| Distinguished researcher and educator in medical sciences (endocrinology and metabolism) and former chair of physiology, where 85 years ago insulin was discovered. He earned the title of Honorary Medical Doctor from Karolinska Institute, Sweden. He is a Fellow of the Royal Society of Canada, and a corresponding member of the Croatian Academy of Sciences and Arts.|
By: Richard Bergman,
Professor Mladen Vranić is distinguished researcher and educator in medical sciences (endocrinology and metabolism) and former chair of physiology, where 85 years ago insulin was discovered. He earned the title of Honorary Medical Doctor Institute, Sweden. He is a Fellow of the Royal Society of Canada, and a corresponding member of the Croatian Academy of Sciences and Arts. He is the only Canadian who got most prestigious awards from American Diabetes association, and 2007 inaugural life achievement award from Canadian Diabetes association.
Mladen Vranic was born in Zagreb in 1930 to Vladimir and Ana, and grew up an only child in an environment strongly influenced by the academic pursuits of his father, who was a mathematician. At different times his father held positions as Professor and Dean in the Faculties of Economics, and Engineering, and in addition lectured on the theory of probability in the Faculty of Science. The Vranic home was a gathering place, not only for colleagues from the Sciences but also from the Arts, including actors from the theatre. It was a wonderful experience for a young person and unique to the culture of Zagreb at the time. Unusual high school experiences were helpful in preparing Vranic' scientific career by forging those aspects of his character that reflected stubbornness, intensity but flexibility. His first year of high school coincided with the German occupation of Jugoslavia, and the fascist Ustase government in Croatia. Mladen's immediate family escaped in 1941 to Crikvenica, which was under Italian occupation. Sadly, however, most of his relatives were killed in the extermination camps of the Ustase or the Nazis. The following year was spent in Italian concentration camps at Kraljevica and Rab, respectively. Interestingly, some of the teachers in these concentration camps became University Professors in Zagreb after the war. Following the collapse of Mussolini's government in Italy in 1943, and because a large part of Croatia was liberated by the Partisans, the family escaped in January 1944 from the island of Rab to Taranto (Italy), which at that time was occupied by the Allied forces. For the last year of the war, his father returned to Croatia to join the Partisan movement, while Mladen, his mother and grandmother stayed in Taranto until the end of the war. These next two years of high school in Taranto were very classical in nature and greatly stimulated a love for literature that Mladen has retained to this day. The circle was complete when he returned to Zagreb for the final three years of high school.
Mladen enrolled into Medical School in Zagreb, where the Department of Physiology had a keen scientific interest in carbohydrate metabolism and diabetes, initiated by Professor Allegretti a few years earlier. This early summer scientific experience in Zagreb was further enhanced by two summer research programmes at the Universities of Vienna and Amsterdam. The only experience Mladen had as a practicing physician was during internship and one year of military service, and since it would have been very difficult to combine clinical practice with basic research he therefore decided to embark on a career as a physiologist. During summers and later, as a research assistant, a close collaboration developed with Drs. Allegretti, Pokrajac, Rabadija and Mihic. The intense teaching of general physiology provided the background for the rest of his career and was a critical early experience for subsequent teaching in the Department of Physiology in Toronto. In medical school, he developed a very close friendship with Dr. Darko Ivancevic (former Head of Nuclear Medicine) and also his family. This friendship and accompanying lengthy discussions on science and many other subjects greatly enriched his life. Since the time that Mladen no longer had relatives in Zagreb, he has felt that this was his Zagreb family.
His Ph.D. thesis reported on his work stimulating the growth of pancreatic islets by cortisol in guinea pigs, providing early evidence that new islet cells sprout from ducts. Clearly, acinar cells were not necessary because hypertrophy of islets could be produced even when all acinar cells were destroyed by ligation of the pancreatic duct. This work was published in Diabetes, his first publication in a top international journal (1). Although he did not pursue this topic further, growth of islets from ductal cells is now being studied with great vigour using modern methodology, since it is a very important topic for the understanding of the life cycle of islet cells in physiology and diabetes. This area of research has become very sophisticated in the last 10 years and Mladen has recently begun a programme about the contrasting effects of exercise training and chronic stress on the dynamics of pancreatic islets and their relationship to the hypothalamic-pituitary-adrenal axis. This could then close the circle of the work begun in Zagreb.
Mladen discussed his work with colleagues at a number of universities in West Germany, but the visit that was to shape his future was with Professor Werner Creutzfeldt, whose father co-discovered Creutzfeldt-Jacob Disease many years earlier. Because he was interested in obtaining a post-doctoral fellowship in the United States, it was suggested that Dr. Creutzfeldt introduce him to Dr. Albert Renold during the next International Diabetes Federation meeting, which was to be held in Geneva. The number of participants at these early meetings was far below that of the present day, so that it was possible for all the participants to undertake a pleasure trip on the lake. As promised, Mladen was introduced to Albert Renold who told him that he would love to accept him at Harvard, but he had just agreed to return to his hometown of Geneva. Nevertheless, he was still to play an important role in Mladen's scientific endeavours after he joined him much later for a sabbatical leave in Geneva.
Following Mladen's initial disappointment, Dr. Creutzfeldt introduced him to Professors Otto and Anka Sirek from the University of Toronto, Canada. Initially, they were very encouraging, indicating that Professor Charles H. Best was very interested in young people and that he would certainly wish to meet with him and hear his presentation at the meeting. Unfortunately, a meeting was not possible and no post-doctoral positions were available. Despite this additional setback, he continued to correspond with the Sireks and to his greatest delight, after many months received an invitation from Professor Best to come to Toronto in January 1963 as a post-doctoral fellow. He was very excited at the prospect since Professor Best, a co-discoverer of insulin, was one of the best-known physiologists of the time, and he began to make preparations for his departure.
The Ministry of the Interior of Croatia agreed to give him a passport, but his wife Magda and 2-year old daughter Iva would have to remain behind. He declined. Finally, fate intervened in the form of Mrs. Savka Dabcevic, who had been a student of his father's in economics and a patron of his mother's beauty salon. Mrs. Dabcevic was a Member of Parliament in 1962 and became President of the Croatian government in 1967. He was extremely grateful for her support. Although initially there was resentment against Croatians who settled in another country, when they met in Toronto a few years ago, he was gratified by the pride she expressed in his achievements. Upon arriving at Montreal Airport, he was interviewed by Immigration Officers and was quite tense when one officer asked him for very specific details of his plans to work with Dr. Best. He was convinced that the information was for the Secret Police and avoided giving any answers. It turned out that this was actually a doctor who was supposed to be conducting a medical examination, but was actually more interested in hearing about his proposed research with Dr. Best.
Three years after their arrival in Canada Mladen and his family returned to Zagreb for a visit. It was an incredibly emotional moment for him and for their parents. He realized how, when living in Croatia, he had taken for granted the beauty of its cities, the Dalmatian Coast and the mountains. On each subsequent visit, he rediscovered some new aspects of Zagreb. His special love is for the incomparable old city. He remembers one poignant incident when he and his father took the lift to the top of Krvavec in the Slovenian Alps. When they told the Hotel Director that they planned to go for a hike, he looked at his father's shoes and exclaimed, “You cannot possibly hike the Alps in these shoes!” He promptly took off his own shoes and made a temporary exchange with Mladen's father. Both were very moved by this warm and generous act. Mladen occasionally felt resentment from some people that he had left Croatia, but he knew that contact with emigrants was not always looked at favorably by the government in power. One exception was Dr. Ivo Padovan, who is now President of the Croatian Academy of Arts & Sciences. In 1967 he stayed with the Vranics while attending a meeting of Otolaryngologists in Toronto. Mladen still remembers his very impressive lecture, and how he greatly strengthened the collaboration in his specialty between the Universities of Zagreb and Toronto. He also encouraged Mladen by taking an interest in his work, which at that time was in its initial stages. They had a great dinner together with Charlie Best and his wife, Margaret and since that time, Ivo and he have remained close friends. Mladen is especially grateful for Padovan's help when his mother was severely ill.
Mladen also developed a close relationship with Zdenko Skrabalo. As mentioned, they collaborated scientifically and he attended many meetings that Zdenko organized. What was especially impressive was the great care with which these meetings were organized, the high quality and especially the warm atmosphere. On one occasion, all members of the Symposium were driving early in the morning on a bus from Dubrovnik along the Dalmatian Coast when they were served freshly dried figs and Grappa. Even more memorable, however, were the splendid dinners prepared by Zdenko's wife, Lidija, in their home. Zdenko not only had a great knowledge of diabetology, but a wide encyclopedic knowledge that was appreciated by all. Under his leadership, the Croatian model of diabetes treatment was initiated and received international recognition. Part of the model was the establishment of a network of treatment centers around the country providing excellent, integrated diabetes care. Zdenko realized that the mobility of scientists was an essential phenomenon that had always existed, and that a close collaboration between his Institute and Mladen's could be of considerable mutual interest. This collaboration also included Suad Efendic. In 1984 the Diabetes Centre of the University of Toronto invited Zdenko to present a lecture on “Diabetes in the Third World”. Prior to the lecture Mladen and Zdenko had attended a meeting together in Washington, and at the airport they suddenly realized to their horror that Zdenko did not have a Canadian visa. The two of them rushed to the Canadian Embassy with very little hope, because the visa needed to be issued instantaneously in order to catch a plane in time for Zdenko to deliver his lecture in Toronto. Fortunately, he had with him the University of Toronto Newspaper, which advertised all the lectures for the week. He showed it to the Canadian official who noticed that above the name of Skrabalo, was the lecture of Dr. Henry Kissinger. He got the visa!
When Mladen met Dr. Best for the first time in Toronto he was very apprehensive. He was even more nervous when he was asked to present a seminar of his work from Zagreb, since he had overheard Dr. Sirek asking Dr. Best what were his first impressions:- “Well,” Best responded, “his English is pretty good but otherwise I don't know.” Following Mladen's presentation, Dr. Best was most enthusiastic - one of the most important encouragement for his future work. Dr. Best was always available for discussions and appointments could be made at short notice. Best played an important role in attracting graduate students, post-doctoral fellows and visiting scientists to the Department of Physiology in the University of Toronto, and it is due to him that Toronto has continued to be a Mecca for diabetes research since the discovery of insulin in 1921 (2). For a while he was in charge of endocrinology teaching to Medical Students. He would introduce Dr. Best for his lecture, “The Discovery of Insulin” and when the class was over, all 250 students would line up to obtain his autograph. Quite an impressive sight! He retired as Chairman of the Department in 1965 and Dr. Haist took over.
During his two post-doctoral years he worked with Drs. Wrenshall and Rapaport. Dr. Wrenshall, both a physicist and physiologist by training, was a pioneer in tracer methodology, which allowed measurement of fluxes of metabolites in vivo quantitatively. Rapaport was a surgeon who came from Romania and at the time was a pioneer of experimental surgery. He did ground breaking research on liver structure and function. His main achievement is known today as “Rapaport's liver acinus”. When he arrived in Toronto after WWII, he began work in experimental surgery and diabetes with Dr. Markoviz. It was rumoured that Dr. Markoviz might have been the famous Canadian medical doctor described in the movie, “Bridge Over the River Kwai”. This work fueled his interest in establishing the first insulin clamp. They removed two-thirds of the pancreas, while the remaining one-third was grafted under the skin of the dog. This graft had its blood supply through a peduncle and was enclosed in a plastic casing. A catheter was introduced simultaneously into the portal vein. At the time of the experiment the graft was removed from the casing and clamping of the peduncle induced instantaneous diabetes while the removal of the clamp restored normal insulin secretion into the portal vein. Most importantly, if the peduncle was cut and exogenous insulin infusion started into the portal vein, then the insulin clamp would be established in a dog that had never been diabetic. On the basis of those experiments he measured for the first time ever, the rate of basal insulin secretion in dogs. He was very enthusiastic when the same value was later reported in man. This preparation also allowed him to investigate the effects of hormones and metabolites independently of insulin secretion. For the first time he demonstrated what is now called “glucose effectiveness”. This means that during glucose tolerance tests, a substantial amount of glucose is removed by the tissues in an insulin-independent process. Insulin release made this removal more efficient but basal insulin secretion sufficed to return glucose to normal after a glucose load. Mladen was very eager to continue with this line of research but he was concerned that it might be difficult to establish this upon his return to Zagreb. Consequently, he thought that the best route would be to try to prolong his stay in Toronto.
Before the Chairman of the Department of Physiology would offer Mladen an academic appointment, he wanted to know that he was competitive enough to be offered a position in the United States. It was suggested that he visit a number of research institutes in the U.S., and to facilitate this a young graduate student in the Department named John Cowan (now President of the Royal Canadian Military College in Kingston, Canada) was enlisted to fly a four-seater Cessna plane from Toronto to Minneapolis, Washington, St. Louis and New York. He was an excellent, local pilot but what Mladen was not told was that this was his very first flying expedition outside of the Toronto area. Mladen's first test was to see whether or not he could endure a few acrobatics - he passed with “flying colours”. It must have made quite an impression at the places they visited, since it was quite puzzling to people how a foreign post-doctoral fellow could afford to engage a plane and a pilot. There were no problems navigating, but while flying around the Empire State Building, John became very annoyed at Mladen's handling of the video camera. When he realized that they might lose control of the plane Mladen decided from then on to follow all of John's instructions with the utmost care. In one incident, the arrangements were so comfortable in the back of the plane and Mladen was so relaxed, that he thought he would read the newspaper - in mid flight, with the cockpit cover open. In an instant, the papers were atomized and it took John years to remove all the bits and pieces from his plane. The most critical outcome of the trip was the offer of an Assistant Professorship in the laboratory of Dr. Rachmiel Levine, one of the great names in the field of diabetes. His book on glucose homeostasis was legendary at the time. Upon Mladen's return to Toronto the news was spread that he was wanted in the U.S. and as a result he was offered a position as Assistant Professor in the Department of Physiology at the University of Toronto. Today, academic appointments and granting of tenure are extremely elaborate procedures with mountains of paperwork. At that time, months after both his appointment and granting of tenure, Dr. Haist remarked that the Department had never received either his M.D. or Ph.D. diplomas. One can only yearn for those times of relaxed trust!
At that time it seemed impossible to become a Landed Immigrant in Canada. It so happened, however, that Mladen's car was insured by a company that once belonged to the Minister of Finance of Canada before he entered politics. The secretary of the insurance company told him that she would write to her former boss to see whether he could help with visas for Mladen and his family. Indeed, he still has the extensive correspondence between the Minister of Finance and the Minister of Immigration - an exchange lasting over 2 years. One day, a Royal Canadian Mounted Police Officer arrived unexpectedly at the door to interview him at great length. Mladen asked whether he also needed to speak to his wife, to which the officer replied, “There is no need.” This was long before the feminist movement swept over the North American continent. There was a second, later visit from the same officer asking the same questions. The accuracy of repeated answers was the test of honesty. At that time, Mladen's memory was better than today, and he was granted the visa. The special benefit was that the secretary of the Insurance Company invited the family to one of the greatest dinners they had ever tasted, reminding him of the fabulous dinner described in Gogol's Dead Souls, especially the generous amount of ice cold vodka that accompanied it.
Life in a new country posed many and varied challenges. His first daughter was 2 1/2 years old and fluent in Croatian. On one visit to relatives in Montreal, she was so frustrated that nobody understood her, she gave endless speeches, in Croatian, to a beautiful German Shepherd dog who showed great understanding. Mladen's wife faced a long period of 7 years to qualify as M.D. and to write the Canadian specialty exams in Physical Medicine and Rehabilitation. In 1971, a particularly emotional and dramatic period devastated Mladen's family. While visiting in Toronto, his mother suffered a massive heart attack on the day that she was due to return to Zagreb. She spent many weeks in the hospital, during which time her own mother, Mladen's grandmother, died in Zagreb. To everyone's amazement, the shock of this news normalized his mother's heart rhythm. During her convalescence, however, Mladen's father was hospitalized in Zagreb with a bleeding ulcer. Immediately following this, Mladen's second daughter, Maja, died of leukemia at the age of 11 months. It was a time of terrible grief.
His work in the field of diabetes has been recognized by a number of awards, including the inaugural Banting & Best Memorial Lecture at the 12th Congress of the International Diabetes Federation in Madrid, Spain (1985). This lectureship was particularly important to him because his work in Canada was initiated by Dr. Best. For Mladen, the most important recognition of his work came when he was awarded the American Diabetes Association's Banting Medal and Lectureship for Distinguished Scientific Achievement. This award was established 60 years ago, following the death of Banting, and one award is given annually. It is generally considered to be the most important international recognition for original research in Diabetes and to date, he is the only researcher working in Canada to have received it. Six weeks before the lecture was scheduled to be given in Washington, D.C., he was riding home from work on his bicycle when he had a collision with a good-looking woman (at least that's how he remembers it), who was also riding her bicycle. The following day, while attending a scientific meeting at Sunnybrook Hospital in Toronto, he suffered a stroke. Luckily, he was immediately whisked into emergency and taken care of. There were two interesting episodes related to the incident. When he began to talk, it was in Croatian and not English. His English wife was very concerned that she would now have to start taking Croatian lessons. When the neurologist came to examine him, he informed his wife that because Mladen could not answer any of the very basic questions that were posed, the prognosis did not look good. It turned out that the neurologist had asked him, in English, about words he had never known in the first place. The test was repeated using questions from the scientific jargon and the diagnosis became excellent. Indeed, after two weeks in hospital he was able to prepare his Banting lecture and then deliver it – with 5,000 people in the audience. After the lecture, he held a reception for many friends, including a sizable group of diabetologists from “Vuk Vrhovac” and Ljubljana. It was on this day that his friends from Ljubljana learned with horror that the Yugoslav army had attacked Slovenia.
Sabbatical at the University of Geneva, Switzerland: As indicated earlier, initial plans to work at Harvard with Albert Renold failed to materialize when Renold became Head of the Institute of Clinical Biochemistry in Geneva. Albert persuaded Mladen, in his inimitable and special way, to spend a year (1976/77) at that unique institution. Albert, who was also Vice President of the University, had made provisions for a special fund for post-doctoral fellowships that was created from salaries of deceased or retired professors (again reminiscent of Gogol). Such funds could be used until replacement appointments were made - a very slow process in Switzerland. The laboratory was housed in a beautiful villa surrounded by flowers and trees. The ideal setting, combined with the presence of Albert attracted a large number of students, fellows and sabbatical professors from all over Europe and North America. Mladen felt as if he had been permanently adopted into a large extended family of diabetologists, all related by virtue of association with Albert and his charming wife, Jacqueline. Together, they provided a support system, which included very generous hospitality in their home - quite unique in Switzerland. One recollection, for example, was an occasion when the lights went out in their apartment and Jacqueline arrived within 15 minutes with a large toolbox to replace the fuse. Albert was fluent in English, French and Italian and it was in part due to his efforts that Diabetes meetings in Europe were held in English, and that Diabetologia and the European Journal of Clinical Investigation were established and also used English exclusively. The University of Geneva had a villa in the Engadines and for two weeks during the Christmas holidays, a number of professors with their families spent time together in a region loved by Nietsche and Giacometti. It is a real paradise for skiers.
Mladen's scientific interests were flourishing. He established the biological effects and control of release of extrapancreatic glucagon and the kinetics of tritiated insulin during exercise as described above. It must have been very stimulating to discuss clinical and basic problems endlessly with scientists like Steve Fajans, Joe Larner and Phil Gorden (former head of NIDDK, Bethesda). A short visit to the Institute from Ed Horton (former Chair of the Department of Medicine at the University of Vermont and currently Professor at Harvard University) initiated a lifelong and very close friendship with Ed and his family.
Geneva was strategically located, giving him an opportunity to visit a large number of European universities. While there, a meeting was organized in Cambridge, England for all Faculty Scholars of the Josiah Macy Foundation. It was a very intimidating experience for him to give a lecture just ahead of Dr. Sanger, who had been awarded the Nobel Prize for the discovery of the structure of insulin. Sanger lectured on the sequence of nucleotides of DNA, which at that time was over 90% complete, and this work later resulted in his second Nobel Prize. Only Sanger and Marie Curie were awarded two Nobel Prizes for science. One of the exciting events was when Dr. Skrabalo invited Albert, Lelio Orci and myself to give the inaugural Vuk Vrhovac Memorial Lectures to commemorate the 50th anniversary of the foundation of the Institute for Diabetes in Zagreb. Vuk Vrhovac was an endocrinologist who visited Toronto soon after the discovery of insulin and realized the importance of dedicating a special institute to this disease. In ensuing years, due to Zdenko and later to Mate Granic and Zeljko Metelko, this became a leading Diabetes Institute.
A sad event during his stay in Geneva was the illness and subsequent death of his father. He was a diabetic and eventually, his diabetes accellerated a generalized atherosclerotic disease. Mladen remained close to his side during the last week of his life, during which time he thanked him for restoring his belief in life. The same night he died. Dr. Devidee, a mathematician and friend, delivered a beautiful speech to a large audience, highlighting Mladen's father's accomplishments and contributions. One fact that Mladen found most remarkable was that his father was responsible for bringing the first computer to Zagreb University, which apparently never worked properly. His father was always trying to convince the other, more theoretical mathematicians, that the computer era had begun. Their reluctance stemmed in part from the fear that computers would interfere with the purity of mathematical thinking. He was very well known as a superb lecturer with a strong sense of humour. An oft-quoted example is when, during an examination, he would urge a student to quickly open the windows, so that all of the stupidities that he uttered could be removed from the room. Unfortunately, this type of humour is no longer politically correct, particularly in North America.
Collaboration with the Department of Endocrinology, Karolinska Institute, Stockholm:
Drs. Suad Efendic and Rolf Luft were keen to introduce tracer methods into their studies of the pathogenesis and pathophysiology of diabetes. Mladen was in Stockholm for over a week but did not see the city at all, as he was literally held hostage in their laboratory. Suad was an old friend who had been a student of medicine in Zagreb when Mladen gave seminars to medical students. He always tells Mladen that his seminars persuaded him to choose science as a career. Thus, Mladen jokingly counts Suad as his first student. For many years, Rolf was either a member or Chair of the Nobel Committee for Medicine and Physiology. He spent 30% of his time every year studying the work of the candidates, and thus was one of the most knowledgeable experts in a large spectrum of medical research. He did important early work in different fields of endocrinology. Mladen was very impressed that Rolf always prepared himself for meetings, something he realized when he saw a stack of his papers in front of him, passages variously underlined, as they prepared to discuss some issues. The collaboration with Suad is now in its 25th year and it has been most productive and enjoyable. Clinical investigations were carried out in Stockholm and animal work in Toronto. Suad is former Chair of the large Department of Molecular Medicine in Stockholm, a member of the Nobel Assembly, the Swedish National Academy of Sciences, and corresponding member of the Croatian Academy of Arts and Science.
Ingmar Bergman's movie, Wild Strawberries, describes the incredible pageantry of awarding honorary degrees at Swedish Universities. Mladen would not have believed that one day he would become part of it. Every year, the Karolinska Institute awards one honorary medical degree to a foreigner, and in 1992, following his nomination by Suad and Rolf, he had the great honour to be chosen. At the ceremony itself, the candidate stands before the Dean while he holds a black, top hat above the head. A signal is then given to an official waiting outside who fires a canon, whereupon the Dean lowers the hat. During the ceremony, degrees are also awarded to graduate students and to professors from Swedish Universities. Hundreds of attendees are dressed in identical formal tailcoats or glittering evening dress. For Mladen, this evening represented the culmination of his collaborative work with Suad, and of his close relationship to the Karolinska Institute. This closeness was further emphasized by his appointment as an Adjunct Professor at the Karolinska. It was on Suad's initiative that a series of Toronto/Stockholm Symposia were begun and held every 3 years.
In 1982, 10 years after being diagnosed with breast cancer, Mladen's wife died. There were meetings in Israel and Kenya later the same year and it was fortuitous that Suad was also participating. At that crucial time in his life, Suad was a great comfort to him, never letting him out of his sight. In addition, to divert his mind from the sorrow, he tried to stimulate him to plan experiments that they would conduct together.
The following year, he became Associate Editor of the American Journal of Physiology, possibly the first non-American in this position. In his early days as a physiologist, he considered a publication in this Journal to be the greatest achievement. Now, he was in the position of making decisions affecting publications of other researchers. He already had some experience, previously serving as Associate Editor of the Canadian Journal of Physiology and Pharmacology and of Metabolism.
Mladen began to play tennis with his Editorial Assistant, Linda, whom he had hired when he took the Associate Editor's position with the American Journal of Physiology. Surprisingly, for anyone who knows how Mladen plays tennis, he won every single game. After Linda and he married and she started to unpack her suitcases, he noticed that the luggage contained various Tennis Championship trophies. Tennis has played a crucial role in their life together. During their sabbatical leave in Oxford, when their daughter Claire was 1 1/2 years old, they were scheduled to play doubles with Gerry and Ann Burrow. Gerry was Chairman of the Department of Medicine at the U. of T. and also on sabbatical leave. He was a first-class tennis player and had defeated Mladen on previous occasions. Mladen told Linda that if they won this match, she could have anything she wanted. After thoroughly defeated them by a score of 6-0, Linda informed him that what she really wanted was another child. Thus, his fourth daughter Anne was born. There were no further opportunities to play with the Burrows, since he became Dean of Medicine and Chancellor at the University of California in San Diego, and then Dean of Medicine at Yale University. This is probably fortunate, because otherwise who knows how big their family would be.
Sabbatical at Oxford University, England: In 1986 an exciting opportunity arose for Mladen to study bioenergetic changes during contraction and recovery in diabetic rat skeletal muscle in Oxford, England. He was invited as a Visiting Research Fellow at Merton College, and with his appointment came a newly renovated 14th century house in the heart of Oxford. The only problem was that there was a very low beam dividing the living room from the dining room. Almost daily, he managed to bang his head as he raced from one room to the other. Sometimes, it actually knocked him to the floor. It hopefully had the desired effect of waking him to face the unexpected challenges of life in Oxford - a fate not unlike that of the mathematicians in Gulliver's Travels. One privilege he had was that of eating with scholars from all fields within the College - and it was free! The dinners were very ceremonial, beginning with port in the Queen's Room (wife of Charles I). This was followed by a multi-course dinner at High Table. Nuts and sweets were served in the next room. They were ritually circulated around the common table so that all could partake. One had to choose seats wisely, however, because once they appeared in front of the very eminent Professor of Roman Law, they would remain there for the duration of the evening. It is said that the sweet wine served had come from the same French vineyards for the last 500 years. The evening would generally finish in the coffee room, where hard liquor was served. Mladen probably wouldn't have survived had he joined in this dinner every evening. One rather odd rule was that one was not allowed to invite one's own wife for these dinners, although he could bring anyone else. He also learned upon arrival that Visiting Fellows could request a Master Key that could open all the doors of the College. Now, Merton College has a vast collection of fine art, old silver and priceless books and Mladen naively thought that he could actually exercise this privilege. He described the horror that he saw in the eyes of the Bursar, who politely informed him that this was really not very practical and would be an absolute catastrophe if he were to lose it! The sad event during their sabbatical stay in Oxford was the serious illness and death of his mother. Mladen has always been very grateful for the wonderful care that she received in the Diabetes Centre in Zagreb.
All previous Chairmen of the Department of Biochemistry in Oxford, where he was working, were Nobel Prize winners. The Department reflected an incredible contrast of facilities. On the one hand, it probably had the greatest concentration of Nuclear Magnetic Resonance equipment in the world, while at the same time there were no pencil sharpeners and an open, antiquated lift elevator called “pater noster”, for the reason that one felt a great need to pray upon entering it.
Another highlight of the Oxford sabbatical was an invitation for a private lunch in the home of the late Professor Sir Isaiah Berlin, one of the greatest liberal intellects of this century. He was the stepfather of Philippe Halban, with whom Mladen had worked during his sabbatical leave in Geneva. The atmosphere was congenial and Sir Isaiah had an extremely warm and inquisitive personality. His most famous and widely read essay is entitled “The Hedgehog and the Fox” from the Greek poet Archilochus, who said, “The fox knows many things, but the hedgehog knows one big thing”. Berlin described Tolstoy as a fox who believed himself to be a hedgehog. Mladen refers to it often in his lectures as a metaphor for metabolic and molecular research. In metabolic research, one deals with control systems, regulation, models and a variety of hormones, metabolites and other factors that continuously interplay to maintain our body near homeostasis. It is a continuous fight between certainty and uncertainty and the models are modified as new discoveries are made. The molecular biologist is more focused and better equipped but has more difficulty in integrating his new findings into complexities of the living body. Physiologists today try to integrate the physiology of organs and tissues with molecular approaches that define the function of the cell. Thus, as with Tolstoy, in the biological sciences it is sometimes difficult to make a clear distinction between the fox and the hedgehog.
Collaboration with the
In 1989 he decided to hold the first of what was to be a series of Symposia jointly organized by the University of Zagreb (Skrabalo and Granic), the University of Toronto (Vranic and Hollenberg) and the Karolinska Institute, Stockholm (Efendic and Luft). The meeting in
The establishment of the
In the last few years Mladen has been a member of the International Advisory Board of the Medical Studies in English, at the University of Zagreb, Croatia. It is a very important endeavor at the school of medicine, and it is directed by the Dean Mrs. N. Cikes and professor D. Jezek. Mladen is involved in the teaching program on a yearly basis. The
Chair of the Department of Physiology,
The Department of Physiology at the
In October 1996 he was the Chairman of the Committee to celebrate the 75th anniversary of the discovery of insulin in the Department of Physiology. Delegates from over 50 countries, including Croatian diabetologists, participated in what was a very strong scientific program that commemorated what Dr. Michael Bliss calls one of the most dramatic adventures in the history of medicine.
An important recognition came in 1997 when he had the honour of being elected as a Corresponding Member of the
There are eight interdependent, projects with the main goal of understanding aspects of the pathogenesis of diabetes, including exercise, stress and hypoglycemia.
1) Extrapancreatic Glucagon
Since the discovery of insulin it was clear that diabetes is related to insulin deficiency. What was not known was whether glucagon, the second hormone of the endocrine pancreas, also played an important role in physiology and diabetes. There were two reasons for this: 1) Glucagon can increase glucose in plasma but only when given at very high concentrations; 2) Diabetes can be induced in animals either by selective chemical destruction of the insulin-producing B-cells or by total pancreatectomy, which removes the B-cells and the glucagon-producing A-cells. If glucagon were the hormone to counteract insulin, one would have expected that total pancreatectomy would induce milder diabetes than the selective destruction of the B-cells, but that was not the case. Dr. Unger from
The most exciting symposium that he attended was a 1974 Conference on Glucagon held at the Santa Ynez ranch in
2) Tracer Methods to Measure Glucose Fluxes
Tracer methods are a necessary tool because a change in glucose turnover can occur independently of the changes of glucose concentration. For example, if the pancreas releases insulin and glucagon at the same time, glucagon will increase glucose production by the liver while insulin will increase glucose uptake to the same degree. Using tracer methodology, Mladen showed glucagon's exquisite potency with only physiological amounts given. This explained why previous workers not using tracer methods believed that glucagon could exert effects only in very high amounts and in many organs, which could not explain its physiological role. Mladen showed that in physiological doses glucagon is very selective, acting only on the liver.
It is easy to measure glucose turnover in steady state. However, if one wishes to learn how various control systems work it is necessary to drive the system out of steady state. Drs. Steele, Altszuler and De Bodo in Brookhaven developed a mathematical model to do just this. Their model was based on certain assumptions regarding the distribution of glucose in extracellular fluid. The problem with their model was that it was not experimentally validated. It had been used only in dogs with uncertainty about the precision of the measurements. The first validations, performed in
The Federation of American Societies of Experimental Biology (FASEB) holds a Symposium every year to consider problems and advances of tracer methodology. he became Chairman and organizer of the Tracer Methodology Study Group in 1972 and continued until 1975. This was a very exciting task, especially when he became the first person asked to edit and publish the Proceedings from this Symposium in Federation Proceedings, a very prestigious and widely read journal.
The main method used to assess insulin's effects in vivo is the euglycemic, hyperinsulinemic clamp developed by Dr. Andres at National Institutes of Health. This is a critical method in diabetes because it can assess the magnitude of insulin resistance. With the clamp combined with tracers, one can assess hepatic glucose production separately from overall glucose utilization. The problem observed in every laboratory was that glucose production measurements were frequently negative, an artefact that invalidated the measurements. With a post-doctoral fellow, Dr. Diane Finegood, and in collaboration with Dr. Richard Bergman of the
Advances in tracer methodology opened the door for very precise investigation of the hormonal interactions and teleology. With Alan Cherrington, then a graduate student, he demonstrated how precisely glucagon and insulin need to interact to increase glucose turnover but maintain glucose homeostasis (8). With Friedrich Kemmer, a postdoctoral fellow from
3) Exercise and Diabetes
Mladen's mentor in
When Berson and Yallow developed the immunoassay for insulin in the sixties, it became evident that during exercise in non-diabetic subjects, insulin in plasma decreases up to 50%. Mladen hypothesized that since blood flow in muscle during exercise can increase by 20-fold or more despite a decrease in plasma insulin, the perfusion of muscle with insulin is maintained. Other laboratories indicated that muscle contraction increases glucose uptake independently of insulin. Mladen concluded that insulin during exercise in vivo is necessary to counterbalance factors that would decrease glucose uptake such as increased fatty acids and catecholamines (11). They then examined the mechanism of exercise-induced hypoglycemia in depancreatized dogs maintained on long-acting insulin. With Kawamori, he was very surprised to find that during exercise, plasma insulin increased dramatically. It was interesting that nobody had made this observation before, although the insulin assay had been available for quite a few years. A friend remarked at the time that what he observed was highly unlikely since it would surely have been noticed before. Nevertheless, he could now for the first time explain the mechanism of the development of hypoglycemia during exercise in insulin-treated patients (12). With increased insulin levels during exercise, glucose production did not increase to match the increased glucose uptake by the muscle. Even when insulin does not increase, the fact that exogenous insulin does not decrease may also inhibit the liver, but to a lesser extent. During his sabbatical leave in
Guilleman's discovery of somatostatin permitted him to study with Dr. B. Issekutz from
He had a very productive and enjoyable collaboration with Dr. Amira Klip. It was known at the time that glucose is transported into various tissues by specialized proteins-glucose transporters. A stunning discovery by Cushman and Kono was that in the fat cell, by far the largest number of transporters is found in cell plasma and that insulin translocates the transporters to the plasma membrane where they exert their function. It was much more difficult to determine glucose transporters in the muscle and Amira was one of the first to develop the methodology required for the muscle. They demonstrated, together with a graduate student D. Dimitrakoudis, that in mild diabetic rats, glucose transporter number is decreased both in plasma membrane and inside the cell and that this was due not to insulin deficiency, but to hyperglycemia. They explored this problem using phlorizin. Since the time of Minkowski, more than 100 years ago, it had been known that phlorizin prevents reabsorption of glucose in the kidney. Therefore, it is possible to normalize glucose in diabetic animals by phlorizin treatment. Plasma glucose is normalized because excessive amounts of glucose are secreted in the urine. When they treated diabetic rats with phlorizin for a few days, glucose concentration normalized and they could normalize not only the number of glucose transporters but also the genetic expression of the gene for glucose transporters in the muscle (20).
This work with Amira continued with a post-doctoral fellow, Dr. Marette. They showed for the first time that most of the glucose transporters are translocated not to the plasma membrane, but to the transverse tubules of the skeletal muscle. This is physiologically very important because transverse tubules represent a larger surface area than the plasma membrane, are exposed to the extracellular milieu and play an important role in transporting ions and nutrients into the muscle fibre. A Ph.D. student in their laboratories, Theos Tsakiridis, demonstrated that the actin network, an important part of the cytoskeleton, is essential for the insulin stimulation of glucose transport and transporters (21). However, they further concluded that this network might be part of the signaling process rather than only a simple vehicle for transport of the vesicles. This was particularly evident when the stimulation of glucose transport was caused by mitochondrial uncoupling of the oxidative chain. This was achieved by dinitrolphenol, which mimics the effect of hypoxia and perhaps exercise. This signaling process was completely different from that with insulin. The key signals required for insulin stimulation, phosphatidylinositol 3-kinase and the actin network were not required when the oxidation chain was uncoupled (22). This observation, with observations from other laboratories explains why the effects of insulin and exercise are additive and why muscular contraction per se can stimulate glucose transport without insulin.
An ongoing collaboration with Errol Marliss from
Insulin deficiency results in increased FFA levels, which according to Randle's hypothesis could inhibit peripheral glucose uptake. Mladen investigated this effect during moderate exercise in dogs with a post-doctoral fellow, Dr. Q. Shi and Dr. K. Yamatani from
His new early concepts regarding metabolic regulations in physiology and diabetes during exercise attracted wide attention. He was invited to organize the first Symposium on “Exercise and Diabetes” sponsored by the Kroc Foundation in 1978, and held in the same place where he had attended the Glucagon Symposium four years earlier (see books edited). This initiated a number of meetings on this topic, held every three years, in both
The last six years we explored the mechanism of preventing hyperglycemia in an animal model of obese diabetic rats (ZDF). These animals have a deficient leptin receptor, and therefore, they eat excessively. With development of obesity, they also develop Type 2 diabetes. In a paper resulting from my D.Sc. in
It is well known that continuous stress deteriorates diabetes and probably can also accelerate the onset of diabetes. Very surprisingly, that is not the case in all types of stress. When we exposed the obese rats to neurogenic stress (rats are put into plastic tubing which restrains their movements), the onset of diabetes was also prevented. Physiological and molecular analysis indicated that this type of stress can decrease body weight and decrease the activity of the Hypothalamic-Pituitary-Adrenal Axis, which both have a beneficial effect. This is in the same line with work of the father of stress, Hans Selye. We indicated that certain types of stress improve, rather than deteriorate the health. Importantly, our work contrasts with common views that all stressors are deleterious for diabetes and illustrates that intermittent exposure to mild stressors and the ensuing adaptations may instead be important for normal physiological functioning by preparing the body to deal with threats to homeostasis (42).
4) The Relative Importance of Portal and Peripheral Insulin in Regulating Glucose Production:
One such example is the control of glucose production. Together with Dr. Adria Giacca, a post-doctoral fellow who came from
5) Stress and Diabetes:
The effects of acute and chronic stress are wide-ranging and it is well known that they can markedly offset metabolic control in diabetes. Together with graduate students, P. Miles and M. Lekas, and post-doctoral fellows, Z.Q. Shi and K. Yamatani, Mladen induced acute stress in dogs by inserting a chronic cannula into the third ventricle (29,30). Carbachol injections mimic the muscarinic action of acetylcholine, which is a major neurotransmitter of the brain. Such an injection induces a release of all counterregulatory hormones (vasopressin, cortisol, catecholamines and glucagon). It is known that some types of stress can selectively suppress insulin secretion but in this model, insulin is not affected. In normal dogs, this stress induces a large increase in glucose turnover with only a 5% change in glucose concentration. Glucose homeostasis is maintained because stress induces an increase in glucose utilization that is independent of insulin. This was the first demonstration of a neuroendocrine pathway that can increase peripheral glucose utilization independently of insulin. In contrast, stress induced a major increase in glucose concentration because glucose uptake did not increase, as shown by graduate student Shirya Rashid. Resistance to stress in diabetes reflects a chronic defect that cannot be improved by acute hyperinsulinemic euglycemic clamps. Similarly to exercise, beta-blockade can in part restore the response of glucose uptake to stress (31). Thus they discovered the mechanism whereby stress in diabetes can offset glucose homeostasis.
6) Protection Against Excessive Hyperglycemia of Muscle and Liver, but not Pancreas
The next important invitation was to deliver the 1995 Solomon Berson Distinguished Lectureship of the American Physiological Society - Endocrinology and Metabolism Section at the Federation of American Societies of Experimental Biology in
The ancient Chinese philosophy of the Yin and the Yang can be used as a metaphor for the balance between active and passive interrelationships. In this philosophy, yin is dark and passive, while yang is light and active. In harmony the two are symbolized as the light and dark halves of a circle, and literally mean the dark and sunny sides of a hill. What is particularly useful with respect to glucose homeostasis is the yin-yang implication of an entire series of opposites, whose interplay (as one increases, the other decreases) defines the actual dynamic process. The thesis of his Berson Lecture was the proposition that in some organs, decreased glucose efficiency is not a defect, but rather a protective mechanism against diabetic complications. Glucose utilization is a result of opposing forces related to the effect of glucose itself, and to the interaction between the effects of glucose and insulin. These interactions are dynamic and reflect a continuum of synergistic and contrasting processes. Most of the complications of diabetes are due to chronic elevation of plasma glucose. Through mass effect, an excessive amount of glucose enters a variety of tissues resulting either in glycosylation of many proteins or in augmentation of otherwise insignificant metabolic pathways. This does not occur in either the muscle or the liver.
In diabetes, glucose uptake in the muscle is not decreased. The defect can be observed by measuring metabolic glucose clearance (MCR), which represents the ratio of glucose utilization to plasma glucose concentration and reflects the efficiency of glucose extraction by the tissues. Glucose clearance is significantly decreased in diabetes, which is one reason for development of hyperglycemia. This was attributed to a toxic effect of hyperglycemia on glucose uptake in peripheral tissues. He suggested that this is mainly an adaptive effect. Together with Dr. Geza Hetenyi, a former Chairman of the Department of Physiology at the
7) Glucose Cycling:
Glucose uptake in the liver is modified by three non-equilibrium reactions:- the glucose cycle, the fructose-6-phosphate cycle and the phosphoenol pyruvate cycle. Suad and Mladen were particularly interested in the glucose cycle in which entry of glucose is accelerated by the enzyme glucokinase, which yields glucose-6 phosphate. Some of the glucose-6 phosphate is then cycled back into glucose through the enzyme glucose-6 phosphatase. Thus through this mechanism a small amount of glucose taken up by the liver is recycled into the blood stream. They found that the activity of glucose cycling was increased in depancreatized and alloxan-induced diabetic dogs, in lean and obese Type-2 diabetic subjects as well as in acromegaly and hyperthyroidism (34,35). The percent increase in post-absorptive glucose cycling is more marked than the increase in glucose production. They suggested, therefore, that measurement of glucose cycling in addition to glucose production could be a valuable tool to assess the early metabolic derangements of glucose intolerance. The mechanism of increased glucose cycling in depancreatized dogs was then investigated (36). With Drs. Shi, Giacca and van der Werve, Chairman of the Department of Nutrition at the
A major acute complication of diabetes is a defective response of glucagon, catecholamines and glucocorticoids to insulin-induced hypoglycemia. The threat of hypoglycemia has increased since the treatment for diabetes has aimed for tight blood glucose control to decrease the risk of diabetic complications. Therefore, it is very important to develop a treatment strategy that would decrease the risk of hypoglycemia. The defect of glucagons and epinephrine response to hypoglycemia is puzzling because both counterregulatory responses are normal or even excessive during some stresses, such as moderate and strenuous exercise (23). Mladen tried to answer this question in dogs and rats by inducing diabetes by alloxan and streptozotocin, respectively. With this treatment, not only are most of the beta-cells destroyed but also the number of islets is markedly reduced. With Drs. Sudha Rastogi and Suad Efendic he showed that although in each islet the number of glucagon cells is greatly increased the total amount of glucagon in pancreas remains unchanged because of the reduction in the number of islet cells. It is well known that the release of glucagon by the pancreas is inhibited by both insulin and somatostatin. Since most beta-cells have been destroyed, somatostatin is the main paracrine inhibitor of the A-cell in diabetes. That is why it is of particular interest that in diabetic islets the ratio of somatostatin to glucagon is markedly increased. An acute insulin injection increased this ratio further. Theirs was the first demonstration that part of the defective mechanism in hypoglycemia may reflect alterations of this ratio in diabetes. Since somatostatin inhibits glucagon release, this could explain why glucagon-producing alpha cells are less sensitive to hypoglycemia, while they remain normally responsive to other stresses (37). The other factor that affects alpha cells is chronic hyperglycemia. With Dr. Shi (38) he then demonstrated that the defective glucagon responses are in part due to chronic hyperglycemia and hyperinsulinemia. Normalization of hypoglycemia without, but not with insulin, restored in part, glucagon's responsiveness in diabetic rats. This occurs because hyperinsulinemia offsets the beneficial effect of normalization of glucose.
Presently, he is investigating with Dr. Steve Matthews, a molecular neuroendocrinologist in the department, and graduate student Owen Chan, the gene expression of stress hormones and their receptors in the brain to find out how diabetes affects the function of the hypothalamic-pituitary-adrenal (HPA) axis and its relationship to sympathoadrenal responses in hypoglycemia. They demonstrated that diabetes increases the activity of the HPA axis, which is evidenced by increased expression of stress hormones and their receptors in the brain and by an increase of peripheral glucocorticoids. The impaired stress responses involved also decreased pituitary and adrenal sensitivity, and the basal hyperactivation of diabetic HPA axis is due to decreased glucocorticoid negative feedback sensitivity. With insulin treatment, glucocorticoid concentration normalizes but central components of the HPA axis remain increased. Since the central HPA axis is also associated with sympathetic activity, this could explain why insulin-treated diabetics retain a defect of the sympathoadrenal response to hypoglycemia. Response of the HPA axis to hypoglycemia is greatly reduced in diabetic rats. Normally during hyperglycemia expression of corticotrophin-releasing hormones increases and the expression of mineralocorticoid hormones decreases. That does not occur in diabetic rats. They also demonstrated that normalization of plasma glucose with or without insulin treatment can normalize the responses of the HPA axis to hypoglycemia. Thus, hyperglycemia and not hypoinsulinemia plays a key role in the fine turning of the HPA axis (39). It is well known that repetitive (antecedent) episodes of hypoglycemia increase the threat of further hypoglycemia episodes. They investigated with graduate student, Karen Inouye, the reason why counterregulatory resonses of epinephrine are deficient (40). They demonstrated that there is a defect of enzyme expression in the adrenal medulla that controls epinephrine and norepinephrine synthesis, which is further jeopardized with antecedent hypoglycemia. This could explain the main defect, which is diminished epinephrine response. This indicates the importance of the regulation of synthesis of those enzymes and opens new possibilities for pharmacological intervention.
When we treated the rats with insulin we could normalize glucagon and epinephrine defects, but the defect of the HPA axis persisted. Our insulin treatment normalized fasting blood sugar, but a moderate defect of fed blood sugar persisted. We therefore concluded that full restoration of counterregulation would only be possible if the control of blood sugar is fully normalized, which at the present time cannot be achieved.
We were then interested whether recurrent restraint stress also increases the threat of hypoglycemia similarly to the effect of episodes of antecedent hypoglycemia. Indeed in diabetic rats, these two effects (antecedent hypoglycemia and antecedent stress) were comparable with respect to the HPA axis. The defect correlated with decreased basal gene expression of PVN AVP and the anterior pituitary POMC mRNA. In these rats, there was practically no glucagon response to hypoglycemia and therefore, recurrent restraint stress could not further jeopardize glucagon responses. However, in contrast to antecedent hypoglycemia, recurrent restraint stress did not impair catecholamines counterregulation.
In this biographical sketch, a long journey has been taken to describe Mladen's research endeavours, which are all related to the physiology and pathophysiology of carbohydrate metabolism with a special emphasis on diabetes. To bring it all together, it would be useful to quote the citation that was read during his induction into the Royal Society of Canada: “He pioneered tracer methods for nonsteady-state glucose turnover, providing a cornerstone for quantifying hormonal interactions in glucoregulation and pathogenesis of diabetes. He established the significance of glucagon-insulin interaction in health and diabetes. His hypothesis concerning factors that determine beneficial or deleterious glucoregulatory effects of exercise in diabetes is universally accepted. He demonstrated by tracer, cellular and molecular methods how muscle, liver and pancreatic a-cells adapt to hyperglycemia: a critical concept in diabetes. By purifying and determining biological activity of stomach glucagon, he provided the first evidence of glucagon's extrapancreatic site, changing prevailing concepts that one hormone is synthesized in one gland.”
Mladen has received several awards and honours for his work:
In closing, Mladen's greatest pride is in his students and post-doctoral fellows who are so well recognized internationally. To mention a few:
Selected Bibliography (from a total of over 290 published papers and chapters)
Conference Proceedings and Books Edited:
In the January issue of Nacional Paper in
This biography of Professor Mladen Vranić has been published in the following monograph:
We express our deep gratitude to Professor Janko Herak and to the Croatian - American Society in Zagreb for permission to present this text for the readers of CROWN.
Also many thanks to Professor Mladen Vranić for providing some biographical supplements concerning his work in the period of 1997-2007.
Mladen Vranic to be inducted in the Canadian Medical Hall of Fame in 2009.
Formated for CROWN by prof.dr. Darko Žubrinić
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