Research and The
The prevalence of diabetes in the Australian population aged 25 years and older is ~7.5 per cent. It is estimated that there are close to one million people with diabetes in Australia . In addition, 16.3 per cent of people have milder glucose abnormalities, known as either impaired glucose tolerance or impaired fasting glycaemia. The number of people with diabetes has trebled since 1981 and there is evidence that the age of onset is becoming progressively younger.
Diabetes is a serious disease. It is closely associated with hypertension, obesity and abnormalities of lipid levels. A fact often not recognised is that diabetes is the major underlying cause of cardiovascular diseases in our community. It is also now the single most common cause of kidney disease requiring dialysis or transplantation, the commonest cause of blindness in working age people, and a major cause of lower limb amputation. The medical, social and economic cost of diabetes is enormous.
There are two main types of diabetes. Type 1 is due to an immunological destruction of insulin-secreting cells in the pancreas, resulting in impaired insulin secretion. Type 2 is due to a combination of impaired insulin secretion and insulin action.
Unfortunately, even the current state of the art treatments for diabetes are not optimal. Our method of stimulating insulin secretion or replacing insulin by injection does not precisely reproduce the body’s natural pattern of insulin secretion. Medications used in treatment do not completely overcome the problem of insulin resistance. Despite concerted efforts from patients and health professionals, metabolic abnormalities in diabetes usually cannot be completely normalised, predisposing people with diabetes to the development of diabetic complications.
Only further research can overcome the serious problems that diabetes imposes on individuals and the community. Much effort has therefore been devoted to studying how diabetes can be better identified and treated. Researchers are also working hard to investigate the causes of diabetic complications and how they can best be prevented.
The following sections summarise some of the recent and ongoing clinical research studies performed at the Diabetes Centre of Royal Prince Alfred Hospital. More basic research programs at the bench top level, and programs linking clinical to basic research are also conducted and are further described in the website of the Department in the University of Sydney (see the University of Sydney web-site at http://www.chs.usyd.edu.au/PG/Research/Central.pdf)
Genetic and metabolic abnormalities of diabetes and its complications
Using the extensive computer database of the Diabetes Centre, which contains information on more than 15,000 patients, it was possible to study the family histories of patients with diabetes in detail. An important finding was that the age of diabetes onset was very strongly related to family history in a reciprocal manner. In every ethnic group studied, individuals who had several family members with diabetes tended to develop diabetes themselves at a very early age. This finding suggests that certain combinations of ‘diabetogenic genes’ characteristic of some families predispose to a higher manifestation rate of diabetes as well as earlier onset. The comprehensive family study also showed that type 2 diabetes has a stronger predilection to maternal transmission. This effect of gender on familial transmission of diabetes gives an important clue to the pathogenesis of type 2 diabetes and needs to be explored further. These observations indicate that screening for diabetes should commence earlier in individuals with a strong family history of diabetes, especially if on the maternal side.
It is well established that type 2 diabetes often exists on a background of coexisting hypertension, dyslipidaemia and central obesity. This complex of clinical features is referred to as Syndrome X or Metabolic Syndrome. An ongoing study has found that about 30% of type 2 patients with diabetes do not have the Metabolic Syndrome and these individuals are relatively protected from suffering from diabetic complications. For example, they develop vascular disease considerably later (about 10 years) than counterparts affected by the Metabolic Syndrome. This “diabetes complication sparing” effect is most apparent in middle age patients. Another study currently being conducted has discovered that the Metabolic Syndrome, often considered to occur concomitantly only with Type 2 diabetes, is surprisingly common in patients with Type 1 diabetes, particularly in the overweight individuals. Similar to the situation mentioned above, Type 1 diabetic patients with the Metabolic Syndrome are more likely to develop diabetic complications. Collectively, these findings have the potential to help us to decide which patients with diabetes require more intensive treatment to prevent the development of diabetic complications.
In collaboration with colleagues in China , studies were conducted to examine the clustering of cardiovascular risk factors in Chinese diabetic patients. It was found that concurrence of diabetes and other cardiovascular risk factors are also common among urban Chinese. Clustering was associated with insulin resistance and the female gender. Many of these patients, especially the blue collar workers, were found to have retinopathy shortly after diagnosis of diabetes, indicating a long period of pre-existing but undiagnosed diabetes. These findings indicate that, with progressive westernisation of lifestyle, China will be exposed to greatly increased risk of diabetes. It emphasises the importance of public health measures to control cardiovascular risk factors and a systematic effort to achieve early diagnosis of diabetes and its complications.
Treatment of diabetes
The Diabetes Centre has participated in several international studies on developing insulin preparations that mimic, more closely, physiological insulin secretion. Glargine and Detemir are two such insulin tested. Both are much more predictable in their effect than insulin previously available and their use is found to be associated with less hypoglycaemia, especially during the sleep period. This represents a considerable improvement in the safety of insulin treatment. As these insulins become increasingly available in Australia , they should greatly facilitate the treatment of diabetes and improve the quality of life for diabetic patients.
As insulin resistance is a fundamental problem in the pathogenesis of type 2 diabetes, there has also been great interest in a new class of oral agent known as the thiazolidinediones, which can specifically improve insulin sensitivity. A study conducted at the Diabetes Centre examined clinical factors that can predict patients’ response and the development of side effects. It was found that indices of insulin resistance such as weight, central obesity and insulin dosage do not accurately predict response. Instead, individual trial is the only means of identifying suitable patients. However, pre-existing obesity was noted to be a strong predictor of weight gain during thiazolidinedione treatment. These findings have improved our selection of patients for this type of treatment.
Until the roles of the thiazolidinedione are better defined, metformin will remain the mainstay of treatment for type 2 diabetes. It has been reported that metformin treatment is often associated with a decrease in the circulating level of Vitamin B12 but the significance of this observation is unclear. For example, it is not established whether it increases the risk of anaemia or neurological deficits (often seen in other forms of Vitamin B12 deficiency) in diabetic patients treated with metformin. Using the sophisticated technique of measuring Sensory Evoked Potentials, we are attempting to determine if Vitamin B12 administration can improve neurotransmission in the peripheral and central nervous system.
Due to the high prevalence of diabetes in the community, it is inevitable that much of the medical care for diabetic patients would have to be provided by general practitioners. The Diabetes Centre has continued to foster a close working relationship with general practitioners through a system of ‘Shared Care’. Much research has been performed to define the factors that make such a system efficient and user-friendly for patients, general practitioners and specialists. In one of the studies, continuity of care and a long-existing relationship between patients and their general practitioners were identified to be pivotal factors to support diabetes Shared Care. It was also shown that different types of doctors require different levels of Shared Care. Due to the prevalence of diabetes and the economic burden of treatment, cost efficiency is important. This is considerably enhanced by recognising heterogeneity of patient and doctor populations and tailoring the Shared Care accordingly.
One of our studies based on data from the Australian Government Health Insurance Commission has allowed the pattern of medical monitoring of diabetes for the whole of NSW to be analysed. In this study, a novel method of relying on Health Insurance Commission record of measurement of HbA1c (a blood test only performed on diabetic patients) in the community – is used to track the pattern of diabetes care in the Australian population. The study indeed demonstrated that the degree of medical monitoring for diabetes in Australia was still short of that advised by recommended guidelines. However, the trend in the last 5 years had shown a steady improvement and, most encouragingly, rural doctors were noted to be performing as well as their city counterparts.
We have also conducted a study to examine in more details the change in pattern of diabetes care provided by referring general practitioners. It was found that over the last decade they have progressively become more proactive in initiating insulin treatment, commencing anti-hypertensive and lipid lowering agents with the result that patients at the time of referral are already on more intensive pharmacological treatment. Consequently, calculation using the Risk Engine of the United Kingdom Prospective Diabetes Study Risk Engine showed that for the patients being managed in the shared care system, compared with earlier time periods, there is predicted to be a progressive fall in the risk of patients developing cardiovascular disease. These results show that our strategy of sharing care with primary care doctors is successful.
Diabetic foot disease
Each year, diabetes is responsible for 3,000 lower-limb amputations in Australia . Additionally, there are many patients who suffer from intractable ulceration, infection and pain in their feet. The Diabetes Centre, therefore, has continued its longstanding interest in the study of diabetic neuropathic and vascular foot diseases. Research in this area is supported by and integrated with RPA’s excellent multi-disciplinary Diabetes High Risk Foot Clinic.
The Diabetes Centre had tested the use of a biosynthetic skin preparation (Apligraf) in the treatment of neuropathic foot ulceration. There is also an ongoing project examining whether application of felt directly onto the skin around an ulcer (as distinct from the conventional method of applying it to inside of shoes) is a better method of deflecting pressure from the ulcer site and allowing it to heal faster. A continuing difficulty is to separate the effects of any specific treatment from good general foot treatment within a multi-disciplinary setting. Detailed biomechanical analysis and muscle strength measurements with the Cybex machine are also being performed to analyse why patients develop neuropathic ulcers at different regions of the foot.
The optimal use of antibiotic therapy has been instrumental in eradicating infection and reducing amputation of the lower limbs in diabetes. What is far less certain is whether antibiotics may also be beneficial in the absence of overt infection. It has been postulated that bacteria produce metalloproteinases which degrade extracellular matrix and thus impair wound healing. As such, antibiotics may promote ulcer healing by reducing bacterial load, even in the absence of overt infection. An ongoing project is using wound fluid and wound biopsies to examine quantitatively the relationship between bacterial count and metalloproteinases, growth factors (particularly connective tissue growth factor) and other parameters of wound healing. This study has the potential of establishing the value of antibiotics in an “uninfected” ulcer and thereby improving our strategies of healing diabetic foot ulcers. It may also help to identify ulcers with high bacterial growth which may be at particular risk of slow ulcer healing. In a parallel study using our primate model of type 1 diabetes, we are examining the effects of connective tissue growth factor deficiency in causing the impairment of wound healing in diabetes (for MMP and growth factor analyses, see the Sydney University website at http://www.chs.usyd.edu.au/PG/Research/Central.pdf)
RPA researchers have completed a comprehensive study on quantitative bone scanning as a means of assessing the severity and progress of acute diabetic neuro-arthropathy of the foot. Neuro-arthropathy represents a devastating and destructive complication of diabetes and underlies many of the amputations. The investigators’ method of quantifying neuro-arthropathy to allow treatment to be assessed has now been incorporated into the Diabetes Centre’s everyday clinical practice.
In another project, the techniques of Doppler ultrasound and photo-plethysmography were used to systematically study how lower-limb arterial calcification, a phenomenon unique to diabetic patients, may affect assessment of peripheral circulation. Due to the calcification, clinicians have always been uncertain whether they can use ankle blood pressure measurement to assess the peripheral vasculature of diabetic patients. It was shown that, in the majority of patients with diabetes, calf and toe artery calcification affects haemodynamic parameters to a similar degree. Only in those patients with arterial calcification to the extent that it produces physiologically impossible levels of ankle blood pressure, was the measurement of toe blood pressure a better alternative. This finding is important and could fundamentally simplify how lower-limb perfusion pressure can be assessed in most patients with diabetes.
Several studies were conducted to broaden the scope of the research and treatment of diabetic foot disease into the community. A prospective follow-up study of 200 patients with diabetes with well defined vascular and nerve status, and their matched controls was completed. This showed a 5 per cent annual incidence of foot ulceration in this group of patients with diabetes. This type of data was previously unavailable for Australian patients in the community setting and confirms the validity of using these risk profiles to pinpoint patients at risk of foot ulceration and amputation. It also allows the determination of numbers of subjects needed to be treated (and therefore the cost incurred) for prevention of one foot ulcer. At a time of limited health care resource, such information is crucial in planning our health care priorities.
An extensive tele-medicine program, linking RPA’s foot clinic with rural areas, has confirmed that training of health professionals and treatment of diabetic patients at such remote sites can be facilitated by simple electronic transmission of visual images of foot disease, resulting in a significant decrease in amputation and hospitalisation.
Many diabetic patients suffer from pain in the feet due to nerve damage and this type of pain is notoriously resistant to treatment. It has therefore attracted much attention in the research of the Diabetes Centre. Analysis of more than 4,000 diabetic patients has shown that conventional testing of sensation transmitted by large nerve fibres, which is commonly used in clinical and electrophysiological examinations, cannot reliably predict which patient will suffer from diabetic neuropathic pain. As pain sensation is transmitted by small nerve fibres, it has previously often been assumed that pain is due to damage of small fibres in the peripheral nerves. An extensive study using a system of computerised assisted sensory examination has enabled the Centre’s researchers to show that abnormalities of these small nerve fibres are particularly likely to play a role in the genesis of pain in patients who have milder degree of large fibre neuropathy.
As a result of these findings, studies are now ongoing to examine, more precisely both numerical and morphological abnormalities of these small nerve fibres. A novel method of skin biopsy to study small nerve fibre numbers and appearance has been developed for this purpose. It allows the nerve structure to be studied non-invasively and results thus far have clearly shown a reduction of small nerve fibres in diabetic patients with painful neuropathy. For any degree of large fibre neuropathy, patients with pain appear to have more severe loss of small nerve fibres.
Another ongoing study is using the technique of laser doppler velocimetry to examine the relationship between abnormalities of protein kinase C, endothelial function and these small nerve fibres.
Although studies of small nerve fibre dysfunction have helped to elucidate the mechanism of painful neuropathy, other factors are likely to be involved. We have used the technique of Magnetic Resonance Spectroscopy to examine brain neurotransmitters in diabetic patients with or without painful neuropathy. Major changes of these brain metabolites due to diabetes have been identified but there were no significant difference between subjects with or without neuropathic pain.
Renal and cardiovascular complications
Kidney and cardiovascular complications are major contributors to the morbidity of diabetes and attract much of our research effort.
An interesting observation is that these diabetic complications are closely related to each other. Patients with diabetic kidney disease are at much increased risk of developing stroke, heart attack and heart failure. In turn, hypertension is the major factor aggravating diabetic kidney disease. Compounds known as cellular adhesion molecules are being studied to see if they could be the factors mediating the relationship between kidney and vascular complications. So far, the promoter regions of the vascular cell adhesion molecule (VCAM) and intercellular adhesion molecule (ICAM) have been cloned and their structures studied in detail to determine if any region of the promoter could be responsible for the increase of VCAM and ICAM expression in diabetes and kidney disease. Interestingly, it was demonstrated that serum from patients with differing degrees of diabetic nephropathy was able to induce the expression of these molecules in proportion to the severity of renal disease. Identification of the substances responsible for this phenomenon could lead to better prevention of vascular disease associated with diabetic nephropathy.
A major research program on metallo-proteinases is also continuing in the department’s laboratory (see the University of Sydney web-site at http://www.chs.usyd.edu.au/PG/Research/Central.pdf) . These enzymes are responsible for degradation of the matrix supporting kidney cells and vascular cells. Their abnormalities can therefore be responsible for renal impairment, vascular disease and their association in diabetes. Studies so far have focused on how high blood glucose can induce a process of advanced glycation of extracellular matrix and circulating proteins and how these processes might exert profound influence on the cascade of matrix degradation, mediated by the metallo-proteinases.
Another study used a tonometer to measure arterial stiffness and wave reflection in diabetic patients. Results clearly show that diabetes leads to an increase in arterial stiffness. This is possibly also related to excessive advanced glycation of the arterial wall and its matrix. The demonstrated arterial stiffness has important implications in the pathogenesis of cardiac failure and hypertension, which are common and serious complications in diabetes. Interestingly there were important gender differences in the development of arterial stiffness in diabetic patients.
Endothelial dysfunction has been postulated to play a central role in causing vascular and cardiac abnormalities of diabetes. In another project, we are now using the technique of laser doppler velocimetry in combination with iontophoresis to examine how endothelial dysfunction correlates with the development diabetic cardiomyopathy in human type 2 diabetes, particularly of the diastolic variety
A major effort continues to study diabetic complications in a colony of baboons with type 1 diabetes Again the emphasis is on how advanced glycation may lead to various diabetic complications and whether the complications can be prevented by aminoguanidine, a compound that inhibits the glycation process. After 10 years of diabetes, these baboons are now developing clinically obvious diabetic kidney disease. In the next couple years, it will be known whether aminoguanidine or a similar agent can prevent this dreaded diabetic complication. Our ongoing studies have also shown that these baboons already have considerable endothelial dysfunction, which is not improved by aminoguanidine treatment.
On a more clinical front, the Diabetes Centre has participated in two major international studies examining the possibility of preventing renal impairment by using a drug known to block the binding of angiotensin to its receptor. These studies have now been completed and clearly show that progression of diabetic nephropathy can be retarded by the use of this agent. This finding is having a great impact on the treatment strategy for people with diabetes and renal impairment.