Effect of glycemic control on microvascular complications in patients with type I diabetes mellitus

Protein glycation in diabetes mellitus

Diabetes mellitus is the ninth leading cause of mortality worldwide. It is a complex disease that manifests as chronic hyperglycemia. Glucose exposure causes biochemical changes at the proteome level as reflected in accumulation of glycated proteins. A prominent example is hemoglobin A1c (HbA1c), a glycated protein widely accepted as a diabetic indicator. Another emerging biomarker is glycated albumin which has demonstrated utility in situations where HbA1c cannot be used. Other proteins undergo glycation as well thus impacting cellular function, transport and immune response. Accordingly, these glycated counterparts may serve as predictors for diabetic complications and thus warrant further inquiry. Fortunately, modern proteomics has provided unique analytic capability to enable improved and more comprehensive exploration of glycating agents and glycated proteins. This review broadly covers topics from epidemiology of diabetes to modern analytical tools such as mass spectrometry to facilitate a better understanding of diabetes pathophysiology. This serves as an attempt to connect clinically relevant questions with findings of recent proteomic studies to suggest future avenues of diabetes research.

The association between diabetes mellitus and incident infections: a systematic review and meta-analysis of observational studies

OBJECTIVE

To quantify the association between diabetes and the risk of incident infections by conducting a systematic review and meta-analysis.

RESEARCH DESIGN AND METHODS

Two reviewers independently screened articles identified from PubMed, EMBASE, Cochrane Library, IPA, and Web of Science databases. Cohort studies (CS) or case-control studies (CCS) evaluating the incidence of infections in adults with diabetes were included. Infections were classified as: skin and soft tissue, respiratory, blood, genitourinary, head and neck, gastrointestinal, bone, viral, and non-specified infections. Study quality was assessed using the Newcastle-Ottawa Quality Assessment Scale. Summary crude and adjusted OR with 95% CIs were calculated using random effects models, stratified by study design. Heterogeneity was measured using the I²statistic and explored using subgroup analyses.

RESULTS

A total of 345 (243 CS and 102 CCS) studies were included. Combining adjusted results from all CS, diabetes was associated with an increased incidence of skin (OR 1.94, 95% CI 1.78 to 2.12), respiratory (OR 1.35, 95% CI 1.28 to 1.43), blood (OR 1.72, 95% CI 1.48 to 2.00), genitourinary (OR 1.61, 95% CI 1.42 to 1.82), head and neck (OR 1.17, 95% CI 1.13 to 1.22), gastrointestinal (OR 1.48, 95% CI 1.40 to 1.57), viral (OR 1.29, 95% CI 1.13 to 1.46), and non-specified (OR 1.84, 95% CI 1.66 to 2.04) infections. A stronger association was observed among CCS: skin (OR 2.64, 95% CI 2.20 to 3.17), respiratory (OR 1.62, 95% CI 1.37 to 1.92), blood (OR 2.40, 95% CI 1.68 to 3.42), genitourinary (OR 2.59, 95% CI 1.60 to 4.17), gastrointestinal (OR 3.61, 95% CI 2.94 to 4.43), and non-specified (OR 3.53, 95% CI 2.62 to 4.75).

CONCLUSION

Diabetes is associated with an increased risk of multiple types of infections. A high degree of heterogeneity was observed; however, subgroup analysis decreased the amount of heterogeneity within most groups. Results were generally consistent across types of infections.

Skeletal muscle as a therapeutic target for delaying type 1 diabetic complications

Type 1 diabetes mellitus (T1DM) is a chronic autoimmune disease targeting the pancreatic beta-cells and rendering the person hypoinsulinemic and hyperglycemic. Despite exogenous insulin therapy, individuals with T1DM will invariably develop long-term complications such as blindness, kidney failure and cardiovascular disease. Though often overlooked, skeletal muscle is also adversely affected in T1DM, with both physical and metabolic derangements reported. As the largest metabolic organ in the body, impairments to skeletal muscle health in T1DM would impact insulin sensitivity, glucose/lipid disposal and basal metabolic rate and thus affect the ability of persons with T1DM to manage their disease. In this review, we discuss the impact of T1DM on skeletal muscle health with a particular focus on the proposed mechanisms involved. We then identify and discuss established and potential adjuvant therapies which, in association with insulin therapy, would improve the health of skeletal muscle in those with T1DM and thereby improve disease management- ultimately delaying the onset and severity of other long-term diabetic complications.

Cental Macular Thickness in Patients with Type 2 Diabetes Mellitus without Clinical Retinopathy

Objective. To compare central macular thickness (CMT) of diabetic patients with type 2 diabetes without clinical retinopathy and healthy subjects. Materials and Methods. Optical coherence tomography (OCT) measurements were performed in 124 eyes of 62 subjects with diabetes mellitus without clinical retinopathy (study group: 39 females, 23 males; mean age: 55.06 ± 9.77 years) and in 120 eyes of 60 healthy subjects (control group: 35 females, 25 males; mean age: 55.78 ± 10.34 years). Blood biochemistry parameters were analyzed in all cases. The data for central macular thickness (at 1 mm), the levels of fasting plasma glucose, and glycosylated hemoglobin (HbA1c) were compared in both groups. Results. The mean central macular thickness was 232.12 ± 24.41 µm in the study group and 227.19 ± 29.94 µm in the control group. The mean HbA1c level was 8.92 ± 2.58% in the study group and 5.07 ± 0.70% in the control group (P = 0.001). No statistically significant relationship was found between CMT, HbA1c, and fasting plasma glucose level in either group (P > 0.05). Conclusions. Central macular thickness was not significantly thicker in patients with type 2 diabetes without clinical retinopathy than in healthy subjects.

Central macular thickness in patients with type 2 diabetes mellitus without clinical retinopathy

Background

An increase in macular thickness due to fluid accumulation in the macula in patients with diabetes mellitus. Optical coherence tomography (OCT) has been shown to be highly reproducible in measuring macular thickness in normal individuals and diabetic patients. OCT can detect subtle changes of macular thickness. The aim of this study is to compare central macular thickness (CMT) of diabetic patients with type 2 diabetes without clinical retinopathy and normal controls, in order to assess possible increased macular thickness associated with diabetes mellitus.

Methods

Optical coherence tomography (OCT) measurements were performed in 124 eyes of 62 subjects with diabetes mellitus without clinically retinopathy (study group: 39 female, 23 male, mean age: 55.06 ± 9.77 years) and in 120 eyes of 60 healthy subjects (control group: 35 female, 25 male, mean age: 55.78 ± 10.34 years). Blood biochemistry parameters were analyzed in all cases. The data for central macular thickness (at 1 mm) and the levels of the fasting plasma glucose and glycosylated hemoglobin (HbA1c) were compared in both groups.

Results

The mean central macular thickness was 232.12 ±24.41 μm in the study group and 227.19 ± 29.94 μm in the control group.

The mean HbA1c level was 8.92 ± 2.58% in the study group and 5.07 ± 0.70% in the control group (p=0.001). No statistically significant relationship was found between CMT, HbA1c, and fasting plasma glucose level in either group (p=0.05).

Conclusions

Central macular thickness was not significantly thicker in patients with type 2 diabetes without clinical retinopathy than in healthy subjects.

Lung function changes related to diabetes mellitus

Diabetic microangiopathy targets the lung as it does other organs. Even though respiratory dysfunction in most patients with diabetes is subclinical and rarely the presenting complaint, there are several reasons why pulmonary assessment is important: (1) Pulmonary function testing noninvasively quantifies physiological reserves in a large microvascular bed that is not clinically devastated by diabetes. (2) Subclinical loss of pulmonary reserves becomes overtly debilitating under conditions of stress, such as with aging, chronic hypoxia due to lung disease or high altitude exposure, or volume overload secondary to cardiac and renal failure. (3) Unlike myocardial or skeletal muscle function, pulmonary indices are largely independent of physical fitness. (4) Interpretation of pulmonary function indices is not complicated by secondary sequelae of diabetic end-organ failure or prior therapy. Lung function could provide useful measures of the progression of systemic microangiopathy. (5) Chronic use of inhaled insulin may affect long-term pulmonary function, while preexisting pulmonary dysfunction may alter the absorption and bioavailability of inhaled insulin. This review will discuss the changes in lung function observed in diabetes, their underlying mechanisms, and their physiological and clinical implications.

The diabetic lung: relevance of alveolar microangiopathy for the use of inhaled insulin

The alveolar-capillary network receives the entire cardiac output and constitutes the largest microvascular organ in the body, making it highly susceptible to systemic microangiopathy. Owing to its large reserves, symptoms and disability develop later in the lung than in smaller microvasculature such as the kidney or retina despite a comparable severity of anatomic involvement. Hence, pulmonary impairment in diabetes mellitus is under-recognized. Nonetheless, respiratory autonomic neuropathy and structural derangement of the thorax and lung parenchyma develop in many asymptomatic diabetic patients; the pathophysiology parallels that in other target organs. Even subclinical loss of alveolar microvascular reserves can be quantified noninvasively from lung diffusing capacity and its components (membrane diffusing capacity and alveolar-capillary blood volume) measured at a given cardiac output at rest or during exercise. The alveolar diffusion-perfusion relation tracks the recruitment of microvascular reserves in a manner independent of physical fitness. This article addresses the importance and pathophysiologic basis of diabetic pulmonary involvement, the assessment of diabetic alveolar microangiopathy, and the relevance of this understanding for the emerging use of inhaled insulin.

Controlled multicenter study on the effect of computer assistance in intensive insulin therapy of type 1 diabetics

This paper describes the results of a controlled multicenter study on the effect of the computer assistance in the intensive insulin therapy. The patient collective consisted of 50 diabetics, randomly divided in two groups with 25 patients per group. The Multiple Subcutaneous Injection (MSI) group was treated with the usually intensive regimen. The treatment in the Computer Assisted Meal Related Insulin Therapy (CAMIT) group was performed with the aid of a specialized pocket computer. Only in the CAMIT group during the study we observed a significant decrease: in the mean blood glucose (BG) with 1.6+/-0.4 mmol/l (P<0.05), in the BG amplitudes by 1.0+/-0.3 mmol/l (P<0.05), and in the hypoglycemia frequency-from 2.0+/-0.4 to 1.2+/-0.3 (P<0.01) hypoglycemic episodes weekly. The HbA(1) values fell in the MSI group by 3.7+/-3.7% and in the CAMIT group significantly by 15.6+/-2.2% (P<0.05). Consequently, the computer-assisted intensive insulin therapy resulted in an improved metabolic control.

Early retinal damage in experimental diabetes: electroretinographical and morphological observations

A growing body of evidence indicates that impairment of retinal function precedes the earliest signs of vascular complications. The aim of this study was to follow the development of retinopathy both functionally and morphologically in a rat model of diabetes mellitus. Diabetes was induced in rats by intravenous injection of streptozotocin (STZ). Age-matched rats raised under similar conditions served as control. The electroretinogram (ERG) was recorded in order to assess retinal function. The expression of glial fibrillary acidic protein (GFAP) in Müller cells was used as a cellular marker for retinal damage. The ERG responses of the diabetic rats were reduced in amplitude compared to the responses recorded from the control rats as early as 2 weeks after onset of diabetes. The b-wave was more affected than the a-wave. GFAP expression in the diabetic retina did not differ from that in the control retina during the first 5 weeks of diabetes. GFAP was demonstrated only in astrocytes in the vitreo-retinal border. After 6-7 weeks of diabetes, GFAP expression in the retinas of the diabetic rats was also detected in the endfeet of the Müller cells. With the progression of diabetes, GFAP expression spreads throughout the entire length of the Müller cells. In the retinas from control rats, GFAP expression was limited to astrocytes and was not detected in Müller cells even at 40 weeks of follow-up. The observations indicate that the functional integrity of retinal cells is compromised already at short time intervals after onset of experimental diabetes in rats.

A comparison of observational studies and randomized, controlled trials

BACKGROUND

For many years it has been claimed that observational studies find stronger treatment effects than randomized, controlled trials. We compared the results of observational studies with those of randomized, controlled trials.

METHODS

We searched the Abridged Index Medicus and Cochrane data bases to identify observational studies reported between 1985 and 1998 that compared two or more treatments or interventions for the same condition. We then searched the Medline and Cochrane data bases to identify all the randomized, controlled trials and observational studies comparing the same treatments for these conditions. For each treatment, the magnitudes of the effects in the various observational studies were combined by the Mantel-Haenszel or weighted analysis-of-variance procedure and then compared with the combined magnitude of the effects in the randomized, controlled trials that evaluated the same treatment.

RESULTS

There were 136 reports about 19 diverse treatments, such as calcium-channel-blocker therapy for coronary artery disease, appendectomy, and interventions for subfertility. In most cases, the estimates of the treatment effects from observational studies and randomized, controlled trials were similar. In only 2 of the 19 analyses of treatment effects did the combined magnitude of the effect in observational studies lie outside the 95 percent confidence interval for the combined magnitude in the randomized, controlled trials.

CONCLUSIONS

We found little evidence that estimates of treatment effects in observational studies reported after 1984 are either consistently larger than or qualitatively different from those obtained in randomized, controlled trials.

Glycemic control and cardiopulmonary function in patients with insulin-dependent diabetes mellitus

BACKGROUND

We studied cardiopulmonary function during exercise in young subjects with long-standing insulin-dependent diabetes mellitus (IDDM) who have no clinical cardiopulmonary disease to determine the relationships of aerobic capacity, gas exchange, ventilatory power requirement, and cardiac output to chronic glycemic control.

METHODS

Eighteen subjects with IDDM and 14 normal control subjects were studied. Nine diabetic subjects received twice daily insulin injections and had chronically elevated levels of glycosylated hemoglobin (hyperglycemic group); 9 other diabetic subjects received insulin via continuous infusion pumps and maintained chronic near-normal levels of glycosylated hemoglobin (normoglycemic group). At the end of at least 7 years of regular follow-up, aerobic capacity was determined by cycle ergometry. Lung volume, diffusing capacity, and cardiac output during exercise were measured by a rebreathing technique. Ventilatory power was measured by the esophageal balloon technique.

RESULTS

Maximal work load and oxygen uptake were markedly impaired in chronically hyperglycemic diabetic patients associated with significant restrictions of lung volume, lung diffusing capacity, and stroke index during exercise. Membrane diffusing capacity was significantly reduced at a given cardiac index. The normoglycemic patients consistently showed less impairment than the hyperglycemic patients.

CONCLUSION

Physiologically significant cardiopulmonary dysfunction develops in asymptomatic patients with long-standing IDDM. Chronic maintenance of near-normoglycemia is associated with improved cardiopulmonary function.

Diabetic complications. The importance of glucose control

The most important question for clinicians caring for diabetic patients, and for the patient themselves, is whether the risk of complications can be altered by careful control of glycemia. Epidemiologic studies showed a strong relationship between glycemia and diabetic complications, in both type I and type II diabetes. There is a continuous relationship between prevailing glycemia and risk of progression of complications, implying that any improvement in glycemic control is beneficial. The debate of the question has ended--glucose control is important.

Diabetic nephropathy

Diabetic nephropathy occurs in approximately 35% of all diabetic patients, both insulin and non-insulin dependent. It accounts for the largest proportion increase of all diseases as a cause for endstage renal disease in the United States. Certain populations, i.e., Pima Indians and Mexican and black Americans, have a higher propensity for developing diabetic nephropathy. The reasons for this increased incidence, however, are unclear. Pathophysiologically, numerous changes in vascular reactivity and renal physiology occur in early diabetes. These include increased sodium avidity, lower threshold for vasoconstriction secondary to angiotensin II and norepinephrine, a greater than 50% of normal increase in renal vasodilation following a protein meal, and loss of renal autoregulation. These differences are not seen in nondiabetic hypertensive subjects. The therapeutic approach to lower elevated arterial pressure in these patients should take these changes in physiology into account. Specifically, antihypertensive agents are preferred that have natriuretic properties and also blunt the effects of vasoconstrictors on both the vasculature and the cellular level, i.e., inhibit mesangial hypertrophy and matrix expansion, the hallmark of diabetes. Ideal agents, therefore, are angiotensin converting enzyme (ACE) inhibitors in the early stages of the disease, and certain calcium antagonists once renal insufficiency occurs. These choices are largely due to the hemodynamic, natriuretic, and anti-proteinuric effects of these agents. Good blood pressure control is essential for preservation of renal function, regardless of agents used. The ACE inhibitors and calcium antagonists of the verapamil and diltiazem groups have demonstrated superior efficacy for preservation of renal function over conventional therapy.

Glycemic control and development of retinopathy in youth-onset insulin-dependent diabetes mellitus. Results of a 12-year longitudinal study

BACKGROUND

In 1979, the authors began a prospective study of the natural history of retinopathy in youth-onset insulin-dependent diabetes mellitus (IDDM). Their major goal was to determine if there was an association between glycemic control and the development and progression of retinopathy.

METHODS

The study consisted of 420 individuals with IDDM (onset younger than 20 years of age) and no retinopathy at baseline. Study subjects were enrolled between 1979 and 1988. Stereo color fundus photographs were obtained annually. Two eye endpoints were recorded: duration when retinopathy was first detected, and when proliferative retinopathy was detected. Glycemic control was assessed by quarterly determinations of glycohemoglobin (GHb). Life-table analyses were performed relating duration of diabetes, sex, GHb, and age of diabetes onset to development of retinopathy.

RESULTS

Retinopathy did not develop before 2 years' duration or before puberty. The prevalence of retinopathy was 50% by 9 years' duration and 100% by 20 years' duration. Retinopathy developed in females approximately 2 years sooner than in males, but plotting duration as postpubertal years resulted in nearly identical rates. Retinopathy developed significantly earlier in subjects with prepubertal onset of diabetes than in subjects with postpubertal onset if duration was plotted as postpubertal years. When separated into three groups based on GHb levels (< 7.5%, 7.5%-9%, > 9%), retinopathy developed approximately 2 years later in subjects in the less than 7.5% GHb group than those in the higher GHb groups. Proliferative retinopathy developed in 11 subjects. Their mean GHb level was higher than the mean GHb for those without proliferative retinopathy (10.9 versus 8.6%; P < 0.01). The higher the level of GHb, the sooner proliferative changes were detected.

CONCLUSION

Long-term glycemic control is significantly related to both development and progression of retinopathy. Prepubertal duration of diabetes is a significant risk factor for the development of retinopathy.

Relationship between diabetes control and pulmonary function in insulin-dependent diabetes mellitus

PURPOSE

To evaluate the effect of different levels of glycemic control on the pulmonary function of subjects with type I insulin-dependent diabetes mellitus.

PATIENTS AND METHODS

Eighteen subjects with type I insulin-dependent diabetes mellitus with no history or physical findings of respiratory disease. Patients were given insulin therapy with a standard twice-daily insulin injection regimen (standard treatment group) or a subcutaneous insulin infusion device (insulin pump) (intensive treatment group). Glycosylated hemoglobin (HbA1c) levels were determined at quarterly intervals in both groups of patients (standard treatment group, n = 10; intensive treatment group, n = 8). Pulmonary function and diffusing capacity for carbon monoxide (DLCO) were measured after 6 years of continuous follow-up.

RESULTS

The average HbA1c in the standard treatment group was significantly higher than that of the intensive treatment group throughout the 6 years of follow-up (p less than 0.001). The forced vital capacity of the standard treatment group was 85 +/- 3% of predicted as compared with 106 +/- 4% of predicted in the intensive treatment group (p less than 0.001). The DLCO was also significantly diminished in the standard treatment group as compared with that in the intensive treatment group (65 +/- 2% versus 87 +/- 4% of predicted) (p less than 0.001).

CONCLUSION

These data confirm previous reports of abnormal respiratory function in subjects with insulin-dependent diabetes mellitus and suggest that long-term near-normoglycemia may be beneficial in preventing the deterioration of pulmonary function associated with diabetes mellitus.

Factors associated with diabetic microangiopathy: a study of 157 type I (insulin-dependent) diabetic patients

The relation between poor glycemic control and the development of diabetic microangiopathy has long been recognized. However hyperglycemia alone cannot account for the striking heterogeneity of diabetic patients regarding the presence or absence of microangiopathic lesions. This study was therefore designed to determine the prevalence of retinopathy, nephropathy, and neuropathy, and to identify the factors respectively associated with these lesions. In 157 patients with type I (insulin-dependent) diabetes, the following parameters were recorded: sex, age, duration of diabetes, body mass index, fasting plasma glucose, HbA1c, blood pressure, antihypertensive treatment, tobacco consumption, urinary albumin excretion, plasma creatinine, and presence of retinopathy and neuropathy. One-half of these patients had retinopathy, 32% neuropathy, and 29% nephropathy. Patients with nephropathy exhibited concomitantly high prevalences of retinopathy (69%) and neuropathy (49%). Among patients with retinopathy, 39% had nephropathy; 79% of those with neuropathy had concomitant retinopathy. For each microangiopathic localization, patients with the disease had significantly higher values (p less than 0.05) than those without for duration of diabetes, prevalence of hypertension, and systolic blood pressure. Stepwise logistic regression analysis showed that the following were independent predictive factors of each localization: for nephropathy, systolic blood pressure; for retinopathy, duration of diabetes; and for neuropathy, duration of diabetes, age, and HbA1c.

Intensified conventional insulin treatment retards the microvascular complications of insulin-dependent diabetes mellitus (IDDM): the Stockholm Diabetes Intervention Study (SDIS) after 5 years

Ninety-six patients with insulin-dependent diabetes mellitus (IDDM) and non-proliferative retinopathy were randomized to intensified conventional treatment (ICT) (n = 44) or regular treatment (RT) (n = 52), and followed up for 5 years. HbA1c decreased from 9.5 +/- 0.2% (mean value +/- SEM) to 7.2 +/- 0.1% in the ICT group, and from 9.4 +/- 0.2% to 8.7 +/- 0.1% in the RT group (difference between the groups, P less than 0.001). Retinopathy increased in both groups (P less than 0.001), but after 5 years it was worse in the RT group (P less than 0.05). The urinary albumin excretion rate was higher in the RT group than in the ICT group after 5 years (239.9 +/- 129.7 micrograms min-1 vs. 46.0 +/- 26.1 micrograms min-1, P less than 0.05). Eight RT patients developed manifest nephropathy, compared with none in the ICT group (P less than 0.01). After 5 years the conduction velocities of the sural (P less than 0.05), peroneal (P less than 0.01) and tibial (P less than 0.001) nerves were lower in the RT group. The respiratory sinus arrhythmia was 12.1 +/- 1.2 beats min-1 in the RT group and 16.7 +/- 1.4 beats min-1 in the ICT group at the end of the study (P less than 0.01). The increases in retinopathy (P less than 0.01), nephropathy (P less than 0.01) and neuropathy (P less than 0.001) were all related to the mean HbA1c value during the study. Smoking habits only influenced the progression of retinopathy (P less than 0.05). Serious hypoglycaemia occurred in 34 ICT patients and 29 RT patients (242 and 98 episodes, respectively) (P less than 0.05). Whereas weight was stable in the RT group, the body mass index increased by 5.8% in the ICT group (P less than 0.01). In conclusion, microvascular complications of diabetes were retarded by intensified conventional insulin treatment. However, such treatment increased the frequency of serious hypoglycaemia, and led to an increase in body weight.

Maturity-onset diabetes of the young (MODY)

This review summarized aspects of the widening scope, phenotypic expression, natural history, recognition, pathogeneses, and heterogenous nature of maturity-onset diabetes of the young (MODY), an autosomal dominant inherited subtype of NIDDM, which can be recognized at a young age. There are differences in metabolic, hormonal, and vascular abnormalities in different ethnic groups and even among Caucasian pedigrees. In MODY patients with low insulin responses, there is a delayed and decreased insulin and C-peptide secretory response to glucose from childhood or adolescence, even before glucose intolerance appears; it may represent the basic genetic defect. The nondiabetic siblings have had normal insulin responses for decades. The fasting hyperglycemia of some MODY has been treated successfully with sulfonylureas for more than 30 years. In a few, after years or decades of diabetes, the insulin and C-peptide responses to glucose are so low that they may resemble those of early Type I diabetes. The rate of progression of the insulin secretory defect over time does distinguish between these two types of diabetes. In contrast are patients from families who have very high insulin responses to glucose despite glucose intolerance and fasting hyperglycemia similar to those seen in patients with low insulin responses. In many of these patients, there is in vivo and in vitro evidence of insulin resistance. Whatever its mechanism, the compensatory insulin responses to nutrients must be insufficient to maintain normal carbohydrate tolerance. This suggests that diabetes occurs only in those patients who have an additional islet cell defect, i.e., insufficient beta cell reserve and secretory capacity. In a few MODY pedigrees with high insulin responses to glucose and lack of evidence of insulin resistance, an insulin is secreted which is a structurally abnormal, mutant insulin molecule that is biologically ineffective. No associations have been found between specific HLA antigens and MODY in Caucasian, black, and Asian pedigrees. Linkage studies of the insulin gene, the insulin receptor gene, the erythrocyte/Hep G2 glucose transporter locus, and the apolipoprotein B locus have shown no association with MODY. Vascular disease may be as prevalent as in conventional NIDDM. Because of autosomal dominant transmission and penetrance at a young age, MODY is a good model for further investigations of etiologic and pathogenetic factors in NIDDM, including the use of genetic linkage strategies to identify diabetogenic genes.

Diabetic microangiopathy, genetics, environment, and treatment

As the major cause of disability and death in insulin-dependent diabetes, microangiopathy is obviously of major concern to diabetologists. Unlike macroangiopathy, which can readily be prevented by means that are currently on hand, the origin and treatment of microangiopathy remain far more problematical. The complexity of this lesion is indicated by the findings in this laboratory that hyperglycemia induced by the rodenticide, vacor, can cause microangiopathy independent of genetic diabetes, yet significant microangiopathic lesions can be detected in genetic diabetic patients before the appearance of hyperglycemia. Further, there is now intriguing evidence based both on basement membrane measurements from our laboratory and on clinical studies showing that significant microangiopathy only rarely occurs prior to the onset of puberty. The evidence that control or even normalization of blood glucose levels does not influence the course of established microangiopathy is becoming increasingly convincing. Five prospective, randomized studies over the past five years have shown that strict regulation of glucose has no consistent benefit on, and in some studies may, at least transiently, accelerate, the retinopathy of diabetes. Moreover, the first controlled study of successful pancreatic transplantation to achieve normalization of blood glucose levels has again demonstrated that established retinopathy is neither prevented nor even delayed by normal glucose levels. This review, therefore, emphasizes that, though hyperglycemia is required for clinically significant microangiopathy to occur, clearly other factors, genetic, environmental, or both, must play major roles in determining the course of microangiopathy. It is toward these nonglycemic factors in the development of diabetic microangiopathy that future research should increasingly be directed.

The relationship between metabolic control and vascular complications of diabetes mellitus

Animal studies strongly support the notion that the microvascular complications of diabetes are a consequence of the metabolic derangements. The evidence from human studies is not nearly as persuasive, but controlled prospective clinical trials are examining this issue more incisively than has been possible previously.

Cryopreserved human fetal pancreas: a source of insulin-producing tissue?

Human fetal pancreata (HFP) were obtained from dilatation and extraction aborted fetuses of 11-18 weeks' gestation. The pancreas was excised under sterile conditions and kept in culture medium at 4 degrees C, prior to stepwise digestion into 50- to 150-micron fragments. The fragmented pieces were allowed to sediment by gravity, then transferred to tissue culture for 24-48 h, and cryopreserved. The freeze-thaw protocol used stepwise equilibration with dimethyl sulfoxide, nucleation of the sample at -10 degrees C, and a slow cooling rate of 0.25 degrees C/min to -40 degrees C, followed by submersion in liquid nitrogen (-196 degrees C). Rapid thawing at 300 degrees C/min from -196 degrees C was employed. Both fresh and frozen-thawed HFP fragments appeared viable as judged by light and electron microscopy, and secreted insulin in a perifusion system upon stimulation with glucose (28 mM) and theophylline (10 mM) or glucose (2.8 mM) and theophylline (10 mM). Six patients with Type I insulin-dependent diabetes mellitus, already requiring immunosuppression for a kidney transplant, had intraportal injection of 20 cryopreserved-thawed and pooled HFP fragments. Up to the 1-year post-transplant follow-up, there has been no evidence of in vivo insulin or C-peptide production. The usefulness of cryopreserved human fetal pancreata as a source of insulin-producing tissue for diabetic patients, therefore, remains to be demonstrated.

Improved diabetes control reduces skeletal muscle capillary basement membrane width in insulin-dependent diabetes mellitus

We studied the relationship between the control of blood glucose and the width of skeletal muscle capillary basement membrane in 54 insulin-dependent diabetic patients. After initial measurement of levels of glycosylated hemoglobin and the width of skeletal muscle capillary basement membrane, the patients were divided into two groups: an intensive treatment group of 30 patients who were treated with continuous subcutaneous insulin infusion and a control group of 24 patients who continued to receive conventional treatment, usually two daily injections of insulin. Both groups have been followed prospectively for periods of time up to 4 years. Within 1 year the intensive treatment group had a significant decrease in glycosylated hemoglobin levels as compared to baseline values reflecting improved control of blood glucose. This level of glycosylated hemoglobin was stable over the remainder of the follow-up period. This group also had a significant reduction in the width of skeletal muscle capillary basement membrane within 1 year and it persisted for the 4 years of observation. The control group of patients had no significant change in their level of glycosylated hemoglobin and the width of the skeletal muscle capillary basement membrane tended to increase with time. It this result in skeletal muscle capillaries applies to those of retinal and renal tissue, meticulous diabetic control for a prolonged period of time may be beneficial in preventing the progression of the microvascular complications of diabetes mellitus.