Association of proinsulin and insulin resistance with coronary artery disease in non-diabetic south Indian men

Cardiometabolic disease in South Asians: A global health concern in an expanding population

Cardiovascular disease (CVD) is one of the main causes of mortality and morbidity worldwide. As an emerging population, South Asians (SAs) bear a disproportionately high burden of CVD relative to underlying classical risk factors, partly attributable to a greater prevalence of insulin resistance and diabetes and distinct genetic and epigenetic influences. While the phenotypic distinctions between SAs and other ethnicities in CVD risk are becoming increasingly clear, the biology of these conditions remains an area of active investigation, with emerging studies involving metabolism, genetic variation and epigenetic modifiers (e.g., extracellular RNA). In this review, we describe the current literature on prevalence, prognosis and CVD risk in SAs, and provide a landscape of translational research in this field toward ameliorating CVD risk in SAs.

Increased carotid intimal media thickness precedes albuminuria in South Indian type 2 diabetic subjects

Introduction Intimal media thickness (IMT) of common carotid artery (CCA) is used as an index of atherosclerosis. IMT is increased in subjects with diabetes and also with diabetic nephropathy.

Aim The study was undertaken in South Indian type 2 diabetic patients with different degrees of albuminuria to see whether albuminuria worsened IMT.

Material and methods IMT was measured by ultrasonography in 273 diabetic subjects with normoalbuminuria (n=91), microalbuminuria (n=92), clinical proteinuria (Prot) (n=90) and in age-matched non-diabetic subjects (n=99). The diabetic subjects were older than the non-diabetic subjects hence IMT was age-adjusted using a linear regression formula.

Results Age-adjusted IMT value in diabetic subjects was significantly higher (0.88±0.3 mm) than in non-diabetic subjects (0.57±0.34 mm) (p<0.001). Mean IMT in normoalbuminuria (0.87±0.26 mm), microalbuminuria (0.90± 0.33 mm) and Prot (0.86±0.39 mm) patients were not significantly different from each other. Male gender, age, diabetes and total cholesterol were independently associated with IMT, while duration of diabetes, hypertension and HbA1C were not.

Conclusion Increased carotid IMT occurred in type 2 diabetes prior to the presence of albuminuria. Further deterioration in IMT did not occur with the presence of albuminuria.

South Asian Ethnicity and Cardiovascular Risk

South Asians (SAs), in their countries or after migration, are at high risk of coronary artery disease (CAD) and mortality compared to other ethnic groups. It has been shown that >90% of CAD global risk could be attributed to 9 modifiable risk factors (RFs) worldwide. However, these conventional RFs may not fully explain this high risk of CAD among SAs. Therefore, attention has been directed toward nonconventional RFs. In this narrative review, we evaluate the conventional and emerging cardiovascular RFs characterizing SAs. These factors may explain the high morbidity and mortality among SAs. Further prospective studies are urgently needed to set algorithms for the optimal management of these RFs in high-risk populations like SAs.

Why Do South Asians Have High Risk for CAD?

South Asians have a higher risk for coronary artery disease (CAD) due to both pathophysiological and life course-related risk factors. We performed a literature search and used qualitative synthesis to present evidence for CAD risk factors among South Asians. A large proportion of the higher risk of South Asians for CAD can be explained by conventional risk factors. However, several conditioning factors such as education, socioeconomic status, and fetal programming, and early life influences may contribute to excess CAD risk in South Asians, suggesting the need for a life course approach. Evidence on unconventional risk factors is provocative but comes from small studies. Large-scale, well-designed epidemiological studies are needed for an in-depth understanding of the CAD risk among South Asians.

Plasma adiponectin does not correlate with insulin resistance and cardiometabolic variables in nondiabetic Asian Indian teenagers

OBJECTIVE

The objectives of this study were to determine age- and sex-specific concentrations of adiponectin in Asian Indian teenagers and adults and to assess whether its blood levels correlated with insulin resistance and other cardiometabolic parameters.

RESEARCH DESIGN AND METHODS

We studied 196 teenagers (94 boys, 102 girls) 12-18 years of age, selected from a cohort of 2,640 individuals from a cross-sectional school-based survey in Chennai, India. For comparison, adiponectin and plasma insulin were measured in 84 healthy adults. Correlation of adiponectin with plasma levels of insulin, proinsulin, insulin resistance, anthropometry, and family history of diabetes were studied.

RESULTS

Adiponectin showed a sex dimorphism, with girls having higher values (in microg/ml) (10.3 +/- 5.0) than boys (8.4 +/- 3.5) (P < 0.0001), and it showed a positive correlation with HDL cholesterol in boys only and not with other lipid parameters, insulin resistance, proinsulin, anthropometry, and family history of diabetes. In the adults, adiponectin correlated with fasting glucose and inversely with triglycerides.

CONCLUSIONS

In Asian Indian adults and teenagers, adiponectin did not correlate directly with measures of insulin sensitivity, overweight, and other cardiometabolic variables. This was at variance with several reports in other populations showing an inverse association of adiponectin with insulin resistance, proinsulin, and BMI, suggesting ethnic differences in the relationship of adiponectin with insulin sensitivity. The role of adiponectin in relation to action of insulin needs more detailed studies in Asian Indians.

[Diabetic cardiomyopathy--a type of coronary artery disease?]

Diabetic cardiomyopathy is a myocardial disease caused by diabetes mellitus unrelated to vascular and valvular pathology or systemic arterial hypertension. Clinical and experimental studies have shown that diabetes mellitus causes myocardial hypertrophy, apoptosis and necrosis, and increases interstitial tissue. The pathophysiology of diabetic cardiomyopathy is incompletely understood and several mechanistical approaches are under debate. Metabolic impairments like hyperglycemia, hyperlipidemia, hyperinsulinemia, and alterations in the cardiac metabolism lead to structural and functional changes which show cellular effects leading to increased oxidative stress, interstitial fibrosis, myocyte death, and disturbances in ion transport and homeostasis. Diastolic dysfunction which consecutively results in systolic dysfunction with increased left ventricular volume and reduced ejection fraction is an early diagnostic parameter. Treatment of diabetic cardiomyopathy does not differ from myocardiopathies of other etiologies and therefore has to follow the appropriate guidelines. Early intervention to reverse metabolic toxicity is the most effective method of prevention.

Reduced postprandial proinsulinaemia and 32-33 split proinsulinaemia after a mixed meal in type 2 diabetic patients following sensitization to insulin with pioglitazone

OBJECTIVE

Reduced insulin sensitivity associated with fasting hyperproinsulinaemia is common in type 2 diabetes. Proinsulinaemia is an established independent cardiovascular risk factor. The objective was to investigate fasting and postprandial release of insulin, proinsulin (PI) and 32-33 split proinsulin (SPI) before and after sensitization to insulin with pioglitazone compared to a group treated with glibenclamide.

DESIGN AND PATIENTS

A randomized double-blind placebo-controlled trial. Twenty-two type 2 diabetic patients were recruited along with 10 normal subjects. After 4 weeks washout, patients received a mixed meal and were assigned to receive pioglitazone or glibenclamide for 20 weeks, after which patients received another identical test meal. The treatment regimes were designed to maintain glycaemic control (HbA1c) at pretreatment levels so that beta-cells received an equivalent glycaemic stimulus for both test meals.

MEASUREMENTS

Plasma insulin, PI, SPI and glucose concentrations were measured over an 8-h postprandial period. The output of PI and SPI was measured as the integrated postprandial response (area under the curve, AUC).

RESULTS

Pioglitazone treatment resulted in a significant reduction in fasting levels of PI and SPI compared to those of the controls. Postprandially, pioglitazone treatment had no effect on the insulin AUC response to the meal but significantly reduced the PI and SPI AUCs. Glibenclamide increased fasting insulin and the postprandial insulin AUC but had no effect on the PI and SPI AUCs.

CONCLUSIONS

Sensitization to insulin with pioglitazone reduces the amount of insulin precursor species present in fasting and postprandially and may reduce cardiovascular risk.

Liver: an alarm for the heart?

BACKGROUND/AIMS

Fatty liver (FL) and coronary artery disease (CAD) have several risk factors in common, which are usually considered to account for their frequent coexistence. The independent association between FL and angiographic CAD was assessed in this case-control study by considering the contribution of their shared risk factors.

METHODS

Three hundred and seventeen adult patients who underwent elective coronary angiography (CAG) were recruited immediately after CAG and classified into either of the two groups A (normal or mildly abnormal CAG; n=85) or B (clinically relevant CAD; n=232). A liver sonography was performed on the same day as CAG.

RESULTS

The groups were significantly different in terms of gender, fasting blood glucose, low-density lipoproteins, diabetes (DM), hypertension and FL. In binary logistic regression, FL was the strongest independent predictor of CAD [P<0.001, odds ratio (OR)=8.48%, 95% confidence interval (CI)=4.39-16.40], followed by DM (P=0.002, OR=2.94) and male gender (P=0.014, OR=2.31). This pattern of associations did not change after clinically significant variables (waist-to-hip ratio, body mass index, triglycerides and high-density lipoproteins) were added to analysis.

CONCLUSION

Fatty liver seems to be a strong independent alarm for the presence of significant CAD.

Coronary artery disease in South Asians: an emerging risk group

Coronary artery disease (CAD) is a leading cause of morbidity and mortality worldwide and was responsible for 7.2 million deaths in 2003. Various studies have pointed out that South Asians have a higher prevalence of CAD as compared with other ethnicities. South Asians may have a genetic predisposition to CAD; however, environmental, nutritional, and lifestyle factors may also be responsible. South Asians have a much higher prevalence of metabolic syndrome, diabetes, insulin resistance (and resultant hyperinsulinemia), central obesity, dyslipidemias (lower high-density lipoprotein, increased lipoprotein[a], higher triglyceride levels), increased thrombotic tendency (increased plasminogen activator inhibitor-1 and decreased tissue plasminogen activator levels), decreased levels of physical activity, and low birth weights ("fetal origins hypothesis"). In addition, the dietary indiscretions and sedentary lifestyle practiced by most South Asians puts them at a higher risk. A multidisciplinary approach involving the population at risk, healthcare personnel, and the government is required to diminish the incidence. Educational programs regarding the genetic predisposition as well as risk factors for CAD, physical activity, and dietary modifications need to be encouraged. There is a need for implementation of newer guidelines as well as a lower threshold for initiating therapeutic interventions in this population. Mass media should be involved to bring about behavioral changes, and these changes should be reinforced at the physician's level.

High incidence of glucose intolerance in Asian-Indian subjects with acute coronary syndrome

OBJECTIVE

The risk of diabetes and coronary heart disease is high in Asian Indians. In this study, we aim to assess 1) the prevalence of hyperglycemia in incident acute coronary syndrome (ACS), 2) the effect of glycemia on the outcome, and 3) the association of plasma levels of insulin and proinsulin with ACS.

RESEARCH DESIGN AND METHODS

A total of 146 nondiabetic subjects (121 men, 25 women) with ACS admitted to two hospitals in 1 year were enrolled. Random blood glucose at admission and a standard oral glucose tolerance test within 3 days were done. Glucose tolerance was categorized as normal glucose tolerance, impaired glucose tolerance (IGT) or impaired fasting glucose, and diabetes. Diabetes was arbitrarily classified further as undiagnosed (HbA1c [A1C] >6.0%) or possibly stress diabetes (A1C <6.0%). Subjects not on antidiabetic treatment were reassessed with a glucose tolerance test between 1 and 2 months. Fasting plasma specific insulin, proinsulin, their molar ratios, and insulin resistance (homeostasis model assessment) were estimated at baseline.

RESULTS

Mean age of the cohort was 55 +/- 10.6 (SD) years. At baseline, 24 (16.4%) had normal glucose tolerance, 67 (45.9%) had IGT or impaired fasting glucose, and 55 (37%) had diabetes (35 [24%] were undiagnosed and 20 [13.7%] had stress diabetes). At follow-up, 53 of 92 responders (57.6%) continued to have IGT or diabetes. Mean baseline plasma insulin, proinsulin and its ratios, and insulin resistance were higher than normal in all subgroups.

CONCLUSIONS

Nondiabetic Asian Indians showed a high prevalence of hyperglycemia following ACS. ACS was associated with insulin resistance and increased levels of specific insulin, proinsulin, and high proinsulin-to-insulin ratios.

Application of monoclonal antibody-based sandwich enzymeimmunoassay in detection of human serum proinsulin

AIM: To develop a highly sensitive and specific ELISA to detect the human serum proinsulin, and to explore the relationship between proinsulin and cardiovascular risk factors in a population-based epidemiological study.

METHODS: The assay was based on two monoclonal antibodies, an anti-C-peptide antibody bound to a microtest plate and a biotin-labeled anti-insulin antibody. The biotin-avidin ELISA was used to measure the serum proinsulin of 1196 subjects who aged 35-59 in Pizhou, Jiangsu Province.

RESULTS: With a detection limit of 0.83 pmol/L, the ELISA covered a standard linear range of 0.83-142 pmol/L, and the human insulin and human C-peptide did not cross-react at 1 200 and 3 960 pmol/L respectively. The inter- and inner-assay coefficient of variation of the ELISA were less than 11.4% and 11.2% respectively. The results of the population-based epidemiological study indicated that the concentration of proinsulin had significantly positive correlations with body mass index (BMI), waist, systolic blood pressure (SBP), diastolic blood pressure (DBP), total cholesterol (TCH), triglycerides (TG), low density lipoprotein cholesterol (LDL-C), and cardiovascular risk factors clustering and negative association with high density lipoprotein cholesterol (HDL-C).

CONCLUSION: The monoclonal-based BA-ELISA can be used to detect serum proinsulin in the clinical and epidemiological study. The mechanism underlying the relationship between proinsulin and cardiovascular risk factors may be related to the fibrinolysis and damages of β-cells.

Diabetic cardiomyopathy: evidence, mechanisms, and therapeutic implications

The presence of a diabetic cardiomyopathy, independent of hypertension and coronary artery disease, is still controversial. This systematic review seeks to evaluate the evidence for the existence of this condition, to clarify the possible mechanisms responsible, and to consider possible therapeutic implications. The existence of a diabetic cardiomyopathy is supported by epidemiological findings showing the association of diabetes with heart failure; clinical studies confirming the association of diabetes with left ventricular dysfunction independent of hypertension, coronary artery disease, and other heart disease; and experimental evidence of myocardial structural and functional changes. The most important mechanisms of diabetic cardiomyopathy are metabolic disturbances (depletion of glucose transporter 4, increased free fatty acids, carnitine deficiency, changes in calcium homeostasis), myocardial fibrosis (association with increases in angiotensin II, IGF-I, and inflammatory cytokines), small vessel disease (microangiopathy, impaired coronary flow reserve, and endothelial dysfunction), cardiac autonomic neuropathy (denervation and alterations in myocardial catecholamine levels), and insulin resistance (hyperinsulinemia and reduced insulin sensitivity). This review presents evidence that diabetes is associated with a cardiomyopathy, independent of comorbid conditions, and that metabolic disturbances, myocardial fibrosis, small vessel disease, cardiac autonomic neuropathy, and insulin resistance may all contribute to the development of diabetic heart disease.