Insulin and coronary artery disease: is syndrome X the unifying hypothesis?

Parental history of coronary artery disease among adults with hypothyroidism: Case controlled study

Background

Thyroid dysfunction has a negative impact on coronary artery diseases (CAD) through several changes in its risk factors like dyslipidemia, glucose intolerance, and components of metabolic syndrome. Parental history of premature CAD may be an important risk factor for their offspring.

Objective

To investigate whether overt and subclinical hypothyroidism and the risk of atherosclerosis are present in adults with parental history of CAD.

Materials and methods

This case control study included 135 hypothyroid patients and 100 age-sex matched controls. Data were analyzed regarding CAD risk factors, hormonal and biochemical measures including retinol Binding Protein-4, fasting serum insulin, high-sensitivity C-reactive protein, lipid profile, fasting serum glucose, and serum malondialdehyde.

Results

Parental history of CAD was significantly higher in overt hypothyroidism than subclinical group (P = 0.001). The level of RBP-4 in hypothyroid patients was significantly higher than euthyroid subjects (P = 0.03), and was higher in hypothyroid patients with positive parental history of CAD (p = 0.01). There were positive relationships between RBP-4 and related cardiovascular risk factors and with hypothyroidism, its sensitivity and specificity were 47.9% and 42.5% respectively. The positive predictive value was 60.8% and the negative predictive value was 30.4%. Hypothyroid patients with parental history of CAD had a risk of 3.7 times more than the euthyroid subjects.

Conclusions

In hypothyroidism patients, parental history of CAD is a predictor of future coronary events and the related risk factors. RBP-4 is positively correlated with waist circumference, BMI, lipid profile, High-sensitivity CRP, MDA, fasting serum glucose, fasting serum insulin, HOMA indices and TSH.

Acute hyperglycemia and oxidative stress: direct cause and effect?

Oxidative stress is increased in Type 2 diabetes and this appears to underlie the development of diabetic complications. Increased oxidative stress is claimed to be triggered directly by acute (sudden-onset) hyperglycemia, but published data do not clearly support a direct cause and effect relationship. In this article, published evidence of a direct prooxidant effect of acute hyperglycemia is presented and discussed in some detail, and conflicts, controversies, and problems are highlighted. Evidence for glucose variability as a possible important trigger of oxidative stress in diabetes is reviewed, with some speculation as to how the field would be advanced if there were more widespread recognition about the role that wide fluctuations in glucose concentration play in diabetic complications. Possible direct or indirect antioxidative effects of various drugs used in the treatment of diabetic subjects are discussed because these may have influenced current understanding of the link between hyperglycemia and oxidative stress. The aims are to reveal the divergence between the available evidence and the accepted view that acute hyperglycemia is a direct trigger of oxidative stress and to suggest areas of research that will help resolve current controversies in this important and challenging area.

On How Insulin May Influence Ageing and Become Atherogenic throughout the Insulin-Like Growth Factor-1 Receptor Pathway: In vitro Studies with Human Vascular Smooth Muscle Cells

BACKGROUND

It is known that growth factors play a role in ageing and atherogenesis, and insulin develops mitogenic activity in vitro.

OBJECTIVES

This study focuses on the pathway by which insulin induces proliferation and mobility in vascular smooth muscle cells (SMCs) compared with that of insulin-like growth factor-1 (IGF-1), because they are two basic phenomena for atherogenesis that could also help to understand the role of insulin in the ageing process.

METHODS

Bromodeoxyuridine DNA incorporation, chemotaxis and the appearance of membrane ruffles were measured in cultured SMCs after incubation with insulin or IGF-1 in the presence of insulin or IGF-1 receptor-blocking antibodies.

RESULTS

Insulin-induced SMC proliferation through the IGF-1 receptors; indeed, the blockade of insulin receptors does not inhibit the mitogenic influence of insulin. On the contrary, insulin-induced cell migration was inhibited by blocking the insulin receptor but not the IGF-1 receptor. Nevertheless, in less differentiated SMCs from non-confluent cultures, the migratory response was significantly higher and insulin lost its receptor specificity. It was stimulated through receptors both for insulin and IGF-1. In these cases the IGF-1 action was similar. Insulin-induced F-actin rearrangements took place through both types of receptors, but IGF-1 was a little more specific through its own receptors.

CONCLUSION

The pathway activated by insulin to induce SMC proliferation is not different from that of IGF-1, whereas the unspecific mechanism inducing mobility in growing cells seems to be related to a higher sensitivity response. Cells with the highest mitotic activity have the highest mobility in which stimulation of receptor specificity is lost for either insulin or IGF-1. Extrapolating these results to in vivo, insulin could become relevant for inducing stabilization and also side effects in ageing.

Reduced antioxidant status in obese children with multimetabolic syndrome

BACKGROUND

In our previous study, the negative correlation found between plasma insulin levels and plasma alpha-tocopherol concentrations suggested that decreased antioxidant vitamin levels and reduced antioxidant capacity might be a characteristic feature of obese children with multimetabolic syndrome (MMS).

OBJECTIVE

To investigate lipid-soluble antioxidant vitamin levels and total antioxidant status (TAS) in obese children with and without MMS and in controls.

SUBJECTS

In total, 16 control children (age: 16.2+/-1.1 y, BMI: 20.7+/-1.9 kg/m(2), body fat (BF): 25.6+/-5.7%; mean+/-s.d.), 15 obese children (age: 13.4+/-2.1 y, BMI: 34.2+/-3.1 kg/m(2), BF: 36.9+/-5.8%,) and 17 obese children without MMS (age: 14.4+/-2.3 y, BMI: 30.4+/-6.2 kg/m(2), BF: 36.3+/-5.8%) were included in the study.

METHODS

Body composition was determined by anthropometric methods. Vitamin analysis was carried out by high-performance liquid chromatography and TAS of the plasma was measured with commercially available kits. Plasma glucose, lipids and insulin were measured by standard laboratory methods.

RESULTS

Plasma alpha-tocopherol and beta-carotene levels corrected for plasma lipids (cholesterol + triglyceride) were significantly (P<0.05) lower in obese children with MMS (2.4 (3.1) micromol/mmol and 12.3 (24.0) pmol/mmol, respectively, median (range from the first to the third quartile)), than in the obese without MMS (3.7 (0.9) micromol/mmol and 48.2 (27.7) pmol/mmol) and in the control group (3.8 (0.7) micromol/mmol and 86.6 (44.5) pmol/mmol). Plasma TAS values of the MMS group (1.2 (0.4) mmol/l) were also significantly (P<0.05) reduced as compared to obese children without MMS (1.62 (0.14) mmol/l) and to controls (1.58 (0.21) mmol/l).

CONCLUSION

Obese children with MMS are prone to oxidative stress. Further investigations are necessary to determine if these children may benefit from vitamin E and beta-carotene supplementation.

Hormonal regulation of interleukin-6 production in human adipocytes

OBJECTIVE

To elucidate the hormonal regulation of interleukin-6 (IL-6) production by human adipose tissue and its relation to leptin.

DESIGN

In vitro study. Human adipocytes were incubated with dexamethasone (with or without RU486), norepinephrine and epinephrine (with or without propranolol), or insulin.

MEASUREMENTS

IL-6 and leptin secretion by human adipocytes.

RESULTS

A gradual increase in IL-6 secretion by adipocytes during differentiation was observed. A positive correlation was found between basal IL-6 release and both glycerol 3-phosphate dehydrogenase activity--a marker of adipocyte differentiation-and leptin release. Dexamethasone decreased IL-6 secretion and increased leptin secretion in a dose-dependent manner. Both catecholamines increased IL-6 and leptin secretion. The effects of dexamethasone and catecholamines on IL-6 and leptin were abrogated by RU486 and propranolol, respectively. Incubation with insulin resulted in a dose-dependent stimulation of IL-6 and leptin secretion.

CONCLUSIONS

IL-6 is produced by human adipocytes and is a potential marker of adipocyte differentiation. Furthermore it is a hormonally regulated cytokine, suppressed by glucocorticoids, and stimulated by catecholamines and insulin in physiological concentrations.

Where thiazolidinediones will fit

Individuals with type 2 diabetes have two defects: insulin resistance, which occurs in the first stages of disease progression, and pancreatic beta-cell failure, which occurs later in the disease. Insulin resistance is the major pathological defect. During the course of the disease, insulin levels are initially elevated to compensate for the increased insulin resistance and then decline as the disease progresses and beta-cells become less responsive. It is necessary to change antidiabetic therapies to address this progression. Current management of type 2 diabetes follows a stepwise treatment program of diet and exercise, monotherapy with oral antidiabetic agents, combination oral therapy and, ultimately, combination therapy with insulin to control blood glucose levels. While control of blood glucose will reduce the risk of microvascular complications, such as microalbuminuria and retinopathy, the incidence of macrovascular complications is not significantly reduced. The introduction of the thiazolidinediones (TZDs) or 'glitazones', a class of agents that offer effective glycemic control and work through the reduction of insulin resistance, offers a new strategy in the management of this condition. These agents have beneficial effects on the pancreatic beta-cell and, in addition, may have potential benefits on the macrovascular complications that commonly occur in these patients.

Hyperglycemia-induced ascorbic acid deficiency promotes endothelial dysfunction and the development of atherosclerosis

Dehydroascorbic acid, the oxidized form of vitamin C, is transported into mammalian cells via facilitative glucose transporters and hyperglycemia inhibits this process by competitive inhibition. This inhibited transport may promote oxidative stress and contribute to the increase in atherosclerotic cardiovascular disease observed in patients with diabetes mellitus. This review explores the importance of this proposed mechanism in light of current research. For example, recent reports suggest that administration of antioxidants, such as vitamin C, may slow atherogenesis by improving endothelium-dependent vasodilation in individuals with abnormal glucose and lipid metabolism, perhaps by preventing the oxidation of nitric oxide, an important regulator of vasomotor tone. Endothelial dysfunction plays a key role in the development of atherosclerosis and endothelial cells may be particularly affected by hyperglycemia-induced ascorbic acid deficiency as they line the interior of blood vessels. In addition, we discuss evidence of several other mechanisms by which vitamin C status may affect the development of atherosclerotic cardiovascular disease, particularly its inverse relationship to multiple cardiovascular disease risk factors and indicators. Given these factors, vitamin C administration is recommended during periods of both acute and chronic hyperglycemia to help preserve endothelial function.

Insulin-leptin-visceral fat relation during weight loss

INTRODUCTION

The relation between insulin-leptin-visceral fat axis during weight loss has not been studied previously.

AIMS

To evaluate the insulin, leptin, and abdominal adiposity relation during weight loss in patients with upper body obesity.

METHODOLOGY

Twenty volunteers (7 men, 13 women) with mean age 50.6+/-6.3 (SD) and upper body obesity (weight 105.4+/-12.3 kg, BMI 35.9+/-2.5 kg/m2) were recruited. Participants were enrolled in a one-arm clinical study using a calorie-deficient diet and an escalating dose regimen of sibutramine, starting with 5 mg daily and increasing in 5-mg increments to 20 mg per day. Body weight, insulin, leptin, glucose, lipids, abdominal computed tomography (CT), and total body electrical conductance (TOBEC) were measured serially at weeks 0, 4, 8, 12, and 24.

RESULTS

Eighteen patients completed the 6-month study: one man and one woman discontinued because of adverse events. With diet and sibutramine, body weight was significantly and continuously reduced throughout the 6-month study. There was a 16.0% (p = 0.0001) reduction in body weight (p < 0.001) and 22.5% (p = 0.0001) decrease in total body fat mass. Abdominal CT scans showed a 28.3% (p = 0.0001) reduction in total abdominal fat, a 26.0% (p = 0.0001) reduction in subcutaneous fat (p < 0.001), and a 31.0% (p = 0.0003) reduction in visceral fat (p < 0.001). There was a 32.0% (p = 0.0008) reduction in leptin levels and 37.9% (p = 0.0001) reduction in insulin levels between baseline and week 4, but no further significant reduction in leptin and insulin levels was observed for the duration of the study. There was a significant correlation between insulin and leptin concentrations throughout the study (p = 0.0001). Leptin was presented as a function of insulin measured at the same time. Significant associations between visceral abdominal fat, subcutaneous fat, and leptin were also observed.

CONCLUSION

In this study, we found that leptin and insulin were related in weight loss. The data suggest that insulin may act as a strong regulator of leptin secretion during weight loss and that circulating leptin levels can be predicted by insulin level. Using sibutramine in conjunction with hypocaloric diet reduced body weight and decreased fat mass significantly. Visceral and subcutaneous abdominal fat depots were shown to decrease. Whether sibutramine exerts any selective reduction of visceral abdominal fat as opposed to total body fat mass will require further clinical investigation.

Polyunsaturated fatty acids in plasma lipids of obese children with and without metabolic cardiovascular syndrome

Previously we reported significantly higher values of gamma-linolenic acid (GLA, 18:3n-6), dihomo-gamma-linolenic acid (DHGLA, 20:3n-6), and arachidonic acid (20:4n-6) in plasma lipid classes in obese children than in nonobese controls. In the present study, fatty acid composition of plasma phospholipids (PL) and sterol esters (STE) was determined by high-resolution capillary gas-liquid chromatography in obese children with and without metabolic cardiovascular syndrome [MCS: defined as simultaneous presence of (i) dyslipidemia, (ii) hyperinsulinemia, (iii) hypertension, and.(iv) impaired glucose tolerance] and in nonobese controls. Fatty acid composition of PL and STE lipids did not differ between obese children without MCS and controls. Obese children with MCS exhibited significantly lower linoleic acid (LA, 18:2n-6) values in PL (17.43 [2.36], % wt/wt, median [range from the first to the third quartile]) than obese children without MCS (19.14 [3.49]) and controls (20.28 13.80]). In contrast, PL GLA values were significantly higher in obese children with (0.13 [0.08]) than in those without MCS (0.08 [0.04]), whereas STE GLA values were higher in obese children with MCS (1.04 [0.72]) than in controls (0.62 [0.48]). DHGLA values in PL were significantly higher in obese children with MCS (4.06 [0.74]) than in controls (2.69 [1.60]). The GLA/LA ratio was significantly higher, whereas the AA/DHGLA ratio was significantly lower in obese children with MCS than in obese children without MCS and in controls. In this study, LA metabolism was affected only in obese children with but not in those without MCS. In obese children with MCS, delta6-desaturase activity appeared to be stimulated, whereas delta5-desaturase activity appeared to be inhibited. Disturbances in LA metabolism may represent an additional health hazard within the multifaceted clinical picture of MCS.

Combined use of insulin and endothelin-1 causes decrease of protein expression of beta-subunit of insulin receptor, insulin receptor substrate-1, and insulin-stimulated glucose uptake in rat adipocytes

Previously, we reported that insulin-stimulated glucose uptake (ISGU) can be inhibited by endothelin (ET-1). However, the mechanism by which ET-1 impairs ISGU in adipocytes remains unclear. This study investigated the effects of ET-1 on insulin action in rat adipocytes in order to elucidate the molecular mechanism of action of ET-1 on ISGU. The results show that ISGU was increased fivefold after 3-h treatment with 1 nM insulin. Treatment with 100 nM ET-1 had no effect on basal glucose uptake. However, ET-1 inhibited approximately 25% of ISGU and 20% of insulin binding after 3-h treatment in the presence of 1 nM insulin. Expression of the beta-subunit of the insulin receptor (IRbeta) and the insulin receptor substrate-1 (IRS-1) in adipocytes was not significantly affected by 1 nM insulin or by 100 nM ET-1, even after 3-h treatment. However, expressions of IRbeta and IRS-1 were dramatically decreased in a dose- and time-dependent manner when adipocytes were treated with both insulin and ET-1. Approximately 50% of IRbeta and 65% of IRS-1 expression levels were suppressed when adipocytes were simultaneously treated with both 1 nM insulin and 100 nM ET-1 for 3 h. These results suggest that the inhibitory effect of ET-1 on ISGU may be mediated via the insulin receptor and suppression of IRbeta/IRS-1 expression.

Hyperinsulinemic hypoalphalipoproteinemia as a new indicator for coronary heart disease

OBJECTIVES

The purpose of this study was to investigate the association among insulin resistance, high density lipoprotein cholesterol (HDL-C) and coronary heart disease (CHD), and to test the hypothesis that HDL-C may ameliorate the adverse effects of insulin.

BACKGROUND

Serum low HDL-C (hypoalphalipoproteinemia) and hyperinsulinemia are independent predictors for CHD, but a strong negative correlation exists between them, as in patients with syndrome X.

METHODS

Fifty-four pairs of cases (M/F: 49/5), defined as patients with angiographically proved CHD, and control subjects (M/F: 49/5) matched with cases with regard to gender and age were included. Insulin resistance was assessed by the homeostasis model assessment (HOMA).

RESULTS

Cases had increased HOMA insulin resistance and lower serum levels of HDL-C than controls. A receiver operating characteristic (ROC) curve analysis indicated that HDL-C and insulin resistance were significant discriminators of CHD (area under ROC curve: 0.72 and 0.69, respectively). The interaction between HDL-C and the association of insulin resistance with CHD was significant: subjects with hyperinsulinemia and high HDL-C had no increased risk of CHD. Multivariate conditional logistic regression analysis showed that hyperinsulinemic hypoalphalipoproteinemia was a stronger indicator for CHD than either HDL-C or insulin resistance alone (-2 log likelihood: 19.0 vs. 12.6 or 15.7).

CONCLUSIONS

Hyperinsulinemic hypoalphalipoproteinemia was a more potent indicator for CHD than either insulin resistance or low serum HDL-C levels alone, and the adverse effects of hyperinsulinemia seem to be ameliorated by high HDL-C levels.