Insulin sensitivity and Lp(alpha) concentrations in normoglycemic offspring of type 2 diabetic parents

Insulin Resistance Index and Proatherogenic Lipid Indices in the Offspring of People with Diabetes

<b><i>Background:</i></b> Diabetes mellitus and cardiovascular diseases significantly contribute to medical morbidity and mortality worldwide, especially in developing countries like Nigeria. Insulin resistance, a characteristic finding of type 2 diabetics and their offspring, is associated with an abnormal lipid metabolism and cardiovascular disease. <b><i>Aims:</i></b> This study therefore aims to determine the pattern of lipid biomarkers of atherogenesis and their relationship with insulin resistance index in young people with a family history of diabetes mellitus. <b><i>Methods:</i></b> This is a cross-sectional study carried out among 150 apparently healthy young adults between 18 and 25 years of age, including 76 with a family history of diabetes mellitus in first- and/or second-degree relatives (YWFH) and 74 with no family history of diabetes mellitus (YWoFH). Anthropometric characteristics, insulin resistance index, plasma glucose, fasting lipid profile (plasma total cholesterol, triglycerides [TG], high-density lipoprotein cholesterol, low-density lipoprotein cholesterol), and serum levels of insulin, lipoprotein(a) [Lp(a)], apolipoprotein B (ApoB), apolipoprotein A-1 (ApoA-1), and ApoB/ApoA-1 ratios were compared in the 2 groups. Plasma glucose, total cholesterol, high-density cholesterol, and TG were measured using standard methods. The Friedewald equation was used to calculate low-density cholesterol. Serum insulin, Lp(a) levels, ApoB, and ApoA-1 were also measured using standard assays. The insulin resistance index was determined using homeostatic model assessment (HOMA). Statistical analysis was performed using SPSS version 20.0. Comparisons between variables were performed using the Mann-Whitney U test, and correlations between variables were performed using Spearman rank correlation coefficients. The level of significance was set at <i>p</i> &#x3c; 0.05. <b><i>Results:</i></b> Offspring of diabetics (YWFH) had a significantly higher median BMI (<i>p</i> = 0.015), waist-to-hip ratio (WHR; <i>p</i> = 0.002), insulin resistance index (<i>p</i> = 0.038), total cholesterol (<i>p</i> = 0.017), TG (<i>p</i> = 0.004), Lp(a) (<i>p</i> = 0.045), ApoB (<i>p</i> = 0.002), and ApoB/ApoA-1 ratio (<i>p</i> = 0.001) than the age-matched control group with no family history of diabetes mellitus (YWoFH). There was no correlation between the insulin resistance index and each of the lipid biomarkers of atherogenesis except Lp(a), with which it was negatively correlated. <b><i>Conclusion:</i></b> This study demonstrates that a positive family history of type 2 diabetes mellitus is associated with a higher insulin resistance index and elevated atherogenic lipid indices; thus, a positive family history of diabetes mellitus in first or second-degree relatives when the index person is not diabetic confirms a significant cardiovascular risk.

Association of matrix γ-carboxyglutamic acid protein levels with insulin resistance and Lp(a) in diabetes: A cross-sectional study

AIMS

The risk of cardiovascular disease (CVD) and mortality is increased in patients with chronic kidney disease (CKD), with a background role of vascular calcification in the development of CVD also reported. Studies have demonstrated that high lipoprotein(a) (Lp(a)) levels accelerate the development of atherosclerolsis and are potentially involved in the vascular calcification. Matrix Gla Protein (MGP) seems to play an important role in vascular calcification. The aim of the study was to examine the potential association of MGP concentrations with Lp(a) and insulin resistance.

METHODS

The study involved 100patients divided in four groups: 25 with both CKD stage 4 and Type2 Diabetes (DM) (Group-A), 25 with CKD4 without DM (Group-B), 25 non uremic patients with DM (Group-C) and 25 healthy subjects (Group-D). Serum glucose, Lp(a), MGP, plasma HBA1c and insulin were measured in all patients. Insulin resistance was estimated by the homeostasis model assessment equation (HOMA-IR).

RESULTS

A significant positive linear association between MGP and Lp(a) levels (r=0.272, p=0.006) was noted, as well as between MGP and HOMA-IR levels (r=0.308, p=0.002). However, no significant linear association between Lp(a) and HOMA-IR levels was recorded. A similar positive association between MGP and insulin levels (r=0.204, p=0.042) was also found.

CONCLUSION

This study concluded that diabetes coexisting with renal disease leads to extreme vascular calcification expressed by elevated MGP levels, resulting in higher frequency of cardiovascular disease in comparison to CKD patients without diabetes. The detected Lp(a) and MGP association in CKD4 patients may also represent the key to the complicated mechanism of their coexisting accelerated atherosclerosis and vascular calcification.

Insulin inhibits human erythrocyte cAMP accumulation and ATP release: role of phosphodiesterase 3 and phosphoinositide 3-kinase

In non-erythroid cells, insulin stimulates a signal transduction pathway that results in the activation of phosphoinositide 3-kinase (PI3K) and subsequent phosphorylation of phosphodiesterase 3 (PDE3). Erythrocytes possess insulin receptors, PI3K and PDE3B. These cells release adenosine triphosphate (ATP) when exposed to reduced O(2) tension via a signaling pathway that requires activation of the G protein, Gi, as well as increases in cAMP. Although insulin inhibits ATP release from human erythrocytes in response to Gi activation by mastoparan 7 (Mas 7), no effect on cAMP was described. Here, we investigated the hypothesis that insulin activates PDE3 in human erythrocytes via a PI3K-mediated mechanism resulting in cAMP hydrolysis and inhibition of ATP release. Incubation of human erythrocytes with Mas 7 resulted in a 62 +/- 7% increase in cAMP (n = 9, P < 0.05) and a 306 +/- 69% increase in ATP release (n = 9, P < 0.05), both of which were attenuated by pre-treatment with insulin. Selective inhibitors of PDE3 (cilostazol) or PI3K (LY294002) rescued these effects of insulin. These results support the hypothesis that insulin activates PDE3 in erythrocytes via a PI3K-dependent mechanism. Once activated, PDE3 limits Mas 7-induced increases in intracellular cAMP. This effect of insulin leads, ultimately, to decreased ATP release in response to Mas 7. Activation of Gi is required for reduced O(2) tension-induced ATP release from erythrocytes and this ATP release has been shown to participate in the matching of O(2) supply with demand in skeletal muscle. Thus, pathological increases in circulating insulin could, via activation of PDE3 in erythrocytes, inhibit ATP release from these cells, depriving the peripheral circulation of one mechanism that could aid in the regulation of the delivery of O(2) to meet tissue metabolic need.

Defects in oxygen supply to skeletal muscle of prediabetic ZDF rats

In humans, prediabetes is characterized by marked increases in plasma insulin and near normal blood glucose levels as well as microvascular dysfunction of unknown origin. Using the extensor digitorum longus muscle of 7-wk inbred male Zucker diabetic fatty rats fed a high-fat diet as a model of prediabetes, we tested the hypothesis that hyperinsulinemia contributes to impaired O(2) delivery in skeletal muscle. Using in vivo video microscopy, we determined that the total O(2) supply to capillaries in the extensor digitorum longus muscle of prediabetic rats was reduced to 64% of controls with a lower O(2) supply rate per capillary and higher O(2) extraction resulting in a decreased O(2) saturation at the venous end of the capillary network. These findings suggest a lower average tissue Po(2) in prediabetic animals. In addition, we determined that insulin, at concentrations measured in humans and Zucker diabetic fatty rats with prediabetes, inhibited the O(2)-dependent release of ATP from rat red blood cells (RBCs). This inability to release ATP could contribute to the impaired O(2) delivery observed in rats with prediabetes, especially in light of the finding that the endothelium-dependent relaxation of resistance arteries from these animals is not different from controls and is not altered by insulin. Computational modeling confirmed a significant 8.3-mmHg decrease in average tissue Po(2) as well as an increase in the heterogeneity of tissue Po(2), implicating a failure of a regulatory system for O(2) supply. The finding that insulin attenuates the O(2)-dependent release of ATP from RBCs suggests that this defect in RBC physiology could contribute to a failure in the regulation of O(2) supply to meet the demand in skeletal muscle in prediabetes.

Beta cell (dys)function in non-diabetic offspring of diabetic patients

AIMS/HYPOTHESIS

The first-degree offspring of patients with type 2 diabetes are prone to develop type 2 diabetes, and have both insulin resistance and beta cell impairment. However, it is still unclear whether both pathophysiological features are inseparably combined and which is the outstanding determinant in the offspring.

METHODS

Glucose metabolism, insulin sensitivity (calculated as M value divided by insulin [M/I]) and beta cell function were studied in the offspring of individuals with type 2 diabetes (n = 187; 57% females; age 43.8 +/- 8.1 years; BMI 26.8 +/- 4.5 kg/m(2)) and in individuals without a family history of type 2 diabetes (controls, n = 519, 55% females; age 43.4 +/- 8.2 years; BMI 26.4 +/- 3.7 kg/m(2), no significant differences between the groups for any characteristic) by performance of 75 g OGTT and 2 h hyperinsulinaemic (40 mU min(-1) m(-2))-isoglycaemic clamp tests. Beta cell function was evaluated by calculating insulinogenic index (IGI) from C-peptide AUC:glucose AUC ratios from the first hour of OGTT (IGI[60 min]) and from the total OGTT (IGI[120 min]).

RESULTS

During the OGTT, the offspring of individuals with type 2 diabetes showed 4-14% higher plasma glucose from 30 to 120 min (p < 0.05) and 20-29% higher serum insulin from 90 to 120 min, but decreased IGI(60 min) and IGI(120 min) (p < 0.05). M/I was 11% lower in the offspring of affected individuals than in controls (p < 0.01). To study the offspring of patients with type 2 diabetes with insulin sensitivity similar to that of the control group, the offspring of affected patients were divided into M/I quartiles. Those in the third M/I quartile showed M/I values and major anthropometric characteristics similar to those of the controls, but insulin AUC and C-peptide AUC values were lower in the first hour and the total OGTT (p < 0.05). The third M/I quartile had lower IGI values at 60 min and 120 min: 11% and 14% lower, respectively (p < 0.02).

CONCLUSIONS/INTERPRETATION

The first-degree offspring of type 2 diabetic patients show insulin resistance and beta cell dysfunction in response to oral glucose challenge. Beta cell impairment exists in insulin-sensitive offspring of patients with type 2 diabetes, suggesting beta cell dysfunction to be a major defect determining diabetes development in diabetic offspring.