Insulin sensitivity, and β-cell function in relation to hemoglobin A1C

Low-density lipoprotein cholesterol levels are associated with first-phase insulin release

AIMS

Prior studies provided evidence that low-density lipoprotein (LDL)-cholesterol-lowering statins reduce cardiovascular events while conveying an increased risk of type 2 diabetes. The aim of this study was to investigate the association between LDL levels and both insulin sensitivity and insulin secretion in a cohort of 356 adult first-degree relatives of patients with type 2 diabetes.

METHODS

Insulin sensitivity was assessed by euglycemic hyperinsulinemic clamp and first-phase insulin secretion was measured by both intravenous glucose tolerance test (IVGTT) and OGTT.

RESULTS

LDL-cholesterol levels were not independently associated with insulin-stimulated glucose disposal. After adjusting for several potential confounders, LDL-cholesterol concentration exhibited a positive independent association with acute insulin response (AIR) during IVGTT and with the OGTT derived Stumvoll first-phase insulin secretion index. When insulin release was adjusted for the underlying degree of insulin sensitivity, using the disposition index (AIR × insulin-stimulated glucose disposal), β-cell function was significantly associated with LDL-cholesterol levels, even after further adjusting for several potential confounders.

CONCLUSIONS

The present results suggest that LDL cholesterol is a positive modulator of insulin secretion. The deterioration in glycemic control observed during treatment with statins might thus be explained by an impairment in insulin secretion due to the cholesterol-lowering effect of statins.

An insight into the mechanisms of COVID-19, SARS-CoV2 infection severity concerning β-cell survival and cardiovascular conditions in diabetic patients

A significantly high percentage of hospitalized COVID-19 patients with diabetes mellitus (DM) had severe conditions and were admitted to ICU. In this review, we have delineated the plausible molecular mechanisms that could explain why there are increased clinical complications in patients with DM that become critically ill when infected with SARS-CoV2. RNA viruses have been classically implicated in manifestation of new onset diabetes. SARS-CoV2 infection through cytokine storm leads to elevated levels of pro-inflammatory cytokines creating an imbalance in the functioning of T helper cells affecting multiple organs. Inflammation and Th1/Th2 cell imbalance along with Th17 have been associated with DM, which can exacerbate SARS-CoV2 infection severity. ACE-2-Ang-(1-7)-Mas axis positively modulates β-cell and cardiac tissue function and survival. However, ACE-2 receptors dock SARS-CoV2, which internalize and deplete ACE-2 and activate Renin-angiotensin system (RAS) pathway. This induces inflammation promoting insulin resistance that has positive effect on RAS pathway, causes β-cell dysfunction, promotes inflammation and increases the risk of cardiovascular complications. Further, hyperglycemic state could upregulate ACE-2 receptors for viral infection thereby increasing the severity of the diabetic condition. SARS-CoV2 infection in diabetic patients with heart conditions are linked to worse outcomes. SARS-CoV2 can directly affect cardiac tissue or inflammatory response during diabetic condition and worsen the underlying heart conditions.

Hemorheological alterations in adults with prediabetes identified by hemoglobin A1c levels

BACKGROUND AND AIMS

A link between increased blood viscosity and type 2 diabetes has been previously reported. Herein, we investigated the association of blood viscosity with prediabetes, identified by glycated hemoglobin A1c (HbA1c) according to the new American Diabetes Association criteria, and subclinical atherosclerosis.

METHODS AND RESULTS

The study cohort includes 1136 non-diabetic adults submitted to anthropometrical evaluation, an oral glucose tolerance test and ultrasound measurement of carotid intima-media thickness (IMT). Whole blood viscosity was estimated using a validated formula based on hematocrit and total plasma proteins. After adjusting for age, and gender, individuals with HbA1c-defined prediabetes (HbA1c 5.7-6.4% [39-47 mmol/mol]) exhibited significantly higher values of hematocrit, and predicted blood viscosity as compared with controls. Increased levels of IMT were observed in subjects with HbA1c-defined prediabetes in comparison to controls. Predicted blood viscosity was positively correlated with age, waist circumference, blood pressure, cholesterol, triglycerides, fibrinogen, white blood cell, HbA1c, fasting and 2-h post-load glucose levels, fasting insulin, IMT and inversely correlated with HDL and Matsuda index of insulin sensitivity. Of the three glycemic parameters, i.e. HbA1c, fasting and 2-h post-load glucose, only HbA1c showed a significant correlation with predicted blood viscosity (β = 0.054, P = 0.04) in a multivariate regression analysis model including multiple atherosclerosis risk factors.

CONCLUSION

The study shows that individuals with HbA1c-defined prediabetes have increased predicted blood viscosity and IMT. The HbA1c criterion may be helpful to capture individuals with an increased risk of diabetes and cardiovascular disease who may benefit from an intensive lifestyle intervention.

Association between hemoglobin glycation index with insulin resistance and carotid atherosclerosis in non-diabetic individuals

Hemoglobin glycation index (HGI), defined as the difference between the observed HbA1c value and the value of HbA1c predicted from plasma glucose levels, represents a measure of the degree of non-enzymatic glycation of hemoglobin and it has been found to be positively associated with micro- and macro-vascular complications in subjects with type 2 diabetes. To investigate the pathophysiological abnormalities responsible for the increased cardiovascular risk of patients with higher HGI, we evaluated the association of HGI with cardio-metabolic characteristics in nondiabetic offspring of type 2 diabetic individuals. Insulin sensitivity, measured by a hyperinsulinemic-euglycemic clamp, cardio-metabolic risk factors including lipid profile, uric acid and inflammatory factors, and ultrasound measurement of carotid intima-media thickness (IMT) were assessed in 387 nondiabetic individuals. Participants were stratified in tertiles according to HGI (high, moderate and low). As compared with subjects with low HGI, those with high HGI displayed an unfavorable cardio-metabolic risk profile having significantly higher values of BMI, waist circumference, triglycerides, uric acid, fasting insulin, inflammatory markers, such as high sensitivity C reactive protein, erythrocytes sedimentation rate, complement C3, fibrinogen, and white blood cell count, and carotid IMT, and lower HDL and insulin-stimulated glucose disposal. In a linear regression analysis model including several atherosclerotic risk factors such as gender, age, BMI, inflammatory factors, lipid profile, insulin-stimulated glucose disposal, fasting insulin, uric acid, and blood pressure, HGI was the major predictor of IMT (β = 0.35; P = 0.001). In a logistic regression analysis adjusted for confounders, individuals with high HGI showed a 2.7-fold increased risk of vascular atherosclerosis (OR 2.72, 95%CI 1.01-7.37) as compared with subjects with low HGI. The present findings support the notion that HGI may be a useful tool to identify a subset of nondiabetic individuals conceivably harboring a higher risk of cardiovascular disease.

One-hour post-load hyperglycemia combined with HbA1c identifies pre-diabetic individuals with a higher cardio-metabolic risk burden

BACKGROUND AND AIMS

Evidence suggests that combining 1-hour plasma glucose ≥155 mg/dl during an oral glucose tolerance test (OGTT) with glycosylated hemoglobin (HbA1c) significantly increases their predictive power for incident diabetes, while their individual and joint associations with cardio-metabolic risk factors remain undefined. Herein, we evaluated whether 1-hour post-load plasma glucose ≥155 mg/dl combined with HbA1c may identify pre-diabetic individuals with a higher cardio-metabolic risk.

METHODS

Anthropometric and metabolic characteristics, insulin sensitivity and insulin secretion assessed by OGTT-derived indexes, carotid intima-media thickness (IMT), pulse pressure, and rate pressure product were evaluated in 1495 individuals.

RESULTS

As compared with subjects with 1-hour post-load glucose <155 mg/dl, individuals with 1-hour post-load glucose ≥155 mg/dl exhibited a significantly worse cardio metabolic profile, both in the group with HbA1c <5.7%, and in the group with prediabetes (HbA1c 5.7-6.4%). Specifically, in both groups, subjects with 1-hour post-load glucose ≥155 mg/dl had higher fasting and 2-h post-load glucose (p < 0.0001 for all in both groups), higher HOMA-IR (p < 0.0001 in both groups), and carotid IMT (p = 0.05 in the group with HbA1c <5.7% and p = 0.03 in the group HbA1c 5.7-6.4%), as well as lower Matsuda index, insulinogenic index and disposition index (p < 0.0001 in both groups), and lower insulin-stimulated glucose disposal (p < 0.0001 in the group with HbA1c <5.7% and p = 0.03 in the group HbA1c 5.7-6.4%).

CONCLUSIONS

Hyperglycemia at 1-hour during an OGTT may be a useful tool to identify a subset of individuals within HbA1c-defined glycemic categories at higher risk of developing type 2 diabetes and cardiovascular disease.

Plasma complement C3 levels are associated with insulin secretion independently of adiposity measures in non-diabetic individuals

BACKGROUND AND AIMS

To evaluate if complement C3 is associated with insulin secretion, as suggested by recent in vitro studies, independently of confounders including adiposity measures.

METHODS AND RESULTS

1010 nondiabetic subjects were stratified into quartiles according to complement C3 values. Insulin secretion was assessed using indexes derived from oral glucose tolerance test (OGTT) in the whole study group and from intravenous glucose tolerance test (IVGTT) in a subgroup (n = 110). Significant differences between quartiles of C3 were observed in body mass index (BMI), waist, fat mass, blood pressure, total cholesterol, high density lipoprotein (HDL), triglycerides, fasting and 2-h post-load glucose, fasting insulin, C reactive protein (hsCRP), fibrinogen, aspartate aminotransferase (AST), alanine aminotransferase (ALT), complement C4, and insulin sensitivity with C3 quartiles exhibiting graded increases in cardio-metabolic risk factors. Differences in insulin secretion indexes between C3 quartiles remained significant after adjustment for age, gender, BMI, insulin sensitivity, blood pressure, total cholesterol, HDL, triglycerides, hsCRP, fibrinogen, and complement C4 levels (P < 0.0001). A multivariable regression analysis revealed that complement C3 is a contributor of insulin secretion, explaining 2.4% and 1.9% of variation of the Stumvoll index for first-phase and second-phase insulin secretion, respectively, and 2.1% of variation of the InsAUC30/GluAUC30 index, independently of gender, age, BMI, waist, fat mass, blood pressure, total cholesterol, HDL, triglycerides, hsCRP, fibrinogen, AST, ALT.

CONCLUSIONS

Complement C3 concentrations are associated with insulin secretion independently of important determinants of glucose homeostasis such as gender, age, adiposity, subclinical inflammation, and insulin sensitivity.

Association between glycemic indices and beta cell function in patients with newly diagnosed type 2 diabetes

OBJECTIVE

To identify the relationship between glycemic indices and β cell function in patients with newly diagnosed type 2 diabetes.

METHODS

The cross-sectional analysis included 61 patients with newly diagnosed type 2 diabetes who received continuous glucose monitoring (CGM) for 72 hours. The association between β cell function and glycemic indices including A1C and glycemic variability was investigated.

RESULTS

A1C (r = -0.405, p = 0.001) and standard deviation of blood glucose (SDBG, r = -0.274, p = 0.032) were significantly correlated to HOMA-β cell function (HBCI), whereas mean amplitude of glycemic excursions (MAGE, r = -0.210, p = 0.104) was not informative. After multiple confounders adjustments, A1C (β = -7.35, p < 0.001), MAGE (β = -4.64, p = 0.040), and SDBG (β = -12.3, p = 0.012) were associated with HBCI.

CONCLUSION

A1C and glycemic variability were both associated with β cell function in patients with newly diagnosed type 2 diabetes. The main limitations of the present study are the cross-sectional design in nature and the limited sample size.