Aging Affects Insulin Resistance, Insulin Secretion, and Glucose Effectiveness in Subjects with Normal Blood Glucose and Body Weight

AIM

Several studies have demonstrated that factors including diabetes, including insulin resistance (IR), glucose effectiveness (GE), and the first and second phase of insulin secretion (FPIS, SPIS) could easily be calculated using basic characteristics and biochemistry profiles. Aging is accompanied by deteriorations of insulin resistance (IR) and insulin secretion. However, little is known about the roles of aging in the different phases of insulin secretion (ISEC), i.e., the first and second phase of insulin secretion (FPIS, SPIS), and glucose effectiveness (GE).

METHODS

In total, 169 individuals (43 men and 126 women) recruited from the data bank of the Meei-Jaw (MJ) Health Screening Center and Cardinal Tien Hospital Data Access Center between 1999 and 2008, with a similar fasting plasma glucose (FPG: 90 mg/dL) and BMI (men: 23 kg/m², women 22 kg/m²) were enrolled. The IR, FPIS, SPIS, and GE were estimated using our previously developed equations shown below. Pearson correlation analysis was conducted to assess the correlations between age and four diabetes factors (DFs: IR, FPIS, SPIS, and GE). The equations that are used to calculate the DF in the present study were built and published by our group.

RESULTS

The age of the participants ranged from 18 to 78 years. Men had higher FPIS but lower HDL-C levels than women (2.067 ± 0.159, 1.950 ± 0.186 μU/min and 1.130 ± 0.306, 1.348 ± 0.357 mmol/dl, accordingly). The results of the Pearson correlation revealed that age was negatively related to the IR and GE in both genders (IR: r = -0.39, p < 0.001 for men, r = -0.24, p < 0.003 for women; GE: r = 0.66, p < 0.001 for men, r = 0.78, p < 0.001 for women). At the same time, the FPIS was also only found to be negatively correlated with age in females (r = -0.238, p = 0.003), but there was no difference in the SPIS and age among both genders.

CONCLUSIONS

We have found that in Chinese subjects with a normal FPG level (90 mg/dL) and body mass index (men: 23 kg/m², women: 22: kg/m²), age is negatively related to the IR and GE among both genders. Only the FPIS was found to be negatively related to age in women. The tightness of their relationships, from the highest to the lowest, are GE, FPIS, and IR. These results should be interpreted with caution because of the small sample size.

Changes in β-Cell Function in Offspring of Type-2 Diabetic Patients, as per Fasting and Two-Hour Plasma Glucose Levels

Background The changes in β-cell function in high-risk populations who are apparently in the normal glucose tolerant stage are still under investigation for designing earlier prevention strategies. This study analyzes changes in β-cell function and insulin sensitivity across fasting and two-hour glucose categories spanning normal glucose tolerance (NGT) to impaired glucose tolerance (IGT), in offspring of subjects with type-2 diabetes mellitus (T2DM) compared to the controls without a known family history of T2DM. Methods Offspring of T2DM patients (cases) and individuals without a family history of T2DM (controls) were the subjects for this cross-sectional study. All participants underwent a 75 g oral glucose tolerance test and blood samples were collected for plasma glucose, insulin, C-peptide and proinsulin, at zero, 30, 60, and 120 minutes.  Results A total of 358 cases (age 23.0 ± 10.8 years, 54% males) and 287 controls (age 28.4 ± 8.10 years, 65% males) were the subjects of this study. Cases and controls were divided into subgroups based on fasting and two-hour glucose categories spanning NGT to IGT. Compared to the reference category of controls (< 80 mg/dL for fasting glucose and < 84 mg/dL for two-hour glucose), cases with IGT had ~60% decline in both β-cell compensation (as measured as disposition index {0-120}) and insulin sensitivity (as measured as whole-body insulin sensitivity index {0-120}); adjusted for age, gender, and body mass index. From lower to higher fasting and two-hour glucose categories, there was a continuous and significant decline in β-cell compensation in both cases and controls. Significant reduction in first-phase insulin secretion, as measured as insulinogenic (0-30) index, was only observed among two-hour glucose categories, not among the fasting glucose categories. In the transition from late NGT cases to IGT cases, there was a significant decline in β-cell compensation, first-phase insulin secretion (more prominent than a decline in overall β-cell secretion) and the changes in whole-body insulin sensitivity were not statistically significant. Conclusions The decline in β-cell compensation was continuous and significant in offspring of subjects with type-2 diabetes and controls without a known family history of diabetes from early normal glucose tolerant ranges to impaired glucose tolerant ranges. Compared to the strictest glucose controlled category of controls, approximately 60% decline was observed in β-cell compensation and insulin sensitivity, in impaired glucose tolerant offspring of subjects with type-2 diabetes mellitus.

Patterns of Insulin Secretion During First-Phase Insulin Secretion in Normal Chinese Adults

BACKGROUND

The increase in diabetes worldwide is alarming. Decreased acute insulin response to intravenous glucose tolerance test (IVGTT) during first-phase insulin secretion (FPIS) is a characteristic of diabetes. However, knowledge of the insulin secretion characteristics identified by different time to glucose peak in subjects with different metabolic state is sparse.

AIMS

This study aimed to find different patterns of FPIS in subjects with normal glucose tolerance (NGT) and analyzed the relationship between insulin secretion patterns and the risk for development of type 2 diabetes mellitus (T2DM).

METHODS

A total of 126 subjects were divided into three groups during a 10-min IVGTT, including NGT with time to glucose peak after 3 min (G1, n = 21), NGT with time to glucose peak at 3 min (G2, n = 95), and prediabetes or diabetes with time to glucose peak at 3 min (G3, n = 10). Glucose, insulin, and C-peptide concentrations at 0, 3, 5, 7, and 10 min during the IVGTT were tested. IVGTT-based indices were calculated to evaluate the insulin secretion and insulin sensitivity.

RESULTS

Age, body mass index (BMI), waist-to-hip ratio, triglyceride (TG), and hemoglobin A1c (HbA1c) of subjects were gradually higher, while high-density lipoprotein cholesterol (HDL-C) was gradually lower from G1 to G3 (p for linear trend <0.05), and the differences between G1 and G2 were also statistically significant (p < 0.05). Glucose peak of most participants in G1 converged at 5 min, and the curves shape of insulin and C-peptide in G2 were the sharpest among three groups. There was no significant difference in all IVGTT-based indices between G1 and G2, but AUC_Ins, AUC_Ins/AUC_Glu, and △Ins₃/△Glu₃ in G2 were the highest, and the p-value for linear trend of those indices among three groups were statistically significant (p < 0.05).

CONCLUSIONS

Two patterns of FPIS were in subjects with NGT, while subjects with later time to glucose peak during FPIS might be less likely to develop T2DM in the future.

First-phase insulin secretion is positively correlated with alanine aminotransferase in young adults

BACKGROUND

Type 2 diabetes (T2D) is known to be one of the most prevalent diseases, and its prevalence is significantly associated with age and metabolic syndrome (MetS). Few studies have been conducted on liver function, MetS and insulin secretion among young adults.

OBJECTIVES

In the present study, we explored the relationship between the liver function enzyme - alanine aminotransferase (ALT) - and first-phase insulin secretion (FPIS) among young adults.

MATERIAL AND METHODS

There were 22,971 men and 28,740 women, aged 18-27 years, assigned to subgroups according to the presence of MetS and quartiles of ALT values. Simple correlation was applied to evaluate their relationship. The difference between the slopes of these relationships and FPIS were statistically analyzed with Chris's calculator.

RESULTS

Most values for metabolic parameters, including ALT and FPIS, were determined to be relatively high in individuals with MetS. By contrast, individuals with MetS had lower high-density-lipoprotein cholesterol (HDL-C) counts and FPIS. Similar results were observed in the quartiles of ALT. Significant positive results were also found in the linear model. Depending on the ALT level, the slope change of FPIS still demonstrated a positive correlation between ALT and FPIS. This correlation was stronger for men than for women.

CONCLUSIONS

A positive correlation between ALT and FPIS exists among young adults. Moreover, this correlation was stronger for men than for women. Both the cause and the effect require further investigation.

Influence of Diabetogenic Factors on Fasting and Postprandial Glucose Levels in Patients with Type 2 Diabetes Mellitus

Background: This study evaluated the relative influence of insulin resistance (IR), first-phase insulin secretion (FPIS), second-phase insulin secretion (SPIS), and glucose effectiveness (GE) in determining the difference between fasting plasma glucose (FPG) and postprandial plasma glucose (PPG) (ΔPG), in a Chinese population with type 2 diabetes (T2D) mellitus. Methods: In total, we enrolled 1213 participants with T2D (479 women). IR, FPIS, SPIS, and GE were estimated by using equations we built previously. ΔPG was defined as FPG - PPG. Results: The relative contribution of the four diabetogenic factors (DFs) was analyzed by multiple linear regression, and GE was the greatest contributor in the ΔPG value (β = 0.171, P < 0.001), whereas IR had the least influence on ΔPG (β = -0.040, P = 0.439). DFs were analyzed by using binary logistic regression to ascertain if ΔPG ≥0 (high fasting plasma glucose, HFG). Three models were built: Model 0: SPIS, Model 1: SPIS + FPIS, and Model 2: Model 1 + GE. Model 2 had the most accurate predictive power; the equation for Model 2 is P = 1/(1 - e^-x), where x = -11.88 + 312.89 × (GE) -1.22 × log(SPIS) +1.63 × log(FPIS). In this equation, P refers to the risk of HFG. Conclusions: For Chinese patients, GE had the most profound effect in determining ΔPG, followed by FPIS, SPIS, and IR. The model suggested that participants with high FPIS, SPIS, and GE would have a high incidence of HFG.

Characteristics of repaglinide and its mechanism of action on insulin secretion in patients with newly diagnosed type-2 diabetes mellitus

This study aims to compare the effect of repaglinide and metformin among Chinese patients with newly diagnosed diabetes, and explore the possible mechanisms by which repaglinide alters insulin secretion.Sixty subjects with glycated hemoglobin (HbA1c) < 10.0% were randomly selected to receive repaglinide or metformin monotherapy for 15 weeks. Blood glucose levels, glycemic variability, β-cell function, and first-phase insulin secretion were compared between these 2 groups at baseline and at 15 weeks. Mouse insulinoma (MIN-6) cells were divided into 3 groups: low glucose, high glucose, and repaglinide 50 nm groups. Cells and cell culture mediums were collected at different timepoints. The expression of pericentrin (PCNT), F-actin, and insulin were tested with immunofluorescence and enzyme-linked immunosorbent assay.All glycemic parameters and variability indexes significantly decreased from baseline to 15 weeks, while no significant difference was found between these 2 groups at baseline or at 15 weeks. Furthermore, there was no significant difference found in fasting insulin and postprandial insulin at baseline and at 15 weeks, while homeostasis model assessment β significantly increased. The first-phase glucose and insulin secretion of the intravenous glucose tolerance test improved in both groups, especially in the repaglinide group. Insulin, PCNT, and F-actin expression in MIN-6 cells decreased after 15 minutes of stimulation with repaglinide, while no difference was observed at 2, 6, and 12 hours. The insulin levels of the cell medium in the repaglinide group remained significantly higher at all timepoints.This study manifests that repaglinide has a noninferiority effect on the glycemic parameters of Chinese patients with newly diagnosed diabetes, when compared with metformin. The PCNT-F-actin pathway plays an important role in the repaglinide regulation process of on-demand insulin secretion.

Immediate enhancement of first-phase insulin secretion and unchanged glucose effectiveness in patients with type 2 diabetes after Roux-en-Y gastric bypass

Roux-en-Y gastric bypass surgery (RYGB) in patients with type 2 diabetes often leads to early disease remission, and it is unknown to what extent this involves improved pancreatic β-cell function per se and/or enhanced insulin- and non-insulin-mediated glucose disposal (glucose effectiveness). We studied 30 obese patients, including 10 with type 2 diabetes, 8 with impaired glucose tolerance, and 12 with normal glucose tolerance before, 1 wk, and 3 mo after RYGB, using an intravenous glucose tolerance test (IVGTT) to estimate first-phase insulin response, insulin sensitivity (Si), and glucose effectiveness with Bergman's minimal model. In the fasting state, insulin sensitivity was estimated by HOMA-S and β-cell function by HOMA-β. Moreover, mixed-meal tests and oral GTTs were performed. In patients with type 2 diabetes, glucose levels normalized after RYGB, first-phase insulin secretion in response to iv glucose increased twofold, and HOMA-β already improved 1 wk postoperatively, with further enhancements at 3 mo. Insulin sensitivity increased in the liver (HOMA-S) at 1 wk and at 3 mo in peripheral tissues (Si), whereas glucose effectiveness did not improve significantly. During oral testing, GLP-1 responses and insulin secretion increased regardless of glucose tolerance. Therefore, in addition to increased insulin sensitivity and exaggerated postprandial GLP-1 levels, diabetes remission after RYGB involves early improvement of pancreatic β-cell function per se, reflected in enhanced first-phase insulin secretion to iv glucose and increased HOMA-β. A major role for improved glucose effectiveness after RYGB was not supported by this study.

Effect of intensive insulin therapy on first-phase insulin secretion in newly diagnosed type 2 diabetic patients with a family history of the disease

Intensive insulin treatment is known to improve β-cell function in the majority of patients with newly diagnosed type 2 diabetes mellitus (T2DM), and family history (FH) is known to be an important independent risk factor for T2DM. Thus, the aim of the present study was to investigate the difference in first-phase insulin secretion and the effect of intensive insulin therapy on the improvement of β-cell function between T2DM patients with and without a FH of diabetes. Patients with newly diagnosed T2DM and healthy controls were divided into groups according to their FH of diabetes. Improvement in β-cell function was evaluated with an arginine stimulation test after two weeks of continuous subcutaneous insulin infusion (CSII). Compared with the control group, the level of fasting insulin and the homeostasis model assessment of insulin resistance (HOMA2-IR) were higher in the DM group, while the homeostasis model assessment of β-cell insulin secretion (HOMA2-%β) and the first-phase peak ratio were lower (P<0.05). In addition, the first-phase peak ratio in the FH- control group was higher compared with that in the FH+ control group (P=0.023). Following CSII, all the patients achieved excellent blood glucose control in 6.2±3.6 days, without severe adverse effects. In the DM groups, the fasting insulin level and HOMA2-IR were lower, while the HOMA2-%β and first-phase peak ratio were higher, when compared with the values prior to treatment, particularly in the FH- DM group. The HOMA2-%β in the FH+ DM group was lower compared with the FH- DM group (P=0.027). Therefore, T2DM patients with and without a FH of the disease were shown to have a good response to CSII in the improvement of insulin resistance and β-cell function; however, the improvements were less significant in patients with a FH compared with patients without a FH of diabetes.