Higher C-Peptide Level During Glucose Clamp Is Associated With Muscle Insulin Resistance in Nonobese Japanese Men

Potential of Fasting C-peptide to Glucose Ratio and Triglyceride Glucose Index as Markers for β-Cell Dysfunction and Insulin Resistance in Patients With Type 2 Diabetes on Insulin Therapy

BACKGROUND

Pathogenesis of type 2 diabetes mellitus (T2DM) is combined from initial insulin resistance (IR) and subsequent β-cell dysfunction. Insulin therapy can replace β-cell function in advanced stages. However excessive insulin therapy increases IR and may expose the patients to risk of cardiovascular disease. We aim to assess β-cell function and IR in patients with type 2 diabetes on insulin therapy by fasting C-peptide to glucose ratio (FCPGR), and triglyceride glucose (TyG) index respectively to support treatment plans.

METHOD

A cross-sectional study was conducted at the Galiawa Diabetes and Endocrinology Teaching Center in Erbil City, Iraq, from June 2023 to January 2024. A convenient sample of 100 patients with T2DM on insulin-based therapy were included after obtaining informed written consent and excluding conditions such as acute illness, uncertain type of diabetes, etc. Each patient was evaluated for anthropometric parameters and current treatment details. Biochemical tests were then carried out to calculate metabolic syndrome (MetS) index score, FCPGR, and TyG index. Finally, patients were divided into four subgroups according to their FCPGR and TyG index and the data were analyzed statistically.

RESULT

The data showed those patients with sufficient β-cell function were 60 (60%), and patients with high TyG index were 95 (95%). There was a significant negative correlation between FCPGR and hemoglobin A1c (HbA1c) (p-value=0.001), while there was a positive correlation between TyG index and HbA1C (p-value=0.001). None of these markers were correlated with BMI (p-value=0.297, and 0.976), duration of T2DM (p-value=0.258, and 0.458), and dose of insulin therapy (p-value=0.901, and 0.477). Patients with sufficient β-cell function and high TyG index had the lowest HbA1C.

CONCLUSION

The study provides valuable insights into the utility of FCPGR and TyG index as biomarkers for β-cell function and insulin resistance in T2DM patients on insulin therapy. The significant correlation with HbA1C underscores their potential in clinical practice. However, the lack of correlation with BMI, disease duration, and insulin dose suggests that further investigation is needed to fully understand these biomarkers' implications across diverse patient profiles.

U-shaped association between plasma C-peptide and sarcopenia: A cross-sectional study of elderly Chinese patients with diabetes mellitus

Limited research exists regarding the relationship between fasting plasma C-peptide levels and sarcopenia. As a result, our study aimed to examine this association in elderly Chinese diabetic patients. This cross-sectional study included 288 elderly patients with diabetes mellitus from the Fourth People's Hospital in Guiyang who were enrolled prospectively between March 2020 and February 2023. The independent variable of interest was fasting plasma C-peptide, while the dependent variable was sarcopenia. Data on several covariates, including demographic factors, lifestyle habits, co-morbidities, anthropometric indicators, and laboratory indicators, were also collected. Of the 288 participants, 27.43% (79/288) had sarcopenia. After adjusting for potential confounding variables, we found a U-shaped association between fasting plasma C-peptide levels and sarcopenia, with inflection points identified at approximately 774 pmol/L and 939 mmol/L. Within the range of 50-744 pmol/L, each 100 pmol/L increase in CysC was associated with a 37% decrease in the odds of sarcopenia (odds ratio [OR], 0.63; 95% confidence interval [CI], 0.49 to 0.83; P < 0.001). Additionally, within the range of 939-1694 pmol/L, each 100 pmol/L increase in fasting plasma C-peptide was associated with a 76% increase in the odds of sarcopenia (odds ratio [OR], 1.76; 95% confidence interval [CI], 1.11 to 2.81; P = 0.017). Our study revealed a U-shaped association between fasting plasma C-peptide levels and the likelihood of sarcopenia, with lower risk in the range of 774-939 pmol/L. These findings may assist in the development of more effective prevention and treatment strategies for sarcopenia in elderly diabetic patients.

A Short-Term High-Fat Diet Worsens Insulin Sensitivity with Changes in Metabolic Parameters in Non-Obese Japanese Men

A short-term high-calorie high-fat diet (HCHFD) impairs insulin sensitivity in non-obese South Asian but not Caucasian men; however, the effect of short-term HCHFD on insulin sensitivity in East Asians is unknown. We recruited 21 healthy non-obese Japanese men to evaluate metabolic parameters and gut microbiota before and after 6-day HCHFD consisting of a regular diet plus a 45% energy excess with dairy fat supplementation. We evaluated tissue-specific insulin sensitivity and metabolic clearance rate of insulin (MCRI) using a two-step hyperinsulinemic euglycemic clamp, glucose tolerance using the glucose tolerance test, and measured ectopic fat in muscle and the liver using ¹H-magnetic resonance spectroscopy. The primary outcome of this study was insulin sensitivity measured by the clamp study. The secondary/exploratory outcomes were other metabolic changes. After HCHFD, levels of circulating lipopolysaccharide binding protein (LBP), a marker of endotoxemia, increased by 14%. In addition, intramyocellular lipid levels in the tibialis anterior and soleus and intrahepatic lipid levels increased by 47%, 31%, and 200%, respectively. Insulin sensitivity decreased by 4% in muscle and 8% in liver. However, even with reduced insulin sensitivity, glucose metabolism was maintained by increased serum insulin concentrations due to lower MCRI and higher endogenous insulin secretion during the clamp. Glucose levels during the meal tolerance test were comparable before and after HCHFD. In conclusion, short-term HCHFD impaired insulin sensitivity in the muscle and livers of non-obese Japanese men with increased LBP and ectopic fat accumulation. Elevated insulin levels from modulated insulin secretion and clearance might contribute to the maintenance of normal glucose metabolism during the clamp and meal tolerance test.

Reduction in C-Peptide Levels and Influence on Pharmacokinetics and Pharmacodynamics of Insulin Preparations: How to Conduct a High-Quality Euglycemic Clamp Study

Objective: The aim of the study was to investigate the different extent of inhibition of endogenous insulin secretion by the reduction of C-peptide levels in an euglycemic clamp study and its effects on the evaluation of pharmacokinetics, pharmacodynamics of insulin preparations, and quality of clamp study to determine the best reduction range of C-peptide levels. Methods: Healthy Chinese male volunteers were enrolled and underwent a single-dose euglycemic clamp test. Participants were subcutaneously injected with long-acting insulin glargine (0.4 IU/kg). Blood samples were collected pretest and up to 24 h post-test to assess pharmacokinetics (PK), pharmacodynamics (PD), and C-peptide levels. Results: We divided the 39 volunteers enrolled in the study into three groups according to the reduction of C-peptide levels: group A (ratio of C-peptide reduction <30%, n = 13), group B (ratio of C-peptide reduction between ≥ 30% and <50%, n = 15), and group C (ratio of C-peptide reduction ≥50%, n = 11); there were significant differences in the three groups (p = 0.000). The upper and lower limits of blood glucose oscillation in group C was statistically lower than the other groups, the range of oscillating glucose levels in group C was -17.0 ± 6.6% to -1.1 ± 6.7%. The AUC_0-24 h in groups A, B, and C were 9.7 ± 2.2, 11.0 ± 2.9, and 11.9 ± 2.1 ng/ml × min, respectively, which indicated an increasing trend in the three groups (P _trend = 0.041). For quality assessment, the average glucose (p = 0.000) and MEFTG (p = 0.001) levels in three groups were significantly different. Conclusion: The different extent of inhibition of endogenous insulin will influence the PK/PD of insulin preparations and the quality of the euglycemic clamp. Furthermore, the ratio of C-peptide reduction should be above 50% to free from the interference of endogenous insulin, and the range of blood glucose levels should be consistently maintained at -10% to 0 in the euglycemic clamp.

Serum C-X-C motif chemokine ligand 14 levels are associated with serum C-peptide and fatty liver index in type 2 diabetes mellitus patients

AIMS/INTRODUCTION

Recent studies have suggested C-X-C motif chemokine ligand 14 (CXCL14), secreted from adipose tissue, to play an important role in the pathogenesis of metabolic syndrome. However, the clinical significance of CXCL14 in humans has not been elucidated. This study aimed to assess correlations between serum CXCL14 levels and clinical parameters in patients with type 2 diabetes mellitus.

MATERIALS AND METHODS

In total, 176 individuals with type 2 diabetes mellitus were recruited. Serum CXCL14 concentrations were determined by enzyme-linked immunosorbent assay. We examined the associations of serum CXCL14 levels with laboratory values, abdominal computed tomography image information, surrogate markers used for evaluating the pathological states of diabetes, obesity and atherosclerosis.

RESULTS

Serum CXCL14 levels correlated positively with body mass index, waist circumference, subcutaneous and visceral fat areas, and serum alanine transaminase, uric acid, total cholesterol, low-density lipoprotein cholesterol, triglycerides and C-peptide (CPR) levels. In contrast, CXCL14 levels correlated inversely with age, pulse wave velocity and serum adiponectin levels. Multiple linear regression analysis showed serum levels of CPR (β = 0.227, P = 0.038) and the fatty liver index (β = 0.205, P = 0.049) to be the only parameters showing independent statistically significant associations with serum CXCL14 levels.

CONCLUSIONS

Serum CXCL14 levels were independently associated with serum CPR and fatty liver index in patients with type 2 diabetes mellitus. In these patients, a high serum CPR concentration might reflect insulin resistance rather than β-cell function, because CXCL14 showed simple correlations with obesity-related parameters. Collectively, these data suggested that serum CXCL14 levels in type 2 diabetes patients might be useful predictors of elevated serum CPR and hepatic steatosis.

Loss of Caveolin-1 Is Associated with a Decrease in Beta Cell Death in Mice on a High Fat Diet

Elevated free fatty acids (FFAs) impair beta cell function and reduce beta cell mass as a consequence of the lipotoxicity that occurs in type 2 diabetes (T2D). We previously reported that the membrane protein caveolin-1 (CAV1) sensitizes to palmitate-induced apoptosis in the beta pancreatic cell line MIN6. Thus, our hypothesis was that CAV1 knock-out (CAV1 KO) mice subjected to a high fat diet (HFD) should suffer less damage to beta cells than wild type (WT) mice. Here, we evaluated the in vivo response of beta cells in the pancreatic islets of 8-week-old C57Bl/6J CAV1 KO mice subjected to a control diet (CD, 14% kcal fat) or a HFD (60% kcal fat) for 12 weeks. We observed that CAV1 KO mice were resistant to weight gain when on HFD, although they had high serum cholesterol and FFA levels, impaired glucose tolerance and were insulin resistant. Some of these alterations were also observed in mice on CD. Interestingly, KO mice fed with HFD showed an adaptive response of the pancreatic beta cells and exhibited a significant decrease in beta cell apoptosis in their islets compared to WT mice. These in vivo results suggest that although the CAV1 KO mice are metabolically unhealthy, they adapt better to a HFD than WT mice. To shed light on the possible signaling pathway(s) involved, MIN6 murine beta cells expressing (MIN6 CAV) or not expressing (MIN6 Mock) CAV1 were incubated with the saturated fatty acid palmitate in the presence of mitogen-activated protein kinase inhibitors. Western blot analysis revealed that CAV1 enhanced palmitate-induced JNK, p38 and ERK phosphorylation in MIN6 CAV1 cells. Moreover, all the MAPK inhibitors partially restored MIN6 viability, but the effect was most notable with the ERK inhibitor. In conclusion, our results suggest that CAV1 KO mice adapted better to a HFD despite their altered metabolic state and that this may at least in part be due to reduced beta cell damage. Moreover, they indicate that the ability of CAV1 to increase sensitivity to FFAs may be mediated by MAPK and particularly ERK activation.

Disruption of fasting and post-load glucose homeostasis are largely independent and sustained by distinct and early major beta-cell function defects: a cross-sectional and longitudinal analysis of the Relationship between Insulin Sensitivity and Cardiovascular risk (RISC) study cohort

BACKGROUND/AIMS

Uncertainty still exists on the earliest beta-cell defects at the bases of the type 2 diabetes. We assume that this depends on the inaccurate distinction between fasting and post-load glucose homeostasis and aim at providing a description of major beta-cell functions across the full physiologic spectrum of each condition.

METHODS

In 1320 non-diabetic individuals we performed an OGTT with insulin secretion modeling and a euglycemic insulin clamp, coupled in subgroups to glucose tracers and IVGTT; 1038 subjects underwent another OGTT after 3.5 years. Post-load glucose homeostasis was defined as mean plasma glucose above fasting levels (δOGTT). The analysis was performed by two-way ANCOVA.

RESULTS

Fasting plasma glucose (FPG) and δOGTT were weakly related variables (stβ = 0.12) as were their changes over time (r = -0.08). Disruption of FPG control was associated with an isolated and progressive decline (approaching 60%) of the sensitivity of the beta-cell to glucose values within the normal fasting range. Disruption of post-load glucose control was characterized by a progressive decline (approaching 60%) of the slope of the full beta-cell vs glucose dose-response curve and an early minor (30%) decline of potentiation. The acute dynamic beta-cell responses, neither per se nor in relation to the degree of insulin resistance appeared to play a relevant role in disruption of fasting or post-load homeostasis. Follow-up data qualitatively and quantitatively confirmed the results of the cross-sectional analysis.

CONCLUSION

In normal subjects fasting and post-load glucose homeostasis are largely independent, and their disruption is sustained by different and specific beta-cell defects.

Characteristics associated with elevated 1-h plasma glucose levels during a 75-g oral glucose tolerance test in non-obese Japanese men

Elevated 1-h plasma glucose (1h-PG; ≥155 mg/dL) during an oral glucose tolerance test is a risk factor for type 2 diabetes. However, the metabolic characteristics of non-obese Asians with elevated 1h-PG are unknown. Thus, we studied 59 non-obese Japanese men with normal glucose tolerance. We divided study participants into the Low 1h-PG group (<155 mg/dL) and the High 1h-PG group (≥155 mg/dL). We compared the metabolic characteristics of the groups, including tissue-specific insulin sensitivity measured using a two-step hyperinsulinemic-euglycemic clamp. Insulinogenic index and adiponectin levels were significantly lower in the High 1h-PG group than in the Low 1h-PG group. Other characteristics, including insulin sensitivity, adiposity and ectopic fat accumulation, were similar between the groups. In conclusion, non-obese Japanese men with high 1h-PG have impaired early-phase insulin secretion and lower adiponectin levels. Insulin resistance and abnormal fat distribution were not evident in this population.