Analysis of factors influencing glucose tolerance in Japanese patients with non-alcoholic fatty liver disease

Dietary Nε-(carboxymethyl)lysine is a trigger of non-alcoholic fatty liver disease under high-fat consumption

The irreversible glycation of proteins produces advanced glycation end products (AGEs) which are triggered to bind the receptor for AGE (RAGE), thereby activating mitogen-activated protein kinase/nuclear factor-κB signaling pathway and stimulating proinflammatory cytokines, ultimately leading to chronic disorders. In this study, we focus the promoting effect of Nε-carboxymethyl-lysine (CML), one of the most dietary AGEs, on non-alcoholic fatty liver disease (NAFLD) and evaluated NAFLD-related biomarkers. Oxidative stress and hepatic steatosis were assessed in oleic acid (OA)-induced HepG2 cells. Using OA-induced HepG2 cells, we show that CML results in oxidative stress and steatosis and drives major changes in hepatic lipid metabolism. Administration of CML exacerbated NAFLD-related symptoms by increasing body and liver weight gain, serum alanine aminotransferase and lipid levels, and insulin resistance in mild high-fat diet-induced mice. Moreover, hepatic histological analysis data, such as staining, western blotting, and RNA-seq, indicate that CML aggravates NAFLD in association with activation of the de novo lipogenesis pathway, consistent with the in vitro assays. Our findings could contribute to model studies related to the prevention and treatment of NAFLD progression due to excessive consumption of dietary AGEs.

The common variant of rs6214 in insulin like growth factor 1 (IGF1) gene: a potential protective factor for non-alcoholic fatty liver disease

PURPOSE

Regarding the central role of insulin resistance in NAFLD, we explored whether insulin-like growth factor 1 (IGF1) and insulin-like growth factor-binding protein 3 (IGFBP3) gene variants were associated with NAFLD susceptibility.

METHODS

IGF1 (rs6214) and IGFBP3 (rs3110697) gene variants were genotyped in 154 cases with biopsy-proven NAFLD and 156 controls using PCR-RFLP method.

RESULTS

The IGF1 rs6214 "AA + AG" genotype compared with the "GG" genotype appeared to be a marker of decreased NAFLD susceptibility (p = .006; OR = 0.47, 95%CI = 0.28-0.80). Furthermore, the IGF1 rs6214 "A" allele was underrepresented in the cases than controls (p = .024; OR = 0.61, 95%CI = 0.40-0.94). However, we observed no significant difference in genotype or allele frequencies between the cases and controls for IGFBP3 gene.

CONCLUSIONS

To our knowledge, these findings suggest, for the first time, that the IGF1 rs6214 "A" allele and "AA + AG" genotype have protective effects for NAFLD susceptibility. Nonetheless, further studies are needed to validate our findings.

RESISTIN GENE POLYMORPHISM AND NONALCOHOLIC FATTY LIVER DISEASE RISK

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) is a chronic liver disease and one of the main global health issues in which liver fat surpasses 5% of hepatocytes without the secondary causes of lipid accumulation or excessive alcohol consumption. Owing to the link between NAFLD and insulin resistance (IR) and obesity and the role of resistin in theses metabolic disorders, we explored the possible association between resistin gene (RETN) variant and NAFLD.

METHODS

A total of 308 unrelated subjects, including 152 patients with biopsy-proven NAFLD and 156 controls were enrolled and genotyped for the RETN gene rs3745367 variant using PCR-RFLP method.

RESULTS

NAFLD patients had higher liver enzymes, systolic blood pressure (SBP), and diastolic blood pressure (DBP) than the controls (P<0.001). However, we observed no significant difference in genotype and allele frequencies between the cases with NAFLD and the controls for the RETN rs3745367 polymorphism either before or after adjustment for confounding factors including age, BMI, sex, smoking status, SBP, and DBP.

CONCLUSION

To our knowledge, this study is the first one that investigated the association between RETN gene rs3745367 variant and biopsy-proven NAFLD. Our findings do not support a role for this gene polymorphism in NAFLD risk in Iranian population; nonetheless, they need to be further investigated in other populations.

INSULIN AND INSULIN RECEPTOR GENE POLYMORPHISMS AND SUSCEPTIBILITY TO NONALCOHOLIC FATTY LIVER DISEASE

ABSTRACT BACKGROUND: Nonalcoholic fatty liver disease (NAFLD) is an increasing global health concern defined by excessive hepatic fat content in the absence of excessive alcohol consumption. OBJECTIVE: Given the pivotal role of insulin resistance in NAFLD, we hypothesized that insulin (INS) and insulin receptor (INSR) gene polymorphisms may be associated with NAFLD risk. METHODS: A total of 312 subjects, including 153 cases with biopsy-proven NAFLD and 159 controls were enrolled in this case-control study. Four polymorphisms in INS (rs3842752, rs689) and INSR (rs1052371, rs1799817) genes were genotyped using PCR-RFLP method. RESULTS: The cases with NAFLD were older and had higher BMI, systolic blood pressure, diastolic blood pressure, as well as higher serum levels of aspartate aminotransferase, alanine aminotransferase, and gamma glutamyl transferase than the controls (P<0.001). The “TT” genotype of INSR rs1799817 compared with “CC” genotype occurred more frequently in the controls than the cases with NAFLD and the difference remained significant after adjustment for confounding factors (P=0.018; OR=0.10, 95%CI=0.02-0.76). However, no significant difference was found for INS rs3842752, INS rs689, and INSR rs1052371 gene polymorphisms between the cases with NAFLD and the controls either before or after adjustment for the confounders. CONCLUSION: These findings corroborate the hypothesis that genetic polymorphisms related to insulin resistance play a role in NAFLD susceptibility. Specifically, the INSR rs1799817 “TT” genotype had a protective effect for NAFLD. However, our results remain to be validated in other studies.

Undercarboxylated osteocalcin correlates with insulin secretion in Japanese individuals with diabetes

BACKGROUND

Undercarboxylated osteocalcin (ucOC) is a secreted protein produced by osteoblasts that regulates insulin secretion and insulin sensitivity in rodents. However, the significance of these effects on glucose metabolism in human remains unknown. Moreover, the pathophysiological roles of ucOC on varying degrees of glucose intolerance, including diabetes need to be elucidated. In the present study, correlations between ucOC and indices of insulin secretion and sensitivity were analyzed in normal glucose tolerance (NGT), impaired glucose metabolism (IGM), and diabetes mellitus (DM) groups.

METHODS

Based on 75 g OGTT data in Japanese individuals without diabetic medication, or medications which may affect ucOC levels, individuals were classified as having normal glucose tolerance (NGT), impaired glucose metabolism (IGM), or diabetes (DM). In each group, 25 individuals were consecutively recruited [total 75 individuals, age: 65 ± 11 (mean ± SD); BMI: 24.9 ± 3.8 kg/m²]. QUICKI and Matsuda index (MI) were calculated as insulin sensitivity indices. Homeostasis model assessment (HOMA)-β and insulinogenic index (IGI) were calculated as insulin secretion indices. UcOC was measured using ECLIA. Normally-distributed log_e-transformed (ln-) values were used for ucOC, HOMA-β, IGI, and MI.

RESULTS

The ucOC was not significantly different among the three groups. The results of multiple regression analysis showed that ln-ucOC did not significantly correlate with age, sex, BMI, waist circumference, fasting plasma glucose, plasma glucose 120 min after glucose loading, fasting plasma immunoreactive insulin, ln-HOMA-β, QUICKI, or ln-MI in any of the three groups. Interestingly, ln-ucOC correlated with ln-IGI (r = 0.422, P = 0.0354) and HbA1c (r = - 0.574, P = 0.0027) only in the DM group. There was no significant correlation between ln-IGI and age, sex, BMI, or HbA1c in the DM group. Further, the results of multiple regression analysis showed that ln-IGI could be independently predicted by BMI (β = 0.598, P = 0.0014) and ln-ucOC (β = 0.641, P = 0.0007) in the DM group (R² = 0.488, P = 0.0006).

CONCLUSION

In our study, ucOC positively correlated with insulin secretion independently of BMI in Japanese individuals with diabetes. These results suggest that ucOC plays more important roles in insulin secretion than in insulin sensitivity in individuals with diabetes.

Fasting plasma mannose levels are associated with insulin sensitivity independent of BMI in Japanese individuals with diabetes

BACKGROUND

Recently, an integrated network analysis has revealed dysregulation in the metabolism of mannose, a glucose epimer, in severely obese individuals without diabetes. In addition, fasting plasma mannose levels (M₀) are associated with insulin resistance independent of BMI. Since the association between mannose and insulin sensitivity (IS) in those with impaired glucose tolerance remains unknown, we aimed to investigate this association in individuals without severe obesity but with varying degrees of glucose tolerance.

METHODS

Based on 75 g OGTT data in Japanese individuals without diabetic medication, individuals were classified as having normal glucose tolerance (NGT), impaired glucose metabolism (IGM), or diabetes (DM). In each group, 25 individuals were consecutively recruited [total 75 individuals, age: 65 ± 11 (mean ± SD); BMI: 24.9 ± 3.8 kg/m²]. QUICKI and Matsuda index (MI) were calculated as IS indices. M₀ was assayed using HPLC. Normally-distributed log_e-transformed (ln-) values were used for MI and leptin.

RESULTS

In the simple regression analysis, ln-MI was negatively correlated with BMI (NGT: r = - 0.639, IGM: r = - 0.466, DM: r = - 0.613) and ln-leptin (NGT: r = - 0.480, IGT: r = - 0.447, DM: r = - 0.593) in all 3 groups. Ln-MI was not significantly correlated with M₀ in NGT (r = 0.241, P = 0.245) and IGT (r = - 0.296, P = 0.152) groups, it was moderately and negatively correlated in the DM group (r = - 0.626, P < 0.001). Similar results were obtained, when QUICKI was used instead of MI as an index of IS. In multiple regression analysis in the DM group, QUICKI (Q) and ln-MI (M) were independently predicted by BMI (Q: β = - 0.413; M: β = - 0.400) and M₀ (Q: β = - 0.413, M: β = - 0.426), accounting for 51.2% (P = 0.0004) and 51.2% (P = 0.0004) of the variability, respectively, which was larger than the prediction for BMI alone (Q: 38.4%, M: 37.6%).

CONCLUSION

Fasting plasma mannose was associated with IS independent of BMI in Japanese individuals with DM.