ObjectiveIncreased hepatic expression of dipeptidyl peptidase 4 (DPP4) is associated with non-alcoholic fatty liver disease (NAFLD). Whether this is causative for the development of NAFLD is not yet clarified. Here we investigate the effect of hepatic DPP4 overexpression on the development of liver steatosis in a mouse model of diet-induced obesity.MethodsPlasma DPP4 activity of subjects with or without NAFLD was analyzed. Wild-type (WT) and liver-specific Dpp4 transgenic mice (Dpp4-Liv-Tg) were fed a high-fat diet and characterized for body weight, body composition, hepatic fat content and insulin sensitivity. In vitro experiments on HepG2 cells and primary mouse hepatocytes were conducted to validate cell autonomous effects of DPP4 on lipid storage and insulin sensitivity.ResultsSubjects suffering from insulin resistance and NAFLD show an increased plasma DPP4 activity when compared to healthy controls. Analysis of Dpp4-Liv-Tg mice revealed elevated systemic DPP4 activity and diminished active GLP-1 levels. They furthermore show increased body weight, fat mass, adipose tissue inflammation, hepatic steatosis, liver damage and hypercholesterolemia. These effects were accompanied by increased expression of PPARγ and CD36 as well as severe insulin resistance in the liver. In agreement, treatment of HepG2 cells and primary hepatocytes with physiological concentrations of DPP4 resulted in impaired insulin sensitivity independent of lipid content.ConclusionsOur results give evidence that elevated expression of DPP4 in the liver promotes NAFLD and insulin resistance. This is linked to reduced levels of active GLP-1, but also to auto- and paracrine effects of DPP4 on hepatic insulin signaling.

The liver plays a key role in glucose homeostasis, lipid and energy metabolism. Its function is primarily controlled by the anabolic hormone insulin and its counterparts glucagon, catecholamines and glucocorticoids. Dysregulation of this homeostatic system is a major cause for development of the metabolic syndrome and type 2 diabetes mellitus. The features of the underlying dynamic molecular network that coordinates systemic nutrient homeostasis are less clear. But recently, considerable progress has been made in elucidating molecular pathways and potential factors involved in the regulation of energy and lipid metabolism and affected in diabetic states. In this review we will focus on important stations in the complex network of molecules that control the balance between glucose production, glucose utilization and regulation of lipid metabolism. Special attention will be paid to the insulin receptor substrate (IRS) proteins with the two major isoforms IRS-1 and IRS-2 as a critical node in hepatic insulin signalling. IRS proteins act as docking molecules to connect tyrosine kinase receptor activation to essential downstream kinase cascades, including activation of the PI-3 kinase or MAPK cascade. IRS-1 and IRS-2 are complementary key players in the regulation of hepatic insulin signalling and expression of genes involved in gluconeogenesis, glycogen synthesis and lipid metabolism. The function of IRS proteins is regulated by their expression levels and posttranslational modifications. This regulation within the dynamic molecular network that coordinates systemic nutrient homeostasis will be outlined in detail under the following conditions: after feeding, during fasting and during exercise. Dysfunction of IRS proteins initially leads to post-prandial hyperglycemia, increased hepatic glucose production, and dysregulated lipid synthesis and is discussed as major pathophysiological mechanism for the development of insulin resistance and type 2 diabetes mellitus. Understanding the molecular regulation and the pathophysiological modifications of IRS proteins is crucial in order to identify new sites for potential intervention to treat or prevent hepatic insulin resistance and type 2 diabetes mellitus.

OBJECTIVE Insulin action in the human brain reduces food intake, improves whole-body insulin sensitivity, and modulates body fat mass and its distribution. Obesity and type 2 diabetes are often associated with brain insulin resistance, resulting in impaired brain-derived modulation of peripheral metabolism. So far, no pharmacological treatment for brain insulin resistance has been established. Since sodium–glucose cotransporter 2 (SGLT2) inhibitors lower glucose levels and modulate energy metabolism, we hypothesized that SGLT2 inhibition may be a pharmacological approach to reverse brain insulin resistance. RESEARCH DESIGN AND METHODS In this randomized, double-blind, placebo-controlled clinical trial, 40 patients (mean ± SD; age 60 ± 9 years; BMI 31.5 ± 3.8 kg/m2) with prediabetes were randomized to receive 25 mg empagliflozin every day or placebo. Before and after 8 weeks of treatment, brain insulin sensitivity was assessed by functional MRI combined with intranasal administration of insulin to the brain. RESULTS We identified a significant interaction between time and treatment in the hypothalamic response to insulin. Post hoc analyses revealed that only empagliflozin-treated patients experienced increased hypothalamic insulin responsiveness. Hypothalamic insulin action significantly mediated the empagliflozin-induced decrease in fasting glucose and liver fat. CONCLUSIONS Our results corroborate insulin resistance of the hypothalamus in humans with prediabetes. Treatment with empagliflozin for 8 weeks was able to restore hypothalamic insulin sensitivity, a favorable response that could contribute to the beneficial effects of SGLT2 inhibitors. Our findings position SGLT2 inhibition as the first pharmacological approach to reverse brain insulin resistance, with potential benefits for adiposity and whole-body metabolism.

Fetal postprandial brain responses were slower in the offspring of women with GDM. This might indicate that gestational diabetes directly affects fetal brain development and may lead to central nervous insulin resistance in the fetus.

We performed the largest randomized, placebo-controlled clinical trial to date (N = 112, 12-week intervention) to investigate the effects and safety of resveratrol supplementation on liver fat content and cardiometabolic risk parameters in overweight and obese and insulin-resistant subjects. At baseline the variability in liver fat content was very large, ranging from 0.09% to 37.55% (median, 7.12%; interquartile range, 3.85%-12.94%). Mean (SD) liver fat content was 9.22 (6.85) % in the placebo group and 9.91 (7.76) % in the resveratrol group. During the study liver fat content decreased in the placebo group (-0.7%) but not in the resveratrol group (-0.03%) (differences between groups: P = .018 for the intention-to-treat [ITT] population; N = 54, resveratrol, N = 54, placebo and P = .0077 for the per protocol [PP] population). No effects of resveratrol supplementation on cardiometabolic risk parameters were observed. Resveratrol supplementation was well tolerated and safe. In conclusion, these data suggest that resveratrol supplementation is safe and that it does not considerably impact liver fat content or cardiometabolic risk parameters in humans.

The number of pregnancies complicated by gestational diabetes (GDM) is increasing worldwide. To identify novel characteristics of GDM, we studied miRNA profiles of maternal and fetal whole blood cells (WBCs) from GDM and normal glucose tolerant (NGT) pregnant women matched for body mass index and maternal age. After adjustment for maternal weight gain and pregnancy week, we identified 29 mature micro-RNAs (miRNAs) up-regulated in GDM, one of which, i.e., miRNA-340, was validated by qPCR. mRNA and protein expression of PAIP1, a miRNA-340 target gene, was found down-regulated in GDM women, accordingly. In lymphocytes derived from the mothers’ blood and treated in vitro, insulin increased and glucose reduced miRNA-340 expression. In fetal cord blood samples, no associations of miRNA-340 with maternal GDM were observed. Our results provide evidence for insulin-induced epigenetic, i.e., miRNA-dependent, programming of maternal WBCs in GDM.

Aims/hypothesis Fetal programming plays an important role in the pathogenesis of type 2 diabetes. The aim of the present study was to investigate whether maternal metabolic changes during OGTT influence fetal brain activity. Methods Thirteen healthy pregnant women underwent an OGTT (75 g). Insulin sensitivity was determined by glucose and insulin measurements at 0, 60 and 120 min. At each time point, fetal auditory evoked fields were recorded with a fetal magnetoencephalographic device and response latencies were determined. Results Maternal insulin increased from a fasting level of 67±25 pmol/l (mean ± SD) to 918±492 pmol/l 60 min after glucose ingestion and glucose levels increased from 4.4±0.3 to 7.4±1.1 mmol/l. Over the same time period, fetal response latencies decreased from 297±99 to 235±84 ms (p=0.01) and then remained stable until 120 min (235±84 vs 251±91 ms, p=0.39). There was a negative correlation between maternal insulin sensitivity and fetal response latencies 60 min after glucose ingestion (r=0.68, p=0.02). After a median split of the group based on maternal insulin sensitivity, fetuses of insulin-resistant mothers showed a slower response to auditory stimuli (283±79 ms) than those of insulin-sensitive mothers (178±46 ms, p=0.03). Conclusions/interpretation Lower maternal insulin sensitivity is associated with slower fetal brain responses. These findings provide the first evidence of a direct effect of maternal metabolism on fetal brain activity and suggest that central insulin resistance may be programmed during fetal development.

GDM, independently of BMI, altered maternal plasma NEFAs and the placental lipid profile. GDM was associated with trophoblast and whole-placenta lipoinflammation; however, this was not accompanied by elevated concentrations of inflammatory cytokines or NEFAs in neonatal cord blood.