Therapeutic Options that Provide Glycemic Control and Weight Loss for Patients with Type 2 Diabetes

Preclinical and Clinical Evidence for a Distinct Regulation of Mu Opioid and Type 1 Cannabinoid Receptor Genes Expression in Obesity

Among endogenous signaling networks involved in both rewarding and homeostatic mechanisms of obesity, a relevant role is played by the endocannabinoid (ECS) and the opioid (EOS) systems. We here studied the transcriptional regulation of ECS and EOS genes in the hypothalamus of Diet-induced obesity rats, a preclinical model of obesity, as well as in humans with obesity and healthy controls. A significant and selective increase in type 1 cannabinoid receptor gene (Cnr1) expression was observed at the beginning of obesity development (5 weeks on high fat diet) as well as after 21 weeks of high diet exposure. After 5 weeks on high fat diet, selective up-regulation of mu opioid receptor gene (Oprm1) expression was also observed. Consistently, epigenetic studies showed a selective and significant decrease in DNA methylation at specific CpG sites at both gene promoters in overweight rats, but only after 5 weeks on high fat diet. Moreover, significantly lower levels of DNA methylation were observed at selected CpG sites of both receptor gene promoters, analyzed in peripheral blood mononuclear cells from younger (<30 years old) humans with obesity, as well as in those with shorter time length from disease onset. Taken together, we here provide evidence of selective, synergistic and time-dependent transcriptional regulation of CNR1 and OPRM1 genes in overweight rats, as well as in human subjects. These alterations in genes regulation could contribute to the development of the obese phenotype, and we thus suggest CNR1 and OPRM1 epigenetic modulation as possible biomarkers of obesity development. Due to the reversible nature of the epigenetic hallmark, our data might also open new avenue to early environmental strategies of intervention.

Weight loss after gastric bypass surgery in human obesity remodels promoter methylation

DNA methylation provides a mechanism by which environmental factors can control insulin sensitivity in obesity. Here, we assessed DNA methylation in skeletal muscle from obese people before and after Roux-en-Y gastric bypass (RYGB). Obesity was associated with altered expression of a subset of genes enriched in metabolic process and mitochondrial function. After weight loss, the expression of the majority of the identified genes was normalized to levels observed in normal-weight, healthy controls. Among the 14 metabolic genes analyzed, promoter methylation of 11 genes was normalized to levels observed in the normal-weight, healthy subjects. Using bisulfite sequencing, we show that promoter methylation of PGC-1α and PDK4 is altered with obesity and restored to nonobese levels after RYGB-induced weight loss. A genome-wide DNA methylation analysis of skeletal muscle revealed that obesity is associated with hypermethylation at CpG shores and exonic regions close to transcription start sites. Our results provide evidence that obesity and RYGB-induced weight loss have a dynamic effect on the epigenome.

Insulin sensitivity and liver glucose production in the rat are influenced by lifetime food restriction

In both humans and rats, food restriction leads to increased insulin sensitivity and predisposition to hypoglycemia. We hypothesized that metabolic responses to hypoglycemic episodes could be altered in food-restricted rats. To test our hypothesis, plasma glucose levels and liver glucose production during insulin-induced hypoglycemia were assessed. Rats either had free access to food (FF group) or were food restricted from birth (FR group). As adults, they were subjected to insulin-induced hypoglycemia after an overnight fast. Plasma glucose was measured before (time 0) the intraperitoneal injection of insulin (1 U/kg) and at regular intervals for 300 minutes. Some FF and FR rats received oral glucose (100 mg/kg) 15 minutes after insulin injection, and the same time intervals were investigated. The FR rats showed a larger decrease and slower recovery of plasma glucose than the FF group, and this was not influenced by oral glucose. Liver glucose production from glycogenolysis and gluconeogenesis (ie, before and during the infusion of L-alanine) was higher and lower, respectively, in the FR rats than in the FF rats, either with or without oral glucose before liver perfusion. Preference for glycogenolysis could be a metabolic adaptation for the maintenance of plasma glucose levels during fasting despite lower food availability in the FR rats. However, long-term FR increased the severity of hypoglycemia and impaired plasma glucose recovery. In addition, hypoglycemia could not be prevented by glucose administration. Therefore, food restriction in individuals with intensive insulin therapy should be more rigorously examined.

Type 2 diabetes comorbidities and treatment challenges: rationale for DPP-4 inhibitors

The management of type 2 diabetes is designed to reduce disease-related complications and improve long-term outcomes. Achieving glycemic control is a critical component of this process. The selection of drug therapy for reducing blood glucose is made more challenging when patients already have complications or comorbid conditions (eg, high risk for hypoglycemia, obesity, renal impairment). Dipeptidyl peptidase-4 (DPP-4) inhibitors are a new class of antihyperglycemic drugs that block degradation of incretin hormones. By enhancing and prolonging incretin effects, DPP-4 inhibitors stimulate glucose-dependent insulin secretion and also reduce glucagon secretion. This results in improved glycemic control, as reflected by decreases in glycated hemoglobin (HbA1c), fasting plasma glucose, and postprandial plasma glucose. Dipeptidyl peptidase-4 inhibitors also have the potential to improve beta-cell function. In randomized clinical trials, the DPP-4 inhibitors saxagliptin and sitagliptin reduced HbA1c by 0.5% to 0.8%, compared with placebo, whether used as monotherapy or in combination with another agent. As initial combination therapy with metformin, saxagliptin and sitagliptin have demonstrated reductions in HbA1c of 2.5% and 1.9%, respectively. The efficacy of the DPP-4 inhibitors was maintained during treatment for up to 2 years, and did not differ in the elderly compared with younger adults. Dipeptidyl peptidase-4 inhibitors offer efficacy similar to other drug classes, and are well tolerated with a lower risk of hypoglycemia, weight-neutral effects, and a low propensity for drug-drug interactions. On the basis of their clinical profiles, the DPP-4 inhibitors are emerging as an attractive option for improving glycemic control in patients with type 2 diabetes. Saxagliptin and sitagliptin are approved for use as initial therapy in combination with metformin, as monotherapy, as well as in combination with metformin, a sulfonylurea, or a thiazolidinedione in patients not adequately controlled by these agents alone.