Serum leptin level is associated with glycaemic control in newly diagnosed type 2 diabetes patients: A 1-year cohort study

Serum leptin, resistin, and adiponectin levels in obese and non-obese patients with newly diagnosed type 2 diabetes mellitus: A population-based study

Disturbances in adipocytokine profiles can contribute to peripheral insulin resistance and impairment of insulin production, which are 2 primary pathophysiological mechanisms involved in type 2 diabetes mellitus (T2DM). Previous studies of disturbed adipocytokine profiles have resulted in ambiguous findings; therefore, we conducted the current study comparing leptin, resistin, and adiponectin concentrations in patients with newly diagnosed T2DM who had normal body mass index (BMI) and those who were obese.We studied a population-based cohort of healthy participants and those with newly diagnosed T2DM. A normal BMI group was randomly selected; age- and sex-matched obese participants were recruited. Circulating leptin, resistin, and adiponectin concentrations were measured and compared between groups using analysis of variance; binary logistic regression analysis was then performed to compare the normal BMI and obese groups.In total, 85 healthy participants and 38 patients with diabetes (19 with normal BMI and 17 who were obese) were enrolled. After adjustment for BMI and waist circumference, the median leptin concentration was higher in the obese group (6.77 (3.89-10.73) ng/mL) than in the normal BMI group (1.69 (0.80-3.89) ng/mL) (P = .007), whereas the median adiponectin concentration was lower in the obese group (1.03 (0.75-2.36) μg/mL vs 3.36 (0.59-7.63) μg/mL, P = .03). In addition, the adiponectin/leptin ratio was higher in the normal BMI group (145.6 (41.3-495.9) ng/mL) than in the obese group (20.55 (8.74-36.94) ng/mL, P = .002).Compared with the normal BMI T2DM group, the obese T2DM group exhibited a disturbed adipocytokine profile in the form of a significantly increased leptin concentration and reduced adiponectin level. Further studies are needed to determine the causal relationship for this difference and evaluate its importance for personalized diabetic treatment.

Chronic hyper-leptinemia induces insulin signaling disruption in adipocytes: Implications of NOS2

Leptin, following its discovery, has developed a formidable interest in the scientific community to delineate its contribution towards overall metabolic homeostasis. Contradictory reports have been published on leptin administration effects on whole body insulin sensitivity. Following late reports, we surveyed human serum leptin levels along with other metabolic parameters including BMI and HOMA-IR. We found a positive correlation between leptin levels and insulin resistance parameters. Considering the presence of the long form of leptin receptor on adipocytes, we explored the effects of chronic physiological hyper-leptinemic exposure on adipocyte insulin sensitivity. Chronic leptin (50ng/ml) treatment in 3T3-L1 adipocytes decreased insulin-induced phosphorylation of nodal insulin signaling proteins along with reduced glucose uptake. Metabolic flux studies indicated mitochondrial dysfunction and reduced oxygen consumption rate. Leptin treatment also increased both cellular and mitochondrial superoxide levels concomitant to increased expression of nitric oxide synthase-2 (NOS2). Further, pharmacological depletion of NOS2 reversed leptin mediated effects on insulin signaling. In-vivo implantation of leptin osmotic pumps in C57BL/6 mice also decreased insulin responsiveness. Interestingly, these effects were lacking in NOS2 knockout strain. In conclusion, our studies put forward a potential link between leptin and adipocyte insulin responsiveness in an NOS2 dependent manner.

Does honey have any salutary effect against streptozotocin - induced diabetes in rats?

BACKGROUND

Diabetes is a global, growing and costly public health problem. In the literature, there are conflicting reports on the effect of consumption of bee honey on diabetes. We assessed the possible effect of a commercially available bee honey (given orally by gavage at doses of 1 g/kg/day for 4 weeks) on the blood concentrations of glucose, insulin and leptin and body weight of rats with streptozotocin-induced diabetes.

METHODS

Thirty-six rats were allocated randomly into six groups equally and treated for 4 weeks as follows: Group.1: non-diabetic rats given distilled water, group.2: non-diabetic rats given honey (1 g/kg), group.3: Diabetic rats given distilled water, group.4: Diabetic rats given honey, group.5: Diabetic rats given insulin (10 IU/kg), and group.6: Diabetic rats given combination of insulin (10 IU/kg) with honey (1 g/kg). The body weight, blood glucose, insulin and leptin concentrations of each rat were measured.

RESULTS

Honey treatment did not significantly affect the glucose, leptin and insulin concentrations of diabetic rats. It did not significantly affect the excessive water intake or urinary output in diabetic rats when compared to the insulin-treated groups. Neither honey nor insulin improved body weight in diabetic rats.

CONCLUSION

Contrary to the reports of a salutary effect of honey in diabetic humans and rodents, our results showed that consumption of honey caused no significant changes in body weight, or glucose and insulin concentrations. However, further studies with different doses and durations of treatment are warranted.

Trivaric acid, a new inhibitor of PTP1b with potent beneficial effect on diabetes

AIM

To screen a potential PTP1b inhibitor from the microbial origin-based compound library and to investigate the potential anti-diabetic effects of the inhibitor in vivo and determine its primary anti-diabetic mechanism in vitro and in silico.

METHODS

PTP1b inhibitory activity was measured using recombination protein as the enzyme and p-NPP as the substrate. The binding of the inhibitor to PTP1b was analysed by docking in silico and confirmed by ITC experiments. The intracellular signalling pathway was detected by Western blot analysis in HepG2 cells. The anti-diabetic effects were evaluated using a diabetic mice model in vivo.

RESULTS

Among 545 microbial origin-based pure compounds tested, trivaric acid, a tridepside, was selected as a PTP1B inhibitor exhibiting strong inhibitory activity with an IC₅₀ of 173nM. Docking and ITC studies showed that trivaric acid was able to spontaneously bind to PTP1b and may inhibit PTP1b by blocking the catalytic domain of the phosphatase. Trivaric acid also enhanced the ability of insulin to stimulate the IR/IRS/Akt/GLUT2 pathway and increase the glucose consumption in HepG2 cells. In diabetic mice, trivaric acid that had been encapsulated into Eudrgit L100-5.5 showed significant anti-diabetic effects, improving insulin resistance, leptin resistance and lipid profile and weight control at doses of 5mg/kg and 50mg/kg.

SIGNIFICANCE

Trivaric acid is a potential lead compound in the search for anti-diabetic agents targeting PTP1b.