Identifying New Treatment Options and Risk Factors for Type 2 Diabetes: The Potential Role of Thymoquinone and Persistent Organic Pollutants

Type 2 Diabetes Mellitus (T2DM) is a metabolic disorder characterized by chronic hyperglycemia, which develops as a consequence of peripheral insulin resistance and defective insulin secretion from pancreatic β-cells. A high calorie diet coupled with physical inactivity are known risk factors for the development of T2DM; however, these alone fail to account for the rapid rise of the disease. Recent attention has turned to the role of environmental pollutants in the development of metabolic diseases. PBDEs (polybrominated diphenyl ethers) are environmental pollutants that have been linked to the development of type 2 diabetes (T2D), however, the precise mechanisms are not clear. In particular, their direct effect on insulin secretion is unknown. In this study, we show that two PBDE congeners, BDE-47 and BDE-85, potentiate glucose-stimulated insulin secretion (GSIS) in INS-1 832/13 cells. This effect of BDE-47 and BDE-85 on GSIS was dependent on thyroid receptor (TR). Both BDE-47 and BDE-85 (10 μM) activated Akt during an acute exposure. The activation of Akt by BDE-47 and BDE-85 plays a role in their potentiation of GSIS, as pharmacological inhibition of PI3K, an upstream activator of Akt, significantly lowers GSIS compared to compounds alone. This study suggests that BDE-47 and BDE-85 directly act on pancreatic β-cells to stimulate GSIS, and that this effect is mediated by the thyroid receptor (TR) and Akt activation. This can cause the β-cells to oversecrete insulin, potentially leading to hyperinsulinemia, insulin resistance, and high blood glucose. In contrast to the potential diabetogenic effects of POPs, there are several naturally-derived compounds which accomplish just the opposite, exerting sensitizing effect on the peripheral tissues and sparing effect on β-cells. TQ, a natural occurring quinone and the main bioactive component of plant Nigella sativa, undergoes intracellular redox cycling and re-oxidizes NADH to NAD+. TQ administration (20 mg/kg/bw/day) to the Diet-Induced Obesity (DIO) mice reduced their diabetic phenotype by decreasing fasting blood glucose and fasting insulin levels, and improved glucose tolerance and insulin sensitivity as evaluated by oral glucose and insulin tolerance tests (OGTT and ITT). Furthermore, TQ decreased serum cholesterol levels and liver triglycerides, increased protein expression of phosphorylated Akt, decreased serum levels of inflammatory markers resistin and MCP-1, and decreased the NADH/NAD+ ratio. These changes were paralleled by an increase in phosphorylated SIRT-1 and AMPKα in liver and phosphorylated SIRT-1 in skeletal muscle. TQ also increased insulin sensitivity in insulin-resistant HepG2 cells via a SIRT-1-dependent mechanism These findings are consistent with the TQ-dependent re-oxidation of NADH to NAD+, which stimulates glucose and fatty acid oxidation and activation of SIRT-1-dependent pathways. Taken together, these results demonstrate that TQ ameliorates the diabetic phenotype in the DIO mouse model of type 2 diabetes

Report from the Scientific Poster Session at the 16th Annual Cardiometabolic Health Congress in National Harbor, USA, 14–17 October 2021

The ever-increasing presence of cardiometabolic risk continues to be a major challenge for health care providers in the United States (US) [...

Report from the Scientific Poster Session at the 16th Annual Cardiometabolic Health Congress in National Harbor, USA, 14–17 October 2021

The ever-increasing presence of cardiometabolic risk continues to be a major challenge for health care providers in the United States (US) [...

TQ normalizes glucose tolerance and insulin sensitivity.

<p>(A) Blood glucose levels in response to oral glucose tolerance test (OGTT). (B) Blood glucose levels in response to insulin tolerance test (ITT). p<0.05 when comparing HFD and LFD (+), and HFD and HFD+TQ (*), using a two-way ANOVA followed by Holm-Sidak post-test. Results are means ± SEM (n = 10–12 mice per treatment group). LFD: low fat diet, HFD: high fat diet, TQ: thymoquinone.</p

TQ improves insulin sensitivity in HepG2 cells via a SIRT-1 dependent mechanism.

<p>HepG2 cells were cultured in high (20 mM) glucose or in growth media containing 5.5 mM glucose for 18 hours, starved with serum-free media for 2 hours, then pre-incubated with vehicle control (0.5% DMSO), nicotinamide (0.5 mM), compound C (20 μM), or with nicotinamide and compound C together for 30 mins, followed by incubation with TQ (10 μM) in the presence or absence of nicotinamide and compound C; or with TQ, resveratrol (50 μM), or AICAR (2 mM) alone for 24 hours in 20mM glucose media. Vehicle-treated cells in 5.5 mM glucose served as control. Insulin (100 nM) was added during the last 30 min. (A) Western blot images of p-Akt, Akt, and β-actin. (B) Protein band quantification using densitometry from three independent experiments. p≤ 0.05 where (*) is significantly different from 5.5G, (#) is significantly different from 20G, and (Δ) is significantly different from 20G + TQ using independent t-tests. 5.5 G: 5.5 mM glucose, 20G: 20 mM glucose, TQ: thymoquinone, R: resveratrol, AIC: AICAR, NIC: nicotinamide, C: compound C.</p

Effects of TQ on Akt and AMPKα protein expression in liver.

<p>(A) Western blot images of Akt, p-Akt, AMPKα and p-AMPKα protein in liver. β-actin was used as a loading control. Western blot images are representative of combined liver lysates from n = 10–12 mice per treatment group. (B) Protein band quantification using densitometry from three independent experiments. p≤0.05 when comparing (+) HFD and LFD, (*) HFD + TQ and HFD, and (#) LFD and LFD + TQ using independent t-tests. LFD: low fat diet, HFD: high fat diet, TQ: thymoquinone.</p

Effects of TQ on triglyceride content in liver and muscle.

<p>(A) Triglyceride concentration in liver. (B) Triglyceride concentration in soleus muscle. (*) p<0.05 when comparing HFD + TQ and HFD using a one-way ANOVA followed by Sidak post-test. Results are means ± SEM (n = 8–12 mice per treatment group). LFD: low fat diet, HFD: high fat diet, TQ: thymoquinone.</p

Effect of TQ on serum glycerol and fatty acids.

<p>Effect of TQ on serum glycerol and fatty acids.</p

Effects of TQ on serum cholesterol.

<p>(A) Total cholesterol serum concentration. (B) HDL cholesterol serum concentration. (C) LDL/VLDL cholesterol serum concentration. p≤0.05 when comparing (+) HFD and LFD, (*) HFD + TQ and HFD using independent t-tests. Results are means ± SEM (n = 6–7 mice per treatment group). LFD: low fat diet, HFD: high fat diet, TQ: thymoquinone, LDL: low-density lipoprotein, HDL: high-density lipoprotein, VLDL: very-low-density lipoprotein.</p

Effects of TQ on SIRT-1 protein expression.

<p>(A) Western blot images of SIRT-1 and p-SIRT-1 protein in liver. β-actin was used as a loading control. (B) Western blot images of SIRT-1 and p-SIRT-1 protein in soleus muscle. β-tubulin was used as a loading control. Western blot images are representative of combined liver and soleus muscle lysates from n = 10–12 mice per treatment group. (C and D) Protein band quantification using densitometry from three independent experiments. p ≤ 0.05 when comparing (+) HFD and LFD and (*) HFD + TQ and HFD using independent t-tests LFD: low fat diet, HFD: high fat diet, TQ: thymoquinone.</p