Protein Kinases Signaling in Pancreatic Beta-cells Death and Type 2 Diabetes

Apigenin potentiates glucose-stimulated insulin secretion through the PKA-MEK kinase signaling pathway independent of K-ATP channels

AIM

Apigenin, a natural bioflavonoid, is reported as an anti-diabetic agent since it possesses the ability to inhibit α-glucosidase activity, cause stimulation of insulin action and secretion, manage ROS, and prevent diabetes complications. Apigenin was identified as a new insulin secretagogue that enhances glucose-stimulated insulin secretion and seems like a better antidiabetic drug candidate. Here we explored the insulinotropic mechanism(s) of apigenin in vitro in mice islets and in vivo in diabetic rats.

METHODS

Size-matched pancreatic islets were divided into groups and incubated in the presence or absence of apigenin and agonists or antagonists of major insulin signaling pathways. The secreted insulin was measured by ELISA. The intracellular cAMP was estimated by cAMP acetylation assay. The acute and chronic effects of apigenin were evaluated in diabetic rats.

RESULTS

apigenin dose-dependently enhanced insulin secretion in isolated mice islets, and its insulinotropic effect was exerted at high glucose concentrations distinctly different from glibenclamide. Furthermore, apigenin amplified glucose-induced insulin secretion in depolarized and glibenclamide-treated islets. Apigenin showed no effect on intracellular cAMP concentration; however, an additive effect was observed by apigenin in both forskolin and IBMX-induced insulin secretion. Interestingly, H89, a PKA inhibitor, and U0126, a MEK kinase inhibitor, significantly inhibited apigenin-induced insulin secretion; however, no significant effect was observed by using ESI-05, an epac2 inhibitor. Apigenin improved glucose tolerance and increased glucose-stimulated plasma insulin levels in diabetic rats. Apigenin also lowered blood glucose in diabetic rats upon chronic treatment.

CONCLUSION

Apigenin exerts glucose-stimulated insulin secretion by modulating the PKA-MEK kinase signaling cascade independent of K-ATP channels.

Therapeutic potential of dietary flavonoid hyperoside against non-communicable diseases: targeting underlying properties of diseases

Non-communicable diseases (NCDs) are a global epidemic with diverse pathogenesis. Among them, oxidative stress and inflammation are the most fundamental co-morbid features. Therefore, multi-targets and multi-pathways therapies with significant anti-oxidant and anti-inflammatory activities are potential effective measures for preventing and treating NCDs. The flavonol glycoside compound hyperoside (Hyp) is widely found in a variety of fruits, vegetables, beverages, and medicinal plants and has various health benefits, especially excellent anti-oxidant and anti-inflammatory properties targeting nuclear factor erythroid 2-related factor 2 (Nrf2) and nuclear factor-κB (NF-κB) signaling pathways. In this review, we summarize the pathogenesis associated with oxidative stress and inflammation in NCDs and the biological activity and therapeutic potential of Hyp. Our findings reveal that the anti-oxidant and anti-inflammatory activities regulated by Hyp are associated with numerous biological mechanisms, including positive regulation of mitochondrial function, apoptosis, autophagy, and higher-level biological damage activities. Hyp is thought to be beneficial against organ injuries, cancer, depression, diabetes, and osteoporosis, and is a potent anti-NCDs agent. Additionally, the sources, bioavailability, pharmacy, and safety of Hyp have been established, highlighting the potential to develop Hyp into dietary supplements and nutraceuticals.

Free fatty acids are associated with muscle dysfunction in Chinese adults with type 2 diabetes

PURPOSE

Muscle dysfunction is considered a sign of poor prognosis in patients with type 2 diabetes (T2D). Thus, early detection of muscle disorders is particularly important in the T2D population. Free fatty acids (FFAs) are clinical indicators of metabolic diseases and muscle function; hence, we aimed to investigate the association between FFAs and muscle function.

METHODS

A total of 160 adult subjects with T2D were characterized and analyzed in this study. Muscle mass and function were measured by walking speed, grip strength and height-adjusted appendicular skeletal muscle mass (ASMM). Partial correlation was applied to explore the correlations between FFAs and muscle indicators. Receiver operating characteristic (ROC) curves were utilized to determine the diagnostic value of FFAs in muscle mass and function.

RESULTS

The FFAs levels were negatively correlated with ASMM (r = -0.347, P = 1.0E-05), grip strength (r = -0.313, P = 7.1E-05) and walking speed (r = -0.167, P = 0.039). Notably, the relationships between FFAs levels and ASMM and walking speed remained significant even after adjusting for age, sex, body mass index (BMI), diabetes duration, and hemoglobin A1C (HbA1c). The combination of conventional indicators, including age, BMI, and HbA1c levels, provided a discrimination of low grip strength with an AUC of 0.648, and low walking speed with an AUC of 0.714. Importantly, when FFAs levels were added to the model, the value of the ROC curve was further improved, with an AUC of 0.785 for low grip strength and 0.755 for low walking speed.

CONCLUSIONS

The current study demonstrated a negative correlation between FFAs and muscle indicators in adult patients with T2D after adjusting for HbA1c levels. FFAs may play an important role in the pathological processes of muscle dysfunction in adults with T2D.