Protective effect of oleanolic acid against beta cell dysfunction and mitochondrial apoptosis: crucial role of ERK-NRF2 signaling pathway.

Pancreatic beta cell dysfunction is a hallmark of diabetes. Our previous results have shown that oleanolic acid (OA) has anti-diabetic potential. However, there is little literature reporting the effect of OA on beta cell dysfunction. The present study was designed to investigate the protective effect of OA against lipotoxicity and the underlying mechanisms. Lepr (db/db) diabetic mice were subjected to fasting blood glucose measurement, intraperitoneal glucose tolerance test after the administration of OA for two weeks. Histopathological observation was conducted by HE staining and transmission electron microscopy assay. Pancreatic islets were isolated from db/db diabetic mice and C57BL/6J mice. Palmitic acid (PA) was used to induce lipotoxicity in vitro. Apoptosis was evaluated in pancreatic islets in diabetic mice and in isolated pancreatic islets and beta-TC3 cells by TUNEL assay. Cellular ATP content, mitochondrial function and redox balance were examined. Phosphorylation of c-Jun NH2-terminal kinase (JNK) and extracellular signal-regulated kinase (ERK) and the activation of nuclear erythroid factor 2 p45-related factor 2 (Nrf2) signaling were evaluated by western blotting. In db/db mice, OA significantly protects beta cell function against lipotoxicity, evidenced by inhibition of apoptosis and improvement of glucose tolerance. In cells, OA administration may protect against PA-induced apoptosis and decrease of GSIS, in which process the activation of Nrf2 is essential. Once Nrf2 is activated, OA could induce GCLc expression, promote the production of GSH, and thus inhibit JNK phosphorylation and solid the antioxidant defense of mitochondria, leading to the inhibition of mitochondrial apoptosis. ERK signaling pathway is responsible for OA-induced activation of Nrf2 and the protective effect of OA. Overall, our study enhances the understanding of the protective effect of OA on beta cell and provides clues for further studies on the underlying mechanisms.

ROS acts as a double-edged sword in the pathogenesis of type 2 diabetes mellitus: is Nrf2 a potential target for the treatment?

Although the clear mechanism of T2DM is still to be elucidated, it has been well established that reactive oxygen species (ROS) derived from multiple sources plays a causal role in multiple types of insulin resistance and contributes to ß-cell dysfunction thus enhances the development and progression of T2DM. What is incomprehensible is that the detrimental ROS also plays a substantial role in the normal insulin signal transduction and glucose-stimulated insulin secretion (GSIS) in ß-cell, which forces us to re-recognize the role of ROS under physiological and pathological conditions in a more broad way. Redox homeostasis is tightly controlled by the transcriptional factor nuclear factor erythroid 2-related factor 2 (Nrf2), whose abnormality is believed to be related with diabetes. Accumulating evidences suggest that there are important cross-talks between Nrf2 and PPARγ, PGC1α, PI3K/Akt on regulating antioxidant enzymes and the development of diabetes. Therefore, these evidences indicate that Nrf2 may be a critical element in taking survival and death decisions when cells are exposed to an oxidant environment. In conclusion, enhancing GSIS and insulin sensitivity through the regulation of Nrf2 levels is a potential avenue for developing new therapeutics. Nrf2 may become a promising target for the treatment of T2DM.

The protective effects of Acanthopanax senticosus Harms aqueous extracts against oxidative stress: role of Nrf2 and antioxidant enzymes.

ETHNOPHARMACOLOGICAL RELEVANCE: Acanthopanax senticosus (Rupr.et Maxim.) Harms, classified into the family of Araliaceae, is used in a variety of diseases in traditional Chinese system of medicine including hypertension, ischemic heart disease and hepatitis. MATERIALS AND METHODS: Different doses (75 mg/kg, 150 mg/kg and 300 mg/kg) of aqueous extracts of Acanthopanax senticosus Harms were evaluated for the antioxidant activity against oxidative stress in mice induced by tert-butyl hydroperoxide (t-BHP) through observating histopathology of the liver and detecting antioxidant enzyme activity, concentration of antioxidant, and related gene and protein expression. RESULTS: Acanthopanax senticosus Harms aqueous extracts (ASE) attenuated the morphological injury of liver induced by t-BHP and increased the activity of antioxidant enzymes and the ratio of GSH/GSSG in serum and liver homogenates. Medium and high doses of ASE also elevated the gene expression of NF-E2-related factor-2 (Nrf2), but not CuZnSOD, MnSOD, catalase (CAT), glutathione peroxidase (GPx) and GCLC. Protein expression results showed that Nrf2 and the antioxidant enzymes were all increased significantly by medium and high doses of ASE. CONCLUSION: The present results indicated that ASE protect against oxidative stress which may be generated via the induction of Nrf2 and related antioxidant enzymes.

RAGE upregulation and nuclear factor-kappaB activation associated with ageing rat cardiomyocyte dysfunction.

Evidence suggests that ageing is a major risk factor for cardiac dysfunction. Interactions between advanced glycation endproducts (AGEs) and the receptor for AGEs (RAGE) are known to cause chronic cellular activation, including activation of nuclear factor-kappaB (NF-kappaB), which has been implicated as a causal factor in the ageing process. To assess whether cardiomyocyte contractile function and the interaction of AGEs with RAGE in the heart are altered in ageing, 25- and 2-month-old male rats were compared. Mechanical properties were assessed in ventricular myocytes using an edge-detection system, including peak twitch amplitude (PTA), time-to-PTA (TPS), time-to-75% relengthening (TR75) and maximal velocity of shortening/relengthening (+/-dL/dt) in ventricular myocytes. AGEs were detected by using a fluorescence assay. The expression of RAGE and NF-kappaB was assessed through a Western blot analysis. Compared with young myocytes, aged myocytes displayed a prolonged TR75 at 1 Hz. With increasing stimulus frequency (from 2 to 4 Hz), aged myocytes' PTA was significantly reduced relative to young myocytes. Aged rat hearts displayed high level of AGEs, RAGE upregulation and NF-kappaB activation. These findings demonstrate impaired cardiomyocyte relaxation and reduced tolerance to increased stimulus frequency in aged rats, which might be associated with enhanced AGEs, RAGE expression, and NF-kappaB activation.