As a first line anti-diabetes drug, the molecular mechanisms by which metformin exerts its pharmacological activities are still under extensive investigations. The Nrf2 signaling plays a crucial role in protecting cells from oxidative damages, and has emerged as a promising target for treatment of diabetes and related complexes in recent years. In the present study, the effect of metformin on Nrf2 signaling was tested in vitro and in vivo, and the possible mechanism was explored. Metformin activated AMPK and Nrf2 signaling and induced the expression of antioxidant genes NQO1 and y-GCSm in C2C12 mouse myoblast cells in a similar concentration- and time-dependent manner. Moreover, overexpression of AMPK significantly elevated the basal and metformin-induced ARE-driven luciferase reporter activities, suggesting the involvement of AMPK in metformin-activated Nrf2 signaling. Finally, metformin activated Nrf2 signaling and induced the expression of antioxidant genes such as HO-1 and SOD, and resulted in increased GSH level in mouse liver and skeletal muscle tissues. Take together, our results clearly demonstrated that metformin activated Nrf2 signaling and enhanced the tissue antioxidant capacity, and provide a new molecular mechanism of action of metformin.
Hematological toxicity （bone marrow suppression） is the most common dose-limiting adverse effect of chemotherapies. The nuclear factor erythroid 2-related factor 2 （Nrf2） is a pivotal coordinator of cellular defensive responses against chemical insults in many tissues including bone marrow. In the present study, the effects of tert-butylhydroquinone （tBHQ） on the expression of Nrf2-regulated genes in peripheral blood cells and cyclophosphamide （CTX）-induced hematotoxicity in mice were investigated. CTX induced apoptosis of peripheral blood nucleated cells and leukopenia in mice, accompanied by mobilization of bone marrow hematopoietic cells, tBHQ treatment induced the expression of Nrf2-regulated genes such as heine oxygenase 1 （HO1） and glutamate-cysteine ligase catalytic subtmit （GCLC） in RAW264.7 mouse macrophage cells and peripheral blood cells both in vitro and in vivo. Interestingly, pretreatment with tBHQ alleviated CTX-induced mouse peripheral blood cell apoptosis and leukopenia in vivo, indicating possible involvement of Nrf2 in the protection against CTX-induced hematotoxicity. This study provides new information on the chemotherapy-induced hematotoxicity, and suggests Nrf2 could serve as a target for the development of chemoprotectants against hematotoxicity.
Colorectal cancer （CRC） is one of the leading causes of cancer-related deaths, and inflammatory bowel diseases and dysregulated cell proliferation play important roles in colorectal carcinogenesis. Therefore, inhibition of inflammatory signaling and cell proliferation is used as a major strategy for chemoprevention of CRC. In the present study, it was found that IC5, a dithiocarbamate derivative, could inhibit the proliferation of LoVo human colon cancer cells in a concentration-dependent manner, with an IC50 of 22 gM. The anti-proliferation effect of IC5 was accompanied by a significant cell cycle arrest in G2/M phase. Further study revealed that IC5 significantly inhibited NF-~B signaling in LoVo cells, suggesting that IC5 could inhibit inflammatory responses. We then evaluated the in vivo efficacy of IC5 to inhibit colitis-associated colorectal carcinogenesis using an azoxymethane （AOM）/dextran sodium sulfate （DSS） mouse model. AOM/DSS treatment resulted in a CRC incidence of 58.3%, while the incidences were decreased to 37.5% and 25% in mice orally administered with 50 and 100 mg/kg IC5, respectively. In addition, IC5 also reduced the plasma levels of alanine aminotransferase and asparatate aminotransferase. Taken together, these results suggested that IC5 could prevent colitis-associated colorectal carcinogenesis, and more attention should be paid to it as a cancer chemopreventive agent in further investigation.
Prenylated flavonoids are mainly distributed in Leguminosae and Moraceae plants, and they have been reported to possess various biological activities. Previously, we have reported a prenylated isoflavonoid, isoangustone A（IAA） from licorice（Glycyrrhiza uralensis）, which induces apoptosis in colorectal cancer cells by disrupting mitochondrial functions. In the present study, we compared a group of flavonoids from licorice with IAA for their anti-proliferation activities and effects on intracellular signaling. The results indicated that the isoprenyl groups on the A and B rings, the hydroxyl groups at the ortho position of isoprenyl on A ring and the conjugated plane of C ring might contribute to the anti-cancer activity of prenylated flavonoids. Based on the above structure-activity relationship, we further identified four prenylated flavonoids with similar anti-cancer activities from licorice. Taken together, our present study established a preliminary structure-activity relationship of anti-cancer prenylated flavonoids, and our data provided important leading compounds from licorice, which deserved further research and development.
Nuclear factor erythroid 2-related factor 2 （Nrf2） controls the expression of a wide array of antioxidant response element （ARE）-driven genes, which are involved in stress response and metabolism regulation. The role of Nrf2/ARE signaling in resistances of cancer cells to radiotherapy and chemotherapy has been widely accepted. However, much less is known about the relevance of Nrf2 to chemotherapy-associated toxicities, such as hepatotoxicity. In the present study, nine chemotherapeutic agents were firstly tested in embryonic fibroblasts （MEFs） and hepatocytes isolated from Nrf2 deficient or wild-type mice. The results indicate that the cytotoxicity of oxaliplatin in hepatocytes was significantly higher than that in MEFs and enhanced by Nrf2 deficiency. Furthermore, oxaliplatin treatment caused more pronounced steatosis and severer liver injury in Nrf2-/- mice compared with wild-type counterparts, as evidenced by dramatically elevated serum transaminase and bilirubin, increased accumulation of fat, inflammatory infiltration and blood congestion. The increased hepatotoxicity in Nrf2 deficient mice was possibly caused by decreased expression of antioxidant genes and glutathione depletion. Our results demonstrated that oxaliplatin-induced hepatotoxicity was significantly impacted by Nrf2 status, therefore Nrf2 could potentially serve as a biomarker to predict or a target to prevent hepatotoxicity of oxaliplatin.
