Rosmarinic acid exerts anti-inflammatory effect and relieves oxidative stress via Nrf2 activation in carbon tetrachloride-induced liver damage

BACKGROUND: Rosmarinic acid (RA) has biological and pharmaceutical properties and shows hepatoprotective potential. However, the hepatoprotective mechanism of RA needs to be further elucidated in vivo and in vitro. OBJECTIVE: This study was aimed to evaluate the protective effect of RA on carbon tetrachloride (CCl(4))-induced liver injury and elucidate the hepatoprotective mechanism of RA in vivo and in vitro. DESIGN: In vivo, the mice were orally administrated with RA (10, 20, and 40 mg/kg bw) daily for 28 consecutive days, and 1% CCl(4) (5 mL/kg bw, dissolved in peanut oil) was used to induce liver injury. In vitro, the big rat liver (BRL) hepatocytes were pretreated with RA (0.2, 0.4, and 0.8 mg/mL) for 3 h, and then the hepatocytes were treated with CC1(4) (final concentration, 14 mM) for 3 h to induce cell injury. The related indexes, including hepatic function, oxidative stress, protein expression of nuclear-factor erythroid 2-related factor 2 (Nrf2) pathway, inflammation, histopathological change, hepatocyte apoptosis, and mitochondrial membrane potential, were evaluated. RESULTS: Oral administration of RA to mice considerably decreased the CCl(4)-induced elevation of serum alanine aminotransferase (ALT), alkaline phosphatase (ALP), triacylglycerols (TG), total cholesterol (TC), total bilirubin (TBIL), hepatic reactive oxygen species (ROS), malondialdehyde (MDA), nitric oxide (NO), 8-hydroxydeoxyguanosine (8-OHdG), tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and interleukin-8 (IL-8). RA also increased the levels of hepatic glutathione (GSH), superoxide dismutase (SOD), and catalase (CAT) and the protein expressions of Nrf2, quinine oxidoreductase (NQO1), and heme oxygenease-1 (HO-1). Histopathological examinations indicated that RA (20 and 40 mg/kg bw) alleviated the liver tissue injury induced by CCl(4). Moreover, RA inhibited the hepatocyte apoptosis caused by CCl(4) based on TUNEL assay. In vitro, RA pretreatment remarkably recovered the cell viability and reduced the CCl(4)-induced elevation of AST, ALT, lactate dehydrogenase (LDH), ROS, and 8-OHdG. Immunohistochemistry staining demonstrated that pretreatment with RA markedly inhibited the expression of IL-6, inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), and Caspase-3 in CCl(4)-treated hepatocytes. Additionally, RA pretreatment significantly decreased the elevation of mitochondrial membrane potential in CCl(4)-treated hepatocytes. CONCLUSIONS: RA exerted a protective effect against CCl(4)-induced liver injury in mice through activating Nrf2 signaling pathway, reducing antioxidant damage, suppressing inflammatory response, and inhibiting hepatocyte apoptosis. RA could attenuate BRL hepatocyte ROS production, DNA oxidative damage, inflammatory response, and apoptosis induced by CCl(4) exposure.