Melatonin activates endoplasmic reticulum stress and apoptosis in rats with diethylnitrosamine-induced hepatocarcinogenesis

Abstract Hepatocellular carcinoma (HCC) is one of the most lethal human cancers worldwide because of its high incidence, its metastatic potential and the low efficacy of conventional treatment. Inactivation of apoptosis is implicated in tumour progression and chemotherapy resistance, and has been linked to the presence of endoplasmic reticulum stress. Melatonin, the main product of the pineal gland, exerts anti-proliferative, pro-apoptotic and antiangiogenic effects in HCC cells, but these effects still need to be confirmed in animal models. Male Wistar rats in treatment groups received diethylnitrosamine (DEN) 50 mg/kg intraperitoneally twice/once a week for 18 weeks. Melatonin was given in drinking water at 1 mg/ kg/d, beginning 5 or 12 weeks after the start of DEN administration. Melatonin improved survival rates and successfully attenuated liver injury, as shown by histopathology, decreased levels of serum transaminases and reduced expression of placental glutathione S-transferase. Furthermore, melatonin treatment resulted in a significant increase of caspase 3, 8 and 9 activities, polyadenosine diphosphate (ADP) ribose polymerase (PARP) cleavage, and Bcl-associated X protein (Bax)/Bcl-2 ratio. Cytochrome c, p53 and Fas-L protein concentration were also significantly enhanced by melatonin. Melatonin induced an increased expression of activating transcription factor 6 (ATF6), C/EBP-homologous protein (CHOP) and immunoglobulin heavy chain-binding protein (BiP), while cyclooxygenase (COX)-2 expression decreased. Data obtained suggest that induction of apoptosis and ER stress contribute to the beneficial effects of melatonin in rats with DEN-induced HCC

Oxidative stress and cell damage in a model of precancerouslesions and advanced hepatocellular carcinoma in rats

Hepatocellular carcinoma (HCC) is the third most frequent cause of cancer deaths through-out the world. This study was aimed to analyze oxidative stress and cell damage in amultistage model of liver carcinogenesis induced by diethylnitrosamine (DEN) in rats.Male Wistar rats weighing 145–150 g were divided into three groups: control, precan-cerous lesions (PL) (which received 100 mg DEN once a week every 6 weeks up to 28weeks), and advanced HCC (50 mg DEN once/twice per week up to 19 weeks). Lipid per-oxidation (TBARS), superoxide dismutase (SOD) activity, and expression of transforminggrowth factor-1 beta (TGF)-1 , endothelial and inducible nitric oxide syntahese (eNOS,iNOS), NADPH quinone oxireductase (NQO)-1, nuclear factor erythroid 2-related factor(NrF)2, kelch-like ECH-associated protein (Keap)1 and heat shock protein (HSP)70 weremeasured. TBARS concentration was augmented in the PL and advanced HCC groups. SODactivity, TGF-1 and Nrf2 expression were higher in animals with precancerous lesions.In advanced HCC, expression of NQO1 and iNOS increased while there was a decrease inHPS70 expression. Data obtained provide evidence for the differential activation of pro-teins involved in oxidative stress and cell damage during progression of carcinogenesis inan animal model of HCC