Regulation of death receptors and their ligands expression by AFB1, FB1 and the both-mycotoxins mixture in rats

VERONICA S. MARY; SILVINA ARIAS; MARTIN G. THEUMER; HECTOR RUBINSTEIN

Cordoba

Congreso; IV Congreso Internacional de Ciencia y Tecnología de los Alimentos; 2012

Ministerio Ciencia y Tecnología Provincia de Córdoba

Aflatoxins and fumonisins are synthesized by fungi Aspergillus and Fusarium, respectively. Aflatoxin B1 (AFB1) and fumonisin B1 (FB1) are the most important in their groups due to these are prevalent forms and their potential toxic effects, including generation of oxidative stress, hepatotoxicity, immunotoxicity and carcinogenicity in humans and animals. Co-exposure to AFB1 and FB1 is a situation that occurs frequently in nature, and has been associated with a high incidence of human hepatocellular carcinoma. However, little is known about the effects induced by both-toxins mixtures. Apoptosis mediated by the FAS/FASL and TNFR/TNFα pathways is an essential mechanism to maintain homeostasis of immune response and tissue, such as liver. This study aims to determinate the effects of AFB1, FB1 and both-mycotoxins mixture on death receptors and their ligands expression on hepatocytes and immune cells from rats, and also to evaluate the involvement of oxidative stress in these effects. FAS expression on the surface of hepatocytes were detected by immunofluorescence, FASL expression on the surface of hepatocytes and immune cells was determined by flow cytometry, and the TNFα production was assessed in immune cells supernatants by ELISA. BRL-3A rat liver cell line was exposed to 20 μM AFB1, 30 μM FB1 and MIX (20 μM AFB1 + 30 μM FB1), and rat spleen mononuclear cells (SMC) were incubated with 20 μM AFB1, 10 μM FB1 and MIX (20 μM AFB1 + 10 μM FB1) for 24 or 48 h. The results of these experiments demonstrate that all mycotoxins treatments increased FAS expression on hepatocytes, being the MIX which produced the least effect. Furthermore, FASL expression was reduced by MIX on hepatocytes and by AFB1 alone or in combination with FB1 on SMC, and the TNFα production was decreased by MIX in SMC. Moreover, antioxidants prevented the alterations in FAS, FASL and TNFα levels induced by AFB1 and MIX, indicating that oxidative stress is involved in the mechanism used by these treatments. These results suggest that AFB1 and FB1 could induce hepatotoxicity through the up-regulation of FAS expression that may lead to increased apoptosis of hepatocytes. However, MIX may induce dysregulation of the FAS/FASL pathway, since although produces a small increase in the expression of FAS, it induces decrease in FASL expression on hepatocytes and immune cells, which would produce a reduction in apoptosis induced by this pathway. Besides, MIX could decrease the apoptosis of hepatocytes reducing the TNFα production, since this cytokine is able to sensitize hepatocytes to Fas ligand-induced apoptosis, addition that it can interact with TNFR. The death receptors pathways are used by immune surveillance in eliminating nascent transformed cells. Therefore, defects in these apoptosis-inducing pathways can eventually lead to the escape of tumour cells, and this mechanism may be involved in the hepatocarcinogenicity induced by the both-mycotoxins mixture.