ETHIONINE TOXICITY IN-VITRO - THE CORRELATION OF DATA FROM RAT HEPATOCYTE SUSPENSIONS AND MONOLAYERS WITH IN-VIVO OBSERVATIONS

The hepato-steatogenic compound ethionine has been used to investigate the correlations between in vivo and in vitro toxicity data. The aim was to find a suitable model of toxicity in hepatocyle suspensions or monolayers in vitro, which could predict the known toxicity of ethioni ne in vivo and which could be implemented in screening compounds of un known toxicity. Thus a variety of markers of cytotoxicity, metabolic c ompetence and liver-specific functions were investigated in rat hepato cyte suspensions and monolayers and compared with in vivo data in the rat. The following markers were measured in the appropriate system: (1 ) Neutral red uptake; 3-(4,5 dimethyl)thiazol-2-yl,-2.5-diphenyl tetra zolium bromide (MTT) reduction; lactate dehydrogenase (LDH), aspartate aminotransferase (AST) and alanine aminotransferase (ALT) leakage (cy totoxicity). (2) ATP levels: protein synthesis and glutathione (GSH) l evels (metabolic competence). (3) Urea and triglyceride synthesis and beta-oxidation (liver specific functions). Ethionine (0-30 mM) did not affect the markers of direct cytotoxicity, except neutral red uptake, which was reduced by 18 and 30 mM ethionine after 20 h in culture. AT P and GSH depletion occurred in hepatocyte suspensions at the highest centrations of ethionine (20 and 30 mM) after 1 h. In monolayers. GSH levels were reduced after 4 h, but not 20 h. Urea synthesis was increa sed in hepatocyte suspensions from I to 3 h by 10-30 mM ethionine and reduced after 20 h in cultured hepatocytes (18-30 mM). Protein synthes is was reduced and beta-oxidation was increased in ethionine-treated h epatocyte suspensions. Unfortunately, there was no measurable effect o n triglyceride accumulation within cells (the major biochemical change in vivo) in either system. Ethionine treated hepatocytes in suspensio n showed the same rate of triglyceride synthesis and transportation ou t of cells as control cells. Thus, hepatocyte suspensions were able to mimic the early biochemical effects of ethionine in vivo (ATP and GSH depletion, inhibition of protein synthesis) and some effects on urea synthesis, but monolayer cultures appeared to be less sensitive to the toxicity of ethionine. However, neither in vitro system was able to m odel the effects of ethionine on the accumulation of triglycerides in vivo.