The use of liver spheroids as an in vitro model for studying induction of the stress response as a marker of chemical toxicity

Stress protein induction has been advocated as a sensitive indicator of com pound-induced toxicity, In monolayer cultures of primary hepatocytes, howev er, the two stress proteins, Hsp25 and Hsp72/3 are upregulated, probably du e to the effect of the isolation procedure and adaptation of the cells to t he culture conditions. The aim of the current studies was to determine whet her liver spheroids would provide an improved experimental model for the st udy of heat shock protein induction in vitro, Primary rat hepatocytes were cultured as liver spheroids and the expression of Hsp25 and Hsp72/3 measure d along with the levels of ATP. GSH and albumin secretion. Hsp72/3 was init ially increased in spheroid culture but returned to in vivo levels after 3 days of culture. Hsp25 was maintained at in vivo levels until day 6 of cult ure, after which levels increased slightly. The effects of the two hepatoto xins, hydrazine and cadmium chloride (CdCl2), were therefore measured on da y 6 of spheroid culture. CdCl2 had no effect on Hsp25 but increased Hsp72/3 at concentrations that affected other biochemical parameters. Hydrazine ca used a rapid reduction in ATP levels and albumin secretion, but did not aff ect Hsp72/3, Hsp25 was slightly induced by hydrazine at later sampling time s at concentrations, however, that affected other biochemical parameters. I t can be concluded that liver spheroids provide a model for studying stress protein expression. However, the increase in stress proteins appears to be a relatively insensitive parameter compared to other more conventionally u sed toxicity endpoints and the response appears to vary with individual tox ins under study. (C) 2000 Elsevier Science Ltd. All rights reserved.