SELECTIVE COLOCALIZATION OF LIPID-PEROXIDATION AND PROTEIN THIOL LOSSIN CHEMICALLY-INDUCED HEPATIC PRENEOPLASTIC LESIONS - THE ROLE OF GAMMA-GLUTAMYL-TRANSPEPTIDASE ACTIVITY

A number of studies indicate that cell proliferation can be modulated by changes in the redox balance of (soluble and protein) cellular thio ls. Free radical processes, including lipid peroxidation (LPO), can af fect such a balance, and a role for LPO in multistage carcinogenesis h as been envisaged. The present study was aimed to assess the relations hips between the protein thiol redox status and the LPO process in che mically induced preneoplastic tissue. The Solt-Farber's initiation-pro motion model of chemical carcinogenesis in the rat liver was used. In fresh cryostat sections, preneoplastic lesions were identified by the reexpression of gamma-glutamyltranspeptidase (GGT) activity. In serial sections, different classes of protein thiols were stained; in additi onal sections, LPO was elicited by various prooxidant mixtures and det ermined thereafter by the hydroxynaphthoic hydrazide-Fast Blue B proce dure. The incubation of sections in the presence of chelated iron plus substrates for GGT activity leads to the development of LPO in select ed section areas closely corresponding to GGT-positive lesions, indica ting the ability of GGT activity to initiate LPO. Protein-reactive thi ols, as well as total protein sulfur, were decreased by 20-25% in cell s belonging to GGT-positive preneoplastic nodules, suggesting the occu rrence of oxidative conditions in vivo. The incubation of additional a djacent sections with the prooxidant mixture H2O2 plus iron(II), in or der to induce the complete oxidation of lipid present in the section, showed a decreased basal concentration of oxidizable lipid substrate i n GGT-rich areas. The decreased levels of both protein thiols and lipi d-oxidizable substrate in GGT-positive nodules suggest that the observ ed GGT-dependent pathway of LPO initiation can be chronically operativ e in vivo during early stages of chemical carcinogenesis, in cells exp ressing GGT as part of their transformed phenotype.