Differences between rats and rabbits in hepatic cytosolic glutathione S-transferase expression in response to nitrogen heterocycle and other inducers

Abstract

Glutathione S-transferase (GST) expression was examined in hepatic cytosol from rats and rabbits treated with 4-picoline, pyrrole, pyridine, pyrazine, imidazole, or piperidine using enzymatic activity, SDS-PAGE, and immunoblot analyses and the results were compared to those obtained with phenobarbital and 3-methylcholanthrene. SDS-PAGE and immunoblot analyses of hepatic cytosol prepared from rats treated with pyrazine revealed the induction of class α (Ya and Yc) and μ (Yb) bands with a corresponding 2.4-fold increase in metabolic activity using 1-chloro-2,4-dinitrobenzene as substrate. A new class α band migrating in the region of the Yc band was observed in the SDS-PAGE and detected in the immunoblot of cytosol from pyrrole-treated rats, whereas treatment with 4-picoline, imidazole, or piperidine failed to alter the expression of the major classes of GST isozymes in this species. SDS-PAGE and immunoblot analyses of rabbit hepatic cytosol revealed a unique species-dependent difference in the expression of GSTs. While phenobarbital and 3-methylcholanthrene induce class α and μ GST expression in rat hepatic cytosol, one of the most interesting observations was that neither of these agents stimulated GST expression in the rabbit. Immunoblot analysis of cytosol isolated from 4-picoline-treated rabbits using GST class α-specific IgG showed the appearance of a novel class α 28-kDa GST band and the concomitant disappearance of a class α 29-kDa GST band. In addition, SDS-PAGE and immunoblot analyses showed that treatment of rabbits with pyrrole, pyrazine, imidazole, or piperidine resulted in the disappearance of this class α 29-kDa GST band with no detectable expression of the class α 28-kDa GST band; the level of the class α 29-kDa band was unaffected by pyridine treatment. In contrast, immunoblot analyses of hepatic cytosol revealed that a 25.5-kDa class μ GST band disappeared following treatment with pyridine, but was unaffected by treatment with other nitrogen heterocycles. The V max of glutathione conjugation to the substrate 1-chloro-2,4-dinitrobenzene decreased by 52, 36, 59, 41, 37, and 32% in hepatic cytosol isolated from 4-picoline-, pyrrole-, pyridine-, pyrazine-, imidazole-, and piperidine-treated rabbits, respectively. The results suggest that nitrogen heterocycles differ in their ability to modulate glutathione S-transferase isozyme expression in rat and rabbit hepatic tissue and that rabbit hepatic GSTs are refractory to induction by agents such as pyrazine, phenobarbital, or 3-methylcholanthrene and hence these xenobiotics do not appear to be bifunctional inducers in this species.