Immunohistochemical studies on early stage of hepatic damage induced by subacute inhalation of toluene vapor in rats.

Toluene is one of the most widely used organic solvents and is commonly recognized as a noxious substance inducing chronically toxic damage to neural, hepatic and renal functions in the workers engaged in printing and painting. Although hepatic cells are generally considered to be vulnerable and susceptible to various organic solvents, particularly chloroform and other halogenated hydrocarbons, the hepatotoxic effects of aromatic hydrocarbons including toluene have not yet been sufficiently characterized. In particular, it still seems unclear whether toluene itself can directly act on hepatic cells, inducing toxic damage to their metabolism and function. To assess the toxic effect of toluene inhalation on rat liver, immunohistochemical analyses of the histological markers for hepatic damage were carried out in animals exposed subacutely to toluene vapor. The immunoreactivities of heat shock proteins (HSP-70 and HSP-90) and cytochrome P4502E1 (CYP2E1) in the liver were analyzed to assess the hepatotoxic damage induced by toluene inhalation, and the expression of these histological markers was shown to be substantially enhanced by the subacute exposure to toluene vapor. Toluene inhalation was furthermore shown to enhance the immunoreactivities of alpha-smooth muscle actin (alpha-SMA), collagen, glucocorticoid receptors (GR) and leptin receptors (Ob-R) in the liver. Additional studies using human hepatoma HepG2 cells showed that toluene can directly induce toxic damage to cells. These findings suggest that toluene inhalation may primarily induce hepatic damage, which may be secondarily exacerbated by the activation of systemic processes possibly connected with glucocorticoids and leptin.