The Role of Inflammatory Cells and Cytochrome P450 in the Potentiation of CCl4-Induced Liver Injury by a Single Dose of Retinol

Evidence suggests that 7 days of retinol pretreatment potentiates chemical-induced liver injury by a mechanism that involves activation of Kupffer cells (KC). These studies were designed to determine if shorter dosing regimens of retinol potentiate carbon tetrachloride (CCl4). Initially, a single dose of retinol was shown to potentiate the hepatotoxicity of CCl4. Male Sprague–Dawley rats were pretreated with all-trans-retinol (75 mg/kg p.o.) 24 hr prior to KC isolation or administration of CCl4(0.2 ml/kg i.p.). KC isolated at 24 hr after retinol released increased amounts of superoxide anion when stimulated with zymosan or phorbol myristate acetate. At 24 hr after CCl4, plasma ALT activities and histological sections of liver were examined. Retinol-pretreated rats showed a significant elevation in both enzyme leakage and centrilobular to midzonal necrosis compared to retinol vehicle controls following CCl4. Although complete protection was not seen, depletion of KC or neutrophils (PMNs) (by gadolinium chloride (GdCl3) or a PMN-depleting antibody, respectively) significantly reduced the hepatotoxicity of 1 day retinol/CCl4liver injury. Immunohistochemical analysis of livers showed significant elevations in positive staining for ED2, ED1, and HIS48 in retinol-pretreated rats given CCl4. GdCl3effectively reduced ED2 staining but did not greatly affect HIS48 staining. Additional studies were performed to estimate the effect of retinol on noninflammatory processes. While total cytochrome P450 was not increased, the activity and concentration of CYP2E1 were both significantly elevated after a single dose of retinol. Hepatocytes isolated from 1-day retinol-treated rats were also more susceptible to CCl4injury, a consequence that is most likely related to elevated CYP2E1 activity. These findings suggest that a single pretreatment with retinol may potentiate CCl4hepatotoxicity by multiple mechanisms which involve increased biotransformation and inflammatory cell activities.