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 chem ical-induced liver injury by a mechanism that involves activation of K upffer cells (KC). These studies were designed to determine if shorter dosing regimens of retinol potentiate carbon tetrachloride (CCl4). In itially, a single dose of retinol was shown to potentiate the hepatoto xicity of CCl4. Male Sprague-Dawley rats were pretreated with all-tran s-retinol (75 mg/kg p.o.) 24 hr prior to KC isolation or administratio n of CCl4 (0.2 ml/kg i.p.). KC isolated at 24 hr after retinol release d increased amounts of superoxide anion when stimulated with zymosan o r phorbol myristate acetate. At 24 hr after CCl4, plasma ALT activitie s and histological sections of liver were examined. Retinol-pretreated rats showed a significant elevation in both enzyme leakage and centri lobular to midzonal necrosis compared to retinol vehicle controls foll owing CCl4. Although complete protection was not seen, depletion of KC or neutrophils (PMNs) (by gadolinium chloride (GdCl3) or a PMN-deplet ing antibody, respectively) significantly reduced the hepatotoxicity o f 1 day retinol/CCl4 liver injury. Immunohistochemical analysis of liv ers showed significant elevations in positive staining for ED2, ED1, a nd HIS48 in retinol-pretreated rats given CCl4. GdCl3 effectively redu ced ED2 staining but did not greatly affect HIS48 staining. Additional studies were performed to estimate the effect of retinol on noninflam matory processes. While total cytochrome P450 was not increased, the a ctivity and concentration of CYP2E1 were both significantly elevated a fter a single dose of retinol. Hepatocytes isolated from 1-day retinol -treated rats were also more susceptible to CCl4 injury, a consequence that is most likely related to elevated CYP2E1 activity. These findin gs suggest that a single pretreatment with retinol may potentiate CCl4 hepatotoxicity by multiple mechanisms which involve increased biotran sformation and inflammatory cell activities. (C) 1996 Academic Press. Inc.