Endotoxin- and inflammation-induced depression of the hepatic drug metabolism in rats

Suppression of cytochrome P450IA1 by interleukin-6 in human HepG2 hepatoma cells

The effects of interleukin-6 (IL-6), the major inducer of the acute-phase reaction, on the expression of cytochrome P450IA1 (CYPIA1) were examined using human HepG2 hepatoma cells. Treatment of cells with IL-6 decreased the level of 3-methylcholanthrene-induced CYPIA1 protein and its mRNA. Nuclear runoff analysis revealed that the effect of IL-6 was largely transcriptional. IL-6 treatment of HepG2 cells increased mRNA for microsomal heme oxygenase, the rate-limiting enzyme in heme catabolism, suggesting that the suppressive effect of IL-6 on CYPIA1 mRNA may be due to a loss of heme. Consistent with this hypothesis, simultaneous treatment of cells with Sn-mesoporphyrin, an inhibitor of heme oxygenase, prevented the IL-6-mediated suppression of CYPIA1. These findings suggest that the suppression of P450IA1 mRNA by IL-6 appears to occur, at least in part, from the decline in free heme content as a result of the induction of heme oxygenase. Our results raise the possibility that other physiological as well as environmental stimuli which affect cellular heme concentrations may also modulate the expression of P450s.

Down-regulation of multiple cytochrome P450 gene products by inflammatory mediators in vivo. Independence from the hypothalamo-pituitary axis

Inflammatory stimuli suppress constitutive hepatic expression of the CYP2C11 and CYP2C12 genes in male and female rat livers, respectively. Because growth hormone (GH) is an important regulator of P450 gene expression in the rat, the effects of bacterial endotoxin injection in hypophysectomized rats were compared to those in normal animals. In intact females, 0.2 mg/kg endotoxin suppressed total P450 and hepatic expression of CYP2C6, CYP2C7, CYP2C12, and CYP2E1 mRNAs, as well as CYP2C12 and CYP2E1 proteins, measured 16 hr later. CYP2C7 and CYP2E1 mRNAs were most affected (17 and 13% of untreated levels, respectively). Endotoxin treatment also induced the mRNA for the hepatic acute phase protein, haptoglobin, to 260% of control female levels. In hypophysectomized females supplemented with GH infusion, endotoxin caused the same or greater effects on expression of the P450 and haptoglobin gene products than were observed in the intact animals. It is concluded that the P450 suppression observed after endotoxin administration can occur independently of an effect on pituitary hormone secretion.

Inflammation, an inducer of metallothionein, inhibits carbon-tetrachloride-induced hepatotoxicity in rats

Inflammation, induced by turpentine (0.1 ml i.m.), protected against carbon tetrachloride (CCl4)-induced hepatotoxicity based on serum activities of sorbitol dehydrogenase. Inflammation was confirmed by elevated serum ceruloplasmin activities, and was associated with high hepatic levels of metallothionein, a zinc protein proposed to protect against CCl4-induced injury. Inflammation suppressed cytochrome P-450 activities, but this was not associated with protection against CCl4-promoted liver microsomal injury as assessed by glucose-6-phosphatase activity loss. Thus, protection against plasma membrane injury did not result primarily from depressed microsomal activation of CCl4. Each effect of inflammation reported here resembled effects of zinc injections. This similarity strengthens the hypothesis that metallothionein protects against CCl4-induced hepatic plasma membrane injury.