Potentiation and suppression of mouse liver cytochrome P-450 isozymes during the acute-phase response induced by bacterial endotoxin

Reversible and persistent consequences of copper deficiency in developing mice

The effect of maternal copper (Cu) deficiency on various proteins was studied to determine if the changes were reversible or persistent with Cu repletion. The functional consequences of these alterations were assessed by exposing the animals to an oxidative stress (endotoxin), and by measuring the formation of benzo[a]pyrene-DNA adducts in vitro. Throughout gestation and lactation, mice were fed a Control diet (10 micrograms Cu/g diet) or a Low Cu diet (1 microgram Cu/g diet). On day 18, the offspring were killed or switched to the Control diet and killed on day 42 following a single injection of saline or endotoxin on day 41. In day-18 offspring, Cu deficiency resulted in decreased hematocrit values, ceruloplasmin activity, liver and tissue Cu levels, and metallothionein concentrations. Cu repletion restored all but metallothionein levels. Early Cu deficiency led to higher brain CuZn superoxide dismutase activity on day 42, and higher levels of brain thiobarbituric acid reactive substances (TBARS) in endotoxin-treated mice. Liver TBARS were lower in day-18 Low Cu offspring and in day-42 Low Cu offspring treated with endotoxin than age-matched Controls. Cytochrome P-450 concentrations were lower in Low Cu, endotoxin-treated males than in Controls. These results show that Cu deficiency-mediated alterations during early development are not immediately reversed with Cu repletion.

Effect of interleukin 6 on phenobarbital induction of cytochrome P-450IIB in cultured rat hepatocytes

Human recombinant interleukin 6 (rhIL-6) caused a dose dependent decrease in the phenobarbital induction of benzyloxyresorufin O-deethylase activity in cultured rat hepatocytes. Decreased enzymatic activity was associated with a decrease in the amount of immunoreactive P-450IIB1/2. rhIL-6 also prevented the PB-induced increase in the steady state level of P-450IIB mRNA. These results suggest that altered P-450 levels observed in vivo during the acute phase reaction may be due to interleukin 6.

Differential effects of recombinant interferon alpha on constitutive and inducible cytochrome P450 isozymes in mouse liver

The hepatic cytochrome P450 (P450)-dependent monooxygenase system is subject to regulation by a variety of xenobiotics and endogenous factors. During infection and inflammation the P450 system is usually suppressed, but the factors responsible for this phenomenon and the P450 isozymes involved have not been identified conclusively. We have studied the effects of a specific inflammatory mediator, recombinant interferon alpha, on the constitutive and inducible expression of P450 isozymes (from the CYP1A, CYP2B, and CYP2C) gene families using isozyme preferred substrates and Western blot analysis. Both increases and decreases in P450 levels occurred in response to interferon alpha. Suppression of constitutive P450 isozyme expression occurred and was shown to involve a decrease in steady-state protein expression. The induction of 7-ethoxyresorufin O-deethylase activity by 3-MC was potentiated whereas induction of 7-pentoxyresorufin- and 7-benzyloxyresorufin O-dealkylases by PB was suppressed by interferon alpha. These data demonstrate that the effects of interferon alpha on the P450-dependent monooxygenase system are complex, involving differential regulation of several isozymes. Both direct and indirect mechanisms may participate in these phenomena.

Enhancing effect of a choline-deficient diet on alterations of hepatic drug-metabolizing enzymes in hepatitis- and hepatoma-predisposed rats (LEC rats)

Marked alterations of hepatic drug-metabolizing enzymes were observed in hepatitis- and hepatoma-predisposed rats (LEC rats) fed a choline-deficient diet. The diet enhanced the development of hepatitis with severe jaundice. The levels of two major classes of cytochrome P-450, P-450PB and P-450MC, were markedly decreased. GST-Yp was dramatically increased, whereas GST-Ya, Yb1 and Yb2 were decreased. LEA rats (the control rats to LEC) fed a choline-deficient diet mimicked LEC rats fed a normal diet in terms of the above enzyme alterations, indicating that hypomethylation is involved in the pathogenesis of hepatitis and hepatoma in LEC rats. Such hypomethylation may initiate the hepatocytes that spontaneously develop hepatitis and hepatoma.

Perturbation of metabolism and disposition of cyclophosphamide by interferon and poly I:C, an interferon inducer, in mice

The effects of interferon and poly I:C on the metabolism and disposition of cyclophosphamide were investigated in mice. Elimination of cyclophosphamide from the blood was decreased in mice treated 24 hr previously with interferon (2.5 x 10(6) U/kg, intraperitoneally) or poly I:C (10 mg/kg, intraperitoneally). The blood half-life of cyclophosphamide in interferon or poly I:C-pretreated mice was prolonged to a first order of disappearance of 29.3 and 41.6 min., respectively, compared to 19.0 min. in control mice. Also, the rate of formation of activated cyclophosphamide was delayed and the peak blood level of activated cyclophosphamide was not as high in poly I:C-pretreated and interferon-pretreated mice as in control mice. The decreased elimination and elevated blood levels of activated cyclophosphamide were reflected by changes in its antitumour activity and toxicity in the mice. In 9,000 x g supernatants prepared from the liver homogenate of mice treated with interferon or poly I:C, the oxidation of cyclophosphamide in vitro has decreased by 29 and 37%, respectively. However, the addition of these agents to normal 9,000 x g supernatant suspensions had no effect on cyclophosphamide oxidation. Modulation of the metabolism and disposition resulted from depressed levels of cytochrome P-450 in the hepatic microsomes of the mice administered interferon or poly I:C.

Factors involved in the depression of hepatic mixed function oxidase during infections with Listeria monocytogenes

A number of infections are capable of depressing the capacity of the liver to metabolize drugs. We have studied a number of factors which could be involved in the depression of cytochrome P-450 and related drug biotransformation enzymes during infections with Listeria monocytogenes. During the course of the infection, drug metabolism and heme content of hepatic microsomes were depressed but heme oxygenase was elevated. A free radical scavenger alpha-tocopherol did not prevent the loss and xanthine oxidase activities did not correlate with the time course of the loss. Infections in susceptible (balb/c) mice produced a larger loss in drug metabolism than in resistant (C57BL/6) mice, and an avirulent strain of the bacteria was without effect. A preparation of hemolysin isolated from Listeria monocytogenes produced a dose-dependent loss of cytochrome P-450 in isolated hepatocytes. These experiments indicate that the loss of drug metabolism during Listeria infections is most likely due to hemolysin released by the bacteria.

Changes in hepatic xenobiotic-metabolising enzymes in mouse liver following infection with Leishmania donovani

Infection of mice with Leishmania donovani resulted in decreased activities of several liver enzymes involved in the metabolism of xenobiotics. Microsomal membranes from infected livers contained reduced amounts of cytochromes P450 and b5 and NADPH-cytochrome P450 reductase. Several cytochrome P450 isoenzymes (P450-PB1, P450-PB3, P450-PCN and P450-UT1) and P450-mediated reactions (aminopyrine demethylase, aniline hydroxylase, benzphentamine demethylase and ethoxycoumarin deethylase) were affected similarly. The metabolism of two carcinogens (nitrosodimethylamine and 7,12-dimethylbenz[a]anthracene) by liver microsomal membrane preparations was also reduced. Leishmania infection caused an increase of cytosolic epoxide hydrolase and microsomal epoxide hydrolase and NADH-cytochrome b5 reductase were unaffected. The results suggest that Leishmania-infected animals are likely to have altered responses to exogenous toxins compared to uninfected animals.

Comparison of propranolol-binding plasma proteins in sheep with those in humans, dogs and rats

Alpha 1-acid glycoprotein (AGP), a plasma protein responsible for the binding of a variety of basic lipophilic drugs including propranolol, is different from other plasma proteins in being nonprecipitable after treatment with 1.2M perchloric acid (PCA). To assess the contribution of AGP to drug disposition in sheep and three other species (rats, dogs, and humans), the binding of [3H]propranolol was measured before and after PCA precipitation. PCA precipitation reduced propranolol binding 14-fold in sheep, compared to 2- to 3-fold in the other species. This implied either that sheep AGP binds less propranolol than other species, or that the AGP in sheep is more precipitable. It was not due to inherently poor propranolol binding, as whole sheep plasma bound a higher fraction than the other species. When samples of PCA-precipitated sheep plasma were analyzed using polyacrylamide gel electrophoresis, the concentration of AGP was 10-20% that of the other species. Phenobarbital induction was used as a tool to examine the changes in the plasma protein profile. Phenobarbital induced propranolol binding and AGP along with two other proteins in sheep. One of these proteins migrated similarly to AGP deglycosylated by peptide-N-glycosidase F. It is postulated that the greater precipitability of propranolol binding in sheep is due to a less glycosylated form of AGP which is not important in other species.

In vivo effects of immunostimulating lipopeptides on mouse liver microsomal cytochromes P-450 and on paracetamol-induced toxicity

Immunomodulating lipopeptides lauroyl-L-Ala-gamma-D-Glu-LL-A2pmNH2-Gly (RP 44.102) and lauroyl-L-Ala-gamma-D-Glu-LL-A2pmNH2 (RP 56.142) were found to protect mice against the hepatotoxicity of paracetamol, which is due to cytochrome P-450 dependent formation of toxic metabolites and radicals. In fact they decreased the amount of hepatic microsomal cytochrome P-450, and the level of CCl4-induced lipid peroxidation. In contrast lauroyl-L-Ala-gamma-D-Glu-DD-A2pmNH2 (RP 53.204), which only differs by the configuration of the two chiral carbons of A2pm (diaminopimelic acid) and is not an immunomodulating agent, failed to protect against poisoning by paracetamol and had no effect on the level of hepatic cytochrome P-450 or the microsomal CCl4-induced lipid peroxidation. This provides a clear connection between the immunostimulating properties of a compound and its effects on xenobiotic biotransformations.

The effects of acute-phase inducers and dimethyl sulphoxide on delta-aminolaevulinate synthase activity in human HepG2 hepatoma cells

The effects of acute-phase inducers and dimethyl sulphoxide (Me2SO) on delta-aminolaevulinate (ALA) synthase in HepG2 cells were examined. Treatment of cells with Me2SO resulted in a significant increase in ALA synthase activity. Interleukin-6 increased ALA synthase activity only slightly, but it substantially potentiated the induction of ALA synthase by Me2SO. These data suggest that ALA synthase activity in liver is altered during acute-phase reactions.

Effect of endotoxin to differentially affect cytochrome P-450 monooxygenase activities of untreated rats and animals induced with phenobarbital or 3-methylcholanthrene

The effect of endotoxin in decreasing the cytochrome P-450-dependent metabolism of aniline, aminopyrine and ethoxycoumarin was examined in untreated rats, and in rats pretreated with either phenobarbital or 3-methylcholanthrene. Ethoxycoumarin metabolism was determined at two substrate concentrations (5 microM and 500 microM) to determine the effect of endotoxin on the high and low affinity enzyme activities. In untreated animals, endotoxin depressed both aniline and ethoxycoumarin metabolism by the high and low affinity enzymes by approximately 70%, but aminopyrine was decreased by only 47%. In phenobarbital pretreated rats, endotoxin decreased enzyme activities less than in untreated animals. Aniline metabolism and low affinity ethoxycoumarin metabolism were decreased by only 24%, and aminopyrine metabolism was decreased by 35%. The high affinity ethoxycoumarin metabolism was least affected, being decreased by only 12%. In 3-methycholanthrene pretreated rats, aniline and ethoxycoumarin (500 microM) metabolism were decreased by approximately 45%, but aminopyrine metabolism was only decreased by 20%. In these animals, endotoxin did not significantly affect the activity of ethoxycoumarin metabolism assayed with the low substrate concentration. Endotoxin decreased total cytochrome P-450 level of untreated rats by 32%, of phenobarbital pretreated rats by 39%, and in 3-methylcholanthrene pretreated animals the decrease was only 21%. Heme oxygenase activity of untreated animals was induced most by endotoxin administration and least in phenobarbital treated rats. The data suggest that endotoxin may differentially affect the various isozymes of cytochrome P-450 associated with the metabolism of aniline, aminopyrine and ethoxycoumarin. The results also suggest that the isozymes associated with these activities in untreated, phenobarbital or 3-methylcholanthrene pretreated rats may differ in their sensitivity to the effect of endotoxin.