The effect of IFN-alpha-Con1 on hepatic cytochrome P-450 and protein synthesis and degradation in hepatic microsomes

Regulation of drug metabolism and disposition during inflammation and infection

The expression and activity of cytochrome P450 (CYP) is altered during periods of infectious disease or when an inflammatory response is activated. Most of the major forms of CYP are affected in this manner and this leads to a decrease in the capacity of the liver and other organs to handle drugs, chemicals and some endogenous compounds. The loss in drug metabolism is predominantly an effect resulting from the production of cytokines and the modulation of the transcription factors that control the expression of specific CYP forms. In clinical medicine numerous examples have been reported indicating the occurrence of compromised drug clearance and changes to pharmacokinetics during disease states with an inflammatory component or during infections. For any drug that is metabolised by CYP and has a narrow therapeutic index, there is a significant risk in placing patients in a position where an infection or inflammatory response might lead to aberrant drug handling and an adverse drug response.

Alteration of drug biotransformation and elimination during infection and inflammation

During infection or inflammation, the expression of cytochrome P450 and its dependent biotransformation pathways are modified. This results in a change in the capacity of the liver to handle drugs and in alterations in the production and elimination of endogenous substances throughout the body. The majority of the CYP isoforms are modified at pre-translational steps in protein synthesis, and, in most cases, cytokines are involved as mediators of the response. Recent information suggests that inflammatory responses that are localized to the CNS cause a loss of CYP within the brain. This is accompanied by a parallel down-regulation of CYP in peripheral organs that is mediated by a signaling pathway between the brain and periphery. This review covers the loss that occurs in the major mammalian CYP families in response to infection/inflammation and the mediator pathways that are key to this response.

Effects of Plasmodium berghei infection on cytochromes P-450 2E1 and 3A2

Metabolism and disposition of most drugs used to treat malaria are substantially altered in malaria infection. Few data are available that specify effects of malaria infection on drug metabolism pathways in humans or animal model systems. In this report, studies were undertaken to determine the effect of Plasmodium berghei infection on cytochrome P-450 (CYP450) 2E1 and 3A2-mediated metabolism and enzyme expression in rat liver microsomes. Malaria infection (MAL) resulted in significant decreases in total cytochrome P-450 content (56%, P < 0.05) and NADPH cytochrome P-450 reductase activity (32%, P < 0.05) as compared to control (CON) rats. Chlorzoxazone 4-hydroxylase activity (CYP2E1-mediated) showed no significant difference between CON and MAL microsomes while testosterone 6-beta-hydroxylase activity (CYP3A2-mediated) was reduced by 41% (P < 0.05) in MAL. Enzyme kinetic studies and immunoblot analysis indicate that the loss of activity for CYP3A2 in malaria infection is due to significantly decreased CYP3A2 protein expression. The altered expression of CYP450s in malaria infection should be taken into account when treating patients with malaria in order to minimize drug-drug interactions or toxicity.

Depression of the hepatic cytochrome P450 by an acute inflammatory reaction: characterization of the nature of mediators in human and rabbit serum, and in the liver

There is increasing evidence suggesting that several mediators are involved in the cascade of events leading to the depression of the cytochrome P450 (P450) by an inflammatory reaction. The present study aimed to confirm the presence of mediators in the serum (RS(INFLA)) and hepatocytes (H(INFLA)) of rabbits with an acute inflammatory reaction, and in the serum of humans with an acute upper respiratory tract viral infection (HS(URTVI)). The inflammatory reaction was induced by the s.c. injection of 5 ml of turpentine. Incubation of RS(INFLA) or HS(URTVI) with H(INFLA) depressed the P450, diminished the formation of theophylline metabolites (3-methylxanthine, 1-methyluric acid, and 1,3-dimethyluric acid), and increased lipid peroxidation. The addition of preheated RS(INFLA) or HS(URTVI) to H(INFLA) did not diminish the amount of P450 or theophylline metabolites, and prevented the increase in lipid peroxidation. Incubating the filtrate of RS(INFLA) or HS(URTVI) dialyzed through membranes with cut-off of 10, 30, 50 and 100 kd, with H(INFLA) showed that rabbit and human mediators have molecular weights ranging from 10 to 30 kd. Incubation of H(INFLA) with hepatocytes from control rabbits (H(CONT)) did not decrease further the P450. However, when RS(INFLA) was added to co-cultured H(CONT) + H(INFLA), the depression of P450 was 37% greater (p<0.05), and the amount of theophylline metabolites generated was around 30% (p<0.05) smaller than that observed when H(CONT) or H(INFLA) were incubated with RS(INFLA). Based on the present results we may speculate that human and rabbit serum mediators are proteins of molecular weights ranging from 10 to 30 kd, and in addition, primed hepatocytes once exposed to the serum mediators release mediators able to depress the P450 in H(CONT).

Down-regulation of the hepatic cytochrome P450 by an acute inflammatory reaction: implication of mediators in human and animal serum and in the liver

1. Infection and inflammation trigger a cascade of mediators that eventually will down-regulate the hepatic cytochrome P450 (P450). The present study aimed to characterize the mediators contained in the serum of rabbits with an acute inflammatory reaction (AIR) induced by the s.c. injection of turpentine (5 ml), and in the serum of humans with an acute upper respiratory tract viral infection. 2. Hepatocytes from control (H(CONT)) rabbits and rabbits with an AIR (H(INFLA)) were isolated and cultured. Compared with H(CONT) in H(INFLA) the production of theophylline metabolites, 3-methylxanthine (3MX), 1-methyluric acid (1MU), and 1,3-dimethyluric acid (1,3DMU) was reduced as was the amount of total P450, while lipid peroxidation was increased. Incubation of H(INFLA) with serum of rabbits with an AIR (RS(INFLA)) for 4 h further reduced the formation of the metabolites of theophylline as well as the amount of P450, and enhanced the lipid peroxidation. RS(INFLA) obtained 6, 12 and 24 h after the injection of turpentine showed the same ability to down-regulate hepatic P450 as the serum obtained at 48 h. 3. The efficacy (Emax) of RS(INFLA) to inhibit the formation of theophylline metabolites differed, i.e. 1,3DMU > 1MU > 3MX, and the potency of serum mediators (IC50) was similar for 3MX and 1MU, but lower for 1,3DMU. 4. Incubation of serum of human volunteers (HS(INFLA)) with a viral infection with H(CONT) or H(INFLA) reduced the production of theophylline metabolites, as well as the amount of P450, and increased the lipid peroxidation. HS(INFLA) depressed 1,3DMU more efficiently than 3MX and 1MU. HS(INFLA) reduced 3MX with greater efficacy than did RS(INFLA). Potency was very variable but not different from rabbits. 5. It is concluded that the serum of rabbits with an AIR or of humans with a viral infection contain several mediators that inhibit noncompetitively various isoenzymes of the hepatic P450. The decrease in P450 induced by HS(INFLA) or RS(INFLA) is closely associated with the increase in lipid peroxidation (r2= 0.8870) suggesting that lipid peroxidation could directly or indirectly be involved in the P450 down-regulation.

Cytochrome P4501A1 and cytochrome P4501A2 are downregulated at both transcriptional and post-transcriptional levels by conditions resulting in interferon-alpha/beta induction

The interferon mediated downregulation of constitutive and inducible cytochrome P450 enzymes occurs through a pretranslational mechanism which depresses the mRNA encoding cytochrome P450s. We measured the transcription rates of CYP1A genes and the turnover of CYP1A mRNA in rats treated with the interferon-alpha/beta inducer polyinosinic acid-polycytidylic acid. The rate of transcription of CYP1A1 and CYP1A2 genes was significantly decreased in hepatic nuclei isolated from male rats treated with polyinosinic acid-polycytidylic acid (10 mg/kg). In addition the rate of degradation of hepatic CYP1A1 and CYP1A2 mRNA was examined following the inhibition of de novo transcription by actinomycin D (1 mg/kg). Messenger RNA levels were analysed by Northern and slot blotting with a 1.2 kb murine CYP1A1 cDNA probe. Interferon significantly augmented the rate of loss of CYP1A1 and CYP1A2 mRNAs suggesting that post-transcriptional degradation of mRNA contributes to the pre-translational events that cause cytochrome P450 downregulation. These results support the involvement of both transcriptional and post-transcriptional mechanisms in the loss of cytochrome P450s mediated by interferon inducers.

Interferon-mediated changes in the expression of CYP1A1 in human B lymphoblastoid (AHH-1 TK +/-) cells

The expression of constitutive and inducible cytochrome P450s has been shown to be downregulated by interferon through an unknown pretranslational mechanism that depresses the mRNA encoding P450 apoproteins. To establish an association between gene transcription and P450 apoprotein downregulation by interferon, we studied the effect of recombinant interferon (IFN-alpha 2a) on CYP1A1 in human B lymphoblastoid cell lines. The cHoI cell line expresses inducible native CYP1A1, while the genetically engineered derivative h1A1 v2 expresses a noninducible extrachromosomal vector-derived human CYP1A1 cDNA lacking the CYP1A1 promoter region. We characterized CYP1A1 activity, apoprotein, and mRNA by ethoxyresorufin O-deethylase activity, Western immunoblotting, and Northern blot analysis, respectively. In cHoI cells, following induction with dibenz[a,h]anthracene, interferon depressed CYP1A1 apoprotein and mRNA levels by 55 and 76%, respectively, with no detectable changes in enzyme activity. In h1A1 v2, however, interferon increased CYP1A1 activity, apoprotein, and mRNA. The depression of CYP1A1 mRNA and apoprotein levels incHoI cells, in contrast with the increase observed in h1A1 v2 cells, suggests that nuclear mechanisms are essential for interferon-mediated depression of inducible P450s. From our preliminary results we propose that interferon-mediated downregulation of CYP1A1 may result from inhibition of gene transcription.

Depression of cytochrome P-450 in mouse liver induced by fractions from Nocardia opaca

We measured the liver cytochrome P-450 content of mice 24 h after they had been injected with the following immunoadjuvants: Nocardia opaca derivatives and peptidoglycans from several bacterial strains. The cell wall fraction was not active, the others diminished liver cytochrome P-450 levels. The dose-response activity varied with the bacterial origin of the peptidoglycans. These findings indicate that the toxicity and efficiency of immunochemotherapeutic protocols can be modified by altering drug metabolism.

The effects of an interferon inducer, polyriboinosinic polyribocytidylic acid on cytochrome P-450 dependent hepatic progesterone metabolism

A time course study on the effects of an interferon inducing agent, polyriboinosinic polyribocytidylic acid (poly rIrC) on the hepatic cytochrome P-450 dependent progesterone metabolism was performed. Administration of a single dose of poly rIrC (10 mg/kg i.p.) to adult male Wistar rats caused a time dependent effect on liver weight, microsomal protein and total cytochrome P-450 levels, as well as the 16 alpha and 6 beta hydroxylation of progesterone. The response was multiphasic, with a maximal depression of both hydroxylase activity 48 hours post-injection, followed by enhanced activity at 72 hours and subsequent return to control activity twenty-four hours later. A second less dramatic rise in the activities followed, bringing the 16 alpha and 6 beta hydroxylase activity to 159% and 141% of their respective control values by 336 hours, at which point of time, the trend appeared to be still on the rise. The enhanced activity at 72 hours was preceded by an increase in serum cortisol and corticosterone levels, the ability of which to enhance the activity of 6 beta hydroxylation of steroids may partly explain the phenomenon.

The suppression of hepatic cytochrome P4504A mRNA mediated by the interferon inducer polyinosinic acid.polycytidylic acid

Interferon and interferon inducers are well known to depress the cytochrome P450-dependent hepatic mixed-function oxidase system and cause a decrease in the capacity of the liver to metabolize drugs and xenobiotics. In this study we have shown that the interferon-mediated changes in an induced form of hepatic cytochrome P450 (CYP4A) are mediated via a depression in the levels of mRNA as assessed by Northern blot and slot blot analyses using a 20-base synthetic oligodeoxyribonucleotide hybridization probe. Rats were pretreated with clofibrate to maximize CYP4A mRNA levels prior to the administration of polyinosinic acid.polycytidylic acid (poly IC), an alpha/beta interferon inducer. Hepatic CYP4A mRNA levels were decreased by 49 and 30% at 6 and 24 hr, respectively, following poly IC administration. In hepatic microsomes cytochrome P450 and functional CYP4A as measured by lauric acid hydroxylation, were not affected at 6 hr, but were depressed by 39 and 27%, respectively, 24 hr following poly IC administration. These results suggest that interferon depresses induced levels of hepatic drug metabolism by lowering the level of cytochrome P450 mRNAs and subsequent synthesis of cytochrome P450 apoproteins.