Importance of T-cell-dependent inflammatory reactions in the decline of microsomal cytochrome P450 concentration in the livers of rats infected with Fasciola hepatica

[Pharmacokinetics characteristics of dexamethasone in Crush syndrome model rats]

Crush syndrome (CS) is characterized by ischemia/reperfusion-induced rhabdomyolysis and subsequent systemic inflammation and has a high mortality rate, even when treated with conventional therapy. In previous studies, we demonstrated that treatment of rats with acute lethal CS using dexamethasone (DEX) had therapeutic effects in laboratory findings and improved the clinical course of CS. However, because the application of DEX in CS therapy is unknown, evaluation of the pharmacokinetic parameters of DEX was considered essential to support its clinical use. Here, we investigated the pharmacokinetic characteristics of DEX in a rat model of CS. Anesthetized rats were subjected to bilateral hind limb compression using rubber tourniquets for 5 h, followed by reperfusion for 0 to 24 h. Rats were divided randomly into 4 groups: saline-treated sham (S) and CS groups and 5.0 mg/kg DEX-treated S (S-DEX) and CS (CS-DEX) groups. Blood and tissue samples were collected for HPLC analysis. In the CS-DEX group, the pharmacokinetic parameters of the area under the concentration-time curve, mean residence time, and distribution volume levels increased significantly compared to the S-DEX group, whereas total body clearance, elimination rate constant, and renal clearance levels decreased significantly. Moreover, decrease of muscle tissue DEX concentration and of CYP3A activity were observed in the CS-DEX group. These results show the pharmacokinetic characteristics of DEX in the rat CS model and support the potential use of DEX in disaster medical care.

Effect of widely used combinations of antiretroviral therapy on liver CYP3A4 activity in HIV-infected patients

AIMS

To evaluate the effects of combined antiretroviral drugs (HAART) on liver CYP3A4 activity using the [(14)C-N-methyl]-erythromycin breath test (ERMBT).

METHODS

HIV-infected patients (31 women, 30 men) with mean (+/- SD) age of 38 +/- 9 years were enrolled and underwent complete clinical and laboratory evaluation. Patients were divided into five groups and were treated with two nucleoside analogues (NAs) and one of the following: nelfinavir alone (n = 13), any ritonavir-boosted protease inhibitor with (n = 8) or without (n = 13) nevirapine, nevirapine alone (n = 15), or a third NA (n = 12). Three or four ERMBTs were performed 7 days prior to (D-7) and at the beginning of treatment (D0), D14 (only for patients taking nevirapine) and on D28.

RESULTS

Mean baseline liver CYP3A4 activity displayed high interindividual variability (47%) but low intraindividual variability (15%). Women had 30% higher ERMBT values than men [2.7 +/- 1.3 vs. 1.9 +/- 0.7; 95% confidence interval (CI) 20.5, 49.5; P = 0.003]. The ERMBT data correlated with body weight, alpha- and beta-globulins and alanin aminotransferases (0.10 < r(s) < 0.20; P < 0.01). Whereas nevirapine had no effect on liver CYP3A4 activity, nelfinavir-based and ritonavir-boosted drug regimens inhibited it by 69% (95% CI 64.7, 72.9; P = 0.005) and by 95% (95% CI 93.3, 96.7; P = 0.001), respectively.

CONCLUSION

Evaluation of the effect of HAART on liver CYP3A4 activity may aid in preventing inappropriate treatment regimens in HIV-infected patients.

The beneficial effect of trolox on sepsis-induced hepatic drug metabolizing dysfunction

Trolox is a hydrophilic analogue of vitamin E. The aim of this study was to investigate its effects on hepatic injury, especially alteration in cytochrome P450 (CYP)-dependent drug metabolism during polymicrobial sepsis. Rats were subjected to polymicrobial sepsis by cecal ligation and puncture (CLP). The rats were treated intravenously with Trolox (2.5 mg/kg) or vehicle, immediately after CLP. Serum aminotransferases and lipid peroxidation levels were markedly increased 24 h after CLP. This increase was attenuated by Trolox. Total CYP content and NADPH-P450 reductase activity decreased significantly 24 h after CLP. This decrease in CYP content was attenuated by Trolox. At 24 h after CLP, there was a significant decrease in the activity of these CYP isozymes: CYP1A1, 1A2, 2B1, and 2E1. However, Trolox differentially inhibited the decrease in CYP isozyme activity. Trolox had little effect on the decrease in CYP1A1 activity but Trolox significantly attenuated decreases in CYP1A2 and 2E1 activities. In fact, Trolox restored CYP2B1 activity to the level of activity found in control rats. Our findings suggest that Trolox reduces hepatocellular damage as indicated by abnormalities in hepatic drug-metabolizing function during sepsis. Our data also indicates that this protection is, in part, caused by decreased lipid peroxidation.

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.

Effect of hypoxia alone or combined with inflammation and 3-methylcholanthrene on hepatic cytochrome P450 in conscious rabbits

1 To investigate the effect of moderate hypoxia alone or combined with an inflammatory reaction or after 3-methylcholanthrene (3MC) pre-treatment on cytochrome P450 (P450), conscious rabbits were exposed for 24 h to a fractional concentration of inspired O2 of 10% (mean PaO2 of 34 mmHg). Hypoxia decreased theophylline metabolic clearance (ClM) from 1.73+/-0.43 to 1.48+/-0.13 ml min-1 kg-1 (P<0. 05), and reduced (P<0.05) the formation clearance of theophylline metabolites, 3-methylxanthine (3MX), 1-methyluric acid (1MU) and 1,3-dimethyluric acid (1,3DMU). Hypoxia reduced the amount of CYP1A1 and 1A2 but increased CYP3A6 proteins. 2 Turpentine-induced inflammatory reaction reduced (P<0.05) the formation clearance of 3MX, 1MU, and 1,3DMU, and diminished the amount of CYP1A1, 1A2 and 3A6 proteins. However, when combined with hypoxia, inflammation partially prevented the decrease in ClM, especially by impeding the reduction of 1,3DMU. The amount of CYP1A1 and 1A2 remained reduced but the amount of CYP3A6 protein returned to normal values. 3 Pre-treatment with 3MC augmented the ClM by 114% (P<0.05) due to the increase in the formation clearance of 3MX, 1MU and 1,3DMU. 3MC treatment increased the amount of CYP1A1 and 1A2 proteins. Pre-treatment with 3MC prevented the hypoxia-induced decrease in amount and activity of the P450. 4 It is concluded that acute moderate hypoxia and an inflammatory reaction individually reduce the amount and activity of selected apoproteins of the P450. However, the combination of hypoxia and the inflammatory reaction restores P450 activity to near normal values. On the other hand, pre-treatment with 3MC prevents the hypoxia-induced depression of the P450.

Decrease in hepatic CYP2C11 mRNA and increase in heme oxygenase activity after intracerebroventricular injection of bacterial endotoxin

We previously reported (Arch. Toxcol. 1998, 72, 492-498) that the differential decrease in the levels of hepatic cytochrome P450 (CYP) isozymes in rats was observed 24 hr after intracerebroventricular (i.c.v.) injection of bacterial lipopolysaccharide (LPS) at the dose ineffective (0.1 microgram) when injected intraperitoneally (i.p.). Among CYP isozymes we examined, the male specific CYP isozyme, CYP2C11 was most severely affected by i.c.v. injection of LPS. In this study, we examined the gene expression of CYP2C11, the total P450 contents, the CYP2C11-dependent activity of imipramine N-demethylase (IMND) and protein of CYP2C11 10 hr after i.c.v. or i.p. injections of LPS. Intracerebroventricular injection of LPS significantly decreased the level of CYP2C11 mRNA (to 63% of saline i.c.v. control), the total P450 contents (to 70% of saline i.c.v. control), the IMND activity (to 74% of saline i.c.v. control), but not protein of CYP2C11 in rat liver. In contrast, i.p. injection of LPS at the same dose as i.c.v. did not significantly affect these parameters. Since CYP is a heme protein, we also measured the activity of heme oxygenase (HO) using the same rat liver microsomes. The HO activity was increased to 166% by i.c.v. injection of LPS and 135% by i.p. injection of LPS compared to corresponding saline control. It is suggested that i.c.v. injection of LPS down-regulates the expression of CYP2C11 at transcriptional level and that both the decrease in CYP2C11 mRNA and the increase in heme degradation may be involved in the decreased level of protein and activity of CYP2C11 by i.c.v. injection of LPS in rat liver.

Liver pathology and immune response in experimental Fasciola hepatica infections of goats

The relationship between the immune response and the pathogenesis of the disease was studied in different primary and secondary experimental Fasciola hepatica infections of goats. The establishment of the infection, measured as percentage of recovered flukes at the necropsy, was similar in primarily and secondarily infected animals (between 19.7% and 24.3%), but the hepatic damage was much more severe in secondarily infected goats, as revealed by the levels of serum hepatic enzymes GGT and LDH. Primary infection evolves to chronic fasciolosis that did not induce the development of resistance, since goats were highly susceptible to secondary infection, showing severe acute and chronic hepatic lesions that led to the death of some animals in each group. The immune response to the infection was proved by the production of specific IgG antibodies to ESP of F. hepatica and the involvement of CD3+ T lymphocytes and lambda IgG+ plasma cells in the hepatic infiltrate. Secondary infection did not induce any difference in either IgG response or in the cellular composition of the infiltrate of hepatic lesions, although this was much more extended. However, neither antibodies nor cell-mediated response were protective: there was no correlation between IgG levels and fluke burden and there was no evidence of cell-mediated killing of the parasite. This suggests the existence of some immune evasion mechanisms in goat infection with F. hepatica. The parasite may depress the local inflammatory and immune response, as suggested by the scarcity of CD3+ T cells in the infiltrate surrounding acute migratory tunnels. Moreover, in secondary infected goats can be suspected an immunological damage of the liver, since a very severe infiltrate of immune cells replaced wide areas of hepatic parenchyma and an immune-mediated damage of hepatocytes could occur.

Fasciola hepatica infection in sheep: changes in liver metabolism

Several aspects of liver function during infection with Fasciola hepatica were examined in sheep four weeks after infection and compared with the changes observed in infected rats. Previously reported respiratory abnormalities in mitochondria isolated from the left lobe of the liver of infected sheep were characterised further. Evidence is presented that the respiratory lesion is located in the mitochondrial electron transport chain and that the aberrant respiratory behaviour is not associated with an increase in nonesterified fatty acids and the depletion of mitochondrial phospholipids, as is the case in the rat. Microsomal membranes, which have also been shown to be depleted of phospholipids in the fluke-infected rat liver, showed no such changes in the sheep. However, in common with the rat, a substantial loss of cytochrome P450 was recorded in microsomes prepared from the left lobe, and the glycogen content of the left lobe was found to be less than 50 per cent of control values. No change was observed in glucose 6-phosphatase activity. All these changes were localised effects, confined to areas of fluke infiltration.