Hepatic drug metabolizing activity in rats with carrageenan-induced inflammation

Effect of experimental diabetes mellitus and arthritis on the pharmacokinetics of hydroxychloroquine enantiomers in rats

PURPOSE

To study the effect of experimental diabetes and arthritis on the pharmacokinetics of hydroxychloroquine (HCQ) enantiomers in rats.

METHODS

The pharmacokinetic studies were carried out following administration of 40 mg/kg of racemic HCQ to diabetic, insulin-treated diabetic, adjuvant arthritic and control rats.

RESULTS

Renal (70% and 62% for R- and S-HCQ, respectively) and non-renal clearance (100% and 145% for R- and S-HCQ, respectively) of HCQ enantiomers were significantly increased in diabetic rats. Diabetes-induced alterations in the disposition of HCQ were reversed by insulin treatment. In arthritic rats, systemic clearance (CL) of HCQ enantiomers was significantly reduced (1.05 +/- 0.15 and 1.3 +/- 0.19 l/h/kg for R- and S-HCQ, respectively) compared to controls (1.69 +/- 0.32 and 1.93 +/- 0.34 l/h/kg for R- and S-HCQ, respectively). The fraction unbound of the R- and S-HCQ were 49.4% and 50.5% lower in platelet rich plasma of arthritic rats compared to healthy rats. Increased blood concentrations of HCQ enantiomers in arthritic rats were significantly related to the degree of inflammation.

CONCLUSIONS

Diabetes significantly increased the CL of both R- and S-HCQ by increasing renal and non-renal clearance. Arthritis caused a significant decrease in CL of HCQ enantiomers through increased binding and a decreased intrinsic clearance. The effect of the diseases on the pharmacokinetics of HCQ, however, was not stereoselective.

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.

Effect of carrageenan-induced granuloma on hepatic cytochrome P-450 isozymes in rats

Carrageenan-induced granuloma was used to study the apoprotein and RNA content, and catalytic activities of several cytochrome P-450 isozymes in liver. This model allowed discrimination between acute and chronic phases of experimental inflammation. The expression of most isozymes studied (CYP2D, CYP2E1, CYP3A1 and CYP4A) was reduced to 20% of the control level during the acute phase and partially recovered (30-60% of control group) during the chronic phase. CYP2B1 content was decreased to 65% of control during the acute and chronic phases of inflammation. RNA (CYP2B1 and CYP2E1) showed a strong depression during the acute phase and recovered during the chronic phase, without differences between isoenzymes. In most cases, there was a good correlation between the apoprotein content of isozymes and related activities. Our results show that the depletion of cytochrome P-450 induced by inflammation depends on the severity of the disease. Experimental inflammation equally affect the transcription of CYP2B1 and CYP2E1, so differences in apoprotein content and related activities between isozymes may due to differential posttranscriptional regulation.

Action of methotrexate on cytochrome P-450 monooxygenases in rats. Study performed with [13C]-aminopyrine micro breath test

The aim of this work was to study the action of methotrexate on the cytochrome P-450 hepatic monooxygenases and to follow the evolution of the metabolic processes with time, after oral and intra-peritoneal administration of these drugs to rats. In order to perform this study, we used a new technique the [13C]-aminopyrine breath test (ABT). At the end of the in vivo study, the rats were sacrificed and the cytochrome P-450 concentration as well as microsomal enzymatic activities of aminopyrine N-demethylase, 7-ethoxyresorufin desalkylase, 7-ethoxycoumarin desalkylase, 7-pentoxyresorufin desalkylase were determined. A histological study of the liver was also carried out. Finally, haematological and biochemical parameters were also determined. In this study, 3 series of 6 rats were used: a control group, a group receiving 70 mg/kg of methotrexate by intra-peritoneal route, and a group of rats treated orally with 1 mg/kg of methotrexate every 2 days. For each observation, the variation of the ABT scores and of the cytochrome P-450 amounts as well as the microsomal aminopyrine N-demethylase activity were in good agreement.

Effects of acute and chronic inflammation on the pharmacokinetics of prednisolone in rats

The effects of acute and chronic stages of carrageenan-induced air-pouch inflammation on the pharmacokinetics of prednisolone were studied in male Wistar rats. Chronic inflammation produced a significant increase in the area under the curve (AUC) of prednisolone compared to control animals (6594 +/- 2144 vs 3530 +/- 2164 micrograms.hr/L). The effect of acute inflammation was not significant (AUC = 4996 +/- 3813). Both acute and chronic inflammation also reduced the in vitro plasma protein binding of prednisolone, the reduction being much greater after chronic inflammation. The AUC of free prednisolone after chronic inflammation was 3141 micrograms.hr/L, compared to 1121 micrograms.hr/L in the control group and 1823 micrograms.hr/L after acute inflammation. The mean values of half-life and apparent volume of distribution at steady-state in each group were similar. These results indicate that prednisolone must be used with caution in the treatment of inflammatory diseases because of higher free concentrations of the steroid.