Aminopyrine N-demethylase Activity Research Articles

Comparison of the florfenicol metabolic rate in Portunus trituberculatus individuals with different body weights

We analysed the metabolic rate of large individuals (LIs) and small individuals (SIs) (based on body weight) of 80-day-old specimens of Portunus trituberculatus injected with 40 mg/kg florfenicol (FLR). The results showed that FLR contents in the gills and hepatopancreas were higher in the SIs than in the LIs. The activities of erythromycin N-demethylase and 7-ethoxyresorufin-O-deethylase related to cytochrome oxidase P450 (CYP) were induced after FLR injection and showed a size-dependent pattern; however, no significant difference in aminopyrine N-demethylase activity was found between the LIs and SIs. The activity of the phase II enzyme glutathione S-transferase (GST) increased in the hepatopancreas after FLR injection, and it was higher in the SIs than the LIs. Moreover, induction of CYP2, CYP3, GST, ABCB and ABCG was observed in the first 24 hr after FLR injection. FLR caused more biomolecular damage in the SIs than the LIs, displaying an obvious body weight- and time-dependent pattern. In summary, the SIs exhibited faster FLR uptake and slower depuration in this species, and FLR caused more biomolecular damage to the SIs.

Effect of Seabuckthorn leaves on Antioxidant and Microsomal Enzymes in poultry birds

In vivo studies on broiler birds were carried out to evaluate effect of aflatoxin and seabuckthorn leaves on microsomal enzyme system, antioxidant enzymes and biochemical parameters i.e. serum triglyceride, total plasma protein, aminopyrine demethylase, aniline hydroxylase, NADPH cytochrome P450 reductase, catalase, LPO, superoxide dismutase, GSH, blood urea nitrogen (BUN) and creatinine levels in poultry. The poultry birds were divided into six groups containing six birds each. Aflatoxin (400 ppb) and seabuckthorn leaves (10000ppm) was administered continuously in poultry feed. Aflatoxin increased serum triglyceride, blood urea nitrogen and creatinine levels where as seabuckthorn leaves supplementation at 10000ppm significantly decreased triglyceride (P<0.05), blood urea nitrogen (P<0.05) and creatinine levels in birds. Toxin decreased liver, kidney and blood superoxide dismutase (SOD), catalase (CAT) and glutathione (GSH) activity, whereas, seabuckthorn leaves (SBTL) increased the activity of these enzymes as compared to control group. The level of lipid peroxidation was significantly increased in the toxin exposed group and decreased in case of SBTL. The activity of Aminopyrine demethylase and Aniline hydroxylase increased, while the activity of NADPH cytochrome P450 reductase is decreased in case of toxin group whereas in case of seabuckthorn leaves exposed group showed no significant change in case of aminopyrine demethylase and NADPH cytochrome P450 reductase, however, the activity of Aniline hydroxylase decreased. On the basis of present study, it could be concluded that the seabuckthorn leaves reduced the effect of Aflatoxin which produced oxidative stress by altering the levels of antioxidant enzymes of liver and kidney in adult poultry birds.

Biotransformation and tissue distribution of protopine and allocryptopine and effects of Plume Poppy Total Alkaloid on liver drug-metabolizing enzymes

In this study, the biotransformation in the plasma, urine and feces of rats following oral administration of protopine (PRO) and allocryptopine (ALL)were explored using HPLC-QqTOF MS. An HPLC-MS/MS method for the determination of tissues was developed and applied to the tissue distribution study in rats following intragastric administration of Plume Poppy Total Alkaloid for 3 weeks. A total of ten PRO metabolites and ten ALL metabolites were characterized in rats in vivo. Among these metabolites, six PRO metabolites and five ALL metabolites were reported for the first time. The predicated metabolic pathways including ring cleavage, demethylation following ring cleavage, and glucuronidation were proposed. The low-concentration residue of PRO and ALL in various tissues was detected at 24 h and 48 h after dosing, which indicated that both compounds could be widely distributed in tissues and exist as low levels of residue. The activities of erythromycin N-demethylase, aminopyrine N-demethylase and NAD (P)H quinone oxidoreductase in female rats can be induced post-dose, but these activities were inhibited in male rats. The proposed biotransformation and residues of PRO and ALL and their effects on enzymes may provide a basis for clarifying the metabolism and interpreting pharmacokinetics.

Evaluation of the efficiency of isolated bacterial consortium PMB11 in removal of colour, degradation and reduction of toxicity from textile dye effluent

AbstractThe aim of the present study was to investigate the textile effluent degrading potential of an isolated bacterial consortium PMB11. The consortium had the capacity to decolourize various textile dyes and textile effluent. Ninetyone percent textile effluent decolourization was observed within 120 hours. The physiochemical characterization of textile effluent indicates reduction in the total hardness (CaCO3), fluorides, chlorides, sulphate, chemical oxygen demand, and biochemical oxygen demand of textile effluent after treatment with consortium PMB11. Induction in the activities of NADHdichlorophenolindophenol reductase, azoreductase, and aminopyrine N-demethylase was observed after decolourization, which indicates involvement of these enzymes in the decolourization and degradation process. The biodegradation of dyes from effluent was confirmed using various analytical techniques, such as UV-Vis spectroscopy, Fourier transform infrared spectroscopy, gas chromatography - mass spectroscopy, and HPLC. A phytotoxicity study was performed to confirm the less toxic nature of the degradation metabolites than the effluent.

Differential Modulation of Xenobiotic-Metabolizing Enzymes in Rats Following Single and Concurrent Exposure to Chlorpyrifos, Arsenic, and Ascorbic Acid

The present study was undertaken to evaluate the subacute toxicity of arsenic (As) and chlorpyrifos (CPF) alone or in combination. In addition, the ameliorative effect of ascorbic acid on As and/or CPF-induced hepatic microsomal xenobiotic metabolizing enzymes in rats was examined. Rats were divided into 9 groups of 6 animals each: control (deionized water), vehicle control (groundnut oil), ascorbic acid (100 mg/kg body weight), As (40 ppm in water), CPF (5 mg/kg body weight), As (40 ppm) + CPF (5 mg/kg body weight), As + ascorbic acid, CPF + ascorbic acid, and As + CPF + ascorbic acid. After 28 d of exposure, rats were sacrificed and liver was extracted for isolation of hepatic microsomes. Exposure to As or CPF alone as well as both of these in combination significantly altered microsomal proteins and activity of phase I and phase II xenobiotic-metabolizing enzymes. Cytochrome P-450 and cytochrome b 5 levels and activities of aniline p-hydroxylase (APH) and uridine diphosphate glucuronosyltransferase (UGT) were significantly decreased in groups treated with As, CPF, and As plus CPF, while glutathione S-transferase (GST) was not markedly altered. Enzymatic activity of aminopyrine N-demethylase (ANDM) was also significantly reduced in As- and CPF-only groups. Co-administration of ascorbic acid effectively countered the As- and CPF-induced alterations in xenobiotic-metabolizing enzymes.

Toxic effects of Triclosan on the detoxification system and breeding of Daphnia magna

The toxic effects of different concentrations of Triclosan (TCS) (1-128 μg/L) on Daphnia magna (D. magna) were investigated by acute (48 h) and chronic (21-day) toxicity tests. The response of antioxidase system and Phase I metabolism process of D. magna exposed to TCS were investigated by measuring a series of biomarkers including glutathione S-transferase (GST), catalase (CAT), superoxide dismutase (SOD), malondialdehyde (MDA), 7-ethoxyresorufin O-deethylase (EROD), Erythromycin N-demethylase (ERND) and Aminopyrine N-demethylase (APND). The 48 h LC50 of TCS was 330 μg/L for D. magna. In the chronic test, total number of neonates per female, body length and the intrinsic rate of natural increase (r) of D. magna increased at the low exposure concentrations (1-16 μg/L) and decreased at the high concentrations (64-128 μg/L), while the total number of molting per adult decreased continually. The GST and CAT activities showed no significant increase in all treatments, and SOD activities were induced after 24-h exposure and inhibited after 48-h exposure at 4-128 μg/L of concentrations. The MDA content increased after 6-h exposure but decreased after 48-h exposure at 4-128 μg/L. EROD activities initially increased after 6-h exposure, but decreased after 24 and 48-h exposure, ERND and APND activities showed a similar temporal pattern among different treatments groups. SOD, MDA and APND were sensitive to TCS, thus they are suitable as potential biomarkers for the exposure to TCS.

Effect of atrazine and chlorpyrifos exposure on cytochrome P450 contents and enzyme activities in common carp gills

Chlorpyrifos (CPF) and atrazine (ATR) are the most widely used organophosphate insecticides and triazine herbicides, respectively, worldwide. This study aimed at investigating the effects of ATR, CPF and mixture on common carp gills following 40-d exposure and 40-d recovery experiments. Cytochrome P450 content, activities of aminopyrine N-demethylase (APND) and erythromycin N-demethylase (ERND) and the mRNA levels of the CYP1 family (CYP1A, CYP1B, and CYP1C) were determined. In total, 220 common carps were divided into eleven groups, and each group was treated with a specific concentration of ATR (4.28, 42.8 and 428μg/L), CPF (1.16, 11.6 and 116μg/L) or ATR–CPF mixture (1.13, 11.3 and 113μg/L). The results showed that P450 content and activities of APND and ERND in fish exposed to ATR and mixture were significantly higher than those in the control group. After the 40-d recovery treatment (i.e., depuration), the P450 content and the activities of APND and ERND in fish decreased to the background levels. A similar tendency was also found in the mRNA levels of the CYP1 family (CYP1A, CYP1B, and CYP1C) in common carp gills. The CPF-treated fish showed no significant difference from the control groups, except for a significant CYP1C induction. These results indicated that CYP enzyme levels are induced by ATR but were only slightly affected by CPF in common carp gills. In addition, the ATR and CPF exposure showed an antagonistic effect on P450 enzymes in common carp gills.

The effects of endosulfan on cytochrome P450 enzymes and glutathione S-transferases in zebrafish (Danio rerio) livers

Endosulfan, an organochlorine pesticide, has been used worldwide in the past decades. The present study was performed to investigate the effect of endosulfan on liver microsomal cytochrome P450 (CYP) enzymes and glutathione S-transferases (GST) in zebrafish. Male and female zebrafish were separated and exposed to a control and four concentrations of endosulfan (0.01, 0.1, 1, and 10μgL−1) and were sampled on days 7, 14, 21, and 28. After exposure to endosulfan, the content of CYP increased and later gradually fell back to control level in most sampling time intervals. A similar tendency was also found in the activities of NADPH-P450 reductase (NCR), aminopyrine N-demethylase (APND) and erythromycin N-demethylase (ERND). GST activities were generally higher in treatment groups than control groups. Regarding sex-based differences, the induction degree of the activity of NCR was generally higher in males than females. Similar differences were also found on the 28th day in the activities of APND and ERND, as well as GST activity on the 7th day. Overall, the present results demonstrate the toxicity at low doses of endosulfan and indicated marked induction of CYP and GST enzymes in zebrafish liver.

Bioremediation Perspective of Navy Blue Rx–Containing Textile Effluent by Bacterial Isolate

ABSTRACT The aim of the present study was to investigate the textile effluent degrading potential of an isolated bacterium, Proteus sp. SUK7. The strain had the capacity to decolorize Navy Blue Rx–containing textile effluent up to 83% within 96 h. The maximum decolorization was observed under static conditions at pH 7.0 and 30°C. Reduction in the chemical oxygen demand (COD) and biological oxygen demand (BOD) of textile effluent was observed after treatment with Proteus sp. SUK7. Induction in the activities of laccase and aminopyrine N-demethylase was observed after decolorization, which indicates involvement of these enzymes in the decolorization process. The presence of various inducers was also found to have a modulatory effect on enzyme activities and the decolorization process. Biodegradation was confirmed using various analytical techniques, such as ultraviolet-visible (UV-Vis) spectroscopy, Fourier transform infrared (FTIR), gas chromatography–mass spectrometry (GC-MS), and high-performance liquid chromatography (HPLC). A phytotoxicity study was performed to confirm the nontoxic nature of the degradation metabolites.

Effectual decolorization and detoxification of triphenylmethane dye malachite green (MG) by Pseudomonas aeruginosa NCIM 2074 and its enzyme system

Malachite green (MG) a complex and resonance-stabilized triphenylmethane (TPM) textile dye, resistant to transformation, was decolorized using Pseudomonas aeruginosa NCIM 2074. The bacteria decolorized MG (50 mg l−1) completely within 5 h into simple metabolic intermediates in aerobic condition at pH 7 and temperature 35 ± 3°C with 53.23% of the COD reduction. Induction in the activities of MG reductase, laccase, and aminopyrine N-demethylase were observed during MG decolorization suggesting these enzymes were involved in the decolorization process. The products after decolorization were examined by UV–Vis, IR spectroscopy, TLC, and HPLC. MG was enzymatically reduced to leucomalachite green (LMG), and further sequential enzymatic reaction converted LMG into N-demethylated and N-oxidized metabolites, including primary and secondary arylamines. The final product formed in this pathway was benzophenone characterized using GC-mass spectroscopy. The cytotoxicity and phytotoxicity study revealed the transformation of MG into non-toxic product by P. aeruginosa NCIM 2074.

In-vitro biotransformation of antipyrine, lignocaine and propranolol in the liver of rats with turpentine-induced inflammation.

In rats with inflammation induced by turpentine injection, changes in drug disposition occur in-vivo and in the perfused isolated liver. Therefore the biotransformation of a low extraction drug, antipyrine, and of two high extraction drugs, lignocaine and propranolol, has been evaluated in the 9000g supernatant fraction of the liver of turpentine-treated rats. Aminopyrine N-demethylase activity and cytochrome P450 content were also measured. Turpentine treatment significantly reduced the in-vitro breakdown of the three drugs; aminopyrine N-demethylase activity and cytochrome P450 content were also decreased. Similar results were found in the proadifen-treated rats, except that in those, the cytochrome P450 content was slightly increased. The changes in drug disposition seen after turpentine-induced inflammation, could therefore be due in part to a change in hepatic enzymatic activity.

Time-dependent effects of Klebsiella pneumoniae endotoxin on hepatic drug-metabolizing enzyme activity in rats.

The time-dependent effects of Klebsiella pneumoniae endotoxin on hepatic cytochrome P450-dependent drug-metabolizing capacity (cytochrome P450 and b5 content, activity of aminopyrine N-demethylase, p-nitroanisole O-demethylase, aniline hydroxylase and benzphetamine N-demethylase) and on the pharmacokinetics of antipyrine have been determined in rats. Measurement of enzyme activity and antipyrine (after intravenous injection of 20 mg kg(-1)) were performed 2, 24 and 96 h after a single intraperitoneal injection of endotoxin (1 mg kg(-1)) and after repeated doses (once daily for 4 days). The contribution of tumour necrosis factor alpha (TNFalpha) to the endotoxin-induced changes was also examined in rats pretreated with granulocyte colony-stimulating factor (G-CSF). The systemic clearance of antipyrine and the activity of hepatic cytochrome P450-dependent drug-metabolizing enzymes were dramatically reduced 24 h after a single injection of endotoxin, but had returned to control levels by 96h. The magnitudes of these decreases in these measurements after repeated doses of endotoxin were similar to those seen 24h after the single dose. The systemic clearance of antipyrine correlated significantly with cytochrome P450 content and aminopyrine N-demethylase activity. In histopathological experiments, moderate hypertrophy of Kupffer cells was observed, with no evidence of severe liver-tissue damage. G-CSF pretreatment suppressed the increased plasma concentrations of TNFalpha produced 2 h after single endotoxin injection, but did not eliminate the endotoxin-induced decrease in the systemic clearance of antipyrine, suggesting that TNFalpha is not the sole component responsible for the reduction of cytochrome P450-mediated drug-metabolizing enzyme activity. These results provide evidence that a single intraperitoneal injection of 1.0 mgkg(-1)K. pneumoniae endotoxin in rats reduces hepatic P450 and b5 levels, and reduces the activity of various cytochrome P450-mediated drug-metabolizing enzymes without causing severe liver-tissue damage. This suggests that the effect of endotoxin on hepatic cytochrome P450-mediated drug-metabolizing isozymes is non-selective.

Inhibition of hepatic microsomal monooxygenase activity by cinchocaine: mechanistic studies and effects of ionization.

The quinoline-based local anaesthetic cinchocaine (dibucaine) was found to be a mixed-type inhibitor of microsomal aminopyrine N-demethylase and 7-ethoxycoumarin O-deethylase activities from control and phenobarbitone-induced rat liver in-vitro. Cinchocaine also elicited a characteristic type I optical difference spectrum in oxidized liver microsomes (Ks = 24 microM; delta Amax = 3.4 X 10(-3) absorbance units (nmol cytochrome P450)-1) but did not appear to bind to the reduced form of the cytochrome. Additional studies indicated that cinchocaine competitively inhibited the type I spectral binding of substrate (aminopyrine) to ferric cytochrome P450. Studies of monooxygenase inhibition by cinchocaine over a relatively narrow pH range (6.5-8.5) indicated that, as might be expected, the un-ionized form of the drug is associated with inhibitory potency superior to that of the ionized form. Thus 40% inhibition of aminopyrine N-demethylase activity was observed with 100 microM cinchocaine at pH 8.0 and 8.5 (24% and 50% un-ionized drug, respectively), whereas only 16% inhibition was observed at pH 6.5 (1% un-ionized drug). These findings suggest that the inhibitory action of cinchocaine is mediated exclusively via an interaction with ferric cytochrome P450 and that the extent of ionization is a determinant of mixed function oxidase inhibition.

Impairment of drug metabolism by the liver in experimental fascioliasis in the rat.

Fascioliasis has been produced in the rat by an oral administration of 20 metacercariae of Fasciola hepatica. Hepatic microsomal cytochrome P450 and b5 contents and both aminopyrine demethylase and aniline hydroxylase activities have been measured during the course of the experimental distomiasis. The cytochrome P450 concentration and microsomal drug metabolizing enzymes generally fell by weeks 3 to 8 post-infestation and recovered to normal values thereafter. For the same period, both the histoenzymatically assayed liver cytochrome oxidase and arylsulphatase activities were reduced whereas there were correlated increases in glutamic pyruvic and glutamic oxaloacetic plasma transaminases. Tissue inflammation and destruction provoked by young histophagous migrating flukes could be responsible for these changes that have already been observed in several hepatic diseases. The possible influence of naturally-induced fasciolasis on liver drug metabolism is discussed.

Induction of hepatic microsomal drug metabolizing enzyme system by levamisole in male mice

To examine the effect of levamisole on the hepatic drug metabolizing enzyme system of mice, levamisole at a dose of 20 mg kg-1 day-1 was administered i.p. for 5 days. Compared with the control values, the levamisole treatment significantly increased the amount of cytochrome P450 and cytochrome b5 and the in-vitro activities of aminopyrine N-demethylase, benzphetamine N-demethylase and aniline hydroxylase. In contrast, there was no change in microsomal NADPH-cytochrome c reductase activity in-vitro or in the relative liver weight and microsomal protein content compared with the corresponding values for control mice. Furthermore, in-vivo induction of drug metabolism was demonstrated by decreased pentobarbitone sleeping times after levamisole pretreatment. These results indicate that certain hepatic microsomal mixed function oxidases of mice are induced by levamisole, the drug that is frequently used as an anthelmintic in veterinary medicine and as an immunostimulant drug in human medicine.

Induction of hepatic CYP enzymes by a subtoxic dose of acetaminophen in rats

Acetaminophen (APAP) is activated by CYP enzymes to N‐acetyl‐benzoquinoneimine, which reacts with cellular macromolecules to initiate liver damage. Alteration of CYP enzyme system by a toxic dose of APAP is well known; however, its potential adverse effect at a lower dose has hardly been explored. Rats were treated with APAP (500 mg/kg, ip) 18 h before a challenge with CCl4. APAP treatment only did not alter serum AST, ALT, or SDH activities. But a prior dose of APAP increased the CCl4 hepatotoxicity significantly. In rats treated with APAP 18 h before, hepatic p‐nitrophenol hydroxylase, p‐nitroanisole O‐demethylase, and aminopyrine N‐demethylase activities were increased significantly. Protein levels of CYP2E1, 3A, 1A1/2, and NADPH CYP reductase were increased, but mRNA expressions of the CYP enzymes were reduced. Ubiquitinated protein expression was suppressed by a prior dose of APAP. The immunoprecipitated CYP proteins were analyzed using a specific Ab against ubiquitin. The ubiquitin‐conjugated proteins in the immunoprecipitated CYP enzymes were decreased, implying that protein stabilization would play an essential role in the induction of CYP enzymes by APAP. These results suggest that a subtoxic dose of APAP may induce CYP enzymes and their metabolizing capacities, thereby influencing the metabolic conversion of xenobiotics that are substrates for the same enzyme systems.

In vivo effects of Faizol Ubat Batuk, a herbal product on aminopyrine metabolism in rat hepatocytes

Traditional medicines, in particular herbal products, have been used abundantly over the years in curing several diseases. Pharmacological interactions of herbal products with modern drugs, however, remain to some extent unknown. Herein, we examined whether co-administration of Faizol Ubat Batuk (FUB), a mixture of aqueous extract of different plants, modifies the metabolism of aminopyrine, a conventional analgesic drug, in rat liver. We used rat hepatocytes outfitted by collagenase perfusion technique. Determination of aminopyrine n-demethylase activity was performed using the Nash colorimetric method, by measuring the amount of formaldehyde produced. Compared to control treatment, FUB significantly increased the hepatic metabolism of aminopyrine in healthy adult male rats. In contrast, the hepatic metabolism of aminopyrine in adult female rats was decreased. Besides, a biphasic effect in n-demethylase activity was observed in young male rats treated with FUB. In a subsequent experiment, FUB did not change the metabolism of aminopyrine in streptozotocin (STZ)-diabetic adult male rats. In conclusion, administration of FUB could affect phase I aminopyrine metabolism in rat heptocytes. In addition, the effects of FUB on hepatic n-demethylase activity were gender and disease dependent.

Characterization of drug metabolizing enzymes and assessment of aging in the gilthead seabream (Sparus aurata) liver

Organic anthropogenic compounds such as polycyclic aromatic hydrocarbons, polychlorinated biphenyls, nitroaromatics, dioxins, various pesticides and natural compounds can enter the aquatic environment. These lipophilic compounds are readily taken up into the tissues of aquatic organisms where biotransformation via Phase I and Phase II metabolism can in part, determine the fate and toxicity of the xenobiotics. In this study on gilthead seabream (Sparus aurata), liver microsomal ethoxyresorufin O-deethylase (EROD), methoxyresorufin O-demethylase (MROD), penthyloxyresorufin O-depenthylase (PROD), benzyloxyresorufin O-debenzylase (BROD), aniline 4-hydroxylase (A4H), N-nitrosodimethylamine N-demethylase (NDMA-DE), aminopyrine N-demethylase (APND), caffeine N-demethylase (CN3D) and erythromycin N-demethylase (ERND) were determined. A4H, ERND, NDMA-ND, EROD and PROD activities increased in gilthead seabream (Sparus aurata) liver microsomes of different ages, while CN3D and APND activities decreased. MROD activities were barely detectable in mature fish whereas BROD activities were not detectable at all ages studied. Results were also recorded at the protein level by Western blotting using anti-CYP1A, CYP2E and CYP3A antibodies. In conclusion, elevated levels of gilthead seabream liver microsomal CYP450 enzyme activities might reveal possible exposure to various exogenous compounds, which might affect the desired responses to drugs, hormones and dietary supplements used during breeding.

Modulation of activities and mRNA expression of cytochrome P450 isoenzymes in rat liver by Sophora flaveacens and coadministration with Veratrum nigrum

To study the modulatory effect of Sophora flaveacens and co-administration with Veratrum nigrum on the activity and mRNA expression of cytochrome P450 isoenzymes in rat liver. Rat liver microsomal cytochrome P450, b5, aminopyrine N-demethylase (APND), p-nitrophenol-hydroxylase (pNPH) activities were quantitated by UV chromatography. The mRNA expression level of five CYP isoenzymes CYP1A1, CYP2B1/2, CYP2C11, CYP2E1 and CYP3A1 were detected by semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR). S. flaveacen and its combination with V. nigrum can dramatically reduce P450 and b5 protein content. Both single and combined use inhibited the activities of aminopyrine N-demethylase. At the mRNA level, the expression of CYP2C11 markedly induced exposure to V. nigrum, while decreased after combination with S. flaveacens. S. flaveacens can induce CYP2B1/2 gene expression, while the Sophora- Veratrum group showed weak inhibition. Both single and co-administrated group have some inhibitory effect on CYP3A1 gene expression, while CYP1A gene expression almost has no change in each group. These results indicated that compatibility of Sophora and Veratrum in a prescription also have herb-herb interactions based on P450. The possible mechanisms of its incompatible effects need to be further analysised via integrating with metabolic studies.

The effect of immunosuppressive agents (FK-506, rapamycin) on renal P450 systems in rat models.

It is well known that cyclosporin, rapamycin and FK-506 (tacrolimus) are metabolized by the liver microsomal cytochrome P450 enzyme system. Although there have been reports of interaction between these drugs and the renal P450 enzyme system, differences among these immunosuppressants has not been comprehensively demonstrated. We have studied the individual capacities of these immunosuppressants to induce renal microsomal P450 enzymes similar to CYP2B4 and CYP4A2 by examining renal function in treated rats, and have correlated the results by means of biochemical, immunological and immunohistochemical assays of renal P450 enzymes. Cyclosporin caused impairment of renal function with an increase in renal-specific P450 content, but FK-506 and rapamycin did not. Laurate omega- and (omega-1)-hydroxylase activity increased in rats treated with rapamycin but decreased in those treated with FK-506. Prostaglandin A1 (PGA1) omega-hydroxylase activity increased in rats treated with FK-506 but was reduced by treatment with cyclosporin. Aminopyrine N-demethylase activity increased in rats treated with cyclosporin or FK-506, but not in those treated with rapamycin. Western-blot analysis revealed significant induction of P450, (similar to CYP2B4 of the rabbit P450 isozyme) in kidneys from rats treated with cyclosporin but not in those from rats receiving FK-506 or rapamycin. Histochemical studies clearly demonstrated a form of P450 such as CYP4A2 in the proximal tubules of rats treated with cyclosporin, but not in those of rats treated with FK-506 or rapamycin. These results show that although cyclosporin has a strong effect on renal P450 systems and induces such a system in kidney cortex (microsomal P450), FK-506 and rapamycin have no substantial effect on the induction of renal P450. These findings might clarify the nephrotoxicity induced by these immunosuppressive drugs.