Investigation of the mechanism by which cyclophosphamide alters cytochrome P450 in male rats

Alteration of endoplasmic reticulum stress, inflammation and anti-oxidative status in cyclophosphamide-damaged liver of Nile tilapia (Oreochromis niloticus)

Cyclophosphamide (CTX) is a common immunosuppressant, and it can also results in liver injury in human and animals. In this study, the CTX-induced liver injury mechanism in tilapia (Oreochromis niloticus) was investigated by studying alteration of endoplasmic reticulum stress (ERS), inflammation and anti-oxidative status. Tilapia was intraperitoneally injected CTX at the doses of 10, 25, 50, 75 and 100 mg·kg^-1, and the blood and liver tissues were collected. The results showed that CTX administration had a significant cytotoxicity on hepatocytes, and increased the liver index. The extensive vacuolar degeneration, unclear cell outline and other histological lesions were also observed. CTX administration markedly decreased the antioxidant ability and enhanced lipid peroxidation in liver. Furthermore, qPCR data showed that CTX administration at 50-100 mg·kg^-1 up-regulated gene expressions of cyp1a, cyp2k1 and cyp3a, and inflammatory response-related genes including rel, relb, nfκb1, il-6, il-8, il-10 and tnf-α. CTX significantly promoted the mRNA levels of ERS-related genes (eif2α, crt, parp1, grp78, ire1, xbp1s and chop) in a dose dependent manner. Additionally, CTX injection at 75-100 mg·kg^-1 could down-regulate gene expressions of anti-oxidative status including nrf2, ucp2, ho-1, gpx3, gstα and cat. Overall results suggested CTX injection induced liver damage which was related to the cytotoxic effect on hepatocytes, decrease of antioxidant capacity, inflammatory response and ERS.

Dynamic Changes of Blood Lipids in Breast Cancer Patients After (Neo)adjuvant Chemotherapy: A Retrospective Observational Study

Background

Previous studies indicated that the (neo)adjuvant chemotherapy for breast cancer can cause significant dyslipidemia in patients, but how long this abnormality can persist is unclear so far. The purpose of this study is to investigate whether (neo)adjuvant chemotherapy has a long-term effect on blood lipids in breast cancer patients.

Methods

A total of 159 newly diagnosed female breast cancer patients receiving the (neo)adjuvant chemotherapy subsequently and 159 female healthy controls were enrolled into the observational study. All participants' blood lipid profiles which included TC, TG, HDL-C, and LDL-C before and at the end of the 1st and 12th month after chemotherapy were retrieved from the electronic medical record system. The blood lipid profiles and the percentage of dyslipidemia before and after chemotherapy in breast cancer patients and controls were compared.

Results

Compared with the baseline before chemotherapy, TC, LDL-C, and TG increased significantly at the end of the 1st month after chemotherapy, but only the abnormal increase in TG (2.98±0.71 mmol/L vs 2.82±0.63 mmol/L, P<0.05) and LDL-C (1.82±0.42 mmol/L vs 1.59±0.42 mmol/L, P<0.05) continued until the 12th month after chemotherapy. Levels of HDL-C in breast cancer patients and all the blood lipid parameters in controls remained stable during the observation period. The percentage of dyslipidemia in breast cancer patients rose from 41.5% at baseline to 54.1% at the 12th month after chemotherapy. Subgroup analysis demonstrated that the increase in dyslipidemia percentage was more pronounced in patients with low body mass index and aged over 50 years.

Conclusion

The (neo)adjuvant chemotherapy used for treating breast cancers can cause significant abnormalities in blood lipid profiles, and the abnormal increase in LDL-C and TG can last at least 12 months after chemotherapy, which indicates long-term management of blood lipid is necessary for those patients.

Role of lupeol and its ester on cyclophosphamide-induced hyperlipidaemic cardiomyopathy in rats

Cyclophosphamide, an alkylating agent widely used in cancer chemotherapy, causes fatal cardiotoxicity. In this study, lupeol, a pentacyclic triterpene isolated from Crataeva nurvala stem bark, and its ester, lupeol linoleate, were investigated for their possible hypocholesterolaemic effects against cyclophosphamide-induced lipidaemic instabilities. Male albino Wistar rats were categorized into 6 groups. Group I served as control. Rats in groups II, V and VI were injected intraperitoneally with a single dose of cyclophosphamide (200 mg kg−1) dissolved in saline. Cyclophosphamide-treated groups V and VI respectively received lupeol and lupeol linoleate (50 mg kg−1), dissolved in olive oil, for 10 days by oral gavage. Groups III and IV served as drug controls and were administered lupeol and lupeol linoleate, respectively. Cyclophosphamide administration induced abnormal changes in serum lipoproteins and lipid fractions in both serum and cardiac tissue. The activity of lipid metabolizing enzymes was distorted significantly in the cyclophosphamide-treated rats. The cyclophosphamide-treated rats also showed extensive intermuscular haemorrhage in histology. Lupeol and its ester reversed the above alterations induced by cyclophosphamide. This study encapsulates the early lipaemic abnormalities in the heart tissue of cyclophosphamide-treated rats. Treatment with lupeol linoleate was more effective than lupeol in rendering protection to the cardiac tissue challenged by cyclophosphamide.

Cyclophosphamide induces mRNA, protein and enzyme activity of cytochrome P450 in rat

The effects of cyclophosphamide (CPA) on CYP enzymes in vivo and its auto induction in rat were investigated in Wistar/Fu male rats at a single dose (40 or 200 mg kg(-1)) or as repeated dose of 200 mg kg(-1) CPA. After a single dose of CPA, mRNAs of CYPs 2B1, 2B2, 3A2, 2C11 were significantly induced up to 220-, 6.7-, 5.0- and 5.8-fold at the low dose CPA, and 4800-, 52-, 22- and 2.5-fold at the high dose. CYP2B1/2 and CYP3A proteins were increased by 4- and 2-fold (low dose) and by 28- and 1.7-fold (high dose). CYP2C11 protein levels were not altered. Microsomal activities of CYP2B, CYP3A and 2C11 were increased by 2-, 1.8- and 1.3-fold at low dose CPA, and 3.2-, 1.7- and 1.6-fold at high dose. A significant (p<0.05) decrease in CPA concentration and a significant (p<0.05) increase in 4-OH-CPA levels were observed with repeated administration of CPA. Acute induction effect on CYP2B1, 2B2, 2C11 and 3A2 and a substantial up regulation of CYP2B1 mRNA were observed after a single dose of CPA, auto induction was observed by repeated administration.

The Effect of Repeated Administration of Cyclophosphamide on Cytochrome P450 2B in Rats

PURPOSE

The prodrug cyclophosphamide (CPA) is activated by cytochrome P450 (CYP) enzymes. CPA is one of the corner stones in all cancer treatment. We have studied the effect of repeated doses of CPA given at different time intervals on the mRNA, protein levels, and enzyme activity of CYPs in rats.

EXPERIMENTAL DESIGN

Two groups of animals (A-75 and A-150) were treated with four doses of CPA (75 and 150 mg/kg, respectively) at short time intervals (6 h). The third group of animals (B-150) was treated with 150 mg/kg at 24-h intervals. Three animals were killed 30 min after administration, and three animals immediately before the next dose.

RESULTS

CYP2B1 and CYP2B2 mRNAs were significantly induced at 6 h after each dose in group A-75 (maximum of 2100-fold and 60-fold after the third dose, respectively), whereas the mRNA levels measured at 6 h postadministration in group A-150 were 1,490-fold and 36-fold after the second dose. In group B-150, no significant induction of mRNA levels was observed. CYP2B1 and CYP2B2 protein levels also increased with increased mRNAs. Plasma levels of 4-hydroxy-CPA measured at 30 min after dose correlated well with the increase in protein levels.

CONCLUSION

Up-regulation of CYP2B mRNA, with a concomitant increase in protein expression and activity, were observed after repeated administration of low doses of CPA compared with that found using higher doses, possibly due to toxicity counteracting induction. These results may help in designing more effective dosing schedules for CPA.

Protective effect of dl-α-lipoic acid on cyclophosphamide induced hyperlipidemic cardiomyopathy

Cyclophosphamide is a potent alkylating agent used in cancer chemotherapy and immunosuppression. The present study is aimed at evaluating the role of a potent antioxidant lipoic acid in cyclophosphamide induced hyperlipidemic cardiomyopathy. Adult male Wistar rats were divided into four treatment groups. Two groups received single intraperitoneal injection of cyclophosphamide (200 mg/kg body weight) to induce cardiotoxicity, one of these groups received lipoic acid treatment (25 mg/kg body weight, orally for 10 days). A vehicle treated control group and a lipoic acid drug control were also included. Cyclophosphamide administration resulted in abnormal elevation of serum lipids. Similarly in the cardiac tissue, the levels of free cholesterol, esterified cholesterol, triglycerides were increased significantly (P<0.05) while the levels of phospholipids and free fatty acids were reduced significantly unlike serum (P<0.05). Serum Low Density Lipoprotein (LDL) and Very Low Density Lipoprotein (VLDL) cholesterol increased significantly (P<0.05) while High Density Lipoprotein (HDL) cholesterol (P<0.05) decreased significantly when compared to controls. These changes corroborated with the abnormal distortion in the activities of lipid metabolizing enzymes in cyclophosphamide treated group. Supplementation of lipoic acid reverted these abnormalities in the lipid levels and activities of lipid metabolizing enzymes to near normalcy after cyclophosphamide administration.

Effect of cyclophosphamide on gene expression of cytochromes p450 and beta-actin in the HL-60 cell line

Many studies have demonstrated that cyclophosphamide (CPA) can affect hepatic cytochrome p450 (CYP) isoenzyme activity in animals. We have investigated the effect of CPA on gene expression of various CYP enzymes as well as beta-actin in the human acute promyelocytic leukemia cell line (HL-60S) and its multidrug-resistant (MDR) phenotype HL-60R. Cells were incubated at different concentrations of CPA ranging between 50 micro g/ml and 5 mg/ml. In determination of cytotoxicity and resistance factor (RF: IC(50) HL-60R/IC(50) HL-60S), concentrations of 100 and 500 micro g/ml CPA were selected to treat HL-60S and HL-60R up to 72 h. CYP gene expression in the cells prior to and after treatment with CPA was determined using semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR) and real-time PCR. Unexposed cell lines did not contain measurable levels of mRNA for CYP2B6, CYP3A4, CYP2C9 and CYP2C19 and no induction was observed after exposure. However, CYP1B1-specific mRNA, which is predominantly expressed in HL-60 cell line, was suppressed after exposure to CPA in a concentration-dependent manner. Beta-actin gene expression was also decreased. The HL-60 RF to CPA was calculated to 0.71, indicating that the multidrug-resistant (MDR) phenotype is not involved in the mechanism of resistance to CPA. No CYPs were induced by CPA in vitro, which probably indicates that the CYP inducibility in blood cells is poor. Our study suggests that suppression of beta-actin gene expression contributes or is involved in the CPA cytotoxicity.

Utility of acetylcysteine in treating poisonings and adverse drug reactions

As recognition of the role of free radicals and reactive toxins in the pathogenesis of disease, poisoning, and adverse drug reactions has evolved, interest in the use of acetylcysteine as a modulator of these effects has steadily increased in recent years. Acetylcysteine is commonly thought to serve as a glutathione precursor and consequently can increase or sustain intracellular glutathione which scavenges reactive oxygen species caused by toxins or subsequent tissue injury. At least 10 additional mechanisms of action for acetylcysteine have been demonstrated in various laboratory models, but a unifying framework of its actions is still to be proposed. This paper reviews the current experimental and therapeutic status of acetylcysteine for the treatment of poisonings and adverse drug reactions. Of the 45 potential uses of acetylcysteine that were identified for the treatment of poisonings or adverse drug reactions, 14 of the toxic effects have little support for its use while promising results have been demonstrated for 27 toxicities. Currently, treatment of acute paracetamol (acetaminophen) poisoning is the only widely accepted clinical indication for acetylcysteine as a treatment for poisoning or adverse drug reactions. In many clinical situations acetylcysteine is used empirically utilising modifications of dosage regimens employed for paracetamol poisoning. Often it is difficult to determine the benefit of therapy with acetylcysteine owing to the nature of the toxicity being treated, the use of other therapies, the presence of comorbid conditions, and the small number of patients studied. The diverse and positive nature of the investigations suggest that there is considerable promise in acetylcysteine as a research tool and pharmacological agent.

Induction of xenobiotic metabolising enzymes in the common brushtail possum, Trichosurus vulpecula, by Eucalyptus terpenes

The mixed function oxidase (MFO) activity and content was studied in the liver of common brushtail possums fed for 10 days on a diet containing a mixture of terpenes found in Eucalyptus leaves on which possums commonly browse. The MFOs were compared to the MFOs in possums fed a control diet of fruits and cereals only. The terpenes chosen were 1,8-cineole, p-cymene, alpha-pinene and limonene. The selected terpenes caused induction of P450 enzymes, as shown by a 53% higher cytochrome P450 content and a 45% increase in aminopyrine demethylase activity in the test animals. Aniline hydroxylase activity was significantly increased, with levels of 2.95 and 1.43 nmol min(-1) mg(-1) microsomal protein in the test and control animals, respectively. There was also a significant increase in androstenedione 16alpha-hydroxylase activity in the test group, 0.85 as compared to 0.50 nmol mg(-1) min(-1) in the control group. Western blot studies using human CYP2E1 and rat CYP2C11 and CYP2C6 antibodies gave CYP2E, CYP2C11 and CYP2C6 immunoreactive bands of greater intensity in the test animals as compared to the control group. This study has shown experimentally that dietary terpenes cause enzyme induction in folivorous marsupials. It also confirms the importance of knowledge of diet when studying xenobiotic metabolising enzymes, particularly in wild animals such as the brushtail possum.

Influence of pretreatment with immunosuppressants on O-demethylation of dextromethorphan in isolated perfused rat liver

Changes in the immune system induced by exogenous or endogenous factors may be accompanied with modifications of the activity of the drug metabolising enzymes in the liver. Some immunostimulatory agents are known to suppress the oxidative metabolism mediated by cytochromes P450. Possible effects of substances which suppress the immune responses of the organism have not been fully understood yet. The present study was undertaken to investigate the influence of immunosuppressants cyclophosphamide and dexamethasone on the CYP2D 1-dependent metabolism of dextromethorphan (DEM) in the isolated perfused liver from male rat donors (Wistar albino, 250-310 g). Recirculatory perfusion system was used with Williams' medium E (Sigma Chemicals Co.) as a perfusion medium (120 mL). DEM was administered as a 1 mg bolus into the perfusion solution at the start of each experiment after 20 min preperfusion. Samples of perfusate for HPLC determination of DEM and its O-demethylated metabolite dextrorphan (DOR) were taken at 15 min intervals for 120 min. The results have shown a rapid conversion of DEM to DOR in the isolated rat liver preparations. Pharmacokinetic parameters in the livers from intact rats were as follows: t1/2 DEM = 19.1+/-4.10 min, k(m) = 0.035+/-0.008 min(-1), Cl(m) = 4.21+/-0.97 mL x min(-1), AUC(DOR) = 2160+/-201 microg x min x L(-1). Pretreatment of rats with dexamethasone (4 mg/kg/day, iv, x 3 days) led to a significant increase in the concentration of dextrorphan in the recirculating solution, but it did not substantially change the kinetic constants of DOR formation (km = 0.036+/-0.004 min(-1), Cl(m) = 4.27+/-0.43 mL x min(-1)). Cyclophosphamide (100 mg/kg, ip, 1 dose on day 5 before perfusion) induced nearly twofold increase in the DOR concentrations in perfusate and thus highly significant (p < 0.01) changes of the kinetic parameters characterizing the increased rate of conversion of DEM to DOR (t1/2 DEM = 12.1+/-0.90 min, km = 0.055+/-0.004 min(-1), Cl(m) = 7.09+/-1.37 mL x min(-1), AUC(DOR) = 3602+/-154 microg x min x L(-1)). Considering that both cyclophosphamide and dexamethasone belong to the most widely used immunosuppressive drugs, their potential to promote the CYP2D-mediated metabolism might have a clinical impact in combined therapy of autoimmune or other diseases.

Hepatic microsomal enzyme activity in the koala and tammar wallaby: high 17beta-hydroxysteroid oxidoreductase activity in koala liver microsomes

We have studied the hepatic microsomal xenobiotic metabolising capacity of koala (Phascolarctos cinereus) and tammar wallaby (Macropus eugenii). Total cytochrome P450 content in hepatic microsomes from koala (0.87 +/- 0.18 nmol/mg protein, n = 4, mean (S.D.) and rat were comparable while tammar wallaby displayed reduced P450 content (0.24 +/- 0.04 nmol/mg protein). Associated microsomal activities (NADPH cytochrome P450 reductase, aminopyrine N-demethylation, aniline hydroxylation, and androstenedione 6beta- and 16alpha-hydroxylation) in koala liver were similar to or reduced relative to rat. Hepatic microsomal NADPH-supported 17beta-hydroxysteroid oxidoreductase (17beta-HSOR) activity was significantly higher in koala (9.99+/-3.08 nmol/mg protein/min) than in tammar wallaby liver (0.86 +/- 0.16 nmol/mg protein/min). However, when NADH was utilised as cofactor the activity was similar in both marsupial species (koala, 1.44 +/- 0.84 nmol/mg protein/min; tammar wallaby, 1.52 +/- 0.44 nmol/mg protein/min). Michaelis-Menten parameters for the kinetics of 17beta-HSOR androstenedione reduction by NADPH and NADH were determined in the koala. The Km for androstenedione was of the order of 1.9-4 microM (n = 4) irrespective of the cofactor used, whilst the Km for NADPH was 0.04-0.05 microM (n = 2) and for NADH was 134-430 microM (n = 2). Potential inhibitors were evaluated for their effects on NADPH-mediated 17beta-HSOR activity with menadione and, to lesser extents, menthone, benzaldehyde and metyrapone eliciting significant inhibition. From detailed kinetic studies menthone was found to be an uncompetitive inhibitor of the activity in koala liver (Ki 220 microM).

Vitamin D metabolite-mediated hypercalcemia in Wegener's granulomatosis

Hypercalcemia may occur during the course of various granuloma-forming diseases. Herein we describe a patient who had symptomatic hypercalcemia as a prominent sign of Wegener's granulomatosis. We observed a direct correlation between the serum levels of 1,25-dihydroxyvitamin D [1,25(OH)2D] and both the serum and the urinary calcium levels. Administration of prednisone and cyclophosphamide led to a substantial decrease in the levels of calcium and serum 1,25(OH)2D, but the serum levels of 25-hydroxyvitamin D remained unchanged. Two months after admission of the patient, the levels of calcium and 1,25(OH)2D increased; after we increased the dose of cyclophosphamide, these levels decreased (the dose of corticosteroids was not changed). We suggest that the excessive synthesis of 1,25(OH)2D was inhibited by a direct or indirect action not only of prednisone but also of cyclophosphamide on the 1 alpha-hydroxylation of 25-hydroxyvitamin D in the activated macrophage of Wegener granulomas. Furthermore, in view of this case and two other recently reported cases, we believe that Wegener's granulomatosis must be definitively added to the list of granulomatous diseases that are responsible for 1,25(OH)2D-mediated hypercalcemia.

The effects of cyclophosphamide on the pharmacokinetics of triiodothyronine in the male rat

In the present study, the possibility that cyclophosphamide or a cyclophosphamide metabolite may be accelerating the clearance of triiodothyronine has been examined. Following administration of exogenous triiodothyronine to saline- and cyclophosphamide-treated rats, the area under the plasma concentration time curve (AUC), apparent clearance (CLapp) and half-life of triiodothyronine were measured. AUC (34.43 +/- 12.34 compared with 33.32 +/- 9.92 nmol h L-1). CLapp (36.30 +/- 12.89 compared with 37.51 +/- 11.16 mL h-1) and half-life (7.50 +/- 1.39 compared with 6.40 +/- 0.96 h) were not significantly different in the control rats compared with the cyclophosphamide-treated rats. As cyclophosphamide does not appear to alter the elimination of triiodothyronine, it is likely that cyclophosphamide or a cyclophosphamide metabolite is acting at the hypothalamo-pituitary axis, reducing the synthesis or release of thyroid stimulating hormone and consequently decreasing the levels of triiodothyronine and thyroxine.

Effect of cyclophosphamide administration on the activity and relative content of hepatic P4502D1 in rat

1. The effects of the administration of the anticancer and immunosuppressive drug, cyclophosphamide, to the rat on hepatic P4502D1 activity and content in the microsomal fraction have been examined. 2. Liver microsomes were obtained from male Hooded Wistar rats administered a single dose (i.p.) of saline or cyclophosphamide (200 mg/kg). Rats receiving cyclophosphamide were killed 1, 4, 7, 10 or 14 days after cyclophosphamide administration. The O-demethylation of dextromethorphan to dextrorphan was used to monitor 2D1 activity. 3. The mean Vmax for dextrorphan formation was reduced significantly (p < 0.0001) 7, 10 and 14 days after cyclophosphamide administration compared with the control group (control, 0.32 +/- 0.07; 7-day, 0.20 +/- 0.08; 10-day, 0.11 +/- 0.02; and 14-day group, 0.15 +/- 0.02 nmol/mg/min). 4. Western blotting revealed that there was a significant reduction (p < 0.0005) in the microsomal relative 2D1 content 10 days after cyclophosphamide administration compared with the control group (control, 1.25 +/- 0.44; and 10-day group, 0.65 +/- 0.14). 5. The activity of reduced nicotinamide adenine dinucleotide phosphate P450 reductase was significantly reduced (p < 0.0001) 7, 10 and 14 days following cyclophosphamide administration (control, 215 +/- 24; 7-day, 102 +/- 20; 10-day, 59 +/- 4 and 14-day group, 76 +/- 8 nmol/mg/min). Cytochrome b5 content was significantly reduced (p < 0.0001) 7 and 10 days following cyclophosphamide administration (control, 0.46 +/- 0.13; 7-day, 0.28 +/- 0.07 and 10-day group, 0.20 +/- 0.03 nmol/mg). 6. The significant reductions in the activity of rat hepatic microsomal 2D1 following cyclophosphamide administration, as seen by the alterations in mean Vmax for dextrorphan formation, do not appear to be due to a single factor, but may result from a combination of several events, including reductions in relative 2D1 content, reduced nicotinamide adenine dinucleotide phosphate P450-reductase activity and cytochrome b5 content.

Cyclophosphamide administered repeatedly to the male rat and as a single dose to the female rat. Its effects on hepatic and pulmonary P450 and associated enzymes

1. Two different aspects of the effects of the cytotoxic agent cyclophosphamide (CP) on rat P450 and associated enzymes have been examined. 2. First, the effects of CP, administered as a single 200 mg/kg dose, on hepatic and pulmonary P450 and some associated enzymes in the female rat have been investigated. Second, the effects of repeat doses of CP (40 mg/kg on days 0-4 with killing on days 5, 8 and 11) to the male rat have been examined. 3. CP decreased the activity of the female rat hepatic enzymes 2A1, 2C6 and/or 2C12 and 2E1, NADPH-P450 oxidoreductase and 17 beta-oxidoreductase and the pulmonary enzyme 2B, 7 days after its administration. The decreases in the activity of the enzymes 2E1 and NADPH-P450 oxidoreductase were accompanied by a corresponding change in the amount of enzyme protein indicating that the alteration in expression of these enzymes occurred via changes in transcription and/or translation or protein degradation. 4. CP also impaired its own activation 7 days after its administration to the female rat. 5. The change in female enzyme profile was accompanied by a reduction in the hormones oestradiol, T4 and T3 7 days after CP administration. 6. Despite an apparent trend for an increase in activity on day 5, a decrease on day 8 and a subsequent increase on day 11, repeat doses of CP to the male rat generally did not alter the P450 isoforms 2A2, 2B1, 2C11, 2E1 and 3A2 or 17 beta-oxidoreductase, NADPH-P450 oxidoreductase and steroid 5 alpha-reductase. 7. Chronic administration of CP to the male rat significantly reduced erythromycin demethylase and NADPH-P450 oxidoreductase 8 days following commencement of dosing and significantly increased 2A2 11 days following commencement of dosing. There was also a statistically significant increase in pulmonary 2B 5 days following commencement of dosing. 8. Plasma testosterone and TSH were unchanged following repeated dosing with CP while T3 was significantly decreased on days 5, 8 and 11 and T4 was significantly decreased on day 8.

Hormonal perturbation as a possible mechanism for the alteration of cytochrome P450 by cyclophosphamide

The mechanism by which the cytotoxic agent cyclophosphamide (CP) alters cytochrome P450 and some associated enzymes in the male rat has been investigated. CP, administered as a high single dose, decreases the activity of the enzymes CYP2C6, CYP2C11, CYP3A2 and CYP2E1 and NADPH P450 reductase and increases the activity of steroid 5 alpha-reductase. CP appears to exert its effect via an indirect mechanism that reaches its maximal effect 7 days after administration. The decreases in the activity of the enzymes CYP2C11, CYP2E1 and CYP3A2 are accompanied via a corresponding change in the amount of enzyme protein indicating that the alteration in expression of these enzymes occurs via changes in transcription and/or translation. Michaelis-Menten analysis confirmed this conclusion for the enzymes CYP2C11 and CYP3A2. The change in enzyme profile is accompanied by a reduction in the hormones, testosterone, TSH, T4 and T3. The reduction in hormone levels is also maximal 7 days after CP administration. To determine whether CP alters enzyme expression in the male rat via perturbation of hormonal regulation, daily replacement doses of hCG and/or T3 were administered for 7 days after a single dose of CP and hepatic CYP and associated enzyme activities assessed. Results indicated that daily hormone replacement with either hCG and/or T3 prevented the changes in expression of the hormone dependent enzymes NADPH P450 reductase, steroid 5 alpha-reductase and CYP3A2 following a single dose of CP. In contrast for other enzymes including the male sex-specific enzyme CYP2C11, the female predominant enzyme CYP2E1 and the sex-independent enzyme CYP2C6, daily replacement of hCG and/or T3 did not prevent the changes that occur 7 days following CP administration. As rats appeared anorexic and dehydrated and significant weight losses were recorded following CP treatment, blood was collected at the time of killing and subjected to biochemical analysis and a complete blood picture to identify any changes in such parameters that may have contributed to the changes in hormones and/or enzyme expression that occurred. However, significant variation in the treatment groups compared with controls for all parameters was not observed to occur except for an anticipated leukopoenia. We have concluded that CP alters the enzymes NADPH P450 reductase, steroid 5 alpha-reductase and CYP3A2 via perturbation of the regulation of these enzymes by testosterone and/or thyroid hormones. However, while interference with regulation by testosterone and/or thyroid hormones may be part of the mechanism by which CP alters CYP2C11 and CYP2E1, other factors are contributing.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of 5-fluorouracil treatment on rat liver microsomal enzymes

1. The effects of the administration of the anticancer drug 5-fluorouracil on P450-mediated metabolizing capacity, and the activity of several related enzymes were examined by comparing two different dosage regimes, i.e. a single ip dose of 5-fluorouracil (120 mg/kg) at 1, 4 and 7 days prior to killing, and a repeated dose regimen of 5-fluorouracil (24 mg/kg/day for 5 consecutive days) with animals being killed at 1, 4 and 7 days after the last 5-fluorouracil dose. 2. Rat liver microsomes were assayed for total P450 content, reduced nicotinamide adenine dinucleotide phosphate-P450-reductase, aminopyrine demethylase, cyclophosphamide 4-hydroxylase, aniline hydroxylase, androstenedione 6 beta- and 16 alpha-hydroxylase and delta 4-3-oxo-steroid 5 alpha-oxidoreductase activity. 3. The animals that received 5-fluorouracil as a single, high dose did not show any alterations in any of the measured parameters at any of the times at which they were killed. 4. The animals that received chronic low doses of 5-fluorouracil, however, showed a statistically significant decrease in androstenedione 6 beta- and 16 alpha-hydroxylase and cyclophosphamide 4-hydroxylase activity and a statistically significant increase in delta 4-3-oxo-steroid 5 alpha-oxidoreductase activity 4 and 7 days after completion of dosing. 5. Immunoquantified P4502C11 and 3A content was also decreased at these time points. These alterations occurred concurrently with depleted plasma testosterone levels in the groups that received repeated low doses of 5-fluorouracil.

The kinetics of the auto-induction of ifosfamide metabolism during continuous infusion

It has often been reported that the oxazaphosphorines ifosfamide and cyclophosphamide induce their own metabolism. This phenomenon was studied in 21 paediatric patients over 35 courses of therapy. All patients received 9 gm-2 of ifosfamide as a continuous infusion over 72 h. Plasma concentrations of parent drug and of the major metabolite in plasma, 3-dechloroethylifosfamide (3DC) were determined, using a quantitative thin-layer chromatography (TLC) technique. A one-compartment model was fitted simultaneously to both ifosfamide and 3DC data. The model included a time-dependent clearance term, increasing asymptotically from an initial value to a final induced clearance and characterised by a first-order rate constant. A time lag, before induction of clearance began, was determined empirically. Metabolite kinetics were characterised by an elimination rate constant for the metabolite and a composite parameter comprising a formation clearance, proportional to the time-dependent clearance of parent drug, divided by the volume of distribution of the metabolite. Thus, the parameters to estimate were the volume of distribution of parent drug (V), initial clearance (Cli), final clearance (Cls), the rate constant for changing clearance (Kc), the elimination rate constant for the metabolite (Km) and Vm/fm, the metabolite volume of distribution divided by the fractional clearance to 3DC. The model of drug and metabolite kinetics produced a good fit to the data in 22 of 31 courses. In a further 4 courses an auto-inductive model for parent drug alone could be used. In the remaining courses, auto-induction could be demonstrated, but there were insufficient data to fit the model. For some patients this was due to a long time lag (up to 54 h) relative to the infusion time. The time lag varied from 6 to 54 (median, 12)h and values for the other parameters were Cli, 3.27 +/- 2.52 lh-1 m-2, Cls, 7.50 +/- 3.03 lh-1 m-2, V, 22.0 +/- 11.0 1 m-2, Kc, 0.086 +/- 0.074 h-1; Km, 0.159 +/- 0.077 h-1 and Vm/fm, 104 +/- 82 1m-2. The values of Kc correspond to a half-life of change in clearance ranging from 2 to 157 h, although for the majority of the patients the half-life was less than 7 h and a new steady-state level was achieved during the 72 h infusion period. This model provides insight into the time course of enzyme induction during ifosfamide administration, which may continue for up to 10 days in some protocols.(ABSTRACT TRUNCATED AT 400 WORDS)