Hepatic Microsomal Enzyme System Research Articles

Evaluation of days-dependent chloramphenicol dosage on rat liver microsomal lipid peroxidation and catalase activity

Drugs and chemical agents can alter the cellular functions associated with the oxidative metabolism, thereby stimulating ROS production. The objective of the this study was the in vivo study of the inhibitory effect of chloramphenicol on hepatic microsomal enzyme system and the effect on lipid peroxidation using the thiobarbituric acid (TBA) reactive as index of peroxidation damage was investigated. The rats were randomly divided into 3 groups; group 1 serves as the control receiving saline water, group 2 receive chloramphenicol at a dose of 28.6 mg/kg body weight/day for 5 days and group 3 for 7 days. Liver protein content, lipid hydroperoxides and catalase activity were all determined. TBARS concentration increased statistically significantly with time of exposure. After 5 days of treatment, the level of TBARS increased by 103.56% with exogenous oxidant and by 141.54% for without oxidant, as compared to the respective control. On day 7, TBARS level in the liver was approximately 90.75% higher than in the control group with oxidant and 117.03% higher than the control without oxidant. The antibiotic elicited significant increase in rat liver lipid peroxidation compared to control. There were decreases in microsomal protein content of the liver in the drug-treated rats when compared with the control rats. It also showed that chloramphenicol treatment affects cytosolic catalase activities. It decreases catalase levels by 15.75% in 5 days dosage treatment and 17.81% in 7 days dosage treatment respectively. There were significance difference (P<0.05) in the treated and control irrespective of the days of dosage. The catalase level in hepatocyte in 5 days and 7 days group was significance at p<0.01. In conclusion, it was evident that treatment of rats for 5 days and 7 days with the therapeutic doses of Chloramphenicol altered antioxidant system and the intensity of effects was concentration/dosage days dependent, it resulted in membrane lipid peroxidation, protein damage, and inhibition of microsomal catalase due to increased generation of free radicals, reactive oxygen species and reactive nitrogen speciesKeywords: Chloramphenicol, rat liver, lipid peroxidation, catalase activity, antioxidant

Disposition Kinetic of Cloxacillin in Healthy and Nephropathic Goats with Immunological and Residual Level in Blood and Tissues

In the present investigation, we evaluated the efficacy of pharmacokinetic profile in healthy as well as nephropathic black-Bengal goats (n=6) of either sex through single intravenous route along with metabolism aspects in all vital organs as well as urine. Nephropathic goats resulted higher B (41.03 ± 3.87 µgmL -1 ), t 1/2 I² (1.17 ± 0.06hr) and low I² (0.59 ± 0.03 hr -1 ) and Cl B (25.70 ± 2.86 mlh -1 kg -1 ) compared to healthy goats. Continuous administration via intramuscular route up to 60 days revealed biochemical, hematological, histopatholocial changes in therapeutic (TP) as well as below therapeutic dosage (HTP) level in black-Bengal goats. Present study also revealed immunosuppressive effect during 60 days continuous intramuscular administration and confirmed stimulatory effect on hepatic microsomal enzyme system.

Suppressive effect of accumulated aluminum trichloride on the hepatic microsomal cytochrome P450 enzyme system in rats

Aluminum (Al) is a low toxicological metal and can accumulate in the liver. The hepatic microsomal cytochrome P450 enzyme system (CYPS) plays important role in the transformation of the toxic materials. It is not clear if the CYPS is affected by Al exposure. Thus, the aim of this study is to investigate the effects of aluminum trichloride (AlCl3) on CYPS in rats. Forty male Wistar rats (5weeks old) weighing 110–120g were randomly allocated and orally exposed to 0, 64.18, 128.36 and 256.72mg/kg body weight (BW) AlCl3 in drinking water for 120days. The body weight (BW) of rats, hepatosomatic index (HSI), hepatic Al content, the concentrations of cytochrome P450 (CYP450), cytochrome B5 (B5), microsomal protein and the activities of NADPH-cytochrome c reductase (CR), aminopyrin N-demethylase (AND), erythromycin N-demethylase (ERND) and aniline-4-hydeoxylase (AH) were assessed at the end of the experiment. The results showed that the increase in Al concentration decreased BW, HIS, concentrations of CYP450, B5, microsomal protein and the activity of CR, AND, ERND and AH in hepatic microsomes. The results revealed that exposure to AlCl3 inhibited the microsomal CYP450 dependent enzyme system of liver. Our findings suggest that long term daily exposure of AlCl3 exerts the suppressive effects and thus may cause dysfunction of hepatic CYP450 dependent enzyme system of rat.

Phenytoin and Cognitive Decline

To the Editor: We read with great interest the article by Naidech et al1 on the association of phenytoin exposure and cognitive disability after subarachnoid hemorrhage. The authors speculate on a number of reasons for this association, to which we would like to add the possibility of a pharmacokinetic interaction compromising the protective effects of nimodipine. Phenytoin induces the hepatic microsomal enzyme system (cytochrome p-450 isozymes). Induction of the CYP isozyme system may …

Effect of the Degree of Hydrogenation of Fish Oil on the Enzymatic Activity and on the Fatty Acid Composition of Hepatic Microsomes from Young and Aged Rats

By modifying the degree of hydrogenation of dietary fat, it is possible to modify the fatty acid composition and the biochemical activity of cellular tissues. The age can be another variable influencing these modifications. The effect of isocaloric diets containing oils with different degrees of hydrogenation: fish oil (FO, 0.3% trans), partially hydrogenated fish oil (PHFO, 29% trans), or highly hydrogenated fish oil (HHFO, 2.3% trans), in the fatty acid composition (cis and trans isomers) of hepatic microsomes from young (70-day-old) and aged (18-month-old) rats, in the microsomal cytochrome P-450 (C-450) content, and in the aminopyrine N-demethylase (AND), aniline hydroxylase (AH), NADPH cytochrome P-450 reductase (NCR), UDP-glucuronyl transferase (UGT), and GSH-S transferase (GST) enzymatic activities were studied. Fatty acid composition and n–6/n–3 ratio of microsomal membranes was modified to a higher extent in young rats. C-450 content and AND activity were reduced when the degree of hydrogenation of dietary fat was increased in the young and the aged rats. AH activity was higher after the PHFO diet in the young rats only. NCR activity was reduced in the young animals when the hydrogenation of the fat was increased. However, in aged rats the enzyme exhibited a higher activity after the PHFO and HHFO diet. UGT and GST activities where not affected by the level of hydrogenation of the dietary fat in both the young and the aged rats. However, UGT activity was higher in the young rats, while GST activity was higher in the aged animals. We conclude that hydrogenation of dietary fat can modify the fatty acid composition of hepatic microsomes, young animals being more sensitive to these changes than aged animals. These effects were also reflected in the amount and/or the activity of some molecular components of the hepatic microsomal mixed-function oxidase enzyme system. Microsomal trans fatty acid composition is not affecting the activity of the enzymes, the age of the animals being the most important factor

홍삼의 사염화탄소 및 갈락토사민 유발 간독성에 대한 치료효과

In this study, we investgated the effect of Red Ginseng (KRG) on liver damage induced by carbon tetrachloride (CTC) and galactosamine (GalN) in rats using indicator enzymes such as serum alanine/aspartate aminotransferases, sorbital dehydrogenase, lactate dehydrogenase, and <TEX>${\gamma}$</TEX>-glutamyltransferase. Treatment of KRG restored these enzyme activities to near normal level compared to CTC or GalN treatment alone. Treatment of KRG also enhanced hepatic microsomal enzyme system, malondialdehyde formation, and depletion of reduced glutathione content, which were reduced by CTC or GalN. We also found that the decreased activities of glutathione S-transferase and glutathine reductase but not <TEX>${\gamma}$</TEX>-glutamycysteine synthetase after KRG treatment restored to normal level. These results indicate that KRG has potent therapeutic activity against CTC- and GalN-induced hepatotoxicity in rat.

Review: therapeutic drug monitoring in pediatrics.

Therapeutic drug monitoring (TDM) can be defined as the measurement of drug concentrations in biologic fluids to assess whether they correlate with the patient’s clinical condition and whether the dosage or dosage intervals need to be changed. This is done to optimize the management of patients receiving drug therapy for the alleviation or prevention of disease. Therapeutic drug monitoring is a relatively new service in the clinical pharmacology and toxicology laboratory and has evolved from being a luxury to a necessity. The principles of TDM were developed in the 1960s. Advances in research and knowledge and increasingly sophisticated laboratory methods led to an expansion of TDM (1–3). A drug must meet the following criteria to be eligible for monitoring: There should be a clinically interpretable correlation between the serum drug concentration and its pharmacologic effect. This usually implies a clinically significant correlation between the serum drug concentration and its concentration in the target tissue (1). There should be a better correlation between the plasma drug concentration and the pharmacologic effect than between the drug dosage and the pharmacologic effect. A narrow margin should exist between serum concentrations that cause toxic effects and concentrations that produce therapeutic effects. The serum concentration resulting from a given drug dose is unpredictable as a result of inter- and intraindividual differences in drug absorption, distribution, and elimination. Such poor correlation between serum concentration and drug dosage has been shown with clomipramine used in treatment of enuresis (2). The pharmacologic effects of drugs are not readily measurable (e.g., suppression of seizure activity is difficult to monitor clinically when administering anticonvulsant drugs). There must be a rapid and reliable method for the analysis of the drug. The criteria for monitoring drugs in children are the same as those for adults (6), but several additional factors must be considered. Neonates, infants, and children undergo major and rapid age-related physiologic and biochemical changes, especially during the first year of life, resulting in different clinical pharmacokinetic and pharmacodynamic parameters from adults (Table 1). Recent indications are that approximately 12% of all drugs prescribed in the United States are for children age 9 years and younger (4). Further, review of drug-dosing habits in neonatal intensive care units has shown that the average number of drugs administered to premature infants weighing less than 1,000 g varies from institution to institution but is usually in the range of 15 to 20 drugs; infants weighing more than 2,500 g usually receive 4 to 10 drugs during their hospital stay. Obviously, drug concentrations in many of these patients need to be monitored by the laboratory, and the possibility of drug interactions needs to be considered. Thus, it is important to have a clear understanding of not only the principles of TDM but also the additional factors inherent in and specific to pediatric clinical pharmacology. Table 1 Pharmacokinetic parameters of drugs commonly used in children When administering drugs to children, age-related differences in drug absorption, distribution, metabolism, and clearance should be taken into account to optimize drug efficacy and to avoid toxicity. There are major differences not only between adults and children but also between neonates and pre- and postpubertal children. The following are some important differences between adults and children: Changes in gastric pH and gastric emptying time during the neonatal period lead to variation in the absorption of many drugs. Differences in body composition (neonates are composed of less body fat and more water) lead to differences in the apparent volume of distribution between neonates, children, and adults (Table 2). Table 2 Some factors affecting drug distribution and disposition Slow total drug clearance in premature infants and neonates is due to immature hepatic and renal function. Immaturity of the hepatic microsomal enzyme system produces slow biotransformation of many drugs in premature infants and neonates, requiring a lower mg/kg dosage to achieve therapeutic concentrations. Greater microsomal enzyme activity in prepubertal children than in postpubertal children and adults necessitates a higher mg/kg dosage to achieve similar serum concentrations of some drugs.

ワルファリンとリファンピシン併用患者のカルテ調査による相互作用の検討

Rifampicin's ability to induce hepatic-microsomal enzymes is well known. As a result, rifampicin has often been implicated in drug interactions by reducing the effectiveness of many drugs that are metabolized by the hepatic-microsomal enzyme system. One such well known interaction is that of rifampicin and warfarin. The concomitant administration of rifampicin and warfarin results in the need for an unusually high maintenance dose of warfarin in order to obtain the desired therapeutic effect.The interaction between warfarin and rifampicin was investigated. The patients treated with rifampicin were selected from the prescription database file made for the prescriptions order entry system, and which contains all the prescriptions filled for the inpatients and outpatients. Thirty patients were treated with rifampicin between July 2000 and June 2001. Four of them used warfarin concomitantly during the study period. Decreased INR values were observed in all patients between 5 and 10 days after the initiation of rifampicin therapy. To maintain proper INR, rifampicin therapy resulted in the need for a two-to three-fold increase in the warfarin dosage. Subsequently, low INR/Dose values were observed during the concomitant use of warfarin and rifampicin (30%-50%). A decrease in the anticoagulant activity of warfarin frequently occurs when rifampicin is used concomitantly. After the initiation and discontinuation of rifampicin therapy, frequent coagulation tests are required in patients treated with warfarin. In conclusion, warfarin should be used with caution when rifampicin is used concomitantly.

Effect of Oxidized Frying Oil and Vitamin C Levels on the Hepatic Xenobiotic-Metabolizing Enzyme System of Guinea Pigs.

The influence of oxidized frying oil (OFO) on the guinea pig hepatic microsomal xenobiotic-metabolizing enzyme system in the presence of different amounts dietary vitamin C was investigated. Weanling male guinea pigs were divided into four groups and were fed 15% oxidized frying oil diets supplemented with vitamin C at 300, 600, or 1,500 mg/kg (experimental diets) or a control diet that contained 15% fresh untreated soybean oil with 300 mg/kg of vitamin C, respectively. After 60 d, guinea pigs were euthanized and phase I and phase II xenobiotic-metabolizing enzymes in the liver were determined. Compared with the fresh oil diet fed the control group, the relative liver weight was higher in the OFO-fed groups. Hepatic microsomal protein and cytochrome P450 contents were significantly higher in OFO-fed guinea pigs than in the control group. Both values increased in response to increased intake of vitamin C. The activities of phase II relative components, including UDP-glucuronyl transferase, UDP-glucuronyl dehydrogenase and beta-glucuronidase, of guinea pigs fed the OFO diets supplemented with 300 mg vitamin C/kg were significantly higher than those of guinea pigs fed the control diet. However, the phase II relative components decreased with increasing vitamin C content in the diet. The results demonstrate that both dietary OFO and vitamin C in guinea pigs induce hepatic xenobiotic-metabolizing enzymes, but the level of induction is modulated by the dietary vitamin C level.

Pharmacokinetics in newborns and infants

Physiologic changes influence the pharmacokinetics of drugs relevant to anesthesia in neonates and infants. The neonatal phase is the phase of life with the most rapid and dramatic changes of organ-functions responsible for pharmacokinetics of most anesthetics. Changes in body composition and the content of plasma proteins influence volume of distribution, the drug distribution to different compartments and the amount of free fraction in plasma. Due to the immaturity of hepatic microsomal enzyme systems there is a decreased metabolism particular of agents which undergo low hepatic extraction like Diazepam, Morphine or some local anesthetics. In the first year of life capacity of the enzymatic systems increases and also clearance increases. Until puberty the clearance of some drugs is greater than the adult level. There are also pharmacodynamic changes like modified sensitivity to some drugs like volatile anesthetics or neuromuscular blocking agents. In summary neonates and infants are a highly heterogenous group with large interindividual differences. Therefore the dosage of anesthetic agents must be individualized to achieve optimal pharmacodynamic effects without toxicity in this age group.

Low Bodyweight Type 2 Diabetes Mellitus

Non-insulin dependent diabetes mellitus (NIDDM) is the most prevalent form of diabetes mellitus (DM) in India. Currently the nomenclature is Type 2 diabetes mellitus (Type 2 DM). About one fourth of these diabetics have a body mass index (BMI) below 19, i.e. low bodyweight Type 2 DM (LB Type 2 DM). They are neither protein deficient nor belong to a poor socio-economic class. LB Type 2 DM more often presents with peripheral neuropathy and infections than coronary artery disease (CAD), hypertension or nephropathy. They achieve good glycemic control with sulphonylurea therapy. The leading causes of death are infection, coma, renal failure and cerebrovascular accident. LB Type 2 DM patients have severe basal hyperglycemia with low circulating levels of insulin while C-peptide levels are similar to those of patients with classic Type 2 DM. Studies on hepatic glucokinase levels and hepatic-microsomal enzyme systems (mixed function oxidase and cytochrome P450) using antipyrine and lidocaine as in vivo probes rev...

Structural Characterization of Two Novel Oxidative Derivatives of Cyclosporine Generated By a Chemical Method

Objectives: To study the generation of cyclosporine derivatives (CMs) by chemical oxidation of the parent compound using hydrogen peroxide. Methods and Results: Hydrogen peroxide was added to cyclosporine (CsA), which was dissolved in ether. After liquid-liquid extraction, CMs were purified by high performance liquid chromatography (HPLC). Detailed structures of CMs were determined by fast atomic bombardment mass spectrometry (FABMS) and nuclear magnetic resonance spectroscopy (NMR). Our results indicated that the parent compound was modified at amino acid number 1 by hydroxylation of the carbon and the formation of a tetrahydrofuran five member ring structure. In addition, these two oxidative products of CsA were determined to be isomeric to each other, differing only in the configuration at one or more carbon atoms. This modification is in contrast to that observed for the formation of the cyclic metabolite of CsA, namely AM1c, by cytochrome P-450 isoenzymes, where the addition of the hydroxyl group occurs on the carbon of amino acid 1. Conclusion: 3 to 4 mg of 2 oxidative derivatives could be produced from 5 mg of CsA by chemical modification of the parent compound. In comparison, biotransformation using the drug-induced hepatic microsomal enzyme system could only produce 0.5 to 1 mg of metabolites/derivatives from 5 mg of CsA.

Toxicity of the brominated flame retardant (tetrabromobisphenol‐A)

The toxicity of tetrabromobisphenol‐A (TBBPA), which is a brominated flame retardant and used in large quantities, was investigated. The threshold for the decrease of body weight was from 0.3 to 3.0 mg/kg/day, and the weight ratio of kidney to body increased from 10 mg/kg/day. The hematocrit value and clotting time decreased, and the cholesterol concentration, blood urea nitrogen (BUN) concentration and choline esterase activity increased. Hemolysis occurred from low concentration (0.5 mg/L) and decreased by metabolization with hepatic microsomal enzyme system. When 500 mg/kg of TBBPA was administrated, TBBPA concentration increased rapidly, but decreased after 4 hr and remained still at 20 hr.

Changes in the activities of hepatic xenobiotic metabolising enzymes after the administration of clenbuterol to female broilers

Clenbuterol is a β 2-agonist drug which in some countries is used illegally to enhance the productivity of various food-producing species, including poultry. This work investigated whether the prolonged exposure of female broilers to clenbuterol modified the activity of hepatic microsomal or cytosolic enzyme systems concerned with the metabolism of drugs, pesticides, carcinogens and endogenous substrates such as sexual steroids. Clenbuterol was added to the birds' diet at concentrations of 1 or 25 ppm for 21 days. There was a dose-related decrease in the concentration of cytochrome P-450, and in the activities of the polycyclic aromatic hydrocarbon-inducible monooxygenases ethoxyresorufm O-de-ethylase and aryl hydrocarbon hydroxylase. The activities of glutathione S-transferase, N-acetyltransferase and uridinediphosphoglucuronyltransferase were not affected by the treatment.

A rifampicin-induced hepatic microsomal enzyme system for the generation of cyclosporine metabolites

A drug-induced rabbit hepatic microsomal enzyme system has been developed to produce milligram quantities of cyclosporine metabolites (CMs). Using a rifampicin-induced microsomal preparation in the presence of a NADPH regenerating system, 60% of the cyclosporine (CsA) was converted to CMs in 2 h. The CMs were recovered by solid phase extraction, and separated by gradient high performance liquid chromatography with two Ultrasphere Ocyl (C8) columns connected in tandem. More than 20 CMs were resolved. The quantities of major CMs produced by 45 mg of microsomal proteins were established by comparing peak areas with known concentrations of authentic CM standards. These major CMs included AM1, AM9, AM19, AM4N, AM1c and the aldehydic isomers (AM1cAL plus AM1AL). Other CMs that were not quantified included AM14N, AM4N9, AM1A, AM1c9, and AM1D1. Several CMs remained to be identified. All CMs were detected by radioimmunoassay using a non-specific CsA antiserum. The purity of the CMs were confirmed by fast atomic bombardment mass spectrometry. Similar findings were observed when erythromycin or trolandomycin was used to induce the hepatic microsomal enzymes. The procedure used to generate CMs was simple. With the enzyme fraction derived from one rabbit liver, 90 to 100 mg of CMs can be obtained. In this study, the metabolite patterns of CsA produced by rabbit liver microsomes were shown to resemble those observed for humans. These results indicate the possibility of using rabbit models to predict CsA biotransformation in man. The CMs generated by this enzyme system can be used to acquire information relevant to the situation in man.

Pharmacokinetics of Tiagabine, a γ‐Aminobutyric Acid‐Uptake Inhibitor, in Healthy Subjects After Single and Multiple Doses

Tiagabine (TGB) HCl, a new antiepileptic compound, is a potent and specific inhibitor of gamma-aminobutyric acid (GABA) uptake. In conjunction with three phase I studies, the pharmacokinetics of TGB were examined in 58 healthy male volunteers. Study I involved single increasing doses (2-24 mg TGB HCl); study II involved doses of 2-10 mg given once daily for 5 days; study III explored one dose daily (6 or 12 mg) for 14 consecutive days. Plasma TGB concentrations were measured by high-performance liquid chromatography (HPLC). Pharmacokinetic parameters were calculated by standard noncompartmental methods. Pharmacokinetic profiles were similar in all three studies and indicated that the processes of absorption and elimination of TGB were linear. The drug was rapidly absorbed, and half-life (t1/2) averaged 5-8 h. The accumulation ratio was fairly low: < 1.4 in most subjects. Secondary peaks in plasma concentration-time profiles suggested enterohepatic recycling. Lack of significant effects on antipyrine clearance indicated that TGB does not induce or inhibit hepatic microsomal enzyme systems.

Induction of hepatic microsomal drug-metabolizing enzymes by methylsulphonyl metabolites of polychlorinated biphenyl congeners in rats

The effect of methylsulphonyl (MeSO 2) metabolites of 2,3′,4′,5-tetrachlorobiphenyl (tetraCB) (IU-70), 2,2′,3′,4′,5-pentachlorobiphenyl (pentaCB) (IU-87), 2,2′,4′,5,5′ -pentaCB (IU-101) and 2,2′,3′,4′,5,5′-hexachlorobiphenyl (hexaCB) (IU-141), on the hepatic microsomal drug-metabolizing enzyme system was investigated in rats. The administration of 3-MeSO 2-2,3′,4′,5-tetraCB (10 μmol/kg), 3-MeSO 2-2,2′,3′,4′,5-pentaCB (0.5 μmol/kg), 3-MeSO 2-2,2′,4′,5,5′-pentaCB (0.5 μmol/kg) and 3-MeSO 2-2,2′,3′,4′,5,5′-hexaCB (2 μmol/kg) to rats significantly increased the contents of cytochromes P-450 and b 5 and the activities of aminopyrine N-demethylase, 7-ethoxycoumarin O-deethylase and benzo[ a]pyrene hydroxylase. From these results, it is suggested that the 3-MeSO 2 derivatives studied are possibly potent phenobarbital-like inducers of microsomal drug-metabolizing enzymes. On the other hand, 4-MeSO 2-2,3′,4′,5-tetraCB, 4-MeSO 2-2,2′,3′,4′,5-pentaCB, 4-MeSO 2-2,2′, 4′,5,5′-pentaCB and 4-MeSO 2-2,2′,3′,4′,5,5′-hexaCB had almost no effect on both cytochrome contents and these enzyme activities. After 96 h, following administration of 2,3′,4′,5-tetraCB, 2,2′,3′,4′,5-pentaCB, 2,2′,4′,5,5′-pentaCB and 2,2′,3′,4′,5,5′-hexaCB

Effect of switching carbamazepine to oxcarbazepine on the plasma levels of neuroleptics. A case report

Carbamazepine was switched to its 10-keto analogue oxcarbazepine among six difficult-to-treat schizophrenic or organic psychotic patients using concomitantly haloperidol, chlorpromazine or clozapine. This change resulted within 2-4 weeks in the 50-200% increase in the plasma levels of these neuroleptics and the appearance of extrapyramidal symptoms. None of the patients showed any clinical deteriotation during the following 3-6 months. The results of this case report support the idea that in contrast with carbamazepine oxcarbazepine does not induce the hepatic microsomal enzyme systems regulating the inactivation of antipsychotic drugs.

Changes of thyroid hormone levels in epileptic patients

We measured serum T3, T4, FT3, FT4 and thyrotropin (TSH) by radioimmunoassay in 150 patients with epilepsy. Of the 150 epileptic patients, 120 cases received single antiepileptic drug, including Sod valproate (VPA), carbamazepine (CBZ), phenytoin (PHT), or MixtBrodsky (MB). Each subgroup consisted of 30 cases. The other 30 were untreated epileptics. The results suggested that there was no significant difference in serum thyroid hormone levels among healthy control group, untreated group, and hepatic non-enzyme-inducing anticonvulsant group (P < 0.05). As compared with the three groups mentioned above, the serum T3, T4, FT3, FT4 concentrations of the enzyme inducer groups were decreased, however, significant decrease was found in PHT group and CBZ group (P < 0.05, P < 0.005). All 12 patients with circulating thyroid hormone concentrations below normal reference values were given enzyme inducer. None of them revealed any clinical manifestation of hypothyroidism. There was no significant difference in serum TSH level among the above 6 groups (P < 0.05), and the serum TSH level of all patients was within normal reference limits. Our study showed that the changes of thyroid hormone in epileptics were due to the effect of some AEDs and not the disease itself. The disparity between the effect of enzyme inducer and that of non-enzyme-inducing anticonvulsants indicated that the hepatic microsomal enzyme system metabolizing thyroid hormone to be induced was the main mechanism for decreased serum thyroid hormone concentrations. Though the serum thyroid hormone levels of the enzyme inducer groups were decreased, no significant increase of the mean serum TSH concentration was found. This implies that AEDs may interfere the HPA function in some way.

Inhibition studies on the involvement of flavoprotein reductases in menadione- and nitrofurantoin-stimulated oxyradical production by hepatic microsomes of flounder (Platichthys flesus).

Inhibitors of mammalian cytochrome P450 and P450 reductase were used to investigate the enzymes in flounder (Platichthys flesus) hepatic microsomes involved in the stimulation of NAD(P)H-dependent iron/EDTA-mediated 2-keto-4-methiolbutyric acid (KMBA) oxidation (hydroxyl radical production) by the redox cycling compounds menadione and nitrofurantoin. Inhibitors were first tested for their effects on flounder microsomal P450 and flavoprotein reductase activities. Ellipticine gave type II difference binding spectra (app. Ks 5.36 microM; delta A max 0.16 nmol-1 P450) and markedly inhibited NADPH-cytochrome c reductase, NADPH-cytochrome P450 reductase, and monooxygenase (benzo[a]pyrene metabolism) activities. 3-aminopyridine adenine dinucleotide phosphate (AADP; competitive inhibitor of P450 reductase) inhibited NADPH-cytochrome c but not NADH-cytochrome c or NADH-ferricyanide reductase activities. Alkaline phosphatase (inhibitor of rabbit P450 reductase) stimulated NADPH-cytochrome c reductase activity seven fold but had less effect on NADH-reductase activities. AADP inhibited nitrofurantoin- and menadione-stimulated KMBA oxidation by 45 and 17%, respectively, indicating the involvement of P450 reductase at least in the former. In contrast, ellipticine had relatively little effect, possibly because, unlike cytochrome c, the smaller xenobiotic molecules can access the hydrophilic binding site of P450 reductase. Alkaline phosphatase stimulated NAD(P)H-dependent basal and xenobiotic-stimulated KMBA oxidation, showing general consistency with the results for reductase activities. Overall, the studies indicate both similarities (ellipticine, AADP) and differences (alkaline phosphatase) between the flounder and rat hepatic microsomal enzyme systems.