Prenatal developmental toxicity study of the basic rubber accelerator, 1,3-di-o-tolylguanidine,in rats

Pregnant rats were given 1,3-di-o-tolylguanidine (DTG) by gavage at 0, 10, 20 or 40 mg/kg bw/day on days 6–19 of pregnancy and the pregnancy outcome was determined on day 20 of pregnancy. At 40 mg/kg bw/day, deaths were observed in four out of 24 females. The incidences of females showing mydriasis at 20 and 40 mg/kg bw/day and showing decreased locomotor activity at 40 mg/kg bw/day were significantly increased. Alopecia, bradypnea, prone position and tremor were also observed at 40 mg/kg bw/day. The maternal body weight gain at 20 and 40 mg/kg bw/day and food consumption at 40 mg/kg bw/day were significantly reduced. A significantly decreased weight of the gravid uterus, increased incidence of postimplantation loss, decreased number of live fetuses, and lowered weights of fetuses and placentae were found at 40 mg/kg bw/day. The incidences of the total number of fetuses with external malformations at 40 mg/kg bw/day and with skeletal malformations at 20 and 40 mg/kg bw/day were significantly increased. Significantly higher incidences of fetuses with brachydactyly and short tail and defects of caudal vertebrae, phalanges and metacarpals were observed at 40 mg/kg bw/day. Delayed ossification was also noted at 40 mg/kg bw/day. The data indicate that DTG is teratogenic at maternal toxic doses and the NOAELs of DTG for maternal and developmental toxicity are 10 mg/kg bw/day in rats.     

Effect of classic and atypical neuroleptics on cytochrome P450 3A (CYP3A) in rat liver

BackgroundCytochrome P450 3A (CYP3A) subfamily is involved in the metabolism of xenobiotics (e.g., drugs) and endogenous substances (e.g., steroids). The aim of the present study was to investigate the influence of classic and atypical neuroleptics on the level and activity of CYP3A in rat liver, measured as a rate of testosterone 2β- and 6β-hydroxylation.MethodsThe reactions were studied in control liver microsomes in the presence of neuroleptics, as well as in the microsomes of rats treated intraperitoneally (ip) with pharmacological doses of the drugs (promazine and thioridazine 10 mg/kg; chlorpromazine 3 mg/kg; haloperidol 0.3 mg/kg; risperidone 0.1 mg/kg; sertindole 0.05 mg/kg) for one day or two weeks (twice a day), in the absence of the neuroleptics in vitro.ResultsThe investigated neuroleptics added in vitro to control liver microsomes produced a moderate or week inhibitory effects on CYP3A activity. After one-day exposure of rats to neuroleptics, only chlorpromazine significantly increased the activity of CYP3A. Chronic treatment of rats with thioridazine diminished the protein level and activity of CYP3A, while risperidone induced this enzyme.ConclusionThe observed changes in the CYP3A expression after prolonged exposition to neuroleptics suggest their influence on the enzyme regulation.     

Prenatal developmental toxicity of gavage or feeding doses of 2-sec-butyl-4,6-dinitrophenol in rats

This study evaluated the prenatal developmental toxicity of the pesticide 2-sec-butyl-4,6-dinitrophenol (dinoseb). Pregnant rats were given dinoseb by gavage at 0, 8.0 or 10 mg/kg bw/day on days 6–15 of gestation, or in the diet at 0, 120 or 200 ppm (0, 6.52 or 8.50 mg/kg bw/day) on days 6–16 of gestation, and litters were evaluated on day 20 of gestation. Maternal toxicity was observed as evidenced by significantly decreased body weight gain and reduced food consumption during the administration period in all the dinoseb-treated groups, and two dams died at 10 mg/kg bw/day. Significantly lower fetal weights and delayed skeletal ossification was observed in the dinoseb-treated groups except for the group fed dinoseb at 120 ppm. The teratogenic potential of the gavage dose of dinoseb was confirmed as evidenced by increased incidences of fetuses with external and skeletal malformations at 10 mg/kg bw/day. The incidence of fetuses with microphthalmia was significantly increased at this dose. On the other hand, feeding doses of dinoseb up to 200 ppm did not induce teratogenicity in this study. These data indicate that dinoseb is teratogenic at maternally toxic doses, but the exposure range of dinoseb at which malformations occur seems to be narrow.     

Effect of strychnine hydrochloride on liver cytochrome P450 mRNA expression and monooxygenase activities in rat

Strychnos nux-vomica L. has been frequently used in traditional Chinese medicine but has high acute toxicity. It is commonly taken with Glycyrrhizae radix to decrease its toxicity but the mechanism of this interaction is unknown. In this work, the mRNA expression and the activity of four cytochrome P450 (CYP) enzymes representative of four subfamilies (CYP1A, CYP3A, CYP2C and CYP2E) were determined ex vivo in rat livers from groups of Wistar rats orally administered strychnine hydrochloride (SH) at three doses (0.1, 0.3 and 0.9 mg/kg/day) alone and, at the highest dose, in combination with glycyrrhetinic acid (GA, 25 mg/kg/day) or liquiritin (LQ, 20 mg/kg/day) once a day for 7 consecutive days. Compared to control, the mRNA expressions of CYP3A1, 1A2 and 2E1 were higher in rats receiving the highest dose of SH but lower for CYP3A1 and CYP2E1 in rats receiving the SH+GA and SH+LQ combinations. CYP2E1 activity was higher and CYP2C, CYP3A and CYP1A2 activities were lower in rats receiving the highest dose of SH. In contrast CYP1A2 and CYP2C activities were higher and CYP2E1 and CYP3A activities lower in rats receiving the SH+GA combination. CYP2E1 and CYP3A activities were also lower in rats receiving the SH+LQ combination. The results show that treatment with SH for 7 days affects the expression and the activity of CYP enzymes and that coadministration of GA and LQ modulates these effects. This modulation may explain the role of Glycyrrhizae radix in reducing the acute toxicity of Strychnos nux-vomica L.CYPs enzymes.     

Safety studies on products from whole coffee fruit

The fruit of the coffee plant, Coffea arabica, has high phenolic antioxidant and phytonutrient content and could be a beneficial food ingredient. However, the fruit has historically been discarded for the favored harvesting of the coffee bean alone. CoffeeBerry® products are derived from the whole fruit and include a ground whole powder, a water extract, and a more recently developed water–ethanol extract. The safety of CoffeeBerry® products was evaluated in three genotoxicity studies, three short-term oral toxicity studies, and a 90-day dietary toxicity study. Bacterial mutagenicity studies and a micronucleus test using murine peripheral cells demonstrated that none of the three products showed mutagenic or genotoxic potential. In the short-term studies, despite palatability issues, female rats showed a tolerance for whole powder and ethanol extract at doses up to 8800 mg/kg bw/day. Male rats also exhibited palatability issues and tolerated lower doses of approximately 4000 mg/kg bw/day ethanol extract via gavage and approximately 2100 mg/kg bw/day whole powder or water extract in the diet. When fed in the diet to Sprague–Dawley rats for 90 days, ethanol extract showed no adverse effects at dietary concentrations of up to 5% (approximately 3446 and 4087 mg/kg bw/day for male and female rats, respectively).     

Pre-clinical safety assessment of the synthetic human milk,nature-identical,oligosaccharide Lacto-N-neotetraose (LNnT)

Lacto-N-neotetraose (LNnT) is a tetrasaccharide naturally occurring in human breast milk, but not in cow’s milk. The safety data generated on a potential new LNnT ingredient produced by chemical synthesis is presented. Standard in vitro genotoxicity tests were performed. LNnT was also administered via gavage in 14-, 28- and 90-day studies at levels corresponding to 0 (control), 1000, 2500 and 5000 mg/kg bw/day in juvenile rats. Fructooligosaccharide (FOS) currently approved for use in infant formulae was used as a reference control at one dose level of 5000 mg/kg bw/day. LNnT was non-mutagenic in in vitro assays. Oral administration up to 5000 mg/kg bw/day to rats over 90 days was not associated with any adverse effects, based on clinical observations, body weight gain, feed consumption, clinical pathology, organ weights and histopathology findings. Regarding gastrointestinal effects, LNnT was better tolerated than FOS during the first 2 weeks of treatment. A No Observed Adverse Effect Level (NOAEL) of 5000 mg/kg bw/day for both male and female rats was identified for LNnT when administered by gavage for 90 days. These findings in the juvenile rat support the safety of LNnT for possible use in infant foods and allow further investigation in clinical studies.     

Characterisation and toxicological assessment of Neutral Methacrylate Copolymer for GRAS evaluation

Neutral Methacrylate Copolymer is a fully polymerised copolymer used in the pharmaceutical industry to permit pH-independent delayed release of active ingredients from oral dosage forms. This function has potential use with food supplements and this article describes available information on the safety of the substance.Oral administration of radiolabelled copolymer to rats resulted in the detection of chemically unchanged copolymer in the faeces, with negligible absorption. Safety studies revealed no adverse toxicity following repeated administration at doses of up to 2000 mg/kg bw/d in a sub-chronic study in rats or 250 mg/kg bw/d in a sub-chronic study in dogs. No reproductive toxicity occurred at up to 2000 mg/kg bw/d in rats or rabbits. The substance shows no evidence of genotoxicity, has low acute toxicity and no irritation or sensitisation potential.An ADI value of 20 mg/kg bw was concluded from two alternative approaches. Daily exposure from use in dietary supplements is estimated as up to 10.0 mg/kg bw in adults and 13.3 mg/kg bw in children. There would therefore appear to be no safety concerns under the intended conditions of use. The information provided is intended to support an evaluation that the substance may be “generally recognized as safe” (GRAS).     

In vitro metabolism and covalent binding of ethylbenzene to microsomal protein as a possible mechanism of ethylbenzene-induced mouse lung tumorigenesis

This study was conducted to determine species differences in covalent binding of the reactive metabolites of ethylbenzene (EB) formed in the liver and lung microsomes of mouse, rat and human in the presence of NADPH. These data further the understanding of the mechanism by which EB causes mouse specific lung toxicity and a follow-up to our earlier report of the selective elevation, although minor, of the ring-oxidized reactive metabolites in mouse lung microsomes (Saghir et al., 2009). Binding assays were also conducted with or without 5-phenyl-1-pentyne (5P1P), an inhibitor of CYP 2F2, and diethyldithiocarbamate (DDTC), an inhibitor of CYP 2E1 to evaluate their role in the formation of the related reactive metabolites. Liver and lung microsomes were incubated with ¹⁴C-EB (0.22 mM) in the presence of 1 mM NADPH under physiological conditions for 60 min. In lung microsomes, binding activity was in the order of mouse (812.4 ± 102.2 pmol/mg protein) >> rat (57.0 ± 3.2 pmol/mg protein). Human lung microsomes had little binding activity (15.7 ± 1.4 pmol/mg protein), which was comparable to the no-NADPH control (9.9–16.7 pmol/mg protein). In liver microsomes, mouse had the highest activity (469.0 ± 38.5 pmol/mg protein) followed by rat (148.3 ± 14.7 pmol/mg protein) and human (89.8 ± 3.0 pmol/mg protein). Presence of 5P1P or DDTC decreased binding across species and tissues. However, much higher inhibition was observed in mouse (86% [DDTC] and 89% [5P1P]) than rat (56% [DDTC] and 59% [5P1P]) lung microsomes. DDTC showed ∼2-fold higher inhibition of binding in mouse and human liver microsomes than 5P1P (mouse = 85% vs. 40%; human = 59% vs. 36%). Inhibition in binding by DDTC was much higher (10-fold) than 5P1P (72% vs. 7%) in rat liver microsomes. These results show species, tissue and enzyme differences in the formation of reactive metabolites of EB. In rat and mouse lung microsomes, both CYP2E1 and CYP2F2 appear to contribute in the formation of reactive metabolites of EB. In contrast, CYP2E1 appears to be the primary CYP isozyme responsible for the reactive metabolites of EB in the liver.     

Inhibitory effects of gypenosides on seven human cytochrome P450 enzymes in vitro

Among the various possible causes for drug interactions, pharmacokinetic factors such as inhibition of drug-metabolizing enzymes, especially cytochrome P450 (CYP) enzymes, are regarded as the most frequent and clinically important. Gypenosides is widely used as functional food and over-the-counter drug in East Asia. In this study, the in vitro inhibitory effects of gypenosides on the major human CYP enzymes (CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, and CYP3A4) activities in human liver microsomes were examined using liquid chromatography–tandem mass spectrometry. Gypenosides showed the strongest inhibition of CYP2D6, followed by CYP2C8, CYP3A4 and CYP2C9. The IC₅₀ values were 1.61 μg/mL, 20.06 μg/mL, 34.76 μg/mL (CYP3A4/midazolam), 46.73 μg/mL (CYP3A4/testosterone), and 54.52 μg/mL, respectively. Gypenosides exhibited competitive inhibition of CYP2D6 (Ki = 1.18). In conclusion, Gypenosides might cause herb–drug interactions via inhibition of CYP2D6. An in vivo study is needed to examine this further.     

An antioxidant,N,N′-diphenyl-p-phenylenediamine (DPPD), affects labor and delivery in rats: A 28-day repeated dose test and reproduction/developmental toxicity test

A 28-day repeated dose toxicity test and reproduction/developmental toxicity test for N,N′-diphenyl-p-phenylenediamine (DPPD) were conducted in [Crl:CD(SD)] SPF rats. Male and female rats were dosed with DPPD by gavage for 28 days at 0, 100, 300, or 1000 mg/kg bw/day or for a total of 42–46 days at 0, 8, 50, or 300 mg/kg bw/day. No significant adverse effects were observed in the repeated dose toxicity study up to 1000 mg/kg bw/day in both sexes. In the reproduction/developmental toxicity study, two females showed piloerection, hypothermia, and pale skin; one died and the other showed dystocia on day 23 of pregnancy at 300 mg/kg bw/day. Another female delivered only three live pups at 300 mg/kg bw/day. A significantly prolonged gestation period was observed at 50 and 300 mg/kg bw/day. The NOAELs of repeated dose toxicity and reproduction/developmental toxicity were considered to be 1000 and 8 mg/kg bw/day, respectively.     

Pre-clinical in vitro and in vivo safety evaluation of bovine whey derived osteopontin,Lacprodan® OPN-10

Lacprodan® OPN-10 is a proprietary whey-based protein product that contains bovine-derived osteopontin (OPN), found in human milk and other bodily tissues. In vitro genotoxicity tests conducted according to accepted guidelines at up to 5000 μg/plate OPN failed to induce genetic mutations in Salmonella typhimurium strains and Escherichia coli strain and did not induce chromosomal aberrations or cytotoxicity in human lymphocytes. Administration of an acute dose of Lacprodan® OPN-10 (2300 mg/kg body weight) to male and female mice did not induce chromosomal damage or mitotic apparatus damage to erythroblasts from bone marrow. Lacprodan® OPN-10 was evaluated in a 13-week oral toxicity study in which rats were fed diets containing 0.5%, 1.0% and 2.0% Lacprodan® OPN-10. No test-article-related clinical observations or toxicological effects on body or organ weights, food consumption, ophthalmic effects, locomotor activity, hematology, clinical chemistry, urinalysis, or pathology were identified. In a teratogenicity study, administration of Lacprodan® OPN-10 up to 2500 mg/kg bw/day via gavage to pregnant rats had no effect on dams or pups. The No Observed Adverse Effect Level (NOAEL) for Lacprodan® OPN-10 in the 13-week toxicity study was 2.0% of the diet (equivalent to 1208 mg/kg bw/day in male rats and 1272 mg/kg bw/day in female rats).     

Estrogenicity of food-associated estrogenic compounds in the fetuses of female transgenic mice upon oral and IP maternal exposure

The present study investigated to what extent seven food-associated in vitro estrogenic compounds can induce estrogenic effects in the fetuses of pregnant female mice with an estrogen receptor (ER)-mediated luciferase (luc) reporter gene system. The luc-induction was determined either 8 h after maternal dosing with a single intraperitoneal (IP) dose or 24 h after the last of a series of 8 daily oral dosages. Three known estrogens, 17β-estradiol (E₂), 17α-ethynylestradiol (EE) and 17β-estradiol 3,17-dipropionate (EP) were used as positive controls at 1 mg/kg bw and DMSO as solvent control. The food-associated estrogenic compounds tested were: bisphenol A (BPA), nonylphenol (NP) both at 50 mg/kg bw, dichlorodiphenyldichloroethylene (p,p′-DDE) at 50 mg/kg bw, quercetin at 16.6 mg/kg bw, and di-isoheptyl phthalate (DIHP), di-(2-ethylhexyl) phthalate (DEHP) and di-(2-ethylhexyl) adipate (DEHA) all at 100 mg/kg bw. Exposure to E₂, EE and EP resulted in significant luc inductions upon both oral and/or IP dosing in a variety of tissues including liver, tibia and femurs, and upon IP dosing also in fetuses.BPA, NP, DEHA, DEHP, DIHP, DDE and quercetin were unable to significantly induce luc activity in fetuses. However, after maternal oral exposure during gestation to NP, BPA and DIHP placental luc activity was significantly lowered.The results indicate that at the current levels of exposure to food-associated estrogenic compounds, estrogenic effects to the fetus are not expected. The significant luc reduction in the placenta, should be further studied for its significance for fetal development and relevance for the human situation.     

Effect of antidepressant drugs on cytochrome P450 2C11 (CYP2C11) in rat liver

BackgroundRat CYP2C11 (besides CYP2C6) can be regarded as a functional counterpart of human CYP2C9. The aim of the present study was to investigate the influence of classic and novel antidepressant drugs on the activity of CYP2C11, measured as a rate of testosterone 2α- and 16α-hydroxylation.MethodsThe reaction was studied in control liver microsomes in the presence of antidepressants, as well as in microsomes from rats treated intraperitoneally (ip) with pharmacological doses of the tested drugs (imipramine, amitriptyline, clomipramine, nefazodone – 10 mg/kg ip; desipramine, fluoxetine, sertraline - 5 mg/kg ip; mirtazapine - 3 mg/kg ip) for one day or two weeks (twice a day), in the absence of antidepressants in vitro.ResultsThe investigated antidepressant drugs added to control liver microsomes produced certain inhibitory effects on CYP2C11 activity, which were moderate (sertraline, nefazodone and clomipramine: K_i = 39, 56 and 66 μM, respectively), modest (fluoxetine and amitriptyline: K_i = 98 and 108 μM, respectively) or weak (imipramine and desipramine: K_i = 191 and 212 μM, respectively). Mirtazapine had no inhibitory effect on CYP2C11 activity. One-day exposure of rats to the antidepressant drugs did not significantly change the activity of CYP2C11 in liver microsomes; however, imipramine, desipramine and fluoxetine showed a tendency to diminish the activity of CYP2C11. Of the antidepressants studied, only desipramine and fluoxetine administered chronically elevated CYP2C11 activity; those effects were positively correlated with the observed increases in the enzyme protein level.ConclusionThree different mechanisms of the antidepressants-CYP2C11 interaction are postulated: 1) a direct inhibition of CYP2C11 shown in vitro by nefazodone, SSRIs and TADs; 2) in vivo inhibition of CYP2C11 produced by one-day treatment with imipramine, desipramine and fluoxetine, which suggests inactivation of the enzyme by reactive metabolites; 3) in vivo induction of CYP2C11 produced by chronic treatment with desipramine and fluoxetine, which suggests their influence on enzyme regulation.     

One-generation reproduction study of esterified propoxylated glycerol (EPG) administered in the feed to CD® (Sprague-Dawley) rats

This one-generation study assessed the potential of esterified propoxylated glycerol (EPG) to affect reproduction and offspring development in rats. Male and female Crl:CD(SD)BR rats (30/sex/group) were exposed to EPG at 0, 0.5, 1, and 2 g/kg bw/day or at 5% (w/w) in the diet prior to (13 weeks), during, and after two consecutive matings. For dams, exposure continued through gestation and lactation; F_1a and F_1b pups were weaned to the respective diet (for up to 91 days). No consistent treatment-related effects were observed in: body weights/gains; feed consumption; clinical observations; mating indices; survival, growth and development of litters, litter sizes, body weights, sex ratios (lower % males/litter at 1 and 2 g/kg bw/day), acquisition of developmental landmarks, behavioral indices, or histology of selected organs. Lower serum vitamin D, liver vitamin A, and liver vitamin E levels were seen in some EPG-treated groups. None of the reductions were judged to be biologically significant. A/G ratio was greater among males receiving 2 g/kg bw/day and 5%. In the absence of any other related effects, the biological significance of this finding is doubtful.     

Taiwan food scandal: The illegal use of phthalates as a clouding agent and their contribution to maternal exposure

In 2011 the Taiwan Food and Drug Administration reported that plasticizers di(2-ethylhexyl) phthalate (DEHP) and di-iso-nonyl phthalate (DiNP), endocrine disruptors, were illegally added to clouding agents used in foods and beverages. 965 products were found contaminated, of which 206 were exported to 22 countries. This study’s purpose was to obtain English names for 28 contaminated products for which DEHP levels were reported, calculate estimated average daily intake (mg/kg/day) for a 50 kg woman consuming one portion, and compare to U.S. and E.U. guidelines for daily intake. We found that drinking just one bottle (500 ml) of sports drinks would result in an average DEHP intake of 0.14 mg/kg bw/day (range 0.091–0.341), which exceeds by several fold government guidelines (0.02–0.06 mg/kg bw/day). One (2 g) serving from 4/14 samples of contaminated dietary supplements exceeds the guideline of 0.02 mg/kg bw/day. In conclusion, consuming even one portion of tainted drinks and some powders would lead to daily intake of DEHP that greatly exceeds established safety guidelines, raising concerns about potential adverse effects, particularly reproductive tract development in the male fetus. Global distribution of DEHP-contaminated and other adulterated products should prompt governments to become proactive in food safety regulations and chemical testing.     

Fipronil induces CYP isoforms in rats

The goal of the present study was to evaluate fipronil effects on the activities of drug metabolizing enzymes in rat liver microsomes. Rats were orally treated with fipronil at doses of 1, 5, 10 and 15 mg/kg bw/day for 6 days. Determinations of cytochrome P450 (CYP) enzyme activities were carried out in hepatic microsomes isolated from treated rats. The activities of some members of CYP2E, CYP1A, CYP2A, CYP2B and CYP3A subfamilies significantly increased after fipronil treatment in a dose-dependent manner as compared to control. The major effects were observed in the O-deethylation of ethoxyresorufin and O-demethylation of methoxyresorufin (reflecting CYP1A1/2 activities), in the O-depenthylation of pentoxyresorufin and 16β-hydroxylation of testosterone (reflecting CYP2B1/2 activities), and in the N-demethylation of erythromycin and 6β-hydroxylation of testosterone (reflecting CYP3A1/2 activities). Immunoblot studies revealed that fipronil increased the apoprotein levels of CYP1A1. Our results suggest that fipronil is an inducer of hepatic phase I CYP enzymes, causing an increased potential to interact with a wide range of xenobiotics or endogenous chemicals that are substrates of the CYP1A, CYP2B and CYP3A subfamilies. Further investigations are required to in vivo evaluate the potential of the metabolite fipronil sulfone as an inducer of phase I CYP enzymes.     

Developmental toxicity study of sodium molybdate dihydrate administered in the diet to Sprague Dawley rats

Molybdenum is an essential nutrient for humans and animals and is a constituent of several important oxidase enzymes. It is normally absorbed from the diet and to a lesser extent from drinking water and the typical human intake is around 2 μg/kg bodyweight per day. No developmental toxicity studies to contemporary standards have been published and regulatory decisions have been based primarily on older studies where the nature of the test material, or the actual dose levels consumed is uncertain.In the current study the developmental toxicity of sodium molybdate dihydrate as a representative of a broad class of soluble molybdenum(VI) compounds, was given in the diet to Sprague Dawley rats in accordance with OECD Test Guideline 414. Dose levels of 0, 3, 10, 20 and 40 mg Mo/kg bw/day were administered from GD6 to GD20. No adverse effects were observed at any dose level on the dams, or on embryofetal survival, fetal bodyweight, or development, with no increase in malformations or variations. Significant increases in serum and tissue copper levels were observed but no toxicity related to these was observed. The NOAEL observed in this study was 40 mg Mo/kg bw/day, the highest dose tested.     

Effects of rifampin on CYP2E1-dependent hepatotoxicity of isoniazid in rats

Isoniazid and rifampin are first line drugs used to prevent and treat tuberculosis. The effects of rifampin co-administration on isoniazid-induced oxidative stress were investigated by the determination of the changes in hepatic metabolizing enzymes and DNA damage. Rats were treated with isoniazid alone (100 mg/kg, i.p.) or co-treated with rifampin (100 mg/kg, i.g.) for 10 or 21 days. Activities of CYP2E1, CYP1A1, CYP3A and glutathione S-transferases (GSTs) were analyzed by specific substrates. DNA oxidative damage by drug treatments was analyzed in precision-cut liver slices by HPLC–MS/MS. Isoniazid significantly increased CYP2E1 activities above control levels after 10 or 21 days treatment (2.25–4.59-fold), indicated by both chlorzoxazone hydroxylase and aniline hydroxylase (p < 0.01). Isoniazid treatment decreased activities of cytosolic total GST, alpha GST and mu GST after 21 days (p < 0.01). No change in activities of CYP1A1, CYP3A, and CYP3A1 mRNA expression was observed after isoniazid treatment. Rifampin co-administration significantly attenuated isoniazid-induced CYP2E1 levels (p < 0.01) and inhibition of mu GST (p < 0.01). Rifampin did not increase the formation of DNA adducts induced by isoniazid. These results suggest that rifampin co-administration does not increase isoniazid-induced oxidative stress through hepatic CYP2E1 during short-term treatment in experimental rats.     

Perazine at therapeutic drug concentrations inhibits human cytochrome P450 isoenzyme 1A2 (CYP1A2) and caffeine metabolism – an in vitro study

The aim of the present study was to estimate the inhibitory effect of perazine, a phenothiazine neuroleptic with piperazine structure in a side chain, on human CYP1A2 activity measured as a rate of caffeine 3-N- and 1-N-demethylation. Moreover, the influence of perazine on other caffeine metabolic pathways such as 7-N-demethylation (CYP1A2, CYP2C8/9, CYP3A4) and 8-hydroxylation (CYP3A4, CYP1A2, CYP2C8/9) was also determined. The Dixon analysis showed that in both human liver microsomes and Supersomes CYP1A2 perazine potently and to a similar degree inhibited caffeine 3-N-demethylation (K_i = 3.5 μM) and 1-N-demethylation (K_i = 5 μM). Perazine moderately diminished the rate of caffeine 7-N-demethylation in Supersomes CYP1A2 (K_i = 11.5 μM) and liver microsomes (K_i = 20 μM), and attenuated C-8-hydroxylation (K_i = 15.5μM) in Supersomes CYP1A2. On the other hand, perazine weakly inhibited caffeine C-8-hydroxylation in liver microsomes (K_i = 98 μM). About 80% of basal CYP1A2 activity was reduced by the therapeutic concentrations of perazine (5–10 μM).The obtained results show that perazine at its therapeutic concentrations is a potent inhibitor of human CYP1A2. Hence, taking account of CYP1A2 contribution to the metabolism of endogenous substances (steroids), drugs (xanthine derivatives, phenacetin, propranolol, imipramine, phenothiazine neuroleptics, clozapine) and carcinogenic compounds, the inhibition of CYP1A2 by perazine may be of physiological, pharmacological and toxicological importance.     

Toxic effects of dietary exposure to T-2 toxin on intestinal and hepatic biotransformation enzymes and drug transporter systems in broiler chickens

The effects of the mycotoxin T-2 on hepatic and intestinal drug-metabolizing enzymes (cytochrome P450) and drug transporter systems (MDR1 and MRP2) in poultry were investigated during this study. Broiler chickens received either uncontaminated feed, feed contaminated with 68 μg/kg or 752 μg/kg T-2 toxin. After 3 weeks, the animals were euthanized and MDR1, MRP2, CYP1A4, CYP1A5 and CYP3A37 mRNA expression were analyzed using qRT-PCR. Along the entire length of the small intestine no significant differences were observed. In the liver, genes coding for CYP1A4, CYP1A5 and CYP3A37 were significantly down-regulated in the group exposed to 752 μg/kg T-2. For CYP1A4, even a contamination level of 68 μg/kg T-2 caused a significant decrease in mRNA expression. Expression of MDR1 was not significantly decreased in the liver. In contrast, hepatic MRP2 expression was significantly down-regulated after exposure to 752 μg/kg T-2. Hepatic and intestinal microsomes were prepared to test the enzymatic activity of CYP3A. In the ileum and liver CYP3A activity was significantly increased in the group receiving 752 μg/kg T-2 compared to the control group. The results of this study show that drug metabolizing enzymes and drug transporter mechanisms can be influenced due to prolonged exposure to relevant doses of T-2.