Our library of drug research abstracts drawn from the medical literature is updated on a regular schedule, and you can be assured that new parafon research articles will be listed here shortly after becoming available to us.
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The influence of a newly developed quinolone: antofloxacin, on CYP activity in rats.
Eur J Drug Metab Pharmacokinet. 2008 Jan-Mar; 33(1): 1-7
Xu X, Liu HY, Liu L, Xie L, Liu XD
To investigate a newly developed quinolone antibiotics, the effect of antofloxacin hydrochloride on cytochrome P450 isoforms in rats was examined. A cocktail approach was adopted. Theophylline (CYP1A2), midazolam (CYP3A), chlorzoxazone (CYP2E1), dextromethorphan (CYP2D6), omeprazole (CYP2C19) and diclofenac (CYP2C9) were used as probes in the study, and own control was adopted. In Protocol 1, probes were given to rats simultaneously by co-administration with antofloxacin. The blood samples were obtained at designated time, and plasma concentrations of the six probes were determined by LC-MS. The pharmacokinetic parameters were calculated and compared in experimental groups in the absence and presence of antofloxacin. The result showed that the presence of antofloxacin resulted in a significant increase in theophylline values of AUC0-T and t1/2 (PAUC0-T = 0.0004 vs control Pt1/2 = 0.005 vs control), indicating that antofloxacin delayed the clearance of theophylline. In Protocol 2, the probes' pharmacokinetic parameters were compared in rats that received six probes before and after 14.5 days of consecutive administration of antofloxacin (15 mg x kg(-1), given orally, twice daily). The results suggested that the AUC0-T of chlorzoxazone was significantly decreased (P = 0.024), while that of dextromethorphan was significantly increased (P = 0.027). In conclusion, these results indicated that antofloxacin may inhibit the activity of CYP1A2, thus delaying the clearance of its substrates, and may have a slight inhibitory effect on CYP2D6 as well as an inductive effect on CYP2E1 following chronic administration.
Cellular Imaging Predictions of Clinical Drug-Induced Liver Injury.
Toxicol Sci. 2008 Jun 3;
Xu JJ, Henstock PV, Dunn MC, Smith AR, Chabot JR, de Graaf D
Drug-induced liver injury (DILI) is the most common adverse event causing drug non-approvals and drug withdrawals. Using drugs as test agents and measuring a panel of cellular phenotypes that are directly linked to key mechanisms of hepatotoxicity, we have developed an in vitro testing strategy that is predictive of many clinical outcomes of DILI. Mitochondrial damage, oxidative stress, and intracellular glutathione, all measured by high content cellular imaging in primary human hepatocyte cultures, are the three most important features contributing to the hepatotoxicity prediction. When applied to over 300 drugs and chemicals including many that caused rare and idiosyncratic liver toxicity in humans, our testing strategy has a true-positive rate of 50-60% and an exceptionally low false-positive rate of 0-5%. These in vitro predictions can augment the performance of the combined traditional preclinical animal tests by identifying idiosyncratic human hepatotoxicants such as nimesulide, telithromycin, nefazodone, troglitazone, tetracycline, sulindac, zileuton, labetalol, diclofenac, chlorzoxazone, dantrolene, and many others. Our findings provide insight to key DILI mechanisms, and suggest a new approach in hepatotoxicity testing of pharmaceuticals.
The effect of isoniazid containing regimen on CYP2E1 during antituberculosis therapy.
Res Commun Mol Pathol Pharmacol. 2005; 117-118: 137-51
Walubo A, Coetsee C, Arti D, Du Plessis JB
Because isoniazid is a selective inducer of CYP2E1 and isoniazid-induced hepatotoxicity is believed to be due to activation of its metabolites by CYP450, this study was undertaken to determine the effect of isoniazid containing regimen on CYP2E1 in TB-patients. The activity of CYP2E1 in 11 newly diagnosed TB-patients (5 F, 6 M) was investigated before (day 0) and during (day 14) treatment for tuberculosis. CYP2E1 activity was measured using the plasma metabolic ratio (MR) of 6-hydroxy-chlorzoxazone to chlorzoxazone, while CYP2E1 quantity in the peripheral lymphocytes was measured using SDS-PAGE. By day 14 of anti-tuberculosis treatment, the activity of CYP2E1 was inhibited by 72% in 8 patients, but increased in 3 patients. The MR for the 8 patients was reduced from (Median & Range) 2.78 (1.1-21.5) on day 0, to 0.75 (0.4-1.22) on day 14, (P = 0.0006). Renal function was normal before and during the investigation. The detection of CYP2E1 by in peripheral lymphocytes was so variable that it could not be correlated with enzyme activity. Nevertheless, its detection in peripheral lymphocytes where normally is not resident indicates that CYP2E1 was induced by isoniazid. These results indicate that during treatment for tuberculosis with isoniazid containing regimen, CYP2E1 is induced but its activity is inhibited by isoniazid.
[Expression of human CYP2E1 in insect cells using bac-to-bac expression system]
Zhejiang Da Xue Xue Bao Yi Xue Ban. 2008 Mar; 37(2): 118-25
Lu K, Zeng S, Yao TW
OBJECTIVE: To obtain recombinant human CYP2E1 and to determine its activity by using the specific probe substrate. METHODS: CYP2E1 cDNA was obtained by RT-PCR using human liver RNA as template. The cloned CYP2E1 cDNA was ligated with pFastBac vector to generate recombinant pFastBac-CYP2E1, which was then transformed into E. coli DH 10 Bac. Recombinant Bacmid-CYP2E1 was generated by transposition. Then Spodoptera frugiperda (Sf9) insect cells was infected with Bacmid-CYP2E1 to generate recombinant baculoviruses carrying human CYP2E1 cDNA. Finally, Sf9 insect cells were triinfected with recombinant baculoviruses carrying human CYP2E1, CYPOR and CYPb5. The activity of the recombinant enzymes was determined using chlorzoxazone as the substrate. RESULT: The Kmand Vmaxof recombinant CYP2E1 to chlorzoxazone was (72.4 +/-8.7) micromol. L(-1) and (2.41 +/-0.10) micromol.min(-1)?g(-1)protein, respectively. CONCLUSION: Active recombinant CYP2E1 has been obtained by bac-to-bac expression system and its activity is similar to previous reports.
J Ethnopharmacol. 2008 May 22; 117(3): 420-6
Tang H, Min G, Ge B, Li Y, Liu X, Jiang S
AIM OF THE STUDY: Chi-Zhi-Huang decoction (PGR) is one of the traditional Chinese medicine (TCM) preparations with unique effect on withdrawing jaundice and has been used to treat icteric patients in China for many years. In this research, we aim at to evaluate the potential activity of PGR in restoring hepatic drug metabolism in a damaged liver. MATERIALS AND METHODS: A cocktail approach with caffeine (10mg/kg), dapsone (10mg/kg) and chlorzoxazone (20mg/kg) respectively as probe drug of cytochrome P450 (CYP) isoform of CYP 1A2, 3A4 and 2E1 was used to evaluate its possible effects on Phase I oxidative metabolism. Pretreated with three dosages of PGR water extract (0.75, 1.5 and 3g/kg, po) for 5 days, male Wistar rats (220-240 g) were intoxicated by phenylisothiocyanate (PITC, 100mg/kg, po) 24h before probes intravenous injection. The pharmacokinetics of the probes in the blood was determined simultaneously by HPLC, and their non-compartmental parameters were used to evaluate the metabolic difference among the groups. Moreover, the levels of liver enzymes (ALT, AST, ALP) and bilirubins were also measured for insight of liver function. RESULTS: The findings in this study suggest that PGR induces CYP 3A4, does not have much effect on CYP 2E1, and inhibits CYP 1A2 at high dosage. CONCLUSION: The current pharmacokinetic approach allowed the protective effects of PGR on oxidative drug metabolism in damaged liver to be systemically examined and will certainly help in the explanation of synergistic effect of the composites formula.
Drug Metab Dispos. 2008 Jul; 36(7): 1233-41
Ahn CY, Bae SK, Jung YS, Lee I, Kim YC, Lee MG, Shin WG
Protein expression of the hepatic CYP2E1 has been reported to be increased in diabetic rats. This enzyme is the primary metabolizer of chlorzoxazone (CZX) to 6-hydroxychlorzoxazone (OH-CZX). Although patients with liver cirrhosis have a higher prevalence of diabetes mellitus, there have been no reported studies on the protein expression of CYP2E1 in rats induced to have liver cirrhosis and diabetes mellitus by injection of N-dimethylnitrosamine followed by streptozotocin [liver cirrhosis with diabetes mellitus (LCD) rats]. Thus, in the present study, the pharmacokinetics of CZX and OH-CZX were evaluated in LCD rats. Compared with control rats, LCD rats had significantly decreased (by 62%) total liver protein and significantly increased (by 124%) protein expression of CYP2E1, but the intrinsic clearance (Cl(int); formation of OH-CZX per milligram protein) was comparable in both groups of rats. As a result, the relative Cl(int) was also comparable for the two groups. Thus, OH-CZX formation in LCD and control rats was expected to be similar. As expected, after i.v. (20 mg/kg) and p.o. (50 mg/kg) administration of CZX, the area under the curve (AUC) of OH-CZX was comparable in control and LCD rats (i.v., 571 +/- 85.8 and 578 +/- 413 microg x min/ml, respectively; p.o., 1540 +/- 338 and 2170 +/- 1070 microg x min/ml, respectively). In LCD rats, the AUC(OH-CZX)/AUC(CZX) ratio was similar to the value in control rats after i.v. and p.o. administration. These results indicate that OH-CZX can be used as a chemical probe to assess the activity of CYP2E1 in LCD rats.
Eur J Drug Metab Pharmacokinet. 2007 Oct-Dec; 32(4): 189-96
Venkatesh P, Harisudhan T, Choudhury H, Mullangi R, Srinivas NR
A uranyl nitrate-induced model of acute renal failure (UN-ARF) for various time periods was used to study its effect on the disposition of several drugs like chlorzoxazone, clarithromycin, vancomycin, methotrexate etc. An attempt to optimize the duration of UN dosing with respect to the pharmacokinetics of etoposide in rats was carried out after intravenous (i.v.) dosing of UN at 5 mg/kg for 1, 3, 5 and 7 days. Irrespective of the duration of UN dosing apart from day 1, ARF was observed, with significantly increased serum levels of creatinine (0.36 +/- 0.11 for controls vs 2.44 +/- 0.72 [day 7] for UN-ARF rats) and urea (33.71 +/- 9.46 for controls vs. 169.2 +/- 9.71 [day 5] for UN-ARF rats) in all the UN-treated groups. It has been reported that ARF may alter the pharmacokinetics (PK) and the exposure of renally eliminated drugs. Further, as exposure to etoposide has a correlation with toxicity, the need to investigate the possible alterations in etoposide pharmacokinetics in the UN-ARF model could be of significance. The PK of etoposide was therefore investigated in control and UN-ARF rats after a single i.v. dose of 25 mg/kg. The concentrations of etoposide in the plasma were determined by high- performance liquid chromatography (HPLC) method with fluorescence detector set at excitation and emission wavelengths of 380 and 520 nm respectively. The metabolic stability of etoposide was investigated in rat liver microsomes prepared from control and UN-ARF treated rats. The PK results showed increased plasma levels and systemic exposure to etoposide (19.97 +/- 2.12 for control vs 29.03 +/- 2.32, 34.45 +/- 3.37, 34.19 +/- 2.98 for 3, 5 and 7day UN-treated groups respectively), i.e. for all UN-ARF groups except for 1-day UN-ARF rats (20.06 +/- 1.53). Incubation with liver microsomes from UN-ARF rats treated for up to 5 days and control rats showed no significant difference in etoposide metabolism suggesting that the CYP3A4 isoenzyme responsible for the metabolism of etoposide was not considerably expressed thereby leading to the conclusion that 3 days UN dosing was sufficient to induce ARF in rats, and that the dose of etoposide required needs to be monitored due to altered PK.
Chem Res Toxicol. 2008 Mar; 21(3): 720-5
Fukami T, Katoh M, Yamazaki H, Yokoi T, Nakajima M
Human P450 2A13 is the most efficient enzyme for catalyzing the metabolism of nicotine and metabolic activation of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). It is conceivable that P450 2A13 also metabolizes chemicals in air pollutants because this enzyme is highly expressed in the respiratory tract. In this study, we investigated the possibility that P450 2A13 can metabolize naphthalene, styrene, and toluene, which are included in air pollutants as well as tobacco smoke, although they were known to be metabolized by P450 1A2 or 2E1. We found that P450 2A13 catalyzed 1- and 2-naphthol formations from naphthalene with higher intrinsic clearances ( kcat/ Km) (3.1- and 2.2-fold, respectively) than P450 1A2 and also more efficiently catalyzed the styrene 7,8-oxide formation from styrene and the benzylalcohol formation from toluene than P450 2E1. The overlapping substrate specificity of P450 2A13 with P450 2E1 was supported by the finding that P450 2A13 catalyzed chlorzoxazone 6-hydroxylation (8-fold higher value of kcat/ Km) and p-nitrophenol 2-hydroxylation (19-fold higher value of kcat/ Km), which are marker activities of P450 2E1. Thus, we found that P450 2A13 metabolizes diverse environmental chemicals and has overlapping substrate specificities of P450 1A2 and 2E1, suggesting that P450 2A13 plays important roles in the local metabolism of environmental chemicals in the respiratory tract related to toxicity or carcinogenicity.
Drugs Aging. 2008; 25(1): 49-59
Lin HY, Liao CC, Cheng SH, Wang PC, Hsueh YS
BACKGROUND: Potentially inappropriate medication use among the elderly in an outpatient setting has been widely reported. However, the potential association between inappropriate medication use and adverse outcomes is seldom examined. OBJECTIVES: To identify the prevalence, risk factors for and adverse outcomes of potentially inappropriate medication use in ambulatory elderly patients with chronic diseases. METHODS: Data for this observational cohort study consisted of computerized claims from a tertiary medical centre in Taiwan to the Bureau of National Health Insurance. Consecutive ambulatory elderly patients aged > or = 65 years who received long-term (3-month) prescriptions for treatment of a chronic disease were recruited from 1 to 31 March 2005. The cohort included 5741 elderly patients who received 7538 long-term prescriptions. Patients who required repeat prescriptions were able to be given the same prescription if their conditions were stable. The prevalence of potentially inappropriate medication use and the incidence of adverse outcomes, including emergency visits, hospitalizations and mortality, were documented for up to 6 months after the first day the patient was recruited. Beers' 2002 criteria were used to determine the potential inappropriateness of prescribed medications. Associations between potentially inappropriate medications and adverse outcomes were examined by multivariate logistic regression analyses controlling for possible confounding factors. RESULTS: The prevalence of potentially inappropriate medication use was 23.7% in the studied hospital. The most frequently prescribed potentially inappropriate medications of high severity (i.e. having a high likelihood of being associated with an adverse effect that was clinically significant) were amiodarone, chlorzoxazone, bisacodyl, nifedipine and amitriptyline. Logistic regression analysis revealed that female sex, advanced age, number of chronic diseases and number of medications taken all significantly increased the likelihood of receiving potentially inappropriate medications. The incidence of adverse outcomes in patients with potentially inappropriate medication use in the studied hospital was 25.1%. Multivariate logistic regression analysis revealed that potentially inappropriate medication use was significantly associated with hospitalization. CONCLUSIONS: Potentially inappropriate medication use is not a rare event in elderly patients and is associated with higher risk of hospitalization in this age group. In order to reduce the possibility of prescribing inappropriate medications, and therefore to reduce the consequent risk of hospitalization, more attention should be paid when prescribing drugs to, in particular, older female patients with multiple chronic illnesses that require treatment with multiple medications.
Chem Biol Interact. 2008 Mar 10; 172(1): 1-10
Rodeiro I, Donato MT, Lahoz A, González-Lavaut JA, Laguna A, Castell JV, Delgado R, Gómez-Lechón MJ
This paper reports cytotoxic effects and changes in the P450 system after exposing rat hepatocytes to four polyphenol-rich products widely used in Cuban traditional medicine (Mangifera indica L. (MSBE), Thalassia testudinum (Tt), Erythroxylum minutifolium and confusum extracts). Effects of mangiferin, the main polyphenol in MSBE, were also evaluated. Cytotoxicity was assayed by the MTT test after exposure of cells to the products (50-1000 microg/mL) for 24 or 72 h. The results showed that 500 microg/mL MSBE was moderately cytotoxic after 72 h, while mangiferin was not. Marked reductions in cell viability were produced by Erythroxylum extracts at concentrations > or = 200 microg/mL, whereas only moderate effects were induced by 1000 microg/mL Tt. Seven specific P450 activities were evaluated after 48 h exposure of cells to the products. MSBE reduced phenacetin O-deethylation (POD; CYP1A2) activity in a concentration-dependent manner (IC(50)=190 microg/mL). No decreases were observed in other activities. In contrast, mangiferin produced reductions in five P450 activities: IC(50) values of 132, 194, >200, 151 and 137 microg/ml for POD (CYP1A2), midazolam 1'-hydroxylation (M1OH; CYP3A1), diclofenac 4'-hydroxylation (D4OH; CYP2C6), S-mephenytoin 4'-hydroxylation (SM4OH), and chlorzoxazone 6-hydroxyaltion (C6OH; CYP2E1), respectively. E. minutifolium, E. confusum and Tt extracts produced small reductions in SM4OH and C6OH activities, but no significant changes were noted in the other P450 activities. On the other hand, all the products increased the benzyloxyresorufin O-debenzylation (BROD; CYP2B1) activity, with MSBE, mangiferin or E. minutifolium showing the highest effects (about 2-fold over control). Our results showed in vitro effects of these natural products on P450 systems, possibly leading to potential metabolic-based interactions.