Publications (25) View all
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Article: Preclinical and clinical evidence for the collaborative transport and renal secretion of an oxazolidinone antibiotic by organic anion transporter 3 (OAT3/SLC22A8) and multidrug and toxin extrusion protein 1 (MATE1/SLC47A1).
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ABSTRACT: N-({(5S)-3-[4-(1,1-dioxidothiomorpholin-4-yl)-3,5-difluorophenyl]-2-oxo-1,3-oxazolidin-5-yl}methyl)acetamide (PNU-288034), an oxazolidinone antibiotic, was terminated in phase I clinical development because of insufficient exposure. Analysis of the drug pharmacokinetic and elimination profiles suggested that PNU-288034 undergoes extensive renal secretion in humans. The compound was well absorbed and exhibited approximately linear pharmacokinetics in the oral dose range of 100 to 1000 mg in human. PNU-288034 was metabolically stable in liver microsomes across species, and unchanged drug was cleared in the urine by an apparent active renal secretion process in rat and monkey (two to four times glomerular filtration rate) but not dog. In vitro studies conducted to characterize the transporters involved demonstrated PNU-288034 uptake by human organic anion transporter 3 (OAT3; K(m) = 44 +/- 5 microM) and human multidrug and toxin extrusion protein 1 (hMATE1; K(m) = 340 +/- 55 microM). The compound was also transported by multidrug resistance P-glycoprotein and breast cancer resistance protein. In contrast, human organic cation transporter 2, human OAT1, and hMATE2-K did not transport PNU-288034. Coadministration of PNU-288034 and the OAT3 inhibitor probenecid significantly increased PNU-288034 plasma area under the curve (170%) and reduced both plasma and renal clearance in monkey. Coadministration of PNU-288034 and cimetidine, a MATE1 inhibitor, also reduced plasma clearance in rat to a rate comparable with probenecid coadministration. Collectively, our results demonstrated a strong in vitro-in vivo correlation for active renal secretion coordinated through the vectorial transport process of OAT3 and MATE1, which ultimately resulted in limiting the systemic exposure of PNU-288034.Journal of Pharmacology and Experimental Therapeutics 09/2010; 334(3):936-44. · 3.83 Impact Factor -
Article: Alteration of testicular steroidogenesis and histopathology of reproductive system in male rats treated with triclosan.
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ABSTRACT: Triclosan (TCS), a chlorophenol, is widely used as a preservative in different types of commercial preparations. The reports on TCS-mediated endocrine disruption are controversial and the present study aimed to elucidate the probable mode of action of TCS as an antiandrogenic compound using a robust study design. Male albino rats, Rattus norvegicus, were treated with three doses of triclosan for a period of 60 days followed by the analysis of various biochemical parameters. RT-PCR analysis demonstrated a significant decrease in mRNA levels for testicular steroidogenic acute regulatory (StAR) protein, cytochrome P450(SCC), cytochrome P450(C17), 3beta-hydroxysteroid dehydrogenase (3beta-HSD), 17beta-hydroxysteroid dehydrogenase (17beta-HSD) and androgen receptor (AR) in TCS treated rats (p<0.05). TCS also induced a perturbed translation of testicular StAR, and AR proteins as shown by Western blot analysis in treated groups of rats. A reduced level of StAR was further indicated by immunohistochemistry in testicular Leydig cells. Further, there was a significant decrease (p<0.05) in the level of serum lutenizing hormone (LH), follicle stimulating hormone (FSH), cholesterol, pregnenolone, and testosterone. In vitro assays demonstrated more than 30% decrease in testicular 3beta-HSD and 17beta-HSD enzyme activities in treated group of animals. Extensive histopathological malformations were observed in the testis and sex accessory tissues of the treated rats. Overall this study showed that TCS decreased the synthesis of androgens followed by reduced sperm production in treated male rats which could be mediated by a decreased synthesis of LH and FSH thus involving hypothalamo-pituitary-gonadal axis.Reproductive Toxicology 01/2009; 27(2):177-85. · 3.23 Impact Factor -
Article: Mechanism-based inactivation of cytochrome P450 2C9 by tienilic acid and (+/-)-suprofen: a comparison of kinetics and probe substrate selection.
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ABSTRACT: In vitro experiments were conducted to compare k(inact), K(I) and inactivation efficiency (k(inact)/K(I)) of cytochrome P450 (P450) 2C9 by tienilic acid and (+/-)-suprofen using (S)-flurbiprofen, diclofenac, and (S)-warfarin as reporter substrates. Although the inactivation of P450 2C9 by tienilic acid when (S)-flurbiprofen and diclofenac were used as substrates was similar (efficiency of approximately 9 ml/min/micromol), the inactivation kinetics were characterized by a sigmoidal profile. (+/-)-Suprofen inactivation of (S)-flurbiprofen and diclofenac hydroxylation was also described by a sigmoidal profile, although inactivation was markedly less efficient (approximately 1 ml/min/micromol). In contrast, inactivation of P450 2C9-mediated (S)-warfarin 7-hydroxylation by tienilic acid and (+/-)-suprofen was best fit to a hyperbolic equation, where inactivation efficiency was moderately higher (10 ml/min/micromol) and approximately 3-fold higher (3 ml/min/micromol), respectively, relative to that of the other probe substrates, which argues for careful consideration of reporter substrate when mechanism-based inactivation of P450 2C9 is assessed in vitro. Further investigations into the increased inactivation seen with tienilic acid relative to that with (+/-)-suprofen revealed that tienilic acid is a higher affinity substrate with a spectral binding affinity constant (K(s)) of 2 microM and an in vitro half-life of 5 min compared with a K(s) of 21 microM and a 50 min in vitro half-life for (+/-)-suprofen. Lastly, a close analog of tienilic acid with the carboxylate functionality replaced by an oxirane ring was devoid of inactivation properties, which suggests that an ionic binding interaction with a positively charged residue in the P450 2C9 active site is critical for recognition and mechanism-based inactivation by these close structural analogs.Drug metabolism and disposition: the biological fate of chemicals 11/2008; 37(1):59-65. · 3.74 Impact Factor -
Article: Disruption of LH-induced testosterone biosynthesis in testicular Leydig cells by triclosan: probable mechanism of action.
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ABSTRACT: Triclosan (TCS) is an antimicrobial chemical widely used in different commercial preparations. The present study demonstrated the mechanism of action of TCS-induced anti-androgenicity in rat Leydig cells. Treatment of purified cells with increasing concentrations of TCS (0.001, 0.01, 0.1, 1 and 10 microM) resulted in a significantly decreased activity of adenylyl cyclase enzyme which was followed by a decreased synthesis of cAMP. This decreased cAMP level resulted in the disruption of entire steroidogenic cascade causing a depressed synthesis of testosterone. However, TCS-induced decrease in the production of testosterone returned to normalcy when cells were treated with forskolin (an adenylyl cyclase activator). Transcription followed by translational of four prominent steroidogenic enzyme/proteins, cytochrome P450 side chain cleavage (P450scc), 3beta-hydroxysteroid dehydrogenase (3beta-HSD), 17beta-hydroxysteroid dehydrogenase (17beta-HSD) and steroidogenic acute regulatory (StAR) protein, also decreased in a dose-dependent manner in TCS-treated Leydig cells as determined by RT-PCR, enzyme assay and Western blot. These results suggested that the disruption of the activity of adenylyl cyclase enzyme by TCS in turn leads to the disruption of intermediate steroidogenic cascade causing a depressed testosterone production. The study further confirmed the anti-androgenic activity of TCS in Leydig cells with highest effective concentration at 1 microM.Toxicology 09/2008; 250(2-3):124-31. · 3.68 Impact Factor -
Article: Spearmint induced hypothalamic oxidative stress and testicular anti-androgenicity in male rats - altered levels of gene expression, enzymes and hormones.
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ABSTRACT: Mentha spicata Labiatae, commonly known as spearmint, can be used for various kinds of illnesses in herbal medicines and food industries. One of the prominent functions of this plant extract is its anti-androgenic activity. The present study investigated the probable correlation between oxidative stress in hypothalamic region and anti-androgenic action of this plant's aqueous extract on rats. Decreased activities of enzymes like superoxide dismutase, catalase, glutathione peroxidase and glutathione reductase in hypothalamus of treated rats indicated spearmint induced oxidative stress. Further RT-PCR and immunoblot analysis demonstrated the decreased expression of some of the steroidogenic enzymes, cytochrome P450scc, cytochrome P450C17, 3beta-Hydroxysteroid dehydrogenase (3beta-HSD), 17beta-Hydroxysteroid dehydrogenase (17beta-HSD) and other related proteins like, steroidogenic acute regulatory protein, androgen receptor and scavenger receptor class B-1. Further, in vitro enzyme assays demonstrated depressed activities of testicular 3beta-HSD and 17beta-HSD enzymes. Histopathology indicated a decreased sperm density in cauda epididymis and degeneration of ductus deference. Our study suggested that spearmint probably induced oxidative stress in hypothalamus resulting in decreased synthesis of LH and FSH which in turn down-regulated the production of testicular testosterone through the disruption of a number of intermediate cascades.Food and Chemical Toxicology 09/2008; 46(12):3563-70. · 3.00 Impact Factor
