RESUMEN
1. The pharmacokinetics, metabolism and excretion of L-NIL-TA, an inducible nitric oxide synthase inhibitor, were investigated in dog. 2. The dose of [14C]L-NIL-TA was rapidly absorbed and distributed after oral and intravenous administration (5 mg kg-1), with Cmax of radioactivity of 6.45-7.07 microg equivalents g-1 occurring at 0.33-0.39-h after dosing. After oral and intravenous administration, radioactivity levels in plasma then declined with a half-life of 63.1 and 80.6-h, respectively. 3. Seven days after oral and intravenous administrations, 46.4 and 51.5% of the radioactive dose were recovered in urine, 4.59 and 2.75% were recovered in faeces, and 22.4 and 22.4% were recovered in expired air, respectively. The large percentages of radioactive dose recovered in urine and expired air indicate that [14C]L-NIL-TA was well absorbed in dogs and the radioactive dose was cleared mainly through renal elimination. The mean total recovery of radioactivity over 7 days was approximately 80%. 4. Biotransformation of L-NIL-TA occurred primarily by hydrolysis of the 5-aminotetrazole group to form the active drug L-N6-(1-iminoethyl)lysine (NIL or M3), which was further oxidized to the 2-keto acid (M5), the 2-hydroxyl acid (M1), an unidentified metabolite (M2) and carbon dioxide. The major excreted products in urine were M1 and M2, representing 22.2 and 21.2% of the dose, respectively.
Asunto(s)
Amidas/farmacocinética , Inhibidores Enzimáticos/farmacocinética , Óxido Nítrico Sintasa/antagonistas & inhibidores , Tetrazoles/farmacocinética , Administración Oral , Amidas/metabolismo , Animales , Biotransformación , Cromatografía Líquida de Alta Presión , Perros , Inhibidores Enzimáticos/metabolismo , Eritrocitos/metabolismo , Heces/química , Femenino , Inyecciones Intravenosas , Pulmón/metabolismo , Masculino , Espectrometría de Masas , Óxido Nítrico Sintasa de Tipo II , Tetrazoles/metabolismoRESUMEN
The time course of induction of microsomal and peroxisomal lipid-metabolizing enzymes in male Wistar rat liver has been investigated following a single i.p. dose of clofibrate (250 mg/kg). The microsomal enzyme, cytochrome P450IVA1, demonstrated a biphasic response to sodium clofibrate administration, the biphasic response consisting of an initial small response, peaking at approximately 30 min post-dose and returning to near baseline values after 2 hr. A second major induction of cytochrome P450IVA1 occurred between 18 and 24 hr post-dose. This biphasic phenomenon for cytochrome P450IVA1 was observed for the enzyme activity (lauric acid hydroxylase), immunodetectable protein (using a specific ELISA method) and at the mRNA level (using a 2.1 kilobase cytochrome P450IVA1 cDNA probe). In contrast, peroxisomal fatty acid beta-oxidation enzymes responded in a monophasic manner to clofibrate administration, peaking approximately 24 hr post-dose. Accordingly, microsomal cytochrome P450IVA1 was induced before the peroxisomal enzymes of fatty acid beta-oxidation. The effect of cycloheximide on the induction of peroxisome proliferation by clofibrate was additionally investigated. The prior administration of cycloheximide to Wistar rats ablated the clofibrate-dependent induction of both cytochrome P450IVA1 and peroxisomal-dependent lipid metabolism and also blocked the corresponding synthesis of enzyme proteins. Cycloheximide additionally inhibited the clofibrate-dependent increase in peroxisomal acyl-CoA oxidase mRNA, but was without effect on the induced cytochrome P450IVA1 mRNA levels, indicating a protein or enzyme dependency for the phenomenon of peroxisome proliferation. Taken collectively, our data strongly argues that the regulation of microsomal cytochrome P450IVA1 and peroxisomal fatty acid beta-oxidation enzymes are closely related, possibly through the initial, clofibrate-dependent regulation of cytochrome P450IVA1.
Asunto(s)
Clofibrato/farmacología , Sistema Enzimático del Citocromo P-450/metabolismo , Microcuerpos/metabolismo , Microsomas Hepáticos/enzimología , Oxigenasas de Función Mixta/metabolismo , Acil-CoA Oxidasa , Animales , Citocromo P-450 CYP4A , Inducción Enzimática/efectos de los fármacos , Oxidorreductasas/metabolismo , RatasRESUMEN
The existence of a postulated hepatic receptor responsible for the peroxisomal proliferation induced in rodents by hypolipidaemic drugs has been investigated. [3H]-nafenopin and [3H]-ciprofibrate were used as labelled ligands and two competitive binding assays, using either a charcoal-dextran or a hydroxylapatite method, were developed to investigate potential binding. In both assay systems, specific displaceable binding of either nafenopin or ciprofibrate to whole homogenate, microsomal and cytosolic fractions of rat liver could not be detected in a variety of buffer systems. A positive control of ligand binding to bovine serum albumin indicated the validity of the binding assays used. In addition, both nafenopin and ciprofibrate exhibited displaceable binding to serum albumin using the hydroxylapatite binding assay and a Scatchard analysis of the binding of [3H]-nafenopin to fatty acid free rat serum albumin yielded a dissociation constant of 5.2 x 10(-7) M and 86 pmol of ligand bound per mg protein. Taken collectively, our data strongly argues against the existence of a specific hepatic peroxisome proliferation receptor and indicates that the peroxisome proliferating hypolipidaemic drugs bind to serum albumin and possibly to other cellular proteins not involved in the activation of genes necessary for peroxisome proliferation.