Carrier-mediated active transport of the glucuronide and sulfate of 6- hydroxy-5,7-dimethyl-2-methylamino-4-(3-pyridylmethyl) benzothiazole (E3040) into rat liver: quantitative comparison of permeability in isolated hepatocytes, perfused liver and liver i

ABSTRACT The hepatic uptake of glucuronic acid and sulfate conjugates of 6-hydroxy-5,7-dimethyl-2-methylamino-4-(3-pyridylmethyl) benzothiazole (E3040), a dual inhibitor of 5-lipoxygenase and thromboxane A 2 synthetase, was investigated in rats. The biliary excretion clearance values for the glucuronide and the sulfate, obtained after i.v. administration of E3040, were similar and corresponded to approximately 30% of the hepatic blood flow rate. The influx clearance values of E3040 conjugates in the presence of 3% bovine serum albumin, measured by a multiple indicator dilution method in the perfused liver, were 1.20 ml/min/g liver for the glucuronide and 0.74 ml/min/g liver for the sulfate, which were twice and equal to the normal hepatic plasma flow rate, respectively, which suggests the presence of an efficient transport system(s). The uptake of E3040 conjugates into the isolated hepatocytes is mediated by Na ϩ -independent active transport system(s), which is inhibited by dibromosulfophthalein and bile acids. The uptake for the sulfate had high-affinity and high-capacity transport activity (K m ϭ 25 M; V max ϭ 7.8 nmol/min/10 6 cells) compared with that for the glucuronide (K m ϭ 59 M; V max ϭ 2.2 nmol/min/10 6 cells). The uptakes of E3040 conjugates (glucuronide, sulfate) exhibited a mutual competitive inhibition. It is suggested that both conjugates share a multispecific organic anion transporter located on the sinusoidal membrane. Conjugative metabolism, such as glucuronidation and sulfation, is an important pathway for the inactivation or detoxification of xenobiotics. On the other hand, conjugative metabolites of certain drugs with pharmacologically active (such as the 6-glucuronide of morphine; In previous studies, we reported the disposition of glucuronide and sulfate of E3040, a novel dual inhibitor of 5-lipoxygenase and thromboxane A 2 synthetase, after administration Received for publication May 24, 1996. ABBREVIATIONS: E3040, 6-hydroxy-5,7-dimethyl-2-methylamino-4-(3-pyridylmethyl) benzothiazole; [ C]E3040, [2- 14 C]6-hydroxy-5,7-dimethyl-2-methylamino-4-(3-pyridylmethyl) benzothiazole dihydrochloride; SD rats, Sprague-Dawley rats; DBSP, dibromosulfophthalein; HEPES, N-2-hydroxyethylpiperazine-NЈ-2-ethanesulfonic acid; MID method, multiple indicator dilution method; HPLC, high-performance liquid chromatography; BSA, bovine serum albumin; TLC, thin-layer chromatography; AUC ϱ , the area under the plasma concentration-time profiles from zero to infinity; CL bile , the biliary excretion clearance; CL renal , the urinary excretion clearance; CL u,renal , the unbound urinary excretion clearance; X bile , the amount excreted into the bile; X urine , the amount excreted into the urine; CL tot , the total body clearance; PS inf , the influx clearance; PS u,inf , the unbound influx clearance; K inf , the influx rate constant; K eff , the efflux rate constant; K seq , the sequestration rate constant; K m , Michaelis constant; V max , maximal uptake rate; P dif , the nonspecific uptake clearance; LUR, the first-pass liver uptake ratio; UWL, the unstirred water layer; PCMBS, p-chloromercuriphenylsulfonic acid; DIDS, 4,4Ј-diisothiocyanatostilbene-2,2Ј-disulfonic acid; FCCP, carbonyl cyanide-p-(trifluoromethoxy)-phenylhydrazone; C/M, cell-to-medium concentration