A survey of the reactivity of in vitro diagnostic bilirubin reagents developed in Japan using artificially prepared bilirubin materials: A comparison of synthetic delta, unconjugated, and taurine-conjugated bilirubin.

BACKGROUND: In vitro diagnostic bilirubin reagents based on oxidation with bilirubin oxidase or vanadic acid for total and direct-reacting bilirubin are widely used in Japan; however, their reactivity to unconjugated and conjugated bilirubin and delta bilirubin has not been completely disclosed by manufacturers. We used artificially prepared bilirubin materials to investigate the reactivity with four in vitro diagnostic bilirubin reagents. METHODS: Porcine unconjugated bilirubin solution, chemically synthesized ditaurobilirubin solution, and chemically synthesized delta bilirubin solution were used as surrogates of naturally occurring unconjugated bilirubin, conjugated bilirubin, and delta bilirubin, respectively. The total bilirubin and direct-reacting bilirubin concentrations were measured by three bilirubin oxidase methods and one vanadic acid method, and the observed concentrations were compared with those obtained by the diazo-based reference measurement procedure. RESULTS: The unconjugated bilirubin and delta bilirubin concentrations were similar when any of the four in vitro diagnostic bilirubin reagents were used during total bilirubin measurement. This was consistent with reference measurement procedure and exhibited a converged inter-method variation. Compared with reference measurement procedure, significantly low ditaurobilirubin concentrations were observed by the in vitro diagnostic bilirubin reagents despite the converged inter-method variation. In delta bilirubin measurement, some reagents reacted doubtfully with unconjugated bilirubin, while showed lower ditaurobilirubin concentrations than its corresponding total bilirubin concentration. Reactivity with delta bilirubin was different for each method including reference measurement procedure. Some reagents were developed to react less with delta bilirubin and others to strongly react with delta bilirubin. CONCLUSIONS: We revealed the reactivity of IVD-TB and IVD-DB reagents to artificially prepared bilirubin materials, and their consistency with reference measurement procedure. The delta bilirubin data results vary depending on the reagents used.

CYP3A4*16 and CYP3A4*18 alleles found in East Asians exhibit differential catalytic activities for seven CYP3A4 substrate drugs.

CYP3A4, the major form of cytochrome P450 (P450) expressed in the adult human liver, is involved in the metabolism of approximately 50% of commonly prescribed drugs. Several genetic polymorphisms in CYP3A4 are known to affect its catalytic activity and to contribute in part to interindividual differences in the pharmacokinetics and pharmacodynamics of CYP3A4 substrate drugs. In this study, catalytic activities of the two alleles found in East Asians, CYP3A4*16 (T185S) and CYP3A4*18 (L293P), were assessed using the following seven substrates: midazolam, carbamazepine, atorvastatin, paclitaxel, docetaxel, irinotecan, and terfenadine. The holoprotein levels of CYP3A4.16 and CYP3A4.18 were significantly higher and lower, respectively, than that of CYP3A4.1 when expressed in Sf21 insect cell microsomes together with human NADPH-P450 reductase. CYP3A4.16 exhibited intrinsic clearances (V(max)/K(m)) that were lowered considerably (by 84-60%) for metabolism of midazolam, carbamazepine, atorvastatin, paclitaxel, and irinotecan compared with CYP3A4.1 due to increased K(m) with or without decreased V(max) values, whereas no apparent decrease in intrinsic clearance was observed for docetaxel. On the other hand, K(m) values for CYP3A4.18 were comparable to those for CYP3A4.1 for all substrates except terfenadine; but V(max) values were lower for midazolam, paclitaxel, docetaxel, and irinotecan, resulting in partially reduced intrinsic clearance values (by 34-52%). These results demonstrated that the impacts of both alleles on CYP3A4 catalytic activities depend on the substrates used. Thus, to evaluate the influences of both alleles on the pharmacokinetics of CYP3A4-metabolized drugs and their drug-drug interactions, substrate drug-dependent characteristics should be considered for each drug.

2-Amino-6-arylthio-9-[2-(phosphonomethoxy)ethyl]purine bis(2,2,2-trifluoroethyl) esters as novel HBV-specific antiviral reagents.

Novel 2-amino-6-arylthio-9-[2-(phosphonomethoxy)ethyl]purine bis(2,2,2-trifluoroethyl) esters were synthesized and evaluated for antihepatitis B virus (HBV) activity in vitro using HB611, HuH-6 cell line, stably transfected with the HBV genome. Among the compounds synthesized, 2-amino-6-phenylthio-9-[2-(phosphonomethoxy)ethyl]purine bis(2,2,2-trifluoroethyl) ester (8), 2-amino-6-(4-methoxyphenylthio)-9-[2-(phosphonomethoxy)ethyl]purine bis(2,2,2-trifluoroethyl) ester (16), 2-amino-6-(3-methoxyphenylthio)-9-[2-(phosphonomethoxy)ethyl]purine bis(2,2,2-trifluoroethyl) ester (17), and 2-amino-6-(2-methoxyphenylthio)-9-[2-(phosphonomethoxy)ethyl]purine bis(2,2,2-trifluoroethyl) ester (18) showed considerably high anti-HBV activity, as represented by IC(50) values of 0.05, 0.03, 0.04, and 0.08 microM, respectively, and exhibited low cytotoxicity, as represented by CC(50) values of more than 1000 microM. It was suggested that these compounds did not have anti-HIV activity, and compound 8 showed only weak anti-HSV-1 activity. An antiviral agent, 9-[2-(phosphonomethoxy)ethyl]adenine (PMEA), which was used as a control in the present study, showed moderate anti-HBV activity, as represented by an IC(50) value of 0.2 microM. Furthermore, compound 16 was administered orally to mice at a dose of 100 mg/kg in order to examine its gastrointestinal absorbability. Consequently, the main active metabolite was observed in mouse plasma, with especially high concentrations in the liver.