Analysis of the Metabolic Pathway of Bosentan and of the Cytotoxicity of Bosentan Metabolites Based on a Quantitative Modeling of Metabolism and Transport in Sandwich-Cultured Human Hepatocytes.

To quantitatively understand the events in the human liver, we modeled a hepatic disposition of bosentan and its three known metabolites (Ro 48-5033, Ro 47-8634, and Ro 64-1056) in sandwich-cultured human hepatocytes based on the known metabolic pathway. In addition, the hepatotoxicity of Ro 47-8634 and Ro 64-1056 was investigated because bosentan is well known as a hepatotoxic drug. A model illustrating the hepatic disposition of bosentan and its three metabolites suggested the presence of a novel metabolic pathway(s) from the three metabolites. By performing in vitro metabolism studies on human liver microsomes, a novel metabolite (M4) was identified in Ro 47-8634 metabolism, and its structure was determined. Moreover, by incorporating the metabolic pathway of Ro 47-8634 to M4 into the model, the hepatic disposition of bosentan and its three metabolites was successfully estimated. In hepatocyte toxicity studies, the cell viability of human hepatocytes decreased after exposure to Ro 47-8634, and the observed hepatotoxicity was diminished by pretreatment with tienilic acid (CYP2C9-specific inactivator). Pretreatment with 1-aminobenzotriazole (broad cytochrome P450 inactivator) also tended to maintain the cell viability. Furthermore, Ro 64-1056 showed hepatotoxicity in a concentration-dependent manner. These results suggest that Ro 64-1056 is directly involved in bosentan-induced liver injury partly because CYP2C9 specifically mediates hydroxylation of the t-butyl group of Ro 47-8634. Our findings demonstrate the usefulness of a quantitative modeling of hepatic disposition of drugs and metabolites in sandwich-cultured hepatocytes. In addition, the newly identified metabolic pathway may be an alternative route that can avoid Ro 64-1056-induced liver injury.

Multiday corticosteroids in cancer chemotherapy delay the diagnosis of and antimicrobial administration for febrile neutropenia: a double-center retrospective study.

BACKGROUND: Medical staff should promptly administer antimicrobials to patients with febrile neutropenia (FN) to decrease the mortality related to cancer chemotherapy. Corticosteroids, which are used in cancer chemotherapy, have a fever-suppressive effect. This effect could lead to a blunt fever response and any local signs of infection, especially in patients receiving multiday corticosteroid administration. The aim of this study was to determine whether multiday corticosteroid administration in cancer chemotherapy delays the diagnosis of and antimicrobial treatment for FN. METHODS: We conducted a double-center retrospective study in Japanese patients with FN. The patients were divided into two groups based on the corticosteroid administration method, i.e., whether administration was multiday or not. To evaluate the degree of masking on FN by corticosteroids, we assessed the correlation between body temperature variation and time of antimicrobial administration after the initiation of chemotherapy. Risk factors for delayed antimicrobial administration were identified by multiple logistic regression analysis. RESULTS: Two hundred thirteen patients were analyzed. The median time required to body temperature reaching 37.5 °C and for antimicrobial administration was longer in the multiday group than in the non-multiday group, with 0.64 and 0.60 days (P = 0.002 and P < 0.001), respectively. Multiday corticosteroid use was identified as an independent risk factor for delayed antimicrobial administration (odds ratio = 3.94; 95% confidence interval = 1.80-8.62; P < 0.001). CONCLUSIONS: Multiday corticosteroid administration in cancer chemotherapy delayed the diagnosis of and antimicrobial administration for FN. Furthermore, it was the only risk factor for delayed antimicrobial administration. We could thus provide evidence that the diagnosis of and antimicrobial administration for FN in patients receiving multiday corticosteroid administration should not be based on body temperature variation alone.

Rat Kidney Slices for Evaluation of Apical Membrane Transporters in Proximal Tubular Cells.

Kidney slice has been often used as a tool reflecting basolateral transport in renal tubular epithelial cells. Recently, we reported that several important apical reabsorptive transporters such as Octn1/2, Sglt1/2, and Pept1/2 were functional in mouse kidney slices as well as transporter activities in basolateral side, which have been well accepted. Because rats are often used for preclinical pharmacodynamic and pharmacokinetic studies as well as mice, it is important to confirm applicability of rat kidney slices for evaluation of apically expressed transporters. The present study investigates usefulness of kidney slices from rats for evaluation of apical membrane transporters for efflux (multidrug resistance 1a, mdr1a) as well as influx (Octn1/2, Sglt1/2, Pept1/2). Na+-dependent uptake of ergothioneine (Octn1), carnitine (Octn2), and methyl-α-D-glucopyranoside (Sglt1/2) by rat kidney slices was observed, and the uptake was decreased by selective inhibitors. In addition, uptake of glycyl-sarcosine (Pept1/2) showed H+-dependence and was decreased by selective inhibitor. Furthermore, accumulation of mdr1a substrate azasetron was increased in the presence of zosuquidar, an mdr1a inhibitor, while strain differences existed. In conclusion, rat kidney slices should be useful for evaluation of renal drug disposition regulated by transporters in apical as well as basolateral membranes of rat renal proximal tubule cells.

Risk factors for oxaliplatin-induced vascular pain in patients with colorectal cancer and comparison of the efficacy of preventive methods.

BACKGROUND: Vascular pain is a common adverse drug reaction in colorectal cancer patients receiving peripheral venous administration of oxaliplatin. The aim of this work was to identify risk factors for vascular pain, and to examine whether currently used treatments reduce its incidence. METHODS: We conducted a multicenter retrospective study in Japanese colorectal cancer patients receiving peripheral venous administration of oxaliplatin. The effects of various treatments (administration of analgesics, addition of dexamethasone to the infusion solution for pH adjustment, dilution of the infusion solution, or use of hot gel for warming the injection site) on the incidence of vascular pain were assessed. Risk factors for vascular pain were identified by multiple logistic regression analysis. RESULTS: One hundred and ninety patients who had received an oxaliplatin-containing regimen via a peripheral venous route were analyzed. None of the preventive methods examined significantly reduced the incidence of vascular pain. BMI (BMI < 22), clinical stage (I-III) and oxaliplatin dosage (130 mg/m2 versus dose reduction) were identified as independent risk factors for development of vascular pain. The incidence of oxaliplatin-induced vascular pain was significantly higher in patients who had two or more risk factors. CONCLUSIONS: BMI, clinical stage and oxaliplatin dosage were identified as independent predictive markers for oxaliplatin-induced vascular pain. Existing treatments for vascular pain are not effective in reducing its incidence.

Usefulness of kidney slices for functional analysis of apical reabsorptive transporters.

Kidney plays a key role in the elimination and reabsorption of drugs and nutrients, however in vitro methods to evaluate renal disposition are limited. In the present study, we investigated usefulness of isolated kidney slice, which had been used for transport only at basolateral membrane of tubular epithelial cells, for evaluation of apical membrane transporters. As transporters that are easy to discriminate between apical and basolateral transports, apical membrane specific and sodium-dependent transporters (SGLTs and OCTNs) and pH-dependent transporters (PEPTs) are selected. Uptake of ergothioneine, carnitine and methyl-α-D-glucopyranoside, which are substrates of apical Octn1, Octn2, and Sglt1/2, respectively, by mice kidney slices showed clear Na+ dependence and reduction by selective inhibitors. In addition, sodium dependence of ergothioneine uptake was negligible in the kidney slice from Octn1-gene deficient mice. Moreover, uptake of PepT1/2 substrate glycyl-sarcosine, was higher than that in the presence of glycyl-leucine, a non-specific Pept inhibitor. The K m and IC 50 values for substrates and inhibitors of each transporter were mostly comparable to those obtained in transporter-transfected cells. In conclusion, it was demonstrated that kidney slices are promising tool to study transporters expressed at the apical membranes as well as basolateral membranes of kidney tubular epithelial cells.