Novel risk assessment of reactive metabolites from discovery to clinical stage.

This study was aimed to predict drug-induced liver injury caused by reactive metabolites. Reactive metabolites covalently bind to proteins and could result in severe outcomes in patients. However, the relation between the extent of covalent binding and clinical hepatotoxicity is still unclear. From a perspective of body burden (human in vivo exposure to reactive metabolites), we developed a risk assessment method in which reactive metabolite burden (RM burden), an index that could reflect the body burden associated with reactive metabolite exposure, is calculated using the extent of covalent binding, clinical dose, and human in vivo clearance. The relationship between RM burden and hepatotoxicity in humans was then investigated. The results indicated that this RM burden assessment exhibited good predictability for sensitivity and specificity, and drugs with over 10 mg/day RM burden have high-risk for hepatotoxicity. Furthermore, a quantitative trapping assay using radiolabeled trapping agents ([35S]cysteine and [14C]KCN) was also developed, to detect reactive metabolite formation in the early drug discovery stage. RM burden calculated using this assay showed as good predictability as RM burden calculated using conventional time- and cost-consuming covalent binding assays. These results indicated that the combination of RM burden and our trapping assay would be a good risk assessment method for reactive metabolites from the drug discovery stage.

The cost and risk of using sodium nitroprusside as a NO donor in chlorophyll fluorescence experiments.

Sodium nitroprusside (SNP) is a widely used nitric oxide (NO) donor chemical, although it has been reported to release cyanide as well as NO during its photolysis. The aim of this work was to examine this potential side effect of SNP. Chlorophyll fluorescence experiments with pea leaves showed that SNP modifies photosynthetic electron transport. The SNP-induced changes were only partially restored in the presence of a NO-specific scavenger. Moreover, a stoichiometric KCN treatment mimicked the outcome caused by the joint application of the NO donor and NO scavenger. These results confirm the cyanide release of SNP and show that both of its photolytic products reduce the photochemical activity of photosystem II in vivo.

An experimental assessment of cyanide challenge dose-response, time-course and recovery of indicative toxicity parameters.

1. Several sub-lethal doses of cyanide were assayed with the aim of obtaining significant differences in the parameters studied. A dose of 4 mg/kg s.c. was selected. 2. Present studies were carried out to determine the time dependence of the effects produced by s.c. administration of a single dose of potassium cyanide as well as the recovery time of some of the toxicity indicative parameters. 3. It was found that cyanide effects continued for at least 3 days; after the parameters had recovered normal values.