Enzymatic reduction of sulphoxide-containing drugs by mammalian tissues and the intestinal microflora

Lee, Shing Cheung (1991) Enzymatic reduction of sulphoxide-containing drugs by mammalian tissues and the intestinal microflora. University of Southampton, Doctoral Thesis.

Abstract

Reduction of the sulphoxide group of drugs has been studied in the tissues of rats and rabbits and the intestinal microflora using four substrates.

In vitro studies showd that the rcductase(s) responsible for the reduction of sulindac was widely distributed in rat tissues, with the highest activities in liver, kidneys and caecum contents. Under anaerobic conditions, the rate of reduction of sulindac by rat liver cytosol was higher than by the microsomal fraction. Sulindac reduction by rat liver cytosol was increased by dithiothreitol and acetaldehyde, indicating that both the thioredoxin system (NADPH-thioredoxin reductasc-thioredoxin) and aldehyde oxidase (a molybdenum hydroxylase) arc present. The thioredoxin system was equally active under aerobic and anaerobic conditions, activity of aldehyde oxidase was greater under anaerobic conditions. The basal reducing activity of the cytosol was completely inhibited by preincubation with menadionc and hydralazine, suggesting that the aldehyde oxidase system may be the dominant enzyme system for sulindac reduction under anaerobic conditions. Both enzyme systems were involved in sulindac reduction by rabbit liver under anaerobic conditions. The reducing activities towards sulphinpyra-zone and diphenyl sulphoxide (DPSO) were low with rat or rabbit liver cytosol and not altered by addition of dithiothreitol. Under anaerobic conditions, acetaldehyde increased the reduction of sulphinpyrazone by rabbit liver cytosol and the reduction of DPSO by rat liver cytosol.

Cytosol from both rat and rabbit kidneys reduced sulindac but not sulphinpyrazone or DPSO. The reduction of sulindac was increased by dithiothreitol but not acetaldehyde, suggesting that the thioredoxin system but not aldehyde oxidase is important in renal tissues.

Extensive reduction was observed when sulindac was incubated with pure cultures of 23 aerobes isolated from human faeces. In Escherichia coli BM1023, the reductases for sulindac were shown to reside mainly in the cytosol. Removal of thioredoxin from cytosolic fractions by gel filtration chromatography resulted in loss of NADPH dependent reducing activity; activity was restored by addition of pure E.coli thioredoxin. Polyclonal antibodies raised against the active site sequence of thioredoxin inhibited the cytosolic reduction of sulindac with NADPH. Partial purification of the enzymes and incubation with four sulphoxide substrates revealed that multiple enzyme systems were present in E.coli', at least two of which are linked to the thioredoxin system.

This record has no associated files available for download.

Contributors

Download statistics