Effects of age, species difference, antibiotics and toxicants on intestinal enzyme activity and genotoxicity

Abstract

Altered intestinal enzyme activity significantly affects the biotransformation and toxicity of many xenobiotics. This article summarizes research, supported by the U.S. Air Force Bioenvironmental Hazards Research Program, that employs a novel gas‐liquid chromatographic assay to investigate the effects of age, species difference, antibiotics, and environmental chemicals on enzyme activity in various regions of the intestinal tract. Significant research findings include the following: (a) age‐dependent alterations in enzyme activity in the gastrointestinal (GI) tract of the developing animal that suggest a changing susceptibility to toxicants during this period; (b) discovery of previously unreported mucosal enzymes in the small intestine that are present in germ‐free rats and are not susceptible to antibiotics; (c) markedly greater intestinal nitroreductase activity and significantly higher bioactivation of the procarcinogen 2,6‐dinitrotoluene (DNT) in CD‐1 mice than in Fischer 344 rats; (d) significantly altered intestinal enzyme activity in rats pretreated with lindane, pentachlorophenol, 2,4,5‐trichlorophenoxyacetic acid (2,4,5‐T), or Aroclor 1254; (e) potentiated DNT genotoxicity by Aroclor 1254 and pentachlorophenol pretreatment; and (f) a transient antagonism of DNT genotoxicity by 2,4,5‐T pretreatment. Enzyme activity in the small intestine may have greater toxicological importance than previously thought in the biotransformation of environmental chemicals and as an indicator of change in the microbial flora.

Possible errors in assay for beta-glycosidase activity

“…Because heat inactivation is not an instantaneous process, there may be some p-nitrophenol reduction to p-aminophenol prior to total heat inactivation. To determine the influence of tissue and microbial nitroreductase enzymes on the analysis of BGr, BGl, and BGa activities, cecal homogenates were incubated anaerobically with the re-spective glycosides of p-nitrophenol in the presence and absence of DCNB, a previously employed substrate, for the determination of nitroreductase activity (3,4). In the absence of DCNB, there was about a twofold decline in the recovery of p-nitrophenol and thus the estimated activity of all three enzymes ( Fig.…”