Abstract 5466: Butyrate effect on expression of quinone oxidoreductase (NQO1) and cytochrome P450 CYP1A1 enzymes

Abstract

Abstract Butyrate is a small chain fatic acid formed by bacterial fermentation of plant foods in guts. It has been shown to induce Quinone Oxidoreductase (NQO1) enzyme in tumor cell lines, which may contribute to the detoxification of dietary carcinogens with out any effect to the expression of carcinogen activation enzymes, such as cytochrome P450 CPY1A1 and epoxide hydrolase. The risk from chemical carcinogens and environmental toxins is dependent on the metabolic balance between bioactivation and detoxification enzymes. Cancer chemoprevention therefore may be achieved through alterations in the expression of these enzymes. There is substantial evidence that chemoprevention comprises multiple intervention methods to impede, arrest, or reverse carcinogenesis at various stages. Transcriptional regulation of activation and detoxification enzymes competing for the carcinogen substrate is strongly affected by intracellular oxidation reduction potential change. Treatment of cells with butyrate causes a change in intracellular redox potential which results in transcriptional regulation of activation and detoxification enzymes. Indicators of redox potential may include the concentration ratio of glutathione (GSH): glutathione disulfide (GSSG), cysteine (CYH): cystine (CYSS) and other redox couples. Treatment of human liver HepG2 cells with sodium butyrate (5mM, 48-72Hr) results in an oxidation of both GSH: GSSG and CYH: CYSS to approximately the same extent up on calculation based on Nernst equation of concentrations determined by HPLC analysis. The present study shows that both the steady-state redox potential of the cysteine/cystine couple (Eh = -155 mV) and GSH/GSSG couple (Eh = -255 mV) in cells are sufficiently oxidized (>40 mV) up on treatment of cells with butyrate. The GSH oxidation, in response to 5mM butyrate at 48 -72 Hr for HepG2 cells were associated with an approximately 3-4-fold increase in mRNA for NQO1 as measured by quantitative PCR and 40-85 fold increase as a luciferase measure for relative change in a of transcriptional activation of NQO1 as comparing to the control respectively. However, CYP1A1 expression was not significantly different from controls. Changes in redox potential may directly release transcriptional proteins from within the cytoplasm for traslocation to the nucleus or alter their affinity for transcription response elements. These possibilities are under investigation using nuclear extracts of HepG2 and HT29 cells treated to alter intracellular redox potential. Surface-enhanced laser desorption/ionization (SELDI) allows rapid identification and quantitation of changes in transcription proteins in response to intracellular redox potential change. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5466. doi:1538-7445.AM2012-5466