Electrochemical Oxidation of Primary Bile Acids: A Tool for Simulating Their Oxidative Metabolism?

Abstract

Bile acids are a subgroup of sterols and important products of cholesterol catabolism in mammalian organisms. Modifications (e.g., oxidation and 7-dehydroxylation) are predominantly exerted by the intestinal microbiota. Bile acids can be found in almost all living organisms, and their concentration and metabolism can be used for the assessment of the pathological and nutritional status of an organism. Electrochemical oxidation is a rapid, relatively inexpensive approach to simulate natural metabolic redox processes in vitro. This technique further allows the identification of oxidative degradation pathways of individual substances, as well as the demonstration of binding studies of generated oxidation products with biologically relevant molecules. When coupling an electrochemical and a high-resolution mass spectrometric system, oxidation products can be generated and identified directly by non-targeted ESI-MS. Here, a method for the generation of oxidation products of the primary bile acids cholic acid and chenodeoxycholic acid was exemplarily developed. Most products and the highest intensities were observed at a pH value of 6. For cholic acid, a high potential of 3 V was necessary, while for chenodeoxycholic acid, a potential of 2.4 V led to a higher number of oxidation products. In a second approach, a binding study with glutathione was performed to simulate phase II metabolism. It was possible to detect signals of free glutathione, free bile acids, and adducts of both reactants. As the resulting mass spectra also showed some new signals of the oxidized bile acid, which could not be observed without glutathione, it can be assumed that glutathione is able to bind reactive oxidation species before reacting with other products.

Keywords

• bile acids
• sterols
• electrochemical oxidation
• EC-MS