A study of the metabolism and metabolomics of polyphenols using isolated rat hepatocytes and liquid chromatography-high resolution mass spectrometry

• Main Author: Omar, Khaled M. K.
• Published: University of Strathclyde 2017
• Subjects: 610
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.750617

Dietary phenolic compounds have been proposed to have significant benefits for health through their anti-oxidant properties. Their metabolism has been well studied; however, it would be advantageous to have knowledge of the metabolites which can be formed from these compounds in order to monitor their presence in physiological fluids such as plasma and urine. Isolated rat hepatocytes contain a full range of enzymes for carrying out phase I, phase II and phase III metabolism of xenobiotics. In this work, isolated rat hepatocytes were used to transform the phenyl propionates ferulic acid and p-coumaric acid and the flavonoids quercetin and hesperidin. The products formed by enzymatic transformation were characterised by liquid chromatography in combination with high resolution mass spectrometry. This was followed by extraction of the data with Sieve software and identification of the metabolites based on their elemental composition. MS2 and MS3 experiments were used to further characterise the metabolites. The phenyl propanoid compounds were mainly sulfated but other transformations such as glucuronidation and glycine conjugation occurred. In addition, the two phenyl propanoid compounds also formed conjugates with glutathione which added across the double bond in the side chain. Quercetin underwent both metabolism and complex degradation in the hepatocyte incubation medium leading to a very complex mixture of metabolites from the intact drug and its chemical degradants. Hesperidin, in contrast to quercetin, underwent a rather simple metabolism being mainly converted to its sulfate. In addition, hydrophilic interaction chromatography in combination with high resolution mass spectrometry was used to study the effects of the phenolic compounds on the hepatocyte metabolome. Quercetin had a strong effect on the metabolome as it depleted the co-factors required for sulfation and glucuronidation. It also had a strong anti-oxidant effect and it appeared to reduce autophagy by the hepatocytes. In conclusion the most interesting compound in the set of compounds studied is quercetin which presents scope for further study.