Study On Phase Ⅱ Metabolites Of Caffeic Acid On Rats

Caffeic acid is a well-known phenolic acid present in a large variety of medicinal plants including Common Thistle (Herba Cirsii Setosi), Japanese Honeysuckle Flower Bud (Flos Lonicerae), Eucommia Bark (Cortex Eucommiae), Common Origanum Herb (Herba Origani Vulgaris), Capillary Wormwood Herb (Herba Artemisiae Capillaris) and Mongolian Dandelion Herb (Herba Taraxaci Mongolici), etc. Its chemical structure is 3-(3,4-Dihydroxyphenyl)-2-propenioic acid. Recent pharmacological studies show that caffeic acid has various bioactivities such as antihypertensive activity, hypoglycemic effect, antiviral and antioxidant qualities, etc. The biological properties of caffeic acid depend on it absorption and metabolism in vivo. However, metabolism of caffeic acid is less studied at home and abroad and only a few studies focus on pharmacokinetics of caffeic acid. In order to elucidate the metabolic information and kinetic disposition of caffeic acid and to provide a basis for its effective material base and development, we further investigated the metabolites of caffeic acid on rats after oral administration.We first determined the phaseⅡmetabolites of caffeic acid in rats urine and their blood samples after oral administration of caffeic acid at a dosage of 100 mg·kg-1 and proposed their structure according to their MS2 spectrum. A total of four main phaseⅡmetabolites were determined in blood samples including two glucuronide conjugates of caffeic acid and two sulfate conjugates of caffeic acid and a total of eight main phaseⅡmetabolites of caffeic acid were determined in rats urine including two methylated metabolites of caffeic acid, two glucuronide conjugates of caffeic acid, two sulfate conjugates of caffeic acid, a glucuronide conjugate of ferulic acid and a sulfate conjugate of ferulic acid. Then, we collected the rats urine after oral administration of caffeic acid and isolated the phaseⅡmetabolites of caffeic acid by macroporous resin, ODS open column, Sephadex LH-20 stepwisely and finally purified by preparative HPLC. A total of six metabolites of caffeic acid were isolated from rat urine. On the basis of spectroscopic analysis including 1H-NMR,13C-NMR, HMBC, HSQC, IR, MS spectra, five phaseⅡmetabolites were characterized as caffeic acid-3-O-β-D-glucuronide, caffeic acid-4-O-β-D-glucuronide, caffeic acid-3-O-sulfate, caffeic acid-4-O-sulfate and ferulic acid. In our study, five phaseⅡmetabolites of caffeic acid above were first obtained from rats urine and their structures were identified on the basis of spectroscopic analysis.In this study, we have systematically made a research on phaseⅡmetabolites of caffeic acid. It is confirmed that caffeic acid is extensively metabolized on rats and caffeic acid glucuronide conjugates are the main phaseⅡmetabolites on rats. Our work on isolation of phaseⅡmetabolites of caffeic acid provides control substance for future qualitative and quantitative research of caffeic acid in vivo and academic evidence for elucidating the metabolic passway of caffeic acid and other phenolic acids.