Plant Glycosides are Natural Prodrugs-Role of Human Intestinal Flora

摘要

Characteristics of traditional medicines are the prescription composed of several natural sources,depending on the physical constitution and symptoms of patients,and the oral route of administration to human,no to be injected and not to be medicines to rats and mice.Hundreds of pharmacological and biochemical researches in vitro have been widely performed and reported,using extracts or components of natural medicines and experimental animals,neglecting the three criteria above described of the traditional medicines.All the components from the traditional medicines inevitably contact with microflora in the gastrointestinal tract after oral administration.Some of them are transformed by bacterial enzymes and then adsorbed through intestinal membrane to portal vein and modified or conjugated in the liver excreted through the bile into digestive tract and metabolized again by the intestinal bacterial enzymes and reabsorbed,so called,enteroheptic circulation of the compounds.Especially glycosides of natural origins are water-soluble,being difficult to be absorbed from intestine and staying long periods of time,suggesting that glycosides itself are low in bio availability and pharmacologically inactive.Based on this hypothesis,we have been working for these twenty years on the metabolites of various plant origins by human intestinal microflora,the isolated bacteria or the mixture of identified bacterium from all human origin.In summary,plant components,glycosides,are in general hydrolyzed by human intestinal flora to the corresponding aglycones.We have identified the responsible bacterium capable if hydrolyzing such glycosides (Table1):sennoside (senna and rhubarb),glycyrrhizin (GL) (licorice),barbaloin (aloe),baicailin (scutellariae radix),ginsenoside (panax ginseng).We have also isolated the respective β-glycosidase from each bacterium and elucidated the metabolic pathways of these glycosides.