Maintenance of a balanced human gut microbiota - an emerging healthcare destination for herbal research

Abstract

The human gastrointestinal tract harbors a complex and dynamic population of micro-organisms known as 'gut microbiota'. The gut micro-organisms exert great influence on us during the states of metabolic/immunological homeostasis as well as manifestation of or protection from diseases. Relative composition of gut microbiota is now known to be influenced by the type of diet, geographic locations and nutritional status of the individuals. Gut microbiota most closely interact with the gastrointestinal tract, liver, skin and central nervous system and hence, aid in physiological functions such as digestion and absorption of nutrients, neuro-transmission, fat metabolism, and immune responses. Accordingly, disturbance in the gut microflora architecture normally lead to several health disorders like obesity, diabetes, hypertension, rheumatoid arthritis, inflammatory bowel disease, nervous depression, anxiety, cognitive decline, Parkinson's Disease etc. The metagenomic studies of human gut flora have suggested that the bulk of the microbial community is made up of nine bacteriophyta namely: Firmicutes, Bacteroidetes, Proteobacteria, Actinobacteria, Fusobacteria, Verrucomicrobia, Cyanobacteria and Spirochaetes. Several studies have also indicated a positive association of gut microbes with bidirectional regulation of intestinal and central nervous system (CNS) through neurotransmitter, endocrine, immune and metabolic pathways. An imbalanced gut microbiota has been shown to affect the progression of CNS diseases, including cerebral ischemia, Alzheimer's disease, disseminated sclerosis and hepatic encephalopathy. In addition, gut microbiota imbalance can also increase intestinal permeability that can lead to liver toxicity and several other pathophysiological complications. Intestinal microbiota contributes to diverse mammalian processes including the metabolic function of the drugs, both traditional as well as modern. A large number of herbal medicines have been found to act in association with gut microbiota because majority of herbal drugs are orally administered and invariably come in direct contact with these microbes. Since most herbal preparations are made up of a large number of plant-derived bioactive metabolites, their precise mode of actions on gut flora, body metabolism and disease management/treatment is often not fully explained. Recent developments in the field of gut metagenomics vis-à-vis bioavailability of herbal ingredients and their pharmacodynamics in disease conditions are providing fresh insights to these associations. Today a general consensus is that most traditional herbals treat disease by three primary modes: getting metabolized into more pharmacologically active metabolites by the action of gut microbiota; regulating the gut microbiota balance in terms of relative population of different bacteria particularly the Firmicutes-to-Bacteroidetes ratio (F/B); and by regulating the synthesis of fermentation products of the gut microbes such as acetate, butyrate and propionate etc. The gut micro-flora architecture and its association with herbal medicines is a hot topic of discussion today. In last five years >13000 papers were published on studies related to gut microbiota. This review is an attempt to summarize our current understanding of this subject with sole intention of sensitizing the researchers' community of medicinal and aromatic plant sciences in India to validate and valorize our existing AYUSH prescriptions in the context of gut microbiota influences for enhancing their global acceptance.