Chapter one - The therapeutic role of microbial metabolites in human health and diseases

Abstract

Microorganisms were known to be the first life on earth, marking their existence as early as 3.5 billion years ago. Microorganisms are the basic foundation of the biosphere. The gut microbiota and the associated metabolites play an inexorable role in human health and disease. The microbial metabolites are of two forms, one is primary metabolites like nucleotides, amino acids, and fermented end products and secondary metabolites are the organic compounds formed at the end of stationary phase. The primary metabolites exert their functional effects on the host through the integration of receptor-mediated metabolite signaling and activation of host intracellular metabolic pathways, whereas the secondary metabolite has no role in the functioning or development of humans. In a healthy individual, beneficial microbiota population is high, when this homeostasis gets altered due to stress, unhealthy food habit, antibiotics, pollution, drugs, infections, or xenobiotics, it may lead to dysbiosis which results in the development of various disorders such as atherosclerosis, diabetes, metabolic syndrome, inflammatory bowel disease, neurological disorder, and colorectal cancer. Microbial dysbiosis leads to alteration in the levels of various metabolites like short-chain fatty acids, bile acids, branched-chain amino acids, trimethylamine N-oxide, phenyl acetyl glutamine, and increase in proinflammatory bacteria. This proinflammatory bacterium carries immunoreactive lipopolysaccharide which can destroy the tight junctions between the host intestinal epithelial cells and forms leaky gut which induces inflammation. Besides their impact on the development of disease, there are some of the microbial metabolites that have therapeutic significance too. Recent researches have proved the therapeutic efficacy of various metabolites in preventing inflammation, apoptosis, hyperresponsiveness of platelets, development of cancerous cell, and regulation of glucose metabolism.