Is inflammageing influenced by the microbiota in the aged gut? A systematic review

Ageing is characterized by a low-grade chronic inflammation marked by elevated circulating levels of inflammatory mediators. This chronic inflammation occurring in the absence of obvious infection has been coined as inflammageing and represents a risk factor for morbidity and mortality in the geriatric population. Also, with ageing, important perturbations in the gut microbiota have been underlined and a growing body of literature has implicated age-related gut dysbiosis as contributing to a global inflammatory state in the elderly. Notwithstanding, very little attention has been given to how gut microbiota impact inflammageing. Here, we investigate the available evidence regarding the association between inflammageing and gut microbiota during ageing. PubMed, Web of Science and Scopus were systematically screened, and seven relevant articles in animals or humans were retrieved. The animal studies reported that Parabacteroides, Mucispirillum, Clostridium and Sarcina positively associate with the pro-inflammatory MCP-1 while Akkermansia, Oscillospira, Blautia and Lactobacillus negatively correlate with MCP-1. Furthermore, "aged"-type microbiota were associated with increased levels of IL6, IL-10, Th1, Th2, Treg, TNF-alpha, TGF-beta, p16, SAMHD1, Eotaxin, and RANTES; activation of TLR2, NF-kappa B and mTOR; and with decreased levels of cyclin E and CDK2. On the other hand, the study on humans demonstrated that bacteria of the phylum Proteobacteria exhibited a positive correlation with IL-6 and IL-8, while Ruminococcus lactaris et rel. portrayed a negative correlation with IL-8. We conclude that changes in "aged"-type gut microbiota are associated with inflammageing.