Gut Microbiota in Lung Cancer: Where Do We Stand?

Abstract

The gut microbiota (GM) is considered to constitute a powerful “organ” capable of influencing the majority of the metabolic, nutritional, physiological, and immunological processes of the human body. To date, five microbial-mediated mechanisms have been revealed that either endorse or inhibit tumorigenesis. Although the gastrointestinal and respiratory tracts are distant physically, they have common embryonic origin and similarity in structure. The lung microbiota is far less understood, and it is suggested that the crosslink between the human microbiome and lung cancer is a complex, multifactorial relationship. Several pathways linking their respective microbiota have reinforced the existence of a gut–lung axis (GLA). Regarding implications of specific GM in lung cancer therapy, a few studies showed that the GM considerably affects immune checkpoint inhibitor (ICI) therapy by altering the differentiation of regulatory T cells and thus resulting in changes in immunomodulation mechanisms, as discovered by assessing drug metabolism directly and by assessing the host immune modulation response. Additionally, the GM may increase the efficacy of chemotherapeutic treatment in lung cancer. The mechanism underlying the role of the GLA in the pathogenesis and progression of lung cancer and its capability for diagnosis, manipulation, and treatment need to be further explored.

Combined Microbiome and Metabolome Analysis Reveals a Novel Interplay Between Intestinal Flora and Serum Metabolites in Lung Cancer

“…Previous studies have shown that the changes of intestinal flora in patients with lung cancer are often related to Firmicutes , Bacteroides , and Proteobacteria ( Zhang et al., 2018 ; Liu et al., 2019 ; Zhuang et al., 2019 ; Zheng et al., 2020 ; Georgiou et al., 2021 ). When using the Kruskal–Wallis algorithm to further identify microbes with different abundances, it was found that the abundance of Firmicutes decreased and Proteobacteria increased in the lung cancer group.…”

Role of the Microbiota in Lung Cancer: Insights on Prevention and Treatment

“…Furthermore, when the intestinal microbiota and its products are translocated through the epithelial barrier and then into the blood flow, they stimulate a toll-like receptor (TLR) response and the subsequent expansion of T lymphocytes into distant tissues. The translocation of bacteria from the gastrointestinal tract can enhance tumor-specific responses through TLRs or the induction of memory responses, as observed for the relationships between Enterococcus hirae and small-cell lung cancer [ 66 , 67 ].…”

“…In addition, anaerobic respiration is observed to increase in lung cancer due to the elective anaerobic qualities of the bacteria that preferentially colonize tumors. They grow in number along with cancer progression, further promoting and stabilizing the hypoxic and proinflammatory tumor environment [ 66 ]. Jin and collaborators showed that lung tumor burden was highly correlated with local bacterial abundance in the airways, but not in the intestinal tract, and deduced a relatively more significant contribution of the local microbiota in lung cancer development.…”

The gut-lung axis: Gut microbiota changes associated with pulmonary fibrosis in mouse models induced by bleomycin

“…A dynamic balance exists between the host and the GM, preventing the occurrence of disease; if this balance is disturbed, many diseases will manifest (Espirito Santo et al, 2021). Research shows that the influence of the GM on its host includes immunological functions, physiological processes, material metabolism, nutritional transformation, inflammatory reactions, and cell aging (Georgiou et al, 2021). The GM has a close relationship with Parkinson's, diabetes mellitus, Alzheimer's, hypertension, non-alcoholic fatty liver disease, atherosclerosis, obesity, chronic lung disease, among others (Chen et al, 2021;Marsland et al, 2015).…”