Molecular Microbiology Research 2024, Vol.14, No.1, 10-19 http://microbescipublisher.com/index.php/mmr 11 knowledge and technologies, new strategies and methods can be provided for the prevention and treatment of chronic diseases. Furthermore, this endeavor seeks to advance the application and development of microbiomics in the medical field, contributing to the realization of personalized medicine. 1 Association Between Microbiota and Chronic Diseases 1.1 Association between microbiota and various chronic diseases Research on the association between microbiota and various chronic diseases reveals their intricate yet crucial connections. These connections are manifested not only in the direct impact of microbiota on the occurrence and development of chronic diseases but also in the interactions between microbiota and various systems within the host. Taking cardiovascular disease as an example, studies have found a close correlation between alterations in the gut microbiota and the risk of cardiovascular disease. Certain gut bacteria can produce metabolites such as trimethylamine N-oxide (TMAO), which promote vascular inflammation and atherosclerosis, while the intake of probiotics may reduce the risk of cardiovascular disease by modulating the balance of gut microbiota (Cingi et al., 2019). In the field of diabetes, research on microbiota has also made remarkable progress. Increasing evidence suggests that dysbiosis of the gut microbiota may lead to insulin resistance and abnormal blood sugar regulation, thereby promoting the development of diabetes. Additionally, some studies have found that alterations in oral microbiota may also be associated with the risk of diabetes. Obesity, as a global health issue, is also closely associated with microbiota. Studies have shown significant differences in the diversity and composition of gut microbiota between obese and healthy individuals, which may be related to metabolic abnormalities and inflammatory responses associated with obesity (Pothmann et al., 2019). Autoimmune diseases are a complex category of diseases often associated with abnormal attacks by the immune system on self-tissues. Research on microbiota provides a new perspective for understanding the pathogenesis of autoimmune diseases. For example, dysbiosis of the gut microbiota may lead to abnormal immune responses to intestinal cells, thereby triggering autoimmune diseases such as inflammatory bowel disease and multiple sclerosis (Chiu et al., 2019). 1.2 Microbiome composition, function, and their metabolic products related to chronic diseases The microbiome, as a vast ecosystem, is characterized by the types and quantities of its microbial species and their relative abundances, which together determine its functionality. These microbes produce various substances through metabolism, including beneficial and potentially harmful compounds. These substances interact with host cells, thereby affecting host health. Studies on microbial communities and their interactions with hosts show that these microbes perform biochemical activities that influence carcinogenesis, tumor progression, and immune therapy responses (Figure 1). During the development of chronic diseases, the composition of the microbiome often changes, with increases in harmful microbes or decreases in beneficial ones potentially triggering or exacerbating disease progression. For example, in the intestines of diabetic patients, a reduction in certain acid-producing bacteria and an increase in bacteria associated with inflammation and insulin resistance are often observed. These changes can lead to metabolic abnormalities in the host, further aggravating the symptoms of diabetes (Figure 1). The function of the microbiome is also directly related to the development of chronic diseases. The microbiome contributes to the maintenance of internal environmental stability in the host by participating in nutrient metabolism, synthesizing vitamins, and regulating immune responses. Impairment of microbiome functions can lead to metabolic imbalances and immune disorders in the host, thus increasing the risk of chronic diseases (Wise et al., 2018).
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