Association between Levels of Trimethylamine N-Oxide and Cancer: A Systematic Review and Meta-Analysis.

Cancer is the second leading cause of death in the world. Reports on the effect of Trimethylamine-N-oxide (TAMO), a small amine oxide generated by gut microbial metabolism of choline, betaine, and carnitine, on cancer are inconsistent. Therefore, this systematic review and meta-analysis summarize the effect of TAMO on cancer incidence. A systematic search was conducted in PubMed, Scopus, Web of Science, and Embase. Data were pooled using the random-effects method and were expressed as weighted mean difference (WMD) and 95% confidence intervals (CI). The pooled results of 16 studies, including 5930 participants, showed that the association between TMAO levels and cancer incidence is insignificant (Odds Ratio: 0.97, 95% CI: (0.64, 1.46), P-value = 0.871). Subgroup analysis showed that urinary TMAO levels were negatively associated with cancer incidence; in contrast, a direct and positive association was observed between serum TMAO levels and cancer incidence. However, "gender" and the "TMAO measuring method" were the potential sources of discrepancies. Meta-regression analysis did not reveal any significant association between duration of studies, age, female ratio, subjects-control, and subjects-case. The present study demonstrates that serum TAMO levels were insignificantly associated with cancer incidence.

Type 2 Diabetes Mellitus and Alzheimer's Disease: A Review of the Potential Links.

Diabetes mellitus and Alzheimer's disease are considered the most prevalent diseases in older ages worldwide. The main pathology of Alzheimer's disease is highly related with accumulation of misfolded proteins that lead to neuronal dysfunction in the brain. On the other hand, diabetes mellitus is associated with alteration of insulin signaling, which could cause the reduction of glucose uptake, metabolic prohibition of energy consuming cells, as well as suppression of glucose to fat conversion in the liver. In spite of having seemingly different pathological features, both diseases share common underlying biological mechanisms. Besides, the epidemiological and environmental links between these two diseases should not be overlooked. In this study, we aim to review shared pathological mechanisms of Alzheimer's disease and diabetes mellitus, including impaired glucose metabolism, increased Amyloid-Beta (Aß) production, impaired lipid metabolism, mitochondrial dysfunction, increased inflammation and elevated oxidative stress. Furthermore, we discuss epidemiological association between these two diseases and also review animal investigations, which have evaluated the potential links between the two diseases.