Abstract：
The gut-brain axis is a crucial interface between the central nervous system and the gut microbiota. Recent evidence shows that exposure to environmental contaminants, such as heavy metals, can cause dysbiosis in gut microbiota, which may affect the gut-brain communication, impacting aspects of brain function and behavior. This systematic review of the literature aims to evaluate whether deleterious effects on brain function due to heavy metal exposure could be mediated by changes in the gut microbiota profile. Animal studies involving exposure to heavy metals and a comparison with a control group that evaluated neuropsychological outcomes and/or molecular outcomes along with the analysis of microbiota composition were reviewed. The authors independently assessed studies for inclusion, extracted data and assessed risk of bias using the protocol of Systematic Review Center for Laboratory Animal Experimentation (SYRCLE) for preclinical studies. A search in 3 databases yielded 16 eligible studies focused on lead (n = 10), cadmium (n = 1), mercury (n = 3), manganese (n = 1), and combined exposure of lead and manganese (n = 1). The animal species were rats (n = 7), mice (n = 4), zebrafish (n = 3), carp (n = 1) and fruit fly (n = 1). Heavy metals were found to adversely affect cognitive function, behavior, and neuronal morphology. Moreover, heavy metal exposure was associated with changes in the abundance of specific bacterial phyla, such as Firmicutes and Proteobacteria, which play crucial roles in gut health. In some studies, these alterations were correlated with learning and memory impairments and mood disorders. The interplay of heavy metals, gut microbiota, and brain suggests that heavy metals can induce direct brain alterations and indirect effects through the microbiota, contributing to neurotoxicity and the development of neuropsychological disorders. However, the small number of papers under review makes it difficult to draw definitive conclusions. Further research is warranted to unravel the underlying mechanisms and evaluate the translational implications for human health.
摘要：
肠-脑轴是中枢神经系统和肠道微生物群之间的重要界面。最近的证据表明，暴露于环境污染物，如重金属，会导致肠道微生物群的生态失调，这可能会影响肠道-大脑的交流，影响大脑功能和行为的方面。这篇系统的文献综述旨在评估重金属暴露对大脑功能的有害影响是否可以通过肠道微生物群的变化来介导。回顾了涉及暴露于重金属的动物研究以及与对照组的比较，该对照组评估了神经心理学结果和/或分子结果以及微生物群组成的分析。作者独立评估了纳入研究，使用临床前研究系统评价实验动物实验中心（SYRCLE）的方案提取数据并评估偏倚风险。在3个数据库中进行的搜索得出了16项针对铅的合格研究（n=10），镉(n=1),汞（n=3），锰(n=1)，铅和锰的联合暴露(n=1)。动物种类为大鼠（n=7），小鼠（n=4），斑马鱼（n=3），鲤鱼(n=1)和果蝇(n=1)。发现重金属会对认知功能产生不利影响，行为，和神经元形态。此外，重金属暴露与特定细菌门的丰度变化有关，如厚壁菌和变形杆菌，在肠道健康中起着至关重要的作用。在一些研究中,这些改变与学习和记忆障碍以及情绪障碍相关。重金属的相互作用，肠道菌群，和大脑表明重金属可以通过微生物群引起直接的大脑改变和间接影响，有助于神经毒性和神经心理障碍的发展。然而,正在审查的文件数量很少，因此很难得出明确的结论。需要进一步的研究来解开潜在的机制，并评估翻译对人类健康的影响。
