Factors affecting arsenic methylation in arsenic-exposed humans: a systematic review and Meta-analysis

Abstract

Objective To explore the regulation and effect factors of arsenic expose and arsenic methylation level, then to provide a reference for study the function of arsenic metabolism in a arsenic poisoning process. Methods A meta-analysis was performed by two researchers. Twenty-five papers satisfying our priori eligibility criteria were included by searching Cochrane library, Pubmed, Springer, Embase and China National Knowledge Infrastructure. Based on the results of heterogeneity, a random or fixed effects model was chosen for the meta-analysis. Results The results showed that the following arsenic metabolites increased (all P < 0.01) following arsenic exposure: inorganic arsenic [iAs; standardized mean difference (SMD): 1.07; 95% confidence interval (CI): 0.61-1.53)], monomethyl arsenic (MMA; SMD: 1.10; 95% CI: 0.81-1.40), dimethyl arsenic (DMA; SMD: 2.50; 95% CI: 1.50-3.69), and total arsenic (TAs, SMD: 3.10; 95% CI: 2.13-4.07). Additionally, the percentages of iAs (iAs%; SMD: 1.00; 95% CI: 0.60-1.40) and MMA (MMA%; SMD: 0.49; 95% CI: 0.21-0.77) also increased, while the percentage of DMA (DMA%; SMD:-0.55; 95% CI:-0.80--0.31) decreased (P < 0.01). The primary methylation index (PMI; SMD:-0.57; 95% CI:-0.94--0.20), and secondary methylation index (SMI; SMD:-0.27; 95% CI:-0.46--0.09) decreased (all P < 0.01). Compared to female, male had higher MMA% (SMD: 0.44; 95% CI: 0.35-0.52), lower DMA% (SMD:-0.33; 95% CI:-0.38--0.28) and SMI (SMD:-0.36; 95% CI:-0.53--0.19). The smoker had higher MMA% (SMD: 0.22; 95% CI: 0.07-0.37) and lower DMA% (SMD:-0.16; 95% CI:-0.26--0.05). The drinker had higher MMA% (SMD: 0.17; 95% CI: 0.07-0.27) and lower DMA% (SMD:-0.24; 95% CI:-0.39--0.10). The older people had higher MMA% (SMD:-0.23; 95% CI:-0.40--0.06). In addition, the body mass index may influence the percentages of MMA (SMD:-0.18; 95% CI:-0.31--0.04, P < 0.01). Conclusion Arsenic exposure, smoking, drinking, and older age can reduce the capacity of arsenic methylation. Arsenic methylation is more efficient in women than in men. Key words: Arsenic; Methylation; Meta-analysis; Humans