Association between ambient particulate matter exposure and mitochondrial DNA copy number: A systematic review and meta-analysis

Background: Ambient particulate matter (PM) has been recognized as inducing oxidative stress, which could contribute to mitochondrial damage and dysfunction. However, studies investigating the association between ambient PM and mitochondria, particularly mitochondrial DNA copy number (mtDNA-CN), have yielded inconsistent results. Methods: We conducted comprehensive literature searches to identify observational studies published before July 17, 2023, examining the association between ambient PM exposure and mtDNA-CN. Meta-analysis using random effects model was employed to calculate the pooled effect estimates for general individual exposures, as well as for prenatal exposure with specific trimester. Additionally, the quality and level of evidence for each exposureoutcome pair was evaluated. Results: A total of 10 studies were included in the systematic review and meta-analysis. The results indicated that general individual exposure to PM 2.5 ( beta = -0.084, 95 % CI: -0.521, 0.353; I 2 = 93 %) and PM 10 ( beta = 0.035, 95 % CI: -0.129, 0.199; I 2 = 95 %) did not significantly affect mtDNA-CN. Prenatal exposure to PM 2.5 ( beta = 0.023, 95 % CI: -0.087, 0.133; I 2 = 0 %) and PM 10 ( beta = 0.006, 95 % CI: -0.135; 0.147; I 2 = 51 %) were also not significantly associated with mtDNA-CN in offspring. The level of evidence for each tested exposure -outcome pair was assessed as "inadequate." Conclusions: The findings of this systematic review and meta -analysis indicate that there is an "inadequate" strength of evidence for the association between general individual or prenatal exposure to ambient PM and mtDNA-CN. Future research necessitates studies with more rigorous design, enhanced control of confounding factors, and improved measures of exposure to substantiate our findings.