Potential roles of air pollutants on the induction and aggravation of rheumatoid arthritis: From cell to bedside studies

Causal associations of air pollution with rheumatoid arthritis: A transethnic Mendelian randomization study

BACKGROUND

Rheumatoid arthritis is a common rheumatic disease, and its onset is closely related to genetic and environmental factors, however, the relationship between air pollution and RA is still hotly debated. Further investigation of the relationship between air pollution and rheumatoid arthritis is conducive to a comprehensive understanding of the risk factors of the disease, providing certain value for the clinical prevention and treatment of RA.

METHODS

We used a Two-Sample Mendelian Randomization approach, integrating the large-scale public genomewide association study, to assess the genetically predicted causal effect of air pollution (including: PM2.5, PM2.5-10, PM10, nitrogen dioxide, nitrogen oxides) on RA in European and European East Asian populations, respectively. Indicators related to air pollution (2,505 individuals to 423,796 individuals), including European and East Asian populations were obtained from the Integrative Epidemiology Unit open GWAS project. Published East Asian RA data were also obtained from the IEU open GWAS project (212,453 individuals), while large-scale publicly available European RA data were obtained from finngen R10 (13,621 cases and 262,844 controls). Inverse variance weighting was used as the primary analytical method, complemented by MR-egger, Weighed median, and Weighted mode results. Cochran Q tested for heterogeneity, and MR-Egger regression analyses were performed to test for multiplicity. leave-one-out analysis allowed for the robustness and reliability were assessed.

RESULTS

No statistically significant effects of PM2.5, PM2.5-10, PM10, nitrogen dioxide, nitrogen oxides and RA were observed in either European or East Asian populations. Results from European data: PM2.5 (IVW OR: 0.71; 95% CI: 0.27-1.91; p = 0.498; number of SNPs: 5), PM2.5-10 (IVW OR: 1.20; 95% CI: 0.61-2.40; p = 0.596; number of SNPs: 15), PM10 (IVW OR: 1.69; 95% CI: 0.84-3.39; p = 0.142; number of SNPs: 9), nitrogen dioxide (IVW OR: 3.88; 95% CI: 0.19-77.77; p = 0.375; number of SNPs: 2), nitrogen oxides (IVW OR: 0.51; 95% CI: 0.16-1.67; p = 0.268; number of SNPs: 4). East Asian data results: PM2.5 (IVW OR: 1.16; 95% CI: 0.98-1.38; p = 0.086; number of SNPs: 4), PM2.5-10 (IVW OR: 1.14; 95% CI: 0.95-1.38; p = 0.166; number of SNPs: 2), PM10 (IVW OR: 0.95; 95% CI: 0.81-1.11; p = 0.503; number of SNPs: 3), nitrogen dioxide (IVW OR: 0.87; 95% CI: 0.76-1.00; p = 0.051; number of SNPs: 6), nitrogen oxides (IVW OR: 0.96; 95% CI: 0.82-1.14; p = 0.671; number of SNPs: 3). No signs of pleiotropy or heterogeneity were observed in the MR-Egger intercept, MR-PRESSO and Cochrane's Q (p>0.05). In addition, no outliers were found in the MR-PRESSO analysis. The results were further validated by leave-one-out tests, confirming the robustness of the findings.

CONCLUSIONS

We performed transethnic MR analysis suggesting that there may not be a genetically predicted causal relationship between air pollution and RA.

Causal Relationships between Air Pollutant Exposure and Bone Mineral Density and the Risk of Bone Fractures: Evidence from a Two-Stage Mendelian Randomization Analysis

A number of studies from the literature have suggested that exposure to air pollutants is associated with a declined bone mineral density (BMD), and increased risks of osteoporosis (OP) and bone fractures. This study was performed to systemically assess the genetically causal associations of air pollutants with site-/age-specific BMD and risk of bone fractures with the implementation of two-sample Mendelian randomization (TSMR) and multivariate Mendelian randomization (MVMR). The TSMR analysis was implemented to infer the causal associations between air pollutants and BMD and the risk of bone fractures, additional MVMR analysis was used to further estimate the direct causal effects between air pollutants and BMD, the occurrence of OP, and bone fractures. The results showed that NOx exposure contributed to lower femoral neck BMD (FN-BMD) (β = -0.71, 95%CI: -1.22, -0.20, p = 0.006) and total body BMD (TB-BMD) (β = -0.55, 95%CI: -0.90, -0.21, p = 0.002). Additionally, exposure to PM10 was found to be associated with a decreased TB-BMD (B β = -0.42, 95%CI: -0.66, -0.18, p = 0.001), further age-specific subgroup analysis demonstrated the causal effect of PM10 exposure on the decreased TB-BMD in a subgroup aged 45 to 60 years (β = -0.70, 95%CI: -1.12, -0.29, p = 0.001). Moreover, the findings of the MVMR analysis implied that there was a direct causal effect between PM10 exposure and the decreased TB-BMD (45 < age < 60), after adjusting for PM2.5 and PM2.5 -10 exposure. Our study provides additional evidence to support the causal associations of higher concentrations of air pollutant exposure with decreased BMD, especially in those populations aged between 45 to 60 years, suggesting that early intervention measures and public policy should be considered to improve public health awareness and promote bone health.