Abstract
OBJECTIVE: To explore the causal relationship between human inhalation injury and circulating inflammatory proteins. METHODS: This research was based on two-sample Mendelian randomization (MR) analysis. With inhalation injury as the exposure factor and circulating inflammatory proteins as the result, data on inhalation injury (216 993 samples) and 91 circulating inflammatory proteins (14 824 samples) were obtained from the genome-wide association study database, and analysis was conducted by two-sample MR analysis methods. Based on linkage disequilibrium analysis, independent site single nucleotide polymorphisms (SNPs) that were significantly associated with inhalation injury were identified as the instrumental variables. The inverse variance weighted (IVW) method was mainly used to analyze the causal relationship between inhalation injury and 91 circulating inflammatory proteins, which were further verified using the weighted median method, weighted pattern method, MR-Egger method, and simple pattern method. Based on the aforementioned IVW method analysis results, SNPs of inhalation injury conformed to the hypothesis were subjected to Cochran's Q test for heterogeneity assessment, the MR-Egger regression test and MR-PRESSO outlier test for assessment of horizontal pleiotropy, and the leave-one-out method analysis for reliability assessment. RESULTS: Six SNPs with a significant threshold (P < 5×10(-5)) were identified as representative instrumental variables of inhalation injury, with F values greater than 10, indicating strong correlated instrumental variables. Based on the 6 inhalation injury SNPs, the IVW method analysis revealed a significant causal relationship between inhalation injury and interleukin-20 (IL-20), IL-20 receptor subunit alpha (IL-20RA), IL-5, and tumor necrosis factor receptor superfamily member 9 (TNFRSF9), with odds ratios of 1.01, 1.01, 1.02, and 1.01, respectively, and 95% confidence intervals of 1.00-1.02, 1.00-1.03, 1.01-1.03, and 1.00-1.03, respectively, P < 0.05. Verification through the weighted median method and MR-Egger method confirmed that the causal relationships between inhalation injury and IL-5 (with odds ratios of 1.02 and 1.03, respectively, confidence intervals of 1.00-1.04 and 1.01-1.04, respectively, P < 0.05) as well as TNFRSF9 (with odds ratios of 1.02 and 1.03, respectively, confidence intervals of 1.00-1.04 and 1.01-1.04, respectively, P < 0.05) were statistically significant. Conversely, verification through the weighted pattern method and simple pattern method indicated that the causal relationships between inhalation injury and IL-20, IL-20RA, IL-5, and TNFRSF9 were not statistically significant (with all P values > 0.05), thus still needing IVW method results as standards. Based on the aforementioned IVW method analysis results, the Cochran's Q test demonstrated there was no significant heterogeneity in the 6 inhalation injury SNPs that had significant causal relationships with IL-20, IL-20RA, IL-5, and TNFRSF9 (with Q values of 2.67, 5.00, 5.17, and 5.29, respectively, P > 0.05); assessments using the MR-Egger regression test along with MR-PRESSO outlier test showed that none of the 6 inhalation injury SNPs that had significant causal relationships with IL-20, IL-20RA, IL-5, and TNFRSF9 had significant horizontal pleiotropy (with intercepts of 0.01, < 0.01, -0.02, and -0.03, respectively, RSSobs values of 3.33, 9.00, 7.88, and 7.26, respectively, P > 0.05); the leave-one-out method analysis showed that the significant causal relationship between inhalation injury and IL-20, IL-20RA, IL-5, and TNFRSF9 was stable and reliable after removing the 6 inhalation injury SNPs one by one. CONCLUSIONS: Through two-sample MR analysis, it is clear that there is a significant causal relationship between inhalation injury and four circulating inflammatory proteins, namely IL-20, IL-20RA, IL-5, and TNFRSF9, suggesting the production of the above four circulating inflammatory proteins is in an increasing trend following inhalation injury.