Plasma apolipoprotein A-IV deficiency as a proteomics-identified diagnostic biomarker for heat stroke: A prospective 2-center study.

PURPOSE: To explore proteomic changes from heat exhaustion (HE) to heat stroke (HS) and identify biomarkers for HS diagnosis. METHODS: This prospective 2-center study, conducted from October 2022 to February 2024, included 18 patients with HS and 23 patients with HE from a hospital in China. We used 4D-data-independent acquisition proteomics to analyze protein expression and identified differentially expressed proteins (DEPs) with a fold change ≥1.5 or ≤0.67, considering p < 0.05 as significant. Bioinformatics and Cytoscape were used to characterize DEP functions and identify key proteins. Receiver operating characteristic curves and least absolute shrinkage and selection operator algorithm were used to assess diagnostic potential, and parallel reaction monitoring validated DEPs. An independent cohort was used to validate biomarkers by enzyme-linked immunosorbent assay. RESULTS: A total of 2604 overlapping proteins were identified, with 176 DEPs screened for significance. These DEPs were predominantly linked to biological processes such as inflammation, immune response, cell signaling, and metabolic regulation. Analysis revealed that apolipoprotein A-IV (APOA4) exhibited the highest area under the curve (AUC) value among the hub proteins and was identified as a significant variable by least absolute shrinkage and selection operator regression. Furthermore, 18 proteins identified through 4-dimensional data-independent acquisition proteomics were confirmed using parallel reaction monitoring. Plasma levels of APOA4 were significantly reduced in HS patients compared to those with HE (p = 0.001). The AUC for diagnosing HS using plasma APOA4 was 0.81, with 77.8% sensitivity and 78.3% specificity. Enzyme-linked immunosorbent assay results corroborated these findings, with plasma APOA4 levels in HS patients being significantly lower than in HE patients, yielding an AUC of 0.74, with 66.7% sensitivity, and 84.2% specificity. CONCLUSION: Plasma APOA4, which was significantly downregulated, may serves as a novel biomarker for the diagnosis of HS.