Characterization of complement C3 as a marker of alpha-amanitin toxicity by comparative secretome profiling

In the human body, proteins secreted into peripheral blood vessels are known as the secretome, and they represent the physiological or pathological status of cells. The unique response of cells to toxin exposure can be confirmed via secretome analysis, which can be used to discover toxic mechanisms or exposure markers. Alpha-amanitin (-AMA) is the most widely studied amatoxin and inhibits transcription and protein synthesis by directly interacting with RNA polymerase II. However, secretory proteins released during hepatic failure caused by -AMA have not been fully characterized. In this study, we analyzed secretome of -AMA-treated Huh-7 cells and mice using a comparative proteomics technique. Overall, 1,505 and 1,440 proteins were identified and quantified, respectively. Among them, 4 and 127 proteins were significantly upregulated and downregulated, respectively. Based on the bioinformatics results for the significantly downregulated proteins, we identified complement component 3 (C3) as a marker for -AMA-induced hepatotoxicity. Through western blot and C3 ELISA assays, we validated -AMA-induced downregulation of C3. In conclusion, using comparative proteomics and molecular biology techniques, we found that -AMA-induced hepatotoxicity reduced C3 levels in the secretome. We expect that this study will aid in identifying new toxic mechanisms, therapeutic targets, and exposure markers of -AMA-induced hepatotoxicity.