Identification of candidate protein biomarkers associated with domoic acid toxicosis in cerebrospinal fluid of California sea lions (Zalophus californianus)

Since 1998, California sea lion stranding events associated with domoic acid toxicosis (DAT) have consistently increased and there are no practical non-lethal clinical tests for the diagnosis of domoic acid toxicosis that can be utilized in a large-scale rehabilitation facility. Proteomic analysis was conducted to discover candidate protein markers of DAT using cerebrospinal fluid (CSF) from stranded sea lions with acute DAT, chronic DAT, or without DAT. A total of 2005 protein families were identified across 40 CSF samples (FDR<0.01) using the annotated California sea lion genome. Of these proteins, 83 were significantly different in abundance across the three groups (p<0.05). Comparisons between all sea lions with DAT versus those without DAT indicated that 119 proteins were significantly different between both groups (p<0.05); whereas, 47 proteins were significantly different between acute DAT and chronic DAT (p<0.05). Significant proteins were assessed as classifiers using ROC curves. Compared to sea lions with non-DAT, those with either acute or chronic DAT displayed higher levels of 14-3-3 proteins and malate dehydrogenase, and lower levels of 5’-3’ exonuclease PLD3, neurosecretory protein VGF, disintegrin and metalloproteinase domain-containing protein, and calsyntenin-1. When comparing acute DAT versus chronic DAT, 4 proteins were identified as good classifiers. Elevated levels of beta-synuclein was detected in acute DAT, and was identified as a high classifier for both comparisons. Many of these proteins have been implicated in a variety of neurodegenerative diseases. These proteins should be considered potential markers for DAT in California sea lions, as well as markers to discriminate between acute or chronic DAT, and should be considered priority for future validation studies as biomarkers.