Species-specific responses to di (2-ethylhexyl) phthalate reveal activation of defense signaling pathways in California sea lion but not in human skeletal muscle cells in primary culture

Higher antioxidant defenses in marine than terrestrial mammals allow them to cope with oxidative stress associated with diving-induced ischemia/reperfusion. Does this adaptation translate to inherent resistance to other stressors? We analyzed oxidative stress indicators in cells derived from human and California sea lion (Zalophus californianus) skeletal muscle upon exposure to di (2-ethylhexyl) phthalate (DEHP). Human abdominal muscle biopsies were collected from healthy women undergoing planned cesarean surgery. California sea lion samples were collected postmortem from stranded animals. Skeletal muscle cells derived from each species were exposed to 1 mM DEHP for 13 days (n = 25) or maintained under control (untreated) conditions (n = 25). Superoxide radical (O₂^•-) production, oxidative damage and antioxidant enzyme activities were measured using spectrophotometric methods. Gene expression was analyzed by RT-qPCR. DEHP exposure increased O₂^•- production and superoxide dismutase (SOD) activity in both species. Glutathione S-transferase (GST) activity and protein carbonyl levels increased in human but not in California sea lion cells. In contrast, glutathione peroxidase (GPx) and catalase (CAT) activities increased in California sea lion but not in human cells exposed to DEHP. In human cells, DEHP increased microsomal GST1 and GST (κ, μ, θ, ω, and ᴢ), while suppressing 8-oxoguanine DNA glycosylase (OGG1), CAT, glutathione reductase (GR), and nuclear factor erythroid 2-related factor 2 (NRF2) expression, suggesting increased oxidative stress and phase two detoxification processes. In California sea lion cells, DEHP increased OGG1, NRF2, GPx2 and SOD3 expression, suggesting activation of antioxidant defenses, which potentially contribute to maintaining redox homeostasis, avoiding oxidative damage.