The efficiency with which β-carotene protects against oxidative stress in chicken embryo fibrobiasts (CEF) at low O2 partial pressures was assessed. Primary cultures of CEF were grown at low O2 partial pressures and oxidatively stressed by exposure to paraquat (PQ). Activities of the antioxidant enzymes superoxide dismutase (EC 1.15.1.1; SOD), catalase (EC 1.11.1.6; CAT) and glutathione peroxidase (EC 1.11.1.9; GSH-Px) were measured as indices of oxidative stress. CEF incubated with 0·25–1·0 mM—PQ for 18 h exhibited increased SOD and CAT activities compared with non-PQ-treated control cells (P < 0·001). No cytotoxicity as indicated by lactate dehydrogenase (EC 1.1.1.27; LDH) release was observed at PQ concentrations below 2·0 mM. Incorporation of added β-carotene into 0·25 mM-PQ-treated cells prevented the PQ-induced increases in SOD and CAT, and activities were similar to those seen in non-PQ-treated control cells. GSH-Px activity decreased relative to its control value on exposure to 0·25 mM-PQ and β-carotene prevented this decrease in a dose-dependent manner. The proportion of LDH released from the CEF treated with β-carotene remained below the control value of 2·5% at all times.

The ability of β-carotene to protect against oxidative stress in vitro was assessed. Primary cultures of chicken embryo fibroblasts (CEF) were oxidatively stressed by exposure to paraquat (PQ). Activities of the antioxidant enzymes superoxide dismutase (SOD; EC 1.15.1.1), catalase (CAT; EC 1.11.1.6) and glutathione peroxidase (GSH-Px; EC 1.11.1.9) were measured as indices of oxidative stress. CEF incubated with 0·25 mM-PQ for 18 h exhibited increased SOD and CAT activities and decreased GSH-Px activity compared with the control (P < 0·001). Incorporation of added β-carotene (0·1 μM) into 0·25 mM-PQ-treated CEF returned SOD activity to that seen in non-PQ-treated cells. β-Carotene (0·1 μM) reduced the CAT activity from that seen in PQ-treated cells and returned the GSH-Px activity to its control value thus protecting the cells against PQ-induced oxidative stress. However, at higher concentrations of β-carotene (10 μM), SOD and CAT activities increased significantly (P < 0·001) relative to non-PQ-treated cells and GSH-Px activity decreased relative to its control value. Similar trends were observed when CEF grown in β-carotene-enricbed media (0·1–10μM) were oxidatively stressed by exposure to 0·25 mM-PQ for 18 h.β-Carotene: Chicken embryo fibroblasts: Oxidative stress Antioxidant enzymes