α-Tocopherol increases caspase-3 up-regulation and apoptosis by β-carotene cleavage products in human neutrophils

It has been found that β-carotene cleavage products (CarCP), besides having mutagenic and toxic effects on mitochondria due to their prooxidative properties, also initiate spontaneous apoptosis of human neutrophils. Therefore, it was expected that antioxidants such as α-tocopherol would inhibit the stimulation of apoptosis and caspase-3 activity by CarCP. However, we found that α-tocopherol increases caspase-3 up-regulation and stimulation of apoptosis of human neutrophils by CarCP. Ascorbic acid does not alter this caspase-3 up-regulating and proapoptotic effect exerted by α-tocopherol. Both α-tocopherol and ascorbic acid, in the absence of CarCP, decrease intracellular caspase-3 activity and spontaneous apoptosis of neutrophils. Uric acid alone or in combination with CarCP does not exert apparent effects on caspase-3 activity and apoptosis. Up-regulating effect of α-tocopherol is not observed in the presence of retinol that markedly stimulates apoptosis by itself, whereas increase of caspase-3 activity is induced by concomitant addition of α-tocopherol and β-ionone, a cyclohexenyl degradation product of β-carotene with shorter aliphatic chain.