The in vitro effect of testosterone on human neutrophil function was investigated. Blood neutrophils from healthy male subjects were isolated and treated with 10 nM, 0.1 and 10 microM testosterone for 24 h. As compared with untreated cells, the testosterone treatment produced a significant decrease of superoxide production as indicated by the measurement of extra- and intracellular superoxide content. An increment in the production of nitric oxide was observed at 0.1 and 10 microM testosterone concentrations, whereas no effect was found for 10 nM. Intracellular calcium mobilization was significantly increased at 10 nM, whereas it was reduced at 10 microM testosterone. There was an increase in phagocytic capacity at 10 nM and a decrease of microbicidal activity in neutrophils treated with testosterone at 10 microM. Glutathione reductase activity was increased by testosterone treatment, whereas no effect was observed in other antioxidant enzyme activities. An increase in the content of thiol groups was observed at all testosterone concentrations. Lipid peroxidation in neutrophils evaluated by levels of TBARS was decreased at 10 nM and 0.1 microM testosterone. These results indicate the antioxidant properties of testosterone in neutrophils as suggested by reduction of superoxide anion production, and lipid peroxidation, and by the increase in nitric oxide production, glutathione reductase activity and the content of thiol groups. Therefore, the plasma levels of testosterone are important regulators of neutrophil function and so of the inflammatory response.

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Taken together our results are supportive to a beneficial effect of astaxanthin-treatment on human neutrophils function as demonstrated by increased phagocytic and fungicide capacity as well as by the reduced superoxide anion and hydrogen peroxide production, however, without affecting neutrophils capacity to kill C. albicans. This process appears to be mediated by calcium released from intracellular storages as well as nitric oxide production.

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