Effect of zinc ions on apoptosis in PBMCs from healthy aged subjects

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Abstract
Immunosenescence features, such as thymic involution, alteration of T-cell repertoire, autoimmunity and accumulation of memory/effector T cells, may be the result, at least in part, of a zinc deficiency, which is often observed during ageing. Zinc, as essential trace element, affects the immune system function and it is an important regulator of apoptosis of immune cells. In this study we addressed the question whether zinc supplementation in vitro at physiological doses can affect spontaneous and oxidative stress-induced apoptosis in peripheral blood mononuclear cells from subjects of three different age groups: young (mean age 28 years), old (mean age 72 years) and nonagenarians. We studied different parameters related to apoptosis (phosphatydilserine exposure, mitochondrial membrane potential, caspase 3 cleavage) and we found that zinc, while decreasing spontaneous apoptosis, can increase oxidative stress-induced apoptosis in an age-related fashion, being this effect more evident in nonagenarians than in old or young subjects. In particular, zinc can increase late apoptosis/necrosis, a phenomenon that could trigger unnecessary inflammation in vivo. We surmise that these age-associated alterations in susceptibility to apoptosis may be due to a different effect of zinc on T cell subsets, that are altered in very old people, and finally that the zinc deficiency, which is often observed in aged subjects, could be a compensatory mechanism to counteract the inflammatory status of the elderly.