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The effect of chronic and acute exercise on thymocyte apoptosis and necrosis in ovariectomized mice given dietary genistein.

AIM
At menopause, many women consume phytoestrogens instead of beginning hormone replacement therapy. Many also start exercise programs for health benefits. Genistein, a soy isoflavone with estrogen-like properties, induces lymphocyte apoptosis in vitro. Aerobic exercise also induces apoptosis in lymphoid cells. The present study was designed to determine the effect of chronic (wheel running, WR) and acute (treadmill) exercise on in vivo apoptosis of thymocytes using an animal model of menopause with supplementation from dietary genistein.


METHODS
Using a randomized design, 99 ovariectomized B6D2F1 mice were fed 250 (GEN) or 0 (C) ppm genistein and given concurrent exercise (voluntary wheel running-WR; or WR followed by a bout of high intensity treadmill running-WR+TREAD) or remained sedentary (SED). After 21 days, mice were sacrificed for measurements of body weights, tissue weights, thymocyte apoptosis and necrosis by annexin-V FITC and propidium iodide staining and flow cytometry, DNA fragmentation by ELISA, and plasma estrogen concentrations by RIA.


RESULTS
WR+TREAD mice had lower percentages of viable and higher percentages of apoptotic and necrotic cells from thymus compared with SED or WR conditions (p<0.001). WR resulted in greater DNA fragmentation in thymus cell lysates than in samples from SED mice (p<0.005). There were no differences in thymocyte apoptosis or DNA fragmentation between GEN and C mice, either independently or interactively with exercise. GEN mice tended to have greater wheel running activity than C mice (0.05<p<0.09, depending on day).


CONCLUSIONS
These findings suggest that 1) intense aerobic exercise increases the percentage of early apoptotic cells in the thymus and 2) dietary genistein is associated with a small increase in voluntary wheel running activity in ovariectomized mice.