Soy isoflavone supplementation elevates erythrocyte superoxide dismutase, but not plasma ceruloplasmin in postmenopausal breast cancer survivors

By DiSilvestro RA, Goodman J., Dy E., LaValle G. Breast Cancer Research and Treatment 89 (2005): 251-255.

Soy isoflavones have been given considerable attention in regard to breast cancer, both for prevention and for increasing risk.

Soy isoflavone antioxidant effects may help prevent breast cancer re-occurrence, but isoflavone estrogen-like actions may increase breast cancer risk. These isoflavone actions can be reflected by effects on two copper enzymes activities, superoxide dismutase 1 (SOD 1), which has antioxidant function relevant to breast cancer prevention, and ceruloplasmin, which has its synthesis up-regulated by estrogen, and for which high values are associated with high breast cancer risk. A soy isoflavone-rich concentrate supplement was examined for effects on these two copper enzyme activities in post-menopausal breast cancer survivors.

Study design

Seven postmenopausal breast cancer survivors (aged 50 – 65 years), who had completed chemotherapy and / or surgery at least 6 months earlier were recruited. Each subject was given soy isoflavone concentrate (SoyLife COMPLEX) and placebo (ground matzo), each for 24 days in a crossover design that included a 2-week washout period. The products were given in capsules at a daily serving of 3 capsules taken twice daily. The daily serving contained 138 mg isoflavones (81 mg daidz(e)in, 42 mg glycit(e)in and 15 mg genist(e)in.

The subjects were blinded as to the order of the treatments (soy or placebo first), which was determined randomly.

Blood and urine samples were analyzed for erythrocyte Cu-Zn SOD activity, for ceruloplasmin (as activity and as immuno-reactive protein) and urinary 8-hydroxy-2′-deoxyguanosine, a DNA oxidation product with relevance to breast cancer.

Results and conclusion

The results showed that supplementation with soy, but not with placebo, produced a statistically significant increase in erythrocyte SOD 1 activities. The increase in SOD 1 activities was not accompanied by a decrease in urinary 8- deoxyhydroxyguanosine. Ceruloplasmin activities and protein were unchanged by both treatments. The increase in SOD-activity could not be related to copper-intake.

In summary, SoyLife COMPLEX showed an antioxidant effect and increased SOD 1 activity considered relevant to reduced breast cancer risk, but not a ceruloplasmin increase associated with estrogenic activity and breast cancer risk. In this pilot study the soy isoflavone concentrate seemed safe and possibly protective in regard to breast cancer risk.

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