Effects of a High Dose, Aglycone-Rich Soy Extract on Prostate-Specific Antigen and Serum Isoflavone Concentrations in Men With Localized Prostate Cancer

Abstract

The efficacy and safety of consuming high-dose isoflavone supplements for prostate cancer is not clear. A double-blind, placebo controlled, randomized trial was conducted in 53 men with prostate cancer enrolled in an active surveillance program. The treatment group consumed a supplement containing 450 mg genistein, 300 mg daidzein, and other isoflavones daily for 6 mo. Prostatespecific antigen (PSA) was measured in both groups at baseline, 3 mo, and 6 mo, and serum concentrations of genistein, daidzein, and equol were assessed at baseline and 6 mo in the treatment group. Following the completion of the 6-mo double-blind study, men were enrolled in a 6-mo open label trial with the same isoflavone-rich supplement, and PSA was measured at 3 and 6 mo. PSA concentrations did not change in either group after 6 mo or after 12 mo when the openlabel study was included. The 6 mo serum concentrations of genistein and daidzein (39.85 and 45.59 μmol/l, respectively) were significantly greater than baseline values and substantially higher than levels previously reported in other studies. Equol levels did not change. Although high amounts of aglycone isoflavones may result in significantly elevated serum concentrations of genistein and daidzein, these dietary supplements alone did not lower PSA levels in men with lowvolume prostate cancer.

Effect of Sulforaphane in Men with Biochemical Recurrence after Radical Prostatectomy

“…Two randomized, double-blind, placebo-controlled short-term isoflavone intervention trials before radical prostatectomy have shown that genistein failed to change the PSA levels significantly, even though it modulated the expression of several genes involved in prostate cancer (43,44). A 6-month double-blind, placebo-controlled intervention study with highdose soy extracts conducted in 53 men with prostate cancer enrolled in an active surveillance program also failed to show lower PSA levels (45). Conversely, soy extracts appear to be more efficient when combined with other compounds.…”

Chemoprotective activity of the isoflavones, genistein and daidzein on mutagenicity induced by direct and indirect mutagens in cultured HTC cells

“…However, intake of an aglycone isoflavone supplement (containing 450 mg genistein, 300 mg daidzein, and other isoflavones daily for 6 months) in a group of 53 prostate cancer patients displayed high plasma levels of genistein (39.85lM) and daidzein (45.59 lM) (deVere White et al 2010). Moreover, data in humans and animals showed that concentrations of flavonoids in the endocrine-responsive tissues including liver, mammary gland, ovary, prostate, and uterus may exceed plasma levels several fold (Gardner et al 2009;Chang et al 2000;Janning et al 2000).…”

Expression of prostate stem cell antigen is downregulated during flavonoid-induced cytotoxicity in prostate cancer cells

“…In prostate cancer, numerous biomarkers have been identified, including PSA, prostate-specific membrane antigen, PSCA, early prostate cancer antigen, B7-H3, chromogranin A, α-methylacyl coenzyme A racemase, glutathione S-transferase P1 (GSTP1), sarcosine, caveolin-1, TMPRSS2-ERG, Ki-67, prostate cancer antigen 3 (PCA3) and disabled homolog 2-interacting protein (35). Previous studies have demonstrated that a number of these biomarkers, including PSA, GSTP1, Ki-67 and PCA3, were the targets by which flavonoids exerted anticancer effects in prostate cancer (36)(37)(38)(39). Using human xenografts grown in mice with severe combined immunodeficiency, it has also been demonstrated that anti-PSCA monoclonal antibodies inhibited the growth and metastasis of tumors (40), thus indicating that PSCA may be an immunotherapeutic target in the treatment of prostate cancer (40,41).…”