Some supplements that should raise testosterone levels contain the synthetic isoflavones methoxyisoflavone and ipriflavone. Those products might work, suggests an in vitro study that Italian doping hunters, associated with the Federazione Medico Sportiva Italiana, published in Drug Testing & Analysis. According to the Italians, both methoxyisoflavone and ipriflavone inhibit aromatase, the enzyme that converts testosterone into estradiol.
Ipriflavone and methoxyisoflavone
Ipriflavone and methoxyisoflavone are synthetic isoflavones. They were invented in the last century by Eastern European chemists, who wanted to make new anabolic agents by tweaking isoflavones such as daidzein, a phyto-estrogen in soy.
Synthetic isoflavones were not successful as a medicine, but they did catch on as a sports supplement.
Ipriflavone and methoxyisoflavone inhibit the action of P450 enzymes such as CYP1A2 and CYP2C9. That is why the Italians wondered whether ipriflavone and methoxyisoflavone also thwart aromatase. Aromatase is the enzyme that converts testosterone into estradiol. And aromatase is, just like CYP1A2 and CYP2C9, a P450 enzyme.
If so, then ipriflavone and methoxyisoflavone may be on the doping list, which also includes agents such as anastrozole and letrozole. Aromatase inhibitors can raise testosterone levels, thereby improving performance.
The researchers put testosterone and aromatase together in test tubes, and then looked at whether they could block the conversion of testosterone to estradiol by adding ipriflavone, methoxyisoflavone and other substances.
Ipriflavone and methoxyisoflavone inhibited the formation of estradiol. Both substances blocked the action of the aromatase enzyme. Daidzein did that too, but to a much lesser extent. The anti-estrogenic effect of methoxyisoflavone and ipriflavone was similar to that of anastrozole.
When the Italians calculated the Ki of methoxyisoflavone and iproflavone based on their tests, they saw that it was equal to the Ki of the pharmacological aromatase inhibitors.
“The results obtained in our in vitro model system show that, in the range of concentrations here considered, methoxyisoflavone, and ipriflavone have a potential for aromatase inhibition similar to that of formestane, anastrozole, and aminoglutethimide”, write the researchers. “Those drugs [are] used in anticancer therapy and banned by the WADA for their effects on steroidogenesis.”
“Clearly, the results here presented are not sufficient to express a final opinion on the opportunity of including synthetic isoflavones on WADA’s Prohibited List, since the actual magnitude of their in vivo effects would certainly be modulated by their pharmacokinetic properties, and especially by their low bioavailability.”
“Nonetheless, we believe their monitoring could still be useful in doping control analysis, also considering the high dosages recommended for synthetic isoflavones in dietary supplements.”