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Aromatase Inhibitor Therapy for Erectile Dysfunction

Aromatase inhibitor therapy may be helpful for some men with erectile dysfunction (ED). Aromatase is an enzyme, especially found in the liver, ovary and adipose tissue, required for the conversion of androgens to estrogens. Specifically, aromatase is responsible for the conversion of the androgens androstenedione and testosterone into the estrogens estrone (E1) and estradiol (E2), respectively. In women, the great majority of testosterone is converted to estradiol and estrone, whereas in men, most of the testosterone stays as testosterone, and only a small percentage is converted to estradiol and estrone.

Aromatase inhibitors prevent the action of the enzyme aromatase. Thus, in the presence of an aromatase inhibitor, the body produces less estradiol (E2) and estrone (E1) and maintains a higher level of testosterone. Aromatase inhibitors have been traditionally used as second-line therapy (after tamoxifen) for the treatment of breast cancer, tumors that usually depend on estrogen for growth.

In men, the effect of 2.5 mg of the aromatase inhibior letrozole suppressed plasma estradiol to concentrations less than 50% of pretreatment values after 2 days, with recovery to approximately pretreatment values after 6 days. These decreases were accompanied by increased gonadotrophin (luteininzing hormone - LH and follicle stimulating hormone - FSH) concentrations, with resultant increases of approximately 50% in plasma testosterone.

In men, aromatase activity appears to increase with age. This is particularly so in men with a high body mass index. Increased aromatase activity in men results in conversion of testosterone into higher levels of estradiol. This is especially a problem if men are taking exogenous testosterone (intramuscular testosterone enanthate or cypionate, or topical 1% testosterone as a hydroalcolic gel) for treatment of hypogonadism. Under such conditions, raising the testosterone in a man with a high aromatase level will elevate the serum estradiol. It is controversial but several investigators believe that elevated estradiol values in men are responsible, in part, for causing persistence of many of the symptoms of "androgen insufficiency", despite receiving testosterone treatment. Some investigators also believe that higher estradiol values are associated with prostate enlargement and there is increasing discussion of the role of estrogen in abnormal prostate tissue growth. High levels of estrogen are also thought to result in male hair loss.

Thus there appears to be a role ("off-label" as it concerns FDA government indications) in the use of aromatase inhibitors in some men with sexual dysfunction and elevated estradiol values.