Benign prostatic hyperplasia--the outcome of age-induced alteration of androgen-estrogen balance?

Abstract

Although human benign prostatic hyperplasia (BPH) is the most common tumor in men, its etiology is still unclear. At present, it is only widely accepted that BPH is under the endocrine control of the testes and strongly associated with aging. Therefore, in the human prostate we describe the impact of aging on the activity of various androgen metabolizing enzymes as well as on the endogenous androgen and estrogen levels. Moreover, the inhibition of 5 alpha-reductase by finasteride (Proscar) will be reported. Among all androgen metabolizing enzymes, within the human prostate 5 alpha-reductase is the most powerful one. Most of the androgen metabolizing enzymes undergo a significant age-dependent alteration. For distinct enzymes, the correlation with age is either negative (e.g. 5 alpha-reductase), or positive. Despite a complex pattern of age-dependent alterations, the dominance of 5 alpha-reductase among all androgen metabolizing enzymes is always maintained. This is underlined by a strong accordance between the age-dependent 5 alpha-reductase activity and the corresponding age-dependent endogenous DHT level. In epithelium, both the 5 alpha-reductase activity and the DHT level decrease with age, whereas in stroma not only the 5 alpha-reductase activity is rather constant over the whole age range but the DHT level as well. In contrast to the relatively unaltered DHT content in the stroma of the human prostate, the estrogen content follows an age-dependent increase. On the other side, in epithelium such a positive correlation between the estrogen level and age is not found. Thus, the age-dependent decrease of the DHT accumulation in epithelium and the concomitant increase of the estrogen accumulation in stroma will lead to a tremendous increase with age of the estrogen/androgen ratio in the human prostate. This could be of pathogenetic importance for BPH development if in fact a balanced androgen/estrogen synergism is necessary for the integrity of the normal human prostate. Finally, it is remarkable that the inhibition of 5 alpha-reductase activity by finasteride (Proscar) is significantly stronger in epithelium than in stroma. Therefore, it is conceivable that the global size-reduction of BPH under finasteride treatment is primarily due to the regression of BPH epithelium.