Previous studies of delta4-androstene-3,17-dione (4-androstenedione) administration in men have not demonstrated sustained increments in testosterone levels, fat-free mass (FFM), and muscle strength; failure to demonstrate androstenedione's androgenic/anabolic effects has stifled efforts to regulate its sales. To determine whether 4-androstenedione has androgenic/anabolic properties, we evaluated its association with androgen receptor (AR) and its effects on myogenesis in vitro. Additionally, we studied the effects of a high dose of 4-androstenedione on testosterone levels, FFM, and muscle strength in hypogonadal men.

We determined the dissociation constant for 4-androstenedione using fluorescence anisotropy measurement of competitive displacement of fluorescent androgen (FA) from AR ligand binding domain (LBD). AR nuclear translocation and myogenic activity of androstenedione were evaluated in mesenchymal, pluripotent C³H10T1/2 cells, in which androgens stimulate myogenesis through an AR-pathway. We determined effects of a high dose of androstenedione (500 mg thrice daily) given for 12-weeks on FFM, muscle strength, and hormone levels in nine healthy, hypogonadal men.

4-Androstenedione competitively displaced FA from AR-LBD with a lower affinity than DHT (Kd 648 ± 21 and 10 ± 0.4 nM, respectively). In C³H10T1/2 cells, 4-androstenedione caused nuclear translocation of AR, and stimulated myogenesis, as indicated by dose-dependent increase in MHC II+ myotube area and up-regulation of MyoD protein. Stimulatory effects of 4-androstenedione on MHC II+ myotubes and MyoD expression were attenuated by bicalutamide, an AR-antagonist. Administration of 1500 mg 4-androstenedione daily to hypogonadal men significantly increased serum androstenedione, total and free testosterone, estradiol, and estrone levels, and suppressed SHBG and HDL cholesterol levels. 4-Androstenedione administration was associated with significant gains in fat-free mass (+1.7 ± 0.5kg, P = 0.012) and muscle strength in bench press (+4.3 ± 3.1kg, P = 0.006) and leg press exercises (+18.8 ± 17.3kg, P = 0.045).

Conclusions. 4-Androstenedione is an androgen that binds AR, induces AR-nuclear translocation, and promotes myogenesis in vitro, with substantially lower potency than DHT. 4-Androstenedione administration in high doses to hypogonadal men increases testosterone levels, FFM, and muscle strength, although at the dose tested, the anabolic effects in hypogonadal men are likely due to its conversion to testosterone.