A novel in vitro model to screen steroid 5 alpha-reductase inhibitors against benign prostatic hyperplasia

A convenient and rapid in vitro model to screen steroid 5 alpha-reductase inhibitors, which are effective in the treatment of benign prostatic hyperplasia (BPH), was developed. In the presence of nicotinamide adenine dinucleotide phosphate (NADPH), steroid 5 alpha-reductase converts testosterone to dihydrotestosterone (DHT) which is a major etiologic factor of BPH. NADPH has characteristic absorbance at 340 nm, and the absorbance spectrum may be used to identify NADPH as a kind of the substrate in this enzymatic reaction. In this paper, NADPH, steroid 5 alpha-reductase, series concentration of testosterone and finasteride, and 4 ml Tris-HCl buffer were continuously incubated together at 37 degrees C and the NADPH OD values were continually measured. The descending rate of NADPH OD340nm value by linear regression from the beginning to the 10th minute is close to the initial velocity of the enzymatic reaction. The precise activity of the steroid 5 alpha-reductase was the slope after subtracting that of the blank control. The inhibition constant (Ki) of steroid 5 alpha-reductase inhibitors could be calculated according to the Lineweaver-Burk plots. Two drug screening models, the most common isotope model and the novel model, were compared in this paper. The result showed that the latter one is more economical, quicker and more effective than the former one.