Comparative GC-MS Based In Vitro Assays of 5α-Reductase Activity Using Rat Liver S9 Fraction

The study evaluated the activity of 5α-reductase (5αR) in rat liver S9 fraction using gas chromatography-mass spectrometry (GC-MS) based in vitro assays. The researchers compared the effectiveness of conventional GC-MS analysis and isotope-dilution GC-MS (GC-IDMS) in detecting 5α-dihydrotestosterone (DHT) when testosterone and the 5αR inhibitor finasteride were present. It was found that DHT was not detectable by conventional GC-MS when testosterone concentration was below 0.2 μM, whereas GC-IDMS successfully evaluated 5αR activity. The study suggested that the combination of S9 fraction and GC-IDMS could be a promising method for assessing 5αR activity in large-scale clinical studies due to the S9 fraction's higher enzyme reactivity and ease of collection compared to microsomal solutions.