Assessment of steroidogenic pathways that do not require testosterone as intermediate

Area of Science:

• Steroid biochemistry
• Endocrinology
• Molecular biology

Background:

• Traditional models posit testosterone (T) as a key intermediate for estradiol (E2) and dihydrotestosterone (DHT) synthesis.
• This T-dependent pathway (Tpath) assumes aromatization and 5α-reduction occur after T formation by 17β-hydroxysteroid dehydrogenase (17β-HSD).

Purpose of the Study:

• To investigate alternative biosynthetic pathways for E2 and DHT that do not require T as an intermediate (noTpath).
• To challenge the established Tpath model based on new biochemical and experimental evidence.

Main Methods:

• Analysis of enzyme kinetics: comparing affinities of aromatase and 5α-reductase for 4-androstenedione (4-dione) versus T.
• Cell-based experiments: using [14C]-labeled DHEA and 4-dione as substrates in SZ95, DU-145, and JEG-3 cell lines with enzyme inhibitors.
• Literature review: examining early studies on 17β-HSD deficiency and steroid metabolism.

Main Results:

• Aromatase and 5α-reductase show higher affinity for 4-dione than T, supporting their action before 17β-HSD.
• Experiments with labeled substrates and inhibitors in cell lines demonstrated E2 and DHT synthesis independent of T.
• Review of historical data on 17β-HSD deficiency supports the physiological relevance of the noTpath.

Conclusions:

• Evidence strongly favors E2 and DHT biosynthesis via pathways where aromatase and 5α-reductase act on precursors before 17β-HSD converts them to T.
• The traditional Tpath is not the sole or necessarily primary route for E2 and DHT synthesis; a T-independent pathway (noTpath) is physiologically functional.