Effects of phenolic compounds on 3ß-hydroxysteroid dehydrogenase activity in human and rat placenta: Screening, mode of action, and docking analysis.

Human 3ß-hydroxysteroid dehydrogenase type I (HSD3B1) and rat type IV (HSD3B4) in placentas catalyze the conversion of pregnenolone to progesterone, which plays a key role in maintaining pregnancy. Many phenolic compounds potentially inhibit HSD3B in placentas as endocrine disruptors. In this study, the effects of 16 phenolic compounds on the activity of human HSD3B1 and rat HSD3B4 were determined and the structure-activity relationship was compared. HSD3B1 in human placental microsomes and HSD3B4 in rat placental microsomes were used to measure their activities and pregnenolone and NAD+ were used as substrates. Of the 16 phenolic compounds, 4-nonylphenol, pentabromophenol, and 2-bromophenol resulted in residual human HSD3B1 activity lower than 50 % and 4-nonylphenol and pentabromophenol resulted in residual rat HSD3B4 activity lower than 50 %. 4-Nonylphenol, pentabromophenol, and 2-bromophenol were mixed inhibitors of human HSD3B1, with Ki values of 2.31, 3.58 and 4.86 µM, respectively, while 4-nonylphenol and pentabromophenol were noncompetitive inhibitors of rat HSD3B4 with Ki values of 20.86 and 141.8 µM. Molecular docking showed that 4-nonylphenol, pentabromophenol, and 2-bromophenol docked to the active sites of human HSD3B1 and rat HSD3B4, and the shift of residue S125 in human HSD3B1 to T125 in rat HSD3B4 could explain the species-dependent difference in their inhibitory potency and mode of action. This study demonstrates that 4-nonylphenol, pentabromophenol, and 2-bromophenol are mixed inhibitors of human placental HSD3B1, while 4-nonylphenol and pentabromophenol are noncompetitive inhibitors of rat HSD3B4, possibly blocking the placental steroidogenesis.

Tetramethyl bisphenol A stimulates proliferation but inhibits fetal Leydig cell function in male rats by targeting estrogen receptor α after in utero exposure.

Tetramethyl bisphenol A (TMBPA) is a widely used flame retardant. TMBPA has been a toxic to Leydig cells in puberty, but it remains unclear whether TMBPA has a similar inhibitor effect on fetal Leydig cells (FLCs). This study reported morphological and functional alterations of FLCs in the testes of male offspring at birth after in utero exposure to TMBPA. Pregnant Sprague Dawley rats were dosed via continuous gavage of TMBPA (0, 10, 50, and 200 mg/kg/day) from gestational day 14 to 21. TMBPA markedly raised serum total testosterone level, testicular volume, and FLC number of male offspring at 200 mg/kg dose. The up-regulation of Insl3, Star, and Cyp11a1 mRNAs was observed after 200 mg/kg TMBPA exposure. After normalization to the number of FLCs, TMBPA significantly reduced Lhcgr and Hsd3b1 expressions at 10 mg/kg, and Cyp17a1 at 200 mg/kg paralleling with their protein levels. TMBPA compromised the expression of Esr1, while increased the expression of Cdk2 and Cdk4 as well as their protein levels. TMBPA particularly increased the phosphorylation of AKT1 and AKT2 at 200 mg/kg. In conclusion, the present study suggests that TMBPA may promote FLC proliferation via ESR1-CDK2/4-AKT pathway, while inhibits the function of FLCs by reducing steroidogenic enzyme activity.

Fluornen-9-bisphenol increases Leydig cell proliferation but inhibits maturation in pubertal male rats via interacting with androgen receptor as an antagonist and estrogen receptor α as an agonist.

Fluornen-9-bisphenol (BPFL) is used as one of the alternatives for bisphenol A. However, whether BPFL has deleterious effects to the male reproductive system and the underlying mechanism remain unknown. Here, we report the effects of BPFL on Leydig cell development in male rats in puberty. Male Sprague-Dawley (28 days old) rats were dosed with 0, 10, 100, 200 mg/kg/day BPFL via gavage for 28 days. BPFL significantly decreased serum testosterone levels at 200 mg/kg while increasing serum luteinizing hormone and follicle-stimulating hormone levels at 200 mg/kg. BPFL markedly increased Leydig cell number but down-regulated the expression of Cyp17a1 and its protein level in Leydig cells at 200 mg/kg. Further study showed that BPFL significantly increased Pcna and Cdk2 expression and increased Leydig cell proliferation at 200 mg/kg. BPFL treatment to immature Leydig cells isolated from 28-day-old male rats for 24 h significantly inhibited testosterone biosynthesis at 50 µM, which was completely reversed by the androgen receptor agonist 7α-methyl-nortestosterone and estrogen receptor α antagonist ICI 182,780. In conclusion, BPFL increases Leydig cell proliferation but inhibits its maturation in male rats in puberty by blocking androgen receptor and activating estrogen receptor α.