Testosterone promotion effect of Eucommia ulmoides staminate flower via the steroidogenic pathway and potential hormonal mechanism

Eucommia ulmoides staminate flowers (EUF), a newly approved functional food in China, have great potential for hormonal regulation. Herein, we aim to demonstrate the chemical composition and pharmacological activity of EUF in testosterone production and hormonal regulation. EUF extract and its components, kaempferol and geniposidic acid, exhibited a strong stimulating effect by increasing testosterone secretion, reducing ROS production, or promoting viability in Leydig cells. Meanwhile, the increased testosterone production was related to the upregulation of mRNA and protein expression of the steroidogenic pathway, such as steroidogenic acute-regulatory protein (StAR), 3β -hydroxysteroid dehydrogenase type 1 (HSD3B1), 17α-hydroxylase/17,20-lyase (CYP17A1), and nuclear receptor subfamily 5 group A member 1 (NR5A1). However, PKA inhibitor H89 or adenylyl cyclase inhibitor SQ22536 could block their effect. The results of transgenic yeast models showed the androgenic agonistic effects of kaempferol and naringenin and the estrogenic agonistic effects of rutin. These results indicated that the testosterone promotional effect of EUF was related to the activation of the steroidogenic pathway and potential hormonal regulation. Kaempferol and geniposidic acid might be the key active ingredients.