Menaquinone-4 enhances testosterone production in rats and testis-derived tumor cells

• Published in: Lipids in health and disease Vol. 10; no. 1; p. 158
• Main Authors: Ito, Asagi, Shirakawa, Hitoshi, Takumi, Naofumi, Minegishi, Yoshihiko, Ohashi, Ai, Howlader, Zakir H, Ohsaki, Yusuke, Sato, Toshiro, Goto, Tomoko, Komai, Michio
• Format: Journal Article
• Language: English
• Published: England BioMed Central Ltd 13-09-2011; BioMed Central; BMC
• Subjects: Animals; Carbon-Carbon Ligases - antagonists & inhibitors; Cell Line, Tumor; Cholesterol; Cholesterol Side-Chain Cleavage Enzyme - metabolism; Cyclic AMP Response Element-Binding Protein - metabolism; Cyclic AMP-Dependent Protein Kinases - antagonists & inhibitors; Cyclic AMP-Dependent Protein Kinases - chemistry; Cyclic AMP-Dependent Protein Kinases - metabolism; Diet; Enzyme-linked immunosorbent assay; Gene expression; Health aspects; I-10 cells; Kinases; Leydig Cells - drug effects; Leydig Cells - metabolism; Liver - drug effects; Liver - metabolism; Male; menaquinone-4; Mice; Nutrition research; Phosphorylation - drug effects; Physiological aspects; Pituitary gland; Plasma; protein kinase A; Protein Kinase Inhibitors - pharmacology; Protein kinases; Protein Processing, Post-Translational - drug effects; Proteins; Rats; Rats, Wistar; Rodents; Science; Specific Pathogen-Free Organisms; testis; Testis - drug effects; Testis - metabolism; Testosterone; Testosterone - blood; Testosterone - metabolism; Tissue Distribution; Up-Regulation - drug effects; Vitamin K; Vitamin K 1 - antagonists & inhibitors; Vitamin K 1 - metabolism; Vitamin K 2 - analogs & derivatives; Vitamin K 2 - pharmacokinetics; Vitamin K 2 - pharmacology; Japan
• ISSN: 1476-511X; 1476-511X
• DOI: 10.1186/1476-511x-10-158

Vitamin K is essential for the posttranslational modification of various Gla proteins. Although it is widespread in several organs, including the testis, the function of vitamin K in these organs is not well characterized. In this study, we investigated the function of vitamin K in the testis and analyzed its role in steroidogenesis.
Eight-week-old male Wistar rats were fed a diet supplemented with menaquinone-4 (MK-4, 75 mg/kg diet), one of the predominant K₂ vitamins present in the testis, for 5 weeks. In vivo testosterone levels of the rats' plasma and testes were measured by enzyme-linked immunosorbent assay, and in vitro testosterone levels of testis-derived tumor cells (I-10 cells) maintained in Ham's F-10 medium with 10% fetal bovine serum were measured following treatment with MK-4 (0 to 100 μM) at several time points. Testosterone and cellular protein levels were analyzed with respect to their effects on steroidogenesis.
Testosterone levels in the plasma and testes of MK-4-fed rats were significantly increased compared to those of control rats, with no obvious differences in plasma luteinizing hormone levels. Secreted testosterone levels from I-10 cells were elevated by MK-4, but not by vitamin K₁, in a dose-dependent manner independent of cAMP treatment. Western blot analysis revealed that expression of CYP11A, the rate-limiting enzyme in steroidogenesis, and phosphorylation levels of protein kinase A (PKA) and the cAMP response element-binding protein were all stimulated by the presence of MK-4. Enhancement of testosterone production was inhibited by H89, a specific inhibitor of PKA, but not by warfarin, an inhibitor of γ-glutamylcarboxylation.
MK-4 stimulates testosterone production in rats and testis-derived tumor cells via activation of PKA. MK-4 may be involved in steroidogenesis in the testis, and its supplementation could reverse the downregulation of testosterone production in elders.