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

Asagi Ito, Hitoshi Shirakawa, Naofumi Takumi, Yoshihiko Minegishi, Ai Ohashi, Zakir H. Howlader, Yusuke Ohsaki, Toshiro Sato, Tomoko Goto, Michio Komai

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35 Citations (Scopus)


Background: 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. Methods. Eight-week-old male Wistar rats were fed a diet supplemented with menaquinone-4 (MK-4, 75 mg/kg diet), one of the predominant K2vitamins 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 M) at several time points. Testosterone and cellular protein levels were analyzed with respect to their effects on steroidogenesis. Results: 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 -glutamylcarboxylation. Conclusions: 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.

Original languageEnglish
Article number158
JournalLipids in Health and Disease
Publication statusPublished - 2011


  • I-10 cells
  • menaquinone-4
  • protein kinase A
  • testis
  • testosterone
  • vitamin K


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