title: Menaquinone-4 enhances testosterone production in rats and testis-derived tumor cells.
abstract: 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 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.
  
  
  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 γ-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.
authors.affiliation: Laboratory of Nutrition, Graduate School of Agricultural Science, Tohoku University, Sendai 981-8555, Japan.
authors.forename: Asagi
authors.initials: A
authors.lastname: Ito
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Shirakawa
authors.forename: Naofumi
authors.initials: N
authors.lastname: Takumi
authors.forename: Yoshihiko
authors.initials: Y
authors.lastname: Minegishi
authors.forename: Ai
authors.initials: A
authors.lastname: Ohashi
authors.forename: Zakir H
authors.initials: ZH
authors.lastname: Howlader
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Ohsaki
authors.forename: Toshiro
authors.initials: T
authors.lastname: Sato
authors.forename: Tomoko
authors.initials: T
authors.lastname: Goto
authors.forename: Michio
authors.initials: M
authors.lastname: Komai
mesh_terms: D000818:Animals; D019735:Carbon-Carbon Ligases / Q000037:antagonists & inhibitors; D045744:Cell Line, Tumor; D002786:Cholesterol Side-Chain Cleavage Enzyme / Q000378:metabolism; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism; D007985:Leydig Cells / Q000187:drug effects / Q000378:metabolism*; D008099:Liver / Q000187:drug effects / Q000378:metabolism; D008297:Male; D051379:Mice; D010766:Phosphorylation / Q000187:drug effects; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D051381:Rats; D017208:Rats, Wistar; D013047:Specific Pathogen-Free Organisms; D013737:Testis / Q000187:drug effects / Q000378:metabolism*; D013739:Testosterone / Q000097:blood / Q000378:metabolism*; D014018:Tissue Distribution; D015854:Up-Regulation / Q000187:drug effects*; D010837:Vitamin K 1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D024482:Vitamin K 2 / Q000031:analogs & derivatives* / Q000493:pharmacokinetics / Q000494:pharmacology
chemical_list: D017362:Cyclic AMP Response Element-Binding Protein; D047428:Protein Kinase Inhibitors; D024482:Vitamin K 2; C030814:menatetrenone; D013739:Testosterone; D010837:Vitamin K 1; D002786:Cholesterol Side-Chain Cleavage Enzyme; D017868:Cyclic AMP-Dependent Protein Kinases; D019735:Carbon-Carbon Ligases; C020660:glutamyl carboxylase