Menaquinone‐4 Enhances Steroidogenesis in Testis Derived Tumor Cells Via the Elevation of cAMP Level

Abstract

Naturally existing vitamin K consists of vitamins K1 and K2. Menaquinone-4 (MK-4), an analog of vitamin K2 and a product of vitamin K1 metabolism, can be detected in several organs, including the testis; however, the function of MK-4 in these tissues has not been well characterized. Recent studies have suggested that vitamin K is involved in enhancing protein kinase A (PKA) activity in several cell types, thus regulating numerous PKA-dependent biological processes. To highlight the effect of vitamin K, we focused on its role in the steroidogenic pathway. Experiments on vitamin K-deficient rats revealed a reduced expression of genes involved in the biosynthesis of cholesterol and steroid hormones in the testis. Moreover, compared with control animals, rats fed on MK-4 diet presented significantly higher testosterone levels in the plasma and testis. These results suggest that vitamin K is involved in the steroidogenic pathway in the testis. Testosterone levels were found to increase in a dose-dependent manner also in cell-based experiments upon addition of MK-4, but such an effect was not observed in vitamin K1 levels. Furthermore, the effect of MK-4 on testosterone production was abolished by the specific PKA inhibitor H89, thus confirming the regulatory role of MK-4 on PKA activation. Here, we describe how MK-4 modulates PKA activation by enhancing intracellular 3′,5′-cyclic adenosine monophosphate (cAMP) levels in testisderived I-10 cells. The presented evidence supports the role of MK-4 in cAMP/PKA signaling and steroidogenesis.

Menaquinone-4 Amplified Glucose-Stimulated Insulin Secretion in Isolated Mouse Pancreatic Islets and INS-1 Rat Insulinoma Cells

“…For the isolation of pancreatic islets from mice, collagenase (Type V, Sigma-Aldrich) with Krebs–Ringer bicarbonate HEPES (KRBH) buffer [1.29 mM NaCl, 5 mM NaHCO 3 , 4.7 mM KCl, 1.2 mM KH 2 PO 4 , 1.2 mM MgSO 4 , 10 mM HEPES (pH 7.4), and 0.1% bovine serum albumin (BSA)] was injected into the pancreas via the common bile duct as described previously [60], followed by enzymatic digestion of the pancreas in the collagenase solution at 37 °C for 15 min in a flask. Next, mechanical digestion was proceeded by gentle pipetting to separate islets from pancreatic tissue.…”

Menaquinone-4 Suppresses Lipopolysaccharide-Induced Inflammation in MG6 Mouse Microglia-Derived Cells by Inhibiting the NF-κB Signaling Pathway

“…Increasing evidence suggests that MK-4 has several unique biological functions such as mediating apoptosis in several cancer cells [20,21,22,23,24,25], promoting growth factor of neuron-like cells [26], enhancing testosterone production [27,28], modulating bile acid synthesis and glucose homeostasis [29], and regulating specific genes via activation of the PXR nuclear receptor [30,31]. Furthermore, vitamin K administration, especially MK-4, was also found to suppress the peripheral inflammation in LPS-induced models [32,33].…”