Enhancement effects of vitamin K1 (phylloquinone) or vitamin K2 (menaquinone-4) on intestinal alkaline phosphatase activity in rats

Abstract

Alkaline phosphatase (ALP) hydrolyzes a variety of monophosphate esters into inorganic phosphoric acid and alcohol at a high optimal pH, and is thought to play an important role in phosphate metabolism. Intestinal ALP, located at the brush border of intestinal epithelial cells, is known to be affected by several kinds of nutrients, but little is known about the physiological function of intestinal ALP. Vitamin K is an essential cofactor for the post-translational carboxylation of glutamate residues into gamma-carboxy glutamate (Gla). Recently, novel functions of vitamin K have been clarified, but no data exist on the relation between vitamin K and intestinal ALP. The aim of this study was to examine the effects of both vitamin Ks (K1: phylloquinone, and K2: menaquinone) on ALP activity. Sprague-Dawley rats (6-wk-old) were divided into three groups: a control, phylloquinone (PK: 600 mg/kg diet), or menaquinone-4 (MK-4: 600 mg/kg diet) diet group. After 3 mo of feeding, we measured intestinal ALP activity by dividing it into five segments. In each segment, both PK and MK-4 increased intestinal ALP activity. The levels of intestinal ALP activity in the duodenum and proximal jejunum from the PK group were significantly higher than in the control group (p<0.05). Moreover, the levels of intestinal ALP activity from the proximal jejunum and distal ileum of the intestine in the MK group were significantly higher than in the control group (p<0.05). In this study, we clarified for the first time that both vitamin K1 and K2 as nutritional factors enhance intestinal ALP activity.