High dose of pyridoxine induces IGFBP-3 mRNA expression in MCF-7 cells and its induction is inhibited by the p53-specific inhibitor pifithrin-α.

It has been reported that supplementation with high-dose vitamin B(6) (B(6)) exerts antitumor effects in rodent models of cancer. However, the mechanism of these effects remains poorly understood. High-dose B(6) also suppresses cell proliferation and induces apoptosis of human breast adenocarcinoma MCF-7 cells. Based on preliminary experiments using DNA microarray analyses, we hypothesized that high-dose pyridoxine (PN) might induce IGF-binding protein-3 (IGFBP-3) expression in MCF-7 cells. In this study, we investigated IGFBP-3 induction by 3 or 10 mM PN using a quantitative real-time PCR method. We found that the induction reached a maximum of 24-fold with 10 mM PN for 72 h compared with non-treated cells. The induction of IGFBP-3 by PN was inhibited by a p53-specific inhibitor, pifithrin-α, in a dose-dependent manner, but was not affected by PD169316 (MAPK inhibitor), AS601245 (c-Jun N-terminal kinase inhibitor) or SL327 (MEK1/2 inhibitor). High-dose PN did not induce p53 mRNA expression. The IGFBP-3 induction by PN seemed to be related to p53 activation.

Promoting effects of Chinese pangolin and wild pink medicines on the mammary gland development in immature mice.

The effects of the mixture of crude aqueous extracts from Chinese pangolin and wild pink (C+P), traditional Chinese medicine, on the proliferation and differentiation of mammary gland epithelium in intact and ovariectomized immature mice were investigated by light and electron microscopy and BrdU immunohistochemistry. Although there were no significant differences in mammary gland fat pad and parenchyma areas between the intact experimental groups, the numbers of duct branchings and buds were significantly larger in the C+W treated mice than in the control mice. The ratio of BrdU immunopositive cells to total epithelial cells was higher in C+W treated intact mice. Ultrastructurally, epithelial cells of the mammary buds and ducts possessed an oval and lucent nucleus, and ribosomes increased in number or developed to a greater degree in C+W treated intact mice than in the control mice. Conversely, there were no significant differences in any measurements of mammary gland between the experimental groups of ovariectomized mice. BrdU immunoreactive cells were never seen and the ultrastructure of mammary epihelial cells indicated the inactive cell phase in both ovariectomied mice. In comparison between the intact and overiectomized mice, the mammary fat pad area was larger in the ovariectomized mice than in the intact mice, although another four measurements were larger in the intact groups. These observations suggest that administration with C+W could promote the development of mammary glands via ovary in immature mice.

Localization of polypyrimidine-tract-binding protein is involved in the regulation of albumin synthesis by branched-chain amino acids in HepG2 cells.

Long-term supplementation of branched-chain amino acids (BCAA) improves hypoalbuminemia in patients with cirrhosis. Our previous findings have suggested that the binding of polypyrimidine-tract-binding protein (PTB) to rat albumin mRNA attenuates its translation. The aim of the present study was to investigate the role of PTB in the regulation of albumin synthesis by BCAA in human hepatoma cells. HepG2 cells were cultured in a medium containing no amino acids (AA-free medium), a medium containing only 1 amino acid (a BCAA: valine, leucine or isoleucine) or a medium containing all 20 amino acids (AA-complete medium). HepG2 cells cultured in AA-complete medium secreted much more albumin than cells cultured in AA-free medium, with no difference in albumin mRNA levels. In cells cultured in AA-free medium, nuclear export of PTB was observed, and the level of the albumin mRNA-PTB complex was greater than in cells cultured in AA-complete medium. Addition of amino acids stimulated nuclear import of PTB. However, addition of amino acids with rapamycin inhibited the nuclear import of PTB. The addition of leucine, but not of valine or isoleucine, to AA-free medium increased albumin secretion and stimulated the nuclear import of PTB. These data indicate that the mammalian target of rapamycin is involved in the regulation of PTB localization and that leucine promotes albumin synthesis by inhibiting the formation of the albumin mRNA-PTB complex.

Antioxidant activity of vitamin B6 delays homocysteine-induced atherosclerosis in rats.

Elevated plasma homocysteine is a risk factor for atherosclerotic disease. In the present study, we have examined whether the oxidative stress due to a low level of vitamin B6 accelerates the development of homocysteine-induced atherosclerosis in rats. First, the effect of homocysteine thiolactone intake (50 mg/kg per d) on vascular integrity, lipid peroxide concentration, endothelial NO synthase (eNOS) expression and biochemical profiles was examined at day 1, day 21 and day 42 (five rats per group). The histochemical staining of the rat aorta showed no change at day 1 and day 21, but the subendothelial space was observed to be enlarged in rat aorta at day 42 with exposure to homocysteine thiolactone. Expression of eNOS was observed in rat aorta at day 42, but not at day 1 and day 21. Serum lipid peroxide concentration and biochemical profiles including glucose cholesterol and triacylglycerol showed no change at any day. Second, the effect of homocysteine thiolactone intake in the presence and absence of vitamin B6 on vascular integrity was examined at day 1 and day 14 (five rats per group). Aortic lesions were observed in vitamin B6-deficient rat aorta at day 14 but not in vitamin B6-supplemented rats. The expression of eNOS was also observed in vitamin B6-deficient rat aorta at day 14. Serum lipid concentrations of the vitamin B6-deficient group significantly increased compared with concentrations of the vitamin B6-supplemented group, though serum concentration of homocysteine did not change between both groups. These results suggest that the oxidative stress caused by a low level of vitamin B6 accelerates the development of homocysteine-induced atherosclerosis in rats.

Effect of high dose of pyridoxine on mammary tumorigenesis.

The effect of high-dose pyridoxine (PN) on mammary tumorigenesis was examined in female Sprague-Dawley rats. The first mammary tumors appeared between 84 and 90 days after 7,12-dimethylbenzanthracene treatment. There was no effect of PN level on tumor incidence at 90 days but at 98, 104, and 111 days. Tumor incidence was lower in the high-dose group (35 mg PN/kg diet) compared with the controls (7 mg PN/kg diet). All tumors were identified as adenocarcinoma and most as papillary type. The number of microcarcinomas in mammary glands of the 35-mg PN group tended to be reduce than that of the 7-mg group. The number of proliferating Ki67-positive cells was significantly reduced by supplementation with PN.

Dietary vitamin B6 suppresses colon tumorigenesis, 8-hydroxyguanosine, 4-hydroxynonenal, and inducible nitric oxide synthase protein in azoxymethane-treated mice.

Recently we reported that the supplementation of vitamin B6 to low vitamin B6 diet caused suppression in colon tumorigenesis and cell proliferation of azoxymethane-treated mice in a dose-dependent manner among 1, 7, and 14 mg pyridoxine HCl/kg diet (J. Nutr. 131: 2204-2207, 2001). To examine the mechanism of the anticolon tumor effect of vitamin B6, male ICR mice were fed the diet containing 1, 7, 14, and 35 mg pyridoxine HCl/kg diet for 22 wk and simultaneously given a weekly injection of azoxymethane for an initial 10 wk. The supplementation of vitamin B6 to a low vitamin B6 diet (1 mg pyridoxine HCl/kg) suppressed the levels of colonic 8-hydroxyguanosine and 4-hydroxynonenal and inducible nitric oxide synthase protein. The results suggest that the preventive effect of vitamin B6 against colon tumorigenesis is at least in part mediated by reducing oxidative stress and nitric oxide production.