Vitamin B6 suppresses growth and expression of albumin gene in a human hepatoma cell line HepG2

Effect of Trace Minerals and B Vitamins on the Proliferation/Cytotoxicity and Mineralization of a Gilthead Seabream Bone-Derived Cell Line

Trace minerals and vitamins are known modulators of bone metabolism, and dietary optimization of these components may improve skeletal development and reduce the occurrence of skeleton deformities in farmed fish. As for larval stages, mineral and water-soluble vitamin nutrition requirements are lacking in research efforts and knowledge is scarce. An in vitro cell system developed from gilthead seabream vertebra and capable of mineralization was used to assess the effect of B vitamins (thiamin and pyridoxine) and trace minerals (copper, manganese, and zinc in a sulfated and chelated form) on cell proliferation and extracellular matrix (ECM) mineralization. Dependent on dose, inhibition of cellular proliferation and/or cytotoxic effects was observed for all nutrients tested and LD₅₀ values were determined: copper, 67.4-69.5 ppm; manganese, 20.9-29.8 ppm; zinc, 37.1-42.8 ppm in sulfated and chelated form respectively; thiamin, 6273 ppm; pyridoxine, 14226 ppm. ECM mineralization was enhanced by mineral (dose and form dependent) and vitamin (dose dependent) supplementation, at non-toxic concentrations below the determined LD_50s. This in vitro work confirmed the mineralogenic action of trace minerals and water-soluble vitamins and provided valuable insights for subsequent in vivo nutritional trials.

Vitamins B6 and cancer

Epidemiologic and laboratory animal studies have suggested that the availability of vitamin B6 modulates cancer risk. The means by which B6 mediates this effect is not known with any surety but it has been reported that high dietary vitamin B6 attenuates and low dietary vitamin B6 increases the risk of cancer. In fact vitamin B6 is widely distributed in foods and overt deficiency of this vitamin is not common. Nevertheless, marginal or secondary vitamin B6 deficiency, which might have an adverse effect on carcinogenesis, is rather common especially among old adults and alcoholics. This chapter addressed currently available information regarding the relationship between vitamin B6 and cancer.

Vitamin B6Suppresses Growth of the Feline Mammary Tumor Cell Line FRM

Growth of FRM cells was inhibited by the addition of pyridoxine in a dose-dependent manner. Use of 5 mM pyridoxine caused an almost complete arrest of cell growth. Pyridoxal was as effective as pyridoxine, but pyridoxamine showed weak inhibitory action. Electron-microscopic examination of control cells revealed large nuclei and cellular membranes with villi, but, in pyridoxine-treated cells, condensed or degraded nuclei were observed. Many vacuoles and cholesterol crystals were widely distributed inside the cellular membrane of pyridoxine-treated cells. One of the vacuoles was identified as a lipid droplet. The DNA ladder was observed in the pyridoxine-treated cells. It is suggested that pyridoxine treatment of FRM cells causes cytolysis of cells by apoptosis.

Effects of vitamin B6 metabolism on oncogenesis, tumor progression and therapeutic responses

Pyridoxal-5'-phosphate (PLP), the bioactive form of vitamin B6, reportedly functions as a prosthetic group for >4% of classified enzymatic activities of the cell. It is therefore not surprising that alterations of vitamin B6 metabolism have been associated with multiple human diseases. As a striking example, mutations in the gene coding for antiquitin, an evolutionary old aldehyde dehydrogenase, result in pyridoxine-dependent seizures, owing to the accumulation of a metabolic intermediate that inactivates PLP. In addition, PLP is required for the catabolism of homocysteine by transsulfuration. Hence, reduced circulating levels of B6 vitamers (including PLP as well as its major precursor pyridoxine) are frequently paralleled by hyperhomocysteinemia, a condition that has been associated with an increased risk for multiple cardiovascular diseases. During the past 30 years, an intense wave of clinical investigation has attempted to dissect the putative links between vitamin B6 and cancer. Thus, high circulating levels of vitamin B6, as such or as they reflected reduced amounts of circulating homocysteine, have been associated with improved disease outcome in patients bearing a wide range of hematological and solid neoplasms. More recently, the proficiency of vitamin B6 metabolism has been shown to modulate the adaptive response of tumor cells to a plethora of physical and chemical stress conditions. Moreover, elevated levels of pyridoxal kinase (PDXK), the enzyme that converts pyridoxine and other vitamin B6 precursors into PLP, have been shown to constitute a good, therapy-independent prognostic marker in patients affected by non-small cell lung carcinoma (NSCLC). Here, we will discuss the clinical relevance of vitamin B6 metabolism as a prognostic factor in cancer patients.

Modulation of gene expression by vitamin B6

The physiologically active form of vitamin B6, pyridoxal 5'-phosphate (PLP), is known to function as a cofactor in many enzymic reactions in amino acid metabolism. Recent studies have shown that, apart from its role as a coenzyme, PLP acts as a modulator of steroid hormone receptor-mediated gene expression. Specifically, elevation of intracellular PLP leads to a decreased transcriptional response to glucocorticoid hormones, progesterone, androgens, and oestrogens. For example, the induction of cytosolic aspartate aminotransferase (cAspAT) in rat liver by hydrocortisone is suppressed by the administration of pyridoxine. The suppression of the cAspAT induction by pyridoxine is caused by a decrease in the expression of the cAspAT gene, which is brought about by inactivation of the binding activity of the glucocorticoid receptor to the glucocorticoid-responsive element in the regulatory region of the cAspAT gene. Vitamin B6 has recently been found to modulate gene expression not only for steroid hormone-responsive or PLP-dependent enzymes but also for steroid- and PLP-unrelated proteins such as serum albumin. Albumin gene expression was found to be modulated by vitamin B6 through a novel mechanism that involves inactivation of tissue-specific transcription factors, such as HNF-1 or C/EBP, by direct interaction with PLP in a similar manner to glucocorticoid receptor. Enhancement of albumin gene expression in the liver by an increased supply of amino acids can be explained by elevated binding of HNF-1 and C/EBP to their DNA-binding sites which, in turn, is caused by a decrease in the intracellular level of PLP by the increased amino acid supply. These findings that vitamin B6 acts as a physiological modulator of gene expression add a new dimension to the hitherto recognized function of vitamin B6 as a cofactor of enzyme action.

Prediagnostic plasma pyridoxal 5'-phosphate (vitamin b6) levels and invasive breast carcinoma risk: the multiethnic cohort

BACKGROUND

Evidence from experimental and epidemiologic studies suggests that vitamin B6 may reduce the risk of breast cancer.

METHODS

We examined the association of prediagnostic plasma concentrations of pyridoxal-5'-phosphate (PLP), an active form of vitamin B6, with postmenopausal breast cancer risk in a case-control study nested in the multiethnic cohort in Hawaii and Southern California, including 706 cases and 706 controls matched on date of birth, ethnicity, study site, date of blood draw, time of blood draw, hours of fasting before blood draw, and use of menopausal hormones. OR and 95% confidence intervals (CI) were calculated using conditional logistic regression models.

RESULTS

Women with plasma PLP concentrations in the highest quartile had a 30% reduced risk of invasive breast cancer (CI: 0.50-0.98) as compared with the women in the lowest PLP quartile (P for trend = 0.02). The association seemed to be limited in cases with hormone receptor-positive tumors (P for heterogeneity = 0.04); and remained unchanged in the analysis restricted to women with blood samples collected more than one year before cancer diagnosis (OR = 0.69; CI: 0.48-0.99; P for trend = 0.03).

CONCLUSIONS

These data suggest that higher circulating levels of vitamin B6 are associated with a reduced risk of invasive postmenopausal breast cancer.

IMPACT

These results, in combination with information from two other prospective studies, suggest a role for vitamin B6 in the prevention of postmenopausal breast cancer. Additional studies are needed to further investigate potential heterogeneity of the vitamin B6 association with breast cancer risk by tumor hormone receptor status.

The expression and activity of cystathionine-γ-lyase and 3-mercaptopyruvate sulfurtransferase in human neoplastic cell lines

The expression and activity of cystathionine γ-lyase (CST) and 3-mercaptopyruvate sulfurtransferase (MPST) were investigated in the human neoplastic cells lines: astrocytoma U373, neuroblastoma SH-SY5Y, melanoma A375, and melanoma WM35. Gene expression analysis demonstrated that the investigated neoplastic cells showed the expression of MPST and what is particularly interesting, the expression of CST. The presence of CST in these cells was confirmed using RT-PCR and western blot analysis. However, in U373 cells, a very low activity of CST was detected. In all the investigated cell lines, the activity of MPST was higher than that of CST, which suggests that in these cells, the main pathway of sulfane sulfur formation is the MPST-catalyzed reaction. RP-HPLC analysis showed a large disparity between the level of cystathionine and GSH in the investigated neoplastic cells. In SH-SY5Y cells, the low level of GSH and low GSH/GSSG ratio corresponded with the highest CST activity. Further investigations could aim at verifying whether the stimulation of CST, at the level of protein or gene expression, could change the proliferation of neoplastic cells.

Pyridoxal phosphate inhibits pituitary cell proliferation and hormone secretion

Pyridoxal phosphate (PLP), a bioactive form of pyridoxine, dose-dependently (10-1000 microm) inhibited cell proliferation in rat pituitary MMQ and GH3 cells and in mouse AtT-20 cells. After 4 d, MMQ cell numbers were reduced by up to 81%, GH3 cell numbers were reduced by up to 64% (P < 0.05), and AtT-20 cell numbers were reduced by up to 90%. Cell proliferation rates recovered and dose-dependently reverted to control levels after PLP withdrawal. After 4 d, PLP (400 and 1000 microm) decreased [3H]thymidine incorporation by up to 71% (P < 0.05). PLP (400-1000 microm) reduced GH3 cell GH and prolactin secretion and AtT-20 cell ACTH secretion (adjusted for cell number) by approximately 70% after 2 d. The 100 microm PLP also inhibited prolactin secretion (65%, P < 0.05) in primary rat pituitary cells treated for 2 d. PLP decreased the percentage of AtT-20 and GH3 cells in S phase and increased those in G0-G1 phase. Furthermore, PLP induced AtT-20 and GH3 cell apoptosis (28 vs. 6, P < 0.05; 26 vs. 3, P < 0.05, respectively) and dose-dependently reduced content of the antiapoptosis gene Bcl-2. These results indicate that pharmacological doses of PLP inhibit pituitary cell proliferation and hormone secretion, in part mediated through PLP-induced cell-cycle arrest and apoptosis. Pyridoxine may therefore be appropriate for testing as a relatively safe drug for adjuvant treatment of hormone-secreting pituitary adenomas.

All-trans retinoic acid down-regulates human albumin gene expression through the induction of C/EBPbeta-LIP

ATRA (all-trans retinoic acid), which is a major bioactive metabolite of vitamin A and a potent regulator of development and differentiation, mediates down-regulation of the human albumin gene. However, the mechanism of ATRA-mediated down-regulation is not well understood. In the present study, deletion analysis and luciferase assays demonstrate that ATRA causes a marked decrease in the activity of the albumin promoter, the region between nt -367 and -167 from the transcription start site, where C/EBP (CCAAT/enhancer-binding protein)-binding sites are tightly packed, is indispensable for ATRA-mediated down-regulation. ChIP (chromatin immunoprecipitation) assays revealed that in vivo binding of C/EBPalpha to the region markedly decreases upon incubation with ATRA, whereas ATRA treatment marginally increases the recruitment of C/EBPbeta. We found that ATRA has the ability to differentially and directly induce expression of a truncated isoform of C/EBPbeta, which is an LIP (liver-enriched transcriptional inhibitory protein) that lacks a transactivation domain, and to increase the binding activity of C/EBPbeta-LIP to its response element. Overexpression of C/EBPbeta-LIP negatively regulates the endogenous expression of albumin, as well as the activity of the albumin promoter induced by C/EBP transactivators such as C/EBPalpha and full-length C/EBPbeta. In conclusion, we propose a novel model for down-regulation of the albumin gene, in which ATRA triggers an increase in the translation of C/EBPbeta-LIP that antagonizes C/EBP transactivators by interacting with their binding sites in the albumin promoter.

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.

Pyridoxal 5'-phosphate is a selective inhibitor in vivo of DNA polymerase alpha and epsilon

Vitamin B(6) compounds such as pyridoxal 5(')-phosphate (PLP), pyridoxal (PL), pyridoxine (PN), and pyridoxamine (PM), which reportedly have anti-angiogenic and anti-cancer effects, were thought to be inhibitors of some types of eukaryotic DNA polymerases. PL moderately inhibited only the activities of calf DNA polymerase alpha (pol alpha), while PN and PM had no inhibitory effects on any of the polymerases tested. On the other hand, PLP, a phosphated form of PL, was potentially a strong inhibitor of pol alpha and epsilon from phylogenetic-wide organisms including mammals, fish, insects, plants, and protists. PLP did not suppress the activities of prokaryotic DNA polymerases such as Escherichia coli DNA polymerase I and Taq DNA polymerase, or DNA-metabolic enzymes such as deoxyribonuclease I. For pol alpha and epsilon, PLP acted non-competitively with the DNA template-primer and competitively with the nucleotide substrate. Since PL was converted to PLP in vivo after being incorporated into human cancer cells, the anti-angiogenic and anti-cancer effects caused by PL must have been caused by the inhibition of pol alpha and epsilon activities after conversion to PLP.

Vitamin B6-mediated suppression of colon tumorigenesis, cell proliferation, and angiogenesis (review)

This review describes current research on the preventive effect of dietary vitamin B(6) against colon tumorigenesis and its possible mechanisms. Studies in cell culture have demonstrated that high levels of vitamin B(6) suppress growth of some cancer cells. From these studies it has been considered that supraphysiological doses of vitamin B(6) suppress tumor growth and metastasis. However, recent rodent study has indicated that azoxymethane-induced colon tumorigenesis in mice is suppressed by moderate doses of dietary vitamin B(6.) Epidemiological studies also support an inverse relationship between vitamin B(6) intake and colon cancer risk. Potential mechanisms underlying the preventive effect of dietary vitamin B(6) have been suggested to include the suppression of cell proliferation, oxidative stress, nitric oxide (NO) synthesis, and angiogenesis.

Antitumor effect of vitamin B6 and its mechanisms

Epidemiological studies have reported an inverse association between vitamin B(6) intake and colon cancer risk. Our recent study has been conducted to examine the effect of dietary vitamin B(6) on colon tumorigenesis in mice. Mice were fed diets containing 1, 7, 14 or 36 mg/kg pyridoxine for 22 weeks, and given a weekly injection of azoxymethane (AOM) for the initial 10 weeks. Compared with the 1 mg/kg pyridoxine diet, 7, 14 and 35 mg/kg pyridoxine diets significantly suppressed the incidence and number of colon tumors, colon cell proliferation and expressions of c-myc and c-fos proteins. Supplemental vitamin B(6) lowered the levels of colonic 8-hydroxyguanosine (8-OHdG), 4-hydroxy-2-nonenal (4-HNE, oxidative stress markers) and inducible nitric oxide (NO) synthase protein. In an ex vivo serum-free matrix culture model using rat aortic ring, supplemental pyridoxine and pyridoxal 5'-phosphate (PLP) had antiangiogenic effect. The results suggest that dietary vitamin B(6) suppresses colon tumorigenesis by reducing cell proliferation, oxidative stress, NO production and angiogenesis.

Vitamin B-6-supplemented diets compared with a low vitamin B-6 diet suppress azoxymethane-induced colon tumorigenesis in mice by reducing cell proliferation

Male ICR mice were examined for the effect of vitamin B-6 [pyridoxine (PN) HCl] on azoxymethane-induced colon tumorigenesis. Mice were fed the diets containing 1, 7, 14 or 35 mg PN HCl/kg for 22 wk, and given a weekly injection of azoxymethane (5 mg/kg body) for the initial 10 wk. Compared with the 1 mg PN HCl/kg diet, 7, 14 and 35 mg PN HCl/kg diets significantly suppressed the incidence and number of colon tumors, colon cell proliferation and expressions of c-myc and c-fos proteins. For some variables, 14 and 35 mg PN HCl/kg diets were more effective than the 7 mg/kg diet. Supplemental vitamin B-6 had no influence on the number of colon apoptotic cells. The results suggest that elevating dietary vitamin B-6 suppresses colon tumorigenesis by reducing cell proliferation.