Vitamin B 6 Modifies the Immune Cross-Talk between Mononuclear and Colon Carcinoma Cells ( vitamin B 6 / PBMC / cytokines / colon cancer cells / cross-talk / cell viability )

The role of vitamin B6 as a key component in a number of biological events has been well established. Based on the relationship between chronic inflammation and carcinogenesis on the one hand, and the interaction between immune and cancer cells expressed by modulated cytokine production on the other hand, the aim of the present work was to examine the possibility that vitamin B6 affects cancer development by an interference in the cross-talk between human peripheral blood mononuclear cells (PBMC) and those from two colon carcinoma cell lines. Both non-stimulated PBMC and mononuclear cells induced for cytokine production by HT-29 and RKO cells from human colon carcinoma lines were incubated without and with 4, 20 and 100 μg/ml of pyridoxal hydrochloride (vitamin B6) and secretion of TNF-α, IL-1β, IL-6, IFN-γ, IL-10, and IL-1ra was examined. Vit B6 caused a dose-dependent decrease in production of all cytokines examined, except for that of IL-1ra. The results indicate that vitamin B6 exerts an immunomodulatory effect on human PBMC. The finding that production of inflammatory cytokines is more pronounced when PBMC are in contact with malignant cells and markedly inhibited by the vitamin suggests an additional way by which vitamin B6 may exert its carcinopreventive effect. Received October 15, 2015. Accepted December 27, 2015. Corresponding author: Hanna Bessler, Laboratory for Immuno logy and Hematology Research, Rabin Medical Center, Hasharon Hospital, 7 Keren Kayemet St, Petah Tiqva, Israel. Phone: (+972) 3-9372480; Fax: (+972) 3-9372388; e-mail: hannab@clalit.org. il Abbreviations: CM – complete medium, FCS – foetal calf serum, HT-29 and RKO – human colon cancer cell lines, IFN-γ – interferon γ, IL – interleukin, MEM – modified Eagle’s medium, PBMC – peripheral blood mononuclear cells, PBS – phosphatebuffered saline, PLP – plasma pyridoxal 5’-phosphate, TNF-α – tumour necrosis factor α, vit B6 – vitamin B6, XTT kit – cell proliferation assay kit. Introduction Pyridoxal 5’-phosphate, the biologically active form of vitamin B6 (vit B6), is a coenzyme that takes an essential part in one-carbon metabolism and in a number of enzymatic activities associated with synthesis and degradation of amino acids, biogenic amines, lipids and carbohydrates, properties thoroughly reviewed by Wu and Lu (2012) and Cellini et al. (2014). Vit B6 is actively integrated with the function of the nervous, immune and endocrine systems and it is not unexpected that its deficiency may be associated with a number of pathological conditions, including epileptic encephalopathy, cardiovascular diseases, rheumatoid arthritis, diabetes, as well as a rather long list of rare inherited diseases (Sakakeeny et al., 2012; Ahmad et al., 2013; Galluzzi et al., 2013; Cellini et al., 2014). A substantial number of studies have shown that vitamins in general, and B6 in particular, are closely connected with prevention and even amelioration of infections. Utilizing the C-reactive protein level and applying precise measurements of pyridoxal-5’-phosphate, Moris et al. (2010) have shown that higher vit B6 intake exerts a marked protective effect against infections. Similar results were obtained by Sakakeeny et al. (2012) in humans and by Selhub et al. (2013), who have reported that in mice with inflammatory bowel disease, vit B6 restriction has been associated with increased severity of their disease. According to the authors, B6 supplementation may alleviate the inflammatory process in the colon, observations that have been supported by other studies (Morris et al., 2010; Benight et al., 2011). Since the link between chronic bowel inflammation and colon cancer seems to be well established, studies have been conducted to elucidate the role of vit B6 in reducing the risk of cancer. In a meta-analysis of prospective studies, Larsson et al. (2010) have shown that for every 100-pmol/ml increase in the blood pyridoxal 5’-phosphate level, the risk of colorectal cancer decreased by 49 %. Komatsu et al. (2003) reported that mice fed with different amounts of pyridoxine showed a dose-dependent decrease in the appearance and number of colon tumours with an increase of vit B6 intake.