Research articleDietary vitamin B6 intake modulates colonic inflammation in the IL10−/− model of inflammatory bowel disease☆,☆☆
Introduction
Vitamin B6 is a water soluble vitamin that exists in several forms including pyridoxal, pyridoxine and pyridoxamine. All three forms may be phosphorylated; however, pyridoxal 5’-phosphate (PLP) is the biologically active form, serving as a cofactor for over 140 distinct enzyme reactions that are involved in the metabolism of proteins, lipids and carbohydrates, the synthesis or metabolism of hemoglobin, neurotransmitters, nucleic acids, one carbon units, immune modulatory metabolites and others [1]. The current RDA for B6 is 1.3 mg/day for men and 1.1 mg/day for women. Plasma concentrations of ≥40 nmol/L total B6 or ≥30 nmol/L PLP [2] are considered to reflect adequacy, and insufficiency is variously defined as either <30- or <20-nmol/L PLP. Although severe vitamin B6 deficiency is rare, low plasma PLP (<20 nmol/L) occurs in 10–16% of the adult US population, depending on age, sex and ethnicity [3].
Over the last decade, it has become quite apparent that a robust relationship exists between vitamin B6 and inflammation, but the mechanistic nature of that relationship remains ill defined. Investigations by our group began with the observation that patients with rheumatoid arthritis (RA) displayed reduced plasma PLP concentrations compared to healthy controls and that, amongst RA patients, PLP was inversely related to the severity of disease and markers of inflammation [4]. Later, within the Framingham Study, we found that plasma PLP was approximately 35% lower in those with elevated C-reactive protein (CRP ≥6 mg/L), an acute-phase reactant, than those with normal CRP (<6 mg/L)[5]. Our analysis of the National Health and Nutrition Examination Survey dataset similarly revealed an inverse relationship between blood levels of B6 and inflammation and, interestingly, also suggested a potential two-way relationship between the two. Overall, the likelihood of having elevated CRP decreased with increasing plasma PLP; however, those with elevated CRP also had lower plasma PLP for a specific B6 intake than those with low CRP, that is, a higher dietary intake of vitamin B6 is required to achieve a set plasma PLP concentration when inflammatory markers are elevated, possibly because PLP is drawn out of the plasma into sites of active inflammation [6]. Using a more comprehensive inflammatory score (consisting of CRP, fibrinogen, IL-6, TNFα, TNFR-2, osteoprotegerin, P-selectin, CD40L, ICAM-1, MCP-1, myeloperoxidase, LPL-A2 mass, LPL-A2 activity and isoprostanes indexed to creatinine.) applied to the Framingham Offspring Cohort, we confirmed that those with elevated inflammatory markers require a higher dietary B6 intake to achieve any given plasma PLP concentration than those with low/normal inflammation [7].
Similar to earlier observations in RA, Saibeni et al. [8] report that plasma PLP concentrations were significantly lower in patients with inflammatory bowel disease (IBD) than controls and that the prevalence of low PLP (<20 nmol/L) was significantly higher amongst patients with active compared to quiescent disease (26.9%, vs. 2.9%; P≤.001).
In addition to data showing that inflammation can deplete plasma vitamin B6, Benight et al. report that B6 inadequacy can attenuate inflammation [9]. Using the dextran sodium sulfate (DSS) model of acute and severe colitis in mice, they demonstrated that the consumption of a diet lacking vitamin B6 (and B12) reduced the risk of mortality as well as disease activity score, weight loss and mucosal expression of iNOS, TNF-α and IL-10 compared to mice fed with adequate B6. It remains to be determined what effect, if any, vitamin B6 supplementation has on disease severity in IBD patients and rodent models. Furthermore, it is not known whether these effects of short-term B6 restriction in an acute colitis model can be recapitulated with long-term inadequacy in chronic IBD models.
Therefore, we sought to test the effect of both vitamin B6 inadequacy and supplementation on the severity of the inflammatory phenotype in a rodent IBD model.
Section snippets
Methods
All animal procedures were approved by the institutional review board of the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University.
IL10 knockout mice (C3Bir.129P2(B6)-Il10tm1Cgn/Lt) were purchased from Jackson laboratory (Bar Harbor, ME, USA). The supplier's colony is maintained in isolators “under conditions which preserve the presence of potentially strain-unique enteric flora required for the development of IBD.” Analysis of fecal samples collected from random mice
Results
After 12 weeks of dietary intervention, plasma PLP concentrations were significantly different between dietary groups (P<.0001). Compared to mice in the control (replete) group, plasma PLP was 85% lower in the deficient mice and 30% higher in supplemented mice, respectively (P<.05). Similarly, colonic PLP content declined in a step-wise fashion with decreasing dietary intake (Fig. 2A). PLP concentrations in plasma and colon were significantly correlated (R=0.47, P=.009).
The body weight of mice
Discussion
Our data clearly indicate that both moderate vitamin B6 supplementation and mild depletion significantly attenuate histological and molecular features of colonic inflammation in the IL10−/− mouse model of IBD (Fig. 3). The results of our deficiency arm are in good agreement with those reported by Benight et al., who show that removing B6 from diets resulted in a significant reduction the in mortality and disease activity index following exposure of mice to 3% DSS [9]. Although our observations
Acknowledgments
Many thanks to Ms. Nellie Desautels and Mr. Gaofeng Bi for their technical assistance. Thank you to Dr. Donald Smith and his animal care team, whose support has been invaluable. Thank you to Dr. Martin Obin and Mr. Alex Histed for your comments and suggestions. A special thank you to Dr. Julie Saba (Children's Hospital Oakland Research Institute) for her insightful comments on our data.
This work was supported by grants from the NIH (J.B.M 5-K05- CA100048-05) and Prevent Cancer Foundation (Z.L).
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The authors report no conflicts of interest.
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Author contributions: Study conception and design, JS, JWC; animal husbandry and care, AB; inflammatory markers, AB; histology, RTB; data analysis JWC; data evaluation and interpretation JS, JC, JBM, ZL; manuscript JS, JWC.