In the present study, we evaluated the effect of vitamin B12 administration on a rat model of AA-induced colitis under the hypothesis that vitamin B12 supplementation is essential in the prevention of IBD. As results, VitB12 treatment in AA colitis group’s values of IL-6, TNF- α, MDA, IL-1β, SOD, GSH were lower than AA colitis control group, but only IL-6 and GSH parameters reached the significant level. Furthermore,inflammation score and a macroscopic score of VitB12 treatment in AA colitis group were also lower than AA colitis control group, but the difference was not statistically significant. Few studies have investigated the association between vitamin B12 and colitis pathogenesis, and, to the best of our knowledge, the present study is the first and only experimental model that examined the effect of vitamin B12 supplementation modulates inflammation in a colitis rat model. Our results signified that although vitamin B12 can influence colitis, their influences seemed to marginal and supplementary.
Clinical trials that aimed to find an association between the pathogenesis of IBD and vitamin B status have also been published, as has an observational prospective trial that investigated the effect of Vitamin B on the course of IBD. The prevalence of hyperhomocysteinemia and the effect of hyperhomocysteinemia on disease activity were assessed via longitudinal follow-up of patients with UC and CD, there was no association between homocysteine levels and disease activity. Instead, the prevalence of hyperhomocysteinemia was higher than in a normal population, although there was no control arm [13]. Retrospective studies have reported a higher prevalence of hyperhomocysteinemia. Erzin et al. [14] reported that 56% of IBD patients, and Peyrin-Biroulet et al. [15] stated that 26% of CD patients have elevated homocysteine levels. Hyperhomocysteinemia can be a result of impaired vitamin absorption due to inflammation, deficiency resulting from a poor diet, and due to a resected or diseased ileum in the CD. Another retrospective study [16] revealed that people with CD had a higher prevalence of vitamin B12 deficiency than did those with UC and a control group. People with prior ileal or ileocolic resection have a particularly higher prevalence. There was no difference between the UC and control groups in this study, a finding that may be interpreted as vitamin B12 deficiency being a result of resection rather than intestinal inflammation. Another study reiterated these results. In a Swiss cohort, only CD patients with stenosis or intestinal surgery had vitamin B12 deficiency [16].
As the studies that assessed the serum folate and vitamin B12 levels of people with IBD patients have produced inconsistent results, meta-analyses have been conducted. The first meta-analysis, determined that people with CD have significantly higher levels of plasma homocysteine than do controls. There was no difference between UC and CD patients [17]. A recently published meta-analysis compared serum folate and vitamin B12 levels in people with IBD and healthy individuals. Interestingly, it found no difference in the mean of vitamin B12, but the folate levels did differ; people with UC patients had significantly lower serum folate levels than controls, but people with CD did not have different levels of folate from the control group [10]. The conflicting results may be due to the methodology used; one of these meta-analyses measured plasma homocysteine levels, while the other considered vitamin B12 and folate levels.
Although resection due to CD or intestinal inflammation can alter the absorption of vitamin B12 or folate, IBD can be a consequence of nutritional deficiency. Homocysteine is a sulfur-containing amino acid that plays a role in two major pathways: remethylation to methionine, which requires folate and vitamin B12, and transsulfuration to cystathionine, which requires vitamin B6. Irrespective of whether it is due to a methyl-deficient diet vitamin B deficient diet, or to genetic defects of enzymes that are involved in homocysteine metabolism (e.g., methyl tetra hydro folatereductase), hyperhomocysteinemia is known as one of the etiologic factors of thrombotic events [18]. It causes vascular inflammation via several mechanisms, one of which is increased production of reactive oxygen species. Similar activation takes place in the intestinal mucosa. Hyperhomocysteinemia promotes microvascular inflammation with aggravating endothelial inflammation, resulting in vascular cell adhesion molecule − 1 upregulation, MCP-1 production, and p38 phosphorylation [19]. This is thought to promote mucosal inflammation and activate several inflammatory and oxidative stress pathways [20].
Antioxidant mechanisms are essential for protecting the colonic mucosa from the harmful effect of inflammation [21]. Increasing antioxidant defense mechanisms in the colon mucosa, via pharmacologic therapies, may be beneficial in IBD treatment. The present study is the first to investigate vitamin B12 as an antioxidant therapy for IBD, although many antioxidant compounds have yielded promising results as such treatment [22]. We expected that vitamin B12 supplementation will decrease the level of homocysteine that modulates inflammation on intestinal mucosa. Our study demonstrated that vitamin B12 supplementation decrease level of IL-6 and GSH in an AA-induced colitis rat model. However, the same results are not observed with all inflammation and oxidative stress biomarkers. Furthermore IS and macroscopic score difference between AA colitis control and VitB12 treatment in AA colitis group were not significant. There are not experimental colitis models that used vitamin B12 supplementation as an antioxidant therapy which we can compare with the present study. One experimental colitis model demonstrated that folate supplementation downregulated homocysteine-induced IL-17 and ROR-γt expression in dextran sulfate sodium (DSS) induced colitis rats that were fed a methionine-deficient diet [23]. Homocysteine activated the p38/cPLA2/COX2/PGE2 pathway and also increased the expression of IL-17 and retinoid-related orphan nuclear receptor-γt (ROR-γt), which is the key transcription factor of IL-17. T helper 17 (Th17) cells, which derive from CD4+ T-cells, play an important role, and an imbalance between T regulatory cells and Th17 appears to be critical for the development of IBD [24, 25]. Although many cytokines play a role in IBD pathogenesis, some studies have suggested that IL-17, which is the cytokine of Th17, contributes to pathogenesis [26]. The present study evaluated the values of nonspecific inflammatory markers such as IL-6, IL-1β etc. Maybe evaluating specific markers of intestinal mucosa such as IL-17 on an experimental colitis model that use antioxidant supplementation will be more beneficial. Furthermore, we used standard diet,not a methyl-deficient diet.
One experimental study on colitis evaluated the role of vitamin B on colitis sequela. In this study, we used dietary vitamin B deficiency and then created an experimental colitis model with DSS infusion. The disease progression and severity were determined by macroscopic changes and inflammation markers. Furthermore, this study determined the in vivo kinetics of the methionine pathway by measuring vitamin B6, vitamin B12, homocysteine and other metabolite levels in colon, plasma, and liver of mice. Interestingly, mortality rates, disease activity index and inflammation markers of mice group that were fed on a control diet were higher when compared with the mice that were fed on a vitamin B deficient diet. This study showed that homocysteine levels were higher in the plasma and colon of the deficient diet mice groups regardless of DSS status. Furthermore, vitamin B6 levels were determined indirectly by calculating its active form of pyridoxalphosphate (PLP). PLP levels were higher in the deficient diet mice groups. This study measured B12 associated metabolites to assess Vitamin B12 deficiency. Methylmalonic acid (MMA) is converted by an enzymatic reaction and requires VitB12 as a cofactor. MMA levels were higher in plasma when compared between the deficient diet mice and the control diet mice groups. Further, this study indicated that remethylation and glycine levels were increased in the deficient mice group. These results indicated that the diet can overcome VitB6 deficiency but not that of VitB12. Folate was included in the diet so homocysteine level was increased due to the deficiency of vitamin B6 and not vitamin B12. Furthermore, this increase did not contribute to the disease progression or inflammation in DSS induced colitis model [27].
Experimental rodent IBD model (IL-10 knockout mice) was used and the effects of vitamin B6 inadequacy and supplementation were monitored on the severity of intestinal inflammation. Mice were randomly assigned to vitamin B6 deficient, replete, and supplementation group. The deficient and supplementation groups both had lower concentrations of molecular and histological markers of inflammation of colon than the replete group. The lower concentrations of histologic and molecular deficiency markers were in accordance with the study conducted by Benignt et al.; however, this study showed that vitamin B6 supplementation ameliorates intestinal inflammation [28]. The results reported by Benignt et al. and us are against the hypothesis of homocysteine contribution due to the nutritional deficiency of colitis pathogenesis and a decrease in its level with nutritional supplementation. Gut microbiota is associated with the pathogenesis of IBD. VitB12 producing bacteria may increase in case of acute intestinal inflammation and intestinal mucosa may absorb more VitB12 but supplementation of VitB12 may not ameliorate intestinal inflammation. We did not measure the level of VitB12 or its metabolites in colon and plasma. Furthermore, acetic acid-induced colitis model represents acute colitis rather than a chronic relapsing and remittent condition so we did not know the effect of vitamin B12 on a chronic colitis model. The effect of vitamin B6 deficiency and supplementation is associated with colitis rather than VitB12.