Co-administration of 1,25-dihydroxyvitamin D3 and infliximab improves colitis in mice by modulating Treg differentiation.

Objectives: The combination of TNF-α inhibitors and vitamin D in colitis remains to be elucidated. In the present study, we revealed the benefit of infliximab (IFX) and vitamin D in a mouse model of Ulcerative colitis (UC). Materials and Methods: A dextran sulfate sodium-induced colitis model was used. The therapeutic effect of the combination was evaluated by symptom and histopathology analysis. The synergistic mechanism was explored by detecting the regulatory effect of the combined therapy on Regulatory T cell (Treg) differentiation. Results: IFX and 1,25-dihydroxyvitamin D3 (VitD3) synergistically prevented the development of colitis by improving clinical signs, pathological and hematological manifestation, and inhibiting intestinal inflammation (decreasing TNF-α, IL-1β, and IL-6). Co-administration of IFX (2.5 mg/kg) with VitD3 or IFX (5.0 mg/kg) with VitD3 was more effective than administration of IFX (2.5 mg/kg, 5.0 mg/kg). There was no difference in therapeutic effect between IFX (5.0 mg/kg) and VitD3+ IFX (2.5 mg/kg) groups or between the VitD3+IFX (5.0 mg/kg) and VitD3+ Azathioprine (AZA) groups. VitD3 or combination therapy showed more powerful regulation of splenetic Treg differentiation and IL-10 production than IFX alone. Moreover, VitD3 alone or in combination induced higher levels of Foxp3 and IL-10 than IFX in colon tissue. In ulcerative colitis patients, serum VitD3 levels positively correlated with Treg levels. Conclusion: VitD3 and IFX synergistically inhibit colitis based on their powerful regulation of Treg differentiation. VitD3 combined with IFX is an alternative therapy for patients who are intolerant to standard doses of IFX or combination of IFX and AZA.