1,25-dihydroxyvitamin D3-3-bromoacetate, a novel vitamin D analog induces immunosuppression through PI3K/Akt/mTOR signaling cascade

- 1,25-dihydroxyvitamin D3-3-bromoacetate (BE) showed immunosuppressive effect.
- BE's immunosuppressive effect is more than that of 1,25-dihydroxyvitamin D3(Vit-D).
- BE induces inhibition of activated memory CD4+ and CD8+ T-cell proliferation.
- BE induces apoptosis of CD3+ T cells more than that of Vit-D.
- Antiproliferative effect of BE is dependent on Akt/mTOR signaling cascade.

PurposeThe molecular mechanism responsible for the immunomodulatory effect of 1,25-dihydroxyvitamin D3 (Vit-D) is still not well elucidated. Unavoidable systemic toxicity of Vit-D has encouraged to develop more potent and less toxic Vit-D analogs, such as 1,25-dihydroxyvitamin D3-3-bromoacetate (BE). Our aim was to explore the immunosuppressive effect of BE and its molecular mechanism in autoimmune diseases.MethodMagnetically sorted CD3+ T cells (T cells) from PBMCs of psoriasis and autoimmune arthritis patients were cultured with/without BE and Vit-D followed by proliferation (MTT, CFSE dilution assays) and apoptosis assays (annexin V). Immunoblot was performed to determine the signaling cascade responsible for the antiproliferative effect.ResultsIn MTT assay, BE (OD: 0.64 ± 0.08) markedly inhibited the anti-CD3/CD28 stimulated proliferation of T cells (OD: 1.8 ± 0.30, p < 0.001) and at equivalent doses, the inhibitory effect was more than that of Vit-D (OD: 0.91 ± 0.11, p < 0.05). The antiproliferative effect of BE was extended to activated CD4+ and CD8+ memory T cells (CD45RA−CD11a+) without much effect on the naïve T cells. BE induced more apoptosis of T cells (45.01 ± 4.27%, p < 0.01) compared to untreated cells (3.45 ± 1.8%), and the proapoptotic effect was markedly more than that of Vit-D (26.1 ± 2.05%, p < 0.05). BE effectively inhibited the anti-CD3/CD28-induced phosphorylation of Akt and mTOR and in both, BE showed more potency than Vit-D (p < 0.05).ConclusionTopical Vit-D is being used successfully in psoriasis for years. However, its potency is less compared to topical corticosteroids. The de novo BE showed significantly more immunosuppression than conventional Vit-D and the immunosuppressive effect is PI3K/Akt/mTOR dependent. Our results indicate that BE could be an effective therapeutic agent for psoriasis and other T-cell-mediated autoimmune diseases.