IntroductionPatients with Systemic Lupus Erythematosus (SLE) have increased cardiovascular risk, endothelial dysfunction, and abnormal endothelial repair mechanisms. Vitamin D deficiency is common in SLE and has been associated with active disease and increased vascular stiffness. Myeloid angiogenic cells (MACs) repair damaged vessels by secretion of angiogenic factors and may be a target for vitamin D. Vitamin D may therefore be a novel therapy to improve cardiovascular risk in SLE patients. This study aimed to determine the effects of vitamin D on endothelial function and repair in patients with SLE.MethodsThe effects of the active form of vitamin D (1,25(OH)2D3) were studied on MACs from vitamin D deficient SLE patients ex vivo. Functional models were developed to study MAC migration, adhesion and interaction with endothelial cells. Additional experiments used a model of healthy MACs treated with IFN-alpha. An observational study of clinically stable vitamin D deficient SLE patients being treated with high dose vitamin D over 3 months was used to investigate the effects of vitamin D on endothelial function as measured by flow-mediated dilatation (FMD).ResultsMACs expressed markers consistent with an M2 macrophage phenotype and they enhanced endothelial network formation in vitro. SLE patients had an increased number of MACs; however, these were dysfunctional compared to healthy controls. Vitamin D increased the number, changed the phenotype and improved the functional capacity of SLE MACs ex vivo. In addition, the angiogenic capacity of SLE MACs was restored toward that of healthy controls via a reduction in the anti-angiogenic cytokine IP10. Vitamin D-treated MACs were also more able to protect endothelial cells against TNF-mediated down-regulation of endothelial nitric oxide synthase (eNOS). In SLE patients treated with vitamin D, there was a strong correlation between the change in serum 25(OH)D and the change in the ratio of endothelium-dependent:independent dilatation (r=-0.650, p=0.006). This was accompanied by an increase in the number of MACs at 3 months (p=0.015). These observations were independent of changes in serum PTH, calcium or lupus disease activity.ConclusionsVitamin D can target MACs and therefore offers a novel approach to improve endothelial repair in patients with SLE. In addition, vitamin D treatment in lupus patients resulted in an improvement in endothelial function, related to the change in vitamin D status. These results suggest that vitamin D could improve surrogate markers of cardiovascular disease and thus reduce cardiovascular risk in this patient group.