Vitamin D does not mitigate monocyte adhesion to vascular endothelial cells in an in vitro pro-inflammatory model

Vitamin D deficiency has been associated with cardiovascular risk factors, including endothelial dysfunction, a critical step in the pathogenesis of atherosclerosis. This study aimed to evaluate the effects of 1α,25-dihydroxycholecalciferol (VD3) on monocyte (THP-1) adhesion to human umbilical vein endothelial cells (HUVECs) under a pro-inflammatory condition. Endothelial cell activation was induced with tumor necrosis factor-alpha (TNF-α, 100 ng/mL), and cells were treated with VD3 at concentrations ranging from 0.1 to 100 nM. Monocyte adhesion was quantified spectrophotometrically, while levels of vascular cell adhesion molecule 1 (VCAM-1), E-selectin, and cluster of differentiation 15 (CD15) were assessed using ELISA. TNF-α significantly increased THP-1 cell adhesion to HUVECs compared to the control group (p < 0.05). Co-treatment with VD3 at all concentrations tested did not reduce monocyte adhesion, showing levels similar to the TNF-α only group, and significantly higher than the negative control (p < 0.05). Furthermore, TNF-α significantly upregulated VCAM-1 expression (p < 0.05), which was unaffected by VD3. E-selectin and CD15 levels remained unchanged under all experimental conditions. These results do not support a modulatory role for VD3 in the early stages of atherogenesis, specifically in reducing endothelial cell activation and monocyte adhesion. While vitamin D has shown beneficial effects in other aspects of cardiovascular health, its impact on vascular inflammation and adhesion processes remains uncertain and needs further investigation. • VD3 does not reduce monocyte adhesion to endothelial cells under TNF-α stimulation • VCAM-1 is upregulated by TNF-α; VD3 co-treatment does not alter this expression • VD3 effects may be masked by strong TNF-α stimulation; context and dose are critical • Findings support the need for standardized protocols in vitamin D and vascular research