Photobiomodulation at 660 nm enhances proliferative activity while preserving viability in human endothelial cells in vitro

Abstract Efficient endothelialization is essential for vascular graft integration and long-term performance, yet strategies to enhance endothelial proliferative activity remain limited. Photobiomodulation (PBM) is a promising noninvasive approach for modulating cell behavior, although its effects on endothelial cells under standard culture conditions remain insufficiently defined. This in this study evaluated the effects of 660 nm PBM at different energy densities on the proliferative activity and viability of human umbilical vein endothelial cells cultured under nonstress conditions. Cells were assigned to four groups: nonirradiated control and PBM-treated groups exposed to 1.0, 4.0, or 7.5 J/cm 2 . Metabolic/proliferative activity and viability were assessed at 24, 48, and 72 h using Alamar Blue, Live/Dead staining, Annexin V/propidium iodide labeling, cell cycle analysis, and Ki67 fluorescence intensity. At 72 h, all irradiated groups showed significantly greater metabolic activity than the control group (1.0 J/cm 2 , p < 0.01; 4.0 and 7.5 J/cm 2 , p < 0.001), whereas viability remained high across all groups (> 95%), with no evidence of cytotoxicity. PBM redistributed cells toward proliferative phases, with a higher proportion of S-phase cells at 1.0 J/cm 2 and greater accumulation in G2/M at 4.0 and 7.5 J/cm 2 . Ki67 fluorescence intensity also increased and was highest at 7.5 J/cm 2 ( p < 0.05). Overall, 660 nm PBM enhanced endothelial proliferative activity while preserving cell viability, with coordinated changes in cell cycle progression and Ki67 fluorescence intensity across different energy densities and the most pronounced overall response at 7.5 J/cm 2 . These findings support PBM as a promising adjunctive strategy for modulating endothelial behavior in vascular tissue engineering and highlight its relevance under standard nonstress culture conditions.