Wavelength-dependent cytokine modulation in metabolically stressed fibroblasts

To investigate the effects of blue- and red-light irradiation on MTT reduction and cytokine concentrations in metabolically stressed L929 fibroblast-like cells, as an in vitro model to explore wavelength-associated biological responses relevant to light exposure during restorative treatments.

L929 fibroblast-like cells were seeded in 96-well black plates with clear, flat bottoms (30,000 cells/well) using Dulbecco's Modified Eagle's Medium (DMEM) supplemented with 10% fetal bovine serum (FBS). After 24 h, the culture medium was replaced with DMEM containing 0.5% FBS to induce metabolic stress. After an additional 24 h, cells were exposed to either blue (452 nm) or red (633 nm) light at a radiant emittance of 200 mW/cm2 for 10, 20, 30, or 60 s (2, 4, 6, or 12 J/cm2). Cells not exposed to light served as controls. MTT reduction (n=3) and cytokine concentrations (n=8) were analyzed using two-way ANOVA followed by Tukey's test for multiple comparisons.

Normalized MTT reduction was numerically higher after red- than blue-light exposure; however, the effect of wavelength did not reach statistical significance (p=0.059), nor exposure time (p=0.057) or the wavelength-by-time interaction (p=0.337). Cytokine concentrations did not show significant overall effects of wavelength, exposure time, or their interaction. In an exploratory maximum-exposure comparison, TNF-α was higher after 60 s of blue-light than in the no-light control (Tukey-adjusted p=0.029), whereas red light did not differ from the control (p=0.101), and blue and red light did not differ from one another (p=0.812).

Under the conditions tested, red light was associated with numerically greater MTT reduction than blue light; however, this difference did not reach statistical significance. Blue light increased TNF-α relative to the no-light control, but the small exploratory cytokine dataset does not establish a wavelength-specific inflammatory response.