A study of the effects of phototherapy dose interval on photobiomodulation of cell cultures.

Background And Objectives: Dosimetry and treatment frequency are controversial phototherapy issues. Efficacy of dose fractionation on photobiomodulation was evaluated in vitro.

Study Design/materials And Methods: Human HEP-2 and murine L-929 cell lines were cultured in complete DMEM media. Photoradiation (670 nm, 5 J/cm2/treatment, 50 J/cm2 total energy delivery), was performed varying treatments per 24 hour period: Group I (Controls)-0, Group II-1/d, Group III-2/d, Group IV-4/d. Cell proliferation was measured using Cyquant (fluorescent DNA content) and MTT (3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyl tetrasolium bromide) assays for 240 hours post therapy. A proliferation index: PI = (#Cells Experimental(t) / #Cells Control(t)) was computed.

Results: MTT assay results demonstrated maximal response in Group III (P < 0.05, n = 3). Cyquant maxima occurred in HEP-2 Groups II and III (P < 0.045) and L-929 Group III (P < 0.091).

Conclusions: Cellular response to dose frequency varies. More frequent treatments (2/24 hours) increased metabolism and proliferation in both cell lines. Further investigation of dose fractionation in phototherapy is warranted.