Relevance of laser irradiance threshold in the induction of alkaline phosphatase in human osteoblast cultures

Abstract

Induction of matrix synthesis by low-level laser has been demonstrated extensively. However, the question of dose- or power intensity-dependency is under-investigated. To address this issue we chose human osteoblast cell cultures and measured their alkaline phosphatase (ALP) activity after laser irradiation. The cell cultures were irradiated periodically by 690 nm radiation via optical transmission fiber-based laser needles, reaching into the culture dishes. The osteoblasts showed no induction of ALP activity when we used a single laser needle stimulation with a laser irradiance of 51 mW/cm(2), an increase of approximately 43% at 102 mW/cm(2) irradiance (two needles per well) and a ninefold increase at 204 mW/cm(2) irradiance (four needles per well), leaving the temperature of the culture medium unaffected. We concluded that the osteoblastic response in ALP activity to a laser stimulus shows a logarithmic relationship, with a distinct threshold, rather than a linear dose-dependency. Secondly, the laser irradiance, rather than the dose, is relevant for the impact of the laser.

Photobiomodulation and bone healing in diabetic rats: evaluation of bone response using a tibial defect experimental model

“…Additionally, some authors have demonstrated that different results can be obtained with the use of different power densities, which could optimize the PBM effects on the target tissue [35,36]. As this study was limited to the investigation of the effects of different fluences, tissue response under different power densities remains to be provided.…”

Laserneedle Acupuncture: A Critical Review and Recent Results

“…18 It was found that invitro studies of human osteoblast cells metabolism could be increased by a factor of 9.1 by laserneedle irradiation. A shift of the osteoblast-osteoclast-activity equilibrium to the bone regeneration side can be induced and maintained by the laserneedle therapy.…”

Laser Phototherapy at High Energy Densities Do Not Stimulate Pre-Osteoblast Growth and Differentiation

“…22 The 102 mW/cm 2 irradiance promoted a 43% increase in ALP production, and the irradiance of 204 mW/cm 2 increased the production of ALP eightfold. 22 These results differ from ours, in which there was no increase in ALP activity with laser. 22 The study by Hirata et al is in accordance with our research.…”

“…21 Many studies showed an increase in ALP activity after laser irradiation. [22][23][24] Haxsen et al performed a study in which osteoblasts were irradiated with a red laser 690 nm, 51, 102, or 204 mW/cm 2 , every 4 h for 24 h in total. 22 The 102 mW/cm 2 irradiance promoted a 43% increase in ALP production, and the irradiance of 204 mW/cm 2 increased the production of ALP eightfold.…”

“…[22][23][24] Haxsen et al performed a study in which osteoblasts were irradiated with a red laser 690 nm, 51, 102, or 204 mW/cm 2 , every 4 h for 24 h in total. 22 The 102 mW/cm 2 irradiance promoted a 43% increase in ALP production, and the irradiance of 204 mW/cm 2 increased the production of ALP eightfold. 22 These results differ from ours, in which there was no increase in ALP activity with laser.…”