How should an increase in alkaline phosphatase activity be interpreted?

Low-level laser therapy, commonly known as LLLT, is the application of low power, monochromatic, and coherent light to injuries and lesions to stimulate healing and give pain relief. There are conflicting reports in the literature regarding the role of ALP. Objective: this study aimed to compare the cellular responses of wounded human skin fibroblasts exposed to doses of 0.5 J/ cm 2, 2.5 J/ cm 2, 5 J/ cm 2, or 16 J/ cm 2 using LLLT with a Helium-Neon laser (632.8 nm, 18.8 mW power output, 2.07 mW/ cm 2 power density, and 3.4 cm diameter spot size or area 9.1 cm 2) to elucidate the role of alkaline phosphatase (ALP) in cell proliferation. Methods: cellular responses to laser irradiation were evaluated using ALP enzyme activity, LDH membrane integrity, neutral red for cell proliferation, optical density at 540 nm, and basic fibroblast growth factor (bFGF) expression. Results: results suggest that an increase in ALP is negatively correlated with cell growth depending on the concentration of growth factors in the medium. Results also indicate that an increase in ALP may be related to cellular damage. Conclusion: since the exact role of ALP is unknown, the ALP enzyme activity assay should be considered in conjunction with other cell proliferation assays such as neutral red, optical density, or more specifically bFGF expression.