Low-Level Laser Irradiation Modulated Viability of Normal and Tumor Human Lymphocytes In Vitro

Abstract Introduction: Laser radiation is a promising strategy against various malignancies. Recent studies have shown that the application of low-power laser therapy (LPLT) at different doses and exposure times could modulate the growth dynamic of tumor cells. Based on the type of laser, LPLT could potentially trigger cell proliferation, differentiation, and apoptosis in different cell lines.Methods: In this study, MTT assay was used to monitor the effect of low and high laser intensities on the viability of normal and cancer lymphocytes. The protein levels of Ki-۶۷ (a proliferation marker) and Caspase-۳ (an apoptosis factor) were measured in human peripheral mononuclear cells (PBMCs) and the B-lymphoblastic cell line (Nalm-۶) using flow cytometry after being-exposed to ۶۳۰-nm LPLT at low (۲, ۴, ۶, and ۱۰ J/cm۲) and high (۱۵, ۳۰, ۶۰, and ۱۲۰ J/cm۲) energy densities in a continuous mode for ۴۸ and ۷۲ hours.Results: By using higher energy densities, ۶۰ and ۱۲۰ J/cm۲, a significant decrease was shown in the viability of Nalm-۶ cells, which reached ۶.۶ and ۱۰.۱% after ۴۸ hours compared to the control cells (P < ۰.۰۵). Notably, Cell exposure to doses ۳۰, ۶۰, and ۱۲۰ J/cm۲ yielded ۷.۵, ۱۲.۹, and ۲۱.۶ cell viability reduction after ۷۲ hours. The collected data showed that the high-intensity parameters of LPLT (۱۵ to ۱۲۰ J/cm۲) promoted significant apoptotic changes in the exposed cells coincided with the activation of Caspase-۳ compared to the none-treated control cells (P < ۰.۰۵). The data further showed the stimulation of the Ki-۶۷ factor both in primary PBMCs and the lymphoblastic cell line treated with LPLT at energy densities of ۴ and ۶ J/cm۲ (P < ۰.۰۵), indicating enhanced cell proliferation. Similar to Nalm-۶ cells, primary PBMCs showed apoptosis after ۴۸ hours of being exposed to doses ۶۰, and ۱۲۰ J/cm۲, indicated by increased Caspase-۳ levels (P < ۰.۰۵). As expected, the Nalm-۶ cells were resistant to cytotoxic effects of laser irradiation in the first ۴۸ hours (P > ۰.۰۵) compared to normal PBMCs. The exposure of Nalm-۶ cells to low-intensity laser intensities increased a proliferation rate compared to the PBMCs treated with the same doses.Conclusion: We showed the potency of LPLT in the induction of apoptosis and proliferation in human primary PBMCs and Nalm-۶ cells in a dose and time-dependent manner after ۷۲ hours. Keywords: Low-power Laser therapy Leukemia Peripheral blood mononuclear cells