Background and Objectives: Mesenchymal stem cells (MSCs) are promising for use in regenerative medicine. Cytostatics can decrease, but low-power laser irradiation (LPLI) can increase the growth of MSCs. The interaction of LPLI, MSCs and cytostatics is not known. This study investigated the effect of four cytostatics (carboplatin, cytarabine, paclitaxel, vincristine), LPLI, and combination of a cytostatic drug and LPLI on murine MSCs (mMSCs). Study Design/Materials and Methods: MMSCs were exposed to LPLI (660nm diode laser; 60mW output power; range of power density: 76-156mW/cm2; range of energy density: 1.9-11.7 J/cm2) and/or a cytostatic drug (carboplatin: 2, 10, 50; cytarabine: 0.4, 10, 50; paclitaxel: 0.4, 2, 10; vincristine: 0.02, 0.1, 0.5 μg/ml, respectively). Cell proliferation was measured after 24, 48, or 72 hours incubation. Results: LPLI at 1.9 J/cm 2 dose increased the proliferation rate with 41% after 48 hours. However, 11.7 J/cm2 LPLI caused 42% inhibition and cytostasis was still detectable after 72 hours. LPLI caused equivalent stimulation in single or in divided doses (3.8 vs. double 1.9 J/cm2 in a 24-hour period). The cytotoxicity of 50 μg/ml carboplatin was eliminated, the inhibitory power of 0.1 μg/ml vincristine was attenuated by 1.9 J/cm2 LPLI even 3 days post-treatment (attenuation > 10%). The 11.7 J/cm2 LPLI enhanced the cytotoxicity of 50 μg/ml cytarabine (from 48% to 73%) and 10 μg/ml paclitaxel (from 37% to 78%). Combination of the ineffective 0.4 μg/ml cytarabine or paclitaxel with the inhibitory 11.7 J/cm2 LPLI exhibited stronger inhibition than the 11.7 J/cm2 LPLI alone (69% and 69% vs. 42%). Conclusions: Low energy density of LPLI increases and high energy density of LPLI decreases the proliferation of mMSCs. Furthermore, LPLI can prevent or attenuate some drug's cytotoxicity and amplify others'. The result depends on the applied energy density, on the type and concentration of the cytostatics.
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