Sridharan, Kaarthik (University medical center, Rostock)



Introduction: Treatment of cells with electromagnetic irradiation (light) can affect their proliferation and differentiation ability. Exposure of cells to light sources with different wavelengths (wavelengths around 415 nm/blue, 540 nm/red, and 810 nm/infrared are most common) appears to have different effects depending on the wavelength, energy intensity and the duration of exposure. Cytochrome c oxidase is believed to be one of the main photon acceptors. In this study, we have developed an experimental setup suitable for irradiating cells (with adipose tissue-derived mesenchymal stem/stromal cells/adMSC) with light of different wavelengths. With this setup, we are investigating the effect of light exposure on the regenerative capacity of adMSC.

Methodology: Since the cell culture media and growth surfaces have specific absorption properties, we measured absorption spectra of different media (with and without fetal calf serum/FCS, with and without phenol red) with different plate formats (clear bottom, with or without lid) and different volumes (50 µl, 100 µl, and 150 µl) using a microplate reader. Using the cell culture medium optimized for light treatment, the adMSC suspension was irradiated with the different wavelengths (blue (430 nm), red (660 nm) and IR (810 nm)) and different exposure times (5, 10 and 15 min). Subsequently, the phenotype, viability, cell number, cell cycle, mitochondrial membrane potential and differentiation ability of the cells were determined.

Results: Since the measurement with black plate with a flat transparent bottom without lid, showed little light scattering, these plates were used for the further analyses. The analysis of absorption spectrum of cell culture media showed that phenol red absorbs light with wavelengths below 600 nm. The media additive FCS showed similar absorption properties. The studies of different filling volumes showed that the absorption capacity increased in direct proportion with increasing filling volume. After optimizing the experimental setup, it was possible to carry out the first experiments on the irradiation of adMSC. Depending on the light source used, different effects occurred. These ranged from changes in cell morphology to reductions in cell number and metabolic activity. We also showed that the effect of light exposure on adMSC also depended on duration and energy input of the light. Further analyses to understand the energy and wavelength-dependent effect on cellular properties are still pending.

Conclusion: Since different materials and compounds have different absorption effects, the experimental setup needs to be adapted to the irradiation conditions. The composition of the media has a direct influence on the light absorption by adMSC, so it has to be adjusted accordingly. Preliminary experiments confirm that the viability and proliferation capacity of adMSC changes depending on the light wavelength and the energy input. With this background knowledge, we can now examine the study of light effects on differentiation and migration ability. These examinations could help to transfer the light treatment to clinical application.

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[2] Chen, Hongli et al, Lasers in medical science vol. 34,4 (2019)


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