Recently, light emitting diodes (LEDs) have been introduced as a potential physical factor for proliferation and differentiation of various stem cells. Among the mesenchymal stem cells human umbilical cord matrix-derived mesenchymal (hUCM) cells are easily propagated in the laboratory and their low immunogenicity make them more appropriate for regenerative medicine procedures. We aimed at this study to evaluate the effect of red and green light emitted from LED on the neural lineage differentiation of hUCM cells in the presence or absence of retinoic acid (RA). Harvested hUCM cells exhibited mesenchymal and stemness properties. Irradiation of these cells by green and red LED with or without RA pre-treatment successfully differentiated them into neural lineage when the morphology of the induced cells, gene expression pattern (nestin, β-tubulin III and Olig2) and protein synthesis (anti-nestin, anti-β-tubulin III, anti-GFAP and anti-O4 antibodies) was evaluated. These data point for the first time to the fact that LED irradiation and optogenetic technology may be applied for neural differentiation and neuronal repair in regenerative medicine.

Light-emitting diodes (LED) have recently been introduced as a potential factor for proliferation of various cell types in vitro. Nowadays, stem cells are widely used in regenerative medicine. Human umbilical cord matrix-derived mesenchymal (hUCM) cells can be more easily isolated and cultured than adult mesenchymal stem cells. The aim of this study was to evaluate the effect of red and green lights produced by LED on the proliferation of hUCM cells. hUCM cells were isolated from the umbilical cord, and light irradiation was applied at radiation energies of 0.318, 0.636, 0.954, 1.59, 3.18, 6.36, 9.54, and 12.72 J/cm(2). Irradiation of the hUCM cells shows a significant (p < 0.05) increase in cell number as compared to controls after 40 h. In addition, cell proliferation on days 7, 14, and 21 in irradiated groups were significantly (p < 0.001) higher than that in the non-irradiated groups. The present study clearly demonstrates the ability of red and green lights irradiation to promote proliferation of hUCM cells in vitro. The energy applied to the cells through LED irradiation is an effective factor with paradoxical alterations. Green light inserted a much profound effect at special dosages than red light.

In an in vitro study, the effect of light polarization on the efficiency of 5-aminolaevulinic acid (ALA) photodynamic therapy (PDT) of basal cell carcinoma (BCC) was investigated. Three states of light polarization (non-polarized, linearly polarized, and circularly polarized) were considered. Cells were exposed to green (532 pm 20 nm) irradiation from light emitting diodes. Cell survival was measured by the colorimetric assay (WST-1) and Trypan blue staining. The colorimetric assay showed a pronounced decrease in the cell viability (up to 30%) using polarized light compared to the non-polarized one in the wavelength region used. Similar results were obtained by the cell counting method (20-30% increase in cell death). The observed effect was dependent on the concentration of photosensitizer. The effect is more expressed in the case of linearly polarized light compared to the circularly polarized one. Results show that the use of polarized light increases the efficiency of in vitro ALA-PDT of BCC. Utilizing polarized light, it is possible to obtain the same effect from PDT by lower concentrations of photosensitizer. Additionally, the concentration dependency of PDT response and photo-bleaching is also reduced.

Photobiomodulation therapy (PBMT) or Low level light Therapy (LLLT), is the stimulatory effect of light on the cell behavior. It has been considered as a potential therapeutic intervention. Glioblastoma is a malignant primary brain tumor without any effective treatment. This in vitro study investigated the effect of PBMT on proliferation rate and vital activity of human glioblastoma U87 cell line. Three different wavelengths were considered: 632 nm (red light, 2.1 mW/cm 2 ), 534 nm (green light, 1.2 mW/cm 2 ), and 457 nm (blue light, 6.5 mW/cm 2 ). The cell behavior was studied during a period of four hours up to 60 hours after irradiation. The irradiated cells were inspected by different assays for cell count, cell viability, cell death, and free radical production rate and were compared with the control non-irradiated ones. The results show a reduction in cell viability for all the three wavelengths. However, the effect is more pronounced for blue light. Cell death assessments, staining and flow cytometry, and NBT assay shows that blue light is not lethal, but that it reduces the free radical production rate. Temporal analysis shows that the maximum effect on cell proliferation will be observed around 48 hours after irradiation. It could be concluded that light, particularly shorter wavelengths, has an inhibitory effect on the in vitro proliferation rate of U87 cell line by affecting the energetics of the cell. The effect is stimulatory and persistent for periods comparable to cell doubling time.

Green LED and three‐dimensional (3D) scaffolds have recently received extensive attentions due to their impact on cell proliferation and differentiation. Melatonin, a circadian rhythm‐regulating hormone, is involved in some physiological phenomena including testosterone biosynthesis. Lower testosterone biosynthesis results in some disorders such as puberty retarding, andropause, and muscle weakness. Therefore, our aim was to investigate the proliferation of Leydig cells and their testosterone‐related Gene expression and secretion under the influence of 3D scaffold, green light and melatonin. The experimental groups of TM3 cells embedded in the 3D scaffold, were exposed to green light, melatonin, both and all three factors. Expression of cell cycle genes including PCNA, CYCLIND1, CDC2 and CDKN1B, and testosterone related genes; GATA4 and RORα were also examined. 3D scaffold enhanced Leydig cells proliferation, and testosterone‐related genes expression. While melatonin decreased cell proliferation and testosterone‐related genes expression. Green light did not significantly change the results but slightly decreased cell proliferation and testosterone synthesis. The combination of green light with melatonin significantly reduced the proliferation rate of TM3 cells and the expression of steroidogenic genes, while the combination of green light with scaffold improved the results. In general, the use of scaffolding enhances proliferation and testosterone‐related genes expression of TM3 Leydig cells. Also, application of green light and scaffolding reduces the deleterious effects of melatonin on these cells.