Effect of photobiomodulation on the viability and functionality of islet cells and pancreatic islet in vitro

During islets transplantation 50% are destroyed at the time of transplantation due to several stresses (ischemia-reperfusion, IBMIR). Light absorption in the near infrared range, Photobiomodulation (PBM), was shown to have a positive impact on wound healing and cell regeneration in different pathologies (e.g., Parkinson’s disease) but few data on pancreatic islets. We studied the impact of PBM (670nm by LED, 2mw/cm²) on MIN6 and rat islets before or during stresses: 1) substrate deprivation (1.5 hours in glucose and serum-free medium for islets, 24 hours for MIN6), 2) cytokines cocktail (24-hour with IL1-β 600IU/mL, IFN-γ 6000IU/mL and TNF-α 6000IU/mL for both), or 3) hypoxia (16 hours, 1% O2 for both), in presence or not of PBM. Viability was checked (confocal microscopy or FACS) and glucose stimulated insulin secretion (GSIS) was performed (index insulin secretion = [insulin] in 16.7mM dextrose/ [insulin] in 2.8mM). For MIN6 the production of superoxide (Mitosox) and mitochondrial membrane potential (TMRM) were performed by FACS. Substrate deprivation-induced islet mortality (25.9 +/- 8.67%, n=12, p<0.001) was reduced if PBM was performed 24h before stress (15.7 +/- 8.34%, p<0.05) or during stress (16.0 +/- 9.19%, p<0.01), as for MIN6. No impact of PBM was observed regarding islets GSIS. Index of MIN6 insulin secretion exposed to substrate deprivation was decreased compared to control (1.07 +/- 0.52 vs. 2.00 +/- 0.55, n=8, p<0.05). If PBM was performed before or during the deprivation stress, MIN6 exhibited similar GSIS than control (p=0.55 and p=0.59). Cytokines-induced islet mortality (34.7 +/- 7.32%, n=5, p<0.05) is reduced if PBM is performed 24 hours before stress (26.9 +/- 4.27%, p<0.05) or during stress (26.7 +/- 4,59%, p<0.05), as for MIN6. Index of islets insulin secretion was decreased compared to control (0.82 +/- 0.22 vs 1.43 +/- 0.50, n=4, p<0.05) and restored only if PBM was applied during the stress (1.66 +/- 0.95, p<0.05). Protective effect of PBM was observed regarding the production of superoxide and restauration of mitochondrial membrane potential of MIN6 stressed by substrate deprivation or cytokines. Hypoxia-induced islet mortality (27.3 +/- 11.9%, n = 8, p<0.01) remained unchanged if PBM was performed during stress (24.2 +/- 11.5%, p=0.923); as for MIN6 cells. Index of islet insulin secretion was decreased by hypoxia compared to control (0.99 +/- 0.05 vs. 1.52 +/- 0.17, n=8, p<0.05) and no effect was observed with PBM; as for MIN6 cells. Exposure of islets to PBM prior or during cytokine exposure and substrate deprivation increase viability and improve functionality of MIN6 and pancreatic islets. Further experiments will be conducted on human islets to confirm these results. So far, our results suggest that islets exposure to PBM could be transposed in clinic as preconditioning of islet after isolation, before transplantation in order to improve their viability and functionality upon transplantation.