Acute application of photobiomodulation does not bring important gains for the muscular performance and functionality of diabetic individuals

Diabetes in spotlight: current knowledge and perspectives of photobiomodulation utilization

Introduction

Diabetes is a global health concern characterized by chronic hyperglycemia resulting from insulinopenia and/or insulin resistance. The rising prevalence of diabetes and its associated complications (ulcers, periodontitis, healing of bone defect, neuropathy, retinopathy, cardiopathy and nephropathy) necessitate innovative therapeutic approaches. Photobiomodulation (PBM), involves exposing tissues and cells to low-energy light radiation, leading to biological effects, largely via mitochondrial activation.

Methods

This review evaluates preclinical and clinical studies exploring the potential of PBM in diabetes and its complications, as well all clinical trials, both planned and completed, available on ClinicalTrials database.

Results

This review highlights the variability in PBM parameters across studies, hindering consensus on optimal protocols. Standardization of treatment parameters and rigorous clinical trials are needed to unlock PBM's full therapeutic potential. 87 clinical trials were identified that investigated PBM in diabetes mellitus (with 5,837 patients planned to be treated with PBM). Clinical trials assessing PBM effects on diabetic neuropathy revealed pain reduction and potential quality of life improvement. Studies focusing on wound healing indicated encouraging results, with PBM enhancing angiogenesis, fibroblast proliferation, and collagen density. PBM's impact on diabetic retinopathy remains inconclusive however, requiring further investigation. In glycemic control, PBM exhibits positive effects on metabolic parameters, including glucose tolerance and insulin resistance.

Conclusion

Clinical studies have reported PBM-induced reductions in fasting and postprandial glycemia without an increased hypoglycemic risk. This impact of PBM may be related to its effects on the beta cells and islets in the pancreas. Notwithstanding challenges, PBM emerges as a promising adjunctive therapy for managing diabetic neuropathy, wound healing, and glycemic control. Further investigation into its impact on diabetic retinopathy and muscle recovery is warranted.

Photobiomodulation therapy on skeletal muscles exposed to diabetes mellitus: a systematic review of animal studies

Diabetes-related muscle damage has been overlooked despite its known association with increased morbidity and mortality in DM individuals. PBMT is a recognized alternative to improve skeletal muscle health in other populations, but its effectiveness in DM is still unclear. To address this issue, we reviewed preclinical studies, available in any language and period, in ten sources of information. The methods were previously registered at PROSPERO (CRD42021271041), based on PRISMA recommendations. Studies in murine models of T1DM or T2DM that reported quantitative analyses of skeletal muscles treated with low-level light therapy could be included after a blind selection process. Most of the seven included studies focus on decompensated T1DM rats with acute muscle injury (cryoinjury or contusion). In these five studies, PBMT improved muscle regeneration, by reducing inflammation and stimulating factors pro-angiogenesis and pro-myogenesis. Some positive effects could also be observed in two studies on muscles without acute injury: control of oxidative stress (T1DM) and reduction of myosteatosis (T2DM). Although infrared laser applied locally appears to be a promising approach, optimal parameters are undefined due to the heterogeneity of outcomes and high risk of bias, which prevented a quantitative synthesis. Several aspects of this growing field have yet to be investigated, particularly regarding the DM model (e.g., aged animals, T2DM), intervention (e.g., comparison with LED), and outcomes (e.g., muscle mass, strength, and function). Future research should aim to improve the internal validity by following guidelines for animal studies and enhance the translatability to clinical trials by using animal models that closely mimic patients with DM in rehabilitation settings.

Optical attenuation coefficient of skin under low compression

In various biomedical optics therapies, knowledge of how light is absorbed or scattered by tissues is crucial. Currently, it is suspected that a low compression applied to the skin surface may improve light delivery into tissue. However, the minimum pressure needed to be applied to significantly increase the light penetration into the skin has not been determined. In this study, we used optical coherence tomography (OCT) to measure the optical attenuation coefficient of the human forearm dermis in a low compression regime (<8k P a). Our results show low pressures such as 4 kPa to 8 kPa are sufficient to significantly increase light penetration by decreasing the attenuation coefficient by at least 1.0m m ^-1.