Wavelength- and irradiance-dependent changes in intracellular nitric oxide level

Unlocking the potential of photobiomodulation therapy for brain neurovascular coupling: The biological effects and medical applications

Photobiomodulation (PBM) therapy stands as an innovative neurostimulation modality that has demonstrated both efficacy and safety in improving brain function. This therapy exerts multifaceted influences on neurons, blood vessels, and their intricate interplay known as neurovascular coupling (NVC). Growing evidence indicates that NVC may present a promising target for PBM intervention. However, the detailed mechanisms underlying its therapeutic benefits remain to be fully understood. This review aims to elucidate the potential metabolic pathways and signaling cascades involved in the modulatory effects of PBM, while also exploring the extensive repertoire of PBM applications in neurologic and psychiatric conditions. The prospects of PBM within the realm of NVC investigation are intensively considered, providing deeper insights into the powerful capabilities of PBM therapy and its potential to revolutionize neurostimulation treatments.

THRA1/PGC-1α/SIRT3 pathway regulates oxidative stress and is implicated in hypertension of maternal hypothyroid rat offspring

Many epidemiologic and animal studies have shown that maternal hypothyroidism is associated with an increased risk of hypertension in offspring in later life. In this study, we established a maternal hypothyroidism rat model to explore the underlying mechanism that contributes to elevated blood pressure in adult male offspring of hypothyroid mothers. The levels of thyroid hormones (THs) in the offspring were measured using ELISA kits. Blood pressure (BP) and depressor response were recorded in conscious, freely moving rats. Vascular reactivity was conducted in isolated mesenteric arteries (MAs) using a myograph. We used real-time quantitative PCR (RT-qPCR) and Western blots to examine the mRNA and protein expression of relevant molecules in MAs. The A7r5 cells were transfected with small interfering RNA (siRNA) to further investigate the gene functions. The following findings were observed: Basal systolic BP and diastolic BP was significantly increased, accompanied by attenuated depressor response and decreased vascular sensitivity to sodium nitroprusside (SNP). Reactive Oxygen Species (ROS) levels in the MAs were enhanced, along with decreased expression of the THRA1/PGC-1α/SIRT3 pathway. In A7r5 cells, triiodothyronine (T3) pretreatment improved the PGC-1α/SIRT3 pathway and reduced ROS levels after H2O2-induced oxidative stress. In contrast, the knockdown of THRA1 or SIRT3 diminished the above effects of T3. Down-regulation of THRA1 contributed to a decline in the PGC-1α/SIRT3 pathway, which causes an increased production of ROS. This indicates that the T3-THRA1/PGC-1α/SIRT3 pathway plays a protective role in the regulation of BP and may be a potential therapeutic strategy against hypertension.

Direct Photobiomodulation Therapy on the Sciatic Nerve Significantly Attenuates Acute Nociceptive Sensitivity Without Affecting Motor Output

OBJECTIVES

Pharmacologic pain treatments lack specific targeting and often produce unwanted side effects (eg, addiction, additional hyperalgesia). We previously established that the direct application of laser irradiation (direct photobiomodulation [PBM]) of the sural nerve reduces thermal hypersensitivity in a rodent model of chronic pain, but not mechanical hypersensitivity. These observations were consistent with a selective reduction in the small-diameter fiber contribution to electrophysiologically measured evoked response after direct PBM of a sensory nerve (saphenous). However, to our knowledge, direct application of laser irradiation has never been performed in an animal model of acute nociceptive pain or on a mixed nerve in which sensory and motor outcomes can be observed.

MATERIALS AND METHODS

In this study, we describe the effects of direct application of laser irradiation (808 nm, 60 mW, 4 minutes) on a mixed nerve (sciatic nerve) in an acute nociceptive pain model (intradermal capsaicin injection) in rats over the course of two weeks. To investigate whether laser irradiation of a mixed nerve alters motor function, in separate experiments, we applied laser irradiation to the sciatic nerve (using the same parameters as in the chronic pain experiments), and force generation of the gastrocnemius was measured.

RESULTS

Capsaicin-induced hypersensitivities to mechanical (pin prick) and thermal (Hargreaves) noxious stimuli, associated with Aδ- and C-fibers, showed a maximal reduction of 70% and 56.2%, respectively, by direct PBM, when compared with a control group (vehicle injection, no PBM) on the same day. This reduction was determined to be significant using a mixed-design analysis of variance with a p value < 0.05. Force generation remained unchanged for up to 120 minutes after laser irradiation. In summary, direct PBM selectively inhibits C- and Aδ-fiber transmission while leaving Aɑ-, Aβ-, and motor-fiber activity intact.

CONCLUSIONS

These results, in conjunction with our previous analyses of laser irradiation effects on the sural nerve in a chronic spared nerve injury pain model, suggest that direct PBM is a promising candidate for treating pain induced by small-diameter fiber activity.

Local and systemic photobiomodulation using a 650 nm LED on skin temperature and hyperalgesia in cellulite: a randomized, placebo-controlled and double-blinded clinical trial

Cellulite is a skin condition that significantly affects women, characterized by "holes" or depressions in the skin, affecting approximately 95% of women at some point in their lives. Cellulite often presents inflammatory symptoms such as increased skin temperature and hyperalgesia. Photobiomodulation, whether applied locally or systemically, has demonstrated important anti-inflammatory effects in various conditions. This study investigates the effects of local and systemic photobiomodulation on hip culottes temperature increases and hyperalgesia in patients with grades 2 to 4 cellulite. Cellulite assessment was carried out using detailed anamnesis, photographic records, algometry, and infrared thermography. Participants received randomized bilateral treatment with or without systemic irradiation using LED photobiomodulation on the hip culottes for four weeks, three times a week. This study aimed to evaluate the effect of photobiomodulation, especially locally applied, together or not with systemic irradiation, on cellulite hyperalgesia and skin temperature among 25 female participants. The group that received only LED treatment showed an increase in pain threshold of 8% and 20% on the right and left sides, respectively, while the group treated with LED + ILIB showed an increase in pain threshold of 32% on both sides. Local photobiomodulation produced a skin temperature decrease of 0.4 °C, while the combination of local and systemic irradiation produced an average skin temperature decrease of 1.2 °C. Our results clearly demonstrate a significantly beneficial effect of LED therapy for cellulite treatment, especially when administered in combination with mILIB, leading to a significant reduction of pain hypersensitivity and skin temperature, indicating a regional subcutaneous improvement of the inflammatory status.

Differential Nitric Oxide Responses in Primary Cultured Keratinocytes and Fibroblasts to Visible and Near-Infrared Light

NO is a crucial signaling molecule involved in skin health, the immune response, and the protection against environmental stressors. This study explores how different wavelengths of light, namely blue (455 nm), red (660 nm), and near infrared (NIR, 850 nm), affect nitric oxide (NO) production in skin cells. Primary keratinocytes and fibroblasts from three donors were exposed to these wavelengths, and NO production was quantified using a DAF-FM fluorescent probe. The results demonstrated that all three wavelengths stimulated NO release, with blue light showing the most pronounced effect. Specifically, blue light induced a 1.7-fold increase in NO in keratinocytes compared to red and NIR light and a 2.3-fold increase in fibroblasts compared to red light. Notably, fibroblasts exposed to NIR light produced 1.5 times more NO than those exposed to red light, while keratinocytes consistently responded more robustly across all wavelengths. In conclusion, blue light significantly boosts NO production in both keratinocytes and fibroblasts, making it the most effective wavelength. Red and NIR light, while less potent, also promote NO production and could serve as complementary therapeutic options, particularly for minimizing potential photoaging effects.

Simultaneous irradiation of 660 and 808 nm on gingival epithelial cells and fibroblasts induces different patterns of oxidative/antioxidative activities: What is the role of the cell type and irradiation parameters?

The aim of this study was to investigate whether simultaneous irradiation at 660 and 808 nm generates different patterns of oxidative/antioxidative activities compared to consecutive irradiation. Primary cultures of gingival keratinocytes and fibroblasts were exposed to a diose laser (660 ± 2 nm and 808 ± 2 nm, 100 mW, 0.09 cm2 spot area) using double irradiation with the two wavelengths (consecutive or simultaneous) for 6, 10, and 20 s. The two irradiation regimens did not increase cell viability in any of the experimental conditions. Lipid peroxidation was increased after consecutive irradiation in epithelial cells, which was not detected after simultaneous irradiation. After 20s of the simultaneous mode, ROS levels increased, but antioxidative balance decreased. In the fibroblasts, the two double irradiations induced ROS reduction, increase in lipid peroxidation, and improvement of antioxidative balance, mainly after the 20 s irradiation time. In conclusion, simultaneous and consecutive irradiation induced distinct oxidative stress modulation in oral epithelial cells and fibroblasts. The imbalance in the oxidative system observed after longer exposures, allied with the absence of a significant increase in the viability of the two cell types, suggests a contraindication for longer simultaneous irradiation in clinical situations that demand cellular stimulation.

Assessing the Impact of High Photon Energy Wavelengths on the Treatment of Chronic Neck and Shoulder Pain

The effect of low-level laser therapy with high photon energy wavelengths, green and violet, for treating chronic musculoskeletal pain was examined in the first-ever clinical trial of its kind. Participants (n = 43) underwent a single 13-minute laser session. The primary measure of effectiveness was the change in initial visual analog pain (VAS) scores observed three minutes posttreatment. The success of a participant was defined in advance as a reduction of ≥30% in VAS scores, while the success of the study was predetermined as achieving a 65 ± 5% success rate among individual participants. Results demonstrated subjects' VAS pain scores decreased from 71.79 to 34.02 (p < 0.0001), while most participants in the study (81.4%) achieved a ≥30% decrease in pain scores. The findings from this clinical investigation provided substantial support for the first Food and Drug Administration clearance (K221987) for the combined application of green and violet lasers.

Photobiomodulation at Defined Wavelengths Regulates Mitochondrial Membrane Potential and Redox Balance in Skin Fibroblasts

Starting from the discovery of phototherapy in the beginning of the last century, photobiomodulation (PBM) has been defined in late 1960s and, since then, widely described in different in vitro models. Robust evidence indicates that the effect of light exposure on the oxidative state of the cells and on mitochondrial dynamics, suggesting a great therapeutic potential. The translational scale-up of PBM, however, has often given contrasting and confusing results, mainly due to light exposure protocols which fail to adequately control or define factors such as emitting device features, emitted light characteristics, exposure time, cell target, and readouts. In this in vitro study, we describe the effects of a strictly controlled light-emitting diode (LED)-based PBM protocol on human fibroblasts, one of the main cells involved in skin care, regeneration, and repair. We used six emitter probes at different wavelengths (440, 525, 645, 660, 780, and 900 nm) with the same irradiance value of 0.1 mW/cm2, evenly distributed over the entire surface of the cell culture well. The PBM was analyzed by three main readouts: (i) mitochondrial potential (MitoTracker Orange staining), (ii) reactive oxygen species (ROS) production (CellROX staining); and (iii) cell death (nuclear morphology). The assay was also implemented by cell-based high-content screening technology, further increasing the reliability of the data. Different exposure protocols were also tested (one, two, or three subsequent 20 s pulsed exposures at 24 hr intervals), and the 645 nm wavelength and single exposure chosen as the most efficient protocol based on the mitochondrial potential readout, further confirmed by mitochondrial fusion quantification. This protocol was then tested for its potential to prevent H2O2-induced oxidative stress, including modulation of the light wave frequency. Finally, we demonstrated that the controlled PBM induced by the LED light exposure generates a preconditioning stimulation of the mitochondrial potential, which protects the cell from oxidative stress damage.

Photophysical Mechanisms of Photobiomodulation Therapy as Precision Medicine

Despite a significant focus on the photochemical and photoelectrical mechanisms underlying photobiomodulation (PBM), its complex functions are yet to be fully elucidated. To date, there has been limited attention to the photophysical aspects of PBM. One effect of photobiomodulation relates to the non-visual phototransduction pathway, which involves mechanotransduction and modulation to cytoskeletal structures, biophotonic signaling, and micro-oscillatory cellular interactions. Herein, we propose a number of mechanisms of PBM that do not depend on cytochrome c oxidase. These include the photophysical aspects of PBM and the interactions with biophotons and mechanotransductive processes. These hypotheses are contingent on the effect of light on ion channels and the cytoskeleton, the production of biophotons, and the properties of light and biological molecules. Specifically, the processes we review are supported by the resonant recognition model (RRM). This previous research demonstrated that protein micro-oscillations act as a signature of their function that can be activated by resonant wavelengths of light. We extend this work by exploring the local oscillatory interactions of proteins and light because they may affect global body circuits and could explain the observed effect of PBM on neuro-cortical electroencephalogram (EEG) oscillations. In particular, since dysrhythmic gamma oscillations are associated with neurodegenerative diseases and pain syndromes, including migraine with aura and fibromyalgia, we suggest that transcranial PBM should target diseases where patients are affected by impaired neural oscillations and aberrant brain wave patterns. This review also highlights examples of disorders potentially treatable with precise wavelengths of light by mimicking protein activity in other tissues, such as the liver, with, for example, Crigler-Najjar syndrome and conditions involving the dysregulation of the cytoskeleton. PBM as a novel therapeutic modality may thus behave as "precision medicine" for the treatment of various neurological diseases and other morbidities. The perspectives presented herein offer a new understanding of the photophysical effects of PBM, which is important when considering the relevance of PBM therapy (PBMt) in clinical applications, including the treatment of diseases and the optimization of health outcomes and performance.

Photobiomodulation and nitric oxide signaling

Nitric oxide (NO) is a well-known gaseous mediator that maintains vascular homeostasis. Extensive evidence supports that a hallmark of endothelial dysfunction, which leads to cardiovascular diseases, is endothelial NO deficiency. Thus, restoring endothelial NO represents a promising approach to treating cardiovascular complications. Despite many therapeutic agents having been shown to augment NO bioavailability under various pathological conditions, success in resulting clinical trials has remained elusive. There is solid evidence of diverse beneficial effects of the treatment with low-power near-infrared (NIR) light, defined as photobiomodulation (PBM). Although the precise mechanisms of action of PBM are still elusive, recent studies consistently report that PBM improves endothelial dysfunction via increasing bioavailable NO in a dose-dependent manner and open a feasible path to the use of PBM for treating cardiovascular diseases via augmenting NO bioavailability. In particular, the use of NIR light in the NIR-II window (1000-1700 nm) for PBM, which has reduced scattering and minimal tissue absorption with the largest penetration depth, is emerging as a promising therapy. In this review, we update recent findings on PBM and NO.

Differential effects of 808-nm light on electron transport chain enzymes in isolated mitochondria: Implications for photobiomodulation initiation

Photobiomodulation is a term for using low-power red to near-infrared light to stimulate a variety of positive biological effects. Though the scientific and clinical acceptance of PBM as a therapeutic intervention has increased dramatically in recent years, the molecular underpinnings of the effect remain poorly understood. The putative chromophore for PBM effects is cytochrome c oxidase. It is postulated that light absorption at cytochrome c oxidase initiates a signaling cascade involving ATP and generation of reactive oxygen species (ROS), which subsequently results in improved cellular robustness. However, this hypothesis is largely based on inference and indirect evidence, and the precise molecular mechanisms that govern how photon absorption leads to these downstream effects remain poorly understood. We conducted low-power PBM-type light exposures of isolated mitochondria to 808 nm NIR light, at a number of irradiances. NIR exposure was found to enhance the activity of complex IV, depress the activity of complex III, and had no effect on the activity of complex II. Further, examining the dose-response of complex IV we found NIR enhancement did not exhibit irradiance reciprocity, indicating the effect on complex IV may not have direct photochemical basis. In summary, this research presents a novel method to interrogate the earliest stages of PBM in the mitochondria, and a unique window into the corresponding molecular mechanism(s) of induction.

Considerations for the Use of Photobiomodulation in the Treatment of Retinal Diseases

Photobiomodulation (PBM) refers to the beneficial effect produced from low-energy light irradiation on target cells or tissues. Increasing evidence in the literature suggests that PBM plays a positive role in the treatment of retinal diseases. However, there is great variation in the light sources and illumination parameters used in different studies, resulting in significantly different conclusions regarding PBM's therapeutic effects. In addition, the mechanism by which PBM improves retinal function has not been fully elucidated. In this study, we conducted a narrative review of the published literature on PBM for treating retinal diseases and summarized the key illumination parameters used in PBM. Furthermore, we explored the potential molecular mechanisms of PBM at the retinal cellular level with the goal of providing evidence for the improved utilization of PBM in the treatment of retinal diseases.

Sometimes less is more: inhibitory infrared light during early reperfusion calms hyperactive mitochondria and suppresses reperfusion injury

Ischemic stroke affects over 77 million people annually around the globe. Due to the blockage of a blood vessel caused by a stroke, brain tissue becomes ischemic. While prompt restoration of blood flow is necessary to save brain tissue, it also causes reperfusion injury. Mitochondria play a crucial role in early ischemia-reperfusion injury due to the generation of reactive oxygen species (ROS). During ischemia, mitochondria sense energy depletion and futilely attempt to up-regulate energy production. When reperfusion occurs, mitochondria become hyperactive and produce large amounts of ROS which damages neuronal tissue. This ROS burst damages mitochondria and the cell, which results in an eventual decrease in mitochondrial activity and pushes the fate of the cell toward death. This review covers the relationship between the mitochondrial membrane potential (ΔΨm) and ROS production. We also discuss physiological mechanisms that couple mitochondrial energy production to cellular energy demand, focusing on serine 47 dephosphorylation of cytochrome c (Cytc) in the brain during ischemia, which contributes to ischemia-reperfusion injury. Finally, we discuss the use of near infrared light (IRL) to treat stroke. IRL can both stimulate or inhibit mitochondrial activity depending on the wavelength. We emphasize that the use of the correct wavelength is crucial for outcome: inhibitory IRL, applied early during reperfusion, can prevent the ROS burst from occurring, thus preserving neurological tissue.

Mammalian complex III heme dynamics studied with pump-probe spectroscopy and red light illuminations

The electronic or molecular mechanisms that initiate photobiomodulation (PBM) in cells are not yet fully understood. The porcine complex III (C-III) of the electron transport chain was characterized with transient absorption spectroscopy (TAS). We then applied our recently developed continuous wave laser coupled TAS procedure (CW-TAS) to investigate the effect of red light irradiances on the heme dynamics of C-III in its c₁ reduced state. The time constants were found to be 3.3 ± 0.3 ps for vibrational cooling of the oxidized state and 4.9 ± 0.4 ps for rebinding of the photodissociated axial ligand of the c₁ reduced state. The analysis of the CW-TAS procedure yielded no significant changes in the C-III heme dynamics. We rule out the possibility of 635 nm CW light at 4.7 mW/cm² inducing a PBM effect on the heme dynamic of C-III, specifically with the photodissociation of its axial ligand.

Incorporation of a Nitric Oxide Donating Motif into Novel PC-PLC Inhibitors Provides Enhanced Anti-Proliferative Activity

Inhibition of phosphatidylcholine-specific phospholipase C (PC-PLC) has previously been shown to be a potential target for novel cancer therapeutics. One downstream consequence of PC-PLC activity is the activation of NF-κB, a nuclear transcription factor responsible for transcribing genes related to oncogenic traits, such as proliferation, angiogenesis, metastasis, and cancer cell survival. Another biological pathway linked to NF-κB is the exogenous delivery of nitric oxide (NO), which decreases NF-κB activity through an apparent negative-feedback loop. In this study, we designed and synthesised 13 novel NO-releasing derivatives of our previously reported class of PC-PLC inhibitors, 2-morpholinobenzoic acids. These molecules contained a secondary benzylamine group, which was readily nitrosylated and subsequently confirmed to release NO in vitro using a DAF-FM fluorescence-based assay. It was then discovered that these NO-releasing derivatives possessed significantly improved anti-proliferative activity in both MDA-MB-231 and HCT116 cancer cell lines compared to their non-nitrosylated parent compounds. These results confirmed that the inclusion of an exogenous NO-releasing functional group onto a known PC-PLC inhibitor enhances anti-proliferative activity and that this relationship can be exploited in order to further improve the anti-proliferative activity of current/future PC-PLC inhibitors.

Transient absorption spectroscopy to explore cellular pathways to photobiomodulation

Photobiomodulation (PBM) describes the use of low irradiance light in the red to near-infrared wavelength range to stimulate biological effects in tissue, and many biological and spectroscopic techniques are used to study PBM. However, these techniques focus on the products or downstream effects rather than the electronic transitions that initiate the PBM processes. This study presents a novel approach to studying low irradiance light exposures on individual proteins and/or protein complexes by combining a continuous wave (CW) laser diode with femtosecond transient absorption spectroscopy (TAS), coined here as CW-TAS, and tests the system on reduced cytochrome c (Cyt c) for proof of principle. TAS was conducted using a 532-nm excitation pump beam and a 350-600 nm supercontinuum probe. CW laser diodes with wavelengths of 450 nm, 635 nm, and 808 nm were interchangeably fiber coupled into the HELIOS Fire. Samples of Cyt c were tested by TAS using a pump power of 15 μW, both with and without CW exposure. CW exposures were carried out with irradiances of 1.60 and 3.20 mW/cm², except for 808 nm, which was only tested at 1.60 mW/cm². Both kinetic and global analyses were performed on the TAS data and the time constants for sets with and without CW exposures were compared. The TAS data for Cyt c with the full dosage of CW exposures did not alter the TAS data distinguishably from the control data. No new electronic transient signals were observed beyond the background when testing Cyt c with the CW exposures. Kinetic analysis confirmed that existing transients did not deviate beyond uncertainty. Global time constants for Cyt c were calculated to be 0.25 ± 0.03 ps and 5.1 ± 0.3 ps for the control study, and the time constants for the CW exposed Cyt c were not significantly different. This study concludes that CW irradiation, at doses delivered, does not alter the transient absorption data of Cyt c. The CW-TAS method provides a new tool for studying PBM effects in other proteins and protein complexes that might respond to the CW wavelengths, such as Complex IV, in future studies.

What is the optimal time-response window for the use of photobiomodulation therapy combined with static magnetic field (PBMT-sMF) for the improvement of exercise performance and recovery, and for how long the effects last? A randomized, triple-blinded, placebo-controlled trial

Background

The optimal time-response window for photobiomodulation therapy (PBMT) using low-level laser therapy (LLLT) and/or light emitting diodes therapy (LEDT) combined with static magnetic fields (sMF) before physical activity still was not fully investigated. The aim of the present study was to investigate the better of four time-response windows for PBMT combined with sMF (PBMT-sMF) use before exercise in humans.

Methods

A prospectively registered, randomized, triple-blinded (volunteers, therapists and assessors) placebo-controlled trial was carried out. Sixty healthy untrained male subjects were randomly allocated to six experimental groups (n = 10 per group): PBMT-sMF 5 mins, PBMT-sMF 3 h, PBMT-sMF 6 h, PBMT-sMF 1-day, placebo, and control. The control group performed all procedures, however did not receive any kind of intervention. PBMT-sMF active or PBMT-sMF placebo was applied precisely in different time points after baseline MVC test to ensure that both MVC tests and eccentric exercise protocol would occur at the same hour of the day in all groups. Then, after five minutes, 3 h, 6 h or 1-day (24 h) of PBMT-sMF treatment (active or placebo) the eccentric exercise protocol was performed. The primary outcome was peak torque obtained from maximum voluntary contraction (MVC). The secondary outcomes were creatine kinase (CK), and delayed onset muscle soreness (DOMS). The primary and secondary outcomes were measured at baseline, immediately after, 1 h, 24 h and 48 h after the eccentric exercise protocol.

Results

Sixty patients were randomized and analyzed to each sequence. The outcomes in absolute values show that all active PBMT-sMF groups increased (p < 0.05) MVC from immediately after to 1 h after eccentric exercise, and decreased (p < 0.05) CK activity at all time points. However, PBMT-sMF 5 mins, 3 h and 6 h groups showed better results in MVC and CK analysis from 24 h to 48 h, and also to DOMS (p < 0.05) at all time points. Participants did not report any adverse events.

Conclusions

PBMT-sMF can be used from 5 min to 6 h before exercise, and the effects can last up to 54 h after treatment. However, the effects start to decrease when a 1-day (24 h) time-response window is used.

Trial registration

NCT03420391. Registered 05 February 2018.