Transcranial low-level laser therapy in an in vivo model of stroke: Relevance to the brain infarct, microglia activation and neuroinflammation

Phototherapy for age-related brain diseases: Challenges, successes and future

Brain diseases present a significant obstacle to both global health and economic progress, owing to their elusive pathogenesis and the limited effectiveness of pharmaceutical interventions. Phototherapy has emerged as a promising non-invasive therapeutic modality for addressing age-related brain disorders, including stroke, Alzheimer's disease (AD), and Parkinson's disease (PD), among others. This review examines the recent progressions in phototherapeutic interventions. Firstly, the article elucidates the various wavelengths of visible light that possess the capability to penetrate the skin and skull, as well as the pathways of light stimulation, encompassing the eyes, skin, veins, and skull. Secondly, it deliberates on the molecular mechanisms of visible light on photosensitive proteins, within the context of brain disorders and other molecular pathways of light modulation. Lastly, the practical application of phototherapy in diverse clinical neurological disorders is indicated. Additionally, this review presents novel approaches that combine phototherapy and pharmacological interventions. Moreover, it outlines the limitations of phototherapeutics and proposes innovative strategies to improve the treatment of cerebral disorders.

Clinical Efficiency of High-Intensity Laser Therapy in Patients With Cervical Radiculopathy: A 12-Week Follow-up, Randomized, Placebo-Controlled Trial

OBJECTIVE

The purpose of this study was to research the clinical effectiveness of high-intensity laser therapy combined with exercise on pain, quality of life, and disability in patients with cervical radiculopathy and compared it with that of placebo and exercise alone.

DESIGN

Ninety participants with cervical radiculopathy were randomized into the following three groups: high-intensity laser therapy + exercise ( n = 30), placebo + exercise ( n = 30), and exercise only ( n = 30). Pain, cervical range of motion, disability, and quality of life (36-item Short Form Health Survey) were assessed at baseline and weeks 4 and 12.

RESULTS

The mean age of the patients (66.7% female) was 48.9 ± 9.3 yrs. Pain intensity in the arm and neck, neuropathic and radicular pain levels, disability, and several parameters of the 36-item Short Form Health Survey showed an improvement in the short and medium term in all three groups. These improvements were greater in the high-intensity laser therapy + exercise group than in the other two groups.

CONCLUSIONS

High-intensity laser therapy + exercise was much more effective in improving medium-term radicular pain, quality of life, and functionality in patients with cervical radiculopathy. Thus, high-intensity laser therapy should be considered for the management of cervical radiculopathy.

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CME OBJECTIVES

At the conclusion of this article, readers will be able to: (1) Define cervical radicular pain and its clinical presentation, and explain the main pathomechanism in cervical radiculopathy (CR); (2) Describe the effects of laser administration on neuropathic pain; and (3) Discuss the clinical significance of coadministration of high-intensity laser therapy (HILT) with exercise (HILT + EX) in CR.

LEVEL

Advanced.

ACCREDITATION

The Association of Academic Physiatrists is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for physicians.The Association of Academic Physiatrists designates this Journal-based CME activity for a maximum of 1.0 AMA PRA Category 1 Credit(s) ™. Physicians should only claim credit commensurate with the extent of their participation in the activity.

Photobiomodulation of Neurogenesis through the Enhancement of Stem Cell and Neural Progenitor Differentiation in the Central and Peripheral Nervous Systems

Photobiomodulation (PBM) is the regulation of biological processes using light energy from sources such as lasers or light-emitting diodes. Components of the nervous system, such as the brain and peripheral nerves, are important candidate PBM targets due to the lack of therapeutic modalities for the complete cure of neurological diseases. PBM can be applied either to regenerate damaged organs or to prevent or reduce damage caused by disease. Although recent findings have suggested that neural cells can be regenerated, which contradicts our previous understanding, neural structures are still thought to have weaker regenerative capacity than other systems. Therefore, enhancing the regenerative capacity of the nervous system would aid the future development of therapeutics for neural degeneration. PBM has been shown to enhance cell differentiation from stem or progenitor cells to near-target or target cells. In this review, we have reviewed research on the effects of PBM on neurogenesis in the central nervous system (e.g., animal brains) and the peripheral nervous system (e.g., peripheral sensory neural structures) and sought its potential as a therapeutic tool for intractable neural degenerative disorders.

The Implications of Microglial Regulation in Neuroplasticity-Dependent Stroke Recovery

Stroke causes varying degrees of neurological deficits, leading to corresponding dysfunctions. There are different therapeutic principles for each stage of pathological development. Neuroprotection is the main treatment in the acute phase, and functional recovery becomes primary in the subacute and chronic phases. Neuroplasticity is considered the basis of functional restoration and neurological rehabilitation after stroke, including the remodeling of dendrites and dendritic spines, axonal sprouting, myelin regeneration, synapse shaping, and neurogenesis. Spatiotemporal development affects the spontaneous rewiring of neural circuits and brain networks. Microglia are resident immune cells in the brain that contribute to homeostasis under physiological conditions. Microglia are activated immediately after stroke, and phenotypic polarization changes and phagocytic function are crucial for regulating focal and global brain inflammation and neurological recovery. We have previously shown that the development of neuroplasticity is spatiotemporally consistent with microglial activation, suggesting that microglia may have a profound impact on neuroplasticity after stroke and may be a key therapeutic target for post-stroke rehabilitation. In this review, we explore the impact of neuroplasticity on post-stroke restoration as well as the functions and mechanisms of microglial activation, polarization, and phagocytosis. This is followed by a summary of microglia-targeted rehabilitative interventions that influence neuroplasticity and promote stroke recovery.

Can transcranial photobiomodulation improve cognitive function? A systematic review of human studies

BACKGROUND

Transcranial photobiomodulation (tPBM) has been studied for over a decade as a possible cognitive intervention.

OBJECTIVE

To evaluate the effect of tPBM for enhancing human cognitive function in healthy adults and remediating impaired cognitive function in adults with cognitive disorders.

METHODS

A systematic literature search from three electronic databases (PubMed, Scopus, Web of Science) was conducted from 1987 to May 2022. The cognitive function being evaluated included learning and memory, attention, executive function, language, and global cognitive function.

RESULTS

Of the 35 studies identified, 29 (82.9 %) studies reported positive improvement in cognitive functions after tPBM. All nine studies on participants with subjective memory complaints, mild cognitive impairment, and dementia, showed positive outcomes. Seven (87.5 %) studies on traumatic brain injury (TBI) patients also showed positive results. A series of clinical trials on stroke patients showed positive trends on improved neurological deficit at first, but was prematurely terminated later at phase III due to the lack of statistical significance. One of the most common protocols for clinical populations employed devices delivering near-infrared light (810 nm), the irradiance of 20-25 mW/cm², and fluence of 1-10 J/cm². While this was common, the reviewed protocols also included other wavelengths of light ranging from visible, red (630-635 nm) to invisible near-infrared maximum wavelengths of 1060-1068 nm.

CONCLUSIONS

tPBM seems to improve cognitive function. However, only half of the reviewed clinical trials were randomized control trials, further investigation is warranted.

Photobiomodulation Attenuated Cognitive Dysfunction and Neuroinflammation in a Prenatal Valproic Acid-Induced Autism Spectrum Disorder Mouse Model

Autism spectrum disorder (ASD) is a neurodevelopmental condition characterized by social communication and interaction disorders, as well as repetitive and restrictive behaviors. To date, no effective treatment strategies have been identified. However, photobiomodulation (PBM) is emerging as a promising treatment for neurological and neuropsychiatric disorders. We used mice exposed to valproic acid (VPA) as a model of ASD and found that pathological behavioral and histological changes that may have been induced by VPA were attenuated by PBM treatment. Pregnant mice that had been exposed to VPA were treated with PBM three times. Thereafter, we evaluated the offspring for developmental disorders, motor function, hyperactivity, repetitive behaviors, and cognitive impairment. PBM attenuated many of the pathological behaviors observed in the VPA-induced ASD mouse model. In addition, pathophysiological analyses confirmed that the increase in activated microglia and astrocytes observed in the VPA-induced ASD mouse model was attenuated by PBM treatment. This suggests that PBM can counteract the behavioral changes caused by neuroinflammation in ASD. Therefore, our data show that PBM has therapeutic potential and may reduce the prevalence of neurodevelopmental disorders such as ASD.

Photobiomodulation for the treatment of neuroinflammation: A systematic review of controlled laboratory animal studies

Background

Neuroinflammation is a response that involves different cell lineages of the central nervous system, such as neurons and glial cells. Among the non-pharmacological interventions for neuroinflammation, photobiomodulation (PBM) is gaining prominence because of its beneficial effects found in experimental brain research. We systematically reviewed the effects of PBM on laboratory animal models, specially to investigate potential benefits of PBM as an efficient anti-inflammatory therapy.

Methods

We conducted a systematic search on the bibliographic databases (PubMed and ScienceDirect) with the keywords based on MeSH terms: photobiomodulation, low-level laser therapy, brain, neuroinflammation, inflammation, cytokine, and microglia. Data search was limited from 2009 to June 2022. We followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guideline. The initial systematic search identified 140 articles. Among them, 54 articles were removed for duplication and 59 articles by screening. Therefore, 27 studies met the inclusion criteria.

Results

The studies showed that PBM has anti-inflammatory properties in several conditions, such as traumatic brain injury, edema formation and hyperalgesia, ischemia, neurodegenerative conditions, aging, epilepsy, depression, and spinal cord injury.

Conclusion

Taken together, these results indicate that transcranial PBM therapy is a promising strategy to treat brain pathological conditions induced by neuroinflammation.

Microglia-mediated neuroinflammation and neuroplasticity after stroke

Stroke remains a major cause of long-term disability and mortality worldwide. The immune system plays an important role in determining the condition of the brain following stroke. As the resident innate immune cells of the central nervous system, microglia are the primary responders in a defense network covering the entire brain parenchyma, and exert various functions depending on dynamic communications with neurons, astrocytes, and other neighboring cells under both physiological or pathological conditions. Microglia activation and polarization is crucial for brain damage and repair following ischemic stroke, and is considered a double-edged sword for neurological recovery. Microglia can exist in pro-inflammatory states and promote secondary brain damage, but they can also secrete anti-inflammatory cytokines and neurotrophic factors and facilitate recovery following stroke. In this review, we focus on the role and mechanisms of microglia-mediated neuroinflammation and neuroplasticity after ischemia and relevant potential microglia-based interventions for stroke therapy.

Synergistic photobiomodulation with 808-nm and 1064-nm lasers to reduce the β-amyloid neurotoxicity in the in vitro Alzheimer's disease models

BACKGROUND

In Alzheimer's disease (AD), the deposition of β-amyloid (Aβ) plaques is closely associated with the neuronal apoptosis and activation of microglia, which may result in the functional impairment of neurons through pro-inflammation and over-pruning of the neurons. Photobiomodulation (PBM) is a non-invasive therapeutic approach without any conspicuous side effect, which has shown promising attributes in the treatment of chronic brain diseases such as AD by reducing the Aβ burden. However, neither the optimal parameters for PBM treatment nor its exact role in modulating the microglial functions/activities has been conclusively established yet.

METHODS

An inflammatory stimulation model of Alzheimer's disease (AD) was set up by activating microglia and neuroblastoma with fibrosis β-amyloid (fAβ) in a transwell insert system. SH-SY5Y neuroblastoma cells and BV2 microglial cells were irradiated with the 808- and 1,064-nm lasers, respectively (a power density of 50 mW/cm2 and a dose of 10 J/cm2) to study the PBM activity. The amount of labeled fAβ phagocytosed by microglia was considered to assess the microglial phagocytosis. A PBM-induced neuroprotective study was conducted with the AD model under different laser parameters to realize the optimal condition. Microglial phenotype, microglial secretions of the pro-inflammatory and anti-inflammatory factors, and the intracellular Ca2+ levels in microglia were studied in detail to understand the structural and functional changes occurring in the microglial cells of AD model upon PBM treatment.

CONCLUSION

A synergistic PBM effect (with the 808- and 1,064-nm lasers) effectively inhibited the fAβ-induced neurotoxicity of neuroblastoma by promoting the viability of neuroblastoma and regulating the intracellular Ca2+ levels of microglia. Moreover, the downregulation of Ca2+ led to microglial polarization with an M2 phenotype, which promotes the fAβ phagocytosis, and resulted in the upregulated expression of anti-inflammatory factors and downregulated expression of inflammatory factors.

Near-infrared light reduces glia activation and modulates neuroinflammation in the brains of diet-induced obese mice

Neuroinflammation is a key event in neurodegenerative conditions such as Alzheimer's disease (AD) and characterizes metabolic pathologies like obesity and type 2 diabetes (T2D). Growing evidence in humans shows that obesity increases the risk of developing AD by threefold. Hippocampal neuroinflammation in rodents correlates with poor memory performance, suggesting that it contributes to cognitive decline. Here we propose that reducing obesity/T2D-driven neuroinflammation may prevent the progression of cognitive decline associated with AD-like neurodegenerative states. Near-infrared light (NIR) has attracted increasing attention as it was shown to improve learning and memory in both humans and animal models. We previously reported that transcranial NIR delivery reduced amyloid beta and Tau pathology and improved memory function in mouse models of AD. Here, we report the effects of NIR in preventing obesity-induced neuroinflammation in a diet-induced obese mouse model. Five-week-old wild-type mice were fed a high-fat diet (HFD) for 13 weeks to induce obesity prior to transcranial delivery of NIR for 4 weeks during 90-s sessions given 5 days a week. After sacrifice, brain slices were subjected to free-floating immunofluorescence for microglia and astrocyte markers to evaluate glial activation and quantitative real-time polymerase chain reaction (PCR) to evaluate expression levels of inflammatory cytokines and brain-derived neurotrophic factor (BDNF). The hippocampal and cortical regions of the HFD group had increased expression of the activated microglial marker CD68 and the astrocytic marker glial fibrillary acidic protein. NIR-treated HFD groups showed decreased levels of these markers. PCR revealed that hippocampal tissue from the HFD group had increased levels of pro-inflammatory interleukin (IL)-1β and tumor necrosis factor-α. Interestingly, the same samples showed increased levels of the anti-inflammatory IL-10. All these changes were attenuated by NIR treatment. Lastly, hippocampal levels of the neurotrophic factor BDNF were increased in NIR-treated HFD mice, compared to untreated HFD mice. The marked reductions in glial activation and pro-inflammatory cytokines along with elevated BDNF provide insights into how NIR could reduce neuroinflammation. These results support the use of NIR as a potential non-invasive and preventive therapeutic approach against chronic obesity-induced deficits that are known to occur with AD neuropathology.

Transcranial photobiomodulation (808 nm) attenuates pentylenetetrazole-induced seizures by suppressing hippocampal neuroinflammation, astrogliosis, and microgliosis in peripubertal rats

Significance: Transcranial photobiomodulation (tPBM) at 808 nm attenuates pentylenetetrazole (PTZ)-induced seizures and convulsive status epilepticus (CSE) in peripubertal rats by protecting neurons from injury and parvalbumin-positive interneurons from apoptosis, and preserving the integrity of perisomatic inhibitory networks. However, the effects of tPBM on neuroinflammation, astrogliosis, and microgliosis in epileptic rat brains are unknown. Thus, further study to unveil these aspects is needed for understanding the phenomena of tPBM on pediatric CSE prevention. Aim: To evaluate the effects of tPBM on neuroinflammation, astrogliosis, and microgliosis in peripubertal rat hippocampus with PTZ-induced seizures and SE. Approach: An 808-nm diode laser was applied transcranially to peripubertal rats prior to PTZ injection. Immunofluorescence staining of neuron-specific enolase (NSE) was used as a marker of neuroinflammation, glial fibrillary acid protein (GFAP) for astrogliosis, ionized calcium-binding adapter molecule 1 (Iba-1) for microgliosis, and mitochondrial cytochrome c oxidase subunit 1 (MT-CO1) for confirming the involvement of cytochrome c oxidase (CCO). Results: tPBM significantly reduced NSE immunoreactivity in CA3 in PTZ-treated rats, GFAP immunoreactivity in CA1, and Iba-1 immunoreactivity in CA3. Enhancement of hippocampal MT-CO1 reflected that tPBM acted in CCO-dependent manner. Conclusions: tPBM (808) attenuated PTZ-induced seizures and SE by suppressing neuroinflammation, astrogliosis, and microgliosis in peripubertal rats.

Photobiomodulation Promotes Hippocampal CA1 NSC Differentiation Toward Neurons and Facilitates Cognitive Function Recovery Involving NLRP3 Inflammasome Mitigation Following Global Cerebral Ischemia

Our recent study revealed that photobiomodulation (PBM) inhibits delayed neuronal death by preserving mitochondrial dynamics and function following global cerebral ischemia (GCI). In the current study, we clarified whether PBM exerts effective roles in endogenous neurogenesis and long-lasting neurological recovery after GCI. Adult male rats were treated with 808 nm PBM at 20 mW/cm² irradiance for 2 min on cerebral cortex surface (irradiance ∼7.0 mW/cm², fluence ∼0.8 J/cm² on the hippocampus) beginning 3 days after GCI for five consecutive days. Cognitive function was evaluated using the Morris water maze. Neural stem cell (NSC) proliferation, immature neurons, and mature neurons were examined using bromodeoxyuridine (BrdU)-, doublecortin (DCX)-, and NeuN-staining, respectively. Protein expression, such as NLRP3, cleaved IL1β, GFAP, and Iba1 was detected using immunofluorescence staining, and ultrastructure of astrocyte and microglia was observed by transmission electron microscopy. The results revealed that PBM exerted a markedly neuroprotective role and improved spatial learning and memory ability at 58 days of ischemia/reperfusion (I/R) but not at 7 days of reperfusion. Mechanistic studies revealed that PBM suppressed reactive astrocytes and maintained astrocyte regeneration at 7 days of reperfusion, as well as elevated neurogenesis at 58 days of reperfusion, as evidenced by a significant decrease in the fluorescence intensity of GFAP (astrocyte marker) but unchanged the number of BrdU-GFAP colabeled cells at the early timepoint, and a robust elevation in the number of DCX-NeuN colabeled cells at the later timepoint in the PBM-treated group compared to the GCI group. Notably, PBM treatment protected the ultrastructure of astrocyte and microglia cells at 58 days but not 7 days of reperfusion in the hippocampal CA1 region. Furthermore, PBM treatment significantly attenuated the GCI-induced immunofluorescence intensity of NLRP3 (an inflammasome component), cleaved IL1β (reflecting inflammasome activation) and Iba1, as well as the colocalization of NLRP3/GFAP or cleaved IL-1β/GFAP, especially in animals subjected to I/R at 58 days. Taken together, PBM treatment performed postischemia exerted a long-lasting protective effect on astrocytes and promoted endogenous neurogenesis in the hippocampal CA1 region, which might contribute to neurological recovery after GCI.

NIR Laser Photobiomodulation Induces Neuroprotection in an In Vitro Model of Cerebral Hypoxia/Ischemia

Brain photobiomodulation (PBM) is an innovative treatment for a variety of neurological conditions, including cerebral ischemia. However, the capability of PBM for ischemic stroke needs to be further explored and its mechanisms of action remain currently unclear. The aim of the present research was to identify a treatment protocol capable of inducing neuroprotection and to investigate the molecular mechanisms activated by a dual-wavelength near infrared (NIR) laser source in an organotypic hippocampal slice model of hypoxia/ischemia. Hippocampal slices were exposed to oxygen and glucose deprivation (OGD) for 30 min followed by NIR laser light (fluence 3.71, 7.42, or 14.84 J/cm²; wavelengths 808 nm and 905 nm) delivered immediately or 30 min or 60 min after OGD, in order to establish a therapeutic window. Neuronal injury was assessed by propidium iodide fluorescence 24 h later. Our results show that NIR laser irradiation attenuates OGD neurotoxicity once applied immediately or 30 min after OGD. Western blot analysis of proteins involved in neuroinflammation (iNOS, COX-2, NFkB subunit p65, and Bcl-2) and in glutamatergic-mediated synaptic activity (vGluT1, EAAT2, GluN1, and PSD95) showed that the protein modifications induced by OGD were reverted by NIR laser application. Moreover, CA1 confocal microscopy revealed that the profound morphological changes induced by OGD were reverted by NIR laser radiation. In conclusion, NIR laser radiation attenuates OGD neurotoxicity in organotypic hippocampal slices through attenuation of inflammatory mechanisms. These findings shed light on molecular definition of NIR neuroprotective mechanisms, thus underlining the potential benefit of this technique for the treatment of cerebral ischemia.