The Catastrophe of Intracerebral Hemorrhage Drives the Capillary-Hemorrhage Dementias, Including Alzheimer's Disease

This review advances an understanding of several dementias, based on four premises. One is that capillary hemorrhage is prominent in the pathogenesis of the dementias considered (dementia pugilistica, chronic traumatic encephalopathy, traumatic brain damage, Alzheimer's disease). The second premise is that hemorrhage introduces four neurotoxic factors into brain tissue: hypoxia of the tissue that has lost its blood supply, hemoglobin and its breakdown products, excitotoxic levels of glutamate, and opportunistic pathogens that can infect brain cells and induce a cytotoxic immune response. The third premise is that where organisms evolve molecules that are toxic to itself, like the neurotoxicity ascribed to hemoglobin, amyloid- (A), and glutamate, there must be some role for the molecule that gives the organism a selection advantage. The fourth is the known survival-advantage roles of hemoglobin (oxygen transport), of A (neurotrophic, synaptotrophic, detoxification of heme, protective against pathogens) and of glutamate (a major neurotransmitter). From these premises, we propose 1) that the brain has evolved a multi-factor response to intracerebral hemorrhage, which includes the expression of several protective molecules, including haptoglobin, hemopexin and A; and 2) that it is logical, given these premises, to posit that the four neurotoxic factors set out above, which are introduced into the brain by hemorrhage, drive the progression of the capillary-hemorrhage dementias. In this view, A expressed at the loci of neuronal death in these dementias functions not as a toxin but as a first responder, mitigating the toxicity of hemoglobin and the infection of the brain by opportunistic pathogens.

Twelve protections evolved for the brain, and their roles in extending its functional life

As human longevity has increased, we have come to understand the ability of the brain to function into advanced age, but also its vulnerability with age, apparent in the age-related dementias. Against that background of success and vulnerability, this essay reviews how the brain is protected by (by our count) 12 mechanisms, including: the cranium, a bony helmet; the hydraulic support given by the cerebrospinal fluid; the strategically located carotid body and sinus, which provide input to reflexes that protect the brain from blood-gas imbalance and extremes of blood pressure; the blood brain barrier, an essential sealing of cerebral vessels; the secretion of molecules such as haemopexin and (we argue) the peptide Aβ to detoxify haemoglobin, at sites of a bleed; autoregulation of the capillary bed, which stabilises metabolites in extracellular fluid; fuel storage in the brain, as glycogen; oxygen storage, in the haemoprotein neuroglobin; the generation of new neurones, in the adult, to replace cells lost; acquired resilience, the stress-induced strengthening of cell membranes and energy production found in all body tissues; and cognitive reserve, the ability of the brain to maintain function despite damage. Of these 12 protections, we identify 5 as unique to the brain, 3 as protections shared with all body tissues, and another 4 as protections shared with other tissues but specialised for the brain. These protections are a measure of the brain's vulnerability, of its need for protection. They have evolved, we argue, to maintain cognitive function, the ability of the brain to function despite damage that accumulates during life. Several can be tools in the hands of the individual, and of the medical health professional, for the lifelong care of our brains.

Glucose Improves the Efficacy of Photobiomodulation in Changing ATP and ROS Levels in Mouse Fibroblast Cell Cultures

In this study, we tested the idea that photobiomodulation-the application of red to near infrared light (~λ = 600-1300 nm) to body tissues-is more effective in influencing cell metabolism when glucose is readily available. To this end, we used a mouse fibroblast (L-929) cell culture model and had two sets of conditions: non-stressed (10% FBS (foetal bovine serum)) and stressed (1% FBS), both either with or without glucose. We treated (or not) cells with photobiomodulation using an 810 nm laser at 15 mW/cm2 (~7.2 J/cm2). Our results showed that photobiomodulation was neither cytotoxic nor effective in enhancing measures of cell viability and proliferation, together with protein levels in any of the cell cultures. Photobiomodulation was, however, effective in increasing adenosine triphosphate (ATP) and decreasing reactive oxygen species (ROS) levels and this was-most importantly-only in conditions where glucose was present; corresponding cultures that did not contain glucose did not show these changes. In summary, we found that the benefits of photobiomodulation, in particular in changing ATP and ROS levels, were induced only when there was glucose available. Our findings lay a template for further explorations into the mechanisms of photobiomodulation, together with having considerable experimental and clinical implications.

Lights for epilepsy: can photobiomodulation reduce seizures and offer neuroprotection?

Epilepsy is synonymous with individuals suffering repeated "fits" or seizures. The seizures are triggered by bursts of abnormal neuronal activity, across either the cerebral cortex and/or the hippocampus. In addition, the seizure sites are characterized by considerable neuronal death. Although the factors that generate this abnormal activity and death are not entirely clear, recent evidence indicates that mitochondrial dysfunction plays a central role. Current treatment options include drug therapy, which aims to suppress the abnormal neuronal activity, or surgical intervention, which involves the removal of the brain region generating the seizure activity. However, ~30% of patients are unresponsive to the drugs, while the surgery option is invasive and has a morbidity risk. Hence, there is a need for the development of an effective non-pharmacological and non-invasive treatment for this disorder, one that has few side effects. In this review, we consider the effectiveness of a potential new treatment for epilepsy, known as photobiomodulation, the use of red to near-infrared light on body tissues. Recent studies in animal models have shown that photobiomodulation reduces seizure-like activity and improves neuronal survival. Further, it has an excellent safety record, with little or no evidence of side effects, and it is non-invasive. Taken all together, this treatment appears to be an ideal treatment option for patients suffering from epilepsy, which is certainly worthy of further consideration.

Remote photobiomodulation targeted at the abdomen or legs provides effective neuroprotection against parkinsonian MPTP insult

Photobiomodulation (PBM)-the irradiation of tissue with low-intensity light-mitigates neuropathology in rodent models of Parkinson's disease (PD) when targeted at the head ('transcranial PBM'). In humans, however, attenuation of light energy by the scalp and skull necessitates a different approach. We have reported that targeting PBM at the body also protects the brain by a mechanism that spreads from the irradiated tissue ('remote PBM'), although the optimal peripheral tissue target for remote PBM is currently unclear. This study compared the neuroprotective efficacy of remote PBM targeting the abdomen or leg with transcranial PBM, in mouse and non-human primate models of PD. In a pilot study, the neurotoxin MPTP was used to induce PD in non-human primates; PBM (670 nm, 50 mW/cm2 , 6 min/day) of the abdomen (n = 1) was associated with fewer clinical signs and more surviving midbrain dopaminergic cells relative to MPTP-injected non-human primates not treated with PBM. Validation studies in MPTP-injected mice (n = 10 per group) revealed a significant rescue of midbrain dopaminergic cells in mice receiving PBM to the abdomen (~80%, p < .0001) or legs (~80%, p < .0001), with comparable rescue of axonal terminals in the striatum. Strikingly, this degree of neuroprotection was at least as, if not more, pronounced than that achieved with transcranial PBM. These findings confirm that remote PBM provides neuroprotection against MPTP-induced destruction of the key circuitry underlying PD, with both the abdomen and legs serving as viable remote targets. This should provide the impetus for a comprehensive investigation of remote PBM-induced neuroprotection in other models of PD and, ultimately, human patients.

A systematic review of the effects of transcranial photobiomodulation on brain activity in humans

In recent years, transcranial photobiomodulation (tPBM) has been developing as a promising method to protect and repair brain tissues against damages. The aim of our systematic review is to examine the results available in the literature concerning the efficacy of tPBM in changing brain activity in humans, either in healthy individuals, or in patients with neurological diseases. Four databases were screened for references containing terms encompassing photobiomodulation, brain activity, brain imaging, and human. We also analysed the quality of the included studies using validated tools. Results in healthy subjects showed that even after a single session, tPBM can be effective in influencing brain activity. In particular, the different transcranial approaches - using a focal stimulation or helmet for global brain stimulation - seemed to act at both the vascular level by increasing regional cerebral blood flow (rCBF) and at the neural level by changing the activity of the neurons. In addition, studies also showed that even a focal stimulation was sufficient to induce a global change in functional connectivity across brain networks. Results in patients with neurological disease were sparser; nevertheless, they indicated that tPBM could improve rCBF and functional connectivity in several regions. Our systematic review also highlighted the heterogeneity in the methods and results generated, together with the need for more randomised controlled trials in patients with neurological diseases. In summary, tPBM could be a promising method to act on brain function, but more consistency is needed in order appreciate fully the underlying mechanisms and the precise outcomes.

The brain's weakness in the face of trauma: How head trauma causes the destruction of the brain

Of all our organs, the brain is perhaps the best protected from trauma. The skull has evolved to enclose it and, within the skull, the brain floats in a protective bath of cerebrospinal fluid. It is becoming evident, however, that head trauma experienced in young adult life can cause a dementia that appears decades later. The level of trauma that induces such destruction is still being assessed but includes levels well below that which cracks the skull or causes unconsciousness or concussion. Clinically this damage appears as dementia, in people who played body-contact sports in their youth or have survived accidents or the blasts of combat; and appears also, we argue, in old age, without a history of head trauma. The dementias have been given different names, including dementia pugilistica (affecting boxers), chronic traumatic encephalopathy (following certain sports, particularly football), traumatic brain injury (following accidents, combat) and Alzheimer's (following decades of life). They share common features of clinical presentation and neuropathology, and this conceptual analysis seeks to identify features common to these forms of brain injury and to identify where in the brain the damage common to them occurs; and how it occurs, despite the protection provided by the skull and cerebrospinal fluid. The analysis suggests that the brain's weak point in the face of trauma is its capillary bed, which is torn by the shock of trauma. This identification in turn allows discussion of ways of delaying, avoiding and even treating these trauma-induced degenerations.

Do astrocytes respond to light, sound, or electrical stimulation?

Astrocytes are not only the most populous cell type in the human brain, but they also have the most extensive and diverse sets of connections, across synapses, axons, blood vessels, as well as having their own internal network. Unsurprisingly, they are associated with many brain functions; from the synaptic transmission to energy metabolism and fluid homeostasis, and from cerebral blood flow and blood-brain barrier maintenance to neuroprotection, memory, immune defenses and detoxification, sleep, and early development. And yet, notwithstanding these key roles, so many current therapeutic approaches to a range of brain disorders have largely neglected their potential involvement. In this review, we consider the role of astrocytes in three brain therapies; two are emerging treatments (photobiomodulation and ultrasound), while the other is well-established (deep brain stimulation). In essence, we explore the issue of whether external sources, such as light, sound, or electricity, can influence the function of astrocytes, as they do neurons. We find that, when taken all together, each of these external sources can influence many, if not, all of the functions associated with astrocytes. These include influencing neuronal activity, prompting neuroprotection, reducing inflammation (astrogliosis) and potentially increasing cerebral blood flow and stimulating the glymphatic system. We suggest that astrocytes, just like neurons, can respond positively to each of these external applications and that their activation could each impart many beneficial outcomes on brain function; they are likely to be key players underpinning the mechanisms behind many therapeutic strategies.

Photobiomodulation for Hypertension and Alzheimer's Disease

Although the cause(s) of Alzheimer's disease in the majority of cases remains elusive, it has long been associated with hypertension. In animal models of the disease, hypertension has been shown to exacerbate Alzheimer-like pathology and behavior, while in humans, hypertension during mid-life increases the risk of developing the disease later in life. Unfortunately, once individuals are diagnosed with the disease, there are few therapeutic options available. There is neither an effective symptomatic treatment, one that treats the debilitating cognitive and memory deficits, nor, more importantly, a neuroprotective treatment, one that stops the relentless progression of the pathology. Further, there is no specific preventative treatment that offsets the onset of the disease. A key factor or clue in this quest for an effective preventative and therapeutic treatment may lie in the contribution of hypertension to the disease. In this review, we explore the idea that photobiomodulation, the application of specific wavelengths of light onto body tissues, can reduce the neuropathology and behavioral deficits in Alzheimer's disease by controlling hypertension. We suggest that treatment with photobiomodulation can be an effective preventative and therapeutic option for this neurodegenerative disease.

A systematic review of the effect of photobiomodulation on the neuroinflammatory response in animal models of neurodegenerative diseases

This systematic review examines the effect of photobiomodulation (PBM), the application of red to near infrared light on body tissues, on the neuroinflammatory response and oxidative stress in animal models of neurodegenerative diseases. The research question and search protocol were prospectively registered on the PROSPERO database. Neurodegenerative diseases are becoming ever more prevalent in the ageing populations across the Western world, with no disease-modifying or neuroprotective treatment options being available. Hence there is a real need for the development of effective treatment options for patients. Inflammatory responses and oxidative stress within the central nervous system have a strong correlation with neuronal cell death. PBM is a non-invasive therapeutic option that has shown efficacy and promising effects in animal models of neurodegenerative disease; many studies have reported neuroprotection and improved behavioural outcomes. To the best of our knowledge, there has been no previous study that has reviewed the anti-inflammatory and the antioxidant effect of PBM in the context of neurodegeneration. This review has examined this relationship in animal models of a range of neurodegenerative diseases. We found that PBM can effectively reduce glial activation, pro-inflammatory cytokine expression and oxidative stress, whilst increasing anti-inflammatory glial responses and cytokines, and antioxidant capacity. These positive outcomes accompanied the neuroprotection evident after PBM treatment. Our review provides further indication that PBM can be developed into an effective non-pharmacological intervention for neurodegenerative diseases.

Shifting patterns of cellular energy production (adenosine triphosphate) over the day and key timings for the effect of optical manipulation

Mitochondria are optically responsive organelles producing energy for cell function via adenosine triphosphate (ATP). But ATP production appears to vary over the day. Here we use Drosophila melanogaster to reveal daily shifts in whole animal ATP production in a tight 24 hours' time series. We show a marked production peak in the morning that declines around midday and remains low through afternoon and night. ATP production can be improved with long wavelengths (>660 nm), but apparently not at all times. Hence, we treated flies with 670 nm light to reveal optimum times. Exposures at 670 nm resulted in a significant ATP increases and a shift in the ATP/adenosine diphosphate (ADP) ratio at 8.00 and 11.00, whilst application at other time points had no effect. Hence, light-induced ATP increases appear limited to periods when natural production is high. In summary, long wavelength influences on mitochondria are conserved across species from fly to human. Determining times for their administration to improve function in ageing and disease are of key importance. This study progresses this problem.

The effect of photobiomodulation on the brain during wakefulness and sleep

Over the last seventy years or so, many previous studies have shown that photobiomodulation, the use of red to near infrared light on body tissues, can improve central and peripheral neuronal function and survival in both health and in disease. These improvements are thought to arise principally from an impact of photobiomodulation on mitochondrial and non-mitochondrial mechanisms in a range of different cell types, including neurones. This impact has downstream effects on many stimulatory and protective genes. An often-neglected feature of nearly all of these improvements is that they have been induced during the state of wakefulness. Recent studies have shown that when applied during the state of sleep, photobiomodulation can also be of benefit, but in a different way, by improving the flow of cerebrospinal fluid and the clearance of toxic waste-products from the brain. In this review, we consider the potential differential effects of photobiomodulation dependent on the state of arousal. We speculate that the effects of photobiomodulation is on different cells and systems depending on whether it is applied during wakefulness or sleep, that it may follow a circadian rhythm. We speculate further that the arousal-dependent photobiomodulation effects are mediated principally through a biophoton – ultra-weak light emission – network of communication and repair across the brain.

Remote Photobiomodulation Treatment for the Clinical Signs of Parkinson's Disease: A Case Series Conducted During COVID-19

Objective: To assess whether remote application of photobiomodulation (PBM) is effective in reducing clinical signs of Parkinson's disease (PD). Background: PD is a progressive neurodegenerative disease for which there is no cure and few treatment options. There is a strong link between the microbiome-gut-brain axis and PD. PBM in animal models can reduce the signs of PD and protect the neurons from damage when applied directly to the head or to remote parts of the body. In a clinical study, PBM has been shown to improve clinical signs of PD for up to 1 year. Methods: Seven participants were treated with PBM to the abdomen and neck three times per week for 12 weeks. Participants were assessed for mobility, balance, cognition, fine motor skill, and sense of smell on enrolment, after 12 weeks of treatment in a clinic and after 33 weeks of home treatment. Results: A number of clinical signs of PD were shown to be improved by remote PBM treatment, including mobility, cognition, dynamic balance, spiral test, and sense of smell. Improvements were individual to the participant. Some improvements were lost for certain participants during at-home treatment, which coincided with a number of enforced coronavirus disease 2019 (COVID-19) pandemic lockdown periods. Conclusions: Remote application of PBM was shown to be an effective treatment for a number of clinical signs of PD, with some being maintained for 45 weeks, despite lockdown restrictions. Improvements in clinical signs were similar to those seen with the application of remote plus transcranial PBM treatment in a previous study. Clinical Trial Registration number: U1111-1205-2035.

A Perspective on the Potential of Opsins as an Integral Mechanism of Photobiomodulation: It's Not Just the Eyes

Objective: To investigate the potential relationship between opsins and photobiomodulation. Background: Opsins and other photoreceptors occur in all phyla and are important in light-activated signaling and organism homeostasis. In addition to the visual opsin systems of the retina (OPN1 and OPN2), there are several non-visual opsins found throughout the body tissues, including encephalopsin/panopsin (OPN3), melanopsin (OPN4), and neuropsin (OPN5), as well as other structures that have light-sensitive properties, such as enzymes, ion channels, particularly those located in cell membranes, lysosomes, and neuronal structures such as the nodes of Ranvier. The influence of these structures on exposure to light, including self-generated light within the body (autofluorescence), on circadian oscillators, and circadian and ultradian rhythms have become increasingly reported. The visual and non-visual phototransduction cascade originating from opsins and other structures has potential significant mechanistic effects on tissues and health. Methods: A PubMed and Google Scholar search was made using the search terms "photobiomodulation", "light", "neuron", "opsins", "neuropsin", "melanopsin", "encephalopsin", "rhodopsin", and "chromophore". Results: This review was examined the influence of neuropsin (also known as kallikrein 8), encephalopsin, and melanopsin specifically on ion channel function, and more broadly on the central and peripheral nervous systems. The relationship between opsins 3, 4, and 5 and photobiomodulation mechanisms was evaluated, along with a proposed role of photobiomodulation through opsins and light-sensitive organelles as potential alleviators of symptoms and accelerators of beneficial regenerative processes. The potential clinical implications of this in musculoskeletal conditions, wounds, and in the symptomatic management of neurodegenerative disease was also examined. Conclusions: Systematic research into the pleotropic therapeutic role of photobiomodulation, mediated through its action on opsins and other light-sensitive organelles may assist in the future execution of safe, low-risk precision medicine for a variety of chronic and complex disease conditions, and for health maintenance in aging.

Improvements in clinical signs of Parkinson's disease using photobiomodulation: a prospective proof-of-concept study

Background

Parkinson’s disease (PD) is a progressive neurodegenerative disease with no cure and few treatment options. Its incidence is increasing due to aging populations, longer disease duration and potentially as a COVID-19 sequela. Photobiomodulation (PBM) has been successfully used in animal models to reduce the signs of PD and to protect dopaminergic neurons.

Objective

To assess the effectiveness of PBM to mitigate clinical signs of PD in a prospective proof-of-concept study, using a combination of transcranial and remote treatment, in order to inform on best practice for a larger randomized placebo-controlled trial (RCT).

Methods

Twelve participants with idiopathic PD were recruited. Six were randomly chosen to begin 12 weeks of transcranial, intranasal, neck and abdominal PBM. The remaining 6 were waitlisted for 14 weeks before commencing the same treatment. After the 12-week treatment period, all participants were supplied with PBM devices to continue home treatment. Participants were assessed for mobility, fine motor skills, balance and cognition before treatment began, after 4 weeks of treatment, after 12 weeks of treatment and the end of the home treatment period. A Wilcoxon Signed Ranks test was used to assess treatment effectiveness at a significance level of 5%.

Results

Measures of mobility, cognition, dynamic balance and fine motor skill were significantly improved (p < 0.05) with PBM treatment for 12 weeks and up to one year. Many individual improvements were above the minimal clinically important difference, the threshold judged to be meaningful for participants. Individual improvements varied but many continued for up to one year with sustained home treatment. There was a demonstrable Hawthorne Effect that was below the treatment effect. No side effects of the treatment were observed.

Conclusions

PBM was shown to be a safe and potentially effective treatment for a range of clinical signs and symptoms of PD. Improvements were maintained for as long as treatment continued, for up to one year in a neurodegenerative disease where decline is typically expected. Home treatment of PD by the person themselves or with the help of a carer might be an effective therapy option. The results of this study indicate that a large RCT is warranted.

Trial registration

Australian New Zealand Clinical Trials Registry, registration number: ACTRN12618000038291p, registered on 12/01/2018.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12883-021-02248-y.

Exploring the Use of Intracranial and Extracranial (Remote) Photobiomodulation Devices in Parkinson's Disease: A Comparison of Direct and Indirect Systemic Stimulations

In recent times, photobiomodulation has been shown to be beneficial in animal models of Parkinson's disease, improving locomotive behavior and being neuroprotective. Early observations in people with Parkinson's disease have been positive also, with improvements in the non-motor symptoms of the disease being evident most consistently. Although the precise mechanisms behind these improvements are not clear, two have been proposed: direct stimulation, where light reaches and acts directly on the distressed neurons, and remote stimulation, where light influences cells and/or molecules that provide systemic protection, thereby acting indirectly on distressed neurons. In relation to Parkinson's disease, given that the major zone of pathology lies deep in the brain and that light from an extracranial or external photobiomodulation device would not reach these vulnerable regions, stimulating the distressed neurons directly would require intracranial delivery of light using a device implanted close to the vulnerable regions. For indirect systemic stimulation, photobiomodulation could be applied to either the head and scalp, using a transcranial helmet, or to a more remote body part (e.g., abdomen, leg). In this review, we discuss the evidence for both the direct and indirect neuroprotective effects of photobiomodulation in Parkinson's disease and propose that both types of treatment modality, when working together using both intracranial and extracranial devices, provide the best therapeutic option.

A day in the life of mitochondria reveals shifting workloads

Mitochondria provide energy for cellular function. We examine daily changing patterns of mitochondrial function and metabolism in Drosophila in vivo in terms of their complex (I-IV) activity, ATP production, glycolysis, and whole fly respiration in the morning, afternoon and night. Complex activity and respiration showed significant and unexpected variation, peaking in the afternoon. However, ATP levels by contrast are >40% greater in the morning and lowest at night when glycolysis peaks. Complex activity modulation was at the protein level with no evidence for differential transcription over the day. Timing differences between increased ATP production and peaks of complex activity may result from more efficient ATP production early in the day leaving complex activity with spare capacity. Optical stimulation of mitochondria is only possible in the mornings when there is such spare capacity. These results provide first evidence of shifts in cellular energy capacity at the organism level. Understanding their translation may be significant to the chosen timing of energy demanding interventions to improve function and health.

"Buckets": Early Observations on the Use of Red and Infrared Light Helmets in Parkinson's Disease Patients

Background: Parkinson's disease is a well-known neurological disorder with distinct motor signs and non-motor symptoms. Objective: We report on six patients with Parkinson's disease that used in-house built photobiomodulation (PBM) helmets. Methods: We used "buckets" lined with light-emitting diodes (LEDs) of wavelengths across the red to near-infrared range (i.e., 670, 810, and 850 nm; n = 5) or an homemade intranasal LED device (660 nm; n = 1). Progress was assessed by the patients themselves, their spouse, or their attending medical practitioners. Results: We found that 55% of the initial signs and symptoms of the six patients showed overall improvement, whereas 43% stayed the same and only 2% got worse. We also found that PBM did not target a specific sign or symptom, with both motor and nonmotor ones being affected, depending on the patient. Conclusions: In summary, our early observations are the first to note the impact of PBM on patients' signs and symptoms over an extended period, up to 24 months, and lays the groundwork for further development to clinical trial.

Pre-conditioning with Remote Photobiomodulation Modulates the Brain Transcriptome and Protects Against MPTP Insult in Mice

Transcranial photobiomodulation (PBM), which involves the application of low-intensity red to near-infrared light (600-1100 nm) to the head, provides neuroprotection in animal models of various neurodegenerative diseases. However, the absorption of light energy by the human scalp and skull may limit the utility of transcranial PBM in clinical contexts. We have previously shown that targeting light at peripheral tissues (i.e. "remote PBM") also provides protection of the brain in an MPTP mouse model of Parkinson's disease, suggesting remote PBM might be a viable alternative strategy for overcoming penetration issues associated with transcranial PBM. This present study aimed to determine an effective pre-conditioning regimen of remote PBM for inducing neuroprotection and elucidate the molecular mechanisms by which remote PBM enhances the resilience of brain tissue. Balb/c mice were irradiated with 670-nm light (4 J/cm² per day) targeting dorsum and hindlimbs for 2, 5 or 10 days, followed by injection of the parkinsonian neurotoxin MPTP (50 mg/kg) over two consecutive days. Despite no direct irradiation of the head, 10 days of pre-conditioning with remote PBM significantly attenuated MPTP-induced loss of midbrain tyrosine hydroxylase-positive dopaminergic cells and mitigated the increase in FOS-positive neurons in the caudate-putamen complex. Interrogation of the midbrain transcriptome by RNA microarray and pathway enrichment analysis suggested upregulation of cell signaling and migration (including CXCR4⁺ stem cell and adipocytokine signaling), oxidative stress response pathways and modulation of the blood-brain barrier following remote PBM. These findings establish remote PBM preconditioning as a viable neuroprotective intervention and provide insights into the mechanisms underlying this phenomenon.

Acquired Resilience: An Evolved System of Tissue Protection in Mammals

This review brings together observations on the stress-induced regulation of resilience mechanisms in body tissues. It is argued that the stresses that induce tissue resilience in mammals arise from everyday sources: sunlight, food, lack of food, hypoxia and physical stresses. At low levels, these stresses induce an organised protective response in probably all tissues; and, at some higher level, cause tissue destruction. This pattern of response to stress is well known to toxicologists, who have termed it hormesis. The phenotypes of resilience are diverse and reports of stress-induced resilience are to be found in journals of neuroscience, sports medicine, cancer, healthy ageing, dementia, parkinsonism, ophthalmology and more. This diversity makes the proposing of a general concept of induced resilience a significant task, which this review attempts. We suggest that a system of stress-induced tissue resilience has evolved to enhance the survival of animals. By analogy with acquired immunity, we term this system 'acquired resilience'. Evidence is reviewed that acquired resilience, like acquired immunity, fades with age. This fading is, we suggest, a major component of ageing. Understanding of acquired resilience may, we argue, open pathways for the maintenance of good health in the later decades of human life.

Photobiomodulation reduces gliosis in the basal ganglia of aged mice

This study explored the effects of long-term photobiomodulation (PBM) on the glial and neuronal organization in the striatum of aged mice. Mice aged 12 months were pretreated with PBM (670 nm) for 20 minutes per day, commencing at 5 months old and continued for 8 months. We had 2 control groups, young at 3 months and aged at 12 months old; these mice received no treatment. Brains were aldehyde-fixed and processed for immunohistochemistry with various glial and neuronal markers. We found a clear reduction in glial cell number, both astrocytes and microglia, in the striatum after PBM in aged mice. By contrast, the number of 2 types of striatal interneurons (parvalbumin⁺ and encephalopsin⁺), together with the density of striatal dopaminergic terminals (and their midbrain cell bodies), remained unchanged after such treatment. In summary, our results indicated that long-term PBM had beneficial effects on the aging striatum by reducing glial cell number; and furthermore, that this treatment did not have any deleterious effects on the neurons and terminations in this nucleus.

Remote tissue conditioning is neuroprotective against MPTP insult in mice

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Remote tissue conditioning is an emerging neuroprotective strategy.

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Remote ischemic conditioning and remote photobiomodulation were tested in MPTP mice.

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Both interventions protected the midbrain against MPTP insult.

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Combining the interventions yielded no added benefit.

Current treatments for Parkinson’s disease (PD) are primarily symptomatic, leaving a need for treatments that mitigate disease progression. One emerging neuroprotective strategy is remote tissue conditioning, in which mild stress in a peripheral tissue (e.g. a limb) induces protection of life-critical organs such as the brain. We evaluated the potential of two remote tissue conditioning interventions – mild ischemia and photobiomodulation – in protecting the brain against the parkinsonian neurotoxin MPTP. Further, we sought to determine whether combining these two interventions provided any added benefit.

Male C57BL/6 mice (n = 10/group) were pre-conditioned with either ischemia of the leg (4 × 5 min cycles of ischemia/reperfusion), or irradiation of the dorsum with 670 nm light (50 mW/cm², 3 min), or both interventions, immediately prior to receiving two MPTP injections 24 hours apart (50 mg/kg total). Mice were sacrificed 6 days later and brains processed for tyrosine hydroxylase immunohistochemistry.

Stereological counts of functional dopaminergic neurons in the substantia nigra pars compacta revealed that both remote ischemia and remote photobiomodulation rescued around half of the neurons that were compromised by MPTP (p < 0.001). Combining the two interventions provided no added benefit, rescuing only 40% of vulnerable neurons (p < 0.01).

The present results suggest that remote tissue conditioning, whether ischemia of a limb or photobiomodulation of the torso, induces protection of brain centers critical in PD. The lack of additional benefit when combining these two interventions suggests they may share common mechanistic pathways. Further research is needed to identify these pathways and determine the conditioning doses that yield optimal neuroprotection.

Evidence for encephalopsin immunoreactivity in interneurones and striosomes of the monkey striatum

In this study, we examined the cellular distribution of encephalopsin (opsin 3; OPN3) expression in the striatum of non-human primates. In addition, because of our long standing interest in Parkinson's disease and neuroprotection, we examined whether parkinsonian (MPTP; 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) insult and/or photobiomodulation (670 nm) had any impact on encephalopsin expression in this key area of the basal ganglia. Striatal sections of control naïve monkeys, together with those that were either MPTP- and/or photobiomodulation-treated were processed for immunohistochemistry. Our results revealed two populations of striatal interneurones that expressed encephalopsin, one of which was the giant, choline acetyltransferase-containing, cholinergic interneurones. The other population had smaller somata and was not cholinergic. Neither cell group expressed the calcium-binding protein, parvalbumin. There was also rich encephalopsin expression in a set of terminals forming striosome-like patches across the striatum. Finally, we found that neither parkinsonian (MPTP) insult nor photobiomodulation had any effect on encephalopsin expression in the striatum. In summary, our results revealed an extensive network of encephalopsin containing structures throughout the striatum, indicating that external light is in a position to influence a range of striatal activities at both the interneurone and striosome level.

Neuroprotective Surgical Strategies in Parkinson's Disease: Role of Preclinical Data

Although there have been many pharmacological agents considered to be neuroprotective therapy in Parkinson's disease (PD) patients, neurosurgical approaches aimed to neuroprotect or restore the degenerative nigrostriatal system have rarely been the focus of in depth reviews. Here, we explore the neuroprotective strategies involving invasive surgical approaches (NSI) using neurotoxic models 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and 6-hydroxydopamine (6-OHDA), which have led to clinical trials. We focus on several NSI approaches, namely deep brain stimulation of the subthalamic nucleus, glial neurotrophic derived factor (GDNF) administration and cell grafting methods. Although most of these interventions have produced positive results in preclinical animal models, either from behavioral or histological studies, they have generally failed to pass randomized clinical trials to validate each approach. We argue that NSI are promising approaches for neurorestoration in PD, but preclinical studies should be planned carefully in order not only to detect benefits but also to detect potential adverse effects. Further, clinical trials should be designed to be able to detect and disentangle neuroprotection from symptomatic effects. In summary, our review study evaluates the pertinence of preclinical models to study NSI for PD and how this affects their efficacy when translated into clinical trials.

No evidence for toxicity after long-term photobiomodulation in normal non-human primates

In this study, we explored the effects of a longer term application, up to 12 weeks, of photobiomodulation in normal, naïve macaque monkeys. Monkeys (n = 5) were implanted intracranially with an optical fibre device delivering photobiomodulation (red light, 670 nm) to a midline midbrain region. Animals were then aldehyde-fixed and their brains were processed for immunohistochemistry. In general, our results showed that longer term intracranial application of photobiomodulation had no adverse effects on the surrounding brain parenchyma or on the nearby dopaminergic cell system. We found no evidence for photobiomodulation generating an inflammatory glial response or neuronal degeneration near the implant site; further, photobiomodulation did not induce an abnormal activation or mitochondrial stress in nearby cells, nor did it cause an abnormal arrangement of the surrounding vasculature (endothelial basement membrane). Finally, because of our interest in Parkinson's disease, we noted that photobiomodulation had no impact on the number of midbrain dopaminergic cells and the density of their terminations in the striatum. In summary, we found no histological basis for any major biosafety concerns associated with photobiomodulation delivered by our intracranial approach and our findings set a key template for progress onto clinical trial on patients with Parkinson's disease.

Widespread brain transcriptome alterations underlie the neuroprotective actions of dietary saffron

Dietary saffron has shown promise as a neuroprotective intervention in clinical trials of retinal degeneration and dementia and in animal models of multiple CNS disorders, including Parkinson's disease. This therapeutic potential makes it important to define the relationship between dose and protection and the mechanisms involved. To explore these two issues, mice were pre-conditioned by providing an aqueous extract of saffron (0.01% w/v) as their drinking water for 2, 5 or 10 days before administration of the parkinsonian neurotoxin MPTP (50 mg/kg). Five days of saffron pre-conditioning provided the greatest benefit against MPTP-induced neuropathology, significantly mitigating both loss of functional dopaminergic cells in the substantia nigra pars compacta (p < 0.01) and abnormal neuronal activity in the caudate-putamen complex (p < 0.0001). RNA microarray analysis of the brain transcriptome of mice pre-conditioned with saffron for 5 days revealed differential expression of 424 genes. Bioinformatics analysis identified enrichment of molecular pathways (e.g. adherens junction, TNFR1 and Fas signaling) and expression changes in candidate genes (Cyr61, Gpx8, Ndufs4, and Nos1ap) with known neuroprotective actions. The apparent biphasic nature of the dose-response relationship between saffron and measures of neuroprotection, together with the stress-inducible nature of many of the up-regulated genes and pathways, lend credence to the idea that saffron, like various other phytochemicals, is a hormetic stimulus, with functions beyond its strong antioxidant capacity. These findings provide impetus for a more comprehensive evaluation of saffron as a neuroprotective intervention.

Effects of a higher dose of near-infrared light on clinical signs and neuroprotection in a monkey model of Parkinson's disease

We have reported previously that intracranial application of near-infrared light (NIr) - when delivered at the lower doses of 25J and 35J - reduces clinical signs and offers neuroprotection in a subacute MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) monkey model of Parkinson's disease. In this study, we explored whether a higher NIr dose (125J) generated beneficial effects in the same MPTP monkey model (n=15). We implanted an NIr (670nm) optical fibre device within a midline region of the midbrain in macaque monkeys, close to the substantia nigra of both sides. MPTP injections (1.8-2.1mg/kg) were made over a five day period, during which time the NIr device was turned on and left on continuously throughout the ensuing three week survival period. Monkeys were evaluated clinically and their brains processed for immunohistochemistry and stereology. Our results showed that the higher NIr dose did not have any toxic impact on cells at the midbrain implant site. Further, this NIr dose resulted in a higher number of nigral tyrosine hydroxylase immunoreactive cells when compared to the MPTP group. However, the higher NIr dose monkeys showed little evidence for an increase in mean clinical score, number of nigral Nissl-stained cells and density of striatal tyrosine hydroxylase terminations. In summary, the higher NIr dose of 125J was not as beneficial to MPTP-treated monkeys as compared to the lower doses of 25J and 35J, boding well for strategies of NIr dose delivery and device energy consumption in a future clinical trial.

Near-infrared light treatment reduces astrogliosis in MPTP-treated monkeys

We have reported previously that intracranial application of near-infrared light (NIr) reduces clinical signs and offers neuroprotection in a subacute MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) monkey model of Parkinson's disease. In this study, we explored whether NIr reduces the gliosis in this animal model. Sections of midbrain (containing the substantia nigra pars compacta; SNc) and striatum were processed for glial fibrillary acidic protein (to label astrocytes; GFAP) and ionised calcium-binding adaptor molecule 1 (to label microglia; IBA1) immunohistochemistry. Cell counts were undertaken using stereology, and cell body sizes were measured using ImageJ. Our results showed that NIr treatment reduced dramatically (~75 %) MPTP-induced astrogliosis in both the SNc and striatum. Among microglia, however, NIr had a more limited impact in both nuclei; although there was a reduction in overall cell size, there were no changes in the number of microglia in the MPTP-treated monkeys after NIr treatment. In summary, we showed that NIr treatment influenced the glial response, particularly that of the astrocytes, in our monkey MPTP model of Parkinson's disease. Our findings raise the possibility of glial cells as a future therapeutic target using NIr.

Turning On Lights to Stop Neurodegeneration: The Potential of Near Infrared Light Therapy in Alzheimer's and Parkinson's Disease

Alzheimer's and Parkinson's disease are the two most common neurodegenerative disorders. They develop after a progressive death of many neurons in the brain. Although therapies are available to treat the signs and symptoms of both diseases, the progression of neuronal death remains relentless, and it has proved difficult to slow or stop. Hence, there is a need to develop neuroprotective or disease-modifying treatments that stabilize this degeneration. Red to infrared light therapy (λ = 600-1070 nm), and in particular light in the near infrared (NIr) range, is emerging as a safe and effective therapy that is capable of arresting neuronal death. Previous studies have used NIr to treat tissue stressed by hypoxia, toxic insult, genetic mutation and mitochondrial dysfunction with much success. Here we propose NIr therapy as a neuroprotective or disease-modifying treatment for Alzheimer's and Parkinson's patients.

Near-infrared light is neuroprotective in a monkey model of Parkinson disease

OBJECTIVE

To examine whether near-infrared light (NIr) treatment reduces clinical signs and/or offers neuroprotection in a subacute 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) monkey model of Parkinson disease.

METHODS

We implanted an optical fiber device that delivered NIr (670 nm) to the midbrain of macaque monkeys, close to the substantia nigra of both sides. MPTP injections (1.5-2.1mg/kg) were made over a 5- to 7-day period, during which time the NIr device was turned on. This was then followed by a 3-week survival period. Monkeys were evaluated clinically (eg, posture, bradykinesia) and behaviorally (open field test), and their brains were processed for immunohistochemistry and stereology.

RESULTS

All monkeys in the MPTP group developed severe clinical and behavioral impairment (mean clinical scores = 21-34; n = 11). By contrast, the MPTP-NIr group developed much less clinical and behavioral impairment (n = 9); some monkeys developed moderate clinical signs (mean scores = 11-15; n = 3), whereas the majority--quite remarkably--developed few clinical signs (mean scores = 1-6; n = 6). The monkeys that developed moderate clinical signs had hematic fluid in their optical fibers at postmortem, presumably limiting NIr exposure and overall clinical improvement. NIr was not toxic to brain tissue and offered neuroprotection to dopaminergic cells and their terminations against MPTP insult, particularly in animals that developed few clinical signs.

INTERPRETATION

Our findings indicate NIr to be an effective therapeutic agent in a primate model of the disease and create the template for translation into clinical trials.

Intracranial application of near-infrared light in a hemi-parkinsonian rat model: the impact on behavior and cell survival

OBJECT The authors of this study used a newly developed intracranial optical fiber device to deliver near-infrared light (NIr) to the midbrain of 6-hydroxydopamine (6-OHDA)-lesioned rats, a model of Parkinson's disease. The authors explored whether NIr had any impact on apomorphine-induced turning behavior and whether it was neuroprotective. METHODS Two NIr powers (333 nW and 0.16 mW), modes of delivery (pulse and continuous), and total doses (634 mJ and 304 J) were tested, together with the feasibility of a midbrain implant site, one considered for later use in primates. Following a striatal 6-OHDA injection, the NIr optical fiber device was implanted surgically into the midline midbrain area of Wistar rats. Animals were tested for apomorphine-induced rotations, and then, 23 days later, their brains were aldehyde fixed for routine immunohistochemical analysis. RESULTS The results showed that there was no evidence of tissue toxicity by NIr in the midbrain. After 6-OHDA lesion, regardless of mode of delivery or total dose, NIr reduced apomorphine-induced rotations at the stronger, but not at the weaker, power. The authors found that neuroprotection, as assessed by tyrosine hydroxylase expression in midbrain dopaminergic cells, could account for some, but not all, of the observed behavioral improvements; the groups that were associated with fewer rotations did not all necessarily have a greater number of surviving cells. There may have been other "symptomatic" elements contributing to behavioral improvements in these rats. CONCLUSIONS In summary, when delivered at the appropriate power, delivery mode, and dosage, NIr treatment provided both improved behavior and neuroprotection in 6-OHDA-lesioned rats.

The mechanical cause of age-related dementia (Alzheimer's disease): the brain is destroyed by the pulse

This review traces evidence that age-related dementia (Alzheimer's disease) results from the destructive impact of the pulse on cerebral vasculature. Evidence is reviewed that the neuropathology of the dementia is caused by the breakdown of small cerebral vessels (silent microbleeds), that the microbleeds result from pulse-induced damage to the cerebral vessels, and that pulse becomes increasingly destructive with age, because of the age-related stiffening of the aorta and great arteries, which causes an increase in the intensity of the pressure pulse. Implications for therapy are discussed, and evidence is reviewed that pulse-induced destruction of the brain, and of another highly vascular organ, the kidney, are becoming the default forms of death, the way we die if we survive the infections, cardiovascular disease, and malignancies, which still, for a decreasing minority, inflict the tragedy of early death.

The effect of different doses of near infrared light on dopaminergic cell survival and gliosis in MPTP-treated mice

We have used the MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) mouse model to explore whether (i) the neuroprotective effect of near infrared light (NIr) treatment in the SNc is dose-dependent and (ii) the relationship between tyrosine hydroxylase (TH)+ terminal density and glial cells in the caudate-putamen complex (CPu). Mice received MPTP injections (50 mg/kg) and 2 J/cm2 NIr dose with either 2 d or 7 d survival period. In another series, with a longer 14 d survival period, mice had a stronger MPTP regime (100 mg/kg) and either 2 J/cm2 or 4 J/cm2 NIr dose. Brains were processed for routine immunohistochemistry and cell counts were made using stereology. Our findings were that in the 2 d series, no change in SNc TH+ cell number was evident after any treatment. In the 7 d series however, MPTP insult resulted in ∼45% reduction in TH+ cell number; after NIr (2 J/cm2) treatment, many cells were protected from the toxic insult. In the 14 d series, MPTP induced a similar reduction in TH+ cell number. NIr mitigated the loss of TH+ cells, but only at the higher dose of 4 J/cm2; the lower dose of 2 J/cm2 had no neuroprotective effect in this series. The higher dose of NIr, unlike the lower dose, also mitigated the MPTP- induced increase in CPu astrocytes after 14 d; these changes were independent of TH+ terminal density, of which, did not vary across the different experimental groups. In summary, we showed that neuroprotection by NIr irradiation in MPTP-treated mice was dose-dependent; with increasing MPTP toxicity, higher doses of NIr were required to protect cells and reduce astrogliosis.

810nm near-infrared light offers neuroprotection and improves locomotor activity in MPTP-treated mice

We explored whether 810nm near-infrared light (NIr) offered neuroprotection and/or improvement in locomotor activity in an acute 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mouse model of Parkinson's disease. Mice received MPTP and 810nm NIr treatments, or not, and were tested for locomotive activity in an open-field test. Thereafter, brains were aldehyde-fixed and processed for tyrosine hydroxylase immunohistochemistry. Our results showed that MPTP-treated mice that were irradiated with 810nm NIr had both greater locomotor activity (∼40%) and number of dopaminergic cells (∼20%) than those that were not. In summary, 810nm (as with 670nm) NIr offered neuroprotection and improved locomotor activity in MPTP-treated mice.

Indirect application of near infrared light induces neuroprotection in a mouse model of parkinsonism - an abscopal neuroprotective effect

We have previously shown near infrared light (NIr), directed transcranially, mitigates the loss of dopaminergic cells in MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine)-treated mice, a model of parkinsonism. These findings complement others suggesting NIr treatment protects against damage from various insults. However one puzzling feature of NIr treatment is that unilateral exposure can lead to a bilateral healing response, suggesting NIr may have 'indirect' protective effects. We investigated whether remote NIr treatment is neuroprotective by administering different MPTP doses (50-, 75-, 100-mg/kg) to mice and treating with 670-nm light directed specifically at either the head or body. Our results show that, despite no direct irradiation of the damaged tissue, remote NIr treatment produces a significant rescue of tyrosine hydroxylase-positive cells in the substantia nigra pars compacta at the milder MPTP dose of 50-mg/kg (∼30% increase vs sham-treated MPTP mice, p<0.05). However this protection did not appear as robust as that achieved by direct irradiation of the head (∼50% increase vs sham-treated MPTP mice, p<0.001). There was no quantifiable protective effect of NIr at higher MPTP doses, irrespective of the delivery mode. Astrocyte and microglia cell numbers in substantia nigra pars compacta were not influenced by either mode of NIr treatment. In summary, the findings suggest that treatment of a remote tissue with NIr is sufficient to induce protection of the brain, reminiscent of the 'abscopal effect' sometimes observed in radiation treatment of metastatic cancer. This discovery has implications for the clinical translation of light-based therapies, providing an improved mode of delivery over transcranial irradiation.

Photobiomodulation inside the brain: a novel method of applying near-infrared light intracranially and its impact on dopaminergic cell survival in MPTP-treated mice

Object

Previous experimental studies have documented the neuroprotection of damaged or diseased cells after applying, from outside the brain, near-infrared light (NIr) to the brain by using external light-emitting diodes (LEDs) or laser devices. In the present study, the authors describe an effective and reliable surgical method of applying to the brain, from inside the brain, NIr to the brain. They developed a novel internal surgical device that delivers the NIr to brain regions very close to target damaged or diseased cells. They suggest that this device will be useful in applying NIr within the large human brain, particularly if the target cells have a very deep location.

Methods

An optical fiber linked to an LED or laser device was surgically implanted into the lateral ventricle of BALB/c mice or Sprague-Dawley rats. The authors explored the feasibility of the internal device, measured the NIr signal through living tissue, looked for evidence of toxicity at doses higher than those required for neuroprotection, and confirmed the neuroprotective effect of NIr on dopaminergic cells in the substantia nigra pars compacta (SNc) in an acute 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of Parkinson disease in mice.

Results

The device was stable in freely moving animals, and the NIr filled the cranial cavity. Measurements showed that the NIr intensity declined as distance from the source increased across the brain (65% per mm) but was detectable up to 10 mm away. At neuroprotective (0.16 mW) and much higher (67 mW) intensities, the NIr caused no observable behavioral deficits, nor was there evidence of tissue necrosis at the fiber tip, where radiation was most intense. Finally, the intracranially delivered NIr protected SNc cells against MPTP insult; there were consistently more dopaminergic cells in MPTP-treated mice irradiated with NIr than in those that were not irradiated.

Conclusions

In summary, the authors showed that NIr can be applied intracranially, does not have toxic side effects, and is neuroprotective.

Photobiomodulation with near infrared light mitigates Alzheimer's disease-related pathology in cerebral cortex - evidence from two transgenic mouse models

INTRODUCTION

Previous work has demonstrated the efficacy of irradiating tissue with red to infrared light in mitigating cerebral pathology and degeneration in animal models of stroke, traumatic brain injury, parkinsonism and Alzheimer's disease (AD). Using mouse models, we explored the neuroprotective effect of near infrared light (NIr) treatment, delivered at an age when substantial pathology is already present in the cerebral cortex.

METHODS

We studied two mouse models with AD-related pathologies: the K369I tau transgenic model (K3), engineered to develop neurofibrillary tangles, and the APPswe/PSEN1dE9 transgenic model (APP/PS1), engineered to develop amyloid plaques. Mice were treated with NIr 20 times over a four-week period and histochemistry was used to quantify AD-related pathological hallmarks and other markers of cell damage in the neocortex and hippocampus.

RESULTS

In the K3 mice, NIr treatment was associated with a reduction in hyperphosphorylated tau, neurofibrillary tangles and oxidative stress markers (4-hydroxynonenal and 8-hydroxy-2'-deoxyguanosine) to near wildtype levels in the neocortex and hippocampus, and with a restoration of expression of the mitochondrial marker cytochrome c oxidase in surviving neurons. In the APP/PS1 mice, NIr treatment was associated with a reduction in the size and number of amyloid-β plaques in the neocortex and hippocampus.

CONCLUSIONS

Our results, in two transgenic mouse models, suggest that NIr may have potential as an effective, minimally-invasive intervention for mitigating, and even reversing, progressive cerebral degenerations.

The impact of near-infrared light on dopaminergic cell survival in a transgenic mouse model of parkinsonism

We have examined whether near-infrared light (NIr) treatment mitigates oxidative stress and increased expression of hyperphosphorylated tau in a tau transgenic mouse strain (K3) that has a progressive degeneration of dopaminergic cells in the substantia nigra pars compacta (SNc). The brains of wild-type (WT), untreated K3 and NIr-treated K3 mice, aged five months (thus after the onset of parkinsonian signs and neuropathology), were labelled immunohistochemically for the oxidative stress markers 4-hydroxynonenal (4-HNE) and 8-hydroxy-2'-deoxyguanosine (8-OHDG), hyperphosphorylated tau (using the AT8 antibody) and tyrosine hydroxylase (TH). The average intensity and area of 4-HNE, 8-OHDG and AT8 immunoreactivity were measured using the MetaMorph software and TH⁺ cell number was estimated using stereology. Our results showed immunoreactivity for 4-HNE, 8-OHDG and AT8 within the SNc was increased in K3 mice compared to WT, and that this increase was mitigated by NIr. Results further showed that TH⁺ cell number was lower in K3 mice than in WT, and that this loss was mitigated by NIr. In summary, NIr treatment reduced the oxidative stress caused by the tau transgene in the SNc of K3 mice and saved SNc cells from degeneration. Our results, when taken together with those in other models, strengthen the notion that NIr treatment saves dopaminergic cells in the parkinsonian condition.