Microglia polarization by mitochondrial metabolism modulation: A therapeutic opportunity in neurodegenerative diseases

Hearing Loss and Alzheimer Disease

Several studies have been done to investigate the role of hearing loss (HL) in cognitive decline. A co-existence of these two conditions has been identified. Recently, thanks to the use of functional MRI and EEG it has been shown that untreated HL can expose patients with cognitive decline to a higher risk of developing Alzheimer Disease (AD). This chapter will discuss the difference between central and peripheral HL, the link between HL and cognition and the relationship between HL and AD. At the end of the chapter the available technologies to treat HL will be discussed as well as their impact on memory and cognition.

The immunometabolic reprogramming of microglia in Alzheimer's disease

Alzheimer's disease (AD) is an age-related neurodegenerative disorder (NDD). In the central nervous system (CNS), immune cells like microglia could reprogram intracellular metabolism to alter or exert cellular immune functions in response to environmental stimuli. In AD, microglia could be activated and differentiated into pro-inflammatory or anti-inflammatory phenotypes, and these differences in cellular phenotypes resulted in variance in cellular energy metabolism. Considering the enormous energy requirement of microglia for immune functions, the changes in mitochondria-centered energy metabolism and substrates of microglia are crucial for the cellular regulation of immune responses. Here we reviewed the mechanisms of microglial metabolic reprogramming by analyzing their flexible metabolic patterns and changes that occurred in their metabolism during the development of AD. Further, we summarized the role of drugs in modulating immunometabolic reprogramming to prevent neuroinflammation, which may shed light on a new research direction for AD treatment.

Treatment of COVID-19 olfactory dysfunction with olfactory training, palmitoylethanolamide with luteolin, or combined therapy: a blinded controlled multicenter randomized trial

PURPOSE

Few evidence-based therapies are available for chronic olfactory dysfunction after COVID-19. This study investigated the relative efficacy of olfactory training alone, co-ultramicronized palmitoylethanolamide with luteolin (um-PEA-LUT, an anti-neuroinflammatory supplement) alone, or combined therapy for treating chronic olfactory dysfunction from COVID-19.

METHODS

This double-blinded controlled, placebo-controlled multicenter randomized clinical trial was conducted in 202 patients with persistent COVID-19 olfactory dysfunction of > 6 month duration. After a screening nasal endoscopy, patients were randomized to: (1) olfactory training and placebo; (2) once daily um-PEA-LUT alone; (3) twice daily um-PEA-LUT alone; or (4) combination of once daily um-PEA-LUT with olfactory training. Olfactory testing (Sniffin' Sticks odor identification test) was performed at baseline and at 1, 2, and 3 months. The primary outcome was recovery of over three points on olfactory testing, with outcomes compared at T0, T1, T2 and T3 across groups. Statistical analyses included one-way ANOVA for numeric data and chi-square for nominal data.

RESULTS

All patients completed the study, and there were no adverse events. At 90 days, odor identification scores improved by > 3 points in 89.2% of patients receiving combined therapy vs. 36.8% receiving olfactory training with placebo, 40% receiving twice daily um-PEA-LUT alone, and 41.6% receiving once daily um-PEA-LUT alone (p < 0.00001). Patients receiving treatment with um-PEA-LUT alone demonstrated subclinical improvement (< 3 point odor identification improvement) more often than patients receiving olfactory training with placebo (p < 0.0001.) CONCLUSIONS: Olfactory training plus once daily um-PEA-LUT resulted in greater olfactory recovery than either therapy alone in patients with long-term olfactory function due to COVID-19.

TRIAL REGISTRATION

20112020PGFN on clinicaltrials.gov.

LEVEL OF EVIDENCE

1b (Individual Randomized Clinical Trial).

Neuroinflammatory disorders of the brain and inner ear: a systematic review of auditory function in patients with migraine, multiple sclerosis, and neurodegeneration to support the idea of an innovative 'window of discovery'

Background

Hearing can be impaired in many neurological conditions and can even represent a forme fruste of specific disorders. Auditory function can be measured by either subjective or objective tests. Objective tests are more useful in identifying which auditory pathway (superior or inferior) is most affected by disease. The inner ear's perilymphatic fluid communicates with the cerebrospinal fluid (CSF) via the cochlear aqueduct representing a window from which pathological changes in the contents of the CSF due to brain inflammation could, therefore, spread to and cause inflammation in the inner ear, damaging inner hair cells and leading to hearing impairment identifiable on tests of auditory function.

Methods

A systematic review of the literature was performed, searching for papers with case-control studies that analyzed the hearing and migraine function in patients with neuro-inflammatory, neurodegenerative disorders. With data extracted from these papers, the risk of patients with neurological distortion product otoacoustic emission (DPOAE) was then calculated.

Results

Patients with neurological disorders (headache, Parkinson's disease, and multiple sclerosis) had a higher risk of having peripheral auditory deficits when compared to healthy individuals.

Conclusion

Existing data lend credence to the hypothesis that inflammatory mediators transmitted via fluid exchange across this communication window, thereby represents a key pathobiological mechanism capable of culminating in hearing disturbances associated with neuroimmunological and neuroinflammatory disorders of the nervous system.

Escalating Bi-Directional Feedback Loops between Proinflammatory Microglia and Mitochondria in Ageing and Post-Diagnosis of Parkinson's Disease

Parkinson's disease (PD) is a chronic and progressive age-related neurodegenerative disease affecting up to 3% of the global population over 65 years of age. Currently, the underlying physiological aetiology of PD is unknown. However, the diagnosed disorder shares many common non-motor symptoms associated with ageing-related neurodegenerative disease progression, such as neuroinflammation, microglial activation, neuronal mitochondrial impairment, and chronic autonomic nervous system dysfunction. Clinical PD has been linked to many interrelated biological and molecular processes, such as escalating proinflammatory immune responses, mitochondrial impairment, lower adenosine triphosphate (ATP) availability, increasing release of neurotoxic reactive oxygen species (ROS), impaired blood brain barrier integrity, chronic activation of microglia, and damage to dopaminergic neurons consistently associated with motor and cognitive decline. Prodromal PD has also been associated with orthostatic hypotension and many other age-related impairments, such as sleep disruption, impaired gut microbiome, and constipation. Thus, this review aimed to present evidence linking mitochondrial dysfunction, including elevated oxidative stress, ROS, and impaired cellular energy production, with the overactivation and escalation of a microglial-mediated proinflammatory immune response as naturally occurring and damaging interlinked bidirectional and self-perpetuating cycles that share common pathological processes in ageing and PD. We propose that both chronic inflammation, microglial activation, and neuronal mitochondrial impairment should be considered as concurrently influencing each other along a continuum rather than as separate and isolated linear metabolic events that affect specific aspects of neural processing and brain function.

Hearing and Ageing

Age-related hearing loss (ARHL), or presbycusis, occurs in most mammals, humans included, with a different age of onset and magnitude of loss. It is associated with two major symptoms: loss of sensitivity to sound, especially for high pitches, and a reduced ability to understand speech in background noise. This phenomenon involves both the peripheral structures of the inner ear and the central acoustic pathways. Several mechanisms have been identified as pro-ageing in the human cochlea. The main one is the oxidative stress. The inner ear physiological degeneration can be affected by both intrinsic conditions, such as genetic predisposition, and extrinsic ones, such as noise exposure. The magnitude of neuronal loss precedes and exceeds that of inner hair cell loss, which is also less important than the loss of outer hair cells. Patients with HL often develop atrophy of the temporal lobe (auditory cortex) and brain gliosis can contribute to the development of a central hearing loss. The presence of white matter hyperintensities (WMHs) on the MRI, which is radiologic representation of brain gliosis, can justify a central HL due to demyelination in the superior auditory pathways. Recently, the presence of WMHs has been correlated with the inability to correctly understand words in elderly with normal auditory thresholds.

Effect of Ultra-Micronized Palmitoylethanolamide and Luteolin on Olfaction and Memory in Patients with Long COVID: Results of a Longitudinal Study

In this study, we investigated whether treatment with palmitoylethanolamide and luteolin (PEA-LUT) leads to improvement in the quantitative or qualitative measures of olfactory dysfunction or relief from mental clouding in patients affected by long COVID. Patients with long COVID olfactory dysfunction were allocated to different groups based on the presence (“previously treated”) or absence (“naïve”) of prior exposure to olfactory training. Patients were then randomized to receive PEA-LUT alone or in combination with olfactory training. Olfactory function and memory were assessed at monthly intervals using self-report measures and quantitative thresholds. A total of 69 patients (43 women, 26 men) with an age average of 40.6 + 10.5 were recruited. PEA-LUT therapy was associated with a significant improvement in validated odor identification scores at the baseline versus each subsequent month; assessment at 3 months showed an average improvement of 10.7 + 2.6, CI 95%: 6–14 (p < 0.0001). The overall prevalence of parosmia was 79.7% (55 patients), with a significant improvement from the baseline to 3 months (p < 0.0001), namely in 31 patients from the Naïve 1 group (72%), 15 from the Naïve 2 group (93.7%), and 9 from the remaining group (90%). Overall, mental clouding was detected in 37.7% (26 subjects) of the cases, with a reduction in severity from the baseline to three months (p = 0.02), namely in 15 patients from the Naïve 1 group (34.8%), 7 from the Naïve 2 group (43.7%), and 4 from the remaining group (40%). Conclusions. In patients with long COVID and chronic olfactory loss, a regimen including oral PEA-LUT and olfactory training ameliorated olfactory dysfunction and memory. Further investigations are necessary to discern biomarkers, mechanisms, and long-term outcomes.

Neuroprotection and Disease Modification by Astrocytes and Microglia in Parkinson Disease

Oxidative stress and neuroinflammation are common bases for disease onset and progression in many neurodegenerative diseases. In Parkinson disease, which is characterized by the degeneration of dopaminergic neurons resulting in dopamine depletion, the pathogenesis differs between hereditary and solitary disease forms and is often unclear. In addition to the pathogenicity of alpha-synuclein as a pathological disease marker, the involvement of dopamine itself and its interactions with glial cells (astrocyte or microglia) have attracted attention. Pacemaking activity, which is a hallmark of dopaminergic neurons, is essential for the homeostatic maintenance of adequate dopamine concentrations in the synaptic cleft, but it imposes a burden on mitochondrial oxidative glucose metabolism, leading to reactive oxygen species production. Astrocytes provide endogenous neuroprotection to the brain by producing and releasing antioxidants in response to oxidative stress. Additionally, the protective function of astrocytes can be modified by microglia. Some types of microglia themselves are thought to exacerbate Parkinson disease by releasing pro-inflammatory factors (M1 microglia). Although these inflammatory microglia may further trigger the inflammatory conversion of astrocytes, microglia may induce astrocytic neuroprotective effects (A2 astrocytes) simultaneously. Interestingly, both astrocytes and microglia express dopamine receptors, which are upregulated in the presence of neuroinflammation. The anti-inflammatory effects of dopamine receptor stimulation are also attracting attention because the functions of astrocytes and microglia are greatly affected by both dopamine depletion and therapeutic dopamine replacement in Parkinson disease. In this review article, we will focus on the antioxidative and anti-inflammatory effects of astrocytes and their synergism with microglia and dopamine.

Hearing loss and dementia: radiologic and biomolecular basis of their shared characteristics. A systematic review

Dementia and hearing loss share radiologic and biologic findings that might explain their coexistence, especially in the elderly population. Brain atrophy has been observed in both conditions, as well as the presence of areas of gliosis. The brain atrophy is usually focal; it is located in the temporal lobe in patients with hearing loss, while it involves different part of brain in patients with dementia. Radiological studies have shown white matter hyperintensities (WMHs) in both conditions. WMHs have been correlated with the inability to correctly understand words in elderly persons with normal auditory thresholds and, the identification of these lesion in brain magnetic resonance imaging studies has been linked with an increased risk of developing cognitive loss. In addition to WMHs, some anatomopathological studies identified the presence of brain gliosis in the elderly's brain. The cause-effect link between hearing loss and dementia is still unknown, despite they might share some common findings. The aim of this systematic review is to analyze radiologic and biomolecular findings that these two conditions might share, identify a common pathological basis, and discuss the effects of hearing aids on prevention and treatment of cognitive decline in elderly patients with hearing loss.

Alzheimer's Disease: New Concepts on the Role of Autoimmunity and NLRP3 Inflammasome in the Pathogenesis of the Disease

Alzheimer's disease (AD), recognized as the most common neurodegenerative disorder, is clinically characterized by the presence of extracellular beta-amyloid (Aβ) plaques and by intracellular neurofibrillary tau tangles, accompanied by glial activation and neuroinflammation. Increasing evidence suggests that self-misfolded proteins stimulate an immune response mediated by glial cells, inducing the release of inflammatory mediators and the recruitment of peripheral macrophages into the brain, which in turn aggravate AD pathology. The present review aims to update the current knowledge on the role of autoimmunity and neuroinflammation in the pathogenesis of the disease, indicating a new target for therapeutic intervention. We mainly focused on the NLRP3 microglial inflammasome as a critical factor in stimulating innate immune responses, thus sustaining chronic inflammation. Additionally, we discussed the involvement of the NLRP3 inflammasome in the gut-brain axis. Direct targeting of the NLRP3 inflammasome and the associated receptors could be a potential pharmacological strategy since its inhibition would selectively reduce AD neuroinflammation.

Could Sars-Cov2 affect MS progression?

A long-term neurologic sequela arising from COVID-19 infection in multiple sclerosis (MS) patients could be related both to the increase of cytokines and the activation of NLRP3 inflammasome by the Sars-CoV2. These two mechanisms may cause a worsening of MS several months after the resolution of the infection.

Can miR-34a be suitable for monitoring sensorineural hearing loss in patients with mitochondrial disease? A case series

Purpose: We aimed at evaluating the feasibility of using MicroRNA (miR)-34a and miR-29b to detect inner ear damage in patients with mitochondrial disease (MD) and sensorineural hearing loss (SNHL).Material and Methods: Three patients with MD and SNHL and seven healthy control subjects were included in this case series. MD patients underwent pure tone audiometry (PTA), distortion product otoacoustic emission (DPOAE) and auditory brain response tests to investigate the specific cochlear and retrocochlear functions; control patients underwent PTA. MiR-34a and miR-29b were extracted from blood in all subjects included in the study. The expression of miR-34a and miR-29b in MD patients and healthy controls were statistically compared, then the expression of these two miRs was compared with DPOAE values.Results: In MD patients, miR-34a was significantly up-regulated compared to healthy controls; miR-34a and DPOAEs were negatively correlated. Conversely, miR-29b was up-regulated only in the youngest patient who suffered from the mildest forms of MD and SNHL, and negatively correlated with DPOAEs.Conclusion: In MD patients, miR-34a and miR-29b might be a marker of inner ear damage and early damage, respectively. Additional studies on larger samples are necessary to confirm these preliminary results.