Neuroinflammation and neurohormesis in the pathogenesis of Alzheimer's disease and Alzheimer-linked pathologies: modulation by nutritional mushrooms

Insights into the Potential Role of Mercury in Alzheimer's Disease

Mercury (Hg), which is a non-essential element, is considered a highly toxic pollutant for biological systems even when present at trace levels. Elevated Hg exposure with the growing release of atmospheric pollutant Hg and rising accumulations of mono-methylmercury (highly neurotoxic) in seafood products have increased its toxic potential for humans. This review aims to highlight the potential relationship between Hg exposure and Alzheimer's disease (AD), based on the existing literature in the field. Recent reports have hypothesized that Hg exposure could increase the potential risk of developing AD. Also, AD is known as a complex neurological disorder with increased amounts of both extracellular neuritic plaques and intracellular neurofibrillary tangles, which may also be related to lifestyle and genetic variables. Research reports on AD and relationships between Hg and AD indicate that neurotransmitters such as serotonin, acetylcholine, dopamine, norepinephrine, and glutamate are dysregulated in patients with AD. Many researchers have suggested that AD patients should be evaluated for Hg exposure and toxicity. Some authors suggest further exploration of the Hg concentrations in AD patients. Dysfunctional signaling pathways in AD and Hg exposure appear to be interlinked with some driving factors such as arachidonic acid, homocysteine, dehydroepiandrosterone (DHEA) sulfate, hydrogen peroxide, glucosamine glycans, glutathione, acetyl-L carnitine, melatonin, and HDL. This evidence suggests the need for a better understanding of the relationship between AD and Hg exposure, and potential mechanisms underlying the effects of Hg exposure on regional brain functions. Also, further studies evaluating brain functions are needed to explore the long-term effects of subclinical and untreated Hg toxicity on the brain function of AD patients.

Hyperbaric oxygen therapy for Alzheimer's dementia with positron emission tomography imaging: a case report

A 58-year-old female was diagnosed with Alzheimer's dementia (AD) which was rapidly progressive in the 8 months prior to initiation of hyperbaric oxygen therapy (HBOT). ¹⁸Fluorodeoxyglucose (¹⁸FDG) positron emission tomography (PET) brain imaging demonstrated global and typical metabolic deficits in AD (posterior temporal-parietal watershed and cingulate areas). An 8-week course of HBOT reversed the patient's symptomatic decline. Repeat PET imaging demonstrated a corresponding 6.5-38% regional and global increase in brain metabolism, including increased metabolism in the typical AD diagnostic areas of the brain. Continued HBOT in conjunction with standard pharmacotherapy maintained the patient's symptomatic level of function over an ensuing 22 months. This is the first reported case of simultaneous HBOT-induced symptomatic and ¹⁸FDG PET documented improvement of brain metabolism in AD and suggests an effect on global pathology in AD.

Resveratrol protects photoreceptors by blocking caspase- and PARP-dependent cell death pathways

Retinal degeneration is a major cause of severe vision loss and irreversible blindness and is characterized by progressive damage to retinal photoreceptor cells. Resveratrol (RSV) serves as an activator of the histone deacetylase, Sirt1, and has been shown to exert anti-oxidative properties. In this study, we mimicked retinal degeneration by subjecting photoreceptors (661 W cells) to glucose deprivation (GD) or light exposure. Under these conditions, we investigated the mechanisms underlying GD- or light exposure-induced cell death and the protective effect of RSV. We found that GD and light exposure resulted in mitochondrial dysfunction, oxidative stress, and cell death. Treatment of injured cells with RSV decreased the production of reactive oxygen species (ROS), improved the ratio of reduced/oxidized glutathione (GSH/GSSG), mitochondrial membrane potential and morphology, and reduced apoptosis. We used the caspase inhibitor, z-VAD-fmk, and a lentiviral-mediated shRNA knockdown of PARP-1 to reveal that GD and light exposure-induced cell death have different underlying mechanisms; GD triggered a caspase-dependent cell death pathway, whereas light exposure triggered a PARP-dependent cell death pathway. The level of caspase-9 and caspase-3, upregulated following GD, were reduced by treatment with RSV. Similarly, the level of PARP-1 and AIF, upregulated following light exposure, were decreased by treatment with RSV. Additionally, treatment with RSV elevated the protein expression and enzymatic activity of Sirt1 and a Sirt1 inhibitor reduced the protective effect of RSV against insult-induced cellular injuries, indicating that RSV's protective effect may involve Sirt1 activation. Finally, we investigated the neuroprotection of RSV in vivo. Administration of RSV to mice under extreme light exposure led to a suppression of the light-induced thinning of the outer nuclear layer (ONL) detected by hematoxylin and eosin (H&E) staining and restored retinal function evaluated by electroretinography (ERG). Taken together, our findings provide evidence that treatment with RSV has neuroprotective effects on both GD and light exposure-induced cell death pathways in photoreceptor cells.

Building Biological Shields via Hormesis

Hormesis offers the potential to build biological shields to protect against a plethora of age-related diseases and acute trauma (e.g., brain traumatic injury) via the implementation of pre- and postconditioning strategies. These strategies have the potential to markedly enhance a broad spectrum of medical and public health practices.

Gut Microbiota and Their Neuroinflammatory Implications in Alzheimer's Disease

The bidirectional communication between the central nervous system (CNS) and the gut microbiota plays a pivotal role in human health. Increasing numbers of studies suggest that the gut microbiota can influence the brain and behavior of patients. Various metabolites secreted by the gut microbiota can affect the cognitive ability of patients diagnosed with neurodegenerative diseases. Nearly one in every ten Korean senior citizens suffers from Alzheimer’s disease (AD), the most common form of dementia. This review highlights the impact of metabolites from the gut microbiota on communication pathways between the brain and gut, as well as the neuroinflammatory roles they may have in AD patients. The objectives of this review are as follows: (1) to examine the role of the intestinal microbiota in homeostatic communication between the gut microbiota and the brain, termed the microbiota–gut–brain (MGB) axis; (2) to determine the underlying mechanisms of signal dysfunction; and (3) to assess the impact of signal dysfunction induced by the microbiota on AD. This review will aid in understanding the microbiota of elderly people and the neuroinflammatory roles they may have in AD.

The intestinal microbiome and Alzheimer's disease: A review

Alzheimer's disease (AD) is an increasingly common neurodegenerative disease. Since the intestinal microbiome is closely related to nervous system diseases, alterations in the composition of intestinal microbiota could potentially contribute to the pathophysiology of AD. However, how the initial interactions with intestinal microbes alter events later in life, such as during neurodegenerative diseases, is still unclear. This review summarizes what is known about the relationship between the intestinal microbiome and AD.

A New Approach to Treating Neurodegenerative Otologic Disorders

Hearing loss, the most common neurological disorder and the fourth leading cause of years lived with disability, can have profound effects on quality of life. The impact of this "invisible disability," with significant consequences, economic and personal, is most substantial in low- and middle-income countries, where >80% of affected people live. Given the importance of hearing for communication, enjoyment, and safety, with up to 500 million affected globally at a cost of nearly $800 billion/year, research on new approaches toward prevention and treatment is attracting increased attention. The consequences of noise pollution are largely preventable, but irreversible hearing loss can result from aging, disease, or drug side effects. Once damage occurs, treatment relies on hearing aids and cochlear implants. Preventing, delaying, or reducing some degree of hearing loss may be possible by avoiding excessive noise and addressing major contributory factors such as cardiovascular risk. However, given the magnitude of the problem, these interventions alone are unlikely to be sufficient. Recent advances in understanding principal mechanisms that govern hearing function, together with new drug discovery paradigms designed to identify efficacious therapies, bode well for pharmaceutical intervention. This review surveys various causes of loss of auditory function and discusses potential neurological underpinnings, including mitochondrial dysfunction. Mitochondria mitigate cell protection, survival, and function and may succumb to cumulative degradation of energy production and performance; the end result is cell death. Energy-demanding neurons and vestibulocochlear hair cells are vulnerable to mitochondrial dysfunction, and hearing impairment and deafness are characteristic of neurodegenerative mitochondrial disease phenotypes. Beyond acting as cellular powerhouses, mitochondria regulate immune responses to infections, and studies of this phenomenon have aided in identifying nuclear factor kappa B and nuclear factor erythroid 2-related factor 2/antioxidant response element signaling as targets for discovery of otologic drugs, respectively, suppressing or upregulating these pathways. Treatment with free radical scavenging antioxidants is one therapeutic approach, with lipoic acid and corresponding carnitine esters exhibiting improved biodistribution and other features showing promise. These compounds are also histone deacetylase (HDAC) inhibitors, adding epigenetic modulation to the mechanistic milieu through which they act. These data suggest that new drugs targeting mitochondrial dysfunction and modulating epigenetic pathways via HDAC inhibition or other mechanisms hold great promise.

Neuroinflammation, Gut Microbiome, and Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease that develops insidiously and causes dementia finally. There are also clinical complications in advanced dementia, such as eating problems, infections, which will lead to the decline of patients' life quality, and the rising cost of care for AD to our society. AD will be important public health challenge. Early detection of AD may be a key issue to prevent, delay, and stop the disease. Gut microbiome and neuroinflammation are closely related with nervous system diseases, although the specific mechanism is not clear. This review introduces the relationship between neuroinflammation, gut microbiome, and AD.