The Cerebral Effect of Ammonia in Brain Aging: Blood-Brain Barrier Breakdown, Mitochondrial Dysfunction, and Neuroinflammation

Ammonium chloride, an environmental pollutant, disrupts melanocyte biology through the regulation of melanosome and autophagy

Ammonium chloride is an indoor environmental pollutant released due to industrial emissions, concrete, indoor bacteria, or other sources. In this study, we characterized molecular mechanisms of ammonium chloride-induced cell damage in melanocyte cells, which are a critical effector for pigmentation. Specifically, we investigated the effects of ammonium chloride on pigmentation and its underlying mechanisms, including its involvement in melanogenesis and autophagy. Based on the experiments, we elucidated that ammonium chloride induced and increased melanogenesis by upregulating MITF via AKT-mediated melanogenic signaling pathways. Moreover, ammonium chloride did not exhibit lysosomotropic activity and inhibited autophagy by activating the AKT-mTOR signaling pathway, suggesting that the pigment-regulating mechanism of ammonium chloride was associated with autophagy in pigmented cells. The findings of this study offer new perspectives on the mechanisms involved in ammonium chloride-induced pigmentation and propose a potential approach to mitigate ammonium chloride-induced side effects like hyperpigmentation and hyperammonemia by employing a combined autophagy inducer.

Glutamine Synthetase: Diverse Regulation and Functions of an Ancient Enzyme

Glutamine synthetase (GS) is a ubiquitous enzyme central to nitrogen metabolism, catalyzing the ATP-dependent formation of glutamine from glutamate and ammonia. Positioned at the intersection of nitrogen metabolism with carbon metabolism, the activity of GS is subject to sophisticated regulation. While the intricate regulatory pathways that govern Escherichia coli GS were established long ago, recent work has demonstrated that homologues are controlled by multiple distinct regulatory patterns, such as the metabolite induced oligomeric state formation in archaeal GS by 2-oxoglutarate. Such work was enabled in large part by advances in cryo-electron microscopy (cryoEM) that allowed greater structural access to this large enzyme complex, such as assessment of the large heterogeneous oligomeric states of GS and protein-interactor-GS complexes. This perspective highlights recent advances in understanding GS regulation, focusing on the dynamic interplay between its oligomeric state, metabolite binding, and protein interactors. These interactions modulate GS activity, influencing cellular processes such as nitrogen assimilation, carbon metabolism, and stress responses. Furthermore, we explore the emerging concept of GS "moonlighting" functions, revealing its roles in palmitoylation, cell cycle regulation, and ion channel modulation. These diverse functions highlight a newfound versatility of GS beyond its primary catalytic role and suggest complex roles in health and disease that warrant further study.

Bioactive Phenolics of Hyoscyamus muticus L. Subsp. Falezlez: A Molecular and Biochemical Approach to Antioxidant and Urease Inhibitory Activities

This study examines the chemical composition, antioxidant properties, and urease inhibitory effects of Hyoscyamus muticus L. subsp. falezlez (Coss.) Maire. Using LC-ESI-MS/MS, 19 distinct phenolic compounds were identified, with chlorogenic acid being the most abundant. The ethanol extract demonstrated notable antioxidant activity, highlighting its potential for therapeutic use. Urease inhibition assays revealed a remarkable 91.35% inhibition by the H. muticus extract, with an IC50 value of 5.6 ± 1.20 μg/mL, indicating its promising role in addressing conditions linked to urease activity. Molecular docking studies further investigated the interaction between H. muticus phenolic compounds and urease, identifying hyperoside as a leading candidate, with a binding energy of -7.9 kcal/mol. Other compounds, such as rutin, luteolin, apigenin, kaempferol, hesperetin, chlorogenic acid, and rosmarinic acid, also demonstrated significant binding affinities, suggesting their potential to disrupt urease function. These findings highlight the therapeutic potential of H. muticus as a source of natural bioactive compounds, offering promising avenues for the development of novel treatments for urease-related disorders and oxidative stress.

A Case of Hyperammonemia Not Attributable to Liver Disease and Treated With IV Ammonia Scavengers

Hyperammonemia is a serious metabolic condition marked by elevated ammonia levels in the blood, leading to neurological damage and systemic complications if untreated. While often associated with liver dysfunction, inborn metabolic errors such as fatty acid oxidation defects, pyruvate metabolism disorders, urea cycle disorders (UCDs), urea splitting bacterial infections, hemato-oncological disorders, and portosystemic shunts are less commonly recognized but significant causes, particularly outside neonatal populations. These metabolic errors, due to partial enzyme deficiencies, may present later in life with atypical symptoms. We report an acute presentation of a female patient in her late fifties with a background of noncirrhotic hyperammonemia of unknown etiology, controlled with oral sodium benzoate. She presented with ataxia, altered mental status, and delusion. The laboratory evaluation revealed significantly elevated ammonia levels, which did not respond to an increased dose of oral sodium benzoate, and she required intravenous ammonia scavengers to achieve acceptable levels. We further discuss several investigations done to establish a cause for her hyperammonemia and a psychiatric diagnosis of erotomania/de Clerambault's syndrome secondary to recurrent hyperammonemia. Although her biochemical workup had some features suggestive of type 2 citrulline deficiency, SLC25A13 mutation analysis for citrin deficiency and an extended R98 panel were negative. Thus, highlighting the complexity of diagnosis of inborn metabolic errors and treatment of metabolic hyperammonemia in the absence of an established diagnosis. It also emphasizes the need for heightened awareness and prompt treatment of inborn metabolic errors in adult patients, following the British Inherited Metabolic Disease Group (BIMDG) management guidelines to prevent severe neurological outcomes. Multidisciplinary management, including liaison with specialists in metabolics, gastroenterology, and dietetics, is crucial for optimizing patient care and outcomes in such complex cases.

Protective effect of menthol against thioacetamide-induced hepatic encephalopathy by suppressing oxidative stress and inflammation, augmenting expression of BDNF and α7-nACh receptor, and improving spatial memory

Hepatic encephalopathy (HE) is a neuropsychiatric syndrome that can occur in people with acute or chronic liver disease. Here, we investigated the effects of menthol, a natural monoterpene, on HE induced by thioacetamide (TA) in male Wistar rats. The rats received 200 mg/kg of TA twice a week for four weeks and were administered 10 mg/kg of menthol intraperitoneally daily for the same period. The results showed that menthol treatment reduced oxidative stress and inflammation in the livers and hippocampi of the rats that received TA. It also lowered the levels of ammonium and liver enzymes AST, ALT, ALP, and GGT in the serum of these animals and prevented liver histopathological damage. In addition, the expression and activity of acetylcholinesterase in the hippocampus of HE model rats were decreased by menthol. Likewise, this monoterpene reduced the expression of TLR4, MyD88, and NF-κB in the hippocampus while increasing the expression of BDNF and α7-nACh receptor. Menthol also reduced neuronal death in the hippocampal cornu ammonis-1 and dentate gyrus regions and reduced astrocyte swelling, which led to improved learning and spatial memory in rats with HE. In conclusion, the study suggests that menthol may have strong protective effects on the liver and brain, making it a potential treatment for HE and neurodegenerative diseases.

Cognitive impairment in patients awaiting kidney and liver transplantation-A clinically relevant problem?

INTRODUCTION

Cognitive impairment (CI) is common in both end-stage kidney disease (ESKD) and alcohol-related liver cirrhosis. The aim of this study was to assess the prevalence and patterns of CI in patients awaiting kidney and liver transplantation, and to identify its determinants.

METHODS

In this cross-sectional, prospective study, 31 consecutive patients with ESKD and 31 consecutive patients with alcohol-related liver cirrhosis, all currently on transplant waiting lists, were screened for cognitive decline using the Addenbrooke's Cognitive Examination. Medical history, demographics, and laboratory test results were also collected.

RESULTS

The prevalence of CI among patients with ESKD and alcohol-related liver cirrhosis was 26% and 90%, respectively. In both groups, memory was the most affected cognitive domain, along with verbal fluency in patients with ESKD, and visuospatial abilities in patients with alcoholic cirrhosis. The most statistically significant increase in the prevalence of CI was found in patients with lower educational attainment, in both alcohol-related liver cirrhosis and ESKD populations as well as in older patients with alcoholic cirrhosis. Furthermore, better cognitive functioning in ESKD patients was associated with higher levels of total lymphocyte count and alanine transaminase (ALT), and in alcohol-related liver cirrhosis patients with higher levels of ALT and aspartate transaminase. A nonsignificant trend toward lower memory domain scores was also observed with increasing ammonia levels and increasing severity of liver disease (higher Child-Pugh scores). Finally, suboptimal performance on the screening test was correlated with the severity of liver disease as assessed by the Model for End-Stage Liver Disease Sodium (MELD-Na), but not at the statistically significant level.

CONCLUSIONS

The prevalence of CI, especially in patients with alcohol-related liver cirrhosis, is high and can be a significant clinical problem, negatively affecting the transplantation process. Routine screening tests in this group would contribute to the implementation of appropriate management, such as rehabilitation program or psychosocial treatments and facilitate the provision of specialized health care.

Association between ambient fine particular matter components and subsequent cognitive impairment in community-dwelling older people: a prospective cohort study from eastern China

BACKGROUND

Fine particular matter (PM2.5) has been associated with dementia, but limited information is available regarding the association between PM2.5 components and dementia.

AIMS

We aimed to identify the major components of PM2.5 that affect cognitive function to further investigate its mechanism of action, and develop a prevention strategy for dementia.

METHODS

In this study, we included 7804 participants aged ≥ 60 years recruited from seven counties in Zhejiang province, eastern China. The participants completed the baseline survey between 2014 and 2015, and were followed up until the end of 2020. We adopted single-component robust Poisson regression models for analyses, and estimated relative risks and 95% confidence intervals describing associations between the chemical constituents of PM2.5 exposure and incident cognitive impairment in those who were free from cognitive impairment at baseline.

RESULTS

Significantly positive associations were observed between sulfate, nitrate, ammonium, and organic matter in PM2.5 and incident cognitive impairment across different exposure periods; the relative risks of 10-year exposure before enrollment ranged from 1.01 to 1.02. However, we did not find a significant association between black carbon and cognitive impairment. The point estimates of the relative risk values did not change substantially after performing the sensitivity analyses.

CONCLUSIONS

Our findings strengthen the idea that long-term exposure to PM2.5 mass and its chemical components is associated with an elevated risk of incident cognitive impairment among older adults.

Creatine supplementation research fails to support the theoretical basis for an effect on cognition: Evidence from a systematic review

Creatine supplementation has been put forward as a possible aid to cognition, particularly for vegans, vegetarians, the elderly, sleep deprived and hypoxic individuals. However, previous narrative reviews have only provided limited support for these claims. This is despite the fact that research has shown that creatine supplementation can induce increased brain concentrations of creatine, albeit to a limited extent. We carried out a systematic review to examine the current state of affairs. The review supported claims that creatine supplementation can increases brain creatine content but also demonstrated somewhat equivocal results for effects on cognition. It does, however, provide evidence to suggest that more research is required with stressed populations, as supplementation does appear to significantly affect brain content. Issues with research design, especially supplementation regimens, need to be addressed. Future research must include measurements of creatine brain content.

Increased intestinal bile acid absorption contributes to age-related cognitive impairment

Cognitive impairment in the elderly is associated with alterations in bile acid (BA) metabolism. In this study, we observe elevated levels of serum conjugated primary bile acids (CPBAs) and ammonia in elderly individuals, mild cognitive impairment, Alzheimer's disease, and aging rodents, with a more pronounced change in females. These changes are correlated with increased expression of the ileal apical sodium-bile acid transporter (ASBT), hippocampal synapse loss, and elevated brain CPBA and ammonia levels in rodents. In vitro experiments confirm that a CPBA, taurocholic acid, and ammonia induced synaptic loss. Manipulating intestinal BA transport using ASBT activators or inhibitors demonstrates the impact on brain CPBA and ammonia levels as well as cognitive decline in rodents. Additionally, administration of an intestinal BA sequestrant, cholestyramine, alleviates cognitive impairment, normalizing CPBAs and ammonia in aging mice. These findings highlight the potential of targeting intestinal BA absorption as a therapeutic strategy for age-related cognitive impairment.

Mitochondrial malfunction and atrophy of astrocytes in the aged human cerebral cortex

How aging affects cells of the human brain active milieu remains largely unknown. Here, we analyze astrocytes and neurons in the neocortical tissue of younger (22-50 years) and older (51-72 years) adults. Aging decreases the amount of reduced mitochondrial cytochromes in astrocytes but not neurons. The protein-to-lipid ratio decreases in astrocytes and increases in neurons. Aged astrocytes show morphological atrophy quantified by the decreased length of branches, decreased volume fraction of leaflets, and shrinkage of the anatomical domain. Atrophy correlates with the loss of gap junction coupling between astrocytes and increased input resistance. Aging is accompanied by the upregulation of glial fibrillary acidic protein (GFAP) and downregulation of membrane-cytoskeleton linker ezrin associated with leaflets. No significant changes in neuronal excitability or spontaneous inhibitory postsynaptic signaling is observed. Thus, brain aging is associated with the impaired morphological presence and mitochondrial malfunction of cortical astrocytes, but not neurons.

Dysregulated cellular redox status during hyperammonemia causes mitochondrial dysfunction and senescence by inhibiting sirtuin-mediated deacetylation

Perturbed metabolism of ammonia, an endogenous cytotoxin, causes mitochondrial dysfunction, reduced NAD+ /NADH (redox) ratio, and postmitotic senescence. Sirtuins are NAD+ -dependent deacetylases that delay senescence. In multiomics analyses, NAD metabolism and sirtuin pathways are enriched during hyperammonemia. Consistently, NAD+ -dependent Sirtuin3 (Sirt3) expression and deacetylase activity were decreased, and protein acetylation was increased in human and murine skeletal muscle/myotubes. Global acetylomics and subcellular fractions from myotubes showed hyperammonemia-induced hyperacetylation of cellular signaling and mitochondrial proteins. We dissected the mechanisms and consequences of hyperammonemia-induced NAD metabolism by complementary genetic and chemical approaches. Hyperammonemia inhibited electron transport chain components, specifically complex I that oxidizes NADH to NAD+ , that resulted in lower redox ratio. Ammonia also caused mitochondrial oxidative dysfunction, lower mitochondrial NAD+ -sensor Sirt3, protein hyperacetylation, and postmitotic senescence. Mitochondrial-targeted Lactobacillus brevis NADH oxidase (MitoLbNOX), but not NAD+ precursor nicotinamide riboside, reversed ammonia-induced oxidative dysfunction, electron transport chain supercomplex disassembly, lower ATP and NAD+ content, protein hyperacetylation, Sirt3 dysfunction and postmitotic senescence in myotubes. Even though Sirt3 overexpression reversed ammonia-induced hyperacetylation, lower redox status or mitochondrial oxidative dysfunction were not reversed. These data show that acetylation is a consequence of, but is not the mechanism of, lower redox status or oxidative dysfunction during hyperammonemia. Targeting NADH oxidation is a potential approach to reverse and potentially prevent ammonia-induced postmitotic senescence in skeletal muscle. Since dysregulated ammonia metabolism occurs with aging, and NAD+ biosynthesis is reduced in sarcopenia, our studies provide a biochemical basis for cellular senescence and have relevance in multiple tissues.

Shared and unique phosphoproteomics responses in skeletal muscle from exercise models and in hyperammonemic myotubes

Skeletal muscle generation of ammonia, an endogenous cytotoxin, is increased during exercise. Perturbations in ammonia metabolism consistently occur in chronic diseases, and may blunt beneficial skeletal muscle molecular responses and protein homeostasis with exercise. Phosphorylation of skeletal muscle proteins mediates cellular signaling responses to hyperammonemia and exercise. Comparative bioinformatics and machine learning-based analyses of published and experimentally derived phosphoproteomics data identified differentially expressed phosphoproteins that were unique and shared between hyperammonemic murine myotubes and skeletal muscle from exercise models. Enriched processes identified in both hyperammonemic myotubes and muscle from exercise models with selected experimental validation included protein kinase A (PKA), calcium signaling, mitogen-activated protein kinase (MAPK) signaling, and protein homeostasis. Our approach of feature extraction from comparative untargeted "omics" data allows for selection of preclinical models that recapitulate specific human exercise responses and potentially optimize functional capacity and skeletal muscle protein homeostasis with exercise in chronic diseases.

Marked Cognitive and Activities of Daily Living Improvement by Shunt Embolization in a Very Old Man with Portosystemic Encephalopathy Mimicking Alzheimer Disease: A Case Report

A 91-year-old man with chronic cognitive impairment underwent shunt embolization for portosystemic encephalopathy (PSE). He experienced intermittent episodes of impaired consciousness and decreased cognitive function and activities of daily living (ADL), for which Alzheimer disease was suspected. On admission, he was in a coma and PSE was diagnosed based on his high ammonia level and the computed tomography findings. After shunt embolization, the patient fully recovered from the impaired consciousness and experienced no recurrence. The patient’s Revised Hasegawa Dementia Scale and Mini-Mental State Examination scores improved significantly from 12 and 17 to 30 and 29 points, respectively. The Barthel Index score also improved from 55/100 to 85/100, suggesting a marked improvement in ADL. PSE progresses slowly in very old patients and may mimic the clinical course of Alzheimer disease but without liver enzyme abnormalities. Therefore, it should be distinguished in every dementia case.

The barrier and interface mechanisms of the brain barrier, and brain drug delivery

Three different barriers are formed between the cerebrovascular and the brain parenchyma: the blood-brain barrier (BBB), the blood-cerebrospinal fluid barrier (BCSFB), and the cerebrospinal fluid-brain barrier (CBB). The BBB is the main regulator of blood and central nervous system (CNS) material exchange. The semipermeable nature of the BBB limits the passage of larger molecules and hydrophilic small molecules, Food and Drug Administration (FDA)-approved drugs for the CNS have been generally limited to lipid-soluble small molecules. Although the complexity of the BBB affects CNS drug delivery, understanding the composition and function of the BBB can provide a platform for the development of new methods for CNS drug delivery. This review summarizes the classification of the brain barrier, the composition and role of the basic structures of the BBB, and the transport, barrier, and destruction mechanisms of the BBB; discusses the advantages and disadvantages of different drug delivery methods and prospects for future drug delivery strategies.

Toxic Metabolites and Inborn Errors of Amino Acid Metabolism: What One Informs about the Other

In inborn errors of metabolism, such as amino acid breakdown disorders, loss of function mutations in metabolic enzymes within the catabolism pathway lead to an accumulation of the catabolic intermediate that is the substrate of the mutated enzyme. In patients of such disorders, dietarily restricting the amino acid(s) to prevent the formation of these catabolic intermediates has a therapeutic or even entirely preventative effect. This demonstrates that the pathology is due to a toxic accumulation of enzyme substrates rather than the loss of downstream products. Here, we provide an overview of amino acid metabolic disorders from the perspective of the ‘toxic metabolites’ themselves, including their mechanism of toxicity and whether they are involved in the pathology of other disease contexts as well. In the research literature, there is often evidence that such metabolites play a contributing role in multiple other nonhereditary (and more common) disease conditions, and these studies can provide important mechanistic insights into understanding the metabolite-induced pathology of the inborn disorder. Furthermore, therapeutic strategies developed for the inborn disorder may be applicable to these nonhereditary disease conditions, as they involve the same toxic metabolite. We provide an in-depth illustration of this cross-informing concept in two metabolic disorders, methylmalonic acidemia and hyperammonemia, where the pathological metabolites methylmalonic acid and ammonia are implicated in other disease contexts, such as aging, neurodegeneration, and cancer, and thus there are opportunities to apply mechanistic or therapeutic insights from one disease context towards the other. Additionally, we expand our scope to other metabolic disorders, such as homocystinuria and nonketotic hyperglycinemia, to propose how these concepts can be applied broadly across different inborn errors of metabolism and various nonhereditary disease conditions.

Role of Creatine Supplementation in Conditions Involving Mitochondrial Dysfunction: A Narrative Review

Creatine monohydrate (CrM) is one of the most widely used nutritional supplements among active individuals and athletes to improve high-intensity exercise performance and training adaptations. However, research suggests that CrM supplementation may also serve as a therapeutic tool in the management of some chronic and traumatic diseases. Creatine supplementation has been reported to improve high-energy phosphate availability as well as have antioxidative, neuroprotective, anti-lactatic, and calcium-homoeostatic effects. These characteristics may have a direct impact on mitochondrion's survival and health particularly during stressful conditions such as ischemia and injury. This narrative review discusses current scientific evidence for use or supplemental CrM as a therapeutic agent during conditions associated with mitochondrial dysfunction. Based on this analysis, it appears that CrM supplementation may have a role in improving cellular bioenergetics in several mitochondrial dysfunction-related diseases, ischemic conditions, and injury pathology and thereby could provide therapeutic benefit in the management of these conditions. However, larger clinical trials are needed to explore these potential therapeutic applications before definitive conclusions can be drawn.

Ionizing Radiation-Induced Brain Cell Aging and the Potential Underlying Molecular Mechanisms

Population aging is occurring rapidly worldwide, challenging the global economy and healthcare services. Brain aging is a significant contributor to various age-related neurological and neuropsychological disorders, including Alzheimer's disease and Parkinson's disease. Several extrinsic factors, such as exposure to ionizing radiation, can accelerate senescence. Multiple human and animal studies have reported that exposure to ionizing radiation can have varied effects on organ aging and lead to the prolongation or shortening of life span depending on the radiation dose or dose rate. This paper reviews the effects of radiation on the aging of different types of brain cells, including neurons, microglia, astrocytes, and cerebral endothelial cells. Further, the relevant molecular mechanisms are discussed. Overall, this review highlights how radiation-induced senescence in different cell types may lead to brain aging, which could result in the development of various neurological and neuropsychological disorders. Therefore, treatment targeting radiation-induced oxidative stress and neuroinflammation may prevent radiation-induced brain aging and the neurological and neuropsychological disorders it may cause.