Methylmalonate Induces Inflammatory and Apoptotic Potential: A Link to Glial Activation and Neurological Dysfunction

Transcriptomics and metabolomics reveal the mechanism of cognitive impairment induced by long-term selenium deficiency in mice

As the aging population increases, cognitive impairment is emerging as a growing health issue worldwide. Low selenium status has been reported to correlate with cognitive decline in older adults. Nonetheless, the impact of prolonged selenium deficiency on cognitive function in adult mice and the underlying mechanisms remain poorly understood. In this research, male C57BL/6 J mice were given either a normal diet (0.2 mg/kg Se) or a selenium-deficient diet (0.02 mg/kg Se) for 24 weeks to evaluate the impact of long-term selenium insufficiency on their cognitive abilities. We performed hippocampus transcriptome sequencing, real-time PCR, Golgi-Cox staining, transmission electron microscopy, western blotting, and untargeted brain metabolomics to uncover the underlying regulatory mechanism. We found that chronic selenium deficiency impaired the capabilities of object recognition, spatial memory, and self-caring in mice, and disrupted the expression of key genes related to cognitive behavior, dendrite morphogenesis, and synaptic plasticity. Additionally, prolonged selenium deficiency compromised neurite integrity, decreased dendritic spine density, impaired synaptic ultrastructure, and reduced synaptic protein expression. Brain metabolomics revealed that differential metabolites (methylmalonic acid, N-acetyl-1-aspartylglutamic acid, and S-adenosylmethionine) may be involved in the process of cognitive impairment. These findings suggest that perturbation in cognition-related transcriptome profiles, lesions in neurites and synapses, and remodeling of the brain metabolic pattern are involved in the cognitive impairment induced by long-term selenium deficiency. Our study offers a new perspective on the pathogenesis of cognitive impairment, highlighting the critical role of selenium supplementation in maintaining healthy cognitive function.

Hypertension may lead to cognitive dysfunction in older adults via methylmalonic acid: evidence from NHANES 2011-2014 population

BACKGROUND

An enriched understanding is necessary concerning the association between hypertension and cognitive impairment in older adults, particularly regarding the potential underlying mechanisms at a biological level. This study aimed to explore the mediating role of methylmalonic acid (MMA) in the hypertension-cognition link in the older population.

METHODS

A total of 2762 adults (age > = 60 years) from the National Health and Nutrition Examination Survey (NHANES) 2011-2014 participated. Cognitive function was assessed using a combination of the Animal Fluency Test (AFT), the Digit Symbol Substitution Test (DSST), and the Consortium to Establish a Registry for Alzheimer's Disease (CERAD) Word List Learning Test. Self-reported hypertension diagnosis, antihypertensive medications use, and blood pressure examinations were used to identify hypertension. Serum MMA (sMMA) levels were collected. Weighted multiple linear regressions and mediation analysis were applied. A subgroup analysis by sex and age was performed.

RESULTS

After adjusting for potential confounding factors, we observed a significant mediating effect of the sMMA level in the hypertension-cognition link, accounting for 11.14% (95% CI 4.09%-14.00%, p < 0.001) of the relationship in older adults. The proportion mediated by the sMMA level in the relationship between hypertension and cognitive function was higher in males (15.23%, 95%CI 1.32%-27.00%, p < 0.001) than in females (6.61%, 95%CI 2.12%-10.00%, p < 0.001). This mediating effect of sMMA was observed only in individuals aged 68 years and older (11.31%, 95%CI 3.80%-16.00%, p < 0.001), with no significant mediation detected in those younger than 68 years.

CONCLUSION

Hypertension may lead to cognitive dysfunction in older adults through MMA. Apart from its role as a biomarker reflecting vitamin B12, MMA may act as an independent neurotoxin capable of inducing brain injury and cognitive impairment. Addressing MMA accumulation, such as through Vitamin B12 supplementation, may have a potential to mitigate hypertension-induced cognitive decline in older adults. Special attention could be paid to hypertensive males with an advanced age (> = 68) to address MMA-related cognitive decline.

Exploration of potential biomarkers for prurigo nodularis based on plasma-metabolome analysis

Prurigo nodularis (PN) is a chronic and debilitating skin disease with severe itching that negatively impacts patients' quality of life and mental state. However, the treatment options for PN remain limited. Global metabolomics analysis can offer effective information on energy metabolism, pathogenesis and potential diagnostic biomarkers. No study on metabolomic analysis of PN has been reported. To further understand the mechanisms of PN and analyse the plasma metabolite profiles in patients with PN. Targeted-metabolome analysis of 306 metabolites in plasma from 18 patients with PN and 19 healthy controls was performed using Liquid Chromatography-tandem Mass Spectrometer analysis. We identified 31 differential metabolites. Most acylcarnitines, long-chain fatty acids, alpha-aminobutyric acid, hydroxybutyric acid and lactic acid among these metabolites were up-regulated in patients with PN; in contrast, glucaric acid, suberic acid, bile acid derivatives and most amino acids were down-regulated. Positive correlations exist between glucaric acid and itching severity and acylcarnitines and insomnia. Suberic acid and the Investigator's Global Assessment (IGA) scores correlate negatively. Metabolite variation reflects the dysregulation of energy metabolism and chronic systematic inflammation in PN. Several metabolites, such as glucaric acid, suberic acid and acylcarnitines, merit further study as potential biomarkers of disease severity in PN.

From Environment to Gene Expression: Epigenetic Methylations and One-Carbon Metabolism in Amyotrophic Lateral Sclerosis

The etiology of the neurodegenerative disease amyotrophic lateral sclerosis (ALS) is complex and considered multifactorial. The majority of ALS cases are sporadic, but familial cases also exist. Estimates of heritability range from 8% to 61%, indicating that additional factors beyond genetics likely contribute to ALS. Numerous environmental factors are considered, which may add up and synergize throughout an individual's lifetime building its unique exposome. One level of integration between genetic and environmental factors is epigenetics, which results in alterations in gene expression without modification of the genome sequence. Methylation reactions, targeting DNA or histones, represent a large proportion of epigenetic regulations and strongly depend on the availability of methyl donors provided by the ubiquitous one-carbon (1C) metabolism. Thus, understanding the interplay between exposome, 1C metabolism, and epigenetic modifications will likely contribute to elucidating the mechanisms underlying altered gene expression related to ALS and to developing targeted therapeutic interventions. Here, we review evidence for 1C metabolism alterations and epigenetic methylation dysregulations in ALS, with a focus on the impairments reported in neural tissues, and discuss these environmentally driven mechanisms as the consequences of cumulative exposome or late environmental hits, but also as the possible result of early developmental defects.

Methylmalonic acid in aging and disease

Metabolic byproducts have conventionally been disregarded as waste products without functions. In this opinion article, we bring to light the multifaceted role of methylmalonic acid (MMA), a byproduct of the propionate metabolism pathway mostly commonly known as a clinical biomarker of vitamin B12 deficiency. MMA is normally present at low levels in the body, but increased levels can come from different sources, such as vitamin B12 deficiency, genetic mutations in enzymes related to the propionate pathway, the gut microbiota, and aggressive cancers. Here, we describe the diverse metabolic and signaling functions of MMA and discuss the consequences of increased MMA levels, such as during the aging process, for several age-related human pathologies.

Clinical and electroencephalogram characteristics of methylmalonic acidemia with MMACHC and MUT gene mutations

OBJECTIVE

This study investigated the clinical, imaging, and electroencephalogram (EEG) characteristics of methylmalonic acidemia (MMA) with nervous system damage as the primary manifestation.

METHODS

From January 2017 to November 2022, patients with nervous system injury as the main clinical manifestation, diagnosed with methylmalonic acidemia by metabolic and genetic testing, were enrolled and analyzed. Their clinical, imaging, and electroencephalogram data were analyzed.

RESULTS

A total of 18 patients were enrolled, including 15 males and 3 females. The clinical symptoms were convulsions, poor feeding, growth retardation, disorder of consciousness, developmental delay, hypotonia, and blood system changes. There were 6 cases (33%) of hydrocephalus, 9 (50%) of extracerebral space widened, 5 (27%) of corpus callosum thinning, 3 (17%) of ventricular dilation, 3 (17%) of abnormal signals in the brain parenchyma (frontal lobe, basal ganglia region, and brain stem), and 3 (17%) of abnormal signals in the lateral paraventricular. In addition, there were 3 cases (17%) of cerebral white matter atrophy and 1 (5%) of cytotoxic edema in the basal ganglia and cerebral peduncle. EEG data displayed 2 cases (11%) of hypsarrhythmia, 3 (17%) of voltage reduction, 12(67%) of abnormal discharge, 13 (72%) of abnormal sleep physiological waves or abnormal sleep structure, 1 (5%) of immature (delayed) EEG development, and 8 (44%) of slow background. There were 2 cases (11%) of spasms, 1 (5%) of atonic seizures, and 1 (5%) of myoclonic seizures. There were 16 patients (89%) with hyperhomocysteinemia. During follow-up, 1 patient was lost to follow-up, and 1 died. In total, 87.5% (14/16) of the children had varying developmental delays. EEG was re-examined in 11 cases, of which 8 were normal, and 3 were abnormal. Treatments included intramuscular injections of vitamin B12, L-carnitine, betaine, folic acid, and oral antiepileptic therapy. Acute treatment included anti-infective, blood transfusion, fluid replacement, and correcting acidosis. The other treatments included low-protein diets and special formula milk powder.

CONCLUSION

Methylmalonic acidemia can affect the central nervous system, leading to structural changes or abnormal signals on brain MRI. Metabolic screening and genetic testing help clarify the diagnosis. EEG can reflect changes in brain waves during the acute phase.

Methylmalonic acidemia: Neurodevelopment and neuroimaging

Methylmalonic acidemia (MMA) is a genetic disease of abnormal organic acid metabolism, which is one of the important factors affecting the survival rate and quality of life of newborns or infants. Early detection and diagnosis are particularly important. The diagnosis of MMA mainly depends on clinical symptoms, newborn screening, biochemical detection, gene sequencing and neuroimaging diagnosis. The accumulation of methylmalonic acid and other metabolites in the body of patients causes brain tissue damage, which can manifest as various degrees of intellectual disability and severe neurological dysfunction. Neuroimaging examination has important clinical significance in the diagnosis and prognosis of MMA. This review mainly reviews the etiology, pathogenesis, and nervous system development, especially the neuroimaging features of MMA.

Methylmalonic acid levels in serum, exosomes, and urine and its association with cblC type methylmalonic acidemia-induced cognitive impairment

Background

The cblC type methylmalonic acidemia is the most common methylmalonic acidemia (MMA) in China. The biochemical characteristics of this disease include elevated methylmalonic acid and homocysteine (HCY), increased propionylcarnitine (C3), decreased free carnitine (C0). In this study, we aimed to clarify the roles of these biomarkers in cblC-MMA induced cognitive impairment and evaluate the capacity of methylmalonic acid in different fluids or exosomes to distinguish cblC-MMA induced cognitive impairment.

Methods

15 non-inherited hyperhomocysteinemia (HHcy) patients, 42 cblC-MMA patients and 57 age- and sex-matched healthy children were recruited in this study. The levels of HCY were detected by an automatic immune analyzer. The levels of acylcarnitines and methylmalonic acid were detected by tandem mass spectrometer.

Results

The main findings were all biomarkers as HCY, acylcarnitines and methylmalonic acid had capacities for distinguishing patients with cblC-MMA induced cognitive impairment from healthy children. The methylmalonic acid in different fluids or exosomes had good performances for distinguishing patients with cblC-MMA induced cognitive impairment from HHcy patients. The methylmalonic acid in serum exosomes and neuronal-derived exosomes were able to distinguishing cblC-MMA patients with cognitive impairment from patients without cognitive impairment. The methylmalonic acid in neuronal-derived exosomes might be helpful to evaluate the severity of cblC-MMA induced cognitive impairment.

Discussion

Methylmalonic acid levels in serum exosomes, especially in serum neuronal-derived exosomes, serve as potential biomarkers for distinguishing cblC-MMA induced cognitive impairment.

Methylmalonic acid induces inflammatory response and redox homeostasis disruption in C6 astroglial cells: potential glioprotective roles of melatonin and resveratrol

Methylmalonic acidemia is a neurometabolic disorder biochemically characterized by the accumulation of methylmalonic acid (MMA) in different tissues, including the central nervous system (CNS). In this sense, it has been shown that high levels of this organic acid have a key role in the progressive neurological deterioration in patients. Astroglial cells actively participate in a wide range of CNS functions, such as antioxidant defenses and inflammatory response. Considering the role of these cells to maintain brain homeostasis, in the present study, we investigated the effects of MMA on glial parameters, focusing on redox homeostasis and inflammatory process, as well as putative mediators of these events in C6 astroglial cells. MMA decreased cell viability, glutathione levels, and antioxidant enzyme activities, increased inflammatory response, and changed the expression of nuclear factor erythroid 2-related factor 2 (Nrf2), nuclear factor kappa B (NFκB), peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), inducible nitric oxide synthase (iNOS), cyclooxygenase 2 (COX-2), and adenosine receptors, suggesting that these transcriptional factors and proteins may underlie the glial responses induced by MMA. Moreover, we also demonstrated the protective roles of melatonin and resveratrol against MMA-induced inflammation and decrease in glutathione levels. In summary, our findings support the hypothesis that astroglial changes are associated with pathogenesis of methylmalonic acidemia. In addition, we showed that these cells might be potential targets for preventive/therapeutic strategies by using molecules, such as melatonin and resveratrol, which mediated glioprotection in this inborn error of metabolism.

Urine Organic Acids as Metabolic Indicators for Global Developmental Delay/Intellectual Disability in Chinese Children

Objective: The purpose of this study was to search for differential metabolites in urine organic acids, and to characterize metabolic features that can be used to identify metabolites for exploration of global developmental delay (GDD)/intellectual disability (ID) etiology and pathogenesis. Methods: We screened positive test results that could explain GDD/ID from 1,253 cases, and the major differential metabolites in 132 urine organic acids from the 1,230 cases with negative results (863 GDD cases, 367 ID cases), and 100 typically developing children (TD). Non-supervisory principal component analysis and orthogonal partial least squares discriminant analysis were used to develop models to distinguish GDD/ID from TD children, and to detect major differential metabolites. Results: We get 23 positive results that could identify the cause of GDD/ID from 1253 cases diagnosed with GDD/ID. Among 1,230 negative results, we get the differential metabolites of the GDD group and the ID group had the same trend compared with the TD group. Twenty four differential metabolites were obtained from the GDD group, and 25 from the ID group (VIP > 1.0, p < 0.01). These differential metabolites were mainly related to the following pathways: the synthesis and degradation of ketone bodies, citrate cycle, alanine, aspartate and glutamate metabolism, pyrimidine metabolism, butanoate metabolism, pyruvate metabolism, fatty acid biosynthesis, valine, leucine and isoleucine degradation. Conclusion: The use of metabolomics research methods to detect urine organic acids of children with GDD/ID can discover differential metabolites, which might be valuable for future research on the etiology, pathogenesis, prognosis and possible interventions of GDD/ID. The significantly altered differential metabolites indicators could therefore be potential diagnostic biomarkers for GDD/ID.

Development and Application of Activity-based Fluorescent Probes for High-Throughput Screening

High-throughput screening facilitates the rapid identification of novel hit compounds; however, it remains challenging to design effective high-throughput assays, partially due to the difficulty of achieving sensitivity in the assay techniques. Among the various analytical methods that are used, fluorescence-based assays dominate owing to their high sensitivity and ease of operation. Recent advances in activity-based sensing/imaging have further expanded the availability of fluorescent probes as monitors for high-throughput screening of result outputs. In this study, we have reviewed various activity-based fluorescent probes used in high-throughput screening assays, emphasizing their structure-related working mechanisms. Moreover, we have explored the possibility of the development of additional and better probes to boost hit identification and drug development against various targets.

Determination of Cytokines and Oxidative Stress Biomarkers in Cognitive Impairment Induced by Methylmalonic Acidemia

OBJECTIVE

Methylmalonic acidemia (MMA) is the most common organic acidemia in children. Many patients with MMA suffered from cognitive impairments. The aim of this study was to identify the significance of cytokines and oxidative stress biomarkers in MMA-induced cognitive impairment.

METHODS

We enrolled 64 children with combined MMA and homocystinuria and 64 age- and sex-matched healthy volunteers. Participants were subsequently classified as with or without cognitive impairments using a uniform neuropsychological assessment test. Serum samples were collected. The serum levels of cytokines and oxidative stress biomarkers were measured using the ELISA or chemical methods.

RESULTS

Compared to control group, the serum levels of tumor necrosis factor (TNF)-α, interleukin (IL)-6, malondialdehyde (MDA), and nitric oxide (NO) in the MMA patients increased markedly (p < 0.05); glutathione (GSH) and superoxide dismutase (SOD) decreased obviously (p < 0.01). The levels of IL-6, TNF-α, NO, and MDA in the serum were negatively associated with DQ or IQ scores. The levels of GSH and SOD in the serum were positively correlated with DQ or IQ scores. After receiver operating characteristic curve analysis, NO was the most useful individual marker for distinguishing the cognitive dysfunction, corresponding to the area under ROC curve (AUC) of 0.82 (95% CI, 0.74-0.91), sensitivity of 76.60%, and specificity of 80.25%. GSH and MDA were also useful for diagnosis of MMA-induced cognitive dysfunction, corresponding to the AUC of 0.80 (95% CI, 0.70-0.89), and 0.73 (95% CI, 0.63-0.82), respectively. The sensitivity and specificity of GSH were 72.34 and 80.25%, respectively. The sensitivity and specificity of MDA were 85.11 and 51.85%, respectively.

CONCLUSIONS

The high-concentration methylmalonic acid in the blood induced immune cells to release pro-inflammatory cytokines such as TNF-α and IL-6. These cytokines and high-concentration methylmalonic acid stimulated the immune cells to produce reactive oxygen species (ROS) and reactive nitrogen species (RNS). The serum methylmalonic acid, cytokines, ROS, and RNS were across the blood-brain barrier and induced cognitive impairment. The small molecule substances such as serum NO, MDA, and GSH participated in the process of neuroinflammation and oxidative stress injury induced by MMA and could be useful for distinguishing the cognitive impairment.

Sustained glial reactivity induced by glutaric acid may be the trigger to learning delay in early and late phases of development: Involvement of p75NTR receptor and protection by N-acetylcysteine

Degeneration of striatal neurons and cortical atrophy are pathological characteristics of glutaric acidemia type I (GA-I), a disease characterized by accumulation of glutaric acid (GA). The mechanisms that lead to neuronal loss and cognitive impairment are still unclear. The purpose of this study was to verify if acute exposure to GA during the neonatal period is sufficient to trigger apoptotic processes and lead to learning delay in early and late period. Besides, whether N-acetylcysteine (NAC) would protect against impairment induced by GA. Pups mice received a dose of GA (2.5 μmol/ g) or saline, 12 hs after birth, and were treated with NAC (250 mg/kg) or saline, up to 21th day of life. Although GA exhibited deficits in the procedural and working memories in 21 and 40-day-old mice, NAC protected against cognitive impairment. In striatum and cortex, NAC prevented glial cells activation (GFAP and Iba-1), decreased NGF, Bcl-2 and NeuN, the increase of lipid peroxidation and PARP induced by GA in both ages. NAC protected against increased p75NTR induced by GA, but not in cortex of 21-day-old mice. Thus, we showed that the integrity of striatal and cortical pathways has an important role for learning and suggested that sustained glial reactivity in neonatal period can be an initial trigger for delay of cognitive development. Furthermore, NAC protected against cognitive impairment induced by GA. This work shows that early identification of the alterations induced by GA is important to avoid future clinical complications and suggest that NAC could be an adjuvant treatment for this acidemia.

Disruption of mitochondrial functions and oxidative stress contribute to neurologic dysfunction in organic acidurias

Organic acidurias (OADs) are inherited disorders of amino acid metabolism biochemically characterized by accumulation of short-chain carboxylic acids in tissues and biological fluids of the affected patients and clinically by predominant neurological manifestations. Some of these disorders are amenable to treatment, which significantly decreases mortality and morbidity, but it is still ineffective to prevent long-term neurologic and systemic complications. Although pathogenesis of OADs is still poorly established, recent human and animal data, such as lactic acidosis, mitochondrial morphological alterations, decreased activities of respiratory chain complexes and altered parameters of oxidative stress, found in tissues from patients and from genetic mice models with these diseases indicate that disruption of critical mitochondrial functions and oxidative stress play an important role in their pathophysiology. Furthermore, organic acids that accumulate in the most prevalent OADs were shown to compromise bioenergetics, by decreasing ATP synthesis, mitochondrial membrane potential, reducing equivalent content and calcium retention capacity, besides inducing mitochondrial swelling, reactive oxygen and nitrogen species generation and apoptosis. It is therefore presumed that secondary mitochondrial dysfunction and oxidative stress caused by major metabolites accumulating in OADs contribute to tissue damage in these pathologies.

Associations of Circulating Methylmalonic Acid and Vitamin B-12 Biomarkers Are Modified by Vegan Dietary Pattern in Adult and Elderly Participants of the Adventist Health Study 2 Calibration Study

BACKGROUND

Elevated plasma methylmalonic acid (MMA) is a functional biomarker of vitamin B-12 status but limited information is available on its prevalence in US vegetarians.

OBJECTIVES

The study examines the prevalence of plasma MMA ≥0.27 µmol/L in those consuming vegetarian diets, its associations with vitamin B-12 intake and biomarkers, and the modifying effect of vegetarian patterns on these associations.

METHODS

In this cross-sectional study (n = 785), concentrations of MMA, vitamin B-12, holotranscobalamin (holoTC), and homocysteine (Hcy) were determined in participants of the calibration substudy of the Adventist Health Study 2 (AHS-2). Vitamin B-12 intake from food, fortified food, and supplements was assessed by six 24-h recalls. Regression models were used to estimate ORs of having high MMA as related to vitamin B-12 status biomarkers, vitamin B-12 intake, and dietary pattern.

RESULTS

The prevalence of low vitamin B-12 status defined by serum vitamin B-12 <148 pmol/L, holoTC <35 pmol/L, MMA ≥0.27 and ≥0.37 μmol/L, or Hcy ≥15 μmol/L, and the OR of having high MMA did not differ by dietary pattern, possibly due to intake from fortified food and supplements. Total daily vitamin B-12 intake in the second tertile range of 4.4-14.5 μg/d reduced the likelihood of elevated MMA by 69%; and a doubling of vitamin B-12 intake was associated with a 4.3% decrease in plasma MMA. The association between log plasma MMA and biomarkers was modified by diet, with the vegan pattern showing an ∼3-fold stronger association with log serum vitamin B-12 and Hcy than did the nonvegetarian pattern.

CONCLUSIONS

The prevalence of vitamin B-12 intake <2.0 μg/d was 15.2% in vegans, 10.6% in lacto-ovo-vegetarians, and 6.5% in nonvegetarians. Given the irreversible neurological consequences of vitamin B-12 inadequacy, the importance of regular supplemental vitamin B-12 intake in adult and elderly individuals is stressed.

Kaolin-induced hydrocephalus causes acetylcholinesterase activity dysfunction following hypothalamic damage in infant rats

In hydrocephalus, the progressive accumulation of cerebrospinal fluid (CSF) causes dilatation of the lateral ventricles affecting the third ventricle and diencephalic structures such as the hypothalamus. These structures play a key role in the regulation of several neurovegetative functions by the production of the hormones. Since endocrine disturbances are commonly observed in hydrocephalic children, we investigated the impact of progressive ventricular dilation on the hypothalamus of infant rats submitted to kaolin-induced hydrocephalus. Seven-day-old infant rats were submitted to hydrocephalus induction by kaolin 20% injection method. After 14 days, the animals were decapitated and brain was collected to analyze mitochondrial function, neuronal activity by acetylcholinesterase (AChE) enzyme, oxidative damage, glial activation, and, neurotransmission-related proteins and anti-apoptotic processes in the hypothalamus. The hydrocephalic animals showed reduction in respiratory rates in the States of phosphorylation (P < 0.01) and non-phosphorylation (P < 0.05); increase in AChE activity in both the cytosol (P < 0.05) and the membrane (P < 0.01); decrease in synaptophysin (P < 0.05) and Bcl-2 (P < 0.05) contents and; increase in protein carbonyl (P < 0.01), GFAP (P < 0.01) and Iba-1 (P < 0.05) levels. The results demonstrate that ventricular dilation causes hypothalamic damage characterized by cholinergic dysfunction and suggests further investigation of the synthesis and secretion of hormones to generate new approaches and to assist in the treatment of hydrocephalic patients with hormonal alterations.

Involvement of the Cholinergic Parameters and Glial Cells in Learning Delay Induced by Glutaric Acid: Protection by N-Acetylcysteine

Dysfunction of basal ganglia neurons is a characteristic of glutaric acidemia type I (GA-I), an autosomal recessive inherited neurometabolic disease characterized by deficiency of glutaryl-CoA dehydrogenase (GCDH) and accumulation of glutaric acid (GA). The affected patients present clinical manifestations such as motor dysfunction and memory impairment followed by extensive striatal neurodegeneration. Knowing that there is relevant striatal dysfunction in GA-I, the purpose of the present study was to verify the performance of young rats chronically injected with GA in working and procedural memory test, and whether N-acetylcysteine (NAC) would protect against impairment induced by GA. Rat pups were injected with GA (5 μmol g body weight^-1, subcutaneously; twice per day; from the 5th to the 28th day of life) and were supplemented with NAC (150 mg/kg/day; intragastric gavage; for the same period). We found that GA injection caused delay procedural learning; increase of cytokine concentration, oxidative markers, and caspase levels; decrease of antioxidant defenses; and alteration of acetylcholinesterase (AChE) activity. Interestingly, we found an increase in glial cell immunoreactivity and decrease in the immunoreactivity of nuclear factor-erythroid 2-related factor 2 (Nrf2), nicotinic acetylcholine receptor subunit alpha 7 (α7nAChR), and neuronal nuclei (NeuN) in the striatum. Indeed, NAC administration improved the cognitive performance, ROS production, neuroinflammation, and caspase activation induced by GA. NAC did not prevent neuronal death, however protected against alterations induced by GA on Iba-1 and GFAP immunoreactivities and AChE activity. Then, this study suggests possible therapeutic strategies that could help in GA-I treatment and the importance of the striatum in the learning tasks.

Ammonia role in glial dysfunction in methylmalonic acidemia

Hyperammonemia is a common finding in patients with methylmalonic acidemia. However, its contribution to methylmalonate (MMA)-induced neurotoxicity is poorly understood. The aim of this study was evaluate whether an acute metabolic damage to brain during the neonatal period may disrupt cerebral development, leading to neurodevelopmental disorders, as memory deficit. Mice received a single intracerebroventricular dose of MMA and/or NH₄Cl, administered 12 hs after birth. The maze tests showed that MMA and NH₄Cl injected animals (21 and 40 days old) exhibited deficit in the working memory test, but not in the reference memory test. Furthermore, MMA and NH₄Cl increased the levels of 2',7'-dichlorofluorescein-diacetate (DCF), TNF-α, IL-1β in the cortex, hippocampus and striatum of mice. MMA and NH₄Cl also increased glial proliferation in all structures. Since the treatment of MMA and ammonia increased cytokines levels, we suggested that it might be a consequence of the glial activation induced by the acid and ammonia, leading to delay in the developing brain and contributing to behavioral alterations. However, this hypothesis is speculative in nature and more studies are needed to clarify this possibility.