Arginine metabolism and the synthesis of nitric oxide in the nervous system

Pathophysiology of Arginases in Cancer and Efforts in Their Pharmacological Inhibition

Arginases are key enzymes that hydrolyze L-arginine to urea and L-ornithine in the urea cycle. The two arginase isoforms, arginase 1 (ARG1) and arginase 2 (ARG2), regulate the proliferation of cancer cells, migration, and apoptosis; affect immunosuppression; and promote the synthesis of polyamines, leading to the development of cancer. Arginases also compete with nitric oxide synthase (NOS) for L-arginine, and their participation has also been confirmed in cardiovascular diseases, stroke, and inflammation. Due to the fact that arginases play a crucial role in the development of various types of diseases, finding an appropriate candidate to inhibit the activity of these enzymes would be beneficial for the therapy of many human diseases. In this review, based on numerous experimental, preclinical, and clinical studies, we provide a comprehensive overview of the biological and physiological functions of ARG1 and ARG2, their molecular mechanisms of action, and affected metabolic pathways. We summarize the recent clinical trials' advances in targeting arginases and describe potential future drugs.

Exploring the clinical connections between epilepsy and diabetes mellitus: Promising therapeutic strategies utilizing agmatine and metformin

PURPOSE

Diabetes mellitus (DM) and epilepsy and the psychological and socio-economic implications that are associated with their treatments can be quite perplexing. Metformin is an antihyperglycemic medication that is used to treat type 2 DM. In addition, metformin elicits protective actions against multiple diseases, including neurodegeneration and epilepsy. Recent studies indicate that metformin alters the resident gut microbiota in favor of species producing agmatine, an arginine metabolite which, in addition to beneficially altering metabolic pathways, is a potent neuroprotectant and neuromodulant.

METHODS

We first examine the literature for epidemiological and clinical evidences linking DM and epilepsy. Next, basing our analyses on published literature, we propose the possible complementarity of agmatine and metformin in the treatment of DM and epilepsy.

RESULTS

Our analyses of the clinical data suggest a significant association between pathogeneses of epilepsy and DM. Further, both agmatine and metformin appear to be multimodal therapeutic agents and have robust antiepileptogenic and antidiabetic properties. Data from animal and clinical studies largely support the use of metformin/agmatine as a double-edged pharmacotherapeutic agent against DM and epilepsy, particularly in their concurrent pathological occurrences.

CONCLUSION

The present review explores the evidences and available data on possible uses of metformin/agmatine as pertinent antidiabetic and antiepileptic agents. Our hope is that this will stimulate further research on the therapeutic actions of these multimodal agents, particularly for subject-specific clinical outcomes.

Agmatine as a novel intervention for Alzheimer's disease: Pathological insights and cognitive benefits

Alzheimer's disease (AD) is a devastating neurodegenerative disorder characterized by progressive cognitive decline and a significant societal burden. Despite extensive research and efforts of the multidisciplinary scientific community, to date, there is no cure for this debilitating disease. Moreover, the existing pharmacotherapy for AD only provides symptomatic support and does not modify the course of the illness or halt the disease progression. This is a significant limitation as the underlying pathology of the disease continues to progress leading to the deterioration of cognitive functions over time. In this milieu, there is a growing need for the development of new and more efficacious treatments for AD. Agmatine, a naturally occurring molecule derived from L-arginine, has emerged as a potential therapeutic agent for AD. Besides this, agmatine has been shown to modulate amyloid beta (Aβ) production, aggregation, and clearance, key processes implicated in AD pathogenesis. It also exerts neuroprotective effects, modulates neurotransmitter systems, enhances synaptic plasticity, and stimulates neurogenesis. Furthermore, preclinical and clinical studies have provided evidence supporting the cognition-enhancing effects of agmatine in AD. Therefore, this review article explores the promising role of agmatine in AD pathology and cognitive function. However, several limitations and challenges exist, including the need for large-scale clinical trials, optimal dosing, and treatment duration. Future research should focus on mechanistic investigations, biomarker studies, and personalized medicine approaches to fully understand and optimize the therapeutic potential of agmatine. Augmenting the use of agmatine may offer a novel approach to address the unmet medical need in AD and provide cognitive enhancement and disease modification for individuals affected by this disease.

Further proof on the role of accumbal nNOS in cocaine-seeking behavior in rats

BACKGROUND

Cocaine use disorder (CUD) remains a severe health problem with no effective pharmacological therapy. One of the potential pharmacological strategies for CUD pharmacotherapy includes manipulations of the brain glutamatergic (Glu) system which is particularly involved in drug withdrawal and relapse. Previous research indicated a pivotal role of ionotropic N-methyl-D-aspartate (NMDA) receptors or metabotropic receptors' type 5 (mGlu5) receptors in controlling the reinstatement of cocaine. Stimulation of the above molecules results in the activation of the downstream signaling targets such as neuronal nitric oxide synthase (nNOS) and the release of nitric oxide.

METHODS

In this paper, we investigated the molecular changes in nNOS in the prefrontal cortex and nucleus accumbens following 3 and 10 days of cocaine abstinence as well as the effectiveness of nNOS blockade with the selective enzyme inhibitor N-ω-propyl-L-arginine hydrochloride (L-NPA) on cocaine seeking in male rats. The effect of L-NPA on locomotor activity in drug-naïve animals was investigated.

RESULTS

Ten-day (but not 3-day) cocaine abstinence from cocaine self-administration increased nNOS gene and protein expression in the nucleus accumbens, but not in the prefrontal cortex. L-NPA (0.5-5 mg/kg) administered peripherally did not change locomotor activity but attenuated the reinstatement induced with cocaine priming or the drug-associated conditioned cue.

CONCLUSIONS

Our findings support accumbal nNOS as an important molecular player for cocaine seeking while its inhibitors could be considered as anti-cocaine pharmacological tools in male rats.

Alterations in glutamate, arginine, and energy metabolism characterize cerebrospinal fluid and plasma metabolome of persons with HIV-associated dementia

OBJECTIVES

HIV-associated dementia (HAD) is the most severe clinical expression of HIV-mediated neuropathology, and the processes underlying its development remain poorly understood. We aimed to exploit high-dimensional metabolic profiling to gain insights into the pathological mechanisms associated to HAD.

DESIGN

In this cross-sectional study, we utilized metabolomics to profile matched cerebrospinal fluid (CSF) and plasma samples of HAD individuals ( n  = 20) compared with neurologically asymptomatic people with HIV (ASYM, n  = 20) and healthy controls (NEG, n  = 20).

METHODS

Identification of plasma and CSF metabolites was performed by liquid-chromatography or gas-chromatography following a validated experimental pipeline. The resulting metabolic profiles were analyzed by machine-learning algorithms, and altered pathways were identified by comparison with KEGG pathway database.

RESULTS

In CSF, HAD patients displayed an imbalance in glutamine/glutamate ratio, decreased levels of isocitrate and arginine, and increased oxidative stress when compared with ASYM or NEG. These changes were confirmed in matched plasma samples, which in addition revealed an accumulation of eicosanoids and unsaturated fatty acids in HAD individuals. Pathway analysis in both biological fluids suggested that alterations in several metabolic processes, including protein biosynthesis, glutamate and arginine metabolism, and energy metabolism, in association to a perturbed eicosanoid metabolism in plasma, may represent the metabolic signature associated to HAD.

CONCLUSION

These findings show that HAD may be associated with metabolic modifications in CSF and plasma. These preliminary data may be useful to identify novel metabolic biomarkers and therapeutic targets in HIV-associated neurological impairment.

Metabolic deregulation associated with aging modulates protein aggregation in the yeast model of Huntington's disease

Huntington's disease is associated with increased CAG repeat resulting in an expanded polyglutamine tract in the protein Huntingtin (HTT) leading to its aggregation resulting in neurodegeneration. Previous studies have shown that N-terminal HTT with 46Q aggregated in the stationary phase but not the logarithmic phase in the yeast model of HD. We carried out a metabolomic analysis of logarithmic and stationary phase yeast model of HD expressing different polyQ lengths attached to N-terminal HTT tagged with enhanced green fluorescent protein (EGFP). The results show significant changes in the metabolic profile and deregulated pathways in stationary phase cells compared to logarithmic phase cells. Comparison of metabolic pathways obtained from logarithmic phase 46Q versus 25Q with those obtained for presymptomatic HD patients from our previous study and drosophila model of HD showed considerable overlap. The arginine biosynthesis pathway emerged as one of the key pathways that is common in stationary phase yeast compared to logarithmic phase and HD patients. Treatment of yeast with arginine led to a significant decrease, while transfer to arginine drop-out media led to a significant increase in the size of protein aggregates in both logarithmic and stationary phase yeast model of HD. Knockout of arginine transporters in the endoplasmic reticulum and vacuole led to a significant decrease in mutant HTT aggregation. Overall our results highlight arginine as a critical metabolite that modulates the aggregation of mutant HTT and disease progression in HD.Communicated by Ramaswamy H. Sarma.

Feature-Based Molecular Networking Facilitates the Comprehensive Identification of Differential Metabolites in Diabetic Cognitive Dysfunction Rats

Cognitive dysfunction is a frequent complication of type 2 diabetes mellitus (T2DM), usually accompanied by metabolic disorders. However, the metabolic changes in diabetic cognitive dysfunction (DCD) patients, especially compared to T2DM groups, are not fully understood. Due to the subtle differences in metabolic alterations between DCD groups and T2DM groups, the comprehensive detection of the untargeted metabolic profiles of hippocampus and urine samples of rats was conducted by LC-MS, considering the different ionization modes and polarities of the examined compounds, and feature-based molecular networking (FBMN) was performed to help identify differential metabolites from a comprehensive perspective in this study. In addition, an association analysis of the differential metabolites in hippocampus and urine was conducted by the O2PLS model. Finally, a total of 71 hippocampal tissue differential metabolites and 179 urine differential metabolites were identified. The pathway enrichment results showed that glutamine and glutamate metabolism, alanine, aspartate, and glutamate metabolism, glycerol phospholipid metabolism, TCA cycle, and arginine biosynthesis in the hippocampus of DCD animals were changed. Seven metabolites (AUC > 0.9) in urine appeared as key differential metabolites that might reflect metabolic changes in the target tissue of DCD rats. This study showed that FBMN facilitated the comprehensive identification of differential metabolites in DCD rats. The differential metabolites may suggest an underlying DCD and be considered as potential biomarkers for DCD. Large samples and clinical experiments are needed for the subsequent elucidation of the possible mechanisms leading to these alterations and the verification of potential biomarkers.

Scutellarin Alleviates Ischemic Brain Injury in the Acute Phase by Affecting the Activity of Neurotransmitters in Neurons

Cerebral ischemic stroke is a common neuron loss disease that is caused by the interruption of the blood supply to the brain. In order to enhance the CIS outcome, both identifying the treatment target of ischemic brain damage in the acute phase and developing effective therapies are urgently needed. Scutellarin had been found to be beneficial to ischemic injuries and has been shown to have potent effects in clinical application on both stroke and myocardial infarction. However, whether scutellarin improves ischemic brain damage in the acute phase remains unknown. In this study, the protective effects of scutellarin on ischemic brain damage in the acute phase (within 12 h) were illustrated. In middle cerebral artery occlusion and reperfusion (MCAO/R) modeling rats, the Z-Longa score was significantly down-regulated by 25% and 23.1%, and the brain infarct size was reduced by 26.95 ± 0.03% and 25.63 ± 0.02% when responding to high-dose and low-dose scutellarin treatments, respectively. H&E and TUNEL staining results indicated that the neuron loss of the ischemic region was improved under scutellarin treatment. In order to investigate the mechanism of scutellarin's effects on ischemic brain damage in the acute phase, changes in proteins and metabolites were analyzed. The suppression of scutellarin on the glutamate-inducing excitatory amino acid toxicity was strongly indicated in the study of both proteomics and metabolomics. A molecular docking experiment presented strong interactions between scutellarin and glutamate receptors, which score much higher than those of memantine. Further, by performing a parallel reaction monitoring-mass spectrometry (PRM-MS) study on both the cortex and hippocampus tissue of the ischemic region, we screened the scutellarin-regulating molecules that are involved in both the release and transportation of neurotransmitters. It was found that the aberrant levels of glutamate receptors, including EAAT2, GRIN1, GRIN2B, and GRM1, as well as of other glutamatergic pathway-involving proteins, including CAMKK2, PSD95, and nNOS, were significantly regulated in the ischemic cortex. In the hippocampus, EAAT2, GRIN1, nNOS, and CAM were significantly regulated. Taken together, scutellarin exerts potent effects on ischemic brain damage in the acute phase by regulating the activity of neurotransmitters and reducing the toxicity of excitatory amino acids in in neurons.

L-arginine homeostasis governs adult neural stem cell activation by modulating energy metabolism in vivo

Neurogenesis in the developing and adult brain is intimately linked to remodeling of cellular metabolism. However, it is still unclear how distinct metabolic programs and energy sources govern neural stem cell (NSC) behavior and subsequent neuronal differentiation. Here, we found that adult mice lacking the mitochondrial urea metabolism enzyme, Arginase-II (Arg-II), exhibited NSC overactivation, thereby leading to accelerated NSC pool depletion and decreased hippocampal neurogenesis over time. Mechanistically, Arg-II deficiency resulted in elevated L-arginine levels and induction of a metabolic shift from glycolysis to oxidative phosphorylation (OXPHOS) caused by impaired attachment of hexokinase-I to mitochondria. Notably, selective inhibition of OXPHOS ameliorated NSC overactivation and restored abnormal neurogenesis in Arg-II deficient mice. Therefore, Arg-II-mediated intracellular L-arginine homeostasis directly influences the metabolic fitness of neural stem cells that is essential to maintain neurogenesis with age.

Molecular insights into sex-specific metabolic alterations in Alzheimer's mouse brain using multi-omics approach

BACKGROUND

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that is characterized by altered cellular metabolism in the brain. Several of these alterations have been found to be exacerbated in females, known to be disproportionately affected by AD. We aimed to unravel metabolic alterations in AD at the metabolic pathway level and evaluate whether they are sex-specific through integrative metabolomic, lipidomic, and proteomic analysis of mouse brain tissue.

METHODS

We analyzed male and female triple-transgenic mouse whole brain tissue by untargeted mass spectrometry-based methods to obtain a molecular signature consisting of polar metabolite, complex lipid, and protein data. These data were analyzed using multi-omics factor analysis. Pathway-level alterations were identified through joint pathway enrichment analysis or by separately evaluating lipid ontology and known proteins related to lipid metabolism.

RESULTS

Our analysis revealed significant AD-associated and in part sex-specific alterations across the molecular signature. Sex-dependent alterations were identified in GABA synthesis, arginine biosynthesis, and in alanine, aspartate, and glutamate metabolism. AD-associated alterations involving lipids were also found in the fatty acid elongation pathway and lysophospholipid metabolism, with a significant sex-specific effect for the latter.

CONCLUSIONS

Through multi-omics analysis, we report AD-associated and sex-specific metabolic alterations in the AD brain involving lysophospholipid and amino acid metabolism. These findings contribute to the characterization of the AD phenotype at the molecular level while considering the effect of sex, an overlooked yet determinant metabolic variable.

L-Citrulline: A novel hypothermic amino acid promoting thermotolerance in heat-exposed chickens

With global warming becoming of increasing concern, poultry farms are experiencing a concomitant increase in heat stress. Chickens are very sensitive to high ambient temperature (HT), so the development of novel nutrients that will help deal with the challenge posed by heat stress is vital. We revealed that L-citrulline (L-Cit) can reduce body temperature in chickens. Orally administered L-Cit solution has been found to provide heat tolerance in chickens and to result in reduced food intake. Heat exposure and oral administration of L-Cit led to increased levels of plasma insulin, whereas heat stress led to a decline in plasma thyroxine. Dietary administration of L-Cit was also shown to be effective to reduce heat stress in broiler chickens. Moreover, L-Cit was found to be metabolized in the liver within 1 h of its administration, and in L-Cit-treated broiler chicks, the Cit-Arginine cycle and the Krebs cycle were found to be active. L-Cit has not yet been approved for inclusion in the poultry diet, so it is important to find alternative sources of L-Cit. Taken together, these findings suggest that L-Cit may serve as an important novel nutrient with the ability to produce heat tolerance in chickens under HT.

Fecal microbiota transplantation can improve cognition in patients with cognitive decline and Clostridioides difficile infection

After fecal microbiota transplantation (FMT) to treat Clostridioides difficile infection (CDI), cognitive improvement is noticeable, suggesting an essential association between the gut microbiome and neural function. Although the gut microbiome has been associated with cognitive function, it remains to be elucidated whether fecal microbiota transplantation can improve cognition in patients with cognitive decline. The study included 10 patients (age range, 63-90 years; female, 80%) with dementia and severe CDI who were receiving FMT. Also, 10 patients (age range, 62-91; female, 80%) with dementia and severe CDI who were not receiving FMT. They were evaluated using cognitive function tests (Mini-Mental State Examination [MMSE] and Clinical Dementia Rating scale Sum of Boxes [CDR-SB]) at 1 month before and after FMT or antibiotics treatment (control group). The patients' fecal samples were analyzed to compare the composition of their gut microbiota before and 3 weeks after FMT or antibiotics treatment. Ten patients receiving FMT showed significantly improvements in clinical symptoms and cognitive functions compared to control group. The MMSE and CDR-SB of FMT group were improved compare to antibiotics treatment (MMSE: 16.00, median, 13.00-18.00 [IQR] vs. 10.0, median, 9.8-15.3 [IQR]); CDR-SB: 5.50, median, 4.00-8.00 [IQR]) vs. 8.0, median, 7.9-12.5, [IQR]). FMT led to changes in the recipient's gut microbiota composition, with enrichment of Proteobacteria and Bacteroidetes. Alanine, aspartate, and glutamate metabolism pathways were also significantly different after FMT. This study revealed important interactions between the gut microbiome and cognitive function. Moreover, it suggested that FMT may effectively delay cognitive decline in patients with dementia.

Potential Utility of Natural Products against Oxidative Stress in Animal Models of Multiple Sclerosis

Multiple sclerosis (MS) is an autoimmune-mediated degenerative disease of the central nervous system (CNS) characterized by immune cell infiltration, demyelination and axonal injury. Oxidative stress-induced inflammatory response, especially the destructive effect of immune cell-derived free radicals on neurons and oligodendrocytes, is crucial in the onset and progression of MS. Therefore, targeting oxidative stress-related processes may be a promising preventive and therapeutic strategy for MS. Animal models, especially rodent models, can be used to explore the in vivo molecular mechanisms of MS considering their similarity to the pathological processes and clinical signs of MS in humans and the significant oxidative damage observed within their CNS. Consequently, these models have been used widely in pre-clinical studies of oxidative stress in MS. To date, many natural products have been shown to exert antioxidant effects to attenuate the CNS damage in animal models of MS. This review summarized several common rodent models of MS and their association with oxidative stress. In addition, this review provides a comprehensive and concise overview of previously reported natural antioxidant products in inhibiting the progression of MS.

First Metabolomic Signature of Blood-Brain Barrier Opening Induced by Microbubble-Assisted Ultrasound

Microbubble (MB)-assisted ultrasound (US) is a promising physical method to increase non-invasively, transiently, and precisely the permeability of the blood-brain barrier (BBB) to therapeutic molecules. Previous preclinical studies established the innocuity of this procedure using complementary analytical strategies including transcriptomics, histology, brain imaging, and behavioral tests. This cross-sectional study using rats aimed to investigate the metabolic processes following acoustically-mediated BBB opening in vivo using multimodal and multimatrices metabolomics approaches. After intravenous injection of MBs, the right striata were exposed to 1-MHz sinusoidal US waves at 0.6 MPa peak negative pressure with a burst length of 10 ms, for 30 s. Then, the striata, cerebrospinal fluid (CSF), blood serum, and urine were collected during sacrifice in three experimental groups at 3 h, 2 days, and 1 week after BBB opening (BBBO) and were compared to a control group where no US was applied. A well-established analytical workflow using nuclear magnetic resonance spectrometry and non-targeted and targeted high-performance liquid chromatography coupled to mass spectrometry were performed on biological tissues and fluids. In our experimental conditions, a reversible BBBO was observed in the striatum without physical damage or a change in rodent weight and behavior. Cerebral, peri-cerebral, and peripheral metabolomes displayed specific and sequential metabolic kinetics. The blood serum metabolome was more impacted in terms of the number of perturbated metabolisms than in the CSF, the striatum, and the urine. In addition, perturbations of arginine and arginine-related metabolisms were detected in all matrices after BBBO, suggesting activation of vasomotor processes and bioenergetic supply. The exploration of the tryptophan metabolism revealed a transient vascular inflammation and a perturbation of serotoninergic neurotransmission in the striatum. For the first time, we characterized the metabolic signature following the acoustically-mediated BBBO within the striatum and its surrounding biological compartments.

Altered Arginine/Nitric Oxide Pathway in Children Diagnosed Attention Deficit Hyperactivity Disorder, and the Effect of 10 Weeks Methylphenidate Treatment

Objective

In this study, we investigated the levels of arginine, nitric oxide (NO), asymmetric dimethylarginine (ADMA), and adrenomedullin that are presumed to play a role in attention deficit hyperactivity disorder (ADHD) etiology, and to compare the findings with healthy controls.

Methods

Thirty ADHD patients and thirty healthy control subjects aged 6−12 years were included in the study. Sociodemographic data form, Schedule for Affective Disorders and Schizophrenia for School Age Children-Present and Lifetime Version; Conners’ Parent/Teacher Rating Scale-Revised Long Form; Children’s Depression Inventory; and The State-Trait Anxiety Inventory for Children were applied to all cases. All participants included in the study were evaluated in terms of their serum arginine, NO, ADMA, and adrenomedullin levels. Subsequently, methylphenidate treatment was started in ADHD patients and blood parameters were tested again in the tenth week of treatment.

Results

At the start of the study, arginine and ADMA levels were significantly higher and NO and adrenomedullin levels were significantly lower in the ADHD group compared to the control group. Post-treatment arginine and ADMA levels were found to be significantly lower than in the pre-treatment period. There were no significant differences in NO and adrenomedullin levels before and after treatment. There was no correlation between scale scores and blood parameters.

Conclusion

These variations in the blood parameters of the ADHD group seem to be worth further investigation. Studies to be conducted with larger sample groups after longer-term treatment may provide new information about the alterations in neurobiological processes related to ADHD etiology and treatment.

Altered Brain Arginine Metabolism and Polyamine System in a P301S Tauopathy Mouse Model: A Time-Course Study

Altered arginine metabolism (including the polyamine system) has recently been implicated in the pathogenesis of tauopathies, characterised by hyperphosphorylated and aggregated microtubule-associated protein tau (MAPT) accumulation in the brain. The present study, for the first time, systematically determined the time-course of arginine metabolism changes in the MAPT P301S (PS19) mouse brain at 2, 4, 6, 8 and 12 months of age. The polyamines putrescine, spermidine and spermine are critically involved in microtubule assembly and stabilization. This study, therefore, further investigated how polyamine biosynthetic and catabolic enzymes changed in PS19 mice. There were general age-dependent increases of L-arginine, L-ornithine, putrescine and spermidine in the PS19 brain (particularly in the hippocampus and parahippocampal region). While this profile change clearly indicates a shift of arginine metabolism to favor polyamine production (a polyamine stress response), spermine levels were decreased or unchanged due to the upregulation of polyamine retro-conversion pathways. Our results further implicate altered arginine metabolism (particularly the polyamine system) in the pathogenesis of tauopathies. Given the role of the polyamines in microtubule assembly and stabilization, future research is required to understand the functional significance of the polyamine stress response and explore the preventive and/or therapeutic opportunities for tauopathies by targeting the polyamine system.

Arginase: An emerging and promising therapeutic target for cancer treatment

Arginase is a key hydrolase in the urea cycle that hydrolyses L-arginine to urea and L-ornithine. Increasing number of studies in recent years demonstrate that two mammalian arginase isoforms, arginase 1 (ARG1) and arginase 2 (ARG2), were aberrantly upregulated in various types of cancers, and played crucial roles in the regulation of tumor growth and metastasis through various mechanisms such as regulating L-arginine metabolism, influencing tumor immune microenvironment, etc. Thus, arginase receives increasing focus as an attractive target for cancer therapy. In this review, we provide a comprehensive overview of the physiological and biological roles of arginase in a variety of cancers, and shed light on the underlying mechanisms of arginase mediating cancer cells growth and development, as well as summarize the recent clinical research advances of targeting arginase for cancer therapy.

Nitric Oxide Synthase activity in major depressive episodes before and after antidepressant treatment: Results of a large case-control treatment study

BACKGROUND

Nitric oxide synthase (NOS) activity, an enzyme potentially involved in the major depressive episodes (MDE), could be indirectly measured by the L-Citrulline/L-Arginine ratio (L-Cit/L-Arg). The aim of this study was: (1) to compare the NOS activity of patients with a MDE to that of healthy controls (HC); (2) to assess its change after antidepressant treatment.

METHODS

A total of 460 patients with a current MDE in a context of major depressive disorder (MDD) were compared to 895 HC for NOS activity (L-Cit/L-Arg plasma ratio). L-Arg and L-Cit plasma levels were measured using a MS-based liquid chromatography method. Depressed patients were assessed at baseline, and after 3 and 6 months of antidepressant treatment for depression severity and clinical response.

RESULTS

Depressed patients had a lower NOS activity than HC at baseline [0.31 ± 0.09 v. 0.38 ± 0.12; 95% confidence interval (CI) -0.084 to -0.062, p < 0.0001]. Lower NOS activity at baseline predicted a higher response rate [odds ratio (OR) = 29.20; 95% CI 1.58-536.37; p = 0.023]. NOS activity in depressed patients increased significantly up to 0.34 ± 0.08 after antidepressant treatment (Est = 0.0034; 95% CI 0.0002-0.0067; p = 0.03).

CONCLUSIONS

Depressed patients have a decreased NOS activity that improves after antidepressant treatment and predicts drug response. NOS activity may be a promising biomarker for MDE in a context of MDD.

Differences of Transport Activity of Arginine and Regulation on Neuronal Nitric Oxide Synthase and Oxidative Stress in Amyotrophic Lateral Sclerosis Model Cell Lines

L-Arginine, a semi-essential amino acid, was shown to delay dysfunction of motor neurons and to prolong the lifespan, upon analysis of transgenic mouse models of amyotrophic lateral sclerosis (ALS). We investigated the transport function of arginine and neuronal nitric oxide synthase (nNOS) expression after pretreatment with L-arginine in NSC-34 hSOD1^WT (wild-type, WT) and hSOD1^G93A (mutant-type, MT) cell lines. [³H]L-Arginine uptake was concentration-dependent, voltage-sensitive, and sodium-independent in both cell lines. Among the cationic amino acid transporters family, including system y+, b^0,+, B^0,+, and y⁺L, system y⁺ is mainly involved in [³H]L-arginine transport in ALS cell lines. System b^0,+ accounted for 23% of the transport in both cell lines. System B^0,+ was found only in MT, and whereas, system y⁺L was found only in WT. Lysine competitively inhibited [³H]L-arginine uptake in both cell lines. The nNOS mRNA expression was significantly lower in MT than in WT. Pretreatment with arginine elevated nNOS mRNA levels in MT. Oxidizing stressor, H₂O₂, significantly decreased their uptake; however, pretreatment with arginine restored the transport activity in both cell lines. In conclusion, arginine transport is associated with system y⁺, and neuroprotection by L-arginine may provide an edge as a possible therapeutic target in the treatment of ALS.

Crosstalk between Neuron and Glial Cells in Oxidative Injury and Neuroprotection

To counteract oxidative stress and associated brain diseases, antioxidant systems rescue neuronal cells from oxidative stress by neutralizing reactive oxygen species and preserving gene regulation. It is necessary to understand the communication and interactions between brain cells, including neurons, astrocytes and microglia, to understand oxidative stress and antioxidant mechanisms. Here, the role of glia in the protection of neurons against oxidative injury and glia–neuron crosstalk to maintain antioxidant defense mechanisms and brain protection are reviewed. The first part of this review focuses on the role of glia in the morphological and physiological changes required for brain homeostasis under oxidative stress and antioxidant defense mechanisms. The second part focuses on the essential crosstalk between neurons and glia for redox balance in the brain for protection against oxidative stress.

Efferocytosis in the Central Nervous System

The effective clearance of apoptotic cells is essential for maintaining central nervous system (CNS) homeostasis and restoring homeostasis after injury. In most cases of physiological apoptotic cell death, efferocytosis prevents inflammation and other pathological conditions. When apoptotic cells are not effectively cleared, destruction of the integrity of the apoptotic cell membrane integrity, leakage of intracellular contents, and secondary necrosis may occur. Efferocytosis is the mechanism by which efferocytes quickly remove apoptotic cells from tissues before they undergo secondary necrosis. Cells with efferocytosis functions, mainly microglia, help to eliminate apoptotic cells from the CNS. Here, we discuss the impacts of efferocytosis on homeostasis, the mechanism of efferocytosis, the associations of efferocytosis failure and CNS diseases, and the current clinical applications of efferocytosis. We also identify efferocytosis as a novel potential target for exploring the causes and treatments of CNS diseases.

Effects of L-arginine and L-citrulline supplementation in reduced protein diets for broilers under normal and cyclic warm temperature

Heat stress causes significant economic losses in the broiler industry. Dietary supplementation of arginine (Arg) and citrulline (Cit) might increase the performance of broilers raised under warm temperature due to vasodilation effects. This study investigated the effects of L-Arg or L-Cit supplementation in broilers fed a reduced protein wheat-based diet deficient in Arg under thermoneutral (NT) and cyclic warm temperature (WT). Ross 308 cockerels (n = 720) were randomly allocated to 4 dietary treatments with 12 replicates of 15 birds per pen from d 7 to 21. The 4 treatments were: normal protein (NP), i.e., 22.3% and 20.9% crude protein in grower and finisher, respectively; reduced protein (RP), i.e., 2.5% lower protein and deficient in Arg; and RP supplemented with 0.28% Arg (RP-Arg) or 0.28% Cit (RP-Cit). A factorial arrangement of treatments was applied during the finisher phase (21 to 35 d). Factors were: diet (4 diets above); and temperature, NT (24 °C) or cyclic WT (33 ± 1 °C for 6 h per day) with 6 replicate pens per treatment. During 7 to 35 d and 21 to 35 d, the birds fed the RP diet had lower body weight gain (BWG) and higher FCR compared to the NP diet (P < 0.01). The addition of Arg or Cit to RP decreased FCR compared to RP (P < 0.01). During 21 to 35 d, the birds exposed to WT had lower feed intake (FI), lower BWG (P < 0.001) but similar FCR (P > 0.05) compared to birds exposed to NT. Diet by temperature interactions were not observed for performance parameters during the period of WT (P > 0.05). On d 35, the RP-fed birds had a lower yield of thigh and drumstick, higher fat pad, lower femur ash, and breaking strength but similar serum uric acid level and higher nitrogen digestibility on d 21 compared to those offered NP (P < 0.05). Supplementation of Arg or Cit to RP resulted in increased femur ash on d 35 (P < 0.05). Thus, feeding the NP diets is necessary to maintain growth performance in broilers regardless of the temperature conditions.

Anti-seizure effects of walnut peptides in mouse models of induced seizure: The involvement of GABA and nitric oxide pathways

Epilepsy is one of the foremost medical disorders. Oxidative stress is a well-known mechanism in epileptogenesis, and many studies suggest that oxidative stress affects the onset and evolution of epilepsy. Here we evaluated the walnut peptide extracts' anti-seizure property in three different mouse seizure models including pentylenetetrazole-induced clonic seizure, chemical kindling, and maximal electroshock. Walnut peptides (20 mg/Kg) were administered by intraperitoneal (IP) injection of mice 60 min before seizure induction in the three models. To delineate the mechanisms of walnut peptides anti-seizure activity, we evaluated the impact of diazepam, flumazenil, and a NOS inhibitor on this activity. Intraperitoneal administration of walnut peptides significantly increased the seizure threshold. Our results also demonstrated that walnut peptides exert their anti-seizure properties through the modulation of benzodiazepine receptors. Thus, walnut peptides may be considered as a new anti-convulsion agent, which can reduce seizure occurrence and slow down seizure progression.

Arginine-dependent immune responses

A growing body of evidence indicates that, over the course of evolution of the immune system, arginine has been selected as a node for the regulation of immune responses. An appropriate supply of arginine has long been associated with the improvement of immune responses. In addition to being a building block for protein synthesis, arginine serves as a substrate for distinct metabolic pathways that profoundly affect immune cell biology; especially macrophage, dendritic cell and T cell immunobiology. Arginine availability, synthesis, and catabolism are highly interrelated aspects of immune responses and their fine-tuning can dictate divergent pro-inflammatory or anti-inflammatory immune outcomes. Here, we review the organismal pathways of arginine metabolism in humans and rodents, as essential modulators of the availability of this semi-essential amino acid for immune cells. We subsequently review well-established and novel findings on the functional impact of arginine biosynthetic and catabolic pathways on the main immune cell lineages. Finally, as arginine has emerged as a molecule impacting on a plethora of immune functions, we integrate key notions on how the disruption or perversion of arginine metabolism is implicated in pathologies ranging from infectious diseases to autoimmunity and cancer.

Inhibition of Urea Transporter (UT)-B Modulates LPS-Induced Inflammatory Responses in BV2 Microglia and N2a Neuroblastoma Cells

Urea is the major nitrogen-containing product of protein metabolism, and the urea cycle is intrinsically linked to nitric oxide (NO) production via the common substrate L-arginine. Urea accumulates in the brain in neurodegenerative states, including Alzheimer's and Huntington's disease. Urea transporter B (UT-B, SLC14A1) is the primary transport protein for urea in the CNS, identified most abundantly in astrocytes. Moreover, enhanced expression of the Slc14a1 gene has been reported under neurodegenerative conditions. While the role of UT-B in disease pathology remains unclear, UT-B-deficient mice display behavioural impairment coupled with urea accumulation, NO disruption and neuronal loss. Recognising the role of inflammation in neurodegenerative disease pathology, the current short study evaluates the role of UT-B in regulating inflammatory responses. Using the specific inhibitor UTBinh-14, we investigated the impact of UT-B inhibition on LPS-induced changes in BV2 microglia and N2a neuroblastoma cells. We found that UTBinh-14 significantly attenuated LPS-induced production of TNFα and IL-6 from BV2 cells, accompanied by reduced release of NO. While we observed a similar reduction in supernatant concentration of IL-6 from N2a cells, the LPS-stimulated NO release was further augmented by UTBinh-14. These changes were accompanied by a small, but significant downregulation in UT-B expression in both cell types following incubation with LPS, which was not restored by UTBinh-14. Taken together, the current evidence implicates UT-B in regulation of inflammatory responses in microglia and neuronal-like cells. Moreover, our findings offer support for the further investigation of UT-B as a novel therapeutic target for neuroinflammatory conditions.

The Role of Amino Acids in Neurotransmission and Fluorescent Tools for Their Detection

Neurotransmission between neurons, which can occur over the span of a few milliseconds, relies on the controlled release of small molecule neurotransmitters, many of which are amino acids. Fluorescence imaging provides the necessary speed to follow these events and has emerged as a powerful technique for investigating neurotransmission. In this review, we highlight some of the roles of the 20 canonical amino acids, GABA and β-alanine in neurotransmission. We also discuss available fluorescence-based probes for amino acids that have been shown to be compatible for live cell imaging, namely those based on synthetic dyes, nanostructures (quantum dots and nanotubes), and genetically encoded components. We aim to provide tool developers with information that may guide future engineering efforts and tool users with information regarding existing indicators to facilitate studies of amino acid dynamics.

Antunes I, Dömling A, H. Elsinga P. Arginase as a Potential Biomarker of Disease Progression: A Molecular Imaging Perspective

Arginase is a widely known enzyme of the urea cycle that catalyzes the hydrolysis of L-arginine to L-ornithine and urea. The action of arginase goes beyond the boundaries of hepatic ureogenic function, being widespread through most tissues. Two arginase isoforms coexist, the type I (Arg1) predominantly expressed in the liver and the type II (Arg2) expressed throughout extrahepatic tissues. By producing L-ornithine while competing with nitric oxide synthase (NOS) for the same substrate (L-arginine), arginase can influence the endogenous levels of polyamines, proline, and NO•. Several pathophysiological processes may deregulate arginase/NOS balance, disturbing the homeostasis and functionality of the organism. Upregulated arginase expression is associated with several pathological processes that can range from cardiovascular, immune-mediated, and tumorigenic conditions to neurodegenerative disorders. Thus, arginase is a potential biomarker of disease progression and severity and has recently been the subject of research studies regarding the therapeutic efficacy of arginase inhibitors. This review gives a comprehensive overview of the pathophysiological role of arginase and the current state of development of arginase inhibitors, discussing the potential of arginase as a molecular imaging biomarker and stimulating the development of novel specific and high-affinity arginase imaging probes.

Altered brain arginine metabolism with age in the APPswe/PSEN1dE9 mouse model of Alzheimer's disease

Amyloid-beta (Aβ) cleaved from amyloid precursor protein (APP) has been proposed to play a central and causative role in the aetiology of Alzheimer's disease (AD). APP_swe/PSEN1_dE9 (APP/PS1) transgenic mice display chronic Aβ accumulation and deposition in the brain. L-arginine is a semi-essential amino acid with a number of bioactive metabolites, and altered arginine metabolism has been implicated in the pathogenesis and/or the development of AD. This study systematically investigated how arginine metabolic profiles changed in the frontal cortex, hippocampus, parahippocampal region and cerebellum of male APP/PS1 mice at 4, 9 and 17 months of age relative to their sex- and age-matched wildtype controls. Immunohistochemistry demonstrated age-related Aβ deposition in the brain. High-performance liquid chromatography and mass spectrometry revealed age-related increases in glutamine, spermidine and spermine in APP/PS1 mice in a region-specific manner. Notably, genotype-related increases in spermine were found in the frontal cortex at the 9-month age point and in the frontal cortex, hippocampus and parahippocampal region at 17 months of age. Given the existing literature indicating the role of polyamines (spermine in particular) in modulating the aggregation and toxicity of Aβ oligomers, increased spermidine and spermine levels in APP/PS1 mice may be a neuroprotective mechanism to combat Aβ toxicity. Future research is required to better understand the functional significance of these changes.

Protein synthesis inhibition promotes nitric oxide generation and activation of CGKII-dependent downstream signaling pathways in the retina

Nitric oxide is an important neuromodulator in the CNS, and its production within neurons is modulated by NMDA receptors and requires a fine-tuned availability of L-arginine. We have previously shown that globally inhibiting protein synthesis mobilizes intracellular L-arginine "pools" in retinal neurons, which concomitantly enhances neuronal nitric oxide synthase-mediated nitric oxide production. Activation of NMDA receptors also induces local inhibition of protein synthesis and L-arginine intracellular accumulation through calcium influx and stimulation of eucariotic elongation factor type 2 kinase. We hypothesized that protein synthesis inhibition might also increase intracellular L-arginine availability to induce nitric oxide-dependent activation of downstream signaling pathways. Here we show that nitric oxide produced by inhibiting protein synthesis (using cycloheximide or anisomycin) is readily coupled to AKT activation in a soluble guanylyl cyclase and cGKII-dependent manner. Knockdown of cGKII prevents cycloheximide or anisomycin-induced AKT activation and its nuclear accumulation. Moreover, in retinas from cGKII knockout mice, cycloheximide was unable to enhance AKT phosphorylation. Indeed, cycloheximide also produces an increase of ERK phosphorylation which is abrogated by a nitric oxide synthase inhibitor. In summary, we show that inhibition of protein synthesis is a previously unanticipated driving force for nitric oxide generation and activation of downstream signaling pathways including AKT and ERK in cultured retinal cells. These results may be important for the regulation of synaptic signaling and neuronal development by NMDA receptors as well as for solving conflicting data observed when using protein synthesis inhibitors for studying neuronal survival during development as well in behavior and memory studies.

The antidepressant effects of l-arginine on chronic mild stress-induced depression by augmenting the expression of brain-derived neurotrophic factor in rats

In the present study, the antidepressant effects of l-arginine in a rat model of chronic mild stress-induced depression were investigated. Animals were divided into group I (sham), group II (control, depression), group III (10 mg/kg l-arginine), group IV (20 mg/kg l-arginine), and group V (10 mg/kg venlafaxine, positive control). The doses were orally administered for 30 consecutive days. Sucrose preference analysis as well as forced swim and open field tests were performed. Serum cortisol, nitric oxide (NO), and monoamine levels in brain tissue were then measured. Brain-derived neurotrophic factor (BDNF) expression was also examined. Supplementation with l-arginine significantly increased the sucrose preference ratio, locomotor activity, and monoamines and decreased serum cortisol and NO levels. The mRNA and protein expression of BDNF in the brain tissue was significantly reduced (>50 %) in control rats. However, supplementation with l-arginine significantly increased BDNF mRNA expression (>50 %) in both groups. Similarly, increased BDNF protein expression after l-arginine treatment was confirmed using Western blot and immunohistochemical analyses. In conclusion, l-arginine supplementation may be effective against chronic stress-induced depression.

Is the Arginase Pathway a Novel Therapeutic Avenue for Diabetic Retinopathy?

Diabetic retinopathy (DR) is the leading cause of blindness in working age Americans. Clinicians diagnose DR based on its characteristic vascular pathology, which is evident upon clinical exam. However, extensive research has shown that diabetes causes significant neurovascular dysfunction prior to the development of clinically apparent vascular damage. While laser photocoagulation and/or anti-vascular endothelial growth factor (VEGF) therapies are often effective for limiting the late-stage vascular pathology, we still do not have an effective treatment to limit the neurovascular dysfunction or promote repair during the early stages of DR. This review addresses the role of arginase as a mediator of retinal neurovascular injury and therapeutic target for early stage DR. Arginase is the ureohydrolase enzyme that catalyzes the production of L-ornithine and urea from L-arginine. Arginase upregulation has been associated with inflammation, oxidative stress, and peripheral vascular dysfunction in models of both types of diabetes. The arginase enzyme has been identified as a therapeutic target in cardiovascular disease and central nervous system disease including stroke and ischemic retinopathies. Here, we discuss and review the literature on arginase-induced retinal neurovascular dysfunction in models of DR. We also speculate on the therapeutic potential of arginase in DR and its related underlying mechanisms.

Silver nanoparticles (Ag-NPs) in the central amygdala protect the rat conditioned by morphine from withdrawal attack due to naloxone via high-level nitric oxide

Repeated injection of morphine during conditioned place preference (CPP) leads to spatial craving due to high-level nitric oxide (NO) in the central nucleus of amygdala (CeA). Silver nanoparticles (Ag-NPs) can produce oxygen-free radicals that lead to NO formation. We aimed to show the Ag-NPs protective effect on naloxone (NLX)-induced morphine withdrawal in the conditioned rats. Wistar rats (300-350 g) were implanted with cannulae in the CeA. After recovery, they were randomly divided into experimental and saline groups. CPP was conducted by three-phase unbiased program. Morphine (0.5-7.5 mg/kg) was injected subcutaneously (s.c.) once/per day during the conditioning phase. Naloxone (NLX) (0.05-0.4 μg/rat) was given, intra-CeA, 10 min before the CPP test. Ag-NPs (0.0001-0.01 μg/rat) were administered alone or prior to the NLX effective dose (0.4 μg/rat), intra-CeA. Conditioning score and withdrawal signs (wet dog shaking and scratching) were obtained and compared with saline group data. All rats' brains were collected in formalin 10% and after 48-72 h stained with NADPH-diaphorase, the NO marker. All data were analyzed by one-way or two-way ANOVA. Morphine (2.5-7.5 mg/kg, s.c.) induced a significant CPP vs. saline (1 mL/kg, s.c.). The single Ag-NPs had no significant effect, whereas the NLX caused meaningful WDS and scratching. However, the NLX pre-treatment in combination with Ag-NPs eliminated these signs. Furthermore, the NO level increased in the CeA. The Ag-NPs may protect the morphine-conditioned rats against the NLX-induced withdrawal symptoms due to high-level NO in the CeA.

Altered plasma levels of arginine metabolites in depression

L-Arginine pathway metabolites appear to play differential roles in the pathogenesis of major depressive disorder (MDD). Studies have revealed an antidepressant and anxiolytic effect of agmatine and putrescine. Possible mechanisms of these effects include inhibition of nitric oxide synthase and N-methyl-D-aspartate receptors. The present study sought to determine whether MDD is associated with altered levels of arginine metabolites and whether these metabolites are associated with depression, anxiety and stress severity. Seventy seven MDD patients 21-65 years of age with a minimum score of 18 on the Hamilton Depression Scale, and 27 age and sex matched healthy controls (HC) were included. Patients with uncontrolled physical diseases, abnormal routine lab tests, other psychiatric diagnoses, or under psychotropic medication were excluded. HC subjects were recruited from the community. Rating instruments included Hamilton Depression and Anxiety Scales, Beck Depression and Anxiety Inventory and Perceived Stress Scale. Fasting blood was drawn between 8:30 and 11:00 a.m. and High Performance Liquid Chromatography (HPLC) was used to measure plasma arginine metabolites. ADMA (Asymmetrical dimethylarginine) and putrescine were significantly lower while SDMA (Symmetric dimethylarginine), agmatine and ornithine were significantly higher in MDD patients (p˂0.05). Depression, anxiety and stress severity were negatively correlated with ADMA and putrescine (p˂0.05). Stress was positively correlated with citrulline, NOHA (N-omega-hydroxy-nor-l-arginine), SDMA, agmatine and ornithine (p˂0.05). Lower putrescine levels predicted depression diagnosis (p = 0.039) and depression severity (p = 0.003). Low ADMA level predicted depression severity as well. Arginine pathway metabolites are associated with the pathophysiology of depression. Putrescine may be a biomarker to predict MDD.

Altered Expression of Urea Cycle Enzymes in Amyloid-β Protein Precursor Overexpressing PC12 Cells and in Sporadic Alzheimer's Disease Brain

Urea cycle enzymes may play important yet poorly characterized roles in Alzheimer's disease (AD). Our previous results showed that amyloid-β (Aβ) affects urea cycle enzymes in rat pheochromocytoma (PC12) cells. The aim of the present study was to investigate the changes in arginases, other urea cycle enzymes, and nitric oxide synthases (NOSs) in PC12 cells transfected with AβPP bearing the double 'Swedish' mutation (APPsw, K670M/N671L) and in postmortem sporadic AD brain hippocampus; the mutation intensifies Aβ production and strongly associates with AD neuropathology. mRNA expression was analyzed using real-time PCR in cell cultures and DNA microarrays in hippocampal CA1 area of human AD brains. Arginase activity was measured spectrophotometrically, and arginine, ornithine, and citrulline levels by high-performance liquid chromatography. Our data demonstrated that the expression and activity of arginases (Arg1 and Arg2), as well as the expression of argininosuccinate synthase (Ass) were significantly reduced in APPsw cells compared to control. However, argininosuccinate lyase (Asl) was upregulated in APPsw cells. Real-time PCR analysis revealed significant elevation of neuronal nitric oxide synthase (Nnos) mRNA in APPsw cells, without changes in the endothelial Enos, whereas inducible Inos was undetectable. The changes were found to follow closely those observed in the human hippocampal CA1 region of sporadic AD brains. The changes in enzyme expression were accompanied in APPsw cells by significantly elevated citrulline, ornithine, and arginine. Our findings demonstrate that AβPP/Aβ alters arginine metabolism and induces a shift of cellular homeostasis that may support the oxidative/nitrosative stress observed in AD.

Promising Neuroprotective Function for M2 Microglia in Kainic Acid-Induced Neurotoxicity Via the Down-Regulation of NF-κB and Caspase 3 Signaling Pathways

Activated microglia have two functional states (M1 and M2) which play dual roles in neurodegenerative diseases. In the present study, we explored a possible neuroprotective function of M2 microglia against kainic acid (KA)-induced neurodegeneration in primary neurons co-cultured with different microglial populations. Neurons were isolated from the hippocampi and cortices of C57BL/6 embryos (embryonic day 16) and microglia were extracted from neonatal pups (postnatal days 0-2). Microglia were either unstimulated (M0-phenotype) or stimulated with lipopolysaccharide and interferon-γ to form the M1-phenotype, or with interleukin (IL)-4, IL-10, and transforming growth factor -β for the M2-phenotype. Neurons were co-cultured with each of the three microglial phenotypes and treated with KA for 24 h. Next, we analyzed the cell survival rate, nitric oxide (NO) levels, and lactate dehydrogenase production, cytokines levels, and expression of nuclear factor κB (NF-κB) and caspase 3 among the three groups before and after KA insult. Our results indicated that M2 microglia played a neuroprotective role in KA-induced neurotoxicity, as demonstrated by high neuronal survival as well as decreased production of NO and pro-inflammatory cytokines. In contrast, neurons co-cultured with M1 microglia exhibited the lowest survival rate as well as increased levels of NO and pro-inflammatory cytokines. Further, the expression of NF-κB and caspase 3 were significantly decreased in M2 microglia co-cultures compared to M1 or M0 microglia co-cultures after KA insult. Therefore, M2 microglia may exert a neuroprotective function in KA-induced neurotoxicity via the down-regulation of NF-κB and caspase 3 signaling pathways.

Altered brain arginine metabolism in a mouse model of tauopathy

Tauopathies consist of intracellular accumulation of hyperphosphorylated and aggregated microtubule protein tau, which remains a histopathological feature of Alzheimer's disease (AD) and frontotemporal dementia. L-Arginine is a semi-essential amino acid with a number of bioactive molecules. Its downstream metabolites putrescine, spermidine, and spermine (polyamines) are critically involved in microtubule assembly and stabilization. Recent evidence implicates altered arginine metabolism in the pathogenesis of AD. Using high-performance liquid chromatographic and mass spectrometric assays, the present study systematically determined the tissue concentrations of L-arginine and its nine downstream metabolites in the frontal cortex, hippocampus, parahippocampal region, striatum, thalamus, and cerebellum in male PS19 mice-bearing human tau P301S mutation at 4, 8, and 12-14 months of age. As compared to their wild-type littermates, PS19 mice displayed early and/or prolonged increases in L-ornithine and altered polyamine levels with age. There were also genotype- and age-related changes in L-arginine, L-citrulline, glutamine, glutamate, and γ-aminobutyric acid in a region- and/or chemical-specific manner. The results demonstrate altered brain arginine metabolism in PS19 mice with the most striking changes in L-ornithine, polyamines, and glutamate, indicating a shift of L-arginine metabolism to favor the arginase-polyamine pathway. Given the role of polyamines in maintaining microtubule stability, the functional significance of these changes remains to be explored in future research.

Arginine Deiminase: Current Understanding and Applications

BACKGROUND

Arginine deiminase (ADI), an arginine catabolizing enzyme, is considered as an anti-tumor agent for the treatment of arginine auxotrophic cancers. However, some obstacles limit its clinical applications.

OBJECTIVE

This review will summarize the clinical applications of ADI, from a brief history to its limitations, and will discuss the different ways to deal with the clinical limitations.

METHOD

The structure analysis, cloning, expression, protein engineering and applications of arginine deiminase enzyme have been explained in this review.

CONCLUSION

Recent patents on ADI are related to ADI engineering to increase its efficacy for clinical application. The intracellular delivery of ADI and combination therapy seem to be the future strategies in the treatment of arginine auxotrophic cancers. Applying ADIs with optimum features from different sources and or ADI engineering, are promising strategies to improve the clinical application of ADI.

Effects of maternal immune activation on brain arginine metabolism of postnatal day 2 rat offspring

l-Arginine is a versatile semi-essential amino acid with a number of bioactive metabolites, and altered arginine metabolism has been implicated in the pathogenesis of schizophrenia. Earlier research has demonstrated that maternal immune activation (MIA; a risk factor for schizophrenia) alters arginine metabolism in the prefrontal cortex and hippocampus of the adult offspring. The present study investigated how MIA affected the levels of l-arginine and its downstream metabolites in the whole forebrain, frontal cortex, hippocampus and cerebellum of male and female rat offspring at the age of postnatal day 2. While no effects were evident in the forebrain, MIA significantly increased l-arginine, glutamate, putrescine, spermidine and spermine levels and the glutamate/GABA ratio, but decreased the glutamine/glutamate ratio, in the frontal cortex, hippocampus and/or cerebellum with no marked sex differences. Cluster analyses revealed that l-arginine and its main metabolites formed distinct groups, which changed as a function of MIA or sex in all four brain regions examined. These results demonstrate, for the first time, that MIA alters brain arginine metabolism in the rat offspring during early neonatal development, and further support the involvement of arginine metabolism in the pathogenesis of schizophrenia.

In human brain ornithine transcarbamylase (OTC) immunoreactivity is strongly expressed in a small number of nitrergic neurons

There is recent evidence for ornithine transcarbamylase (OTC) expression in adult human brain. We decided to immunocytochemically map OTC throughout brain, and to further characterize OTC-immunopositive neurons. By using double immunolabeling technique for OTC and neuronal nitric oxide synthase (nNOS) OTC protein expression was revealed in a small subset of nitrergic (nNOS) neurons. Since citrulline (the reaction product of OTC) enhances the bioavailability of L-arginine, the substrate of nNOS, it is conceivable that OTC activity supports NO production in nitrergic neurons.

Effects of Aging and Tocotrienol-Rich Fraction Supplementation on Brain Arginine Metabolism in Rats

Accumulating evidence suggests that altered arginine metabolism is involved in the aging and neurodegenerative processes. This study sought to determine the effects of age and vitamin E supplementation in the form of tocotrienol-rich fraction (TRF) on brain arginine metabolism. Male Wistar rats at ages of 3 and 21 months were supplemented with TRF orally for 3 months prior to the dissection of tissue from five brain regions. The tissue concentrations of L-arginine and its nine downstream metabolites were quantified using high-performance liquid chromatography and liquid chromatography tandem mass spectrometry. We found age-related alterations in L-arginine metabolites in the chemical- and region-specific manners. Moreover, TRF supplementation reversed age-associated changes in arginine metabolites in the entorhinal cortex and cerebellum. Multiple regression analysis revealed a number of significant neurochemical-behavioral correlations, indicating the beneficial effects of TRF supplementation on memory and motor function.