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Fukuyama K, Motomura E, Okada M. A Novel Gliotransmitter, L-β-Aminoisobutyric Acid, Contributes to Pathophysiology of Clinical Efficacies and Adverse Reactions of Clozapine. Biomolecules 2023; 13:1288. [PMID: 37759688 PMCID: PMC10526296 DOI: 10.3390/biom13091288] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2023] [Revised: 08/18/2023] [Accepted: 08/22/2023] [Indexed: 09/29/2023] Open
Abstract
Clozapine is listed as one of the most effective antipsychotics and has been approved for treating treatment-resistant schizophrenia (TRS); however, several type A and B adverse reactions, including weight gain, metabolic complications, cardiotoxicity, convulsions, and discontinuation syndromes, exist. The critical mechanisms of clinical efficacy for schizophrenia, TRS, and adverse reactions of clozapine have not been elucidated. Recently, the GABA isomer L-β-aminoisobutyric acid (L-BAIBA), a protective myokine in the peripheral organs, was identified as a candidate novel transmission modulator in the central nervous system (CNS). L-BAIBA activates adenosine monophosphate-activated protein kinase (AMPK) signalling in both the peripheral organs and CNS. Activated AMPK signalling in peripheral organs is an established major target for treating insulin-resistant diabetes, whereas activated AMPK signalling in the hypothalamus contributes to the pathophysiology of weight gain and metabolic disturbances. Clozapine increases L-BAIBA synthesis in the hypothalamus. In addition, the various functions of L-BAIBA in the CNS have recently been elucidated, including as an activator of GABA-B and group-III metabotropic glutamate (III-mGlu) receptors. Considering the expressions of GABA-B and III-mGlu receptors (localised in the presynaptic regions), the activation of GABA-B and III-mGlu receptors can explain the distinct therapeutic advantages of clozapine in schizophrenia or TRS associated with N-methyl-D-aspartate (NMDA) receptor disturbance compared with other atypical antipsychotics via the inhibition of the persistent tonic hyperactivation of thalamocortical glutamatergic transmission in the prefrontal cortex. L-BAIBA has also been identified as a gliotransmitter, and a detailed exploration of the function of L-BAIBA in tripartite synaptic transmission can further elucidate the pathophysiology of effectiveness for treating TRS and/or specific adverse reactions of clozapine.
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Affiliation(s)
| | | | - Motohiro Okada
- Department of Neuropsychiatry, Division of Neuroscience, Graduate School of Medicine, Mie University, Tsu 514-8507, Japan; (K.F.); (E.M.)
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Fukuyama K, Motomura E, Okada M. Enhanced L-β-Aminoisobutyric Acid Is Involved in the Pathophysiology of Effectiveness for Treatment-Resistant Schizophrenia and Adverse Reactions of Clozapine. Biomolecules 2023; 13:biom13050862. [PMID: 37238731 DOI: 10.3390/biom13050862] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2023] [Revised: 05/14/2023] [Accepted: 05/17/2023] [Indexed: 05/28/2023] Open
Abstract
Clozapine is an effective antipsychotic for the treatment of antipsychotic-resistant schizophrenia; however, specific types of A/B adverse effects and clozapine-discontinuation syndromes are also well known. To date, both the critical mechanisms of clinical actions (effective for antipsychotic-resistant schizophrenia) and the adverse effects of clozapine remain to be elucidated. Recently, we demonstrated that clozapine increased the synthesis of L-β-aminoisobutyric acid (L-BAIBA) in the hypothalamus. L-BAIBA is an activator of the adenosine monophosphate-activated protein kinase (AMPK), glycine receptor, GABAA receptor, and GABAB receptor (GABAB-R). These targets of L-BAIBA overlap as potential targets other than the monoamine receptors of clozapine. However, the direct binding of clozapine to these aminoacidic transmitter/modulator receptors remains to be clarified. Therefore, to explore the contribution of increased L-BAIBA on the clinical action of clozapine, this study determined the effects of clozapine and L-BAIBA on tripartite synaptic transmission, including GABAB-R and the group-III metabotropic glutamate receptor (III-mGluR) using cultured astrocytes, as well as on the thalamocortical hyper-glutamatergic transmission induced by impaired glutamate/NMDA receptors using microdialysis. Clozapine increased astroglial L-BAIBA synthesis in time/concentration-dependent manners. Increased L-BAIBA synthesis was observed until 3 days after clozapine discontinuation. Clozapine did not directly bind III-mGluR or GABAB-R, whereas L-BAIBA activated these receptors in the astrocytes. Local administration of MK801 into the reticular thalamic nucleus (RTN) increased L-glutamate release in the medial frontal cortex (mPFC) (MK801-evoked L-glutamate release). Local administration of L-BAIBA into the mPFC suppressed MK801-evoked L-glutamate release. These actions of L-BAIBA were inhibited by antagonists of III-mGluR and GABAB-R, similar to clozapine. These in vitro and in vivo analyses suggest that increased frontal L-BAIBA signaling likely plays an important role in the pharmacological actions of clozapine, such as improving the effectiveness of treating treatment-resistant schizophrenia and several clozapine discontinuation syndromes via the activation of III-mGluR and GABAB-R in the mPFC.
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Affiliation(s)
- Kouji Fukuyama
- Department of Neuropsychiatry, Division of Neuroscience, Graduate School of Medicine, Mie University, Tsu 514-8507, Japan
| | - Eishi Motomura
- Department of Neuropsychiatry, Division of Neuroscience, Graduate School of Medicine, Mie University, Tsu 514-8507, Japan
| | - Motohiro Okada
- Department of Neuropsychiatry, Division of Neuroscience, Graduate School of Medicine, Mie University, Tsu 514-8507, Japan
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Fukuyama K, Motomura E, Okada M. A Candidate Gliotransmitter, L-β-Aminoisobutyrate, Contributes to Weight Gain and Metabolic Complication Induced by Atypical Antipsychotics. Nutrients 2023; 15:nu15071621. [PMID: 37049464 PMCID: PMC10097171 DOI: 10.3390/nu15071621] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2023] [Revised: 03/15/2023] [Accepted: 03/23/2023] [Indexed: 03/29/2023] Open
Abstract
Lurasidone and quetiapine are effective atypical mood-stabilizing antipsychotics, but lurasidone and quetiapine are listed as lower-risk and high-risk for weight gain/metabolic complications, respectively. The pathophysiology of the discrepancy of metabolic adverse reactions between these antipsychotics remains to be clarified. The GABA isomer, β-aminoisobutyric acid (BAIBA) enantiomer, was recently re-discovered as myokine via an AMP-activated protein kinase activator (AMPK) enhancer and inhibitory gliotransmitter. Notably, activation of AMPK in peripheral organs improves, but in the hypothalamus, it aggravates metabolic disturbances. Therefore, we determined effects of chronic administration of lurasidone and quetiapine on intracellular and extracellular levels of the BAIBA enantiomer. L-BAIBA is a major BAIBA enantiomer in the hypothalamus and astrocytes, whereas L-BAIBA only accounted for about 5% of total plasma BAIBA enantiomers. Chronic lurasidone administration did not affect body weight but decreased the L-BAIBA level in hypothalamus and cultured astrocytes, whereas chronic quetiapine administration increased body weight and the L-BAIBA level in hypothalamus and astrocytes. Contrary, neither lurasidone nor quetiapine affected total plasma levels of the BAIBA enantiomer since D-BAIBA levels were not affected by these antipsychotics. These results suggest that activation of intracellular L-BAIBA signaling is, at least partially, involved in the pathophysiology of metabolic adverse reaction of quetiapine. Furthermore, this study also demonstrated that lurasidone and quetiapine suppressed and enhanced astroglial L-BAIBA release induced by ripple-burst stimulation (which physiologically contributes to cognitive memory integration during sleep), respectively. Therefore, L-BAIBA probably contributes to the pathophysiology of not only metabolic adverse reactions, but also a part of clinical action of lurasidone or quetiapine.
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Opposing effects of clozapine and brexpiprazole on β-aminoisobutyric acid: Pathophysiology of antipsychotics-induced weight gain. SCHIZOPHRENIA (HEIDELBERG, GERMANY) 2023; 9:8. [PMID: 36750570 PMCID: PMC9905547 DOI: 10.1038/s41537-023-00336-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/01/2023] [Accepted: 01/26/2023] [Indexed: 02/09/2023]
Abstract
Clozapine is one of the most effective antipsychotics and has the highest risk of weight gain and metabolic complications; however, the detailed pathophysiology of its clinical action and adverse reactions remains to be clarified. Therefore, the present study determined the chronic effects of clozapine (high risk of weight gain) and brexpiprazole (relatively low risk of weight gain) on intracellular and extracellular levels of β-aminoisobutyric acid (BAIBA) enantiomers, which are endogenous activators of AMP-activated protein kinase (AMPK). L-BAIBA is the dominant BAIBA enantiomer in the rat hypothalamus and cultured astrocytes, whereas L-BAIBA accounts for only approximately 5% of the total plasma BAIBA enantiomers. L-BAIBA displayed GABAB receptor agonistic action in the extracellular space and was released through activated astroglial hemichannels, whereas in the intracellular space, L-BAIBA activated AMPK signalling. Chronic administration of the effective doses of clozapine increased intracellular and extracellular levels of L-BAIBA in the hypothalamus and cultured astrocytes, whereas that of brexpiprazole decreased them. These results suggest that enhancing hypothalamic AMPK signalling by increasing intracellular L-BAIBA levels is, at least partially, involved in the pathophysiology of clozapine-induced weight gain and metabolic complications.
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Jarzebska N, Georgi S, Jabs N, Brilloff S, Maas R, Rodionov RN, Zietz C, Montresor S, Hohenstein B, Weiss N. Kidney and liver are the main organs of expression of a key metabolic enzyme alanine:glyoxylate aminotransferase 2 in humans. ATHEROSCLEROSIS SUPP 2020; 40:106-112. [PMID: 31818439 DOI: 10.1016/j.atherosclerosissup.2019.08.041] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
BACKGROUND The metabolic syndrome is a cluster of cardiovascular risk factors and is highly predictive for development of cardiovascular diseases. An association between elevated plasma levels of the endogenous inhibitor of nitric oxide synthases asymmetric dimethylarginine (ADMA) and risk of cardiovascular diseases has been demonstrated in numerous epidemiological studies. ADMA can be catabolized by dimethylarginine dimethylaminohydrolase (DDAH) or metabolized through a much less understood alternative pathway by alanine:glyoxylate aminotransferase 2 (AGXT2) with the formation of α-keto-δ-(N,N-dimethylguanidino)valeric acid (ADGV). Previous RT-PCR and Western Blot studies suggested that Agxt2 is expressed in the mouse kidney and liver at comparable levels, while Northern Blot and in-situ RNA-hybridisation experiments demonstrated that the kidney is the main organ of Agxt2 expression in rats. Given this discrepancy, the goal of the current study was to analyse the expression of AGXT2 in human tissues. MATERIAL AND METHODS We analyzed AGXT2 expression in human tissues from a normal tissue bank by RT-PCR and further validated the results by Western Blot. We also performed immunohistochemical staining for AGXT2 and double fluorescent staining with an anti-AGXT2 antibody and a monoclonal anti-mitochondrial antibody. RESULTS We saw the strongest expression of AGXT2 in the kidney and liver and confirmed this results on protein level. By IHC staining we were able to show that AGXT2 is present in the convoluted tubule in the kidney and in the liver hepatocytes. The double fluorescent staining revealed mitochondrial localization of AGXT2. CONCLUSIONS Our current data suggest that both hepatocytes and kidney tubular epithelial cells are the major sources of AGXT2 in humans. We also demonstrated the mitochondrial localization of human AGXT2 enzyme.
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Affiliation(s)
- Natalia Jarzebska
- University Center for Vascular Medicine & Department of Medicine III - Section Angiology, University Hospital Carl Gustav Carus, Technische Universität Dresden, Dresden, Germany; Department of Anesthesiology and Intensive Care Medicine, Pulmonary Engineering Group, University Hospital Carl Gustav Carus, Technische Universität Dresden, Germany
| | - Sophia Georgi
- University Center for Vascular Medicine & Department of Medicine III - Section Angiology, University Hospital Carl Gustav Carus, Technische Universität Dresden, Dresden, Germany
| | - Normund Jabs
- University Center for Vascular Medicine & Department of Medicine III - Section Angiology, University Hospital Carl Gustav Carus, Technische Universität Dresden, Dresden, Germany
| | - Silke Brilloff
- University Center for Vascular Medicine & Department of Medicine III - Section Angiology, University Hospital Carl Gustav Carus, Technische Universität Dresden, Dresden, Germany
| | - Renke Maas
- Institute of Experimental and Clinical Pharmacology and Toxicology, Friedrich-Alexander-University Erlangen-Nürnberg (FAU), Erlangen, Germany
| | - Roman N Rodionov
- University Center for Vascular Medicine & Department of Medicine III - Section Angiology, University Hospital Carl Gustav Carus, Technische Universität Dresden, Dresden, Germany
| | - Christian Zietz
- Institute of Pathology, University Hospital Carl Gustav Carus, Technische Universität Dresden, Dresden, Germany
| | - Sabrina Montresor
- University Center for Vascular Medicine & Department of Medicine III - Section Angiology, University Hospital Carl Gustav Carus, Technische Universität Dresden, Dresden, Germany
| | - Bernd Hohenstein
- Division of Nephrology, Department of Internal Medicine III, University Hospital Carl Gustav Carus, Technische Universität Dresden, Dresden, Germany
| | - Norbert Weiss
- University Center for Vascular Medicine & Department of Medicine III - Section Angiology, University Hospital Carl Gustav Carus, Technische Universität Dresden, Dresden, Germany.
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The Second Life of Methylarginines as Cardiovascular Targets. Int J Mol Sci 2019; 20:ijms20184592. [PMID: 31533264 PMCID: PMC6769906 DOI: 10.3390/ijms20184592] [Citation(s) in RCA: 34] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2019] [Revised: 09/13/2019] [Accepted: 09/15/2019] [Indexed: 02/07/2023] Open
Abstract
Endogenous methylarginines were proposed as cardiovascular risk factors more than two decades ago, however, so far, this knowledge has not led to the development of novel therapeutic approaches. The initial studies were primarily focused on the endogenous inhibitors of nitric oxide synthases asymmetric dimethylarginine (ADMA) and monomethylarginine (MMA) and the main enzyme regulating their clearance dimethylarginine dimethylaminohydrolase 1 (DDAH1). To date, all the screens for DDAH1 activators performed with the purified recombinant DDAH1 enzyme have not yielded any promising hits, which is probably the main reason why interest towards this research field has started to fade. The relative contribution of the second DDAH isoenzyme DDAH2 towards ADMA and MMA clearance is still a matter of controversy. ADMA, MMA and symmetric dimethylarginine (SDMA) are also metabolized by alanine: glyoxylate aminotransferase 2 (AGXT2), however, in addition to methylarginines, this enzyme also has several cardiovascular protective substrates, so the net effect of possible therapeutic targeting of AGXT2 is currently unclear. Recent studies on regulation and functions of the enzymes metabolizing methylarginines have given a second life to this research direction. Our review discusses the latest discoveries and controversies in the field and proposes novel directions for targeting methylarginines in clinical settings.
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Beta-Aminoisobutyric Acid as a Novel Regulator of Carbohydrate and Lipid Metabolism. Nutrients 2019; 11:nu11030524. [PMID: 30823446 PMCID: PMC6470580 DOI: 10.3390/nu11030524] [Citation(s) in RCA: 69] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2019] [Revised: 02/22/2019] [Accepted: 02/26/2019] [Indexed: 01/04/2023] Open
Abstract
The prevalence and incidence of metabolic syndrome is reaching pandemic proportions worldwide, thus warranting an intensive search for novel preventive and treatment strategies. Recent studies have identified a number of soluble factors secreted by adipocytes and myocytes (adipo-/myokines), which link sedentary life style, abdominal obesity, and impairments in carbohydrate and lipid metabolism. In this review, we discuss the metabolic roles of the recently discovered myokine β-aminoisobutyric acid (BAIBA), which is produced by skeletal muscle during physical activity. In addition to physical activity, the circulating levels of BAIBA are controlled by the mitochondrial enzyme alanine: glyoxylate aminotransferase 2 (AGXT2), which is primarily expressed in the liver and kidneys. Recent studies have shown that BAIBA can protect from diet-induced obesity in animal models. It induces transition of white adipose tissue to a “beige” phenotype, which induces fatty acids oxidation and increases insulin sensitivity. While the exact mechanisms of BAIBA-induced metabolic effects are still not well understood, we discuss some of the proposed pathways. The reviewed data provide new insights into the connection between physical activity and energy metabolism and suggest that BAIBA might be a potential novel drug for treatment of the metabolic syndrome and its cardiovascular complications.
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Burdin DV, Kolobov AA, Brocker C, Soshnev AA, Samusik N, Demyanov AV, Brilloff S, Jarzebska N, Martens-Lobenhoffer J, Mieth M, Maas R, Bornstein SR, Bode-Böger SM, Gonzalez F, Weiss N, Rodionov RN. Diabetes-linked transcription factor HNF4α regulates metabolism of endogenous methylarginines and β-aminoisobutyric acid by controlling expression of alanine-glyoxylate aminotransferase 2. Sci Rep 2016; 6:35503. [PMID: 27752141 PMCID: PMC5067591 DOI: 10.1038/srep35503] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2016] [Accepted: 09/30/2016] [Indexed: 02/07/2023] Open
Abstract
Elevated levels of circulating asymmetric and symmetric dimethylarginines (ADMA and SDMA) predict and potentially contribute to end organ damage in cardiovascular diseases. Alanine-glyoxylate aminotransferase 2 (AGXT2) regulates systemic levels of ADMA and SDMA, and also of beta-aminoisobutyric acid (BAIB)-a modulator of lipid metabolism. We identified a putative binding site for hepatic nuclear factor 4 α (HNF4α) in AGXT2 promoter sequence. In a luciferase reporter assay we found a 75% decrease in activity of Agxt2 core promoter after disruption of the HNF4α binding site. Direct binding of HNF4α to Agxt2 promoter was confirmed by chromatin immunoprecipitation assay. siRNA-mediated knockdown of Hnf4a led to an almost 50% reduction in Agxt2 mRNA levels in Hepa 1–6 cells. Liver-specific Hnf4a knockout mice exhibited a 90% decrease in liver Agxt2 expression and activity, and elevated plasma levels of ADMA, SDMA and BAIB, compared to wild-type littermates. Thus we identified HNF4α as a major regulator of Agxt2 expression. Considering a strong association between human HNF4A polymorphisms and increased risk of type 2 diabetes our current findings suggest that downregulation of AGXT2 and subsequent impairment in metabolism of dimethylarginines and BAIB caused by HNF4α deficiency might contribute to development of cardiovascular complications in diabetic patients.
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Affiliation(s)
- Dmitry V Burdin
- Department of Physiology, Saint Petersburg State University, 199034 Saint Petersburg, Russia
| | - Alexey A Kolobov
- Department of Biochemistry, Saint Petersburg State University, 199034 Saint Petersburg, Russia
| | - Chad Brocker
- National Cancer Institute, NIH, Bethesda, MD, 20892, USA
| | | | - Nikolay Samusik
- Stanford University School of Medicine, Stanford, CA, 94305, USA
| | - Anton V Demyanov
- Institute of Highly Pure Biopreparations, 197110 Saint Petersburg, Russia
| | - Silke Brilloff
- University Center for Vascular Medicine, Technische Universität Dresden, 01307 Dresden, Germany
| | - Natalia Jarzebska
- University Center for Vascular Medicine, Technische Universität Dresden, 01307 Dresden, Germany
| | | | - Maren Mieth
- Institute of Experimental and Clinical Pharmacology and Toxicology, Friedrich-Alexander-University Erlangen-Nürnberg (FAU), 91054 Erlangen, Germany
| | - Renke Maas
- Institute of Experimental and Clinical Pharmacology and Toxicology, Friedrich-Alexander-University Erlangen-Nürnberg (FAU), 91054 Erlangen, Germany
| | - Stefan R Bornstein
- Department of Internal Medicine III, University Hospital Carl Gustav Carus, Technische Universität Dresden, 01307 Dresden, Germany
| | - Stefanie M Bode-Böger
- Institute of Clinical Pharmacology, Otto-von-Guericke University, 39120 Magdeburg, Germany
| | - Frank Gonzalez
- National Cancer Institute, NIH, Bethesda, MD, 20892, USA
| | - Norbert Weiss
- University Center for Vascular Medicine, Technische Universität Dresden, 01307 Dresden, Germany
| | - Roman N Rodionov
- University Center for Vascular Medicine, Technische Universität Dresden, 01307 Dresden, Germany
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Rodionov RN, Jarzebska N, Weiss N, Lentz SR. AGXT2: a promiscuous aminotransferase. Trends Pharmacol Sci 2014; 35:575-82. [PMID: 25294000 DOI: 10.1016/j.tips.2014.09.005] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2014] [Revised: 09/09/2014] [Accepted: 09/11/2014] [Indexed: 12/11/2022]
Abstract
Alanine-glyoxylate aminotransferase 2 (AGXT2) is a multifunctional mitochondrial aminotransferase that was first identified in 1978. The physiological importance of AGXT2 was largely overlooked for three decades because AGXT2 is less active in glyoxylate metabolism than AGXT1, the enzyme that is deficient in primary hyperoxaluria type I. Recently, several novel functions of AGXT2 have been 'rediscovered' in the setting of modern genomic and metabolomic studies. It is now apparent that AGXT2 has multiple substrates and products and that altered AGXT2 activity may contribute to the pathogenesis of cardiovascular, renal, neurological, and hematological diseases. This article reviews the biochemical properties and physiological functions of AGXT2, its unique role at the intersection of key mitochondrial pathways, and its potential as a drug target.
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Affiliation(s)
- Roman N Rodionov
- University Center for Vascular Medicine and Department of Internal Medicine, Division of Angiology, University Hospital 'Carl Gustav Carus', Technische Universität Dresden, Fetscherstrasse 42, 01307 Dresden, Germany
| | - Natalia Jarzebska
- University Hospital 'Carl Gustav Carus', Technische Universität Dresden, Fetscherstrasse 42, 01307 Dresden, Germany
| | - Norbert Weiss
- University Center for Vascular Medicine and Department of Internal Medicine, Division of Angiology, University Hospital 'Carl Gustav Carus', Technische Universität Dresden, Fetscherstrasse 42, 01307 Dresden, Germany
| | - Steven R Lentz
- Department of Internal Medicine, University of Iowa Carver College of Medicine, 200 Hawkins Drive, Iowa City, IA 52242, USA.
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Caplin B, Leiper J. Endogenous nitric oxide synthase inhibitors in the biology of disease: markers, mediators, and regulators? Arterioscler Thromb Vasc Biol 2012; 32:1343-53. [PMID: 22460557 DOI: 10.1161/atvbaha.112.247726] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The asymmetric methylarginines inhibit nitric oxide synthesis in vivo by competing with L-arginine at the active site of nitric oxide synthase. High circulating levels of asymmetric dimethylarginine predict adverse outcomes, specifically vascular events but there is now increasing experimental and epidemiological evidence that these molecules, and the enzymes that regulate this pathway, play a mechanistic role in cardiovascular diseases. Recent data have provided insight into the impact of altered levels of these amino acids in both humans and rodents, however these reports also suggest a simplistic approach based on measuring, and modulating circulating asymmetric dimethylarginine alone is inadequate. This review outlines the basic biochemistry and physiology of endogenous methylarginines, examines both the experimental and observational evidence for a role in disease pathogenesis, and examines the potential for therapeutic regulation of these molecules.
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Affiliation(s)
- Ben Caplin
- Centre for Nephrology, UCL Medical School, Royal Free Campus 2nd Floor, Rowland Hill St, London NW3 2PF.
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Rodionov RN, Murry DJ, Vaulman SF, Stevens JW, Lentz SR. Human alanine-glyoxylate aminotransferase 2 lowers asymmetric dimethylarginine and protects from inhibition of nitric oxide production. J Biol Chem 2009; 285:5385-91. [PMID: 20018850 DOI: 10.1074/jbc.m109.091280] [Citation(s) in RCA: 87] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Elevated blood concentrations of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric-oxide (NO) synthase, are found in association with diabetes, hypertension, congestive heart failure, and atherosclerosis. ADMA levels are controlled by dimethylarginine dimethylaminohydrolases (DDAHs), cytosolic enzymes that hydrolyze ADMA to citrulline and dimethylamine. ADMA also has been proposed to be regulated through an alternative pathway by alanine-glyoxylate aminotransferase 2 (AGXT2), a mitochondrial aminotransferase expressed primarily in the kidney. The goal of this study was to define the subcellular localization of human AGXT2 and test the hypothesis that overexpression of human AGXT2 protects from ADMA-induced inhibition in nitric oxide (NO) production. AGXT2 was cloned from human kidney cDNA and overexpressed in COS-7 cells and human umbilical vein endothelial cells with a C-terminal FLAG epitope tag. Mitochondrial localization of human AGXT2 was demonstrated by confocal microscopy and a 41-amino acid N-terminal mitochondrial cleavage sequence was delineated by N-terminal sequencing of the mature protein. Overexpression of human AGXT2 in the liver of C57BL/6 mice using an adenoviral expression vector produced significant decreases in ADMA levels in plasma and liver. Overexpression of human AGXT2 also protected endothelial cells from ADMA-mediated inhibition of NO production. We conclude that mitochondrially localized human AGXT2 is able to effectively metabolize ADMA in vivo resulting in decreased ADMA levels and improved endothelial NO production.
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Affiliation(s)
- Roman N Rodionov
- Department of Internal Medicine, The University of Iowa Carver College of Medicine, Iowa City, Iowa 52242, USA
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Monico CG, Persson M, Ford GC, Rumsby G, Milliner DS. Potential mechanisms of marked hyperoxaluria not due to primary hyperoxaluria I or II. Kidney Int 2002; 62:392-400. [PMID: 12110000 DOI: 10.1046/j.1523-1755.2002.00468.x] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
BACKGROUND Hyperoxaluria may be idiopathic, secondary, or due to primary hyperoxaluria (PH). Hepatic alanine:glyoxylate aminotransferase (AGT) or glyoxylate/hydroxypyruvate reductase (GR/HPR) deficiency causes PHI or PHII, respectively. Hepatic glycolate oxidase (GO) is a candidate enzyme for a third form of inherited hyperoxaluria. METHODS Six children were identified with marked hyperoxaluria, urolithiasis, and normal hepatic AGT (N = 5) and GR/HPR (N = 4). HPR was below normal and GR not measured in one. Of an affected sibling pair, only one underwent biopsy. GO mutation screening was performed, and dietary oxalate (Diet(ox)), enteric oxalate absorption (EOA) measured using [13C2] oxalate, renal clearance (GFR), fractional oxalate excretion (FE(ox)) in the children, and urine oxalate in first-degree relatives (FDR) to understand the etiology of the hyperoxaluria. RESULTS Mean presenting age was 19.2 months and urine oxalate 1.3 +/- 0.5 mmol/1.73 m2/24 h (mean +/- SD). Two GO sequence changes (T754C, IVS3 - 49 C>G) were detected which were not linked to the hyperoxaluria. Diet(ox) was 42 +/- 31 mg/day. EOA was 9.4 +/- 3.6%, compared with 7.6 +/- 1.2% in age-matched controls (P = 0.33). GFR was 90 +/- 19 mL/min/1.73 m2 and FE(ox) 4.2 +/- 1.4. Aside from the two brothers, hyperoxaluria was not found in FDR. CONCLUSIONS These patients illustrate a novel form of hyperoxaluria and urolithiasis, without excess Diet(ox), enteric hyper-absorption, or hepatic AGT, GR/HPR deficiency. Alterations in pathways of oxalate synthesis, in liver or kidney, or in renal tubular oxalate handling are possible explanations. The affected sibling pair suggests an inherited basis.
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Affiliation(s)
- Carla G Monico
- Division of Nephrology, General Clinical Research Center, Mayo Clinic Rochester, Minnesota 55905, USA.
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