Disability and persistent motor deficits are linked to structural crossed cerebellar diaschisis in chronic stroke.

Brain imaging has significantly contributed to our understanding of the cerebellum being involved in recovery after non-cerebellar stroke. Due to its connections with supratentorial brain networks, acute stroke can alter the function and structure of the contralesional cerebellum, known as crossed cerebellar diaschisis (CCD). Data on the spatially precise distribution of structural CCD and their implications for persistent deficits after stroke are notably limited. In this cross-sectional study, structural MRI and clinical data were analyzed from 32 chronic stroke patients, at least 6 months after the event. We quantified lobule-specific contralesional atrophy, as a surrogate of structural CCD, in patients and healthy controls. Volumetric data were integrated with clinical scores of disability and motor deficits. Diaschisis-outcome models were adjusted for the covariables age, lesion volume, and damage to the corticospinal tract. We found that structural CCD was evident for the whole cerebellum, and particularly for lobules V and VI. Lobule VI diaschisis was significantly correlated with clinical scores, that is, volume reductions in contralesional lobule VI were associated with higher levels of disability and motor deficits. Lobule V and the whole cerebellum did not show similar diaschisis-outcome relationships across the spectrum of the clinical scores. These results provide novel insights into stroke-related cerebellar plasticity and might thereby promote lobule VI as a key area prone to structural CCD and potentially involved in recovery and residual motor functioning.

Developmental dynamics of homoarginine, ADMA and SDMA plasma levels from birth to adolescence.

Guanidino compounds such as dimethylarginines (SDMA, ADMA) and L-homoarginine ((L-)hArg) can interfere with bioavailability and function of the main NO-donor L-arginine (L-Arg). High ADMA and SDMA but low L-hArg concentrations have been associated with cardio- and cerebrovascular events and mortality in adults. The role of guanidino compounds in paediatric patients remains less clear. We, therefore, compared guanidino compound levels in plasma samples of 57 individuals with chronic kidney disease (CKD) and 141 individuals without CKD from the age of 0 to 17 years, including patients with different comorbidities by correlation and regression analyses. We found highest hArg, SDMA and ADMA concentrations in neonates (Kruskal-Wallis, p < 0.001 for all). From the age of 1 year on, hArg levels increased, whereas SDMA und ADMA levels further decreased in children. SDMA and ADMA are higher in children with CKD independent of GFR (mean factor 1.92 and 1.38, respectively, p < 0.001 for both), and SDMA is strongly correlated with creatinine concentration in children with CKD (Spearman's rho 0.74, p < 0.001). We provide guanidino compound levels in a large sample covering all paediatric age groups for the first time. Our data can be used to assess the role of guanidino compounds such as hArg in disease states, i.e. cerebro- and cardiovascular disorders in childhood and adolescence.

Blood neurofilament light chain in Parkinson's disease.

Blood neurofilament light chain (NfL) is an easily accessible, highly sensitive and reliable biomarker for neuroaxonal damage. Currently, its role in Parkinson's disease (PD) remains unclear. Here, we demonstrate that blood NfL can distinguish idiopathic PD from atypical parkinsonian syndromes (APS) with high sensitivity and specificity. In cross-sectional studies, some found significant correlations between blood NfL with motor and cognitive function, whereas others did not. In contrast, prospective studies reported very consistent associations between baseline blood NfL with motor progression and cognitive worsening. Amongst PD subtypes, especially postural instability and gait disorder (PIGD) subtype, symptoms and scores are reliably linked with blood NfL. Different non-motor PD comorbidities have also been associated with high blood NfL levels suggesting that the neuroaxonal damage of the autonomic nervous system as well as serotonergic, cholinergic and noradrenergic neurons is quantifiable. Numerous absolute NfL cutoff levels have been suggested in different cohort studies; however, validation across cohorts remains weak. However, age-adjusted percentiles and intra-individual blood NfL changes might represent more valid and consistent parameters compared with absolute NfL concentrations. In summary, blood NfL has the potential as biomarker in PD patients to be used in clinical practice for prediction of disease severity and especially progression.

The heterogeneity of Parkinson's disease.

The heterogeneity of Parkinson's disease (PD), i.e. the various clinical phenotypes, pathological findings, genetic predispositions and probably also the various implicated pathophysiological pathways pose a major challenge for future research projects and therapeutic trail design. We outline several pathophysiological concepts, pathways and mechanisms, including the presumed roles of α-synuclein misfolding and aggregation, Lewy bodies, oxidative stress, iron and melanin, deficient autophagy processes, insulin and incretin signaling, T-cell autoimmunity, the gut-brain axis and the evidence that microbial (viral) agents may induce molecular hallmarks of neurodegeneration. The hypothesis is discussed, whether PD might indeed be triggered by exogenous (infectious) agents in susceptible individuals upon entry via the olfactory bulb (brain first) or the gut (body-first), which would support the idea that disease mechanisms may change over time. The unresolved heterogeneity of PD may have contributed to the failure of past clinical trials, which attempted to slow the course of PD. We thus conclude that PD patients need personalized therapeutic approaches tailored to specific phenomenological and etiologic subtypes of disease.

Cortical thickness of contralesional cortices positively relates to future outcome after severe stroke.

Imaging studies have evidenced that contralesional cortices are involved in recovery after motor stroke. Cortical thickness (CT) analysis has proven its potential to capture the changes of cortical anatomy, which have been related to recovery and treatment gains under therapy. An open question is whether CT obtained in the acute phase after stroke might inform correlational models to explain outcome variability. Data of 38 severely impaired (median NIH Stroke Scale 9, interquartile range: 6-13) acute stroke patients of 2 independent cohorts were reanalyzed. Structural imaging data were processed via the FreeSurfer pipeline to quantify regional CT of the contralesional hemisphere. Ordinal logistic regression models were fit to relate CT to modified Rankin Scale as an established measure of global disability after 3-6 months, adjusted for the initial deficit, lesion volume, and age. The data show that CT of contralesional cortices, such as the precentral gyrus, the superior frontal sulcus, and temporal and cingulate cortices, positively relates to the outcome after stroke. This work shows that the baseline cortical anatomy of selected contralesional cortices can explain the outcome variability after severe stroke, which further contributes to the concept of structural brain reserve with respect to contralesional cortices to promote recovery.

Combined Short-Pulse and Directional Deep Brain Stimulation of the Thalamic Ventral Intermediate Area for Essential Tremor.

OBJECTIVE: Novel deep brain stimulation (DBS) systems allow directional and short-pulse stimulation to potentially improve symptoms and reduce side effects. The aim of this study was to investigate the effect of short-pulse and directional stimulation, in addition to a combination of both, in the ventral intermediate thalamus (VIM)/posterior subthalamic area (PSA) on tremor and stimulation-induced side effects in patients with essential tremor. MATERIALS AND METHODS: We recruited 11 patients with essential tremor and VIM/PSA-DBS. Tremor severity (Fahn-Tolosa-Marin), ataxia (International Cooperative Ataxia Rating Scale), and paresthesia (visual analog scale) were assessed with conventional omnidirectional and directional stimulation with pulse width of 60 µs and 30 µs. RESULTS: All stimulation conditions reduced tremor. The best directional stimulation with 60 µs reduced more tremor than did most other stimulation settings. The best directional stimulation, regardless of pulse width, effectively reduced stimulation-induced ataxia compared with the conventional stimulation (ring 60 µs) or worst directional stimulation with 60 µs. All new stimulation modes reduced occurrence of paresthesia, but only the best directional stimulation with 30 µs attenuated paresthesia compared with the conventional stimulation (ring 60 µs) or worst directional stimulation with 60 µs. The best directional stimulation with 30 µs reduced tremor, ataxia, and paresthesia compared with conventional stimulation in most patients. Correlation analyses indicated that more anterior stimulation sites are associated with stronger ataxia reduction with directional 30 µs than with conventional 60 µs stimulation. CONCLUSION: Directional and short-pulse stimulation, and a combination of both, revealed beneficial effects on stimulation-induced adverse effects.

Diabetes, Glycated Hemoglobin (HbA1c), and Neuroaxonal Damage in Parkinson's Disease (MARK-PD Study).

BACKGROUND: Diabetes is associated with incidence and prevalence of Parkinson's disease (PD). Furthermore, glycated hemoglobin (HbA1c) levels have been linked with motor function and progression. OBJECTIVES: We evaluated the relationship between prevalent diabetes and HbA1c levels with serum neurofilament light chain (NfL) levels as marker of neuroaxonal damage. METHODS: NfL concentrations were analyzed with Simoa in serum of 195 PD patients with available HbA1c values. Motor (MDS-UPDRS III, Hoehn & Yahr [H&Y]) and cognitive (Montreal Cognitive Assessment [MoCA]) function was assessed and vascular comorbidities were documented from medical records. RESULTS: PD patients with prevalent diabetes had higher serum NfL levels and lower MoCA scores independent of age, body mass index (BMI), and vascular risk factors. Furthermore, diabetes was associated with higher H&Y stages in unadjusted and age/BMI-adjusted models. Higher HbA1c levels were associated with increased NfL in unadjusted and age/BMI-adjusted models. CONCLUSIONS: In PD patients, diabetes and high HbA1c are associated with increased neuroaxonal damage and cognitive impairment. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson Movement Disorder Society.

Population kinetics of homoarginine and optimized supplementation for cardiovascular risk reduction.

Homoarginine is an endogenous amino acid whose levels are reduced in patients with renal, cardio- and cerebrovascular disease. Moreover, low homoarginine concentrations independently predict morbidity and mortality in these patients. Besides endogenous synthesis, homoarginine is also a constituent of the human diet. The objective of the present study was to analyze the kinetics of orally supplemented homoarginine in human plasma by means of a pharmacometric approach. We developed a pharmacometric model to evaluate different dosing regimens, especially the regimen of 125 mg once weekly, based on a previous clinical study (n = 20). The model was adapted to account for differences in baseline homoarginine plasma concentrations between healthy and diseased individuals. A novel dosing regimen of 25 mg once daily led to higher attainment of homoarginine reference concentrations using clinical trial simulations. With 25 mg/day, the trough concentration of only 6% of the older and 3.8% of the younger population was predicted to be below the target concentration of 2.0-4.1 µmol/L. In synopsis, the new dosing regimen recapitulates the kinetics of homoarginine in healthy individuals optimally.

Serum neurofilament light chain and postural instability/gait difficulty (PIGD) subtypes of Parkinson's disease in the MARK-PD study.

The PIGD (postural instability / gait difficulty) subtype of Parkinson´s disease (PD) is associated with faster cognitive and motor decline. So far, there are no quantifiable biomarkers to aid clinical subtyping. Neurofilament light chain (NfL) is a highly specific marker of neuro-axonal damage and can be assessed in blood. Here, we investigated if serum NfL concentrations are associated with PIGD subtype and PIGD scores in PD patients at advanced disease stages. Furthermore, we evaluated if serum NfL is associated with motor and cognitive function assessed with MDS-UPDRS part III and Montreal cognitive assessment (MoCA). Serum NfL levels were analyzed with Single Molecule Assays (Simoa) in blood of 223 PD patients from the bioMARKers in Parkinson's Disease (MARK-PD) study. Serum NfL concentrations were higher in PIGD patients independent of age, sex and disease duration. In linear regression analysis, serum NfL levels were associated with MoCA, MDS-UPDRS III and PIGD scores in unadjusted models, but remained significant after adjustment only with PIGD scores. In conclusion, increased serum NfL levels were associated with PIGD subtype and PIGD scores in patients with advanced PD.

Serum Sphingosine-1-Phosphate Levels Are Associated With Severity and Outcome in Patients With Cerebral Ischemia.

BACKGROUND AND PURPOSE: The aim of this study was to examine whether sphingosine-1-phosphate (S1P) levels in patients with acute stroke are associated with stroke severity and outcome. METHODS: In a prospective stroke cohort (MARK-STROKE), 374 patients with acute ischemic stroke or transient ischemic attack were enrolled (mean age: 67.9±13.0 years, sex: 64.7% male), and serum-S1P at admission was analyzed with tandem mass spectrometry. In addition to cross-sectional analyses, 79 adverse events (death, stroke, myocardial infarction, rehospitalization) were recorded in 270 patients during follow-up. Regression analyses were adjusted for age, sex, low-density lipoprotein cholesterol, and vascular risk factors. Results were validated in an independent stroke cohort with 219 patients with acute ischemic stroke (CIRCULAS). RESULTS: Low serum-S1P was associated with higher National Institutes of Health Stroke Scale score at admission and with anterior circulation nonlacunar infarcts determined by multivariate regression analyses. During a follow-up of 294±170 days, patients with S1P in the lowest tertile (<1.33 µmol/L) had more adverse events (Kaplan-Meier analysis, P=0.048 for trend). In adjusted Cox regression analysis, the lowest S1P tertile was associated with a worse outcome after stroke (hazard ratio, HR 0.51 [95% confidence interval 0.28-0.92]). Results were confirmed in an independent cohort, ie, low S1P levels were associated with higher National Institutes of Health Stroke Scale, larger infarct volumes and worse outcome after 90 days (ß-coefficient: -0.03, P=0.026; ß-coefficient: -0.099, P=0.009 and odds ratio 0.52 [0.28-0.96], respectively). CONCLUSIONS: Our findings imply a detrimental role of low S1P levels in acute stroke and therefore underpin the therapeutic potential of S1P-mimics.

Sphingosine-1-Phosphate, Motor Severity, and Progression in Parkinson's Disease (MARK-PD).

BACKGROUND: Treatment with sphingosine-1-phosphate (S1P) agonists confers neuroprotective effects in animal models of Parkinson's disease (PD). OBJECTIVES: We assessed the association of serum S1P levels with motor and cognitive symptoms in patients with PD. METHODS: S1P concentrations were analyzed with liquid chromatography-tandem mass spectrometry (LC-MS/MS) in serum of 196 PD patients and in 196 age- and sex-matched controls. Motor (Unified Parkinson's disease rating scale III [UPDRS III], Hoehn and Yahr) and cognitive (Montreal Cognitive Assessment [MoCA]) function were assessed at baseline. Follow-up data was available from 64 patients (median [interquartile range], 513 [381-677] days). RESULTS: S1P levels were lower in PD patients compared with controls, that is 1.75 (1.38-2.07) and 1.90 (1.59-2.18) µmol/L, respectively (P = 0.001). In PD patients, lower S1P concentrations were associated with higher UPDRS III scores and Hoehn and Yahr stage. In the follow-up cohort, S1P concentrations below the median were associated with faster motor decline (hazard ratio: 4.78 [95% CI, 1.98, 11.50]), but not with cognitive worsening. CONCLUSIONS: Our observations reveal an association of S1P with PD. © 2021 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Trimethyllysine, vascular risk factors and outcome in acute ischemic stroke (MARK-STROKE).

Trimethyllysine (TML) is involved in the generation of the pro-atherogenic metabolite trimethylamine-N-oxide (TMAO) by gut microbiota. In clinical studies, elevated TML levels predicted major adverse cardiovascular events (MACE) in patients with acute or stable coronary artery disease (CAD). In contrast to cardiovascular patients, the role of TML in patients with acute cerebral ischemia is unknown. Here, we evaluated circulating TML levels in 374 stroke patients from the prospective biomarkers in stroke (MARK-STROKE) study. Compared with 167 matched healthy controls, acute ischemic stroke patients had lower median TML plasma concentrations, i.e. 0.71 vs. 0.47 µmol/L (p < 0.001) and this difference persisted after adjusting for age and sex. TML plasma concentrations were associated with age, serum creatinine, glucose, cholesterol and lysine. Patients with prevalent arterial hypertension, atrial fibrillation or a history of myocardial infarction had increased TML levels, but this observation was not independent of age, sex and GFR. In 274 patients, follow-up data were available. During a median follow-up of 284 [25th-75th percentile: 198, 431] days, TML was not associated with incident MACE (stroke, myocardial infarction, death). In summary, our data suggests a different role of TML in acute ischemic stroke compared with CAD patients.

Subclinical Cardiac Microdamage, Motor Severity, and Cognition in Parkinson's Disease.

BACKGROUND: We assessed if cardiac blood markers are associated with motor and cognitive function in patients with Parkinson's disease (PD). METHODS: High-sensitivity troponin I and N-terminal pro-B-type natriuretic peptide (NT-proBNP) were evaluated in 285 PD patients. Furthermore, N-terminal pro-B-type natriuretic peptide levels were analyzed in 570 age, sex and cardiovascular risk factor matched healthy controls. Motor (UPDRS, Hoehn &Yahr) and cognitive function (Montreal Cognitive Assessemtn) were assessed at baseline in all 285 patients and after 1 year in 101 patients. RESULTS: N-terminal pro-B-type natriuretic peptide were significantly increased in 285 PD patients compared with 570 matched healthy controls. In PD patients, increased high-sensitivity troponin I and N-terminal pro-B-type natriuretic peptide levels were associated with worse motor function at baseline and also with motor decline after 1 year. N-terminal pro-B-type natriuretic peptide and high-sensitivity troponin I were inversely associated with cognitive function at baseline only in unadjusted models. CONCLUSIONS: Subclinical cardiac microdamage is associated with motor severity in PD patients. © 2020 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.

Creatine, guanidinoacetate and homoarginine in statin-induced myopathy.

Our study evaluated the effect of creatine and homoarginine in AGAT- and GAMT-deficient mice after simvastatin exposure. Balestrino and Adriano suggest that guanidinoacetate might explain the difference between AGAT- and GAMT-deficient mice in simvastatin-induced myopathy. We agree with Balestrino and Adriano that our data shows that (1) creatine possesses a protective potential to ameliorate statin-induced myopathy in humans and mice and (2) homoarginine did not reveal a beneficial effect in statin-induced myopathy. Third, we agree that guanidinoacetate can be phosphorylated and partially compensate for phosphocreatine. In our study, simvastatin-induced damage showed a trend to be less pronounced in GAMT-deficient mice compared with wildtype mice. Therefore, (phospo) guanidinoacetate cannot completely explain the milder phenotype of GAMT-deficient mice, but we agree that it might contribute to ameliorate statin-induced myopathy in GAMT-deficient mice compared with AGAT-deficient mice. Finally, we agree with Balestino and Adriano that AGAT metabolites should further be evaluated as potential treatments in statin-induced myopathy.

Muscle phenotype of AGAT- and GAMT-deficient mice after simvastatin exposure.

Statin-induced myopathy affects more than 10 million people worldwide. But discontinuation of statin treatment increases mortality and cardiovascular events. Recently, L-arginine:glycine amidinotransferase (AGAT) gene was associated with statin-induced myopathy in two populations, but the causal link is still unclear. AGAT is responsible for the synthesis of L-homoarginine (hArg) and guanidinoacetate (GAA). GAA is further methylated to creatine (Cr) by guanidinoacetate methyltransferase (GAMT). In cerebrovascular patients treated with statin, lower hArg and GAA plasma concentrations were found than in non-statin patients, indicating suppressed AGAT expression and/or activity (n = 272, P = 0.033 and P = 0.039, respectively). This observation suggests that statin-induced myopathy may be associated with AGAT expression and/or activity in muscle cells. To address this, we studied simvastatin-induced myopathy in AGAT- and GAMT-deficient mice. We found that simvastatin induced muscle damage and reduced AGAT expression in wildtype mice (myocyte diameter: 34.1 ± 1.3 µm vs 21.5 ± 1.3 µm, P = 0.026; AGAT expression: 1.0 ± 0.3 vs 0.48 ± 0.05, P = 0.017). Increasing AGAT expression levels of transgenic mouse models resulted in rising plasma levels of hArg and GAA (P < 0.01 and P < 0.001, respectively). Simvastatin-induced motor impairment was exacerbated in AGAT-deficient mice compared with AGAT-overexpressing GAMT-/- mice and therefore revealed an effect independent of Cr. But Cr supplementation itself improved muscle strength independent of AGAT expression (normalized grip strength: 55.8 ± 2.9% vs 72.5% ± 3.0%, P < 0.01). Homoarginine supplementation did not affect statin-induced myopathy in AGAT-deficient mice. Our results from clinical and animal studies suggest that AGAT expression/activity and its product Cr influence statin-induced myopathy independent of each other. The interplay between simvastatin treatment, AGAT expression and activity, and Cr seems to be complex. Further clinical pharmacological studies are needed to elucidate the underlying mechanism(s) and to evaluate whether supplementation with Cr, or possibly GAA, in patients under statin medication may reduce the risk of muscular side effects.

Major central nervous system complications after allogeneic stem cell transplantation: A large retrospective study on 888 consecutive adult patients.

OBJECTIVES: Major complications affecting the central nervous system (CNS) present a challenge after allogeneic stem cell transplantation (allo-SCT). METHODS: Incidence, risk factors, and outcome were retrospectively analyzed in 888 patients in a monocentric study. RESULTS: Cumulative incidence (CI) of major CNS complications at 1 year was 14.8% (95%CI 12.3%-17.2%). Median follow-up is 11 months. CNS complications were documented in 132 patients: in 36 cases, classified metabolic; 26, drug-related neurotoxicity (14 attributed to cyclosporine A, 4 to antilymphocyte globulin); 11, cerebrovascular (ischemic n = 8, bleeding n = 3); 9, infections; 9, psychiatric; and 9, malignant. The cause of CNS symptoms remained unclear for 37 patients (28%). Multivariate analysis demonstrated an association of CNS complication with patient age (P < .001). The estimated OS of patients with any CNS complication was significantly lower than in patients without neurological complications (P < .001), and the CI of non-relapse mortality (NRM) was higher for patients with CNS complication (P < .001). A significant negative impact on survival can only be demonstrated for metabolic CNS complications and CNS infections (NRM, P < .0001 and P = .0003, respectively), and relapse (P < .0001). CONCLUSION: CNS complications after allo-SCT are frequent events with a major contribution to morbidity and mortality. In particular, the situations of unclear neurological complications need to be clarified by intensive research.

Low homoarginine/SDMA ratio is associated with poor short- and long-term outcome after stroke in two prospective studies.

BACKGROUND: Guanidino compounds, including asymmetric dimethylarginine (ADMA), symmetric dimethylarginine (SDMA), and L-homoarginine (hArg), have been associated with cardio- and cerebrovascular events and risk. We aimed to study if low hArg/ADMA and hArg/SDMA ratios are associated with mortality and outcome after stroke. METHODS: In two prospective cohorts of acute stroke patients from Germany and the UK, we analyzed hArg, ADMA, and SDMA to determine hArg/ADMA and hArg/SDMA ratios. The guanidino compound levels were associated with mortality, adverse events, and neurological impairment, i.e., National Institutes of Health Stroke Scale (NIHSS) and modified Rankin Scale (mRS). RESULTS: During 7.4 years, high hArg/ADMA and hArg/SDMA ratios were both associated with a reduction in all-cause mortality in patients with ischemic stroke in a UK stroke cohort (hArg/ADMA: hazard ratio (HR) 0.75 [95% confidence interval (CI) 0.62-0.92]; n = 394; P = 0.006; hArg/SDMA: HR 0.68 [0.54-0.85]; n = 394; P = 0.001). In a German stroke cohort, patients with high hArg/SDMA ratio experienced fewer adverse events compared with those with low hArg/SDMA ratios within 30 days after stroke (HR 0.73 [0.57-0.92]; n = 135; P = 0.009), whereas hArg/ADMA was not predictive. Furthermore, hArg/SDMA ratios inversely correlated with the degree of neurological impairment (NIHSS) (r = - 0.27; P = 0.001; n = 138). Lower hArg/SDMA ratios were also found in dependent (mRS 3-6) compared with independent patients (mRS < 3; P = 0.007; n = 138), whereas hArg/ADMA did not. CONCLUSION: These results from two prospective stroke studies reveal that hArg/SDMA ratio could prove a valuable blood-based biomarker to discriminate patients with poor short- and long-term outcome, increased neurological impairment, and severe disability after stroke.

Arginine Derivatives in Cerebrovascular Diseases: Mechanisms and Clinical Implications.

The amino acid L-arginine serves as substrate for the nitric oxide synthase which is crucial in vascular function and disease. Derivatives of arginine, such as asymmetric (ADMA) and symmetric dimethylarginine (SDMA), are regarded as markers of endothelial dysfunction and have been implicated in vascular disorders. While there is a variety of studies consolidating ADMA as biomarker of cerebrovascular risk, morbidity and mortality, SDMA is currently emerging as an interesting metabolite with distinct characteristics in ischemic stroke. In contrast to dimethylarginines, homoarginine is inversely associated with adverse events and mortality in cerebrovascular diseases and might constitute a modifiable protective risk factor. This review aims to provide an overview of the current evidence for the pathophysiological role of arginine derivatives in cerebrovascular ischemic diseases. We discuss the complex mechanisms of arginine metabolism in health and disease and its potential clinical implications in diverse aspects of ischemic stroke.

Homoarginine- and Creatine-Dependent Gene Regulation in Murine Brains with l-Arginine:Glycine Amidinotransferase Deficiency.

l-arginine:glycine amidinotransferase (AGAT) and its metabolites homoarginine (hArg) and creatine have been linked to stroke pathology in both human and mouse studies. However, a comprehensive understanding of the underlying molecular mechanism is lacking. To investigate transcriptional changes in cerebral AGAT metabolism, we applied a transcriptome analysis in brains of wild-type (WT) mice compared to untreated AGAT-deficient (AGAT-/-) mice and AGAT-/- mice with creatine or hArg supplementation. We identified significantly regulated genes between AGAT-/- and WT mice in two independent cohorts of mice which can be linked to amino acid metabolism (Ivd, Lcmt2), creatine metabolism (Slc6a8), cerebral myelination (Bcas1) and neuronal excitability (Kcnip3). While Ivd and Kcnip3 showed regulation by hArg supplementation, Bcas1 and Slc6a8 were creatine dependent. Additional regulated genes such as Pla2g4e and Exd1 need further evaluation of their influence on cerebral function. Experimental stroke models showed a significant regulation of Bcas1 and Slc6a8. Together, these results reveal that AGAT deficiency, hArg and creatine regulate gene expression in the brain, which may be critical in stroke pathology.

Evidence by GC-MS that lysine is an arginase-catalyzed metabolite of homoarginine in vitro and in vivo in humans.

l-Homoarginine (hArg) is biosynthesized from l-arginine (Arg) and l-lysine (Lys) by arginine:glycine amidinotransferase (AGAT). AGAT also catalyzes the formation of guanidinoacetate (GAA) from Arg and glycine (Gly). GAA is converted to creatine (N-methyl guanidinoacetate) by guanidinoacetate N-methyl-transferase (GAMT). Low circulating and excretory concentrations of hArg are associated with worse cardiovascular outcome and mortality. hArg is a poor substrate of nitric oxide synthase (NOS) and a weak inhibitor of arginase. The metabolism of hArg in humans is little investigated. Previously, we found that orally administered hArg (125 mg/day) increased the plasma concentration of hArg, but not of Arg, the substrate of NOS, in healthy subjects. We newly analyzed the plasma samples collected in that study for Lys and other amino acids. Repeated measures ANOVA revealed statistically significant differences between the groups (P = 0.008) with respect to plasma Lys concentration which increased by about 8% after a 4-week hArg supplementation. In vitro, recombinant human arginase and bovine liver arginase I were demonstrated by a specific and sensitive stable-isotope GC-MS assay to hydrolyze hArg to Lys. Our results suggest that Lys is a metabolite of hArg produced by the hydrolytic activity of arginase. Arginase may play a key role in hArg homeostasis in humans.