Las concentraciones de glutamina y citrulina reflejan la síntesis del óxido nítrico en el sistema nervioso humano / Glutamine and citrulline concentrations reflect nitric oxide synthesis in the human nervous system

INTRODUCCIÓN: Aunque la citrulina es producida por la sintasa del óxido nítrico (NO) al activarse el receptor glutamatérgico NMDA, nitritos y nitratos (NOx) son considerados los mejores marcadores de síntesis del NO pues citrulina es también metabolizada por otras enzimas. En este estudio se realizó un análisis de correlaciones de concentraciones de citrulina y NOx en líquido cefalorraquídeo humano para evaluar la proporción en que la citrulina refleja la síntesis del NO y la neurotransmisión glutamatérgica. MÉTODOS: Se incluyeron pacientes con trastornos neurológicos agudos a los que se realizó punción lumbar (n = 240). Se determinó la concentración de NOx y aminoácidos por HPLC. RESULTADOS: NOx no fue diferente por la presencia de infección (p = 0,110) o inflamación (p = 0,349). La regresión múltiple mostró que NOx correlacionó con glutamina (r = -0,319, p < 0,001) y citrulina (r = 0,293, p = 0,005) pero no con el cociente citrulina/arginina (r = -0,160, p = 0,173). El ANCOVA confirmó que NOx está asociado con citrulina (F = 7,6, p = 0,007) pero no con el cociente citrulina/arginina (F = 2,2; p = 0,136), ni con la infección (F = 1,8; p = 0,173) o la inflamación (F = 1,4; p = 0,227). NOx no correlacionó con arginina ni con glutamato. CONCLUSIONES: Esto sugiere que citrulina refleja parte de la síntesis del NO a pesar de la contribución de otras vías metabólicas. Además, este estudio muestra que la glutamina es un modulador importante de la actividad de la NOS, y que arginina y glutamato no correlacionan con la concentración de NOx

INTRODUCTION: Although citrulline is produced by nitric oxide (NO) synthase upon activation of the NMDA glutamate receptor, nitrite and nitrate (NOx) concentration is considered the best marker of NO synthesis, as citrulline is also metabolised by other enzymes. This study analyses the correlation between human cerebrospinal fluid NOx and citrulline concentrations in order to determine the extent to which citrulline reflects NO synthesis and glutamatergic neurotransmission. METHODS: Participants were patients with acute neurological diseases undergoing lumbar puncture (n = 240). NOx and amino acid concentrations were determined by HPLC. RESULTS: NOx concentrations did not vary significantly where infection (p = 0,110) or inflammation (p = 0,349) were present. Multiple regression analysis showed that NOx concentration was correlated with glutamine (r = -0,319, p < 0,001) and citrulline concentrations (r = 0,293, p = 0,005) but not with the citrulline/arginine ratio (r = -0,160, p = 0,173). ANCOVA confirmed that NOx concentration was correlated with citrulline concentration (F = 7,6, p = 0,007) but not with the citrulline/arginine ratio (F = 2,2, p = 0,136), or presence of infection (F=1,8, p = 0,173) or inflammation (F = 1,4, p = 0,227). No association was found between NOx and arginine or glutamate concentrations. CONCLUSION: The results suggest that CSF citrulline concentration reflects NOx synthesis to some extent, despite the contribution of other metabolic pathways. In addition, this study shows that glutamine is an important modulator of NO synthase activity, and that arginine and glutamate are not correlated with NOx

Glutamine and citrulline concentrations reflect nitric oxide synthesis in the human nervous system. / Las concentraciones de glutamina y citrulina reflejan la síntesis del óxido nítrico en el sistema nervioso humano.

INTRODUCTION: Although citrulline is produced by nitric oxide (NO) synthase upon activation of the NMDA glutamate receptor, nitrite and nitrate (NOx) concentration is considered the best marker of NO synthesis, as citrulline is also metabolised by other enzymes. This study analyses the correlation between human cerebrospinal fluid NOx and citrulline concentrations in order to determine the extent to which citrulline reflects NO synthesis and glutamatergic neurotransmission. METHODS: Participants were patients with acute neurological diseases undergoing lumbar puncture (n=240). NOx and amino acid concentrations were determined by HPLC. RESULTS: NOx concentrations did not vary significantly where infection (p=0,110) or inflammation (p=0,349) were present. Multiple regression analysis showed that NOx concentration was correlated with glutamine (r=-0,319, p<0,001) and citrulline concentrations (r=0,293, p=0,005) but not with the citrulline/arginine ratio (r=-0,160, p=0,173). ANCOVA confirmed that NOx concentration was correlated with citrulline concentration (F=7,6, p=0,007) but not with the citrulline/arginine ratio (F=2,2, p=0,136), or presence of infection (F=1,8, p=0,173) or inflammation (F=1,4, p=0,227). No association was found between NOx and arginine or glutamate concentrations. CONCLUSION: The results suggest that CSF citrulline concentration reflects NOx synthesis to some extent, despite the contribution of other metabolic pathways. In addition, this study shows that glutamine is an important modulator of NO synthase activity, and that arginine and glutamate are not correlated with NOx.

Dexamethasone significantly attenuates sub-arachnoid hemorrhage-induced elevation in cerebrospinal fluid citrulline and leukocytes.

AIM: Cerebral vasospasm is a leading cause of death and disability following aneurysmal subarachnoid hemorrhage (SAH). Nitric oxide (NO) is a potent mediator of vasodilation, and citrulline is a known contributor to NO production. The leukocytosis inflammatory response can increase vasoconstrictive compounds that may also contribute to vasospasm. Dexamethasone is a glucocorticosteroid commonly administered after SAH, which may alter the production of leukocytes and citrulline. The goal of this project was to study the effects of dexamethasone on leukocytosis, citrulline, and angiographic vasospasm. METHODS: Experimental SAH was induced in 18 New Zealand white rabbits. Intravenous dexamethasone was administered to one group (N.=9) at 2 mg/kg/day. A placebo group (N.=9) was given a saline infusion with otherwise identical procedures. CSF citrulline, leukocytes, protein, and glucose, as well as plasma citrulline were measured at baseline and 3 days post-SAH in a blinded fashion. Basilar artery angiography was performed at baseline and repeated 3 days post-SAH. RESULTS: The change in CSF citrulline from day 0 to day 3 was significantly lower in the dexamethasone group compared to controls (P=0.002). The change in CSF white blood cells was also significantly lower (P=0.005). There was no significant change in plasma citrulline levels or angiographic vasospasm. CONCLUSION: Dexamethasone significantly decreases CSF citrulline and CSF leukocytosis after experimental SAH. It is possible this could lead to a relative vasoconstriction and vasodilation, respectively. These processes could cancel-out opposing effects of dexamethasone on cerebral vasospasm, partially contributing to the recognized, multifactorial, inconsistent effects of glucocorticoids on vasospasm.

Unrecognized citrullinemia mimicking encephalitis in a 14-year-old boy: unexpected result through the use of a standardized lumbar puncture protocol.

Citrullinemia is a urea cycle disorder caused by deficiency of argininosuccinate synthetase. Late onset forms can remain undiscovered until a decompensation that can resemble encephalitis. Herein, we report a 14-year old patient with suspected encephalitis with fluctuating episodes of confusion. EEG mainly showed bilateral slowing with some spikes plus spike waves; and was interpreted as suspicious for encephalitis. Brain MRI was normal. Leukocytes in CSF were slightly elevated. Treatment for a CNS infectious disease was begun. Symptoms did not resolve and there were several episodes of confusion, so a repeat lumbar puncture was performed according to a standardized protocol including an amino acid profile. An elevation of citrulline in CSF was found, which ultimately led to the diagnosis of a late onset citrullinemia. The establishment of this diagnosis will protect the patient from the sequelae of unrecognized and thus untreated episodes of hyperammonemia. Thus, following a standardized lumbar puncture protocol can be essential to detect patients with otherwise unrecognized underlying metabolic disorders that are not suspected because of clinical symptoms. In addition, it is important to stress that an ammonia concentration should be determined in any patient with neurological signs like confusion.

Association of an endogenous inhibitor of nitric oxide synthase with cerebral vasospasm in patients with aneurysmal subarachnoid hemorrhage.

OBJECT: Delayed cerebral vasospasm after subarachnoid hemorrhage (SAH) may be evoked by the decreased availability of nitric oxide (NO). Increased cerebrospinal fluid (CSF) levels of asymmetric dimethyl-L-arginine (ADMA), an endogenous inhibitor of NO synthase (NOS), have been associated with the course and degree of cerebral vasospasm in a primate model of SAH. In this study, the authors sought to determine if similar changes in CSF ADMA levels are observed in patients with SAH, and whether these changes are associated with NO and NOS metabolite levels in the CSF and the presence of cerebral vasospasm. METHODS: Asymmetric dimethyl-L-arginine, L-arginine, L-citrulline, and nitrite levels were measured in CSF and serum samples collected during the 21-day period after a single aneurysmal SAH in 18 consecutive patients. Samples were also obtained in a control group consisting of seven patients with Chiari malformation Type I and five patients with spontaneous intracerebral hemorrhage without SAH. Vasospasm, defined as a greater than 11% reduction in the anterior circulation vessel diameter ratio compared with the ratio calculated from the initial arteriogram, was assessed on cerebral arteriography performed around Day 7. RESULTS: In 13 patients with SAH, arteriographic cerebral vasospasm developed. Cerebrospinal fluid ADMA levels in patients with SAH were higher than in those in the control group (p < 0.001). The CSF ADMA level remained unchanged in the five patients with SAH without vasospasm, but was significantly increased in patients with vasospasm after Day 3 (6.2 +/- 1.7 microM) peaking during Days 7 through 9 (13.3 +/- 6.7 microM; p < 0.001) and then gradually decreasing between Days 12 and 21 (8.8 +/- 3.2 microM; p < 0.05). Nitrite levels in the CSF were lower in patients with vasospasm compared to patients without vasospasm (p < 0.03). Cerebrospinal fluid ADMA levels positively correlated with the degree of vasospasm (correlation coefficient [CC] = 0.88, p = 0.0001; 95% confidence interval [CI] 0.74-0.95) and negatively correlated with CSF nitrite levels (CC = -0.55; p = 0.017; 95% CI -0.81 to -0.12). CONCLUSIONS: These results support the hypothesis that ADMA is involved in the progression of cerebral vasospasm. Asymmetric dimethyl-L-arginine and its metabolizing enzymes may be a future target for treatment of cerebral vasospasm after SAH.

Arginine, citrulline and nitrate concentrations in the cerebrospinal fluid from patients with acute hydrocephalus.

Citrulline and nitric oxide (NO) are synthesized by NO synthase (NOS) in a 1:1-stoichiometry. In this study, we determined by HPLC arginine and citrulline concentrations by fluorescence detection and nitrate levels by UV absorbance detection in the cerebrospinal fluid (CSF) from patients with acute hydrocephalus that underwent ventricular drainage. We found increased citrulline concentration (50.6+/-17.2 versus 20.9+/-2.0 microM) and decreased arginine/citrulline molar ratio (0.42+/-0.11 versus 1.12+/-0.16) in hydrocephalus patients, while arginine and nitrate concentrations and citrulline/nitrate molar ratio remained with little change. Citrulline has been determined as a marker of NOS activity in some studies, but it remains to be determined the extent at which this statement holds true, since other biochemical pathways also regulate the concentration of this amino acid. Our results suggest that citrulline is primarily synthesized from NOS in acute hydrocephalus. The evaluation of sample deproteinization by addition of methanol for the analysis of amino acids in CSF is also reported.

Cerebrospinal fluid and plasma concentrations of nitric oxide metabolites are increased in dementia with Lewy bodies.

We compared cerebrospinal fluid (CSF) and plasma concentrations of nitric oxide metabolites (NO(-)(x)) in 22 patients with dementia with Lewy bodies (DLB) and 13 matched controls. We found a pronounced increase in NO(-)(x) CSF and plasma levels in DLB patients. No changes were found in L-arginine and L-citrulline levels in CSF or plasma. There was no correlation between CSF and plasma levels and age, age of onset, duration of the disease or scores of the MiniMental State Examination. These findings reveal that excessive nitric oxide production may be related to the pathogenesis of DLB.

L-glutamate, L-arginine and L-citrulline levels in cerebrospinal fluid of Parkinson's disease, multiple system atrophy, and Alzheimer's disease patients.

Alterations in neuronal nitric oxide (NO) production may play a role in the pathophysiology of Parkinson's disease (PD) Alzheimer's disease (AD), and multiple system atrophy (MSA). The biosynthesis of NO is dependent on the availability of L-arginine, the substrate for NO-synthase (NOS), and on L-glutamate, which stimulates NO synthesis via the NMDA receptor. In this process L-citrulline is formed. We measured the levels of these amino acids in cerebrospinal fluid (CSF) of 108 PD patients, 12 AD patients, 15 MSA patients and 21 healthy subjects. A slight but statistically significant elevation of CSF L-citrulline was found in MSA patients, while CSF L-glutamate was found to be significantly decreased in AD patients. We found no significant changes in L-arginine levels. Although the relation between the CSF levels of these amino acids and neuronal NO production is still unclear, our findings suggest that AD is associated with a decrease in NO synthesis.

Vasodilation by intrathecal lipopolysaccharide of the cerebral arteries after subarachnoid haemorrhage in dogs.

To investigate the influence of inducible nitric oxide synthase on cerebral arteries after subarachnoid haemorrhage (SAH) in vivo, lipopolysaccharide (LPS), a major inducer of inducible nitric oxide synthase, was injected intracisternally into control and SAH model dogs. Intracisternal injection of LPS (0.5 mg) produced a long-lasting, submaximal vasodilation of the basilar artery of control dogs on angiography. This effect became significant at 4 hours after LPS injection and plateaued after 6 hours. This vasodilation was reduced by N(G)-monomethyl-L-arginine. Vasopressin slightly suppressed the vasodilation, while bradykinin increased it. The concentration of L-arginine in CSF decreased after LPS injection, while that of L-citrulline increased. In cytokines, the concentration of tumour necrosis factor-alpha; (TNF-alpha;) in CSF increased transiently at 4 hours after LPS injection, while interleukin-1 beta, interleukin-6, interferon-gamma, did not change. These data suggest that vasodilation by LPS is mainly due to nitric oxide predominantly synthesized by an inducible nitric oxide synthase, proximally induced by TNF-alpha. Our data make it unlikely that SAH itself induces the inducible nitric oxide synthase in vascular tissue, since isolated endothelium-denuded basilar artery from SAH model dogs did not respond to L-arginine. In SAH model dogs, the degree of vasodilation by LPS differed with the severity of vasospasm. Vasodilation was much greater in mild than in severe vasospasm in dogs, and was increased by superoxide dismutase. These findings suggest that the induction of inducible nitric oxide synthase or its activity may be less effective in severe vasospasm.

Bovine citrullinaemia: a clinical, pathological, biochemical and genetic study.

Calves affected with citrullinaemia are clinically normal immediately after birth. In the majority of calves the clinical course of the disease was similar. Within 24 hours of birth they become depressed; then within 3 to 4 days were observed to wander aimlessly or stand with their head pressed against a wall or fence. By day 4 to 5 they become recumbent, developed convulsions, followed by collapse and death. Oedema of the cerebral cortex is a consistent histological lesion. Citrulline concentration in blood, cerebrospinal fluid, eye fluid and cerebral tissue is greatly elevated. Information gathered from pedigrees of affected calves indicate that the defect is widely disseminated throughout the Australian Friesian population.

Citrulline as a diagnostic parameter and a major amino acid constituent of cerebrospinal fluid in hepatic coma.

Free amino acids of cerebrospinal fluid and serum in hepatic coma have been studied. Citrulline was found to form about 80% of the total free amino acids in cerebrospinal fluid, whereas serum contained slightly higher levels of tyrosine, methionine, phenylalanine and glutamine. The higher level of citrulline in cerebrospinal fluid may be attributed to the inhibition of argininosuccinic acid synthetase in this disease.

[Normal range of free amino acids in cerebrospinal fluid of children (author's transl)]. / Verhalten der freien Aminosäuren im Liquor cerebrospinalis von Kindern

UNLABELLED: Free amino acids were determined quantitatively in cerebrospinal fluid of 80 boys and 69 girls (ages 1 month-14years). On the basis of the cliniclal criterions these children were considered to be ""healthy''. The total number of examined children was 2000. Cerebrospinal fluid was mixed with an equal volume of 5% sulphosalicylic acid and the amino acids were separated by ion exchange column chromatography. RESULTS: 1. The sexspecific investigation of the 1 month -2 years old children showed that the boys had a statistical significant hgher concentration of lysine and that no statistical significant differences existed between the groups of 2-14 years old children. 2. The age specific comparison revealed that the amino acid concentrations ofaspartic acid, citrulline, histidine, lysine, serine, threonine and tyrosine were in the cerebrospinal fluid of the younger boys statistical significant higher as compared to the older boys and that the concentration of serine in the cerebrospinal fluid of the younger girls was statistical significant higher than in the group of older girls.