Hyperaggregability and impaired nitric oxide production in platelets from postmenopausal women.

OBJECTIVE: Cardiovascular mortality increases after menopause in women. Nitric oxide is essential for proper platelet function inhibiting its aggregation and maintaining vascular haemostasis. Here, we investigated whether platelet function and intraplatelet l-arginine-nitric oxide pathway are impaired in postmenopausal women. STUDY DESIGN: Cross-sectional. MAIN OUTCOMES MEASURES: Blood was collected from 16 premenopausal and 12 postmenopausal women without any additional risk factor for cardiovascular disease. Platelet reactivity was measured by light transmission aggregometry. l-Arginine-nitric oxide pathway was assessed measuring transmembrane l-[(3)H]-arginine transport, nitric oxide synthase activity by the citrulline assay, and arginase activity by the conversion of l-[(14)C]arginine to l-[(14)C]-urea. The activity of antioxidant enzymes was measured by spectrophotometric assays. Protein expression was determined by Western blotting. RESULTS: Platelet aggregation was increased in postmenopausal compared to premenopausal women. Postmenopausal women demonstrated reduced plasma levels of l-arginine, a lower nitric oxide synthase activity, similar endothelial and inducible nitric oxide synthase expression, and a compensatory increase in l-arginine transmembrane transport. Arginase expression and activity did not differ between groups. In regard to oxidative stress, no differences between groups were observed NAPDH oxidase subunits expression and protein carbonylation. However, the activity of the antioxidant enzyme superoxide dismutase and catalase protein levels in platelets were higher in postmenopausal women. CONCLUSION: Postmenopausal women present increased platelet reactivity, which may be due to a reduction in intraplatelet nitric oxide synthesis. Platelet hyperaggregability is known to be associated with arterial and venous thromboembolic event; therefore, it may contribute to the heightened risk of cardiovascular adverse events in this population.

Chronic exercise leads to antiaggregant, antioxidant and anti-inflammatory effects in heart failure patients.

BACKGROUND: Heart failure (HF) patients are at an increased risk of thrombotic events. Here, we investigated the effects of exercise training on platelet function and factors involved in its modulation in HF. DESIGN AND METHODS: Thirty HF patients were randomized to 6 months of supervised exercise training or to a control group that remained sedentary. Exercise training consisted of 30 min of moderate-intensity treadmill exercise, followed by resistance and stretching exercises, performed three times a week. Blood was collected before and after the intervention for platelet and plasma obtainment. RESULTS: Peak VO2 increased after exercise training (18.0 ± 2.2 vs. 23.8 ± 0.5 mlO2/kg/min; p < 0.05). Exercise training reduced platelet aggregation induced by both collagen and ADP (approximately -6%; p < 0.05), as well as platelet nitric oxide synthase activity (0.318 ± 0.030 vs. 0.250 ± 0.016 pmol/10(8) cells; p < 0.05). No difference in the above-mentioned variables were observed in the control group. No significant difference was observed in intraplatelet cyclic guanosine monophosphate levels among groups. There was a significant increase in the activity of the antioxidant enzymes superoxide dismutase and catalase in plasma and platelets, resulting in a decrease in both lipid and protein oxidative damage. Systemic levels of the inflammatory markers C-reactive protein, fibrinogen, and tumour necrosis factor α were also reduced in HF after training. CONCLUSIONS: Our results suggest that regular exercise training is a valuable adjunct to optimal medical management of HF, reducing platelet aggregation via antioxidant and anti-inflammatory effects, and, therefore, reducing the risk of future thrombotic events.

Platelet activation, oxidative stress and overexpression of inducible nitric oxide synthase in moderate heart failure.

1. Chronic heart failure (CHF) is a common disabling disorder associated with thromboembolic events, the genesis of which is not yet fully understood. Nitric oxide (NO), derived from the vascular endothelium and platelets, has an important role in the physiological regulation of blood flow. It is generated from the amino acid L-arginine via NO synthase (NOS). 2. The main objective of the present study was to investigate NO production and its relationship with platelet aggregation, oxidative stress, inflammation and related amino acids in patients with moderate CHF. The expression and activity of NOS isoforms were analysed by western blotting and conversion of L-[(3)H]-arginine to L-[(3)H]-citrulline, respectively, in CHF patients (n = 12) and healthy controls (n = 15). Collagen- and ADP-induced platelet aggregation, oxidative stress (thiobarbituric acid-reactive substances (TBARS) formation and superoxide dismutase (SOD) activity) and plasma levels of amino acids and inflammatory markers (fibrinogen and C-reactive protein (CRP)) were also determined. 3. Both collagen- and ADP-induced platelet aggregation were increased in CHF patients compared with controls. Platelets from CHF patients did not show any changes in NOS activity in the presence of overexpression of inducible NOS. Systemic and intraplatelet TBARS production was elevated, whereas SOD activity was decreased in CHF patients. l-arginine plasma concentrations were lower in CHF patients than in controls. Systemic levels of CRP and fibrinogen were increased in CHF patients. 4. The results show that, in patients with moderate CHF, there is platelet activation and reduced intraplatelet NO bioavailability due to oxidative stress, which suggests a role for platelets in the prothrombotic state.

Increased nitric oxide production in platelets from severe chronic renal failure patients.

Nitric oxide (NO) production occurs through oxidation of the amino acid L-arginine by NO synthase (NOS). NO inhibits platelet activation by increasing the levels of cyclic guanosine monophosphate (cGMP), thus maintaining vascular homeostasis. Our group previously demonstrated (da Silva et al. 2005) an enhancement of the L-arginine-NO-cGMP pathway in platelets taken from chronic renal failure (CRF) patients on haemodialysis associated with reduced platelet aggregation. We investigate the platelet L-arginine-NO-cGMP pathway, platelet function, and inflammation from patients in CRF on conservative treatment. A total of 42 CRF patients and 42 controls (creatinine clearance = 27 ± 3 vs. 93 ± 1 mL per min per 1.73 m2, respectively) participated in this study. NOS activity and expression and cGMP concentration were measured in platelets. Platelet aggregation induced by collagen or ADP was evaluated and plasma levels of fibrinogen were determined by the Clauss method. A marked increase in basal NOS activity was seen in undialysed CRF patients compared with controls, accompanied by an elevation of fibrinogen plasma levels. There were no differences in expression of NOS and in cGMP levels. In this context, platelet aggregation was not affected. We provide the first evidence of increased intraplatelet NO biosynthesis in undialysed CRF patients, which can be an early marker of future haemostatic abnormalities during dialysis treatment.

Insulin resistance in obesity and metabolic syndrome: is there a connection with platelet l-arginine transport?

OBJECTIVE: Nitric oxide (NO) is a short-lived gaseous messenger with multiple physiological functions including regulation of blood flow, platelet adhesion and aggregation inhibition. NO synthases (NOS) catalyze the conversion of cationic amino acid L-arginine in L-citrulline and NO. Despite an increasing prevalence of obesity and metabolic syndrome (MetS) in the last decades, the exact mechanisms involved in the pathogenesis and cardiovascular complications are not fully understood. We have examined the effects of obesity and MetS on the L-arginine-NO-cGMP pathway in platelets from a population of adolescents. MATERIALS: A total of twenty six adolescent patients (13 with obesity and 13 with MetS) and healthy volunteers (n=14) participated in this study. Transport of L-arginine, NO synthase (NOS) activity and cGMP content in platelets were analyzed. Moreover, platelet function, plasma levels of L-arginine, metabolic and clinical markers were investigated in these patients and controls. RESULTS: L-arginine transport (pmol/10(9) cells/min) in platelets via system y(+)L was diminished in obese subjects (20.8±4.7, n=10) and MetS patients (18.4±3.8, n=10) compared to controls (52.3±14.8, n=10). The y(+)L transport system correlated negatively to insulin levels and Homeostasis Model Assessment of Insulin Resistance (HOMA IR) index. No differences in NOS activity and cGMP content were found among the groups. Moreover, plasma levels of L-arginine were not affected by obesity or MetS. DISCUSSION: Our study provides the first evidence that obesity and MetS lead to a dysfunction of L-arginine influx, which negatively correlates to insulin resistance. These findings could be a premature marker of future cardiovascular complications during adulthood.

Exercise training in doxorubicin-induced heart failure: effects on the L-arginine-NO pathway and vascular reactivity.

Heart failure (HF) is the end-stage of cardiovascular disease and is associated with a high incidence of thrombotic events. Nitric oxide (NO) mediates vasodilation and prevents platelet activation, providing an important antithrombotic effect. The aim of this study was to investigate the effects of aerobic training on survival, platelet L-arginine-NO pathway, and vasodilator properties in doxorubicin (DOX)-induced HF. Sprague Dawley rats were randomly assigned to saline/sedentary (SAL/SED), saline/exercise (SAL/EX), DOX/sedentary (DOX/SED), and DOX/exercise (DOX/EX) groups. Four weeks after intraperitoneal DOX injection (1mg/kg(-1)/d(-1); 10 days), shortening fraction in DOX/SED and DOX/EX was significantly reduced. Treadmill exercise was performed during 6 weeks, 5 days/week(-1), 30minutes/day(-1), 50% to 60% of maximum velocity. Survival was higher in DOX/EX (67%) than DOX/SED (33%). No differences were observed in intraplatelet L-arginine transport assessed by incubation with L- [(3)H]-arginine, nor in NOS activity measured by the conversion of L- [(3)H]-arginine into L- [(3)H]-citrulline among the groups. Vasodilation response to acetylcholine was impaired in DOX/SED and DOX/EX; in nitroglycerine, it was limited to DOX/SED. Aerobic training reduced mortality in DOX-induced HF animals and restored vascular smooth muscle relaxation properties. However, it did not ameliorate intraplatelet NO bioavailability and endothelial function during the period studied.

Nitric oxide and oral diseases: can we talk about it?

Nitric oxide (NO) is a short-lived intercellular messenger with multiple biological implications, such as regulation of blood pressure, inhibition of platelet adhesion and aggregation, bacterial-challenge and cytokine stimulation, and regulation of mineralized tissue function. NO synthase (NOS) catalyses the conversion of cationic amino acid L-arginine to L-citrulline and NO. Recently there is an increasing interest in the role of NO in the physiopathology of periodontal disease (PD). PD is a chronic inflammatory disease of the attachment structures of the teeth, which is found in 40-50% of most adult populations worldwide and may result in tooth loss. The potential sources of NO in periodontum are inflammatory cells, keratinocytes, fibroblasts, osteoclastics and blood vessels. Etiological periodontitis factors, such as inflammatory cytokines and periodontopathogens are evolved in enhanced NO levels, which may be part of a nonspecific natural defense mechanism or may lead to periodontal damage. This review gives detail of recent research data focusing on NO bioavailability and its involvement in periodontitis pathogenesis and the modulation of NO for better control of this disease.

Oxidative stress, l-arginine-nitric oxide and arginase pathways in platelets from adolescents with anorexia nervosa.

Anorexia nervosa (AN) is associated with high cardiovascular mortality. Nitric oxide (NO) inhibits platelet function and regulates the cardiovascular homeostasis. The aim of this study was to investigate the l-arginine-NO-GMPc and arginase pathways and oxidative stress in platelets from patients with AN. Intraplatelet l-arginine transport, NOS expression and activity, cGMP levels, platelet aggregation, arginase expression and oxidative stress were measured in adolescent patients with AN (n=11) and healthy controls (n=12). Plasma l-arginine levels were significantly reduced in AN. l-arginine transport, NOS activity and cGMP basal levels were reduced in platelets associated with unchanged platelet aggregability. The expression of NOS isoforms was not affected. TBARS production was diminished, while the activity of superoxide dismutase was elevated in AN patients. There was an overexpression of arginase II in AN. Alterations of l-arginine-NO-GMPc and arginase pathways in platelets can be early predictors of the incidence of cardiovascular disease into adult life in AN.

Platelet aggregation in arterial hypertension: is there a nitric oxide-urea connection?

1. Systemic arterial hypertension (SAH) is a major independent risk factor for cardiovascular disease. The physiopathology of SAH is multifactorial, complex and remains to be elucidated. Nitric oxide (NO) is an important regulator of vascular and haemostatic functions. The cationic amino acid l-arginine serves as the substrate for NO synthases (NOS) and arginase, an enzyme of the urea cycle. We have previously reported inhibition of l-arginine transport in erythrocytes and platelets in hypertension. 2. The aim of the present study was to investigate the l-arginine-NO pathway and urea cycle in platelets and their role in platelet function and systemic inflammatory responses in SAH patients. The expression and activity of NOS and arginase in platelets, platelet aggregation and plasma levels of C-reactive protein (CRP) were evaluated in 20 SAH patients and 18 age-matched healthy volunteers. 3. There was a reduction of NOS activity in hypertensive patients that was associated with activation of platelet aggregability induced by collagen, but not by ADP. Platelets from SAH patients exhibited compensatory overexpression of inducible NOS, but not endothelial NOS. Intraplatelet arginase activity in SAH patients was not affected, but systemic concentrations of CRP were increased compared with controls. 4. It is likely that diminished NO bioavailability in SAH contributes to cardiovascular complications. Our findings may provide the basis for developing new therapeutic approaches for the treatment of hypertension.

Dengue fever activates the L-arginine-nitric oxide pathway: an explanation for reduced aggregation of human platelets.

In patients with Dengue fever, a viral inflammatory syndrome, haemorrhage is a significant pathological feature, yet the underlying mechanisms remain unclear. Nitric oxide (NO) is an important regulator of platelet function, inhibiting aggregation, recruitment and adhesion to the vascular endothelium. We have investigated whether changes in the activity of the L-arginine-NO pathway in human platelets may account for increased bleeding in patients with Dengue fever. A total of 16 patients with Dengue fever and 18 age-matched healthy volunteers participated in the study. Collagen induced platelet aggregation in a dose-dependent manner in both Dengue patients and controls, but the degree of platelet aggregation was significantly reduced in the patient group. Elevated rates of L-arginine transport in Dengue fever patients were associated with enhanced NO synthase activity and elevated plasma fibrinogen levels. The present study provides the first evidence that Dengue fever is associated with increased L-arginine transport and NO generation and reduced platelet aggregation.

Modulation of the cationic amino acid transport system y+L by surface potential, ouabain and thrombin in human platelets: effects of uremia.

BACKGROUND: Nitric oxide (NO), a key endogenous mediator involved in the maintenance of platelet function, is synthesized from the amino acid L-arginine. We have shown that L-arginine transport in platelets is rate-limiting for NO synthesis. A disturbance in the L-arginine-NO pathway in platelets was previously described in chronic renal failure (CRF) patients. METHODS: Detailed kinetic studies were performed in platelets from controls (n = 60) and hemodialysis patients (n = 26). RESULTS: The transport of L-arginine in platelets is mediated via system y+L, which is competitively inhibited by L-leucine in the presence of Na+ and by the irreversible inhibitor pCMB. In platelets, system y+L is markedly stimulated by an Na+/K+-ATPase inhibitor, ouabain, and by changes in surface potential, while it is downregulated by intraplatelet amino acid depletion (zero-trans) and by thrombin. In CRF patients, activation of L-arginine transport was limited to well-nourished patients compared to malnourished patients and controls, where it was reduced and did not differ significantly among the groups under zero-trans conditions. CONCLUSION: Our results provide the first evidence that system y+L in platelets is modulated by zero-trans conditions, surface potential, thrombin and intraplatelet Na+ concentration. Our findings suggest that enhanced transport in CRF involves increased L-arginine exchange with intraplatelet neutral amino acids.

Inhibitory effects of endogenous L-arginine analogues on nitric oxide synthesis in platelets: role in platelet hyperaggregability in hypertension.

1. An increase in plasma concentrations of endogenous L-arginine analogues, which are inhibitors of nitric oxide (NO) synthesis, may be involved in platelet activation and the increased risk of thrombosis in essential hypertension. Nitric oxide is synthesised in platelets from the amino acid L-arginine by inducible and constitutive isoforms of NO synthase (NOS), which leads to increased levels of cGMP. 2. In the present study, we investigated basal intraplatelet cGMP levels, platelet aggregation and pro-inflammatory biomarkers in hypertensive patients. The effects of endogenous (N(G)-monomethyl-L-arginine (L-NMMA) and asymmetric dimethylarginine (ADMA); both at 1 mmol/L) and exogenous (aminoguanidine and N(G)-nitro-L-arginine; both at 1 mmol/L) L-arginine analogues and the neutral amino acid L-leucine (1 mmol/L) in inhibiting NOS activity in platelets were also investigated. 3. Twelve healthy controls and 18 hypertensive patients participated in the study. Platelet aggregation induced by collagen was increased in hypertensive patients (95 +/- 5%) compared with controls (72 +/- 5%). Basal NOS activity and intraplatelet cGMP levels were reduced in hypertensive platelets. Moreover, ADMA, L-NMMA and L-leucine were effective inhibitors of NO synthesis in both hypertensive and control platelets. Essential hypertension led to an inflammatory response, with increased plasma concentrations of fibrinogen, C-reactive protein and cytokines. 4. These findings provide evidence that, in essential arterial hypertension, the enhanced plasma levels of endogenous L-arginine analogues ADMA and L-NMMA, potent inhibitors of L-arginine transport and NO synthesis in platelets, may play a role in increased platelet aggregation via a cGMP-dependent mechanism.

Nitric oxide, malnutrition and chronic renal failure.

The conditionally essential amino acid L-arginine is the substrate for nitric oxide (NO) synthesis, a key second messenger involved in physiological functions including endothelium-dependent vascular relaxation and inhibition of platelet adhesion and aggregation. Extracellular L-arginine transport seems to be essential for the production of NO by the action of NO synthases (NOS), even when the intracellular levels of L-arginine are available in excess (L-arginine paradox). Chronic renal failure (CRF) is a complex clinical condition associated with accelerated atherosclerosis and thrombosis leading to cardiovascular events. Various studies document that markers of malnutrition and inflammation, such as low body mass index (BMI), C-reactive protein (CRP) and interleukin-6 (IL-6), are strong independent predictors of cardiovascular mortality in patients with end-stage renal disease (ESRD). There is considerable literature demonstrating that a disturbance in the nitric oxide control mechanism plays a role in mediating the haemodynamic and haemostatic disorders present in CRF. Endogenous analogues of L-arginine, ADMA and L-NMMA, which can inhibit NO synthesis and L-arginine transport, are increased whilst L-arginine is reduced in plasma from all stages of CRF patients. In this context, the uptake of L-arginine in blood cells is increased in undialysed CRF patients and in patients treated by CAPD and haemodialysis. In platelets obtained from haemodialysis patients, the activation of L-arginine transport and NO production was limited to well-nourished patients. Impairment in nitric oxide bioactivity, coupled with malnutrition and inflammation, may contribute to increased incidence of atherothrombotic events in CRF. This article summarizes the current knowledge of L-arginine-nitric oxide pathway and malnutrition in CRF and briefly describes possible therapeutic interventions.

Platelet nitric oxide synthesis in uremia and malnutrition: a role for L-arginine supplementation in vascular protection?

L-arginine is the physiological precursor for nitric oxide (NO) synthesis, and availability and transport of L-arginine modulate the rates of NO biosynthesis in circulating blood cells and the vasculature. NO is involved in many vascular functions such as vasodilation and inhibition of platelet aggregation and adhesion. We have established that reduced plasma L-arginine and NO production and increased tumour necrosis factor-alpha (TNF-alpha), fibrinogen, and C-reactive protein levels in malnourished uremic patients are associated with increased aggregability of platelets. Our findings may explain the increased cardiovascular mortality in patients with deficient nutritional status, leading to inflammation, oxidative stress, impaired L-arginine-NO signalling, and platelet activation. The aim of this review is to evaluate whether disturbances in the L-arginine-NO signalling pathway in chronic renal failure and atherosclerosis are affected by malnutrition and inflammation. We have included a brief overview of membrane transporters mediating influx of L-arginine and other cationic amino acids, as these transporters are involved in the potential benefits of L-arginine supplementation and platelet function in malnourished uremic patients.

Plasma amino acid profile and L-arginine uptake in red blood cells from malnourished uremic patients.

BACKGROUND: Patients with end-stage chronic renal failure (CRF) (uremia) have a high prevalence of inflammation, malnutrition, and oxidative stress. All of these features seem to be associated with the increased cardiovascular mortality observed in these patients. Nitric oxide (NO) is involved in the pathogenesis of CRF. The present study investigates the effects of nutritional status on L-arginine transport (NO precursor), plasma amino acid profile, and concentration of tumor necrosis factor (TNF)-alpha in uremic patients on hemodialysis (HD). METHODS: A total of 32 uremic patients on regular HD and 16 healthy controls were included in this study. Kinetic studies of L-arginine transport, mediated by cationic transport systems y(+) and y(+)L into red blood cells, plasma concentrations of amino acids (measured by high-performance liquid chromatography), and plasma TNF-alpha level (evaluated by enzyme-linked immunosorbent assay), were analyzed in malnourished and well-nourished patients (isolated by body mass index). RESULTS: L-arginine influx by system y(+) in red blood cells (micromol/L cells(-1)h(-1)) was increased in both malnourished (377 +/- 41) and well-nourished (461 +/- 63) patients with CRF compared with controls (287 +/- 28). Plasma levels of all cationic amino acids (L-arginine, L-ornithine, and L-lysine) were low in uremic patients compared with controls. Among the uremic population, the reduction in plasma cationic amino acids levels was greater in malnourished patients. L-cysteine and L-glutamate, precursors of glutathione, were dramatically increased in plasma from uremic patients, independently of nutritional status. In addition, TNF-alpha concentration in plasma was enhanced in malnourished uremic patients (3.4 +/- 0.7 pg/mL) compared with controls (1.2 +/- 0.1 pg/mL) and well-nourished patients (1.9 +/- 0.1 pg/mL). CONCLUSIONS: Our results suggest an increased catabolism of cationic amino acids, inflammatory markers, and oxidative stress in CRF, especially in malnourished patients. The reduced plasma concentration of plasma L-arginine is counterbalanced by enhanced rates of transport, resulting in an activation of NO synthesis in uremia.

Uremia, atherothrombosis and malnutrition: the role of L-arginine-nitric oxide pathway.

The uraemic syndrome is a complex condition that results from an accumulation of multiple waste compounds, combined with failure of the endocrine and homeostatic functions of the kidney in end-stage chronic renal failure (CRF) patients. Recently it has become clear that uraemia is a microinflammatory condition with a significant increase in inflammation markers. Malnutrition is a common pathological condition which exacerbates cardiovascular mortality in uraemic patients. Inadequate diet and a state of persistent catabolism play major roles in uraemic malnutrition, yet the underlying mechanisms have not been completely clarified. Malnourished patients present elevated levels of circulating cytokines, further aggravating the oxidative and inflammatory characteristics of uraemia. It has been suggested that abnormalities in nitric oxide bioactivity, coupled with malnutrition and inflammation, may contribute to increased incidence of atherothrombotic events in uraemia. Amongst the earliest indications of nutritional deficiency are low concentrations of plasma amino acids, including L-arginine, the precursor for nitric oxide (NO) synthesis. Atherosclerosis is an inflammatory disorder and NO is an important mediator of inflammation. There is a close association between thrombosis and platelet aggregation, and NO is involved in all stages of platelet activation. L-arginine inhibits platelet aggregation both in vitro and in vivo, while L-NMMA (NG-monomethyl-L-arginine), an endogenous L-arginine analogue and inhibitor of NO synthase (NOS), increases platelet activation and adhesion. The majority of studies in animal models and human patients indicate that the systemic production of NO is increased in uraemia. CRF patients show reduced plasma concentration of L-arginine, and the enhancement of L-arginine transport is essential to maintain increased NO synthesis in platelets taken from these patients. The present review provides an overview of recent advances in the understanding of the association among malnutrition, chronic inflammation and the L-arginine-nitric oxide pathway in uraemic patients, and related potential interventions that could improve clinical outcome in chronic renal failure.

O papel da via L-arginina-óxido nítrico em doenças pulmonares / The role of L-arginine-nitric oxide pathway in pulmonary diseases

O óxido nítrico (NO) é um gás inorgânico com uma meia vida curta, que vem sendo associado a importantes funções fisiológicas, incluindo neurotransmissão, vasodilatação, atividade citotóxica do sistema imune e agregação plaquetária. O NO é sintetizado, a partir do aminoácido catiônico L-arginina, por uma família de enzimas: óxido nítrico sintases (NOS). Existem três isoformas de NOS: neuronal (nNOS), induzível (iNOS) e endotelial (eNOS). A liberação inapropriada deste mediador, ou uma reduzida disponibilidade de L-arginine, tem sido associada à patogênese de várias doenças. A asma e a hipertensão arterial pulmonar (HAP) são doenças com alta morbi-mortalidade, e o completo entendimento e adequado tratamento dessas enfermidades permanece sendo um desafio. Evidência recente sugere que um distúrbio da via L-arginina-NO esteja envolvido na fisiopatologia da asma e da HAP. Este artigo revisa o conhecimento atual sobre a via L-arginina-NO, na asma e na HAP, e descreve, sucintamente, as possíveis intervenções terapêuticas.

Effects of nutritional status on the L-arginine-nitric oxide pathway in platelets from hemodialysis patients.

BACKGROUND: Malnutrition is a common feature in chronic renal failure and adversely affects patient morbidity and mortality. We here investigate the effects of nutritional status on the L-arginine-nitric oxide signaling pathway and platelet function in chronic renal failure patients on regular hemodialysis. METHODS: Platelet aggregation was correlated with plasma amino acid profiles, L-arginine transport, and nitric oxide synthase (NOS) activity determined by conversion of L-[(3)H]-arginine to L-[(3)H]-citrulline and accumulation of intracellular cyclic guanosine monophospate (cGMP) in platelets from malnourished and well-nourished chronic renal failure patients on regular hemodialysis (N = 78). RESULTS: Transport of L-arginine (pmol/10(9)cells/min) via y(+) L system was increased in well-nourished (104 +/- 15) compared to controls (57 +/- 11) or malnourished chronic renal failure patients (55 +/- 13). Basal NOS activity (pmol/10(8)cells) was enhanced in well-nourished chronic renal failure patients (0.51 +/- 0.01) compared to controls (0.18 +/- 0.01) or malnourished chronic renal failure patients (0.08 +/- 0.03). In addition, basal cGMP levels are elevated in platelets from well-nourished chronic renal failure compared to malnourished uremic patients. Platelet aggregation induced by collagen is impaired in well-nourished chronic renal failure patients compared to malnourished patients and controls. Plasma L-arginine levels are reduced in chronic renal failure patients and even lower in malnourished patients. CONCLUSION: Our findings provide the first evidence that L-arginine transport via the high affinity system y(+) L and nitric oxide synthesis are only stimulated in platelets from well-nourished chronic renal failure patients, leading to impaired platelet aggregation. The absence of this adaptive response in the l-arginine-nitric oxide pathway in platelets from malnourished chronic renal failure patients may account for the enhanced occurrence of thrombotic events in these patients.

Diminished L-arginine bioavailability in hypertension.

L-Arginine is the precursor of NO (nitric oxide), a key endogenous mediator involved in endothelium-dependent vascular relaxation and platelet function. Although the concentration of intracellular L-arginine is well above the Km for NO synthesis, in many cells and pathological conditions the transport of L-arginine is essential for NO production (L-arginine paradox). The present study was designed to investigate the modulation of L-arginine/NO pathway in systemic arterial hypertension. Transport of L-arginine into RBCs (red blood cells) and platelets, NOS (NO synthase) activity and amino acid profiles in plasma were analysed in hypertensive patients and in an animal model of hypertension. Influx of L-arginine into RBCs was mediated by the cationic amino acid transport systems y+ and y+L, whereas, in platelets, influx was mediated only via system y+L. Chromatographic analyses revealed higher plasma levels of L-arginine in hypertensive patients (175+/-19 micromol/l) compared with control subjects (137+/-8 micromol/l). L-Arginine transport via system y+L, but not y+, was significantly reduced in RBCs from hypertensive patients (60+/-7 micromol.l(-1).cells(-1).h(-1); n=16) compared with controls (90+/-17 micromol.l(-1).cells(-1).h(-1); n=18). In human platelets, the Vmax for L-arginine transport via system y+L was 86+/-17 pmol.10(9) cells(-1).min(-1) in controls compared with 36+/-9 pmol.10(9) cells(-1).min(-1) in hypertensive patients (n=10; P<0.05). Basal NOS activity was decreased in platelets from hypertensive patients (0.12+/-0.02 pmol/10(8) cells; n=8) compared with controls (0.22+/-0.01 pmol/10(8) cells; n=8; P<0.05). Studies with spontaneously hypertensive rats demonstrated that transport of L-arginine via system y+L was also inhibited in RBCs. Our findings provide the first evidence that hypertension is associated with an inhibition of L-arginine transport via system y+L in both humans and animals, with reduced availability of L-arginine limiting NO synthesis in blood cells.