L-arginine improves endothelial function and reduces LDL oxidation in patients with stable coronary artery disease

BACKGROUND: We investigated the effects of oral L-arginine on endothelial function, intravascular oxidative stress, and circulating inflammatory markers in patients with stable coronary artery disease (CAD). METHODS: Thirty-one stable CAD patients were randomly assigned to oral L-arginine (10 g) or vitamin C (500 mg, an antioxidant, as active control) daily for 4 weeks, with crossover to the alternate therapy after 2 weeks off therapy, in this study. Brachial artery endothelial function studies were performed and serum concentrations of lipids and inflammatory markers were measured at baseline, at the end of each 4-week treatment period and at the 2-week wash-out period. Susceptibility of low-density lipoprotein (LDL) particles to oxidation, a marker of oxidative stress, was determined in 11 patients at random before and after 4-week treatment of oral L-arginine. RESULTS: We demonstrates that consumption of either L-arginine or vitamin C significantly increased brachial artery flow-mediated dilatation (mean diameter change from baseline of 4.87%, P<0.0001 and of 3.17%, P=0.0003, respectively). Neither oral L-arginine nor vitamin C affected lipid profiles and circulating levels of inflammatory markers. However, in the 11 patients whose LDL susceptibility to oxidation was determined, lag time significantly increased by 27.1% (P=0.045) after consumption of L-arginine for 4 weeks. CONCLUSIONS: Oral L-arginine supplement improved endothelial function and reduced LDL oxidation in stable CAD patients.     

Nitric oxide release in the nucleus tractus solitarius during and after bilateral common carotid artery occlusion

1. The purpose of the present study was to investigate the effect of bilateral common carotid artery occlusion (BCCAO) on cardiovascular responses and nitric oxide (NO) formation in the nucleus tractus solitarius (NTS). 2. Twenty-three adult cats were anaesthetized intraperitoneally with urethane (400 mg/kg) and alpha-chloralose (40 mg/kg). The femoral artery was cannulated to allow monitoring of systemic arterial pressure (SAP) and heart rate (HR). The femoral vein was cannulated for intravenous drug administration. 3. Extracellular NO levels in the NTS were measured by in vivo voltammetry using an NO microsensor combined with a microcomputer-controlled apparatus. 4. Microinjection of l-arginine (30 nmol) into the NTS produced hypotension and NO release. This effect of l-arginine was not changed by 2 min of BCCAO. 5. Bilateral common carotid artery occlusion produced increases in SAP and NO levels. These effects were more apparent in vagotomized than in intact animals. 6. The onset latency of BCCAO-induced changes in SAP levels (8.4 +/- 2.5 s) was longer than that for changes in NO (4.7 +/- 1.7 s). 7. Bilateral common carotid artery occlusion induced hypertension and NO release in the NTS of intact and vagotomized animals. These cardiovascular and NO responses to BCCAO were significantly attenuated by NG-nitro-l-arginine methyl ester (10 mg/kg, i.v.) and MK-801 (2.5 mg/kg, i.v.). These data suggest that NO synthase and activation of N-methyl-d-aspartate receptors are involved in the cardiovascular and NO responses to BCCAO.     

Treatment of psoriasis with topical NG-monomethyl-L-arginine, an inhibitor of nitric oxide synthesis

A double blind left, right comparative study was carried out in 17 psoriatic subjects to examine the influence of a topically applied inhibitor of nitric oxide (NO) synthesis on the pathogenic events of psoriasis. The inhibitor NG-monomethyl-L-arginine (L-NMMA) in aqueous cream BP was applied to one plaque while aqueous cream BP alone served as control. Compared with the control, the L-NMMA-treated side showed significant (77%) inhibition of NO production and a reduction in blood flow, confirming its bioavailability. L-NMMA significantly reduced staining for endothelial cells and intercellular adhesion molecule 1, while CD1a-positive Langerhans cells and CD8-positive suppressor cytotoxic T cells increased. CD4-positive lymphocytes and epidermal proliferation, as indicated by Ki-67 staining, were unaffected by this degree of inhibition of NO synthesis, and correspondingly significant clinical improvement was not found.     

Pharmacokinetic-pharmacodynamic profile of systemic nitric oxide-synthase inhibition with L-NMMA in humans

AIMS: It has been demonstrated that inhibition of endothelium derived nitric oxide with NG-monomethyl-L-arginine (L-NMMA) results in a different cardiac and peripheral vascular response. The purpose of this study was to investigate the pharmacokinetic-pharmacodynamic profile of L-NMMA and pharmacokinetic interactions with L-arginine in healthy subjects. METHODS: Plasma pharmacokinetics were analysed from two different studies: In study 1, 3 mg kg-1 L-NMMA was administered i.v. over 5 min and systemic haemodynamics, cardiac output (CO), fundus pulsation amplitude (FPA), and NO-exhalation (exhNO) were measured at baseline and 15, 65, 95, 155, and 305 min after start of drug administration (n=7). In study 2, 17 mg kg-1 min-1 of the physiologic substrate for nitric oxide synthase, L-arginine, was coinfused i.v. over 30 min with a primed constant infusion of 50 microg kg-1 min-1 L-NMMA (n=8). RESULTS: Bolus infusion of L-NMMA resulted in a maximum plasma concentration of 12. 9+/-3.4 microg ml-1 (mean+/-s.d.) with elimination half-life of 63. 5+/-14.5 min and clearance of 12.2+/-3.5 ml min-1 kg-1 and caused a small hypertensive response, decreased CO by 13%, FPA by 26%, exhNO by 46% and increased systemic vascular resistance by 16% (P<0.05 each) 15 min after start of drug administration. Although only limited data points were available in the L-NMMA plasma concentration range between 0 and 4 microg ml-1, drug effects over time were in good agreement with an Emax model (r2>0.98 each), which also suggested that concentrations producing half-maximum effects were higher for FPA than for CO and exhNO. The coinfusion with L-arginine caused a nearly two-fold increase in plasma L-NMMA levels, indicating a pharmacokinetic interaction. CONCLUSIONS: In the absence of a systemic hypertensive response, L-NMMA significantly decreased CO, exhNO, and FPA. The concentration calculated to produce a half maximal effect was equivalent for exhNO and CO, but markedly higher for FPA. Furthermore, measurement of FPA is susceptible to changes in L-NMMA levels at small plasma concentrations.     

Effects of L-arginine and phosphodiesterase-5 inhibitor, sildenafil, on inflammation and airway responsiveness of sensitized BP2 mice

Nitric oxide (NO) levels are elevated in the exhaled breath of asthmatic patients and NO is considered as a biomarker of airway inflammation. However, the functions of NO in the airways are not completely understood. L-arginine, as the substrate of NO synthases, is the precursor of NO which stimulates guanylate cyclase and leads to the formation of cyclic GMP (cGMP). Sildenafil, a phosphodiestérase-5 (PDE-5) inhibitor, prevents the degradation of cGMP. In this study the effects of L-arginine and sildenafil treatment, alone or in combination, were evaluated in ovalbumin-sensitized BP2 mice. These effects concerning the airway responsiveness to inhaled methacholine (MCh) were evaluated by whole-body plethysmography (WBP), the inflammatory response evaluated by bronchoalveolar lavage fluid (BALF) analyses and lung tissue biopsies (eosinophilic inflammation associated with lung remodelling), and NO metabolite measurements (by Griess reaction) in BALF. Ovalbumin sensitization induced: (a) an inflammatory reaction with eosinophil and neutrophil influx in BALF and lung; and (b) an increased bronchial responsiveness to MCh. L-arginine treatment [50 mg/kg intraperitoneally (i.p.), for 7 days] increased the relative amount of eosinophils and neutrophils in BALF, had a tendency to increase the airway responsiveness to inhaled MCh and increased the NO metabolite level in BAL. Sildenafil treatment (20 mg/kg i.p. for 7 days) did not affect the airway responsiveness to MCh and had a lower effect compared with L-arginine on inflammatory reactions. The combination of the two treatments resulted in a dramatic enhancement of the airway responsiveness to inhaled MCh. The relative amount of eosinophils was increased and lung histology showed obvious worsened tissular lesions such as epithelial shedding and hypertrophy, hyperplasia of smooth muscle cells, and fibrosis. These findings are consistent with the notion that NO production plays a role in the development of airway inflammation and hyperresponsiveness of sensitized mice and highlighted the potential risk of the L-arginine dietary complement or PDE5 treatment in asthmatic patients.     

Characterization of cationic amino acid transport systems in rat erythrocytes: lack of effect of uraemia on L-arginine influx

1. Chronic renal failure (CRF) is associated with the abnormal regulation of nitric oxide (NO) synthesis at the systemic level. The transport of L-arginine, upregulated in blood cells from uraemic patients, modulates NO synthesis in this pathological condition. The model of partial nephrectomy in rats is widely accepted as a valid model of uraemia. Because there are no reports of L-arginine transport in blood cells from uraemic rats, the aim of the present study was to investigate L-arginine transport in red blood cells (RBCs) from these rats. 2. The kinetics of L-arginine transport in RBC and plasma and the amino acid profiles of RBC were investigated in control, sham-operated and subtotally nephrectomized rats. 3. L-Arginine transport was mediated via the cationic amino acid transport system y+ and a transport system with kinetics resembling the human system y+L. In control RBC, the apparent Ki for L-leucine inhibition of L-arginine transport via system y+L was 0.16 +/- 0.02 and 4.8 +/- 2 mmol/L in the presence of Li+ and Na+, respectively. 4. The Vmax values for L-arginine transport via system y+L and system y+ were similar in RBC from control sham-operated and uraemic rats. Moreover, L-arginine concentrations in plasma and RBC were not affected by uraemia. 5. The findings of the present study provide the first evidence that L-arginine transport in rat erythrocytes is mediated by two distinct cationic transport systems with characteristics of systems y+ and y+L, which accept neutral amino acids only in the presence of Li+. In contrast with previous studies in uraemic patients, plasma levels and maximal transport rates of L-arginine were not altered in this rat model of CRF.     

L-Arginine and melatonin interaction in rat intestinal ischemia--reperfusion

We investigated the combinative effects of L-arginine and melatonin on the contractile responses of terminal ileum after the intestinal ischemia-reperfusion (I/R), in vivo. Male rats were subjected to mesenteric ischemia (30 min) followed by reperfusion (180 min). We have observed a dramatic decrease in spontaneous basal activity and Ach-induced contractile response. Our data clearly showed that the contractility decrease was ameliorated by L-arginine but not by L-NAME. Melatonin has reversed the inhibition of contractility caused by I/R injury in part. We did not observe an augmentation in the contractility of ileum when we use melatonin and L-arginine in combination, in fact, melatonin decreased the protective effect of L-arginine in intestinal I/R injury.     

Endothelial nitric oxide synthase is a critical factor in experimental liver fibrosis

Reduced expression of endothelial nitric oxide synthase (eNOS) in chronic liver disease can reduce hepatic perfusion and accelerate fibrosis. The relationship between eNOS expression and liver fibrogenesis remains unclear. We investigated whether l -arginine attenuated chronic liver fibrosis through eNOS expression. Chronic liver injury was induced by administration of carbon tetrachloride (CCl₄) to mice for 8 weeks. 5-Methylisothiourea hemisulphate (SMT), an iNOS inhibitor, or l -arginine, a NOS substrate were injected subcutaneously. CCl₄-induced hepatotoxicity, oxidative stress and accumulation of collagen were detected in the liver. The expression levels of inducible NOS (iNOS) and nuclear factor kappa-B (NF-κB) activity in the liver after CCl₄ treatment were increased but eNOS expression and activator protein-1 (AP-1) activity were decreased. Both SMT and l -arginine effectively reduced CCl₄ induced oxidative stress and collagen formation, but l -arginine showed a significantly greater suppression of collagen formation, iNOS expression and NF-κB activity. l -Arginine also restored the level of eNOS and AP-1 activity. l -Arginine was more effective than SMT in suppressing liver fibrosis. l -Arginine might improve NO production which facilitates hepatic blood flow and thus retards liver fibrogenesis. Our results showed that the reduced eNOS expression in CCl₄-treated mice was reversed by l -arginine. Furthermore, l -arginine also reversed the reduced AP-1 activity, an eNOS promoter.     

URINARY NO3− EXCRETION AS AN INDICATOR OF NITRIC OXIDE FORMATION IN VIVO DURING ORAL ADMINISTRATION OF l-ARGININE OR l-NAME IN RATS

• 1 Endothelium-derived nitric oxide (NO), a major modulator of vascular tone, is synthesized from the terminal guanidino nitrogen of l -arginine. This reaction is inhibited by analogues of l -arginine, such as N-nitro-l -arginine methyl ester (l -NAME). Many of the biological effects of NO are mediated by the second messenger cGMP. NO is rapidly oxidized to NO₃^? which, like cGMP, is eliminated via excretion into the urine. In a placebo controlled study, we investigated whether oral bolus administration of l -arginine and l -NAME affects the urinary excretion rates of NO₃^? and cGMP in Munich Wistar Frömmter (MWF) rats.
• 2 Twenty MWF rats were kept in metabolic cages and received l -arginine (3 g/kg body weight), l -NAME (50mg/kg), or placebo (0.9% saline) in randomized order. Urine samples were sequentially collected for 10 h and analysed for creatinine, NO₃^? and cGMP.
• 3 l -Arginine induced a slight, but prolonged increase in urine flow, whereas l -NAME induced an early, transient increase in urine flow which was followed by a decrease. Creatinine clearance decreased by 65% after l -NAME, but was not affected by l -arginine or placebo.
• 4 Urinary NO₃^? and cGMP excretion rates transiently increased after l -arginine (NO₃^?: + 29%; cGMP: + 16%) for 4–5h, whereas l -NAME induced an immediate, pronounced and lasting inhibition of urinary NO₃^? and cGMP excretion (NO₃^?:-76%; cGMP:-46%). Urinary NO₃^? and cGMP excretions were significantly correlated (r = 0.755; P< 0.001).
• 5 Urinary excretion rates of NO₃^? and cGMP, expressed as μmol/h, were correlated to urine flow (mL/h; r = 0.617 and 0.649, respectively; both P<0.05), whereas after correction by urinary creatinine (μmol/mmol creatinine) no correlation with urine flow was observed, indicating that these excretion rates were independent of renal excretory function. Thus we conclude that changes in the urinary excretion rates of NO₃^? and cGMP represent changes in NO production rates in vivo when expressed in relation to urinary creatinine. Urinary NO₃^? and cGMP excretion is modulated by acute NO synthase inhibition or substrate provision.