The interaction of receptor-type protein tyrosine phosphatases sigma and zeta1 controls cardiac fibroblast migration

Background

Among cardiovascular diseases as a major health burden heart failure (HF) plays a central role. Our screening of patients with HF either from ischemic – or dilatative cardiomyopathy has shown that receptor-type protein tyrosine phosphatase sigma (PTPRσ) and zeta1 (PTPRz1) are upregulated compared to healthy hearts. Inhibition of PTPRσ is known to be necessary for autonomic reinnervation after myocardial infarction [1] and for various functions in the nervous system [2]. Most recently the loss of PTPRz1 in knockout-mice has been shown to lead to impaired morphogenesis with postnatal systolic and diastolic heart failure [3].

Purpose

A crucial step in myocardial remodeling and the development of HF is fibroblast migration into the wound, where they differentiate into myofibroblasts, producing extracellular matrix proteins and forming the scar. Up to now no information is available on the role of PTPRσ and PTPRz1 in fibroblast migration and myocardial remodeling.

Methods

Neonatal cardiac fibroblasts are transfected with either scrambled-, PTPRσ-, PTPRz1-siRNA or a combination thereof. A scratch wound is inflicted at confluency of the cells. The number of migrated cells, relative to the control, is determined microscopically after 48 hours. Transfected fibroblasts are seeded into transwells to examine their transmigration. After 48 hours the number of transmigrated cells, relative to the control, is determined after DAPI staining. N=4, statistical analysis is performed using Kruskal-Wallis Test with Dunn's multiple comparison.

Results

In the scratch assay a PTPRz1 knockdown resulted in a significant increase in migrating cells (1 vs. 1,355±0,1144, p=0,0265). This promigratory effect is not present in PTPRσ knockdown cells, independent of the PTPRz1 expression (1 vs. 1,032±0,1654 and 1 vs. 1,073±0,08597, both p>0,9999). In transmigration there is a fourfold increase in transmigrated cells after PTPRz1 knockdown (1 vs 4,046±0,4865, p=0,05). Like in migration this effect is reversed after downregulation of PTPRσ (1 vs 0,9834±0,3844 and 1 vs. 1,345±0,6584, both p>0,9999).

Conclusion

PTPRσ and PTPRz1 are differentially regulated during the pathogenesis of heart failure. While a knockdown of PTPRz1 leads to an increase in fibroblast migration and transmigration, downregulation of PTPRσ inhibits this effect. These results indicate an antimigratory role for PTPRz1. We hypothesize that PTPRσ and PTPRz1 interact through shared intracellular effector molecules, affecting fibroblast migration, an important step in myocardial remodeling and the development of HF. Further investigations will be conducted to identify these shared effector molecules of PTPRσ and PTPRz1 to find a way to influence heart failure through regulation of receptor-type protein tyrosine phosphatases.

Funding Acknowledgement

Type of funding sources: Public Institution(s). Main funding source(s): Carl von Ossietzky University Oldenburg

Bicarbonate-buffered ultrafiltration during pediatric cardiac surgery prevents electrolyte and acid-base balance disturbances

Pediatric cardiopulmonary bypass is still a challenge because of electrolyte disturbances and inflammation. Many investigations deal with different types of hemofiltration to reduce these potentially harmful side effects. We tested the hypothesis of whether bicarbonate-buffered hemofiltration of the priming solution minimizes electrolyte and acid-base disturbances during the initiation of cardiopulmonary bypass and whether bicarbonate-buffered hemofiltration performed during cardiopulmonary bypass could reduce cytokine levels. Twenty children younger than 2 years of age (mean age 166 ± 191 days; mean weight 6.42 ± 3.22 kg) scheduled for pediatric cardiac surgery with cardiopulmonary bypass were enrolled in this prospective clinical study. Cardiopulmonary bypass circuits were primed with a bicarbonate-buffered hemofiltration solution, gelatin and 1 unit of packed red blood cells. The priming was hemofiltered using an ultrahemofilter until approximately 1000 mL of ultrafiltrate was restored with the buffered solution. Further hemofiltration was performed throughout the whole bypass time, especially during rewarming. Blood gas analyses and inflammatory mediators were monitored during the operation. Blood gas analysis results after initiation of cardiopulmonary bypass and throughout the entire study remained within the physiologic ranges. Even potassium decreased from 4.0 ± 0.3 to 3.4 ± 0.4 mmol.l−1 after initiation of cardiopulmonary bypass. Plasma levels of tumor necrosis factor alpha decreased significantly (47 ± 44 vs. 24 ± 21 pg.mL−1) whereas complement factor C3a (5.0 ± 2.9 vs. 16.8 ± 6.6 ng.mL−1) and interleukin-6 (7.3 ± 15.2 vs. 110 ± 173 pg.mL−1) increased despite hemofiltration. In conclusion, this study shows that bicarbonate-buffered ultrafiltration is an efficient, simple and safe method for performing hemofiltration, both of the priming solution and during the entire bypass time. The use of a physiological restitution solution prevents electrolyte and acid-base balance disturbances. The elimination of inflammatory mediators seems to be as effective as other ultrafiltration methods.

Local anaesthetics inhibit signalling of human NMDA receptors recombinantly expressed in Xenopus laevis oocytes: role of protein kinase C

BACKGROUND

N-methyl-D-aspartate (NMDA)-receptor activation contributes to postoperative hyperalgesia. Studies in volunteers have shown that intravenous local anaesthetics (LAs) prevent the development of hyperalgesic pain states. One potential explanation for this beneficial effect is the inhibition of NMDA receptor activation. Therefore, we studied the effects of LA on NMDA receptor function.

METHODS

The human NR1A/NR2A NMDA receptor was expressed recombinantly in Xenopus laevis oocytes. Peak currents were measured by voltage clamp in Mg- and Ca2+-free, Ba2+-containing Tyrode's solution. Holding potential was -70 mV. Oocytes were stimulated with glutamate/glycine (at EC50) with or without 10 min prior incubation in bupivacaine, levobupivacaine, S-(-)-ropivacaine, or lidocaine (all at 10(-9)-10(-4) M), procaine (10(-4) M), R-(+)-ropivacaine (10(-4) M), QX314 (permanently charged, 5 x 10(-4) M) extracellularly or intracellularly or benzocaine (permanently uncharged, 5 x 10(-3) M). We also determined the effect of the protein kinase C (PKC) inhibitors chelerythrine (5 x 10(-5) M), calphostin C (3 x 10(-6) M) and Ro 31-8220 (10(-7) M), and the effect of PKC activation with phorbolester (10(-6) M).

RESULTS

Non-injected oocytes were unresponsive to agonist application, but oocytes expressing NMDA receptors responded with inward currents (1.1+/-0.08 microA). All LA concentration-dependently inhibited agonist responses. The inhibition was reversible and stereoselective. Intracellular QX314 reduced responses to 59% of control, but extracellular QX314 was without effect. Benzocaine reduced responses to 33% of control. PKC inhibitors had no additional inhibitory effect beyond that of bupivacaine. The effect of PKC activation was abolished in the presence of bupivacaine.

CONCLUSION

All LA tested inhibited the activation of human NMDA receptors in a concentration dependent fashion. This effect may contribute to reduced hyperalgesia and opiate tolerance observed after systemic administration of LA. The effect is independent of the charge of LA; site of action is intracellular. The mechanism of action may be mediated by inhibition of PKC.

Comparison of electrical velocimetry and transoesophageal Doppler echocardiography for measuring stroke volume and cardiac output † †Declaration of interest. This study was supported by Osypka Medical GmbH, Berlin, Germany

BACKGROUND

Impedance cardiography (ICG) has been used extensively to estimate stroke volume (SV) and cardiac output (CO) from changes of thoracic electrical bioimpedance (TEB). However, studies comparing ICG with reference methods have questioned the reliability of this approach. Electrical velocimetry (EV) provides a new algorithm to calculate CO from variations in TEB. As the transoesophageal Doppler echocardiographic quantification of CO (TOE-CO) has emerged as a reliable method, the purpose of this study was to determine the limits of agreement between CO estimations using EV (EV-CO) and TOE-CO.

METHODS

Standard ECG electrodes were used for non-invasive EV-CO measurements. These were placed on 37 patients scheduled for coronary artery surgery necessitating transoesophageal echocardiography monitoring. Simultaneous EV-CO and TOE-CO measurements were recorded after induction of anaesthesia. EV-CO was calculated using the Bernstein-Osypka equation. TOE-CO was measured across the aortic valve using continuous-wave Doppler echocardiography and a triangular orifice model.

RESULTS

A significant high correlation was found between the TOE-CO and the EV-CO measurements (r2=0.86). Data were related linearly. The slope of the line (1.10 (se 0.07)) was not significantly different from unity, and the point at which it intersected the ordinate (-0.46 (0.32) litre min(-1)) was not significantly different from zero. Bland-Altman analysis revealed a bias of 0.18 litre min(-1) with narrow limits of agreement (-0.99 to 1.36 litre min(-1)).

CONCLUSIONS

The agreement between EV-CO and TOE-CO is clinically acceptable, and these two techniques can be used interchangeably.

Effective systolic orifice area of the aortic valve: implications for Doppler echocardiographic cardiac output determinations

BACKGROUND

Substantial research using echocardiography has established that stroke volume (SV) or cardiac output (CO) can be measured non-invasively at the level of the aortic valve (AV) with high accuracy. Stroke volume is the product of the velocity time integral occurring at the sampling site and the effective systolic AV orifice area (AVOAeff). Nevertheless, a generally accepted method for the determination of AVOAeff is still lacking.

METHODS

Aortic valve OAeff was measured in 228 consecutive patients scheduled for coronary artery surgery. Two widely adopted methods were applied to approximate the constantly changing orifice area of the AV: (1) the circular orifice model (AVOA-CM), and (2) the triangular orifice model (AVOA-TM). Aortic valve OA-CM assumes the shape of a circle as an appropriately time averaged geometrical model, and AVOA-TM takes the shape of an equilateral triangle for granted.

RESULTS

The AV was easily imaged by echocardiography in both short- and long-axis views in all patients. Relying on AVOA-CM, AVOAeff was 3.49+/-0.77 cm2. AVOA-TM estimates were 2.80+/-0.55 cm2 (mean+/-SD). The results did not agree (bias analysis).

CONCLUSIONS

The echocardiographic measurement of SV or CO at the level of the AV has to be reconsidered.

Arg123-Tyr166 domain of human ApoA-I is critical for HDL-mediated inhibition of macrophage homing and early atherosclerosis in mice

Atherosclerosis was studied in apolipoprotein E (apoE) knockout mice expressing human apolipoprotein A-I (apoA-I) or an apoA-I/apolipoprotein A-II (apoA-II) chimera in which the Arg123-Tyr166 central domain of apoA-I was substituted with the Ser12-Ala75 segment of apoA-II. High density lipoprotein (HDL) cholesterol levels were identical in apoA-I and apoA-I/apoA-II mice, but at 4 months, plaques were 2.7-fold larger in the aortic root of the apoA-I/apoA-II mice (P<0.01). The macrophage-to-smooth muscle cell ratio of lesions was 2.1-fold higher in apo-I/apoA-II mice than in apoA-I mice (P<0.01). This was due to a 2.7-fold higher (P<0.001) in vivo macrophage homing in the aortic root of apoA-I/apoA-II mice. Plasma platelet-activating factor acetyl hydrolase activity was lower (P<0.01) in apoA-I/apoA-II mice, resulting in increased oxidative stress, as evidenced by the higher titer of antibodies against oxidized low density lipoprotein (P<0.01). Increased oxidative stress resulted in increased stimulation of ex vivo macrophage adhesion by apoA-I/apoA-II beta-very low density lipoprotein and decreased inhibition of beta-very low density lipoprotein-induced adhesion by HDL from apoA-I/apoA-II mice. The cellular cholesterol efflux capacity of HDL from apoA-I/apoA-II mice was very similar to that of apoA-I mice. Thus, the Arg123-Tyr166 central domain of apoA-I is critical for reducing oxidative stress, macrophage homing, and early atherosclerosis in apoE knockout mice independent of its role in HDL production and cholesterol efflux.

Deletion of the hypoxia-response element in the vascular endothelial growth factor promoter causes motor neuron degeneration

Hypoxia stimulates angiogenesis through the binding of hypoxia-inducible factors to the hypoxia-response element in the vascular endothelial growth factor (Vegf) promotor. Here, we report that deletion of the hypoxia-response element in the Vegf promotor reduced hypoxic Vegf expression in the spinal cord and caused adult-onset progressive motor neuron degeneration, reminiscent of amyotrophic lateral sclerosis. The neurodegeneration seemed to be due to reduced neural vascular perfusion. In addition, Vegf165 promoted survival of motor neurons during hypoxia through binding to Vegf receptor 2 and neuropilin 1. Acute ischemia is known to cause nonselective neuronal death. Our results indicate that chronic vascular insufficiency and, possibly, insufficient Vegf-dependent neuroprotection lead to the select degeneration of motor neurons.

Adenovirus-Mediated Gene Transfer of Human Platelet-Activating Factor–Acetylhydrolase Prevents Injury-Induced Neointima Formation and Reduces Spontaneous Atherosclerosis in Apolipoprotein E–Deficient Mice

Background —Atherosclerosis is characterized by an early inflammatory response involving proinflammatory mediators such as platelet-activating factor (PAF)-like phospholipids, which are inactivated by PAF-acetylhydrolase (PAF-AH). The effect of adenovirus-mediated expression of PAF-AH on injury-induced neointima formation and spontaneous atherosclerosis was studied in apolipoprotein E–deficient mice.

Methods and Results —Intravenous administration of an adenovirus (5×10 8 plaque-forming units) directing liver-specific expression of human PAF-AH resulted in a 3.5-fold increase of plasma PAF-AH activity at day 7 ( P <0.001); this was associated with a 2.4- and 2.3-fold decrease in malondialdehyde-modified LDL autoantibodies and the lysophosphatidylcholine/phosphatidylcholine ratio, respectively ( P <0.001 for both). Non-HDL and HDL cholesterol levels in PAF-AH –treated mice were similar to those of control virus-treated mice. Seven days after virus injection, endothelial denudation of the common left carotid artery was induced with a guidewire. Neointima formation was assessed 18 days later. PAF-AH gene transfer reduced oxidized lipoproteins by 82% ( P <0.001), macrophages by 69% ( P =0.006), and smooth muscle cells by 84% ( P =0.002) in the arterial wall. This resulted in a 77% reduction ( P <0.001) of neointimal area. Six weeks after adenovirus-mediated gene transfer, spontaneous atherosclerotic lesions in the aortic root were analyzed. PAF-AH gene transfer reduced atherosclerotic lesions by 42% ( P =0.02) in male mice, whereas a nonsignificant 14% reduction was observed in female mice. Basal and PAF-AH activity after gene transfer were higher in male mice than in female mice ( P =0.01 and P =0.04, respectively).

Conclusions —Gene transfer of PAF-AH inhibited injury-induced neointima formation and spontaneous atherosclerosis in apolipoprotein E–deficient mice. Our data indicate that PAF-AH, by reducing oxidized lipoprotein accumulation, is a potent protective enzyme against atherosclerosis.

Regional anaesthesia in patients at coronary risk for noncardiac and cardiac surgery

This review presents a brief overview about the role of regional anaesthesia in patients at risk for myocardial ischemia and/or infarction after cardiac and noncardiac surgical procedures. It includes pathophysiological insights in the problems of plaque rupture and the possible interactions by the use of regional anaesthesia. Special emphasis is put on the subject of thoracic epidural anaesthesia with newer studies showing improvement in relief of angina and improvement of global systolic and diastolic function in patients with coronary artery disease.

HDL-associated PAF-AH reduces endothelial adhesiveness in apoE-/- mice

Macrophage infiltration into the subendothelial space at lesion prone sites is the primary event in atherogenesis. Inhibition of macrophage homing might therefore prevent atherosclerosis. Since HDL levels are inversely correlated with cardiovascular risk, their effect on macrophage homing was assessed in apoE-deficient (apoE-/-) mice. Overexpression of human apolipoprotein AI in apoE-/- mice increased HDL levels 3-fold and reduced macrophage accumulation in an established assay of leukocyte homing to aortic root endothelium 3.2-fold (P<0.005). This was due to reduced in vivo betaVLDL oxidation, reduced betaVLDL triggered endothelial cytosolic Ca2+ signaling through PAF-like bioactivity, lower ICAM-1 and VCAM-1 expression, and diminished ex vivo leukocyte adhesion. Adenoviral gene transfer of human PAF-acetylhydrolase (PAF-AH) in apoE-/- mice increased PAF-AH activity 1.5-fold (P<0.001), reduced betaVLDL-induced ex vivo macrophage adhesion 3.5-fold (P<0.01), and reduced in vivo macrophage homing 2.6-fold (P<0.02). These inhibitory effects were observed in the absence of increased HDL cholesterol levels. In conclusion, HDL reduces macrophage homing to endothelium by reducing oxidative stress via its associated PAF-AH activity. This protective mechanism is independent of the function of HDL as cholesterol acceptor. Modulation of lipoprotein oxidation by PAF-AH may prevent leukocyte recruitment to the vessel wall, a key feature in atherogenesis.

Perflubron emulsion delays blood transfusions in orthopedic surgery. European Perflubron Emulsion Study Group

BACKGROUND

Fluorocarbon emulsions have been proposed as temporary artificial oxygen carriers. The aim of the present study is to compare the effectiveness of perflubron emulsion with the effectiveness of autologous blood or colloid infusion for reversal of physiologic transfusion triggers.

METHODS

A multinational, multicenter, randomized, controlled, single-blind, parallel group study was performed in 147 orthopedic patients. Patients underwent acute normovolemic hemodilution with colloid to a target hemoglobin of 9 g/dl with an inspiratory oxygen fraction (FIO2) of 0.40. Patients were then randomized into one of four treatment groups after having reached any of the protocol-defined transfusion triggers including tachycardia (heart rate > 125% of posthemodilution rate or > 110 bpm), hypotension (mean arterial pressure < 75% of posthemodilution level or < or = 60 mmHg), elevated cardiac output (> 150% of posthemodilution level) or decreased mixed venous oxygen partial pressure (PVO2; < 38 mmHg). Treatments in the four groups were 450 ml autologous blood harvested during acute normovolemic hemodilution given at FO2 = 0.40; 450 ml colloid at FIO2 = 1.0; 0.9 g/kg perflubron emulsion with colloid (total = 450 ml) at FIO2 = 1.0; and 1.8 g/kg perflubron emulsion with colloid (total = 450 ml) at FIO2 = 1.0. The primary endpoint was duration of transfusion-trigger reversal. A secondary end-point was percentage of transfusion-trigger reversal.

RESULTS

Perflubron emulsion was well tolerated with no serious adverse event attributed to drug treatment. Duration of reversal was longest in the 1.8 g/kg perflubron group (median, 80 min; 95% confidence interval, 60-100 min; P = 0.014 vs. autologous blood, P < 0.001 vs. colloid) followed by the 0.9 g/kg perflubron group (median, 59 min; 95% confidence interval, 40-90 min), the autologous blood group (median, 55 min; 95% confidence interval, 30-70 min) and the colloid group (median, 30 min; 95% confidence interval, 27-60 min). Percentage of reversal was also highest in the 1.8 g/kg perflubron group (97%; P < 0.001 vs. autologous blood; P = 0.014 vs. colloid), followed by 0.9 g/kg perflubron (82%), colloid (76%), and autologous blood (60%).

CONCLUSIONS

Perflubron emulsion (1.8 g/kg) combined with 100% oxygen ventilation is more effective than autologous blood or colloid infusion in reversing physiologic transfusion triggers.

Circulating activated platelets assist THP-1 monocytoid/endothelial cell interaction under shear stress

Circulating complexes of leukocytes and activated platelets are markers for atherosclerosis, but their interaction with the arterial endothelial lining has not been studied. Therefore, the effect of activated platelets on rolling and adhesion of labeled human THP-1 monocytoid cells to human umbilical vein endothelial cell (HUVEC) monolayers was studied by epifluorescence microscopy in a parallel plate flow chamber. In the absence of activated platelets, THP-1 rolling on resting HUVEC was negligible at shear rates greater than 300 s(-1). Activation of HUVEC with 100 nmol/L phorbol myristate acetate (PMA) increased THP-1 cell adhesion at shear rates less than 400 s(-1). Therefore, a shear rate of 400 s(-1) was identified as a threshold for THP-1 adhesion. THP-1 rolling on activated HUVEC was reduced by 64% after L-selectin inhibition but was not affected by P-selectin inhibition. The addition of 1 to 50 thrombin receptor-activating peptide (TRAP)-activated platelets per THP-1 cell enhanced interactions between THP-1 cells and HUVEC, resulting in a steep bell-shaped dose-response curve, with a peak of 10 +/- 3 rolling cells/50 seconds at 3 platelets per THP-1 cell (P <.01 v control) with a concomitant 2- to 3-fold increase of firmly adhering cells (P <.01 v control). In reconstituted blood, low numbers of activated platelets had the same effect on THP-1 rolling and adhesion. P-selectin inhibition reduced platelet/THP-1 cell interaction in suspension and deposition of the complexes on the endothelial monolayer. Inhibition of both P- and L-selectin reduced THP-1/HUVEC interactions to 14% (P <.01, n = 4). Sialidase digestion and removal of terminal sialic acid residues from HUVEC or THP-1 cells but not from platelets abolished the platelet mediated augmentation of THP-1 cell adhesion. Thus, THP-1 rolling on HUVEC is shear-dependent and largely mediated by L-selectin. P-selectin expressed on activated platelets increases monocytoid cell adhesion to endothelial cells at shear rates found in coronary arteries through interactions with both endothelial and monocytoid cells and may facilitate macrophage accumulation in the vessel wall.

Inhibition of plasminogen activators or matrix metalloproteinases prevents cardiac rupture but impairs therapeutic angiogenesis and causes cardiac failure

Cardiac rupture is a fatal complication of acute myocardial infarction lacking treatment. Here, acute myocardial infarction resulted in rupture in wild-type mice and in mice lacking tissue-type plasminogen activator, urokinase receptor, matrix metalloproteinase stromelysin-1 or metalloelastase. Instead, deficiency of urokinase-type plasminogen activator (u-PA-/-) completely protected against rupture, whereas lack of gelatinase-B partially protected against rupture. However, u-PA-/- mice showed impaired scar formation and infarct revascularization, even after treatment with vascular endothelial growth factor, and died of cardiac failure due to depressed contractility, arrhythmias and ischemia. Temporary administration of PA inhibitor-1 or the matrix metalloproteinase-inhibitor TIMP-1 completely protected wild-type mice against rupture but did not abort infarct healing, thus constituting a new approach to prevent cardiac rupture after acute myocardial infarction.

Inhaled prostaglandin E1 for treatment of acute lung injury in severe multiple organ failure

Acute lung injury is characterized by hypoxemia due to pulmonary ventilation/perfusion-mismatching. I.v. administered prostaglandin E1 (PGE1), a vasodilator with a high pulmonary clearance, has been studied in acute lung injury. Inhalation of the vasodilators nitric oxide and prostacyclin improved oxygenation by selective dilation of the pulmonary vasculature in ventilated lung areas. In the present study, PGE1 inhalation was used for treatment of acute lung injury. Fifteen patients with acute lung injury defined as PaO2/fraction of inspired oxygen (FIO2) <160 mm Hg were treated with PGE1 inhalation in addition to standard intensive care. The drug was continuously delivered via a pneumatic nebulizer. Acute physiology and chronic health evaluation system II and multiple organ failure scores were (mean +/- SEM) 33 +/- 2 and 10 +/- 0.3, respectively. Inhaled PGE1 was administered for 103 +/- 17 h at a dose of 41 +/- 2 microg/h. The PaO2/FIO2 ratio increased from 105 +/- 9 to 160 +/- 17 mm Hg (P < 0.05) and to 189 +/- 25 mm Hg (P < 0.05) after 4 h and 24 h, respectively. PGE1 inhalation decreases in mean pulmonary artery pressure and central venous pressure were not statistically significant. Mean arterial pressure, pulmonary capillary wedge pressure, cardiac output, and heart rate remained unchanged. Intensive care unit mortality was 40%. The present data suggest that inhaled PGE1 is an effective therapeutic option for improving oxygenation in patients with acute lung injury. Whether inhaled PGE1 will increase survival in acute lung injury should be investigated in a controlled prospective trial.

IMPLICATIONS

In patients with severe acute lung injury and multiple organ failure, inhaled prostaglandin E1 improved oxygenation and decreased venous admixture without affecting systemic hemodynamic variables. Controlled clinical trials are warranted.

Arterio-venous carboxyhemoglobin difference suggests carbon monoxide production by human lungs

Carbon monoxide is hypothesized to be produced by the enzyme heme oxygenase predominantly in liver and spleen, bound to hemoglobin, and excreted by the lungs. Thus, venous carboxyhemoglobin is expected to be higher or equal to arterial carboxyhemoglobin. Unspecific inflammatory stimuli have been shown to induce heme oxygenase in lung tissue possibly leading to pulmonary carbon monoxide production. Arterial and central venous carboxyhemoglobin levels were measured in critically ill patients on the third day of ICU stay (n = 59) as well as in otherwise healthy humans prior to orthopedic surgery (n = 29). Arterial and central venous carboxyhemoglobin were higher in ICU patients than in healthy humans, respectively. In both groups, arterial carboxyhemoglobin was significantly higher than central venous carboxyhemoglobin. The arteriovenous carboxyhemoglobin differences were similar in both groups. The data suggest (a) increased CO-generation in critical illness and (b) pulmonary CO-production in healthy and critically ill humans.

LDL hypercholesterolemia is associated with accumulation of oxidized LDL, atherosclerotic plaque growth, and compensatory vessel enlargement in coronary arteries of miniature pigs

The association between accumulation of oxidized low density lipoprotein (LDL) and (1) progression of atherosclerotic plaques and (2) compensatory enlargement was assessed in the coronary arteries of LDL-hypercholesterolemic miniature pigs. In miniature pigs fed a 4% cholesterol diet, LDL cholesterol levels increased from 27+/-3.5 mg/dL (mean+/-SEM, n=36) to 250+/-28 mg/dL (n=10), 260+/-15 mg/dL (n=6), and 260+/-17 mg/dL (n=10) at 6, 14, and 24 weeks, respectively. Mean intimal areas of lesions in the left anterior descending coronary artery of hypercholesterolemic pigs were 0.16+/-0.046 mm2 at 6 weeks (n=10) and increased 5.4-fold (n=6, P<.05) and 10.6-fold (n=10, P<.001) at 14 and 24 weeks, respectively. Plaque growth was associated with an increase in mean internal elastic lamina area, from 1.44+/-0.17 to 4.38+/-0.52 mm2 (P=.007) and in mean luminal area from 1.42+/-0.15 mm2 in control pigs to 4.38+/-0.52 mm2 in pigs fed a cholesterol diet for 24 weeks (P=.007 vs control). Levels of total LDL in the intima, measured immunocytochemically, were 0.031+/-0.0098, 0.11+/-0.057 (P< or =.05), and 0.43+/-0.082 U (P<.001) at 6, 14, and 24 weeks, respectively. Corresponding levels of oxidized LDL were 0.034+/-0.023, 0.11+/-0.050 (P<.05), and 0.44+/-0.065 U (P<.001), respectively, suggesting that virtually all LDL in the intima is oxidized. Levels of oxidized LDL in the lesions were correlated with the intimal areas (r=.85, P<.0001) but were independent of plasma levels of LDL cholesterol and of oxidized LDL. Plaque levels of oxidized LDL were also correlated with internal elastic lamina areas (r=.72, P<.0001) and with luminal areas (r=.50, P=.0098). Plaque growth in the coronary arteries of LDL-hypercholesterolemic miniature pigs is associated with (1) an increase in plaque levels of oxidized LDL at constant plasma levels of LDL cholesterol and of oxidized LDL and (2) compensatory vessel enlargement proportional to plaque levels of oxidized LDL.

Adhesiveness of mononuclear cells in hypercholesterolemic humans is normalized by dietary L-arginine

Hypercholesterolemia reduces vascular nitric oxide (NO) activity. This dysfunction may promote endothelial monocyte interaction, as NO is a potent inhibitor of cell adhesion. We have previously shown that in hypercholesterolemic (HC) rabbits, chronic oral supplementation of L-arginine (Arg) restores NO activity and inhibits monocyte-endothelial cell interaction, in association with a reduction in atherogenesis. We hypothesized that enhancement of endothelial NO activity in HC humans would reduce monocyte adhesiveness. We used a functional binding assay to assess the adhesiveness of human mononuclear cells (MNCs) ex vivo to determine the effects of hypercholesterolemia and L-arginine administration. MNCs from HC subjects adhered in greater numbers (50% more cells per high-power field; P < .0001) than cells derived from normocholesterolemic (NC) subjects. To determine whether enhancement of endogenous NO activity could inhibit mononuclear cell adhesiveness, in a double-blinded placebo-controlled study, oral arginine HCl (8.4 g/d) was administered to HC subjects. Over a course of 2 weeks, this treatment abolished the increased adhesiveness of HC MNCs (160 +/- 11% versus 104 +/- 5%; before and after 2 weeks of Arg treatment; results expressed as a percentage of the binding values obtained using cells derived from paired NC individuals). By contrast, MNC adhesion remained significantly elevated in placebo-treated HC subjects. To examine whether endothelium-derived NO could act as a paracrine modulator of monocyte behavior, monocytes were exposed to NO donors or cocultered in the presence of endothelial cells exposed to antagonists of NO synthase in the presence or absence of L-arginine. NO donors inhibited monocyte adhesiveness. Furthermore, the adhesiveness of monocytes cocultured with endothelial cells was increased by antagonists of NO synthase; this effect was reversed by L-arginine. This study shows that the adhesiveness of human MNCs is increased by hypercholesterolemia. The increase in adhesiveness was reversed in vivo by administration of the NO precursor L-arginine. NO donors or endothelium-derived NO inhibits the adhesiveness of monocytes in vitro, supporting the hypothesis that the effects of L-arginine are mediated by NO.

Dietary L-arginine supplementation normalizes platelet aggregation in hypercholesterolemic humans

OBJECTIVES

The present study was designed to test the hypothesis that long-term dietary supplementation with the nitric oxide precursor L-arginine would enhance vascular or platelet-derived nitric oxide activity, or both, and thereby inhibit platelet reactivity in hypercholesterolemic humans.

BACKGROUND

We have shown that reduced vascular activity of nitric oxide in hypercholesterolemic rabbits can be restored by L-arginine supplementation. The improvement in nitric oxide activity is associated with an inhibition of platelet aggregation ex vivo. This effect is most likely due to increased elaboration of endothelium- or platelet-derived nitric oxide, or both, because the inhibition of platelet reactivity was associated with elevation of intraplatelet cyclic guanosine monophosphate and was reversed by the nitric oxide synthase antagonist N-methyl-arginine.

METHODS

In a double-blinded, randomized, placebo-controlled trial, hypercholesterolemic patients were assigned to L-arginine hydrochloride, 8.4 g/day orally, or placebo for 2 weeks. Platelet-rich plasma was obtained for aggregometry induced by collagen (1 to 10 micrograms/ml) at four points: baseline, after 2 weeks of treatment, after a 2-week washout and after a long-term washout of 16 weeks on average. Aggregation was quantified by light transmittance and expressed as a percent transmittance observed with platelet-poor plasma.

RESULTS

Compared with normocholesterolemic control subjects, platelets from hypercholesterolemic subjects stimulated with 5 micrograms/ml of collagen showed increased aggregability (68.6% in hypercholesterolemic patients vs. 54.5% in normocholesterolemic control subjects, p < or = 0.02). After 2 weeks of treatment with L-arginine (but not placebo), platelet reactivity was modestly reduced; this effect persisted for 2 weeks after discontinuation of arginine (52.6% in arginine-treated patients vs. 65.1% in normocholesterolemic control subjects, p = 0.07). After 18 weeks (i.e., 16 weeks after discontinuing arginine treatment), the platelets of hypercholesterolemic patients once again became hyperaggregable, and the extent of platelet aggregation was significantly increased compared with the 4-week point (73.6% after vs. 52.6% during arginine treatment, p < 0.01). No significant change in platelet reactivity was seen in placebo-treated hypercholesterolemic patients throughout the study. L-Arginine treatment was well tolerated without side effects.

CONCLUSIONS

This double-blinded, placebo-controlled study demonstrates that dietary supplementation with L-arginine can modestly attenuate the increased platelet reactivity seen in hypercholesterolemic patients. The data are consistent with our previous studies in hypercholesterolemic animals, demonstrating that L-arginine restores endogenous nitric oxide activity and inhibits platelet aggregation. Enhancement of endogenous nitric oxide activity is a potential novel therapeutic strategy worthy of further study.

Dexamethasone-induced sodium influx in human lymphocytes

We evaluated the direct effects of glucocorticoids on intracellular sodium content and cellular transport systems. Cytosolic free sodium concentration ([Na+]i) was measured in intact human lymphocytes using the sodium-sensitive fluorescent dye sodium-binding benzofuran-isophthalate. Administration of dexamethasone for 60 min increased lymphocytic [Na+]i from 17.6 +/- 2.0 mmol/L to 24.3 +/- 3.9 nmol/L (n = 12; P < 0.01). The dexamethasone-induced [Na+]i increase was abolished in the absence of extracellular sodium, by mifepristone and by actinomycin D. The dexamethasone-induced [Na+]i increase was also seen after inhibition of Na+,K(+)-ATPase by 1 mmol/L ouabain. The present results indicate that dexamethasone produces a trans-plasma membrane sodium influx probably by early occurring genomic effects.

Filling state of intracellular Ca2+ pools triggers trans plasma membrane Na+ and Ca2+ influx by a tyrosine kinase-dependent pathway

The relations between the filling state of intracellular calcium stores that are regulated by the endoplasmic Ca(2+)-ATPase and trans plasma membrane sodium and calcium influx were investigated. The effects of specific inhibition of endoplasmic Ca(2+)-ATPase by thapsigargin, cyclopiazonic acid, and 2,5-di-(tert-butyl)-1,4-benzohydroquinone (BHQ) on cytosolic free sodium concentration ([Na+]i) and cytosolic free calcium concentration ([Ca2+]i) were evaluated in lymphocytes from healthy subjects using the fluorescent dyes sodium-binding benzofuran isophthalate and fura2. The specific inhibition of endoplasmic Ca(2+)-ATPase by thapsigargin, cyclopiazonic acid, or BHQ increased lymphocytic [Na+]i and [Ca2+]i. The thapsigargin-induced [Na+]i increase was abolished in the absence of external sodium, indicating that thapsigargin induced a trans plasma membrane sodium influx. In the absence of external calcium the thapsigargin-induced [Ca2+]i increase was significantly reduced, whereas the thapsigargin-induced [Na+]i increase remained the same. This finding indicates that the filling state of intracellular calcium pools rather than the elevation of [Ca2+]i per se regulates the plasma membrane permeability for sodium in lymphocytes. The inhibition of the tyrosine kinase by genistein inhibited the thapsigargin-induced increases of both [Na+]i and [Ca2+]i in lymphocytes. The present study shows that the filling state of intracellular thapsigargin-sensitive calcium pools regulates trans plasma membrane sodium and calcium influx via a tyrosine kinase-dependent pathway.

L-arginine attenuates platelet reactivity in hypercholesterolemic rabbits

Platelets are capable of producing nitric oxide (NO) through the L-arginine-NO synthase pathway. Acute exposure to supraphysiological concentrations of L-arginine in vitro increases the production of NO by platelets and is associated with an increase in platelet cyclic GMP (cGMP) levels and a reduction in platelet aggregation. The purpose of this study was to determine if chronic oral administration of L-arginine decreases platelet aggregation in hypercholesterolemic animals and to determine if this effect is mediated by the metabolism of L-arginine to NO. Male New Zealand White rabbits were fed normal chow (Con), a 1% cholesterol diet (Chol), or a 1% cholesterol diet supplemented with a sixfold enrichment of dietary L-arginine (Arg) or L-methionine (Met). After 10 weeks, cholesterol levels were equally increased in Chol and Arg animals, whereas plasma arginine levels were doubled in the Arg group. There was no difference in maximum aggregation initiated by ADP (100 mumol/L) between washed platelets from Con, Met, and Chol animals, but aggregation of platelets from Arg animals was significantly decreased (P < .05). In aggregating platelets from Arg animals, cGMP levels were significantly higher than the other groups (P < .05). When platelets were incubated ex vivo with the NO synthase inhibitor NG-monomethyl-L-arginine, the effects of dietary L-arginine were reversed. Chronic dietary supplementation of L-arginine decreases platelet aggregation in hypercholesterolemic rabbits. This effect appears to be due to the metabolism of L-arginine to NO.

Increased cytosolic sodium and reduced Na,K-ATPase activity in transgenic rats

The transgenic rat TGR(mRen2)27 is a new monogenetic model in hypertension research that develops fulminant hypertension after the mouse Ren-2d renin gene has been integrated into its genome. To evaluate the molecular mechanism of development of hypertension in this animal model, we measured cytosolic free sodium concentration in intact lymphocytes from seven transgenic rats and eight age-matched normotensive Sprague-Dawley rats using the novel sodium-sensitive fluorescent dye sodium-binding benzofuranisophthalate. Resting cytosolic sodium was significantly higher in transgenic rats compared with Sprague-Dawley rats (31.7 +/- 2.2 versus 18.2 +/- 0.4 mmol/L, mean +/- SEM, P < .001). Inhibition of Na,K-ATPase by 0.5 mmol/L ouabain for 5 minutes significantly increased lymphocytic cytosolic sodium in Sprague-Dawley rats to 36.5 +/- 3.4 mmol/L (P < .001 compared with resting value), whereas no significant change could be observed in transgenic rats (35.4 +/- 0.6 mmol/L), indicating that Na,K-ATPase is less responsive in transgenic rats. The Na,K-ATPase activity from erythrocytes was measured with an enzyme-linked assay. Na,K-ATPase activity was significantly reduced in transgenic rats compared with Sprague-Dawley rats (4.0 +/- 0.3 versus 8.1 +/- 0.6 U/L, P < .001). We concluded that reduced Na,K-ATPase activity leads to elevated cytosolic sodium in this model of genetic hypertension.