Nitric oxide: an endogenous modulator of leukocyte adhesion

A newly developed solution enhances thirty-hour preservation in a canine lung transplantation model

Ischemia and reperfusion cause the production of oxygen free radicals. These damage grafts or disrupt normal vascular homeostatic mechanisms, with a parallel reduction in endothelial nitric oxide and adenosine 3',5'-cyclic monophosphate levels. We hypothesized that lung preservation failure may be related to these events. To improve lung preservation, we prepared a new ET-Kyoto solution, which contains N-acetylcysteine (a radical scavenger), nitroglycerin (to elevate the nitric oxide level), and dibutyryl adenosine 3',5'-cyclic monophosphate (to elevate the adenosine 3',5'-cyclic monophosphate level) and examined its efficacy in a canine single-lung transplantation model. Lungs were flushed with new ET-Kyoto solution (group I, n = 9), basal ET-Kyoto solution (group II, n = 6), basal ET-Kyoto solution plus ethanol and propylene glycol (solvents of nitroglycerin; group III, n = 6), or low-potassium dextran glucose solution (group IV, n = 6), and stored at 4 degrees C for 30 hours. After left single-lung transplantation, the right main bronchus and right pulmonary artery were ligated and the functions of the transplanted lung were assessed for 6 hours. Arterial oxygen tension was significantly higher in group I than in groups II, III, and IV (p < 0.05). Peak inspiratory pressure and wet-to-dry lung weight ratio were significantly lower in group I than in groups II and IV (p < 0.01). Histologic and ultrastructural studies showed better preservation in group I than in groups II, III, and IV. We conclude that the new ET-Kyoto solution provides enhanced 30-hour lung preservation.

Nitric oxide reduces tumor cell adhesion to isolated rat postcapillary venules

Adhesion of circulating tumor cells to microvascular endothelium plays an important role in tumor metastasis to distant organs. The purpose of this study was to determine whether nitric oxide (NO) would attenuate tumor cell adhesion (TCA) to naive or lipopolysaccharide (LPS)-treated postcapillary venules. A melanoma cell line, RPMI 1846, was shown to be much more adhesive to postcapillary venules isolated from rat mesentery than to corresponding precapillary arterioles. Although venules exposed to LPS for 4 h demonstrated an increased adhesivity for the melanoma cells, TCA to LPS-treated arterioles was not altered. Isolated venules exposed to DETA/NO (1 mM), an NO donor, for 30 min prior to tumor cell perfusion prevented the increment in adhesion induced by LPS and attenuated TCA to naive postcapillary venules. While L-arginine (100 microM), an NO precursor, failed to decrease TCA to naive postcapillary venules, this treatment abolished LPS-stimulated TCA to postcapillary venules. The effect of L-arginine was reversed by administration of N(omega)-nitro-L-arginine methyl ester (L-NAME, 100 microM), an NO synthase (NOS) inhibitor. These observations indicate that both exogenous and endogenous NO modulate TCA to postcapillary venules. To assess the role of NO-induced activation of cGMP in the reduction in TCA produced by DETA/NO, two additional series of experiments were conducted. In the first series, LY-83583 (10 microM), a guanylyl cyclase inhibitor, was shown to completely reverse the effect of DETA/NO on TCA to both naive and LPS-activated postcapillary venules. On the other hand, administration of 8-bromoguanosine 3',5'-cyclic monophosphate (8-B-cGMP) (1 mM), a cell permeant cGMP analog, mimicked the effect of DETA/NO and reduced TCA to LPS-stimulated postcapillary venules. These data suggest that (a) tumor cells are more likely to adhere to postcapillary venules than to corresponding precapillary arterioles, (b) LPS enhances TCA to postcapillary venules, (c) both exogenously applied (DETA/NO) and endogenously generated (L-arginine) NO attenuate the enhanced adhesion induced by LPS, but only DETA/NO reduced TCA to naive postcapillary venules, and (d) the NO-induced reduction in TCA to LPS-activated postcapillary venules occurs by a cGMP-dependent mechanism.

Glyceryl trinitrate prevents neutrophil activation but not thromboxane release following ischaemia-reperfusion injury

The aim of this study was to determine whether glyceryl trinitrate (GTN) has a protective effect on neutrophil-mediated lung injury in a model of aortic occlusion (30 min) and reperfusion (120 min). Sprague-Dawley rats were randomized into control (n = 11), ischaemia-reperfusion (IR) (n = 12), and IR treated with GTN (2 micrograms kg-1 min-1) during reperfusion (n = 10). Myeloperoxidase (MPO) activity measured pulmonary neutrophil influx. Pulmonary endothelial permeability was measured by wet:dry weight ratio, bronchoalveolar lavage (BAL) protein and neutrophil counts. Neutrophil superoxide release was measured by flow cytometry in a further IR versus GTN experiment (n = 6 in each group). The significant increase in MPO activity produced by IR to a level of 7.99 units g-1 was prevented by GTN which reduced the level to 4.73 units g-1. The increase in pulmonary microvascular leakage after reperfusion was also prevented by GTN: BAL protein without GTN was 992 micrograms ml-1 and with GTN 579 micrograms ml-1; BAL neutrophil count without GTN was 3219 cells mm-3 and with GTN 820 cells mm-3; the wet:dry lung weight ratio without GTN was 3.8 and with GTN 3.3. Neutrophil superoxide release increased significantly after 40 min of reperfusion in the untreated IR group (P < 0.05). This increase was prevented in the GTN-treated group. GTN administration had no effect on plasma thromboxane production during revascularization. These data suggest that GTN administration during the reperfusion phase has the potential to decrease pulmonary microvascular injury.

Inhaled nitric oxide improves lung allograft function after prolonged storage

Morbidity caused by early allograft dysfunction, manifested by a progressive increase in pulmonary vascular resistance and a decrease in oxygenation, remains a serious problem in lung transplantation. Inhalation of nitric oxide, an essential homeostatic molecule, has been shown to have beneficial effects on a variety of acute lung injuries. The purpose of the present study was to investigate the effect of inhaled nitric oxide on posttransplant function of canine left lung allografts. Fourteen dogs underwent left lung allotransplantation. Donors received systemic heparin and prostaglandin E1 followed by pulmonary artery flush with modified Euro-Collins solution. Donor left lungs were stored for 18 hours at 1 degree C and subsequently implanted. Immediately after reperfusion, the contralateral right main pulmonary artery and bronchus were ligated. The chest was closed and recipients turned to the supine position for the 6-hour assessment period. Hemodynamic and arterial and venous blood gas analyses were made at 15-minute intervals at an inspired oxygen fraction of 1.0 and 5 cm of water positive end-expiratory pressure. Animals were killed at the end of the assessment. Allograft myeloperoxidase activity assays and wet/dry weight ratios were done. In group I (n = 5), nitric oxide gas was administered continuously at concentrations of 60 to 70 ppm before reperfusion and throughout the 6-hour assessment period. In group II (n = 5), nitric oxide administration was initiated at the same concentration after reperfusion injury had developed. Group III animals (n = 4) received no nitric oxide. Significant improvement in gas exchange was apparent in group I. At the end of the 6-hour assessment period, mean arterial oxygen tension was 253.8 +/- 44.7 mm Hg and 114.9 +/- 25.5 mm Hg in groups I and III, respectively (p < 0.05). Group II animals had no improvement in oxygenation with nitric oxide. Systemic hemodynamics were unaffected by nitric oxide. However, an immediate decrease in pulmonary vascular resistance was noted. Group I myeloperoxidase activity was significantly lower than that in control group III (0.24 +/- 0.06 versus 0.36 +/- 0.04 units, respectively; p < 0.05).

Effects of angiotensin II infusion and inhibition of nitric oxide synthase on the rat aorta

In previous studies, we showed that in vivo infusion of angiotensin II (Ang II) to adult rats induced vascular changes in gene expression, and this effect did not depend solely on blood pressure elevation. To determine whether nitric oxide can influence the effects of Ang II on the vessel wall, we administered to rats Ang II separately or in combination with the arginine analogue N omega-nitro-L-arginine methyl ester, which inhibits nitric oxide synthase chronically when given in vivo. We measured changes in aortic medial thickness, the association of macrophages with the endothelial surface of the aorta, the presence of proliferating cell nuclear antigen in the intima and adventitia as an index of aortic cell cycle changes, and the expression of immunodetectable fibronectin as an index of changes in the extra-cellular matrix. After 18 days of nitric oxide inhibition, the major changes were increased medial thickness and a 3.5-fold increase in the number of adherent macrophages. Rats treated with two different doses of Ang II for 3 days had a fivefold and threefold increase in the number of proliferating cells from the intimal and adventitial regions, respectively. Combined treatment resulted in increased medial thickness, intimal and adventitial cell proliferation, and macrophage adherence. An increased and altered pattern of fibronectin distribution was found in all treatment groups. Losartan administration prevented the effects of Ang II but not of nitric oxide inhibition, whereas administration of L-arginine, prevented both intimal macrophage adherence and increased adventitial proliferation in rats given combined treatment. The data suggest that nitric oxide selectively influences macrophage association with the arterial wall, whereas Ang II and nitric oxide may have opposing effects on arterial cell proliferation.

Atherosclerosis and the vascular biology of aging

With advancing age, a series of structural, architectural and compositional modifications take place in the vasculature. The diameter of the vessels tends to increase, and thickening of intimal and medial layers is often observed. In the subendothelial space, blood-derived leukocytes and an increased amount of "activated" smooth muscle cells are present. Extracellular matrix accumulates and becomes particularly rich in glycosaminoglycans. Collagen content increases, while elastin fibers appear progressively disorganized, thinner, and frequently fragmented. These changes in the normal architecture of the vessel wall, that could be referred to as "the vasculopathy of aging", are likely to be the consequence of adaptive mechanisms to maintain normal conditions of flow, mechanical stress and/or wall tension. Although many of these features are similar to the histological findings of the atherosclerotic vessels, atherosclerosis and age-related "vasculopathy" are two distinct phenomena. Nonetheless, several experimental observations in animal models suggest a special link between "the vasculopathy of aging" and atherosclerotic disease, and suggest a particular predisposition of the old vessel to develop the atherosclerotic lesion. Compared to vessels from young animals, older ones show a greater reactivity to mechanical injury and to chronic insults. This may reflect changes in the biology of the vessels that are "intrinsic" to the aging process. Indeed, aging affects the function and responsiveness of the endothelium and vascular smooth muscle cells. Endothelial permeability is increased with age, while ability to produce vasoactive substances declines. Smooth muscle cells from old individuals show a growth advantage over the young ones, and display an increased ability to migrate toward chemoattractants. Moreover, the accumulation of advanced glycation end products (AGEs) occurring with aging can trigger a series of cellular events, such as cellular oxidative stress, expression of leukocyte adhesion molecules, endothelial transmigration of monocytes, and smooth muscle cell chemotaxis, all considered important prelesional events in the atherogenesis process. Taken together, the changes occurring with aging, while unproven to initiate lesion formation per se, are likely to accelerate the development of the atherosclerotic plaque and contribute to increased severity of this disease in the elderly.

Downregulation of nitrovasodilator-induced cyclic GMP accumulation in cells exposed to endotoxin or interleukin-1 beta

1. Induction of nitric oxide synthase (iNOS) results in overproduction of nitric oxide (NO), which may be a principal cause of the massive vasodilatation and hypotension observed in septic shock. Since NO-induced vasorelaxation is mediated via the soluble isoform of guanylate cyclase (sGC), the regulation of sGC activity during shock is of obvious importance, but yet poorly understood. The aim of the present study was to investigate the activation of sGC by sodium nitroprusside (SNP) before and after exposure of rat aortic smooth muscle cells to endotoxin (LPS) or interleukin-1 beta (IL-1 beta). 2. Exposure of rat aortic smooth muscle cells to SNP (10 microM) elicited up to 200 fold increases in cyclic GMP. This effect was attenuated by 30-70% in IL-1 beta- or LPS-pretreated cells, in a pretreatment time-and IL-1 beta- or LPS-concentration-dependent manner. When, however, cells were exposed to IL-1 beta or LPS and then stimulated with the particulate guanylate cyclase activator, atriopeptin II, no reduction in cyclic GMP accumulation was observed. 3. Pretreatment of rats with LPS (5 mg kg-1, i.v.) for 6 h led to a decrease in aortic ring SNP-induced cyclic GMP accumulation. 4. The IL-1 beta-induced reduction in SNP-stimulated cyclic GMP accumulation in cultured cells was dependent on NO production, as arginine depletion abolished the downregulation of cyclic GMP accumulation in response to SNP. 5. Reverse-transcriptase-polymerase chain reaction analysis revealed that the ratio of steady state mRNA for the alpha, subunit of sGC to glyceraldehyde phosphate dehydrogenase was decreased in LPS- or IL-1 beta-treated cells, as compared to vehicle-treated cells. 6. Protein levels of the alpha 1 sGC subunit remained unaltered upon exposure to LPS or IL-1 beta, suggesting that the early decreased cyclic GMP accumulation in IL-1 beta- or LPS-pretreated cells was probably due to reduced sGC activation. Thus, the observed decreased responsiveness of sGC to NO stimulation following cytokine or LPS challenge may represent an important homeostatic mechanism to offset the extensive vasodilatation seen in sepsis.

Ca(2+)-dependent nitric oxide release in endothelial but not R3230Ac rat mammary adenocarcinoma cells

We have characterized the ability of several cell types associated with the microvasculature of solid tumors to release nitric oxide (NO.) in response to increases in cytosolic Ca2+ concentration ([Ca2+]c). EA.hy926 immortalized human umbilical vein endothelial cells (EC), rat fibroblasts (RFL), and tumorigenic cells isolated from R3230Ac rat mammary adenocarcinoma (MaC) were treated with thapsigargin (TG), an inhibitor of Ca(2+)-ATPase. NO. output was measured via a chemiluminescence detection system. Baseline NO. output was detectable only for EC. TG caused a significant increase in EC NO. output that could be blocked with NG-monomethyl-L-arginine and restored with L-arginine. TG did not stimulate NO. release from RFL or MaC cells, despite elevating [Ca2+]c in all cells. A Ca(2+)-dependent isoform of NO synthase (eNOS) was detected by immunoblot only in EC. These data indicate that EC, but not RFL or MaC, are capable of Ca(2+)-dependent NO. release and suggest that any Ca(2+)-dependent NO. release within this tumor is primarily of endothelial (and not tumorigenic cell) origin.

Supplemental L-arginine HCl augments bacterial phagocytosis in human polymorphonuclear leukocytes

That L-arginine (L-Arg) augments the host response to acute bacterial sepsis suggests that this amino acid intervenes early in the immune response, perhaps via the nitric oxide synthetase (NOS) pathway. The effect of L-Arg supplementation on in vitro phagocytosis of fluorescein-labeled, heat-killed Staphylococcus aureus by peripheral blood neutrophils (PMNs) from 12 normal human volunteers was studied. Separated PMNs were incubated for 2 h with labeled bacteria, with and without supplemental L-Arg, D-arginine, glycine, and/or the NOS inhibitors L-canavanine, aminoguanidine, or L-NG-nitroarginine methyl ester. PMNs were fixed and extracellular fluorescence quenched with crystal violet. By flow cytometry and confocal microscopy, L-Arg supplementation was shown to result in a highly significant increase in PMN bacterial phagocytosis, the maximal effect being seen with L-Arg 380 microM and falling off with higher concentrations. This augmentation was completely abrogated by NOS inhibitors in molar excess, but inhibitors alone did not suppress phagocytosis below that of unsupplemented controls. Neither D-arginine nor glycine affected phagocytosis; the L-Arg effect was stereospecific and not related to utilization of L-Arg as an energy source. L-Arg supplementation significantly enhances bacterial phagocytosis in human neutrophils, perhaps by effects on cytoskeletal phenomena, and this appears to be mediated through NOS activity. Phagocytosis by nonspecific immune cells which intervene early in the response to sepsis is critically important, and beneficial effects of L-Arg on the clinical course of sepsis may be due at least in part to augmentation of phagocyte function.

Intrathecal infusion of the nitric oxide synthase inhibitor N-methyl L-arginine after experimental spinal cord injury in guinea pigs

The potential role of nitric oxide (NO) production in secondary pathologic processes that follow spinal cord injury was examined in a guinea pig model that shows secondary loss of function for at least 3 days after trauma. Lateral compression injury of the lower thoracic cord was performed under ketamine/xylazine/acepromazine anesthesia. A fine polyethylene cannula was inserted through an incision in the dura rostral to the injury and run along the dorsal subdural space to the lesion level. The tube was connected to an osmotic pump delivering 1 microL/h of a 10 mM solution of either N-methyl-L-arginine or N-methyl-D-arginine in normal saline (pH 7.2). N-Methyl-L-arginine blocks both constitutive and inducible forms of NO synthase (NOS), present in neurons and inflammatory cells, respectively: N-methyl-D-arginine is the inactive stereoisomer. Two groups of 10 animals were used. Behavioral analysis and somatosensory evoked potential measurements were performed daily for 3 days, then the animals were fixed and survival of white matter at the center of the injury was evaluated, using toluidine-blue stained, 1 microns plastic sections. No significant difference was found between treated and control groups in degree or rate of secondary loss of spinal cord function or in the cross-sectional area of surviving white matter. These data do not support the hypothesis that local NO production by phagocytes, neurons, or other cells plays a significant role in secondary pathology of injury in this model.

Shear stress modulates expression of Cu/Zn superoxide dismutase in human aortic endothelial cells

A major determinant of the level of cellular superoxide anion (O2-.) is the dismutation of O2-. to hydrogen peroxide by the enzyme superoxide dismutase (SOD). Three forms of SOD exist, but in endothelial cells, the major form outside of the mitochondria is the cytosolic copper/zinc-containing superoxide dismutase (Cu/Zn SOD). Since fluid shear stress is an important determinant of the function and structure of endothelial cells in vivo, we examined the effect of laminar shear stress on the expression of Cu/Zn SOD in cultured human aortic endothelial cells. Laminar shear stress of 0.6 to 15 dyne/cm2 increased Cu/Zn SOD mRNA in a time- and dose-dependent manner in human aortic endothelial cells. Shear stress also increased both Cu/Zn SOD protein content and the enzyme activity. Nuclear runon assays showed that nuclei from human aortic endothelial cells exposed to laminar shear stress had a 1.6-fold greater transcriptional activity of the Cu/Zn SOD gene compared with cells not exposed to shear, indicating that an increase in Cu/Zn SOD mRNA induced by laminar shear stress is at least in part mediated by increased transcription. In contrast, shear stress had no effect on Cu/Zn SOD mRNA levels in human aortic smooth muscle cells. These findings show that physiological levels of shear stress increase expression of Cu/Zn SOD in the endothelium. This adaptation to shear stress might augment the effect of locally produced NO. and thereby promote the antiatherogenic and anti-inflammatory properties of the endothelial cell.

Failure of L-NAME to cause inhibition of nitric oxide synthesis: role of inducible nitric oxide synthase

We addressed the hypothesis that administration of nitric oxide synthase inhibitor, NG -nitro-L-arginine methyl ester (L-NAME) does not result in a sustained suppression of nitric oxide (NO) synthesis, because of a compensatory expression of inducible nitric oxide synthase (iNOS). L-NAME was administered in the drinking water (0.1-1.0 mg/ml) for 7 days to guinea pigs and rats. Nitric oxide synthesis was assessed by [1] ex vivo formation of nitrite in blood vessels and intestine [2] tissue levels of cGMP [3] iNOS gene expression by RT-PCR [4] NADPH diaphorase staining [5] direct assessment of NO release in tissue explants using a microelectrode/electrochemical detection system. Chronic L-NAME administration elevated intestinal cGMP and nitrite levels in guinea pigs (p < 0.05). In rats, intestinal nitrite levels were comparable in control and L-NAME treatment groups, whereas direct assessment of NO release defined a marked increase in the L-NAME group. Chronic L-NAME resulted in an induction of iNOS gene expression in rats and guinea pigs and novel sites of NADPH diaphorase staining in the intestine. We conclude that iNOS expression is responsible for a compensatory increase or normalization of NO synthesis during sustained administration of L-NAME.

Phase variation in Francisella tularensis affecting intracellular growth, lipopolysaccharide antigenicity and nitric oxide production

Many microbial pathogens, such as Mycobacterium spp. and Salmonella spp., use macrophage intracellular growth or antigenic variation as mechanisms for avoiding the host immune system. In this work we present evidence to show that the intracellular pathogen Francisella tularensis uses phase variation to alter antigenicity and the host macrophage nitric oxide response simultaneously, thereby modulating its intracellular growth. The lipopolysaccharide (LPS) and lipid A of F. tularensis fails to stimulate production of significant levels of nitric oxide (NO) by rat macrophages. However, spontaneous variants of F. tularensis expressing an antigenically distinct LPS induce rat macrophages to produce increased levels of NO, thereby suppressing microbial intramacrophage growth. Similarly, lipid A isolated from these variants stimulates increased levels of NO production. A reverse phase shift can occur, which returns the LPS to the original antigenic form, reduces NO production, and restores intramacrophage growth. These findings represent the first demonstration of a phase-variation phenomenon which modulates intracellular growth and an innate immune response. Furthermore, these results suggest that a microbial pathogen can exploit macrophage NO production for its own benefit, perhaps by prolonging the host-pathogen association during the acute phase of disease or during the process of establishing a carrier state.

Nitric oxide inhalation decreases pulmonary platelet and neutrophil sequestration during extracorporeal circulation in the pig

OBJECTIVE

The inhibiting effect of nitric oxide on the aggregation and adhesion of neutrophils and platelets has been well documented in vitro. In vivo evidence, however, is more scant. In this study, we studied the effects of inhaled nitric oxide on pulmonary cellular sequestration in our sham hemodialysis model. Accumulation of neutrophils and platelets in the lungs has been shown to be an early event in this model.

DESIGN

Prospective, randomized, controlled study.

SETTING

Animal laboratory at a university medical center.

SUBJECTS

Twenty-six anesthetized, mechanically ventilated pigs.

INTERVENTIONS

111Indium-oxine was used to selectively label neutrophils or platelets and the activity over the lungs was followed dynamically with a gamma camera. Sham hemodialysis, using a cuprophan hollow-fiber dialyzer, was instituted via catheters in the femoral vessels. The animals were divided into two main groups: a) the nitric oxide recipient group (n = 12, with platelets labeled in seven animals and neutrophils labeled in five animals); and b) the control group (n = 14, with platelets labeled in seven animals and neutrophils labeled in seven animals). The animals in the former group were given 50 parts per million of nitric oxide in the inspiratory gas from the beginning of dialysis and for 30 mins onward.

MEASUREMENTS AND MAIN RESULTS

Inhalation of nitric oxide attenuated the increase in activity over the lungs in both the neutrophil and platelet groups during sham hemodialysis. In addition, an inhibiting effect on the increase in pulmonary pressure was noted.

CONCLUSION

Apart from the effects of nitric oxide on central hemodynamics in this model, the scintigraphic findings indicate an in vivo effect of nitric oxide on the accumulation of platelets and neutrophils in the lungs, probably due to inhibition of the adhesion and/or aggregation of these cells.

Cold restraint stress-induced gastric mucosal dysfunction. Role of nitric oxide

The objectives of this study were to determine the cold restraint stress-induced changes in gastric mucosal permeability and to assess whether nitric oxide synthesis inhibition affects gastric mucosal integrity after cold-restraint administration. Cold-restraint stress caused multiple gastric lesions in 90% of animals. The lesion index was found to be 3.87 +/- 0.97 mm. Gastric mucosal permeability to the [51CR]EDTA molecule was significantly elevated in the cold-restraint group compared to control. In order to evaluate the role of nitric oxide in cold restraint stress-induced gastropathy, L-arginine analog NG-nitro-L-arginine methyl ester (L-NAME) was given as a bolus (10 mg/kg, intravenously) and infused at a rate of 2 mg/ml/hr for 2 hr after cold-restraint administration. L-NAME greatly exacerbated gastric mucosal dysfunction associated with cold-restraint stress. D-NAME, the biologically inactive enantiomer, did not enhance mucosal dysfunction, whereas L-arginine, the substrate for nitric oxide, reversed the effect of L-NAME. In an additional group of experiments, effects of cold-restraint stress and L-NAME on net transmucosal fluid flux as well as tissue myeloperoxidase activity (MPO) were assessed. Cold-restraint stress administration significantly reduced the absorptive capacity of stomach, whereas L-NAME treatment did not affect the stress-induced alterations on net fluid absorption. Furthermore, L-NAME treatment did not affect the cold restraint stress-induced changes in tissue MPO activity. Our results suggest that gastric barrier function is altered after cold-restraint stress and nitric oxide production is important in minimizing mucosal barrier dysfunction associated with cold-restraint stress administration. Our results also indicate that L-NAME-induced alterations on mucosal permeability are not related to net transmucosal fluid flux and tissue neutrophils.

Effect of human hemoglobin on systemic and regional hemodynamics in a porcine model of endotoxemic shock

OBJECTIVE

Excessive release of nitric oxide has been implicated as being an important factor contributing to systemic arterial hypotension in septic shock. Hemoglobin is an effective nitric oxide scavenger. The purpose of this study was to test the hypothesis that treatment with cross-linked human hemoglobin can ameliorate systemic arterial hypotension and improve organ perfusion in a porcine model of normodynamic endotoxemic shock.

DESIGN

Prospective, randomized, controlled trial.

SETTING

Laboratory at a university medical center.

SUBJECTS

Fourteen, male, random-bred swine.

INTERVENTIONS

All animals were challenged with Escherichia coli lipopolysaccharide (400 microg/kg) infused from t = 0 to 90 mins. Pigs in group 1 (n = 7) were infused with cross-linked human hemoglobin (150 mg/kg) at t = 30 mins. Pigs in group 2 (n = 7) were infused at t = 30 mins with 150 mg/kg of dextran (average molecular weight 70,000 daltons) as a 5% (weight per volume) solution.

MEASUREMENTS AND MAIN RESULTS

After infusion of endotoxin, mean arterial pressure decreased significantly (p < .05) but baseline cardiac index was maintained in both groups. In hemoglobin-treated pigs (group 1), mean arterial pressure was higher than in controls (group 2) from t = 60 to 120 mins (p < .05). There were no significant differences between the two groups in systemic vascular resistance index, renal blood flow, mesenteric blood flow, systemic oxygen delivery, or systemic oxygen extraction. Ileal mucosal blood flow was lower (p < .07) in group 1 than in group 2. Mean pulmonary arterial pressure increased relative to baseline in both groups, but was significantly greater in group 1 as compared with group 2. Compared with controls, infusion of hemoglobin significantly exacerbated endotoxin-induced arterial hypoxemia (p < .05).

CONCLUSIONS

Treatment with hemoglobin improved mean arterial pressure in endotoxemic swine without significantly impairing blood flow to the renal or mesenteric vascular beds. Infusion of hemoglobin, however, significantly exacerbated endotoxin-induced pulmonary hypertension and arterial hypoxemia. Additional pharmacologic strategies may be necessary to ameliorate the potential adverse pulmonary effects of administering hemoglobin solutions to patients with sepsis.

Inhibition of inducible nitric oxide synthase prevents myocardial and systemic vascular barrier dysfunction during early cardiac allograft rejection

NO is produced during cardiac allograft rejection by expression of inducible NO synthase (iNOS) in the rejecting heart. Recent evidence indicates that NO modulates vascular permeability under both physiological and pathophysiological conditions. The present study explored the effects of early acute cardiac allograft rejection, and specifically the effects of NO, on myocardial and systemic vascular barrier function using a quantitative double-tracer permeation method in a rat cardiac transplant model. Early allograft rejection increased albumin permeation twofold to fivefold in the allograft heart and systemic vasculature (brain, lung, sciatic nerve, diaphragm, retina, muscle, kidney, and uvea) compared with isografts and controls. There were no detectable differences in regional blood flow or hemodynamics, suggesting that increased albumin permeation resulted from increased vascular permeability. iNOS mRNA was expressed in the allograft heart and native lung and was associated with increased serum nitrite/nitrate levels. iNOS inhibition with aminoguanidine prevented or attenuated allograft heart and systemic vascular barrier dysfunction and reduced allograft serum nitrite/nitrate levels to isograft values. Aminoguanidine did not affect the mild histological changes of rejection present in allografts. These data demonstrate the novel observations that (1) endothelial barrier function is compromised in the systemic vasculature, particularly in the brain, remote from the site of allograft rejection; (2) allograft vascular barrier dysfunction is associated with increased NO production and iNOS mRNA expression in the affected tissues (eg, native lung and grafted heart); and (3) inhibition of NO production by iNOS prevents vascular barrier dysfunction in the allograft heart and systemic vasculature.

Lack of effect of recombinant human superoxide dismutase on cold ischemia-induced arteriosclerosis in syngeneic rat aortic transplants

Prolonged cold ischemia time and the generation of free oxygen radicals during reperfusion are risk factors for allograft arteriosclerosis. Growth factors are the main pro-proliferative mediators of smooth muscle cells in classical and in allograft arteriosclerosis. Superoxide dismutase is an enzyme that catalyzes the dismutation of superoxide anions into hydrogen peroxide. This study was designed to investigate which smooth muscle cell growth factor contribute to the formation of arteriosclerosis in syngenic vascular grafts with prolonged ischemia time, and whether perioperative intravenous administration of recombinant human superoxide dismutase (rh-SOD) prevents arteriosclerosis in these grafts. DA aortas were transplanted into DA recipients. One group of transplants was made with a short ex vivo ischemia time (15 min), while the other group transplant grafts was stored for 24 hr in cold saline. In addition to morphometric quantitation of the histological alterations, RNA isolated from grafts with short cold ischemia time in a semiquantitative polymerase chain reaction specific for various known smooth muscle cell growth factors. Syngeneic grafts with prolonged cold ischemia time showed severe intimal thickening and prominent medical necrosis, which were not seen in control groups. Approximately 3-fold levels of insulin-like growth factor-1 were found in ischemic syngeneic grafts compared with non-ischemic syngenic grafts, whereas epidermal growth factor levels were slightly lower. No changes in other growth factor mRNAs were found. Perioperative treatment with rh-SOD did not have significant effect on the extent of intimal thickening nor on the intensity of medial necrosis in grafts with prolonged ischemia time, and administration of rh-SOD did not change the expression level of insulin-like growth factor-1 in the grafts, either.

Differential localization of allograft nitric oxide synthesis: comparison of liver and heart transplantation in the rat model

Nitric oxide (NO) is a free radical with a diversity of cellular origins and potential functions. Within the realm of solid organ transplantation, NO has been the focus of much attention. Discordant reports have documented both suppression and potentiation of the alloimmune response. In addition to questions regarding its functional role, little is known of the cellular origins of NO in acute rejection of vascularized allografts. To address this question, acute rejection models of rat heterotopic heart and orthotopic liver transplantation were chosen. When compared with naive controls and isografted animals, acute rejection in both heart and liver transplantation was associated with elevated systemic levels of the NO metabolite, nitrite. This was accompanied by increased graft content of iNOS protein as determined by immunoblot analysis of protein extracts. Expression of iNOS mRNA was localized with in situ hybridization. In both heart and liver transplantation, iNOS mRNA was found in the inflammatory infiltrate accompanying acute rejection. In addition, hepatocytes also expressed iNOS mRNA in the rejecting liver allograft. In contrast, cardiac myocytes in the rejecting heart allograft did not stain for iNOS mRNA. These results indicate that organ-specific, differential cellular expression of iNOS occurs in the acutely rejecting allograft. Transcriptional regulation of iNOS may vary among various organs according to the local cellular milieu. In addition, there may be a variable allograft specific response to acute rejection which may modify the associated immunologic biology.

Additive effect of nitric oxide and prostaglandin-E2 synthesis inhibitors in endotoxin-induced uveitis in the rabbit

The involvement of nitric oxide (NO) and prostaglandin E2 (PGE2) was investigated in a model of intraocular inflammation induced by intravitreal injection of endotoxin (lipopolysaccharide, LPS, 10 ng) in rabbits. The severity of uveitis, the myeloperoxidase (MPO) activity in iris-ciliary body, and the protein concentration in aqueous humor were determined. Nitric oxide synthase (NOS) and cyclooxygenase (COX) activities were assessed respectively by nitrite and PGE2 levels in aqueous humor. Treatment with inhibitors of NOS (NG-nitro-L-arginine methyl ester, L-NAME, 50 mg/kp i.p.) or COX (diclofenac, 30 micrograms, topically), alone or in combination, were compared to a saline-treated group. Diclofenac or L-NAME alone reduced or delayed the intensity of uveitis, and partially decreased the protein concentration in aqueous humor; diclofenac, but not L-NAME, partially reduced the polymorphonuclear leukocyte infiltration in the iris ciliary body as indicated by the MPO activity. Treatment with both inhibitors in combination diminished the clinical uveitis, the disruption of the blood-aqueous barrier and the MPO activity in the iris-ciliary body. We conclude that NO and PGE2 have additive effects in endotoxin-induced uveitis in rabbits, and that the inhibition of both pathways would improve the therapeutical management of uveitis.

Aging progressively impairs endothelium-dependent vasodilation in forearm resistance vessels of humans

Studies in experimental models suggest that endothelium-derived nitric oxide is reduced with aging, and this circumstance may be relevant to atherogenesis. The aim of this study was to determine whether increasing age resulted in altered endothelium-dependent vasodilation in the forearm resistance vessels of healthy humans. Forearm blood flow was measured in 119 healthy subjects, aged 19 to 69 years, by venous occlusion plethysmography. Brachial artery infusions of methacholine chloride (0.03 to 10.0 microgram/min) were used to assess endothelium-dependent vasodilation and of sodium nitroprusside (0.03 to 10.0 microgram/min) to assess endothelium-independent vasodilation. The slope of the dose-blood flow response relation was calculated in each subject for each drug. Univariate and multiple stepwise regression analyses were used to relate vascular reactivity to selected variables, including age, lipids, and blood pressure. Endothelium-dependent vasodilation was progressively impaired with increasing age, assessed as a reduction in slope from 2.25 +/- 0.16 to 0.34 +/- 0.11 (mL/100 mL tissue per minute)/(microgram/min) (P <.001). The decline in endothelium-dependent vasodilation was already evident by the fourth decade (age 30 to 39 years). Endothelium-independent vasodilation did not change with age. Age, total cholesterol, and low-density lipoprotein cholesterol were univariate predictors of endothelium-dependent vasodilation. Age remained the most significant predictor of endothelium-dependent vasodilator responses by multiple stepwise regression analysis. From these observations, it can be concluded that endothelium-dependent vasodilation declines steadily with increasing age in healthy human subjects. Age is a strong univariate and multivariate predictor of endothelium-dependent vasodilation. This finding may be a marker for more widespread endothelial dysfunction.

L-arginine depletion inhibits glomerular nitric oxide synthesis and exacerbates rat nephrotoxic nephritis

Nitric oxide (NO) synthesis is induced in glomeruli in glomerulonephritis; its role in the pathogenesis of glomerular injury is unknown. Interpretation of its role using the currently available analogues of L-arginine as in vivo inhibitors of NO is complicated by their lack of specificity for inducible NO synthase (iNOS). As NO synthesis by iNOS depends on extracellular L-arginine, we have here examined effects of L-arginine depletion on glomerular NO synthesis and the course of accelerated nephrotoxic nephritis (NTN). Arginase, which converts L-arginine to urea and L-ornithine, was used to achieve L-arginine depletion. A single dose of i.v. arginase produced complete depletion of plasma arginine for four hours. Two forms of NTN were induced in preimmunised rats by nephrotoxic globulin: (1) the systemic form of the model by intravenous nephrotoxic globulin; or (2) the unilateral form of model by left kidney perfusion with nephrotoxic globulin, which avoids the complications of systemic administration of nephrotoxic globulin. Arginase reduced plasma arginine levels and the synthesis of nitrite (the stable end-product of NO) by NTN glomeruli (95% inhibition). Proteinuria was exacerbated. There was no effect on early (24 hr) leukocyte infiltration. In the systemic form of the model arginine depletion by i.v. arginase increased glomerular thrombosis at 24 hours, and the severity of histological changes at four days, accompanied by systemic hypertension. In the unilateral form of the model, where i.v. arginase did not induce hypertension, there was no increase in thrombosis or histological severity of nephritis. These results show that arginine depletion, which inhibits glomerular NO synthesis in NTN, leads to increased proteinuria. Where injury is severe, or accompanied by systemic hypertension, the disease is further exacerbated by glomerular thrombosis. These results suggest that NO has an important role in limiting acute glomerular injury.

Vascular gene transfer of the human inducible nitric oxide synthase: characterization of activity and effects on myointimal hyperplasia

BACKGROUND

Nitric oxide (NO) has been shown to decrease myointimal hyperplasia in injured blood vessels. We hypothesize inducible No synthase (iNOS) gene transfer even at low efficiency will provide adequate local no production to achieve this goal.

MATERIALS AND METHODS

A retroviral vector containing the human iNOS cDNA (DFGiNOS) was used to transfer the iNOS gene into vascular cells and isolated blood vessels to answer the following questions: can vascular endothelial and smooth muscle cells support iNOS activity and will low efficiency iNOS gene transfer suppress myointimal hyperplasia in injured porcine arteries?

RESULTS

DFGiNOS-infected sheep pulmonary artery endothelial cells (SPAEC) expressed significant iNOS mRNA and protein, releasing nitrite levels of 155.0 +/- 10.7 nmol/mg protein/24 h vs. 5.5 +/- 1.1 by control cells. Transduced rat smooth muscle cells (RSMC) also expressed abundant iNOS mRNA and protein, but, in contrast to SPAEC, NO synthesis was dependent on exogenous tetrahydrobiopterin (BH4) (291.8 +/- 10.4 nmol nitrite/mg protein/24 hr with BH4, 37.7 +/- 2.6 without BH4). Only porcine arteries infected with DFGiNOS following balloon injury exhibited a 3-fold increase in total NO synthesis and a 15-fold increase in cGMP levels over control vessels in a BH4 dependent fashion, despite only a 1% gene transfer efficiency. Transfer of iNOS completely prevented the 53% increase in myointimal thickness induced by balloon catheter injury; the administration of a NOS inhibitor reversed this effect.

CONCLUSIONS

These in vitro findings suggest that vascular iNOS gene transfer may be feasible. Furthermore, a low gene transfer efficiency may be sufficient to inhibit myointimal hyperplasia following arterial balloon injury, although a source of BH4 may be required.

Aggravation of experimental allergic encephalomyelitis (EAE) by administration of nitric oxide (NO) synthase inhibitors

Macrophages constitute a large proportion of the inflammatory cells that infiltrate the central nervous system (CNS) of animals with EAE. Through the production of inflammatory mediators these infiltrating macrophages can contribute to the regulation of the immune reaction within the CNS, that eventually results in neurological deficits associated with EAE. NO, a free radical produced by macrophages and other cell types, has been put forward as such an immune mediator. In the present study we show that macrophages isolated from the CNS of Lewis rats with clinical signs of EAE produce elevated amounts of NO. We treated rats, in which EAE was induced, with N(omega) -nitro-L-arginine-methylester or N(g)-monomethyl-L-arginine, inhibitors of NO synthase, either systemically via intraperitoneal injection, or intracerebrally via a cannula placed in the lateral ventricle. Both treatments resulted in a marked aggravation of clinical signs of EAE. These data point to an important role of NO, produced by infiltrating macrophages, as an immune-suppressor in the disease process during EAE.

Regulation of expression of the endothelial cell nitric oxide synthase

1. Recent studies have provided insight into how the expression of endothelial cell nitric oxide synthase (ecNOS) is regulated. 2. The promoter of ecNOS has several features that are compatible with a constitutively expressed, so-called 'house keeping' gene. These include absence of a TATA box and the presence of Sp1 binding sites located near the transcription start site. The promoter also contains a number of putative binding domains which suggests that it may be regulated by a variety of transcription factor mediated signals. 3. Studies of cultured endothelial cells suggest that ecNOS expression is modulated by shear stress, transforming growth factor beta, inhibition of protein kinase C and the state of proliferation. These experiments indicate that although the ecNOS is a 'constitutively expressed' gene, its content in the endothelium is subject to modest degrees of regulation that may have important physiological and pathophysiological implications.

Cardioprotective actions of oligotide, a single stranded polydeoxyribonucleotide complex, in myocardial ischaemia and reperfusion injury

1. The efficacy of oligotide, a single stranded polydeoxyribonucleotide complex, was examined in a feline model of myocardial ischaemia (MI: 90 min) and reperfusion (R: 270 min). Oligotide (15 mg kg-1 bolus) was administered intravenously 80 min after occlusion of the left anterior descending (LAD) coronary artery (i.e., 10 min prior to R) and continued for an additional 280 min (10 mg kg-1 h-1 infusion). 2. Oligotide-treated cats showed significantly smaller myocardial necroses and lower cardiac myeloperoxidase activities (significantly lower neutrophil infiltration) in the necrotic zone as compared to MI+R cats receiving only vehicle. 3. LAD coronary arteries isolated from MI+R cats exhibited a significant endothelial dysfunction (i.e., reduced endothelium-dependent relaxation), and significantly increased adherence of polymorphonuclear neutrophils (PMNs) ex vivo. However, oligotide significantly preserved endothelial function and attenuated PMN adherence in ischaemic LAD coronary arteries. 4. Oligotide attenuated P-selectin expression on thrombin-stimulated platelets as well as PMN adherence to thrombin-stimulated coronary endothelium. Immunohistochemical examination in vivo revealed that oligotide treatment also significantly inhibited coronary endothelial P-selectin expression after 90 min MI and 20 min R. 5. Oligotide exerted a significant cardioprotection in MI+R injury. The mechanism appears to be related to attenuation of PMN-endothelial interaction and eventual infiltration into the ischaemic myocardium.

Generation of nitric oxide and superoxide during reperfusion after focal cerebral ischemia in rats

We investigated the levels of nitrosyl hemoglobin (HbNO) in rat jugular blood by electron spin resonance (ESR) spectroscopy during and after middle cerebral artery occlusion. The levels of plasma nitric oxide (NO) end products, nitrate plus nitrate, were compared with the levels of HbNO. Small amounts of HbNO were detected in sham-operated rats (n=4) and those subjected to 2 h of occlusion (n=4), whereas nitrite plus nitrate was increased only in the latter (P<0.01; vs.sham). Upon reperfusion after 2 h of occlusion both HbNO and nitrite plus nitrate clearly increased after 15 min (n=4) and 30 min (n=6) reperfusion (P<0.01; vs.occlusion). Administration of superoxide dismutase (5 mg/kg) significantly increased HbNO (P<0.05) but not plasma nitrate plus nitrate (n=5). The increase in HbNO suppressed by administration of NG-nitro-L-arginine methyl ester (20mg/kg; n=4,P<0.01), and this suppression could be reversed by L-arginine (200 mg/kg) (n=4). The present study clearly showed that the L-arginine-NO synthase pathway was activated during reperfusion after focal cerebral ischemia and indicated the involvement of a reaction between NO and superoxide during early reperfusion.

A new side effect of inhaled nitric oxide in neonates and infants with pulmonary hypertension: functional impairment of the neutrophil respiratory burst

INTRODUCTION

Inhaled nitric oxide (NO) may be beneficial in the treatment of pulmonary hypertension, both of the newborn and in the adult respiratory distress syndrome. Up to now, serious systemic side effects have not been reported.

OBJECTIVE

The effect of inhaled NO on superoxide anion production by neutrophils.

DESIGN

Prospective study of a consecutive series of 15 neonates and infants.

SETTING

Neonatal and paediatric ICUs with a total of 17 beds (university hospital).

MEASUREMENTS AND RESULTS

Superoxide anion production was determined by a flow cytometric method using dihydrorhodamine 123 (DHR) as an oxidative probe after the priming of neutrophils with N-formyl-methionyl- leucylphenylalanine (fMLP) or with Escherichia coli. The generated fluorescence was expressed as relative fluorescence intensity (RFI). Inhalation of NO for more than 24 h reduced the superoxide anion production by neutrophils stimulated with E. coli to below baseline values before NO inhalation (mRFI = 158 +/- 25 vs 222 +/- 24; P = 0.03). This decrease was more pronounced after more than 72 h (mRFI = 133 +/- 17). At this time, superoxide anion production by fMLP-stimulated neutrophils was also decreased (mRFI = 40 +/- 3, vs 57 +/- 5; P = 0.03). The reduced capacity of superoxide production persisted throughout therapy with NO and lasted up to more than 4 days after the end of NO inhalation.

CONCLUSION

The results suggest that inhalation of NO in patients with pulmonary hypertension causes reduced superoxide anion production by neutrophils stimulated with E. coli or with fMLP. To determine the clinical importance of this systemic side effect with respect to bacterial infections, a randomized controlled study is necessary.

The role of the microcirculation in multiple organ dysfunction syndrome (MODS): a review and perspective

Major advances in intensive care medicine during the past two decades have altered the spectrum of disease encountered by intensive care physicians, anaesthesiologists, traumatologists and pathologists. One of the most important manifestations of severe trauma or infections is the multiple organ dysfunction syndrome (MODS), a life-threatening condition that often ends in multiple organ failure (MOF) and death. Evidence gathered from clinical and morphological observations in humans, taken together with experimental animal studies and a vast accumulation of in vitro data, clearly indicate that the microcirculation lies at the centre of this complex process, which results in peripheral vascular insufficiency, inadequate oxygen delivery to vital organs, and hence, severe organ dysfunction. The multifunctional nature of the endothelium makes it a prime candidate for study of the pathomechanisms of MODS. This paper reviews the evidence for the hypothesis that the microcirculation, and in particular its endothelial component, has a central role in the pathogenesis of MODS. The evidence is reviewed principally from the standpoints of classical morbid anatomy and cell pathobiology.

Chronic inhalation of nitric oxide inhibits neointimal formation after balloon-induced arterial injury

Systemic and local intravascular NO administration inhibits neointimal formation after vascular injury in animal models. NO appears to attenuate smooth muscle proliferation both directly and indirectly by preventing the release of growth factors. Inhalation of low concentrations of NO dilates pulmonary vascular smooth muscle but does not cause systemic vasodilatation. Recently, NO inhalation was found to inhibit platelet function in vivo. We studied the effects of NO inhalation on neointimal formation after balloon-induced injury of the adult rat carotid artery. Beginning 60 minutes before carotid injury, rats breathed either air with 0 or 80 ppm NO for 14 days. Rats were killed, carotid arteries were fixed and paraffin-embedded, and neointimal formation was measured by analyzing the ratio of intimal to medial areas (I/M ratio) in carotid artery cross sections. Intimal hyperplasia was evident in both groups of animals, but I/M ratios were 43% less in animals breathing 80 ppm NO for 2 weeks than in animals breathing air alone (0.78 +/- 0.12 and 1.37 +/- 0.11 [mean +/- SE], respectively; P < .02). Similarly, 1 week after carotid injury, neointimal formation was less in rats breathing 80 ppm NO than in rats breathing air alone (I/M ratio, 0.39 +/- 0.11 versus 0.76 +/- 0.06; P < .02). Breathing 20 ppm NO for 2 weeks or 80 ppm NO for 1 week followed by air alone for 1 week did not attenuate neointimal formation measured at 14 days. In anesthetized rats breathing 80 ppm NO or air alone for 1 hour, neither systemic blood pressure nor bleeding time differed. These observations demonstrate that inhaling 80 ppm NO inhibits neointimal formation after balloon-induced carotid artery injury in rats. NO inhalation may represent a safe and novel method of preventing restenosis after percutaneous angioplasty.

The vascular biology of nitric oxide and its role in atherogenesis

Nitric oxide (NO), the biologically active component of endothelium-derived relaxing factor, has critical roles in the maintenance of vascular homeostasis. Decreased endothelial NO production, as a result of endothelial dysfunction, occurs in the early phases of atherosclerosis. NO appears to inhibit atherogenesis by inhibiting leukocyte and platelet activation and by inhibiting smooth muscle cell proliferation. Endothelial denudation is a prominent feature of vascular injury associated with percutaneous angioplasty, and decreased NO production appears to contribute to the restenosis process. Manipulation of the NO/cGMP signal transduction system may provide novel therapeutic approaches for limiting atherogenesis and neointimal proliferation in the future.

Time dependence of Na-nitroprusside administration in the prevention of neutrophil infiltration in the rat ischemic kidney

The aim of this study was to determine the ideal time of administration of Na-nitroprusside to prevent neutrophil infiltration in ischemically damaged kidneys. Sprague-Dawley rats were subjected to 75 min of renal warm ischemia and contralateral nephrectomy. The animals were divided into 7 groups: the ischemic control (IC), which received normal saline, the sham group without warm ischemia and the experimental groups, which received intravenous Na-nitroprusside (NP) (5 mg/kg) at 75, 30, 15, and 5 min prior to reperfusion. Another experimental group was given verapamil (V) (5 mg/kg) as a NO-independent vasodilator 5 min prior to reperfusion. The final evaluation included survival at seven days, serum creatinine (SCr) and blood urea nitrogen (BUN) daily for 3 days, and neutrophil infiltration determined by the presence of myeloperoxidase (MPO) in renal tissue at 2 hr after reperfusion. Histological damage was assessed at 24 hr. There were significant improvements in all parameters when the Na-NP was administered at 75, 30, and 15 min prior to reperfusion when compared with the control group (p < 0.05). There were no differences either in survival or renal function when the 5 min group was compared with the IC or V groups. It is concluded then, that Na-NP can be administered as late as 15 min before reperfusion and still have a protective effect. It appears that the mechanism of protection of Na-NP is due to blocking of one of the steps of the interaction between leukocytes and endothelium--migration. Furthermore, the verapamil (a NO-independent vasodilator) and Na-NP5 (a NO-dependent vasodilator) groups did not show a beneficial effect in these severely ischemically damaged kidneys, which might be one more reason to believe that Na-NP could be interacting at the level of leukocyte-endothelial cell interaction.

Cellular localization and effect of nitric oxide synthesis in a rat model of orthotopic liver transplantation

Nitric oxide (NO) is a multifunctional free radical with a variety of described biochemical and physiological roles. The immunologic relationships between organ transplantation and NO synthesis are unknown. While a number of in vitro and in vivo models have demonstrated an immunomodulatory role for NO, results suggest both an immunosuppressive and immunostimulatory function. In order to better delineate the role of NO in liver transplantation, the Kamada model of rat OLT with strain combinations simulating acute rejection and spontaneous hyporesponsiveness was chosen. In this setting, both acute rejection and spontaneous hyporesponsiveness were associated with increased levels of plasma NO metabolites and allograft expression of the enzyme, NO synthase (iNOS). The extent of expression was significantly greater with acute rejection. Using in situ hybridization, iNOS mRNA was localized to both infiltrating inflammatory cells and hepatocytes in the context of acute rejection. In contrast, iNOS mRNA expression was isolated to the hepatocytes in the hyporesponsive state. To specifically delineate the role of hepatocyte-derived NO, NO synthesis was ablated in the spontaneous hyporesponsiveness model and resulted in significant elevation of serum transaminase values with accompanying histologic evidence of increased periportal inflammatory infiltration. Our results suggest that the site of NO production varies according to the immunologic status of the liver allograft, and hepatocyte-derived NO may be protective in the hyporesponsive state.

Gas-generating systems in acute renal allograft rejection in the rat. Co-induction of heme oxygenase and nitric oxide synthase

Gases are now viewed as biologic messengers, and in this regard, carbon monoxide and nitric oxide are incriminated in signaling processes in neural tissue. Carbon monoxide is generated by heme oxygenase (HO), an enzyme inducible by heme, cytokines, and oxidative stress and considered an antioxidant response; nitric oxide is generated by nitric oxide synthase, an enzyme also inducible by cytokines. Since mononuclear cells infiltrate the acutely rejecting kidney, and foster within the kidney oxidative stress and a cytokine-enriched milieu, we examined the expression of these enzymes in acute renal allograft rejection (AR) (Brown Norway kidney to a Lewis rat; n = 17) and in control isografts (Lewis kidney to a Lewis rat; n = 17). No immunosuppressives were used. We found marked induction of HO mRNA and protein in renal allografts at day 5 after transplantation. Prominent expression of HO protein, as detected by immunofluorescence, was observed in the mononuclear cells infiltrating the renal allograft. More than 80% of these cells were macrophages, as identified by positive staining with ED1 antibody. ED1+ cells were rare in isografts and did not stain for HO. We also found co-expression of mRNA and protein for the inducible isoform of nitric oxide synthase (iNOS) in AR at day 5 after transplantation. Induction of HO and iNOS may reflect the cellular effect of diverse cytokines elaborated in the rejecting kidney. HO may enable the macrophage to degrade heme-containing proteins released from erythrocytes and other damaged cells; alternatively, induction of HO may defend the macrophage against oxidant injury. Increased nitric oxide, as a result of iNOS activity, may antagonize the vasoconstrictive effects of a number of mediators (i.e., thromboxane and endothelin) present in acute rejection; conversely, nitric oxide may prove cytotoxic through a number of recognized effects. Our studies provide the first demonstration of the induction of HO in the rejecting renal allograft as well as the first demonstration in vivo for the induction of HO in macrophages at the site of an inflammatory response. Such expression, linked as it is to the expression of iNOS, indicates that the macrophage mimics the behavior of neural cells by generating these gaseous messengers; thus, neural cells are not alone in deploying these mediators. Through a number of effects, these products of HO and iNOS may influence the nature and severity of tissue injury in AR.

Autocrine growth inhibition of IL-1 beta-treated cultured human aortic smooth muscle cells: possible role of nitric oxide

This study was designed to investigate whether interleukin (IL)-1 beta would stimulate nitric oxide (NO) production in cultured aortic vascular smooth muscle cells (VSMCs), and to determine the basic effect of the liberated NO on VSMC proliferation. NO production was estimated from nitrite concentration of culture medium in multi-well plates, determined by the Griess method. VSMCs were IL-1 beta-pretreated in insert cups, and co-cultured with untreated VSMC in the wells. 3H-thymidine (3H-Tdr) incorporation into the VSMC in wells was evaluated for VSMC proliferative activity. IL-1 beta stimulated NO production in VSMCs in a concentration-dependent manner. This effect was further enhanced by the addition of a membrane-permeable cyclic adenosine monophosphate derivative, dibutyryl cyclic AMP (db-cAMP), and was significantly reduced by concomitant use of an NO synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME). IL-1 beta-pretreated VSMCs significantly inhibited 3H-Tdr incorporation of the co-cultured VSMC. This inhibitory effect was significantly enhanced by the addition of db-cAMP, while this inhibition was significantly decreased by preincubation with L-NAME, and was abolished in the L-arginine-free medium. These results suggest that, in human VSMC, IL-1 beta stimulates NO production that is enhanced by intracellular cAMP accumulation, and that the liberated NO inhibits further VSMC proliferation in an autocrine fashion.

Nitric oxide attenuates neutrophil-mediated myocardial contractile dysfunction after ischemia and reperfusion

With the knowledge of NO as an antiadhesion molecule, we performed studies to investigate the effects of NO on postischemic polymorphonuclear leukocyte (PMN)-medicated myocardial contractile dysfunction. Studies were performed with isolated perfused rat hearts subjected to 20 minutes of global ischemia and 45 minutes of reperfusion. Human PMNs (50 million) were infused over the first 5 minutes of reperfusion, and the recovery of left ventricular function was compared with baseline values. Infusion of PMNs alone (n = 10) led to a 61% reduction in left ventricular developed pressure (LVDP) and a 57% reduction in the pressure-rate product (PRP) at 45 minutes of reperfusion. Infusion of an NO donor, CAS-754 (n = 9), resulted in 80.2 +/- 6.7% recovery of LVDP and 77.0 +/- 8.6% recovery of PRP. Treatment with L-arginine (2.5 mmol/L, n = 10) resulted in a similar improvement in the postischemic contractile state of the heart. In contrast, NG-nitro-L-arginine methyl ester (L-NAME) treatment (250 mumol/L, n = 10) resulted in an exacerbation of contractile dysfunction, as evidence by a 93% reduction in LVDP at 45 minutes of reperfusion and a 91% reduction in PRP. The deleterious effects of L-NAME were prevented by L-arginine coperfusion. We failed to observe any cardioprotective effects when NO or L-arginine was administered to hearts subjected to 25 minutes of ischemia and 45 minutes of reperfusion in the absence of PMNs. In conclusion, PMN-mediated myocardial contractile dysfunction is attenuated by NO and exacerbated by blockade of NO synthesis.

Platelet activation and interactions with the microvasculature

Platelet adherence to structurally or functionally damaged endothelium and its subsequent activation are multifaceted events. Regulation of the rate and extent of platelet adhesion is under local control by the platelets and endothelium. Even in the absence of platelet adhesion to endothelium or subendothelium, there is a complex hemostatic balance of coagulation and anticoagulation. This is mediated by the manufacture, release, and inactivation of various procoagulant and anticoagulant compounds, predominantly by the platelets and endothelium. The relationship between the two in maintaining the homeostasis of coagulation and other processes is complex. This review focuses on the structure, function, and interaction of endothelium, subendothelium, and platelets and on their vasoactive and pro-/anticoagulant functions.

Endothelial dysfunction in preeclampsia. Part II: Reducing the adverse consequences of endothelial cell dysfunction in preeclampsia; therapeutic perspectives

Next to low-dose Aspirin there appear to be several new and promising pharmacologie approaches for reducing the adverse consequences of endothelial cell dysfunction in preeclampsia. Among these are selective thromboxane-A2 synthetase and/or thromboxane-A2 receptor antagonists, stable prostacyclin analogues, selective S(erotonin)2-receptor blockers, nitrovasodilators, glycoprotein IIb/IIIa antagonists, hirudin, and ticlopidine. Early-onset preeclampsia appears to be associated with certain disorders that are likely to provoke an arterial thrombotic process by impairing the normal endothelial cell-platelet interactions. Especially heterozygous hyperhomocysteinemia, protein S deficiency and anticardiolipin antibodies appear to be fairly common. The management of these 3 separate disease entities will be discussed.

Monosodium urate crystals promote neutrophil adhesion via a CD18-independent and selectin-independent mechanism

The primary objective of this study was to determine whether monosodium urate (MSU) crystals induced neutrophil adhesion to cellular substrata and, if so, then to elucidate the molecular mechanisms involved. Human umbilical vein endothelial cells (HUVEC), as well as various other cellular substrata, were treated with various sized MSU crystals, washed, and then coincubated in the presence of neutrophils for 60 min. HUVEC exposed to MSU crystals but not to silica crystals or uric acid promoted neutrophil adhesion in a dose- and size-dependent manner, an event also observed with monolayers of rabbit synovial cells and rat intestinal epithelial cells. The increased neutrophil adhesion could not be attenuated by anti-CD18, anti-intracellular adhesion molecule-1, or various anti-selectin antibodies, despite the fact that scanning electron microscopy revealed that neutrophils were adhering primarily to the endothelial cells rather than to exposed crystals. CD18-deficient neutrophils adhered to MSU crystal-treated HUVEC as effectively as their CD18-positive counterparts. The neutrophil adhesion was temperature dependent but did not require protein synthesis. Additionally, HUVEC phagocytosis of crystals was necessary for subsequent neutrophil-endothelial cell interactions to transpire. Pretreatment of endothelial cells and neutrophils with colchicine significantly reduced the adhesive interaction. Our data demonstrate that exposure of endothelial and other cells to MSU crystals promotes neutrophil adhesion that occurs by a firm CD18-independent and selectin-independent adhesive mechanism.

Effects of estrogen on atherosclerosis formation and serum nitrite/nitrate concentrations in cholesterol-fed ovariectomized rabbits

This study was to examine the effects of estrogen replacement on atherosclerosis formation in ovariectomized cholesterol-fed rabbits. We also examined serum levels of nitrite/nitrate, stable metabolites of nitric oxide, to investigate the involvement of nitric oxide. Female New Zealand White rabbits were ovariectomized and divided into 3 groups; 1) fed a normal diet (ND group, n=5), 2) fed a 1% cholesterol diet (CD group, n=6), or 3) fed a 1% cholesterol diet and received estrogen replacement (CD+E group, n=7). After 3 months, the rabbits were sacrificed to examine atherosclerosis formation. Atherosclerosis was not observed in ND. The oil red 0 positive area in the aorta was significantly greater in CD than in CD+E (CD, 17.3+/-2.2; CD+E, 9.3+/-0.8%, p<0.05). Stenosis of the coronary artery was also significantly greater in CD than in CD+E (CD, 30.6+/-9.7; CD+E, 6.7+/-2.9%, p <0.05). There was no significant difference in serum lipids between CD and CD+E. Serum nitrite/nitrate levels were significantly lower in CD than in ND (ND, 37.6+/-3.6; CD, 25.3+/-3.1 microM, p<0.05). There was a non-significant trend towards higher nitrite/nitrate levels after estrogen replacement (CD+E, 34.4+/-3.8 microM, p=0.08 vs. CD). These results suggest that direct actions on vascular wall including nitric oxide production contribute to the anti-atherogenic effects of estrogen.