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1Consiglio Nazionale delle Ricerca Institute of Clinical Physiology, Faculty of Medicine, University of Pisa, Pisa; and 2Department of Pharmaceutical Science, University of Padova, Padua, Italy
Submitted 21 October 2005 ; accepted in final form 17 February 2006
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ABSTRACT |
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 TOP ABSTRACT METHODSRESULTSDISCUSSIONGRANTSREFERENCES |
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lipid peroxides; vasodilation; capillary perfusion
Polyethylene glycol (PEG) is a water-soluble polymer, has no electric charge and no affinity for any specific organ, is nonimmunogenic and nontoxic, and differs in average molecular weight (19, 27, 34). PEG repairs neuronal membranes and inhibits free radical production in in vitro and in vivo models of spinal cord injury (22, 35). Recent findings demonstrated that PEG has a beneficial effect in early and long-term cold I/R injury, in renal medulla injury, and in the isolated perfused rat kidney (13, 20). Moreover, PEG interferes with the coagulation system and reduces platelet adhesion in vitro and in vivo (3, 15). PEG forms a molecular barrier on the glycocalyx, preventing acute platelet deposition on damaged arteries, and grafting of pericardium with PEG inhibits calcium deposits and reduces adhesion of platelets and leukocytes to the surface (12, 37). Therefore, by application of PEG with end groups reactive to protein-free amine to improve biostability, it is possible to reduce inflammation and control water content of endothelial cells (28, 32, 38).
We hypothesized that PEG could repair endothelial cell damage during postischemic reperfusion. Furthermore, we developed a novel macromolecular donor of NO in which 1, 8, and 16 NO-releasing molecules were covalently bound to PEG (PG1, PG8, and PG16, respectively). The NO-releasing molecule is butanediol mononitrate (BDMN), which is conjugated to the carboxylic groups of PEG derivatives by an ester linkage. PG8 and PG16 were obtained by preparation of PEG-dendron polymers, which allow circumvention of the common low loading of linear PEGs, in which only the two hydroxyl groups at the end chain can be used for drug linking. The dendritic structures were synthesized at the level of PEG ends by use of 
-glutamic acid as branching moiety; -glutamic acid doubles the number of carboxylic groups at each generation step of the dendrons and, thus, increases the drug/polymer payload (28). We examined the effects of PEG and mono-8–16-PEGylated compounds and their activity in the hamster cheek pouch by visualization with the intravital fluorescent microscopy technique (4–8). After treatment, the diameter, RBC velocity, and flow changes in arterioles were evaluated, as well as plasma lipid peroxidation, vascular permeability, leukocyte adhesion, and changes in perfused capillary length (PCL) (4, 7). Experiments were also carried out to measure the influence of I/R, with and without treatment, on plasma vWF concentration (2). To investigate the mechanisms contributing to the effects of the PEG compounds, the hamster cheek pouch was treated with the NO synthase inhibitor NG-monomethyl-L-arginine (L-NMMA) in addition to PEG-NO before I/R.
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METHODS |
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Glu-(Glu)2-(BDMN)4]2 (PG8) and PEG 10,000-[Glu-(Glu)2-(Glu)4-(BDMN)8]2 (PG16), dendrimeric structures were built at the hydroxyl groups of HO-PEG-OH (10,000 Da) with -glutamic acid as branching moiety, as reported elsewhere (26). BDMN was linked to the PEG dendrons PEG 10,000-[Glu-(Glu)2-(COOH)4]2 and PEG 10,000-[Glu-(Glu)2-(Glu)4-(COOH)8]2, as reported for PG1. The PEG compounds were characterized by 1H NMR spectroscopy, and nitrite concentration produced in the medium was determined using the Griess reaction (Active Motif, Rixensart, Belgium). Human umbilical vein endothelial cells were incubated with the PEG-NO conjugates and cultured in minimum essential medium without fetal bovine serum for 24 h. Briefly, 300 µl of the medium were centrifuged, and 70 µl of the supernatant were mixed with the nitrate reductase and cofactors for 30 min at room temperature and then with 50 µl of Griess reagent A and 50 µl of Griess reagent B for 20 min. The absorbance was measured on a spectrophotometer at 540 nm. Experimental preparation and protocols. Male Syrian hamsters (80–100 g body wt; Charles River) were anesthetized by pentobarbital sodium injection (50 mg/kg body wt ip). The animals were tracheotomized, and the right carotid artery and femoral vein were cannulated for measurement of blood pressure and injection of the phosphorescent probes and supplementary doses of anesthetic. Animal handling and care followed the guidelines of the Italian Research Council for the care and use of animals in laboratories (published by Italian Government Regulation Official Bulletin 116.92).
We used five groups of animals subjected to I/R: the control group (I/R, n = 10) was subjected to I/R; the PG (n = 10) group was treated with PEG 5,000 or PEG 10,000, and the PG1 (n = 5), PG8 (n = 5), and PG16 (n = 10) groups were treated with PG1, PG8, and PG16, respectively. Before I/R, all the animals were intravenously injected with PEG or PEG-NO at 0.5 mg/0.5 ml, a dose that, in a pilot study, was found to decrease arterial blood pressure. The decrease in blood pressure was prolonged during the time of observation (data not shown). Ischemia was induced by application of an atraumatic microvascular clip on the proximal part of the cheek pouch for 30 min. The clamp was removed, and the microcirculation was reperfused for 30 min. For measurement of vWF, a control [sham (S)] group (n = 3) was followed without treatment for 90 min to determine whether anesthesia and surgical treatment increased the vWF level.
In a second series of experiments, the hamster cheek pouch was superfused with a superfusate solution containing L-NMMA (LIR group, n = 5; Sigma, St. Louis, MO) at a final concentration of 10–5 M. The cheek pouch was superfused 30 min before ischemia and throughout the 60 min of reperfusion. Topical administration was used to avoid systemic effects. L-NMMA was added to the superfusate reservoir contemporaneously with PEG (LPG group, n = 5) or PG8 (LPG8 group, n = 5) injection. Control animals (IR group, n = 3) received equivalent amounts of physiological saline during I/R.
In a third series of experiments, two groups of animals were subjected to I/R: the control (I/R) group (n = 4) was treated with saline, and the 2PG8 group (n = 4) was treated with PG8 (0.5 mg/0.5 ml iv) before I/R. In these groups, the reperfusion was allowed to persist for 5 h for measurement of lipid peroxidation within a period of observation equivalent to the half-life of PEG-NO compounds.
The left cheek pouch was exteriorized and fixed on a Plexiglas microscope stage, and a thin black blade was inserted through a small incision between the upper and lower layers of the pouch (4, 5). The cheek pouch was superfused with Ringer solution (pH 7.35 at 36°C, equilibrated with 5% CO2-95% N2). The temperature of the water-heated Plexiglas stage was maintained at 37°C. The hamster cheek pouch was observed with a fluorescence microscope (Orthoplan, Leica Microsystem, Wetzlar, Germany) through a x4 (0.14 NA) or x20 (0.25 NA) objective and a x10 eyepiece. Epi-illumination of the microvessels after injection of fluorescein isothiocyanate-dextran 150,000 [FITC, 500 mg/kg iv, as 5% (wt/vol) solution, in 5 min] was supplied by a 150-W xenon lamp through filter sets appropriate for FITC (I2 Ploemopak filter block, Leitz) and acridine red (N2, Leica) and a heat filter (Leitz KG1). The image was projected onto a silicone-intensified target low-light-level camera (COHU 5253), observed on a video monitor, and recorded by a video recorder (U-Matic VO 5800 PS, Sony). Video images were videotaped, and microvascular measurements were made offline by a computer-assisted imaging software system (MIP Image, Consiglio Nazionale delle Ricerca Institute of Clinical Physiology).
Measurements of microvascular parameters. All animals were injected with acridine red (1 mg/100 g iv) for visualization of the leukocytes and platelets at baseline and after reperfusion (4). The number of adherent leukocytes in venules was expressed as the number per 100-µm length of venule (16 ± 8 µm diameter, >250 µm long). In each animal, five arterioles and five venules were recorded on videotape.
PCL, defined as capillary segments through which RBC traveled in a 
30-s period, was assessed in a 
0.5-mm2 region. PCL (cm–1), defined as the total length of RBC-perfused capillaries divided by the area of the microscopic field of view, was evaluated by measurement and addition of the length of capillaries through which RBC traveled (7). PCL was measured using our laboratory imaging software system.
Microvessel diameters (D) were measured by an image shearing system (digital image shearing monitor, model 907, IPM, San Diego, CA). RBC velocity was determined using dual-slit cross-correlation (velocity tracker model 102 B, IPM). The measured centerline velocities were normalized to vessel size to obtain the mean RBC velocity (V) (6, 7). Blood flow (
) was calculated from the measured parameters as follows: = V x 
(D/2)2.
Fluorescence intensity of vascular permeability in the perivascular space was quantified by normalization to baseline gray levels: NGL = (I – Ir)/Ir, where I is the average baseline gray level and Ir is fluorescence intensity at the end of the reperfusion period (5, 6). Gray levels, ranging from 0 to 255, were determined by the MIP Image program. The window used to measure average fluorescence intensity was 50 µm long and 50 µm wide.
Measurement of lipid peroxides. The d-ROMs assay kit (Diacron, Parma, Italy) allows measurement of the total amount of plasma hydroperoxides (6). The d-ROMs assay is based on Fenton's reaction or on radical formation during lipid peroxidation. The peroxy and alkoxy radicals produced, the quantity of which is directly proportional to the quantity of plasma peroxides, are trapped by a chromogen (N,N-diethyl-p-phenyldiamine) that forms a colored stable radical that is detectable spectrophotometrically at 505 nm. The concentration of the colored complex is directly correlated to the concentration of hydroperoxides. Ten microliters of a chromogenic substance and 1 ml of the kit buffer were mixed with 10 µl of blood for 1 min at 37°C. The results are expressed in arbitrary units (1 AU = 0.08 mg/100 ml H2O2). Blood samples were taken from the cannulated carotid artery at baseline and during reperfusion.
Measurement of vWF. The vWF levels were determined in stored plasma with an enzyme immunoassay kit for human vWF (Gradipore, Sydney, Australia) that cross-reacts with vWF of different mammalian species. Samples were obtained from the femoral artery catheter at baseline, after the vessel was unclamped, and after 30 min of reperfusion and stored at –80°C. Plasma levels of vWF were expressed as percentage of the controlled lyophilized pooled human plasma supplied with the kit. Sham-operated animals (sham group, n = 3) were used to determine the level of vWF secretion induced by anesthesia and surgical treatment.
Mean arterial blood pressure [transducer (model P10E2, Viggo-Spectramed, Oxnard, CA) connected to a catheter in the carotid artery] and heart rate were monitored by a Gould Windograf recorder (model 13-6615-10S). Data were recorded and stored in a computer.
Values are means ± SD. GraphPad software (San Diego, CA) was used to analyze statistical differences. Statistical differences between groups at the same times were determined by the Kruskall-Wallis test followed by Dunn's test. Friedman's two-way analysis of variance by rank, used to determine differences between groups at different times, was followed by Dunnett's test. Differences were considered significant at P < 0.05.
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RESULTS |
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-glutamic acid, and BDMN. In vitro NO determination from PEG-NO compounds showed an increase in nitrite/nitrate release in cell supernatants. Conversely, no significant increase was observed when the cells were incubated with PEG or the PEG-NO conjugates were incubated with medium alone. Table 1 shows the main parameters characterizing the PEG conjugates.
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Effects of I/R.
Arterioles were divided according to the branching order: fourth-order (A4) arterioles (n = 30), with 13.0 ± 7.0 µm diameter, 1.20 ± 0.20 mm/s RBC velocity, and 0.23 ± 0.09 nl/s blood flow, and second- to-third-order (A2–A3) arterioles (n = 25), with 47.8 ± 5.9 µm diameter, 2.22 ± 0.34 mm/s RBC velocity, and 5.00 ± 1.10 nl/s blood flow. In the I/R group, the diameter, RBC velocity, and blood flow of the arterioles decreased significantly during reperfusion (P < 0.01 vs. baseline; 
Figs. 1–3). These changes were associated with a marked increase in vascular permeability in postcapillary and collecting venules during reperfusion (baseline 0.04 ± 0.02 normalized gray levels, P < 0.01; Fig. 4). The number of leukocytes adhering to postcapillary venules increased significantly compared with baseline (P < 0.01; Fig. 5). PCL decreased significantly compared with baseline (baseline 1.4 ± 0.3 cm–1, P < 0.01; Fig. 6). The plasma levels of vWF, expressed as percentage of the controlled lyophilized pooled human plasma, increased significantly after ischemia and reperfusion (P < 0.01; Fig. 7). Plasma lipid peroxides measured at baseline (220 ± 55 AU, n = 15) increased significantly at 5 and 15 min of reperfusion (P < 0.05; Fig. 8). After 30 min of reperfusion, lipid peroxide levels began to decrease significantly.
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Figs. 1–3). Vascular permeability decreased significantly in the PG group (Fig. 4) compared with the I/R group. The number of leukocytes adhering to postcapillary venules increased after reperfusion but was less than in the I/R group (Fig. 5). PCL (baseline 1.5 ± 0.5 cm–1) increased significantly compared with the I/R group after reperfusion (P < 0.05; Fig. 6). After PEG treatment, plasma vWF did not change significantly compared with baseline at 5 and 30 min of reperfusion (Fig. 7). After treatment with PEG, lipid peroxides were significantly lower in the PG group than in the I/R group (Fig. 8; P < 0.01): –38% and –25% at 5 and 15 min of reperfusion, respectively (P < 0.05 vs. I/R group). In the LPG group, the decrease in arteriolar diameter (–57% vs. baseline, P < 0.01) and capillary perfusion (–49% vs. baseline, P < 0.01) was less marked than in the LIR group. Lipid peroxide production was maintained at normal levels after 5 min of reperfusion, whereas it increased at 15 and 30 min of reperfusion and was lower than in the LI/R group (Fig. 9).
Effects of PEG-NO on I/R injury.
In the PG1, PG8, and PG16 groups, arteriolar diameter and RBC velocity and flow increased significantly compared with the I/R group. There was a significant dilation in A2–A3 and A4 arteriolar diameter and RBC velocity and flow increased compared with the I/R group (P < 0.05; Figs. 1–3). In the PG8 group, permeability was reduced in venules and capillaries after reperfusion (P < 0.05 vs. I/R group; Fig. 4), whereas PG16 significantly increased permeability. PEG-NO significantly decreased leukocyte adhesion in venules compared with the I/R group, but the decrease was more pronounced in the PG8 group (Fig. 5). In the PG1 and PG8 groups, PCL (baseline 1.5 ± 0.7 cm–1) increased significantly compared with the I/R group, with a greater increase in the PG8 group (P < 0.05; Fig. 6). After PG1 and PG8, plasma vWF decreased significantly at 5 and 30 min of reperfusion compared with the I/R group. With PG16, a significant decrease at 5 min of reperfusion was followed by a slight increase at 30 min of reperfusion (Fig. 7). After treatment with PEG-NO, the increase in lipid peroxidation was significantly lower than in the I/R group (Fig. 8). Lipid peroxides returned to normal values at 30 min of reperfusion (–53% and –30% for PG1 and –57% and –34% for PG8 at 5 and 15 min of reperfusion, respectively, P < 0.05 vs. I/R group); after PG16, they increased significantly at 30 min of reperfusion (–63%, –12%, and +48% at 5, 15, and 30 min of reperfusion, respectively; P < 0.05 vs. the I/R group). After PG8 injection, lipid peroxides did not change significantly compared with baseline, although the period of reperfusion was extended for 5 h (Fig. 10).
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DISCUSSION |
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PEG showed no significant effect under control conditions; after postischemic reperfusion, it reduced oxidative stress and increased arteriolar diameter and capillary perfusion. Furthermore, PEG attenuated coagulation by decreasing vWF concentration and leukocyte adhesion. In agreement with our data, administration of PEG immediately after spinal cord injury in guinea pigs resulted in a marked decrease in oxidative stress (22). The authors suggested that the effect of PEG on oxidative stress is dependent on its capacity to repair the membrane, and not on the scavenging capacity intrinsic to the polymer. Another mechanism that has been suggested is PEG repair of the membrane by reduction of calcium influx and, thereby, inhibition of free radical formation. Inhibition of excessive formation of lipid peroxides during reperfusion has been shown to decrease membrane viscosity of endothelial cells and, therefore, capillary resistance (4, 5). The correlation between the decrease in lipid peroxidation and cell fluidity was clearly observed in capillary endothelial cells (18, 29). Our findings show a significant vasodilation associated with increased flow at early reperfusion after PEG injection, which might increase the membrane fluidity in endothelial cells in response to the increased shear stress.
Here, we show that PG8 inhibited arteriolar vasoconstriction and decreased oxidative stress, which improved capillary perfusion after postischemic reperfusion in the hamster cheek pouch microcirculation. Moreover, although the period of reperfusion was extended for 5 h, there was no increase in lipid peroxidation after PG8 treatment. These results are in agreement with the previously reported significant reduction in the severity of I/R injury by NO donors (5). However, NO donors in clinical use are limited by their rapid NO release, poor distribution to the endothelial cells of the target tissue, and toxic effects (31). In previous studies, we used the NO donor 2,2'-(hydroxynitrosohydrazino)bis-etanamine (DETA-NO), which is a potent blood pressure-lowering drug under baseline conditions. Conversely, when we measured arterial blood pressure as an indicator of the vasodilating effect, PEG-NO induced a slight but significant and persistent reduction, whereas PEG did not induce a reduction. PEG compounds could have several advantages over other NO donors because of the controlled release of NO and their well-known ability to interact with cell membranes. These compounds represent circulating endogenous reservoirs of NO with controlled half-life. The release half-life of NO from PEG compounds depends on the fate of the polymer in the body, so their half-life and biodistribution mainly depend on the molecular weight and architecture of PEG. According to our measurements, the half-life of PEG-NO compounds ranged from 1 h for the monoderivative to 5–6 h for the dendrimeric compounds PG8 and PG16 (34).
A previous study showed that NO deficiency contributes to an imbalance between oxidative stress and NO signaling in vascular cells, providing a plausible mechanism for adverse consequences of the low NO level after I/R in the hamster cheek pouch (5, 7). Furthermore, hypoxia- and ischemia-induced decreases in blood flow involve responses linked to NO level and excessive oxidative stress, which are also known to modulate oxygen tension in arterioles (4, 6). These changes are associated with an increase in vWF concentration, vascular permeability, and leukocyte adhesion. The mechanism behind the beneficial PG8 effects on microvascular dysfunction could be linked to a better balance between NO and lipid peroxidation of endothelial vascular cells after postischemic reperfusion. However, the observation that L-NMMA did not completely block the effects on arteriolar vasodilation and capillary perfusion of PG8 suggests that PEG-NO compounds elicit other specific effects on vascular function that modulate protection against I/R-induced injury. L-NMMA did not completely prevent arteriolar dilation after PEG-NO or PEG administration; therefore, it is likely that this agent causes vasodilation via NO activation of guanylyl cyclase, because L-NMMA blocks NO release via inhibition of NO synthase, a process only partially affected by PG8. After L-NMMA, lipid peroxidation increased after 15 min of reperfusion; this effect was reduced to some extent in the presence of PEG or PG8. Therefore, some beneficial effects of PEG-NO compounds could be linked to PEG activities on the endothelial surface layer.
It is well known that PEG is a colloid and quickly changes the way proteins interact with each other and with water in the glycocalyx (32, 38). In a study on a model bioadhesion system, Bruinsma et al. (9) reported giant vesicles in contact with a lipid bilayer and showed that PEG-lipids mimic the inhibiting effect of the cell glycocalyx on adhesion. The endothelial surface layer consists of a matrix of molecular chains extending from the surface of the glycocalyx that senses the shear stress and, thus, contributes to vascular permeability and to the activation of coagulation factors by modulating platelet and leukocyte interactions with the endothelium (14, 36). There is mounting evidence that the damage to the glycocalyx completely inhibits shear stress-induced NO production (14, 24). After ischemia, oxidative stress and oxidized LDL reduce endothelial glycocalyx through a mechanism that leads to increased shedding, resulting in increased permeability and adhesiveness of platelets and leukocytes to endothelial cells (11, 25, 39). In a previous study, we showed significant changes in vasodilation associated with reduction of shear stress in arterioles after postischemic reperfusion that regulate production of vasoactive factors (6, 8). Our present study demonstrates that PEG significantly improved vasodilation during postischemic reperfusion. One possible explanation is that insertion of PEG into the endothelial surface layer of microvessels makes the membranes more responsive to shear stress, which is responsible for vasodilation, and more resistant to oxidative stress.
However, it is also possible to speculate on alternative mechanisms of PEG-NO, such as changes in the water boundary around endothelial cells. Because of the high flexibility, hydrophilicity, and large number of water molecules integrated into its chains, PEG presents a hydrodynamic volume greater than would be expected from its molecular weight and has high protein-rejecting properties (19, 32, 34). PEG has an apparent molecular weight 5–10 times higher than of that of a globular protein of comparable mass, as shown by gel permeation chromatography (23). This explains the stabilizing property of PEG and provides the basis for the decreased immunogenicity and the antigenicity conveyed to a conjugate (1). This extensive water integration can help form a stable water layer around the PEG chain, creating a microenvironment in which the drugs or the surroundings are more protected. Therefore, the effect of PEG could be related to the formation and maintenance of a stable water structure on the endothelial surface, which could be crucial in modulating the activity of shear stress-mediated mechanisms. The absence of this "protective" water layer during I/R could influence flow velocity, allow substances to aggregate on the wall, and increase vascular permeability.
Moreover, our results demonstrate an increase of vWF immediately after early reperfusion. In agreement with our data, other authors demonstrated in rats that the plasma concentration of vWF rose after 30 min of intestinal ischemia followed by 15 min of reperfusion (2). Moreover, hypoxia, and also reoxygenation, induced release of vWF endothelial secretory granules in cultured cells (30). In our model, PEG decreased leukocyte adhesion and vWF concentration in systemic blood, thus showing that PEG interferes significantly with coagulation during reperfusion. Indeed, leukocytes are activated in I/R injury, leading to an excessive production of free radicals and adherence to the endothelial surface, further enhancing the production of free radicals, which leads to microvascular injury (25). PEG-NO reduced lipid peroxides, which amplify leukocyte adherence and promote plasma vWF concentration, and thus further counteracted the lack of capillary perfusion.
PEG can act as the surface masking polymer because of its recognized ability to reduce protein absorption and its use as a pharmacological adjuvant when administered in vivo (12). On the other hand, there is evidence that PEG improves renal medulla injury and decreases the activation of cytokine and adhesion molecule cascade during early and long-term cold I/R (13). Our results suggest that PEG could limit the adhesion of leukocytes among the macromolecular components of the glycocalyx and prevent release of vWF secretory granules. Because leukocytes cannot roll along the endothelial cells, adhesion of platelets and leukocytes cannot be enhanced by reperfusion-induced damage.
It is well known that PEG reduces osmotic cell swelling and permeability in different models (20, 21). In particular, PEG is able to seal and repair minute holes in the membrane and, thus, immediately reverse a transient increase in vascular permeability subsequent to acute spinal cord injury (22). In our study, PEG reduced lipid peroxidation and, thus, blocked a further increase in vascular permeability during postischemic reperfusion.
After reperfusion, there was a greater increase in vascular permeability, leukocyte adhesion, and vWF concentration and a decrease in capillary perfusion in animals treated with PG16 than in those treated with PG8. Interestingly, with PG16 after 15 min of reperfusion, there was an increase in lipid peroxidation, which started to decrease after 30 min of reperfusion. We speculate that higher doses of NO molecules over a longer period of time could interact with free radicals to produce peroxynitrite during reoxygenation. In tissues exposed to hypoxia and reoxygenation, high levels of NO are toxic. For many years, it has been largely recognized that oxidative stress markedly increases in I/R; yet a number of clinical trials were unable to validate the antioxidant treatment (40). Accumulating evidence suggests that, besides oxidative stress, NO-mediated nitrative stress plays a critical role in I/R injury. Indeed, a high concentration of NO is deleterious and induces apoptotic cell death in cultured cells (10). Therefore, we can suggest that PG16 may determine excessive nitrative stress, thus decreasing the protective effect.
Together, our findings provide evidence of a protective role for PG8 because of the level of NO and the stabilizing effect of PEG on endothelial cells. Furthermore, the microvascular effects exerted by the PEG-NO compounds differ among each other in terms of their efficacy; however, this study is a first attempt to control the NO level in the endothelial cells by utilization of PEG-NO compounds. Despite the protective role of PEG compounds in the treatment of I/R injury, some issues need to be addressed in future studies. In particular, we did not measure the plasma concentration of derivatives of these compounds in vivo after postischemic reperfusion; such measurements were beyond the scope of the present study.
In conclusion, our data provide evidence that PEG attenuates alterations in blood flow, thus increasing capillary perfusion and reducing plasma vWF level and leukocyte adhesion on postcapillary venules during I/R injury. The protective effects of PEG-NO are mediated by the increased NO level but could also be related to the hydrophilicity of PEG or the ability of PEG to insert into the endothelial surface layer, which makes it more resistant to oxidative stress and preserves shear stress-mediated vasodilation during I/R. The newly developed NO donor appears to have better and longer-lasting effects on vasodilation than PEG alone, on preventing plasma vWF and leukocyte adhesion increase, and on dampening the decrease in capillary perfusion. These results appear quite relevant, because PEG-NO could have promise as a compound for treatment of endothelial cell dysfunction during I/R.
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FOOTNOTES |
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The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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  S. Bertuglia Intermittent hypoxia modulates nitric oxide-dependent vasodilation and capillary perfusion during ischemia-reperfusion-induced damage Am J Physiol Heart Circ Physiol, April 1, 2008; 294(4): H1914 - H1922. [Abstract] [Full Text] [PDF]
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P < 0.05 vs. PG, PG1, and PG16.
