The damaging potential of leukocyte activation in the microcirculation

No-reflow after recanalization in ischemic stroke: From pathomechanisms to therapeutic strategies

Endovascular reperfusion therapy is the primary strategy for acute ischemic stroke. No-reflow is a common phenomenon, which is defined as the failure of microcirculatory reperfusion despite clot removal by thrombolysis or mechanical embolization. It has been reported that up to 25% of ischemic strokes suffer from no-reflow, which strongly contributes to an increased risk of poor clinical outcomes. No-reflow is associated with functional and structural alterations of cerebrovascular microcirculation, and the injury to the microcirculation seriously hinders the neural functional recovery following macrovascular reperfusion. Accumulated evidence indicates that pathology of no-reflow is linked to adhesion, aggregation, and rolling of blood components along the endothelium, capillary stagnation with neutrophils, astrocytes end-feet, and endothelial cell edema, pericyte contraction, and vasoconstriction. Prevention or treatment strategies aim to alleviate or reverse these pathological changes, including targeted therapies such as cilostazol, adhesion molecule blocking antibodies, peroxisome proliferator-activated receptors (PPARs) activator, adenosine, pericyte regulators, as well as adjunctive therapies, such as extracorporeal counterpulsation, ischemic preconditioning, and alternative or complementary therapies. Herein, we provide an overview of pathomechanisms, predictive factors, diagnosis, and intervention strategies for no-reflow, and attempt to convey a new perspective on the clinical management of no-reflow post-ischemic stroke.

The role of adhesive receptor patterns on cell transport in complex microvessels

Cell transport is governed by the interaction of fluid dynamic forces and biochemical factors such as adhesion receptor expression and concentration. Although the effect of endothelial receptor density is well understood, it is not clear how the spacing and local spatial distribution of receptors affect cell adhesion in three-dimensional microvessels. To elucidate the effect of vessel shape on cell trajectory and the arrangement of endothelial receptors on cell adhesion, we employed a three-dimensional deformable cell model that incorporates microscale interactions between the cell and the endothelium. Computational cellular adhesion models are systematically altered to assess the influence of receptor spacing. We demonstrate that the patterns of receptors on the vessel walls are a key factor guiding cell movement. In straight microvessels, we show a relationship between cell velocity and the spatial distribution of adhesive endothelial receptors, with larger receptor patches producing lower translational velocities. The joint effect of the complex vessel topology seen in microvessel shapes such as curved and bifurcated vessels when compared to straight tubes is explored with results which showed the spatial distribution of receptors affecting cell trajectory. Our findings here represent demonstration of the previously undescribed relationship between receptor pattern and geometry that guides cellular movement in complex microenvironments.

Myofibre injury induces capillary disruption and regeneration of disorganized microvascular networks

Injury to skeletal muscle disrupts myofibres and their microvascular supply. While the regeneration of myofibres is well described, little is known of how the microcirculation is affected by skeletal muscle injury or its recovery during regeneration. Nevertheless, the microvasculature must also recover to restore skeletal muscle function. We aimed to define the nature of microvascular damage and time course of repair during muscle injury and regeneration induced by the myotoxin BaCl₂ . To test the hypothesis that microvascular disruption occurred secondary to myofibre injury, isolated microvessels were exposed to BaCl₂ or the myotoxin was injected into the gluteus maximus (GM) muscle of mice. In isolated microvessels, BaCl₂ depolarized smooth muscle cells (SMCs) and endothelial cells while increasing intracellular calcium in SMCs but did not elicit death of either cell type. At 1 day post-injury (dpi) of the GM, capillary fragmentation coincided with myofibre degeneration while arteriolar and venular networks remained intact; neutrophil depletion before injury did not prevent capillary damage. Perfused capillary networks reformed by 5 dpi in association with more terminal arterioles and were dilated through 10 dpi. With no change in microvascular area or branch point number in regenerating capillary networks, fewer capillaries aligned with myofibres and were no longer organized into microvascular units. By 21 dpi, capillary orientation and microvascular unit organization were no longer different from uninjured GM. We conclude that following their disruption secondary to myofibre damage, capillaries regenerate as disorganized networks that remodel into microvascular units as regenerated myofibres mature. KEY POINTS: Skeletal muscle regenerates after injury; however, the nature of microvascular damage and repair is poorly understood. Here, the myotoxin BaCl₂ , a standard experimental method of acute skeletal muscle injury, was used to investigate the response of the microcirculation to local injury of intact muscle. Intramuscular injection of BaCl₂ induced capillary fragmentation with myofibre degeneration; arteriolar and venular networks remained intact. Direct exposure to BaCl₂ did not kill microvascular endothelial cells or smooth muscle cells. Dilated capillary networks reformed by 5 days post-injury (dpi) in association with more terminal arterioles. Capillary orientation remained disorganized through 10 dpi. Capillaries realigned with myofibres and reorganized into microvascular units by 21 dpi, which coincides with the recovery of vasomotor control and maturation of nascent myofibres. Skeletal muscle injury disrupts its capillary supply secondary to myofibre degeneration. Reorganization of regenerating microvascular networks accompanies the recovery of blood flow regulation.

Anthracycline Cardiotoxicity: It Is Possible to Teach an Old Dog Some New Tricks

Anthracyclines have proved to be one of the most effective chemotherapeutic agents in the treatment of numerous solid tumors and hematologic malignancies in both adult and pediatric patients. Their clinical benefit, however, is sometimes hampered by the development of cardiotoxicity, a process that still remains elusive despite decades of investigation. It has been postulated that anthracycline-induced cardiotoxicity is mediated in part by reactive oxygen species and redox cycling. This article reviews anthracycline cardiotoxicity in terms of historical significance, epidemiology, current detection strategies, prevention strategies, and patient care after anthracycline-based chemotherapy.

Liposomal Curcumin is Better than Curcumin to Alleviate Complications in Experimental Diabetic Mellitus

Curcumin (CC) is known to have anti-inflammatory and anti-oxidative properties and has already been tested for its efficiency in different diseases including diabetes mellitus (DM). New formulations and route administration were designed to obtain products with higher bioavailability. Our study aimed to test the effect of intraperitoneal (i.p.) administration of liposomal curcumin (lCC) as pre-treatment in streptozotocin(STZ)-induced DM in rats on oxidative stress, liver, and pancreatic functional parameters. Forty-two Wistar-Bratislava rats were randomly divided into six groups (seven animals/group): control (no diabetes), control-STZ (STZ-induced DM —60 mg/100g body weight a single dose intraperitoneal administration, and no CC pre-treatment), two groups with DM and CC pre-treatment (1mg/100g bw—STZ + CC1, 2 mg/100g bw—STZ + CC2), and two groups with DM and lCC pre-treatment (1 mg/100g bw—STZ + lCC1, 2 mg/100g bw—STZ + lCC1). Intraperitoneal administration of Curcumin in diabetic rats showed a significant reduction of nitric oxide, malondialdehyde, total oxidative stress, and catalase for both evaluated formulations (CC and lCC) compared to control group (p < 0.005), with higher efficacy of lCC formulation compared to CC solution (p < 0.002, excepting catalase for STZ + CC2vs. STZ + lCC1when p = 0.0845). The CC and lCC showed hepatoprotective and hypoglycemic effects, a decrease in oxidative stress and improvement in anti-oxidative capacity status against STZ-induced DM in rats (p < 0.002). The lCC also proved better efficacy on MMP-2, and -9 plasma levels as compared to CC (p < 0.003, excepting STZ + CC2 vs. STZ + lCC1 comparison with p = 0.0553). The lCC demonstrated significantly better efficacy as compared to curcumin solution on all serum levels of the investigated markers, sustaining its possible use as adjuvant therapy in DM.

MICROVASCULAR FLOW ABNORMALITIES ASSOCIATED WITH RETINAL VASCULITIS: A Potential of Mechanism of Retinal Injury

PURPOSE

To investigate the structural optical coherence tomography and related microvascular flow characteristics in eyes with retinal vasculitis.

METHODS

Regions involved with perivascular infiltration in eyes with retinal vasculitis, but no evidence of large vessel occlusion were evaluated with optical coherence tomography (OCT), OCT angiography, and fluorescein angiography.

RESULTS

Ten eyes of 5 patients with a variety of etiologies of retinal vasculitis were evaluated. These patients did not have either cotton wool spots or deeper placoid areas of retinal ischemia. Around large vessels there was perivascular infiltration with leakage and staining seen during fluorescein angiography. Structural OCT showed slight thickening with loss of visualization of normal retinal laminations. OCT angiography showed a lack of flow signal in capillary sized vessels in the same areas. Treatment resulted in a rapid thinning of the affected areas, with the inner and middle layers of the retina becoming thinner than surrounding uninvolved areas. OCT angiography did not show a return of capillary perfusion in these regions. The thickness change in the structural OCT as shown by a heat map had a pattern mimicking the original perivascular infiltration around large retinal vessels.

CONCLUSION

Capillary level perfusion abnormalities can develop in regions adjacent to large vessel inflammatory infiltrate that result in retinal thinning without the development of usual stigmata of acute microvascular flow obstruction such as cotton wool spots. This suggests that retinal damage may occur in retinal vasculitis that would not be recognized without using OCT-based imaging modalities.

Biomechanics of the Circulating Tumor Cell Microenvironment

Circulating tumor cells (CTCs) exist in a microenvironment quite different from the solid tumor tissue microenvironment. They are detached from matrix and exposed to the immune system and hemodynamic forces leading to the conclusion that life as a CTC is "nasty, brutish, and short." While there is much evidence to support this assertion, the mechanisms underlying this are much less clear. In this chapter we will specifically focus on biomechanical influences on CTCs in the circulation and examine in detail the question of whether CTCs are mechanically fragile, a commonly held idea that is lacking in direct evidence. We will review multiple lines of evidence indicating, perhaps counterintuitively, that viable cancer cells are mechanically robust in the face of exposures to physiologic shear stresses that would be encountered by CTCs during their passage through the circulation. Finally, we present emerging evidence that malignant epithelial cells, as opposed to their benign counterparts, possess specific mechanisms that enable them to endure these mechanical stresses.

Optical coherence tomography angiography

Optical coherence tomography (OCT) was one of the biggest advances in ophthalmic imaging. Building on that platform, OCT angiography (OCTA) provides depth resolved images of blood flow in the retina and choroid with levels of detail far exceeding that obtained with older forms of imaging. This new modality is challenging because of the need for new equipment and processing techniques, current limitations of imaging capability, and rapid advancements in both imaging and in our understanding of the imaging and applicable pathophysiology of the retina and choroid. These factors lead to a steep learning curve, even for those with a working understanding dye-based ocular angiography. All for a method of imaging that is a little more than 10 years old. This review begins with a historical account of the development of OCTA, and the methods used in OCTA, including signal processing, image generation, and display techniques. This forms the basis to understand what OCTA images show as well as how image artifacts arise. The anatomy and imaging of specific vascular layers of the eye are reviewed. The integration of OCTA in multimodal imaging in the evaluation of retinal vascular occlusive diseases, diabetic retinopathy, uveitis, inherited diseases, age-related macular degeneration, and disorders of the optic nerve is presented. OCTA is an exciting, disruptive technology. Its use is rapidly expanding in clinical practice as well as for research into the pathophysiology of diseases of the posterior pole.

Anthracycline Chemotherapy and Cardiotoxicity

Anthracycline chemotherapy maintains a prominent role in treating many forms of cancer. Cardiotoxic side effects limit their dosing and improved cancer outcomes expose the cancer survivor to increased cardiovascular morbidity and mortality. The basic mechanisms of cardiotoxicity may involve direct pathways for reactive oxygen species generation and topoisomerase 2 as well as other indirect pathways. Cardioprotective treatments are few and those that have been examined include renin angiotensin system blockade, beta blockers, or the iron chelator dexrazoxane. New treatments exploiting the ErbB or other novel pro-survival pathways, such as conditioning, are on the cardioprotection horizon. Even in the forthcoming era of targeted cancer therapies, the substantial proportion of today's anthracycline-treated cancer patients may become tomorrow's cardiac patient.

Retinal Neurodegeneration in the Course of Diabetes-Pathogenesis and Clinical Perspective

Diabetic retinopathy is generally considered as a microvascular disease which develops as a result of chronic hyperglycaemia. However, the neuronal apoptosis and reactive gliosis are recently postulated as early changes in diabetic retinopathy. This phenomenon is described as a neurodegeneration and suggests that diabetic retinopathy should be recognized as a neurovascular complication. In this review, we discuss the mechanisms leading to the neurodegeneration of the retina in diabetic patients including: low-grade inflammatory process, oxidative stress, activation of polymorphonuclear neutrophils, glutamate excitotoxicity and imbalance in the neuroprotective factors. Secondly, we point out the clinical significance of measuring the retinal neurodegeneration.

Dynamic regulation of plasma matrix metalloproteinases in human diabetic ketoacidosis

BACKGROUND

Diabetic ketoacidosis (DKA) in children is associated with cerebrovascular-related complications. We recently reported that DKA facilitates leukocyte adherence to the brain microvascular endothelium. Adhered leukocytes can release enzymes that instigate vascular dysfunction. Our aims were to measure plasma levels of leukocyte-derived matrix metalloproteinases (MMPs) from DKA patients and to correlate plasma MMP concentrations with DKA severity.

METHODS

Plasma was obtained from children with type 1 diabetes, either in DKA (n = 16) or insulin controlled (CON; n = 16). Antibody microarray and gelatin zymography were used to quantify plasma MMPs and their endogenous tissue inhibitors (TIMPs). MMP concentrations were correlated with DKA severity (blood pH). Quantitative PCR of leukocyte mRNA was used to help determine the origin of plasma MMPs.

RESULTS

DKA was associated with altered plasma levels of ↓MMP-2 (P < 0.001), ↑MMP-8 (P < 0.001), ↑MMP-9 (P < 0.05), and ↑TIMP-4 (P < 0.001), as compared with CON. Elevated MMP-8 and MMP-9 were both positively correlated with DKA severity (P < 0.05). DKA was associated with increased leukocyte mRNA for MMP-8, MMP-9, and TIMP-4 (P < 0.005).

CONCLUSION

MMPs are dynamically regulated during DKA. Plasma MMP-8 and MMP-9 concentrations correlate with DKA severity and are known to degrade brain microvascular endothelial cell tight junctions. Thus, leukocyte-derived MMPs might contribute to DKA-associated cerebrovascular complications.

Cardio-protective effects of pentraxin 3 produced from bone marrow-derived cells against ischemia/reperfusion injury

BACKGROUND

Inflammation is one of major mechanisms contributing to the pathogenesis of myocardial ischemia/reperfusion (I/R) injury. Pentraxin 3 (PTX3), produced in response to inflammatory signals, acts as a humoral arm of the innate immunity. Here we investigated the role of PTX3 produced from bone marrow-derived cells in myocardial I/R injury using PTX3-deficient (PTX3KO) mice.

METHODS AND RESULTS

PTX3KO mice and wild-type littermate (WT) mice were lethally irradiated and injected with bone marrow (BM) cells, generating four types of mice (WT(WT-BM), WT(PTX3KO-BM), PTX3KO(WT-BM) and PTX3KO(PTX3KO-BM)). Six weeks after BM transplantation, the myocardial I/R procedure (45 min of left descending coronary artery ligation followed by 48 h of reperfusion) was performed. Infarct size was greater in WT and PTX3KO mice with BM from PTX3KO donor (WT(PTX3KO-BM) and PTX3KO(PTX3KO-BM)) compared with WT and PTX3KO mice with BM from WT donor (WT(WT-BM) and PTX3KO(WT-BM)). Localization of PTX3 was observed in neutrophils and macrophages in WT and PTX3KO mice with BM from WT donor (WT(WT-BM) and PTX3KO(WT-BM)), while only in endothelial cells in WT mice with BM from PTX3KO donor (WT(PTX3KO-BM)). Infiltration of neutrophils and generation of reactive oxygen species (ROS) at ischemic border zones were greater in PTX3KO mice with BM from PTX3KO donor (PTX3KO(PTX3KO-BM)) than PTX3KO mice with BM from WT donor (PTX3KO(WT-BM)). Plasma levels and cardiac expressions of interleukin-6 were higher in PTX3KO mice with BM from PTX3KO donor (PTX3KO(PTX3KO-BM)) than PTX3KO mice with BM from WT donor (PTX3KO(WT-BM)). However, no significant differences in infarct size, infiltration of neutrophils, generation of ROS and plasma and cardiac levels of interleukin-6 were observed between WT and PTX3KO mice with BM from WT donor and between WT and PTX3KO mice with BM from PTX3KO donor. These results indicated that the lack of PTX3 produced from BM-derived cells, and not from cardiac resident cells, exacerbated myocardial injury after I/R.

CONCLUSION

PTX3 produced from bone marrow-derived cells plays a crucial role in cardiac protection against myocardial I/R injury by attenuating infiltration of neutrophils, generation of ROS and inflammatory cytokine.

Curcuminoids limit neutrophil-mediated reperfusion injury in experimental stroke by targeting the endothelium

OBJECTIVE

We sought to test the hypothesis that turmeric-derived curcuminoids limit reperfusion brain injury in an experimental model of stroke via blockade of early microvascular inflammation during reperfusion.

METHODS

Male Sprague Dawley rats subjected to MCAO/R were treated with turmeric-derived curcuminoids (vs. vehicle) 1 hour prior to reperfusion (300 mg/kg ip). Neutrophil adhesion to the cerebral microcirculation and measures of neutrophil and endothelial activation were assayed during early reperfusion (0-4 hours); cerebral infarct size, edema, and neurological function were assessed at 24 hours. Curcuminoid effects on TNFα-stimulated human brain microvascular endothelial cell (HBMVEC) were assessed.

RESULTS

Early during reperfusion following MCAO, curcuminoid treatment decreased neutrophil rolling and adhesion to the cerebrovascular endothelium by 76% and 67% and prevented >50% of the fall in shear rate. The increased number and activation state (CD11b and ROS) of neutrophils were unchanged by curcuminoid treatment, while increased cerebral expression of TNFα and ICAM-1, a marker of endothelial activation, were blocked by >30%. Curcuminoids inhibited NF-κB activation and subsequent ICAM-1 gene expression in HBMVEC.

CONCLUSION

Turmeric-derived curcuminoids limit reperfusion injury in stroke by preventing neutrophil adhesion to the cerebrovascular microcirculation and improving shear rate by targeting the endothelium.

Protein Kinase C Epsilon Contributes to NADPH Oxidase Activation in a Pre-Eclampsia Lymphoblast Cell Model

Pre-eclampsia is a pregnancy-specific disorder characterised by hypertension and proteinuria, which in severe cases results in multi-system disturbances. The maternal syndrome is associated with a pro-inflammatory state, consisting of leukocyte activation, which is thought to contribute to the widespread endothelial dysfunction. We previously showed increased activation of NADPH oxidase in pre-eclampsia, in both neutrophils and B-lymphoblast cell lines (B-LCLs). In this study, the mechanism by which NADPH oxidase activity is increased in pre-eclampsia was further investigated. NADPH oxidase activity was found to be increased in phorbol-12-myristate-13-acetate (PMA) stimulated B-LCLs isolated from women with pre-eclampsia. This correlated with an increase in protein kinase C (PKC) substrate phosphorylation, p47-phox phosphorylation (a regulatory component of NADPH oxidase) and p47-phox directed-kinase activity. Using ion exchange and hydroxyapatite chromatography we identified a major peak of PMA regulated p47-phox kinase activity. Chromatography fractions were probed for PKC isoforms. We found the major peak of p47-phox kinase activity could not be separated from the elution profile of PKC epsilon. Using a peptide inhibitor of PKC epsilon, PMA-induced reactive oxygen species (ROS) production could be reduced to that of a normal B-LCL. These data suggest a pro-inflammatory role for PKC epsilon in the pathogenesis of pre-eclampsia.

Exaggerated neutrophil-mediated reperfusion injury after ischemic stroke in a rodent model of type 2 diabetes

OBJECTIVE

We tested the hypothesis that both chronic and acute inflammatory processes contribute to worse reperfusion injury and stroke outcome in an experimental model of T2DM.

MATERIALS AND METHODS

Twelve- to thirteen-week-old male Zucker Diabetic Fatty (ZDF) rats vs. Zucker Lean Controls (ZLC) rats were tested at baseline and after middle cerebral artery occlusion (ischemia) and reperfusion (I-R). Neutrophil adhesion to the cerebral microcirculation, neutrophil expression of CD11b, infarction size, edema, neurologic function, sICAM, and cerebral expression of neutrophil-endothelial inflammatory genes were measured.

RESULTS

At baseline, CD11b and sICAM were significantly increased in ZDF vs. ZLC animals (p < 0.05). After I-R, significantly more neutrophil adhesion and cell aggregates were observed in ZDF vs. ZLC (p < 0.05); infarction size, edema, and neurologic function were significantly worse in ZDF vs. ZLC (p < 0.05). CD11b and sICAM-1 remained significantly increased in ZDFs (p < 0.05), and cerebral expression of IL-1β, GRO/KC, E-selectin, and sICAM were significantly induced in ZDF, but not ZLC groups (p < 0.05) after 2.5 hours of reperfusion.

CONCLUSION

Both sides of the neutrophil-endothelial interface appear to be primed prior to I-R, and remain significantly more activated during I-R in an experimental model of T2DM. Consequently, reperfusion injury appears to play a significant role in poor stroke outcome in T2DM.

Sickle cell disease: old discoveries, new concepts, and future promise

The discovery of the molecular basis of sickle cell disease was an important landmark in molecular medicine. The modern tools of molecular and cellular biology have refined our understanding of its pathophysiology and facilitated the development of new therapies. In this review, we discuss some of the important advances in this field and the impediments that limit the impact of these advances.

Successful reperfusion for acute ST elevation myocardial infarction is associated with a decrease in WBC count

BACKGROUND

Elevated white blood cell (WBC) count on admission in patients with ST segment elevation myocardial infarction (STEMI) has been associated with an adverse prognosis. Whether successful reperfusion by primary percutaneous coronary intervention (PCI) is associated with a decrease in WBC count is unknown.

METHODS

In this subanalysis of the On-TIME trial, WBC count was measured on admission and 6 h and 24 h after primary PCI for STEMI (n = 364). Angiographic measurements of reperfusion, including TIMI-flow and myocardial blush grade, were compared with changes in WBC count.

RESULTS

Restoration of TIMI 3 flow by primary PCI was associated with a significant decrease in median WBC count (11.5 (9.7-14.2), 10.7 (9.0-12.5), 9.9 (8.5-11.5) at baseline, 6 h and 24 h), whereas after unsuccessful PCI (TIMI < 3 flow) WBC count remained elevated (12.5 (9.5-14.6), 12.1 (9.9-14.4), and 11.4 (9.2-15.2)). Improved myocardial blush was also related to a decrease in WBC count. After multivariate analysis, improved myocardial perfusion (TIMI 3 flow and myocardial blush grade 3) was an independent predictor of a decrease of WBC count after PCI.

CONCLUSION

Impaired myocardial reperfusion after primary PCI for STEMI is associated with persistent WBC elevation.

The evaluation of the protective action of antioxidants on small intestine of rabbits experimentally injured by ischemia and reperfusion

PURPOSE

The aim of this study was to ascertain the possibility of diminishing ischemia-reperfusion injury by intravenous application of the chosen antioxidants: vitamin C, mannitol, and N-acetylcysteine.

METHODS

The study was performed on New Zealand Red male rabbits, which were divided into 6 groups of 8. In group 1, 5 segments of the small intestine were taken for histopathologic examination (normal intestine). In group 2, segments of the small intestine were taken for histopathologic examination after 3 hours of closure of the superior mesenteric artery (ischemic intestine). In group 3, after 3 hours of closure of the superior mesenteric artery, 1 hour of reperfusion took place. In this group, blood flow in the superior mesenteric artery was measured within the first 30 minutes, and segments of the small intestine were taken for histopathologic examination after 60 minutes of the reperfusion. In groups 4, 5, and 6 the procedure was similar to that in group 3, but additionally the rabbits were given antioxidants intravenously: in group 4, vitamin C, 250 mg/kg; in group 5, 20% mannitol, 3 mL/kg; and in group 6, N-acetylcysteine, 100 mg/kg.

RESULTS

All the chosen antioxidants had a beneficial influence on the blood flow in the superior mesenteric artery. The blood flow in the groups with antioxidants after 30 minutes of the reperfusion was 53% to 57% of initial values compared with 27% of initial values in group 3. In histopathologic evaluation, protective action of the antioxidants was seen in the groups with vitamin C and mannitol.

CONCLUSIONS

Application of the chosen antioxidants reduces injury of the rabbit small intestine caused by reperfusion after 3 hours of closure of the superior mesenteric artery.

Role of nitric oxide in leukocyte-independent endothelial damage during experimental endotoxemia

Endothelial damage during early endotoxemia has been shown to be leukocyte independent. Platelet-activating factor and serotonin receptor antagonism has been shown to reduce leukocyte-independent macromolecular leakage significantly. Nevertheless, the exact mechanisms involved in leukocyte-independent endothelial dysfunction are unknown. Therefore, it was the aim of the study to investigate the effects of nitric oxide (NO) on leukocyte-independent endothelial damage during endotoxemia. In male Wistar rats, venular wall shear rate, macromolecular efflux, and leukocyte-endothelial interaction were determined in mesenteric postcapillary venules using intravital microscopy at baseline and at 60 and 120 min after start of the experiment. The animals received fucoidin to prevent leukocyte-endothelial interaction. The experiments were divided into three parts. In part 1, we investigated the effects of the NO-inhibitor L-NAME on leukocyte-independent endothelial damage during endotoxemic and nonendotoxemic conditions. The efficiency of the NO-donor (SIN-1) used, part 2, was investigated by the inhibitory properties of SIN-1 on NO-inhibition-induced macromolecular efflux. Finally, part 3, we analyzed the effects of the NO-donor SIN-1 on endothelial damage during endotoxemia. Both the combined challenge of the animals with L-NAME and endotoxin and the challenge with L-NAME alone resulted in a strong increase in macromolecular efflux, showing significant differences to control groups at an earlier time point than endotoxin challenge alone. Interestingly, combined L-NAME and endotoxin challenge, L-NAME challenge alone, and endotoxin challenge alone showed a similar macromolecular efflux at the end of the experiment. SIN-1 prevented both the increase in macromolecular efflux seen after L-NAME challenge (part 2) and was highly effective in preventing significantly the increase in macromolecular leakage that is seen during leukocyte-independent endotoxemia (part 3). In conclusion, our data indicate that during early states of endotoxemia endogenous NO preserves endothelial integrity in a leukocyte-independent setting. Exogenous NO prevents endothelial damage during early leukocyte-independent endotoxemia. Summarizing these data, endothelial integrity during leukocyte-independent endotoxemia is a NO-mediated event.

Epinephrine as a mediator of pulmonary neutrophil sequestration

Neutrophil-mediated lung injury is a potential complication of trauma and sepsis. Concomitant with trauma and sepsis, there is an immediate and sustained systemic elevation of catecholamines including epinephrine. In the absence of trauma or sepsis, we examined whether epinephrine contributes to the accumulation of neutrophils in the lung. Eight- to 12-week-old male CF-1 mice were injected i.p. with 0.2 mL of normal saline or epinephrine (0.1-5.0 mg/kg). An unmanipulated control group was included to examine the stress of i.p. injection. Animals were sacrificed at predetermined time points, and lung and spleen were harvested. PMN accumulation was assessed by using a myeloperoxidase (MPO) assay, which is an indirect marker for neutrophil presence. Morphometric analysis of lung tissue was performed by a pathologist blinded to the groups. Increasing epinephrine doses resulted in a significantly increased accumulation of pulmonary neutrophils compared with normal saline. The stress of normal saline injection also resulted in a significantly greater pulmonary neutrophil accumulation than unmanipulated controls. The effects of epinephrine on pulmonary neutrophil accumulation were greatest at 2 h, but they were not significantly different from saline-injected controls by 12 h. These results correlated with histological analysis. There were no significant differences in spleen MPO activity between groups, suggesting an organ-specific mechanism of epinephrine-induced pulmonary neutrophil sequestration. In the absence of trauma, shock, or infection, epinephrine results in the accumulation of neutrophils in murine lungs. The finding that "injection stress" increased lung neutrophil sequestration suggests the possibility that this mechanism may be physiologically relevant. Thus, epinephrine release in trauma may set the stage for development of neutrophil-mediated acute lung injury.

Adenosine deaminase inhibition attenuates microvascular dysfunction and improves survival in sepsis

The ability of increased endogenous adenosine to mitigate microvascular derangements in sepsis was studied. Pentostatin (2'-deoxycoformycin), an inhibitor of adenosine deaminase, was administered to mice immediately after induction of sepsis by cecal ligation and puncture. Intravital video microscopy of cremasteric postcapillary venules was performed. Leukocyte rolling and adhesion were significantly increased in septic mice compared with control mice. Treatment of septic mice with pentostatin significantly decreased leukocyte rolling and adhesion (6.02 +/- 0.09 versus 1.72 +/- 0.12 rolling cells/min, 2.07 +/- 0.04 versus 0.62 +/- 0.05 adherent cells/100 microm per minute; p < 0.001). Albumin leakage (ratio) was significantly attenuated in septic animals treated with pentostatin (0.42 +/- 0.05 versus 0.21 +/- 0.04; p < 0.01). Circulating levels of interleukin-6, tumor necrosis factor-alpha, and soluble tumor necrosis factor type II receptor were decreased in septic mice treated with pentostatin. Survival was significantly improved at 48 hours in mice treated with pentostatin. These results suggest an important role for adenosine in modulating both leukocyte-dependent and -independent mechanisms of endothelial injury in sepsis. Exploiting the advantageous action of endogenous adenosine represents a potentially useful and novel therapeutic approach for the treatment of sepsis.

Influence of serotonin-receptor antagonism on mast cell activation during endotoxemia

INTRODUCTION: Mast cells have been implicated in the aetiology of many diseases and are particularly important in evoking leukocyte-endothelial interactions during endotoxemia. Mast cell activity can be modified by histamine. There are only little data available whether serotonin (5-HT), another amine, is involved in alterations of mast cell activity, too. The aim of the study was to investigate the effects of the 5-HT-receptor antagonists methysergide (5-HT(1/2/7)-receptor antagonist), and ketanserin (5-HT(2A)-receptor antagonist) on mesenteric mast cell activation during endotoxemia. MATERIALS AND METHODS: In male Wistar rats, mast cell activity was determined in the mesentery using intravital microscopy. Rats were randomised in four groups of 12 animals each. Animals underwent laparotomy and the mesentery was exposed beneath an in-vivo videomicroscope. After baseline measurment endotoxemia was induced by continuous intravenous infusion of 2 mg/kg/h endotoxin (ETX group). Animals in the ETX/5-HT(1/2)-ANT group received methysergide (1 mg/kg body weight), animals in the ETX/5-HT(2A)-ANT group received ketanserin (1 mg/kg body weight) additionally prior to laparotomy and to the procedure described above. Animals in saline group served as controls and received equivalent volumes of NaCl 0.9%. Activated mast cells were stained by superfusion of the mesentery with ruthenium red. RESULTS: The relative mast cell activity to baseline value increased significantly in all groups. Values of the ETX-group versus the ETX/5-HT(1/2)-ANT group, the ETX/5-HT(2A)-ANT group, and the saline group were significantly higher at 120 min. CONCLUSIONS: Serotonin receptor antagonism using the 5-HT(1/2/7)-receptor antagonist methysergide or the 5-HT(2A)-receptor antagonist ketanserin reduces endotoxin-induced mast cell activation in-vivo, most probably via the 5-HT(2A)-receptor subtype.

Activation of leukocytes during the uteroplacental passage in preeclampsia

Endothelial dysfunction and inflammation appear to play a major role in the pathogenesis of preeclampsia. We hypothesize that a chronic inflammation in the decidua and placenta during preeclampsia may lead to a local leukocyte activation in this compartment. Venous blood was sampled simultaneously from antecubital and uterine veins during cesarean sections in 30 women with preeclampsia, 29 with uncomplicated pregnancies, and from 17 nonpregnant women. The expression of adhesion molecules and complement-related markers on neutrophils and monocytes was analyzed by flow cytometry. In patients with preeclampsia, neutrophil expression of the integrins CD11a, CD11b, and CD11c and of the complement related markers CD35 and CD59 was significantly higher in samples from uterine than from antecubital veins. No differences were found in nonpregnant women. On monocytes the expression of the Sialyl Lewis(x) antigen, the integrins CD11a, CD11c, and CD49d, and the complement-related markers CD46 and CD59 was higher in samples from uterine than from antecubital veins during preeclampsia, but not in uncomplicated pregnancies, whereas in nonpregnant women CD31 was decreased. Our findings suggest activation of neutrophils and monocytes taking place during the uteroplacental passage in preeclamptic, but not in normal pregnancies. Such a local inflammatory response involving enhanced leukocyte/endothelial interaction may contribute to the pathogenesis of this disorder.

Methysergide attenuates leukocyte-independent plasma extravasation during endotoxemia

PURPOSE

During endotoxemia, the early endothelial damage has been shown to be leukocyte independent. Therefore, it was the aim of our study to investigate the role of serotonin in mediating leukocyte-independent microvascular permeability during endotoxemia. Microvascular permeability was determined after inhibition of the L-selectin mediated leukocyte adherence by fucoidin and after inhibition of serotonin effects by the serotonin (5HT)-receptor antagonist methysergide.

MATERIALS AND METHODS

In male Wistar rats, leukocyte rolling, leukocyte adherence, and macromolecular leakage were determined in mesenteric postcapillary venules using intravital microscopy. After pretreatment with the serotonin-receptor antagonist methysergide, animals in the FUCO/ETX/5HT-ANT group received a continuous infusion of endotoxin. Animals in the FUCO/ETX group underwent the same procedure but received saline 0.9% instead of methysergide. In both groups, leukocyte adherence was prevented by administration of fucoidin. Animals in the saline group received volume-equivalent saline 0.9%.

RESULTS

In the endotoxin-challenged groups, fucoidin prevented leukocyte rolling and reduced leukocyte adherence to values comparable to saline group. In the FUCO/ETX group, macromolecular leakage increased significantly, starting at 60 minutes. Values in the saline group increased slightly, being significant at 120 minutes, whereas vascular permeability remained unchanged in the FUCO/ETX/5HT-ANT group. Differences in macromolecular leakage between the FUCO/ETX-group versus the FUCO/ETX/5HT-ANT group and the saline group were significant at 120 minutes. Differences in macromolecular leakage between the FUCO/ETX/5HT-ANT group and the saline group were not significant.

CONCLUSIONS

The leukocyte-independent endothelial damage during early endotoxemia can be inhibited efficiently by the 5-HT-receptor antagonist methysergide, indicating that serotonin plays an important role in that pathophysiology.

Role of platelet-activating factor in leukocyte-independent plasma extravasation and mast cell activation during endotoxemia

BACKGROUND

Independently from leukocyte adherence, endothelial factors and mast cell activation seems to promote microvascular permeability. Platelet-activating factor (PAF) has been shown to play a significant role in endotoxin-induced leukocyte adherence. The aim of our study was to investigate if there is also a role for PAF in mediating leukocyte-independent microvascular permeability changes and activation of mast cells during endotoxemia. Therefore, during endotoxemia microvascular permeability and mast cell activation were determined after inhibition of L-selectin-mediated leukocyte adherence by fucoidin and after inhibition of PAF effects by the PAF receptor antagonist BN52021.

MATERIALS AND METHODS

In male Wistar rats, red cell velocity (V(RBC)), venular wall shear rate, microvascular permeability, leukocyte adherence, and mast cell activation were determined in mesenteric postcapillary venules using intravital microscopy at baseline and 60 and 120 min after start of a continuous infusion of endotoxin (ETX; 2 mg/kg/h, Escherichia coli O26:B6) (ETX group). Animals in the FUCO/ETX group received fucoidin (25 mg/kg body wt) in addition to the procedure described above. Animals in the FUCO/ETX/PAF-ANT group received fucoidin and the PAF receptor antagonist BN52021 (5 mg/kg body wt) prior to the continuous endotoxin infusion. Control animals (control group) received only equivalent volumes of NaCl 0.9%.

RESULTS

There were no microhemodynamic and macrohemodynamic differences between groups. In all endotoxin-challenged groups macromolecular leakage and mast cell activity increased significantly, starting at 60 min. Both macromolecular leakage and mast cell activity were significantly higher in the FUCO/ETX group than in the FUCO/ETX/PAF-ANT group and control group. Differences in macromolecular leakage between groups were significant at 120 min. Differences in mast cell activity between groups were significant at 60 and 120 min.

CONCLUSIONS

The results of our study demonstrate a leukocyte-independent plasma extravasation that can be inhibited by the PAF receptor antagonist BN52021, indicating the involvement of PAF in the pathophysiology of leukocyte-independent microvascular damage during early endotoxemia. Mast cell activity seems to precede leukocyte-independent macromolecular leakage.

Leukocyte-independent plasma extravasation during endotoxemia

OBJECTIVES

To determine the meaning of leukocyte-endothelial interactions for the development of endotoxin-induced vascular leakage.

DESIGN

Randomized, blinded, controlled trial.

SETTING

Experimental laboratory.

SUBJECTS

Twenty-four male Wistar rats.

INTERVENTIONS

After application of fucoidin to prevent leukocyte rolling and adherence (25 mg/kg; n = 8; fucoidin/LPS group) or saline 0.9% (n = 8; LPS group), animals were given an intravenous infusion of endotoxin (Escherichia coli lipopolysaccharide 026:B6; 2 mg/kg/hr) over 120 mins. Animals in the control group (n = 8) received an equivalent volume of saline 0.9%.

MEASUREMENTS AND MAIN RESULTS

Leukocyte rolling and leukocyte adherence, red cell velocity, vessel diameters, venular wall shear rate, volumetric blood flow, and macromolecular leakage were determined in mesenteric postcapillary venules using in vivo videomicroscopy at baseline, 60 mins, and 120 mins after start of a continuous endotoxin infusion. Fucoidin prevented leukocyte rolling (baseline, 3+/-2 rollers; 120 mins, 3+/-1 rollers; not significant vs. baseline; p < .01 vs. LPS group) and reduced the adherence of leukocytes at baseline and during endotoxemia and showed only a slight increase in adherent leukocytes (baseline, 100+/-38 cells/mm2; 120 mins, 244+/-68 cells/mm2; p < .05 vs. baseline; p < .01 vs. LPS group). In the LPS group, endotoxin exposure induced a marked increase in adherent leukocytes (baseline, 248+/-24 cells/mm2; 120 mins, 560+/-57 cells/mm2; p < .01). Leukocyte adherence in control animals (control group) did not increase significantly. Macromolecular leakage, expressed as the ratio of perivenular to intravenular fluorescence intensity after injection of fluorescence-labeled albumin, increased from 0.16+/-0.03 to 0.49+/-0.04 (p < .01 vs. baseline; p < .05 vs. control) during the infusion of endotoxin in the LPS group. Fucoidin application did not diminish the extravasation of albumin (baseline, 0.09+/-0.03; 120 mins, 0.61+/-0.10; p < .01 vs. baseline; p < .01 vs. control).

CONCLUSIONS

These results demonstrate that despite a significant reduction of adherent leukocytes to the endothelium by fucoidin, there is no reduction in macromolecular leakage, indicating that leukocyte-endothelial interactions only play a minor role for the development of macromolecular leakage and microvascular damage in the early phase of endotoxemia.

Pycnogenol in chronic venous insufficiency

Forty patients with chronic venous insufficiency (CVI) and varices of the legs were selected and double-blindly randomly assigned to a treatment with Pycnogenol (French maritime pine bark extract), 100 mg x 3/day or a placebo for 2 months, according to a double-blind experimental design. The effects of the treatment were evaluated by scoring the symptomatology with a semi-quantitative scale, and the venous blood flow by means of a hand-held Doppler ultrasound. The tolerability was evaluated by recording the adverse effects and by means of hematology and blood chemistry parameters, before and at the end of the treatment. Pycnogenol treatment induced a significant reduction in subcutaneous edema as well as heaviness and pain in the legs, on both after 30 and 60 days, the evaluation time periods. Approximately 60% of patients treated with Pycnogenol(R) experienced a complete disappearance of edema (the most rapidly disappearing symptom) and pain at the end of the treatment, while almost all the patients reported a reduction in leg heaviness which disappeared in approximately 33% of patients. These changes were statistically significant. No effect was observed in the placebo-treated subjects. No effect on the venous blood flow was observed in either of the experimental groups.

Leukocyte accumulation and hemodynamic changes in the cerebral microcirculation during early reperfusion after stroke

BACKGROUND AND PURPOSE

Leukocytes contribute to cerebral ischemia-reperfusion injury. However, few experimental models examine both in vivo behavior of leukocytes and microvascular rheology after stroke. The purpose of the present study was to characterize patterns of leukocyte accumulation in the cerebral microcirculation and to examine the relationship between leukocyte accumulation and microcirculatory hemodynamics after middle cerebral artery occlusion and reperfusion (MCAO-R).

METHODS

Male rats (250 to 350 g) were anesthetized and ventilated. Tail catheters were inserted for measurement of arterial blood gases and administration of drugs. Body temperature was maintained at 37 degrees C. Animals were subjected to 2 hours of MCAO by the filament method. A cranial-window preparation was performed, and the brain was superfused with warm, aerated artificial cerebrospinal fluid. Reperfusion was initiated by withdrawing the filament, and the pial microcirculation was observed by use of intravital fluorescence microscopy. Leukocyte accumulation in venules, arterioles, and capillaries; leukocyte rolling in venules; and leukocyte venular shear rate were assessed during 1 hour of reperfusion.

RESULTS

We found significant leukocyte adhesion in cerebral venules during 1 hour of reperfusion after 2 hours of MCAO. Leukocyte trapping in capillaries and adhesion to arterioles after MCAO-R tended to increase compared with controls, but the increase was not significant. We also found that shear rate was significantly reduced in venules during early reperfusion after MCAO.

CONCLUSIONS

A model using the filament method of stroke and fluorescence microscopy was used to examine white-cell behavior and hemodynamics in the cerebral microcirculation after MCAO-R. We observed a significant increase in leukocyte rolling and adhesion in venules and a significant decrease in blood shear rate in the microcirculation of the brain during early reperfusion. Leukocytes may activate and damage the blood vessels and surrounding brain cells, which contributes to an exaggerated inflammatory component to reperfusion. The model described can be used to examine precisely blood cell-endothelium interactions and hemodynamic changes in the microcirculation during postischemic reperfusion. Information from these and similar experiments may contribute to our understanding of the early inflammatory response in the brain during reperfusion after stroke.

Skeletal muscle blood flow after prolonged tourniquet ischaemia and reperfusion with and without intervening reoxygenation: an experimental study in rats using laser Doppler perfusion imaging

The total, safe, time available for operating during tourniquet ischaemia is thought to be prolonged by short, intervening episodes of reperfusion. However, animal experiments have suggested that this may cause a reduction of the postischaemic reperfusion injury. The purpose of the present study was to investigate the effect on final postischaemic reperfusion of intermittent, short periods of reperfusion compared with that of prolonged, continuous tourniquet ischaemia. A rat tourniquet model of total limb ischaemia and laser Doppler imaging to measure postischaemic microvascular perfusion in skeletal muscle was used in a total of 25 anaesthetised rats. Four were non-ischaemic controls. In 21 rats one hind leg was made totally ischaemic by a tourniquet. Fourteen were exposed to uninterrupted periods of either 1.5 hours or three hours, and seven to interrupted total ischaemia of three hours, with a 20 minutes reperfusion interval after 1.5 hours of ischaemia. The postischaemic blood flow was monitored 20 minutes after release of the tourniquet. Postischaemic skeletal muscle blood flow was significantly reduced after three hours of continuous ischaemia compared with the group that had an intervening short period of reoxygenation. The postischaemic reperfusion after three hours of ischaemia with a short reperfusion interval was not reduced after ischaemia compared with either that in controls or to that in the group exposed to only 1.5 hours of tourniquet ischaemia. These findings support the clinical practice of using intervening periods of reperfusion to prolong the total tourniquet time that can safely be used. There were no adverse effects on postischaemic reperfusion from intermittent reoxygenation.

Neutrophils in galactose-fed dogs: suppressed apoptosis and increased adhesion to retinal capillary endothelial cells

Dogs fed a diet containing 30% galactose develop diabetes-like retinal capillary changes. As retinal capillary occlusion is commonly observed in diabetic retinopathy, neutrophil apoptosis and the interaction of neutrophils with retinal capillary endothelial cells were investigated. Neutrophils were isolated with Ficoll-Hypaque centrifugation from dogs fed a 30% galactose diet and dogs fed a normal, control diet containing 30% non-nutrient filler. Apoptosis of neutrophils was microscopically examined after incubation at 37 degrees C for 3 hours with either 100 U/mL tumor necrosis factor alpha (TNF-alpha), 2 microg/mL cycloheximide or 50 ng/mL phorbol 12-myristate 13-acetate (PMA). Neutrophil adhesion to dog retinal capillary endothelial cells was examined by counting the cells attached to the surface of endothelial cells after the incubation in the presence of either 100 U/mL TNF-alpha or 5 microg/mL lipopolysaccharides (LPS) at 37 degrees C for 3 hours. With all three stimulants TNF-alpha, cycloheximide and PMA, the rate of apoptosis was significantly lower for neutrophils isolated from galactose-fed dogs compared to control dogs fed a normal diet. Preincubation of neutrophils from control dogs in medium containing 30% galactose for 3 hours did not affect the rate of apoptosis. Neutrophil adhesion to retinal capillary endothelial cells induced by incubation in the presence of either 100 U/mL TNF-alpha or 5 microg/ml LPS was significantly higher with neutrophils isolated from galactose-fed dogs than those from control dogs. The data indicate that long-term galactose feeding is essential with development of various neutrophil dysfunctions. These neutrophil changes may contribute to the development of retinal microangiopathy associated with diabetes and galactosemia.

A comparison of free radical-induced vascular and skeletal muscle damage in immunocompetent and neutropenic rats

BACKGROUND

Intraarterial infusion of the free radical donor tert. -butyl-hydroperoxide (tert.-BuOOH) into one extremity of the rat induces vascular permeability and considerable skeletal muscle damage. However, it remains unclear what the role of polymorphonuclear neutrophils (PMNs) is in oxidative stress-related processes. Therefore, we investigated possible differences between neutropenic and normal animals in this model.

METHODS

Neutropenia was induced in male rats by intraperitoneal administration of cyclophosphamide. tert.-BuOOH was continuously infused intraarterially into one hindlimb of normal or neutropenic nonanesthetized rats for 24 h. The control neutropenic rats were infused with the same volume of saline. After the infusion, 99mTc-IgG was administered intravenously followed by scintigraphic imaging analysis of the left/right uptake ratio of the hindlimbs and by gamma counting of the tissue samples of the gastrocnemius and gluteus maximus muscles. Samples of these muscles were analyzed by light microscopy.

RESULTS

The uptake ratios were significantly increased in the normal and neutropenic tert.-BuOOH-infused animals as compared with the saline-infused neutropenic rats (P < 0.05). The uptake ratios were significantly higher in normal than in neutropenic tert.-BuOOH-infused rats (P < 0.05). Histological analysis of the saline infused skeletal muscles showed unaffected skeletal muscles with intact arterioles and arteries. In the gastrocnemius and gluteus maximus muscles of the normal tert. -BuOOH-infused and neutropenic rats, similar morphological damage was observed.

CONCLUSIONS

PMNs can increase, to some extent, the vascular permeability of the free radical damaged small arteries and arterioles of a tert.-BuOOH-infused hindlimb. However, in the present animal model, tert.-BuOOH alone can induce oxidative stress-related abnormalities with skeletal muscle tissue damage that is mainly independent of the presence of PMNs.

Hypertonic saline resuscitation reduces neutrophil margination by suppressing neutrophil L selectin expression

Hypertonic saline (HS) reduces hemorrhage-induced lung injury by suppressing the neutrophil oxidative burst and reducing lung neutrophil influx. This study investigated whether this is caused by the effects of HS on endothelial adhesion molecule expression, the production of chemoattractants in the lung, or a direct effect of HS on neutrophil selectin expression.

METHODS

BALB/c mice were made to hemorrhage to 40 mm Hg for 1 hour and resuscitated with shed blood and either 4 mL/kg 7.5% HS or two times the shed blood volume of lactated Ringer's solution (LRS). Neutrophil L selectin expression was determined by flow cytometry, total neutrophil counts were obtained by differential staining, and pulmonary endothelial P and E selectin expression was evaluated by immunohistochemistry. Chemoattractants in lung lavages were determined with a modified Boyden chamber migration assay.

RESULTS

Chemotactic activity of lavage fluid of HS-treated animals was not significantly different from that of LRS-treated animals, and endothelial P and E selectin expression was not altered by HS resuscitation. Neutrophils of HS-treated animals, however, expressed significantly less L selectin than those of LRS-treated mice. Concomitantly, circulating neutrophil counts of LRS-treated animals were significantly decreased compared with those of HS-treated mice.

CONCLUSION

HS had little effect on endothelial selectin expression and chemoattractant production in the lung. HS significantly decreased neutrophil L selectin expression, however. This suggests that HS resuscitation may reduce lung injury by preventing neutrophil L selectin expression and endothelial adhesion.

Development of vascular complications in diabetes

Chronic complications of diabetes are dominated by disorders of the vascular system. They are a much larger burden on both diabetic patients and overall medical costs than diabetes itself. Large vessel problems are far more frequent than microvascular disorders. Loss of arterial elasticity alters arterial flow patterns and increases microcirculatory peak flow rates. Hyperglycemia may directly disrupt elastin formation. Diabetic leg artery disease may be generated by nerve damage, reversing this interactive contribution sequence. The major anatomic feature of microangiopathy in long-term diabetes is an unevenly distributed thickening of the intima of smaller arterioles. The thickening is primarily due to accumulation of type IV (basement membrane) collagen. Arterioles change local vessel diameter to adjust blood distribution to meet current needs. The thickening compromises the maximum local blood flow that may be achieved by this means. Compromise of maximal arteriolar dilatation does not disrupt exercising muscle but in the kidney, retina, and possibly in nerve, local circumstances can generate serious damage. Each of these system's responses has unique features that mediate its vulnerability, but all these organs show arteriolar hyalinization. The increased arteriolar accumulation of type IV collagen appears to be a response to the tangential force generated by flow over local endothelial cells. An increase in peak arteriolar wall force is mediated by a diabetes-specific doubling of erythrocyte membrane curvature change resistance. Red cell aggregation rate determines the rate of damage. The same nonspecific burden may also predispose to heart disease and stroke. Intensive metabolic control improves red cell deformability and protects against arteriolar damage. Therapies that address the rheologic problem more directly may add to the effectiveness of good diabetes control in the future.

The relative safety of MRI contrast agent in acute necrotizing pancreatitis

OBJECTIVE

To validate the safety of gadolinium-diethylenetriamine pentaacetic acid (GD-DTPA) by measuring its effect on pancreatic capillary perfusion and acinar injury in acute pancreatitis.

BACKGROUND

Contrast-enhanced computed tomography (CECT) is proposed as a gold standard for early evaluation of acute necrotizing pancreatitis. However, iodinated contrast media used for CECT have been shown in these circumstances to reduce pancreatic capillary flow and increase necrosis and mortality. Recent reports suggest that post-GD MRI provides images comparable to CECT in the assessment of severe acute pancreatitis.

METHODS

Necrotizing pancreatitis was induced in 14 Wistar rats by intraductal glycodeoxycholic acid (10 mM/L) and intravenous caerulein (5 microg/kg/h) over 6 hours. Intravital microscopic quantitation of pancreatic capillary blood flow was performed using fluorescein isothiocyanate-labeled erythrocytes after induction of pancreatitis and 30 and 60 minutes after an intravenous bolus of either Ringer's solution or GD-DTPA (0.2 mL/kg).

RESULTS

The two study groups were comparable with regard to mean arterial pressure, heart rate, arterial blood gases, hematocrit, amylase, lipase, and trypsinogen activation peptide production throughout the experiment. GD-DTPA did not reduce capillary flow (1.93 +/- 0.05 nL/capillary/min) compared to animals infused with Ringer's solution (1.90 +/- 0.06 nL/capillary/min).

CONCLUSIONS

Intravenous injection of GD-DTPA does not further impair pancreatic microcirculation or increase acinar injury in acute necrotizing pancreatitis. Because of this advantage over CT contrast medium, further development of MRI as a staging tool in acute pancreatitis seems desirable.

Blood flow structuring and its alterations in capillaries of the cerebral cortex

Various manifestations of blood flow structuring were investigated in rabbit cerebral cortex capillaries, which possess the most narrow lumina of all parts of the body. Blood flow structuring in the capillaries was characterized by the presence of a stable and comparatively large parietal plasma layer, which changed insignificantly under control and ischemic conditions, but disappeared when blood stasis developed inside the capillaries. The axial core of the blood flow in the capillaries, which occupied almost two-thirds of the intracapillary volume under normal conditions, consisted of significantly deformed (stretched along the microvessels' axes) and nonaggregated erythrocytes. During ischemia the shape of the erythrocytes did not change appreciably; only the blood plasma intervals between them increased significantly, demonstrating reduction of the local hematocrit. During primary blood stasis caused by enhanced intravascular erythrocyte aggregation, typical blood flow structuring became significantly disturbed: red cells filled the whole, or almost the whole, capillary lumina and did not leave visible space for plasma inside the microvessel lumina. We concluded that normal blood flow structuring is a deciding factor in the blood rheological properties of microvessels. Its disturbance, caused by fast accumulation of erythrocytes in the capillary lumina, results in blood rheological disorders and in a slow down to a full stop of the blood flow, despite a preserved arteriolovenular pressure difference.

Increased nitric oxide deactivation by polymorphonuclear leukocytes in patients with intermittent claudication

PURPOSE

Local activation of polymorphonuclear leukocytes (PMNLs) is considered an important aspect of the pathogenesis of intermittent claudication, although concrete mechanisms of their effects on circulatory homeostasis in peripheral atherosclerotic disease remain unclear. This study evaluated the ability of PMNLs to deactivate nitric oxide (NO), a key regulator of regional circulation, as a possible factor determining PMNL involvement into ischemic disorders in patients who have intermittent claudication before and after vascular reconstruction.

METHODS

A total of 57 patients who had peripheral occlusive disease in an aortofemoral segment before surgical treatment (group 1) and 65 patients who had similar occlusive lesions and other clinical and demographic data 6 to 12 months after undergoing inflow vascular reconstruction (group 2) were examined. All patients from group 2 had anatomically patent grafts; their satisfaction and level of function after surgical treatment were assessed by a five-point questionnaire. The sex- and age-matched control group included 35 subjects. NO activity was bioassayed by measuring its ability to increase cyclic guanosine monophosphate (cGMP) accumulation in rat fetal lung-cultured fibroblasts (RFL-6 cells). The ability of PMNLs to deactivate NO was characterized as the percent decrease in NO-induced cGMP accumulation in RFL-6 cells.

RESULTS

Stimulated PMNLs caused inhibition of the activity of authentic NO; accumulation of cGMP induced by sodium nitroprusside was not affected. PMNLs from patients with peripheral atherosclerotic disease either before or after vascular reconstruction had a more marked capacity of NO inactivating than the cells from healthy subjects. For both groups of patients, levels of PMNL-induced NO deactivation were higher for patients with diabetes, and especially both diabetes and arterial hypertension. For both groups of patients, there was no correlation between levels of PMNL-induced NO deactivation and resting ankle-brachial indexes (ABIs). In contrast, close correlation was revealed between levels of PMNL-induced NO deactivation and postexercise ABIs and percent decrease in resting ABIs after exercise in patients evaluated either before or after surgical treatment.

CONCLUSIONS

The ability of stimulated PMNLs to deactivate NO is elevated in peripheral occlusive disease and may be implicated in the pathogenesis of intermittent claudication. In patients who underwent successful recanalization of magistral arteries, levels of PMNL-induced NO deactivation remained higher than in control subjects. The increase in the ability of PMNL to deactivate NO positively correlated to ABI decreases after exercise in patients with peripheral occlusive disease either before or after surgical treatment.

Calcium-channel blockers preserve coronary endothelial reactivity after ischemia-reperfusion

BACKGROUND

Calcium-channel blockers have been reported to improve myocardial recovery after ischemia-reperfusion, but their effects on coronary blood flow regulation remain to be defined. Experiments were designed to evaluate the effects of calcium antagonists on coronary artery vasoregulation exposed to ischemia-reperfusion.

METHODS

Three groups of hearts (n = 6) were pretreated with a 10-minute infusion of either diltiazem, verapamil, or nifedipine at concentrations of 10(-9) mol/L to 10(-6) mol/L and exposed to 30 minutes of no-flow ischemia and 45 minutes of reperfusion. Another group (n = 6) received no pretreatment and was used as control. Endothelium-dependent and -independent relaxations were tested by assessing coronary flow increase to 5-hydroxytryptamine (10(-6) mol/L) and sodium nitroprusside (10(-5) mol/L) infusion, respectively. Left ventricular pressure, its first derivative, and coronary basal flow were recorded before and after ischemia as well as during calcium antagonist infusion.

RESULTS

Endothelium-dependent relaxation after ischemia was significantly improved with all three drugs in a dose-dependent fashion; nifedipine was found to be the more potent. Endothelium-independent relaxation was also significantly preserved with calcium antagonists regardless of the type, whereas left ventricular hemodynamics were not. During perfusion, nifedipine was found to have the most negative inotropic effect and to be the most potent vasodilator on the coronary circulation. Diltiazem was the less effective drug on both left ventricular hemodynamics and coronary circulation.

CONCLUSIONS

This study indicates that preischemic infusion of calcium antagonists enhance endothelium-dependent and -independent coronary artery relaxation in the isolated rat heart model in a dose- and drug-dependent fashion. This can be achieved at low doses without affecting left ventricular hemodynamics and should contribute to preserve coronary artery autoregulation.

Nitric oxide modulation of transcellular biosynthesis of cys-leukotrienes in rabbit leukocyte-perfused heart

1. We have studied the role of nitric oxide (NO) in the regulation of the transcellular biosynthesis of sulphidopeptide leukotrienes (cys-LT) generated upon neutrophil-vascular wall interactions and their functional consequences, in the spontaneously beating, cell-perfused, heart of the rabbit. 2. Hearts were perfused under recirculating conditions (50 ml) with 5 x 10(6) purified human neutrophils (PMNL), and challenged with 0.5 microM A-23187 for 30 min. Coronary perfusion pressure (CPP) and left-ventricular end-diastolic pressure (LVEDP) were monitored. Cys-LT formation was measured by reversed phase high performance liquid chromatography (h.p.l.c.) and u.v. spectral analysis. Myeloperoxidase (MPO) enzyme activity, assayed in aliquots of the recirculating buffer, was used as a marker of PMNL, adhesion to the coronary endothelium. 3. Basal CPP and LVEDP values averaged 45 +/- 1.4 mmHg and 5 +/- 0.1 mmHg, respectively; A-23187 triggered an increase in CPP (134 +/- 9 mmHg, at 30 min) which was significantly attenuated by pretreatment with L-arginine, 100 microM (90 +/- 3 mmHg, at 30 min). Pretreatment with NG-monomethyl-L-arginine, 10 microM (L-NMMA), induced a marked increase in CPP (290 +/- 40 mmHg, at 20 min) and in LVEDP (47 +/- 16 mmHg), so pronounced that it caused cardiac arrest in systole in 5 out of 6 hearts and these were prevented by L-arginine, 100 microM, (CPP 115 +/- 10 mmHg, LVEDP 6 +/- 1.1 mmHg, at 30 min). 4. The increase in CPP was accompanied by the release of cys-LT in the circulating buffer, which was reduced significantly by L-arginine. Pretreatment with L-NMMA, caused a marked rise in cys-LT concentrations which was prevented by L-arginine. 5. Neither L-arginine nor L-NMMA affected directly the A-23187-induced arachidonic acid (AA) metabolism in isolated PMNL alone. 6. Pretreatment with L-NMMA caused a prompt drop in myeloperoxidase (MPO), activity, suggesting rapid adhesion of PMNL to the coronary wall; this effect was significantly blunted by L-arginine. 7. This study suggests that NO provides cardioprotection in an organ model of transcellular metabolism of cys-LT by preventing PMNL adhesion to the coronary intima.

Experimental antileukocyte interventions in cerebral ischemia

White blood cells (WBCs) play vital roles in host defense. Recently, increasing interest has been directed toward the question of whether WBCs, particularly polymorphonuclear leukocytes, could also act as mediators of secondary brain damage in the setting of focal and global cerebral ischemia with and without reperfusion. Considerable insight into the importance of WBC-mediated tissue injury has been gained from studies employing antileukocyte interventions in experimental cerebral ischemia. The purpose of this article is to survey the different approaches taken to interfere with WBC inflammatory function. Emphasis is laid on a discussion of the efficacy of these interventions, their effects and side effects on cerebral and systemic parameters, and the power of evidence they provide for identification of WBCs as important factors in cerebral ischemia. The role of WBCs has been investigated in a great variety of global and focal cerebral ischemia models with and without reperfusion, leading to sometimes contradictory results. In the light of currently available data, it seems likely that WBCs contribute to secondary brain damage in the scenario of experimental transient focal cerebral ischemia, if the insult is not too severe.