Heparin modulates integrin-mediated cellular adhesion: specificity of interactions with alpha and beta integrin subunits.

Heparin is known to influence the growth, proliferation, and migration of vascular cells, but the precise mechanisms are unknown. We previously demonstrated that unfractionated heparin (UH) binds to the platelet integrin alpha(IIb)beta(3), and enhances ligand binding. To help define the specificity and site(s) of heparin-integrin interactions, we employed the erythroleukemic K562 cell line, transfected to express specific integrins (alpha(v)beta(3), alpha(v)beta(5), and alpha(IIb)beta(3)). By comparing K562 cells expressing a common alpha subunit (Kalpha(v)beta(3), Kalpha(v)beta(5)) with cells expressing a common beta subunit (Kalpha(v)beta(3), Kalpha(IIb)beta(3)), we observed that heparin differentially modulated integrin-mediated adhesion to vitronectin. UH at 0.5-7.5 microg/ml consistently enhanced the adhesion of beta(3) expressing cells (Kalpha(v)beta(3),Kalpha(IIb)beta(3)). In contrast, UH at 0.5-7.5 microg/ml inhibited Kalpha(v)beta(5) adhesion. Experiments using integrin-blocking antibodies, appropriate control ligands, and nontransfected native K562 cells revealed that heparin's actions were mediated by the specific integrins under study. Preincubation of heparin with Kalpha(v)beta(3) cells enhanced adhesion, while preincubation of heparin with the adhesive substrate (vitronectin) had minimal effect. There was a structural specificity to heparin's effect, in that a low molecular weight heparin and chondroitin sulfate showed significantly less enhancement of adhesion. These findings suggest that heparin's modulation of integrin-ligand interactions occurs through its action on the integrin. The inhibitory or stimulatory effects of heparin depend on the beta subunit type, and the potency is dictated by structural characteristics of the glycosaminoglycan.

beta1-integrin-ligand disengagement induces in vitro capillary tube disruption mediated by p38 MAPK activity.

BACKGROUND: Disrupting cell-matrix interactions may lead to capillary injury as seen in sepsis and transplant rejection. Previously, we demonstrated capillary disruption mediated by beta1-integrin-ligand disengagement. We now determine whether p38 mitogen-activated protein kinase (MAPK) and extracellular signal-regulated kinase (ERK) pathways are involved in this capillary injury. METHODS: Endothelial capillaries on Matrigel were preincubated with a p38 MAPK inhibitor (SB203580), ERK pathway inhibitor (PD98059), or dimethyl sulfoxide. Subsequently, a beta1-integrin blocking (P5D2) or an irrelevant antibody was added. After 24 hours, capillary integrity was quantified as capillary intersections/well. Antibody-treated cell lysates then were immunoprecipitated with either a phospho-p38 MAPK or phospho-ERK1/2 antibody. Kinase activity was measured with ATF-2 and Elk-1 fusion proteins as substrates for p38 MAPK and ERK, respectively, followed by Western blotting. RESULTS: P5D2 disrupted capillary tubes. Increased p38 MAPK activity at 8 hours and ERK activity at 2 and 8 hours were seen in P5D2-treated lysates. Preincubation with SB203580, but not with PD98059 or DSMO, significantly reduced capillary tube disruption. CONCLUSIONS: The beta1-integrin-ligand disengagement resulted in capillary disruption and stimulated p38 MAPK and ERK activity. In spite of activation of both pathways, the p38 MAPK but not the ERK pathway inhibitor prevented beta1-integrin antibody effects. Inhibiting p38 MAPK may mitigate capillary injury associated with sepsis and transplant rejection.

Popliteal vascular injury during total knee arthroplasty.

BACKGROUND: Popliteal vascular injury during total knee arthroplasty (TKA) is rare. Although the etiology, management, and outcome of this injury have not been systematically studied, several anecdotal reviews and small case series have suggested a high morbidity, with tourniquet injury as a predominant etiology. METHODS: We surveyed 190 members of a major regional vascular society concerning their experiences with popliteal vascular injuries sustained during TKA, specifically regarding the presentation, mechanisms of injury, diagnostic studies, surgical exposure and methods of repair, and outcomes. RESULTS: Thirteen surgeons provided data (6.8% response rate) on 19 patients with TKA-related popliteal artery injuries. In contrast to the historical literature, sharp, direct trauma was the predominant etiology of vascular injury. Vascular reconstructive techniques varied, with arterial bypass being the most common. There was no mortality in this series. Eighty-four percent (16/19) of the patients had full recoveries. Limb loss occurred in 2 of the 19 patients (10.5%). CONCLUSION: Popliteal vascular injuries during TKA are primarily the result of direct trauma to the vessel. Prompt diagnosis, extensile vascular exposure through a medial knee surgical incision, and standard reconstructive techniques offer a good prognosis for this limb-threatening complication.

Distal venous arterialization for limb salvage--a case report.

The reperfusion of an ischemic limb in the absence of suitable target artery remains a formidable task. The authors report a case of an ischemic limb in patient whose distal arteries were identified intraoperatively as unsuitable for conventional revascularization. A distal arteriovenous fistula was created between the already arterialized in situ greater saphenous vein conduit and the inframalleolar superficial venous system of the foot. The flow through the superficial venous system salvaged the limb and continues to perfuse the foot 4 years post-operatively with resolution of rest pain.

Anticoagulants: to bleed or not to bleed, that is the question.

Thromboembolic vascular diseases remain the main cause of death in Western industrialized societies. Anticoagulants retard the formation, growth, and embolization of thrombi and are effective agents in the prevention and treatment of thromboembolic disease. Anticoagulants in venous thromboembolism have been investigated extensively with rigorous randomized, controlled trials, while the roles for anticoagulants in arterial thromboembolism generally have evolved through natural history studies and empirical practice. Thus, many current guidelines for anticoagulant use in arterial disease are based on successful established routines and rational therapy. To effectively balance the efficacy and risks of anticoagulation, the vascular surgeon needs a thorough understanding of anticoagulant drugs, their mechanisms of action, and their proven and unproven indications. Since the first use of heparin in arterial surgery, a variety of new and different anticoagulants have become available, including low-molecular-weight heparins, heparin-like drugs, hirudins, and thrombin inhibitors. Despite their diverse actions, they all inhibit some portion of the plasma coagulation cascade, thus distinguishing them from platelet inhibitors or fibrinolytics. Every interference with the coagulation cascade carries a risk of minor, major, or fatal hemorrhage. To date, no drug or therapeutic strategy has succeeded fully in dissociating its antithrombotic effects from its risks of bleeding.

Anorexia in space and possible etiologies: an overview.

Space travelers experience a flight duration-dependent loss in weight and body mass while in a microgravity environment, despite the absence of increased energy expenditure. Anorexia in space can lead to in-flight caloric deficits of 1330 kcal per 70 kg astronaut per day in the presence of abundant food and has a critical effect on endurance and performance. Microgravity, alterations in the light-and-dark cycle, and exposure to radiation energy are the environmental stresses believed to influence appetite, food intake, and gastrointestinal function during space flight. Review of data and recent studies in rodents during microgravity showed a release of stress hormones and complex neuroendocrine and physiologic changes involving the modulation of hypothalamic activity, food intake-related hormones, and cytokines. The shift of dietary preference to carbohydrates, which occurs in astronauts, denotes a stress physiologic response and augments free-plasma tryptophan concentration in the brain, the precursor of the potent anorexic agent, serotonin (5-HT). Alterations of other neuroendocrine mediators, including corticotropin-releasing factor (CRF), coordinate the stress response, leading to a decrease in appetite and gastrointestinal function. Our laboratories used the antiorthostatic tail-suspension technique to successfully mimic some of these anorexia-related stress responses and to directly demonstrate the role of 5-HT in microgravity-related decreased food intake and delayed gastric emptying. Further rodent studies from our laboratories demonstrated the adverse effect of altered dark-and-light cycles on food intake and body weight. Radiation energy, through its documented effects on appetite, probably contributes to the decreased caloric intake by astronauts. Modulation of hypothalamic activity, 5-HT, and CRF play a critical role in anorexia related to microgravity and circadian rhythm alterations. Specific gene knockout mice (e.g., 5-HT or CRF and their respective receptors) may prove fruitful in defining the pathways by which anorexia in space occurs. An understanding of these pathophysiologic problems as they relate to appetite, food intake, gastric emptying and gastrointestinal function, sufficiently to derive successful practical solutions, may lead to a quantitative enhancement of physiologic well-being and performance status, serving as a productive countermeasure in space.