摘要:

Background The binding of urokinase-type plasminogen activator (uPA) to its receptor (uPAR) on cell surfaces has the potential to influence degradation of extracellular matrix (ECM). Thus, uPA bound to monocyte/macrophages and its interactions with plasminogen activator inhibitors types 1 and 2 (PAI-1 and PAI-2) may modify atherogenesis by altering cell-associated proteolytic activity, degradation of ECM, and neointimal formation at sites of vascular injury.Methods and Results To determine whether the expression of proteins on the surface of cells involved in fibrinolysis changes in human cells in response to mediators implicated in atherogenesis, we exposed U937 cells (an immortal human monocyte-like cell line) to transforming growth factor- beta (TGF- beta) and to thrombin. Induction of uPAR mRNA occurred with TGF- beta (5 ng/mL) in a time-dependent fashion (P=.05; n=4). Thrombin (5 National Institutes of Health (NIH) U/mL) increased uPAR mRNA by 2.8-fold above control (n=4) without altering PAI-1 mRNA or protein synthesis (n=4). The increase in uPAR gene expression in cells exposed to either TGF- beta or thrombin translated into a functional increase in cell-surface proteolytic activity. Under control conditions, U937 cells expressed PAI-2 but not PAI-1 mRNA. PAI-2 mRNA expression increased (P<.05; n=4) with thrombin (5 NIH U/mL) but was suppressed by TGF- beta (5 ng/mL). TGF- beta induced PAI-1 mRNA within 6 hours accompanied by a 9-fold increase in PAI-1 protein from 6 hours (2.3+-1.9 ng/mL) to 24 hours (20.0+-9.6 ng/mL, P=.005; n=3) paralleled by increased synthesis as shown in metabolic labeling experiments with Sulfur-35-methionine and immunoprecipitation of labeled PAI-1. PAI-1 mRNA and protein expression were seen in human coronary artery atherectomy specimens as well and were localized to analogous monocyte/macrophages and to smooth muscle cells as judged from results of in situ hybridization and immunocytochemistry studies.Conclusions The results indicate that there is induction of PAI-1 and uPAR in U937 cells exposed to TGF- beta and thrombin. In atheroma, analogous processes may modulate early migration of luminal monocytes into the subintimal space and proteolysis of ECM. Thus, cell surface, monocyte-directed fibrinolysis may influence atherosclerosis, restenosis, or both. (Circulation. 1994;90:1927-1934.)

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Background Several epidemiological studies have shown an inverse relation between high-density lipoprotein (HDL) cholesterol levels and coronary heart disease. Recently, observational studies have suggested a similar inverse relation between HDL and restenosis after coronary balloon angioplasty. Despite these observations, it is unclear whether this inverse relation reflects a direct vascular protective effect of HDL or apolipoprotein (apo) A-I, the major apolipoprotein component of HDL. Therefore, to determine whether HDL directly influences neointima formation, we investigated the effect of recombinant apo A-I Milano (apo A-I M), a mutant of human apo A-I with Arg-173 to Cys substitution, on intimal thickening after balloon injury in cholesterol-fed rabbits.Methods and Results Cholesterol feeding was initiated 18 days before injury and continued until the time of death. Eight rabbits received intravenous injections of 40 mg of apo A-I M linked to a phospholipid carrier on alternate days, beginning 5 days before and continuing for 5 days after balloon injury of femoral and iliac arteries. Eight rabbits received the carrier alone, and four received neither apo A-I M nor the carrier. Three weeks after balloon injury, apo A-I M-treated rabbits had significantly reduced intimal thickness compared with the two control groups (mean+-SD): 0.49+-0.29 versus 1.14+-0.38 mm2and 1.69+-0.43 mm2, P<.002 by ANOVA). The intima-to-media ratio was also significantly reduced by apo A-I M (0.7+-0.2 versus 1.5+-0.5 and 2.1+-0.1, P<.002 by ANOVA) compared with the two controls. The fraction of intimal lesion covered by macrophages, as identified by immunohistochemistry using macrophage-specific monoclonal antibody, was significantly less in apo A-I M-treated rabbits compared with carrier-treated animals (25.3+-17% versus 59.4+-12.3%, P<.005). Aortic cholesterol content, measured in an additional 10 rabbits, did not differ significantly between apo A-I M-treated animals (n=5) and carrier-treated controls (n=5).Conclusions Apo A-I M significantly reduced intimal thickening and macrophage content after balloon injury in cholesterol-fed rabbits without a change in arterial total cholesterol content. Although the precise mechanism of action remains to be defined, these findings are consistent with a direct vascular effect of apo A-I, which could have potential therapeutic implications. (Circulation. 1994;90:1935-1941.)

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Background After a brief episode of ischemia, myocardial function may be depressed for prolonged periods despite reperfusion. The mechanisms of postischemic dysfunction differ depending on the experimental model. Regional ischemia and reperfusion in the intact animal provide a clinically relevant model, but experimental variables are difficult to control. Experimental conditions can be well controlled in isolated cardiac muscle and myocyte preparations, but these models are limited by the assumptions used to mimic ischemia and reperfusion. This study combines the unique advantages of both preparations. We characterized in vivo alterations in regional two-dimensional finite strains with ischemia and reperfusion produced in the intact animal, then isolated cardiac myocytes from the region with postischemic dysfunction to characterize in vitro function of postischemic myocytes.Methods and Results In seven anesthetized rabbits, three piezoelectric crystals were inserted in a triangular array to measure two-dimensional finite strains around the large coronary artery in the left ventricular anterior free wall. After 15 minutes of ischemia and reperfusion, strains were depressed at a stable level (approximately) 30% to 40% below control values between 1 and 6 hours after reperfusion. The direction of maximal shortening deformations was midway between circumferential and longitudinal directions during control and did not shift after reperfusion. In a second group of five rabbits, cardiac myocytes were isolated from the region with postischemic dysfunction after 15 minutes of ischemia and 45 minutes of reperfusion. We compared in vitro function in 45 postischemic myocytes with 48 cardiac myocytes isolated from five normal rabbits. Each rabbit (postischemic and control) contributed 9+-1 (SD) myocytes to the study. All myocytes were studied within 1 hour after myocyte isolation ((approximately) 3 to 5 hours after reperfusion for postischemic myocytes). Myocytes were stimulated at 0.5 Hz and perfused with 2 mmol/L (Ca2+) Tyrode's solution to measure unloaded cell shortening. There was significantly less shortening in postischemic myocytes (12.4+-2.1%) than control myocytes (16.2+-1.2%). Maximal cell length (Lmax) was significantly longer in postischemic (134+-7 microns) than control myocytes (122+-7 microns), as was minimum cell length (Lmin) (118+-8 versus 103+-9 microns, respectively). The duration of shortening (time from stimulation to Lmin) was significantly shorter in postischemic (279+-56 milliseconds) than control myocytes (405+-44 milliseconds). Peak rates of cell shortening (-dL/dt) and lengthening (+dL/dt) did not differ.Conclusions In rabbits, 15 minutes of ischemia produced a stable depression in finite strains for 1 to 6 hours after reperfusion, with shortening deformations reduced by (approximately) 30% to 40% without a shift in direction. Cardiac myocytes isolated from postischemic myocardium display functional impairments in vitro similar to those measured in vivo, with an (approximately) 25% reduction in unloaded myocyte shortening and decreased contraction duration. This indicates that ischemia and reperfusion induce intrinsic impairments in contractility independently of external loading conditions. This model may be useful for examining cellular mechanisms of postischemic myocardial dysfunction. (Circulation. 1994;90:1942-1950.)

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Background Platelet-dependent thrombosis can be effectively inhibited by intravenous administration of direct thrombin antagonists. However, an increased propensity for abnormal bleeding has been associated with systemic administration of these agents. The goal of this study was to determine whether local delivery of a potent thrombin inhibitor, d-Phe- l-Pro-l-Arg chloromethyl ketone (PPACK), could inhibit platelet-dependent thrombosis without altering systemic hemostatic function.=2.5 mg/mL for 15 minutes produced sustained inhibition of platelet-dependent thrombosis with no change in hemostatic measurements.Conclusions These results indicate that local delivery of the direct antithrombin PPACK, by either boundary layer infusion or static application techniques, effectively inhibits platelet-dependent thrombosis at doses that are several orders of magnitude less than the systemic dose required for an equivalent antithrombotic effect. In contrast to the systemic administration of PPACK, local delivery produced maximal inhibition of thrombosis without alterations in hemostasis. (Circulation. 1994;90:1951-1955.)

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Background Although the indirect thrombin inhibitor heparin and the more potent direct inhibitor hirudin are useful in preventing thrombosis, a substantial opportunity remains for improving the thrombus selectivity of thrombin inhibitors.Methods and Results To explore the effect of targeting an antithrombin to the surface of a clot, we covalently linked recombinant hirudin to the Fab' (or IgG) of a monoclonal antibody (59D8) that selectively binds to an epitope on fibrin that becomes exposed only after thrombin cleaves fibrinopeptide B. Antibody-coupled hirudin bound to an immobilized peptide of the fibrin beta -chain amino-terminal sequence and inhibited the peptidolytic activity of thrombin more efficiently than free hirudin. Thrombin inhibition dependent on binding to immobilized fibrin monomer was enhanced 1100-fold (P<.0001). Hirudin-59D8 Fab' was 10 times more effective than hirudin in inhibiting fibrin deposition on experimental clot surfaces in fibrinogen solution (P<.0001) and human plasma (P<.0001). The more effective inhibition of thrombin by the conjugate was supported by significantly diminished concentrations of fibrinopeptide A in the plasma supernatant of the clot (P=.0001). Inhibition of clotting by an uncoupled mixture of hirudin and 59D8 Fab' was indistinguishable from that by hirudin alone, indicating that the conjugate's greater inhibitory activity was due to the covalent linkage between antibody and hirudin.Conclusions Fibrin-targeted hirudin (in comparison with unmodified hirudin) significantly reduces fibrin deposition on the surface of experimental clots. (Circulation. 1994;90: 1956-1963.)

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Background Estrogen replacement therapy reduces the risk of coronary heart disease in postmenopausal women, and estrogen treatment modulates endothelium-dependent vasodilation in ovariectomized, atherosclerotic monkeys. Estradiol-17 beta also induces relaxation in isolated rabbit coronary arteries as well as cerebral basilar arteries. The estrogen concentrations required to induce such relaxation are in the pharmacological range (10 sup -6 to 10 sup -5 mol/L).Methods and Results The present study was designed to test whether the sensitivity and specificity of the relaxing response of coronary vascular smooth muscle to exogenous estradiol-17 beta is dependent on the sex hormone status of the animal. In coronary artery rings contracted with PGF2alpha (3 x 10 sup -5 mol/L), estradiol-17 beta caused significant relaxation at a physiological estrogen concentration (10 sup -9 mol/L), in coronary artery rings from oophorectomized, estrogen-treated and acutely estrogen-withdrawn rabbits only. Relaxation induced by estradiol-17 beta at lower concentrations (10 sup -9 to 10 sup -6 mol/L) in these rings was 20+-6%, 42+-8%, 54+-9%, and 75+-8%, respectively, compared with 4+-2%, 12+-5%, 16+-7%, and 25+-12% and 5+-2%, 12+-5%, 18+-8%, and 23+-10% in rings from estrogen-maintained and oophorectomized rabbits, respectively (P<.01). The relaxation in coronary artery rings from estrogen-treated and acutely estrogen-withdrawn rabbits was endothelium and nitric oxide dependent since it was abolished by endothelium removal and the nitric oxide synthase inhibitor Nomega-nitro-l-arginine.Conclusions This study demonstrates that estrogen-induced, endothelium-dependent relaxation of coronary arteries may, in some species, depend on the sex hormone status of the animal. These findings may help to better understand the effects of ovarian steroids in the coronary circulation of females. (Circulation. 1994;90:1964-1968.)

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Background Major risk factors for accelerated allograft arteriosclerosis include humoral and cellular immune response, hyperlipidemia, and viral infections. We demonstrated earlier that rat cytomegalovirus (RCMV) infection doubles smooth muscle cell proliferation and intimal thickening of rat aortic allografts. In this study, the effects of 9-(1,3-dihydroxy-2-propoxymethyl)guanine (DHPG) on RCMV-enhanced rat allograft arteriosclerosis are investigated.Methods and Results Aortic allografts from the DA to the WF rat strain were used. The recipients were inoculated with 105plaque-forming units of RCMV 1 day after transplantation. Two groups of RCMV-infected rats were treated with DHPG with an initial dose of 20 mg/kg IP and a maintenance dose of 10 mg/kg IP twice a day for a period of 14 days. In the DHPG prophylaxis group (n=22), the drug administration started 1 day before infection, and in the DHPG treatment group (n=17), 7 days after infection. One group of infected rats was left untreated (n=21). The grafts were removed 7 and 14 days and 1, 3, and 6 months after transplantation. In the DHPG prophylaxis group, no virus could be recovered by plaque assays. In the treatment group, 50% of rats were virus-positive at 1 month and 40% at 3 months. DHPG prophylaxis prevented the infiltration of inflammatory cells and their proliferation in the adventitia of RCMV-infected recipients (P<.01), with a 60% reduction in the interleukin-2 receptor expression (P<.05) and a 30% decrease in major histocompatibility complex class II expression (P=NS). DHPG prophylaxis did not significantly alter the levels of insulin-like growth factor-1, epidermal growth factor, platelet-derived growth factor-BB, transforming growth factor- beta1, acidic fibroblast growth factor, and basic fibroblast growth factor messages in the allograft vascular wall. Early media necrosis was reduced. Arteriosclerotic alterations and proliferation of smooth muscle cells were both reduced 50% to 70% by DHPG prophylaxis (P<.05 at 3 months). The responses in the DHPG treatment group were quite similar but less impressive and statistically nonsignificant.Conclusions We consider it likely that DHPG inhibits arteriosclerotic alterations primarily by reducing the infectious virus and thereby the inflammatory response in the allograft vascular wall; another possibility is a direct antiproliferative effect on smooth muscle cell replication. A dose-dependent inhibitory effect of DHPG on smooth muscle cell replication was recorded in an in vitro study. (Circulation. 1994;90:1969-1978.)

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Background Conventional balloon angioplasty of intracoronary thrombus is associated with a high incidence of abrupt closure, distal embolization, and no-reflow phenomenon. The purpose of this study was to assess a new technique for treating intracoronary thrombus consisting of the local delivery of urokinase directly to the angioplasty site with urokinase-coated hydrogel balloons.Methods and Results We assessed local urokinase delivery using hydrogel balloons in four protocols. First, we evaluated the pharmacokinetics of urokinase delivery in vitro using Iodine-125-labeled urokinase to measure drug loading onto hydrogel balloons, drug retention by the hydrogel polymer during blood exposure, and drug transfer from the balloon surface to the arterial wall during balloon dilatation. Second, we measured Iodine-125-urokinase washoff from the hydrogel balloon in the intact circulation and intramural drug delivery during in vivo balloon angioplasty in 10 anesthetized New Zealand rabbits. Third, we assessed the effect of local urokinase delivery on Indium-111-labeled platelet deposition after balloon angioplasty in vivo in 13 porcine carotid or iliac arteries dilated with urokinase-coated balloons and compared them with contralateral control arteries dilated with saline-coated balloons. Finally, we determined the clinical efficacy of urokinase-coated balloons in 15 patients with intracoronary thrombus, including 7 who demonstrated abrupt thrombotic closure after conventional angioplasty. Between 241 and 1509 U urokinase could be loaded onto hydrogel balloons ranging in size from 2 to 8 mm. In vitro and in vivo studies demonstrated that hydrogel balloons absorbed significantly more urokinase and demonstrated less drug washoff than nonhydrogel balloons (P<.01). Similarly, both in vitro and in vivo studies demonstrated urokinase transfer from the hydrogel to the arterial wall during balloon angioplasty, with greater intramural drug deposition with larger balloons (P<.01). Local urokinase delivery after in vivo porcine angioplasty decreased Indium-111-labeled platelet deposition by 47% compared with contralateral control vessels (P=.03). Use of urokinase-coated balloons in patients with intracoronary thrombus resulted in thrombus dissolution and reversal of abrupt closure in all cases, without evidence of distal embolization.Conclusions With the use of hydrogel-coated balloons, urokinase can be delivered locally to an angioplasty site. This technique decreases platelet deposition after in vivo balloon angioplasty and is efficacious in treating intracoronary thrombus in patients, including those with abrupt thrombotic closure. (Circulation. 1994;90:1979-1988.)

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Background Besides cardiac load, the renin-angiotensin system (RAS) and aldosterone may regulate collagen accumulation during maturation or hypertrophic growth. The effect of cardiac volume overload on both left ventricular (LV) and right ventricular (RV) collagen and elastin and the possible role of the RAS in such changes have not yet been assessed.Methods and Results In the present study we assessed (1) the effects of 4 to 10 weeks of volume overload by an aortocaval shunt or minoxidil on LV and RV collagen and elastin and (2) the potential of the angiotensin-converting enzyme inhibitor enalapril and the angiotensin II receptor blocker losartan to prevent and regress volume overload-induced changes in cardiac collagen and elastin. Cardiac volume overload by aortocaval shunt or minoxidil treatment decreased LV collagen accumulation as compared with control rats. In contrast, RV collagen accumulation was potentiated during the initial weeks but not during chronic aortocaval shunt. Enalapril and losartan prevented the relative decreases in LV collagen content and concentration induced by a shunt. Losartan also reversed the decrease in LV collagen content by aortocaval shunt. Neither blocker significantly affected the enhanced RV collagen accumulation during the initial weeks of shunt, but both blockers further potentiated RV collagen accumulation during chronic volume overload. Aortocaval shunt for 4 weeks but not 10 weeks enhanced LV and RV elastin accumulation. This initial increase in LV and RV elastin content was blocked by both enalapril and losartan.Conclusions Cardiac volume overload, even when accompanied by increased plasma renin activity, decreases LV collagen accumulation, suggesting that in contrast to the stimulatory effect of systolic wall stress, increased diastolic wall stress inhibits collagen accumulation. In support of this concept, enalapril and losartan decreased LV preload and maintained LV collagen accumulation. In contrast to LV collagen, RV collagen accumulation was potentiated during the initial weeks of volume overload, possibly related to acute RV pressure overload shortly after aortocaval shunt and its decrease with chronic shunt. Enalapril and losartan had minimal effect on the enhanced RV collagen during the initial weeks of aortocaval shunt but potentiated RV collagen during chronic shunt, possibly by decreasing RV diastolic pressures. Altogether, these data suggest that during cardiac volume overload, the RAS affects cardiac collagen primarily by its hemodynamic effects. The RAS, however, may potentiate RV and LV elastin accumulation during the initial weeks of volume overload since both enalapril and losartan block this increase. (Circulation. 1994;90:1989-1996.)

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Background Single premature beats were introduced in the reentrant circuit during stable atrial flutter in the canine sterile pericarditis model to test the hypotheses that (1) despite the fact that the reentrant circuit is functionally determined, there is a fully excitable gap; (2) the excitable gap in the reentrant circuit is not uniform; and (3) inhomogeneities of conduction in the reentrant circuit explain the effects of premature beats.Methods and Results A multiplexing system was used to record 190 unipolar electrograms from the right atrial free wall during 18 atrial flutter episodes in 9 dogs. In all 18 episodes, premature stimuli captured the atrial flutter reentrant circuit. At the longest coupling intervals, the return cycle at the site closest to the pacing site did not prolong. As the coupling interval of the premature stimulus decreased, the return cycle then progressively increased, associated with changes in conduction in the reentrant circuit that were not uniform. The result was that coupling intervals associated with introduction of the premature beat also were not constant. The mean duration of the total (ie, fully plus partially) excitable gap was 12+-4 ms in areas of slow conduction, and it was always shorter than the total excitable gap in other areas (22+-6 ms, P<.001). The mean duration of the fully excitable gap based on analysis of the return cycle was 4+-1 ms in the reentrant circuit. In 13 of 18 atrial flutter episodes, a premature stimulus terminated atrial flutter by causing block of the orthodromic wave front of the premature beat in an area of slow conduction. The mean coupling interval that caused orthodromic block was 113+-5 ms (recorded at the site just proximal to the area of block), and it was always longer than the delivered stimulus coupling interval at the pacing site (96+-8 ms, P<.001).Conclusions We conclude that in this functionally determined atrial flutter reentrant circuit in the canine sterile pericarditis model, (1) a fully excitable gap is present in at least part of the reentrant circuit; (2) the duration of the excitable gap in the reentrant circuit is shortest in areas of slow conduction; and (3) when a premature beat encounters the partially excitable gap of the reentrant circuit, it results in changes in conduction such that the coupling intervals are not uniform throughout in the reentrant circuit. (Circulation. 1994;90:1997-2014.)

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID