Charles L. Lucore

Factors Responsible for Impaired Fibrinolysis in Obese Subjects and NIDDM Patients

Accelerated atherosclerosis is the leading cause of death in patients with non-insulin-dependent diabetes mellitus (NIDDM). Impaired endogenous fibrinolytic activity may accelerate atherosclerosis by exposing vascular luminal wall surfaces to persistent and recurrent thrombi and clot-associated mitogens. This study was conducted to further characterize endogenous fibrinolysis in lean and obese nondiabetic subjects and in NIDDM patients and to identify mechanisms responsible for the alterations identified. Obese and diabetic subjects had threefold elevations of plasma concentrations of plasminogen activator inhibitor type 1 (PAI-1) compared with values in lean control subjects. Despite the lack of significant differences in plasma concentrations of tissue-type plasminogen activator in the obese and diabetic subjects, both basal and stimulated endogenous fibrinolytic activities were decreased. The decreases were associated with increased activity of PAI-1 in plasma, in turn correlated with increased concentrations of immunoreactive insulin and C-peptide. These results are consistent with our previous observations demonstrating direct stimulatory effects of insulin and its precursors on cellular expression of PAI-1 in vitro and observations by others demonstrating decreased basal fibrinolytic activity in NIDDM patients. Impaired endogenous fibrinolytic activity could lead to prolonged or recurrent exposure of luminal surfaces of vessel walls to microthrombi and clot-associated mitogens that may accelerate atherosclerosis in hyperinsulinemic subjects.

Fibrinopeptide A levels indicative of pulmonary vascular thrombosis in patients with primary pulmonary hypertension.

Although the mechanisms involved in the pathophysiology of primary pulmonary hypertension have not yet been delineated, thrombosis has been implicated. This study was designed to determine whether thrombin activity as reflected by plasma concentrations of fibrinopeptide A (FPA), a marker of the action of thrombin on fibrinogen, is increased in patients with primary pulmonary hypertension. To evaluate fibrinolytic activity, we measured plasma concentrations of tissue-type plasminogen activator, plasminogen activator inhibitor-1, and cross-linked fibrin degradation products. We studied 31 patients with primary pulmonary hypertension. Plasma FPA concentrations measured by radioimmunoassay, were elevated to 87.4 +/- 36.9 ng/ml (mean +/- SEM). Fifteen minutes after administration of heparin (5,000 U), FPA concentrations decreased to 6.8 +/- 1.4 ng/ml (p less than 0.001 compared with preheparin levels). In 21 of 30 patients (70%), FPA concentrations after heparin administration were less than half the preheparin levels, a response consistent with inhibition of thrombin by heparin and the short half-life of FPA. Despite evidence for marked thrombin activity, plasma concentrations of cross-linked fibrin degradation products were normal in all but four patients. Plasminogen activator inhibitor-1 activity was elevated in 19 of the 27 patients in whom it was measured, potentially limiting the fibrinolytic response. The elevations of FPA indicate that thrombin activity is increased in vivo in patients with primary pulmonary hypertension. Thus, sequential assays of plasma markers of thrombosis and fibrinolysis in vivo may help identify those patients who may benefit from treatment with anticoagulants.

Rural Interhospital Transfer of ST-Elevation Myocardial Infarction Patients for Percutaneous Coronary Revascularization The Stat Heart Program

Background— In Europe, interhospital transfer of ST-elevation myocardial infarction (STEMI) patients for primary percutaneous coronary intervention (PCI) from non–PCI-capable (STEMI-referral) to PCI-capable (STEMI-accepting) facilities has been shown to be a superior reperfusion strategy compared with on-site fibrinolysis. The feasibility of such programs in the United States remains poorly defined. Methods and Results— We describe an observational cohort of 230 consecutive presumed STEMI patients who underwent interhospital transfer between January 2005 and March 2007 among 6 STEMI-referral and 2 STEMI-accepting hospitals in rural central Illinois. A standard treatment protocol using rapid interhospital transfer for primary PCI or rescue PCI after full-dose intravenous fibrinolysis (in event of unanticipated transfer delays) was initiated by the STEMI-referral emergency department physician. Three time intervals were evaluated: STEMI-referral care (door 1 to departure), transport time (door 1 departure to STEMI-accepting hospital arrival [door 2]), and STEMI-accepting hospital care (door 2 to balloon). Primary PCI was performed in 165 STEMI-confirmed patients (87.7%), whereas fibrinolysis was required in 16 patients (8.5%), with 56% undergoing rescue PCI. The median door 1–to-departure time was 46 minutes (25th and 75th percentiles, 32 and 62 minutes); approximately two thirds of this delay was attributable to the wait for transport arrival and departure. The transport and door 2–to-balloon times were 29 minutes (25th and 75th percentiles, 25 and 35 minutes) and 35 minutes (25th and 75th percentiles, 32 and 46 minutes), respectively. The door 1–to-balloon time was 117 minutes (25th and 75th percentiles, 98 and 137 minutes), with 12.2% and 58% of patients achieving a time of ≤90 and ≤120 minutes, respectively. No adverse clinical events occurred during interhospital transport. Conclusion— In rural US communities, emergency department physician–initiated interhospital transfer of STEMI patients for primary or rescue PCI is feasible and was safely executed with achievement of timely reperfusion when performed within coordinated healthcare networks.

Biochemical determinants of clearance of tissue-type plasminogen activator from the circulation.

Biochemical modification of tissue-type plasminogen activator (t-PA) designed to alter pharmacokinetics and pharmacodynamics offers promise for development of pharmaceuticals particularly suitable for treatment of specific disorders and for induction of coronary thrombolysis by intramuscular as well as intravenous administration. Accordingly, to identify biochemical determinants of clearance of t-PA from the circulation, we injected rabbits intravenously with three different preparations of t-PA synthesized from the same human gene and expressed in Chinese hamster ovary cells cultured under disparate conditions. Influences of glycosylation on clearance were defined by experiments with enzymatically treated t-PA in which clearance was assessed with concomitant administration of selected neoglycoproteins that compete with t-PA for specific glycoprotein receptors. The role of an intact active catalytic site, as reflected by differences in clearance with and without prior treatment of t-PA with the protease inhibitor PPACK, was defined also. Results indicate that clearance is altered by inhibition of the active site and that the nature and extent of glycosylation--not evident simply by analysis of peptide structure--influence clearance as well. These findings suggest that mannose/N-acetylglucosamine-specific glycoprotein receptors expressed on hepatic reticuloendothelial cells participate in clearance of t-PA from the circulation but that galactose-specific glycoprotein receptors probably do not. The observations may explain differences in clearance seen with different preparations of t-PA that have been seen in clinical pilot studies and may identify biochemical determinants of clearance amenable to modification for development of agents with potentially desirable, specific biological properties.

Potential attenuation of fibrinolysis by growth factors released from platelets and their pharmacologic implications

Increased concentrations of the fast-acting tissue-type plasminogen activator (t-PA) inhibitor attenuate the fibrinolytic activity of pharmacologically administered activators of the fibrinolytic system such as t-PA. Accordingly, it was hypothesized that augmentation of synthesis and elaboration of inhibitor from the liver, leading to increased concentrations of inhibitor in plasma, or from endothelial cells in the vicinity of thrombi undergoing lysis, leading to increased concentrations locally, may contribute to failure of pharmacologically induced thrombolysis or to early reocclusion. Because platelets are rich in transforming growth factor beta and epidermal growth factor-like activity, it was thought that release of growth factors from platelets activated in vivo could mediate increases of the inhibitor in plasma by stimulating its formation in the liver and its local release from endothelial cells in the vicinity of thrombi. If so, fibrinolysis might be rendered more effective by concomitant prevention of platelet growth factor release. Transforming growth factor beta, a major constituent of platelets, increased concentrations of the t-PA inhibitor messenger ribonucleic acid (mRNA) in human hepatoma cells in a specific and dose-dependent manner. A peak effect was seen with 5 ng/ml and a 10-fold increase in 6 hours. Release of inhibitor protein into conditioned media increased as well. Induction of the inhibitor mRNA increase was elicited by exposure as brief as 30 minutes. Cycloheximide, an inhibitor of protein synthesis, was not inhibitory. The mechanisms responsible differed from those seen with epidermal growth factor, shown previously in the laboratory to increase inhibitor mRNA. In addition, the 2 factors were synergistic. Platelet lysates elicited effects simulating those of the purified growth factors.(ABSTRACT TRUNCATED AT 250 WORDS)

Induction of endothelial cell expression of the plasminogen activator inhibitor type 1 gene by thrombosis in vivo.

BackgroundWe have shown previously that products from activated platelets can augment synthesis of plasminogen activator inhibitor type 1 (PAI-1) in cultured endothelial and hepatoma (Hep G2) cells in vitro and increase plasma PAI-1 activity in vivo in rabbits. Accordingly, the effects of activation of platelets associated with thrombosis and thrombolysis in vivo on plasma PAI-1 activity and expression of the PAI-1 gene in endothelium, liver, and other organs were characterized. Methods and ResultsEndothelial injury giving rise to platelet-rich thrombi was induced with electrical stimulation in carotid arteries in rabbits. Clot lysis and recanalization were induced subsequently with intravenous tissue-type plasminogen activator (t-PA) and verified with Doppler flow probes. Plasma PAI-1 activity (mean ± SD) increased from 6 ± 2 arbitrary units (AU)/ml to 129 ± 48 AU/ml (n=15) within several hours after recanalization. When t-PA had failed to induce recanalization, the increase was much less (from 7 ± 2 to 42 ± 23 AU/ml, n=11). To define mechanisms responsible for these changes, PAI-1 messenger RNA (mRNA) was evaluated by Northern blot analysis and localized in tissues by in situ hybridization. Strong and consistent induction of PAI-1 mRNA was evident in aorta, heart, and liver of animals subjected to thrombosis (twofold to threefold increases compared with values in controls), particularly in those in which thrombolysis had been induced (fourfold to sixfold). After thrombolysis, an intense, PAI-1 mRNA-specific signal was detected in endothelium of aorta, liver, and heart, with less intense signals in endothelium of lung, adrenals, and kidneys. ConclusionsThe increases in plasma PAI-1 activity follow a preceding increase in endothelial cell expression of the PAI-1 gene as reflected by PAI-1 mRNA levels. Thus, increased synthesis of endothelial cell PAI-1 after thrombosis and thrombolysis may attenuate endogenous fibrinolysis early after coronary thrombolysis, thereby potentiating early, thrombotic reocclusion.

Dependence of fibrinolytic activity on the concentration of free rather than total tissue-type plasminogen activator in plasma after pharmacologic administration.

To identify factors responsible for the decline of plasma tissue-type plasminogen activator (t-PA)-specific activity that we have observed after infusions of the activator and to define the potential usefulness of selected variants of t-PA in obviating them in patients with infarction, serial plasma samples from patients (n = 4) and rabbits (n = 15) given t-PA were assayed for total t-PA antigen, t-PA activity, and free as opposed to type-1 plasminogen activator inhibitor (PAI-1)--complexed t-PA. In patients, attenuation of t-PA specific activity after infusions was evident with concentrations of total t-PA antigen that were as much as sevenfold greater than pretreatment values (62 compared with 9 ng/ml). Attenuation of t-PA activity corresponded with the disappearance of free t-PA from plasma and was associated with persistence of complexes of t-PA with PAI-1. In normal rabbits (n = 4) given wild-type t-PA by bolus injection, PAI-1 activity was 4 +/- 1 arbitrary units/ml. Attenuation of t-PA activity was not evident until 60 minutes after injection at a time when total plasma t-PA antigen concentration was as low as 13 +/- 8 ng/ml. Under these conditions, plasma t-PA was composed predominantly of free t-PA. In rabbits (n = 5) given lipopolysaccharide to increase plasma PAI-1 activity to 193 +/- 84 arbitrary units/ml, the specific activity of t-PA was attenuated as early as 15 minutes after injection at a time when total t-PA antigen concentration was as high as 164 +/- 79 ng/ml. As was the case with samples from patients, attenuation was associated with the disappearance of free t-PA and the persistence of complexes of t-PA with PAI-1. A genetically engineered variant of t-PA with comparable specific activity and a comparable rate constant of association with PAI-1 but designed to persist in the circulation manifested prolonged clearance from plasma of normal rabbits (n = 3) (t1/2 = 24.6 +/- 1.6 minutes compared with an alpha phase t1/2 of 1.9 minutes for wild-type t-PA). The variant lacked the epidermal growth factor and kringle one domains and contained a duplicated kringle two domain.(ABSTRACT TRUNCATED AT 400 WORDS)

Impact of abciximab and coronary stenting on outcomes and costs of percutaneous coronary interventions in a community hospital.

ObjectiveTo assess costs and outcomes of coronary stenting and balloon angioplasty with and without adjunctive treatment with abciximab for 3758 consecutive elective percutaneous coronary interventions at a single community center over the 2.5‐year period between 1 January 1995 and 30 June 1997. ResultsAbciximab was more common among patients who had recently suffered myocardial infarction, patients with unstable angina, and patients with more complex coronary lesions. Use of abciximab in conjunction with balloon angioplasty or stenting and stenting alone was associated with significant reductions in incidence of major adverse cardiovascular events in hospital. Multivariate analysis indicated that use of abciximab and stenting were associated with significant independent effects on risk of an event. Hospital costs were increased for patients administered abciximab, treated with stenting, or both. Total costs and costs inclusive of those incurred in catheterization laboratory and pharmacy increased significantly with increasing complexity of lesions. Multivariate regression analysis (baseline cost US

Quantification of free tissue-type plasminogen activator in plasma from patients undergoing coronary thrombolysis

5621) identified death (US

Interactions of tissue-type plasminogen activator with plasma inhibitors and their pharmacologic implications.

16 098), emergency revascularization (US