Saratin, an inhibitor of von Willebrand factor-dependent platelet adhesion, decreases platelet aggregation and intimal hyperplasia in a rat carotid endarterectomy model

PURPOSE

Post-carotid endarterectomy, thrombosis, and intimal hyperplasia may be decreased by the inhibition of platelet adhesion and activation. In this study, a novel agent, saratin, was used to inhibit platelet-to-collagen adhesion in a rat carotid endarterectomy model. Saratin is a recombinant protein isolated from the saliva of the medicinal leech Hirudo medicinalis, which is thought to act by binding to collagen, and inhibits von Willebrand factor-collagen interaction under conditions of increased shear and therefore, the adherence and activation of platelets at the vessel wall. Saratin has the advantage of being a nonsystemic, site-specific topical application.

METHODS

A rat carotid endarterectomy model was used in which an open technique with arteriotomy and intimectomy was used. Saratin was applied to the endarterectomized surface of the carotid artery before arterial closure. End point measurements included platelet adhesion, thrombosis rate, intimal hyperplasia development, bleeding times, and platelet counts. Electron micrographs of carotid arteries were used for quantitative analysis of platelet aggregation and platelet counts. Intimal hyperplasia and thrombosis were assessed with computer-assisted morphometric analysis of elastin-stained carotid artery sections with direct measurement of the intimal hyperplasia area.

RESULTS

The topical application of saratin significantly decreased platelet adhesion compared with controls at 3 hours after carotid endarterectomy (64 +/- 17 vs 155 +/- 33 platelets per grid, P = .05), and 24 hours after carotid endarterectomy (35 +/- 11 vs 149 +/- 37 platelets per grid, P = .0110), respectively. A percent luminal stenosis, as a measure of intimal hyperplasia, was significantly decreased with saratin application compared with controls (10.9% +/- 1.8% vs 29.8% +/- 6.8%, P = .0042). This decrease in intimal hyperplasia formation correlated with the inhibition of platelet adhesion. Thirty-three percent of control arteries were found to be thrombosed 2 weeks after carotid endarterectomy compared with a 0% thrombosis rate in the saratin-treated group (P = .0156). No increased bleeding was encountered along the arterial suture line in the saratin group. Bleeding times and systemic platelet counts were not found to change significantly in the saratin-treated rats compared with control rats at 3 and 24 hours after endarterectomy.

CONCLUSION

Saratin significantly decreased platelet adhesion, intimal hyperplasia, luminal stenosis, and thrombosis after carotid endarterectomy in rats. Saratin did not increase suture line bleeding or bleeding times, and did not decrease platelet counts. Saratin may serve as a topical agent to be used for the site-specific inhibition of thrombosis and intimal hyperplasia after vascular manipulation.

Increasing levels of dietary homocystine with carotid endarterectomy produced proportionate increases in plasma homocysteine and intimal hyperplasia

PURPOSE

The role that homocysteine may play in post-carotid endarterectomy (CEA) restenosis due to intimal hyperplasia is not well understood. This study was designed to investigate the effects of different levels of dietary homocystine on: (1) plasma homocysteine; (2) post-CEA intimal hyperplasia; and (3) levels of the methyl donor S-adenosylmethionine (SAM) and its counterpart S-adenosylhomocysteine (SAH) in the homocysteine pathway.

METHODS

Male rats were fed specialized diets for 2 weeks pre- and post-CEA. Groups included control (0 homocystine added, n=9), 1.5 (1.5 g/kg homocystine added, n=10), 3.0 (3.0 g/kg homocystine added, n=9), and 4.5 (4.5 g/kg homocystine added, n=11). The rats underwent a surgical carotid endarterectomy. Endpoints included; plasma homocysteine, intimal hyperplasia, replicative index using with alpha-SM actin and BrdU, hepatic SAM levels, SAH levels, and the hepatic activities of methylenetetrahydrofolate reductase (MTHFR) and cystathionine beta-synthase (CBS).

RESULTS

Increasing dietary homocystine produced a proportionate increase in plasma homocysteine and an increase in intimal hyperplasia. Regression analysis of plasma homocysteine levels and intimal hyperplasia showed a significant correlation (r=0.71,P=0.003). Plasma homocysteine levels above 15 microM were associated with significant increases in intimal hyperplasia above 6.5% (P=0.04). Elevation of plasma homocysteine levels to moderate levels (5-25 microM) resulted in significant post-CEA intimal hyperplasia. Cellular analysis of the area of intimal hyperplasia in all diet groups showed comparable amounts of cells positive for alpha-SM actin. However, with increasing levels of dietary homocystine and plasma homocysteine there was an increase in replicative index (P<0.001) as determined by BrdU staining. Increasing dietary homocystine increased plasma homocysteine and was followed by increases in the replicative index thus producing increased intimal hyperplasia and lumenal stenosis. In hepatic measurements the 1.5 and 3.0 g/kg homocystine diets caused: increased liver activity of MTHFR (P=0.03) and decreased hepatic levels of SAM, SAH and SAM/SAH ratios compared to controls. Homocystine treatment did not cause significant alterations in CBS levels (P=0.992). These studies also showed no correlation of the MTHFR and CBS enzymes with plasma homocysteine levels or intimal hyperplasia. However, hepatic levels of SAM showed significant negative correlations with plasma homocysteine (r=-0.58; P=0.006) and with BrdU percentages of cellular proliferation (r=-0.69; P=0.06).

CONCLUSION

The degree of post-CEA intimal hyperplasia in a rat model is directly related to the plasma level of homocysteine. The hyperplastic effects of homocysteine may be mediated in part by a physiological insufficiency of methyl donors as shown by decreases in SAM. Thus, increasing levels of plasma homocysteine enhanced and accelerated the smooth muscle cell response after CEA which led to increased intimal hyperplasia and lumenal stenosis.

Increased intimal hyperplasia after carotid endarterectomy in spontaneously hypertensive rats

This study evaluated the effects of hypertension on postoperative intimal hyperplasia using a rat carotid endarterectomy (CEA) model with spontaneously hypertensive rats (SHR) and normotensive Sprague-Dawley rats (SD). SHR and SD rats underwent left carotid exposure and CEA via an arteriotomy, scoring and removal of the intima, followed by arteriotomy closure. The rats were then sacrificed two weeks postoperatively. The left carotid artery was harvested and underwent elastin and double immunohistochemical staining. The percent of lumenal stenosis was calculated using morphometric measurements, and stained cells within the intimal hyperplasia were counted. The means and standard deviation of the means were calculated, and the two groups were compared using a 2-sample t test. The systolic blood pressure was 228 +/-35 mm Hg in the SHR group and 108 +/-8 mm Hg in the SD group (p<0.00001). The percent of lumenal stenosis was 82.6 +/-17.1% in the SHR group and 21.2 +/-13.7% in the SD rats (p value <0.0001). The percentage of cells staining for a-SM actin was equal in the SHR group and the SD group (> 91%) but the percentage of these cells staining for BrdU was 38.2 +/-8.4% in the SHR group and 10.7 +/-5.8% in the SD group (p< 0.00001). Hypertension in the SHR rats was associated with an increased lumenal stenosis due to increased intimal hyperplasia. The increased intimal hyperplasia was due to enhanced and accelerated replication of smooth muscle cells. Hypertension may be associated with increased restenosis rates after CEA.

Missed injuries in a rural area trauma center

BACKGROUND

Missed injuries can lead to delays. In the rural environment, where patients are frequently seen in multiple hospitals prior to reaching the trauma center, different problems arise.

METHODS

Level-1 trauma center admissions from January 1993 through June 1995 were reviewed. Missed injuries were those not identified within 24 hours of injury. Data extracted included demographics, mechanism, severity and outcome. Comparisons were made between missed injury patients and typical trauma patients.

RESULTS

Of 3,996 patients, 70 missed injuries were identified in 56 patients. Compared with typical trauma patients, missed injury patients suffered more blunt trauma, were more severely injured, had longer intensive care unit and hospital stays, and a lower mortality rate. Transferred patients accounted for 60% of missed injuries.

CONCLUSIONS

Transferred patients with blunt injury have the highest risk for missed injury. Delayed transports and prior examination may contribute to complacency. All trauma patients must be repeatedly evaluated thoroughly, and all diagnostic studies reviewed for adequacy.

Severe acidosis alone does not predict mortality in the trauma patient

BACKGROUND

Because severe acidosis is an indicator of poor prognosis in trauma patients, medical records of these patients were analyzed to determine whether aggressive resuscitation was appropriate.

PATIENTS AND METHODS

Data from a level 1 trauma center registry were reviewed retrospectively to identify patients with a pH < or = 7.0. Thirty-seven patients were identified. Severely acidotic patients were compared to average trauma patients in terms of demographics, resuscitation, injury, and outcome. Surviving acidotic patients were also compared to nonsurviving acidotic patients.

RESULTS

Half of the severely acidotic group survived initial resuscitation with approximately one third surviving to leave the hospital. There were no chronically disabled survivors. Nonsurviving acidotic patients were more unstable, more neurologically depressed, and more severely injured. Resuscitation efforts did not consume excessive hospital resources.

CONCLUSION

Severe acidosis alone is not a sufficiently powerful predictor of outcome to justify withholding resuscitation; however, when combined with coma and shock, this condition had no survivors in this small series.

Thrombin inhibition enhances tissue-type plasminogen activator-induced thrombolysis and delays reocclusion

The objectives of this study were to test the hypotheses that thrombin inhibitors 1) enhance tissue-type plasminogen activator (t-PA)-induced coronary thrombolysis and 2) prevent or delay coronary artery reocclusion. Seventy-one dogs developed occlusive coronary thrombi after introducing a copper coil into the left anterior descending coronary artery (LAD). Coronary blood flows were monitored by an externally positioned pulsed Doppler flow probe. t-PA was given with or without heparin at different times after LAD occlusions. In some experiments, hirugen, a synthetic hirudin-based peptide and specific thrombin inhibitor, was given as 4 mg/kg i.v. bolus and 3 mg.kg-1.h-1 i.v. infusion at 30 min after LAD occlusion with t-PA and a bolus of heparin. Thrombolysis times were significantly shorter in t-PA- and heparin-treated dogs than in dogs treated with t-PA alone. Reocclusion times were significantly longer in t-PA- and heparin-treated dogs than in dogs treated with t-PA alone. Continuous heparin infusions prolonged reocclusion times to greater than 180 min in all treated dogs. The addition of hirugen to t-PA plus one bolus heparin prolonged reocclusion times to 90 +/- 6 min in dogs with 30-min thrombi. Thus heparin enhances t-PA-induced thrombolysis and delays reocclusion. Addition of a specific thrombin inhibitor, such as hirugen, to heparin enhances its effect on delaying reocclusion.

Use of a tunneling device to aid in positioning of a graft

A tunneling device can be used to ensure easy placement of a prosthetic or autogenous graft. This can be done without the danger of the graft twisting, kinking or having the clips and ties pulled off. The often frustrating problem of ensuring that the arterial graft lies properly in position can be greatly simplified with the use of this technique.

Thrombolytic therapy: enhancement by platelet and platelet-derived mediator antagonists

Coronary thrombolysis is the treatment of choice for patients with acute Q wave myocardial infarcts who have no contraindication to such therapy. However, the time required for thrombolysis to occur and the possibility of reocclusion of the infarct-related artery following thrombolytic therapy are problems. The time required for thrombolysis to occur with currently available agents ranges from 40 to 60 minutes and the frequency of reocclusion of the infarct-related artery after tissue-type plasminogen activator is 10 to 20%. We review experimental studies and clinical evaluations in which attempts have been made to develop adjunctive therapies that when coupled with available thrombolytic interventions might shorten the time to thrombolysis and delay or prevent reocclusion. From the studies done to date, it appears that a combination of thromboxane synthesis inhibitor and receptor antagonist with a serotonin receptor antagonist and heparin shortens the time to thrombolysis and delays or prevents coronary artery reocclusion in experimental canine models with copper coil-induced coronary artery thrombi. A monoclonal antibody to the platelet glycoprotein IIb/IIIa receptor given with tissue plasminogen activator and heparin also shortens the time to thrombolysis and delays or prevents reocclusion in experimental canine models. A mutant tissue plasminogen activator with a glycosylation defect and prolonged systemic clearance delays coronary artery reocclusion following lysis of three-hours coronary thrombi, induced by a copper coil. Thrombin inhibitors, including heparin, and synthetic inhibitors, given with tissue plasminogen activator and aspirin, appear to shorten the time to thrombolysis and delay or prevent coronary artery reocclusion in experimental canine models.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of new antiplatelet agents as adjunctive therapies in thrombolysis

Coronary thrombolysis is the treatment of choice for patients with acute Q-wave myocardial infarcts who have no contraindications to such therapy. However, the time required for thrombolysis and the possibility of reocclusion of the infarct-related artery remain problematic. Herein are described experimental animal studies and clinical evaluations in which attempts have been made to develop adjunctive therapies that, when coupled with available thrombolytic interventions, might shorten the time to thrombolysis and delay or prevent reocclusion. From the studies conducted to date, it is clear that a combined thromboxane synthesis inhibitor and receptor antagonist with a serotonin receptor antagonist and heparin shorten the time to thrombolysis and delay or prevent coronary artery reocclusion in experimental canine models with copper coil-induced coronary artery thrombi. A monoclonal antibody to the platelet glycoprotein IIb/IIIa receptor coupled with tissue plasminogen activator (t-PA) and heparin also shortens the time to thrombolysis and delays or prevents reocclusion in experimental canine models. Thrombin inhibitors, including heparin and synthetic inhibitors, given with t-PA and aspirin, appear to shorten the time to thrombolysis and delay or prevent coronary artery reocclusion in experimental canine models. Aspirin coupled with intravenous streptokinase reduces mortality in patients with presumed acute myocardial infarction, and a combination of heparin and t-PA results in infarct-artery patency more frequently than t-PA without heparin. Data from these studies are encouraging with regard to the possibility of developing effective and relatively safe thrombolytic regimens that shorten the time to thrombolysis and delay or prevent coronary artery reocclusion.

Potential usefulness of combined thromboxane A2 and serotonin receptor blockade for preventing the conversion from chronic to acute coronary artery disease syndromes

Evidence suggests that unstable angina, non-Q-wave myocardial infarction and Q-wave myocardial infarcts represent a continuum, such that transient reduction in coronary blood flow associated with platelet aggregation and dynamic vasoconstriction at sites of coronary artery stenosis and endothelial injury lead to abrupt development of unstable angina. Factors potentially responsible for the conversion from chronic to acute coronary artery disease include endothelial injury at sites of stenosis. The endothelial injury may be the result of plaque fissuring or ulceration, hemodynamic factors (including systemic arterial hypertension or flow shear stress), infection, smoking, coronary arteriography or balloon angioplasty. Clinical and experimental animal studies suggest that interference with thromboxane and serotonin contributions to platelet aggregation and dynamic coronary artery constriction may prevent chronic coronary artery disease syndromes from converting to acute disease. To protect against this process may require both thromboxane and serotonin receptor antagonists or a combination of thromboxane synthesis inhibitor and receptor antagonist with a serotonin receptor antagonist. Further studies are needed to test this hypothesis.

Evidence that combined thromboxane A2 and serotonin receptor blockade might prevent coronary artery thrombosis and the conversion from chronic to acute coronary heart disease syndromes

Evidence that combined thromboxane A2 and serotonin blockade may prevent coronary artery thrombosis and the conversion from chronic to acute coronary heart disease syndromes is considered. Available data from clinical and experimental animal studies are consistent with the hypothesis that interference with thromboxane and serotonin's contributions to platelet aggregation and dynamic coronary artery constriction might prevent the conversion from chronic to acute disorders, including the development of unstable angina and myocardial infarction in some patients at risk. Substantial protection preventing the conversion from stable to unstable angina and myocardial infarction may very well require both thromboxane and serotonin receptor antagonists or the combination of a thromboxane synthesis inhibitor and receptor antagonist with a serotonin receptor antagonist. Future clinical studies should test this hypothesis directly.

Specific platelet mediators and unstable coronary artery lesions. Experimental evidence and potential clinical implications

We have speculated previously that the abrupt conversion from chronic stable to unstable angina and the continuum to acute myocardial infarction may result from myocardial ischemia caused by progressive platelet aggregation and dynamic vasoconstriction themselves caused by local increases in thromboxane and serotonin at sites of coronary artery stenosis and endothelial injury. Platelet aggregation and dynamic coronary artery vasoconstriction probably result from the local accumulation of thromboxane and serotonin and also relative decreases in the local concentrations of endothelially derived vasodilators and inhibitors of platelet aggregation, such as endothelium-derived relaxing factor (EDRF) and prostacyclin. With severe reductions in coronary blood flow caused by these mechanisms, platelet aggregates may increase, and an occlusive thrombus composed of platelets and white and red blood cells in a fibrin mesh may develop. When coronary arteries are occluded or narrowed for a sufficient period of time by these mechanisms, myocardial necrosis, electrical instability, or sudden death may occur. We believe that unstable angina and acute myocardial infarction are a continuum in relation to the process of coronary artery thrombosis and vasoconstriction. When the period of platelet aggregation or dynamic vasoconstriction at sites of endothelial injury and coronary artery stenosis is brief, unstable angina or non-Q wave infarction may occur. However, when the coronary artery obstruction by these mechanisms is prolonged for several hours, Q wave myocardial infarction results. Chronic endothelial injury and coronary artery stenosis are probably associated with the accumulation of platelets, white and red blood cells, and a fibrin mesh at the site of stenosis and endothelial injury.

Combined aortobifemoral and femoropopliteal bypass in the management of patients with extensive atherosclerosis

Certain patients have atherosclerosis in both aortoiliac and femoropopliteal segments of the arterial tree and thus do not have a good result from reconstruction of the aortoiliac segment. No method has been developed to identify these patients and we do not know whether, by combining a femoropopliteal bypass with an aortobifemoral bypass, the results can be improved. We present a series of 153 patients with severe multilevel occlusive disease treated by simultaneous reconstruction and followed for up to 6.5 years. The cumulative patency of the femoropopliteal bypasses was 80% at four years. Functional and symptomatic improvement was excellent, and operative mortality was low when one considers the age and poor general condition of the patients.