Thomas F. Lindsay

Groups IV, V, and X Phospholipases A2s in Human Neutrophils ROLE IN EICOSANOID PRODUCTION AND GRAM-NEGATIVE BACTERIAL PHOSPHOLIPID HYDROLYSIS

The bacterial tripeptide formyl-Met-Leu-Phe (fMLP) induces the secretion of enzyme(s) with phospholipase A2 (PLA2) activity from human neutrophils. We show that circulating human neutrophils express groups V and X sPLA2 (GV and GX sPLA2) mRNA and contain GV and GX sPLA2 proteins, whereas GIB, GIIA, GIID, GIIE, GIIF, GIII, and GXII sPLA2s are undetectable. GV sPLA2 is a component of both azurophilic and specific granules, whereas GX sPLA2 is confined to azurophilic granules. Exposure to fMLP or opsonized zymosan results in the release of GV but not GX sPLA2 and most, if not all, of the PLA2 activity in the extracellular fluid of fMLP-stimulated neutrophils is due to GV sPLA2. GV sPLA2 does not contribute to fMLP-stimulated leukotriene B4 production but may support the anti-bacterial properties of the neutrophil, because 10–100 ng per ml concentrations of this enzyme lead to Gram-negative bacterial membrane phospholipid hydrolysis in the presence of human serum. By use of a recently described and specific inhibitor of cytosolic PLA2-α (group IV PLA2α), we show that this enzyme produces virtually all of the arachidonic acid used for the biosynthesis of leukotriene B4 in fMLP- and opsonized zymosan-stimulated neutrophils, the major eicosanoid produced by these pro-inflammatory cells.

Salvage of skeletal muscle with free radical scavengers

Extensive skeletal muscle necrosis may occur after prolonged ischemia to the lower extremity, with serious consequences both locally and systemically. The extent of necrosis is a combination of cellular damage that occurs during both the period of ischemia and the period of reperfusion. The purpose of this study was to reduce the extent of reperfusion-induced muscle necrosis by therapeutic interventions administered only during the initial period of reperfusion. Indeed, the pretreatment of patients who have an acute arterial occlusion is rarely possible and only interventions applicable to the reperfusion phase would be clinically relevant. By perfusing the isolated gracilis muscle in a controlled manner with reduced oxygen concentrations alone and in combination with free radical scavengers, we were able to reduce the extent of muscle necrosis. By means of controlled oxygen delivery alone, muscle necrosis was reduced from 87% +/- 8% in the control muscle to 67% +/- 9% (p less than 0.05) in the treated muscle. The combination of reduced oxygen delivery and free radical scavengers reduced necrosis from 78% +/- 8% in the control muscle to 53% +/- 7% (p less than 0.01) on the experimental side. We conclude that controlled oxygen delivery and free radical scavengers can reduce skeletal muscle necrosis occurring after prolonged normothermic ischemia.

Mesenteric arterial bypass grafts: Early and late results and suggested surgical approach for chronic and acute mesenteric ischemia

BACKGROUND The purposes of this study were to determine the early and late results of placement of arterial bypass grafts in the treatment of chronic and acute intestinal ischemia and to ascertain whether multiple grafts provide better late results than a single graft. METHODS Records of 34 patients who underwent mesenteric vascular graft placement were retrospectively reviewed. RESULTS All 21 patients with chronic ischemia had a history of intestinal angina and weight loss. Food fear was reported by 33% of patients; also, diarrhea in 57%, constipation in 29%, acalculous cholecystitis in 19%, ischemic gastritis or peptic ulcer in 19%, and elevation of liver enzymes in 22% were reported. Angiogram showed more than 50% stenosis or occlusion of the superior mesenteric artery (SMA) in 100% of patients, celiac artery in 90%, and inferior mesenteric artery in 90%. Although not described previously, a reduction in collateral flow from the internal iliac arteries was caused by severe pelvic disease in 56% of patients. There were no in-hospital deaths. The rate of survival at 1 year was 100%; at 2 years it was 93% +/- 6%, at 3 years 86% +/- 9%, at 5 years 79% +/- 11%, and at 10 years 50% +/- 15%. During follow-up, graft thrombosis occurred in three patients. Of the patients who underwent only a single SMA or celiac bypass, two of five died of bowel infarction; only one of 16 patients who underwent both celiac and SMA bypass had to undergo a repeat surgical procedure because of graft occlusion. Three of 16 retrograde bypasses thrombosed, compared with zero of five prograde bypasses. In nine patients who underwent placement of mesenteric bypass grafts because of acute ischemia caused by acute mesenteric thrombosis, the early mortality rate was 22%; the two deaths were the result of bowel ischemia. The cumulative survival rate was 78% +/- 14% at 1 month, 65% +/- 17% at 1 year, and 52% +/- 16% at 5 years. One of the two late deaths was due to graft thrombosis and bowel infarction. Three of four patients who underwent concomitant mesenteric bypass at the time of aneurysm repair or aortobifemoral bypass survived the surgical procedure. CONCLUSIONS When chronic and acute mesenteric ischemia are diagnosed and treated with a bypass graft, the early and late results are good. Complete revascularization of the SMA and celiac artery or pelvis or both and prograde bypass may reduce the risk of late bowel ischemia.

Coronary bypass and carotid endarterectomy: does a combined approach increase risk? A metaanalysis

BACKGROUND Patients with concomitant carotid and coronary artery disease present a surgical dilemma. We compared the stroke and mortality rates for combined coronary artery bypass grafting and carotid endarterectomy in which both procedures were performed under a single anesthetic, versus a staged approach, in which coronary artery bypass grafting and carotid endarterectomy were performed separately. METHODS A computerized MEDLINE search supplemented with a manual bibliographic review was performed for all peer-reviewed English language publications that contained both combined and staged coronary artery bypass grafting/carotid endarterectomy patient cohorts. Outcomes of interest were stroke, death, and stroke or death; aggregation of outcome rates was performed with the Mantel-Haenszel method. RESULTS Sixteen studies were identified with a total of 844 combined patients and 920 staged patients. None of the studies was completely randomized. The combined surgical group had a higher prevalence of unstable angina; the two groups had a similar prevalence of symptomatic carotid disease and severe carotid stenosis. Meta-analysis revealed a significantly increased risk of the composite end point, stroke or death, for patients undergoing combined procedures (relative risk 1.49; 95% confidence interval 1.03-2.15; p = 0.034). There was also a trend toward increased risk during combined procedures for the end points of stroke (relative risk 1.50; 95% confidence interval 0.97-2.32; p = 0.068) and death (relative risk 1.55; 95% confidence interval 0.94-2.53; p = 0.084) considered separately. The crude event rates for stroke were 6.0% versus 3.2% for combined versus staged procedure, 4.7% versus 2.9% for death, and 9.5% versus 5.7% for stroke or death. Two of the 16 individual studies showed a statistically significant increase in the risk of stroke or death for combined procedure (p < 0.05). CONCLUSIONS Combined coronary artery bypass grafting and carotid endarterectomy may be associated with a higher risk of stroke or death than staged procedures. A randomized trial needs to be performed to determine the optimal management of patients with concomitant carotid and coronary artery disease.

The Use of Antiplatelet Therapy in the Outpatient Setting: Canadian Cardiovascular Society Guidelines

Antiplatelet agents are a cornerstone of therapy for patients with atherosclerotic vascular disease. There is presently a lack of comprehensive guidelines focusing on the use of antiplatelet drugs in patients currently manifesting or at elevated risk of cardiovascular disease. The Canadian Antiplatelet Therapy Guidelines Committee reviewed existing disease-based guidelines and subsequently published literature and used expert opinion and review to develop guidelines on the use of antiplatelet therapy in the outpatient setting. This full document has been summarized in an Executive Summary published in the Canadian Journal of Cardiology and may be found at http://www.ccs.ca/. Antiplatelet therapy appears to be generally underused, perhaps in part because of a lack of clear, evidence-based guidance. Here, we provide specific guidelines for secondary prevention in patients discharged from hospital following acute coronary syndromes, post-percutaneous coronary intervention, post-coronary artery bypass grafting, patients with a history of transient cerebral ischemic events or strokes, and patients with peripheral arterial disease. Issues related to primary prevention are also addressed, in addition to special clinical contexts such as diabetes, heart failure, chronic kidney disease, pregnancy/lactation, and perioperative management. Recommendations are provided regarding pharmacologic interactions that may occur during combination therapy with warfarin, clopidogrel and proton-pump inhibitors, or acetylsalicylic acid and nonsteroidal anti-inflammatory drugs, as well as for the management of bleeding complications.

The effect of ischemia/reperfusion on adenine nucleotide metabolism and xanthine oxidase production in skeletal muscle

Prolonged ischemia to skeletal muscle as occurs after an acute arterial occlusion results in alterations in adenine nucleotide metabolism. Adenosine triphosphate continues to be used for cellular functions, and an ischemia-induced degradation of phosphorylated adenine nucleotides is initiated. In this experiment we demonstrated the time-dependent aspect of adenine nucleotide depletion during ischemia and the production of large quantities of soluble precursors. In addition, we studied the rate of conversion of xanthine dehydrogenase to xanthine oxidase, a potential source of oxygen-free radicals, after controlled periods of total normothermic ischemia (4 hours and 5 hours) and during the reperfusion phase. During ischemia complete depletion of creatine phosphate occurred in both groups, and adenosine triphosphate fell from 22.1 +/- 1.3 to 10.3 +/- 1.4 mumol/gm dry weight after 4 hours and from 21.6 +/- 0.7 to 3.9 +/- 0.8 mumol/gm dry weight after 5 hours (p less than 0.05). During reperfusion, creatine phosphokinase resynthesis occurred in both groups, but adenosine triphosphate levels were not significantly increased (p greater than 0.05). A washout of lipid soluble products of adenine nucleotide metabolism occurred equally in both groups. The relationship between phosphorylated adenine nucleotides as measured by the energy charge potential fell significantly in both groups (p less than 0.05), but after the shorter period of ischemia (4 hours it returned to normal during early reperfusion but did not after 5 hours of ischemia. There was 21% +/- 4% necrosis after 4 hours and 51% +/- 8% after 5 hours of ischemic stress when assessed at 48 hours. In conclusion, the degree of adenine nucleotide degeneration as determined primarily by the length of the ischemic period, may be the most important determinant of the ultimate extent of skeletal muscle ischemic necrosis that results from an acute interruption of circulation.

Twenty-five percent albumin prevents lung injury following shock/resuscitation.

ObjectiveTo evaluate novel indications for the use of human albumin solutions in the prevention and treatment of acute lung injury following shock/resuscitation and to test the hypothesis that 25% human albumin is an effective resuscitation fluid as well as an immunomodulatory agent protective against lung injury in our model. DesignA previously developed rodent model of acute lung injury in which resuscitated shock primes for increased lung injury in response to a small dose of intratracheal lipopolysaccharide. SettingUniversity-affiliated hospital. SubjectsSprague Dawley rats weighing 300–350 g. InterventionsAnimals were bled to a mean arterial pressure of 40 mm Hg and maintained in a shock phase for 1 hr. Animals then were resuscitated by transfusion of the shed blood plus an equal volume of Ringer’s lactate or their shed blood plus 3 mL/kg volume of 25% albumin or their shed blood plus 15 mL/kg of 5% human albumin over a period of 2 hrs. To test for the possible role of 25% albumin as an antioxidant, we also performed resuscitation with Ringer’s lactate supplemented with N-acetylcysteine or 25% albumin depleted of its antioxidant properties by N-ethylmaleimide. Mean arterial pressure was monitored continuously. One hour after resuscitation, 100 &mgr;g of lipopolysaccharide in 200 &mgr;L of saline was administered intratracheally. Measurements and Main ResultsResuscitation with 25% albumin significantly reduced transpulmonary protein flux, bronchoalveolar lavage fluid neutrophil counts, and the degree of histopathological injury compared with resuscitation with Ringer’s lactate or 5% albumin. To delineate the underlying mechanism of this beneficial effect, the production of cytokine-induced neutrophil chemoattractant as well as nuclear translocation of its critical transcription factor nuclear factor-&kgr;B was measured. Both cytokine-induced neutrophil chemoattractant messenger RNA concentrations and nuclear factor-&kgr;B translocation were diminished following 25% albumin resuscitation. Furthermore, 25% albumin significantly decreased lipid peroxidation in plasma as measured by 8-isoprostane concentrations. N-ethylmaleimide modified 25% albumin, possessing lesser antioxidant activity, exhibited an attenuated protection from lung injury. ConclusionsResuscitation with 25% albumin attenuates lung injury in this rat model. The beneficial effect was due to reduced neutrophil sequestration. The antioxidant properties of the 25% albumin preparation appeared to be partially responsible for the effects observed. These studies suggest a novel role for 25% albumin as an anti-inflammatory agent in neutrophil-mediated diseases, such as acute respiratory distress syndrome.

Quantitation of postischemic skeletal muscle necrosis: Histochemical and radioisotope techniques

Skeletal muscle necrosis will result from prolonged periods of ischemia. The purpose of this study was to develop a method to estimate the extent of necrosis using nitroblue tetrazolium staining and technetium scanning. The bilateral canine gracilis muscle preparation with total vascular isolation was exposed to 4 hr of complete normothermic ischemia followed by reperfusion. After 45 hr of reperfusion 99mTc pyrophosphate (PYP) was injected and 3 hr later the muscles were harvested, cut into six slices, and stained with nitroblue tetrazolium. Biopsies were taken from tetrazolium-positive and -negative areas for electron microscopy to confirm the ability of the stain to distinguish viable from necrotic muscle. Computerized planimetry of the staining pattern was used to estimate the extent of necrosis as a percentage of the total muscle. Electron microscopy confirmed the validity of nitroblue tetrazolium to discriminate between viable and necrotic skeletal muscle in this experimental model. After 4 hr of ischemia the percentage necrosis was 30.2 +/- 6.1% (mean +/- SEM, n = 12), there was no difference in the extent of necrosis in left vs right paired muscles, using tetrazolium staining or technetium PYP uptake. There was a statistically significant correlation between the percentage necrosis and the density of 99mTc PYP uptake per muscle (r = 0.83, P less than 0.001) and per slice (r = 0.94, P less than 0.001). This study demonstrates the ability of tetrazolium staining to accurately differentiate between viable and necrotic skeletal muscle and provides a reproducible method for estimating the extent of necrosis in the gracilis muscle model.

The surgical and functional outcome of limb-salvage surgery with vascular reconstruction for soft tissue sarcoma of the extremity.

BackgroundThis study compared the surgical, oncological, and functional outcomes of patients undergoing limb-salvage surgery for extremity soft tissue sarcoma with vascular resection and reconstruction with the outcomes of those undergoing limb-salvage without vascular reconstruction.MethodsNineteen patients were identified from a prospective soft-tissue sarcoma database who underwent vascular resection and reconstruction as part of their limb-salvage surgery and who were followed up for at least 1 year or until death. Each of these 19 patients was case-matched to 2 additional patients on the basis of tumor location, size, and depth; patient age; and timing of radiation. To compare functional outcome, a subset of patients was case-matched with additional criteria including wound-complication status, motor nerve sacrifice, similar preoperative function as determined by the Toronto Extremity Salvage Score, and no metastases at diagnosis or the 1-year follow-up.ResultsPatients in the vascular reconstruction group were more likely to require a muscle transfer (53% vs. 18%; P = .008), experience a wound complication (68% vs. 32%; P = .03), experience deep venous thrombosis (26% vs. 0; P = .003), experience significant limb edema (87% vs. 20%; P = .001), and ultimately require an amputation (16% vs. 3%; P = .07). Patients who underwent vascular reconstruction had only slightly lower Toronto Extremity Salvage Score scores 1 year after surgery (78.5 vs. 84.2; P = .35). There were no significant differences in local or systemic tumor relapse between the two groups.ConclusionsVascular reconstruction is a feasible option in limb-salvage surgery for soft tissue sarcoma but is associated with an increased risk for postoperative complications, including amputation. Although function is not significantly worse after vascular reconstruction, the results are less predictable.

Canadian Cardiovascular Society Position Statement on the Management of Thoracic Aortic Disease

This Canadian Cardiovascular Society position statement aims to provide succinct perspectives on key issues in the management of thoracic aortic disease (TAD). This document is not a comprehensive overview of TAD and important elements of the epidemiology, presentation, diagnosis, and management of acute aortic syndromes are deliberately not discussed; readers are referred to the 2010 guidelines published by the American Heart Association, American College of Cardiology, American Association for Thoracic Surgery, and other stakeholders. Rather, this document is a practical guide for clinicians managing adult patients with TAD. Topics covered include size thresholds for surgical intervention, emerging therapies, imaging modalities, medical and lifestyle management, and genetics of TAD. The primary panel consisted of experts from a variety of disciplines that are essential for comprehensive management of TAD patients. The methodology involved a focused literature review with an emphasis on updates since 2010 and the use of Grading of Recommendations Assessment, Development, and Evaluation methodology to arrive at specific recommendations. The final document then underwent review by a secondary panel. This document aims to provide recommendations for most patients and situations. However, the ultimate judgement regarding the management of any individual patients should be made by their health care team.