Producing physicians for south Texas

South Texas, one of the fastest growing regions in the country, remains among the most medically underserved, in part, because few students from South Texas enter medical school. To address this issue and to increase the diversity of the matriculant pool, Baylor College of Medicine (BCM) and The University of Texas-Pan American (UT-PA) established in 1994 the Premedical Honors College (PHC), a rigorous undergraduate program at UT-PA for students from South Texas high schools. Students who complete all PHC requirements and BCM prerequisites are accepted into BCM upon graduation from UT-PA. Those in good standing receive counseling, enrichment experiences, and tuition and fee waivers from UT-PA and BCM. The program is increasing the number of students from South Texas universities matriculating into medical school, and is expanding the involvement of local physicians in undergraduate education, heightening visibility for partner institutions, and becoming an effective, replicable bachelor of science/doctor of medicine model.

Cytokines and the microcirculation in ischemia and reperfusion

The intense inflammatory reaction following reperfusion of the infarcted myocardium has been implicated as a factor in extension of injury. However, this inflammatory reaction is also critical to tissue repair. The cellular responses that mediate these functions are orchestrated by sequential induction and/or release of cytokines resulting in a closely regulated cytokine cascade. This paper reviews research on these cytokine cascades, their cellular origin, and factors which control the cellular response to their presence. Factors examined include leukotaxis, phenotypic transition of leukocytes, adhesion molecule induction and the role of cytokines in tissue repair and scar formation.

A Ras-dependent pathway regulates RNA polymerase II phosphorylation in cardiac myocytes: implications for cardiac hypertrophy

Despite extensive evidence implicating Ras in cardiac muscle hypertrophy, the mechanisms involved are unclear. We previously reported that Ras, through an effector-like function of Ras GTPase-activating protein (GAP) in neonatal cardiac myocytes (M. Abdellatif et al., J. Biol. Chem. 269:15423-15426, 1994; M. Abdellatif and M. D. Schneider, J. Biol. Chem. 272:527-533, 1997), can up-regulate expression from a comprehensive set of promoters, including both cardiac cell-specific and constitutive ones. To investigate the mechanism(s) underlying these earlier findings, we have used recombinant adenoviruses harboring a dominant negative Ras (17N Ras) allele or the N-terminal domain of GAP (nGAP), responsible for the Ras-like effector function. Inhibition of endogenous Ras reduced basal levels of [3H]uridine and [3H]phenylalanine incorporation into total RNA, mRNA, and protein, with parallel changes in apparent cell size. In addition, 17N Ras markedly inhibited phosphorylation of the C-terminal domain (CTD) of RNA polymerase II (pol II), known to regulate transcript elongation, accompanied by down-regulation of its principal kinase, cyclin-dependent kinase 7 (Cdk7). In contrast, nGAP elicited the opposite effects on each of these parameters. Furthermore, cotransfection of constitutively active Ras (12R Ras) with wild-type pol II, rather than a truncated mutant lacking the CTD, demonstrated that Ras activation of transcription was dependent on the pol II CTD. Consistent with a potential role for this pathway in the development of cardiac myocyte hypertrophy, alpha1-adrenergic stimulation similarly enhanced pol II phosphorylation and Cdk7 expression, where both effects were inhibited by dominant negative Ras, while pressure overload hypertrophy led to an increase in both hyperphosphorylated and hypophosphorylated pol II in addition to Cdk7.

Dominant-negative effect of a mutant cardiac troponin T on cardiac structure and function in transgenic mice

Hypertrophic cardiomyopathy (HCM) is a disease of sarcomeric proteins. The mechanism by which mutant sarcomeric proteins cause HCM is unknown. The leading hypothesis proposes that mutant sarcomeric proteins exert a dominant-negative effect on myocyte structure and function. To test this, we produced transgenic mice expressing low levels of normal or mutant human cardiac troponin T (cTnT). We constructed normal (cTnT-Arg92) and mutant (cTnT-Gln92) transgenes, driven by a murine cTnT promoter, and produced three normal and five mutant transgenic lines, which were identified by PCR and Southern blotting. Expression levels of the transgene proteins, detected using a specific antibody, ranged from 1 to 10% of the total cTnT pool. M-mode and Doppler echocardiography showed normal left ventricular dimensions and systolic function, but diastolic dysfunction in the mutant mice evidenced by a 50% reduction in the E/A ratio of mitral inflow velocities. Histological examination showed cardiac myocyte disarray in the mutant mice, which amounted to 1-15% of the total myocardium, and a twofold increase in the myocardial interstitial collagen content. Thus, the mutant cTnT-Gln92, responsible for human HCM, exerted a dominant-negative effect on cardiac structure and function leading to disarray, increased collagen synthesis, and diastolic dysfunction in transgenic mice.

Stem cell factor induction is associated with mast cell accumulation after canine myocardial ischemia and reperfusion

BACKGROUND

Myocardial infarction is associated with an intense inflammatory reaction leading to healing and scar formation. Because mast cells are a significant source of fibrogenic factors, we investigated mast cell accumulation and regulation of stem cell factor (SCF), a potent growth and tactic factor for mast cells, in the healing myocardium.

METHODS AND RESULTS

Using a canine model of myocardial ischemia and reperfusion, we demonstrated a striking increase of mast cell numbers during the healing phase of a myocardial infarction. Mast cell numbers started increasing after 72 hours of reperfusion, showing maximum accumulation in areas of collagen deposition (12.0+/-2.6-fold increase; P<0.01) and proliferating cell nuclear antigen (PCNA) expression. The majority of proliferating cells were identified as alpha-smooth muscle actin-positive myofibroblasts or factor VIII-positive endothelial cells. Mast cells did not appear to proliferate. Using a nuclease protection assay, we demonstrated induction of SCF mRNA within 72 hours of reperfusion. Immunohistochemical studies demonstrated that a subset of macrophages was the source of SCF immunoreactivity in the infarcted myocardium. SCF protein was not found in endothelial cells and myofibroblasts. Intravascular tryptase-positive, FITC-avidin-positive, CD11b-negative mast cell precursors were noted in the area of healing and in the cardiac lymph after 48 to 72 hours of reperfusion.

CONCLUSIONS

Mast cells increase in number in areas of collagen deposition and PCNA expression after myocardial ischemia. The data provide evidence of mast cell precursor infiltration into the areas of cellular injury. SCF is induced in a subset of macrophages infiltrating the healing myocardium. We suggest an important role for SCF in promoting chemotaxis and growth of mast cell precursors in the healing heart.

Resident cardiac mast cells degranulate and release preformed TNF-alpha, initiating the cytokine cascade in experimental canine myocardial ischemia/reperfusion

BACKGROUND

Neutrophil-induced cardiomyocyte injury requires the expression of myocyte intercellular adhesion molecule (ICAM)-1 and ICAM-1-CD11b/CD18 adhesion. We have previously demonstrated interleukin (IL)-6 activity in postischemic cardiac lymph; IL-6 is the primary stimulus for myocyte ICAM- 1 induction. Furthermore, we found that induction of IL-6 mRNA occurred very early on reperfusion of the infarcted myocardium. We hypothesized that the release of a preformed upstream cytokine induced IL-6 in leukocytes infiltrating on reperfusion.

METHODS AND RESULTS

Constitutive expression of TNF-alpha and not IL-1beta was demonstrated in the normal canine myocardium and was localized predominantly in cardiac mast cells. Mast cell degranulation in the ischemic myocardium was documented by demonstration of a rapid release of histamine and TNF-alpha in the cardiac lymph after myocardial ischemia. Histochemical studies with FITC-labeled avidin demonstrated degranulating mast cells only in ischemic samples of canine myocardium. Immunohistochemistry suggested that degranulating mast cells were the primary source of TNF-alpha in the ischemic myocardium. In situ hybridization studies of reperfused myocardium localized IL-6 mRNA in infiltrating mononuclear cells and in mononuclear cells appearing in the postischemic cardiac lymph within the first 15 minutes of reperfusion. Furthermore, isolated canine mononuclear cells incubated with postischemic cardiac lymph demonstrated significant induction of IL-6 mRNA, which was partially blocked with a neutralizing antibody to TNF-alpha.

CONCLUSIONS

Cardiac mast cells degranulate after myocardial ischemia, releasing preformed mediators, such as histamine and TNF-alpha. We suggest that mast cell-derived TNF-alpha may be a crucial factor in upregulating IL-6 in infiltrating leukocytes and initiating the cytokine cascade responsible for myocyte ICAM-1 induction and subsequent neutrophil-induced injury.

Pathophysiologically relevant concentrations of tumor necrosis factor-alpha promote progressive left ventricular dysfunction and remodeling in rats

BACKGROUND

Although patients with heart failure express elevated circulating levels of tumor necrosis factor-alpha (TNF-alpha) in their peripheral circulation, the structural and functional effects of circulating levels of pathophysiologically relevant concentrations of TNF-alpha on the heart are not known.

METHODS AND RESULTS

Osmotic infusion pumps containing either diluent or TNF-alpha were implanted into the peritoneal cavity of rats. The rate of TNF-alpha infusion was titrated to obtain systemic levels of biologically active TNF-alpha comparable to those reported in patients with heart failure (approximately 80 to 100 U/mL), and the animals were examined serially for 15 days. Two-dimensional echocardiography was used to assess changes in left ventricular (LV) structure (remodeling) and LV function. Video edge detection was used to assess isolated cell mechanics, and standard histological techniques were used to assess changes in the volume composition of LV cardiac myocytes and the extracellular matrix. The reversibility of cytokine-induced effects was determined either by removal of the osmotic infusion pumps on day 15 or by treatment of the animals with a soluble TNF-alpha antagonist (TNFR:Fc). The results of this study show that a continuous infusion of TNF-alpha led to a time-dependent depression in LV function, cardiac myocyte shortening, and LV dilation that were at least partially reversible by removal of the osmotic infusion pumps or treatment of the animals with TNFR:Fc.

CONCLUSIONS

These studies suggest that pathophysiologically relevant concentrations of TNF-alpha are sufficient to mimic certain aspects of the phenotype observed in experimental and clinical models of heart failure.

Adenoviral delivery of E2F-1 directs cell cycle reentry and p53-independent apoptosis in postmitotic adult myocardium in vivo

Irreversible exit from the cell cycle precludes the ability of cardiac muscle cells to increase cell number after infarction. Using adenoviral E1A, we previously demonstrated dual pocket protein- and p300-dependent pathways in neonatal rat cardiac myocytes, and have proven that E2F-1, which occupies the Rb pocket, suffices for these actions of E1A. By contrast, the susceptibility of adult ventricular cells to viral delivery of exogenous cell cycle regulators has not been tested, in vitro or in vivo. In cultured adult ventricular myocytes, adenoviral gene transfer of E2F-1 induced expression of proliferating cell nuclear antigen, cyclin-dependent protein kinase 4, cell division cycle 2 kinase, DNA synthesis, and apoptosis. In vivo, adenoviral delivery of E2F-1 by direct injection into myocardium induced DNA synthesis, shown by 5'-bromodeoxyuridine incorporation, and accumulation in G2/M, by image analysis of Feulgen-stained nuclei. In p53(-)/- mice, the prevalence of G1 exit was more than twofold greater; however, E2F-1 evoked apoptosis and rapid mortality comparably in both backgrounds. Thus, the differential effects of E2F-1 on G1 exit in wild-type versus p53-deficient mice illustrate the combinatorial power of viral gene delivery to genetically defined recipients: E2F-1 can override the G1/S checkpoint in postmitotic ventricular myocytes in vitro and in vivo, but leads to apoptosis even in p53(-)/- mice.

Gene recombination in postmitotic cells. Targeted expression of Cre recombinase provokes cardiac-restricted, site-specific rearrangement in adult ventricular muscle in vivo

Mouse models of human disease can be generated by homologous recombination for germline loss-of-function mutations. However, embryonic-lethal phenotypes and systemic, indirect dysfunction can confound the use of knock-outs to elucidate adult pathophysiology. Site-specific recombination using Cre recombinase can circumvent these pitfalls, in principle, enabling temporal and spatial control of gene recombination. However, direct evidence is lacking for the feasibility of Cre-mediated recombination in postmitotic cells. Here, we exploited transgenic mouse technology plus adenoviral gene transfer to achieve Cre-mediated recombination in cardiac muscle. In vitro, Cre driven by cardiac-specific alpha-myosin heavy chain (alphaMyHC) sequences elicited recombination selectively at loxP sites in purified cardiac myocytes, but not cardiac fibroblasts. In vivo, this alphaMyHC-Cre transgene elicited recombination in cardiac muscle, but not other organs, as ascertained by PCR analysis and localization of a recombination-dependent reporter protein. Adenoviral delivery of Cre in vivo provoked recombination in postmitotic, adult ventricular myocytes. Recombination between loxP sites was not detected in the absence of Cre. These studies demonstrate the feasibility of using Cre-mediated recombination to regulate gene expression in myocardium, with efficient induction of recombination even in terminally differentiated, postmitotic muscle cells. Moreover, delivery of Cre by viral infection provides a simple strategy to control the timing of recombination in myocardium.

Noninvasive determination of pulse-wave velocity in mice

Some transgenic mice have abnormal vascular function, but arterial geometry and dynamics are difficult to evaluate. To examine whether ultrasonic velocimetry could be used to determine arterial pulse-wave velocity (PWV) in mice, a custom-made 20-MHz pulsed Doppler instrument was used to obtain blood flow velocity signals from the aortic arch and the abdominal aorta 4 cm downstream. The upstroke (foot) of the velocity wave was timed at each site with respect to the R wave of the electrocardiogram, and PWV was calculated by dividing the separation distance by the difference in R-foot times. Doppler determinations were compared with invasive tonometry, and PWV was altered pharmacologically. It was found that the upstrokes of pressure (by tonometry) and velocity were coincident (+/-1 ms) and that PWV could be calculated by either method on exposed vessels. With the use of Doppler methods, pulse transit time was determined noninvasively with +/-1-ms resolution in 140 of 142 attempts in 82 mice. The calculated PWV in mice ranged from 220 to 850 cm/s with vasodilating anesthetics producing the low values and vasoconstricting agents producing the higher values. Thus PWV can be determined noninvasively in mice, is similar to that in other mammals, and responds as expected to vasoactive agents.

Induction of monocyte chemoattractant protein-1 in the small veins of the ischemic and reperfused canine myocardium

BACKGROUND

Healing after myocardial infarction is characterized by the presence of macrophages in the infarcted area. Since augmented monocyte influx has been implicated as a potential mechanism for improved healing after reperfusion, we wished to study the induction of monocyte chemoattractant protein-1 (MCP-1) during reperfusion.

METHODS AND RESULTS

The cDNA for MCP-1 was cloned from a canine jugular vein endothelial cell (CJVEC) library and exhibited 78% identity with the deduced amino acid sequence of human MCP-1. Samples of myocardium were taken from control and ischemic segments after 1 hour of ischemia and various times of reperfusion; total RNA was isolated from myocardial samples and probed with a cDNA probe for canine MCP-1. Induction of MCP-1 mRNA occurred only in previously ischemic segments within the first hour of reperfusion, peaked at 3 hours, and persisted throughout the first 2 days of reperfusion. In the absence of reperfusion, no significant MCP-1 induction was seen. Both ischemic (but not preischemic) cardiac lymph and human recombinant TNF-alpha induced MCP-1 in CJVECs. MCP-1 was identified by immunostaining on infiltrating cells and venular (but not arterial) endothelium by 3 hours. In contrast, in situ hybridization showed MCP-1 mRNA to be confined to the endothelium of small veins (venules) 10 to 70 microns in diameter.

CONCLUSIONS

MCP-1 mRNA is induced in the endothelium of a specific class of small veins immediately after reperfusion. MCP-1 induction is confined to the previously ischemic area that has been reperfused. We suggest a significant role for MCP-1 in monocyte trafficking in the reperfused myocardium.

Complement C5a, TGF-beta 1, and MCP-1, in sequence, induce migration of monocytes into ischemic canine myocardium within the first one to five hours after reperfusion

BACKGROUND

Recent studies suggest that reperfusion promotes healing of formerly ischemic heart tissue even when myocardial salvage is no longer possible. Since monocyte-macrophage infiltration is the hallmark of the healing infarct, we have attempted to identify mechanisms that attract monocytes into the heart after reperfusion of ischemic canine myocardium.

METHODS AND RESULTS

Isolated autologous 99mTc-labeled mononuclear leukocytes injected into the left atrium localized preferentially in previously ischemic myocardium within the first hour after reperfusion. Histological studies revealed CD64+ monocytes in small venules and the perivascular connective tissue within the first hour after reperfusion. Flow cytometric analysis of cells in cardiac lymph showed systematically increasing numbers of neutrophils and monocytes between 1 and 4 hours after reperfusion; monocyte enrichment was eventually greater than neutrophil enrichment. Monocyte chemotactic activity in cardiac lymph collected in the first hour after reperfusion was wholly attributable to C5a. Transforming growth factor (TGF)-beta 1 contributed significantly to this chemotactic activity after 60 to 180 minutes, and after 180 minutes, monocyte chemotactic activity in lymph was largely dependent on monocyte chemoattractant protein (MCP)-1 acting in concert with TGF-beta 1.

CONCLUSIONS

Beginning in the first 60 minutes after reperfusion, C5a, TGF-beta 1, and MCP-1, acting sequentially, promote infiltration of monocytes into formerly ischemic myocardium. These events may promote the healing of myocardial injury facilitated by reperfusion.

Hemodynamic effects of different pacing ratios in chronic dynamic double cardiomyoplasty

BACKGROUND

Dynamic cardiomyoplasty is being used clinically worldwide, and evaluated by a clinical trial (phase III) in the United States. Some centers stimulate the skeletal muscle wrap with every heart beat (1:1 [muscle:heart]), whereas others use every other heart beat (1:2). Recent concern over the possible deleterious effects of too-frequent stimulation of the muscles motivated the attempt to evaluate, in a canine model of chronic, double cardiomyoplasty, the effects of two different pacing ratios on several hemodynamic parameters of interest.

METHODS

Double cardiomyoplasty was performed using both latissimus dorsi muscles in 11 dogs. Fatigue resistance was achieved using the clinical transformation protocol. At a final experiment, acute cardiac failure was induced by administration of propranolol. Hemodynamic measurements of eight physiologic variables were averaged over complete pacing cycles, including the nonpaced beat at a 1:2 pacing ratio.

RESULTS

The net effects of latissimus dorsi muscle stimulation at each of two pacing ratios were compared using nonparametric statistics. With the exception of left ventricular pressure (p = 0.0262) and its first derivative, dP/dt (p = 0.0099), there was no significant difference between hemodynamic performance at the two pacing ratios.

CONCLUSIONS

In this canine model, pacing every other beat produces hemodynamic results that are statistically similar to pacing every beat. Less frequent stimulation of the latissimus dorsi muscle may preserve its function and improve clinical results without compromising hemodynamic benefit.

Assessment of myocardial viability with 99mTc sestamibi in patients undergoing cardiac transplantation. A scintigraphic/pathological study

BACKGROUND

99mTc sestamibi and 201 Tl are tracers that allow equivalent detection of myocardial infarction. However, because sestamibi does not undergo as much time-dependent redistribution as does 201Tl, it has been considered suboptimal for the detection of myocardial viability.

METHODS AND RESULTS

Fifteen consecutive patients with ischemic cardiomyopathy who underwent orthotopic cardiac transplantation received an intravenous injection of 99mTc sestamibi at 1 to 6 hours before transplantation. Rotational tomography of the excised, intact, native hearts was performed to quantify the extent of myocardial hypoperfusion. The hearts were then sliced and reimaged on a gamma camera, followed by pathological quantification of the extent and severity of scarred and normal myocardium. Samples of normally and abnormally perfused myocardium underwent gamma well counting to determine tissue radioactivity and were examined under light microscopy for delineation of myocardial structure after trichrome staining. The mean extent of scintigraphic scar quantified through the use of rotational tomography was 45 +/- 14% of the left ventricle and correlated closely with pathological scar size (r = .89), despite a slight overestimation. Scintigraphic scar size determined with planar imaging of the individual myocardial slices also correlated closely with pathological scar size (r = .88). A good correlation existed between tissue 99mTc sestamibi activity determined through well counting and histological evidence of myocardial viability (r = .89). Most hypokinetic and 40% of akinetic/dyskinetic myocardial segments contained scintigraphically and histologically normal myocardium.

CONCLUSIONS

99mTc sestamibi scintigraphy can be used to accurately quantify the extent of myocardial scarring. Furthermore, the relative sestamibi activity in perfusion defects, measured several hours after administration, is a good indicator of myocardial viability determined with microscopy.

Noninvasive indexes of cardiac systolic and diastolic function in hyperthyroid and senescent mouse

The mouse is a common model for transgenic manipulation, however, their small size has made hemodynamic study difficult. A noninvasive 10-MHz pulsed Doppler probe was used to measure aortic and mitral flow velocities in anesthetized, intact mice to study the effects of aging and hypethyroidism (induced by thyroxine) one systolic and diastolic cardiac function. In 10 hyperthyroid mice peak aortic velocity (PAV, an index of systolic function) was 34% higher than in 10 control mice (108 +/- 2 vs. 80 +/- 3 cm/s, P < 0.05). The ratio of early to late mitral filling velocity (E/A ratio, an index of diastolic function) was 47% higher (5.6 +/- 0.8 vs. 3.8 +/- 0.2, P < 0.05) in the hyperthyroid mice. In six old (30 mo) mice PAV was similar to eight young (4 mo) mice (73 +/- 3 vs. 75 +/- 3 cm/s), but the E/A ratio was 59% lower (1.8 +/- 0.3 vs. 4.4 +/- 0.4, P < 0.05). Despite a wide range of observed heart rates, the systolic and diastolic parameters of the groups were clearly separated. We conclude that cardiac systolic and diastolic function in mice, measured by pulsed Doppler ultrasound, are similar to larger species both in magnitude and in their response to hyperthyroidism and aging.

Myocardial ischemia and reperfusion: a murine model

Myocardial ischemia followed by reperfusion promotes a complex series of inflammatory reactions as noted in a variety of large animal studies. With development of genetically altered mice, there is intense interest in developing murine models to study mechanisms operative in cardiovascular disease. We developed a mouse model to study coronary artery occlusion and reperfusion effects and the method required to perform these studies both acutely and chronically. In mice, we applied a left anterior descending coronary artery occlusion either permanently or for 30 or 60 min followed by reperfusion allowing flow through the previously occluded coronary artery bed. Reperfusion was documented visually as well as by using Doppler ultrasound and histopathological techniques. The area at risk (AAR) and infarct size (IS) were assessed by EVans blue dye and triphenyltetrazolium chloride staining with computerized planimetry using an image analysis software program. The infarct as percentage of AAR and IS as percentage of the left ventricle in 13 mice with permanent occlusion was 68.6 +/- 4.4 and 28.0 +/- 2.8%, respectively. Reperfusion after occlusions of 60 and 30 min resulted in a significant decrease in IS as a percentage of the AAR compared with permanent occlusion. Histological examination of the ischemic and reperfused myocardium shows infiltration of leukocytes into the ischemic region as well as contraction bands classically associated with reperfusion. This new model allows assessment of AAR, IS, cardiac function, and pathophysiology in the mouse. With the current technology to develop genetically altered mice for overexpression or targeted mutations of various genes, this model is used to understand the complex pathophysiology of ischemia and reperfusion injury.

Neutrophil sequestration and pulmonary dysfunction in a canine model of open heart surgery with cardiopulmonary bypass. Evidence for a CD18-dependent mechanism

BACKGROUND

Previous studies documented an inflammatory reaction to cardiopulmonary bypass with neutrophil (PMN) sequestration in the lungs, contributing to microvascular injury and postoperative pulmonary dysfunction. This study explored the hypothesis that the beta 2 integrin CD18, a leukocyte adhesion molecule, mediates this response.

METHODS AND RESULTS

Fifteen adult, mixed-breed dogs underwent 90 minutes of cardiopulmonary bypass with 3 hours of subsequent recovery. Seven additional dogs were treated before cardiopulmonary bypass with a 1-mg/kg IV bolus of R15.7 IgG, a monoclonal antibody to CD18. Both groups were compared with 5 sham bypass control dogs. Bypassed dogs demonstrated an increased number of PMNs sequestered in the lungs 3 hours after bypass compared with sham bypass control dogs (1466 +/- 75 versus 516 +/- 43 PMN/mm2 alveolar surface area, mean +/- SEM, P < .001). Also, when PMNs from bypass dogs were compared with those from sham dogs, they produced more H2O2 (305 +/- 45 versus 144 +/- 48 amol H2O2 per phagocyte per 20 minutes, P < .05). Bypass dogs had significantly decreased arterial oxygenation 3 hours after the procedure compared with shams (457 +/- 20 versus 246 +/- 49 mm Hg, P < .05), and they had a significantly increased lung wet-to-dry weight ratio (5.38 +/- 0.14 versus 4.54 +/- 0.15, P = .003), demonstrating a significant increase in lung water. R15.7 markedly attenuated pulmonary PMN accumulation in bypass dogs (412 +/- 73 PMN/mm2, P < .001) and significantly inhibited PMN production of H2O2 (146 +/- 18 amol H2O2 per phagocyte per 20 minutes, P < .05) Bypass dogs pretreated with R15.7 also had improved oxygenation (445 +/- 28 mm Hg, P < .05) and tended to have less lung water accumulation after bypass (4.99 +/- 0.20).

CONCLUSIONS

Pulmonary dysfunction after cardiopulmonary bypass is caused, at least in part, by a neutrophil-mediated, CD18-dependent mechanism.

Induction of interleukin-6 synthesis in the myocardium. Potential role in postreperfusion inflammatory injury

BACKGROUND

Neutrophil-induced injury of myocardial cells requires the expression of intercellular adhesion molecule-1 (ICAM-1) on the myocyte surface and is mediated by ICAM-1-CD11b/CD18 adhesion. We have previously shown that interleukin-6 (IL-6) cytokine activity, present in cardiac lymph, induces ICAM-1 on isolated cardiac myocytes. Furthermore, in previous in vivo studies, we have also shown ICAM-1 mRNA induction in the myocardium within the first hour of reperfusion in the previously ischemic viable zone. We hypothesized that induction of IL-6 synthesis in the myocardium was an integral part of the reaction to injury resulting from ischemia and reperfusion and was associated with induction of ICAM-1 on myocardial cells.

METHODS AND RESULTS

In this study, cloned canine IL-6 cDNA was used as a molecular probe to study the regulation of IL-6 in an awake canine model of myocardial ischemia and reperfusion. IL-6 mRNA was induced in ischemic and reperfused segments of myocardium preferentially in segments previously exposed to severe ischemia. Peak levels of IL-6 mRNA were reached within 3 hours of reperfusion. At the same time, IL-6 mRNA and ICAM-1 mRNA were found in the same myocardial segments. In contrast to hearts that were ischemic for 1 hour and reperfused for 3 hours, nonreperfused hearts after 4 hours of persistent ischemia demonstrated minimal induction of ICAM-1 or IL-6 despite similar degrees of injury and blood flow reductions during ischemia. After 24 hours of persistent ischemia, levels of IL-6 mRNA were comparable to those observed in hearts that were ischemic for 1 hour and subsequently reperfused for 24 hours.

CONCLUSIONS

Our results demonstrate induction of IL-6 mRNA in the myocardium and that this synthesis is accelerated by reperfusion. Evidence is also provided to show that peak IL-6 mRNA precedes that of ICAM-1 mRNA. These findings are compatible with our hypothesis that IL-6 is important in the induction of ICAM-1 in the area of ischemia. In addition, these studies suggest that the necessary factors to promote adhesive interactions between transmigrated neutrophils and cardiac myocytes are present in reperfused myocardium.

Role of early reperfusion in the induction of adhesion molecules and cytokines in previously ischemic myocardium

Our studies in vitro demonstrate that neutrophil mediated injury of isolated cardiac myocytes requires the presence of ICAM-1 on the surface of the myocyte and CD11b/CD18 activation on the neutrophil. In post-ischemic cardiac lymph, there is rapid appearance of C5a activity during the first hours of reperfusion. Interleukin-6 activity is present throughout the first 72 h of reperfusion and is sufficient to induce ICAM-1 on the surface of the cardiac myocyte. In situ hybridization studies suggest that ICAM-1 mRNA is found in viable myocardial cells on the edge of the myocardial infarction within 1 h of reperfusion. ICAM-1 protein expression on cardiac myocytes is seen after 6 h of reperfusion, and increases thereafter. Non-ischemic tissue demonstrates no early induction of ICAM-1 mRNA or ICAM-1 protein on myocardial cells. In our most recent experiments, we have determined that reperfusion is an absolute requirement for the early induction of myocardial ICAM-1 mRNA in previously ischemic myocardial cells. To further assess this, we have cloned and sequenced a canine interleukin-6 (IL-6) cDNA. The data suggest that early induction of IL-6 mRNA is also reperfusion dependent as it could be demonstrated in the same ischemic and reperfused segments in which ICAM-1 mRNA was found. Peak expression of IL-6 mRNA occurred much earlier than that for ICAM-1 mRNA. Similar experiments were then performed with a molecular probe for interleukin-8 (IL-8). This chemokine is a potent neutrophil stimulant and has a higher degree of specificity for neutrophils than classic chemoattractants such as C5a.(ABSTRACT TRUNCATED AT 250 WORDS)

Neutrophil activation and adhesion molecule expression in a canine model of open heart surgery with cardiopulmonary bypass

OBJECTIVE

The aim was to determine whether, in a canine model, changes in surface expression of the neutrophil adhesion molecules CD11b/CD18 and L-selectin during and after open heart surgery with cardiopulmonary bypass can be used to identify subjects at risk for postoperative pulmonary dysfunction.

METHODS

Adult mixed breed dogs underwent cardiopulmonary bypass and were compared to "sham bypass" controls. Flow cytometry was performed on blood from the two groups of dogs and changes in CD11b/CD18 adhesion molecules and L-selectin were investigated.

RESULTS

Flow cytometry on blood from bypass dogs showed increased CD18 expression during and after cardiopulmonary bypass and a reciprocal decrease in L-selectin expression. Sham animals showed no significant change. In the bypass animals, changes in adhesion molecule expression were not evenly distributed across the population of circulating neutrophils; however, they were indicative of a percentage of activated cells. There was a significant negative linear relationship between the percentage of activated cells and arterial oxygenation 3 h after bypass (r = -0.80, P < 0.001). From this analysis, 11 animals were identified as "high" responders and seven as "low" responders, with different patterns of cellular activation and oxygenation during and after bypass. High responders had an average of 40(SEM 5)% activated cells during bypass with a persistently raised percentage of activated cells [38(3)%] 3 h later, whereas low responders had only 22(6)% activated cells during bypass and 11(2)% activated cells 3 h after bypass. High responder animals had a marked and continued deterioration in PO2 after bypass [to 25(6)% of baseline 3 h after bypass] whereas low responder animals showed recovery of oxygenation after the first hour postbypass and improved to 80(8)% of baseline at 3 h.

CONCLUSIONS

Changes in adhesion molecule expression serve as a marker of neutrophil activation during cardiopulmonary bypass. The percentage of activated neutrophils in the circulation within 3 h after cardiopulmonary bypass may be predictive of an ongoing inflammatory process that is linked to pulmonary dysfunction.

Noninvasive measurement of ascending aortic blood velocity in mice

Mice are useful models in numerous research protocols, but monitoring cardiovascular parameters in small animals is difficult. Therefore we evaluated the use of 20-MHz pulsed Doppler ultrasound to measure ascending aortic blood velocity in intact anesthetized mice. Using a 0.5-mm-diameter 20-MHz transducer applied to the right sternal border, we recorded audio Doppler signals from the ascending aorta of 31 mice [24.4 +/- 1.5 (SD) g body wt]. The signals were played back at speed into a fast Fourier transform analyzer from which we measured heart rate (453 +/- 96 beats/min), ejection time (38 +/- 3%), peak velocity (90 +/- 11 cm/s), mean velocity (23 +/- 4 cm/s), rise time (7.3 +/- 2 ms), stroke distance (29 +/- 7 mm), and acceleration (163 +/- 63 m/s2) from the spectral envelopes. We determined aortic diameter (1.2 +/- 0.2 mm) and Doppler angle (0-20 degrees) in six mice by molding the aortic root and major systemic vessels with casting resin infused at 100 mmHg pressure. For an aortic diameter of 1.2 mm, cardiac output was estimated to be 14.8 ml/min and stroke volume to be 33 microliters. To verify the origin of the signals and to test responsiveness to known stimuli, we measured velocity signals from the aorta and other nearby vessels and varied heart rate and aortic velocity by warming or by infusion of isoproterenol in three open-chest animals. For the noninvasive applications, acoustic coupling was adequate through the moistened fur, and aortic velocity signals were obtained in all animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Interleukin-8 gene induction in the myocardium after ischemia and reperfusion in vivo

Neutrophil adhesion and direct cytotoxicity for cardiac myocytes require chemotactic stimulation and are dependent upon CD18-ICAM-1 binding. To characterize the potential role of IL-8 in this interaction, canine IL-8 cDNA was cloned and the mature recombinant protein expressed in Escherichia coli BL21 cells. Recombinant canine IL-8 markedly increased adhesion of neutrophils to isolated canine cardiac myocytes. This adhesion resulted in direct cytotoxicity for cardiac myocytes. Both processes were specifically blocked by antibodies directed against CD18 and IL-8. In vivo, after 1 h of coronary occlusion, IL-8 mRNA was markedly and consistently induced in reperfused segments of myocardium. IL-8 mRNA was not induced in control (normally perfused) myocardial segments. Minimal amounts of IL-8 mRNA were detected after 3 or 4 h of ischemia without reperfusion. Highest levels of induction were evident in the most ischemic myocardial segments. IL-8 mRNA peaked in the first 3 h of reperfusion and persisted at high levels beyond 24 h. IL-8 staining was present in the inflammatory infiltrate near the border between necrotic and viable myocardium, as well as in small veins in the same area. These findings provide the first direct evidence for regulation of IL-8 in ischemic and reperfused canine myocardium and support the hypothesis that IL-8 participates in neutrophil-mediated myocardial injury.

Free oxygen radicals contribute to platelet aggregation and cyclic flow variations in stenosed and endothelium-injured canine coronary arteries

OBJECTIVES

The purpose of this study was to test the hypothesis that free oxygen radicals contribute to platelet aggregation and cyclic flow variations in stenosed and endothelium-injured coronary arteries.

BACKGROUND

Although free oxygen radicals, such as superoxide anion and hydrogen peroxide, have been shown to alter platelet function in vitro, the potential role of free oxygen radicals has not been fully described in an in vivo model of coronary artery thrombosis.

METHODS

Cyclic flow variations were produced in dogs by an external constrictor placed at the site of the left anterior descending coronary artery with injured endothelium. Blood flow in this artery was monitored by a pulsed Doppler flow probe. If cyclic flow variations were observed during postoperative days, dogs intravenously received superoxide dismutase plus catalase. In anesthetized dogs that did not develop an episode of cyclic flow variations, the effect of intracoronary infusion of xanthine plus xanthine oxidase or hydrogen peroxide on arterial blood flow velocity was studied. In platelet studies, the effect of free oxygen radicals and radical scavengers on platelet aggregation was examined.

RESULTS

In conscious dogs with cyclic flow variations, superoxide dismutase plus catalase significantly reduced cyclic flow variations (n = 7), whereas saline infusion had no effect (n = 7). The infusion of xanthine plus xanthine oxidase or hydrogen peroxide significantly induced cyclic flow variations in four of six dogs or in five of seven dogs, respectively. In vitro platelet studies showed that xanthine plus xanthine oxidase or hydrogen peroxide significantly enhanced platelet aggregation, and superoxide dismutase or catalase significantly inhibited such aggregation.

CONCLUSIONS

Reduction of free radical formation decreases platelet aggregation and may eliminate cyclic flow variations, whereas promotion of free radical generation enhances platelet aggregation and may induce cyclic flow variations. Thus, free oxygen radicals are an important mediator in this model.

Cardiolipin-protein complexes and initiation of complement activation after coronary artery occlusion

Specific rabbit anti-cardiolipin (anti-CL) antibodies were used to investigate the hypothesis that cardiolipin, associated with mitochondrial membrane proteins, binds C1 and facilitates activation of the complement cascade following reperfusion of ischemic myocardium. By immunoelectron microscopy, anti-CL localized to subsarcolemmal mitochondria, emerging through breaks in membranes of damaged cardiac myocytes. Anti-CL reacted with > 15 mitochondrial constituents, most of which comigrated with the proteins that bind C1q in transblots of subsarcolemmal mitochondria, fractionated by polyacrylamide gel electrophoresis under reducing conditions in the presence of sodium dodecyl sulfate. A subset of the C1q-binding proteins > 24 to 37 kDa served as stable sites for assembly of C3, C5, and C9. Cardiac lymph, collected during the first hour after reperfusion of ischemic myocardium, contained proteins of diverse size that reacted with both anti-CL and C1q. Cardiac lymph, collected before occlusion and 4 to 5 hours after reperfusion, in comparison, had few if any C1q or anti-CL reactive proteins. Treatment with phospholipase suppressed the C1q-binding activity and anti-CL reactivity of the proteins in reperfusion lymph and those with similar properties in mitochondrial extracts. Our data suggest that during ischemia, mitochondria, extruded through breaks in the sarcolemma, unfold and release membrane fragments in which cardiolipin and protein are intimately associated. By binding C1 and supplying sites for the assembly of later-acting complement components, these fragments provide the means to disseminate the complement-mediated inflammatory response to ischemic injury.