Parenteral administration of an activating monoclonal antibody to the alpha1beta1 integrin in dogs

In mice, monoclonal antibody (mAb) to the alpha1 integrin abrogate gastro-intestinal damage during graft-versus-host-disease (GVHD), suggesting anti alpha1 mAb as candidates for treatment in humans as well. Our current data show that one such reagent, mAb 1B3.1, when immobilized to plastic wells via rabbit- anti murine (ram) immunoglobulin (Ig) induces a protein kinase-dependent spreading of activated human T cells. Furthermore, it significantly increases the proliferative response, and expression of interleukin-2 (IL-2) receptors (R) and CD69, of resting T cells, expressing minimal integrin on the cell surface, to sub-optimal stimulation by anti-CD3 mAb. We found, in addition, that mAb 1B3.1 a) immuno-precipitates alpha1beta1 integrins from cell-surface iodinated canine epithelial cells b) is highly reactive with canine T cells after their activation and c) inhibits adhesion of canine T cells to collagen IV. Despite the potential ability of the mAb to co-activate T cells in vitro, two dogs that received 4 injections of 0.5-0.3 mg/Kg of mAb 1B3.1 remained healthy, developing only marginal transient lymphopenia. Injection of 0.75mg/Kg in a third dog induced a more marked lymphopenia, and an additional dose of 1.0 mg/Kg 2 weeks later was followed by gastrointestinal hemorrhage. importantly, the lymphopenia was associated with a greater and more persistent decrease of CD8+ than of CD4+ T cells, leading to an increase in the CD4/CD8 ratio 24 hours after the injection. Thus, despite it's co-activating effects in vitro, administration of this mAb in vivo is feasible when appropriately dosed, and may have immuno-modulatory effects.

Basic fibroblast growth factor induces myocardial hypertrophy following acute infarction in rats

Basic fibroblast growth factor (bFGF) is a potent mitogen which induces growth of collateral vessels in ischaemic and infarcted myocardium. The effect of systemically administered bFGF on left ventricular (LV) function, myocardial hypertrophy and LV remodelling following acute myocardial infarction (MI) have not yet been fully investigated. Thirty Sprague-Dawley male rats were randomized to receive bFGF (0.5 mg) or rat albumin intraperitoneally for 1 week, beginning immediately after the induction of MI. Five animals served as controls and did not undergo any operation. Animals were killed 6 weeks after surgery and the hearts were perfused and fixed at physiological pressure. Transverse cross-sections from infarcted areas were stained with antibodies against proliferating cell nuclear antigen (PCNA) and Masson-trichrome and analysed with a coloured-image analyser for LV area (mm2), LV cavity diameter (mm), infarcted area (%), and wall thickness (mm) in infarcted and non-infarcted regions. LV area was similar in MI rats and in controls (41.7 +/- 6.9 and 43.0 +/- 1.5 mm2, respectively) and was significantly larger in MI bFGF-treated (MI/bFGF) animals (47.6 +/- 7.1 mm2) (P = 0.023). LV cavity diameter was significantly larger in the MI group than in MI/bFGF and control animals (6.0 +/- 0.8, 4.9 +/- 1.4, and 4.4 +/- 0.8 mm, respectively, P = 0.018). Wall thickness in the non-infarcted region was significantly smaller in MI animals (1.4 +/- 0.3 mm) than in MI/bFGF animals (1.6 +/- 0.4 mm) and the control group (1.6 +/- 0.1 mm) (P = 0.015). The ratio between LV cavity diameter/non-MI wall thickness was higher in MI than in control and MI/bFGF groups (4.8 +/- 1.6, 2.7 +/- 0.6 and 3.3 +/- 1.8, respectively, P = 0.03). Proliferating endothelial cells were significantly more abundant in infarcted than in normal areas in both MI and MI/bFGF groups, but with no significant differences between the groups. Intraperitoneal administration of bFGF did not cause any untoward extracardiac effects. Thus, systemic bFGF administration following acute MI in rats prevents dilatation of the LV, induces hypertrophy of the non-infarcted myocardium and exerts no untoward effects on extracardiac organs.

Percutaneous multielectrode endocardial mapping during ventricular tachycardia in the swine model

BACKGROUND

Identification of critical areas within the ventricular tachycardia circuit is a prerequisite for catheter ablation. Currently, mapping during ventricular tachycardia, usually performed with standard catheters, is difficult and time-consuming and can be used only in patients with hemodynamically stable tachycardia.

METHODS AND RESULTS

A total of 43 pigs underwent closed-chest induction of myocardial infarction. A basket-shaped catheter carrying 64 electrodes was deployed in the left ventricle during normal sinus rhythm. Unipolar pacing at 3 mA was successful in 78% of the basket catheter electrodes, demonstrating good electrode-tissue contact. Hemodynamic and echocardiographic measurements did not reveal any significant interference with myocardial or valvular function during or after catheter deployment. One hundred eighteen episodes of monomorphic ventricular tachycardia were induced in 28 pigs through right ventricular stimulation, 81 of which were mapped and analyzed. Ventricular tachycardia mapping was rapid, requiring only several beats and < 10 seconds to complete. Presystolic potentials, a possible target for ablation, were identified in 58% of the tachycardia episodes mapped. Pathological examination revealed only minor valvular and endocardial catheter-induced lesions immediately after mapping and none a month later.

CONCLUSIONS

The multielectrode catheter enables rapid and safe percutaneous endocardial mapping of ventricular tachycardia in the swine model. Exploration of the clinical potential of the multielectrode catheter seems warranted.

The effect of low molecular weight heparin (fragmin) on myocardial neutrophil accumulation and infarct size in a rat model of myocardial infarction

BACKGROUND

Heparin molecules possess immunomodulating properties, which are thought to complement their established antithrombotic activity. The purpose of this study was to evaluate whether the antiinflammatory properties of low molecular weight heparin (LMWH) can attenuate polymorphonuclear neutrophil accumulation and infarct size in a rat model of myocardial infarction.

METHODS

Myocardial infarction was induced by ligating the left main coronary artery. LMWH (fragmin 500 anti-FXa u/kg) or vehicle (saline) were administered subcutaneously thirty minutes prior to coronary artery occlusion. Significant anticoagulant activity was attained with LMWH for more than eight hours. Twenty-four hours later, neutrophil accumulation and infarct size were determined by measuring left ventricular free wall myeloperoxidase and residual creatine kinase activity, respectively.

RESULTS

As compared with rats administered vehicle, myeloperoxidase activity was insignificantly decreased in rats treated with LMWH (1.24 +/- 0.28 u/g vs 1.66 +/- 0.15 u/g, P = 0.16. Infarct size was also not significantly different between the groups (62.48 +/- 3.5% and 50.67 +/- 7.2% of left ventricular free wall with vehicle and LMWH, respectively, P = 0.1).

CONCLUSION

The authors conclude that LMWH does not significantly reduce myocardial neutrophil accumulation and infarct size twenty-four hours after myocardial infarction in the rat.

Alteration of lipid profile in hyperlipidemic rabbits by allicin, an active constituent of garlic

BACKGROUND

The effect of garlic on the serum lipid profile has been the subject of controversy. This study was therefore designed to examine the effects of allicin, an active constituent of garlic, on the lipid profile in a rabbit model.

METHODS

Allicin was produced by reacting alliin, synthesized in our laboratory, with purified alliinase. Nineteen New Zealand White rabbits were fed a cholesterol-rich diet (0.25% cholesterol) for 18 weeks. Ten rabbits received freshly produced allicin (3 mg/kg orally) starting at 8 weeks, and nine received placebo. There was no significant difference between the lipid profiles of the two groups at baseline up to 8 weeks.

RESULTS

From day 28 of allicin supplementation a significant difference was found between the allicin and placebo groups in the graph regression lines describing the influence of allicin on serum cholesterol: Y = 41.39 + 8.69 multiplied by day (control) versus Y = -877.24 + 17.67 multiplied by day (allicin). The same trend was found for low-density lipoprotein concentrations: Y = 10.3 + 8.4 multiplied by (control) versus Y = -750.4 + 15.7 multiplied by day (allicin). The serum high-density lipoprotein levels also differed significantly between the groups: Y = 20.29 + 0.24 multiplied by day (control) versus Y = -109.9 + 1.65 multiplied by day (allicin).

CONCLUSIONS

Our results indicate that allicin has a beneficial effect on the serum lipid profile in hyperlipidemic rabbits, and should be further tested clinically.

Exogenous insulin-like growth factor II enhances post-infarction regional myocardial function in swine

OBJECTIVES

Insulin-like growth factor II (IGF-II) promotes cardiac myocyte growth and contractility in vitro. This study was designed to investigate the effect of exogenous IGF-II on regional myocardial function at the area of infarct in the pig.

METHODS

Myocardial infarction was induced in 12 female anaesthetized pigs by affigel blue beads, embolizing microvessels of the left anterior descending coronary artery distribution. In the experimental group (n = 6), IGF-II (0.12 microgram.kg-1 in two animals and 0.6 microgram.kg-1 in four) was incorporated into the beads and delivered by them to the infarct area. Myocardial function was followed echocardiographically, and the excised heart was analysed immunohistochemically and histopathologically.

RESULTS

Myocardial function in injured zones, inversely related to an echocardiographic segmental wall motion score (mean +/- SEM), was similar between the two groups at baseline, but at 4 weeks post-infarction was significantly (P = 0.008) reduced in the control group (0.58 +/- 0.38 vs 3.42 +/- 0.84), in contrast to nearly baseline values in the experimental group (0.58 +/- 0.33 vs 1.17 +/- 0.42, P = 0.41). Cardiac performance in injured segments was significantly better after myocardial injury in the experimental group (P = 0.04). Tissue samples from both groups (4 weeks post-infarction), stained with haematoxylin and eosin demonstrated peri-infarct myocyte hypertrophy, corresponding to regions selectively stained by an antibody for CD56, which highlights growing cardiac myocytes. By image analysis semi-quantification, staining for CD56 was significantly (P = 0.04) higher in the peri-infarct region of the experimental group, as compared with controls (106.5 +/- 2.8 vs 92 +/- 4.4 gray level units). Microvessels stained for von-Willebrand factor were similar in number in both groups (P = 0.8), as were mesenchymal cells stained for vimentin (P = 0.7).

CONCLUSIONS

Exogenous IGF-II, delivered to the infarct area ameliorates regional cardiac function in the pig, perhaps by inducing peri-infarct myocyte growth.

A closed-chest pig model of sustained ventricular tachycardia

The goal of this study was to develop and explore a closed-chest animal model of sustained VT. Seven of 11 domestic pigs had successful induction of myocardial infarction by injection of agarose gel microbeads into the left anterior descending coronary artery through an inflated balloon angioplasty catheter. Four of the first five pigs died and seem to represent a "learning experience." During a 3- to 50-day follow-up period, each pig underwent 1-3 electrophysiological studies. Sustained, monomorphic VT was induced 1-4 times in 5 of the 7 pigs (a total of 19 episodes), was reproducible during the same study in all pigs, and could be repetitively induced during successive studies in some. Ventricular fibrillation was induced less frequently (nine episodes) and was successfully terminated by DC shock in eight episodes. We conclude that a closed-chest pig model of VT is feasible and is associated with a relatively high induction rate of sustained, monomorphic, and reproducible VT and a relatively low mortality rate.

Decreased thickening of normal myocardium with transient increased wall thickness during stress echocardiography with atrial pacing

Stress echocardiography is used increasingly in the evaluation of coronary artery disease. The echocardiographic evaluation of ischemia is based on stress-induced changes in wall motion and wall thickening of the ischemic segments. Studies have demonstrated that left ventricular volumetric changes may induce changes in wall thickness. The aim of the study was to evaluate whether significant changes in ventricular volume, wall thickness, and wall thickening occur during stress echocardiography with atrial pacing. Seven German Landrace female pigs were studied 4 weeks after the induction of a small myocardial infarction. Echocardiographic measurements were conducted in noninfarcted segments on the short-axis view at baseline and during atrial pacing at 120, 150, and 180 beats/min. End-diastolic circumferential area decreased from 12.3 +/- 2.0 cm2 at baseline to 8.9 +/- 1.9 cm2 at 180 beats/min of atrial pacing (p < 0.01). Mean wall thickness (interventricular septal plus posterior wall thickness divided by 2) increased markedly and progressively from 6.7 +/- 0.6 mm at baseline to 9.8 +/- 1.0 mm at 180 beats/min (p < 0.01). The increase in wall thickness correlated inversely with end-diastolic area (r = -0.57; p < 0.01). Percent systolic thickening decreased from 38.9 +/- 12.0 at baseline to 14.9 +/- 7.4 at 180 beats/min of atrial pacing (p < 0.01). The decrease in percent wall thickening correlated with the increase in wall thickness (r = -0.71; p < 0.01). In conclusion, this study shows that a marked increase in wall thickness (pseudohypertrophy) and decrease in percent systolic thickening are observed during rapid atrial pacing in normal myocardium and do not indicate stress-induced left ventricular dysfunction.

The applicability of color-labeled microspheres in a rabbit model of ischemia-reperfusion

This study was designed to examine the ability of color-labeled microspheres to depict different states of myocardial perfusion in a rabbit model of ischemia-reperfusion. A thread was passed under the left anterior descending artery (LAD) and the first left marginal artery of anesthetized New Zealand White rabbits. Blue-labeled microspheres (500/g body wt) were injected into the left atrium. The thread was tightened in rabbits belonging to the experimental group (n = 8), and red-labeled microspheres (500/g body wt) were injected. The snare was loosened, and yellow-labeled microspheres (500/g body wt) were injected before (n = 5) or after (n = 3) methylene blue injection. In animals belonging to the "sham" group (n = 4 and n = 2, respectively), the sequence of injections was similar, but the snare was not tightened. The animals were euthanized, and 0.3-1 g sections were cut from ischemic and nonischemic regions, as determined by methylene blue in the experimental subgroups and from the corresponding regions in the "sham" subgroups. The tissue samples were digested with 4 M KOH, ethanol 70%, and ultrasonication, and the microspheres were recovered by vacuum filtration. The dye was chemically removed from the microspheres, and the photometric absorption of each sample was determined. There was no significant difference between the experimental and "sham" groups in baseline uptake of blue-labeled microspheres. Rabbits belonging to the experimental subgroups had significantly lower mean uptake of red microspheres during ischemia relative to "sham" (0.51 +/- 0.08 vs 1.06 +/- 0.24 and 0.36 +/- 0.19 vs 0.91 +/- 0.12, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Electrical injury in the femoral artery of rabbits as a model for arterial thrombosis: a pilot study

Electrical stimulation was delivered to the femoral artery of 20 rabbits to examine whether endothelial injury results in a consistent formation of arterial thrombosis. The arterial patency was monitored throughout the experiment by flowmeter and was visualized by femoral angiography in 5/20 cases. The arterial segments remained totally occluded in 7/20 (35%), partially occluded in 9/20 (45%), and patent in 4/20 (20%) rabbits following stimulation with 200 microA anodal current for 180 minutes. The average time of electrical stimulation needed to achieve total occlusion (n = 7) was 110 +/- 49 minutes. Alternating occlusion and recanalization of the artery (cyclic flow variation) was observed in 12 rabbits, with total occlusion ensuing in 6/12 cases. Intravenous administration of recombinant tissue-type plasminogen activator (20 micrograms/kg/min for sixty minutes) resulted in femoral reflow and subsequent reocclusion in 2/5 cases. Histopathologic examination disclosed arterial thrombi composed of platelets, fibrin, and red blood cells. Thus, according to these data this technique was found to induce arterial thrombosis following electrical stimulation of the rabbit femoral artery but was inconsistent regarding the arterial patency.

Low molecular weight heparin (Fragmin) prevents early reocclusion following femoral artery thrombolysis with rt-PA in rabbits

The purpose of this study was to evaluate the effect of low molecular weight heparin Fragmin on thrombolysis with tissue-type plasminogen activator (rt-PA) and to compare its effect to that of standard heparin. A rabbit thrombosis model was used, consisting of a blood clot produced in an isolated femoral artery segment with superimposed endothelial damage and distal stenosis. Thirty rabbits were randomized to three treatment groups with rt-PA (30 micrograms.kg-1.min-1 for 60 min and no additional therapy), rt-PA with i.v. standard heparin (200 IU.kg-1 bolus and then 70 IU.kg-1 hourly) and rt-PA with s.c. Fragmin (a single dose of 500 IU.kg-1) prior to rt-PA administration. In six of 10 rabbits given rt-PA only, recanalization was observed which was persistent in three. In eight of 10 rabbits given rt-PA with intravenous heparin, reflow was achieved, which was persistent in three. Fragmin resulted in recanalization in eight of 10 rabbits, with persistent patency in each recanalized rabbit. Reflow time was not shortened with either standard heparin or Fragmin compared with rt-PA alone (64 +/- 41, 56 +/- 18, 50 +/- 23 min respectively), (P = 0.7). Persistent reocclusion after reflow was not observed with Fragmin (0/8) but was present with both standard heparin (5/8, P = 0.03 vs Fragmin) and rt-PA alone (3/6, P = 0.05 vs Fragmin). Thus, in the femoral artery of the rabbit, Fragmin, unlike standard heparin, was found to prevent reocclusion following rt-PA thrombolysis.

Transurethral needle ablation (TUNA) of the prostate using low-level radiofrequency energy: an animal experimental study

Transurethral needle ablation of the canine prostate using low level radiofrequency energy was examined for efficacy and safety in a two-stage experimental study. Eleven mongrel dogs were treated via the bladder neck and prostatic urethra using a specially designed catheter through which needle antennas were advanced into the prostatic tissue. A radiofrequency energy source was connected to the catheter and used to create tissue ablation. In the first 5 dogs this was found to be feasible. Necrotic lesions were created around the needle antennas. Typically, lesions were 1 cm in diameter and conical in shape. The actual size of the lesion was directly related to power level used, time of ablation and length of needle deployment. In the next 6 dogs temperatures were simultaneously measured in the prostatic urethra and rectum. The dogs were sacrificed 0, 2, 2, 14, 28 and 30 days following the experiments and the bladder, prostate and anterior rectal wall were removed en bloc and examined macroscopically and histopathologically for any changes. It was found that urethral temperatures increased to 46.1 degrees C on the average while rectal temperature did not rise during the entire experiment. The lesions found in the prostate were similar to those found in the first 5 dogs. No macroscopic or histopathologic changes were noted at the bladder base, anterior rectal wall or in the distal prostatic urethra. It was concluded that prostatic tissue ablation in the canine model can be achieved safely and could justify the start of human trials.