Characterization of Siglec-5 (CD170) expression and functional activity of anti-Siglec-5 antibodies on human phagocytes

OBJECTIVE

The Siglec family of proteins consists of at least 10 members with immunoglobulin and lectin domains and with similar sialic acid-binding properties. Many Siglec family members are expressed on hematopoietic cells and are involved in cell/cell interactions. Some family members are suspected of regulating cellular processes through specific signaling pathways. Monoclonal antibodies were generated against specific epitopes of Siglec-5 (CD170) and were used to determine expression of Siglec-5 on normal blood and marrow cells and cell lines. The antibodies also were used to elucidate functional activity for Siglec-5 on blood neutrophils.

METHODS

Flow cytometry and ELISA were used to determine the specificity of the monoclonal antibodies for Siglec-5 and to determine expression patterns. Chemiluminescence assays were employed to measure the oxidative burst activity of whole blood or purified neutrophils following treatment with the anti-Siglec-5 antibodies.

RESULTS

Cell surface expression analysis demonstrated that the protein was expressed on gated human neutrophil and monocyte populations, both in the blood and bone marrow. Expression on neutrophils was enhanced by one-hour treatment with fMLP or TNF-alpha. Epitope-specific anti-Siglec-5 monoclonal antibodies did not directly activate human neutrophils; however, antibody binding augmented neutrophil oxidative burst activity as determined by fMLP-induced luminol-dependent chemiluminescence.

CONCLUSION

Data demonstrating expression of Siglec-5 on cells of the myelomonocytic lineage and alteration of its expression by inflammatory stimuli suggest a role for this protein in cell/cell interactions following microbial exposure.

Aortomyoplasty counterpulsation: experimental results and early clinical experience

BACKGROUND

Presently the only clinical method of skeletal muscle augmentation of the heart is achieved by wrapping muscle around the cardiac ventricles and then stimulating the muscle to contract synchronously with cardiac systole. Intraaortic balloon counterpulsation provides diastolic counterpulsation in the short-term with the known benefits of increasing diastolic pressure and reducing ventricular afterload. Using protocols already in existence for dynamic cardiomyoplasty we have investigated the long-term use of extraaortic skeletal muscle-powered counterpulsation.

METHODS

In five alpine goats the right latissimus dorsi muscle (LDM) was used to achieve a wrap around the ascending aorta, which had been augmented with an elliptic pericardial patch. Electrostimulation protocols were commenced after 2 weeks and continued for 12 to 24 months. At this time baseline hemodynamic measurements were made with and without stimulation of the LDM. Acute cardiac depression was induced and further measurements were made, again with and without stimulation of the LDM.

RESULTS

Results in the basal state demonstrated improvement in all parameters with stimulation and a 23% increase of the subendocardial viability index. After induction of cardiac depression there was a 52% increase in cardiac output, 39% decrease in systemic vascular resistance, and 27% increase in subendocardial viability index. Histologic studies demonstrated tight adhesion between the aortic wall and the LDM, no dilatation of the aortic wall, and no deleterious effects in the aortic wall of the chronic intermittent constriction. Histochemical staining demonstrated transformation of the muscle fibers of the LDM flap into type 1 oxidative muscle fibers.

CONCLUSIONS

In conclusion, our present study demonstrates that in this animal model aortomyoplasty produces a chronic counterpulsation with preservation of aortic architecture. With induction of heart failure aortomyoplasty provided an effective means of cardiac assistance. The use of the ascending aorta to achieve diastolic counterpulsation may be an efficient use of skeletal muscle energy to augment the heart in selected clinical cases. Early clinical experience is described in this article.

Benefits of aortic and pulmonary counterpulsation using dynamic latissimus dorsi myoplasty

BACKGROUND

Intraaortic and pulmonary artery counterpulsation are useful techniques to support circulation during either left or right ventricular dysfunction. Electrically stimulated skeletal muscles wrapped around the aorta, used as means of cardiac failure treatment, have proved to be an effective method of handling experimental left ventricular failure. In this article we report an induced cardiac failure model in acute open chest dogs and describe the hemodynamic improvement of simultaneous aortic and pulmonary artery counterpulsation.

METHODS

This was achieved with a bilateral latissimus dorsi muscle flap, stimulated with a software written in C++ for Windows. Dynamic aortomyoplasty was performed using the left latissimus dorsi muscle flap around the descending aorta, and dynamic pulmonaromyoplasty was achieved wrapping the pulmonary trunk with the right latissimus dorsi muscle flap. In all animals blood pressures and cardiac output were measured after cardiac failure induced by a high-dose of propranolol hydrochloride (3 mg/kg intravenously) before and after latissimus dorsi muscle flap stimulation.

RESULTS

Aortopulmonary counterpulsation resulted in a significant increase in mean aortic pressure, mean pulmonary pressure, and cardiac output. In addition, a significant decrease was observed in end-diastolic left ventricular pressure, systemic vascular resistance, and pulmonary vascular resistance. Subendocardial viability index (diastolic pressure-time index/systolic tension-time index) in aortomyoplasty and tension time index in pulmonaromyoplasty showed significant improvement when cardiac assistance was performed by electrical stimulation of both muscles (p = 0.037 and p = 0.001, respectively).

CONCLUSIONS

Treatment of experimentally induced cardiac failure using aortopulmonary counterpulsation allows effective hemodynamic improvement in open-chest dogs.

Coronary stenting with a new ultra-short balloon expandable device: early and late animal results

The early and late effects of a new balloon-expandable coronary stent (Boneau II) were studied in 16 adult mongrel dogs. Thirty-three balloon-expandable stents were deployed using standard transfemoral coronary angioplasty technique. Single stents were placed in eight dogs and multiple (two to four) stents were placed in eight dogs. Intravenous heparin (3,000 units) was administered at the beginning of the procedure. Aspirin, dipyridamole, dextran, and warfarin were not administered before or after the procedure. All stent deployments were successful. Angiographic or pathologic examinations were performed within 24 hr of deployment on two of the dogs, at 2 weeks on two of the dogs, at 2 months on three of the dogs, at 6 months on six of the dogs, and at 1 year on three of the dogs. All successfully deployed stents were noted to be widely patent. There was no evidence of side-branch vessel occlusion. There was no evidence of acute or late vessel thrombosis. Histologic examination at 2 months showed a mean intimal thickness of 153 microns. The stainless steel Boneau II coronary stent is relatively short and easily deployed. This balloon-expandable coronary stent was successfully deployed in normal canine arteries without the use of anticoagulation or antiplatelet therapy before or after the procedure. The Boneau II intracoronary stent has a very low thrombogenic potential in dogs.

Assessment of smooth muscle contribution to descending thoracic aortic elastic mechanics in conscious dogs

Early investigators found contradictory evidence that vascular smooth muscle activation reduces the elastic modulus of the arterial wall under isotonic conditions but increases it under isometric conditions, concomitant with increased pulse-wave velocity. We examined the individual contributions of aortic constituents to the elastic modulus of the aortic wall to determine if isobaric analysis produces an accurate assessment of vascular smooth muscle activation. We used a modified Maxwell model assuming an incremental elastic modulus (Einc) composed of the elastic modulus of elastin fibers (EE), the elastic modulus of collagen fibers (EC) affected by the fraction of collagen fibers (fC) recruited to support wall stress, and the elastic modulus of the vascular smooth muscle (ESM) according to the following formula: Einc = EE+EC x fC+ESM.Einc was assessed in eight conscious dogs using descending thoracic aortic pressure (microtransducer) and diameter (sonomicrometry) measurements. Stress-strain relations in the control state and during activation of smooth muscle by continuous administration of phenylephrine (5 micrograms.kg-1 x min-1) were obtained by transient occlusions of the descending aorta and inferior vena cava. Results were as follows: EE was 4.99 +/- 1.58 x 10(6) dynes/cm2 (mean +/- SD), and EC was 965.8 +/- 399.8 x 10(6) dynes/cm2, assessed during the control state. Phenylephrine administration increased the theoretical pulse-wave velocity (Moens-Korteweg equation) from 5.25 +/- 1.03 m/s during the control state to 7.57 +/- 2.53 m/s (P < .005). Active muscle exhibited a unimodal stress-strain curve with a maximum stress of 0.949 +/- 0.57 x 10(6) dynes/cm2 at a corresponding strain value of 1.299 +/- 0.083. The maximum value observed corresponded, on the pressure-diameter curve of the active artery, to a pressure of 234.28 +/- 46.6 mm Hg and a diameter of 17.94 +/- 1.6 mm. The maximum ESM derived from the stress-strain relation of the active muscle was 8.345 +/- 7.56 x 10(6) dynes/cm2 at a strain value of 1.283 +/- 0.079. This point was located at 208.01 +/- 40.8 mm Hg and 17.73 +/- 1.41 mm on the active pressure-diameter curve. During activation of vascular smooth muscle, Einc decreased (P < .05) when plotted against internal pressure but increased (P < .05) when plotted against strain, over the operative range.(ABSTRACT TRUNCATED AT 400 WORDS)

Preventive effect of chronic converting enzyme inhibition on aortic stiffening induced by renovascular hypertension in conscious dogs

OBJECTIVE

The aim was to assess the influence of the renin-angiotensin system on the geometrical and elastic properties of the aorta in conscious dogs, using a model of renovascular hypertension, and to examine the effects of inhibition of the system by the angiotensin converting enzyme inhibitor spirapril.

METHODS

The aortic elastic behaviour in response to renovascular hypertension was studied in 15 conscious dogs instrumented with a pressure microtransducer and a pair of ultrasonic diameter dimension gauges in the upper descending thoracic aorta. Renovascular hypertension was induced by surgical occlusion of one renal artery and stenosis of the other. One day after renal surgery, dogs were randomly assigned to two groups receiving for two months either the new angiotensin converting enzyme inhibitor spirapril (n = 8) or a placebo capsule (n = 7). The two groups of dogs were compared to a control group of normotensive dogs (n = 7). After two months of treatment the elastic properties of the aorta were studied by computation of the beat to beat pressure-diameter hysteresis loops obtained during transient increase of pressure induced by bolus doses of angiotensin. The aortic pressure-diameter (P-D) relationship, obtained over a wide range, was fitted by an exponential fit (P = alpha.e beta D), where beta is the stiffness index. A decomposition of the P-D curve according to a biphasic model of the parallel arrangement of elastin and collagen enabled two pressure-diameter elastic moduli to be obtained, one representing the resistance to stretch at low pressure levels (elastic fibres and smooth muscle), and the other representing the resistance to stretch at the highest pressures (collagen fibres).

RESULTS

The pressure-diameter curve of the placebo group was shifted to the left compared to the curves of the control and spirapril groups, showing that renovascular hypertension was associated with isobaric reduction of aortic diameter. The stiffness index beta was higher (p < 0.05) in the placebo group [0.605(SD 0.304) mm-1] than in either the control group [0.362(0.126) mm-1] or the spirapril group [0.348(0.083) mm-1], suggesting that renovascular hypertension was associated with aortic stiffening. The biphasic analysis showed that the collagen pressure-diameter elastic modulus was unaffected by spirapril, whereas the elastin pressure-diameter elastic modulus was significantly reduced by converting enzyme inhibitor with respect to the placebo (p < 0.05).

CONCLUSIONS

Chronic converting enzyme inhibition by spirapril prevents the isobaric aortic diameter reduction induced by renovascular hypertension in conscious dogs and decreases aortic stiffness, in particular by changing the elastic behaviour of the elastin fibres rather than of the collagen fibres.

Assessment of elastin and collagen contribution to aortic elasticity in conscious dogs

The elastic behavior of total elastin (EE) and collagen (EC) and the recruitment of collagen fibers (FC) supporting wall stress at a given transmural pressure level were assessed in seven conscious dogs using descending thoracic aortic pressure (microtransducer) and diameter (sonomicrometer) measurements. Stress-strain relationships values calculated at control and during bolus administration of angiotensin and nitroglycerin enabled quantification of angiotensin and nitroglycerin enabled quantification of elastic moduli of elastin (EE = 4.868 +/- 1.753 x 10(6) dyn/cm2; means +/- SD) and collagen (EC = 1,306 +/- 637 x 10(6) dyn/cm2) according to a biphasic model of elastin and collagen parallel arrangement. The FC was found to be 6.1 +/- 2.6% at a pressure level of 118 +/- 16 mmHg. Values for EE and EC were similar to those reported in in vitro studies and showed scarce variability. This approach provides a quantitative evaluation of elastin and collagen moduli in conscious animals and also permits the evaluation of FC, which may be of interest in studies of connective tissue diseases involving the aortic wall.