Intramural delivery of agent via a novel drug-delivery sleeve. Histological and functional evaluation

BACKGROUND

The infusion sleeve is a novel drug-delivery catheter system designed to deliver an agent under controlled conditions into the arterial wall at the site of angioplasty. The purpose of the present study was to characterize the delivery agent via the infusion sleeve in ex vivo and in vivo models.

METHODS AND RESULTS

The delivery of horseradish peroxidase via the infusion sleeve was studied in a porcine explanted heart model. Under physiological conditions, arteries underwent balloon injury (approximately 10% overstretch), after which horseradish peroxidase (2.5 mL) was delivered at specific pressures. Cross-sectional analysis demonstrated greater staining when the agent was delivered at increasing pressures. The infusion sleeve was evaluated in an in vivo canine coronary model. With an infusion sleeve loaded over a standard dilatation catheter through a 9F guide, overstretch balloon injury was performed, after which fluoresceinated heparin was delivered. Animals were killed 2 hours after delivery. Fluoresceinated heparin-treated segments demonstrated high fluorescence signals, localizing with smooth muscle cell nuclei with less activity in the interstitium. The functional significance of intramural heparin delivery was studied in a porcine carotid model. In the presence of 111In-labeled platelets, arteries underwent overstretch injury followed by delivery of heparin (50 or 100 units/kg) or vehicle. Platelet deposition was reduced at 30 minutes (57%, P < .01) and 12 hours (39%, P = .06) compared with saline controls.

CONCLUSIONS

Agent delivery via the infusion sleeve is pressure dependent; transmural delivery is possible with minimal disruption of arterial wall architecture; the infusion sleeve is compatible with standard angioplasty equipment; and heparin delivery at the site of balloon injury significantly reduces platelet deposition in a porcine model for a minimum of 12 hours.

A novel nucleotide-based thrombin inhibitor inhibits clot-bound thrombin and reduces arterial platelet thrombus formation

A novel thrombin inhibitor based on single-stranded (ss) deoxynucleotides with the sequence GGTTGGTGTGGTTGG (thrombin aptamer) has been recently discovered. In this study, we tested its efficacy in inhibiting clot-bound thrombin activity and platelet thrombus formation in an ex vivo whole artery angioplasty model. The thrombin aptamer showed a specific dose-dependent inhibition of thrombin-induced platelet aggregation (0.5 U/mL) in human platelet-rich plasma, with an IC50 of approximately 70 to 80 nmol/L. In an in vitro clot-bound thrombin assay system, heparin, used at clinically relevant concentrations of 0.2 U/mL and 0.4 U/mL, was ineffective in inhibiting clot-bound thrombin (6.5% and 34.9% inhibition at 0.2 U/mL and 0.4 U/mL, respectively). In contrast, the thrombin aptamer at an equivalent anticoagulant concentration inhibited clot-bound thrombin (79.7% inhibition). In an ex vivo whole artery angioplasty model, the thrombin aptamer markedly suppressed the generation of fibrinopeptide A (FPA), whereas heparin at 2 U/mL was ineffective. Compared with a scrambled ssDNA control, the thrombin aptamer reduced platelet deposition by 34.5% +/- 5% (mean +/- SEM, n = 4, P = .09) at low shear rates (approximately 200 s-1) and 61.3% +/- 11% (mean +/- SEM, n = 4, P = .05) at high shear rates (approximately 850 s-1). Thrombin aptamers based on ssDNA molecules represent a new class of thrombin inhibitors with potent anticoagulant and antithrombotic properties.

Ultrasonic energy. Effects on vascular function and integrity

BACKGROUND

Ultrasonic energy transmitted via flexible wire probes provides a new means of ablating atherosclerotic plaque. We studied the effects of ultrasonic energy (20 kHz) delivered via a ball-tipped wire probe on arterial vasomotor behavior in rabbit thoracic aortas in a perfused whole-vessel model.

METHODS AND RESULTS

After precontraction with phenylephrine (10(-5) M) or KCl (60 mM), the effects of ultrasonic energy (0.7-5.5 W x 60 seconds, 42-330 J) on arterial vasomotor behavior were measured using long-axis ultrasonic vessel imaging of the proximal (ultrasonic probe-treated) and distal (untreated) control segments. The efficacy of plaque ablation at these same probe-tip power outputs was evaluated in atherosclerotic, human cadaver iliofemoral arteries. Ultrasonic energy caused dose (energy)-dependent relaxation in rabbit aortas after precontraction with phenylephrine in arteries with endothelium (n = 8) and without endothelium (n = 8) (p less than 0.001 versus ultrasound treated at power outputs of 2.9 and 5.5 W). There was no difference in the relaxation dose responses between endothelialized and endothelially denuded segments (p = NS). Ultrasonic energy also caused significant relaxation (67 +/- 8%) after voltage-dependent precontraction with 60 mM KCl. Temperature measurements revealed less than 1 degrees C warming of the vessel wall during as long as 2 minutes of treatment at a power output of 5.5 W. Pathological examination showed no smooth muscle injury at (moderate) power outputs that caused arterial relaxation. At probe-tip power outputs of 2.9-5.5 W, ultrasonic energy recanalized two of two totally occluded cadaveric iliofemoral vessel segments. The ultrasonic ablation catheter was also demonstrated to cause arterial relaxation in a recanalized canine femoral artery in vivo.

CONCLUSIONS

Ultrasonic energy delivered via a flexible-wire probe produces dose-dependent, endothelium-independent smooth muscle relaxation capable of reversing both receptor-mediated and voltage-dependent vasoconstriction in vitro. At moderate power outputs, this relaxation response does not appear to be due to thermal effects or irreversible smooth muscle cell injury. This vasorelaxant effect of ultrasonic energy is also apparent in vivo, at doses that effectively ablate atherosclerotic plaque, and may improve the safety of arterial recanalization using ultrasonic energy.

Roles of thrombin and platelet membrane glycoprotein IIb/IIIa in platelet-subendothelial deposition after angioplasty in an ex vivo whole artery model

BACKGROUND

Platelet deposition at the site of injury caused by balloon angioplasty is associated with acute closure and restenosis.

METHODS AND RESULTS

In a new ex vivo whole artery angioplasty model, we examined the roles of thrombin inhibition with D-Phe-Pro-ArgCH2Cl (PPACK) and inhibition of the platelet membrane fibrinogen receptor glycoprotein IIb/IIIa (GPIIb/IIIa) with monoclonal antibody 7E3 on platelet deposition at the site of balloon injury. Fresh rabbit aortas were mounted in a perfusion chamber. One half of the mounted arterial segment was dilated with a standard angioplasty balloon catheter and the uninjured half served as the control segment. The vessels were perfused with human blood at physiological pressure and shear rates of 180-250 second-1 for 30 minutes. Platelet deposition was measured using 111In-labeled platelets and scanning electron microscopy. With heparin (2 units/ml) anticoagulation, 8.2 +/- 2.2 x 10(6) platelets/cm2 were deposited at the site of balloon injury compared with 0.7 +/- 0.2 x 10(6) platelets/cm2 on uninjured segments (p less than 0.02, n = 7). PPACK was tested at a concentration (10 microM) that totally inhibited platelet aggregation in response to thrombin. 7E3 was tested at a concentration (10 micrograms/ml) that totally inhibited platelet aggregation. Platelet deposition at the site of balloon injury was reduced 47% by PPACK and 70% by 7E3 compared with heparin.

CONCLUSIONS

At shear rates seen in nonstenotic coronary arteries, PPACK and 7E3 are more effective than heparin in reducing platelet deposition at the site of balloon injury. The significant inhibition of platelet deposition by PPACK demonstrates the importance of heparin-resistant thrombin in platelet thrombus formation. The 7E3 results suggest that approximately 70% of platelet deposition at the site of balloon injury is GPIIb/IIIa dependent and that the remaining 30% results from non-GPIIb/IIIa-mediated platelet-subendothelial adhesion. Finally, the ex vivo whole artery system is a useful model for studying platelet-vessel wall interactions under physiologically defined parameters.

Nature of the glomerular capillary injury in human membranous glomerulopathy

A differential solute clearance technique was used to evaluate glomerular capillary wall function in 20 patients with membranous glomerulopathy and massive proteinuria. The clearance of inulin, the filtration fraction, and the fractional clearance of uncharged dextrans of a radius of 28-48 A were depressed significantly below control values in 20 healthy volunteers (P less than 0.01). In contrast, the fractional clearance of dextrans of radius greater than 50 A was elevated markedly. A theoretical model of solute transport that depicts the major portion of the glomerular capillary wall as an isoporous membrane and the minor portion as a nondiscriminatory shunt pathway revealed the calculated glomerular ultrafiltration coefficient to be five times lower and mean pore radius of the major membrane component to be 4 A smaller than control values. However, the fraction of filtrate volume permeating the shunt pathway was three- to fourfold above control values and correlated strongly in individual patients with the fractional clearance of albumin (r = 0.76) and of IgG (r = 0.80). Lowering renal plasma flow by 24% during indomethacin therapy in seven patients resulted in a 74% reduction in proteinuria accompanied by a corresponding diminution of filtrate formed through the shunt pathway. Morphometric analysis of glomerular ultrastructure revealed the magnitude of depression of the glomerular filtration rate and of urinary protein leakage to be related strongly to changes in the epithelial layer of the glomerular capillary wall, but not to the density of subepithelial immune deposits. We conclude that glomerular capillaries in membranous glomerulopathy are characterized by a loss of ultrafiltration capacity and of barrier size-selectivity, and that subepithelial immune deposits do not provide a structural basis for these functional alterations.

Resident characteristics and staff behavior in two hospitals for mentally retarded adults

Results of part of a study aimed at evaluating the implications of different nurse staffing levels were reported. Two samples of 30 patients were observed in the two hospitals and measures were obtained of the proportion of time they were involved in adaptive and maladaptive activities, the frequency with which they interacted in particular ways with the nursing staff, and their Adaptive Behavior Scale scores. When these various measures were examined, we found that those patients who needed more attention received it but not necessarily of the appropriate type. While such results are understandable and even perhaps predictable, they do serve to reveal a situation deserving remedial attention. We in fact suggested that one possible means of countering this tendency to ignore the less attractive patients is for the nursing staff to be assigned much smaller groups of patients than is customary.

Nurses' expectations for accomplishment of mentally retarded patients

As part of a larger study into the pattern of care delivered to hospitalized mentally retarded adults, an attitude survey was undertaken. Factor analysis on questionnaires returned by 696 nurses yielded a three factor solution. One factor, concerned with the expectations that nurses hold of the potential level of patient accomplishment, was examined. Different grades of staff were found to hold significantly different views on a scale ranging from "optimist" to "pessimist". Results from 30 hospitals showed that, after correcting for this grade effect, there were substantial institutional differences.