Transvenous procurement of pulmonary artery smooth muscle and endothelial cells using a novel endoarterial biopsy catheter in a canine model

A Bioinformatic Algorithm based on Pulmonary Endoarterial Biopsy for Targeted Pulmonary Arterial Hypertension Therapy

Background

Optimal pharmacological therapy for pulmonary arterial hypertension (PAH) remains unclear, as pathophysiological heterogeneity may affect therapeutic outcomes. A ranking methodology based on pulmonary vascular genetic expression analysis could assist in medication selection and potentially lead to improved prognosis.

Objective

To describe a bioinformatics approach for ranking currently approved pulmonary arterial antihypertensive agents based on gene expression data derived from percutaneous endoarterial biopsies in an animal model of pulmonary hypertension.

Methods

We created a chronic PAH model in Micro Yucatan female swine by surgical anastomosis of the left pulmonary artery to the descending aorta. A baseline catheterization, angiography and pulmonary endoarterial biopsy were performed. We obtained pulmonary vascular biopsy samples by passing a biopsy catheter through a long 8 French sheath, introduced via the carotid artery, into 2- to 3-mm peripheral pulmonary arteries. Serial procedures were performed on days 7, 21, 60, and 180 after surgical anastomosis. RNA microarray studies were performed on the biopsy samples.

Results

Utilizing the medical literature, we developed a list of PAH therapeutic agents, along with a tabulation of genes affected by these agents. The effect on gene expression from pharmacogenomic interactions was used to rank PAH medications at each time point. The ranking process allowed the identification of a theoretical optimum three-medication regimen.

Conclusion

We describe a new potential paradigm in the therapy for PAH, which would include endoarterial biopsy, molecular analysis and tailored pharmacological therapy for patients with PAH.

Assessment of microRNA and gene dysregulation in pulmonary hypertension by endoarterial biopsy

MicroRNAs (miRNAs) may regulate a number of genes, each of which may have a variety of functions. We utilized an endoarterial biopsy catheter to assess the dysregulation of miRNAs in a porcine shunt model of pulmonary hypertension (PH). Two Yucatan micropigs underwent surgical anastomosis of the left pulmonary artery to the descending aorta. Endoarterial biopsy samples were obtained at baseline, and at regular intervals during the progression of PH. RNA, isolated from biopsy samples, was analyzed by Illumina miRNA expression microarrays (containing ∼1200 human miRNAs), Affymetrix Porcine GeneChips, Bioconductor, and GeneSpring. We examined a total of 925 genes in a PH whole genome microarray. Biopsy samples showed that 39 miRNAs were downregulated and 34 miRNAs were upregulated compared to baseline. The number of PH-associated genes reported to be controlled by each of the dysregulated miRNAs was in the range of 1–113. The five miRNAs that had the largest number of PH-associated genes were: miR-548c-3p, miR-520d-3p, miR-130a-5p, miR-30a-3p, and miR-let-7g-3p. Several of the dysregulated miRNAs have been associated with molecular pathways and biologic processes involved in PH. Among 29 miRNAs, which were predicted to be dysregulated by a systems biology approach, we found four that were dysregulated in our porcine shunt model. An endoarterial biopsy technique was successful in showing that a large number of miRNAs are dysregulated in a porcine shunt model of PH. Many of these miRNAs control multiple PH-associated genes, molecular pathways, and biologic processes. Endoarterial biopsy offers potential experimental and clinical diagnostic value.

Challenges in the development of chronic pulmonary hypertension models in large animals

Pulmonary hypertension (PH) results in significant morbidity and mortality. Chronic PH animal models may advance the study of PH's mechanisms, evolution, and therapy. In this report, we describe the challenges and successes in developing three models of chronic PH in large animals: two models (one canine and one swine) utilized repeated infusions of ceramic microspheres into the pulmonary vascular bed, and the third model employed a surgical aorto-pulmonary shunt. In the canine model, seven dogs underwent microsphere infusions that resulted in progressive elevation of pulmonary arterial pressure over a few months. In this model, pulmonary endoarterial tissue was obtained for histology. In the aorto-pulmonary shunt swine model, 17 pigs developed systemic level pulmonary pressures after 2-3 months. In this model, pulmonary endoarterial tissue was sequentially obtained to assess for changes in gene and microRNA expression. In the swine microsphere infusion model, three pigs developed only a modest chronic increase in pulmonary arterial pressure, despite repeated infusions of microspheres (up to 40 in one animal). The main purpose of this model was for vasodilator testing, which was performed successfully immediately after acute microsphere infusions. Chronic PH in large animal models can be successfully created; however, a model's characteristics need to match the investigational goals.

Vascular histomolecular analysis by sequential endoarterial biopsy in a shunt model of pulmonary hypertension

The molecular mechanisms of pulmonary arterial hypertension (PAH) remain ill-defined. The aims of this study were to obtain sequential endoarterial biopsy samples in a surgical porcine model of PAH and assess changes in histology and mRNA expression during the disease progression. Differentially expressed genes were then analyzed as potential pharmacological targets. Four Yucatan micro-pigs underwent surgical anastomosis of the left pulmonary artery to the descending aorta. Endovascular samples were obtained with a biopsy catheter at baseline (before surgery) and from the left lung 7, 60, and 180 days after surgery. RNA was isolated from biopsy samples, amplified and analyzed. Dysregulated genes were linked to drugs with potential to treat or prevent PAH. With the development of PAH in our model, we identified changes in histology and in the expression of several genes with known or investigational inhibitors and several novel genes for PAH. Gene dysregulation displayed time-related variations during disease progression. Endoarterial biopsy provides a new method of assessing pulmonary vascular histology and gene expression in PAH. This analysis could identify novel applications for existing and new PAH drugs. The detection of stage- and disease-specific variation in gene expression could lead to individualized therapies.

Increased expression of endoarterial vascular cell adhesion molecule-1 mRNA in an experimental model of lung transplant rejection: diagnosis by pulmonary arterial biopsy

BACKGROUND

Early detection of rejection after lung transplantation may prevent allograft failure. This study determines if mRNA from the cell adhesion molecules intercellular adhesion molecule-1, vascular cell adhesion molecule (VCAM)-1, and E-selectin in pulmonary endovascular tissue samples could be markers of early rejection.

METHODS

Single left lung transplants were performed in five dogs. Each dog was treated for 2 weeks with immunosuppression, after which rejection was allowed to occur. Percutaneous biopsies from 2- to 3-mm distal branch pulmonary arteries were obtained in each dog from the normal and the transplanted lungs at the end of immunosuppression therapy and periodically (2-4 times) for 1 to 3 weeks until euthanasia. Levels of cell adhesion molecule mRNA in the biopsy samples were quantitated by reverse-transcriptase polymerase chain reaction and normalized to beta-actin mRNA levels.

RESULTS

Between three and five pulmonary endoarterial biopsy samples were obtained from each lung at each catheterization procedure. There was a significant increase in VCAM-1 mRNA levels in the biopsies of the transplanted lungs (which were undergoing rejection) compared with the native right lungs in all dogs. Progressive increases in VCAM-1 mRNA were observed with longer rejection times. VCAM-1 mRNA changes were detected earlier than histologic changes of rejection.

CONCLUSIONS

In pulmonary endoarterial biopsy samples obtained in a canine lung transplant model, there was a progressive increase in VCAM-1 mRNA levels with increasing rejection. Changes in VCAM-1 mRNA were observed earlier than histologic changes of rejection. VCAM-1 quantitation by endoarterial biopsy may be useful in surveillance and early diagnosis of rejection in patients who undergo lung transplantation.

Balloon angioplasty and stenting of multiple intralobar pulmonary arterial stenoses in adult patients

Balloon angioplasty and stent placement for pulmonary arterial stenoses in children are well-established therapies. In contrast, management of isolated peripheral pulmonary arterial stenoses in adults remains relatively unexplored. Four women (ages 18-63 years) with multiple discrete intralobar pulmonary arterial stenoses were treated with balloon angioplasty. Initially, 4-5 stenoses were dilated in each patient. The mean minimum diameter of the stenoses increased from 1.3 to 3.1 mm (P < 0.001), and the mean ratio of right ventricular to aortic systolic pressure decreased from 0.92 to 0.62 (P < 0.05). Each patient had marked symptomatic improvement. However, three patients developed recurrence of symptoms 4-24 months after angioplasty, and two had angiographic evidence of restenosis at previously dilated sites. These restenoses were treated with repeat angioplasty or stent implantation (three stents in each patient). One of these two patients developed near-occlusive restenosis of the stents and had successful bilateral lung transplantation. The other patient had a third catheterization with successful implantation of three additional stents. The third patient with recurrent symptoms died 2 years later, without further intervention. Transcutaneous catheter therapy for multiple intralobar pulmonary arterial stenoses in adults is highly successful acutely, but restenosis is common within several months. For some patients, balloon angioplasty and stent implantation may provide definitive management, while for others these procedures may serve as a bridge to lung transplantation.

Percutaneous pulmonary endoarterial biopsy in an experimental model of pulmonary hypertension

STUDY OBJECTIVES

The aims of this study were: to evaluate the performance of a novel arterial biopsy catheter in obtaining pulmonary endovascular samples in hypertensive dogs; to compare the results of pulmonary endoarterial biopsy in hypertensive vs normotensive dogs; and to assess the histologic changes in the hypertensive model.

DESIGN AND INTERVENTIONS

Thirty-four dogs (27 with normal pulmonary arterial pressures and seven with pulmonary hypertension) were catheterized through an external jugular vein to obtain endovascular biopsy samples from distal pulmonary arteries 2 to 3 mm in luminal diameter. To induce pulmonary hypertension, seven dogs were given repeated infusions of 0.6- to 0.9-mm ceramic microspheres into the superior vena cava. Endoarterial samples were obtained at pulmonary systolic arterial pressures ranging from 10 to 110 mm Hg.

MEASUREMENTS AND RESULTS

Sixty-two biopsy catheterization procedures were performed in the 34 dogs. After 12 initial procedures of technique refinement, endoarterial samples were obtained in each of the last 50 procedures (21 in normotensive dogs and 29 in hypertensive dogs). The average number of endovascular biopsy samples retrieved was 7.1 (range, 2 to 12) from a mean of 8.6 (range, 2 to 15) biopsy attempts per catheterization (success rate=83%). The average biopsy piece measured 1.13 mm in length, 0.33 mm in depth, and up to 1.0 mm in width. The biopsy success rates and endoarterial sample sizes were similar in normotensive and hypertensive dogs. Smooth muscle cells and endothelial cells were grown from the biopsy samples. There were no significant procedural complications, except for one self-limited hemorrhage. Histologically, samples obtained from dogs with pulmonary hypertension showed characteristic changes when compared with biopsies from normotensive dogs.

CONCLUSION

This new endoarterial biopsy catheter was safe and effective when used to obtain pulmonary endoarterial samples in dogs with normal and experimentally elevated pulmonary arterial pressures. The quality and quantity of the biopsy samples allowed identification of pathologic changes.