Reverse remodeling of pulmonary arteries by high-dose prostaglandin I₂ therapy: A case report

Abstract

Idiopathic pulmonary arterial hypertension (IPAH) is characterized by pulmonary vascular remodeling. We have reported that high-dose prostaglandin I₂ (PGI₂) therapy markedly improved hemodynamics in IPAH patients and that PGI₂ induced apoptosis of pulmonary artery smooth muscle cells obtained from IPAH patients. PGI₂ is thought to have reverse remodeling effects, although it has not been histologically confirmed. In a case series, we examined the reverse pulmonary vascular remodeling effects of PGI₂ in lung tissues obtained from an IPAH patient treated with high-dose PGI₂ and an IPAH patient not treated with PGI₂. Apoptotic cells were detected in small pulmonary arteries of the IPAH patient treated with high-dose PGI₂ but not in those from the IPAH patient not treated with PGI₂. Media of peripheral pulmonary arteries were thick in the IPAH patient not treated with PGI₂. On the other hand, media of peripheral pulmonary arteries were thin in the IPAH patient treated with high-dose PGI₂. The single case report suggested that high-dose PGI₂ therapy has the potential for reverse pulmonary vascular remodeling by induction of apoptosis and reduction of medial hypertrophy. Accumulation of cases is needed for the application to generalized effect of high-dose PGI₂.

<Learning objective: Reverse pulmonary vascular remodeling would provide further improvement in patients with IPAH. High-dose PGI₂ therapy has the potential for reverse pulmonary vascular remodeling in patients with IPAH.>

Introduction

Idiopathic pulmonary arterial hypertension (IPAH) is characterized by vasoconstriction and vascular remodeling of pulmonary arteries [1]. Reverse remodeling as well as vasodilatation of pulmonary arteries would be desirable in patients with IPAH. We have reported that high-dose intravenous prostaglandin I₂ (PGI₂) therapy (>40 ng/kg/min) resulted in marked reduction in mean pulmonary artery pressure [2] and that PGI₂ induced apoptosis of cultured pulmonary artery smooth muscle cells (PASMCs) obtained from patients with IPAH [3]. These results suggest that high-dose intravenous PGI₂ therapy would reverse pulmonary vascular remodeling by induction of apoptosis in PAH-PASMCs, although it has not been histologically confirmed. We experienced a patient with IPAH who underwent cadaveric lung transplantation (CLT), although his clinical condition and hemodynamics were improved by high-dose intravenous PGI₂ monotherapy. We examined the reverse pulmonary vascular remodeling effects of PGI₂ in lung tissues obtained from patients with IPAH treated with high-dose PGI₂ or not treated with PGI₂.

Materials and methods

Lung tissues were obtained from two patients with IPAH at lung transplantation. As controls, lung tissues were obtained at lung lobectomy from a patient with lung cancer who had no pulmonary hypertension. All human subject protocols were approved by the Human Ethics Committee of Okayama University Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences, and written informed consent was obtained from all patients before the procedure. Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assays were performed on frozen sections with an ApopTag fluorescein in situ apoptosis detection kit (Chemicon International Inc., Temecula, CA, USA). Nuclear morphology was examined by labeling with 4′,6-diamidino-2-phenylindole (DAPI) (0.5 μL/mL). For identification of SMCs, α-smooth muscle actin mouse monoclonal antibody was used. The primary antibody was detected with rabbit anti-mouse immunoglobulin TRITC (DakoCytomation, Glostrup, Denmark). Tissues were analyzed using a fluorescence microscope (LSM5 EXCITER, Carl Zeiss Microimaging Inc., Oberkochen, Germany and Olympus IX71, Olympus Optical Co. Ltd., Tokyo, Japan). Morphometric analysis was performed on Elastica van Gieson-stained sections from paraffin-embedded blocks by standard techniques. Pulmonary arteries of 100–300 μm in external diameter were examined.

Results

A 21-year-old man whose mother had died from pulmonary hypertension (PH) was diagnosed with familial PAH at the age of 9 years and had received intravenous PGI₂ therapy from the age of 16 years. PGI₂ dose had been gradually increased to 115 ng/kg/min over a period of about four years. Although mean pulmonary artery pressure decreased from 106 mmHg to 45 mmHg and symptoms were improved, he received CLT because of the appearance of a donor. In lung tissues obtained from the patient, apoptotic cells were detected in pulmonary arteries of his lung (Fig. 1). We also obtained lung tissues from a patient with IPAH who was not treated with PGI₂ and from a patient with lung cancer. A 28-year-old woman was diagnosed with IPAH at the age of 22 years. Mean pulmonary artery pressure was 60 mmHg and she had received intravenous PGI₂ therapy at the age of 25 years. However, the therapy was discontinued due to interstitial lung disease induced by PGI₂ as previously described [4]. The patient was treated with an endothelin receptor antagonist and phosphodiesterase-5 inhibitor after the interstitial lung disease had been cured. However, mean pulmonary artery pressure was 59 mmHg at the age of 27 years and CLT was performed because of the appearance of a donor. No apoptotic cells were found in lung tissues obtained from the patient who had not received PGI₂ therapy (Fig. 2A) or in lung tissues obtained from the non-PAH patient (Fig. 2B). Media of peripheral pulmonary arteries were thick in a patient with IPAH who had not received PGI₂ therapy (Fig. 2C). On the other hand, media of peripheral pulmonary arteries were thin in a patient with IPAH treated with high-dose PGI₂ (Fig. 3) and a non-PAH patient (Fig. 2D).

Fig. 1.

Pulmonary arteries stained by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay in a patient treated with high-dose prostaglandin I₂. Green is TUNEL-positive. Red is α-smooth muscle actin. Blue is 4′,6-diamidino-2-phenylindole. Bar = 100 μm. Arrows indicated TUNEL-positive cells.

Fig. 2.

Pulmonary arteries stained by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay and Elastica van Gieson staining in a patient not treated with prostaglandin I₂ (PGI₂) and in a non-pulmonary arterial hypertension (PAH) patient. Upper panel: TUNEL assay. Lower panel: Elastica van Gieson staining. (A and C) A 28-year-old woman who had not received PGI₂ therapy. (B and D) A non-PAH patient.

Fig. 3.

Pulmonary arteries stained by Elastica van Gieson staining in a patient treated with high-dose prostaglandin I₂. Arrows indicated the peripheral pulmonary arteries. Media of peripheral pulmonary arteries were thick.

Discussion

The pulmonary vasculature has been analyzed in almost all cases by autopsy in patients who died from progression of PH, and there have been few studies in which the pulmonary vasculature in patients whose clinical condition and hemodynamics improved was analyzed. In the present study, we analyzed the pulmonary vasculature in patients who received high-dose PGI₂ therapy and whose clinical condition and hemodynamics improved. It was histologically confirmed that pulmonary vascular remodeling was reversible in patients with IPAH. Two case reports have shown that reduction in pulmonary flow caused a change in pulmonary vasculature in native lungs of patients with IPAH who had undergone single-lung transplantation 5, 6. Recently, pathological features of PAH patients treated with current medications were reported [7]. No significant differences were detected in medial thickness between patients with IPAH and controls. Thus, current medications for PAH have the potential for reversal of medial hypertrophy. In this study, improvement of hemodynamics, presence of apoptotic cells, and less medial hypertrophy were observed in a patient who received high-dose PGI₂ therapy. These results suggest that high-dose PGI₂ has the potential for reverse pulmonary vascular remodeling by reduction of medial hypertrophy. On the other hand, increased intimal thickness was observed in patients treated with currently recommended medications [7]. Reverse intimal hypertrophy will be a target for therapy of PAH in the future.

We previously reported that PGI₂ at a high concentration (1.0 ng/mL) significantly induced apoptosis of cultured pulmonary artery SMCs obtained from patients with IPAH. However, PGI₂ at a low concentration (0.5 ng/mL) did not significantly induce apoptosis [3]. The dose of PGI₂ at a high concentration fitted to 100 ng/kg/min PGI₂ in clinical settings by calculation from circulating blood volume of 50 kg body weight in humans. Thus, we consider that reverse remodeling of the pulmonary arteries would be a direct effect of high-dose PGI₂.

In this case report, TUNEL-positive cells were stained with antibodies against α-SMA which are markers for SMC and media of peripheral pulmonary arteries were thin in a patient treated with high-dose PGI₂. We previously reported that PGI₂ at a high concentration induced apoptosis of cultured PASMCs obtained from patients with IPAH [3]. Therefore, TUNEL-positive cells have characteristics of PASMCs.

Limitation

Apoptotic cells were detected in only one IPAH patient with high-dose PGI₂ therapy. Accumulation of cases is needed for the application to the generalized effect of high-dose PGI₂.

In conclusion, the single case report suggested that high-dose PGI₂ therapy has the potential for reverse pulmonary vascular remodeling by induction of apoptosis and reduction of medial hypertrophy.

Conflict of interest

Authors declare no conflict of interest.