Furegrelate, a thromboxane synthase inhibitor, blunts the development of pulmonary arterial hypertension in neonatal piglets

Abstract

The development of pulmonary arterial hypertension (PAH) in pediatric patients has been linked to the production of the arachidonic acid metabolite, thromboxane A(2) (TxA(2)). The present study evaluated the therapeutic effect of furegrelate sodium, a thromboxane synthase inhibitor, on the development of PAH in a neonatal piglet model. Three-day-old piglets were exposed to 21 days of normoxia (N; 21% F(I)O(2)) or chronic hypoxia (CH; 10% F(I)O(2)). A third group of piglets received the oral TxA(2) synthase inhibitor, furegrelate (3 mg/kg, 2 or 3 times daily) at the induction of CH. In vivo hemodynamics confirmed a 2.55-fold increase of the pulmonary vascular resistance index (PVRI) in CH piglets (104±7 WU) compared to N piglets (40±2 WU). The CH piglets treated twice daily with furegrelate failed to show improved PVRI, but furegrelate three times daily lowered the elevated PVRI in CH piglets by 34% to 69±5 WU and ameliorated the development of right ventricular hypertrophy. Microfocal X-ray computed tomography (CT) scanning was used to estimate the diameter-independent distensibility term, α (% change in diameter per Torr). Pulmonary arterial distensibility in isolated lungs of CH piglets (α=1.0±0.1% per Torr) was lower than that of N piglets (α=1.5±0.1% per Torr) indicative of vascular remodeling. Arterial distensibility was partially restored in furegrelate-treated CH piglets (α =1.2±0.1% per Torr) and microscopic evidence showing muscularization of small pulmonary arteries also was less prominent in these animals. Finally, isolated lungs of furegrelate-treated piglets showed lower basal and vasodilator-induced transpulmonary pressures compared to CH animals. These findings suggest that pharmacological inhibition of TxA(2) synthase activity by furegrelate blunts the development of hypoxia-induced PAH in an established neonatal piglet model primarily by preserving the structural integrity of the pulmonary vasculature.

Keywords: furegrelate; hypoxia; neonatal pulmonary arterial hypertension; pulmonary arterial hypertension; thromboxane A2; thromboxane synthase; vasoconstriction.

Figure 1

(A) Values of resting pulmonary vascular resistance index (PVRI) in neonatal piglets exposed for three weeks to normoxia (N), chronic hypoxia (CH) or chronic hypoxia + furegrelate twice daily (CH + F_BID) or three times daily (CH + F_TID). Sample sizes were 19, 26, 6 and 13, respectively. FNx01Significant difference (P<0.05) from PVRI of N piglets. †Significant difference (P<0.05) from PVRI of CH piglets. (B) Mean arterial pressure (MAP) in the same groups of animals showed no significant difference between groups. Values are mean±S.E.M.

Figure 2

(A) Individual values of 11-dehydro TxB₂, a stable metabolite of TxA₂, in urine samples from neonatal piglets exposed for 3 weeks to normoxia (N), chronic hypoxia (CH) or chronic hypoxia + furegrelate three times daily (CH + F_TID). Each symbol represents a single animal. (B) Average urinary 11-dehydro TxB₂ values for the animals in A. Sample sizes were 8, 6 and 4, respectively. Values are mean±S.E.M.

Figure 3

(A) Computer-generated three-dimensional images of pulmonary arterial trees from neonatal piglets exposed for 3 weeks to normoxia (N), chronic hypoxia (CH) or chronic hypoxia + furegrelate three times daily (CH + F_TID). (B) Comparison of distensibility coefficients between the pulmonary circulations of N, CH and CH + F_TID piglets. Sample sizes were 15, 7 and 6, respectively. *Significant difference (P<0.05) between N and CH. †Significant difference (P<0.05) between CH and CH + F_TID. Values are mean±S.E.M.

Figure 4

(A) Histological sections comparing percent medial thickness (%MT) of small pulmonary arteries in lungs from neonatal piglets exposed for 3 weeks to normoxia (N), chronic hypoxia (CH) or chronic hypoxia + furegrelate three times daily (CH + F_TID). (B) Average %MT values for arteries of N, CH and CH + F_TID piglets. *Significant difference (P<0.05) between N and CH. † = Significant difference (P<0.05) between CH and CH + F_TID. Sample sizes were 103 arteries from 4 piglets (N), 192 arteries from 4 piglets (CH), and 184 arteries from 4 piglets (CH + F_TID). Values are mean±S.E.M.

Figure 5

Resting ∆P_tp in isolated lungs of piglets exposed to normoxia (N), chronic hypoxia (CH) or CH + furegrelate three times daily (CH + F_TID). Lungs were perfused with control (Con) solution before nifedipine (10 μmol/L) and papaverine (15 mg/kg bolus) were added to induce dilation (N+P). *Significant difference (P<0.05) between N and CH piglets for the same measurement. †Significant difference (P<0.05) between CH and CH + F_TID piglets for the same measurement. #Significant difference (P<0.05) between control (Con) and vasodilator challenge (N+P) in the same animal group.