Effect of the sphingosine kinase 1 selective inhibitor, PF-543 on arterial and cardiac remodelling in a hypoxic model of pulmonary arterial hypertension

Abstract

Recent studies have demonstrated that the expression of sphingosine kinase 1, the enzyme that catalyses formation of the bioactive lipid, sphingosine 1-phosphate, is increased in lungs from patients with pulmonary arterial hypertension. In addition, Sk1−/− mice are protected from hypoxic-induced pulmonary arterial hypertension. Therefore, we assessed the effect of the sphingosine kinase 1 selective inhibitor, PF-543 and a sphingosine kinase 1/ceramide synthase inhibitor, RB-005 on pulmonary and cardiac remodelling in a mouse hypoxic model of pulmonary arterial hypertension. Administration of the potent sphingosine kinase 1 inhibitor, PF-543 in a mouse hypoxic model of pulmonary hypertension had no effect on vascular remodelling but reduced right ventricular hypertrophy. The latter was associated with a significant reduction in cardiomyocyte death. The protection involves a reduction in the expression of p53 (that promotes cardiomyocyte death) and an increase in the expression of anti-oxidant nuclear factor (erythroid-derived 2)-like 2 (Nrf-2). In contrast, RB-005 lacked effects on right ventricular hypertrophy, suggesting that sphingosine kinase 1 inhibition might be nullified by concurrent inhibition of ceramide synthase. Therefore, our findings with PF-543 suggest an important role for sphingosine kinase 1 in the development of hypertrophy in pulmonary arterial hypertension.

Sphingosine Kinase 1: A Potential Therapeutic Target in Pulmonary Arterial Hypertension?

“…These findings are consistent with the observation that the selective and potent SphK1 inhibitor, PF-543 (at nM concentrations) had no effect on vascular remodeling in a mouse hypoxic model of pulmonary hypertension [33]. Of note, chronic Ang-II-induced hypertensive Sphk1 −/− mice exhibit less aortic and mesenteric artery contractility in response to phenylephrine or noradrenaline, suggesting that SphK1 also functions downstream of 1 adrenoceptors [6].…”

“…In addition, RB-005 had no significant inhibitory effect on RVP or vascular remodeling in hypoxic-treated mice [33], suggesting that the failure to remove SphK1 by proteasomal degradation from these hypoxic vessels prevents the inhibitor from reversing or blocking vascular remodeling. In addition, a weak inhibitor of SphK1, such as SKi, has been shown to induce accelerated proteasomal degradation of SphK1 via activation of the proteasome in human prostate cancer cells [7].…”

“…The resistance of SphK1 to 'direct' inducers as seen for RB-005 in hypoxic-treated mice [33], might also occur in other models of pulmonary hypertension, with observed differences in the modulation of vascular remodeling and blood pressure. For example, SphK1 is regulated by acetylation [46] and this can occur at the same lysine residues as ubiquitination.…”

“…In this regard, the basilar artery from Sphk1 Sphk1 is an up-stream regulator of SOC [32]. Intracellular S1P was also reported to mediate an effect on SOC-dependent Ca 2+ influx independently of S1P receptors as the S1P 1/3 receptor antagonist (VPC23019) and S1P 2/4 antagonist (JTE-013) failed to modify the response [33]. Taken together with other findings described above, S1P appears to act both extracellularly (via S1P 2 ) and intracellularly (via SOC) to regulate blood pressure changes.…”

“…This is based on the strong correlation between the concentrations of inhibitor required to induce proteasomal degradation in human PASMC with the K i for inhibition of the catalysis of S1P formation by purified human SphK1 [43]. Another 'direct' SphK1 inhibitor, RB-005 (10 mg/kg i/v) [33] has been found to induce the proteasomal degradation of SphK1 in human PASMC in vitro and in pulmonary vessels from mice (10 mg/kg, i/v) exposed to normoxia, but failed to reduce SphK1 expression in the pulmonary vessels of mice treated with hypoxia for 3 weeks [33].…”