Background: Pulmonary arterial hypertension (PAH) is a deadly disease characterized by increased pulmonary arterial pressure, vascular occlusion and inflammation. Recently, a robust increase in oxidized lipids have been demonstrated, including 15-hydroxyeicosatetraenoic acids (15HETE), in the lungs and plasma of PAH patients and animal models. We hypothesized that diets rich in 15HETE is sufficient to cause PH in wild type mice. We also examined whether 15HETE or its metabolites are required to cause PH by comparing the effect of 15HETE with 15HETE methyl ester (15HETE-ME), a stable form of 15HETE that is not easily metabolized.
Methods: C57BL/6 male mice were fed for 3 weeks (5μg/day) with 15HETE, 15HETE-ME, or regular chow diet (n=8-21 mice/group). PH development was followed via weekly echocardiography. Right ventricular systolic pressure (RVSP) via direct heart catheterization and RV hypertrophy index were measured. Lung morphology, lipid deposit and inflammation were assessed using H&E, Oil red O staining and RT-qPCR.
Results: Echocardiography revealed the first sign of PH in mice on 15HETE diet after one week and a significant decrease in the pulmonary acceleration time after 2 weeks of treatment (16.6±1.9 vs. 21.2±1.4 msec, p<0.05). Mice on 15HETE diet also had higher RVSP (31.3±1.1 vs. 38.4±2.3 mmHg, p<0.05), which was concomitant with higher RV hypertrophy index (0.26 ± 0.02 vs. 0.33 ±0.02, p<0.05) without any sign of dysfunction (RVFS 35±2 vs. 34±1%). Pulmonary arteriolar thickness was also increased in mice on 15HETE diet compared to regular diet (35.1±0.8 vs 53.4±1%, p<0.05). We also found an infiltration of CD8+ (1±0.1 vs. 1.5±0.14, p<0.05) and CD69+ (1±0.1 vs. 1.6±0.2, p<0.05) cells, demonstrating an activation of CD8+ into cytotoxic T cells. Our new model of PH is not a model of atherosclerosis as there was no plaque in aorta of the mice on 15HETE diet. Finally, mice on 15HETE-ME diet also developed PH as RVSP was higher compared to control (31.3±1.1 vs. 39±3 mmHg, p<0.05), and similar to what was seen in 15HETE, confirming 15HETE itself and not its metabolites is sufficient to cause PH in wild type mice.
Conclusions: we have developed a physiologically relevant animal model to study PH as a consequence of oxidized lipids overload as it occurs in human.