Rapid clearance of circulating haptoglobin from plasma during acute pulmonary embolism in rats results in HMOX1 up-regulation in peripheral blood leukocytes

Background: Acute pulmonary embolism (PE) causes pulmonary hypertension (PH) via several mechanisms including pulmonary vasospasm. We hypothesize that PE with associated PH leads to alterations in plasma protein concentrations indicative of disease severity and prognosis. Objective: To identify plasma proteins altered in abundance by PE in rats. Methods: Plasma samples were obtained from rats at 2, 6 and 18 h after experimental PE produced with intrajugular injection of polystyrene beads at three different levels of severity (mild, moderate and severe). Total plasma protein was separated using two-dimensional sodium dodecylsulfate-polyacrylamide gel electrophoresis (2D SDS-PAGE) and candidate protein spots altered in expression by PE were identified by mass spectroscopy. Haptoglobin identity and amount was verified by western blot analysis. Results: The PE model produced a dose-dependent increase in right ventricular systolic pressure (RVSP) (mmHg) at 2 h: mild 39 +/- 1.7, moderate 40 +/- 1.8 and severe 51 +/- 1.3 mmHg, coincident with significant increases in free plasma (hemoglobin). Combined 2D SDS-PAGE and Western blot analysis indicated time-and dose-dependant loss of plasma haptoglobin levels in response to acute PE. Haptoglobin (HP) was essentially absent from plasma within 2 h of severe PE. Clearance of HP from plasma was accompanied by increased expression of heme oxygenase-1 (hmox1) in peripheral blood leukocytes and in HMOX1 enzyme activity in the liver. Conclusions: PE that causes pulmonary hypertension is associated with haptoglobin depletion and up-regulation of HMOX1 enzyme.