Elevated cardiac hemoglobin expression is associated with a pro-oxidative and inflammatory environment in primary mitral regurgitation

Abstract

Background: Primary mitral regurgitation (PMR) is associated with oxidative and inflammatory myocardial damage. We reported greater exosome hemoglobin (Hb) in pericardial fluid (PCF) versus plasma, suggesting a cardiac source of Hb.

Objective: Test the hypothesis that Hb is produced in the PMR heart and is associated with increased inflammation.

Methods and results: Hb gene expression for subunits alpha (HBA) and beta (HBB) was assessed in right atria (RA), left atria (LA) and left ventricular (LV) tissue from donor hearts (n = 10) and PMR patient biopsies at surgery (n = 11). PMR patients (n = 22) had PCF and blood collected for macrophage markers, pro-inflammatory cytokines, and matrix metalloproteinases (MMPs). In-situ hybridization for HBA mRNA and immunohistochemistry for Hb-alpha (Hbα) and Hb-beta (Hbβ) protein was performed on PMR tissue.

Results: HBA and HBB genes are significantly increased (>4-fold) in RA, LA, and LV in PMR vs. normal hearts. In PMR tissue, HBA mRNA is expressed in both LV cardiomyocytes and interstitial cells by in-situ hybridization; however, Hbα and Hbβ protein is only expressed in interstitial cells by immunohistochemistry. PCF oxyHb is significantly increased over plasma along with low ratios (<1.0) of haptoglobin:oxyHb and hemopexin:heme supporting a highly oxidative environment. Macrophage chemotactic protein-1, tumor necrosis factor-α, interleukin-6, and MMPs are significantly higher in PCF vs. plasma.

Conclusion: There is increased Hb production in the PMR heart coupled with the inflammatory state of the heart, suggests a myocardial vulnerability of further Hb delivery and/or production during cardiac surgery that could adversely affect LV functional recovery.

Keywords: Haptoglobin; Hemoglobin; Hemopexin; Inflammation; Oxidative stress; Primary mitral regurgitation.