Increased expression of oxidation-specific epitopes and apoptosis are associated with haptoglobin genotype: possible implications for plaque progression in human atherosclerosis.

Abstract

OBJECTIVES:

The purpose of this study was to test the hypothesis that increased oxidative stress is associated with apoptosis in human plaques with the haptoglobin (Hp) 2-2 genotype.

BACKGROUND:

Intraplaque hemorrhage releases free hemoglobin (Hb). Impaired Hb clearance induces oxidative stress leading to plaque progression. The binding of Hp to Hb attenuates iron-induced oxidative reactions.

METHODS:

Twenty-six human aortic plaques were Hp genotyped. Hp2-2 plaques (n = 13) were compared with control (Hp1-1/2-1) (n = 13). The iron grade was measured by Perl's staining. Immunostaining was used to detect oxidation-specific epitopes (OSEs) reflecting oxidized phospholipids and malondialdehyde-like epitopes. The percentages of apoptotic cells and apoptotic morphological features were quantified. DNA fragmentation and active caspase-3 were measured by in situ end-labeling and immunohistochemistry, respectively.

RESULTS:

In Hp2-2 plaques, iron content was increased (1.22 ± 0.15 vs. 0.54 ± 0.08; p < 0.0001) along with expression of oxidized phospholipid- (78.9 ± 5.8 vs. 38.8 ± 3.8; p < 0.0001), and malondialdehyde-like OSEs (93.9 ± 7.9 vs. 54.7 ± 3.9; p < 0.0001). The total percentages of apoptotic cells (11.9 ± 0.44 vs. 3.5 ± 0.28; p < 0.0001), nuclear fragmentation (11.8 ± 0.50 vs. 3.3 ± 0.26; p < 0.0001), nuclear condensation (10.9 ± 0.58 vs. 3.4 ± 0.20; p < 0.0001), chromatin margination (14.2 ± 0.57 vs. 6.5 ± 0.37; p < 0.0001), cytoplasmic blebs (1.6 ± 0.28 vs. 0.8 ± 0.14; p < 0.002), and eosinophilia (10.8 ± 0.74 vs. 4.2 ± 0.27; p < 0.0001) were increased in Hp2-2 plaques. Furthermore, DNA fragmentation (119.9 ± 1.40 vs. 57.5 ± 0.80; p < 0.001), and active caspase-3 density (84.7 ± 7.62 vs. 50.6 ± 7.49; p < 0.004) were increased in Hp2-2 plaques. Logistic regression analysis identified correlation between the percentage of apoptotic cells and the density of OSEs (r = 0.56; p < 0.003).

CONCLUSIONS:

These findings provide insights into genetic predisposition to oxidative stress and the relationship between OSEs and macrophage apoptosis that may explain advanced atherosclerosis in human Hp2-2 plaques.

• Authors: K-Raman Purushothaman, Meerarani Purushothaman, Andrew P Levy, Patrick A Lento, Solene Evrard, Jason C Kovacic, Karen C Briley-Saebo, Sotirios Tsimikas, Joseph L Witztum, Prakash Krishnan, Annapoorna Kini, Zahi A Fayad, Valentin Fuster, Samin K Sharma, Pedro R Moreno
• Journal: Journal of the American College of Cardiology (J Am Coll Cardiol) Vol. 60 Issue 2 Pg. 112-9 (Jul 10 2012) ISSN: 1558-3597 [Electronic] United States
• PMID: 22766337 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
• Copyright: Copyright © 2012 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.

Chemical References

• Epitopes
• Haptoglobins
• Iron
• Caspase 3

Topics

• Aged
• Alleles
• Apoptosis (physiology)
• Caspase 3 (metabolism)
• Coronary Artery Disease (genetics, metabolism)
• DNA Fragmentation
• Disease Progression
• Epitopes (metabolism)
• Female
• Genetic Predisposition to Disease
• Genotype
• Haptoglobins (genetics)
• Humans
• Immunohistochemistry
• Iron (metabolism)
• Macrophages (metabolism)
• Male
• Middle Aged
• Oxidative Stress (genetics)
• Plaque, Atherosclerotic (genetics, metabolism)
• Rupture, Spontaneous