Haptoglobin Genotype Is a Determinant of Iron, Lipid Peroxidation, and Macrophage Accumulation in the Atherosclerotic Plaque

Abstract

Objective-Intraplaque hemorrhage increases the risk of plaque rupture and thrombosis. The release of hemoglobin (Hb) from extravasated erythrocytes at the site of hemorrhage leads to iron deposition, which may increase oxidation and inflammation in the atherosclerotic plaque. The haptoglobin (Hp) protein is critical for protection against Hb-induced injury. Two common alleles exist at the Hp locus and the Hp 2 allele has been associated with increased risk of myocardial infarction. We have demonstrated decreased anti-oxidative and anti-inflammatory activity for the Hp 2 protein. We tested the hypothesis that the Hp 2-2 genotype is associated with increased oxidative and macrophage accumulation in atherosclerotic plaques. Methods and Results-The murine Hp gene is a type 1 Hp allele. We created a murine type 2 Hp allele and targeted its insertion to the Hp locus by homologous recombination. Atherosclerotic plaques from C57Bl/6 ApoE Ϫ/Ϫ Hp 2-2 mice were associated with increased iron (Pϭ0.008), lipid peroxidation (4-hydroxynonenal and ceroid) and macrophage accumulation (Pϭ0.03) as compared with plaques from C57Bl/6 ApoE Ϫ/Ϫ Hp 1-1 mice. Conclusions-Increased iron, lipid peroxidation and macrophage accumulation in ApoEϪ/Ϫ Hp 2-2 plaques suggests that the Hp genotype plays a critical role in the oxidative and inflammatory response to intraplaque hemorrhage. Key Words: atherosclerotic plaque Ⅲ hemoglobin Ⅲ inflammation Ⅲ iron Ⅲ macrophages T he major cause of acute coronary thrombosis is atherosclerotic plaque rupture and the precursor lesion has been termed the high-risk plaque. [1][2][3][4][5][6] Pathological features of highrisk plaques include a large lipid necrotic core, thin fibrous cap, inflammatory infiltrate, and intraplaque hemorrhage. [1][2][3][4][5][6] Extracorpuscular hemoglobin (Hb) released from red blood cells after intra-plaque hemorrhage represents a potent stimulus for inflammation within the plaque. It is becoming apparent that the frequency of microvascular hemorrhages has been severely underestimated and may occur in up to 40% of all advanced atherosclerotic plaques. 7 An important defense mechanism to counteract the effects of intra-plaque hemorrhage is mediated by haptoglobin (Hp), an abundant serum protein whose primary function is to bind to extracorpuscular Hb, thereby attenuating its oxidative and inflammatory potential. 8 Hp also promotes the clearance of extracorpuscular Hb via the CD163 scavenger receptor present on macrophages. 9 This scavenging pathway is the only mechanism that exists for removing free Hb released at extravascular sites, ie, at sites of hemorrhage within the atherosclerotic plaque.In humans there exist 2 classes of alleles for Hp, designated 1 and 2. The Hp polymorphism is a common polymorphism. In the western world, 16% of the population is Hp 1-1 (homozygous for the Hp 1 allele), 36% is Hp 2-2 (homozygous for the Hp 2 allele), and 48% is Hp 2-1 (heterozygote). 8 The Hp 2 allele is found only in humans. All other mammals, including higher primates have only th...

Age-related Accumulation of Non-heme Ferric and Ferrous Iron in Mouse Ovarian Stroma Visualized by Sensitive Non-heme Iron Histochemistry

“…The characteristics of these cells in aged mouse ovaries were shared with foam cells, which are located in atherosclerotic foci. In foam cells, lipid peroxidation, ceroid accumulation, and autofluorescence have been observed (Lee et al 1998;Shashkin et al 2005;Levy et al 2007). Therefore, we identified the enlarged stromal cells in aged ovaries as macrophages with characteristics of foam cells.…”

Haptoglobin 2-2 Genotype Is Associated with Increased Risk of Type 2 Diabetes Mellitus in Northern Chinese

“…We also propose that the role of Hp in T2DM risk might lies in its ability to act as an antioxidant (Mustafa et al, 2004;Quaye et al, 2006). Free Hb-induced oxidation is more effectively inhibited by Hp1-1 compared with Hp2-2, which has been reported to be a less effective antioxidant in vitro and in vivo (Okazaki and Nagai, 1997;Melamed-Frank et al, 2001;Mustafa et al, 2004;Asleh et al, 2005;Levy et al, 2007;Milman et al, 2008;Nakhoul et al, 2009). With the lower anti-oxidative potential, those with Hp2-2 genotype may therefore have the higher risk for T2DM.…”

“…The dysfunction of endothelial cells is one of the characteristic of early stage type 2 diabetes mellitus (T2DM) (Sjoholm and Nystrom, 2005;Quaye et al, 2006). Thus, Hp functions as an antioxidant and an important vascular endothelial protector by binding Hb and preventing LDL oxidation (Mustafa et al, 2004;Asleh et al, 2005Asleh et al, , 2006Levy et al, 2007Levy et al, , 2010.…”

“…In healthy men, the Hp2-2 type is related to the highest serum iron and ferritin levels compared to other Hp types (Fagoonee et al, 2005). Although each type of Hp protein can bind to free Hb, the Hp1-1 has the highest affinity for free Hb, and is superior to the Hp2-2 protein in neutralizing its oxidative effects (Okazaki and Nagai, 1997;Melamed-Frank et al, 2001;Asleh et al, 2005;Levy et al, 2007;Milman et al, 2008). The functional differences among the Hp types have important biological and clinical consequences.…”

Pharmacogenomic effect of vitamin E on kidney structure and function in transgenic mice with the haptoglobin 2-2 genotype and diabetes mellitus

“…This directly affects the polymeric distribution of the circulating Hp polymers found in the serum of these mice. We recently overcame all of these problems by producing a transgenic mouse with a genetically engineered murine (as opposed to human) Hp 2 allele and targeted insertion of this murine Hp 2 gene to the murine Hp locus by homologous recombination (26). In this study, we report on the use of these mice to study the development and progression of DN.…”