Haptoglobin is an abundant hemoglobin-binding protein present in the plasma. The function of haptoglobin is primarily to determine the fate of hemoglobin released from red blood cells after either intravascular or extravascular hemolysis. There are two common alleles at the Hp genetic locus denoted 1 and 2. There are functional differences between the Hp 1 and Hp 2 protein products in protecting against hemoglobin-driven oxidative stress that appear to have important clinical significance. In particular, individuals with the Hp 2-2 genotype and diabetes mellitus appear to be at significantly higher risk of microvascular and macrovascular complications. A pharmacogenomic strategy of administering high dose antioxidants specifically to Hp 2-2 DM individuals may be clinically effective.

Objective-Clinical trials of vitamin E have failed to demonstrate a decrease in cardiovascular events. However, these studies did not address possible benefit to subgroups with increased oxidative stress. Haptoglobin (Hp), a major antioxidant protein, is a determinant of cardiovascular events in patients with Type 2 diabetes mellitus (DM). The Hp gene is polymorphic with 2 common alleles, 1 and 2. The Hp 2 allelic protein product provides inferior antioxidant protection compared with the Hp 1 allelic product. We sought to test the hypothesis that vitamin E could reduce cardiovascular events in DM individuals with the Hp 2-2 genotype, a subgroup that comprises 2% to 3% of the general population. Methods and Results-1434 DM individuals Ն55 years of age with the Hp 2-2 genotype were randomized to vitamin E (400 U/d) or placebo. The primary composite outcome was myocardial infarction, stroke, and cardiovascular death. At the first evaluation of events, 18 months after initiating the study, the primary outcome was significantly reduced in individuals receiving vitamin E (2.2%) compared with placebo (4.7%; Pϭ0.01) and led to early termination of the study. xtensive preclinical and observational studies showing the apparent benefit from vitamin E in preventing cardiovascular events created an atmosphere in which more than 40% of cardiologists were routinely prescribing high dose vitamin E. 1 Over the past 10 years, several prospective randomized clinical trials have investigated whether vitamin E supplementation provides cardiovascular protection. 2-9 The overwhelming consensus from these studies is that vitamin E supplementation does not provide cardiovascular benefit. 10 -11 To the contrary, meta-analysis of these studies suggests high dose vitamin E supplementation may increase mortality, 12 and several opinion articles have called for a moratorium on prescription of high dose vitamin E supplements. 10 -12 A possible explanation for why these studies failed in spite of solid preclinical data are the inadequate nature of patient selection in these studies. 13 High-dose antioxidant therapy may only provide benefit to individuals who suffer from particularly high levels of oxidative stress. Conclusions-VitaminThe haptoglobin (Hp) genotype may help identify patients with high levels of oxidative stress and who may benefit from antioxidant therapy with vitamin E. 14 The Hp gene is polymorphic with 2 common classes of alleles denoted 1 and 2. 15 We and others have demonstrated that the Hp 2 allele protein product is an inferior antioxidant compared with the Hp 1 allele protein product. 16 -20 These differences in antioxidant protection are profoundly accentuated in the diabetic state resulting in a marked relative increase in oxidative stress in Hp 2 transgenic mice and Hp 2-2 individuals with DM. 16 -20 The distribution of the 3 Hp genotypes in Western societies is approximately 16% Hp 1-1, 36% Hp 2-2, and 48% Hp 2-1. 15 We have demonstrated an interaction between the Hp genotype and DM on the development of cardi...

Abstract-We have recently demonstrated in multiple independent population-based longitudinal and cross sectional analyses that the haptoglobin 2-2 genotype is associated with an increased risk for diabetic cardiovascular disease. The chief function of haptoglobin (Hp) is to bind to hemoglobin and thereby prevent hemoglobin-induced oxidative tissue damage. This antioxidant function of haptoglobin is mediated in part by the ability of haptoglobin to prevent the release of iron from hemoglobin on its binding. We hypothesized that there may be diabetes-and haptoglobin genotypedependent differences in the amount of catalytically active redox active iron derived from hemoglobin. We tested this hypothesis using several complementary approaches both in vitro and in vivo. First, measuring redox active iron associated with haptoglobin-hemoglobin complexes in vitro, we demonstrate a marked increase in redox active iron associated with Hp 2-2-glycohemoglobin complexes. Second, we demonstrate increased oxidative stress in tissue culture cells exposed to haptoglobin 2-2-hemoglobin complexes as opposed to haptoglobin 1-1-hemoglobin complexes, which is inhibitable by desferrioxamine by either a chelation or reduction mechanism. Third, we demonstrate marked diabetes-dependent differences in the amount of redox active iron present in the plasma of mice genetically modified expressing the Hp 2 allele as compared with the Hp 1 allele. Taken together these data implicate redox active iron in the increased susceptibility of individuals with the Hp 2 allele to diabetic vascular disease. Key Words: diabetes Ⅲ oxidative stress Ⅲ iron Ⅲ haptoglobin Ⅲ hemoglobin T he haptoglobin (Hp) gene locus on chromosome 16q22 is polymorphic with two common alleles existing in man, denoted 1 and 2. 1 We have recently established in multiple independent population-based longitudinal and cross sectional studies that the haptoglobin genotype is an independent risk factor for diabetic cardiovascular disease. 2-6 Specifically, we have demonstrated that diabetic individuals homozygous for the haptoglobin 2 allele (Hp 2-2) are at significantly greater risk of developing cardiovascular disease as compared with diabetic individuals homozygous for the haptoglobin 1 allele (Hp 1-1) with an intermediate risk being found in the heterozygote. 3 Haptoglobin is an antioxidant as a direct result of its ability to prevent hemoglobin-driven oxidation. 7 The stoichiometric binding of haptoglobin to hemoglobin not only stabilizes the heme iron moiety in hemoglobin (Hb) 8 but also promotes its scavenging by the CD163 macrophage receptor by receptormediated endocytosis. 9 We have recently demonstrated that the ability of haptoglobin to protect against hemoglobindriven oxidative injury is abrogated when hemoglobin becomes glycated, a process that is markedly accelerated in the diabetic state. 10 Glycohemoglobin-haptoglobin complexes are catalytically redox active and therefore the rate at which haptoglobin-hemoglobin complexes are cleared from the serum and extravascular ...

OBJECTIVE-Pharmacogenomics is a key component of personalized medicine. The Israel Cardiovascular Events Reduction with Vitamin E Study, a prospective placebo-controlled study, recently demonstrated that vitamin E could dramatically reduce CVD in individuals with diabetes and the haptoglobin (Hp) 2-2 genotype (40% of diabetic individuals). However, because of the large number of clinical trials that failed to demonstrate benefit from vitamin E coupled with the lack of a mechanistic explanation for why vitamin E should be beneficial only in diabetic individuals with the Hp 2-2 genotype, enthusiasm for this pharmacogenomic paradigm has been limited. In this study, we sought to provide such a mechanistic explanation based on the hypothesis that the Hp 2-2 genotype and diabetes interact to promote HDL oxidative modification and dysfunction.RESEARCH DESIGN AND METHODS-Hb and lipid peroxides were assessed in HDL isolated from diabetic individuals or mice with the Hp 1-1 or Hp 2-2 genotypes. HDL function was assessed based on its ability to promote cholesterol efflux from macrophages. A crossover placebo-controlled study in Hp 2-2 diabetic humans and in Hp 1-1 and Hp 2-2 diabetic mice assessed the ability of vitamin E to favorably modify these structural and functional parameters.RESULTS-Hb and lipid peroxides associated with HDL were increased and HDL function was impaired in Hp 2-2 diabetic individuals and mice. Vitamin E decreased oxidative modification of HDL and improved HDL function in Hp 2-2 diabetes but had no effect in Hp 1-1 diabetes.CONCLUSIONS-Vitamin E significantly improves the quality of HDL in Hp 2-2 diabetic individuals.