Intensive lifestyle intervention in type 2 diabetes and risk of incident coronary artery disease for the common haptoglobin phenotypes: the Look AHEAD study.

BACKGROUND: Intensive glycemic control reduced coronary artery disease (CAD) events among the Action to Control Cardiovascular Disease Risk in Diabetes (ACCORD) participants with the haptoglobin (Hp) 2-2 phenotype only. It remains unknown whether Hp phenotype modifies the effect of an intensive lifestyle intervention (ILI) on CAD in type 2 diabetes. METHODS: Haptoglobin phenotype was measured in 4542 samples from the Action for Health in Diabetes (Look AHEAD) study. Cox regression models assessed the effect of ILI (focused on weight loss from caloric restriction and physical activity) versus diabetes support and education (DSE) on CAD events in each phenotype group, and within pre-specified subgroups including race/ethnicity, sex, history of cardiovascular disease, diabetes medication use, and diabetes duration. RESULTS: 1590 (35%) participants had the Hp2-2 phenotype. The ILI did not lower glycated hemoglobin (%HbA1c) to < 6.5% in either phenotype, with a peak significant difference between treatment arms of 0.5% [non-Hp2-2] and 0.6% [Hp2-2]. The cumulative CAD incidence was 13.4% and 13.8% in the DSE arm and 12.2% and 13.6% in the ILI arm for non-Hp2-2 and Hp2-2 groups, respectively. Compared to DSE, the ILI was not associated with CAD among participants without (HR = 0.95, 95% CI 0.78-1.17) or with (0.89, 0.68-1.19) the Hp2-2 phenotype (p-interaction between Hp phenotype and ILI = 0.58). After Bonferroni correction, there were no significant results among any subgroups. CONCLUSIONS: Hp phenotype did not modify the effect of the weight loss ILI on risk of CAD in Look AHEAD, potentially because it did not substantially impact glycemic control among participants with or without the Hp2-2 phenotype. Further research is needed to determine if these results are conclusive.

Molecular Insights into IQSEC2 Disease.

Recent insights into IQSEC2 disease are summarized in this review as follows: (1) Exome sequencing of IQSEC2 patient DNA has led to the identification of numerous missense mutations that delineate at least six and possibly seven essential functional domains present in the IQSEC2 gene. (2) Experiments using IQSEC2 transgenic and knockout (KO) mouse models have recapitulated the presence of autistic-like behavior and epileptic seizures in affected animals; however, seizure severity and etiology appear to vary considerably between models. (3) Studies in IQSEC2 KO mice reveal that IQSEC2 is involved in inhibitory as well as stimulatory neurotransmission. The overall picture appears to be that mutated or absent IQSEC2 arrests neuronal development, resulting in immature neuronal networks. Subsequent maturation is aberrant, leading to increased inhibition and reduced neuronal transmission. (4) The levels of Arf6-GTP remain constitutively high in IQSEC2 knockout mice despite the absence of IQSEC2 protein, indicating impaired regulation of the Arf6 guanine nucleotide exchange cycle. (5) A new therapy that has been shown to reduce the seizure burden for the IQSEC2 A350V mutation is heat treatment. Induction of the heat shock response may be responsible for this therapeutic effect.

Daily Brief Heat Therapy Reduces Seizures in A350V IQSEC2 Mice and Is Associated with Correction of AMPA Receptor-Mediated Synaptic Dysfunction.

Purposeful induction of fever for healing, including the treatment of epilepsy, was used over 2000 years ago by Hippocrates. More recently, fever has been demonstrated to rescue behavioral abnormalities in children with autism. However, the mechanism of fever benefit has remained elusive due in large part to the lack of appropriate human disease models recapitulating the fever effect. Pathological mutations in the IQSEC2 gene are frequently seen in children presenting with intellectual disability, autism and epilepsy. We recently described a murine A350V IQSEC2 disease model, which recapitulates important aspects of the human A350V IQSEC2 disease phenotype and the favorable response to a prolonged and sustained rise in body core temperature in a child with the mutation. Our goal has been to use this system to understand the mechanism of fever benefit and then develop drugs that can mimic this effect and reduce IQSEC2-associated morbidity. In this study, we first demonstrate a reduction in seizures in the mouse model following brief periods of heat therapy, similar to what was observed in a child with the mutation. We then show that brief heat therapy is associated with the correction of synaptic dysfunction in neuronal cultures of A350V mice, likely mediated by Arf6-GTP.

IQSEC2 mutation associated with epilepsy, intellectual disability, and autism results in hyperexcitability of patient-derived neurons and deficient synaptic transmission.

Mutations in the IQSEC2 gene are associated with drug-resistant, multifocal infantile and childhood epilepsy; autism; and severe intellectual disability (ID). We used induced pluripotent stem cell (iPSC) technology to obtain hippocampal neurons to investigate the neuropathology of IQSEC2-mediated disease. The neurons were characterized at three-time points during differentiation to assess developmental progression. We showed that immature IQSEC2 mutant dentate gyrus (DG) granule neurons were extremely hyperexcitable, exhibiting increased sodium and potassium currents compared to those of CRISPR-Cas9-corrected isogenic controls, and displayed dysregulation of genes involved in differentiation and development. Immature IQSEC2 mutant cultured neurons exhibited a marked reduction in the number of inhibitory neurons, which contributed further to hyperexcitability. As the mutant neurons aged, they became hypoexcitable, exhibiting reduced sodium and potassium currents and a reduction in the rate of synaptic and network activity, and showed dysregulation of genes involved in synaptic transmission and neuronal differentiation. Mature IQSEC2 mutant neurons were less viable than wild-type mature neurons and had reduced expression of surface AMPA receptors. Our studies provide mechanistic insights into severe infantile epilepsy and neurodevelopmental delay associated with this mutation and present a human model for studying IQSEC2 mutations in vitro.

Housing of A350V IQSEC2 pups at 37 °C ambient temperature prevents seizures and permits the development of social vocalizations in adulthood.

OBJECTIVES: Mutations in the human IQSEC2 gene are associated with drug-resistant epilepsy and severe behavioral dysfunction. We have focused on understanding one human IQSEC2 missense mutation (A350V) for which we have created a corresponding A350V IQSEC2 mouse model by CRISPR which demonstrates seizures when the mice are 15-20 days old and impaired social vocalizations in adulthood. We observed that a child with the A350V mutation stops having seizures when experiencing a fever of greater than 38 °C. In this study, we first sought to determine if we could recapitulate this phenomenon in A350V 15-20 day old mice using a previously established protocol to raise body temperature to 39 °C achieved by housing the mice at 37 °C. We then sought to determine if mice in whom seizure activity had been prevented as pups would develop social vocalization activity in adulthood. METHODS: 15-20 day old A350V male mice were housed either at 37 °C or 22 °C. Ultrasonic vocalizations of these mice were assessed at 8-10 weeks in response to a female stimulus. RESULTS: Housing of 15-20 day old A350V mice at 37 °C resulted in a reduction in lethal seizures to 2% (1/41) compared to 45% (48/108) in mice housed at 22 °C, p = 0.0001. Adult A350V mice who had been housed at 37 °C as pups displayed a significant improvement in the production of social vocalizations. CONCLUSION: Raising the body temperature by raising the ambient temperature might provide a means to reduce seizures associated with the A350V IQSEC2 mutation and thereby allow for an improved neurodevelopmental trajectory.

Haptoglobin Phenotype Is Associated With High-Density Lipoprotein-Bound Hemoglobin Content and Coronary Endothelial Dysfunction in Patients With Mild Nonobstructive Coronary Artery Disease.

Objective- Coronary endothelial dysfunction (ED) is an early stage of atherosclerosis and is associated with impaired high-density lipoprotein (HDL) function. A functional polymorphism at the haptoglobin (Hp) gene locus (rs72294371) has been associated with marked differences in HDL structure and function. We sought to determine whether Hp phenotype was associated with coronary ED and whether the amount of hemoglobin (Hb) tethered to HDL via Hp was Hp-type dependent and associated with ED. Approach and Results- Microvascular and epicardial coronary endothelial function was assessed in 338 individuals with nonobstructive coronary artery disease. Microvascular ED was defined as <50% change in coronary blood flow and epicardial ED as ≥20% decrease in coronary artery diameter after intracoronary acetylcholine infusion. The amount of Hb bound to HDL was measured by ELISA after HDL purification from plasma samples using immune-affinity chromatography. One hundred and seventy of the individuals in this study (50.3%) were diagnosed with microvascular ED, 143 (42.3%) with epicardial ED, and 67 (19.7%) had diabetes mellitus (DM). Hp phenotype was significantly associated with microvascular ( P=0.01) and epicardial ED ( P=0.04) among DM individuals. There was a significant and inverse correlation between the amount of HDL-bound Hb and change in coronary blood flow (r=-0.40; P<0.0001) and in coronary artery diameter (r=-0.44; P<0.0001) in response to acetylcholine infusion. Hb content of HDL was significantly increased in individuals with Hp 2-2 and DM. In a logistic regression model, Hp 2-2 phenotype was associated with microvascular ED (odds ratio, 1.9; P=0.03) and the amount of HDL-bound Hb was an independent predictor of both microvascular (odds ratio, 4.6 for each 1-SD increase; P<0.0001) and epicardial (odds ratio, 2.2; P<0.0001) ED. Conclusions- Hp phenotype is significantly associated with coronary ED in DM individuals. This association is likely related to increased Hb tethering to HDL via Hp 2-2 in DM.

The Role of Haptoglobin Polymorphism in Cardiovascular Disease in the Setting of Diabetes.

Atherosclerotic cardiovascular disease (CVD) is the major cause of morbidity and mortality in individuals with diabetes mellitus (DM). Preclinical models have suggested that excessive oxidative stress and hyperglycemia are directly responsible for this pathological association. However, numerous clinical trials involving the administration of high doses of the antioxidant vitamin E or attempts at strict glycemic control have failed to show a significant reduction of CVD in DM patients. We describe here a possible explanation for the failure of these trials, that being their lack of proper patient selection. The haptoglobin (Hp) genotype is a major determinant of the risk of CVD in the setting of DM. Treatment of individuals with the high-risk Hp genotype with antioxidants or aggressive glycemic control has shown benefit in several small studies. These studies suggest a precision medicine-based approach to preventing diabetes complications. This approach would have a profound effect on the costs of diabetes care and could dramatically reduce morbidity from diabetes.

IQSEC2-Associated Intellectual Disability and Autism.

Mutations in IQSEC2 cause intellectual disability (ID), which is often accompanied by seizures and autism. A number of studies have shown that IQSEC2 is an abundant protein in excitatory synapses and plays an important role in neuronal development as well as synaptic plasticity. Here, we review neuronal IQSEC2 signaling with emphasis on those aspects likely to be involved in autism. IQSEC2 is normally bound to N-methyl-D-aspartate (NMDA)-type glutamate receptors via post synaptic density protein 95 (PSD-95). Activation of NMDA receptors results in calcium ion influx and binding to calmodulin present on the IQSEC2 IQ domain. Calcium/calmodulin induces a conformational change in IQSEC2 leading to activation of the SEC7 catalytic domain. GTP is exchanged for GDP on ADP ribosylation factor 6 (ARF6). Activated ARF6 promotes downregulation of surface α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptors through a c-jun N terminal kinase (JNK)-mediated pathway. NMDA receptors, AMPA receptors, and PSD-95 are all known to be adversely affected in autism. An IQSEC2 transgenic mouse carrying a constitutively active mutation (A350V) shows autistic features and reduced levels of surface AMPA receptor subunit GluA2. Sec7 activity and AMPA receptor recycling are presented as two targets, which may respond to drug treatment in IQSEC2-associated ID and autism.

Interaction Between the Haptoglobin Genotype and Vitamin E on Cardiovascular Disease in Diabetes.

PURPOSE OF REVIEW: Despite compelling evidence regarding the importance of oxidant stress in the development of vascular complications and observational studies suggesting that vitamin E may be protective from these complications, multiple clinical trials have failed to show benefit from vitamin E supplementation in the prevention of vascular complications in diabetes. One possible explanation for this failure of vitamin E may have been inappropriate patient selection. This review seeks to provide the clinical evidence and mechanistic basis for why a subset of individuals defined by their haptoglobin (Hp) genotype may derive cardiovascular protection by vitamin E supplementation. RECENT FINDINGS: Clinical trial data from the HOPE, ICARE, and WHS studies is presented showing a pharmacogenomic interaction between the Hp genotype and vitamin E on the development of CVD. Specifically, in individuals with diabetes and the Hp2-2 genotype, vitamin E has been shown to be associated with an approximately 35% reduction in CVD. Cardioprotection by vitamin E in individuals with the Hp2-2 genotype appears to be mediated in part by an improvement in HDL functionality as demonstrated in three independent trials in both type 1 diabetes and type 2 diabetes. Vitamin E may provide benefit in reducing CVD in Hp2-2 individuals with diabetes. However, in order for this pharmacogenomic algorithm to be accepted as a standard of care and used clinically, an additional large prospective study will need to be performed.

Haptoglobin genotype-dependent differences in macrophage lysosomal oxidative injury.

The major function of the Haptoglobin (Hp) protein is to control trafficking of extracorpuscular hemoglobin (Hb) thru the macrophage CD163 receptor with degradation of the Hb in the lysosome. There is a common copy number polymorphism in the Hp gene (Hp 2 allele) that has been associated with a severalfold increased incidence of atherothrombosis in multiple longitudinal studies. Increased plaque oxidation and apoptotic markers have been observed in Hp 2-2 atherosclerotic plaques, but the mechanism responsible for this finding has not been determined. We proposed that the increased oxidative injury in Hp 2-2 plaques is due to an impaired processing of Hp 2-2-Hb complexes within macrophage lysosomes, thereby resulting in redox active iron accumulation, lysosomal membrane oxidative injury, and macrophage apoptosis. We sought to test this hypothesis in vitro using purified Hp-Hb complex and cells genetically manipulated to express CD163. CD163-mediated endocytosis and lysosomal degradation of Hp-Hb were decreased for Hp 2-2-Hb complexes. Confocal microscopy using lysotropic pH indicator dyes demonstrated that uptake of Hp 2-2-Hb complexes disrupted the lysosomal pH gradient. Cellular fractionation studies of lysosomes isolated from macrophages incubated with Hp 2-2-Hb complexes demonstrated increased lysosomal membrane oxidation and a loss of lysosomal membrane integrity leading to lysosomal enzyme leakage into the cytoplasm. Additionally, markers of apoptosis, DNA fragmentation, and active caspase 3 were increased in macrophages that had endocytosed Hp 2-2-Hb complexes. These data provide novel mechanistic insights into how the Hp genotype regulates lysosomal oxidative stress within macrophages after receptor-mediated endocytosis of Hb.

Conformational analysis of the IQSEC2 protein by statistical thermodynamics.

Mutations in the IQSEC2 gene result in severe intellectual disability, epilepsy and autism. The primary function of IQSEC2 is to serve as a guanine exchange factor (GEF) controlling the activation of ARF6 which in turn mediates membrane trafficking and synaptic connections between neurons. As IQSEC2 is a large intrinsically disordered protein little is known of the structure of the protein and how this influences its function. Understanding this structure and function relationship is critical for the development of novel therapies to treat IQSEC2 disease. We therefore sought to identify IQSEC2 conformers in unfolded and folded states and analyze how conformers differ when binding to ARF6 and thereby influence GEF catalysis. We simulated the folding process of IQSEC2 by accelerated molecular dynamics (aMD). Following the ensemble method of Gibbs, we proposed that the number of microstates in the ensemble replicating a protein macroscopic system is the total number of MD snapshots sampled on the production MD trajectory. We divided the entire range of reaction coordinate into a series of consecutive, non-overlapping bins. Thermal fluctuations of biomolecules in local equilibrium states are Gaussian in form. To predict the free energy and entropy of different conformational states using statistical thermodynamics, the density of states was estimated taking into account how many MD snapshots constitute each conformational state. IQSEC2 dimers derived from the most stable folded and unfolded conformers of IQSEC2 were generated by protein-protein docking and then used to construct IQSEC2-ARF6 encounter complexes. We suggest that IQSEC2 folding and dimerization are two competing processes that may be used by nature to regulate the process of GDP exchange on ARF6 catalyzed by IQSEC2.

Molecular modeling of ARF6 dysregulation caused by mutations in IQSEC2.

IQSEC2 gene mutations are associated with epilepsy, autism, and intellectual disability. The primary function IQSEC2, mediated via its Sec 7 domain, is to act as a guanine nucleotide exchange factor for ARF6. We sought to develop a molecular model, which may explain the aberrant Sec 7 activity on ARF6 of different human IQSEC2 mutations. We integrated experimental data of IQSEC2 mutants with protein structure prediction by the RaptorX server combined with molecular modeling and molecular dynamics simulations. Normally, apocalmodulin (apoCM) binds to IQSEC2 resulting in its N-terminal fragment inhibiting access of its Sec 7 domain to ARF6. An increase in Ca2+ concentration destabilizes the interaction of IQSEC2 with apoCM and removes steric hindrance of Sec 7 binding with ARF6. Mutations at amino acid residue 350 of IQSEC2 result in loss of steric hindrance of Sec 7 binding with ARF6 leading to constitutive activation of ARF6 by Sec 7. On the other hand, a mutation at amino acid residue 359 of IQSEC2 results in constitutive hindrance of Sec 7 binding to ARF6 leading to the loss of the ability of IQSEC2 to activate ARF6. These studies provide a model for dysregulation of IQSEC2 Sec 7 activity by mutant IQSEC2 proteins.Communicated by Ramaswamy H. Sarma.

Haptoglobin phenotype and intensive glycemic control for coronary artery disease risk reduction in people with type two diabetes: The Veterans Affairs Diabetes Trial.

Background: Intensive glycemic control reduced the risk of coronary artery disease (CAD) events among White ACCORD study participants with the haptoglobin (Hp)2-2 phenotype, and not among participants without the Hp2-2 phenotype. It is unknown whether these results persist in a population with more severe diabetes. Methods: Haptoglobin phenotype was measured in 1746 (97 %) samples from the Veterans Affairs Diabetes Trial (VADT) randomized controlled trial. Multivariable-adjusted Cox regression models assessed the effect of intensive therapy on CAD risk among participants with and without the Hp2-2 phenotype separately and when stratified within pre-specified race/ethnicity-based subgroups. Time-varying (achieved) HbA1c data (<7.0 % or ≥8.0 % compared to 7.0-7.9, updated every 3 months) were also analyzed in relation to CAD risk within each phenotype. Results: 567 (32.5 %) participants had the Hp2-2 phenotype. Compared to standard therapy, intensive glycemic control was not associated with risk of CAD among participants with the non-Hp2-2 or the Hp2-2 phenotype or for any race/ethnicity-based group. Compared to HbA1c of 7.0-7.9 %, having HbA1c <7.0 % was not associated with CAD risk for either phenotype or among any race/ethnicity-based group. Having HbA1c ≥8.0 % was associated with an increased risk of CAD among Hispanic participants without the Hp2-2 phenotype (HR= 3.61, 95 % CI: 1.54-8.41, p-interaction=0.53). Conclusion: The effect of intensive glycemic therapy on CAD events was not dependent on Hp phenotype in the VADT study of veterans with severe diabetes who may represent a population where Hp phenotype information would not be useful for personalizing diabetes management. However, further research is needed to determine if these results are conclusive.

Haptoglobin Phenotype and Intensive Glycemic Control for Coronary Artery Disease Risk Reduction in People With Type 2 Diabetes: The ADVANCE Study.

OBJECTIVE: Intensive glycemic control reduced coronary artery disease (CAD) events among the Action to Control Cardiovascular Risk in Diabetes (ACCORD) study participants with the haptoglobin (Hp)2-2 phenotype but not in participants without the Hp2-2 phenotype. It is unknown whether and how these results translate across different demographic/clinical characteristics and treatment strategies. RESEARCH DESIGN AND METHODS: Haptoglobin phenotype was measured in available samples from the Action in Diabetes and Vascular Disease: Preterax and Diamicron MR Controlled Evaluation (ADVANCE) biomarker case-cohort study. Weighted multivariable-adjusted Cox regression models were used to evaluate the association between intensive glycemic control (HbA1c target of ≤6.5%) versus standard therapy (based on local guidelines) and major CAD events among participants with (n = 1,327) and without (n = 2,077) the Hp2-2 phenotype separately and within prespecified stratifications by sex, race, previous cardiovascular disease (CVD), diabetes duration, and HDL-cholesterol. RESULTS: While the hazard ratios (HRs) were in the hypothesized differing directions, compared with standard therapy, intensive glycemic control was not significantly associated with risk of CAD events among participants without (1.04, 95% CI 0.82-1.32) or with (0.84, 0.63-1.14, Pinteraction = 0.27) the Hp2-2 phenotype overall. Intensive therapy was associated with lower CAD risk among participants with the Hp2-2 phenotype who had no previous CVD (0.47, 0.29-0.76, Pinteraction = 0.01). CONCLUSIONS: Our findings suggest that intensive glycemic control contributes to the prevention of major CAD events among ADVANCE participants with the Hp2-2 phenotype and no previous CVD and are in alignment with our hypothesis that intensive glycemic control may be beneficial in a subset of people with the Hp2-2 phenotype.

Vitamin E in the prevention of cardiovascular disease: the importance of proper patient selection.

Vitamin E is a naturally occurring fat-soluble antioxidant which has been proposed as a treatment for both primary and secondary protection against cardiovascular (CV) events. Promising data from observational epidemiological studies associating higher vitamin E dietary intake with lower risk of CV events have not been validated in randomized controlled clinical trials assessing the effect of vitamin E on CV outcomes. While the pendulum of medical opinion has swung to suggest that high dose vitamin E supplements have no place in the treatment and prevention of CV disease, new data is emerging that allows identification of a specific target population for this treatment, namely patients with diabetes mellitus and the haptoglobin genotype 2-2. This review details the scientific basis and clinical evidence related to the effect of vitamin E on CV outcomes, and the importance of proper patient selection in gaining therapeutic benefit from this intervention.

An enzyme linked immunosorbent assay (ELISA) for the determination of the human haptoglobin phenotype.

BACKGROUND: Haptoglobin (Hp) is an abundant serum protein which binds extracorpuscular hemoglobin (Hb). Two alleles exist in humans for the Hp gene, denoted 1 and 2. Diabetic individuals with the Hp 2-2 genotype are at increased risk of developing vascular complications including heart attack, stroke, and kidney disease. Recent evidence shows that treatment with vitamin E can reduce the risk of diabetic vascular complications by as much as 50% in Hp 2-2 individuals. We sought to develop a rapid and accurate test for Hp phenotype (which is 100% concordant with the three major Hp genotypes) to facilitate widespread diagnostic testing as well as prospective clinical trials. METHODS: A monoclonal antibody raised against human Hp was shown to distinguish between the three Hp phenotypes in an enzyme linked immunosorbent assay (ELISA). Hp phenotypes obtained in over 8000 patient samples using this ELISA method were compared with those obtained by polyacrylamide gel electrophoresis or the TaqMan PCR method. RESULTS: Our analysis showed that the sensitivity and specificity of the ELISA test for Hp 2-2 phenotype is 99.0% and 98.1%, respectively. The positive predictive value and the negative predictive value for Hp 2-2 phenotype is 97.5% and 99.3%, respectively. Similar results were obtained for Hp 2-1 and Hp 1-1 phenotypes. In addition, the ELISA was determined to be more sensitive and specific than the TaqMan method. CONCLUSIONS: The Hp ELISA represents a user-friendly, rapid and highly accurate diagnostic tool for determining Hp phenotypes. This test will greatly facilitate the typing of thousands of samples in ongoing clinical studies.

The Relationship Between Time-Varying Achieved HbA1c and Risk of Coronary Events Depends on Haptoglobin Phenotype Among White and Black ACCORD Participants.

OBJECTIVE: Intensive glycemic therapy reduced coronary artery disease (CAD) events among White participants in the Action to Control Cardiovascular Risk in Diabetes (ACCORD) study with the haptoglobin (Hp)2-2 phenotype, while participants without the Hp2-2 phenotype had no CAD benefit. The association between achieved glycated hemoglobin (HbA1c) and CAD for each Hp phenotype remains unknown. RESEARCH DESIGN AND METHODS: Achieved HbA1c was similar in each phenotype throughout the study. Prospectively collected HbA1c data (categorized as <6.0%, 6.0-6.5%, 6.6-6.9%, or ≥8.0% compared with 7.0-7.9%) from the ACCORD study, updated every 4 months over a median of 4.7 years, were analyzed in relation to CAD in the Hp2-2 (n = 3,322) and non-Hp2-2 (n = 5,949) phenotypes separately overall, and within White (63%, 37% Hp2-2) and Black (19%, 26% Hp2-2) participants using Cox proportional hazards regression with time-varying covariables. RESULTS: Compared with HbA1c of 7.0-7.9%, having HbA1c ≥8.0% was associated with CAD risk among White (adjusted HR [aHR] 1.43, 95% CI 1.03-1.98) and Black (2.86, 1.09-7.51) participants with the Hp2-2 phenotype, but not when all Hp2-2 participants were combined overall (1.30, 0.99-1.70), and not among participants without the Hp2-2 phenotype. HbA1c <7.0% was not associated with a lower risk of CAD for any Hp phenotype. CONCLUSIONS: Achieving HbA1c >8.0% compared with 7.0-7.9% was consistently associated with incident CAD risk among White and Black ACCORD participants with the Hp2-2 phenotype, while no association was observed among participants without the Hp2-2 phenotype. We found no evidence that HbA1c concentration <7.0% prevents CAD in either Hp phenotype group.

Relationship Between Time-Varying Achieved High-Density Lipoprotein Cholesterol and Risk of Coronary Events Depends on Haptoglobin Phenotype Within the ACCORD Lipid Study.

Background The Hp (haptoglobin)2-2 phenotype (~40% of people) is associated with dysfunctional high-density lipoprotein (HDL) that is heavily oxidized in hyperglycemia, which may explain why raising HDL-cholesterol (HDL-C) does not reliably prevent coronary artery disease (CAD) in diabetes. Methods and Results In this observational study using longitudinal data from the ACCORD (Action to Control Cardiovascular Risk in Diabetes) lipid trial, time-varying (achieved) HDL-C updated at 4, 8, and 12 months, and annually thereafter over a mean of 4.7 years, was analyzed in relation to risk of CAD and secondary outcomes using Cox proportional hazards regression with time-varying covariables among participants with (n=1781) and without (n=3191) the Hp2-2 phenotype. HDL-C did not differ between the phenotypes throughout the study. Having low HDL-C (<40 mg/dL for male participants and <50 mg/dL for female participants) was associated with a greater risk of CAD compared with non-low HDL-C among participants with the non-Hp2-2 phenotype (hazard ratio [HR], 1.48 [95% CI, 1.18-1.87]) but not among the Hp2-2 phenotype (HR, 0.97 [95% CI, 0.70-1.35]; P interaction=0.03). Similarly, an inverse relationship was observed between HDL-C quintiles and CAD risk among participants without the Hp2-2 phenotype, whereas no significant inverse relationship was observed among participants with the Hp2-2 phenotype (P interaction=0.38). Among the Hp2-2 phenotype group, having low HDL-C was associated with higher risk of CVD mortality (HR, 2.09 [95% CI, 1.05-4.13]), and compared with the lowest HDL-C quintile, higher quintiles were associated with lower risk of CVD mortality and congestive heart failure. Conclusions Hp phenotype modified the association between HDL-C and risk of CAD in the ACCORD lipid study, suggesting that HDL dysfunction in the Hp2-2 phenotype may hinder CAD-protective properties of HDL-C.

Is it time to screen for the haptoglobin genotype to assess the cardiovascular risk profile and vitamin E therapy responsiveness in patients with diabetes?

Diabetes mellitus (DM) carries an increased risk for cardiovascular complications. Haptoglobin (Hp) is an abundant plasma protein with an antioxidant function by virtue of its ability to block the oxidative activity of extracorpuscular hemoglobin. There exist two common functional alleles at the Hp genetic locus, denoted 1 and 2, with three Hp genotypes (Hp 1-1, 2-1, and 2-2). The Hp protein expressed in Hp 2-2 individuals is markedly inferior in protecting against hemoglobin-induced oxidative stress. Hp 2-2 DM individuals have been shown to be at increased risk for the development of diabetes complications, particularly diabetic cardiovascular disease (CVD). We review the biological mechanisms underlying the interaction between the Hp genotype and DM on CVD and the accumulating evidence in favor of Hp genotyping all individuals with DM and providing antioxidant vitamin E supplementation specifically to Hp 2-2 DM individuals to reduce their CVD morbidity and mortality.

Haptoglobin genotype and its role in determining heme-iron mediated vascular disease.

Haptoglobin (Hp) is a hemoglobin (Hb) binding protein whose major function is to prevent heme-iron mediated oxidation. The polymorphic nature of the Hp gene results in varying levels of antioxidant function associated with the protein products. Multiple clinical studies have now determined that the Hp 2-2 genotype is associated with an increased risk of developing vascular complications in patients suffering from diabetes. The mechanism for this phenomenon is a decrease in antioxidant capability associated with the Hp 2-2 protein. Specifically, heme iron associated with the Hp2-2/Hb complex is more redox active than other Hp type complexes and has been shown in a number of systems to lead to increased levels of oxidative stress in the form of oxidized lipids and decreased lipoprotein function. In addition, Hp 2-2/Hb complexes are cleared less efficiently from the circulation, leading to a buildup of iron in the plasma and in tissues. Recent analyses from clinical studies utilizing vitamin E treatment have shown beneficial results specifically in the diabetic Hp 2-2 genotype population. The use of vitamin E in the treatment of Hp 2-2 diabetics has the potential to greatly reduce medical costs and improve quality of life in the ever-growing diabetic population.