Oxidation of low-density lipoprotein by hemoglobin stems from a heme-initiated globin radical: antioxidant role of haptoglobin

HDL dysfunction in diabetes: causes and possible treatments

HDL is known to be inversely correlated with cardiovascular disease due to its diverse antiatherogenic functions. These functions include cholesterol efflux and reverse cholesterol transport, antioxidative and anti-inflammatory activities. However, HDL has been shown to undergo a loss of function in several pathophysiological states, as in the acute phase response, obesity and chronic inflammatory diseases. Some of these diseases were also shown to be associated with increased risk for cardiovascular disease. One such disease that is associated with HDL dysfunction and accelerated atherosclerosis is diabetes mellitus, a disease in which the HDL particle undergoes diverse structural modifications that result in significant changes in its function. This review will summarize the changes that occur in HDL in diabetes mellitus and how these changes lead to HDL dysfunction. Possible treatments for HDL dysfunction are also briefly described.

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.

Lipid rafts and redox regulation of cellular signaling in cholesterol induced atherosclerosis

Redox mediated signaling mechanisms play crucial roles in the pathogenesis of several cardiovascular diseases. Atherosclerosis is one of the most important disorders induced mainly by hypercholesterolemia. Oxidation products and related signaling mechanisms are found within the characteristic biomarkers of atherosclerosis. Several studies have shown that redox signaling via lipid rafts play a significant role in the regulation of pathogenesis of many diseases including atherosclerosis. This review attempts to summarize redox signaling and lipid rafts in hypercholesterolemia induced atherosclerosis.

Methaemalbumin formation in sickle cell disease: effect on oxidative protein modification and HO-1 induction

Normally, cell free haemoglobin is bound by haptoglobin and efficiently cleared. However, the chronic haemolysis in sickle cell disease (SCD) overwhelms haptoglobin binding capacity and protein turnover, resulting in elevated cell free haemoglobin. Cell free haemoglobin acts as both a scavenger of vasoactive nitric oxide and a pro-oxidant. In addition, methaemoglobin (metHb) releases the haem moiety, which can bind to albumin to form methaemalbumin (metHSA). This study used electron paramagnetic resonance to detect metHSA in SCD plasma and demonstrated that haptoglobin prevents haem transfer from metHb to HSA. MetHSA may either provide a second line of defence against haemoglobin/haem-mediated oxidation or contribute to the pro-oxidant environment of SCD plasma. We demonstrated that HSA inhibited oxidative protein modification induced by metHb. Additionally, we showed that while metHb induced haem oxygenase 1 (HO-1), an indicator of oxidative stress, HSA attenuated metHb induction of this enzyme, thereby limiting the potential benefits of HO-1. Furthermore, HO-1 induction by metHSA was less than HO-1 induction by equimolar metHb not bound to albumin. Our findings confirm the presence of metHSA in SCD and suggest that haem transfer from metHb to HSA reduces the oxidative effects of free haemoglobin/haem on endothelium with both beneficial (reduced protein oxidation) and potentially harmful (reduced HO-1 induction) outcomes.

Macrophage infiltration and smooth muscle cells content associated with haptoglobin genotype in human atherosclerotic carotid plaques

We assessed the association between the haptoglobin (Hp) genotype and 2 common indicators of atherosclerotic plaque instability: macrophage infiltration and the smooth muscle cell (SMC) content. A total of 70 consecutive patients who underwent carotid endarterectomy were included in the study. For immunohistochemical study the anti-CD68 and anti-a-actin antibodies were used on adjacent serial sections; 36 plaques from patients with the Hp 1-1 or 2-1 genotype and 34 plaques from patients with the Hp 2-2 genotype were analyzed. The macrophage content (CD68+) was significantly higher in the Hp 2-2 group compared with that in the Hp 1-1 or 2-1 group (P < .001). In plaques from patients with diabetes, the SMC content was significantly lower in the Hp 2-2 group (P = .034). Carotid plaques from diabetic patients with Hp 2-2 genotype had higher macrophage infiltration and lower SMC content. Both parameters are indicators of atherosclerotic plaque instability.

Haemoglobin-induced oxidative stress is associated with both endogenous peroxidase activity and H2O2 generation from polyunsaturated fatty acids

Patients with increased haemolytic haemoglobin (Hb) have 10-20-times greater incidence of cardiovascular mortality. The objective of this study was to evaluate the role of Hb peroxidase activity in LDL oxidation. The role of Hb in lipid peroxidation, H(2)O(2) generation and intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) was assessed using NaN(3), a peroxidase inhibitor, catalase, a H(2)O(2) decomposing enzyme and human umbilical vein endothelial cells (HUVECs), respectively. Hb induced H(2)O(2) production by reacting with LDL, linoleate and cell membrane lipid extracts. Hb-induced LDL oxidation was inhibited by NaN(3) and catalase. Furthermore, Hb stimulated ICAM-1 and VCAM-1 expression, which was inhibited by the antioxidant, probucol. Thus, the present study suggests that the peroxidase activity of Hb produces atherogenic, oxidized LDL and oxidized polyunsaturated fatty acids (PUFAs) in the cell membrane and reactive oxygen species (ROS) formation mediated Hb-induced ICAM-1 and VCAM-1 expression.

The genetics of vascular complications in diabetes mellitus

Prospective identification of which individuals with diabetes mellitus (DM) are at greatest risk for developing cardiovascular disease (CVD) complications would have considerable public health importance by allowing the allocation of limited resources to be focused on those individuals who would most benefit from aggressive intervention. Over the past 20 years genetic disease association studies have demonstrated that polymorphisms at specific genetic loci may identify those individuals at greatest risk for developing CVD in the setting of DM. This article reviews the evidence accumulated to date on four polymorphic loci with the aim of explaining how these polymorphisms modify the risk for CVD in DM by modifying the functional activity of a specific gene. Use of the knowledge of these genetic differences among individuals in targeting drug therapy (pharmacogenomics) is also discussed.

Prediction of diabetic retinopathy: role of oxidative stress and relevance of apoptotic biomarkers

Diabetic retinopathy (DR) is the foremost cause of blindness in working-aged worldwide; it is characterized by vascular and neuronal degeneration. Features of DR include leukocyte adhesion, increased vascular permeability, neovascularization and neuronal cell death. Early diagnosis and intervention are important to prevent or at least ameliorate the development of DR. Recent reports indicate that pathophysiological mechanisms leading to diabetic retinopathy include oxidative stress and retinal cell death cascades. Circulating biomarkers of oxidative stress such as malondialdehyde (MDA), thiobarbituric acid reacting substances (TBARS), conjugated diene (CD), advanced oxidation protein products (AOPP), protein carbonyl, 8-hydroxydeoxyguanosin (8-OHdG), nitrotyrosine, and F(2) isoprostanes and pro-apoptosis molecules (caspase-3, Fas, and Bax) are associated with increased susceptibility to develop DR in diabetic subjects. Thus, identification of oxidative stress and cell death biomarkers in diabetic patients could be in favor of predicting, diagnosis, and prevention of DR, and to target for novel therapeutic interventions.

Hemoglobin can attenuate hydrogen peroxide-induced oxidative stress by acting as an antioxidative peroxidase

Hemoglobin is considered a potentially toxic molecule when released from erythrocytes during hemolysis, inflammation, or tissue injury. The mechanisms of toxicity involve reduced nitric oxide bioavailability and oxidative processes both occurring at the heme prosthetic groups. When the endogenous oxidant H(2)O(2) reacts with Hb, transient radicals are generated during the peroxidative consumption of H(2)O(2). If not neutralized, these radicals can lead to tissue toxicity. The net biologic effect of extracellular Hb in an H(2)O(2)-rich environment will therefore be determined by the balance of H(2)O(2) decomposition (potential protective effect) and radical generation (potential damaging effect). Here we show that Hb can protect different cell types from H(2)O(2)-mediated cell death and the associated depletion of intracellular glutathione and ATP. Importantly, Hb blunts the transcriptional oxidative-stress response induced by H(2)O(2) in human vascular smooth muscle cells (VSMCs). Based on spectrophotometric and quantitative mass spectrometry analysis, we suggested a novel mechanism in which Hb redox-cycles H(2)O(2) and simultaneously internalizes the radical burden, with irreversible structural globin changes starting with specific amino acid oxidation involving the heme proximate betaCys93 and ultimately ending with protein precipitation. Our results suggest that complex interactions determine whether extracellular Hb, under certain circumstances, acts a protective or a damaging factor during peroxidative stress conditions.

Lipoprotein modification and macrophage uptake: role of pathologic cholesterol transport in atherogenesis

Low-density lipoprotein (LDL) is a major extracellular carrier of cholesterol and, as such, plays important physiologic roles in cellular function and regulation of metabolic pathways. However, under pathologic conditions of hyperlipidemia, oxidative stress and/or genetic disorders, specific components of LDL become oxidized or otherwise modified, and the transport of cholesterol by modified LDL is diverted from its physiologic targets toward excessive cholesterol accumulation in macrophages and the formation of macrophage "foam" cells in the vascular wall. This pathologic deposition of modified lipoproteins and the attendant pro-inflammatory reactions in the artery wall lead to the development of atherosclerotic lesions. Continued accumulation of immunogenic modified lipoproteins and a pro-inflammatory milieu result in the progression of atherosclerotic lesions, which may obstruct the arterial lumen and/or eventually rupture and thrombose, causing myocardial infarction or stroke. In this review, we survey mechanisms of LDL modification and macrophage lipoprotein uptake, including results of recent in vivo experiments, and discuss unresolved problems and controversial issues in this growing field. Future directions in studying foam cell formation may include introducing novel animal models, such as hypercholesterolemic zebrafish, enabling dynamic in vivo observation of macrophage lipid uptake.

Neutralization of toxic haem by Porphyromonas gingivalis haemoglobin receptor

Free haem is known to be toxic to organs, tissues and cells. It enhances permeability by binding to a cell membrane, which leads to cell death, and damages lipids, proteins and DNA through the generation of reactive oxygen species. Lysine- and arginine-specific gingipains (Kgp and RgpA/B) are major proteinases that play an important role in the pathogenicity of a black-pigmented periodontopathogen named Porphyromonas gingivalis. One of the adhesin domains of gingipain, HbR could bind haem as an iron nutrient source for P. gingivalis. Using erythrocyte and its membrane as a model, results from the present study demonstrate that recombinant HbR expressed in Escherichia coli could inhibit haem-induced haemolysis, probably through removing haem from the haem-membrane complex and lowering free haem toxicity by mediating dimerization of haem molecules. The ability to protect a cell membrane from haem toxicity is a new function for HbR.

Haptoglobin genotype and endothelial function in diabetes mellitus: a pilot study

Endothelial function (EnF) is impaired in patients with diabetes mellitus (DM) due in large part to an increase in oxidative stress. Haptoglobin (Hp) is a potent antioxidant protein which is encoded by two different alleles (1 and 2) with the Hp 1 protein being a superior antioxidant to the Hp 2 protein. We hypothesized that DM individuals with the Hp 2-2 genotype would have greater endothelial dysfunction as compared to DM individuals with the Hp 1-1 genotype. We studied EnF in 16 Hp 2-2, 14 Hp 1-1 DM individuals and 14 healthy subjects. DM patients' groups were matched in terms of age, cardiovascular risk factors and metabolic characteristics. EnF was assessed using post-ischemic reactive hyperemia and strain gauge plethysmography and expressed either as the maximal flow after the ischemic period or as the area under the flow-time curve (AUC). We showed that EnF indices, AUC and maximal flow, were also higher in the healthy and Hp 1-1 groups compared with Hp 2-2 genotype group (615 +/- 60 and 600 +/- 40 vs. 450 +/- 50 ml dl(-1), 29 +/- 2.6 and 25 +/- 3 vs. 14 +/- 1.8 ml min(-1) dl(-1), P < 0.003 and P < 0.05, for AUC and maximal flow, one-way ANOVA, respectively). We concluded that Hp 2-2 diabetic patients had a worse EnF than controls and Hp 1-1 diabetic subjects.

The reaction of cell-free oxyhemoglobin with nitrite under physiologically relevant conditions: Implications for nitrite-based therapies

Nitric oxide (NO*) participates in the regulation of a wide array of biological processes and its deficit contributes to the severity of many diseases. Recently, a role of NO deficiency that occurs as a result of intravascular hemolysis and increases in levels of cell-free hemoglobin in the pathway of chronic anemic pathologies has been suggested. Experimental evidence for deoxyhemoglobin-catalyzed reduction of nitrite to NO* leads to the possibility of nitrite infusion-based therapies to correct NO* deficits. However, the presence of plasma hemoglobin also raises the possibility of deleterious free radical-mediated oxidative damage from the reaction between nitrite and oxyhemoglobin in the vasculature. We show that the conditions required for the reaction between nitrite and oxyhemoglobin to exhibit free radical-mediated autocatalytic kinetics are highly unlikely to occur in the plasma compartment, even during extensive hemolysis and with pharmacological nitrite doses. Although the presence of haptoglobin enhances the rate of the reaction between nitrite and oxyhemoglobin, common plasma antioxidants-ascorbate and urate, as well as catalase-prevent autocatalysis. Our findings suggest that pharmacological doses of nitrite are unlikely to cause free radical or ferrylhemoglobin formation in plasma originating from the reaction of nitrite with cell-free oxyhemoglobin in vivo.

Pharmacogenomic application of the haptoglobin genotype in the treatment of HDL dysfunction

An emerging paradigm of research has suggested that in the setting of diabetes mellitus (DM) the quality or function of high-density lipoprotein (HDL) may be a determinant of cardiovascular disease risk. Specific structural modifications of HDL protein and lipid components, resulting from oxidative modification, have been proposed to mediate HDL’s loss of the ability to promote cholesterol efflux (reverse cholesterol transport), serve as an antioxidant and anti-inflammatory agent. Therefore, inhibiting HDL oxidative modification would be expected to improve its function and provide cardioprotection. Nevertheless, antioxidant strategies to reduce cardiovascular events from atherosclerosis in DM have failed. It has been proposed that this failure may have been due to the inadequate nature of patient selection. High dose antioxidant therapy may only provide benefit to a subset of DM individuals with oxidatively modified HDL. We will review evidence that haptoglobin (Hp) identifies such individuals who can be successfully treated with vitamin E. These data will suggest that a pharmacogenomic approach utilizing the Hp genotype may be useful in identifying individuals who will benefit from antioxidant therapy.

The effects of genetic and seasonal factors on reproductive success

OBJECTIVE

To search for possible effects of two polymorphisms and of the solar cycle of illumination on reproductive success.

DESIGN

Study of haptoglobin (Hp) and ACP1 polymorphisms in consecutive puerperae and analysis of phenotype distribution in relation to time of conception.

SETTING

The Maternity Department of Penne Hospital, Penne, Italy.

PATIENT(S)

Three hundred sixty-eight consecutive healthy pueperae from the Caucasian population.

RESULT(S)

The distribution of Hp and ACP1 phenotypes depends on the phase of the solar cycle at conception. Women homozygous for Hp with low ACP1 activity are more likely to conceive in the first part of the year. Women heterozygous for Hp with medium-high ACP1 activity are more likely to conceive in the last part of the year.

CONCLUSION(S)

In the first months of the year there is a steady increase in solar illumination, and this phase corresponds to the best period for reproduction in most plants and animals. This period is also the coldest in the Italian latitudes. Although humans are not seasonal breeders, it is possible that women having a genetic background best adapted to the metabolic demand of the cold period of the year will respond better to reproductive stimuli, resulting in a higher probability of conceiving in the first part of the year.

Pharmacogenomics in prevention of diabetic cardiovascular disease: utilization of the haptoglobin genotype in determining benefit from vitamin E

Numerous large clinical trials have been carried out over the past several years testing the ability of the antioxidant vitamin E to prevent diabetic cardiovascular disease. Meta-analysis of these studies has demonstrated that vitamin E does not provide any cardiovascular protection and may be associated with an increase in mortality. However, these studies did not address possible benefit to subgroups with increased oxidative stress. In this review we provide supporting clinical evidence and a mechanistic basis for utilizing a genetic marker, the haptoglobin genotype, in determining whether vitamin E therapy may or may not be beneficial for a given patient with diabetes.

Heme, heme oxygenase, and ferritin: how the vascular endothelium survives (and dies) in an iron-rich environment

Iron-derived reactive oxygen species are involved in the pathogenesis of numerous vascular disorders. One abundant source of redox active iron is heme, which is inherently dangerous when it escapes from its physiologic sites. Here, we present a review of the nature of heme-mediated cytotoxicity and of the strategies by which endothelium manages to protect itself from this clear and present danger. Of all sites in the body, the endothelium may be at greatest risk of exposure to heme. Heme greatly potentiates endothelial cell killing mediated by leukocytes and other sources of reactive oxygen. Heme also promotes the conversion of low-density lipoprotein to cytotoxic oxidized products. Hemoglobin in plasma, when oxidized, transfers heme to endothelium and lipoprotein, thereby enhancing susceptibility to oxidant-mediated injury. As a defense against such stress, endothelial cells upregulate heme oxygenase-1 and ferritin. Heme oxygenase opens the porphyrin ring, producing biliverdin, carbon monoxide, and a most dangerous product-redox active iron. The latter can be effectively controlled by ferritin via sequestration and ferroxidase activity. These homeostatic adjustments have been shown to be effective in the protection of endothelium against the damaging effects of heme and oxidants; lack of adaptation in an iron-rich environment led to extensive endothelial damage in humans.

Role of redox regulation and lipid rafts in macrophages during Ox-LDL-mediated foam cell formation

Hyperlipidemias and small dense LDLs in patients with high-triglyceride low-HDL syndromes lead to a prolonged half life of apoB-containing particles. This is associated with reactive oxygen species (ROS) activation and leads to formation of oxidized LDL (Ox-LDL). Generators of ROS in macrophages (MACs) include myeloperoxidase (MPO)-mediated respiratory burst and raft-associated NADPH-oxidase. The intracellular oxidant milieu is involved in cellular signaling pathways, like ion-transport systems, protein phosphorylation, and gene expression. Lipid oxidation through ROS can amplify foam cell formation through Ox-LDL uptake, leading to formation of ceramide (Cer)-rich lipid membrane microdomains, and is associated with expansion of the lysosomal compartment and an upregulation of ABCA1 and other genes of the AP3 secretory pathway. Ox-LDL may also affect cell-surface turnover of Cer-backbone sphingolipids and apoE-mediated uptake by LRP-family members. In contrast, HDL-mediated lipid efflux causes disruption of lipid membrane microdomains and prevents foam cell formation. Oxidation of HDL through MPO leads to a failure of lipid efflux and enhancement of MAC loading. Therefore, lipid rafts and oxidation processes are important in regulation of MAC foam cell formation and atherosclerosis, and the balance between oxidant and antioxidant intracellular systems is critically important for efficient MAC function.

Purification and characterization of a recombinant rat prohaptoglobin expressed in baculovirus-infected Sf9 insect cells

To generate hemoglobin-free full-length haptoglobin the cDNA encoding rat haptoglobin alphabeta subunits was cloned into shuttle vector pVT-Bac-His and used to produce a recombinant baculovirus Autographa californica Nuclear Polyhedrosis Virus (AcNPV) as an expression vector, named HpAcNPV. Recombinant virus was used to infect Spodoptera frugiperda (Sf9) insect cells. The 50 kDa protein expressed was mostly secreted into the culture medium at relatively high titer (15 microg/mL) and was found to be rat prohaptoglobin having a vector-derived N-terminal extension of 37 amino acids, containing both a hexahistidine tag and an enterokinase recognition sequence. The protein was successfully purified by a three step procedure including nickel-linked agarose and DEAE-Sepharose chromatography steps. Hemoglobin was not detected in the purified preparations. Purified recombinant rat prohaptoglobin protein was also found to be glycosylated, and to be capable of forming a complex with rat hemoglobin in vitro.

Immunochemical property of human haptoglobin phenotypes: determination of plasma haptoglobin using type-matched standards

OBJECTIVES

Haptoglobin (Hp) phenotypes 1-1, 2-1, and 2-2 are associated with inflammatory diseases. Since their biochemical structures are rather heterogeneous, it is necessary to accurately determine the plasma Hp levels.

DESIGN AND METHODS

Immunodiffusion, immunoturbidimetric, and noncompetitive ELISA were conducted to determine the differences in immunoreactivity among Hp phenotypes and to verify that such difference may significantly affect the outcome of Hp determinations. A novel ELISA using phenotype-matched calibrators was performed to compared with a commercial GenWay ELISA kit using a single calibrator in normal healthy males.

RESULTS

In immunodiffusion and immunoturbidimetric assays, the immunoreactivity of Hp 1-1 was markedly higher than 2-1 and 2-2, while an opposite result was observed using an ELISA. The latter was primarily due to the repeated antigenic epitopes in polymeric 2-1 and 2-2. Thus, Hp levels could be significantly over- or underestimated depending on the method. An accurate ELISA could be achieved when using each type-specific Hp calibrator matched to each type subject. We show the mean levels of Hp 1-1 subjects (n=16; 184+/-42 mg/dL) to be significantly and differentially greater than 2-1 (n=28; 153+/-55 mg/dL) (p<0.05) and 2-2 (n=24; 93+/-54 mg/dL) (p<0.01) subjects.

CONCLUSIONS

Due to the diverse immunochemical structure among the Hp types, phenotyping should be performed in all the patients and a type-matched Hp calibrator should be used in clinical Hp determination.

Short Communication: Cellular Localization of Haptoglobin mRNA in the Experimentally Infected Bovine Mammary Gland

Expression of haptoglobin (Hp) mRNA, one of the major acute phase proteins in cattle, was demonstrated in homogenates of the bovine mammary gland. The aim of this study was to localize Hp mRNA expression within the udder at the cellular level during the first 24 h of infection with Escherichia coli. For this purpose, 3 quarters of 3 cows were subsequently inoculated with E. coli at 6, 12, and 24 h preslaughter; the fourth quarter received saline at 24 h preslaughter as a control. After slaughter, tissue samples of each quarter were collected for analyses by in situ hybridization and real-time reverse-transcription PCR. Haptoglobin mRNA expression was allocated to the alveolar epithelium of the mammary gland. Quantification of Hp-positive cells in in situ hybridization of Hp mRNA from tissue homogenates and of Hp protein in milk confirmed increasing concentrations within 24 h of infection.

Methemoglobin--it's not just blue: a concise review

Hemoglobin has functions besides carrying oxygen to the tissues, and regulates vascular tone and inflammation via a redox couple with methemoglobin. Hemoglobin has iron in the reduced valance Fe(II) and methemoglobin has iron in the oxidized valance Fe (III), with a free energy capable of producing water from oxygen. In generating methemoglobin the couple functions as a nitrite reductase. The degree of oxidation of hemoglobin senses the oxygen level in the blood and uses its ability to produce nitric oxide from nitrite to control vascular tone, increasing blood flood when the proportion of oxygenated hemoglobin falls. Additional cardiovascular damage is produced by methemoglobin mediated oxidation of light density lipoproteins, accelerating arteriosclerosis. In addition, the release of heme from methemoglobin is an important factor in inflammation. These physiologic functions are paralleled by the well-described role in the oxidation of various drugs resulting in methemoglobinemia.

Haptoglobin genotype is a regulator of reverse cholesterol transport in diabetes in vitro and in vivo

Two common alleles exist at the haptoglobin (Hp) locus, and the Hp2 allele is associated with an increased incidence of cardiovascular disease, specifically in diabetes mellitus (DM). Oxidative stress is increased in Hp2 mice and humans with DM. Oxidative modification of the apolipoprotein A-I inhibits reverse cholesterol transport. We sought to test the hypothesis that reverse cholesterol transport is impaired in Hp2 DM mice and humans. In vitro, using serum from non-DM and DM individuals, we measured cholesterol efflux from (3)H-cholesterol-labeled macrophages. In vivo, we injected (3)H-cholesterol-loaded macrophages intraperitoneally into non-DM and DM mice with the Hp1-1 or Hp2-2 genotype and monitored (3)H-tracer levels in plasma, liver, and feces. In vitro, in DM individuals only, we observed significantly decreased cholesterol efflux from macrophages incubated with serum from Hp2-1 or Hp2-2 as compared with Hp1-1 individuals (P<0.01). The interaction between Hp type and DM was recapitulated using purified Hp and glycated Hb. In vivo, DM mice loaded with (3)H-cholesterol-labeled macrophages had a 40% reduction in (3)H-cholesterol in plasma, liver, and feces as compared with non-DM mice (P<0.01). The reduction in reverse cholesterol transport associated with DM was significantly greater in Hp2-2 mice as compared with Hp1-1 mice (54% versus 25% in plasma; 52% versus 27% in liver; 57% versus 32% in feces; P<0.03). reverse cholesterol transport is decreased in Hp2-2 DM. This may explain in part the increased atherosclerotic burden found in Hp2-2 DM individuals.

Application of pharmacogenomics in the prevention of diabetic cardiovascular disease: Mechanistic basis and clinical evidence for utilization of the haptoglobin genotype in determining benefit from antioxidant therapy

Atherosclerotic cardiovascular disease (CVD) and diabetic vascular disease have been associated with an increase in oxidative stress. Mechanistic studies in vitro and in animals have demonstrated a direct role for oxidatively modified protein and lipid molecules in the pathophysiology of these diseases. As a result of this oxidation hypothesis numerous studies have been carried out over the past 5-10 years testing the ability of antioxidant vitamins to decrease the incidence of these diseases. The general consensus from these studies, involving over 200,000 individuals, has been that antioxidant vitamins do not provide any vascular protection. Moreover, several of these studies have demonstrated that antioxidant supplementation may be associated with an increased incidence of disease and mortality. One reason why these antioxidant vitamins may have failed to demonstrate benefit may have been due to inappropriate patient selection. In this review we provide supporting clinical evidence and a mechanistic basis for utilizing a genetic marker, the haptoglobin (Hp) genotype, in determining whether antioxidant vitamin therapy may or may not be beneficial for a given patient with diabetes.

Inflammation inhibitors were remarkably up-regulated in plasma of severe acute respiratory syndrome patients at progressive phase

Severe acute respiratory syndrome (SARS) is a severe infectious disease that has affected many countries and regions since 2002. A novel member of the coronavirus, SARS‐CoV, has been identified as the causative agent. However, the pathogenesis of SARS is still elusive. In this study, we used 2‐D DIGE and MS to analyze the protein profiles of plasma from SARS patients, in the search for proteomic alterations associated with the disease progression, which could provide some clues to the pathogenesis. To enrich the low‐abundance proteins in human plasma, two highly abundant proteins, albumin and IgG, were first removed. By comparing the plasma proteins of SARS patients with those of a normal control group, several proteins with a significant alteration were found. The up‐regulated proteins were identified as alpha‐1 acid glycoprotein, haptoglobin, alpha‐1 anti‐chymotrypsin and fetuin. The down‐regulated proteins were apolipoprotein A‐I, transferrin and transthyretin. Most of the proteins showed significant changes (up‐ or down‐regulated) in the progressive phase of disease, and there was a trend back to normal level during the convalescent phase. Among these proteins, the alterations of fetuin and anti‐chymotrypsin were further confirmed by Western blotting. Since all the up‐regulated proteins identified above are well‐known inflammation inhibitors, these results strongly suggest that the body starts inflammation inhibition to sustain the inflammatory response balance in the progression of SARS.

Influence of human haptoglobin polymorphism on oxidative stress induced by free hemoglobin on red blood cells

BACKGROUND

An in vitro study was conducted to determine whether haptoglobin phenotypes differed in their protective effect against oxidative stress induced by extracellular hemoglobin on red blood cells.

METHODS

Conjugated dienes and thiobarbituric acid-reactive substances (TBARS) were determined in human red blood cell membranes in the presence of hemoglobin and various concentrations of each type of purified haptoglobin. In addition, the release of K+ and lactate dehydrogenase from red blood cells was measured.

RESULTS

A protective effect of haptoglobin was observed in terms of results obtained for the four parameters examined, with significant differences (p<0.001) between the three haptoglobin types; type 1-1 was the most active and type 2-2 the least active. A proportion of oxidative damage was not sensitive to haptoglobin, but to desferrioxamine (an iron chelator), indicating the participation of two actors, hemoglobin and free iron, in the oxidative stress of membrane lipids.

CONCLUSIONS

The antioxidant role of haptoglobin and the phenotype dependence were confirmed for preventing possible oxidative damage induced by free hemoglobin and iron release during its catabolism.

Present status of outcome prediction of invasive coronary treatment by using genetic markers

A growing number of studies suggest that the outcome after invasive coronary treatment may be in part genetically determined. Here, we review the present status of outcome prediction of invasive coronary treatments by using genetic markers. Although some studies found an association between one or another genetic marker with one or another clinical endpoint, many other studies found no such relations; to date, none of the genetic markers that have been investigated in association studies are used in routine clinical practice to prospectively assess the prognosis following invasive coronary treatment or to decide upon therapeutic strategies. Many associations between genetic markers and certain clinical endpoints were initially reported in small studies but could not be confirmed in larger ones. Some of these discrepancies may be explained by publication bias. Some genetic variants may have true effects on clinical endpoints, which, albeit biologically interesting, do not bear much clinical relevance. On the other hand, many-if not most-studies that have been published to date are more or less grossly underpowered and very rarely report on the results of an a priori power analysis. Thus, there is still a need for further high-quality studies designed to investigate the specific contribution of genetic factors to the outcome after invasive coronary interventions.

Hemodialysis reduces inhibitory effect of plasma ultrafiltrate on LDL oxidation and subsequent endothelial reactions

Oxidative modification of low-density lipoprotein (LDL) and its deleterious effect on endothelium is implicated in the pathogenesis of atherosclerosis. Endothelium responds to such an insult by upregulating the synthesis of heme oxygenase-1 (HO-1) and ferritin. Endothelial cell damage and dysfunction have been observed in patients with chronic kidney disease (CKD) on maintenance hemodialysis (HD). We studied the effect of low-molecular-weight components of uremic plasma on LDL oxidation and LDL-oxidation-provoked endothelial cell reactions, such as the induction of cytotoxicity and the upregulation of cell-protective HO-1 and ferritin. Plasma ultrafiltrate (molecular weight<5000 Da) from CKD patients on HD or when treated conservatively exhibited a pronounced inhibition on heme-mediated oxidative modification of LDL. Endothelial cell cytotoxicity provoked by LDL oxidation was also attenuated by plasma ultrafiltrate from CKD patients. During HD treatment, a dramatic drop occurred in the retardation of oxidative reactions, and a loss of endothelial cytoprotection exerted by plasma ultrafiltrate was noted. The upregulation of HO-1 and ferritin in response to oxidative stress of LDL was blunted by uremic plasma ultrafiltrate that was released by the end of HD. The decreased antioxidant capacity of ultrafiltrate after HD occurred as a consequence of the intradialytic removal of L-ascorbic acid, uric acid, bilirubin, 3-indoxyl sulfate, indoxyl-beta-D-glucuronide, p-cresol, and phenol. Intradialytic removal of L-ascorbic acid, uric acid, bilirubin, 3-indoxyl sulfate, indoxyl-beta-D-glucuronide, p-cresol, and phenol increases the risk of LDL oxidation and subsequent endothelial cell damage, which underlines the importance of activation of cytoprotective HO-1 and ferritin in endothelium.

Heme, heme oxygenase and ferritin in vascular endothelial cell injury

Iron-derived reactive oxygen species are implicated in the pathogenesis of numerous vascular disorders including atherosclerosis, microangiopathic hemolytic anemia, vasculitis, and reperfusion injury. One abundant source of redox active iron is heme, which is inherently dangerous when released from intracellular heme proteins. The present review concerns the involvement of heme in vascular endothelial cell damage and the strategies used by endothelium to minimize such damage. Exposure of endothelium to heme greatly potentiates cell killing mediated by polymorphonuclear leukocytes and other sources of reactive oxygen. Free heme also promotes the conversion of low-density lipoprotein (LDL) into cytotoxic oxidized products. Only because of its abundance, hemoglobin probably represents the most important potential source of heme within the vascular endothelium; hemoglobin in plasma, when oxidized, transfers heme to endothelium and LDL, thereby enhancing cellular susceptibility to oxidant-mediated injury. As a defense against such toxicity, upon exposure to heme or hemoglobin, endothelial cells up-regulate heme oxygenase-1 and ferritin. Heme oxygenase-1 is a heme-degrading enzyme that opens the porphyrin ring, producing biliverdin, carbon monoxide, and the most dangerous product - free redox active iron. The latter can be effectively controlled by ferritin via sequestration and ferroxidase activity. Ferritin serves as a protective gene by virtue of antioxidant, antiapoptotic, and antiproliferative actions. These homeostatic adjustments have been shown effective in the protection of endothelium against the damaging effects of exogenous heme and oxidants. The central importance of this protective system was recently highlighted by a child diagnosed with heme oxygenase-1 deficiency, who exhibited extensive endothelial damage.

Carbonylated proteins in bronchoalveolar lavage of patients with sarcoidosis, pulmonary fibrosis associated with systemic sclerosis and idiopathic pulmonary fibrosis

Oxygen-derived free radicals produced by phagocytes have been postulated to contribute to lung tissue damage occurring during diffuse lung diseases (DLD). The two-dimensional electrophoretic (2-DE) analysis of bronchoalveolar lavage (BAL) protein composition revealed different protein profiles in sarcoidosis (S), idiopathic pulmonary fibrosis (IPF) and systemic sclerosis (SSc) with a significant increase of low molecular weight proteins in IPF. Some of these proteins are involved in antioxidant processes. The aims of this report were to analyse the oxidative stress occurring in patients with DLD through determination of BAL protein carbonyl content and to identify target proteins of oxidation by a proteomic approach (2-DE combined with immunoblotting with specific antibodies for carbonyl groups). Carbonylated proteins detected by enzyme-linked immunosorbent assay (ELISA) were increased in BAL of patients with S, IPF and SSc compared to healthy controls with a significant difference for S and IPF. The proteomic approach to the analysis of BAL revealed that protein carbonylation was a process involving specific carbonylation-sensitive proteins and that in IPF a greater number of proteins target of oxidation were present. In conclusion, to our knowledge, this is the first report providing a database of proteins target of oxidation in BAL of patients with sarcoidosis, idiopathic pulmonary fibrosis and systemic sclerosis.

Vascular damage by unstable hemoglobins: The role of heme-depleted globin

The study compared the damage inflicted to endothelial cells (ECs) by intact hemoglobin (Hb) and isolated chains. To compare optional in vivo contact of acellular Hb with the endothelium, oxy-forms of Hb and its isolated alpha- and beta-chains existing in the thalassemias were added to primary confluent cultures of bovine aorta EC. Cell damage was followed by morphological changes or leakage of lactic dehydrogenase and pre-inserted 51Cr from the cells, followed for 27 h. Under these experimental conditions, Hb did not affect the cells but its chains inflicted damage, beta- more than alpha-chains. Based on the literature and our data, we hypothesized that hemin and/or globin should be responsible for the increased endothelial damage by beta-chains. While hemin hardly affected ECs, globin, unlike the plasma protein hemopexin, was harmful. Since hemin release leaves globin with a large hydrophobic surface, the globin-damage appears to result from adsorptive pinocytosis to endothelial membrane.

Secretion of ferritin by iron-laden macrophages and influence of lipoproteins

Increasing evidence supports a role of cellular iron in the initiation and development of atherosclerosis. We and others reported earlier that iron-laden macrophages are associated with LDL oxidation, angiogenesis, nitric oxide production and apoptosis in atherosclerotic processes. Here we have further studied perturbed iron metabolism in macrophages, their interaction with lipoproteins and the origin of iron accumulation in human atheroma. In both early and advanced human atheroma lesions, hemoglobin and ferritin accumulation correlated with the macrophage-rich areas. Iron uptake into macrophages, via transferrin receptors or scavenger receptor-mediated erythrophagocytosis, increased cellular iron and accelerated ferritin synthesis at both mRNA and protein levels. The binding activity of iron regulatory proteins was enhanced by desferrioxamine (DFO) and decreased by hemin and iron compounds. Iron-laden macrophages exocytosed both iron and ferritin into the culture medium. Exposure to oxidized low-density lipoprotein (oxLDL, >or=50 microg/mL) resulted in <20% apoptosis of iron-laden human macrophages, but cells remained impermeable after a 24 h period and an increased excretion of ferritin could be observed by immunostaining techniques. Exposure to high-density lipoprotein (HDL) significantly decreased ferritin excretion from these cells. We conclude: (i) erythrophagocytosis and hemoglobin catabolism by macrophages contribute to ferritin accumulation in human atherosclerotic lesions and; (ii) iron uptake into macrophages leads to increased synthesis and secretion of ferritin; (iii) oxidized LDL and HDL have different effects on these processes.

Haptoglobin Genotype– and Diabetes-Dependent Differences in Iron-Mediated Oxidative Stress In Vitro and In Vivo

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 genotype–dependent 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.

In vivo and in vitro studies establishing haptoglobin as a major susceptibility gene for diabetic vascular disease

Hemoglobin (Hb) released during hemolysis is a potent oxidant. Extracorpuscular Hb may enter the vessel wall and mediate low-density lipoprotein oxidation, thereby promoting the development and progression of atherosclerosis. Haptoglobin (Hp) is an antioxidant protein as a result of its ability to bind Hb and block Hb-induced oxidative damage. Hp also facilitates the removal of Hb from the extravascular compartment via the CD163 macrophage scavenger receptor. In man, there are two common alleles for Hp denoted 1 and 2, and correspondingly, three different possible genotypes: Hp1-1, Hp2-1, and Hp2-2. We have recently demonstrated in several longitudinal studies that Hp genotype is an independent risk factor for diabetic vascular complications. Specifically, we have shown that diabetic individuals with Hp2-2 are more likely to develop nephropathy, retinopathy, and cardiovascular disease as compared with those with Hp2-1 or Hp1-1. Mechanistically, we have found significant Hp type differences in the antioxidant and CD163-mediated scavenging and activation functions of the different Hp protein types. Furthermore, we have demonstrated that these functions are modified in the diabetic state. In this review, we focus on the clinical studies associating the Hp polymorphism and diabetic vascular complications, and the molecular basis behind this interaction.

Convulsive disorder and genetic polymorphism. Association of idiopathic generalized epilepsy with haptoglobin polymorphism

Haptoglobin is a polymorphic protein that is well known for its hemoglobin (Hb)-binding property. The protein shows gross differences in molecular size among genotypes, resulting in different degrees of diffusion in central nervous system tissue. Since the breakdown of erythrocytes in the intracerebral fluid results in Hb-mediated free OH radical formation, lipid peroxidation, and increased neuronal excitability, a differential diffusion of haptoglobin phenotypes in the intracerebral fluid might result in a different degree of protection from oxidative damage. We have studied two samples of children with idiopathic generalized epilepsy from two different Italian populations. In both samples the haptoglobin *1/*1 genotype is much less represented in epileptic children than in controls. These observations suggest that subjects carrying the Hp*1/*1 genotype, that has the lowest molecular size and diffuses more readily in the interstitial cerebral fluid, are more protected against idiopathic generalized epilepsy than those with other haptoglobin genotypes.

Why heme needs to be degraded to iron, biliverdin IXalpha, and carbon monoxide?

A large amount of hemoglobin is degraded daily to heme and globin and is replenished by biosynthesis in the bone marrow erythroblasts. "Free heme" can be dissociated from apohemoglobin in vitro and, conversely, native hemoglobin can be renatured from them. Then why does heme need to be degraded to iron, biliverdin IXalpha, and carbon monoxide in vivo? Free heme, i.e., a protein-unbound heme, exists in cells at a very minute concentration and exerts regulatory functions such as the repression of nonspecific delta-aminolevulinate synthase expression and the induction of microsomal heme oxygenase-1 (HO-1). The latter gene expression occurs by way of free heme-mediated derepression of Bach1, a mammalian heme-responsive transcription factor that suppresses the activation of the HO-1 gene. All these events occur at free heme concentrations below 1 microM. In contrast, free heme concentration greater than 1 microM can be toxic because it catalyzes the production of reactive oxygen species. To cope with this problem, the body is equipped with various defense mechanisms against high free heme concentrations. HO is one of the major players in these mechanisms, and it catabolizes free heme to iron, biliverdin IXalpha, and carbon monoxide. These three metabolites of heme by HO reactions have additional important functions and are involved in various critical cellular events. Thus, the breakdown of heme to smaller elements has its own significance in essential cellular metabolism.

Oxidized low-density lipoprotein, iron stores, and haptoglobin polymorphism

BACKGROUND

In vitro experimental studies demonstrated that iron promotes free radical-induced low-density lipoprotein (LDL) oxidation.

OBJECTIVE

To test the hypothesis that circulating oxidized LDL (oxLDL) levels might be associated with body iron stores (serum ferritin) and iron-related genetic markers (hemochromatosis gene C282Y mutation, haptoglobin polymorphism).

METHODS

We investigated 381 (176 males, 205 females, age 45 +/- 6 years) healthy Caucasians. Serum oxLDL, assayed by a mAb-4E6-based enzyme-linked immunosorbent assay (ELISA), was expressed as oxLDL/LDL ratio to adjust for serum LDL-cholesterol concentration. Hemochromatosis gene C282Y mutation analysis was performed by a Taqman-based polymerase chain reaction (PCR) assay. Haptoglobin (Hp) phenotypes (Hp 1-1, Hp 2-1, Hp 2-2) were determined by starch gel electrophoresis.

RESULTS

In stepwise multivariate regression analysis, gender (P < 0.0001), current smoking (P < 0.0001), HDL-cholesterol (P = 0.0001), ferritin (P = 0.0051), body mass index (BMI) (P = 0.0063), and Hp phenotype (P = 0.0331) independently predicted oxLDL/LDL ratio in the total group. In men, smoking (P < 0.0001), ferritin (P = 0.0052), Hp phenotype (P = 0.0063), and HDL-cholesterol (P = 0.0127) were independent determinants of oxLDL/LDL ratio. In women, only body mass index (P < 0.0001), HDL-cholesterol (P = 0.0005), and smoking (P = 0.0025) were significantly associated with oxLDL/LDL ratio. The C282Y mutation (wild-type versus C282Y heterozygotes) was not associated with oxLDL/LDL ratio in both sexes.

CONCLUSION

Serum ferritin concentration and Hp polymorphism are independently associated with circulating oxLDL levels in males.

Haptoglobin polymorphisms and iron homeostasis in health and in disease

Haptoglobin (Hpt) is a plasma protein with hemoglobin-binding capacity. It is a well-known marker of hemolysis. Hpt is also an acute-phase protein that functions as a bacteriostatic agent, an inhibitor of prostaglandin synthesis and angiogenesis. However, the best-known biological function of Hpt is capture of hemoglobin (Hb). The identification of functional differences in haptoglobin molecules resulting from relatively common polymorphisms has further elucidated the importance of haptoglobin in iron homeostasis and in disease processes influenced by iron metabolism. In this review the effect of Hpt polymorphism on these different disease entities will be discussed.

Oxidation of low-density lipoprotein by hemoglobin-hemichrome

Hemoglobin and myoglobin are inducers of low-density lipoprotein oxidation in the presence of H(2)O(2). The reaction of these hemoproteins with H(2)O(2) result in a mixture of protein products known as hemichromes. The oxygen-binding hemoproteins function as peroxidases but as compared to classic heme-peroxidases have a much lower activity on small sized and a higher one on large sized substrates. A heme-globin covalent adduct, a component identified in myoglobin-hemichrome, was reported to be the cause of myoglobin peroxidase activity on low-density lipoprotein. In this study, we analyzed the function of hemoglobin-hemichrome in low-density lipoprotein oxidation. Oxidation of lipids was analyzed by formation of conjugated diene and malondialdehyde; and oxidation of Apo-B protein was analyzed by development of bityrosine fluorescence and covalently cross-linked protein. Hemoglobin-hemichrome has indeed triggered oxidation of both lipids and protein, but unlike myoglobin, hemichrome has required the presence of H(2)O(2). In correlation to this, we found that unlike myoglobin, hemichrome formed by hemoglobin/H(2)O(2) does not contain a globin-heme covalent adduct. Nevertheless, hemoglobin-hemichrome remains oxidatively active towards LDL, indicating that other components of the oxidatively denatured hemoglobin should be considered responsible for its hazardous activity in vascular pathology.