Comparison of laboratory parameters as risk factors for the presence and the extent of coronary or carotid atherosclerosis: the significance of apolipoprotein B to apolipoprotein all ratio

Bilirubin, cardiovascular diseases and cancer: epidemiological perspectives

Owing to a potent antioxidant property of bilirubin, a growing interest has been drawn to the potential protective effects of bilirubin against oxidative stress-related diseases. This article evaluates associations of bilirubin with atherosclerotic diseases and cancer. Serum bilirubin has consistently been shown to be inversely associated with diverse atherosclerotic diseases, mostly among men in different populations. A limited number of prospective studies have shown a U-shaped or reversed J-shaped relationship between bilirubin and coronary heart disease in men and no evident association in women. Few studies have provided evidence supportive of a protective association between bilirubin and cancer risk. The findings on bilirubin-related genetic polymorphisms are inconsistent in relation to coronary heart disease and cancer.

Plasma bilirubin and UGT1A1*28 are not protective factors against first-time myocardial infarction in a prospective, nested case-referent setting

BACKGROUND

Bilirubin, an effective antioxidant, shows a large variation in levels between individuals and has been positively associated with reduced cardiovascular disease risk. A major reason for the variability is a common promoter polymorphism, UGT1A1*28, which reduces the transcription of the enzyme that conjugates bilirubin, UDP-glucuronosyltransferase 1A1. The aim of the study was to evaluate a possible protective effect of plasma bilirubin and the UGT1A1*28 polymorphism against myocardial infarction in a prospective case-referent setting.

METHODS AND RESULTS

Subjects (n=618) with a first-ever myocardial infarction (median event age, 60.5 years; median lag time, 3.5 years) and 1184 matched referents were studied. Plasma bilirubin was lower in cases versus referents. Despite a strong gene-dosage effect on bilirubin levels in both cases and referents, the UGT1A1*28 polymorphism did not influence the risk of myocardial infarction. Among multiple other variables, serum iron showed one of the strongest associations with bilirubin levels.

CONCLUSIONS

We found no evidence for a protective effect of the UGT1A1*28 polymorphism against myocardial infarction and consequently neither for bilirubin. The lower bilirubin levels in cases might be caused by decreased production, increased degradation, or increased elimination.

Socioeconomic position and inflammatory and immune biomarkers of cardiovascular disease: applications to the Panel Study of Income Dynamics

Biomarkers are an important aspect of research linking psychosocial stress and health. This article aims to characterize the biological pathways that may mediate the relationship between socioeconomic position (SEP) and cardiovascular disease (CVD) and address opportunities for further research within the Panel Study of Income Dynamics (PSID), with a focus on psychosocial stressors related to SEP. We review the literature on CVD biomarkers, including adhesion and proinflammatory molecules (interleukin-6, other cytokines, C-reactive proteins, fibrinogen, etc.) and microbial pathogens. The impact of socioeconomic determinants and related psychosocial stressors on CVD biomarkers mediated by behavioral and central nervous system pathways are described. We also address measurement and feasibility issues, including specimen collection methods, processing and storage procedures, laboratory error, and within-person variability. In conclusion, we suggest that PSID consider adding important assessments of specific CVD biomarkers and mediating behavioral measures, health, and medications that will ultimately address many of the gaps in the literature regarding the relationship between SEP and cardiovascular health.

Inhibitors of the heme oxygenase - carbon monoxide system: on the doorstep of the clinic?

The past decade has seen substantial developments in our understanding of the physiology, pathology, and pharmacology of heme oxygenases (HO), to the point that investigators in the field are beginning to contemplate therapies based on administration of HO agonists or HO inhibitors. A significant amount of our current knowledge is based on the judicious application of metalloporphyrin inhibitors of HO, despite their limitations of selectivity. Recently, imidazole-based compounds have been identified as potent and more selective HO inhibitors. This 'next generation' of HO inhibitors offers a number of desirable characteristics, including isozyme selectivity, negligible effects on HO protein expression, and physicochemical properties favourable for in vivo distribution. Some of the applications of HO inhibitors that have been suggested are treatment of hyperbilirubinemia, neurodegenerative disorders, certain types of cancer, and bacterial and fungal infections. In this review, we address various approaches to altering HO activity with a focus on the potential applications of second-generation inhibitors of HO.

Gilbert syndrome, UGT1A1*28 allele, and cardiovascular disease risk: possible protective effects and therapeutic applications of bilirubin

Serum bilirubin has been shown to be inversely related to cardiovascular disease (CVD) in both retrospective and prospective studies. Meta-analysis of existing studies has also confirmed that serum bilirubin concentrations are inversely related to CVD. Less information is known about the protective effects of slightly elevated serum bilirubin concentrations. In this review, we will focus primarily on the association of serum bilirubin and CVD and the possible protective roles of bilirubin, heme oxygenase (HO), and bilirubin UDP-glucuronosyltransferase (UGT1A1). HO and biliverdin reductase control the formation of bilirubin, whereas UGT1A1 controls bilirubin conjugation and clearance. Because of the health and therapeutic implications of slightly elevated serum bilirubin concentrations, we will discuss the recent prospective studies on cardiovascular risk in individuals with Gilbert syndrome (GS) as well as those with the UGT1A1*28 allele. Such individuals have decreased hepatic bilirubin UDP-glucuronosyltransferase activity, decreased bilirubin clearance, and increased serum bilirubin concentrations. Lastly, we will discuss some of the therapeutic approaches that could be used to increase serum bilirubin concentrations to prevent CVD and other oxidative and inflammatory diseases.

Apolipoprotein AII is a regulator of very low density lipoprotein metabolism and insulin resistance

Apolipoprotein AII (apoAII) transgenic (apoAIItg) mice exhibit several traits associated with the insulin resistance (IR) syndrome, including IR, obesity, and a marked hypertriglyceridemia. Because treatment of the apoAIItg mice with rosiglitazone ameliorated the IR and hypertriglyceridemia, we hypothesized that the hypertriglyceridemia was due largely to overproduction of very low density lipoprotein (VLDL) by the liver, a normal response to chronically elevated insulin and glucose. We now report in vivo and in vitro studies that indicate that hepatic fatty acid oxidation was reduced and lipogenesis increased, resulting in a 25% increase in triglyceride secretion in the apoAIItg mice. In addition, we observed that hydrolysis of triglycerides from both chylomicrons and VLDL was significantly reduced in the apoAIItg mice, further contributing to the hypertriglyceridemia. This is a direct, acute effect, because when mouse apoAII was injected into mice, plasma triglyceride concentrations were significantly increased within 4 h. VLDL from both control and apoAIItg mice contained significant amounts of apoAII, with approximately 4 times more apoAII on apoAIItg VLDL. ApoAII was shown to transfer spontaneously from high density lipoprotein (HDL) to VLDL in vitro, resulting in VLDL that was a poorer substrate for hydrolysis by lipoprotein lipase. These results indicate that one function of apoAII is to regulate the metabolism of triglyceride-rich lipoproteins, with HDL serving as a plasma reservoir of apoAII that is transferred to the triglyceride-rich lipoproteins in much the same way as VLDL and chylomicrons acquire most of their apoCs from HDL.

The Heme Catabolic Pathway and its Protective Effects on Oxidative Stress‐Mediated Diseases

Bilirubin, the principal bile pigment, is the end product of heme catabolism. For many years, bilirubin was thought to have no physiological function other than that of a waste product of heme catabolism--useless at best and toxic at worst. Although hyperbilirubinemia in neonates has been shown to be neurotoxic, studies performed during the past decade have found that bilirubin has a number of new and interesting biochemical and biological properties. In addition, there is now a strong body of evidence suggesting that bilirubin may have a beneficial role in preventing oxidative changes in a number of diseases including atherosclerosis and cancer, as well as a number of inflammatory, autoimmune, and degenerative diseases. The results also suggest that activation of the heme oxygenase and heme catabolic pathway may have beneficiary effects on disease prevention either through the action of bilirubin or in conjunction with bilirubin. If so, it may be possible to therapeutically induce heme oxygenase, increase bilirubin concentrations, and lower the risk of oxidative stress-related diseases.

Atherosclerotic risk factors and carotid stiffness in elderly asymptomatic HD patients

Several studies showed that carotid atherosclerosis and stiffness are independent prognostic factors of cardiovascular morbidity and mortality in the general population and in end-stage renal disease patients. However, the impact of established risk factors on carotid structural and elastic properties in non-diabetic elderly hemodialysis patients with negative history for cardiovascular disease has not been fully elucidated. In this paper, we investigated the effect of established and potential risk factors on carotid atherosclerosis and stiffness. Thirty stable, non-symptomatic, non-diabetic patients, aged 65-years and older (mean age 71.4+/-4.15, range 65-79) on hemodialysis for more than 6 months, were included. All patients underwent B-mode ultrasonography of common carotid artery estimating intima-media wall thickness and wall-to-lumen ratio bilaterally and checking for the presence of plaques. Carotid elasticity was evaluated by compliance, distensibility, and the incremental elastic modulus (Einc), whereas systemic arterial stiffening was evaluated by the augmentation index provided by tonometry of radial artery. Our results showed that presence of carotid plaques and wall thickening were frequent findings in this population (76% and 73.3%, respectively) and they were positively associated with fibrinogen (P<0.005), diastolic blood pressure (P<0.004), visceral obesity (P<0.001) and bio-intact PTH (i-PTH) (P=0.03). Overall, systemic and carotid stiffness were strongly correlated with hs-CRP (P=0.018), serum ferritin (P=0.02) with age (P=0.03), lipids (P=0.03) and i-PTH (P=0.05). In conclusion, our findings show that stiffening and atherosclerosis in non-symptomatic elderly HD patients are very common and they are related not only to hemodynamic changes (diastolic blood pressure), inflammation (hs-CRP, fibrinogen, ferritin) or metabolic dysfunction (increased i-PTH, abnormal lipid profile), but also to abnormal fat deposition (increased waist to hip ratio and waist circumference). Considering the high morbidity and mortality of elderly patients, close monitoring of these parameters could be useful to prevent cardiovascular events.

The Inverse Association of Elevated Serum Bilirubin Levels with Subclinical Carotid Atherosclerosis

BACKGROUND

Serum bilirubin is negatively associated with the development of coronary heart disease. In the present study, we have focused on the analysis of intima-media thickness (IMT) of the common carotid artery in hyper- and normobilirubinemic subjects.

METHODS

The study was performed on 111 men without manifested atherosclerosis. In all subjects, complete biochemical tests were determined along with the examination of IMT by carotid ultrasound.

RESULTS

The mean IMT in hyperbilirubinemic subjects as compared with controls was substantially lower (p=0.017), and hyperbilirubinemic men also had very low age-adjusted prevalence odds ratios for having IMT above the 50th percentiles of controls, even after adjustment for selected vascular risk factors (p=0.034).

CONCLUSIONS

In the present study, we demonstrate the inverse relationship between serum bilirubin and IMT in healthy men.

Associations between inflammatory markers, traditional risk factors, and complications in patients with type 2 diabetes mellitus

OBJECTIVE

Inflammatory markers predict cardiovascular events in a wide range of patients. Two factors, fibrinogen (FIB) and high-sensitivity C reactive protein (CRP), are currently entering clinical practice as cardiovascular risk predictors. In patients with type 2 diabetes mellitus, we sought to examine the relationship between macrovascular disease, urinary albumin/creatinine ratio (ACR), and FIB or CRP, as well as the relationship of FIB and CRP with traditional risk predictors of these complications of diabetes.

METHODS

In 202 consecutive patients with type 2 diabetes mellitus from a diabetes clinic, clinical and biochemical data were obtained and a cross-sectional analysis was performed.

RESULTS

Patients with macrovascular disease had higher FIB (P=.02) but not higher CRP. They were older, more likely to have retinopathy or elevated serum creatinine, had higher ACR and lower HDL cholesterol. They were more likely to be treated with statins, beta-blockers, and ASA. Adjustment for statin therapy did not result in significant differences in CRP levels according to macrovascular disease status. Both FIB (P=.01) and CRP (P=.02) were significantly higher in patients with ACR whose values were in the proteinuria range. In multivariate analysis, both FIB (P=.001) and CRP (P=.03) were positively correlated with ACR, but no association was seen between CRP and ACR when FIB was entered in the model. Other factors positively associated with ACR were age, diastolic blood pressure, retinopathy, and hemoglobin A1c (HbA1c). FIB and CRP were strongly correlated (R=.49, P< or =.001) and this effect was independent of statin therapy. CRP was positively associated with body mass index (BMI), serum triglycerides, and sulfonylurea therapy and negatively associated with metformin therapy. Patients on statin therapy had significantly higher FIB and lower CRP. Women on hormone replacement therapy (HRT) had significantly lower FIB and higher CRP.

CONCLUSIONS

In patients with diabetes: (1) the two markers, FIB and CRP, are interrelated; (2) FIB is significantly associated with presence of microvascular disease, independent of CRP; (3) CRP is strongly associated with metabolic factors but not with complications of diabetes, independently of FIB; (4) statins and HRT were divergently associated with CRP and FIB as HRT was associated with lower FIB and higher CRP, while statins showed the reverse association; and (5) CRP and FIB provide different information about the characteristics and consequences of diabetes mellitus because of divergent associations with biological indicators and therapeutic agents.

A genome scan for loci influencing anti-atherogenic serum bilirubin levels

Epidemiological studies have shown an association of decreased serum bilirubin levels with coronary artery disease. Two segregation analyses in large pedigrees have suggested a major gene responsible for high bilirubin levels occurring in about 12% of the population. Based on a recessive model from a previous segregation analysis, we performed a genome scan using 587 markers genotyped in 862 individuals from 48 Utah pedigrees to detect loci linked to high bilirubin levels. As a complementary approach, non-parametric linkage (NPL) analysis was performed. These two methods identified four regions showing evidence for linkage. The first region is on chromosome 2q34-37 with multipoint LOD and NPL scores of 3.01 and 3.22, respectively, for marker D2S1363. This region contains a previously described gene, uridine diphosphate glycosyltransferase 1, which has been associated with high bilirubin levels. A polymorphism in the promoter of this gene was recently shown to be responsible for Gilbert syndrome which is associated with mild hyperbilirubinemia. The other regions were found on chromosomes 9q21, 10q25-26, and 18q12 with maximum NPL scores of 2.39, 1.55, and 2.79, respectively. Furthermore, we investigated in these pedigrees the association between bilirubin levels and coronary artery disease. One-hundred and sixty-one male and 41 female subjects had already suffered a coronary artery disease event. Male patients showed significantly lower bilirubin concentrations than age-matched controls. This association, however, was not observed in females. These results provide evidence that loci influencing bilirubin variation exist on chromosomes 2q34-37, 9q21, 10q25-26, and 18q12 and confirms the association of low bilirubin levels with coronary artery disease in males.

Association of lipids, lipoproteins, apolipoproteins and paraoxonase enzyme activity with premature coronary artery disease

BACKGROUND AND DESIGN

The association of serum apolipoprotein (apo) A-I and apo B concentrations and paraoxonase (PON) enzyme activity with angiographically determined coronary artery disease (CAD) was investigated in Iranian non-diabetic patients with premature CAD and control participants in a sex- and age-matched case-control study.

METHODS

The study population consisted of 59 non-diabetic patients with premature CAD and 55 CAD control participants. Premature CAD was defined as the presence of angiographically proven coronary stenosis (> or =50% involvement) in men and women younger than 55 and 65 years, respectively. Apolipoprotein concentrations were measured by immunoturbidometric assay and paraoxonase/arylesterase activities by spectrophotometric assay of p-nitrophenol/phenol production following addition of paraoxon/phenylacetate to serum.

RESULTS

In CAD patients, increased concentrations of total cholesterol (215 +/- 43 compared with 193 +/- 43, P < 0.001), low-density lipoprotein cholesterol (137 +/- 46 compared with 116 +/- 39, P < 0.05) and apo B (102 +/- 24 compared with 84 +/- 17, P < 0.001) and a decreased ratio of apo A-I/apo B (1.7 +/- 0.4 compared with 2.0 +/- 0.6, P < 0.001) were observed compared to the control group. Other study variables were not significantly different between the two groups. On multiple logistic regression analysis, the only marker for discrimination between the CAD+ group and the CAD- control group was apo B level.

CONCLUSIONS

In Iranian non-diabetic patients with premature CAD, the concentration of apo B is a better marker than traditional lipids in discriminating between CAD+ and CAD- patients. The lack of significant difference in PON activity between CAD patients and control participants supports the concept of interethnic variability in PON activity and gene polymorphism observed in other studies.

Relationship between the sialic acid content of low-density lipoprotein (LDL) and autoantibodies to oxidized LDL in the plasma of healthy subjects and patients with atherosclerosis

To determine whether the sialic acid (SA) content of the low-density lipoprotein (LDL) is related to the plasma concentration of autoantibodies to oxidized LDL (oxLDL), we measured the SA content of LDL and the concentrations of oxLDL and autoantibodies to oxLDL in plasma of 20 apparently healthy subjects and 20 patients with advanced coronary atherosclerosis. In the healthy subjects the SA content of LDL correlated positively with plasma concentration of autoantibodies to oxLDL. In agreement with the literature the decreased SA content of LDL was associated with an increased fraction of oxLDL; a decreased fraction of oxLDL was associated with an increased plasma concentration of autoantibodies to oxLDL. In the patients the SA content of LDL and plasma concentrations of oxLDL and autoantibodies to oxLDL were not related. We conclude that the SA content of LDL correlates positively with plasma concentration of autoantibodies to oxLDL in healthy subjects. However, this association may vary depending on the stage of atherogenesis. Although our results suggest dependence of LDL SA content on the clearance of oxidatively modified (desialylated and oxidized) LDL from blood by autoantibodies to oxLDL, the mechanisms regulating the SA content of LDL await further studies.

Elevated C-reactive protein constitutes an independent predictor of advanced carotid plaques in dyslipidemic subjects

Inflammation plays a key role in the physiopathology of atherosclerosis. C-reactive protein (CRP) has been found to predict cardiac events in healthy subjects and in patients with coronary heart disease. However, the relationship between CRP and subclinical atherosclerosis is not well established. We examined the potential relationship between CRP and common carotid artery intima-media thickness and carotid plaques in dyslipidemic subjects. Dyslipidemic patients (n=1051) were recruited for the study. All patients had a complete clinical examination and systematically underwent ultrasonographic evaluation of the extracranial carotid arteries on a duplex system. The serum concentration of CRP was measured by using a sensitive immunoradiometric assay. In a univariate model, a strong positive relationship was found between CRP and the severity of carotid stenosis (P<0.0001). In multivariate analysis, the association between CRP and the degree of carotid atherosclerosis remained significant for advanced plaques (P=0.0007) in male subjects only. Significant correlations were found between CRP and body mass index (P<0.0001) and between CRP and other markers associated with the metabolic syndrome. In this large dyslipidemic population, elevated CRP is an independent predictor of advanced carotid plaques in male subjects. Body mass index and other markers of the metabolic syndrome (HDL cholesterol, triglycerides, diabetes, and high blood pressure) are significant determinants of CRP levels in this population.