editorial; monocytes; cardiovascular outcomes; inflammation
ABO blood groups have been associated with various disease phenotypes, particularly cardiovascular diseases. Cardiovascular diseases are the most common causes of death in developed countries and their prevalence rate is rapidly growing in developing countries. There have been substantial historical associations between non-O blood group status and an increase in some cardiovascular disorders. Recent GWASs have identified ABO as a locus for thrombosis, myocardial infarction, and multiple cardiovascular risk biomarkers, refocusing attention on mechanisms and potential for clinical advances. As we highlight in this paper, more recent work is beginning to probe the molecular basis of the disease associations observed in these observational studies. Advances in our understanding of the physiologic importance of various endothelial and platelet-derived circulating glycoproteins are elucidating the mechanisms through which the ABO blood group may determine overall cardiovascular disease risk. The role of blood group antigens in the pathogenesis of various cardiovascular disorders remains a fascinating subject with potential to lead to novel therapeutics and prognostics and to reduce the global burden of cardiovascular diseases.
Adiposity-associated inflammation and insulin resistance are strongly implicated in the development of type 2 diabetes and atherosclerotic cardiovascular disease. This article reviews the mechanisms of adipose inflammation, because these may represent therapeutic targets for insulin resistance and for prevention of metabolic and cardiovascular consequences of obesity. The initial insult in adipose inflammation and insulin resistance, mediated by macrophage recruitment and endogenous ligand activation of Toll-like receptors, is perpetuated through chemokine secretion, adipose retention of macrophages, and elaboration of pro-inflammatory adipocytokines. Activation of various kinases modulates adipocyte transcription factors, including peroxisome proliferator-activated receptor-γ and NFκB, attenuating insulin signaling and increasing adipocytokine and free fatty acid secretion. Inflammation retards adipocyte differentiation and further exacerbates adipose dysfunction and inflammation. Paracrine and endocrine adipose inflammatory events induce a local and systemic inflammatory, insulin-resistant state promoting meta-bolic dyslipidemia, type 2 diabetes, and cardiovascular disease. Developing therapeutic strategies that target both adipose inflammation and insulin resistance may help to prevent type 2 diabetes and cardiovascular disease in the emerging epidemic of obesity.
type 2 diabetes; insulin resistance; adiposity-associated inflammation; adipose tissue; insulin; fatty acids
In this issue of the JCI, Vaisar et al. studied the proteome of HDL (see the related article beginning on page 746). They reveal, quite unexpectedly, that HDL is enriched in several proteins involved in the complement cascade, as well as in a variety of protease inhibitors, supporting the concept that HDL plays a role in innate immunity and in the regulation of proteolytic cascades involved in inflammatory and coagulation processes. The protein makeup of HDL also appears to be altered in patients with coronary artery disease. HDL proteomics is in its infancy, and preliminary findings will need to be confirmed using standardized approaches in larger clinical samples. However, this approach promises to better elucidate the relationship of HDL to atherosclerosis and its complications and could eventually help in the development of biomarkers to predict the outcome of interventions that alter HDL levels and functions.
Psoriasis is a Th-1/17 mediated inflammatory disease associated with increased risk of cardiovascular disease (CVD). Inflammation may modulate lipoprotein particle number and directly impair HDL functions, in particular reverse cholesterol transport (RCT). We sought to study how chronic in vivo inflammation modulates lipoprotein particle composition using nuclear magnetic resonance spectroscopy (NMR) and HDL efflux in psoriasis.
Methods and Results
We prospectively enrolled a consecutive sample of patients with psoriasis (n=122) and compared lipoprotein and metabolic risk factors to patients without psoriasis (n=134). Fasting lipids, insulin, glucose were measured by standard assays, and lipoprotein concentration and size were measured by NMR. In a random subset (n=100 each group), HDL efflux capacity was quantified using a validated ex vivo system involving the incubation of macrophages with apolipoprotein B-depleted serum from patients. Traditional lipid concentrations were similar in both groups except for HDL concentration which was lower in psoriasis (43 mg/dL (36–58) vs 50 (42–62), p<0.01). However, NMR showed an atherogenic profile in psoriasis similar to that observed in diabetes, with significant increase in LDL particle concentration [1210.5 (1002–1498) vs 1115 (935–1291), p=0.03] with decrease in LDL size [20.6 (20.3–21.1) vs 21.3 (20.6–21.1), p<0.001] beyond CV risk factors and HOMA-IR (p=0.001). Finally, HDL efflux capacity was lower in psoriasis compared to controls in fully adjusted models (beta −0.14, p=0.001).
These data support a more atherogenic lipoprotein profile by NMR and decreased HDL efflux capacity in psoriasis patients compared to controls beyond CVD risk factors. The abnormal lipoprotein particle composition and HDL efflux capacity in psoriasis may provide a link between psoriasis and CVD.
inflammation; atherosclerosis; HDL efflux; cholesterol; lipoprotein particles
Assessment of vascular disease has evolved from mere indirect and direct measurements of luminal stenosis to sophisticated imaging methods to depict millimeter structural changes of the vasculature. In the near future, the emergence of multimodal molecular imaging strategies may enable robust therapeutic and diagnostic (‘theragnostic’) approaches to vascular diseases that comprehensively consider structural, functional, biological and genomic characteristics of the disease in individualized risk assessment, early diagnosis and delivery of targeted interventions. This review presents a summary of recent preclinical and clinical developments in molecular imaging and theragnostic applications covering diverse atherosclerosis events such as endothelial activation, macrophage infammatory activity, plaque neovascularization and arterial thrombosis. The main focus is on molecular targets designed for imaging platforms commonly used in clinical medicine including magnetic resonance, computed tomography and positron emission tomography. A special emphasis is given to vascular ultrasound applications, considering the important role this imaging platform plays in the clinical and research practice of the vascular medicine specialty.
atherosclerosis plaque; imaging based therapeutic delivery systems; molecular imaging; theragnostics; thrombosis; vascular ultrasound
Inflammation may directly impair HDL functions, in particular reverse cholesterol transport (RCT), but limited data support this concept in humans.
Methods and Results
We employed low-dose human endotoxemia to assess the effects of inflammation on HDL and RCT-related parameters in vivo. Endotoxemia induced remodelling of HDL with depletion of pre-β1a HDL particles determined by 2-D gel electrophoresis (-32.2 ± 9.3% at 24h, p<0.05) as well as small (-23.0 ± 5.1%, p<0.01, at 24h) and medium (-57.6 ± 8.0% at 16h, p<0.001) HDL estimated by nuclear magnetic resonance (NMR). This was associated with induction of class II secretory phospholipase A2 (~36 fold increase) and suppression of lecithin:cholesterol acyltransferase activity (-20.8 ± 3.4% at 24h, p<0.01) and cholesterol ester transfer protein mass (-22.2 ± 6.8% at 24h, p<0.001). The HDL fraction, isolated following endotoxemia, had reduced capacity to efflux cholesterol in vitro from SR-BI and ABCA1, but not ABCG1 transporter cell models.
These data support the concept that “atherogenic-HDL dysfunction” and impaired RCT occur in human inflammatory syndromes, largely independent of changes in plasma HDL-C and ApoA-I levels.
inflammation; atherosclerosis; cholesterol; lipoproteins; macrophages
Elevated plasma fibrinogen is a prothrombotic risk factor for cardiovascular disease (CVD). Recent small studies report that fibrinogen oxidative modifications, specifically tyrosine residue nitration, can occur in inflammatory states and may modify fibrinogen function. HDL cholesterol is inversely related to CVD and suggested to reduce the oxidation of LDL cholesterol, but whether these antioxidant functions extend to fibrinogen modifications is unknown. We used a recently validated ELISA to quantify nitrated fibrinogen during experimental human endotoxemia (N=23) and in a cohort of healthy adults (N=361) who were characterized for inflammatory and HDL parameters as well as subclinical atherosclerosis measures, carotid artery intima-medial thickness (IMT) and coronary artery calcification (CAC). Fibrinogen nitration increased following endotoxemia and directly correlated with accelerated ex vivo plasma clotting velocity. In the observational cohort, nitrated fibrinogen was associated with levels of CRP and serum amyloid A. Nitrated fibrinogen levels were not lower with increasing HDL cholesterol and did not associate with IMT and CAC. In humans, fibrinogen nitration was induced during inflammation and was correlated with markers of inflammation and clotting function but not HDL cholesterol or subclinical atherosclerosis in our modest sample. Inflammation-induced fibrinogen nitration may be a risk factor for promoting CVD events.
Fibrinogen; Nitration; Intima-medial thickness; Coronary artery calcification; High-density lipoprotein (HDL)
Atherosclerosis is a complex and heritable disease involving multiple cell types and the interactions of many different molecular pathways. The genetic and molecular mechanisms of atherosclerosis have in part been elucidated by mouse models; at least 100 different genes have been shown to influence atherosclerosis in mice. Importantly, unbiased genome-wide association studies have recently identified a number of novel loci robustly associated with atherosclerotic coronary artery disease (CAD). Here we review the genetic data elucidated from mouse models of atherosclerosis, as well as significant associations for human CAD. Furthermore, we discuss in greater detail some of these novel human CAD loci. The combination of mouse and human genetics has the potential to identify and validate novel genes that influence atherosclerosis, some of which may be candidates for new therapeutic approaches.
CAD; Lipids; Mice; GWAS; Genome-wide
Coronary artery calcification (CAC) is associated with increased mortality risk in the general population. Although individuals with chronic kidney disease (CKD) are at markedly increased mortality risk, the incidence, prevalence, and prognosis of CAC in CKD is not well-understood.
Cross-sectional observational study.
Setting and Participants
Analysis of 1,908 participants who underwent coronary calcium scanning as part of the multi-ethnic CRIC (Chronic Renal Insufficiency Cohort) Study.
Estimated glomerular filtration rate (eGFR) computed using the Modification of Diet in Renal Disease (MDRD) Study equation, stratified by race, sex and diabetic status. eGFR was treated as a continous variable and a categorical variable compared to the reference range of >60 ml/min/1.73 m2
CAC detected using CT scans using either an Imatron C-300 electron beam computed tomography scanner or multi-detector CT scanner. CAC was computed using the Agatston score, as a categorical variable. Analyses were performed using ordinal logistic regression.
We found a strong and graded relationship between lower eGFR and increasing CAC. In unadjusted models, ORs increased from 1.68 (95% CI, 1.23–2.31) for eGFR from 50–59 to 2.82 (95% CI, 2.06–3.85) for eGFR of <30. Multivariable adjustment only partially attenuated the results (OR, 1.53; 95% CI, 1.07–2.20) for eGFR<30.
Use of eGFR rather than measured GFR.
We demonstrated a graded relationship between severity of CKD and CAC, independent of traditional risk factors. These findings supports recent guidelines that state that if vascular calcification is present, it should be considered as a complementary component to be included in the decision making required for individualizing treatment of CKD.
Technological advances facilitating the acquisition of large arrays of biomarker data have led to new opportunities to understand and characterize disease progression over time. This creates an analytical challenge, however, due to the large numbers of potentially informative markers, the high degrees of correlation among them, and the time-dependent trajectories of association. We propose a mixed ridge estimator, which integrates ridge regression into the mixed effects modeling framework in order to account for both the correlation induced by repeatedly measuring an outcome on each individual over time, as well as the potentially high degree of correlation among possible predictor variables. An expectation-maximization algorithm is described to account for unknown variance and covariance parameters. Model performance is demonstrated through a simulation study and an application of the mixed ridge approach to data arising from a study of cardiometabolic biomarker responses to evoked inflammation induced by experimental low-dose endotoxemia.
biomarkers; cardiovascular disease (CVD); mixed effects; repeated measures; ridge regression
Leukocyte infiltration of adipose is a critical determinant of obesity-related metabolic diseases. Fractalkine (CX3CL1) and its receptor (CX3CR1) comprise a chemokine system involved in leukocyte recruitment and adhesion in atherosclerosis, but its role in adipose inflammation and type 2 diabetes is unknown.
RESEARCH DESIGN AND METHODS
CX3CL1 mRNA and protein were quantified in subcutaneous adipose and blood during experimental human endotoxemia and in lean and obese human adipose. CX3CL1 cellular source was probed in human adipocytes, monocytes, and macrophages, and CX3CL1-blocking antibodies were used to assess its role in monocyte-adipocyte adhesion. The association of genetic variation in CX3CR1 with metabolic traits was determined in a community-based sample. Finally, plasma CX3CL1 levels were measured in a case-control study of type 2 diabetes.
Endotoxemia induced adipose CX3CL1 mRNA (32.7-fold, P < 1 × 10−5) and protein (43-fold, P = 0.006). Obese subjects had higher CX3CL1 levels in subcutaneous adipose compared with lean (0.420 ± 0.387 vs. 0.228 ± 0.187 ng/mL, P = 0.04). CX3CL1 was expressed and secreted by human adipocytes and stromal vascular cells. Inflammatory cytokine induction of CX3CL1 in human adipocytes (27.5-fold mRNA and threefold protein) was completely attenuated by pretreatment with a peroxisome proliferator–activated receptor-γ agonist. A putative functional nonsynonymous single nucleotide polymorphism (rs3732378) in CX3CR1 was associated with adipose and metabolic traits, and plasma CX3CL1 levels were increased in patients with type 2 diabetes vs. nondiabetics (0.506 ± 0.262 vs. 0.422 ± 0.210 ng/mL, P < 0.0001).
CX3CL1-CX3CR1 is a novel inflammatory adipose chemokine system that modulates monocyte adhesion to adipocytes and is associated with obesity, insulin resistance, and type 2 diabetes. These data provide support for CX3CL1 as a diagnostic and therapeutic target in cardiometabolic disease.
We tested whether genetic factors distinctly contribute to either development of coronary atherosclerosis or, specifically, to myocardial infarction in existing coronary atherosclerosis.
We did two genome-wide association studies (GWAS) with coronary angiographic phenotyping in participants of European ancestry. To identify loci that predispose to angiographic coronary artery disease (CAD), we compared individuals who had this disorder (n=12 393) with those who did not (controls, n=7383). To identify loci that predispose to myocardial infarction, we compared patients who had angiographic CAD and myocardial infarction (n=5783) with those who had angiographic CAD but no myocardial infarction (n=3644).
In the comparison of patients with angiographic CAD versus controls, we identified a novel locus, ADAMTS7 (p=4·98×10−13). In the comparison of patients with angiographic CAD who had myocardial infarction versus those with angiographic CAD but no myocardial infarction, we identified a novel association at the ABO locus (p=7·62×10−9). The ABO association was attributable to the glycotransferase-deficient enzyme that encodes the ABO blood group O phenotype previously proposed to protect against myocardial infarction.
Our findings indicate that specific genetic predispositions promote the development of coronary atherosclerosis whereas others lead to myocardial infarction in the presence of coronary atherosclerosis. The relation to specific CAD phenotypes might modify how novel loci are applied in personalised risk assessment and used in the development of novel therapies for CAD.
The PennCath and MedStar studies were supported by the Cardiovascular Institute of the University of Pennsylvania, by the MedStar Health Research Institute at Washington Hospital Center and by a research grant from GlaxoSmithKline. The funding and support for the other cohorts contributing to the paper are described in the webappendix.
Metabolic syndrome (MS) definitions predict cardiovascular events beyond traditional risk factors in type 2 diabetic (DM) as well as non-diabetics subjects. We and other have shown that apolipoprotein B (apoB) and non-HDL cholesterol (non-HDL-C) are associated with coronary artery calcification (CAC) in DM. However, the relative value of MS, apoB lipoproteins and estimates of insulin resistance is unknown in predicting atherosclerosis in DM. We performed cross sectional analyses of white subjects in 2 community based studies (N= 611 type 2 diabetic subjects, N= 803 non-diabetic subjects) using multivariate analysis of traditional risk factors and then adding MS, apoB and homeostatic model assessment for insulin resistance (HOMA-IR). Incremental value was tested with likelihood ratio testing. Beyond traditional risk, HOMA-IR [Tobit regression ratio 1.86 (p=0.002)], apoB [1.55 (p=0.001)] and MS [2.37 (p=0.007)] were independently associated with CAC. In nested models, HOMA-IR added value to apoB [1.72 (p=0.008)], MS [1.72 (p=0.011)] and both apoB and MS [1.64 (p=0.021)]. ApoB showed a similar pattern when added to HOMA-IR [1.51 (p=0.004)], MS [1.46 (p=0.005)] and both HOMA-IR and MS [1.48 (p=0.006)]. MS added to apoB [1.99 (p=0.032)], but not HOMA-IR [1.54 (p=0.221)] or both apoB and HOMA-IR [1.32 (p=0.434)]. In conclusion, insulin resistance estimates add value to MS and apoB in predicting CAC scores in DM and warrant further evaluation in clinic for identification of DM patients at higher risk for atherosclerotic cardiovascular disease.
insulin resistance; apolipoprotein B; coronary artery calcification; type 2 diabetes
Plasma C-reactive protein (CRP) is associated with cardiovascular disease (CVD) but effects may vary by gender and degree of CVD risk. Whether CRP has value as a CVD risk marker in type-2 diabetes (T2DM) is unclear. We examined whether CRP has gender differences in the association of coronary artery calcium (CAC) in diabetic and non diabetic samples without clinical CVD.
We performed cross-sectional analyses of gender influence on CRP association with CAC in the Penn Diabetes Heart Study (N = 1299 with T2DM), the Study of Inherited Risk of Coronary Atherosclerosis (N = 860 non diabetic subjects), and a combined sample.
Female gender was associated with higher plasma CRP in diabetic and non-diabetic samples after adjustment for covariates. There was a strong interaction by gender in the association of CRP with CAC (interaction p < 0.001). In diabetic women, CRP was associated with higher CAC even after further adjustment for age, race, medications, metabolic syndrome, Framingham risk score, and body mass index [Tobit ratio 1.60, 95% CI (1.03-2.47)]. Although this relationship was attenuated in non diabetic women, the combined sample maintained this association in fully adjusted models [1.44, 95% CI (1.13-1.83)]. There was no association of CRP with CAC in either diabetic or non diabetic men.
CRP may be a useful marker of cardiovascular risk in women, particularly in diabetic women who otherwise have no known CVD. Prospective studies are needed to better assess gender differences in CRP utility and the use of CRP in T2DM.
Coronary artery calcium; C-reactive protein; Diabetes; Gender
Genome-wide association studies (GWAS) in over 100,000 people have revealed novel loci associated with coronary artery disease (CAD) and myocardial infarction (MI) which present exciting opportunities to discover novel disease pathways. One such recently identified locus is on chromosome 10q11, near the gene for the chemokine CXCL12 which has been implicated in cardiovascular disease (CVD) in both mouse and human studies. These GWAS demonstrate that CXCL12 may emerge as a potential therapeutic target for atherosclerosis and thrombosis.
CXCL12; atherosclerosis; GWAS; cardiovascular disease; inflammation
Glycated hemoglobin (HbA1c), used to monitor and diagnose diabetes, is influenced by average glycemia over a 2- to 3-month period. Genetic factors affecting expression, turnover, and abnormal glycation of hemoglobin could also be associated with increased levels of HbA1c. We aimed to identify such genetic factors and investigate the extent to which they influence diabetes classification based on HbA1c levels.
RESEARCH DESIGN AND METHODS
We studied associations with HbA1c in up to 46,368 nondiabetic adults of European descent from 23 genome-wide association studies (GWAS) and 8 cohorts with de novo genotyped single nucleotide polymorphisms (SNPs). We combined studies using inverse-variance meta-analysis and tested mediation by glycemia using conditional analyses. We estimated the global effect of HbA1c loci using a multilocus risk score, and used net reclassification to estimate genetic effects on diabetes screening.
Ten loci reached genome-wide significant association with HbA1c, including six new loci near FN3K (lead SNP/P value, rs1046896/P = 1.6 × 10−26), HFE (rs1800562/P = 2.6 × 10−20), TMPRSS6 (rs855791/P = 2.7 × 10−14), ANK1 (rs4737009/P = 6.1 × 10−12), SPTA1 (rs2779116/P = 2.8 × 10−9) and ATP11A/TUBGCP3 (rs7998202/P = 5.2 × 10−9), and four known HbA1c loci: HK1 (rs16926246/P = 3.1 × 10−54), MTNR1B (rs1387153/P = 4.0 × 10−11), GCK (rs1799884/P = 1.5 × 10−20) and G6PC2/ABCB11 (rs552976/P = 8.2 × 10−18). We show that associations with HbA1c are partly a function of hyperglycemia associated with 3 of the 10 loci (GCK, G6PC2 and MTNR1B). The seven nonglycemic loci accounted for a 0.19 (% HbA1c) difference between the extreme 10% tails of the risk score, and would reclassify ∼2% of a general white population screened for diabetes with HbA1c.
GWAS identified 10 genetic loci reproducibly associated with HbA1c. Six are novel and seven map to loci where rarer variants cause hereditary anemias and iron storage disorders. Common variants at these loci likely influence HbA1c levels via erythrocyte biology, and confer a small but detectable reclassification of diabetes diagnosis by HbA1c.
We sought to replicate the association between the kinesin-like protein 6 (KIF6) Trp719Arg polymorphism (rs20455) and clinical coronary artery disease (CAD).
Recent prospective studies suggest that carriers of the 719Arg allele in KIF6 are at increased risk of clinical CAD compared with non-carriers.
The KIF6 Trp719Arg polymorphism (rs20455) was genotyped in nineteen case-control studies of non-fatal CAD either as part of a genome-wide association study or in a formal attempt to replicate the initial positive reports.
Over 17 000 cases and 39 000 controls of European descent as well as a modest number of South Asians, African Americans, Hispanics, East Asians, and admixed cases and controls were successfully genotyped. None of the nineteen studies demonstrated an increased risk of CAD in carriers of the 719Arg allele compared with non-carriers. Regression analyses and fixed effect meta-analyses ruled out with high degree of confidence an increase of ≥2% in the risk of CAD among European 719Arg carriers. We also observed no increase in the risk of CAD among 719Arg carriers in the subset of Europeans with early onset disease (<50 years of age for males and <60 years for females) compared with similarly aged controls as well as all non-European subgroups.
The KIF6 Trp719Arg polymorphism was not associated with the risk of clinical CAD in this large replication study.
kinesin-like protein 6; KIF6; coronary artery disease; myocardial infarction; polymorphism
To determine whether insulin sensitizers lower androgen levels and whether androgen suppression improves insulin resistance in non-diabetic postmenopausal women.
Randomized, double-blind, placebo-controlled study
Clinical and Translational Research Center of a university hospital
Thirty-five postmenopausal women aged 50-79 yr with insulin resistance and higher testosterone levels
Subjects were randomized to metformin plus leuprolide placebo (LP), leuprolide plus metformin placebo (MP), or LP plus MP in a 1:1:1 fashion over a 12 week period.
Main Outcome Measures
Insulin sensitivity (M) assessed by euglycemic-hyperinsulinemic clamp and free testosterone by equilibrium dialysis.
In those randomized to metformin, free testosterone decreased by 19% (p=0.02) compared to placebo, along with an expected improvement in M. Total testosterone also decreased significantly (p=0.001) whereas sex hormone binding globulin (SHBG) did not change. In those randomized to leuprolide, the percent change in M was not different from placebo (p=0.56), despite a 48% relative decrease in free testosterone levels (p<0.001).
These data are the first to establish a causal link between insulin resistance and testosterone in postmenopausal women. They confirm that treatment of insulin resistance decreases testosterone production in this population and demonstrate that pharmacologic lowering of testosterone does not affect insulin resistance.
Testosterone; insulin resistance; polycystic ovary syndrome; metabolic syndrome; aging; elderly; women
We performed a meta-analysis of 14 genome-wide association studies of coronary artery disease (CAD) comprising 22,233 cases and 64,762 controls of European descent, followed by genotyping of top association signals in 60,738 additional individuals. This genomic analysis identified 13 novel loci harboring one or more SNPs that were associated with CAD at P<5×10−8 and confirmed the association of 10 of 12 previously reported CAD loci. The 13 novel loci displayed risk allele frequencies ranging from 0.13 to 0.91 and were associated with a 6 to 17 percent increase in the risk of CAD per allele. Notably, only three of the novel loci displayed significant association with traditional CAD risk factors, while the majority lie in gene regions not previously implicated in the pathogenesis of CAD. Finally, five of the novel CAD risk loci appear to have pleiotropic effects, showing strong association with various other human diseases or traits.
Lp(a), implicated in both atherogenesis and thrombosis pathways, varies significantly by demographic and metabolic factors, providing challenges for its use in Coronary Heart Disease (CHD) risk. The purpose of this study was to investigate whether type-2 diabetic subjects, relative to non-diabetics, might benefit more from Lp(a) measurement in the prediction of CHD risk, as measured by coronary artery calcium (CAC).
We performed cross sectional analyses in two community-based studies: the Penn Diabetes Heart Study [N=1299 with type-2 diabetes] and the Study of Inherited Risk of Coronary Atherosclerosis [N=860 without diabetes].
Blacks had 2–3 fold higher Lp(a) levels than whites in diabetic and non-diabetic samples. There was significant difference by gender (interaction p<0.001), but not race, in the association of Lp(a) with CAC in type-2 diabetic subjects. In age and race adjusted analysis of diabetic women, Lp(a) was associated with CAC [Tobit regression ratio 2.76 (95% CI 1.73–4.40), p<0.001]. Adjustment for exercise, medications, Framingham risk score, metabolic syndrome, BMI, CRP and hemoglobin A1c attenuated this effect, but the association of Lp(a) with CAC remained significant [2.25, (1.34–3.79), p=0.002]. This relationship was further maintained in women stratified by race, or by the use of HRT or lipid lowering drugs. In contrast, Lp(a) was not associated with CAC in diabetic men, nor in non-diabetic men and women.
Lp(a) is a strong independent predictor of CAC in type-2 diabetic women, regardless of race, but not in men. Lp(a) does not relate to CAC in men or women without type-2 diabetes.
Coronary artery calcium; Lipoprotein(a); Gender; Subclinical atherosclerosis
Pathway-based association methods have been proposed to be an effective approach in identifying disease genes, when single-marker association tests do not have sufficient power. The analysis of quantitative traits may be benefited from these approaches, by sampling from two extreme tails of the distribution. Here we tested a pathway association approach on a small genome-wide association study (GWAS) on 653 subjects with extremely high high-density lipoprotein cholesterol (HDL-C) levels and 784 subjects with low HDL-C levels. We identified 102 genes in the sterol transport and metabolism pathways that collectively associate with HDL-C levels, and replicated these association signals in an independent GWAS. Interestingly, the pathways include 18 genes implicated in previous GWAS on lipid traits, suggesting that genuine HDL-C genes are highly enriched in these pathways. Additionally, multiple biologically relevant loci in the pathways were not detected by previous GWAS, including genes implicated in previous candidate gene association studies (such as LEPR, APOA2, HDLBP, SOAT2), genes that cause Mendelian forms of lipid disorders (such as DHCR24), and genes expressing dyslipidemia phenotypes in knockout mice (such as SOAT1, PON1). Our study suggests that sampling from two extreme tails of a quantitative trait and examining genetic pathways may yield biological insights from smaller samples than are generally required using single-marker analysis in large-scale GWAS. Our results also implicate that functionally related genes work together to regulate complex quantitative traits, and that future large-scale studies may benefit from pathway-association approaches to identify novel pathways regulating HDL-C levels.
GWAS; lipid; HDL-C; pathway analysis; cholesterol; sterol transport; sterol metabolism; genetic association
Resistin causes insulin resistance and diabetes in mice whereas in humans it is linked to inflammation and atherosclerosis. Few human genetic studies of resistin in inflammation and atherosclerosis have been performed. We hypothesized that the −420C>G putative gain-of-function resistin variant would be associated with inflammatory markers and atherosclerosis but not with metabolic syndrome or adipokines in humans.
Design and methods
We examined the association of three resistin polymorphisms, −852A>G, −420C>G and +157C>T, and related haplotypes with plasma resistin, cytokines, C-reactive protein (CRP), adipokines, plasma lipoproteins, metabolic syndrome and coronary artery calcification (CAC) in nondiabetic Caucasians (n = 851).
Resistin levels were higher, dose-dependently, with the −420G allele (CC 5·9 ± 2·7 ng/ml, GC 6·5 ± 4·0 ng/ml and GG 7·2 ± 4·8 ng/ml, trend P = 0·04) after age and gender adjustment [fold higher for GC + GG vs. CC; 1·07 (1·00–1·15), P < 0·05)]. The −852A>G single nucleotide polymorphism (SNP) was associated with higher soluble tumour necrosis factor-receptor 2 (sol-TNFR2) levels in fully adjusted models [1·06 (95% CI 1·01–1·11), P = 0·01)]. The estimated resistin haplotype (GGT) was associated with sol-TNFR2 (P = 0·04) and the AGT haplotype was related to CRP (P = 0·04) in the fully adjusted models. Resistin SNPs and haplotypes were not associated with body mass index (BMI), fasting glucose, insulin resistance, metabolic syndrome, adipokines or CAC scores.
Despite modest associations with plasma resistin and inflammatory biomarkers, resistin 5′ variants were not associated with metabolic parameters or coronary calcification. This suggests that resistin is an inflammatory cytokine in humans but has little influence on adiposity, metabolic syndrome or atherosclerosis.
Fatty acid–binding proteins (FABPs) 4 and 5 play coordinated roles in rodent models of inflammation, insulin resistance, and atherosclerosis, but little is known of their role in human disease. The aim of this study was to examine the hypothesis that plasma adipocyte and macrophage FABP4 and FABP5 levels would provide additive value in the association with metabolic and inflammatory risk factors for cardiovascular disease as well as subclinical atherosclerosis. Using the Penn Diabetes Heart Study (PDHS; n = 806), cross-sectional analysis of FABP4 and FABP5 levels with metabolic and inflammatory parameters and with coronary artery calcium, a measure of subclinical coronary atherosclerosis, was performed. FABP4 and FABP5 levels had strong independent associations with the metabolic syndrome (for a 1-SD change in FABP levels, odds ratio [OR] 1.85, 95% confidence interval [CI] 1.43 to 2.23, and OR 1.66, 95% CI 1.41 to 1.95, respectively) but had differential associations with metabolic syndrome components. FABP4 and FABP5 were also independently associated with C-reactive protein and interleukin-6 levels. FABP4 (OR 1.26, 95% CI 1.05 to 1.52) but not FABP5 (OR 1.13, 95% CI 0.97 to 1.32) was associated with the presence of coronary artery calcium. An integrated score combining FABP4 and FABP5 quartile data had even stronger associations with the metabolic syndrome, C-reactive protein, interleukin-6, and coronary artery calcium compared to either FABP alone. In conclusion, this study provides evidence for an additive relation of FABP4 and FABP5 with the metabolic syndrome, inflammatory cardiovascular disease risk factors, and coronary atherosclerosis in type 2 diabetes mellitus. These findings suggest that FABP4 and FABP5 may represent mediators of and biomarkers for metabolic and cardiovascular disease in type 2 diabetes mellitus.