CYP7A1 encodes cholesterol 7α-hydroxylase an enzyme crucial to cholesterol homeostasis. Its transcriptional activity is down-regulated by fenofibrate. The goal of this study was to determine the effect of CYP7A1 polymorphisms on lipid changes in response to fenofibrate. We examined associations of three tagging single nuclear polymorphisms (SNP) (i6782C>T, m204T>G, 3U12536A>C) at CYP7A1 with triglyceride (TG) and HDL-C responses to a 3-week treatment with fenofibrate 160 mg/d in 864 US White participants from the Genetics of Lipid Lowering Drugs and Diet Network (GOLDN) study. The m204T>G variant significantly associated TG and HDL-C responses to fenofibrate. Individual homozygous for the common T allele of m204T>G SNP displayed both the greater reduction of TG (−32% for TT, −28% for GT, −25% for GG, P = 0.004) and an increase of HDL-C response compared to non-carriers (4.1% for TT, 3.4% for GT, 1.2% for GG, P = 0.01). Conversely, individuals homozygous for the minor allele of i6782C>T showed greater increase of HDL-C response compared to non-carriers (2.8% CC, 4.5% for CT, 5.8% for TT, P=0.02) albeit no significant effect on TG response. Our data suggest that common variants at CYP7A1 locus modulate the TG lowering and HDL-C raising effects of fenofibrate, and contribute to the interindividual variation of the drug responses.
CYP7A1; polymorphism; TG response; fenofibrate
Past studies have demonstrated that single nucleotide polymorphisms (SNPs) of the sodium-bicarbonate co-transporter gene (SLC4A5) are associated with hypertension. We tested the hypothesis that SNPs in SLC4A5 are associated with salt-sensitivity of blood pressure (BP) in 185 Caucasians consuming an isocaloric constant diet with a randomized order of 7 days low Na+ (10 mmol/d) and 7 days high Na+ (300 mmol/d) intake. Salt-sensitivity was defined as a ≥7mm Hg increase in mean arterial pressure (MAP) during a randomized transition between high and low Na+ diet.
A total of 35 polymorphisms in 17 candidate genes were assayed, 25 of which were tested for association. Association analyses with salt-sensitivity revealed three variants that associated with salt-sensitivity, two in SLC4A5 (P <0.001), and one in GRK4 (P = 0.020). Of these, two SNPs in SLC4A5 (rs7571842 and rs10177833) demonstrated highly significant results and large effects sizes, using logistic regression. These two SNPs had P values of 1.0×10−4 and 3.1×10−4 with odds ratios of 0.221 and 0.221 in unadjusted regression models, respectively, with the G allele at both sites conferring protection. These SNPs remained significant after adjusting for BMI and age, (P = 8.9×10−5 and 2.6×10−4 and odds ratios 0.210 and 0.286, respectively). Further, the association of these SNPS with salt-sensitivity was replicated in a second hypertensive population. Meta-analysis demonstrated significant associations of both SNPs with salt-sensitivity [rs7571842 (P=1.2×10−5); rs1017783 (P=1.1×10−4)]. In conclusion, SLC4A5 variants are strongly associated with salt-sensitivity of BP in two separate Caucasian populations.
Genetics-human; Genetics-association studies; Cardiovascular disease; Hypertension (Kidney); Blood Pressure; Sodium-bicarbonate co-transporter; Salt-sensitivity; Hypertension; Genetics
Prior evidence suggests a link between inflammation and hypertension. Interleukin-6 (IL-6) has been implicated in animal studies to play an important role in angiotensin II (ANGII) mediated hypertension. The aim of this study was to examine the relationship of IL-6 and renin-angiotensin system (RAS) activity in human hypertension.
Data from 385 hypertensives and 196 normotensives are included in this report. Blood pressure and laboratory evaluation were performed on liberal and low sodium diets. IL-6 response to an ANGII infusion was evaluated to assess the effect of acute RAS activation.
Hypertensives had higher baseline IL-6 and C-reactive protein (CRP) compared with normotensives on both diets. IL-6 increased in response to ANGII in hypertensives and normotensives (28% in hypertensives, 31% in normotensives, p = < 0.001 for change from baseline). In the setting of RAS activation by a low salt diet, multivariate regression analysis adjusted for age, BMI, gender, race and hypertension status demonstrated an independent positive association of PRA with CRP (beta = 0.199, p<0.0001). There was no significant difference in IL-6 or CRP levels between liberal and low sodium diets.
These findings confirm an association between hypertension and inflammation and provide human data supporting previous evidence from animal studies that IL-6 plays a role in ANGII mediated hypertension. Notably, compared to levels on a liberal sodium diet, neither IL-6 or CRP were higher with activation of the RAS by a low salt diet indicating that a low sodium diet is not inflammatory despite increased RAS activity.
hypertension; inflammation; sodium; angiotensin; CRP; IL-6
A shift towards overall larger very low-density lipoprotein (VLDL), and smaller low-density lipoprotein and high-density lipoprotein (HDL) diameters occurs in insulin resistance (IR), which reflects shifts in the distribution of the subfraction concentrations. Fenofibrate, indicated for hypertriglyceridemia, simultaneously reduces IR and shifts in lipoprotein diameter. Individual responses to fenofibrate vary, and we conducted a genome-wide association study to identify genetic differences that could contribute to such differences.
Association analysis was conducted between single nucleotide polymorphisms (SNPs) on the Affymetrix 6.0 array and fasting particle diameter responses to a 12-week fenofibrate trial, in 817 related Caucasian participants of the Genetics of Lipid Lowering Drugs and Diet Network. Linear models were conducted, which adjusted for age, sex and study center as fixed effects, and pedigree as a random effect. The top three SNPs associated with each fraction were examined subsequently for associations with changes in subfraction concentrations.
SNPs in AHCYL2 and CD36 genes reached, or closely approached, genome-wide levels of significance with VLDL and HDL diameter responses to fenofibrate, respectively (P=4 × 10−9 and 8 × 10−8). SNPs in AHCYL2 were associated with a decrease in the concentration of the large VLDL subfraction only (P = 0.002). SNPs associated with HDL diameter change were not associated with a single subfraction concentration change (P > 0.05) indicating small shifts across all subfractions.
We report novel associations between lipoprotein diameter responses to fenofibrate and the AHCYL2 and CD36 genes. Previous associations of these genes with IR emphasize the role of IR in mediating lipoprotein response to fenofibrate.
AHCYL2; CD36; fenofibrate; inflammation; insulin resistance; insulin signaling; lipoprotein diameter; methylation; PPARγ; subclass
Fenofibrate therapy reduces serum triglycerides (TG) and increases high-density lipoprotein-cholesterol (HDL-C) and thus addresses the atherogenic dyslipidemia associated with metabolic syndrome (MetS). Our hypothesis is that genetic factors contribute to the variability of lipid response to fenofibrate differently in subjects with MetS and without MetS.
We investigated the association in 25 candidate genes with lipid responses to a 3-weeks trial on fenofibrate in subjects with and without MetS. We employed growth curve mixed models to generate the response phenotypes to fenofibrate in TG, HDL-C, and low-density lipoprotein-cholesterol (LDL-C) and examined the genetic associations accounting for family dependencies.
After correcting for multiple testing (p<0.05) and accounting for significant differences in the association effect sizes between subjects with and without MetS (p<0.05), variants of APOA5 (rs662799) and APOE (rs429358) were associated with HDL-C and LDL-C responses in MetS subjects, while APOA4 (rs675)was associated with TG response in non-MetS subjects. There was also suggestive evidence that MetS may interact with APOA4 (p=0.017), APOA5 (p=0.06), and APOE (p=0.09) to the variation to lipid responses.
Genetic effects that contributed to the variability of lipid responses to fenofibrate may differ in subjects with and without MetS. This research may provide guidance for more personalized and effective therapies.
Serum- and glucocorticoid-inducible kinase 1 (SGK1) plays a central role in epithelial sodium channel (ENaC)-dependent Na+ transport in the distal nephron. We hypothesized that SGK1 gene variants may contribute to the effect of dietary salt intake on BP in humans with hypertension, and consequentially influence renin-angiotensin-aldosterone (RAA) system activity. Our study population included 421 hypertensive Caucasian participants of the HyperPath group who had completed a dietary salt protocol with measurement of BP and RAA system activity. Three SGK1 tagging single nucleotide polymorphisms (SNPs) from the HapMap CEU population captured the genetic variation in the SGK1 region. Assuming an additive genetic model, two SNPs (rs2758151 and rs9402571) were associated with BP and plasma renin activity (PRA) effects of dietary salt intake. Major alleles were associated with higher systolic BP on high salt and decreased PRA on low salt. In contrast, low salt neutralized genotype differences. Similar, non-significant trends were observed in a normotensive population (N=152). Genotype was also associated with two salt-sensitive subtypes of hypertension. SGK1 genetic variants are associated with salt sensitivity of BP and PRA in human hypertension. Genotype status at these SGK1 variants may identify individuals prone to salt-sensitive hypertension.
SGK1; polymorphism; renin; salt sensitivity
Extreme obesity is associated with health and cardiovascular disease risks. Although gastric bypass surgery induces rapid weight loss and ameliorates many of these risks in the short term, long-term outcomes are uncertain.
To examine the association of Roux-en-Y gastric bypass (RYGB) with weight loss, diabetes mellitus, and other health risks 6 years after surgery.
Design, Setting, and Participants
A prospective Utah-based study conducted between July 2000 and June 2011 of 1156 severely obese (body mass index [BMI] ≥35) participants aged 18–72 years (82% women; mean BMI 45.9; 95% CI, 31.2–60.6) who sought and received RYGB surgery (n=418), sought but did not have surgery (n=417; control group 1), or were randomly selected from a population-based sample not seeking weight loss surgery (n=321; control group 2).
Main Outcome Measures
Weight loss, diabetes, hypertension, dyslipidemia, and health-related quality of life were compared between participants having RYGB surgery and control participants using propensity score adjustment.
Six years after surgery, patients who received RYGB surgery (with 92.6% follow-up) lost 27.7% (95% CI, 26.6%–28.9%) of their initial body weight compared with 0.2% (95% CI, -1.1% to 1.4%) gain in control group 1 and 0% (95% CI, −1.2 to 1.2%) in control group 2. Weight loss maintenance was superior in patients who received RYGB surgery, with 94% (95% CI, 92%–96%) and 76% (95% CI, 72%–81%) of patients receiving RYGB surgery maintaining at least 20% weight loss 2 and 6 years after surgery, respectively. Diabetes remission rates 6 years after surgery were 62% (95% CI, 49%–75%) in the RYGB surgery group, 8% (95% CI, 0%–16%) in control group 1, and 6% (95% CI, 0%–13%) in control group 2, with remission odds ratios (ORs) of 16.5 (95% CI, 4.7–57.6; P<.001) vs control group 1 and 21.5 (95% CI, 5.4–85.6; P<.001) vs control group 2. The incidence of diabetes throughout the course of the study was reduced after RYGB surgery (2%; 95% CI, 0%–4%; versus 17%; 95% CI, 10%–24%; OR, 0.11; 95% CI, 0.04–0.34 compared with control group 1 and 15%; 95% CI, 9%–21%; OR, 0.21; 95% CI, 0.06–0.67 compared with control group 2; both P<.001). The numbers of participants with bariatric surgery-related hospitalizations were 33 (7.9%), 13 (3.9%), and 6 (2.0%) for RYGB surgery group and 2 control groups, respectively.
Among severely obese patients, compared with nonsurgical control patients, the use of RYGB surgery was associated with higher rates of diabetes remission and lower risk of cardiovascular and other health outcomes over 6 years.
Hypertension represents a complex heritable disease in which environmental factors may directly affect gene function via epigenetic mechanisms. The aim of this study was to test the hypothesis that dietary salt influences the activity of a histone modifying enzyme, lysine-specific demethylase 1 (LSD-1), which in turn is associated with salt-sensitivity of blood pressure (BP).
Animal and human studies were performed. Salt-sensitivity of LSD-1 expression was assessed in wild-type and LSD-1 heterozygote knockout (LSD-1+/−) mice. Clinical relevance was tested by multivariate associations between single nuclear polymorphisms (SNPs) in the LSD-1 gene and salt-sensitivity of BP, with control of dietary sodium, in a primary African-American hypertensive cohort and two replication hypertensive cohorts (Caucasian and Mexican-American).
LSD1 expression was modified by dietary salt in wild-type mice with lower levels associated with liberal salt intake. LSD-1+/− mice expressed lower LSD-1 protein levels than wild-type mice in kidney tissue. Similar to LSD-1+/− mice, African-American minor allele carriers of two LSD-1 SNPs displayed greater change in systolic BP in response to change from low to liberal salt diet (rs671357, p=0.01; rs587168, p=0.005). This association was replicated in the Hispanic (rs587168, p=0.04) but not the Caucasian cohort. Exploratory analyses demonstrated decreased serum aldosterone concentrations in African-American minor allele carriers similar to findings in the LSD-1+/− mice, decreased alpha-EnaC expression in LSD-1+/− mice, and impaired renovascular responsiveness to salt loading in minor allele carriers.
The results of this translational research study support a role for LSD1 in the pathogenesis of salt-sensitive hypertension.
Hypertension; Salt-sensitivity; LSD1; Genetics; Epigenetic
Vitamin D and serum lipid levels are risk factors for cardiovascular disease. We sought to determine if vitamin D (25OHD) interacts at established lipid loci potentially explaining additional variance in lipids.
1060 individuals from Utah families were used to screen 14 loci for SNPs potentially interacting with dietary 25OHD on lipid levels. Identified putative interactions were evaluated for 1) greater effect size in subsamples with winter measures, 2) replication in an independent sample, and 3) lack of gene-environment interaction for other correlated dietary factors. Maximum likelihood models were used to evaluate interactions. The replicate sample consisted of 2890 individuals from the Family Heart Study. Putative 25OHD receptor binding site modifying SNPs were identified and allele-specific, 25OHD-dependent APOA5 promoter activity examined using luciferase expression assays. An additional sample with serum 25OHD measures was analyzed.
An rs3135506-25OHD interaction influencing HDL-C was identified. The rs3135506 minor allele was more strongly associated with low HDL-C in individuals with low winter dietary 25OHD in initial and replicate samples (p=0.0003 Utah, p=0.002 Family Heart); correlated dietary factors did not explain the interaction. SNP rs10750097 was identified as a putative causative polymorphism, was associated with 25OHD-dependent changes in APOA5 promoter activity in HEP3B and HEK293 cells (p<0.01), and showed similar interactions to rs3135506 in family cohorts. Linear interactions were not significant in samples with serum 25OHD measures; however, genotype-specific differences were seen at deficient 25OHD levels.
A 25OHD receptor binding site modifying APOA5 promoter polymorphism is associated with lower HDL-C in 25OHD deficient individuals.
HDL CHOLESTEROL; TRIGLYCERIDE; VITAMIN D; APOLIPOPROTEIN A5; GENE-ENVIRONMENT INTERACTION; CARDIOVASCULAR DISEASE RISK; CAUSATIVE VARIANT
Insulin resistance (IR) is a complex disorder caused by an interplay of both genetic and environmental factors. Recent studies identified a significant interaction between body mass index (BMI) and the rs1800795 polymorphism of the Interleukin-6 (IL-6) gene that influences both IR and onset of type 2 diabetes mellitus (T2DM) with obese individuals homozygous for the C allele demonstrating the highest level of IR and greatest risk for T2DM. Replication of a gene-environment interaction is important to confirm the validity of the initial finding and extends the generalizability of the results to other populations. Thus, the objective of this study was to replicate this gene-environment interaction on IR in a hypertensive population and perform a meta-analysis with prior published results.
Material and Methods
The replication analysis was performed using Caucasian individuals with hypertension (HTN) from the HyperPATH cohort (N=311), genotyped for rs1800795. Phenotype studies were conducted after participants consumed two diets: high sodium (HS) (200mmol/day) and low sodium (LS) (10mmol/day) for 7 days each. Measurements for plasma glucose, insulin, and IL-6 were obtained after 8 hours of fasting. IR was characterized by the homeostatic model assessment (HOMA-IR).
In HyperPATH, BMI was a significant effect modifier of the relationship between rs1800795 and HOMA-IR; higher BMI was associated with higher HOMA-IR among homozygote CC individuals when compared to major allele G carriers (p=0.003). Further, the meta-analysis in 1028 individuals confirmed the result demonstrating the same significant interaction between rs1800795 and BMI on HOMA-IR (p=1.05×10−6).
This rare replication of a gene-environment interaction extends the generalizability of the results to HTN while highlighting this polymorphism as a marker of IR in obese individuals.
Interleukin-6 gene; Hypertension; Obesity; Insulin Resistance
Despite evidence in support of anti-inflammatory and triglyceride-lowering effects of fenofibrate, little is known about genetic determinants of the observed heterogeneity in treatment response. This study provides the first genome-wide examination of fenofibrate effects on systemic inflammation.
Biomarkers of inflammation were measured in participants of the Genetics of Lipid Lowering Drugs and Diet Network (GOLDN, n=1092) before and after a 3-week daily treatment with 160 mg of fenofibrate. Two inflammatory patterns (hsCRP-IL6 and MCP1-TNF-α) were derived using principal component analysis. Associations between single nucleotide polymorphisms on the Affymetrix 6.0 chip and phenotypes were assessed using mixed linear models, adjusted for age, sex, study center, and ancestry as fixed effects and pedigree as a random effect.
Before fenofibrate treatment, the strongest evidence for association was observed for polymorphisms near or within the IL2RA gene with the hsCRP-IL6 pattern (rs7911500, P=5×10−9 and rs12722605, P=5×10−8). Associations of the MCP1-TNF-α pattern with loci in several biologically plausible genes (CYP4F8 (rs3764563), APBB1IP (rs1775246), COL13A1 (rs2683572), and COMMD10 (rs1396485)) approached genome-wide significance (P=3×10−7, 5×10−7, 6×10−7, and 7×10−7 respectively) before fenofibrate treatment. After fenofibrate treatment, the rs12722605 locus in IL2RA was also associated with the MCP1-TNF-α pattern (P=3×10−7). The analyses of individual biomarker response to fenofibrate did not yield genome-wide significant results, but the rs6517147 locus near the immunologically relevant IFNAR2 gene was suggestively associated with IL6 (P=7×10−7).
We have identified several novel biologically relevant loci associated with systemic inflammation before and after fenofibrate treatment.
fenofibrate; inflammation; genome-wide association study
Variants in the gene encoding the γ-subunit of the epithelial sodium channel (SCNN1G) are associated with both Mendelian and quantitative effects on blood pressure. Here, in four cohorts of 1611 white European families comprising a total of 8199 individuals, we undertook staged testing of candidate SNPs for SCNN1G (supplemented with imputation based on data from the 1000 Genomes Project) followed by a meta-analysis in all families of the strongest candidate. We also examined relationships between the genotypes and relevant intermediate renal phenotypes as well as expression of SCNN1G in human kidneys. We found that an intronic SNP of SCNN1G (rs13331086) was significantly associated with age-, sex- and BMI-adjusted blood pressure in each of the four populations (P < 0.05). In an inverse variance-weighted meta-analysis of this SNP in all four populations each additional minor allele copy was associated with a 1 mmHg increase in systolic blood pressure and 0.52 mmHg increase in diastolic blood pressure (SE = 0.33, P = 0.002 for SBP; SE = 0.21, P = 0.011 for DBP). The same allele was also associated with higher 12-h overnight urinary potassium excretion (P = 0.04), consistent with increased epithelial sodium channel activity. Renal samples from hypertensive subjects showed a non-significant (P = 0.07) 1.7-fold higher expression of SCNN1G compared with normotensive controls. These data provide genetic and phenotypic evidence in support of a role for a common genetic variant of SCNN1G in blood pressure determination.
blood pressure; genetics; meta-analysis; risk factors; cardiovascular diseases
Trans fatty acids (TFA) lower HDL and increase triglyceride concentrations while polyunsaturated fatty acids (PUFA) lower triglycerides and may decrease HDL concentrations. The effect of the interaction between trans fat and PUFA on lipids is uncertain.
Men and women (n = 1032) in the Genetics of Lipid-Lowering Drugs and Diet Network (GOLDN) study were included. Fatty acids in erythrocyte membranes were measured with gas chromatography while data on potential confounders were obtained from questionnaires. To test the interaction between total erythrocyte PUFA (ePUFA) and TFA (eTFA) on lipid concentrations we distributed eTFA into tertiles and dichotomized ePUFA at the median concentration.
For the 1st, 2nd and 3rd tertiles of eTFA, multivariate-adjusted means±s.e.m for HDL were 46.2±1.1, 46.3±1.1 and 45.5±1.0 mg/dL among those with low ePUFA, respectively, while they were 50.0±1.1, 46.9±1.1 and 44.7±1.1 mg/dL among those with high ePUFA, respectively (P for interaction = 0.01). For the 1st, 2nd and 3rd tertiles of eTFA, multivariate-adjusted means±s.e.m for triglycerides were 178.6±11.3, 144.7±10.9 and 140.8±10.6, respectively, among those with low ePUFA, while they were 133.8±11.3, 145.7±10.9 and 149.3±11.5, respectively, among those with high ePUFA (P for interaction = 0.005). Results for VLDL were similar to those for triglycerides. No significant interactions were observed for LDL or total cholesterol.
The relation between trans fat and HDL, VLDL and triglycerides may depend on PUFA. The benefit of avoiding trans fat may be greater among individuals with higher PUFA intake. Supplementation with PUFA among individuals with relatively high trans fat intake may have limited benefits on lipid profiles.
Objective and methods
A loss-of-function cytosine (C) for thymidine (T) transition at nucleotide 8590 of CYP4A11 has been associated with increased blood pressure in humans. We tested the hypothesis that CYP4A11 T8590C genotype is associated with salt sensitivity in the International Hypertensive Pathotype cohort.
CYP4A11 T8590C genotype was associated with hypertension in whites. Among normotensive individuals, CYP4A11 T8590C genotype was associated with mean arterial pressure (MAP) during both high and low salt diets, such that there was no relationship between genotype and salt sensitivity of blood pressure. Among hypertensive individuals, CYP4A11 T8590C genotype did not associate with MAP during high salt intake, whereas MAP decreased with increasing number of C alleles during salt restriction. Consequently, among hypertensive individuals, change in MAP with salt restriction was greatest in individuals homozygous for the C allele (−10.9 ± 9.9, −11.1 ± 12.3, and −18.8 ± 12.0 mmHg in TT, CT, and CC groups, respectively, P = 0.02). In both normotensive and hypertensive individuals, individuals homozygous for the C allele exhibited an attenuated increase in renal blood flow during high salt. CYP4A11 genotype did not affect pressor responses to Angiotensin II in normotensive or hypertensive individuals.
The loss-of-function CYP4A11 8590C allele is associated with a diagnosis of hypertension and, in normotensive individuals, with higher blood pressure regardless of salt intake. Among hypertensive individuals, the C allele is associated with salt-sensitive blood pressure. Impaired renal vasodilation during high salt intake may contribute to salt sensitivity. Studies are needed to determine whether CYP4A11 T8590C genotype predicts responses to medications that affect sodium homeostasis in hypertensive individuals.
blood pressure; CYP4A11; dietary salt intake; hypertension; renal blood flow; salt sensitivity
The renin gene has been previously reported to be associated with essential hypertension in a variety of ethnic groups. However, no studies have systematically evaluated the relationship between single nucleotide polymorphisms (SNPs) representing coverage of the entire renin gene and hypertension risk. To evaluate the association between renin gene variation and hypertension we investigated data on HyperPath cohort with 570 hypertensive and 222 normotensive Caucasian subjects. Six tagging SNPs and resultant haplotypes were tested for associations with hypertension risk, followed by mean arterial pressure (MAP), plasma renin activity (PRA) and the change in MAP in response to angiotensin II infusion (AngII ΔMAP). The A allele of SNP rs6693954 and the haplotype containing rs6696954A were significantly associated with higher risk for hypertension (OR=1.98, P=0.0001; OR=1.63 P=0.0005, respectively). The same haplotype block was also associated with altered PRA levels and blunted AngII ΔMAP (global P value=0.02, 0.047, respectively). Our results confirm that polymorphisms in the REN are associated with increased risk for hypertension in an independent cohort, and that the underlying mechanism may reside in the interaction of renin activity and vascular responsiveness to angiotensin II.
Renin; SNP; haplotype; blood pressure and Hypertension
Iron overload is associated with increased diabetes risk. We therefore investigated the effect of iron on adiponectin, an insulin-sensitizing adipokine that is decreased in diabetic patients. In humans, normal-range serum ferritin levels were inversely associated with adiponectin, independent of inflammation. Ferritin was increased and adiponectin was decreased in type 2 diabetic and in obese diabetic subjects compared with those in equally obese individuals without metabolic syndrome. Mice fed a high-iron diet and cultured adipocytes treated with iron exhibited decreased adiponectin mRNA and protein. We found that iron negatively regulated adiponectin transcription via FOXO1-mediated repression. Further, loss of the adipocyte iron export channel, ferroportin, in mice resulted in adipocyte iron loading, decreased adiponectin, and insulin resistance. Conversely, organismal iron overload and increased adipocyte ferroportin expression because of hemochromatosis are associated with decreased adipocyte iron, increased adiponectin, improved glucose tolerance, and increased insulin sensitivity. Phlebotomy of humans with impaired glucose tolerance and ferritin values in the highest quartile of normal increased adiponectin and improved glucose tolerance. These findings demonstrate a causal role for iron as a risk factor for metabolic syndrome and a role for adipocytes in modulating metabolism through adiponectin in response to iron stores.
Concentrations of 1,25-hydroxyvitamin D have been positively associated with dietary sodium and salt-sensitivity (SS) of blood pressure (BP), and inversely with plasma renin activity (PRA). We investigated the association between PRA and 25-hydroxyvitamin D (25OHD), the most clinically relevant vitamin D metabolite, and whether 25OHD associates with SS of BP in renin phenotypes of hypertension.
We performed cross-sectional analyses on 223 Caucasian subjects with hypertension maintained in high and low dietary sodium balance. Subjects were distinguished as having low-renin (LR) or normal-renin (NR) hypertension. Multivariable linear regression was used to evaluate adjusted relationships.
Increasing 25OHD concentrations were inversely associated with PRA (p<0.05) on both salt diets. Furthermore, 25OHD was associated with SS of BP in LR hypertension (β=0.62, p=0.04), but not in NR hypertension (β=0.06, p=0.59). In an adjusted multivariable interaction model, renin status (LR vs NR) was a significant effect modifier of the relationship between 25OHD and SS of BP (p=0.04).
Our findings suggest that 25OHD is inversely associated with PRA and positively associated with SS of BP in LR hypertension subjects. These results extend and support prior evidence indicating an interaction between dietary sodium, the RAS, and vitamin D that influences BP in hypertension.
VITAMIN D; RENIN; SODIUM; BLOOD PRESSURE; HYPERTENSION
The purpose of this study was to clarify the association of the angiotensinogen gene (AGT) with insulin sensitivity using SNP and haplotype analyses in a Caucasian cohort.
Material and Methods
A candidate gene association study was conducted in Caucasians with and without hypertension (N=449). Seventeen single nucleotide polymorphisms (SNPs) of the AGT gene and their haplotypes were analyzed for an association with HOMA-IR. Multivariate regression model accounting for age, gender, BMI, hypertension status, study site, and sibling relatedness was used to test the hypothesis.
Nine of the seventeen SNPs were significantly associated with lower HOMA-IR levels. Homozygous minor allele carriers of the most significant SNP rs2493134 (GG), a surrogate for the gain of function mutation rs699 [AGT p.M268T], had significantly lower HOMA-IR levels (p=0.0001) than heterozygous or homozygous major allele carriers (GC, AA). Direct genotyping of rs699 in a subset of the population showed similar results with minor allele carriers exhibiting significantly decreased HOMA-IR levels (p=0.003). Haplotype analysis demonstrated that haplotypes rs2493137A|rs5050A|rs3789678G|rs2493134A and rs2004776G|rs11122576A|rs699T|rs6687360G were also significantly associated with HOMA-IR (p=0.0009, p=0.02) and these results were driven by rs2493134 and rs699.
This study confirms an association between the AGT gene and insulin sensitivity in Caucasian humans. Haplotype analysis extends this finding and implicates SNPs rs2493134 and rs699 as the most influential. Thus, AGT gene variants, previously shown to be associated with AGT levels, are also associated with insulin sensitivity; suggesting a relationship between the AGT gene, AGT levels, and insulin sensitivity in humans.
insulin resistance; hypertension; angiotensinogen; genetics
Low salt (LS) diet activates the renin-angiotensin-aldosterone and sympathetic nervous systems, both of which can increase insulin resistance (IR). We investigated the hypothesis that LS diet is associated with an increase in IR in healthy subjects.
Healthy individuals were studied after 7 days of LS diet (urine sodium <20 mmol/day) and 7 days of high salt (HS) diet (urine sodium >150 mmol/day) in a random order. IR was measured after each diet and compared statistically, unadjusted and adjusted for important covariates.
One hundred fifty two healthy men and women, age 39.1 ± 12.5 years (range 18–65), body mass index (BMI) 25.3 ± 4.0 kg/m2, were included in this study. Mean (SD) homeostasis model assessment (HOMA) was significantly higher on LS compared with HS diet (2.8 ± 1.6 Vs 2.4 ± 1.7; P <0.01). Serum aldosterone (21.0 ± 14.3 Vs 3.4 ± 1.5 ng/dl; p<0.001), 24 hour urine aldosterone (63.0 ± 34.0 Vs 9.5 ± 6.5 µg/day; p<0.001) and 24 hour urine norepinephrine excretion (78.0 ± 36.7 Vs 67.9 ± 39.8 µg/day; p<0.05) were higher on LS diet compared with HS diet. LS diet was significantly associated with higher HOMA independent of age, gender, blood pressure, BMI, serum sodium and potassium, serum angiotensin II, plasma renin activity, serum and urine aldosterone, and urine epinephrine and norepinephrine.
Low salt diet is associated with an increase in IR. The impact of our findings on the pathogenesis of diabetes and cardiovascular disease needs further investigation.
HOMA; Renin - angiotensin - Aldosterone; Salt intake
Several genes that influence HDL-C, LDL-C, and triglyceride levels have been identified. The effects of genetic polymorphisms on lipid levels may be age dependent. We replicated 17 of these previously identified associations and then used cross-sectional and longitudinal analysis to investigate age-SNP interaction effects. The rs646776 SNP at the SORT1 locus showed an age interaction that was significant in cross-sectional analyses of 1350 individuals from Utah (p=0.0003) and in 2977 individuals from the NHLBI Family Heart Study (p=0.007) as well as in longitudinal analysis of a subsample of 1099 individuals from the Utah cohort that had been followed for over 20 years (p=0.0001). The rs646776 genotype-specific difference in LDL-C levels was significantly greater for younger individuals than for older individuals. These findings may help elucidate the mode of action of the SORT1 gene and impact potential therapeutic interventions targeting this pathway.
SORTILIN 1; AGE-GENE INTERACTION; CARDIOVASCULAR DISEASE; CARDIOVASCULAR GENETICS; HERITABILITY
25-hydroxyvitamin D (25[OH]D) deficiency and excess activity of the renin-angiotensin system (RAS) are both associated with cardiovascular disease. Vitamin D interacts with the vitamin D receptor (VDR) to negatively regulate renin expression in mice; however, human studies linking genetic variation in the VDR with renin are lacking. We evaluated: 1) whether genetic variation in the VDR at the Fok1 polymorphism was associated with plasma renin activity (PRA) in a population of hypertensives and a separate population of normotensives; and 2) whether the association between Fok1 genotype and PRA was independent of 25(OH)D levels.
Genetic association study, assuming an additive model of inheritance, of 375 hypertensive and 146 normotensive individuals from the HyperPATH cohort, who had PRA assessments after 1 week of high dietary sodium balance (HS) and l week of low dietary sodium balance (LS).
The minor allele (T) at the Fok1 ploymorphism was significantly associated with lower PRA in hypertensives (LS: β= −0.22, P<0.01; HS: β= −0.19, P<0.01); when repeated in normotensives, a similar relationship was observed (LS: β= −0.17, P<0.05; HS: β= −0.18, P=0.14). In multivariable analyses, both higher 25(OH)D levels and the T allele at Fok1 were independently associated with lower PRA in hypertensives, however, 25(OH)D was not associated with PRA in normotensives.
Genetic variation at the Fok1 polymorphism of the VDR gene, in combination with 25(OH)D levels, was associated with PRA in hypertension. These findings support the vitamin D-VDR complex as a potential regulator of renin activity in humans.
vitamin D; renin; polymorphism; Fok1; VDR
Prior studies have suggested that circulating adiponectin concentrations are associated positively with vitamin D and negatively with body-mass index (BMI), but have not accounted for the influence of the renin-angiotensin-aldosterone system (RAAS) in this relationship. This is particularly relevant because increased RAAS activity is associated with obesity and is known to lower adiponectin levels. We evaluated the association between adiponectin and 25-hydroxyvitamin D (25[OH]D) after controlling RAAS activity with dietary sodium equilibration, and also evaluated whether this relationship was influenced by BMI.
Cross-sectional study of 115 hypertensive Caucasian men from the HyperPATH Consortium.
To manipulate RAAS activity, all subjects underwent one week of high sodium (HS) diet to suppress RAAS, and one week of low sodium (LS) diet to stimulate RAAS. Linear regression was used to evaluate the association between adiponectin and 25(OH)D, and the effect of BMI on this relationship, in each dietary condition.
Adiponectin was higher on HS, where circulating RAAS activity was low, when compared to LS (HS=2.9 versus LS=2.4 µg/mL, p<0.0001). 25(OH)D levels were positively associated with adiponectin, and BMI was a statistically significant effect modifier of the relationship between 25(OH)D and adiponectin on both diets (p-interaction < 0.01 between BMI and 25[OH]D).
Higher 25(OH)D concentrations were independently associated with higher adiponectin levels, particularly when BMI was high. Dietary sodium balance and circulating RAAS activity did not appear to affect this relationship. Future studies should explore whether vitamin D supplementation increases adiponectin levels in obesity.
Background and Aims
Epidemiologic studies have suggested beneficial effects of flavonoids on cardiovascular disease. Cocoa and particularly dark chocolate are rich in flavonoids and recent studies have demonstrated blood pressure lowering effects of dark chocolate. However, limited data are available on the association of chocolate consumption and the risk of coronary heart disease (CHD). We sought to examine the association between chocolate consumption and prevalent CHD.
We studied in a cross-sectional design 4,970 participants aged 25 to 93 years who participated in the National Heart, Lung, and Blood Institute (NHLBI) Family Heart Study. Chocolate intake was assessed through a semi-quantitative food frequency questionnaire. We used generalized estimating equations to estimate adjusted odds ratios.
Compared to subjects who did not report any chocolate intake, odds ratios (95% CI) for CHD were 1.01 (0.76-1.37), 0.74 (0.56-0.98), and 0.43 (0.28-0.67) for subjects consuming 1-3 times/month, 1-4 times/week, and 5+ times/week, respectively (p for trend <0.0001) adjusting for age, sex, family CHD risk group, energy intake, education, non-chocolate candy intake, linolenic acid intake, smoking, alcohol intake, exercise, and fruit and vegetables. Consumption of non-chocolate candy was associated with a 49% higher prevalence of CHD comparing 5+/week vs. 0/week [OR=1.49 (0.96-2.32)].
These data suggest that consumption of chocolate is inversely related with prevalent CHD in a general population.
epidemiology; carbohydrate; nutrition; cardiovascular disease
Both resistin and vitamin D have been associated with the renin-angiotensin-aldosterone system (RAAS). We investigated the association between resistin and the RAAS, and resistin and vitamin D under controlled dietary sodium conditions.
Retrospective cross-sectional study of subjects from the HyperPATH Consortium, who were maintained in high dietary sodium (HS) and low dietary sodium (LS) balance for one week each.
Caucasian subjects with hypertension (n=177).
25-hydroxyvitamin D (25[OH]D) levels were used to assess vitamin D status. Plasma resistin and RAAS measures were evaluated on each dietary intervention.
Resistin levels were significantly higher in LS, where RAAS activity was high, when compared to HS balance, where RAAS activity was suppressed (6.36 vs. 5.86 µg/L, p<0.0001); however, resistin concentrations were not associated with plasma renin activity or serum aldosterone on either diet. 25(OH)D levels were positively and independently associated with resistin in both dietary conditions (HS: β=0.400, p-trend=0.027; LS: β=0.540, p-trend=0.014).
Dietary sodium loading reduced resistin levels, possibly by suppressing the RAAS; however, circulating RAAS components were not related to resistin concentrations within each specific dietary sodium condition. 25(OH)D was positively associated with resistin and may be involved in resistin regulation through an unknown mechanism. Further studies to better understand resistin regulation in human hypertension are warranted.
resistin; renin; angiotensin; sodium; vitamin D
Background and Aims
While a diet rich in anti-oxidant has been favorably associated with coronary disease and hypertension, limited data have evaluated the influence of such diet on subclinical disease. Thus, we sought to examine whether chocolate consumption is associated with calcified atherosclerotic plaque in the coronary arteries (CAC).
In a cross-sectional design, we studied 2,217 participants of the NHLBI Family Heart Study. Chocolate consumption was assessed by a semi-quantitative food-frequency questionnaire and CAC was measured by cardiac CT. We defined prevalent CAC using an Agatston score of at least 100 and fitted generalized estimating equations to calculate prevalence odds ratios of CAC.
There was an inverse association between frequency of chocolate consumption and prevalent CAC. Odds ratios (95% CI) for CAC were 1.0 (reference), 0.94 (0.66-1.35), 0.78 (0.53-1.13), and 0.68 (0.48-0.97) for chocolate consumption of 0, 1-3 times per month, once per week, and 2+ times per week, respectively (p for trend 0.022), adjusting for age, sex, energy intake, waist-hip ratio, education, smoking, alcohol consumption, ratio of total-to-HDL-cholesterol, non-chocolate candy, and diabetes mellitus. Controlling for additional confounders did not alter the findings. Exclusion of subjects with coronary heart disease or diabetes mellitus did not materially change the odds ratio estimates but did modestly decrease the overall significance (p = 0.07).
These data suggest that chocolate consumption might be inversely associated with prevalent CAC.
Chocolate; diet; epidemiology; coronary calcium; subclinical disease