Development of a Proton Nuclear Magnetic Resonance Spectroscopic Method for Determining Plasma Lipoprotein Concentrations and Subspecies Distributions from a Single, Rapid Measurement

We are developing a method for quantifying plasma lipoproteins by proton nuclear magnetic resonance (NMR) spectroscopy that offers advantages over existing clinical methods. We showed that the major lipoproteins have distinct NMR properties sufficient to permit their concentrations to be extracted from a computer lineshape analysis of the plasma lipid methyl resonance envelope (Clin Chem 1991; 37:377-86). We have now discovered that the spectra of the subspecies within each lipoprotein class are different enough to influence the composite spectrum of that class and hence the spectrum of whole plasma. By including spectra representative of these subspecies as additional components in the lineshape-fitting analysis, a complete concentration profile of very-low-density, low-density (LDL), and high-density (HDL) lipoproteins plus the subspecies distributions within these classes can be simultaneously generated. A pilot study of 30 plasma samples of widely varied composition demonstrated good agreement between NMR-derived values and lipoprotein lipid concentrations and LDL and HDL subspecies distributions determined by gradient-gel electrophoresis.

Bidirectional Mendelian randomization to explore the causal relationships between body mass index and polycystic ovary syndrome

STUDY QUESTION

What are the causal relationships between polycystic ovary syndrome (PCOS) and body mass index (BMI)?

SUMMARY ANSWER

Bidirectional Mendelian randomization analyses suggest that increased BMI is causal for PCOS while the reverse is not the case.

WHAT IS KNOWN ALREADY

The contribution of obesity to the pathogenesis of PCOS is controversial. To date, published genetic studies addressing this question have generated conflicting results and have not utilized the full extent of known single nucleotide polymorphisms associated with body mass index (BMI).

STUDY DESIGN, SIZE, DURATION

This cross-sectional Mendelian randomization (MR) and genetic association study was conducted in 750 individuals of European origin and with PCOS and 1567 BMI-matched controls.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Cases and controls were matched for BMI as well as for distribution of weight categories (normal weight, overweight, obese). Two-sample MR using inverse variance weighting (IVW) was conducted using a 92-SNP instrument variable for BMI with PCOS as the outcome, followed by two-sample MR with a 16-SNP instrument variable for PCOS with BMI as the outcome. Sensitivity analyses included MR-Egger and maximum likelihood methods. Secondary analyses assessed associations of genetic risk scores and individual SNPs with PCOS, BMI and quantitative androgen-related and glucose homeostasis-related traits.

MAIN RESULTS AND THE ROLE OF CHANCE

Each standard deviation genetically higher BMI was associated with a 4.89 (95% CI 1.46-16.32) higher odds of PCOS. Conversely, genetic risk of PCOS did not influence BMI. Sensitivity analyses yielded directionally consistent results. The genetic risk score of 92 BMI SNPs was associated with the diagnosis of PCOS (OR 1.043, 95% CI 1.009-1.078, P = 0.012). Of the 92 BMI risk variants evaluated, none were associated individually with PCOS after considering multiple testing. The association of FTO SNP rs1421085 with BMI was stronger in women with PCOS (β = 0.071, P = 0.0006) than in controls (β = 0.046, P = 0.065).

LIMITATIONS, REASONS FOR CAUTION

The current sample size, while providing good power for MR and genetic risk score analyses, had limited power to demonstrate association of individual SNPs with PCOS. Cases and controls were not matched for age; however, this was mitigated by adjusting analyses for age. Dietary and lifestyle data, which could have been used to explore the greater association of the FTO SNP with BMI in women with PCOS, was not available.

WIDER IMPLICATIONS OF THE FINDINGS

Increasing BMI appears to be causal for PCOS but having PCOS does not appear to affect BMI. This study used the most comprehensive set of SNPs for BMI currently available. Prior studies using fewer SNPs had yielded conflicting results and may have been confounded because cases and controls were not matched for weight categories. The current results highlight the potential utility of weight management in the prevention and treatment of PCOS.

STUDY FUNDING/COMPETING INTEREST(S)

National Institutes of Health Grants R01-HD29364 and K24-HD01346 (to R.A.), Grant R01-DK79888 (to M.O.G.), Grant U54-HD034449 (to R.S.L.), Grant U19-HL069757 (to R.M.K.). The funders had no influence on the data collection, analyses or conclusions of the study. No conflict of interests to declare.

TRIAL REGISTRATION NUMBER

N/A.

Pathways and mechanisms linking dietary components to cardiometabolic disease: thinking beyond calories

Calories from any food have the potential to increase risk for obesity and cardiometabolic disease because all calories can directly contribute to positive energy balance and fat gain. However, various dietary components or patterns may promote obesity and cardiometabolic disease by additional mechanisms that are not mediated solely by caloric content. Researchers explored this topic at the 2017 CrossFit Foundation Academic Conference 'Diet and Cardiometabolic Health - Beyond Calories', and this paper summarizes the presentations and follow-up discussions. Regarding the health effects of dietary fat, sugar and non-nutritive sweeteners, it is concluded that food-specific saturated fatty acids and sugar-sweetened beverages promote cardiometabolic diseases by mechanisms that are additional to their contribution of calories to positive energy balance and that aspartame does not promote weight gain. The challenges involved in conducting and interpreting clinical nutritional research, which preclude more extensive conclusions, are detailed. Emerging research is presented exploring the possibility that responses to certain dietary components/patterns are influenced by the metabolic status, developmental period or genotype of the individual; by the responsiveness of brain regions associated with reward to food cues; or by the microbiome. More research regarding these potential 'beyond calories' mechanisms may lead to new strategies for attenuating the obesity crisis.

New Pharmacogenomics Research Network: An Open Community Catalyzing Research and Translation in Precision Medicine

The goal of pharmacogenomics research is to discover genetic polymorphisms that underlie variation in drug response. Increasingly, pharmacogenomics research involves large numbers of patients and the application of new technologies and methodologies to enable discovery. The Pharmacogenomics Research Network (PGRN) has become a community-driven network of investigators spanning scientific and clinical disciplines. Here, we highlight the activities and types of resources that enable PGRN members to enhance and drive basic and translational research in pharmacogenomics.

Candidate-Gene Study of Functional Polymorphisms in SLCO1B1 and CYP3A4/5 and the Cholesterol-Lowering Response to Simvastatin

Cholesterol‐lowering response to 40 mg simvastatin daily for 6 weeks was examined for associations with common genetic polymorphisms in key genes affecting simvastatin metabolism (CYP3A4 and CYP3A5) and transport (SLCO1B1). In white people (n = 608), SLCO1B1 521C was associated with lesser reductions of total and low‐density lipoprotein cholesterol. Associations between SLCO1B1 521C and cholesterol response were not detected in African Americans (n = 333). Associations between CYP3A4*22 or CYP3A5*3 and cholesterol response were not detected in either race, and no significant race‐gene or gene‐gene interactions were detected. As several of the analyses may have been underpowered (especially the analyses in the African American cohort), the findings not suggesting an association should not be considered conclusive and warrant further investigation. The finding regarding SLCO1B1 521C in whites was consistent with several previous reports. SLCO1B1 521C resulted in a diminished cholesterol‐lowering response, but a marginal effect size limits utility for predicting simvastatin response.

The clinical pharmacogenetics implementation consortium guideline for SLCO1B1 and simvastatin-induced myopathy: 2014 update

Simvastatin is among the most commonly used prescription medications for cholesterol reduction. A single coding single-nucleotide polymorphism, rs4149056T>C, in SLCO1B1 increases systemic exposure to simvastatin and the risk of muscle toxicity. We summarize evidence from the literature supporting this association and provide therapeutic recommendations for simvastatin based on SLCO1B1 genotype. This article is an update to the 2012 Clinical Pharmacogenetics Implementation Consortium guideline for SLCO1B1 and simvastatin-induced myopathy.

Characterization of statin dose response in electronic medical records

Efforts to define the genetic architecture underlying variable statin response have met with limited success, possibly because previous studies were limited to effect based on a single dose. We leveraged electronic medical records (EMRs) to extract potency (ED50) and efficacy (Emax) of statin dose-response curves and tested them for association with 144 preselected variants. Two large biobanks were used to construct dose-response curves for 2,026 and 2,252 subjects on simvastatin and atorvastatin, respectively. Atorvastatin was more efficacious, was more potent, and demonstrated less interindividual variability than simvastatin. A pharmacodynamic variant emerging from randomized trials (PRDM16) was associated with Emax for both. For atorvastatin, Emax was 51.7 mg/dl in subjects homozygous for the minor allele vs. 75.0 mg/dl for those homozygous for the major allele. We also identified several loci associated with ED50. The extraction of rigorously defined traits from EMRs for pharmacogenetic studies represents a promising approach to further understand the genetic factors contributing to drug response.

Pharmacometabolomics of statin response

Statins reduce risk of cardiovascular disease (CVD) by decreasing plasma low-density lipoprotein (LDL) concentrations, as well as reducing inflammation and improving endothelial function. Despite their documented efficacy, there is considerable interindividual variation in effects of statins on CVD biomarkers. In the studies summarized here, we used complementary metabolomics platforms to define global effects of a statin (simvastatin) on metabolism and to identify markers indicative of mechanisms that contribute to variation in plasma LDL response to statin treatment.

The clinical pharmacogenomics implementation consortium: CPIC guideline for SLCO1B1 and simvastatin-induced myopathy

Cholesterol reduction from statin therapy has been one of the greatest public health successes in modern medicine. Simvastatin is among the most commonly used prescription medications. A non-synonymous coding single-nucleotide polymorphism (SNP), rs4149056, in SLCO1B1 markedly increases systemic exposure to simvastatin and the risk of muscle toxicity. This guideline explores the relationship between rs4149056 (c.521T>C, p.V174A) and clinical outcome for all statins. The strength of the evidence is high for myopathy with simvastatin. We limit our recommendations accordingly.

The emerging role of electronic medical records in pharmacogenomics

Health-care information technology and genotyping technology are both advancing rapidly, creating new opportunities for medical and scientific discovery. The convergence of these two technologies is now facilitating genetic association studies of unprecedented size within the context of routine clinical care. As a result, the medical community will soon be presented with a number of novel opportunities to bring functional genomics to the bedside in the area of pharmacotherapy. By linking biological material to comprehensive medical records, large multi-institutional biobanks are now poised to advance the field of pharmacogenomics through three distinct mechanisms: (i) retrospective assessment of previously known findings in a clinical practice-based setting, (ii) discovery of new associations in huge observational cohorts, and (iii) prospective application in a setting capable of providing real-time decision support. This review explores each of these translational mechanisms within a historical framework.

Pathophysiology of triglyceride-rich lipoproteins in atherothrombosis: clinical aspects

Invasive and noninvasive arterial imaging are important techniques used to study atherosclerosis and, specifically, to evaluate the atherogenecity of triglyceride-rich lipoproteins (TRL). Serial coronary angiography trials show significant benefit from lowering low-density lipoprotein cholesterol (LDL-C) which serves to retard lesion progression. Even with aggressive LDL-C reduction, however, up to half of patients demonstrate continued progression of atherosclerosis. Angiographic studies reveal that lowering LDL-C has the most impact on severe lesions, those > or = 50% diameter stenosis, whereas TRL (and their apolipoprotein markers) have been identified as a driving factor behind progression of mild-to-moderate lesions < 50% diameter stenosis. Quantitative coronary angiography (QCA) has demonstrated that progression of mild-to-moderate lesions are among the most significant predictors of clinical coronary events, and that lowering TRL reduces progression of coronary artery disease to the same degree as the lowering of LDL-C.

Estrogen receptor genotypes, menopausal status, and the lipid effects of tamoxifen

Tamoxifen induces important changes in serum lipid profiles in some women; however, little information is available to predict which women will experience improved lipid profiles during tamoxifen therapy. As part of a multicenter prospective observational trial in 176 breast cancer patients, we tested the hypothesis that tamoxifen-induced lipid changes were associated with genetic variants in candidate target genes (CYP2D6, ESR1, and ESR2). Tamoxifen lowered low-density lipoprotein cholesterol (P<0.0001) by 23.5 mg/dl (13.5-33.5 mg/dl) and increased triglycerides (P=0.006). In postmenopausal women, the ESR1-XbaI and ESR2-02 genotypes were associated with tamoxifen-induced changes in total cholesterol (P=0.03; GG vs GA/AA) and triglycerides (P=0.01; gene-dose effect), respectively. In premenopausal women, the ESR1-XbaI genotypes were associated with tamoxifen-induced changes in triglycerides (P=0.002; gene-dose effect) and high-density lipoprotein (P=0.004; gene-dose effect). Our results suggest that estrogen receptor genotyping may be useful in predicting which women would benefit more from tamoxifen.

The pharmacogenetics research network: from SNP discovery to clinical drug response

The NIH Pharmacogenetics Research Network (PGRN) is a collaborative group of investigators with a wide range of research interests, but all attempting to correlate drug response with genetic variation. Several research groups concentrate on drugs used to treat specific medical disorders (asthma, depression, cardiovascular disease, addiction of nicotine, and cancer), whereas others are focused on specific groups of proteins that interact with drugs (membrane transporters and phase II drug-metabolizing enzymes). The diverse scientific information is stored and annotated in a publicly accessible knowledge base, the Pharmacogenetics and Pharmacogenomics Knowledge base (PharmGKB). This report highlights selected achievements and scientific approaches as well as hypotheses about future directions of each of the groups within the PGRN. Seven major topics are included: informatics (PharmGKB), cardiovascular, pulmonary, addiction, cancer, transport, and metabolism.

Apo B versus cholesterol in estimating cardiovascular risk and in guiding therapy: report of the thirty-person/ten-country panel

There is abundant evidence that the risk of atherosclerotic vascular disease is directly related to plasma cholesterol levels. Accordingly, all of the national and transnational screening and therapeutic guidelines are based on total or LDL cholesterol. This presumes that cholesterol is the most important lipoprotein-related proatherogenic risk variable. On the contrary, risk appears to be more directly related to the number of circulating atherogenic particles that contact and enter the arterial wall than to the measured concentration of cholesterol in these lipoprotein fractions. Each of the atherogenic lipoprotein particles contains a single molecule of apolipoprotein (apo) B and therefore the concentration of apo B provides a direct measure of the number of circulating atherogenic lipoproteins. Evidence from fundamental, epidemiological and clinical trial studies indicates that apo B is superior to any of the cholesterol indices to recognize those at increased risk of vascular disease and to judge the adequacy of lipid-lowering therapy. On the basis of this evidence, we believe that apo B should be included in all guidelines as an indicator of cardiovascular risk. In addition, the present target adopted by the Canadian guideline groups of an apo B <90 mg dL(-1) in high-risk patients should be reassessed in the light of the new clinical trial results and a new ultra-low target of <80 mg dL(-1) be considered. The evidence also indicates that the apo B/apo A-I ratio is superior to any of the conventional cholesterol ratios in patients without symptomatic vascular disease or diabetes to evaluate the lipoprotein-related risk of vascular disease.

Subclasses of Low-Density Lipoprotein and Very Low-Density Lipoprotein in Familial Combined Hyperlipidemia: Relationship to Multiple Lipoprotein Phenotype

Objective— The present study addresses the presence of distinct metabolic phenotypes in familial combined hyperlipidemia (FCHL) in relation to small dense low-density lipoprotein (sd LDL) and very low-density lipoprotein (VLDL) subclasses.

Methods and Results— Hyperlipidemic FCHL relatives (n=72) were analyzed for LDL size by gradient gel electrophoresis. Pattern B LDL (sd LDL, particle size <258 Å) and pattern A LDL (buoyant LDL, particle size ≥258 Å) were defined. Analyses showed bimodal distribution of LDL size associated with distinct phenotypes. Subjects with predominantly large, buoyant LDL showed a hypercholesterolemic phenotype and the highest apo B levels. Subjects with predominantly sd LDL showed a hypertriglyceridemic, low high-density lipoprotein (HDL) cholesterol phenotype, with moderately elevated apoB, total cholesterol level, and LDL cholesterol level. Subjects with both buoyant LDL and sd LDL (pattern AB, n=7) showed an intermediate phenotype, with high normal plasma triglycerides. VLDL subfraction analysis showed that the sd LDL phenotype was associated with a 10-times higher number of VLDL1 particles of relatively lower apo AI and apo E content, as well as smaller VLDL2 particles, in combination with increased plasma insulin concentration in comparison to pattern A.

Conclusions— The present observations underscore the importance of the VLDL triglyceride metabolic pathway in FCHL as an important determinant of the phenotypic heterogeneity of the disorder.

An apolipoprotein influencing triglycerides in humans and mice revealed by comparative sequencing

Comparison of genomic DNA sequences from human and mouse revealed a new apolipoprotein (APO) gene (APOAV) located proximal to the well-characterized APOAI/CIII/AIV gene cluster on human 11q23. Mice expressing a human APOAV transgene showed a decrease in plasma triglyceride concentrations to one-third of those in control mice; conversely, knockout mice lacking Apoav had four times as much plasma triglycerides as controls. In humans, single nucleotide polymorphisms (SNPs) across the APOAV locus were found to be significantly associated with plasma triglyceride levels in two independent studies. These findings indicate that APOAV is an important determinant of plasma triglyceride levels, a major risk factor for coronary artery disease.

DIETARY ANDGENETICEFFECTS ONLOW-DENSITYLIPOPROTEINHETEROGENEITY

We have tested whether differences in distribution and dietary responsiveness of low-density lipoprotein (LDL) subclasses contribute to the variability in the magnitude of LDL-cholesterol reduction induced by diets low in total and saturated fat and high in carbohydrate. Our studies have focused on a common, genetically influenced metabolic profile, characterized by a predominance of small, dense LDL particles (subclass pattern B), that is associated with a two- to threefold increase in risk for coronary artery disease. We have found that healthy normolipidemic individuals with this trait show a greater reduction in LDL cholesterol and particle number in response to low-fat, high-carbohydrate diets than do unaffected individuals (subclass pattern A). Moreover, such diets result in reduced LDL particle size, with induction of pattern B in a substantial proportion of pattern A men. Recent studies have indicated that this response is under genetic influence. Future identification of the specific genes involved may lead to improved targeting of dietary therapies aimed at reducing cardiovascular disease risk.

Molecular signal transduction by conformational transmission: use of tetrasubstituted perhydroanthracenes as transducers

2,3,6,7-Tetrasubstituted cis-anti-cis perhydroanthracenes have been studied as conformational transducers for molecular signal transduction. 2,2'-Bipyridine groups attached to the perhydroanthracene through ether linkages were chosen as receptor substituents, while pyrene groups were selected as effectors. A chelation-induced triple ring flip of the perhydroanthracene could be achieved by the complexation of zinc(II) ions at the bipyridine sites of ligands 13 and 15. It was found that two pyrene substituents attached to the perhydroanthracene via a linker with an E double bond and an ester group could be used to monitor the triple ring flip. In the equatorial positions, the pyrenes are sufficiently close to form an excimer in the excited state, giving a fluorescence signal at 480 nm. In the axial positions, they are far away from each other and give mainly a monomer fluorescence signal at 380 nm. Both the bipyridine receptor and the pyrene effector are present in compound 33. The conformational switching 34-->35 (the two conformers of 33) has successfully been used for a signal transduction over a signal distance of 2 nm.

Familial factors in the antihypertensive response to lisinopril

BACKGROUND

Although it is widely recognized that there are familial elements in the pathogenesis of hypertension, remarkably little is known about the influence of family history on response to specific antihypertensive agents.

METHODS

This study was designed to address that issue by comparing the depressor response to lisinopril in a dose range of 10 to 40 mg in 74 patients enrolled as sibling pairs. Because all patients were treated with lisinopril, ambulatory blood pressure monitoring (ABPM), an objective measure not influenced by the investigators, was used to assess the primary blood pressure (BP) outcome variable.

RESULTS

Diastolic BP was highly correlated between sibling pairs at baseline (r = 0.476; P < .03) and on treatment (r = 0.524; P = .0021). Ethnicity/race had a striking influence on lisinopril dose and response rate. Among African American patients, 23 of 28 reached the top dose of 40 mg/day, whereas only 14 of 36 Caucasian patients reached that dose level. Among Caucasians, 92% responded, and only 48% of African Americans. Responders were characterized by being younger and heavier, having significantly lower microalbuminuria at baseline, higher baseline renal plasma flow (RPF), and higher urinary kallikrein.

CONCLUSION

Among Caucasians, the presence of a hypertensive sibling predicts a striking therapeutic response to angiotensin converting enzyme inhibition.

Atherogenic lipoprotein phenotype and diet-gene interactions

Studies employing analysis of LDL subclasses have demonstrated heterogeneity of the LDL response to low fat, high carbohydrate diets in healthy nonobese subjects. In individuals with a genetically influenced atherogenic lipoprotein phenotype, characterized by a predominance of small dense LDL (LDL subclass pattern B), lowering of plasma LDL cholesterol levels by diets with < or =24% fat has been found to represent a reduction in numbers of circulating mid-sized and small LDL particles, and hence an expected lowering of cardiovascular disease risk. In contrast, in the majority of healthy individuals with larger LDL (pattern A, found in approximately 70% of men and a larger percentage of women), a significant proportion of the low fat diet-induced reduction in plasma LDL cholesterol is made by depletion of the cholesterol content of LDL particles. This change in LDL composition is accompanied by a shift from larger to smaller LDL particle diameters. Moreover, with progressive reduction of dietary fat and isocaloric substitution of carbohydrate, an increasing number of subjects with pattern A convert to the pattern B phenotype. Studies in families have indicated that susceptibility to induction of pattern B by low fat diets is under genetic influence. Thus, diet-gene interactions affecting LDL subclass patterns may contribute to substantial interindividual variability in the effects of low fat diets on coronary heart disease risk.

Lipoprotein candidate genes for multivariate factors of the insulin resistance syndrome: a sib-pair linkage analysis in women twins

The insulin resistance syndrome (IRS) is characterized by a combination of interrelated coronary heart disease risk factors, including low high-density lipoprotein cholesterol (HDLC) levels, obesity and increases in triglyceride (TG), systolic and diastolic blood pressure (BP), small low-density lipoprotein particles (LDL-size), and fasting and postload plasma insulin and glucose. Using factor analysis, we previously identified multivariate factors based on data from women participating in the Kaiser Permanente Women Twins Study: 1) Weight/Fat, 2) Insulin/Glucose, 3) Lipids, and 4) BP. The purpose of this study is to evaluate evidence for genetic linkage between the multivariate factors and candidate genes. Quantitative sib-pair analysis based on the factor scores with markers for 9 candidate genes was carried out based on data from 126 pairs of dizygotic (DZ) women twins from the second exam of the Kaiser Permanente Women Twins study. Suggestive evidence for linkage was found for the Weight/fat factor and the Apo E gene (p = 0.01), and stronger evidence for linkage with the Lipid factor and the cholesterol ester transfer protein (p = 0.002) gene. Therefore, the CETP gene appears to influence covariation in LDL size, TG, and HDL, and may account for a portion of the well-established statistical and metabolic associations observed between these risk factors.

Enhanced oxidative susceptibility and reduced antioxidant content of metabolic precursors of small, dense low-density lipoproteins

PURPOSE

Elevated plasma concentrations of low-density lipoproteins (LDL) increase risk for coronary heart disease. However, lipoprotein profiles rich in small, dense LDL particles confer greater risk than those that mainly consist of large, buoyant LDL. This may be due, in part, to the greater oxidative susceptibility of small, dense LDL. In the current studies, we tested whether differences in the oxidative behavior of buoyant and dense LDL arise from differences in their immediate metabolic precursors, intermediate-density lipoproteins.

SUBJECTS AND METHODS

We compared the properties of intermediate-density lipoproteins and buoyant and dense LDL subfractions in 9 subjects with the large, buoyant LDL phenotype versus 6 with the small, dense LDL phenotype. Oxidative susceptibility was evaluated based on conjugated diene formation and parinaric acid oxidation induced by copper. Antioxidants (ubiquinol-10 and alpha-tocopherol) were measured by high-performance liquid chromatography.

RESULTS

Oxidative susceptibility was increased and antioxidant concentrations were decreased with increasing lipoprotein density (intermediate intermediate-density lipoproteins to buoyant LDL to dense LDL). Intermediate-density lipoproteins from subjects with the small, dense LDL phenotype had a greater oxidative susceptibility (by the parinaric acid test) and lower antioxidant concentrations than corresponding particles from subjects with the large, buoyant LDL phenotype.

CONCLUSIONS

Differences in oxidative susceptibility between large, buoyant and small, dense LDL particles are apparent in their lipoprotein precursors. These results suggest that lipoprotein oxidative susceptibility may be metabolically programmed and that intermediate-density lipoproteins may contribute to the increased risk associated with the small, dense LDL phenotype.

High-density lipoprotein cholesterol esterification and transfer rates to lighter density lipoproteins mediated by cholesteryl ester transfer protein in the fasting and postprandial periods are not altered in type 1 diabetes mellitus

Background: Diabetes mellitus is associated with atherosclerosis that has, in part, been ascribed to abnormalities in the reverse cholesterol transport system. Methods: We determined, in the fasting and post-alimentary periods, rates of HDL cholesterol esterification and transfer to apoB-containing lipoproteins, cholesteryl ester transfer protein (CETP) concentration, and apoB lipoprotein size in 10 type 1 diabetics and 10 well-matched controls. Autologous HDL was labeled with [14C]cholesterol and incubated at 37 degrees C during a period of 30 min for measurement of the cholesterol esterification rate (CER), as well as for 24 h for measurement of the endogenous HDL [14C]cholesteryl ester ([14C]CE) transfer rate to apoB-containing lipoproteins after 2- and 4-h incubations with the subject's own plasma. Exogenous cholesteryl ester transfer activity (CETA) was estimated by incubation of the participant's plasma (CETP source) with [14C]CE-HDL and VLDL from a pool of plasma donors. ApoB lipoprotein size was determined using non-denaturing polyacrylamide gradient gel electrophoresis of whole plasma. Results: Contrary to previous studies, we showed that even not well-controlled type 1 diabetics did not differ from lipid-matched, non-diabetic subjects in HDL-[14C]cholesterol esterification rate, transfer rates, or CETP concentration. CETP concentration correlates with the exogenous method of [14C]CE transfer and with the endogenous method only when the latter is corrected for plasma triacylglycerol (TG) concentration. In addition, during the postprandial phase, diabetic patients' VLDL are smaller and IDL size increases less than in controls. Conclusion: In type 1 diabetes mellitus, CETA is not altered when the plasma levels of donor and/or acceptor lipoproteins are within the normal range.

Increased low density lipoprotein degradation in aorta of irradiated mice is inhibited by preenrichment of low density lipoprotein with alpha-tocopherol

We previously reported that upper thoracic exposure to ionizing radiation (IR) accelerates fatty streak formation in C57BL/6 mice and that such effects are inhibited by overexpression of the antioxidant enzyme CuZn-superoxide dismutase (SOD). Notably, IR-accelerated lesion formation is strictly dependent on a high fat diet (i.e., atherogenic lipoproteins) but does not involve alterations in circulating lipid or lipoprotein levels. We thus proposed that IR promotes changes in the artery wall that enhance the deposition of lipoprotein lipids. To address this hypothesis, we examined the effects of IR on aortic accumulation and degradation of low density lipoproteins (LDL). Ten-week-old C57BL/6 mice were exposed to a single (8-Gy) dose of (60)Co radiation to the upper thoracic area or were sham irradiated (controls) and were then placed on the high fat diet. Five days postexposure, the mice received either (125)I-labeled LDL ((125)I-LDL) (which was used to measure intact LDL) or (125)I-labeled tyramine cellobiose ((125)I-TC)-LDL (which was used to measure both intact and cell-degraded LDL) via tail vein injection. On the basis of trichloroacetic acid (TCA)-precipitable counts in retroorbital blood samples, > or =95% of donor LDL was cleared within 24 h and there were no differences in time-averaged plasma concentrations of the two forms of LDL among irradiated and control mice. Aortic values increased markedly within the first hour and thereafter exhibited a slow increase up to 24 h. There were no differences between irradiated and control mice at 1 h, when values primarily reflected LDL entry, but a divergence was observed thereafter. At 24 h, (125)I-TC-associated counts were 1.8-fold higher in irradiated mice (P = 0.10). In contrast, (125)I-LDL-associated counts were 30% lower in irradiated mice (P< 0.05), suggesting that most of the retained (125)I-TC was associated with LDL degradation products. Consistent with the proposed involvement of oxidative or redox-regulated events, IR-induced LDL degradation was lower in SOD-transgenic than wild-type mice (P<0.05). The importance of LDL oxidation was suggested by observations that IR-induced LDL degradation was significantly reduced by preenriching LDL with alpha-tocopherol. On the basis of these results, we propose that IR elicits SOD-inhibitable changes in the artery wall that enhance LDL oxidation and degradation leading to the deposition of LDL-borne lipids. These studies provide additional support for the role of oxidation in lipoprotein lipid deposition and atherogenesis and suggest that IR promotes an arterial environment that stimulates this process in vivo.

Induction and maintenance of the neuronal cholinergic phenotype in the central nervous system by BMP-9

Bone morphogenetic proteins (BMPs) have multiple functions in the developing nervous system. A member of this family, BMP-9, was found to be highly expressed in the embryonic mouse septum and spinal cord, indicating a possible role in regulating the cholinergic phenotype. In cultured neurons, BMP-9 directly induced the expression of the cholinergic gene locus encoding choline acetyltransferase and the vesicular acetylcholine transporter and up-regulated acetylcholine synthesis. The effect was reversed upon withdrawal of BMP-9. Intracerebroventricular injection of BMP-9 increased acetylcholine levels in vivo. Although certain other BMPs also up-regulated the cholinergic phenotype in vitro, they were less effective than BMP-9. These data indicate that BMP-9 is a differentiating factor for cholinergic central nervous system neurons.

Heritability of factors of the insulin resistance syndrome in women twins

The insulin resistance syndrome (IRS) is characterized by a combination of interrelated coronary heart disease (CHD) risk factors, including low high-density lipoprotein cholesterol (HDL-C) levels, obesity and increases in triglyceride (TG), blood pressure, small low-density lipoprotein particles (LDL), and both fasting and postload plasma insulin and glucose. Using factor analysis, we previously identified 3 uncorrelated factors that explained 66% of the variance among these variables, based on data from women participating in examination 2 of the Kaiser Permanente Women Twins Study in Oakland, CA during 1989-1990. The factors were interpreted as: 1) body mass/fat distribution, 2) insulin/glucose, and 3) lipids: TG, HDL-C, LDL peak particle diameter. In this analysis, heritability of each of the factors was estimated based on data from 140 monozygotic and 96 dizygotic pairs of non-diabetic women twins. Heritability estimates were calculated using the classical approach, the analysis of variance (ANOVA) approach, and the maximum likelihood approach. For the body mass/fat distribution factor heritability estimates suggest moderate genetic influences; 0.61 (P < 0.001), 0.14 (P > 0.05), and 0.71 (P < 0.001), respectively. The insulin/glucose factor appeared to be highly heritable, with estimates of 0.87, 0.92, and 0.57 (all P < 0.001), respectively. The heritability estimates for the lipid factor were moderate and consistent across methods: 0.25 (P < 0.10), 0.32 (P < 0.05), and 0.30 (P < 0.05), respectively. These results are consistent with genetic influences on each of the 3 "factors," and suggest that both genetic and environmental effects are involved in the clustering of IRS risk factors.

Cardiovascular fitness, body composition, and lipoprotein lipid metabolism in older men

BACKGROUND

Lipoprotein lipids in older individuals are affected by family history of coronary artery disease (CAD), obesity, diet, and physical activity habits.

METHODS

The relationship of obesity and physical fitness (VO2max) to lipoprotein lipids and postheparin lipases was examined in a cross-sectional study of 12 lean (LS) and 26 obese (OS) sedentary men and 18 master athletes (MAs) aged 65+/-1 years (mean +/- SE). The men were healthy, had no family history of CAD, and were weight stable on AHA diets at the time of study.

RESULTS

VO2max was similar in LS and OS men but higher in the MAs. The OS men had a higher percentage of body fat (%BF), waist circumference, and waist:hip ratio (WHR) than the MA and LS men, but MA and LS men differed only in waist circumference. Total and LDL-C levels were comparable, but HDL-C, HDL2-C, and %HDL2b subspecies were higher in MAs than in OS and LS men, and in LS than in OS men. Triglyceride (TG) was similar in MAs and LS men but higher in OS men. Across groups, two multiple regression analyses models (VO2max, %BF, and WHR or waist circumference) showed that %BF and VO2max independently predicted HDL-C and HDL2, whereas WHR predicted TG (r2 = .45) more strongly than waist circumference (r2 = .39). Postheparin lipoprotein lipase activity (LPL) was comparable among groups and correlated independently with VO2max. Total postheparin lipolytic activity (PHLA), hepatic lipase activity (HL), and HL:PHLA ratio were similar in MAs and LS men but higher in OS men. In both multiple regression analysis models, only %BF predicted HL activity and the HL:PHLA ratio. The HL:PHLA ratio independently predicted HDL-C, HDL2-C, %HDL2b, %HDL3 subspecies, and the cholesterol:HDL-C ratio, whereas LPL activity predicted TG.

CONCLUSIONS

Increased fitness and reduced total and abdominal fatness in MAs are associated with lower HL and higher LPL activities, which may mediate their higher HDL-C and lower TG levels relative to their sedentary peers.