Conifer desiccation in the 2021 NW heatwave confirms the role of hydraulic damage

The unprecedented heatwave which hit the Pacific northwest of North America in late June-early July 2021 impacted ecosystems and communities, yet evidence for and analysis of this impact are still missing. Here we bring a unique dataset quantifying the impact on conifer trees, which are keystone species of many northwest ecosystems. Moreover, we take advantage of this exceptional event as a broad, extreme, 'field experiment' to test a fundamental theory in plant physiology and prepare our forests for a harsher future. Overall, the data collected confirm the role of hydraulic vulnerability in drought-induced injury to trees.

Effects of sample aging on total cholesterol values determined by the automated ferric chloride-sulfuric acid and Liebermann-Burchard procedures

To investigate the comparability of three commonly used methods for determination of total cholesterol in plasma in several studies, we used fresh plasma samples as well as plasmas and reference sera that had been stored frozen at −15 degrees C for as long as several years. Duplicate determinations by the manual method of Abell et al. (J. Biol. Chem. 195: 357, 1952) were compared with estimates from one to five continuous-flow analyzers by the ferric chloride-sulfuric acid procedure and also with estimates from five to 13 continuous-flow analyzers by the Liebermann-Burchard procedure with calibrator, as part of the laboratory standardization activities of the Lipid Research Clinics. The agreement among all three procedures was generally within acceptable limits (within 5% of the manual method) when plasmas or sera were fresh or had been frozen for less than one month. Results by the manual method of Abell et al. agreed well with those by the automated Liebermann-Burchard method for samples that had been stored at −15 degrees C for as long as two years. However, the automated ferric chloride-sulfuric acid procedure often showed unacceptably high values (as compared with those from the manual method) for samples that had been stored frozen for a year or more. With the ferric chloride-sulfuric acid method, measured cholesterol concentration increased about 2.5% per year of storage for at least two years. We conclude that reference sera of plasmas that have been kept in long-term frozen storage (−15 degrees C) are not suitable for ongoing standardization of the automated ferric chloride-sulfuric acid assay for cholesterol.

Effects of Extended-Release Niacin on Quartile Lp-PLA2 Levels and Clinical Outcomes in Statin-treated Patients with Established Cardiovascular Disease and Low Baseline Levels of HDL-Cholesterol: Post Hoc Analysis of the AIM HIGH Trial

Background:

Lipoprotein-associated phospholipase A2 (LpPLA2) is an inflammatory marker that has been associated with the presence of vulnerable plaque and increased risk of cardiovascular (CV) events.

Objective:

To assess the effect of extended-release niacin (ERN) on Lp-PLA2 activity and clinical outcomes.

Methods:

We performed a post hoc analysis in 3196 AIM-HIGH patients with established CV disease and low baseline levels of high-density lipoprotein cholesterol (HDL-C) who were randomized to ERN versus placebo on a background of simvastatin therapy (with or without ezetimibe) to assess the association between baseline Lp-PLA2 activity and the rate of the composite primary end point (CV death, myocardial infarction, stroke, hospitalization for unstable angina, and symptom-driven revascularization).

Results:

Participants randomized to ERN, but not those randomized to placebo, experienced a significant 8.9% decrease in LpPLA2. In univariate analysis, the highest quartile of LpPLA2 activity (>208 nmol/min/mL, Q4) was associated with higher event rates compared to the lower quartiles in the placebo group (log rank P = .032), but not in the ERN treated participants (log rank P = .718). However, in multivariate analysis, adjusting for sex, diabetes, baseline LDL-C, HDL-C, and triglycerides, there was no significant difference in outcomes between the highest Lp-PLA2 activity quartile versus the lower quartiles in both the placebo and the ERN groups.

Conclusion:

Among participants with stable CV disease on optimal medical therapy, elevated Lp-PLA2 was associated with higher CV events; however, addition of ERN mitigates this effect. This association in the placebo group was attenuated after multivariable adjustment, which suggests that Lp-PLA2 does not improve risk assessment beyond traditional risk factors.

Structural basis of the lipid transfer mechanism of phospholipid transfer protein (PLTP)

Human phospholipid transfer protein (PLTP) mediates the transfer of phospholipids among atheroprotective high-density lipoproteins (HDL) and atherogenic low-density lipoproteins (LDL) by an unknown mechanism. Delineating this mechanism would represent the first step towards understanding PLTP-mediated lipid transfers, which may be important for treating lipoprotein abnormalities and cardiovascular disease. Here, using various electron microscopy techniques, PLTP is revealed to have a banana-shaped structure similar to cholesteryl ester transfer protein (CETP). We provide evidence that PLTP penetrates into the HDL and LDL surfaces, respectively, and then forms a ternary complex with HDL and LDL. Insights into the interaction of PLTP with lipoproteins at the molecular level provide a basis to understand the PLTP-dependent lipid transfer mechanisms for dyslipidemia treatment.

Low-Density Lipoprotein Inhibits Secretion of Phospholipid Transfer Protein in Human Trophoblastic BeWo Cells

Human plasma phospholipid transfer protein (PLTP) plays an important role in lipoprotein metabolism. In this study, we investigated the effects of lipoproteins on the secretion of PLTP in cultured BeWo choriocarcinoma cells. Low-density lipoproteins (LDLs) decreased PLTP secretion in a dose- and time-dependent manner, whereas very low density lipoproteins and high-density lipoproteins (HDLs) had little effect. LDL suppression of PLTP secretion was not altered by the inhibition of both LDL receptor and LDL receptor–related protein with receptor-associated protein. Mitogen-activated protein kinase (MAPK) kinase (MEK) inhibitor, U0126, could abolish the LDL-mediated inhibition of PLTP secretion. Furthermore, LDL, but not HDL, could stimulate the expression of MAPK phosphatase-1 (MKP-1) in BeWo cells that resulted in the inactivation of p44/p42 extracellular signal-regulated kinase (ERK) 1 and 2, the family members of MAPKs. These results support the conclusion that LDL-mediated suppression of PLTP secretion in BeWo cells is through a LDL receptor-independent MAPK signaling pathway.

Mortality reduction in patients treated with long-term intensive lipid therapy: 25-year follow-up of the Familial Atherosclerosis Treatment Study-Observational Study

BACKGROUND

Cardiovascular disease (CVD) begins early in life and is associated with both the number of risk factors present and length of exposure to these risk factors including hyperlipidemia.

OBJECTIVES

The clinical benefit of intensive lipid therapy over 25 years was investigated in the Familial Atherosclerosis Treatment Study-Observational Study.

METHODS

Of 175 coronary artery disease subjects with mean low-density lipoprotein cholesterol (LDL-C) of 191 mg/dL and mean age of 50 years, who completed the randomized and placebo-controlled Familial Atherosclerosis Treatment Study, 100 chose receiving lipid management by their physicians (usual care [UC]) and 75 elected to receive an intensive treatment [IT] for lipid management with lovastatin (40 mg/d), niacin (2.5 g/d), and colestipol (20 g/d) from 1989 to 2004, followed by double therapy with simvastatin (40-80 mg/d) and niacin from 2005 to 2006 and by triple therapy of ezetimibe 10 mg and simvastatin 40 to 80 mg/d plus niacin during 2007 to 2012. Deaths from CVD, non-CVD, and any cause were compared between UC and IT using Cox proportional hazards model.

RESULTS

UC and IT groups were similar in risk factors with the exception that IT had more severe coronary artery disease. Mean LDL-C levels were 167 mg/dL from 1988 to 2004, 97 from 2005 to 2006, and 96 from 2007 to 2012 in surviving subjects receiving UC. IT lowered LDL-C to 119, 97, and 83 mg/dL in the 3 periods, respectively. Compared with UC, IT significantly reduced total mortality (11.1 vs 26.3 per 1000 person years [PY], hazard ratio [HR] = 0.45, 95% confidence interval [CI]: 0.26-0.77, P = .003) and CVD mortality (10.6 vs 27.7 per 1000 PY, HR = 0.34, 95% CI: 0.15-0.80, P = .009). The non-CVD mortality was also reduced but was not of statistical significance (6.8 vs 12.7 per 1000 PY, HR = 0.55, 95% CI: 0.27-1.14, P = .11).

CONCLUSIONS

Long-term intensive lipid therapy significantly reduced total and cardiovascular mortality in Familial Atherosclerosis Treatment Study-Observational Study. These results support the importance of lifetime risk management to improve long-term outcome.

Relationship of baseline HDL subclasses, small dense LDL and LDL triglyceride to cardiovascular events in the AIM-HIGH clinical trial

BACKGROUND AND AIMS

Previous results of the AIM-HIGH trial showed that baseline levels of the conventional lipid parameters were not predictive of future cardiovascular (CV) outcomes. The aims of this secondary analysis were to examine the levels of cholesterol in high density lipoprotein (HDL) subclasses (HDL2-C and HDL3-C), small dense low density lipoprotein (sdLDL-C), and LDL triglyceride (LDL-TG) at baseline, as well as the relationship between these levels and CV outcomes.

METHODS

Individuals with CV disease and low baseline HDL-C levels were randomized to simvastatin plus placebo or simvastatin plus extended release niacin (ERN), 1500 to 2000 mg/day, with ezetimibe added as needed in both groups to maintain an on-treatment LDL-C in the range of 40-80 mg/dL. The primary composite endpoint was death from coronary disease, nonfatal myocardial infarction, ischemic stroke, hospitalization for acute coronary syndrome, or symptom-driven coronary or cerebrovascular revascularization. HDL-C, HDL3-C, sdLDL-C and LDL-TG were measured at baseline by detergent-based homogeneous assays. HDL2-C was computed by the difference between HDL-C and HDL3-C. Analyses were performed on 3094 study participants who were already on statin therapy prior to enrollment in the trial. Independent contributions of lipoprotein fractions to CV events were determined by Cox proportional hazards modeling.

RESULTS

Baseline HDL3-C was protective against CV events (HR: 0.84, p = 0.043) while HDL-C, HDL2-C, sdLDL-C and LDL-TG were not event-related (HR: 0.96, p = 0.369; HR: 1.07, p = 0.373; HR: 1.05, p = 0.492; HR: 1.03, p = 0.554, respectively).

CONCLUSIONS

The results of this secondary analysis of the AIM-HIGH Study indicate that levels of HDL3-C, but not other lipoprotein fractions, are predictive of CV events, suggesting that the HDL3 subclass may be primarily responsible for the inverse association of HDL-C and CV disease.

Lipoprotein (a) measurements for clinical application

The high degree of size heterogeneity of apo(a), the distinct protein component of lipoprotein (a) [Lp(a)], renders the development and selection of specific antibodies directed to apo(a) more difficult and poses significant challenges to the development of immunoassays to measure its concentration in plasma or serum samples. Apo(a) is extremely variable in size not only between but also within individuals because of the presence of two different, genetically determined apo(a) isoform sizes. Therefore, the antigenic determinants per particle available to interact with the antibodies will vary in the samples and the calibrators, thus contributing to apo(a) size-dependent inaccuracy of different methods. The lack of rigorous validation of the immunoassays and common means of expressing Lp(a) concentrations hinder the harmonization of results obtained by different studies and contribute to the lack of common cut points for identification of individuals at risk for coronary artery disease or for interventions aimed at reducing Lp(a) levels. The aim of our review is to present and critically evaluate the issues surrounding the measurements of Lp(a), their impact on the clinical interpretation of the data, and the obstacles we need to overcome to achieve the standardization of Lp(a) measurements.

Inhibition of thrombin generation in human plasma by phospholipid transfer protein

Background

Plasma phospholipid transfer protein (PLTP) transfers lipids between donors and acceptors (e.g., from HDL to VLDL) and modulates lipoprotein composition, size, and levels. No study has reported an assessment of the effects of PLTP on blood clotting reactions, such as reflected in thrombin generation assays, or on the association of venous thrombosis (VTE) risk with PLTP activity.

Methods

The in vitro effects of PLTP on blood coagulation reactions and the correlations between plasma PLTP activity levels and VTE were studied.

Results

Recombinant (r) PLTP concentration-dependently inhibited plasma thrombin generation and factor XII-dependent kallikrein generation when sulfatide was used to stimulate factor XII autoactivation in plasma. However, rPLTP did not inhibit thrombin generation in plasma induced by factor XIa or tissue factor, implicating an effect of PLTP on contact activation reactions. In purified systems, rPLTP inhibited factor XII autoactivation stimulated by sulfatide in the presence of VLDL. In surface plasmon resonance studies, purified factor XII bound to immobilized rPLTP, implying that rPLTP inhibits factor XII-dependent contact activation by binding factor XII in the presence of lipoproteins. Analysis of plasmas from 40 male patients with unprovoked VTE and 40 matched controls indicated that low PLTP lipid transfer activity (≤25th percentile) was associated with an increased risk of VTE after adjustment for body mass index, plasma lipids, and two known thrombophilic genetic risk factors.

Conclusion

These data imply that PLTP may be an antithrombotic plasma protein by inhibiting generation of prothrombotic factor XIIa in the presence of VLDL. This newly discovered anticoagulant activity of PLTP merits further clinical and biochemical studies.

Electronic supplementary material

The online version of this article (doi:10.1186/s12959-015-0054-0) contains supplementary material, which is available to authorized users.

PLTP activity inversely correlates with CAAD: effects of PON1 enzyme activity and genetic variants on PLTP activity

Recent studies have failed to demonstrate a causal cardioprotective effect of HDL cholesterol levels, shifting focus to the functional aspects of HDL. Phospholipid transfer protein (PLTP) is an HDL-associated protein involved in reverse cholesterol transport. This study sought to determine the genetic and nongenetic predictors of plasma PLTP activity (PLTPa), and separately, to determine whether PLTPa predicted carotid artery disease (CAAD). PLTPa was measured in 1,115 European ancestry participants from a case-control study of CAAD. A multivariate logistic regression model was used to elucidate the relationship between PLTPa and CAAD. Separately, a stepwise linear regression determined the nongenetic clinical and laboratory characteristics that best predicted PLTPa. A final stepwise regression considering both nongenetic and genetic variables identified the combination of covariates that explained maximal PLTPa variance. PLTPa was significantly associated with CAAD (7.90 × 10(-9)), with a 9% decrease in odds of CAAD per 1 unit increase in PLTPa (odds ratio = 0.91). Triglyceride levels (P = 0.0042), diabetes (P = 7.28 × 10(-5)), paraoxonase 1 (PON1) activity (P = 0.019), statin use (P = 0.026), PLTP SNP rs4810479 (P = 6.38 × 10(-7)), and PCIF1 SNP rs181914932 (P = 0.041) were all significantly associated with PLTPa. PLTPa is significantly inversely correlated with CAAD. Furthermore, we report a novel association between PLTPa and PON1 activity, a known predictor of CAAD.

HDL-3 is a superior predictor of carotid artery disease in a case-control cohort of 1725 participants

Background

Recent data suggest that high‐density lipoprotein cholesterol (HDL‐C) levels are likely not in the causative pathway of atheroprotection, shifting focus from HDL‐C to its subfractions and associated proteins. This study's goal was to determine which HDL phenotype was the better predictor of carotid artery disease (CAAD).

Methods and Results

HDL‐2 and HDL‐3 were measured in 1725 participants of European ancestry in a prevalent case‐control cohort study of CAAD. Stratified analyses were conducted for men (n=1201) and women (n=524). Stepwise linear regression was used to determine whether HDL‐C, HDL‐2, HDL‐3, or apolipoprotein A1 was the best predictor of CAAD, while adjusting for the confounders of censored age, diabetes, and current smoking status. In both men and women, HDL‐3 was negatively associated with CAAD (P=0.0011 and 0.033 for men and women, respectively); once HDL‐3 was included in the model, no other HDL phenotype was significantly associated with CAAD. Addition of paraoxonase 1 activity to the aforementioned regression model showed a significant and independent (of HDL‐3) association with CAAD in men (P=0.001) but not in the smaller female subgroup.

Conclusions

This study is the first to contrast the associations of HDL‐2 and HDL‐3 with CAAD. We found that HDL‐3 levels were more predictive of CAAD status than HDL‐2, HDL‐C, or apolipoprotein A1. In addition, for men, paraoxonase 1 activity improved the overall model prediction for CAAD independently and additively with HDL‐3 levels. Further investigation into the molecular mechanisms through which HDL‐3 is associated with protection from CAAD is warranted.

Lipoprotein lipase (LPL) is associated with neurite pathology and its levels are markedly reduced in the dentate gyrus of Alzheimer's disease brains

Lipoprotein lipase (LPL) is involved in regulation of fatty acid metabolism, and facilitates cellular uptake of lipoproteins, lipids and lipid-soluble vitamins. We evaluated LPL distribution in healthy and Alzheimer’s disease (AD) brain tissue and its relative levels in cerebrospinal fluid. LPL immunostaining is widely present in different neuronal subgroups, microglia, astrocytes and oligodendroglia throughout cerebrum, cerebellum and spinal cord. LPL immunoreactivity is also present in leptomeninges, small blood vessels, choroid plexus and ependymal cells, Schwann cells associated with cranial nerves, and in anterior and posterior pituitary. In vitro studies have shown presence of secreted LPL in conditioned media of human cortical neuronal cell line (HCN2) and neuroblastoma cells (SK-N-SH), but not in media of cultured primary human astrocytes. LPL was present in cytoplasmic and nuclear fractions of neuronal cells and astrocytes in vitro. LPL immunoreactivity strongly associates with AD-related pathology, staining diffuse plaques, dystrophic and swollen neurites, possible Hirano bodies and activated glial cells. We observed no staining associated with neurofibrillary tangles or granulovacuolar degeneration. Granule cells of the dentate gyrus and the associated synaptic network showed significantly reduced staining in AD compared to control tissue. LPL was also reduced in AD CSF samples relative to those in controls.

Relationship of apolipoproteins A-1 and B, and lipoprotein(a) to cardiovascular outcomes: the AIM-HIGH trial (Atherothrombosis Intervention in Metabolic Syndrome with Low HDL/High Triglyceride and Impact on Global Health Outcomes)

OBJECTIVES

This study sought to examine the relationship between baseline and on-study apolipoproteins (apo) A-1 and B and lipoprotein(a) [Lp(a)] levels and the development of subsequent cardiovascular (CV) events in the AIM-HIGH (Atherothrombosis Intervention in Metabolic Syndrome with Low HDL/High Triglyceride and Impact on Global Health Outcomes) trial.

BACKGROUND

Niacin has been reported to lower apoB and Lp(a) and to raise apoA-1.

METHODS

Individuals with CV disease and low baseline levels of high-density lipoprotein cholesterol were randomized to simvastatin plus placebo or simvastatin, plus extended-release niacin ([ERN], 1,500 to 2,000 mg/day), with ezetimibe added as needed, in both groups, to maintain an on-treatment low-density lipoprotein cholesterol in the range of 40 to 80 mg/dl. Hazard ratios (HRs) were used to evaluate the relationship between levels of apoA-1, apoB, and Lp(a), and CV events in each treatment group.

RESULTS

Baseline apoB and the apoB/apoA-I ratio were significantly predictive of CV events only for the placebo group (HR: 1.17 [p = 0.018] and HR: 1.19 [p = 0.016]). Baseline and on-study Lp(a) were predictive of CV events in both simvastatin plus placebo (baseline HR: 1.24 [p = 0.002] and on-study HR: 1.21 [p = 0.017]) and the simvastatin plus ERN group (baseline HR: 1.25 [p = 0.001] and on-study HR: 1.18 [p = 0.028]). The ERN modestly increased 1-year apoA-1 (7%), decreased apoB (13%), decreased the ApoB/ApoA-1 ratio (19%), and decreased Lp(a) 21%, but did not reduce CV events.

CONCLUSIONS

Lp(a) was associated with increased CV risk in both treatment groups indicating that it contributes to residual CV risk. However, there was no evidence that ERN reduced CV risk, despite favorable lipoprotein changes.

Linkage and association of phospholipid transfer protein activity to LASS4

Phospholipid transfer protein activity (PLTPa) is associated with insulin levels and has been implicated in atherosclerotic disease in both mice and humans. Variation at the PLTP structural locus on chromosome 20 explains some, but not all, heritable variation in PLTPa. In order to detect quantitative trait loci (QTLs) elsewhere in the genome that affect PLTPa, we performed both oligogenic and single QTL linkage analysis on four large families (n = 227 with phenotype, n = 330 with genotype, n = 462 total), ascertained for familial combined hyperlipidemia. We detected evidence of linkage between PLTPa and chromosome 19p (lod = 3.2) for a single family and chromosome 2q (lod = 2.8) for all families. Inclusion of additional marker and exome sequence data in the analysis refined the linkage signal on chromosome 19 and implicated coding variation in LASS4, a gene regulated by leptin that is involved in ceramide synthesis. Association between PLTPa and LASS4 variation was replicated in the other three families (P = 0.02), adjusting for pedigree structure. To our knowledge, this is the first example for which exome data was used in families to identify a complex QTL that is not the structural locus.

PLTP regulates STAT3 and NFκB in differentiated THP1 cells and human monocyte-derived macrophages

Phospholipid transfer protein (PLTP) plays an important role in regulation of inflammation. Previously published studies have shown that PLTP binds, transfers and neutralizes bacterial lipopolysaccharides. In the current study we tested the hypothesis that PLTP can also regulate anti-inflammatory pathways in macrophages. Incubation of macrophage-like differentiated THP1 cells and human monocyte-derived macrophages with wild-type PLTP in the presence or absence of tumor necrosis factor alpha (TNFα) or interferon gamma (IFNγ) significantly increased nuclear levels of active signal transducer and activator of transcription 3, pSTAT3(Tyr705) (p<0.01). Similar results were obtained in the presence of a PLTP mutant without lipid transfer activity (PLTP(M159E)), suggesting that PLTP-mediated lipid transfer is not required for activation of the STAT3 pathway. Inhibition of ABCA1 by chemical inhibitor, glyburide, as well as ABCA1 RNA inhibition, reversed the observed PLTP-mediated activation of STAT3. In addition, PLTP reduced nuclear levels of active nuclear factor kappa-B (NFκB) p65 and secretion of pro-inflammatory cytokines in conditioned media of differentiated THP1 cells and human monocyte-derived macrophages. Our data suggest that PLTP has anti-inflammatory capabilities in macrophages.

Role of plasma phospholipid transfer protein in lipid and lipoprotein metabolism

The understanding of the physiological and pathophysiological role of PLTP has greatly increased since the discovery of PLTP more than a quarter of century ago. A comprehensive review of PLTP is presented on the following topics: PLTP gene organization and structure; PLTP transfer properties; different forms of PLTP; characteristics of plasma PLTP complexes; relationship of plasma PLTP activity, mass and specific activity with lipoprotein and metabolic factors; role of PLTP in lipoprotein metabolism; PLTP and reverse cholesterol transport; insights from studies of PLTP variants; insights of PLTP from animal studies; PLTP and atherosclerosis; PLTP and signal transduction; PLTP in the brain; and PLTP in human disease. PLTP's central role in lipoprotein metabolism and lipid transport in the vascular compartment has been firmly established. However, more studies are needed to further delineate PLTP's functions in specific tissues, such as the lung, brain and adipose tissue. Furthermore, the specific role that PLTP plays in human diseases, such as atherosclerosis, cancer, or neurodegenerative disease, remains to be clarified. Exciting directions for future research include evaluation of PLTP's physiological relevance in intracellular lipid metabolism and signal transduction, which undoubtedly will advance our knowledge of PLTP functions in health and disease. This article is part of a Special Issue entitled Advances in High Density Lipoprotein Formation and Metabolism: A Tribute to John F. Oram (1945-2010).

Impact of site-specific N-glycosylation on cellular secretion, activity and specific activity of the plasma phospholipid transfer protein

The plasma phospholipid transfer protein (PLTP) plays a key role in lipid and lipoprotein metabolism. It has six potential N-glycosylation sites. To study the impact of these sites on PLTP secretion and activity, six variants containing serine to alanine point mutations were prepared by site-directed mutagenesis and expressed in Chinese hamster ovary Flp-In cells. The apparent size of each of the six PLTP mutants was slightly less than that of wild type by Western blot, indicating that all six sites are glycosylated or utilized. The size of the carbohydrate at each N-glycosylation site ranged from 3.14 to 4.2kDa. The effect of site-specific N-glycosylation removal on PLTP secretion varied from a modest enhancement (15% and 60%), or essentially no effect, to a reduction in secretion (8%, 14% and 32%). Removal of N-glycosylation at any one of the six glycosylation sites resulted in a significant 35-78% decrease in PLTP activity, and a significant 29-80% decrease in PLTP specific activity compared to wild type. These data indicate that although no single N-linked carbohydrate chain is a requirement for secretion or activity, the removal of the carbohydrate chains had a quantitative impact on cellular secretion of PLTP and its phospholipid transfer activity.

Lipoprotein(a) levels, apo(a) isoform size, and coronary heart disease risk in the Framingham Offspring Study

The aim of this study was to assess the independent contributions of plasma levels of lipoprotein(a) (Lp(a)), Lp(a) cholesterol, and of apo(a) isoform size to prospective coronary heart disease (CHD) risk. Plasma Lp(a) and Lp(a) cholesterol levels, and apo(a) isoform size were measured at examination cycle 5 in subjects participating in the Framingham Offspring Study who were free of CHD. After a mean follow-up of 12.3 years, 98 men and 47 women developed new CHD events. In multivariate analysis, the hazard ratio of CHD was approximately two-fold greater in men in the upper tertile of plasma Lp(a) levels, relative to those in the bottom tertile (P < 0.002). The apo(a) isoform size contributed only modestly to the association between Lp(a) and CHD and was not an independent predictor of CHD. In multivariate analysis, Lp(a) cholesterol was not significantly associated with CHD risk in men. In women, no association between Lp(a) and CHD risk was observed. Elevated plasma Lp(a) levels are a significant and independent predictor of CHD risk in men. The assessment of apo(a) isoform size in this cohort does not add significant information about CHD risk. In addition, the cholesterol content in Lp(a) is not a significant predictor of CHD risk.

Different phospholipid transfer protein complexes contribute to the variation in plasma PLTP specific activity

Phospholipid transfer protein (PLTP) facilitates the transfer of phospholipids among lipoproteins. Over half of the PLTP in human plasma has been found to have little phospholipid transfer activity (inactive PLTP). We recently observed that plasma PLTP specific activity is inversely correlated with high-density lipoprotein (HDL) level and particle size in healthy adults. The purpose of this study was to evaluate the factors that contribute to the variation in plasma PLTP specific activity. Analysis of the specific activity of PLTP complexes in nine plasma samples from healthy adults revealed two clusters of inactive PLTP complexes with mean molecular weights (MW) of 342kDa and 146kDa. The large and small inactive PLTP complexes represented 52±8% (range 39-63%) and 8±8% (range 1-28%) of the plasma PLTP, respectively. Active PLTP complexes had a mean MW of 207kDa and constituted 40±6% (range 33-50%) of the plasma PLTP. The specific activity of active PLTP varied from 16 to 32μmol/μg/h. These data demonstrate for the first time the existence of small inactive plasma PLTP complexes. Variation in the amount of the two clusters of inactive PLTP complexes and the specific activity of the active PLTP contribute to the variation in plasma PLTP specific activity.

Phospholipid transfer protein in human plasma associates with proteins linked to immunity and inflammation

Phospholipid transfer protein (PLTP), which associates with apolipoprotein A-I (the major HDL protein), plays a key role in lipoprotein remodeling. Because its level in plasma increases during acute inflammation, it may also play previously unsuspected roles in the innate immune system. To gain further insight into its potential physiological functions, we isolated complexes containing PLTP from plasma by immunoaffinity chromatography and determined their composition. Shotgun proteomics revealed that only 6 of the 24 proteins detected in the complexes were apolipoproteins. The most abundant proteins were clusterin (apoJ), PLTP itself, coagulation factors, complement factors, and apoA-I. Remarkably, 20 of the 24 proteins had known protein-protein interactions. Biochemical studies confirmed two previously established interactions and identified five new ones between PLTP and proteins. Moreover, clusterin, apoA-I, and apoE preserved the lipid-transfer activity of recombinant PLTP in the absence of lipid, indicating that these interactions may have functional significance. Unexpectedly, lipids accounted for only 3% of the mass of the PLTP complexes. Collectively, our observations indicate that PLTP in human plasma resides on lipid-poor complexes dominated by clusterin and proteins implicated in host defense and inflammation. They further suggest that protein-protein interactions drive the formation of PLTP complexes in plasma.

Effects of combination lipid therapy on coronary stenosis progression and clinical cardiovascular events in coronary disease patients with metabolic syndrome: a combined analysis of the Familial Atherosclerosis Treatment Study (FATS), the HDL-Atherosclerosis Treatment Study (HATS), and the Armed Forces Regression Study (AFREGS)

We examined the impact of metabolic syndrome (MS) on coronary stenosis progression and major cardiovascular (CV) events and investigated the mitigating effects of low-density lipoprotein (LDL) cholesterol lowering and LDL cholesterol lowering plus high-density lipoprotein (HDL) cholesterol increasing. This analysis combined individual patient data from 445 subjects who participated in 3 double-blinded, randomized, placebo-controlled trials (FATS, HATS, and AFREGS) comparing intensive lipid therapy to placebos on coronary stenosis progression by quantitative coronary angiography and on major CV events. The primary end points were change in mean proximal coronary diameter stenosis (Delta%S(prox)) over 3 years and the frequency of the predefined composite of coronary artery disease death, nonfatal myocardial infarction, stroke, and revascularization due to worsening ischemia. Patients with MS had 50% more rapid coronary stenosis progression and 64% increased CV event frequency compared to those without. More rapid coronary stenosis progression was significantly and independently associated with a 3.5-fold increased event risk (p <0.001). Combination lipid therapy significantly decreased stenosis progression by 83% (Delta%S(prox) 0.5 vs 2.9, p <0.001) in patients with MS and induced a small net regression in those without (Delta%S(prox) -0.3 vs 2.0, p <0.001). Combination therapy decreased the event rate by 54% (13% vs 28%, p = 0.03) in those with MS and by 82% (3% vs 17%, p = 0.002) without. On average, each 10% decrease in LDL cholesterol or 10% increase in HDL cholesterol was significantly associated with a 0.3 Delta%S(prox) decrease. Each 10% decrease in LDL cholesterol or 10% increase in HDL cholesterol was associated with 11% (p = 0.02) or 22% (p <0.001) event risk decrease. In conclusion, patients with MS have significantly more rapid coronary stenosis progression and a higher frequency of CV events. Greater stenosis progression rate is associated with a higher event rate. LDL cholesterol-lowering and HDL cholesterol-increasing therapies independently and significantly decrease coronary stenosis progression and decrease CV events.

Phospholipid transfer protein reduces phosphorylation of tau in human neuronal cells

Tau function is regulated by phosphorylation, and abnormal tau phosphorylation in neurons is one of the key processes associated with development of Alzheimer's disease and other tauopathies. In this study we provide evidence that phospholipid transfer protein (PLTP), one of the main lipid transfer proteins in the brain, significantly reduces levels of phosphorylated tau and increases levels of the inactive form of glycogen synthase kinase-3beta (GSK3 beta) in HCN2 cells. Furthermore, inhibition of phosphatidylinositol-3 kinase (PI3K) reversed the PLTP-induced increase in levels of GSK3 beta phosphorylated at serine 9 (pGSK3 beta(Ser9)) and partially reversed the PLTP-induced reduction in tau phosphorylation. We provide evidence that the PLTP-induced changes are not due to activation of Disabled-1 (Dab1), insofar as PLTP reduced levels of total and phosphorylated Dab1 in HCN2 cells. We have also shown that inhibition of tyrosine kinase activity of insulin receptor (IR) and/or insulin-like growth factor 1 (IGF1) receptor (IGFR) reverses the PLTP-induced increase in levels of phosphorylated Akt (pAkt(Thr308) and pAkt(Ser473)), suggesting that PLTP-mediated activation of the PI3K/Akt pathway is dependent on IR/IGFR receptor tyrosine kinase activity. Our study suggests that PLTP may be an important modulator of signal transduction pathways in human neurons.

Genetic and nongenetic sources of variation in phospholipid transfer protein activity

Phospholipid transfer protein (PLTP) belongs to the lipid transfer/lipopolysaccharide-binding protein gene family. Expression of PLTP has been implicated in the development of atherosclerosis. We evaluated the effects of PLTP region tagging single nucleotide polymorphisms (SNPs) on the prediction of both carotid artery disease (CAAD) and PLTP activity. CAAD effects were evaluated in 442 Caucasian male subjects with severe CAAD and 497 vascular disease-free controls. SNP prediction of PLTP transfer activity was evaluated in both a subsample of 87 subjects enriched for an allele of interest and in a confirmation sample of 210 Caucasian males and females. Hemoglobin A1c or insulin level predicted 11-14% of age- and sex-adjusted PLTP activity. PLTP SNPs that predicted approximately 11-30% of adjusted PLTP activity variance were identified in the two cohorts. For rs6065904, the allele that was associated with CAAD was also associated with elevated PLTP activity in both cohorts. SNPs associated with PLTP activity also predicted variation in LDL-cholesterol and LDL-B level only in the replication cohort. These results demonstrate that PLTP activity is strongly influenced by PLTP region polymorphisms and metabolic factors.

Differential effects of simvastatin and pravastatin on expression of Alzheimer's disease-related genes in human astrocytes and neuronal cells

Inhibitors of HMG-CoA reductase (statins) are widely used medications for reduction of cholesterol levels. Statin use significantly reduces risk of cardiovascular disease but has also been associated with lower risk of other diseases and conditions, including dementia. However, some reports suggest that statins also have detrimental effects on the brain. We provide evidence that simvastatin and pravastatin have significantly different effects on expression of genes related to neurodegeneration in astrocytes and neuroblastoma (SK-N-SH) cells in culture. Simvastatin significantly reduced expression of ABCA1 in astrocytes and neuroblastoma cells (by 79% and 97%, respectively; both P < 0.001). Pravastatin had a similar but attenuated effect on ABCA1 in astrocytes (-54%, P < 0.001) and neuroblastoma cells (-70%, P < 0.001). Simvastatin reduced expression of apolipoprotein E in astrocytes (P < 0.01). Furthermore, both statins reduced expression of microtubule-associated protein tau in astrocytes (P < 0.01), while both statins increased its expression in neuroblastoma cells (P < 0.01). In SK-N-SH cells, simvastatin significantly increased cyclin-dependent kinase 5 and glycogen synthase kinase 3beta expression, while pravastatin increased amyloid precursor protein expression. Our data suggest that simvastatin and pravastatin differentially affect expression of genes involved in neurodegeneration and that statin-dependent gene expression regulation is cell type specific.

PLTP is present in the nucleus, and its nuclear export is CRM1-dependent

Phospholipid transfer protein (PLTP), one of the key lipid transfer proteins in plasma and cerebrospinal fluid, is nearly ubiquitously expressed in cells and tissues. Functions of secreted PLTP have been extensively studied. However, very little is known about potential intracellular PLTP functions. In the current study, we provide evidence for PLTP localization in the nucleus of cells that constitutively express PLTP (human neuroblastoma cells, SK-N-SH; and human cortical neurons, HCN2) and in cells transfected with human PLTP (Chinese hamster ovary and baby hamster kidney cells). Furthermore, we have shown that incubation of these cells with leptomycin B (LMB), a specific inhibitor of nuclear export mediated by chromosome region maintenance 1 (CRM1), leads to intranuclear accumulation of PLTP, suggesting that PLTP nuclear export is CRM1-dependent. We also provide evidence for entry of secreted PLTP into the cell and its translocation to the nucleus, and show that intranuclear PLTP is active in phospholipid transfer. These findings suggest that PLTP is involved in novel intracellular functions.

SAA and PLTP activity in plasma of periodontal patients before and after full-mouth tooth extraction

OBJECTIVE

To assess whether treatment of advanced periodontal disease affects plasma levels of serum amyloid A (SAA) and phospholipid transfer protein (PLTP) activity.

DESIGN

We measured the levels of SAA and PLTP activity in plasma of 66 patients with advanced periodontal disease before and after treatment by full-mouth tooth extraction (FME).

RESULTS

At baseline, median SAA levels in our study population were within the normal range (2.7 microg ml(-1)) but SAA was elevated (>5 microg ml(-1)) in 18% of periodontitis patients. Three months after FME, SAA levels were significantly reduced (P = 0.04). SAA did not correlate with any of the periodontal disease parameters. PLTP activity was elevated in patients with periodontitis, compared to the PLTP activity reference group (age-matched systemically healthy adults, n = 29; 18 micromol ml(-1) h(-1)vs 13 micromol ml(-1) h(-1), respectively, P = 0.002). PLTP activity inversely correlated with average periodontal pocket depth (PPD) per tooth (r(s) = -0.372; P = 0.002). Three months after FME, median PLTP activity did not change significantly.

CONCLUSIONS

Full-mouth tooth extraction significantly reduces SAA, a marker of inflammation, while it does not affect plasma PLTP activity. However, the inverse correlation between PLTP activity and average PPD suggests that increased PLTP activity may limit periodontal tissue damage.

Human plasma phospholipid transfer protein specific activity is correlated with HDL size: implications for lipoprotein physiology

To gain further insights into the relationship between plasma phospholipid transfer protein (PLTP) and lipoprotein particles, PLTP mass and phospholipid transfer activity were measured, and their associations with the level and size of lipoprotein particles examined in 39 healthy adult subjects. No bivariate correlation was observed between PLTP activity and mass. PLTP activity was positively associated with cholesterol, triglyceride, apo B and VLDL particle level (r(s)=0.40-0.56, p< or =0.01) while PLTP mass was positively associated with HDL-C, large HDL particles, and mean LDL and HDL particle sizes (r(s)=0.44-0.52, p<0.01). Importantly, plasma PLTP specific activity (SA) was significantly associated with specific lipoprotein classes, positively with VLDL, IDL, and small LDL particles (r(s)=0.42-0.62, p< or =0.01) and inversely with large LDL, large HDL, and mean LDL and HDL particle size (r(s)=-0.42 to -0.70, p< or =0.01). After controlling for triglyceride levels, the correlation between PLTP mass or SA and HDL size remained significant. In linear models, HDL size explained 45% of the variability of plasma PLTP SA while triglyceride explained 34% of the PLTP activity. Thus, in healthy adults a significant relationship exists between HDL size and plasma PLTP SA (r(s)=-0.70), implying that HDL particle size may modulate PLTP SA in the vascular compartment.

Multiple SNPs within and surrounding the apolipoprotein E gene influence cerebrospinal fluid apolipoprotein E protein levels

The epsilon4 allele of the apolipoprotein E gene (APOE) is associated with increased risk and earlier age at onset in late onset Alzheimer's disease (AD). Other factors, such as expression level of apolipoprotein E protein (apoE), have been postulated to modify the APOE related risk of developing AD. Multiple loci in and outside of APOE are associated with a high risk of AD. The aim of this exploratory hypothesis generating investigation was to determine if some of these loci predict cerebrospinal fluid (CSF) apoE levels in healthy non-demented subjects. CSF apoE levels were measured from healthy non-demented subjects 21-87 years of age (n=134). Backward regression models were used to evaluate the influence of 21 SNPs, within and surrounding APOE, on CSF apoE levels while taking into account age, gender, APOE epsilon4 and correlation between SNPs (linkage disequilibrium). APOE epsilon4 genotype does not predict CSF apoE levels. Three SNPs within the TOMM40 gene, one APOE promoter SNP and two SNPs within distal APOE enhancer elements (ME1 and BCR) predict CSF apoE levels. Further investigation of the genetic influence of these loci on apoE expression levels in the central nervous system is likely to provide new insight into apoE regulation as well as AD pathogenesis.

Prevalence and determinants of elevated apolipoprotein B and dense low-density lipoprotein in youths with type 1 and type 2 diabetes

OBJECTIVE

The objective of the study was to assess the prevalence and determinants of elevated apolipoprotein B (apoB) and dense low-density lipoprotein (LDL) in United States youth with type 1 or type 2 diabetes.

METHODS

We conducted cross-sectional analyses of apoB concentrations, LDL density, and prevalence of elevated apoB levels and dense LDL from the SEARCH for Diabetes in Youth study, a six-center U.S.-based study of youth with diabetes onset younger than 20 years of age (2657 with type 1 and 345 with type 2).

RESULTS

Among youth with type 1 diabetes, 11% had elevated apoB (>or=100 mg/dl, 1.95 mm/liter), 8% had dense LDL (relative flotation rateor=130 mg/dl, 3.36 mm/liter). In contrast, among youth with type 2 diabetes, 36% had elevated apoB, 36% had dense LDL, but only 23% had elevated LDL-cholesterol. Dense LDL and apoB each increased with hemoglobin A1c in both types. Among type 1 diabetics in poor glycemic control (hemoglobin A1c>or=9.5%), 28% had elevated apoB, and 18% had dense LDL, whereas 72% of poorly controlled type 2 diabetics had elevated apoB and 62% had dense LDL.

CONCLUSIONS

In youth with type 1 diabetes, elevated apoB and dense LDL were not highly prevalent, whereas elevated apoB and dense LDL were common lipoprotein abnormalities in youth with type 2 diabetes. The prevalence of these risk factors substantially increased with poor glycemic control in both groups, stressing the importance of achieving and maintaining an optimal glucose control.

An amphipathic helical region of the N-terminal barrel of phospholipid transfer protein is critical for ABCA1-dependent cholesterol efflux

Phospholipid lipid transfer protein (PLTP) mimics high-density lipoprotein apolipoproteins in removing cholesterol and phospholipids from cells through the ATP-binding cassette transporter A1 (ABCA1). Because amphipathic alpha-helices are the structural determinants for ABCA1 interactions, we examined the ability of synthetic peptides corresponding to helices in PLTP to remove cellular cholesterol by the ABCA1 pathway. Of the seven helices tested, only one containing PLTP residues 144-163 (p144), located at the tip of the N-terminal barrel, promoted ABCA1-dependent cholesterol efflux and stabilized ABCA1 protein. Mutating methionine 159 (Met-159) in this helix in PLTP to aspartate (M159D) or glutamate (M159E) nearly abolished the ability of PLTP to remove cellular cholesterol and dramatically reduced PLTP binding to phospholipid vesicles and its phospholipid transfer activity. These mutations impaired PLTP binding to ABCA1-generated lipid domains and PLTP-mediated stabilization of ABCA1 but increased PLTP binding to ABCA1. PLTP interactions with ABCA1 also mimicked apolipoproteins in activating Janus kinase 2; however, the M159D/E mutants were also able to activate this kinase. Structural analyses showed that the M159D/E mutations had only minor effects on PLTP conformation. These findings indicate that PLTP helix 144-163 is critical for removing lipid domains formed by ABCA1, stabilizing ABCA1 protein, interacting with phospholipids, and promoting phospholipid transfer. Direct interactions with ABCA1 and activation of signaling pathways likely involve other structural determinants of PLTP.

Evidence mounts for a role of the kidney in lipoprotein(a) catabolism

Numerous studies have suggested a role of the kidney in lipoprotein(a) (Lp(a)) catabolism, but direct evidence is still lacking. Frischmann et al. demonstrate that the marked elevation of Lp(a) observed in hemodialysis patients results from a decrease in Lp(a) clearance rather than an increase in Lp(a) production, consistent with the notion that the kidney degrades Lp(a). More studies are needed to prove the biological relevance.

Effect of statins on Alzheimer's disease biomarkers in cerebrospinal fluid

BACKGROUND

Treatment with HMG-CoA reductase inhibitors ("statins") has been variably associated with a reduced risk of Alzheimer's disease (AD) in epidemiologic studies and reduced amyloid-beta (Abeta) deposition in animal models of AD. Putative neuroprotective effects of statins may vary in relation to their ability to penetrate into the central nervous system (CNS).

METHODS

We measured levels of cerebrospinal fluid (CSF) AD biomarkers following 14 weeks of treatment with simvastatin (a CNS permeant statin; n=10) at 40 mg/day or pravastatin (a CNS impermeant statin; n=13) at 80 mg/day in hypercholesterolemic subjects without dementia.

RESULTS

Simvastatin, but not pravastatin, reduced CSF levels of phospho-tau-181 (p-tau181) in all subjects. There were no differences in CSF levels of total tau, Abeta42, Abeta40, soluble amyloid beta protein precursor (sAbetaPP) alpha or beta, or F2-isoprostanes.

CONCLUSIONS

Statins may modulate the phosphorylation of tau in humans and this effect may depend on the CNS availability of the statin. These results suggest another mechanism by which statins may act to reduce the risk of AD.

Statins of different brain penetrability differentially affect CSF PLTP activity

BACKGROUND/AIMS

Phospholipid transfer protein (PLTP) and apolipoprotein E (apoE) are key proteins involved in lipoprotein metabolism in the peripheral circulation and in the brain. Several epidemiological studies suggested that use of 3-hydroxyl-3-methylglutaryl-coenzyme A reductase inhibitors (statins) reduces risk of Alzheimer's disease (AD). However, the effects of statins of differing blood-brain barrier (BBB) penetrability on brain-derived molecules in cognitively normal individuals are largely unknown.

METHODS

To assess the effect of statins on these indices as a function of BBB penetration, cerebrospinal fluid (CSF) and plasma PLTP activity and apoE concentration were measured in cognitively intact, modestly hypercholesterolemic adults randomly allocated to treatment with either pravastatin, which does not penetrate BBB (80 mg/day, n = 13), or simvastatin, which penetrates BBB (40 mg/day, n = 10).

RESULTS

Simvastatin significantly increased CSF PLTP activity (p = 0.005). In contrast, pravastatin had no such effect. In the pravastatin-treated group, CSF apoE concentration decreased significantly (p = 0.026), while the simvastatin-treated group showed a tendency towards lower CSF apoE levels, with CSF apoE concentration lowered in 8 of 10 subjects.

CONCLUSION

Our data indicate that statins differentially affect two key lipid transfer proteins in the brain, and that effect on PLTP activity depends on statin BBB penetrability.

Active plasma phospholipid transfer protein is associated with apoA-I- but not apoE-containing lipoproteins

Plasma phospholipid transfer protein (PLTP) is a multifaceted protein with diverse biological functions. It has been shown to exist in both active and inactive forms. To determine the nature of lipoproteins associated with active PLTP, plasma samples were adsorbed with anti-A-I, anti-A-II, or anti-E immunoadsorbent, and PLTP activity was measured in the resulting plasma devoid of apolipoprotein A-I (apoA-I), apoA-II, or apoE. Anti-A-I and anti-A-II immunoadsorbents removed 98 +/- 1% (n = 8) and 38 +/- 25% (n = 7) of plasma PLTP activity, respectively. In contrast, only 1 +/- 5% of plasma PLTP activity was removed by anti-E immunoadsorbent (n = 7). Dextran sulfate (DS) cellulose did not bind apoA-I, but it removed 83 +/- 5% (n = 4) of the PLTP activity in plasma. In size-exclusion chromatography, PLTP activity removed by anti-A-I or anti-A-II immunoadsorbent was associated primarily with particles of a size corresponding to HDL, whereas a substantial portion of the PLTP activity dissociated from DS cellulose was found in particles larger or smaller than HDL. These data show the following: 1) active plasma PLTP is associated primarily with apoA-I- but not apoE-containing lipoproteins; 2) active PLTP is present in HDL particles with and without apoA-II, and its distribution between these two HDL subpopulations varies widely among individuals; and 3) DS cellulose can remove active PLTP from apoA-I-containing lipoproteins, and this process creates new active PLTP-containing particles in vitro.

Phospholipid transfer protein activity is associated with inflammatory markers in patients with cardiovascular disease

Plasma phospholipid lipid transfer protein (PLTP) has several known key functions in lipoprotein metabolism. Recent studies suggest that it also may play a role in the inflammatory response. Inflammatory cell activity contributes to the development of atherosclerosis. To seek further evidence for the association of PLTP with inflammation, we studied the relationship between PLTP activity and five inflammatory markers [C-reactive protein (CRP), serum amyloid A (SAA), interleukin 6 (IL-6), white blood cells (WBC), and fibrinogen] in 93 patients with low HDL and cardiovascular disease (CVD). Plasma PLTP activity had the strongest correlation with CRP (r=0.332, P<0.001) followed by SAA (r=0.239, P=0.021). PLTP, CRP, and SAA were significantly associated with body mass index (BMI), insulin or glucose, apolipoprotein (apo) B, and/or apo E level (r=0.264-0.393, P<0.01). PLTP, SAA, and IL-6 also were associated with the concentration of HDL particles without apo A-II [Lp(A-I)](r=0.373-0.472, P<0.005, n=56), but not particles with apo A-II. Smoking was associated with increased PLTP activity, CRP, and WBC, and hypertension with increased PLTP activity. In linear models, CRP remained significantly associated with PLTP after adjustment of CVD risk factors and insulin resistance. Also, much of the variability of plasma PLTP activity was explained by CRP, BMI, Lp(A-I), smoking, glucose, and blood pressure. These findings show for the first time that plasma PLTP activity is associated positively with CRP in CVD, a state of chronic inflammation.

Reduced CSF PLTP activity in Alzheimer's disease and other neurologic diseases; PLTP induces ApoE secretion in primary human astrocytes in vitro

Phospholipid transfer protein (PLTP) plays a pivotal role in cellular lipid efflux and modulation of lipoprotein metabolism. PLTP is distributed widely in the central nervous system (CNS), is synthesized by glia and neurons, and is active in cerebrospinal fluid (CSF). The aims of this study were to test the hypothesis that patients with Alzheimer's disease (AD) have altered PLTP-mediated phospholipid transfer activity in CSF, and to examine the potential relationship between PLTP activity and apolipoprotein E (apoE) levels in CSF. We assessed PLTP activity and apoE concentration in CSF of patients with probable AD (n = 50), multiple sclerosis (MS; n = 9), other neurologic diseases (n = 21), and neurologically healthy controls (n = 40). PLTP activity in AD was reduced compared to that in controls (P < 0.001), with approximately half of the AD patients with PLTP activity values below all controls. Patients with MS had lower PLTP activity than AD patients (P < 0.001). PLTP activity was highly correlated with PLTP mass, as estimated by Western blot (r = 0.006; P < 0.01). CSF PLTP activity positively correlated with apoE concentration in AD (R = 0.435; P = 0.002) and controls (R = 0.456; P = 0.003). Anti-apoE immunoaffinity chromatography and Western blot analyses indicated that some CSF PLTP is associated with apoE-containing lipoproteins. Exogenous addition of recombinant PLTP to primary human astrocytes significantly increased apoE secretion to the conditioned medium. The findings of reduced PLTP activity in AD CSF, and the observation that PLTP can influence apoE secretion in astrocytes suggest a potential link between alterations in the brain lipid metabolism and AD pathogenesis.

Emerging roles for phospholipid transfer protein in lipid and lipoprotein metabolism

PURPOSE OF REVIEW

This review highlights the recent key advances in our understanding of the role of phospholipid transfer protein in lipid and lipoprotein metabolism.

RECENT FINDINGS

The overexpression of human phospholipid transfer protein in mice is associated with an increase in atherosclerosis. This is consistent with earlier studies using mouse models suggesting that phospholipid transfer protein was pro-atherogenic. The presence of phospholipid transfer protein in macrophages and atherosclerotic lesions suggests that it could be either anti-atherogenic by facilitating lipid efflux or pro-atherogenic by facilitating lipid retention. Phospholipid transfer protein may also be a key player in reverse cholesterol transport, as it interacts with the adenosine triphosphate-binding cassette transporter A1 and facilitates lipid efflux from peripheral cells. Both the release of chymase, a neutral protease, from mast cells and the oxidation of HDL by hypochlorous acid can impair the function of phospholipid transfer protein in reverse cholesterol transport. Studies of phospholipid transfer protein-mediated phospholipid transfer activity in humans support a role for phospholipid transfer protein in hypertriglyceridemia, obesity, diabetes, inflammation and coronary artery disease, and in the modulation of LDL particle density and size. Furthermore, recent evidence suggests that phospholipid transfer protein may play a role in reproductive processes, in lipid and lipoprotein metabolism in the central nervous system, and in neurodegenerative disease.

SUMMARY

Phospholipid transfer protein is emerging as a multifaceted and multifunctional player in lipid and lipoprotein metabolism, but much additional work will be required to understand the significance of these recent findings for clinical practice.

Safety and tolerability of simvastatin plus niacin in patients with coronary artery disease and low high-density lipoprotein cholesterol (The HDL Atherosclerosis Treatment Study)

The high-density lipoprotein (HDL)-Atherosclerosis Treatment Study showed that simvastatin plus niacin (mean daily dose 13 mg and 2.4 g, respectively) halt angiographic atherosclerosis progression and reduce major clinical events by 60% in patients with coronary artery disease (CAD) who have low HDL, in comparison with placebos, over 3 years. How safe and well-tolerated is this combination? One hundred sixty patients with CAD, including 25 with diabetes mellitus, with mean low-density lipoprotein cholesterol of 128 mg/dl, HDL cholesterol of < or =35 mg/dl (mean 31), and mean triglycerides of 217 mg/dl were randomized to 4 factorial combinations of antioxidant vitamins or their placebos and simvastatin plus niacin or their placebos. Patients were examined monthly or bimonthly for 38 months; side effects (gastrointestinal upset, nausea, anorexia, vision, skin, and energy problems, or muscle aches) were directly queried and recorded. Aspartate aminotransferase, creatine phosphokinase (CPK), uric acid, homocysteine, and fasting glucose levels were regularly monitored. A safety monitor reviewed all side effects and adjusted drug dosages accordingly. Patients who received simvastatin plus niacin and those on placebo had similar frequencies of clinical or laboratory side effects: any degree of flushing (30% vs 23%, p = NS), symptoms of fatigue, nausea, and/or muscle aches (9% vs 5%, p = NS), aspartate aminotransferase (SGOT) > or =3 times upper limit of normal (3% vs 1%, p = NS), CPK > or =2 times upper limit of normal (3% vs 4%, p = NS), CPK > or =5 times upper limit of normal, new onset of uric acid > or =7.5 mg/dl (18% vs 15%, p = NS), and homocysteine > or =15 micromol/L (9% vs 4%, p = NS). Glycemic control among diabetics declined mildly in the simvastatin-niacin group but returned to pretreatment levels at 8 months and remained stable for rest of the study. This combination regimen was repeatedly described by 91% of treated patients and 86% of placebo subjects as "very easy" or "fairly easy" to take. Thus, the simvastatin plus niacin regimen is effective, safe, and well tolerated in patients with or without diabetes mellitus.

Quantitative Trait Locus Mapping of Genes That Regulate Phospholipid Transfer Activity in SM/J and NZB/BlNJ Inbred Mice

OBJECTIVE

Phospholipid transfer protein (PLTP), an important protein in the transfer of phospholipids between lipoprotein particles and in the remodeling of HDL, is regulated at both the transcriptional and the protein level. We performed quantitative trait locus (QTL) analysis to identify genomic loci regulating PLTP activity in mice.

METHODS AND RESULTS

Plasma PLTP activity was measured in 217 male F2 progeny from a SM/J x NZB/B1NJ intercross. Two QTL for plasma PLTP activity in mice fed chow (Pltpq1 and Pltpq2) were found on chromosomes 3 (34 cM, logarithm of odds [LOD] 3.5) and 10 (66 cM, LOD 4.1); two additional QTL in mice fed atherogenic diet (Pltpq3 and Pltpq4) were found on chromosomes 9 (56 cM, LOD 4.5) and 15 (34 cM, LOD 5.0); and one QTL (Pltiq1) for the inducibility of PLTP activity was found on chromosome 4 (70 cM, LOD 3.7). Several candidate genes for these 5 QTL were tested by sequence comparison and expression studies.

CONCLUSIONS

We identified five significant loci involved in PLTP activity in the mouse and provided supporting evidence for the candidacy of Nr1h4 and Apof as the genes underlying Pltpq2.

Report of the National Heart, Lung, and Blood Institute Workshop on Lipoprotein(a) and Cardiovascular Disease: Recent Advances and Future Directions

It has been estimated that ∼37% of the US population judged to be at high risk for developing coronary artery disease (CAD), based on the National Cholesterol Education Program guidelines, have increased plasma lipoprotein(a) [Lp(a)], whereas Lp(a) is increased in only 14% of those judged to be at low risk. Therefore, the importance of establishing a better understanding of the relative contribution of Lp(a) to the risk burden for CAD and other forms of vascular disease, as well as the underlying mechanisms, is clearly evident. However, the structural complexity and size heterogeneity of Lp(a) have hindered the development of immunoassays to accurately measure Lp(a) concentrations in plasma. The large intermethod variation in Lp(a) values has made it difficult to compare data from different clinical studies and to achieve a uniform interpretation of clinical data. A workshop was recently convened by the National Heart, Lung, and Blood Institute (NHLBI) to evaluate our current understanding of Lp(a) as a risk factor for atherosclerotic disorders; to determine how future studies could be designed to more clearly define the extent to which, and mechanisms by which, Lp(a) participates in these processes; and to present the results of the NHLBI-supported program for the evaluation and standardization of Lp(a) immunoassays. This report includes the most recent data presented by the workshop participants and the resulting practical and research recommendations.

Phospholipid transfer protein interacts with and stabilizes ATP-binding cassette transporter A1 and enhances cholesterol efflux from cells

Phospholipid lipid transfer protein (PLTP) is ubiquitously expressed in animal tissues and plays multiple roles in lipoprotein metabolism, but the function of peripheral PLTP is still poorly understood. Here we show that one of its possible functions is to transport cholesterol and phospholipids from cells to lipoprotein particles by a process involving PLTP interactions with cellular ATP-binding cassette transporter A1 (ABCA1). When ABCA1 was induced in murine macrophages or ABCA1-transfected baby hamster kidney cells, PLTP gained the ability to promote cholesterol and phospholipid efflux from cells. Although PLTP alone had lipid efflux activity, its maximum activity was observed in the presence of high density lipoprotein particles. Pulsechase studies showed that the interaction of PLTP with ABCA1-expressing cells played a role in promoting lipid efflux. Overexpression of ABCA1 dramatically increased binding of both PLTP and apoA-I to common sites on the cell surface. Both PLTP and apoA-I were covalently cross-linked to ABCA1, each protein blocked cross-linking of the other, and both PLTP and apoA-I stabilized ABCA1 protein. These results are consistent with PLTP and apoA-I binding to ABCA1 at the same or closely related sites. Thus, PLTP mimics apolipoproteins in removing cellular lipids by the ABCA1 pathway, except that PLTP acts more as an intermediary in the transfer of cellular lipids to lipoprotein particles.

PLTP activity decreases with weight loss: changes in PLTP are associated with changes in subcutaneous fat and FFA but not IAF or insulin sensitivity

Phospholipid transfer protein (PLTP) activity is elevated in obese and diabetic subjects. No prospective studies have examined the effect of weight loss on PLTP activity and assessed whether the resultant changes in activity are related to changes in body weight, insulin resistance, or both. PLTP activity was measured at baseline in 46 subjects (body mass index = 19-64 kg/m2) and after diet-induced weight loss in 19 of the obese subjects. Total body fat mass (FM) by dual-energy X-ray absorptiometry, intraabdominal fat (IAF), and abdominal subcutaneous fat (SQF) by CT scan, insulin sensitivity (SI) by frequently sampled intravenous glucose tolerance test, leptin, and lipids were determined. At baseline, PLTP activity correlated with FM (r = 0.36, P = 0.02) and SQF (r = 0.31, P = 0.045), but not with IAF (r = 0.16, P = 0.32) or SI (r = 0.10, P = 0.52). With diet-induced weight loss (16 +/- 7.3 kg), PLTP activity significantly decreased 9.1% (P = 0.002). The change in PLTP activity correlated with the change in SQF (r = 0.55, P = 0.014) (33.6% decrease), but not with IAF (r = 0.09, P = 0.73) or SI (r = 0.18, P = 0.44), and was highly correlated with the change in nonesterified fatty acid (NEFA) (r = 0.71, P < 0.001). In conclusion, elevated PLTP activity in obese subjects is likely a result of increased body fat, reflected by SQF, and is influenced by NEFAs but is not directly related to insulin resistance.