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.

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.

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.

Functional analysis of the transcriptional activity of the mouse phospholipid transfer protein gene.

Phospholipid transfer protein (PLTP) plays an important role in the metabolism of plasma high density lipoprotein. The mouse gene encoding PLTP and its promoter region has been cloned in our laboratory. The present study was conducted to functionally analyze the transcriptional regulation of the mouse PLTP gene. The results indicated that DNA sequences between -245 and -69 were responsible for the full promoter activity and binding motifs for transcription factor Sp1 and AP-2 within this functional promoter region were synergistically essential for the basal transcription. The transcriptional activity of this gene was significantly increased by chenodeoxycholic acid and fenofibrate, suggesting that transcription factor farnesoid X-activated receptor (FXR) and peroxisome proliferator-activated receptor (PPAR) are likely involved in the transcriptional regulation. DNA sequence analysis suggests that DNA sequences from -407 to -395 and from -393 to -381 are homologous to the recognition motifs of FXR, and those from -859 to -847 and from -309 to -297 are similar to the potential binding motif for PPAR. These findings provide a molecular basis for further investigation of the physiological function and regulation of the PLTP gene in mice.

Plasma phospholipid transfer protein activity in patients with low HDL and cardiovascular disease treated with simvastatin and niacin.

Plasma phospholipid transfer protein (PLTP) is an important modulator of high-density lipoprotein (HDL) metabolism, regulating its particle size, composition, and mass. In patients with low HDL and cardiovascular disease (CVD), plasma PLTP activity is positively correlated with the concentration of HDL particles containing apo A-I but not apo A-II (Lp(A-1)). We recently completed a study to determine the effect of simvastatin and niacin (S-N) therapy on disease progression/regression in these patients, and found that this therapy selectively increased Lp(A-I). To determine if PLTP was also increased with this drug therapy, we measured the PLTP activity in the plasma of 30 of these patients obtained at baseline and after 12 months of therapy, and compared the changes to a similar group of 31 patients who received placebo for the drugs. No significant increase in PLTP activity was observed in either group of patients. However, changes in apo A-I and A-II between these two time points were correlated with the corresponding change in PLTP activity. The correlation coefficients were r=0.57 (P=0.001) and r=0.43 (P=0.02) for apo A-I, and r=0.54 (P=0.002) and r=0.41 (P=0.02) for apo A-II in the placebo and S-N group, respectively. At baseline, PLTP activity correlated positively with the percent of plasma apo A-I associated with Lp(A-I) (r=0.38, P=0.04) and the amounts of apo A-I in these particles (r=0.43, P=0.02). These relationships persisted in patients who took placebo for 12 months (r=0.46, P=0.009 and r=0.37, P=0.04, respectively), but was attenuated in those treated with S-N. These data indicate that S-N-induced increase in Lp(A-I) was PLTP-independent. It also confirms our previous observation that an interrelationship exists between PLTP and apo-specific HDL particle subclasses in CVD patients with low HDL, and that this relationship is altered by drug intervention.

Antioxidant supplements block the response of HDL to simvastatin-niacin therapy in patients with coronary artery disease and low HDL.

One strategy for treating coronary artery disease (CAD) patients with low HDL cholesterol (HDL-C) is to maximally increase the HDL-C to LDL-C ratio by combining lifestyle changes with niacin (N) plus a statin. Because HDL can prevent LDL oxidation, the low-HDL state also may benefit clinically from supplemental antioxidants. Lipoprotein changes over 12 months were studied in 153 CAD subjects with low HDL-C randomized to take simvastatin and niacin (S-N), antioxidants (vitamins E and C, beta-carotene, and selenium), S-N plus antioxidants (S-N+A), or placebo. Mean baseline plasma cholesterol, triglyceride, LDL-C, and HDL-C levels of the 153 subjects were 196, 207, 127, and 32 mg/dL, respectively. Without S-N, lipid changes were minor. The S-N and S-N+A groups had comparably significant reductions (P

Glucose regulates the transcription of human genes relevant to HDL metabolism: responsive elements for peroxisome proliferator-activated receptor are involved in the regulation of phospholipid transfer protein.

Phospholipid transfer protein (PLTP) plays an important role in human plasma HDL metabolism. Clinical data have recently indicated that plasma PLTP activity and mass were both higher in diabetic patients concomitant with hyperglycemia. The present study shows that high glucose increases both PLTP mRNA and functional activity in HepG2 cells, due to a significant increase in the promoter activity of human PLTP gene. The glucose-responsive elements are located between -759 and -230 of the PLTP 5'-flanking region, within which two binding motifs (-537 to -524 and -339 to -327) for either peroxisome proliferator-activated receptor or farnesoid X-activated receptor are involved in this glucose-mediated transcriptional regulation. This finding suggests that high glucose upregulates the transcription of human PLTP gene via nuclear hormone receptors. In addition, high glucose increases mRNA levels for several genes that are functionally important in HDL metabolism, including human ATP-binding cassette transporter A1, apolipoprotein A-I, scavenger receptor BI, and hepatic lipase. The functional promoter activities of these genes are enhanced by high glucose in three cell lines tested, indicating that glucose may also regulate these genes at the transcriptional level. Our findings provide a molecular basis for a role of hyperglycemia in altered HDL metabolism.

Electron-beam tomography coronary calcium scores are superior to Framingham risk variables for predicting the measured proximal stenosis burden.

Previous studies of electron-beam tomography (EBT) have correlated coronary calcium scores with simplistic visual estimates of disease severity. In a clinical trial designed to evaluate 2 treatment strategies in coronary artery disease (CAD) patients with low levels of high-density lipoprotein cholesterol, we used quantitative coronary angiography to measure composite proximal stenosis burden from the baseline coronary angiogram and assessed the traditional Framingham risk variables in 146 patients. Stenosis burden is the sum, per patient, of percent stenosis for the worst lesion found in each of 9 standard proximal coronary segments. EBT estimates of coronary calcium (Agatston score, calcium volume score) were obtained for 115 of these patients. Stenosis burden was correlated with the calcium scores and risk variables. The best traditional correlates of stenosis burden were smoking status (r = 0.31, p = 0.001), prior myocardial infarction (r = 0.24, p = 0.005), body mass index (r = 0.23, p = 0.005), pack-years smoking (r = 0.20, p = 0.05), and age (r = 0.17, p = 0.04). With adjustment for age, all these correlations improved (eg, body mass index x age [r = 0.28, p = 0.001]). In addition, total cholesterol x age (r = 0.22, p = 0.008), fibrinogen x age (r = 0.19, p = 0.03), and systolic blood pressure x age (r = 0.18, p = 0.03) became significant correlates. Spearman correlations of the calcium scores with stenosis burden were considerably greater (Agatston: r = 0.62, p <0.0001; calcium volume: r = 0.63, p <0.0001). In multivariate regression analysis, calcium score, body mass index, and history of myocardial infarction were independent correlates of stenosis burden (R(2) = 0.45). At a given point in time, the EBT coronary calcium scores are greatly superior to the Framingham risk factors in predicting the measured proximal stenosis burden. Agatston and calcium volume scores are comparably predictive of stenosis burden.

Simvastatin and niacin, antioxidant vitamins, or the combination for the prevention of coronary disease.

BACKGROUND: Both lipid-modifying therapy and antioxidant vitamins are thought to have benefit in patients with coronary disease. We studied simvastatin-niacin and antioxidant-vitamin therapy, alone and together, for cardiovascular protection in patients with coronary disease and low plasma levels of HDL. METHODS: In a three-year, double-blind trial, 160 patients with coronary disease, low HDL cholesterol levels and normal LDL cholesterol levels were randomly assigned to receive one of four regimens: simvastatin plus niacin, vitamins, simvastatin-niacin plus antioxidants; or placebos. The end points were arteriographic evidence of a change in coronary stenosis and the occurrence of a first cardiovascular event (death, myocardial infarction, stroke, or revascularization). RESULTS: The mean levels of LDL and HDL cholesterol were unaltered in the antioxidant group and the placebo group; these levels changed substantially (by -42 percent and +26 percent, respectively) in the simvastatin-niacin group. The protective increase in HDL2 with simvastatin plus niacin was attenuated by concurrent therapy with antioxidants. The average stenosis progressed by 3.9 percent with placebos, 1.8 percent with antioxidants (P=0.16 for the comparison with the placebo group), and 0.7 percent with simvastatin-niacin plus antioxidants (P=0.004) and regressed by 0.4 percent with simvastatin-niacin alone (P<0.001). The frequency of the clinical end point was 24 percent with placebos; 3 percent with simvastatin-niacin alone; 21 percent in the antioxidant-therapy group; and 14 percent in the simvastatin-niacin-plus-antioxidants group. CONCLUSIONS: Simvastatin plus niacin provides marked clinical and angiographically measurable benefits in patients with coronary disease and low HDL levels. The use of antioxidant vitamins in this setting must be questioned.

Use of a reference material proposed by the International Federation of Clinical Chemistry and Laboratory Medicine to evaluate analytical methods for the determination of plasma lipoprotein(a).

BACKGROUND: As part of the NIH/National Heart, Lung and Blood Institute Contract for the Standardization of Lipoprotein(a) [Lp(a)] Measurements, a study was performed in collaboration with the IFCC Working Group for the Standardization of Lp(a) Assays. The aims of the study, performed with the participation of 16 manufacturers and 6 research laboratories, were to evaluate the IFCC proposed reference material (PRM) for its ability to transfer an accuracy-based value to the immunoassay calibrators and to assess concordance in results among different methods. METHODS: Two different purified Lp(a) preparations with protein mass concentrations determined by amino acid analysis were used to calibrate the reference method. A Lp(a) value of 107 nmol/L was assigned to PRM. After uniformity of calibration was demonstrated in the 22 evaluated systems, Lp(a) was measured on 30 fresh-frozen sera covering a wide range of Lp(a) values and apolipoprotein(a) [apo(a)] sizes. RESULTS: The among-laboratory CVs for these samples (6-31%) were, in general, higher than those obtained for PRM (2.8%) and the quality-control samples (14%, 12%, and 9%, respectively), reflecting the broad range of apo(a) sizes in the 30 samples and the sensitivity of most methods to apo(a) size heterogeneity. Thus, although all of the assays were uniformly calibrated through the use of PRM, no uniformity in results was achieved for the isoform-sensitive methods. CONCLUSIONS: Linear regression analyses indicated that to various degrees, apo(a) size heterogeneity affects the outcome of the immunochemical methods used to measure Lp(a). We have also shown that the inaccuracy of Lp(a) values determined by methods sensitive to apo(a) size significantly affects the assessment of individual risk status for coronary artery disease.

Genetic control of HDL levels and composition in an interspecific mouse cross (CAST/Ei x C57BL/6J).

Strain CAST/Ei (CAST) mice exhibit unusually low levels of high density lipoproteins (HDL) as compared with most other strains of mice, including C57BL/6J (B6). This appears to be due in part to a functional deficiency of lecithin:cholesterol acyltransferase (LCAT). LCAT mRNA expression in CAST mice is normal, but the mice exhibit several characteristics consistent with functional deficiency. First, the activity and mass of LCAT in plasma and in HDL of CAST mice were reduced significantly. Second, the HDL of CAST mice were relatively poor in phospholipids and cholesteryl esters, but rich in free cholesterol and apolipoprotein A-I (apoA-I). Third, the adrenals of CAST mice were depleted of cholesteryl esters, a phenotype similar to that observed in LCAT- and acyl-CoA:cholesterol acyltransferase-deficient mice. Fourth, in common with LCAT-deficient mice, CAST mice contained triglyceride-rich lipoproteins with "panhandle"-like protrusions. To examine the genetic bases of these differences, we studied HDL lipid levels in an intercross between strain CAST and the common laboratory strain B6 on a low fat, chow diet as well as a high fat, atherogenic diet. HDL levels exhibited complex inheritance, as 12 quantitative trait loci with significant or suggestive likelihood of observed data scores were identified. Several of the loci occurred over plausible candidate genes and these were investigated. The results indicate that the functional LCAT deficiency is unlikely to be due to variations of the LCAT gene. Our results suggest that novel genes are likely to be important in the control of HDL metabolism, and they provide evidence of genetic factors influencing the interaction of LCAT with HDL.

Lipopolysaccharide-binding protein and phospholipid transfer protein release lipopolysaccharides from gram-negative bacterial membranes.

Although animals mobilize their innate defenses against gram-negative bacteria when they sense the lipid A moiety of bacterial lipopolysaccharide (LPS), excessive responses to this conserved bacterial molecule can be harmful. Of the known ways for decreasing the stimulatory potency of LPS in blood, the binding and neutralization of LPS by plasma lipoproteins is most prominent. The mechanisms by which host lipoproteins take up the native LPS that is found in bacterial membranes are poorly understood, however, since almost all studies of host-LPS interactions have used purified LPS aggregates. Using native Salmonella enterica serovar Typhimurium outer membrane fragments (blebs) that contained (3)H-labeled lipopolysaccharide (LPS) and (35)S-labeled protein, we found that two human plasma proteins, LPS-binding protein (LBP) and phospholipid transfer protein (PLTP), can extract [(3)H]LPS from bacterial membranes and transfer it to human high-density lipoproteins (HDL). Soluble CD14 (sCD14) did not release LPS from blebs yet could facilitate LBP-mediated LPS transfer to HDL. LBP, but not PLTP, also promoted the activation of human monocytes by bleb-derived LPS. Whereas depleting or neutralizing LBP significantly reduced LPS transfer from blebs to lipoproteins in normal human serum, neutralizing serum PLTP had no demonstrable effect. Of the known lipid transfer proteins, LBP is thus most able to transfer LPS from bacterial membranes to the lipoproteins in normal human serum.

Effect of weight loss with reduction of intra-abdominal fat on lipid metabolism in older men.

How weight loss improves lipid levels is poorly understood. Cross-sectional studies have suggested that accumulation of fat in intra-abdominal stores (IAF) may lead to abnormal lipid levels, increased hepatic lipase (HL) activity, and smaller low density lipoprotein (LDL) particle size. To determine what effect loss of IAF would have on lipid parameters, 21 healthy older men underwent diet-induced weight loss. During a period of weight stability before and after weight loss, subjects underwent studies of body composition, lipids, measurement of postheparin lipoprotein and HL lipase activities, cholesteryl ester transfer protein activity, and insulin sensitivity (Si). After an average weight loss of 10%, reductions in fat mass, IAF, and abdominal s.c. fat were seen, accompanied by reductions in levels of triglyceride, very low density lipoprotein cholesterol, apolipoprotein B, and HL activity. High density lipoprotein-2 cholesterol and Si increased. In those subjects with pattern B LDL at baseline, LDL particle size increased. Cholesteryl ester transfer protein activity did not change. Changes in IAF and Si correlated with a decrease in HL activity (although not independently of each other). In summary, in men undergoing diet-induced weight loss, only loss of IAF was found to be associated with a reduction in HL, which is associated with beneficial effects on lipid levels.

PLTP activity in premenopausal women. Relationship with lipoprotein lipase, HDL, LDL, body fat, and insulin resistance.

Plasma phospholipid transfer protein (PLTP) is thought to play a major role in the facilitated transfer of phospholipids between lipoproteins and in the modulation of high density lipoprotein (HDL) particle size and composition. However, little has been reported concerning the relationships of PLTP with plasma lipoprotein parameters, lipolytic enzymes, body fat distribution, insulin, and glucose in normolipidemic individuals, particularly females. In the present study, 50 normolipidemic healthy premenopausal females were investigated. The relationships between the plasma PLTP activity and selected variables were assessed. PLTP activity was significantly and positively correlated with low density lipoprotein (LDL) cholesterol (r(s) = 0.53), apoB (r(s) = 0.44), glucose (r(s) = 0.40), HDL cholesterol (r(s) = 0.38), HDL(3) cholesterol (r(s) = 0.37), lipoprotein lipase activity (r(s) = 0.36), insulin (r(s) = 0.33), subcutaneous abdominal fat (r(s) = 0.36), intra-abdominal fat (r(s) = 0.29), and body mass index (r(s) = 0.29). HDL(2) cholesterol, triglyceride, and hepatic lipase were not significantly related to PLTP activity. As HDL(2) can be decreased by hepatic lipase and hepatic lipase is increased in obesity with increasing intra-abdominal fat, the participants were divided into sub-groups of non-obese (n = 35) and obese (n = 15) individuals and the correlation of PLTP with HDL(2) cholesterol was re-examined. In the non-obese subjects, HDL(2) cholesterol was found to be significantly and positively related to PLTP activity (r(s) = 0.44). Adjustment of the HDL(2) values for the effect of hepatic lipase activity resulted in a significant positive correlation between PLTP and HDL(2) (r(s) = 0.41), indicating that the strength of the relationship between PLTP activity and HDL(2) can be reduced by the opposing effect of hepatic lipase on HDL(2) concentrations. We conclude that PLTP-facilitated lipid transfer activity is related to HDL and LDL metabolism, as well as lipoprotein lipase activity, adiposity, and insulin resistance.

Plasma lipoproteins promote the release of bacterial lipopolysaccharide from the monocyte cell surface.

When bacterial lipopolysaccharide (LPS) enters the bloodstream, it is thought to have two general fates. If LPS binds to circulating leukocytes, it triggers innate host defense mechanisms and often elicits toxic reactions. If instead LPS binds to plasma lipoproteins, its bioactivity is largely neutralized. This study shows that lipoproteins can also take up LPS that has first bound to leukocytes. When monocytes were loaded with [(3)H]LPS and then incubated in plasma, they released over 70% of the cell-associated [(3)H]LPS into lipoproteins (predominantly high density lipoprotein), whereas in serum-free medium the [(3)H]LPS remained tightly associated with the cells. The transfer reaction could be reproduced in the presence of pure native lipoproteins or reconstituted high density lipoprotein. Plasma immunodepletion experiments and experiments using recombinant LPS transfer proteins revealed that soluble CD14 significantly enhances LPS release from the cells, high concentrations of LPS-binding protein have a modest effect, and phospholipid transfer protein is unable to facilitate LPS release. Essentially all of the LPS on the monocyte cell surface can be released. Lipoprotein-mediated LPS release was accompanied by a reduction in several cellular responses to the LPS, suggesting that the movement of LPS from leukocytes into lipoproteins may attenuate host responses to LPS in vivo.

DNA sequences responsible for reduced promoter activity of human phospholipid transfer protein by fibrate.

Phospholipid transfer protein (PLTP) plays an important role in plasma lipid and lipoprotein metabolism. We have previously cloned and characterized the promoter region of the human PLTP gene. The present study was conducted to determine if the promoter activity of the human PLTP gene is affected by fibrate, a hypolipidemic drug, and to identify DNA sequences that are responsible for the effect. The results indicated that the promoter activity of the PLTP gene was significantly reduced by fenofibrate, and the area that was mainly responsive to the reducing effect by fibrate was located between -377 and -230 of the 5'-flanking region. The DNA sequence analysis suggested that each area of the DNA sequences from -342 to -323 and from -322 to -299 has two repeated sequences, which are inverted and homologous to the recognition motif of peroxisome proliferator-activated receptor (PPAR), namely the PPAR-responsive element (PPRE). Mutagenesis of these PPRE-like sequences, especially that at -322 to -299, abolished most of the reducing effects of fibrate on the PLTP promoter activity. These findings strongly suggest that the PPRE-like elements are responsible for the reduced promoter activity of the human PLTP gene by fibrate.

Phospholipid transfer protein enhances removal of cellular cholesterol and phospholipids by high-density lipoprotein apolipoproteins.

High-density lipoprotein (HDL) apolipoproteins remove excess cholesterol from cells by an active transport pathway that may protect against atherosclerosis. Here we show that treatment of cholesterol-loaded human skin fibroblasts with phospholipid transfer protein (PLTP) increased HDL binding to cells and enhanced cholesterol and phospholipid efflux by this pathway. PLTP did not stimulate lipid efflux in the presence of albumin, purified apolipoprotein A-I, and phospholipid vesicles, suggesting specificity for HDL particles. PLTP restored the lipid efflux activity of mildly trypsinized HDL, presumably by regenerating active apolipoproteins. PLTP-stimulated lipid efflux was absent in Tangier disease fibroblasts, induced by cholesterol loading, and inhibited by brefeldin A treatment, indicating selectivity for the apolipoprotein-mediated lipid removal pathway. The lipid efflux-stimulating effect of PLTP was not attributable to generation of prebeta HDL particles in solution but instead required cellular interactions. These interactions increased cholesterol efflux to minor HDL particles with electrophoretic mobility between alpha and prebeta. These findings suggest that PLTP promotes cell-surface binding and remodeling of HDL so as to improve its ability to remove cholesterol and phospholipids by the apolipoprotein-mediated pathway, a process that may play an important role in enhancing flux of excess cholesterol from tissues and retarding atherogenesis.

Introduction of the human PLTP transgene suppresses the atherogenic diet-induced increase in plasma phospholipid transfer activity in C57BL/6 mice.

The human plasma phospholipid transfer protein (PLTP) has been shown to facilitate the transfer of phospholipids between lipoproteins and convert high-density lipoproteins into larger and smaller particles in vitro. To explore the lipid transport function in vivo, transgenic C57BL/6 mice that express the human PLTP gene, driven by its natural promoter, were generated. Little difference in PLTP activity and lipoprotein lipids was observed between transgenic mice and non-transgenic control mice fed the chow diet. In response to an atherogenic high-fat, high-cholesterol, cholic acid containing diet, the PLTP activity increased significantly with time in control mice (62% in males and 34% in females after the high-fat diet for 18 weeks). In contrast, the PLTP activity did not change appreciably in the transgenic mice fed the atherogenic diet. Thus, the introduction of the human transgene suppressed the diet-induced increase in plasma PLTP activity, as evidenced by a decrease in PLTP mRNA in a variety of tissues. High-density lipoprotein levels decreased in mice fed the atherogenic diet, but there was a proportionally greater decrease in transgenic animals than in controls. After 18 weeks on the atherogenic diet, the transgenic animals had high-density lipoprotein-cholesterol and PLTP activity approximately one-half of that of control animals. Non-denaturing gradient gel electrophoresis of plasma indicated that the atherogenic diet decreased the high-density lipoprotein size distribution in control mice. However, high-density lipoprotein particle size distribution of the transgenic mice was shifted to smaller particles compared with control animals (P < 0.001). These findings suggest that PLTP activity can modulate the effects of an atherogenic diet on high-density lipoproteins.

Relationship between plasma phospholipid transfer protein activity and HDL subclasses among patients with low HDL and cardiovascular disease.

Low levels of high density lipoproteins (HDL) are associated with an increased risk for premature cardiovascular disease. The plasma phospholipid transfer protein (PLTP) is believed to play a critical role in lipoprotein metabolism and reverse cholesterol transport by remodeling HDL and facilitating the transport of lipid to the liver. Plasma contains two major HDL subclasses, those containing both apolipoproteins (apo) A-I and A-II, Lp(A-I, A-II), and those containing apo A-I but not A-II, Lp(A-I). To examine the potential relationships between PLTP and lipoproteins, plasma PLTP activity, lipoprotein lipids, HDL subclasses and plasma apolipoproteins were measured in 52 patients with documented cardiovascular disease and low HDL levels. Among the patients, plasma PLTP activity was highly correlated with the percentage of plasma apo A-I in Lp(A-I) (r=0.514, p < 0.001) and with the apo A-I, phospholipid and cholesterol concentration of Lp(A-I) (r=0.499, 0.478, 0.457, respectively, p < 0.001). Plasma PLTP activity was also significantly correlated with plasma apo A-I (r=0.413, p=0.002), HDL cholesterol (r=0.308, p=0.026), and HDL, and HDL3 cholesterol (r=0.284 and 0.276, respectively, p < 0.05), but no significant correlation was observed with Lp(A-I, A-I), plasma cholesterol, triglycerides, or apo B, very low density lipoprotein cholesterol or low density lipoprotein cholesterol. These associations support the hypothesis that PLTP modulates plasma levels of Lp(A-I) particles without significantly affecting the levels of Lp(A-I, A-II) particles.

Relationship between phospholipid transfer protein activity and HDL level and size among inbred mouse strains.

Because of the paucity of data on phospholipid transfer protein (PLTP) activity and lipoprotein phospholipid in mouse strains, plasma PLTP activity (PLTA), plasma phospholipid and cholesterol, HDL phospholipid and cholesterol, and HDL size distribution were determined in 15 inbred mouse strains. The 15 inbred mouse strains differed in their relatedness to one another and consisted of six largely unrelated groups: Castaneus, Swiss, C57BL, AKR, DBA, and NZB. Lipid and PLTA analyses were performed on plasma pools from male and female mice that had fasted for 4 h prior to blood draw. Among the representative unrelated strains fed the chow diet, there was a highly significant relationship between PLTA and plasma phospholipid (r(s) = 0.727, P < 0.01), HDL phospholipid (r(s) = 0.762, P < 0.01), HDL cholesterol (r(s) = 0.699, P < 0.02), percentage of large HDL particles (r(s) = 0.699, P < 0.02), and HDL peak size (r(s) = 0.776, P < 0.01). Similar results were obtained among these strains fed a high fat, high cholesterol diet. PLTA increased in all strains fed the high fat diet (chix = 94%, range 6 to 221%). Strain SM having relatively low PLTA and HDL was crossed with strain NZB having high PLTA and HDL. The F1 progeny from this cross were backcrossed to strain SM and 41 male backcross progeny collected. Among these individual backcrossed animals, PLTA was highly correlated with plasma phospholipid (r(s) = 0.508, P = 0.001), HDL phospholipid (r(s) = 0.566, P < 0.001), HDL cholesterol (r(s) = 0.532, P < 0.001), and percentage of large HDL particles (r(s) = 0.446, P = 0.020). Therefore, we conclude that PLTP is a determinant of HDL level and size in mice.-Albers, J. J., W. Pitman, G. Wolfbauer, M. C. Cheung, H. Kennedy, A-Y. Tu, S. M. Marcovina, and B. Paigen. Relationship between phospholipid transfer protein activity and HDL level and size among inbred mouse strains.