Lipid Transfer Protein Activity Research Articles

The effect of thermal processing on the IgE reactivity of the non‐specific lipid transfer protein from apple, Mal d 3

Non-specific lipid transfer proteins (LTPs) are involved in allergy to fresh and processed fruits. We have investigated the effect of thermal treatment and glycation on the physico-chemical and IgE-binding properties of the LTP from apple (Mal d 3). Mal d 3 was purified from apple peel and the effect of heating in the absence and presence of glucose investigated by CD spectroscopy, electrospray and MALDI-TOF mass spectrometry. IgE reactivity was determined by RAST and immunoblot inhibition, SPT and basophil histamine release test. The identity and IgE reactivity of purified Mal d 3 was confirmed. Mild heat treatment (90 degrees C, 20 min) in the absence or presence of glucose did not alter its IgE reactivity. More severe heat treatment (100 degrees C, 2 h) induced minor changes in protein structure, but a significant decrease in IgE-binding (30-fold) and biological activity (100- to 1000-fold). Addition of glucose resulted in up to four glucose residues attached to Mal d 3 and only a 2- and 10-fold decrease of IgE-binding and biological activity, respectively. Only severe heat treatment caused a significant decrease in the allergenicity of Mal d 3 but glycation had a protective effect. The presence of sugars in fruits may contribute to the thermostability of the allergenic activity of LTP in heat-processed foods.

Lipid Transfer Proteins Enhance Cell Wall Extension in Tobacco

Plant cells are enclosed by a rigid cell wall that counteracts the internal osmotic pressure of the vacuole and limits the rate and direction of cell enlargement. When developmental or physiological cues induce cell extension, plant cells increase wall plasticity by a process called loosening. It was demonstrated previously that a class of proteins known as expansins are mediators of wall loosening. Here, we report a type of cell wall-loosening protein that does not share any homology with expansins but is a member of the lipid transfer proteins (LTPs). LTPs are known to bind a large range of lipid molecules to their hydrophobic cavity, and we show here that this cavity is essential for the cell wall-loosening activity of LTP. Furthermore, we show that LTP-enhanced wall extension can be described by a logarithmic time function. We hypothesize that LTP associates with hydrophobic wall compounds, causing nonhydrolytic disruption of the cell wall and subsequently facilitating wall extension.

Type 2 diabetes mellitus is associated with differential effects on plasma cholesteryl ester transfer protein and phospholipid transfer protein activities and concentrations

Background: Human plasma contains two lipid transfer proteins, cholesteryl ester transfer protein (CETP) and phospholipid transfer protein (PLTP), which are crucial in reverse cholesterol transport. Methods: Plasma CETP and PLTP activity levels and concentrations in 16 type 2 diabetic patients and 16 matched healthy subjects were determined, and these data were correlated to clinical variables, including insulin sensitivity and lipid levels. Results: Plasma triglycerides were higher (p<0.02) and high‐density lipoprotein (HDL) cholesterol (p<0.02) was lower in diabetic patients. Plasma CETP activity and concentrations were not significantly different between diabetic and healthy subjects, but CETP specific activity was lower in diabetic patients (p<0.001). Multiple regression analysis showed that plasma CETP activity was positively related to CETP concentration (p=0.0001) and negatively to the diabetic state (p<0.002) or to HbA1c (p<0.02). PLTP activity (p<0.05) and specific activity were higher (p<0.05), whereas there was no difference in PLTP concentration between the two groups. There was no significant bivariate correlation between PLTP concentration and activity, in either healthy or diabetic subjects. Multiple regression analysis did disclose positive relationships of PLTP activity with PLTP concentration (p=0.0001), plasma triglycerides (p=0.0001) and waist/hip ratio (p=0.0001), but not with the diabetic state or HbA1c. Conclusions: Neither CETP nor PLTP activity was independently associated with insulin sensitivity. Specific CETP activity is decreased in type 2 diabetes mellitus. In contrast, specific PLTP activity is higher in diabetes, as a result of the association of plasma PLTP activity with plasma triglycerides and obesity. Measurement of both plasma lipid transfer protein activity and mass levels may thus provide extra information in diabetes mellitus.

Effects of medium-chain fatty acids and oleic acid on blood lipids, lipoproteins, glucose, insulin, and lipid transfer protein activities

Dietary medium-chain fatty acids (MCFAs) are of nutritional interest because they are more easily absorbed from dietary medium-chain triacylglycerols (MCTs) than are long-chain fatty acids from, for example, vegetable oils. It has generally been claimed that MCFAs do not increase plasma cholesterol, although this claim is poorly documented. We compared the effects of a diet rich in either MCFAs or oleic acid on fasting blood lipids, lipoproteins, glucose, insulin, and lipid transfer protein activities in healthy men. In a study with a double-blind, randomized, crossover design, 17 healthy young men replaced part of their habitual dietary fat intake with 70 g MCTs (66% 8:0 and 34% 10:0) or high-oleic sunflower oil (89.4% 18:1). Each intervention period lasted 21 d, and the 2 periods were separated by a washout period of 2 wk. Blood samples were taken before and after the intervention periods. Compared with the intake of high-oleic sunflower oil, MCT intake resulted in 11% higher plasma total cholesterol (P = 0.0005), 12% higher LDL cholesterol (P = 0.0001), 32% higher VLDL cholesterol (P = 0.080), a 12% higher ratio of LDL to HDL cholesterol (P = 0.002), 22% higher plasma total triacylglycerol (P = 0.0361), and higher plasma glucose (P = 0.033). Plasma HDL-cholesterol and insulin concentrations and activities of cholesterol ester transfer protein and phospholipid transfer protein did not differ significantly between the diets. Compared with fat high in oleic acid, MCT fat unfavorably affected lipid profiles in healthy young men by increasing plasma LDL cholesterol and triacylglycerol. No changes in the activities of phospholipid transfer protein and cholesterol ester transfer protein were evident.

Glycolipid intermembrane transfer is accelerated by HET-C2, a filamentous fungus gene product involved in the cell-cell incompatibility response.

Among filamentous fungi capable of mycelial growth, het genes play crucial roles by regulating heterokaryon formation between different individuals. When fusion occurs between fungal mycelia that differ genetically at their het loci, the resulting heterokaryotic cells are quickly destroyed. It is unclear how het gene products of Podospora anserina trigger heterokaryon incompatibility. One unexplored possibility is that glycosphingolipids play a role because the het-c2 gene encodes a protein that displays 32% sequence identity and an additional 30% similarity to the mammalian glycolipid transfer protein. Here, P. anserina protoplasts containing wild-type het-c2 genes were shown to have greater glycosphingolipid transfer activity than protoplasts with disrupted het-c2 genes, a condition previously linked to altered cell compatibility following hyphal fusion. The observed glycolipid transfer activity could not be accounted for by nonspecific lipid transfer protein activity. Direct assessment showed that purified, recombinant HET-C2 accelerates the intermembrane transfer of glycolipid in vitro, but that the HET-C2 activity is mitigated much less by negatively charged membranes than the mammalian glycolipid transfer protein. The findings are discussed within the context of HET-C2 being a member of an emerging family of ancestral sphingolipid transfer proteins that play important roles in cell proliferation and accelerated death.

High intakes of vegetables, berries, and apples combined with a high intake of linoleic or oleic acid only slightly affect markers of lipid peroxidation and lipoprotein metabolism in healthy subjects , ,

A high consumption of vegetables and fruit is associated with decreased risk of ischemic heart disease and several cancers. The pathophysiology of these diseases involves free radical mechanisms. Diet may either enhance or diminish oxidative stress in the body. We studied the effects of high and low intakes of vegetables, berries, and apples on markers of lipid peroxidation and lipoprotein metabolism in subjects consuming diets high in linoleic or oleic acid. For 6 wk, healthy men and women (n = 77; aged 19-52 y) consumed 1 of 4 controlled isoenergetic diets rich in either linoleic acid (11% of energy) or oleic acid (12% of energy) and containing either 815 or 170 g vegetables, berries, and apples/10 MJ. Nineteen healthy volunteers served as control subjects. Several markers of dietary compliance (plasma fatty acids, vitamin C, carotenoids, and quercetin), lipid peroxidation [ex vivo LDL oxidation, plasma and LDL thiobarbituric acid-reactive substances, paraoxonase (EC 3.1.8.1), and urinary 8-iso-prostaglandin F(2)(alpha)], and lipoprotein metabolism (plasma lipids, apolipoproteins, and lipid transfer protein activities) were measured from samples collected before and at the end of the experimental period. Plasma fatty acid composition and antioxidant concentrations showed that compliance with the diets was good. However, there were no significant differences between the diets in the markers of lipid peroxidation and lipoprotein metabolism. In healthy volunteers with adequate vitamin intakes, 6-wk diets differing markedly in the amounts of linoleic and oleic acid and vegetables, berries, and apples did not differ in their effects on lipid peroxidation or lipoprotein metabolism.

Effects of acylation on the structure, lipid binding, and transfer activity of wheat lipid transfer protein.

Study of the effect of protein chemical acylation on their functional properties or activity often brings valuable information regarding structure-function relationships. We performed such work on wheat lipid transfer protein, LTP1, to investigate the role of grafted acyl chains on the lipid binding and transfer properties. LTP1 was acylated by using anhydride derivatives of various chain lengths from C2 to C6. Only the chemical modifications with hexanoic acid yielded a marked effect on the tertiary structure and a slight change in the secondary structure. The affinity of the modified proteins for myristoyl-lysophosphatidylcholine was similar to that of the native protein accompanied by a slight decrease in stoichiometry. Interestingly, the acylation of LTP1 enhanced the lipid transfer activity by at least a factor of 10 for hexanoic chain length. Finally, the grafting of acyl chains was investigated by means of molecular modelling, and an attempt is made to correlate with our experimental data.

Plasma lipases and lipid transfer proteins increase phospholipid but not free cholesterol transfer from lipid emulsion to high density lipoproteins.

BackgroundPlasma lipases and lipid transfer proteins are involved in the generation and speciation of high density lipoproteins. In this study we have examined the influence of plasma lipases and lipid transfer protein activities on the transfer of free cholesterol (FC) and phospholipids (PL) from lipid emulsion to human, rat and mouse lipoproteins. The effect of the lipases was verified by incubation of labeled (3H-FC,14C-PL) triglyceride rich emulsion with human plasma (control, post-heparin and post-heparin plus lipase inhibitor), rat plasma (control and post-heparin) and by the injection of the labeled lipid emulsion into control and heparinized functionally hepatectomized rats.ResultsIn vitro, the lipase enriched plasma stimulated significantly the transfer of 14C-PL from emulsion to high density lipoprotein (p<0.001) but did not modify the transfer of 3H-FC. In hepatectomized rats, heparin stimulation of intravascular lipolysis increased the plasma removal of 14C-PL and the amount of 14C-PL found in the low density lipoprotein density fraction but not in the high density lipoprotein density fraction. The in vitro and in vivo experiments showed that free cholesterol and phospholipids were transferred from lipid emulsion to plasma lipoproteins independently from each other. The incubation of human plasma, control and control plus monoclonal antibody anti-cholesteryl ester transfer protein (CETP), with 14C-PL emulsion showed that CETP increases 14C-PL transfer to human HDL, since its partial inhibition by the anti-CETP antibody reduced significantly the 14C-PL transfer (p<0.05). However, comparing the nontransgenic (no CETP activity) with the CETP transgenic mouse plasma, no effect of CETP on the 14C-PL distribution in mice lipoproteins was observed.ConclusionsIt is concluded that: 1-intravascular lipases stimulate phospholipid transfer protein mediated phospholipid transfer, but not free cholesterol, from triglyceride rich particles to human high density lipoproteins and rat low density lipoproteins and high density lipoproteins; 2-free cholesterol and phospholipids are transferred from triglyceride rich particles to plasma lipoproteins by distinct mechanisms, and 3 - CETP also contributes to phospholipid transfer activity in human plasma but not in transgenic mice plasma, a species which has high levels of the specific phospholipid transfer protein activity.

Low plasma lecithin:cholesterol acyltransferase and lipid transfer protein activities in growth hormone deficient and acromegalic men: role in altered high density lipoproteins

Growth hormone (GH) deficiency and acromegaly may be associated with increased cardiovascular risk. Little is known about alterations in high density lipoproteins (HDL) in these conditions. Lecithin:cholesterol acyl transferase (LCAT) has the ability to esterify free cholesterol (FC) in HDL. Cholesteryl ester transfer protein (CETP) is able to transfer cholesteryl esters (CE) from HDL to very low and low density lipoproteins (VLDL and LDL). During phospholipid transfer protein (PLTP) -mediated HDL remodelling, small pre β-HDL particles are generated which serve as acceptors for cellular cholesterol and provide the initial LCAT-substrate. We documented plasma lipids, LCAT, CETP and PLTP activity levels as well as plasma cholesterol esterification (EST) and cholesteryl ester transfer (CET) in 12 adult men with acquired GH deficiency, 12 acromegalic men and 24 healthy male subjects. All GH deficient and acromegalic patients received conventional hormonal replacement therapy if necessary. VLDL+LDL cholesterol and plasma triglycerides were higher in GH deficient ( P<0.01 and P<0.05) and acromegalic patients ( P<0.05 and P<0.01) than in healthy subjects. HDL cholesterol and HDL CE were lower ( P<0.05 for both) and the HDL FC/CE ratio was higher ( P<0.01) in these patient groups compared to healthy subjects. Plasma LCAT, CETP and PLTP activity levels were lower in acromegalic patients (P<0.01 for all) and CETP activity was lower in GH deficient patients ( P<0.01) compared to healthy subjects. Plasma EST and CET were decreased in both acromegalic ( P<0.01 for both) and GH deficient patients ( P<0.05 for both). Multiple regression analysis demonstrated independent negative relationships of plasma insulin-like growth factor I with plasma LCAT ( P=0.0001), CETP ( P=0.009) and PLTP activity levels ( P=0.021). Plasma LCAT ( P=0.0001) and CETP activity ( P=0.0001) were also negatively associated with (substitution therapy for) adrenal insufficiency. In conclusion, GH deficient and acromegalic patients show abnormalities in HDL, consistent with impaired LCAT action. Decreases in plasma EST and CET in such patients, as well as a low PLTP activity in acromegaly suggest that reverse cholesterol transport may be impaired, contributing to increased cardiovascular risk.

Effect of growth hormone replacement therapy on plasma lecithin:cholesterol acyltransferase and lipid transfer protein activities in growth hormone-deficient adults

The effects of growth hormone (GH) replacement on plasma lecithin:cholesterol acyltransferase (LCAT), cholesteryl ester transfer protein (CETP), and phospholipid transfer protein (PLTP), factors involved in high density lipoprotein (HDL) metabolism, are unknown. We carried out a 6 months study in 24 GH-deficient adults who were randomized to placebo (n = 8), low dose GH (1 U daily, n = 8), and high dose GH (2 U daily, n = 8), followed by a 6 months open extension study with high dose GH (1 dropout). No significant changes in plasma lipoproteins, LCAT, CETP, and PLTP activities, cholesterol esterification (EST) and cholesteryl ester transfer (CET) were observed after placebo. After 6 months of GH (combined data, n = 24), very low + low density lipoprotein (VLDL + LDL) cholesterol (P < 0.05) and apolipoprotein B (P < 0.05) decreased, whereas HDL cholesterol and HDL cholesteryl ester increased (P < 0.05). Prolonged treatment showed comparable effects. Plasma apolipoprotein A-I and Lp[a] remained unchanged. Plasma LCAT (P < 0.01) and CETP activities (P < 0.01), as well as EST (P < 0.01) and CET decreased (P < 0.01) after 12 months of GH (n = 15), but PLTP activity did not significantly change. Changes in EST and CET after 12 months of treatment were independently related to changes in plasma LCAT (P = 0.001 and CETP activity (P = 0.01).In conclusion, GH replacement therapy improves the lipoprotein profile in GH-deficient adults. Chronic GH replacement lowers plasma LCAT and CETP activities, contributing to a decrease in cholesterol esterification and cholesteryl ester transfer. These effects may have consequences for HDL metabolism and reverse cholesterol transport.

The role of altered high-density lipoproteins in the low plasma lecithin cholesterol acyltransferase and lipid transfer protein activity found in growth hormone-deficient men with acromegaly

The role of altered high-density lipoproteins in the low plasma lecithin cholesterol acyltransferase and lipid transfer protein activity found in growth hormone-deficient men with acromegaly

Net mass transfer of plasma cholesteryl esters and lipid transfer proteins in normolipidemic patients with peripheral vascular disease.

The role of plasma cholesteryl ester transfer and lipid transfer proteins in atherosclerosis is unclear. Recent data suggest both antiatherogenic and atherogenic properties for cholesteryl ester transfer protein (CETP). The overall effect of CETP on atherosclerosis may thus vary depending on individual lipid metabolism. To test whether lipid transfer parameters are of importance even in patients without major lipid risk factors for atherosclerosis, CETP mass and activity, net mass transfer of cholesteryl esters between endogenous lipoproteins (CET), and phospholipid transfer protein (PLTP) activity were determined in plasma from 18 normolipidemic male patients with peripheral vascular disease and 21 controls. Furthermore, lecithin: cholesterol acyltransferase (LCAT) activity was tested. The results show that CETP mass, CETP activity, and LCAT activity are not different between patients and controls. However, specific CETP activity (CETP activity/CETP mass) is lower in the patients (P < .02). On the contrary, higher CET is observed in patients' plasma (P < .001). Increased plasma PLTP activity (P = .052) is demonstrable in the patients. If the data of all subjects are combined, CET correlates positively with triglycerides ([TG], r = .45, P < .001) and with PLTP activity (r = .32, P < .05) but negatively with specific CETP activity (r = -.37 P < .05). CET and specific CETP activity remain significantly different in TG-matched patients and controls and are more strongly interrelated (r = -.71, P < .001), suggesting a higher and selective influence of lipid transfer inhibitor(s) on CET and CETP activity in the patients. CET allows the best discrimination between patients and controls in univariate and multivariate analysis. Eighty-eight percent of the subjects are correctly classified by CET as a single parameter. The results suggest that increased CET in the patients may reflect atherogenic alterations in TG metabolism and/or in lipid transfer protein activities despite normal fasting lipoprotein levels.

Influence of insulin sensitivity and the TaqIB cholesteryl ester transfer protein gene polymorphism on plasma lecithin:cholesterol acyltransferase and lipid transfer protein activities and their response to hyperinsulinemia in non-diabetic men

Lecithin:cholesteryl acyl transferase (LCAT), cholesteryl ester transfer protein (CETP), phospholipid transfer protein (PLTP), and lipoprotein lipases are involved in high density lipoprotein (HDL) metabolism. We evaluated the influence of insulin sensitivity and of the TaqIB CETP gene polymorphism (B1B2) on plasma LCAT, CETP, and PLTP activities (measured with exogenous substrates) and their responses to hyperinsulinemia. Thirty-two non-diabetic men without hyperlipidemia were divided in quartiles of high (Q1) to low (Q4) insulin sensitivity. Plasma total cholesterol, very low + low density lipoprotein cholesterol, triglycerides, and apolipoprotein (apo) B were higher in Q4 compared to Q1 (P < 0.05 for all), whereas HDL cholesterol and apoA-I were lowest in Q4 (P < 0.05 for both). Plasma LCAT activity was higher in Q4 than in Q1 (P < 0.05) and PLTP activity was higher in Q4 than in Q2 (P < 0.05). Insulin sensitivity did not influence plasma CETP activity. Postheparin plasma lipoprotein lipase activity was highest and hepatic lipase activity was lowest in Q1. Insulin infusion decreased PLTP activity (P < 0.05), irrespective of the degree of insulin sensitivity. The CETP genotype exerted no consistent effects on baseline plasma lipoproteins and LCAT, CETP, and PLTP activities. The decrease in plasma PLTP activity after insulin was larger in B1B1 than in B2B2 homozygotes (P < 0.05).▪These data suggest that insulin sensitivity influences plasma LCAT, PLTP, lipoprotein lipase, and hepatic lipase activities in men. As PLTP, LCAT, and hepatic lipase may enhance reverse cholesterol transport, it is tempting to speculate that high levels of these factors in association with insulin resistance could be involved in an antiatherogenic mechanism. A possible relationship between the CETP genotype and PLTP lowering by insulin warrants further study.—Riemens, S. C., A. Van Tol, B. K. Stulp, and R. P. F. Dullaart. Influence of insulin sensitivity and the TaqIB cholesteryl ester transfer protein gene polymorphism on plasma lecithin:cholesterol acyltransferase and lipid transfer protein activities and their response to hyperinsulinemia in non-diabetic men. J. Lipid Res. 1999. 40: 1467–1474.

Altered Composition of High Density Lipoproteins in Women With the Polycystic Ovary Syndrome

Rajkhowa, M.; Neary, R. H.; Kumpatla, P.; Game, F. L.; Jones, P. W.; Obhrai, M. S.; Clayton, R. N. Author Information

Altered composition of high density lipoproteins in women with the polycystic ovary syndrome.

Women with polycystic ovary syndrome (PCOS) appear at increased cardiovascular risk due in part to a dyslipidemia characterized by increased plasma triglyceride and reduced high density lipoprotein (HDL) cholesterol levels. This is a detailed exploratory study of HDL composition in 35 obese [body mass index (BMI), > 27] and 22 nonobese subjects with PCOS and in 14 healthy obese and 18 nonobese women. Although we found reduced levels of total and HDL2 cholesterol in obese women with PCOS, HDL composition was modified by depletion of lipid relative to protein, with reduced ratios of HDL total cholesterol and HDL phospholipids to apolipoprotein A-I (apoA-I) compared to those in obese controls (P = 0.008 and P = 0.012, respectively). This was explained by reduced cholesterol (P = 0.004) and phospholipid (although not significant, P = 0.07) in HDL with no change in the content of apoA-I, its major protein. Obesity, insulin resistance, and hyperandrogenemia are features of PCOS and potentially affect lipid metabolism. Insulin sensitivity was assessed by the reduction in endogenous glucose concentration after exogenous insulin; the insulin, glucose, and fatty acid responses to oral glucose; and the fasting insulin concentration. When age, BMI, free androgen index, insulin sensitivity determined by all methods, and the presence of PCOS were subjected to stepwise multivariate regression analysis, the presence of PCOS was the most consistent predictor of lipid-depleted HDL (HDL total cholesterol/apoA-I and HDL phospholipids/apoA-I). We speculate that altered activity of hepatic lipase or lipid transfer protein could explain this aspect of the dyslipidemia. Obesity has an important influence on the lipid profile. Obese PCOS and control subjects had higher levels of cholesterol, triglyceride, apoB, and fatty acids than their lean counterparts, and BMI proved the best predictor of blood levels on multiple regression analysis. In contrast, lean PCOS patients had normal sensitivity to insulin and lipid profiles similar to those of the lean controls and did not manifest the HDL abnormalities. Although in PCOS, correlations were obtained between the free androgen index and cholesterol, triglyceride, and apoB levels and between the integrated glucose and insulin responses after oral glucose and fasting fatty acid and triglyceride levels, when age and adiposity were included as covariates only fatty acids and the integrated glucose response remained significantly correlated. Among the controls, total, low density lipoprotein cholesterol, triglycerides, and apoB were related to aspects of insulin sensitivity independent of age and BMI. Lipid metabolism in PCOS is dependent on several related factors, but subjects with PCOS who are obese show a specific reduction in HDL lipid, suggesting a reduced capacity for cholesterol removal from tissues with diminished antiatherogenic potential. Efforts should be directed toward reducing obesity in PCOS to improve the metabolic disturbance in addition to ameliorating the presenting symptoms.

The cholesterol-raising diterpenes from coffee beans increase serum lipid transfer protein activity levels in humans

Cafestol and kahweol–diterpenes present in unfiltered coffee— strongly raise serum VLDL and LDL cholesterol and slightly reduce HDL cholesterol in humans. The mechanism of action is unknown. We determined whether the coffee diterpenes may affect lipoprotein metabolism via effects on lipid transfer proteins and lecithin:cholesterol acyltransferase in a randomized, double-blind cross-over study with 10 healthy male volunteers. Either cafestol (61–64 mg/day) or a mixture of cafestol (60 mg/day) and kahweol (48–54 mg/day) was given for 28 days. Serum activity levels of cholesterylester transfer protein, phospholipid transfer protein and lecithin:cholesterol acyltransferase were measured using exogenous substrate assays. Relative to baseline values, cafestol raised the mean (±S.D.) activity of cholesterylester transfer protein by 18±12% and of phospholipid transfer protein by 21±14% (both P<0.001). Relative to cafestol alone, kahweol had no significant additional effects. Lecithin:cholesterol acyltransferase activity was reduced by 11±12% by cafestol plus kahweol ( P=0.02). It is concluded that the effects of coffee diterpenes on plasma lipoproteins may be connected with changes in serum activity levels of lipid transfer proteins.

Administration of Long-Term Tamoxifen Therapy Modifies the Plasma Lipoprotein—Lipid Concentration and Lipid Transfer Protein I Activity in Postmenopausal Women with Breast Cancer

Tamoxifen remains one of the most effective agents in the treatment of breast cancer. However, the development of persistent side effects from chronic administration of tamoxifen remains a concern. The objective of this project was to investigate the effect of long-term tamoxifen therapy (2 years) on the plasma lipoprotein concentration and lipid transfer activity in postmenopausal women diagnosed with breast cancer. Two distinct populations of breast cancer patients were recruited for this study: postmenopausal women diagnosed with breast cancer that have never been on tamoxifen and postmenopausal women diagnosed with breast cancer that have been on tamoxifen (20 mg once daily) for 2 years (n=18 each group). Blood was collected for total and lipoprotein cholesterol (C) and triglyceride (TG) analysis by established enzymatic assays prior to and 2 years following the initial tamoxifen dose. To determine the effect of tamoxifen administration on lipid transfer between lipoprotein fractions, lipid transfer protein (LTP I) activity was measured. A significant decrease in total and low-density lipoprotein (LDL) cholesterol levels and a moderate increase in high-density lipoprotein (HDL) triglyceride levels were observed in plasma samples from postmenopausal women with breast cancer who were administered tamoxifen for 2 years. No significant differences in total and lipoprotein C and TG plasma levels were observed in samples from women with breast cancer that never received tamoxifen. LTP I activity was significantly decreased in patients receiving tamoxifen compared to patients who never received tamoxifen. These specific tamoxifen-induced effects may be important for a number of reasons. Although the apparent decrease in total C and LDL-C levels are favorable for reducing the risk of cardiovascular disease, the elevated levels of HDL-TG have been related to the increased risk of ischemic heart disease. Furthermore, understanding how tamoxifen influences LTP I activity provides valuable insight into how the administration of tamoxifen modifies plasma lipoprotein—lipid levels.

Higher high density lipoprotein cholesterol associated with moderate alcohol consumption is not related to altered plasma lecithin: cholesterol acyltransferase and lipid transfer protein activity levels

Lecithin:cholesterol acyltransferase (LCAT), cholesteryl ester transfer protein (CETP) and phospholipid transfer protein (PLTP) are important factors involved in HDL metabolism. Altered plasma activity levels of these factors could play a role in the increase in high density lipoprotein (HDL) cholesterol associated with moderate alcohol consumption. We measured plasma LCAT, CETP and PLTP activities with exogenous substrate assays, as well as lipoproteins and HDL lipids in 6 alcohol-abstaining men, 18 matched men who used ⪯ 1 and 18 men who used > 1 alcohol-containing drinks per day. Plasma cholesterol and triglycerides were similar in the three groups. HDL total cholesterol, HDL cholesteryl ester, HDL free cholesterol and HDL triglycerides were higher in the alcohol drinkers compared to the abstainers (all P < 0.05). No differences in plasma LCAT, CETP and PLTP activity levels were observed between the three groups. Analysis of covariance also demonstrated that the use of alcohol was associated with higher HDL cholesterol ( P < 0.04), whereas plasma LCAT, CETP and PLTP activity levels were not related to alcohol consumption. Furthermore, HDL cholesteryl ester was positively associated with LCAT activity ( P < 0.001), PLTP activity ( P < 0.01) and alcohol intake ( P < 0.04) and negatively with plasma triglycerides ( P < 0.001) and CETP activity ( P < 0.03), indicating that alcohol influenced HDL cholesteryl ester independently from these biochemical parameters. The higher HDL cholesterol associated with moderate alcohol consumption is, therefore, unlikely to be caused by an effect on plasma LCAT, CETP or PLTP activity levels.

Plasma cholesteryl ester transfer activity is modulated by the phase transition of the lipoprotein core

Previous studies have shown that lipid transfer protein (LTP) activity is strongly temperature dependent, demonstrating a dramatic rise in activity near 37 degrees C. We have investigated the origin of this rapid rise in LTP activity. LTP-mediated transfers of radiolabeled cholesteryl ester (CE) from LDL to HDL, HDL to LDL, LDL to biotin-LDL, HDL to biotin-HDL, and between liposomes were determined as a function of assay temperature. Only assays containing LDL demonstrated this rapid rise in CE transfer activity. In contrast, TG transfer was almost linear with assay temperature. As human LDL CE undergoes a thermal phase transition near 37 degrees C, we investigated whether the rapid rise in CE transfer was dependent on this transition. Monkey LDL were isolated from animals consuming diets containing cholesterol and enriched in saturated, monounsaturated, or polyunsaturated fatty acids. With these LDL as substrate, the CE transfer between 21 degrees and 49 degrees C could be described by two straight lines, the intersection of which defined the inflection temperature. Among eight LDL samples, the inflection temperature was highly correlated with the CE phase transition determined by differential scanning calorimetry (r2 = 0.86). Both calorimetry and CE transfer activity inflection values were correlated with the saturated + monoene/polyene ratio of the LDL cholesteryl esters (r2 = 0.733 and 0.612, respectively). For LDL with inflection temperatures below 37 degrees C, CE transfer activity at 37 degrees C increased 10-14% for each 1 degree C decrease in the inflection temperature. We conclude that LTP activity is markedly affected by the physical state of the core CE. Diets rich in saturated fatty acids may result in LDL that are poor LTP substrates, which may hinder LTP's ability to promote normal lipoprotein remodeling.

Inhibition of oleic acid incorporation into a non‐lipid fraction by chloroacetamide herbicides

Oleic acid is incorporated into an insoluble fraction left over after lipid extraction in Scenedesmus acutus. This incorporation is extremely sensitive to the chloroacetamide herbicide, metazachlor (I50= ca 20 nM). Therefore, factors influencing the incorporation of radioactivity from oleic acid into this non‐lipid fraction were investigated. S. acutus cells were cultivated under various conditions with or without inhibitors and [14C]‐oleic acid was supplied to the algae; the lipids were extracted and the radioactivity incorporated in the remaining fraction monitored. The inhibition seemed specific for chloroacetamides and related classes since it was also observed with alachlor, dimethenamid and mefenacet (an oxyacetamide). In contrast, it could not be found with diuron, oryzalin, nor could it be observed with a non‐herbicidal metazachlor derivative or iodoacetamide. Incorporation of oleic acid into that fraction required meta‐bolically active cells and was stimulated by light. Other fatty acids (16:0, 18:2, and 18:3) were also incorporated into the non‐lipid fraction but their incorporation was not inhibited by metazachlor. Among other components, the fraction contains proteins. However, a possible specific effect of chloroacetamides on the binding of oleic acid to proteins or on the in vitro activity of lipid transfer proteins could not be detected. Not much is known yet about mechanism and chemistry of oleic acid incorporation but this finding opens a new path for investigations towards the primary target of these herbicides.