The influence of letrozole on serum lipid concentrations in postmenopausal women with primary breast cancer who have completed 5 years of adjuvant tamoxifen (NCIC CTG MA.17L).

BACKGROUND: The purpose of this study was to evaluate changes in serum lipid parameters {cholesterol, high-density lipoprotein (HDL) cholesterol, low-density lipoprotein (LDL) cholesterol, triglycerides and lipoprotein(a) [Lp(a)]}, in postmenopausal women receiving letrozole or placebo after adjuvant tamoxifen for early stage breast cancer (NCIC CTG MA.17L). PATIENTS AND METHODS: MA.17L is a substudy of MA.17, a randomized, double-blind, placebo-controlled trial of letrozole 2.5 mg taken daily for 5 years in postmenopausal women with primary breast cancer completing approximately 5 years of prior adjuvant tamoxifen. Patients consenting to participate in this companion study had blood drawn and lipid parameters (total cholesterol, HDL cholesterol, LDL cholesterol, Lp(a), triglycerides) evaluated at baseline, 6 months, 12 months and yearly thereafter until completion of protocol therapy. It was required that women be non-hyperlipidemic and not taking lipid-lowering drugs at time of entry on this trial. RESULTS: Three hundred and forty seven women were enrolled in the study. The letrozole and the placebo groups demonstrated marginally significant differences in the percentage change from baseline in HDL cholesterol at 6 months (P=0.049), in LDL cholesterol at 12 months (P=0.033) and triglycerides at 24 months (P=0.036). All comparisons of lipid parameters at other time points were not significantly different between the two treatment groups. No statistically significant differences in the number of patients exceeding the thresholds defined for the lipid parameters were found between the two treatment groups. CONCLUSIONS: The MA.17 trial demonstrated a significant improvement in disease-free survival with the use of letrozole as extended adjuvant therapy post tamoxifen. Results from this study suggests that letrozole does not significantly alter serum cholesterol, HDL cholesterol, LDL cholesterol, triglycerides or Lp(a) in non-hyperlidiemic postmenopausal women with primary breast cancer treated up to 36 months following at least 5 years of adjuvant tamoxifen therapy. These findings further support the tolerability of extended adjuvant letrozole in postmenopausal women following standard tamoxifen therapy.

Elucidating the microbial component of natural attenuation.

Microbial reactions are a key determinant in natural attenuation. However, providing unequivocal evidence of the extent of their involvement is challenging. Several approaches are being developed to meet this challenge, including the use of contaminant-specific transformation products, carbon- or hydrogen-based stable isotopic analysis and reactive transport modeling. These approaches emphasize the ongoing need to integrate strategically between temporally and spatially variant geochemical conditions, the ecological characteristics of the resident microbial communities and their resultant pollutant-transformation capabilities.

Assessing the plasma pharmacokinetics, tissue distribution, excretion and effects on cholesterol pharmacokinetics of a novel hydrophilic compound, FM-VP4, following administration to rats.

PURPOSE: The purpose of this project was to 1) assess the disposition kinetics of [3H]-cholesterol following co-administration with a novel hydrophilic compound, FM-VP4, and 2) determine the pharmacokinetics, tissue distribution and excretion of [3H]FM-VP4 following single oral (150 mg/kg which includes 100 mCi of radiolabel) and intravenous (15 mg/kg which includes 10 mCi of radiolabel) doses. METHODS: Following an overnight fast (12-16 h) and 48 h post-surgery, adult male Sprague Dawley rats were divided into six treatment groups (n=4/group). Groups received single oral doses of 25 mCi/ml [3H]cholesterol alone or with 5, 10, 20, 50 and 100 mg/kg FM-VP4 at 0700 h. Ten percent Intralipid was used to solubilize and co-administer [3H]-cholesterol and FM-VP4. LC-MS analysis confirmed minimal cholesterol and vegetable stanol content within 10% Intralipid. Thin layer chromatography was used to confirm that the majority of radioactivity measured in plasma was associated with either esterified or unesterified cholesterol. In a second study pharmacokinetics of [3H]FM-VP4 were studied following intravenous or orally gavaged doses (n=8). Tissues, urine and feces were also collected in FM-VP4 kinetics study to measure tissue distribution of radioactivity. Plasma [3H]-cholesterol and [3H]FM-VP4 were tested for radioactivity. RESULTS: FM-VP4 co-administration significantly decreased [3H]-cholesterol AUC0-48h and Cmax, and increased CL/F and Vd/F of [3H]-cholesterol as compared to controls in a dose-dependent manner. Following oral administration of [3H]FM-VP4, the majority of radioactivity following was recovered in the feces and gastrointestinal (GI) tract. The compound exhibited an oral bioavailability of 6.5%. Following IV administration, a two-compartment pharmacokinetic model was observed and the majority of the radioactivity was recovered in the GI tract. CONCLUSIONS: FM-VP4 reduces plasma concentration of [3H]-cholesterol in fasting rats. [3H]FM-VP4 has a very low oral bioavailability.

Assessing plasma lipid levels, body weight, and hepatic and renal toxicity following chronic oral administration of a water soluble phytostanol compound, FM-VP4, to gerbils.

The purpose of this project was to determine the effect of a FM-VP4 when incorporated into the diet or drinking water on plasma lipids, body weight, and hepatic and renal function following chronic oral administration to gerbils. Gerbils were administered water and food daily containing either no FM-VP4 (controls; n=6), 2% or 4% FM-VP4 incorporated into the gerbil diet (n=6 each treatment group) or 2% or 4% FM-VP4 dissolved in the drinking water (n=6 each treatment group). Body weight and food and water intake were monitored weekly. Following 8 weeks of this regiment blood was obtained via a cardiac puncture and all animals were sacrificed humanely. Plasma obtained from this blood was analyzed for total cholesterol, total triglyceride and high-density lipoprotein (HDL)-cholesterol levels by standard enzymatic and precipitation techniques. Low-density lipoprotein (LDL)-cholesterol levels were determined by the Friedewald equation. The plasma was also analyzed for changes in hepatic enzyme (aspartate aminotransferase [AST] and alanine aminotransferase [ALT]) and plasma creatinine (renal function) concentrations. 2% and 4% FM-VP4 administration incorporated both into the diet and in the drinking water resulted in a significant decrease in total plasma cholesterol and LDL cholesterol concentration compared to controls. Animals administered 4% FM-VP4 in either their diet or drinking water had significantly lower body weight following the 8 weeks of treatment compared to the other groups. Significant differences in daily water intake was observed in all treatment groups with the exception of the 2% FM-VP4 in diet group compared to controls. Significant differences in daily food intake were observed in gerbils administered 2% FM-VP4 in the drinking water and 4% FM-VP4 in the diet and drinking water groups compared to controls. A significant decrease in total plasma triglyceride concentration was observed in gerbils administered 4% FM-VP4 in their drinking water compared to controls. A significant increase in HDL cholesterol concentrations was observed in gerbils administered 2% FM-VP4 in their diet and 4% FM-VP4 in their drinking water compared to controls. No significant elevations in AST, ALT and creatinine concentrations were reported for all treatment groups compared to controls. These findings suggest that FM-VP4 significantly decrease plasma lipids and body weight with no apparent hepatic or renal toxicity.

Effects of a novel hydrophilic phytostanol analog on plasma lipid concentrations in gerbils.

This study was designed to determine the effects of a novel hydrophilic phytostanol analog, FM-VP4, on total plasma cholesterol, total plasma triglyceride, low-density lipoprotein (LDL) cholesterol, and high-density lipoprotein (HDL) cholesterol concentrations after acute oral administration to gerbils. Gerbils were administered a standard gerbil diet for 4 continuous weeks, and daily water and food intake was monitored and replaced. The diet contained either no FM-VP4 (control) or FM-VP4 at the following concentrations: 0.25, 0.50, 1.0, or 2.0% w/w; six gerbils were fed each diet formulation. After 4 weeks of receiving a single diet formulation, blood was obtained from each gerbil by cardiac puncture and the animals were sacrificed humanely. Plasma obtained from this blood was analyzed for total cholesterol, total triglyceride, and HDL cholesterol levels by standard enzymatic and precipitation techniques. LDL cholesterol levels were calculated using the Friedewald equation. Administration of dietary FM-VP4 resulted in significant decreases in total plasma cholesterol and LDL cholesterol concentrations compared with controls. Dietary FM-VP4 at concentrations of 1% and 2% (w/w) decreased total plasma cholesterol by 3.4 mmol/L compared with controls. This decrease was entirely due to the loss of cholesterol from the LDL pool because LDL cholesterol was decreased by 3.3 and 3.2 mmol/L after 1% and 2% (w/w) FM-VP4, respectively. There were no significant changes in plasma triglyceride or HDL cholesterol concentrations after the administration of FM-VP4. Animals administered 1% or 2% (w/w) FM-VP4 also had significantly lower body weight after 4 weeks of treatment compared with the other groups. However, no unusual behavior was observed in these animals. No major differences in daily water or food intake were observed throughout the study. These findings indicate that FM-VP4 decreases total and LDL cholesterol concentrations.

Overexpression of acyl-coA binding protein and its effects on the flux of free fatty acids in McA-RH 7777 cells.

Overexpression of acyl-CoA binding protein (ACBP) was induced in a rat hepatoma cell line (McA-RH 7777) by stable integration of rat ACBP cDNA. The transfected cells (ACBP-27) had 3.5-fold higher concentrations of ACBP than control cells (14 vs. 4 ng/microg DNA). Both ACBP-27 and control cells were cultured in the presence of various concentrations of radiolabeled palmitic acid; and the effects of ACBP on lipogenesis and beta-oxidation were studied. Incubation of the cells with 100 microM palmitic acid resulted in 42% greater incorporation of the fatty acid in ACBP-27 cells as compared to that in the control cells. This increased incorporation of the fatty acid was observed predominantly in the triglyceride fraction. Higher concentrations of palmitic acid (200 to 400 microM) were associated with a significant decrease in the production of 14CO2 in the ACBP-27 cell line than in the control cells, while lower concentrations had no effect. Our data suggest a role for ACBP in the partitioning of fatty acids between esterification reactions leading to the formation of neutral lipids and beta-oxidation. ACBP may play a regulatory role by influencing this important branch point in intermediary lipid metabolism.

Probing the 121-136 domain of lecithin:cholesterol acyltransferase using antibodies.

Lecithin:cholesterol acyltransferase (LCAT) catalyzes the esterification of plasma lipoprotein cholesterol in mammals as part of the reverse cholesterol transport pathway. Studies of the natural mutations of LCAT revealed a region that is highly sensitive to mutations (residues 121-136) and it is highly conserved in six animal species. The purpose of these studies was to investigate the reactivity of wild type and several mutated forms of LCAT, with a series polyclonal antibodies to further characterize this specific domain (residues 121-136). Two polyclonal antibodies directed against the whole enzyme, one against human plasma LCAT and the other against purified recombinant LCAT, and one site specific polyclonal antibody, directed against the 121-136 region of LCAT, were employed. All three antibodies reacted with a recombinant form of purified LCAT; however, only the polyclonal antibodies directed against the whole enzyme were able to recognize the LCAT when it was adsorbed to a hydrophobic surface in a solid phase immunoassay, or when bound to HDL in a sink immunoassay. These findings indicate that the epitope(s) of the 121-136 region are not accessible to antibodies under these conditions. Three mutant forms of LCAT, representing alterations in the 121-136 region, were also examined for their immunoreactivity with the same panel of antibodies and compared to the wild-type enzyme. These studies demonstrate that in its native configuration the 121-136 region of LCAT is likely to reside on a surface of LCAT. Furthermore, mutations within this region appear to markedly impact the exposure of epitopes at additional sites. These findings suggest that the 121-136 region could play an important role in enzyme interaction with its hydrophobic lipoprotein substrates as mutations within this region appear to alter enzyme conformation, catalytic activity, and the specificity of LCAT.

Assessing plasma pharmacokinetics of cholesterol following oral coadministration with a novel vegetable stanol mixture to fasting rats.

The purpose of this project was to assess the plasma pharmacokinetics of [(3)H]cholesterol following coadministration of a novel vegetable stanol mixture composed of sitostanol and campestanol (FCP-3P4) to fasting rats. Following an overnight fast (12-16 h) and 48 h post-surgery, adult male Sprague Dawley rats were divided into six treatment groups and received a single-dose oral gavage at 0700 h of either: [(3)H]cholesterol (25 microCi/mL), FCP-3P4 (5 mg/kg) + [(3)H]cholesterol (25 microCi/mL), FCP-3P4 (12.5 mg/kg) + [(3)H]cholesterol (25 microCi/mL), FCP-3P4 (25 mg/kg) + [(3)H]cholesterol (25 microCi/mL), FCP-3P4 (50 mg/kg) + [(3)H]cholesterol (25 microCi/mL), or FCP-3P4 (100 mg/kg) + [(3)H]cholesterol (25 microCi/mL). Intralipid (10%) was the vehicle used to solubilize and coadminister [(3)H]cholesterol and FCP-3P4. Liquid chromatography-mass spectrometry analysis confirmed minimal cholesterol and vegetable stanol content within 10% Intralipid. Analysis of plasma pharmacokinetics was initiated by sampling 0.5 mL of blood prior to and 0.25, 0.5 1.0, 2.0, 4.0, 6.0, 8.0, 10, 24, 28, 32, and 48 h post-oral gavage. Plasma samples were obtained by centrifugation of the blood samples and analyzed for [(3)H]cholesterol radioactivity. Pharmacokinetics analysis was performed by standard noncompartmental methods using statistical moment theory. Thin-layer chromatography was used to confirm that the majority of radioactivity measured in plasma was cholesterol (in the form of esterified or unesterified cholesterol). Greater than 90% of the radioactivity measured in all plasma samples was cholesterol-associated (in the form of either esterified or unesterified cholesterol). The coadministration of FCP-3P4 significantly decreased the area under the curve of [(3)H]cholesterol concentration versus time from 0 to 48 h (AUC(0-48h)) and maximum concentration (C(max)) in a dose-dependent manner. However, coadministration of FCP-3P4 at 25, 50, and 100 mg/kg resulted in a significant increase in apparent total body clearance (CL/F, where F is the bioavailability constant), apparent volume of distribution (V(d)/F), and oral absorption rate constant (k(a)) of [(3)H]cholesterol compared with controls. These findings suggest that the novel vegetable stanol mixture, FCP-3P4, modifies the plasma pharmacokinetics of [(3)H]cholesterol in fasting rats on oral coadministration.

Extensive lifestyle management intervention following cardiac rehabilitation: pilot study.

Long-term management of the lifestyles of cardiac patients who have completed a cardiac rehabilitation program (CRP), and the risks that may develop for future health problems, have not been extensively reported. The purpose of this pilot study of graduates of CRPs was to: (a) assess lifestyle and risk factor trends, (b) test certain protocols, and (c) identify the challenges and limitations in managing lifestyles and risk factors. A convenience sample of 49 people with ischemic heart disease (IHD) was randomized to a Lifestyle Management Intervention (LMI) group and a Usual Care (UC) group and followed for 6 months. Patients assigned to the LMI group underwent six additional exercise sessions and participated in telephone follow-ups and a counseling session. Patients in the UC group were assessed at baseline and at the end of 6 months. Of the original 49 participants, 17 in the LMI group and 19 in the UC group completed the study. Patients in the LMI group showed significant reductions in total cholesterol and LDL-C from baseline at 6 months. Diastolic blood pressure was decreased significantly in the UC group. The study identified the challenges of lifestyle intervention and found that favorable risk factor modifications are possible for patients who have completed a CRP.

Characterization of the effects of mutations in the putative branchpoint sequence of intron 4 on the splicing within the human lecithin:cholesterol acyltransferase gene.

We have previously identified a point mutation (intervening sequence (IVS) 4: T --> C) in the branchpoint consensus sequence of intron 4 of the lecithin:cholesterol acyltransferase (LCAT) gene in patients with fish-eye disease. To investigate the possible mechanisms responsible for the defective splicing, we made a series of mutations in the branchpoint sequence and expressed these mutants in HEK-293 cells followed by the analysis of pre-mRNA splicing using reverse transcriptase-polymerase chain reaction as well as LCAT activity assay. The results reveal that 1) the mutation of the branchpoint adenosine to any other nucleotide completely abolishes splicing; 2) the insertion of a normal branch site into the intronic sequence of the natural (IVS4-22c) or the branchpoint (IVS4-20t) mutant completely restores splicing; 3) the natural mutation can be partially rescued by making a single nucleotide change (G --> A) within the branchpoint consensus sequence; and 4) other single base changes, particularly around the branchpoint adenosine residue, significantly decrease the efficiency of splicing and thus enzyme activity. Surprisingly, the nucleotide transversion at the last position of the branchpoint sequence (i.e. IVS4-25a or -25g) results in a 2.7-fold increase in splicing efficiency. Therefore, these observations clearly establish the functional significance of the branchpoint sequence of intron 4 for the splicing of the human LCAT mRNA precursors.

Biochemical and compositional analyses of recombinant lecithin:cholesterol acyltransferase (LCAT) obtained from a hepatic source.

Lecithin:cholesterol acyltransferase (LCAT) is an important plasma glycoprotein which plays a central role in lipid metabolism. This protein is responsible for generation of cholesteryl esters in plasma and it has been proposed to play a pivotal role in the reverse cholesterol transport pathway. Structural and functional studies of LCAT have employed various expression systems for production of recombinant LCAT (rLCAT). However, recent studies have shown some differences in the oligosaccharide structure and composition of rLCAT. In this study, we have generated a new hepatic based expression system using McArdle-RH7777 (Mc-7777) cells to produce a recombinant protein most similar to human plasma LCAT. The expressed glycoprotein was compared to the LCAT expressed in previously characterized baby hamster kidney (BHK) cells. Both proteins were compared on the basis of their carbohydrate structure and composition as well as their functional properties. Although the functional properties of both glycoproteins were similar, the carbohydrate structure was significantly different. While BHK-LCAT contained bi-, tri-, and tetraantennary structures, Mc-7777 LCAT presented only biantennary oligosaccharide structures. The difference in glycosylation pattern of rLCAT from Mc-7777 and BHK cells underlines the importance of appropriate expression system, both in vivo and in vitro.

Apolipoprotein A-I (R151C)Paris is defective in activation of lecithin: cholesterol acyltransferase but not in initial lipid binding, formation of reconstituted lipoproteins, or promotion of cholesterol efflux.

ApoA-I(R151)Paris is a natural apolipoprotein (apo) A-I variant that is associated with low levels of high-density lipoprotein cholesterol (HDL-cholesterol) and the partial deficiency of lecithin:cholesterol acyl-transferase (LCAT) in the plasma of heterozygous carriers. We compared the abilities of recombinant normal apoA-I and recombinant apoA-I(R151C)Paris to clear an emulsion of dimyristoylphosphatidylcholine (DMPC), to form reconstituted lipoproteins with dipalmitoylphosphatidylcholine (DPPC), to activate LCAT, and to promote efflux of biosynthetic cholesterol from porcine aortic smooth muscle cells (SMCs) or of exogenous cholesterol from lipid-loaded mouse peritoneal macrophages. Recombinant apoA-I(R151C)Paris occurred in monomeric and dimeric forms at a ratio of 60:40. Normal apoA-I and apoA-I(R151C)Paris cleared DMPC emulsions at equal rates. Both isoforms associated completely with DPPC during cholate dialysis. Normal apoA-I formed one single particle with a mean diameter of 9.3 nm, whereas apoA-I(R151)Paris gave rise to three particles with mean diameters of 9.3 nm (containing 74% of apoA-I), 10.6 nm, and 12.1 nm, respectively. Compared to normal apoA-I, apoA-I(R151C)Paris had a reduced LCAT-cofactor activity with a 60% lower Vmax/Km ratio due to a 50% higher affinity constant, Km. During incubations for 10 min and 360 min, normal apoA-I/DPPC complexes and apoA-I(R151C)Paris/DPPC complexes were equally efficient in releasing biosynthetic cholesterol from SMCs. In the lipid-free form, apoA-I(R151C)Paris induced normal hydrolysis of cholesteryl esters and normal cholesterol efflux from lipid-loaded mouse-peritoneal macrophages. In conclusion, in addition to its ability to form homo- and heterodimers, apoA-I(R151C)Paris is characterized by defective LCAT-cofactor activity but by normal lipid binding and cholesterol-efflux-promoting abilities.

A first British case of fish-eye disease presenting at age 75 years: a double heterozygote for defined and new mutations affecting LCAT structure and expression.

Fish-eye disease is a familial syndrome with corneal opacification, major high density lipoprotein (HDL) deficiency in plasma, significant cholesterol esterification in plasma on non-HDL lipoproteins, generally without premature coronary disease. This first British male case from unrelated British parents had infarcts when aged 49 and 73 years but was asymptomatic at age 81 years, with plasma cholesterol 4.3-7.1 mmol/litre, triglycerides 1.8-2.2 mmol/litre, HDL cholesterol < 0.1 mmol/litre, apolipoprotein A-I < 0.16 g/litre, lipoprotein(a) 0.61 g/litre. Cholesterol esterification was impaired using HDL-3 and A-I proteoliposomes but not using VLDL/IDL/LDL. The findings are those of LCAT deficiency with the classic fish-eye disease defect. Most of the 22 reported cases were homozygous or heterozygous for a Thr-Ile mutation at codon 123 of the lecithin:cholesterol acyltransferase (LCAT) gene. This patient was a double heterozygote for this mutation and a second new incompletely defined mutation affecting LCAT expression as defined by reduced mass and activity in plasma.

Cyclosporine transfer from low- and high-density lipoproteins is partially influenced by lipid transfer protein I triglyceride transfer activity.

PURPOSE: The purpose of this study was to determine if lipid transfer protein (LTP I) facilitated triglyceride (TG) transfer activity regulates the plasma lipoprotein distribution of cyclosporine (CSA). METHODS: To assess the influence of drug concentration and incubation time on the plasma lipoprotein distribution of CSA, 3H-CSA (50 to 1000 ng/ml) was incubated in human plasma for 5 to 120 minutes at 37 degrees C. To determine if LTP I facilitated TG transfer activity regulates the plasma lipoprotein distribution of CSA, 3H-Triolein (TG)- or 3H-CSA-enriched high-density lipoproteins (HDL) or low-density lipoproteins (LDL) were incubated in T150 buffer (50 mM Tris-HCl, 150 mM NaCl, 0.02% Sodium Azide, 0.01% Disodium EDTA), pH 7.4 which contained a 3H-Triolein (TG) or 3H-CSA-free lipoprotein counterpart +/- exogenous LTP I (1.0 microg protein/ml) or in delipidated human plasma which contained 1.0 microg protein/ml of endogenous LTP I for 90 minutes at 37 degrees C. These experiments were repeated in the presence of a monoclonal antibody TPI (15 microg protein/ml) directed against LTP I. RESULTS: No differences in CSA lipoprotein distribution were observed following incubation of the drug at varying concentrations and incubation times in human plasma. The percent transfer of TG from HDL to LDL and LDL to HDL was greater in T150 buffer than in human plasma. However, the percent transfer of CSA from only LDL to HDL was greater in T150 buffer than in human plasma. Furthermore, undetectable 3H-CSA transfer from HDL to LDL in T150 buffer containing purified LTP I was observed. In addition, when the percent transfer of TG and CSA were determined in the presence of TPI, the percent transfer of TG and CSA from only LDL to HDL were significantly decreased in T150 buffer and human plasma compared to controls. CONCLUSIONS: These findings suggest that the transfer of CSA between different lipoprotein particles is only partially influenced by LTP I facilitated TG transfer activity.

Separation of liposomes from plasma components using fast protein liquid chromatography.

We describe an efficient method for separating liposomes (large unilamellar vesicles, 120-150 nm diameter) from plasma lipoproteins employing fast protein liquid chromatography (FPLC). This method resolves very low density lipoprotein (VLDL), low-density lipoprotein, high-density lipoprotein, and other plasma components. Selective detection of liposomes (large unilamellar vesicles, 120-150 nm diameter) was achieved using either radiolabeled or fluorescent lipid probes. The liposomes were found to coelute with the earliest FPLC-eluting lipoprotein fraction, VLDL. The remaining plasma lipoprotein and protein components eluted at later times and were resolved from liposomes and VLDL. In order to separate VLDL from liposomes, we selectively precipitated the VLDL fraction from plasma using tungstophosphoric acid and magnesium chloride, prior to separation by FPLC. Furthermore, we demonstrate that this technique can be used to separate liposomes from lipoproteins in plasma samples collected after intravenous administration of liposomes to mice. This technique has wide application in studies of liposome stability in blood and, in particular, for the characterization of liposomal drug carrier systems.

Multiple dysfunctions of two apolipoprotein A-I variants, apoA-I(R160L)Oslo and apoA-I(P165R), that are associated with hypoalphalipoproteinemia in heterozygous carriers.

ApoA-I(R160L)Oslo and apoA-I(P165R) are naturally occurring apolipoprotein (apo) A-I variants that are associated with low HDL-cholesterol in heterozygous carriers. We characterized the capacity of these variants to bind lipid, to activate lecithin:cholesterol acyltransferase (LCAT), and to promote efflux of biosynthetic cholesterol from porcine aortic smooth muscle cells (SMCs) or exogenous cholesterol from lipid-loaded mouse peritoneal macrophages. During cholate dialysis, normal apoA-I and both variants associated completely with dipalmitoylphosphatidylcholine (DPPC) and formed rLpA-I of identical size. However, both apoA-I(P165R) and apoA-I(R160L)Oslo showed a reduced capacity to clear a turbid emulsion of dimyristoylphosphatidylcholine (DMPC). Compared to normal apoA-I, the LCAT-cofactor activity of apoA-I(P165R) and apoA-I(R160L)Oslo as defined by the ratio of Vmax to appKm was reduced significantly by 62% and 29%, respectively (here and throughout the text, the apparent Km is given as Michaelis-Menten kinetics do not take particle binding into account and therefore would result in errors with an interfacial enzyme such as LCAT; Vmax estimates are not affected by this error). ApoA-I/DPPC complexes induced biphasic cholesterol efflux from SMCs with a fast and a slow efflux component. Compared to rLpA-I reconstituted with wild type apoA-I, rLpA-I with apoA-I(P165R) or apoA-I(R160L)Oslo were significantly less effective in promoting cholesterol efflux from SMCs in incubations of 10 min duration but equally effective in incubations of 6 h duration. Lipid-free apoA-I did not induce efflux of biosynthetic cholesterol from SMCs but induced hydrolysis of cholesteryl esters and cholesterol efflux from acetyl-LDL-loaded mouse peritoneal macrophages. In the lipid-free form, both apoA-I variants promoted normal cholesterol efflux from murine peritoneal macrophages. We conclude that amino acid residues arginine 160 and proline 165 of apoA-I contribute to the formation of a domain that is very important for initial lipid binding and contributes to LCAT-activation and promotion of initial cholesterol efflux but not to the stabilization of preformed rLpA-I.

Pharmacokinetics, distribution in serum lipoproteins and tissues, and renal toxicities of amphotericin B and amphotericin B lipid complex in a hypercholesterolemic rabbit model: single-dose studies.

The purpose of this study was to determine if a relationship exists among total serum and lipoprotein cholesterol concentration, the severity of amphotericin B (AmpB)-induced renal toxicity, and the serum pharmacokinetics of AmpB in hypercholesterolemic rabbits administered AmpB and AmpB lipid complex (ABLC). After 10 days of cholesterol-enriched diet (0.50% [wt/vol]) or regular rabbit diet (control), each rabbit was administered a single intravenous bolus of AmpB or ABLC (1.0 mg/kg of body weight). Blood samples were obtained before administration and serially thereafter for the assessment of serum pharmacokinetics, kidney toxicity, and serum lipoprotein distribution. Rabbits were humanely sacrificed after all blood samples were obtained, and tissues were harvested for drug analysis. Before drug treatment, cholesterol-fed rabbits demonstrated marked increases in total serum cholesterol and low-density lipoprotein (LDL) cholesterol levels compared with levels in rabbits on a regular diet. No significant differences in triglyceride levels were observed. A significant increase in serum creatinine levels was observed in cholesterol-fed and regular diet-fed rabbits administered AmpB. However, the magnitude of this increase was 2.5-fold greater in cholesterol-fed rabbits than in regular diet-fed rabbits. No significant differences in triglyceride levels were observed. A significant increase in serum creatinine levels was observed in cholesterol-fed and regular diet-fed rabbits administered ABLC. Whereas AmpB pharmacokinetics were significantly altered in cholesterol-fed rabbits administered free AmpB, similar AmpB pharmacokinetics were observed in both rabbit groups administered ABLC. Renal AmpB levels were significantly increased in cholesterol-fed rabbits administered AmpB compared with those in all other groups. Hepatic and lung AmpB levels were elevated in cholesterol-fed rabbits administered free AmpB compared to controls. In addition, hepatic, lung, and spleen AmpB levels were significantly decreased in cholesterol-fed rabbits administered ABLC compared to controls. An increased percentage of AmpB was recovered in LDL-very-low-density lipoprotein fraction when free AmpB was administered to cholesterol-fed rabbits compared with those in all other groups. These findings suggest that increases in cholesterol, specifically, LDL cholesterol levels, modify the disposition and renal toxicity of free AmpB. However, the pharmacokinetics and renal toxicity of ABLC were independent of elevations in total and LDL cholesterol levels.

Transmission of two novel mutations in a pedigree with familial lecithin:cholesterol acyltransferase deficiency: structure-function relationships and studies in a compound heterozygous proband.

Two novel mutations were identified in a compound heterozygous male with lecithin:cholesterol acyltransferase (LCAT) deficiency. Exon sequence determination of the LCAT gene of the proband revealed two novel heterozygous mutations in exons one (C110T) and six (C991T) that predict non-conservative amino acid substitutions (Thr13Met and Pro307Ser, respectively). To assess the distinct functional impact of the separate mutant alleles, studies were conducted in the proband's 3-generation pedigree. The compound heterozygous proband had negligible HDL and severely reduced apolipoprotein A-I, LCAT mass, LCAT activity, and cholesterol esterification rate (CER). The proband's mother and two sisters were heterozygous for the Pro307Ser mutation and had low HDL, markedly reduced LCAT activity and CER, and the propensity for significant reductions in LCAT protein mass. The proband's father and two daughters were heterozygous for the Thr13Met mutation and also displayed low HDL, reduced LCAT activity and CER, and more modest decrements in LCAT mass. Mean LCAT specific activity was severely impaired in the compound heterozygous proband and was reduced by 50% in individuals heterozygous for either mutation, compared to wild type family members. It is also shown that the two mutations impair both catalytic activity and expression of the circulating protein.

T-->G or T-->A mutation introduced in the branchpoint consensus sequence of intron 4 of lecithin:cholesterol acyltransferase (LCAT) gene: intron retention causing LCAT deficiency.

Previous mutations associated with lecithin:cholesteryl acyltransferase (LCAT) deficiency syndromes have been identified in the coding regions of the LCAT gene. However, recently, an intron mutation was found in a family in which three sisters presented with fish-eye disease (FED). The probands were shown to be heterozygotes for a mutation in intron 4. The respective T-->C nucleotide substitution, 22 bases upstream of the 3'-splice site, causes a null allele as the result of complete intron retention. Since the natural mutation occurs in a putative branchpoint consensus sequence of the intron, it was hypothesized that the point mutation may disrupt the splicing of the pre-mRNA. To further study the functional significance of the above thymine residue in the branchpoint sequence, we introduced other nucleotides at this position, i.e., LCAT Int-4 MUT-1 (T-->G) and LCAT Int-4 MUT-2 (T-->A). After stable transfection of the mutated pNUT-LCAT minigenes into BHK cells, we could detect neither LCAT activity nor LCAT protein in the culture medium of the pNUT-LCAT Int-4 MUT-1 and pNUT-LCAT Int-4 MUT-2 cell lines, as was previously described for the natural mutation. To determine the effects of the introduced mutations on pre-mRNA splicing, total RNA from transfected BHK cells was used for RT-PCR analysis. All BHK cell lines were shown to transcribe the integrated LCAT minigenes. However, the sizes of these LCAT messengers indicated that intron 4 was retained in the pNUT-LCAT Int-4 MUT-1 and pNUT-LCAT Int-4 MUT-2 cell lines. Subsequent sequence analysis of the RT-PCR products demonstrated that the unspliced intronic sequences contained the introduced mutations. In conclusion, the observed retention of intron 4 of the LCAT gene is the result of the specific loss of a thymine residue two bases upstream of the branchpoint adenosine residue in the putative branchpoint consensus sequence. The results confirm that a single base change in the branchpoint consensus sequence of an intron can cause human disease although this sequence is poorly conserved in mammals.

Characterization of recombinant human plasma lecithin: cholesterol acyltransferase (LCAT): N-linked carbohydrate structures and catalytic properties.

The major N-linked carbohydrate structures were determined for recombinant human plasma lecithin:cholesterol acyltransferase (LCAT). The analysis of the structure of oligosaccharides by fast atom bombardment mass spectrometry (FAB-MS) and linkage analysis was preceded by reduction and carboxymethylation of the intact glycoproteins and digestion with trypsin and proline specific endopeptidase. The N-glycans were subsequently released from the glycopeptides by PNGase F digestion and the oligosaccharides were separated using a C18 Sep-pak cartridge. The data from the combination of FAB spectrometry and linkage analysis show that the N-linked glycans present on recombinant LCAT (rLCAT) were composed primarily of triantennary and tetraantennary structures with and without core fucosylation. A minor population of glycans (less than 5%) contained up to three repeats of N-acetyllactosamine in one or more antennae. The LCAT activities of both recombinant and circulating forms of plasma LCAT were determined using low molecular weight and lipoprotein substrates. The catalytic behavior of these two enzyme forms were found to be very similar if not identical. These findings validate the concept that the recombinant enzyme can serve as an appropriate model for structure/function studies of LCAT and provide the foundation for subsequent structural studies.