Cholesteryl ester transfer protein facilitates the movement of water-insoluble drugs between lipoproteins: a novel biological function for a well-characterized lipid transfer protein

The potential of cholesteryl ester transfer protein as a therapeutic target

INTRODUCTION

Over recent decades, attempts to ascertain the pro-atherogenic nature of plasma cholesteryl ester transfer protein (CETP) and to establish the relevance of its pharmacological blockade as a promising high density lipoproteins-raising and anti-atherogenic therapy have been disappointing.

AREAS COVERED

The current review focuses on CETP as a multifaceted protein, on genetic variations at the CETP gene and on their possible consequences for cardiovascular risk in human populations. Specific attention is given to physiological modulation of endogenous CETP activity by the apoC1 inhibitor. Finally, the rationale behind the need for selection of patients to treat is discussed in the light of recent studies.

EXPERT OPINION

At this stage one can only speculate on the clinical outcome of pharmacological CETP inhibitors in high-risk populations, but recent advances give cause to adjust the expectations from now on. The CETP effect is probably largely influenced by the overall metabolic state, and whether CETP blockade may be relevant or not in promoting cholesterol disposal is still questioned. The possible need for a careful stratification of patients to treat with CETP inhibitors is outlined. Finally, manipulation of CETP activity should be considered with caution in the context of sepsis and infectious diseases.

Defective triglyceride biosynthesis in CETP-deficient SW872 cells

We previously reported that reducing the expression of cholesteryl ester transfer protein (CETP) disrupts cholesterol homeostasis in SW872 cells and causes an ∼50% reduction in TG. The causes of this reduced TG content, investigated here, could not be attributed to changes in the differentiation status of CETP-deficient cells, nor was there evidence of endoplasmic reticulum (ER) stress. In short-term studies, the total flux of oleate through the TG biosynthetic pathway was not altered in CETP-deficient cells, although mRNA levels of some pathway enzymes were different. However, the conversion of diglyceride (DG) to TG was impaired. In longer-term studies, newly synthesized TG was not effectively transported to lipid droplets, yet this lipid did not accumulate in the ER, apparently due to elevated lipase activity in this organelle. DG, shown to be a novel CETP substrate, was also inefficiently transferred to lipid droplets. This may reduce TG synthesis on droplets by resident diacylglycerol acyltransferase. Overall, these data suggest that the decreased TG content of CETP-deficient cells arises from the reduced conversion of DG to TG in the ER and/or on the lipid droplet surface, and enhanced TG degradation in the ER due to its ineffective transport from this organelle.

Emerging risk biomarkers in cardiovascular diseases and disorders

Present review article highlights various cardiovascular risk prediction biomarkers by incorporating both traditional risk factors to be used as diagnostic markers and recent technologically generated diagnostic and therapeutic markers. This paper explains traditional biomarkers such as lipid profile, glucose, and hormone level and physiological biomarkers based on measurement of levels of important biomolecules such as serum ferritin, triglyceride to HDLp (high density lipoproteins) ratio, lipophorin-cholesterol ratio, lipid-lipophorin ratio, LDL cholesterol level, HDLp and apolipoprotein levels, lipophorins and LTPs ratio, sphingolipids, Omega-3 Index, and ST2 level. In addition, immunohistochemical, oxidative stress, inflammatory, anatomical, imaging, genetic, and therapeutic biomarkers have been explained in detail with their investigational specifications. Many of these biomarkers, alone or in combination, can play important role in prediction of risks, its types, and status of morbidity. As emerging risks are found to be affiliated with minor and microlevel factors and its diagnosis at an earlier stage could find CVD, hence, there is an urgent need of new more authentic, appropriate, and reliable diagnostic and therapeutic markers to confirm disease well in time to start the clinical aid to the patients. Present review aims to discuss new emerging biomarkers that could facilitate more authentic and fast diagnosis of CVDs, HF (heart failures), and various lipid abnormalities and disorders in the future.

Validation of the reconstituted high-density lipoprotein (rHDL) drug delivery platform using dilauryl fluorescein (DLF)

Dilauryl fluorescein (DLF) is a lipid soluble molecule that becomes fluorescent when lauric acid is removed by hydrolysis The purpose of these studies was to evaluate DLF as a potential probe for the function of reconstituted high-density lipoproteins (rHDL) as hydrophobic drug transport vehicles. The DLF containing rHDL nanoparticles were characterized regarding their physical/chemical properties, including molecular diameter, molecular weight, chemical composition, and buoyant density. We investigated the uptake of DLF from rHDL in cells that overexpress the scavenger receptor (SR-B1), known to facilitate the selective cellular uptake of cholesteryl esters from HDL. These studies show that DLF can be incorporated into rHDL and redistributed in the plasma compartment. In addition, these studies demonstrated an enhanced uptake and hydrolysis of DLF from rHDL by cells that overexpress the SR-B1 receptor, suggesting the involvement of a receptor mediated mechanism. The incorporation of DLF into the rHDL nanoparticles appear to protect against hydrolysis in the systemic circulation based on the lower rate of rHDL/DLF hydrolysis compared with the free DLF during incubation with human plasma. DLF may thus be used as a probe to track the movement and metabolism of HDL core constituents, including cancer chemotherapeutic agents.

Lactobacillus gasseri [corrected] CHO-220 and inulin reduced plasma total cholesterol and low-density lipoprotein cholesterol via alteration of lipid transporters

This randomized, double-blind, placebo-controlled, and parallel-designed study was conducted to investigate the effect of a synbiotic product containing Lactobacillus gasseri [corrected] CHO-220 and inulin on lipid profiles of hypercholesterolemic men and women. Thirty-two hypercholesterolemic men and women with initial mean plasma cholesterol levels of 5.7±0.32 mmol/L were recruited for the 12-wk study. The subjects were randomly allocated to 2 groups; namely the treatment group (synbiotic product) and the control group (placebo), and each received 4 capsules of synbiotic or placebo daily. Our results showed that the mean body weight, energy, and nutrient intake of the subjects did not differ between the 2 groups over the study period. The supplementation of synbiotic reduced plasma total cholesterol and low-density lipoprotein (LDL)-cholesterol by 7.84 and 9.27%, respectively, compared with the control over 12 wk. Lipoproteins were subsequently subfractionated and characterized. The synbiotic supplementation resulted in a lower concentration of triglycerides in the very low, intermediate, low, and high-density lipoprotein particles compared with the control over 12 wk. The concentration of triglycerides in lipoproteins is positively correlated with an increased risk of atherosclerosis. Our results showed that the synbiotic might exhibit an atheropreventive characteristic. Cholesteryl ester (CE) in the high-density lipoprotein particles of the synbiotic group was also higher compared with the control, indicating greater transport of cholesterol in the form of CE to the liver for hydrolysis. This may have led to the reduced plasma total cholesterol level of the synbiotic group. The supplementation of synbiotic also reduced the concentration of CE in the LDL particles compared with the control, leading to the formation of smaller and denser particles that are more easily removed from blood. This supported the reduced LDL-cholesterol level of the synbiotic group compared with the control. Our present study showed that the synbiotic product improved plasma total- and LDL-cholesterol levels by modifying the interconnected pathways of lipid transporters. In addition, although Lactobacillus gasseri [corrected] CHO-220 could deconjugate bile, our results showed a statistically insignificant difference in the levels of conjugated, deconjugated, primary, and secondary bile acids between the synbiotic and control groups over 12 wk, indicating safety from bile-related toxicity.

Reversible flow of cholesteryl ester between high-density lipoproteins and triacylglycerol-rich particles is modulated by the fatty acid composition and concentration of triacylglycerols

We determined the influence of fasting (FAST) and feeding (FED) on cholesteryl ester (CE) flow between high-density lipoproteins (HDL) and plasma apoB-lipoprotein and triacylglycerol (TG)-rich emulsions (EM) prepared with TG-fatty acids (FAs). TG-FAs of varying chain lengths and degrees of unsaturation were tested in the presence of a plasma fraction at d > 1.21 g/mL as the source of CE transfer protein. The transfer of CE from HDL to FED was greater than to FAST TG-rich acceptor lipoproteins, 18% and 14%, respectively. However, percent CE transfer from HDL to apoB-containing lipoproteins was similar for FED and FAST HDL. The CE transfer from HDL to EM depended on the EM TG-FA chain length. Furthermore, the chain length of the monounsaturated TG-containing EM showed a significant positive correlation of the CE transfer from HDL to EM (r = 0.81, P < 0.0001) and a negative correlation from EM to HDL (r = -041, P = 0.0088). Regarding the degree of EM TG-FAs unsaturation, among EMs containing C18, the CE transfer was lower from HDL to C18:2 compared to C18:1 and C18:3, 17.7%, 20.7%, and 20%, respectively. However, the CE transfer from EMs to HDL was higher to C18:2 than to C18:1 and C18:3, 83.7%, 51.2%, and 46.3%, respectively. Thus, the EM FA composition was found to be the rate-limiting factor regulating the transfer of CE from HDL. Consequently, the net transfer of CE between HDL and TG-rich particles depends on the specific arrangement of the TG acyl chains in the lipoprotein particle core.

Disposition of amphotericin B in the isolated perfused rat liver

The hepatic disposition and biliary excretion of amphotericin B were investigated in the isolated perfused rat liver (IPRL). Bolus dose of 50 μg, 99 μg and 198 μg amphotericin B in lipoprotein-free perfusate and 198 μg amphotericin B in perfusate with 1 μM high-density lipoprotein (HDL) or 1 μM low-density lipoprotein (LDL) were examined in the IPRL. Amphotericin B concentration in perfusate was measured using a validated HPLC assay. Amphotericin B was eliminated from the perfusate in a biexponential manner. The hepatic clearance (CLH) increased in proportion to the dose administered (0.27±0.05 mL min−1 at low dose, 0.54±0.23 mL min−1 at medium dose and 1.06±0.24 mL min−1 at high dose), indicating non-linear hepatic disposition of amphotericin B. The hepatic extraction ratio of amphotericin B was very low (0.066±0.015). Tissue-to-perfusion partition coefficient, calculated at 120 min, increased 1.5 fold from 9.8±1.7 at low dose to 15.9±6.4 at high dose, suggesting the significant uptake and extensive retention of amphotericin B in the liver. Biliary excretion made only minor contribution to amphotericin B elimination in the IPRL, representing around 1–3% of the dose administered. No metabolites were detected in perfusate, bile and liver samples. The hepatic disposition of amphotericin B was not affected by the presence of HDL and LDL in the perfusate. In conclusion, the hepatic disposition of amphotericin B demonstrates restrictive elimination and is concentration-dependent, consistent with carrier-mediated uptake, and lipoproteins do not influence amphotericin B hepatobiliary disposition.

Defining targets for investigating the pharmacogenomics of adverse drug reactions to antifungal agents

Adverse drug reactions (ADRs) associated with antifungal therapy are major problems in patients with invasive fungal infections. Whether by clinical history or patterns of genetic variation, the identification of patients at risk for ADRs should result in improved outcomes while minimizing deleterious side effects. A major contributing factor to ADRs with antifungal agents relates to drug distribution, metabolism and excretion. Genetic variation in key genes can alter the structure and expression of genes and gene products (e.g., proteins). Thus far, the effort has focused on identifying polymorphisms with either empirical or predicted in silico functional consequences; the best candidate genes encode phase I and II drug-metabolizing enzymes (e.g., CYP2C19 and N-acetyltransferase), plasma proteins (albumin and lipoproteins) and drug transporters (P-glycoprotein and multidrug resistance proteins), which can affect the disposition of antifungal agents, eventually leading to dose-dependent (type A) toxicity. Less is known regarding the key genes that interact with antifungal agents, resulting in idiosyncratic (type B) ADRs. The possible role of certain gene products and genetic polymorphisms in the toxicities of antifungal agents are discussed in this review. The preliminary data address the following: low-density lipoproteins and cholesteryl ester transfer protein in amphotericin B renal toxicity; toll-like receptor 1 and 2 in amphotericin B infusion-related ADRs; phosphodiesterase 6 in voriconazole visual adverse events; flavin-containing monooxygenase, glutathione transferases and multidrug resistance proteins 1 and 2 in ketoconazole and terbinafine hepatotoxicity; CYP enzymes and P-glycoprotein in drug interactions between azoles and coadministered medications; multidrug resistance proteins 8 and 9 on 5-flucytosine bone marrow toxicity; and mast cell activation in caspofungin histamine release. This will focus on high-priority candidate genes, which could provide a starting point for molecular studies to elucidate the potential mechanisms for understanding toxicity associated with antifungal drugs as well as identifying candidate genes for large population prospective genetic association studies.

Disturbed lipids, lipoproteins and triglyceride-rich lipoproteins as well as fasting and nonfasting non-high-density lipoprotein cholesterol in post-renal transplant patients

Serum levels of lipids and lipoproteins were determined in 98 post-renal transplant fasting patients, and lipids and non-high density lipoprotein-cholesterol (non-HDL-C) and lipid ratios in the same post-renal transplant non-fasting patients were compared. The reference group was 87 healthy subjects. All patients were divided into two groups: patients with dyslipidemia (n = 69) and patients with normolipidemic (n = 29). The post-renal transplant patients (TX) with dyslipidemia had a significantly increased concentration of triglyceride (TG), low-density lipoprotein-cholesterol (LDL-C), non-HDL-C, apoB, and TRL and lipid ratios, and decreased HDL-C level and lipoprotein ratios. The lipids, lipoproteins, and lipoprotein ratios were significantly beneficial in TX patients with normolipidemic than in those with dyslipidemia. However, TRL concentration and lipid ratios were significantly increased and apoAI/apoCIII significantly decreased as compared to the reference group. The TX patients with dyslipidemia showed a significant correlation between TG and apoB:CIII (r = 0.562, p < 0.001) and apoCIII (r = 0.380, p < 0.004), but those with normolipidemic showed a significant correlation only between TG and apoCIII (r = 0.564, p < 0.008). Regression and Bland-Altman analyses showed excellent correlation between fasting and nonfasting non-HDL-C levels (r = 0.987, R(2) + 0.987) in TX patients both with dyslipidemia and normolipidemic. We think the finding that nonfasting labs that are reliable for non-HDL-C as well as total cholesterol is important, as fasting labs are not always available. Disturbances of lipids, lipoproteins, and TRLs depend not only on the kind of treatment, but due to multiple factors can accelerate cardiovascular complications in post-renal transplant patients with dyslipidemia and also with normolipidemic. Further studies concerning this problem should be completed.

Human pharmacogenomic variations and their implications for antifungal efficacy

Pharmacogenomics is defined as the study of the impacts of heritable traits on pharmacology and toxicology. Candidate genes with potential pharmacogenomic importance include drug transporters involved in absorption and excretion, phase I enzymes (e.g., cytochrome P450-dependent mixed-function oxidases) and phase II enzymes (e.g., glucuronosyltransferases) contributing to metabolism, and those molecules (e.g., albumin, A1-acid glycoprotein, and lipoproteins) involved in the distribution of antifungal compounds. By using the tools of population genetics to define interindividual differences in drug absorption, distribution, metabolism, and excretion, pharmacogenomic models for genetic variations in antifungal pharmacokinetics can be derived. Pharmacogenomic factors may become especially important in the treatment of immunocompromised patients or those with persistent or refractory mycoses that cannot be explained by elevated MICs and where rational dosage optimization of the antifungal agent may be particularly critical. Pharmacogenomics has the potential to shift the paradigm of therapy and to improve the selection of antifungal compounds and adjustment of dosage based upon individual variations in drug absorption, metabolism, and excretion.

The association of common SNPs and haplotypes in the CETP and MDR1 genes with lipids response to fluvastatin in familial hypercholesterolemia

OBJECTIVE

To examine whether genetic polymorphisms in the cholesteryl-ester transfer protein (CETP) and the P-glycoprotein drug transporter (MDR1), are associated with variable lipid response to fluvastatin.

METHODS

Lipid levels were determined in a compliance-monitored clinical study at baseline and following 20 weeks of treatment with 40 mg dose of fluvastatin in 76 FH patients. CETP and MDR1 SNP genotyping was performed and linear regression was used to examine the associations between common SNPs and haplotypes and lipid response.

RESULTS

Treatment with 40 mg of fluvastatin resulted in mean low density lipoprotein cholesterol (LDL-C) reduction of 21.5%; mean triglyceride (TG) reduction of 8.3%; and a mean high-density lipoprotein cholesterol (HDL-C) increase of 13.4%. Five tagging SNPs in both genes were used to reconstruct five and six haplotypes accounting for 71.4% and 90.2% of the observed haplotypes in the CETP and MDR1 genes, respectively. CETP-H13 and MDR1-h4 were associated with an increase in LDL-C response. CETP-H5 was significantly associated with decreased TG and HDL-C response, whereas MDR1-h10 was associated with decreased TG response. A multivariate regression model indicated an independent additive effect of CETP-H5 and MDR1-h10 on the level of TG response.

CONCLUSIONS

CETP and MDR1 have independent effects on lipid changes following fluvastatin treatment. The results of this study may lead to an improved understanding of the genetic determinants of lipids response to treatment.

Unidirectional Inhibition of Lipid Transfer Protein I-Mediated Transfer of Cholesteryl Esters Between High-Density and Low-Density Lipoproteins by Amphotericin B Lipid Complex

PURPOSE

The purpose of this study was to determine whether Fungizone or amphotericin B lipid complex (ABLC; ABELCET) affects the transfer of cholesteryl ester (CE) by lipid transfer protein I (LTP I; also known as cholesteryl ester transfer protein) between HDL and LDL (bidirectional transfer HDL to LDL and LDL to HDL).

METHODS

Increasing concentrations of either Fungizone or ABELCET (1.25-12.5 microg AmpB/ml) were incubated with HDL and [3H]CE-LDL or [3H]CE-HDL and LDL (the amount of each fraction added was equivalent to 10 microg of cholesterol) and LTP I in delipidated human plasma at 37 degrees C for 90 min. As a positive control, TP2, a monoclonal antibody directed against LTP-1, was added instead of drug. After incubation, manganese and phosphate reagents were then added to precipitate out all of the LDL. The supernatant, consisted of only HDL, was counted for radioactivity to determine the amount of CE transferred from LDL. Similarly, the precipitate consisted of only LDL, was counted for radioactivity to determine the amount of CE transferred from HDL.

RESULTS

For Fungizone, the transfer of cholesteryl ester (CE) between HDL and LDL were not significantly different compared to nontreated controls. For ABELCET, CE transfer from HDL to LDL was significantly decreased at 12.5 microg AmpB/ml compared to control. However, transfer from LDL to HDL was not significantly different compared to non-treated controls. Similar results were observed with the major lipid component of ABELCET, dimyristoylphosphatidylcholine. CE transfer from HDL to LDL and LDL to HDL was significantly decreased when using the positive control (TP2).

CONCLUSIONS

Fungizone does not affect LTP I-mediated transfer of CE between HDL and LDL. ABELCET inhibits transfer from HDL to LDL, but has no effect on CE transfer from LDL to HDL. This uni-directional inhibition may contribute to the high recovery of AmpB in HDL but the very low presence of drug in the LDL fraction following ABELCET incubation.

Lipid transfer protein transports compounds from lipid nanoparticles to plasma lipoproteins

Nanometer-sized lipid emulsion particles with a diameter of 25-50 nm, called Lipid Nano-Sphere (LNS), are expected as a promising drug carrier to show prolonged plasma half-life of an incorporating drug. In terms of successful drug delivery using LNS, a drug should be incorporated into the lipid particles and remain within the particle, not only in the formulation in vitro but also after administration into the systemic blood circulation. In this study, we showed that phospholipids and some water-insoluble molecules also moved from lipid particles to plasma lipoproteins or albumin in serum and plasma half-lives of these compounds did not reflect that of the drug carriers. It was suggested that phospholipid or its derivative were transferred from LNS particles to plasma lipoproteins by lipid transfer proteins (LTP) in the circulation. These phenomena leaded to unsuccessful delivery of the drug with lipid-particulate drug carriers. On the other hand, lipophilic derivatives with cholesterol pro-moiety tested in this study were not released from LNS particles and showed prolonged plasma half-lives. Lipophilicity is known to be an important parameter for incorporating drugs into lipid particles but substrate specificity for LTP seems to be another key to success promising drug design using lipid emulsion particulate delivery system.