Plasma lipoproteins as drug carriers: pharmacological activity and disposition of the complex of beta-sitosteryl-beta-D-glucopyranoside with plasma lipoproteins

Mannose-Coated Reconstituted Lipoprotein Nanoparticles for the Targeting of Tumor-Associated Macrophages: Optimization, Characterization, and In Vitro Evaluation of Effectiveness

Reconstituted high-density lipoprotein nanoparticles (rHDL NPs) have been utilized as delivery vehicles to a variety of targets, including cancer cells. However, the modification of rHDL NPs for the targeting of the pro-tumoral tumor-associated macrophages (TAMs) remains largely unexplored. The presence of mannose on nanoparticles can facilitate the targeting of TAMs which highly express the mannose receptor at their surface. Here, we optimized and characterized mannose-coated rHDL NPs loaded with 5,6-dimethylxanthenone-4-acetic acid (DMXAA), an immunomodulatory drug. Lipids, recombinant apolipoprotein A-I, DMXAA, and different amounts of DSPE-PEG-mannose (DPM) were combined to assemble rHDL-DPM-DMXAA NPs. The introduction of DPM in the nanoparticle assembly altered the particle size, zeta potential, elution pattern, and DMXAA entrapment efficiency of the rHDL NPs. Collectively, the changes in physicochemical characteristics of rHDL NPs upon the addition of the mannose moiety DPM indicated that the rHDL-DPM-DMXAA NPs were successfully assembled. The rHDL-DPM-DMXAA NPs induced an immunostimulatory phenotype in macrophages pre-exposed to cancer cell-conditioned media. Furthermore, rHDL-DPM NPs delivered their payload more readily to macrophages than cancer cells. Considering the effects of the rHDL-DPM-DMXAA NPs on macrophages, the rHDL-DPM NPs have the potential to serve as a drug delivery platform for the selective targeting of TAMs.

Structure, metabolism and biological functions of steryl glycosides in mammals

Steryl glycosides (SGs) are sterols glycosylated at their 3β-hydroxy group. They are widely distributed in plants, algae, and fungi, but are relatively rare in bacteria and animals. Glycosylation of sterols, resulting in important components of the cell membrane SGs, alters their biophysical properties and confers resistance against stress by freezing or heat shock to cells. Besides, many biological functions in animals have been suggested from the observations of SG administration. Recently, cholesteryl glucosides synthesized via the transglycosidation by glucocerebrosidases (GBAs) were found in the central nervous system of animals. Identification of patients with congenital mutations in GBA genes or availability of respective animal models will enable investigation of the function of such endogenously synthesized cholesteryl glycosides by genetic approaches. In addition, mechanisms of the host immune responses against pathogenic bacterial SGs have partially been resolved. This review is focused on the biological functions of SGs in mammals taking into consideration their therapeutic applications in the future.

Steryl Glycosides in Fungal Pathogenesis: An Understudied Immunomodulatory Adjuvant

Invasive fungal infections pose an increasing threat to human hosts, especially in immunocompromised individuals. In response to the increasing morbidity and mortality of fungal infections, numerous groups have shown great strides in uncovering novel treatment options and potential efficacious vaccine candidates for this increasing threat due to the increase in current antifungal resistance. Steryl glycosides are lipid compounds produced by a wide range of organisms, and are largely understudied in the field of pathogenicity, especially to fungal infections. Published works over the years have shown these compounds positively modulating the host immune response. Recent advances, most notably from our lab, have strongly indicated that steryl glycosides have high efficacy in protecting the host against lethal Cryptococcal infection through acting as an immunoadjuvant. This review will summarize the keystone studies on the role of steryl glycosides in the host immune response, as well as elucidate the remaining unknown characteristics and future perspectives of these compounds for the host-fungal interactions.

Determination of stigmasterol, β-sitosterol and stigmastanol in oral dosage forms using high performance liquid chromatography with evaporative light scattering detection

A validated and repeatable high performance liquid chromatography (HPLC) method with online evaporative light scattering (ELSD) was developed for the analysis of two sterols, stigmasterol, beta-sitosterol and a stanol, stigmastanol, found to be common in many herbal formulations and health care supplements. The method is based on the separation of the three marker compounds on a C8 column (Phenomenex Luna, 5 microm, 150 mmx4.6 mm i.d.) using methanol:water (95:5 v/v) as the mobile phase, and a flow rate of 1 ml/min to separate all the marker compounds within 12 min. Cholesterol (50 microg/ml) was used as internal standard and methanol as the extraction solvent. The ELSD response parameters were optimised and the limits of detection (LOD) and quantification (LOQ) were calculated to be 2 and 5 microg/ml, respectively, which is more sensitive than obtained by photo diode array detection (5 and 7 microg/ml). Using ELSD, the percentage relative standard deviation (%R.S.D.) of intra-day and inter-day (3 days) precision for each marker was better than 3%, the accuracy data were within 97-103% and the recovery data were found to be within 95-107% for the five commercially available products examined. This method was used to assay commercially available products formulated as oral dosage forms purported to contain African Potato and associated sterols and stanol and proved to be suitable for the routine analysis and quality control of such products.

A nanometer lipid emulsion, lipid nano-sphere (LNS), as a parenteral drug carrier for passive drug targeting

We attempted to develop an artificial lipoprotein-like particle, lipid nano-sphere (LNS), incorporating dexamethasone palmitate (DMP). LNS is 25-50 nm in diameter and is composed of soybean oil and egg lecithin. Potential drug carriers were compared with a conventional fat emulsion for intravenous nutrition, lipid microsphere (LM, d=200-300 nm), which is already used clinically. LM easily entered reticuloendothelial systems, such as the liver, and was rapidly cleared from the circulation. However, LNS showed much higher plasma levels of DMP after intravenous administration to rats and recovered more than 80% of the injected dose in the perfusate in single-pass rat liver perfusion. The calculated volume for the distribution of the lipid emulsion within the liver showed that LNS underwent fenestration and was distributed into the Disse space in the liver. Because of the lower uptake of LNS particles by the liver, LNS showed good recovery from the liver and prolonged the plasma half-life of DMP after intravenous injection. In addition, higher efficiency in the targeting of DMP into inflammation sites and higher anti-inflammatory efficacy were observed in LNS. Thus, LNS easily and selectively passed through the leaky capillary wall by passive diffusion depending on the plasma concentration. Nanometer-sized lipid emulsion particles, LNS, seem to be a promising carrier system for passive drug targeting of lipophilic drugs.

Regional intestinal absorption of FITC-dextran 4,400 with nanoparticles based on beta-sitosterol beta-D-glucoside in rats

Nanoparticles (NP) are potential carriers for drug delivery to the targeted intestine. NP based on beta-sitosterol beta-D-glucoside (Sit-G) enhanced the colon-specific absorption of FITC-dextran 4,400 (FD-4), because the concentration-dependent increase of bioavailability appeared in only the colon. In a permeation study, the absorption enhancement in the colon was suppressed in the following conditions: (1) the addition of Sit-G NP to serosa; (2) a permeation study at 4 degrees C; (3) the addition of endocytosis inhibitor, cytochalasin B. NP based on sitosterol, the aglycon of Sit-G, did not increase the FD-4 colonic permeation. The addition of Sit-G NP to the mucosal side induced a decrease of transepithelial resistance (TEER), but this phenomenon was suppressed by an inhibitor of Na(+)-dependent specific glucose transporter, phrolidzin, which did not affect FD-4 permeation. These findings suggested that absorption enhancement by Sit-G NP may not be due to opening of a tight junction, but might be related to endocytosis via glucose residue of Sit-G.

Suppressors of cancer cell proliferation from fig (Ficus carica) resin: isolation and structure elucidation

A mixture of 6-O-acyl-beta-D-glucosyl-beta-sitosterols, the acyl moeity being primarily palmitoyl and linoleyl with minor amounts of stearyl and oleyl, has been isolated as a potent cytotoxic agent from fig (Ficuscarica) latex and soybeans. Identity was established by spectroscopic methods (NMR, MS) and confirmed by chemical synthesis. Both the natural and the synthetic compounds showed in vitro inhibitory effects on proliferation of various cancer cell lines.

Enhanced delivery of AZT to macrophages via acetylated LDL

It is known that infected macrophages play an important role in HIV pathogenesis acting as a reservoir for dissemination of the virus to various organs. Enhanced and/or specific delivery of anti-HIV agents to infected cells is expected to improve their therapeutic index by increasing efficacy and reducing toxicity. Acetylated low density lipoproteins (AcLDL) are known to be taken up by macrophages via scavenger receptors and appear to be good carriers for targeting drug molecules to macrophages. This study investigated the delivery of 3'-azido-3'-deoxythymidine (AZT), an anti-HIV agent, to macrophages using AcLDL. Since the incorporation of AZT into AcLDL was found to be low, several derivatives of AZT including 5'-O-13-oxamyristate-AZT (5'-O-oxaMyr-AZT) have been synthesized as prodrugs. The prodrugs were incorporated into AcLDL using two different methods, namely the contact method and the microemulsion method. Our results demonstrated that the microemulsion method was more effective. The physicochemical properties of the AcLDL/prodrug complex were evaluated by electrophoresis and electron microscopy (EM). Incubation of the complex with plasma resulted in little distribution of the incorporated drug molecules from AcLDL to other components of the plasma, suggesting that the complex was quite stable. Cellular uptake studies using J774.A and U937 demonstrated that AcLDL/prodrug was taken up about 10 times more than AZT. The presence of excess AcLDL was found to inhibit the cellular uptake of AcLDL/5'-O-oxaMyr-AZT by macrophages while excess high density lipoprotein (HDL) or low density lipoprotein (LDL) was found to have little effect, suggesting that the AcLDL/prodrug complex is taken up into macrophages via the scavenger receptor.

Preparation of a complex of dexamethasone palmitate-low density lipoprotein and its effect on foam cell formation of murine peritoneal macrophages

In the early progression of atherosclerosis, LDL migrates in the subendothelial space of the artery and plays an important role in foam cell formations of macrophages. LDL may serve as a carrier of site-specific delivery of drugs to atherosclerotic lesions. In this exploratory study, dexamethasone palmitate (DP) was incorporated in LDL, and an inhibitory effect of this complex on foam cell formations was examined. LDL was isolated from human plasma, and the DP-LDL complex was prepared by incubation in the presence of Celite 545. No degradation nor modification of LDL was observed. The DP/LDL molar ratio of the complex was 35-50:1. Foam cell formations of murine macrophages were induced by incubation with oxidized LDL. When macrophages were pretreated with the DP-LDL complex, accumulation of cholesterol ester in the macrophages induced by oxidized LDL, i.e., an index of foam cell formation, was decreased. These findings indicated that the DP-LDL complex showed similar characteristics to LDL, and the DP-LDL complex inhibited foam cell formations of macrophages in vitro. This study provides the basis for further study of the DP-LDL complex as a drug-carrier complex for treatment of atherosclerosis.

Drug targeting using low density lipoprotein (LDL): physicochemical factors affecting drug loading into LDL particles

Low density lipoprotein (LDL) has been found suitable as a targeting carrier for cytotoxic drugs. However, higher drug loading into LDL particles without disrupting their native integrity remains a major obstacle. The purpose of this study is to investigate the different physicochemical factors that may affect drug loading and to characterize LDL-drug conjugates. Doxorubicin (Dox) and 3', 5'-O-dipalmitoyl-5-iodo-2'-deoxyuridine (dpIUdR) were used as reference cytotoxic drugs. Drugs were loaded into LDL particles using the dry film method with or without surfactants, liposomal and the direct addition method. The effects of incubation temperature, time and stoichiometry of LDL-drug conjugates on drug loading were investigated. The LDL-drug conjugates were evaluated for their stability and characterized by differential scanning calorimetry (DSC), denatured gel (SDS-PAGE), and electron microscopy (EM). We have suitably incorporated 45+/-10 Dox and 150+/-25 dpIUdR molecules/LDL particle. A seven-fold increase in Dox incorporation was achieved with the liposomal preparation compared to the dry film method. A 4- to 6-h incubation at 37 degreesC was suitable to restore the native structure of LDL particles. No apo B fragmentation of LDL particles was noted on denatured gel. DSC studies showed no change in the Tm of the LDL and the LDL-drug conjugates. An increase in particle size of LDL-dpIUdR, not LDL-Dox was observed in EM compared to the native LDL which may be related to higher incorporation of dpIUdR. The results indicate that physicochemical factors significantly affect drug loading efficiency and may need to be considered to optimize drug incorporation into LDL particles.

beta-Sitosterol and beta-sitosterol glucoside stimulate human peripheral blood lymphocyte proliferation: implications for their use as an immunomodulatory vitamin combination

The phytosterols, beta-sitosterol (BSS), and its glucoside (BSSG) enhance the in vitro proliferative response of T-cells stimulated by sub-optimal concentrations of phytohaemagglutinin (PHA) several fold at extremely low concentrations (femtogram level). A 100:1 (mass:mass) ratio of BSS:BSSG (termed essential sterolin formulation, ESF) showed higher stimulation than the individual sterols at the same concentration. In vivo activity of ESF was also demonstrated when volunteers ingested ESF for 4 weeks. Proliferation of their T-cells, stimulated maximally with PHA, was significantly enhanced (20-920%) when compared to baseline values. In vitro, ESF (1 microgram.ml) was able to significantly enhance the expression of CD25 and HLA-Dr activation antigens on T-cells and increased the secretion, into the medium, of IL-2 and gamma interferon. NK-cell activity was also increased by BSS and BSSG alone, but with EST a higher activity was always found at different effector:target ratios (100:1 12:1).

Physicochemical characterization of a synthetic lipid emulsion for hepatocyte-selective delivery of lipophilic compounds: application to polyiodinated triglycerides as contrast agents for computed tomography

A synthetic lipid emulsion (LE) has been developed with physicochemical properties that closely resemble those of a specific class of naturally-occurring lipoproteins known as chylomicron remnants. The formulation has the potential to serve as a hepatocyte-selective delivery system for any lipophilic or amphipathic compounds that can be associated with the internal lipid phase of the emulsion. In the present studies, a lipophilic polyiodinated triglyceride (ITG) was successfully incorporated into the delivery vehicle to form a stable chylomicron-remnant-like emulsion capable of localizing material to the liver following intravenous injection. The preferred ITG-LE formulation was shown to have a mean particle diameter of less than 200 nm and a particle size stability profile in excess of 12 months. The viscosity, pH, and osmolality of the formulation also appeared favorable for safe and convenient intravenous injection. The particle size profile, chemical properties, and high degree of incorporation of ITG into the emulsion suggest that the ITG-LE formulation holds substantial promise as a hepatocyte-selective imaging agent for computed tomography of the liver. Biodistribution, elimination, and computed tomography (CT) imaging results in animals corroborated the hepatocyte-selective nature of the ITG-LE formulation.

Synthesis of the cholesteryl ester prodrugs cholesteryl ibuprofen and cholesteryl flufenamate and their formulation into phospholipid microemulsions

Phospholipid micoremulsions have been suggested as a drug-delivery system for hydrophobic compounds. In this study hydrophobicity was achieved by derivatizing with cholesterol. Cholesteryl ibuprofen (3) and cholesteryl flufenamate (4) were synthesized. 3 was isolated as an amorphous, white solid with a melting range of 114-120 degrees C. 4 was isolated as a crystalline, white solid with a melting range of 145-148 degrees C. The proposed structures of 3 and 4 were supported by IR, NMR, MS, and organic microanalysis. Phospholipid:cholesteryl ester microemulsions were prepared by the addition of a 1-propanol solution of the cholesteryl ester, other lipids, and phospholipid to a rapidly mixing KCl/KBr solution. The hydrophobic phase was modified by the addition of cholesteryl oleate or triolein to study the effect of the fluidity of the hydrophobic core on the formation of the microemulsions. The results indicated that a molar ratio of 75:25 and a total lipid concentration of 60 mg/mL consistently gave microemulsions with a mean size of 100-150 nm. In addition, the formation of eutectic mixtures of 3 and 4 with cholesteryl oleate were determined to be 16% (w/w) for 3 and 12% (w/w) for 4; melting points were 35.2 and 45.2 degrees C, respectively. The solubilities of 3 and 4 in triolein were determined to be 13.2% (w/w) and 11.5% (w/w), respectively. Other investigators have shown that if the core of a phospholipid:cholesteryl estermicroemulsion exists in a liquid state at physiologic temperature, the turnover of the cholesteryl esters from these microemulsions occurs at a faster rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of steroid hormone association with human plasma lipoproteins

Partition coefficient analysis, equilibrium dialysis, and computer simulation were used to evaluate associations of twelve steroid hormones (androstanediol, androstenediol, androstenedione, androsterone, dehydroepiandrosterone, dihydrotestosterone, estradiol, estriol, estrone, hydroxyprogesterone, progesterone, and testosterone) with human plasma high density lipoproteins (HDL), low density lipoproteins (LDL), and very low density lipoproteins (VLDL). It was determined that partitioning of steroid hormones (SH) between the aqueous medium and the surfaces of lipoproteins (LP) was the initial (first order) SH-LP interaction. For some SH, especially dehydroepiandrosterone, significant second order interactions, which may involve chemical conversions, were detected. The first order binding values of the twelve SH with three LP were combined with the corresponding binding values of SH with sex hormone-binding globulin, corticosteroid-binding globulin, and albumin in a 6 X 12 matrix. The computer program TRANSPORT was used to analyze the matrix and determine the distribution of each SH among six different binding agents in the "normal" male. It was concluded that LP are important vehicles for SH conveyance in plasma and may also be important for SH entry into cells.

Metabolism of sitosteryl beta-D-glucoside and its nutritional effects in rats

[4-14C]Sitosteryl beta-D-glucoside, intragastrically administered to rats, was not absorbed by the intestinal mucosa. At three hr after the application, radioactivity was concentrated almost exclusively in the digesta of stomach, small intestine as well as cecum and colon, whereas only low proportions of radioactively labeled compounds were found in the various tissues of the gastrointestinal tract. Minor proportions of labeled metabolites of [4-14C]sitosteryl beta-D-glucoside, such as sitosterol and sitosteryl esters, were formed in the small intestine in vivo and in slices of small intestine in vitro. In the tissues of cecum and colon as well as the digesta derived from them, high proportions of labeled coprositostanol, i.e. 24 alpha-ethyl-5 beta-cholestan-3 beta-ol, that obviously had been formed by bacterial degradation of the substrate were detected. The feeding of sitosteryl beta-D-glucoside (0.5 g/kg body weight X day) over a period of four weeks did not alter significantly body weights or organ weights of rats. Analyses of steryl lipids of the various organs and tissues confirmed the findings obtained with the radioactive substrate: neither sitosteryl beta-D-glucoside nor sitosterol or sitosteryl esters derived therefrom had been transported in appreciable amounts to organs and tissues outside the alimentary canal during the feeding period. Minor proportions of unmetabolized sitosteryl beta-D-glucoside were detected in the tissues of stomach and intestine, whereas large proportions of the substrate were found in feces of rats that had received the sitosteryl beta-D-glucoside-containing diet; coprositostanol was found in feces of these animals in high proportions as well.(ABSTRACT TRUNCATED AT 250 WORDS)