Uptake of cholesterol by the retina occurs primarily via a low density lipoprotein receptor-mediated process.

PURPOSE: In this study we examined the uptake of circulating lipoproteins into the retina, using a naturally fluorescent cholesterol analog for imaging and deuterated cholesterol for quantification by mass spectroscopy. The purpose of this study was to better understand cholesterol uptake, transport and homeostasis in the retina. METHODS: Human low density lipoprotein (LDL) and high density lipoprotein (HDL) were labeled with the fluorescent cholesterol analog cholesta-5,7,9(11)-trien-3beta-ol (CTL) and deuterated cholesterol (25,26,26,26,27,27,27-[2H]cholesterol, D7Ch). Rats were injected intravenously with CTL-LDL, CTL-HDL and D7Ch-LDL. Fluorescent confocal microscopy was used to image the uptake of CTL and mass spectroscopy was used to quantify D7Ch. Immunohistochemistry and fluorescent confocal microscopy were used to localize apoB (an LDL marker protein) and LDL receptor (LDLR) protein in rat and monkey retinas. RESULTS: CTL-specific fluorescence was imaged by confocal microscopy in the retinal pigment epithelium (RPE), choriocapillaris and parts of the neural retina within 2 h post-injection and was visualized in the photoreceptor outer segments by 4 h. Replacing LDL with HDL as the CTL carrier gave a less robust and more delayed labeling of retinal layers. Human apolipoprotein B (apoB) was also localized in the rat choriocapillaris and RPE by 4 h post-injection. Human apoB was detected by immunoblot analysis in the rat retina primarily as a about 70 kDa protein, suggesting proteolytic degradation. LDL-mediated uptake of cholesterol was quantified by mass spectroscopy using deuterated cholesterol in place of CTL. In addition, apoB and LDLR were localized in monkey retina by immunohistochemistry. CONCLUSIONS: The retina is capable of rapid uptake of circulating LDL via an LDLR-mediated process primarily occurring in the RPE and also possibly Müller cells. Despite the dominance of HDL over LDL in rat serum, LDL appears to be the preferred carrier for cholesterol transport to and uptake by the retina. The results also suggest that blood-borne LDL represents a significant contributor to the steady-state levels of cholesterol and possibly other lipids in the retina.

[Liver targeting of cationic liposomes modified with soybean-derived sterylglucoside in vitro].

AIM: To construct a liposomal liver targeting delivery system by adding soybean-derived sterylglucoside (SG) to the cationic liposomes. METHODS: The physico-chemical properties of SG modified cationic lipsomes were investigated using fluorescein sodium (FS) as a model drug, as well as the interaction of SG modified liposomes with HepG2 2. 2. 15 cells in the point of involvement of asialoglycoprotein receptor (ASGP-R) mediated transfection. Liver targeting of modified cationic liposomes were also investigated using liver perfusing technique, and hepatocytes and non-hepatocytes were separated and examined after perfusing. RESULTS: All the formula yielded high incorporation efficiency (83.12% - 91.74%), small particle size (93.0 - 124.4 nm). The zeta potential of blank liposomes all showed positive values. The transfection efficiency of FS entrapped in SG-liposomes with HepG2 2.2. 15 was significantly higher than that of liposomes without modification. The transfection of SG-liposomes were reduced significantly by the 20/30 mmol galactose as a competitor of ASGP-R. All the cationic liposomes showed high level of liver uptake of FS. Compared with the uptake of non-hepatocytes of each respectively, only SG/Brij-35 liposomes showed difference in FS uptake by hepatocytes (P < 0.05). CONCLUSION: It showed that SG/Brij-35 modified cationic liposomes are potentially useful drug carrier to liver but may be affected by different modification.

Application of sterylglucoside-containing particles for drug delivery.

Recent advances in biotechnology have promoted biomolecular targeting of drugs, peptides and genes in the treatment and management of major diseases and infections. Therapeutic development of drugs and delivery systems may have various objectives: Systemic drugs require optimal delivery and uptake at target sites; peptide drugs require alternative routes of administration, such as nasal or intestinal absorption; gene medicines need to be delivered efficiently, safely and selectively to diseased areas. The propensity of ligand-modified liposomes to carry drugs and genes to desirable sites has been extensively examined and current reports show considerable progress in this field. Sterylglucoside (SG) is a novel absorption-enhancer of peptide drugs across nasal and intestinal mucosae. Physico-chemical properties and biodistribution of liposomes incorporating SG were studied and compared against the profiles of aglycon and sitosterol derivatives of SG. It was shown that SG particles aided colon drug delivery and increased bioavailability of peptide drugs after nasal and intestinal administration. In addition, they were able to enhance anticancer effects in liver cancer chemotherapy. Biological fate and interaction of SG with hepatocytes support the novel proposition of liver-targeting SG-liposomes.

[Biodistribution and hepatocytes targeting of cationic liposomes surface-modified with sterylglucoside and golyethylene glycol].

AIM: To investigate the biodistribution and the hepatocytes targeting of cationic liposome containing 3beta[N-( N',N'-dimethylaminoethane) carbamoyl] cholesterol (DC-Chol) and surface-modified liposomes with sterylglucoside (SG) and polyethylene glycol-distearoylphosphatidylethanolamine (PEG-DSPE). METHODS: Cationic liposomes (CL) composed of DC-Chol and dipalmitoylphosphatidylcholine (DPPC), SG/PEG modified cationic liposome (SG/PEG-CL), both contained trace 3H-cholesterol (3H-Chol) as radiolabel, were prepared. The liposomes encapsulating 125I-labled antisense oligodeoxynucleotide (125I-asODN) (SG/PEG-CL-asODN) were also prepared. The biodistribution of CL, SG/PEG-CL, SG/PEG-C2-asODN as well as 125I-asODN solution, were studied. The radioactivities in hepatocytes and non-hepatocytes after administration of CL and SG/PEG-CL were determined by infuseing method. RESULTS: CL and SG/PEG CL significantly aggregated in liver. The distribution of SG/PEG CL was significantly higher in hepatocytes (P < 0.01) and lower in non-hepatocytes (P < 0.01) than that of CL. The concentrations of SG/PEG-CL-asODN in liver and spleen were significantly higher than that of asODN solution (P < 0.01). CONCLUSION: Cationic liposome modified with SG/PEG changed the distribution of asODN. Cationic liposome can target hepatocytes more effective after being modified with SG.

[Transformation of 3beta-(2-hydroxyethoxy)-5alpha-cholest-8(14)-en-15-one in a polar metabolite in HepG2 hepatoma cells]. / Prevrashchnie 3beta-(2-gidroksiétoksi)5alpha-kholest-8(14)-en-15-ona v poliarnyi metabolit v kletkakh gepatomy HepG2.

Incubation of 3 beta-(2-hydroxy-2[3H]-ethoxy)-5 alpha-cholest-8(14)-en-15-one with Hep G2 cells led to the accumulation of a radioactive polar product in the culture medium, which was identified as 3 beta-(2-hydroxyethoxy)-15-keto-5 alpha-cholest-8(14)-ene-24-oic acid. Its structure was confirmed by a chemical counter synthesis. The labeled ketosterol was rapidly (tau 1/2 = 6 min) and reversibly bound by Hep G2 cells. The intracellular concentration of 15-ketosterol decreased during incubation mainly due to the formation of a polar metabolite, secreted to the medium. The level of cholesterol biosynthesis was 22 +/- 5% of the control value in Hep G2 cells at a 15-ketocholesterol concentration in the medium of 30 microM. However, further incubation for 3 h in the medium without the ketosterol led to restoration of the level of biosynthesis to 85 +/- 11% of the control value. These results suggest that inhibition of the cholesterol biosynthesis by 15-ketocholesterol in Hep G2 cells depends on the intracellular concentration of the inhibitor, which, in turn, is determined by the rate of its conversion into the polar metabolite. The English version of the paper: Russian Journal of Bioorganic Chemistry, 2003, vol. 29, no. 6; see also http://www.maik.ru.

Collagen-stimulated unidirectional translocation of cholesterol in human platelet membranes.

When human platelets are stimulated with collagen or thrombin, the asymmetric distribution of membrane lipids is disrupted as phosphatidylserine and phosphatidylethanolamine translocate from the inner monolayer to the outer monolayer. Coincident with the stimulus-dependent rearrangement of membrane phospholipids is a rapid redistribution of cholesterol from the outer to the inner membrane monolayer. This redistribution of cholesterol was observed when the stimulus was collagen or ADP. The data presented here show that epinephrine stimulation does not promote cholesterol translocation but does potentiate collagen-promoted movement of cholesterol. To investigate the process of cholesterol translocation, experiments were performed to determine whether collagen stimulated reverse cholesterol movement; i.e. from the inner to the outer monolayer. For this study, the fluorescent sterol cholestatrienol (C-3) was incorporated into platelet membranes by exchange from cholesterol-containing phosphatidylcholine small unilamellar vesicles. C-3 was then removed selectively from the outer monolayer by treatment of the platelets with bovine serum albumin (BSA). During the subsequent incubation of BSA-treated platelets, C-3 moved spontaneously into the outer from the inner monolayer. This translocation had an apparent half-time of approximately 25 min and was unaltered by the presence of collagen. These results suggest that collagen treatment of platelets selectively facilitates the inward movement of the sterol. We have hypothesized that cholesterol translocation may be thermodynamically driven as a result of an unfavorable entropy, resulting in cholesterol translocation out of an environment becoming enriched in phosphatidylethanolamine. The unidirectional nature of collagen-promoted cholesterol movement from the phosphatidylethanolamine-rich outer monolayer is consistent with this interpretation.

3 beta-Chlorosteroids: artefacts and possible contaminants in food and feed--toxicological effects in mice.

3 beta-Chlorosteroids, such as cholesteryl beta-chloride and sitosteryl beta-chloride, are formed during the production of protein hydrolysates, which are useful flavour enhancers. These chlorinated steroids may also attract attention as environmental contaminants if they are released from liquid crystal display devices. The effects of orally administered 3 beta-chlorosteroids were tested in female NMRI mice. The animals were fed cholesteryl beta-chloride or sitosteryl beta-chloride at doses of 1 mg and 10 mg/animal/day, that is, 33 mg and 330 mg/body weight/day, over a period of 3 months. Feed intake, body weight and organ weights of the animals, as well as concentration of 3 beta-chlorosteroids in faeces and various organs and tissues showed that cholesteryl beta-chloride and sitosteryl beta-chloride are not acutely toxic compounds. However, chronic toxicity cannot be excluded because small amounts of 3 beta-chlorosteroids, in particular cholesteryl beta-chloride, were absorbed by the intestinal tract and accumulated in adipose tissue. Histopathological examination of sections of organs and tissues showed no indication of irreversible cell damage in the stomach, duodenum, liver, kidneys and spleen caused by the chlorinated steroids.

Studies on intestinal absorption, distribution and metabolism of 3 beta-chloro[4-14C]cholest-5-ene and 3 beta-chloro[4-14C]stigmast-5-ene in mice.

A method for the analysis of 3 beta-chloro steroids by high-performance liquid chromatography is described. These compounds are known to occur in commercial protein hydrolysates. The gastro-intestinal absorption, distribution and metabolism of chlorinated steroids were studied after their intragastric application to mice. At 2 hr after stomach intubation of 3 beta-chloro[4-14C]cholest-5-ene and 3 beta-chloro-[4-14C]stigmast-5-ene, large proportions of radioactivity had passed through the small intestine and were found to be concentrated in the contents of the caecum and colon. Very small amounts of 3 beta-chlorocholest-5-ene were absorbed by the intestinal mucosa and distributed to organs and tissues outside the alimentary canal, whereas intestinal permeability of 3 beta-chlorostigmast-5-ene was negligible. After administration of labelled 3 beta-chlorocholest-5-ene, the highest value of radioactivity, 120 Bq/g tissue, outside the intestinal tract was detected in liver. Altogether, less than 0.5% of the total radioactivity applied to the animals was found to be transported through the intestinal wall and less than 0.5% of the total radioactivity was detected in various metabolites. In general, 3 beta-chlorostigmast-5-ene was transported in smaller proportions and metabolized to a lesser extent than the corresponding cholesterol derivative. Moreover, metabolites of the two radioactive substrates formed by enzymatic attack of enteric micro-organisms were not detected in the contents of the caecum and colon. It appears that 3 beta-chlorinated steroids are fairly stable products that are metabolized poorly both by the cells of the intestinal mucosa and by enteric micro-organisms of mice.