Suppression of liver uptake of liposomes by dextran sulfate 500

Rediscovery of mononuclear phagocyte system blockade for nanoparticle drug delivery

Rapid uptake of nanoparticles by mononuclear phagocyte system (MPS) significantly hampers their therapeutic efficacy. Temporal MPS blockade is one of the few ways to overcome this barrier - the approach rediscovered many times under different names but never extensively used in clinic. Using meta-analysis of the published data we prove the efficacy of this technique for enhancing particle circulation in blood and their delivery to tumours, describe a century of its evolution and potential combined mechanism behind it. Finally, we discuss future directions of the research focusing on the features essential for successful clinical translation of the method.

Mechano-boosting nanomedicine antitumour efficacy by blocking the reticuloendothelial system with stiff nanogels

Nanomedicine has been developed for cancer therapy over several decades, while rapid clearance from blood circulation by reticuloendothelial system (RES) severely limits nanomedicine antitumour efficacy. We design a series of nanogels with distinctive stiffness and investigate how nanogel mechanical properties could be leveraged to overcome RES. Stiff nanogels are injected preferentially to abrogate uptake capacity of macrophages and temporarily block RES, relying on inhibition of clathrin and prolonged liver retention. Afterwards, soft nanogels deliver doxorubicin (DOX) with excellent efficiency, reflected in high tumour accumulation, deep tumour penetration and outstanding antitumour efficacy. In this work, we combine the advantage of stiff nanogels in RES-blockade with the superiority of soft nanogels in drug delivery leads to the optimum tumour inhibition effect, which is defined as mechano-boosting antitumour strategy. Clinical implications of stiffness-dependent RES-blockade are also confirmed by promoting antitumour efficacy of commercialized nanomedicines, such as Doxil and Abraxane.

Advanced strategies to evade the mononuclear phagocyte system clearance of nanomaterials

Nanomaterials are promising carriers to improve the bioavailability and therapeutic efficiency of drugs by providing preferential drug accumulation at their sites of action, but their delivery efficacy is severely limited by a series of biological barriers, especially the mononuclear phagocytic system (MPS)-the first and major barrier encountered by systemically administered nanomaterials. Herein, the current strategies for evading the MPS clearance of nanomaterials are summarized. First, engineering nanomaterials methods including surface modification, cell hitchhiking, and physiological environment modulation to reduce the MPS clearance are explored. Second, MPS disabling methods including MPS blockade, suppression of macrophage phagocytosis, and macrophages depletion are examined. Last, challenges and opportunities in this field are further discussed.

Boosting nanomedicine performance by conditioning macrophages with methyl palmitate nanoparticles

Surface PEGylation, biological camouflage, shape and stiffness modulation of nanoparticles as well as liver blockade and macrophage depletion have all improved the blood longevity of nanomedicines. Yet, the mononuclear phagocytic system still recognizes, sequesters, and processes the majority of blood borne particles. Here, the natural fatty acid methyl palmitate is combined with endogenous blood components - albumin - realizing ∼200 nm stable, spherical nanoparticles (MPN) capable of inducing a transient and reversible state of dormancy into macrophages. In primary bone marrow derived monocytes (BMDM), the rate of internalization of 5 different particles, ranging in size from 200 up to 2000 nm, with spherical and discoidal shapes, and made out of lipids and polymers, was almost totally inhibited after an overnight pre-treatment with 0.5 mM MPN. Microscopy analyses revealed that MPN reversibly reduced the extension and branching complexity of the microtubule network in BMDM, thus altering membrane bulging and motility. In immunocompetent mice, a 4 h pre-treatment with MPN was sufficient to redirect 2000 nm rigid particles from the liver to the lungs realizing a lung-to-liver accumulation ratio larger than 2. Also, in mice bearing U87-MG tumor masses, a 4 h pre-treatment with MPN enhanced the therapeutic efficacy of docetaxel-loaded nanoparticles significantly inhibiting tumor growth. The natural liver sequestering function was fully recovered overnight. This data would suggest that MPN pre-treatment could transiently and reversibly inhibit non-specific particle sequestration, thus redirecting nanomedicines towards their specific target tissue while boosting their anti-cancer efficacy and imaging capacity.

Directing Nanoparticle Biodistribution through Evasion and Exploitation of Stab2-Dependent Nanoparticle Uptake

Up to 99% of systemically administered nanoparticles are cleared through the liver. Within the liver, most nanoparticles are thought to be sequestered by macrophages (Kupffer cells), although significant nanoparticle interactions with other hepatic cells have also been observed. To achieve effective cell-specific targeting of drugs through nanoparticle encapsulation, improved mechanistic understanding of nanoparticle-liver interactions is required. Here, we show the caudal vein of the embryonic zebrafish ( Danio rerio) can be used as a model for assessing nanoparticle interactions with mammalian liver sinusoidal (or scavenger) endothelial cells (SECs) and macrophages. We observe that anionic nanoparticles are primarily taken up by SECs and identify an essential requirement for the scavenger receptor, stabilin-2 ( stab2) in this process. Importantly, nanoparticle-SEC interactions can be blocked by dextran sulfate, a competitive inhibitor of stab2 and other scavenger receptors. Finally, we exploit nanoparticle-SEC interactions to demonstrate targeted intracellular drug delivery resulting in the selective deletion of a single blood vessel in the zebrafish embryo. Together, we propose stab2 inhibition or targeting as a general approach for modifying nanoparticle-liver interactions of a wide range of nanomedicines.

Improved Tumor Uptake by Optimizing Liposome Based RES Blockade Strategy

Minimizing the sequestration of nanomaterials (NMs) by the reticuloendothelial system (RES) can enhance the circulation time of NMs, and thus increase their tumor-specific accumulation. Liposomes are generally regarded as safe (GRAS) agents that can block the RES reversibly and temporarily. With the help of positron emission tomography (PET), we monitored the in vivo tissue distribution of ⁶⁴Cu-labeled 40 × 10 nm gold nanorods (Au NRs) after pretreatment with liposomes. We systematically studied the effectiveness of liposome administration by comparing (1) differently charged liposomes; (2) different liposome doses; and (3) varying time intervals between liposome dose and NR dose. By pre-injecting 400 μmol/kg positively charged liposomes into mice 5 h before the Au NRs, the liver and spleen uptakes of Au NRs decreased by 30% and 53%, respectively. Significantly, U87MG tumor uptake of Au NRs increased from 11.5 ± 1.1 %ID/g to 16.1 ± 1.3 %ID/g at 27 h post-injection. Quantitative PET imaging is a valuable tool to understand the fate of NMs in vivo and cationic liposomal pretreatment is a viable approach to reduce RES clearance, prolong circulation, and improve tumor uptake.

Prolonging the circulatory retention of SPIONs using dextran sulfate: in vivo tracking achieved by functionalisation with near-infrared dyes

The rapid reticuloendothelial system (RES) mediated clearance of superparamagnetic iron oxide nanoparticles (SPIONs) from circulation is considered a major limitation of their clinical utility. We aimed to address this by using dextran sulfate 500 (DSO4 500), a Kupffer cell blocking agent, to prolong SPIONs circulatory time. Blood concentrations of SPIONs are difficult to quantify due to the presence of haemoglobin. We therefore developed methods to functionalise SPIONs with near-infrared (NIR) dyes in order to trace their biodistribution. Two SPIONs were investigated: Nanomag®-D-spio-NH(2) and Ferucarbotran. Nanomag®-D-spio-NH(2) was functionalised using NHS (N-hydroxysuccinimide) ester NIR dye and Ferucarbotran was labelled using periodate oxidation followed by reductive amination or a combination of EDC (ethyl(dimethylaminopropyl) carbodiimide )/NHS and click chemistries. Stability after conjugation was confirmed by dynamic light scattering (DLS), superconducting quantum interference device (SQUID) and transmission electron microscopy (TEM). In vivo experiments with the functionalised SPIONs showed a significant improvement in SPIONs blood concentrations in mice pre-treated with dextran sulfate sodium salt 500 (DSO4 500).

Gadolinium chloride augments tumor-specific imaging of targeted quantum dots in vivo

Nonspecific sequestration of nanoparticles by the reticulo-endothelial system (RES) results in the degradation of image quality of nanoparticle-based imaging. We demonstrate that gadolinium chloride (GdCl3) pretreatment inactivates RES macrophages, thereby increasing circulatory time and amplifying the tumor-specific signal of conjugated nanoparticles in vivo. The experimental results were validated using compartmental modeling, and the rate parameters for the observed kinetics pattern were estimated. This pretreatment strategy could have broad applicability across biomedical applications utilizing theranostic nanoparticles that are sequestered by the RES.

Inverse targeting of diclofenac sodium to reticuloendothelial system-rich organs by sphere-in-oil-in-water (s/o/w) multiple emulsion containing poloxamer 403

Sphere-in-oil-in-water (s/o/w) multiple emulsions containing diclofenac sodium were prepared by gelatinization of inner aqueous phase. A further modified version (s/o/wp) of s/o/w was formulated by adding 5.0% w/v poloxamer 403 to the external aqueous phase during the second step of emulsification in order to affect the adsorptive coating on the surface (s/o/wp). The inverse targeting of reticuloendothelial system (RES) rich organs was compared with a non reticuloendothelial system after intravenous administration of s/o/w multiple emulsion (treatment I) and poloxamer containing s/o/wp multiple emulsion (treatment II). The amount of diclofenac sodium in the plasma and various organs was measured to elucidate the effect of inverse targeting to RES and targeting to other tissues in terms of the incorporated drug. After i.v. administration, the half life (34.65 vs.16.26 h) and apparent volume of distribution of diclofenac sodium (2815 vs. 1671.5 ml/kg) were significantly higher in treatment II than in treatment I. It is concluded that the amount of drug in RES rich organs (spleen, liver) were significantly lower than the values in non-RES organs such as lungs, inflammatory tissue (synovial fluid) in treatment II than in treatment I.

Prolonged circulation of menatetrenone by emulsions with hydrogenated castor oils in rats

Previously, we reported that plasma half-lives of a drug incorporated in lipid emulsions prepared with soybean oil (SO), a long-chain triglyceride, and hydrogenated castor oils (HCOs) (SO/HCOs) were markedly longer, while those as SO/polyoxyethylene sorbitan esters (SO/PSs) were similar, compared to that as SO/egg yolk phosphatides (SO/EYP) [J. Pharm. Pharmacol. 54 (2002) 1357; J. Drug Target. 11 (2003) 37]. In the present study, lipid emulsions were prepared with Miglyol 812 (MO), a medium-chain triglyceride, and HCOs, and the kinetics of the incorporated drug, menatetrenone, were examined. The plasma half-lives and the liver uptake of menatetrenone as MO/polyoxyethylene-(10)-hydrogenated castor oils (MO/HCO10s) were similar to and larger than those as MO/EYP, respectively. On the other hand, the plasma half-lives and liver uptake of menatetrenone as MO/polyoxyethylene-(20)-hydrogenated castor oils (MO/HCO20s) or MO/polyoxyethylene-(60)-hydrogenated castor oils (MO/HCO60s) were markedly longer and lower than those as MO/EYP, respectively. The pretreatment of dextran sulfate 500,000, a reticuloendothelial system suppressor, raised the plasma concentration and inhibited liver uptake of menatetrenone as MO/HCO10, but not for MO/HCO20. These findings suggest that the minimum number of oxyethylene units within HCOs for the prolonged plasma circulation of menatetrenone was 20 for MO/HCOs, similarly to SO/HCOs.

Promotion of xenogeneic hematopoietic chimerism in rodents by mononuclear phagocyte depletion

The successful establishment of tolerance toward pig tissues in primates through hematopoietic progenitor cell engraftment is restricted by the rapid disappearance of these cells in the recipient following infusion. We developed and tested the hypothesis that phagocytes of the reticuloendothelial system are responsible for the rapid clearance of infused pig hematopoietic cells using a mouse model. Mice received non-myeloablative conditioning and, on various days, were injected with medronate-encapsulated liposomes (M-L) or control blank liposomes, followed by the intravenous infusion of miniature swine hematopoietic cells. M-L were well-tolerated in mice (n=100) at levels that deplete mononuclear phagocytes. Depletion of mononuclear phagocytes in normal Balb/c mice as well as in severe combined immune deficient mice increased the accumulation of pig hematopoietic cells in the bone marrow (BM) by 10-fold when measured 24 h after the infusion of the cells. Colony-forming unit analysis showed an increased accumulation of pig hematopoietic progenitors in the BM of mice that were infused with medronate-liposomes. We conclude that depletion of mononuclear phagocytes by M-L has the potential to lower the barrier to the establishment of mixed chimerism and tolerance induction in xenotransplantation.

A simple method for preparation of immuno-magnetic liposomes

A simple and readily manoeuverable method for preparing immuno-magnetic liposomes that indigenously contain binding sites for attaching other molecules like antibodies on their exterior surface is described. In this method magnetic unilamellar vesicles are prepared from a mixture of phosphatidylcholine, cholesterol, small amounts of a linear chain aldehyde and colloidal particles of magnetic iron oxide, using a reverse phase evaporation technique. The aldehyde (dedecanal) molecules align themselves among the lipid molecules in the bilayer with their aldehyde groups exposed to the aqueous phase, allowing straight attachment of antibody molecules (human-antimouse IgG-FITC in this case) in one single step. The success of this approach is confirmed by fluorescence microscopy as well as binding of the resulting immuno-magnetic liposomes to their corresponding target cells.

Low molecular weight dextran sulfate prevents complement activation and delays hyperacute rejection in pig-to-human xenotransplantation models

Dextran sulfate of 5000 molecular weight (DXS 5000) is known to block complement activation as well as the intrinsic coagulation cascade by potentiation of C inhibitor. The effect of DXS 5000 on hyperacute rejection (HAR) was tested in pig-to-human xenotransplantation models. For in vitro testing, a cytotoxicity assay was used with the pig kidney cell line PK15 as target cells and fresh, undiluted human serum as antibody and complement source. Ex vivo pig lung perfusion was chosen to assess DXS 5000 in a physiologic model. Pig lungs were perfused with fresh, citrate-anticoagulated whole human blood to which 1 or 2 mg/ml DXS 5000 were added; the lungs were ventilated and the blood de-oxygenated. Pulmonary vascular resistance (PVR) and blood oxygenation (deltapO2) were monitored throughout the experiment. Autologous pig blood and human blood without DXS 5000 served as controls. In the PK 15 assay DXS 5000 led to a complete, dose-dependent inhibition of human serum cytotoxicity with an average IC50 of 43 +/- 18 microg/ml (n=8). Pig lungs perfused with untreated human blood (n=2) underwent HAR within 105 +/- 64 min, characterized by increased PVR, decrease of deltapO2, and generalized edema. Microscopically, capillary bleeding as well as deposition of human antibodies, complement and fibrin could be observed. Addition of DXS 5000 (n=4) prolonged lung survival to 170 +/- 14 min for 1 mg/ml and 250 +/- 42 min for 2 mg/ml. and PVR values as well as edema formation were comparable to control lungs that were perfused with autologous pig blood (n=2). Activation of complement (activation products in serum, deposition on lung tissue) and the coagulation system (fibrin monomers) were significantly diminished as compared to human blood without DXS 5000. Binding of anti-Gal antibodies was not influenced, and in vitro experiments showed no evidence of complement depletion by DXS 5000. In conclusion, DXS 5000 is an efficient complement inhibitor in pig-to-human xenotransplantation models and therefore a candidate for complement-inhibitory/anti-inflammatory therapy either alone or in combination with other substances and warrants further investigation.

Alkyl-polyacrylate esters are strong mucosal adjuvants

Synthetic polymers were examined for their potency to enhance mucosal immune responses to inactivated antigens. Aqueous solutions of polyacrylic acid with a MW of 450 kDa (p[AA]) or an butyl-ester thereof with 16% esterification (Butyl16-p[AA]) plus antigen were administered twice intranasally in mice with a 2 week interval. The frequency of IgA-antibody secreting cells (ASCs) in lung cell suspensions was determined 1 week after the second immunisation. Both polymers significantly enhanced the IgA response against inactivated Newcastle disease virus (iNDV), inactivated influenza virus strain MRC-11 (iMRC-11), haemagglutinin/neuraminidase subunits of influenza virus strain A/Texas (HA/NA) and bovine serum albumin (BSA). Butyl16-p(AA) was significantly more effective than non-derivatised p(AA), cholera toxin B subunit (CTB) or liposomes. The factor of increase in IgA-ASCs varied from <10- to >100-fold and depended on the type of antigen, the dose of antigen and the adjuvant. Extremely high responses of about 10,000 IgA-ASCs per million lung cells were detected after immunisation with 5 microg HA/NA plus 50 microg Butyl16-p(AA). Intranasal immunisation with Butyl16-p(AA) resulted in high IgA responses, not only in the lungs, but also in the spleen and in high IgG responses in these organs. We concluded that alkyl-esters of polyacrylate are an interesting, novel category of mucosal adjuvants.

Effect of composition on biological fate of oil particles after intravenous injection of O/W lipid emulsions

Plasma concentrations of oil particles after intravenous injection of oil-in-water (O/W) lipid emulsions were monitored based on the plasma concentration of phospholipids (PL) and triglycerides (TG), and the light scattering intensity (LSI) of plasma. Previously, we found that their time profiles after injection of the standard O/W lipid emulsion composed of soybean oil (SO) and egg yolk phosphatides (EYP) were similar and suggested that the oil particles with diameter of about 200 nm were entrapped by reticuloendothelial system (RES). Herein, in order to develop a delivery system to avoid the RES uptake by using the lipid emulsions, biological fate of lipid emulsions with oil particles of various sizes or those emulsified by surfactants with polyoxyethylene segments were subjected to the investigations. Lipid emulsions with oil particles of various sizes (about 150-550 nm) were prepared by altering EYP content. The oil particles were stable in plasma in vitro, but oil particle size decreased time-dependently after intravenous injection. Plasma clearance of oil particles depended on their initial size and was decreased by pretreatment with dextran sulfate 500 (DS500), a known RES suppressor. These results suggested that oil particles are still entrapped by RES, even for small-sized oil particles (about 150 nm). Lipid emulsion with small-sized oil particles was also prepared using medium chain triglycerides. The oil particles were stable in vitro, but the time profiles of plasma concentrations of PL and TG, and LSI of plasma were different, and oil particle size decreased time-dependently after intravenous injection. Plasma clearance of the oil particles also depended on their initial size and was decreased by DS500, suggesting that in vivo instability could be due to RES-mediated processes. Artificial surfactants with polyoxyethylene segments, HCO-60 (HCO60) and polysorbate 80 (PS80), were used for RES avoidance. HCO60 resulted in drastic reduction of the plasma clearance of the oil particles for both lipid emulsions composed of soybean oil and medium chain triglycerides. The time-dependent decrease of oil particle size after intravenous injection was marginal. In contrast, PS80 could not prolong the circulation time of the oil particles, and their size decreased time-dependently after intravenous injection.

O/W lipid emulsions for parenteral drug delivery. III. Lipophilicity necessary for incorporation in oil particles even after intravenous injection

The potential usefulness of oil-in-water (O/W) lipid emulsions as injectable drug delivery systems was examined. Plasma concentrations of oil particles after intravenous injection of a standard lipid emulsion composed of soybean oil and egg yolk phosphatides were monitored based on the plasma concentrations of phospholipids and triglycerides, and the light scattering intensity of the plasma. Their time profiles were similar to each other, and the oil particle size decreased time-dependently. Pretreatment with dextran sulfate, a known reticuloendothelial system (RES) suppressor, resulted in marked reduction of the plasma clearance of the oil particles and of the time-dependent alteration of oil particle size, suggesting that oil particles were trapped by RES. The lipophilicity of the drug needed for its incorporation in the oil particles even after intravenous injection was found to be clog P > 8, where clog P is the calculated logarithm of the partition coefficient between n-octanol and water. In the case of sudan II (clog P = 5.4), the release from the oil particles was very quick after intravenous injection, resulting in slight alteration in biodistribution when compared with its micellar solution. In contrast, menatetrenone (clog P = 9.5) was selectively delivered to the liver, lungs and spleen, being consistent with the oil particles taken up by RES.

Prolonging the circulation time and modifying the body distribution of intravenously injected polystyrene nanospheres by prior intravenous administration of poloxamine-908. A 'hepatic-blockade' event or manipulation of nanosphere surface in vivo?

Intravenously injected uncoated small (60 nm) and large (250 nm) size model polystyrene particles (which are cleared rapidly from the blood by macrophages of the reticuloendothelial system) can be converted to long-circulatory and splenotropic particles in vivo, respectively, if such particles are injected shortly (up to 3 h) after an appropriate dose of the block polymer non-ionic surfactant, poloxamine-908. Evidence indicates that small and large size polystyrene beads can acquire a coating of poloxamine-908 and/or poloxamine-protein complexes in vivo. The adsorption of such complexes on to the bead surface could explain their altered body distribution since small and large size polystyrene beads that were precoated with poloxamine-908 exhibit similar biodistribution following i.v. injection.

Lung specific stealth liposomes: stability, biodistribution and toxicity of liposomal antitubercular drugs in mice

Liposomes with enhanced affinity towards lung tissue were prepared for the development of more effective chemotherapy against tuberculosis. Modification of surface of stealth liposomes by tagging O-stearylamylopectin (O-SAP) resulted in the increased affinity of these liposomes towards lung tissue of mice. Liposomes containing egg phosphatidylcholine (ePC), cholesterol (CH), dicetylphosphate (DCP), O-SAP and monosialogangliosides (GM1)/distearylphosphatidylethanolamine-poly(ethylene glycol) 2000 (DSPE-PEG 2000) were found to be most stable in serum. Tissue distribution of these liposomes showed more accumulation in lungs than in reticuloendothelial systems (RES) of normal and tuberculous mice. Pre administration of PC and CH (2:1.5) liposomes before the injection of lung specific stealth liposomes further enhanced their uptake in lungs. In vivo stability of these liposomes demonstrated the slow and controlled release of their encapsulated contents. Isoniazid and rifampicin encapsulated in liposomes were less toxic to peritoneal macrophages as compared to free drugs. Further, encapsulated drugs also demonstrated reduced in vivo toxicity in comparison to free drug(s). These findings suggest liposomes to be better drug delivery vehicles for experimental tuberculosis.

Physicochemical and pharmacokinetic characteristics of plasmid DNA/cationic liposome complexes

The objectives of this study were (i) to characterize the plasmid DNA encoding the chloramphenicol acetyltransferase reporter gene (pCAT) complexed with cationic liposomes (Lipofectin and LipofectACE) in terms of particle size and zeta potential, (ii) to compare pharmacokinetic characteristics, and (iii) to study the hepatic uptake mechanisms. DNA/LipofectACE complexes showed a negative zeta potential of -36 mV at 1:5 w/w ratio, but a positive zeta potential of (19 mV at 1:10 w/w ratio. Lipofectin samples showed a positive zeta potential) of 21-28 mV at these ratios. These preparations showed a wide particle size distribution ranging from 600 to 1200 nm. Following intravenous injection of 1:10 w/w ratio [32P]pCAT/liposome complexes at a dose of 0.1 mg DNA/kg into the tail vein of mice, radioactivity was rapidly eliminated from the plasma and almost 50-60% of the dose was taken up by the liver within 5 min after administration. Plasmid DNA/liposome complexes were predominantly taken up by the liver nonparenchymal cells. The hepatic uptake was inhibited by preceding administration of dextran sulfate (DS), but not by polycytidic acid (poly[C]) and polyinosinic acid (poly[I]), suggesting the involvement of a phagocytic process. We suggest that these complexes are preferentially taken up by the liver nonparenchymal cells mainly via Kupffer cell phagocytosis.

Endocytosis of hyaluronan in rat Kupffer cells

The binding, uptake and degradation of hyaluronan (HA) labelled with 3H in its acetyl group were studied in cultured rat Kupffer cells (KC). At 4 degrees C the binding increased with increasing concentrations of HA in the culture medium up to at least 1 microgram/ml, when saturation occurred. Binding could be prevented efficiently by the addition of an excess of unlabelled HA, and to a lesser extent by chondroitin sulphate and oligosaccharide fragments of HA, consisting of four sugars or more. The labelled HA bound to the cells could be removed by incubating the cells with Streptomyces hyaluronidase, or trypsin, indicating that the HA-binding sites are located on the cell surface. At 37 degrees C HA was internalized in a concentration-dependent manner, and degradation products appeared in the supernatant after 1-5 h, depending on the concentration applied. At 50 ng of free HA/ml, each KC accumulated 60 ag of the polysaccharide/min in the first 1 h, and degraded a total amount of 10 fg of HA during an 8 h period. Addition of the negatively charged polysaccharide dextran sulphate reduced binding, and to an even greater extent internalization, of HA in KC, while no effect was observed with dextran. Depletion of intracellular potassium caused a marked reduction in the rate of endocytosis of cell-membrane-associated HA into KC, without affecting binding. Addition of KCl to the culture medium returned endocytosis of [3H]HA to normal levels. There was no effect on binding and a partial effect on internalization by depletion of bivalent cations or in the presence of EDTA. The degradation of [3H]HA by KC cultures was abolished in the presence of weak bases, NH4Cl and chloroquine, supporting the idea that HA is endocytosed into lysosomes prior to degradation. The fluid-phase marker [14C]sucrose was internalized in the cells at much lower rate than was HA. Rates of binding, internalization and degradation of HA in KC point therefore to a specific endocytosis followed by an intracellular degradation to low-M(r) compounds. It was estimated that, under physiological conditions, KC only clear a minor proportion of circulating HA.

Bone marrow uptake of liposome-entrapped spin label after liver blockade with empty liposomes

Using an ESR spectrometer, we studied the time course of the uptake of the liposome-entrapped spin label 2,2,6,6-tetramethylpiperidine-N-oxyl-4-trimethylammonium in liver, spleen, and bone marrow following reticuloendothelial liver blockade. Our results show that suppression of the phagocytic activity of the liver increases the delivery of liposomes to the spleen and bone marrow without substantially altering uptake by the liver.

Hepatic metabolism of colloidal gold-low-density lipoprotein complexes in the rat: evidence for bulk excretion of lysosomal contents into bile

Rats were treated with 17 alpha-ethinyl estradiol to induce high levels of low-density lipoprotein receptors in hepatocytes. When these rats were given intravenous injections of low-density lipoprotein-colloidal gold complexes, most of the gold (labeled with 195Au) appeared to be taken up by Kupffer cells, as were complexes of colloidal gold with albumin or polyvinylpyrrolidone. However, when these rats were also administered gadolinium chloride, which blocks Kupffer cell activity, most of the low-density lipoprotein-gold (but not gold complexed with albumin or polyvinylpyrrolidone) was taken up into hepatocytes by receptor-mediated endocytosis and concentrated in peribiliary lysosomes, as determined by electron microscopy. Colloidal gold taken up as a complex with low-density lipoprotein was excreted into the feces via the common bile duct at a maximal rate of about 5% daily, 4 to 12 days after injection. Thereafter, the rate of gold excretion fell off until reaching a plateau after 3 weeks. At this late time, most of the colloidal gold was shown by electron microscopy to be in Kupffer cells, whereas earlier (6 days after injection) it was contained mainly in older hepatocytic lysosomes, identified by lipofuscin granules. It is concluded that, in rats, hepatocytic lysosomes empty most of their contents into bile every week or two, apparently by exocytosis.

Suppression of liver uptake of orally fed liposomes by injection (i.p.) of dextran sulfate 500

125Iodine labelled human immunoglobulin-G encapsulated liposomes were administered orally to rats. Distribution of radioactivity was checked in various tissues and in portal blood. The effect of dextran sulfate (DS 500,000 m. wt., liver blockade agent) injection (i.p.) on the liver uptake of liposomes and on the amount of liposomes appearing in the portal blood from the gastrointestinal tract have been studied. An increased amount of radioactivity was observed in the portal blood and the amount of radioactivity in the liver decreased appreciably after injection of dextran sulfate. In both the cases the action of dextran sulfate started 2 hours after injection and reached maximum at 12 hour, falling slightly at 24 hour.

Immune clearance of liposomes inhibited by an anti-Fc receptor antibody in vivo

In a study designed to evaluate the potential for in vivo manipulation of the circulation and tissue distribution of injected liposomes, mice were passively injected with antidinitrophenyl (anti-DNP) monoclonal antibodies of the IgG2a or IgG2b subclasses or were immunized with the nitrophenyl hapten bound to a protein carrier. They were then injected i.v. with 125I- and carboxyfluorescein-labeled, DNP-bearing liposomes. Circulation time of the DNP-bearing liposomes was markedly reduced in actively and passively immune mice, with increased deposition of liposomes in the liver. The increased clearance of liposomes could be abrogated by injection of a monoclonal antibody directed against the murine IgG Fc receptor (2.4G2). The results suggest that clearance of ligand-bearing reagent in the face of an immune response may be modified by specific immunologic manipulation in vivo.

Effect of a selected suppression of the reticuloendothelial system on the distribution of model carrier particles

The distribution of small labeled latex test particles has been studied after intravenous administration to the rabbit using the noninvasive technique of gamma scintigraphy. The reticuloendothelial system was suppressed using polystyrene latex particles and dextran sulfate as blocking agents. Both materials gave rise to significant uptake of particles in the lungs of the order of 60% of the administered dose. The effect seen with suppression with latex particles remained unaltered over an 8-d period, while for suppression with dextran sulfate the effect was transient, and particles that were initially deposited in the lungs were subsequently redistributed to the liver. The results are discussed in terms of previous studies on reticuloendothelial suppression using different agents, test colloids, and animal models.