Binding sites and endocytosis of heparin and polylysine are changed when the two molecules are given as a complex to Chinese hamster ovary cells

Thermodynamics of lipid interactions with cell-penetrating peptides

Cationic peptides are efficiently taken up by biological cells through different pathways, which can be exploited for delivery of intracellular drugs. For example, their endocytosis is known since 1967, and this typically produces entrapment of the peptides in endocytotic vesicles. The resulting peptide (and cargo) degradation in lysosomes is of little therapeutic interest. Beside endocytosis (and various subtypes thereof), cationic cell-penetrating peptides (CPPs) may also gain access to cytosol and nucleus of livings cells. This process is known since 1988, but it is poorly understood whether the cytosolic CPP appearance requires an active cellular machinery with membrane proteins and signaling molecules, or whether this translocation occurs by passive diffusion and thus can be mimicked with model membranes devoid of proteins or glycans. In the present chapter, protocols are presented that allow for testing the membrane binding and disturbance of CPPs on model membranes with special focus on particular CPP properties. Protocols include vesicle preparation, lipid quantification, and analysis of membrane leakage, lipid polymorphism ((31)P NMR), and membrane binding (isothermal titration calorimetry). Using these protocols, a major difference among CPPs is observed: At low micromolar concentration, nonamphipathic CPPs, such as nona-arginine (WR(9)) and penetratin, have only a poor affinity for model membranes with a lipid composition typical of eukaryotic membranes. No membrane leakage is induced by these compounds at low micromolar concentration. In contrast, their amphipathic derivatives, such as acylated WR(9) (C(14), C(16), C(18)) or amphipathic penetratin mutant p2AL (Drin et al., Biochemistry 40:1824-1834, 2001), bind and disturb lipid model membranes already at low micromolar peptide concentration. This suggests that the mechanism for cytosolic CPP delivery (and potential toxicity) differs among CPPs despite their common name.

Surfen, a small molecule antagonist of heparan sulfate

In a search for small molecule antagonists of heparan sulfate, we examined the activity of bis-2-methyl-4-amino-quinolyl-6-carbamide, also known as surfen. Fluorescence-based titrations indicated that surfen bound to glycosaminoglycans, and the extent of binding increased according to charge density in the order heparin > dermatan sulfate > heparan sulfate > chondroitin sulfate. All charged groups in heparin (N-sulfates, O-sulfates, and carboxyl groups) contributed to binding, consistent with the idea that surfen interacted electrostatically. Surfen neutralized the anticoagulant activity of both unfractionated and low molecular weight heparins and inhibited enzymatic sulfation and degradation reactions in vitro. Addition of surfen to cultured cells blocked FGF2-binding and signaling that depended on cell surface heparan sulfate and prevented both FGF2- and VEGF(165)-mediated sprouting of endothelial cells in Matrigel. Surfen also blocked heparan sulfate-mediated cell adhesion to the Hep-II domain of fibronectin and prevented infection by HSV-1 that depended on glycoprotein D interaction with heparan sulfate. These findings demonstrate the feasibility of identifying small molecule antagonists of heparan sulfate and raise the possibility of developing pharmacological agents to treat disorders that involve glycosaminoglycan-protein interactions.

Glycan antagonists and inhibitors: a fount for drug discovery

Glycans, the carbohydrate chains of glycoproteins, proteoglycans, and glycolipids, represent a relatively unexploited area for drug development compared with other macromolecules. This review describes the major classes of glycans synthesized by animal cells, their mode of assembly, and available inhibitors for blocking their biosynthesis and function. Many of these agents have proven useful for studying the biological activities of glycans in isolated cells, during embryological development, and in physiology. Some are being used to develop drugs for treating metabolic disorders, cancer, and infection, suggesting that glycans are excellent targets for future drug development.

Thermodynamic studies and binding mechanisms of cell-penetrating peptides with lipids and glycosaminoglycans

Cell-penetrating peptides (CPPs) traverse the membrane of biological cells at low micromolar concentrations and are able to take various cargo molecules along with. Despite large differences in their chemical structure, CPPs share the structural similarity of a high cationic charge density. This property confers to them the ability to bind electrostatically membrane constituents such as anionic lipids and glycosaminoglycans (GAGs). Controversies exist, however, about the biological response after the interaction of CPPs with such membrane constituents. Present review compares thermodynamic binding studies with conditions of the biological CPP uptake. It becomes evident that CPPs enter biological cells by different and probably competing mechanisms. For example, some amphipathic CPPs traverse pure lipid model membranes at low micromolar concentrations--at least in the absence of cargos. In contrast, no direct translocation at these conditions is observed for non-amphipathic CPPs. Finally, CPPs bind GAGs at low micromolar concentrations with potential consequences for endocytotic pathways.

Inducing a change in the pharmacokinetics and biodistribution of poly-L-lysine in rats by complexation with heparin

The aim of our study was to induce changes in the plasma elimination half-life (t(1/2)(elim)), rate and extent of urinary excretion, and biodistribution of a model macromolecule, poly-L-lysine, in rats following complexation with heparin. Male Sprague-Dawley rats were dosed intravenously with either unfractionated [(3)H]heparin, FITC-labelled poly-L-lysine, or an [(3)H]heparin:FITC-labelled poly-L-lysine complex. Serum and blood concentration vs time and urinary excretion profiles were determined as well as the resulting patterns of biodistribution to liver, spleen, kidney, and muscle tissue. While the mean values for the total body clearance of poly-L-lysine and the complex were not significantly different, the volume of distribution and the half-life associated with elimination from the serum were increased greater than 2-fold for the complex compared with free poly-L-lysine. The rate and extent of elimination in the urine followed the relative rank order; heparin > poly-L-lysine> heparin:poly-L-lysine complex. Thirty minutes following intravenous administration, there was significantly more tissue deposition/uptake of the complex in the liver, kidney, and muscle, but not the spleen, when compared with poly-L-lysine administered alone. Complexation of heparin to poly-L-lysine effectively increased the fraction of an administered dose of poly-L-lysine that was deposited in liver, kidney, and muscle tissue. Due to the macromolecular complex being nontoxic and uncharged, potentially it might serve as a suitable carrier for both conventional and peptidic drugs to increase drug distribution to liver, kidney, or muscle tissue.

Efficiency of protein transduction is cell type-dependent and is enhanced by dextran sulfate

Protein transduction domains (PTDs), both naturally occurring and synthetic, have been increasingly utilized to deliver biologically active agents to a variety of cell types in vitro and in vivo. We report that in addition to previously characterized arginine-rich PTDs, including TAT, lysine homopolymers were able to mediate transduction of a wide variety of cell types, as measured by flow cytometric and enzymatic assays. The efficiency of PTD-mediated transduction was influenced by the cell type tested, although polylysine homopolymers demonstrate levels of internalization that consistently exceeded those of TAT and arginine homopolymers. Transduction of arginine/lysine-rich PTDs occurred at 4 degrees C and following depletion of cellular ATP pools, albeit generally at reduced levels. Although transduction was reduced in Chinese hamster ovary mutant lines deficient in either heparan sulfate or glycosaminoglycan synthesis, uptake was restored to wild-type levels by incubating target cells with dextran sulfate. The enhancement of transduction by dextran sulfate suggests that electrostatic interactions play an important first step in the process by which PTDs and their cargo traverse the plasma membrane.

Proteolytic processing in a non-lysosomal compartment is required for transcytosis of protein-polylysine conjugates in cultured Madin-Darby canine kidney cells

The transcytosis of horseradish peroxidase, as well as its poly(L-lys) and poly(D-lys) thioether conjugates, was investigated in Strain I Madin-Darby canine kidney (MDCK) cell monolayers grown on 0.4 microns pore size polycarbonate membranes in Costar Transwells. The 3 types of HRP had almost identical rates of transport during the first 2 hr of incubation. However, a significant increase of basal-to-apical transport was detected beginning at 3 hr only in Transwells containing the poly(L-lys) conjugate. This increase was inhibited by colchicine (2 microM) and by the Bowman-Birk protease inhibitor (0.1 mg/ml), but not by NH4Cl (10 mM) or chloroquine (0.1 mM). The increase was abolished either by prior trypsinization of the conjugate or by incubation at 4 degrees C. Ultrafiltration studies indicated that the transcytosed poly(L-lys) conjugate was smaller in size than the original conjugate. These results indicate that the conjugate was processed during transcytosis in a non-lysosomal proteolytic compartment, where its poly(L-lys) moiety was selectively degraded, allowing active peroxidase to be released into the apical medium.

Receptor-mediated magnetic carriers: basis for targeting

A new magnetic microsphere carrier has been formulated that may localize drugs by both biochemical and physical means. The microspheres, prepared from the polysaccharide chitosan, are designed to bind to anionic glycosaminoglycan receptors on the surface of capillary endothelial cells. The microspheres were formulated to have a controlled cationic character and had a mean diameter of 0.70 micron and a magnetite content of 16% (w/w). Formation of complexes between chitosan and heparin and between the microspheres and heparin has been demonstrated. Heparin served as a model glycosaminoglycan. The chitosan:heparin complex ratio was found to be 1:1 based on charge and was formed between ammonium ions on the chitosan and SO3- groups on heparin. Neutralization of the charge on the microspheres prevented their complexation with heparin. The rationale for the use of the delivery system and its potential limitation are discussed.

Binding of polycation DEAE-dextran to Chinese hamster ovary cells induces reversible Ca2+ influx and inhibits capping of concanavalin A acceptor proteins

Binding of the polycation DEAE-dextran to the cell surface of HA-1 CHO cells caused a marked increase in 45Ca2+ exchange influx. The effect was fairly selective for Ca2+, undirectional (efflux was not increased) and was rapidly reversed by treatment with polyanion dextran sulfate. 45Ca2+ influx could not be stimulated by treatment with multivalent lectins or fibronectin. In addition to stimulating 45Ca2+ flux, DEAE-dextran inhibited the capping of concanavalin-A acceptor proteins. Inhibition of capping occurred over the same DEAE-dextran concentration range (20-200 micrograms/ml) which stimulated 45Ca2+ uptake, possibly implicating increased cellular [Ca2+] in the inhibition of concanavalin A acceptor protein capping in this cell type. The profound effect of DEAE-dextran on cellular Ca2+ uptake and the rapid reversal of the effect by dextran sulfate might make the polycation a useful agent for the induction of transient increases in cellular [Ca2+].

Chondrogenesis of limb bud mesenchyme in vitro: stimulation by cations

To analyze the nature of cell-cell interactions in chondrogenesis, two cations that influence these interactions, calcium and poly-L-lysine (PL), were tested for their effects on chondrogenesis in vitro. High density cultures of chick limb bud mesenchyme (Hamilton-Hamburger stages 23/24), were exposed to culture media containing calcium (0.6-3.3 mM) or PL (1-10 micrograms/ml). Both cations stimulated chondrogenesis in a dose-dependent manner, and also promoted cartilage formation in normally non-chondrogenic, low cell density cultures. Chondrogenesis was assayed based on cartilage nodule number, [35S]sulfate incorporation, and expression of type II collagen as detected by immunohistochemistry. The calcium effect was not mimicked by other divalent cations (Cd, Co, Ni, Mg, Mn, and Sr). The effect of PL was dependent on its Mr (greater than or equal to 14K) and charge, and was mimicked by poly-D-lysine but not by lysine or other analogs of PL or lysine (epsilon-amino caproic acid, lysozyme, poly-L-arginine, and spermidine). Calcium and PL probably act by different mechanisms since their effects were additive, and required their presence on different days of culture: calcium acted on Day 1, and PL on Day 2. It is proposed that calcium may play a role in the cell aggregation phase of chondrogenesis whereas PL, or a naturally occurring polypeptide of similar nature, may promote chondrogenesis by crosslinking specific anionic components of the cell surface or extracellular matrix.

Binding and endocytosis of heparin by human endothelial cells in culture

Binding of heparin and low molecular weight heparin fragments (CY 222, Mr range 1500-8000) to human vascular endothelial cells was studied. Primary culture of human umbilical vein endothelial cells and either 125I or 3H-labeled heparin or [125I]CY 222 were used. Slow, saturable and specific binding was found. No other tested glycosaminoglycan, excepting a highly sulfated heparan fraction, was able to compete for heparin binding. Two groups of binding sites for [3H]heparin could be distinguished: one with high affinity (Kd = 0.12 microM) and another with lower affinity (Kd = 1.37 microM) and a relative large capacity of binding (1.16 X 10(7) molecules/cell) was calculated. The Kd for unlabeled heparin, as calculated from competition experiments, was 0.23 microM. Much lower affinity was calculated for unlabeled low molecular weight heparin fragments CY 222 (Kd = 4.3 microM) from competition experiments with [125I]CY 222. The binding reversibility was only partial for unfractionated heparin. Even by chasing with unlabeled compound, a fraction of 25-30% was not dissociable from endothelial cells. This fraction was much lower if incubation was carried out at 4 degrees C. The addition of basic proteins (histones) to the incubation medium greatly enhanced the undissociable binding at 37 degrees C, but not at 4 degrees C. The undissociable fraction of heparin was not available to degradation by purified microbial heparinase. These results suggest that a fraction of bound heparin is internalized by the vascular endothelium.