Permeabilization and calcium-dependent activation of rabbit polymorphonuclear leukocytes by poly-L-arginine

Design, synthesis, and biocompatibility of an arginine-based polyester

Polycations are very useful in biotechnology. However, most existing polycations have high toxicity that significantly limits their clinical translation. We designed poly(ethylene argininylaspartate diglyceride) (PEAD) that is based on arginine, aspartic acid, glycerol, and ethylene glycol. A set of in vitro assays demonstrated that PEAD exhibited no cytotoxicity at 1 mg/mL, which is at least 100 times higher than the widely used polycation-polyethylenimine. Subcutaneous injection of 1 mg PEAD in rats did not cause an adverse response acutely or after 4 weeks. Zeta potential measurements revealed that PEAD has high affinity to biological polyanions such as DNA and hyaluronic acid. This polycation represents a new platform of biocompatible polycations that may lead to clinical innovations in gene therapy, controlled release, tissue engineering, biosensors, and medical devices.

The role of calcium ions in DEAE-dextran-induced stimulation of neutrophil migration

The polycation DEAE-dextran caused a strong enhancement of non-directed migration of rabbit peritoneal neutrophils. The activating effect on migration was completely annulled in the presence of the polyanion poly-D-glutamic acid, indicating that the effect depended on the positive charge of the macromolecule. Chemotaxis activated by the chemotactic peptide fMLP was only slightly affected by the polycation. In contrast with fMLP-activation, stimulation of migration by DEAE-dextran was dependent on the presence of extracellular Ca2+. DEAE-dextran also stimulated migration of electroporated neutrophils. The stimulation was absent when calcium was not present; the increase of migration was strongest at Ca(2+)-concentrations between 100 nM and 1 microM Ca2+. This indicates that the requirement for extracellular Ca2+ in intact cells is a reflection of the intracellular requirement. Several types of calcium blockers gave a moderate inhibition of DEAE-dextran activated migration. Activation of migration by DEAE-dextran of electroporated neutrophils was completely inhibited by calcium channel blockers, at very low concentrations. The results suggest that both Ca(2+)-fluxes across the plasma membrane and Ca2+ from intracellular stores are required for DEAE-activated migration, and that the calcium from the intracellular source is required on a place where the extracellular Ca2+ has no, or limited, admittance.

Killing of endothelial cells and release of arachidonic acid. Synergistic effects among hydrogen peroxide, membrane-damaging agents, cationic substances, and proteinases and their modulation by inhibitors

51Chromium-labeled rat pulmonary artery endothelial cells (EC) cultivated in MEM medium were killed, in a synergistic manner, by mixtures of subtoxic amounts of glucose oxidase-generated H2O2 and subtoxic amounts of the following agents: the cationic substances, nuclear histone, defensins, lysozyme, poly-L-arginine, spermine, pancreatic ribonuclease, polymyxin B, chlorhexidine, cetyltrimethyl ammonium bromide, as well as by the membrane-damaging agents phospholipases A2 (PLA2) and C (PLC), lysolecithin (LL), and by streptolysin S (SLS) of group A streptococci. Cytotoxicity induced by such mixtures was further enhanced by subtoxic amounts either of trypsin or of elastase. Glucose-oxidase cationized by complexing to poly-L-histidine proved an excellent deliverer of membrane-directed H2O2 capable of enhancing EC killing by other agonists. EC treated with rabbit anti-streptococcal IgG were also killed, in a synergistic manner, by H2O2, suggesting the presence in the IgG preparation of cross-reactive antibodies. Killing of EC by the various mixtures of agonists was strongly inhibited by scavengers of hydrogen peroxide (catalase, dimethylthiourea, MnCl2), by soybean trypsin inhibitor, by polyanions, as well as by putative inhibitors of phospholipases. Strong inhibition of cell killing was also observed with tannic acid and by extracts of tea, but less so by serum. On the other hand, neither deferoxamine, HClO, TNF, nor GTP gamma S had any modulating effects on the synergistic cell killing. EC exposed either to 6-deoxyglucose, puromycin, or triflupromazin became highly susceptible to killing by mixtures of hydrogen peroxide with several of the membrane-damaging agents. While maximal synergistic EC killing was achieved by mixtures of H2O2 with either PLA2, PLC, LL, or with SLS, a very substantial release of [3H]arachidonic acid (AA), PGE2, and 6-keto-PGF occurred only if a proteinase was also added to the mixture of agonists. The release of AA from EC was markedly inhibited either by scavengers of H2O2, by proteinase inhibitors, by cationic agents, by HClO, by tannic acid, and by quinacrin. We suggest that cellular injury induced in inflammatory and infectious sites might be the result of synergistic effects among leukocyte-derived oxidants, lysosomal hydrolases, cytotoxic cationic polypeptides, proteinases, and microbial toxins, which might be present in exudates. These "cocktails" not only kill cells, but also solubilize AA and several of its metabolites. However, AA release by the various agonists can be also achieved following attack by leukocyte-derived agonists on dead cells. It is proposed that treatment by "cocktails" of adequate antagonists might be beneficial to protect against cellular injury in vivo.

Strontium and barium induce exocytosis in electropermeabilized neutrophils

Calcium, strontium and barium induced an exocytotic response in electropermeabilized rabbit neutrophils while magnesium was without any effect. The extent of enzyme release was found to depend upon the concentration of these cations. For all cations, an optimum concentration was found with the same maximum enzyme release. At concentrations higher than optimum a decrease in lysozyme release was observed. Efficiency to induce enzyme release was in the order: Ca2+ > Sr2+ > Ba2+. Enzyme release was significantly enhanced by guanosine-5'-[gamma-thio]triphosphate (GTP gamma S) resulting in a shift to the left of the dose/response curve. The enhancement by GTP gamma S was strongest with Ca2+, was less with Sr2+, and was very little with Ba2+. The time course of lysozyme release was the same for Ca2+, Sr2+, and Ba2+ in the presence and absence of GTP gamma S when suboptimal cation concentrations were used. A decrease in responsiveness to the effectors after electropermeabilization was observed with Ca2+, Sr2+ and Ba2+ in the presence and absence of GTP gamma S. The lysozyme release induced by the different cations was not inhibited by the protein kinase C inhibitor staurosporine and was slightly affected by pertussis toxin. Ca2+ and Sr2+, but not Ba2+, potentiated formyl-methionyl-leucyl-phenylalanine (fMet-Leu-Phe) induced enzyme release in intact neutrophils. The divalent cation ionophore A23187 induced enzyme release in the presence of Ca2+ and Sr2+ but not in the presence of Ba2+. The results obtained with electropermeabilized neutrophils indicate that Sr2+ and Ba2+ can act as substitutes for Ca2+ in activating exocytosis, and that permeabilized neutrophils provide the best tool to investigate the effects of alkaline earth ions in exocytosis.

Exocytosis in electropermeabilized neutrophils. Responsiveness to calcium and guanosine 5'-[gamma-thio]triphosphate

Electropermeabilized neutrophils were used to study the exocytotic response in rabbit neutrophils. Enzyme release from electropermeabilized neutrophils could be induced by elevating the Ca2+ concentration. Ca(2+)-induced secretion was significantly enhanced by guanosine 5'-[gamma-thio]triphosphate (GTP[S]) in a concentration-dependent manner. The effect of GTP[S] could be blocked by guanosine 5'-[beta-thio]diphosphate (GDP[S]) and was not affected by pertussis toxin. GTP[S] did not induce enzyme release in the absence of Ca2+. Induction of an exocytotic response did not require addition of ATP. However, neutrophils permeabilized in the absence of ATP became refractory to stimulation due to a reduction in their affinity for Ca2+. Responsiveness to the effectors Ca2+ or Ca2+ + GTP[S] could be prolonged or restored by ATP. ATP was not the only agent that prolonged responsiveness; other nucleotides and inorganic phosphates were also effective. The protein kinase C inhibitors staurosporine and 1-O-hexadecyl-2-methyl-sn-glycerol did not inhibit exocytosis and had only a small effect on the prolongation and restoration of responsiveness by ATP. A hypothesis is presented suggesting that the loss of responsiveness is caused by dephosphorylation and that the restoration or prolongation of responsiveness is not mediated by protein kinase C. It is possible that an as yet unidentified Ca(2+)-binding protein is dephosphorylated, resulting in a decrease in Ca2+ affinity.

Protamine-induced permeability changes in the neutrophil plasma membrane as the basis of activation of exocytosis

Protamine induces a gradual change in plasma membrane permeability in rabbit neutrophils, which is evident from the increase of indol fluorescence, and the leakage of quin2 from quin2-loaded neutrophils. The influx of extracellular Ca2+ into the neutrophil provides an explanation for exocytosis which occurs in the presence of Ca2+ and protamine. The dependence of exocytosis on Ca2+ concentration follows the same pattern as is observed in neutrophils permeabilized by other means. In the absence of Ca2+, and in the presence of protamine, La3+ has an activating effect on exocytosis. At higher concentrations La3+ inhibits exocytosis that occurs in the presence of Ca2+ and protamine, as do some other metal ions. The resemblance between the membrane effects of a number of toxins, as reported in literature, and protamine-induced membrane damage suggests that they occur via the same mechanism.

Cytochalasin B-induced superoxide production in polycation-treated neutrophils

Cytochalasin B alone induces little superoxide production in intact rabbit peritoneal neutrophils. The cytochalasin causes a strong production of superoxide in cells treated with membrane-permeabilizing polycations. Several polycations were able to express the activating effect of cytochalasin B. Especially the poly-L-arginine with a molecular weight of 24,000 proved to be effective. The effectiveness of some polycations is limited because they inactivate the superoxide-generating oxidase system of the neutrophil. Cytochalasin B-induced superoxide production starts at poly-L-arginine concentrations that cause a change of membrane permeability. At the concentrations of cytochalasin B used in our experiments, the binding of [3H]cytochalasin B is not enhanced in poly-L-arginine-treated cells as compared with control cells. Activation of superoxide production by cytochalasin B in polycation-treated neutrophils occurs both in the presence or absence of extracellular Ca2+. When the cells are pretreated with agents that known to interfere with intracellular Ca2+, the subsequent activation is strongly inhibited, suggesting a role for intracellular Ca2+ in cytochalasin B-induced activation. It is suggested that cytochalasin B alone is not able to activate all the steps that eventually result in complete activation of the superoxide-generating oxidase and that membrane perturbation by polycation provides activation of the remaining steps.

Changes of plasma membrane permeability in neutrophils treated with polycations

The effects of the polycations poly-L-arginine, poly-L-lysine, and poly-ethyleneimine on rabbit neutrophil membrane permeability were compared. LDH release, quin2 release from quin2-loaded cells, and increase of indo 1 fluorescence were considered as measures for changes in membrane permeability. All polycations cause abundant LDH release. Quin2 release occurs more rapidly than LDH release, and the increase of indo 1 fluorescence is even faster. Apparently polycation-induced permeability changes occur gradually, allowing the influx (or efflux) of small molecules more rapidly than larger ones. A number of divalent and trivalent cations inhibit polycation-induced LDH and quin2 release in a way that resembles the inhibition of other cytotoxic agents described in literature. In the absence of extracellular Ca2+, the polycations induce little lysozyme release. In the presence of extracellular Ca2+, there is abundant lysozyme release, indicating that the influx of Ca2+ causes exocytosis. Exocytosis still occurs when Ca2+ is added some time after polycation addition, indicating that polycation treatment leaves the cells largely intact. All polycations tested have in common that they cause gradual changes in the permeability of the plasma membrane only, which opens the possibility to use them as membrane-permeabilizing agents for the study of Ca(2+)-induced exocytosis.

Induction of superoxide production in rabbit neutrophils by a stable analogue of GTP

Treatment of rabbit neutrophils with the stable GTP analogue GTP gamma S results in generation of superoxide. Whereas poly-L-arginine, an agent known to damage the plasma membrane, has only a small effect by itself, a strong and synergistic enhancement of superoxide generation is obtained in the presence of GTP gamma S and poly-L-arginine. The effect is potentiated in the presence of NADPH. Other nucleotides, such as GTP, are not effective in inducing superoxide generation. The results indicate that the stable guanine nucleotide GTP gamma S may activate superoxide production in rabbit neutrophils, and that this effect is evident if the plasma membrane has been permeabilized by poly-L-arginine, allowing an easy entry of GTP gamma S into the cell.

The involvement of ionic interactions during asbestos-induced enzyme release from polymorphonuclear leukocytes

Chrysotile asbestos permeabilizes the plasma membrane of rabbit polymorphonuclear leukocytes (PMNs) which is evident from the release of the cytoplasmic enzyme lactate dehydrogenase (LDH) from the cell. When Ca2+ is present in the medium exocytosis is observed, evident from the release of the granule associated enzyme lysozyme which is not liberated in the absence of Ca2+. Asbestos-induced enzyme release is inhibited by polyanions or by removal of positive charges on asbestos, and resembles enzyme release induced by synthetic polycations. Pretreatment of PMNs with neuraminidase does not affect the ability of asbestos to induce enzyme release from these cells. Asbestos induces release of glucose from glucose-loaded liposomes, and this effect can be inhibited by the polyanion poly-D-glutamic acid. The results are compatible with the view that positive charges play a decisive role in the interaction between PMNs and asbestos, and that the primary target of asbestos could be the lipid bilayer of the membrane. The interaction results in a permeabilized plasma membrane. When Ca2+ is present in the medium it moves into the cell and causes exocytosis of the granule enzyme lysozyme. Inhibition of cytotoxicity by polyanion may cause a diminished Ca2+-influx and hence inhibition of lysozyme release.