Effects of benzyl alcohol on transferrin and low density lipoprotein receptor mediated endocytosis in leukemic guinea pig B lymphocytes

Modulation of cytokine gene expression by cathelicidin BMAP-28 in LPS-stimulated and -unstimulated macrophages

Apart from direct bacterial killing, antimicrobial host defence peptides (HDPs) exert various other biological activities that also include modulation of immune responses to infection. The bovine cathelicidin BMAP-28 has been extensively studied with regard to its direct antibacterial activity while little is known about its effects on immune cell function. We have investigated its ability to affect inflammatory pathways and to influence the proinflammatory response induced by LPS in RAW 264.7 macrophages, in terms of modulation of TLR4 activation and cytokine gene induction. BMAP-28 on its own elicited ERK1/2, p38 and NF-κB activation leading to upregulation of IL-1β gene expression in these cells, suggesting it has the capacity to activate selected cellular pathways through direct effects on macrophages. As expected based on its in vitro LPS-binding properties, BMAP-28 blocked LPS-induced cytokine gene expression when added to the cell culture in combination with LPS. However it enhanced the induction of IL-1β and IL-6 genes and suppressed that of IFN-β when added prior to or following LPS stimulation over a 30-60 min time interval, or when co-administered with taxol as another TLR4 stimulant. It did not inhibit the expression of IFN-β induced by the TLR3 ligand poly(I:C). Overall these results, and the fact that BMAP-28 increased the LPS-stimulated activation of NF-κB while diminishing that of IRF-3, suggest that the peptide potentiates the early TLR4-mediated proinflammatory cytokine response while inhibiting the TLR4/TRAM/TRIF signaling pathway leading to IRF-3 activation and IFN-β gene expression. Using a TLR4-specific antibody we also found that BMAP-28 decreased the LPS-induced internalization of surface TLR4 required for initiating the TRAM/TRIF signaling pathway, which provides a mechanism for the inhibitory effect of the peptide on the TLR4/TRAM/TRIF pathway.

Membrane cholesterol modulates the fluid shear stress response of polymorphonuclear leukocytes via its effects on membrane fluidity

Continuous exposure of polymorphonuclear leukocytes (PMNLs) to circulatory hemodynamics points to fluid flow as a biophysical regulator of their activity. Specifically, fluid flow-derived shear stresses deactivate leukocytes via actions on the conformational activities of proteins on the cell surface. Because membrane properties affect activities of membrane-bound proteins, we hypothesized that changes in the physical properties of cell membranes influence PMNL sensitivity to fluid shear stress. For this purpose, we modified PMNL membranes and showed that the cellular mechanosensitivity to shear was impaired whether we increased, reduced, or disrupted the organization of cholesterol within the lipid bilayer. Notably, PMNLs with enriched membrane cholesterol exhibited attenuated pseudopod retraction responses to shear that were recovered by select concentrations of benzyl alcohol (a membrane fluidizer). In fact, PMNL responses to shear positively correlated (R(2) = 0.96; P < 0.0001) with cholesterol-related membrane fluidity. Moreover, in low-density lipoprotein receptor-deficient (LDLr(-/-)) mice fed a high-fat diet (a hypercholesterolemia model), PMNL shear-responses correlated (R(2) = 0.5; P < 0.01) with blood concentrations of unesterified (i.e., free) cholesterol. In this regard, the shear-responses of PMNLs gradually diminished and eventually reversed as free cholesterol levels in blood increased during 8 wk of the high-fat diet. Collectively, our results provided evidence that cholesterol is an important component of the PMNL mechanotransducing capacity and elevated membrane cholesterol impairs PMNL shear-responses at least partially through its impact on membrane fluidity. This cholesterol-linked perturbation may contribute to dysregulated PMNL activity (e.g., chronic inflammation) related to hypercholesterolemia and causal for cardiovascular pathologies (e.g., atherosclerosis).

Effects of Heparin Administration on Trypanosoma brucei gambiense Infection in Rats

We examined whether heparin administration influences in vivo trypanosome proliferation in infected rats. Administration of heparin every 8 hr via cardiac catheter inhibited growth of Trypanosoma brucei gambiense and prolonged survival of treated rats. Heparin administration increased lipoprotein lipase activity, high-density lipoprotein (HDL) concentration in the blood, and haptoglobin messenger RNA content of the liver. The presence of heparin in culture media did not directly affect proliferation of trypanosomes in vitro. However, the addition of plasma from infected rats treated with heparin to culture media decreased the number of trypanosomes. This effect was decreased by incubating the trypanosomes with benzyl alcohol, a known inhibitor of receptor-mediated endocytosis of lipoprotein. These data suggested that heparin administration reduced the number of trypanosomes in infected rats. Trypanosome lytic factor, a HDL and haptoglobin-related protein, protects humans and some animals from infection by Trypanosoma brucei brucei. In rats, increases in HDL and haptoglobin may affect the proliferation of T. b. gambiense.

Benzyl alcohol differently affects fluid phase endocytosis and exocytosis in renal epithelial cells

The effects of benzyl alcohol, a local anaesthetic commonly used for modification of membrane fluidity, on fluid phase endocytosis and on exocytosis have been investigated in MDCK cells. Fluid phase endocytosis in confluent cells monolayer grown on solid support was determined, at 37 degrees C, by the uptake of the fluorescent dye Lucifer Yellow (LY). Exocytosis was estimated from the release of LY by cells preloaded with the dye. Addition of benzyl alcohol resulted in a concentration dependent inhibition of fluid phase endocytosis. For 30 mM benzyl alcohol, the inhibition obtained (83%) compared with that produced by preincubating the cells in a solution made hypertonic with 0.25 M sucrose. The inhibitory effect of benzyl alcohol was reversed within 30 min by washing. Endocytosis inhibition by benzyl alcohol was also observed in LLC-PK1 cells and OK cells, two renal epithelial cell lines of proximal tubule origin. In contrast, benzyl alcohol had no effect on exocytosis in LLC-PK1 cells, a limited but significant (15% at 30 mM) stimulatory effect on exocytosis in MDCK cells and a marked stimulatory effect (75% at 30 mM) in OK cells. These data demonstrate that benzyl alcohol affects endocytosis and exocytosis processes in renal epithelial cells. They suggest that membrane fluidity may alter membrane trafficking in living renal epithelial cells.

Quantitative comparison between aminophospholipid translocase activity in human erythrocytes and in K562 cells

Spin-labeled phospholipids were used to determine the transbilayer movement of phospholipids in human erythrocytes, in K562 cells and in human neonatal red cells. The erythroleukemia cell line, K562, as well as human neonatal red cells, which are rich in reticulocytes, were considered as representative of human erythrocyte precursor cells. In the nucleated cells, the difference between outside-inside movement of aminophospholipids and that of phosphatidylcholine or sphingomyelin analogues allowed us to discriminate between lipid internalization due to aminophospholipid translocase activity and to endocytosis. From the initial rates of aminophospholipid inward movement, we inferred that the activity of the aminophospholipid translocase is higher in the precursor cells than in mature erythrocytes.

Influence of conjugation of doxorubicin to transferrin on the iron uptake by K562 cells via receptor-mediated endocytosis

The influence of conjugation of doxorubicin to holotransferrin on the receptor-mediated endocytosis of and on the iron uptake from transferrin was studied using K562 cells. 125I-labelled transferrin and doxorubicin-transferrin conjugates were used in the binding, dissociation, and ligand-exchange experiments at 0 degree C, and 59Fe,125I-labelled (double-labelled) ligands were used in the endocytosis, iron uptake, and recycling experiments at 37 degrees C. The binding affinity of conjugates was about half of that of transferrin. Binding of 125I-labelled ligands was blocked by both unlabelled ligands to the same degree, however, it was not blocked at all by an 8000-fold excess of doxorubicin. After saturation bindings, slightly more 125I-labelled conjugates dissociated from the surface of cells than transferrin. Exchange of 125I-labelled ligands for unlabelled ligands resulted in different EC50 values (defined as the concentration of unlabelled ligand at which half as much radioligand is exchanged for unlabelled ligand as would be exchanged at infinitely high concentration of unlabelled ligand under similar assay conditions). While transferrin exchanged transferrin with an EC50 value close to the binding affinity, conjugates exchanged conjugates with much lower efficiency. The heterolog exchange experiments yielded EC50 values inbetween the two extrema. For studying iron uptake, K562 cells were loaded with the double-labelled ligands either at 37 degrees C (endosome-loading only) or at 0 degree C (surface-loading only). Results obtained for the endocytosis of, the iron uptake from, and the recycling of double-labelled ligands indicate that (a) the rate of iron uptake is smaller from conjugates than from transferrin, (b) there are at least two parallel recycling processes for both ligand.receptor complexes, and (c) each time constant characterizing the different steps of iron uptake via receptor-mediated endocytosis is smaller for conjugates than for transferrin (or, the half times characterizing the different steps are higher for conjugates than for transferrin). Endocytosis and iron uptake were unaffected by free doxorubicin (12.5 microM) or colchicine (1 mM). Benzyl alcohol (30 mM) slowed down the rate of both endocytosis and iron uptake, while dithiothreitol (5 mM) decreased the rate of iron uptake and increased the rate of endocytosis. N-Ethylmaleimide (1 mM) completely stopped both endocytosis and iron uptake. The results suggest that the binding of conjugates to the surface of cells is governed by the binding of the transferrin part of conjugates to the transferrin receptor. However, conjugation of doxorubicin to transferrin seems to influence all properties of transferrin.(ABSTRACT TRUNCATED AT 400 WORDS)

Enhancement of intracellular uncoating of adenovirus in HeLa cells in the presence of benzyl alcohol as a membrane fluidizer

The early extra- and intra-cellular interaction between adenovirus type 2 and HeLa cells was studied in the presence of benzyl alcohol as a fluidizing agent. The process of virus attachment and internalization were not affected at 5-15 mM of benzyl alcohol at 25 degrees C. Under the same conditions an enhancement by 45% at the most was demonstrated for the cell-mediated virion uncoating. By completely blocking virion internalization with 50 mM azide the uncoating was reduced to 20% of the normal level. The remaining surface-located uncoating was not affected by benzyl alcohol. It was demonstrated that an enhancement of the intracellular virion uncoating was followed by a raised production of the hexon antigen, which was interpreted as an increase in the specific infectivity of the virus.

Effect of benzyl alcohol on phospholipid transverse mobility in human erythrocyte membrane

The effect of benzyl alcohol on the transverse mobility and repartition of phospholipids in the human erythrocyte membrane was investigated using electron spin resonance and morphological modification of red blood cells. Transmembrane internalization rates and equilibrium distribution in red blood cells of short-chain spin-labeled phosphatidylcholine, phosphatidylethanolamine and phosphatidylserine were strongly modified by treatment with 10-70 mM benzyl alcohol. A dual effect was observed: (a) at 4 degrees C and 37 degrees C there was an N-ethylmaleimide-sensitive, long lasting and fully reversible increase in the spin-labeled phosphatidylserine and phosphatidylethanolamine internalization rate; (b) at 37 degrees C, an enhancement of N-ethylmaleimide-insensitive fluxes of all the labeled phospholipids through the membrane occurred. Both effects were dose-dependent. Erythrocytes submitted to benzyl alcohol incubation also showed dose-dependent shape changes: an immediate one from discocytes to echinocytes, followed by a slower N-ethylmaleimide- and ATP-dependent change to stomatocytes. Moreover, benzyl alcohol treatment was shown to lead to enhanced hydrolysis of intracellular ATP. All the effects of benzyl alcohol can be described as an accumulation of labeled phosphatidylethanolamine (and labeled phosphatidylcholine at 37 degrees C) in the inner leaflet. This can be interpreted as a perturbation of the erythrocyte membrane, leading to an energy-consuming specific increase in aminophospholipid translocase activity, in addition to a slow and passive bidirectional flux of all phospholipids at 37 degrees C.

The influence of transferrin binding to L2C guinea pig leukemic lymphocytes on the endocytosis cycle kinetics of its receptor

The parameters regulating the internalization and recycling of transferrin-specific receptors were determined in guinea pig leukemic B lymphocytes, in the absence or presence of ligand. We show that after the cells were purified, 45-56% of the total receptors were on the cell surface. In the absence of transferrin, unoccupied receptors are quickly internalized (rate constant, 0.12 min-1) whereas their recycling is much slower (rate constant, 0.026 min-1). This difference between endocytosis and recycling rates leads to a balanced receptor distribution with only 22% of the total receptors outside after incubation of the cells for 20-30 min at 37 degrees C. The internalization rate of occupied receptors, measured in the presence of transferrin is faster (rate constant, 0.21 min-1) than that of unoccupied receptors calculated in the absence of transferrin (0.12 min-1; see above). On the other hand, mere binding of transferrin to its receptor, without internalization, arrested by cytoplasm acidification, is sufficient to induce a large increase (by a factor of seven) in the recycling rate of unoccupied internal receptors from 0.026 min-1 to 0.17 min-1. Thus, in these lymphocytes, transferrin mobilizes internal receptors by modifying the kinetic rates of internalization and recycling, leading to a new equilibrium between external and internal receptors.