Cell surface chemistry of arterial endothelium and blood monocytes in the normolipidemic rabbit

Chemical mapping of the luminal surface of normal rabbit aortic and coronary endothelium was investigated cytochemically to establish a baseline for further comparison with the biochemical changes possibly induced by the experimental hypercholesterolemia. Morphometric analysis showed that in the aortic endothelium the plasma membrane exposes a large number of uniformly-distributed positively-charged groups of high pKa, and a heterogeneous pattern of dense anionic groups of low pKa. Among the latter, only a third was represented by neuraminidase-cleavable sialic acids. These are constituted by various classes of N-, and O-substituted sialyl residues in glycoconjugates, most frequent being those non-O-acetylated at C8 or C9. Among the oligosaccharides detected with lectins, very abundant were the glycoconjugates containing mannosyl and subterminal galactosyl, whereas N-acetyl-glucosamine, terminal galactosyl and N-acetyl-galactosaminyl moieties were rather poorly represented. The density of the latter two markedly increased after its unmasking by neuraminidase treatment. Coated pits contained both anionic and cationic sites, but only few sialic acids and saccharide residues in significantly lower amounts than plasma membrane. The membrane of plasmalemmal vesicles displayed a high number of cationic sites and mannosyl residues, but very few anionic groups, sialyl residues, and galactosyl and N-acetyl-galactosaminyl moieties. Coronary endothelium displayed a chemical pattern similar to aorta, with some differences, especially in the frequency of some oligosaccharides. Vena cava was low in acidic groups but rather rich in galactose. Plasmalemmal vesicles were only occasionally labeled by the probes used. Monocyte surface exhibited a high density of anionic sites, and binding sites for wheat germ agglutinin and Ricinus communis agglutinin. No mononuclear cells were observed adhering to endothelial surface.

Prelesional events in atherogenesis. Changes induced by hypercholesterolemia in the cell surface chemistry of arterial endothelium and blood monocytes, in rabbit

We investigated the modifications that diet-induced hypercholesterolemia, in rabbit, can produce in the cell surface charge and chemistry of arterial endothelium (E) and blood monocytes (M). Weekly, up to 8 weeks, after blood samples were taken for lipid analysis and blood cell preparation, the vasculature was washed free of blood and the endothelial luminal surface (ES) exposed to cytochemical probes for detecting charged groups, sialoconjugates and oligosaccharides. After fixation in situ, specimens collected from lesion-prone regions (aortic arch and coronary artery) and vena cava, were processed for electron microscopy. Morphometric analysis of tracer distribution on endothelium of nonlesional and lesional areas occurring in various stages of structural alterations, showed a remarkable resistance of the cell coat to very high level of serum cholesterol. In nonlesional zones the E surface charge and glycoconjugates were not significantly changed. In lesional areas, including those with forming fatty streaks, while cationic sites, galactosyl-, and N-acetyl-galactosaminyl residues were not altered whereas mannosyl moieties increased in density. A reduction in anionic groups and sialoconjugates appeared only after advanced extracellular and intracellular accumulation of lipoprotein-derived material and stromal proliferation developed in the intima. Moreover, these ES changes were usually restricted to the relatively rare E cells heavily loaded with lipid inclusions. The modulations were generally paralleled by comparable variations in the M surface. Regardless the extent of surface charge reduction, monocytes continued to migrate and foam cells to egress from the vessel wall. The results suggest that the onset and progression of early intimal lesions are not preceded but followed by significant restricted alterations in cell surface charge and glycoconjugates of arterial endothelium and monocytes.

Charge effect on binding, uptake and transport of ferritin through fenestrated endothelium

The binding, uptake and transport of hydrosoluble macromolecules as a function of their electric charge have been investigated in mouse pancreatic exocrine fenestrated endothelium. After intravenous injection of ferritin derivatives with different isoelectric points (3.7, 4.5, 7.0 and 8.4) specimens of pancreas were collected at 5, 25, 45 and 60 min and processed for electron microscopy. Although the concentrations (10 mg/ml) and injected volumes (1 ml/100 g body weight) were identical, the tracers with similar molecular weight (Mr approximately 960,000), but with different net electric charge, followed different routes in endocytotic and transcytotic processes. The endothelial cell internalizes ferritins into multivesicular bodies and lysosomes. While anionic ferritins are endocytosed via plasmalemmal vesicles (fluid phase endocytosis), the cationic derivatives are taken up exclusively by coated pits (adsorptive endocytosis). The anionic and neutral macromolecules seem to be transcytosed via plasmalemmal vesicles. The circulating polycations are aggregated by plasma proteins and transcytosed as such either in fluid phase by large vacuoles, or by adsorption on the coated structures. The first mechanism is physiological, the latter probably appears in unusual conditions by which the endothelium participates in the plasma clearance. Our findings indicate that, for the transport of macromolecules, the capillary endothelium can be accounted not only as a size barrier but also as a selective-differentiated charge barrier with complex and multiple mechanisms for the modulation of its transport systems. The endocytotic and transcytotic processes undergo the effect of net electric charge of the plasma components.

Cationic heme undecapeptide as stain for detecting glycosaminoglycans on cellulose acetate strips

A rapid and sensitive method has been developed for detecting glycosaminoglycans on cellulose acetate strips. The method is based on the electrostatic interactions between glycosaminoglycans and cationic heme undecapeptide. The complexes are identified by peroxidatic reaction using 3,3'-diaminobenzidine as H2 donor. The detection limit is 2.5-10 ng for sulfated glycosaminoglycans and 60 ng for hyaluronic acid. The sensitivity of this method is higher than of those using Alcian blue or toluidine blue (500 ng).

Anionized and cationized hemeundecapeptides as probes for cell surface charge and permeability studies: differentiated labeling of endothelial plasmalemmal vesicles

To obtain small membrane markers easily accessible to the charged groups of the cell surface, we prepared, from hemeundecapeptide (HUP), three derivatives that maintain the peroxidatic activity: the anionized hemeundecapeptide, Mr 1,963, estimated diameter 1.68 nm, pl 3.5, for the detection of basic groups; and both a cationized hemeundecapeptide containing predominantly tertiary amino groups, Mr 2,215, estimated diameter 1.75 nm, pl 9.0, and a cationized hemeundecapeptide containing only primary amino groups, Mr 2,271, estimated diameter 1.75 nm, pl 10.6, for labeling acidic residues. The markers were perfused in situ in mice to label the luminal surface of fenestrated endothelium of pancreatic capillaries. Specimens were processed through the cytochemical reaction for peroxidatic activity and examined by electron microscopy. The anionized HUP and HUP (pl 4.85) marked the plasmalemma proper, the coated pits, and the membrane and diaphragms of plasmalemmal vesicles and transendothelial channels. The cationized HUP containing predominantly tertiary amino groups (pl 9.0) decorated all cell surface components with the exception of plasmalemmal vesicles and channels; the latter were, however, labeled by the cationized HUP containing only primary groups (pl 10.6), which suggests that these structures contain on their luminal surface very weak acidic residues of high pKa values. The fact that the membrane of plasmalemmal vesicles can discriminate against permeant cationic macromolecules only up to a pl of approximately 9.0 indicates that in the electrostatic restriction there is a charge limit. In the case of fenestrated capillary endothelium, the upper charge limit seems to be a pl of approximately 9.0. In these vessels, the charge discrimination is effective for molecules as small as 2 nm.