Effect of sialidase on blood group specificity of hog submaxillary glycoproteins

Exploration of the Sialic Acid World

Sialic acids are cytoprotectors, mainly localized on the surface of cell membranes with multiple and outstanding cell biological functions. The history of their structural analysis, occurrence, and functions is fascinating and described in this review. Reports from different researchers on apparently similar substances from a variety of biological materials led to the identification of a 9-carbon monosaccharide, which in 1957 was designated "sialic acid." The most frequently occurring member of the sialic acid family is N-acetylneuraminic acid, followed by N-glycolylneuraminic acid and O-acetylated derivatives, and up to now over about 80 neuraminic acid derivatives have been described. They appeared first in the animal kingdom, ranging from echinoderms up to higher animals, in many microorganisms, and are also expressed in insects, but are absent in higher plants. Sialic acids are masks and ligands and play as such dual roles in biology. Their involvement in immunology and tumor biology, as well as in hereditary diseases, cannot be underestimated. N-Glycolylneuraminic acid is very special, as this sugar cannot be expressed by humans, but is a xenoantigen with pathogenetic potential. Sialidases (neuraminidases), which liberate sialic acids from cellular compounds, had been known from very early on from studies with influenza viruses. Sialyltransferases, which are responsible for the sialylation of glycans and elongation of polysialic acids, are studied because of their significance in development and, for instance, in cancer. As more information about the functions in health and disease is acquired, the use of sialic acids in the treatment of diseases is also envisaged.

Terminal Sialic Acid Residues on Human Glycophorin A Are Recognized by Porcine Kupffer Cells

BACKGROUND

We have previously shown that recognition of human erythrocytes by porcine Kupffer cells is mediated by a carbohydrate-dependent mechanism. The present study explores the possible ligands existing on human glycophorin A and tests their ability to inhibit erythrocyte rosette formation.

METHODS

Human erythrocytes were tested for ABO and MN specificity and used as targets in a 51Chromium quantitative erythrocyte rosette assay. Monosaccharides present on human glycophorin A, neuraminyl lactoses, bovine and porcine submaxillary mucins (BSM and PSM), and hyaluronic acid as well as proteoglycan N-linked glycosidase F(PNGaseF)- and sialidase A-treated human erythrocyte glycoproteins (hEGP) and human erythrocytes were all tested for inhibitory potential in the rosetting assay.

RESULTS

Porcine Kupffer-cell recognition of human erythrocytes was insensitive to differences in blood groups A, B, O, or MN. At 30 mM, the monosaccharide, N-acetylneuraminic acid, and the trisaccharide mixture, neuraminyl lactoses, disrupted human erythrocyte recognition by 25% and 30%, respectively. A dilution of BSM but not PSM inhibited the rosetting assay by 17% (.2 mg/mL), 33% (1 mg/mL), and 53% (2 mg/mL). The same dilution of hyaluronic acid had no effect on rosetting. Removal of N-linked oligosaccharides from hEGP with PNGaseF did not impair its ability to inhibit the rosetting assay. In contrast, removal of sialic acid completely abrogated its inhibitory ability. Treatment of whole human erythrocytes with sialidase A likewise prevented recognition by porcine Kupffer cells.

CONCLUSIONS

Terminal sialic acid on human erythrocytes is a target recognized by porcine Kupffer cells, suggesting a role for a sialic-acid receptor in innate cellular recognition of xenogeneic epitopes. Inasmuch as this work reveals a carbohydrate-recognition mechanism for cellular rejection, we shed light on a potential new boundary that will need to be overcome within xenotransplantation.

Effect of sialidase on the viability of erythrocytes in circulation

Sialic acid has been detected on the erythrocyte surface of a number of different species of animals. The objective of this investigation was to determine the physiological significance of these sialyl residues to the viability of erythrocytes in circulation. Methods have been described for the determination of total sialic acid on red blood cells and the conditions under which it may be released with sialidase. Chicken, dog, goat, and rabbit were chosen for these studies because of the differences in the amount (3 X 10(6) - 72 X 10(6) resides per erythrocyte), and type (N-acetyl-or N-glycolyl-neuraminic acids) of sialic acid found on the surface of their erythrocytes. Radioactive tagging with Na251CrO4 was used to monitor the effect of sialidase on the viability of erythrocytes upon autologous transfusion. By the two criteria used to assess the viability of erythrocytes-the percentage of erythrocytes surviving 24 hr after the autologous transfusion, and the half-life of those red blood cells in circulation that survive the first 24 h after the autologous transfusion, and the half-life of those red blood cells in circulation that survive the first 24 hr-it is apparent that the presence of sialic acid on the cell surface is crucial for the survival of nonnucleated mammalian erythrocytes. The loss of viability of dog erythrocytes can be elicited by the removal of approximately 10% of the total sialic acid. In marked contrast to the behavior of mammalian erythrocytes, sialidase-treated chicken erythrocytes appear to retain their viability in circulation.