Preparation and immunological studies of protein conjugates of N-acylneuraminic acids

Chefalo, Peter J.; Pan, Yu; Nagy, Nancy; Harding, Clifford V.; Guo, Zhongwu

doi:10.1023/b:glyc.0000033997.01760.b9

Cited by 35 publications

(29 citation statements)

References 37 publications

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“…proposed by Guo and colleagues (45). If these modified Sias incorporate into leukemic cells as efficiently as Neu5Gc, they may provide an advantage over our proposed Neu5Gc targeting, which could damage other normal cells that already have low levels of Neu5Gc.…”

Section: Discussionmentioning

confidence: 79%

Effects of Natural Human Antibodies against a Nonhuman Sialic Acid That Metabolically Incorporates into Activated and Malignant Immune Cells

Nguyen

Tangvoranuntakul

Varki

2005

The Journal of Immunology

136

144

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Humans are genetically incapable of producing the mammalian sialic acid N-glycolylneuraminic acid (Neu5Gc), due to an inactivating mutation in the enzyme synthesizing it. Despite this, human cells and tissues appear capable of metabolically incorporating Neu5Gc from exogenous sources, including dietary red meat and dairy products. All normal humans studied are now shown to have circulating Abs against Neu5Gc, with marked differences in isotype levels. The question arises whether such Abs can adversely affect Neu5Gc-expressing human cells or tissues. In this study, we show that although normal human PBMC do not incorporate Neu5Gc during in vitro incubation, activated T cells do. Primary human leukemia cells and human leukemic cell lines are even more efficient at incorporation. Human sera containing naturally high levels of anti-Neu5Gc IgG Abs (hereafter abbreviated GcIg) deposited complement on Neu5Gc-expressing leukemic cells and activated T cells, but not on normal cells. The binding of GcIg resulted in complement-mediated cytotoxicity, which was inhibited by heat inactivation. Low anti-Neu5Gc IgG-containing human sera did not mediate any of these effects. Mixed killing assays confirmed the 15-fold selective killing of leukemic cells over PBMC by GcIg following Neu5Gc feeding. This approach could potentially serve as novel way to target malignant cells for death in vivo using either natural Abs or anti-Neu5Gc Abs prepared for this purpose. Further studies are needed to determine whether deposition of natural GcIg and complement can also target healthy proliferating immune cells for death in vivo following incorporation of dietary Neu5Gc.

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Section: Discussionmentioning

confidence: 79%

Effects of Natural Human Antibodies against a Nonhuman Sialic Acid That Metabolically Incorporates into Activated and Malignant Immune Cells

Nguyen

Tangvoranuntakul

Varki

2005

The Journal of Immunology

136

144

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“…Thus, the mechanism by which Neu5Gc is incorporated into human cells is of potentially great importance. Further studies of this process are also relevant both to the ongoing attempts by various groups to incorporate different kinds of unnatural sialic acids into cultured cells (43,(71)(72)(73) and also to our efforts to understand how exogenous dietary Neu5Gc gain entry into normal human tissues. In this regard it is of note that Neu5Gc accumulation appears to be enhanced in naturally occurring tumors and in fetal tissues.…”

Section: The Lysosomal Sialic Acid Transporter Is Required For Exportmentioning

confidence: 99%

Mechanism of Uptake and Incorporation of the Non-human Sialic Acid N-Glycolylneuraminic Acid into Human Cells*

Bardor¹,

Nguyen

Díaz

et al. 2005

Journal of Biological Chemistry

343

321

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N-Glycolylneuraminic acid (Neu5Gc) is a widely expressed sialic acid in mammalian cells. Although humans are genetically deficient in producing Neu5Gc, small amounts are present in human cells in vivo. A dietary origin was suggested by human volunteer studies and by observing that free Neu5Gc is metabolically incorporated into cultured human carcinoma cells by unknown mechanisms. We now show that free Neu5Gc uptake also occurs in other human and mammalian cells. Inhibitors of certain non-clathrin-mediated endocytic pathways reduce Neu5Gc accumulation. Studies with human mutant cells show that the lysosomal sialic acid transporter is required for metabolic incorporation of free Neu5Gc. Incorporation of glycosidically bound Neu5Gc from exogenous glycoconjugates (relevant to human gut epithelial exposure to dietary Neu5Gc) requires the transporter as well as the lysosomal sialidase, which presumably acts to release free Neu5Gc. Thus, exogenous Neu5Gc reaches lysosomes via pinocytic/endocytic pathways and is exported in free form into the cytosol, becoming available for activation and transfer to glycoconjugates. In contrast, N-glycolylmannosamine (ManNGc) apparently traverses the plasma membrane by passive diffusion and becomes available for conversion to Neu5Gc in the cytosol. This mechanism can also explain the metabolic incorporation of chemically synthesized unnatural sialic acids, as reported by others. Finally, to our knowledge, this is the first example of delivery to the cytosol of an extracellular small molecule that cannot cross the plasma membrane, utilizing fluid pinocytosis and a specific lysosomal transporter. The approach could, thus, potentially be generalized to any small molecule that has a specific lysosomal transporter but not a plasma membrane transporter.Sialic acid (Sia) 1 is a generic name for a family of acidic nine carbon sugars typically found as the outermost units of glycan chains on the vertebrate cellular glycocalyx and on secreted glycoproteins (1, 2). Their location and widespread occurrence on all vertebrate cells allow them to be involved in processes such as pathogen binding, inflammation, immune response, and tumor metastasis (3-8).There are more than 50 kinds of Sias known in nature (2, 9, 10). Most are derived via biosynthetic modification of a Sia called N-acetylneuraminic acid (Neu5Ac) (3,4,9). The addition of a single oxygen atom to the N-acetyl group of Neu5Ac gives a very common variation called N-glycolylneuraminic acid (Neu5Gc). The surfaces of most primate cell types studied to date are dominated by two major Sias, which are Neu5Ac and Neu5Gc (11,12).For a Sia molecule to get attached to glycoconjugates it must first be activated by conversion to the sugar nucleotide derivative cytidine monophosphate-Sia (CMP-Sia). Thus, Sias are converted to CMP-Sias in the nucleus, which then return to the cytosol to be transported into the Golgi apparatus, where they serve as high energy donors for attaching Sias to newly synthesized glycoconjugates on their way to the cell surfac...

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“…Aldehyde-functionalized glycosides or linkers have been conjugated to lysine amino groups via reductive amination [65]. In order to reduce steric hindrance and increase the loading with glycosides spacer arms have been introduced [66].…”

Section: Modifications Of Lysine Side-chainsmentioning

confidence: 99%

Recent Developments in Neoglycopeptide Synthesis

Brimble

Miller

Williams

2011

Amino Acids, Peptides and Proteins in Organic Chemistry

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Preparation and immunological studies of protein conjugates of N-acylneuraminic acids

Cited by 35 publications

References 37 publications

Effects of Natural Human Antibodies against a Nonhuman Sialic Acid That Metabolically Incorporates into Activated and Malignant Immune Cells

Effects of Natural Human Antibodies against a Nonhuman Sialic Acid That Metabolically Incorporates into Activated and Malignant Immune Cells

Mechanism of Uptake and Incorporation of the Non-human Sialic Acid N-Glycolylneuraminic Acid into Human Cells*

Recent Developments in Neoglycopeptide Synthesis

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