N-Acetylmannosamine is a hexosamine monosaccharide. It is a neutral, stable naturally occurring compound. N-Acetylmannosamine is also known as N-Acetyl-D-mannosamine monohydrate, (which has the CAS Registry Number: 676347-48-1), N-Acetyl-D-mannosamine which can be abbreviated to ManNAc or, less commonly, NAM). ManNAc is the first committed biological precursor of N-acetylneuraminic acid (Neu5Ac, sialic acid) (Figure 1). Sialic acids are the negatively charged, terminal monosaccharides of carbohydrate chains that are attached to glycoproteins and glycolipids (glycans).


Sialylation of recombinant proteins

There is normally some level of glycan sialylation within a glycoprotein, but with the observation that incomplete sialylation can lead to reduced therapeutic activity, it becomes relevant to assess the cell-lines and culture media to “humanise” the glycoprotein to improve performance and yield and reduce manufacturing costs. Keppler et al.demonstrated that the GNE enzyme was rate limiting in human hematopoietic cell lines and affected efficiency in cell surface sialylation. The activity of the GNE enzyme is now recognised as one of the defining features in the efficient production of sialylated recombinant glycoprotein therapeutic drugs. Improved sialylation after the addition of ManNAc and other supporting ingredients to the culture medium not only increases manufacturing yield, but also improves therapeutic efficacy by increasing solubility, increasing half-life and reducing immunogenicity by reducing the formation of antibodies  to the therapeutic glycoprotein 

Therapeutic potential

When the GNE epimerase kinase does not function correctly in the human body thereby reducing the available ManNAc, it is reasonable to assume that treatment with ManNAc could assist with improving health benefits. The therapeutic potential for ManNAc is currently being assessed in several diseases in which therapy could benefit from its ability to enhance the biosynthesis of sialic acid.

GNE myopathy

The disease GNE myopathy [formerly known as hereditary Inclusion Body Myopathy (HIBM), and Distal Myopathy with Rimmed Vacuoles (DMRV)] is manifested as progressive muscle weakness. GNE myopathy is a rare genetic disorder caused by hyposialylated muscle proteins and glycosphingolipids because there is insufficient metabolic ManNAc to form the Neu5Ac terminal sugar. There is no available therapy to treat GNE myopathy.

Kidney diseases

There is a growing body of evidence that reduced activity of the GNE enzyme in the sialylation pathway in kidney tissue could contribute to several glomerular kidney diseases, due to the lack of the Neu5Ac terminal sugar on several kidney glycoproteins.

Three kidney diseases that affect both children and adults are minimal change disease (MCD), focal segmental glomerulosclerosis (FSGS) and membranous nephropathy (MN). These diseases are characterized by proteinuria (protein in the urine) and in the case of FSGS, a tendency to progressive scarring of the glomerulus (the filtering units of the kidneys) that leads to end-stage kidney disease. Several therapies are available for these diseases, but these therapies do not provide lasting reduction in proteinuria for many subjects and there can be severe side-effects.

There is now substantial pre-clinical evident correlating with human kidney biopsy samples, that some patients with MCD, FSGS or MN have kidney sialic acid insufficiency on their glomerular proteins. ManNAc therapy may increase sialic acid production and subsequently increase sialylation of glomerular proteins.

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