Sialic acid analysis is a regulatory requirement laid out in the ICH Q6B guidelines for characterization of biopharmaceuticals.
Sialic acids are negatively charged monosaccharides found on the non-reducing termini of glycans. They are important for the stability and 3D confirmation of glycoproteins and are involved in many biological interactions. Sialic acids often have a pivotal functional impact: for example sialylation of the N-glycans on IgG increases anti-inflammatory activity; O-acetylated sialic acids can change ligand interactions and affect degradation (O-acetylated sialic including Neu5, 9Ac2 are found on EPO); and the presence of sialic acids also increase the serum half life of glycoproteins by preventing uptake by the asialoglycoprotein-receptor located on liver cells.
A diverse range of sialic acids are found in nature, but the two major sialic acids found on N-glycans and O-glycans in biopharmaceuticals are N-acetyl-neuraminic acid (Neu5Ac, or NANA) and N-glycolyl-neuraminic acid (Neu5Gc, or NAGA). Humans cannot synthesise Neu5Gc and its presence on a drug can lead to immune reactions such as chronic inflammation. Anti-Neu5Gc antibodies have been detected in normal human sera, and can neutralize any Neu5Gc containing biopharmaceutical, thus lowering the drug’s efficacy. It is important to be aware that the choice of cell line can greatly influence the type of sialic acids present on a biopharmaceutical, for instance a large proportion of the sialic acids on mouse IgG are often Neu5Gc.
It is therefore imperative, for drug safety and efficacy, to monitor both the level and types of sialic acids during all stages of the product life cycle as well as QC batch to batch consistency.