Impact of surfactants on the stability of therapeutic peptides under interfacial stress

Peptide therapeutics are prone to aggregation, denaturation, and interfacial adsorption, which can compromise product quality, reduce potency, increase immunogenicity, and shorten shelf life. Although surfactants are widely used to stabilize protein biologics, their use in commercial parenteral peptide formulations appears to be more selective. Specifically, the literature does not provide a clear rationale for using surfactants in this context, and their effects on peptides remain poorly understood. Here, we investigate the effects of three common surfactants, polysorbate 80 (PS80), polysorbate 20 (PS20), and poloxamer 188 (PX188), on the conformational stability, oligomerization, and aggregation of liraglutide as the primary model peptide, followed by exploratory evaluation of semaglutide and glucagon, under agitation stress. For liraglutide, which forms dynamic oligomers that are not intrinsically stable under agitation stress, SEC and CD reveal extensive aggregation and structural rearrangement in the presence of both PS80 and PX188, with PS80 driving more rapid aggregation. NMR shows strong, specific interactions between liraglutide and PS80 but not PX188, suggesting different mechanisms: PS80 perturbs the native oligomer via peptide-surfactant interactions, whereas PX188 likely promotes aggregation through interfacial stress. Consistent with this, PS20, with its shorter, less hydrophobic chain, caused less disruption than PS80, underscoring the importance of surfactant-peptide interaction strength. In contrast, semaglutide, which forms more stable oligomers, showed only limited changes in aggregation behavior in the presence of surfactants. For glucagon, which has a strong intrinsic tendency to fibrillate, surfactants modestly changed aggregation rates but did not prevent fibril formation. It is worth noting that, unlike therapeutic monoclonal antibodies, which primarily adopt monomeric structures stabilized by extensive intramolecular and interdomain interactions, peptides drugs are more flexible and therefore more susceptible to perturbation by surfactants. Overall, surfactant effects on peptide stability are highly molecule-dependent and reflect a balance among peptide-peptide and peptide-surfactant interactions, surfactant-mediated interfacial stress, and the intrinsic stability of peptide oligomers.