Peptide aggregation (revision 18)
Old revision·20:18, 17 May 2025·TFA_Counterion
| Peptide aggregationDegradation route | |
|---|---|
| Reversible form | Self-association into defined oligomers |
| Irreversible form | Amyloid-like fibrils, amorphous particles |
| Detected by | Size-exclusion chromatography, light scattering, visual inspection |
| Topic infobox · conventions | |
Peptide aggregation is the association of peptide molecules with one another. It ranges from reversible self-association into defined oligomers, which may be a stabilising feature of a formulation, to irreversible formation of amyloid-like fibrils or amorphous particles, which is a degradation route.[1]
The distinction between the two is central and is frequently lost. Liraglutide self-associates into heptamers in its formulation, and that association contributes to its duration of action; human amylin forms fibrils, which is why it could not be developed as a medicine without engineering. Both are "aggregation" in a loose sense and they are not the same phenomenon.[2]
Aggregation is driven by concentration, by pH near the isoelectric point, by hydrophobic surface exposure, by agitation at air–liquid interfaces, and by temperature. It is the degradation route most likely to be visible: a solution that has gone faintly hazy after reconstitution has changed.[1]
Mechanisms
[edit]Aggregation proceeds through partially unfolded or conformationally exposed states rather than from the native state directly. Anything that increases the population of such states — heat, interfaces, shear, extremes of pH — increases the rate.[1]
Nucleation-dependent aggregation, characteristic of amyloid formation, shows a lag phase during which nuclei form, followed by rapid growth. The lag is why a solution can appear stable for a period and then change quickly, and why seeding with pre-formed aggregate abolishes the lag entirely — a relevant consideration when material is drawn repeatedly from one container.
Interfacial aggregation is the mechanism most often encountered in handling. The air–liquid interface presents a hydrophobic surface at which peptides adsorb and unfold, so shaking a vial is substantially worse than swirling it. The same applies to repeated passage through a narrow needle.[3]
Detection
[edit]| Method | Detects | Limitation |
|---|---|---|
| Visual inspection | Visible particles, haze | Insensitive to soluble oligomers |
| Size-exclusion chromatography | Soluble aggregates | Dissociating conditions can hide reversible species |
| Dynamic light scattering | Particle size distribution | Dominated by the largest particles present |
| Reverse-phase HPLC | Little or nothing | Aggregates often dissociate on the column |
The last row is the important one for reading certificates. A reverse-phase purity determination is run under denaturing conditions with organic solvent and acid; aggregates dissociate and are counted as monomer. A high purity figure by that method says nothing about aggregation state.[3]
Size-exclusion chromatography is the ordinary determination for aggregate content, and its result depends on the mobile phase: a dissociating buffer will report a cleaner profile than a native one on the same material. For an amylin analogue or an acylated incretin peptide, which one was used is a material question.[1]
See also
References
- ^ a b c d Manning MC, Chou DK, Murphy BM, Payne RW, Katayama DS. "Stability of protein pharmaceuticals: an update." Pharmaceutical Research 27(4):544–575 (2010). DOI:10.1007/s11095-009-0045-6. PMID 20143256.
- ^ Westermark P, Andersson A, Westermark GT. "Islet amyloid polypeptide, islet amyloid, and diabetes mellitus." Physiological Reviews 91(3):795–826 (2011). PMID 21742788.
- ^ a b United States Pharmacopeia, General Chapter <1503>, Quality Attributes of Synthetic Peptide Drug Substances.