What I am working with: dulaglutide · 4 °C.
This is a procedural question rather than a theoretical one, and I would like the procedure rather than the theory.
What I have done so far is read the label documentation where it exists and the two pharmacopoeial monographs that are publicly available, which cover the licensed presentation and say nothing about a research one.
What would you do, and what would you check afterwards?
Whatever the refrigerated figure is, divide it by about 0.9. 4 °C is the condition the rule of thumb is anchored to, so it is the baseline rather than a multiplier: everything else in this thread is quoted relative to it. So a preparation with a twenty-eight day refrigerated figure has roughly 30 days at 4 °C on the same assumption — an order-of-magnitude answer, not a shelf life, and it says nothing about sterility, which has its own clock. "Within specification" also needs a specification: purity, content, or both, and at what limit. Without that the question has no numerical answer at all.
Stated carefully, aggregation is a physical process and is the one most often caused by handling rather than by time.
Adsorption onto glass and plastic is significant at low concentrations — micrograms per millilitre — and negligible at milligrams per millilitre. It is the usual explanation for an apparent loss in a dilute preparation.
Deamidation converts asparagine or glutamine to the corresponding acid via a succinimide intermediate, adding one dalton. It is base-catalysed, accelerates above neutral pH and is the dominant aqueous pathway for many peptides.
Metal-catalysed oxidation of methionine is documented across peptide and protein formulations and is why chelators appear in some formulations.
Apparent loss in a dilute preparation is usually adsorption rather than degradation and is worth ruling out first.
Swirl, never shake. Aggregation is a handling problem more than a time problem.
HPLC purity, identity confirmation and quantified content on the vial you actually hold. Reports arrive with the chromatogram attached, not just a number.
Submit a sampleFounded 1998. ISO 9001 and cGMP certified, 1,500+ staff and 200+ patents. The synthesis house behind a great many of the vials that get sent out for testing - batch-specific documentation with every order.
Visit GL BiochemWorth being precise here: asparagine and glutamine are the deamidation risk, and methionine is the oxidation risk.
Oxidation targets methionine, cysteine and tryptophan, adding sixteen daltons per oxygen. It is catalysed by trace metals and promoted by dissolved oxygen and by light.
To be exact about it, freeze-thaw cycling drives aggregation through concentration at the ice interface and pH shifts as buffer components crystallise out at different rates. Each cycle costs something.
Adsorption losses at low concentrations are quantified in formulation studies and are the reason carrier proteins are used in dilute preparations.
The caveat is that none of these pathways can be seen by looking at a vial, and a clear solution can be substantially degraded.
At dilute concentrations, suspect adsorption before you suspect chemistry.
edited 30 Jul 2024 by h_pergande — clarified the distinction between purity and content
Start with the sequence, because which pathways are available depends on which residues are present.
A mass spectrum resolves most of this: minus eighteen is dehydration or succinimide, plus one is deamidation, plus sixteen is oxidation, and an unchanged mass with a shifted retention time is an isomer.
Hydrolysis cleaves the backbone, most readily at aspartate-proline and aspartate-glycine sequences, and is acid-catalysed. In a dry solid it barely proceeds at all.
Nothing here is medical advice, and research-use compounds are not approved for human use.
A mass spectrum names the pathway. Plus one, plus sixteen, minus eighteen.
Answer first: the degradation pathways worth knowing are hydrolysis, deamidation, oxidation, aggregation and adsorption, and each has a different trigger and a different mitigation.
Aggregation is physical: peptides unfold at air-liquid interfaces and associate. Shaking maximises that interface, which is why swirling and shaking produce visibly different outcomes on the same vial.
Aggregation at air-liquid interfaces is established from surface-tension and particle-count studies and is the basis for anti-agitation handling guidance.
Sequence determines which pathways apply, so general statements are general.
Cold, dry, dark, still. Those four words cover most of the mitigation.
This is answerable from the chemistry rather than from anecdote, which is unusual and welcome.
Light exposure matters for tryptophan-containing sequences and for anything with a chromophore. Amber vials and a closed box are free mitigations.
Deamidation via the succinimide intermediate is well characterised, with sequence-dependent rates highest for asparagine-glycine motifs.
The caveat is that "within specification" and "unchanged" are different claims. A vial can lose a few per cent of content and still be usable for its purpose while no longer matching its certificate.
Sequence decides which pathways are even available. Check the residues.
Ask PeptideStack is a static archive. Posting is closed, but the norms are worth stating: answer the question that was asked, show your working, cite the trial or the certificate, and say plainly where the evidence runs out.