What I have: cagrilintide · 10 mg/mL · eight weeks.
I would rather be corrected now than propagate something wrong.
I am specifically not interested in a testimonial; I am interested in a measurement.
How well supported is this claim?
eight weeks is 56 days and, on a weekly schedule, 8 stopper punctures out of one vial at 10 mg/mL. Set the chemical question aside for a moment, because the puncture count is the one with a convention attached: 56 days is 2 times the twenty-eight days conventionally allowed for a preserved multi-dose preparation once it has been entered. Chemically, 10 mg/mL is high enough that adsorption to the glass is a rounding error and low enough that it is not protecting you from anything. What 8 withdrawals do add is 8 opportunities to introduce air, 8 coring events on the same stopper, and a headspace that grows with every draw — none of which show up on a certificate and all of which are avoided by splitting into aliquots at reconstitution.
The relevant point is that a mass shift of plus one dalton is deamidation and plus sixteen is oxidation, so degradation is often visible in a mass spectrum if anyone looks.
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.
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.
Deamidation via the succinimide intermediate is well characterised, with sequence-dependent rates highest for asparagine-glycine motifs.
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.
Analytical standards and reagents with traceable certificates. Every quantitative result you read inherits the accuracy of the standard behind it.
Shop standardsStart with the sequence, because which pathways are available depends on which residues are present.
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.
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.
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.
Sequence decides which pathways are even available. Check the residues.
edited 27 Nov 2024 by micron22 — added the citation requested in comments
Answer first: the degradation pathways worth knowing are hydrolysis, deamidation, oxidation, aggregation and adsorption, and each has a different trigger and a different mitigation.
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.
Stated carefully, light exposure matters for tryptophan-containing sequences and for anything with a chromophore. Amber vials and a closed box are free mitigations.
Sequence determines which pathways apply, so general statements are general.
Cold, dry, dark, still. Those four words cover most of the mitigation.
The honest answer is that most reported "degradation" is adsorption and dilution error rather than chemistry.
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.
Aggregation at air-liquid interfaces is established from surface-tension and particle-count studies and is the basis for anti-agitation handling guidance.
A mass spectrum names the pathway. Plus one, plus sixteen, minus eighteen.
The short version: water enables most of it, oxygen enables oxidation, surfaces enable adsorption, and agitation enables aggregation.
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.
Adsorption losses at low concentrations are quantified in formulation studies and are the reason carrier proteins are used in dilute preparations.
Swirl, never shake. Aggregation is a handling problem more than a time problem.
edited 28 Sept 2024 by h_pergande — removed a claim I could not source
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.