Is there any published stability data for mazdutide at 4 °C?

Details up front: mazdutide · 4 °C.

I would rather be corrected now than propagate something wrong.

I am specifically not interested in a testimonial; I am interested in a measurement.

Is this actually true, and what is the evidence?

Probably not at 4 °C specifically, because that is not where stability programmes take their readings. Accelerated work is conventionally run at 25 °C and 40 °C, with the refrigerated condition as the control, so 4 °C sits between or beyond the published points and what you will find is bracketing rather than a measurement. 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. Whatever you find, check what was measured before you use it: a paper reporting purity at 4 °C has not measured content, and the two fail at different rates for different reasons.

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.

Degradation pathway by condition

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.

Sequence determines which pathways apply, so general statements are general.

At dilute concentrations, suspect adsorption before you suspect chemistry.

In practice, asparagine and glutamine are the deamidation risk, and methionine is the oxidation risk.

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.

Aggregation at air-liquid interfaces is established from surface-tension and particle-count studies and is the basis for anti-agitation handling guidance.

Swirl, never shake. Aggregation is a handling problem more than a time problem.

The short version: water enables most of it, oxygen enables oxidation, surfaces enable adsorption, and agitation enables aggregation.

Light exposure matters for tryptophan-containing sequences and for anything with a chromophore. Amber vials and a closed box are free mitigations.

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.

Metal-catalysed oxidation of methionine is documented across peptide and protein formulations and is why chelators appear in some formulations.

Cold, dry, dark, still. Those four words cover most of the mitigation.

Answering this needs the physical state, since a dry powder is protected from most of these and a solution is protected from none.

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.

Adsorption losses at low concentrations are quantified in formulation studies and are the reason carrier proteins are used in dilute preparations.

Apparent loss in a dilute preparation is usually adsorption rather than degradation and is worth ruling out first.

A mass spectrum names the pathway. Plus one, plus sixteen, minus eighteen.

edited 25 Oct 2024 by meniscus_film — added the method parameters