GLP-3 in the laboratory

Published research context

Incretin peptides are among the most heavily studied signalling molecules in metabolic research. Published work spans receptor binding and selectivity assays, receptor internalisation and signalling bias in cultured cell lines, and whole animal studies in rodent models of metabolic disturbance. The receptor is a class B G protein coupled receptor, and a large share of the literature concerns how different ligands engage it.

The limitation worth stating plainly is that the bulk of mechanistic work in this area is carried out in cell culture and in rodent models. Findings in those systems describe the systems themselves. They are not statements about people, and this material is not supplied for any use involving people.

For a laboratory setting up work in this area, the practical questions are usually receptor source and assay format, whether albumin is present in the buffer given that acylated analogues bind it, and how the peptide is handled so that the concentration in the well is the concentration intended.

How each lot is characterised

Two measurements carry most of the weight for a peptide of this class. Purity is determined by reversed phase high performance liquid chromatography with ultraviolet detection at 214 nanometres, the wavelength at which the peptide bond itself absorbs, so the detector responds to peptide material rather than to any single side chain. The result is reported as the area of the main peak as a percentage of total integrated area.

Identity is determined by electrospray ionisation mass spectrometry. The observed average mass is compared against the theoretical mass calculated from the sequence and any modification. A lot is accepted when the observed value falls within the stated tolerance of the theoretical value, which for this class is a fraction of a dalton.

The certificate of analysis for each fill size also records appearance, net peptide content determined by amino acid analysis, water content by Karl Fischer titration, and the counter ion. The lot number printed on the vial label resolves to the published certificate for that lot, so the document and the material in hand can always be matched.

Handling on the bench

The unopened vial is stored at minus twenty degrees, dark and desiccated. Lyophilised peptide is considerably more stable than the same material in solution, so the powder should stay dry until the moment it is needed.

Allow the vial to reach room temperature before opening, so that atmospheric moisture does not condense onto cold powder. Reconstitute with bacteriostatic water, adding the solvent slowly down the vial wall rather than directly onto the cake, and swirl gently to dissolve. Shaking a peptide solution introduces shear and an air interface, both of which encourage aggregation.

Once in solution, refrigerate and divide into single use aliquots. Repeated freeze and thaw cycles are the most common avoidable cause of loss of material in peptide work, because each cycle concentrates solutes at the ice boundary and exposes the molecule to an expanding interface. Acylated peptides in particular are prone to adsorbing onto plastic surfaces, so low binding tubes and tips are worth using where the working concentration is low.

Specification