Kisspeptin-10 Nasal Solution

This is Kisspeptin-10 supplied as a buffered, preserved aqueous solution rather than as a lyophilized cake. The peptide itself is the same molecule described on the Kisspeptin-10 product page; what differs is the formulation around it.

Kisspeptin-10 is the C-terminal decapeptide of the KISS1 gene product, annotated on UniProt Q15726 as residues 112 to 121 of the precursor, which is also why the literature calls it metastin 45-54. The same annotation marks that decapeptide as the region essential for receptor binding and activation. Its receptor is KISS1R (UniProt Q969F8), a class A G-protein-coupled receptor also published under the names GPR54, AXOR12 and OT7T175 - four names, one accession.

The C-terminal amide is part of the identity rather than a finishing detail: it is the RFamide motif that defines this ligand family, recorded by UniProt as a phenylalanine amide at residue 121 and by FDA GSRS as a registered phenylalanylamide modification at position 10. Ohtaki and colleagues reported the amidation in the Nature paper that identified the peptide in 2001.

That makes the des-amido form the impurity that matters, and it is only about one dalton away. Worse, the arginine-9 citrulline analogue has the identical formula and the identical monoisotopic mass to that des-amido species, so accurate mass alone cannot separate the two - confirmation needs fragmentation or sequencing. The same one-dalton shift also arises from deamidation at either asparagine, which means a single mass reading has three plausible explanations and distinguishes none of them.

The peptide has one tryptophan, one tyrosine and two phenylalanines, so unlike most of the short peptides in this catalogue it has a genuine chromophore and absorbance at 280 nm is a usable concentration method. It contains no cysteine and no methionine; Trp3 is the oxidation-prone residue instead.

One documented cleavage route runs inside the decapeptide rather than at an end. UniProt Q15726 records matrix metalloproteinases 2 and 9 cutting between precursor residues 118 and 119, which are positions 7 and 8 of this peptide - the glycine-leucine bond. Tomita and colleagues confirmed it in the Journal of Medicinal Chemistry in 2008 by building alkene and hydroxyethylene isosteres of that one bond and measuring the resulting resistance. Separately, Liu and colleagues characterised the principal decomposition product in plasma as the peptide with its N-terminal tyrosine removed, using a validated mass-spectrometry assay.

A word on what is in the solution, since that is what makes this a different product from the powder. A nasal-grade peptide solution is three things beyond the peptide and water: a tonicity agent, a buffer and a preservative. The tonicity agent - sodium chloride in some marketed products, a polyol or sugar such as sorbitol or dextrose in others - sets the osmolality of the solution, and the choice is chemical rather than cosmetic, because a salt also contributes ionic strength that screens charge and shifts apparent side-chain acidity while a polyol contributes none and additionally stabilises the compact state of a peptide by preferential exclusion from its hydration shell. The buffer, typically a citrate, acetate, succinate or citrate-phosphate system in the pH range roughly 4.5 to 6.8, holds the pH near the minimum of the peptide's own degradation rate, since amide hydrolysis is acid-catalysed and asparagine deamidation is base-catalysed and each has a different pH optimum; without a buffer, dissolved carbon dioxide and leachables from the container would move the pH over shelf life. The preservative, usually benzalkonium chloride at roughly one to two parts in ten thousand, is a quaternary ammonium surfactant whose permanently charged head adsorbs to the anionic surface of a microbial envelope and whose alkyl tail then partitions into the bilayer and destroys its permeability barrier; it is present because a near-neutral aqueous solution containing a peptide and a sugar is itself a growth medium, and a container that is opened more than once meets the organisms in the air around it. A chelating agent such as disodium edetate is frequently the fourth component, sequestering the trace iron and copper that would otherwise drive the tryptophan oxidation described above.