GHK-Cu levels have been observed to decline with age. Research continues to explore its role in tissue biology, skin biology and ageing-related science.
GHK-Cu
GHK is a naturally occurring tripeptide, glycyl-L-histidyl-L-lysine, first isolated from human plasma in the 1970s. It has a high affinity for copper(II) ions, and the complex it forms with them is what is referred to as GHK-Cu. The copper is not an additive; it is part of what the molecule is.
The observation that started the field was an age-related one: plasma concentrations of GHK reported in younger adults are substantially higher than those reported in older adults. That decline prompted decades of investigation into what the peptide does while it is present. Gene expression work has examined its influence across a broad set of pathways rather than a single target, which is unusual for a molecule this small.
The literature spans copper coordination chemistry, cell culture models of tissue remodelling, and analyses of gene expression profiles. Reviews by Pickart, who first isolated the peptide, consolidate several decades of that work. Much of the applied research concerns topical and wound-model contexts rather than systemic administration.