GHK-Cu: identity, copper chemistry and published research

GHK-Cu is one of the best-known small peptides in the research literature, and also one of the most loosely described. The same three letters appear in coordination-chemistry papers, in fibroblast and keratinocyte studies, in rat wound models, in gene-expression analyses and in cosmetic-ingredient marketing. This explainer sets out what the compound is, how it holds copper, which experimental models it has been studied in, what those studies report, and where the evidence stops.

What is GHK-Cu?

GHK is the tripeptide glycyl-L-histidyl-L-lysine: glycine at the N-terminus, histidine in the middle and lysine at the C-terminus (one-letter sequence G-H-K). The free peptide has the molecular formula C14H24N6O4 and a molecular weight of 340.38 g/mol, and is registered under CAS 49557-75-7 (PubChem CID 73587).

GHK-Cu is the same tripeptide bound to a copper(II) ion. PubChem lists the 1:1 complex under the name prezatide copper, CAS 89030-95-5 (CID 71587328), with a molecular weight of about 403 g/mol for the complex ion as drawn, before any counter-ion is counted. PubChem also holds an entry for a complex of one copper ion with two GHK molecules (CAS 130120-56-8). Commercial material is usually a salt, often an acetate, so the formula weight on a label can sit above either figure.

In practice this means three different things can be sold or described as “GHK-Cu”: the 1:1 complex, the 1:2 complex, and a salt of either. Before comparing a batch with a paper, check which form the certificate describes, its CAS number and whether the molecular weight includes counter-ions. Our guide to reading a peptide Certificate of Analysis covers those fields in more detail, and the same checks apply to any GHK-Cu offered by a supplier such as the EuroPeps research-peptide shop.

Where does GHK come from?

The peptide entered the literature in 1973, when Pickart and Thaler reported a tripeptide in human serum that prolonged the survival of normal liver cells and stimulated the growth of neoplastic liver cells in culture (Pickart and Thaler, 1973). Later work described GHK as a tripeptide isolated from plasma with an affinity for copper(II) (Maquart et al., 1988).

One proposed origin is proteolysis of the extracellular matrix. Maquart and colleagues pointed out that the GHK triplet occurs in the α2(I) chain of type I collagen, and suggested that proteases at a site of tissue damage might release it (Maquart et al., 1988). That is a hypothesis drawn from sequence, not a demonstrated pathway. A 2015 review also reports that GHK is present in saliva and urine and that its plasma level declines with age (Pickart et al., 2015).

How does GHK bind copper?

GHK is a strong copper(II) chelator. Crystal and solution studies show that the complex behaves differently in the two states. In the solid state, copper(II)-GHK crystallises as a dimer, with the fourth equatorial position taken by a labile oxygen atom from a carboxylate. In solution it is a monomer in which copper is bound by three nitrogen atoms: the free N-terminal amine of glycine, the deprotonated amide nitrogen between glycine and histidine, and a nitrogen of the histidine imidazole ring. The fourth equatorial position is labile and can be occupied by other ligands such as glycine or histidine, forming ternary complexes (Hureau et al., 2011).

The same study compared GHK with DAHK, the copper-binding Asp-Ala-His-Lys motif found at the N-terminus of serum albumin. Copper exchange between DAHK molecules was very slow, whereas exchange involving GHK was fast, which the authors attributed to a complex of one copper ion with two GHK molecules. Both complexes were redox-inert under moderate potentials, but copper(II)-GHK could be converted electrochemically to copper(I) at around −0.62 V (versus Ag/AgCl), with release of the copper ion (Hureau et al., 2011).

Binding strength has been measured directly. Using isothermal titration calorimetry with glycine as a weaker competing ligand, Trapaidze and colleagues found that both peptides bind copper(II) predominantly in a 1:1 ratio, with conditional dissociation constants at pH 7.4 of 7.0 × 10⁻¹⁴ M for GHK and 2.6 × 10⁻¹⁴ M for DAHK. The binding energetics of the two peptides differed, with a larger enthalpic contribution for GHK (Trapaidze et al., 2012). Affinity in this range is why GHK is often described as a copper carrier, and why the copper status of a sample matters when interpreting any experiment with it.

Which research models has GHK-Cu been studied in?

The primary literature falls into four groups:

• Cultured fibroblasts, mostly dermal fibroblasts, used to measure synthesis of collagen, glycosaminoglycans and matrix-remodelling enzymes.
• Cultured keratinocytes and skin-equivalent models, three-dimensional cultures in which keratinocytes form a layered epithelium on a dermal substrate.
• Gene-expression analyses, including computational screening of public expression databases and follow-up experiments in cultured lung fibroblasts.
• Rat wound models, chiefly the wound chamber: a stainless-steel mesh cylinder implanted under the skin of the back, which fills with new connective tissue over several weeks and can be sampled for analysis.

What do studies in cultured fibroblasts describe?

In fibroblast cultures, GHK-Cu was associated with higher collagen synthesis. The effect began between 10⁻¹² and 10⁻¹¹ M, was greatest at 10⁻⁹ M and did not depend on a change in cell number (Maquart et al., 1988). The low concentration range is often quoted; it comes from a single early study.

A later study from the same laboratory looked at matrix breakdown as well as synthesis. In dermal fibroblast cultures, GHK-Cu raised levels of matrix metalloproteinase-2 (MMP-2) in the conditioned medium together with MMP-2 messenger RNA, and also raised secretion of the tissue inhibitors of metalloproteinases TIMP-1 and TIMP-2. Copper ions on their own reproduced the MMP-2 effect, but GHK without copper did not (Siméon et al., 2000). That observation matters for anyone designing an experiment: some activity attributed to GHK-Cu may belong to the copper rather than the peptide, so a copper-salt control is informative.

What do studies in keratinocytes describe?

In monolayer cultures of keratinocytes, GHK-Cu was associated with greater cell proliferation. In skin-equivalent models, basal cells became more cuboidal when GHK-Cu was added, and immunohistochemistry showed more cells positive for proliferating cell nuclear antigen (PCNA) and for p63, which the authors describe as a putative stem-cell marker. Expression of integrins α6 and β1 was higher, which the authors confirmed by Western blotting (Kang et al., 2009).

The same group then tested copper-free GHK in the same models and reported similar findings: more proliferation in monolayer culture, more cuboidal basal cells, stronger integrin staining along the basement membrane and more PCNA- and p63-positive cells (Choi et al., 2012). Read beside the fibroblast MMP-2 study, this leaves the role of copper model-dependent and unresolved.

What do gene-expression studies describe?

The most rigorous gene-expression study of GHK did not start from the peptide at all. Campbell and colleagues profiled gene expression in lung tissue from smokers with chronic obstructive pulmonary disease, taking eight regions from each of eight lungs (64 samples) and quantifying emphysema severity in each region by micro-CT. They identified 127 genes whose expression tracked regional emphysema severity. Querying the Connectivity Map, a public database of expression profiles from cultured cell lines exposed to small molecules, they found GHK among the compounds whose profile ran opposite to that signature (Campbell et al., 2012).

They then tested the prediction in culture. In lung fibroblasts, GHK reproduced gene expression patterns induced by transforming growth factor beta (TGFβ), was associated with organisation of the actin cytoskeleton and raised expression of integrin β1. In collagen I gel assays, adding GHK or TGFβ restored contraction and remodelling by fibroblasts derived from lungs with COPD, compared with fibroblasts from former smokers without COPD (Campbell et al., 2012). The authors called for further studies of mechanism and of what such a reversal means for disease progression.

Broader gene-count statements come from review articles. A 2015 review states that GHK can up- or down-regulate at least 4,000 genes (Pickart et al., 2015), and a 2018 review interprets this kind of data as explaining the range of activities reported for the peptide (Pickart and Margolina, 2018). A count of that kind describes changes in measured messenger RNA in profiling experiments; on its own it does not show that the corresponding proteins or cell behaviours change.

What do rat wound models describe?

The central in-vivo study used the wound-chamber model in rats. Chambers received repeated additions of either saline or GHK-Cu at several concentrations; at the end of the experiment their contents were analysed. In the GHK-Cu chambers there were concentration-dependent rises in dry weight, DNA, total protein, collagen and glycosaminoglycan content. Collagen synthesis rose about twice as much as synthesis of non-collagen proteins, messenger RNAs for type I and type III collagen were higher, and TGFβ messenger RNA was unchanged. The relative amount of dermatan sulphate was also higher. A control tripeptide, L-glutamyl-L-histidyl-L-proline, had no significant effect (Maquart et al., 1993).

A follow-up in the same model in Sprague-Dawley rats tracked matrix metalloproteinases over the course of repair. MMP-9 and MMP-2 were the main gelatinolytic activities. GHK-Cu did not change interstitial collagenase activity, but MMP-9 expression persisted in the chamber tissue until day 22 in GHK-Cu chambers, and pro-MMP-2 and active MMP-2 were higher at the later time points, days 18 and 22 (Siméon et al., 1999). Together the two papers describe GHK-Cu in this model as acting on both matrix deposition and remodelling.

Reviews also cite work in mice, pigs and dogs and in other tissue sites (Pickart et al., 2015). Those studies are not covered individually here and are best read in the original papers, with attention to the model, the compound form and the controls used.

How does the research literature relate to the cosmetic-ingredient literature?

GHK-Cu is widely used as a cosmetic ingredient, and its research and cosmetic literatures are easily confused. They are different kinds of evidence.

The research literature summarised above measures defined endpoints, such as collagen synthesis, enzyme levels, messenger RNA or histology, in named models under controlled conditions. The cosmetic literature evaluates finished formulations, typically with appearance-based endpoints. Findings in cultured fibroblasts or rat wound chambers do not transfer to a formulation applied to intact tissue: the peptide has to cross the stratum corneum, survive the formulation and reach the relevant cells at a relevant concentration.

Penetration has been measured in vitro. In flow-through diffusion cells, an aqueous solution of GHK-copper diacetate was applied to isolated stratum corneum, heat-separated epidermis and dermatomed human skin, and copper in the tissue and receptor fluid was measured by inductively coupled plasma mass spectrometry over 48 hours. The permeability coefficient through dermatomed tissue was about 2.43 × 10⁻⁴ cm/h (Hostynek et al., 2011). The study measured copper, not the intact peptide, so it does not show how much GHK crossed the tissue unchanged.

A second point concerns authorship. Two of the most cited reviews of GHK, from 2015 and 2018, are narrative reviews written by the group that first described the peptide (Pickart et al., 2015; Pickart and Margolina, 2018). They are useful maps of the literature, but they are not systematic reviews, and their broad summaries are no substitute for the primary studies.

What remains unresolved?

• The role of copper. In fibroblasts, copper alone reproduced the MMP-2 effect while copper-free GHK did not; in keratinocytes and skin-equivalent models, copper-free GHK gave findings similar to GHK-Cu. Which activities need the complex, the free peptide or the free metal is not settled.
• Concentration. The often-quoted picomolar to nanomolar range for collagen synthesis comes from one early fibroblast study. How culture concentrations relate to those in plasma or in tissue is not established.
• Replication. The fibroblast and wound-chamber studies cited here come from one laboratory in Reims, and the two keratinocyte studies from one group in Korea. Independent replication with modern methods and defined compound forms is limited.
• Compound definition. Many papers do not report the salt form, copper-to-peptide ratio or purity of the material used, which makes comparison between studies and with commercial batches difficult.
• Gene-expression versus function. Expression signatures, including Connectivity Map hits, generate hypotheses; few have been followed through to protein-level and functional readouts in the way the emphysema study did.
• Human data. The primary literature reviewed here is cell-culture, tissue-profiling and rat work; the cosmetic literature measures formulations, not the compound, and does not answer the questions above.

For a researcher, the practical summary is narrow: GHK-Cu is a well-characterised copper(II) complex with a defined coordination chemistry; in cultured fibroblasts, keratinocyte models, lung fibroblasts and rat wound chambers, it has been associated with changes in extracellular-matrix synthesis, remodelling enzymes and gene expression; and the open questions about copper, concentration and replication are large enough that any new experiment should define its compound form and include copper and peptide controls.