GHK-Cu copper peptide: what it is, how it differs from GHK, and what the research actually measured

What the GHK-Cu peptide is#

GHK is a tripeptide: three amino acids, glycine, histidine and lysine, joined in that order (Gly-His-Lys). GHK-Cu is the same tripeptide bound to a copper(II) ion. The two names are often used interchangeably in search results and vendor listings, but they describe two different chemical forms, and the difference matters when a lot is tested.

The tripeptide was first reported in 1973 by Loren Pickart and Martin Thaler, who described a tripeptide in human serum that prolonged the survival of normal liver cells and stimulated growth in neoplastic (tumor-derived) liver cells in culture.^[1] Later work identified it as a copper-binding peptide. A 2018 review by Pickart and Margolina describes GHK as a natural component of human plasma, with a reported concentration of about 200 ng/mL at age 20 falling to about 80 ng/mL by age 60.^[2] The same sequence also occurs inside the α2 chain of type I collagen, a point that shaped how early researchers thought about it.^[3]

GHK vs GHK-Cu: identifiers, CAS number and molecular weight#

Most confusion about the "GHK-Cu molecular weight" or the "GHK-Cu CAS number" comes from mixing up the free tripeptide and its copper complex. PubChem keeps separate records for them:

The free tripeptide record is CID 73587,^[4] the neutral copper complex is CID 165429100,^[5] and the record under the nonproprietary name prezatide copper is CID 71587328.^[6] The National Library of Medicine's MeSH vocabulary lists GHK-Cu, copper(II)GHK and Iamin as entry terms under glycyl-histidyl-lysine and gives the registry number 49557-75-7, noting that it refers to the L-isomer of the tripeptide.^[7] A separate CAS number for the copper complex circulates in supplier catalogs; we could not verify it in PubChem and do not list it here.

The same logic applies to molecular weight. The copper complex weighs more than the free peptide by the mass of the copper atom less the two displaced hydrogens, and any salt counterion adds further mass. A single weight quoted without saying which form it describes cannot be checked against a test report. The GHK-Cu product page states the form supplied, and each lot's Certificate of Analysis should state which form its expected mass refers to.

Why researchers study GHK-Cu#

Interest has followed three threads. The first is copper: GHK binds copper(II) tightly, and copper is a cofactor for enzymes involved in connective tissue. The second is collagen, both because the GHK sequence is part of a collagen chain and because early fibroblast experiments measured collagen output. The third, more recent, is gene expression, where GHK turned up in computational searches of large public datasets. Each thread has its own small group of primary studies, and they are summarized below with the system each one used.

The primary studies, and what each measured#

Cell culture: Maquart et al., FEBS Letters, 1988#

This study used fibroblasts grown from human foreskin explants. The authors measured radiolabeled proline incorporation into collagen and non-collagen proteins, collagen hydroxyproline and procollagen mRNA after 24-hour exposure to GHK-Cu across a range of very low concentrations. They reported increased collagen secretion, with stimulation beginning at picomolar concentrations and peaking at about 10^-9 M, and no change in cell number or viability. GHK without copper produced about the same effect, and copper ions alone did not. The authors pointed out the GHK triplet in the α2 chain of type I collagen and proposed that enzymes at a wound site might release it. That proposal was a hypothesis, not something the experiment tested.^[3]

Rat wound chamber: Maquart et al., Journal of Clinical Investigation, 1993#

The same group moved to rats. Stainless-steel wire-mesh cylinders were implanted under the skin of the back to create a wound chamber, and GHK-Cu at several concentrations, saline or a control tripeptide was delivered into the chamber. The chamber contents were analyzed for dry weight, total protein, collagen, DNA, glycosaminoglycans and the mRNAs for collagens and TGF-β. The authors reported concentration-dependent increases in dry weight, DNA, protein, collagen and glycosaminoglycans, higher type I and type III collagen mRNA with no change in TGF-β mRNA, and no significant effect from the control tripeptide. This was an animal model of extracellular-matrix accumulation in rats.^[8]

Rat ischemic wounds: Canapp et al., Veterinary Surgery, 2003#

Twenty-four adult male rats were divided into three groups: a topical GHK-Cu gel, the gel vehicle alone, and no treatment. Six-millimeter full-thickness wounds were made within an ischemic skin flap on each rat's back, wound margins were traced daily for 13 days, and biopsies on days 6, 10 and 13 were analyzed for TNF-α and the matrix metalloproteinases MMP-2 and MMP-9. The authors reported smaller wound areas in the GHK-Cu group than in untreated controls on several days, and lower TNF-α, MMP-2 and MMP-9 concentrations in the biopsies. The study was in rats, with 24 animals in total.^[9]

Gene expression: Campbell et al., Genome Medicine, 2012#

This study started from human lung tissue, not from GHK. The authors profiled gene expression in 64 tissue samples taken from eight regions of each of eight lungs, six from patients with severe COPD and two from donors, and built a gene signature associated with emphysema severity. They then queried the Connectivity Map, a public database of gene-expression responses of cultured cells to many compounds, and found that GHK's expression profile ran opposite to that signature. Follow-up experiments used cultured primary human lung fibroblasts and measured gene expression, actin and integrin-β1 staining and collagen-gel contraction. Everything involving GHK was done in cultured cells or in database analyses; no person or animal received GHK in this work.^[10]

Pickart and Margolina later extended the Connectivity Map approach and reported that GHK was associated with an expression change of 50% or more in 31.2% of human genes in those datasets.^[2] The review itself cautions that computer-based gene findings often lack supporting biological data, and these figures describe cell-line responses in a database, not effects measured in tissue.

Topical formulation studies in people#

The only human data for GHK-Cu come from small studies of cosmetic creams and serums applied to skin. The 2018 review summarizes several of them: a 12-week facial cream study in 71 women with photoaged skin that measured skin density, thickness and wrinkle parameters; a 12-week eye-area cream study in 41 women compared with a placebo and a vitamin K cream; and an 8-week randomized, double-blind study comparing a GHK-Cu serum with a different cosmetic peptide product and with the carrier alone, measuring wrinkle volume and depth.^[2] The review reports these studies briefly and does not give participant numbers for several of them. Its authors list their affiliation as Skin Biology, a skin-care research company, which a reader should weigh when assessing the summary.

What has not been studied#

Outside topical cosmetic products, there are no controlled human studies of GHK-Cu in the sources reviewed here. The wound findings come from rats, the collagen findings from cultured fibroblasts and rat wound chambers, and the gene-expression findings from cell lines and database analyses. None of these has been followed by a controlled human trial of the same question.

• No controlled human trials outside topical cosmetic formulations.
• No FDA-approved drug containing GHK-Cu.
• Mechanistic statements about collagen release at wound sites, and gene-level effects, are hypotheses from cell, animal and computational work.
• Much of the summary literature comes from a small number of groups, including authors linked to the original discovery.

The FDA has addressed GHK-Cu in the context of pharmacy compounding. Its list of bulk drug substances that may present significant safety risks includes GHK-Cu for injectable routes of administration in the section for substances that were nominated and then withdrawn by the nominator, which the agency describes as substances previously in Category 2 of its interim policies. The stated concerns are that compounded injectable drugs containing GHK-Cu may pose a risk of immunogenicity and that there are limited data in humans to inform safety-related considerations.^[11]

What a GHK-Cu Certificate of Analysis should show#

Because GHK-Cu is a metal complex rather than a plain peptide, a report that gives only an HPLC purity figure leaves the main question open. A useful report addresses both the peptide and the copper:

1. Identity of the peptide. Mass spectrometry confirming the GHK sequence, with the report stating whether the observed mass is the free tripeptide or the copper complex.
2. Copper content or complex characterization. A measured copper content, or a copper-to-peptide ratio, against the expected one copper per peptide. Without it, the vial could hold uncomplexed peptide, excess copper salt, or both.
3. Purity by HPLC, with the chromatogram, so related peptide impurities are visible.
4. Form and appearance. Which salt or counterion is present, and the appearance; the copper complex is blue, as noted on the product page.
5. Lot number, method, laboratory and date, matching the vial.

Our guide to reading a Certificate of Analysis explains each of these fields in more detail, and the COA library lists every Renuvia lot with its current testing status. Stability of the lyophilized powder is covered in storing lyophilized peptides.