The laboratory entry
GHK-Cu in a collagen culture
The phrase that earns my confidence here is unusually precise: collagen synthesis changed without a change in the number of cells.
The collagen experiment
In the 1988 experiment in human fibroblast cultures, GHK-Cu stimulated collagen synthesis. The response began between 10^-12 and 10^-11 M and reached its maximum at 10^-9 M. Those are concentrations in a cell-culture experiment, describing what the investigators put into the culture medium.
The increase occurred independently of any change in cell number. For me, the interest sits in that distinction. A dish containing more cells could produce more material simply because there were more cells doing the work. Here, the reported result points to a change in collagen production without that explanation.
The experiment earns a particular kind of credit from me: it makes a collagen effect worth investigating. The result has enough detail to argue with. It leaves open how the same compound behaves in a finished topical preparation, how much reaches its target and which visible change, if any, follows.
Gene-expression results
A 2018 review of GHK and gene-expression data ranges much further. It reports that approximately 31.2% of human genes showed a change at a 50%-or-greater threshold in the analysis. Its evidence includes database analysis and cell-culture validation, with changes involving tissue repair, protein quality control and antioxidant programmes.
I become more demanding as the reach of the argument grows. A broad gene-expression signature offers many possible explanations to test. It also leaves many opportunities to mistake a molecular change for a desirable outcome. The percentage describes the analysis and its threshold; it gives no percentage improvement in somebody’s skin.
The simpler collagen experiment is easier for me to place. Its population was cultured human fibroblasts, its exposure was in the medium and its outcome was collagen synthesis. The gene analysis adds a field of possible mechanisms. Deciding which of those mechanisms matters in an applied preparation requires another experiment.
The gene figure has a threshold attached: 50%-or-greater change. I give that qualifier as much weight as the headline percentage.
From culture medium to a topical preparation
The topical GHK review identifies skin permeability as a central difficulty. That makes the next step in the argument a formulation question. Putting a compound into culture medium and applying a preparation to skin create different conditions.
The original collagen result gets the largest share of my confidence. For the applied question, the useful next stops are the delivery experiment and the reported skin outcomes. Each supplies a different piece of the preparation.