AHK

AHK is the tripeptide alanyl-histidyl-lysine (C15H26N6O4, MW 354.41, CAS 126828-32-8). It is structurally parallel to GHK, the better-known copper-binding tripeptide, differing in its first residue — alanine rather than glycine — and like GHK it is used mainly as a copper complex, AHK-Cu.

AHK-Cu has a genuinely specific piece of human-tissue evidence behind it, which is unusual in cosmetic peptides. In a study of human hair follicles cultured ex vivo, AHK-Cu at 10⁻¹² to 10⁻⁹ M stimulated elongation of the follicles and proliferation of dermal papilla cells. Dermal papilla cells are the specialised fibroblasts that govern hair follicle morphogenesis and growth, so this is a mechanistically relevant target rather than a generic proliferation readout.

The apoptosis findings are worth reporting precisely, because they are often overstated. At 10⁻⁹ M, AHK-Cu reduced the number of apoptotic dermal papilla cells, but that reduction was

not statistically significant . What did change was the molecular signature: the Bcl-2/Bax ratio rose and cleaved caspase-3 and PARP fell — consistent with reduced apoptotic signalling even though the cell count difference did not reach significance.

The limiting factor for every topical peptide is delivery. Peptides are hydrophilic and relatively large, while the stratum corneum is a lipophilic barrier built to exclude exactly such molecules. A peptide that performs well in a fibroblast culture has not thereby been shown to reach fibroblasts through intact skin. Reviews of cosmeceutical peptides identify this permeability gap — not receptor pharmacology — as the principal open problem, and note that formulation strategies such as oil-in-water and water-in-oil-in-water emulsions are used to try to close it with uncertain success.

The supporting study is ex vivo and in vitro at picomolar-to-nanomolar concentrations applied directly to tissue and cells — conditions a topical product must actually achieve at the follicle to be comparable, which skin permeability makes uncertain. The anti-apoptotic cell-count result did not reach statistical significance. No controlled clinical trial of topical AHK for hair growth or skin appearance was located.

AHK is the tripeptide Ala-His-Lys (C15H26N6O4, MW 354.41, CAS 126828-32-8, PubChem CID 7408502). The histidine imidazole and the N-terminal amine provide the copper-coordinating chemistry; the biologically studied form is the copper complex AHK-Cu rather than the free peptide.