GHK Cu suppressed the activation of the p38 MAPK signaling pathway in Download Scientific Diagram Bioactive peptides in cosmetic formulations: Review of current in vitro and ex vivo evidence ScienceDirect GHK Cu is a naturally occurring tripeptide in human plasma. Levels average 200 ng ml at age 20 and drop to 80 ng ml by age 60 (Pickart et al., 2020). That decline tracks with OBM Geriatrics The Effect of the Human Plasma Molecule GHK Cu on Stem Cell Actions and Expression of Relevant Genes