What is the safe topical dosing, duration, and contraindications for the copperbinding peptide GHKCu for wound healing or antiaging? Rational modification of PROTACs for tumor selective protein degradation 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 Nanoengineered Self Assembling Peptides with Increased Proteolytic Stability Promote Wound Healing ACS Applied Materials & Interfaces