However, we have also pointed out some shortfalls in this evidence
Free Cu2+ is toxic (Fenton reactions, hydroxyl radicals), but the GHK-Cu complex is stable, diffusible and delivers copper in a targeted manner to copper-dependent metalloenzymes: lysyl oxidase (collagen/elastin crosslinking), Cu/Zn superoxide dismutase (SOD1, antioxidant defence), tyrosinase (controlled melanogenesis), dopamine-beta-hydroxylase
Metabolism & Elimination Limited characterization of specific metabolic pathways has been published for both peptides: CJC-1295 (NO DAC): Peptidase-mediated degradation represents primary metabolic pathway Four amino acid substitutions provide enhanced resistance to dipeptidyl peptidase-IV Metabolites and degradation products not fully characterized in published literature Clearance from circulation within hours despite sustained pharmacodynamic effects Ipamorelin: Clearance of 0.078 L/h/kg in human pharmacokinetic studies Rapid elimination from plasma following distribution phase Metabolic pathways likely involve proteolytic cleavage at peptide bonds No significant accumulation observed with repeated dosing in animal models A notable pharmacokinetic-pharmacodynamic disconnect exists: despite relatively short plasma half-lives (30 minutes to 2 hours), growth hormone secretory effects persist for 6+ hours, suggesting either active metabolites, tissue retention, or persistent receptor signaling cascade activation
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