Histidine and Histidinamide Prevent Copper-Induced Oxidative Stress and Cell Death in Skin Keratinocytes

Unbound free copper ions are a significant concern in biological systems, as they can catalyze the production of reactive oxygen species (ROS), leading to oxidative stress and subsequent cell death. While copper is essential as a cofactor for many enzymes, its dysregulation can be highly detrimental, particularly in tissues like the skin, which are constantly exposed to environmental factors. Current strategies for mitigating copper-induced toxicity often involve metal chelators, but identifying specific compounds that offer both potent chelation and cytoprotective effects without adverse reactions remains a challenge. This study investigates amino acids as potential safe and effective chelators to protect skin cells.

Researchers conducted an in vitro study to evaluate the copper chelation activities and cytoprotective effects of 20 free amino acids and 20 amidated amino acids in cultured HaCaT keratinocytes. Cells were exposed to CuSO4 (0.4-1.0 mM) to induce cell death and oxidative stress. The primary interventions were individual amino acids, including histidine (1.0 mM), histidinamide (1.0 mM), cysteine (1.0 mM), and cysteinamide (1.0 mM). Key endpoints included cell viability, ROS production, glutathione oxidation, lipid peroxidation, and protein carbonylation. EDTA and GHK-Cu were used as reference compounds to benchmark chelation and protective effects.

Among the free amino acids, cysteine demonstrated the highest copper chelation activity, followed by histidine and glutamic acid. Similarly, cysteinamide exhibited the highest chelation among amidated amino acids, with histidinamide ranking second. Exposure to CuSO4 (0.4-1.0 mM) induced cell death in a concentration-dependent manner in HaCaT cells. Notably, at a concentration of 1.0 mM, only histidine and histidinamide effectively prevented the cell death caused by 1.0 mM CuSO4. In stark contrast, cysteine and cysteinamide, despite their superior copper-chelating activities, showed no cytoprotective effects. Reference compounds EDTA and GHK-Cu also failed to provide cytoprotection. > Histidine and histidinamide uniquely suppressed the CuSO4-induced ROS production, glutathione oxidation, lipid peroxidation, and protein carbonylation in HaCaT cells, indicating a broader protective mechanism beyond simple chelation. These specific amino acids demonstrated a distinct ability to mitigate multiple markers of oxidative damage.