Zinc (II) complexes with amino acids as new active ingredients of anti-acne preparations

USince zinc compounds have a number of beneficial properties for the skin, including accelerating wound healing, antimicrobial, sebostatic and demulcent activities, we decided to test a new group of zinc compounds as potential candidates for anti-acne applications.
Our research focuses on zinc (II) complexes of the general formula [Zn(AA)2], where AA represents an amino acid (L-Glu, Gly, L-His, L-Pro, L-Met, and L-Trp). Firstly, we designed and performed complexes’ syntheses; we confirmed compounds’ chemical structure and composition by 1H NMR spectroscopy , elemental analysis, and by single-crystal X-ray diffraction. In the next stage of the research the antibacterial properties of the zinc complexes were determined against the anaerobic strain of Cutibacterium acnes, three Gram-positive strains, viz. S. aureus ATCC 6538, S. epidermidis ATCC 12228, and S. pyogenes ATCC 19615, and two Gram-negative bacteria, viz. E. coli ATCC 25992 and P. aeruginosa ATCC 2785.Then, the cytotoxicity of the zinc complexes was evaluated against human skin fibroblasts (1BR.3.N cell line) and human epidermal keratinocyte cell lines. Based on the satisfactory results of these studies, two compounds, i.e. zinc complexes of glycine and histidine, were selected to create original gel formulations with a potential anti-acne effect. Physicochemical stability, microbiological purity (referring to PN-EN ISO standards) and efficacy of the preservative system (according to Ph. Eur. 10 methodology) for the prepared formulations were evaluated. Skin tolerance was determined in a group of 25 healthy volunteers by the patch test.
To sum up, the preparations containing zinc(II) complexes with glycine and histidine as active substances can be topically used in the treatment of acne skin due to their high antibacterial activity against C. acnes and low cytotoxicity for the skin cells. In the future, we plan to confirm our assumptions by testing the zinc-amino acids preparations on a group of volunteers with acne symptoms.
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