Heptapeptide Semax demonstrates high affinity for copper(II) ions, protecting neuroblastoma and endothelial cells from metal-induced cytotoxicity.

The dysregulation of metal ions, known as dys-homeostasis, is a critical factor implicated in the pathology of several neurodegenerative disorders. The brain is a specialized organ that actively concentrates metal ions, making it particularly vulnerable to imbalances. An excess of certain metals, like copper, can induce cellular toxicity and contribute to cognitive decline. The regulatory peptide Semax, an analog of the adrenocorticotropic hormone fragment ACTH(4-10), is already known for its neuroprotective activities and its positive effects on learning and cognitive brain functions. Understanding its interaction with metal ions could reveal a novel mechanism for its neuroprotective properties and offer new therapeutic avenues for metal-associated neurotoxicity.

This in vitro study investigated the metal-binding capabilities and protective effects of Semax. Researchers performed an equilibrium study to characterize the interaction between Semax and copper(II) ions (Cu²⁺), identifying the types of complexes formed at different pH levels and their coordination chemistry. To assess the peptide's protective ability, they used an MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay to measure cell viability. The assay was conducted on two distinct cell lines: human SH-SY5Y neuroblastoma cells and RBE4 rat brain endothelial cells. These cells were exposed to copper to induce cytotoxicity, both with and without the presence of Semax, to determine if the peptide could mitigate the metal's toxic effects.

The equilibrium study confirmed that Semax has a high affinity for copper(II) ions. It forms three distinct complex species with copper. Two minor species, [CuL] and [CuLH-1]-, coexist in the pH range from 3.6 to 5. As the pH rises above 5, a single complex, [CuLH-2]2-, becomes the predominant species. In this stable form, the donor atoms are arranged around the copper ion in a 4N planar coordination mode, indicating a strong and specific binding interaction. Most significantly, the MTT assay revealed a protective effect against metal-induced damage.

The presence of Semax resulted in a reduced copper-induced cytotoxicity in both the SH-SY5Y neuroblastoma cell line and the RBE4 endothelial cell line. The study demonstrates that by chelating copper ions, Semax can effectively neutralize their toxic potential in relevant neural and vascular cell models, providing a biochemical basis for its observed neuroprotective activities.

Written by TitrateLab, separately from the study summarized above.