Potencial neurotóxico de um possível produto de transformação do L-BMAA: O ácido 1-metil-2-oxoimidazolina-4-carboxílico como indutor de neurodegeneração

Abstract

L-BMAA is a non-proteinogenic amino acid produced as a secondary metabolite by some plants and cyanobacteria species, gaining prominence for its association with a high incidence of neurodegenerative diseases on the island of Guam in the 1980s. Its relationship with neurodegenerative processes was linked to the hyperstimulation of ionotropic L-Glu receptors, interfering with calcium homeostasis and inducing cell death. Later studies, using in vitro models, confirmed that its toxicity is dependent on the carbonate ion, capable of forming additives with L-BMAA under physiological conditions. In previous work, a possible marker with m/z 145 was identified, which was related to the formation of a guanidine ring (1-methyl-2-oxoimidazoline-4-carboxylic acid) - cyclic BMAA. Similarly, other endogenous and exogenous compounds are related to the hyperstimulation of iGluRs and, consequently, neurodegenerative processes. Initially, a comprehensive review was conducted addressing the neurotoxic potential and structure-activity relationship of five iGluR agonists, including LBMAA, ß-ODAP, domoic acid, quinolinic acid, and L-homocysteic acid. Furthermore, a synthesis route for cyclic BMAA was proposed, and its toxicity was evaluated in vitro against the BV-2 microglial cell line using MTT assays, ROS assessment, mitochondrial membrane potential, and fluorescence-based cell death mechanism analysis. As a result, the compound was synthesized with 86% purity, and its chemical structure was confirmed by Nuclear Magnetic Resonance (NMR) and High-Resolution Mass Spectrometry (HRMS). Concentrations of 0.21 ± 0.12 and 0.8 ± 0.09 mM were defined as the LD25 and LD50 for BV- 2 cells, respectively. Both the MTT assay and morphological analysis of cells after 24 hours of treatment demonstrated a dose-dependent effect. Fluorescence assays further revealed the acute effects of cyclic BMAA, such as induction of apoptosis and increased ROS. In summary, this work demonstrates the possibility of this compound having a novel toxicity effect, which may be the key to explaining the effects demonstrated for over 40 years, related to the highest known rate of neurodegeneration in the world. [resumo fornecido pelo autor]