Quantitative structure–activity relationship for 4-hydroxy-2-alkenal induced cytotoxicity in L6 muscle cells

Lipid peroxidation is one of the most important sources of endogenous toxic metabolites. 4-Hydroxy-2-nonenal (HNE) and 4-hydroxy-2-hexenal (HHE) are produced in several oxidative stress associated diseases from peroxidation of n-6 and n-3 polyunsaturated fatty acids, respectively. Both are able to form covalent adducts with many biomolecules. Particularly, proteins adduction can induce structural and conformational changes and impair biological function, which may be involved in the toxicity of hydroxy-alkenals. The aim of this study was to compare the effect of 4-hydroxy-2-alkenals to several chemically related derivatives in order to clarify the physico-chemical requirement of their toxicity. L6 muscle cells were treated with HHE, HNE and parent derivatives (acetal derivative, trans-alkenals and alkanals). Viability and necrosis were estimated using MTT, LDH and caspase-3 tests. Log LC50 (Lethal Concentration 50) was then tested for correlation with adducts formation (estimated using dinitrophenylhydrazine) and several molecular descriptors in order to establish quantitative structure–toxicity relationship (QSTR) models. The rank of derivatives toxicity, based on LC50 was: hydroxy-alkenals > acetal derivatives ≈ 2-alkenals > alkanals and a high correlation was found between log LC50 and protein carbonylation. Moreover, log LC50 was correlated to the electrophilic descriptor LUMO (lowest unoccupied molecular orbital) as well as with electronegativity-related molecular descriptors such as number of oxygen atoms, partial negative surface area (PNSA3) and partial positive surface area (PPSA3). Together, these results point out the important role of the electrophilic structure and adduct formation in hydroxy-alkenals toxicity. Our present study demonstrates that 4-hydroxy-2-alkenals dramatic effects on cell viability are due to covalent adducts formation, particularly Michael adducts. This capacity is related to the electrophilic structure and reactive CC double bond, making it highly accessible for nucleophilic addition. The present study suggests that nucleophilic scavengers might protect cells against electrophile compounds and might be of possible therapeutic value in oxidative stress associated diseases.