Determination of the antioxidant activity and antibacterial effect of the α-lipoic acid-NHS molecule in fisheries products

Abstract

Alpha-lipoic acid plays significant roles in metabolic pathways and provides substantial antioxidant defense. In this study, the N-hydroxysuccinimide ester derivative (alpha-lipoic acid-NHS) was examined for antioxidant performance and inhibitory effects on Gram-negative and Gram-positive bacterial strains isolated from aquatic environments. Antioxidant performance was evaluated using DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging and CUPRAC (cupric ion reducing) assays. Additionally, The compound's ability to mitigate oxidative stress was evaluated by quantifying reactive oxygen species (ROS) levels with the 8-OHdG ELISA method at different alpha-lipoic acid-NHS concentrations. Antibacterial activity was tested against four reference pathogens (Staphylococcus aureus, Aeromonas hydrophila, Salmonella enterica, Escherichia coli) and four environmental isolates (Bacillus cereus, B. toyonensis, Oceanisphaera sediminis, Pseudomonas putida) using the microdilution method. The results showed that alpha-lipoic acid-NHS exhibited negligible antioxidant activity in both DPPH and CUPRAC assays. In terms of antibacterial effects, however, complete inhibition of growth was observed in some bacterial strains at higher concentrations (5-10 mM). While ROS levels decreased modestly with increasing alpha-lipoic acid-NHS, this effect did not correlate with chemical antioxidant test results, suggesting the reduction was not due to direct antioxidant action. In conclusion, alpha-lipoic acid-NHS does not function as an effective direct radical scavenger but may exert indirect antioxidant effects and moderate antibacterial activity. It may have potential as a supportive compound in antioxidant systems and antibacterial therapies rather than as a standalone therapeutic agent.