Additive Effects of N-Acetylcysteine and [R₄W₄] Combination Treatment on Mycobacterium avium

Mycobacterium avium is an opportunistic pathogen and a leading contributor to nontuberculous mycobacterial infections in immunocompromised individuals. However, treatment duration, antibiotic toxicity, and resistance present challenges in the management of mycobacterium infections, prompting the need for novel treatment. N-acetylcysteine (NAC) has demonstrated potent antimycobacterial activity, while antimicrobial peptides such as the cyclic [R₄W₄] have shown additive effects when combined with first-line antibiotics. This study aimed to investigate the mechanism and efficacy of NAC and [R₄W₄] combination therapy against M. avium. A membrane depolarization assay was used to evaluate the effects of NAC and [R₄W₄] on M. avium cell membrane integrity. Antimycobacterial activity was assessed by treating cultures with varying concentrations of NAC, [R₄W₄], a combination, or a sham treatment. The same regimens were applied to M. avium-infected THP-1-derived macrophages to assess intracellular efficacy. NAC and [R₄W₄] each disrupted the M. avium membrane potential, with enhanced effects in combination. The combination treatment significantly reduced M. avium survival in both the culture and infected macrophages compared with NAC alone and untreated controls. [R₄W₄] and NAC also demonstrated potent antibacterial activity, while the lowest MIC and the combination of [R₄W₄] and NAC displayed additive effects, indicating an improved bacterial inhibition compared to individual treatments. These findings demonstrate the additive activity of NAC and [R₄W₄] against M. avium in vitro and suggest that combining antioxidant compounds with antimicrobial peptides may represent a promising strategy for treating mycobacterial infections.