Polymyxin antibiotics induce nephrotoxicity through the selective inhibition of Complex I-dependent respiration in mouse and rat mitochondria.

Colistin and polymyxin B are last-resort antibiotics for the treatment of infections caused by multidrug-resistant Gram-negative bacteria; however, their clinical use is limited by considerable nephrotoxicity. Mitochondrial dysfunction has been proposed as one mechanism that contributes to polymyxin-induced kidney injury, but the precise mitochondrial target remains unclear. In the present study, we investigated the effects of colistin and polymyxin B on mitochondrial respiratory complexes. NMRI mice were treated subcutaneously with colistin or polymyxin B (20 mg/kg) every 8 h for a total of six times, which resulted in the accumulation of colistin and polymyxin B 29 and 40 μg/g kidney tissue, respectively. Both polymyxins increased the expression of markers of tubular damage up to 29-fold and induced mitochondrial dysfunction in the kidney. In in vitro experiments using mitochondria from intact kidneys, low concentrations of colistin inhibited Complex I-dependent respiration in the OXPHOS state, with an IC₅₀ of approximately 5 μg/mL. This effect was Complex I-specific because at 5 μg/mL, colistin and polymyxin B did not impair respiration supported by other respiratory chain complexes or compromise mitochondrial membrane integrity. Similar Complex I inhibition by polymyxins was detected in vitro in rat kidney mitochondria. In conclusion, our findings identify mitochondrial Complex I as a sensitive target of colistin and polymyxin B and suggest that inhibition of Complex I-dependent respiration is a key driver of polymyxin-induced nephrotoxicity. This mechanism provides a toxicological framework for understanding interactions between polycationic peptide antibiotics and mitochondrial respiration and may support the selection and optimisation of safer antimicrobial peptides.