Prolonged linezolid therapy induces progressive mitochondrial dysfunction in human peripheral blood mononuclear cells

Background Linezolid commonly causes hematologic toxicity, especially thrombocytopenia, during extended treatment. This effect is linked to the inhibition of mitochondrial protein synthesis, which impairs oxidative phosphorylation and cellular energy production. Although reduced complex IV activity has been observed in long-term therapy, the connection between treatment duration and mitochondrial dysfunction in humans remains insufficiently defined. Methods Forty patients were included and stratified by treatment duration: 2–7 days (group 1), 8–14 days (group 2) and more than 14 days (group 3). To evaluate mitochondrial function in peripheral blood mononuclear cells (PBMCs) from patients treated with linezolid for different durations, Seahorse XF was used. To assess protein expression changes associated with mitochondrial toxicity, LC-MS/MS was used. Differentially expressed proteins were identified in R based on fold-change thresholds (|log₂FC|≥0.58) and p < 0.05, and results were visualized with volcano plots and STRING interaction networks. Results All the groups were similar in terms of variables and characteristics. Mitochondrial respiration declined progressively with treatment duration and platelet counts showed a parallel reduction. Proteomic analysis identified one cluster of downregulated protein in group 2 of patients and two in group 3; they were involved in mitochondrial ATP synthesis—mainly subunits of complexes I and IV of the respiratory chain—supporting a concordant functional and molecular pattern of mitochondrial impairment. Conclusions Prolonged linezolid treatment was associated with progressive mitochondrial dysfunction, as reflected by both functional assays and proteomic profiles. Concordant changes in respiration and protein expression support mitochondrial involvement in linezolid-related toxicity and suggest that, in addition to previously reported alterations in complex IV, complex I proteins may also be affected in treated patients.