Myoglobin induces oxidative stress and decreases endocytosis and monolayer permissiveness in cultured kidney epithelial cells without affecting viability.

BACKGROUND: Muscle degradation caused by severe burn releases myoglobin (Mb), which accumulates in the kidney (termed myoglobinuria). Mb is a pro-oxidant.

AIM: To demonstrate that Mb promotes oxidative stress and dysfunction in cultured Madin-Darby canine kidney type II (MDCK II) cells.

METHODS: The glutathione redox ratio was used to monitor oxidative stress. Regulation of antioxidant response genes was determined with RT-PCR. Propidium iodide and annexin V staining were markers of necrosis and apoptosis, respectively. Mitochondrial function was assessed by monitoring mitochondrial depolarisation. Endocytosis was determined with immune fluorescence microscopy, and monolayer permeability was monitored with labelled inulin.

RESULTS: Kidney epithelial cells exposed to (0-100 muM) Mb showed a dose-dependent decrease in the glutathione redox ratio indicative of enhanced oxidative stress. In parallel, the expression of antioxidant genes for superoxide dismutase (SOD)-1/2, inducible haemoxygenase (HO-1) and catalase (CAT) increased in MDCK II cells, coupled with increases in corresponding activity. Notably, apoptosis and necrosis remained unaffected. However, transferrin endocytosis and monolayer permeability decreased significantly, while clathrin distribution and mitochondrial function were unaffected.

CONCLUSION: Low concentrations of Mb promote oxidative stress in kidney epithelial cells that manifest as subtle changes to function without decreasing viability. Whether this impairs kidney function in burns patients is not clear.