Indoxyl Sulfate Contributes to Uremic Sarcopenia by Inducing Apoptosis in Myoblasts

Uremic sarcopenia is a complication of chronic kidney disease, particularly in its later stages, which leads to musculoskeletal disability. Uremic toxins have been linked to the pathogenesis of several manifestations of uremic syndrome. We sought to investigate whether indoxyl sulphate (IS), a protein-bound uremic toxin, is implicated in the development of uremic sarcopenia.

Myoblasts were exposed to IS at normal (0.6 mg/L, IS_0.6), uremic (53 mg/L, IS₅₃) or maximum uremic (236 mg/L, IS₂₃₆) concentrations for 24, 48 and 72 h. Cell viability was evaluated by MTT assay and by 7-aminoactinomycin D staining. ROS generation and apoptosis were evaluated by flow cytometry. MyoD and myogenin mRNA expression was evaluated by qRT-PCR and myosin heavy chain expression by immunocytochemistry.

Myoblast viability was reduced by IS236 in a time-dependent pattern (p <0.05; 84.4, 68.0, and 63.6%). ROS production was significantly higher (p <0.05) in cells exposed to IS₅₃ and IS₂₃₆ compared to control (untreated cells). The apoptosis rate was significantly higher in cells treated with IS₅₃ and IS₂₃₆ than in control after 48h (p <0.05; 4.7 ± 0.1% and 4.6 ± 0.3% vs. 3.1 ± 0.1%, respectively) and 72h (p <0.05; 9.6 ± 1.1% and 10.4 ± 0.3% vs. 3.1 ± 0.7%, respectively). No effect was observed on MyoD, myogenin, myosin heavy chain expression, and markers of myoblast differentiation at any IS concentration tested or time-point experiment.

These data indicate that IS has direct toxic effects on myoblast by decreasing its viability and increasing cell apoptosis. IS may be a potential target for treating uremic sarcopenia.