Mitochondrial dysfunction and oxidative stress in patients with chronic kidney disease

Abstract

Mitochondria abnormalities in skeletal muscle may contribute to frailty and sarcopenia, commonly present in patients with chronic kidney disease (CKD). Dysfunctional mitochondria are also a major source of oxidative stress and may contribute to cardiovascular disease in CKD We tested the hypothesis that mitochondrial structure and function worsens with the severity of CKD Mitochondrial volume density, mitochondrial DNA (mtDNA) copy number, BNIP3, and PGC1α protein expression were evaluated in skeletal muscle biopsies obtained from 27 subjects (17 controls and 10 with CKD stage 5 on hemodialysis). We also measured mtDNA copy number in peripheral blood mononuclear cells (PBMCs), plasma isofurans, and plasma F2-isoprostanes in 208 subjects divided into three groups: non-CKD (eGFR>60 mL/min), CKD stage 3-4 (eGFR 60-15 mL/min), and CKD stage 5 (on hemodialysis). Muscle biopsies from patients with CKD stage 5 revealed lower mitochondrial volume density, lower mtDNA copy number, and higher BNIP3 content than controls. mtDNA copy number in PBMCs was decreased with increasing severity of CKD: non-CKD (6.48, 95% CI 4.49-8.46), CKD stage 3-4 (3.30, 95% CI 0.85-5.75, P = 0.048 vs. non-CKD), and CKD stage 5 (1.93, 95% CI 0.27-3.59, P = 0.001 vs. non-CKD). Isofurans were higher in patients with CKD stage 5 (median 59.21 pg/mL, IQR 41.76-95.36) compared to patients with non-CKD (median 49.95 pg/mL, IQR 27.88-83.46, P = 0.001), whereas F2-isoprostanes did not differ among groups. Severity of CKD is associated with mitochondrial dysfunction and markers of oxidative stress. Mitochondrial abnormalities, which are common in skeletal muscle from patients with CKD stage 5, may explain the muscle dysfunction associated with frailty and sarcopenia in CKD Further studies are required to evaluate mitochondrial function in vivo in patients with different CKD stages.

Keywords: BNIP3; PGC1α; chronic kidney disease; mitochondria; mitochondrial DNA copy number; oxidative stress; skeletal muscle.

Figure 1

Representative electron micrograph of skeletal muscles from a healthy control (A) and patients with CKD stage 5 on maintenance hemodialysis (CKD 5/MHD). (A) Normal subsarcolemmal mitochondria. (B) Mitochondria with signs of swelling. (C) Double membrane structure compatible with auto‐phagosome. (D) Lipofuscin pigment (scale bar = 500 μm).

Figure 2

(A) Mitochondrial volume density (MVD) in controls with normal kidney function (N = 17) and patients with CKD stage 5 on maintenance hemodialysis (CKD 5/MHD, N = 10) in the vastus lateralis. (B) Frequency distribution of MVD in individual myofibers showed a greater proportion of fibers with lower MVD in patients with CKD stage 5.

Figure 3

(A) Mitochondrial DNA (mtDNA) copy number in the vastus lateralis in controls with normal kidney function (N = 8) and patients with CKD stage 5 on maintenance hemodialysis (CKD5/MHD, N = 10). (B) Representative Western blots of BCL‐2/adenovirus interacting protein 3 BNIP3 in the vastus lateralis in controls and patients with CKD5/MHD (N = 9 in each group); Coomassie blue staining was used as loading control. (C) Optical densities were calculated using the NIH software image J.

Figure 4

Mitochondrial DNA (mtDNA) copy number in peripheral blood mononuclear cells (PBMCs) in patients with different stages of CKD. Patients were divided into three groups according to eGFR: Non‐CKD (eGFR > 60 mL/min, N = 28), CKD 3–4 (eGFR between 15 and 60 mL/min, N = 17), and CKD 5/MHD (eGFR < 15 mL/min on maintenance hemodialysis, N = 42). P values were adjusted for gender, age, BMI, and history of diabetes.

Figure 5

Plasma lactate levels in patients with different stages of chronic kidney disease (CKD). Patients were divided in three groups according to eGFR: Non‐CKD (eGFR > 60 mL/min, N = 109), CKD 3–4 (eGFR between 15 and 60 mL/min, N = 35), and CKD 5/MHD (eGFR < 15 mL/min on maintenance hemodialysis, N = 42). P values were adjusted for gender, age, BMI, and history of diabetes. Normal lactate concentrations are less than 2 mmol/L.

Figure 6

Mitochondrial complex I activity, F2‐isoprostanes, and isofurans in kidneys from mice treated with doxorubicin. Mice were treated with a single IP injection of either vehicle (N = 10) or doxorubicin (20 mg/kg, N = 10). Kidneys were collected 72 h later. Complex I activity was normalized to the amount of protein in mitochondria pellets.

Figure 7

F2‐isoprostanes and isofurans in patients with different stages of chronic kidney disease (CKD). Patients were divided in three groups according to eGFR: Non‐CKD (eGFR > 60 mL/min, N = 74), CKD 3–4 (eGFR between 15 and 60 mL/min, N = 26), and CKD5/MHD (eGFR < 15 mL/min on maintenance hemodialysis, N = 61). P values were adjusted for gender, age, BMI, and history of diabetes. Normal values in healthy controls for F2‐isoprostanes and isofurans are 35 ± 6 pg/mL and 43 ± 5 pg/mL, respectively.