Table 1.
Animal characteristics of lean and diabetic ZDF rats after 2 weeks of treatment with water or 30, 100 or 300 mg/kg body weight/day metformin (MET30, MET100 and MET300, respectively).
Figure 1.
In vivo oxidative capacity of tibialis anterior (TA) muscle, assessed by 31P MRS.
Representative examples of 31P MR spectra obtained during rest with 32 averages (A) and at the end of the electrical-stimulation protocol with 4 averages (B). (C) Representative examples of relative PCr concentrations during rest, muscle stimulation and recovery (time resolution = 20 s) for a water-treated diabetic rat (open symbols) and a diabetic rat treated with metformin at 300 mg/kg body weight/day (filled symbols). PCr concentrations are expressed as a percentage of the resting PCr concentration. Mono-exponential functions (dark lines) were fit to the recovery data and the PCr recovery rate constants were 0.63 and 0.21 min-1 for the water-treated and metformin-treated animal, respectively. (D) Rate constants of PCr recovery, kPCr, after electrical stimulation in TA muscle of lean and diabetic rats treated with water or 30, 100 or 300 mg/kg body weight/day metformin (MET30, MET100 and MET300 respectively). Data is represented as mean ± SD (n = 6 per group). kPCr was significantly lower in diabetic rats compared with lean rats, independent of treatment regimen (ANOVA: P<0.001). In addition, treatment had a significant effect on kPCr, independent of genotype, and a pairwise analysis of differences is provided by Bonferroni-corrected post-hoc tests: * P<0.001 when compared with water-treated animals, † P<0.001 when compared with MET30-treated animals, ‡ P<0.001 when compared with MET100-treated animals.
Table 2.
Metabolite concentrations and pH in TA muscle measured by 31P MRS of lean and diabetic ZDF rats after 2 weeks of treatment with water or 30, 100 or 300 mg/kg body weight/day metformin (MET30, MET100 and MET300, respectively).
Figure 2.
Relative mitochondrial-DNA copy number of lean and diabetic rats after 2 weeks of treatment with either water or metformin (300 mg/kg bodyweight/day).
Data is represented as mean ± SD (n = 6 per group).
Figure 3.
O2 consumption rates determined in mitochondria isolated from TA muscle of lean and diabetic rats treated with water or 30, 100 or 300 mg/kg body weight/day metformin (MET30, MET100 and MET300, respectively) for 2 weeks, fueled by pyruvate plus malate (Complex I-dependent substrate).
Respiratory capacity was determined in the OXPHOS state, when mitochondrial respiration is coupled to ATP synthesis; the LEAK-state, when the system is limited by ADP; and the ETS state, after uncoupling of the ETS from ATP synthesis. Data is represented as mean ± SD (n = 6 per group). For the OXPHOS state, the interaction between genotype and treatment was borderline significant and for the LEAK and ETS state, the interaction between genotype and treatment was significant. A pairwise analysis of differences is provided by Bonferroni-corrected two-sided unpaired t-tests: * P<0.05 when compared with water-treated animals of the same genotype, † P<0.05 when compared with MET30-treated animals of the same genotype, ‡ P<0.05 when compared with MET100-treated animals of the same genotype, # P<0.05 when compared with lean animals of the same treatment regimen.
Table 3.
Respiratory control ratios (RCR's) in mitochondria isolated from TA muscle of lean and diabetic rats treated with water or 30, 100 or 300 mg/kg body weight/day metformin (MET30, MET100 and MET300, respectively) for 2 weeks, fueled by pyruvate plus malate (Complex I-dependent substrate) and succinate plus rotenone (Complex II-dependent substrate).
Figure 4.
O2 consumption rates determined in mitochondria isolated from TA muscle of lean and diabetic rats treated with water or 30, 100 or 300 mg/kg body weight/day metformin (MET30, MET100 and MET300 respectively) for 2 weeks, fueled by succinate plus rotenone (Complex II-dependent substrate).
Respiratory capacity was determined in the OXPHOS state, when mitochondrial respiration is coupled to ATP synthesis; and the LEAK-state, when the system is limited by ADP. Data is represented as mean ± SD (n = 6 per group). For the OXPHOS state, the interaction between genotype and treatment was significant and a pairwise analysis of differences is provided by Bonferroni-corrected two-sided unpaired t-tests: ‡ P<0.05 when compared with MET100-treated animals of the same genotype.
Figure 5.
O2 flux measured in mitochondria isolated from TA muscle of lean and diabetic ZDF rats after 5 min of incubation with metformin (1 mM), normalized to O2 flux measured in isolated mitochondria without addition of metformin.
Respiratory capacity was determined in the OXPHOS state, when mitochondrial respiration is coupled to ATP synthesis, fueled with either pyruvate plus malate (Complex I respiration) or succinate plus rotenone (Complex II respiration). Data is represented as mean ± SD (n = 6 per group). Incubation with metformin significantly lowered OXPHOS respiration fueled with pyruvate plus malate, independent of genotype (ANOVA: * P<0.001). Metformin did not affect Complex II respiration.