Background and Significance:
Metabolic heart disease(MHD) is common in patients with obesity, type 2 diabetes and/or metabolic syndrome. We found cardiac mitochondrial dysfunction in mice with obesity-related MHD due to consumption of a high fat high sucrose (HFHS) diet. The effects of diet-induced obesity on cardiac energetics and pump function in the intact organ are largely unknown.
Hypothesis:
We tested the hypothesis that cardiac mitochondrial dysfunction due to HFHS diet for one month impairs energetic and contractile reserve in the intact heart.
Methods and Results:
Mice were fed a HFHS or control diet (CD) for 1 month. In isolated cardiac mitochondria from HFHS-fed mice (vs. CD) the maximal rate of ATP synthesis was decreased for complex I (down by 42%; p<0.05) and II (down by 37%; p<0.05) substrates. We measured myocardial energetics in isolated perfused hearts using 31P NMR spectroscopy at baseline (450 bpm, 2 mM Ca++) and high workload (600 bpm, 4 mM Ca++) in HFHS (n=7) and CD (n=8) hearts. In HFHS-fed hearts, myocardial ATP concentration was the same at baseline (10.5±0.4 vs 10.4±0.5 mM) and high workload (7.4±0.9 vs. 7.5±0.5 mM) as that of CD hearts. However, in HFHS-fed hearts the concentration of phosphocreatine, which reflects energy reserve, was decreased at baseline (13±0.7 vs. 17.5±0.8 mM; p<0.01) and decreased further at high workload (down to 7.3±0.7; p<0.01 vs. baseline and p<0.01 vs. CD at 10.5±0.4 mM) - indicating a mismatch between ATP production and utilization. In HFHS hearts, the diastolic pressure-volume relationship was shifted upward and leftward at baseline, indicative of diastolic dysfunction. In HFHS hearts, baseline systolic function was preserved (rate pressure product 41,600±2,200 vs. 41,000±2,000 mmHg/min), but was decreased at high workload (54,800±7,200 vs. 85,300±4,300 mmHg/min; p<0.01 vs. CD), reflecting an impaired contractile reserve.
Conclusion:
Consumption of a HFHS diet for one month causes cardiac mitochondrial dysfunction with reduced ATP synthesis leading to impaired energetic reserve in the intact heart. Diastolic dysfunction at rest and the impaired ability to increase systolic function with increased work demands may result from impaired energetics in MHD.