Mitochondrial inefficiencies and anoxic ATP hydrolysis capacities in diabetic rat heart

Abstract

As ~80% of diabetic patients die from heart failure, an understanding of diabetic cardiomyopathy is crucial. Mitochondria occupy 35-40% of the mammalian cardiomyocyte volume and supply 95% of the heart's ATP, and diabetic heart mitochondria show impaired structure, arrangement, and function. We predict that bioenergetic inefficiencies are present in diabetic heart mitochondria; therefore, we explored mitochondrial proton and electron handling by linking oxygen flux to steady-state ATP synthesis, reactive oxygen species (ROS) production, and mitochondrial membrane potential (ΔΨ) within rat heart tissues. Sprague-Dawley rats were injected with streptozotocin (STZ, 55 mg/kg) to induce type 1 diabetes or an equivalent volume of saline (control, n = 12) and fed standard rat chow for 8 wk. By coupling high-resolution respirometers with purpose-built fluorometers, we followed Magnesium Green (ATP synthesis), Amplex UltraRed (ROS production), and safranin-O (ΔΨ). Relative to control rats, the mass-specific respiration of STZ-diabetic hearts was depressed in oxidative phosphorylation (OXPHOS) states. Steady-state ATP synthesis capacity was almost one-third lower in STZ-diabetic heart, which, relative to oxygen flux, equates to an estimated 12% depression in OXPHOS efficiency. However, with anoxic transition, STZ-diabetic and control heart tissues showed similar ATP hydrolysis capacities through reversal of the F1F0-ATP synthase. STZ-diabetic cardiac mitochondria also produced more net ROS relative to oxygen flux (ROS/O) in OXPHOS. While ΔΨ did not differ between groups, the time to develop ΔΨ with the onset of OXPHOS was protracted in STZ-diabetic mitochondria. ROS/O is higher in lifelike OXPHOS states, and potential delays in the time to develop ΔΨ may delay ATP synthesis with interbeat fluctuations in ADP concentrations. Whereas diabetic cardiac mitochondria produce less ATP in normoxia, they consume as much ATP in anoxic infarct-like states.

Role of Oxygen Free Radicals, Nitric Oxide and Mitochondria in Mediating Cardiac Alterations During Liver Cirrhosis Induced by Thioacetamide

“…The uncoupling of mitochondrial respiration and oxidative phosphorylation, producing the decrease in respiratory control ratio, was evident by 3 months, at which time cirrhosis is evident histologically in the liver. A similar decrease in respiratory control ratio has been observed in failed human myocardial tissue [39], and diabetic hearts were also shown to have lower ATP levels and compromised mitochondrial respiration [40]. An important feature of cellular injury is activation of the mitochondrial permeability transition (MPT) pore, which can be induced by oxidative stress [41].…”

Mitochondrial glycerol 3-phosphate facilitates bumblebee pre-flight thermogenesis

“…ATP production was measured simultaneously with respiration rates using Magnesium Green™ (MgG, ThermoFisher Scientific, Waltham, MA, USA) fluorescence (ex/em, 503 nm/530 nm), based on previous work 32–34 . Flight muscle was prepared as previously described before being added to the chamber.…”

“…PM and G3P-supported respiration protocols were conducted as described above. ATP production signal was calibrated based on previous work by conducting a separate titration of ATP and ADP up to 5 mM 32 . ATP production rates were then determined by expressing this change in ATP concentration over time in Excel (Microsoft, Redmond, WA, USA).…”

Mitochondrial dysfunction and its impact on diabetic heart

“…In chronic Type 1 diabetes (OVE26 mice) mice model, it was demonstrated that mice had evidence of mitochondrial biogenesis that was coupled to a reduction in mitochondrial function and mitochondrial ultrastructural defects [57]. Mitochondrial state III respiration is significantly reduced in type 2 diabetic animal models (db/db and ob/ob) [58–60]. Furthermore, there is evidence for increased cardiac mitochondrial biogenesis with ultrastructural defects in insulin resistance and diabetes animals [59, 61–64].…”