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Contribution of Ketone Oxidation on Energy Production in the Failing Heart

  • Author / Creator
    Pherwani, Simran A
  • One third of all deaths in Canada are due to cardiovascular diseases, including heart failure. Cardiovascular diseases have a considerable economic burden, and drastically impact the health and quality of life of Canadians. Heart failure (HF) is a clinical condition where the heart is unable to adequately pump blood throughout the body, limiting nutrient and 02 delivery. Individuals with type 2 diabetes (T2D) are at high risk of developing HF. A class of anti-diabetic drugs, sodium glucose co-transporter 2 inhibitors (SGLT2i), have recently been shown to improve HF outcomes in clinical trials with individuals with HF regardless of the presence of type 2 diabetes (T2D). SGLT2i are expressed in the proximal tubule of the kidney and are involved in 90% of the reabsorption of filtered glucose. SGLT2 inhibition prevents glucose reabsorption and reentry into the circulation, improving glycemic control. The EMPAREG-OUTCOMES trial in 2019 showed that the SGLT2i, empagliflozin, decreased hospitalization and deaths due to cardiovascular causes such as HF in T2D patients at high risk for cardiovascular events. The DAPA-HF trial in 2020 showed that the SGLT2i, dapagliflozin, also improved cardiac outcomes; however, in both the presence or absence of T2D. This was followed shortly after by the EMPEROR trial in 2021 which confirmed these observations with empagliflozin. However, it has not yet been fully established how exactly SGLT2i act to improve cardiac function, and the mechanisms responsible for their cardioprotective effects remain unclear. The failing heart exhibits a decrease in mitochondrial oxidative phosphorylation, namely glucose oxidation rates, resulting in decreased energy production in the heart. Increased evidence has shown that circulating ketones as well as cardiac ketone utilization increases in heart failure. Additionally, SGLT2i have been shown to increase circulating ketone levels. Therefore, we hypothesized that SGLT2i improve cardiac function by providing the failing heart with an extra source of fuel in the form of ketones. Thus, the purpose of this study was to determine whether increased energetics through providing ketones as an extra fuel to the failing heart is responsible for the improvement in cardiac function and cardiovascular outcomes seen in SGLT2i clinical trials, and to address a possible mechanism behind the cardioprotective effects. 8-week old C57BL6/N mice underwent a transverse aortic constriction (TAC) or sham surgery to induce pressure overload hypertrophy over 3 weeks, following which mice were randomized to receive either dapagliflozin (1mg/kg BW) or not in their drinking water for 4 weeks. Biweekly body weight and blood glucose and ketone measurements were taken. Echocardiography was done at 3 weeks and 6 weeks post surgery to assess cardiac function, and a glucose tolerance test (GTT) was done at the 6-week time point. After the 7-week protocol, mice were subjected to ex-vivo isolated working heart perfusions, where their hearts were perfused with radiolabelled Betahydroxybutyrate (BOHB), palmitate, or glucose to assess substrate oxidation and glycolytic rates. Hearts were perfused at physiological conditions of these substrates as well as concentrations seen following treatment (i.e. BOHB levels observed in vivo with Dapagliflozin treatment): this was 0.2 mM and 0.6 mM BOHB, respectively. Protein expression of ketone oxidation enzymes, as well as inflammation markers in the mouse heart were measured using immunoblotting. We did not observe an improvement in in vivo cardiac function; however, we did observe an increase in cardiac efficiency with DAPA treatment in HF, alongside increased ATP production due to increased glucose and BOHB oxidation rates. Additionally, we did not observe any significant improvement in circulating ketone levels with treatment, or in cardiac energy metabolism with dapagliflozin treatment at both 0.2 mM and 0.6 mM BOHB. Therefore, our results suggest that the beneficial cardiovascular effects of SGLT2i may not be due to fuel use and improved energetics as hypothesized, as we did not observe any significant changes in substrate oxidative rates with dapagliflozin. Since we observed a trend towards an increase in NLRP3/NALP3 inflammasome protein expression, we believe there is value in exploring the NLRP3/NALP3 inflammasome pathway as a potential mechanism through which SGLT2i may be acting.

  • Subjects / Keywords
  • Graduation date
    Fall 2021
  • Type of Item
    Thesis
  • Degree
    Master of Science
  • DOI
    https://doi.org/10.7939/r3-2dz6-3t18
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.