Inhibition of Serine Palmitoyl Transferase I Reduces Cardiac Ceramide Levels and Increases Glycolysis Rates following Diet-Induced Insulin Resistance

Objective: Diet-induced obesity (DIO) leads to an accumulation of intra-myocardial lipid metabolites implicated in causing cardiac insulin resistance and contractile dysfunction. One such metabolite is ceramide, and our aim was to determine the effects of inhibiting de novo ceramide synthesis on cardiac function and insulin stimulated glucose utilization in mice subjected to DIO. Materials and Methods: C57BL/6 mice were fed a low fat diet or subjected to DIO for 12 weeks, and then treated for 4 weeks with either vehicle control or the serine palmitoyl transferase I (SPT I) inhibitor, myriocin. In vivo cardiac function was assessed via ultrasound echocardiography, while glucose metabolism was assessed in isolated working hearts. Results: DIO was not associated with an accumulation of intra-myocardial ceramide, but rather, an accumulation of intra-myocardial DAG (2.63±0.41 vs. 4.80±0.97 nmol/g dry weight). Nonetheless, treatment of DIO mice with myriocin decreased intra-myocardial ceramide levels (50.3±7.7 vs. 26.9±2.7 nmol/g dry weight) and prevented the DIO-associated increase in intra-myocardial DAG levels. Interestingly, although DIO impaired myocardial glycolysis rates (7789±1267 vs. 2671±326 nmol/min/g dry weight), hearts from myriocin treated DIO mice exhibited an increase in glycolysis rates. Conclusions: Our data reveal that although intra-myocardial ceramide does not accumulate following DIO, inhibition of de novo ceramide synthesis nonetheless reduces intra-myocardial ceramide levels and prevents the accumulation of intra-myocardial DAG. These effects improved the DIO-associated impairment of cardiac glycolysis rates, suggesting that SPT I inhibition increases cardiac glucose utilization. © 2012 Ussher et al.published_or_final_versio

Empagliflozin Prevents Worsening of Cardiac Function in an Experimental Model of Pressure Overload-Induced Heart Failure

This study sought to determine whether the sodium/glucose cotransporter 2 (SGLT2) inhibitor empagliflozin improved heart failure (HF) outcomes in nondiabetic mice. The EMPA-REG OUTCOME (Empagliflozin, Cardiovascular Outcome Event Trial in Type 2 Diabetes Mellitus Patients) trial demonstrated that empagliflozin markedly prevented HF and cardiovascular death in subjects with diabetes. However, despite ongoing clinical trials in HF patients without type 2 diabetes, there are no objective and translational data to support an effect of SGLT2 inhibitors on cardiac structure and function, particularly in the absence of diabetes and in the setting of established HF. Male C57Bl/6 mice were subjected to either sham or transverse aortic constriction surgery to induce HF. Following surgery, mice that progressed to HF received either vehicle or empagliflozin for 2 weeks. Cardiac function was then assessed in vivo using echocardiography and ex vivo using isolated working hearts. Although vehicle-treated HF mice experienced a progressive worsening of cardiac function over the 2-week treatment period, this decline was blunted in empagliflozin-treated HF mice. Treatment allocation to empagliflozin resulted in an improvement in cardiac systolic function, with no significant changes in cardiac remodeling or diastolic dysfunction. Moreover, isolated hearts from HF mice treated with empagliflozin displayed significantly improved ex vivo cardiac function compared to those in vehicle-treated controls. Empagliflozin treatment of nondiabetic mice with established HF blunts the decline in cardiac function both in vivo and ex vivo, independent of diabetes. These data provide important basic and translational clues to support the evaluation of SGLT2 inhibitors as a treatment strategy in a broad range of patients with established HF

Myriocin treatment of DIO mice decreases intra-myocardial ceramide levels and prevents the accumulation of intra-myocardial DAG.

<p><i>A:</i> Intra-myocardial TAG, <i>B:</i> ceramide, <i>C:</i> long chain acyl CoA, and <i>D:</i> DAG levels in low fat fed and DIO mice treated with vehicle control or myriocin. Values represent mean ± SE (n = 4–8). Differences were determined using a one-way ANOVA followed by Bonferroni post-hoc analysis. *<i>P</i><0.05, significantly different from vehicle control counterpart. ^†<i>P</i><0.05, significantly different from low fat fed counterpart.</p

Cardiac PDH activity is not impaired in DIO mice treated with myriocin.

<p><i>A:</i> Cardiac PDH activity in control and myriocin treated DIO Mice. <i>B:</i> % decrease in cardiac PDH activity relative to low fat fed counterparts. <i>C</i>: Cardiac PDK4 protein expression is increased in control treated DIO mice, but not myriocin treated DIO mice. Values represent mean ± SE (n = 6). Differences were determined using an unpaired Student’s two-tailed t-test or a one-way ANOVA followed by a Bonferroni’s post-hoc analysis. *<i>P</i><0.05, significantly different from DIO control mice. ^†<i>P</i><0.05, significantly different from low fat fed counterpart.</p

Plasma Lipids in DIO and <i>db/db</i> mice.

<p>Plasma TAG and FFA levels ad libitum were measured in DIO and <i>db/db</i> mice treated with vehicle control or myriocin (n = 4–7). Values represent means ± SE.</p

H⁺ production in hearts from DIO mice.

<p>H⁺ production was calculated in control and myriocin treated DIO mice by subtracting the rate of glucose oxidation from the rate of glycolysis and multiplying by two. Values represent mean ± SE (n = 6–7). Differences were determined using an unpaired Student’s two-tailed t-test. *<i>P</i> = 0.13.</p

Insulin resistance in mice following DIO.

<p><i>A:</i> 12 weeks of DIO results in significant increases in body weight in mice. <i>B:</i> This increase in body weight resulted in whole body glucose intolerance, and <i>C:</i> insulin resistance. Values represent mean ± SE (n = 10–11). Glucose and insulin were administered via intraperitoneal injection. Differences were determined using an unpaired Student’s two-tailed t-test or two-way ANOVA followed by a Bonferroni’s post-hoc analysis. *<i>P</i><0.05, significantly different from low fat fed counterpart. ^†<i>P</i><0.05, significantly different from low fat fed counterpart at 12 weeks post-diet.</p