Abstract P364: Liraglutide Protects Against Angiotensin-induced Diastolic Dysfunction And Is Associated With Altered Acetyl-coa Metabolism

Background: The mechanisms underlying diastolic dysfunction remain complicated and poorly understood. Previously implicated mechanisms include increased interstitial fibrosis and oxidative damage, altered calcium handling, and mitochondrial dysfunction. In this study, we investigate changes in the cardiac metabolic profile from mice with Angiotensin-II (Ang)-induced diastolic dysfunction. Because treatment with the GLP-1 agonist liraglutide (Lira) relieves Ang-induced diastolic dysfunction, we examined altered metabolites in Ang and Ang+Lira mice to identify metabolic pathways involved. Methods: 8-wk mice were implanted with Ang pumps (1000 ng/kg/min) +/- Lira (0.2 mg/kg/day) therapy for 4 wks and compared to sham mice. Baseline and 4-wk echocardiography was performed. Hearts were collected for RNA-sequencing, Western blot, histology, radiolabeled palmitate assay, and targeted metabolomics by liquid chromatography-mass spectrometry to assess metabolic changes. Results: After Ang treatment, mice had significant diastolic dysfunction but only mild hypertrophy based on echo and histologic measures and no evidence of systolic change. Compared to sham mice, Ang mice had reduced E/A (Sham, 2.67±0.40; Ang, 1.71±0.11; p<0.05) and peak reverse longitudinal strain rate (rLSR;Sham, 8.48±0.65/s; Ang, 6.081±0.33/s; p<0.05, consistent with diastolic dysfunction. Ang+Lira mice had improved E/A (3.57±0.50, p<0.01 vs. Ang) and rLSR (8.65±0.68/s, p<0.01 vs Ang). Targeted metabolomic analysis of hearts found significantly increased accumulation of Acetyl-CoA in Ang mice (peak area 0.14±0.02) compared to sham (0.04±0.02 ,p<0.05) that is restored by Lira therapy (0.02±0.01 ,p<0.05 vs sham and Ang). A radiolabeled palmitate oxidation assay found decreased palmitate oxidation in both Ang and Ang+Lira mice compared to sham, but interestingly, also demonstrated significantly lower acid soluble metabolite oxidation in the Ang+Lira mice vs. Ang alone. Conclusions: We found that Ang-treated mice accumulate myocardial Acetyl-CoA, suggesting a defect in TCA flux. Lira resolves the increase in Acetyl-CoA and improved measures of diastolic dysfunction. This data may implicate a novel metabolic pathway in the development of diastolic disease.

Cold acclimation enhances UCP1 content, lipolysis, and triacylglycerol resynthesis, but not mitochondrial uncoupling and fat oxidation, in rat white adipocytes

The objective of this study was to investigate whether cold-induced browning of the subcutaneous (Sc) inguinal (Ing) white adipose tissue (WAT) increases the capacity of this tissue to oxidize fatty acids through uncoupling protein 1 (UCP1)-mediated thermogenesis. To accomplish that, rats were acclimated to cold (4°C for 7 days). Subsequently, interscapular and aortic brown adipose tissues (iBAT and aBAT, respectively), epididymal (Epid), and Sc Ing WAT were used for adipocyte isolation. In BAT adipocytes, cold acclimation increased UCP1 content and palmitate oxidation either in the absence or presence of oligomycin, whereas in Sc Ing adipocytes glucose and palmitate oxidation were not affected, although multilocular adipocytes were formed and UCP1 content increased upon cold acclimation in the WAT. Furthermore, isoproterenol-stimulated cold Sc Ing adipocytes exhibited significantly lower rates of palmitate oxidation than control cells when exposed to oligomycin. These findings provide evidence that, despite increasing UCP1 levels, cold acclimation essentially reduced mitochondrial uncoupling-mediated fat oxidation in Sc Ing adipocytes. Conversely, glycerol kinase and phosphoenolpyruvate carboxykinase levels, isoproterenol-induced lipolysis, as well as glycerol and palmitate incorporation into lipids significantly increased in these cells. Therefore, instead of UCP1-mediated mitochondrial uncoupling, cold acclimation increased the capacity of Sc Ing adipocytes to export fatty acids and enhanced key components of the triacylglycerol resynthesis pathway in the Sc Ing WAT.

Increased ketone body oxidation provides additional energy for the failing heart without improving cardiac efficiency

AimsThe failing heart is energy-starved and inefficient due to perturbations in energy metabolism. Although ketone oxidation has been shown recently to increase in the failing heart, it remains unknown whether this improves cardiac energy production or efficiency. We therefore assessed cardiac metabolism in failing hearts and determined whether increasing ketone oxidation improves cardiac energy production and efficiency.Methods and resultsC57BL/6J mice underwent sham or transverse aortic constriction (TAC) surgery to induce pressure overload hypertrophy over 4-weeks. Isolated working hearts from these mice were perfused with radiolabelled β-hydroxybutyrate (βOHB), glucose, or palmitate to assess cardiac metabolism. Ejection fraction decreased by 45% in TAC mice. Failing hearts had decreased glucose oxidation while palmitate oxidation remained unchanged, resulting in a 35% decrease in energy production. Increasing βOHB levels from 0.2 to 0.6 mM increased ketone oxidation rates from 251 ± 24 to 834 ± 116 nmol·g dry wt−1 · min−1 in TAC hearts, rates which were significantly increased compared to sham hearts and occurred without decreasing glycolysis, glucose, or palmitate oxidation rates. Therefore, the contribution of ketones to energy production in TAC hearts increased to 18% and total energy production increased by 23%. Interestingly, glucose oxidation, in parallel with total ATP production, was also significantly upregulated in hearts upon increasing βOHB levels. However, while overall energy production increased, cardiac efficiency was not improved.ConclusionsIncreasing ketone oxidation rates in failing hearts increases overall energy production without compromising glucose or fatty acid metabolism, albeit without increasing cardiac efficiency.

Fibroblast growth factor 21 and exercise-induced hepatic mitochondrial adaptations

Exercise stimulates hepatic mitochondrial adaptations; however, the mechanisms remain largely unknown. Here we tested whether FGF21 plays an obligatory role in exercise induced hepatic mitochondrial adaptations by testing exercise responses in FGF21 knockout mice. FGF21 knockout (FGF21-KO) and wild-type (WT) mice (11–12 wk of age) had access to voluntary running wheels for exercise (EX) or remained sedentary for 8 wk. FGF21 deficiency resulted in greater body weight, adiposity, serum cholesterol, insulin, and glucose concentrations compared with WT mice ( P < 0.05). In addition, hepatic mitochondrial complete palmitate oxidation, β-hydroxyacyl-CoA dehydrogenase (β-HAD) activity, and nuclear content of PGC-1α were 30–50% lower in FGF21-KO mice compared with WT mice ( P < 0.01). EX effectively lowered body weight, adiposity, serum triglycerides, free fatty acids, and insulin and normalized mitochondrial complete palmitate oxidation in the FGF21-KO mice, whereas the reduced hepatic β-HAD activity and lowered nuclear content of PGC-1α in FGF21-KO mice were not restored by EX. In addition, EX increased hepatic CPT-1α mRNA expression and ACC phosphorylation (a marker of increased AMPK activity) and reduced hepatic triacylglycerol content in both genotypes. However, FGF21-KO mice displayed a lower EX-induced increase in the mRNA expression of the hepatic gluconeogenic gene, PEPCK, compared with WT. In conclusion, FGF21 does not appear necessary for exercise-induced systemic and hepatic mitochondrial adaptations, but the increased adiposity, hyperinsulinemia, and impairments in hepatic mitochondrial function induced by FGF21 deficiency can be partially rescued by daily wheel running exercise.

Leukemia inhibitory factor increases glucose uptake in mouse skeletal muscle

Members of the IL-6 family, IL-6 and ciliary neurotrophic factor (CNTF), have been shown to increase glucose uptake and fatty acid oxidation in skeletal muscle. However, the metabolic effects of another family member, leukemia inhibitory factor (LIF), are not well characterized. Effects of LIF on skeletal muscle glucose uptake and palmitate oxidation and signaling were investigated in ex vivo incubated mouse soleus and EDL muscles from muscle-specific AMPKα2 kinase-dead, muscle-specific SOCS3 knockout, and lean and high-fat-fed mice. Inhibitors were used to investigate involvement of specific signaling pathways. LIF increased muscle glucose uptake in dose (50-5,000 pM/l) and time-dependent manners with maximal effects at the 30-min time point. LIF increased Akt Ser473 phosphorylation (P) in soleus and EDL, whereas AMPK Thr172 P was unaffected. Incubation with parthenolide abolished LIF-induced glucose uptake and STAT3 Tyr705 P, whereas incubation with LY-294002 and wortmannin suppressed both basal and LIF-induced glucose uptake and Akt Ser473 P, indicating that JAK and PI 3-kinase signaling is required for LIF-stimulated glucose uptake. Incubation with rapamycin and AZD8055 indicated that mammalian target of rapamycin complex (mTORC)2, but not mTORC1, also is required for LIF-stimulated glucose uptake. In contrast to CNTF, LIF stimulation did not alter palmitate oxidation. LIF-stimulated glucose uptake was maintained in EDL from obese insulin-resistant mice, whereas soleus developed LIF resistance. Lack of SOCS3 and AMPKα2 did not affect LIF-stimulated glucose uptake. In conclusion, LIF acutely increased muscle glucose uptake by a mechanism potentially involving the PI 3-kinase/mTORC2/Akt pathway and is not impaired in EDL muscle from obese insulin-resistant mice.

Abstract 689: Cystathionine-Beta-Synthase Deficiency Induces Cardiac Hypertrophy and Contributes to Diminished Fatty Acid Oxidation in Mice with Diet-Induced Obesity

Obesity-related cardiac lipid accumulation is associated with lipotoxicity and dysfunction. Cysteine is required for the synthesis of the antioxidant glutathione, which can be supplied by the transsulfuration of homocysteine by cystathionine-beta-synthase (Cbs). Cbs+/- mice with diet-induced obesity had greater glucose intolerance and lipotoxicity in the heart. Our objective was to determine the functional effects and mechanisms of cardiac lipotoxicity in Cbs+/- mice with diet-induced obesity. Cbs+/- and Cbs+/+ mice were fed a control diet or a high-fat diet (HFD) from weaning for 20 weeks. As expected, Cbs+/+ and Cbs+/- mice fed the HFD had greater final body weights, visceral (retroperitoneal and epididymal) and subcutaneous (inguinal) adiposity compared to mice fed the control diet. Cbs+/- mice had greater heart weights accompanied by higher concentrations of long chain polyunsaturated fatty acids arachidonic acid, 20:4n6 (AA) and docosahexaenoic acid, 22:6n3 (DHA) in the heart compared to Cbs+/+ mice. Mice fed the HFD had higher AA, but lower DHA concentrations in the heart compared to mice fed the control diet, with the greatest effect in Cbs+/- mice. Isolated working hearts revealed a reduced heart rate and cardiac output in Cbs+/- mice fed the control diet compared to Cbs+/+ mice. Independent of diet, Cbs+/- mice also had reduced aortic flow compared to Cbs+/+ mice, with a higher coronary flow only in Cbs+/- mice fed the HFD. Working hearts also revealed that Cbs+/- mice had lower palmitate oxidation rates compared to Cbs+/+ mice, with higher palmitate oxidation and glycolysis rates in mice fed the HFD compared to mice fed the control diet. Cbs+/- mice had a lower ratio of phosphorylated-AMP activated protein kinase alpha (AMPKα)/AMPKα expression (regulator of cellular energy) in heart compared to Cbs+/+ mice, and this occurred to a greater extent in those fed the HFD. Furthermore, we observed a higher ratio of collagen type 1(COL1α1)/ collagen type 3 (COL3α1) expression (implicated in myocardial stiffness) in heart, only in Cbs+/- mice fed the HFD. Collectively, these findings suggest that cardiac lipotoxicity in Cbs+/- mice with obesity is associated with cardiac hypertrophy, impaired cardiac fatty acid metabolism, and cardiac dysfunction.

Gender-Related Effects on Substrate Utilization and Metabolic Adaptation in Hairless Spontaneously Hypertensive Rat

Cold exposure of rats leads to ameliorated glucose and triglyceride utilization with females displaying better adaptation to a cold environment. In the current study, we used hairless rats as a model of increased thermogenesis and analyzed gender-related effects on parameters of lipid and glucose metabolism in the spontaneously hypertensive (SHR) rats. Specifically, we compared hairless coisogenic SHR-Dsg4 males and females harboring mutant Dsg4 (desmoglein 4) gene versus their SHR wild type controls. Two way ANOVA showed significant Dsg4 genotype (hairless or wild type) x gender interaction effects on palmitate oxidation in brown adipose tissue (BAT), glucose incorporation into BAT determined by microPET, and glucose oxidation in skeletal muscles. In addition, we observed significant interaction effects on sensitivity of muscle tissue to insulin action when Dsg4 genotype affected these metabolic traits in males, but had little or no effects in females. Both wild type and hairless females and hairless males showed increased glucose incorporation and palmitate oxidation in BAT and higher tissue insulin sensitivity when compared to wild type males. These findings provide evidence for gender-related differences in metabolic adaptation required for increased thermogenesis. They are consistent with the hypothesis that increased glucose and palmitate utilization in BAT and muscle is associated with higher sensitivity of adipose and muscle tissues to insulin action.

TBC1D1 reduces palmitate oxidation by inhibiting β-HAD activity in skeletal muscle

In skeletal muscle the Rab-GTPase-activating protein TBC1D1 has been implicated in the regulation of fatty acid oxidation by an unknown mechanism. We determined whether TBC1D1 altered fatty acid utilization via changes in protein-mediated fatty acid transport and/or selected enzymes regulating mitochondrial fatty acid oxidation. We also determined the effects of TBC1D1 on glucose transport and oxidation. Electrotransfection of mouse soleus muscles with TBC1D1 cDNA increased TBC1D1 protein after 2 wk ( P < 0.05), without altering its paralog AS160. TBC1D1 overexpression decreased basal palmitate oxidation (−22%) while blunting 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR)-stimulated palmitate oxidation (−18%). There was a tendency to increase fatty acid esterification (+10 nmol·g−1·60 min−1, P = 0.07), which reflected the reduction in fatty acid oxidation (−12 nmol·g−1·60 min−1). Concomitantly, basal (+21%) and AICAR-stimulated glucose oxidation (+8%) were increased in TBC1D1-transfected muscles relative to their respective controls ( P < 0.05), independent of changes in GLUT4 and glucose transport. The reductions in TBC1D1-mediated fatty acid oxidation could not be attributed to changes in the transporter FAT/CD36, muscle mitochondrial content, CPT1 expression or the expression and phosphorylation of AS160, acetyl-CoA carboxylase, or AMPK. However, TBC1D1 overexpression reduced β-HAD enzyme activity (−18%, P < 0.05). In conclusion, TBC1D1-mediated reduction of muscle fatty acid oxidation appears to occur via inhibition of β-HAD activity.

Combining metformin and aerobic exercise training in the treatment of type 2 diabetes and NAFLD in OLETF rats

Here, we sought to compare the efficacy of combining exercise and metformin for the treatment of type 2 diabetes and nonalcoholic fatty liver disease (NAFLD) in hyperphagic, obese, type 2 diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rats. OLETF rats (age: 20 wk, hyperglycemic and hyperinsulinemic; n = 10/group) were randomly assigned to sedentary (O-SED), SED plus metformin (O-SED + M; 300 mg·kg−1·day−1), moderate-intensity exercise training (O-EndEx; 20 m/min, 60 min/day, 5 days/wk treadmill running), or O-EndEx + M groups for 12 wk. Long-Evans Tokushima Otsuka (L-SED) rats served as nonhyperphagic controls. O-SED + M, O-EndEx, and O-EndEx + M were effective in the management of type 2 diabetes, and all three treatments lowered hepatic steatosis and serum markers of liver injury; however, O-EndEx lowered liver triglyceride content and fasting hyperglycemia more than O-SED + M. In addition, exercise elicited greater improvements compared with metformin alone on postchallenge glycemic control, liver diacylglycerol content, hepatic mitochondrial palmitate oxidation, citrate synthase, and β-HAD activities and in the attenuation of markers of hepatic fatty acid uptake and de novo fatty acid synthesis. Surprisingly, combining metformin and aerobic exercise training offered little added benefit to these outcomes, and in fact, metformin actually blunted exercise-induced increases in complete mitochondrial palmitate oxidation and β-HAD activity. In conclusion, aerobic exercise training was more effective than metformin administration in the management of type 2 diabetes and NAFLD outcomes in obese hyperphagic OLETF rats. Combining therapies offered little additional benefit beyond exercise alone, and findings suggest that metformin potentially impairs exercise-induced hepatic mitochondrial adaptations.