Distinct oxygenases and their oxylipin products have been shown to participate in thermogenesis by mediating physiological adaptations required to sustain body temperature. Since the role of the lipoxygenase (LOX) family in cold adaptation remains elusive, we aimed to investigate whether, and how, LOX activity is required for cold adaptation and to identify LOX-derived lipid mediators that could serve as putative cold mimetics with therapeutic potential to combat diabetes. By utilizing mass-spectrometry-based lipidomics in mice and humans, we demonstrated that cold and β3-adrenergic stimulation could promote the biosynthesis and release of 12-LOX metabolites from brown adipose tissue (BAT). Moreover, 12-LOX ablation in mouse brown adipocytes impaired glucose uptake and metabolism, resulting in blunted adaptation to the cold in vivo. The cold-induced 12-LOX product 12-HEPE was found to be a batokine that improves glucose metabolism by promoting glucose uptake into adipocytes and skeletal muscle through activation of an insulin-like intracellular signaling pathway.

Liraglutide, a glucagon-like peptide-1 receptor (GLP-1R) agonist used for the treatment of T2D, has been shown to alleviate diabetic cardiomyopathy (DbCM) in experimental T2D, which was associated with increased myocardial glucose oxidation. To determine whether this increase in glucose oxidation is necessary for cardioprotection, we hypothesized that liraglutide’s ability to alleviate DbCM would be abolished in mice with cardiomyocyte-specific deletion of pyruvate dehydrogenase (PDH; Pdha1 CM−/− mice), the rate-limiting enzyme of glucose oxidation. Male Pdha1 CM−/− mice and their α-myosin heavy chain Cre expressing littermates (αMHC Cre mice) were subjected to experimental T2D via 10 weeks of high-fat diet supplementation, with a single low-dose injection of streptozotocin (75 mg/kg) provided at week 4. All mice were randomized to treatment with either vehicle control or liraglutide (30 µg/kg) twice daily during the final 2.5 weeks, with cardiac function assessed via ultrasound echocardiography. As expected, liraglutide treatment improved glucose homeostasis in both αMHC Cre and Pdha1 CM−/− mice with T2D, in the presence of mild weight loss. Parameters of systolic function were unaffected by liraglutide treatment in both αMHC Cre and Pdha1 CM−/− mice with T2D. However, liraglutide treatment alleviated diastolic dysfunction in αMHC Cre mice, as indicated by an increase and decrease in the e′/a′ and E/e′ ratios, respectively. Conversely, liraglutide failed to rescue these indices of diastolic dysfunction in Pdha1 CM−/− mice. Our findings suggest that increases in glucose oxidation are necessary for GLP-1R agonist mediated alleviation of DbCM. As such, strategies aimed at increasing PDH activity may represent a novel approach for the treatment of DbCM.

Growth differentiation factor 15 (GDF15) is a peptide with utility in obesity, as it decreases appetite and promotes weight loss. Because obesity increases the risk for type 2 diabetes (T2D) and cardiovascular disease, it is imperative to understand the cardiovascular actions of GDF15, especially since elevated GDF15 levels are an established biomarker for heart failure. As weight loss should be encouraged in the early stages of obesity-related prediabetes/T2D, where diabetic cardiomyopathy is often present, we assessed whether treatment with GDF15 influences its pathology. We observed that GDF15 treatment alleviates diastolic dysfunction in mice with T2D independent of weight loss. This cardioprotection was associated with a reduction in cardiac inflammation, which was likely mediated via indirect actions, as direct treatment of adult mouse cardiomyocytes and differentiated THP-1 human macrophages with GDF15 failed to alleviate lipopolysaccharide-induced inflammation. Therapeutic manipulation of GDF15 action may thus have utility for both obesity and diabetic cardiomyopathy.

HomeJournal of the American Heart AssociationAhead of PrintPharmacological Inhibition of Succinyl Coenzyme A:3‐Ketoacid Coenzyme A Transferase Alleviates the Progression of Diabetic Cardiomyopathy Open AccessRapid CommunicationPDF/EPUBAboutView PDFView EPUBSections ToolsAdd to favoritesDownload citationsTrack citationsPermissions ShareShare onFacebookTwitterLinked InMendeleyReddit Jump toOpen AccessRapid CommunicationPDF/EPUBPharmacological Inhibition of Succinyl Coenzyme A:3‐Ketoacid Coenzyme A Transferase Alleviates the Progression of Diabetic Cardiomyopathy Amanda A. Greenwell, Seyed Amirhossein Tabatabaei Dakhili, Cory S. Wagg, Christina T. Saed, Jordan S.F. Chan, Kunyan Yang, Indiresh A. Mangra‐Bala, Magnus J. Stenlund, Farah Eaton, Keshav Gopal, Jason R.B. Dyck, Gary D. Lopaschuk and John R. Ussher Amanda A. GreenwellAmanda A. Greenwell https://orcid.org/0000-0003-0355-2938 , Faculty of Pharmacy and Pharmaceutical Sciences, , University of Alberta, , Edmonton, , AB, , Canada, , Cardiovascular Research Institute, , University of Alberta, , Edmonton, , AB, , Canada, , Alberta Diabetes Institute, , University of Alberta, , Edmonton, , AB, , Canada, , Seyed Amirhossein Tabatabaei DakhiliSeyed Amirhossein Tabatabaei Dakhili https://orcid.org/0000-0002-8104-5029 , Faculty of Pharmacy and Pharmaceutical Sciences, , University of Alberta, , Edmonton, , AB, , Canada, , Cardiovascular Research Institute, , University of Alberta, , Edmonton, , AB, , Canada, , Alberta Diabetes Institute, , University of Alberta, , Edmonton, , AB, , Canada, , Cory S. WaggCory S. Wagg , Cardiovascular Research Institute, , University of Alberta, , Edmonton, , AB, , Canada, , Alberta Diabetes Institute, , University of Alberta, , Edmonton, , AB, , Canada, , Department of Pediatrics, , University of Alberta, , Edmonton, , AB, , Canada, , Christina T. SaedChristina T. Saed https://orcid.org/0000-0002-4469-330X , Faculty of Pharmacy and Pharmaceutical Sciences, , University of Alberta, , Edmonton, , AB, , Canada, , Cardiovascular Research Institute, , University of Alberta, , Edmonton, , AB, , Canada, , Alberta Diabetes Institute, , University of Alberta, , Edmonton, , AB, , Canada, , Jordan S.F. ChanJordan S.F. Chan https://orcid.org/0009-0006-1567-8772 , Faculty of Pharmacy and Pharmaceutical Sciences, , University of Alberta, , Edmonton, , AB, , Canada, , Cardiovascular Research Institute, , University of Alberta, , Edmonton, , AB, , Canada, , Alberta Diabetes Institute, , University of Alberta, , Edmonton, , AB, , Canada, , Kunyan YangKunyan Yang https://orcid.org/0000-0002-5586-5875 , Faculty of Pharmacy and Pharmaceutical Sciences, , University of Alberta, , Edmonton, , AB, , Canada, , Cardiovascular Research Institute, , University of Alberta, , Edmonton, , AB, , Canada, , Alberta Diabetes Institute, , University of Alberta, , Edmonton, , AB, , Canada, , Indiresh A. Mangra‐BalaIndiresh A. Mangra‐Bala https://orcid.org/0009-0007-2259-1664 , Faculty of Pharmacy and Pharmaceutical Sciences, , University of Alberta, , Edmonton, , AB, , Canada, , Cardiovascular Research Institute, , University of Alberta, , Edmonton, , AB, , Canada, , Alberta Diabetes Institute, , University of Alberta, , Edmonton, , AB, , Canada, , Magnus J. StenlundMagnus J. Stenlund https://orcid.org/0009-0006-7009-2168 , Faculty of Pharmacy and Pharmaceutical Sciences, , University of Alberta, , Edmonton, , AB, , Canada, , Cardiovascular Research Institute, , University of Alberta, , Edmonton, , AB, , Canada, , Alberta Diabetes Institute, , University of Alberta, , Edmonton, , AB, , Canada, , Farah EatonFarah Eaton https://orcid.org/0000-0002-8251-8908 , Faculty of Pharmacy and Pharmaceutical Sciences, , University of Alberta, , Edmonton, , AB, , Canada, , Cardiovascular Research Institute, , University of Alberta, , Edmonton, , AB, , Canada, , Alberta Diabetes Institute, , University of Alberta, , Edmonton, , AB, , Canada, , Keshav GopalKeshav Gopal https://orcid.org/0000-0002-3320-2990 , Faculty of Pharmacy and Pharmaceutical Sciences, , University of Alberta, , Edmonton, , AB, , Canada, , Cardiovascular Research Institute, , University of Alberta, , Edmonton, , AB, , Canada, , Alberta Diabetes Institute, , University of Alberta, , Edmonton, , AB, , Canada, , Jason R.B. DyckJason R.B. Dyck https://orcid.org/0000-0002-7045-2884 , Cardiovascular Research Institute, , University of Alberta, , Edmonton, , AB, , Canada, , Alberta Diabetes Institute, , University of Alberta, , Edmonton, , AB, , Canada, , Department of Pediatrics, , University of Alberta, , Edmonton, , AB, , Canada, , Gary D. LopaschukGary D. Lopaschuk https://orcid.org/0000-0003-1010-0454 , Cardiovascular Research Institute, , University of Alberta, , Edmonton, , AB, , Canada, , Alberta Diabetes Institute, , University of Alberta, , Edmonton, , AB, , Canada, , Department of Pediatrics, , University of Alberta, , Edmonton, , AB, , Canada, and John R. UssherJohn R. Ussher * Correspondence to: John R. Ussher, 2‐020E Katz Group Centre for Pharmacy and Health Research, Faculty of Pharmacy and Pharmaceutical Sciences, University of Alberta, Edmonton, AB T6G 2R3 Canada. Email: E-mail Address: [email protected] https://orcid.org/0000-0001-9574-5707 , Faculty of Pharmacy and Pharmaceutical Sciences, , University of Alberta, , Edmonton, , AB, , Canada, , Cardiovascular Research Institute, , University of Alberta, , Edmonton, , AB, , Canada, , Alberta Diabetes Institute, , University of Alberta, , Edmonton, , AB, , Canada, Originally published27 Mar 2024https://doi.org/10.1161/JAHA.123.032697Journal of the American Heart Association. 2024;0:e032697Previous studies have demonstrated that the antipsychotic agent, pimozide, can improve hyperglycemia in type 2 diabetes (T2D) secondary to inhibition of the ketone oxidation enzyme, succinyl CoA (coenzyme A):3‐ketoacid CoA transferase (SCOT).1 Given that T2D is associated with a diabetic cardiomyopathy (DbCM) often characterized by diastolic dysfunction,2 we aimed to assess the actions of SCOT inhibition on DbCM pathogenesis. As human studies have suggested that increased ketone oxidation is an adaptive response in heart failure,3 strategies to improve glycemia via decreasing ketone oxidation may inadvertently worsen DbCM and increase risk for heart failure as a consequence.All animal procedures were conducted in accordance with the regulations of the Canadian Council on Animal Care and approved by the University of Alberta Health Sciences Animal Welfare Committee. The data presented in this study are available from the corresponding author upon reasonable request.Male C57BL/6J mice were subjected to T2D via high‐fat diet supplementation for 12‐weeks, with streptozotocin (75 mg/kg) administered at week 4 (Figure [A]), whereas their lean counterparts were provided standard chow. A cohort of mice at study completion had their hearts isolated and perfused in the working mode to assess metabolism. Myocardial glycolysis and glucose oxidation were decreased in mice with T2D, whereas palmitate oxidation was unchanged (Figure [B]). Notably, myocardial ketone (β‐hydroxybutyrate [βOHB]) oxidation was also impaired in mice with T2D, which was paradoxically associated with an increase in myocardial SCOT activity (Figure [B, C]). Protein expression profiling of ketone oxidation revealed a decrease in βOHB dehydrogenase 1, which may explain the reduction of myocardial βOHB oxidation (Figure [D]).Download figureDownload PowerPointFigure Figure . Pimozide treatment inhibits SCOT activity and attenuates diastolic dysfunction in mice with experimental T2D.A, Experimental model of T2D and study design. B, Myocardial energy metabolism during aerobic perfusion of isolated working mouse hearts perfused with Krebs Henseleit solution containing 11 mM glucose, 1.2 mM palmitate and 0.8 mM βOHB, with the appropriate radiolabeled tracers for the measurement of glycolysis ([5‐3H]glucose), glucose oxidation ([U‐14C]glucose), fatty acid oxidation ([9,10‐3H]palmitate), and ketone body oxidation ([3‐14C]βOHB) (n=3–6). C, SCOT activity in myocardial tissue assessed via monitoring the ultraviolet absorbance at 313 nM to measure the rate of acetoacetyl CoA formation (n=4, 5). D, Representative immunoblots and myocardial protein expression of ACAT1, BDH1, and SCOT (n=5, 10). E, Intraperitoneal glucose tolerance in response to an overnight fast following 2 weeks of treatment with VC or pimozide (n=13, 16). F, Total body weight, fat mass, and lean mass measured using an EchoMRI machine following 4 weeks of treatment with VC or pimozide (n=10, 14). G, SCOT activity in myocardial tissue from VC‐ and pimozide‐treated mice with T2D (n=4, 5). Cardiac structural and functional parameters assessed by ultrasound echocardiography in mice following 4 weeks of treatment with VC or pimozide (n=8–14). This includes assessment of systolic function using M‐Mode echocardiography to measure (H) EF, (I) FS, and (J) LV mass normalized to lean body mass. Diastolic function was assessed by pulsed wave Doppler to determine the (K) E/A ratio; and by tissue Doppler to measure the (L) e′/a′ ratio. Diastolic function was also assessed by determination of the (M) E/e′ ratio and (N) LA size (measured as the maximal anteroposterior LA diameter by M‐mode imaging in the parasternal long‐axis view). O, Picrosirius red representative images and quantification of perivascular and interstitial fibrosis in 3 transverse sections of diastole‐arrested hearts using ImageJ (n=3, 4). P, Wheat‐germ agglutinin representative images and quantification of cardiomyocyte cross‐sectional area using widefield fluorescence microscopy to capture images from 5 μm transverse sections at the midsegment of the heart arrested in diastole, with 30 to 50 cardiomyocytes averaged from the heart at the same level (n=3, 4). Q, Myocardial PDH phosphorylation at serine‐232 and representative images (n=4, 5). R, Relative mRNA expression of gene markers of inflammation (nucleotide‐binding domain‐like receptor protein 3 (Nlrp3), interleukin‐1β (Il1b), interleukin‐6 (Il6), C‐C motif chemokine ligand 2 (Ccl2), C‐C motif chemokine ligand 5 (Ccl5), and tumor necrosis factor α (Tnfa) (n=4, 6). S, Myocardial spermidine and spermine content determined by applying a targeted quantitative metabolomics approach using a combination of direct injection MS with a reverse‐phase LC‐MS/MS custom assay (n=5). T, Myocardial triacylglycerol content assessed by the Bligh and Dyer method following homogenization of frozen myocardial tissue in a 2:1 chloroform:methanol solution (n=5, 6). U, Study summary illustration. Values represent mean±SEM. Differences were determined using several nonparametric tests, including exact 2‐sample Fisher–Pitman permutation tests (panels [B, C right, D, F, G, R, S, T]), a Kruskal–Wallis test with Dunn's multiple comparison test (α: 0.05 threshold for P value comparison) (panels [O, P]), or a Kolmogrov–Smirnov tests with a Bonferroni–Dunn's multiple comparisons test (α: 0.05 threshold for P value comparison) (panels [H, I, J, K, L, M left, N left, Q]). Parametric testing was used after confirmation of normal distribution of the samples by the Shapiro–Wilk normality test and then a repeated measures 2‐way ANOVA (panels [C left, E, M right, N right]) was performed followed by a Bonferroni post hoc analysis (α: 0.05 threshold for P value comparison). Panel M right pre‐post P values; Lean VC (P>0.999), Lean pimozide (P>0.999), T2D VC (P=0.223), T2D pimozide (P=0.002). Panel N right pre‐post P values; Lean VC (P>0.999), Lean pimozide (P=0.602), T2D VC (P=0.526), T2D pimozide (P<0.0001). Data analysis was completed using GraphPad Prism 10 software. Red color font was used to specify P values that indicated a significant difference (P<0.05). *P<0.05, significantly different from lean counterpart. ^P<0.05, significantly different from pretreatment counterpart. AcAc‐CoA indicates acetoacetyl CoA; ACAT1, AcAc‐CoA thiolase; βOHB, β‐hydroxybutyrate; BDH1, β‐hydroxybutyrate dehydrogenase 1; CoA, coenzyme A; DbCM, diabetic cardiomyopathy; EF, ejection fraction; FS, fractional shortening; IPGTT, intraperitoneal glucose tolerance test; LA, left atrial; LBM, lean body mass; LC, liquid chromatography; LV, left ventricular; MS, mass spectrometry; NAD, nicotinamide adenine dinucleotide; NADH, nicotinamide adenine dinucleotide + hydrogen; PDH, pyruvate dehydrogenase; PMZ, pimozide; SCOT, succinyl CoA:3‐ketoacid CoA transferase; Spd, spermidine; Spn, spermine; STZ, streptozotocin; T2D, type 2 diabetes; TAG, triacylglycerol; TCA, tricarboxylic acid; and VC, vehicle control. The illustrations in panels [A] and [U] were created with BioRender.com.Consistent with previous studies,1 pimozide treatment for 2 weeks in mice with T2D (10 mg/kg every 48 hours via oral gavage) improved glucose tolerance versus their vehicle control (VC; corn oil) treated counterparts independent of changes in body weight (Figure [E, F]). As expected, pimozide treatment of mice with T2D decreased myocardial SCOT activity (Figure [G]).Pimozide treatment for 4 weeks did not worsen systolic function in mice with T2D, as left ventricular ejection fraction and fractional shortening were similar to their VC‐treated counterparts (Figure [H, I]). Intriguingly, we observed a reduction in corrected left ventricular mass (assessed via M‐mode echocardiography as previously described4), and although the E/A and e′/a′ ratios were not altered via pimozide treatment, the E/e′ ratio decreased, indicative of an improvement in diastolic function (Figure [J–M]). Left atrial enlargement is also associated with diastolic dysfunction2 and was abolished following pimozide treatment of mice with T2D, providing further evidence to suggest an alleviation of DbCM pathogenesis (Figure [N]). Although mice with T2D displayed increases in interstitial and perivascular fibrosis, as well as increased cardiomyocyte cross‐sectional area, this was not attenuated via treatment with pimozide (Figure [O, P]).As previous studies demonstrated that the mechanism of improved glycemia in response to SCOT inhibition involved increases in muscle activity of pyruvate dehydrogenase,1 the rate‐limiting enzyme of glucose oxidation, we next assessed myocardial pyruvate dehydrogenase status. Inhibitory pyruvate dehydrogenase phosphorylation at serine‐232 in the heart was unaffected by pimozide treatment in mice with T2D (Figure [Q]); thus it is unlikely that an enhancement of myocardial glucose oxidation underlies the cardioprotective effects of SCOT inhibition. In addition to serving as a fuel source, βOHB is also a signaling molecule whose accumulation in response to SCOT inhibition could amplify its signaling effects. Indeed, βOHB has anti‐inflammatory properties, but a suppression of cardiac inflammation in our study is also unlikely, given that gene expression of interleukin‐6 was the only inflammatory marker to demonstrate a trend toward reduction (Figure [R]). Interestingly, myocardial spermidine and spermine content were increased by pimozide treatment (Figure [S]). As these polyamines induce cardioprotection in the setting of DbCM by decreasing oxidative stress and cardiomyocyte apoptosis,5 they may contribute to how pimozide alleviates diastolic dysfunction. Conversely, we failed to detect caspase 3 cleavage in the hearts of our mice (data not shown), suggesting that our model of T2D is associated with negligible cardiomyocyte apoptosis. Pimozide treatment also decreased myocardial triacylglycerol content (Figure [T]), which may be secondary to a pimozide‐mediated increase in fatty acid oxidation.1 Thus, it will be important for future studies to interrogate whether SCOT inhibition directly affects elements of cardiac lipotoxicity.Overall, our results reveal that myocardial ketone oxidation is downregulated in DbCM, which appears to be an adaptive response. Indeed, we demonstrated that pharmacological SCOT inhibition, which further decreases ketone oxidation, did not induce heart failure with preserved ejection fraction in mice with T2D but rather improved diastolic function. As pimozide may prolong the QT interval, future studies will need to assess whether using pimozide to decrease ketone oxidation may affect cardiac arrhythmias, for which people with T2D are at increased risk. However, we previously observed that direct treatment of the isolated heart with pimozide had no effect on heart rate.1 Therefore, strategies aimed at decreasing ketone oxidation in T2D may not only improve glycemia but also alleviate DbCM through mechanisms that remain incompletely understood (Figure [U]).Sources of FundingThis study was supported by an End Diabetes Award from Diabetes Canada to JRU. Amanda A. Greenwell was supported by a Vanier Canada Graduate Scholarship from the Canadian Institutes of Health Research. John R. Ussher is a Tier 2 Canada Research Chair (Pharmacotherapy of Energy Metabolism in Obesity).DisclosuresNone.AcknowledgmentsJohn R. Ussher is the guarantor of the work and had full access to all data presented in this study and thus takes full responsibility for the integrity of the data and its analysis.Footnotes* Correspondence to: John R. Ussher, 2‐020E Katz Group Centre for Pharmacy and Health Research, Faculty of Pharmacy and Pharmaceutical Sciences, University of Alberta, Edmonton, AB T6G 2R3 Canada. Email: jussher@ualberta.caThis article was sent to Sakima A. Smith, MD, MPH, Associate Editor, for review by expert referees, editorial decision, and final disposition.For Sources of Funding and Disclosures, see page 4.References1 Al Batran R, Gopal K, Capozzi ME, Chahade JJ, Saleme B, Tabatabaei‐Dakhili SA, Greenwell AA, Niu J, Almutairi M, Byrne NJ, et al. Pimozide alleviates hyperglycemia in diet‐induced obesity by inhibiting skeletal muscle ketone oxidation. Cell Metab. 2020; 31:909–919.e8. doi: 10.1016/j.cmet.2020.03.017CrossrefMedlineGoogle Scholar2 Ritchie RH, Abel ED. Basic mechanisms of diabetic heart disease. Circ Res. 2020; 126:1501–1525. doi: 10.1161/CIRCRESAHA.120.315913LinkGoogle Scholar3 Lopaschuk GD, Karwi QG, Tian R, Wende AR, Abel ED. Cardiac energy metabolism in heart failure. Circ Res. 2021; 128:1487–1513. doi: 10.1161/CIRCRESAHA.121.318241LinkGoogle Scholar4 Gopal K, Al Batran R, Altamimi TR, Greenwell AA, Saed CT, Tabatabaei Dakhili SA, Dimaano MTE, Zhang Y, Eaton F, Sutendra G, et al. FoxO1 inhibition alleviates type 2 diabetes‐related diastolic dysfunction by increasing myocardial pyruvate dehydrogenase activity. Cell Rep. 2021; 35:108935. doi: 10.1016/j.celrep.2021.108935CrossrefMedlineGoogle Scholar5 Wang Y, Chen J, Li S, Zhang X, Guo Z, Hu J, Shao X, Song N, Zhao Y, Li H, et al. Exogenous spermine attenuates rat diabetic cardiomyopathy via suppressing ROS‐p53 mediated downregulation of calcium‐sensitive receptor. Redox Biol. 2020; 32:101514. doi: 10.1016/j.redox.2020.101514CrossrefMedlineGoogle Scholar eLetters(0)eLetters should relate to an article recently published in the journal and are not a forum for providing unpublished data. Comments are reviewed for appropriate use of tone and language. Comments are not peer-reviewed. Acceptable comments are posted to the journal website only. Comments are not published in an issue and are not indexed in PubMed. Comments should be no longer than 500 words and will only be posted online. References are limited to 10. Authors of the article cited in the comment will be invited to reply, as appropriate.Comments and feedback on AHA/ASA Scientific Statements and Guidelines should be directed to the AHA/ASA Manuscript Oversight Committee via its Correspondence page.Sign In to Submit a Response to This Article Previous Back to top Next FiguresReferencesRelatedDetails Article InformationMetrics Copyright © 2024 The Authors. Published on behalf of the American Heart Association, Inc., by Wiley BlackwellThis is an open access article under the terms of the Creative Commons Attribution‐NonCommercial‐NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non‐commercial and no modifications or adaptations are made.https://doi.org/10.1161/JAHA.123.032697PMID: 38533954 Manuscript receivedNovember 17, 2023Manuscript acceptedFebruary 20, 2024Originally publishedMarch 27, 2024 Keywordsdiabetic cardiomyopathydiastolic functionketone metabolismsuccinyl CoA:3‐ketoacid CoA transferasetype 2 diabetesPDF download SubjectsBasic Science ResearchMetabolism

AIMS:Recent studies have demonstrated that stimulating pyruvate dehydrogenase (PDH, gene Pdha1), the rate-limiting enzyme of glucose oxidation, can reverse obesity-induced non-alcoholic fatty liver disease (NAFLD), which can be achieved via treatment with the antianginal ranolazine. Accordingly, our aim was to determine whether ranolazine's ability to mitigate obesity-induced NAFLD and hyperglycaemia requires increases in hepatic PDH activity.METHODS:We generated liver-specific PDH-deficient (Pdha1Liver-/- ) mice, which were provided a high-fat diet for 12 weeks to induce obesity. Pdha1Liver-/- mice and their albumin-Cre (AlbCre ) littermates were randomized to treatment with either vehicle control or ranolazine (50 mg/kg) once daily via oral gavage during the final 5 weeks, following which we assessed glucose and pyruvate tolerance.RESULTS:Pdha1Liver-/- mice exhibited no overt phenotypic differences (e.g. adiposity, glucose tolerance) when compared to their AlbCre littermates. Of interest, ranolazine treatment improved glucose tolerance and mildly reduced hepatic triacylglycerol content in obese AlbCre mice but not in obese Pdha1Liver-/- mice. The latter was independent of changes in hepatic mRNA expression of genes involved in regulating lipogenesis.CONCLUSIONS:Liver-specific PDH deficiency is insufficient to promote an NAFLD phenotype. Nonetheless, hepatic PDH activity partially contributes to how the antianginal ranolazine improves glucose tolerance and alleviates hepatic steatosis in obesity.

During periods of prolonged fasting/starvation, the liver generates ketones [i.e., β-hydroxybutyrate (βOHB)] that primarily serve as alternative substrates for ATP production. Previous studies have demonstrated that elevations in skeletal muscle ketone oxidation contribute to obesity-related hyperglycemia, whereas inhibition of succinyl CoA:3-ketoacid CoA transferase (SCOT), the rate-limiting enzyme of ketone oxidation, can alleviate obesity-related hyperglycemia. As circulating ketone levels are a key determinant of ketone oxidation rates, we tested the hypothesis that increases in circulating ketone levels would worsen glucose homeostasis secondary to increases in muscle ketone oxidation. Accordingly, male C57BL/6J mice were subjected to high-fat diet-induced obesity, whereas their lean counterparts received a standard chow diet. Lean and obese mice were orally administered either a ketone ester (KE) or placebo, followed by a glucose tolerance test. In tandem, we conducted isolated islet perifusion experiments to quantify insulin secretion in response to ketones. We observed that exogenous KE administration robustly increases circulating βOHB levels, which was associated with an improvement in glucose tolerance only in obese mice. These observations were independent of muscle ketone oxidation, as they were replicated in mice with a skeletal muscle-specific SCOT deficiency. Furthermore, the R-isomer of βOHB produced greater increases in perifusion insulin levels versus the S-isomer in isolated islets from obese mice. Taken together, acute elevations in circulating ketones promote glucose-lowering in obesity. Given that only the R-isomer of βOHB is oxidized, further studies are warranted to delineate the precise role of β-cell ketone oxidation in regulating insulin secretion.NEW & NOTEWORTHY It has been demonstrated that increased skeletal muscle ketone metabolism contributes to obesity-related hyperglycemia. Since increases in ketone supply are key determinants of organ ketone oxidation rates, we determined whether acute elevations in circulating ketones following administration of an oral ketone ester may worsen glucose homeostasis in lean or obese mice. Our work demonstrates the opposite, as acute elevations in circulating ketones improved glucose tolerance in obese mice.

Despite significant progress in understanding the pathogenesis of type 2 diabetes (T2D), it remains difficult to manage. Hence, new therapeutic options targeting unique mechanisms of action are required. We have previously observed that elevated skeletal muscle succinyl CoA:3-ketoacid CoA transferase (SCOT) activity, the rate-limiting enzyme of ketone oxidation, contributes to the hyperglycemia characterizing obesity and T2D. Moreover, we identified that the typical antipsychotic agent, pimozide, is a SCOT inhibitor that can alleviate obesity-induced hyperglycemia. We have now extended those observations herein, using computer-assisted in silico modelling and in vivo pharmacology studies that highlight SCOT as a noncanonical target shared amongst the diphenylbutylpiperidine (DPBP) drug class, which includes penfluridol and fluspirilene. All 3 DPBPs tested (pimozide, penfluridol, and fluspirilene) improved glycemia in obese mice. While the canonical target of the DPBPs is the dopamine 2 receptor, studies in obese mice demonstrated that acute or chronic treatment with a structurally unrelated antipsychotic dopamine 2 receptor antagonist, lurasidone, was devoid of glucose-lowering actions. We further observed that the DPBPs improved glycemia in a SCOT-dependent manner in skeletal muscle, suggesting that this older class of antipsychotic agents may have utility in being repurposed for the treatment of T2D.

Background: Nonalcoholic fatty liver disease (NAFLD) increases risk for obesity-related insulin resistance and type 2 diabetes. Recent studies have demonstrated that stimulating pyruvate dehydrogenase (PDH) , the rate-limiting enzyme in glucose oxidation, can reverse obesity-induced NAFLD. Moreover, our lab has observed that treatment with the antianginal drug, ranolazine, augments hepatic PDH activity, leading to a reversal of obesity-induced glucose intolerance and NAFLD in mice. Our aim herein was to determine whether ranolazine's ability to mitigate obesity-induced NAFLD and hyperglycemia requires increases in hepatic PDH activity. Methods: We generated liver-specific PDH deficient (PDHLiver-/-) mice by crossing floxed Pdha1 mice with albumin-Cre (Alb-Cre) mice. PDHLiver-/- and Alb-Cre mice were placed on a high-fat diet for 12-weeks to induce obesity, whereas their lean controls were fed a low-fat diet. Mice were randomized to treatment with either vehicle control or ranolazine (50 mg/kg) once daily via oral gavage for 5-weeks, following which we assessed glucose homeostasis and hepatic steatosis. Results: Lean PDHLiver-/- mice exhibited no overt phenotypic differences (e.g. adiposity, glucose tolerance) from their Alb-Cre littermates, though a mild but nonsignificant worsening of pyruvate tolerance was observed. Similar findings were observed in obese PDHLiver-/- mice compared to their Alb-Cre littermates. Of interest, ranolazine treatment produced mild improvements in glucose tolerance in obese Alb-Cre mice, but not in obese PDHLiver-/- mice. However, this improvement in ranolazine treated Alb-Cre mice appears to be independent of decreases in hepatic triacylglycerol content. Conclusions: Although hepatic PDH activity appears to contribute to the glucose-lowering actions of ranolazine, this appears to be dissociated from its actions on hepatic steatosis, and impaired hepatic PDH activity per se is not sufficient to produce an NAFLD phenotype. Disclosure C. T. Saed: None. S. Tabatabaei dakhili: None. A. A. Greenwell: None. J. S. F. Chan: None. K. Yang: None. K. Gopal: None. F. Eaton: None. J. R. Ussher: None.

Purpose: Despite significant progress in understanding the pathogenesis of type 2 diabetes (T2D) , it remains difficult to manage, hence, new therapeutic options are required. We previously observed that elevated skeletal muscle succinyl CoA:3-ketoacid CoA transferase (SCOT) activity, the rate-limiting enzyme of ketone (KB) oxidation, contributes to obesity-induced hyperglycemia. Moreover, we identified that the antipsychotic agent, pimozide, is a SCOT inhibitor with glucose-lowering actions. In silico molecular modeling determined that a wide range of DPBPs can theoretically inhibit SCOT activity, therefore, we determined whether the DPBP drug class could be repurposed for the treatment of T2D. Methods: 8-week-old male wild-type and muscle-specific/brain-specific SCOT knockout (SCOTMuscleKO, SCOTBrainKO) mice were subjected to experimental obesity via consumption of a high fat, high sugar diet for 12-weeks. Lean control mice received a low fat, low sugar diet. At 8-weeks, lean and obese mice were treated with DPBPs (penfluridol, fluspirilene, pimozide (10mg/kg)) once every 2 days via oral gavage for 14-days, following which circulating KB levels and glucose homeostasis were assessed. To rule out a contribution of the canonical actions of DPBPs as dopamine 2 (D2) receptor antagonists to DPBP-mediated glucose-lowering, obese mice were treated with the structurally unrelated D2 receptor antagonist, lurasidone (10 mg/kg) . Results: All tested DPBPs improved glucose homeostasis in obese mice through a mechanism dependent on the inhibition of both brain and muscle SCOT activity. Treatment with lurasidone failed to improve glycemia in obese mice, thus consistent with a SCOT-dependent mechanism of action. Conclusions: Our findings suggest all DPBPs have glucose-lowering actions and therefore may have clinical utility in being repurposed for the treatment of T2D. Disclosure S. Tabatabaei dakhili: None. C. A. Velazquez: None. P. A. Crawford: Advisory Panel; Abbott Diabetes, Johnson & Johnson Global Services. M. Glover: None. R. Al batran: None. J. R. Ussher: None. R. Abou farraj: None. A. A. Greenwell: None. C. T. Saed: None. K. Yang: None. K. Gopal: None. J. S. F. Chan: None. C. Lee: None. F. Eaton: None. Funding Canadian Institutes of HealthResearch

Opsin3 (Opn3) is a transmembrane heptahelical G protein-coupled receptor (GPCR) with the potential to produce a nonvisual photoreceptive effect. Interestingly, anatomical profiling of GPCRs reveals that Opn3 mRNA is highly expressed in adipose tissue. The photosensitive functions of Opn3 in mammals are poorly understood, and whether Opn3 has a role in fat is entirely unknown. In this study, we found that Opn3-knockout (Opn3-KO) mice were prone to diet-induced obesity and insulin resistance. At the cellular level, Opn3-KO brown adipocytes cultured in darkness had decreased glucose uptake and lower nutrient-induced mitochondrial respiration than wild-type (WT) cells. Light exposure promoted mitochondrial activity and glucose uptake in WT adipocytes but not in Opn3-KO cells. Brown adipocytes carrying a defective mutation in Opn3's putative G protein-binding domain also exhibited a reduction in glucose uptake and mitochondrial respiration in darkness. Using RNA-sequencing, we identified several novel light-sensitive and Opn3-dependent molecular signatures in brown adipocytes. Importantly, direct exposure of brown adipose tissue (BAT) to light in living mice significantly enhanced thermogenic capacity of BAT, and this effect was diminished in Opn3-KO animals. These results uncover a previously unrecognized cell-autonomous, light-sensing mechanism in brown adipocytes via Opn3-GPCR signaling that can regulate fuel metabolism and mitochondrial respiration. Our work also provides a molecular basis for developing light-based treatments for obesity and its related metabolic disorders.