A high-fat diet supplemented with medium-chain triglycerides ameliorates hepatic steatosis by reducing ceramide and diacylglycerol accumulation in mice.

Non-alcoholic fatty liver disease (NAFLD) is projected to be the most common chronic liver disease worldwide and is closely linked to obesity, insulin resistance and type 2 diabetes. Currently, no pharmacological treatments are available to treat NAFLD, and lifestyle modification, including dietary interventions, is the only remedy. Therefore, we conducted a study to determine whether supplementation with medium-chain triglycerides (MCTs), containing a mixture of C8 and C10 (60/40), attenuates NAFLD in obese and insulin-resistant mice. To achieve that, we fed C57BL/6 male mice a high-fat diet (HFD) for 12 weeks to induce obesity and hepatic steatosis, after which obese mice were assigned randomly either to remain on the HFD or to transition to an HFD supplemented with MCTs (HFD + MCTs) or a low-fat diet (LFD) for 6 weeks as another dietary intervention model. Another group of mice was kept on an LFD throughout the study and used as a lean control group. Obese mice that transitioned to HFD + MCTs exhibited improvement in glucose and insulin tolerance tests, and the latter improvement was independent of changes in adiposity when compared with HFD-fed mice. Additionally, supplementation with MCTs significantly reduced hepatic steatosis, improved liver enzymes and decreased hepatic expression of inflammation-related genes to levels similar to those observed in obese mice transitioned to an LFD. Importantly, HFD + MCTs markedly lowered hepatic ceramide and diacylglycerol content and prevented protein kinase C-ε translocation to the plasma membrane. Our study demonstrated that supplementation with MCTs formulated mainly from C8 and C10 effectively ameliorated NAFLD in obese mice.

Loss of muscle PDH induces lactic acidosis and adaptive anaplerotic compensation via pyruvate-alanine cycling and glutaminolysis.

Pyruvate dehydrogenase (PDH) is the rate-limiting enzyme for glucose oxidation that links glycolysis-derived pyruvate with the tricarboxylic acid (TCA) cycle. Although skeletal muscle is a significant site for glucose oxidation and is closely linked with metabolic flexibility, the importance of muscle PDH during rest and exercise has yet to be fully elucidated. Here, we demonstrate that mice with muscle-specific deletion of PDH exhibit rapid weight loss and suffer from severe lactic acidosis, ultimately leading to early mortality under low-fat diet provision. Furthermore, loss of muscle PDH induces adaptive anaplerotic compensation by increasing pyruvate-alanine cycling and glutaminolysis. Interestingly, high-fat diet supplementation effectively abolishes early mortality and rescues the overt metabolic phenotype induced by muscle PDH deficiency. Despite increased reliance on fatty acid oxidation during high-fat diet provision, loss of muscle PDH worsens exercise performance and induces lactic acidosis. These observations illustrate the importance of muscle PDH in maintaining metabolic flexibility and preventing the development of metabolic disorders.

Knowledge Translation in Glomerulonephritis: Successes in Translational Research From the Bench to Bedside.

Purpose of review: Glomerulonephritis refers to a rare group of diseases characterized by glomerular inflammation, which collectively are a common cause of kidney failure. Until recently, there was a lack of high-quality clinical trials to inform the care of patients with glomerulonephritides. We identified examples of successful translational research spanning from basic science to clinical applications, and highlight gaps in implementation science. Sources of information: The focus of our review was derived from discussions between health care professionals, researchers, and patient partners. We also performed literature searches pertaining to the treatment of glomerulonephritis in PubMed and Google Scholar. Methods: Examples of successful knowledge translation were generated through review of new evidence in the past 5 years and by iterative discussions by the authors. We then conducted a narrative review of several themes related to knowledge translation in glomerulonephritis. This was complemented by an interview with a patient partner to provide an example of a patient's perspective living with glomerulonephritis. Key findings: We summarized selected recent advances in glomerulonephritis and its knowledge translation in the following domains: (1) identification of auto-antibodies in membranous nephropathy and minimal change disease; (2) clinical trials of novel targeted therapies for IgA nephropathy and lupus nephritis, which have led to approval of new treatments; (3) developments in research networks and clinical trials in glomerulonephritis; (4) recognition of the importance in developing standardized patient reported outcome measures in clinical trials; and (5) barriers in knowledge translation including access to medication. Limitations: A systematic search of the literature and formal assessment of quality of evidence were beyond the scope of this review.

Motif de la revue: La glomérulonéphrite désigne un groupe rare de maladies qui se caractérisent par une inflammation des glomérules. Collectivement, ces maladies sont une cause fréquente d'insuffisance rénale. Jusqu'à récemment, il n'y avait pas d'essais cliniques de grande qualité pour guider les soins des patients atteints de glomérulonéphrites. Nous avons répertorié des exemples de recherches translationnelles réussies, allant de la recherche fondamentale aux applications cliniques, et nous avons mis en évidence les lacunes dans l'application de la science. Sources: L'essentiel de notre examen est dérivé de discussions entre les professionnels de la santé, les chercheurs et les patients partenaires. Nous avons également procédé à une revue de la littérature sur PubMed et Google Scholar portant sur le traitement de la glomérulonéphrite. Méthodologie: Des exemples d'application réussie des connaissances ont été générés par un examen des récentes données probantes (cinq dernières années) et par des discussions itératives entre les auteurs. Nous avons ensuite procédé à une revue narrative de plusieurs thèmes liés à l'application des connaissances en contexte de glomérulonéphrite. Cette démarche a été complétée par une entrevue avec une patiente partenaire, afin de fournir le point de vue d'une personne vivant avec une glomérulonéphrite. Principaux résultats: Nous avons résumé certaines des avancées récentes de la recherche sur la glomérulonéphrite et l'application des connaissances dans les domaines suivants: 1) l'identification d'auto-anticorps dans la glomérulonéphrite membraneuse et la néphropathie à lésion glomérulaire minime; 2) les essais cliniques portant sur de nouvelles thérapies ciblées pour la néphropathie à IgA et la néphrite lupique qui ont conduit à l'approbation de nouveaux traitements; 3) les développements dans les réseaux de recherche et les essais cliniques sur la glomérulonéphrite; 4) la reconnaissance de l'importance d'élaborer des mesures normalisées pour les résultats rapportés par les patients dans les essais cliniques; 5) les obstacles à l'application des connaissances, y compris l'accès aux médicaments. Limites: Une recherche systématique de la documentation et l'évaluation officielle de la qualité des preuves dépassaient la portée de cet examen.

The antianginal ranolazine fails to improve glycaemia in obese liver-specific pyruvate dehydrogenase deficient male mice.

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.

Defective muscle ketone body oxidation disrupts BCAA catabolism by altering mitochondrial branched-chain aminotransferase.

Ketone bodies are an endogenous fuel source generated primarily by the liver to provide alternative energy for extrahepatic tissues during prolonged fasting and exercise. Skeletal muscle is an important site of ketone body oxidation that occurs through a series of reactions requiring the enzyme succinyl-CoA:3-ketoacid-CoA transferase (SCOT/Oxct1). We have previously shown that deleting SCOT in the skeletal muscle protects against obesity-induced insulin resistance by increasing pyruvate dehydrogenase (PDH) activity, the rate-limiting enzyme of glucose oxidation. However, it remains unclear whether inhibiting muscle ketone body oxidation causes hypoglycemia and affects fuel metabolism in the absence of obesity. Here, we show that lean mice lacking skeletal muscle SCOT (SCOTSkM-/-) exhibited no overt phenotypic differences in glucose and fat metabolism from their human α-skeletal actin-Cre (HSACre) littermates. Of interest, we found that plasma and muscle branched-chain amino acid (BCAA) levels are elevated in SCOTSkM-/- lean mice compared with their HSACre littermates. Interestingly, this alteration in BCAA catabolism was only seen in SCOTSkM-/- mice under low-fat feeding and associated with decreased expression of mitochondrial branched-chain aminotransferases (BCATm/Bcat2), the first enzyme in BCAA catabolic pathway. Loss- and gain-of-function studies in C2C12 myotubes demonstrated that suppressing SCOT markedly diminished BCATm expression, whereas overexpressing SCOT resulted in an opposite effect without influencing BCAA oxidation enzymes. Furthermore, SCOT overexpression in C2C12 myotubes significantly increased luciferase activity driven by a Bcat2 promoter construct. Together, our findings indicate that SCOT regulates the expression of the Bcat2 gene, which, through the abundance of its product BCATm, may influence circulating BCAA concentrations.NEW & NOTEWORTHY Most studies investigated ketone body metabolism under pathological conditions, whereas the role of ketone body metabolism in regulating normal physiology has been relatively understudied. To address this gap, we used lean mice lacking muscle ketone body oxidation enzyme SCOT. Our work demonstrates that deleting muscle SCOT has no impact on glucose and fat metabolism in lean mice, but it disrupts muscle BCAA catabolism and causes an accumulation of BCAAs by altering BCATm.

The Antipsychotic Dopamine 2 Receptor Antagonist Diphenylbutylpiperidines Improve Glycemia in Experimental Obesity by Inhibiting Succinyl-CoA:3-Ketoacid CoA Transferase.

Despite significant progress in understanding the pathogenesis of type 2 diabetes (T2D), the condition 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 now extend those observations here, using computer-assisted in silico modeling and in vivo pharmacology studies that highlight SCOT as a noncanonical target shared among the diphenylbutylpiperidine (DPBP) drug class, which includes penfluridol and fluspirilene. All three 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.

An isoproteic cocoa butter-based ketogenic diet fails to improve glucose homeostasis and promote weight loss in obese mice.

High-fat and very low-carbohydrate based ketogenic diets have gained considerable popularity as a nonpharmacological strategy for obesity, due to their potential to enhance weight loss and improve glucose homeostasis. However, the effectiveness of a ketogenic diet toward metabolic health is equivocal. To better understand the impact of ketogenic diets in obesity, male and female mice were fed a 60% cocoa butter-based high-fat diet for 16-wk to induce obesity, following which mice were transitioned to either an 85% cocoa butter fat-based ketogenic diet, a 10% cocoa butter fat-based low-fat diet, or maintained on a high-fat diet for an additional 8-wk. All experimental diets were matched for sucrose and protein content and contained an identical micronutrient profile, with complex carbohydrates being the primary carbohydrate source in the low-fat diet. The transition to a ketogenic diet was ineffective at promoting significant body fat loss and improving glucose homeostasis in obese male and female mice. Alternatively, obese male and female mice transitioned to a low-fat and high-complex carbohydrate diet exhibited beneficial body composition changes and improved glucose tolerance that may, in part, be attributed to a mild decrease in food intake and a mild increase in energy expenditure. Our findings support the consumption of a diet low in saturated fat and rich in complex carbohydrates as a potential dietary intervention for the treatment of obesity and obesity-induced impairments in glycemia. Furthermore, our results suggest that careful consideration should be taken when considering a ketogenic diet as a nonpharmacological strategy for obesity.NEW & NOTEWORTHY It has been demonstrated that ketogenic diets may be a nutritional strategy for alleviating hyperglycemia and promoting weight loss in obesity. However, there are a number of inconsistencies with many of these studies, especially with regard to the macronutrient and micronutrient compositions of the diets being compared. Our work demonstrates that a ketogenic diet that is both micronutrient-matched and isoproteic with its comparator diets fails to improve glycemia or promote weight loss in obese mice.

FoxO1 inhibition alleviates type 2 diabetes-related diastolic dysfunction by increasing myocardial pyruvate dehydrogenase activity.

Type 2 diabetes (T2D) increases the risk for diabetic cardiomyopathy and is characterized by diastolic dysfunction. Myocardial forkhead box O1 (FoxO1) activity is enhanced in T2D and upregulates pyruvate dehydrogenase (PDH) kinase 4 expression, which inhibits PDH activity, the rate-limiting enzyme of glucose oxidation. Because low glucose oxidation promotes cardiac inefficiency, we hypothesize that FoxO1 inhibition mitigates diabetic cardiomyopathy by stimulating PDH activity. Tissue Doppler echocardiography demonstrates improved diastolic function, whereas myocardial PDH activity is increased in cardiac-specific FoxO1-deficient mice subjected to experimental T2D. Pharmacological inhibition of FoxO1 with AS1842856 increases glucose oxidation rates in isolated hearts from diabetic C57BL/6J mice while improving diastolic function. However, AS1842856 treatment fails to improve diastolic function in diabetic mice with a cardiac-specific FoxO1 or PDH deficiency. Our work defines a fundamental mechanism by which FoxO1 inhibition improves diastolic dysfunction, suggesting that it may be an approach to alleviate diabetic cardiomyopathy.

Barth syndrome-related cardiomyopathy is associated with a reduction in myocardial glucose oxidation.

Heart failure presents as the leading cause of infant mortality in individuals with Barth syndrome (BTHS), a rare genetic disorder due to mutations in the tafazzin (TAZ) gene affecting mitochondrial structure and function. Investigations into the perturbed bioenergetics in the BTHS heart remain limited. Hence, our objective was to identify the potential alterations in myocardial energy metabolism and molecular underpinnings that may contribute to the early cardiomyopathy and heart failure development in BTHS. Cardiac function and myocardial energy metabolism were assessed via ultrasound echocardiography and isolated working heart perfusions, respectively, in a mouse model of BTHS [doxycycline-inducible Taz knockdown (TazKD) mice]. In addition, we also performed mRNA/protein expression profiling for key regulators of energy metabolism in hearts from TazKD mice and their wild-type (WT) littermates. TazKD mice developed hypertrophic cardiomyopathy as evidenced by increased left ventricular anterior and posterior wall thickness, as well as increased cardiac myocyte cross-sectional area, though no functional impairments were observed. Glucose oxidation rates were markedly reduced in isolated working hearts from TazKD mice compared with their WT littermates in the presence of insulin, which was associated with decreased pyruvate dehydrogenase activity. Conversely, myocardial fatty acid oxidation rates were elevated in TazKD mice, whereas no differences in glycolytic flux or ketone body oxidation rates were observed. Our findings demonstrate that myocardial glucose oxidation is impaired before the development of overt cardiac dysfunction in TazKD mice, and may thus represent a pharmacological target for mitigating the development of cardiomyopathy in BTHS.NEW & NOTEWORTHY Barth syndrome (BTHS) is a rare genetic disorder due to mutations in tafazzin that is frequently associated with infantile-onset cardiomyopathy and subsequent heart failure. Although previous studies have provided evidence of perturbed myocardial energy metabolism in BTHS, actual measurements of flux are lacking. We now report a complete energy metabolism profile that quantifies flux in isolated working hearts from a murine model of BTHS, demonstrating that BTHS is associated with a reduction in glucose oxidation.

The GLP-1 Receptor Agonist Liraglutide Increases Myocardial Glucose Oxidation Rates via Indirect Mechanisms and Mitigates Experimental Diabetic Cardiomyopathy.

BACKGROUND: Type 2 diabetes (T2D) increases risk for cardiovascular disease. Of interest, liraglutide, a therapy for T2D that activates the glucagon-like peptide-1 receptor to augment insulin secretion, reduces cardiovascular-related death in people with T2D, though it remains unknown how liraglutide produces these actions. Notably, the glucagon-like peptide-1 receptor is not expressed in ventricular cardiac myocytes, making it likely that ventricular myocardium-independent actions are involved. We hypothesized that augmented insulin secretion may explain how liraglutide indirectly mediates cardioprotection, which thereby increases myocardial glucose oxidation. METHODS: C57BL/6J male mice were fed either a low-fat diet (lean) or were subjected to experimental T2D and treated with either saline or liraglutide 3× over a 24-hour period. Mice were subsequently euthanized and had their hearts perfused in the working mode to assess energy metabolism. A separate cohort of mice with T2D were treated with either vehicle control or liraglutide for 2 weeks for the assessment of cardiac function via ultrasound echocardiography. RESULTS: Treatment of lean mice with liraglutide increased myocardial glucose oxidation without affecting glycolysis. Conversely, direct treatment of the isolated working heart with liraglutide had no effect on glucose oxidation. These findings were recapitulated in mice with T2D and associated with increased circulating insulin levels. Furthermore, liraglutide treatment alleviated diastolic dysfunction in mice with T2D, which was associated with enhanced pyruvate dehydrogenase activity, the rate-limiting enzyme of glucose oxidation. CONCLUSIONS: Our data demonstrate that liraglutide augments myocardial glucose oxidation via indirect mechanisms, which may contribute to how liraglutide improves cardiovascular outcomes in people with T2D.

Chronically Elevating Circulating Ketones Can Reduce Cardiac Inflammation and Blunt the Development of Heart Failure.

BACKGROUND: Previous studies have shown beneficial effects of acute infusion of the primary ketone body, ß-hydroxybutyrate, in heart failure (HF). However, whether chronic elevations in circulating ketones are beneficial remains unknown. METHODS: To chronically elevate circulating ketones in mice, we deleted the expression of the ketolytic, rate-limiting-enzyme, SCOT (succinyl-CoA:3-ketoacid-CoA transferase 1; encoded by Oxct1), in skeletal muscle. Tamoxifen-inducible skeletal muscle-specific Oxct1Muscle-/- knockout (n=32) mice and littermate controls (wild type; WT; n=35) were subjected to transverse aortic constriction (TAC) surgery to induce HF. RESULTS: Deletion of SCOT in skeletal, but not cardiac muscle resulted in elevated concentrations of fasted circulating ß-hydroxybutyrate in knockout mice compared with WT mice (P=0.030). Five weeks following TAC, WT mice progressed to HF, whereas knockout mice with elevated fasting circulating ketones were largely protected from the TAC-induced effects observed in WT mice (ejection fraction, P=0.011; mitral E/A, P=0.012). Furthermore, knockout mice with TAC had attenuated expression of markers of sterile inflammation and macrophage infiltration, which were otherwise elevated in WT mice subjected to TAC. Lastly, addition of ß-hydroxybutyrate to isolated hearts was associated with reduced NLRP3 (nucleotide-binding domain-like receptor protein 3)-inflammasome activation, which has been previously shown to play a role in contributing to HF-induced cardiac inflammation. CONCLUSIONS: These data show that chronic elevation of circulating ketones protects against the development of HF that is associated with the ability of ß-hydroxybutyrate to directly reduce inflammation. These beneficial effects of ketones were associated with reduced cardiac NLRP3 inflammasome activation, suggesting that ketones may modulate cardiac inflammation via this mechanism.

Pimozide Alleviates Hyperglycemia in Diet-Induced Obesity by Inhibiting Skeletal Muscle Ketone Oxidation.

Perturbations in carbohydrate, lipid, and protein metabolism contribute to obesity-induced type 2 diabetes (T2D), though whether alterations in ketone body metabolism influence T2D pathology is unknown. We report here that activity of the rate-limiting enzyme for ketone body oxidation, succinyl-CoA:3-ketoacid-CoA transferase (SCOT/Oxct1), is increased in muscles of obese mice. We also found that the diphenylbutylpiperidine pimozide, which is approved to suppress tics in individuals with Tourette syndrome, is a SCOT antagonist. Pimozide treatment reversed obesity-induced hyperglycemia in mice, which was phenocopied in mice with muscle-specific Oxct1/SCOT deficiency. These actions were dependent on pyruvate dehydrogenase (PDH/Pdha1) activity, the rate-limiting enzyme of glucose oxidation, as pimozide failed to alleviate hyperglycemia in obese mice with a muscle-specific Pdha1/PDH deficiency. This work defines a fundamental contribution of enhanced ketone body oxidation to the pathology of obesity-induced T2D, while suggesting pharmacological SCOT inhibition as a new class of anti-diabetes therapy.

l-Citrulline supplementation improves glucose and exercise tolerance in obese male mice.

NEW FINDINGS: What is the central question of the study? Does the action of l-citrulline, which has been shown to augment performance in animals and athletes, possibly via increasing mitochondrial function, translate to obese animals, and does this improve glycaemia? What is the main finding and its importance? Chronic supplementation with l-citrulline improves not only exercise capacity, but also glycaemia in obese mice, which would be beneficial as obese individuals are at increased risk for type 2 diabetes. However, l-citrulline supplementation also caused a mild impairment in insulin signalling and insulin tolerance in obese mice. ABSTRACT: l-Citrulline is an organic α-amino acid that has been shown to have a number of salutary actions on whole-body physiology, including reducing muscle wasting and augmenting exercise and muscle performance. The latter has been suggested to arise from elevations in mitochondrial function. Because enhancing mitochondrial function has been proposed as a novel strategy to mitigate insulin resistance, our goal was to determine whether supplementation with l-citrulline could also improve glycaemia in an experimental mouse model of obesity. We hypothesized that l-citrulline treatment would improve glycaemia in obese mice, and this would be associated with elevations in skeletal muscle mitochondrial function. Ten-week-old C57BL/6J mice were fed either a low-fat (10% kcal from lard) or a high-fat (60% kcal from lard) diet, while receiving drinking water supplemented with either vehicle or l-citrulline (0.6 g l-1 ) for 15 weeks. Glucose homeostasis was assessed via glucose/insulin tolerance testing, while in vivo metabolism was assessed via indirect calorimetry, and forced exercise treadmill testing was utilized to assess endurance. As expected, obese mice supplemented with l-citrulline exhibited an increase in exercise capacity, which was associated with an improvement in glucose tolerance. Consistent with augmented mitochondrial function, we observed an increase in whole body oxygen consumption rates in obese mice supplemented with l-citrulline. Surprisingly, l-citrulline supplementation worsened insulin tolerance and reduced insulin signalling in obese mice. Taken together, although l-citrulline supplementation improves both glucose tolerance and exercise capacity in obese mice, caution must be applied with its broad use as a nutraceutical due to a potential deterioration of insulin sensitivity.

Dietary-Induced Obesity, Hepatic Cytochrome P450, and Lidocaine Metabolism: Comparative Effects of High-Fat Diets in Mice and Rats and Reversibility of Effects With Normalization of Diet.

The effects of a high-fat diet on mRNA and protein of cytochrome P450 (CYP) enzymes in rats and mice and its impact on lidocaine deethylation to its main active metabolite, monoethylglycinexylidide (MEGX), in rats were investigated. The effect of a change in diet from high-fat to standard diet was also evaluated. Plasma biochemistry, mRNA, protein expression for selected CYP, and the activity of lidocaine deethylation were determined. The high-fat diet curtailed the activity and the expression of the majority of CYPs (CYP1A2, CYP3A1, CYP2C11, CYP2C12, and CYP2D1), mRNA levels (Cyp1a2 and Cyp3a2), and MEGX maximal formation rate (Vmax). Mice showed complementary results in their protein expressions of cyp3a and 1a2. Switching the diet back to standard chow in rats for 4 weeks reverted the expression levels of mRNA and protein back to normal levels as well as the maximum formation rates of MEGX. Female and male rodents showed similar patterns in CYP expression and lidocaine metabolism in response to the diets, although MEGX formation was faster in male rats. In conclusion, diet-induced obesity caused general decreases in CYP isoforms not only in rats but also in mice. The effects were shown to be reversible in rats by normalizing the diet.

Role of Cytochrome p450 and Soluble Epoxide Hydrolase Enzymes and Their Associated Metabolites in the Pathogenesis of Diabetic Cardiomyopathy.

A plethora of studies have demonstrated that cardiomyopathy represents a serious source of morbidity and mortality in patients with diabetes. Yet, the underlying mechanisms of diabetic cardiomyopathy are still poorly understood. Of interest, cytochrome P450 2J (CYP2J) and soluble epoxide hydrolase (sEH) are known to control the maintenance of cardiovascular health through the regulation of cardioprotective epoxyeicosatrienoic acids (EETs) and its less active products, dihydroxyeicosatrienoic acids (DHETs). Therefore, we examined the role of the aforementioned pathway in the development of diabetic cardiomyopathy. Our diabetic model initiated cardiomyopathy as indexed by the increase in the expression of hypertrophic markers such as NPPA. Furthermore, diabetic cardiomyopathy was associated with a low level of cardiac EETs and an increase of the DHETs/EETs ratio both in vivo and in cardiac cells. The modulation in EETs and DHETs was attributed to the increase of sEH and the decrease of CYP2J. Interestingly, the reduction of sEH attenuates cardiotoxicity mediated by high glucose in cardiac cells. Mechanistically, the beneficial effect of sEH reduction might be due to the decrease of phosphorylated ERK1/2 and p38. Overall, the present work provides evidence that diabetes initiates cardiomyopathy through the increase in sEH, the reduction of CYP2J, and the decrease of cardioprotective EETs.

Impaired branched chain amino acid oxidation contributes to cardiac insulin resistance in heart failure.

BACKGROUND: Branched chain amino acids (BCAA) can impair insulin signaling, and cardiac insulin resistance can occur in the failing heart. We, therefore, determined if cardiac BCAA accumulation occurs in patients with dilated cardiomyopathy (DCM), due to an impaired catabolism of BCAA, and if stimulating cardiac BCAA oxidation can improve cardiac function in mice with heart failure. METHOD: For human cohorts of DCM and control, both male and female patients of ages between 22 and 66 years were recruited with informed consent from University of Alberta hospital. Left ventricular biopsies were obtained at the time of transplantation. Control biopsies were obtained from non-transplanted donor hearts without heart disease history. To determine if stimulating BCAA catabolism could lessen the severity of heart failure, C57BL/6J mice subjected to a transverse aortic constriction (TAC) were treated between 1 to 4-week post-surgery with either vehicle or a stimulator of BCAA oxidation (BT2, 40 mg/kg/day). RESULT: Echocardiographic data showed a reduction in ejection fraction (54.3 ± 2.3 to 22.3 ± 2.2%) and an enhanced formation of cardiac fibrosis in DCM patients when compared to the control patients. Cardiac BCAA levels were dramatically elevated in left ventricular samples of patients with DCM. Hearts from DCM patients showed a blunted insulin signalling pathway, as indicated by an increase in P-IRS1ser636/639 and its upstream modulator P-p70S6K, but a decrease in its downstream modulators P-AKT ser473 and in P-GSK3ß ser9. Cardiac BCAA oxidation in isolated working hearts was significantly enhanced by BT2, compared to vehicle, following either acute or chronic treatment. Treatment of TAC mice with BT2 significantly improved cardiac function in both sham and TAC mice (63.0 ± 1.8 and 56.9 ± 3.8% ejection fraction respectively). Furthermore, P-BCKDH and BCKDK expression was significantly decreased in the BT2 treated groups. CONCLUSION: We conclude that impaired cardiac BCAA catabolism and insulin signaling occur in human heart failure, while enhancing BCAA oxidation can improve cardiac function in the failing mouse heart.

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

AIMS: The 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 RESULTS: C57BL/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 ß-hydroxybutyrate (ßOHB), 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 ßOHB 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 ßOHB levels. However, while overall energy production increased, cardiac efficiency was not improved. CONCLUSIONS: Increasing ketone oxidation rates in failing hearts increases overall energy production without compromising glucose or fatty acid metabolism, albeit without increasing cardiac efficiency.

The antianginal ranolazine mitigates obesity-induced nonalcoholic fatty liver disease and increases hepatic pyruvate dehydrogenase activity.

Obese individuals are often at risk for nonalcoholic fatty liver disease (NAFLD), insulin resistance, type 2 diabetes (T2D), and cardiovascular diseases such as angina, thereby requiring combination therapies for their comorbidities. Ranolazine is a second-line antianginal agent that also improves glycemia, and our aim was to determine whether ranolazine modifies the progression of obesity-induced NAFLD. Twelve-week-old C57BL/6J male mice were fed a low-fat or high-fat diet for 10 weeks and then treated for 30 days with either vehicle control or ranolazine (50 mg/kg via daily s.c. injection). Glycemia was monitored via glucose/pyruvate/insulin tolerance testing, whereas in vivo metabolism was assessed via indirect calorimetry. Hepatic triacylglycerol content was quantified via the Bligh and Dyer method. Consistent with previous reports, ranolazine treatment reversed obesity-induced glucose intolerance, which was associated with reduced body weight and hepatic steatosis, as well as increased hepatic pyruvate dehydrogenase (PDH) activity. Ranolazine's actions on hepatic PDH activity may be directly mediated, as ranolazine treatment reduced PDH phosphorylation (indicative of increased PDH activity) in HepG2 cells. Therefore, in addition to mitigating angina, ranolazine also reverses NAFLD, which may contribute to its documented glucose-lowering actions, situating ranolazine as an ideal antianginal therapy for obese patients comorbid for NAFLD and T2D.

Glucagon-like peptide-1 receptor action in the vasculature.

Glucagon-like peptide-1 receptor (GLP-1R) agonists augment insulin secretion and are thus used clinically to improve glycemia in subjects with type 2 diabetes (T2D). As recent data reveal marked improvements in cardiovascular outcomes in T2D subjects treated with the GLP-1R agonists liraglutide and semaglutide in the LEADER and SUSTAIN-6 clinical trials respectively, there is growing interest in delineating the mechanism(s) of action for GLP-1R agonist-induced cardioprotection. Of importance, negligible GLP-1R expression in ventricular cardiac myocytes suggests that cardiac-independent actions of GLP-1R agonists may account for the reduced death rates from cardiovascular causes in T2D subjects enrolled in the LEADER trial. Conversely, vascular smooth muscle cells (VSMCs) appear to express the canonical GLP-1R, and GLP-1/GLP-1R agonists exhibit a number of salutary actions on the vascular endothelium that could potentially contribute to GLP-1R agonists directly improving cardiovascular outcomes in subjects with T2D. We review herein the described actions of GLP-1/GLP-1R agonists on the vascular endothelium, which include antiproliferative actions on VSMCs and endothelial cells, reductions in oxidative stress, and increases in nitric oxide generation. GLP-1 also increases microvascular recruitment and microvascular blood flow. Taken together, such actions may explain the antihypertensive and/or antiatherosclerotic actions attributed to GLP-1/GLP-1R agonists in preclinical and clinical studies. Nonetheless, further mechanistic studies are still necessary to determine the relative importance of such actions in accounting for reductions in macrovascular cardiovascular disease in human subjects with T2D treated with GLP-1R agonists.