Malonyl-CoA decarboxylase is not a substrate of AMP-activated protein kinase in rat fast-twitch skeletal muscle or an islet cell line.

The AMP-activated protein kinase (AMPK) plays an important role in fuel metabolism in exercising skeletal muscle and possibly in the islet cell with respect to insulin secretion. Some of these effects are due to AMPK-mediated regulation of cellular malonyl-CoA content, ascribed to the ability of AMPK to phosphorylate and inactivate acetyl-CoA carboxylase (ACC), reducing malonyl-CoA formation. It has been suggested that AMPK may also regulate malonyl-CoA content by activation of malonyl-CoA decarboxylase (MCD). We have investigated the potential regulation of MCD by AMPK in exercising skeletal muscle, in an islet cell line, and in vitro. Three rat fast-twitch muscle types were studied using two different contraction methods or after exposure to the AMPK activator AICAR. Although all muscle treatments resulted in activation of AMPK and phosphorylation of ACC, no stimulus had any effect on MCD activity. In 832/13 INS-1 rat islet cells, two treatments that result in the activation of AMPK, namely low glucose and AICAR, also had no discernable effect on MCD activity. Last, AMPK did not phosphorylate in vitro either recombinant MCD or MCD immunoprecipitated from skeletal muscle or heart. We conclude that MCD is not a substrate for AMPK in fast-twitch muscle or the 832/13 INS-1 islet cell line and that the principal mechanism by which AMPK regulates malonyl-CoA content is through its regulation of ACC.     

Coordinate regulation of malonyl-CoA decarboxylase,sn-glycerol-3-phosphate acyltransferase,and acetyl-CoA carboxylase by AMP-activated protein kinase in rat tissues in response to exercise

Changes in the concentration of malonyl-CoA in many tissues have been related to alterations in the activity of acetyl-CoA carboxylase (ACC), the rate-limiting enzyme in its formation. In contrast, little is known about the physiological role of malonyl-CoA decarboxylase (MCD), an enzyme responsible for malonyl-CoA catabolism. In this study, we examined the effects of voluntary exercise on MCD activity in rat liver, skeletal muscle, and adipose tissue. In addition, the activity of sn-glycerol-3-phosphate acyltransferase (GPAT), which like MCD and ACC can be regulated by AMP-activated protein kinase (AMPK), was assayed. Thirty min after the completion of a treadmill run, MCD activity was increased approximately 2-fold, malonyl-CoA levels were reduced, and ACC and GPAT activities were diminished by 50% in muscle and liver. These events appeared to be mediated via activation of AMPK since: 1) AMPK activity was concurrently increased by exercise in both tissues; 2) similar findings were observed after the injection of 5-amino 4 imidazole carboxamide, an AMPK activator; 3) changes in the activity of GPAT and ACC paralleled that of MCD; and 4) the increase in MCD activity in muscle was reversed in vitro by incubating immunoprecipitated enzyme from the exercised muscle with protein phosphatase 2A, and it was reproduced by incubating immunopurified MCD from resting muscle with purified AMPK. An unexpected finding was that exercise caused similar changes in the activities of ACC, MCD, GPAT, and AMPK and the concentration of malonyl-CoA in adipose tissue. In conclusion: MCD, GPAT, and ACC are coordinately regulated by AMPK in liver and adipose tissue in response to exercise, and except for GPAT, also in muscle. The results suggest that AMPK activation plays a major role in regulating lipid metabolism in many cells following exercise. They also suggest that in each of them, it acts to increase fatty acid oxidation and decrease its esterification.     

Regulation of cardiac malonyl-CoA content and fatty acid oxidation during increased cardiac power

Myocardial fatty acid oxidation is regulated by carnitine palmitoyltransferase I (CPT I), which is inhibited by malonyl-CoA. Increased cardiac power causes a fall in malonyl-CoA content and accelerated fatty acid oxidation; however, the mechanism for the decrease in malonyl-CoA is unclear. Malonyl-CoA is formed by acetyl-CoA carboxylase (ACC) and degraded by malonyl-CoA decarboxylase (MCD); thus a fall in malonyl-CoA could be due to activation of MCD, inhibition of ACC, or both. This study assessed the effects of increased cardiac power on malonyl-CoA content and ACC and MCD activities. Anesthetized pigs were studied under control conditions and during increased cardiac power in response to dobutamine infusion and aortic constriction alone, under hyperglycemic conditions, or with the CPT I inhibitor oxfenicine. An increase in cardiac power was accompanied by increased myocardial O(2) consumption, decreased malonyl-CoA concentration, and increased fatty acid oxidation. There were no differences among groups in activity of ACC or AMP-activated protein kinase (AMPK), which physiologically inhibits ACC. There also were no differences in V(max) or K(m) of MCD. Previous studies have demonstrated that AMPK can be inhibited by protein kinase B (PKB); however, PKB was activated by dobutamine and the elevated insulin that accompanied hyperglycemia, but there was no effect on AMPK activity. In conclusion, the fall in malonyl-CoA and increase in fatty acid oxidation that occur with increased cardiac work were not due to inhibition of ACC or activation of MCD, suggesting alternative regulatory mechanisms for the work-induced decrease in malonyl-CoA concentration.     

Fenofibrate lowers abdominal and skeletal adiposity and improves insulin sensitivity in OLETF rats

The effect of peroxisome proliferator-activated receptor (PPAR)-alpha activators on the liver is well established, but the other effects on muscle and adipose tissue about lipid metabolism and insulin sensitivity are not clear. We investigated whether PPAR-alpha activation affects adiposity of skeletal muscle as well as adipose tissue and improves insulin sensitivity in spontaneous type 2 diabetes model, Otsuka Long-Evans Tokushima Fatty (OLETF) rats. Thirty-three weeks of aged, 20 male OLETF rats were divided into two groups. Control group (n=10) was fed with chow and treatment group (n=10) with chow contained fenofibrate for 7 weeks. At the age of 40 weeks, all rats were examined with MRI, intravenous glucose tolerance test, and then sacrificed for measurement of fat mass and RNA analyses. The total fat (the sum of subcutaneous, mesenteric, epididymal, and retroperitoneal fat pads) measured by dissection was significantly reduced in treatment group. The signal intensity of muscular adiposity was significantly decreased in treatment group. The mRNA levels of FAT/CD36 and mitochondrial carnitine palmitoyltransferase I (M-CPT I) in liver were remarkably increased. Fasting plasma insulin and leptin levels, insulin response after intravenous glucose loading and homeostasis model assessment insulin resistance (HOMA(IR)) index were lowered in treatment group. Fenofibrate increase mitochondrial fatty acid beta-oxidation in liver but not in skeletal muscle and lower the plasma levels of triglyceride and free fatty acid. It might result in reduction of adiposity of truncal adipose tissue and skeletal muscle. We suggest that reduction of adiposity in trunk and skeletal muscle might improve insulin sensitivity.     

PPAR Agonist-Induced Reduction of Mcp1 in Atherosclerotic Plaques of Obese,Insulin-Resistant Mice Depends on Adiponectin-Induced Irak3 Expression

Synthetic peroxisome proliferator-activated receptor (PPAR) agonists are used to treat dyslipidemia and insulin resistance. In this study, we examined molecular mechanisms that explain differential effects of a PPARα agonist (fenofibrate) and a PPARγ agonist (rosiglitazone) on macrophages during obesity-induced atherogenesis. Twelve-week-old mice with combined leptin and LDL-receptor deficiency (DKO) were treated with fenofibrate, rosiglitazone or placebo for 12 weeks. Only rosiglitazone improved adipocyte function, restored insulin sensitivity, and inhibited atherosclerosis by decreasing lipid-loaded macrophages. In addition, it increased interleukin-1 receptor-associated kinase-3 (Irak3) and decreased monocyte chemoattractant protein-1 (Mcp1) expressions, indicative of a switch from M1 to M2 macrophages. The differences between fenofibrate and rosiglitazone were independent of Pparγ expression. In bone marrow-derived macrophages (BMDM), we identified the rosiglitazone-associated increase in adiponectin as cause of the increase in Irak3. Interestingly, the deletion of Irak3 in BMDM (IRAK3^−/− BMDM) resulted in activation of the canonical NFκB signaling pathway and increased Mcp1 protein secretion. Rosiglitazone could not decrease the elevated Mcp1 secretion in IRAK3^−/− BMDM directly and fenofibrate even increased the secretion, possibly due to increased mitochondrial reactive oxygen species production. Furthermore, aortic extracts of high-fat insulin-resistant LDL-receptor deficient mice, with lower adiponectin and Irak3 and higher Mcp1, showed accelerated atherosclerosis. In aggregate, our results emphasize an interaction between PPAR agonist-mediated increase in adiponectin and macrophage-associated Irak3 in the protection against atherosclerosis by PPAR agonists.     

AMP-activated protein kinase and coordination of hepatic fatty acid metabolism of starved/carbohydrate-refed rats

Acute increases in the concentration of malonyl-CoA play a pivotal role in mediating the decrease in fatty acid oxidation that occurs in many tissues during refeeding after a fast. In this study, we assess whether such increases in malonyl-CoA in liver could be mediated by malonyl-CoA decarboxylase (MCD), as well as acetyl-CoA carboxylase (ACC). In addition, we examine how changes in the activity of ACC, MCD, and other enzymes that govern fatty acid and glycerolipid synthesis relate temporally to alterations in the activities of the fuel-sensing enzyme AMP-activated protein kinase (AMPK). Rats starved for 48 h and refed a carbohydrate chow diet for 1, 3, 12, and 24 h were studied. Refeeding caused a 40% decrease in the activity of the alpha1-isoform of AMPK within 1 h, with additional decreases in AMPKalpha1 activity and a decrease in AMPKalpha2 occurring between 1 and 24 h. At 1 h, the decrease in AMPK activity was associated with an eightfold increase in the activity of the alpha1-isoform of ACC and a 30% decrease in the activity of MCD, two enzymes thought to be regulated by AMPK. Also, the concentration of malonyl-CoA was increased by 50%. Between 1 and 3 h of refeeding, additional increases in the activity of ACC and decreases in MCD were observed, as was a further twofold increase in malonyl-CoA. Increases in the activity (60%) and abundance (12-fold) of fatty acid synthase occurred predominantly between 3 and 24 h and increases in the activity of mitochondrial sn-glycerol-3-phosphate acyltransferase (GPAT) and acyl-CoA:diaclyglycerol acyltransferase (DGAT) at 12 and 24 h. The results strongly suggest that early changes in the activity of MCD, as well as ACC, contribute to the increase in hepatic malonyl-CoA in the starved-refed rat. They also suggest that the changes in these enzymes, and later occurring increases in enzymes regulating fatty acid and glycerolipid synthesis, could be coordinated by AMPK.     

Cardiomyocyte-specific knockout of endothelin receptor a attenuates obesity cardiomyopathy

Endothelin (ET)-1 is implicated in the pathophysiology of cardiovascular diseases although its role in obesity anomalies has not been fully elucidated. This study was designed to examine the impact of ET-1 receptor A (ET_A) ablation on obesity-induced changes in cardiac geometry and contractile function, as well as the mechanisms involved with a focus on autophagy. Cardiomyocyte-specific ET_A receptor knockout (ETAKO) and WT mice were fed either low-fat (10% calorie from fat) or high-fat (45% calorie from fat) diet for 24?weeks. Glucose tolerance test was examined to confirm insulin resistance. High-fat diet intake compromised myocardial geometry (enlarged left ventricular diameters in systole and diastole), morphology (cardiac hypertrophy, increased wall thickness and interstitial fibrosis), contractile function (reduced fractional shortening, ejection fraction and cardiomyocyte shortening) and intracellular Ca²⁺ handling, the effect of which was significantly attenuated by ETAKO. TUNEL staining revealed overt apoptosis in high-fat-fed group, the effect was reverted by ETAKO. Western blot analysis noted that high-fat intake downregulated leptin receptor and PPARγ, insulin signaling (elevated basal/dampened insulin-stimulated phosphorylation of Akt and IRS1), phosphorylation of AMPK, ACC, upregulated GATA-4, ANP, NFATc3, PPARα, m-TOR/p70s6k signaling, which were attenuated by ETAKO with the exception of AMPK/ACC. Furthermore, high-fat intake suppressed cardiac autophagy, which was abrogated by ETAKO. In cultured murine cardiomyocytes, palmitic acid challenged mimicked high-fat diet-induced hypertrophic and autophagic responses, the effect of which were abolished by the ET_A receptor antagonist BQ123 or mTOR inhibitor rapamycin. These results suggest that inhibition of ET_A rescues high-fat intake-induced cardiac anomalies possibly through autophagy regulation.     

Adiponectin is required for PPARγ-mediated improvement of endothelial function in diabetic mice

Rosiglitazone is a PPARγ agonist commonly used to treat diabetes. In addition to improving insulin sensitivity, rosiglitazone restores normal vascular function by a mechanism that remains poorly understood. Here we show that adiponectin is required to mediate the PPARγ effect on vascular endothelium of diabetic mice. In db/db and diet-induced obese mice, PPARγ activation by rosiglitazone restores endothelium-dependent relaxation of aortae, whereas diabetic mice lacking adiponectin or treated with an anti-adiponectin antibody do not respond. Rosiglitazone stimulates adiponectin release from fat explants, and subcutaneous fat transplantation from rosiglitazone-treated mice recapitulates vasodilatation in untreated db/db recipients. Mechanistically, adiponectin activates AMPK/eNOS and cAMP/PKA signaling pathways in aortae, which increase NO bioavailability and reduce oxidative stress. Taken together, these results demonstrate that adipocyte-derived adiponectin is required for PPARγ-mediated improvement of endothelial function in diabetes. Thus, the adipose tissue represents a promising target for treating diabetic vasculopathy.     

Long-term high-fat diet-induced obesity decreases the cardiac leptin receptor without apparent lipotoxicity

AimsLeptin resistance has been associated with cardiac lipotoxicity; however, whether leptin resistance is a risk factor associated with cardiac lipotoxicity at different time points in diet-induced obesity is unclear. The objective of this study was to evaluate this relationship.Main methodsMale Wistar rats were fed a normal chow diet (12% from fat) or a high-fat diet (49% from fat) for 15 and 45 weeks, respectively. The adiposity index, body weight and co-morbidities were evaluated. Heart lipotoxicity was assessed by analyzing cardiac function and morphological changes as well as cardiac triglyceride, ceramide and lipid hydroperoxide accumulations. Cardiac apoptosis was examined using the TUNEL method. Leptin function was determined by examining plasma leptin levels, cardiac leptin receptors (OB-R) and related phosphorylations of AMP-activated kinase protein (AMPK) and Acetyl CoA carboxylase (ACC).Key findingsThe diet-induced obesity was characterized by an elevated adiposity index, body weight and leptin levels at both 15 and 45 weeks. There was no difference between groups in the cardiac triglyceride or lipid hydroperoxide levels. Interestingly, ceramide levels decreased in obese animals in both experimental periods. The cardiac morphological and functional parameters were not altered. Although down-regulation of OB-R has occurred in chronic obesity, it did not adversely affect AMPK or ACC phosphorylation.SignificanceThe development of obesity via long-term feeding of a high-fat diet to rats does not result in cardiac lipotoxicity but promotes the down-regulation of OB-R. However, this does not result in altered levels of AMPK or ACC phosphorylations in this animal model.     

Activation of malonyl-CoA decarboxylase in rat skeletal muscle by contraction and the AMP-activated protein kinase activator 5-aminoimidazole-4-carboxamide-1-beta -D-ribofuranoside

Alterations in the concentration of malonyl-CoA, an inhibitor of carnitine palmitoyltransferase I, have been linked to the regulation of fatty acid oxidation in skeletal muscle. During contraction decreases in muscle malonyl-CoA concentration have been related to activation of AMP-activated protein kinase (AMPK), which phosphorylates and inhibits acetyl-CoA carboxylase (ACC), the rate-limiting enzyme in malonyl-CoA formation. We report here that the activity of malonyl-CoA decarboxylase (MCD) is increased in contracting muscle. Using either immunopurified enzyme or enzyme partially purified by (NH(4))(2)SO(4) precipitation, 2-3-fold increases in the V(max) of MCD and a 40% decrease in its K(m) for malonyl-CoA (190 versus 119 micrometer) were observed in rat gastrocnemius muscle after 5 min of contraction, induced by electrical stimulation of the sciatic nerve. The increase in MCD activity was markedly diminished when immunopurified enzyme was treated with protein phosphatase 2A or when phosphatase inhibitors were omitted from the homogenizing solution and assay mixture. Incubation of extensor digitorum longus muscle for 1 h with 2 mm 5-aminoimidazole-4-carboxamide-1-beta-d-ribofuranoside, a cell-permeable activator of AMPK, increased MCD activity 2-fold. Here, too, addition of protein phosphatase 2A to the immunopellets reversed the increase of MCD activity. The results strongly suggest that activation of AMPK during muscle contraction leads to phosphorylation of MCD and an increase in its activity. They also suggest a dual control of malonyl-CoA concentration by ACC and MCD, via AMPK, during exercise.     

High-fat diet offsets the long-lasting effects of running-wheel access on food intake and body weight in OLETF rats

We have previously demonstrated that running-wheel access normalizes the food intake and body weight of Otsuka Long-Evens Tokushima Fatty (OLETF) rats. Following 6 wk of running-wheel access beginning at 8 wk of age, the body weight of OLETF rats remains reduced, demonstrating a lasting effect on their phenotype. In contrast, access to a high-fat diet exacerbates the hyperphagia and obesity of OLETF rats. To determine whether diet modulates the long-term effects of exercise, we examined the effects of high-fat diet on food intake and body weight in OLETF rats that had prior access to running wheels for 4 wk. We found that 4 wk of running exercise significantly decreased food intake and body weight of OLETF rats. Consistent with prior results, 4 wk of exercise also produced long-lasting effects on food intake and body weight in OLETF rats fed a regular chow. When running wheels were relocked, OLETF rats stabilized at lower levels of body weight than sedentary OLETF rats. However, access to a high-fat diet offset these effects. When OLETF rats were switched to a high-fat diet following wheel relocking, they significantly increased food intake and body weight, so that they reached levels similar to those of sedentary OLETF rats fed a high-fat diet. Gene expression determination of hypothalamic neuropeptides revealed changes that appeared to be appropriate responses to the effects of diet and running exercise. Together, these results demonstrate that high-fat diet modulates the long-lasting effects of exercise on food intake and body weight in OLETF rats.     

β‐Adrenergic‐AMPK Pathway Phosphorylates Acetyl‐CoA Carboxylase in a High‐epinephrine Rat Model,SPORTS

We established a new animal model called SPORTS (Spontaneously‐Running Tokushima‐Shikoku) rats, which show high‐epinephrine (Epi) levels. Recent reports show that Epi activates adenosine monophosphate (AMP)–activated protein kinase (AMPK) in adipocytes. Acetyl‐CoA carboxylase (ACC) is the rate‐limiting enzyme in fatty acid synthesis, and the enzymatic activity is suppressed when its Ser‐79 is phosphorylated by AMPK. The aim of this study was to investigate the in vivo effect of Epi on ACC and abdominal visceral fat accumulation. We divided both 6‐week male control and SPORTS rats into two groups, which were fed either normal diet or high fat and sucrose (HFS) diet for 16 weeks. At the end of diet treatment, retroperitoneal fat was collected for western blotting and histological analysis. Food intake was not different among the groups, but SPORTS rats showed significantly lower weight gain than control rats in both diet groups. After 10 weeks of diet treatment, glucose tolerance tests (GTTs) revealed that SPORTS rats had increased insulin sensitivity. Furthermore, SPORTS rats had lower quantities of both abdominal fat and plasma triglyceride (TG). In abdominal fat, elevated ACC Ser‐79 phosphorylation was observed in SPORTS rats and suppressed by an antagonist of β‐adrenergic receptor (AR), propranolol, or an inhibitor of AMPK, Compound C. From these results, high level of Epi induced ACC phosphorylation mediated through β‐AR and AMPK signaling pathways in abdominal visceral fat of SPORTS rats, which may contribute to reduce abdominal visceral fat accumulation and increase insulin sensitivity. Our results suggest that β‐AR‐regulated ACC activity would be a target for treating lifestyle‐related diseases, such as obesity.     

Hepatic expression of malonyl-CoA decarboxylase reverses muscle, liver and whole-animal insulin resistance

Lipid infusion or ingestion of a high-fat diet results in insulin resistance, but the mechanism underlying this phenomenon remains unclear. Here we show that, in rats fed a high-fat diet, whole-animal, muscle and liver insulin resistance is ameliorated following hepatic overexpression of malonyl-coenzyme A (CoA) decarboxylase (MCD), an enzyme that affects lipid partitioning. MCD overexpression decreased circulating free fatty acid (FFA) and liver triglyceride content. In skeletal muscle, levels of triglyceride and long-chain acyl-CoA (LC-CoA)-two candidate mediators of insulin resistance-were either increased or unchanged. Metabolic profiling of 36 acylcarnitine species by tandem mass spectrometry revealed a unique decrease in the concentration of one lipid-derived metabolite, beta-OH-butyrate, in muscle of MCD-overexpressing animals. The best explanation for our findings is that hepatic expression of MCD lowered circulating FFA levels, which led to lowering of muscle beta-OH-butyrate levels and improvement of insulin sensitivity.     

Globular adiponectin resistance develops independently of impaired insulin-stimulated glucose transport in soleus muscle from high-fat-fed rats

High-fat (HF) diets induce insulin resistance and alter lipid metabolism, although controversy exists regarding the impact of saturated vs. polyunsaturated fats. Adiponectin (Ad) stimulates fatty acid (FA) oxidation and improves insulin sensitivity in humans and rodents, due in part to the activation of AMP-activated protein kinase (AMPK) and subsequent deactivation of acetyl coenzyme A carboxylase (ACC). In genetically obese, diabetic mice, this acute stimulatory effect on AMPK in muscle is lost. The ability of a HF diet to induce skeletal muscle Ad resistance has not been examined. The purpose of this study was to determine whether Ad's effects on FA oxidation and AMPK/ACC would be reduced following different HF diets, and if this coincided with the development of impaired maximal insulin-stimulated glucose transport. Rats were fed a control (10% kcal fat, CON), high unsaturated fat (60% kcal safflower oil, SAFF), or high saturated fat diet (60% kcal lard, LARD) for 4 wk. Following the dietary intervention, glucose transport, lipid metabolism, and AMPK/ACC phosphorylation were measured in the presence and absence of globular Ad (gAd, 2.5 microg/ml) in isolated soleus muscle. LARD rats showed reduced rates of maximal insulin-stimulated glucose transport compared with CON and SAFF (+68 vs. +172 and +184%, P < or = 0.001). gAd increased pACC (+25%, P < or = 0.01) and FA oxidation (+28%, P < or = 0.05) in CON rats, but not in either HF group. Thus 4 wk of HF feeding results in the loss of gAd stimulatory effect on ACC phosphorylation and muscle FA oxidation, and this can occur independently of impaired maximal insulin-stimulated glucose transport.     

Increased malonyl-CoA and diacylglycerol content and reduced AMPK activity accompany insulin resistance induced by glucose infusion in muscle and liver of rats

Glucose infusion in rats for 1-4 days results in insulin resistance and increased triglyceride, whole tissue long-chain fatty acyl-CoA (LCA-CoA), and malonyl-CoA content in red skeletal muscle. Despite this, the relation between these alterations and the onset of insulin resistance has not been defined. We aimed to 1) identify whether the changes in these lipids and of diacylglycerol (DAG) precede or accompany the onset of insulin resistance in glucose-infused rats, 2) determine whether the insulin resistance is associated with alterations in AMP-activated protein kinase (AMPK), and 3) assess whether similar changes occur in liver and in muscle. Hyperglycemia (17-18 mM) was maintained by intravenous glucose infusion in rats for 3 or 5 h; then euglycemia was restored and a 2-h hyperinsulinemic clamp was performed. Significant (P < 0.01) muscle and liver insulin resistance first appeared in red quadriceps and liver of the glucose-infused group at 5 h and was associated with a twofold increase in DAG and malonyl-CoA content and a 50% decrease in AMPK and acetyl-CoA carboxylase (ACC) phosphorylation and AMPK activity. White quadriceps showed qualitatively similar changes but without decreases in AMPK or ACC phosphorylation. Triglyceride mass was increased at 5 h only in liver, and whole tissue LCA-CoA content was not increased in liver or either muscle type. We conclude that the onset of insulin resistance induced by glucose oversupply correlates temporally with increases in malonyl-CoA and DAG content in all three tissues and with reduced AMPK phosphorylation and activity in red muscle and liver. In contrast, it was not associated with increased whole tissue LCA-CoA content in any tissue or triglyceride in muscle, although both are observed at later times.     

Modulation of metabolic and cardiac dysfunctions by insulin sensitizers and angiotensin receptor blocker in rat model of type 2 diabetes mellitus

The objective of this study was to investigate the modulation of metabolic dysfunctions, adiponectin levels, and cardiac dysfunctions of type 2 diabetes mellitus (T2DM) by a combination of the insulin sensitizer rosiglitazone and angiotensin receptor blocker telmisartan in an experimental rat model. Fifty male adult Sprague-Dawley rats were divided equally into 5 groups. Group I: fed normal chow; served as normal control group. Groups II-V: fed a high-fat diet (HFD) for 2 weeks, followed by injection of streptozotocin (STZ; 35 mg/kg) to create a model of T2DM. Group II: treated with vehicle. Group III: treated with rosiglitazone (4 mg/kg). Group IV: treated with telmisartan (5 mg/kg). Group V: treated with both agents. Untreated HFD-STZ rats showed elevated fasting blood glucose, insulin, homeostasis model assessment (HOMA) index, triglycerides (TGs), low-density lipoprotein cholesterol (LDL), and total serum cholesterol (TC), with a decrease in high-density lipoprotein cholesterol (HDL) and adiponectin levels (p < 0.001). Rosiglitazone exerted more improvement in all parameters than telmisartan did, and a combination of both did not augment the improvement further, except for TGs and adiponectin. For the isolated atrial study, a combination of rosiglitazone and telmisartan corrected the responses of the atria of HFD-STZ rats to the negative inotropic effect induced by adenosine better than either one did alone, whereas this combination, surprisingly, significantly attenuated the positive inotropic response to β-adrenoreceptor and α-adrenoreceptor agonists. In conclusion, rosiglitazone significantly improved the metabolic and cardiac dysfunctions in T2DM. Moreover, a combination of rosiglitazone and telmisartan offered more improvement in serum TGs and adiponectin, and restored the atrial inotropic response to adenosine. Surprisingly, this combination significantly attenuates the positive inotropic response to α1-adrenoreceptor and β-adrenoreceptor agonists.     

Effect of diet composition on coenzyme A and its thioester pools in various rat tissues

Three coenzyme A (CoA) molecular species, i.e., acetyl-CoA, malonyl-CoA, and nonesterified CoA (CoASH), in 13 types of fasted rat tissue were analyzed. A relatively larger pool size of total CoA, consisting of acetyl-CoA, malonyl-CoA, and CoASH, was observed in the medulla oblongata, liver, heart, and brown adipose tissue. Focusing on changes in the CoA pool size in response to the nutrient composition of the diet given, total CoA pools in rats continuously fed a high-fat diet for 4 weeks were significantly higher in the hypothalamus, cerebellum, and kidney, and significantly lower in the liver and skeletal muscle than those of rats fed a high-carbohydrate or high-protein diet. In particular, reductions in the liver were remarkable and were caused by decreased CoASH levels. Consequently, the total CoA pool size was reduced by approximately one-fifth of the hepatic contents of rats fed the other diets. In the hypothalamus, which monitors energy balance, all three CoA molecular species measured were at higher levels when rats were fed the high-fat diet. Thus, it was of interest that feeding rats a high-fat diet affected the behaviors of CoA pools in the hypothalamus, liver, and skeletal muscle, suggesting a significant relationship between CoA pools, especially malonyl-CoA and/or CoASH pools, and lipid metabolism in vivo.     

Effects of PPARgamma and PPARalpha agonists on serum leptin levels in diet-induced obese rats.

Leptin and peroxisome proliferator-activated receptors are two important adipose tissue factors involved in energy metabolism regulation. It has been shown that PPARgamma agonists decrease leptin levels. However, the effects of PPARalpha agonists on leptin have not been investigated much. The aim of this study was to compare the effects of a PPARgamma agonist rosiglitazone (RSG) and PPARalpha agonist gemfibrozil (G) on body weight and serum insulin and leptin levels in diet-induced obese rats. Male Wistar rats were divided into six groups according to diet and drug therapy. After four weeks, serum glucose, triglyceride, insulin and leptin levels were significantly decreased in the high-fat-fed and RSG-treated groups compared to the group fed a high-fat diet only (162 +/- 19 vs. 207 +/- 34 mg/dl, 58 +/- 20 vs. 112 +/- 23 mg/dl, 3.1 +/- 1.0 vs. 15.2 +/- 4.0 ng/ml, 1.6 +/- 0.5 vs. 3.6 +/- 1.6 ng/ml, respectively). However, these parameters were not statistically different in RSG animals treated with a standard diet compared to the standard diet group. The high fat+RSG group gained much more weight compared to high-fat and high-fat+G groups (p > 0.05). Additionally, serum glucose, insulin and leptin levels were significantly decreased in the high-fat-fed and G-treated group compared to high-fat group (149 +/- 19 vs. 207 +/- 34 mg/dl, 57 +/- 16 vs. 112 +/- 23 mg/dl, 4.3 +/- 2.1 vs. 15.2 +/- 4.0 ng/ml, 1.6 +/- 0.4 vs. 3.6 +/- 1.6 ng/ml, respectively). These results suggest that PPARalpha agonists may decrease serum glucose, insulin and leptin levels as PPARgamma agonists do in diet-induced obese rats.     

Contribution of malonyl-CoA decarboxylase to the high fatty acid oxidation rates seen in the diabetic heart

Myocardial glucose oxidation is markedly reduced in the uncontrolled diabetic. We determined whether this was due to direct biochemical changes in the heart or whether this was due to altered circulating levels of insulin and substrates that can be seen in the diabetic. Isolated working hearts from control or diabetic rats (streptozotocin, 55 mg/kg iv administered 6 wk before study) were aerobically perfused with either 5 mM [(14)C]glucose and 0.4 mM [(3)H]palmitate (low-fat/low-glucose buffer) or 20 mM [(14)C]glucose and 1.2 mM [(3)H]palmitate (high-fat/high-glucose buffer) +/-100 microU/ml insulin. The presence of insulin increased glucose oxidation in control hearts perfused with low-fat/low-glucose buffer from 553 +/- 85 to 1,150 +/- 147 nmol x g dry wt(-1) x min(-1) (P < 0. 05). If control hearts were perfused with high-fat/high-glucose buffer, palmitate oxidation was significantly increased by 112% (P < 0.05), but glucose oxidation decreased to 55% of values seen in the low-fat/low-glucose group (P < 0.05). In diabetic hearts, glucose oxidation was very low in hearts perfused with low-fat/low-glucose buffer (9 +/- 1 nmol x g dry wt(-1) x min(-1)) and was not altered by insulin or high-fat/high-glucose buffer. These results suggest that neither circulating levels of substrates nor insulin was responsible for the reduced glucose oxidation in diabetic hearts. To determine if subcellular changes in the control of fatty acid oxidation contribute to these changes, we measured the activity of three enzymes involved in the control of fatty acid oxidation; AMP-activated protein kinase (AMPK), acetyl-CoA carboxylase (ACC), and malonyl-CoA decarboxylase (MCD). Although AMPK and ACC activity in control and diabetic hearts was not different, MCD activity and expression in all diabetic rat heart perfusion groups were significantly higher than that seen in corresponding control hearts. These results suggest that an increased MCD activity contributes to the high fatty acid oxidation rates and reduced glucose oxidation rates seen in diabetic rat hearts.