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.     

Airway cellularity, lipid laden macrophages and microbiology of gastric juice and airways in children with reflux oesophagitis

Background and methods

Human metapneumovirus (hMPV) is a recently discovered respiratory virus associated with bronchiolitis, pneumonia, croup and exacerbations of asthma. Since respiratory viruses are frequently detected in patients with acute exacerbations of COPD (AE-COPD) it was our aim to investigate the frequency of hMPV detection in a prospective cohort of hospitalized patients with AE-COPD compared to patients with stable COPD and to smokers without by means of quantitative real-time RT-PCR.

Results

We analysed nasal lavage and induced sputum of 130 patients with AE-COPD, 65 patients with stable COPD and 34 smokers without COPD. HMPV was detected in 3/130 (2.3%) AE-COPD patients with a mean of 6.5 × 10⁵ viral copies/ml in nasal lavage and 1.88 × 10⁵ viral copies/ml in induced sputum. It was not found in patients with stable COPD or smokers without COPD.

Conclusion

HMPV is only found in a very small number of patients with AE-COPD. However it should be considered as a further possible viral trigger of AE-COPD because asymptomatic carriage is unlikely.     

Metformin counters the insulin-induced suppression of fatty acid oxidation and stimulation of triacylglycerol storage in rodent skeletal muscle

The present study examined the acute effects of metformin on fatty acid (FA) metabolism in oxidative soleus (SOL) and glycolytic epitrochlearis (EPT) rodent muscle. SOL and EPT were incubated for either 30 or 180 min in the absence or presence of 2 mM metformin and with or without insulin (10 mU/ml). Metformin did not alter basal FA metabolism but countered the effects of insulin on FA oxidation and incorporation into triacylglyerol (TAG). Specifically, metformin prevented the insulin-induced suppression of FA oxidation in SOL but did not alter FA incorporation into lipid pools. In contrast, in EPT metformin blunted the incorporation of FA into TAG when insulin was present but did not alter FA oxidation. In SOL, metformin resulted in a 50% increase in AMP-activated protein kinase alpha2 activity and prevented the insulin-induced increase in malonyl-CoA content. In both fiber types, basal and insulin-stimulated glucose oxidation were not significantly altered by metformin. All effects were similar regardless of whether they were measured after 30 or 180 min. Because increased muscle lipid storage and impaired FA oxidation have been associated with insulin resistance in this tissue, the ability of metformin to reverse these abnormalities in muscle FA metabolism may be a part of the mechanism by which metformin improves glucose clearance and insulin sensitivity. The present data also suggest that increased glucose clearance is not due to its enhanced subsequent oxidation. Additional studies are warranted to determine whether chronic metformin treatment has similar effects on muscle FA metabolism.     

A role for period 2 in cardioprotection

How adenosine receptors protect the ischemic heart is not completely understood. Eckle et al. (2012) now show that signaling through adenosine receptor 2b (Adora2b) stabilizes a circadian rhythm protein, period 2 (Per2), resulting in the stabilization of hypoxia-inducible factor-1α (HIF-1α), upregulation of glycolysis, and cardioprotection from ischemia.     

Metabolic response to an acute jump in cardiac workload: effects on malonyl-CoA, mechanical efficiency, and fatty acid oxidation

Inhibition of myocardial fatty acid oxidation can improve left ventricular (LV) mechanical efficiency by increasing LV power for a given rate of myocardial energy expenditure. This phenomenon has not been assessed at high workloads in nonischemic myocardium; therefore, we subjected in vivo pig hearts to a high workload for 5 min and assessed whether blocking mitochondrial fatty acid oxidation with the carnitine palmitoyltransferase-I inhibitor oxfenicine would improve LV mechanical efficiency. In addition, the cardiac content of malonyl-CoA (an endogenous inhibitor of carnitine palmitoyltransferase-I) and activity of acetyl-CoA carboxylase (which synthesizes malonyl-CoA) were assessed. Increased workload was induced by aortic constriction and dobutamine infusion, and LV efficiency was calculated from the LV pressure-volume loop and LV energy expenditure. In untreated pigs, the increase in LV power resulted in a 2.5-fold increase in fatty acid oxidation and cardiac malonyl-CoA content but did not affect the activation state of acetyl-CoA carboxylase. The activation state of the acetyl-CoA carboxylase inhibitory kinase AMP-activated protein kinase decreased by 40% with increased cardiac workload. Pretreatment with oxfenicine inhibited fatty acid oxidation by 75% and had no effect on cardiac energy expenditure but significantly increased LV power and LV efficiency (37 +/- 5% vs. 26 +/- 5%, P < 0.05) at high workload. In conclusion, 1) myocardial fatty acid oxidation increases with a short-term increase in cardiac workload, despite an increase in malonyl-CoA concentration, and 2) inhibition of fatty acid oxidation improves LV mechanical efficiency by increasing LV power without affecting cardiac energy expenditure.     

Phosphorylation control of cardiac acetyl-CoA carboxylase by cAMP-dependent protein kinase and 5'-AMP activated protein kinase.

Acetyl-CoA carboxylase (ACC) is regarded in liver and adipose tissue to be the rate-limiting enzyme for fatty acid biosynthesis; however, in heart tissue it functions as a regulator of fatty acid oxidation. Because the control of fatty acid oxidation is important to the functioning myocardium, the regulation of ACC is a key issue. Two cardiac isoforms of ACC exist, with molecular masses of 265 kDa and 280 kDa (ACC265 and ACC280). In this study, these proteins were purified from rat heart and used in subsequent phosphorylation and immunoprecipitation experiments. Our results demonstrate that 5' AMP-activated protein kinase (AMPK) is able to phosphorylate both ACC265 and ACC280, resulting in an almost complete loss of ACC activity. Although cAMP-dependent protein kinase phosphorylated only ACC280, a dramatic loss of ACC activity was still observed, suggesting that ACC280 contributes most, if not all, of the total heart ACC activity. ACC280 and ACC265 copurified under all experimental conditions, and purification of heart ACC also resulted in the specific copurification of the alpha2 isoform of the catalytic subunit of AMPK. Although both catalytic subunits of AMPK were expressed in crude heart homogenates, our results suggest that alpha2, and not alpha1, is the dominant isoform of AMPK catalytic subunit regulating ACC in the heart. Immunoprecipitation studies demonstrated that specific antibodies for both ACC265 and ACC280 were able to coimmunoprecipitate the alternate isoform along with the alpha2 isoform of AMPK. Taken together, the immunoprecipitation and the purification studies suggest that the two isoforms of ACC in the heart exist in a heterodimeric structure, and that this structure is tightly associated with the alpha2 subunit of AMPK.     

Malonyl-CoA mediates leptin hypothalamic control of feeding independent of inhibition of CPT-1a

Hypothalamic fatty acid metabolism is involved in central nervous system controls of feeding and energy balance. Malonyl-CoA, an intermediate of fatty acid biosynthesis, is emerging as a significant player in these processes. Notably, hypothalamic malonyl-CoA has been implicated in leptin's feeding effect. Leptin treatment increases malonyl-CoA level in the hypothalamic arcuate nucleus (Arc), and this increase is required for leptin-induced decrease in food intake. However, the intracellular downstream mediators of malonyl-CoA's feeding effect have not been identified. A primary biochemical action of malonyl-CoA is the inhibition of the acyltransferase activity of carnitine palmitoyltransferase-1 (CPT-1). In the hypothalamus, the predominant isoform of CPT-1 that possesses the acyltransferase activity is CPT-1 liver type (CPT-1a). To address the role of CPT-1a in malonyl-CoA's anorectic action, we used a recombinant adenovirus expressing a mutant CPT-1a that is insensitive to malonyl-CoA inhibition. We show that Arc overexpression of the mutant CPT-1a blocked the malonyl-CoA-mediated inhibition of CPT-1 activity. However, the overexpression of this mutant did not affect the anorectic actions of leptin or central cerulenin for which an increase in Arc malonyl-CoA level is also required. Thus, CPT-1a does not appear to be involved in the malonyl-CoA's anorectic actions induced by leptin. Furthermore, long-chain fatty acyl-CoAs, substrates of CPT-1a, dissociate from malonyl-CoA's actions in the Arc under different feeding states. Together, our results suggest that Arc intracellular mechanisms of malonyl-CoA's anorectic actions induced by leptin are independent of CPT-1a. The data suggest that target(s), rather than CPT-1a, mediates malonyl-CoA action on feeding.     

Identification of a small Na/H exchanger-like message in the rabbit myocardium

We examined the Na⁺/H⁺ exchanger message in isolated perfused rabbit hearts using Northern blot analysis with cDNA encoding for the rabbit cardiac Na⁺/H⁺ exchanger. A cDNA probe from the coding region of the rabbit myocardial Na⁺/H⁺ exchanger hybridized to mRNA of 5 kb under high stringency, and to a second 3.8 kb mRNA species under low stringency. When Northern blots were re-probed with a section of the 3′-untranslated region of the cDNA, the 5 kb message was apparent while the smaller 3.8 kb message was not. If isolated working rabbit hearts were subjected to ischemia we observed increases in the 3.8 kb message. Overall, the results show that a 3.8 kb mRNA product, which is homologous to the amiloride sensitive Na⁺/H⁺ exchanger, exists in the myocardium and increases during ischemia in the myocardium.     

Myocardial triglyceride turnover during reperfusion of isolated rat hearts subjected to a transient period of global ischemia.

Triglyceride turnover in reperfused/ischemic rat hearts was investigated. Hearts were initially perfused under aerobic conditions for a 1-h "pulse" perfusion with 1.2 mM [1-14C]palmitate to label the endogenous lipid pools, followed by a 30-min period of no-flow ischemia or a 10-min period of retrograde perfusion (control). Hearts were then reperfused under aerobic conditions with buffer containing 1.2 mM [9,10-3H]palmitate. All buffers contained 11 mM glucose and 500 microunits/ml insulin. Rates of endogenous triglyceride lipolysis and synthesis were measured during reperfusion, whereas rates of exogenous palmitate oxidation were measured both prior to ischemia and during reperfusion following ischemia. During reperfusion of ischemic hearts, a 20% increase in exogenous fatty acid oxidation rates was seen compared with pre-ischemic rates. Despite an initial burst of endogenous fatty acid oxidation, no acceleration of steady state endogenous triglyceride lipolysis was seen compared with their nonischemic hearts. In contrast, a significant increase in triglyceride synthesis was observed. Triglyceride turnover was also measured in a series of hearts reperfused following ischemia in the absence of exogenous fatty acids. A significant enhancement of functional recovery was seen compared with hearts reperfused with 1.2 mM palmitate. In addition, a significant increase in fatty acid oxidation from endogenous triglyceride lipolysis was observed. We conclude that the heart quickly recovers its ability to oxidize exogenous fatty acids during reperfusion and that although triglyceride lipolysis is not accelerated during reperfusion of ischemic hearts in the presence of 1.2 mM palmitate, a significant increase in triglyceride synthesis does occur.