Myocardial phospholipid metabolism in alloxan diabetic rats

Alloxan diabetes in rats was found to decrease the level of phospholipids in the heart. Measurement of specific phosphatides showed that the decrease was restricted only to phosphatidylethanolamine and lysophosphatidylcholine. Study of $\text{in}$$\text{vivo}$ incorporation of ³²Pi indicated an impairment of phosphatidylethanolamine synthesis and conversion of phosphatidylcholine into lysophosphatidyl choline in the heart of diabetic rats. Treatment of diabetic rats with insulin restored the levels of phosphatidylethanolamine and lysophosphatidylcholine and incorporation of ³²Pi into these phosphatides to almost normal.     

Myocardial substrate metabolism influences left ventricular energetics in vivo

The myocardial oxygen consumption (MVO(2)) to left ventricular pressure-volume area (PVA) relationship is assumed unaltered by substrates, despite varying phosphate-to-oxygen ratios and possible excess MVO(2) associated with fatty acid consumption. The validity of this assumption was tested in vivo. Left ventricular volumes and pressures were assessed with a combined conductance-pressure catheter in eight anesthetized pigs. MVO(2) was calculated from coronary flow and arterial-coronary sinus O(2) differences. Metabolism was altered by glucose-insulin-potassium (GIK) or Intralipid-heparin (IH) infusions in random order and monitored with [(14)C]glucose and [(3)H]oleate tracers. Profound shifts in glucose and fatty acid oxidation were observed. Contractility, coronary flow, and slope of the MVO(2)-PVA relationship were unchanged during GIK and IH infusions. MVO(2) at zero PVA (unloaded MVO(2)) was 0.16 +/- 0.13 J x beat(-1) x 100 g(-1) higher during IH compared with GIK infusion (P = 0.001), a 48% increase. The study demonstrates a marked energetic advantage of glucose oxidation in the myocardium, profoundly affecting the MVO(2)-PVA relationship. This may in part explain the "oxygen-wasting" effect of lipid-enhancing interventions such as adrenergic drugs and ischemia.     

Myocardial ischaemia inhibits mitochondrial metabolism of 4-hydroxy-trans-2-nonenal

Myocardial ischaemia is associated with the generation of lipid peroxidation products such as HNE (4-hydroxy-trans-2-nonenal); however, the processes that predispose the ischaemic heart to toxicity by HNE and related species are not well understood. In the present study, we examined HNE metabolism in isolated aerobic and ischaemic rat hearts. In aerobic hearts, the reagent [(3)H]HNE was glutathiolated, oxidized to [(3)H]4-hydroxynonenoic acid, and reduced to [(3)H]1,4-dihydroxynonene. In ischaemic hearts, [(3)H]4-hydroxynonenoic acid formation was inhibited and higher levels of [(3)H]1,4-dihydroxynonene and [(3)H]GS-HNE (glutathione conjugate of HNE) were generated. Metabolism of [(3)H]HNE to [(3)H]4-hydroxynonenoic acid was restored upon reperfusion. Reperfused hearts were more efficient at metabolizing HNE than non-ischaemic hearts. Ischaemia increased the myocardial levels of endogenous HNE and 1,4-dihydroxynonene, but not 4-hydroxynonenoic acid. Isolated cardiac mitochondria metabolized [(3)H]HNE primarily to [(3)H]4-hydroxynonenoic acid and minimally to [(3)H]1,4-dihydroxynonene and [(3)H]GS-HNE. Moreover, [(3)H]4-hydroxynonenoic acid was extruded from mitochondria, whereas other [(3)H]HNE metabolites were retained in the matrix. Mitochondria isolated from ischaemic hearts were found to contain 2-fold higher levels of protein-bound HNE than the cytosol, as well as increased [(3)H]GS-HNE and [(3)H]1,4-dihydroxynonene, but not [(3)H]4-hydroxynonenoic acid. Mitochondrial HNE oxidation was inhibited at an NAD(+)/NADH ratio of 0.4 (equivalent to the ischaemic heart) and restored at an NAD(+)/NADH ratio of 8.6 (equivalent to the reperfused heart). These results suggest that HNE metabolism is inhibited during myocardial ischaemia owing to NAD(+) depletion. This decrease in mitochondrial metabolism of lipid peroxidation products and the inability of the mitochondria to extrude HNE metabolites could contribute to myocardial ischaemia/reperfusion injury.     

Myocardial energy metabolism in ischemic preconditioning and cardioplegia: A metabolic control analysis

For both, cardioplegia (CP) and ischemic preconditioning (IP), increased ischemic tolerance with reduction in infarct size is well documented. These cardioprotective effects are related to a limitation of high energy phosphate (HEP) depletion. As CP and IP have to be assumed to act by different mechanisms, their effects on myocardial HEP metabolism cannot be assumed to be identical. Therefore, a systematic analysis of myocardial HEP metabolism for both procedures and their combination was performed, addressing the question whether there are different effects on myocardial HEP metabolism by IP and CP. In this study, metabolic control analysis was used to analyze the regulation of HEP metabolism. In open chest pigs subjected to 45 min LAD occlusion (index ischemia), CP and IP preserved myocardial ATP (control (C) 0.14 ± 0.05 μmol/g wwt; CP: 0.95 ± 0.14, IP: 0.61 ± 0.12; p<0.05 C vs. CP and IP) and reduced myocardial necrosis (infarct size IA/RA: C: 90.0 ± 3.0%; CP: 0.0 ± 0.0% but patchy necroses; IP: 5.05 ± 2.1%; p<0.05 C vs. CP and IP). The effects on HEP metabolism, however, were different: CP acted predominantly by slowing down the breakdown of phosphocreatine (PCr) during early phases of ischemia (C: ΔPCr 0–2 min: 5.24 ± 0.32 μmol/g wwt; CP: ΔPCr 0–2 min: 3.38 ± 0.23 μmol/g wwt, p<0.05 vs. C), leaving ATP breakdown during later stages unaffected (C: ΔATP 5–45 min: 1.77 ± 0.11 μmol/g wwt CP: ΔATP 5–45 min: 1.59 ± 0.28 μmol/g wwt, n.s. vs. C). In contrast to CP, in IP PCr breakdown was even increased (IP: ΔPCr 0–2 min: 7.06 ± 0.34 μmol/g wwt, p<0.05 vs. C), but ATP depletion greatly attenuated (IP: ΔATP 5–45 min: 0.48 ± 0.10 μmol/g wwt, p<0.05 vs. C and CP). Combining IP and CP yielded an additive effect with slowing down the breakdown of both PCr (IP+CP: ΔPCr 0–2 min: 5.09± 0.35 μmol/g wwt, p<0.05 vs. C and IP) and ATP (IP+CP: ΔATP 5–45 min: 0.56 ± 0.48 μmol/g wwt, p<0.05 vs. C and CP), resulting in a higher ATP content at the end of index ischemia (1.86 ± 0.46 μmol/g wwt, p<0.05 vs. C, CP and IP). Compared to IP, combining IP+CP achieved also a further reduction in infarct size (IA/RA: 0.0 ± 0.0%, p<0.05 vs IP) and—compared to CP—a disappearance of the patchy necroses. {The concept of major differences in myocardial HEP metabolism during CP and IP is further supported at a molecular level by metabolic control analysis. CP but not IP slowed down the CK reaction velocity at high PCr levels. In contrast to CP exerting a continuous decline in vATPase for any given ATP level, in IP myocardium ATPase reaction velocity was even increased at higher ATP contents, whereas a marked decrease in ATPase reaction velocity was found if ATP levels decreased. The equilibrium of the CK-reaction remained unchanged following CP, whereas IP induced a changing CK equilibrium, which was the more shifted towards PCr the more myocardial HEP content decreased. The data demonstrate different effects of CP and IP on myocardial HEP metabolism, i.e. PCr and ATP breakdown as well as the apparent equilibrium of the creatine kinase (CK)-reaction. For these reasons the combination of the two protective interventions has an additive effect. (Mol Cell Biochem 278: 222–232, 2005)     

Myocardial function and energy substrate metabolism in the insulin-resistant JCR:LA corpulent rat.

Alterations in myocardial energy substrate utilization contribute to the development of cardiomyopathic changes in insulin-dependent and non-insulin-dependent diabetic rats. Energy substrate utilization and contractile function, however, have not been characterized in insulin-resistant diabetes. In this study, we studied these parameters in the insulin-resistant obese JCR:LA-cp rat homozygous for the corpulent gene (cp/cp). Homozygous (+/+) or heterozygous (+/cp) lean non-insulin-resistant rats were used as controls. Isolated working hearts from cp/cp and lean control rats were perfused with Krebs-Henseleit buffer containing either 11 mM [U-14C]glucose and 0.4 mM palmitate or 11 mM glucose and 0.4 mM [1-14C]palmitate. Unlike control hearts, hearts from cp/cp rats were found to require high doses of insulin and Ca2+ concentrations of less than or equal to 1.75 mM to maintain mechanical function. In the presence of 2,000 microU/ml insulin, contractile function from cp/cp rat hearts was not depressed in the presence of either 1.25 or 1.75 mM Ca2+. Steady-state glucose oxidation rates in hearts perfused with 1.25 mM Ca2+ and 2,000 microU/ml insulin were 811 +/- 86 (SE) and 612 +/- 51 nmol.min-1.g dry wt-1 in cp/cp and control rats, respectively. Palmitate oxidation was 307 +/- 47 and 307 +/- 47 nmol.min-1.g dry wt-1 in cp/cp and lean control hearts, respectively. Under these perfusion conditions, 40% of myocardial ATP production was derived from glucose, whereas 60% was derived from palmitate in both cp/cp and control rats.(ABSTRACT TRUNCATED AT 250 WORDS)     

Myocardial lipid metabolism in cardiac hyper- and hypo-function. Studies on triiodothyronine-treated and transplanted rat hearts.

Lipid composition of the myocardium and in vitro lipid metabolism were studied in hearts from young rats after 30 days of treatment with triiodothyronine (100 microgram/kg per day) and in heterotopically isotransplanted hearts of inbred adult rats 6 days after surgery. The former served as an experimental model of cardiac hyperfunction, while the latter, empty beating hearts, served as a model of cardiac hypofunction. In hearts from hyperthyroid animals the concentration of phosphatidylcholine, phosphatidylethanolamine, cardiolipin, and the incorporation of 14C-labelled palmitic and erucic acid into these phospholipids were increased significantly as compared with controls. In contrast, the triglyceride concentration and the incorporation of palmitate into triglyceride was significantly decreased. In transplanted hearts, the phospholipid concentration and the incorporation of 14C-labelled fatty acids into phospholipids were significantly decreased as compared with the hearts of the inbred host rats of the same age. The results indicate that the mechanical performance of the heart affects the phospholipid composition, which may be a reflection of increased or decreased proliferation of subcellular membranes in sustained cardiac hyper- or hypo-function.     

Myocardial angiogenesis

Coronary angiogenesis and collateral growth are chronic adaptations to myocardial ischemia, which are aimed at restoring coronary blood flow and salvaging myocardium in an ischemic region. Although we have assumed that myriad numbers of growth factors are involving in this adaptation, details in the underlying mechanisms, i.e., number of angiogenic factors, angiostatic factors, their receptors/signaling cascades, interactions/crosstalk among the signaling pathways and receptors, and the time course of expression/function of a particular factor or pathway during the successful adaptation are still unclear; they are, probably, harmonized like a symphony. Although there is as of yet no consensus about the mechanisms and causal factors for these cononary adaptations to ischemia, recent evidence strongly suggests that a balance between growth factors and growth inhibitors is critical. In this review we introduce vascular endothelial growth factor, angiopoietins, and angiostatin, as factors playing pivotal roles in coronary angiogenesis and collateral growth.