Long-chain acyl-coenzyme A esters and fatty acids directly link metabolism to K(ATP) channels in the heart

Exploring the Role of Surface and Mitochondrial ATP-Sensitive Potassium Channels in Cancer: From Cellular Functions to Therapeutic Potentials

ATP-sensitive potassium (KATP) channels are found in plasma membranes and mitochondria. These channels are a type of ion channel that is regulated by the intracellular concentration of adenosine triphosphate (ATP) and other nucleotides. In cell membranes, they play a crucial role in linking metabolic activity to electrical activity, especially in tissues like the heart and pancreas. In mitochondria, KATP channels are involved in protecting cells against ischemic damage and regulating mitochondrial function. This review delves into the role of KATP channels in cancer biology, underscoring their critical function. Notably responsive to changes in cellular metabolism, KATP channels link metabolic states to electrical activity, a feature that becomes particularly significant in cancer cells. These cells, characterized by uncontrolled growth, necessitate unique metabolic and signaling pathways, differing fundamentally from normal cells. Our review explores the intricate roles of KATP channels in influencing the metabolic and ionic balance within cancerous cells, detailing their structural and operational mechanisms. We highlight the channels' impact on cancer cell survival, proliferation, and the potential of KATP channels as therapeutic targets in oncology. This includes the challenges in targeting these channels due to their widespread presence in various tissues and the need for personalized treatment strategies. By integrating molecular biology, physiology, and pharmacology perspectives, the review aims to enhance the understanding of cancer as a complex metabolic disease and to open new research and treatment avenues by focusing on KATP channels. This comprehensive approach provides valuable insights into the potential of KATP channels in developing innovative cancer treatments.

Structural basis of the activation of TRPV5 channels by long-chain acyl-Coenzyme-A

Long-chain acyl-coenzyme A (LC-CoA) is a crucial metabolic intermediate that plays important cellular regulatory roles, including activation and inhibition of ion channels. The structural basis of ion channel regulation by LC-CoA is not known. Transient receptor potential vanilloid 5 and 6 (TRPV5 and TRPV6) are epithelial calcium-selective ion channels. Here, we demonstrate that LC-CoA activates TRPV5 and TRPV6 in inside-out patches, and both exogenously supplied and endogenously produced LC-CoA can substitute for the natural ligand phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) in maintaining channel activity in intact cells. Utilizing cryo-electron microscopy, we determined the structure of LC-CoA-bound TRPV5, revealing an open configuration with LC-CoA occupying the same binding site as PI(4,5)P2 in previous studies. This is consistent with our finding that PI(4,5)P2 could not further activate the channels in the presence of LC-CoA. Our data provide molecular insights into ion channel regulation by a metabolic signaling molecule.

PGRMC1 Ablation Protects from Energy-Starved Heart Failure by Promoting Fatty Acid/Pyruvate Oxidation

Heart failure (HF) is an emerging epidemic with a high mortality rate. Apart from conventional treatment methods, such as surgery or use of vasodilation drugs, metabolic therapy has been suggested as a new therapeutic strategy. The heart relies on fatty acid oxidation and glucose (pyruvate) oxidation for ATP-mediated contractility; the former meets most of the energy requirement, but the latter is more efficient. Inhibition of fatty acid oxidation leads to the induction of pyruvate oxidation and provides cardioprotection to failing energy-starved hearts. One of the non-canonical types of sex hormone receptors, progesterone receptor membrane component 1 (Pgrmc1), is a non-genomic progesterone receptor associated with reproduction and fertility. Recent studies revealed that Pgrmc1 regulates glucose and fatty acid synthesis. Notably, Pgrmc1 has also been associated with diabetic cardiomyopathy, as it reduces lipid-mediated toxicity and delays cardiac injury. However, the mechanism by which Pgrmc1 influences the energy-starved failing heart remains unknown. In this study, we found that loss of Pgrmc1 inhibited glycolysis and increased fatty acid/pyruvate oxidation, which is directly associated with ATP production, in starved hearts. Loss of Pgrmc1 during starvation activated the phosphorylation of AMP-activated protein kinase, which induced cardiac ATP production. Pgrmc1 loss increased the cellular respiration of cardiomyocytes under low-glucose conditions. In isoproterenol-induced cardiac injury, Pgrmc1 knockout resulted in less fibrosis and low heart failure marker expression. In summary, our results revealed that Pgrmc1 ablation in energy-deficit conditions increases fatty acid/pyruvate oxidation to protect against cardiac damage via energy starvation. Moreover, Pgrmc1 may be a regulator of cardiac metabolism that switches the dominance of glucose-fatty acid usage according to nutritional status and nutrient availability in the heart.

Impacts of a high-fat diet on the metabolic profile and the phenotype of atrial myocardium in mice

AIMS

Obesity, diabetes, and metabolic syndromes are risk factors of atrial fibrillation (AF). We tested the hypothesis that metabolic disorders have a direct impact on the atria favouring the formation of the substrate of AF.

METHODS AND RESULTS

Untargeted metabolomic and lipidomic analysis was used to investigate the consequences of a prolonged high-fat diet (HFD) on mouse atria. Atrial properties were characterized by measuring mitochondria respiration in saponin-permeabilized trabeculae, by recording action potential (AP) with glass microelectrodes in trabeculae and ionic currents in myocytes using the perforated configuration of patch clamp technique and by several immuno-histological and biochemical approaches. After 16 weeks of HFD, obesogenic mice showed a vulnerability to AF. The atrial myocardium acquired an adipogenic and inflammatory phenotypes. Metabolomic and lipidomic analysis revealed a profound transformation of atrial energy metabolism with a predominance of long-chain lipid accumulation and beta-oxidation activation in the obese mice. Mitochondria respiration showed an increased use of palmitoyl-CoA as energy substrate. APs were short duration and sensitive to the K-ATP-dependent channel inhibitor, whereas K-ATP current was enhanced in isolated atrial myocytes of obese mouse.

CONCLUSION

HFD transforms energy metabolism, causes fat accumulation, and induces electrical remodelling of the atrial myocardium of mice that become vulnerable to AF.

Association of body mass index with left ventricular diastolic dysfunction among ambulatory individuals with diabetes mellitus in rural Uganda: a cross-sectional study

Background

Left ventricular diastolic dysfunction (LVDD) is a recognized complication of diabetes mellitus that precedes and is a risk factor for heart failure. We aimed to determine the prevalence of LVDD and its association with body mass index in ambulatory adults with diabetes mellitus in rural Uganda.

Methods

We conducted a cross-sectional study, over 5 months, to enroll 195 ambulatory Ugandan adults living with diabetes mellitus for at least five years at Mbarara Regional Referral Hospital. We collected demographic, and clinical data and measured body mass index (BMI). Echocardiography was performed to determine LVDD by assessing the mitral inflow ventricular filling velocities (E/A and E/è ratios), tricuspid regurgitant jet peak velocity, and left atrium maximum volume index. We used logistic regression to estimate the odds ratio for the association of LVDD with BMI and evaluated the variation of associations by age and hypertension status.

Results

Of the 195 participants, 141 (72.31%) were female, the mean age was 62 [standard deviation, 11.50] years, and the median duration of diabetes diagnosis was 10 [interquartile range, 7, 15] years. Eighty-six percent (n = 168) had LVDD with the majority (n = 127, 65.1%) of participants in the grade 1 category of LVDD. In the adjusted model, the odds of LVDD for each 1 kg/m² increase in BMI was 1.11 [95% confidence interval 1.00, 1.25, p = 0.04]. The adjusted odds of LVDD among individuals aged ≥ 50 years with BMI ≥ 25 kg/m² was 13.82 times the odds of LVDD in individuals aged < 50 years with BMI < 25 kg/m².

Conclusion

LVDD is prevalent and positively associated with BMI among ambulatory Ugandan adults living with diabetes mellitus for at least five years. The association was higher for older overweight/obese than younger individuals with normal weight. Future studies should focus on the effect of weight loss on LVDD as a possible target for the prevention of heart failure.

The versatile regulation of K2P channels by polyanionic lipids of the phosphoinositide and fatty acid metabolism

Work over the past three decades has greatly advanced our understanding of the regulation of K_ir K⁺ channels by polyanionic lipids of the phosphoinositide (e.g., PIP₂) and fatty acid metabolism (e.g., oleoyl-CoA). However, comparatively little is known regarding the regulation of the K_2P channel family by phosphoinositides and by long-chain fatty acid–CoA esters, such as oleoyl-CoA. We screened 12 mammalian K_2P channels and report effects of polyanionic lipids on all tested channels. We observed activation of members of the TREK, TALK, and THIK subfamilies, with the strongest activation by PIP₂ for TRAAK and the strongest activation by oleoyl-CoA for TALK-2. By contrast, we observed inhibition for members of the TASK and TRESK subfamilies. Our results reveal that TASK-2 channels have both activatory and inhibitory PIP₂ sites with different affinities. Finally, we provided evidence that PIP₂ inhibition of TASK-1 and TASK-3 channels is mediated by closure of the recently identified lower X-gate as critical mutations within the gate (i.e., L244A, R245A) prevent PIP₂-induced inhibition. Our findings establish that K⁺ channels of the K_2P family are highly sensitive to polyanionic lipids, extending our knowledge of the mechanisms of lipid regulation and implicating the metabolism of these lipids as possible effector pathways to regulate K_2P channel activity.

Lipid metabolism and its implications for type 1 diabetes-associated cardiomyopathy

Diabetic cardiomyopathy was first defined over four decades ago. It was observed in small post-mortem studies of diabetic patients who suffered from concomitant heart failure despite the absence of hypertension, coronary disease or other likely causal factors, as well as in large population studies such as the Framingham Heart Study. Subsequent studies continue to demonstrate an increased incidence of heart failure in the setting of diabetes independent of established risk factors, suggesting direct effects of diabetes on the myocardium. Impairments in glucose metabolism and handling receive the majority of the blame. The role of concomitant impairments in lipid handling, particularly at the level of the myocardium, has however received much less attention. Cardiac lipid accumulation commonly occurs in the setting of type 2 diabetes and has been suggested to play a direct causal role in the development of cardiomyopathy and heart failure in a process termed as cardiac lipotoxicity. Excess lipids promote numerous pathological processes linked to the development of cardiomyopathy, including mitochondrial dysfunction and inflammation. Although somewhat underappreciated, cardiac lipotoxicity also occurs in the setting of type 1 diabetes. This phenomenon is, however, largely understudied in comparison to hyperglycaemia, which has been widely studied in this context. The current review addresses the changes in lipid metabolism occurring in the type 1 diabetic heart and how they are implicated in disease progression. Furthermore, the pathological pathways linked to cardiac lipotoxicity are discussed. Finally, we consider novel approaches for modulating lipid metabolism as a cardioprotective mechanism against cardiomyopathy and heart failure.

Modulation of Potassium Channel Activity in the Balance of ROS and ATP Production by Durum Wheat Mitochondria-An Amazing Defense Tool Against Hyperosmotic Stress

In plants, the existence of a mitochondrial potassium channel was firstly demonstrated about 15 years ago in durum wheat as an ATP-dependent potassium channel (PmitoKATP). Since then, both properties of the original PmitoKATP and occurrence of different mitochondrial potassium channels in a number of plant species (monocotyledonous and dicotyledonous) and tissues/organs (etiolated and green) have been shown. Here, an overview of the current knowledge is reported; in particular, the issue of PmitoKATP physiological modulation is addressed. Similarities and differences with other potassium channels, as well as possible cross-regulation with other mitochondrial proteins (Plant Uncoupling Protein, Alternative Oxidase, Plant Inner Membrane Anion Channel) are also described. PmitoKATP is inhibited by ATP and activated by superoxide anion, as well as by free fatty acids (FFAs) and acyl-CoAs. Interestingly, channel activation increases electrophoretic potassium uptake across the inner membrane toward the matrix, so collapsing membrane potential (ΔΨ), the main component of the protonmotive force (Δp) in plant mitochondria; moreover, cooperation between PmitoKATP and the K(+)/H(+) antiporter allows a potassium cycle able to dissipate also ΔpH. Interestingly, ΔΨ collapse matches with an active control of mitochondrial reactive oxygen species (ROS) production. Fully open channel is able to lower superoxide anion up to 35-fold compared to a condition of ATP-inhibited channel. On the other hand, ΔΨ collapse by PmitoKATP was unexpectedly found to not affect ATP synthesis via oxidative phosphorylation. This may probably occur by means of a controlled collapse due to ATP inhibition of PmitoKATP; this brake to the channel activity may allow a loss of the bulk phase Δp, but may preserve a non-classically detectable localized driving force for ATP synthesis. This ability may become crucial under environmental/oxidative stress. In particular, under moderate hyperosmotic stress (mannitol or NaCl), PmitoKATP was found to be activated by ROS, so inhibiting further large-scale ROS production according to a feedback mechanism; moreover, a stress-activated phospholipase A2 may generate FFAs, further activating the channel. In conclusion, a main property of PmitoKATP is the ability to keep in balance the control of harmful ROS with the mitochondrial/cellular bioenergetics, thus preserving ATP for energetic needs of cell defense under stress.

Long-chain acyl-CoA esters in metabolism and signaling: Role of acyl-CoA binding proteins

Long-chain fatty acyl-CoA esters are key intermediates in numerous lipid metabolic pathways, and recognized as important cellular signaling molecules. The intracellular flux and regulatory properties of acyl-CoA esters have been proposed to be coordinated by acyl-CoA-binding domain containing proteins (ACBDs). The ACBDs, which comprise a highly conserved multigene family of intracellular lipid-binding proteins, are found in all eukaryotes and ubiquitously expressed in all metazoan tissues, with distinct expression patterns for individual ACBDs. The ACBDs are involved in numerous intracellular processes including fatty acid-, glycerolipid- and glycerophospholipid biosynthesis, β-oxidation, cellular differentiation and proliferation as well as in the regulation of numerous enzyme activities. Little is known about the specific roles of the ACBDs in the regulation of these processes, however, recent studies have gained further insights into their in vivo functions and provided further evidence for ACBD-specific functions in cellular signaling and lipid metabolic pathways. This review summarizes the structural and functional properties of the various ACBDs, with special emphasis on the function of ACBD1, commonly known as ACBP.

Role of microangiopathy in diabetic cardiomyopathy

Although heart disease due to diabetes is mainly associated with complications of the large vessels, microvascular abnormalities are also considered to be involved in altering cardiac structure and function. Three major defects, such as endothelial dysfunction, alteration in the production/release of hormones, and shift in metabolism of smooth muscle cells, have been suggested to produce damage to the small arteries and capillaries (microangiopathy) due to hyperglycemia, and promote the development of diabetic cardiomyopathy. These factors may either act alone or in combination to produce oxidative stress as well as changes in cellular signaling and gene transcription, which in turn cause vasoconstriction and structural remodeling of the coronary vessels. Such alterations in microvasculature produce hypoperfusion of the myocardium and thereby lower the energy status resulting in changes in Ca(2+)-handling, apoptosis, and decreased cardiac contractile force. This article discusses diabetes-induced mechanisms of microvascular damage leading to cardiac dysfunction that is characterized by myocardial dilatation, cardiac hypertrophy as well as early diastolic and late systolic defects. Metabolic defects and changes in neurohumoral system due to diabetes, which promote disturbances in vascular homeostasis, are highlighted. In addition, increase in the vulnerability of the diabetic heart to the development of heart failure and the signaling pathways integrating nuclear factor κB and protein kinase C in diabetic cardiomyopathy are also described for comparison.

Stable isotope dilution liquid chromatography/mass spectrometry analysis of cellular and tissue medium- and long-chain acyl-coenzyme A thioesters

RATIONALE

Acyl-Coenzyme A (CoA) thioesters are the principal form of activated carboxylates in cells and tissues. They are employed as acyl carriers that facilitate the transfer of acyl groups to lipids and proteins. Quantification of medium- and long-chain acyl-CoAs represents a significant bioanalytical challenge because of their instability.

METHODS

Stable isotope dilution liquid chromatography/selected reaction monitoring-mass spectrometry (LC/SRM-MS) provides the most specific and sensitive method for the analysis of CoA species. However, relevant heavy isotope standards are not available and they are challenging to prepare by chemical synthesis. Stable isotope labeling by essential nutrients in cell culture (SILEC), developed originally for the preparation of stable isotope labeled short-chain acyl-CoA thioester standards, has now been extended to medium-chain and long-chain acyl-CoAs and used for LC/SRM-MS analyses.

RESULTS

Customized SILEC standards with >98% isotopic purity were prepared using mouse Hepa 1c1c7 cells cultured in pantothenic-free media fortified with [(13) C3 (15) N1 ]-pantothenic acid and selected fatty acids. A SILEC standard in combination with LC/SRM-MS was employed to quantify cellular concentrations of arachidonoyl-CoA (a representative long-chain acyl-CoA) in two human colon cancer cell lines. A panel of SILEC standards was also employed in combination LC/SRM-MS to quantify medium- and long-chain acyl-CoAs in mouse liver.

CONCLUSIONS

This new SILEC-based method in combination with LC/SRM-MS will make it possible to rigorously quantify medium- and long-chain acyl-CoAs in cells and tissues. The method will facilitate studies of medium- and long-chain acyl-CoA dehydrogenase deficiencies as well as studies on the role of medium- and long-chain acyl-CoAs in cellular metabolism.

Structural determinants of the transient receptor potential 1 (TRPV1) channel activation by phospholipid analogs

The transient receptor potential vanilloid 1 (TRPV1) ion channel is a polymodal protein that responds to various stimuli, including capsaicin (the pungent compound found in chili peppers), extracellular acid, and basic intracellular pH, temperatures close to 42 °C, and several lipids. Lysophosphatidic acid (LPA), an endogenous lipid widely associated with neuropathic pain, is an agonist of the TRPV1 channel found in primary afferent nociceptors and is activated by other noxious stimuli. Agonists or antagonists of lipid and other chemical natures are known to possess specific structural requirements for producing functional effects on their targets. To better understand how LPA and other lipid analogs might interact and affect the function of TRPV1, we set out to determine the structural features of these lipids that result in the activation of TRPV1. By changing the acyl chain length, saturation, and headgroup of these LPA analogs, we established strict requirements for activation of TRPV1. Among the natural LPA analogs, we found that only LPA 18:1, alkylglycerophosphate 18:1, and cyclic phosphatidic acid 18:1, all with a monounsaturated C18 hydrocarbon chain activate TRPV1, whereas polyunsaturated and saturated analogs do not. Thus, TRPV1 shows a more restricted ligand specificity compared with LPA G-protein-coupled receptors. We synthesized fatty alcohol phosphates and thiophosphates and found that many of them with a single double bond in position Δ9, 10, or 11 and Δ9 cyclopropyl group can activate TRPV1 with efficacy similar to capsaicin. Finally, we developed a pharmacophore and proposed a mechanistic model for how these lipids could induce a conformational change that activates TRPV1.

Oleic acid inhibits the K(ATP) channel subunit Kir6.1 and the K(ATP) current in human umbilical artery smooth muscle cells

BACKGROUND

The objective of the present study was to determine the effect of various concentrations of oleic acid (OA) on KATP channel expression and the potential relationship to exogenous nitrogen monoxide and protein kinase C levels.

METHODS

Human umbilical artery smooth muscle cells (HUASMCs), between the 7th and 10th passages, were divided into control group, OA group (final OA concentration of 0, 50, 100 or 200 μmol/L), nitric oxide (NO) intervention group, protein kinase C inhibitor group or GF-109203X (GFX) intervention group. Western immunoblotting was used to detect the protein expression of the KATP channel subunit Kir6.1. Also, quantitative real-time polymerase chain reaction analysis to determine Kir6.1 messenger RNA levels and whole-cell patch clamping to measure KATP currents were performed.

RESULTS

The results suggested that OA inhibited Kir6.1 protein and messenger RNA expression in HUASMCs. Under a high concentration of potassium (140 mmol/L), 100 μmol/L OA significantly reduced ATP-sensitive potassium current density, whereas a low extracellular concentration of potassium (5.4 mmol/L) did not influence KATP density. Pretreatment with either exogenous NO or GFX weakened the OA-induced inhibition of KATP in HUASMCs.

CONCLUSIONS

The study demonstrated that OA inhibited Kir6.1, a KATP channel subunit, in HUASMCs, and indirectly inhibited the KATP current. In addition, the results indicated that NO and/or GFX partially reversed OA inhibition in HUASMCs.

Acute regional left atrial ischemia causes acceleration of atrial drivers during atrial fibrillation

BACKGROUND

The mechanisms by which acute left atrial ischemia (LAI) leads to atrial fibrillation (AF) initiation and perpetuation remain unclear.

OBJECTIVE

To investigate the electrophysiological mechanisms of AF perpetuation in the presence of regional atrial ischemia.

METHODS

LAI (90-minute ischemia) was obtained in isolated sheep hearts by selectively perfusing microspheres into the left anterior atrial artery. Two charge-coupled device cameras and several bipolar electrodes enabled recording from multiple atrial locations: with a dual-camera setup (protocol 1, n = 10, and protocol 1', n = 4, for biatrial or atrioventricular camera setups, respectively), in the presence of propranolol/atropine (1 μM) added to the perfusate after LAI (protocol 2, n = 3) and after a pretreatment with glibenclamide (10 μM; protocol 3, n = 4).

RESULTS

Spontaneous AF occurred in 41.2% (7 of 17) of the hearts that were in sinus rhythm before LAI. LAI caused action potential duration shortening in both the ischemic (IZ) and nonischemic (NIZ) zones by 21% ± 8% and 34% ± 13%, respectively (pacing, 5 Hz; P<.05 compared to baseline). Apparent impulse velocity was significantly reduced in the IZ but not in the NIZ (-65% ± 19% and 9% ± 18%; P = .001 and NS, respectively). During LAI-related AF, a significant NIZ maximal dominant frequency increase from 7.4 ± 2.5 to 14.0 ± 5.5 Hz (P<.05) was observed. Glibenclamide, an ATP-sensitive potassium current (IKATP) channel blocker, averted LAI-related maximal dominant frequency increase (NIZ: LAI vs glibenclamide 14.0 ± 5.5 Hz vs 5.9 ± 1.3 Hz; P<.05). An interplay between spontaneous focal discharges and rotors, locating at the IZ-NIZ border zone, maintained LAI-related AF.

CONCLUSIONS

LAI leads to an IKATP conductance-dependent action potential duration shortening and spontaneous AF maintained by both spontaneous focal discharges and reentrant circuits locating at the IZ border zone.

Adipose tissue biology and cardiomyopathy: translational implications

It is epidemiologically established that obesity is frequently associated with the metabolic syndrome and poses an increased risk for the development of type 2 diabetes mellitus and cardiovascular disease. The molecular links that connect the phenomenon of obesity, per se, with insulin resistance and cardiovascular disease are still not fully elucidated. It is increasingly apparent that fully functional adipose tissue can be cardioprotective by reducing lipotoxic effects in other peripheral tissues and by maintaining a healthy balance of critical adipokines, thereby allowing the heart to maintain its full metabolic flexibility. The present review highlights both basic and clinical findings that emphasize the complex interplay of adipose tissue physiology and adipokine-mediated effects on the heart exerted by either direct effects on cardiac myocytes or indirect actions via central mechanisms through sympathetic outflow to the heart.

Comparative proteomic analysis of the ATP-sensitive K+ channel complex in different tissue types

ATP-sensitive K(+) (K(ATP)) channels are expressed ubiquitously, but have diverse roles in various organs and cells. Their diversity can partly be explained by distinct tissue-specific compositions of four copies of the pore-forming inward rectifier potassium channel subunits (Kir6.1 and/or Kir6.2) and four regulatory sulfonylurea receptor subunits (SUR1 and/or SUR2). Channel function and/or subcellular localization also can be modified by the proteins with which they transiently or permanently interact to generate even more diversity. We performed a quantitative proteomic analysis of K(ATP) channel complexes in the heart, endothelium, insulin-secreting min6 cells (pancreatic β-cell like), and the hypothalamus to identify proteins with which they interact in different tissues. Glycolysis is an overrepresented pathway in identified proteins of the heart, min6 cells, and the endothelium. Proteins with other energy metabolic functions were identified in the hypothalamic samples. These data suggest that the metabolo-electrical coupling conferred by K(ATP) channels is conferred partly by proteins with which they interact. A large number of identified cytoskeletal and trafficking proteins suggests endocytic recycling may help control K(ATP) channel surface density and/or subcellular localization. Overall, our data demonstrate that K(ATP) channels in different tissues may assemble with proteins having common functions, but that tissue-specific complex organization also occurs.

Predictors and prevention of diabetic cardiomyopathy

Despite our cognizance that diabetes can enhance the chances of heart failure, causes multiorgan failure,and contributes to morbidity and mortality, it is rapidly increasing menace worldwide. Less attention has been paid to alert prediabetics through determining the comprehensive predictors of diabetic cardiomyopathy (DCM) and ameliorating DCM using novel approaches. DCM is recognized as asymptomatic progressing structural and functional remodeling in the heart of diabetics, in the absence of coronary atherosclerosis and hypertension. The three major stages of DCM are: (1) early stage, where cellular and metabolic changes occur without obvious systolic dysfunction; (2) middle stage, which is characterized by increased apoptosis, a slight increase in left ventricular size, and diastolic dysfunction and where ejection fraction (EF) is <50%; and (3) late stage, which is characterized by alteration in microvasculature compliance, an increase in left ventricular size, and a decrease in cardiac performance leading to heart failure. Recent investigations have revealed that DCM is multifactorial in nature and cellular, molecular, and metabolic perturbations predisposed and contributed to DCM. Differential expression of microRNA (miRNA), signaling molecules involved in glucose metabolism, hyperlipidemia, advanced glycogen end products, cardiac extracellular matrix remodeling, and alteration in survival and differentiation of resident cardiac stem cells are manifested in DCM. A sedentary lifestyle and high fat diet causes obesity and this leads to type 2 diabetes and DCM. However, exercise training improves insulin sensitivity, contractility of cardiomyocytes, and cardiac performance in type 2 diabetes. These findings provide new clues to diagnose and mitigate DCM. This review embodies developments in the field of DCM with the aim of elucidating the future perspectives of predictors and prevention of DCM.

Cardiac ryanodine receptor in metabolic syndrome: is JTV519 (K201) future therapy?

Metabolic syndrome is characterized by a combination of obesity, hypertension, insulin resistance, dyslipidemia, and impaired glucose tolerance. This multifaceted syndrome is often accompanied by a hyperdynamic circulatory state characterized by increased blood pressure, total blood volume, cardiac output, and metabolic tissue demand. Experimental, epidemiological, and clinical studies have demonstrated that patients with metabolic syndrome have significantly elevated cardiovascular morbidity and mortality rates. One of the main and frequent complications seen in metabolic syndrome is cardiovascular disease. The primary endpoints of cardiometabolic risk are coronary and peripheral arterial disease, myocardial infarction, congestive heart failure, arrhythmia, and stroke. Alterations in expression and/or functioning of several key proteins involved in regulating and maintaining ionic homeostasis can cause cardiac disturbances. One such group of proteins is known as ryanodine receptors (intracellular calcium release channels), which are the major channels through which Ca(2+) ions leave the sarcoplasmic reticulum, leading to cardiac muscle contraction. The economic cost of metabolic syndrome and its associated complications has a significant effect on health care budgets. Improvements in body weight, blood lipid profile, and hyperglycemia can reduce cardiometabolic risk. However, constant hyperadrenergic stimulation still contributes to the burden of disease. Normalization of the hyperdynamic circulatory state with conventional therapies is the most reasonable therapeutic strategy to date. JTV519 (K201) is a newly developed 1,4-benzothiazepine drug with antiarrhythmic and cardioprotective properties. It appears to be very effective in not only preventing but also in reversing the characteristic myocardial changes and preventing lethal arrhythmias. It is also a unique candidate to improve diastolic heart failure in metabolic syndrome.

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.

The glycolytic enzymes glyceraldehyde 3-phosphate dehydrogenase and enolase interact with the renal epithelial K+ channel ROMK2 and regulate its function

BACKGROUND/AIMS

ROMK channels mediate potassium secretion and regulate NaCl reabsorption in the kidney. The aim was to study the functional implications of the interaction between ROMK2 (Kir1.1b) and two glycolytic enzymes, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and enolase-α, which were identified as potential regulatory subunits of the channel complex.

METHODS

We performed a membrane yeast-two-hybrid screen of a human kidney cDNA library with ROMK2 as a bait. Interaction of ROMK2 with GAPDH and enolase was verified using GST pull-down, co-immunoprecipitation, immunohistochemistry and co-expression in Xenopus oocytes.

RESULTS

Confocal imaging showed co-localisation of enolase and GAPDH with ROMK2 in the apical membrane of the renal epithelial cells of the thick ascending limb. Over-expression of GAPDH or enolase-α in Xenopus oocytes markedly reduced the amplitude of ROMK2 currents but did not affect the surface expression of the channels. Co-expression of the glycolytically inactive GAPDH mutant C149G did not have any effect on ROMK2 current amplitude.

CONCLUSION

Our results suggest that the glycolytic enzymes GAPDH and enolase are part of the ROMK2 channel supramolecular complex and may serve to couple salt reabsorption in the thick ascending limb of the loop of Henle to the metabolic status of the renal epithelial cells.

Effect of diabetes on alteration of metabolism in cardiac myocytes: therapeutic implications

Diabetic cardiomyopathy is a distinct entity in humans. It leads to ventricular dysfunction independent of and additive to coronary artery disease and hypertension. Clinical and experimental studies have pointed to the role of metabolic derangements in the development of diabetic cardiomyopathy. Altered insulin signaling in diabetes leads to decreased myocyte glucose uptake and utilization, associated with an increased concentration of free fatty acids. This results in decreased glucose oxidation and increased fatty acid oxidation. Fatty acids increase mitochondrial oxygen consumption for ATP production and stimulate the uncoupling proteins in mitochondria. These proteins decrease the mitochondrial protein gradient, leading to fall in ATP production. The resultant defect in myocardial energy production impairs myocyte contraction and diastolic function. This is the hallmark of diabetic cardiomyopathy at earlier stages. In later stages diabetes impairs the myocyte ischemic defense mechanism, leading to increased cardiovascular morbidity and mortality. Other factors contributing toward causation of diabetic cardiomyopathy are collagen accumulation leading to reduced myocardial compliance, accumulation of advanced glycation end product-modified extracellular matrix proteins with subsequent inelasticity of vessel walls and myocytes, abnormal myocardial calcium handling leading to altered mechanics, endothelial dysfunction, cardiac autonomic neuropathy, and impairment of ischemic preconditioning. Trimetazidine acts a metabolic switch, favoring glucose over free fatty acids as the substrate for metabolism in cardiac myocytes.

The diabetic cardiomyopathy

Diabetic cardiomyopathy has been defined as "a distinct entity characterized by the presence of abnormal myocardial performance or structure in the absence of epicardial coronary artery disease, hypertension, and significant valvular disease". The diagnosis stems from the detection of myocardial abnormalities and the exclusion of other contributory causes of cardiomyopathy. It rests on non-invasive imaging techniques which can demonstrate myocardial dysfunction across the spectra of clinical presentation. The presence of diabetes is associated with an increased risk of developing heart failure, and the 75% of patients with unexplained idiopathic dilated cardiomyopathy were found to be diabetic. Diabetic patients with microvascular complications show the strongest association between diabetes and cardiomyopathy, an association that parallels the duration and severity of hyperglycemia. Metabolic abnormalities (that is hyperglycemia, hyperinsulinemia, and hyperlipemia) can lead to the cellular alterations characterizing diabetic cardiomyopathy (that is myocardial fibrosis and/or myocardial hypertrophy) directly or indirectly (that is by means of renin-angiotensin system activation, cardiac autonomic neuropathy, alterations in calcium homeostasis). Moreover, metabolic abnormalities represent, on a clinical ground, the main therapeutic target in the patients with diabetes since the diagnosis of diabetes is made. Since diabetic cardiomyopathy is highly prevalent in the asymptomatic type 2 diabetic patients, screening for its presence at the earliest stage of development can lead to prevent the progression to chronic heart failure. The most sensitive test is standard echocardiogram, while a less expensive pre-screening method is the detection of microalbuminuria.

Syntaxin-1A inhibits KATP channels by interacting with specific conserved motifs within sulfonylurea receptor 2A

We previously demonstrated that syntaxin (Syn)-1A is present in the sarcolemma of rat cardiomyocytes and binds sulfonylurea receptor (SUR) 2A nucleotide binding folds (NBFs) to inhibit ATP-sensitive potassium (K(ATP)) channel. Here, we examined for the precise domains within the NBFs of SUR2A that may interact with Syn-1A. Specifically, we tested truncated NBF protein segments encompassing the conserved motifs Walker A (W(A)), signature/Linker (L), and Walker B (W(B)). In vitro binding results indicate that the domains encompassing W(A) and L of NBF-1 and all three conserved motifs of NBF-2 bound Syn-1A. Electrophysiological studies, employing inside-out patch-clamp recordings from SUR2A/Kir6.2 expressing HEK cells and mouse cardiomyocytes, show that W(B) and L of NBF-1 and all three NBF-2 truncated protein segments reduced Syn-1A inhibition of SUR2A/K(ATP) channels. Remarkably, these same NBF-1 and -2 truncated proteins could independently disrupt the intimate FRET interactions of full length SUR2A (-mCherry) and Syn-1A (-EGFP). These results taken together indicate that Syn-1A possibly maintains inhibition of cardiac ventricular K(ATP) channels by binding to large regions of NBF-1 and NBF-2 to stabilize the NBF-1-NBF-2 heterodimer formation and prevent ATP-binding and ATP hydrolysis. Since K(ATP) channels are closely coupled to metabolic states, we postulate that these very intimate Syn-1A-SUR2A interactions are critically important for myocardial protection during stress, in which profound changes in metabolic factors (pH, ATP) could modulate these Syn-1A-SUR2A interactions.

Diabetic cardiomyopathy--fact or fiction?

Epidemiologic as well as clinical studies confirm the close link between diabetes mellitus and heart failure. Diabetic cardiomyopathy (DCM) is still a poorly understood "entity", however, with several contributing pathogenetic factors which lead in different stages of diabetes to characteristic clinical phenotypes. Hyperglycemia with a shift from glucose metabolism to increased beta-oxidation and consecutive free fatty acid damage (lipotoxicity) to the myocardium, insulin resistance, renin-angiotensin-aldosterone system (RAAS) activation, altered calcium homeostasis and structural changes from the natural collagen network to a stiffer matrix due to advanced glycation endproduct (AGE) formation, hypertrophy and fibrosis contribute to the respective clinical phenotypes of DCM. We propose the following classification of cardiomyopathy in diabetic patients: a) Diastolic heart failure with normal ejection fraction (HFNEF) in diabetic patients often associated with hypertrophy without relevant hypertension. Relevant coronary artery disease (CAD), valvular disease and uncontrolled hypertension are not present. This is referred to as stage 1 DCM. b) Systolic and diastolic heart failure with dilatation and reduced ejection (HFREF) in diabetic patients excluding relevant CAD, valvular disease and uncontrolled hypertension as stage 2 DCM. c) Systolic and/or diastolic heart failure in diabetic patients with small vessel disease (microvascular disease) and/or microbial infection and/or inflammation and/or hypertension but without CAD as stage 3 DCM. d) If heart failure may also be attributed to infarction or ischemia and remodeling in addition to stage 3 DCM the term should be heart failure in diabetes or stage 4 DCM. These clinical phenotypes of diabetic cardiomyopathy can be separated by biomarkers, non-invasive (echocardiography, cardiac magnetic resonance imaging) and invasive imaging methods (levocardiography, coronary angiography) and further analysed by endomyocardial biopsy for concomitant viral infection. The role of specific diabetic drivers to the clinical phenotypes, to macro- and microangiopathy as well as accompanying risk factors or confounders, e.g. hypertension, autoimmune factors or inflammation with or without viral persistence, need to be identified in each individual patient separately. Thus hyperglycemia, hyperinsulinemia and insulin resistance as well as lipotoxicity by free fatty acids (FFAs) are the factors responsible for diabetic cardiomyopathy. In stage 1 and 2 DCM diabetic cardiomyopathy is clearly a fact. However, precise determination of to what degree the various underlying pathogenetic processes are responsible for the overall heart failure phenotype remains a fiction.

K(ATP) channel-dependent metaboproteome decoded: systems approaches to heart failure prediction, diagnosis, and therapy

Systems biology provides an integrative platform by which to account for the biological complexity related to cardiac health and disease. In this way, consequences of ATP-sensitive K(+) (K(ATP)) channel deficiency for heart failure prediction, diagnosis, and therapy were resolved recently at a proteomic level. Under stress-free conditions, knockout of the Kir6.2 K(ATP) channel pore induced metabolic proteome remodelling, revealing overrepresentation of markers of cardiovascular disease. Imposed stress precipitated structural and functional defects in Kir6.2-knockout hearts, decreasing survival and validating prediction of disease susceptibility. In the setting of hypertension, a leading risk for heart failure development, proteomic analysis diagnosed the metabolism-centric impact of K(ATP) channel deficiency in disease. Bioinformatic interrogation of K(ATP) channel-dependent proteome prioritized heart-specific adverse effects, exposing cardiomyopathic traits of aggravated contractility, fibrosis, and ventricular hypertrophy. In dilated cardiomyopathy induced by Kir6.2-knockout pressure overload, proteomic remodelling was exacerbated, underlying a multifaceted molecular pathology that indicates the necessity for a broad-based strategy to achieve repair. Embryonic stem cell intervention in cardiomyopathic K(ATP) channel knockout hearts elicited a distinct proteome signature that forecast amelioration of adverse cardiac outcomes. Functional/structural measurements validated improved contractile performance, reduced ventricular size, and decreased cardiac damage in the treated cohort, while systems assessment unmasked cardiovascular development as a prioritized biological function in stem cell-reconstructed hearts. Thus, proteomic deconvolution of K(ATP) channel-deficient hearts provides definitive evidence for the channel's homeostatic contribution to the cardiac metaboproteome and establishes the utility of systems-oriented approaches to predict disease susceptibility, diagnose consequences of heart failure progression, and monitor therapy outcome.

Activation of the plant mitochondrial potassium channel by free fatty acids and acyl-CoA esters: a possible defence mechanism in the response to hyperosmotic stress

The effect of free fatty acids (FFAs) and acyl-CoA esters on K(+) uptake was studied in mitochondria isolated from durum wheat (Triticum durum Desf.), a species that has adapted well to the semi-arid Mediterranean area and possessing a highly active mitochondrial ATP-sensitive K(+) channel (PmitoK(ATP)), that may confer resistance to environmental stresses. This was made by swelling experiments in KCl solution under experimental conditions in which PmitoK(ATP) activity was monitored. Linoleate and other FFAs (laurate, palmitate, stearate, palmitoleate, oleate, arachidonate, and the non-physiological 1-undecanesulphonate and 5-phenylvalerate), used at a concentration (10 μM) unable to damage membranes of isolated mitochondria, stimulated K(+) uptake by about 2-4-fold. Acyl-CoAs also promoted K(+) transport to a much larger extent with respect to FFAs (about 5-12-fold). In a different experimental system based on safranin O fluorescence measurements, the dissipation of electrical membrane potential induced by K(+) uptake via PmitoK(ATP) was found to increase in the presence of 5-phenylvalerate and palmitoyl-CoA, both unable to elicit the activity of the Plant Uncoupling Protein. This result suggests a direct activation of PmitoK(ATP). Stimulation of K(+) transport by FFAs/acyl-CoAs resulted in a widespread phenomenon in plant mitochondria from different mono/dicotyledonous species (bread wheat, barley, triticale, maize, lentil, pea, and topinambur) and from different organs (root, tuber, leaf, and shoot). Finally, an increase in mitochondrial FFAs up to a content of 50 nmol mg(-1) protein, which was able to activate PmitoK(ATP) strongly, was observed under hyperosmotic stress conditions. Since PmitoK(ATP) may act against environmental/oxidative stress, its activation by FFAs/acyl-CoAs is proposed to represent a physiological defence mechanism.

Early administration of trimetazidine may prevent or ameliorate diabetic cardiomyopathy

Diabetic cardiomyopathy is a type of cardiac dysfunction resulting from diabetes, independent of vascular or valvular pathology. It clinically manifests initially as asymptomatic diastolic dysfunction and then progresses to symptomatic heart failure. Two major contributors to the development of diabetic cardiomyopathy, which are unique to diabetes, are hyperglycemia and diabetes-related alterations in myocardial metabolism. Diabetes mellitus is characterized by reduced glucose and lactate metabolism and enhanced fatty acid metabolism, which are the early consequences of the disease. Studies on the effect of intensive glucose control on heart failure events in patients with diabetes have been conducted with neutral results. However, no study on the effect of metabolic modulators on the prevention of heart failure has been reported. Trimetazidine, a 3-ketoacyl coenzyme A thiolase (3-KAT) inhibitor, shifts cardiac energy metabolism from free fatty acid oxidation to glucose oxidation by inhibiting mitochondrial long-chain 3-KAT, and is used clinically as an effective antianginal agent. Studies have shown that trimetazidine improves heart function in patients with idiopathic cardiomyopathy and in diabetic patients with cardiac ischemia or heart failure. In addition to being effective, trimetazidine has only mild side effects. Therefore, instead of routine administration of trimetazidine for the treatment of diabetic cardiomyopathy, we hypothesize that the early application of trimetazidine may prevent or ameliorate diabetic cardiomyopathy. In addition to life style modifications, ACEI, ARB, and beta-blockers, which have been recommended in the past, trimetazidine should be administered to those patients with impaired glucose tolerance or patients in the early course of diabetes. In this way, we may reduce the prevalence of heart failure and improve the long-term survival of patients with diabetes through early normalization of the myocardial substrate metabolism.

Muscle KATP channels: recent insights to energy sensing and myoprotection

ATP-sensitive potassium (K(ATP)) channels are present in the surface and internal membranes of cardiac, skeletal, and smooth muscle cells and provide a unique feedback between muscle cell metabolism and electrical activity. In so doing, they can play an important role in the control of contractility, particularly when cellular energetics are compromised, protecting the tissue against calcium overload and fiber damage, but the cost of this protection may be enhanced arrhythmic activity. Generated as complexes of Kir6.1 or Kir6.2 pore-forming subunits with regulatory sulfonylurea receptor subunits, SUR1 or SUR2, the differential assembly of K(ATP) channels in different tissues gives rise to tissue-specific physiological and pharmacological regulation, and hence to the tissue-specific pharmacological control of contractility. The last 10 years have provided insights into the regulation and role of muscle K(ATP) channels, in large part driven by studies of mice in which the protein determinants of channel activity have been deleted or modified. As yet, few human diseases have been correlated with altered muscle K(ATP) activity, but genetically modified animals give important insights to likely pathological roles of aberrant channel activity in different muscle types.

Diabetic cardiomyopathy: signaling defects and therapeutic approaches

Diabetes mellitus is the world's fastest growing disease with high morbidity and mortality rates, predominantly as a result of heart failure. A significant number of diabetic patients exhibit diabetic cardiomyopathy; that is, left ventricular dysfunction independent of coronary artery disease or hypertension. The pathogenesis of diabetic cardiomyopathy is complex, and is characterized by dysregulated lipid metabolism, insulin resistance, mitochondrial dysfunction and disturbances in adipokine secretion and signaling. These abnormalities lead to impaired calcium homeostasis, ultimately resulting in lusitropic and inotropic defects. This article discusses the impact of these hallmark factors in diabetic cardiomyopathy, and concludes with a survey of available and emerging therapeutic modalities.

Diabetic Cardiomyopathy: Mechanisms and Therapeutic Targets

The incidence and prevalence of diabetes mellitus are each increasing rapidly in our society. The majority of patients with diabetes succumb ultimately to heart disease, much of which stems from atherosclerotic disease and hypertension. However, cardiomyopathy can develop independent of elevated blood pressure or coronary artery disease, a process termed diabetic cardiomyopathy. This disorder is a complex diabetes-associated process characterized by significant changes in the physiology, structure, and mechanical function of the heart. Here, we review recently derived insights into mechanisms and molecular events involved in the pathogenesis of diabetic cardiomyopathy.

ATP-sensitive K+ channel knockout induces cardiac proteome remodeling predictive of heart disease susceptibility

Forecasting disease susceptibility requires detection of maladaptive signatures prior to onset of overt symptoms. A case-in-point are cardiac ATP-sensitive K+ (K(ATP)) channelopathies, for which the substrate underlying disease vulnerability remains to be identified. Resolving molecular pathobiology, even for single genetic defects, mandates a systems platform to reliably diagnose disease predisposition. High-throughput proteomic analysis was here integrated with network biology to decode consequences of Kir6.2 K(ATP) channel pore deletion. Differential two-dimensional gel electrophoresis reproducibly resolved >800 protein species from hearts of asymptomatic wild-type and Kir6.2-knockout counterparts. K(ATP) channel ablation remodeled the cardiac proteome, significantly altering 71 protein spots, from which 102 unique identities were assigned following hybrid linear ion trap quadrupole-Orbitrap tandem mass spectrometry. Ontological annotation stratified the K(ATP) channel-dependent protein cohort into a predominant bioenergetic module (63 resolved identities), with additional focused sets representing signaling molecules (6), oxidoreductases (8), chaperones (6), and proteins involved in catabolism (6), cytostructure (8), and transcription and translation (5). Protein interaction mapping, in conjunction with expression level changes, localized a K(ATP) channel-associated subproteome within a nonstochastic scale-free network. Global assessment of the K(ATP) channel deficient environment verified the primary impact on metabolic pathways and revealed overrepresentation of markers associated with cardiovascular disease. Experimental imposition of graded stress precipitated exaggerated structural and functional myocardial defects in the Kir6.2-knockout, decreasing survivorship and validating the forecast of disease susceptibility. Proteomic cartography thus provides an integral view of molecular remodeling in the heart induced by K(ATP) channel deletion, establishing a systems approach that predicts outcome at a presymptomatic stage.

5-Hydroxydecanoate and coenzyme A are inhibitors of native sarcolemmal KATP channels in inside-out patches

BACKGROUND

5-Hydroxydecanoate (5-HD) inhibits preconditioning, and it is assumed to be a selective inhibitor of mitochondrial ATP-sensitive K(+) (mitoK(ATP)) channels. However, 5-HD is a substrate for mitochondrial outer membrane acyl-CoA synthetase, which catalyzes the reaction: 5HD + CoA + ATP --> 5-HD-CoA (5-hydroxydecanoyl-CoA) + AMP + pyrophosphate. We aimed to determine whether the reactants or principal product of this reaction modulate sarcolemmal K(ATP) (sarcK(ATP)) channel activity.

METHODS

Single sarcK(ATP) channel currents were measured in inside-out patches excised from rat ventricular myocytes. In addition, sarcK(ATP) channel activity was recorded in whole-cell configuration or in giant inside-out patches excised from oocytes expressing Kir6.2/SUR2A.

RESULTS

5-HD inhibited (IC(50) approximately 30 microM) K(ATP) channel activity, albeit only in the presence of (non-inhibitory) concentrations of ATP. Similarly, when the inhibitory effect of 0.2 mM ATP was reversed by 1 microM oleoyl-CoA, subsequent application of 5-HD blocked channel activity, but no effect was seen in the absence of ATP. Furthermore, we found that 1 microM coenzyme A (CoA) inhibited sarcK(ATP) channels. Using giant inside-out patches, which are weakly sensitive to "contaminating" CoA, we found that Kir6.2/SUR2A channels were insensitive to 5-HD-CoA. In intact myocytes, 5-HD failed to reverse sarcK(ATP) channel activation by either metabolic inhibition or rilmakalim.

GENERAL SIGNIFICANCE

SarcK(ATP) channels are inhibited by 5-HD (provided that ATP is present) and CoA but insensitive to 5-HD-CoA. 5-HD is equally potent at "directly" inhibiting sarcK(ATP) and mitoK(ATP) channels. However, in intact cells, 5-HD fails to inhibit sarcK(ATP) channels, suggesting that mitochondria are the preconditioning-relevant targets of 5-HD.

Cardiac sarcolemmal K(ATP) channels: Latest twists in a questing tale!

Reconstitution of K(ATP) channel activity from coexpression of members of the pore-forming inward rectifier gene family (Kir6.1, KCNJ8, and Kir6.2 KCNJ11) with sulfonylurea receptors (SUR1, ABCC8, and SUR2, ABCC9) of the ABCC protein sub-family, has led to the elucidation of many details of channel gating and pore properties, as well as the essential roles of Kir6.2 and SUR2 subunits in generating cardiac ventricular K(ATP). However, despite this extensive body of knowledge, there remain significant holes in our understanding of the physiological role of the cardiac K(ATP) channel, and surprising new findings keep emerging. Recent findings from genetically modified animals include the apparent insensitivity of cardiac sarcolemmal channels to nucleotide levels, and unenvisioned complexities of the subunit make-up of the cardiac channels. This topical review focuses on these new findings and considers their implications.

Proteomic profiling of KATP channel-deficient hypertensive heart maps risk for maladaptive cardiomyopathic outcome

KCNJ11 null mutants, lacking Kir6.2 ATP-sensitive K(+) (K(ATP)) channels, exhibit a marked susceptibility towards hypertension (HTN)-induced heart failure. To gain insight into the molecular alterations induced by knockout of this metabolic sensor under hemodynamic stress, wild-type (WT) and Kir6.2 knockout (Kir6.2-KO) cardiac proteomes were profiled by comparative 2-DE and Orbitrap MS. Despite equivalent systemic HTN produced by chronic hyperaldosteronism, 114 unique proteins were altered in Kir6.2-KO compared to WT hearts. Bioinformatic analysis linked the primary biological function of the K(ATP) channel-dependent protein cohort to energetic metabolism (64% of proteins), followed by signaling infrastructure (36%) including oxidoreductases, stress-related chaperones, processes supporting protein degradation, transcription and translation, and cytostructure. Mapped protein-protein relationships authenticated the primary impact on metabolic pathways, delineating the K(ATP) channel-dependent subproteome within a nonstochastic network. Iterative systems interrogation of the proteomic web prioritized heart-specific adverse effects, i.e., "Cardiac Damage", "Cardiac Enlargement", and "Cardiac Fibrosis", exposing a predisposition for the development of cardiomyopathic traits in the hypertensive Kir6.2-KO. Validating this maladaptive forecast, phenotyping documented an aggravated myocardial contractile performance, a massive interstitial fibrosis and an exaggerated left ventricular size, all prognostic indices of poor outcome. Thus, Kir6.2 ablation engenders unfavorable proteomic remodeling in hypertensive hearts, providing a composite molecular substrate for pathologic stress-associated cardiovascular disease.

Telomere biology in heart failure

The incidence and prevalence of cardiovascular disease increases progressively with advancing age. Cardiovascular disease is a major cause of morbidity and mortality in Western Countries. In the near future, as the population ages, it is expected that the population prevalence of cardiovascular disease will increase dramatically, imposing a major social and economical burden on society. Not only is age closely related to the development and progression of cardiovascular disease, but genetic and environmental factors also play an important role. Recently, a chromosomal mechanism, telomere shortening, has been considered a driving force by which genetic and environmental factors jointly affect biological aging, and possibly the risk for developing age-associated diseases. Telomeres are the extreme ends of chromosomes and shorten progressively during every cell cycle and therefore can be considered an indicator of biological age. In heart failure, telomere length is severely reduced. In the current review, we will discuss the emerging role of telomere biology in the pathophysiology of heart failure.

Bioinformatic profiling of the transcriptional response of adult rat cardiomyocytes to distinct fatty acids

Diabetes mellitus, obesity, and dyslipidemia increase risk for cardiovascular disease, and expose the heart to high plasma fatty acid (FA) levels. Recent studies suggest that distinct FA species are cardiotoxic (e.g., palmitate), while others are cardioprotective (e.g., oleate), although the molecular mechanisms mediating these observations are unclear. The purpose of the present study was to investigate the differential effects of distinct FA species (varying carbon length and degree of saturation) on adult rat cardiomyocyte (ARC) gene expression. ARCs were initially challenged with 0.4 mM octanoate (8:0), palmitate (16:0), stearate (18:0), oleate (18:1), or linoleate (18:2) for 24 h. Microarray analysis revealed differential regulation of gene expression by the distinct FAs; the order regarding the number of genes whose expression was influenced by a specific FA was octanoate (1,188) > stearate (740) > palmitate (590) > oleate (83) > linoleate (65). In general, cardioprotective FAs (e.g., oleate) increased expression of genes promoting FA oxidation to a greater extent than cardiotoxic FAs (e.g., palmitate), whereas the latter induced markers of endoplasmic reticulum and oxidative stress. Subsequent RT-PCR analysis revealed distinct time- and concentration-dependent effects of these FA species, in a gene-specific manner. For example, stearate- and palmitate-mediated ucp3 induction tended to be transient (i.e., initial high induction, followed by subsequent repression), whereas oleate-mediated induction was sustained. These findings may provide insight into why diets high in unsaturated FAs (e.g., oleate) are cardioprotective, whereas diets rich in saturated FAs (e.g., palmitate) are not.

Fatty acids and insulin modulate myocardial substrate metabolism in humans with type 1 diabetes

OBJECTIVE

Normal human myocardium switches substrate metabolism preference, adapting to the prevailing plasma substrate levels and hormonal milieu, but in type 1 diabetes, the myocardium relies heavily on fatty acid metabolism for energy. Whether conditions that affect myocardial glucose use and fatty acid utilization, oxidation, and storage in nondiabetic subjects alter them in type 1 diabetes is not well known.

RESEARCH DESIGN AND METHODS

To test the hypotheses that in humans with type 1 diabetes, myocardial glucose and fatty acid metabolism can be manipulated by altering plasma free fatty acid (FFA) and insulin levels, we quantified myocardial oxygen consumption (MVo(2)), glucose, and fatty acid metabolism in nondiabetic subjects and three groups of type 1 diabetic subjects (those studied during euglycemia, hyperlipidemia, and a hyperinsulinemic-euglycemic clamp) using positron emission tomography.

RESULTS

Type 1 diabetic subjects had higher MVo(2) and lower myocardial glucose utilization rate/insulin than control subjects. In type 1 diabetes, glucose utilization increased with increasing plasma insulin and decreasing FFA levels. Myocardial fatty acid utilization, oxidation, and esterification rates increased with increasing plasma FFA. Increasing plasma insulin levels decreased myocardial fatty acid esterification rates but increased the percentage of fatty acids going into esterification.

CONCLUSIONS

Type 1 diabetes myocardium has increased MVo(2) and is insulin resistant during euglycemia. However, its myocardial glucose and fatty acid metabolism still responds to changes in plasma insulin and plasma FFA levels. Moreover, insulin and plasma FFA levels can regulate the intramyocardial fate of fatty acids in humans with type 1 diabetes.

Effect of adenosine triphosphate-sensitive potassium channel inhibitors on coronary metabolic vasodilation

The ATP-sensitive potassium (K(ATP)) channel is a distinct type of potassium ion channel that is found in the vascular smooth muscle cells of a variety of mammalian species, including humans. The activity of K(ATP) channels is determined by many factors including cellular ATP and ADP levels, thus providing a link between cellular metabolism and vascular tone through its effects on membrane potential. Experimental studies using inhibitors of K(ATP) channels, such as the sulfonuylurea class of drugs, indicate that these channels modulate coronary vascular tone including the hyperaemia induced by increased myocardial metabolism. This review examines the evidence linking K(ATP) channels to the regulation of coronary vascular tone and the potential clinical implications of pharmacologic therapies that act on K(ATP) channels.

Modulation of hSlo BK current inactivation by fatty acid esters of CoA

Lipid metabolism influences membrane proteins, including ion channels, in health and disease. Fatty acid esters of CoA are important intermediates in fatty acid metabolism and lipid biosynthesis. In the present study, we examined the effect of acyl-CoAs on hSlo BK currents. Arachidonoyl-CoA (C(20)-CoA) induced beta2-dependent inhibition of hSlo-alpha current when applied intracellularly but not extracellularly. This action was also mimicked by other long-chain acyl-CoAs such as oleoyl-CoA (C(18)-CoA) and palmitoyl-CoA (C(16)-CoA), but not acetyl-CoA (C(2)-CoA, shorter chain), suggesting that the length of acyl chains, rather than CoA headgroups, is critical. When hSlo-alpha inactivation was induced by a free synthetic cationic beta2 NH2-terminus inactivation ball peptide, long-chain acyl-CoAs inhibited hSlo-alpha current and facilitated inactivation. The precursor fatty acids also facilitated the ball peptide-induced inactivation in a chain length-dependent manner, whereas sphingosine (positively charged) slowed this inactivation. When the beta2-induced inactivation was compared with that of the ball peptide, there was a negative shift in the steady state inactivation, slower recovery, and a reduced voltage-dependence of inactivation onset. These data suggest that electrostatic interactions with the cytosolic inactivation domain of beta2 mediate acyl-CoA modulation of BK currents. BK channel inactivation may be a specific target for lipid modulation in physiological and pathophysiological conditions.

Alchemy in the soup: transforming metabolic signals to excitability

The intersection of cell metabolism with electrical signaling links the environment and cell function over time scales ranging from milliseconds to lifetimes. In responding to cellular metabolites, adenosine triphosphate (ATP)-sensitive potassium (K(ATP)) channels are an important component of this intersection. Recent studies have begun to delineate the roles of K(ATP) channels in multiple tissues and the far-reaching consequences of aberrant K(ATP) channel activity and disturbed sensing of cell metabolism.

Cardiovascular actions of insulin

Insulin has important vascular actions to stimulate production of nitric oxide from endothelium. This leads to capillary recruitment, vasodilation, increased blood flow, and subsequent augmentation of glucose disposal in classical insulin target tissues (e.g., skeletal muscle). Phosphatidylinositol 3-kinase-dependent insulin-signaling pathways regulating endothelial production of nitric oxide share striking parallels with metabolic insulin-signaling pathways. Distinct MAPK-dependent insulin-signaling pathways (largely unrelated to metabolic actions of insulin) regulate secretion of the vasoconstrictor endothelin-1 from endothelium. These and other cardiovascular actions of insulin contribute to coupling metabolic and hemodynamic homeostasis under healthy conditions. Cardiovascular diseases are the leading cause of morbidity and mortality in insulin-resistant individuals. Insulin resistance is typically defined as decreased sensitivity and/or responsiveness to metabolic actions of insulin. This cardinal feature of diabetes, obesity, and dyslipidemia is also a prominent component of hypertension, coronary heart disease, and atherosclerosis that are all characterized by endothelial dysfunction. Conversely, endothelial dysfunction is often present in metabolic diseases. Insulin resistance is characterized by pathway-specific impairment in phosphatidylinositol 3-kinase-dependent signaling that in vascular endothelium contributes to a reciprocal relationship between insulin resistance and endothelial dysfunction. The clinical relevance of this coupling is highlighted by the findings that specific therapeutic interventions targeting insulin resistance often also ameliorate endothelial dysfunction (and vice versa). In this review, we discuss molecular mechanisms underlying cardiovascular actions of insulin, the reciprocal relationships between insulin resistance and endothelial dysfunction, and implications for developing beneficial therapeutic strategies that simultaneously target metabolic and cardiovascular diseases.

Activation of inwardly rectifying potassium (Kir) channels by phosphatidylinosital-4,5-bisphosphate (PIP2): Interaction with other regulatory ligands

All members of the inwardly rectifying potassium channels (Kir1-7) are regulated by the membrane phospholipid, phosphatidylinosital-4,5-bisphosphate (PIP(2)). Some are also modulated by other regulatory factors or ligands such as ATP and G-proteins, which give them their common names, such as the ATP sensitive potassium (K(ATP)) channel and the G-protein gated potassium channel. Other more non-specific regulators include polyamines, kinases, pH and Na(+) ions. Recent studies have demonstrated that PIP(2) acts cooperatively with other regulatory factors to modulate Kir channels. Here we review how PIP(2) and co-factors modulate channel activities in each subfamily of the Kir channels.

C16:0 sulfatide inhibits insulin secretion in rat beta-cells by reducing the sensitivity of KATP channels to ATP inhibition

Sulfatide (3'-sulfo-beta-galactosyl ceramide) is a glycosphingolipid present in mammalians in various fatty acid isoforms of which the saturated 16 carbon-atom length (C16:0) is more abundant in pancreatic islets than in neural tissue, where long-chain sulfatide isoforms dominate. We previously reported that sulfatide isolated from pig brain inhibits glucose-induced insulin secretion by activation of ATP-sensitive K+ channels (K(ATP) channels). Here, we show that C16:0 sulfatide is the active isoform. It inhibits glucose-stimulated insulin secretion by reducing the sensitivity of the K(ATP) channels to ATP. (The half-maximal inhibitory concentration is 10.3 and 36.7 micromol/l in the absence and presence of C16:0 sulfatide, respectively.) C16:0 sulfatide increased whole-cell K(ATP) currents at intermediate glucose levels and reduced the ability of glucose to induce membrane depolarization, reduced electrical activity, and increased the cytoplasmic free Ca2+ concentration. Recordings of cell capacitance revealed that C16:0 sulfatide increased Ca2+-induced exocytosis by 215%. This correlated with a stimulation of insulin secretion by C16:0 sulfatide in intact rat islets exposed to diazoxide and high K+. C24:0 sulfatide or the sulfatide precursor, beta-galactosyl ceramide, did not affect any of the measured parameters. C16:0 sulfatide did not modulate glucagon secretion from intact rat islets. In betaTC3 cells, sulfatide was expressed (mean [+/-SD] 0.30 +/- 0.04 pmol/microg protein), and C16:0 sulfatide was found to be the dominant isoform. No expression of sulfatide was detected in alphaTC1-9 cells. We conclude that a major mechanism by which the predominant sulfatide isoform in beta-cells, C16:0 sulfatide, inhibits glucose-induced insulin secretion is by reducing the K(ATP) channel sensitivity to the ATP block.

Cytoplasmic accumulation of long-chain coenzyme A esters activates KATP and inhibits Kir2.1 channels

Long-chain fatty acids acyl coenzyme A esters (LC-CoA) are obligate intermediates of fatty acid metabolism and have been shown to activate K(ATP) channels but to inhibit most other Kir channels (e.g. Kir2.1) by direct channel binding. The activation of K(ATP) channels by elevated levels of LC-CoA may be involved in the pathophysiology of type 2 diabetes, the hypothalamic sensing of circulating fatty acids and the regulation of cardiac K(ATP) channels. However, LC-CoA are effectively buffered in the cytoplasm and it is currently not clear whether their free concentration can reach levels sufficient to affect Kir channels in vivo. Here, we report that extracellular oleic acid complexed with albumin at an unbound concentration of 81 +/- 1 nm strongly activated K(ATP) channels and inhibited Kir2.1 channels in Chinese hamster ovary (CHO) cells as well as endogenous Kir currents in human embryonic kidney (HEK293) cells. These effects were only seen in the presence of a high concentration of glucose (25 mm), a condition known to promote the accumulation of LC-CoA by inhibiting their mitochondrial uptake via carnitine-palmitoyl-transferase-1 (CPT1). Accordingly, pharmacological inhibition of CPT1 by etomoxir restored the effects of oleic acid under low glucose conditions. Finally, triacsin C, an inhibitor of the acyl-CoA synthetase, which is necessary for LC-CoA formation, abolished the effects of extracellular oleic acid on the various Kir channels. These results establish the direct regulation of Kir channels by the cytoplasmic accumulation of LC-CoA, which might be of physiological and pathophysiological relevance in a variety of tissues.