Activated peroxisomal fatty acid metabolism improves cardiac recovery in ischemia-reperfusion

Metabolites-mediated posttranslational modifications in cardiac metabolic remodeling: Implications for disease pathology and therapeutic potential

The nonenergy - producing functions of metabolism are attracting increasing attention, as metabolic changes are involved in discrete pathways modulating enzyme activity and gene expression. Substantial evidence suggests that myocardial metabolic remodeling occurring during diabetic cardiomyopathy, heart failure, and cardiac pathological stress (e.g., myocardial ischemia, pressure overload) contributes to the progression of pathology. Within the rewired metabolic network, metabolic intermediates and end-products can directly alter protein function and/or regulate epigenetic modifications by providing acyl groups for posttranslational modifications, thereby affecting the overall cardiac stress response and providing a direct link between cellular metabolism and cardiac pathology. This review provides a comprehensive overview of the functional diversity and mechanistic roles of several types of metabolite-mediated histone and nonhistone acylation, namely O-GlcNAcylation, lactylation, crotonylation, β-hydroxybutyrylation, and succinylation, as well as fatty acid-mediated modifications, in regulating physiological processes and contributing to the progression of heart disease. Furthermore, it explores the potential of these modifications as therapeutic targets for disease intervention.

Nitric oxide and mitochondrial function in cardiovascular diseases

Nitric oxide (NO) has been highlighted as an important factor in cardiovascular system. As a signaling molecule in the cardiovascular system, NO can relax blood vessels, lower blood pressure, and prevent platelet aggregation. Mitochondria serve as a central hub for cellular metabolism and intracellular signaling, and their dysfunction can lead to a variety of diseases. Accumulating evidence suggests that NO can act as a regulator of mitochondria, affecting mitochondrial function and cellular activity, which in turn mediates the onset and progression of disease. However, there is a lack of comprehensive understanding of how NO regulates mitochondrial function in the cardiovascular system. This review aims to summarize the regulation of mitochondrial function by nitric oxide in cardiovascular related diseases, as well as the multifaceted and complex roles of NO in the cardiovascular system. Understanding the mechanism of NO mediated mitochondrial function can provide new insights for the prevention and treatment of cardiovascular diseases.

Andrographolide Attenuates Myocardial Ischemia-Reperfusion Injury in Mice by Up-Regulating PPAR-α

Andrographolide (AGP), a bioactive diterpene lactone, is an active constituent extracted from Andrographis paniculata. It has many biological activities, such as antioxidant, antitumor, antivirus, anti-inflammation, hepatoprotection, and cardioprotection. The aim of the present study is to investigate the cardioprotective effects of AGP in a mouse model of myocardial ischemia-reperfusion injury (MIRI). Adult male C57BL/6 J mice were pre-treated orally with AGP (25 mg/kg) for six days. After 30 min of the left anterior descending coronary artery occlusion followed by 24 h of reperfusion, mice received an additional dose of AGP. The results showed that: (i) AGP pretreatment significantly reduced myocardial infarct size and cardiac injury biomarkers in MIRI mice and improved left ventricular ejection fraction (EF) and fractional shortening (FS); (ii) AGP pretreatment attenuated MIRI-induced oxidative stress imbalance in MIRI mice by increasing total antioxidant capacity (T-AOC) and reducing the levels of hydrogen peroxide (H2O2), nitric oxide (NO), malondialdehyde (MDA), and dihydroethidium (DHE); (iii) AGP pretreatment increased Bcl-2 expression and decreased caspase-3 and Bax expression in ischemic myocardial tissue, along with a reduction in TUNEL-positive cells. Further analysis showed that stimulation by I/R decreased peroxisome proliferator-activated receptor-α (PPAR-α) expression in ischemic cardiac tissue, which was prevented by AGP administration. Moreover, administration of the PPAR-α antagonist GW6471 (1 mg/kg) abolished the protective effect of AGP on oxidative stress and apoptosis in the ischemic heart tissue of mice stimulated by ischemia-reperfusion. Taken together, these results suggest that AGP attenuates MIRI-induced cardiac injury by up-regulating PPAR-α expression, thereby preventing oxidative stress and cellular apoptosis.

Heart Failure: A Deficiency of Energy-A Path Yet to Discover and Walk

Heart failure is a complex syndrome and our understanding and therapeutic approach relies mostly on its phenotypic presentation. Notably, the heart is characterized as the most energy-consuming organ, being both a producer and consumer, in order to satisfy multiple cardiac functions: ion exchange, electromechanical coordination, excitation-contraction coupling, etc. By obtaining further knowledge of the cardiac energy field, we can probably better characterize the basic pathophysiological events occurring in heart disease patients and understand the metabolic substance changes, the relationship between the alteration of energy production/consumption, and hence energetic deficiency not only in the heart as a whole but in every single cardiac territory, which will hopefully provide us with the opportunity to uncover the beginning of the heart failure process. In this respect, using (a) newer imaging techniques, (b) biomedicine, (c) nanotechnology, and (d) artificial intelligence, we can gain a deeper understanding of this complex syndrome. This, in turn, can lead to earlier and more effective therapeutic approaches, ultimately improving human health. To date, the scientific community has not given sufficient attention to the energetic starvation model. In our view, this review aims to encourage scientists and the medical community to conduct studies for a better understanding and treatment of this syndrome.

Mitochondria-Associated Organelle Crosstalk in Myocardial Ischemia/Reperfusion Injury

Organelle damage is a significant contributor to myocardial ischemia/reperfusion (I/R) injury. This damage often leads to disruption of endoplasmic reticulum protein regulatory programs and dysfunction of mitochondrial energy metabolism. Mitochondria and endoplasmic reticulum are seamlessly connected through the mitochondrial-associated endoplasmic reticulum membrane (MAM), which serves as a crucial site for the exchange of organelles and metabolites. However, there is a lack of reports regarding the communication of information and metabolites between mitochondria and related organelles, which is a crucial factor in triggering myocardial I/R damage. To address this research gap, this review described the role of crosstalk between mitochondria and the correlative organelles such as endoplasmic reticulum, lysosomal and nuclei involved in reperfusion injury of the heart. In summary, this review aims to provide a comprehensive understanding of the crosstalk between organelles in myocardial I/R injury, with the ultimate goal of facilitating the development of targeted therapies based on this knowledge.

Hydroxymethylglutaryl-CoA reductase activity is essential for mitochondrial β-oxidation of fatty acids to prevent lethal accumulation of long-chain acylcarnitines in the mouse liver

BACKGROUND AND PURPOSE

Statins are competitive inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase (HMGCR), and exert adverse effects on mitochondrial function, although the mechanisms underlying these effects remain unclear. We used a tamoxifen-induced Hmgcr-knockout (KO) mouse model, a multi-omics approach and mitochondrial function assessments to investigate whether decreased HMGCR activity impacts key liver energy metabolism pathways.

EXPERIMENTAL APPROACH

We established a new mouse strain using the Cre/loxP system, which enabled whole-body deletion of Hmgcr expression. These mice were crossed with Rosa26Cre mice and treated with tamoxifen to delete Hmgcr in all cells. We performed transcriptomic and metabolomic analyses and thus evaluated time-dependent changes in metabolic functions to identify the pathways leading to cell death in Hmgcr-KO mice.

KEY RESULTS

Lack of Hmgcr expression resulted in lethality, due to acute liver damage caused by rapid disruption of mitochondrial fatty acid β-oxidation and very high accumulation of long-chain (LC) acylcarnitines in both male and female mice. Gene expression and KO-related phenotype changes were not observed in other tissues. The progression to liver failure was driven by diminished peroxisome formation, which resulted in impaired mitochondrial and peroxisomal fatty acid metabolism, enhanced glucose utilization and whole-body hypoglycaemia.

CONCLUSION AND IMPLICATIONS

Our findings suggest that HMGCR is crucial for maintaining energy metabolism balance, and its activity is necessary for functional mitochondrial β-oxidation. Moreover, statin-induced adverse reactions might be rescued by the prevention of LC acylcarnitine accumulation.

Renal Mitochondrial ATP Transporter Ablation Ameliorates Obesity-Induced CKD

SIGNIFICANCE STATEMENT

This study sheds light on the central role of adenine nucleotide translocase 2 (ANT2) in the pathogenesis of obesity-induced CKD. Our data demonstrate that ANT2 depletion in renal proximal tubule cells (RPTCs) leads to a shift in their primary metabolic program from fatty acid oxidation to aerobic glycolysis, resulting in mitochondrial protection, cellular survival, and preservation of renal function. These findings provide new insights into the underlying mechanisms of obesity-induced CKD and have the potential to be translated toward the development of targeted therapeutic strategies for this debilitating condition.

BACKGROUND

The impairment in ATP production and transport in RPTCs has been linked to the pathogenesis of obesity-induced CKD. This condition is characterized by kidney dysfunction, inflammation, lipotoxicity, and fibrosis. In this study, we investigated the role of ANT2, which serves as the primary regulator of cellular ATP content in RPTCs, in the development of obesity-induced CKD.

METHODS

We generated RPTC-specific ANT2 knockout ( RPTC-ANT2-/- ) mice, which were then subjected to a 24-week high-fat diet-feeding regimen. We conducted comprehensive assessment of renal morphology, function, and metabolic alterations of these mice. In addition, we used large-scale transcriptomics, proteomics, and metabolomics analyses to gain insights into the role of ANT2 in regulating mitochondrial function, RPTC physiology, and overall renal health.

RESULTS

Our findings revealed that obese RPTC-ANT2-/- mice displayed preserved renal morphology and function, along with a notable absence of kidney lipotoxicity and fibrosis. The depletion of Ant2 in RPTCs led to a fundamental rewiring of their primary metabolic program. Specifically, these cells shifted from oxidizing fatty acids as their primary energy source to favoring aerobic glycolysis, a phenomenon mediated by the testis-selective Ant4.

CONCLUSIONS

We propose a significant role for RPTC-Ant2 in the development of obesity-induced CKD. The nullification of RPTC-Ant2 triggers a cascade of cellular mechanisms, including mitochondrial protection, enhanced RPTC survival, and ultimately the preservation of kidney function. These findings shed new light on the complex metabolic pathways contributing to CKD development and suggest potential therapeutic targets for this condition.

Decreased long-chain acylcarnitine content increases mitochondrial coupling efficiency and prevents ischemia-induced brain damage in rats

Long-chain acylcarnitines (LCACs) are intermediates of fatty acid oxidation and are known to exert detrimental effects on mitochondria. This study aimed to test whether lowering LCAC levels with the anti-ischemia compound 4-[ethyl(dimethyl)ammonio]butanoate (methyl-GBB) protects brain mitochondrial function and improves neurological outcomes after transient middle cerebral artery occlusion (MCAO). The effects of 14 days of pretreatment with methyl-GBB (5 mg/kg, p.o.) on brain acylcarnitine (short-, long- and medium-chain) concentrations and brain mitochondrial function were evaluated in Wistar rats. Additionally, the mitochondrial respiration and reactive oxygen species (ROS) production rates were determined using ex vivo high-resolution fluorespirometry under normal conditions, in models of ischemia-reperfusion injury (reverse electron transfer and anoxia-reoxygenation) and 24 h after MCAO. MCAO model rats underwent vibrissae-evoked forelimb-placing and limb-placing tests to assess neurological function. The infarct volume was measured on day 7 after MCAO using 2,3,5-triphenyltetrazolium chloride (TTC) staining. Treatment with methyl-GBB significantly reduced the LCAC content in brain tissue, which decreased the ROS production rate without affecting the respiration rate, indicating an increase in mitochondrial coupling. Furthermore, methyl-GBB treatment protected brain mitochondria against anoxia-reoxygenation injury. In addition, treatment with methyl-GBB significantly reduced the infarct size and improved neurological outcomes after MCAO. Increased mitochondrial coupling efficiency may be the basis for the neuroprotective effects of methyl-GBB. This study provides evidence that maintaining brain energy metabolism by lowering the levels of LCACs protects against ischemia-induced brain damage in experimental stroke models.

Energy metabolism: A critical target of cardiovascular injury

Cardiovascular diseases are the main killers threatening human health. Many studies have shown that abnormal energy metabolism plays a key role in the occurrence and development of acute and chronic cardiovascular diseases. Regulating cardiac energy metabolism is a frontier topic in the treatment of cardiovascular diseases. However, we are not very clear about the choice of different substrates, the specific mechanism of energy metabolism participating in the course of cardiovascular disease, and how to develop appropriate drugs to regulate energy metabolism to treat cardiovascular disease. Therefore, this paper reviews how energy metabolism participates in cardiovascular pathophysiological processes and potential drugs aimed at interfering energy metabolism.It is expected to provide good suggestions for promoting the clinical prevention and treatment of cardiovascular diseases from the perspective of energy metabolism.

Cardiomyocyte tetrahydrobiopterin synthesis regulates fatty acid metabolism and susceptibility to ischaemia-reperfusion injury

NEW FINDINGS

What is the central question of this study? What are the physiological roles of cardiomyocyte-derived tetrahydrobiopterin (BH4) in cardiac metabolism and stress response? What is the main finding and its importance? Cardiomyocyte BH4 has a physiological role in cardiac metabolism. There was a shift of substrate preference from fatty acid to glucose in hearts with targeted deletion of BH4 synthesis. The changes in fatty-acid metabolic profile were associated with a protective effect in response to ischaemia-reperfusion (IR) injury, and reduced infarct size. Manipulating fatty acid metabolism via BH4 availability could play a therapeutic role in limiting IR injury.

ABSTRACT

Tetrahydrobiopterin (BH4) is an essential cofactor for nitric oxide (NO) synthases in which its production of NO is crucial for cardiac function. However, non-canonical roles of BH4 have been discovered recently and the cell-specific role of cardiomyocyte BH4 in cardiac function and metabolism remains to be elucidated. Therefore, we developed a novel mouse model of cardiomyocyte BH4 deficiency, by cardiomyocyte-specific deletion of Gch1, which encodes guanosine triphosphate cyclohydrolase I, a required enzyme for de novo BH4 synthesis. Cardiomyocyte (cm)Gch1 mRNA expression and BH4 levels from cmGch1 KO mice were significantly reduced compared to Gch1flox/flox (WT) littermates. Transcriptomic analyses and protein assays revealed downregulation of genes involved in fatty acid oxidation in cmGch1 KO hearts compared with WT, accompanied by increased triacylglycerol concentration within the myocardium. Deletion of cardiomyocyte BH4 did not alter basal cardiac function. However, the recovery of left ventricle function was improved in cmGch1 KO hearts when subjected to ex vivo ischaemia-reperfusion (IR) injury, with reduced infarct size compared to WT hearts. Metabolomic analyses of cardiac tissue after IR revealed that long-chain fatty acids were increased in cmGch1 KO hearts compared to WT, whereas at 5 min reperfusion (post-35 min ischaemia) fatty acid metabolite levels were higher in WT compared to cmGch1 KO hearts. These results indicate a new role for BH4 in cardiomyocyte fatty acid metabolism, such that reduction of cardiomyocyte BH4 confers a protective effect in response to cardiac IR injury. Manipulating cardiac metabolism via BH4 could play a therapeutic role in limiting IR injury.

Right ventricular energy metabolism in a porcine model of acute right ventricular pressure overload after weaning from cardiopulmonary bypass

Acute right ventricular pressure overload (RVPO) occurs following congenital heart surgery and often results in low cardiac output syndrome. We tested the hypothesis that the RV exhibits limited ability to modify substrate utilization in response to increasing energy requirements during acute RVPO after cardiopulmonary bypass (CPB). We assessed the RV fractional contributions (Fc) of substrates to the citric acid cycle in juvenile pigs exposed to acute RVPO by pulmonary artery banding (PAB) and CPB. Sixteen Yorkshire male pigs (median 38 days old, 12.2 kg of body weight) were randomized to SHAM (Ctrl, n = 5), 2-h CPB (CPB, n = 5) or CPB with PAB (PAB-CPB, n = 6). Carbon-13 (13 C)-labeled lactate, medium-chain, and mixed long-chain fatty acids (MCFA and LCFAs) were infused as metabolic tracers for energy substrates. After weaning from CPB, RV systolic pressure (RVSP) doubled baseline in PAB-CPB while piglets in CPB group maintained normal RVSP. Fc-LCFAs decreased significantly in order PAB-CPB > CPB > Ctrl groups by 13 C-NMR. Fc-lactate and Fc-MCFA were similar among the three groups. Intragroup analysis for PAB-CPB showed that the limited Fc-LCFAs appeared prominently in piglets exposed to high RVSP-to-left ventricular systolic pressure ratio and high RV rate-pressure product, an indicator of myocardial oxygen demand. Acute RVPO after CPB strongly inhibits LCFA oxidation without compensation by lactate oxidation, resulting in energy deficiency as determined by lower (phosphocreatine)/(adenosine triphosphate) in PAB-CPB. Adequate energy supply but also metabolic interventions may be required to circumvent these RV energy metabolic abnormalities during RVPO after CPB.

Acylcarnitines: Nomenclature, Biomarkers, Therapeutic Potential, Drug Targets, and Clinical Trials

Acylcarnitines are fatty acid metabolites that play important roles in many cellular energy metabolism pathways. They have historically been used as important diagnostic markers for inborn errors of fatty acid oxidation and are being intensively studied as markers of energy metabolism, deficits in mitochondrial and peroxisomal β -oxidation activity, insulin resistance, and physical activity. Acylcarnitines are increasingly being identified as important indicators in metabolic studies of many diseases, including metabolic disorders, cardiovascular diseases, diabetes, depression, neurologic disorders, and certain cancers. The US Food and Drug Administration-approved drug L-carnitine, along with short-chain acylcarnitines (acetylcarnitine and propionylcarnitine), is now widely used as a dietary supplement. In light of their growing importance, we have undertaken an extensive review of acylcarnitines and provided a detailed description of their identity, nomenclature, classification, biochemistry, pathophysiology, supplementary use, potential drug targets, and clinical trials. We also summarize these updates in the Human Metabolome Database, which now includes information on the structures, chemical formulae, chemical/spectral properties, descriptions, and pathways for 1240 acylcarnitines. This work lays a solid foundation for identifying, characterizing, and understanding acylcarnitines in human biosamples. We also discuss the emerging opportunities for using acylcarnitines as biomarkers and as dietary interventions or supplements for many wide-ranging indications. The opportunity to identify new drug targets involved in controlling acylcarnitine levels is also discussed. SIGNIFICANCE STATEMENT: This review provides a comprehensive overview of acylcarnitines, including their nomenclature, structure and biochemistry, and use as disease biomarkers and pharmaceutical agents. We present updated information contained in the Human Metabolome Database website as well as substantial mapping of the known biochemical pathways associated with acylcarnitines, thereby providing a strong foundation for further clarification of their physiological roles.

Beyond rare disorders: A new era for peroxisomal pathophysiology

Metabolism is emerging as a central influencer of multiple disease states in humans. Peroxisomes are central metabolic organelles whose decreased function gives rise to severe peroxisomal diseases. Recently, it is becoming clear that, beyond such rare inborn errors, the deterioration of peroxisomal functions contributes to multiple and prevalent diseases such as cancer, viral infection, diabetes, and neurodegeneration. Despite the clear importance of peroxisomes in common pathophysiological processes, research on the mechanisms underlying their contributions is still sparse. Here, we highlight the timeliness of focusing on peroxisomes in current research on central, abundant, and society-impacting human pathologies. As peroxisomes are now coming into the spotlight, it is clear that intensive research into these important organelles will enable a better understanding of their contribution to human health, serving as the basis to develop new diagnostic and therapeutic approaches to prevent and treat human diseases.

Meldonium Ameliorates Hypoxia-Induced Lung Injury and Oxidative Stress by Regulating Platelet-Type Phosphofructokinase-Mediated Glycolysis

Hypoxic environments at high altitudes influence the long-term non-altitude health of residents, by inducing changes in metabolism and the mitochondria, severe lung injury, and endangering life. This study was aimed to determine whether meldonium can ameliorate hypoxia-induced lung injury and investigate its possible molecular mechanisms. We used Swiss mice and exposed type Ⅱ alveolar epithelial cell to hypobaric hypoxic conditions to induce lung injury and found that meldonium has significant preventive effect, which was associated with the regulation of glycolysis. We found using human proteome microarrays assay, molecular docking, immunofluorescence and pull-down assay that the target protein of meldonium is a platelet-type phosphofructokinase (PFKP), which is a rate-limiting enzyme of glycolysis. Also, meldonium promotes the transfer of nuclear factor erythroid 2-related factor 2 (Nrf2) from the cytoplasm to the nucleus, which mitigates oxidative stress and mitochondrial damage under hypoxic condition. Mechanistically, meldonium ameliorates lung injury by targeting PFKP to regulate glycolysis, which promotes Nrf2 translocation from the cytoplasm to the nucleus to alleviate oxidative stress and mitochondrial damage under hypoxic condition. Our study provides a novel potential prevention and treatment strategy against hypoxia-induced lung injury.

Pharmacological activation of PPARβ/δ preserves mitochondrial respiratory function in ischemia/reperfusion via stimulation of fatty acid oxidation-linked respiration and PGC-1α/NRF-1 signaling

Myocardial ischemia/reperfusion (I/R) injury leads to significant impairment of cardiac function and remains the leading cause of morbidity and mortality worldwide. Activation of peroxisome proliferator-activated receptor β/δ (PPARβ/δ) confers cardioprotection via pleiotropic effects including antioxidant and anti-inflammatory actions; however, the underlying mechanisms are not yet fully elucidated. The aim of this study was to investigate the effect of PPARβ/δ activation on myocardial mitochondrial respiratory function and link this effect with cardioprotection after ischemia/reperfusion (I/R). For this purpose, rats were treated with the PPARβ/δ agonist GW0742 and/or antagonist GSK0660 in vivo. Mitochondrial respiration and ROS production rates were determined using high-resolution fluororespirometry. Activation of PPARβ/δ did not alter mitochondrial respiratory function in the healthy heart, however, inhibition of PPARβ/δ reduced fatty acid oxidation (FAO) and complex II-linked mitochondrial respiration and shifted the substrate dependence away from succinate-related energy production and towards NADH. Activation of PPARβ/δ reduced mitochondrial stress during in vitro anoxia/reoxygenation. Furthermore, it preserved FAO-dependent mitochondrial respiration and lowered ROS production at oxidative phosphorylation (OXPHOS)-dependent state during ex vivo I/R. PPARβ/δ activation was also followed by increased mRNA expression of components of FAO -linked respiration and of transcription factors governing mitochondrial homeostasis (carnitine palmitoyl transferase 1b and 2-CPT-1b and CPT-2, electron transfer flavoprotein dehydrogenase -ETFDH, peroxisome proliferator-activated receptor gamma co-activator 1 alpha- PGC-1α and nuclear respiratory factor 1-NRF-1). In conclusion, activation of PPARβ/δ stimulated both FAO-linked respiration and PGC-1α/NRF -1 signaling and preserved mitochondrial respiratory function during I/R. These effects are associated with reduced infarct size.

Long-chain fatty acid oxidation and respiratory complex I deficiencies distinguish Barth Syndrome from idiopathic pediatric cardiomyopathy

Barth syndrome (BTHS) is an X-linked disorder that results from mutations in the TAFAZZIN gene, which encodes a phospholipid transacylase responsible for generating the mature form of cardiolipin in inner mitochondrial membranes. BTHS patients develop early onset cardiomyopathy and a derangement of intermediary metabolism consistent with mitochondrial disease, but the precise alterations in cardiac metabolism that distinguish BTHS from idiopathic forms of cardiomyopathy are unknown. We performed the first metabolic analysis of myocardial tissue from BTHS cardiomyopathy patients compared to age- and sex-matched patients with idiopathic dilated cardiomyopathy (DCM) and nonfailing controls. Results corroborate previous evidence for deficiencies in cardiolipin content and its linoleoyl enrichment as defining features of BTHS cardiomyopathy, and reveal a dramatic accumulation of hydrolyzed (monolyso-) cardiolipin molecular species. Respiratory chain protein deficiencies were observed in both BTHS and DCM, but a selective depletion of complex I was seen only in BTHS after controlling for an apparent loss of mitochondrial density in cardiomyopathic hearts. Distinct shifts in the expression of long-chain fatty acid oxidation enzymes and the tissue acyl-CoA profile of BTHS hearts suggest a specific block in mitochondrial fatty acid oxidation upstream of the conventional matrix beta-oxidation cycle, which may be compensated for by a greater reliance upon peroxisomal fatty acid oxidation and the catabolism of ketones, amino acids, and pyruvate to meet cardiac energy demands. These results provide a comprehensive foundation for exploring novel therapeutic strategies that target the adaptive and maladaptive metabolic features of BTHS cardiomyopathy.

Protective Effects of Meldonium in Experimental Models of Cardiovascular Complications with a Potential Application in COVID-19

Right ventricular (RV) and left ventricular (LV) dysfunction is common in a significant number of hospitalized coronavirus disease 2019 (COVID-19) patients. This study was conducted to assess whether the improved mitochondrial bioenergetics by cardiometabolic drug meldonium can attenuate the development of ventricular dysfunction in experimental RV and LV dysfunction models, which resemble ventricular dysfunction in COVID-19 patients. Effects of meldonium were assessed in rats with pulmonary hypertension-induced RV failure and in mice with inflammation-induced LV dysfunction. Rats with RV failure showed decreased RV fractional area change (RVFAC) and hypertrophy. Treatment with meldonium attenuated the development of RV hypertrophy and increased RVFAC by 50%. Mice with inflammation-induced LV dysfunction had decreased LV ejection fraction (LVEF) by 30%. Treatment with meldonium prevented the decrease in LVEF. A decrease in the mitochondrial fatty acid oxidation with a concomitant increase in pyruvate metabolism was noted in the cardiac fibers of the rats and mice with RV and LV failure, respectively. Meldonium treatment in both models restored mitochondrial bioenergetics. The results show that meldonium treatment prevents the development of RV and LV systolic dysfunction by enhancing mitochondrial function in experimental models of ventricular dysfunction that resembles cardiovascular complications in COVID-19 patients.

Metabolic Impairment in Coronary Artery Disease: Elevated Serum Acylcarnitines Under the Spotlights

Coronary artery disease (CAD) remains the leading cause of death worldwide. Expanding patients' metabolic phenotyping beyond clinical chemistry investigations could lead to earlier recognition of disease onset and better prevention strategies. Additionally, metabolic phenotyping, at the molecular species level, contributes to unravel the roles of metabolites in disease development. In this cross-sectional study, we investigated clinically healthy individuals (n = 116, 65% male, 70.8 ± 8.7 years) and patients with CAD (n = 54, 91% male, 67.0 ± 11.5 years) of the COmPLETE study. We applied a high-coverage quantitative liquid chromatography-mass spectrometry approach to acquire a comprehensive profile of serum acylcarnitines, free carnitine and branched-chain amino acids (BCAAs), as markers of mitochondrial health and energy homeostasis. Multivariable linear regression analyses, adjusted for confounders, were conducted to assess associations between metabolites and CAD phenotype. In total, 20 short-, medium- and long-chain acylcarnitine species, along with L-carnitine, valine and isoleucine were found to be significantly (adjusted p ≤ 0.05) and positively associated with CAD. For 17 acylcarnitine species, associations became stronger as the number of affected coronary arteries increased. This implies that circulating acylcarnitine levels reflect CAD severity and might play a role in future patients' stratification strategies. Altogether, CAD is characterized by elevated serum acylcarnitine and BCAA levels, which indicates mitochondrial imbalance between fatty acid and glucose oxidation.

Energy substrate metabolism and mitochondrial oxidative stress in cardiac ischemia/reperfusion injury

The heart is the most metabolically flexible organ with respect to the use of substrates available in different states of energy metabolism. Cardiac mitochondria sense substrate availability and ensure the efficiency of oxidative phosphorylation and heart function. Mitochondria also play a critical role in cardiac ischemia/reperfusion injury, during which they are directly involved in ROS-producing pathophysiological mechanisms. This review explores the mechanisms of ROS production within the energy metabolism pathways and focuses on the impact of different substrates. We describe the main metabolites accumulating during ischemia in the glucose, fatty acid, and Krebs cycle pathways. Hyperglycemia, often present in the acute stress condition of ischemia/reperfusion, increases cytosolic ROS concentrations through the activation of NADPH oxidase 2 and increases mitochondrial ROS through the metabolic overloading and decreased binding of hexokinase II to mitochondria. Fatty acid-linked ROS production is related to the increased fatty acid flux and corresponding accumulation of long-chain acylcarnitines. Succinate that accumulates during anoxia/ischemia is suggested to be the main source of ROS, and the role of itaconate as an inhibitor of succinate dehydrogenase is emerging. We discuss the strategies to modulate and counteract the accumulation of substrates that yield ROS and the therapeutic implications of this concept.

Meldonium: Pharmacological, toxicological, and analytical aspects

Meldonium is the active molecule from Mildronate® with similar chemical structure to an amino acid, and it is known as (3-(2,2,2-trimethylhydrazine) propionate) (CAS 76144-81-5). This pharmaceutical substance is approved in Eastern Europe for cerebral and myocardial ischemia and has been on the World Doping Association’s banned substances list since January 2016. The goal of this review is to relate the use of meldonium as a doping agent, considering its pharmacological, toxicological, and analytical aspects. This review is based on the scientific literature from digital platforms. The main mechanism of action of meldonium is based on a decrease in l-carnitine levels and increase of peroxisomes activity in the cytosol. Females were more susceptible to the substance in animal experiments for toxicological tests. There is currently no report in the scientific literature about acute or chronic intoxication cases by meldonium in humans. Based on the literature findings, meldonium showed ergogenic effect in animals and human volunteers. For anti-doping analysis, urine is the biological matrix of choice, and dilute-and-shoot is the most common sample treatment in addition to liquid chromatography–mass spectrometry analysis. Other approaches could be used to determine meldonium levels, mainly for screening tests, such as l-carnitine or gamma-butyrobetaine levels.

Altered mitochondrial metabolism in the insulin-resistant heart

Obesity-induced insulin resistance and type 2 diabetes mellitus can ultimately result in various complications, including diabetic cardiomyopathy. In this case, cardiac dysfunction is characterized by metabolic disturbances such as impaired glucose oxidation and an increased reliance on fatty acid (FA) oxidation. Mitochondrial dysfunction has often been associated with the altered metabolic function in the diabetic heart, and may result from FA-induced lipotoxicity and uncoupling of oxidative phosphorylation. In this review, we address the metabolic changes in the diabetic heart, focusing on the loss of metabolic flexibility and cardiac mitochondrial function. We consider the alterations observed in mitochondrial substrate utilization, bioenergetics and dynamics, and highlight new areas of research which may improve our understanding of the cause and effect of cardiac mitochondrial dysfunction in diabetes. Finally, we explore how lifestyle (nutrition and exercise) and pharmacological interventions can prevent and treat metabolic and mitochondrial dysfunction in diabetes.

The Potential Role of Protein Tyrosine Phosphatase, Receptor Type C (CD45) in the Intestinal Ischemia-Reperfusion Injury

This study was designed to identify several key genes and their functions in preventing or ameliorating intestinal ischemia-reperfusion (IR) injury, which could provide rationale for further exploring the regulatory mechanisms or clinical treatment for intestinal IR injury. The microarray GSE37013 of human intestinal IR injury was downloaded from Gene Expression Omnibus database. The differentially expressed genes (DEGs) with changes of reperfusion time were screened using Short Time-series Expression Miner, followed by function enrichment analysis, protein-protein interaction (PPI) network, and module construction. Subsequently, the key DEGs were identified with VEEN analysis based on the significant results of function enrichment analysis and PPI module. Finally, the gene-drug interactions were predicted using DGIdb 2.0. The DEGs of intestinal IR injury were significantly divided into three clusters with changes of reperfusion time. The genes in the three clusters were mainly enriched in transmembrane transport, defense responses, and cellular component assembly related pathways, respectively. There were 121 nodes and 281 interactions in PPI network, including one significant submodule. Protein tyrosine phosphatase, receptor type C (PTPRC) was a hub code both in PPI network and in submodule. A total of eight key DEGs were identified but only PTPRC was predicted to be interacted with eight drugs, such as infliximab. Totally, eight key genes associated with intestinal IR were identified; PTPRC especially was the most prominent potential drug target. These findings provided several potential therapeutic targets or potential breakthrough area in the study of intestinal IR injury.

Landscape of heart proteome changes in a diet-induced obesity model

Obesity is a pandemic associated with a high incidence of cardiovascular disease; however, the mechanisms are not fully elucidated. Proteomics may provide a more in-depth understanding of the pathophysiological mechanisms and contribute to the identification of potential therapeutic targets. Thus, our study evaluated myocardial protein expression in healthy and obese rats, employing two proteomic approaches. Male Wistar rats were established in two groups (n = 13/group): control diet and Western diet fed for 41 weeks. Obesity was determined by the adipose index, and cardiac function was evaluated in vivo by echocardiogram and in vitro by isolated papillary muscle analysis. Proteomics was based on two-dimensional gel electrophoresis (2-DE) along with mass spectrometry identification, and shotgun proteomics with label-free quantification. The Western diet was efficient in triggering obesity and impaired contractile function in vitro; however, no cardiac dysfunction was observed in vivo. The combination of two proteomic approaches was able to increase the cardiac proteomic map and to identify 82 differentially expressed proteins involved in different biological processes, mainly metabolism. Furthermore, the data also indicated a cardiac alteration in fatty acids transport, antioxidant defence, cytoskeleton, and proteasome complex, which have not previously been associated with obesity. Thus, we define a robust alteration in the myocardial proteome of diet-induced obese rats, even before functional impairment could be detected in vivo by echocardiogram.

Redox Signaling from and to Peroxisomes: Progress, Challenges, and Prospects

SIGNIFICANCE

Peroxisomes are organelles that are best known for their role in cellular lipid and hydrogen peroxide (H₂O₂) metabolism. Emerging evidence suggests that these organelles serve as guardians and modulators of cellular redox balance, and that alterations in their redox metabolism may contribute to aging and the development of chronic diseases such as neurodegeneration, diabetes, and cancer. Recent Advances: H₂O₂ is an important signaling messenger that controls many cellular processes by modulating protein activity through cysteine oxidation. Somewhat surprisingly, the potential involvement of peroxisomes in H₂O₂-mediated signaling processes has been overlooked for a long time. However, recent advances in the development of live-cell approaches to monitor and modulate spatiotemporal fluxes in redox species at the subcellular level have opened up new avenues for research in redox biology and boosted interest in the concept of peroxisomes as redox signaling platforms.

CRITICAL ISSUES

This review first introduces the reader to what is known about the role of peroxisomes in cellular H₂O₂ production and clearance, with a focus on mammalian cells. Next, it briefly describes the benefits and drawbacks of current strategies used to investigate the complex interplay between peroxisome metabolism and cellular redox state. Furthermore, it integrates and critically evaluates literature dealing with the interrelationship between peroxisomal redox metabolism, cell signaling, and human disease.

FUTURE DIRECTIONS

As the precise molecular mechanisms underlying many of these associations are still poorly understood, a key focus for future research should be the identification of primary targets for peroxisome-derived H₂O₂.

Dietary rescue of lipotoxicity-induced mitochondrial damage in Peroxin19 mutants

Mutations in peroxin (PEX) genes lead to loss of peroxisomes, resulting in the formation of peroxisomal biogenesis disorders (PBDs) and early lethality. Studying PBDs and their animal models has greatly contributed to our current knowledge about peroxisomal functions. Very-long-chain fatty acid (VLCFA) accumulation has long been suggested as a major disease-mediating factor, although the exact pathological consequences are unclear. Here, we show that a Drosophila Pex19 mutant is lethal due to a deficit in medium-chain fatty acids (MCFAs). Increased lipolysis mediated by Lipase 3 (Lip3) leads to accumulation of free fatty acids and lipotoxicity. Administration of MCFAs prevents lipolysis and decreases the free fatty acid load. This drastically increases the survival rate of Pex19 mutants without reducing VLCFA accumulation. We identified a mediator of MCFA-induced lipolysis repression, the ceramide synthase Schlank, which reacts to MCFA supplementation by increasing its repressive action on lip3. This shifts our understanding of the key defects in peroxisome-deficient cells away from elevated VLCFA levels toward elevated lipolysis and shows that loss of this important organelle can be compensated by a dietary adjustment.

Peroxisomes are organelles that contain several enzymes and fatty acids required for many metabolic tasks in the cell, and upon peroxisome loss, their educts accumulate. One example is the accumulation of very-long-chain fatty acids (VLCFAs) with a chain length of more than 20 carbons. These fatty acids cannot be oxidized in mitochondria but are exclusively degraded in peroxisomes. Lowering increased VLCFA levels is sometimes attempted as a treatment option for human disorders with peroxisomal dysfunction, although its effectiveness remains unclear. Here, we have analyzed this process in Drosophila melanogaster and found that peroxisomal loss results not only in VLCFA accumulation but also in a reduction of medium-chain fatty acids (MCFAs). We could show that this is due to a state of high lipolysis and increased mitochondrial activity. By supplementation with MCFAs from coconut oil, we were able to rescue mitochondrial damage and lethality observed in peroxisome-deficient flies. We found that this process is mediated by the ceramide synthase Schlank, which acts as a transcription factor and shuttles between nuclear membrane and endoplasmic reticulum (ER) in response to MCFA availability. We conclude that peroxisome loss triggers the accumulation of free fatty acids and mitochondrial damage in flies and that these effects can be rescued by a diet rich in MCFAs.

Peroxisomes in cardiomyocytes and the peroxisome / peroxisome proliferator-activated receptor-loop

It is well established that the heart is strongly dependent on fatty acid metabolism. In cardiomyocytes there are two distinct sites for the β-oxidisation of fatty acids: the mitochondrion and the peroxisome. Although the metabolism of these two organelles is believed to be tightly coupled, the nature of this relationship has not been fully investigated. Recent research has established the significant contribution of mitochondrial function to cardiac ATP production under normal and pathological conditions. In contrast, limited information is available on peroxisomal function in the heart. This is despite these organelles harbouring metabolic pathways that are potentially cardioprotective, and findings that patients with peroxisomal diseases, such as adult Refsum’s disease, can develop heart failure. In this article, we provide a comprehensive overview on the current knowledge of peroxisomes and the regulation of lipid metabolism by PPARs in cardiomyocytes. We also present new experimental evidence on the differential expression of peroxisome-related genes in the heart chambers and demonstrate that even a mild peroxisomal biogenesis defect (Pex11α-/- ) can induce profound alterations in the cardiomyocyte’s peroxisomal compartment and related gene expression, including the concomitant deregulation of specific PPARs. The possible impact of peroxisomal dysfunction in the heart is discussed and a model for the modulation of myocardial metabolism via a peroxisome/PPAR-loop is proposed.

Acute and long-term administration of palmitoylcarnitine induces muscle-specific insulin resistance in mice

Acylcarnitine accumulation has been linked to perturbations in energy metabolism pathways. In this study, we demonstrate that long-chain (LC) acylcarnitines are active metabolites involved in the regulation of glucose metabolism in vivo. Single-dose administration of palmitoylcarnitine (PC) in fed mice induced marked insulin insensitivity, decreased glucose uptake in muscles, and elevated blood glucose levels. Increase in the content of LC acylcarnitine induced insulin resistance by impairing Akt phosphorylation at Ser473. The long-term administration of PC using slow-release osmotic minipumps induced marked hyperinsulinemia, insulin resistance, and glucose intolerance, suggesting that the permanent accumulation of LC acylcarnitines can accelerate the progression of insulin resistance. The decrease of acylcarnitine content significantly improved glucose tolerance in a mouse model of diet-induced glucose intolerance. In conclusion, we show that the physiological increase in content of acylcarnitines ensures the transition from a fed to fasted state in order to limit glucose metabolism in the fasted state. In the fed state, the inability of insulin to inhibit LC acylcarnitine production induces disturbances in glucose uptake and metabolism. The reduction of acylcarnitine content could be an effective strategy to improve insulin sensitivity. © 2017 BioFactors, 43(5):718-730, 2017.

Circulating acylcarnitine profile in human heart failure: a surrogate of fatty acid metabolic dysregulation in mitochondria and beyond

Heart failure (HF) is associated with metabolic perturbations, particularly of fatty acids (FAs), which remain to be better understood in humans. This study aimed at testing the hypothesis that HF patients with reduced ejection fraction display systemic perturbations in levels of energy-related metabolites, especially those reflecting dysregulation of FA metabolism, namely, acylcarnitines (ACs). Circulating metabolites were assessed using mass spectrometry (MS)-based methods in two cohorts. The main cohort consisted of 72 control subjects and 68 HF patients exhibiting depressed left ventricular ejection fraction (25.9 ± 6.9%) and mostly of ischemic etiology with ≥2 comorbidities. HF patients displayed marginal changes in plasma levels of tricarboxylic acid cycle-related metabolites or indexes of mitochondrial or cytosolic redox status. They had, however, 22-79% higher circulating ACs, irrespective of chain length (P < 0.0001, adjusted for sex, age, renal function, and insulin resistance, determined by shotgun MS/MS), which reflects defective mitochondrial β-oxidation, and were significantly associated with levels of NH₂-terminal pro-B-type natriuretic peptide levels, a disease severity marker. Subsequent extended liquid chromatography-tandem MS analysis of 53 plasma ACs in a subset group from the primary cohort confirmed and further substantiated with a comprehensive lipidomic analysis in a validation cohort revealed in HF patients a more complex circulating AC profile. The latter included dicarboxylic-ACs and dihydroxy-ACs as well as very long chain (VLC) ACs or sphingolipids with VLCFAs (>20 carbons), which are proxies of dysregulated FA metabolism in peroxisomes. Our study identified alterations in circulating ACs in HF patients that are independent of biological traits and associated with disease severity markers. These alterations reflect dysfunctional FA metabolism in mitochondria but also beyond, namely, in peroxisomes, suggesting a novel mechanism contributing to global lipid perturbations in human HF.NEW & NOTEWORTHY Mass spectrometry-based profiling of circulating energy metabolites, including acylcarnitines, in two cohorts of heart failure versus control subjects revealed multiple alterations in fatty acid metabolism in peroxisomes in addition to mitochondria, thereby highlighting a novel mechanism contributing to global lipid perturbations in heart failure.Listen to this article's corresponding podcast at http://ajpheart.podbean.com/e/acylcarnitines-in-human-heart-failure/.

The Peroxisome-Mitochondria Connection: How and Why?

Over the past decades, peroxisomes have emerged as key regulators in overall cellular lipid and reactive oxygen species metabolism. In mammals, these organelles have also been recognized as important hubs in redox-, lipid-, inflammatory-, and innate immune-signaling networks. To exert these activities, peroxisomes must interact both functionally and physically with other cell organelles. This review provides a comprehensive look of what is currently known about the interconnectivity between peroxisomes and mitochondria within mammalian cells. We first outline how peroxisomal and mitochondrial abundance are controlled by common sets of cis- and trans-acting factors. Next, we discuss how peroxisomes and mitochondria may communicate with each other at the molecular level. In addition, we reflect on how these organelles cooperate in various metabolic and signaling pathways. Finally, we address why peroxisomes and mitochondria have to maintain a healthy relationship and why defects in one organelle may cause dysfunction in the other. Gaining a better insight into these issues is pivotal to understanding how these organelles function in their environment, both in health and disease.

Carnitine and γ-Butyrobetaine Stimulate Elimination of Meldonium due to Competition for OCTN2-mediated Transport

Meldonium (3-(2,2,2-trimethylhydrazinium)propionate) is the most potent clinically used inhibitor of organic cation transporter 2 (OCTN2). Inhibition of OCTN2 leads to a decrease in carnitine and acylcarnitine contents in tissues and energy metabolism optimization-related cardioprotective effects. The recent inclusion of meldonium in the World Anti-Doping Agency List of Prohibited Substances and Methods has raised questions about the pharmacokinetics of meldonium and its unusually long elimination time. Therefore, in this study, the rate of meldonium washout after the end of the treatment was tested with and without administration of carnitine, γ-butyrobetaine (GBB) and furosemide to evaluate the importance of competition for OCTN2 transport in mice. Here, we show that carnitine and GBB administration during the washout period effectively stimulated the elimination of meldonium. GBB induced a more pronounced effect on meldonium elimination than carnitine due to the higher affinity of GBB for OCTN2. The diuretic effect of furosemide did not significantly affect the elimination of meldonium, carnitine and GBB. In conclusion, the competition of meldonium, carnitine and GBB for OCTN2-mediated transport determines the pharmacokinetic properties of meldonium. Thus, due to their affinity for OCTN2, GBB and carnitine but not furosemide stimulated meldonium elimination. During long-term treatment, OCTN2-mediated transport ensures a high muscle content of meldonium, while tissue clearance depends on relatively slow diffusion, thus resulting in the unusually long complete elimination period of meldonium.

Long-chain acylcarnitines determine ischaemia/reperfusion-induced damage in heart mitochondria

The accumulation of long-chain fatty acids (FAs) and their CoA and carnitine esters is observed in the ischaemic myocardium after acute ischaemia/reperfusion. The aim of the present study was to identify harmful FA intermediates and their detrimental mechanisms of action in mitochondria and the ischaemic myocardium. In the present study, we found that the long-chain acyl-CoA and acylcarnitine content is increased in mitochondria isolated from an ischaemic area of the myocardium. In analysing the FA derivative content, we discovered that long-chain acylcarnitines, but not acyl-CoAs, accumulate at concentrations that are harmful to mitochondria. Acylcarnitine accumulation in the mitochondrial intermembrane space is a result of increased carnitine palmitoyltransferase 1 (CPT1) and decreased carnitine palmitoyltransferase 2 (CPT2) activity in ischaemic myocardium and it leads to inhibition of oxidative phosphorylation, which in turn induces mitochondrial membrane hyperpolarization and stimulates the production of reactive oxygen species (ROS) in cardiac mitochondria. Thanks to protection mediated by acyl-CoA-binding protein (ACBP), the heart is much better guarded against the damaging effects of acyl-CoAs than against acylcarnitines. Supplementation of perfusion buffer with palmitoylcarnitine (PC) before occlusion resulted in a 2-fold increase in the acylcarnitine content of the heart and increased the infarct size (IS) by 33%. A pharmacologically induced decrease in the mitochondrial acylcarnitine content reduced the IS by 44%. Long-chain acylcarnitines are harmful FA intermediates, accumulating in ischaemic heart mitochondria and inducing inhibition of oxidative phosphorylation. Therefore, decreasing the acylcarnitine content via cardioprotective drugs may represent a novel treatment strategy.

Pharmacological effects of meldonium: Biochemical mechanisms and biomarkers of cardiometabolic activity

Meldonium (mildronate; 3-(2,2,2-trimethylhydrazinium)propionate; THP; MET-88) is a clinically used cardioprotective drug, which mechanism of action is based on the regulation of energy metabolism pathways through l-carnitine lowering effect. l-Carnitine biosynthesis enzyme γ-butyrobetaine hydroxylase and carnitine/organic cation transporter type 2 (OCTN2) are the main known drug targets of meldonium, and through inhibition of these activities meldonium induces adaptive changes in the cellular energy homeostasis. Since l-carnitine is involved in the metabolism of fatty acids, the decline in its levels stimulates glucose metabolism and decreases concentrations of l-carnitine related metabolites, such as long-chain acylcarnitines and trimethylamine-N-oxide. Here, we briefly reviewed the pharmacological effects and mechanisms of meldonium in treatment of heart failure, myocardial infarction, arrhythmia, atherosclerosis and diabetes.

Decreased acylcarnitine content improves insulin sensitivity in experimental mice models of insulin resistance

The important pathological consequences of insulin resistance arise from the detrimental effects of accumulated long-chain fatty acids and their respective acylcarnitines. The aim of this study was to test whether exercise combined with decreasing the content of long-chain acylcarnitines represents an effective strategy to improve insulin sensitivity in diabetes. We used a novel compound, 4-[ethyl(dimethyl)ammonio]butanoate (methyl-GBB), treatment and exercise to decrease acylcarnitine contents in the plasma and muscles in the insulin resistance models of high fat diet (HFD) fed C57BL/6 mice and db/db mice. The methyl-GBB treatment induced a substantial decrease in all acylcarnitine concentrations in both fed and fasted states as well as when it was combined with exercise. In the HFD fed mice methyl-GBB treatment improved both glucose and insulin tolerance. Methyl-GBB administration, exercise and the combination of both improved insulin sensitivity and reduced blood glucose levels in db/db mice. Methyl-GBB administration and the combination of the drug and exercise activated the PPARα/PGC1α signaling pathway and stimulated the corresponding target gene expression. Insulin insensitivity in db/db mice was not induced by significantly increased fatty acid metabolism, while increased insulin sensitivity by both treatments was not related to decreased fatty acid metabolism in muscles. The pharmacologically reduced long-chain acylcarnitine content represents an effective strategy to improve insulin sensitivity. The methyl-GBB treatment and lifestyle changes via increased physical activity for one hour a day have additive insulin sensitizing effects in db/db mice.

Inhibition of L-carnitine biosynthesis and transport by methyl-γ-butyrobetaine decreases fatty acid oxidation and protects against myocardial infarction

BACKGROUND AND PURPOSE

The important pathological consequences of ischaemic heart disease arise from the detrimental effects of the accumulation of long-chain acylcarnitines in the case of acute ischaemia-reperfusion. The aim of this study is to test whether decreasing the L-carnitine content represents an effective strategy to decrease accumulation of long-chain acylcarnitines and to reduce fatty acid oxidation in order to protect the heart against acute ischaemia-reperfusion injury.

KEY RESULTS

In this study, we used a novel compound, 4-[ethyl(dimethyl)ammonio]butanoate (Methyl-GBB), which inhibits γ-butyrobetaine dioxygenase (IC₅₀ 3 μM) and organic cation transporter 2 (OCTN2, IC₅₀ 3 μM), and, in turn, decreases levels of L-carnitine and acylcarnitines in heart tissue. Methyl-GBB reduced both mitochondrial and peroxisomal palmitate oxidation rates by 44 and 53% respectively. In isolated hearts treated with Methyl-GBB, uptake and oxidation rates of labelled palmitate were decreased by 40%, while glucose oxidation was increased twofold. Methyl-GBB (5 or 20 mg·kg(-1)) decreased the infarct size by 45-48%. In vivo pretreatment with Methyl-GBB (20 mg·kg(-1)) attenuated the infarct size by 45% and improved 24 h survival of rats by 20-30%.

CONCLUSIONS AND IMPLICATIONS

Reduction of L-carnitine and long-chain acylcarnitine content by the inhibition of OCTN2 represents an effective strategy to protect the heart against ischaemia-reperfusion-induced damage. Methyl-GBB treatment exerted cardioprotective effects and increased survival by limiting long-chain fatty acid oxidation and facilitating glucose metabolism.

Suppression of intestinal microbiota-dependent production of pro-atherogenic trimethylamine N-oxide by shifting L-carnitine microbial degradation

AIMS

Trimethylamine-N-oxide (TMAO) is produced in host liver from trimethylamine (TMA). TMAO and TMA share common dietary quaternary amine precursors, carnitine and choline, which are metabolized by the intestinal microbiota. TMAO recently has been linked to the pathogenesis of atherosclerosis and severity of cardiovascular diseases. We examined the effects of anti-atherosclerotic compound meldonium, an aza-analogue of carnitine bioprecursor gamma-butyrobetaine (GBB), on the availability of TMA and TMAO.

MAIN METHODS

Wistar rats received L-carnitine, GBB or choline alone or in combination with meldonium. Plasma, urine and rat small intestine perfusate samples were assayed for L-carnitine, GBB, choline and TMAO using UPLC-MS/MS. Meldonium effects on TMA production by intestinal bacteria from L-carnitine and choline were tested.

KEY FINDINGS

Treatment with meldonium significantly decreased intestinal microbiota-dependent production of TMA/TMAO from L-carnitine, but not from choline. 24hours after the administration of meldonium, the urinary excretion of TMAO was 3.6 times lower in the combination group than in the L-carnitine-alone group. In addition, the administration of meldonium together with L-carnitine significantly increased GBB concentration in blood plasma and in isolated rat small intestine perfusate. Meldonium did not influence bacterial growth and bacterial uptake of L-carnitine, but TMA production by the intestinal microbiota bacteria K. pneumoniae was significantly decreased.

SIGNIFICANCE

We have shown for the first time that TMA/TMAO production from quaternary amines could be decreased by targeting bacterial TMA-production. In addition, the production of pro-atherogenic TMAO can be suppressed by shifting the microbial degradation pattern of supplemental/dietary quaternary amines.

Long-chain acylcarnitine content determines the pattern of energy metabolism in cardiac mitochondria

In the heart, a nutritional state (fed or fasted) is characterized by a unique energy metabolism pattern determined by the availability of substrates. Increased availability of acylcarnitines has been associated with decreased glucose utilization; however, the effects of long-chain acylcarnitines on glucose metabolism have not been previously studied. We tested how changes in long-chain acylcarnitine content regulate the metabolism of glucose and long-chain fatty acids in cardiac mitochondria in fed and fasted states. We examined the concentrations of metabolic intermediates in plasma and cardiac tissues under fed and fasted states. The effects of substrate availability and their competition for energy production at the mitochondrial level were studied in isolated rat cardiac mitochondria. The availability of long-chain acylcarnitines in plasma reflected their content in cardiac tissue in the fed and fasted states, and acylcarnitine content in the heart was fivefold higher in fasted state compared to the fed state. In substrate competition experiments, pyruvate and fatty acid metabolites effectively competed for the energy production pathway; however, only the physiological content of acylcarnitine significantly reduced pyruvate and lactate oxidation in mitochondria. The increased availability of long-chain acylcarnitine significantly reduced glucose utilization in isolated rat heart model and in vivo. Our results demonstrate that changes in long-chain acylcarnitine contents could orchestrate the interplay between the metabolism of pyruvate-lactate and long-chain fatty acids, and thus determine the pattern of energy metabolism in cardiac mitochondria.

Mildronate, the inhibitor of L-carnitine transport, induces brain mitochondrial uncoupling and protects against anoxia-reoxygenation

The preservation of mitochondrial function is essential for normal brain function after ischaemia-reperfusion injury. l-carnitine is a cofactor involved in the regulation of cellular energy metabolism. Recently, it has been shown that mildronate, an inhibitor of l-carnitine transport, improves neurological outcome after ischaemic damage of brain tissues. The aim of the present study was to elucidate the mitochondria targeted neuroprotective action of mildronate in the model of anoxia-reoxygenation-induced injury. Wistar rats were treated daily with mildronate (per os; 100mg/kg) for 14 days. The acyl-carnitine profile was determined in the brain tissues. Mitochondrial respiration and the activities of carnitine acetyltransferase (CrAT) and tricarboxylic acid (TCA) cycle enzymes were measured. To assess tolerance to ischaemia, isolated mitochondria were subjected to anoxia followed by reoxygenation. The mildronate treatment significantly reduced the concentrations of free l-carnitine (FC) and short-chain acyl-carnitine (AC) in brain tissue by 40-76%, without affecting the AC:FC ratio. The activities of CrAT and TCA cycle enzymes were slightly increased after mildronate treatment. Despite partially induced uncoupling, mildronate treatment did not affect mitochondrial bioenergetics function under normoxic conditions. After exposure to anoxia-reoxygenation, state 3 respiration and the respiration control ratio were higher in the mildronate-treated group. The results obtained demonstrate that mildronate treatment improves tolerance against anoxia-reoxygenation due to an uncoupling preconditioning-like effect. Regulating l-carnitine availability provides a potential novel target for the treatment of cerebral ischaemia and related complications.