Glycine protects cardiomyocytes against lethal reoxygenation injury by inhibiting mitochondrial permeability transition

The use of amino acids and their derivates to mitigate against pesticide-induced toxicity

Exposure to pesticides induces oxidative stress and deleterious effects on various tissues in non-target organisms. Numerous models investigating pesticide exposure have demonstrated metabolic disturbances such as imbalances in amino acid levels within the organism. One potentially effective strategy to mitigate pesticide toxicity involves dietary intervention by supplementing exogenous amino acids and their derivates to augment the body's antioxidant capacity and mitigate pesticide-induced oxidative harm, whose mechanism including bolstering glutathione synthesis, regulating arginine-NO metabolism, mitochondria-related oxidative stress, and the open of ion channels, as well as enhancing intestinal microecology. Enhancing glutathione synthesis through supplementation of substrates N-acetylcysteine and glycine is regarded as a potent mechanism to achieve this. Selection of appropriate amino acids or their derivates for supplementation, and determining an appropriate dosage, are of the utmost importance for effective mitigation of pesticide-induced oxidative harm. More experimentation is required that involves large population samples to validate the efficacy of dietary intervention strategies, as well as to determine the effects of amino acids and their derivates on long-term and low-dose pesticide exposure. This review provides insights to guide future research aimed at preventing and alleviating pesticide toxicity through dietary intervention of amino acids and their derivates.

Right Ventricular Subclinical Dysfunction in SLE Patients Correlates with Metabolomic Fingerprint and Organ Damage

Systemic lupus erythematosus (SLE) is a chronic inflammatory disease, and several studies have suggested possible early RV involvement. Aim of the study was to evaluate the 3D echo parameters of the right ventricle (RV) and the metabolomic profile to correlate both with SLE severity. Forty SLE patients, free of cardiovascular disease, were enrolled and the following 3D parameters were evaluated: the RV ejection fraction (RV-EF), longitudinal strain of the interventricular septum (Septal LS), longitudinal strain of the free wall (Free-LS) and the fractional area change (FAC). In addition, a metabolomic analysis was performed. Direct correlations were observed between TAPSE values and the RV 3D parameters. Then, when splitting the population according to the SDI value, it was found that patients with higher cumulative damage (≥3) had significantly lower FAC, RV-EF, Septal LS, and Free-LS values; the latter three parameters showed a significant correlation with the metabolic profile of the patients. Furthermore, the division based on SDI values identified different metabolic profiles related to the degree of RV dysfunction. The RV dysfunction induced by the chronic inflammatory state present in SLE can be identified early by 3D echocardiography. Its severity seems to be related to systemic organ damage and the results associated with a specific metabolic fingerprint constituted by 2,4-dihydroxybutyric acid, 3,4-dihydroxybutyric acid, citric acid, glucose, glutamine, glycine, linoleic acid, oleic acid, phosphate, urea, and valine.

Glycine protects the male reproductive system against lead toxicity via alleviating oxidative stress, preventing sperm mitochondrial impairment, improving kinematics of sperm, and blunting the downregulation of enzymes involved in the steroidogenesis

Lead (Pb) is a highly toxic heavy metal widely dispersed in the environment because of human industrial activities. Many studies revealed that Pb could adversely affect several organs, including the male reproductive system. Pb-induced reproductive toxicity could lead to infertility. Thus, finding safe and clinically applicable protective agents against this complication is important. It has been found that oxidative stress plays a fundamental role in the pathogenesis of Pb-induced reprotoxicity. Glycine is the simplest amino acid with a wide range of pharmacological activities. It has been found that glycine could attenuate oxidative stress and mitochondrial impairment in various experimental models. The current study was designed to evaluate the role of glycine in Pb-induced reproductive toxicity in male mice. Male BALB/c mice received Pb (20 mg/kg/day; gavage; 35 consecutive days) and treated with glycine (250 and 500 mg/kg/day; gavage; 35 consecutive days). Then, reproductive system weight indices, biomarkers of oxidative stress in the testis and isolated sperm, sperm kinetic, sperm mitochondrial indices, and testis histopathological alterations were monitored. A significant change in testis, epididymis, and Vas deferens weight was evident in Pb-treated animals. Markers of oxidative stress were also significantly increased in the testis and isolated sperm of the Pb-treated group. A significant disruption in sperm kinetic was also evident when mice received Pb. Moreover, Pb exposure caused significant deterioration in sperm mitochondrial indices. Tubular injury, tubular desquamation, and decreased spermatogenic index were histopathological alterations detected in Pb-treated mice. It was found that glycine significantly blunted oxidative stress markers in testis and sperm, improved sperm mitochondrial parameters, causing considerable higher velocity-related indices (VSL, VCL, and VAP) and percentages of progressively motile sperm, and decreased testis histopathological changes in Pb-exposed animals. These data suggest glycine as a potential protective agent against Pb-induced reproductive toxicity. The effects of glycine on oxidative stress markers and mitochondrial function play a key role in its protective mechanism.

A designer mixture of six amino acids promotes the extracellular matrix gene expression in cultured human fibroblasts

The deterioration of the skin is caused by dermatological disorders, environmental conditions, and ageing processes. One incisive strategy for supervising the skin ageing process is implementing healthy nutrition, preserving a balanced diet and a good supply of food supplements. Here, we compared H-Pro-Hyp-OH peptide, hydrolysed collagen, and an original mixture of six amino acids (we named 6aa)-including glycine, l-alanine, l-proline, l-valine, l-leucine, and l-lysine-effects on the production of extracellular matrix (ECM) components, particularly the elastin, fibronectin, collagen 1, and collagen 4. Treatment of BJ human skin fibroblasts with the 6aa mixture upregulated elastin, fibronectin, and collagen 1 gene expression, without affecting the expression of anti-reactive oxygen species enzymes. Moreover, the mTOR signaling pathway seems to be involved, at least in part. Collectively, these results suggest that the six amino acid mixture exerts beneficial effects in human skin fibroblasts.

Protection function of 18β-glycyrrhetinic acid on rats with high-altitude pulmonary hypertension based on 1H NMR metabonomics technology

18β-Glycyrrhetinic acid (GA) is the triterpenoid aglycone component of glycyrrhizic acid, a natural product of traditional Chinese medicine, and has been proven to possess a variety of pharmacological effects. The protection function and the mechanism of GA on rats with high-altitude pulmonary hypertension (HAPH) are studied using proton nuclear magnetic resonance (1H NMR) metabonomics technology and biochemical analysis. An HAPH model is established, and 60 male rats are randomly divided into the following groups: Control(normal saline, 0.4 mL/100 g), model (normal saline, 0.4 mL/100 g), Nifedipine (nifedipine, 2.7 mg/kg), and high-, medium-, and low-dose GA groups (100, 50, and 25 mg/kg GA designated as GA.H, GA.M, and GA.L, respectively). Serum biochemical indicators of rats in each group are measured, and pathological changes in the pulmonary artery are observed. 1H NMR metabonomics technology is used for serum analysis. Results show that GA can significantly reduce pulmonary arterial pressure and malondialdehyde levels and increase the glutathione peroxidase and superoxide dismutase activities in HAPH rats. Pathological results show that GA can alleviate pulmonary artery injuries of HAPH rats. Metabolomics analytical findings show that GA can alleviate the metabolic disorder of HAPH rats through anti-oxidation and anti-inflammatory effects, improve their bodies' ability to resist hypoxia, and restore various metabolic pathways (energy metabolism, amino acid metabolism, and lipid metabolism). GA has potential therapeutic effects on HAPH rats, but its target needs to be further studied.

Subtle Role for Adenylate Kinase 1 in Maintaining Normal Basal Contractile Function and Metabolism in the Murine Heart

Aims

Adenylate kinase 1 (AK1) catalyses the reaction 2ADP ↔ ATP + AMP, extracting extra energy under metabolic stress and promoting energetic homeostasis. We hypothesised that increased AK1 activity would have negligible effects at rest, but protect against ischaemia/reperfusion (I/R) injury.

Methods and Results

Cardiac-specific AK1 overexpressing mice (AK1-OE) had 31% higher AK1 activity (P = 0.009), with unchanged total creatine kinase and citrate synthase activities. Male AK1-OE exhibited mild in vivo dysfunction at baseline with lower LV pressure, impaired relaxation, and contractile reserve. LV weight was 19% higher in AK1-OE males due to higher tissue water content in the absence of hypertrophy or fibrosis. AK1-OE hearts had significantly raised creatine, unaltered total adenine nucleotides, and 20% higher AMP levels (P = 0.05), but AMP-activated protein kinase was not activated (P = 0.85). ¹H-NMR revealed significant differences in LV metabolite levels compared to wild-type, with aspartate, tyrosine, sphingomyelin, cholesterol all elevated, whereas taurine and triglycerides were significantly lower. Ex vivo global no-flow I/R, caused four-of-seven AK1-OE hearts to develop terminal arrhythmia (cf. zero WT), yet surviving AK1-OE hearts had improved functional recovery. However, AK1-OE did not influence infarct size in vivo and arrhythmias were only observed ex vivo, probably as an artefact of adenine nucleotide loss during cannulation.

Conclusion

Modest elevation of AK1 may improve functional recovery following I/R, but has unexpected impact on LV weight, function and metabolite levels under basal resting conditions, suggesting a more nuanced role for AK1 underpinning myocardial energy homeostasis and not just as a response to stress.

1H NMR serum metabolomic profiling of patients at risk of cardiovascular diseases performing stress test

Cardiovascular diseases are the leading cause of death worldwide. Changes in lifestyle and/or pharmacological treatment are able to reduce the burden of coronary artery diseases (CAD) and early diagnosis is crucial for the timely and optimal management of the disease. Stress testing is a good method to measure the burden of CAD but it is time consuming and pharmacological testing may not fully mimic exercise test. The objectives of the present project were to characterize the metabolic profile of the population undergoing pharmacological and exercise stress testing to evaluate possible differences between them, and to assess the capacity of ¹H NMR spectroscopy to predict positive stress testing. Pattern recognition was applied to ¹H NMR spectra from serum of patients undergoing stress test and metabolites were quantified. The effects of the stress test, confounding variables and the ability to predict ischemia were evaluated using OPLS-DA. There was an increase in lactate and alanine concentrations in post-test samples in patients undergoing exercise test, but not in those submitted to pharmacological testing. However, when considering only pharmacological patients, those with a positive test result, showed increased serum lactate, that was masked by the much larger amount of lactate associated to exercise testing. In conclusion, we have established that pharmacological stress test does not reproduce the dynamic changes observed in exercise stress. Although there is promising evidence suggesting that ¹H NMR based metabolomics could predict stress test results, further studies with much larger populations will be required in order to obtain a definitive answer.

Atherosclerosis Linked to Aberrant Amino Acid Metabolism and Immunosuppressive Amino Acid Catabolizing Enzymes

Cardiovascular disease is the leading global health concern and responsible for more deaths worldwide than any other type of disorder. Atherosclerosis is a chronic inflammatory disease in the arterial wall, which underpins several types of cardiovascular disease. It has emerged that a strong relationship exists between alterations in amino acid (AA) metabolism and the development of atherosclerosis. Recent studies have reported positive correlations between levels of branched-chain amino acids (BCAAs) such as leucine, valine, and isoleucine in plasma and the occurrence of metabolic disturbances. Elevated serum levels of BCAAs indicate a high cardiometabolic risk. Thus, BCAAs may also impact atherosclerosis prevention and offer a novel therapeutic strategy for specific individuals at risk of coronary events. The metabolism of AAs, such as L-arginine, homoarginine, and L-tryptophan, is recognized as a critical regulator of vascular homeostasis. Dietary intake of homoarginine, taurine, and glycine can improve atherosclerosis by endothelium remodeling. Available data also suggest that the regulation of AA metabolism by indoleamine 2,3-dioxygenase (IDO) and arginases 1 and 2 are mediated through various immunological signals and that immunosuppressive AA metabolizing enzymes are promising therapeutic targets against atherosclerosis. Further clinical studies and basic studies that make use of animal models are required. Here we review recent data examining links between AA metabolism and the development of atherosclerosis.

Metabolic changes in mice cardiac tissue after low-dose irradiation revealed by 1H NMR spectroscopy

Ionizing radiation may cause cardiotoxicity not only at high, but even at low (considered as harmless) doses, yet the molecular mechanisms of the heart's response to low doses are not clear. In this work, we used high-resolution nuclear magnetic resonance (NMR) spectroscopy to detect the early and late effects of radiation on the metabolism of murine hearts. The hearts of C57Bl/6NCrl female mice were irradiated in vivo with single 0.2 Gy or 2 Gy doses using 6 MV photons, then tissues were collected 48 h and 20 weeks after exposure. The most distinct changes in the profile of polar metabolites were detected 48 h after irradiation with 2 Gy, and included increased levels of pantothenate and glutamate as well as decreased levels of alanine, malonate, acetylcarnitine, glycine and adenosine. Significant effects of the 2 Gy dose were also observed 20 weeks after irradiation and included decreased levels of glutamine and acetylcarnitine when compared with age-matched controls. Moreover, several differences were observed between hearts irradiated with 2 Gy and analyzed either 48 h or 20 weeks after the exposure, which included changes in levels of acetylcarnitine, alanine, glycine, glutamate, glutamine, formate, myo-inositol and trimethylamine. No statistically significant effects induced by the 0.2 Gy dose were observed 20 weeks after irradiation. In general, radiation-affected compounds were associated with energy metabolism, fatty acid beta-oxidation, oxidative stress and damage to cell structures. At the same time, radiation-related effects were not detected at the level of tissue histology, which indicated a higher sensitivity of metabolomics-based tests for cardiac tissue response to radiation.

The CO-releasing molecule CORM-3 protects adult cardiomyocytes against hypoxia-reoxygenation by modulating pH restoration

Several studies have reported that CORM-3, a water-soluble carbon monoxide releasing molecule, elicits cardioprotection against myocardial infarction but the mechanism remains to be investigated. Numerous reports indicate that inhibition of pH regulators, the Na⁺/H⁺ exchanger (NHE) and Na⁺/HCO₃^- symporter (NBC), protect cardiomyocytes from hypoxia/reoxygenation injury by delaying the intracellular pH (pHi) recovery at reperfusion. Our goal was to explore whether CORM-3-mediated cytoprotection involves the modulation of pH regulation. When added at reoxygenation, CORM-3 (50 μM) reduced the mortality of cardiomyocytes exposed to 3 h of hypoxia and 2 h of reoxygenation in HCO₃^--buffered solution. This effect was lost when using inactive iCORM-3, which is depleted of CO and used as control, thus implicating CO as the mediator of this cardioprotection. Interestingly, the cardioprotective effect of CORM-3 was abolished by switching to a bicarbonate-free medium. This effect of CORM-3 was also inhibited by 5-hydroxydecanoate, a mitochondrial ATP-dependent K⁺ (mK_ATP) channel inhibitor (500 μM) or PD098059, a MEK1/2 inhibitor (10 μM). In additional experiments and in the absence of hypoxia-reoxygenation, intracellular pH was monitored in cardiomyocytes exposed to cariporide to block NHE activity. CORM-3 inhibited alkalinisation and this effect was blocked by PD098059 and 5-HD. In conclusion, CORM-3 protects the cardiomyocyte against hypoxia-reoxygenation injury by inhibiting a bicarbonate transporter at reoxygenation, probably the Na⁺/HCO₃^- symporter. This cardioprotective effect of CORM-3 requires the activation of mK_ATP channels and the activation of MEK1/2.

Metabolic remodeling of cardiomyocytes identified in phosphoinositide-dependent kinase 1-deficient mice

Metabolic remodeling plays an essential role in the pathophysiology of heart failure (HF). Many studies have shown that the disruption of phosphoinositide-dependent protein kinase-1 (PDK1) caused severe and lethal HF; however, the metabolic pattern of PDK1 deletion remains ambiguous. ¹H nuclear magnetic resonance-based metabolomics was applied to explore the altered metabolic pattern in Pdk1-deficient mice. Principle component analysis showed significant separation as early as 4 weeks of age, and dysfunction of metabolism precedes a morphological change in Pdk1-deficient mice. A time trajectory plot indicated that disturbed metabolic patterns were related to the pathological process of the HF in Pdk1-deficient mice, rather than the age of mice. Metabolic profiles demonstrated significantly increased levels of acetate, glutamate, glutamine, and O-phosphocholine in Pdk1 deletion mice. Levels of lactate, alanine, glycine, taurine, choline, fumarate, IMP, AMP, and ATP were significantly decreased compared with controls. Furthermore, PDK1 knockdown decreased the oxygen consumption rate in H9C2 cells as determined using a Seahorse XF96 Analyzer. These findings imply that the disruption of metabolism and impaired mitochondrial activity might be involved in the pathogenesis of HF with PDK1 deletion.

The footprints of mitochondrial impairment and cellular energy crisis in the pathogenesis of xenobiotics-induced nephrotoxicity, serum electrolytes imbalance, and Fanconi's syndrome: A comprehensive review

Fanconi's Syndrome (FS) is a disorder characterized by impaired renal proximal tubule function. FS is associated with a vast defect in the renal reabsorption of several chemicals. Inherited and/or acquired conditions seem to be connected with FS. Several xenobiotics including many pharmaceuticals are capable of inducing FS and nephrotoxicity. Although the pathological state of FS is well described, the exact underlying etiology and cellular mechanism(s) of xenobiotics-induced nephrotoxicity, serum electrolytes imbalance, and FS are not elucidated. Constant and high dependence of the renal reabsorption process to energy (ATP) makes mitochondrial dysfunction as a pivotal mechanism which could be involved in the pathogenesis of FS. The current review focuses on the footprints of mitochondrial impairment in the etiology of xenobiotics-induced FS. Moreover, the importance of mitochondria protecting agents and their preventive/therapeutic capability against FS is highlighted. The information collected in this review may provide significant clues to new therapeutic interventions aimed at minimizing xenobiotics-induced renal injury, serum electrolytes imbalance, and FS.

Circulating mediators of remote ischemic preconditioning: search for the missing link between non-lethal ischemia and cardioprotection

Acute myocardial infarction (AMI) is one of the leading causes of mortality and morbidity worldwide. There has been an extensive search for cardioprotective therapies to reduce myocardial ischemia-reperfusion (I/R) injury. Remote ischemic preconditioning (RIPC) is a phenomenon that relies on the body's endogenous protective modalities against I/R injury. In RIPC, non-lethal brief I/R of one organ or tissue confers protection against subsequent lethal I/R injury in an organ remote to the briefly ischemic organ or tissue. Initially it was believed to be limited to direct myocardial protection, however it soon became apparent that RIPC applied to other organs such as kidney, liver, intestine, skeletal muscle can reduce myocardial infarct size. Intriguing discoveries have been made in extending the concept of RIPC to other organs than the heart. Over the years, the underlying mechanisms of RIPC have been widely sought and discussed. The involvement of blood-borne factors as mediators of RIPC has been suggested by a number of research groups. The main purpose of this review article is to summarize the possible circulating mediators of RIPC, and recent studies to establish the clinical efficacy of these mediators in cardioprotection from lethal I/R injury.

Autocatalytic cycle in the pathogenesis of diabetes mellitus: biochemical and pathophysiological aspects of metabolic therapy with natural amino acids on the example of glycine

In this work systematization (classification) of biochemical and physiological processes that cause disorders in the human body during the development of diabetes mellitus is carried out. The development of the disease is considered as the interaction and mutual reinforcement of two groups of parallel processes. The first group has a molecular nature and it is associated with impairment of ROS-regulation system which includes NADPH oxidases, RAGE receptors, mitochondria, cellular peroxireductase system and the immune system. The second group has a pathophysiological nature and it is associated with impairment of microcirculation and liver metabolism. The analysis of diabetes biochemistry based on different published references yields a creation of a block diagram evaluating the disease development over time. Two types of autocatalytic processes were identified: autocatalysis in the cascade of biochemical reactions and "cross-section" catalysis, in which biochemical and pathophysiological processes reinforce each other. The developed model has shown the possibility of using pharmacologically active natural metabolite glycine as a medicine inhibiting the development of diabetes. Despite the fact that glycine is a substitute amino acid the drop in the glycine blood concentration occurs even in the early stages of diabetes development and can aggravate the disease. It is shown that glycine is a potential blocker of key autocatalytic cycles, including biochemical and pathophysiological processes. The analysis of the glycine action based on the developed model is in complete agreement with the results of clinical trials in which glycine has improved blood biochemistry of diabetic patients and thereby it prevents the development of diabetic complications.

Comparative effect of selenium and glycine on hydrogen peroxide-induced cell death and activation of macrophage U937 cells

The effects of selenium and glycine (either separately or in combination) on hydrogen peroxide-induced cell death on U937 cells and activation of U937-derived macrophages were investigated. In the first instance, U937 cells were incubated with or without selenium (Se) or glycine (GLY) or both (Se + GLY) for 24 h before exposure to hydrogen peroxide. Control cells were not incubated with Se, GLY or exposed to hydrogen peroxide. Cell viability was later assessed via trypan blue and MTT assays. For the other experiment, U937 cells were transformed to the macrophage form using phorbol 12-myristate 13-acetate before incubating with or without Se, GLY, Se + GLY. Contents were subsequently exposed to hydrogen peroxide and 24 h later assessed for the production of TNF-α, IL-1, IL-6 and the expression of iNOS and NF-κB. The results revealed that hydrogen peroxide caused significant cell death which was ameliorated by both Se and GLY. Pre-incubation of the cells with both Se and GLY did not significantly enhance cell numbers compared to GLY (p > 0.05). On the other hand, Se and GLY reduced hydrogen peroxide-mediated production of TNF-α, IL-1, IL-6 and expression of iNOS and NF-κB. Incubating the U937-derived macrophages with Se + GLY significantly ameliorated hydrogen peroxide-mediated activation of macrophages when compared to pre-treatments with Se or GLY (p < 0.05). The findings demonstrate that both Se and GLY reduced hydrogen peroxide-induced alterations in U937 cells and U937-derived macrophages. Implications of the findings are discussed.

Remote ischemic conditioning provides humoural cross-species cardioprotection through glycine receptor activation

AIMS

Remote ischaemic conditioning (RIC) releases a humoural factor able to exert cross-species cardioprotection when plasma dialysate is applied to isolated hearts. However, the exact chemical nature of this factor is currently unknown.

METHODS AND RESULTS

RIC (4 × 5min femoral occlusion/5min reperfusion) was applied to 10 male pigs, and blood was taken before and after the manoeuvre. Discriminant analysis of ¹H-NMR spectra (n = 10-12) obtained from plasma dialysates (12-14 kDa cut-off) allowed to demonstrate a different metabolic profile between control and postRIC samples, with lactate (2.671 ± 0.294 vs. 3.666 ± 0.291 μmol/mL, P = 0.020), succinate (0.062 ± 0.005 vs. 0.082 ± 0.008 μmol/mL, P = 0.035) and glycine (0.055 ± 0.009 vs. 0.471 ± 0.151 μmol/mL, P = 0.015) being the main responsible for such differences. Plasma dialysates were then given to isolated mice hearts submitted to global ischaemia (35 min) and reperfusion (60 min), for 30 min before ischaemia or during the first 15 min of reflow. Infarct size was significantly reduced when postRIC dialysate was applied before ischaemia as compared with hearts pretreated with control dialysate (44.81 ± 3.22 vs. 55.55 ± 2.53%, P = 0.012, n = 12). Blockade of glycine receptors with strychnine 10 μM inhibited the protective effect caused by pretreatment with postRIC dialysate (52.76 ± 6.94 vs. 51.92 ± 5.78%, P-NS, n = 5), whereas pretreatment with glycine 3 mmol/L, but not succinate 100 μmol/L, mimicked RIC protection (41.90 ± 4.50% in glycine-treated vs. 61.51 ± 5.16 and 64.73 ± 4.47% in succinate-treated and control hearts, respectively, P < 0.05, n = 4-7).

CONCLUSIONS

RIC releases glycine and exerts cross-species cardioprotection against infarction through glycine receptor activation.

Multifarious Beneficial Effect of Nonessential Amino Acid, Glycine: A Review

Glycine is most important and simple, nonessential amino acid in humans, animals, and many mammals. Generally, glycine is synthesized from choline, serine, hydroxyproline, and threonine through interorgan metabolism in which kidneys and liver are the primarily involved. Generally in common feeding conditions, glycine is not sufficiently synthesized in humans, animals, and birds. Glycine acts as precursor for several key metabolites of low molecular weight such as creatine, glutathione, haem, purines, and porphyrins. Glycine is very effective in improving the health and supports the growth and well-being of humans and animals. There are overwhelming reports supporting the role of supplementary glycine in prevention of many diseases and disorders including cancer. Dietary supplementation of proper dose of glycine is effectual in treating metabolic disorders in patients with cardiovascular diseases, several inflammatory diseases, obesity, cancers, and diabetes. Glycine also has the property to enhance the quality of sleep and neurological functions. In this review we will focus on the metabolism of glycine in humans and animals and the recent findings and advances about the beneficial effects and protection of glycine in different disease states.

Metabolic Signature of Remote Ischemic Preconditioning Involving a Cocktail of Amino Acids and Biogenic Amines

BACKGROUND

Remote ischemic preconditioning (RIPC) is an attractive therapeutic procedure for protecting the heart against ischemia/reperfusion injury. Despite evidence of humoral mediators transported through the circulation playing a critical role, their actual identities so far remain unknown. We sought to identify plasmatic RIPC-induced metabolites that may play a role.

METHODS AND RESULTS

Rat plasma samples from RIPC and control groups were analyzed using a targeted metabolomic approach aimed at measuring 188 metabolites. Principal component analysis and orthogonal partial least-squares discriminant analysis were used to identify the metabolites that discriminated between groups. Plasma samples from 50 patients subjected to RIPC were secondarily explored to confirm the results obtained in rats. Finally, a combination of the metabolites that were significantly increased in both rat and human plasma was injected prior to myocardial ischemia/reperfusion in rats. In the rat samples, 124 molecules were accurately quantified. Six metabolites (ornithine, glycine, kynurenine, spermine, carnosine, and serotonin) were the most significant variables for marked differentiation between the RIPC and control groups. In human plasma, analysis confirmed ornithine decrease and kynurenine and glycine increase following RIPC. Injection of the glycine and kynurenine alone or in combination replicated the protective effects of RIPC seen in rats.

CONCLUSIONS

We have hereby reported significant variations in a cocktail of amino acids and biogenic amines after remote ischemic preconditioning in both rat and human plasma.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT01390129.

The role of glycine in regulated cell death

The cytoprotective effects of glycine against cell death have been recognized for over 28 years. They are expressed in multiple cell types and injury settings that lead to necrosis, but are still not widely appreciated or considered in the conceptualization of cell death pathways. In this paper, we review the available data on the expression of this phenomenon, its relationship to major pathophysiologic pathways that lead to cell death and immunomodulatory effects, the hypothesis that it involves suppression by glycine of the development of a hydrophilic death channel of molecular dimensions in the plasma membrane, and evidence for its impact on disease processes in vivo.

Role of connexin 43 in cardiovascular diseases

Gap junctions (GJs) channels provide the basis for intercellular communication in the cardiovascular system for maintenance of the normal cardiac rhythm, regulation of vascular tone and endothelial function as well as metabolic interchange between the cells. They allow the transfer of small molecules and may enable slow calcium wave spreading, transfer of "death" or of "survival" signals. In the cardiomyocytes the most abundant isoform is Connexin 43 (Cx43). Alterations in Cx43 expression and distribution were observed in myocardium disease; i.e. in hypertrophic cardiomyopathy, heart failure and ischemia. Recent reports suggest the presence of Cx43 in the mitochondria as well, at least in the inner mitochondrial membrane, where it plays a central role in ischemic preconditioning. In this review, the current knowledge on the relationship between the remodeling of cardiac gap junctions and cardiac diseases are summarized.

Metabolomic approach to profile functional and metabolic changes in heart failure

Background

Heart failure (HF) is characterized by a series of adaptive changes in energy metabolism. The use of metabolomics enables the parallel assessment of a wide range of metabolites. In this study, we appraised whether metabolic changes correlate with HF severity, assessed as an impairment of functional contractility, and attempted to interpret the role of metabolic changes in determining systolic dysfunction.

Methods

A 500 MHz proton nuclear magnetic resonance (¹H-NMR)-based analysis was performed on blood samples from three groups of individuals: 9 control subjects (Group A), 9 HF patients with mild to moderate impairment of left ventricle ejection fraction (LVEF: 41.9 ± 4.0 %; Group B), and 15 HF patients with severe LVEF impairment (25.3 ± 10.3 %; Group C). In order to create a descriptive model of HF, a supervised orthogonal projection on latent structures discriminant analysis (OPLS-DA) was applied using speckle tracking-derived longitudinal strain rate as the Y-variable in the multivariate analysis.

Results

OPLS-DA identified three metabolic clusters related to the studied groups achieving good values for R² [R²(X) = 0.64; R²(Y) = 0.59] and Q² (0.39). The most important metabolites implicated in the clustering were 2-hydroxybutyrate, glycine, methylmalonate, and myo-inositol.

Conclusions

The results demonstrate the suitability of metabolomics in combination with functional evaluation techniques in HF staging. This innovative tool should facilitate investigation of perturbed metabolic pathways in HF and their correlation with the impairment of myocardial function.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-015-0661-3) contains supplementary material, which is available to authorized users.

Evaluation of toxicological effects induced by tributyltin in clam Ruditapes decussatus using high-resolution magic angle spinning nuclear magnetic resonance spectroscopy: Study of metabolic responses in heart tissue and detection of a novel metabolite

Tributyltin (TBT) is a highly toxic pollutant present in many aquatic ecosystems. Its toxicity in mollusks strongly affects their performance and survival. The main purpose of this study was to elucidate the mechanisms of TBT toxicity in clam Ruditapes decussatus by evaluating the metabolic responses of heart tissues, using high-resolution magic angle-spinning nuclear magnetic resonance (HRMAS NMR), after exposure to TBT (10^-9, 10^-6 and 10^-4 M) during 24 h and 72 h. Results show that responses of clam heart tissue to TBT exposure are not dose dependent. Metabolic profile analyses indicated that TBT 10^-6 M, contrary to the two other doses tested, led to a significant depletion of taurine and betaine. Glycine levels decreased in all clam groups treated with the organotin. It is suggested that TBT abolished the cytoprotective effect of taurine, betaine and glycine thereby inducing cardiomyopathie. Moreover, results also showed that TBT induced increase in the level of alanine and succinate suggesting the occurrence of anaerobiosis particularly in clam group exposed to the highest dose of TBT. Taken together, these results demonstrate that TBT is a potential toxin with a variety of deleterious effects on clam and this organotin may affect different pathways depending to the used dose. The main finding of this study was the appearance of an original metabolite after TBT treatment likely N-glycine-N'-alanine. It is the first time that this molecule has been identified as a natural compound. Its exact role is unknown and remains to be elucidated. We suppose that its formation could play an important role in clam defense response by attenuating Ca²⁺ dependent cell death induced by TBT. Therefore this compound could be a promising biomarker for TBT exposure.

Protection against myocardial ischemia-reperfusion injury in clinical practice

Even when reperfusion therapy is applied as early as possible, survival and quality of life are compromised in a considerable number of patients with ST-segment elevation acute myocardial infarction. Some cell death following transient coronary occlusion occurs during reperfusion, due to poor handling of calcium in the sarcoplasmic reticulum-mitochondria system, calpain activation, oxidative stress, and mitochondrial failure, all promoted by rapid normalization of intracellular pH. Various clinical trials have shown that infarct size can be limited by nonpharmacological strategies--such as ischemic postconditioning and remote ischemic conditioning--or by drugs--such as cyclosporine, insulin, glucagon-like peptide-1 agonists, beta-blockers, or stimulation of cyclic guanosine monophosphate synthesis. However, some clinical studies have yielded negative results, largely due to a lack of consistent preclinical data or a poor design, especially delayed administration. Large-scale clinical trials are therefore necessary, particularly those with primary clinical variables and combined therapies that consider age, sex, and comorbidities, to convert protection against reperfusion injury into a standard treatment for patients with ST-segment elevation acute myocardial infarction.

Effects of glycine supplementation on myocardial damage and cardiac function after severe burn

BACKGROUND

Glycine has been shown to participate in protection from hypoxia/reoxygenation injury. However, the cardioprotective effect of glycine after burn remains unclear. This study aimed to explore the protective effect of glycine on myocardial damage in severely burned rats.

METHODS

Seventy-two Wistar rats were randomly divided into three groups: normal controls (C), burned controls (B), and glycine-treated (G). Groups B and G were given a 30% total body surface area full-thickness burn. Group G was administered 1.5 g/(kg d) glycine and group B was given the same dose of alanine via intragastric administration for 3d. Serum creatine kinase (CK), lactate dehydrogenase (LDH), aspartate transaminase (AST), and blood lactate, as well as myocardial ATP and glutathione (GSH) content, were measured. Cardiac contractile function and histopathological changes were analyzed at 12, 24, 48, and 72 hours.

RESULTS

Serum CK, LDH, AST, and blood lactate increased, while myocardial ATP and GSH content decreased in both burned groups. Compared with group B, the levels of CK, LDH, and AST significantly decreased, whereas blood lactate as well as myocardial ATP and GSH content increased in group G. Moreover, cardiac contractile function inhibition and myocardial histopathological damage in group G significantly decreased compared with group B.

CONCLUSION

Myocardial histological structure and function were damaged significantly after burn. Glycine is beneficial to myocardial preservation by improving cardiomyocyte energy metabolism and increasing ATP and GSH abundance.

Glycine, a simple physiological compound protecting by yet puzzling mechanism(s) against ischaemia-reperfusion injury: current knowledge

Ischaemia is amongst the leading causes of death. Despite this importance, there are only a few therapeutic approaches to protect from ischaemia-reperfusion injury (IRI). In experimental studies, the amino acid glycine effectively protected from IRI. In the prevention of IRI by glycine in cells and isolated perfused or cold-stored organs (tissues), direct cytoprotection plays a crucial role, most likely by prevention of the formation of pathological plasma membrane pores. Under in vivo conditions, the mechanism of protection by glycine is less clear, partly due to the physiological presence of the amino acid. Here, inhibition of the inflammatory response in the injured tissue is considered to contribute decisively to the glycine-induced reduction of IRI. However, attenuation of IRI recently achieved in experimental animals by low-dose glycine treatment regimens suggests additional/other (unknown) protective mechanisms. Despite the convincing experimental evidence and the large therapeutic width of glycine, there are only a few clinical trials on the protection from IRI by glycine with ambivalent results. Thus, both the mechanism(s) behind the protection of glycine against IRI in vivo and its true clinical potential remain to be addressed in future experimental studies/clinical trials.

Glycine attenuates myocardial ischemia-reperfusion injury by inhibiting myocardial apoptosis in rats

Glycine is a well-documented cytoprotective agent. However, whether it has a protective effect against myocardial ischemia-reperfusion injury in vivo is still unknown. By using an open-chest anesthetized rat model, we found that glycine reduced the infarct size by 21% in ischemia-reperfusion injury rats compared with that in the vehicle-treated MI/R rats. The left ventricular ejection fraction and fractional shortening were increased by 19.11% and 30.98%, respectively, in glycine-treated rats. The plasma creatine kinase levels in ischemia-reperfusion injury rats decreased following glycine treatment. Importantly, administration of glycine significantly inhibited apoptosis in post-ischemia-reperfusion myocardium, which was accompanied by suppression of phosphorylated p38 mitogen-activated protein kinase and c-Jun NH2-terminal kinase, as well as the Fas ligand. These results suggest that glycine attenuates myocardial ischemia-reperfusion injury in vivo by inhibiting cardiomyocytes apoptosis.

Cardioprotection from ischemia/reperfusion injury: basic and translational research

Because ischemic heart diseases (IHDs) are a major cause of mortality and heart failure, novel therapeutic approaches are expected to improve the clinical outcomes of patients with IHDs such as acute myocardial infarction and ischemic heart failure. Brief episodes of nonlethal ischemia and reperfusion before sustained ischemia or at the onset of reperfusion can reduce ischemia-reperfusion injury. These ischemic conditioning phenomena are termed "ischemic preconditioning" and "ischemic postconditioning", respectively. Furthermore, brief episodes of nonlethal ischemia and reperfusion applied to the organ or tissue distal to the heart reduce myocardial infarct size, known as "remote ischemic conditioning". The cardioprotection afforded by these ischemic conditionings can be used to treat patients with acute myocardial infarction or cardiac operations. Extensive research has determined that autacoids (eg, adenosine, bradykinin opioid) and cytokines, their respective receptors, kinase signaling pathways and mitochondrial modulation are involved in ischemic conditioning. Modification of these factors by pharmacological agents mimics the cardioprotection by ischemic conditioning and provides a novel therapeutic intervention for IHDs. Here, the potential mechanisms of ischemic conditioning and its "proof-of-concept" translational studies are reviewed. In the near future, large, multicenter, randomized, placebo-controlled, clinical trials will be required to determine whether pharmacological and ischemic conditioning can improve the clinical outcomes of patients with IHDs.

Calcium-mediated cell death during myocardial reperfusion

Reperfusion may induce additional cell death in patients with acute myocardial infarction receiving primary angioplasty or thrombolysis. Altered intracellular Ca(2+) handling was initially considered an essential mechanism of reperfusion-induced cardiomyocyte death. However, more recent studies have demonstrated the importance of Ca(2+)-independent mechanisms that converge on mitochondrial permeability transition (MPT) and are shared by cardiomyocytes and other cell types. This article analyses the importance of Ca(2+)-dependent cell death in light of these new observations. Altered Ca(2+) handling includes increased cytosolic Ca(2+) levels, leading to activation of calpain-mediated proteolysis and sarcoplasmic reticulum-driven oscillations; this can induce hypercontracture, but also MPT due to the privileged Ca(2+) transfer between sarcoplasmic reticulum and mitochondria through cytosolic Ca(2+) microdomains. In the opposite direction, permeability transition can worsen altered Ca(2+) handling and favour hypercontracture. Ca(2+) appears to play an important role in cell death during the initial minutes of reperfusion, particularly after brief periods of ischaemia. Developing effective and safe treatments to prevent Ca(2+)-mediated cardiomyocyte death in patients with transient ischaemia, by targeting Ca(2+) influx, intracellular Ca(2+) handling, or Ca(2+)-induced cell death effectors, is an unmet challenge with important therapeutic implications and large potential clinical impact.

Glycine preconditioning to ameliorate pulmonary ischemia reperfusion injury in rats

This study examines the impact of glycine (Gly) preconditioning on ischemia reperfusion (IR)-induced pulmonary mitochondrial injury to research the previously, in pig lungs, demonstrated Gly-dependent amelioration of pulmonary IR injury. IR injury was induced in rat lungs by 30 min pulmonary hilum clamping followed by 60 min reperfusion time. Rats were subjected to controls, shams and two study groups (IR30/60, Gly-IR30/60) receiving 37.5 mg Gly i.v. or not before IR induction. The wet/dry-weight ratio, mitochondria viability (MV), membrane integrity (MI), respiratory chain complex (RCC) activities, mitochondrial membrane potential (ΔΨm) and cytochrome C (Cyt C) content were analysed. In IR30/60, RCC and MV were impaired; Cyt C loss and MI combined with matrix metalloproteinase-9 (MMP-9) activation and ΔΨm alteration were observed when compared with controls. In Gly-IR30/60, complex II function and mitochondrial viability were protected during IR, and MMP-9 activation combined with tissue-water content accumulation and ΔΨm alteration were ameliorated. Cyt C loss, mitochondrial membranes damage, tissue GSH oxidation or neutrophil sequestration was not extenuated in Gly-IR30/60. Gly ameliorates IR-associated mitochondrial dysfunction and decay of viability and normalizes ΔΨm but does not protect from Cyt C liberation and mitochondrial membrane damage. Our data suggest that the previously described effect of Gly preconditioning results at least partially from mitochondrial protection. A dose-finding study is necessary to improve results of Gly preconditioning.

Contribution of delayed intracellular pH recovery to ischemic postconditioning protection

Ischemic postconditioning (PoCo) has been proven to be a feasible approach to attenuate reperfusion injury and enhance myocardial salvage in patients with acute myocardial infarction, but its mechanisms have not been completely elucidated yet. Recent studies demonstrate that PoCo may delay the recovery of intracellular pH during initial reperfusion, and that its ability to limit infarct size critically depends on this effect. Prolongation of postischemic intracellular acidosis inhibits hypercontracture, mitochondrial permeability transition, calpain-mediated proteolysis, and gap junction-mediated spread of injury during the first minutes of reflow. This role of prolonged acidosis does not exclude the participation of other pathways in PoCo-induced cardioprotection. On the contrary, it may allow these pathways to act by preventing immediate reperfusion-induced cell death. Moreover, the existence of interactions between intracellular acidosis and endogenous protection signaling cannot be excluded and needs to be investigated. The role of prolonged acidosis in PoCo cardioprotection has important implications in the design of optimal PoCo protocols and in the translation of cardioprotective strategies to patients with on-going myocardial infarction receiving coronary reperfusion.

Mitochondria and GSK-3beta in cardioprotection against ischemia/reperfusion injury

The mitochondrion is a powerhouse of the cell, a platform of cell signaling and decision-maker of cell death, including death by ischemia/reperfusion. Ischemia shuts off ATP production by mitochondria, and cell viability is compromised by energy deficiency and build-up of cytotoxic metabolites during ischemia. Furthermore, the mitochondrial permeability transition pore (mPTP) is primed by ischemia to open upon reperfusion, leading to reperfusion-induced cell necrosis. mPTP opening can be suppressed by ischemic preconditioning (IPC) and other interventions that induce phosphorylation of GSK-3beta. Activation of the mitochondrial ATP-sensitive K(+) channel (mK(ATP) channel) is an important signaling step in a trigger phase of IPC, which ultimately enhances GSK-3beta phosphorylation upon reperfusion, and this channel functions as a mediator of cytoprotection as well. The mitochondrial Ca(2+)-activated K(+) channel appears to play roles similar to those of the mK(ATP) channel, though regulatory mechanisms of the channels are different. Phosphorylated GSK-3beta inhibits mPTP opening presumably by multiple mechanisms, including preservation of hexokinase II in mPTP complex, prevention of interaction of cyclophilin-D with adenine nucleotide translocase, inhibition of p53 activation and attenuation of ATP hydrolysis during ischemia. However, cytoprotective signaling pathways to GSK-3beta phosphorylation and other mPTP regulatory factors are modified by co-morbidities, including type 2 diabetes, and such modification makes the myocardium refractory to IPC and other cardioprotective agents. Regulatory mechanisms of mPTP, and their alterations by morbidities frequently associated with ischemic heart disease need to be further characterized for translation of mitochondrial and mPTP biology to the clinical arena.

Lethal myocardial reperfusion injury: a necessary evil?

Despite being the most effective means of limiting infarct size, coronary reperfusion comes at a price and induces additional damage to the myocardium. Lethal reperfusion injury (death of myocytes that were viable at the time of reperfusion) is an increasingly acknowledged phenomenon. There are many interconnected mechanisms involved in this type of cell death. Calcium overload (generating myocyte hypercontracture), rapid recovery of physiological pH, neutrophil infiltration of the ischemic area, opening of the mitochondrial permeability-transition-pore (PTP), and apoptotic cell death are among the more important mechanisms involved in reperfusion injury. The activation of a group of proteins called reperfusion injury salvage kinases (RISK) pathway confers protection against reperfusion injury, mainly by inhibiting the opening of the mitochondrial PTP. Many interventions have been tested in human trials triggered by encouraging animal studies. In the present review we will explain in detail the main mechanism involved in reperfusion injury, as well as the various approaches (pre-clinical and human trials) performed targeting these mechanisms. Currently, no intervention has been consistently shown to reduce reperfusion injury in large randomized multicenter trials, but the research in this field is intense and the future is highly promising.

Glycine pretreatment ameliorates liver injury after partial hepatectomy in the rat

BACKGROUND

Living donor liver transplantation subjects the donor to a major hepatectomy. Pharmacological or nutritive protection of the liver during the procedure is desirable to ensure that the remnant is able to maintain sufficient function. The aim of our study was to analyze the effects of pretreatments with alpha-tocopherol (vitamin E), the flavonoid silibinin and/or the amino acid L-glycine on the donor in a rat model.

METHODS

Male Wistar rats were pretreated with L-glycine (5% in chow, 5 days), alpha-tocopherol (100 mg/kg body weight by gavage, 3 days) and/or silibinin (100 mg/kg body weight, i.p., 5 days). Thereafter, 90% partial hepatectomy was performed without portal vein clamping.

RESULTS

Glycine pretreatment markedly decreased transaminase release (AST, 12 hr: glycine 1292 +/- 192 U/L, control 2311 +/- 556 U/L, p < .05; ALT, 12 hr: glycine 1013 +/- 278 U/L, control 2038 +/- 500 U/L, p < .05), serum ALP activity and serum bilirubin levels (p < .05). Prothrombin time was reduced, and histologically, liver injury was also decreased in the glycine group. Silibinin pretreatment was less advantageous and pretreatment with alpha-tocopherol at this very high dose showed some adverse effects. Combined, i.e., triple pretreatment was less advantageous than glycine alone. Liver resection induced HIF-1alpha accumulation and HIF-1alpha accumulation was also decreased by glycine pretreatment.

CONCLUSION

The decrease of liver injury and improvement of liver function after pretreatment with glycine suggests that glycine pretreatment might be beneficial for living liver donors as well as for patients subjected to partial hepatectomy for other reasons.

Postconditioning and protection from reperfusion injury: where do we stand? Position paper from the Working Group of Cellular Biology of the Heart of the European Society of Cardiology

Ischaemic postconditioning (brief periods of ischaemia alternating with brief periods of reflow applied at the onset of reperfusion following sustained ischaemia) effectively reduces myocardial infarct size in all species tested so far, including humans. Ischaemic postconditioning is a simple and safe manoeuvre, but because reperfusion injury is initiated within minutes of reflow, postconditioning must be applied at the onset of reperfusion. The mechanisms of protection by postconditioning include: formation and release of several autacoids and cytokines; maintained acidosis during early reperfusion; activation of protein kinases; preservation of mitochondrial function, most strikingly the attenuation of opening of the mitochondrial permeability transition pore (MPTP). Exogenous recruitment of some of the identified signalling steps can induce cardioprotection when applied at the time of reperfusion in animal experiments, but more recently cardioprotection was also observed in a proof-of-concept clinical trial. Indeed, studies in patients with an acute myocardial infarction showed a reduction of infarct size and improved left ventricular function when they underwent ischaemic postconditioning or pharmacological inhibition of MPTP opening during interventional reperfusion. Further animal studies and large-scale human studies are needed to determine whether patients with different co-morbidities and co-medications respond equally to protection by postconditioning. Also, our understanding of the underlying mechanisms must be improved to develop new therapeutic strategies to be applied at reperfusion with the ultimate aim of limiting the burden of ischaemic heart disease and potentially providing protection for other organs at risk of reperfusion injury, such as brain and kidney.

Glycine and glycine receptor signalling in non-neuronal cells

Glycine is an inhibitory neurotransmitter acting mainly in the caudal part of the central nervous system. Besides this neurotransmitter function, glycine has cytoprotective and modulatory effects in different non-neuronal cell types. Modulatory effects were mainly described in immune cells, endothelial cells and macroglial cells, where glycine modulates proliferation, differentiation, migration and cytokine production. Activation of glycine receptors (GlyRs) causes membrane potential changes that in turn modulate calcium flux and downstream effects in these cells. Cytoprotective effects were mainly described in renal cells, hepatocytes and endothelial cells, where glycine protects cells from ischemic cell death. In these cell types, glycine has been suggested to stabilize porous defects that develop in the plasma membranes of ischemic cells, leading to leakage of macromolecules and subsequent cell death. Although there is some evidence linking these effects to the activation of GlyRs, they seem to operate in an entirely different mode from classical neuronal subtypes.

Glycine inhibits the LPS-induced increase in cytosolic Ca2+ concentration and TNFalpha production in cardiomyocytes by activating a glycine receptor

AIM

Previous studies have demonstrated that glycine (GLY) markedly reduces lipopolysaccharide (LPS)-induced myocardial injury.However, the mechanism of this effect is still unclear. The present study investigated the effect of GLY on cytosolic calcium concentration([Ca2+]c) and tumor necrosis factor-alpha (TNFalpha) production in cardiomyocytes exposed to LPS, as well as whether the glycine-gated chloride channel is involved in this process.

METHODS

Neonatal rat cardiomyocytes were isolated, and the [Ca2+]c and TNFalpha levels were determined by using Fura-2 and a Quantikine enzyme-linked immunosorbent assay, respectively. The distribution of the GLY receptor and GLY-induced currents in cardiomyocytes were also investigated using immunocytochemistry and the whole-cell patch-clamp technique, respectively.

RESULTS

LPS at concentrations ranging from 10 ng/mL to 100 microg/mL significantly stimulated TNFalpha production. GLY did not inhibit TNFalpha production induced by LPS at concentrations below 10 ng/mL but did significantly decrease TNFalpha release stimulated by 100 microg/mL LPS and prevented an LPS-induced increase in [Ca2+]c, which was reversed by strychnine, a glycine receptor antagonist. GLY did not block the isoproterenol-induced increase in [Ca2+]c, but did prevent the potassium chloride-induced increase in [Ca2+]c in cardiomyocytes.Strychnine reversed the inhibition of the KCl-stimulated elevation in [Ca2+]c by GLY. In chloride-free buffer, GLY had no effect on the dipotassium hydrogen phosphate-induced increase in [Ca2+]c. Furthermore, GLY receptor alpha1 and beta subunit-immunoreactive spots were observed in cardiomyocytes, and GLY-evoked currents were blocked by strychnine.

CONCLUSION

Cardiomyocytes possess the glycine-gated chloride channel, through which GLY prevents the increase in [Ca2+]c and inhibits the TNFalpha production induced by LPS at high doses in neonatal rat cardiomyocytes.

Effect of intracellular lipid droplets on cytosolic Ca2+ and cell death during ischaemia-reperfusion injury in cardiomyocytes

Lipid droplets (LD) consist of accumulations of triacylglycerols and have been proposed to be markers of ischaemic but viable tissue. Previous studies have described the presence of LD in myocardium surviving an acute coronary occlusion. We investigated whether LD may be protective against cell death secondary to ischaemia-reperfusion injury. The addition of oleate-bovine serum albumin complex to freshly isolated adult rat cardiomyocytes or to HL-1 cells resulted in the accumulation of intracellular LD detectable by fluorescence microscopy, flow cytometry and (1)H-nuclear magnetic resonance spectroscopy. Simulated ischaemia-reperfusion of HL-1 cells (respiratory inhibition at pH 6.4 followed by 30 min of reperfusion) resulted in significant cell death (29.7+/-2.6% of total lactate dehydrogenase release). However, cell death was significantly attenuated in cells containing LD (40% reduction in LDH release compared with control cells, P=0.02). The magnitude of LD accumulation was inversely correlated (r(2)=0.68, P=0.0003) with cell death. The protection associated with intracellular LD was not a direct effect of the fatty acids used to induce their formation, because oleate added 30 min before ischaemia, during ischaemia or during reperfusion did not form LD and did not protect against cell death. Increasing the concentration of free oleate during reperfusion progressively decreased the protection afforded by LD. HL-1 cells labelled with fluo-4, a Ca(2+)-sensitive fluorochrome, fluorescence within LD areas increased more throughout simulated ischaemia and reperfusion than in the cytosolic LD-free areas of the same cells. As a consequence, cells with LD showed less cytosolic Ca(2+) overload than control cells. These results suggest that LD exert a protective effect during ischaemia-reperfusion by sequestering free fatty acids and Ca(2+).

Acidic reoxygenation protects against endothelial dysfunction in rat aortic rings submitted to simulated ischemia

Ischemia-reperfusion causes endothelial dysfunction. Prolongation of acidosis during initial cardiac reperfusion limits infarct size in animal models, but the effects of acidic reperfusion on vascular function are unknown. The present work analyzes the effects of acidic reoxygenation on vascular responses to different agonists in rat aortic rings. Arterial rings obtained from Sprague-Dawley rat aorta were placed in organ baths containing a Krebs solution oxygenated at 37 degrees C (pH 7.4). After equilibration (30 mN, 1 h), the effects of acidosis (pH 6.4) on aortic responses to acetylcholine and norepinephrine were initially assessed under normoxic conditions. Thereafter, the effects of acidosis during hypoxia (1 h) or reoxygenation on aortic responses to acetylcholine, norepinephrine, or sodium nitroprusside were analyzed and compared with those observed in control rings. Acidosis did not modify aortic responses to acetylcholine or adrenaline during normoxia. In contrast, rings submitted to hypoxia and reoxygenated at pH 7.4 showed a reduction in vasodilator responses to acetylcholine and in contractions to norepinephrine with no change in responses to sodium nitroprusside. Reoxygenation at pH 6.4 did not modify the depressed response to norepinephrine but enhanced the recovery of acetylcholine-induced vasorelaxation. Cumulative concentration-response curves to acetylcholine showed an increased responsiveness to this drug in rings reoxygenated at a low pH. This functional improvement was associated with the preservation of aortic cGMP content after stimulation of reoxygenated rings with acetylcholine. In conclusion, acidic reoxygenation preserves endothelial function in arterial rings submitted to simulated ischemia, likely through the preservation of cGMP signaling.