Label-free quantitative SWATH-MS proteomic analysis of adult myocardial slices in vitro after biomimetic electromechanical stimulation

A special in vitro model maintained with ultrathin cardiac slices with a preserved architecture, multi-cellularity, and physiology of the heart tissue was used. In our experiments, we performed label-free quantitative SWATH-MS proteomic analysis of the adult myocardial slices in vitro after biomimetic electromechanical stimulation. Rat myocardial slices were stretched to sarcomere lengths (SL) within the physiological range of 1.8–2.2 μm. Electromechanically stimulated slices were compared with slices cultured without electromechanical stimulation (unloaded and nonstimulated-TW) on a liquid–air interface and with fresh myocardial slices (0 h-C). Quantitative (relative) proteomic analyses were performed using a label-free SWATH-MS technique on a high-resolution microLC-MS/MS TripleTOF 5600+ system (SCIEX). The acquired MS/MS spectra from the DDA LC–MS/MS analyses of the rat heart samples were searched against the UniProt Rattus norvegicus database (version of 15.05.2018) using the Paragon algorithm incorporated into ProteinPilot 4.5 (SCIEX) software. The highest number of differential proteins was observed in the TW group—121 when compared to the C group. In the 1.8 and 2.2 groups, 79 and 52 proteins present at a significantly different concentration from the control samples were found, respectively. A substantial fraction of these proteins were common for two or more comparisons, resulting in a list of 169 significant proteins for at least one of the comparisons. This study found the most prominent changes in the proteomic pattern related to mitochondrial respiration, energy metabolism, and muscle contraction in the slices that were stretched and fresh myocardial slices cultured without electromechanical stimulation.

Impaired L-arginine metabolism marks endothelial dysfunction in CD73-deficient mice

Changes in the ecto-5′-nucleotidase activity—an extracellular nucleotide catabolic enzyme may lead to the inflammation and endothelial dysfunction. We investigated the effect of CD73 deletion on the endothelial function and l-arginine metabolism in various age groups of mice. 1-,3-,6-, and 12-month-old, male C57BL/6 J wild type (WT) and C57BL/6 J CD73−/− (CD73−/−) mice were used. Blood samples were used for the analysis of adenine nucleotide concentrations. Serum samples were analyzed for the concentration of amino acids, Interleukin 6 (IL-6), Intercellular Adhesion Molecule 1 (ICAM-1), Vascular Cell Adhesion Molecule 1 (VCAM-1), and endothelial nitric oxide synthase (eNOS) level. Serum and aortic nitrate/nitrite, as well as aortic arginase and NOS activity in endothelial cells (EC) were evaluated. CD73 deletion led to age-dependent increase in IL-6, ICAM-1, and VCAM-1 concentration compared to WT. All CD73−/− mice age groups were characterized by reduced l-Arginine concentration and eNOS level. Significantly lower NOS activity was noticed in EC isolated from CD73−/− mice lungs in comparison to EC isolated from WT lungs. The l-Arginine/ADMA ratio in the CD73−/− decreased in age-dependent manner in comparison to WT. The nitrate/nitrite ratio was reduced in serum and in aortas of 6-month-old CD73−/− mice as compared to WT. The ornithine/arginine and ornithine/citrulline ratios were increased in CD73−/− compared to controls. Blood (erythrocyte) Adenosine-5′-triphosphate and Adenosine-5′-diphosphate levels were reduced in favor to higher blood Adenosine-5′-monophosphate concentration in CD73−/− mice in comparison to WT. The CD73 deletion leads to the development of age-dependent endothelial dysfunction in mice, associated with impaired l-arginine metabolism. CD73 activity seems to protect endothelium.

Nicotinamide metabolism alterations in bladder cancer: Preliminary studies

OBJECTIVES

Cancer is one of the main cause of death in Western countries. Inflammation plays an important role in the pathogenesis of cancer. Nicotinamide (NA) - known for its anti-inflammatory properties - participates in the processes related to the cell cycle regulation and DNA repair, which are relevant in cancer development. This study aimed to investigate the nicotinamide metabolism alterations in bladder cancer.

METHODS

Blood and plasma samples of patients with bladder cancer were collected. Blood pyridine and adenine nucleotides concentration were measured using high performance liquid chromatography (HPLC). Plasma nicotinamide metabolites concentration were determined using high performance liquid chromatography - mass spectrometry (LC/MS).

RESULTS

Our results indicated that the development of bladder cancer caused significant decrease in the concentration of N-methylnicotinamide (MetNA) (0.07 ± 0.02 vs 0.1 ± 0.03 µmol/l) and an increase in the concentration of N-methyl-2-pyridone-5-carboxamide (Met2PY) - one of the final nicotinamide metabolites: (1.1 ± 0.15 vs 0.7 ± 0.07 µmol/l) in comparison to the control. The association between the stage of cancer and the increase in both, Met2PY and Met4PY levels was observed. Blood ATP and NAD levels were significantly decreased in bladder cancer patients as compared to the control (970.8 ± 77.84 vs 1165.00 ± 57.76 µmol/l; 45.86 ± 2.98 vs 53.06 ± 2.28 µmol/l respectively).

CONCLUSIONS

Bladder cancer development caused substantial changes in nicotinamide metabolism, such as decreased plasma MetNA and increased Met2PY concentration. Analysis of the nicotinamide and its metabolites concentrations - as new biomarkers - may allow to track the course of pathological processes in cancer.

Activities of purine converting enzymes in heart, liver and kidney mice LDLR-/- and Apo E-/

Nucleotide metabolism plays a major role in a number of vital cellular processes such as energetics. This, in turn, is important in pathologies such as atherosclerosis. Three month old atherosclerotic mice with knock outs for LDLR and apolipoprotein E (ApoE) were used for the experiments. Activities of AMP-deaminase (AMPD), ecto5'-nucleotidase (e5NT), adenosine deaminase (ADA), purine nucleoside phosphorylase (PNP) were measured in heart, liver and kidney cortex and medulla by analysing conversion of substrates into products using HPLC. The activity of ecto5'-nucleotidase differ in hearts of LDLR^-/- and ApoE^-/- mice with no differences in ADA and AMPD activity. We noticed highest activity of e5NT in kidney medulla of the models. This model of atherosclerosis characterize with an inhibition of enzyme responsible for production of protective adenosine in heart but not in other organs and different metabolism of nucleotides in kidney medulla.

Deletion of CD73 in mice leads to aortic valve dysfunction

Aortic stenosis is known to involve inflammation and thrombosis. Changes in activity of extracellular enzyme - ecto-5'-nucleotidase (referred also as CD73) can alter inflammatory and thrombotic responses. This study aimed to evaluate the effect of CD73 deletion in mice on development of aortic valve dysfunction and to compare it to the effect of high-fat diet. Four groups of mice (normal-diet Wild Type (WT), high-fat diet WT, normal diet CD73-/-, high-fat diet CD73-/-) were maintained for 15weeks followed by echocardiographic analysis of aortic valve function, measurement of aortic surface activities of nucleotide catabolism enzymes as well as alkaline phosphatase activity, mineral composition and histology of aortic valve leaflets. CD73-/- knock out led to an increase in peak aortic flow (1.06±0.26m/s) compared to WT (0.79±0.26m/s) indicating obstruction. Highest values of peak aortic flow (1.26±0.31m/s) were observed in high-fat diet CD73-/- mice. Histological analysis showed morphological changes in CD73-/- including thickening and accumulation of dark deposits, proved to be melanin. Concentrations of Ca²⁺, Mg²⁺ and PO₄^3- in valve leaflets were elevated in CD73-/- mice. Alkaline phosphatase (ALP) activity was enhanced after ATP treatment and reduced after adenosine treatment in aortas incubated in osteogenic medium. AMP hydrolysis in CD73-/- was below 10% of WT. Activity of ecto-adenosine deaminase (eADA), responsible for adenosine deamination, in the CD73-/- was 40% lower when compared to WT. Deletion of CD73 in mice leads to aortic valve dysfunction similar to that induced by high-fat diet suggesting important role of this surface protein in maintaining heart valve integrity.

AMP-regulated protein kinase activity in the hearts of mice treated with low- or high-fat diet measured using novel LC-MS method

AMP-regulated protein kinase (AMPK) is involved in regulation of energy-generating pathways in response to the metabolic needs in different organs including the heart. The activity of AMPK is mainly controlled by AMP concentration that in turn could be affected by nucleotide metabolic pathways. This study aimed to develop a procedure for measurement of AMPK activity together with nucleotide metabolic enzymes and its application for studies of mice treated with high-fat diet. The method developed was based on analysis of conversion of AMARA peptide to pAMARA by partially purified heart homogenate by liquid chromatography/mass spectrometry (LC/MS). Activities of the enzymes of nucleotide metabolism were evaluated by analysis of conversion of substrates into products by HPLC. The method was applied for analysis of hearts of mice fed 12 weeks with low- (LFD) or high-fat diet (HFD). The optimized method for AMPK activity analysis (measured in presence of AMP) revealed change of activity from 0.089 ± 0.035 pmol/min/mg protein in LFD to 0.024 ± 0.002 in HFD. This coincided with increase of adenosine deaminase (ADA) activity from 0.11 ± 0.02 to 0.19 ± 0.06 nmol/mg tissue/min and decrease of AMP-deaminase (AMPD) activity from 1.26 ± 0.35 to 0.56 ± 0.15 nmol/mg tissue/min for LFD and HFD, respectively. We have proven quality of our LC/MS method for analysis of AMPK activity. We observed decrease in AMPK activity in the heart of mice treated with high-fat diet. However, physiological consequences of this change could be modulated by decrease in AMPD activity.

Functional analysis of expression of human ecto-nucleoside triphosphate diphosphohydrolase-1 and/or ecto-5'-nucleotidase in pig endothelial cells

Adenine nucleosides and nucleotides are important signaling molecules involved in control of key mechanisms of xenotransplant rejection. Extracellular pathway that converts ATP and ADP to AMP, and AMP to adenosine mainly mediated by ecto-nucleoside triphosphate diphosphohydrolase 1, (ENTPD1 or CD39) and ecto-5'-nucleotidase (E5NT or CD73) respectively, is considered as important target for xenograft protection. To clarify feasibility of combined expression of human ENTPD1 and E5NT and to study its functional effect we transfected pig endothelial cell line (PIEC) with both genes together. To do this we have produced a dicistronic construct bearing F2A sequence in frame between human E5NT and human ENTPD1 coding sequences. PIEC cells were mock-transfected as transfection control or transfected with plasmids encoding human ENTPD1 or human E5NT. PIEC cells were exposed to 50 μM ATP or 50 μM ADP or 50 μM AMP. Conversion of extracellular substrates into products (ATP/ADP/AMP/adenosine) was measured by HPLC in the media collected at specific time intervals. Following addition of AMP, production of adenosine in the medium of E5NT/ENTPD1- and E5NT- transfected cells increased to 14.2±1.1 and 24.5±3.4 μM respectively while it remained below 1 μM in controls and in ENTPD1-transfected cells. A marked increase of adenosine formation from ADP or ATP was observed only in E5NT/ENTPD1-transfected cells (11.7±0.1 and 5.7±2.2 μM respectively) but not in any other condition studied. This study indicates feasibility and functionality of combined expression of human E5NT and ENTPD1 in pig endothelial cells using F2A sequence bearing construct.

Effect of nitrosative stress on extracellular nucleotide metabolism in endothelial cells

Mechanisms of free radical injury involve chemical modification of proteins, lipid derivatives and nucleic acids and consequent loss of its function. However, specific targets and exact sequence of events has not been fully clarified. We determined whether extracellular enzymes that are involved in adenosine formation such as ecto-5'nucleotidase (e5N) and removal such as extracellular form of adenosine deaminase (eADA) could be affected by peroxynitrite. We used intact cell assay system that involves exposure of cultured HMEC-1 cells to substrates followed by HPLC analysis of conversion of substrates into products. We found that e5N and ADA activities decreased by 20-40% after incubation for 20 or 60 minutes with 30 μM peroxynitrite. Decrease of cellular ATP and NAD was also observed. We conclude that besides other cytotoxic effects modification of extracellular enzymes of nucleotide metabolism could be important target for free radical injury.

Nucleotide metabolic mismatches in mammalian hearts: implications for transplantation

Introduction

Human donor organ shortages have led surgeons and scientists to explore the use of animals as alternative organ sources. Acute thrombovascular rejection (AVR) is the main hurdle in xenotransplantation. Disparities in nucleotide metabolism in the vessels of different species may contribute significantly to the microvascular component of AVR.

Methods

We evaluated the extent of nucleotide metabolism mismatch in selected organs and endothelial cells of different mammals with particular focus on the changes in activity of ecto-5’-nucleotidase (E5’N) elicited by exposure of porcine hearts or endothelial cells to human blood (ex vivo) or human plasma (in vitro).

Results

E5’N activity in the rat heart was significantly higher than in other species. We noted a significant difference (p<0.001) in E5’N activity between human and pig endothelial cell lines. Initial pig aortic endothelial E5’N activity decreased in vitro after a three-hour exposure to human and porcine plasma while remaining constant in controls. Ex vivo perfusion with fresh human blood for four hours resulted in a significant decrease of E5’N activity in both wild type and transgenic pig hearts overexpressing human decay accelerating factor (p<0.001).

Conclusions

This study provides evidence that mismatches in basal mammalian metabolic pathways and humoral immunity interact in a xenogeneic environment. Understanding the role of nucleotide metabolism and signalling in xenotransplantation may identify new targets for genetic modifications and may lead to the development of new therapies extending graft survival.

AMP-activated protein kinase (AMPK)-dependent and -independent pathways regulate hypoxic inhibition of transepithelial Na+ transport across human airway epithelial cells

BACKGROUND AND PURPOSE

Pulmonary transepithelial Na(+) transport is reduced by hypoxia, but in the airway the regulatory mechanisms remain unclear. We investigated the role of AMPK and ROS in the hypoxic regulation of apical amiloride-sensitive Na(+) channels and basolateral Na(+) K(+) ATPase activity.

EXPERIMENTAL APPROACH

H441 human airway epithelial cells were used to examine the effects of hypoxia on Na(+) transport, AMP : ATP ratio and AMPK activity. Lentiviral constructs were used to modify cellular AMPK abundance and activity; pharmacological agents were used to modify cellular ROS.

KEY RESULTS

AMPK was activated by exposure to 3% or 0.2% O(2) for 60 min in cells grown in submerged culture or when fluid (0.1 mL·cm(-2) ) was added to the apical surface of cells grown at the air-liquid interface. Only 0.2% O(2) activated AMPK in cells grown at the air-liquid interface. AMPK activation was associated with elevation of cellular AMP:ATP ratio and activity of the upstream kinase LKB1. Hypoxia inhibited basolateral ouabain-sensitive I(sc) (I(ouabain) ) and apical amiloride-sensitive Na(+) conductance (G(Na+) ). Modification of AMPK activity prevented the effect of hypoxia on I(ouabain) (Na(+) K(+) ATPase) but not apical G(Na+) . Scavenging of superoxide and inhibition of NADPH oxidase prevented the effect of hypoxia on apical G(Na+) (epithelial Na(+) channels).

CONCLUSIONS AND IMPLICATIONS

Hypoxia activates AMPK-dependent and -independent pathways in airway epithelial cells. Importantly, these pathways differentially regulate apical Na(+) channels and basolateral Na(+) K(+) ATPase activity to decrease transepithelial Na(+) transport. Luminal fluid potentiated the effect of hypoxia and activated AMPK, which could have important consequences in lung disease conditions.

Metabolism of 4-pyridone-3-carboxamide-1-β-D-ribonucleoside (4PYR) in rodent tissues and in vivo

Our previous studies identified 4-pyridone-3-carboxamide-1-β-D-ribonucleoside (4PYR) phosphates in human erythrocytes. We demonstrated formation of these nucleotides by phosphorylation of 4PYR and potential toxicity due to disruption of erythrocyte energy balance. This study aimed to evaluate the ability of the other cell types to phosphorylate 4PYR to characterize function and toxicity of these compounds. Homogenates of rat heart, kidneys, and liver were used to study the rate of 4PYR phosphorylation in the presence of ATP. In another experiment, 4PYR was administered into mouse as repeated subcutaneous injections and into rats as intraperitoneal infusion. After 7 days, heart, liver, kidney, lungs, and skeletal muscle were collected, and the concentration of 4PYR nucleotides was evaluated. HPLC was used to measure 4PYR and 4PYR nucleotides in homogenate and specimens from in vivo experiments. 4PYR was rapidly phosphorylated by the liver homogenate (390 ± 27 nmol/min/g wet wt). Significant rates were reported in the heart and kidneys' homogenates: 34.3 ± 4.3 nmol/min/g and 33.2 ± 9.2 nmol/min/g, respectively. Phosphorylation of 4PYR was almost completely inhibited by adenosine kinase inhibitor 5'-iodotubercidin. Administration of 4PYR in vivo resulted in accumulation of 4PYR monophosphate in the liver, heart, skeletal muscle, and lung (20-220 nmol/g dry wt) except kidney (<1 nmol/g). In contrast to erythrocytes, no 4PYR triphosphate formation (<1 nmol/g) was observed in any of the organs studied. We conclude that not only the erythrocytes but also other cell types are capable of phosphorylating 4PYR to form 4PYR monophosphate. Potential toxicity or physiological role of 4PYR in peripheral organs could be considered, but mechanisms will be different from that in erythrocytes.

Protection of mouse heart against hypoxic damage by AMP deaminase inhibition

Clinical observation in patients with heart disease indicates that reduced activity of AMP deaminase could be protective in heart failure and ischemic heart disease. This study evaluated the effect of 3-[2-(3-carboxy-4-bromo-5,6,7,8-tetrahydronaphthyl)ethyl]-3,6,7,8-tetrahydroimidazo [4,5-d][1,3]diazepin-8-ol, an AMP deaminase inhibitor (AMPDI) in the mouse heart subjected to hypoxia. ApoE/LDLR knock-out mice were subjected to reduced oxygen tension in breathing air. AMPDI was infused before hypoxia in the treated group. We observed amelioration of elcetrocardiographic changes during hypoxia in the treated group that are consistent with a protective effect.

Biological efficiency of AMP deaminase inhibitor: 3-[2-(3-carboxy-4-bromo-5,6,7,8-tetrahydronaphthyl)ethyl]-3,6,7,8-tetrahydroimidazo[4,5]-[1,3]diazepin-8-OL

AMP deaminase could be a potential target for treatment of heart disease but experimental evaluation of this concept is difficult due to limited availability of inhibitors with proven efficiency in biological systems. This study evaluated the effect of 3-[2-(3-carboxy-4-bromo-5,6,7,8-tetrahydronaphthyl)ethyl]-3,6,7,8-tetrahydroimidazo [4,5-d][1,3]diazepin-8-ol, an AMP deaminase inhibitor (AMPDI) on the pathways of nucleotide metabolism in perfused rat heart. We show that AMPDI at 0.3 mM concentration effectively inhibits AMP deaminase in this experimental model.

Cardiac muscle AMP-deaminase from a 10-year-old male heterozygous for the AMPD1 C34T mutation

A C34T mutation in the AMPD1 gene is proposed to cause local or systemic augmentations in blood adenosine level and improvement of prognoses in heart diseases like congestive heart failure or heart ischemic disease. This study examines some physico-chemical properties of AMP-deaminase isolated from cardiac muscle of a 10-year-old boy heterozygote for this mutation.

Cytoprotective effects of nicotinamide derivatives in endothelial cells

Following discovery of NAD(+)-dependent reactions that control gene expression, cytoprotection, and longevity, there has been a renewed therapeutic interest in precursors, such as nicotinamide and its derivatives. We tested 20 analogues of nicotinamide for their ability to protect endothelial cells from peroxynitrite stress and their effect on poly (ADP-ribose) polymerase (PARP) activity. Several nicotinamide derivatives protected endothelial cells from peroxynitrite-induced depletion of cellular NAD(+) and ATP concentrations, but only some of these compounds inhibited PARP. We conclude that some nicotinamide derivatives provide protection of endothelial cells against peroxynitrite-induced injury independent of inhibition of PARP activity. Preservation of the NAD(+) pool was a common effect of these compounds.

Modulation of AMP deaminase in rat hearts subjected to ischemia and reperfusion by purine riboside

Changes in AMP deaminase (AMPD) activity influence heart function and progression of heart disease, but the underlying mechanism is unknown. We evaluated the effect of purine riboside (Purr) on the activity of AMPD in perfused rat hearts and in isolated rat cardiomyocytes. Brief perfusion of the pre-ischemic heart with 200 micro M Purr resulted in activation of AMPD, more pronounced degradation of the adenine nucleotides, and reduced recovery of the adenine nucleotide pool during reperfusion. Brief incubation of rat cardiomyocytes with 200 micro M Purr also activated AMPD, while prolonged exposure resulted in enzyme inhibition. We conclude that Purr activates AMPD, whereas metabolites of this compound may inhibit the enzyme.

Metabolism of 4-pyridone-3-carboxamide-1-beta-D-ribonucleoside triphosphate and its nucleoside precursor in the erythrocytes

We recently discovered new nucleotides (4-pyridone-3-carboxamide-1-beta -D-ribonucleoside phosphates) in human erythrocytes. To establish the precursor compound and pathways of nucleotide derivative formation and breakdown, human erythrocytes were incubated for 3 hours with 0.3 mM 4-pyridone-3-carboxamide-1-beta-D-ribonucleoside (4PYR) and erythrocyte concentrations of 4PYR and adenine nucleotides were followed. 4PYR triphosphate increased from 16.1 +/- 0.6 micro M to 74.9 +/- 9.17 and 4PYR monophosphate increased from 5 micro M to 254.7 +/- 13.9 micro M. Conversely, incubation with 0.3 mM 4-pyridone-3-carboxamide (4PY) did not lead to additional 4PYR nucleotide formation. 4PYR nucleotides were catabolized to 4PYR. We conclude that 4PYR nucleotides are formed in erythrocytes by nucleoside kinase-mediated 4PYR phosphorylation and catabolized by 5'nucleotidase-mediated dephosphorylation.

Pharmacological inhibition of AMP-deaminase in rat cardiac myocytes

Because mutation of AMP deaminase 1 gene leading to reduced AMP deaminase activity may result in protection of cardiac function in patients with heart disease, inhibitors of AMP deaminase (AMPD) may have therapeutic applications. This study evaluated the effect of a specific inhibitor of AMP deaminase 3-[2-(3-carboxy-4-bromo-5,6,7,8-tetrahydronaphthyl)ethyl]-3,6,7,8-tetrahydroimidazo [4,5-d][1,3]diazepin-8-ol (AMPDI) on the isolated human enzyme and on nucleotide catabolism in rat cardiomyocytes. AMPDI effectively inhibited isolated human AMPD with an IC(50) = 0.5 micro M. AMPDI was much less effective with isolated cardiomyocytes (IC(50) = 0.5 mM). AMPDI is a very effective inhibitor of AMPD that despite lower efficiency in the cell system examined could be useful for in vivo studies.

4-pyridone-3-carboxamide ribonucleoside triphosphate accumulating in erythrocytes in end stage renal failure originates from tryptophan metabolism

We recently identified an erythrocyte nucleotide accumulating in end-stage renal disease as 4-pyridone-3-carboxamide ribonucleotide triphosphate (4PYTP), a nucleotide never described previously. Plasma tryptophan concentration has been previously reported to be reduced in patients in chronic renal failure that is in turn associated with elevated precursors of tryptophan metabolism, including L -kynurenine and quinolinic acid, both of which have been implicated in the neurotoxic manifestations of chronic renal failure. Here we compare mean erythrocyte 4PYTP, and plasma tryptophan concentrations, in controls and four patient groups with renal impairment (10 per group) and confirmed a reduction in plasma tryptophan in patients on dialysis that corrected with renal transplantation. We found: An inverse correlation between plasma tryptophan and red cell 4PYTP concentrations (R(2)=0.44, P<0.001) when all patients were grouped together. Restoration of both tryptophan and 4PYTP concentrations to control values was only achieved following renal transplantation. 4PYTP was absent from erythrocytes in Molybdenum cofactor (MoCF) deficiency implicating aldehyde oxidase/dehydrogenase, a Molybdenum requiring enzyme. High 4PYTP erythrocyte concentrations in adenine or hypoxanthine-phosphoribosyltransferase deficient patients in severe uremia (113 microM and 103 microM), confirmed the lack of involvement of either enzyme in 4PYTP formation. We propose that 4PYTP is formed by a novel route involving the oxidation of the intermediates of NAD turnover from quinolinic acid by aldehyde oxidase.

HPLC/tandem ion trap mass detector methods for determination of inosine monophosphate dehydrogenase (IMPDH) and thiopurine methyltransferase (TPMT)

The efficiency of Mycophenolate mofetil (MMF) and Azathioprine (AZA) as immunosuppressive agents depends on the activity of 2 enzymes, inosine monophosphate dehydrogenase (IMPDH) and thiopurine methyltransferase (TPMT) respectively. We present preliminary evaluation of nonradioactive methods that apply HPLC with ion-trap mass detection to measure the activities of IMPDH in peripheral blood mononuclear cells (PBMC) and TPMT in the erythrocytes (RBC). We found IMPDH activity of 0.9 +/- 0.2 nmol/hour/10(6) PBMC and TPMT activity of 19.9 +/- 4.7 nmol/hour/ml RBC in healthy subjects. These methods, following its further validation, could be useful for monitoring the activity in a clinical and experimental setting.

Stimulatory effects of atorvastatin on extracellular nucleotide degradation in human endothelial cells

Endothelial degradation of extracellular nucleotides is known to be an important mechanism in regulation of thrombosis, inflammation and immune response. It is possible that this pathway is a target for pleiotropic drugs such as atorvastatin. We studied therefore the effect of atorvastatin on extracellular nucleotide degradation in human endothelial cells. Atorvastatin treatment of human umbilical vein endothelial cells (HUVEC) and human microvascular endothelial cells (HMEC-1) resulted in significant increase in ATP breakdown and adenosine formation both if analysed in intact cell studies and as enzyme activity in cell lysates. We conclude that one of the beneficial effects of atorvastatin may include acceleration of extracellular nucleotide breakdown. This will attenuate nucleotide mediated pro-inflammatory effect and stimulate protective mechanisms of adenosine.

Differences in activities of the enzymes of nucleotide metabolism and its implications for cardiac xenotransplantation

Xenotransplantation is one be possible solution for a severe shortage of human organs available for transplantation. However, only a few studies addressed metabolic compatibility of transplanted animal organs. Our aim was to compare activities of adenosine metabolizing enzymes in the heart of different species that are relevant to clinical or experimental xenotransplantation. We noted fundamental differences: ecto-5' nucleotidease (E5' N) activity was 4-fold lower in pig and baboon hearts compared to the human hearts while mouse activity was compatible with human and rat activity was three times higher than human. There also were significant differences in AMP-deaminase (AMPD), adenosine deaminase (ADA) and purine nucleoside phosphorylase (PNP) activities. We conclude that differences in nucleotide metabolism may contribute to organ dysfunction after xenotransplantation.

Liquid chromatographic/mass spectrometric procedure for measurement of NAD catabolites in human and rat plasma and urine

Monitoring level of the metabolites of the coenzyme NAD such as nicotinamide and its oxidized and methylated derivatives is important due to therapeutic applications of these compounds and monitoring of oxidative stress. We evaluated feasibility of using HPLC with electrospray ion-trap mass detection for single run separation and quantitation of all the NAD metabolites. We achieved good separation and retention of all the metabolites of interest using reversed-phase with ion-pairing. Single ion monitoring or tandem MS were used for detection and quantitation of the specific compounds with good linearity. The method was able to detect all the physiological metabolites in plasma samples of rats and humans or in urine. However, full validation is necessary before this method could be routinely applied.

Prevention of adriamycin induced heart failure by an increase in endogenous adenosine production

Adenosine (Ado) triggers several protective mechanisms that may attenuate development of heart failure, both locally and systemically. We developed a procedure allowing sustained increase in endogenous Ado production by the combined application of Ado metabolism inhibitors and nucleotide precursors. We found that our procedure attenuate the development of heart failure induced by adriamycin.

The effect of N-methyl-2-pyridone-5-carboxamide--A nicotinamide catabolite on poly ADP-rybosylation and oxidative stress injury in endothelial cells

This study evaluated the effect of nicotinamide (NA) and its endogenous metabolite 2PY (N-methyl-2-pyridone-5-carboxamide) on the activity of poly (ADP-ribose) polymerase (PARP) and on peroxynitrite-induced injury in endothelial cells. 2PY and NA inhibited isolated PARP with half-maximal constants of 0.53 mM and 0.025 mM, respectively. Exposure to peroxynitrite caused a decrease of the NAD pool in cultured endothelial cells to below 10% of initial level. Addition of 2PY or NA provided partial protection from peroxynitrite-induced NAD depletion, with NA being more effective. 2PY and NA also provide protection from ATP depletion. We conclude that NA as well as 2PY protect from oxidative stress injury in endothelial cells by inhibition of PARP and protection from NAD depletion. This, in turn, protects energetics, allowing maintaining cellular ATP.

AMPD1 C34T mutation selectively affects AMP-deaminase activity in the human heart

Possession of the nonsense mutation in AMPD 1 C34T gene has been linked to improved survival in patients with heart failure, possibly by promoting the formation of adenosine. This mutation is known to decrease the activity of AMP-deaminase in skeletal muscle. We have found that the AMPD1 mutation decreases the activity of AMP-deaminase in the heart without changing the activity of any other enzymes of adenine nucleotide metabolism. Protective mechanism of this mutation may be thus induced by local cardiac metabolic changes.

Purine metabolism in pigs and humans and its implications for xenotransplantation

We compared concentrations of nucleotide substrates and activities of enzymes of nucleotide metabolism in pig and human blood, heart, and kidney. The most important difference was lower ecto-5-nucleotidase (ESN) activity in both pig hearts and kidney. Furthermore, higher hypoxanthine, inosine, adenine, and uracil, but lower uridine and uric acid concentrations were observed in pig blood as compared to human. A twofold increase in UTP concentration has been observed in pig hearts following 4 h perfusion with human blood. Purine metabolism is an important target for genetic and pharmacological manipulation during xenotransplantations.

Exposure to human blood inactivates swine endothelial ecto-5'-nucleotidase

Ecto-5'-nucleotidase (E5'N) is an extracellular enzyme forming anti-inflammatory and immunosuppressive adenosine. We evaluated whether confrontation of pig heart and endothelial cells with human blood changes the activity of E5'N. Pig hearts were perfused ex vivo with fresh human blood for 4 h. Pig aortic endothelial cells (PAEC) were incubated in vitro with human plasma for 3 h. Ex vivo perfusion of pig heart with fresh human blood resulted in a decrease in E5'N activity to 62% and 61% of initial in wild-type and transgenic pig hearts, respectively. PAEC activity of E5'N decreased to 71% and 50% of initial after 3 h exposure to heat-inactivated and active complement human plasma, respectively, while it remained constant in controls. Pig heart activity of E5'N decreased following exposure to human blood, which may affect adenosine production and exacerbate hyperacute and vascular rejection.

Expression of human ecto 5' nucleotidase in pig endothelial cells and its implication for adenosine production and xenotransplantation

Human endothelial activity of ecto-5'-nucleotidase (E5'N) is several times higher than in pig endothelial cells. This may have implication for xenotransplantation due to the role this enzyme plays in conversion of pro-inflammatory and pro-aggreggatory nucleotides into anti-inflammatory and antiaggregatory adenosine. We have shown in this study that human E5'N can be functionally expressed in pig endothelial cells leading to increased adenosine production from both extracellular AMP and ATP. We suggest that E5'N expression in transgenic pigs for xenotransplantation may help to prolong graft survival.

Lidoflazine combined with nucleotide precursors increases ATP content and adenosine production in cardiomyocytes

We have previously identified that the nucleoside transport blocker dipyridamole increases adenosine production but may cause depletion of the nucleotide pool in cardiomyocytes during extended exposure and that this effect was abolished by co-administration of adenine and ribose. The present study aimed to establish whether lidoflazine, a newer generation of nucleoside transport inhibitor with calcium antagonist properties, would cause a similar effect. We conclude that lidoflazine did not affect the nucleotide pool while the combined application of lidoflazine with precursors of nucleotide resynthesis increased ATP concentration and further enhanced adenosine production.

Association of improved cardiac function in donors with C34T mutation of the AMP deaminase 1 gene

Possession of the C34T mutation in AMP deaminase (AMPD1) gene has been shown to be associated with attenuation of the progression of heart failure and improved survival in ischemic heart disease. In this study, we examined the frequency of the mutation in the heart with good and poor cardiac function and in healthy controls. We found that there was no difference in the frequency of the mutation between the patients with heart failure and healthy controls. However, the frequency of the mutation in the healthy donor hearts was much higher when compared to healthy controls or donors with failing hearts.

An unusual pyridine nucleotide accumulating in erythrocytes: its identity and positive correlation with degree of renal failure

We have investigated an unusual nucleotide that accumulates, with precursors, in the erythrocytes of patients in uraemia. This nucleotide is related chemically to the NAD breakdown product, N1-methyl-2-pyridone-5-carboxamide (Me2Py), found in high concentrations in the plasma of uraemic patients. Both Me2Py and the nucleotide accumulate to high concentrations in the blood during uraemia: our investigations of samples from renal out-patients have provided information on a plausible link between the two compounds.

Elevation of the adenylate pool in rat cardiomyocytes by S-adenosyl-L-methionine

Rapid resynthesis of the adenylate pool in cardiac myocytes is important for recovery of contractility and normal function of regulatory mechanisms in the heart. Adenosine and adenine are thought to be the most effective substrates for nucleotide synthesis, but the possibility of using other compounds has been studied very little in cardiomyocytes. In the present study, the effect of S-adenosyl-L-methionine (SAM) on the adenylate pool of isolated cardiomyocytes was investigated and compared to the effect of adenine and adenosine. Adult rat cardiomyocytes were isolated using the collagenase perfusion technique. The cells were incubated in the presence of adenine derivatives for 90 min followed by nucleotide determination by HPLC. The concentrations of adenine nucleotides expressed in nmol/mg of cell protein were initially 22.1 +/- 1.4, 4.0 +/- 0.3 and 0.70 +/- 0.08 for ATP, ADP and AMP, respectively (n = 10, +/- S.E.M.), and the total adenylate pool was 26.8 +/- 1.6. In the presence of 1.25 mM SAM in the medium, the adenylate pool increased by 5.2 +/- 0.4 nmol/mg of cell protein, but only if 1 mM ribose was additionally present in the medium. No changes were observed with SAM alone. A similar increase (by 4.9 +/- 0.6 nmol/mg protein) was observed after incubation with 1.25 mM adenine plus 1 mM ribose, but no increase was observed if ribose was omitted. Adenosine at 0.1 or 1.25 mM concentrations also caused an increase in the adenylate pool (by 5.2 +/- 1.0 and 5.2 +/- 0.9 nmol/mg protein, respectively), which in contrast to the SAM or adenine was independent of the additional presence of ribose. Thus, S-adenosyl-L-methionine could be used as a precursor of the adenylate pool in cardiomyocytes, which is as efficient in increasing the adenylate pool after 90 min of incubation as adenosine or adenine. Nucleotide synthesis from SAM involves the formation of adenine as an intermediate with its subsequent incorporation by adenine phosphoribosyltransferase.

Role of endogenous endothelin on coronary reflow after cardioplegic arrest

OBJECTIVE

Endothelin plays a role in the regulation of basal coronary tone. We hypothesized that low coronary reflow and reduced cardiac function after prolonged ischemia may be due to increased release of endogenous endothelin.

METHODS

Using an isolated perfused rat heart, we examined the effect of the addition of various endothelin antagonists during reperfusion after 4 hours of cardioplegic arrest at 4 degrees C. Hearts were freeze-clamped at the end of reperfusion for analysis of high-energy phosphate levels. Results are expressed as the percentages of preischemic values.

RESULTS

The addition of bosentan or Ro61-0612 (nonselective endothelin antagonists) resulted in a significant increase in the recovery of coronary flow after 30 minutes of reperfusion (100.9% vs 85.3% [P =.03] and 122.4% vs 83.7% [P <.001], respectively, versus controls). The addition of PD155080 (endothelin A antagonist) had a similar effect (129.5% vs 91.4%, P =.008). BQ788 (endothelin B antagonist) and phosphoramidon (endothelin-converting enzyme inhibitor) had no effect. Myocardial adenosine triphosphate levels were significantly (12.1%) higher after reperfusion with Ro61-0612 (18.1 +/- 0.4 micromol/g vs 16.2 +/- 0.5 micromol/g, P =.01). There was no difference in the recovery of cardiac mechanical function with any of the antagonists studied.

CONCLUSION

These results suggest that endogenous endothelin plays a role in low coronary reflow after prolonged cardioplegic arrest but does not impair recovery of myocardial function.

Overexpression of interleukin-1 receptor antagonist provides cardioprotection against ischemia-reperfusion injury associated with reduction in apoptosis

BACKGROUND

Interleukin-1 (IL-1) plays a role in mediating acute inflammation during ischemia-reperfusion (I/R) injury in the heart, which leads to both necrosis and apoptosis of cardiomyocytes. IL-1 receptor antagonist (IL-1ra) is known to inhibit the effects of IL-1alpha and IL-1beta, resulting in attenuated inflammatory injury, and to protect cells from IL-1beta-induced apoptosis in vitro. We hypothesized that IL-1ra overexpression would provide cardioprotection by reducing inflammation-mediated myocardial damage including apoptosis after I/R injury in vivo.

METHODS AND RESULTS

Rat hearts were transfected with human secreted-type IL-1ra gene by intracoronary infusion of Hemagglutinating Virus of Japan liposome and were heterotopically transplanted. IL-1ra overexpression in these hearts was confirmed by enzyme immunoassay and immunohistochemistry. Myocardial tolerance of the transplanted heart was evaluated with the use of a novel system in which the heart, existing within the recipient's abdomen, was given 30 minutes of ischemia by left coronary artery occlusion and 24 hours of reperfusion. Consequently, infarct size was decreased in IL-1ra-transfected hearts compared with control-transfected ones (26.9+/-3.2% versus 46.2+/-3.0%, P=0.001), corresponding to lower myocardial myeloperoxidase activity (2.20+/-0.69 versus 6.82+/-1.19 U/g wet wt, P<0.001) and decreased neutrophil infiltration in histological study. Terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling and DNA-laddering studies demonstrated that cardiomyocyte apoptosis was attenuated in IL-1ra-transfected hearts (21.4+/-3.3 versus 41.4+/-3.4%, P=0.002), correlating with reduced post I/R upregulation of Bax, Bak, and caspase-3.

CONCLUSIONS

IL-1ra introduced by gene transfection protected myocardium from I/R injury by attenuating the inflammatory response, which was associated with decreased apoptosis. This suggests a potentially important role of IL-1/IL-1ra in myocardial I/R injury and the value of IL-1ra-gene therapy for myocardial preservation.

Protection from reperfusion injury after cardiac transplantation by inhibition of adenosine metabolism and nucleotide precursor supply

BACKGROUND

Adenosine (Ado) triggers numerous protective mechanisms in the heart that may attenuate ischemia-reperfusion injury in cardiac grafts. We aimed to establish whether sustained increase in endogenous Ado production by the combined application of Ado metabolism inhibitors and nucleotide precursors attenuates reperfusion injury in transplanted hearts.

METHODS AND RESULTS

Rat hearts were collected after the infusion of St Thomas' Hospital cardioplegic solution, stored at 4 degrees C for 4 hours, and heterotopically transplanted into the abdomen of recipient rats. A solution containing Ado deaminase inhibitor erythro-9(2-hydroxy-3-nonyl)adenine, Ado kinase inhibitor 5'-aminoadenosine, and nucleotide precursors adenine and ribose was administered at the time of reperfusion in the treated group, whereas saline was administered to control animals. After 1 or 24 hours, mechanical function of the transplanted hearts was evaluated in an ex vivo perfusion system followed by the determination of myocardial ATP with related metabolites and measurement of the activity of neutrophil-specific enzyme myeloperoxidase in cardiac homogenates. After 24 hours of reperfusion, maximum left ventricular developed pressure increased from 87.0+/-6.8 mm Hg (mean+/-SEM) in controls to 118.1+/-8.2 mm Hg in the treated group (P<0.05), ATP increased from 11.0+/-0.8 micromol/g dry wt in controls to 15.1+/-1.2 micromol/g dry wt in the treated group (P<0.01), and myeloperoxidase activity decreased from 2.23+/-0.60 U/g wet wt in controls to 0.58+/-0.12 U/g wet wt in the treated group (P<0.001). No differences in cardiac function, ATP, or myeloperoxidase activity were observed between the treated group and controls after 1 hour of reperfusion.

CONCLUSIONS

The administration of Ado metabolism inhibitors with nucleotide precursors causes a sustained increase in endogenous Ado production and exerts a potent protective effect against reperfusion injury in transplanted hearts. Improved cardiac function and elevated ATP concentration were accompanied by complete amelioration of neutrophil infiltration in treated hearts, suggesting that reduction in postischemic inflammation could be an important mechanism of this protective effect.

Cell transplantation for the treatment of acute myocardial infarction using vascular endothelial growth factor-expressing skeletal myoblasts

BACKGROUND

Vascular endothelial growth factor (VEGF) is a promising reagent for inducing myocardial angiogenesis. Skeletal myoblast transplantation has been shown to improve cardiac function in chronic heart failure models by regenerating muscle. We hypothesized that transplantation of VEGF-expressing myoblasts could effectively treat acute myocardial infarction by providing VEGF-induced cardioprotection through vasodilatation in the early phase, followed by angiogenesis effects in salvaging ischemic host myocardium combined with the functional benefits of newly formed, skeletal myoblast-derived muscle in the later phase.

METHODS AND RESULTS

Primary rat skeletal myoblasts were transfected with the human VEGF(165) gene using hemagglutinating virus of Japan-liposome with >95% transfection efficiency. Four million of these myoblasts (VEGF group), control-transfected myoblasts (control group), or medium only (medium group) was injected into syngeneic rat hearts 1 hour after left coronary artery occlusion. Myocardial VEGF-expression increased for 2 weeks in the VEGF group, resulting in enhanced angiogenesis without the formation of tumors. Grafted myoblasts had differentiated into multinucleated myotubes within host myocardium. Infarct size (33.3+/-1.4%, 38.1+/-1.4%, and 43.7+/-1.6% for VEGF, control, and medium groups, respectively; P=0.0005) was significantly reduced with VEGF treatment, and cardiac function improved in the VEGF group (maximum dP/dt: 4072.0+/-93.6, 3772.5+/-101.1, and 3482.5+/-90.6 mm Hg/s in the 3 groups, respectively; P=0.0011; minimum dP/dt: -504.2+/-68.5, -2311.3+/-57.0, and -2124.0+/-57.9 mm Hg/s, respectively; P=0.0008).

CONCLUSIONS

This combined strategy of cell transplantation with gene therapy could be of importance for the treatment of acute myocardial infarction.

Heat shock protein 70 gene transfection protects mitochondrial and ventricular function against ischemia-reperfusion injury

BACKGROUND

Upregulation of heat shock protein 70 (HSP70) is beneficial in cardioprotection against ischemia-reperfusion injury, but the mechanism of action is unclear. We studied the role of HSP70 overexpression through gene therapy on mitochondrial function and ventricular recovery in a protocol that mimics clinical donor heart preservation.

METHODS AND RESULTS

Hemagglutinating virus of Japan (HVJ)-liposome technique was used to transfect isolated rat hearts via intracoronary infusion of either the HSP70 gene (HSP group, n=16) or no gene (CON group, n=16), which was heterotopically transplanted into recipient rats. Four days after surgery, hearts were either perfused on a Langendorff apparatus for 30 minutes at 37 degrees C (preischemia studies [n=8/group]) or perfused for 30 minutes at 37 degrees C, cardioplegically arrested for 4 hours at 4 degrees C, and reperfused for 30 minutes at 37 degrees C (postischemia studies [n=8/group]). Western blotting and immunohistochemistry confirmed HSP70 upregulation in the HSP group. Postischemic mitochondrial respiratory control indices (RCIs) were significantly better preserved in HSP than in CON hearts: NAD(+)-linked RCI values were 9.54+/-1.1 versus 10.62+/-0.46 before ischemia (NS) but 7.98+/-0.69 versus 1.28+/-0.15 after ischemia (P<0.05), and FAD-linked RCI values were 6.87+/-0.88 versus 6.73+/-0.93 before ischemia (NS) but 4.26+/-0.41 versus 1.34+/-0.13 after ischemia (P<0.05). Postischemic recovery of mechanical function was greater in HSP than in CON hearts: left ventricular developed pressure recovery was 72.4+/-6.4% versus 59.7+/-5.3% (P<0.05), maximum dP/dt recovery was 77.9+/-6.6% versus 52.3+/-5.2% (P<0.05), and minimum dP/dt recovery was 72.4+/-7.2% versus 54.8+/-6.9% (P<0.05). Creatine kinase release in coronary effluent after reperfusion was 0.20+/-0.04 versus 0.34+/-0.06 IU. min(-1). g wet wt(-1) (P<0.05) in HSP versus in CON hearts.

CONCLUSIONS

HSP70 upregulation protects mitochondrial function after ischemia-reperfusion injury; this was associated with improved preservation of ventricular function. Protection of mitochondrial function may be important in the development of future cardioprotective strategies.