Metabolic changes induced by ischemia and cardioplegia: a study employing cardiac microdialysis in pigs

Study on the Active Constituents and Molecular Mechanism of Zhishi Xiebai Guizhi Decoction in the Treatment of CHD Based on UPLC-UESI-Q Exactive Focus, Gene Expression Profiling, Network Pharmacology, and Experimental Validation

As one of the most common clinical cardiovascular diseases (CVDs), coronary heart disease (CHD) is the most common cause of death in the world. It has been confirmed that Zhishi Xiebai Guizhi decoction (ZXGD), a classical prescription of the traditional Chinese medicine (TCM), has achieved certain effects in the treatment of CHD; however, the mechanism still remains controversial. In this paper, an integrated approach, including UPLC-UESI-Q Exactive Focus, gene expression profiling, network pharmacology, and experimental validation, was introduced to systematically investigate the mechanism of ZXGD in the treatment of CHD. First, UPLC-UESI-Q Exactive Focus was applied to identify the chemical compounds of ZXGD. Then, the targets of the components for ZXGD were predicted by MedChem Studio software embed in the integrative pharmacology-based research platform of TCM, and the differentially expressed genes (DEGs) of CHD were obtained by gene expression profiling in gene expression omnibus database. The common genes of the above two genes were obtained by Venn analysis as the targets of GXGD in treatment with CHD. Third, the core targets were screened out by protein-protein interaction network analysis, and the kyoto encyclopedia of genes and genomes pathway enrichment analysis was performed by the database for annotation, visualization, and integrated discovery bioinformatics resources. After that, the formula-herb-compound-target-pathway network was constructed to explore the mechanism of ZXGD in the treatment of CHD. Finally, molecular docking and the vitro experiment were carried out to validate some key targets. As a result, a total of 39 compounds, 12 core targets, and 4 pathways contributed to ZXGD for the treatment of CHD. This study preliminarily provided a foundation for the study on the mechanism against CHD for ZXGD and may be a reference for the compatibility mechanism and the extended application of TCM compound prescription.

Guanosine, a guanine-based nucleoside relaxed isolated corpus cavernosum from mice through cGMP accumulation

In corpus cavernosum (CC), guanosine triphosphate (GTP) is converted into cyclic guanosine monophosphate (cGMP) to induce erection. The action of cGMP is terminated by phosphodiesterases and efflux transporters, which pump cGMP out of the cell. The nucleotides, GTP, and cGMP were detected in the extracellular space, and their hydrolysis lead to the formation of intermediate products, among them guanosine. Therefore, our study aims to pharmacologically characterize the effect of guanosine in isolated CC from mice. The penis was isolated and functional and biochemical analyses were carried out. The guanine-based nucleotides GTP, guanosine diphosphate, guanosine monophosphate, and cGMP relaxed mice corpus cavernosum, but the relaxation (90.7 ± 12.5%) induced by guanosine (0.000001-1 mM) was greater than that of the nucleotides (~ 45%, P < 0.05). Guanosine-induced relaxation was not altered in the presence of adenosine type 2A and 2B receptor antagonists. No augment was observed in the intracellular levels of cyclic adenosine monophosphate in tissues stimulated with guanosine. Inhibitors of nitric oxide synthase (L-NAME, 100 μM) and soluble guanylate cyclase (ODQ, 10 μM) produced a significant reduction in guanosine-induced relaxation in all concentrations studied, while in the presence of tadalafil (300 nM), a significant increase was observed. Pre-incubation of guanosine (100 μM) produced a 6.6-leftward shift in tadalafil-induced relaxation. The intracellular levels of cGMP were greater when CC was stimulated with guanosine. Inhibitors of ecto-nucleotidases and xanthine oxidase did not interfere in the response induced by guanosine. In conclusion, our study shows that guanosine relaxes mice CC and opens the possibility to test its role in models of erectile dysfunction.

Guanosine exerts antiplatelet and antithrombotic properties through an adenosine-related cAMP-PKA signaling

BACKGROUND

Guanosine is a natural product and an endogenous nucleoside that has shown to increase during myocardial ischemia. Platelets are critically involved in ischemic coronary events. It remains unknown, however, whether guanosine may affect platelet activation and function. We sought to investigate the potential antiplatelet and antithrombotic properties of guanosine and decipher the mechanisms behind.

METHODS

We firstly assessed the effects of guanosine on platelet activation/aggregation upon stimulation with several platelet agonists including adenosine diphosphate (ADP), collagen, arachidonic acid (AA), and TRAP-6. Guanosine antithrombotic potential was also evaluated both in vitro (Badimon perfusion chamber) and in vivo (murine model). In addition we assessed any potential effect on bleeding. At a mechanistic level we determined the release of thromboxane B2, intraplatelet cAMP levels, the binding affinity on platelet membrane, and the activation/phosphorylation of protein kinase A (PKA), phospholipase C (PLC) and PKC.

RESULTS

Guanosine markedly inhibited platelet activation/aggregation-challenged by ADP and, although to a lesser extent, also reduced platelet aggregation challenged by collagen, AA and TRAP-6. Guanosine significantly reduced thrombus formation both in vitro and in vivo without significantly affects bleeding. Guanosine antiplatelet effects were associated with the activation of the cAMP/PKA signaling pathway, and a reduction in thromboxane B2 levels and PLC and PKC phosphorylation. The platelet aggregation and binding affinity assays revealed that guanosine effects on platelets were mediated by adenosine.

CONCLUSION

Guanosine effectively reduces ADP-induced platelet aggregation and limits thrombotic risk. These antithrombotic properties are associated with the activation of the cAMP/PKA signaling pathway.

Extracellular guanosine regulates extracellular adenosine levels

The aim of this investigation was to test the hypothesis that extracellular guanosine regulates extracellular adenosine levels. Rat preglomerular vascular smooth muscle cells were incubated with adenosine, guanosine, or both. Guanosine (30 μmol/l) per se had little effect on extracellular adenosine levels. Extracellular adenosine levels 1 h after addition of adenosine (3 μmol/l) were 0.125 ± 0.020 μmol/l, indicating rapid disposition of extracellular adenosine. Extracellular adenosine levels 1 h after addition of adenosine (3 μmol/l) plus guanosine (30 μmol/l) were 1.173 ± 0.061 μmol/l, indicating slow disposition of extracellular adenosine. Cell injury increased extracellular levels of endogenous adenosine and guanosine, and the effects of cell injury on endogenous extracellular adenosine were modulated by altering the levels of endogenous extracellular guanosine with exogenous purine nucleoside phosphorylase (converts guanosine to guanine) or 8-aminoguanosine (inhibits purine nucleoside phosphorylase). Extracellular guanosine also slowed the disposition of extracellular adenosine in rat preglomerular vascular endothelial cells, mesangial cells, cardiac fibroblasts, and kidney epithelial cells and in human aortic and coronary artery vascular smooth muscle cells and coronary artery endothelial cells. The effects of guanosine on adenosine levels were not mimicked or attenuated by 5-iodotubericidin (adenosine kinase inhibitor), erythro-9-(2-hydroxy-3-nonyl)-adenine (adenosine deaminase inhibitor), 5-aminoimidazole-4-carboxamide (guanine deaminase inhibitor), aristeromycin (S-adenosylhomocysteine hydrolase inhibitor), low sodium (inhibits concentrative nucleoside transporters), S-(4-nitrobenzyl)-6-thioinosine [inhibits equilibrative nucleoside transporter (ENT) type 1], zidovudine (inhibits ENT type 2), or acadesine (known modulator of adenosine levels). Guanosine also increases extracellular inosine, uridine, thymidine, and cytidine, yet decreases extracellular uric acid. In conclusion, extracellular guanosine regulates extracellular adenosine levels.

Exogenous carbon monoxide does not affect cell membrane energy availability assessed by sarcolemmal calcium fluxes during myocardial ischaemia-reperfusion in the pig

Carbon monoxide is thought to be cytoprotective and may hold therapeutic promise for mitigating ischaemic injury. The purpose of this study was to test low-dose carbon monoxide for protective effects in a porcine model of acute myocardial ischaemia and reperfusion. In acute open-thorax experiments in anaesthetised pigs, pretreatment with low-dose carbon monoxide (5% increase in carboxyhaemoglobin) was conducted for 120 min before localised ischaemia (45 min) and reperfusion (60 min) was performed using a coronary snare. Metabolic and injury markers were collected by microdialysis sampling in the ventricular wall. Recovery of radio-marked calcium delivered locally by microperfusate was measured to assess carbon monoxide treatment effects during ischaemia/reperfusion on the intracellular calcium pool. Coronary occlusion and ischaemia/reperfusion were analysed for 16 animals (eight in each group). Changes in glucose, lactate and pyruvate from the ischaemic area were observed during ischaemia and reperfusion interventions, though there was no difference between carbon monoxide-treated and control groups during ischaemia or reperfusion. Similar results were observed for glycerol and microdialysate ⁴⁵Ca(2+) recovery. These findings show that a relatively low and clinically relevant dose of carbon monoxide did not seem to provide acute protection as indicated by metabolic, energy-related and injury markers in a porcine myocardial ischaemia/reperfusion experimental model. We conclude that protective effects of carbon monoxide related to ischaemia/reperfusion either require higher doses of carbon monoxide or occur later after reperfusion than the immediate time frame studied here. More study is needed to characterise the mechanism and time frame of carbon monoxide-related cytoprotection.

Glutamate release predicts ongoing myocardial ischemia of rat hearts

BACKGROUND

Glutamate metabolism is associated with myocardial ischemia-reperfusion, but it is not clear whether glutamate reveals ongoing ischemia (OI). We evaluated whether microdialysis would detect OI induced by coronary artery ligation in a rat cardiac transplantation model.

MATERIAL AND METHODS

A total of 24 Fischer 344 rats underwent syngeneic heterotopic cardiac transplantation. Of these, 16 rats underwent ligation of the left anterior coronary artery (LAD) of the heart to induce ongoing ischemia (OI), of which eight grafts received intra-aortally Gabapentin (12 mg/graft), a glutamate-release inhibitor and eight grafts with transplantation only served as the control. With a microdialysis catheter samples for glucose, lactate, pyruvate, glutamate, and glycerol were analysed spectrophotometrically. Histology and aquaporin 7 evaluations were performed after graft harvesting.

RESULTS

Glutamate was elevated after 15 min of reperfusion in OI as compared with Control (14.31 +/- 5.03 microM vs 6.75 +/- 2.21 microM, p = 0.05), respectively. Glycerol remained high in OI (61.89 +/- 46.13 microM to 15.84 +/- 0.85 microM, p = ns) and low in Control (12.33 +/- 3.36 microM to 5.52 +/- 0.25 microM, p = ns). Gabapentin decreased glutamate release from 7.32 +/- 1.57 microM to 2.71 +/- 0.64 microM, (p < 0.05) and resulted in decrease of glycerol levels from 24.64 +/- 4.03 microM to 10.43 +/- 2.49 microM, (p < 0.05) in OI. The expression of aquaporin 7 and histology confirmed OI.

CONCLUSIONS

We suggest that glutamate release may be used as an early indicator of OI after cardiac arrest.

A UPLC-MS/MS application for profiling of intermediary energy metabolites in microdialysis samples--a method for high-throughput

Research within the field of metabolite profiling has already illuminated our understanding of a variety of physiological and pathological processes. Microdialysis has added further refinement to previous models and has allowed the testing of new hypotheses. In the present study, a new ultra-performance liquid chromatography/electrospray-tandem mass spectrometry (UPLC-ESI-MS/MS) method for the simultaneous detection and quantification of intermediary energy metabolites in microdialysates was developed. The targeted metabolites were mainly from the citric acid cycle in combination with pyruvic acid, lactic acid, and the ATP (adenosine triphosphate) hydrolysis product adenosine along with metabolites of adenosine. This method was successfully applied to analyze the microdialysates obtained from an experimental animal study giving insight into the hitherto unknown concentration of many interstitial energy metabolites, such as succinic acid and malic acid. With a total cycle time of 3 min, injection to injection, this method permits analysis of a much larger number of samples in comparison with conventional high performance liquid chromatography/tandem mass spectrometry HPLC-MS/MS strategies. With this novel combination where microdialysis and high sensitivity UPLC-MS/MS technique is combined within cardiologic research, new insights into the intermediary energy metabolism during ischemia-reperfusion is now feasible.

Prevention of atrial fibrillation following cardiac surgery: basis for a novel therapeutic strategy based on non-hypoxic myocardial preconditioning

Atrial fibrillation is the most common complication of cardiac surgical procedures performed with cardiopulmonary bypass. It contributes to increased hospital length of stay and treatment costs. At present, preventive strategies offer only suboptimal benefits, despite improvements in anesthesia, surgical technique, and medical therapy. The pathogenesis of postoperative atrial fibrillation is considered to be multifactorial. However oxidative stress is a major contributory factor representing the unavoidable consequences of ischemia/reperfusion cycle occurring in this setting. Considerable evidence suggests the involvement of reactive oxygen species (ROS) in the pathogenic mechanism of this arrhythmia. Interestingly, the deleterious consequences of high ROS exposure, such as inflammation, cell death (apoptosis/necrosis) or fibrosis, may be abrogated by a myocardial preconditioning process caused by previous exposure to moderate ROS concentration known to trigger survival response mechanisms. The latter condition may be created by n-3 PUFA supplementation that could give rise to an adaptive response characterized by increased expression of myocardial antioxidant enzymes and/or anti-apoptotic pathways. In addition, a further reinforcement of myocardial antioxidant defenses could be obtained through vitamins C and E supplementation, an intervention also known to diminish enzymatic ROS production. Based on this paradigm, this review presents clinical and experimental evidence supporting the pathophysiological and molecular basis for a novel therapeutic approach aimed to diminish the incidence of postoperative atrial fibrillation through a non-hypoxic preconditioning plus a reinforcement of the antioxidant defense system in the myocardial tissue.

An anaesthetic protocol in the young domestic pig allowing neuromuscular blockade for studies of cardiac function following cardioplegic arrest and cardiopulmonary bypass

BACKGROUND

Neuromuscular blockade should, for ethical reasons, not be allowed in animal experiments unless the use is strongly motivated. Beforehand, the anaesthetic protocol must be documented without muscle relaxation in the species studied. Documentation is difficult to obtain from the scientific literature. When focusing on cardiac function over time, in particular, the ideal anaesthetic protocol should cause no or minor alterations in cardiac variables.

METHODS

We intended to document an anaesthetic protocol involving ventilation with N(2)O combined with loading doses and continuous infusions of pentobarbital, fentanyl and midazolam in seven pigs by applying potentially painful stimuli every 15 min for 7 h. Subsequently, left ventricular global and regional function was studied with conductance catheter and strain rate imaging by echocardiography in eight pigs with pancuronium included.

RESULTS

Pigs without pancuronium were completely immobilized and unresponsive to potentially painful stimuli and sternotomy, with no accumulation or degradation of anaesthetic agents. With pancuronium included, left ventricular preload gradually decreased together with reduction of cardiac index from 3.52 +/- 0.14 at 2 h to 2.84 +/- 0.11 L min(-1). m(-2) (+/-SEM) after 7 h of observation. Preload recruitable stroke work decreased after 7 h, whereas peak systolic strain in the anterior left ventricular wall and load-independent indices of diastolic function were not significantly altered.

CONCLUSION

In specific experimental protocols, the anaesthetic protocol described could allow the use of muscular paralysis in young domestic pigs, for instance when involving hypothermic cardiopulmonary bypass, cardioplegic arrest and reperfusion.