Ribose-enhanced myocardial recovery following ischemia in the isolated working rat heart

Buyang Huanwu Decoction Alleviates Atherosclerosis by Regulating gut Microbiome and Metabolites in Apolipoprotein E-deficient Mice fed with High-fat Diet

ABSTRACT

The traditional Chinese herbal prescription Buyang Huanwu decoction (BHD), effectively treats atherosclerosis. However, the mechanism of BHD in atherosclerosis remains unclear. We aimed to determine whether BHD could alleviate atherosclerosis by altering the microbiome-associated metabolic changes in atherosclerotic mice. An atherosclerotic model was established in apolipoprotein E-deficient mice fed high-fat diet, and BHD was administered through gavage for 12 weeks at 8.4 g/kg/d and 16.8 g/kg/d. The atherosclerotic plaque size, composition, serum lipid profile, and inflammatory cytokines, were assessed. Mechanistically, metabolomic and microbiota profiles were analyzed by liquid chromatography-mass spectrometry and 16S rRNA gene sequencing, respectively. Furthermore, intestinal microbiota and atherosclerosis-related metabolic parameters were correlated using Spearman analysis. Atherosclerotic mice treated with BHD exhibited reduced plaque area, aortic lumen occlusion, and lipid accumulation in the aortic root. Nine perturbed serum metabolites were significantly restored along with the relative abundance of microbiota at the family and genus levels but not at the phylum level. Gut microbiome improvement was strongly negatively correlated with improved metabolite levels. BHD treatment effectively slows the progression of atherosclerosis by regulating altered intestinal microbiota and perturbed metabolites.

Integrated Functions of Cardiac Energetics, Mechanics, and Purine Nucleotide Metabolism

Purine nucleotides play central roles in energy metabolism in the heart. Most fundamentally, the free energy of hydrolysis of the adenine nucleotide adenosine triphosphate (ATP) provides the thermodynamic driving force for numerous cellular processes including the actin-myosin crossbridge cycle. Perturbations to ATP supply and/or demand in the myocardium lead to changes in the homeostatic balance between purine nucleotide synthesis, degradation, and salvage, potentially affecting myocardial energetics and, consequently, myocardial mechanics. Indeed, both acute myocardial ischemia and decompensatory remodeling of the myocardium in heart failure are associated with depletion of myocardial adenine nucleotides and with impaired myocardial mechanical function. Yet there remain gaps in the understanding of mechanistic links between adenine nucleotide degradation and contractile dysfunction in heart disease. The scope of this article is to: (i) review current knowledge of the pathways of purine nucleotide depletion and salvage in acute ischemia and in chronic heart disease; (ii) review hypothesized mechanisms linking myocardial mechanics and energetics with myocardial adenine nucleotide regulation; and (iii) highlight potential targets for treating myocardial metabolic and mechanical dysfunction associated with these pathways. It is hypothesized that an imbalance in the degradation, salvage, and synthesis of adenine nucleotides leads to a net loss of adenine nucleotides in both acute ischemia and under chronic high-demand conditions associated with the development of heart failure. This reduction in adenine nucleotide levels results in reduced myocardial ATP and increased myocardial inorganic phosphate. Both of these changes have the potential to directly impact tension development and mechanical work at the cellular level. © 2024 American Physiological Society. Compr Physiol 14:5345-5369, 2024.

Evaluation of the anti-ischemic effects of D-ribose during dobutamine stress echocardiography: a pilot study

D-Ribose, a pentose sugar, has shown to improve myocardial high-energy phosphate stores depleted by ischemia. This study investigated the ability of D-Ribose with low dose dobutamine to improve the contractile response of viable myocardium to dobutamine and to assess the efficacy of D-ribose in reducing stress-induced ischemia. Twenty-six patients with ischemic cardiomyopathy completed a two-day, randomized, double blind crossover trial comparing the effects of D-Ribose and placebo on regional wall motion. On the first study day, either D-Ribose or placebo was infused for 4.5 hours. Low (5 and 10 μ/kg/min) and subsequently, high (up to 50 μ/kg/min) dose dobutamine echocardiography was then performed. On the second study day, patients crossed over to the alternative article for a similar 4.5 hours infusion time period and underwent a similar evaluation. The wall motion response during low dose dobutamine was the same with D-Ribose and placebo in 77% of segments (203/263, Kappa = 0.37). In segments with discordant responses, more segments improved with D-Ribose than with placebo (41 vs. 19 segments, p = 0.006). With high dose dobutamine infusion, the wall motion response (ischemia vs. no ischemia) was the same with D-Ribose and placebo in 83% of interpretable segments (301/363, kappa = 0.244). In segments with discordant responses, there were more ischemic segments with placebo compared to D-Ribose (36 vs. 26, p = 0.253). Nineteen patients developed ischemia during the dobutamine and placebo infusion and 13 patients had ischemia during dobutamine and D-ribose infusion (p = 0.109). D-Ribose improved contractile responses to dobutamine in viable myocardium with resting dysfunction but had no significant effect in reducing the frequency of stress-induced wall motion abnormalities.

Preservation of diastolic function in monocrotaline-induced right ventricular hypertrophy in rats

During ischemic heart diseases and when heart failure progresses depletion of myocardial energy stores occurs. D-Ribose (R) has been shown to improve cardiac function and energy status after ischemia. Folic acid (FA) is an essential cofactor in the formation of adenine nucleotides. Therefore, we assessed whether chronic R-FA administration during the development of hypertrophy resulted in an improved cardiac function and energy status. In Wistar rats (n = 40) compensatory right ventricular (RV) hypertrophy was induced by monocrotaline (30 mg/kg; MCT), whereas saline served as control. Both groups received a daily oral dose of either 150 mg.kg(-1).day(-1) dextrose (placebo) or R-FA (150 and 40 mg.kg(-1).day(-1), respectively). In Langendorff-perfused hearts, RV and left ventricular (LV) pressure development and collagen content as well as total RV adenine nucleotides (TAN), creatine content, and RV and LV collagen content were determined. In the control group R-FA had no effect. In the MCT-placebo group, TAN and creatine content were reduced, RV and LV diastolic pressure-volume relations were steeper, RV systolic pressures were elevated, RV and LV collagen content was increased, and RV-LV diastolic interaction was altered compared with controls. In the MCT-R-FA group, TAN, RV and LV diastolic stiffness, RV and LV collagen content, and RV-LV diastolic interaction were normalized to the values in the control group while creatine content remained depressed and RV systolic function remained elevated. In conclusion, the depression of energy status in compensated hypertrophic myocardium observed was partly prevented by chronic R-FA administration and accompanied by a preservation of diastolic function and collagen deposition.

Role of Adenosine as Adjunctive Therapy in Acute Myocardial Infarction

Although early reperfusion and maintained patency is the mainstay therapy for ST elevation myocardial infarction, experimental studies demonstrate that reperfusion per se induces deleterious effects on viable ischemic cells. Thus "myocardial reperfusion injury" may compromise the full potential of reperfusion therapy and may account for unfavorable outcomes in high-risk patients. Although the mechanisms of reperfusion injury are complex and multifactorial, neutrophil-mediated microvascular injury resulting in a progressive decrease in blood flow ("no-reflow" phenomenon) likely plays an important role. Adenosine is an endogenous nucleoside found in large quantities in myocardial and endothelial cells. It activates four well-characterized receptors producing various physiological effects that attenuate many of the proposed mechanisms of reperfusion injury. The cardio-protective effects of adenosine are supported by its role as a mediator of pre- and post-conditioning. In experimental models, administration of adenosine in the peri-reperfusion period results in a marked reduction in infarct size and improvement in ventricular function. The cardioprotective effects in the canine model have a narrow time window with the drug losing its effect following three hours of ischemia. Several small clinical studies have demonstrated that administration of adenosine with reperfusion therapy reduces infarct size and improves ventricular function. In the larger AMISTAD and AMISTAD II trials a 3-h infusion of adenosine as an adjunct to reperfusion resulted in a striking reduction in infarct size (55-65%). Post hoc analysis of AMISTAD II showed that this was associated with significantly improved early and late mortality in patients treated within 3.17 h of symptoms. An intravenous infusion of adenosine for 3 h should be considered as adjunctive therapy in high risk-patients undergoing reperfusion therapy.

Using fructose-1,6-diphosphate during hypothermic rabbit-heart preservation: a high-energy phosphate study

BACKGROUND

In this study, we evaluated the effects of fructose-1,6-diphosphate (FDP) on high-energy phosphate metabolism during 18-hour hypothermic rabbit-heart preservation.

METHODS

Under general anesthesia and artificial ventilation, hearts from 42 adult New Zealand white rabbits were harvested, flushed, and preserved in St. Thomas solution at 4(o)C for 18 hours. In the study group (n = 15), FDP (5 mmol/liter) was added to the St. Thomas solution, whereas in the control group (n = 17), fructose (5 mmol/liter) was added. Another 10 hearts did not undergo hypothermic storage, but were used as the normal group for high-energy phosphate concentration comparison.

RESULTS

After 18 hours of hypothermic preservation, myocardial high-energy phosphate content decreased in both preservation groups. In the study group, left ventricular adenosine triphosphate (ATP) content was 33% of that in the normal hearts, but in the control group, ATP decreased to 14% of normal. Adenosine diphosphate (ADP) content, energy charge, and ATP-to-ADP ratio showed similar decreases. The high-energy phosphate profile (content in the atria and ventricles and the ratio of ATP to ADP to AMP) was maintained in the study group but not in the control group. High-energy phosphate metabolites such as inosine monophosphate (IMP), inosine, and hypoxanthine increased in both preservation groups, but the increase was more prominent in the control group.

CONCLUSION

Adding FDP to St. Thomas solution attenuated the depletion of high-energy phosphate concentration in the preserved hearts. This difference was especially prominent in the left and right ventricles. The protective effect of FDP during hypothermic heart preservation deserves further study.

The benefits of ribose in cardiovascular disease

Cardiovascular disease still ranks as the leading cause of death in men and women. Adults have tried to lower their risk of cardiovascular disease by improving their diet, quitting smoking, controlling blood pressure and exercising regularly. Additionally, many adults have turned to nutriceutical or natural products. Myocardial ischemia, produces a depression in myocardial tissue levels of high energy compounds, along with a compromise in myocardial function. Ribose, a naturally occurring sugar, has been extensively investigated, both in animal and clinical studies, as an agent to enhance the recovery of these depressed energy compounds. Results of these studies have been promising in enhancing the recovery of these energy molecules along with an improvement in myocardial function. Therefore, ribose should be considered as a potential agent in the treatment of ischemic cardiovascular disease.

Preischemic administration of ribose to delay the onset of irreversible ischemic injury and improve function: studies in normal and hypertrophied hearts

Compared with normal hearts, those with pathology (hypertrophy) are less tolerant of metabolic stresses such as ischemia. Pharmacologic intervention administered prior to such stress could provide significant protection. This study determined, firstly, whether the pentose sugar ribose, previously shown to improve postischemic recovery of energy stores and function, protects against ischemia when administered as a pretreatment. Secondly, the efficacy of this same pretreatment protocol was determined in hearts with pathology (hypertrophy). For study 1, Sprague-Dawley rats received equal volumes of either vehicle (bolus i.v. saline) or ribose (100 mg/kg) before global myocardial ischemia. In study 2, spontaneously hypertensive rats (SHR; blood pressure approximately 200/130) with myocardial hypertrophy underwent the same treatment protocol and assessments. In vivo left ventricular function was measured and myocardial metabolites and tolerance to ischemia were assessed. In normal hearts, ribose pretreatment significantly elevated the heart's energy stores (glycogen), and delayed the onset of irreversible ischemic injury by 25%. However, in vivo ventricular relaxation was reduced by 41% in the ribose group. In SHR, ribose pretreatment did not produce significant elevations in the heart's energy or improvements in tolerance to global ischemia, but significantly improved ventricular function (maximal rate of pressure rise (+dP/dt(max)), 25%; normalized contractility ((+dP/dt)/P), 13%) despite no change in hemodynamics. Thus, administration of ribose in advance of global myocardial ischemia does provide metabolic benefit in normal hearts. However, in hypertrophied hearts, ribose did not affect ischemic tolerance but improved ventricular function.

No effects of oral ribose supplementation on repeated maximal exercise and de novo ATP resynthesis

A double-blind randomized study was performed to evaluate the effect of oral ribose supplementation on repeated maximal exercise and ATP recovery after intermittent maximal muscle contractions. Muscle power output was measured during dynamic knee extensions with the right leg on an isokinetic dynamometer before (pretest) and after (posttest) a 6-day training period in conjunction with ribose (R, 4 doses/day at 4 g/dose, n = 10) or placebo (P, n = 9) intake. The exercise protocol consisted of two bouts (A and B) of maximal contractions, separated by 15 s of rest. Bouts A and B consisted of 15 series of 12 contractions each, separated by a 60-min rest period. During the training period, the subjects performed the same exercise protocol twice per day, with 3-5 h of rest between exercise sessions. Blood samples were collected before and after bouts A and B and 24 h after bout B. Knee-extension power outputs were approximately 10% higher in the posttest than in the pretest but were similar between P and R for all contraction series. The exercise increased blood lactate and plasma ammonia concentrations (P < 0.05), with no significant differences between P and R at any time. After a 6-wk washout period, in a subgroup of subjects (n = 8), needle-biopsy samples were taken from the vastus lateralis before, immediately after, and 24 h after an exercise bout similar to the pretest. ATP and total adenine nucleotide content were decreased by approximately 25 and 20% immediately after and 24 h after exercise in P and R. Oral ribose supplementation with 4-g doses four times a day does not beneficially impact on postexercise muscle ATP recovery and maximal intermittent exercise performance.

[5-3H]glucose overestimates glycolytic flux in isolated working rat heart: role of the pentose phosphate pathway

We set out to study the pentose phosphate pathway (PPP) in isolated rat hearts perfused with [5-3H]glucose and [1-14C]glucose or [6-14C]glucose (crossover study with 1- then 6- or 6- then 1-14C-labeled glucose). To model a physiological state, hearts were perfused under working conditions with Krebs-Henseleit buffer containing 5 mM glucose, 40 microU/ml insulin, 0.5 mM lactate, 0.05 mM pyruvate, and 0.4 mM oleate/3% albumin. The steady-state C1/C6 ratio (i.e., the ratio from [1-14C]glucose to [6-14C]glucose) of metabolites released by the heart, an index of oxidative PPP, was not different from 1 (1.06 +/- 0.19 for 14CO2, and 1.00 +/- 0.01 for [14C]lactate + [14C]pyruvate, mean +/- SE, n = 8). Hearts exhibited contractile, metabolic, and 14C-isotopic steady state for glucose oxidation (14CO2 production). Net glycolytic flux (net release of lactate + pyruvate) and efflux of [14C]lactate + [14C]pyruvate were the same and also exhibited steady state. In contrast, flux based on 3H2O production from [5-3H]glucose increased progressively, reaching 260% of the other measures of glycolysis after 30 min. The 3H/14C ratio of glycogen (relative to extracellular glucose) and sugar phosphates (representing the glycogen precursor pool of hexose phosphates) was not different from each other and was <1 (0.36 +/- 0.01 and 0.43 +/- 0.05 respectively, n = 8, P < 0.05 vs. 1). We conclude that both transaldolase and the L-type PPP permit hexose detritiation in the absence of net glycolytic flux by allowing interconversion of glycolytic hexose and triose phosphates. Thus apparent glycolytic flux obtained by 3H2O production from [5-3H]glucose overestimates the true glycolytic flux in rat heart.

D-Ribose as a supplement for cardiac energy metabolism

Metabolic support for the heart has been an attractive concept since the pioneering work of Sodi-Pallares et al. four decades ago.* Recently, interest has increased in the use of over-the-counter supplements and naturally occurring nutriceuticals for enhancement of cardiac and skeletal muscle performance. These include amino acids such as creatine, L-carnitine, and L-arginine, as well as vitamins and cofactors such as alpha-tocopherol and coenzyme Q. Like these other molecules, D-ribose is a naturally occurring compound. It is the sugar moiety of ATP and has also received interest as a metabolic supplement for the heart. The general hypothesis is that under certain pathologic cardiac conditions, nucleotides (particularly ATP, ADP, and AMP) are degraded and lost from the heart. The heart's ability to resynthesize ATP is then limited by the supply of D-ribose, which is a necessary component of the adenine nucleotide structure. In support of this hypothesis, recent reports have used D-ribose to increase tolerance to myocardial ischemia. Its use in patients with stable coronary artery disease improves time to exercise-induced angina and electrocardiographic changes. In conjunction with thallium imaging or dobutamine stress echocardiography, D-ribose supplementation has been used to enhance detection of hibernating myocardium. In this article, we review the biochemical basis for using supplemental D-ribose as metabolic support for the heart and discuss the experimental evidence for its benefit.

Physiologic effects of extracellular superoxide dismutase transgene overexpression on myocardial function after ischemia and reperfusion injury

OBJECTIVE

Myocardial injury after ischemia and reperfusion may be mediated, in part, by oxygen-derived free radicals. In this study the protective effects of extracellular superoxide dismutase overexpression were directly assessed in the hearts of transgenic mice, after ischemia and reperfusion injury, using an isolated work-performing murine heart preparation and computerized analysis of functional data.

METHODS

A blinded study was performed to compare cardiac function in the hearts of both transgenic mice with a 3.5-fold overexpression of myocardial extracellular superoxide dismutase (n = 6, 22 to 26 gm) and littermate controls (n = 8, 22 to 26 gm). Preload-dependent cardiac output, contractility, heart rate, stroke work, and stroke volume were evaluated in the two groups before and after a 6-minute period of normothermic ischemia.

RESULTS

No differences were found between extracellular superoxide dismutase hearts and control hearts in any parameter of myocardial function before ischemia. After ischemia, decreases in cardiac output occurred in both groups; however, this decrease was larger in control mice compared with extracellular superoxide dismutase mice. A higher percentage of recovery was also observed in the contractility, heart rate, stroke work, and stroke volume of extracellular superoxide dismutase hearts compared with control hearts.

CONCLUSION

After global normothermic ischemia and subsequent reperfusion, decreases in cardiac function occurred in both extracellular superoxide dismutase and control mice; however, a higher percentage of recovery was observed in the extracellular superoxide dismutase overexpressed hearts. These data suggest that extracellular superoxide dismutase transgene overexpression significantly improves preservation of myocardial function after ischemia and reperfusion injury.

Regulation of and intervention into the oxidative pentose phosphate pathway and adenine nucleotide metabolism in the heart

The capacity of the oxidative pentose pathway (PPP) in the heart is limited, since the activity of glucose-6-phosphate dehydrogenase (G-6-PD), the first and regulating enzyme of this pathway, is very low. Two mechanisms are involved in the regulation of this pathway. Under normal conditions, G-6-PD is inhibited by NADPH. This can be overcome in the isolated perfused rat heart by increasing the oxidized glutathione and by elevating the NADP+/NADPH ratio. Besides this rapid control mechanism, there is a long-term regulation which involves the synthesis of G-6-PD. The activity of G-6-PD was elevated in the rat heart during the development of cardiac hypertrophy due to constriction of the abdominal aorta and in the non-ischemic part of the rat heart subsequent to myocardial infarction. The catecholamines isoproterenol and norepinephrine stimulated the activity of myocardial G-6-PD in a time- and dose-dependent manner. The isoproterenol-induced stimulation was cAMP-dependent and due to increased new synthesis of enzyme protein. The G-6-PD mRNA was elevated by norepinephrine. As a consequence of the stimulation of the oxidative PPP, the available pool of 5-phosphoribosyl-1-pyrophosphate (PRPP) was expanded. PRPP is an important precursor substrate for purine and pyrimidine nucleotide synthesis. The limiting step in the oxidative PPP, the G-6-PD reaction, can be bypassed with ribose. This leads to an elevation of the cardiac PRPP pool. The decline in ATP that is induced in many pathophysiological conditions was attenuated or even entirely prevented by i.v. infusion of ribose. In two in vivo rat models, the overloaded and catecholamine-stimulated heart and the infarcted heart, the normalization of the cardiac adenine nucleotide pool by ribose was accompanied by an improvement of global heart function. Combination of ribose with adenine or inosine in isoproterenol-treated rats was more effective to restore completely the cardiac ATP level within a short period of time than either intervention alone.

Circulatory assist techniques in cardiogenic shock: metabolic aspects

Assisted circulation in severe cardiogenic shock was evaluated using a reservoir and a single pump without an oxygenator in 88 dogs. Study groups included: no treatment, substrates only (cysteine, ribose), nitroprusside, left ventricular (LV) + right atrial (RA) bypass + substrates, LV + RA bypass, left atrial (LA) + RA bypass, LA bypass, LV bypass, LV + RA + fluosol. Metabolic studies of O2 consumption, acid and alkaline phosphatase, lactate, creatine phosphokinase (CPK), myocardial depressant factor (MDF), and tissue adenosine triphosphate (ATP) were done in the course of 4-hour treatment periods followed by 2-hour observation periods. Best survival at 4-hour and 6-hour levels were achieved in LV + RA bypass. Cysteine and ribose reduced survival when added to the pump supported (LV + RA bypass) group. Cysteine/ribose improved survival over the no treatment group. O2 consumption increased significantly in the groups with best survival but remained unchanged from control or shock levels when cysteine/ribose were added. Unusually high levels of CPK, acid and alkaline phosphatase, and MDF occurred in both groups receiving cysteine/ribose, indicating significant organ damage correlating with poor survival. Lactate levels were less predictive. Heart tissue ATP levels were higher in groups with good survival. Liver ATP levels were lower in high survival groups. Lung ATP did not differ between groups.

The oxidative pentose phosphate pathway in the heart: regulation, physiological significance, and clinical implications

The capacity of the oxidative pentose phosphate pathway (PPP) in the heart is small, since the activity of glucose-6-phosphate dehydrogenase (G-6-PD), the first and rate-limiting enzyme, is very low. Basically, two mechanisms are involved in the regulation of this pathway. Under normal conditions, G-6-PD is inhibited by NADPH. This can immediately be overcome in the isolated perfused rat heart by increasing the oxidized glutathione and by elevating the NADP+/NADPH ratio. Apart from this rapid control mechanism, there exists a long-term regulation which involves the synthesis of G-6-PD. All catecholamines that were administered stimulated the activity of myocardial G-6-PD in a time- and dose-dependent manner. This stimulation was due to increased new synthesis of enzyme protein, since the G-6-PDmRNA was specifically enhanced. As a consequence of the stimulation of the oxidative PPP, the available pool of 5-phosphoribosyl-1-pyrophosphate (PRPP) was elevated which serves as an important precursor substrate for purine and pyrimidine nucleotide synthesis. The limiting step in the oxidative PPP can be bypassed by ribose which leads to an elevation of the cardiac PRPP pool. The decline in the ATP that is induced in many pathophysiological conditions can be attenuated or even entirely prevented by i.v. infusion of ribose. In some experimental in vivo rat models such as in the overloaded and catecholamine-stimulated heart and in the non-ischemic region of the infarcted heart, the normalization of the metabolic situation was accompanied by an improvement of global heart function. Ribose application has been shown to be beneficial in several clinical disease states such as myoadenylate deaminase deficiency and McArdle's disease. Moreover, ribose facilitated thallium-201 redistribution and markedly improved the detection of reversible ischemic injury of the pig and human heart.

Ribose infusion accelerates thallium redistribution with early imaging compared with late 24-hour imaging without ribose

To determine if early (4-h) thallium-201 imaging with ribose infusion would enhance detection of thallium redistribution better than late (24-h) imaging without ribose infusion, 15 patients with coronary artery disease underwent thallium stress tests by both methods within 2 weeks. All 15 patients had quantitative coronary angiography. After immediate postexercise planar imaging during the first of two exercise tests, patients were randomized to receive either intravenous ribose (3.3 mg/kg per min) or a control infusion of saline solution for 30 min. Images performed at 4 h for the ribose study were compared with those at 24 h for the saline control study. During the second test, exercise was carried to the same rate-pressure product and each patient received the opposite infusion. Four-hour postexercise images after ribose infusion identified 21 reversible defects not seen in the 24-h saline study. Three reversible defects were seen only in saline studies, but not with ribose at 4 h (p less than 0.01); 15 reversible defects were seen with both tests. When analyzed with respect to the 31 vascular territories supplied by a coronary artery with a greater than 50% stenosis, 8 territories had reversible defects present in the ribose but not the saline study and the saline study did not demonstrate reversible defects in territories that were seen in the ribose study (p less than 0.01). In 14 of these territories, reversible defects were seen with both tests. In 6 of 15 patients, additional vascular territories with reversible defects were identified after ribose infusion. It is concluded that ribose enhances the detection of thallium redistribution at 4 h compared with 24-h control images in patients with coronary artery disease and, therefore, substantially improves the identification of viable ischemic myocardium.

Biochemical changes induced in the myocardial cell during cardioplegic arrest supplemented with creatine phosphate

The purpose of this work was to evaluate the biochemical changes in the myocardial cell using cardioplegia supplemented with creatine phosphate (CP). Many previous studies have demonstrated the beneficial effect of CP on the ischemic myocardium and its mechanism of action has been assumed to be mainly extracellular. Based on the assumption that CP could also exert some influence on myocardial cellular metabolism, this investigation was carried out. Forty patients undergoing mitral valve replacement were divided into two groups: group 1 was treated with standard cardioplegic solution, and group 2 was treated with cardioplegic solution enriched with CP at a concentration of 10 mmol/L. Samples of papillary muscle, obtained from the removed valve, were studied by means of biochemical methods in order to assess the enzyme activities and the metabolites of the different biochemical pathways related to energy metabolism in the myocardial cell. One papillary muscle sample was used to determine enzyme activities spectrophotometrically; another was used to evaluate metabolite concentrations by spectrophotometric or spectrophotofluorimetric methods. The rate of spontaneous functional recovery after rewarming and weaning from cardiopulmonary bypass (CPB) also was evaluated. In group 2, the Vmax of enzymatic activities was significantly greater (hexokinase, malate dehydrogenase, glutamate dehydrogenase, total NADH cytochrome c reductase) and a better functional state of the heart was observed after CPB. On the basis of the clinical and biochemical data, it is concluded that the myocardium was better preserved when CP was added to the cardioplegic solution. Therefore, the results suggest a possible interaction of exogenous CP with cellular metabolism.

Role of adenosine in the treatment of myocardial stunning

Adenosine is an endogenous nucleoside produced from the breakdown of adenosine triphosphate (ATP) that possesses a number of complex cellular and metabolic effects that could ameliorate postischemic contractile dysfunction (myocardial stunning). Potential mechanisms include the repletion of high-energy phosphate stores, reduced myocardial oxygen consumption, a decrease in oxygen-derived free radicals, restoration of calcium homeostasis, and an increase in regional myocardial blood flow. Experimental studies have shown that adenosine can reduce myocardial stunning with or without a concomitant increase in the total myocardial ATP stores. Adenosine may be a useful pharmacologic strategy in the prevention and treatment of ventricular dysfunction following episodes of regional or global ischemia, although further studies are needed to clarify the precise cellular mechanisms involved.

31P-NMR study of cardiac preservation: St. Thomas' Hospital cardioplegic solution versus UW preservation solution

Ex vivo cardiac preservation was evaluated by measuring the catabolism of high-energy phosphate (ATP and creatine phosphate, CrP) using 31P-NMR spectroscopy. After cardioplegic arrest St. Thomas' Hospital cardioplegic solution (group A), and University of Wisconsin (UW) preservation solution (group B) were tested. The hearts were mounted in the 4.7 T horizontal bore magnet of the NMR spectrometer and were continuously perfused with the test solution under 25 cm H2O pressure for 6 h at 10 degrees C. Peak heights of the beta-phosphate of ATP and CrP were measured and expressed as percentages of the initial value. For both group A and group B. ATP declined less rapidly during preservation than CrP. In group A, ATP remained constant for 60 min while CrP decreased from the onset of preservation. After 6 h of preservation 28.3% of ATP and 24.5% of CrP remained (group A). On the other hand, in group B, levels of both ATP and CrP remained much more stable: CrP did not decrease during the first 3 h of preservation, while ATP started to decrease after 5 h. At the end of preservation 76.1% of ATP and 71.5% of CrP were still present. We conclude that UW solution is superior to St. Thomas' Hospital solution for the preservation of high-energy phosphates during 6 h cardiac preservation with continuous hypothermic low-flow perfusion.

Pressure-controlled reperfusion improves postischemic recovery of LV-hypertrophied rat hearts

The influence of pressure-controlled postischemic reperfusion (Rp) on functional and metabolic parameters in hearts of sham-operated rats and hypertrophied hearts of rats with aortic constriction were studied. Hypertrophied hearts are considered to be more susceptible to ischemia. The hearts were perfused in the Langendorff-technique for thirty minutes at 35 degrees C with Krebs-Henseleit bicarbonate buffer at a perfusion pressure (PP) of 75 mmHg and for five minutes at 15 degrees C with St. Thomas' Hospital cardioplegic solution at a PP of 60 mmHg. After a period of global ischemia of forty minutes' duration at 15 degrees C, reperfusion was started either abruptly (aRp: PP 75 mmHg immediately) or gently (gRp: PP 75 mmHg within thirty minutes); it lasted for forty-five minutes. Intraventricular peak systolic pressure (ISP) was monitored and energy-rich compounds (ATP, ADP, AMP, CrP, free Cr) were analyzed. In normal hearts, metabolic recovery was not affected by the mode of reperfusion, but functional recovery (ISP) averaged 88% of the preischemic control value after gRp as compared with 73% after aRp. In hypertrophied hearts, gentle reperfusion ameliorated both metabolic and functional recovery. At forty-five minute recovery, CrP averaged 5.1 mumol/g ww after aRp and 6.6 mumol/g ww after gRp (p less than 0.01), and ISP amounted to 73% of the preischemic control after aRp and to 85% after gRp.

Myocardial adenine nucleotide metabolism in pediatric patients during hypothermic cardioplegic arrest and normothermic ischemia

Quantitative assessment of high-energy phosphate levels, including degradation or utilization during ischemia, has not previously been performed in infants and children. Animal experiments suggest that high-energy phosphate metabolism varies with maturation. To help answer these questions, 24 patients aged 2 months to 8 years underwent myocardial biopsy immediately after the institution of cardiopulmonary bypass (16 to 20 degrees C). Additional samples were obtained at 16 and 45 minutes after aortic cross-clamping and administration of cardioplegia (St. Thomas's solution) (in vivo ischemia). Seven patients also underwent major myocardial resection. Resected specimens were placed in a 37 degrees C bath and divided into equal-sized samples that were removed at ten-minute intervals (in vitro ischemia). All samples were immersed in liquid nitrogen and analyzed for adenine nucleotide pool metabolites using high-performance liquid chromatography. Levels of adenosine triphosphate were high before cross-clamping but diminished during the period of protected ischemia. Adenosine triphosphate loss was much more pronounced in patients less than 18 months old (p less than 0.05) and was associated with accumulation of adenosine monophosphate and inosine, a finding not seen in patients more than 18 months old (p less than 0.05). The same trends documented during in vivo ischemia were noted during in vitro ischemia. Immaturity of 5'-nucleotidase results in accumulation of adenosine monophosphate during ischemia. It is known that 5'-nucleotidase is present in neonatal myocardial cell membranes and absent from the cytosol.(ABSTRACT TRUNCATED AT 250 WORDS)

Enhanced high energy phosphate recovery with ribose infusion after global myocardial ischemia in a canine model

High energy phosphate levels are depressed following global ischemia and require several days to completely recover. Short-term methods to enhance ATP recovery have included infusion of ATP precursors, inhibition of enzymes that catabolize AMP, and membrane transport stabilization. Several precursors have been used to augment adenine nucleotide synthesis including adenosine, inosine, adenine, and ribose. Because of the short-term nature of previous experiments, recovery had been incomplete and the effects in the intact animal unknown. The purpose of this study was to determine the effects of ribose infusion in a long-term model of global ischemia and attempt to identify the precursor which limits myocardial ATP regeneration in the intact animal. Global myocardial ischemia (20 min, 37 degrees C) was produced in dogs on cardiopulmonary bypass. With reperfusion either ribose (80 mM) in normal saline or normal saline alone was infused at 1 ml/min into the right atrium and the animals were followed for 24 hr. Ventricular biopsies were obtained through an indwelling ventricular cannula prior to ischemia, at the end of ischemia, and 4 and 24 hr postischemia and analyzed for adenine nucleotides and creatine phosphate levels. Radiolabeled microspheres were used to measure myocardial and renal blood flows and no significant difference was found between ribose-treated control groups. In both groups, myocardial ATP levels fell by at least 50% at the end of ischemia. No significant ATP recovery occurred after 24 hr in the control dogs, but in the ribose-treated animals, ATP levels rebounded to 85% of control by 24 hr.(ABSTRACT TRUNCATED AT 250 WORDS)

High-energy phosphates, myocardial contractile function and material properties after short periods of oxygen deficiency

To investigate myocardial performance and diastolic properties after repeated periods of oxygen deficiency auxotonic and isovolumic measurements were performed after three periods (4 min) of asphyxia in Wistar rats (n = 19). Additionally, the response of the peak isovolumic left ventricular pressure to postextrasystolic potentiation was measured. The hemodynamic results were compared to the levels of high-energy phosphates. Already after 15 min of recovery from asphyxia auxotonic measures of systolic function were completely normal compared to the control group (n = 19). Isovolumic measurements after 20 min of postasphyctic recovery, however, demonstrated a considerable reduction of the peak left ventricular pressure (226.5 +/- 7.5 mm Hg vs. 262.6 +/- 3.4 mm Hg in controls, mean +/- SEM (p less than 0.01) indicating persistence of decreased postischemic contractile performance. The relative effect of postextrasystolic potentiation was similar in both groups, but could not compensate for the reduced performance of the postasphyctic hearts: the absolute postextrasystolic peak isovolumic pressure of the postasphyctic hearts was lower than the value of the regular isovolumic peak pressure in the controls. Diastolic properties (pressure/volume and stress/strain relationships) of the postasphyctic myocardium remained unchanged. The total sum of the adenine-nucleotides decreased from 7.2 +/- 0.2 to 5.6 +/- 0.3 mumol/gww (p less than 0.01). ATP was reduced from 4.8 +/- 0.2 to 3.9 +/- 0.3 mumol/gww (p less than 0.01). Phosphocreatine was elevated to 7.0 +/- 0.6 mumol/gww, x +/- SEM (p less than 0.01). Our results demonstrated normal postasphyctic basal hemodynamics and material properties. Thus, the energy supply was sufficient to maintain steady state conditions - in spite of decreased overall adenine-nucleotide levels. Isovolumic measurements and postextrasystolic potentation tests, however, indicated that the contractile performance of the postischemic myocardium was still reduced. This functional limitation cannot be explained by altered material properties and is probably not causally related to the decreased overall ATP content.

Effects of fluid resuscitation on cardiac dysfunction following thermal injury

To test the hypothesis that low cardiac output in burns is secondary to hypovolemia, the effects of resuscitation on isovolumic contracting rat heart following a full-thickness burn were studied. Sprague-Dawley rats were randomly assigned into three groups: (1) Sham burn, (2) 30% body surface area burn nonresuscitated, (3) 30% body surface area burn with 15 cc Ringer's lactate/180 g body wt ip at the time of burn resuscitated. Twenty hours postburn, the hearts were mounted on a Lagendorff perfusion apparatus. A balloon-tipped catheter placed in the left ventricle measured pressure and dp/dt. Coronary flow was determined. Myocardial samples for ATP and water were obtained. Left ventricular function was evaluated by recording peak systolic pressure, end diastolic pressure, and maximum +/- dp/dt while balloon volume was increased to 0.3 cc. Results are with end diastolic volume constant at 0.15 cc. Compared to sham burn, burn nonresuscitated generated lower peak systolic pressure +/- dp/dt and higher end diastolic pressure while hearts from burn resuscitated generated the same as sham burn. Coronary flow and tissue water content was similar in all. ATP content was lower in burn nonresuscitated. Our data support that impaired systolic and diastolic function in burn nonresuscitated hearts is associated with lower ATP levels not seen in burn resuscitated and reperfusion of burn nonresuscitated hearts does not reverse the myocardial depressant effect.

Myocardial preservation 1987: what is the state of the art?

The principles of myocardial preservation by hypothermic cardioplegia are: to induce cardiac arrest rapidly, to minimize energy requirements and prevent ischaemic damage during arrest, and to avoid reperfusion injury after arrest. These principles are put into practice by infusing an effective cold cardioplegic solution at the beginning of ischaemia and then every 20-30 min throughout ischaemia. Myocardial temperature should be maintained below 15 degrees C in all areas of the myocardium by topical cooling, efficient venous drainage and cardiac venting. The use of an oxygenated blood-based cardioplegic solution produces a modest improvement in myocardial recovery compared with a non-oxygenated crystalloid solution. During coronary reperfusion after arrest, ventricular distension should be avoided and coronary pressure should be sufficiently high to perfuse all areas of the myocardium, especially in patients with coronary stenoses. Developing areas in myocardial preservation include metabolic supplementation of the myocardium, the use of free radical scavengers, the prevention of atrial arrythmias and the use of coronary sinus cardioplegia. The increasing numbers of high risk patients presenting for surgery should stimulate the surgeon to adhere closely to the basic principles of myocardial preservation and to apply existing cardioplegic techniques meticulously. It should also challenge the investigator to increase basic understanding and improve methodology in this important area of cardiac surgery.

Intermittent reperfusion extends myocardial preservation for transplantation

A protocol was developed to compare prolonged heart preservation by hypothermic storage with prolonged hypothermic storage interrupted by a period of reperfusion. Hearts from adult mongrel dogs were excised after administration of 4 degrees C crystalloid cardioplegia. Group A hearts (N = 7) underwent 7.5 hours of ischemia at 4 degrees C followed by 1.5 hours of reperfusion and rewarming (A0). Group B hearts (N = 8) underwent 3 hours of ischemia at 4 degrees C, 1.5 hours of reperfusion and rewarming (B1), 3 additional hours of ischemia at 4 degrees C following repeat cardioplegia, and finally 1.5 hours of reperfusion and rewarming (B2). During reperfusion, hearts were defibrillated and left ventricular (LV) function was assessed by measuring isovolumic peak systolic pressure and maximum positive rate of rise of LV pressure (+dP/dtmax) with an intraventricular balloon. LV biopsy samples for adenosine triphosphate (ATP) assay were obtained before ischemia and after each rewarming period. One Group A heart could not be defibrillated and studied. All Group B hearts completed the protocol. LV function, as assessed by peak pressure and +dP/dtmax, at B1 and B2 exceeded values obtained at A0, but the differences were not statistically significant. The mean ATP level was 63.4 +/- 7.7% of baseline at B1 and 79.7 +/- 4.3% of baseline at B2 (p less than .03). The mean ATP level was 57.9 +/- 5.9% of baseline at A0 (p less than .007, B2 vs. A0). It is presumed that intermittent reperfusion allows repletion of substrate stores, which results in improved myocardial protection.(ABSTRACT TRUNCATED AT 250 WORDS)

Myocardial protection

Early studies of myocardial protection were designed to minimize ischemic injury. The next class and generation of investigations will most likely be designed to accelerate recovery following known myocardial injury. Such techniques will play an important role in allowing operations on acutely injured and ischemic myocardium and will be important in the treatment of postischemic injury when such injury occurs during the course of complex cardiac operations. Surgical aspects of myocardial metabolism are still rudimentary and many empiric observations require further exploration into the mechanisms by which such applications work.

Repeated short periods of regional myocardial ischemia: effect on local function and high energy phosphate levels

The effect of recurrent periods of ischemia on the myocardium was investigated in 15 open-chest dogs. Ischemia was produced by 3 minutes of proximal occlusion of the left anterior descending coronary artery. Each occlusion was followed by reperfusion of 3 minutes duration. Forty occlusions with a total of 120 minutes of ischemia were performed, and regional function (sonomicrometry) as well as high energy phosphates (needle biopsies) were determined at the end of the 5th, 20th, and 40th period of ischemia and reperfusion. The first periods of ischemia had a cumulative effect both on regional postischemic function (44% and 59% respectively of preischemic control after 20 occlusions) and on the ATP content, but with increasing number of occlusions the additive effects became smaller (ATP reduction/mumol/g w w/per occlusion). The ATP breakdown per occlusion was diminished with increasing number of periods of ischemia, and no significant adenosine was measured in the ischemic myocardium. Higher than normal postischemic creatine phosphate levels (9.1 mumol/g w w at the 40th reperfusion vs. 6.7 mumol/g w w control) indicated a functioning oxidative phosphorylation in the presence of an ATP utilization problem at the sarcomere level, because indicators of the cellular energy level (energy charge, free energy change of ATP hydrolysis) quickly normalized during reperfusion. Stunned myocardium is therefore not a problem of energy supply but rather of energy utilization. Reduced ATP utilization and regional dysfunction are the expressions of the same cellular defect which resides either in the ATP-splitting contractile apparatus or in the electromechanical coupling. Contractile dysfunction during reperfusion protects the heart against subsequent periods of ischemia because ATP turnover is reduced.

Myocardial preservation

The principles used to develop techniques for myocardial preservation in cardiac surgery have been successfully applied to the protection of the donor heart in transplant surgery. This article reviews the latest advances in myocardial preservation during cardiac surgery and shows how they have been adopted in current cardiac transplant techniques.

Long term model for evaluation of myocardial metabolic recovery following global ischemia

Myocardial ATP levels remain depressed following significant periods of ischemia (Isc) despite reperfusion (Rpf). Neither the rate of in vivo ATP return following global Isc nor the factors which influence recovery have been defined. In order to determine the time course to complete the return of ATP levels and evaluate methods of enhancing recovery of ATP levels, we have devised a chronic canine model of global Isc. In this model serial ventricular biopsies can be taken in the awake animal over several days without reoperation which allows an investigation of the recovery of the myocardium following a uniform global insult to be performed. Recovery of ATP levels has been shown to depend, at least in part, on the availability of precursors and the activity of the ATP regenerating enzymes. Because complete recovery of ATP levels takes days, short term (hours) models have limitations. Previous attempts at enhancing ATP recovery following Isc have been only partially successful because either the degree of depression was not great or the period of observation was short, resulting in incomplete return. To identify the best precursor choice, we previously measured the activity of the AMP regenerating enzymes, adenosine kinase (AdK) (adenosine----AMP) and adenine phosphoribosyl transferase (APRT) (adenine----AMP). Because APRT activity was 20 fold higher than AdK with similar Km values for substrates, it appeared that adenine (A) is preferred to adenosine for AMP regeneration in the dog's myocardium. The formation of 5-phosphoribosyl 1-pyrophosphate (PRPP) may also be rate limiting and, therefore, the effect of ribose (R) on ATP recovery was also evaluated. Recovery of ATP levels was assessed in three groups: (1) normal saline (NS), (2) A (20 mM) in normal saline (A/NS) or (3) A with R (80 mM) in normal saline (A/R) were infused (1.0 ml/min) into the right atrium of dogs for 48 hours following Isc. In all groups, ATP levels fell to between 46-60% of pre-Isc levels during Isc. In the NS dogs, ATP levels continued to fall slightly to 46% pre-Isc levels during the first four hours of Rpf after Isc. By 24 hours no appreciable recovery had occurred and the measured ATP was only 51% of the pre-Isc value. Even by seven days, ATP had not returned fully, and by extrapolation, complete recovery required 9.9 +/- 1.4 days. Treated dogs showed, however, that ATP recovery could be significantly enhanced.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of adenosine and AICAR on ATP content and regional contractile function in reperfused canine myocardium

We investigated whether the postischemic acceleration of adenosine triphosphate (ATP) synthesis by means of precursor infusion is beneficial for the contractile function of reperfused myocardium. A coronary artery was occluded for 45 min in 21 dogs to produce a marked but reversible ischemia. During the following 3 hours of reperfusion either adenosine (n = 6) or AICAR (5-amino-imidazole-4-carboxamide-riboside) (n = 6) was infused intracoronarily by a small transfemoral catheter positioned in the LAD. ATP repletion by adenosine was nearly 50% of the deficit caused by the previous ischemia, the effect of AICAR on steady-state tissue ATP concentration was insignificant. Regional systolic function of these both groups was compared to that of a control group (n = 9) receiving only a saline infusion. We measured the regional function by subendocardially implanted ultrasound transducers using the transit time method. All three groups showed a reduction to about 25% of the initial segment shortening at the end of ischemia, followed by a quick recovery to half of the preocclusion segment shortening after reopening of the vessel. No further changes were observed in the control series during the 3 hours of reperfusion (50 +/- 10% SE segment shortening at the end). With adenosine infusion - in spite of the resulting considerable ATP elevation - no significant change of segmental contractile function occurred (44 +/- 5% SE segment shortening). Only the AICAR treated group differed from control. It produced a continuous deterioration during reflow resulting in a holosystolic bulging of -20% +/- 10% SE at the end of 3 hours of reperfusion. Our results show that there is no correlation between different ATP tissue levels achieved by adenosine infusion and systolic function in reperfused myocardium after regional reversible ischemia. We hypothesize that reperfusion dyskinesia is caused by a failure of energy utilisation rather than of energy supply.

Recent advances in cardiopulmonary bypass and the clinical application of myocardial protection

Basic scientific research has provided the impetus to develop cardioplegic solutions that offer excellent myocardial preservation. Future research will continue to develop methods for better delivery of cardioplegia to all myocardial regions. In addition, earlier detection of evolving ischemic damage during aortic cross-clamping might provide a basis for earlier intervention to reverse developing myocardial injury. At the present time, the cardiac surgeon has many cardioplegic solutions and delivery systems from which to choose. Only by understanding the principles involved in myocardial preservation will the surgeon be able to develop a system that will work best in his or her clinical practice.

Concepts and techniques of myocardial protection for adult open heart surgery

Discussions of myocardial protection are often limited to the subject of cardioplegia. However, numerous aspects of operative and perioperative care are of comparable importance. This article outlines the broad topic of myocardial protection, provides strategies for its practical implementation, and reports the author's personal results.

Metabolic and functional effects of phosphoenolpyruvate and adenosine triphosphate on rat hearts subjected to global ischemia

The effect of phosphoenolpyruvate (PEP) and adenosine triphosphate (ATP) administered during ischemia was investigated, using the paracorporeal rat heart model. During 15 min of global ischemia the hearts were perfused twice with PEP and ATP (supplemented) or with NaCl only (non-supplemented). In hearts that were freeze-clamped after the ischemic period (group A), the myocardial content of high-energy phosphates showed only minor differences between hearts with and without supplemention. In the supplemented hearts there was increased myocardial content of pyruvate and, to some extent, of lactate, indicating that PEP was metabolized to pyruvate and partly to lactate. In groups B and C the hearts were reperfused for 40 min before freeze-clamping. The non-supplemented hearts showed higher energy content and better left ventricular performance and, concomitantly, the creatine kinase isoenzyme MB (CK-MB) efflux was less than for the supplemented hearts. A clear inverse relationship between left ventricular performance and CK-MB efflux indicated that CK-MB served as a marker of cell integrity. These results contrasted with previus finding of an unequivocally positive effect from PEP and ATP administration. Possible explanations are discussed.