Biomedical subjects
M Karmazyn
Publications and source records attributed to M Karmazyn.
Mechanisms of protection of the ischemic and reperfused myocardium by sodium-hydrogen exchange inhibition.
Sodium-hydrogen exchange (Na-H exchange) is a major regulator of intracellular pH and is one of the major mechanisms for restoring pH after ischemia-induced intracellular acidosis. However, activation of Na-H exchange during ischemia and reperfusion is also involved in paradoxical induction of cell injury. This likely reflects the fact that activation of the exchanger is closely coupled to sodium influx and, as a consequence, to elevation in intracellular calcium concentrations through sodium-calcium exchange. In addition to intracellular acidosis, other factors can also stimulate the exchanger, including various autocrine and paracrine factors, such as endothelin-1, angiotensin II, alpha(1)-adrenergic agonists, as well as toxic agents, such as hydrogen peroxide and lysophosphatidylcholine. Although at least six Na-H exchange isoforms have thus far been identified, it appears that the 1 subtype, termed NHE1, is the predominant isoform in the mammalian myocardium. Effective pharmacological inhibitors of Na-H exchange, including those that are NHE1 specific, have been extensively demonstrated to protect the ischemic and reperfused myocardium in terms of improved systolic and diastolic function, preservation of cellular ultrastructure, attenuation of the incidence of arrhythmias, and reduction of apoptosis. Moreover, the salutary effects of these agents have been demonstrated using a variety of experimental models as well as animal species, suggesting that the role of Na-H exchange in mediating injury is not species specific. Thus, Na-H exchange represents an important target for pharmacological intervention in attenuation of ischemia and reperfusion-induced cardiac injury. Coupled with the low potential for toxicity of the agents, Na-H exchange inhibition could emerge as an effective therapeutic strategy in cardiac disorders, particularly involving conditions associated with ischemia and reperfusion.
The antifungal antibiotic clotrimazole potently inhibits L-type calcium current in guinea-pig ventricular myocytes.
The antimycotic agent clotrimazole (CLT) is a promising potential therapeutic agent for a variety of diseases including cancer. Although it is known that CLT alters calcium homeostasis in many cell types, its cardiac effects are virtually unknown. We investigated the effects of CLT on L-type calcium current (ICa,L) and action potentials in guinea-pig ventricular myocytes. CLT (5, 25 and 50 microM) inhibited basal ICa,L by 16, 59 and 93%, respectively. The inhibitory effect of CLT was rapid and the peak effect was attained within 3 min. At a concentration of 25 microM, the inhibitory effect of CLT was partially reversible whereas the response to 50 microM CLT persisted following drug withdrawal. CLT abbreviated action potential duration at 50 and 90% of repolarization and suppressed the plateau significantly. These results indicate that CLT may have important cardiac effects at concentrations used to induce the antiproliferative action of the drug.
Cardioprotective effects of propofol and sevoflurane in ischemic and reperfused rat hearts: role of K(ATP) channels and interaction with the sodium-hydrogen exchange inhibitor HOE 642 (cariporide).
BACKGROUND: Sodium ion-hydrogen ion (Na(+)-H(+)) exchange inhibitors are effective cardioprotective agents. The N(+)-H(+) exchange inhibitor HOE 642 (cariporide) has undergone clinical trials in acute coronary syndromes, including bypass surgery. Propofol and sevoflurane are also cardioprotective via unknown mechanisms. The authors investigated the interaction between propofol and HOE 642 in the ischemic reperfused rat heart and studied the role of adenosine triphosphate-sensitive potassium (K(ATP)) channels in the myocardial protection associated with propofol and sevoflurane. METHODS: Isolated rat hearts were perfused by the Langendorff method at a constant flow rate, and left ventricular function and coronary pressures were assessed using standard methods. Energy metabolites were also determined. To assess the role of K(ATP) channels, hearts were pretreated with the K(ATP) blocker glyburide (10 microM). Hearts were then exposed to either control buffer or buffer containing HOE 642 (5 microM), propofol (35 microM), sevoflurane (2.15 vol%), the K(ATP) opener pinacidil (1 microM), or the combination of propofol and HOE 642. Each heart was then subjected to 1 h of global ischemia followed by 1 h of reperfusion. RESULTS: Hearts treated with propofol, sevoflurane, pinacidil, or HOE 642 showed significantly higher recovery of left ventricular developed pressure and reduced end-diastolic pressures compared with controls. The combination of propofol and HOE 642 provided superior protection toward the end of the reperfusion period. Propofol, sevoflurane, and HOE 642 also attenuated the onset and magnitude of ischemic contracture and preserved high-energy phosphates (HEPs) compared with controls. Glyburide attenuated the cardioprotective effects of sevoflurane and abolished the protection observed with pinacidil. In contrast, glyburide had no effect on the cardioprotection associated with propofol treatment. CONCLUSION: HOE 642, propofol, and sevoflurane provide cardioprotection via different mechanisms. These distinct mechanisms may allow for the additive and superior protection observed with the combination of these anesthetics and HOE 642.
Orally administered NHE1 inhibitor cariporide reduces acute responses to coronary occlusion and reperfusion.
Na+/H+ exchange (NHE) mediates myocardial ischemic and reperfusion injury. We examined the effects of dietary administration of the potent and selective NHE1 inhibitor cariporide on acute responses to coronary artery ligation and reperfusion in the anesthetized rat. Male Sprague-Dawley rats received control rat chow or an identical diet containing 3 parts per million of cariporide for 1 wk before 225 min of occlusion of the left main coronary artery or 45 min of occlusion followed by 180 min of reperfusion. Hearts were excised and divided into left ventricle, right ventricle, and interventricular septum for analysis of NHE1 mRNA expression and apoptosis by staining with terminal deoxynucleotidyl transferase-mediated nick end labeling. Ischemia and reperfusion were associated with a threefold elevation in NHE1 mRNA expression in control animals that was significantly reduced in cariporide-fed rats. Cariporide reduced mortality from 26% of animals to 0%. The incidence of all arrhythmias was significantly reduced, including ventricular fibrillation (from 42 to 0%) and ventricular tachycardia (from 81 to 15%), as well as the number of ventricular premature beats (from 70 +/- 12 to 17 +/- 6). Cariporide moderately reduced apoptosis only in the reperfused left ventricle to values not significantly greater than those in sham-operated animals, and this was associated with a significantly higher ratio of Bcl-2 to Bax. This study suggests that NHE inhibition with dietary cariporide represents an effective management of acute postinfarction responses.
LPS pretreatment ameliorates peritonitis-induced myocardial inflammation and dysfunction: role of myocytes.
Peritonitis induced by cecal ligation and puncture (CLP) produces a systemic inflammatory response that can be largely mitigated by pretreatment of the animals with lipopolysaccharide (LPS tolerance). Although cells of myeloid origin and endothelial cells have been shown to contribute to the development of LPS tolerance, little is known regarding the potential role of parenchymal cells in this phenomenon. The major aim of the present study was to assess whether cardiac parenchymal cells (myocytes) contribute to the development of LPS tolerance. Six hours after induction of CLP rats were neutropenic and acidotic, the myocardium contained a leukocyte infiltrate [myeloperoxidase (MPO) activity was increased], and myocardial contractile function was impaired (left ventricular developed pressure was decreased). In animals that were pretreated with LPS these manifestations of sepsis were largely reversed. Further studies focused on the responses of cardiac myocytes to CLP and whether myocytes contributed to the development of LPS tolerance. Myocytes were isolated from rat hearts 6 h after induction of CLP. These myocytes 1) exhibited an impaired ability to shorten in response to pacing, 2) contained the nuclear transcription factor NF-kappaB in their nuclei, 3) increased their surface levels of intercellular adhesion molecule-1 (ICAM-1), and 4) were hyperadhesive for neutrophils. All of these events did not occur in myocytes obtained from animals that were pretreated with LPS before induction of CLP. These findings indicate that LPS tolerance can be induced in myocytes with respect to polymorphonuclear leukocyte adhesion, presumably by an inability of CLP to mobilize NF-kappaB to the myocyte nuclei and, thereby, preventing an increase in surface levels of ICAM-1.
Modulation of Na+/H+ exchange isoform 1 mRNA expression in isolated rat hearts.
Na+/H+ exchange (NHE) has been demonstrated to mediate myocardial ischemia and reperfusion injury as well as injury produced by hydrogen peroxide (H2O2) or lysophosphatidylcholine (LPC). However, changes in gene expression in response to injurious factors have not been extensively studied. We examined Na+/H+ exchange isoform 1 (NHE-1) expression using Southern detection of the RT-PCR product in response to 30 min of global ischemia with or without reperfusion in isolated rat hearts or to 30 min of exposure to either H2O2 (100 microM) or LPC (5 microM). We also determined whether ischemic preconditioning (2x 5-min ischemia) alters basal NHE-1 expression or the subsequent response to insult. Ischemia with or without reperfusion increased NHE-1 expression approximately sevenfold (P < 0.05), whereas either H2O2 or LPC increased expression approximately twofold. Preconditioning reduced NHE-1 message by approximately 70% (P < 0.05) and significantly attenuated the effects of ischemia, H2O2, or LPC. The internal standard, beta-globin was unaffected by any treatment. Our results indicate that NHE-1 expression is rapidly increased in response to ischemia with or without reperfusion as well as in response to H2O2 or LPC. In contrast, preconditioning was associated with downregulation of NHE-1. These results may be important in furthering our understanding of NHE-1 in cardiac disease states and suggest that the antiporter adapts rapidly to cardiac conditions associated with pathology.
Protective effects against hydrogen peroxide-induced toxicity by activators of the ATP-sensitive potassium channel in isolated rat hearts.
Activation of ATP-sensitive (KATP) channels has been shown to exert protective effects on the ischemic and reperfused myocardium. Reactive oxygen species are thought to mediate, at least in part, this form of cardiac injury. Using isolated perfused rat hearts, we therefore studied whether KATP activation exerts any effect on the direct deleterious effects of either 200 microM hydrogen peroxide or a free radical generating system consisting of purine plus xanthine oxidase in terms of function and energy metabolite status. On their own, hydrogen peroxide or the combination of purine plus xanthine oxidase treatment resulted in a time-dependent depression of myocardial contractility, which reached over 90% after 30 min perfusion, an effect which was associated with approximately 1000% elevation in left ventricular end-diastolic pressure (LVEDP). The KATP channel opener cromakalim (0.5 microM) significantly attenuated the hydrogen peroxide-induced loss in systolic function throughout the treatment period, and reduced the elevation in LVEDP with significant attenuation 10, 15 and 20 min after hydrogen peroxide addition. Contractile dysfunction produced by hydrogen peroxide was associated with significantly reduced tissue ATP, creatine phosphate and glycogen content to approximately 70, 60 and 70% of control, respectively. The depletion of these metabolites was significantly attenuated to 35, 23 and 23% of control, respectively, in the presence of cromakalim. The protective effects of cromakalim against contractile dysfunction, as well as depletion in intermediary energy metabolites, was abolished in the presence of the KATP channel antagonist glibenclamide (1 microM). However, glibenclamide on its own failed to alter the cardiac response to hydrogen peroxide with respect to any parameter. The responses to the free radical generating system consisting of purine plus xanthine oxidase was unaffected by cromakalim. Our study shows that KATP channel activation selectively protects against the cardiotoxic influence of hydrogen peroxide, and may explain, in part, the salutary effects of KATP activators in myocardial ischemia.
Hydrogen peroxide induced impairment of post-ischemic ventricular function is prevented by the sodium-hydrogen exchange inhibitor HOE 642 (cariporide).
OBJECTIVE: Sodium-hydrogen exchange (NHE) activation is a major mechanism of cardiac injury produced by ischemia and reperfusion. In addition, NHE may mediate the direct effects of hydrogen peroxide (H2O2) in normally perfused hearts. The present study was done to determine whether H2O2 at low concentrations producing mild myocardial depression affects post-ischemic recovery of function and to determine the ability of the NHE inhibitor HOE 642 to modulate this effect. METHODS: Isolated Langendorff-perfused rat hearts with a left ventricular balloon inflated to an initial end-diastolic pressure of 5 mmHg were subjected to 90 min of global zero-flow ischemia followed by 60 min reperfusion. In Study 1, hearts were randomized for perfusion with or without H2O2 (20 microM) for 15 min before ischemia and throughout reperfusion. In Study 2, identical experiments were done except that the hearts were pretreated with the NHE inhibitor HOE 642 (5 microM). Function was assessed by determining intraventricular pressures. RESULTS: Recovery of developed pressure in Study 1 after 10 min reperfusion was 60.3 +/- 8% of pre-ischemic values in control hearts whereas this was reduced to 29.9 +/- 10% in hearts treated with H2O2 (P < 0.05). After 60 min of reperfusion recovery of developed pressure was 80.3 +/- 5.2% and 60.7 +/- 7% in control and H2O2-treated hearts, respectively (P < 0.05). Recovery of rates of pressure development (+dP/dt) and relaxation (-dP/dt) paralleled the effects seen with developed pressure. Moreover, these effects were associated with significantly elevated end-diastolic pressure during the last 20 min of reperfusion. In Study 2, HOE 642 completely prevented the deleterious effect of H2O2, both with respect to ventricular recovery and to the elevation in end-diastolic pressure during reperfusion. CONCLUSIONS: Our results show that very low concentrations of H2O2 significantly impair recovery of function in this rat model of myocardial ischemia-reperfusion. Moreover, our results suggest that this effect is likely dependent on NHE activity and can be prevented by treatment with the NHE inhibitor HOE 642.
Augmented retinal endothelin-1, endothelin-3, endothelinA and endothelinB gene expression in chronic diabetes.
PURPOSE: Endothelins (ETs) belong to a family of vasoactive peptides implicated in several disorders of the microvasculature. In the present study, we investigated ET-1 and ET-3 peptide mRNAs and ETA, ETB receptor mRNAs in the retina of diabetic BB/W rats and age-matched, non-diabetic control animals, following six months of diabetes. METHODS: Total mRNA was extracted from each retina and was subjected to reverse transcriptase polymerase chain reaction for ET-1, ET-3, ETA and ETB. Simultaneously, beta-globin was amplified and used as a housekeeping gene. The products were analyzed on agarose gels and the specificity of the amplification was established by hybridization with amplification-specific biotinylated oligoprobes. For quantification, the products from the linear phase of amplification were subjected to serial dilution slot-blot hybridization and densitometry. RESULTS: ETs and their receptor mRNA expressions were present in the retina. Retinas from the diabetic animals showed significant increases in ET-1, ET-3 ET(A), ET(B) mRNA expressions compared to those from control rats. CONCLUSIONS: These findings indicate that retinal ET-1, ET-3, ET(A) and ET(B) mRNA expression in increased in the chronically diabetic BB/W rat. Augmented gene expression of ETs and their receptors potentially may be of importance in the pathogenesis of retinal microangiopathy in diabetes.
The myocardial sodium-hydrogen exchanger (NHE) and its role in mediating ischemic and reperfusion injury.
A major mechanism by which the heart adapts to intracellular acidosis during ischemia and recovers from the acidosis after reperfusion is through the sodium-hydrogen exchanger (NHE). There are at least 5 NHE isoforms thus-far identified with the NHE-1 subtype representing the major one found in the mammalian myocardium. This 110 kDa glycoprotein extrudes protons concomitantly with Na influx in a 1:1 stoichiometric relationship rendering the process electroneutral. Although NHE is critical for the maintenance of intracellular pH during acid loading conditions such as ischemia, there is convincing evidence that it also plays a pivotal role in mediating tissue injury during ischemia and reperfusion. The mechanism for this paradoxical deleterious role of NHE reflects the fact that under conditions of tissue stress, including ischemia, Na-K adenosine triphosphate (ATP)ase is inhibited thereby limiting Na extrusion resulting in an elevation in intracellular Na concentrations. The latter effect, in turn, will increase intracellular Ca concentrations via Na-Ca exchange. In addition, NHE-1 expression in the diseased myocardium is increased suggesting that elevated production of the antiporter represents a long-term adaptive process in an attempt by the cardiac cell to regulate intracellular pH which, paradoxically, contributes to cardiac pathology. Extensive studies using NHE inhibitors such as amiloride or its analogs, or more specific compounds including 3-methylsulphonyl-4-piperidinoloenzoyl-guanidine methanesulphonate (HOE 694) or 4-isopropyl-3-methylsulphonylbenzcyl-guanidine methane sulphonate (HOE 642) have consistently shown protective effects against ischemic and reperfusion injury in a large variety of experimental models and animal species particularly in terms of attenuating contractile dysfunction. Such studies have contributed greatly to the overwhelming evidence that NHE activation mediates ischemic and reperfusion injury. Indeed, HOE 642 (Cariporide) is currently undergoing clinical evaluation in high risk cardiac patients. Moreover, there is now emerging evidence that NHE may be involved in mediating cardiotoxicity directly produced by various ischemic metabolites such as lipid amphiphiles or reactive oxygen species. In this regard, we have demonstrated that NHE inhibitors can effectively attenuate the cardiac injury produced by lysophosphatidylcholine and hydrogen peroxide. In addition, it now appears that NHE inhibition reduces apoptosis in the ischemic myocardium, a process which may be of importance in the subsequent development of postinfarction heart failure. In conclusion, NHE represents an important adaptive process in response to intracellular acidosis resulting in a paradoxical contribution to cardiac tissue injury.
Hydrogen peroxide-induced stimulation of L-type calcium current in guinea pig ventricular myocytes and its inhibition by adenosine A1 receptor activation.
Hydrogen peroxide (H2O2) produces complex cardiac effects that may involve altered calcium homeostasis. The cardiotoxic effects of H2O2 can be attenuated by adenosine A1 receptor agonists. The present study examined the effect of H2O2 on L-type Ca++ current (ICa,L) in guinea pig ventricular myocytes under two different recording conditions and the influence of adenosine receptor agonists. H2O2 (100 microM), did not have any significant effect on ICa,L, under conventional whole cell patch configuration. However, when recorded under nystatin perforated patch configuration, H2O2 caused a gradual and significant increase (84 +/- 14%) in ICa,L compared to control values. N6-cyclopentyladenosine (CPA), an adenosine A1 receptor agonist, significantly attenuated the effect of H2O2. The inhibitory effect of N6-cyclopentyladenosine was antagonized by 8cyclopentyl-1, 3-dipropylxanthine, an adenosine A1 receptor antagonist. The A2A and A3 receptor agonists, 2-p-(2-Carboxyethyl)phenethylamino-5'- N - ethylcarboxamidoadenosine (CGS-21680) and 1-deoxy-1-[6-[[(3-iodophenyl)methyl]amino]-9H-purin-9-yl]-N-methyl-be ta-D-ribofuranuronamide, respectively, did not modulate the enhancement of ICa,L by H2O2. Moreover the effects of N6-cyclopentyladenosine were mimicked by the protein kinase C inhibitor bisindolylmaleimide. Thus, our results demonstrate a potent stimulatory effect of H2O2 on ICa,L in guinea pig ventricular myocytes. We further demonstrate that adenosine A1 receptor activation attenuates this effect. Our results suggest a potential basis for altered calcium homeostasis in response to H2O2 as well as the salutary effects of A1 receptor activation against H2O2-induced cardiotoxicity.
Differential effects of endothelin-1 on basal and isoprenaline-enhanced Ca2+ current in guinea-pig ventricular myocytes.
1. We examined the effect of endothelin-1 (ET-1) on basal and isoprenaline-enhanced L-type Ca2+ current (ICa,L) in guinea-pig ventricular myocytes under nystatin-perforated patch configuration. 2. ET-1 at concentrations of 1, 5 and 10 nM had little effect on basal ICa,L. However, ICa,L enhanced by isoprenaline (500 nM) was significantly attenuated by 5 nM ET-1 by more than 50%. This effect was reversed upon washout. ICa,L enhanced by forskolin was also decreased by ET-1. 3. The inhibitory effect of ET-1 against isoprenaline was completely blocked by the ETA receptor antagonist BQ-123 (1 microM). In myocytes incubated with pertussis toxin (PTX, 2 micrograms ml-1) for 5 h, ET-1 did not inhibit isoprenaline-enhanced ICa,L. 4. Although ET-1 has been shown to activate specific protein kinase C (PKC) isoforms, a significant inhibitory effect of ET-1 was maintained in the presence of the PKC inhibitor bisindolylmaleimide (20 nM). The nitric oxide (NO) donor SIN-1 (10 microM) attenuated but failed to prevent the ET-1 effect. 5. In summary, our results demonstrate that ET-1 is devoid of any significant effects on basal ICa,L. However, it exerts a potent inhibitory effect against isoprenaline-enhanced ICa,L. This effect is mediated through ETA receptors coupled to PTX-sensitive G-proteins and occurs in the presence of PKC inhibition and NO generation.
A rapid ischemia-induced apoptosis in isolated rat hearts and its attenuation by the sodium-hydrogen exchange inhibitor HOE 642 (cariporide).
Apoptosis is a potentially important myocardial response to pathology including ischemia and reperfusion. Na-H exchange (NHE) represents an important mechanism for mediating such injury. The present study was done to determine if NHE inhibition can affect early apoptosis in an acute model of ischemia and reperfusion. Isolated rat hearts were subjected to zero-flow ischemia for various durations with or without subsequent 30 min of reperfusion. Nick-end-labelling of biotin-dUTP (TUNEL staining), as well as DNA extraction followed by agarose gel electrophoresis, were used to semiquantify apoptotic cells and identify DNA laddering, respectively. Apoptosis first appeared after 10 min of ischemia and reached a maximum level after 30 min. The number of apoptotic cells after 30 min of ischemia was 31 +/- 3 per 100 high power microscopic fields, whereas in reperfused hearts the number of cells was 34 +/- 3. To determine the effect of NHE inhibition, hearts were pretreated 15 min prior to ischemia with HOE 642, a potent and specific inhibitor of the isoform (NHE-1) found in myocardium. HOE 642 significantly reduced the number of apoptotic cells in the ischemic and reperfused heart to 2 +/- 1 and 6 +/- 1, respectively (P<0.05 from untreated hearts). DNA laddering was not observed with electrophoretic DNA analysis, likely owing to the small number of apoptotic cells involved. Hearts recovered nearly 100% of function in both groups, although there was a significantly higher recovery after 1 and 2 min of reperfusion in those hearts treated with HOE 642. Our study shows that apoptosis, albeit very mild in nature, can be rapidly induced in isolated hearts by a relatively brief period of ischemia without reperfusion, which can be markedly attenuated by the NHE inhibitor HOE 642. The ability of HOE 642 to markedly attenuate apoptosis may be important in terms of understanding the drug's cardioprotective properties as well as the overall role of NHE in heart disease.
The Na-H exchanger revisited: an update on Na-H exchange regulation and the role of the exchanger in hypertension and cardiac function in health and disease.
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Interaction between anesthetics and the sodium-hydrogen exchange inhibitor HOE 642 (cariporide) in ischemic and reperfused rat hearts.
BACKGROUND: Sodium (Na+)-hydrogen (H+) exchange (NHE) inhibitors are effective cardioprotective agents. The potent NHE inhibitor HOE 642 (cariporide) is being evaluated clinically in high-risk patients, including those having coronary artery bypass. Volatile anesthetics are also cardioprotective, most likely via different mechanisms. The potential interaction between anesthetics and HOE 642 was investigated. METHODS: Electrically paced isolated rat hearts were perfused at constant flow. Left ventricular developed pressure and end-diastolic pressure were monitored as determinants of function. Hearts were subjected to 60 min each of total ischemia followed by reperfusion. Isoflurane (0.93 minimum alveolar concentration [MAC]), sevoflurane (1.03 MAC), or sufentanil (1.2 nM) was added 15 min before ischemia and throughout reperfusion, either alone or in combination with HOE 642 (5 microM). The effect of HOE 642 alone was also studied. At the end of reperfusion, hearts were freeze-clamped for subsequent determination of tissue metabolites. RESULTS: In control hearts, left ventricular developed pressure recovered to 40% of preischemia values, whereas left ventricular end-diastolic pressure increased by 650% after reperfusion. Sevoflurane, isoflurane, or HOE 642 alone significantly enhanced left ventricular developed pressure recovery to more than 90%, although recovery with HOE 642 was more rapid and accompanied by significantly reduced left ventricular end-diastolic pressure. HOE 642 plus volatile anesthetics produced additive effects, with left ventricular developed pressure recovering by more that 100%, although left ventricular end-diastolic pressure was not further reduced. Sufentanil had no effect in terms of developed pressure, but protection with HOE 642 was maintained. HOE 642 with or without volatile anesthetics also preserved adenosine triphosphate levels. CONCLUSIONS: Isoflurane, sevoflurane, and HOE 642 enhance ventricular recovery, but the effect of HOE 642 is also associated with reduced contracture and adenosine triphosphate preservation. A combination of the NHE inhibitor and either volatile agent confers additive and superior protection, which could be relevant for the establishment of ideal cardioprotective strategies during surgery.
Na(+)-H+ exchange inhibition protects against mechanical, ultrastructural, and biochemical impairment induced by low concentrations of lysophosphatidylcholine in isolated rat hearts.
Lysophophatidylcholine (LysoPC) accumulates rapidly in the ischemic myocardium and is an important mediator of ischemia-induced cell injury. Na(+)-H+ exchange (NHE) inhibition has been demonstrated to protect the ischemic and reperfused myocardium. We determined whether NHE inhibition can also modulate cardiotoxicity produced by LysoPC (3 and 5 mumol/L) in isolated rat hearts. At 3 mumol/L, LysoPC produced a depression in left ventricular developed pressure (LVDP) and elevation in left ventricular end-diastolic pressure (LVEDP), which were 19 +/- 7% and 1290 +/- 205% of pre-LysoPC values, respectively, after 30 minutes of treatment. In the presence of the NHE inhibitor 4-isopropyl-3-methylsulfonylbenzoyl-guanidine methanesulfonate (HOE 642, 5 mumol/L), LVDP was reduced to only 80.8 +/- 8.6%, and LVEDP increased to 270 +/- 32% (P < .05 for both parameters). LysoPC significantly depressed tissue ATP, creatine phosphate, and glycogen contents and increased lactate levels, all of which were significantly attenuated by HOE 642. Moreover, marked LysoPC-induced ultrastructural abnormalities, including mitochondrial and myofibrillar disruption, were totally prevented by HOE 642. This protection was mimicked by another NHE inhibitor, methylisobutylamiloride (5 mumol/L). HOE 642 was also effective against injury produced by 5 mumol/L LysoPC although, generally, the protection was less marked than that observed against 3 mumol/L; LVDP depression after 30 minutes was 10.1 +/- 4.3% and 41.4 +/- 10.4% of pre-LysoPC values in control and HOE 642-treated hearts, respectively (P < .05), whereas corresponding LVEDP elevations were 1629 +/- 393% and 990 +/- 144% (P > .05). In myocytes superfused with bicarbonate-free buffer subjected to acid loading by NH4Cl pulsing, pH recovery (as measured by acid flux) was significantly stimulated by 3 mumol/L LysoPC, indicative of NHE activation. Our study shows that cardiac injury produced by low concentrations of LysoPC can be effectively attenuated by NHE inhibition. The results also suggest that the beneficial effects of NHE inhibitors on the ischemic myocardium may be, at least partially, mediated by inhibiting the deleterious effects of LysoPC.
Effect of sodium-hydrogen exchange inhibition on functional and metabolic impairment produced by oxidative stress in the isolated rat heart.
Sodium-hydrogen exchange (NHE) represents an important process mediating myocardial ischemic and reperfusion injury, and NHE inhibitors have been shown to be effective cardioprotective agents against this form of injury. The precise mechanisms by which NHE inhibition protect the heart are not known and we therefore postulated that attenuation of oxidative stress could contribute to such protection. Accordingly, we examined whether the potent and specific NHE inhibitor 4-isopropyl-3-methylsulphonylbenzoyl-guanidine methanesulphonate (HOE 642, 5 microM) can protect isolated rat hearts against mechanical and biochemical impairment produced by either hydrogen peroxide (150 or 200 microM) or a free radical generating system consisting of purine (4.6 or 9.2 mM) and xanthine oxidase (20 or 40 U/L). HOE 642 significantly delayed and attenuated both the depression in left ventricular developed pressure (LVDP) as well as the elevation in left ventricular end-diastolic pressure (LVEDP) produced by both concentrations of hydrogen peroxide, although greater protection was generally seen against the lower hydrogen peroxide concentration, particularly with respect to LVEDP. Hydrogen peroxide, at both concentrations, significantly reduced high energy phosphate and glycogen contents and elevated lactate levels, all of which were significantly attenuated by HOE 642. In contrast, HOE 642 had no effect on functional impairment produced by either concentration of the free radical generating system. At its lower concentration, the combination of purine plus xanthine oxidase had no effect on energy metabolites, although a significant reduction in high energy phosphate stores was seen with the higher concentration. However, this was unaffected by HOE 642. The protective effect of HOE 642 was mimicked by another NHE inhibitor, methylisobutylamiloride (MIA, 5 microM). Our study therefore shows that NHE inhibition selectively protects against functional and metabolic impairment produced by hydrogen peroxide. Since hydrogen peroxide formation has been implicated in the development of ischemic and reperfusion injury, it is possible that the protective effect of NHE inhibition against this form of oxidative stress may explain in part the basis for the well-established salutary actions of NHE inhibitors in the ischemic and reperfused myocardium. Since HOE 642 failed to modify the response to free radical generators, it is unlikely that the protective effects of NHE inhibitors can be explained by a free radical scavenging mechanism.