Protective effect of amiloride against reperfusion damage as evidenced by inhibition of accumulation of free fatty acids in working rat hearts

To examine whether amiloride protects against ischemia-induced or reperfusion-induced damage to the heart, mechanical and metabolic studies were performed in the isolated, working rat heart. Ischemia decreased both mechanical function and the tissue levels of high-energy phosphates and increased the tissue levels of free fatty acids (FFAs). Reperfusion restored the levels of high-energy phosphates but further increased FFA accumulation. For this reason, accumulation of FFAs was used as an indicator of both ischemia-induced and reperfusion-induced damage. Drugs were added to the perfusion solution 5 min before ischemia until the end of ischemia (pre) or until 10 min after reperfusion (pre + post). Diltiazem (1 or 5 mumol/L pre) decreased the mechanical function of the non-ischemic heart and attenuated both ischemia-induced and reperfusion-induced accumulation of FFAs. Amiloride (50 mumol/L pre) did not affect the mechanical function of the non-ischemic heart or attenuate ischemia-induced or reperfusion-induced FFA accumulation effectively. However, amiloride (50 mumol/L pre + post) did markedly attenuate the reperfusion-induced accumulation of FFAs. In conclusion, diltiazem attenuates both ischemia-induced and reperfusion-induced myocardial damage, probably through its energy-sparing effect as a result of a decrease in mechanical function before ischemia. In contrast, amiloride attenuates only the reperfusion-induced myocardial damage through mechanisms other than the energy-sparing effect.

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.

Cardioprotective effect of K-7259, a novel dilazep derivative, against ischemia-reperfusion damage in isolated, working rat hearts

Global ischemia (15 min) followed by reperfusion (10, 20 or 30 min) was performed in isolated, working rat hearts. Ischemia depressed mechanical function, which was not restored by reperfusion of 20 min. Preischemic administration of K-7259 (N,N'-bis[4-(3,4,5-trimethoxyphenyl)butyl]homopiperazine dihydrochloride) (1, 5 or 10 microM) decreased the function before ischemia, but it attenuated the ischemia-induced dysfunction during reperfusion (20 min). Postischemic administration of K-7259 (10 microM) or dilazep (20 microM) also attenuated the ischemia-induced dysfunction during reperfusion (30 min). Ischemia-reperfusion (10 min) increased the tissue malondialdehyde level, and postischemic administration of K-7259 (10 microM) or dilazep (20 microM) attenuated the malondialdehyde accumulation. K-7259 has a cardioprotective effect when given either before or after ischemia.

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.

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.

A new approach to the development of anti-ischemic drugs. Substances that counteract the deleterious effect of lysophosphatidylcholine on the heart

Lysophosphatidylcholine (LPC) is an amphiphilic metabolite that can be produced from membrane-phospholipids by activation of phospholipase A2 (PLA2), and it accumulates in the heart during ischemia and reperfusion. It is known that LPC is an arrhythmogenic substance. Recent studies have revealed that LPC produces mechanical and metabolic derangements in perfused working rat hearts, and Ca(2+)-overload in isolated cardiac myocytes. Thus, LPC possesses an ischemia-like effect on the heart. LPC accumulated in the myocardium activates phospholipase A2, establishing a vicious circle; i.e. LPC itself has an ability to produce another LPC. Therefore, a drug that has an anti-LPC effect would protect or improve ischemia/reperfusion damage. This article will review the effect of LPC in relation to ischemia, and consider a possibility of developing new anti-ischemic drugs on the basis of the anti-LPC action.

K-7259, a novel dilazep derivative, and d-propranolol attenuate H2O2-induced cell damage

We studied the effects of dilazep, K-7259 (a novel derivative of dilazep) and d-propranolol on the change in cell shape and accumulation of nonesterified fatty acids (NEFA) induced by hydrogen peroxide (H2O2) in isolated rat cardiac myocytes. Myocytes were incubated in a Krebs-Ringer bicarbonate buffer containing 2 mM diethyltriamine pentaacetic acid (DETAPAC) and 2mM FeSO4 for 10 min, and then treated with 2mM H2O2 for 50 min. Before the treatment with H2O2, the percentage of the number of rod-shaped cells to that of total cells was 66 +/- 2%, and decreased to 35 +/- 3%, 25 +/- 4% and 14 +/- 2%, after 30, 40 and 50 min of the H2O2 treatment, respectively. The levels of NEFA (lauric, myristic, palmitoleic, arachidonic, linoleic, palmitic, oleic and stearic acids) increased after the treatment with H2O2. In the absence of FeSO4 and DETAPAC, however, H2O2 did not have these effects, and therefore all the experiments with drugs were performed in the presence of Fe2SO4 and DETAPAC. K-7259 (30 microM) and d-propranolol (50 microM) attenuated both the changes in cell shape and accumulation of NEFA induced by H2O2, whereas dilazep (30 or 50 microM) did not. N-(2-mercaptopropionyl)glycine (2 mM), an .OH scavenger, inhibited the H2O2-induced changes completely. These results suggest that K-7259 and d-propranolol attenuate the H2O2-induced changes in cell shape and accumulation of NEFA, probably because of their .OH-scavenging effect.

A study on dilazep: II. Dilazep attenuates lysophosphatidylcholine-induced mechanical and metabolic derangements in the isolated, working rat heart

The effects of dilazep, d-propranolol and lidocaine on the mechanical and metabolic changes induced by lysophosphatidylcholine (LPC) were studied in isolated, perfused working rat heart. After a stabilization period, the heart was perfused for 5 min with LPC (10 microM) alone, LPC plus dilazep (5, 10 or 20 microM), LPC plus d-propranolol (30 or 50 microM) or LPC plus lidocaine (30 or 100 microM) and then perfused with normal Krebs-Henseleit bicarbonate (KHB) buffer for a further 20 min. Perfusion with LPC for 5 min followed by KHB for 20 min irreversibly decreased cardiac mechanical function, decreased the tissue levels of adenosine triphosphate and creatine phosphate significantly, and increased the tissue levels of lactate and free fatty acids including arachidonic acid. Dilazep or d-propranolol significantly attenuated the mechanical and metabolic changes induced by LPC, but lidocaine did not. These results indicate that the exogenous LPC causes ischemia-like changes, suggesting that LPC is one of the important factors in producing ischemia-reperfusion derangements in terms of mechanical and metabolic functions, and that both dilazep and d-propranolol can prevent the LPC-induced myocardial damage.

A study on dilazep: I. Mechanism of anti-ischemic action of dilazep is not coronary vasodilation but decreased cardiac mechanical function in the isolated, working rat heart

In the isolated, perfused working rat heart, ischemia (15 min) decreased the mechanical function and the tissue levels of adenosine triphosphate and creatine phosphate and increased the levels of lactate and free fatty acids. Reperfusion (20 min) did not restore the mechanical function, but restored incompletely the levels of metabolites, with the exception of free fatty acids, which increased further during reperfusion. Dilazep was given 5 min before starting ischemia until the end of ischemia. Dilazep at 5 or 10 microM decreased the cardiac mechanical function, but did not affect coronary flow in the pre-ischemic heart. Dilazep at 5 or 10 microM accelerated the recovery of mechanical function and coronary flow during reperfusion, and it attenuated metabolic changes induced by ischemia and reperfusion. Dilazep at 1 microM neither decreased the pre-ischemic mechanical function nor restored the mechanical function during reperfusion, although it attenuated the accumulation of free fatty acids during reperfusion. These results suggest that dilazep attenuates both ischemia- and reperfusion-induced myocardial damage and that the anti-ischemic action of dilazep is not due to coronary vasodilation but probably due to an energy-sparing effect and other effects that remain to be studied.

Protective effect of crataegus extract on the cardiac mechanical dysfunction in isolated perfused working rat heart

The effect of the water-soluble fraction of Crataegus (Crataegus extract) on the cardiac mechanical and metabolic function was studied in the isolated, perfused working rat heart during ischemia and reperfusion. Ischemia (15 min) was produced by removing afterload pressure, and reperfusion (20 min) was produced by returning it to the original pressure. In the control (no drug) heart, ischemia decreased mechanical function to the lowest level, which did not recover even after the end of reperfusion. Crataegus extract (0.01 or 0.05%) was applied to the heart from 5 min before ischemia through the first 10 min after reperfusion. With the high concentration of Crataegus extract (0.05%) the mechanical function recovered during reperfusion incompletely without increasing coronary flow, but the low concentration of Crataegus extract (0.01%) did not. In the heart treated with the high concentration of Crataegus extract, the reperfusion-induced recovery of the energy metabolism was accelerated, and the level of lactate during ischemia was lower than that in the control heart, although the myocardial levels of free fatty acids during ischemia and reperfusion were not greatly affected. These results demonstrate that Crataegus extract (0.05%) has a cardioprotective effect on the ischemic-reperfused heart, and that the cardioprotective effect is not accompanied by an increase in coronary flow.

Cardioprotective effect of d-propranolol in ischemic-reperfused isolated rat hearts

In the isolated, perfused working rat heart, ischemia (15 min) decreased mechanical function and also the tissue levels of ATP and creatine phosphate, and increased the tissue levels of lactate and free fatty acids including arachidonic acid. Reperfusion (20 min) did not restore mechanical function, but restored changes of metabolites incompletely except for free fatty acids, which changed further during reperfusion. Drugs were given 5 min before ischemia until the end of ischemia or for the first 10 min after reperfusion. Both dl- and d-propranolol (10 and 30 microM) decreased mechanical function, accelerated the recovery of mechanical function during reperfusion following ischemia, and attenuated ischemia reperfusion-induced metabolic changes. The attenuation of reperfusion-induced metabolic changes was more marked when these drugs were present during reperfusion. d-Propranolol showed a cardioprotection similar to that by dl-propranolol. Timolol (50 microM) did not accelerate the recovery of mechanical function during reperfusion, and did not attenuate the reperfusion-induced metabolic changes. These results suggest that d-propranolol, like dl-propranolol, has a cardioprotective effect which is probably due to its membrane stabilizing (or sodium channel blocking) action.

Cardioprotective effect of pindolol in ischemic-reperfused isolated rat hearts

The effects of pindolol and timolol on ischemia reperfusion damage were studied in isolated working rat hearts. Ischemia (15 min) decreased the mechanical function and the energy state, and increased the tissue levels of free fatty acids (FFA). During reperfusion (20 min), the mechanical function did not recover, but the energy state recovered incompletely, whereas FFA increased further. Pindolol (50 microM) accelerated recovery of the mechanical function and the energy state that had been decreased by ischemia during reperfusion, and inhibited the accumulation of FFA during ischemia and reperfusion, especially when it was applied during the whole period of reperfusion. Timolol (50 microM), however, did not accelerate recovery of the mechanical function and the energy state during reperfusion, although it attenuated FFA accumulation during reperfusion. The pindolol-induced recovery of the mechanical function during reperfusion was reduced by timolol. The results suggest that the intrinsic sympathomimetic activity of pindolol may play an important role, at least in part, in producing the cardioprotective effect, especially during reperfusion.