Captopril and ramiprilat protect against free radical injury in isolated working rat hearts

Protective Role of Ramipril and Candesartan against Myocardial Ischemic Reperfusion Injury: A Biochemical and Transmission Electron Microscopical Study

The present study was designed to investigate the role of combined administration of Ramipril and Candesartan against in vitro myocardial ischemic reperfusion injury in rat. Male Wistar albino rats were divided into five groups (n = 6) and treated with saline (10 mL/kg), Ramipril (2 mg/kg), Candesartan (1 mg/kg), and the combination of both drugs, respectively 24 h before induction of global ischemia (5 min of stabilization, 9 min of global ischemia, and 12 min of reflow). Combination of Ramipril and Candesartan when compared to the monotherapy significantly increased the levels of superoxide dismutase, reduced glutathione, catalase, and nitric oxide and decreased the levels of thiobarbituric acid reactive substances. In addition, the superior protective role of combination of Ramipril and Candesartan on ischemia induced myocardial damage was further confirmed by well preserved myocardial tissue architecture in light microscopy and transmission electron microscopy analysis studies. The combination was proved to be effective in salvaging the myocardial tissue against ischemic reperfusion injury when compared to the monotherapy of individual drugs and further investigations on protective mechanism of drugs by increasing the nitric oxide level at molecular levels are needed.

Ramipril protects the endothelium from high glucose-induced dysfunction through CaMKKβ/AMPK and heme oxygenase-1 activation

This study aims to investigate the effects of ramipril (RPL) on endothelial dysfunction associated with diabetes mellitus using cultured human aortic endothelial cells (HAECs) and a type 2 diabetic animal model. The effect of RPL on vasodilatory function in fat-fed, streptozotocin-treated rats was assessed. RPL treatment of 8 weeks alleviated insulin resistance and inhibited the decrease in endothelium-dependent vasodilation in diabetic rats. RPL treatment also reduced serum advanced glycation end products (AGE) concentration and rat aorta reactive oxygen species formation and increased aorta endothelium heme oxygenase-1 (HO-1) expression. Exposure of HAECs to high concentrations of glucose induced prolonged oxidative stress, apoptosis, and accumulation of AGEs. These effects were abolished by incubation of ramiprilat (RPT), the active metabolite of RPL. However, treatment of HAECs with STO-609, a CaMKKβ (Ca(2+)/calmodulin-dependent protein kinase kinase-β) inhibitor; compound C, an AMPK (AMP-activated protein kinase) inhibitor; and Zn(II)PPIX, a selective HO-1 inhibitor, blocked these beneficial effects of RPT. In addition, RPT increased nuclear factor erythroid 2-related factor-2 (Nrf-2) nuclear translocation and activation in a CaMKKβ/AMPK pathway-dependent manner, leading to increased expression of the Nrf-2-regulated antioxidant enzyme, HO-1. The inhibition of CaMKKβ or AMPK by pharmaceutical approach ablated RPT-induced HO-1 expression. Taken together, RPL ameliorates insulin resistance and endothelial dysfunction in diabetes via reducing oxidative stress. These effects are mediated by RPL activation of CaMKK-β, which in turn activates the AMPK-Nrf-2-HO-1 pathway for enhanced endothelial function.

Antioxidant effect of captopril and enalapril on reactive oxygen species-induced endothelial dysfunction in the rabbit abdominal aorta

BACKGROUND

Reactive oxygen species (ROS) are known to be related to cardiovascular diseases. Many studies have demonstrated that angiotensin-converting enzyme inhibitors have beneficial effects against ROS. We investigated the antioxidant effect of captopril and enalapril in nitric oxide mediated vascular endothelium-dependent relaxations.

MATERIALS AND METHODS

Isolated rabbit abdominal aorta ring segments were exposed to ROS by electrolysis of the organ bath medium (Krebs-Henseleit solution) after pretreatment with various concentrations (range, 10(-5) to 3×10(-4) M) of captopril and enalapril. Before and after electrolysis, the endothelial function was measured by preconstricting the vessels with norepinephrine (10(-6) M) followed by the cumulative addition of acetylcholine (range, 3×10(-8) to 10(-6) M). The relevance of the superoxide anion and hydrogen peroxide scavenging effect of captopril and enalapril was investigated using additional pretreatments of diethyldithiocarbamate (DETCA, 0.5 mM), an inhibitor of Cu/Zn superoxide dismutase, and 3-amino-1,2,4-triazole (3AT, 50 mM), an inhibitor of catalase.

RESULTS

Both captopril and enalapril preserved vascular endothelium-dependent relaxation after exposure to ROS in a dose-dependent manner (p<0.0001). Pretreatment with DETCA attenuated the antioxidant effect of captopril and enalapril (p<0.0001), but pretreatment with 3AT did not have an effect.

CONCLUSION

Both captopril and enalapril protect endothelium against ROS in a dose-dependent fashion in isolated rabbit abdominal aortas. This protective effect is related to superoxide anion scavenging.

Captopril normalizes insulin signaling and insulin-regulated substrate metabolism in obese (ob/ob) mouse hearts

The goal of this study was to determine whether inhibiting the renin-angiotensin system would restore insulin signaling and normalize substrate use in hearts from obese ob/ob mice. Mice were treated for 4 wk with Captopril (4 mg/kg x d). Circulating levels of free fatty acids, triglycerides, and insulin were measured and glucose tolerance tests performed. Rates of palmitate oxidation and glycolysis, oxygen consumption, and cardiac power were determined in isolated working hearts in the presence and absence of insulin, along with levels of phosphorylation of Akt and AMP-activated protein kinase (AMPK). Captopril treatment did not correct the hyperinsulinemia or impaired glucose tolerance in ob/ob mice. Rates of fatty acid oxidation were increased and glycolysis decreased in ob/ob hearts, and insulin did not modulate substrate use in hearts of ob/ob mice and did not increase Akt phosphorylation. Captopril restored the ability of insulin to regulate fatty acid oxidation and glycolysis in hearts of ob/ob mice, possibly by increasing Akt phosphorylation. Moreover, AMPK phosphorylation, which was increased in hearts of ob/ob mice, was normalized by Captopril treatment, suggesting that in addition to restoring insulin sensitivity, Captopril treatment improved myocardial energetics. Thus, angiotensin-converting enzyme inhibitors restore the responsiveness of ob/ob mouse hearts to insulin and normalizes AMPK activity independently of effects on systemic metabolic homeostasis.

Captopril and L-arginine have a synergistic cardioprotective effect in ischemic-reperfusion injury in the isolated rat heart

OBJECTIVES

The present study was designed to evaluate the possible effect of the combined administration of both captopril (Cap) and L-arginine (L-a) in the isolated ischemic rat heart model.

BACKGROUND

Recent studies suggest that L-arginine and angiotensin-converting enzyme (ACE) inhibitors possess independent cardioprotective effects in ischemic hearts. The pharmacological effect of the combination of both drugs has not yet been investigated in the ischemic myocardium.

METHODS

Using the modified Langendorf model, rats were perfused with either Cap 360 micromol/L (n = 6) or (L-a) 3mmol/L (n = 6), both captopril and L-arginine (Cap+L-a) (n = 8), or saline control (Con) (n = 8). The study design included 30 minutes of perfusion, 30 minutes of global ischemia, and 30 minutes of reperfusion thereafter.

RESULTS

Hearts treated with both Cap+L-a demonstrated an improved performance in all parameters. After 10 minutes of reperfusion, the P(max) in the Cap+L-a group was 98 +/- 8 mmHg (P <.001), 59 +/- 14 mmHg in the Cap group (P <.02), and 44.3 +/- 10 mmHg in the L-a group (P = NS), compared with only 42 +/- 8 mmHg in the control. After 10 minutes of reperfusion the dP/dt(min) was: in the Cap+L-a group: -1,650 +/- 223 mmHg/s (P <. 006); in the Cap group: -1,051 +/- 302 mmHg/s (P <.03); in the L-a group: -870 +/- 131 mmHg/s (P = NS), compared with only -487 +/- 131 mmHg/s in the control. Coronary flow was significantly increased in all 3 groups: Cap+L-a group: 22.3 +/- 1.5 mL/min (P <.001); Cap group: 18 +/- 1.6 mL/min (P <.01); L-a group: 19.8 +/- 0.9 mL/min (P <.02), compared with 12.6 +/- 0.9 mL/min in the Con group. Total NO level was significantly increased in the Cap+L-a group: 13.4 +/- 2 micromol (P <.03) vs. 6.1 +/- 1 micromol for the L-a group. NO levels of both the Cap group and the Con group were beneath detectable values.

CONCLUSION

Combined administration of captopril and L-arginine has a synergistic, protective effect on heart function and coronary flow that may be mediated by enhanced NO production.

Oxygen radical system in chronic infarcted rat heart: the effect of combined beta blockade and ACE inhibition

In vitro experiments suggest that beta blockade and angiotensin-converting enzyme (ACE) inhibition may protect the failing heart by reduction of myocardial oxidative stress. To test this hypothesis in an in vivo model, the beta blocker metoprolol (350 mg) and the ACE inhibitor ramipril (1 mg) were given either alone or in combination to rats (per kilogram body weight per day) for 6 weeks after myocardial infarction. Left ventricular end-diastolic pressure (LVEDP), contractile function of papillary muscles, enzymatic antioxidative defense (indicated by the activities of the superoxide dismutase isoenzymes and glutathione peroxidase), and the extent of lipid peroxidation were studied. Placebo-treated rats showed cardiac hypertrophy, increased LVEDP, lower rates of contraction and relaxation, as well as a deficit in the myocardial antioxidative defense associated with increased lipid peroxide levels, when compared with sham-operated animals. Combined beta blockade and ACE inhibition improved the antioxidative defense, reduced hypertrophy and LVEDP, and enhanced rates of contraction. Thus prolonged beta blockade and ACE inhibition after infarction may decrease myocardial oxidative stress and thereby could be beneficial in heart failure.

Pretreatment with ramiprilat induces cardioprotection against free radical injury in guinea-pig isolated heart: involvement of bradykinin, protein kinase C and prostaglandins

1. Pretreatment with ramiprilat, an angiotensin-converting enzyme (ACE) inhibitor, induced cardioprotection and its possible mechanism of action was investigated in guinea-pig Langendorff perfused heart. 2. Superoxide anion (*O2-), produced by hypoxanthine and xanthine oxidase, and the 1,1-diphenyl-2-picryl-hydrazyl (DPPH) free radical were used for triggering free radical injury in cardiac tissue. 3. 1,1-Diphenyl-2-picryl-hydrazyl and *O2- significantly reduced left ventricular developed pressure (LVDP), +/-dP/dt(max), heart rate and coronary flow. Left ventricular end-diastolic pressure (LVEDP) was elevated and lactate dehydrogenase (LDH) leakage and the formation of thiobarbituric acid-reactive substances (TBARS) formation were significantly increased. 4. Pretreatment with ramiprilat induced cardioprotection against DPPH and *O2- free radical injury. Cardiac functions (LVDP, LVEDP and +/-dP/dt(max)) were significantly improved. Both LDH and TBARS were reduced. 5. HOE 140 (a selective bradykinin B2 receptor antagonist), calphostin C (a protein kinase C (PKC) inhibitor) and indomethacin (a cyclo-oxygenase inhibitor) all abolished the cardiac protective effect of ramiprilat. However, N(G)-nitro-L-arginine methyl ester, a nitric oxide synthase inhibitor, had no effect. 6. In conclusion, ramiprilat pretreatment induces cardioprotection against either DPPH or *O2- free radical injury. The protective effect depends on activation of B2 receptors and PKC. Prostaglandin synthesis is also involved.

Ramipril-induced delayed myocardial protection against free radical injury involves bradykinin B2 receptor-NO pathway and protein synthesis

1. The aim of the present study was to examine whether ramipril induces delayed myocardial protection against free radical injuries ex vivo and to determine the possible role of the bradykinin B2-nitric oxide (NO) pathway, prostaglandins(PGs) and protein synthesis in this delayed adaptive response. 2. Rats were pretreated with ramipril (10 or 50 microg kg(-1), i.v.) and hearts were isolated after 24, 48 and 72 h. Langendorff hearts were subjected to 1,1-diphenyl-2-picryl-hydrazyl (DPPH) free radical-induced injury. 3. Left ventricular developed pressure (LVDP) and its maximal increase velocity (+ dP/dtmax), coronary flow (CF), heart rate (HR), lactate dehydrogenase (LDH) in coronary effluent and thiobarbituric acid reactive substances (TBARS) in the myocardium were measured. 4. The results showed that in the DPPH control group, 20 min after free radical-induced injury, LVDP, +dP/dtmax, CF, HR declined, whereas TBARS and LDH increased significantly. The above cardiac function parameters were significantly improved in RAM-pretreated rats after 24 and 48 h. 5. Pretreatment with HOE 140, the selective bradykinin B2 receptor antagonist, NG-nitro-L-arginine, the NO synthase inhibitor, and actinomycin D, the RNA transcription inhibitor, prior to ramipril injection abolished the beneficial effects of ramipril at 24 h while indomethacin, a cyclooxygenase inhibitor, pretreatment had no effect on ramipril-induced delayed protection. 6. In conclusion, ramipril induces delayed myocardial protection against free radical injury in the rat heart. This delayed protection was sustained for 48 h, is associated with the bradykinin B2 receptor-NO pathway and depends on protein but not prostaglandin synthesis.

Possible mechanism of captopril induced endothelium-dependent relaxation in isolated rabbit aorta

The mechanism of captopril, an angiotensin converting enzyme (ACE) inhibitor with sulfhydryl group (SH) in its structure, to produce an endothelium-dependent vasorelaxation was studied. In rabbit aorta with intact endothelium and precontracted with phenylephrine, captopril and superoxide dismutase (SOD) produced dose-dependent relaxation. Lisinopril, an ACE inhibitor without a -SH group in its structure, did not produce endothelium-dependent relaxation. It was observed that captopril, like SOD, produced the relaxation by protecting the EDRF from getting inactivated by superoxide anions as pyrogallol and methylene blue inhibited both the captopril and SOD-mediated relaxation. The free radical scavenging action of captopril is further substantiated by the observation that captopril, but not lisinopril, inhibited FeCl3/ascorbic acid-induced lipid peroxidation in whole tissue homogenates of rabbit aorta to a level comparable to that of SOD. These results suggest that endothelium-dependent vasodilation produced by captopril may be due to its ability to scavenge superoxide anion and this property may be ascribed to the -SH group present in its structure.

Hydralazine, but not captopril, decreases free radical production and apoptosis in neurons and thymocytes

The effects of captopril and hydralazine, two commonly used antihypertensive drugs, on free radical generation and the onset of apoptosis in neuron and thymocyte preparations from 10-12 day old rats have been studied. Apoptosis was induced in neurons by kainate or N-methyl-D-aspartate and in thymocytes by heat shock. Intracellular free radical production was measured by 2',7'-dichlorofluorescein fluorescence, and apoptotic cells were detected by cell staining with fluorescein-labelled annexin V. Captopril was found to have no effect on intracellular free radical generation and also had no significant effect on the early stages of apoptosis in neurons and thymocytes. In contrast, hydralazine was found to decrease free radical generation in both neurons and thymocytes, and it also significantly decreased the numbers of apoptotic cells when neurons and thymocytes were stimulated for apoptosis. Hydralazine had a greater effect on decreasing free radical generation in neurons than in thymocytes, but it had a more pronounced effect on decreasing apoptosis in thymocytes compared to neurons, suggesting that apoptosis, under our experimental conditions, may not solely be triggered by free radical generation. These results contrast with earlier reports that captopril is a free radical scavenger and can decrease apoptosis in T-lymphocytes and cardiomyocytes, and the results obtained with hydralazine are in apparent disagreement with earlier reports that this drug is a free radical generator and can cause intracellular damage suggestive of enhanced free radical formation.

Protective effect of the angiotensin-converting enzyme inhibitor captopril on postischemic myocardial damage in perfused rat heart

This study was undertaken to examine whether a sulfhydryl-containing angiotensin-converting enzyme (ACE) inhibitor, captopril, improves postischemic cardiac function and myocardial metabolism in the perfused working rat heart, and to elucidate the mechanism by which captopril protects the myocardium from postischemic damage. Isolated rat hearts were perfused by the working heart technique for 15 min. Ischemia was then induced for 30 min by lowering the afterload pressure and coronary flow to zero. After ischemia, hearts were reperfused for 30 min by returning afterload pressure to 60 mmHg. Captopril, a non-sulfhydryl-containing ACE inhibitor, enalapril, or a type 1 angiotensin II receptor antagonist, DuP 753, was added to the perfusate 5 min before ischemia, and the treatment was continued during the first 10-min period of reperfusion. In all groups there was no significant difference in pressure-rate product, coronary flow, tissue levels of ATP, total adenine nucleotides (TANs), energy charge potential (ECP), or creatine phosphate (CrP) before and during ischemia. During reperfusion following ischemia, captopril significantly improved the recovery of pressure-rate product, coronary flow, and tissue levels of ATP, TAN, ECP, and CrP, but neither enalapril nor DuP 753 had an effect. In conclusion, captopril improved postischemic cardiac function and myocardial metabolism in the perfused rate heart and its effect was independent of the blunting of angiotensin II formation.

Captopril in cardioplegia and reperfusion: protective effects on the ischemic heart

BACKGROUND

Previous studies have shown that long-term treatment with the angiotensin-converting enzyme inhibitor captopril attenuates left ventricular dilatation and improves survival after extensive myocardial infarction. However, there is only sparse evidence of the immediate effects of the drug on hearts undergoing global ischemia and reperfusion. The purpose of this study was to investigate the direct effect of captopril, given in cardioplegia or after ischemia, on the functional recovery of the reperfused myocardium.

METHODS

Isolated rat hearts undergoing warm cardioplegic arrest followed by 1 hour of global ischemia and 30 minutes of reperfusion were studied using the modified Langendorff model.

RESULTS

After ischemia, hearts receiving captopril (360 mumol/L) either in the cardioplegic solution (n = 9) or during reperfusion (n = 9) developed higher pressure (p < 0.001), greater first derivative of the rise in left ventricular pressure (p < 0.01 and p < 0.001, respectively), greater first derivative of the fall in left ventricular pressure (p < 0.001 and p < 0.002), higher pressure-time integral (p < 0.001), greater coronary flow (p < 0.001), and higher oxygen consumption values (p < 0.001 and p < 0.003) compared with the control group (n = 9). Hearts receiving captopril both in the cardioplegia and during reperfusion (n = 9) had the best recovery of all three groups and lower levels of creatine kinase (47.8 +/- 5.9 U/L versus 73.3 +/- 5.6 U/L; p < 0.01) compared with the control group.

CONCLUSIONS

Captopril given in cardioplegia and in reperfusion has a favorable, protective, and additive effect on the recovery of isolated rat hearts undergoing global ischemia and reperfusion; hemodynamic performance improves, coronary flow and oxygen consumption increase, and myocardial damage decreases.

Cardioprotective effect of angiotensin-converting enzyme inhibitors in patients with coronary artery disease

Clinical and experiments study with angiotensin-converting enzyme (ACE) inhibitors suggest that these agents may improve coronary artery disease by acting at multiple sites in the series of events leading to end-stage heart disease. These agents reduce blood pressure, improve prognosis and symptoms in patients with severe heart failure and in patients after acute myocardial infarction with left ventricular dysfunction. They are useful in the early, acute phase of myocardial infarction. More recently, ACE inhibitors have been shown to reduce in vitro vascular hypertrophy, to attenuate arteriosclerosis, and to maintain endothelium function. Whether these effects occur at clinical levels is still uncertain. The exciting clinical data have led to the proposal that alteration of ACE activity, particularly in tissue, is an important factor in development and progression of CAD. The ACE system is complex, with endocrine, paracrine, and autocrine effects. ACE is present in cardiac and vascular tissue. Therefore, the beneficial effects of ACE inhibitors can be classified as "cardio" and "vasculo" protective. This article summarizes a number of independent and complementary mechanisms pointing to a role of ACE and ACE inhibition in coronary artery disease.

Ramiprilat attenuates hypoxia/reoxygenation injury to cardiac myocytes via a bradykinin-dependent mechanism

Isolated rat neonatal cardiac myocytes were subjected to immersion in hypoxic (PO2 < 2 mm Hg), glucose-free Tyrode's solution for 5 h followed by concomitant reoxygenation and staining with the membrane-impermeant fluorophore, propidium iodide, in normoxic (PO2 > 150 mm Hg), serum-free culture media for 15 min in order to assess sarcolemmal damage indicative of myocyte viability due to hypoxia/reoxygenation injury. Prior to hypoxic exposure, cells were pretreated for 90 min with the angiotensin-converting enzyme inhibitor cyclopenta[b]pyrrole-2-carboxylic acid, 1-[2-[(1-carboxy-3-phenylpropyl)amino]-l-oxopropyl]octahydro-[2S-[1[R* (R*)]2 alpha, 3a beta, 6a beta]] (ramiprilat), concomitantly with ramiprilat and H-D-Arg-Arg-Pro-Hyp-Gly-Thi-Ser-D-Tic-Oic-Arg-OH (bradykinin B2 receptor antagonist HOE 140), the bioactive peptide Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg (bradykinin) or concomitantly with bradykinin and HOE 140. Hypoxia/reoxygenation injury to untreated control cardiac myocytes was characterized by a significant loss of sarcolemmal integrity measured at 75 +/- 4% of total cell fluorescence (mean +/- S.E., n = 42 cultures). Compared to propidium iodide staining of the above untreated control myocytes, those pretreated with 30 or 100 microM ramiprilat showed a significant reduction of propidium iodide staining to 45 +/- 9% and 40 +/- 8% (n = 9, P < 0.05) of untreated controls, respectively. Pretreatment with the protective concentrations of ramiprilat concomitant with 10 microM HOE 140 abolished the significant reduction in propidium iodide staining observed with ramiprilat alone. Similarly, pretreatment with 10 or 100 nM bradykinin significantly reduced propidium iodide staining to 35 +/- 5% and 60 +/- 10% (n = 6, P < 0.05) of the untreated hypoxic controls, respectively. In addition, concomitant pretreatment with protective concentrations of bradykinin and 10 microM HOE 140 also abolished the significant reduction in propidium iodide staining observed with bradykinin alone. The results indicate that the angiotensin-converting enzyme inhibitor ramiprilat has a protective effect on isolated cardiac myocytes exposed to hypoxia/reoxygenation and that this effect is most likely related to a local action of bradykinin on the cardiac myocyte via the activation of the kinin B2 receptor.

Effects of the angiotensin converting enzyme inhibitor captopril on experimental autoimmune encephalomyelitis

Angiotensin converting enzyme (ACE)1 mediates inflammation, participates in T cell stimulation by certain antigenic peptides, and influences the permeability of the blood brain barrier (BBB). ACE is elevated in multiple sclerosis (MS), an autoimmune disease of the central nervous system (CNS), characterized by increased BBB permeability. ACE inhibitor captopril suppresses certain immune functions and inhibits inflammatory or autoimmune diseases. We studied the effect of captopril on Lewis rat EAE, an animal model of MS. Fourteen rats with EAE were treated with captopril 30 mg/kg daily from immunization to day 21 post-immunization, and compared with 14 untreated rats. Severity scores and lymphocyte reactivity to myelin basic protein and mitogen were measured. There was a statistically significant (p < 0.05) difference between the mean and cumulative clinical scores of captopril-treated and untreated animals. Lymphocytes from captopril treated EAE rats at the peak of disease severity had diminished responses to MBP and concanavalin A. The data suggest a significant beneficial effect of captopril in Lewis rat EAE. Further studies including other inhibitors of ACE or of other peptidases with immune, inflammatory or BBB role, may identify potentially valuable immunopharmacologic agents.

Cardiac hypertrophy-related gene expression in spontaneously hypertensive rats: crucial role of angiotensin AT1 receptor

Angiotensin converting-enzyme inhibitors (alacepril and imidapril) or an AT1-receptor antagonist (SC-52458) was administered to 10-week-old spontaneously hypertensive rats (SHR) for 7 days, and cardiac mRNA levels for contractile proteins and atrial natriuretic polypeptide (ANP) were comprehensively measured. The expression of skeletal alpha-actin and ANP was selectively enhanced in the heart of vehicle-treated SHR compared with Wistar-Kyoto rats (WKY), thereby suggesting that the phenotypic modulation of myocytes occurred at the early stage of hypertension. The above-mentioned three drugs similarly suppressed these enhanced gene expressions, nearly to the control levels. In contrast, although the treatment with hydralazine lowered the blood pressure of SHR similarly, hydralazine did not suppress ANP expression at all and only partially suppressed skeletal alpha-actin. Moreover, alacepril did not affect these gene expressions in WKY. Thus, AT1 receptor may be crucial for phenotypic modulation in the heart of SHR.

Oxygen-free radicals and myocardial nerve fibers endings

Previous data from our laboratory have shown that electrolysis-induced oxygen free radicals (OFR) and ischemia/reperfusion (I/R) injury both produced a significant decrease of myocardial noradrenaline (NA) stocks in the isolated perfused rat heart. Therefore, we carried out the present study by immuno- and fluorescence histochemistry techniques to demonstrate the possibility that fibers nerve endings of the heart may be injured and to evaluate the subsequent damages. Isolated rat hearts were perfused according to the Langendorff technique and subdivided into i) control; ii) electrolyzed (two platinum electrodes, DC current, 10 mA, 1 min); iii) xanthine and xanthine oxidase (X-XO) perfusion for 30 min, and iv) 30 min global ischemia followed by 5 min reperfusion. Results indicate that in the last three groups myocardial fibers were altered. However, in electrolyzed hearts and those submitted to X-XO perfusion, but not in the I/R model, a disruption of many of the nerve fibers could be noted. Thus, NA leakage may be due to a neural injury when OFR are generated exogenously, whereas in the I/R model NA overflow may be explained by a metabolic dysfunction such as the inversion of the uptake I carrier. The major conclusion of this study is that OFR as generated exogenously (by electrolysis or by X-XO) cannot be considered to closely mimic the conditions of I/R injury, at least as concerns neural injury.

The effect of angiotensin-converting enzyme inhibitors on human neutrophil chemotaxis in vitro

1. Myocardial 'reperfusion injury' has been partly attributed to the production of free radicals which are cytotoxic towards cells. Neutrophils are recruited by ischaemic tissue and are one source of free radicals. Angiotensin-converting enzyme (ACE) inhibitors can reduce 'reperfusion injury' and we decided to determine if ACE inhibitors might contribute to this effect by inhibiting neutrophil chemotaxis. 2. The effects of captopril (a thiol containing ACE inhibitor) and enalaprilat (a nonthiol ACE inhibitor) and N-mercaptopropionyl glycine (MPG) (a simple thiol) on neutrophil chemotaxis were tested in an in vitro Boyden chamber assay. 3. The chemotactic response of human neutrophils to fMLP was reduced by 27.6% with MPG (n = 8; P < 0.05), by 13.2% with enalaprilat (n = 8; P = 0.075) and by 5.2% with captopril (n = 8; P = 0.66) at 5 microM (therapeutic concentration.) 4. Neutrophil chemotaxis was significantly decreased with 50 microM and 500 microM MPG and enalaprilat and 500 microM captopril. 5. Supratherapeutic concentrations of ACE inhibitors can reduce neutrophil chemotaxis at high concentrations and this effect does not appear to be -SH dependent.

Comparison of the free radical-scavenging ability of captopril and ascorbic acid in an in-vitro model of lipid oxidation. Implications for reperfusion injury and ACE inhibitor therapy

The free radical-scavenging activity of captopril and ascorbic acid was determined by assessing their ability to inhibit the peroxidation of linoleic acid in sodium dodecyl sulphate (SDS) micelles at 37 degrees C. The extent of peroxidation was monitored polarographically using an oxygen electrode to determine oxygen consumption rates. Ascorbic acid was observed to inhibit the peroxidation in a concentration-dependent fashion with an IC50 value of 17 microM. In contrast, the addition of captopril at concentrations up to 500 microM did not result in any detectable inhibition. Unlike ascorbic acid, no synergistic effect, as evidenced by the duration of inhibition, was observed with captopril/alpha-tocopherol mixtures. Measurements of the partitioning of captopril between SDS micelles and the aqueous phase show that 37% of the bulk captopril concentration is localized within the micellar phase; this indicates that phase separation of captopril from the lipid peroxyl radicals is not the cause of the observed lack of inhibitory activity.

Does captopril treatment before thrombolysis in acute myocardial infarction attenuate reperfusion damage? Short-term and long-term effects

Several experimental studies carried out on animals and on isolated heart preparations show that captopril can reduce post-ischemic reperfusion injury. Our study was aimed at investigating the effects of captopril before thrombolysis in acute myocardial infarction (AMI) and included 259 patients, hospitalized within 4 h of the onset of symptoms. Patients were randomly subdivided into two groups: the first group (131 patients, Group A, pretreatment) received 6.25 mg captopril orally about 15 min before i.v. administration of urokinase (2 million), the second group (128 patients, Group B, late-treatment), received captopril about 3 days after thrombolytic treatment. Captopril doses were later increased in both groups according to blood pressure. All patients were subdivided according to the localization of infarction. Anterior AMI was shown by 166 patients (84 from Group A and 82 from Group B); 93 patients showed inferior AMI (47 from Group A and 46 from Group B). Ventricular hyperkinetic arrhythmias (VHAs) due to reperfusion were evaluated during the first 2 h. VHAs occurred in 11.9% of patients with anterior AMI in Group A vs. 37.8% in Group B (P < 0.001). CK peak normalization time in the group with anterior AMI was achieved after 58 +/- 2 h in Group A vs. 71 +/- 2 h in Group B (P < 0.001). CK peak was 1719 +/- 152 in Group A vs. 2184 +/- 164 U/l in Group B, (P < 0.039). Late arrhythmias, higher than Lown's Class 2 were found to occur in 15.4% of patients with anterior AMI of Group A vs. 31.7% in Group B (P < 0.022), at predischarge Holter test.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of captopril on myocardial protection during cardioplegia

The study aimed at checking effects exerted by captopril (C) on human myocardial ACE system as well as the role played by tissue ACE inhibition in reducing reperfusion damage. A human experimental model was used during cardioplegia due to aorto-coronary-by-pass (CABG). Fifty-four patients with coronary artery disease affecting 3 vessels having suffered from acute myocardial infarction anterior (AMI-ant), homogeneous as far as ejection fraction (35-55%), number of grafts (3), clamping time, age and sex, were randomised in a double blind experiment, and were given captopril or placebo (P). A total of 4 mg/l Captopril was mixed into the cardioplegic solution with blood according to the method of Buckberg (Buckberg GD. J Thorac Cardiovasc Surg 1987; 93: 127-139). Eight samples (blood/perfusate) were obtained from each patients and norepinephrine (NE), epinephrine (E) were assayed using an HPLC technique. Angiotensin I was assayed by RIA. CK was also assayed (units/ml). Blood/perfusate samples were taken during CABG: (1) pre-pump; (2) pump sample; (3) pump preclamping; (4) coronary sinus; (5) coronary sinus sample during reperfusion; (6) coronary sinus during warm reperfusion; (7) after clamping sample; (8) after decanulation;

RESULTS

Captopril group (29 patients): angiotensin I: (1) 8.15; (2) 7.0; (3) 7.31; (4) 8.45; (5) 8.93; (6) 8.73; (7) 9.07; (8) 9.40; versus placebo: (1) 7.09, (2) 7.43; (3) 7.80; (4) 9.31; (5) 9.01; (6) 8.35; (7) 8.85; (8) 8.07 ng/ml, probability, not significant.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardioprotection by ramiprilat in isolated rabbit hearts

The anti-ischemic properties of the ACE inhibitor ramiprilat (ram) were investigated in electrically driven Langendorff hearts from rabbits whose endogenous angiotensin-I content has been previously shown to be very low (constant pressure: 70 cm H2O, Tyrode solution, Ca2+ 1.8 mmol/l). Cumulative concentration-response curves showed that the reduction in global coronary flow (CF) by exogenous angiotensin-I was concentration dependently inhibited by ram (P < 0.05). Myocardial ischemia (MI) was induced by occlusion of a left coronary artery branch and MI was quantified by NADH surface fluorescence photography. MI was significantly enlarged (+23%) (P < 0.05) by exogenous angiotensin-I (6 x 10(-9) mol/l). Addition of ram (10(-8) mol/l) to the perfusion buffer simultaneously with angiotensin-I, completely prevented the reduction of CF by angiotensin-I (P > 0.05) and significantly diminished MI even below control values (-25%) (P < 0.05). In the absence of exogenous angiotensin-I, ram alone (10(-8) mol/l) did not significantly enhance CF (P > 0.05), supporting findings demonstrating a very low endogenous angiotensin-I content in isolated rabbit hearts. However, ram alone (10(-8) mol/l) significantly diminished MI (-24%) (P < 0.05). We conclude that ram does possess direct cardioprotective properties that are independent of the inhibition of angiotensin-II generation but that may be related to potentiation of the effects of bradykinin.

Enhanced expression of superoxide dismutase messenger RNA in viral myocarditis. An SH-dependent reduction of its expression and myocardial injury

The oxygen free radical system has been reported to be activated by influenza virus infection in the lungs. However, the involvement of oxygen radicals in viral myocarditis is still unknown. Captopril, an angiotensin-converting enzyme (ACE) inhibitor and potent free radical scavenger with a sulfhydryl group, was effective for the treatment of viral myocarditis, while enalapril, an ACE inhibitor without a sulfhydryl group, was not effective against acute myocarditis. In this study, we investigated the role of oxygen radicals in the pathogenesis of viral myocarditis and the therapeutic effects of agents with a sulfhydryl group. 4-wk-old BALB/c mice were inoculated with the encephalomyocarditis virus, and treated with captopril or N,2-mercapto-propionyl glycine (MPG), a sulfhydryl-containing amino acid derivative without ACE inhibiting property, from days 4 to 14. On day 14, captopril and MPG significantly improved survival of mice and myocardial injury (necrosis, cellular infiltration, and calcification) in a dose-dependent manner compared with the infected control group. Thus, captopril and MPG were effective for the treatment of virus-induced myocarditis. Furthermore, a striking induction of manganese superoxide dismutase (Mn-SOD) and copper/zinc SOD (Cu/Zn-SOD) mRNAs in infected hearts was found (8-13-fold for Mn-SOD and 4-11-fold for Cu/Zn-SOD) when compared with age-matched uninfected mice hearts. MPG completely inhibited the increase of both mRNAs, even when treatment was started on day 4. Thus, oxygen radicals may play an important role in the pathogenesis of viral myocarditis, and a therapeutic approach by eliminating oxygen radicals seems possible.

Elevated breath pentane in heart failure reduced by free radical scavenger

Pentane, a product of lipid peroxidation, has been detected in situations involving ischemic injury. Such injury may be limited if lipid peroxidation can be controlled by antioxidants. The role of lipid peroxidation in chronic heart failure (CHF) was assessed by measuring breath pentane in patients with CHF vs. age matched controls. The effect of a free radical scavenger on pentane released during CHF was also measured. Pentane levels were correlated with the daily dose of captopril, a sulfhydril-containing drug used to treat CHF, which is an angiotensin converting enzyme inhibitor. To separate the scavenging effects of captopril from the pharmacologic effects of converting enzyme inhibitors, a crossover study using a nonsulfhydril inhibitor was used. Patients with CHF excreted (p < 0.005) high concentrations of pentane (5.7 +/- 2.1 vs. control 3.6 +/- 1.2 nmol/l). Patients treated with captopril also had significantly higher (p < 0.05) excretion of pentane than the control patients (4.7 +/- 1.3 vs. 3.6 +/- 1.2 nmol/l). The dose of captopril was inversely proportional to the concentration of pentane excreted (r = 0.55, p < 0.05). Pentane excretion during captopril therapy was significantly lower before (p < 0.01) and after (p < 0.02) nonsulfhydril inhibitor therapy.

CONCLUSION

breath pentane is elevated in CHF and it can be reduced by a free radical scavenger. This reduction of pentane excretion is not a converting enzyme inhibitor class effect.

Reduction of myocardial infarct size by ramiprilat is independent of angiotensin II synthesis inhibition

The angiotensin-converting enzyme inhibitor ramiprilat, the angiotensin II receptor antagonist losartan, angiotensin II, ramiprilat plus angiotensin II, or saline (N = 6 each group), were administered i.v. in anesthetized, open-chest rabbit preparations of acute myocardial ischemia. Animals were instrumented for measurement of systemic hemodynamics and left ventricular +dP/dtmax, then subjected to 30 min of left anterior descending coronary artery occlusion (marginal branch) followed by 2 h of reperfusion. Ramiprilat (50 micrograms/kg), losartan (10 mg/kg), or saline were administered prior to reperfusion, and angiotensin II (2.5 ng/kg per min) was infused 15 min prior to occlusion and throughout the remainder of the experiment. Losartan was supplemented (10 mg/kg) after 1 h of reperfusion. These non-hypotensive doses of ramiprilat and losartan were demonstrated to significantly antagonize the systemic pressor effects of i.v. challenge with angiotensin I (15% of control, maximum) and II (5% of control, maximum), respectively, for the duration of the experiment. Systemic hemodynamic and +dP/dtmax changes due to occlusion/reperfusion or drug administration were similar between treatment groups. Infarct size was measured post-experimentally using tetrazolium staining and is reported as a percent of area at risk. Infarct size/area at risk (%) was significantly lower in rabbits administered ramiprilat only (20 +/- 6%*) or ramiprilat plus angiotensin II (26 +/- 5%*), compared to those receiving saline (41 +/- 6%), angiotensin II (51 +/- 4%), or losartan (52 +/- 4%, mean +/- S.E.M., * P < 0.05). These data indicate that direct angiotensin II receptor stimulation or receptor antagonism does not alter the degree of myocardial necrosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin converting enzyme inhibitors as oxygen free radical scavengers

The authors have compared the ability of two non-SH-containing angiotensin converting enzyme (ACE) inhibitors (enalaprilat and lisinopril) with an -SH containing ACE inhibitor (captopril) to scavenge the hydroxyl radical (.OH). All three compounds were able to scavenge .OH radicals generated in free solution at approximately diffusion-controlled rates (10(10) M-1 s-1) as established by the deoxyribose assay in the presence of EDTA. The compounds also inhibited deoxyribose degradation in reaction mixtures which did not contain EDTA but not so effectively. This later findings also suggests that they have some degree of metal-binding capability. Chemiluminescence assays of oxidation of hypoxanthine by xanthine oxidase in the presence of luminol, confirm that the three ACE inhibitors are oxygen free radical scavengers. Our results indicate that the presence of a sulphydryl group in the chemical structure of ACE inhibitors is not relevant for their oxygen free radical scavenging ability.

Exacerbation of left ventricular ischemic diastolic dysfunction by pressure-overload hypertrophy. Modification by specific inhibition of cardiac angiotensin converting enzyme

Hearts with compensatory pressure-overload hypertrophy show an increased intracardiac activation of angiotensin II that may contribute to ischemic diastolic dysfunction. We studied whether pressure-overload hypertrophy in response to aortic banding would result in exaggerated diastolic dysfunction during low-flow ischemia and whether the specific inhibition of the cardiac angiotensin converting enzyme by enalaprilat would modify systolic and diastolic function during ischemia and reperfusion in either hypertrophied or nonhypertrophied hearts. Isolated, red blood cell-perfused isovolumic nonhypertrophied and hypertrophied rat hearts were subjected to enalaprilat (2.5 x 10(-7) M final concentration) infusion during 20 minutes of baseline perfusion and during 30 minutes of low-flow ischemia and 30 minutes of reperfusion. Coronary flow per gram was similar in nonhypertrophied and hypertrophied hearts during baseline perfusion, ischemia, and reperfusion. At baseline, left ventricular developed pressure was higher in hypertrophied than nonhypertrophied hearts in untreated groups (224 +/- 8 versus 150 +/- 9 mm Hg; p less than 0.01) and in enalaprilat-treated groups (223 +/- 9 versus 145 +/- 8 mm Hg; p less than 0.01). During low-flow ischemia, left ventricular developed pressure was depressed but similar in all groups. All groups showed deterioration of diastolic function; however, left ventricular end-diastolic pressure increased to a significantly higher level in untreated hypertrophied than in nonhypertrophied hearts (65 +/- 7 versus 33 +/- 3 mm Hg; p less than 0.001). Enalaprilat had no effect in nonhypertrophied hearts, but it significantly attenuated the greater increase in left ventricular end-diastolic pressure in hypertrophied hearts treated with enalaprilat compared with no drug (65 +/- 7 versus 50 +/- 5 mm Hg; p less than 0.01). The beneficial effect could not be explained by differences in coronary blood flow per gram left ventricular weight, glycolytic flux as reported by lactate production, myocardial water content, oxygen consumption, and tissue levels of glycogen and high energy phosphate compounds. During reperfusion, all hearts showed a partial recovery of developed pressure to 70-74% of initial values. No effect of enalaprilat could be detected during reperfusion on systolic and diastolic function or restoration of tissue levels of high energy compounds. In conclusion, our experiments show that hypertrophied red blood cell-perfused hearts manifest a severe impairment of left ventricular diastolic relaxation in response to low-flow ischemia in comparison with control hearts. Further, our experiments support the hypothesis that the enhanced conversion of angiotensin I to angiotensin II in rats with pressure-overload hypertrophy contributes to the enhanced sensitivity of hypertrophied hearts to diastolic dysfunction during low-flow ischemia.

Pharmacokinetic optimisation of angiotensin converting enzyme (ACE) inhibitor therapy

Angiotensin converting enzyme (ACE) inhibitors are increasingly used to treat hypertension and congestive heart failure. Recently, several new ACE inhibitors with pharmacokinetic features different from earlier agents such as captopril or enalapril have come into use. This review discusses the use of pharmacokinetics to optimise ACE inhibitory therapy in various patient groups. Among the pharmacokinetic characteristics of ACE inhibitors the route of excretion and to a lesser degree the half-life appear to be the most clinically relevant. There is no evidence that being a prodrug offers a significant clinical advantage. The importance of varying tissue penetration also remains to be determined. Knowledge of ACE inhibitor pharmacokinetics is particularly important in patients with renal or hepatic dysfunction in whom the major route of excretion of these agents is impaired. This might also be the case in elderly patients or those with severe congestive heart failure. However, for most ACE inhibitors, major changes in the drug dosage (amount or interval) are necessary only when the glomerular filtration rate falls below 30 ml/min (1.80 L/h). The occurrence of adverse effects due to overdosage or drug interactions may be prevented by adapting the prescription of an ACE inhibitor to its pharmacokinetic characteristics.

Beneficial effect of beraprost, a prostacyclin-mimetic agent, on post-hypoxic recovery of cardiac function and metabolism in rabbit isolated hearts

1. The present study was undertaken to determine whether beraprost, a stable prostacyclin-mimetic agent, may exert a beneficial effect on post-hypoxic recovery of cardiac function and metabolism. Isolated rabbit hearts were perfused by the Langendorff method for 20 min under glucose-free hypoxic conditions, followed by 45 min reoxygenation in the presence of glucose, and their functional and metabolic changes with or without beraprost-treatment were examined. 2. Hypoxic insult induced cessation of cardiac contractile force, depletion of myocardial high-energy phosphates, accumulation of tissue calcium, and release of creatine kinase and ATP metabolites. Subsequent reoxygenation resulted in a poor recovery of cardiac contractile force (less than 10% of the pre-hypoxic value), a poor restoration of high-energy phosphates, and increase in calcium content. A further release of creatine kinase and ATP metabolites from the heart was observed during reoxygenation. 3. Treatment with 0.45 microM beraprost during the whole hypoxic period resulted in a significant suppression of the increase in tissue calcium, and the release of creatine kinase and ATP metabolites during hypoxic perfusion. This treatment also elicited a significant post-hypoxic recovery of the cardiac contractile force and the tissue high-energy phosphates. Reoxygenation-induced release of creatine kinase and ATP metabolites was also prevented by treatment with beraprost. 4. When hearts were treated with prostacyclin sodium (0.50 microM) in the same manner for the purpose of comparison, similar improvement of post-hypoxic contractile and metabolic recovery were observed. 5. These results demonstrate that treatment with either beraprost or prostacyclin is beneficial for post-hypoxic recovery of cardiac function and metabolism. Since the observed effects on post-hypoxic contractile recovery were exerted at a concentration of approximately 0.50 microM of these agents (a concentration far from the physiological range) the underlying mechanism appears to be different from the physiological action of prostacyclin.

Influence of ACE inhibitors on free radicals and reperfusion injury: pharmacological curiosity or therapeutic hope?

1. The currently available evidence shows that thiol containing ACE inhibitors are free radical (FR) scavengers in vitro; in particular the OH. radical is effectively scavenged by these compounds. There is also good evidence that, in vivo, ACE inhibitors can preserve myocardial contractile function following a period of reversible ischaemia (by directly protecting myocytes and/or preserving coronary flow through protection of endothelial cells). These in vivo benefits are probably also due to FR scavening, mainly due to the presence of a thiol group but, also as a consequence of augmented prostanoid production. 2. Use of more relevant animal models and testing of a range of doses of ACE inhibitors might be undertaken before clinical investigation is considered. Because of its nature, however, the existence and importance of reperfusion injury in man will only be proven or disproven by pharmacological intervention. One option is to compare a thiol containing agent with absent or minimal haemodynamic effects with placebo as an adjunct to thrombolysis. This is the simplest approach. An alternative approach is to conduct a comparative study of a -SH containing ACE inhibitor and a non -SH containing ACE inhibitor given prior to thrombolysis. There are many problems with either approach. The lack of reliable measures of FR activity in man and difficulty in measuring accurately left ventricular function post-myocardial infarction means that mortality is likely to be the only reliable end-point in such a study.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of the ability of the angiotensin-converting enzyme inhibitor captopril to scavenge reactive oxygen species

Captopril, an inhibitor of angiotensin-converting enzyme, has been suggested to have additional cardioprotective action because of its ability to act as an antioxidant. The rates of reaction of captopril with several biologically-relevant reactive oxygen species were determined. Captopril reacts slowly, if at all, with superoxide (rate constant less than 10(3) M-1 s-1) or hydrogen peroxide (rate constant less than M-1 s-1). It does not inhibit peroxidation of lipids stimulated by iron ions and ascorbate or by the myoglobin/H2O2 system. Indeed, mixtures of ferric ion and captopril can stimulate lipid peroxidation. Captopril reacts rapidly with hydroxyl radical (rate constant greater than 10(9) M-1 s-1) but might be unlikely to compete with most biological molecules for OH because of the low concentration of captopril that can be achieved in vivo during therapeutic use. Captopril did not significantly inhibit iron ion-dependent generation of hydroxyl radicals from hydrogen peroxide. By contrast, captopril is a powerful scavenger of hypochlorous acid: it was able to protect alpha 1-antiproteinase (alpha 1 AP) against inactivation by this species and to prevent formation of chloramines from taurine. We suggest that the antioxidant action of captopril in vivo is likely to be limited, and may be restricted to protection against damage by hypochlorous acid derived from the action of neutrophil myeloperoxidase.