Protective ability and binding affinity of captopril towards serum albumin in an in vitro glycation model of diabetes mellitus

One-quarter of adult population in different world regions are reported to live with hypertension, of whom, a high percentage had a diabetes mellitus (DM). This co-morbid state is believed to act synergistically on accelerating the long-term diabetic complications. Therefore, adequate treatment of high blood pressure is essential for diabetic patients, and should be always directed to their benefits. Albumin glycation is still the most important explanation for the pathogenesis of chronic diabetic complications. Our in vitro experiments induce non-enzymatic glycation of bovine serum albumin (BSA) under physiological conditions. The levels of advanced glycation end products (AGEs) were measured by their characteristic intrinsic fluorescence. Additions of captopril at concentrations from 5 to 50 microM caused 10-47% reduction in the formation of AGEs. Captopril binding properties of native and glycosylated BSA were characterized, and its affinity towards the native albumin was unaltered by the in vitro glycation. Therefore, we concluded that captopril could protect against albumin glycation, and it has a similar binding affinities towards native and glcosylated protein. Anti-glycation effect may help to attenuate the serious long-term diabetes related complications. Besides, the unchanged pharmacokinetic parameters provide an essential extra beneficial effect for diabetic hypertensive patients.     

Antioxidant effects of angiotensin-converting enzyme (ACE) inhibitors: free radical and oxidant scavenging are sulfhydryl dependent, but lipid peroxidation is inhibited by both sulfhydryl- and nonsulfhydryl-containing ACE inhibitors.

With an assay that generates free radicals (FR) through photooxidation of dianisidine sensitized by riboflavin, 4 x 10(-5) M captopril, epicaptopril (SQ 14,534, captopril's stereoisomer), zofenopril, and fentiapril [all sulfhydryl (-SH)-containing angiotensin-converting enzyme (ACE) inhibitors] were shown effective scavengers of nonsuperoxide free radicals whereas non-SH ACE inhibitors were not. Captopril was a more effective FR scavenger at pH 5.0 than at pH 7.5. Captopril (2 x 10(-5) M) also scavenged the other toxic oxygen species hydrogen peroxide and singlet oxygen and inhibited microsomal lipid peroxidation. Finally, captopril reduced the amount of superoxide anion-radical detected after neutrophils in whole blood were activated with zymosan, probably by inhibiting leukocyte superoxide production.     

Captopril inhibits the oxidative modification of apolipoprotein B-100 caused by myeloperoxydase in a comparative in vitro assay of angiotensin converting enzyme inhibitors

The oxidative modification of low-density lipoproteins (LDL) is a key event in the formation of atheromatous lesions. Indeed, oxidized derivatives accumulate in the vascular wall and promote a local inflammatory process which triggers the progression of the atheromatous plaque. Myeloperoxidase (MPO) has been mentioned as a major contributor to this oxidative process. It takes part in the oxidation both of lipids by chlorination and peroxidation and of apolipoprotein B-100. Based on recent observations with several anti-inflammatory and thiol-containing drugs, the present study was designed to test the hypothesis that anti-hypertensive agents from the angiotensin converting enzyme (ACE) inhibitors group inhibit the oxidative modifications of Apo B-100 caused by MPO. Captopril, ramipril, enalapril, lisinopril and fosinopril were assessed by measuring: their inhibiting effect on the MPO/H(2)O(2)/Cl(-) system, the accumulation of compound II, which reflects the inhibition of the synthesis of HOCl and the LDL oxidation by MPO in presence of several concentrations of ACE inhibitors. Only captopril, a thiol-containing ACE inhibitor, was able to significantly decrease the oxidative modification of LDL in a dose dependent manner and this by scavenging HOCl. This efficient anti-hypertensive drug therefore appears to also protect against the atherosclerotic process by this newly documented mechanism.     

Effect of captopril, enalaprilat and mercaptopropionyl glycine (MPG) on the oxidative activity of human isolated neutrophils.

1. Neutrophil NADPH oxidase produces the superoxide anion (O2-) anion radical from oxygen. The thiol containing ACE inhibitor, captopril has been reported to inhibit isolated NADPH oxidase. The above effect of captopril, if present in intact cells, could contribute to the ability of this drug to alleviate neutrophil-mediated tissue damage. We have, therefore, investigated the effect of captopril on the oxidative activity of intact human isolated neutrophils. 2. The effects of captopril on neutrophil oxidative activity were compared with those of enalaprilat (a non-thiol ACE inhibitor) and N-mercaptopropionyl glycine (MPG) (a simple thiol). 3. The oxidative response of PMA-stimulated neutrophils measured by lucigenin chemiluminescence was not affected by any of these test agents. The thiol captopril and MPG (but not enalaprilat) caused an initial delay in luminol chemiluminescence production by PMA-stimulated neutrophils. 4. Captopril and MPG (but not enalaprilat) increased, rather than decreased oxygen uptake, when added to PMA-stimulated neutrophils. Thiol oxidation was determined to be, at least partly, responsible for the excess oxygen uptake observed. 5. NADPH oxidase activity in intact neutrophils was not affected by captopril, MPG or enalaprilat. The inhibition of NADPH oxidase activity is unlikely to contribute to the therapeutic effects of captopril and other thiols.     

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.     

Sulfhydryl group in angiotensin converting enzyme inhibitors and superoxide radical formation.

The superoxide radical scavenging effects of the SH group in the captopril molecule has been proposed to be the basis of the "cadioprotective" effect of this angiotensin converting enzyme (ACE) inhibitor in animal models of myocardial injury. We determined the effects of captopril, another ACE inhibitor with an SH group (SQ 26,703), its stereoisomer without ACE inhibitory effect but with an SH group (SQ 14,534), another ACE inhibitor without a SH group (enalaprilat), and N-acetylcysteine on superoxide radical generation by human neutrophils and by the purine-xanthine oxidase reaction. None of the compounds examined decreased superoxide radicals in therapeutic concentrations; however, SH-containing agents directly reduced spectrophotometric absorbance of ferricytochrome C. Thus, SH-containing agents with or without ACE inhibitory effects do not scavenge superoxide radicals.     

Clinical pharmacokinetics and selective pharmacodynamics of new angiotensin converting enzyme inhibitors: an update

The angiotensin converting enzyme (ACE) inhibitors are widely used in the management of essential hypertension, stable chronic heart failure, myocardial infarction (MI) and diabetic nephropathy. There is an increasing number of new agents to add to the nine ACE inhibitors (benazepril, cilazapril, delapril, fosinopril, lisinopril, pentopril, perindopril, quinapril and ramipril) reviewed in this journal in 1990. The pharmacokinetic properties of five newer ACE inhibitors (trandolapril, moexipril, spirapril, temocapril and imidapril) are reviewed in this update. All of these new agents are characterised by having a carboxyl functional groups and requiring hepatic activation to form pharmacologically active metabolites. They achieve peak plasma concentrations at similar times (t(max)) to those of established agents. Three of these agents (trandolapril, moexipril and imidapril) require dosage reductions in patients with renal impairment. Dosage reductions of moexipril and temocapril are recommended for elderly patients, and dosages of moexipril should be lower in patients who are hepatically impaired. Moexipril should be taken 1 hour before meals, whereas other ACE inhibitors can be taken without regard to meals. The pharmacokinetics of warfarin are not altered by concomitant administration with trandolapril or moexipril. Although imidapril and spirapril have no effect on digoxin pharmacokinetics, the area under the concentration-time curve of imidapril and the peak plasma concentration of the active metabolite imidaprilat are decreased when imidapril is given together with digoxin. Although six ACE inhibitors (captopril, enalapril, fosinopril, lisinopril, quinapril and ramipril) have been approved for use in heart failure by the US Food and Drug Administration, an overview of 32 clinical trials of ACE inhibitors in heart failure showed that no significant heterogeneity in mortality was found among enalapril, ramipril, quinapril, captopril, lisinopril, benazepril, perindopril and cilazapril. Initiation of therapy with captopril, ramipril, and trandolapril at least 3 days after an acute MI resulted in all-cause mortality risk reductions of 18 to 27%. Captopril has been shown to have similar morbidity and mortality benefits to those of diuretics and beta-blockers in hypertensive patients. Captopril has been shown to delay the progression of diabetic nephropathy, and enalapril and lisinopril prevent the development of nephropathy in normoalbuminuric patients with diabetes. ACE inhibitors are generally characterised by flat dose-response curves. Lisinopril is the only ACE inhibitor that exhibits a linear dose-response curve. Despite the fact that most ACE inhibitors are recommended for once-daily administration, only fosinopril, ramipril, and trandolapril have trough-to-peak effect ratios in excess of 50%.     

Relative Lipophilicities and Structural-Pharmacological Considerations of Various Angiotensin-Converting Enzyme (ACE) Inhibitors

Lipophilicities of seven structurally diverse angiotensin-converting enzyme (ACE) inhibitors, viz., captopril, zofenoprilat, enalaprilat, ramiprilat, lisinopril, fosinoprilat, and ceronapril (SQ29852), were compared by determining their octanol-water distribution coefficients (D) under physiological pH conditions. The distribution coefficients of zofenopril, enalapril, ramipril and fosinopril, which are the prodrug forms of zofenoprilat, enalaprilat, ramiprilat, and fosinoprilat, respectively, were also determined. Attempts were made to correlate lipophilicities with the reported data for oral absorption, protein binding, ACE inhibitory activity, propensity for biliary excretion, and penetration across the blood-brain barrier for these therapeutic entities. Better absorption of prodrugs compared to their respective active forms is in agreement with their greater lipophilicities. Captopril, lisinopril, and ceronapril are orally well absorbed despite their low lipophilicities, suggesting involvement of other factors such as a carrier-mediated transport process. Of all the compounds studied, the two most lipophilic ACE inhibitors, fosinoprilat and zofenoprilat, exhibit a rank-order correlation with respect to biliary excretion. This may explain the dual routes of elimination (renal and hepatic) observed with fosinoprilat in humans. The more lipophilic compounds also exhibit higher protein binding. Both the lipophilicity and a carrier-mediated process may be involved in penetration of some of these drugs into brain. For structurally similar compounds, in vitro ACE inhibitory activity increased with the increase in lipophilicity. However, no clear correlation between lipophilicity and ACE inhibitory activity emerged when different types of inhibitors are compared, possibly because their interactions with enzymes are primarily ionic in nature.     

Effects of ACE inhibitors on oxidation of human low density lipoprotein.

Oxidation of low density lipoprotein (LDL) may be instrumental in the development of atherosclerosis. We have examined the effect of the angiotensin converting enzyme (ACE) inhibitors captopril and quinaprilat and the -SH containing compound N-acetylcysteine on LDL oxidation. Oxidation of isolated human LDL was initiated with CuCl2. Conjugated diene formation (monitored spectrophotometrically at 234 nm) gave a measure of LDL oxidation. Captopril inhibited LDL oxidation but quinaprilat did not. The lag phase to the rapid increase in absorbance at 234 nm determined was 109 (65-157) min median and range for control samples and rose to 209 (168-305) min with captopril 10 microM, a ratio of 2.1:1 for drug to control (P = 0.01). N-acetylcysteine had a similar effect to captopril (drug to control lag time ratio 2.0:1, with NAC 10 microM), i.e. suggesting resistance to oxidation was due to the -SH group of both drugs. Captopril may have a potentially anti-atherosclerotic property not shared by other ACE inhibitors.     

Impairment of endothelium-dependent relaxation of rat aortas by homocysteine thiolactone and attenuation by captopril

To explore the effects of angiotensin-converting enzyme (ACE) inhibitors on endothelial dysfunction induced by homocysteine thiolactone (HTL). Both endothelium-dependent relaxation and nondependent relaxation of thoracic aortic rings in rats induced by acetylcholine (Ach) or sodium nitroprusside (SNP) and biochemical parameters including malondialdehyde (MDA) and nitric oxide (NO) were measured in rat isolated aorta. Exposure of aortic rings to HTL (3 to 30 mM) for 90 minutes made a significant inhibition of endothelium-dependent relaxation induced by Ach, decreased contents of NO, and increased MDA concentration in aortic tissue. After incubation of aortic rings with captopril (0.003 to 0.03 mM) attenuated the inhibition of endothelium-dependent relaxation (EDR) and significantly resisted the decrease of NO content and elevation of MDA concentration caused by HTL (30 mmol/L) in aortic tissues, a similarly protective effect was observed when the aortic rings were incubated with both N-acetylcysteine (0.05 mM). Treatment with enalaprilat (0.003 to 0.01 mM) made no significant difference with the HTL (30 mM) group regarding EDR, but enalaprilat (0.03 mM) and losartan (0.03 mM) could partly restore the EDR in response to HTL (30 mM). Captopril was more effective than enalaprilat and losartan in attenuation of the inhibition of on acetylcholine-stimulated aortic relaxation by HTL in the same concentration. Moreover, superoxide dismutase (SOD, 200 U/mL), which is a scavenger of superoxide anions, apocynin (0.03 mM), which is an inhibitor of NADPH oxidase, and l-Arginine (3 mmol/L), a precursor of nitric oxide (NO), could reduce HTL (30 mM)-induced inhibition of EDR. After pretreatment with not only the NO synthase inhibitor Nomega-nitro-l-arginine methyl ester (L-NAME, 0.01 mM) but also the free sulfhydryl group blocking agent p-hydroxymercurybenzoate (PHMB, 0.05 mM) could abolish the protection of captopril and N-acetylcysteine, respectively. These results suggest that mechanisms of endothelial dysfunction induced by HTL may include the decrease of NO and the generation of oxygen free radicals and that captopril can restore the inhibition of EDR induced by HTL in isolated rat aorta, which may be related to scavenging oxygen free radicals and may be sulfhydryl-dependent.     

The effect of saturation of ACE binding sites on the pharmacokinetics of enalaprilat in man.

1. Eight healthy male volunteers received oral enalapril, 10 mg, in the presence and absence of pretreatment with captopril, 50 mg, twice daily for 5 days. 2. Enalaprilat pharmacokinetics were characterised after both doses of enalapril to investigate the effect of saturating ACE binding sites by pretreatment with captopril. 3. The pharmacokinetics of enalaprilat were best described by a one compartment model with zero order input incorporating saturable binding to plasma and tissue ACE. 4. Values of AUC (0.72 h) for enalaprilat were 419 +/- 97 and 450 +/- 87 ng ml-1 h in the presence and absence of captopril, respectively. The difference was not statistically significant nor were there any other differences in model parameters. 5. Induction of ACE by captopril resulting in an increase in the number of ACE binding sites, may have obscured any effect of captopril on the occupancy of ACE binding sites by enalapril.     

Increased bradykinin levels accompany the hemodynamic response to acute inhibition of angiotensin-converting enzyme in dogs with heart failure.

To determine the short-term effects of angiotensin-converting enzyme (ACE) inhibition on hemodynamics and circulating levels of norepinephrine, angiotensin, and bradykinin, responses to enalaprilat and perindoprilat were examined at doses of 0.03, 0.3, and 1 mg/kg in permanently instrumented conscious dogs with pacing-induced heart failure (right ventricular pacing, 240-250 beats/min, 3 weeks). All doses of the two inhibitors produced similar decrease in mean aortic pressure and increase in cardiac output. Neither inhibitor affected plasma norepinephrine level. Both compounds induced a similar 60-80% decrease in blood angiotensin II level, a similar two- to eightfold increase in blood angiotensin I level, and a 80-95% decrease in the angiotensin II/angiotensin I ratio. There were also a fourfold to 10-fold increase in blood bradykinin-(1-9) level, a twofold increase in blood bradykinin-(1-7) level, and a 70-85% decrease in bradykinin-(1-7)/bradykinin-(1-9) ratio. In addition, the changes in total peripheral resistance induced by the two ACE inhibitors were weakly but significantly correlated with the changes in blood angiotensin II or blood bradykinin-(1-9). Thus whatever the specificity of enalaprilat and perindoprilat, both inhibitors produced similar acute hemodynamic effects in dogs with heart failure, which was associated with marked decrease in circulating angiotensin II level and increase in bradykinin-(1-9) level. This study, which measures for the first time in heart failure the blood bradykinin level after ACE inhibitors, indicates, in concert with angiotensin II reduction, a role for increased bradykinin-(1-9) level in mediating short-term hemodynamic effects of ACE inhibition in this model of heart failure.     

Comparison of angiotensin-converting enzyme inhibitors in the rat in perfused hindlimbs and in vivo.

To investigate the role of local renin angiotensin systems in the functional responses to angiotensin I and II, the effects of angiotensin I and angiotensin II on resistance were measured in perfused hindlimbs of rats under normal conditions and during infusion of enalaprilate, lisinopril, zabiciprilate and captopril at two infusion rates. The angiotensin-converting enzyme (ACE) inhibitors significantly increased ED50 and decreased maximal resistance changes of angiotensin I dose dependently, without effects on angiotensin II responses. Captopril increased the ED50 of angiotensin I significantly more than did the other ACE inhibitors at a low infusion rate. The ACE inhibitors, except for lisinopril, increased the ED50 of angiotensin I pressor responses in vivo to the same extent, and were similarly potent to inhibit plasma ACE activity at 15 min after injection. The ratio of the doses of the ACE inhibitors used in vivo was the same as in perfused hindlimbs. These results suggest that, in the hindlimbs, angiotensin I causes ACE-dependent vasoconstriction. Captopril may be more effective to inhibit local ACE than the other ACE inhibitors investigated.     

ACE inhibitors and AII receptor antagonists in the treatment and prevention of bone marrow transplant nephropathy

Radiation nephropathy has emerged as a major complication of bone marrow transplantation (BMT) when total body irradiation (TBI) is used as part of the regimen. Classically, radiation nephropathy has been assumed to be inevitable, progressive, and untreatable. However, in the early 1990's, it was demonstrated that experimental radiation nephropathy could be treated with a thiol-containing ACE inhibitor, captopril. Further studies showed that enalapril (a non-thiol ACE inhibitor) was also effective in the treatment of experimental radiation nephropathy, as was an AII receptor antagonist. Studies also showed that ACE inhibitors and AII receptor antagonists were effective in the prophylaxis of radiation nephropathy. Interestingly, other types of antihypertensive drugs were ineffective in prophylaxis, but brief use of a high-salt diet in the immediate post-irradiation period decreased renal injury. A placebo-controlled trial of captopril to prevent BMT nephropathy in adults is now underway. Since excess activity of the renin-angiotensin system (RAS) causes hypertension, and hypertension is a major feature of radiation nephropathy; an explanation for the efficacy of RAS antagonism in the prophylaxis of radiation nephropathy would be that radiation leads to RAS activation. However, current studies favor an alternative explanation, namely that the normal activity of the RAS is deleterious in the presence of radiation injury. On-going studies suggest that efficacy of RAS antagonists may involve interactions with a radiation-induced decrease in renal nitric oxide activity or with radiation-induced tubular cell proliferation. We hypothesize that while prevention (prophylaxis) of radiation nephropathy with ACE inhibitors, AII receptor antagonists, or a high-salt diet work by suppression of the RAS, the efficacy of ACE inhibitors and AII receptor antagonists in treatment of established radiation nephropathy depends on blood pressure control.     

Studies on the Magnitude and the Mechanism of Cough Potentiation by Angiotensin-Converting Enzyme Inhibitors in Guinea-pigs: Involvement of Bradykinin in the Potentiation

One adverse effect of the angiotensin-converting enzyme (ACE) inhibitors used for treatment of hypertension and congestive heart failure is the production of dry coughs. Imidapril is a new type of ACE inhibitor with a very low incidence of coughs. The magnitude and the mechanism of cough potentiation of imidapril and other ACE inhibitors has been studied in guinea-pigs. In normal guinea-pigs single and repeated dosing of imidapril at 0.1 to 100 mg kg^?1 had no effect on capsaicin- or citric acid-induced coughs. Single and repeated dosing of enalapril and captopril at 10 to 30 mg kg^?1, respectively, significantly increased the number of capsaicin-induced coughs. Repeated dosing of 1 mg kg^?1 enalapril also significantly augmented the capsaicin cough. In bronchitic guinea-pigs imidapril also had no effect on the coughs induced by the two stimulants. Enalapril and captopril significantly increased the number of coughs induced not only by capsaicin but also by citric acid. Lower doses of enalapril were enough to augment the capsaicin-induced coughs, whereas medium to large doses failed to augment the cough irrespective of the protocol of administration. Bradykinin-induced discharges of the vagal afferents from the lower airway were significantly increased by enalaprilat but not by imidaprilat. Capsaicin-induced discharges of the afferents were, on the other hand, significantly depressed by enalaprilat, but not by imidaprilat. Interestingly, enalaprilat depression of the discharges was significantly reversed by Hoe-140, a bradykinin B₂ receptor blocker. In guinea-pigs pretreated with a low dose of enalapril, arterial infusion of bradykinin significantly potentiated the coughs induced by capsaicin. The results indicated that imidapril was less potent than enalapril and captopril in potentiating cough responses induced by capsaicin and citric acid in guinea-pigs, and further suggest that bradykinin might be a key substance in the mechanism of the potentiation of coughs associated with ACE inhibitors.     

Captopril-induced reversal of nitroglycerin tolerance: role of sulfhydryl group vs. ACE-inhibitory activity.

The angiotensin-converting enzyme (ACE) inhibitor captopril has been shown to reverse vascular tolerance to nitroglycerin (NTG). Whether captopril reverses NTG tolerance by providing sulfhydryl (SH) groups or by inhibiting ACE is not clear. To examine this issue, we treated rat aortic rings with buffer, captopril (SH +, ACE inhibitory activity +), enalaprilat (SH-, ACE inhibitory activity +), or N-acetylcysteine (NAC, SH+, ACE inhibitory activity-) prior to their contraction with epinephrine and subsequent relaxation with NTG. Previous exposure of NTG-treated rings resulted in marked resistance to the vasorelaxant effect of a subsequent exposure to NTG in buffer-treated rings. Both NAC and captopril, but not enalaprilat, potentiated the vasorelaxant effects of NTG during the first exposure of vascular rings to NTG and also prevented the development of tolerance to NTG during a second exposure. Buffer-treated rings showed an inability to accumulate cyclic guanosine monophosphate (GMP) in response to a second exposure to NTG. In contrast, both NAC and captopril-pretreated rings demonstrated a persistence of cyclic GMP accumulation during the second NTG exposure. The endothelium-dependent vasodilator acetylcholine (ACh) caused relaxation of the NTG-tolerant rings and also induced cyclic GMP accumulation in these rings. In other experiments, we found that prior exposure of vascular rings to ACh did not cause resistance to the subsequent vasorelaxant effects of ACh. NAC, captopril, and enalaprilat did not modulate the effects of ACh during either the first or subsequent exposures to ACh. In addition, indomethacin did not influence the "protective" effects of NAC or captopril against NTG tolerance.(ABSTRACT TRUNCATED AT 250 WORDS)     

Does luminol chemiluminescence detect free radical scavengers?

Thiol compounds have been reported to abolish hypoxanthine/xanthine oxidase induced luminol chemiluminescence and this effect has been attributed to scavenging of superoxide (O2-)/(H2O2) produced from hypoxanthine/xanthine oxidase. Yet other workers have reported that thiol compounds have shown little, if any, reactivity towards O2-/H2O2. The aim of this study was to examine the discrepancy between these two sets of findings further. Captopril (a thiol angiotensin-converting enzyme (ACE) inhibitor) and MPG (a simple thiol) were observed to abolish hypoxanthine/xanthine oxidase induced chemiluminescence. The reactivity of captopril and MPG towards O2-/H2O2 was then determined by measurement of thiol oxidation in captopril and MPG after their incubation with hypoxanthine/xanthine oxidase. Incubation (at 10 min, 37 degrees C) with 4 mM hypoxanthine/0.03 u ml-1 xanthine oxidase resulted in 7% and 20% thiol oxidation in captopril and MPG (at 1 mM) respectively. Captopril and MPG, therefore, appeared to be ineffective scavengers of oxidants produced by hypoxanthine/xanthine oxidase. Captopril and MPG also did not affect urate production or oxygen consumption by xanthine oxidase which indicated that captopril and MPG quench luminol chemiluminescence by a mechanism that excludes the inhibition of xanthine oxidase. Hypoxanthine/xanthine oxidase induced luminol chemiluminescence may, therefore, be an unsuitable method for measuring free radical scavenging activity by drugs.     

Effect of angiotensin-converting enzyme inhibitors and nitroxy groups on human coronary resistance vessels in vitro

We investigated the interaction between nitroxy groups and angiotensin-converting enzyme (ACE) inhibitors to assess the role of sulfhydryl groups and adenosine triphosphate (ATP)-sensitive potassium channels in vasodilation of human coronary resistance vessels in vitro. Coronary resistance vessels were resected from the right atrial appendage of 27 patients undergoing open heart surgery. The vessel ends were inserted into a microglass pipette with the internal pressure maintained at 40 mm Hg. Nitroglycerin did not change the vasoresponse, whereas nicorandil induced a concentration-dependent vasodilation that was not affected by methylene blue, but was markedly inhibited by glibenclamide. The ACE inhibitors, captopril, with a sulfhydryl group (1 x 10(-6) M), and enalaprilat, without a sulfhydryl group (1 x 10(-6) M), were added to either nitroglycerin or nicorandil to assess the incremental response of the sulfhydryl group to vasodilation. The addition of captopril or L-cysteine (1 x 10(-6) M) enhanced the activity of both nitroglycerin and nicorandil, whereas addition of enalaprilat did not. The responses of nicorandil and nitroglycerin to captopril and were similar. Cromakalim was not enhanced by L-cysteine or captopril. The response of nitroglycerin was not enhanced by captopril or L-cysteine after addition of N(G)-monomethyl-L-ARGININE (L-NMMA). Both nitroglycerin and nicorandil exhibited an increase in vasodilation in the presence of an ACE inhibitor containing a sulfhydryl group. The mechanism of the vasodilatory action in the coronary resistance vessels may involve the opening of an ATP-sensitive potassium channel and subsequent guanylate cyclase activation. These interactions have important clinical implications.     

Effect of SQ29,852, a new angiotensin converting enzyme (ACE) inhibitor with a phosphonic acid group, on the activity of angiotensin converting enzyme from human kidney

1. An in vitro experiment was carried out to compare the inhibitory effect of SQ29,852 on human renal angiotensin converting enzyme (ACE) with those of captopril, enalapril and enalaprilat. 2. SQ29,852 strongly inhibited human renal ACE; its IC50 value was 1.5 x 10(-8) M. In terms of the IC50, SQ29,852's efficacy was about 1/10 of that of captopril and 1/28 of that of enalaprilat, but it was about 14 times more potent than enalapril. 3. SQ29,852 showed no inhibitory effects on cathepsin D, urinary kallikrein, renal renin, pepsin, trypsin and chymotrypsin. Its ACE-specificity was higher than that of captopril. 4. ACE inhibition by SQ29,852 was shown to be competitive, as revealed by Lineweaver-Burk plots. The affinity of SQ29,852 to ACE was shown to be high by a Ki value of 1.2 x 10(-8) M.     

The effect of captopril on inflammation-induced liver injury in male rats

Abstract

Activation of macrophages-induced by lipopolysaccharide (LPS) is accompanied by the production of reactive oxygen species and inflammatory cytokines to induce hepatic injury. Renin–angiotensin system may play a role in liver damage. In the current study, the effect of captopril on the injury of inflammation-induced liver was investigated. The rats were divided into (1) Control, (2) LPS, and (3–5) LPS as well as 10, 50, or 100?mg/kg captopril for 2 weeks. Captopril decreased NO metabolites, IL-6, and MDA, while it increased CAT, SOD, and total thiol in the liver. Captopril also attenuated AST, ALT, and ALK-P, whereas it increased albumin and total protein in serum. As an ACE inhibitor, captopril improved liver function and attenuated inflammation and oxidative stress induced by LPS injection.