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

Vibrational Spectroscopic Studies on the Disulfide Formation and Secondary Conformational Changes of Captopril–HSA Mixture after UV-B Irradiation

The effects of pH and ultraviolet-B (UV-B) irradiation on the secondary structure of human serum albumin (HSA) in the absence or presence of captopril were investigated by an attenuated total reflection (ATR)/Fourier transform infrared (FTIR) spectroscopy. The UV-B exposure affecting the stability of captopril before and after captopril-HSA interaction was also examined by using confocal Raman microspectroscopy. The results indicate that the transparent pale-yellow solution for captopril-HSA mixture in all pH buffer solutions, except pH 5.0 approximately 7.0, changed into a viscous form then a gel form with UV-B exposure time. The secondary structural transformation of HSA in the captopril-HSA mixture with or without UV-B irradiation was found to shift the maxima amide I peak in IR spectra from 1652 cm(-1) assigned to alpha-helix structure to 1622 cm(-1) because of a beta-sheet structure, which was more evident in pH 3.0, 8.0 or 9.0 buffer solutions. The Raman shift from 1653 cm(-1) (alpha-helix) to 1670 cm(-1) (beta-sheet) also confirmed this result. Captopril dissolved in distilled water with or without UV-B irradiation was determined to form a captopril disulfide observed from the Raman spectra of 512 cm(-1), which was exacerbated by UV-B irradiation. There was little disulfide formation in the captopril-HSA mixture even with long-term UV-B exposure, but captopril might interact with HSA to change the protein secondary structure of HSA whether there was UV-B irradiation or not. The pH of the buffer solution and captopril-HSA interaction may play more important roles in transforming the secondary structure of HSA from alpha-helix to beta-sheet in the corresponding captopril-HSA mixture than UV-B exposure. The present study also implies that HSA has the capability to protect the instability of captopril in the course of UV-B irradiation. In addition, a partial unfolding of HSA induced by pH or captopril-HSA interaction under UV-B exposure is proposed.

Cardioprotective effect of orally administered angiotensin-converting enzyme inhibitor against ischemia. Reperfusion injury in the isolated rat heart

Angiotensin-converting enzyme inhibitors are reported to be cardioprotective against ischemia/reperfusion injury. Few studies have been made, however, on the cardioprotectiveness of orally administered angiotensin-conrerting enzyne inhibitors. Wistar rats were pretreated with oral delapril--30 mg/kg/day in the low-dose group and 90 mg/kg/day in the high-dose group--for one week. Cardiac function recovery was assessed after ischemia/reperfusion in the isolated working heart model. Rat hearts in the high-dose group were also reperfused with a solution containing nitro-L-arginine methyl ester, a nitric-oxide synthase inhibitor. Oral pretreatment of delapril did not affect baseline cardiac function. The percentage of cardiac output recovery for controls was 22 +/- 4.5%, for the low-dose group 44 +/- 6.5% (P < 0.05 versus controls), and for the high-dose group 76 +/- 5.3% (P < 0.001 versus controls and low-dose). Although coronary vascular resistance at the end of reperfusion showed no difference, mean coronary vascular resistance early after reperfusion was significantly lower (P < 0.0001) in both delapril groups than in control. In the high-dose group, reperfusion with L-NAME significantly increased coronary vascular resistance after ischemia/reperfusion and attenuated the cardioprotectiveness of delapril (P < 0.05 versus without nitro-L-arginine methyl ester). We thus found that oral administration of delapril was cardioprotective dose-dependently against ischemia/reperfusion injury. Nitric oxide appeared to be involved in the mechanism behind this cardioprotective effect.

Enalapril and moexipril protect from free radical-induced neuronal damage in vitro and reduce ischemic brain injury in mice and rats

Angiotensin-converting enzyme inhibitors have been demonstrated to protect spontaneously hypertensive rats from cerebral ischemia. The present study investigated the protective effect of enalapril and moexipril in models of permanent focal cerebral ischemia in normotensive mice and rats. To elucidate the mechanism of neuroprotection the influence of these angiotensin-converting enzyme inhibitors on glutamate-, staurosporine- or Fe2+/3+-induced generation of reactive oxygen species and neuronal cell death in primary cultures from chick embryo telencephalons was studied. Treatment with moexipril or enalapril dose-dependently reduced the percentage of damaged neurons, as well as mitochondrial reactive oxygen species generation induced by glutamate, staurosporine or Fe2+/3+. Furthermore, moexipril and enalapril attenuated staurosporine-induced neuronal apoptosis as determined by nuclear staining with Hoechst 33258. In mice, 1 h pretreatment with enalapril (0.03 mg/kg) or moexipril (0.3 mg/kg) significantly reduced brain damage after focal ischemia as compared to control animals. Additionally, moexipril (0.01 mg/kg) was able to reduce the infarct volume in the rat model after focal cerebral ischemia. The results of the present study indicate that the angiotensin-converting enzyme inhibitors enalapril and moexipril promote neuronal survival due to radical scavenging properties.

Inhibitory effects of a subdepressor dose of L-158,809, an angiotensin II type 1 receptor antagonist, on cardiac hypertrophy and nephropathy via the activated human renin-angiotensin system in double transgenic mice with hypertension

The effects of L-158,809, an angiotensin II type 1 receptor antagonist, on cardiac hypertrophy and nephropathy were examined using Tsukuba hypertensive mice (THM) carrying both human renin and angiotensinogen genes. Nine male THM aged 20 weeks were assigned to each of a no-dosage group and an L-158,809 dosage group, and L-158,809 was administered for 8 weeks. Nine age-matched male C57BL/6 mice were used as normal control animals. At 28 weeks of age, all of the mice were euthanized. Systolic blood pressure, urinary volume, water intake volume, urinary albumin excretion, heart weight and kidney weight to body weight ratios and a glomerulosclerosis index were measured. In the no-dosage group, the values of all of these parameters were larger than those in the control mice. In the L-158,809 group, all of the parameters showed significant improvement, except for blood pressure, which was not significantly different from that in the no-dosage group. These results suggest that the renin-angiotensin system played a crucial role in the cardiac hypertrophy and nephropathy in THM, and that L-158,809 exhibited strong curative effects on cardiac hypertrophy and nephropathy by blocking the angiotensin II type 1 receptor.