Achim Möller

Reduction of myocardial infarction by calpain inhibitors A-705239 and A-705253 in isolated perfused rabbit hearts

Abstract Two novel calpain inhibitors (A-705239 and A-705253) were studied in isolated perfused rabbit hearts subjected to 60-min occlusion of the ramus interventricularis of the left coronary artery (below the origin of the first diagonal branch), followed by 120 min of reperfusion. The inhibitors were added to the perfusion fluid in various final concentrations from the beginning of the experiments before the coronary artery was blocked. Hemodynamic monitoring and biochemical analysis of perfusion fluid from the coronary outflow were carried out. Myocardial infarct size and the area at risk (transiently non-perfused myocardium) were determined from left ventricular slices after a special staining procedure with Evans blue and 2,3,5-triphenyltetrazolium chloride. The infarcted area (dead myocardium) was 77.9±2.3% of the area at risk in untreated controls (n=12). The infarct size was significantly reduced in the presence of both calpain inhibitors. The best effect was achieved with 10-8 M A-705253 (n=8), which reduced (p<0.001) the infarcted area to 49.3±3.9% of the area at risk, corresponding to an infarct reduction of 61.8%. No statistical difference was observed between the experimental groups in coronary perfusion, left ventricular pressure, and in the release of lactate dehydrogenase and creatine kinase from heart muscle.

A novel water-soluble and cell-permeable calpain inhibitor protects myocardial and mitochondrial function in postischemic reperfusion.

Abstract The effects of the novel calpain inhibitor A-705239 were studied in isolated perfused rabbit hearts subjected to 45 min of global ischemia, followed by 60 min of reperfusion. During 15 min of perfusion the inhibitor accumulated in myocardial tissue up to 16 times the concentration in the perfusate. Almost complete recovery and survival of heart function (90%) was seen with an inhibitor concentration of 10 8 M in the perfusion fluid when the compound was administered prior to ischemia. Left ventricular pressure amplitude and coronary flow showed significantly higher values during reperfusion in the presence of the inhibitor. A-705239 significantly reduced the release of creatine kinase, from 166±49 U/l in untreated hearts to 44±10 U/l, and diminished the release of lactate dehydrogenase from 118±20 U/l in untreated hearts to 63±4 U/l. Mitochondrial dysfunction following ischemia and reperfusion was markedly attenuated by the inhibitor. Thus, the state 3 respiration rate only decreased to 4.2 in contrast to 2.6 nmol O2/(min×mg s.w.) in untreated hearts, reflecting a reduced damage of oxidative phosphorylation. Furthermore, in the presence of the inhibitor the inner mitochondrial membranes became less permeable as indicated by a smaller leak respiration. The excellent properties of A-705239 should make this compound a valuable tool for further pharmacological studies.

Human μ-calpain: Simple isolation from erythrocytes and characterization of autolysis fragments

Abstract Heterodimeric calpain, consisting of the large (80 kDa) and the small (30 kDa) subunit, was isolated and purified from human erythrocytes by a highly reproducible fourstep purification procedure. Obtained material is more than 95% pure and has a specific activity of 6 7 mU/mg. Presence of contaminating proteins could not be detected by HPLC and sequence analysis. During storage at 80 C the enzyme remains fully activatable by Ca 2+ , although the small subunit is partially processed to a 22 kDa fragment. This novel autolysis product of the small subunit starts with the sequence 60 RILG and is further processed to the known 18 kDa fragment. Active forms and typical transient and stable autolysis products of the large subunit were identified by protein sequencing. In caseinzymograms only the activatable forms 80 kDa+30 kDa, 80 kDa+22 kDa and 80 kDa+18 kDa displayed caseinolysis.

Calpain inhibitor A-558693 in experimental focal cerebral ischemia in rats

Abstract Objectives: Calpains are intracellular proteases, which are activated in various cerebral injuries. We studied the expression of μ-calpain in a model of focal cerebral ischemia/reperfusion and the efficacy of the calpain inhibitor A-558693. Methods: A transient occlusion of the middle cerebral artery was produced in male Wistar rats by using the suture model with 3 hours of ischemia and 24 hours of reperfusion. Six animals were given the calpain inhibitor and six animals were treated with placebo. The infarct size was determined by the loss of the calpain substrate microtubule-associated protein-2 (MAP-2) immunohistochemistry using volumetry in serial slices of the brains. Furthermore μ-calpain positive-stained cells were detected by immunohistochemistry and western blotting. Results: In placebo-treated animals the μ-calpain expression was significantly increased in the ischemic hemisphere compared with the contralateral non-ischemic hemisphere (88.6 versus 10.5% in the basal ganglia, 60.7 versus 10.7% in the cortex, p<0.001, respectively) with a subsequent loss its substrate MAP-2. However, the use of the calpain inhibitor A-558693 did not significantly change the μ-calpain expression, nor significantly reduce the infarct volume. Discussion: The present data indicate that μ-calpain proteolysis plays an important role in the chain of events following cerebral ischemia. However, the calpain inhibitor A-558693 failed to prevent these changes.