Activity profile of calpains I and II in chronically infarcted rat myocardium – influence of the calpain inhibitor CAL 9961

Abstract

1 The calpains have been proposed to be activated following cardiac ischaemia and to contribute to myocyte damage after myocardial infarction (MI). In this study, the activity of calpains I and II in the infarcted and non-infarcted rat myocardium and the action of the selective calpain inhibitor, CAL 9961, has been investigated. 2 MI was induced by permanent ligation of the left coronary artery. One, 3, 7 and 14 days post MI, the enzymes calpain I and II were separated from homogenates of the interventricular septum (IS) and left ventricular free wall (LVFW) by chromatography on DEAE-Sepharose. The activity of the calpains was measured in sham-operated and MI animals chronically treated with placebo or CAL 9961 (15 mg kg 71 d 71 s.c.) in a synthetic substrate assay. Treatment was started 3 days before MI induction. 3 Calpain I activity reached highest values in IS 14 days post MI, whereas maximum activity of calpain II was measured in LVFW 3 days post MI. In experiments in vitro, CAL 9961 completely inhibited both calpains. In vivo, chronic treatment of MI animals with CAL 9961 partially prevented the increase in calpain I activity in IS and reduced calpain II activity in LVFW to sham levels. 4 Our ®ndings demonstrate that calpains I and II are activated after MI, however, both enzymes di er in their regional and temporal activation within the infarcted myocardium. Chronic inhibition of these enzymes with CAL 9961 might limit the calpain-induced myocardial damage and preserve cardiac structural integrity post MI.

Calpain-dependent Cleavage of N-cadherin Is Involved in the Progression of Post-myocardial Infarction Remodeling

“…One of the major obstacles for the study of calpains has been the lack of reliable methods to measure calpain activity accurately in vivo. Previous reports demonstrated that expression levels or enzymatic activities of calpains were increased in the hearts after MI (17)(18)(19)(20)(21), but these results must be interpreted cautiously. Obviously, the protein content of calpains does not necessary correlate with their proteolytic activity, and the in vitro enzymatic assays using homogenized tissue samples after the addition of Ca 2ϩ merely indicate the proteolytic capacity of calpains, not the calpain activity in situ.…”

“…During acute ischemia, the intracellular Ca 2ϩ is elevated mainly through Ca 2ϩ entry by reverse mode Na ϩ / Ca 2ϩ exchanger (15,16), leading to the assumption that calpain activation during an acute phase may exacerbate myocardial cell death. Meanwhile, it has been reported that enzymatic activities as well as mRNA and protein levels of calpains are elevated in a chronic phase (17)(18)(19)(20)(21), suggesting that calpain activation may be implicated in the progression of left ventricular (LV) remodeling after MI. Indeed, several reports have demonstrated that calpain inhibitors reduced infarct size and prevented LV dysfunction after MI in animal models (22,23), but there are significant limitations to these pharmacological approaches.…”

Calpain inhibition preserves myocardial structure and function following myocardial infarction

“…2A). A recent study (40) showed that in postinfarct heart, m-calpain activity level was higher in the beginning (3 days following an MI) and -calpain was higher in 2-wk post-MI heart. Overall, all these studies indicate that calpain enrichment observed in the border zone of 4-day MI mice might be primarily contributed by m-calpain, although the possible contribution by the cleaved (active) form of -calpain could not be ruled out from these studies.…”

Cardiomyocyte Degeneration With Calpain Deficiency Reveals a Critical Role in Protein Homeostasis

“…Nevertheless, it is important to determine whether this might be the case, not only for the mechanistic insight to be gained, but because pharmacological calpain inhibition is being pursued as a means of limiting cardiac ischemic injury. 11,12 Here, to identify the conse-quences of calpain activity on myocardial protein degradation and function, we used genetic techniques to positively and negatively modulate calpain activity in cultured cardiac myocytes and in vivo mouse hearts. The results suggest that calpain 1 can promote ubiquitination of myocardial proteins and is positioned at the apex of an essential degradative pathway that prevents pathological accumulation of select misfolded or damaged proteins.…”