Cyclo-oxygenase-2 (COX-2) expression at the site of recent myocardial infarction: friend or foe?

Abstract

Background: Cyclo-oxygenase-2 (COX-2) is induced in cardiomyocytes only in response to stress, such as ischaemia.

Objective: To assess COX-2 expression at the site of recent myocardial infarction.

Methods: COX-2 expression was evaluated by specific immunostaining in cardiomyocytes from 23 subjects who died 10-60 days after acute myocardial infarction. The relation between COX-2 myocardial expression and apoptotic rate was investigated. Cardiomyocyte apoptotic rate was defined as the number of cells co-expressing in situ end labelling of DNA fragmentation (TUNEL) and immunostaining for activated caspase-3.

Results: COX-2 expression was found in cardiomyocytes at the site of infarction in nine of 23 cases (39%). It was associated with fivefold higher apoptotic rates (median 17.9% (interquartile range 11.0-25.4%) v 3.7% (0.6-12.8%); p = 0.016), and apoptotic rate increased progressively from mild to intense COX-2 staining (p for trend 0.009). COX-2 expression co-localised with TUNEL nuclear staining in myocytes, and there was a high concordance between COX-2 and hypoxia induced factor 1-alpha staining (78%, p = 0.021) and between COX-2 and bax (83%, p = 0.014). Subjects showing myocardial COX-2 expression were more likely to have enlarged hearts (p = 0.050), and intense COX-2 staining was strictly associated with symptomatic heart failure (p = 0.035).

Conclusions: COX-2 is expressed in cardiomyocytes in nearly 40% of cases at the site of recent acute myocardial infarction, even late after the index event. Its expression was associated with extremely high apoptotic rates. These findings suggest a potential cause-effect link between COX-2 expression and enhanced myocardial apoptosis in ischaemic cardiomyopathy.

Figure 1

Intense cyclo-oxygenase-2 (COX-2) myocardial staining. Intense cytoplasmic staining is shown in several cardiomyocytes at the site of infarction, using a primary anti-COX-2 antibody (goat polyclonal sc-1745, Santa Cruz Biotechnology, California, USA, at a 1:100 dilution, according to the results of titration experiments for optimal dilutions), and with a secondary reaction using the streptavidin–biotin system (Dako, Carpintera, California, USA), with diaminobenzidine as the final chromogen.

Figure 2

Cardiomyocyte apoptosis. An apoptotic cardiomyocyte co-staining for DNA fragmentation (TUNEL) and activated caspase-3 is shown.

Figure 3

Peri-infarct apoptotic rate according to myocardial expression of cyclo-oxygenase-2 (COX-2). A significantly higher apoptotic rate was found in subjects with versus without COX-2 expression at the site of recent infarction, especially with intense COX-2 expression (++). Kruskal–Wallis test, p  =  0.047; Mann–Whitney U test, p  =  0.016 (comparing patients with versus without COX-2 expression); p value for trend  =  0.009 (univariate ANOVA analysis considering the three groups separately). The box represents the median value and the vertical bars are the interquartile range.

Figure 4

Cyclo-oxygenase-2 (COX-2) co-localises with markers of apoptosis. Double positive staining (nuclear staining for DNA fragmentation at TUNEL, and cytoplasmic staining for COX-2) within the same cardiomyocyte is shown.

Figure 5

Cyclo-oxygenase-2 (COX-2) expression, unfavourable cardiac remodelling, and heart failure. (A) Patients with myocardial COX-2 expression at site of infarction showed a greater transverse diameter to wall thickness ratio, which is a marker of unfavourable cardiac remodelling. (B) Subjects with symptomatic heart failure were more likely to have intense peri-infarct COX-2 expression than the others. The box represents the median value; vertical bars show interquartile range.