Protective role of cyclooxygenase-2 inhibition in bacteria-induced myocyte failure

Trupti A. Patel, Siân E. Harding, *Timothy D. Warner and Jane A. Mitchell, Myocardial Systems Biology and Cardiothoracic Pharmacology, Critical Care, National Heart and Lung Institute, Imperial College London, Dovehouse Street, London SW3 6LY, UK. *The William Harvey Research Institute, Barts and the London, Queen Mary’s School of Medicine and Dentistry, London EC1M 6BQ, UK.

Our understanding of the mechanisms underlying the myocardial dysfunction of sepsis remains incomplete. We have shown that bacteria induce contractility changes in isolated cardiomyocytes (Patel et al., current meeting). Cyclooxygenase ( COX) inhibitors have recently been implicated in cardiovascular deaths (Bresalier R.S. et al., 2005; Nussmeier N.A. et al., 2005). Thus, the aims of this study were to investigate the role of COX enzymes in bacteria-induced myocyte dysfunction after incubation with whole heat-killed Gram positive Staphylococcus aureus (SA).

Ventricular myocytes were isolated from adult male Sprague Dawley rats (250-350g) and cultured for 24h with SA (107-108 colony forming units/mL) with and without the COX-2 selective inhibitor rofecoxib (3 x 10-6M) or the non-selective COX inhibitor naproxen (10 -4M). Myocytes that were capable of contraction upon electrical stimulation (0.5Hz, 1mM Ca2+) and proportions of non-contracting and arrhythmic cells were counted. A contraction was detectable when shortening with each beat was ≥ 0.25%. Contraction amplitude, time to peak contraction ( TTP), time to 50% relaxation (R50) and time to 90% relaxation (R90) were measured via a video camera using software from IonOptix. Data was analysed by paired t-test or one-way ANOVA with Tukey post hoc test.

At 24h, SA reduced the proportion of viable myocytes that had contractile activity (Con, 59.9 ± 3.2%; SA 42.8 ± 5.6%; P<0.01, n=7), an effect that was reversed by culturing with naproxen (SA + naproxen, 65.2 ± 7.4%, n=7). Contraction amplitude, TTP, R50 and R90 did not differ between treatment groups. In the presence of rofecoxib, SA no longer produced a significant decrease in the proportion of contracting myocytes (Con, 60.3 ± 4.4%, SA, 43.0 ± 6.1%, SA + rofecoxib, 54.8 ± 3.8%, n=10). Moreover, rofecoxib significantly increased the contraction amplitude (percentage shortening) of SA-treated myocytes but not control (Con, 2.5 ± 0.3% vs. Con + rofecoxib, 2.0 ± 0.3%, n.s.d.; SA, 2.1 ± 0.3% vs.SA + rofecoxib, 2.9 ± 0.4%, P< 0.01, n=34-40 myocytes). TTP, R50, R90 were unaffected. The concentration-response curves of isoprenaline (10-10– 10-7M) did not differ between SA and control. However, superfusing SA-treated myocytes with rofecoxib sustained the increase in contraction amplitude at all doses of isoprenaline, with no effect on control myocytes.

In conclusion, this study demonstrates that the decrease in contractility of ventricular myocytes induced by SA is, at least, in part, mediated by COX-2 products. The protective effect seen here of rofecoxib suggests that future COX-2 selective drugs may have cardioprotective functions in some forms of heart disease.

Bresalier R.S. et al. (2005) N Engl J Med., 352(11),1092-102.
Nussmeier N.A. et al. (2005) N Engl J Med., 352(11),1081-91.