Proinflammatory cytokines such as tumor necrosis factor (TNF)-alpha and interleukin (IL)-1 beta have been implicated in the pathogenesis of myocardial dysfunction in ischemia-reperfusion injury, sepsis, chronic heart failure, viral myocarditis, and cardiac allograft rejection. Although circulating TNF-alpha and IL-1 beta are both often elevated in septic shock, it remains unknown whether TNF-alpha or IL-1 beta are the factors induced during sepsis that directly depress human myocardial function, and if so, whether the combination synergistically depresses myocardial function. Furthermore, the mechanism(s) by which these cytokines induce human myocardial depression remain unknown. We hypothesized the following: a) TNF-alpha and IL-1 beta directly depress human myocardial function; b) together, TNF-alpha and IL-1 beta act synergistically to depress human myocardial function; and c) inhibition of ceramidase or nitric oxide synthase attenuates myocardial depression induced by TNF-alpha or IL-1 beta by limiting proximal cytokine signaling or production of myocardial nitric oxide (NO).
Prospective, randomized, controlled study.
Experimental laboratory in a university hospital.
Freshly obtained human myocardial trabeculae.
Human atrial trabeculae were obtained at the time of cardiac surgery, suspended in organ baths, and field simulated at 1 Hz, and the developed force was recorded. After a 90-min equilibration, TNF-alpha (1.25, 12.5, 125, or 250 pg/mL for 20 mins), IL-1 beta (6.25, 12.5, 50, or 200 pg/mL for 20 mins), or TNF-alpha (1.25 pg/mL) plus IL-1 beta (6.25 pg/mL) were added to the bath, and function was measured for the subsequent 100 mins after the 20-min exposure. To assess the roles of the sphingomyelin and NO pathways in TNF-alpha and IL-1 beta cross-signaling, the ceramidase inhibitor N-oleoyl ethanolamine (1 [micro sign]M) or the NO synthase inhibitor NG-monomethyl-L-arginine (10 [micro sign]M) was added before TNF-alpha (125 pg/mL) or IL-1 beta (50 pg/mL).
Measurements and Main Results
TNF-alpha and IL-1 beta each depressed human myocardial function in a dose-dependent fashion (maximally depressing to 16.2 + 1.9% baseline developed force for TNF-alpha and 25.7 + 6.3% baseline developed force for IL-1 beta), affecting systolic relatively more than diastolic performance (each p < .05). However, when combined, TNF-alpha and IL-1 beta at concentrations that did not individually result in depression (p > .05 vs. control) resulted in contractile depression (p < .05 vs. control). Inhibition of myocardial sphingosine or NO release abolished the myocardial depressive effects of either TNF-alpha or IL-1 beta.
TNF-alpha and IL-1 beta separately and synergistically depress human myocardial function. Sphingosine likely participates in the TNF-alpha and IL-1 beta signal leading to human myocardial functional depression. Therapeutic strategies to reduce production or signaling of either TNF-alpha or IL-1 beta may limit myocardial dysfunction in sepsis. (Crit Care Med 1999; 27:1309-1318)