Cellular mechanisms of acute septic cardiomyopathy: cardiodepressive profiles of endotoxin, tumor necrosis factor α and interleukin-1 in the cardiomyocyte
© Current Science Ltd 1997
Published: 1 March 1997
Aim of study
Cardiodepression in sepsis and septic shock is mainly attributed to endotoxin-induced release of tumor necrosis factor α (TNFα) and interleukin 1 (IL-1) into the circulation It is supposed that the negative inotropic action of these cytokines in the heart is mediated by induction of inducible nitric oxide synthase (iNOS). When applied in vivo, endotoxin and TNFα indeed mimic the cardiovascular pattern of sepsis. Elevated levels of TNFα and IL-1 are measured in sepsis. The purpose of this study was to compare the cardiodepressive profiles of endotoxin. TNFα and IL-1 on the cardiomyocyte level and determine whether or not their effects are mediated by nitric oxide (NO).
Spontaneously beating neonatal rat cardiomyocytes were cultured in the presence of endotoxin (1–10 μg/ml), IL–1 (20–100 U/ml) or TNFα (10–1000 U/ml) for 24-72 h. Spontaneous beating as well as electrically triggered contractions (yielding values of pulsation amplitude) were monitored and recorded by means of a photo-optical device. Nitrite in the cell culture supernatant as a measure of NO production was determined by the Grieβ reaction. iNOS in cardiomyocytes was measured by reverse transcriptase polymerase chain reaction (RT-PCR). Cell-associated IL-1-activity was determined by a bioassay.
Both endotoxin and TNF and IL-1 block β-adrenergic response in isolated cardiomyocytes after a 24 h culture-period. In neither case, morphological signs of cytotoxicity were observed, as determined by phase contrast microscopy. iNOS is induced by IL-1 (100 U/ml, 24 h) and endotoxin (1 μg/ml, 24 h); both signals are suppressed by simultaneous administration of dexamethasone (0.1 μM). Nitrite content of the supernatant is enhanced by IL-1 (42.0 ± 5.8 nmol/mg protein: control: 29.9 ± 3.0; P < 0.05) and endotoxin (≥ 1 μg/ml) (both suppressible by dexamethasone, 0.1 μM). IL-1 (100 U /ml) does not significantly increase basal contractile frequency in cardiomyocytes. TNFα in high concentration (1000 U/ml, 6 h/24 h) only very weakly induces iNOS (RT-PCR) in RCM, the signal is suppressed by simultaneous application of dexamethasone (0.1 μM). In the presence of the pathophysiologically relevant TNFα concentration of 10 U/ml, mRNA for iNOS in minimal amounts is evidenced after 6 h of culture, but no longer after 24 h. NO production was not enhanced by TNFα (10 U/ml, 24 h) (absence and presence of dexamethasone). After stimulation with endotoxin (10 μg/ml, 24 h) cell-associated IL-1 activity is enhanced in rat cardiomyocytes.
Endotoxin has a direct effect on rat cardiomyocytes in vitro, as evidenced by contractile disturbance. iNOS induction and increase in cell-associated IL-1-activity. Although both endotoxin and IL-1 and TNFα block β-adrenergic response in cardiomyocytes, only endotoxin and IL-1 lead to an increased NO production in these cells, whereas TNFα-cardiodepression seems to be independent of NO.