Isoproterenol Inhibits Bacterial Lipopolysaccharide-Stimulated Release of Tumor Necrosis Factor-α from Human Heart Tissue

Abstract

Recent evidence suggests that inflammatory cytokines, particularly tumor necrosis factor a (TNF-α), may play a role in heart disease. Elevated plasma levels of the cytokine have been reported in congestive heart failure and severe angina and after myocardial infarction. The exact role of TNF-α in heart disease and how production is stimulated and regulated in the heart are current areas of investigation. Regarding regulation of production, isoproterenol elevates cyclic AMP and inhibits TNF-α release in macrophages. Therefore we hypothesized that stimulation of β-adrenergic receptors of the sympathetic nervous system would inhibit release of the cytokine from heart tissue. With Institutional Review Board approval and patient consent atrial tissue was obtained during preparation for cardiac bypass. The tissue was divided into segments, placed in culture medium, and incubated for various times in the presence or absence of lipopolysaccharide (LPS) (20 μg/mL) and/or isoproterenol (1 μM). The medium was removed and analyzed for biologically active TNF-α by the L929 cell cytotoxicity assay. Tissue samples were weighed and TNF-α release was expressed as pg TNF-α/mg tissue. Initially, to determine the time course of release, measurements were made at 2, 5, 10, 15, 30, 60, 120, 180, and 360 minutes after the addition of LPS. Elevated TNF-α levels in the culture medium were reliably detected at 360 minutes after exposure to LPS. In atrial tissue obtained from seven patients TNF-α released into the culture medium at 360 minutes was 6 ± 3 pg/mg tissue. In the presence of LPS, levels of the cytokine in the culture medium increased to 604 ± 233 pg/mg tissue (P < 0.05 vs LPS alone). When isoproterenol and LPS were simultaneously added to the culture medium release of TNF-α was reduced by 87 per cent to 82 ± 40 pg/mg tissue (P < 0.05 vs LPS alone). Our results show that activation of the β-adrenergic receptor inhibits myocardial production of TNF-α. This finding suggests that the sympathetic nervous system inhibits production of the cytokine and that impaired sympathetic function in heart failure may play a role in the elevated levels of TNF-α.