N-acetylcysteine prevents the deleterious effect of tumor necrosis factor-(alpha) on calcium transients and contraction in adult rat cardiomyocytes.

Background: The negative effect of tumor necrosis factor-alpha (TNF-alpha) on heart contraction, which is mediated by sphingosine, is a major component in heart failure. Because the cellular level of glutathione may limit sphingosine production via the inhibition of the Mg-dependent neutral sphingomyelinase (N-SMase), we hypothesized that cardiac glutathione status might determine the negative contractile response to TNF-alpha.

Methods And Results: We examined the effects of TNF-alpha in isolated cardiomyocytes obtained from control rats or rats that were given the glutathione precursor N-acetylcysteine (NAC, 100 mg IP per animal). In cardiomyocytes obtained from control rats, 25 ng/mL TNF-alpha increased reactive oxygen species generation and N-SMase activity (500% and 34% over basal, respectively) and decreased the amplitude of [Ca(2+)](i) in response to electrical stimulation (22% below basal). NAC treatment increased cardiac glutathione content by 42%. In cardiomyocytes obtained from NAC-treated rats, 25 ng/mL TNF-alpha had no effect on reactive oxygen species production or N-SMase activity but increased the amplitude of [Ca(2+)](i) transients and contraction in response to electrical stimulation by 40% to 50% over basal after 20 minutes. This was associated with a hastened relaxation (20% reduction in t(1/2) compared with basal) and an increased phosphorylation of both Ser(16)- and Thr(17)-phospholamban residues (260% and 115% of maximal isoproterenol effect, respectively).

Conclusions: It is concluded that cardiac glutathione status, by controlling N-SMase activation, determines the severity of the adverse effects of TNF-alpha on heart contraction. Glutathione supplementation may therefore provide therapeutic benefits for vulnerable hearts.