N -Acetylcysteine Prevents the Deleterious Effect of Tumor Necrosis Factor-α on Calcium Transients and Contraction in Adult Rat Cardiomyocytes

Abstract

Background-The negative effect of tumor necrosis factor-␣ (TNF-␣) 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-␣. Methods and Results-We examined the effects of TNF-␣ 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-␣ increased reactive oxygen species generation and N-SMase activity (500% and 34% over basal, respectively) and decreased the amplitude of [Ca 2ϩ ] 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-␣ had no effect on reactive oxygen species production or N-SMase activity but increased the amplitude of [Ca 2ϩ ] 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-␣ on heart contraction. Glutathione supplementation may therefore provide therapeutic benefits for vulnerable hearts.

Neutral sphingomyelinase inhibition participates to the benefits of N-acetylcysteine treatment in post-myocardial infarction failing heart rats

“…H 2 0 2 and lipid peroxidation by-products were quantified in LV homogenates using the Amplex Red Hydrogen Peroxide Kit (A22188) (Molecular Probes) and the Lipid peroxidation kit (Calbiochem), respectively. N-SMase activity was determined in LV homogenates as previously described [11].…”

“…We previously reported that glutathione status determines TNF-α adverse effects in heart [11,12]. Herein we addressed the question as to whether glutathione deficiency might be causally linked to the exacerbated TNF-α activation occurring in well-established CHF, as this was observed in several other chronic diseases including HIV infection [13,14], neurodegeneration [1,15], muscular fatigue [14], rheumatoid arthritis [3] and chronic lung diseases [16,17].…”

“…In its both reduced (GSH) and oxidized (GSSG) forms, glutathione serves as a natural inhibitor of N-SMase [25], which hydrolyzes sphingomyelin into ceramide, controlling the sphingolipid signaling cascade [26][27][28] and mediating TNF-α apoptotic [29] and negative inotropic effects in cardiomyocytes [11,30,31]. Downstream ceramide generation, the ordered cascade of events in N-SMase pathway comprises downregulation of the prosurvival factor Bcl-2, resulting into a decrease of the proapoptotic Bax/ prosurvival Bcl-2 protein ratio that in turn elicits activation of caspase-3 [32].…”

NADPH oxidase-derived superoxide impairs calcium transients and contraction in aged murine ventricular myocytes

“…Perfusion of isolated rabbit hearts with hydrogen peroxide increased cytosolic calcium concentration (Corretti et al, 1991) and TNF-α or ischemia induce changes in calcium handling that are normalized by application of ROS scavengers (Cailleret et al, 2004;Dworschak et al, 2004).…”

Why is the world so poorly prepared for a pandemic of hypervirulent avian influenza?

“…One of the important downstream signal transduction mechanisms is activation of two different sphingomyelinases (with different localization), which are called neutral and acid sphingomyelinase (38,49 Á51). The sphingomyelinases cleave sphingomyelin to ceramide and phosphocholine, and ceramide (N-acylsphingosine) can subsequently be degraded to a fatty acid'/sphingosine; these molecules (especially ceramide and sphingosine) may be regarded as functioning as second messengers of TNF-a (40,50). Ceramide is important not only as a signal molecule in its own right, but also as a precursor of other molecules that have signal function, such as lactosylceramide (51).…”