Inhibition of LPS-mediated activation in rat Kupffer cells by N-acetylcysteine occurs subsequent to NF-kappaB translocation and requires protein synthesis.

Abstract

Activation of the resident hepatic macrophage population, Kupffer cells, leads to production of mediators that initiate, potentiate, and modulate hepatic injury. Recent studies have shown that activation of the pluripotent transcription factor nuclear factor-kappaB (NF-kappaB) is an important step in the induction of inflammatory cytokines, chemokines, growth factors, cell adhesion proteins, and cytokine receptors, thus efforts have been focused to modulate its activity. A common observation in diverse experimental systems is that oxidant stress activates NF-kappaB and antioxidant drugs prevent activation and subsequent inflammatory gene transcription. However, we have recently shown that the inhibitory effect of N-acetylcysteine (NAC) is independent of its role as a substrate of glutathione synthesis and NAC can inhibit Kupffer cell activation at points beyond the initiation of activation. The goal of this study was to characterize the mechanism for NAC-mediated inhibition of Kupffer cell activation. We show for the first time that this process requires a cellular synthetic response to prevent both NF-kappaB and tumor necrosis factor alpha (TNF-alpha) mRNA activation. Furthermore, NAC-mediated inhibition occurs after degradation of IkappaB-alpha and nuclear translocation of NF-kappaB. These data suggest that inhibition of Kupffer cell activation by NAC is a nuclear event and offers a potential approach to modulate Kupffer cell activation during hepatic injury.