Thiopental and Nuclear Factor B: Some Questions

To the Editor:—In their very interesting study, Loop et al. demonstrate an inhibitory effect of thiopental on nuclear factor B (NFB) activation in T cells. However, we missed some essential background information in the discussion. First, the concentration of thiopental used in this study is much higher than plasma concentrations noted in clinical practice or in other models presenting inhibitory effects of thiopental on interferon (IFN) production. Second, the fact that thiopental suppresses NFB translocation in T cells may not directly reflect general immune suppression. Regulation of cytokines in T cells is simplified in this article and may lead to false interpretation. Therefore, it would be helpful to give some more information beyond that provided by the authors in their statement that “other transcription factors may be involved.” Cytokine expression is regulated in a cell-type and stimuli-specific manner. This might explain why Loop et al. were not able to demonstrate any effect of propofol on cytokine production or NFB activation, whereas Takaono et al. describe inhibition of interleukin 6 (IL-6) production in lipopolysaccharide-stimulated peripheral blood mononuclear cells after propofol treatment. In the same study, thiopental (up to 200 g/ l) had no significant effect on IL-6 production. Furthermore, the ability of transcription factors to bind DNA and modulate gene transcriptions is tightly regulated in normal cells. There are four transcription factors that play a major role in the regulation of inflammatory gene expression: activator protein 1, activating transcription factor 2, signal transducers and activators of transcription, and NFB (and, in T cells, nuclear factor of activated T cells [NFAT]). The pattern of their activation regulates expression of inflammatory mediators. Inhibition of one transcription factor may include enhanced activation of another factor. Loop et al. show that thiopental reduces the production of IL-2, IL-6, and IFNin phorbol-12-myristate-13acetate–stimulated peripheral blood mononuclear cells. The authors conclude that this is due to the inhibitory effect of thiopental on NFB activation. However, the transcription of IL-2 and IFNrequires the activation of NFAT and activator protein 1 more than that of NFB. This is of importance since NFAT is also required for transcription of IL-10, an antiinflammatory cytokine induced by thiopental. In this regard it also must be mentioned that the regulation of IFNseems to be different in Jurkat cells than in “normal” T cells. In addition, the presentation of NFAT binding in the presence of other anesthetics would have been very interesting since it has been shown that ketamine decreases cytokine production in whole blood preparations at concentrations comparable to those used by Loop et al. Furthermore, it has been shown that ketamine suppresses endotoxin-induced NFB activation in other models. Therefore, it is surprising that Loop et al. do not see any effect of ketamine on NFB activation in T cells or on cytokine production in peripheral blood mononuclear cells.