Kuo P C, Abe K Y
Department of Surgery, University of Maryland Medical Systems, Baltimore, USA.
Surgery. 1996 Aug;120(2):309-14. doi: 10.1016/s0039-6060(96)80303-5.
In a system of rat hepatocytes in primary culture, inhibition of cytokine-mediated nitric oxide (NO) production has been shown to be protective in states of oxidative stress. In the absence of oxidative injury, inhibition of NO synthesis has been associated with decreased intracellular levels of reduced glutathione.
To further characterize the role of NO in hepatocyte glutathione metabolism, cytokine-mediated NO synthesis was inhibited by addition of a competitive substrate inhibitor. Reduced glutathione, NO metabolites, and enzyme activity and steady-state mRNA levels of the rate-limiting enzyme for reduced glutathione (GSH) synthesis, gamma-glutamylcysteine synthetase, were determined in the presence and absence of the substrate inhibitor. A diffusible cyclic guanosine monophosphate (cGMP) analog, 8-bromo-cGMP, was added in selected instances to determine the potential role of soluble guanylyl cyclase in glutathione metabolism.
Inhibition of cytokine-induced NO synthesis was associated with depletion of glutathione. These levels were restored in the presence of pharmacologic concentrations of a NO donor. Along with decreased glutathione levels, gamma-glutamylcysteine synthetase enzyme activity and steady state mRNA levels were also decreased with inhibition of NO synthesis. Addition of 8-bromo-cGMP did not alter glutathione content or gamma-glutamylcysteine synthetase enzyme activity and steady-state mRNA levels.
In this system of cultured rat hepatocytes, cytokine-mediated NO synthesis may be protective in states of oxidative stress through regulation of glutathione synthesis.
在原代培养的大鼠肝细胞系统中，细胞因子介导的一氧化氮（NO）生成的抑制已被证明在氧化应激状态下具有保护作用。在无氧化损伤的情况下，NO合成的抑制与细胞内还原型谷胱甘肽水平降低有关。
为了进一步明确NO在肝细胞谷胱甘肽代谢中的作用，通过添加竞争性底物抑制剂来抑制细胞因子介导的NO合成。在存在和不存在底物抑制剂的情况下，测定还原型谷胱甘肽、NO代谢产物以及还原型谷胱甘肽（GSH）合成的限速酶γ-谷氨酰半胱氨酸合成酶的酶活性和稳态mRNA水平。在特定情况下添加可扩散的环磷酸鸟苷（cGMP）类似物8-溴-cGMP，以确定可溶性鸟苷酸环化酶在谷胱甘肽代谢中的潜在作用。
细胞因子诱导的NO合成的抑制与谷胱甘肽的消耗有关。在存在药理浓度的NO供体时，这些水平得以恢复。随着谷胱甘肽水平的降低，γ-谷氨酰半胱氨酸合成酶的酶活性和稳态mRNA水平在NO合成受到抑制时也降低。添加8-溴-cGMP并未改变谷胱甘肽含量、γ-谷氨酰半胱氨酸合成酶的酶活性和稳态mRNA水平。
在这个培养的大鼠肝细胞系统中，细胞因子介导的NO合成可能通过调节谷胱甘肽合成在氧化应激状态下具有保护作用。
