Oxidative stress and inflammation are fundamental for the onset of aging and appear to be causatively linked. Previously, we reported that hepatocytes from aged rats, compared with young rats, are hyperresponsive to interleukin-1b (IL-1b) stimulation and exhibit more potent c-Jun N-terminal kinase (JNK) activation and attenuated interleukin-1 receptor-associated kinase-1 (IRAK-1) degradation. An age-related increase in the activity of neutral sphingomyelinase-2 (NSMase-2), a plasma membrane enzyme, was found to be responsible for the IL-1b hyperresponsiveness. The results reported here show that increased NSMase activity during aging is caused by a 60-70% decrease in hepatocyte GSH levels. GSH, at concentrations typically found in hepatocytes from young animals, inhibits NSMase activity in a biphasic dose-dependent manner. Inhibition of GSH synthesis in young hepatocytes activates NSMase, causing increased JNK activation and IRAK-1 stabilization in response to IL-1b, mimicking the hyperresponsiveness typical for aged hepatocytes. Vice versa, increased GSH content in hepatocytes from aged animals by treatment with N-acetylcysteine inhibits NSMase activity and restores normal IL-1b response. Importantly, the GSH decline, NSMase activation, and IL-1b hyperresponsiveness are not observed in aged, calorie-restricted rats. In summary, this report demonstrates that depletion of cellular GSH during aging plays an important role in regulating the hepatic response to IL-1b by inducing NSMase-2 activity. Increased basal inflammation is a phenomenon emblematic of the aging process. It is characterized by increased concentrations of serum markers such as C-reactive protein and serum amyloid A (1) as well as by the activation of proinflammatory signaling molecules such as c-Jun N-terminal kinase (JNK) (2), nuclear factor-kB (NF-kB) (3), and CCAAT/enhancer binding proteins a and b (4). According to the oxidative stress hypothesis of aging, changes in mitochondrial functions and the deterioration of antioxidant defense mechanisms lead to an imbalance in the production and neutralization of free radicals, which in turn induces tissue damage and inflammation. Indeed, oxidative stress seems to play a fundamental role in the onset of aging-associated inflammation, because a decline in reactive oxygen species (ROS) generation brought about by calorie restriction (5) or by antioxidant supplementation decreases the expression of various inflammatory markers in aged animals. It has been proposed that the excess ROS generated during aging stimulate the secretion of proinflammatory cytokines, thus creating a proinflammatory environment (5). However, despite the fact that basal levels of some cytokines, such as tumor necrosis factor-a (TNF-a) and interleukin-6 (IL-6), seem to increase with age, these increases are modest, and it is not yet clear whether they are sufficient to evoke an inflammatory response. Moreover, the systemic concentrations of other cytokines, including interleukin-1b (IL1b), remain unchanged in healthy elder...