Protein modifications, such as carbonylation, nitration and formation of lipid peroxidation adducts, e.g. 4-hydroxynonenal (HNE), are products of oxidative damage attributed to reactive oxygen species (ROS). The mitochondrial respiratory chain Complexes I and III have been shown to be a major source of ROS in vitro. Additionally, modifications of the respiratory chain Complexes (I-V) by nitration, carbonylation and HNE adduct decrease their enzymatic activity in vitro. However, modification of these respiratory chain complex proteins due to in vivo basal level ROS generation has not been investigated. In this study, we show a basal level of oxidative damage to specific proteins of adult bovine heart submitochondrial particle (SMP) complexes, and find that most of these proteins are localized in the mitochondrial matrix. We postulate that electron leakage from respiratory chain complexes and subsequent ROS formation may cause damage to specific complex subunits and contribute to long-term accumulation of mitochondrial dysfunction.

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For both men and women, ischemic heart disease is one of the leading causes of death in the United States today, and its pathobiology has been attributed to many factors, including proinflammatory cytokines. Interleukin (IL) 2 -18 is a pleiotropic cytokine belonging to the IL-1 family (1-5), whose expression is up-regulated in numerous immune, infectious, and inflammatory conditions (1-5), which may further amplify the inflammatory cascade by inducing additional cytokines, chemokines, and adhesion molecules (1-5). Elevated plasma IL-18 levels have been detected in patients with acute coronary syndromes (6), and a direct correlation between IL-18 levels and the severity of myocardial dysfunction has been reported. Circulating IL-18 levels have been shown to be independent predictors of coronary events in humans, with increased basal levels of IL-18 observed in individuals who later developed coronary events (7). Increased circulating IL-18 levels have also been measured during heart failure as well as in stroke patients (8, 9). IL-18 signals via the IL-18 receptor, a heterodimer consisting of a ligand binding ␣-subunit and a signal-transducing ␤-subunit (10, 11). Binding of IL-18 to IL-18R␣ recruits IL-18R␤, and this activated complex initiates pleiotropic signal transduction events. Similar to IL-1 receptor antagonist that blocks IL-1 signaling, IL-18-binding protein (IL-18BP) binds IL-18 with high affinity, inhibits IL-18 bioavailability (12), neutralizes IL-18 effects, and thus reduces inflammation. Interestingly, transgenic mice overexpressing human IL-18BP exhibit reduced inflammation and disease severity (13).Cytotoxic free radicals and proinflammatory cytokines are produced during ischemia/reperfusion (I/R) injury. Using isolated adult rat cardiomyocytes, we have recently described NF-B-dependent IL-18 and IL-18R␤ expression following hydrogen peroxide and TNF-␣ treatment in vitro (14). Moreover, although IL-18BP gene expression under basal conditions in these cells is undetectable, TNF-␣ and H 2 O 2 each induce IL-18BP mRNA in a delayed but persistent manner (14), which suggests tight regulation of IL-18 bioavailability. However, the precise role of IL-18 in I/R injury and its regulation in vivo are incompletely understood, and the signal transduction path-* This work was supported in part by the Research Service of the Department of Veterans Affairs. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

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