Actin levels are shown as loading control. liver tissue was observed after IP plus I/R in normal mice but not in CT-1Cnull mice. Oxidative stress, a process involved in IP-induced hepatoprotection, was found to stimulate CT-1 release from isolated hepatocytes. Interestingly, brief ischemia followed by short reperfusion Rabbit Polyclonal to LAMP1 caused mild serum transaminase elevation and strong STAT3 activation in normal and IL-6Cdeficient mice, but failed to activate STAT3 Ibutamoren mesylate (MK-677) and provoked marked hypertransaminasemia in CT-1Cnull animals. In conclusion, CT-1 is an essential endogenous defense of the liver against I/R and is a key mediator of the protective effect induced by IP. Ischemia-reperfusion (I/R) damage develops when liver blood flow is interrupted, or severely diminished, for a long period of time and then restarted. Ischemia may induce cell death by itself by causing ATP depletion, but mainly primes the cells for the more intense damage that occurs when the liver is reperfused (1). Upon reentry of oxygen, uncoupled dysfunctional mitochondria produce large amounts of oxygen-free radicals, intense oxidative stress, and mitochondrial permeability transition leading to cell death (1). Ibutamoren mesylate (MK-677) On reperfusion activation of Kupffer cells also occurs, leading to abundant production of reactive oxygen species and proinflammatory cytokines, further enhancing organ damage (1). I/R injury can cause cell death by apoptosis or necrosis (1) depending on the intensity of ATP depletion. I/R liver damage is of great clinical importance because it can cause primary graft nonfunction after liver transplantation and may critically compromise the function of the remaining liver after major hepatic resections (2). The development of new therapeutic approaches to control I/R injury may benefit from better understanding of the defensive mechanisms set into motion in the liver when it is subjected to ischemic insults. In the liver, and in various tissues, it has been shown that a short period of ischemia protects efficiently against subsequent I/R injury (3). This phenomenon, known as ischemic preconditioning (IP), indicates that a brief ischemic insult triggers a protective biological reaction in the liver which is associated with inhibition of proapoptotic pathways (3, Ibutamoren mesylate (MK-677) 4). Although several mechanisms have been invoked, there is increasing evidence supporting that a sublethal oxidative stress, as occurs during a short ischemic interval, plays a crucial role in the induction of IP (4). In this regard recent reports have demonstrated that the protective effect granted by IP on subsequent ischemic injury can be mimicked by treatment with H2O2 or an H2O2 analogue (5, 6). However, the downstream effectors of the protective action of reactive oxygen species are still not known. Cardiotrophin (CT)-1 is member of the IL-6 family of cytokines that binds to a specific receptor that contains gp130 and leukemia inhibitory factor receptor (7). gp130 is common to the receptor complex of other members of IL-6 superfamily and is required for both ligand binding and signal transduction (7). CT-1 is expressed by both parenchymal and nonparenchymal liver cells and exerts potent antiapoptotic effects on hepatocytes (8). In these cells, as in cardiomyocytes and neurons, CT-1 activates cell survival signaling pathways including STAT3, extracellular-regulated kinase (Erk)1/2, and protein kinase B (Akt) (8C10). In the present work we have analyzed the possible role of CT-1 as a natural defense of the liver against I/R injury. RESULTS AND DISCUSSION Treatment with recombinant CT-1 reduces I/R liver injury To determine if CT-1 was able to attenuate I/R injury, 400 g/kg of body weight of recombinant rat CT-1 (rCT-1) was administered to Wistar rats 10 min before clamping the artery of the medium and left liver lobes. Samples were obtained at 6 h of reperfusion after 1 h of ischemia. We found that although untreated rats showed a marked rise of serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) and exhibited large areas of necrosis in the liver biopsy, those that were pretreated with CT-1 showed little variation of Ibutamoren mesylate (MK-677) transaminases and no relevant histological changes in the liver parenchyma (Fig. 1, A and B). Subsequent determination of transaminases levels at 12 h of reperfusion showed maintained low values in rats pretreated with rCT-1 but high levels in untreated animals (unpublished data). Open in a separate window Figure 1. CT-1 defends the liver against I/R damage. (A) AST and ALT levels in the serum of rats after 1 h ischemia and 6 h reperfusion (I/R), sham-operated animals, or rats that were treated with CT-1 (400 g/kg of weight, i.v.) 10 min before I/R. Values are means SD; 8 rats were used per Ibutamoren mesylate (MK-677) treatment..