In this study, we sought to determine whether p38MAPK-dependent HO-1 expression plays a critical role in the tropisetron-mediated hepatoprotection after trauma-hemorrhage. The present results indicated that at 24 h after trauma-hemorrhage, plasma AST and ALT concentrations, hepatic MPO activity, and CINC-1, CINC-3, ICAM-1, IL-6, TNF-α, and MIP-1α levels were all markedly increased in male rats. The salutary effects of tropisetron at doses of 0.1, 0.3, 1, and 3 mg/kg were evaluated for liver injury after trauma-hemorrhage. We found similar beneficial effects when tropisetron was administered at dosages of 1 or 3 mg/kg and poor results at dosages of 0.1 or 0.3 mg/kg. Administration of a single dose of tropisetron (1 mg/kg) during resuscitation could attenuate the increase in inflammatory parameters. Tropisetron administration also prevented the trauma-hemorrhage-induced decrease in hepatic p-p38 MAPK expression. A difference in the magnitude of HO-1 expression in the livers of male rats, with or without tropisetron treatment after trauma-hemorrhage, was also found. Co-administration of the p38 MAPK inhibitor (SB-203580) or HO inhibitor (chromium-mesoporphyrin) with tropisetron after trauma-hemorrhage abolished the tropisetron-induced effects described above. These results collectively suggest that the salutary effects of tropisetron are mediated via p38MAPK-dependent HO-1 expression.
The liver is a large solid abdominal organ, and liver damage can result in serious inflammation and life threatening conditions. Previous studies have shown that hepatic injury is associated with increased neutrophil accumulation 
. The infiltration of neutrophils in the liver is also accompanied by increased expression of local cytokines, chemokines, and adhesion molecules 
. IL-6 is an important pro-inflammatory mediator in hepatic damage and is required for chemokine production and adhesion molecule expression. Liver injury or hypoxia causes marked increases in hepatic IL-6 expression 
. In this study, hepatic IL-6, TNF-α, and MIP-1α levels were significantly attenuated in the animals treated with tropisetron after trauma-hemorrhage. Tissue MPO activity is an important indicator of neutrophil infiltration, and it has been correlated with CINC-1 and CINC-3 expression after trauma-hemorrhage 
. Our results showed that trauma-hemorrhage results in a significant increase in hepatic cytokine/chemokine levels and ICAM-1 expression, which are accompanied by elevated hepatic MPO activity. However, tropisetron administration after trauma-hemorrhage attenuated these pro-inflammatory mediators and alleviated hepatic injury.
Our previous studies have shown that the p38 MAPK pathway attenuates overproduction of pro-inflammatory cytokines, chemokines, and adhesion molecules and neutrophil accumulation after trauma-hemorrhage 
. P38 MAPK phosphorylation has been reported to activate protective effects in various organs, including the intestine, liver, and heart, after trauma-hemorrhage 
. In this study, we found that the tropisetron-induced attenuation of hepatic injury was likely mediated by increases in p38 MAPK activation, which was blocked by the p38 MAPK inhibitor SB-203580. Consistent with some studies, our results showed that trauma-hemorrhagic shock led to a significant decrease of p38 MAPK activation 
. However, this result has serious discrepancies with other reports 
. Sato et al. have shown that hemorrhagic shock induces p38 MAPK activation in a male Wistar rat model of hemorrhagic shock without trauma or resuscitation 
. Li et al. indicate that hemorrhagic shock increases phosphorylation of p38γ MAPK, but decreases phosphorylation of p38α MAPK in a female C57BL6/J mice model of hemorrhagic shock/resuscitation without trauma 
. Other study shows that hemorrhagic shock increases p38 MAPK expression in a male C57BL6/J mice model of hemorrhagic shock/resuscitation without trauma 
. The animal model applied in our study is male Sprague-Dawley rat model of trauma-hemorrhagic shock with resuscitation. The mechanisms responsible for the divergent responses remain unknown. Previous studies have also shown that p38 MAPK activation contributes to the protection of cell/tissue following injury 
. In human monocytes, the increase in p38 MAPK activation is associated with the alcohol-induced attenuation of TNF-α production and augmentation of IL-10 secretion 
. Other reports also indicate that p38 MAPK activation protects glomerular epithelial cells against complement-mediated cell injury and regulates mucosal recovery in ischemic-injured ileum 
. The roles of p38 MAPK on tissue or organ function after injury might be complex. The possible reasons might be related to different species and various animal models among those studies. However, it remained to be determined in further studies.
Induction of HO-1 plays an important role in organ protection against oxidative stress, inflammation and biological toxicity 
. A growing body of evidence indicates that HO-1 expression is up-regulated after trauma-hemorrhage and that its induction might play a critical role in the preservation of organ microcirculatory function and cytoprotection 
. Previous studies have shown that p38 MAPK activation leads to the induction of HO-1 
. Our results also suggest that the salutary effects of tropisetron are mediated via p38 MAPK-dependent HO-1 up-regulation. Our finding that treatment with SB-203580 abolished the tropisetron-induced up-regulation of HO-1 after trauma-hemorrhage suggests that tropisetron administration after trauma-hemorrhage up-regulates HO-1 via the p38 MAPK-related pathway. Our data showed that p38 MAPK activation might have organ protective effects in a rodent model of trauma-hemorrhagic shock. However, some reports indicate that p38 MAPK activation is harmful to organ functions in hemorrhagic shock 
. The p38 MAPK activation might initiate the activation of HO-1 and have no direct organ protective effect. HO-1 might have direct organ protective effects. Further studies are required to elucidate the precise mechanism.
5-HT3 receptor antagonists are often used for prevention or treatment of nausea and vomiting 
. Previous studies have shown that tropisetron possesses anti-inflammatory properties 
, which are related to the inhibition of pro-inflammatory mediator release from various tissues 
. However, little is known about the role of tropisetron in trauma-hemorrhage. In the present study, tropisetron played a role in regulating the production of pro-inflammatory mediators. The ability of tropisetron to modulate expression of inflammatory cytokines, as well as chemokines and adhesion molecules, suggests a role for tropisetron in the regulation of hepatic inflammation. Our study further indicates that tropisetron administration after trauma-hemorrhage decreases pro-inflammatory mediator levels and likely attenuates liver injury through p38 MAPK-mediated up-regulation of HO-1.
From our study, tropisetron-induced organ protective effects are partially mediated via activation of hepatic p38 MAPK-dependent HO-1 pathway in a rodent model of trauma-hemorrhagic shock. However, some reports suggest that p38 MAPK activation is essential to induce organ dysfunction following hemorrhagic shock 
. The role of p38 MAPK remains unclear. Further study is needed to evaluate the precise role of p38 MAPK. It would be more convincing if the knockout animal or siRNA is introduced to future studies.
In conclusion, the results of this study indicate that tropisetron administration alleviates hepatic injury and pro-inflammatory mediator production after trauma-hemorrhage. The decrease in hepatic injury after tropisetron treatment is likely due to a reduction in hepatic neutrophil accumulation associated with down-regulation of CINC-1, CINC-3, ICAM-1, IL-6, TNF-α, and MIP-1α. Inhibition of hepatic pro-inflammatory mediators production by tropisetron appears to contribute to the decrease in hepatic expression of chemokines and adhesion molecules. Blockade of p38 MAPK activation or HO-1 expression and the associated deterioration of other parameters suggest that the reduction of inflammation in the liver is partially mediated via a p38 MAPK dependent HO-1 pathway. Although the precise mechanism of the salutary effects of tropisetron in attenuating hepatic injury after trauma-hemorrhage remains unclear, our studies provides evidence that the p38 MAPK-dependent up-regulation of HO-1 may be critical in tropisetron-mediated hepatoprotection after trauma-hemorrhage. These findings also have implications for the potential use of tropisetron as a clinical adjunct for trauma-hemorrhage treatment.