Relieving Effect of Quercetin on Ischemia / Reperfusion-Induced Liver Damage in an Animal Model

Japan) were reared on a specific pathogen-free diet and randomly divided into two groups (n=8 for each). The control group was reared on the standard CE-2 rodent diet (CLEA Japan Inc., Japan) without quercetin, while the quercetin-treated group was reared on the CE-2 diet with quercetin (Sigma, USA). Quercetin was dissolved in distilled water and injected intraperitoneally (100 mg/kg) 24 h before the I/R experiment. Both groups were fasted for 12 h before the experiment.


Introduction
Ischemia/reperfusion (I/R)-induced liver damage can be a problem in surgeries such as liver resection and liver transplantation [1][2][3].I/R-induced liver damage can include liver tissue damage and microcirculatory disturbance caused by the production of reactive oxygen species (ROS) through the activation of Kupffer cells, hypercytokinemia, and protease through activated neutrophils [2][3][4][5].
Quercetin is a flavonoid found in fruit and vegetables that has a strong antioxidative stress effect through the scavenging of free radicals [4][5][6][7][8].Its protective effect with regard to post-I/R organ damage has been reported for various organs, such as the heart [9], brain [7], kidneys [10], and gastrointestinal tract, and its antioxidant effect is considered to be the primary mechanism of action [4,6,7,10,11].Here, we examine the effect of quercetin, which has a strong antioxidative stress effect, on I/R-induced liver damage using an animal model.

Experimental animal model and drug
Eight-week-old male F344 (Fisher) rats (CLEA Japan Inc.,

Liver histology findings
In the control group, hepatic microcirculatory disturbance, liver cell degeneration and necrosis, and focal hemorrhage were observed (Figure 1).In the quercetin-treated group, liver cell structure was maintained, and findings were insignificant (Figure 2).

Discussion
Previously, both oral [5] and intramuscular administration [4,8] of quercetin has been reported to reduce I/R-induced liver damage in animal models.In our study, intraperitoneal administration of quercetin showed a similar relieving effect on I/R injury.I/R-induced liver damage occurs in two phases [1].In the early phase within 2 h of reperfusion, ROS and cytokines such as TNF-α are significantly involved in liver damage [1][2][3].Our study involved blood and histological examination 1 h after initiating reperfusion; thus, the protective effect of quercetin was examined in the early phase.However, the significant decrease in nitrotyrosine yield and TNF-α suggested that quercetin had an antioxidant and cytokine suppression effect.
Nitrotyrosine is a good indicator of oxidative stress, and two pathways are known to be involved in its production.The first is the nitration of tyrosine residues by peroxynitrite, which is the product of a reaction between superoxides and nitric oxide (NO) [1,7].The second is nitration through the catalytic reaction of myeloperoxidase (MPO) and nitrite, which is a metabolite of NO [12].Therefore, in the present study, the mechanism underlying the significant decrease in nitrotyrosine yield in the quercetintreated group may be explained by several pathways, as follows: 1) Quercetin has a ROS scavenger effect that may lead to the scavenging of superoxides [4][5][6]8] 2) Some studies have reported that quercetin inhibits NO production [2,10,11,13].Further, because NO has a vasodilatory effect, it may also have a protective effect on I/R-induced hepatic microcirculatory disturbance [1].However, because peroxynitrite produced by the reaction between NO and superoxides is highly detrimental to tissues [1,7], the suppression of NO may reduce tissue damage.
3) Quercetin is also reported to have an inhibitory effect on MPO activity [4]; thus, the administration of quercetin may inhibit MPO activity.
In addition, after I/R, a rapid increase in blood levels of TNF-α occurs and causes hepatocellular damage and hepatic microcirculatory disturbance as a result of its cytotoxic effect [1,3,4].In the present study, quercetin significantly decreased blood levels of TNF-α, which may have contributed to the alleviation of I/R-induced liver damage in the early phase [1,14].

Conclusion
Our study result demonstrates that quercetin treatment reduces I/R-induced liver damage possibly through both antioxidant and cytokine inhibitory pathways.

Table 1 :
Comparison of serum AST/ALT levels, TNF-α, and nitrotyrosine yield in the control and quercetin-treated groups.