Korea has a long history of traditional oriental medicine whose materials are derived from nature. Yeonsan Ogye (YO) is one of Korea's native poultry species which has many positive effects such as prevention of anemia, coronary heart disease, and treatment of deep-seated sore [12]. Recently, Kim et al. have reported that YO extracts have various biological activities including antiinflammation, anti-oxidation, and immuno-enhancement in cell line [3]. Bioactive peptides are generally defined as a small peptide with hormone or drug-like physiological activity and many animal and plant food proteins are used as sources of bioactive peptides [45]. A study using the bioactive peptides of Ogye was performed in vitro; suggested that Ogye peptides have anti-oxidative effects [6]. However, the anti-oxidant capacity of bioactive Yeonsan Ogye peptides (YOPs), which has potential for use as an anti-oxidant functional food, has not been studied yet in animal model.

Therefore, in this study, we have investigated the change of hepatic anti-oxidant index levels of three-week-old Sprague-Dawley male rats depending on the amount of YOPs to their feed.

There were no differences in the initial and final body weights, weight gain, food intake, food efficiency ratio, and organ weight at day killed including liver, kidney, spleen, thymus, and epididymal fat among all of the groups (Table 1).

To confirm whether the YOPs leads to the regulation of anti-oxidative reaction, we measured the level of NO and MDA, and the activity of SOD and CAT which is known as anti-oxidant indexes in a rat's liver. The measurement of MDA is widely used as an indicator of oxidative stress, and SOD and CAT denotes anti-oxidant enzymes [8]. During the inflammatory process, NO and superoxide are produced from immune cells, and these may react together producing oxidative active molecule, which can cause lipid oxidation [9].

Fig. 1 indicated the hepatic level of NO and MDA and the hepatic activity of SOD and CAT of 3 groups (Fig. 1). The hepatic NO level in the Y500 (8.36 ± 0.38 µmol/mg protein) group was significantly lower than that in the control (9.71 ± 0.66 µmol/mg protein) and Y250 (10.34 ± 0.57 µmol/mg protein) groups (p < 0.05, Fig. 1A). As Compared with in the Y250 (6.46 ± 0.37 nmol/mg protein) group, the hepatic MDA level was decreased in the Y500 (4.33 ± 0.28 nmol/mg) group (p < 0.01, Fig. 1B). These results were partially different from the study that treated the extract of YO in rat's macrophage, showing that the levels of NO and cytokine were decreased whereas there was no difference in dose of extracts [3]. And our results were similar with other research which evaluated the effect of bovine lactoferricin to inhibition of inducible NO synthase mRNA expression in human articular chondrocyte [10]. Moreover, the result of MDA was also similar to other study when investigating the effect of bioactive peptide on the level of MDA. Carnosine known as bioactive peptide in some species of vertebrates leads to the reduction of hepatic MDA level in rats [11]. Although few studies that using YOPs were conducted, we can consider that YOPs may have abilities to regulate NO and MDA production, and may have the effectiveness is higher as YOPs dose is higher.

The statistical significance of hepatic SOD and CAT activities which concern as anti-oxidant enzymes among the groups did not occur in this study (Fig. 1C and 1D). According to oxidative stress pathway, anti-oxidative effect on free radical removal could explain in two ways; first is that promoting the activities of anti-oxidant enzymes, and second is that anti-oxidants themselves removing free radicals [12].

Therefore we speculate that YOPs seems to have a role as an anti-oxidant itself. Moreover, one may speculate two possibilities about these results. First, toxic products known as free radicals may not be enough generated in liver to increase the activity of SOD and CAT, because we used healthy animal models. Second, the reduction of NO and MDA may be attributed to other mechanisms unrelated to those of the anti-oxidants. To investigate these possibilities, experiments should be added to whether or not hydrogen peroxide, hydroxyl radicals, and superoxide radicals should be produced.

According to these results, we conclude that YOPs can cause hepatic anti-oxidation. The strength of this study is being the first to demonstrate YOPs' efficacy. This study is worthwhile based on the results for further researches of YOPs, and it is also meaningful in contributing to the development of functional foods with YOPs which may have anti-oxidative effects. In this study, we experimented with male rats to exclude the effects of hormonal changes according to menstrual cycle in female rats. However further study using both gender rats should be conducted as a preclinical study to examine the efficacy of YOPs.