In vitro and in vivo antioxidant activities of three major polyphenolic compounds in pomegranate peel: Ellagic acid, punicalin, and punicalagin

Pomegranates is abundant in polyphenols and is well-known for its antioxidant activity. Punicalagin (PG) is a major poly-phenolic compound in the pomegranate peel. In certain conditions, PG can be hydrolyzed to punicallin (PL) and ellagic acid (EA), and PL can be further hydrolyzed to EA. PG, PL, and EA all play important roles in the antioxidant activity of pomegranate peels. This study was conducted to compare the in vitro antioxidant activity and in vivo anti-oxidative stress effects of PG, PL, and EA. For the in vitro test, 2,2-diphenyl-1-picrylhydrazyl radical (DPPH center dot) and superoxide anion (O-2(-)) scavenging capacities, ferric-reducing antioxidant power (FRAP), and lipid peroxidation (LPO) inhibition capacities of PG, PL, and EA were tested. For the in vivo test, oxidatively stressed mice, which were induced by oxidized fish oil, were administrated PG, PL or EA (10 mg kg(-1) d(-1)) for 21 days. The results showed that the in vitro antioxidant activity trends were EA>PG>PL>Trolox in scavenging DPPH center dot, PG>PL>EA approximate to Trolox in scavenging O-2(-), EA>PG approximate to PL>Trolox in FRAP, and Trolox>PG>EA>PL in LPO inhibition. In the in vivo test, the EA treatment increased the average daily weight gain and total antioxidant capacity (T-AOC) in the plasma (P<0.05), liver (P<0.05), and intestine (P<0.05) in oxidatively stressed mice. It increased the superoxide dismutase (SOD) activity in the liver (P<0.05) and intestine (P<0.05). It increased the glutathione peroxidase (GSH-Px) activity in the intestine (P<0.05) and the intestinal villus height to crypt depth ratio (P<0.05). EA treatment decreased the malondialdehyde (MDA) content in the plasma (P<0.05), liver (P<0.05), and intestine (P<0.05) and the mRNA expressions of the pro -inflammatory factors, TNF-alpha (P<0.05), IFN-gamma (P<0.05) and IL-6 (P<0.05). PL increased the SOD (P<0.05) and GSH-Px activities (P<0.05) in the intestine and decreased the MDA content (P<0.05) and the mRNA expressions of TNF-a (P<0.05) and IL-6 (P<0.05) in the intestine. PG increased the SOD activity (P<0.05) and GSH-Px activity (P<0.05) in the intestine and decreased the MDA content in the intestine (P<0.05) and IL-6 mRNA expression in the intestine (P<0.05). In summary, EA, PL, and PG all had powerful in vitro antioxidant capacities, and they had different antioxidant advantages in acting against different types of radicals; EA was more effective than PL and PG in protecting against oxidative injury in vivo, especially for intestinal injury. These findings suggest that multiple polyphenol compounds in pomegranate peel may exert superior antioxidant activity than single purified polyphenols; when using pomegranate peels as health-promoting additive in animal feed, raising EA content by methods of hydrolysis or fermentation in advance could achieve better effects.