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The intracellular antioxidant activities of diosmetin were evaluated by cellular antioxidant activity (CAA) assay, 2,2-azobis(2-amidinopropane) dihydrochloride (AAPH)-induced erythrocyte hemolysis assay and cupric chloride (CuCl2)-induced plasma oxidation assay. The results showed that diosmetin exhibits strong cellular antioxidant activity (EC50 = 7.98 μmol, CAA value = 58 μmol QE/100 μmol). It was also found that diosmetin treatment could effectively attenuate AAPH-induced erythrocyte hemolysis (91.0% inhibition at 100 μg/mL) and CuCl2-induced plasma oxidation through inhibition of intracellular reactive oxygen species (ROS) generation. Diosmetin could significantly restore AAPH-induced increase of intracelluar antioxidant enzyme (SOD, GPx, and CAT) activities to normal levels, as well as inhibit intracellular malondialdehyde (MDA) formation. Thus, the intracellular antioxidant detoxifying mechanism of diosmetin is associated with both nonenzymatic and enzymatic defense systems.

We showed in our previous study that docosahexaenoic acid-rich phosphatidylethanolamine in the external layer of small-size liposomes, as a model for biomembranes, protected its docosahexaenoic acid from 2,2'-azobis(2-amidinopropane)dihydrochloride- (AAPH-) mediated lipid peroxidation in vitro. Besides phosphatidylethanolamine, both phosphatidylserine and an alkenyl-acyl analogue of phosphatidylethanolamine, phosphatidylethanolamine plasmalogen, are reported to possess characteristic antioxidant activities. However, there are few reports about the relationship between the protective activity of phosphatidylethanolamine plasmalogen and/or phosphatidylserine against lipid peroxidation and their distribution in a phospholipid bilayer. Furthermore, it is unclear whether phosphatidylethanolamine plasmalogen and/or phosphatidylserine protect their component polyunsaturated fatty acids (PUFAs) from lipid peroxidation. In the present study, we examined the relationship between the transbilayer distribution of aminophospholipids, such as phosphatidylethanolamine rich in arachidonic acid, phosphatidylethanolamine plasmalogen, and phosphatidylserine, and the oxidative stability of their component PUFAs. The transbilayer distribution of these aminophospholipids in liposomes was modulated by coexisting phosphatidylcholine bearing two types of acyl chain: dipalmitoyl or dioleoyl. The amounts of these primary aminophospholipids in the external layer became significantly higher in liposomes containing dioleoylphosphatidylcholine than in those containing dipalmitoylphosphatidylcholine. Phosphatidylethanolamine rich in arachidonic acid, phosphatidylethanolamine plasmalogen or phosphatidylserine in the external layer of liposomes, as well as external docosahexaenoic acid-rich phosphatidylethanolamine, were able to protect their component PUFAs from AAPH-mediated lipid peroxidation.

This paper presents a simple, convenient method for determining the efficiency of antioxidants in aqueous systems. Production of conjugated diene hydroperoxide by oxidation of linoleic acid in an aqueous dispersion is monitored at 234 nm. 2, 2'-Azobis(2-amidinopropane) dihydrochloride is used as a free radical initiator. Among 12 antioxidants tested, phenolic compounds proved to be the most efficient, both kinetically and in terms of the inhibition time (T(inh)). Applied to wort, malt, and hops, the method confirmed a significant antioxidant activity in such products, especially hops. This assay can be used to follow oxidative changes throughout the brewing process and to understand the contribution of each raw material.

This study investigated the antioxidative activity of green tea extract, and a green tea tannin mixture and its components, under conditions of radical generation using the hydrophilic azo compound, 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH) to generate peroxyl radicals at a constant and measurable rate in the cultured renal epithelial cell line, LLC-PK(1), which is susceptible to oxidative damage. Treatment with AAPH decreased cell viability and increased the formation of thiobarbituric acid-reactive substances. However, green tea extract, and the tannin mixture and its components, comprising (-)-epigallocatechin 3-O-gallate (EGCg), (-)-gallocatechin 3-O-gallate (GCg), (-)-epicatechin 3-O-gallate (ECg), (-)-epigallocatechin (EGC), (+)-gallocatechin (GC), (-)-epicatechin (EC), and (+)-catechin (C), showed protective activity against AAPH-induced cellular damage. The tannin mixture and its components exhibited higher antioxidative activity than the green tea extract. Furthermore, EGCg and GCg had higher activity than EGC and GC, respectively. In particular, EGCg exerted the most significant cellular protective activity against AAPH. These results indicate that green tea tannin may inhibit cellular loss and lipid peroxidation resulting from the peroxyl radical generated by AAPH, and that the chemical structure of tannin is also involved in the activity, suggesting that the O-dihydroxy structure in the B ring and the galloyl groups are important determinants for radical scavenging and antioxidative potential.