No abstract

Recently, we proposed an oxygen radical absorbance capacity method that directly quantifies the antioxidant’s scavenging capacity against free radicals and evaluated the radical scavenging abilities for water soluble antioxidant compounds. In this study, we determined the radical scavenging abilities of lipophilic antioxidants which were solubilized by cyclodextrin in water. Commonly employed fluorescence-based method measures the antioxidant’s protection capability for the fluorescent probe, while we directly quantify free-radical level using electron paramagnetic resonance spin trapping technique. In addition, the spin trapping-based method adopted controlled UV-photolysis of azo-initiator for free radical generation, but in fluorescence-based method, thermal decomposition of azo-initiator was utilized. We determined the radical scavenging abilities of seven well-known lipophilic antioxidants (five flavonoids, resveratrol and astaxanthin), using methylated β-cyclodextrin as a solubilizer. The results indicated that the agreement between spin trapping-based and fluorescence-based values was only fair partly because of a large variation in the previous fluorescence-based data. Typical radical scavenging abilities in trolox equivalent unit are: catechin 0.96; epicatechin 0.94; epigallocatechin gallate 1.3; kaempferol 0.37; myricetin 3.2; resveratrol 0.64; and astaxanthin 0.28, indicating that myricetin possesses the highest antioxidant capacity among the compounds tested. We sorted out the possible causes of the deviation between the two methods.

The oxygen radical absorbance capacity (ORAC) method employs a water soluble azo-radical initiator, AAPH (2,2’-azobis(2-amidinopropane) dihydrochloride) as a free radical generator, by which the fluorescent probe fluorescein is damaged to result in the loss of fluorescence. Antioxidants can protect the probe from the damage and the degree of protection is quantified. Because AAPH has been used as a lipid-peroxidation reagent, “oxygen radical” in ORAC is generally accepted as peroxyl radicals; however, in the present spin trapping experiments using a newly developed spin trap, CYPMPO, there was no indication of peroxyl-radical formation in AAPH decomposition in aqueous media. These spin trapping studies demonstrated that alkoxyl (RO·) radical adduct was the sole product of AAPH decomposition. In contrast, alkyl-peroxyl (ROO·) radical was spin-trapped during the decomposition of a lipid soluble azo-radical initiator AIBN (azobis(isobutyronitrile)) in non-aqueous media. We speculate that alkyl-peroxyl radicals are short-lived in water, rapidly converted into alkoxyl radicals. Although the possibility that ORAC method monitors peroxyl-radical scavenging activity cannot be completely eliminated, spin trapping evidence strongly indicates that ORAC method is a scavenging capacity assay for alkoxyl radicals.

When cyclic nitrones, such as 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), 4-phenyl-5,5-dimethyl-1- pyrroline-N-oxide (PDMPO), and 3,3,5,5-tetramethyl-1-pyrroline-N-oxide (M4PO) were mixed with hydrogen tetrachloro aurate(III), DMPOX (5,5-dimethyl-1-pyrrolid-2-one-N-oxyl) type free radicals appeared with the precipitation of Au(0). The reaction did not proceed with noncyclic nitrones, such as N-tert-butyl-α-phenyl-nitrone (PBN) and α-(4-pyridyl-1-oxide)-N-tert-butyl-nitrone (POBN). The order of the HAuCl4 decrease was DMPO > PDMPO > M4PO. The reaction was depressed by the addition of chloride or hydroxide ions. 1-Hydroxy-5,5-dimethyl-1-pyrrolid-2-one (HDMPN), the precursor of DMPOX, was also oxidized to DMPOX by HAuCl4. Every step of the gold reduction from Au(III) to Au(0) can be used for the oxidation of HDMPN to DMPOX. Based on these and previous results, the reaction was assumed to proceed by the following scheme consisting of a ligand exchange interaction of AuCl4– with >N+–O– in DMPO, then nucleophilic addition of a water molecule to DMPO, then the stepwise intramolecular transfer of three electrons from DMPO to Au(III), and finally the precipitation of Au(0). Key words: ESR, nitrone, spin traps, DMPO, DMPOX, gold(III) ion.

Correspondence istics of our case deserve additional comments. The myelodysplastic changes seen in apparently non-leukaemic bone marrow cells and the hypoplastic presentation coupled with pancytopenia suggest that AML might have followed a preleukaemic state. Cases of AML following myelodysplastic syndromes (MDS) have been recently recognized (Hehlmann et al, 1981; Eridani et d, 1985; Neame et al, 1985). This, like other evidences (Editorial, 1983), may indicate that some cases of MDS are the result of a defect of the pluripotential stem cell. A hypoplastic presentation has been reported in both AML (Howe et al, 1982) and common ALL (Breatnach et al, 198 1). Hypocellular acute and leukaemia and monosomy 7 are regarded as bad prognostic characteristics in AML (Borgstrom et al, 1980; Howe et ul, 1982). The excellent response to therapy in this patient suggests that intensive post-remission chemotherapy schemes designed for AML might be of value in these cases. Servicio de