Biomedical subjects
A C Woollard
Publications and source records attributed to A C Woollard.
Lipid hydroperoxide measurement by oxidation of Fe2+ in the presence of xylenol orange. Comparison with the TBA assay and an iodometric method.
Study of the role of hydroperoxides and lipid peroxidation in disease requires simple and sensitive methods for direct hydroperoxide measurement. We report on a technique for measuring hydroperoxide which relies upon the rapid hydroperoxide-mediated oxidation of Fe2+ under acidic conditions. Fe3+ forms a chromophore with xylenol orange which absorbs strongly at 560 nm, yielding an apparent E560 (for H2O2, butyl hydroperoxide and cumene hydroperoxide) of 4.3 X 10(4) M-1 cm-1. The assay was validated in a study of liposomal lipid peroxidation and shown to give results comparable with those obtained by an iodometric method or by measuring conjugated dienes. The assay involving thiobarbituric acid, by comparison, underestimates lipid peroxidation and does not measure hydroperoxide per se.
Hydrogen peroxide production during experimental protein glycation.
The accumulation of hydrogen peroxide (H2O2) during incubations of protein with glucose (experimental glycation) has previously been too low for direct measurement although it is suggested to be the precursor of protein-damaging hydroxylating agents. We have thus developed a simple H2O2-measuring technique which relies upon the rapid peroxide-mediated oxidation of Fe2+ to Fe3+ (catalysed by sorbitol) under acidic conditions followed by reaction of the latter cation with the dye, xylenol orange. We have used the method to demonstrate that incubation mixtures of protein and glucose generates nanomolar levels of hydrogen peroxide in the presence of protein under physiological conditions of pH and temperature.
Antioxidant characteristics of some potential anticataract agents. Studies of aspirin, paracetamol, and bendazac provide support for an oxidative component of cataract.
It is conceivable that drugs with anticataract potential possess antioxidant activity. Using defined chelating agents and reducing agents in a number of assays for antioxidant activity, we have demonstrated that paracetamol, aspirin, bendazac, and its metabolite 5-hydroxybendazac possess substantial reducing and/or metal-chelating activity. We found that paracetamol and 5-hydroxybendazac reduced the diphenylpicrylhydrazyl free radical; inhibited butyl peroxide-induced erythrocyte lysis as well as the haematin-catalyzed oxidative coupling of 4-aminoantipyrine and phenol by butyl peroxide. Furthermore, paracetamol, bendazac, and aspirin competed with 3-(2-pyridyl)-5,6-Diphenyl-1,2,4-triazine-4', 4"-disulphonic acid (ferrozine) for ferrous ion.
Abnormal redox status without increased lipid peroxidation in sugar cataract.
In conflict with a previous report, we find that phenolic inhibitors of lipid peroxidation (butylated hydroxytoluene [BHT] and butylated hydroxyanisole [BHA]) do not have significant inhibitory effect on galactosemic cataract formation. This is consistent with the lack of enhancement of stable products of lipid peroxidation (measured by the thiobarbituric acid assay) in the lenses of galactosemic rats. This does not imply that oxidative stress plays no role in galactosemic cataract formation (indeed, we find that galactosemic lens homogenates contain increased amounts of an Fe2+ oxidant, possibly a peroxide), but rather that BHT- and BHA-inhibitable lipid peroxidation specifically has no role to play. In instances where drugs appear to inhibit galactosemic cataract formation, other effects caused by the drugs, e.g., inhibition of feeding or induction of general detoxification pathways, must be considered.