Does luminol chemiluminescence detect free radical scavengers?
Thiol compounds have been reported to abolish hypoxanthine/xanthine oxidase induced luminol chemiluminescence and this effect has been attributed to scavenging of superoxide (O2-)/(H2O2) produced from hypoxanthine/xanthine oxidase. Yet other workers have reported that thiol compounds have shown little, if any, reactivity towards O2-/H2O2. The aim of this study was to examine the discrepancy between these two sets of findings further. Captopril (a thiol angiotensin-converting enzyme (ACE) inhibitor) and MPG (a simple thiol) were observed to abolish hypoxanthine/xanthine oxidase induced chemiluminescence. The reactivity of captopril and MPG towards O2-/H2O2 was then determined by measurement of thiol oxidation in captopril and MPG after their incubation with hypoxanthine/xanthine oxidase. Incubation (at 10 min, 37 degrees C) with 4 mM hypoxanthine/0.03 u ml-1 xanthine oxidase resulted in 7% and 20% thiol oxidation in captopril and MPG (at 1 mM) respectively. Captopril and MPG, therefore, appeared to be ineffective scavengers of oxidants produced by hypoxanthine/xanthine oxidase. Captopril and MPG also did not affect urate production or oxygen consumption by xanthine oxidase which indicated that captopril and MPG quench luminol chemiluminescence by a mechanism that excludes the inhibition of xanthine oxidase. Hypoxanthine/xanthine oxidase induced luminol chemiluminescence may, therefore, be an unsuitable method for measuring free radical scavenging activity by drugs.
Clapperton
M
M
Bioengineering Unit, University of Strathclyde, Glasgow.
McMurray
J
J
Fisher
A C
AC
Dargie
H J
HJ
D000975:Antioxidants / Q000378:metabolism; D002216:Captopril / Q000494:pharmacology; D016166:Free Radical Scavengers / Q000032:analysis*; D066298:In Vitro Techniques; D008163:Luminescent Measurements; D008165:Luminol; D013438:Sulfhydryl Compounds / Q000494:pharmacology*; D013481:Superoxides / Q000378:metabolism; D014969:Xanthine Oxidase / Q000037:antagonists & inhibitors
D000975:Antioxidants; D016166:Free Radical Scavengers; D013438:Sulfhydryl Compounds; D013481:Superoxides; D008165:Luminol; D002216:Captopril; D014969:Xanthine Oxidase