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GENERATION OF FREE RADICALS DURING PHOTOSENSITIZATION OF HYPOCRELLIN A AND THEIR EFFECTS ON CARDIAC MEMBRANES
Author(s) -
Zang LunYi,
Misra Bibhu R.,
Misra Hara P.
Publication year - 1992
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1992.tb02188.x
Subject(s) - chemistry , ascorbic acid , radical , electron paramagnetic resonance , lipid peroxidation , photochemistry , superoxide dismutase , spin trapping , superoxide , microsome , malondialdehyde , nuclear chemistry , antioxidant , biochemistry , enzyme , food science , nuclear magnetic resonance , physics
— Hypocrellin A (HA), a peryloquinone derivative, has recently been isolated from a fungus Hypocrella bambusae . This lipid soluble pigment, in combination with phototherapy, has been used to treat many skin diseases including the keloids caused by scalding and burns. We have studied the effects of photosensitized HA on biomembranes using pig heart microsomes. Photosensitization of HA was found to peroxidize the membrane lipids in the cardiac microsomes. The photodamage imposed by HA depended not only on the concentration of HA but also on the time of irradiation and pH of the system. Superoxide dismutase (SOD), ascorbic acid, β‐carotene and 5,5‐dimethyl‐1‐pyrroline‐ N ‐oxide (DMPO) inhibited the lipid peroxidation ˜50, ˜50, ˜30 and ˜97%. respectively. Spin trapping in combination with EPR spectroscopic techniques was used to identify the reactive free radicals during the photoreaction. Formation of superoxide anion radical, (O 2 ), was identified by the SOD‐inhibitable DMPO‐O 2 ‐ ‐ EPR spectrum. Both SOD and ascorbic acid inhibited the EPR signal intensity in a dose‐dependent manner with rate constants of 6.78 × 10 8 M −1 s −1 1.82 × 10 4 M −1 S −1 respectively. The lifetime of O 2 , under these conditions, was found to be 1.1 s. Photoirradiation of HA yielded a HA free radical with a g = 2.002 which was not suppressed by SOD but in the presence of reductants such as ascorbic acid and catechol the spectrum was completely suppressed. The increase of the EPR signal intensity and malondialdehyde formation with increasing pH may be due, in part, to the production of predominant *HA − species at high pH which would be more reactive with oxygen to yield O 2 . These results indicate that the lipid peroxidation of the cardiac membranes observed during photooxidation of HA may arise, in part, from the interaction of membrane lipids with reactive species of oxygen and HA free radical produced during the photo‐irradiation