Generation of Free Radicals During Photosensitization of Hypocrellin a and Their Effects on Cardiac Membranes

Abstract

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, beta-carotene and 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) inhibited the lipid peroxidation approximately 50, approximately 50, approximately 30 and approximately 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, (O2-.), was identified by the SOD-inhibitable DMPO-O2- EPR spectrum. Both SOD and ascorbic acid inhibited the EPR signal intensity in a dose-dependent manner with rate constants of 6.78 x 10(8) M-1 s-1 and 1.82 x 10(4) M-1 s-1, respectively. The lifetime of O2-., 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 septum 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 O2-.. 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.

Environmental photodegradation of pyrimidine fungicides — Kinetics of the visible-light-promoted interactions between riboflavin and 2-amino-4-hydroxy-6-methylpyrimidine

“…2): (i) irradiating in the presence of 10 µg mL -1 of SOD, an enzyme that behaves as a quencher of superoxide anion (O 2 . − )-mediated photooxidations when used in similar concentrations (19)(20)(21)(22) (relative rate = 0.78); (ii) irradiating in the presence of 1 mM sodium azide, a well known selective physical quencher of O 2 ( 1 ∆g) (4) (relative rate = 0.41); and (iii) irradiating the system AHMPD-Rf but with a concentration of AHMPD of 40 mM or higher (relative rate for 40 mM AHMPD = 0.61). No oxygen uptake was detected when 5 mM AHMPD was replaced by similar concentrations of 2-aminopyrimidine, 4-hydroxypyrimidine, or 6-methylpyrimidine.…”

Novel Therapeutic and Diagnostic Applications of Hypocrellins and Hypericins

“…Thus a Type I process is suggested to be involved in some photosensitizing processes of hypocrellins and hypericins, either as a supplemental or, in some cases, a predominant role 1–5 . A Type I (free radical) process has been described for the hypocrellin A‐induced photodamage of cardiac membranes, 68 and for the hypericin‐induced photoinactivation of tyrosine protein kinase (TPK) ( vide infra ).…”

Optimization of hypocrellin B derivative amphiphilicity and biological activity

“…PDT activity of hypocrellins is ascribed to photogenerated semiquinone anion radical and reactive oxygen species [14,24] . Ability of photogenerating semiquinone anion radicals by THB, compounds 1 and 2 in an argonsaturated DMSO solution was evaluated based on EPR measurements.…”