Substituent effects in the free radical reactions of silybin: radiation-induced oxidation of the flavonoid at neutral pH.

Abstract

Silybin dihemisuccinate sodium salt, a flavonoid used in human therapy of liver dysfunction, has an inhibitory effect in vivo on radiation-induced deactivation of enzymes and peroxidation of membrane lipids in rat liver microsomes. The reactivity of silybin and its phenolic OH groups towards free radicals (OH, N3., (SCN)2.-, Cl3CO2.) in aqueous solution was studied by pulse radiolysis. Absorption spectra for the phenoxyl-type radicals were assigned using structurally similar models. The one-electron reduction potential for silybin at pH 7 (E07 = 0.76 V), determined using the p-methoxy-phenoxyl/phenolate redox couple as reference standard (E07 = 0.72 V, Lind et al. 1990), is related to the 3'-methoxy-4'-OH structure, the exclusive target for one-electron oxidation at pH 7, while the 7-OH and 5-OH groups are prevented from oxidation by 4-keto substitution and intramolecular H-bonding, respectively. The free radical reactivity of silybin compares favourably with poly-OH-substituted flavonoids; however, the latter compounds have been reported to generate potentially toxic oxygen species at a biologically relevant pH.

• Authors: I György, S Antus, A Blázovics, G Földiák
• Journal: International journal of radiation biology (Int J Radiat Biol) Vol. 61 Issue 5 Pg. 603-9 (May 1992) ISSN: 0955-3002 [Print] England
• PMID: 1349624 (Publication Type: Journal Article)

Chemical References

• Free Radicals
• Hydroxides
• Silymarin
• Hydroxyl Radical

Topics

• Animals
• Free Radicals
• Hydroxides
• Hydroxyl Radical
• Male
• Microsomes, Liver (drug effects, enzymology, radiation effects)
• Oxidation-Reduction
• Pulse Radiolysis
• Rats
• Rats, Inbred Strains
• Silymarin (pharmacology)