Topical delivery of retinyl ascorbate: 4. Comparative anti-oxidant activity towards DPPH.
The free radical scavenging properties of retinyl ascorbate (RA-AsA) were determined by monitoring the decomposition of 2,2-diphenyl-1-picrylhydrazyl (DPPH) as a function of time and in comparison with ascorbic acid (AsA), ascorbic acid palmitate (AsA-Pal), retinoic acid (RA), retinol (ROL) and retinol palmitate (Rol-Pal). The rate constant of RA-AsA (mean3+/-SD) was 4.9+/-0.3 M(-1) s(-1), and indicated greater potency as an antioxidant compared to the rest of the test compounds (AsA 3.4+/-0.4 M(-1) s(-1), AsA-Pal, 2.9+/-0.2 M(-1) s(-1), RA 1.4+/-0.3 M(-1) s(-1), ROL 1.3+/-0.1 M(-1) s(-1), Rol-Pal exhibited insignificant activity). The decomposition rate constant of DPPH, 5+/-0.6 x 10(-8) M(-1) s(-1), in ethanol and BHA, 154+/-3 M(-1) s(-1) were both used as control. The compound RA-2-carboxy-2-hydroxy-ethanoate was isolated by prep-TLC and was identified, by 13C and 1HNMR spectroscopy, as the major by-product from the reaction of RA-AsA with DPPH, which was also found to be potent antioxidant, 2.1+/-0.2 M(-1) s(-1). This suggests that oxidation of AsA moiety did not lead to the production of erythrulose species, which could cause deleterious modifications of cellular proteins.
Abdulmajed
Kasem
K
Welsh School of Pharmacy, Cardiff University, Cardiff, CF10 3XF, UK.
McGuigan
Chris
C
Heard
Charles M
CM
D000287:Administration, Topical; D001205:Ascorbic Acid / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000737:chemistry*; D001713:Biphenyl Compounds / Q000737:chemistry*; D004224:Diterpenes; D016166:Free Radical Scavengers / Q000737:chemistry*; D006834:Hydrazines / Q000737:chemistry*; D010851:Picrates; D012176:Retinoids; D000084562:Retinyl Esters; D014212:Tretinoin / Q000737:chemistry; D014801:Vitamin A / Q000031:analogs & derivatives / Q000737:chemistry
D001713:Biphenyl Compounds; D004224:Diterpenes; D016166:Free Radical Scavengers; D006834:Hydrazines; D010851:Picrates; D012176:Retinoids; D000084562:Retinyl Esters; C504062:retinyl ascorbate; D014801:Vitamin A; C014794:retinol palmitate; D014212:Tretinoin; C004931:1,1-diphenyl-2-picrylhydrazyl; D001205:Ascorbic Acid