Pharmaceutical Research, Vol. 19, No. 7, July 2002 (© 2002)
Trommer, H.1; Böttcher, R.2; Pöppl, A.2; Hoentsch, J.2; Wartewig, S.3; Neubert, R. H. H.1,4
1
Martin-Luther-University Halle-Wittenberg, School of Pharmacy,
Institute of Pharmaceutics and Biopharmaceutics,
Wolfgang-Langenbeck-Straße 4, D-06120 Halle (Saale), Germany.
2
University of Leipzig, Department of Physics and Earth Sciences,
Institute of Experimental Physics II,
Linnéstraße 5, D-04103 Leipzig, Germany.
3
Institute of Applied Dermatopharmacy,
Wolfgang-Langenbeck-Straße 4, D-06120 Halle (Saale), Germany.
4
To whom correspondence should be addressed.
(e-mail:
neubert@pharmazie.uni-halle.de)
Purpose.
The effects of ascorbic acid on Stratum corneum lipid models following
ultraviolet irradiation were studied adding iron ions as transition
metal catalysts.
Methods.
Lipid peroxidation was quantified by the thiobarbituric acid assay.
The qualitative changes were studied on a molecular level by mass
spectrometry.
To elucidate the nature of free radical involvement we carried out
electron paramagnetic resonance studies.
The influence of ascorbic acid on the concentration of hydroxyl radicals
was examined using the spin trapping technique.
Moreover, we checked the vitamin's ability to react with stable radicals.
Results.
Ascorbic acid was found to have prooxidative effects in all lipid systems
in a concentration dependent manner.
The degradation products of ascorbic acid after its prooxidative action
were detected.
The concentration of the hydroxyl radicals in the Fenton assay was
decreased by ascorbic acid.
The quantification assay of
Conclusions.
Considering human skin and its constant exposure to UV light and oxygen,
an increased pool of iron ions in irradiated skin and the depletion of
co-antioxidants, the administration of ascorbic acid in cosmetical
formulations or in sunscreens could unfold adverse effects among the
Stratum corneum lipids.
KEY WORDS: ascorbic acid; thiobarbituric acid assay;
mass spectrometry; EPR; oxidative stress.
Introduction
Ascorbic acid is a hydrophilic hexuronic acid lacton.
Because humans have lost the ability to synthesize ascorbic acid, it must
be provided as an essential micronutrient from food.
The most well-known biochemical function of ascorbic acid is the protection
of the prolyl and lysyl hydroxylases.
This seems to be essential for the synthesis of stable collagen
molecules.
Furthermore, ascorbic acid has been shown to be a neuromodulator, an
antiviral substance and immunostimulant, and a radical scavenger.
Most of the chemical and biochemical properties of ascorbic acid are
related to its oxoenediol structure and can be explained by its
participation in biochemical redox processes.
Ascorbic acid is a diabasic acid and in aqueous solution a strong
reducing compound.
Despite the high number of publications dealing with the vitamin, and the
relatively simple chemical structure of the molecule, other properties of
the molecule are not yet fully understood.
Conflicting data has lead to controversy in the literature, and at present
even the daily human intake is still under debate.
Further sources of controversy are the interactions of vitamin C with
reactive oxygen species (ROS), as both antioxidant and prooxidant
properties have been reported.
Recently, genotoxic effects were suggested to be a result of the ability
of ascorbic acid to decompose lipid hydroperoxides to DNA damaging
secondary products raising the question why add ascorbic acid to drug
formulation for topical application.
In the skin, ascorbic acid is part of the antioxidative network of the
Stratum corneum and therefore, along with lipophilic antioxidants,
proteins, and other biomolecules, a target to the oxidative stressors
of the environment.
A decrease in the concentration of ascorbic acid was measured in murine
Stratum corneum following ozone exposure.
In this paper, therefore, the mechanism of the redox behavior of ascorbic
acid is studied using Stratum corneum lipid model systems to test its
actions on exposure to UV light.
As the biggest organ of the human body, the skin is constantly exposed
to both ultraviolet radiation and oxygen.
The degradation of ascorbic acid caused by UV-light was studied at a
molecular level using electrospray ionization mass spectrometry
(ESI-MS).
The advantages of the soft electrospray ionization (ESI) avoiding early
fragmentation and the ion trap possibilities of full scan mass
spectrometry (MS), MA/MS, and multiple state MS experiments allowed the
identification of the ascorbic acid decomposition products as well as the
lipid peroxidation products.
Electron paramagnetic resonance (EPR) spectroscopy is being used more
frequently in pharmaceutical research because of the unique information
which can be obtained by EPR spectrums of both in vivo and
in vitro experiments.
We used the spin trapping method by