The Photostability and Photostabilization of trans-Resveratrol

Sep 1, 2011 | Contact Author | By: Craig Bonda, Jean Zhang and Anna Pavlovic, The HallStar Company
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Title: The Photostability and Photostabilization of trans-Resveratrol
resveratrolx polyphenolx hydroxyl groupx benzenex antioxidantx reactive oxygen speciesx isomerx stilbenesx trans-x cis-x photoisomerizationx
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Keywords: resveratrol | polyphenol | hydroxyl group | benzene | antioxidant | reactive oxygen species | isomer | stilbenes | trans- | cis- | photoisomerization

Abstract: In this study, the effects of ultraviolet radiation (UVR) on trans-resveratrol were documented, finding that UV radiation causes it to undergo rapid and extensive photoisomerization and some photodecomposition. The antioxidant activity of trans-resveratrol is correspondingly reduced. However, in the presence of ethylhexyl methoxycrylene, a photostabilizer used in sunscreens, the effects of UV exposure on trans-resveratrol are minimized, thereby preserving its antioxidant activity and, presumably, its bioavailability.

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C Bonda, J Zhang and A Pavlovic, The Photostability and Photostabilization of trans-Resveratrol, Cosm & Toil 126(9) 652 (2011)

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What happens to certain skin care active ingredients after they are applied to the skin and exposed to sunlight? Do they function as intended? Or do they undergo chemical or structural changes that render them less effective or even ineffective?

Previously, the skin care active ingredients retinol (vitamin A) and retinyl palmitate were studied by these authors, finding that exposure to UVR caused them to lose their structural and, to some extent, their chemical integrity.1 In this article, similar stability studies on trans-resveratrol are reported.

Resveratrol is a polyphenol that occurs naturally in at least 72 plant species.2 Dietary sources include peanuts, peanut butter, the seeds and skins of grapes and wine. Resveratrol is a member of the stilbene family of chemicals, whose members exhibit two aromatic rings connected by a methylene bridge. Resveratrol exists in two isomeric forms, trans- and cis- (see Figure 1) and as the glucoside piceid, also called polydatin. The trans- isomer is the more common and is believed to be more stable and biologically active.3

Resveratrol is an antioxidant, a compound that inhibits or counteracts an oxidizing agent. Oxidizing agents include free radicals, which are atoms or molecules with an unpaired electron. Examples of free radicals include superoxide anion (O2), peroxyl radical (COO˙) and hydroxyl radical (˙OH). Other highly reactive oxidizing agents include molecular oxygen (O2), singlet oxygen and hydrogen peroxide (H2O2).4 Oxidizing agents that contain oxygen are referred to as reactive oxygen species (ROS). Each is capable of initiating and propagating a free radical “chain reaction” with potentially damaging consequences for cellular membranes, proteins and DNA.5

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Table 1. Formulas for 0.1% trans-Resveratrol compositions tested

Table 1. Formulas for 0.1% <em>trans</em>-Resveratrol compositions tested

Test formulations were prepared as o/w emulsions. The formulas and preparative procedures can be found in Table 1.

Table 2. Chromatographic separation conditions and pump programs

Table 2. Chromatographic separation conditions and pump programs

Chromatographic separation was achieved using an C18 column under the conditions summarized in Table 2.

Table 3. Results of HPLC photostability studies

Table 3. Results of HPLC photostability studies

Table 3 summarizes the areas of each peak and their ratios in the three experiments.

Table 4. Percent of trans-resveratrol remaining over time when the compositions containing it are spread on glass, incubated at 37˚C and protected from light.

Table 4. Percent of trans-resveratrol remaining over time when the compositions containing it are spread on glass, incubated at 37˚C and protected from light.

Table 4 shows that the percent of trans-resveratrol remaining by HPLC after being spread in a thin layer on glass and incubated at 37oC for 2, 4, and 16 hours was 99.30%, 99.93% and 98.79%, respectively.

Table 5: Results of DPPH assay of antioxidant activity

Table 5: Results of DPPH assay of antioxidant activity

Table 5 resents the raw data collected from the DPPH assay of antioxidant activity of a 0.005% methanolic solution of trans-resveratrol before and after irradiation with 5 MED.

Figure 1. Resveratrol occurs naturally as trans- and cis- isomers, as well as a glucoside called polydatin or piceid.

Figure 1. Resveratrol occurs naturally as <em>trans-</em> and <em>cis-</em> isomers, as well as a glucoside called polydatin or piceid.

Resveratrol exists in two isomeric forms, trans- and cis- (see Figure 1) and as the glucoside piceid, also called polydatin.

Figure 2. UV absorption curves for trans- and cis- isomers of resveratrol as recorded by the DAD of the HPLC instrument.

<p>Figure 2. UV absorption curves for <em>trans-</em> and <em>cis-</em> isomers of resveratrol as recorded by the DAD of the HPLC instrument.

Both isomers absorb in the solar UV range between 290 nm and 400 nm, indicating the potential for destructive photochemical reactions. The trans- isomer absorbs UV with a broad peak between 304 nm and 321 nm and a molar extinction coefficient of about 30,000. The cis- isomer absorbs UV with a peak at 286 nm and a molar extinction coefficient of about 15,000.

Figure 3. A portion of the HPLC chromatogram that recorded the measurement of 0.1% trans-resveratrol in a skin care composition before being irradiated with UVR.

Figure 3. A portion of the HPLC chromatogram that recorded the measurement of 0.1% <em>trans</em>-resveratrol in a skin care composition before being irradiated with UVR.

The preservative phenoxyethanol (orange) is used as the internal standard.

Figure 4. After exposure to 5 MED of UVR, about half of the trans-resveratrol (blue) is converted to the cis- isomer (green) and some unidentified photoproducts (purple).

Figure 4. After exposure to 5 MED of UVR, about half of the <em>trans</em>-resveratrol (blue)  is converted to the <em>cis</em>- isomer (green) and some unidentified photoproducts (purple).

Figures 3, 4 and 5 are the relevant portions of the HPLC chromatograms recorded before irradiation with no EHMC, after 5 MED with no EHMC, and after 5 MED with 4% EHMC, respectively.

Figure 5. In the presence of the photostabilizer EHMC (yellow), UVR-induced isomerization of trans-resveratrol is strongly inhibited, although a small amount of the cis- isomer (green) is visible.

Figure 5. In the presence of the photostabilizer EHMC (yellow), UVR-induced isomerization of <em>trans</em>-resveratrol is strongly inhibited, although a small amount  of the <em>cis</em>- isomer (green) is visible.

Figures 3, 4 and 5 are the relevant portions of the HPLC chromatograms recorded before irradiation with no EHMC, after 5 MED with no EHMC, and after 5 MED with 4% EHMC, respectively.

Figure 6. The antioxidant activity of trans-resveratrol before (red) and after (green) UVR with 5 MED.

Figure 6. The antioxidant activity of <em>trans</em>-resveratrol before (red) and after (green) UVR with 5 MED.

The steeper the curve, the greater the antioxidant activity. As the graph shows, UVR has reduced the antioxidant activity of the trans-resveratrol solution. Also shown are the trend lines (logarithmic regression), their equations, and the “R squared,” a statistical measure of how well the trend line matches the actual data. A perfect fit is R2 = 1. In both cases the trend lines are very close fits to the data.

Figure 7. Results of the qualitative fluorescence quenching experiment.

Figure 7. Results of the qualitative fluorescence quenching experiment.

The bottom three spots contain the negative controls—i.e., solutions of 0.2% trans-resveratrol in ethyl acetate with, from left, 0%, 1% and 2% of a non-photoactive diluent. The top three test spots shown, from left, with 0%, 1% and 2% EHMC.

Figure 8. The percentage of 0.1% trans-resveratrol in two formulations following exposure to UVR in the absence and presence of EHMC at 4%.

Figure 8. The percentage of 0.1% <em>trans</em>-resveratrol in two formulations following exposure to UVR in the absence and presence of EHMC at 4%.

Formulators who want their trans-resveratrol products to deliver biological benefits should include a proven photostabilizer to preserve the structural integrity of trans-resveratrol (see Figure 8).

Footnotes (CT1109 Bonda)

a Product was purchased from Sigma-Aldrich Company Ltd., Gillingham, Dorset, UK.
b Product was provided by DSM, Heerlen, Netherlands.
c SolaStay S1 (INCI: Ethylhexyl Methoxycrylene) is a product manufactured by The HallStar Company, Chicago, USA.
d The Cary 50 UV-Visible Spectrophotometer is a device manufactured by Agilent Technologies, Santa Clara, Calif., USA.
e The Dynamic Absorbance Detector (DAD), part of the HP Agilent 1100 HPLCis manufactured by Agilent Technologies, Santa Clara, Calif., USA.
f The Model 16S Solar Simulator with a PMA 2105 UV-B DCS Detector controlled by a PMA 2100 microprocessor-based controller used for this study is a device from Solar Light Co., Glenside, Penn., USA.
g The HP Agilent 1100 HPLC is a system manufactured by Agilent Technologies, Santa Clara, Calif., USA.
h ChemStation for LC 3D is produced by Agilent Technologies, Santa Clara, Calif., USA.
i The Apollo C18 column (4.6 x 150 mm, with a 5-µm particle size) is manufactured by Alltech Associates, Deerfield, Ill., USA.
j 4420-221 Aluminum-backed Flexible Silica TLC Plates are manufactured by Whatman Plc, Kent, UK.
k ENF-240C is a lamp manufactured by Spectroline, Westbury, N.Y., USA. m D70 SLR is an archived camera model manufactured by Nikon, Tokyo.

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