2005 ANNUAL SCIENTIFIC SEMINAR 355 Eumelanin & Pheomelanin: Eumelanin is best known for its photoprotective role in the skin. Photoprotection is afforded by the ability of melanin to serve as a physical barrier that scatters incident UV light, and as a filter that reduces the penetration of UV light through the epidermis. An important property of eumelanin is its ability to scavenge free radicals, and to function as a superoxide dismutase that reduces reactive oxygen to hydrogen peroxide. Therefore, decrease in eumelanin increases the risk of skin damage from oxidative stress, This can be counter acted by selecting an anti-aging ingredient(s) or a skin lightening ingredient with built-in broad-spectrum antioxidant functionality. Pheomelanin, which is yellow-reddish in color, differs from eumelanin that the building blocks are derived from cysteinyl-DOP A. Epidemiological data indicate individuals with fair skin are more susceptible to skin cancers than their darker counterparts as pheomelanin exhibits a greater phototoxicity than eumelanin. In contrast to eumelanin, pheomelanin is photolabile and potentially phototoxic. This detrimental effect can also be prevented by supplementing with broad-spectrum antioxidant(s). Skin Lightening & Anti-Aging Ingredients: A wide range of polyphenolics are known to have skin lightening and also anti-aging properties. Melanin inhibitory activities of natural polyphenolics, such as anthaquinones, arylbenzofurans, chalcones, coumarins, flavonoids, stilbenes, low-molecular weight tannins,etc., have been reported. Skin lightening agents can inhibit melanin biosynthesis by blocking various points of the pathways and are thus useful in lightening human skin. Skin lightening agents can also be used to treat local hyperpigmentation or spots that are caused by local increase in melanin synthesis or uneven distribution. In order to show the interlink between the skin lightening and anti-aging ingredients, we have chosen two standardized plant extracts belonging to two types of polyphenolics, namely, flavonoids of G/ycyrrhiza glabra (Licorice, Glabridin as the active) and low molecular-weight tannins (1,000) of Phyllanthus emb/ica (Emblica). Work done in our laboratory and elsewhere has shown that both products are very effective skin lightening and anti-aging agents due to their broad-spectrum antioxidant and chelating activities. Licorice is also an excellent tyrosinase inhibitor. Inhibitory concentration (IC50) of peroxidase/H202 and Fe2+/H202 induced conversion of DOPA to DOPAchrome for Licorice and Emblica and their antioxidant activity profiles are summarized in Table 1. Clinical trials have shown their effectiveness both as skin lightening and anti-aging ingredients. Table 1: Comparative In-Vitro Skin Lightening and Antioxidant Activity Profile Skin Lightening Efficiency Antioxidant Activity IC�¾ (µg/ml) IC so¾ (µg/ml) Peroxidase / Tyrosinase / Tyrosinase / Fe"+IH202 Singlet oxygen Superoxide L-DOPA L-DOPA tyrosine anion radical Emblica 500 140 70 690 60 12 Licorice 430 10 IO 455 20 43 Koiic acid 220 35 10 150 Pro-oxidant Pro-oxidant Hydroquinone 610 230 JO Melanin i 107 400 Ascorbic acid 88 63 30 105 Pro-oxidant 27 MAP No activity No activity No activity Melanin i 500 No activity Conclusion: What is really needed to create true skin lightening products with anti-aging benefits is to select one or more natural polyphenolics. Tyrosinase inhibitory activity is not a prerequisite to have skin lightening effect. Inhibition of alternate oxidative pathways, namely, peroxidase/H202 and Fe2+/H202 can also provide desired skin lightening activity. Skin lightening ingredients can also work by other mechanisms. For anti-aging activity, we do need ingredients with a quencher for ROS, a chelator for iron and copper and an inhibitor for matrix metalloprotease. Oxidative pathways in melanogenesis and the UV­ induced oxidative stress are the interlinkage between skin lightening and anti-aging ingredients. References l. Valverde P, P Maiining, C Todd, CJ McNeil, & AJ Thody, Exp Dermatol, 40: 1312-1316, 1999. 2. Berneburg M, H Plettenberg, & J Krutmann, Photodermatol Photoimun Photomed, 16: 239-244, 2000. 3. Okun MR, Physio/ Chem Phys Med NMR, 28:91-100, 1996. 4. Nappi AJ, E Vass, J Biol Chem, 276:11214-11222, 2001.
356 JOURNAL OF COSMETIC SCIENCE CORRELATING SENSORY PERCEPTION TO THE RHEOLOGICAL PARAMETERS OF EMULSIONS: A PREDICTIVE MODEL FOR FUTURE PRODUCT DEVELOPMENT? Introduction Andrew M. DiMuzio, Eric S. Abrutyn and Maggie Y. Cantwell Kao Brands Company, Cincinnati, OH Although the rheological characteristics and consumer skinfeel properties of emulsions have both been studied extensively oyer the last few decades, very few published studies have been devoted to finding a correlation between the two. Brummer and GoderskJ [ 1] broke down the skin feeling aspects into two groups: "Primary" (initial application) and ·'Secondary" (final rub-in). They correlated a product's '·primary" skin feeling with two rheological measurements: maximwn (zero-shear) viscosity, and yield value. "Secondary," skin feeling was correlated with the product's viscosity at approximately 5000 sec·'. Products that fell within the limits for each of these parameters were deemed pleasant-feeling, while those that fell outside those limits were deemed unsatisfactory. Lee ct al [2] found a correlation between the G'/G' crosso,·er point stress (what they tenncd a "critical shear stress") and a skin feeling index score. Wortel ct al [3] used mullirnriatc methods to determine that cohesi,eness scores could be correlated to the combination of yield Yalue and dynamic Yiscpsity. For the present study, we :uc anempting to find if there are any other rheological parameters that could be correlated with skinfcel, and whether more than one arc working in concert to generate a particular feeling on the skin. Materials and Methods Rheological Anal�sis: Six different o/w emulsions (with widely differing skinfeel properties) were analyzed al 25 ° C with an AR-1000 rheometer (T.A. Instruments). using a ..io mm serrated parallel plate. a 1000 micron gap, and a solYcnt trap (to pre,·ent edge drying). Three tests were performed on each sample: Stress Sweep, Creep. and Flow. During stress sweeps, the samples were exposed to increased oscillatory stresses, ranging from 0.1 to 200 Pa (log mode, 20 points per decade. I Hz), until the samples yielded. For creep tests, a stress value from within the linear viscoelastic region (L VR, obtained from the stress sweep) was chosen, and applied to the sample for 30 minutes, then rcmO\cd. with the sample being allowed to rccoYcr for 90 minutes. For flow tests, a two-step method was used. A steady-state flow test was employed from 10-100 Pa, while a continuous ramp was employed from 1-1000 sec· 1 These 2 data sets were then merged to produce one continuous flow curve. ScnsOQ' Panel Analysis: All emulsion samples were submitted to a Skinfecl Spectrum TM DcscriptiYe Analysis panel, which uses physical intensity references for each product attribute, strict protocols for manipulation, and precisely defined terms to discriminate and describe the sensory properties of a giYen sample [-' l Scores arc gi\·cn for characteristics such as spreadability, firmness, and cohesiveness, with an intcnsitJ scale of 0-100 ( 100 = Very High). Data is then analyzed for significance. Data Analysis: Rheological and sensory panel data were analyzed (utilizing univari:He and multirnriate techniques) for correlation and regression with Minitab statistical software. Results and Discussion In aJI, 4-' rheological data points were obtained for each emulsion, and these were run against 21 sensory data points. Using regression anaJysis, we were able to uncover a number of interesting correlations (Sec Table 1). Cohesiveness, for example, correlates negatively with gel strength at the G' == G" crossover point (fable 2, Figure I). Three of the five correlations involve multiple variables each of these three incorporate data derived from the Creep analysis (relaxation time, equilibrium compliance, and minimwn [recovery] strain).
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