301 ALOE-EMODIN INHIBITS PROLIFERATION OF ADULT HUMAN KERATINOCYTES results demonstrate that growth inhibition in keratinocyte cultures was not a consequence of cell necrosis, as demonstrated by LDH release assay (Figure 1B). Clearly, the mecha- nisms of AE antiproliferative effect are complex and cell-specifi c. It seems that keratinocytes are more sensitive to antiproliferative effect of AE than com- monly used tumor cell lines. We fi nd this information particularly relevant, having in mind the fact that aloe extracts containing anthraquinones including AE are frequently applied to the skin. We demonstrated antiproliferative effect of AE at the 5 μM concen- tration, which corresponds to 1.35 ppm w/w in the cultivation medium (Figure 1A). In fact, the average AE IC50 value for the tested keratinocyte cultures was calculated to be 1.1 ppm (Table I). The industry-established standard for the anthraquinone contents in the products for the nonmedicinal use, frequently marketed as wound or burn healing promoting products, is 50 ppm (3) exceeding by far demonstrated IC50. Therefore, AE present in such preparations may be detrimental in all conditions requiring epithelization including burns, wounds, and ulcers. On the other hand, one can keep in mind that ob- served antiproliferative effect of the AE can in fact be benefi cial in hyperproliferative skin diseases such as psoriasis. To determine benefi cial and adverse effects of AE present in the aloe extracts, further ex- periments should be conducted, preferentially on the skin explants. Another set of ex- periments with head-to-head comparison of aloe extracts preparations with and without AE, possibly in clinical setting, could be warranted to delineate the net effect of AE on human skin. Also, the manufacturers should carefully screen raw materials and fi nal prod- ucts for the AE contents and label them properly. ACKNOWLEDGMENT This work was supported by the Ministry of Science of the Republic of Serbia (grant no. 175038). Figure 2. Aloe-emodin (AE) induces keratinocyte apoptosis. Keratinocytes from 10 different donors (labeled 1–10) were incubated for 6 h in the absence (0) or presence of 5 μM AE and the number of apoptotic cells was determined by fl ow cytometry. ∗∗p 0.01.

JOURNAL OF COSMETIC SCIENCE 302 REFERENCES (1) H. Yao, Y. Chen, S. Li, L. Huang, W. Chen, and X. Lin, Promotion proliferation effect of a polysaccha- ride from Aloe barbadensis Miller on human fi broblasts in vitro, Int. J. Biol. Macromol., 45, 152–156 (2009). (2) C. E. Turner, D. A. Williamson, P. A. Stroud, and D. J. Talley, Evaluation and comparison of commer- cially available Aloe vera L. products using size exclusion chromatography with refractive index and multi-angle laser light scattering detection, Int. Immunopharmacol., 4, 1727–1737 (2004). (3) Cosmetic Ingredient Review Expert Panel, Final report on the safety assessment of Aloe Andongensis Extract, Aloe Andongensis Leaf Juice, Aloe Arborescens Leaf Extract, Aloe Arborescens Leaf Juice, Aloe Arborescens Leaf Protoplasts, Aloe Barbadensis Flower Extract, Aloe Barbadensis Leaf, Aloe Barbadensis Leaf Extract, Aloe Barbadensis Leaf Juice, Aloe Barbadensis Leaf Polysaccharides, Aloe Barbadensis Leaf Water, Aloe Ferox Leaf Extract, Aloe Ferox Leaf Juice, and Aloe Ferox Leaf Juice Extract, Int. J. Toxicol., 26 Suppl 2, 1–50 (2007). (4) D. Wolfl e, C. Schmutte, J. Westendorf, and H. Marquardt, Hydroxyanthraquinones as tumor promot- ers: Enhancement of malignant transformation of C3H mouse fi broblasts and growth stimulation of primary rat hepatocytes, Cancer Res., 50, 6540–6544 (1990). (5) S. Popadic, Z. Ramic, L. Medenica, M. Mostarica Stojkovic, V. Trajkovic, and D. Popadic, Antiprolif- erative effect of vitamin A and D analogues on adult human keratinocytes in vitro, Skin Pharmacol. Physiol., 21, 227–234 (2008). (6) S. Mijatovic, D. Maksimovic-Ivanic, J. Radovic, D. Miljkovic, G. N. Kaludjerovic, T. J. Sabo, and V. Trajkovic, Aloe emodin decreases the ERK-dependent anticancer activity of cisplatin, Cell Mol. Life Sci., 62, 1275–1282 (2005). (7) P. L. Kuo, T. C. Lin, and C. C. Lin, The antiproliferative activity of aloe-emodin is through p53-dependent and p21-dependent apoptotic pathway in human hepatoma cell lines, Life Sci., 71, 1879–1892 (2002). (8) J. Guo, B. Xiao, S. Zhang, D. Liu, Y. Liao, and Q. Sun, Growth inhibitory effects of gastric cancer cells with an increase in S phase and alkaline phosphatase activity repression by aloe-emodin, Cancer Biol. Ther., 6, 85–88 (2007).