Comparative studies on the chemical and enzymatic stability of alpa-and beta-arbutin

Authors: AVONTO, CRISTINA - University Of Mississippi; WANG, YAN-HONG - University Of Mississippi; AVULA, BHARATHI - University Of Mississippi; WANG, MEI - University Of Mississippi; RUA, DIEGO - Us Food & Drug Administration (FDA); KHAN, IKHLAS - University Of Mississippi

Submitted to: Planta Medica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/2/2015
Publication Date: 10/7/2015
Publication URL: http://handle.nal.usda.gov/10113/62600
Citation: Avonto, C., Wang, Y., Avula, B., Wang, M., Rua, D., Khan, I.A. 2015. Comparative studies on the chemical and enzymatic stability of alpa-and beta-arbutin. Planta Medica. 38:187-193. doi: 10.1111/ics.12275

Interpretive Summary: In summary, in the present work we propose an innovative approach to assess the stability of a-arbutin and ß-arbutin as potential source of the toxic compound hydroquinone. Several analytical approaches has been combined, including NMR, HPLC and optical rotation. Both arbutins were found to be quite stable under mild storage conditions both in solutions and in cosmetic formulations stored for 16 months. On the other hand, both compounds were unstable under strong hydrolytic conditions and a potential source of hydroquinone. Metabolic degradation of both arbutins also need to be considered as a potential hazard, although the potential release or accumulation of hydroquinone in the skin after topical application of arbutins may not necessarily occur, as other oxidative metabolic pathways other than enzymatic hydrolysis may be involved.

Technical Abstract: Alpha and beta arbutin are glycoside derivatives used as skin whitening agents. Both compounds interfere with tyrosinases activity in a fashion similar to their aglycone hydroquinone. Hydroquinone has been associated with ochronosis and possible carcinogenic effect. Due to their structural similarity to hydroquinone, both arbutins may be regarded as potential sources of the toxic aglycone after chemical or metabolic conversion. There is a lack of information regarding the stability and safety of a-arbutin as cosmetic ingredient, thus stability studies to compare both arbutins were here performed using HPLC-PDA, NMR and optical rotation. Solutions of pure compounds and cosmetic formulations were analyzed for potential epimerization or hydrolysis to produce hydroquinone. Metabolic degradation was investigated using pear peels as a biological model. Both arbutins were found to be stable under mild storage conditions in solutions (in the absence of stabilizers) as well as in cosmetic formulations stored for 16 months. Both compounds were unstable under hydrolytic conditions, which led to the release of hydroquinone. Enzymatic degradation of both arbutins was also observed, although the potential release or accumulation of hydroquinone in the skin after topical application may not necessarily occur.