Preparation of carotenoid extracts and nanoemulsions from Lycium barbarum L. and their effects on growth of HT-29 colon cancer cells

Lycium barbarum L., a traditional Chinese herb widely used in Asian countries, has been demonstrated to be protective against chronic diseases such as age-related macular degeneration. The objectives of this study were to determine the carotenoid content in L. barbarum by highperformance liquid chromatography-mass spectrometry, followed by preparation of a carotenoid nanoemulsion to evaluate the mechanism. of inhibition on HT-29 colon cancer cells. The highest extraction yield of carotenoids was attained by employing a solvent system of hexane-ethanolacetone (1: 1: 1, v/v/v). Nine carotenoids, including neoxanthin (4.47 mu g g(-1)), all-transzeaxanthin and its cis-isomers (1666.3 mu g g-1), all-trans-a-cryptoxanthin (51.69 mu g g(-1)), alltrans- a-carotene and its cis-isomers (20.11 mu g g(-1)), were separated within 45 min and quantified using a YMC C-30 column and a gradient mobile phase of methanol-water (9: 1, v/v) (A) and methylene chloride (B). A highly stable carotenoid nanoemulsion composed of Capryol (TM) 90, Transcutol (R) HP, Tween 80 and deionized water was prepared with a mean particle size of 15.1 nm. Characterization of zeaxanthin standard, blank nanoemulsion, carotenoid extract and carotenoid nanoemulsion by differential scanning calorimetry curves and Fourier transform infrared spectra revealed a good dispersion of zeaxanthin-dominated carotenoid extract with no significant chemical change after incorporation into nanoemulsion. The in vitro release kinetic study showed a higher release profile at pH 5.2 than at physiological pH 7.4, suggesting a rapid release of carotenoids in the acidic environment (pH 4.5-6.5) characteristic of tumors. Both the carotenoid nanoemulsion and the extract were effective at inhibiting growth of HT-29. colon cancer cells, with an IC50 of 4.5 and 4.9 mu g ml(-1), respectively. Also, both treatments could upregulate p53 and p21 expression and down-regulate CDK2, CDK1, cyclin A and cyclin B expression and arrest the cell cycle at G(2)/M. The study may form a basis for further exploration of L. barbarum nanoemulsion in cancer treatment.