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

Abstract

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 high-performance 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–ethanol–acetone (1:1:1, v/v/v). Nine carotenoids, including neoxanthin (4.47 μ g g −1 ), all- trans -zeaxanthin and its cis -isomers (1666.3 μ g g −1 ), all- trans - β -cryptoxanthin (51.69 μ g g −1 ), all- trans - β -carotene and its cis -isomers (20.11 μ 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 ® 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 IC 50 of 4.5 and 4.9 μ g ml −1 , respectively. Also, both treatments could up-regulate 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.