Lutein and zeaxanthin: use of in vitro models to examine digestive stability, absorption, and photoprotective activity in human lens epithelial cells
Lutein and zeaxanthin are selectively accumulated in the lens and macular region of the retina. It has been suggested that these xanthophylls protect ocular tissues against ultraviolet radiation and reactive oxygen species that can cause cataracts and age-related macula degeneration. Insights regarding the absorption of dietary xanthophylls for delivery to ocular tissues are limited. My first objective was to examine factors affecting the transfer of lutein and zeaxanthin from foods to micelles during simulated digestion Test foods included spinach, wolfberry, orange pepper, squash, mango and lutein supplement. Micellarization of lutein and zeaxanthin during the small intestinal phase of digestion exceeded that of beta-carotene and was greater for xanthophylls in oil-based supplements than in spinach. Xanthophyll esters were decreased and non-esterified xanthophylls increased during simulated digestion as a result of cholesterol esterase activity. The efficiency of micellarization of free and esterified forms of the xanthophylls differed with micellarization of free zeaxanthin/lutein > zeaxanthin/lutein mono-esters > zeaxanthin/lutein di-esters. Apical uptake of lutein from micelles by human intestinal cells was linear for 4 hours. Stimulation of chylomicron synthesis was associated with secretion of only 7.6 +/- 0.1% of cellular lutein. The activities of acquired xanthophylls within enterocytes merits investigation. Although a photoprotective effect of xanthophylls in ocular tissue has been proposed, direct support is lacking. Therefore, the second objective of my study was to examine the effects of xanthophylls on lipid peroxidation and the mitogen-activated stress signaling pathways in human lens epithelial (HLE) cells following UVB irradiation. Pre-treatment of cultures with either 2 micromol/L lutein, zeaxanthin and astaxanthin for 4h before exposure to 300 J/m2 UVB radiation decreased lipid peroxidation and attenuation of c-JUN NH2-terminal kinase (JNK) and p38 by 47-57%, 50-60% and 25-32%, respectively. Significant inhibition of UVB-induced activation of JNK and p38 was observed for cells containing < 0.20 and 0.30 nmol xanthophyll/mg protein, respectively, whereas greater than 2.3 nmol alpha-TC/mg protein was required to significantly decrease UVB-induced stress signaling. These data suggest that physiological concentrations of xanthophylls protect cultured human lens epithelial cells against UVB irradiation. In vivo assessment of the photoprotective activities of xanthophylls is warranted.
School:The Ohio State University
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:caco 2 cells in vitro model lutein photoprotection uvb xanthophylls zeaxanthin
Date of Publication:01/01/2004