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M.–P.G. Agbaga, S.R. Brush, K. Henry, M.H. Elliott, M.R. Al–Ubaidi, R.E. Anderson; N–3 Polyunsaturated Fatty Acid Metabolism In 661W Cells . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3736.
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© ARVO (1962-2015); The Authors (2016-present)
Vertebrate retinas are highly enriched in long–chain polyunsaturated fatty acids (PUFA), especially docosahexaenoic acid (22:6n3) with largest amounts found in the rod outer segments (ROS). However, most studies on retinal fatty acid composition come from rod rather than cone outer segments; hence there is very limited data on the lipid environment of the cones. In this study, we investigated the fatty acid composition of an immortalized cone–like photoreceptor cell line, 661W cells, to determine if these cells have the machinery to generate 22:6n3 from n–3 PUFA precursors alpha–linolenic acid (18:3n3) and docosapentaenoic acid (22:5n3).
661W cells were plated at a density of 2 x 106cells/ml in DMEM supplemented with 10% calf serum and antibiotics, and treated for 72 hrs with different concentrations of the sodium salts of either 18:3n3, 22:5n3, or 22:6n3. After the 72 hrs, cells were collected; washed, and total lipids were extracted and converted to fatty acid methyl esters (FAMEs), which were analyzed by gas–liquid chromatography.
661W cells grown in DMEM without fatty acids supplementation have low levels of 22:6n3. Supplementation with 18:3n3 led to its internalization and subsequent conversion to 20:5n3 and 22:5n3; however, no appreciable accumulation of 22:6n3 was observed. Similarly, when incubated with 22:5n3, the cells incorporated and converted it to 24:5n3, as well as retroconverted a small amount to 20:5n3, but conversion to 22:6n3 was very low. When incubated with 22:6n3, however, cells rapidly incorporated it into glycerolipids; some was also retroconverted to 20:5n3.
661W cells possess the metabolic machinery for elongation, desaturation, and retroconversion of fatty acids from n–3 fatty acid precursors. However, they are not able to make 22:6n3 from appropriate precursors. The metabolic block seems to be in the activity of Δ6–desaturase, the enzyme that converts 24:5n3 to 24:6n3.
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