Journal of Lipid Research, Vol 34, 2077-2090, Copyright © 1993 by Lipid Research, Inc.
Fatty acid metabolism studies of human epidermal cell cultures
CL Marcelo and WR Dunham
Department of Dermatology, University of Michigan Medical School, Ann Arbor 48109-0528.
Adult human epidermal keratinocytes grow rapidly in medium that is
essential fatty acid (EFA)-deficient. In this medium they exhibit decreased
amounts of the fatty acids, 18:2, 20:3, 20:4, and contain increased amounts
of monounsaturated fatty acids. [14C]- and [3H]acetate and radiolabeled
fatty acids, 16:0, 18:2, and 20:4 were used to study the fatty acid
metabolism of these cells. Label from acetate appeared in 14- to 20-carbon
fatty acids, both saturated and monounsaturated. No label was seen in the
essential fatty acid 18:2, 18:3, and 20:4. Radiolabel from [9,
10-3H]palmitic acid (16:0) was detected in 16:0, 16:1, 18:0, and 18:1.
[14C]linoleic acid (18:2) was converted to 18:3, 20:2, 20:3, and 20:4,
demonstrating delta 6 and delta 5 desaturase activity in keratinocytes.
Label from acetate, 16:0, or 18:2 was found mostly in the cellular
phospholipids while only one third of the label from [14C]arachidonic was
found in the phospholipids. [14C]acetate and [14C]18:2 time course data
were used to construct a model of the metabolism of these reactants, using
coupled, first-order differential equations. The data show that
EFA-deficient keratinocytes metabolize fatty acids using pathways
previously found in liver; they suggest the positioning of 18:2 desaturase
and 18:3 elongase near the plasma membrane; they indicate that for the
synthesis of nonessential fatty acids the formation of 18:0 from 16:0 is
the rate- determining step; and they show that the conversion of 18:2 to
20:3 is rapid. These experiments demonstrate a method to study lipid enzyme
kinetics in living cells.
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