DIFFERENTIAL UTILIZATION OF LINOLEIC AND ARACHIDONIC-ACID BY CULTUREDHUMAN KERATINOCYTES

The essential fatty acid, linoleic acid (LA), is required for the epid ermal barrier and LA is also the precursor fatty acid for arachidonic acid (AA). Both fatty acids are imported from systemic sources, becaus e AA is also not synthesized in the epidermis. The present studies wer e undertaken to compare the uptake and incorporation into cellular lip id of these fatty acids and to determine whether they compete with one another in these processes in relation to keratinocyte differentiatio n. The incorporation of [C-14]LA and/or [C-14]AA into phospholipids an d triglycerides was examined in keratinocytes cultured under submerged and lifted conditions. In submerged (less well-differentiated) cultur es, more LA was incorporated into phospholipids than AA, while AA was incorporated into triglycerides to a greater extent. When given togeth er, neither fatty acid influenced the total and/or relative uptake and lipid distribution of the other. Compared to submerged cultures, the uptake of LA increased 2-fold in lifted (differentiated) cultures, whi le the uptake of AA was unchanged. Lifting increased the proportion of AA incorporated into phospholipids, but did not alter the distributio n of LA among phospholipids or triglycerides. These data suggest that the essential fatty acids, LA and AA, which are destined for different metabolic roles within the keratinocyte do not compete with one anoth er during their uptake and distribution among cellular lipid species. Furthermore, as keratinocytes differentiate in culture, their increase d requirement for LA for the synthesis of barrier lipids may be achiev ed through the preferentially enhanced uptake and lipid incorporation.