Journal of Lipid Research, Vol 29, 1065-1077, Copyright © 1988 by Lipid Research, Inc.
Fatty acids of pulmonary surfactant phosphatidylcholine from fetal rabbit lung tissue in culture. Biosynthesis of n-10 monoenoic fatty acids
KJ Longmuir, C Resele-Tiden and ME Rossi
Department of Physiology and Biophysics, College of Medicine, University of California, Irvine 92717.
We have previously reported that fetal rabbit lung tissue in organ culture
produces a lamellar body material (pulmonary surfactant) with a lower
percentage of disaturated phosphatidylcholine than is typically found in
rabbit lung in vivo (Longmuir, K.J., C. Resele-Tiden, and L. Sykes. 1985.
Biochim. Biophys. Acta. 833: 135-143). This investigation was conducted to
identify all fatty acids present in the lamellar body phosphatidylcholine,
and to determine whether the low level of disaturated phosphatidylcholine
is due to excessive unsaturated fatty acid at position sn-1, sn-2, or both.
Fetal rabbit lung tissue, 23 days gestation, was maintained in culture for
7 days in defined (serum-free) medium. Phospholipids were labeled in
culture with [1-14C]acetate or [U- 14C]glycerol (to follow de novo fatty
acid biosynthesis), or with [1- 14C]palmitic acid (to follow incorporation
of exogenously supplied fatty acid). Radiolabeled fatty acid methyl esters
obtained from lamellar body phosphatidylcholine were first separated by
reverse-phase thin-layer chromatography (TLC) into two fractions of 1) 14:0
+ 16:1 and 2) 16:0 + 18:1. Complete separation of the individual saturated
and monoenoic fatty acids was achieved by silver nitrate TLC of the two
fractions. Monoenoic fatty acid double bond position was determined by
permanganate-periodate oxidation followed by HPLC of the carboxylic acid
phenacyl esters. Lamellar body phosphatidylcholine contained four monoenoic
fatty acids: 1) palmitoleic acid, 16:1 cis-9; 2) oleic acid, 18:1 cis-9; 3)
cis-vaccenic acid, 18:1 cis-11; and 4) 6-hexadecenoic acid, 16:1 cis-6. In
addition, 8-octadecenoic acid, 18:1 cis-8, was found in the fatty acids of
the tissue homogenate. The abnormally low disaturated phosphatidylcholine
content in lamellar body material was the result of abnormally high levels
of monoenoic fatty acid (principally 16:1 cis-9) found at position sn-2.
Position sn-1 contained normal levels of saturated fatty acid. The
biosynthesis of the unusual n-10 fatty acids was observed from the start of
culture throughout the entire 7-day culture period, and was observed in
incubations of tissue slices of day 23 fetal rabbit lung. This is the first
report of the biosynthesis of n-10 fatty acids (16:1 cis-6 and 18:1 cis-8)
in a mammalian tissue other than skin, where these fatty acids are found in
the secretory product (sebum) of sebaceous glands.