In vitro metabolism of 14C-polyunsaturated fatty acids in midgut gland and ovary cells from Penaeus kerathurus Forskâl at the beginning of sexual maturation

Abstract

The incorporation and metabolism via the desaturase/elongase pathway of [1- 14C]18:2(n-6) linoleic acid (LA), [1- 14C]18:3(n-3) linolenic acid (LNA), [1- 14C]20:4(n-6) arachidonic acid (AA) and [1- 14C]20: 5(n-3) eicosapentaenoic acid (EPA) were studied in midgut gland and ovary cell suspensions from wild-caught adult females of Penaeus kerathurus Forskål at the beginning of sexual maturation. The incorporation and recovery of radioactivity in total lipids of midgut gland cells was greater for [1- 14C]LA and [1- 14C]LNA than for [1- 14C]AA or [1- 14C]EPA, indicating a preferential retention of C 18-polyunsaturated fatty acids (PUFAs) in this organ. The recovery of radioactivity from all PUFA decreased during the time course. The incorporation of [1- 14C]PUFAs into total polar lipids in midgut gland cells increased during the time course (from 33.4% to 65.2%) with a concomitant decrease into total neutral lipids. These changes were due to significantly increased incorporation into phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidylinositol (PI), with significantly decreased incorporation into triacylglycerol (TAG). [1- 14C]AA and [1- 14C]EPA were preferentially incorporated into PI, and [1- 14C]EPA was more important in phospholipid synthesis in midgut gland cells than [1- 14C]-labeled LA, LNA or AA. The incorporation and recovery of radioactivity in total lipids from ovary cells was significantly lower than in midgut gland cells but significantly increased during the time course with all the [1- 14C]PUFAs. The distribution of radioactivity from [1- 14C]AA and [1- 14C]EPA in ovary cells showed preferential retention into polar lipid classes compared with [1- 14C]LA or [1- 14C]LNA, and the general pattern was of net synthesis of PC at the expense of PE, free fatty acid and TAG. The results indicated that midgut gland and ovary cells have only a limited ability to convert C 18-PUFA to C 20- and C 22-highly unsaturated fatty acid. The recovery of radioactivity in 22:6(n-3) was ∼10-fold greater with [1- 14C]EPA than with [1- 14C]LNA as precursor. Substantial amounts of radioactivity were recovered in 24:5(n-6), 24:5(n-3) and 24:6(n-3), particularly in cells incubated with [1- 14C]EPA, indicating that the conversion of EPA to DHA in both organs may occur by a pathway using Δ 6-desaturase activity rather than by a Δ 4-desaturation