Effect of polyunsaturated fatty acids on the growth of fish cells in culture

Cell proliferation and long chain polyunsaturated fatty acid metabolism in a cell line from southern bluefin tuna (Thunnus maccoyii)

Southern bluefin tuna (SBT, Thunnus maccoyii) aquaculture is a highly valuable industry, but research on these fish is hampered by strict catch quotas and the limited success of captive breeding. To address these limitations, we have developed a SBT cell line (SBT-E1) and here we report on fatty acid metabolism in this cell line. The SBT-E1 cells proliferated well in standard Leibovitz's L-15 cell culture medium containing fetal bovine serum (FBS) as the source of fatty acids. Decreasing the FBS concentration decreased the cell proliferation. Addition of the C(18) polyunsaturated fatty acids (PUFA) α-linolenic acid (ALA, 18:3n-3) or linoleic acid (LNA, 18:2n-6) to the cell culture medium had little effect on the proliferation of the cells, whereas addition of the long-chain PUFA (LC-PUFA) arachidonic acid (ARA, 20:4n-6), eicosapentaenoic acid (EPA, 20:5n-3) or docosahexaenoic acid (DHA, 22:6n-3) significantly reduced the proliferation of the cells, especially at higher concentrations and especially for DHA. Addition of vitamin E to the culture medium overcame this effect, suggesting that it was due to oxidative stress. The fatty acid profiles of the total lipid from the cells reflected those of the respective culture media with little evidence for desaturation or elongation of any of the fatty acids. The only exceptions were EPA and ARA, which showed substantial elongation to 22:5n-3 and 22:4n-6, respectively, and DHA, which was significantly enriched in the cells compared with the culture medium. The results are discussed in light of the dietary PUFA requirements of SBT in the wild and in aquaculture.

Stimulation of proliferation of an essential fatty acid-deficient fish cell line by C20 and C22 polyunsaturated fatty acids and effects on fatty acid composition

Recently we reported the development of a fish cell line, EPC-EFAD, derived from the carp (Cyprinus carpio) epithelial papilloma line, EPC, that could survive and proliferate in essential fatty acid-deficient (EFAD) medium. The EPC-EFAD cell line may be a useful model system in which to study the cellular biochemical effects of EFA deficiency and has advantages in studies of polyunsaturated fatty acid (PUFA) and eicosanoid metabolism in fish in that the complications introduced by culture in relatively n-6 PUFA-rich mammalian sera are removed. In the present study, the effects on cell proliferation rate of supplementing EPC-EFAD cells with various n-3 and n-6 PUFA were investigated to determine the possible role(s) of PUFA in cell growth and division. The selectivity of incorporation of specific PUFA into individual glycerophospholipid classes and the feasibility of reproducing in vivo fatty acid compositions in vitro were also investigated. Proliferation of the EPC-EFAD cell line was stimulated by arachidonic (20:4 n-6), eicosapentaenoic (20:5 n-3) and docosahexaenoic (22:6 n-3) fatty acids but not by 18:2 n-6 or 18:3 n-3. The differential effects of PUFA on cellular proliferation may be related to the lack of significant delta 5 desaturase activity in the cells at 22 degrees C and may implicate a role for eicosanoids in the mechanism of stimulation of proliferation. PUFA supplementation increased the cytotoxic effects of longer term culture, an effect that was partly alleviated by inclusion of vitamin E in the culture medium. The cells could generally be supplemented with PUFA to produce cellular fatty acid compositions in vitro that were similar to in vivo compositions.

Development of an in vitro model of essential fatty acid deficiency in fish cells

Levels of eicosapentaenoic acid (EPA; 20:5, n-3) greatly exceed those of arachidonic acid (AA; 20:4, n-6) in the tissue phospholipids of most fish species. Despite this, it is 20:4, n-6-derived eicosanoids that are produced predominantly in fish cells. The development of an essential fatty acid (EFA)-deficient fish cell line would greatly assist the study of this selectivity and so several fish cell lines were cultured in EFA-deficient (EFAD) media. All n-3 and n-6 polyunsaturated fatty acids (PUFA) and total PUFA were considerably reduced in all lines, except turbot fin (TF) in which total n-9 PUFA doubled from 13.8% to 27.5% of total fatty acids. In the topminnow hepatocarcinoma cell line (PLHC-1), there was almost complete depletion of both n-3 and n-6 PUFA and in TF cells, no n-3 PUFA were detected. In the carp epithelial papilloma cell line (EPC), both n-6 and n-3 PUFA were reduced by approximately 70%. The reduced PUFA in cells cultured in EFAD media was compensated to a large extent in most cell lines by significantly increased percentages of monounsaturated fatty acids, particularly 18:1, n-9. Total n-9 PUFA were significantly increased in all cell lines by culture in EFAD media, with 20:2, n-9 significantly increased in all cell lines. There were relatively small increases, but often significant, in 20:3, n-9 in all cell lines. Of the cell lines investigated, only EPC and PLHC-1 showed proliferation after four passages in EFAD medium, although the growth rates were reduced in comparison with media supplemented with serum, but EPC was the only cell line able to survive and proliferate in long-term culture on EFAD medium. The EFAD-EPC line is a potentially useful model system for the study of the effects of EFA deficiency on cell structure and function and eicosanoid metabolism in fish.

Influence of fatty acids and bovine serum albumin on the growth of human hepatoma and immortalized human kidney epithelial cells

The protective influence of bovine serum albumin against growth inhibition caused by fatty acids was studied in human hepatoma (HepG2) and immortalized human kidney epithelial (IHKE) cells. In general, growth inhibition by unsaturated fatty acids (0.15 mmol/liter) increased with increasing number of double bonds. For HepG2 cells crude albumin (1 g/100 ml) did not greatly modify growth inhibition by arachidonic, eicosapentaenoic, and docosahexaenoic acid. With oleic, linoleic, and linolenic acids, crude and defatted albumin stimulated cell growth. In contrast, for IHKE cells both albumins counteracted growth inhibition by unsaturated fatty acids to approximately the same extent. When HepG2 cells were cultured in the presence of saturated fatty acids (0.3 mmol/liter), C2, C6, and C8 had no or little inhibitory effect. C10 and C12 inhibited cell growth appreciably, whereas C14, and especially C16, had poor inhibitory effects. Crude albumin counteracted growth inhibition by all these fatty acids. In contrast, defatted albumin had little or no effect (except against C10 and C12), and even increased the growth inhibition by C14 and C16. With unsaturated fatty acids there seemed to be an inverse relationship between cell growth and the concentration of thiobarbituric acid reactive substances (TBARS) in media. Vitamin E abolished growth inhibition (and the increase in TBARS concentration) by unsaturated fatty acids. The complex interaction between fatty acids and albumins calls for great caution when interpreting data on growth effects.

Cytoprotective effect of tocopherols in hepatocytes cultured with polyunsaturated fatty acids

When highly unsaturated fatty acids are added to cell cultures, it can become important to include antioxidants in the culture medium to prevent cytotoxic peroxidation. To find an optimal antioxidant for this purpose, the effect of 50 microM alpha-tocopherol, gamma-tocopherol, alpha-tocopheryl acetate, alpha-tocopheryl acid succinate, or alpha-tocopheryl phosphate, or of 1 microM N,N'-diphenyl-1,4-phenylenediamine, was investigated with respect to the agent's ability to prevent lactate dehydrogenase leakage in long-term rat hepatocyte cultures supplemented with 0.5 mM highly unsaturated fatty acids. Formation of thiobarbituric acid reactive substances in the cultures was also measured. alpha-Tocopheryl acid succinate was found to be the most effective cytoprotective compound, followed by N,N'-diphenyl-1,4-phenylenediamine, alpha-tocopherol, gamma-tocopherol and alpha-tocopheryl acetate, and alpha-tocopheryl phosphate was without effect.