Immunology 110(3): 348-357

Dihomo-γ-linolenic acid inhibits tumour necrosis factor-α production by human leucocytes independently of cyclooxygenase activity

Condition and Disease Specific Research Department, Numico Research B.V., Wageningen, the Netherlands

Correspondence: Laura M'Rabet, Numico Research B.V., Bosrandweg 20, 6704 PH, Wageningen, the Netherlands. E-mail: ln.hcraeser-ocimun@tebarm.arual

Condition and Disease Specific Research Department, Numico Research B.V., Wageningen, the Netherlands

Received 2003 May 5; Revised 2003 Jul 21; Accepted 2003 Sep 2.

Abstract

Dietary oils (such as borage oil), which are rich in γ-linolenic acid (GLA), have been shown to be beneficial under inflammatory conditions. Dihomo-GLA (DGLA) is synthesized directly from GLA and forms a substrate for cyclooxygenase (COX) enzymes, resulting in the synthesis of lipid mediators (eicosanoids). In the present study, the immunomodulatory effects of DGLA were investigated and compared with those of other relevant fatty acids. Freshly isolated human peripheral blood mononuclear cells (PBMC) were cultured in fatty acid (100 µm)-enriched medium for 48 hr. Subsequently, cells were stimulated with lipopolysaccharide (LPS) for 20 hr and the cytokine levels were measured, in supernatants, by enzyme-linked immunosorbent assay (ELISA). Phospholipids were analysed by gas chromatography. Fatty acids were readily taken up, metabolized and incorporated into cellular phospholipids. Compared with the other fatty acids tested, DGLA exerted pronounced modulatory effects on cytokine production. Tumour necrosis factor-α (TNF-α) and interleukin (IL)-10 levels were reduced to 60% of control levels, whereas IL-6 levels were not affected by DGLA. Kinetic studies showed that peak levels of TNF-α, occurring early after LPS addition, were inhibited strongly, whereas IL-10 levels were not affected until 15 hr after stimulation. Both the reduction of cytokine levels and the decrease in arachidonic acid levels in these cells, induced by DGLA, were dose dependent, suggesting a shift in eicosanoid-subtype synthesis. However, although some DGLA-derived eicosanoids similarly reduced TNF-α levels, the effects of DGLA were probably not mediated by COX products, as the addition of indomethacin did not alter the effects of DGLA. In conclusion, these results suggest that DGLA affects cytokine production by human PBMC independently of COX activation.

Abstract

Data show one representative sample out of three. Intersample variation for the different fatty acids analysed was < 5%.

AA, arachidonic acid; DHA, docosahexaenoic acid; DPA, docosapentaenoic acid; DGLA, dihomo-γ-linolenic acid; EPA, eicosapentaenoic acid; GLA, γ-linolenic acid; LA, linoleic acid; LNA, α-linolenic acid; SA, stearidonic acid.

Acknowledgments

We thank Erik Hogenkamp from Numico Research B.V. (Wageningen, the Netherlands) for his technical assistance and the fatty acid analysis of human serum.

Acknowledgments

Abbreviations

AA	arachidonic acid (20:4n-6)
BF₃	boron trifluoride
ccTXA₂	carbocyclic-thromboxane-A₂
COX	cyclooxygenase
DGLA	dihomo-γ-linolenic acid (20:3n-6)
DHA	docosahexaenoic acid (22:6n-3)
DMSO	dimethylsulphoxide
ELISA	enzyme-linked immunosorbent assay
EPA	eicosapentaenoic acid (20:5n-3)
FCS	fetal calf serum
GLA	γ-linolenic acid (18:3n-6)
IL	interleukin
LA	linoleic acid (18:2n-6)
LNA	α-linolenic acid (18:3n-3)
LPS	lipopolysaccharide
LTB₄	leukotriene B₄
PBMC	peripheral blood mononuclear cells
PBS	phosphate-buffered saline
PGE	prostaglandin E
PUFA	polyunsaturated fatty acid
SA	stearidonic acid (18:4n-3)
TNF-α	tumour necrosis factor-α
TXB	thromboxane B

Abbreviations

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