Differential metabolism of dihomo-gamma-linolenic acid and arachidonic acid by cyclo-oxygenase-1 and cyclo-oxygenase-2: implications for cellular synthesis of prostaglandin E1 and prostaglandin E2.
Prostaglandin (PG) E(1) has been shown to possess anti-inflammatory properties and to modulate vascular reactivity. These activities are sometimes distinct from those of PGE(2), suggesting that endogenously produced PGE(1) may have some beneficial therapeutic effects compared with PGE(2). Increasing the endogenous formation of PGE(1) requires optimization of two separate processes, namely, enrichment of cellular lipids with dihomo-gamma-linolenic acid (20:3 n-6; DGLA) and effective cyclo-oxygenase-dependent oxygenation of substrate DGLA relative to arachidonic acid (AA; 20:4 n-6). DGLA and AA had similar affinities (K(m) values) and maximal reaction rates (V(max)) for cyclo-oxygenase-2 (COX-2), whereas AA was metabolized preferentially by cyclo-oxygenase-1 (COX-1). To overcome the kinetic preference of COX-1 for AA, CP-24879, a mixed Delta(5)/Delta(6) desaturase inhibitor, was used to enhance preferential accumulation of DGLA over AA in cells cultured in the presence of precursor gamma-linolenic acid (18:3 n-6). This protocol was tested in two cell lines and both yielded a DGLA/AA ratio of approx. 2.8 in the total cellular lipids. From the enzyme kinetic data, it was calculated that this ratio should offset the preference of COX-1 for AA over DGLA. PGE(1) synthesis in the DGLA-enriched cells was increased concurrent with a decline in PGE(2) formation. Nevertheless, PGE(1) synthesis was still substantially lower than that of PGE(2). It appears that employing a dietary or a combined dietary/pharmacological paradigm to augment the cellular ratio of DGLA/AA is not an effective route to enhance endogenous synthesis of PGE(1) over PGE(2), at least in cells/tissues where COX-1 predominates over COX-2.
Levin
Galit
G
Department of Biochemistry, George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv 69978, Israel.
Duffin
Kevin L
KL
Obukowicz
Mark G
MG
Hummert
Susan L
SL
Fujiwara
Hideji
H
Needleman
Philip
P
Raz
Amiram
A
D015126:8,11,14-Eicosatrienoic Acid / Q000378:metabolism*; D000527:Alprostadil / Q000096:biosynthesis*; D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism*; D051545:Cyclooxygenase 1; D051546:Cyclooxygenase 2; D015232:Dinoprostone / Q000096:biosynthesis*; D007527:Isoenzymes / Q000378:metabolism*; D007700:Kinetics; D008565:Membrane Proteins; D051379:Mice; D011451:Prostaglandin-Endoperoxide Synthases / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D014407:Tumor Cells, Cultured
D007527:Isoenzymes; D008565:Membrane Proteins; D011994:Recombinant Proteins; D016718:Arachidonic Acid; D051545:Cyclooxygenase 1; D051546:Cyclooxygenase 2; D011451:Prostaglandin-Endoperoxide Synthases; C496512:Ptgs1 protein, mouse; D000527:Alprostadil; D015126:8,11,14-Eicosatrienoic Acid; D015232:Dinoprostone