Mead acid eicosanoids - the family is complete
Taka
metabolized to everything claimed to be the "essential" derivative of
the arachidonic acid (AA) or EPA:
1) The COX metabolite like PGE2:
Prostaglandin E2-like activity of 20:3n-9 platelet lipoxygenase end-
product.
Lagarde M, Burtin M, Rigaud M, Sprecher H, Dechavanne M, Renaud S.
5,8,11-Icosatrienoic acid (20:3n-9), a fatty acid associated with
platelet hyperactivity, was oxygenated by platelet lipoxygenase. The
end-product of this pathway was purified by high-performance liquid
chromatography (HPLC) and characterized as 12-hydroxy-5,8,10-
icosatrienoic acid [12-OH-20:3(5,8,10)] by capillary gas-liquid mass
spectrometry. When tested upon platelet aggregation, 12-
OH-20:3(5,8,10) exhibited a biphasic effect. At low concentrations
(below 5 X 10(-7) M) it potentiated aggregation but inhibited it at
higher levels, a pattern similar to that obtained with prostaglandin
E2. However, since the amounts of 12-OH-20:3(5,8,10) generated under
thrombin stimulation are in the range of concentrations with
potentiating effects, it seems that the 12-OH derivative is
responsible for the hyperaggrebility of 20:3n-9-rich platelets.
PMID: 3918886
J Biol Chem. 1986 May 25;261(15):6719-24.
Calcium-dependent oxidation of 5,8,11-icosatrienoic acid by the
cyclooxygenase enzyme system.
Elliott WJ, Morrison AR, Sprecher H, Needleman P.
Mead (5,8,11-icosatrienoic) acid was found to be metabolized by the
cyclooxygenase enzyme system of ram seminal vesicle microsomes in a
calcium-dependent manner. Although the enzyme converted Mead acid to
products more slowly and less completely than the isomeric 8,11,14-
icosatrienoic acid, both oxidations were inhibitable by indomethacin.
Experiments using purified cyclooxygenase confirmed the participation
of this enzyme system in the calcium-dependent oxidation. The products
of the oxidation were separated by high performance liquid
chromatography and analyzed by ultraviolet and gas chromatography-mass
spectrometry. The spectra obtained were consistent with the products
having the structures 13-hydroxy-5,8,11-icosatrienoate (the major
product), 11-hydroxy-5,8,12-icosatrienoate, 9-hydroxy-5,7,11-
icosatrienoate, and two isomeric 8,11-dihydroxy-5,9,12-
icosatrienoates. No prostaglandin-like, cyclized products could be
identified. This report is only the second to illustrate a calcium-
dependent oxidation of a polyunsaturated fatty acid by a
cyclooxygenase enzyme system and further extends the metabolic
potential of Mead acid.
PMID: 3084488
J Chromatogr B Biomed Sci Appl. 1997 Mar 7;690(1-2):332-7.
Oxygenation of 5,8,11-eicosatrienoic acid by prostaglandin H
synthase-2 of ovine placental cotyledons: isolation of 13-
hydroxy-5,8,11-eicosatrienoic and 11-hydroxy-5,8,12-eicosatrienoic
acids.
Oliw EH, Hornsten L, Sprecher H.
Department of Pharmaceutical Biosciences. Uppsala University
Biomedical Center.
Prostaglandin H synthase-1 of ram vesicular glands metabolises 5,8,11-
eicosatrienoic (Mead) acid to 13R-hydroxy-5,8,11-eicosatrienoic and to
11R-hydroxy-5,8,12-eicosatrienoic in a 5:1 ratio. We wanted to
determine the metabolism of this fatty acid by prostaglandin H
synthase-2. Western blot showed that microsomes of sheep and rabbit
placental cotyledons contained prostaglandin H synthase-2, while
prostaglandin H synthase-1 could not be detected. Microsomes of sheep
cotyledons metabolised [1-14C]5,8,11-eicosatrienoic acid to many polar
metabolites and diclofenac (0.05 mM) inhibited the biosynthesis. The
two major metabolites were identified as 13-hydroxy-5,8,11-
eicosatrienoic and 11-hydroxy-5,8,12-eicosatrienoic acids. They were
formed in a ratio of 3:2, which was not changed by aspirin (2 mM).
5,8,11-Eicosatrienoic acid is likely oxygenated by removal of the pro-
S hydrogen at C-13 and insertion of molecular oxygen at either C-13 or
C-11, which is followed by reduction of the peroxy derivatives to 13-
hydroxy-5,8,11-eicosatrienoic and 11-hydroxy-5,8,12-eicosatrienoic
acids, respectively. Prostaglandin H synthase-1 and -2 oxygenate
5,8,11-eicosatrienoic acid only slowly compared with arachidonic acid.
PMID: 9106061
2) 5-LOX leukotriene metabolites like LTB4:
J Biol Chem. 1983 Nov 10;258(21):12797-800.
Products derived from 5,8,11-eicosatrienoic acid by the 5-lipoxygenase-
leukotriene pathway.
Jakschik BA, Morrison AR, Sprecher H.
Analysis of products derived from 5,8,11-eicosatrienoic acid via the 5-
lipoxygenase-leukotriene pathway showed that this fatty acid is
readily converted to leukotriene (LT)A3. When 10,000 X g supernatant
from rat basophilic leukemia cell homogenates was incubated with 30
microM fatty acid, 5,8,11-eicosatrienoic acid produced 6.2 +/- 1.1
nmol of LTA3 and arachidonic acid 15.5 +/- 1.9 nmol of LTA4 (n = 4).
However, only insignificant amounts of LTB3 were formed (0.15 +/- 0.04
nmol of LTB3 and 4.2 +/- 0.4 nmol of LTB4, n = 4). These data indicate
that the LTA-hydrolase requires not only the three double bonds of the
triene but also the double bond at C-14 to efficiently convert LTA to
LTB. These findings have significant implications for essential fatty
acid deficiency.
J Biol Chem. 1984 Oct 10;259(19):11784-9.
Leukotriene B formation by neutrophils from essential fatty acid-
deficient rats.
Stenson WF, Prescott SM, Sprecher H.
Analysis of neutrophil phospholipids from rats fed an essential fatty
acid-deficient diet revealed a 33% reduction in arachidonate and a 90%
reduction in linoleate compared to neutrophil phospholipids of rats
fed a normal diet. The neutrophil phospholipids from rats fed the
essential fatty acid-deficient diet also contained significant amounts
of 5,8,11-eicosatrienoate, a fatty acid not found in the neutrophils
of rats fed a normal diet. Analysis of the production of leukotrienes
of the B series by ionophore-stimulated neutrophils from rats fed an
essential fatty acid-deficient diet revealed a 87% reduction in
leukotriene B4 compared to neutrophils from rats fed a normal diet
even though the arachidonate content was reduced by only 34%.
Essential fatty acid-deficient neutrophils converted endogenous 5,8,11-
eicosatrienoic acid to leukotriene A3 and its nonenzymatic degradation
products, but little or no leukotriene B3 was formed. Neutrophils from
rats fed a normal diet incubated with ionophore and exogenous 5,8,11-
eicosatrienoate also produced leukotriene A3 and its nonenzymatic
degradation products but little or no leukotriene B3. Exogenous 5,8,11-
eicosatrienoate incubated with ionophore-stimulated normal neutrophils
caused a dose-dependent inhibition of leukotriene A hydrolase
resulting in diminished production of leukotriene B4 from endogenous
arachidonate. Assays of leukotriene A hydrolase in the 10,000 X g
supernatant fraction of a homogenate of RBL-1 cells revealed that a
lipoxygenase metabolite of 5,8,11-eicosatrienoate rather than 5,8,11-
eicosatrienoate itself is the inhibitor of leukotriene A hydrolase.
Thus the finding that leukotriene B4 production by neutrophils from
essential fatty acid-deficient rats is diminished out of proportion to
the decrease in arachidonate content appears to be due to inhibition
of leukotriene A hydrolase by a lipoxygenase metabolite.
3) P450 epoxygenase HETE-like metabolites:
Arch Biochem Biophys. 1993 Sep;305(2):288-97.
Oxygenation of 5,8,11-eicosatrienoic acid by prostaglandin
endoperoxide synthase and by cytochrome P450 monooxygenase: structure
and mechanism of formation of major metabolites.
Oliw EH, Hornsten L, Sprecher H, Hamberg M.
Department of Pharmaceutical Biosciences, Uppsala University
Biomedical Center, Sweden.
Incubation of 5,8,11-[1-14C]eicosatrienoic acid with prostaglandin
endoperoxide synthase of ram vesicular gland microsomes led to
formation of a number of polar metabolites. Four major compounds were
characterized by chemical and physical methods and found to be: (11R)-
hydroxy-5,8,12-eicosatrienoic acid, 8,9,11-trihydroxy-5,12-
eicosadienoic acid (two diastereoisomers), and 8,9-epoxy-11-
hydroxy-5,12-eicosadienoic acid. On the basis of previous studies on
the mechanism of prostaglandin biosynthesis it seemed likely that the
initial step of conversion of 5,8,11-eicosatrienoic acid consisted of
removal of the pro-S hydrogen from C-13. The resulting carbon-centered
radical was apparently attacked by dioxygen at C-13 to provide a (13R)-
(hydro)peroxy derivative, which served as the precursor of (13R)-
hydroxyeicosatrienoic acid. Alternatively, attack by dioxygen occurred
at C-11 to produce an (11R)-peroxy radical. This intermediate was
further converted to (11R)-hydroxyeicosatrienoic acid by reduction,
into two 8,9,11-trihydroxy-5,12-eicosadienoic acids by successive
cyclization, oxygenation, and reduction, and into the epoxy-hydroxy
acid by cyclization and intramolecular epoxidation. The relative
abundance of (13R)-hydroxy-5,8,11-eicosatrienoic acid, (11R)-
hydroxy-5,8,12-eicosatrienoic acid, and the epoxy alcohol plus the two
8,9,11-triols was 51, 9, and 40%, respectively. The oxygenation at
C-13 and C-11 of 5,8,11-eicosatrienoic acid was inhibited by 90% in
the presence of diclofenac, an inhibitor of prostaglandin endoperoxide
synthase. The two diastereomeric 8,9,11-trihydroxy acids and the epoxy-
hydroxy acid are novel oxylipins and their formation provides
independent chemical evidence for the existence of an 11-peroxy
radical intermediate in prostaglandin endoperoxide synthase catalysis.
Oxygenation of 5,8,11-eicosatrienoic acid by cytochrome P450 from
liver microsomes of cynomolgus monkeys and phenobarbital-treated rats
was also investigated. The metabolites formed included 19- and 20-
hydroxyeicosatrienoic acid, 8,9- and 11,12-dihydroxyeicosadienoic
acids (formed by enzymatic hydrolysis of the corresponding epoxides),
and (12R)-hydroxy-5,8,10-hydroxyeicosatrienoic acid.
PMID: 8373167
4) The very long chain PUFAs like DHA for brain, sperm:
Biochim Biophys Acta. 1995 Oct 26;1259(1):82-8.
Studies on the metabolism of [1-14C]5.8.11-eicosatrienoic (Mead) acid
in rat hepatocytes.
Retterstøl K, Woldseth B, Christophersen BO.
Institute of Clinical Biochemistry, University of Oslo,
Rikshospitalet, Norway.
The oxidation, esterification and formation of chain elongated and
desaturated products of [1-14C]5,8,11-eicosatrienoic (Mead) acid was
studied. Liver cells from essentially fatty acid deficient (EFAD) and
control rats were used. The metabolism of [1-14C]20:4, n-6 and
[1-14C]20:5, n-3 were studied under the same experimental conditions.
More 20:3, n-9 than 20:4, n-6 and 20:5, n-3 was oxidised both in EFAD
and control cells. 20:3, n-9 was elongated to [14C]22:3, n-9 in both
cell types and significant amounts of [14C]22:4, n-9 were formed in
EFAD cells. Less 20:3, n-9 was esterified in phospholipids and more in
triacylglycerol than observed with 20:4, n-6 and 20:5, n-3 in both
cell types. 20:3, n-9 was mainly esterified in phosphatidylcholine and
little was esterified in phosphatidylethanolamine compared to 20:4,
n-6 and 20:5, n-3. In comparison, 20:3, n-9 was rather efficiently
esterified in phosphatidylinositol as 18:0-20:3. [14C]22:4, n-9 formed
from 20:3, n-9 in EFAD hepatocytes was esterified in triacylglycerol,
not in phospholipids, unlike [14C]22:5, n-6 and [14C]22:6, n-3 which
were mainly esterified in phospholipids.
PMID: 7492619
Biochim Biophys Acta. 1998 May 20;1392(1):59-72.
A comparative study of the metabolism of n-9, n-6 and n-3 fatty acids
in testicular cells from immature rat.
Retterstøl K, Haugen TB, Woldseth B, Christophersen BO.
Institute of Clinical Biochemistry, National Hospital, University of
Oslo, N-0027 Oslo, Norway.
Dietary 18 and 20-carbon fatty acids of the n-6 and the n-3 families
are metabolized to 22:5,n-6 and 22:6,n-3 by a sequence of specific
desaturases and chain elongation via 24-carbon intermediates. This
pathway is regulated so that more 22:6,n-3 than 22:5,n-6 is found in
the tissues. Rat testis is an exception since 22:5,n-6 is present in
large proportions in this organ. Therefore rat testis appears to be
interesting for studies of the detailed synthesis of 22:5,n-6 compared
with that of 22:6,n-3. By using fresh preparations of rat testicular
cells from 19-day-old rats enriched in Sertoli cells, we compared the
metabolism of 1-14C-labelled n-3, n-6 and n-9 fatty acids. The
testicular cells actively synthesized 22:6,n-3 and 22:5, n-6, but not
22:4,n-9 from the 18 and 20-carbon precursors. Of 200 mol 14C-labelled
C18 and C20 fatty acids added initially, approximately 20-40 mol were
found as 24-carbon intermediates after 24 h of incubation. This
indicates that the balanced capacity of elongation, desaturation and
chain shortening favours the accumulation of 24-carbon intermediates
in these cells. One exception was [1-14C]20:3,n-9 which was
efficiently elongated to 22:3,n-9 but not to C24 fatty acids. Our data
suggests that the poor elongation of n-9 fatty acids from C22- to C24
may be an important hindrance in the synthesis of 22:4,n-9. The
efficient synthesis of 22:5,n-6 may also partly explain why this is
the major 22-carbon fatty acid in rat testis. Copyright 1998 Elsevier
Science B.V. All rights reserved.
PMID: 9593823
Taka
mont...@lycos.com
LOX product that is similar to PGE2, which is a COX-2 product,
correct? I remember a study that found Mead acid is made into mostly
LTA3 - any idea why they didn't talk about this?
Taka
I think they mean functionally similar, not structurally similar.
Besides LTA3, mead acid can be made into LTB3, LTC3, LTD3, LTE3, 5S,
12S-diHETE as well as the 12-OH-20:3(5,8,10) derivative described in
the first study. The enzymes responsible are:
Mead acid -> LTA3: 5-LOX
Mead acid -> 12-OH-20:3(5,8,10): 12-LOX
LTA3 -> LTB3: LTA4H (PMID: 15134534)
LTA3 is apparently made in leukocytes while12-OH-20:3(5,8,10) is made
in platelets.
Taka
mont...@lycos.com
products were LTA3. I don't remember what kinds of cells were used,
but a pubmed search should clear it up (for those interested).
However, the really glaring thing here is that there is a claim that
you can find in textbooks being used today that Mead acid is
insufficient, and a simple animal experiment could be done to
demonstrate that this is not accurate. The M.I.T. experiment in the
1940s were very good - they even noticed how oleic acid was helpful in
the "essential fatty acid" context (rather than omega 3s and/or 6s).