Anti-Inflammatory Effects of Epoxyeicosatrienoic Acids
Epoxyeicosatrienoic acids (EETs) are generated by the activity of both selective and also more general cytochrome p450 (CYP) enzymes on arachidonic acid and inactivated largely by soluble epoxide hydrolase (sEH), which converts them to their corresponding dihydroxyeicosatrienoic acids (DHETs). EETs have been shown to have a diverse range of effects on the vasculature including relaxation of vascular tone, cellular proliferation, and angiogenesis as well as the migration of smooth muscle cells. This paper will highlight the growing evidence that EETs also mediate a number of anti-inflammatory effects in the cardiovascular system. In particular, numerous studies have demonstrated that potentiation of EET activity using different methods can inhibit inflammatory gene expression and signalling pathways in endothelial cells and monocytes and in models of cardiovascular diseases. The mechanisms by which EETs mediate their effects are largely unknown but may include direct binding to peroxisome proliferator-activated receptors (PPARs), G-protein coupled receptors (GPCRs), or transient receptor potential (TRP) channels, which initiate anti-inflammatory signalling cascades.
Hindawi Publishing Corporation
International Journal of Vascular Medicine
Volume 2012, Article ID 605101, 7 pages
Review A rticle
Anti-Inﬂammatory Effects of Epoxyeicosatrienoic Acids
Scott J. Thomson, Ara Askari, and David Bishop-Bailey
Translational Medicine and Therapeutics, William Harvey Research Institute, Barts and The London School of Medicine and Dentistry,
Queen Mary University of London, Charterhouse Square, London EC1M 6BQ, UK
Correspondence should be addressed to Scott J. Thomson, firstname.lastname@example.org
Received 30 May 2012; Accepted 20 June 2012
Academic Editor: Ken-ichi Aihara
Copyright © 2012 Scott J. Thomson et al. This is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly
Epoxyeicosatrienoic acids (EETs) are generated by the activity of both selective and also more general cytochrome p450
(CYP) enzymes on arachidonic acid and inactivated largely by soluble epoxide hydrolase (sEH), which converts them to their
corresponding dihydroxyeicosatrienoic acids (DHETs). EETs have been shown to have a diverse range of eﬀects on the vasculature
including relaxation of vascular tone, cellular proliferation, and angiogenesis as well as the migration of smooth muscle cells. This
paper will highlight the growing evidence that EETs also mediate a number of anti-inﬂammatory eﬀects in the cardiovascular
system. In par ticular, numerous studies have demonstrated t hat potentiation of EET activity using diﬀerent methods can inhibit
inﬂammatory gene expression and signalling pathways in endothelial cells and monocytes and in models of cardiovascular
diseases. The mechanisms by which EETs mediate their eﬀects are largely unknown but may include direct binding to peroxisome
proliferator-activated receptors (PPARs), G-protein coupled receptors (GPCRs), or transient receptor potential (TRP) channels,
which initiate anti-inﬂammatory signalling cascades.
Cardiovascular diseases such as atherosclerosis have a strong
inﬂammatory component. Inﬂammation in the vascular
wall may be initiated by endothelial dysfunction and
the accumulation of toxic oxidised circulating lipids .
Inﬂammatory mediators such as TNFα and IL-1β secreted,
which induces the upregulation of cell adhesion molecules,
facilitates leukocyte recruitment in to the vascular wall [2, 3]
and stimulates vascular smooth muscle cell migration and
proliferation . Circulating monocytes not only respond
to inﬂammatory stimuli by producing large amounts of
inﬂammatory mediators but they are also crucial for eﬀective
activation of lymphocytes and adaptive immunity. The hall-
mark of advanced unstable atherosclerotic lesions is that they
are monocyte/macrophage rich and highly inﬂammatory.
Inﬂammatory responses are normally promptly termi-
nated since excessive or prolonged inﬂammation can lead
to chronic pathological conditions such as cardiovascular
diseases, Crohn’s disease, rheumatoid ar thritis, or cancer.
Although there have been many new treatments recently
developed to combat inﬂammatory diseases, some of these
treatments are either very expensive and/or not eﬀective
in subsets of patients. Therefore, it is important to con-
tinue to investigate mechanisms that regulate inﬂammatory
responses as they may open up novel therapeutic targets.
There is a growing list of evidence that the epoxygenase
pathway of arachidonic acid metabolism, which generates
epoxyeicosatrienoic acids (EETs), exerts anti-inﬂammatory
eﬀects that may be harnessed to treat disease. This paper
will summarise that evidence and highlight outstanding
questions that remain to be answered.
2. Overview of the Epoxygenase Pathway of
Arachidonic Acid Metabolism
Arachidonic acid is an omega-6 polyunsaturated long chain
fatty acid that contains 20 carbon atoms and four cis-
double bonds and possesses a carboxyl group and a methyl
group at respective ends of the molecule. The double bonds
are located between carbons 5-6, 8-9, 11-12, and 14-15
relative to the carboxyl group. Therefore, its chemical name
is all-cis-5,8,11,14-eicosatetraenoic acid and its lipid name
2 International Journal of Vascular Medicine
is 20 : 4 (n-6). The cis-conﬁguration of the four double
bonds causes the arachidonic acid backbone to signiﬁcantly
bend. In contrast, double bonds in the trans-conﬁguration
or saturated arachidonic acid result in structurally unbent or
Experiments performed more than 30 years ago showed
that incubations of radio-labelled arachidonic acid with
microsomal preparations derived from a variety of tissues
including liver [5, 6], kidney , hypothalamus , and
anterior pituitary  resulted in the for m ation of EETs.
This “epoxygenase” reaction required cytochrome p450
(CYP) enzymes and utilised NADPH and oxygen in a 1 : 1
stoichiometric ratio . One atom of molecular oxygen
is incorporated into one of the four double bonds of
arachidonic acid retaining the cis-geometry and yielding
four potential EETs, that is, 5,6-EET, 8,9-EET, 11,12-EET,
or 14,15-EET, respectively. Furthermore, each EET can be
present in either the S/R or R/S stereoconﬁguration, thus
eight potential EETs can be formed.
2.1. Epoxygenation of Arachidonic Acid Performed by Spe-
ciﬁc CYPs. CYP enzymes catalyze the oxidation of organic
substances, as well as xenobiotics. Altogether, 57 putative
CYP genes have been identiﬁed in man (by comparison
mice have 103 and rat 89 CYP, resp.) that are divided into
15 subfamilies . Attempts have been made to classify
human CYP genes by substrate; however, a more systematic
nomenclature is generally used since the true physiological
roles of many of these genes are still unknown . To
date, at least 12 human CYP genes have been reported to
possess epoxygenase activity, although most studies have
been focussed on the CYP2C and CYP2J families, which are
considered the major epoxygenase enzymes.
2.2. CYP2C. One of the earliest studies using recombinant
human CYP compared the metabolic proﬁles of the CYP2C8
and CYP2C9 enzymes , which are 77% identical at the
amino acid level. Despite their high similarity, CYP2C8 and
CYP2C9 exhibit both regio- and stereoselective diﬀerences
in their epoxygenation of arachidonic acid. For instance,
CYP2C8 produced only 14,15-EET and 11,12-EET at a
1.25 : 1 ratio, which represented 68% of the total metabolites
measured. By contrast, CYP2C9 produced 14,15-EET 11,12-
EET and 8,9-EET at a ratio of 2.3 : 1 : 0.5, which represented
69% of total metabolites. Furthermore, with respect to stere-
oselectivity, CYP2C8 was 81% selective for the 11(R),12(S)-
EET conﬁguration, whereas CYP2C9 was 70% selective for
the 11(S),12(R)-EET conﬁguration . These CYP enzymes
also carry out other reactions including allylic hydroxylation
on arachidonic acid and other fatty acids.
2.3. CYP2J2. Epoxygenase activity of human CYP2J2 was
ﬁrst demonstrated by the Zeldin lab, who initially cloned
and characterised the gene . Recombinant CYP2J2
metabolised arachidonic acid to all four potential epoxy-
genase products, with 14,15-EET being the predominant
metabolite formed. CYP2J2 was found to be highly expressed
in the heart, and EETs were produced in similar proportions
as recombinant CYP2J2 suggesting that CYP2J2 played a
major role in EET generation in the heart in vivo .
CYP2J2 expression is also seen in kidney, liver and muscle
tissues , and, to a lesser extent, in the gut .
2.4. Other CYPs. A comprehensive comparison study by
Rifkind and colleagues examined the epoxygenase activity of
a panel of 10 CYP proteins by overexpressing them in HepG2
cells and measuring metabolic products. CYP 2C8, 2C9,
1A2, and 2E1 principally produced epoxygenase products. By
contrast, CYP2D6 was inactive, while CYPs 2A6, 3A3, 3A4,
and 3A5 had minimal epoxygenase activity . CYP3A4
has also been shown to make the epoxygenase products 8,9-
EET, 11,12-EET, and 14,15-EET, respectively, in several breast
cancer cell lines . Other CYPs that have been shown
to possess epoxygenase activity include CYP1A, CYP2B1
and CYP2B2  and CYP2B12 , CYP2C8, CYP2C9,
CYP2D18 , CYP2N1 and CYP2N2 , and rat CYP4A2
and 4A3 . The full extent of the epoxygenase activity
of these enzymes and the physiological consequences of any
activity is, however, poorly understood.
3. Soluble Epoxide Hydrolase
Once formed, EETs are unstable because the y are rapidly
metabolised. The main catabolic pathway is the conversion of
EETs into dihydroxyeicosatrienoic acid (DHETs), catalysed
by soluble epoxide hydrolase (sEH) . DHETs are gen-
erally considered to be less active; however, they have been
shown to exert vasodilatory eﬀects on coronary arteries .
DHETS are far more polar than their corresponding EETs
and quickly diﬀuse out of tissues as the 1, diols or conjugates
of them. Other pathways of EET metabolism include chain
elongation, β-oxidation, and ω-oxidation . 5,6 EET and
8,9 EET are substrates for COX enzymes  and can also be
incorporated into membrane phospholipids. DHETs have a
lower binding aﬃnity for phospholipids which may account
for its relatively increased plasma levels .
Recently, the damaging cardiovascular risk factor homo-
cysteine has been shown to upregulate sEH in endothelial
cells and promote a proinﬂammatory environment . In
contrast, elevating the levels of endogenous CYP products by
removing (sEH knockout mice) or inhibiting soluble epoxide
hydrolase (sEH-1) has been shown to reduce neointima for-
mation , atherosclerosis and abdominal aortic aneurysm
development, dyslipidaemia in hyperlipidaemic mice ,
and reduce hypertension  and diabetes indiﬀerent
mouse models. A number of sEH inhibitors have now been
developed and are moving towards clinical trials for a variety
of disorders related to cardiovascular disease.
4. Epoxygenases in Vascular and
CYP2C mediated generation of 11,12 EET has also been
documented in porcine coronary arteries , and CYP2C
enzymes have been found expressed in endothelial cells ,
International Journal of Vascular Medicine 3
and in primary human monocytes and M1 (CYP2C8) and
M2 macrophages (CYP2C8 and CYP2C9) .
CYP2J2 immunoreactivity is seen in the endothelial and
smooth muscle cell layers of human coronary arteries , as
well as in the human monocytic cell lines THP-1 and U937,
primary monocytes and M1 and M2 macrophages ,
and the endothelial cell line EA hy.926s . Interestingly,
neither CYP2J2 nor CYP2C8 mRNA expression was detected
in human polymorphonuclear cells . More recently, the
increased risk of coronary artery disease was shown to be
associated with a polymorphism in the promoter of CYP2J2
gene in some populations, which decreases the expression of
the enzyme .
5. Epoxygenases and EETs
EETs have been shown to exert multiple biological eﬀects
on the vasculature including proproliferation and angio-
genic eﬀects . EETs have also been hypothesized as
endothelium-derived hyperpolarizing factors, as they hyper-
polarize and relax vascular smooth muscle cells by activat-
ing calcium-activated potassium channels . However,
a number of the anti-inﬂammator y activities of EETs on
inﬂammatory cells, as discussed below, appear independent
of any cellular hyper polarisation .
5.1. Endothelial Cells. Overexpression of CYP2J2 in human
and bovine endothelial cells inhibits TNFα-induced
VCAM-1  and VCAM-1 promoter activity in reporter
assays . Treatment with the epoxygenase inhibitor
SKF525A reversed the eﬀects of CYP2J2 overexpression on
VCAM-1 promoter activity . Exogenous EETs also exert
the same eﬀects as CYP2J2 overexpression, although diﬀerent
EETs can have diﬀerent selectivities. In human endothelial
cells, 11,12-EET signiﬁcantly inhibited VCAM-1 expression
in response to TNFα,IL-1α, or LPS. By contrast, 14,15-EET
had negligible eﬀect, while 5,6-EET, 8,9-EET, and 11,12-
DHET all inhibited to varying degrees but to a lesser extent
than 11,12-EET. 11,12-EET also inhibited TNFα-induced
E-selectin and ICAM-1 expression . Mice engineered
to overexpress the human epoxygenase genes CYP2J2 or
CYP2C8, respectively, were generated to investigate their
roles in endothelial cells. Primary pulmonary endothelial
cells derived from these mice showed reduced levels of LPS-
induced adhesion molecule and chemokine gene expression.
Furthermore, these anti-inﬂammatory eﬀects were inhibited
by treatment with the epoxygenase inhibitor MS-PPOH and
a putative EET receptor antagonist 14,15-EEZE .
5.2. Monocytic Cells. Similar to endothelial cells, EET activity
has also been shown to antagonise inﬂammatory signals in
monocytic cells. Phorbol ester treatment of THP-1 led to
a 4-fold increase in CYP2J2 expression between 3–7 days
after stimulation, suggesting that endogenous expression
of CYP2J2 may regulate inﬂammatory responses in these
cells . Addition of 8,9-EET or 11,12-EET inhibited
basal TNF secretion from THP1 cells by about 90% and
40%, respect ively . Similarly, the epoxygenase inhibitor
SKF525A led to a concentration-dependent superinduc tion
of LPS-induced PGE
in rat monocytes and COX-2 in mouse
and human monocytes . Consistent with these ﬁnd-
ings, exogenous 11,12-EET dose dependently inhibited LPS-
and attenuated SKF-mediated superinduc-
tion. 11,12-EET also inhibited LPS-induced COX-2 activity
and expression . EETs can, therefore, both compete with
arachidonic acid for the binding site in COX enzymes as
well as inhibit the inﬂammation induced induction of COX-
2 expression. A study found that EETs were detected in
human peritoneal macrophages under basal conditions, but
not following zymosan treatment, which caused a shift to
prostaglandin synthesis .
5.3. Leukocyte Endothelial Cell Interactions. Several studies
have demonstrated that EETs can regulate functional inter-
action between leukocytes and endothelial cells. Treatment
of endothelial cells with 14,15-EET signiﬁcantly enhanced
attachment of the monocytic cell line U937 [ 43]. Pretreat-
ment of endothelial cells with EETs alone or in combi-
nation with PMA had neglig ible eﬀects on adherence of
PMNs. However, cotreatment of EETs and PMA led to a
concentration-dependent decrease in adherence of PMNs
when cocultured with endothelial cells . 11,12-EET, but
not 14,15-EET, was shown to inhibit adherence of monocytic
cells in an ex vivo model. Mice were treated with TNFα
alone or in combination with either 11,12-EET or 14,15-EET,
and carotid arteries were remove d and incubated with U937
cells. The l evel of inhibition of adherent cells was comparable
to that of treatment with a blocking VCAM-1 antibody
. PBMCs derived from mice systemically overexpressing
human CYP2J2 via in vivo gene delivery were signiﬁcantly
less adherent to TNFα-treated HUVECs compared to control
5.4. In Vivo Models. There have been conﬂicting reports
on the eﬀects of EETs i n acute models of inﬂammation in
vivo. Rats injected with TNFα showed elevated plasma levels
of adhesion molecules and inﬂammatory cytokines, and
decreased levels of the anti-inﬂammatory mediator IL-10.
However, these eﬀects were sig niﬁcantly reduced by systemic
overexpression of human CYP2J2 , suggesting that EETs
act as anti-inﬂammatory mediators. Similarly, TNFα-treated
human bronchi also showed reduced inﬂammation when
treated with 14,15-EET . LPS responses of wild-ty pe
mice have also been compared to sEH
−/− null mice or mice
that had endothelial-speciﬁc overexpression of the human
CYP2J2 or CYP2C8. All three genetically modiﬁed mice
had reduced levels of inﬂammatory gene expression and
neutrophil recruitment in the lung following LPS injection.
Moreover, these eﬀects correlated with decreased ac tivation
of the key transcription factor NF-κB. By contrast,
another study found that to sEH
−/− null mice were not
protected from LPS-induced inﬂammatory gene expression
or neutrophil recruitment in the liver, and that treatment
with the sEH inhibitor AUDA also had minimal eﬀect liver
inﬂammation, despite higher levels of endogenous EETs .
4 International Journal of Vascular Medicine
This suggests that either the eﬀects of EETs are organ speciﬁc,
or that liver is more susceptible to endotoxin shock.
6. Mechanisms of EET Action
6.1. NF-κB Inhibition. The mechanisms by which EETs
mediate their anti-inﬂammatory eﬀects remain ill-deﬁned,
but there are several reports that they can inhibit activation
of NF-κB, a key transcription factor for inﬂammatory gene
induction. In mammals NF-κB comprises ﬁve subunits, with
the RelA (p65) subunit being expressed in most cell types.
Under basal conditions, NF-κB dimers are localised in the
cytoplasm due to interactions with IκB (inhibitor of NF-
κB) proteins. Signalling cascades induced by inﬂammator y
descend on the IKK (inhibitor of NF-κB kinase) complex,
which phosphorylates IκB. This tags IκBforsubsequent
ubiquitination and degradation by the proteosome, which, in
turn, facilitates NF-κB nuclear t ranslocation where it binds
to its cognate binding elements to activate transcription
11,12-EET inhibits NF-κBreporteractivityinboth
HEK293 cells  a nd human endothelial cells fol-
lowing stimulation. Furthermore, 11,12-EET also inhibited
TNFα-induced RelA nuclear translocation, IκBα degrada-
tion, and IKKα activity, respectively , indicating that
EET-mediated inhibition of NF-κB occurs upstream of IKK.
Interestingly, 14,15-EET was also shown to inhibit the
TNFα-induced degradation of IκBα in primary human lung
tissue buthadnoeﬀect on NF-κBreporteractivity
in HEK293s, suggesting that 14,15-EET may act in a cell
type-speciﬁc manner. Similarly, 8,9-EET and 11,12-EET
inhibited NF-κB reporter gene activity in HEK293 cells .
In contrast to CYP2J2, CYP2C9 increased NF-κBactivity
in human vascular endothelium via sup eroxide generation,
potentially giving this CYP a proinﬂammatory proﬁle .
6.2. STAT3. EETs can also activate STAT3 in human breast
cancer cell lines, with 14,15-EET promoting STAT3 tyrosine-
705 phosphorylation and nuclear translocation . Acti-
vation of STAT3 was shown to be dependent on cell
proliferation, which led the authors to conclude that 14,15-
EET may be involved in an autocrine/paracrine pathway
driving cell growth. Interestingly, the anti-inﬂammatory
eﬀects of IL-10 in macrophages are also dependent on STAT3
tyrosine-705 phosphorylation . Taken together, these
results suggest that the anti-inﬂammatory eﬀects of EETs
may be mediated by activation of STAT3, in addition to the
inhibition of NF-κB.
6.3. EETs as PPAR Agonists. PPARs are a subfamily of the
nuclear receptor superfamily that comprises three ligand-
activated tr anscription factors: PPARα (NR1C1), PPARβ/δ
(NR1C2), and PPARγ (NR1C3). Upon ligand binding, they
form heterodimers with the retinoid X receptor and bind to
speciﬁc response elements in gene promoters to upregulate
gene transcription . PPARs have been show n to regulate
diverse physiological processes such a s fatty acid and glucose
metabolism, angiogenesis, and cellular proliferation and
diﬀerentiation, in addition to inﬂammation. PPAR ligands
include a variety of fatty acids, and there has been recent
evidence that metabolites of the epoxygenase pathway can
activate PPAR receptors.
The omega -alcohol of 14,15-EET, 20,14,15-HEET, or a
1 : 4 mixture of the omega-alcohols of 8,9- and 11,12-EETs
activated human and mouse PPARα in transient transfection
assays, suggesting a role for them as endogenous ligands
for these orphan nuclear receptors . Overexpression of
human CYP2J2 in HEK293 cells resulted in a synergistic
activation of PPARα,-β/δ and, -γ reporter gene activity .
8,9-EET and 11,12-EET, but not 14,15-EET, (in contrast to
its hydroxy metabolite 20,14,15-HEET) were able to induce
PPARα reporter activity . Furthermore, IL-1β-induced
NF-κB reporter ac tivity and COX-2 mRNA induction in
HEK293 cells was signiﬁcantly inhibited cells expressing of
CYP2J2 and PPARα.
Competition and direct binding assays subsequently
revealed that EETs bind to the ligand-binding domain of
PPARγ with K(d) in the μM range. In the presence of the
sEH inhibitor AUDA, EETs increased PPARγ transcription
activity in endothelial cells and 3T3-L1 preadipocytes. In
endothelial cells, AUDA enhanced, but overexpression of
sEH reduced laminar ﬂow-induced PPARγ activity, EET
generation, and the inhibition of VCAM-1 expression .
PPARs, therefore, represent a viable receptor target for the
anti-inﬂammatory eﬀects of EETs. However, it should be
noted that AUDA may exert multiple eﬀects in addition to
sEH inhibition. It has b een shown to act both as a PPAR
agonist  and a EET mimetic ; therefore, results using
AUDA should be cautiously interpreted.
6.4. GPCRs. ForsometimeithasbeensuggestedthatEETs
might mediate many of their eﬀects v ia binding to a putative
G-protein coupled receptor(s) (GPCRs). For example, 11,12-
EET produced a 0.5- to 10-fold increase in the activity of the
KCa channels in smooth muscle cells derived from bovine
coronary arteries, which was dependent on the presence of
GTP . Furthermore, blocking antibodies against GSα,
but not Gβγ or anti-Giα, were able to inhibit the activation
induced by 11,12-EET . Using radio-ligand binding,
14,15-EET has been shown to have a high aﬃ
nity for a
receptor expressed on guinea pig-derived mononuclear cells,
which was purported to be a G-protein coupled receptor
that stimulated cAMP production . This putative GPCR-
cAMP pathway remains elusive but may represent a novel
anti-inﬂammatory pathway by which EETs act.
6.5. TRPV1 and EETs. TRPV4 is a cation channel of the
“transient receptor potential” (TRP) family that functions
as a Ca
entry channel, that is expressed in smooth muscle
cells, endothelial cells, as well as in perivascular nerves.
CYP-dependent generation of 5,6-EET can activate TRPV4
in murine endothelial cells and is a possible contributing
mechanism to the hyperpolarising eﬀects of EETs .
Additionally, 11,12-EET can ac tivate TRPV4 channels in
smooth muscle cells from rat cerebral arteries , and 5,6-
EET and 8,9-EET can a ctivate TRPV4 in human endothelial
International Journal of Vascular Medicine 5
cells . Although activated by EETs, there is little evidence
that ac tivation of TRPV4 is anti-inﬂammatory, though it
does lead to vasodilation via nitric oxide, prostacyclin,
and intermediate/small conductance K+ channel-dependent
pathways, and in vascular smooth muscle, large conductance
K+ channel activation, and hyperpolarization .
7. Summary and Outlook
More than 100 metabolites der ived from arachidonic acid
have been described, with the best characterised com-
ing from the COX and LOX pathways which generate
prostanoids and leukotrienes, respectively . Knowledge
of these pathways has led to several important therapeutic
breakthroughs such as COX inhibitors which are used to
treat pain and inﬂammation and leukotriene antagonists
that have been used to treat asthma. By contrast, much less
is known about the epoxygenase pathway of arachidonic
acid metabolism, although as outlined in this paper, EETs
can exert a number of cardio-protective anti-inﬂammatory
eﬀects on vascular cells such as endothelial cells and
monocytes. These include inhibition of proinﬂammatory
mediators and cell adhesion molecules. Indeed, a recent
study has measured epoxygenase products in atherosclerotic
patients . Compared to healthy volunteers, both obese
and nonobese CAD patients had signiﬁcantly higher plasma
EETs , suggesting that this is a compensation mechanism
to protect against ongoing vascular inﬂammation.
Although elevating epoxygenase products via sEH inhi-
bition have been shown to be beneﬁcial in a wide variety
of animal models of cardiovascular disease, the mecha-
nisms through which these eﬀects are mediated are still
largely unknown, although NF-κBandSTAT3haveboth
been implicated. However, several fundamental question
regarding the role of EETs in vascular inﬂammation remain
unanswered. Firstly, it is clear that CYP epoxygenases can act
on substrates other than arachidonic acid, such as cardio-
protective ﬁsh oils. Eicosapentaenoic acid for example is an
omega-3 long chain fatty acid that diﬀers from arachidonic
acid by the addition of one extra double bond at the 17-
18 carbon position. Epoxygenation of eicosapentaenoic acid
by CYP enzymes generates 17,18-epoxyeicosatrienoic acid,
which has a hyperpolarising eﬀect on bronchial smooth
muscle cells in vitro and in vivo . Similarly, linoleic
acid, which is the major dietary fat, can be epoxygenated
by CYP enzymes resulting in potent metabolites which
are probably proinﬂammatory in nature. However, little is
known regarding the function of many of these alternative
“epoxygenase” metabolites have on the cardiovascular system
during inﬂammation. Secondly, the full range of epoxy-
genase ac tivity by CYP enzymes in healthy and diseased
physiological settings is still not completely understood and
remains a signiﬁcant barrier to progress in the ﬁeld. Thirdly,
and probably most importantly, deﬁnitive identiﬁcation of
a speciﬁc receptor that mediates the activities of EETs
is essential to fully understand the epoxygenase pathway,
and will help to elucidate new therapies for cardiovascular
diseases in the future.
This work was supported by the British Heart Foundation
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