Clinical Science (1994) 87, 173-178 (Printed in Great Britain)
I73
Complex modulation of cytokine induction by endotoxin
and tumour necrosis factor from peritoneal macrophages
of rats by diets containing fats of different saturated,
monounsaturated and polyunsaturated fatty acid
composition
P. S. TAPPIA and R. F. GRIMBLE
Department of Human Nutrition, School of 6iological Sciences. University of Southampton.
Southampton, U.K.
(Received 27 September 1993/21 February 1994; accepted 8 March 1994)
1. Responses to cytokines and other inflammatory
stimuli have been shown to be enhanced by fats rich
in n-6 polyunsaturated fatty acids and suppressed
by fats rich in n - 3 polyunsaturated fatty acids and
oleic acid or poor in n-6 polyunsaturated fatty
acids.
2. Corn oil is rich and coconut oil, olive oil and
butter are poor in n - 6 polyunsaturated fatty acids.
Olive oil and butter are rich in oleic acid. Fish oil is
rich in n - 3 polyunsaturated fatty acids.
3. The present study examines the effects of feeding
standard chow or corn, coconut, fish and olive oils
and butter for 4 and 8 weeks on subsequent cytokine
production by peritoneal macrophages of rats.
4. Tumour necrosis factor production in response to a
lipopolysaccharide stimulus and interleukin-1 and
interleukin-6 production in response to a tumour
necrosis factor challenge were studied.
5. All fats produced a small, but statistically insignificant, reduction in tumour necrosis factor production, which was greatest for olive oil at 8 weeks.
6. After 4 weeks, fish and olive oil significantly
reduced interleukin-1 production. After 8 weeks,
coconut oil suppressed production of the cytokine,
and the inhibitory effect of fish oil was still apparent.
After 8 weeks, corn and olive oil enhanced
interleukin-1 production.
7. After 4 weeks of feeding, fish and olive oil enhanced interleukin-6 production. After 8 weeks, the
enhancement by these fats increased, and corn oil and
butter also enhanced production. Coconut oil produced no modulatory effect.
8. Only in the cases of the effect of fish and coconut
oil in interleukin-1 production, corn oil on interleukin1 and interleukind production and olive oil in tumour
necrosis factor production, were the effects of fats on
cytokine production in concordance with their modu~~
~
~
latory effects on responses to cytokines and other
inflammatory agents in v i v a
INTRODUCTION
Cytokines
such
as
interleukin-1
(IL-l),
interleukin-6 (IL-6) and tumour necrosis factor
(TNF) initiate and mediate many of the metabolic
and immunological changes which occur in response
to infection, trauma and chronic inflammatory
disease. The molecules are produced mainly from
macrophages, fibroblasts and endothelial cells. IL-1,
T N F and IL-6 act on a wide range of target tissues
and may bring about effects in a synergistic manner.
Furthermore, IL-1 and T N F can stimulate IL-6
production [l-31.
Although IL-1 and T N F are essential components
of the immune system, they can, when produced in
excessive amounts, or in the wrong context, contribute to the pathology of disease processes [4-61.
Fish oil exerts an anti-inflammatory effect on a
range of diseases in which cytokines play a part.
Symptoms in rheumatoid arthritis, inflammatory
bowel disease and psoriasis are ameliorated by
dietary supplementation with fish oil or eicosapentaenoic acid (EPA) [7-91. Dietary fats may potentially modulate cytokine biology by altering the
sensitivity of cytokine-producing cells to inflammatory stimuli and by changing the sensitivity
of target cells to the actions of cytokines. Consumption of fish oil supplements for a period of 6 or
more weeks will reduce the ability of monocytes,
from healthy subjects, to produce IL-1, IL-6 and
T N F in response to bacterial endotoxin [lo, 111.
The same phenomenon has been observed for IL-1
and T N F production by monocytes from rheumatoid patients [lo]. When palm oil was substituted
~
Key words: cytokine production, dietary fats, interleukin-I, interleukin-6. polyunsaturated fatty acids, n -6, tumour necrosis factor.
Abbreviations: EPA, eicorapentaenoic acid; 11-1, interleukin-I; IL-2, interleukin-2; lL-6. interleukin4 LA, linoleic acid; LPS, lipopolysaccharide; MTl,
3-(4,MimethylthiuoCZ-yl)-Z,Miphenyltetrazolium bromide; PUFA, polyunsaturated fatty acid; TNF. tumour necrosis factor.
Correspondence: Dr P. S. Tappia, Department of Human Nutrition, University of Southampton. Basset Crescent East, Southampton SO16 7PX, U.K.
I74
P. S. Tappia and R. F. Grimble
for 70% of the total dietary fat of a group of healthy
subjects for a 6 week period, a small depression was
found in the production of T N F by whole blood in
response to endotoxin in uitro [12]. A substantial
number of studies on experimental animals has
shown that a wide range of fats may modulate
cytokine-mediated responses to a range of inflammatory stimuli (for reviews see [13-153). In
essence, fats rich in EPA or low in linoleic acid (LA)
exert an anti-inflammatory influence, and fats rich
in LA may exert a pro-inflammatory influence. In
addition, fats rich in oleic acid reduce the responses
of animals to endotoxin and T N F [16, 171. The
present study examines the pro- and antiinflammatory potential of a range of fats on cytokine production from rat peritoneal macrophages in
response to endotoxin and TNF. Macrophages were
derived from rats fed diets containing fats rich in
LA (corn oil), poor in LA (coconut oil and butter),
rich in oleic acid (butter and olive oil) and rich in
EPA (fish oil).
MATERIALS A N D METHODS
Table I. Fatty acid composition of diets
Composition (g/kg of diet)
Fatty acid
Diet.. . Chow*
Euttert
Coconut
oilt
Corn
oil?
Fish
oil$
Olive
oilt
40.4
13.4
9.0
2.3
0.4
8.5
6.3
0.2
0.0
6.3
16.1
4.2
8.9
15.7
8.3
0.2
1.6
16.8
11.3
0.0
0.1
15.0
2.7
1.2
74.0
0.0
0.0
0.6
13.4
2.2
0.3
28.7
41.8
1.5
0.0
0.0
0.0
c20.4 (n - 6)
0.2
1.4
3.2
0.4
1.0
7.6
7.1
0.6
1.3
c l Q I (n - 3)
0.0
2.4
7.8
19.5
8.0
1.9
22.3
5.8
1.2
0.0
0.0
cll 6 (o - 3 )
0.0
0.0
Cl1.0
c14.0
c16.0
CI8.0
c16.1 (”-7)
CI8.l ( “ - 9 )
c181(n-6)
CI8 3 (“-3)
0.0
0.0
14.8
0.8
0.0
0.0
0.0
*Special Diet Services technical information.
tComputed from [17a].
$W. Vas Dias. personal communication.
bottomed cages at 22°C on a 12h light/l2 h dark
cycle, with free access to food and water. The fatty
acid composition of the diets is shown in Table 1.
Materials
Naphthol Blue Black, formalin, PBS, SDS, actinomycin D, thioglycollate and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT)
were obtained from Sigma Chemical Co., Poole,
Dorset, U.K. Fungizone, gentamicin, foetal calf
serum, RPMl 1640 medium and Dulbecco’s Minimum Essential Medium were obtained from
Gibco, Paisley, Scotland, U.K. [ 3H]Thymidine was
obtained from ICN Biomedicals Ltd, High Wycombe,
Bucks, U.K.
Animals and diets
Thirty-six weanling male Wistar rats were maintained for either 4 or 8 weeks on a diet composed of
either standard rat chow (23g of fatikg of diet;
Special Diets Services, Witham, Essex, U.K.) or one
of five synthetic diets (lOOg/kg of diet) comprising
of butter fat (Dairy Crest, Surbition, Surrey, U.K.),
coconut oil (Booker Foodstuffs, Downton, Wilts,
U.K.), corn oil (Mazola/CPC, Esher, Surrey, U.K.),
fish oil (MaxEPA; Sevenseas Healthcare, Hull, U.K.)
and olive oil.
In all diets, 10% of the fat was provided as corn
oil to prevent essential fatty acid deficiency. The
diets were otherwise identical and adequate in protein (177g of casein/kg of diet, 285g of starch/kg of
diet), fibre (1OOg of cellulose powder/kg of diet),
vitamins and minerals (50g of vitamin free vitamin
and mineral mixture/kg of diet (Special Diets
Services, supplemented with appropriate levels of
vitamin E to provide 90mg of vitamin E/kg of diet).
Care was taken with respect to storage and allocation of the diets to minimize susceptibility to
oxidation. The animals were housed in wire-
Isolation and cultivation of macrophages
Peritoneal macrophage collection was performed
by a modification of the method of Castro and
Lefkowitz [18]. Thioglycollate broth ( 1 ml) was injected intraperitoneally into male Wistar rats. After
a period of 96 h, animals were killed by cervical
dislocation and immobilized ventral side up.
Approximately 30ml of heparinized PBS was injected into the peritoneum and gently massaged.
The heparinized PBS was withdrawn and centrifuged at 400g,,, for 20min at 4°C. After centrifugation, the pellet was gently resuspended in 25vol. of
RPMl 1640 medium containing 10% (v/v) foetal
calf serum. Macrophages were purified by adherence
to plastic petri dishes by placing the petri dishes
into a humidified incubator for 3 h at 37°C under
5% CO,. After incubation, petri dishes were washed
three times with PBS to remove non-adherent cells
and RPMl 1640 medium was added to achieve a
concentration of 1 x lo6 cells/ml. Either lipopolysaccharide (LPS, to a final concentration of long/
ml) or T N F (to a final concentration of 2.5ng/ml)
was added and the petri dishes were returned to a
humidified incubator at 37°C under 5% CO,. In ‘a
pilot study concentrations of 10 ng and 2.5 ng/ml of
LPS and TNF, respectively, were found to elicit
optimal cytokine production from macrophages derived from chow-fed rats. After 5 h, T N F levels in
culture medium (of macrophages stimulated with
LPS) were measured and petri dishes were returned
for a further 13 h (overnight) incubation. After this
period levels of IL-6 and IL-1 in the culture
medium were determined.
Influence of fats on cytokine production
Assay for TNF in culture medium
T N F levels in supernatants were determined by
employing a modification of the assay described by
Aggarwal et al. [19]. Briefly, 2 x lo4 L929 cells in
0.1 ml of RPMl 1640 [containing 10% (v/v) foetal
calf serum, 1% (v/v) fungizone and 0.4% (v/v) gentamicin] were incubated the day before in a 96-well
flat-bottomed microtitre plate (Nunc). Serial dilutions of test supernatants (0.1 ml) were added to the
plate in the presence of actinomycin D at a final
concentration of 1 pg/ml. Plates were incubated at
37°C for 24h after which cells were stained with
0.1ml of Naphthol Blue Black stain [0.05% NBB,
9% (v/v) acetic acid, 0.1 mol/l sodium acetate] for
30min. Cells were then fixed with 0.1 ml of formalin
fixative [lo% (v/v) formalin, 9% (v/v) acetic acid,
0.1 mol/l sodium acetate] for 15min after which
plates were washed and inverted on to absorbent
paper to dry. Sodium hydroxide (50 mmol/l, 0.15 ml)
was added to each well, and the absorbance at
620nm was measured. One unit of T N F activity
was defined as the amount required to lyse 50% of
the L929 target cells.
Assay for 11-1 in culture medium
The bioassay for IL-1 utilized the ability of this
cytokine to induce interleukin-2 (IL-2) production
by a subclone, NOB-I, of the murine thymoma cellline EL4.6.1. This line produces IL-2 in response to
IL-1, which is measured using CTLL cells (murine
T cell-line). Briefly, IL-1 in supernatants was measured as follows: l x lo5 cells in 0.1 ml of RPMl
1640 medium [supplemented with 10% (v/v) foetal
calf serum, 1% (v/v) fungizone and 0.4% (v/v) gentamicin] were incubated in a 96-well flat-bottomed
microtitre plate, to which was added 0.1 ml of
serially diluted test supernatants, and incubated for
24h at 37°C in a humidified COz incubator. After
this period, 50p1 of the supernatant from each well
was added to a 50pl (5 x lo3 cells) cell suspension of
CTLL cells in RPMl 1640 medium [supplemented
with 10% (v/v) foetal calf serum, 1% (v/v) fungizone
and 0.4% (v/v) gentamicin] already preincubated in
a 96-well flat-bottomed microtitre plate. The plate
was incubated further for 24 h at 37°C in a humidified COz incubator, after which 0.5pCi of
C3H]thymidine was added to each well and the
plates were incubated for 8h. C3H]Thymidine incorporation into CTLL cells was determined by
liquid scintillation counting.
Assay for lL-6 in culture medium
IL-6 concentrations in culture supernatants were
estimated by employing a bioassay based on the
proliferative effect of this cytokine on the IL-6dependent murine hybridoma cell line, B9. Briefly,
3 x lo3 cells in 0.1ml of RPMl 1640 medium
[supplemented with 10% (v/v) foetal calf serum, 1%
(v/v) fungizone and 0.4% (v/v) gentamicin] were
I75
5
=
4
\
M
‘3
Y
F
1
I
0
Butter
Olive oil
Chow
Fish oil
Corn oil Coconut oil
Fig. I. Effect of different dietary fats on macrophage T N F producand 8 weeks
of feeding. Weanling rats
tion after.4 weeks (0)
were maintained on 10% (w/w) fat diets for 4 and 8 weeks. Macrophages
were then harvested and stimulated with endotoxin (IOng/ml) for Sh, after
which TNF in the culture medium was determined. Data are meansfSEM
(m)
incubated in a 96-well flat-bottomed microtitre
plate. To each well, 0.1 ml of serially diluted test
supernatant was added and the plates was incubated for approximately 72 h at 37°C in a humidified 5% CO, incubator. After this incubation, 1Opl
of MTT (5mg/ml in PBS, filter-sterilized and
stored in darkness) was added to each well and
incubated for a further 4.5 h, followed by the addition of 25pl of acid SDS [lo% (w/v) SDS dissolved
in 0.02mol/l HCl] per well and a 1 h incubation in
darkness at room temperature. Absorbance was
recorded at 570 nm.
RESULTS
Fig. 1 shows the effect of 10% fat diets on T N F
production, after an endotoxin challenge, by macrophages derived from animals after 4 and 8 weeks of
feeding. After 4 weeks of feeding T N F production is
reduced in animals consuming all the synthetic diets
containing fat, compared with production from
macrophages derived from chow-fed rats. The same
degree of reduction (approximately 33%) occurred
and there were no differences between fats. However, after feeding the diet containing olive oil for 8
weeks a marked suppression of T N F production
(47%) occurred compared with production by
macrophages derived from chow-fed animals.
Fig. 2 shows the effect of 10% fat diets on IL-6
production by macrophages challenged with TNF,
after rats had been fed the synthetic diets for 4 and
8 weeks. After 4 weeks, differences in responses of
macrophages from rats fed the various fats were
apparent. Cells from animals fed diets containing
fish and olive oil produced significantly more IL-6
in response to T N F than cells derived from animals
fed the other diets. Production by macrophages
from animals fed fish and olive oil was 22% greater
in both instances than from macrophages derived
P. S. Tappia and R. F. Grirnble
I76
**
***
41
I
Chow
Fish oil
Corn oil
Coconut oil
**
***
Butter
Olive oil
*
I
T
1
Fig. 2 Effect of different dietary fats on macrophage 114 production
and 8 weeks (H) of feeding. Weanling rats were
after 4 weeks
maintained on 10% (w/w) fat diets for 4 and 8 weeks. Macrophages were
then harvested and stimulated with recombinant human TNF (2.5ng/ml) for
24h. after which 11-6 in the culture medium was determined. Data are
means+SEM from six experiments with three animals per group.
Values which are statistically significantly different from those for the
corresponding chow-fed group by analysis of variance are indicated:
*P < 0.05, **P < 0.01, ***P <0.001.
(a)
from animals fed chow. However, after 8 weeks,
olive and fish oil exerted a greater stimulatory effect
on IL-6 production than at 4 weeks, and inclusion
of butter and fish oil in the diets also resulted in
greater production of the cytokine than was the case
for cells from chow-fed animals. Relative to production by cells from the latter animals, those from the
groups receiving corn, olive and fish oils and butter
produced loo%, 65%, 58% and 65% greater
amounts of the cytokine in response to TNF, respectively. The changes in production by cells from
animals at 8 weeks, compared with those from
animals at 4 weeks, was a decline of 10% by those
from the chow-fed groups, and increases of 64%,
lo%, 35% and 35% by macrophages from corn, fish
and olive oil and butter groups, respectively. A
decline of 6% occurred in production by cells from
the coconut oil group.
Fig. 3 shows the effect of the various dietary
treatments on TNF-stimulated macrophage IL-1
production after rats had been fed the synthetic
diets for 4 and 8 weeks. After 4 weeks of feeding,
IL-1 production was reduced by all fats, in particular in animals fed fish and olive oil. Significant
reductions of 26% and 16% were caused by the fish
and olive oil, respectively, compared with chow-fed
animals. After 8 weeks of feeding, a similar phenomenon to that which occurred for IL-6 became
evident. Fish oil suppressed IL-1 production by 31%
as compared with chow-fed animals. In animals fed
corn oil enhancement of production occurred. An
elevation of 50% was observed as compared with
values from chow-fed animals and represented an
increase of 27% compared with IL-1 production
after 4 weeks. IL-1 production was also significantly
reduced by 39%. Compared with values from
chow-fed animals, production was 10% greater than
Chow
Fish oil
Corn oil
Coconut oil
Butter
Fig. 3. Effect of different dietary fats on macrophage 11-1production
and 8 weeks ( ) of feeding. Weanling rats were
after 4 weeks (0)
maintained on 10% (w/w) fat diets for 4 and 8 weeks. Macrophages were
than harvested and stimulated with recombinant human TNF (2.5 ng/ml) for
24h, after which 11-1 in the culture medium was determined. Data are
means f SEM from six experiments with three animals per group. Values
which are statistically significantly different from those of the Corresponding
chow-fed group by analysis of variance are indicated: *Pi0.05, **P<O.OI.
that observed after 4 weeks. In the butter-fed animals IL-1 production was further suppressed by
19% compared with values from chow-fed animals.
In animals fed on olive oil for 8 weeks a significant
increase (46%) in IL-1 production was observed,
which represented an increase of 159% compared
with production by cells from animals fed olive oil
for 4 weeks.
DISCUSSION
The pattern of cytokine release from macrophages
and other cells in response to inflammatory stimuli
is complex. Rapid production of IL-1 and T N F is
followed by a relatively slower release of IL-6.
Furthermore, T N F and IL-1 have the capacity to
induce production of each other and of IL-6. In the
present study the final concentration of T N F and
IL-1 in the incubation medium may have arisen in
part because of such a phenomenon. It is clear from
the results of the present study that dietary fats may
modulate these events in a complex manner. The
modulatory effects produced by the various fats
depend upon the length of time that they are fed to
the experimental animals and the fatty acid composition of the dietary fat. During the 8 weeks period
over which the experiment was conducted, the ability of macrophages, derived from animals fed chow,
to produce T N F in response to endotoxin rose by a
small percentage that was statistically nonsignificant. The ability of T N F to induce IL-1 from
these cells rose by a small, but insignificant, extent,
and IL-6 production was unaffected by the age of
the animals. If cytokine production by cells from
chow-fed animals is used as a benchmark, it can be
seen that T N F production in response to endotoxin
is suppressed by all dietary fats after 4 weeks of
Influence of fats on cytokine production
feeding; however, by 8 weeks, only cells from animals fed olive oil remained suppressed. In each case,
however, the suppression caused by dietary fat did
not reach statistical significance. All fats had major
modulatory effects on the ability of T N F to induce
IL-I and IL-6 production. The modulatory effects
varied between fats at 4 and 8 weeks of dietary
exposure and over the time course of the study.
Induction of IL-1 at 4 weeks was suppressed by
fish and olive oil, with non-significant inhibitory
effects being produced by other fats. At 8 weeks,
however, a dichotomy was observed in the effects,
whereby further suppression was caused. Feeding
fish oil and coconut oil produced a major inhibitory
influence. However, corn and olive oil, at this time,
produced a major enhancement of production.
Induction of IL-6 by T N F at 4 weeks was enhanced
by fish and olive oil, whereas corn and coconut oil
and butter were without effects. However, at 8
weeks of feeding, the stimulatory effect of fish oil
and olive oil had increased, and corn oil and butter
now enhanced production. From these patterns of
change, it can be seen that for some fats, such as
corn oil, coconut oil and butter, modulatory effects
are not seen until 8 weeks of exposure to dietary
change. Fish oil, however, produces consistent
effects on IL-1 and 1L-6 production, which increase
in intensity between 4 and 8 weeks of feeding. While
olive oil produces opposite effects on IL-1 at 4 and
8 weeks, it influences IL-6 induction in a stimulatory manner at both time points. Furthermore, the
effect increases in intensity between the two experimental time points. Coconut oil had no influence on
IL-6 induction while affecting that of IL-I. Conversely, butter exerted no major influence on IL-I
production but stimulated that of IL-6. Olive oil
exerted opposing effects on IL-1 and IL-6 induction
at 4 weeks, and fish oil did likewise at the two
experimental time points. While olive oil exerted an
opposing influence on IL-1 and IL-6 after 4 weeks
feeding, at 8 weeks it enhanced production of both
cytokines.
From the complex interplay of fats on the ability
of peritoneal macrophages to produce IL-1 and IL6 in response to T N F stimulation, it can be deduced
thet no single cellular mechanism can explain the
modulatory influence of all fats on cytokine production. In studies by others [lo, 203, changes in
eicosanoid generation and membrane fluidity have
been suggested as possible mechanisms. Studies in
uitro have shown that prostaglandins of the 2- and
3-series suppress and leukotrienes enhance IL- 1
production by macrophages [2l, 223. In the present
study reduced synthesis of leukotriene B, by substitution of EPA into membrane phospholipids
and reduction in arachidonic acid content, respectively, could explain the reductions caused by
fish and coconut oils of IL-1 induction by TNF.
The enhanced production of IL-6 in response to
T N F that is caused by feeding butter, olive oil and
fish oil might be explained by removal of the
177
inhibitory influence of prostaglandin E, by reduction in the arachidonic acid content, or enhancement of the EPA content, of membrane phospholipids. However, the stimulatory influence of
corn oil feeding in IL-6 production clearly cannot
be explained by such a mechanism, unless enhanced
leukotriene production was a consequence of feeding this fat.
The hypothesis that fish oil suppresses IL-1 and
T N F production by reduction in synthesis of leukotrienes of the 4-series is further thrown into doubt
by the studies on T N F and IL-1 in mice fed the fat
for 16 days. Enhanced production of both cytokines
by peritoneal macrophages stimulated with endotoxin was noted. Prostaglandin E, production by
stimulated cells was reduced and release of IL-I and
T N F were negatively correlated with prostaglandin
E, production [21]. However, in studies in which
prostaglandin E, and prostaglandin E, production
by peritoneal macrophages was manipulated by
diets which were enriched by feeding fats that were
either rich in n-3 or n-6 polyunsaturated fatty
acids (PUFAs), both eicosanoids suppressed T N F
production to an equal extent [23].
Studies in animals and humans indicate that fats
rich in PUFAs, and a-tocopherol exert complex
modulatory effects upon immune function. When
mice were fed diets that contained a-tocopherol at
concentrations which are considered adequate for
chow-fed animals, reductions in tissue a-tocopherol
occurred if n-3 and n-6 PUFAs were added to
the diet in concentrations of 50g/kg [24]. These
authors [24] proposed that diets rich in PUFAs
increase the requirement for a-tocopherol. A
number of studies have shown that consumption of
increased levels of the vitamin can enhance immune
function and cytokine production [25]. Thus, reductions in immune function, brought about by
dietary n-3 and n-6 PUFAs, may, in part, be due
to reduced a-tocopherol status. Indeed, in rats fed
diets rich in maize oil, depressed lymphocyte responses to mitogens were restored, in part, by
dietary a-tocopherol supplementation [26].
In the present study, a reduction in tissue concentrations of a-tocopherol in rats fed fish oil, might
play a part in the reduction of IL-1 production in
response to TNF. However, in a study on elderly
subjects, vitamin E supplementation had no effect
on IL-1 production from peripheral blood mononuclear cells while reducing plasma lipid peroxide
concentrations and enhancing IL-2 production from
peripheral blood mononuclear cells in response to a
conconavalin A challenge [27]. In the present study
dietary concentrations were 2-3 times the concentration required by chow-fed rats. While no
measurements of a-tocopherol status were performed it is unlikely that reduced vitamin E status
contributed to the influence of fish oil on IL-6
production and of maize oil on IL-I and IL-6
production as enhanced responses occurred.
Inflammatory responses to infection and trauma
I78
P. S. Tappia and R. F. Grimble
are a consequence of cytokine production. Many
studies have shown that responses to inflammatory
agents are modified by fats. Corn oil enhances and
olive oil and butter suppresses metabolic responses
to endotoxin injection [16]. Fish oil, coconut oil
and butter suppress metabolic effects of T N F [13].
Fish oil reduces the anorexic effects of IL-1 in rats
[28], the anorectic influence of neoplasia in rats
[29] and the febrile response to 1L-1 and burn
injury in guinea-pigs [30, 311. While the results of
the present study demonstrating an inhibitory
influence of olive oil on endotoxin-induced T N F
production of fish and coconut oil on TNF-induced
IL-1 production, and a stimulatory effect of corn oil
on IL-I and IL-6 production, may directly contribute to these observations in uiuo, the stimulatory
effects of all fats except coconut oil in TNF-induced
IL-6 production may not. The overall intensity of
inflammatory responses depends upon the level of
cytokine production as well as the sensitivity of
target tissues to these molecules. Changes in target
tissue sensitivity to the actions of cytokines may
therefore play a significant part in antiinflammatory properties of fish oil, olive oil and
coconut oil demonstrated in the studies in uiuo cited
above.
ACKNOWLEDGMENTS
We are grateful for financial support for these
studies from the Ministry of Agriculture, Fisheries
and Food. We thank Seven Seas Limited, Marfleet,
Hull, for the gift of MaxEPA, and Professor A.
Shenkin, Department of Clinical Biochemistry,
Royal Liverpool University Hospital, for the gift of
IL-Qdependent murine B9 hybridoma cells. We
thank Jane Byers for secretarial assistance.
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