180s Biochemical Society Transactions (1 996) 24
lnternctive effects of diebuy cholesteml and snhrrrted fat on low
density lipopmkin eholes(eml
ANDREW M. SALTER, JENNIFER S. BRUCE, ANDREW J.
BENNETT*, E. HEATHER MANGlAPANE and DAVID A.
WHITE*,
Department of Applied Biochemistry & Food Science,
University of Nottingham, Sutton Bonington Campus,
Loughborough, UK, LEI2 5 R D
*Departmentof Biochemistry,University of Nottingham Medical
School, Nottingham, UK, NG7 2UH
It is well established that dietary saturated fat and, to a lesser
extent, dietary cholesterol can influence plasma concentrations
of low density lipoprotein (LDL) cholesterol [I]. However, it is
not known whether these two dietary factors act independently.
Furthermore, it is clear that not all saturated fatly acids have the
same effect. In the present study we have looked at the effect
of the three main dietary saturated fatly acids, myristic (C14:0),
palmitic (C16:O) and stearic (C18:O) acids, at three different
dietary cholesterol concentrations (0.005,O.12, and 0.24%,w/w),
on LDL metabolism in the male Golden Syrian Hamster. We
have previously shown that these relatively modest dietary
cholesterol concentrations increase plasma LDL concentrations
when incorporated into low fat chow -based diet [2].
Nine groups of six animals were fed semi-synthetic diets
for 28 days containing 20% (w/w) dietary fat. This consisted of
10% triolein and IOYOtrimyristin (diet TM), tripalmitin (diet TP)
or tristearin (diet TS). Cholesterol was dissolved in the melted
fat prior to the mixing of the diets. Animals fed the tristearin rich diet consumed significantly more food than those fed diets
containing the two other fats (p<O.OOI). On the 27th day
animals were fasted overnight and blood was collected the
following morning by cardiac puncture. Livers were flushed
with saline, snap frozen in liquid N, and stored at -40°C until
further analysis. Plasma lipoprotein, hepatic LDL receptor
mRNA and hepatic cholesterol ester were determined as
previously described [3). LDL cholesterol concentrations are
shown in table 1
Table 1 : Plasma LDL cholesterol (mM) concentrations for each
of the arows of animals
dietan, chol.
TM
TP
TS
0.005%
0.75+0.I59
0.78k0.156
0.67M.I74
0.12%
0.99i0.285
0.81*0.075
0.56*0.110
0.24%
0.83M.126
l.15M.242
0.70M.162
Two way analysis of variance (ANOVA) showed that
there was an interactive effect of dietary cholesterol and dietary
fat such that, no significant difference between the fats was seen
at 0 005% cholesterol, TM was significantly different from TS
at 0 12% cholesterol (p<O 01) and TP was significantly different
from TS at 0 24% cholesterol (p<O 01) Thus, the data confirms
that stearic acid does not increase plasma LDL cholesterol like
other saturated fats but also indicates that the effects of myristic
and palmitic acids are dependent on the amount of cholesterol
in the diet
Table 2 shows that hepatic LDL receptor mRNA
concentrations decreased wth increasing dietary cholesterol
concentrations with those in the 0.005% groups being
significantly lower than the 0.12% and 0.24% (both p<O.OOI)
groups and the 0.12% groups lower than the 0.24% groups
(p<O.OI). Surprisingly the LDL receptor mRNA concentrations
were lower in the TS groups than the TM (p<O.Ol) and TP
(p<O.OOI) groups. However this may relate to the higher food
intake, and hence higher cholesterol intake of the TS fed
animals.
Table 2. HeDatic mRNA (attomoledue RNA) concentrations for
the LDL receDtor (r) gene for each aroup of animals.
dietary chol.
TM
TP
TS
0.005%
4.29M.797
4.21*0.462
3.24*0.409
0.12%
3.04M.142
3.26M.416
2.41M.391
0.24%
2.16M.616
2.4W0.442
2.17i0.449
Further analysis of the data showed that in animals fed
the TP diets, but not the TM or TS diets, LDL cholesterol
correlated with hepatic LDLr mRNA concentrations (p<0.05).
Hepatic cholesterol ester stores were found to increase
with increasing cholesterol in the diet but there was a significant
effect of the type of dietary saturated fat (table 3). As such, the
amount of cholesterol stored in the livers of TP -fed animals was
significantly greater than in TM fed animals at 0.24% dietary
cholesterol (p<O.OOI) and TS -fed animals at 0.12% (piO.05)
and 0.24% (p<O.OOI) dietary cholesterol. For all dietary fats
there was a strong correlation between hepatic cholesterol ester
and hepatic LDL receptor mRNA concentrations (p<O.OOl).
Table 3 HeDatic cholesterol ester concentrations !mde wet
weieht) for each aroup of animals
~
dietary chol.
TM
TP
TS
0.005%
4.4*0.99
2.1k0.78
2.8i0.91
0.12%
21.3*3.12
17.8*2.68
32.2*8.71
0.24%
48.1*12.72
27.3*5.68
48.3k11.45
We conclude that feeding modest amounts of cholesterol
to hamsters leads to the accumulation of cholesterol ester in the
liver and that this is associated with a down -regulation of LDL
receptor gene expression. However, only in animals fed palmitic
acid -rich diet was there a correlation between LDL receptor
mRNA concentrations and plasma LDL cholesterol. In animals
fed myristic or stearic acid -rich diets, factors other than hepatic
LDL receptor expression must be important in regulating LDL
cholesterol concentrations.
1) Grundy, S.M. & Denke,M.A. (1990) J Lipid Res 31, 1149-
1172
2) Sessions,V.A. & Salter,A.M. ( 1 994) Biochim Biophys Acta
121 I , 207-214
3) Bennett, A.J., Billett,M.A., Salter,A.M., Mangiapane, E.H.,
Bruce, J.S., Anderton, K.L., Marenah, C.B., Lawson, N. &
White, D.A. (1995) Biochem J, 31 I , 167-173