N-3 versus N-3 PUFA dictate blood fats

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Hi All,

The below abstract that is not pdf-available seems

to report that n-3 fatty acids are reported to induce

better blood lipid levels than n-6 fatty acids such as

linoleic acid, which has similar action. Some here

justifiably use psyllium to improve satiation and

blood lipids, I believe. Psyllium was shown in the

Ann Nutr Metabol paper to act better with a diet

in which n-3 fats were predominant. Cholesterol

was added to the diet at two levels.

0.1% cholesterol is about equal to the RDA for

a 2000 calorie/day CR diet?

The abstract does not describe the dietary fat

components, but a reference from the same authors

that is pdf-available from me does describe them.

The details are described at the end of this

post and appear to represent the article of our

greatest possible interest.

Experiments were done in the hamster animal model

system. Rats are the rodents often used to study lipids

in such systems, but hamsters appear to be better in

respect to correlating with human lipidology.

Therefore, between the first abstract on

psyllium and lipids and the paper describing

the diet components, are two pdf-available

to all paper citations and excerpts on the

hamster model system.

Although the Ann Nutr Metab paper is not pdf-available,

the authors had previously used the same animal

model system to study the effects of n-3 and n-6 fatty

acids on cholesterol in the hamster model system

and therefore may be in our interest, as suggested

by the pdf excerpts below at the end of this message.

The largest pdf excerpts for the paper that

may interest us most is at the end of this post.

First, here are the two papers describing the

hamster model system from the paper at the end of

the message. For a comparison before this of rats

and hamster, see:

hamster: A small European rodent (Cricetus frumentarius). It is

remarkable for having a pouch on each side of the jaw, under the

skin, and for its migrations.

A common name used to describe a subfamily of the muridae. Four of

the more common genera are cricetus, cricetulus, mesocricetus, and

phodopus.

All hamsters are seed and plant feeders, store food, hibernate in

winter, and breed throughout the year under laboratory conditions.

rat: One of the several species of small rodents of the genus Mus

and allied genera, larger than mice, that infest houses, stores, and

ships, especially the Norway, or brown, rat (M. andrinus). These

were introduced into Anerica from the Old World.

And, now, the relevance to the human system of hamster,

there are:

26 Spady DK,Dietschy JM:Interaction of dietary

cholesterol and triglycerides in the regulation

of hepatic low density lipoprotein transport in

the hamster.J Clin Invest 1988;81:300 –309.

http://www.pubmedcentral.nih.gov/articlerender.fcgi?

tool=pubmed & pubmedid=2448340

... The hamster has proved to be a good model in which to

study these regulatory mechanisms since its concentration of

plasma LDL-cholesterol responds to changes in dietary lipid

intake in a manner that is essentially identical to that seen in

man (15). Furthermore, the kinetics of LDL-cholesterol pro-duction

and degradation have been worked out in detail in this

species (13) so that it is possible, in quantitative terms, to

identify the reason why a particular dietary or pharmacologi-cal

manipulation results in a change in the steady state plasma

LDL-cholesterol concentration.

... 15. Spady, D. K., and J. M. Dietschy. 1985. Dietary saturated

triacylglycerols suppress hepatic low density lipoprotein receptor

activ-ity

in the hamster. Proc. Natl. Acad. Sci. USA. 82:4526-4530.

http://www.pubmedcentral.nih.gov/picrender.fcgi?

artid=391135 & action=stream & blobtype=pdf

... Selection of the male hamster as

the animal of choice for these studies was dictated by several

recent observations. Rates of cholesterol synthesis in the

whole animal in species such as the rat are exceptionally high

(120 mg/day per kg of body weight), whereas the hamster

and man have much lower rates (9). Of greater importance,

the rate of sterol synthesis in the liver of the hamster is

disproportionately low and in the range found in biopsy

specimens of human liver (9, 10). Because of this very limited

synthetic capacity, the liver of man and, particularly, the

male hamster cannot readily adapt to changes in cholesterol

flux and so alters rates of LDL transport in response to

changes in diet or to a pharmacological challenge (4, 7). Thus,

hamster and man are similar in having significant levels of

circulating LDL-cholesterol, in their intrinsically low rates of

hepatic cholesterol synthesis, in their response to different

diets and drugs, and in the manner in which they handle

biliary sterol secretion (9, 11, 12). ....

Now, here is the Medline abstract for the psyllium and PUFA paper.

Ann Nutr Metab. 2004 Nov 22;48(6):374-380 [Epub ahead of print]

Effects of Psyllium on Plasma Total and Lipoprotein Cholesterol

and Hepatic

Cholesterol in Hamsters Fed n-3 PUFA or n-6 PUFA with High

Cholesterol Levels.

Liu YC, Liu SY, Lin MH.

... n-3 polyunsaturated fatty acids (PUFA) diet ...

n-3 PUFA plus psyllium (8%, wt/wt) diet

combined with variable levels of cholesterol (0, 0.05, 0.1%, wt/wt)

or a

cholesterol-enriched (0.2%, wt/wt) n-3 PUFA or n-6 PUFA diet that

contained

either 8% methyl cellulose or psyllium for 4 weeks. In the n-3 PUFA-

fed

hamsters, we have found that psyllium was able to reduce plasma total

cholesterol and low density lipoprotein (LDL)-cholesterol

significantly when

0.1% cholesterol was added to the diet. In contrast, the effects of

psyllium

were not seen in the n-3 PUFA-fed hamsters without dietary

cholesterol or with

0.05% dietary cholesterol. However, no matter in the presence of

psyllium or

not, the increase of plasma total cholesterol, very-low-density

lipoprotein

(VLDL)-cholesterol, LDL-cholesterol and high-density lipoprotein

(HDL)-cholesterol levels was depend on the content of dietary

cholesterol.

Although the cholesterol diet increased the liver total cholesterol

level, 80 g

psyllium/kg diet resulted in a significantly lower concentration of

liver total

cholesterol in the cholesterol-fed hamsters. In the second

experiment, we have

also found that psyllium feeding lowered significantly plasma total

cholesterol

and VLDL-cholesterol concentrations in hamsters fed n-3 PUFA but not

in those

fed n-6 PUFA. However, the levels of plasma total cholesterol, VLDL-

cholesterol

and LDL-cholesterol levels of the (n-6) PUFA-fed hamsters were

significantly

lower than those in the (n-3) PUFA-fed hamsters in the absence or

presence of

dietary psyllium. Our data also showed that hamsters fed both high-

cholesterol

n-3 PUFA and n-6 PUFA diets had a significant decrease in hepatic

cholesterol

with intake of psyllium. Liver total cholesterol concentrations were

significantly lower in n-3 PUFA-fed hamsters compared with the n-6

PUFA-fed

groups. ...

PMID: 15564767 [PubMed - as supplied by publisher]

Now, here is the longer paper detailing the effect of n-3 PUFA or

n-6 PUFA with various cholesterol levels in hamsters.

What may be in our interest, is that it appeared that in Fig. 1

the weights

of the hamsters were for about 0.04% cholesterol in the diet, not

significantly

38% higher for the n-3 versus n-6 PUFA. In Fig. 2, the plasma

cholesterol was

at 0-0.0.25% cholesterol in the diet significantly greater for the n-

3 PUFA and

for the 0.1 and 0.2% cholesterol diet significantly greater for the n-

6 PUFA.

for Fig. 3, blood LDL levels were in the same pattern as was total

cholesterol

in Fig. 2, but more than the level at 0.2% dietary cholesterol. HDL

was about

40-100% better in its increased level when using n-6 PUFA in the diet.

Ann Nutr Metab. 2004 Sep-Oct;48(5):321-8. Epub 2004 Oct 01.

The amount of dietary cholesterol changes the mode of effects of

(n-3)

polyunsaturated fatty acid on lipoprotein cholesterol in hamsters.

Lin MH, Lu SC, Huang PC, Liu YC, Liu SY.

... polyunsaturated fatty acids (PUFA) ...

cholesterol content (0, 0.025, 0.05, 0.1 and 0.2%, w/w) with either

(n-3) PUFA

(21 g/100 g fatty acids) or (n-6) PUFA (37.4 g/100 g fatty acids) fat

for 6

weeks. In hamsters fed the nonatherogenic diet (0 or 0.025% dietary

cholesterol), very low density lipoprotein (VLDL)-cholesterol levels

in the

(n-3) PUFA group were not significantly different from those in the

(n-6) PUFA

group, and low density lipoprotein (LDL)-cholesterol levels in the (n-

3) PUFA

group were significantly lower than those in the (n-6) PUFA group. In

contrast,

in hamsters fed the atherogenic diet (0.1 or 0.2% dietary

cholesterol), VLDL-

and LDL-cholesterol levels in the (n-3) PUFA group were significantly

higher

than those in the (n-6) PUFA group, in a dose-dependent manner. When

the

hamsters were fed with 0, 0.025, 0.05, 0.1 or 0.2% (w/w) dietary

cholesterol,

high density lipoprotein (HDL) cholesterol concentration was

significantly lower

in the (n-3) PUFA group than those in the (n-6) PUFA group. Hepatic

cholesteryl

esters were significantly lower, while hepatic microsomal acyl-

coenzyme

A:cholesterol acyltransferase activity and VLDL-cholesteryl esters

were

significantly higher in hamsters fed (n-3) PUFA with the atherogenic

diet (0.1

or 0.2% dietary cholesterol) than in those fed (n-6) PUFA with the

atherogenic

diet. Our results demonstrate that the amount of dietary cholesterol

is an

important factor in determining the mode and extent of effects of

dietary (n-3)

PUFA, especially on VLDL- and LDL-cholesterol levels. When dietary

cholesterol

intake was above 0.1% (w/w), the plasma cholesterol-lowering effect

of (n-3)

PUFA disappeared, and instead, it showed a cholesterol-increasing

effect.

However, the effects of dietary (n-3) PUFA on HDL-cholesterol are

independent of

dietary cholesterol content.

PMID: 15467282 [PubMed - in process]

... the response to dietary (n-3)PUFA

among different animal species is highly variable.Differ-

ent animal species also vary greatly in their response to

dietary cholesterol.Considerable interest has centered on

the hamster as a model for studying lipoprotein metabo-

lism.This is because cholesterol metabolism in this spe-

cies resembles that in human beings in several respects,

including the response to dietary cholesterol and fat [26 ].

...The test diets had similar fatty acid compositions

with the PUFA/SFA ratio set to be 1.0,except that 18 g linoleic acid/

100 g fatty acids in the (n-6)PUFA diet was replaced by (n-3)PUFA,

mainly EPA and DHA,in the (n-3)PUFA diet.The amounts of

PUFA,monounsaturated fatty acids (MUFA)and SFA were compa-

rable in both the (n-6)PUFA and (n-3)PUFA groups.The cholester-

ol concentration of the fish oil was determined,and the dietary cho-

lesterol level was adjusted to be the same for both the (n-6)PUFA

and (n-3)PUFA groups.All diets were supplemented with 0.005 g

D,L -alpha-tocopherol/kg and stored in the dark at –20 ° C. ...

Table 1. Fatty acid composition of the test diets

Fatty acid g/100 g fatty acids

(n-6)PUFA (n-3)PUFA

8:0 3.1 2.6

10:0 2.4 2.0

12:0 12.5 10.5

14:0 6.5 8.8

16:0 11.7 12.8

16:1(n-7)–3.6

18:0 4.6 3.5

18:1(n-9)17.9 13.4

18:2(n-6)37.4 19.2 = linoleic acid

18:3(n-3)3.9 2.4

18:4(n-3)–1.7

20:1(n-9)–1.4

20:4(n-6)–0.9

20:5(n-3)–10.9 = EPA

22:1(n-9)–0.7

22:5(n-3)–1.3

22:6(n-3)–4.6 = DHA

SFA 41 40

PUFA 41 41

MUFA 18 19

(n-6)PUFA 37 20

(n-3)PUFA 4 21

PUFA/SFA,g/g 1 1

... Results

Body Weight Gain and Liver Weight

The gain in body weight,liver weight and liver-to-body

weight ratio of hamsters fed diets differing in fat composi-

tion were similar across all groups (fig.1).There were

gradual increases of the liver weight and liver-to-body

weight ratio with increasing intake of dietary cholesterol

in hamsters fed both (n-6)and (n-3)PUFA diets (fig.1).

Plasma and Lipoprotein Cholesterol

When no dietary cholesterol was given or dietary cho-

lesterol was maintained at 0.025%(w/w),plasma choles-

terol concentration was significantly lower (p !0.05)in

the (n-3)PUFA group compared to the (n-6)PUFA group

(fig.2).The lower plasma cholesterol level observed in

hamsters fed (n-3)PUFA essentially reflected a reduced

amount of cholesterol carried in both LDL and HDL frac-

tions (fig.3).However,VLDL-and LDL-cholesterol con-

centrations in the hamsters ingesting the (n-3)PUFA diet

were significantly higher than in those ingesting the (n-6)

PUFA diet when dietary cholesterol intake was above

0.1%(fig.3).In the following time course study,our data

demonstrate that 1 week of feeding high cholesterol

(0.1%,w/w)diet containing (n-3)PUFA was sufficient to

produce the maximum increasing of VLDL-and LDL-

cholesterol concentrations by the diet and to observe max-

imum differences between the diet groups (fig.4).How-

ever,the percentage increase of VLDL-and LDL-choles-

terol concentrations (compared to (n-6)PUFA group)

gradually decreased toward the end of the 6-week feeding

period.In the first week,the percentage increase of

VLDL-cholesterol level was 108%,but in the sixth week,

it was reduced to 40%.The percentage increase of LDL-

cholesterol level was 40%in the first week,but in the sixth

week,it was reduced to 20%(fig.4).HDL-cholesterol lev-

els were significantly lower in the (n-3)PUFA group than

those in the (n-6)PUFA group when the hamsters were

fed with 0,0.025,0.05,0.1 or 0.2%cholesterol (fig.3).In

hamsters consuming the (n-3)PUFA diets,there were no

changes in HDL-cholesterol levels with increasing choles-

terol intake.However,the HDL-cholesterol level in (n-6)

PUFA group was significantly increased at 0.2%choles-

terol intake.

Hepatic Cholesteryl Esters

The hepatic cholesteryl ester content increased pro-

gressively in a dose-dependent fashion as the dietary cho-

lesterol intake increased in both (n-6)and (n-3)PUFA

groups (fig.5).The esterified cholesterol concentration

was significantly less in the (n-3)PUFA group than in the

(n-6)PUFA group.

Hepatic Microsomal ACAT Activity

Hepatic cholesteryl esters were significantly lower,

while hepatic microsomal ACAT activity and VLDL-cho-

lesteryl esters were significantly higher in hamsters fed the

(n-3)PUFA diet with high cholesterol intake (0.1 or 0.2%)

than in those fed the (n-6)PUFA diet with high cholester-

ol intake (0.1 or 0.2%)(table 2).

Characteristics of Plasma VLDL

The molar ratio of the core lipids (cholesteryl esters/

triglycerides:CE/TG)with cholesterol feeding increased

more dramatically in the (n-3)PUFA-fed hamsters

(fig.6).In hamsters fed the atherogenic diet (0.1 or 0.2%

dietary cholesterol),the molar ratios of the core lipids

(CE/TG)in the (n-3)PUFA group were significantly high-

er than those in the (n-6)PUFA group.The molar ratios of

the total surface to core lipid components (phospholipids

+free cholesterol/triglycerides +cholesteryl esters:PL +

FC/TG +CE)were higher in the (n-3)PUFA group than

those in the (n-6)PUFA group regardless of the concen-

trations of dietary cholesterol (fig.7).

Discussion

This most striking finding of this study was the ability

of the amount of dietary cholesterol to change the mode of

effects of (n-3)PUFA on lipoprotein cholesterol in ham-

sters.This study showed that dietary (n-3)PUFA was

more beneficial than (n-6)PUFA in lowering plasma cho-

lesterol concentration when hamsters were fed with the

nonatherogenic diet (0 or 0.025%dietary cholesterol)for

6 weeks.The lowering occurred mainly in the LDL and

HDL fractions.A previous study [25 ]also observed a

more hypocholesterolemic effect with (n-3)PUFA after 4

weeks 'feeding of a cholesterol-free diet when compared

to (n-6)PUFA.However,the hypocholesterolemic effect

of (n-3)PUFA was only in the HDL fraction.The differ-

ence in the lipoprotein fractions of the hypocholester-

olemic effect of (n-3)PUFA may be due to the differences

in the feeding duration.In contrast,in hamsters fed the

atherogenic diet (0.1 or 0.2%dietary cholesterol)for 6

weeks,(n-3)PUFA induces hypercholesterolemia more

than (n-6)PUFA,the increase being in the VLDL and

LDL fractions.The results support our earlier observa-

tions [25 ]made in hamsters fed an (n-3)PUFA-or (n-6)

PUFA-rich diet supplemented with 5 g/kg cholesterol.

These studies demonstrated that increases in LDL-choles-

terol (LDL-C)and VLDL-cholesterol (VLDL-C)with

(n-3)PUFA consumption when compared to (n-6)PUFA

are dependent on dietary cholesterol.Surette et al.[23 ]

also observed 90%greater VLDL-C and LDL-C concen-

trations in hamsters ingesting a (n-3)PUFA diet contain-

ing 0.1%cholesterol compared with those consuming an

oleic acid-rich diet.However,HDL-cholesterol (HDL-C)

levels were significantly lower in the (n-3)PUFA group

than those in the (n-6)PUFA group whether the dietary

cholesterol was added in the diet or not.This parallels sev-

eral other controlled animal and human feeding trials

where a decrease in HDL-C has been observed with fish

oil consumption [34 –37 ].The decrease in cholesterol con-

centration observed in the HDL fraction with (n-3)PUFA

consumption was very comparable in the groups of ham-

sters with increasing consumption of dietary cholesterol.

Thus,while (n-3)PUFA-induced changes in LDL-C and

VLDL-C are dependent on dietary cholesterol,changes in

HDL-C are not.

Of the two PUFA treatments,(n-3)PUFA was more

significant in increasing LDL-C levels without a signifi-

cant change in HDL-C levels,thus increasing the LDL/

HDL ratio (n-6 PUFA:0.58,0.70,0.76,0.94,0.67;n-3

PUFA:0.35,0.61,1.04,1.79,2.33).High LDL/HDL

ratios are associated with an increased risk of vascular dis-

ease [38 ]and therefore a dietary (n-3)PUFA might be

disadvantageous in reducing the risk of experiencing this

disease with increasing intake of dietary cholesterol.

There are two important implications of this study

with respect to human nutrition.First,these data suggest

that the detrimental effect of (n-3)PUFA on LDL-C could

be minimized if the intake of cholesterol could be reduced

to 0.05%.The data obtained in the hamsters fed 0.05%

cholesterol are particularly relevant to the human situa-

tion since this load of cholesterol corresponds to the

intake of F 125 mg of cholesterol per 1,000 kcal of dietary

intake.Second,given the likelihood that Western diets

will always contain at least several hundred milligrams of

cholesterol each day,the alternative way in which to

remain at the reasonably low LDL-C level is to be certain

that the diet contains (n-6)PUFA that effectively block

the deleterious effects of the dietary cholesterol.

Another interesting observation we made in this study

was that hamsters of the (n-3)PUFA group had signifi-

cantly lower hepatic cholesteryl ester concentrations than

hamsters of the (n-6)PUFA group with increasing dietary

cholesterol.The combination of higher dietary cholesterol

delivery to the liver and decreased hepatic cholesteryl

ester formation may reveal the underlying result for the

decreased LDL-receptor activity in animals consuming

n-3 PUFA and cholesterol.

Several human and animal studies [39,40 ]have re-

cently reported that fish oil feeding induced changes in

lipoprotein composition and particle size.In our study,

based on the greater ratio of surface lipids to core lipids of

VLDL in the (n-3)PUFA group,the particle size of VLDL

in the (n-3)PUFA group is probably smaller than those in

the (n-6)PUFA group.Nigon et al.[41 ]demonstrated

that larger or smaller LDL particles had a lower LDL-

receptor binding affinity than medium-sized LDL parti-

cles and might have a slower turnover rate.Therefore,the

increase in LDL-C observed in hamsters fed the (n-3)

PUFA with the atherogenic diet (0.1 or 0.2 dietary choles-

terol)can be at least partially explained by a reduced

hepatic receptor-mediated uptake of LDL.

Although cholesteryl esters were significantly lower,

hepatic microsomal ACAT activity and VLDL-cholester-

yl esters were significantly higher in hamsters fed (n-3)

PUFA with the atherogenic diet (0.1 or 0.2%dietary cho-

lesterol)than in those fed (n-6)PUFA with the atherogen-

ic diet.It is feasible to postulate that (n-3)PUFA some-

how stimulated the hepatic cholesteryl esters secretion

under the challenge of dietary cholesterol.The marked

decline in hepatic cholesteryl ester can be partly ac-

counted for by the increased level of secretion of choles-

teryl ester in the VLDL particles.

Cheers, Al Pater