Mon, 17 May 2004 11:02:54 -0400 in article
<[email hidden]> "Dr. Andrew B. Chung, MD/PhD"
Quoted message said:Matti Narkia said:The study
Kurowska EM, Manthey JA. Hypolipidemic effects and
absorption of citrus polymethoxylated flavones in
hamsters with diet-induced hypercholesterolemia. J Agric
Food Chem. 2004 May 19;52(10):2879-86. PMID: 15137829
[PubMed - in process] <URL:http://www.ncbi.nlm.nih.gov/e-
ntrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&li-
st_uids=15137829>
found that compounds called polymethoxylated flavones
(PMFs), which are found in the peels of tangerines and
oranges and also in smaller amounts in the juices of
these fruits, could be better than drugs for lowering
cholesterol.
Comments in
Orange, tangerine peels could be better than drugs for
lowering cholesterol <URL:http://www.eurekalert.org/pub_releases/2004-05/acs-
otp051104.php>
--
Matti Narkia
Then, why were you advocating higher cholesterol levels
(for the brain) earlier?
Do I need to explain you that there is a difference between
serum cholesterol level and brain cholesterol synthesis
status? Too bad, but here we go: Brain needs cholesterol for
its proper functioning as shown by the studies presented.
Additionally, these studies show that brain manufactures its
own cholesterol in glias. Also, in general, serum
cholesterol cannot pass through the blood-brain-barrier
(this may, however, be a little more complicated, because
astrocytes have LDL-receptors). Therefore serum cholesterol
level and brain cholesterol synthesis status can be largely
independent of each other, unless serum cholesterol level
has been reduced for example by a drug which can pass
through blood-brain-barrier and thus also potentially affect
brain's cholesterol synthesis. Many statins for instance
cannot get through blood-brain-barrier, but some can.
It is possible that serum cholesterol level is high, but
brain is cholesterol deficient.
References:
Edmond J. Essential polyunsaturated fatty acids and the
barrier to the brain: the components of a model for
transport. J Mol Neurosci. 2001 Apr-Jun;16(2-3):181-93;
discussion 215-21. Review. PMID: 11478373 [PubMed -
indexed for MEDLINE] <URL:http://www.ncbi.nlm.nih.gov/ent-
rez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_-
uids=11478373>
"... First, discrete studies have demonstrated that
cholesterol and the nonessential fatty acids, (palmitic,
oleic, stearic) do not enter the brain parenchyma. ..."
Bjorkhem I, Lutjohann D, Breuer O, Sakinis A, Wennmalm A.
Importance of a novel oxidative mechanism for elimination of
brain cholesterol. Turnover of cholesterol and 24(S)-
hydroxycholesterol in rat brain as measured with 18O2
techniques in vivo and in vitro. J Biol Chem. 1997 Nov 28;272(48):30178-
84. PMID: 9374499 [PubMed - indexed for MEDLINE]
<URL:http://www.jbc.org/cgi/content/full/272/48/30178>
"The largest pool and concentration of cholesterol in
the body is found in the brain. Being a constituent of
myelin and cell membranes cholesterol is important for
the function of this organ and an inborn defect in
cholesterol synthesis is associated with serious
neurological and mental dysfunctions (1).
Brain cholesterol is efficiently protected from exchange
with circulating lipoproteins by the blood-brain barrier
(2). In accordance with this, most recent studies have
favored the view that the majority of brain cholesterol
is synthesized locally although at a low rate (for a
review, see Ref. 3). Using in vivo and in vitro
techniques the estimated half-life of cholesterol has
been found to be 4-6 months in rats (4, 5).
The protection of brain cholesterol from exchange with
circulating lipoprotein by the blood-brain barrier is
not absolute (6, 7) but this exchange seems to be low in
relation to the local synthesis of cholesterol. To what
extent there is a flux of unmetabolized cholesterol in
the opposite direction from the brain into the
circulation, is not known. If the blood-brain barrier is
equally effective in both directions to prevent flux of
cholesterol, there is a need for another more specific
mechanism for elimination of cholesterol from the brain
to compensate for the synthesis under steady-state
conditions. ..."
--
Matti Narkia
