Question for Chris M. - LDL receptors in endothelium?

[Guest guest]

In Malcom Kendrick's book and in this online article

(http://www.thincs.org/Malcolm.emigration.htm) he states that the endothelium

does not

have receptors for LDL (normal LDL - he doesn't mention oxidized LDL). He comes

to the

conclusion that LDL can't penetrate the endothelium because of this, unless LDL

concentrations are extremely high (above 580 mg/dl).

I know you've done a lot of research in this area - what's your take on this?

Also, elsewhere in the book he expresses skepticism (disbelief, actually) that

HDL can

penetrate the fibrous cap of an atheroma, " suck " out the cholesterol, get back

out and

then transport the cholesterol to the liver. Here's a quote:

" Firstly, atherosclerotic plaques are almost universally covered over by a

lining, or cap

separating the plaque from the bloodstream, and this cap is impermeable to HDL.

Secondly, a great deal of the cholesterol in plaque is in clefts, even crystals

(how do you

think Virchow recognized it 150 years ago?). It is not free and floating about

inside a

plaque, and you would need a pneumatic drill to extract it, and I can't see HDL

wielding a

pickaxe to a cholesterol cleft. Thirdly, no one has explained, or identified,

any sort of

mechanism by which HDL gets cholesterol out of the plaque. It just sort of...

does it.

Speaking personally, I always like to see some sort of plausible biological

mechanism to

explain why something works. "

Is there such a mechanism? I am not particularly well-versed in biochemistry,

though I

have a pretty good understanding of physiology and pathophysiology. I have also

wondered about this question, and I'm hoping you may be able to shed some light

on it.

Thanks,

Chris