Journal of Lipid Research, Vol 26, 273-282, Copyright © 1985 by Lipid Research, Inc.
The in vitro formation of HDL2 during the action of LCAT: the role of triglyceride-rich lipoproteins
H Dieplinger, R Zechner and GM Kostner
We examined the effects of lecithin:cholesterol acyl transferase (LCAT) and
of lipoprotein lipase (LPL) on the conversion of high density lipoproteins
(HDL) towards fractions of lower densities using the analytical
ultracentrifuge. Freshly isolated whole plasma was incubated for 24 h at 37
degrees C in the presence or absence of active enzyme systems. In some
cases, lipoproteins were removed by selective precipitations;
alternatively, we added triglyceride-rich lipoproteins (TGRLP) or
Intralipid to the incubations. The results are as follows. 1) The
incubation of whole plasma containing active LCAT leads to a conversion of
HDL3 to a fraction of lower density, notably HDL2a. If LCAT is inhibited,
the conversion is far less pronounced. 2) If very low and low density
lipoproteins are removed by phosphotungstate precipitation and the
supernatant is incubated with LCAT, HDL3 shifts towards higher densities.
3) The presence of phosphatidylcholine/cholesterol liposomes or the
presence of blood cells as a source of additional LCAT substrate had only
little influence on the HDL conversion in our system. 4) The addition of
TGRLP or of Intralipid at minimal ratios of 2.5:1 caused an almost complete
conversion of HDL3 to HDL2b. This conversion was dependent on active LCAT.
5) LPL also caused a shift of HDL3 to HDL2a if TGRLP was present. HDL2b,
however, was not formed by LPL unless LCAT was active.