In Vitro Modulation of Serum Lipoproteins in a Patient with Liver Cirrhosis by Lipoprotein Deficient Fractions from a Normal Control

Abstract

To investigate the possible mechanism of serum lipoprotein (LP) abnormalities in cirrhotics, the following in vitro experiment was carried out. Serum LPs from the patient were isolated by sequential ultracentrifugation at d. 1.21g/ml and inactivated by heat treatment at 56°C 30min after subsequent dialysis against saline. LP deficient fraction (LPDF) from serum and postheparin plasma (PHP) from a healthy control was obtained by the same procedure at 4°C. The LPs were incubated with equal amount of the LPDF at 37°C for 6hr. The activity of lipoprotein lipase (LPL) and lecithin: cholesterol acyltransferase (LCAT) was inhibited by 1M NaCl and 2mM parachloromercuriphenyl sulfonate respectively. The resulting mixtures were isolated to record LP profiles and to perform chemical analyses by single-step density gradient ultra-centrifugation.
Most significant changes among the mixtures were observed in a PHP·LPDF containing system which possessed LPL, hepatic triglyceride lipase (H-TGL) and LCAT, wheareas there were no appreciable changes in other systems.
The results from the PHP·LPDF containing system were as follows.
1) In LP profiles, the absorbance of low density lipoproteins₂ (LDL₂) and high density lipoproteins₂ (HDL₂) shifted to heavier density and HDL₃ peak which was not usually detectable in cirrhotics appeared.
2) Total amount of LPs showed parallel changes with the LP profiles.
3) With respect to the percent chemical composition of each LP fraction, the significant changes were an increase in protein of very low density lipoprotein (VLDL)+intermediate density lipoprotein (IDL), an increase in total cholesterol (TC) and a decrease in triglycerides (TG) of LDL₂, an increase in protein and a decrease in TG of HDL₂ and an increase in protein and a decrease in TG and phospholipids of HDL₃. In addition, an elevation in cholesteryl ester/TC ratio was found in LDL₂, HDL₂ and HDL₃.
4) Apoprotein (apo) A-I/A-II ratio was elevated in both HDL₂ and HDL₃ subfractions.
These in vitro results suggest that lipoprotein abnormalities in cirrhotics could be partially normalized by the treatment with LPDF from healthy PHP which contains LPL, H-TGL and LCAT.