Journal of Lipid Research, Vol 30, 1943-1952, Copyright © 1989 by Lipid Research, Inc.
Lovastatin treatment inhibits sterol synthesis and induces HMG-CoA reductase activity in mononuclear leukocytes of normal subjects
BG Stone, CD Evans, WF Prigge, WC Duane and RL Gebhard
Department of Medicine, VA Medical Center, Minneapolis, MN 55417.
The mechanism by which competitive inhibitors of 3-hydroxy-3-
methylglutaryl coenzyme A (HMG-CoA) reductase decrease serum cholesterol is
incompletely understood. The few available data in humans suggest that
chronic administration of the competitive inhibitor, lovastatin, decreases
serum cholesterol with little or no change in total body sterol synthesis.
To further define the effect of lovastatin on cholesterol synthesis in
normal subjects, we investigated the effect of a single oral dose of
lovastatin and a 4-week treatment period of lovastatin on mononuclear
leukocyte (ML) sterol synthesis as a reflection of total body sterol
synthesis. In parallel, we measured serum lipid profiles and HMG-CoA
reductase activity in ML microsomes that had been washed free of
lovastatin. ML sterol synthesis did not significantly decrease (23 +/- 5%,
mean +/- SEM) at 3 h after a single 40-mg dose of lovastatin. With a single
oral 80-mg dose, ML sterol synthesis decreased by 57 +/- 10% (P less than
0.05) and remained low for the subsequent 6 h. With both doses, total
HMG-CoA reductase enzyme activity in microsomes prepared from harvested
mononuclear leukocytes was induced 4.8-fold (P less than 0.01) over
baseline values. Both the 20-mg bid dose and the 40-mg bid dose of
lovastatin administered for a 4-week period decreased serum cholesterol by
25-34%. Lovastatin at 20 mg bid decreased ML sterol synthesis by 23 +/- 6%
(P less than 0.02) and increased ML HMG-CoA reductase 3.8 times (P less
than 0.001) the baseline values. Twenty four hours after stopping
lovastatin, ML sterol synthesis and HMG-CoA reductase enzyme activity had
returned to the baseline values. The higher dose of lovastatin (40 mg bid)
decreased ML sterol synthesis by 16 +/- 3% (P less than 0.05) and induced
HMG-CoA reductase to 53.7 times (P less than 0.01) the baseline value at 4
weeks. Stopping this higher dose effected a rebound in ML sterol synthesis
to 140 +/- 11% of baseline (P less than 0.01), while HMG-CoA reductase
remained 12.5 times baseline (P less than 0.01) over the next 3 days. No
rebound in serum cholesterol was observed. From these data we conclude that
in normal subjects lovastatin lowers serum cholesterol with only a modest
effect on sterol synthesis. The effect of lovastatin on sterol synthesis in
mononuclear leukocytes is tempered by an induction of HMG-CoA reductase
enzyme quantity, balancing the enzyme inhibition by lovastatin.(ABSTRACT
TRUNCATED AT 400 WORDS)