The effect of mevalonate on 3-hydroxy-3-methylglutaryl-CoA reductase activity and the absolute rate of cholesterol biosynthesis in human monocyte-derived macrophages

Functional Interplay Between the Macrophage Scavenger Receptor Class B Type I and Pitavastatin (NK-104)

Background— Scavenger receptor class B type I (SR-BI), a receptor for high-density lipoprotein (HDL), plays an important role in the bidirectional cholesterol exchange between cells and HDL particles and the atherosclerotic lesion development. Enhancement of SR-BI expression significantly reduces, whereas lack of SR-BI expression accelerates, the atherosclerotic lesion development in proatherogenic mice. Statins, a class of inhibitors for 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, significantly suppress de novo cholesterol synthesis and reduce the incidence of coronary heart disease. Statins also display multiple pleiotropic effects independently of cholesterol synthesis in the vascular cells. Here, we investigated the effects of pitavastatin (NK-104), a newly synthesized statin, on macrophage SR-BI expression.

Methods and Results— We found that pitavastatin significantly increased SR-BI mRNA and protein expression in a macrophage cell line in a concentration- and time-dependent manner. It also increased SR-BI expression in both mouse peritoneal and human monocyte-derived macrophages. Associated with increased SR-BI expression, pitavastatin enhanced macrophage HDL binding, uptake of [ 14 C]cholesteryl oleate/HDL, and efflux of [ 3 H]cholesterol to HDL. Pitavastatin abolished the inhibition of macrophage SR-BI expression by cholesterol biosynthetic intermediates. It also restored SR-BI expression inhibited by lipopolysaccharide and tumor necrosis factor-α through its inactivation of the transcription factor nuclear factor-κB.

Conclusions— Our data demonstrate that pitavastatin can stimulate macrophage SR-BI expression by reduction of cholesterol biosynthetic intermediates and antiinflammatory action and suggest additional pleiotropic effects of statins by which they may reduce the incidence of coronary heart disease.

1,25-Dihydroxyvitamin D3-induced HL-60 macrophages: regulation of cholesterol and LDL metabolism

Differentiation of human promyelocytic leukemic HL-60 cells with 1,25-dihydroxyvitamin D3 (D3) results in macrophages which exhibit specific and saturable receptor-mediated processing of both native and modified low density lipoprotein (LDL). Analysis of binding kinetics demonstrated that macrophages bind LDL and acetyl-LDL with similar affinities, yet possess significantly different numbers of receptors (55 +/- 6 x 10(3) LDL receptors/cell vs 79 +/- 7 x 10(3) acetyl-LDL receptors/cell). D3-induced HL-60 macrophages challenged with LDL or acetyl-LDL exhibited suppression of HMG-CoA reductase activity as well as a significant induction in the incorporation of [14C]oleate into cholesteryl ester compared with macrophages incubated with lipoprotein depleted serum. Maximum increases in ACAT activity were obtained in macrophages incubated with 25-hydroxycholesterol plus LDL or acetyl-LDL. The increase in ACAT activity in macrophages challenged with acetyl-LDL paralleled the increase in cellular cholesterol content and the increase of oil red O lipid stainable material, imparting the macrophages with a foamy appearance. The data indicate that D3-induced HL-60 macrophages are a useful model for the study of lipoprotein--macrophage interactions as related to foam cell development and atherogenesis.

Lipoprotein receptors of HL-60 macrophages. Effect of differentiation with tetramyristic phorbol acetate and 1,25-dihydroxyvitamin D3

The human promyelocytic leukemic cell line HL-60 is a unique model for studies of the effects of macrophage differentiation on the expression and regulation of lipoprotein receptors. Undifferentiated HL-60 cells express a regulated low density lipoprotein (LDL) receptor and lack the acetylated LDL (acetyl-LDL) scavenger receptor. HL-60 macrophages differentiated with tetramyristic phorbol acetate failed to degrade LDL and acetyl-LDL via receptor-mediated processes. Differentiation with 1,25-dihydroxyvitamin D3 (D3) induced macrophages exhibiting specific saturable receptors for LDL and acetyl-LDL. The LDL receptor of D3-induced macrophages was found to exhibit specificity for apolipoprotein B- and E-containing lipoproteins, to be calcium dependent, and to be inhibited by pronase and chloroquine. Maximal degradation of acetyl-LDL was achieved within 2 days of D3 treatment and was specific for acetyl-LDL, was calcium independent, was inhibited by chloroquine, and was sensitive to pronase and fucoidin treatment. Incubation of D3-induced macrophages with LDL or acetyl-LDL resulted in reductions in sterol synthesis and receptor-mediated degradation of LDL; the scavenger receptor pathway was unaltered. These results demonstrate that D3-induced HL-60 macrophages exhibit patterns of sterol and lipoprotein metabolism and regulation that make them a useful model system for in vitro studies of lipoprotein-macrophage interactions related to foam cell development and atherogenesis.