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HMG-CoA reductase inhibitors reduce acetyl LDL endocytosis in mouse peritoneal macrophages
F Bernini1, N Scurati, G Bonfadini
1Institute of Pharmacology and Pharmacognosy, University of Parma, Italy.
Abstract:
We previously reported that mevalonate starvation elicited by hydroxymethyl glutaryl coenzyme A (HMG-CoA) reductase inhibitors reduced cholesterol accumulation promoted in murine macrophages by acetylated LDL (AcLDL). In the present study we investigated the cellular mechanism of this effect. Our results indicate that the HMG-CoA reductase inhibitors fluvastatin and simvastatin reduce, in a concentration-dependent manner, more than 50% of the 125I-AcLDL degradation by macrophages. This effect was not due to a decrease of lysosomal enzyme activity, and it was paralleled by the retention of AcLDL-associated cholesteryl ester in the incubation medium. The ability of fluvastatin to inhibit AcLDL degradation was completely overcome by mevalonate and its derivative geranylgeraniol. Evaluation at 4 degrees C of 125I-AcLDL binding to plasma membrane suggested that the inhibitory effect of fluvastatin on lipoprotein catabolism was not due to a decreased expression of scavenger receptors. Fluorescent microscope analysis of cellular internalization of AcLDL labeled with the fluorochrome 3,3'-dioctadecyl indocarbocyanine demonstrated that fluvastatin inhibits lipoprotein endocytosis, an effect reversed by mevalonate. Studies performed with native 125I-LDL indicated that fluvastatin did not inhibit but rather increased the degradation of LDL taken up by the normal LDL receptor. These results exclude a generalized depression of the cellular endocytotic activity by the drug. The ability of fluvastatin to reduce AcLDL catabolism and cholesterol esterification was more pronounced in cholesterol-enriched macrophages compared with normal cells. In conclusion, the present results demonstrate that HMG-CoA reductase inhibitors may reduce the in vitro cholesterol accumulation in macrophages by inhibiting AcLDL endocytosis.
Insights
Hydroxymethyl glutaryl coenzyme A (HMG-CoA) reductase inhibitors, like fluvastatin, reduce cholesterol accumulation in macrophages by inhibiting acetylated LDL (AcLDL) endocytosis. This mechanism involves blocking AcLDL uptake rather than affecting lysosomal enzymes or scavenger receptors.
Area of Science:
- Biochemistry
- Cell Biology
- Pharmacology
Background:
- Mevalonate starvation, induced by HMG-CoA reductase inhibitors, was previously shown to reduce cholesterol accumulation in macrophages.
- Acetyl-low-density lipoprotein (AcLDL) promotes cholesterol accumulation in macrophages.
Purpose of the Study:
- To investigate the cellular mechanism by which HMG-CoA reductase inhibitors reduce cholesterol accumulation promoted by AcLDL in macrophages.
- To determine if fluvastatin and simvastatin affect AcLDL degradation, binding, or internalization.
Main Methods:
- Macrophages were treated with fluvastatin or simvastatin and incubated with radiolabeled AcLDL (125I-AcLDL).
- AcLDL degradation, binding to scavenger receptors, and cellular internalization were measured.
- The effects of mevalonate and geranylgeraniol on AcLDL metabolism were assessed.
- LDL receptor-mediated uptake of native LDL was also studied.
Main Results:
- HMG-CoA reductase inhibitors significantly reduced AcLDL degradation by macrophages in a concentration-dependent manner.
- This reduction was associated with retained cholesteryl ester in the incubation medium, not decreased lysosomal activity.
- Mevalonate and geranylgeraniol reversed the inhibitory effect of fluvastatin on AcLDL degradation.
- Fluvastatin inhibited AcLDL endocytosis but not its binding to scavenger receptors or LDL receptor-mediated uptake of native LDL.
- The inhibitory effect was more pronounced in cholesterol-enriched macrophages.
Conclusions:
- HMG-CoA reductase inhibitors reduce in vitro cholesterol accumulation in macrophages primarily by inhibiting AcLDL endocytosis.
- The mechanism does not involve decreased lysosomal enzyme activity, scavenger receptor expression, or generalized endocytosis inhibition.
- Mevalonate supplementation can overcome the inhibitory effects of these drugs on AcLDL metabolism.