Elsevier

Biochemical Pharmacology

Volume 64, Issue 4, 15 August 2002, Pages 645-648
Biochemical Pharmacology

Short communication
G protein-coupled receptor for nicotinic acid in mouse macrophages

https://doi.org/10.1016/S0006-2952(02)01220-0Get rights and content

Abstract

The use of the HDL-elevating drug nicotinic acid in the treatment and prevention of atherosclerotic disease is limited by the frequent induction of skin flushing. The therapeutic effects of nicotinic acid are attributed to inhibition of lipolysis in adipose tissue via a G protein-coupled receptor, whereas the mechanism of flush induction by release of prostaglandin D2 from macrophages is not understood. In this study, we investigated if macrophages contain nicotinic acid receptors. Specific guanine nucleotide sensitive binding sites for [3H]nicotinic acid were detected in membranes from mouse RAW 264.7 macrophages. Nicotinic acid and related heterocycles stimulated activation of pertussis toxin-sensitive G proteins. The rank orders of potency in macrophage membranes were identical for inhibition of [3H]nicotinic acid binding and G protein activation, and were pharmacologically indistinguishable from that of the G protein-coupled nicotinic acid receptor in spleen membranes. These results indicate that the effects of nicotinic acid on macrophages, spleen and probably adipocytes are mediated via an identical, unique G protein-coupled receptor.

Introduction

The ability of the hypolipidemic drug nicotinic acid to elevate high density lipoprotein cholesterol to a greater extent than other drugs is of particular interest in the treatment of atherosclerotic diseases [1]. Nicotinic acid and its metabolically stable derivative acipimox inhibit adenylate cyclase in adipocytes through a pertussis toxin-sensitive G protein [2], [3], which leads to decreased phosphorylation of hormone-sensitive lipase and inhibition of its activity. Skin flushing is a common side effect of nicotinic acid. Flushing is prevented or attenuated by cyclooxygenase inhibitors, which, however, do not affect the lipid-lowering effect of nicotinic acid [4]. This vasodilation has been attributed to the release of prostaglandin D2 in skin [5]. Since the prostaglandin D2 release is not accompanied by a release of histamine, it is assumed that the cell type which releases the prostaglandin is not the mast cell [5]. The formation of prostaglandin D2 has been attributed largely to a glutathione-requiring prostaglandin D synthase localized mainly in antigen-presenting cells [6]. However, there is no direct evidence for the presence of nicotinic acid receptors in these cells in skin. Since the activation of nicotinic acid receptors in skin macrophages might be the reason for the release of prostaglandin D2, the present study was set up to investigate if macrophages express G protein-coupled receptors for nicotinic acid, which have been characterized previously in rat adipocyte and spleen membranes [7], or if a nicotinic acid binding site distinct from this receptor is detectable.

Section snippets

Materials and methods

RAW 264.7 mouse macrophages (European Collection of Cell Cultures) were cultured in Dulbecco’s modified Eagle’s medium (DMEM) with 2 mM glutamine, 100 U/mL penicillin, 200 μg/mL streptomycin and 10% fetal bovine serum (FBS) in 175 cm2 flasks at 37° in the presence of 5% CO2. Confluent cultures were split 1:15 every 3–4 days. Incubations with pertussis toxin (50 ng/mL) were performed for 20 hr. Membranes from adherent and nonadherent cells were prepared separately after mechanical removal of adherent

Results and discussion

Membranes from adherent and nonadherent RAW 264.7 macrophages displayed specific [3H]nicotinic acid binding. The affinity of [3H]nicotinic acid measured in saturation experiments was identical to that previously found for the nicotinic acid receptor in rat adipocyte and spleen membranes [7] (Table 1). The density of [3H]nicotinic acid binding sites in mouse macrophage membranes was considerably lower than in membranes from adipocytes or spleen (Table 1). Competition experiments with

Acknowledgements

The authors are grateful to Eugen Heinz for expert technical assistance. Acipimox was a generous gift from Pharmacia-Upjohn.

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