Pravastatin down-regulates inflammatory mediators in human monocytes in vitro

Abstract

There is experimental evidence that pravastatin, which is designed to inhibit the rate-limiting enzyme of cholesterol synthesis, can affect cell metabolism and proliferation. We therefore studied the effects of pravastatin on the generation of inflammatory mediators in non-stimulated and stimulated primary human monocytes in vitro. In our experimental model, pravastatin induced a dose-dependent inhibition of monocyte cholesterol synthesis (up to 67%), up-regulation of low density lipoprotein receptor mRNA (by about 35%) and reduction in intracellular cholesterol accumulation. In parallel, exposure of non-stimulated monocytes to various doses of pravastatin resulted in inhibition of monocyte chemoattractant protein-1 protein expression (up to 15-fold), reduction of tumour necrosis factor alpha (TNF-α) levels (up to 2.4-fold) and a total loss of metalloproteinase-9 activity in stimulated cells. Pravastatin at concentrations of 5, 100 and 500 μM caused an inhibition of TNF-α-induced cellular oxygen consumption from 2.4- to 5.5-fold. These data extend the findings of potential anti-inflammatory actions of statins and also suggest the possibility for pravastatin use in a broader spectrum of inflammatory situations.

Introduction

Clinical and experimental studies have shown that reduction in plasma cholesterol, particularly low density lipoprotein (LDL) cholesterol, by treatment with statins can induce regression of vascular atherosclerosis and reduction of cardiovascular-related morbidity Desager and Horsmans, 1996, Corsini et al., 1998. Statins are competitive hydroxy-3-metyl glutaryl coenzyme A (HMG-CoA) reductase inhibitors that inhibit the synthesis of cholesterol from mevalonic acid by suppressing the conversion of HMG-CoA (Corsini et al., 1999). They also enhance the expression of LDL receptors, increase incorporation of LDL and reduce serum levels of cholesterol (Ma et al., 1986). Various studies have shown that specific statins can inhibit cholesterol accumulation in macrophages thereby reducing their activity Weber et al., 1997, Bocan et al., 1994, can inhibit platelet aggregation leading to decreased platelet thrombus formation Faggiotto and Paoletti, 1999, Carvalho et al., 1974 and influence vascular smooth muscle cell migration and proliferation (Weissberg et al., 1996). These diverse effects of statins on the biological processes contributing to atherosclerotic plaque development suggest that the benefit from treatment with statins cannot be only explained by a reduction in plasma total or LDL cholesterol levels Wheeler, 1998, Kendall and Toescu, 1999.

Current knowledge suggest that atherosclerosis is an inflammatory process and that the initiation and progression of the lesions involves cellular migration, proliferation and production of a significant number of pro-inflammatory factors such as chemokines, cytokines, reactive oxygen species, and growth factors by all of the cell types within the artery wall (Plutzky, 1999). Monocytes are among the first cells to accumulate in early atherosclerotic lesions. Macrophage infiltration into the atherosclerotic lesion has been linked to activation of the transcription factor nuclear factor-κB (NF-κB) and synthesis of numerous NF-κB-dependent gene products including free radicals, cytokines, chemokines and metalloproteinases Brand et al., 1996, Thurberg and Collins, 1998. Recent reports have shown that statins such as lovastatin and atorvastatin through the inhibition of NF-κB activity can reduce pro-inflammatory cytokine and chemokine expression in smooth muscle cells and mononuclear cells and therefore play a role in the stabilisation of the lesion (Ortego et al., 1999).

Pravastatin is a hydrophilic, anionic drug and selective inhibitor of HMG-CoA reductase (Pan, 1991). The drug has been shown to reduce plasma LDL cholesterol concentrations in experimental animals as well as in humans Koga et al., 1990, Parker et al., 1990. The inhibition by pravastatin of macrophage cholesterol synthesis, both in vivo and in vitro, was shown to be associated with enhanced cellular uptake of native LDL, but not the acetylated LDL or oxidized LDL (Keidar et al., 1994). Pravastatin was found to reduce macrophage content, calcification and new vessel formation in atherosclerotic plaques in cholesterol-fed rabbits and in atherosclerotic monkeys Shiomi et al., 1995, Williams et al., 1998, suggesting that this drug can reduce inflammation and enhance plaque stability. It was also shown that pravastatin activates endothelial nitric oxide synthase (Kaesemeyer et al., 1999) and inhibits platelet aggregation and thrombus formation in an injured artery (Lacoste and Lam, 1996), in addition to its lipid-lowering effect. Results from the Long-term Intervention with Pravastatin in Ischaemic Disease (LIPID) Study Group, showed that patients with a broad range of initial cholesterol levels (4.0–7.0 mM) had a reduced morbidity and mortality on treatment (The Lipid Study Group, 1998), thus high-lightning mechanisms of pravastatin additional to its lipid-lowering properties.

The aim of the present study was to correlate the effects of pravastatin on cellular lipid metabolism and generation of pro-inflammatory molecular species in non-stimulated and stimulated human monocytes in culture.