Inhibitory effect of statins on inflammatory cytokine production from human bronchial epithelial cells

Abstract

Statins are 3-hydroxy-3-methylglutaryl-co-enzyme A reductase inhibitors of cholesterol biosynthesis, and have been reported to exert pleiotropic effects on cellular signalling and cellular functions involved in inflammation. Recent reports have demonstrated that previous statin therapy reduced the risk of pneumonia or increased survival in patients with community-acquired pneumonia. However, the precise mechanisms responsible for these effects are unclear. In the present study, we examined the effects of statins on cytokine production from lipopolysaccharide (LPS)-stimulated human bronchial epithelial cells (BEAS-2B). Interleukin (IL)-6 and IL-8 mRNA expression and protein secretion in LPS-stimulated cells were inhibited significantly by the lipophilic statin pitavastatin and the hydrophilic statin pravastatin. As these inhibitory effects of statin were negated by adding mevalonate, the anti-inflammatory effects of statins appear to be exerted via the mevalonic cascade. In addition, the activation levels of Ras homologue gene family A (RhoA) in BEAS-2B cells cultured with pitavastatin were significantly lower than those without the statin. These results suggest that statins have anti-inflammatory effects by reducing cytokine production through inhibition of the mevalonic cascade followed by RhoA activation in the lung.

Fig. 1

The inhibitory effects of pitavastatin (PTV) on inflammatory cytokine production. Interleukin (IL)-6, IL-8 and granulocyte–macrophage colony-stimulating factor (GM-CSF) mRNA expression in lipopolysaccharide (LPS)-stimulated BEAS-2B cells was inhibited significantly by PTV (1 nM, 10 nM, 100 nM) in a dose-dependent manner (a,c,e). IL-6 and IL-8 secretion, but not GM-CSF secretion, by LPS-stimulated BEAS-2B cells was also reduced significantly by PTV in a dose-dependent manner (b,d,f); *P < 0·05, **P < 0·001, compared with the cells cultured without PTV (white column).

Fig. 2

The effects of exogenous mevalonate on the cytokine production. Interleukin (IL)-6 and IL-8 mRNA expression, but not granulocyte–macrophage colony-stimulating factor (GM-CSF) mRNA expression, in lipopolysaccharide (LPS)-stimulated BEAS-2B cells was inhibited significantly at various concentrations of pravastatin (PRV) (a,c,e). IL-6 and IL-8 secretion by LPS-stimulated BEAS-2B cells was also reduced significantly by PRV in a dose-dependent manner (b,d). GM-CSF secretion was reduced only by 10 µM PRV (f); *P < 0·05, **P < 0·001, compared with the cells cultured without PRV (white column).

Fig. 3

Reverse effects of exogenous mevalonate (MEV) to the pitavastatin (PTV) inhibition. The inhibitory effects of PTV (10 nM) on lipopolysaccharide (LPS)-induced interleukin (IL)-6, IL-8 and granulocyte–macrophage colony-stimulating factor (GM-CSF) cytokine mRNA expression and production, except GM-CSF production, were negated by treatment with 10 mM of MEV (a–e); *P < 0·05, **P < 0·001, compared between the groups.

Fig. 4

The reduction of Ras homologue gene family A (RhoA) activation by pitavastatin. The lipopolysaccaride (LPS)-induced activation levels of RhoA in BEAS-2B cells cultured with pitavastatin (PTV) (100 nM) were significantly lower than those without the statin; **P < 0·001, compared with the cells cultured without PTV (white column).