Pharmacological inhibitors of the mevalonate pathway activate pro-IL-1 processing and IL-1 release by human monocytes.

OBJECTIVE: The effects of statins (3-hydroxy-3-methylglutaryl coenzyme A reductase-HMGR-inhibitors) on the inflammatory response remain unclear. HMGR is implicated in the mevalonate pathway, directly upstream of cholesterol biosynthesis. We studied the impairment by this pathway of cytokine production by peripheral blood mononuclear cells (PBMCs) and THP-1 cells. The aim was to identify a specific cytokine "signature" of cells under simvastatin treatment in order to link pharmacological inhibition of the mevalonate pathway and inflammation.
METHODS: Normal human PBMCs and THP-1 cells were cultured with inhibitors of HMGR (simvastatin), geranylgeranyltransferase (GGTI-298), farnesyltransferase (FTI-277), and/or caspase-1 (Z-VAD(Ome)-FMK). Following culture, cytokine production, caspase-1 activity, IL-1beta mRNA and Rac-1 activity were determined.
RESULTS: Pharmacological inhibition of the mevalonate pathway specifically enhanced the release of IL-1alpha, IL-1beta and IL-18 and inhibited IL-1ra production by LPS-activated PBMCs and THP-1 cells. Simvastatin did not modify pro-IL-1beta expression, but enhanced caspase-1 activity, the enzyme responsible for IL-1beta and IL-18 maturation. GGTI-298 also enhanced IL-1-family cytokine production, showing that geranylgeranylation is involved in caspase-1 activation. Additionally, simvastatin enhanced Rac-1 activity.
CONCLUSION: Pharmacological inhibition of the mevalonate pathway by statins highlighted the specific induction of the proinflammatory cytokines of the IL-1 family whose maturation is either directly (i.e. IL-1beta and IL-18), or indirectly (i.e. IL-1alpha) dependant on caspase-1.