VIP downregulates cytokine secretion and TLR-4 expression in THP-1 monocytes

Objectives: Vasoactive intestinal peptide (VIP) ameliorates gram negative sepsis and joint remodelling due to rheumatoid arthritis in animal models by inhibiting the production of inflammatory cytokines. VIP is produced in GCF during periodontal disease but it is not known whether VIP has any effect on pro-inflammatory cytokine networks induced by pathogenic oral bacteria such as Porphyromonas gingivalis. The aim of our study was to assess the effect of VIP on pro-inflammatory pathways in human monocytes exposed to P.gingivalis strain W50 LPS. Methods: THP-1 cells were differentiated into monocytes by treatment with vitamin D3. Cytokine production in cell culture was measured by ELISA and cellular location of transcription factors by scanning confocal microscopy using fluorescently labelled antibodies. Toll-like receptor (TLR) expression was determined by FACS analysis. Results: VIP significantly (P<0.05) downregulated production of TNF-α and IL-18 by monocytes stimulated with P.gingivalis LPS. Furthermore, the downregulation of these cytokines coincided with decreased or absent nuclear translocation of the transcription factors NFκB and c-jun in the same cells. P.gingivalis LPS upregulated TLR4 expression in monocytes but this was significantly inhibited by co-incubation with VIP. P.gingivalis LPS only had a minimal effect on TLR2 expression. Conclusions: We conclude that VIP downregulates P.gingivalis LPS-stimulated pro-inflammatory events in monocytes. The action of VIP may be mediated by inhibition of NFκB and c-jun activation and downregulation of TLR4 expression. These observations may inform therapeutic strategies aimed at immunomodulation in periodontal disease. Supported by a Clinician Scientist award (to PMP) from the UK Department of Health.