Identification of novel anti-inflammatory natural compounds and their underlying mechanisms using in vitro/in vivo dermatitis models

Abstract

Dysregulated immune responses play a major role in the development and progression of diverse inflammatory disorders. Several drugs are available to treat these conditions, but their usage is often limited by either low efficacy or severe adverse effects. Therefore, there remains a continuing need to develop novel anti-inflammatory drugs. In recent reports, flavonoid and phenolic compounds have been demonstrated to possess beneficial effects in inflammatory conditions. In this study we demonstrated the anti-inflammatory potential of a newly synthesized flavonoid macakurzin C derivative, CPD 14, and a natural phenolic compound, coniferyl aldehyde (CA) using in vitro and in vivo systems. CPD 14 significantly suppressed the release and expression of inflammatory mediators in lipopolysaccharide (LPS)-stimulated murine macrophages and IFN-γ/TNF-α-stimulated human keratinocytes. Down regulation of nuclear factor-κB (NF-κB) signaling and induction of nuclear factor-erythroid 2-related factor-2/hemeoxygenase-1 (Nrf2/HO-1) pathway were found to be responsible for the anti-inflammatory effects of CPD 14. To demonstrate the in vivo relevance, phorbol 12-myristate 13-acetate (TPA)-induced acute skin inflammation and oxazolone-induced chronic dermatitis models were employed. Topical application of CPD 14 exhibited strong skin protection in both acute and chronic models of inflammation, where chemical-induced inflammatory parameters and the expression of inflammatory mediators were markedly suppressed by CPD 14.

CA potently inhibited nitric oxide (NO) generation and expression of inducible nitric oxide synthase (iNOS) in LPS-activated macrophages and IFN-γ/TNF-α-stimulated HaCaT cells. Regarding the underlying mechanism, NF-κB and mitogen-activated protein kinase (MAPK) pathways, typical intracellular pathways for iNOS regulation, were not affected by CA. CA potently suppressed Janus kinase 2 (JAK2) and signal transducers and activators of transcription 1 (STAT1) phosphorylation, and subsequent nuclear translocation of p-STAT1. The in vivo relevance was analyzed after topical and systemic application of CA in TPA-induced ear edema and carrageenan (CRG)-induced paw edema models, respectively. Topically applied CA produced significant protection against TPA-induced ear edema along with suppressed histopathological changes. Systemic administration of CA also produced significant protection against CRG-induced paw edema in rats, where CRG-induced iNOS and STAT1 phosphorylation were suppressed by CA.

Collectively, we propose that CPD 14 and CA are the potential therapeutic options for the conditions associated with excessive inflammation.

Key words: Synthetic flavonoid, coniferyl aldehyde, anti-inflammatory activity, TPA-induced acute inflammation, oxazolone-induced atopic dermatitis, carrageenan-induced paw edema