Abstract
Psoriasis is a chronic autoimmune disease mediated by dysregulated immune responses in dendritic cells (DC) and T cells. The stress-response enzyme heme oxygenase-1 (HO-1) has been described as protective in animal models of psoriasis, however, implementation of HO-1-based therapies is hindered by the lack of clinically-suitable HO-1 inducers. The plant-derived polyphenols, carnosol and curcumin, have been identified as candidate HO-1 inducers however there has been little investigation into their effects on human immune cells. We demonstrate that treatment of human DC with these polyphenols limits DC maturation, reduces pro-inflammatory cytokine production, and prevents induction of allospecific T cell responses, in a manner partially dependent on carbon monoxide (CO). We also characterised their effects in ex-vivo psoriasis PBMC and report that curcumin, but not carnosol, strongly reduces T cell proliferation and cytokine poly-functionality, with reduced expression of psoriatic cytokines IFNγ, IL-17, GM-CSF and IL-22. This study therefore supports reports highlighting the therapeutic potential of curcumin in psoriasis by providing insight into its immunological effects on healthy human DC and psoriasis PBMC. We also demonstrate, for the first time, the anti-inflammatory effects of carnosol in human immune cells.
Highlights
Psoriasis is a chronic autoimmune disease of the skin affecting 2–3% of the population, which manifests as red, scaly plaques with associated pruritus and pain[1]
In order to confirm that carnosol and curcumin are non-toxic in vitro and capable of upregulating heme oxygenase-1 (HO-1) in human dendritic cells (DC) at the concentrations used in this study, DC were treated with carnosol or curcumin (2.5–10 μM) and examined for cell viability and HO-1 expression
The basal expression of HO-1 was reduced in LPS-stimulated DC (Fig. 1D, lane 2), this was overcome in the presence of carnosol or curcumin (Fig. 1D, lanes 3–8)
Summary
Psoriasis is a chronic autoimmune disease of the skin affecting 2–3% of the population, which manifests as red, scaly plaques with associated pruritus and pain[1]. We demonstrate that treatment with carnosol or curcumin prior to stimulation with lipopolysaccharide (LPS) limits DC maturation, reduces production of pro-inflammatory cytokines and attenuates proliferation of allogeneic T cells.
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