Anti-inflammatory activity of Persicaria tinctoria extract against the environmental toxic stress-induced inflammation in HaCaT keratinocytes

Abstract

Persicaria tinctoria is one of the representative natural dyes and has been commonly used in traditional medicines. The anti-inflammatory activity of Persicaria tinctoria has been reported for oxidative stress-induced models. However, the effect of Persicaria tinctoria on the environmental toxic stress-induced inflammation is not investigated. In this study, the anti-inflammatory activity and its molecular mechanism of Persicaria tinctoria methanol extract (PE) were evaluated in both the ultraviolet B (UVB)-irradiated and the cadmium/nickel-induced inflammation models in HaCaT keratinocytes. UVB is a major environmental stress to promote skin aging. Nickel, cadmium, lead and other divalent cations are adsorbed or existed in particulate matters (PMs), which are major air pollutants in the environment. PE significantly inhibited PGE2 synthesis in UVB-irradiated HaCaT cells in a concentration-dependent manner. The effects of indigo, indigo carmine, indirubin and thioindigo, major chemical compounds associated with the natural chemicals in Persicaria tinctoria, were evaluated to identify the causative ingredient on the UVB-induced PGE2 up-regulation in HaCaT cells. Indigo and thioindigo significantly inhibited the production of PGE2 in HaCaT cells. Indirubin and indigo carmine had no effect on the UVB-induced PGE2 upregulation in sub-cytotoxic concentrations. To elucidate the molecular mechanisms, the cellular phosphorylation levels of ERK, PI3K/AKT and STAT3 were measured in the indigo and/or thioindigo treated HaCaT cells. Indigo and thioindigo inhibited the phosphorylation of ERK and PI3K/AKT signaling pathways. In addition, indigo suppressed the activation of STAT3 signaling pathway. These results suggest indigoid compounds are partly responsible for the anti-inflammatory activity of PE in the UVB-induced PGE2 up-regulation model in HaCaT keratinocytes. Scanning electron microscope (SEM) observations and energy dispersive X-ray spectroscopy (EDS) analysis were performed to study the morphology, size and elemental composition of particulate matters (PMs) collected in 2015. The detected elements and components in PMs were pollens, microorganisms, sylvites, crystalline sulfides, silicon dioxide fly ash, heavy metals and carbon solid particles originated from anthropogenic sources. Among them, sulfites and heavy metals were chosen as PM-associated inflammatory inducers. The effects of sodium bisulfite, lead chloride, nickel chloride, cadmium chloride or cobalt chloride on the production of PGE2 were evaluated in HaCaT keratinocytes. In HaCaT cells, cadmium chloride significantly increased PGE2 synthesis. Although nickel chloride, cobalt chloride and lead chloride tended to increase PGE2, the level of the PGE2 upregulation was not enough to use the pharmacological screen. PE, indigo and thioindigo significantly attenuated the cadmium-induced PGE2 synthesis in HaCaT cells. As the UVB-induced model, indigo and thioindigo inhibited the phosphorylation of ERK and PI3K/AKT. Therefore, PE and its indigoid compounds, indigo and thioindigo, are candidates for an effective anti-inflammatory agent against the environmental toxic stress-induced inflammation in HaCaT keratinocytes.