Cis‐urocanic acid suppresses UV‐B‐induced interleukin‐6 secretion and cytotoxicity in human corneal and conjunctival epithelial cells in vitro

Abstract

PurposeUrocanic acid (UCA) is a major ultraviolet (UV)-absorbing endogenous chromophore in the epidermis and is also an efficacious immunosuppressant. The anti-inflammatory and cytoprotective effects of cis-UCA were studied in ocular surface cell cultures exposed to UV-B irradiation. MethodsHuman corneal epithelial cells (HCE-2) and human conjunctival epithelial cells (HCECs) were incubated with 10, 100, 1,000, and 5,000 μg/ml cis-UCA with and without a single UV-B irradiation dose. The concentrations of IL-1β, IL-6, IL-8, and TNF-α in the culture medium and caspase-3 activity in the cell extract sampled were measured by enzyme-linked immunosorbent assay (ELISA). Cell viability was measured by the colorimetric MTT (3-(4,5-dimethyldiazol- 2-yl)-2,5-diphenyltetrazolium bromide) assay. ResultsUV-B irradiation multiplied interleukin IL-6 and IL-8 secretion levels in HCE-2 cells and HCECs as analyzed with ELISA. Cell viability as measured by the MTT assay declined by 30%–50% in HCE-2 cells and by 20%–40% in HCECs after UV-B irradiation. Moreover, UV-B increased caspase-3 activity in both cell types as analyzed with ELISA. Treatment with 100 μg/ml cis-UCA completely suppressed IL-6 and IL-8 secretion, decreased caspase-3 activity, and improved cell viability against UV-B irradiation. No significant effects on IL-6 or IL-8 secretion, caspase-3 activity, or viability of the non-irradiated cells were observed with 100 μg/ml cis-UCA in both cell types. The 5,000 μg/ml concentration was toxic. ConclusionsThese findings indicate that cis-UCA may represent a promising anti-inflammatory and cytoprotective treatment option to suppress UV-B-induced inflammation and cellular damage in human corneal and conjunctival epithelial cells.

Quercetin alleviates 4-hydroxynonenal-induced cytotoxicity and inflammation in ARPE-19 cells

“…The assay was performed according to the manufacturer's instructions. Moreover, the ability of cells to metabolize 3-(4,5-dimethyldiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) was assayed as described previously (Viiri et al, 2009). …”

Cis‐urocanic acid inhibits SAPK/JNK signaling pathway in UV‐B exposed human corneal epithelial cells in vitro

“…In addition, after UV stimulation, MnSOD expression has been shown to be UV dose-dependent, exerting diminishing expression in high UV-B doses [10]. However, at the same time, UV-B exposure induces the NF-κB-related proinflammatory cytokines IL-6 and IL-8 in HCE-2 cells [47]. Our research shows that both JNK and NF-κB pathways are activated by UV-B.…”

“…Consistently with an earlier study with epidermal cells [51], the inhibition of JNK pathway seems to be a critical target in the regulation of apoptosis also in human corneal epithelial cells. While cis-UCA was present in the culture medium during UV-B irradiation of the cells, it was inferred from previous experience [47] that the cis-UCA concentration used in the current experiment does not appreciably block the transmission of UV-B photons.…”

“…We have previously shown that cis-UCA suppresses UV-Binduced cytokine expression and improves cell viability against UV-B irradiation in human ocular cells [47]. In the present study, we further investigated the mechanisms of these actions.…”

“…Moreover, cis-UCA neither photobinds to DNA [43,44] nor is able to enhance UV photocarcinogenesis [45], whereas it may suppress immunological recognition of tumor antigens in specific experimental conditions [46]. In our previous study, we have showed that cis-UCA suppresses UV-B-induced interleukin (IL)-6 and IL-8 secretion and cytotoxicity in human corneal and conjunctival cells in vitro [47]. However, the molecular targets of cis-UCA action remain to be resolved.…”