Effect of curcumin on acidic pH-induced expression of IL-6 and IL-8 in human esophageal epithelial cells (HET-1A): role of PKC, MAPKs, and NF-κB

Abstract

Human esophageal epithelial cells play a key role in esophageal inflammation in response to acidic pH during gastroesophageal reflux disease (GERD), increasing secretion of IL-6 and IL-8. The mechanisms underlying IL-6 and IL-8 expression and secretion in esophageal epithelial cells after acid stimulation are not well characterized. We investigated the role of PKC, MAPK, and NF-kappaB signaling pathways and transcriptional regulation of IL-6 and IL-8 expression in HET-1A cells exposed to acid. Exposure of HET-1A cells to pH 4.5 induced NF-kappaB activity and enhanced IL-6 and IL-8 secretion and mRNA and protein expression. Acid stimulation of HET-1A cells also resulted in activation of MAPKs and PKC (alpha and epsilon). Curcumin, as well as inhibitors of NF-kappaB (SN-50), PKC (chelerythrine), and p44/42 MAPK (PD-098059) abolished the acid-induced expression of IL-6 and IL-8. The JNK inhibitor SP-600125 blocked expression/secretion of IL-6 but only partially attenuated IL-8 expression. The p38 MAPK inhibitor SB-203580 did not inhibit IL-6 expression but exerted a stronger inhibitory effect on IL-8 expression. Together, these data demonstrate that 1) acid is a potent inducer of IL-6 and IL-8 production in HET-1A cells; 2) MAPK and PKC signaling play a key regulatory role in acid-mediated IL-6 and IL-8 expression via NF-kappaB activation; and 3) the anti-inflammatory plant compound curcumin inhibits esophageal activation in response to acid. Thus IL-6 and IL-8 expression by acid may contribute to the pathobiology of mucosal injury in GERD, and inhibition of the NF-kappaB/proinflammatory cytokine pathways may emerge as important therapeutic targets for treatment of esophageal inflammation.

Trypsin impaired epithelial barrier function and induced IL-8 secretion through basolateral PAR-2: a lesson from a stratified squamous epithelial model

“…Previous research using esophageal monolayer cells showed that weak acid could upregulate IL-8 gene expression (18,28). However, in our model, 24 h continuous weak acid (pH 4, 5, and 6) apical stimulation did not affect IL-8 production or TEER.…”

Protective Effects of Chlorogenic Acid against Experimental Reflux Esophagitis in Rats

“…COX-2 inhibitors such as celecoxib significantly reduced the severity of chronic esophagitis (Hayakawa et al, 2006). Nuclear factor-kappa B, mitogen-activated protein kinases and protein kinase C activation are known to be involved in the regulation of acid-induced upregulation of these inflammatory mediators in vitro (Rafiee et al, 2009). In the present study, serum levels of TNF-α and iNOS and COX-2 protein expressions in esophageal tissues were increased by RE, and CGA attenuated these increases.…”

Dickkopf-1, the Wnt antagonist, is induced by acidic pH and mediates epithelial cellular senescence in human reflux esophagitis

“…Total cell extracts were prepared and subjected to Western blotting, as previously described (40). Cytoplasmic and nuclear fractions were prepared using the NE-PER kit according to the manufacturer's protocol (Pierce/Thermo Scientific, Rockford, IL).…”

“…Mucosal biopsies of equal size were cultured in 0.5 ml of RPMI medium for 24 h, as previously described (40). Dkk1 secretion was assessed in tissue and cell culture media by ELISA (R & D Systems) according to the manufacturer's protocol.…”