Aims/hypothesis The aim of this study was to determine the impact of the common food additive carrageenan (E407) on glucose tolerance, insulin sensitivity and insulin signalling in a mouse model and human hepatic cells, since carrageenan is known to cause inflammation through interaction with toll-like receptor (TLR)4, which is associated with inflammation in diabetes. Methods Male C57BL/6J mice were given carrageenan (10 mg/l) in their drinking water, and underwent a glucose tolerance test (GTT), an insulin tolerance test (ITT) and an ante-mortem intraperitoneal insulin injection. HepG2 cells were exposed to carrageenan (1 mg/l×24 h) and insulin. Levels of phospho(Ser473)-protein kinase B (Akt), phospho (Ser307)-IRS1, phosphoinositide 3-kinase (PI3K) activity and phospho(Ser32)-inhibitor of κB (IκBα) were determined by western blotting and ELISA. Results Glucose tolerance was significantly impaired in carrageenan-treated 12-week-old mice compared with untreated controls at all time points (n=12; p<0.0001). Baseline insulin and insulin levels at 30 min after taking glucose during the GTT were significantly higher following carrageenan treatment. During the ITT, glucose levels declined by more than 80% in controls, but not in carrageenan-treated mice. Carrageenan exposure completely inhibited insulininduced increases in phospho-(Ser473)-Akt and PI3K activity in vivo in mouse liver and in human HepG2 cells. Carrageenan increased phospho(Ser307)-IRS1 levels, and this was blocked when carrageenan-induced inflammation was inhibited. Conclusion This is the first report of the impact of carrageenan on glucose tolerance and indicates that carrageenan impairs glucose tolerance, increases insulin resistance and inhibits insulin signalling in vivo in mouse liver and human HepG2 cells. These effects may result from carrageenan-induced inflammation. The results demonstrate extra-colonic manifestations of ingested carrageenan and suggest that carrageenan in the human diet may contribute to the development of diabetes.

Two members of the SLC26 gene family, SLC26A3 or DRA (downregulated in adenoma) and SLC26A6 (putative anion transporter 1, PAT1), are known to play a major role in apical Cl(-)/OH(-) (HCO(3)(-)) exchange process in the human intestine. We have previously shown the inhibitory effects of IFN-gamma (30 ng/ml, 24 h) on both SLC26A3 and A6 expression and promoter activity. We also demonstrated that the effects of IFN-gamma on SLC26A6 gene expression were mediated via IRF-1 transcription factor. However, the molecular mechanisms underlying the transcriptional modulation of SLC26A3 gene expression by IFN-gamma in the intestine are not known. The present studies were, therefore, designed to elucidate the signaling mechanisms and transcription factor(s) involved in mediating the inhibitory effects of IFN-gamma on DRA promoter (p--1183/+114) activity. Deletion analysis indicated that the IFN-gamma response element is located within the -1183 to -790 region, and sequence analysis of this region revealed the presence of potential gamma-activated site (GAS), a binding site (-933/-925 bp) for signal transducer and activator of transcription factor 1 (STAT1). Mutations in the potential GAS element abrogated the inhibitory effects of IFN-gamma. These studies provide evidence for the involvement of STAT1 in the inhibition of SLC26A3 gene expression by IFN-gamma in the human intestine.

To determine the impact of B cell leukemia/lymphoma (BCL) 10 on the phosphorylation of crucial mediators in NF-B-mediated inflammatory pathways, human colonic epithelial cells were exposed to carrageenan (CGN), a sulfated polysaccharide commonly used as a food additive and known to induce NF-B nuclear translocation by both canonical and noncanonical pathways. Phosphorylations of intermediates in inflammatory cascades, including NF-B-inducing kinase (NIK) at Thr 559 , transforming growth factor-␤-activating kinase ( B cell leukemia/lymphoma; nuclear factor-B