Intestinal alkaline phosphatase in the colonic mucosa of children with inflammatory bowel disease

AIM： To investigate intestinal alkaline phosphatase （iAP） in the intestinal mucosa of children with inflammatory bowel disease （IBD）. METHODS： Colonic biopsy samples were taken from 15 newly diagnosed IBD patients and from 10 healthy controls. In IBD patients, specimens were obtainedboth from inflamed and non-inflamed areas. The lAP mRNA and protein expression was determined by reverse transcription-polymerase chain reaction and Western blotting analysis, respectively. Tissue localiza- tion of lAP and Toll-like receptor （TLR） 4 was investi- gated by immunofluorescent staining. RESULTS： The lAP protein level in the inflamed muco- sa of children with Crohn＇s disease （CD） and ulcerative colitis （UC） was significantly decreased when compared with controls （both P 〈 0.05）. Similarly, we found a significantly decreased level of lAP protein in the in- flamed mucosa in CD compared with non-inflamed mucosa in CD （P 〈 0.05）. In addition, the iAP protein level in inflamed colonic mucosa in patients with UC was decreased compared with non-inflamed mucosa in patients with CD （P 〈 0.05）. lAP protein levels in the non-inflamed mucosa of patients with CD were similar to controls, lAP mRNA expression in inflamed colonic mucosa of children with CD and UC was not significant- ly different from that in non-inflamed colonic mucosa with CD. Expression of lAP mRNA in patients with non- inflamed mucosa and in controls were similar. Co-local- ization of lAP with TLR4 showed intense staining with a dotted-like pattern, lAP was present in the inflamed and non-inflamed mucosa of patients with CD, UC, and in control biopsy specimens, irrespective of whether it was present in the terminal ileum or in the colon. However, the fluorescent signal of TLR4 was more pro- nounced in the colon compared with the terminal ileum in all groups studied. CONCLUSION： Lower than normal lAP protein levels in inflamed mucosa of IBD patients may indicate a role for lAP in inflammatory lesions in IBD. Based on our results, administration of exogenous lAP enzyme to pa- tients with the active form of IBD may be a therapeutic option.

Interplay between intestinal alkaline phosphatase, diet, gut microbes and immunity

Intestinal alkaline phosphatase (IAP) plays an essential role in intestinal homeostasis and health through interactions with the resident microbiota, diet and the gut. IAP’s role in the intestine is to dephosphorylate toxic microbial ligands such as lipopolysaccharides, unmethylated cytosine-guanosine dinucleotides and flagellin as well as extracellular nucleotides such as uridine diphosphate. IAP’s ability to detoxify these ligands is essential in protecting the host from sepsis during acute inflammation and chronic inflammatory conditions such as inflammatory bowel disease. Also important in these complications is IAP’s ability to regulate the microbial ecosystem by forming a complex relationship between microbiota, diet and the intestinal mucosal surface. Evidence reveals that diet alters IAP expression and activity and this in turn can influence the gut microbiota and homeostasis. IAP’s ability to maintain a healthy gastrointestinal tract has accelerated research on its potential use as a therapeutic agent against a multitude of diseases. Exogenous IAP has been shown to have beneficial effects when administered during ulcerative colitis, coronary bypass surgery and sepsis. There are currently a handful of human clinical trials underway investigating the effects of exogenous IAP during sepsis, rheumatoid arthritis and heart surgery. In light of these findings IAP has been marked as a novel agent to help treat a variety of other inflammatory and infectious diseases. The purpose of this review is to highlight the essential characteristics of IAP in protection and maintenance of intestinal homeostasis while addressing the intricate interplay between IAP, diet, microbiota and the intestinal epithelium.

Microbiota-host interplay at the gut epithelial level,health and nutrition

Growing evidence suggests the implication of the gut microbiota in various facets of health and disease. In this review, the focus is put on microbiota-host molecular cross-talk at the gut epithelial level with special emphasis on two defense systems： intestinal alkaline phosphatase（IAP） and inducible heat shock proteins（iHSPs）. Both IAP and iHSPs are induced by various microbial structural components（e.g. lipopolysaccharide, flagellin, CpG DNA motifs）,metabolites（e.g. n-butyrate） or secreted signal molecules（e.g., toxins, various peptides, polyphosphate）. IAP is produced in the small intestine and secreted into the lumen and in the interior milieu. It detoxifies microbial components by dephosphorylation and, therefore, down-regulates microbe-induced inflammation mainly by inhibiting NF-κB pro-inflammatory pathway in enterocytes. IAP gene expression and enzyme activity are influenced by the gut microbiota. Conversely, IAP controls gut microbiota composition both directly, and indirectly though the detoxification of pro-inflammatory free luminal adenosine triphosphate and inflammation inhibition. Inducible HSPs are expressed by gut epithelial cells in proportion to the microbial load along the gastro-intestinal tract. They are also induced by various microbial components, metabolites and secreted molecules. Whether iHSPs contribute to shape the gut microbiota is presently unknown. Both systems display strong anti-inflammatory and anti-oxidant properties that are protective to the gut and the host. Importantly, epithelial gene expressions and protein concentrations of IAP and iHSPs can be stimulated by probiotics, prebiotics and a large variety of dietary components, including macronutrients（protein and amino acids, especially L-glutamine, fat, fiber）, and specific minerals（e.g. calcium）and vitamins（e.g. vitamins K1 and K2）. Some food components（e.g. lectins, soybean proteins, various polyphenols） may inhibit or disturb these systems. The general cel ular and molecular mechanisms involved in the microbiota-host epithelial crosstalk and subsequent gut protection through IAP and iHSPs are reviewed along with their nutritional modulation.Special emphasis is also given to the pig, an economically important species and valuable biomedical model.