IAP is involved in the maintenance of normal gut microbial homeostasis and may have therapeutic potential against dysbiosis and pathogenic infections.

Ramasamy, S., S. Singh, P. Taniere, M. J. S. Langman, and M. C. Eggo. Sulfide-detoxifying enzymes in the human colon are decreased in cancer and upregulated in differentiation. Am J Physiol Gastrointest Liver Physiol 291: G288 -G296, 2006. First published February 23, 2006 doi:10.1152/ajpgi.00324.2005.-H 2S is highly toxic and selectively inhibits butyrate oxidation in colonocytes. Ineffective detoxification may result in mucosal insult, inflammation, and ultimately in colorectal cancer (CRC). Rhodanese can detoxify H 2S and is comprised of two isoenzymes: thiosulfate sulfurtransferase (TST) and mercaptopyruvate sulfurtransferase (MST). Using specific antisera to discriminate TST from MST, we found that only TST could detoxify H2S. In sections of normal colon, both enzymes were located on the luminal mucosal surface, and they were expressed in the colonocytes but not in the mucin-secreting goblet cells. Expression of both enzymes was focally lost in ulcerative colitis and markedly reduced in advanced colon cancer, the disease progression correlating with the decreased expression of MST and TST. In HT-29 cells, a human colon cancer cell line, TST activity and expression were significantly increased by butyrate and by histone deacetylase inhibition, agents that promote HT-29 cell differentiation. Sulfide (0.1 mM) also increased TST activity, but higher sulfide concentrations (0.3-3 mM) were toxic. Preincubation in butyrate to increase TST expression, decreased sensitivity of the cells to sulfide toxicity. We conclude that decreased expression of TST (or MST) is a tumor marker for CRC. TST expression is increased in colonocyte differentiation. Dysregulation of TST expression and activity resulting in inability to effectively detoxify could be a factor in the cell loss and inflammation that accompany ulcerative colitis and ultimately then in CRC. colorectal cancer; thiosulfate sulfurtransferase; butyrate; HT-29 IN THE HUMAN COLON, anaerobic bacteria produce hydrogen sulfide (H 2 S) (25), which inhibits the oxidation of short-chain fatty acids (SCFA) (18,19). SCFAs are the main energy source (Ͼ70% ) for colonocytes (18) and also contribute 5-10% of the total energy supplies in humans. Inhibition of their oxidation in the colon will result in colonocyte starvation and death, resulting in inflammation. This, the "energy deficiency" hypothesis of Roediger (18), is postulated to lead to ulcerative colitis (UC). Many studies have shown that patients with UC have increased colorectal cancer (CRC) risk, with Prior et al. (16) estimating this as an 11-fold excess. On the basis of these studies, we suggest that the expression of enzymes important in sulfide detoxification is essential to preserve a healthy mucosa and that derangements in expression may accompany UC and CRC.We recently showed that colonic mucosal rhodanese can detoxify hydrogen sulfide (15) and thus might protect against mucosal injury. Rhodanese is a mitochondrial enzyme, present in all living organisms from bacteria to humans, and is thought to play a cen...

Intestinal alkaline phosphatase (IAP) is a small intestinal brush border enzyme that has been shown to function as a gut mucosal defense factor, but its precise mechanism of action remains unclear. We investigated the effects of IAP on specific bacteria and bacterial components to determine its molecular targets. Purulent fluid from a cecal ligation and puncture model, specific live and heat-killed bacteria (Escherichia coli, Salmonella typhimurium, and Listeria monocytogenes), and a variety of proinflammatory ligands (LPS, CpG DNA, Pam-3-Cys, flagellin, and TNF) were incubated with or without calf IAP (cIAP). Phosphate release was determined by using a malachite green assay. The various fluids were applied to target cells (THP-1, parent HT-29, and IAP-expressing HT-29 cells) and IL-8 secretion measured by ELISA. cIAP inhibited IL-8 induction by purulent fluid in THP-1 cells by >35% (P < 0.005). HT29-IAP cells had a reduced IL-8 response specifically to gram-negative bacteria; >90% reduction compared with parent cells (P < 0.005). cIAP had no effect on live bacteria but attenuated IL-8 induction by heat-killed bacteria by >40% (P < 0.005). cIAP exposure to LPS and CpG DNA caused phosphate release and reduced IL-8 in cell culture by >50% (P < 0.005). Flagellin exposure to cIAP also resulted in reduced IL-8 secretion by >40% (P < 0.005). In contrast, cIAP had no effect on TNF or Pam-3-Cys. The mechanism of IAP action appears to be through dephosphorylation of specific bacterial components, including LPS, CpG DNA, and flagellin, and not on live bacteria themselves. IAP likely targets these bacterially derived molecules in its role as a gut mucosal defense factor.