Increased potency of a novel complement factor 5a receptor antagonist in a rat model of inflammatory bowel disease

We have previously shown that complement factor 5a(C5a) plays a role in the pathogenesis of 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced colitis in rats by using the selective, orally active C5a antagonist AcF-[OP(D-Cha) WR]. This study tested the efficacy and potency of a new C5a antagonist, hydrocinnamate (HC)-[OP(D-Cha) WR], which has limited intestinal lumenal metabolism, in this model of colitis. Analogs of AcF-[OP(D-Cha) WR] were examined for their susceptibility to alimentary metabolism in the rat using intestinal mucosal washings. One metabolically stable analog, HC-[OP(D-Cha)WR], was then evaluated pharmacokinetically and investigated at a range of doses (0.03 - 10 mg/kg/ day p.o.) in the 8-day rat TNBS- colitis model, against the comparator drug AcF-[OP(D-Cha) WR]. Using various amino acid substitutions, it was determined that the AcF moiety of AcF-[OP(D-Cha) WR] was responsible for the metabolic instability of the compound in intestinal mucosal washings. The analog HC-[OP( D-Cha) WR], equiactive in vitro to AcF-[OP(D-Cha) WR], was resistant to intestinal metabolism, but it displayed similar oral bioavailability to AcF-[OP(D-Cha) WR]. However, in the rat TNBS- colitis model, HC-[OP(D-Cha) WR] was effective at reducing mortality, colon edema, colon macroscopic scores, and increasing food consumption and body weights, at 10- to 30- fold lower oral doses than AcF-[OP( D-Cha) WR]. These studies suggest that resistance to intestinal metabolism by HC-[OP(D-Cha) WR] may result in increased local concentrations of the drug in the colon, thus affording efficacy with markedly lower oral doses than AcF-[OP(D-Cha) WR] against TNBS-colitis. This large increase in potency and high efficacy of this compound makes it a potential candidate for clinical development against intestinal diseases such as inflammatory bowel disease.

Systemic regulation of intestinal iron absorption

The intestinal absorption of the essential trace element iron and its mobilization from storage sites in the body are controlled by systemic signals that reflect tissue iron requirements. Recent advances have indicated that the liver-derived peptide hepcidin plays a central role in this process by repressing iron release from intestinal enterocytes, macrophages and other body cells. When iron requirements are increased, hepcidin levels decline and more iron enters the plasma. It has been proposed that the level of circulating diferric transferrin, which reflects tissue iron levels, acts as a signal to alter hepcidin expression. In the liver, the proteins HFE, transferrin receptor 2 and hemojuvelin may be involved in mediating this signal as disruption of each of these molecules decreases hepcidin expression. Patients carrying mutations in these molecules or in hepcidin itself develop systemic iron loading (or hemochromatosis) due to their inability to down regulate iron absorption. Hepcidin is also responsible for the decreased plasma iron or hypoferremia that accompanies inflammation and various chronic diseases as its expression is stimulated by pro-inflammatory cytokines such as interleukin 6. The mechanisms underlying the regulation of hepcidin expression and how it acts on cells to control iron release are key areas of ongoing research.

A survey of the intestinal transcriptomes of the hookworms, Necator americanus and Ancylostoma caninum, using tissues isolated by laser microdissection microscopy

The gastrointestinal tracts of multi-cellular blood-feeding parasites are targets for vaccines and drugs. Recently, recombinant vaccines that interrupt the digestion of blood in the hookworm gut have shown efficacy, so we explored the intestinal transcriptomes of the human and canine hookworms, Necator americanus and Ancylostoma caninum, respectively. We used Laser Microdissection Microscopy to dissect gut tissue from the parasites, extracted the RNA and generated cDNA libraries. A total of 480 expressed sequence tags were sequenced from each library and assembled into contigs, accounting for 268 N. americanus genes and 276 A. caninum genes. Only 17% of N. americanus and 36% of A. caninum contigs were assigned Gene Ontology classifications. Twenty-six (9.8%) N. americanus and 18 (6.5%) A. caninum contigs did not have homologues in any databases including dbEST-of these novel clones, seven N. americanus and three A. caninum contigs had Open Reading Frames with predicted secretory signal peptides. The most abundant transcripts corresponded to mRNAs encoding cholesterol-and fatty acid-binding proteins, C-type lectins, Activation-Associated Secretory Proteins, and proteases of different mechanistic classes, particularly astacin-like metallopeptidases. Expressed sequence tags corresponding to known and potential recombinant vaccines were identified and these included homologues of proteases, anti-clotting factors, defensins and integral membrane proteins involved in cell adhesion. (c) 2006 Australian Society for Parasitology Inc Published by Elsevier Ltd. All fights reserved.