Oral efficacy of a leukotriene B4 receptor antagonist in colitic cotton-top tamarins

Blockade of LTB(4) /BLT(1) pathway improves CD8(+) T-cell-mediated colitis

BACKGROUND

Leukotriene B4 (LTB(4) ) has chemotactic properties for activated T cells expressing the high-affinity receptor BLT(1) . This study investigated whether the LTB(4) antagonist (CP-105,693), selective for BLT(1) receptor, could protect mice from colitis mediated by specific cytotoxic CD8(+) T lymphocytes (CTL).

METHODS

Virus-specific colitis was induced in C57Bl/6 mice transferred with lymphoid cells from P14 TcR Tg mice which are specific to class I GP33 peptide of LCMV. Mice were immunized with GP33-pulsed dendritic cells and colitis was elicited by intrarectal administration of the peptide. Colitis was evaluated by body weight loss and macroscopic and histological analysis of colon. In vivo priming of specific CD8(+) CTL was determined using interferon (IFN)-γ ELISPOT and in vivo CTL assays. In some experiments mice were treated with a selective LTB(4) receptor antagonist.

RESULTS

Immunization with GP33-pulsed dendritic cells (DCs) induced priming of specific CD8(+) CTL, as shown by the presence of IFN-γ-producing CD8(+) T cells in colon draining lymph nodes and in vivo CTL assays. Intrarectal challenge with GP33 induced severe colitis and recruitment of granzyme B(+) P14 CD8(+) cells in colon. Treatment with the specific LTB(4) receptor antagonist before elicitation of colitis reduced the severity of colitis and decreased the frequency of specific effectors.

CONCLUSIONS

Colitis can be induced by IFN-γ-producing cytotoxic CD8(+) CTL specific for viral antigen. Blockade of the LTB(4) /BLT(1) pathway by a selective BLT(1) receptor antagonist attenuates colitis by inhibiting CD8(+) effectors recruitment in colon. These data illustrate the therapeutic potential of LTB(4) receptor selective antagonists in protection from CD8(+) T-cell-mediated intestinal inflammation.

Involvement of endogenous leukotriene B4 and platelet-activating factor in polymorphonuclear leucocyte recruitment to dermal inflammatory sites in rats

A critical role for leukotriene B(4) (LTB(4)) and/or platelet-activating factor (PAF) in regulating polymorphonuclear cell (PMN) trafficking to inflammatory sites has been reported in a number of experimental inflammatory models. In vitro, newly synthesized LTB(4) and PAF were shown to act in an autocrine/paracrine or intracrine fashion to enhance intracellular arachidonic acid availability and leukotriene biosynthesis. This suggested potentially cooperative effects of these lipid mediators in regulating PMN extravasation. The present study aimed to elucidate whether endogenous LTB(4) and PAF may both act to regulate plasma extravasation and PMN trafficking to inflammatory sites in experimental inflammation. With this aim, we have used selective and potent PAF and LTB(4) receptor antagonist pretreatments in dermal and pulmonary inflammation models in rats. Our results show additive inhibitory effects of dual LTB(4) and PAF receptor blockade in either PAF- or LTB(4)-elicited cutaneous PMN accumulation compared to single-drug administration. Furthermore, the combined administration of the drugs inhibited the PMN accumulation induced by the chemically unrelated soluble agonists tumour necrosis factor-alpha and C5a. Finally, in a model of pulmonary inflammation induced by the intravenous injection of Sephadex beads, lung neutrophilia was reduced by 63% following the administration of LTB(4) and PAF antagonists, in contrast with the lack of effect of single drug administration. Our results strongly support a role of both endogenous LTB(4) and PAF in regulating PMN trafficking to inflammatory sites in various experimental conditions.

Cytochrome P-450 4F18 is the leukotriene B4 omega-1/omega-2 hydroxylase in mouse polymorphonuclear leukocytes: identification as the functional orthologue of human polymorphonuclear leukocyte CYP4F3A in the down-regulation of responses to LTB4

Leukotriene B(4) (LTB(4)) is a potent chemoattractant for polymorphonuclear leukocytes (PMN) and other cells. Human PMN inactivate LTB(4) by omega-oxidation catalyzed by cytochrome P-450 (CYP) 4F3A. The contribution of the enzymatic inactivation of LTB(4) by CYP4Fs to down-regulating functional responses of cells to LTB(4) is unknown. To elucidate the role of CYP4F-mediated inactivation of LTB(4) in terminating the responses of PMN to LTB(4) and to identify a target for future genetic studies in mice, we have identified the enzyme that catalyzes the omega-1 and omega-2 oxidation of LTB(4) in mouse myeloid cells as CYP4F18. As determined by mass spectrometry, this enzyme catalyzes the conversion of LTB(4) to 19-OH LTB(4) and to a lesser extent 18-OH LTB(4). Inhibition of CYP4F18 resulted in a marked increase in calcium flux and a 220% increase in the chemotactic response of mouse PMN to LTB(4). CYP4F18 expression was induced in bone marrow-derived dendritic cells by bacterial lipopolysaccharide, a ligand for TLR4, and by poly(I.C), a ligand for TLR3. However, when bone marrow-derived myeloid dendritic cells trafficked to popliteal lymph nodes from paw pads, the expression of CYP4F18 was down-regulated. The results identify CYP4F18 as a critical protein in the regulation of LTB(4) metabolism and functional responses in mouse PMN and identify it as the functional orthologue of human PMN CYP4F3A.

Gastrointestinal tract antigenic profile of cotton-top tamarin, Saguinus oedipus, is similar to that of humans with inflammatory bowel disease

As an animal model for human inflammatory bowel disease and colorectal cancer, the cotton-top tamarin remains controversial. Demonstration of antigenic similarity to the human would enhance its validity. Using colonic extracts and washings, we compared binding of seven monoclonal antibodies reactive with bowel and cancer antigens in both tamarins and humans with inflammatory bowel disease. Additionally, telomerase activity was tested for. Expression of a mucin antigen specific to human cancer was increased in tamarin colonic washings as well as aminoproteoglycans and EGFR in tamarin extracts, as compared to those of humans with inflammatory bowel disease (P < 0.005). An adenoma-associated antigen and k-ras p21 protein were negative in the tamarin. A trend to greater telomerase activity exists in tamarins. The antigenic similarity validates this model for human inflammatory bowel disease and colorectal cancer. A trend to increased telomerase activity in tamarins is consistent with the greater predisposition to cancer in these animals.

In vitro investigation of the effect of prostaglandins and nonsteroidal anti-inflammatory drugs on contractile activity of the equine smooth muscle of the dorsal colon, ventral colon, and pelvic flexure

OBJECTIVES

To determine the in vitro effect of prostaglandin E2 (PGE2), PGF2alpha, PGI2; and nonsteroidal anti-inflammatory drugs (NSAID; ie, flunixin meglumine, ketoprofen, carprofen, and phenylbutazone) on contractile activity of the equine dorsal colon, ventral colon, and pelvic flexure circular and longitudinal smooth muscle.

ANIMALS

26 healthy horses.

PROCEDURE

Tissue collected from the ventral colon, dorsal colon, and pelvic flexure was cut into strips and mounted in a tissue bath system where contractile strength was determined. Incremental doses of PGE2, PGF2alpha,, PGI2, flunixin meglumine, carprofen, ketoprofen, and phenylbutazone were added to the baths, and the contractile activity was recorded for each location and orientation of smooth muscle.

RESULTS

In substance P-stimulated tissues, PGE2 and PGF2alpha enhanced contractility in the longitudinal smooth muscle with a decrease or no effect on circular smooth muscle activity. Prostaglandin I2 inhibited the circular smooth muscle response with no effect on the longitudinal muscle. The activity of NSAID was predominantly inhibitory regardless of location or muscle orientation.

CONCLUSIONS AND CLINICAL RELEVANCE

In the equine large intestine, exogenous prostaglandins had a variable effect on contractile activity, depending on the location in the colon and orientation of the smooth muscle. The administration of NSAID inhibited contractility, with flunixin meglumine generally inducing the most profound inhibition relative to the other NSAID evaluated in substance P-stimulated smooth muscle of the large intestine. The results of this study indicate that prolonged use of NSAID may potentially predispose horses to develop gastrointestinal tract stasis and subsequent impaction.

Carboxy-substituted cinnamides: a novel series of potent, orally active LTB4 receptor antagonists

A series of carboxy-substituted cinnamides were investigated as antagonists of the human cell surface leukotriene B4 (LTB4) receptor. Binding was determined through measurement of [3H]LTB4 displacement from human neutrophils. Receptor antagonism was confirmed through a functional assay, which measures inhibition of Ca2+ release in human neutrophils. Potent antagonists were discovered through optimization of a random screening hit, a p-(alpha-methylbenzyloxy)cinnamide, having low-micromolar activity. Substantial improvement of in vitro potency was realized by the attachment of a carboxylic acid moiety to the cinnamide phenyl ring through a flexible tether, leading to identification of compounds with low-nanomolar potency. Modification of the benzyloxy substituent, either through ortho-substitution on the benzyloxy phenyl group or through replacement of the ether oxygen with a methylene or sulfur atom, produced achiral antagonists of equal or greater potency. The most potent compounds in vitro were assayed for oral activity using the arachidonic acid-induced mouse ear edema model of inflammation. Several compounds in this series were found to significantly inhibit edema formation and myeloperoxidase activity in this model up to 17 h after oral administration. Representatives of this series have been shown to be potent and long-acting orally active inhibitors of the LTB4 receptor.