Eicosanoids and inflammatory bowel disease: regulation and prospects for therapy

Ganglioside Alters Phospholipase Trafficking, Inhibits NF-κB Assembly, and Protects Tight Junction Integrity

Background and Aims: Dietary gangliosides are present in human milk and consumed in low amounts from organ meats. Clinical and animal studies indicate that dietary gangliosides attenuate signaling processes that are a hallmark of inflammatory bowel disease (IBD). Gangliosides decrease pro-inflammatory markers, improve intestinal permeability, and reduce symptoms characteristic in patients with IBD. The objective of this study was to examine mechanisms by which dietary gangliosides exert beneficial effects on intestinal health. Methods: Studies were conducted in vitro using CaCo-2 intestinal epithelial cells. Gangliosides were extracted from milk powder and incubated with differentiated CaCo-2 cells after exposure to pro-inflammatory stimuli. Gut barrier integrity was assessed by electron microscopy, epithelial barrier function was examined by measuring transepithelial electric resistance, and content of HBD-2, IL-23, NF-κB, and sPLA₂ was assessed by ELISA. Results: Ganglioside attenuated the decrease in integrity of tight junctions induced by pro-inflammatory stimuli and improved epithelial barrier function (P < 0.05). Ganglioside decreased the basolateral secretion of sPLA₂ (P ≤ 0.05), lowered HBD-2 and IL-23 levels (P ≤ 0.05), and inhibited NF-κB activation (P ≤ 0.05). Conclusions: In summary, the present study indicates that ganglioside GD3 improves intestinal integrity by altering sPLA₂ trafficking, and the production of pro-inflammatory mediators is mitigated by decreasing assembly of the NF-κB complex. Dietary gangliosides may have promising potential beneficial effects in IBD as decreased inflammatory signaling, improved intestinal integrity, and maintenance of epithelial barrier function have been demonstrated in vitro.

Recent discoveries on absorption of dietary fat: Presence, synthesis, and metabolism of cytoplasmic lipid droplets within enterocytes

Dietary fat provides essential nutrients, contributes to energy balance, and regulates blood lipid concentrations. These functions are important to health, but can also become dysregulated and contribute to diseases such as obesity, diabetes, cardiovascular disease, and cancer. Within enterocytes, the digestive products of dietary fat are re-synthesized into triacylglycerol, which is either secreted on chylomicrons or stored within cytoplasmic lipid droplets (CLDs). CLDs were originally thought to be inert stores of neutral lipids, but are now recognized as dynamic organelles that function in multiple cellular processes in addition to lipid metabolism. This review will highlight recent discoveries related to dietary fat absorption with an emphasis on the presence, synthesis, and metabolism of CLDs within this process.

Protective effect of Bauhinia tomentosa on acetic acid induced ulcerative colitis by regulating antioxidant and inflammatory mediators

Inflammatory bowel diseases (IBD), including Crohn's disease and Ulcerative colitis (UC), are life-long and recurrent disorders of the gastrointestinal tract with unknown etiology. The present study is designed to evaluate the ameliorative effect of Bauhinia tomentosa during ulcerative colitis (UC). Three groups of animals (n=6) were treated with B. tomentosa (5, 10, 20 mg/kg B.wt respectively) for 5 consecutive days before induction of UC. UC was induced by intracolonic injection of 3% acetic acid. The colonic mucosal injury was assessed by macroscopic scoring and histological examination. Furthermore, the mucosal content of lipid peroxidation (LPO), reduced glutathione (GSH), nitric oxide (NO), glutathione peroxidase (GPx) and superoxide dismutase (SOD) activity confirms that B. tomentosa could significantly inhibit colitis in a dose dependent manner. The myeloperoxidase (MPO), tumor necrosis factor (TNF-α), inducible nitric oxide synthase (iNOS) expression studies and lactate dehydrogenase (LDH) assay also supported that B. tomentosa could significantly inhibit experimental colitis. The effect was comparable to the standard drug sulfasalazine. Colonic mucosal injury parallels with the result of histological and biochemical evaluations. The extracts obtained from B. tomentosa possess active substances, which exert marked protective effects in acute experimental colitis, possibly by regulating the antioxidant and inflammatory mediators.

Intestinal inflammation in TNBS sensitized rats as a model of chronic inflammatory bowel disease

An enteritis, based on a delayed-type hypersensitivity reaction, was induced in TNBS (2,4,4-trinitrobenzenesulphonic acid) sensitized rats by multiple intrajejunal challenge with TNBS via an implanted catheter. This treatment induced chronic inflammation of the distal small intestine characterized by intense hyperaemia, oedema and gut wall thickening as assessed by macroscopic scoring and weighing a defined part of the dissected intestine. Histologically, the inflammatory response included mucosal and submucosal cell infiltration by lymphocytes and histiocytes, transmural granulomatous inflammation with multinucleated cells and activated mesenteric lymph nodes. Ex vivo stimulated release of the inflammatory mediator LTB₄ in the dissected part of the intestine was increased following TNBS treatment. Drug treatment with sulphasalazine or 5-aminosalicylic acid improved the enteritis score and attenuated TNBS induced oedema formation and LTB₄ production. The applicability and relevance of this new model are discussed with respect to drug development and basic research of inflammatory bowel diseases.

Sequential release of cytokines, lipid mediators and nitric oxide in experimental colitis

The object of this study was to establish whether different pro- and anti-inflammatory mediators were formed in colonic tissue from experimental colitis depending on the course of the disease. Concentrations of mediators of inflammation were examined in colonic tissue in dextran induced colitis in mice. Initial inflammation was produced by 5 days treatment of 10% dextran sodium sulfate (DSS) in drinking water, followed by a further 9 day period of 2% DSS in an attempt to produce a milder chronic inflammation. The degree of inflammation was scored by a standardized macroscopic and histological examination. Initially, a 60% maximum inflammation score was observed at day 4. At this time inflammation was associated with the release of interleukin-lβ (IL-1β) and tumour necrosis factor-α (TNFα), whereas both prostaglandins 6kPGF_1α and PGE₂ and nitric oxide (NO) markedly decreased. Then a 25% inflammation score was reached which coincided with an increased production of platelet-activating factor (PAF). No significant changes were observed in leukotriene B₄ and C₄ formation. In conclusion, pro-inflammatory cytokines IL-1β and TNFα are considered to be primary mediators, whereas PAF, eicosanoids and NO may reflect secondary mediators in experimental colitis.

Role of eicosanoids on intestinal epithelial homeostasis

The intestinal epithelium is a highly dynamic system that is continuously renewed by a process involving cell proliferation and differentiation. Moreover, it is the main interface with the external environment, and maintenance and regulation of the epithelial structure and epithelial barrier function are key determinants of digestive health and host well being. The tight junction, a multiprotein complex composed of transmembrane proteins associated with the cytoskeletal peri-junctional ring of actin and myosin, is an essential component of this barrier that is strictly regulated in a spatio-temporal manner by a complex signaling network. Defects in the intestinal epithelial barrier function have been observed in inflammatory bowel disease, and a classic example of the connection between inflammation and cancer is the increased risk of colorectal cancer in patients with inflammatory bowel disease. In recent years, several molecules have emerged as critical players contributing to inflammation-associated colorectal cancer. For example, eicosanoids derived from arachidonic acid are proposed as mediators involved in the regulation of epithelial structure/function. Interestingly, the tissue concentration of eicosanoids increases during mucosal inflammation and colorectal cancer development. This overview focuses on the physiological and physiopathological roles of eicosanoids in cell growth/cell differentiation/apoptosis and in the paracellular permeability of the intestinal epithelium. A better understanding of these processes will foster new ideas for the development of therapies for these chronic disorders.

5-Lipoxygenase-derived lipid mediators are not required for the development of NSAID-induced inflammatory bowel disease in IL-10-/- mice

Leukotrienes are potent lipid mediators derived from the metabolism of arachidonic acid by the enzyme 5-lipoxygenase (5-LO). Elevated levels of the proinflammatory leukotriene LTB(4) have been found in preclinical models of inflammatory bowel disease (IBD) as well as in colon tissue from individuals with IBD. We therefore determined the extent to which absence of 5-LO-derived lipid mediators would alter the colitis in IL-10(-/-) mice, a model of human IBD. IL-10(-/-)/5-LO(-/-) mice were generated and were healthy. Absence of 5-LO did not alter the development of spontaneous colitis in IL-10-deficient mice. We then evaluated the extent to which absence of 5-LO would alter the development of NSAID-induced colitis in IL-10(-/-) mice. Absence of 5-LO did not delay the onset or alter the severity of inflammation in NSAID-treated IL-10(-/-) mice. At an early time point, 3 days after NSAID treatment was initiated, a qualitative increase in the number of dendritic cells and CD4(+) T cells was noted in the colons of IL-10(-/-)/5-LO(-/-); however, this difference was no longer present after 14 days of NSAID treatment. Absence of 5-LO did not alter the degree of neutrophil infiltration into the in this model. Absence of 5-LO does not alter the development of IFN-gamma producing Th1-type CD4(+) T cells or IL-17 producing CD4(+) T cells. Absence of 5-LO-derived mediators did not alter the expression of the adhesion molecules ICAM-1 and P-selectin. Development of colitis in IL-10(-/-) mice was associated with increased levels of the 5-LO-derived anti-inflammatory lipoxin LXA(4). These studies demonstrate that 5-LO-derived leukotrienes are not required for the development or maintenance of spontaneous or NSAID-induced colonic inflammation in IL-10(-/-) mice.

Increased interleukin-10 production and Th2 skewing in the absence of 5-lipoxygenase

Eicosanoids (prostaglandins and leukotrienes) are important mediators of inflammatory responses. These lipid mediators may also regulate the production of peptide mediators of the immune system. In this study, we investigated the effect of the absence of 5-lipoxygenase (5-LO)-derived leukotrienes on interleukin (IL)-10 production. IL-10 is a key regulator of immune and inflammatory responses, and previous studies have suggested that prostaglandins effect their immunosuppressive functions in part by stimulation of IL-10 production. We therefore investigated whether leukotriene production would have a similar role in regulation of IL-10 production. We have made the striking observation that absence of 5-LO-derived leukotrienes results in increased IL-10 production with a concomitant decrease in the production of pro-inflammatory cytokines, including tumour necrosis factor (TNF)-alpha and IL-12. Moreover, T-cell cytokine production in the absence of 5-LO-derived leukotrienes results in increased IL-4 production and decreased interferon (IFN)-gamma production. This may be in part secondary to increased IL-10 production and its effects on dendritic cell function resulting in altered T-cell differentiation. These findings indicate that, in addition to the central role leukotrienes play in the acute inflammatory response, endogenous leukotrienes are also important regulators of inflammatory cytokine production, via regulation of IL-10 production and in vivo differentiation of T cells.

Involvement of 5-lipoxygenase in spinal cord injury

A traumatic spinal cord injury (SCI) induces a sequelae of events which conduce biochemical and cellular alterations. Here we compare the degree of spinal cord injury caused by the application of vascular clips, in mice lacking the 5-lipoxygenase and in the corresponding wild-type mice. Biochemical, immunohistochemical and functional studies revealed respectively an increase of neutrophils infiltration, of IL-1beta, TNF-alpha immunoreactivity, apoptosis (measured by Annexin-V staining) and loss of hind legs movement in SCI operated 5-LO wild-type mice. In contrast, the degree of (1) neutrophil infiltration at different time points, (2) cytokine expression (TNF-alpha and IL-1beta), (3) histological damage, (4) apoptosis, was markedly reduced in the tissues obtained from SCI operated 5-LO deficient mice and (5) the motor recovery was ameliorated.

5-lipoxygenase knockout mice exhibit a resistance to acute pancreatitis induced by cerulein

Here we compare the degree of pancreatitis caused by cerulein in mice lacking 5-lipoxygenase (5-LO) and in the corresponding wild-type mice. Intraperitoneal injection of cerulein in mice resulted in severe, acute pancreatitis characterized by oedema, neutrophil infiltration and necrosis and elevated serum levels of amylase and lipase. Infiltration of pancreatic and lung tissue with neutrophils (measured as increase in myeloperoxidase activity) was associated with enhanced lipid peroxidation (increased tissue levels of malondialdehyde). Immunohistochemical examination demonstrated a marked increase in immunoreactivity for intracellular adhesion molecule-1 (ICAM-1), P-selectin and E-selectin in the pancreas and lung of cerulein-treated mice. In contrast, the degree of (1) pancreatic inflammation and tissue injury (histological score), (2) up-regulation/expression of P-selectin, E-selectin and ICAM-1, and (3) neutrophil infiltration was markedly reduced in pancreatic and lung tissue obtained from cerulein-treated 5-LO-deficient mice. These findings support the view that 5-LO plays an important, pro-inflammatory role in the acute pancreatitis caused by cerulein in mice.

5-Lipoxygenase knockout mice exhibit a resistance to pleurisy and lung injury caused by carrageenan

In the present study, by comparing the responses in wild-type (WT) mice and mice lacking [knockout (KO)] the 5-lipoxygenase (5-LO), we investigated the role played by 5-LO in the development of acute inflammation. When compared with carragenan-treated 5-LOWT mice, 5-LOKO mice, which had received carrageenan, exhibited a reduced degree of pleural exudation, polymorphonuclear cell migration. Lung myeloperoxidase activity, an index of neutrophil infiltration, was significantly reduced in 5-LOKO mice in comparison with 5-LOWT. Lung-tissue sections from carrageenan-treated 5-LOWT mice showed positive staining for intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), P-selectin, and E-selectin, which were mainly localized around vessels. The intensity and degree of ICAM-1, VCAM-1, P-selectin, and E-selectin were markedly reduced in tissue section from carrageenan-5-LOKO mice, which also improved the histological status of the inflamed lungs. Taken together, our results clearly demonstrate that 5-LO modulates neutrophil infiltration in the acute lung inflammation.

Efficacy and safety of oral ridogrel in the treatment of ulcerative colitis: two multicentre, randomized, double-blind studies

BACKGROUND

Ridogrel at low doses inhibits thromboxane synthase. Oral ridogrel, from 5 mg once daily to 150 mg twice daily, improves the endoscopic appearance of colonic mucosa and clinical manifestations in mild to moderate ulcerative colitis.

AIM

One US trial and one international trial were conducted to determine the effect of ridogrel on mild to severe active ulcerative colitis.

METHODS

Two 12-week, double-blind, randomized, parallel-group trials were conducted. A US trial compared 0.5 mg, 2.5 mg and 5 mg of ridogrel once daily with placebo. An international trial compared 0.5 mg of ridogrel once daily with 2.5 mg and 5.0 mg of ridogrel once daily and 800 mg of mesalazine (known as mesalamine in the USA) three times daily. The primary efficacy outcome measure was the rate of complete remission.

RESULTS

In the US trial, complete remission was achieved in 20.8% of patients in the 0.5 mg ridogrel group, 17.9% in the 2.5 mg ridogrel group, 20.6% in the 5.0 mg ridogrel group and 13.6% in the placebo group. In the international trial, 14.4% of patients in the 0.5 mg ridogrel group, 19.6% in the 2.5 mg ridogrel group, 19.4% in the 5.0 mg ridogrel group and 16.4% in the mesalazine group experienced complete remission. In the international trial, rates of complete remission at the end-point were greater in the 2.5 mg and 5.0 mg ridogrel groups than in the 0.5 mg ridogrel group, but the differences were not statistically significant. In the US trial, rates of complete remission at the end-point were greater in the 2.5 mg and 5.0 mg ridogrel groups than in the placebo group, but the differences were not statistically significant. Approximately 30% of the patients in each group discontinued treatment before the 12-week end-point owing to a lack of therapeutic response. All doses of ridogrel were well tolerated and comparable with placebo or mesalazine in terms of safety.

CONCLUSIONS

No significant differences in the primary efficacy outcome measure were found between either the 2.5 mg or the 5.0 mg dose of ridogrel and placebo in the US trial and between either the 2.5 mg or the 5.0 mg dose of ridogrel and the 0.5 mg dose of ridogrel, a surrogate dose for placebo, in the international trial. There was no clear indication in either trial of an effective dose of ridogrel in the treatment of ulcerative colitis.

Eicosanoids and the large intestine

During the past three decades, many studies have been conducted to determine the precise role of eicosanoids in colorectal physiology and pathophysiology. This research has increased our understanding of bioactive lipid signaling, and may contribute to the development of more effective therapeutic modalities for digestive diseases in the future. The purpose of this report is to provide a brief overview of the role of eicosanoids in the colon and rectum. This information has been organized according to both functional and disease-related categories. The role of eicosanoids in colonic secretion, motility, inflammatory bowel disease, and colorectal neoplasia will be discussed.

ANTI-INFLAMMATORY ACTIVITY OF PHYCOCYANIN EXTRACT IN ACETIC ACID-INDUCED COLITIS IN RATS

The anti-inflammatory effect of c-phycocyanin extract was studied in acetic acid-induced colitis in rats. Phycocyanin (150, 200 and 300 mg kg-1 p.o.) was administered 30 min before induction of colitis with enema of 1 ml of 4% acetic acid per rat. Twenty-four hours later myeloperoxidase (MPO) activity was determined as well as histopathological and ultrastructural studies were carried out in colonic tissue. Phycocyanin substantially reduced MPO activity which was increased in the control colitis group. Also, histopathological and ultrastructural studies showed inhibition in inflammatory cell infiltration and reduction to some extent in colonic damage in rats treated with phycocyanin. The probable role of antioxidative and the scavenging properties of phycocyanin against reactive oxygen species in the anti-colitic effect is discussed in this paper. To our knowledge this is the first report on the anti-inflammatory effect of phycocyanin in an experimental model of colitis.(c) 1999 The Italian Pharmacological Society.

Role of the 5-lipoxygenase-activating protein (FLAP) in murine acute inflammatory responses

Leukotrienes are potent inflammatory mediators synthesized from arachidonic acid (AA) predominately by cells of myeloid origin. The synthesis of these lipids is believed to be dependent not only on the expression of the enzyme 5-lipoxygenase (5-LO), which catalyzes the first steps in the synthesis of leukotrienes, but also on expression of a nuclear membrane protein termed the 5-LO-activating protein (FLAP). To study the relationship of these two proteins in mediating the production of leukotrienes in vivo and to determine whether the membrane protein FLAP has additional functions in various inflammatory processes, we have generated a mouse line deficient in this protein. FLAP-deficient mice develop normally and are healthy. However, an array of assays comparing inflammatory reactions in FLAP-deficient mice and in normal controls revealed that FLAP plays a role in a subset of these reactions. Although examination of DTH and IgE-mediated passive anaphylaxis showed no difference between wild-type and FLAP-deficient animals, mice without FLAP possessed a blunted inflammatory response to topical AA and had increased resistance to platelet-activating factor-induced shock compared to controls. Also, edema associated with Zymosan A-induced peritonitis was markedly reduced in animals lacking FLAP. To determine whether these differences relate solely to a deficit in leukotriene production, or whether they reflect an additional role for FLAP in inflammation, we compared the FLAP-deficient mice to 5-LO-deficient animals. Evaluation of mice lacking FLAP and 5-LO indicated that production of leukotrienes during inflammatory responses is dependent upon the availability of FLAP and did not support additional functions for FLAP beyond its role in leukotriene production.

The effect of a selective 5-lipoxygenase inhibitor, zileuton, on tissue damage in acute colonic inflammation in rats

Though the mechanism of tissue damage induced by colonic inflammation in ulcerative colitis is unknown, it has been established that the inflammatory mediator and potent neutrophil (PMN) chemotaxin, leukotriene B4(LTB4), is present in elevated amounts in the inflamed mucosa. The unique role of 5-lipoxygenase in the production of leukotrienes has made it a target for inhibition. This study used a rat model of acute colonic inflammation induced by a single IP injection of Mitomycin-C to test the efficacy of a specific and potent 5-lipoxygenase inhibitor zileuton in the treatment of colonic inflammation. We hypothesized that after inducing colitis in rats with mitomycin-C, the administration of oral zileuton would inhibit leukotriene production, thus preventing PMN infiltration and subsequent tissue damage. Zileuton decreased colonic tissue damage as measured by Histological score. However, zileuton did not significantly decrease neutrophil infiltration measured by mucosal PMN or myeloperoxidase (MPO) levels. Although zileuton was successful in significantly decreasing the frequency of severe colitis in our model, the fact that the decrease in PMN count and MPO level was not statistically significant suggests that another mechanism may be involved in its anti-inflammatory effect.

Mediators of inflammation in chronic inflammatory bowel disease

A distinguishing feature of inflammatory bowel disease (IBD) is its apparently spontaneous, chronic relapsing course. Despite extensive research over several decades the etiology of IBD remains unknown, but evidence has accumulated to suggest that the mucosal inflammatory response may be caused by (i) a defective mucosal barrier function resulting in an abnormally increased exposure to luminal antigens and toxins, (ii) an appropriate immunologic response to an unusual infection, antigen or toxin, or (iii) an inappropriate immunological response to ubiquitous antigens or stimuli. In recent years, the identification of established and potential mediators of inflammation has expanded to include eicosanoids, platelet activating factor, biogenic amines, kinins, complement-derived peptides, chemotactic peptides, cytokines, neuropeptides, and reactive metabolites of oxygen and nitrogen. Thus, the study of the inflammatory process has become ever more complex. Until the predisposing and trigger factors have been identified the achievement of a more rational and effective approach to therapy in IBD relies on interruption of the mechanisms responsible for excess mediator formation. As summarized in this review on the role of soluble mediators of inflammation, several Danish gastroenterologists have been profoundly engaged in basic and clinical research in the past 25 years to place some pieces of the confusing puzzle of IBD.

Eicosanoids and the gastrointestinal tract

Determining the role of eicosanoids in gastrointestinal physiology and pathophysiology has been an active area of investigation over the past 20 years. The landmark discovery of prostaglandin endoperoxide synthase and other enzymes involved in the production of arachidonic acid products (lipoxygenases and epoxygenases) ushered in a new era of research. The goal of this review is to distill a large body of work pertaining to studies of eicosanoids in the gastrointestinal tract. This review has been organized according both to functional (secretion and motility) and disease-related (inflammation, mucosal injury, and neoplasia) effects. The aim of this article is to present a clear summary of this area of gastroenterology so that future research can be directed in a logical and productive manner.

Effects of intracolonic acetic acid on responses to colorectal distension in the rat

The present study was undertaken to examine the effects of chemical irritation of the colon on responses to noxious colorectal distension (CRD) in the rat. Pressor and abdominal visceromotor (electromyographic, EMG) responses to CRD were examined in chronically instrumented, unanesthetized rats before and at 6 and 24 h after intracolonic instillation of 5% acetic acid (HAc) or saline. The magnitude of the visceromotor response to phasic CRD (80 mmHg, 20 s) was significantly greater in HAc- than in saline-treated rats at both 6 and 24 h. This was accompanied by a significant increase in the resting EMG activity in both groups, but not between groups. There was, however, no change produced in either the resting mean arterial pressure (MAP) or the magnitude of the pressor response to CRD by HAc treatment. Signs of colonic inflammation (leukocyte infiltration) were examined periodically after HAc treatment, but were apparent only at 24 h. It is concluded that mechanical (distension) and chemical irritation (HAc) of the colon can elicit changes in the basal visceromotor activity and the visceromotor response to CRD. These changes seem to reflect an alteration in the sensitivity of the colon to noxious stimuli.

Metabolic disposition of leukotriene B4 (LTB4) and oxidation-resistant analogues of LTB4 in conscious rabbits

1. The kinetics of leukotriene B4 (LTB4), after single i.v. injections of doses of 0.1 to 1 micrograms kg-1, were investigated in conscious rabbits and compared with those of the omega- and beta-oxidation resistant bioactive analogues, 20, 20, 20-trifluoro-LTB4 (20-F3-LTB4) and 3-thio-LTB4, respectively. 2. Immunoreactive LTB4 (IR-LTB4) elimination was first-order, as shown by a constant systemic clearance (ClLTB4) and a proportional increase in the area under the curve (AUC) of the plasma concentration versus time curve over the dose-range studied. Our results showed a good correlation between observed steady-state plasma concentrations (Css) of IR-LTB4 after continuous infusion of LTB4 and those predicted by using the mean estimated ClLTB4 of 93 +/- 4 ml min-1 kg-1, further confirming the linearity of IR-LTB4 elimination. 3. The half-life (t1/2) or IR-LTB4 increased from 0.47 +/- 0.02 to 0.63 +/- 0.04 min as a consequence of a change in the apparent volume of distribution (Vd) from 72 +/- 5 to 109 +/- 13 ml kg-1, for the 0.1 and 1 micrograms kg-1 doses injected, respectively. 4. Single i.v. injections of [3H]-LTB4 (4.7 ng kg-1) were administered, and the decay of plasma [3H]-LTB4 following h.p.l.c. purification was used to estimate the kinetic parameters. The kinetic parameters of [3H]-LTB4 were characterized by a mean systemic clearance (Cl) of 96 +/- 11 ml min-1 kg-1, a t1/2 of 0.53 +/- 0.03 min, and an apparent Vd of 85 +/- 9 ml kg-1, similar to the parameters obtained after LTB4 boluses. 5. The disposition of LTB4 analogues, whether resistant to Omega- or to Beta-oxidation in vitro, did not differ significantly from the disposition of the LTB4 molecule. The half-lives of 20-F3-LTB4 and 3-thio-LTB4 in the circulation were 0.52 +/- 0.07 min and 0.70 +/- 0.11 min, respectively.6. In summary, our results showed that LTB4, as well as Omega-oxidation- and Beta-oxidation-resistant analogues were cleared very rapidly from the rabbit circulation and indicate that in situ, metabolism in blood is not a rate-limiting factor for the elimination of LTB4.

Review article: thromboxanes in inflammatory bowel disease--pathogenic and therapeutic implications

Recent work suggests that thromboxanes may play a major pathogenic role in inflammatory bowel disease. Thromboxanes are produced in excess not only in inflamed mucosa but also in Crohn's disease, by uninflamed bowel and by isolated intestinal and peripheral blood mononuclear cells. Their cellular source is likely to include platelets, neutrophils, endothelial and epithelial cells as well as mononuclear cells, possible stimuli to their overproduction being chemotactic peptides, lipopolysaccharide, leukotrienes, platelet activating factor, interleukin-1, bradykinin and angiotensin II. The pro-inflammatory effects of thromboxanes are both direct (diapedesis and activation of neutrophils, mucosal ulceration, reduction of suppressor T-cell activity) and indirect (vasoconstriction, platelet activation). Although corticosteroids and aminosalicylates inhibit thromboxane synthesis, this action does not necessarily explain their therapeutic effect in inflammatory bowel disease. Selective thromboxane synthesis inhibitors and receptor antagonists, however, ameliorate experimental colitis in animals. Picotamide and ridogrel are dual thromboxane pathway blockers already used in man. Drugs of this type could prove useful not only for the prevention of systemic thrombo-embolism but also for suppressing intestinal mucosal inflammation in patients with inflammatory bowel disease.

NPC 15669, an inhibitor of neutrophil recruitment, is efficacious in acetic acid-induced colitis in rats

BACKGROUND

The efficacy of the leukocyte recruitment inhibitor, N-[9H-2,7-dimethylfluoren-9-ylmethoxy)carbonyl]-L-leucine (NPC 15669) was compared with drugs used to treat inflammatory bowel diseases in a rat model, acetic acid-induced colitis.

METHODS

Colonic damage assessed by visual inspection, histological quantitation of tissue injury, vascular permeability, myeloperoxidase (MPO) accumulation, and synthesis of inflammatory mediators were measured.

RESULTS

Intrarectal pretreatment with NPC 15669 results in a significant reduction of all measured indices of inflammation. The median effective dose (ED50) of NPC 15669 for inhibition of MPO accumulation and vascular permeability is 13.2 mg/kg and 31 mg/kg, respectively. The active moiety of sulfasalazine, 5-aminosalicylic acid (5-ASA), the antioxidant/5-lipoxygenase inhibitor, nordihydroguaiaretic acid (NDGA) and the corticosteroids dexamethasone and hydrocortisone, yielded ED50 values (MPO accumulation) of 68 mg/kg, 95 mg/kg, 0.7 mg/kg, and 13 mg/kg, respectively. When formulated suspensions of NPC 15669, 5-ASA, or dexamethasone were used, potency was increased 10-40-fold. Furthermore, NPC 15669 (10 mg/kg) administered 7 hours after acetic acid and evaluated 24 hours after acetic acid administration significantly attenuated neutrophil influx (70% inhibition of MPO accumulation), whereas 5-ASA (100 mg/kg) displayed no therapeutic effects.

CONCLUSIONS

NPC 15669 may be useful in the treatment of inflammatory disorders.

Inverse regulation of alpha- and beta-adrenoceptors during trinitrobenzenesulfonic acid (TNB)-induced inflammation in guinea-pig small intestine

The hypothesis has been raised that intestinal motor disturbances induced by inflammation of the digestive tract may reflect alterations in intestinal cell-membrane receptors. This question has been addressed herein for adrenoceptors by performing [3H]prazosin, [3H]rauwolscine and [3H]DHA binding studies on guinea-pig jejunal smooth-muscle membrane preparations from both healthy controls and 3, 6, and 10 days after TNB-induced intestinal inflammation. Each of the adrenoceptor subtype-selective radioligands used bound selectively to a single saturable class of sites, with no significant (p < 0.05) variation of dissociation constant (KD) values along the inflammatory process. In contrast maximal binding capacities (Bmax) for the different radioligands varied moderately but significantly (p < 0.05 and p < 0.01) according to the time after TNB injection. The alpha-adrenoceptors were significantly upregulated, respectively from (mean +/- SE in fmoles/mg of proteins) 27 +/- 3.8 (controls) to 91 +/- 3.1 (day 10) for the alpha 1-subtype, and from 26 +/- 2.7 (controls) to 102 +/- 5.9 (day 10) for the alpha 2-subtype. In contrast beta-adrenoceptors were down-regulated from 384 +/- 34.6 (controls) to 158 +/- 17.2 (day 10). These findings highlighted an apparently inverse pathological regulation of intestinal alpha- and beta- adrenoceptor densities. They suggest that changes in intestinal adrenoceptors, probably resulting from functional denervation of the inflamed bowel tissue, may contribute to the altered intestinal motility observed in inflammatory bowel diseases.

New developments in the pharmacotherapy of inflammatory bowel disease

In this article the clinical features and aetiology of inflammatory bowel diseases are described and current pharmacotherapeutic possibilities are explored. Also reviewed are recent developments and future prospects for the pharmacotherapy of inflammatory bowel diseases, including aminosalicylates, corticosteroids, immunosuppressants, lipoxygenase inhibitors, fish oil, sucralfate, bismuth compounds, free radical scavengers, (hydroxy)chloroquine, sodium cromoglycate and methotrexate.

Increased protein tyrosine kinase activity of the colonic mucosa in ulcerative colitis

The protein tyrosine kinase (PTK) activity was measured in the inflamed colonic mucosa of 12 patients with ulcerative colitis and in the normal colonic mucosa of 12 control patients with colon cancer. The specific PTK activity in the particulate fraction obtained from ulcerative colitis mucosa was significantly increased compared with that of normal mucosa (5.10 +/- 0.60 pmol/min/mg versus 2.12 +/- 0.44 pmol/min/mg protein; p less than 0.05). Inflamed ulcerative colitis mucosa also showed a significantly higher total PTK activity in the particulate fraction than normal mucosa (2.60 +/- 0.42 pmol/min/g versus 0.91 +/- 0.16 pmol/min/g tissue; p less than 0.05). Mucosal samples from ulcerative colitis patients were divided into those with mild and those with severe inflammation on histologic examination (n = 6 each). The particulate PTK activity of severely inflamed mucosa was significantly higher than that of mildly inflamed mucosa (p less than 0.05). These results suggest that colonic inflammation in ulcerative colitis is associated with alterations in cellular PTK activity.

5-lipoxygenase inhibitors and their anti-inflammatory activities

A wide variety of agents have been reported as 5-LO inhibitors. The majority of the series appear to be lipophilic reducing agents, including phenols, partially saturated aromatics, and compounds containing heteroatom-heteroatom bonds. Many of these are not selective 5-LO inhibitors, but often affect CO and other LOs as well. In vivo systemic activity for many of these has been, in general, disappointing, probably because of poor bioavailability caused by lipophilicity and metabolic instability (oxidation, and conjugation of phenolic compounds). However, topically a number of agents have shown promise for skin inflammation, with Syntex's lonapalene the most advanced of these. Most results published to date appear more disappointing in the allergy/asthma field. More excitingly, a few structural types are selective 5-LO inhibitors which have shown systemic activity in vivo and in the clinic. Abbott's zileuton (136) appears to be one of the leading compounds in this category, along with other hydroxamates such as BW-A4C (129) from Burroughs-Wellcome. Recent selective non-reducing agents such as Wyeth-Ayerst's Wy-50,295 (143) and the similar ICI compounds such as ICI 216800 (145) also hold promise. The enantiospecific effects of (106) and (145) are especially interesting for the design of new inhibitors. If compounds like these validate the hypothesis that inhibition of 5-LO will have a significant anti-inflammatory effect, a redoubling of effort throughout the industry to find second- and third-generation selective agents may be expected. Part of the difficulty in interpreting and comparing the 5-LO literature is the plethora of test methods and activity criteria. As pointed out in the introduction, inhibition of product release from cells, often stimulated with A23187, has commonly been used to demonstrate 5-LO inhibition. However, this type of assay cannot be assumed to be diagnostic for 5-LO inhibition. Only if specificity for 5-LO product generation and (ideally) activity in cell-free enzymes is also shown should mechanistic interpretations be made. Recently, a new class of compounds was found at Merck which inhibited LT biosynthesis without inhibiting 5-LO, but apparently by a novel, specific mechanism. L-655,240 (169) and L-663,536 (MK-886) (170) were both active in human ISN, with IC50 values in the low micromolar range. Both also orally inhibited GPB (< 1 mg/kg). MK-886 was effective in Ascaris-induced asthma in squirrel monkeys, in rat carrageenan pleurisy, in rat Arthus pleurisy, and (topically) in guinea-pig ear oedema induced by A23187.(ABSTRACT TRUNCATED AT 400 WORDS)

Role of reactive oxygen species in intestinal diseases

It is well known that reactive oxygen metabolites are generated during several pathologies, and that they are able to disturb many cellular processes and eventually lead to cellular injury. After intestinal ischemia, reactive oxygen species are produced when the ischemic tissue is reperfused. The enzyme xanthine oxidase is thought to play a key role in this process. As a result of this oxygen radical production, the permeability of the endothelium and the mucosa increases, allowing infiltration of inflammatory leukocytes into the ischemic area. Moreover, reactive oxygen species are also indirectly involved in leukocyte activation. In turn, these inflammatory cells respond with the production of oxygen radicals, which play an important role in the development of tissue injury. Thus, intestinal ischemia and reperfusion evokes an inflammatory response. Also during chronic intestinal inflammatory diseases, reactive oxygen metabolites are proposed to play an important role in the pathology. Scavenging of reactive oxygen species will thus be beneficial in these disorders.

Optical isomers of a leukotriene B4 antagonist have differential effects on granulocyte diapedesis in the guinea pig dermis

Leukotriene B4 (LTB4) is a proinflammatory product of arachidonic acid metabolism that has been implicated in a number of inflammatory diseases. When injected intradermally into the guinea pig, LTB4 has been shown to elicit a dose-dependent infiltration of granulocytes as assessed by the level of the neutrophil marker enzyme myeloperoxidase. SC-41930 [7-[3-(4-acetyl-3-methoxy-2-propylphenoxy)propoxy]-3,4-dihydro-8- propyl-2H-1-benzopyran-2-carboxylic acid] is a potent LTB4 receptor antagonist. When compounds were coadministered along with LTB4 (35 ng) into the dermal site, racemic SC-41930, (+)-SC-41930, and (-)-SC-41930 each inhibited granulocyte accumulation with ED50 values of 340 +/- 30, 98 +/- 5.7, and 1000 +/- 142 ng, respectively; when given intravenously inhibited with ED50 values of 0.5 +/- 0.06, 0.3 +/- 0.04, and 1.4 +/- 0.19 mg/kg, respectively; and when given intragastrically inhibited with ED50 values of 1.7 +/- 0.20, 1.4 +/- 0.23, and 3.0 +/- 0.41 mg/kg, respectively.

The antiinflammatory agent SC-41930 inhibits granulocyte infiltration of the rodent dermis induced by 6-trans-leukotriene B4

Granulocyte diapedesis in response to the generation of defined chemotaxins such as leukotriene B4 (LTB4), 12(R)-hydroxyeicosatetraenoic acid [12(R)-HETE], C5a, platelet activating factor and others is a hallmark of the inflammatory process that is thought to contribute to the tissue pathology seen in a number of diseases. 6-trans-LTB4 arises through the myeloperoxidase (MPO)-dependent metabolism of sulfidopeptide leukotrienes and through the action of 5-lipoxygenase on 12(R)-HETE. The intradermal (i.d.) injection of 6-trans-LTB4 induces a dose and time dependent influx of granulocytes into the guinea-pig (Hartley) dermis. When various doses of the LTB4 receptor antagonist and antiinflammatory agent, SC-41930 (7-[3-(4-acetyl-3-methoxy-2-propylphenoxy)-propoxy]-3,4-dihydro- 8-propyl-2H-1-benzopyran-2-carboxylic acid) given 30 min ahead of i.d. injection of 6-trans-LTB4 (10 micrograms/i.d. site), granulocyte infiltration, as assessed by dermal levels of the neutrophil marker enzyme MPO was inhibited with an ED50 value of 9.8 mg/kg in the guinea-pig. When various doses (10-25 micrograms) 6-trans-LTB4 were injected in the mouse (CD-1) dermis, there was a dose-related increase in granulocyte accumulation at 4 h. Furthermore when mice were pretreated (-30 min) with SC-41930 (1 mg/kg) orally, the trafficking of granulocytes was inhibited (p less than .01) as assessed by dermal MPO levels. SC-41930 orally inhibits 6-trans-LTB4-induced granulocyte accumulation in the guinea-pig more potently than against the response to 12(R)-HETE(ED50:13.4 mg/kg) but less potently than against LTB4 (ED50:0.6 mg/kg). These multiple activities may contribute to this compound's potential as an inflammatory agent.

Potential role of histamine monochloramine in a rabbit model of ileitis

Histamine chloramines, derived from the chlorination of histamine by granulocyte-derived oxidants, are potential mediators of intestinal injury and dysfunction in states of atopy or inflammation. We assessed the ability of histamine monochloramine to increase epithelial permeability in rabbit distal small intestine and determined whether the conditions for histamine chloramine formation are favorable in a rabbit model of ileitis. Epithelial permeability, quantified by the blood-to-lumen clearance of 51Cr-labeled ethylenediaminetetraacetic acid, was enhanced by luminal perfusion with either histamine or histamine monochloramine (10 microM), although the latter was twice as effective (p less than 0.05). In a rabbit model of ileitis induced by a luminal solution of acetic acid (200 mM) and casein (10 mg/ml) there was a marked increase in epithelial permeability and in the release into the lumen of histamine, myeloperoxidase, 6-keto-prostaglandin F1 alpha and protein. These results suggest that the conditions are favorable for histamine chloramine formation and that histamine and histamine chloramine may impair the integrity of the epithelial barrier.