Picotamide inhibition of excess in vitro thromboxane B2 release by colorectal mucosa in inflammatory bowel disease

Effect of pharmaceutical interventions targeting thromboxane receptors and thromboxane synthase in cardiovascular and renal diseases

The present review focuses on the roles of thromboxane A2 (TxA2) in arterial thrombosis, atherogenesis, vascular stent-related ischemic events and renal proteinuria. Particular emphasis is laid on therapeutic interventions targeting the TxA2 (TP) receptors and TxA2 synthase (TS), including dual TP-receptor antagonists and TS inhibitors. Their significant inhibitory efficacies on arterial thrombogenesis, atherogenesis, restenosis after stent placement, vasoconstriction and proteinuria indicate novel and improved treatments for cardiovascular and selected renal diseases. New therapeutic interventions of the TxA2 pathway may also be beneficial for patients with poor biological antiplatelet drug response, for example, to aspirin and/or clopidogrel. These new TP/TS agents offer novel improved treatments to efficiently and simultaneously interfere with thrombogenesis and atherogenesis, and to enlarge the existing panel of platelet inhibitors for efficient prophylaxis and treatment of arterial thrombosis and renal proteinuria.

NV-52

NV-52, a synthetic flavonoid derivative, is a selective thromboxane synthase (TXS) inhibitor that is being developed as a treatment for inflammatory bowel disease. NV-52 selectively inhibits TXS in vitro in physiological relevant concentrations, causing a reduction in thromboxane B(2) of </= 40% in association with an increase in prostaglandin E(2). NV-52 is effective in suppressing colonic inflammation in a murine model of inflammatory bowel disease. NV-52 has not demonstrated any toxicity in in vitro and animal toxicological studies, and has been administered to normal volunteers in a Phase I clinical trial without detectable adverse effects. NV-52 is well absorbed and a single dose of 400 mg p.o. produced a plasma concentration that is comparable with the concentrations that have been shown to produce significant TXS inhibition in vitro.

Paradox of simultaneous intestinal ischaemia and hyperaemia in inflammatory bowel disease

This review has focused on evidence regarding intestinal perfusion of inflammatory bowel disease (IBD). Basic investigation has defined an altered microvascular anatomy in the affected IBD bowel, which corresponds with diminished mucosal perfusion in the setting of chronic, long-standing inflammation. Diminished perfusion is linked to impaired wound healing, and may contribute to the continued refractory mucosal damage, which characterizes IBD. Alterations in vascular anatomy and physiology in IBD suggests additional possible mechanisms by which micro-vessels may contribute to the initiation and perpetuation of IBD. This begs the following questions: will angiogenesis within the gut lead to sustained inflammation, does the growing vasculature generate factors that transform the surrounding tissue and does angiogenesis generate vascular anastomosis within the gut, with shunting of blood away from the mucosal surface, impairment of metabolism and potentiation of gut damage? Further studies are required to define the mechanisms that underlie the vascular dysfunction and its role in pathophysiology of IBD.

Platelets in inflammatory bowel disease: clinical, pathogenic, and therapeutic implications

Both Crohn's disease (CD) and ulcerative colitis (UC) are associated with abnormalities of platelet number and function. In the peripheral circulation the state of platelet activation is typically increased, and inflammatory bowel disease (IBD)-involved mucosa frequently contains platelet aggregates within mucosal microthrombi. The relevance of platelet dysfunction to IBD pathogenesis is still unclear, but there is solid evidence demonstrating that platelets, in addition to their traditional role in hemostasis, can also function as potent proinflammatory cells. Upon activation, platelets secrete a large number of biologically active molecules able to induce or amplify an inflammatory process through many of the same cellular and molecular pathways conventionally utilized by immune cells mediating IBD. The aim of this article is to review data on the existence of platelet dysfunction in IBD, substantiate platelets' inflammatory potential, discuss the implications of abnormal platelet activity for chronic intestinal inflammation, and consider the potential benefits of platelet modulation for treatment of IBD.

Thromboxane synthase immunohistochemistry in inflammatory bowel disease

BACKGROUND

Thromboxanes are produced in excess in inflammatory bowel disease. Preliminary reports suggest that ridogrel, a thromboxane synthase inhibitor, is anti-inflammatory and may have therapeutic benefits in patients with ulcerative colitis.

AIMS

To investigate the immunohistochemical expression of thromboxane synthase in the colorectal mucosa of patients with inflammatory bowel disease.

METHODS

Immunostaining of colonic biopsies from patients with inflammatory bowel disease (n = 13) and controls (n = 5) was performed using a monoclonal antibody to human thromboxane synthase. The extent of staining in cells of the lamina propria was compared in patient and control groups, and was assessed in relation to disease activity scored macroscopically and histologically.

RESULTS

The percentage of cells in the lamina propria staining for thromboxane synthase was higher in patients with active inflammatory bowel disease than in those with inactive disease or in controls (p = 0.02 and p = 0.002, respectively). There was a direct correlation between disease activity, measured endoscopically and histologically, and the percentage of lamina propria cells staining for thromboxane synthase (R = 0.71, p = 0.001 and R = 0.72, p = 0.001, respectively).

CONCLUSIONS

Increased thromboxane synthase expression in lamina propria cells occurs in active inflammatory bowel disease. It is possible that this results in increased thromboxane synthesis, which may in turn contribute to mucosal inflammation and intramucosal thrombogenesis.

Lack of efficacy of ridogrel, a thromboxane synthase inhibitor, in a placebo-controlled, double-blind, multi-centre clinical trial in active Crohn's disease

BACKGROUND

Thromboxanes are produced in excess and platelets are activated in active Crohn's disease. Preliminary reports have suggested that ridogrel, a dual thromboxane synthase inhibitor and receptor antagonist, may have therapeutic benefit in patients with inflammatory bowel disease.

AIMS

To investigate the efficacy of ridogrel in patients with active Crohn's disease.

PATIENTS AND METHODS

This was an international, multicentre, randomized, double-blind, placebo-controlled trial of 5 mg/day oral ridogrel for 12 weeks in 85 patients with moderately active Crohn's disease. Sixty patients were randomized to receive ridogrel, and 25 to placebo. The Crohn's disease activity index (CDAI) was used to assess disease activity: remission was defined as a CDAI < 150. Changes in clinical condition, as assessed by the Harvey-Bradshaw index, global evaluation by the investigator and the patient, and blood measures of inflammation, were used as secondary outcomes.

RESULTS

The patients' mean (s.d.) CDAI at recruitment was 277 (68) in the ridogrel treated group and 265 (70) in the placebo group. At their final assessment, 20 out of 60 (35%) patients who had been given ridogrel in an intention-to-treat analysis and seven out of 25 (28%) patients given placebo were in remission (no significant difference). No significant differences in Harvey- Bradshaw index or global evaluation were noted between patients given ridogrel and those given placebo. Adverse events were similar in both groups.

CONCLUSION

A 5-mg dose of oral ridogrel was not more effective than placebo in inducing remission in patients with moderately active Crohn's disease. If thromboxane synthesis and platelet function are to be targeted for the treatment of Crohn's disease, more potent agents require development and assessment.

Increased serum levels of eotaxin in patients with inflammatory bowel disease

BACKGROUND

The CC-chemokines eotaxin and eotaxin-2, produced by epithelial and phagocytic cells, are potent and selective chemoattractants for eosinophils and basophils. The eosinophil is a potent inflammatory cell thought to play an important role in the pathogenesis of inflammatory bowel disease (IBD). In this study we investigated the serum concentrations of eotaxin and eotaxin-2 in patients with Crohn disease and ulcerative colitis.

METHODS

Thirty-one patients with Crohn disease, 35 patients with ulcerative colitis and 41 control patients were studied. Eotaxin and eotaxin-2 serum levels were measured with solid phase sandwich enzyme-linked immunosorbent assays.

RESULTS

Significantly increased serum eotaxin levels were observed in both patients with Crohn disease (289.4+/-591.5 pg/ml) and ulcerative colitis (207.0+/-243.4 pg/ml) when compared with controls (138.0+/-107.8 pg/ml) (P < 0.01). Moreover, patients with active Crohn disease and ulcerative colitis showed significantly higher serum eotaxin levels than patients with quiescent disease (434.0+/-776.8 pg/ml versus 113.8+/-65.4 pg/ml in Crohn disease and 295.7+/-337.1 versus 121.2+/-91.9 pg/ml in ulcerative colitis, P < 0.05). In contrast, there was no significant difference in eotaxin-2 serum levels among patients with Crohn disease (863.5+/-448.2 pg/ml), ulcerative colitis (1028.3+/-431.4 pg/ml) and controls (981.4+/-539.4 pg/ml).

CONCLUSIONS

Eotaxin is significantly increased in serum of patients with active Crohn disease and ulcerative colitis, suggesting that this cytokine may play a role in the pathogenesis of IBD.

Ridogrel enemas in distal ulcerative colitis

OBJECTIVE

To evaluate the effect of Ridogrel enemas (Janssen Research Foundation, Beerse, Belgium) on disease activity and mucosal inflammatory mediators in patients with active left-sided ulcerative colitis.

DESIGN AND METHODS

Eleven patients with active left-sided ulcerative colitis were evaluated in an open non-placebo-controlled pilot study. All patients were treated with Ridogrel enemas (300 mg/40 ml once daily) over four weeks. A disease activity score based on clinical, endoscopic and histological criteria was obtained before and after treatment with Ridogrel. The concentrations of thromboxane B2 (TxB2), prostaglandin E2 (PGE2), interleukin-6 (IL-6) and tumour necrosis factor alpha (TNF-alpha) were measured in mucosal biopsies before and after treatment.

RESULTS

One patient discontinued treatment because of progression of disease, the other ten patients tolerated the Ridogrel enemas well. Mucosal TxB2 concentration decreased significantly in all patients. The mucosal concentrations of the other inflammatory mediators (PGE2, IL-6 and TNF-alpha) were unaltered. The disease score decreased in five patients. However, clinical improvement was not always associated with a decrease in endoscopic and/or histological scores.

CONCLUSIONS

This pilot study shows that Ridogrel enemas selectively reduce mucosal TxB2 concentration.

Pathogenesis of Crohn's disease

In the absence of a single initiating aetiological factor, most workers envisage Crohn's disease as the manifestation of poorly regulated immune and inflammatory processes within the gut wall. Initially these responses may arise as a response to common antigens associated with the gut--bacterial products being amongst the most obvious candidates. In genetically predisposed individuals there is overexpression both of local immune response mechanisms in the gut wall (T-cells, B-cells and macrophages) and of systemic inflammatory cells (predominantly polymorphonuclear leukocytes), which are attracted into the inflamed gut through activation of adhesion molecules on the vascular endothelium. As a consequence a large number of pro-inflammatory processes are expressed in the gut wall, inadequately checked by the normal counter-inflammatory processes that should serve to limit inflammation. Defining the relative importance of the individual processes, and identifying critical steps that could be inhibited or enhanced for therapeutic purposes, is a major challenge of Crohn's disease research.