Thromboxanes: selective biosynthesis and distinct biological properties

The prostaglandin endoperoxide ring structure alone does not establish suitability as a substrate for thromboxane synthetase, but the degree of unsaturation and carbon chain length are also essential features. Thus, human platelet microsomes can synthesize thromboxane A2, thromboxane A3, but not thromboxane A1 from their respective endoperoxides. The potent vasoconstrictor property of thromboxanes can be dissociated from its capacity to produce platelet aggregation. Furthermore, thromboxane formation is not an essential process in platelet aggregation. The observations indicate the remarkable structural specificity of both the synthetic enzymes, cyclooxygenase and thromboxane synthetase, as well as the vascular and platelet receptor sites.     

Scintigraphic evaluation of experimental colitis in rabbits

Scintigraphic techniques are frequently used for evaluation of inflammatory bowel disease. The radiopharmaceutical of choice is labeled leukocytes. In this study, two new agents, 111In-labeled polyethylene glycol-coated liposomes and 111In-labeled human nonspecific gamma globulin (immunoglobulin G; IgG), were compared with 111In-leukocytes in a rabbit model of colitis. METHODS: In rabbits, acute colitis was induced by colonic instillation of trinitrobenzene sulfonic acid at 25 cm from the anal sphincter. After 24 hr, 15 MBq of the radiopharmaceuticals was injected intravenously in groups of four rabbits. Twenty-four hours after injection, the animals were killed and macroscopic abnormalities were scored in seven consecutive affected colonic segments of 5 cm each (0 = normal, 1 = inflammation, 2 = ulcers). The ex vivo uptake was measured in the normal ascending colon and the affected colonic segments. The colitis index (CI, affected-to-normal colon-uptake ratio) was calculated. RESULTS: Histologically, an acute, patchy, transmural colitis was observed at the site of instillation and the distal colon. The CI of all agents in colitis lesions correlated with the severity of the abnormalities. With increasing severity, the CI for liposomes was 1.86 +/- 0.24, 4.88 +/- 0.42 and 7.42 +/- 0.54 (r2 = 0.68, p < 0.001); for leukocytes 1.77 +/- 0.32, 3.10 +/- 0.58 and 5.54 +/- 0.83 (r2 = 0.31, p < 0.01); for IgG 1.60 +/- 0.29, 2.81 +/- 0.21 and 2.65 +/- 0.21 (r2 = 0.29, p < 0.02). CONCLUSION: Indium-111-labeled-leukocytes, -IgG and -liposomes all show increased uptake in inflamed colonic tissue. Indium-111-liposomes showed the highest CI, which correlates best with the morphological abnormalities. Indium-111-leukocytes and 111In-liposomes are superior to 111In-IgG for this indication.     

Effect of indomethacin and atropine in experimental asthma in conscious guinea pigs

Pulmonary mechanics were measured in unanesthetized guinea pigs sensitized to horseradish peroxidase (HRP) before and during two aerosolized challenges of this antigen. During the first challenge the pulmonary resistance increased in all animals. Prior to second challenge the animals received either atropine (0.2 mg/kg) or indomethacin (10 mg/kg) intraperitoneally. We found that during the second challenge the indomethacin group had an increase in pulmonary resistance slightly greater or similar to that during the first exposure to the antigen, while the animals treated with atropine had a significantly diminished response (P less than 0.05). In five guinea pigs sensitized to HRP but challenged with a nonspecific aerosal made up of rabbit albumin, we found that pulmonary resistance increased in some animals and that this increase could be partially blocked by atropine. These results show that indomethacin has no effect on this model of allergic airways disease. They also confirm the importance of the vagus nerves in allergic bronchoconstriction and in addition show that nonspecific hyperirritability can be induced in some animals by immunization.     

Hepatocyte tight-junctional permeability is increased in rat experimental colitis

BACKGROUND & AIMS: Hepatobiliary complications occur in inflammatory bowel disease and may be caused by the translocation of intestinal toxins from portal blood into bile through leaky hepatocyte tight junctions. The role of tight junctions in the pathogenesis of hepatobiliary complications in experimental inflammatory bowel disease was investigated. METHODS: Colitis was induced in rats by intracolonic instillation of trinitrobenzene sulfonic acid. The function of hepatocellular tight junctions was evaluated in perfused livers by measuring early (paracellular) horseradish peroxidase excretion into the bile and by electron microscopy and semiquantitative analysis of lanthanum penetration through the tight junction and into bile canaliculi. Immunofluorescent localization of cingulin and ZO-1 was used to study the structure of hepatocyte junctions. RESULTS: Colitis was associated with increased serum bilirubin and bile acid concentrations, a 2.5-fold increase in paracellular biliary excretion of horseradish peroxidase, and a ninefold increase in lanthanum permeability. Liver histology and cingulin and ZO-1 localizations were similar to normal liver. CONCLUSIONS: Experimental colitis is associated with hepatobiliary complications and an increased hepatocyte tight junctional permeability to horseradish peroxidase and lanthanum. Subtle alterations in tight junction function may be involved in the pathogenesis of hepatobiliary injuries in inflammatory bowel disease.     

Endothelial proliferation in experimental granulomatous colitis. Autoradiography and immunohistochemistry studies

The time sequence and magnitude of endothelial cell proliferation was investigated in an experimental model of granulomatous colitis in rats, induced by intramural inoculations of mycobacterium Bacillus Calmette-Guerin. Colonic tissues were assessed by gross examination, histopathology, autoradiography, and immunohistochemistry. Gross examination of the colonic tissue showed thickening of the colonic wall, erythema, hemorrhage, and scattered ulcers. Histopathological findings were characterized by an acute transmural inflammation, progressing to chronic inflammation accompanied by regenerative changes in the glandular epithelium, goblet cell depletion, mucosal atrophy and fibrosis. Well-developed noncaseating granulomas were first observed at day 5 and were found to be a dominant feature up to day 17. Autoradiographic studies showed increased endothelial cell labeling up to 17% at 48 hr, compared to less than 1% labeling in control animals. Immunostaining for factor VIII-related antibody, an endothelial cell marker, showed increased numbers of microvessels and individual positive cells located in areas of inflammation as early as 24 hr. At day 5 these individual cells along with dilated neocapillaries were found surrounding the granulomas. This model of granulomatous colitis mimics many features of the human disease state. The early increase in endothelial cell proliferation that precedes granuloma formation during the course of the inflammatory response may suggest that the events leading to the expression of granulomatous colitis are dependent on endothelial proliferation.     

Pathophysiological role of nitric oxide in rat experimental colitis

Overproduction of nitric oxide (NO) by inducible nitric oxide synthase (iNOS) may contribute to the pathophysiology of ulcerative colitis. A 2,4,6-trinitrobenzenesulfonic acid sodium salt (TNBS) colitis model was established to examine the effect of selective iNOS inhibition, by S-(2-aminoethyl) isothiouronium bromide (ITU), on colonic mucosal cell damage and inflammation. Rats, killed 7 days after TNBS, had increased colonic mucosal levels of iNOS and interleukin-8 (IL-8), in addition to severe colonic inflammation which was characterized by significantly increased colon weight, damage score and colonic myeloperoxidase activity (MPO) (a marker of neutrophil influx). TNBS-treated rats had markedly decreased body weight and thymus weight. Administration of colitic rats with ITU significantly inhibited iNOS activity/expression and tended to reduce mucosal levels of IL-8, but no effect on MPO activity was observed. Following ITU therapy, colitic rats had reduced colonic damage and losses in body weight and thymus weight were reversed. Improvement of TNBS colitis by ITU suggested that excess NO, produced by iNOS, may have contributed to the initiation/amplification of colonic disease, by mechanisms including enhancement of IL-8 release. NO-mediated enhancement of pro-inflammatory cytokine release was further investigated in vitro. Lipopolysaccharide (LPS) and interferon-gamma (IFN-gamma) stimulated release of nitrite, lactate dehydrogenase (LDH), TNF alpha, IL-1 beta and IL-8 from rat peritoneal macrophages, all of which were significantly reduced by ITU. This suggests that NO-mediated cell damage enhances pro-inflammatory mediator release from macrophages. In addition, enhancement of IL-8 and TNF alpha release was also partially NO-dependent in activated peritoneal neutrophils. Therefore, the amelioration of TNBS colitis by ITU could include inhibition of NO-mediated pro-inflammatory cytokine release.     

Ticlopidine, diarrhea and lymphocytic colitis

Perforation into the heart is a rare ulcer complication in a hiatal hernia. Because of the massive bleeding, medical help is often in vain. The case of a 73-year-old patient reported by our department confirms this. Endoscopic treatment was not possible because of the extraordinary amount of blood in the stomach, and the high intraoperative blood loss was lethal. If gastric ulcers occur in upper regions of the stomach, the possibility of the presence of an paraesophageal hernia and elective surgical treatment must be considered.     

Effect of indomethacin and sodium meclofenamate on the renal concentrating defect in experimental enterococcal pyelonephritis in rats

The present studies have confirmed a severe urinary concentrating defect early in the course of experimental enterococcal pyelonephritis. This defect in maximum concentrating ability was almost completely reversed immediately following indomethacin or sodium meclofenamate intravenously. This effect of indomethacin and sodium meclofenamate was transient and was not associated with a fall in numbers of enterococci per gram of kidney. Injection of indomethacin or sodium meclofenamate in noninfected rats had no effect on maximum renal concentrating ability. The potential mechanisms by which indomethacin and sodium meclofenamate, inhibitors of renal prostaglandin synthesis, could reverse a defect in maximum urinary concentration are discussed.     

Direct evidence of oxidative damage in acute and chronic phases of experimental colitis in rats

During inflammatory colitis in man and experimental animals, the production of free radicals increases. This study evaluated the histological pattern and biochemical parameters of oxidative damage during acute and chronic colitis induced by 2,4,-trinitrobenzenesulfonic acid + ethanol in rats. On the samples of scraped mucosa of six groups of rats, one not treated, one killed after 1 hr, and those killed one, two, four, and eight weeks after the induced-damage, we determined the histological and superoxide dismutase activity and the concentration of lipoperoxides, malonyldialdheyde, and reduced glutathione. After 1 hr, the mucosal damage and superoxide dismutase activity were slight; glutathione, lipoperoxides, and malonyldialdheyde were significantly increased. At one week, the histological damage was severe, decreasing progressively, and significantly correlated to superoxide dismutase activity. Lipoperoxides and malonyldialdheyde were high throughout the study. Glutathione was significantly increased at one and two weeks and dramatically decreased thereafter. Therefore, in experimental colitis the cascade of free-radical production induces a constant self-maintaining lipoperoxidation and consumes the cellular antioxidant capability.     

Pharmacokinetics of indomethacin and indomethacin metabolites administered continuously to patients with healthy or damaged kidneys

After oral administration of 75 mg Indomethacin dlimination half-life of the unchanged drug is not altered in patients with severely impaired renal function. In patients with renal insufficiency half-life of Indomethacin plus metabolites is twice that of the normal value. Repeated daily administration of 75 mg for 8 days does not influence Indomethacin kinetics. In the control group and in patients with moderate by impaired renal function Indomethacin half-life does not change during chronic administration.     

Both the lymphotoxin and tumor necrosis factor pathways are involved in experimental murine models of colitis

BACKGROUND & AIMS: Membrane lymphotoxin (LT) alpha/beta, a member of the tumor necrosis factor (TNF) family of immune regulatory molecules, is involved both in the development of secondary lymphoid tissues and the maintenance of organized lymphoid tissues in the adult. Defects observed in the mucosal immune system in animals with a genetically disrupted LTalpha/beta pathway coupled with the expression of LTalpha/beta in activated T cells motivated an examination of the importance of this pathway in experimental colitis. METHODS: Soluble LTbeta receptor (LTbetaR) immunoglobulin fusion protein was used to inhibit the LTalpha/beta/light axis in two independent rodent models of colitis: CD45RBhi CD4(+)-reconstituted SCID mice and bone marrow-transplanted tg26 mice (BM --> tg26). RESULTS: Treatment with LTbetaR immunoglobulin attenuated the development of both the clinical and histological manifestations of the disease in these two murine models of colitis. Given the success of TNF inhibitors in the treatment of human Crohn's disease, the effects of LTbetaR immunoglobulin have been compared with antibody to TNF in the BM --> tg26 model, and both treatments were equally efficacious. CONCLUSIONS: The LT pathway plays a role in the development of colitis as important as that of the TNF system and, therefore, represents a potential novel intervention point for the treatment of inflammatory bowel disease.     

Associated ulcerative colitis, sclerosing cholangitis, and insulin-dependent diabetes mellitus

We report two young men with clinical and laboratory evidence of macroscopic ulcerative colitis, sclerosing cholangitis, and insulin-dependent diabetes mellitus. The first patient presented at age 15 with vomiting, abdominal pain, weight loss, and abnormal liver function test results. Liver biopsy and endoscopic retrograde cholangiopancreatography (ERCP) demonstrated sclerosing cholangitis. Colonoscopy with biopsy revealed ulcerative colitis which responded to sulfasalazine. Diabetes occurred at age 18 and insulin therapy was begun. The second patient was 19 at presentation with diarrhea, hematochezia, and weight loss. Proctosigmoidoscopy revealed ulcerative colitis, and sulfasalazine led to clinical remission. Three months later he developed diabetes requiring insulin therapy. At age 28, he developed elevated alkaline phosphatase, and ERCP revealed sclerosing cholangitis. At age 37 he expired from adenocarcinoma that metastasized to the liver. Literature review revealed only one possible case report of this association with microscopic asymptomatic ulcerative colitis in that patient. Statistical analysis suggests that this association is real rather than a chance occurrence. An autoimmune process may be involved and a specific histocompatibility locus antigen (HLA) type may exert a regulatory influence.     

A study of colonic mucins in two kinds of experimental colitis model in rat

We investigated the quantitative changes in colonic mucins of rats with colitis. Male Wistar rats were treated with dextran sodium sulfate (DSS) or N-ethylmaleimide (NEM) to induce colitis. Both DSS and NEM caused depletion of goblet cells, infiltration of inflammatory cells and erosion at the colonic mucosa around the anus. Though the goblet cells decreased, colonic mucins increased in the distal colon. These phenomena may explain the clinical features of human ulcerative colitis, namely the goblet cell depletion and the mucous stool. The increase of colonic mucins may be a compensatory function of the colon tissue in response to the localized decrease of mucin production.     

Interactions of indomethacin with lysosomes and proteins

The stabilizing action of indomethacin on lysosomes and protein in vivtro was studied. The magnitude of the stabilizing action on lysosomes was greater than that of aspirin or oxyphenbutazone, similar to that of phenylbutazone, but less than that of prednisolone. The stabilizing action of indomethacin on lysosomes possibly may contribute to its anti-inflammatory properties.