Assay of prostaglandin-like substances in faeces and their measurement in ulcerative colitis

Simultaneous Quantitation of Lipid Biomarkers for Inflammatory Bowel Disease Using LC-MS/MS

Eicosanoids are key mediators and regulators of inflammation and oxidative stress that are often used as biomarkers for severity and therapeutic responses in various diseases. We here report a highly sensitive LC-MS/MS method for the simultaneous quantification of at least 66 key eicosanoids in a widely used murine model of colitis. Chromatographic separation was achieved with Shim-Pack XR-ODSIII, 150 × 2.00 mm, 2.2 µm. The mobile phase was operated in gradient conditions and consisted of acetonitrile and 0.1% acetic acid in water with a total flow of 0.37 mL/min. This method is sensitive, with a limit of quantification ranging from 0.01 to 1 ng/mL for the various analytes, has a large dynamic range (200 ng/mL), and a total run time of 25 min. The inter- and intraday accuracy (85-115%), precision (≥85%), and recovery (40-90%) met the acceptance criteria per the US Food and Drug Administration guidelines. This method was successfully applied to evaluate eicosanoid metabolites in mice subjected to colitis versus untreated, healthy control mice. In summary, we developed a highly sensitive and fast LC-MS/MS method that can be used to identify biomarkers for inflammation and potentially help in prognosis of the disease in inflammatory bowel disease (IBD) patients, including the response to therapy.

Altered colonic mucosal Polyunsaturated Fatty Acid (PUFA) derived lipid mediators in ulcerative colitis: new insight into relationship with disease activity and pathophysiology

Objectives

Ulcerative colitis (UC) is a relapsing inflammatory disorder of unconfirmed aetiology, variable severity and clinical course, characterised by progressive histological inflammation and with elevation of eicosanoids which have a known pathophysiological role in inflammation. Therapeutic interventions targetting eicosanoids (5-aminosalicylates (ASA)) are effective first line and adjunctive treatments in mild-moderate UC for achieving and sustaining clinical remission. However, the variable clinical response to 5-ASA and frequent deterioration in response to cyclo-oxygenase (COX) inhibitors, has prompted an in depth simultaneous evaluation of multiple lipid mediators (including eicosanoids) within the inflammatory milieu in UC. We hypothesised that severity of inflammation is associated with alteration of lipid mediators, in relapsing UC.

Design

Study was case-control design. Mucosal lipid mediators were determined by LC-MS/MS lipidomics analysis on mucosal biopsies taken from patients attending outpatients with relapsing UC. Univariate and multivariate statistical analyses were used to investigate the association of mucosal lipid mediators, with the disease state and severity graded histologically.

Results

Levels of PGE₂, PGD₂, TXB₂, 5-HETE, 11-HETE, 12-HETE and 15-HETE are significantly elevated in inflamed mucosa and correlate with severity of inflammation, determined using validated histological scoring systems.

Conclusions

Our approach of capturing inflammatory mediator signature at different stages of UC by combining comprehensive lipidomics analysis and computational modelling could be used to classify and predict mild-moderate inflammation; however, predictive index is diminished in severe inflammation. This new technical approach could be developed to tailor drug treatments to patients with active UC, based on the mucosal lipid mediator profile.

Mechanism of action of 5-arninosalicylic acid

5-Aminosalicylic Acid (5-ASA) has been used for over 50 years in the treatment of inflammatory bowel disease in the pro-drug form sulphasalazine (SASP). SASP is also used to treat rheumatoid arthritis. However whether the therapeutic properties of SASP are due to the intact molecule, the 5-ASA or sulphapyridine components is unknown. Several mechanisms of action have been proposed for 5-ASA and SASP including interference in the metabolism of arachidonic acid to prostaglandins and leukotrienes, scavenging,of reactive oxygen species, effects on leucocyte function and production of cytokines. However, it is unlikely that the anti-inflammatory properties of SASP and 5-ASA are due to several different properties but more likely that a single property of 5-ASA explains the theraapeutic effects of 5-ASA and SASP. Reactive oxygen species (ROS) are involved in the metabolism of prostaglandins and leukotrienes and can act as second messengers, and so the scavenging of ROS may be the single mechanism of action of 5-ASA that gives rise to its antiinflammatory effects in both inflammatory bowel disease and rheumatoid arthritis.

Effect of nimesulide on acetic acid- and leukotriene-induced inflammatory bowel disease in rats

Inflammatory bowel disease (IBD) is a relapsing inflammation of intestine, which is mediated by release of inflammatory mediators. Both cyclo-oxygenase product prostaglandin (PGE2) and lipo-oxygenase product leukotriene (LTB4), may contribute to the pathogenesis of the inflammatory response. Nimesulide, a preferential COX-2 inhibitor was evaluated for its efficacy against experimental colitis in two different models (acetic acid- and LTB4-induced IBD) in rats. Inflammatory response was induced by intrarectal single administration of acetic acid or LTB4. Nimesulide (9 and 18 mg/kg, p.o.) significantly prevented development of inflammatory changes, decreased myeloperoxidase (MPO) activity, and also restored the altered contractility response of the isolated colon segment to KCl. The results suggested the involvement of both cyclo-oxygenase (COX) and lipo-oxygenase-mediated proinflammatory agents in colonic inflammatory process associated with IBD. Further, this study suggests that such therapeutic interventions may be of value in the treatment of IBD.

Electrical behaviour of interleukin-1 beta (IL-1 beta) and prostaglandin-E2 (PGE2) on colonic myenteric neurones

Abstract Intracellular recordings were used to examine the effects on electrical and synaptic behaviour of interleukin (IL)-1beta and prostaglandin E2(PGE2) on myenteric neurones of the guinea-pig colon. Application of IL-1beta and PGE2resulted in a concentration-dependent slow depolarization with enhanced spike discharge in, respectively, 45% (21/47) and 83% (33/41) of the impaled colonic neurones. Administration of IL-1beta in three neurones (6%) elicited a hyperpolarization. Responses remained during tetrodotoxin application, indicative of a direct effect of both substances on the impaled neurones. The effects of IL-1beta remained in the presence of indomethacine, a prostaglandin synthase inhibitor. Responses were seen in both nitric oxide synthase- and choline acetyl transferase-immunoreactive neurones. IL-1beta evoked a 26% reduction of the fast excitatory postsynaptic potential. These results indicate that the application of IL-1beta and PGE2evoke direct excitatory actions on a subset of myenteric neurones. For IL-1beta, direct inhibition and presynaptic inhibition of the fast excitatory postsynaptic potential has also been found. In the distal colon, responses to IL-1beta are not mediated through PGE2pathways.

Roles of secretory phospholipases A(2) in inflammatory diseases and trauma

Six distinct secretory small molecular weight phospholipases A(2) (PLA(2)) have been cloned and characterized from human tissues. Two of them, pancreatic group IB PLA(2) (PLA(2)-IB) and synovial-type group IIA PLA(2) (PLA(2)-IIA) have been studied as to their association to various inflammatory diseases. PLA(2)-IB is a digestive enzyme synthesized by pancreatic acinar cells. In acute pancreatitis, which is characterized by destruction of pancreatic tissue, PLA(2)-IB is released into the circulation, but its role in pancreatic and other tissue damage is still hypothetical. The concentration of PLA(2)-IIA increases in blood plasma in generalized inflammatory response resulting from infections, chronic inflammatory diseases, acute pancreatitis, trauma and surgical operations. PLA(2)-IIA is synthesized in a number of gland cells and is present in cellular secretions on mucosal surfaces including Paneth cells of intestinal mucosa, prostatic gland cells and seminal plasma, and lacrimal glands and tears. PLA(2)-IIA is expressed in hepatoma-derived cells in vitro and hepatocytes in vivo. PLA(2)-IIA is regarded as an acute phase protein and seems to function as an antibacterial agent especially effective against Gram-positive bacteria. Other putative functions in the inflammatory reaction include hydrolysis of cell membrane phospholipids and release of arachidonic acid for prostanoid synthesis.

Morphological and functional changes in the colonic epithelial cells in a rabbit model of colitis

A rabbit model of TNBS-colitis was used to study the effect of intestinal inflammation on epithelial cell function. Epithelial cells were isolated using a non-enzymatic isolation method without any apparent contamination with infiltrating immune cells. The isolated cells were found to be viable using dye exclusion studies, unidirectional Na+ -fluxes, proliferation assays and morphological studies. The cells, however, showed morphological changes that suggested the presence of increased number of secretory vesicles. This increase correlated well with the increase observed in ion and water secretion as measured by the short-circuit current. Finally, in the colitic tissue the number of PGE2 receptors was greatly reduced with no changes observed in the affinity of PGE2 to its receptor. The reduced number of PGE2 receptors might be due to sensitization of the receptor. In conclusion, we have demonstrated that morphologically and functionally normal epithelial cells can be isolated from the rabbit inflamed distal colon.

n-3 fatty acids only delay early relapse of ulcerative colitis in remission

Relapse prevention by dietary n-3 fatty acids (5.1 g/day) was studied in a double-blind, placebo-controlled trial of 64 patients with ulcerative colitis in remission and off steroids. 5-ASA compounds were stopped three months after randomization and clinical disease activity monitored for two years. Macroscopic and histologic activity and extension was assessed by colonoscopy at entry and at exit. Both treatment groups were well matched at start. Nine patients on placebo and eight on n-3 fatty acids stopped taking their medication prematurely. Actuarial relapse-free survival was improved by n-3 fatty acids only during months 2 and 3 (2P < 0.05-0.01), but cumulative relapse rate at two years was similar for those taking placebo (18/33 = 55%) and n-3 fatty acids (18/31 = 58%). There was also no consistent difference in clinical, macroscopic, and histologic disease activity between treatment groups. The n-3 fatty acids temporarily retard, but do not prevent, relapse of ulcerative colitis.

Intracolonic administration of zileuton, a selective 5-lipoxygenase inhibitor, accelerates healing in a rat model of chronic colitis

BACKGROUND

5-Lipoxygenase products play a part in inflammatory response.

AIMS

The effect of intracolonic administration of zileuton (a 5-lipoxygenase inhibitor) on colonic damage and eicosanoid local release was assessed in a rat model of colitis.

METHODS

Ninety rats with trinitrobenzenesulphonic acid induced colitis were randomised to receive placebo, 5-aminosalicylic acid (50 mg/kg), or zileuton (50 mg/kg) intracolonically for four weeks. Local eicosanoid release was monitored by intracolonic dialysis throughout the study. The colon was removed for macroscopic and histological assessment at weeks 1, 2, and 4 after colitis induction in 10 rats of each group.

RESULTS

Zileuton significantly reduced macroscopic damage score after four weeks of treatment in comparison with the other two groups (p = 0.034). In addition, zileuton administration significantly increased the intracolonic release of both thromboxane B2 at week 1 (p = 0.05) and prostaglandin E2 at weeks 2 and 4 (p < 0.05). Zileuton and 5-aminosalicylic acid decreased leukotriene B4 release by 90% at day 3.

CONCLUSIONS

Intracolonic zileuton, compared with 5-aminosalicylic acid and placebo, seems to improve the course of the disease in a model of chronic colitis. This effect may be related to an increased and maintained production of prostaglandin E2 together with inhibition of leukotriene B4 synthesis.

Depressed T cell reactivity to recall antigens in Crohn's disease before and after surgical resection

Earlier studies regarding possible primary immune disturbances participating in the pathogenesis of Crohn's disease yielded conflicting results. Peripheral blood lymphocyte subsets and lymphocyte proliferative responses to five soluble recall antigens and to the polyclonal stimulator phythaemagglutinin were therefore measured in 17 patients with active Crohn's disease, before and six months after surgical resection of the inflamed intestine and in 16 healthy controls. Lymphocyte proliferation in response to all five recall antigens was significantly lower in patients than in controls. No significant differences with controls were detected after surgery. Addition of indomethacin to phythaemagglutinin stimulated lymphocyte cultures had a stronger proliferation enhancing effect in patients than in controls, resulting in comparable proliferative responses in both groups. When both indomethacin and prostaglandin E2 were added, inhibition of reactivity by prostaglandin E2 was stronger in patients' cultures. This suggests a higher sensitivity to inflammatory prostaglandins in Crohn's disease. The degree of lymphocyte stimulation by antigens correlated positively with the percentage of circulating memory T cells (CD 45 RA-). The percentage of activated (HLA-DR+) CD8 cells was higher in patients than in controls. The CD4/CD8 ratio, which was not significantly different between patients and controls, correlated significantly with disease activity and characteristics, even in the postoperative phase. These findings suggest that immune abnormalities in Crohn's disease fluctuate with and are probably secondary to inflammatory activity.

Alterations in the mucosal immune system in ulcerative colitis and Crohn's disease

Emphasis is now being placed upon obtaining a better understanding of the regulatory cytokines that normally downregulate acute intestinal inflammation. These inhibitory cytokines appear to be missing or not functioning properly in patients with inflammatory bowel disease (IBD), thereby leading to perpetuation of inflammation. As we obtain an increased understanding of immune and inflammatory regulatory processes in the intestine, we will be able to devise better future therapeutic strategies for use in our IBD patients.

In vitro changes in the properties of rabbit colonic muscularis mucosae in colitis

BACKGROUND

The muscularis mucosae is the muscle layer closet to the site of elevated inflammatory mediator production in inflammatory bowel disease. Thus, it is the first muscle layer subject to their influence.

METHODS

Using a rabbit trinitrobenzene sulfonic acid model of colitis, changes in the properties of the muscularis mucosae resulting from the inflammatory process were studied in vitro.

RESULTS

Animals developed a mild colitis-like inflammation that was confined to the epithelium, lamina propria, and submucosa. Colitic muscularis mucosae contractile responses to leukotriene D4 and prostaglandins E2 and F2 alpha were significantly attenuated relative to the maximum tissue response to acetylcholine, whereas responses to histamine, substance P, and vasoactive intestinal polypeptide were unchanged. In addition, the stress-generating capacity of the colitic muscularis mucosae was compromised in a stimulus-independent manner and passive tension increased relative to active tension.

CONCLUSIONS

The muscularis mucosae undergoes two significant alterations in colitis: (a) a selective desensitization to the effects of arachidonic acid metabolites and (b) an impairment of its excitation-contraction coupling mechanism. A loss of the ability of the muscularis mucosae to cause mucosal movement and alter luminal surface area may be an important early stage in the pathophysiology of inflammatory bowel disease.

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.

A comparison in vitro of human and rabbit distal colonic muscle responses to inflammatory mediators

The present study compared in vitro the motor responses of human and rabbit distal colonic longitudinal and circular muscle to acetylcholine, histamine, leukotrienes B4 and D4, and prostaglandins E2 and F2 alpha. The active and passive mechanical properties of these muscles were also evaluated. All muscle types were contracted by acetylcholine and histamine. Longitudinal muscle from both species was contracted by prostaglandin E2 and prostaglandin F2 alpha, although rabbit muscle was more sensitive. Prostaglandin E2 relaxed the majority of both human and rabbit circular muscle preparations that were studied. Prostaglandin F2 alpha first relaxed and then contracted circular muscle from both species. Leukotriene B4 had no effect on any tissue studied. Leukotriene D4 caused transient relaxations in a proportion of all muscle types, but the relaxations were not concentration-related. Contractile responses did not differ under isotonic recording conditions, but relaxations were much more clearly defined. Based on experiments using atropine, phentolamine and propranolol, and pyrilamine or tetrodotoxin, it was concluded that the responses of both human and rabbit distal colonic muscles to these inflammatory mediators have a similar pharmacological basis. All muscle types exhibited low passive tension and developed active tension in the range 0.8-1.2 Lo. These data strongly support the belief that after the onset of an induced colitis, the rabbit colon has value as a predictive model for the study of inflammatory mediator-induced colonic motility changes in humans.

Supplementation with n-3 fatty acids from fish oil in chronic inflammatory bowel disease--a randomized, placebo-controlled, double-blind cross-over trial

Thirty-nine patients with chronic inflammatory bowel disease were studied in a 7-month, double-blind, placebo controlled cross-over trial of dietary supplementation with fish oil, which provided about 3.2 g n-3 fatty acids per day. At control, biopsies from inflamed mucosa contained higher levels of arachidonic acid than uninvolved mucosa. Dietary n-3 fatty acids were well tolerated and incorporated into plasma and enteric mucosa phospholipids at the expense of n-6 fatty acids. The arachidonic acid-derived prostanoid generation was reduced by fish oil and the extension and severity of macroscopic bowel involvement was moderately improved. In patients with Crohn's disease, clinical activity was unchanged by fish-oil supplementation. In patients with ulcerative colitis, clinical disease activity fell during fish oil supplementation and thereafter; this was not significant however. Despite a moderate reduction in inflammatory lipid mediators by dietary n-3 fatty acids and limited morphological improvement in chronic inflammatory bowel disease, the clinical benefit seems to be confined to patients with ulcerative colitis.

Effects of sulfasalazine and a sulfasalazine analogue on the formation of lipoxygenase and cyclooxygenase products

A sulfasalazine analogue, 5'-(2,4-dichlorobenzoyl)2'-hydroxyphenylacetic acid (CL 42A), potently inhibited the formation of 5-lipoxygenase products (leukotrienes B4 and C4 and 5-hydroxyeicosatetraenoic acid) by human leukocytes. Half-maximal inhibition of leukotriene production was obtained with 5 and 10 microM CL 42A after stimulation with serum-treated zymosan or ionophore A23187, respectively. CL 42A was equipotent to nordihydroguaiaretic acid and about 50 times more potent than sulfasalazine and benoxaprofen in studies on the inhibition of LTB4 formation in leukocyte suspensions stimulated with serum-treated zymosan. Furthermore, CL 42A had no inhibitory effect on the production of 15-hydroxyeicosatetraenoic acid after incubation of human leukocytes with ionophore A23187 in the presence of exogenous arachidonic acid. Sulfasalazine inhibited the synthesis of 5-lipoxygenase products (5-hydroxyeicosatetraenoic acid and leukotriene B4: IC50 250 microM, leukotriene C4: IC50 100 microM) in a concentration-dependent manner but had no effect on 15-hydroxyeicosatetraenoic acid formation. The metabolites of sulfasalazine, sulfapyridine and 5-aminosalicylic acid, and the isomer, 4-aminosalicylic acid, were all less potent than sulfasalazine as inhibitors of leukotriene formation. Both CL 42A (IC50 20 microM) and sulfasalazine (IC50 500 microM) inhibited the synthesis of thromboxane B2 and hydroxyheptadecatrienoic acid in human platelet suspensions after arachidonic acid stimulation. However, while CL 42A inhibited cyclooxygenase, the inhibitory effect of sulfasalazine was exerted mainly on thromboxane synthase. The platelet formation of 12-hydroxyeicosatetraenoic acid was not inhibited by CL 42A whereas sulfasalazine had a weak inhibitory effect.

Therapeutic potential of fish oil in the treatment of ulcerative colitis

In a pilot study six patients with active ulcerative colitis and six healthy controls were given fish oil (MaxEPA) containing 3-4 g of eicosapentaenoic acid daily for a period of 12 weeks. There was a significant improvement in the patients' symptoms and histological appearance of the rectal mucosa by the end of the treatment period. There was significant fall in neutrophil chemiluminescence during treatment in patients, whereas no change was observed in the control group. Neutrophil leukotriene B4 levels fell significantly during treatment. Serum from patients receiving fish oil was significantly less chemotactic for neutrophils compared with control serum. Eicosapentaenoic acid inhibited neutrophil chemotaxis and chemiluminescence in vitro. The omega-3 fatty acids, which occur naturally in fish oils, may exert a beneficial effect by decreasing the production of inflammatory mediators.

Exaggerated prostaglandin production by colonic smooth muscle in rabbit colitis

Enhanced production of arachidonic acid metabolites by colonic mucosa has been reported in ulcerative colitis as well as in experimental models of colitis. However, production of these compounds by colonic smooth muscle from colitis subjects has not been described. To evaluate arachidonic acid metabolism in colonic tissue, we studied the production of prostaglandin E2 (PGE2) by mucosa and muscularis propria in two experimental models of acute colitis in which inflammation was virtually confined to the mucosa. Colitis was induced in New Zealand white rabbits by either of two methods, dinitrochlorobenzene (DNCB) sensitization or formalin followed by intravenous soluble immune complexes (F-IC). Arachidonic acid metabolites were identified from in vitro incubations of tissue with [14C] arachidonic acid by thin layer chromatography followed by autoradiography. The major eicosanoid metabolites of colitis mucosa and muscularis were 14C-labeled prostaglandin E2, prostaglandin F2a and 6-keto prostaglandin F1 alpha. PGE2 was quantitated from incubations without labeled arachidonic acid by radio-immunoassay. PGE2, expressed as picograms per milligram protein per 20 min (mean +/- SEM), was increased in F-IC mucosa (1093 +/- 141 vs 645 +/- 189, P less than 0.05) and DNCB mucosa (1354 +/- 487 vs 527 +/- 222, P less than 0.05) compared to normals. PGE2 production by uninflamed colitis muscularis propria was also increased five- to eightfold compared to normals for F-IC muscularis (1594 +/- 329 vs 189 +/- 35, P less than 0.005) and DNCB muscularis (1287 +/- 171 vs 225 +/- 72, P less than 0.005). Thus, the adjacent inflammation in colonic mucosa may induce increased eicosanoid production by the uninflamed smooth muscle.(ABSTRACT TRUNCATED AT 250 WORDS)

Chemotactic activity in inflammatory bowel disease. Role of leukotriene B4

An important histologic feature of inflammatory bowel disease (IBD) is infiltration of the colonic mucosa with neutrophils. To investigate the nature of the chemotactic agents responsible for this infiltration, colonic mucosa from three normals and nine patients with inflammatory bowel disease (seven ulcerative colitis, two Crohn's colitis) was assayed for chemotactic activity for human neutrophils in vitro in a Boyden chamber. There was more (greater than 10-fold more) chemotactic activity in homogenates of inflammatory bowel disease mucosa than in homogenates of normal colonic mucosa. Analysis of the chemotactic activity in the inflammatory bowel disease mucosa revealed that most was lipid extractable. Moreover, when the lipid extract was fractionated by reverse-phase high-pressure liquid chromatography, the only fraction with significant chemotactic activity was the fraction that coeluted with leukotriene B4. The chemotactic response to IBD mucosa was blocked by anti-LTB4 antisera. The amount of chemotactic activity in lipid extracts of different inflammatory bowel disease specimens correlated well with the concentration of leukotriene B4 measured by UV absorbance (250 ng/g of mucosa). These data suggest that leukotriene B4 is an important stimulus to neutrophil chemotaxis in inflammatory bowel disease and, thus, may play a major role in the amplification of the inflammatory response in this condition.

In vivo production of leukotriene B4 and leukotriene C4 in rabbit colitis. Relationship to inflammation

Leukotriene B4, a proinflammatory compound, recently has been identified as the major metabolite of arachidonic acid in tissue incubations of human and animal colitis. To determine the relationship of inflammation to the in vivo production of leukotrienes, rabbit colitis was induced by formalin enema followed by intravenous infusion of immune complexes, and serial samples were collected by rectal dialysis. Leukotrienes B4 and C4 were measured by radioimmunoassay after high-pressure liquid chromatography. Prostaglandin E2 was assayed after Sephadex chromatography. Leukotrienes were not detected in control animals. Eicosanoid production progressively increased during development of inflammation and correlated with severity of inflammatory cell infiltration (p less than 0.01). Methylprednisolone decreased prostaglandin E2 but did not significantly reduce leukotrienes or inflammation. These data demonstrate that in vivo production of leukotrienes B4 and C4 correlates with indices of inflammation, consistent with the concept that these eicosanoids contribute to the inflammation of colitis.

Prostaglandins and the gastrointestinal mucosa: are they important in its function, disease, or treatment?

In 1971 interest in the role of prostaglandins in the gastrointestinal tract was stimulated by the publication of two hypotheses--that aspirin damaged the gastric mucosa by inhibiting prostaglandin synthesis (1) and that cholera toxin caused diarrhea by stimulating it (2). Subsequent research into the gastrointestinal actions of prostaglandins has been considerable and now impinges on clinical practice. This paper reviews the involvement of prostaglandins and related compounds in mucosal protection, in ulcer healing, in diarrhea, and in gastrointestinal inflammation, with particular reference to the growing body of human data.

Increased metabolism of arachidonic acid in an immune model of colitis in guinea-pigs

Inflammation of the guinea-pig colon was produced by skin sensitization and subsequent intracolonic challenge with the chemical hapten, dinitrochlorobenzene. Metabolism of [14C]-arachidonic acid by homogenates of control colon was very low, although metabolites co-migrating on thin layer chromatography (t.l.c.) with prostaglandin E2 (PGE2), PGF2 alpha, PGD2, 6-keto-PGF1 alpha, thromboxane B2 (TXB2), HHT and 11-, 12-, 15-HETE were formed. There was an overall 3 fold increase in metabolism of [14C]-arachidonic acid by homogenates of inflamed mucosa. The greatest increase in metabolite formation was of PGE2, with smaller increases in HHT, 11-, 12-, 15-HETE, PGD2, TXB2, PGF2 alpha and 6-keto-PGF1 alpha. The formation of these metabolites was inhibited both by indomethacin and the dual pathway inhibitor, BW755C. The formation of immunoreactive PGE2, TXB2 and 6-keto-PGF1 alpha was also increased in homogenates of inflamed guinea-pig colon. The small level of immunoreactive LTB4 detected in control colon was not changed in inflamed colonic tissue. The dinitrochlorobenzene model of colitis offers a means of studying arachidonic acid metabolism in an immune-mediated inflammatory response in intestinal tissue.

[Eicosanoids and phospholipases]

Prostaglandins, thromboxanes, and leukotrienes have been implicated to play an important role in physiology as well as in a growing list of pathophysiologic conditions. These oxidation products of 8.11.14-eicosatrienoic-, 5.8.11.14.-eicosatetraenoic-, and 5.8.11.14.17.-pentaenoic acids have been collectively designated eicosanoids. Many clinically important diseases are associated with altered eicosanoid biosynthesis. Furthermore, a series of hormones are known to induce acutely formation of eicosanoids, suggesting a crucial role in a multitude of tissue responses including phenomena such as secretion, platelet aggregation, chemotaxis, and smooth muscle contraction. The major precursor for the eicosanoids seems to be 5.8.11.14.-eicosatetraenoic acid or arachidonic acid. Virtually all of arachidonic acid however is present in esterified form in complex glycerolipids. Since cyclooxygenase and the lipoxygenases utilize arachidonic acid in its free form, a set of acylhydrolases is required to liberate arachidonic acid from membrane lipids before eicosanoid formation can occur. It became only recently apparent that a minor acidic phospholipid, phosphatidylinositol, comprising only 5%-10% of the phospholipid mass in mammalian cells, plays an important role in arachidonic acid metabolism. Phosphatidylinositol--after phosphorylation to phosphatidylinositolphosphate and phosphatidylinositolbisphosphate--appears to be hydrolyzed by specific phospholipases C generating 1-stearoyl-2-arachidonoyl-diglyceride. Diglyceride serves as substrate for diglyceride lipase to form monoglyceride and free fatty acid. Alternatively diglyceride is phosphorylated by diglyceride kinase yielding phosphatidic acid, which is believed to be reincorporated into phosphatidylinositol. In addition to phosphatidylinositol phosphatidylcholine, phosphatidylethanolamine and phosphatidic acid may contribute to arachidonic acid release. These phospholipids are substrates for phospholipases A2 generating free arachidonic acid and the respective lysophospholipid. Understanding of the biochemistry of arachidonic acid liberation may be critical in developing strategies of pharmacological intervention in a variety of pathological conditions.

Biosynthesis of lipoxygenase and cyclo-oxygenase products from [14C]-arachidonic acid by human colonic mucosa

The human colon synthetises several prostanoids which may have a role in inflammatory bowel diseases. As lipoxygenase products of arachidonate metabolism have been implicated in inflammatory processes, we have now investigated the formation of both lipoxygenase and cyclo-oxygenase metabolites from [14C]-arachidonic acid [(14C]-AA) by human colonic tissue. Homogenates of human colonic mucosa were incubated with [14C]-AA and after extraction into diethyl ether, separated by thin layer chromatography using two solvent systems that allowed resolution of cyclo-oxygenase and lipoxygenase products. The predominant cyclo-oxygenase products, as identified by their chromatographic mobility, were PGE2 greater than PGF2 alpha greater than PGD2 greater than TXB2 greater than 6-keto-PGF1 alpha. The formation of these products was inhibited both by indomethacin (1-10 microM) and the dual pathway inhibitor, BW755C (1-30 microM). The predominant lipoxygenase products formed, which had the chromatographic mobility of 11-, 12-, 15-HETE (which ran together) were inhibited by BW755C (19 microM) but not by indomethacin (3 microM). Further resolution of this TLC band, performed using normal phase HPLC, indicated that both 12-HETE and 15-HETE were major lipoxygenase products formed by human colonic homogenate. The present findings indicate that human colonic tissue can convert [14C]-AA into lipoxygenase as well as cyclo-oxygenase products and support the suggestion that lipoxygenase products may have a role in inflammatory bowel disease.

Imbalance of prostacyclin and thromboxane synthesis in Crohn's disease

Synthesis of prostanoids in Crohn's disease was investigated using rectal biopsy specimens maintained in organ culture. As with ulcerative colitis increased synthesis of prostaglandin (PG)E2 was observed when the mucosa was inflamed, compared with uninflamed mucosa in Crohn's disease, and with control biopsy specimens. In contrast with ulcerative colitis differences from control specimens were observed even in the absence of inflammation. There was a raised synthesis of thromboxane (Tx)B2 (stable breakdown product of TxA2); concentrations of 6-keto PGF1 alpha (stable breakdown product of prostacyclin) were unchanged and hence the ratio of 6-keto PGF1 alpha/TxB2 was reduced. These changes might lead to an altered cytoprotective capacity or reduced suppressor cell activity, such as has previously been reported in intestinal lymphocytes in Crohn's disease.

Release of slow-reacting substance of anaphylaxis and leukotriene C4-like immunoreactivity from guinea pig colonic tissue

Colonic mucosa, muscularis propria and subserosa from ovalbumin-sensitized guinea pigs were incubated and challenged with antigen in vitro. Slow-reacting substance of anaphylaxis (SRS-A) was determined biologically as well as radioimmunologically in terms of leukotriene (LT) C4-like immunoreactivity. Before antigenic challenge release of immunoreactive LTC4 by all tissues was below or close to the detection limit of the radioimmunoassay. After addition of antigen colonic mucosa released considerable amounts of LTC4-like immunoreactivity, while muscularis propria and subserosa were less active. The biological activity of the SRS-A formed after challenge was antagonized by FPL 55712. Contrary to LTC4-like immunoreactivity release of 6-keto-prostaglandin (PG) F1 alpha was predominant in the subserosa and smaller amounts were released from the smooth muscular and mucosal layers. Synthesis of SRS-A and LTC4-like immunoreactivity, respectively, as well as synthesis of 6-keto-PGF1 alpha was inhibited by the dual inhibitor of lipoxygenase and cyclooxygenase BW755c. The results suggest a role for LTs as local mediators of inflammatory reactions in colonic disease states, particularly those with possible involvement of immunological processes.

Antiabsorptive effects of 16,16 dimethyl prostaglandin E2 in isolated rat colon

Ulcerative colitis is distinguished by abundant prostaglandin E2 (PGE 2) in the stools and by severe diarrhea. To determine whether luminal PGE2 alters normal colonic absorption, NA+ and Cl-transport across isolated rat proximal colon were studied before and after 16,16 dimethyl PGE2 (dmPGE2) addition to flux chambers. Luminal administration of dmPGE2 significantly reduced the net mucosal to serosal fluxes of Na+ and Cl-. These antiabsorptive tive effects of dmPGE2 on NA+ and Cl- active transport were reflected by a reduced metabolic rate of colonic tissue slices incubated with dmPGE2. Addition of dmPGE2 significantly reduces oxidation of glucose by the colon. Structurally, dmPGE2 reduced the length of colonic mucosal microvilli, thereby decreasing absorptive surface area. These results suggest that PGE2 released into the colonic lumen of patients with ulcerative colitis exerts antiabsorptive effects on the colon and in this way contributes to the associated diarrhea.

A method for the bioassay of intestinal secretory activity in the conscious rat: studies with arachidonic acid and prostaglandin E2

A method to study the kinetics of intestinal absorption and secretion in the unanesthetized rat is described. This procedure consists of the perfusion of the small intestine with isotonic NaCl-KCl-[36Cl]NaCl and polyethylene glycol-6000 as a nonabsorbable marker. Secretagogues [arachidonic acid (AA) or PGE2] were administered by continuous infusion via the superior mesenteric artery. Samples of perfusate, taken every 15 min, were analyzed for Na, Cl, 36Cl, K, and PEG-6000 to calculate solute and volume movement. In control rats, net absorption of water and electrolytes increased steadily throughout the 2-hr duration of the perfusion. Water, Na, and Cl moved across the intestine in parallel proportions. Net absorption of K was lower than that of the other electrolytes. AA, at the intraarterial dose of 1 mg/kg/hr did not produce a significant effect; at 4 mg/kg/hr it impaired net absorption, and at 8 mg/kg/hr it gradually enhanced net secretion of both water and electrolytes, especially K. Secretion was also demonstrated with the intraarterial infusion of PGE2 (312 microgram/kg). It is concluded that this new rat model is suitable for the bioassay of intestinal secretory stimulants and can be used for the search of intestinal antisecretory drugs.

Effect of prednisolone on prostaglandin synthesis by rectal mucosa in ulcerative colitis: investigation by laminar flow bioassay and radioimmunoassay

The effect of two concentrations of prednisolone on synthesis of prostaglandin E2 (PGE2) by 40 rectal biopsies in organ culture was investigated using both laminar flow bioassay and radioimmunoassay (RIA). Prednisolone (concentration 8.33 x 10(-7)M) reduced mean synthesis of PGE2 to 36.4% of control values (measured by bioassay) or 26.2% of control values (measured by RIA). With prednisolone (concentration 5.66 X 10(-4) M) synthesis of PGE2 was 7.7% of control values (RIA). The two concentrations are similar respectively to those achieved in plasma after oral prednisolone and delivered topically by prednisolone enemata. Inhibition of PG synthesis may thus explain prednisolone's anti-inflammatory action in the treatment of ulcerative colitis.

Studies of prostaglandins and sulphasalazine in ulcerative colitis

Specific evidence is presented of the release of prostaglandins from the colon in active ulcerative colitis. An increase in the levels of bioassayed prostaglandin-like activity in the stools and colo-rectal venous plasma from patients with active ulcerative colitis is described. Radioimmunoassay confirms the presence of prostaglandin E and prostaglandin F in the stools in colitis. Increased urinary levels of prostaglandin F metabolite occur in patients with active colitis and return to normal as the disease becomes quiescent. Sulphasalazine and its faecal metabolite, 5-aminosalicylic acid, were shown by an indirect method (reduction of the tone of the isolated rat fundus strip) to inhibit prostaglandin biosynthesis in vitro. In contrast, sulphasalazine was without effect on the urinary excretion of prostaglandin F metabolite in 7 healthy subjects. In 2 patients with colitis withdrawal of sulphasalazine was associated with increasing levels of stool prostaglandin-like activity and urinary prostaglandin F metabolite excretion. Indomethacin, given to 3 patients with chronically active ulcerative colitis, unresponsive to standard medical treatment, was associated with a decreased urinary excretion of prostaglandin F metabolite but was without clinical benefit. The possible mode of action of sulphasalazine as a prostaglandin inhibitor in colitis is discussed along with the potential use of other prostaglandin inhibitors.

Stimulation of rat colonic mucosal prostaglandin synthesis by calcium and carbamylcholine: relationship to alterations in cyclic nucleotide metabolism

The present study examined the relationships between prostaglandin (PG) synthesis and cyclic nucleotide metabolism in rat colonic mucosal slices. Ca2+, Ca2+ plus A23187 and carbamylcholine all increased [14C]-arachidonate release from prelabeled slices and stimulated production of PGE. Actions of A23187 and carbamylcholine required Ca2+ and were suppressed by tetracaine or mepacrine, whose known actions include inhibition of acyl hydrolase activity. Exogenous arachidonate or linoleate stimulated PGE synthesis in the absence of Ca2+ or in the presence of the inhibitors, suggesting a role for Ca2+ dependent acyl hydrolase activity in the mediation of the actions of Ca2+, A23187 and carbamylcholine on PGE synthesis. Accumulation of both cAMP and cGMP in colonic mucosal slices was enhanced by carbamylcholine, Ca2+, Ca2+ plus A23187, arachidonate or linoleate. Stimulatory actions of each of these agents on PGE production and cyclic nucleotide accumulation were inhibited by O2 exclusion or indomethacin (100 micrograms/ml). The results support a role for local PG production in the mediation of carbamylcholine and Ca2+ actions on cyclic nucleotides. Endogenous ionic, neurohumoral and dietary factors may modulate colonic mucosal PG synthesis and cyclic nucleotide content, and thereby influence the physiologic expression of the actions of these putative local cellular regulators.

Therapeutic efficacy of sulfasalazine and its metabolites in patients with ulcerative colitis and Crohn's disease

We studied the therapeutic efficacy of sulfasalazine and its metabolites sulfapyridine and 5-aminosalicylic acid in nine patients with Crohn's disease and in 23 patients with ulcerative colitis. In a randomized, controlled trial, we treated 11 patients for six weeks with 1 g of sulfasalazine three times a day, seven patients with 0.5 g of sulfapyridine three times a day, and 14 patients with 0.5 g of 5-aminosalicylic acid suppositories three times a day. The clinical state of the disease was characterized by an activity index, quality of stool, and remission rate. In addition, we monitored plasma levels of sulfapyridine, 5-aminosalicylic acid, and their acetylated metabolites. The initial activity index (mean +/- S.D.) was significantly reduced by sulfasalazine (from 245 +/- 129 to 100 +/- 71; P < 0.001) and by 5-aminosalicylic acid (from 251 +/- 65 to 90 +/- 93; P < 0.0001), but sulfapyridine was without benefit. Stool quality was also improved by sulfasalazine (82 per cent of the cases) and by 5-aminosalicylic acid (79 per cent). The highest remission rate was achieved with 5-aminosalicylic acid (86 per cent), followed by sulfasalazine (64 per cent) and sulfapyridine (14 per cent). Our investigations show that 5-aminosalicylic acid is the active moiety of sulfasalazine and that this effective metabolite may be an alternative to sulfasalazine in inflammatory bowel disease.

Rectal mucosal prostaglandin E2 release and its relation to disease activity, electrical potential difference, and treatment in ulcerative colitis

In vivo rectal dialysis was used to study rectal mucosal release of immunoreactive prostaglandin E2-like material and its relation to disease activity, rectal electrical potential difference (PD), and treatment in 24 patients with ulcerative colitis. In untreated colitics in remission and in relapse, median values for apparent mucosal prostaglandin E2 (PGE2) release were increased three-fold (P < 0.05) and 13-fold (P < 0.002) respectively over that found in control subjects. In patients in remission during treatment with sulphasalazine and/or corticosteroids, median apparent PGE2 release was similar to that of controls, but in colitics in relapse, despite treatment, it was greatly increased (P< 0.002). Ulcerative colitis in relapse was associated with a significant reduction in rectal PD(P < 0.002); in patients with quiescent ulcerative colitis, a smaller reduction was found (P < 0.05). In nine patients studied serially before and during treatment, there were associations between changes in disease activity assessed sigmoidoscopically, in PD and in apparent mucosal PGE2 release. Furthermore, rectal mucosal PGE2 release and PD were linearly correlated (P < 0.01). These findings indicate that mucosal PGE2 release is markedly enhanced in active ulcerative colitis, and they confirm the value of rectal PD as a guide to disease activity. In addition, they suggest that rectal dialysis may be a useful way of studying rectal prostaglandin metabolism in man.

A prostaglandin-like activity in small intestine and postirradiation gastrointestional syndrome

A correlation between the postirradiation increase of the small intestine motility and the prostaglandin-like activity in this organ during gastrointestional syndrome was observed. Indomethacin decreased the elevated motility of intestine and reduced the prostaglandin-like activity in this syndrome.

Capacity-limited gut wall metabolism of 5-aminosalicylic acid, a therapeutically active metabolite of sulfasalazine, in rats

The metabolic fate of 5-aminosalicylic acid (reported to be the active therapeutic moiety of sulfasalazine) was assessed in fasting rats as a function of dose (25-200 mg/kg) and administration route (oral, intraperitoneal, and intravenous). 5-Aminosalicylic acid is subject to both capacity-limited presystemic (apparently during first passage through the intestinal epithelium) and systemic acetylation. The possibility exists that 5-aminosalicylic acid also is acetylated presystemically after oral sulfasalazine administration to patients with inflammatory bowel disease. Any alteration in the absorption activity if N-acetyl-5-aminosalicylic acid is inactive or less active than 5-amino-salicylic acid.

Determination of prostaglandin synthetase activity in rectal biopsy material and its significance in colonic disease

A method is described for determining prostaglandin synthetase activity in milligram amounts of tissue. The procedure is based on the conversion of 14C-arachidonic acid to prostaglandin E2 and F2alpha-like substances. High levels of prostaglandin synthetase activity occurred in the inflamed mucosa of patients with ulcerative colitis and fell during successful drug therapy, but it is not yet known whether the cause of the inflammation first involves increased PG synthetase activity, or whether inflammation caused increase of PG synthetase.