The effect of 16,16-dimethyl prostaglandin E2 on proliferation of an intestinal goblet cell line and its synthesis and secretion of mucin glycoproteins

Structural and Molecular Tear Film Changes in Glaucoma

The Tear Film (TF) is a trilaminar and dynamic fluid covering the entire Ocular Surface (OS), consisting of a mucus, aqueous, and lipid layer deeply interacting between them. Because of its structure and functions, TF plays a pivotal role in the preservation of the OS integrity and the quality of vision. Medical therapy for glaucoma is recognized to profoundly disturb the OS homeostasis by altering all components of the ocular surface unit, including TF. The presence of preservatives, the number of daily eye drops instillations, and the duration of therapy are the main contributors to TF changes. From the physio-pathological side, TF alterations are induced by toxic and allergic mechanisms and result from goblet cell and Meibomian gland loss, dysfunction of accessory lacrimal glands, and epithelial disruption. In detail, TF changes are represented by mucus layer thinning, reduced mucin concentration, aqueous layer volume reduction, and lipid layer thinning with increased tear evaporation. Hyper- osmolarity and instability represent the main hallmarks of these changes and are an expression of a iatrogenic form of dry eye. TF undergoes also molecular modifications that primarily reflect a therapy- or disease-induced inflammatory status of the OS. Over the last years, this field of research aimed a progressively growing interest since molecular variations may be considered as potential candidate biomarkers of glaucoma. The aim of this review is to report the main TF changes occurring during glaucoma, exploring the relationship they may have with the glaucoma-related ocular surface disease and the patient quality of life, and their utility as potential biomarkers of disease.

Irinotecan-Induced Mucositis Is Associated with Goblet Cell Dysregulation and Neural Cell Damage in a Tumour Bearing DA Rat Model

Irinotecan-induced mucositis is a major oncological problem. Goblet cells secrete mucus, protecting the intestinal mucosa, with secretion altered during mucositis. The enteric nervous system is involved in regulating gut motility and secretion. The aim of this study was to determine whether enteric neural cells and goblet cells are altered following irinotecan treatment. Tumour-bearing Dark Agouti rats were administered a single dose of 175 mg/kg of irinotecan intraperitoneally and 0.01 mg/kg atropine subcutaneously. Experimental and untreated control rats were killed at times 6, 24, 48, 72, 96 and 120 h after treatment. Jejunum and colon samples were formalin fixed. Haematoxylin and eosin staining, Alcian Blue-PAS staining, and immunohistochemistry with S-100 antibody (neural cell marker) were carried out. Statistical analyses were carried out using Kruskal-Wallis test with Dunns post test, Mann Whitney U test and nonlinear regression. Total goblet cells decreased at 72 h compared with controls in the colon (p < 0.05). The percentage of cavitated goblet cells decreased compared to all other time points at 120 h in the colon. The number of S-100 positive cells in the submucosal plexus decreased in the colon (p = 0.0046) and in the myenteric plexus of the jejunum and colon (p = 0.0058 and p = 0.0022, respectively), when comparing treated with control. Enteric ganglia in the myenteric plexus of the jejunum decreased at 24 h and 96 h. Irinotecan-induced mucositis is associated with increases in mucus secretion, and enteric neural cell change. These changes may contribute to the pathophysiology of mucositis through the dysregulation of neural signalling.

Conjunctival goblet cells density and preservative-free tafluprost therapy for glaucoma: an in vivo confocal microscopy and impression cytology study

PURPOSE

To evaluate the density of conjunctival goblet cells (GCs) in glaucomatous patients treated with preservative-free (PF) tafluprost, using laser scanning confocal microscopy (LSCM) and impression cytology (IC).

METHODS

Thirty glaucomatous patients (30 eyes) naive for therapy and thirty healthy subjects (30 eyes) were enrolled. Conjunctiva was examined by means of Heidelberg Retina Tomography/Rostock cornea module. Afterwards, the specimens for IC were obtained. Patients were randomized to PF-tafluprost (Group 1) or preserved latanoprost (Group 2) and controls to the vehicle of latanoprost (Group 3) or physiological buffered saline solution (Group 4). Both LSCM and IC were performed at baseline, and after the 1st and 6th months of therapy, GC density (GCD) (cells/mm(2) ) was the main outcome measurement.

RESULTS

  Baseline. Mean GCD was 240.69 ± 25.43 and 232.65 ± 23.52, for LSCM, and 162.10 ± 23.44 and 164.71 ± 21.03 for IC in Group 1 and 2, respectively. GC density values were not significantly different in Group 3 and 4 (p > 0.05%). Month one. Mean GCD increased to 284.16 ± 43.88 and 230.62 ± 48.32 in Group 1 (p < 0.001) and to 297.86 ± 26.87 and 221.78 ± 43.02 in Group 2 (p < 0.05), measured with LSCM and IC, respectively. In Group 3, GCD decreased to 205.88 ± 25.04 and 139.54 ± 17.37 measured with LSCM and IC, respectively (p < 0.05). Month six. Mean GCD did not change in Group 1 (p > 0.05) whereas it decreased in Group 2 (p < 0.05), compared to month 1. In Group 3, GCD further decreased to 166.32 ± 22.31 and 120.76 ± 11.66, measured with LSCM and IC, respectively (p < 0.05); in Group 4, mean GCD did not change during the study period (p > 0.05).

CONCLUSIONS

Treatment with PF tafluprost was associated with an increase in conjunctival GCD in glaucomatous eyes naïve for therapy. Further studies are mandatory to verify this finding because its validation may have important consequences in the medical management of glaucoma.

Cyclooxygenase-2 expression and cell proliferation are increased in MUC2-positive area of columnar-lined esophagus

Columnar-lined esophagus is composed of intestinal type and gastric type epithelium. Only the specialized or intestinal type columnar epithelium is susceptible to the development of esophageal adenocarcinoma. The aim of the present paper was to evaluate the expression of cyclooxygenase (COX) and microsomal prostaglandin E synthase (mPGES) in gastric-type and intestinal-type metaplasia in columnar-lined esophagus and compare these with cell proliferation. Biopsy specimens of 30 columnar-lined esophagus patients were collected, and immunohistochemistry was performed for secretory mucins (MUC2, MUC5AC), COX, mPGES and cell proliferation (Ki-67). The MUC2-positive area had higher COX-2 expression and cell proliferation than the MUC5AC-positive area. There was a close correlation between COX-2 expression and cell proliferation. In contrast, the expression of COX-1, mPGES-1 and -2 was similar between intestinal metaplasia and gastric metaplasia. In conclusion, intestinal-type columnar-lined esophagus possesses COX-2 expression and a higher proliferation potential, suggesting that esophageal adenocarcinoma may arise from specialized columnar-lined esophagus.

Core 3 synthase is down-regulated in colon carcinoma and profoundly suppresses the metastatic potential of carcinoma cells

The core 3 structure of the O-glycan, GlcNAcbeta1-3GalNAcalpha1-Ser/Thr, an important precursor in the biosynthesis of mucin-type glycoproteins, is synthesized by beta1,3-N-acetylglucosaminyltransferase 6 (beta3Gn-T6; core 3 synthase). We generated an anti-beta3Gn-T6 mAb (G8-144 mAb) and performed immunohistochemical analyses. In normal stomach and colon, beta3Gn-T6 was strongly expressed in the Golgi region of epithelia. In contrast, its expression was markedly down-regulated in gastric and colorectal carcinomas. Tissue specimens from a familial adenomatous polyposis patient showed a clear correlation between the down-regulation of beta3Gn-T6 expression and the degree of dysplasia/neoplasia. In vitro, the level of beta3Gn-T6 transcript was increased according to the differentiation of Caco-2 cells. These results suggested that the expression of beta3Gn-T6 is closely regulated during differentiation and dedifferentiation. beta3Gn-T6 would be a useful marker for distinguishing between benign adenomas and premalignant lesions. HT1080 FP-10 cells stably transfected with the beta3Gn-T6 gene showed a decrease in the core 1 structure, Galbeta1,3GalNAcalpha1-Ser/Thr, probably due to competition between the core 1 synthase and core 3 synthase. The migration activity of the transfectants was markedly lower than that of mock transfectants in vitro, and lung metastasis after i.v. injection of the transfectants into nude mice was significantly suppressed. These findings indicated that the core structures of O-glycans are profoundly involved in the metastatic capacity of cancer cells.

Prostaglandin EP receptors: Targets for treatment and prevention of colorectal cancer?

The importance of the prostaglandin (PG) synthesis pathway, particularly the rate-limiting enzymatic step catalyzed by cyclooxygenase, to colorectal carcinogenesis and development of novel anticolorectal cancer therapy is well established. The predominant PG species in benign and malignant colorectal tumors is PGE2. PGE2 acts via four EP receptors termed EP1 to EP4. Recently, EP receptors have been identified as potential targets for treatment and/or prevention of colorectal cancer. This review summarizes existing knowledge of the expression and function of the EP receptor subtypes in human and rodent intestine during tumorigenic progression and describes the current literature on targeting EP receptor signaling during intestinal tumorigenesis.

Interleukin-1beta induces MUC2 and MUC5AC synthesis through cyclooxygenase-2 in NCI-H292 cells

Interleukin-1beta (IL-1beta) has been implicated in the pathogenesis of inflammatory diseases of the airway. In this study, we investigated the regulation of MUC2 and MUC5AC expression and of their regulatory mechanisms through cyclooxygenase-2 (COX-2) and prostaglandin E(2) (PGE(2)). Cells activated by IL-1beta showed increased COX-2, MUC2, and MUC5AC expressions at both the mRNA and protein levels. Mucin production was blocked by the selective COX-2 inhibitor NS398, and PGE(2) directly induced MUC2 and MUC5AC expression at both the mRNA and protein levels in a dose-dependent manner. These results suggest a role for PGE(2) in IL-1beta-induced mucin synthesis in NCI-H292 cells. To investigate the roles of molecules upstream of COX-2 in mucin regulation, we examined the role of mitogen-activated protein kinases (MAPKs). Cells activated by IL-1beta showed increased extracellular signal-regulated kinase (ERK)1/2 and p38 phosphorylation, and IL-1beta-induced MUC2 and MUC5AC production was blocked by the ERK pathway inhibitor PD98059 or the p38 inhibitor SB203580. The inhibition of both MAPKs reduced IL-1beta-induced COX-2 expression and PGE(2) synthesis. Furthermore, the addition of PGE(2) to cells overcame the inhibitory effects of both MAPK inhibitors in IL-1beta-induced mucin production. These results indicate that in human pulmonary epithelial cells, IL-1beta activates ERK or p38 to induce COX-2 production, which in turn induces MUC2 and MUC5AC production.

Molecular cloning and characterization of a novel UDP-GlcNAc:GalNAc-peptide beta1,3-N-acetylglucosaminyltransferase (beta 3Gn-T6), an enzyme synthesizing the core 3 structure of O-glycans

The core 3 structure of the O-glycan, GlcNAcbeta1-3GalNAcalpha1-serine/threonine, an important precursor in the biosynthesis of mucin-type glycoproteins, is synthesized by UDP-N-acetylglucosamine:GalNAc-peptide beta1,3-N- acetylglucosaminyltransferase (beta3Gn-T; core 3 synthase). The core 3 structure is restricted in its occurrence to mucins from specific tissues such as the stomach, small intestine, and colon. A partial sequence encoding a novel member of the human beta3Gn-T family was found in one of the data bases. We cloned a complementary DNA of this gene and named it beta3Gn-T6. The putative amino acid sequence of beta3Gn-T6 retains the beta3Gn-T motifs and is predicted to comprise a typical type II membrane protein. The soluble form of beta3Gn-T6 expressed in insect cells showed beta3Gn-T activity toward GalNAcalpha-p-nitrophenyl and GalNAcalpha1-serine/threonine. The beta1,3-linkage between GlcNAc and GalNAc of the enzyme reaction product was confirmed by high performance liquid chromatography and NMR analyses. beta3Gn-T6 effectively transferred a GlcNAc to the GalNAc residue on MUC1 mucin, resulting in the synthesis of a core 3 structure. Real time PCR analysis revealed that the beta3Gn-T6 transcript was restricted in its distribution, mainly to the stomach, colon, and small intestine. We concluded that beta3Gn-T6 is the most logical candidate for the core 3 synthase, which plays an important role in the synthesis of mucin-type O-glycans in digestive organs.

The human prostanoid DP receptor stimulates mucin secretion in LS174T cells

This study demonstrates the localization of the prostaglandin (PG)D(2) receptor (DP) within the mucous-secreting globlet cells of the human colon by in situ hybridization, which suggests a role for DP in mucous secretion. Selective high affinity ligands were used, therefore, to evaluate DP regulation of mucous secretion in LS174T human colonic adenocarcinoma cells. The expression of hDP in LS174T cells was confirmed at the mRNA level by reverse transcriptase-polymerase chain reaction, and at the protein level by radioligand binding assays and signal transduction (cyclic AMP accumulation) assays. PGD(2) and the highly selective DP-specific agonist L-644,698 ((4-(3-(3-(3-hydroxyoctyl)-4-oxo-2-thiazolidinyl) propyl) benzoic acid) (racemate)), but not PGE(2) competed for [(3)H]-PGD(2)-specific binding to LS174T cell membranes (K:(i) values of 0.4 nM and 7 nM, respectively). The DP-specific agonists PGD(2), PGJ(2), BW245C (5-(6-carboxyhexyl)-1-(3-cyclohexyl-3-hydroxypropylhydantoin)), and L-644,698 showed similar potencies in stimulating cyclic AMP accumulation (EC(50) values: 45 - 90 nM) and demonstrated the expected rank order of potency. PGE(2) also elicited cyclic AMP production in this cell line (EC(50) value: 162 nM). The activation of cyclic AMP production by PGD(2) and L-644,698, but not PGE(2), was inhibited by the selective DP antagonist BW A868C. Thus, PGD(2) and L-644,698 act through hDP in LS174T cells. PGD(2), L-644,698 and PGE(2) (an established mucin secretagogue) potently stimulated mucin secretion in LS174T cells in a concentration-dependent manner (EC(50)<50 nM). However, BW A868C effectively antagonized only the mucin secretion mediated by PGD(2) and L-644,698 and not PGE(2). These data support a role for the DP receptor in the regulation of mucous secretion.

Cellular distribution of prostanoid EP receptors mRNA in the rat gastrointestinal tract

The inhibition of PGE(2) synthesis resulting from sustained NSAIDs therapy has been linked to gastrointestinal irritations and ulceration. The multiple physiological effects of PGE(2) in the gut are mediated through the activation of four receptors termed EP(1-4). The aim of the study was to determine the precise distribution of the four prostaglandin E(2) receptors in the rat stomach, small intestine, and colon. We used non-radioactive in situ hybridization techniques on paraffin-embedded tissue. Mucous cells of the stomach and goblet cells of the small intestine and colon were found to express mRNA for all four EP subtypes. A positive hybridization signal for EP(1), EP(3), and EP(4) was detected in the parietal cells of the stomach whereas the chief cells expressed low levels of EP(1) and EP(3). The EP(1) and EP(3) receptor mRNA could also be detected in the muscularis mucosa, longitudinal muscle and enteric ganglias of the stomach and small intestine. However, close examination of the enteric ganglias indicated that most of the positive labeling was localized to the glial cells, although some neurons did express EP(3). In conclusion, we have detailed the distribution of prostanoid EP receptors in the gut at the cellular level, giving new insights to the role of prostaglandins in gastrointestinal functions.

Secretagogue response of goblet cells and columnar cells in human colonic crypts

Crypts of Lieberkühn were isolated from human colon, and differential interference contrast microscopy distinguished goblet and columnar cells. Activation with carbachol (CCh, 100 microM) or histamine (10 microM) released contents from goblet granules. Stimulation with prostaglandin E(2) (PGE(2), 5 microM) or adenosine (10 microM) did not release goblet granules but caused the apical margin of columnar cells to recede. Goblet volume was lost during stimulation with CCh or histamine ( approximately 160 fl/cell), but not with PGE(2) or adenosine. Three-quarters of goblet cells were responsive to CCh but released only 30% of goblet volume. Half-time for goblet volume release was 3.7 min. PGE(2) stimulated a prolonged fluid secretion that attained a rate of approximately 350 pl/min. Columnar cells lost approximately 50% of apical volume during maximal PGE(2) stimulation, with a half-time of 3.3 min. In crypts from individuals with ulcerative colitis, goblet cells were hypersensitive to CCh for release of goblet volume. These results support separate regulation for mucus secretions from goblet cells and from columnar cells, with control mechanisms restricting total release of mucus stores.

Prostaglandin E(2) stimulates rat and human colonic mucin exocytosis via the EP(4) receptor

BACKGROUND & AIMS

Mucins form an integral part of innate host defenses against intestinal pathogens and irritants. However, the mechanisms whereby mucin secretion is regulated during inflammation are poorly understood. Because prostaglandin E(2) (PGE(2)) is prominent during intestinal inflammation, we investigated its receptor-signaling pathway coupled to mucin exocytosis in the colonic epithelial cell line LS174T and rat colon.

METHODS

Reverse-transcription polymerase chain reaction (RT-PCR) and [(3)H]PGE(2) binding assays were used to identify the PGE(2) receptors (EP). Intracellular cyclic adenosine monophosphate ([cAMP](i)) was quantified by enzyme immunoassay. Mucins were metabolically labeled with [(3)H]glucosamine, and mucin secretion was quantified by Sepharose 4B column chromatography, immunoblot analysis, and cesium chloride density gradient centrifugation.

RESULTS

RT-PCR and DNA sequence analysis identified EP(2), EP(3), and EP(4) receptors. Mucin secretion and [cAMP](i) production by LS174T cells were stimulated dose-dependently by PGE(2), the EP(4)-receptor agonist 1-OH-PGE(1), and the EP(3)/EP(4) agonist M&B28767 and were inhibited with the adenylate cyclase inhibitor SQ22536. The EP(1), EP(2), and EP(3)/EP(1)-receptor agonists iloprost, butaprost, and sulprostone, respectively, had no effect. Similar results were obtained in rat colonic loop studies confirming that the EP(4) receptor is linked to mucin exocytosis in vivo. [(3)H]PGE(2) binding to cell membranes identified a high-affinity binding site that was competitively inhibited by M&B28767 (EP(3)/EP(4)) > 1-OH-PGE(1) (EP(4)) > sulprostone (EP(3)/EP(1)) > butaprost (EP(2)).

CONCLUSIONS

PGE(2) coupling to the EP(4) receptor stimulates [cAMP](i)-dependent mucin exocytosis.

Secretagogue response of goblet cells and columnar cells in human colonic crypts

Crypts of Lieberkühn were isolated from human colon, and differential interference contrast microscopy distinguished goblet and columnar cells. Activation with carbachol (CCh, 100 microM) or histamine (10 microM) released contents from goblet granules. Stimulation with prostaglandin E2 (PGE2, 5 microM) or adenosine (10 microM) did not release goblet granules but caused the apical margin of columnar cells to recede. Goblet volume was lost during stimulation with CCh or histamine (approximately 160 fl/cell), but not with PGE2 or adenosine. Three-quarters of goblet cells were responsive to CCh but released only 30% of goblet volume. Half-time for goblet volume release was 3.7 min. PGE2 stimulated a prolonged fluid secretion that attained a rate of approximately 350 pl/min. Columnar cells lost approximately 50% of apical volume during maximal PGE2 stimulation, with a half-time of 3.3 min. In crypts from individuals with ulcerative colitis, goblet cells were hypersensitive to CCh for release of goblet volume. These results support separate regulation for mucus secretions from goblet cells and from columnar cells, with control mechanisms restricting total release of mucus stores.

A novel biological role for prostaglandin D2 is suggested by distribution studies of the rat DP prostanoid receptor

We report the cloning, functional expression and cell-specific localization of the rat homologue of the prostaglandin D2 receptor (DP). In situ hybridization, utilizing multiple digoxigenin-labelled riboprobes and their complementary sense controls, was performed to determine the detailed distribution of DP receptor mRNA in the central nervous system and the gastrointestinal tract. Within the brain, the leptomeninges and choroid plexus expressed DP receptor mRNA. Transcripts detected in the spinal cord were localized to the sensory and motor neurons of the dorsal and ventral horns, respectively, suggesting a role for the DP receptor in the modulation of central nervous system processes, including pain transmission. Within the gastrointestinal tract (stomach, duodenum, ileum and colon) signals were highly localized to the mucous-secreting goblet cells and the columnar epithelium. These findings suggest a novel biological role for prostaglandin D2-mediated activity at the DP receptor, namely mucous secretion. In addition, radioligand binding assays (saturation analyses and equilibrium competition assays) and functional assays (measuring cAMP accumulation) were performed to characterize the recombinant rat DP receptor expressed in human embryonic kidney (HEK) 293(EBNA) cells. A single site of binding (K(D) = 14 nM, Bmax = 115 fmol/mg protein) was measured for prostaglandin D2-specific binding to the rat DP receptor. Prostaglandin D2 proved to be a potent agonist at the rat DP receptor (EC50 = 5 nM). The rank order of efficacy for DP receptor specific agonists [prostaglandin D2 = prostaglandin J2 = BW 245C (5-(6-carboxyhexyl)-1-(3-cyclohexyl-3-hydroxypropylhydantoin)) > L-644,698 ((4-(3-(3-(3-hydroxyoctyl)-4-oxo-2-thiazolidinyl) propyl) benzoic acid) (racemate)] reflected the affinity with which the ligands bound to the receptor.

Effects of neurotransmitters, gut hormones, and inflammatory mediators on mucus discharge in rat colon

The effect of potential mediators of mucus secretion was investigated in the isolated vascularly perfused rat colon by using a sandwich enzyme-linked immunosorbent assay for rat colonic mucin and by histochemical analysis. Bethanechol (100-200 microM), bombesin (100 nM), and vasoactive intestinal peptide (VIP, 100 nM) provoked a dramatic mucin discharge (maximal response at 900, 900, and 600% of control loops, respectively). VIP-stimulated mucin secretion was abolished by tetrodotoxin, whereas atropine was without effect. In contrast, both tetrodotoxin and atropine significantly decreased mucin release induced by bombesin. Isoproterenol or calcitonin gene-related peptide was without effect. Serotonin (1-5 microM) and peptide YY (10 nM) evoked mucin discharge, whereas glucagon-like peptide-1 did not release mucin. Finally, bromolasalocid (20 microM), interleukin-1beta (0.25 nM), sodium nitroprusside (1 mM), and dimethyl-PGE2 (2.5 microM) induced mucus discharge. The results demonstrated a good correlation between the immunological method and histological analysis. In conclusion, these findings suggest a role for the enteric nervous system, the enteroendocrine cells, and resident immune cells in mediation of colonic mucus release.

Effects of PGE2 and of different synthetic PGE derivatives on the glycosylation of pig gastric mucins

The glycosylation of pig gastric mucins, discharged in response to prostaglandin (PG) E2 and to three synthetic PGE-derivatives (misoprostol, nocloprost, rioprostil) was compared. After a 20 h culture period in the absence or presence of 1 micromol/l of one of the PGs, mucins were isolated by gel chromatography and their glycosylation characterized by their linkage to a panel of lectins. For all tested PGs, a significantly increased lectin linkage to mucin glycoproteins of high molecular weight was detected; no significant effects were observed for low molecular weight glycoproteins. Within the stimulatory pattern, major effects were found for the linkage of peanut agglutinin and soybean agglutinin, suggesting predominant effects on the expression of galactose and N-acetyl-galactosamine. Only minor effects were found for sialic acid, mannose, N-acetyl-glucosamine and fucose expression, as evidenced by the linkage of Sambucus nigra agglutinin, Concanavalin A, Datura stramonium agglutinin and Ulex europaeus I agglutinin. All PGs exerted a similar stimulatory pattern. However, at the indicated concentration, misoprostol (281 +/- 36% of control) rendered a significantly higher overall effect than PGE2 (208 +/- 31%), whereas the increases induced by nocloprost (237 +/- 35%) and rioprostil (202 +/- 35%) were not significantly different from the PGE2 effects. These results, suggesting similar stimulatory effects of PGE2 and of the tested synthetic PGs on glycosylation of mucin oligosaccharides, discharged from mucous cells during an in vitro culture, may, at least in part, explain clinical findings that during an impairment of the endogenous PG synthesis, the tested synthetic PGs are effective exogenous substitutes for endogenous E-type prostaglandins and act as anti-ulcer drugs.

Effect of lipoxygenase inhibition on mucous glycoprotein secretion from chinchilla middle ear epithelial cells in vitro

Lipoxygenase is an enzyme that metabolizes arachidonic acid down to leukotrienes. Recent studies have shown that the enzyme is implicated in mucous glycoprotein (MGP) secretion stimulated by inflammatory mediators in the airways, suggesting its possible role in secretion of MGP from middle ear epithelial cells. To investigate a correlation between MGP secretion and the arachidonic acid metabolites, we examined the effects of nordihydroguaretic acid (NDGA, both a cyclooxygenase and lipoxygenase inhibitor), low-dose indomethacin (an inhibitor of cyclooxygenase), and A63162 (an inhibitor of lipoxygenase) on MGP secretion in cultured chinchilla middle ear epithelial cells. It was found that lipoxygenase inhibition led to reduction of MGP secretion from cultured chinchilla middle ear epithelial cells, while cyclooxygenase inhibition did not. Both cyclooxygenase and lipoxygenase inhibition resulted in profound blockage of MGP secretion in baseline and platelet activating factor-stimulated MGP secretion. It was concluded, therefore, that MGP secretion was linked to arachidonic acid metabolites, especially lipoxygenase products.

Eicosanoid production by parasites:

In this review, Adam Belley and Kris Chadee discuss eicosanoid production by various parasites and propose roles they may play in pathogenesis and immunomodulation. The commonality between parasites is prostaglandin production and, therefore, special attention is given to the cyclooxygenase pathway, highlighting the enzymes and functions of prostaglandins.

Bradykinin modulates mucin secretion but not synthesis from an intestinal goblet cell line

The effect of the inflammatory mediator bradykinin on glycoprotein synthesis and mucin secretion in the human colonic adenocarcinoma cell line HT29-18N2 was examined. Bradykinin, at a threshold of 0.01 microM, accelerated the rate of mucin discharge as assessed by a mucin-specific ELISA. Using immunofluorescence microscopy, a thick meshwork of extracellular mucus was observed over bradykinin-treated monolayers but not mock-treated controls. Morphometric analysis of bradykinin-treated monolayers revealed no decreases in intracellular mucin stores or any other easily discernable morphological alteration. The ability of the cyclooxygenase inhibitors indomethacin and naproxen to decrease the response to bradykinin by approximately 68% indicates the effect is mediated, at least partially, through the generation of prostaglandins. Bradykinin did not alter the rate of incorporation of 3H-glucosamine into newly synthesized glycoproteins. Bradykinin-accelerated mucin secretion may be linked to the depletion of intracellular mucin stores in the inflammatory bowel disease ulcerative colitis.