Gastrointestinal toxicity of nonsteroidal antiinflammatory drugs.
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Anti-Inflammatory Agents, Non-Steroidal↗
Biomedical subjects
M M Wolfe
Publications and source records attributed to M M Wolfe.
Structure of the rat glucose-dependent insulinotropic polypeptide receptor gene.
The Glucose-dependent insulinotropic polypeptide receptor (GIPR) is a member of the secretin-vasoactive intestinal polypeptide family of G-protein coupled receptors possessing seven transmembrane domains. We report here the cloning and the exon-intron structure of the rat GIPR gene, along with the identification and characterization of its 5'-flanking region. The coding region of the GIPR gene spans approximately 10.2 kilobases and contains 13 exons. Three additional exons, two encoding either 5' or 3' untranslated sequences and one contained in a novel alternatively spliced mRNA, were identified. The 5'-flanking sequences contained a number of transcription factor binding motifs, including a cAMP response element, an octamer binding site, three SP1 sites and an initiator element. However, neither a CAAT motif nor TATA box were found. Transient transfection assays demonstrated that the 5'-flanking region of the GIPR gene can efficiently promote transcription in RIN38 cells and that deletion of 50 base pairs containing a potential SPI binding sites leads to a 2.4-fold loss of transcriptional activity. In addition, transient transfection experiments comparing the relative promoter activities of 5'-flanking sequences of the GIPR gene in RIN38 and rat-2 cells suggests that distal negative regulatory sequences may control cell-specific expression.
Animals↗
Effect of GIP and GLP-1 antagonists on insulin release in the rat.
Glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 (GLP-1) are potent insulinotropic peptides released from the small intestine. To examine their relative contribution to postprandial insulin release, a specific GIP antagonist (ANTGIP) and a GLP-1 antagonist, exendin-(9-39)-NH2, were infused into rats after an intragastric glucose meal. In control rats, plasma glucose and insulin levels rose gradually during the first 20 min and then decreased. Exendin-(9-39)-NH2 administration inhibited postprandial insulin secretion by 32% at 20 min and concomitantly increased plasma glucose concentrations. In contrast, ANTGIP treatment not only induced a 54% decrease in insulin secretion but also a 15% reduction in plasma glucose levels 20 min after the glucose meal. In vivo studies in rats demonstrated that glucose uptake in the upper small intestine was significantly inhibited by the ANTGIP, an effect that might account for the decrease in plasma glucose levels observed in ANTGIP-treated rats. When the two antagonists were administered to rats concomitantly, no potentiating effect on either insulin release or plasma glucose concentration was detected. Glucose meal-stimulated GLP-1 release was not affected by ANTGIP administration, whereas postprandial glucagon levels were diminished in rats receiving exendin-(9-39)-NH2. The results of these studies suggest that GIP and GLP-1 may share a common mechanism in stimulating pancreatic insulin release. Furthermore, the GIP receptor appears to play a role in facilitating glucose uptake in the small intestine.
Absorption↗
Gastrin-mediated effects of omeprazole on rat colon mucosa.
BACKGROUND: Omeprazole increases circulating gastrin levels, which in turn may affect the growth and differentiation of colon mucosa. Chloride transport mechanisms in normal colon were analyzed as markers for possible trophic actions of endogenous hypergastrinemia. METHODS: Four groups of Fischer rats were studied for 10 days. Group 1 (baseline) received no treatment. Group 2 received omeprazole only. Group 3 received omeprazole plus vehicle. Group 4 received omeprazole plus CCK-B gastrin receptor antagonist (GRA) L740,093 in vehicle. On day 10 serum gastrin was assayed. Colon mucosa was analyzed for protein and DNA content. Semiquantitative Northern analysis measured levels of messenger RNA (mRNA) encoding for key Cl- transporters: Na-K-Cl cotransporter (Cl- secretion in crypts), Cl-/HCO3- exchanger (Cl- absorption in villi), and Na/K adenosine triphosphatase (not directly involved in Cl- transport). RESULTS: Omeprazole increased gastrin levels, which were not altered by vehicle or GRA. Omeprazole increased protein, DNA, and Na/K adenosine triphosphatase mRNA levels, with no effect by GRA. In contrast, omeprazole decreased Na-K-Cl and Cl-/HCO3- mRNA levels, effects that were partly reversed by GRA. CONCLUSIONS: Omeprazole augments growth index values of colon mucosa independent of serum gastrin. Against a background of omeprazole-induced achlorhydria hypergastrinemia appears to influence differentiation rather than growth of normal colon mucosa.
Animals↗
Future trends in the development of safer nonsteroidal anti-inflammatory drugs.
Gastrointestinal (GI) adverse events, ranging from mild to life-threatening, are well-recognized sequelae to nonsteroidal anti-inflammatory drug (NSAID) use. Recent improvements in our knowledge of the mechanisms responsible for NSAID-associated gastropathy have enabled several experimental approaches to decreasing the risk of these events. Whereas such strategies as preassociation of NSAIDs to zwitterionic phospholipids to prevent NSAID-mucosal interactions and concomitant administration of trefoil peptides to stimulate mucosal defense pathways represent novel approaches, their clinical feasibility remains to be determined. Other strategies that appear more immediately promising in the reduction of NSAID-associated GI toxicity are the coupling of NSAIDs to nitric oxide (NO)-releasing compounds and the introduction of NSAIDs that are preferential or specific for cyclo-oxygenase-2 (COX-2), the isoform implicated in the inflammatory response. Clinical trials of several specific COX-2 inhibitors, as well as European clinical data for a preferential COX-2 inhibitor, meloxicam, suggest that COX-2 inhibitors provide an advantage over standard NSAIDs in terms of GI tolerability. However, as recent observations have implicated COX-2 as an integral component in the maintenance of physiologic homeostasis, careful scrutiny of both the beneficial and the deleterious effects of the selective COX-2 inhibitors is requisite before their approval and widespread use. Furthermore, based on the physiologic importance of COX-2, the preferential inhibitors may ultimately prove to represent the optimal compromise for the treatment of various arthritides.
Animals↗
Functional GIP receptors are present on adipocytes.
In addition to its important role in maintaining glucose homeostasis, it has recently become apparent that glucose-dependent insulinotropic polypeptide (GIP) is also involved in different steps of lipid metabolism. GIP has been shown to stimulate the release of lipoprotein lipase from fat, as well as increase the rate of fat incorporation into adipose tissue. Moreover, GIP has been shown to increase the clearance rate of chylomicrons in the circulation and to inhibit the action of glucagon. Despite evidence for GIP effects on fat tissue, GIP receptors have not been identified in fat cells or tissues. The present study was undertaken to identify GIP receptors in isolated adipocytes, as well as to identify GIP receptors in the established fat cell line, differentiated 3T3-L1. RNAse protection analysis demonstrated the presence of GIP receptor transcripts in rat adipocytes. A polyclonal GIP receptor antiserum directed at the N-terminus of the receptor detected the presence of GIP receptors in both rat fat and differentiated 3T3-L1 cells by Western blot analysis. Moreover, [125I] GIP binding assays revealed both specific and displaceable GIP binding sites in differentiated 3T3-L1 cells (IC50 = 10(-9) M). When undifferentiated 3T3-L1 cells, which appear to express relatively few GIP receptors, were incubated in the presence of GIP, no effect on intracellular cAMP accumulation was detected. In contrast, the inclusion of 10 nM GIP in the incubation medium increased cAMP accumulation in rat fat cells and differentiated 3T3-L1 cells. This increase in cAMP accumulation was abolished with the specific GIP receptor antagonist GIP(7-30)NH2. The results of these studies indicate that GIP receptors are present in fat cells and are up-regulated when 3T3-L1 cells undergo differentiation to become adipocytes. Furthermore, the increase in intracellular cAMP accumulation detected upon ligand binding indicates that these receptors are functional.
3T3 Cells↗
Cell-specific expression of the glucose-dependent insulinotropic polypeptide gene in a mouse neuroendocrine tumor cell line.
Glucose-dependent insulinotropic polypeptide (GIP) is a 42-amino acid gastrointestinal regulatory peptide that, in the presence of glucose, stimulates insulin secretion. GIP is expressed in K cells of the small intestine and in cells of the submandibular salivary gland. Using a rat GIP cDNA as a specific probe, we screened a number of established cell lines for the expression of GIP mRNA. STC-1 cells, a cell line derived from a mouse neuroendocrine tumor, were found to express high levels of GIP mRNA. GIP-specific transcripts were not detected in other cell lines tested, which included cells of intestinal, salivary, and endocrine origin. Analysis of GIP-luciferase fusions identified two promoters, a distal and a proximal promoter, upstream of the translation initiation codon for GIP. The distal promoter, located upstream of position +1, corresponds to the principal promoter of the GIP gene and can promote cell-specific transcription. Sequential deletion and site-directed mutational analysis of the distal promoter demonstrated that the sequence between -193 and -182 determines cell-specific expression of GIP. Contained in this region is a consensus GATA motif, suggesting that a member of the GATA family of DNA-binding proteins is involved in the cell-specific regulation of the GIP gene.
Animals↗
NSAIDs and the gastrointestinal mucosa.
In the United States, these double-edged drugs cause as many as 20,000 deaths a year. To blunt their harmful effects, two promising strategies are being pursued: concurrent administration of prostaglandin analogues to support gastric homeostasis, and the development, or identification among existing NSAIDs, of an agent that targets inflammatory prostaglandins while sparing the homeostatic ones.
Animals↗
Postprandial stimulation of insulin release by glucose-dependent insulinotropic polypeptide (GIP). Effect of a specific glucose-dependent insulinotropic polypeptide receptor antagonist in the rat.
Glucose-dependent insulinotropic polypeptide (GIP) is a 42-amino acid peptide produced by K cells of the mammalian proximal small intestine and is a potent stimulant of insulin release in the presence of hyperglycemia. However, its relative physiological importance as a postprandial insulinotropic agent is unknown. Using LGIPR2 cells stably transfected with rat GIP receptor cDNA, GIP (1-42) stimulation of cyclic adenosine monophosphate (cAMP) production was inhibited in a concentration-dependent manner by GIP (7-30)-NH2. Competition binding assays using stably transfected L293 cells demonstrated an IC50 for GIP receptor binding of 7 nmol/liter for GIP (1-42) and 200 nmol/liter for GIP (7-30)-NH2, whereas glucagonlike peptide-1 (GLP-1) binding to its receptor on ++betaTC3 cells was minimally displaced by GIP (7-30)-NH2. In fasted anesthetized rats, GIP (1-42) stimulated insulin release in a concentration-dependent manner, an effect abolished by the concomitant intraperitoneal administration of GIP (7-30)-NH2 (100 nmol/ kg). In contrast, glucose-, GLP-1-, and arginine-stimulated insulin release were not affected by GIP (7-30)-NH2. In separate experiments, GIP (7-30)-NH2 (100 nmol/kg) reduced postprandial insulin release in conscious rats by 72%. It is concluded that GIP (7-30)-NH2 is a GIP-specific receptor antagonist and that GIP plays a dominant role in mediating postprandial insulin release.
Animals↗
Chronic desensitization of the glucose-dependent insulinotropic polypeptide receptor in diabetic rats.
Rats were rendered diabetic by streptozotocin, after which serum glucose-dependent insulinotropic polypeptide (GIP) levels, duodenal mucosal GIP content, and GIP mRNA levels were nine times, 50% and 80%, respectively, greater than in control rats. To determine whether an increase in GIP gene expression might induce chronic desensitization of its receptor, normal rats were subjected to continuous intravenous GIP infusion. Serum GIP levels increased gradually in GIP-infused rats, and by 4 h a threefold increase was detected. In response to GIP infusion, the serum insulin concentration increased at 30 min, followed by a gradual decrease, and at 4 h, no increase in insulin levels was detected despite a sustained elevated serum GIP level. The response to glucagon-like peptide-1 (GLP-1) was preserved, a reporter cell line (LGIPR2) stably transfected with rat GIP receptor cDNA was studied. GIP stimulated adenosine 3', 5'-cyclic monophosphate (cAMP) production in LGIPR2 cells, which was first detected after 1 h of stimulation, reached maximum level at 4 h, and returned to basal concentrations by 16 h. Additional stimulation with GIP at 16 h did not affect cAMP generation, indicating desensitization of the GIP receptor by the ligand. In contrast, a response to prostaglandin E1 or forskolin in GIP-desensitization was a receptor-specific process. The results of these studies indicate that GIP gene expression is enhanced in diabetic animals and that elevated serum GIP level induces chronic desensitization of the GIP receptor in vivo and in a stably transfected cell line.
Animals↗
Glucose-dependent insulinotropic peptide (GIP) gene expression in the rat salivary gland.
Previous studies have indicated that following nutrient ingestion, GIP is released principally from the upper small intestine. In addition to its presence in the rat small intestine, GIP transcripts have also been localized to the submandibular salivary gland (SSG). The present studies were directed to further characterize expression of the GIP gene in the SSG. Pregnant rats were sacrificed at gestational days 18 and 20, followed by the removal of rat fetuses. The duodenum pancreas, and SSG were then excised from the fetuses, as well as from neonatal pups at ages 1, 3, 7, 10, 14, and 21 days. RNA was extracted and measured by Northern blot analysis using specific rat GIP probes. GIP transcripts were first detected in the duodenum in the 18-day fetus and reached maximum levels at birth. In contrast, GIP mRNA was not observed in the SSG until 10 days postnatally and was not detected at all in either the fetal or neonatal pancreas. In situ hybridization of the SSG using an 35S-labelled antisense GIP RNA probe demonstrated expression of the GIP gene to be limited to ductal cells, with no transcripts present in acini. In separate experiments, rats fasted overnight were given water or 10% glucose. While no changes were detected in water-fed rats following oral glucose ingestion, small, but significant increases in SSG GIP gene expression were detected at 60 and 240 min. The results of these initial studies suggest the possibility of a functional role for GIP in the rat salivary gland by the demonstration of GIP mRNA in the SSG by Northern analysis and in situ hybridization, as well as by an increase in SSG GIP gene expression following a glucose meal.
Animals↗
Liquid-phase combinatorial synthesis.
A concept termed liquid-phase combinatorial synthesis (LPCS) is described. The central feature of this methodology is that it combines the advantages that classic organic synthesis in solution offers with those that solid-phase synthesis can provide, through the application of a linear homogeneous polymer. To validate this concept two libraries were prepared, one of peptide and the second of nonpeptide origin. The peptide-based library was synthesized by a recursive deconvolution strategy [Erb, E., Janda, K. D. & Brenner, S. (1994) Proc. Natl. Acad. Sci. USA 91, 11422-11426] and several ligands were found within this library to bind a monoclonal antibody elicited against beta-endorphin. The non-peptide molecules synthesized were arylsulfonamides, a class of compounds of known clinical bactericidal efficacy. The results indicate that the reaction scope of LPCS should be general, and its value to multiple, high-throughput screening assays could be of particular merit, since multimilligram quantities of each library member can readily be attained.
Amino Acid Sequence↗
Nonsteroidal antiinflammatory drugs and the gastrointestinal tract. The double-edged sword.
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Anti-Inflammatory Agents, Non-Steroidal↗
Effects of hypochlorhydria and hypergastrinemia on structure and function of gastrointestinal cells. A review and analysis.
Since hypochlorhydria can induce hypergastrinemia, and gastrin has a trophic effect on some gastrointestinal cells, states that cause elevated plasma gastrin levels are of interest in terms of effects on cell growth and function. This article reviews the relationship between gastric mucosal cells during periods of acid stimulation and inhibition and analyses the effects of hypochlorhydria and hypergastrinemia on gastric and colonic cells and tumors. Hypochlorhydria releases the inhibitory effect of antral gastrin cells, inducing them to release gastrin in the presence of peptides or amino acids in the gastric lumen or in response to antral distension. Gastrin stimulates the oxyntic mucosa, which may lead to hyperplasia of enterochromaffin-like cells, resulting in enterochromaffin-like carcinoid tumors in aged rats and, rarely, in patients with chronic atrophic gastritis or gastrinomas. In addition to hypergastrinemia, other factors appear to be required for the progression of enterochromaffin-like hyperplasia to carcinoids; genetic factors may be involved. Gastrin elevations due to antisecretory drug therapy are indirectly proportional to the degree of acid inhibition and are reversible upon cessation of therapy. The gastrin levels during omeprazole therapy are similar to those caused by gastric vagotomy. Available evidence does not support a relationship between hypergastrinemia and the occurrence or growth of gastric carcinoma or colonic tumors.
Achlorhydria↗
Role of luminal ammonia in the development of gastropathy and hypergastrinemia in the rat.
BACKGROUND/AIMS: Chronic infection with Helicobacter pylori causes persistent elevations in gastric juice ammonia levels. Thus, we studied the effects of experimentally induced increases in gastric juice ammonia levels on gastric structure and function and gastrin homeostasis. METHODS: Rats were fed either normal chow or the diet supplemented (20 g/dL) with ammonium or sodium acetate. RESULTS: Long-term dietary ammonium loading for 2 weeks or longer resulted in a 1.5-2-fold increase in the weight and mucosal thickness of the stomach and proximal duodenum with evidence of mild gastritis and enterochromaffinlike cell hyperplasia. The ammonium-containing diet also induced a significant 2-3-fold increase in both circulating gastrin levels of fed rats and an increase in the postprandial gastrin responses over control values. Antral gastrin levels were also markedly elevated by long-term ingestion of the test diet, which was increased 3-4-fold over control values in fasted animals and less so after meal stimulation. Consistent with these findings, gastrin-specific messenger RNA was increased 2.5-3-fold in the antrum of ammonium fed rats, whereas actin-specific messenger RNA was not affected or decreased. Animals fed a diet supplemented with 20 g/dL sodium acetate sustained modest increases in mucosal thickness and serum and antral gastrin concentration, suggesting that nonspecific gastric injury and inflammation is also a factor that influences G-cell function. CONCLUSIONS: Long-term exposure of the antral mucosa to elevated levels of ammonia in the gastric juice in the presence of gastritis, conditions similar to that occurring in subjects infected with H. pylori, seem to be causative factors in the development of G-cell hyperfunction.
Acetates↗
Measurement of anterior and posterior circulation flow contributions to cerebral blood flow. An ultrasound-derived volumetric flow analysis.
Ultrasound-derived volumetric flow analysis may be useful in answering questions of basic physiological interest in the cerebrovascular circulation. Using this technique, the authors have sought to describe quantitatively the complete concurrent flow relations among all four arteries supplying the brain. The aim of this study of normal subjects was to determine the relative flow contributions of the anterior (internal carotid arteries) and posterior (vertebral arteries) cerebral circulation. Comparisons between the observed and theoretically expected anterior and posterior flow distribution would provide an opportunity to assess traditional rheological conceptions in vivo. Pulsed color Doppler ultrasonography was used to measure mean flow rates in the internal carotid and vertebral arteries in 21 normal adults. The anterior circulation (internal carotid arteries bilaterally) carried 82% of the brain's blood supply and comprised 67% of the total vascular cross-sectional area. These values demonstrate precise concordance between observations in vivo and the theoretically derived (Hagen-Poiseuille) expected flow distribution. These cerebrovascular findings support the traditional conception of macroscopic blood flow. Further studies using ultrasound-derived volumetric analysis of the brain's arterial flow relations may illuminate the vascular pathophysiology underlying aging, cerebral ischemia, and dementias.
Adult↗
Regulation of glucose-dependent insulinotropic peptide gene expression by a glucose meal.
Glucose-dependent insulinotropic peptide (GIP) enhances insulin secretion by pancreatic beta-islet cells. Its release has been demonstrated predominantly after the ingestion of carbohydrate and fat. We have recently cloned a rat intestinal GIP cDNA and in the present studies have used this cDNA as a probe for measuring rat duodenal GIP mRNA after nutrient administration. Rats were fasted overnight, after which they were permitted to drink water or 10% glucose. The duodenum was then removed, GIP mRNA was measured by Northern hybridization analysis, and duodenal mucosa and serum GIP levels were determined by radioimmunoassay. In response to oral 10% glucose, duodenal mucosal GIP mRNA concentrations increased from 2 to 4 h, and at the end of 4 h a threefold increase was detected. Serum and mucosal GIP concentrations increased earlier, starting at 60 min, and levels remained elevated at 4 h. In separate studies, nuclear run-on assays were performed to compare the effects of glucose and water ingestion on transcription of the GIP gene. Whereas no increase in GIP gene transcription was detected in rats ingesting water, the rate of transcription doubled in glucose-fed rats. Actin gene transcription was nearly identical in both groups, indicating genomic specificity. The results of these studies indicate that duodenal GIP gene expression is stimulated at both the pre- and posttranslational levels by glucose-containing meals. These studies further suggest that the release of GIP from cellular storage granules might account for the initial increase in serum GIP levels after oral glucose ingestion.
Animals↗
The effect of recombinant cytokines on [14C]-aminopyrine accumulation by isolated canine parietal cells.
Interleukin-1 (IL-1) and tumor necrosis factor-alpha (TNF-alpha) have been shown to inhibit basal and pentagastrin-stimulated gastric secretion in rats and histamine-stimulated secretion in dogs. IL-1 also reduces the severity of ethanol and stress-induced gastroduodenal damage. The aim of this study was to examine the effects of human recombinant IL-1 alpha and TNF-alpha on enzymatically dispersed and enriched (> 90%) parietal cells stimulated with histamine, histamine plus 3-isobutyl-1-methylxanthine (IMX) or carbachol (all 10(-5) M). Acid secretion was assessed indirectly by quantitating [14C]-aminopyrine (AP) accumulation. IL-1 alpha (500 and 1000 ng/ml) inhibited histamine-stimulated AP uptake by 53% and 60% respectively, and it inhibited IL-1 alpha (1500 ng/ml) by 69%. IL-1 alpha (500 and 1000 ng/ml) inhibited histamine plus IMX-stimulated AP uptake by 36% and 34%, respectively. IL-1 alpha (500 ng/ml) also inhibited carbachol-stimulated AP accumulation. TNF-alpha (100 and 250 ng/ml) inhibited histamine-stimulated AP accumulation by 38% and 36%, respectively. TNF-alpha also significantly inhibited histamine/IMX- and carbachol-stimulated AP uptake (P < or = .01). Indomethacin did not affect IL-1 alpha-induced inhibition. These results show that IL-1 alpha and TNF-alpha inhibit histamine- and carbachol-stimulated isolated parietal cell secretion and that, for IL-1 alpha, this effect does not depend on mucosal prostaglandin synthesis.
1-Methyl-3-isobutylxanthine↗