Secretory changes associated with chemically-induced duodenal ulceration: simultaneous measurements of acid, pepsin, base and pancreatic enzymes in rats with chronic gastric fistula

A Review on the Antimutagenic and Anticancer Effects of Cysteamine

Cancer is one of the leading causes of death worldwide. First-line treatments usually include surgery, radiotherapy, and/or systemic therapy. These methods can be associated with serious adverse events and can be toxic to healthy cells. Despite the new advances in cancer therapies, there is still a continuous need for safe and effective therapeutic agents. Cysteamine is an aminothiol endogenously synthetized by human cells during the degradation of coenzyme-A. It has been safely used in humans for the treatment of several pathologies including cystinosis and neurodegenerative diseases. Cysteamine has been shown to be a potent antimutagenic, anticarcinogenic, and antimelanoma in various in vitro and in vivo studies, but a review on these aspects of cysteamine's use in medicine is lacking in the current literature. The efficacy of cysteamine has been shown in vitro and in vivo for the treatment of different types of cancer, such as gastrointestinal cancer, pancreatic cancer, sarcomas, hepatocellular carcinoma, and melanoma, leading to the significant reduction of lesions and/or the increase of survival time. Although the mechanisms of action are not fully understood, possible explanations are (i) free radical scavenging, (ii) alteration of the tumor cell proliferation by affecting nucleic acid and protein synthesis or inhibition of DNA synthesis, and (iii) hormone regulation. In conclusion, regarding the high safety profile of cysteamine and the current literature data presented in this article, cysteamine might be considered as an interesting molecule for the prevention and the treatment of cancer. Further clinical studies should be performed to support these data in humans.

Detection of duodenal ulcer-associated genes in rats

We assessed the expression of about 8,000 known or unknown genes in the preulcerogenic stages of cysteamine-induced duodenal ulceration in rats, in comparison with the toxic but nonulcerogen ethanolamine. The most prominent gene changes were confirmed by custom gene blots, reverse transcriptase polymerase chain reaction (RT-PCR), real-time PCR, radio-immunoassay, Western blot, or enzyme-linked immunosorbent assay (ELISA), and the levels of their expression in other gastrointestinal organs such as ileum and colon were identified by real-time PCR. The time-course study after cysteamine showed 40 genes with marked changes, belonging to cell surface antigens, transcription factors, DNA binding proteins, ion channels, transport proteins, cellular receptors, and expressed sequence tags (i.e., unknown genes). In comparison with ethanolamine, these 40 genes changed by cysteamine only may represent ulcer-associated genes, such as endothelin receptor B, endothelin 1, caspase 3, transcription factors egr-1, Sp1, the angiogenic growth factors vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF), and especially egr-1 and endothelin receptor B (ETRB) showed no changes in ileum and colon.

CONCLUSIONS

(1) These data suggest that duodenal ulcerogenesis may require the interaction of several genes leading to endothelial and epithelial cell injury, mucosal erosion, and ulcer; (2) these new findings may offer a new approach to the identification of potential ulcerogenic genes and provide new insights into the molecular mechanisms of duodenal ulceration.

Effects of a new sigma ligand, JO 1784, on cysteamine ulcers and duodenal alkaline secretion in rats

BACKGROUND

The ulceroprotective effects of JO 1784 [(+)-N-cyclopropyl-methyl-N-methyl-1,4-diphenyl-1-ethyl-but-3-en-1-yl amine, hydrochloride], a new specific and highly selective sigma ligand, were examined in rats.

METHODS

Different models of gastric ulcers (4-hour restraint stress, aspirin, ethanol, and taurocholate) and cysteamine-induced duodenal ulcers were used. The gastric acid secretion (4-hour Shay rat preparation) and the duodenal bicarbonate secretion were also studied.

RESULTS

JO 1784 elicited a potent protection against duodenal ulcers but had a weaker protective effect on any of the gastric ulceration models tested. It displayed no gastric antisecretory activity but induced a dose-dependent stimulation of duodenal bicarbonate secretion. Haloperidol, hexamethonium, tetrodotoxin, bivagotomy (but not atropine), and the intravenous but not intracerebroventricular administration of devazepide, a cholecystokinin A antagonist, inhibited the stimulatory effect of JO 1784.

CONCLUSION

These results show that JO 1784, a selective sigma ligand, is a potent protector of the duodenal mucosa. This activity may be related to its stimulating effect on bicarbonate secretion, which is driven through a complex nervous mechanism involving muscarinic synapses, vagal afferent fibers, and peripheral cholecystokinin receptors. This drug might open a new specific way in the treatment of duodenal ulcers.

Effect of duodenal ulcerogens cysteamine, mepirizole, and MPTP on duodenal myoelectric activity in rats

Increased gastric acid secretion, enhanced acid delivery to the duodenum, and reduced alkaline secretion in the proximal duodenum are relatively well-established pathophysiologic abnormalities in duodenal ulcer. Impaired duodenal motility, however, may also contribute to duodenal ulceration by altering the distribution of acid and alkaline secretions along the upper digestive tract. We tested the hypothesis that the duodenal ulcerogens cysteamine, MPTP, and mepirizole modify duodenal motility in the rat and that motility changes might be a common and early alteration in experimental duodenal ulceration. All three duodenal ulcerogens rapidly produced extensive changes in duodenal myoelectric activity and reduced the frequency of myoelectric slow waves. Cysteamine induced marked hypermotility for at least 6 hr; MPTP rapidly decreased motility and fragmented the myoelectric migrating pattern. Mepirizole induced biphasic changes: an early hypermotility phase of about 30 min was followed by profound hypomotility. These results indicate that marked alterations of duodenal motility are common during experimental duodenal ulceration. In light of the differential effect of the ulcerogens on duodenal motility, it remains to be determined how these changes influence acid neutralization in the proximal duodenum. Nevertheless, our results suggest that all three duodenal ulcerogens, which are different in structure, alter duodenal motility.

Cysteamine-induced reduction in gastrointestinal somatostatin: evidence for a region-specific loss in immunoreactivity

Administration of cysteamine (beta-mercaptoethylamine; 2-aminoethanethiol) to rats has been shown to decrease the levels of somatostatin-like immunoreactivity (SLI) in the gastrointestinal tract and pancreas but its mode of action is unclear. In the current study the effect of cysteamine on gastrointestinal and pancreatic SLI has been studied using two antisera with different regional specificities. In addition, the in vitro effect of cysteamine on SS-14 and SS-28 has been studied by high-performance liquid chromatography (HPLC). Characterization of the two antisera (AS 26.3.2 and AS 1001) with a range of analogs of SS-14 revealed that both were directed against the midportion of the molecule but that AS 1001 was also sensitive to changes at the N- and C-termini. Tissue extracts from cysteamine-treated rats measured with AS 26.3.2 showed no significant change for the stomach, jejunum or pancreas but duodenal levels were reduced. With AS 1001 SLI levels were reduced in all tissues. Gel permeation chromatography of stomach extracts measured with AS 1001 showed a reduction in both SS-14 and SS-28. With AS 26.3.2 an increase in SLI eluting prior to the SS-14 peak occurred explaining why no significant reduction in total SLI was detected. With duodenal extracts the elution profiles with AS 1001 reflected the large reduction in total SLI whereas with AS 26.3.2 a smaller reduction occurred. Both SS-14 and SS-28 were reduced. HPLC analysis of SS-14 and SS-28 following incubation with cysteamine in vitro showed a time-dependent decrease in both somatostatin species with absorbance at 280 nm was measured. New peptide peaks which developed were not all detectable by radioimmunoassay with either antibody. The results suggest that cysteamine causes a change in the structure of somatostatin which probably first involves a reduction of the disulphide bridge and then the N- and C-terminal regions of the molecule thus making it unmeasurable by antisera sensitive to changes in these regions.

Role of prostanoids in experimental duodenal ulcer in rat

The purposes of this study were to determine whether inhibition of cyclooxygenase is a mechanism by which cysteamine and mepirizole produce duodenal ulcers, identify qualitative or quantitative differences in prostanoid production between gastric mucosa and duodenum, and determine whether differences in cyclooxygenase sensitivity to inhibition by aspirin exist between these two tissues. In fed female rats, gastric mucosal prostaglandin E2 (PGE2) and prostacyclin (PGI2) generation was 235 +/- 25 and 832 +/- 40 ng/g/min, respectively, whereas full-thickness duodenal PGE2 and PGI2 generation was 665 +/- 46 and 662 +/- 49 ng/g/min, respectively. Over an intraperitoneal dose range of 0-25 mg/kg, aspirin-induced cyclooxygenase inhibition was dose-dependent and similar for the two tissues. Duodenal ulceration (16.7 mm2) produced by cysteamine, 425 mg/kg, was associated with a 46% reduction in duodenal PGE2 generation, while having no effect on PGI2 generation; however, cysteamine, 213 mg/kg, produced no visible duodenal mucosa injury yet reduced duodenal PGE2 generation 39% compared to control values. In fed male rats, gastric mucosal PGE2 and PGI2 generation was 179 +/- 18 and 813 +/- 61 ng/g/min, respectively, whereas duodenal PGE2 and PGI2 generation was 321 +/- 27 and 454 +/- 38 ng/g/min, respectively. Duodenal ulceration (7.7 +/- 2.3 mm2) produced by oral mepirizole was associated with a 63% reduction in duodenal PGE2 generation compared to control values, while having no effect on PGI2 generation. Subcutaneous aspirin, 100 mg/kg, which reduced duodenal PGE2 generation to a greater degree than either ulcerogen, given in conjunction with pentagastrin, did not produce visible duodenal ulceration.(ABSTRACT TRUNCATED AT 250 WORDS)

Gastric mucosal protection by new aryl sulfhydryl drugs

Alkyl sulfhydryl drugs protect against acute gastric hemorrhagic mucosal lesions. We tested the protective effect of cyclic drugs containing oxidized (KT1-32, KT1-39, KT1-94), or reduced (KT1-66, KT1-109, KT1-293, KT1-720, KT1-756) sulfhydryls. The most potent protective agents (KT1-32, KT1-109, KT1-720, KT1-756) were investigated in detail. Drugs were administered intragastrically to fasted rats 30 min before 100% ethanol (1 ml) or acidified aspirin (10 mg/100 g), and mucosal lesions were measured planimetrically 1 hr later. Control rats receiving only ethanol had lesions involving 14.5% of the glandular mucosa. KT1-32, KT1-109, KT1-720, or KT1-756 (10 mg/100 g) reduced lesions to 0.7, 2.7, 1.8, or 0.7% of glandular stomach respectively. Aspirin-induced lesions involved 1.52% of the glandular mucosa and 10 mg/100 g of KT1-32, KT1-109, or KT1-720, or 2 mg/100 g of KT1-756 diminished the damage to 0.13, 0.02, or 0.04, or 0.00%, respectively. Indomethacin interfered with protection against ethanol by KT1-109, while the sulfhydryl alkylator N-ethylmaleimide abolished protection by both KT1-32 and KT1-109. Among the drugs investigated in detail, KT1-756 increased gastric acid output, while KT1-720 and KT1-756 significantly enhanced pepsin secretion. All four compounds studied in detail (ie, KT1-32, KT1-109, KT1-720, KT1-756) decreased the extent of vascular lesions in the gastric mucosa as revealed by monastral blue 1 min after ethanol. Thus, the mechanism of gastric mucosal protection by these novel aryl sulfhydryl compounds cannot be ascribed to an antisecretory effect, but may be related to prevention of vascular injury.

From cysteamine to MPTP: structure-activity studies with duodenal ulcerogens

Cysteamine is the first chemical identified that induces acute and chronic duodenal ulcers in rodents. Structure-activity studies with cysteamine, propionitrile and their derivatives, as well as with analogues of toluene, revealed numerous alkyl and aryl duodenal ulcerogens. Among these, one of the most interesting from an etiologic and pathogenetic point of view is the dopaminergic neurotoxin MPTP, which shows structural similarities with toluene. The chemically-induced duodenal ulcers are similar and localized on the anterior and posterior wall of the duodenal bulb. Both cysteamine and MPTP affect endogenous dopamine; MPTP is especially potent in depleting central dopamine and inducing lesions in the substantia nigra. MPTP given in high doses induces Parkinson's disease-like syndrome and gastric ulcers. Cysteamine and propionitrile also cause dyskinesia in large and multiple doses. The motility disorders and duodenal ulcers are abolished by dopamine agonists. Cysteamine and MPTP have been known to increase and decrease gastric acid secretion, respectively. However, both compounds induced duodenal dysmotility, decreased bicarbonate production, and reduced its delivery from distal to proximal duodenum. These factors decrease acid neutralization in the duodenal bulb and contribute to duodenal ulceration. Thus, studies with animal models may reveal endogenous mediators and specific receptors which might be involved in the pathogenesis of duodenal ulceration. Specific structure-activity studies in toxicology may lead to new insights in the pathogenesis and pharmacology of a poorly understood human disorder such as duodenal ulceration.

The effect of muscarinic and beta-adrenergic blockade on cysteamine-induced gastrin secretion by the isolated perfused rat stomach

Cysteamine-induced duodenal ulceration in rats is accompanied by increased circulating gastrin. Although cysteamine appears to exert a direct action on the gastrin cell some groups have provided evidence for an involvement of the autonomic nervous system. The current experiments were performed to determine whether beta-adrenergic or cholinergic (muscarinic) pathways are involved in the acute effect of cysteamine on gastrin secretion in the isolated perfused rat stomach. Cysteamine (1 mM) increased gastrin (IRG) secretion to a maximum ranging between 100% and 192% above basal. A cysteamine concentration of 5mM resulted in peak levels ranging between 150% and 1050% above basal. Addition of atropine or propranalol did not influence the responses obtained. The present results, therefore, do not support a role for either cholinergic or beta-adrenergic pathways in cysteamine-induced gastrin release at the level of the stomach and suggest that in vivo such autonomic effects are mediated extrinsically.

Effect of lapachol, a naphthaquinone isolated from Tectona grandis, on experimental peptic ulcer and gastric secretion

Lapachol, a naphthaquinone isolated from the roots of Tectona grandis given at a dose of 5 mg kg-1 p.o. twice daily for 3 days was found to have an anti-ulcerogenic effect on subsequently induced experimental gastric and duodenal ulcers in rats and guinea-pigs. Its action appears to be associated with an effect on the protein content of gastric juice, and it reversed aspirin-induced changes in peptic activity, protein and sialic acid.

Development and significance of cysteamine and propionitrile models of duodenal ulcer

Cysteamine is widely used in rodents to induce duodenal ulcer. Herein, the pathogenesis of duodenal ulceration in its earliest stages was reviewed using findings from cysteamine- and propionitrile-induced duodenal ulcer in rodent models, especially taking into account changes in the secretion of gastric acid, duodenal and pancreatic bicarbonate as well as gastroduodenal motility. The effect of cysteamine-HCl in inducing ulcers in rats is circadian rhythm-dependent. The effect is greatest from just before the end of diurnal rest to just after the start of nocturnal activity. The chronobiologic effect may be in part due to the circadian rhythm-dependent increased gastric acid production from cysteamine. Titratable acidity was found to be twice as great in the gastric juice of rodents when cysteamine was given by injection at 2000 (just after the start of nocturnal activity) in comparison to when given at 0800 or 1200 (at the beginning or middle span of daily rest). Further studies have shown that adrenalectomy of rats 7 days before cysteamine administration obliterated the observed circadian susceptibility to ulcer formation. Duodenal ulceration, at least in the cysteamine model, appears to be under chronobiologic neuroendocrine control or influence, seemingly mediated by the adrenal glands.

Mechanisms of mucosal injury in the stomach and duodenum: time-sequence analysis of morphologic, functional, biochemical and histochemical studies

This review is based on results from our laboratory and those published by others, and is focused on the early stages of pathogenesis that can be studied mostly in animals. Gastric mucosal injury is analysed on the examples of ethanol- and aspirin-induced lesions. Ethanol (50-100%) rapidly penetrates the mucosa, causes directly and/or indirectly (e.g., release of vasoactive products) endothelial damage in superficial and deep capillaries and venules. The vascular damage results in increased vascular permeability and decrease in blood flow leading to complete circulatory standstill in superficial capillaries 1-2 min after intragastric administration of concentrated ethanol. The direct chemical damage to surface mucosal epithelium is then followed by hypoxia and deep hemorrhagic necrosis in 1-5 min (erosion or ulcer). Unionized aspirin initiates a similar and complex yet slower progressing and less extensive erosion than alcohol. Duodenal erosion and ulcer produced by cysteamine, mepirizole or MPTP are preceded by excess acid in the proximal duodenum. This could be due to increased gastric acid output (1-4 hr), decreased bicarbonate secretion or duodenal dysmotility (0.5-8 hr) preventing the proper mix of acid and base in duodenal bulb. Necrosis and desquamation of absorptive cells in duodenal villi are evident 2-4 hr, followed by villus amputation (4-8 hr), erosion and ulcer (8-24 hr). The pathogenesis of gastroduodenal mucosal injury can thus be reconstructed from results obtained with animal models and from human studies. The results should serve as a basis to design protective drugs that are active on the basis of pathogenetic events.

Effects of indomethacin on the duodenal mucosa of rats: comparative study with cysteamine

Effects of indomethacin and cysteamine on the duodenal mucosa of rats were studied microscopically (using scanning electron microscopy) and also functionally. Indomethacin (5 mg/kg, s.c.) induced no microscopic damage to the duodenal epithelium for up to 6 hr after administration. Indomethacin had no effects on gastric H+ output and the amount of H+ in the duodenum, but did reduce the duodenal HCO3- secretion (both basal and 10 mM-HCl stimulated). PGE2 contents in the duodenal mucosa were markedly reduced by indomethacin for 6 hr. These results suggest that reductions of duodenal HCO3- secretion and endogenous prostaglandins per se do not impair the H+ disposal system of the duodenum and so do not damage the epithelial cells. In contrast, cysteamine (100 mg/kg, s.c.) produced microscopic damage to the duodenal epithelium as early as 2 hr later. Cysteamine significantly increased gastric H+ output and reduced duodenal HCO3- secretion, resulting in an increased amount of H+ in the duodenum 3 hr later. Cysteamine had no effect on PGE2 contents in the duodenum. The time lag between damage formation and functional changes suggests that the earliest damage caused by cysteamine occurs by mechanisms other than erosive action of H+ emptied by the stomach. The increased amount of H+ may contribute to an enhancement of the initial damage.

Protection by metals against ethanol-induced gastric mucosal injury in the rat. Comparative biochemical and pharmacologic studies implicate protein sulfhydryls

Recent evidence suggests a role of endogenous sulfhydryls (SHs) in gastric "cytoprotection." Because divalent metals bind to or oxidize SH groups, their effect on ethanol-induced gastric erosions was studied. For comparative biochemical studies the SH cysteamine, the glutathione depletor diethylmaleate. and SH alkylating agent N-ethylmaleimide (NEM) were also used. Rats pretreated with CdCl2, ZnCl2, or Cu(NO3)2 6 h before absolute ethanol showed a significant dose-dependent decrease in the mucosal lesions. Copper was effective in preventing the lesions up to 15 min before the ethanol. Iron and manganese were active at 30 min, but not at 6 h before the ethanol lesions. Indomethacin administration decreased the protection afforded by iron, manganese, and cadmium, but did not modify that by lead and copper. N-ethylmaleimide abolished the protection by iron, manganese, and cadmium, but did not affect the protection caused by lead and copper when given after the metals. However, when NEM was given before lead and copper, it diminished the protection. Secretory studies revealed that cadmium and zinc slightly inhibited gastric acid secretion, but a similar reduction of acid output by cimetidine did not decrease the ethanol-induced gastric erosions. Biochemical studies of endogenous SH showed that the protective metals and NEM decreased the glutathione concentration in the nonprotein fraction, whereas these metals diminished and NEM, which antagonizes mucosal protection, elevated the cysteine concentration in the protein fraction of the gastric mucosa. The common factor with the protective agents thus seems to be the blocking of protein SH by binding or oxidation by protective agents. These endogenous SHs may mediate cellular responses to injury.

Modulation of somatostatin binding sites in cytosol of rabbit gastric fundic mucosa by cysteamine administration

Cysteamine, when given in vivo to rabbits, depleted immunoreactive somatostatin in rabbit gastric fundic mucosa. Depletion of immunoreactive somatostatin was associated with both an increase in the number and a decrease in the affinity of the low-affinity somatostatin binding sites. The in vitro incubation of cysteamine (0.1 mM) with the cytosolic fraction did not result in any modification of somatostatin binding. These results suggest that a decrease in the endogenous immunoreactive somatostatin might lead to up-regulation of somatostatin binding sites in the gastric fundic mucosa.

Duodenal ulcerogens cysteamine and propionitrile induce gastroduodenal motility alterations in the rat

The effects of the duodenal ulcerogens cysteamine and propionitrile on gastroduodenal myoelectric activity and intraluminal pressure in the fasted rat as well as on contractility of isolated gut muscle strips were investigated. Duodenal ulcerogens, unlike the nonulcerogen but toxic analogue ethanolamine, caused an early disruption of the myoelectric migrating complex, a marked increase in the spiking activity, and a decrease in the frequency of the slow waves in the duodenum. Both the increased spiking activity and the decreased slow wave frequency were dose dependent for cysteamine. Manometrically recorded contractions at the stomach corpus, midantrum, and antropyloric region as well as in the proximal duodenum of the conscious rat showed decreased contractions at the corpus and midantrum and an increase at the pyloric and duodenal sites during an intravenous infusion of cysteamine. In vitro studies demonstrated that circularly or longitudinally cut muscle strips taken from different regions of the stomach and duodenum responded to cysteamine with increased contractility. In summary, the duodenal ulcerogens cysteamine and propionitrile rapidly induce motor abnormalities in the stomach and duodenum of the rat. In vitro studies suggest that a cholinergic mechanism may be involved. It is possible that motor changes play a role in the pathogenesis of the experimentally induced duodenal ulcers.