RESUMEN

AIMS: To investigate the expression of pepsinogen A3 (Pg3) encoding genes in the gastric mucosa of normal controls and subjects with atrophic gastritis and gastric cancer. METHODS: One hundred and fifty nine patients underwent upper gastrointestinal endoscopy with sampling of gastric biopsy specimens and serum. Pg3 isoproteins were determined by electrophoresis in serum and gastric mucosal biopsy specimens. Pg3 encoding genes were assessed by PCR in DNA obtained from peripheral blood. RESULTS: One hundred and one subjects (82 normal histology/chronic gastritis, 17 atrophic gastritis, two gastric cancer) showed a pepsinogen phenotype with presence of Pg3 and a corresponding pepsinogen genotype with presence of Pg3 encoding genes. Fifty eight subjects showed a phenotype lacking Pg3. In 39 of them (23 normal histology/chronic gastritis, 11 atrophic gastritis, five gastric cancer), a corresponding genotype without Pg3 encoding genes was found. However, in the remaining 19 subjects (4 normal histology/chronic gastritis, nine atrophic gastritis, six gastric cancer); Pg3 encoding genes were demonstrable in the absence of Pg3 production. CONCLUSIONS: Unexpressed Pg3 encoding genes can be shown in many cases of atrophic gastritis and gastric cancer, but rarely in healthy controls and subjects with superficial gastritis. The correlation of atrophic gastritis and gastric cancer with a pepsinogen phenotype lacking Pg3 can be explained by loss of expression of Pg3 encoding genes throughout the complete gastric mucosa. The mechanism of such loss and the importance as a marker for premalignant degeneration have to be elucidated.

Asunto(s)

Asunto(s)

RESUMEN

Interactions between viscum album (Iscador) and DNA were studies by amplification of specific human pepsinogen A gene promoter sequences by polymerase chain reaction (PCR). Gel retardation assays showed no binding of Viscum album to these promoter sequences. Incubation of plasmid constructs consisting of human pepsigen A promoter fragments coupled to thechloramphenicol acetyl-transferase (CAT) reporter gene with Iscador had no effect on transcriptional activity. Promoter sequences incubated with Iscador became insensitive to methylation by specific DNA methyltransferases by destruction of DNA methyltransferase activity

Asunto(s)

RESUMEN

The molecular mechanisms underlying the regulation of pepsinogen A (PGA) gene expression in mammalian cells are poorly understood. In this paper we describe the structural and functional analysis of the pepsinogen A gene promoter in the pig. By genomic Southern analyses we demonstrate that, in contrast with human PGA genes which are amplified and organized in haplotypes, only a single PGA gene is present per haploid porcine genome. With the aim of identifying promoter elements mediating the gastric mucosa cell-specific transcription of the PGA gene in pig, we isolated a PGA gene from a porcine genomic library. The nucleotide sequence of the first exon and 1.7 kb of the upstream DNA region were determined and compared with the corresponding regions of the human PGA gene encoding isozymogen Pg5. In order to study the promoter activity of the PGA gene a functional assay was developed: we succeeded in obtaining primary monolayer cultures of porcine gastric mucosal chief cells, suitable for transfection. Fragments of 5'-flanking and noncoding first exon sequences of the porcine and human PGA genes were linked to the chloramphenicol acetyltransferase (CAT) gene. The transcriptional activity of these hybrid genes was assessed in transient expression assays upon transfection (lipofection) of gastric and nongastric cells. Whereas PGA 5'-flanking sequences showed no promoter activity in nongastric cell types, the DNA region from -205 to +21 was found to be sufficient to direct expression of the porcine PGA constructs in a cell-specific manner. Further deletion analysis of the proximal promoter fragment identified several regions (-205 to -167, -127 to -67 and +2 to +21) acting synergistically in the transcriptional regulation of the PGA gene. In contrast, all human PGA-CAT constructs used failed to show promoter activity in porcine gastric chief cells, indicating species-specific control of PGA gene expression. In addition, the transcriptional activity of the porcine PGA promoter in chief cells from pig was completely abolished by in vitro CpG methylation. Footprint analyses of the proximal promoter fragment using nuclear extracts from either porcine gastric mucosal chief cells or liver revealed some notable differences between both extracts, which might reflect the interaction with (a) cell-specific factor(s).

Asunto(s)

RESUMEN

The protective effect of extracts of mistletoe Viscum album (Iscador) with reference to carcinogenesis was tested on in vitro cultured porcine gastric chief cells. Putative protection against in vitro methylation of lambda DNA by N-methyl-N-nitro-N-nitrosoguanidine (MNNG) was studied with restriction endonucleases. Preparations of Iscador from mistletoe grown on oak as host tree had a high cytotoxic effect on gastric chief cells, with an LC50 after 24hrs that ranged between 0.01 and 0.03 mg/ml. At 0.01 mg/ml, Iscador was also found to protect lambda DNA from methylation or destruction by MNNG. During the course of this study a high variability was found both in cytotoxicity and protection rate against methylation which we attribute to batch to batch differences. Thus the LC50 for Iscador MH86L12 was 0.005 mg/ml, while for MH87 D24 it was 0.05 mg/ml after 24hrs. The Iscador batch W frf 50 mg/ml, which was made from a fresh plant extract at the Hiscia Institute, showed less variability. Results are therefore given for this batch of Iscador only

Asunto(s)

RESUMEN

The heterogeneous group of proteinases known as pepsinogens are synthesized, stored, and upon appropriate stimulation released from gastric mucosal chief cells. Under the acidic conditions of the lumen of the stomach, the proenzymes, pepsinogens, are converted to "pepsin", which plays an important physiologic role as a digestive enzyme. The potential roles for pepsin in upper gastrointestinal diseases such as gastric or duodenal ulcer and gastroesophageal reflux disease along with the recent development of in vitro gastric gland and isolated chief cell preparations have renewed interest in the study of the control of pepsinogen synthesis and secretion. In this article the authors briefly summarize current knowledge of the biology of pepsinogens and emphasize more recent findings concerning the control of the chief cell, which is related to the synthesis and secretion of pepsinogens in vitro.

Asunto(s)

RESUMEN

We have studied the effect of tripotassium dicitrato bismuthate on the peptic activity of gastric juice, both basal and pentagastrin-stimulated, from five healthy volunteers using porcine pepsin solution as a control. Tripotassium dicitrato bismuthate showed no inhibition of the proteolytic activity of either the pure porcine or the human pepsin in the gastric juice. The ulcer healing efficacy of tripotassium dicitrato bismuthate is unlikely to be related to a gastric anti-protease effect.

Asunto(s)

RESUMEN

The actions of hydrochloric acid, natural PGE1, PGE2 and a synthetic commercial PGE1 preparation, Enisoprost (Searle) on pepsinogen synthesis and secretion were studied in canine chief cell monolayer cultures. Hydrochloric acid, applied directly to the apical surface of chief cells using culture plate inserts (Millipore) had no effect on secretion, nor did it affect the action of any secretagogue in the basolateral medium. All prostaglandins tested showed significant stimulation of pepsinogen secretion. Basal secretion of pepsinogen after 90 min was 9.4 (1.3)% to total initial monolayer content. At 10(-6) M, PGE1 stimulated secretion was 26.1 (3.8)%; PGE2 27.9 (4)% and Enisoprost 28.8 (4.2)% of initial pepsinogen content. Stimulations by all tested prostaglandins were additive with carbachol (10(-4) M) and CCK (10(-9) M), but not with VIP (10(-6) M), dbcAMP (10(-3) M) or forskolin (10(-6) M) responses. All three prostaglandins stimulated pepsinogen synthesis as measured by 14C labelled amino acid incorporation into pepsinogen. Time course experiments were similar to those for forskolin and showed shorter time delays between stimulus and increased synthesis rate than carbachol but longer than dbcAMP. Stimulated pepsinogen secretion was inhibited by high pepsin concentrations (greater than 800 micrograms/ml) in the medium. The inhibited abolished simultaneous carbachol induced stimulation of synthesis but prostaglandin or forskolin stimulation only after two hours. Combined with the shorter response time, as compared with carbachol, these data support our previous findings that potent stimulators of cAMP production can stimulate pepsinogen synthesis directly by stimulation of mRNA synthesis, independently from an increased secretion. The additivity of effects with carbachol or CCK and similarity with forskolin stimulated synthesis supports the suggestion that the actions of prostaglandins are mediated by cAMP.

Asunto(s)

RESUMEN

We have studied pepsinogen synthesis and secretion in primary monolayer cultures of canine gastric chief cells. Monolayers were formed after approximately 48 hr. Pepsinogen synthesis was studied by adding 14C-labeled amino acids to the culture medium. Basal secretion of de novo synthesized pepsinogen after 4 hr was 4 +/- 1.2% of total newly synthesized pepsinogen. Basal secretion of stored pepsinogen after 90 min was 8 +/- 1.4% of total pepsinogen content. Carbachol, dbcAMP, forskolin, VIP, CCK-8, and the phorbol ester 12-O-tetradecanoyl-phorbol-13-acetate all stimulated secretion of de novo synthesized pepsinogen and preformed pepsinogen. Only additive interactions were found. dbcAMP caused a peak outburst of stored pepsinogen in the first 10 min. Carbachol stimulation was time dependent. Stimulation of de novo synthesized pepsinogen secretion was time dependent for both carbachol and dbcAMP. dbcAMP caused an immediate 10-fold increase in pepsinogen synthesis, but carbachol did so only after a lag time of 30 min. This was identical to the time necessary for the appearance of labeled pepsinogen in the medium. Addition of atropine after 2 hr resulted in a return to basal synthesis. Stimulated pepsinogen synthesis was always observed concomitant with stimulated pepsinogen secretion. These results show that most external stimuli for pepsinogen synthesis are dependent upon prior depletion of pepsinogen stores, which then triggers synthesis, while stimulation of cAMP production stimulates pepsinogen synthesis more directly.

Asunto(s)

RESUMEN

Gastrotropin (GT), a protein previously isolated from porcine ileal mucosa, with a molecular mass of 14,054 daltons, was extracted from canine ileum and purified to homogeneity. The canine and porcine peptides had similar relative molecular mass, charge, hydrophobicity, and amino acid compositions. Direct Edman degradation yielded no free amino acids, indicating a blocked NH2-terminus, and a partial sequence determination of the CNBr fragments demonstrated a high degree of homology with porcine GT. Previous studies have indicated that GT is a potent enterooxyntin, and to further characterize these observations we have investigated the actions of both porcine and canine GT on isolated enriched preparations of guinea pig and dog parietal and chief cells. The results of these studies demonstrate that GT is present in more than one species and that the cellular response to porcine and canine GT is identical. The efficacies of canine and porcine GT preparations in stimulating pepsinogen secretion and [14C]aminopyrine uptake were identical and equal to those of cholecystokinin octapeptide (CCK8) and pentagastrin. GT was 100-fold more potent than either of these two major secretagogues. Maximal [14C]aminopyrine accumulation was observed with 10(-8) M GT, with an ED50 of 2 x 10(-9) M compared to pentagastrin, which caused maximal accumulation at 10(-6) M and had an ED50 of 5 x 10(-8) M. Maximal pepsinogen secretion was observed with 10(-7) M GT, with an ED50 of 10(-10) M, compared to 10(-6) M for CCK8, with an ED50 of 10(-8) M. The maximal chief cell response to GT was unaffected by the addition of CCK8 or carbachol, but responded additively with forskolin, indicating that GT uses the same transduction mechanism as CCK8 and carbachol and does not involve the activation of adenylate cyclase. The ED50 values observed with both parietal and chief cells in these studies were close to the basal circulating levels of GT (3.5 x 10(-9) M) in adult pigs. These results clearly demonstrate that GT is a potent component of the enterooxyntin factor identified in studies of the role of the small bowel in the regulation of gastric secretion.

Asunto(s)

RESUMEN

Changes have been studied in human and rat pepsinogen phenotypes induced by N'-methyl-N'nitro-N-nitrosoguanidine (MMNG) in in vitro rat experiments and in vivo cultures of human and rat isolated gastric chief cells. In vivo the fastest migrating electrophoretic band decreased or disappeared as early as 3 weeks after the start of MNNG treatment. The changes, observed in 17 of 32 rats receiving MNNG, were permanent and consistently associated with pronounced histopathologic changes seen 10 months later (17 of 17). Comparable phenotypic changes were observed after 7 days only in MNNG-treated rat chief cell cultures. In human chief cell cultures a decrease of the Pg3 band, which is consistent with the "carcinogenic" phenotype, was observed in two of six preparations treated with MNNG. This early preceding change in phenotype preceding tumor formation may be useful as a diagnostic tool for the onset of gastric cancer.

Asunto(s)

RESUMEN

The relationship between electrophoretic pepsinogen A (PGA) patterns from urine and gastric mucosa was studied in healthy volunteers and in patients with various gastric disorders. Discrepancies between urinary and gastric PGA patterns were found in 63.3% of the individuals. In 9% of the subjects with these discrepancies, the phenotype class in urine was different from that in gastric mucosa. The differences were found in all diagnostic groups. The highest frequency of differences was found in patients with gastric ulcer. The differences were not related to the serum PGA level. More than 80% of the differences were caused by a lower relative intensity of pepsinogen A fraction 5 (Pg5) in urine than in gastric mucosa. The possible origin of differences in PGA isozymogen patterns was studied by organ culture of gastric biopsies. In vitro synthesis and secretion of pepsinogens were studied by electrophoresis and autoradiography. The synthesis rate of PGA in biopsies of 1-2 mm diameter was 40-100 ng/hr. Posttranslational modification of PGA isozymogens was demonstrated. Pg2 and part of Pg4 probably are secondary products of Pg3 and Pg5, respectively. In some individuals the secretion rate of Pg3 was low compared to the other isozymogens. The conversion of Pg3 into Pg2 and the differential secretion of the isozymogens may explain some of the discrepancies between gastric and urinary PGA patterns.

Asunto(s)

RESUMEN

Precursors of the gastric proteases pepsinogen A (pepsinogen I) and pepsinogen C (pepsinogen II) and slow-moving protease were demonstrated in biopsy specimens from Barrett's epithelium in 21 of 22 patients with Barrett's esophagus; in 14 of them, in variable combinations at different sites. In 13 of 19 patients (68.4%) with detectable pepsinogen A, different isozymogen patterns were found between the Barrett's epithelium and the gastric corpus mucosa. Discrepancies consisted mainly of a stronger pepsinogen 5 band in the Barrett's epithelium, with a higher incidence in biopsy specimens with features of dysplasia than with no or indefinite dysplasia; the difference was, however, not statistically significant. Zymograms of 69 biopsy specimens from Barrett's epithelium were correlated with the histologic type: pepsinogen A and C were most frequently found in the fundic type, least often in the specialized intestinal type. In control gastric corpus biopsy specimens, pepsinogen A and C as well as slow-moving protease were always detectable. The observed variability of gastric protease patterns, in particular of pepsinogen A isozymograms, may be due to differences in expression within the pepsinogen A cluster, suggesting a deregulation of gene expression or partial deletion of the pepsinogen A gene cluster.

Asunto(s)

RESUMEN

In this paper the role of pepsinogen has been reviewed in its physiological and clinical aspects. Although acid secretion has traditionally received far more attention clinically and has therefore been studied in great detail, the development of cellular systems has recently seen a revival in interest of pepsinogen secretion. These systems have made it possible to study pepsinogen secretion in more detail. Although many questions remain unanswered, a picture of a stimulus-secretion coupling mechanism of the chief cell has emerged that resembles in many aspects the pancreatic acinar cell, but also possesses some unique features of its own. The chief cell monolayer culture has also made it possible to study pepsinogen synthesis, and these studies seem to have solved the old controversy of whether or not modulation of pepsinogen synthesis occurs as a result of increased secretion. It now seems that pepsinogen synthesis does indeed increase in response to stimulated secretion. In addition to physiological studies, this review has discussed clinical aspects of the human pepsinogens in various gastric disorders. The clinical implications of genetic heterogeneity of the human pepsinogens are especially intriguing. Relationships between certain PGA phenotypes and certain gastric disorders have been described and some studies have tried to evaluate the relevance of these findings for diagnostic purposes. So far, it seems that PGA phenotyping alone has only limited diagnostic value, but, in combination with serum PGA determinations, could be of additional help in the diagnosis of gastric malignancy. In addition, various studies suggest that the ratio of serum PGA and PGC levels may be helpful in determining the histological status of the gastric mucosa. A very promising possibility in solving the many problems involved in exact genotype determinations through phenotyping is the recent availability of cDNA probes. With this technique, the question of whether the association between PGA phenotypes and gastric malignancy is primary or secondary may be solved in the near future. In view of the very poor prognosis for gastric cancer, further studies concerning the relationships between gastric cancer, serum pepsinogen levels, and PGA phenotypes or genotypes will hopefully lead to the possibility of an earlier diagnosis for gastric malignancy.

Asunto(s)

RESUMEN

Gastric mucosal pepsinogen A phenotype, serum pepsinogen A level, serum pepsinogen C level, serum pepsinogen A/pepsinogen C ratio, and serum gastrin level were evaluated as potential markers for gastric cancer or its precursors in 19 healthy volunteers and 341 patients from the gastroscopy program. Gastric cancer, atrophic gastritis, and intestinal metaplasia of the stomach were associated with pepsinogen A phenotypes, characterized by an intense fraction 5, and with a low serum pepsinogen A level (less than 25 micrograms/l), a low serum pepsinogen A/pepsinogen C ratio (less than 1.5), and a high serum gastrin level (greater than 79 ng/l). The specificity of pepsinogen A phenotypes with an intense fraction 5 for gastric cancer or its precursors was 95.1% with a sensitivity of 20.4%. The sensitivity and specificity of the noninvasive tests were evaluated with the receiver operating characteristic. For clinical purposes, a serum pepsinogen A/pepsinogen C ratio less than 1.8 is the most suitable test, with a sensitivity of 74% and a specificity of 76% for gastric cancer or its precursors, with a reference population of patients with benign gastric disorders. However, the sensitivity and specificity of the single or combined tests are too low for population screening purposes.

Asunto(s)

RESUMEN

Electrophoretic pepsinogen A patterns were determined in gastric fundic mucosa biopsies from 601 patients with various gastric disorders and 25 healthy volunteers. Pepsinogen A patterns with an intense fraction 5 appeared to be associated with gastric cancer and premalignant changes of the stomach (p less than 10(-9)). In 60 individuals pepsinogen A patterns were determined in normal mucosa from different parts of the stomach. No differences were found between these patterns. In 29 out of 59 gastric cancer patients pepsinogen A could be demonstrated in the macroscopically malignant tissue. In two cases a different pattern compared with uninvolved fundic mucosa was observed. During a follow up study, major changes in the pepsinogen A pattern were observed in 7 out of 56 patients. In 8.6% of the examined patients urinary pepsinogen A patterns differed considerably as compared with the pattern observed in the gastric fundus. The results suggest that the highly significant association between intense Pg5 (the product of the D gene) and gastric cancer or its precursors may be caused by genetic as well as non-genetic factors.

Asunto(s)

RESUMEN

The effect of omeprazole on gastric acid and pepsin secretion and fasting serum gastrin and serum pepsinogen I levels was studied in 12 healthy volunteers. Omeprazole, 40 mg enteric-coated granules, or placebo was given once daily for nine days in a double-blind crossover study design. Twenty-four hours after a single dose of omeprazole, mean basal and mean pentagastrin-stimulated acid output decreased significantly. This effect was more pronounced after nine days of treatment. Basal pepsin output was significantly reduced only in those subjects with basal anacidity during omeprazole treatment. Stimulated pepsin output was slightly reduced after a single dose but unaltered after nine days of omeprazole. Fasting serum gastrin and serum pepsinogen I levels increased significantly during omeprazole treatment. It is concluded that omeprazole is a potent and selective inhibitor of gastric acid secretion, probably without a direct effect on pepsin secretion. However, in cases of basal anacidity during omeprazole administration, basal pepsin secretion is reduced. During omeprazole treatment, fasting serum levels of gastrin and pepsinogen I rise.

Asunto(s)

RESUMEN

Total human pepsinogen (PG) was isolated from gastric fundic mucosa and PGA (formerly called PGI) from urine, using standard ion-exchange and gel filtration techniques. Gastric PGA was separated from PGC (formerly called PGII) either by immunoaffinity or high resolution ion-exchange chromatography (fast protein liquid chromatography, Pharmacia, Uppsala, Sweden). The individual PGA isozymogens 2, 3, 4 and 5 could be isolated to homogeneity with the aid of the same ion-exchanger. Evidence was obtained for the existence of secondary modifications of the PGA fractions 3, 4 and 5, electrophoretically overlapping the primary (genetic) isozymogens.

Asunto(s)

RESUMEN

Regulation mechanisms of pepsinogen (EC 3.4.23.) synthesis and secretion were studied by following newly synthesized [14C]-labeled pepsinogen during culture of isolated rabbit gastric glands. Omeprazole, a substituted benzimidazole, while almost completely abolishing acid production at 10(-4) M, strongly stimulated secretion of preformed and newly synthesized pepsinogen. Although the pepsinogen synthesis at this concentration of omeprazole was reduced to about 55% of the control rate, a two-fold absolute increase of total secreted pepsinogen was found. This increase was not due to a non specific leakage through disruption of chief cell membranes, as no increase of lactate dehydrogenase in the culture medium could be demonstrated. The stimulated secretion was influenced neither by 10(-3) M cimetidine, 10(-3) sodium thiocyanate nor 10(-4) M atropine. No additivity was found between the carbachol (10(-4) M) or dibutyryl cyclic AMP (10(-3) M) and the omeprazole induced pepsinogen secretion.

Asunto(s)

RESUMEN

Serum pepsinogen A (pepsinogen I) levels and urinary pepsinogen A phenotypes were studied in relation to ABO blood group, age and sex in 700 healthy blood donors. There was no relation between urinary pepsinogen A phenotypes and serum pepsinogen A levels. It is concluded that serum PGA levels and PGA phenotypes are independent factors in predisposition to gastroduodenal disorders. Serum pepsinogen A levels were higher in males than in females and rose with increasing age. The ABO blood groups were not related to pepsinogen A phenotypes. Blood group O individuals showed higher serum pepsinogen A levels compared with blood group A. Pepsinogen A phenotypes with intensity of fraction 5 were more frequent in males compared with females.

Asunto(s)