Cellular origin and release of intrinsic factor from isolated rat gastric mucosal cells

Murine experimental autoimmune gastritis models refractive to development of intrinsic factor autoantibodies, cobalamin deficiency and pernicious anemia

Researchers have developed murine lymphopenic, non-lymphopenic, transgenic, spontaneous and infectious agent based models to induce an experimental autoimmune gastritis (EAG) for the study of human organ-specific autoimmune disease. These models result in a chronic inflammatory mononuclear cell infiltrate in the gastric mucosa, destruction of parietal and zymogenic cells with autoantibodies reactive to the gastric parietal cells and the gastric H+/K+ ATPase (ATP4), arguably hallmarks of a human autoimmune gastritis (AIG). In the case of AIG, it is well documented that, in addition to parietal cell antibodies being detected in up to 90% of patients, up to 70% have intrinsic factor antibodies with the later antibodies considered highly specific to patients with pernicious anemia. This is the first report specifically investigating the occurrence of intrinsic factor antibodies, cobalamin deficiency and pernicious anemia in EAG models. We conclude, in contrast to AIG, that, in the three EAG models examined, intrinsic factor is not selected as a critical autoantigen.

Vitamin B12 transporters

The uptake of vitamin B12 from the intestine into the circulation is perhaps the most complex uptake mechanism of all the vitamins, involving no less than five separate VB12-binding molecules, receptors and transporters. Each molecule involved in uptake has a separate affinity and specificity for VB12 as well as a separate cell receptor. Thus VB12 is initially bound by haptocorrin in the stomach, then by IF in the small intestine. An IF receptor is then involved in uptake of the IF-VB12 complex by the intestinal epithelial cell, with the subsequent proteolytic release of VB12 and subsequent binding to TcII. The TcII receptor then transports the TcII-VB12 complex across the cell, whence it is released into the circulation. It is surprising, then, that despite its complexity, it has been possible to harness the vitamin VB12 uptake mechanism to enhance the oral uptake of peptides, proteins, and nanoparticles.

Expression of intrinsic factor and pepsinogen in the rat stomach identifies a subset of parietal cells

Morphological and functional heterogeneity of parietal cells has been thought to be due to different maturation positions within the gastric gland. Morphodynamic studies have shown that 2% of parietal cells in mice derive from a pre-neck (chief) cell precursor. Intrinsic factor (IF) and pepsinogen, markers of rat chief cells, were used to determine if these proteins identified a subset of parietal cells that might reflect origin from the pre-neck cell lineage. The zymogenic region of the rat stomach and gradient-isolated fractions enriched in parietal and chief cells were fixed in 10% buffered Formalin or in Bouin's solution. Immunostaining was performed using indirect immunoperoxidase histochemistry and double-labeled immunofluorescence with antibodies raised against human IF, pepsinogen II, and H(+)-K(+)-adenosinetriphosphatase (H(+)-K(+)-ATPase). In intact tissue, parietal (H(+)-K(+)-ATPase-positive) cells were found starting at the upper edge of the isthmus, but parietal cells positive for IF and pepsinogen were only found from just below the isthmus and neck region to the base of the gastric gland. Three to four percent of isolated parietal cells were positive for these ectopic markers. This subset of cells was also positive for H(+)-K(+)-ATPase. Thus products of rat chief cells are expressed in a subset of parietal cells. The percentage of positive cells is similar to that predicted to be derived from the pre-neck (chief) precursor lineage in the mouse. The distribution of these cells to the lower neck and base of the gland suggests that the expression of chief cell products is consistent with either predetermination by lineage or parietal cell maturation or with both processes.

Regulation of mucus secretion by cells isolated from the rat gastric mucosa

1. A suspension of cells, containing about 30% mucous cells, was isolated from the rat fundic mucosa, and was pre-incubated with D-[6-3H]glucosamine. 3H-labelled material subsequently released into the medium was separated by Fast Protein Liquid Chromatography on a Superose 6 column. 2. A sharp peak of labelled high molecular weight material eluted from the column close to the void volume. This material was identified as mucous glycoprotein by its similar chromatographic behaviour to partially purified rat gastric mucous glycoprotein, by its resistance to complete degradation by papain and by its behaviour on treatment with dithiothreitol. On a caesium chloride density gradient the labelled material was virtually all located between densities of 1.35 and 1.53 g/ml. with the main peak at 1.40 g/ml. 3. A broad peak of lower molecular weight material was also eluted from the column. The release of this unidentified material did not seem to be closely associated with the release of mucous glycoprotein from the cells. 4. Release of mucous glycoprotein was stimulated by secretin (half-maximally effective concentration 2.3 nM, 84% stimulation above basal release at 100 nM), and by isoprenaline (half-maximally effective concentration 34 nM, 33% stimulation at 1 microM). Carbachol (0.5 nM) produced a significant (18-29%) stimulation of mucus secretion, but gastrin (100 nM), histamine (0.5 mM) and epidermal growth factor (200 nM) were without effect. 5. The preparation should prove useful in the identification of the agents which regulate gastric mucus secretion.

Immunohistochemical survey of cobalamin-binding proteins

Dietary cobalamin is bound to intrinsic factor (IF) and nonintrinsic factor (R protein) in the gastrointestinal tract. Distribution of IF has previously been described only in the stomach (parietal, chief cells), duodenum (mucous cells), and pancreatic juice. Cells containing R protein have been reported to be more widespread, including mucin-secreting cells of the intestinal tract. To further clarify the cells producing these cobalamin binders in the various organs, we surveyed a number of tissues in four species, with monospecific antisera raised against rat IF and hog R protein, using indirect immunoperoxidase histochemistry. A positive staining pattern was confirmed after blocking with the appropriate protein purified to homogeneity. Strong IF staining was noted over chief cells in the rat stomach, with weaker but substantial staining in the parietal cells as well. Intrinsic factor was found only in parietal cells in all other species examined. R protein was found in parietal cells of all species tested, except in the hog, where mucous cells of the basal crypt stained. The area of the brush border and apical cytoplasm in small intestinal epithelial cells was also positive for both IF and R protein, probably reflecting uptake. Accessory digestive organs, such as salivary gland and pancreas were also positive for both IF and R protein in the secretory ducts. Accessory digestive organs contribute to the secretion of IF as well as R protein, but the physiologic importance of this IF secretion is not clear.

Naturally occurring opioid peptides modulate H+-production by isolated rat parietal cells

The rationale for the present study was to determine the effects of naturally occurring opioid peptides on H+-production by isolated rat parietal cells as indirectly measured by [14C]-aminopyrine uptake. In crude preparations (18 to 25% parietal cells) and in enriched (80 to 90%) parietal cell fractions stimulation by submaximal histamine- or dibutyryl cAMP-concentrations (10(-6)-10(-4) mol/l) was augmented by 20-30% in the presence of methionine-enkephalin (Met-Enk) and Met-Enk Arg6Phe7 (10(-7) to 10(-5) mol/l). This augmentation was blocked by the opiate receptor antagonist (-)naloxone (10(-6) mol/l) suggesting specificity of the action of Met-Enk and Met-Enk Arg6Phe7. At 10(-6) mol/l (-)naloxone did not exert nonspecific toxic effects. Yet, even in the absence of exogenous opioids, histamine-induced H+-production was inhibited by 3 X 10(-5) or 10(-4) mol/l (-)naloxone. Since similar inhibition occurred with (+)naloxone, an inactive stereoisomer which does not interact with opiate receptors, effects of (-)naloxone at concentrations above 10(-5) mol/l must be considered nonspecific. We conclude that Met-Enk and Met-Enk Arg6Phe7 have no effect on basal, but augment stimulated H+-production by a direct effect on the parietal cells. At nontoxic concentrations (-)naloxone antagonizes this augmentation indicating that it is mediated by specific opiate receptors on the parietal cells.

[Isolated human gastric mucosa cells--studies on physiologic and pharmacologic regulatory mechanisms]

Cells were isolated by use of collagenase, EDTA and pronase form human gastric mucosa obtained at peptic ulcer surgery (n = 61) or at Whipple's operations (n = 6). Enriched parietal cell fractions were prepared by isopycnic centrifugation with Percoll. H+ production, intracellular instrinsic factor and histamine content were maximal in the low density fraction containing 75% parietal cells and--among other nonparietal cell types--mast cells. H+ production, intrinsic factor secretion and adenylate cyclase-activity responded to histamine stimulation in a concentration dependent manner. Response was blocked by histamine H2 receptor antagonists (rantidine, famotidine). Dibutyryl cAMP and the phosphodiesterase inhibitor IMX were the most powerful stimuli whereas carbachol, hexoprenaline and pentagastrin were less effective. Prostaglandin E2 and 6-keto-PGF2 alpha occurred in the highest concentrations in the low density cell fraction. PG production increased linearly for 15 min and seemed to be influenced by the intracellular calcium level.

Effects of hormones (calcitonin, GIP) and pharmacological antagonists (ranitidine and famotidine) on isolated rat parietal cells

The rationale for the present study was to compare calcitonin and gastric inhibitory polypeptide (GIP) versus two histamine H2 receptor antagonists with respect to their potency of inhibiting parietal cell functions. Adenylate cyclase activity and acid production ([14C]aminopyrine uptake) of isolated rat parietal cells were stimulated by histamine. At 10(-7) and 10(-6) mol/l, calcitonin and GIP reduced the response to histamine by 10-20% following noncompetitive kinetics. Ranitidine and famotidine (MK 208) inhibited the response to histamine by about 50% at 10(-7)-10(-6) mol/l, and at 10(-5) mol/l abolished the histamine effect. On a molar basis famotidine turned out to be 6 times more potent than ranitidine. Both antagonists revealed competitive kinetics. Our data suggest direct inhibition of the parietal cells by the tested compounds which were shown to interfere at the adenylate cyclase cAMP system or at the histamine H2 receptor. However, compared to the histamine H2 receptor antagonists, hormonal inhibition is less pronounced and mediated by a different mechanism.

The influence of omeprazole on the synthesis and secretion of pepsinogen in isolated rabbit gastric glands

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.

Prostaglandin formation by isolated gastric parietal and nonparietal cells of the rat

Rat gastric cells isolated by pronase and subdivided by Percoll into 3 fractions (F1, F2, F3) were used to study prostaglandin E2 (PGE2) formation and, as an indirect measure of parietal cell H+ production, [14C]-aminopyrine uptake. Cells that had not been fractionated, with 20 to 25% parietal cells, contained at 0 degree C 1.7 +/- 0.35 (s.e.mean) ng PGE2 10(8) cells-1. During incubation at 37 degrees C these cells steadily synthesized up to 4.36 +/- 0.73 ng PGE2 10(8) cells-1 from endogenous substrate. Indomethacin in concentrations higher than 10(-6) mol 1(-1) inhibited this basal formation completely, but 10(-4) mol 1(-1) did not reduce the cellular PGE2 level below 1.4 +/- 0.2 ng 10(8) cells-1. Arachidonic acid in concentrations higher than 10(-5) mol 1(-1) evoked an abundant formation of PGE2, and 10(-4) mol 1(-1) built up a plateau of over 7.5 +/- 1.65 ng PGE2 10(8) cells-1 within 15 min. PGE2 formation in cell fractions increased significantly with the number of parietal cells per assay tube. Indomethacin (10(-8) to 10(-4) mol 1(-1] did not influence the histamine-stimulated uptake of [14C]-aminopyrine, while arachidonic acid (10(-5) to 10(-4) mol 1(-1] inhibited this process. PGE2 formation in response to arachidonic acid was prevented by indomethacin, but the inhibition of aminopyrine uptake by arachidonic acid could not be prevented by indomethacin. The data suggest that isolated gastric cells of the rat sustain constant PGE2 synthesis in vitro, which is more pronounced in parietal than in mucosal and chief cells. PGE2 may exert different effects within distinct gastric cell types.

Intrinsic factor secretion from isolated human gastric mucosal cells

Human gastric mucosal cells were isolated from the resected fundic mucosa of peptic ulcer patients. The intracellular content and secretion of intrinsic factor were estimated by binding to cyano[57Co]cobalamin. The content was maximal in the enriched parietal cell fraction which also displayed the highest H+ production as measured by amino[14C] pyrine uptake. Secretagogues evoked full response after 15 min of incubation: pentagastrin (181% of basal secretion), carbachol (208%), histamine (250%) and dibutyryl cyclic adenosine monophosphate (304%). The phosphodiesterase inhibitor isobutylmethylxanthine was slightly more effective even than dibutyryl cAMP. The response to histamine was abolished by ranitidine, indicating activation of adenylate cyclase via histamine H2 receptors, but remained unaffected by atropine, which in turn blocked the carbachol effect, whereas ranitidine was ineffective. The mean formation rate was 8.4 fmol intrinsic factor/10(6) cells per h under basal conditions and 14.3 fmol in response to histamine.