A review of the status of omeprazole: the Hambury workshop.
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Humans↗
Biomedical subjects
G Sachs
Publications and source records attributed to G Sachs.
Pharmacological aspects of acid secretion.
The secretion of gastric acid is regulated both centrally and peripherally. The finding that H2-receptor antagonists are able to reduce or abolish acid secretion due to vagal, gastrinergic, and histaminergic stimulation shows that histamine plays a pivotal role in stimulation of the parietal cell. In the rat, the fundic histamine is released from the ECL cell, in response to gastrin, acetylcholine, or epinephrine, and histamine release is inhibited by somatostatin or by the H3-receptor ligand, R-alpha-methyl histamine. The parietal cell has a muscarinic, M3, receptor responsible for [Ca]i regulation. Blockade of muscarinic receptors by atropine can be as effective as H2-receptor blockade in controlling acid secretion. However, general effects on muscarinic receptors elsewhere produce significant side effects. The different receptor pathways converge to stimulate the gastric H+,K(+)-ATPase, the pump responsible for acid secretion by the stomach. This enzyme is an alpha,beta heterodimer, present in cytoplasmic membrane vesicles of the resting cell and in the canaliculus of the stimulated cell. It has been shown that acid secretion by the pump depends on provision of K+Cl- efflux pathway becoming associated with the pump. As secretion occurs only in the canaliculus, this K+Cl- pathway is activated only when the pump inserts into the canalicular membrane. Transport by the enzyme involves reciprocal conformational changes in the cytoplasmic and extracytoplasmic domain. These result in changes in sidedness and affinity for H3O+ and K+, enabling active H+ for K+ exchange. The acid pump inhibitors of the substituted benzimidazole class, such as omeprazole, are concentrated in the canaliculus of the secreting parietal cell and are activated there to form sulfenamides. The omeprazole sulfenamide, for example, reacts covalently with two cysteines in the extracytoplasmic loops between the fifth and sixth transmembrane and the seventh and eighth transmembrane segments of the alpha subunit of the H+,K(+)-ATPase, forming disulfide derivatives. This inhibits ATP hydrolysis and H+ transport, resulting in effective, long-lasting regulation of acid secretion. Therefore, this class of acid pump inhibitor is significantly more effective and faster acting than the H2 receptor antagonists. K+ competitive antagonists bind to the M1 and M2 transmembrane segments of the alpha subunit of the acid pump and also abolish ATPase activity. These drugs should also be able to reduce acid secretion more effectively than receptor antagonists and provide shorter acting but complete inhibition of acid secretion.
Amino Acid Sequence↗
Gastrin-stimulated changes in Ca2+ concentration in parietal cells depends on adenosine 3',5'-cyclic monophosphate levels.
BACKGROUND & AIMS: The parietal cell has secretory receptors for histamine and acetylcholine, whereas the functional nature of the gastrin/cholecystokinin B receptor is controversial. This study in isolated gastric glands investigates the cholecystokinin B receptor-induced intracellular calcium concentration ([Ca]i) response in enterochromaffin-like (ECL) and parietal cells as a function of adenosine 3',5'-cyclic monophosphate pathways. METHODS: The responses of [Ca]i in ECL and parietal cells of perfused rabbit or rat calcium orange-loaded gastric glands were determined using confocal microscopy. ECL cells were identified by position, size, and autofluorescence and parietal cells by position and size. RESULTS: Gastrin (1 mumol/L) produced an elevation of [Ca]i levels in both ECL and parietal cells. In the presence of 100 mumol/L cimetidine, the ECL cell response to gastrin was not affected but the [Ca]i response of the parietal cell was abolished. With dibutyryl adenosine 3',5' phosphate in addition to cimetidine, the response of the parietal cell [Ca]i to gastrin was restored in both the rat and rabbit. CONCLUSIONS: The [Ca]i response of the parietal but not the ECL cell to the addition of gastrin seems to depend on the presence of normal or elevated intracellular adenosine 3',5'-cyclic monophosphate levels. Therefore, H2 receptor activity may be permissive for the effect of gastrin on parietal cell function.
Animals↗
Turnover of the gastric H+,K(+)-adenosine triphosphatase alpha subunit and its effect on inhibition of rat gastric acid secretion.
BACKGROUND & AIMS: The rate of turnover and the effect of inhibition of acid secretion on the turnover of gastric H+,K(+)-adenosine triphosphatase (ATPase) is unknown. The aim of this study was to determine the turnover of the alpha subunit of gastric H+,K(+)-ATPase in rats under control conditions and during inhibition of acid secretion by ranitidine or omeprazole. METHODS: The turnover of the alpha subunit of the ATPase was determined by measuring the loss of incorporated 35S-methionine. This was compared with the rate of recovery of K(+)-stimulated ATPase activity in the omeprazole-treated animals. RESULTS: The half-life of the alpha subunit was 54 hours. A 1-week treatment with omeprazole had no significant effect, but the half-life increased to 125 hours (P < 0.01) after continuous ranitidine infusion. After omeprazole treatment, K(+)-stimulated ATPase activity recovered with a half-time of 15 hours. CONCLUSIONS: The turnover of the gastric ATPase subunit was independent of omeprazole inhibition but was prolonged by ranitidine. The effect of ranitidine suggests that the resting pump in tubulovesicles may turn over more slowly than the stimulated pump in the secretory canaliculus. The rapid recovery of ATPase activity compared with turnover after omeprazole is caused by both H+,K(+)-ATPase synthesis and loss of covalently bound drug.
Animals↗
Lytic effector cell activity and major depressive disorder in patients with breast cancer: a prospective study.
The study examined lymphokine-activated killer cell (LAK) and natural killer (NK) cell activity in breast cancer patients prior to surgery as compared to effector cell lysis in patients with non-malignant breast tumors, further in connection with lifetime diagnosis of major depression, severity of current depression, anxiety and coping styles. Follow up studies covered a period of 6 and 12 months. Prior to surgery, life time diagnosis of major depressive disorder, trait anxiety and coping styles did not discriminate patients as far as effector cell lysis is concerned. LAK activity but not NK activity was reduced in patients with actual depressive symptoms (P < 0.01) and high state anxiety (P < 0.05). These findings support the hypothesis that LAK activity is a state marker of actually existing depression and anxiety prior to surgery. Affective rather than coping measures showed significant differences in LAK activity. For LAK activity, 1 year after surgery the only predicting factors were Tamoxifen therapy and chemotherapy.
Adult↗
Carbon monoxide generation in carbon dioxide absorbents.
Several cases of unexpected high carboxyhemoglobin (COHb) levels in patients undergoing general anesthesia were observed. To avoid carbon monoxide (CO) intoxication, the use of high fresh gas flows and frequent changes of the absorbent were recommended. However, due to economic and ecologic considerations, low-flow anesthetic techniques have advantages. Thus, the subject urgently needed to be reexamined. In 1001 patients undergoing enflurane or isoflurane anesthesia, blood samples were taken 30 min after fresh gas flow reduction to 0.5 L/min and analyzed for COHb. The absorbent canisters, containing soda lime, were used for several days. The statistical mean and SD of COHb was 1.17% +/- 0.97% in the range of 0%-7.6%. There was no statistical difference between the COHb values when broken down by the duration of use of the absorbent canisters. In no case were dangerously high COHb levels observed. As recently revealed, only dry absorbents produce CO if exposed to volatile anesthetics containing a CHF2-moiety. Thus, all measures must be avoided that dry out the absorbent. Low-flow anesthesia preserves the moisture content of the absorbent and, thus, seems to be a factor protecting from CO generation.
Adsorption↗
Review article: the continuing development of proton pump inhibitors with particular reference to pantoprazole.
Inhibition of the gastric proton pump is gaining acceptance as the treatment of choice for severe gastrooesophageal reflux disease, and for treatment of duodenal and gastric ulceration. Three of these drugs are now available (omeprazole, lansoprazole and pantoprazole) and more are being developed. Proton pump inhibitors share the same core structure, but differ in terms of substituents on this core. The substitutions are able to modify some important chemical properties of the compounds. For example, pantoprazole is significantly more acid-stable than omeprazole or lansoprazole. E3810 is significantly less stable than the other compounds. We present an explantation for this finding that depends on the relative pK values for the pyridine and benzimidazole nitrogens, especially the former. Pantoprazole formulated in an enteric-coated tablet displays high bioavailability and linear pharmacokinetics whether on single or multiple dose regimens. Although all three proton pump inhibitors provide a similar chemical conversion to sulphenamides, which are highly reactive cysteine reagents, these reagents derivatize different cysteines in the extracytoplasmic or membrane domain of the pump and inhibit the pump at different rates. Whereas the differences in chemical reactivity can be explained by the solution chemistry of the compounds, selective derivatization of different cysteines on the protein argues for an involvement of pump structure in response to the presence of the proton pump inhibitor on its luminal surface. This suggests that the proton pump inhibitors, which were originally designed to take advantage of only the highly acidic space generated in the parietal cell by the production of the sulphenamide, are made even more selective by the protein they target. Pantoprazole is metabolized by a combination of phase I and phase II metabolism, and has also been shown to have a very low potential for drug interaction. Studies of acid secretion in man have shown this compound to be an effective and long lasting inhibitor of acid secretion. The pharmacodynamics explain the cumulative effect of repeated doses and maximal acid secretory capacity with a once daily dosage.
2-Pyridinylmethylsulfinylbenzimidazoles↗
The pharmacology of the gastric acid pump: the H+,K+ ATPase.
The gastric H+,K+ ATPase--the gastric acid pump--is the molecular target for the class of antisecretory drugs called the proton-pump inhibitors (PPIs). These compounds--omeprazole, lansoprazole, and pantoprazole--contain, as their core structure, 2-pyridyl methylsulfinyl benzimidazole. The H+,K+ ATPase is a heterodimer composed of a 1034-amino acid catalytic alpha peptide and a glycosylated 291-amino acid beta subunit. The alpha subunit probably contains 10 membrane-spanning sequences; the beta, a single transmembrane segment. The PPIs have a pKa of about 4.0; hence they accumulate only in the acidic secretory canaliculus of the stimulated parietal cell. Here they undergo conversion to a cationic sulfenamide, which then reacts with available cysteines on the extracytoplasmic face of the alpha subunit. Omeprazole reacts and forms disulfide bonds with cys813(822) and cys892; lansoprazole, with cys813(822), cys892, and cys321; and pantoprazole, with cys813 and -822. The antisecretory effect of the drugs reflects their short plasma half-life (approximately 60 min), the number of active pumps during that time, and the recovery of pumps following biosynthesis and reversal of inhibition. These drugs also show synergism with either amoxicillin or clari- thromycin in eradicating Helicobacter pylori, an organism shown to be important in duodenal and gastric ulcer disease. Their action is probably due to elevation of pH in the environment of the organism, rather than to any direct action.
Amino Acid Sequence↗
Expression of gastric and colonic H(+)-K(+)-ATPase in the rat kidney.
Enzymatic and microperfusion studies have indicated that an ATP-dependent H+/K+ exchange process is present in the collecting duct of the mammalian kidney. Immunochemical staining has also provided evidence for expression of a gastric-type H(+)-K+ adenosine triphosphatase (H(+)-K(+)-ATPase). Rat kidney mRNA was probed with use of the polymerase chain reaction (PCR) to determine the presence of an H(+)-K(+)-ATPase. cDNA made with mRNA isolated from the kidneys of rats maintained on a low-K diet was used as template in PCR reactions with primers encompassing the cDNA sequence of the alpha-subunit of the gastric H(+)-K(+)-ATPase and the 5' and 3' ends of the colonic H(+)-K(+)-ATPase. The resulting products, 300-700 bp in size, hybridized with probes directed against either the gastric or colonic sequences of the H(+)-K(+)-ATPase. Sequencing of the individual PCR products showed identity with the appropriate regions of the alpha-subunits of the gastric H(+)-K(+)-ATPase and colonic H(+)-K(+)-ATPase. These data indicate that the rat kidney expresses mRNAs encoding both gastric and colonic H(+)-K(+)-ATPases.
Animals↗
Gastric acid secretion.
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Amino Acid Sequence↗
A program to reduce onset distress in unselected type I diabetic patients: effects on psychological variables and metabolic control.
This paper reports the results of a prospective controlled trial of a program addressing reduction of onset distress and better future adaptation in adults who were enrolled at the time of diagnosis of type I diabetes mellitus. Patients were assigned randomly to either standard intensive treatment and patient education with the distress reduction program (N = 10) or to standard intensive treatment and patient education without this program (N = 13). Prospective follow-up of patients with multiple validated measures of treatment outcome showed less anxious coping behavior, less depression and less denial at the 9-month follow-up and less denial at the 15-month follow-up in the group with the distress reduction program, but no differences in metabolic control between the two groups at any time. We conclude that our program has a positive impact on the crisis at diabetes onset; the lower denial in the treatment group may lead to improved regimen adherence in the long term.
Adaptation, Psychological↗
Characterization of potassium and chloride channels in the basolateral membrane of bovine nonpigmented ciliary epithelial cells.
PURPOSE: The pigmented epithelial (PE) and the nonpigmented epithelial (NPE) cells of the ciliary body may function as a syncytium for secretion of the aqueous humor, with solute and water entering through the PE and leaving through the NPE cell. Secretion across the basolateral membrane of the NPE cell was postulated to depend on coupling sodium extrusion through the NaK-ATPase to efflux through Cl channels. In the current study, the authors used single-channel patch clamp techniques to characterize the ion channels present in the basolateral membrane of the NPE cell. METHODS: Mild enzymatic digestion of the bovine ciliary process was used to obtain pairs or clusters of NPE cells that were coupled to their neighbor PE cells. Cells were dispersed immediately onto a coverslip, bathed in a HEPES-buffered saline, and imaged with an inverted microscope. With the anatomic relationship between cells still intact, a patch-pipette electrode was applied to the basolateral surface of the NPE cell. Single-channel currents were then characterized in 52 cells by using either the cell-attached or excised versions of the patch-clamp technique. RESULTS: A calcium-dependent "maxi" K channel was found in approximately 33% of the patches. It was activated by depolarizing voltage steps in cell-attached patches and was relatively inactive near the resting potential. When excised from the cell, it was activated by high levels of bath calcium and, in symmetrical K solutions (150 mM), showed a linear current-voltage (I-V) relationship with a slope conductance of approximately 150 pS. This channel was highly selective to K over Na and was blocked by barium (2 mM) or quinine (1 mM). In cell-attached recordings, a smaller conductance Cl channel was observed in 73% of the patches. The channel currents were inward at resting potential and outward with depolarizing voltage steps, with a pipette reversal potential of approximately -23 mV. The current-voltage relationship of this channel was nearly linear with a slope conductance of approximately 24 pS. When pipette Na and K were replaced with N-methyl-D-glucamine, this channel produced an inward current showing a high selectivity for Cl. This Cl-selective channel was activated by dibutyryl-cyclic adenosine monophosphate (cAMP) but not by elevation of intracellular calcium with ionomycin or by anisosmotic cell swelling. CONCLUSIONS: Two ion channels were found in the NPE basolateral membrane: One was K selective, the other was Cl selective. The cAMP-activated Cl channel may be important in supplying the counterion for Na extrusion across the basolateral surface of the NPE cell, whereas the calcium-dependent maxi K channel may be useful for membrane hyperpolarization to increase the driving force for Cl exit.
Animals↗
Progress in therapy of ulcer disease.
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Anti-Bacterial Agents↗
Disease-related worries and concerns: a study on out-patients with inflammatory bowel disease.
OBJECTIVE: To investigate the relationship between inflammatory bowel disease (IBD) patients' disease-related worries and concerns and their disease-related data, sociodemographic variables and perceived information level with respect to IBD. STUDY DESIGN: Prospective evaluation of disease-related concerns. SETTING: Out-patient IBD clinic of a university hospital. STUDY POPULATION: The study included 105 patients with IBD (72 with Crohn's disease and 33 with ulcerative colitis). MEASUREMENTS: Worries and concerns were measured using the standardized 25-item rating form of IBD patient concerns; actual disease activity was assessed by physicians using the Crohn's disease and clinical activity indices. Sociodemographic and other disease-related data were collected using a structured questionnaire. Patients' perceived information level was measured using a visual analogue scale. RESULTS: The issues of greatest concern to our patients were, in descending order of importance, having an ostomy bag (mean score +/- SD 63.6 +/- 38), the effects of medication (53.1 +/- 34), having surgery (51.6 +/- 36), the uncertain nature of the disease (46.5 +/- 32) and energy level (41.5 +/- 34). Patients with ulcerative colitis scored higher with respect to concern about loss of bowel control (P < 0.03). Disease-related worries and concerns correlated poorly with disease-related data (actual disease activity, severity of the course of IBD, diagnosis, disease duration or location, medication) but showed a significant negative correlation with patients' perceived information level about IBD (t = 0.2, P < 0.004). Lower information-level scores were associated with greater concerns. CONCLUSION: We conclude that the patients' information level about IBD and disease-related concerns have to be considered in clinical practice. Better information about IBD and psychosomatic counselling for patients who show high levels of concern may improve their quality of life and clinical care.
Adolescent↗
Cloning and expression of the rabbit gastric CCK-A receptor.
Cholecystokinin stimulates pancreatic zymogen secretion by binding with high affinity to a receptor on the pancreatic acinar cell. This receptor has been cloned and shown to be a CCK-A subtype. CCK also stimulates pepsinogen secretion from the gastric chief cell with high affinity. Using polymerase chain reaction with primers from the known sequence of the rat pancreatic CCK-A receptor cDNA, we prepared a 600 bp product from rat and rabbit stomach cDNA. From Southern analysis these represented a fragment of a gastric CCK-A receptor. PCR was then used to amplify a rabbit lambda ZAP II gastric epithelial cDNA library with the same primers, and the product was identified by sequencing as representing a CCK-A receptor fragment. When this PCR product was used to screen the library, ten positive clones were identified in a screening of 4.10(5) plaques, and several of these were sequenced. All had essentially the same sequence contained within 2 of these clones consisted of 427 amino acids and was 92% homologous (87% identity) to the known rat pancreatic CCK-A sequence but only 43% homologous to the gastric CCK-B sequence. The cDNA was subcloned into a pcDNA1 expression vector and transiently expressed in the human embryonic kidney cell line, HK 293. The responses of intracellular Ca2+ in these transfected cells to CCK and gastrin were monitored using video imaging. On the average 40% of the cells responded to CCK-8 by a transient elevation of [Ca2+]i followed by a steady state plateau. CCK was a high and gastrin a low affinity ligand for this signal, corresponding to the actions of these ligands on pepsinogen secretion from chief cells and somatostatin release from D cells. Hence from sequence and second messenger responses, the clone represents the CCK-A receptor presumably responsible for pepsinogen secretion by gastric chief cells and somatostatin release from gastric D cells.
Amino Acid Sequence↗
Biochemical identification of transmembrane segments of the Ca(2+)-ATPase of sarcoplasmic reticulum.
The transmembrane segments of sarcoplasmic reticulum Ca(2+)-ATPase were determined by trypsinization of cytoplasmic side-out intact sarcoplasmic reticulum vesicles. The membrane portion of tryptic digest comprising the transmembrane fragments, joined by the intravesicular segments, was separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis after labeling with fluorescein 5-maleimide in the presence of sodium dodecyl sulfate. In this way, seven fluorescent bands of tryptic fragments below 11 kDa were observed which were derived from 4 pairs of membrane spanning segments and one hydrophobic sequence at the C-terminal end. Two peptides of 10.8 and 10.6 kDa had the identical N-terminal sequence beginning at Glu826, representing the transmembrane segments M7 and M8 and their connecting loop. A band at 8.1 kDa contained one peptide beginning at Tyr36 (M1/loop/M2). A 7.7-kDa peptide starting at Leu253 (M3/loop/M4) and a 7.3-kDa peptide beginning at Ala752 (M5/loop/M6) were also observed. A band at 6.7 kDa contained two peptides, one beginning at Ser48 (M1/loop/M2) and another beginning at Tyr763 (M5/loop/M6). In addition, a 4-kDa peptide beginning at Met925 was observed. The size of this peptide did not allow for a complete pair of transmembrane segments, but this peptide could have been derived from trypsinolysis between the last pair of membrane spanning segments. These data therefore provide biochemical evidence for at least 8 transmembrane segments and perhaps two more at the C-terminal end of the enzyme.
Amino Acid Sequence↗
Topological analysis of H+,K(+)-ATPase using in vitro translation.
The membrane topology of the alpha subunit of the H+,K(+)-ATPase was investigated by using in vitro transcription/translation of DNA sequences encoding fusion proteins that contained possible membrane-spanning segments. The vectors consisted of DNA sequences encoding (a) either the first 101 (M0 vectors) or the first 139 (M1 vectors) amino acids of the N-terminal region of the alpha subunit of the ATPase, (b) a variable region, and then (c) the C-terminal 177 amino acids of the C-terminal region of the beta subunit, with five N-linked glycosylation sites. The variable region of the fusion protein contained the cDNA sequences representing the possible eight or 10 membrane-spanning segments either alone or in various combinations. Transcription/translation was performed in the presence of [35S]methionine using a coupled reticulocyte lysate in the absence and presence of microsomes. The fusion protein was identified by autoradiography following separation using SDS-polyacrylamide gel electrophoresis. Glycosylation of a translated sequence corresponded to membrane insertion and translocation of the C-terminal beta sequence. This method allowed analysis of signal anchor sequences using the M0 vector. The presence of a stop transfer sequence in the variable segment of the M1 vector resulted in inhibition of translocation of the C-terminal beta sequence. The sequences for the first four membrane segments could act as either signal anchor or stop transfer sequences. Therefore, this region of the alpha subunit has four membrane-spanning segments that are co-inserted with translation. The sequence corresponding to membrane segment M8 acted as a stop transfer sequence. The sequence corresponding to membrane segment M9 acted as a signal anchor sequence, and that corresponding to membrane segment M10 acted as a stop transfer sequence. The sequences representing the fifth, sixth, and seventh (M5, M6, and M7) membrane segments were unable to co-insert into the membrane. These data verify the first four and the eight membrane-spanning segments of the alpha subunit of the gastric H+,K(+)-ATPase and provide evidence for translational insertion of an additional pair of membrane-spanning segments, M9 and M10. It appears that insertion of membrane segments M5, M6, and M7 is determined differently from the other membrane-spanning segments. In combination with other methods, this in vitro transcription/translation method is useful for defining the membrane topology of the P type ATPases.
Amino Acid Sequence↗
Identification of a region of the H,K-ATPase alpha subunit associated with the beta subunit.
The gastric H,K-ATPase consists of an alpha, beta heterodimer. To determine which part of the alpha subunit is associated with the beta subunit, hog gastric vesicles were trypsinized, which left most of the beta subunit undigested. The vesicles were solubilized with either C12E8 (polyoxyethylene 8 lauryl ester) or Nonidet P-40 and then passed over a wheat germ agglutinin column, which retained the beta subunit. Among the fragments of membrane spanning segments obtained by digestion in the absence of K+, only one peptide fragment of the alpha subunit coeluted with the beta subunit, representing only the M7 and M8 membrane spanning segments of the alpha subunit along with their extracytoplasmic connecting loop. With K+ present during digestion, the fragments at 19-21 kDa and at 9.4 kDa were retained on the column, representing the M7 to C-terminal end and the M5/loop/M6 sector of the enzyme. These results provide biochemical evidence that a region of the alpha subunit containing the M7/loop/M8 sector is bound to the beta subunit under both digestion conditions; but when the C-terminal 180-amino acid sector of the alpha subunit remains intact, as found in the presence of K+, there is an additional retention of the M5/loop/M6 sector of the alpha subunit.
Amino Acid Sequence↗