Carbonic anhydrases and mucosal vanilloid receptors help mediate the hyperemic response to luminal CO2 in rat duodenum.

BACKGROUND & AIMS: The duodenal mucosa is exposed to PCO(2) >200 mm Hg due to the luminal mixture of gastric acid with secreted bicarbonate, which augments mucosal protective mechanisms. We examined the hyperemic response to elevated luminal PCO(2) in the duodenum of anesthetized rats luminally exposed to high CO(2) saline to help elucidate luminal acid-sensing mechanisms. METHODS: Blood flow was measured by laser Doppler, and intracellular pH of epithelial cells by measured by ratio microimaging. The permeant carbonic anhydrase (CA) inhibitor methazolamide, relatively impermeant CA inhibitor benzolamide, vanilloid receptor antagonist capsazepine, or sodium-hydrogen exchanger 1 (NHE-1) inhibitor dimethyl amiloride were perfused with or without the high CO(2) solution. RESULTS: The high CO(2) solution increased duodenal blood flow, which was abolished by pretreatment with methazolamide or capsazepine or by dimethyl amiloride coperfusion. Sensory denervation with capsaicin also abolished the CO(2) effects. Benzolamide dose-dependently inhibited CO(2)-induced hyperemia and at 100 nmol/L inhibited CO(2)-induced intracellular acidification. The membrane-bound CA isoforms IV, IX, XII, and XIV and cytosolic CA II and the vanilloid receptor 1 (TRPV1) were expressed in duodenum and stomach. Dorsal root ganglion and nodose ganglion expressed all isoforms except for CA IX. CONCLUSIONS: The duodenal hyperemic response to luminal CO(2) is dependent on cytosolic and membrane-bound CA isoforms, NHE-1, and TRPV1. CO(2)-induced intracellular acidification was inhibited by selective extracellular CA inhibition, suggesting that CO(2) diffusion across the epithelial apical membrane is mediated by extracellular CA. NHE-1 activation preceding TRPV1 stimulation suggests that luminal CO(2) is sensed as H(+) in the subepithelium.

Epithelial carbonic anhydrases facilitate PCO2 and pH regulation in rat duodenal mucosa.

The duodenum is the site of mixing of massive amounts of gastric H+ with secreted HCO3-, generating CO2 and H2O accompanied by the neutralization of H+. We examined the role of membrane-bound and soluble carbonic anhydrases (CA) by which H+ is neutralized, CO2 is absorbed, and HCO3- is secreted. Rat duodena were perfused with solutions of different pH and PCO2 with or without a cell-permeant CA inhibitor methazolamide (MTZ) or impermeant CA inhibitors. Flow-through pH and PCO2 electrodes simultaneously measured perfusate and effluent pH and PCO2. High CO2 (34.7 kPa) perfusion increased net CO2 loss from the perfusate compared with controls (pH 6.4 saline, PCO2 approximately 0) accompanied by portal venous (PV) acidification and PCO2 increase. Impermeant CA inhibitors abolished net perfusate CO2 loss and increased net HCO3- gain, whereas all CA inhibitors inhibited PV acidification and PCO2 increase. The changes in luminal and PV pH and [CO2] were also inhibited by the Na+-H+ exchanger-1 (NHE1) inhibitor dimethylamiloride, but not by the NHE3 inhibitor S3226. Luminal acid decreased total CO2 output and increased H+ loss with PV acidification and PCO2 increase, all inhibited by all CA inhibitors. During perfusion of a 30% CO2 buffer, loss of CO2 from the lumen was CA dependent as was transepithelial transport of perfused 13CO2. H+ and CO2 loss from the perfusate were accompanied by increases of PV H+ and tracer CO2, but unchanged PV total CO2, consistent with CA-dependent transmucosal H+ and CO2 movement. Inhibition of membrane-bound CAs augments the apparent rate of net basal HCO3- secretion. Luminal H+ traverses the apical membrane as CO2, is converted back to cytosolic H+, which is extruded via NHE1. Membrane-bound and cytosolic CAs cooperatively facilitate secretion of HCO3- into the lumen and CO2 diffusion into duodenal mucosa, serving as important acid-base regulators.

Mechanism of augmented duodenal HCO(3)(-) secretion after elevation of luminal CO(2).

The proximal duodenum is exposed to extreme elevations of P(CO(2)) because of the continuous mixture of secreted HCO(3)(-) with gastric acid. These elevations (up to 80 kPa) are likely to place the mucosal cells under severe acid stress. Furthermore, we hypothesized that, unlike most other cells, the principal source of CO(2) for duodenal epithelial cells is from the lumen. We hence examined the effect of elevated luminal P(CO(2)) on duodenal HCO(3)(-) secretion (DBS) in the rat. DBS was measured by the pH-stat method. For CO(2) challenge, the duodenum was superfused with a high Pco(2) solution. Intracellular pH (pH(i)) of duodenal epithelial cells was measured by ratio microfluorometry. CO(2) challenge, but not isohydric solutions, strongly increased DBS to approximately two times basal for up to 1 h. Preperfusion of the membrane-permeant carbonic anhydrase inhibitor methazolamide, or continuous exposure with indomethacin, fully inhibited CO(2)-augmented DBS. Dimethyl amiloride (0.1 mM), an inhibitor of the basolateral sodium-hydrogen exchanger 1, also inhibited CO(2)-augumented DBS, although S-3226, a specific inhibitor of apical sodium-hydrogen exchanger 3, did not. DIDS, an inhibitor of basolateral sodium-HCO(3)(-) cotransporter, also inhibited CO(2)-augemented DBS, as did the anion channel inhibitor 5-nitro-2-(3-phenylpropylamino) benzoic acid. CO(2) decreased epithelial cell pH(i), followed by an overshoot after removal of the CO(2) solution. We conclude that luminal CO(2) diffused in the duodenal epithelial cells and was converted to H(+) and HCO(3)(-) by carbonic anhydrase. H(+) initially exited the cell, followed by secretion of HCO(3)(-). Secretion was dependent on a functioning basolateral sodium/proton exchanger, a functioning basolateral HCO(3)(-) uptake mechanism, and submucosal prostaglandin generation and facilitated hydration of CO(2) into HCO(3)(-) and H(+).

Cystic fibrosis gene mutation reduces epithelial cell acidification and injury in acid-perfused mouse duodenum.

BACKGROUND & AIMS: Dysfunction of the cystic fibrosis transmembrane regulator (CFTR) is associated with diminished duodenal HCO3- secretion, despite a reported lack of clinical duodenal ulceration in affected subjects. We hypothesized that duodenal epithelial cells expressing a mutant CFTR have enhanced resistance to acid-induced injury. To test this hypothesis, we measured duodenal epithelial cell intracellular pH (pHi), injury, and acid back-diffusion in response to a luminal acid challenge in transgenic mice. METHODS: A murine colony was established for the CFTR DeltaF508 (DeltaF) mutation. Epithelial cell pH i was measured by microscopy with a trapped, fluorescent pH-sensitive dye in living C57BL/6 and DeltaF/DeltaF, +/DeltaF, and +/+ mice. In vivo confocal microscopy confirmed the localization of the dye in the cytoplasm of the epithelial cells. Epithelial injury was measured fluorometrically using propidium iodide. Duodenal epithelial bicarbonate secretion and proton permeability were measured by back-titration. Bicarbonate secretion and acid back-diffusion were measured in a perfused duodenal loop. RESULTS: Basal and post-acid exposure bicarbonate secretion were reduced in DeltaF/DeltaF mice, although acid back-diffusion was similar to controls. Epithelial pHi of CFTR DeltaF/DeltaF mice during luminal acid exposure was significantly higher than pHi in +/DeltaF, +/+, or C57BL/6 mice. Acid-related epithelial injury was markedly less in DeltaF/DeltaF mice in comparison with the other groups. CONCLUSIONS: Increased cellular buffering power of the epithelial cells of DeltaF/DeltaF mice likely protects against acidification and injury during acid exposure. We speculate that this protective mechanism partially underlies the perceived relative lack of peptic ulceration in patients affected by cystic fibrosis.

Hepatobiliary cystadenocarcinoma with cystadenoma elements of the gall bladder in an old man.

Hepatobiliary cystadenoma and cystadenocarcinoma of the gall bladder have rarely been reported. An 88-year-old Japanese man was admitted to our clinic because of hypochondralgia and jaundice. Imaging techniques revealed hemobilia and a multilocular cystic tumor in the fundus of the gall bladder, and cholecystectomy was performed. Grossly, the tumor (3.5 x 3 x 3 cm) was multicystic, containing seromucous fluid. The tumor was located in the fibromuscular layer and subserosa of the gall bladder fundus, and protruded into the serosal surface, not into gall bladder lumen. The mucosa appeared free of tumor involvement, and no gall stones were recognized. Microscopically, the tumor was located in the fibromuscular layer, subserosa and tiny focus of the mucosal surface. The tumor consisted of mucin-rich benign columnar cells, dysplastic mucous cells, malignant papillotubular cells and invasive carcinoma cells. Malignant and atypical tumor cells were located in the center of the tumor and in the tiny area of the mucosal surface, while benign tumor cells were located in the peripheral portions of the tumor and in the serosal side. Neither ovarian stroma-like mesenchymal stroma nor an oncocytic change in tumor cells was recognized. Non-tumorous gall bladder showed chronic cholecystitis. Immunohistochemically, benign and carcinoma cells were positive for cytokeratins, epithelial membrane antigen, CA19-9, MUC1, MUC5AC and MUC6, and carcinoma cells were also positive for carcinoembryonic antigen and p53 protein. The present case indicates that hepatobiliary cystadenocarcinoma without mesenchymal stroma may occur in the gall bladder of old men, and suggests that hepatobiliary cystadenoma without mesenchymal stroma may transform into hepatobiliary cystadenocarcinoma in the gall bladder.

Spontaneous rupture of peripancreatic lymph node with hepatocellular carcinoma metastasis: report of an autopsy case with massive peritoneal bleeding.

Hepatocellular carcinoma (HCC) has a tendency for fatal spontaneous rupture leading to massive hemorrhage. The majority of such ruptures of HCC occur in the liver, while a few previous studies showed that such HCC rupture developed at metastatic sites including the lung, pleura, spleen, and peritoneum. We here report a case of hepatitis C virus-related HCC with spontaneous rupture of a peripancreatic lymph node with HCC metastases. A 61-year-old Japanese man died of hepatic failure after therapy for cirrhosis and HCC for 6 years. At autopsy, the liver showed diffuse multinodular HCC in both lobes. Metastases were found in lumbar vertebral bones and abdominal lymph nodes of the hepatic hilar, peripancreatic and perigastric regions. One lymph node (4 cm in diameter) around the pancreatic head was found ruptured, and blood coagula (100 g) was present around the ruptured node. Pure blood of 2000 ml was noted in the peritoneal cavity. Cirrhosis was not recognized. Histologically, the liver tumors and metastases in the lumbar vertebral bones and abdominal lymph nodes were poorly-differentiated HCC of Edmondson's grade III. The ruptured lymph node was almost replaced by poorly-differentiated HCC, and the ruptured site showed hemorrhage, breakdown of the capsule, and ischemic changes. Non-tumorous liver showed chronic hepatitis C. The immediate cause of death was suggested to be circulatory insufficiency due to rupture of the lymph node and/or hepatic failure. The present case showed that abdominal lymph nodes with HCC metastases may rupture and cause severe hemorrhage in the peritoneal cavity, leading to death.

Significant role of ceramide pathway in experimental gastric ulcer formation in rats.

Ceramides have emerged as key participants in the signaling pathway of cytokines and apoptosis. We previously revealed that phorbol 12-myristate 13-acetate (PMA) induced experimental ulcers in rat gastric mucosa. In this study, we investigated the role of ceramide in ulcer formation and its relation to the activation of transcription factors and apoptosis. PMA was subserosally injected to rat glandular stomach. Fumonisin B1 (FB1), an inhibitor of ceramide synthase, was administered together with the PMA. The time course of ceramide content was quantified using thin layer chromatography and the number of apoptotic cells was determined by immunohistochemistry. The activation of transcription factor nuclear factor-kappaB (NF-kappaB) or activator protein-1 (AP-1) was evaluated using an electrophoretic mobility shift assay. The administration of FB1 attenuated PMA-induced gastric ulcer formation in a dose-dependent manner. Before the ulcers became obvious, the ceramide content (C18 and C24 ceramide) increased significantly in the gastric wall. The activation of NF-kappaB and AP-1 and an increase in the number of apoptotic cells were also observed. Both of these were significantly inhibited by the coadministration of FB1. However, NF-kappaB inhibitors attenuated gastric ulcer formation without affecting the ceramide content or the number of apoptotic cells. Ceramide formation in the stomach significantly contributes to PMA-induced tissue damage, possibly via the activation of transcription factors and an increase in apoptosis in the gastric mucosa. However, after the increase in ceramide levels, the NF-kappaB and apoptosis pathways may be separately involved in ulcer formation.

Nuclear factor-kappaB and TNF-alpha mediate gastric ulceration induced by phorbol myristate acetate.

Phorbol esters induce inflammation in rodents by activating protein kinase C. We determined whether nuclear factor-kappaB (NF-kappaB) and tumor necrosis factor-alpha (TNF-alpha) play role in the formation of gastric ulcer induced by phorbol-12-myristate-13-alphacetate (PMA) in rats. Subserosally injected PMA dose-dependently induced gastric mucosal ulcer. Activation of NF-kappaB in the gastric mucosa corresponding to the PMA injection sites was observed before the ulcers became obvious as assessed by an in situ fluorescence DNA binding assay and electrophoretic mobility shift assay. The NF-kappaB activation and subsequent ulcer formation were significantly inhibited by injection of pyrrolidine dithiocarbamate, proteasome inhibitor (MG132), or NF-kappaB decoy. Antibody against TNF-alpha significantly inhibited ulcer formation without attenuating NF-kappaB activation. These results suggest that both NF-kappaB activation followed by TNF-alpha release contribute to tissue damage in PMA-induced gastric ulcer formation.