Effect of bile salts on carbonic anhydrase from rat and human gastric mucosa

Transcriptome Profiling of Placenta through Pregnancy Reveals Dysregulation of Bile Acids Transport and Detoxification Function

Placenta performs the function of several adult organs for the fetus during intrauterine life. Because of the dramatic physiological and metabolic changes during pregnancy and the strong association between maternal metabolism and placental function, the possibility that variation in gene expression patterns during pregnancy might be linked to fetal health warrants investigation. Here, next-generation RNA sequencing was used to investigate the expression profile, including mRNAs and long non-coding RNAs (lncRNAs) of placentas on day 60 of gestation (G60), day 90 of gestation (G90), and on the farrowing day (L0) in pregnant swine. Bioinformatics analysis of differentially expressed mRNAs and lncRNAs consistently showed dysregulation of bile acids transport and detoxification as pregnancy progress. We found the differentially expressed mRNAs, particularly bile salt export pump (ABCB11), organic anion-transporting polypeptide 1A2 (OATP1A2), carbonic anhydrase II (CA2), Na⁺-HCO₃⁻ cotransporter (NBC1), and hydroxysteroid sulfotransferases (SULT2A1) play an important role in bile acids transport and sulfation in placentas during pregnancy. We also found the potential regulation role of ALDBSSCG0000000220 and XLOC_1301271 on placental SULT2A1. These findings have uncovered a previously unclear function and its genetic basis for bile acids metabolism in developing placentas and have important implications for exploring the potential physiological and pathological pathway to improve fetal outcomes.

Structural elucidation of the hormonal inhibition mechanism of the bile acid cholate on human carbonic anhydrase II

The carbonic anhydrases (CAs) are a family of mostly zinc metalloenzymes that catalyze the reversible hydration/dehydration of CO2 into bicarbonate and a proton. Human isoform CA II (HCA II) is abundant in the surface epithelial cells of the gastric mucosa, where it serves an important role in cytoprotection through bicarbonate secretion. Physiological inhibition of HCA II via the bile acids contributes to mucosal injury in ulcerogenic conditions. This study details the weak biophysical interactions associated with the binding of a primary bile acid, cholate, to HCA II. The X-ray crystallographic structure determined to 1.54 Å resolution revealed that cholate does not make any direct hydrogen-bond interactions with HCA II, but instead reconfigures the well ordered water network within the active site to promote indirect binding to the enzyme. Structural knowledge of the binding interactions of this nonsulfur-containing inhibitor with HCA II could provide the template design for high-affinity, isoform-specific therapeutic agents for a variety of diseases/pathological states, including cancer, glaucoma, epilepsy and osteoporosis.

Cell biology of laryngeal epithelial defenses in health and disease: preliminary studies

Esophageal epithelium has intrinsic antireflux defenses, including carbonic anhydrases (CAs I to IV) that appear to be protective against gastric reflux. This study aimed to investigate the expression and distribution of CA isoenzymes in laryngeal epithelium. Laryngeal biopsy specimens collected from the vocal fold and interarytenoid regions were analyzed by Western blotting and immunofluorescence. Carbonic anhydrases I and II were expressed by the majority of samples analyzed. In contrast, CA III was differentially expressed in the interarytenoid samples and was not detected in any vocal fold samples. The expression of CA III was increased in esophagitis as compared to normal esophageal tissue. Carbonic anhydrase I and III isoenzymes were distributed cytoplasmically in the basal and lower prickle cell layers. The laryngeal epithelium expresses some CA isoenzymes and has the potential to protect itself against laryngopharyngeal reflux. Laryngeal tissue may be more sensitive to injury due to reflux damage than the esophageal mucosa because of different responses of CA isoenzymes.

The distribution of carbonic anhydrase II in human, pig and rat oesophageal epithelium

Carbonic anhydrase II (CA II) is present in human oesophageal epithelial cells and probably involved in protecting the mucosa against acidic gastric refluxate. If this is the case, then it is likely that the enzyme will be more concentrated at or near the gastro-oesophageal junction. To answer this question, and determine whether CA II is present and similarly distributed in other species, we also examined the oesophageal epithelium of the rat and pig. In the rat, CA II was largely absent from the oesophageal epithelium, but present in the stratified squamous epithelium of the gastric forestomach as an approximately 2 mm-long collar around the entrance to the corpus, a site that roughly corresponds to the gastro-oesophageal junction in other animals. The enzyme was present mainly in basal and prickle cells. In upper and middle pig oesophagus, CA II was largely confined to basal cells and isolated groups of stratified superficial prickle cells. CA II-containing epithelial cells were highly concentrated in the thickened epithelium at the gastro-oesophageal junction (about four-times thicker than upper or middle). Reactive cells were present throughout the depth of the epithelium, but noticeably more concentrated in the basal and superficial prickle cell layers. CA II was also prominent in the most superficial cell layers in islands of the oesophageal mucosa within the gastric cardia. In man, CA II was confined largely to the basal half of the epithelium in the upper and middle regions of oesophagus. The distribution of CA II at the gastro-oesophageal junction took different forms. In general, there were more CA II-reactive cells at or closer to the lumen. The superficial prickle cell layers tended to exhibit more CA II than the deeper layers, with basal and epibasal cells containing little or no enzyme. In other regions of the same specimens, CA II-containing cells were present from the basal to the most luminal layers. If CA II in oesophageal epithelial cells in the region of the gastro-oesophageal junction (or in the case of the rat the forestomach/corpus junction) is important in the defence against refluxate, then it is in a vulnerable site, since bile salts are potent inhibitors of the enzyme. The action of bile salts on CA II may be an important factor in the initiation of oesophageal disease.

Scintigraphic assessment of interdigestive duodenogastric reflux in humans: distinguishing between duodenal and biliary reflux material

BACKGROUND

Late duodenal phase III is characterized by retroperistalsis. The physiologic function of this phenomenon is unknown. Our aim was to study the relationship between duodenal motility and the transport of duodenal contents from the biliary tract and the duodenum by using a double-isotope technique.

METHODS

Manometric analysis of the direction of interdigestive duodenal pressure waves was performed in 12 volunteers. Duodenal marker was infused directly into the proximal duodenum, and bile marker was infused intravenously for 2 h. Radionuclide activity was examined for regions corresponding to the stomach, gallbladder, and duodenum.

RESULTS

In phase II, antegrade pressure waves dominated with propulsion of both markers to the jejunum. Retroperistalsis occurred in 90% of the activity fronts and was always (100%) followed by retropulsion of duodenal marker to the stomach. A clear-cut reflux of bile marker was seen in only 17% of the activity fronts. The incidence rate of duodenogastric reflux was highest in phase III (P=0.008) compared with phase II with an infrequent (P=0.002) admixture of bile. Bile marker contents increased abruptly in the gallbladder during phase III.

CONCLUSIONS

Late phase III acts as a retroperistaltic pump, retropelling duodenal contents to the stomach. In this physiologic duodenogastric reflux. bile is avoided by deviation to the gallbladder, probably by a phase lll-associated occlusion of the sphincter Oddi.

Fiberoptic technique for 24-hour bile reflux monitoring. Standards and normal values for gastric monitoring

Physiologic bile reflux was assessed in 27 in vivo test with healthy volunteers to define a standardized protocol and normal values for 24-hour enterogastric bile reflux monitoring (protocol with supine, upright, and meal phases and a free diet avoiding alcohol, smoking, and coffee, evaluation with different thresholds of absorbance units: 0.14, 0.25). In vitro tests with bile-sodium solutions demonstrated a linear dependence of absorbance for bilirubin up to 600 mumol/liter (range of the fiberoptic device: 0.0-1.0). Fluids and food might interfere with absorbances below 0.25 (exception: coffee). In vivo bile often remains in the stomach for more than 1 hr; these events were defined as reflux episodes. The upper limits for physiologic bile reflux are a percentage of total time of bile reflux of 28.2% and an average absorbance during a reflux episode of 0.62 (95th percentile with threshold 0.25). Comparing bile with pH monitoring (absorbance > 0.25 and/or pH > 4), an increase of bilirubin was found most frequently with constant pH (45%) or an increase of pH with constant bilirubin (36%). The hypothesis was drawn that bile and duodenal or pancreatic secretions may separately contribute to duodenogastric reflux.