Carbonic anhydrase in the alimentary tract. Roles of the different isozymes and salivary factors in the maintenance of optimal conditions in the gastrointestinal canal

Carbonic Anhydrases in Metazoan Model Organisms: Molecules, Mechanisms, and Physiology

During the past three decades, mice, zebrafish, fruit flies, and Caenorhabditis elegans have been the primary model organisms used for the study of various biological phenomena. These models have also been adopted and developed to investigate the physiological roles of carbonic anhydrases (CAs) and carbonic anhydrase-related proteins (CARPs). These proteins belong to eight CA families and are identified by Greek letters: α, β, γ, δ, ζ, η, θ, and ι. Studies using model organisms have focused on two CA families, α-CAs and β-CAs, which are expressed in both prokaryotic and eukaryotic organisms with species-specific distribution patterns and unique functions. This review covers the biological roles of CAs and CARPs in light of investigations performed in model organisms. Functional studies demonstrate that CAs are not only linked to the regulation of pH homeostasis, the classical role of CAs but also contribute to a plethora of previously undescribed functions.

Molecular cloning and characterization of secretory carbonic anhydrase VI in pufferfish (Takifugu rubripes)

Carbonic anhydrase VI (CA VI) has been characterized as a secretory isozyme in mammals. Our present study confirmed the occurrence of CA VI in pufferfish (Takifugu rubripes). In this study, genomic sequence information for the CA VI of pufferfish was used for molecular cloning. We cloned a 1821 bp cDNA sequence, which consisted of a complete coding sequence of 1623bp and a deduced amino acid sequence of 540 amino acids from the open reading frame. A BLAST search indicated that this protein exhibits 53%, 79%, and 67% identity with human, tilapia, and gar CA VI, respectively. It also shows 63%-77% identity with other fish CA VI-like sequences (zebrafish, Asian arowana, salmon, and large yellow croaker). Moreover, alignment of two or more sequences revealed that the protein sequence of pufferfish CA VI has 34%-37% identity with mammalian and fish CA II sequences. An NH₂-terminal signal peptide of 18 amino acids in length was predicted in the pufferfish CA VI sequence. Three potential N-linked glycosylation sites and two cysteine residues (Cys-28 and Cys-209) that are likely to form one disulfide bond were present in pufferfish CA VI. In silico and phylogenetic analyses revealed that pufferfish CA VI is an extracellular secretory protein. Active site analysis indicated that this protein is a low-activity CA isozymes due to a characteristic Val/Ile substitution at position 207. Homology modeling of puffer CA VI was performed using the crystal structure of human carbonic anhydrase XIV as a template structure, based on high similarity. Reverse transcription-polymerase chain reaction (PCR), quantitative PCR and in situ hybridization results revealed that, the pufferfish CA VI is highly expressed in liver tissue.

Carbonic anhydrase II: a novel biomarker for pseudomyxoma peritonei

Altered expression of carbonic anhydrase (CA) II is associated with human carcinogenesis. We analysed CA II protein expression in 89 patients with pseudomyxoma peritonei (PMP) and correlated its association against survival. We determined the expression of CA II by immunohistochemistry and then scored the staining results. The correlations of CA II expression with Peritoneal Cancer Index (PCI) and tumour grade were examined. The effect of CA II and tumour grade on survival was investigated. Positive CA II expression was found in 58 patients (65%) and absent in 31 patients (35%). High-grade (HG) morphology was associated with a loss of CA II expression (p = 0.048). The mean CA II immunostaining intensity score was 1.00 ± 1.1 (median 1, range 0-3) for HG morphology and 1.54 ± 1.1 (median 2, range 0-3) for low-grade (LG) morphology. The 5-year overall survival (OS) for those patients with CA II expression was 80% and 59% for those without (p < 0.001). The 5-year OS rates for those patients with HG morphology and positive CA II expression was 72% and 31% for those with negative CA II expression (p = 0.044). This study suggests that the expression of CA II acts as independent prognostic biomarker for survival in PMP.

Identification of in vivo Pellicle Constituents by Analysis of Serum Immune Responses

Human acquired enamel pellicle is composed of molecules that selectively adsorb from saliva onto tooth surfaces and provides a protective interface between the tooth enamel and the oral environment. To identify the micro-amounts of components present in pellicle, we immunized mice with in vivo-formed human acquired enamel pellicle and analyzed the serum immune responses. Selective reactivities of the serum (OD > 1.0 above background) against albumin, amylase, carbonic anhydrase II, sIgA, IgG, IgM, lactoferrin, lysozyme, proline-rich proteins, statherin, histatin 1, and mucous glycoprotein 1 were observed. We further confirmed the presence of proline-rich proteins, lactoferrin, lysozyme, and carbonic anhydrase II by probing in vivo pellicle with specific polyclonal anti-sera. The polyclonal antibody approach provided a powerful method for the identification of various pellicle proteins, including some which show mineral homeostasis or antimicrobial activity.

Altered gene expression in the lower respiratory tract of Car6 (-/-) mice

From birth, the respiratory tract mucosa is exposed to various chemical, physical, and microbiological stress factors. Efficient defense mechanisms and strictly regulated renewal systems in the mucosa are thus required. Carbonic anhydrase VI (CA VI) is the only secreted isoenzyme of the α-CA gene family. It is transported in high concentrations in saliva and milk into the alimentary tract where it contributes to optimal pH homeostasis. Earlier study of transcriptomic responses of Car6 (-/-) mice has shown changes in the response to oxidative stress and brown fat cell differentiation in the submandibular gland. It has been suggested that CA VI delivered to the mucosal surface of the bronchiolar epithelium is an essential factor in defense and renewal of the lining epithelium. In this study, the transcriptional effects of CA VI deficiency were investigated in both trachea and lung of Car6 (-/-) mice using a cDNA microarray analysis. Functional clustering of the results indicated significant changes of gene transcription in the lower airways. The altered biological processes included antigen transport by M-cells, potassium transport, muscle contraction, and thyroid hormone synthesis. Immunohistochemical staining confirmed the absence of CA VI in the submandibular gland of Car6 (-/-) mice. Immunostaining of the trachea and lung samples revealed no differences between the knockout and wild type groups nor were any morphological changes observed. The present findings can help us to recognize novel functions for CA VI-one of the major protein constituents of saliva and milk.

Synthesis of Schiff base derivatives of 4-(2-aminoethyl)-benzenesulfonamide with inhibitory activity against carbonic anhydrase isoforms I, II, IX and XII

Schiff base derivatives were obtained by reaction of 4-(2-aminoethyl)benzenesulfonamide with aromatic aldehydes. The corresponding secondary amine derivatives were also prepared by reduction of the imine compounds with NaBH4. These derivatives were investigated as inhibitors of four human carbonic anhydrase (CA, EC 4.2.1.1) isoforms, the cytosolic isozymes hCA I and II, as well as, the transmembrane, tumor-associated hCA IX and XII. Some of the newly synthesised compounds showed effective inhibitory activities against these CA isozymes. Many low nanomolar inhibitors were detected against all isoforms among the secondary amines whereas the Schiff bases were by far less active compared to the corresponding reduced derivatives among all investigated isoforms.

The role of carbonic anhydrase VI in bitter taste perception: evidence from the Car6⁻/⁻ mouse model

Background

Carbonic anhydrase VI (CA VI) is a secretory isozyme of the α-CA gene family. It is highly expressed in the salivary and mammary glands and secreted into saliva and milk. Although CA VI was first described as a gustatory protein, its exact functional roles have remained enigmatic. Interestingly, polymorphism of the CA6 gene was recently linked to bitter taste perception in humans. In this study, we compared the preference of Car6^−/− and wild-type mice for different taste modalities in an IntelliCage monitoring environment. Morphologies of taste buds, tongue papillae, and von Ebner’s glands were evaluated by light microscopy. Cell proliferation and rate of apoptosis in tongue specimens were examined by Ki67 immunostaining and fluorescent DNA fragmentation staining, respectively.

Results

The behavioral follow up of the mice in an IntelliCage system revealed that Car6^−/− mice preferred 3 μM quinine (bitter) solution, whereas wild type mice preferred water. When the quinine concentration increased, both groups preferentially selected water. Histological analysis, Ki67 immunostaining and detection of apoptosis did not reveal any significant changes between tongue specimens of the knockout and wild type mice.

Conclusions

Our knockout mouse model confirms that CA VI is involved in bitter taste perception. CA VI may be one of the factors which contribute to avoidance of bitter, potentially harmful, substances.

Safety of carbonic anhydrase inhibitors

INTRODUCTION

Carbonic anhydrase (CA) inhibitors have an impressive safety record despite the multiple functions that CA isozymes serve because they are not fully inhibited with most dosing. While reducing the targeted CA-dependent process sufficiently for disease control, residual activity and uncatalyzed rates in combination with compensations are adequate to avoid lethal consequences. Some drugs have in vitro selectivity differences against the 13 active isozymes, but none are convincingly selective in vivo or clinically. Efforts to synthesize selective inhibitors should result in safer drugs with fewer side effects.

AREAS COVERED

This review will focus on approved drugs with CA-inhibiting activity, whether used directly for this purpose or others. Side effects are discussed in relation to various organ systems and the disease being treated. Causes of side effects are considered, and strategies for symptom reduction are given.

EXPERT OPINION

Common side effects of paresthesias, dyspepsia, lassitude and fatigue in 30 - 40% of patients are generally tolerable or abate, but if not can be partially relieved by bicarbonate supplementation. The most important safety concerns are severe acidosis, respiratory failure and encephalopathy in patients with renal, pulmonary and hepatic disease where caution is critical, as is also the case in persons with sulfa drug allergies.

Membrane associated carbonic anhydrase IV (CA IV): a personal and historical perspective

Carbonic anhydrase IV is one of 12 active human isozymes and one of four expressed on the extracellular surfaces of certain endothelial and epithelial cells. It is unique in being attached to the plasma membrane by a glycosyl-phosphatiydyl-inositol (GPI) anchor rather than by a membrane-spanning domain. It is also uniquely resistant to high concentrations of sodium dodecyl sulfate (SDS), which allows purification from tissues by inhibitor affinity chromatography without contamination by other isozymes. This unique resistance to SDS and recovery following denaturation is explained by the two disulfide bonds. The 35-kDa human CA IV is a "high activity" isozyme in CO2 hydration activity, like CA II, and has higher activity than other isozymes in catalyzing the dehydration of HCO3 (-). Human CA IV is also unique in that it contains no oligosaccharide chains, where all other mammalian CA IVs are glycoproteins with one to several oligosaccharide side chains.Although CA IV has been shown to be active in mediating CO2 and HCO3 (-) transport in many important tissues like kidney and lung, and in isolated cells from brain and muscle, the gene for CA IV appears not to be essential. The CA IV knockout mouse produced by targeted mutagenesis, though slightly smaller and produced in lower than expected numbers, is viable and has no obvious mutant phenotype. Conversely, several dominant negative mutations in humans are associated with one form of reitinitis pigmentosa (RP-17), which we attribute to unfolded protein accumulation in the choreocapillaris, leading to apoptosis of cells in the overlying retina.

Synthesis and carbonic anhydrase inhibitory properties of novel cyclohexanonyl bromophenol derivatives

The Naturally occurring novel cyclohexanonyl bromophenol 2(R)-2-(2,3,6-tribromo-4,5-dihydroxybenzyl)cyclohexanone (4) was synthesized as a racemic compound. Cyclohexylphenyl methane derivatives (10-17) with Br, OMe, CO, and OH were also obtained. Inhibition of four human carbonic anhydrase (hCA, EC 4.2.1.1) isozymes I, II, IV, and VI, with compounds 2-4, 8, and 10-26 was investigated. These compounds were found to be promising carbonic anhydrase inhibitors and some of them showed interesting inhibitory activity. Some of the compounds investigated here showed effective hCA inhibitory activity, and might be used as leads for generating novel carbonic anhydrase inhibitors which are valuable drug candidates for the treatment of glaucoma, epilepsy, gastric and duodenal ulcers, neurological disorders, and osteoporosis.

In vitro inhibition of α-carbonic anhydrase isozymes by some phenolic compounds

Carbonic anhydrase inhibitors (CAIs) are a class of pharmaceuticals used as antiglaucoma agents, diuretics, antiepileptics, in the management of mountain sickness, gastric and duodenal ulcers, neurological disorders or osteoporosis. We report here the inhibitory capacities of some phenolic compounds against three human CA isozymes (hCA I, hCA II, and hCA VI) and the gill carbonic anhydrase of the teleost fish Dicentrarchus labrax (European seabass) (dCA). The isozymes showed quite diverse inhibition profiles with these compounds. These data may lead to design novel CAIs with a diverse inhibition mechanism compared to sulfonamide/sulfamate inhibitors.

Expression of hypoxic marker CA IX is regulated by site-specific DNA methylation and is associated with the histology of gastric cancer

The hypoxic marker carbonic anhydrase (CA) IX has been recognized as a tumor-associated protein and is essential for cancer development. However, because CA IX expression does not always correlate with hypoxia, its regulatory mechanism remains unclear. The objective of the present study was to clarify the role and regulation of CA IX expression in gastric cancer. The immunohistochemical expression of CA IX and hypoxia-inducible factor-1α was assessed in 77 patients with gastric cancer. A methylation-sensitive restriction enzyme method was used to quantify site-specific methylation at -74 bp in the CA9 promoter in tissue from patients with gastric cancer and in corresponding normal tissue. CA9 expression in cell lines was strongly dependent on methylation status but not hypoxic stimuli. In tissue from patients with gastric cancer, the quantity of methylation was significantly correlated with the protein expression (P = 0.003). Moreover, the methylation value was significantly lower in intestinal-type compared with diffuse-type cancer (P = 0.003). Compared with normal mucosa, intestinal-type cancer demonstrated significant hypomethylation, whereas diffuse-type cancer exhibited hypermethylation. In conclusion, expression of CA IX in gastric cancer is predominantly regulated by methylation of a single CpG rather than by hypoxia. Furthermore, epigenetic alterations in CA9 differ between the intestinal and diffuse types of gastric cancer.

Markers of bile duct tumors

Biliary tract carcinomas are relatively rare, representing less than 1% of cancers. However, their incidence has increased in Japan and in industrialized countries like the USA. Biliary tract tumors have a poor prognosis and a high mortality rate because they are usually detected late in the course of the disease; therapeutic treatment options are often limited and of minimal utility. Recent studies have shown the importance of serum and molecular markers in the diagnosis and follow up of biliary tract tumors. This review aims to introduce the main features of the most important serum and molecular markers of biliary tree tumors. Some considerable tumor markers are cancer antigen 125, carbohydrate antigen 19-9, carcinoembryonic antigen, chromogranin A, mucin 1, mucin 5, alpha-fetoprotein, claudins and cytokeratins.

In Vitro inhibition of human carbonic anhydrase I and II isozymes with natural phenolic compounds

Inhibition of two human cytosolic carbonic anhydrase (hCA, EC 4.2.1.1) isozymes I and II with some natural phenolic derivatives was investigated using the esterase assay with 4-nitrophenyl acetate as substrate. Resveratrol, catechin, silymarin, dobutamin, and curcumin showed K(I) values in the range of 4.47-9.47 mm for hCA I and of 2.86-7.44 μm against hCA II, respectively. These natural product phenols were generally competitive inhibitors with 4-nitrophenylacetate as substrate. Some natural phenols investigated here showed effective hCA II inhibitory effects, in the same range as the clinically used sulfonamide acetazolamide, and might be used as leads for generating enzyme inhibitors possibly targeting other CA isoforms that have not been yet assayed for their interactions with such agents.

Analysis of a shortened form of human carbonic anhydrase VII expressed in vitro compared to the full-length enzyme

Carbonic anhydrase (CA) enzymes are expressed in all organs of the mammalian body where they participate in important physiological functions. CA VII is a cytosolic isozyme which may be expressed as two forms according to the recent GenBank data. We designed a present study to express and characterize the human CA VII forms: full-length CA VII and short form (predicted to lack 56 residues from the N-terminus). Reverse transcriptase PCR analysis revealed mRNAs for both CA VII forms in the human brain. These different forms were expressed as recombinant proteins to investigate their biochemical properties. The full-length CA VII was used to raise a polyclonal antiserum in a rabbit, and the antiserum was then employed in western blot analyses and immunohistochemistry of mouse tissues. Data from mass spectrometry and comparative modeling showed that CA VII protein contains a single intramolecular disulfide bridge (Cys-56 to Cys-180) which is lacking in the short form. The computer model suggested distinctly different folding for the different forms. The more exposed structure and the absence of the disulfide bridge in the short form could make this protein more susceptible to degradation. In fact, this was realized in several protein purification efforts in which the short form readily degraded during the experimental procedures. From these results, we conclude that the full-length CA VII is a predominant active form in human brain and also in other tissues. In addition to the brain, CA VII is expressed in several other organs including the stomach, duodenum, colon, liver, and skeletal muscle. The distribution pattern suggests multiple functions for CA VII in different organs.

Carbonic anhydrase inhibitors. Inhibition of human erythrocyte isozymes I and II with a series of antioxidant phenols

The inhibition of two human cytosolic carbonic anhydrase (hCA, EC 4.2.1.1) isozymes I and II, with a series of phenol derivatives was investigated by using the esterase assay, with 4-nitrophenyl acetate as substrate. 2,6-Dimethylphenol, 2,6-diisopropylphenol (propofol), 2,6-di-t-butylphenol, butylated hydroxytoluene, butylated hydroxyanisole, vanillin, guaiacol, di(2,6-dimethylphenol), di(2,6-diisopropylphenol), di(2,6-di-t-butylphenol), and acetazolamide showed K(I) values in the range of 37.5-274.5 microM for hCA I and of 0.29-113.5 microM against hCA II, respectively. All these phenols were non-competitive inhibitors with 4-nitrophenylacetate as substrate. Some antioxidant phenol derivatives investigated here showed effective hCA II inhibitory effects, in the same range as the clinically used sulfonamide acetazolamide, and might be used as leads for generating enzyme inhibitors possibly targeting other CA isoforms which have not been yet assayed for their interactions with such agents.

In vitro inhibition of salicylic acid derivatives on human cytosolic carbonic anhydrase isozymes I and II

The inhibition of two human cytosolic carbonic anhydrase (hCA, EC 4.2.1.1) isozymes, hCA I and II, with a series of salicylic acid derivatives was investigated by using the esterase method with 4-nitrophenyl acetate as substrate. IC(50) values for sulfasalazine, diflunisal, 5-chlorosalicylic acid, dinitrosalicylic acid, 4-aminosalicylic acid, 4-sulfosalicylic acid, 5-sulfosalicylic acid, salicylic acid, acetylsalicylic acid (aspirin) and 3-metylsalicylic acid were of 3.04 microM, 3.38 microM, 4.07 microM, 7.64 microM, 0.13 mM, 0.29 mM, 0.42 mM, 0.56 mM, 2.71 mM and 3.07 mM for hCA I and of 4.49 microM, 2.70 microM, 0.72 microM, 2.80 microM, 0.75 mM, 0.72 mM, 0.29 mM, 0.68 mM, 1.16 mM and 4.70 mM for hCA II, respectively. Lineweaver-Burk plots were also used for the determination of the inhibition mechanism of these substituted phenols, most of which were noncompetitive inhibitors with this substrate. Some salicylic acid derivatives investigated here showed effective hCA I and II inhibitory activity, and might be used as leads for generating enzyme inhibitors eventually targeting other isoforms which have not been assayed yet for their interactions with such agents.

Annexin A4: A novel molecular marker for gastric cancer with Helicobacter pylori infection using proteomics approach

Helicobacter pylori was reported to be an important risk factor for the carcinogenesis of gastric cancer. Here, we used a proteomic approach to find differentially expressed proteins between the normal and tumor tissue of gastric cancer patients infected with H. pylori. In our results, we found annexin A4 was over-expressed in patients infected with H. pylori and was found in tumor cells, and over-expressed in gastric cancer SCM-1 cells after H. pylori infection. Ca(2+ ) can be induced by H. pylori and interact with annexin A4 Ca(2+) binding site to block the calmodulin-activated chloride conductance activation; therefore, it produces a new environment that benefits the malignant existence of H. pylori and raises the risk for gastric cancer. We also found interleuken-8 (IL-8) expression levels were increased in H. pylori infected SCM-1 cells. Combined with previous reports and our results, we summarize that the over-expression of annexin A4 in SCM-1 cells with H. pylori infection may subsequently induce IL-8 which can further cause tumor angiogenesis. In this paper, we show that annexin A4 is a potential novel molecular marker for gastric cancer with H. pylori infection, and our results may provide a new insight in the development of new anti-cancer drugs.

Expression of carbonic anhydrases IX and XII during mouse embryonic development

BACKGROUND

Of the thirteen active carbonic anhydrase (CA) isozymes, CA IX and XII have been linked to carcinogenesis. It has been suggested that these membrane-bound CAs participate in cancer cell invasion, which is facilitated by an acidic tumor cell environment. Since active cell migration is a characteristic feature of embryonic development, we set out to explore whether these isozymes are expressed in mouse embryos of different ages. The studies were focused on organogenesis stage.

RESULTS

Immunohistochemistry demonstrated that both CA IX and XII are present in several tissues of the developing mouse embryo during organogenesis. Staining for CA IX revealed a relatively wide distribution pattern with moderate signals in the brain, lung, pancreas and liver and weak signals in the kidney and stomach. The expression pattern of CA XII in the embryonic tissues was also relatively broad, although the intensity of immunostaining was weak in most tissues. The CA XII-positive tissues included the brain, where the most prominent staining was seen in the choroid plexus, and the stomach, pancreas, liver and kidney.

CONCLUSION

Membrane-bound CA isozymes IX and XII are expressed in various tissues during mouse organogenesis. These enzymes may regulate ion and pH homeostasis within the developing embryo.

Laryngeal epithelial defenses against laryngopharyngeal reflux: investigations of E-cadherin, carbonic anhydrase isoenzyme III, and pepsin

OBJECTIVES

This is the third annual report of an international research network studying the cellular impact of laryngopharyngeal reflux (LPR) on laryngeal epithelium. The objective of this study was to investigate the presence of E-cadherin (epithelial cadherin; the intercellular junctional complex protein) in relation to the presence of (intracellular) pepsin and carbonic anhydrase isoenzyme III (CAIII).

METHODS

Fifty-four laryngeal biopsy specimens from 18 LPR patients were studied by immunohistochemistry and Western blotting for pepsin, E-cadherin, and CAIII. These data were compared to those from normal control subjects analyzed in another research study.

RESULTS

Intracellular pepsin was detected in LPR patients, but not in controls. E-cadherin expression was reduced in patients with LPR. Carbonic anhydrase III expression was not found in the vocal fold or in the majority of samples taken from the ventricle of LPR patients and was inversely associated with E-cadherin membranous expression.

CONCLUSIONS

The findings of depleted E-cadherin and CAIII and the presence of pepsin appear to correlate with LPR. The reduced protective response indicated by the reduced expression of CAIII may play an important role in the disruption of the intercellular barrier associated with the down-regulation of E-cadherin.

Gastric pit cell hyperplasia and glandular atrophy in carbonic anhydrase IX knockout mice: studies on two strains C57/BL6 and BALB/C

Carbonic anhydrase (CA) isoenzyme IX is a hypoxia-inducible enzyme, which is expressed in the human and rodent gastrointestinal tract and overexpressed in several different tumors. Functionally, it has probably an effect on proliferation and differentiation of gastrointestinal epithelial cells. It may also participate in gastric morphogenesis, since a recent study has shown gastric pit cell hyperplasia and glandular atrophy in CA IX-knockout mice. However, it is not known whether CA IX produces morphological changes in the gastric mucosa, which can turn into a dysplasia or malignancy in the presence of some carcinogenic factors. High-salt diet is considered such a factor which has been shown to modulate Helicobacter pylori-associated carcinogenesis. We produced two strains of CA IX-knockout mice, C57/BL6 and BALB/c, and the mice ate either standard or high-salt feed for 20 weeks. Stomach samples were collected from 40 Car 9(-/-) knockout mice and 37 wildtype littermates, and the tissue sections were examined for histology. CA IX-deficiency caused gastric pit cell hyperplasia and glandular atrophy in both BALB/c and C57/BL6 strains. Excess dietary salt had no significant effect on the severity of pit cell hyperplasia. No dysplasia was found in any of the groups. In C57/BL6 mice, CA IX-deficiency was associated with gastric submucosal inflammation. The results indicate that CA IX-deficiency provides a useful model to study the mechanisms of gastric morphogenesis and epithelial integrity. Further studies are needed to see whether CA IX has a role in the regulation of immune response. The findings suggest that although CA IX-deficiency is not a tumor-promoting factor per se, it induces glandular atrophy in the body mucosa, a lesion which is considered to be a preneoplastic alteration in the stomach.

Carbonic anhydrase gene expression in CA II-deficient (Car2-/-) and CA IX-deficient (Car9-/-) mice

Using real-time PCR and immunohistochemistry, we have examined the expression of carbonic anhydrase isozymes (CA) I, II, III, IV, IX, XII, XIII and XIV in the brain, kidney, stomach and colon of the wild-type, CA II-deficient (Car2-/-), and CA IX deficient (Car9-/-) mice. The expression of Car4, Car12, Car13 and Car14 mRNAs did not show any significant deviations between the three groups of mice, whereas both groups of CA deficient mice showed decreased expression levels of Car1 in the colon and Car3 in the kidney. The Car2 mRNA level was greatly reduced but not completely abolished in all four tissues from the Car2-/- mice in which no CA II protein was expressed. Sequencing the Car2 cDNA isolated from C57BL6 Car2-/- mice revealed two nucleotide differences from the wild-type C57BL6 mice. One is a silent polymorphism found in Car2 mRNA from wild-type DBA mice, which is the strain that provided the original mutagenized chromosome. The second change is a mutation that causes prematurely terminated translation at codon 155 (Gln155X). Car9 mRNA and CA IX protein expression levels were up-regulated about 2.5- and 3.6-fold, respectively, in the stomach of the Car2-/- mice. These results suggest that the loss of function of cytosolic CA II in the stomach of Car2-/- mice leads to up-regulation of an extracellular CA, namely CA IX, which is expressed on the cell surface of the gastric epithelium.

Expression of a novel carbonic anhydrase, CA XIII, in normal and neoplastic colorectal mucosa

Background

Carbonic anhydrase (CA) isozymes may have an important role in cancer development. Some isozymes control pH homeostasis in tumors that appears to modulate the behaviour of cancer cells. CA XIII is the newest member of the CA gene family. It is a cytosolic isozyme which is expressed in a number of normal tissues. The present study was designed to investigate CA XIII expression in prospectively collected colorectal tumor samples.

Methods

Both neoplastic and normal tissue specimens were obtained from the same patients. The analyses were performed using CA XIII-specific antibodies and an immunohistochemical staining method. For comparison, the tissue sections were immunostained for other cytosolic isozymes, CA I and II.

Results

The results indicated that the expression of CA XIII is down-regulated in tumor cells compared to the normal tissue. The lowest signal was detected in carcinoma samples. This pattern of expression was quite parallel for CA I and II.

Conclusion

The down-regulation of cytosolic CA I, II and XIII in colorectal cancer may result from reduced levels of a common transcription factor or loss of closely linked CA1, CA2 and CA13 alleles on chromosome 8. Their possible role as tumor suppressors should be further evaluated.

Carbonic anhydrases in normal gastrointestinal tract and gastrointestinal tumours

Carbonic anhydrases (CAs) catalyse the hydration of CO₂ to bicarbonate at physiological pH. This chemical interconversion is crucial since HCO₃^- is the substrate for several biosynthetic reactions. This review is focused on the distribution and role of CA isoenzymes in both normal and pathological gastrointestinal (GI) tract tissues. It has been known for many years that CAs are widely present in the GI tract and play important roles in several physiological functions such as production of saliva, gastric acid, bile, and pancreatic juice as well as in absorption of salt and water in intestine. New information suggests that these enzymes participate in several processes that were not envisioned earlier. Especially, the recent reports on plasma membrane-bound isoenzymes IX and XII have raised considerable interest since they were reported to participate in cancer invasion and spread. They are induced by tumour hypoxia and may also play a role in von Hippel-Lindau (VHL)-mediated carcinogenesis.

Localization, morphology and function of the mitochondria-rich cells in relation to transepithelial Na(+)-transport in chicken lower intestine (coprodeum)

The correlation between morphology of the mitochondria-rich cells (MR cells) in chicken lower intestine, coprodeum, and dietary sodium levels, has been investigated, using hens with differing dietary intake of NaCl and plasma aldosterone levels. Additionally, the function of the MR cells was evaluated in relation to proton secretion/exchange. Epithelium from the coprodeum was examined by optical, transmission and scanning electron microscopy, and Na(+)-transport across the coprodeal epithelium was measured electrophysiologically in Ussing-chambers. To investigate the function of MR cells, lectin-, enzyme- and immunohistochemistry methods were used. The MR cells were generally located in the epithelium on the upper parts of the sides of mucosal folds. Long microvilli, high but variable toluidine blue affinity/electrondensity and numerous mitochondria were the main features distinguishing them from the surrounding epithelial cells. Two main MR cell types were observed, differing in microvillous morphology, diameter and toluidine blue affinity/electrondensity. This probably reflected differences in maturity and activity. The MR cells expressed a positive carbonic anhydrase reaction and a proton exchange similar to the absorptive intestinal epithelial cells, but exhibited no specific demonstrable proton secretion. A close correlation between the ultrastructure of the MR-cells, dietary sodium levels, plasma aldosterone and transepithelial Na-transport was observed.

Transmembrane carbonic anhydrase isozymes IX and XII in the female mouse reproductive organs

BACKGROUND

Carbonic anhydrase (CA) classically catalyses the reversible hydration of dissolved CO2 to form bicarbonate ions and protons. The twelve active CA isozymes are thought to regulate a variety of cellular functions including several processes in the reproductive systems.

METHODS

The present study was designed to investigate the expression of transmembrane CAs, CA IX and XII, in the mouse uterus, ovary and placenta. The expression of CA IX and XII was examined by immunoperoxidase staining method and western blotting. CA II and XIII served as positive controls since they are known to be present in the mouse reproductive tract.

RESULTS

The data of our study indicated that CA XII is expressed in the mouse endometrium. Only very faint signal was observed in the corpus luteum of the ovary and the placenta remained mainly negative. CA IX showed weak reaction in the endometrial epithelium, while it was completely absent in the ovary and placenta.

CONCLUSION

The conservation of CA XII expression in both mouse and human endometrium suggests a role for this isozyme in reproductive physiology.

Mice with a targeted disruption of the AE2 Cl-/HCO3- exchanger are achlorhydric

The AE2 Cl-/HCO3- exchanger is expressed in numerous cell types, including epithelial cells of the kidney, respiratory tract, and alimentary tract. In gastric epithelia, AE2 is particularly abundant in parietal cells, where it may be the predominant mechanism for HCO3- efflux and Cl- influx across the basolateral membrane that is needed for acid secretion. To investigate the hypothesis that AE2 is critical for parietal cell function and to assess its importance in other tissues, homozygous null mutant (AE2(-/-)) mice were prepared by targeted disruption of the AE2 (Slc4a2) gene. AE2(-/-) mice were emaciated, edentulous (toothless), and exhibited severe growth retardation, and most of them died around the time of weaning. AE2(-/-) mice exhibited achlorhydria, and histological studies revealed abnormalities of the gastric epithelium, including moderate dilation of the gastric gland lumens and a reduction in the number of parietal cells. There was little evidence, however, that parietal cell viability was impaired. Ultrastructural analysis of AE2(-/-) gastric mucosa revealed abnormal parietal cell structure, with severely impaired development of secretory canaliculi and few tubulovesicles but normal apical microvilli. These results demonstrate that AE2 is essential for gastric acid secretion and for normal development of secretory canalicular and tubulovesicular membranes in mouse parietal cells.

Expression of hypoxia-inducible, membrane-bound carbonic anhydrase isozyme XII in mouse tissues

Carbonic anhydrase (CA) XII is a membrane-associated enzyme that has been demonstrated to be normally expressed in some human tissues, to be upregulated in some cancers, and to be a hypoxia-inducible gene product. In mouse, CA XII has been recently localized in the kidney. In the present study, we investigated CA XII gene and protein expression in other mouse tissues, with the kidney serving as a positive control for the reagents. The expression of CA XII mRNA was examined using polymerase chain reaction (PCR) amplification of commercial cDNAs produced from selected mouse tissues. A strong positive signal for CA XII mRNA was detected in the kidney, and weak signals were obtained in the testis and lung. Heart, spleen, liver, and skeletal muscle were negative. Immunohistochemical staining was performed using a mouse CA XII-specific antibody and biotin-streptavidin complex method. The results showed high expression of CA XII in the kidney, as expected. It was also highly expressed in the surface epithelial cells of the colon, whereas it was absent in the stomach, proximal small intestine, pancreas, liver, heart, and skeletal muscle. The maturing sperm cells showed a weak staining in a pattern that most probably indicates expression in the developing acrosomal membrane. The high expression in the kidney and colon suggests a role for CA XII in the maintenance of body ion and pH homeostasis in the mouse. However, the present findings demonstrated that CA XII has a very limited distribution in mouse tissues outside these two organs.

Characterization of CA XIII, a novel member of the carbonic anhydrase isozyme family

The carbonic anhydrase (CA) gene family has been reported to consist of at least 11 enzymatically active members and a few inactive homologous proteins. Recent analyses of human and mouse databases provided evidence that human and mouse genomes contain genes for still another novel CA isozyme hereby named CA XIII. In the present study, we modeled the structure of human CA XIII. This model revealed a globular molecule with high structural similarity to cytosolic isozymes, CA I, II, and III. Recombinant mouse CA XIII showed catalytic activity similar to those of mitochondrial CA V and cytosolic CA I, with k(cat)/K(m) of 4.3 x 10(7) m(-1) s(-1), and k(cat) of 8.3 x 10(4) s(-1). It is very susceptible to inhibition by sulfonamide and anionic inhibitors, with inhibition constants of 17 nm for acetazolamide, a clinically used sulfonamide, and of 0.25 microm, for cyanate, respectively. Using panels of cDNAs we evaluated human and mouse CA13 gene expression in a number of different tissues. In human tissues, positive signals were identified in the thymus, small intestine, spleen, prostate, ovary, colon, and testis. In mouse, positive tissues included the spleen, lung, kidney, heart, brain, skeletal muscle, and testis. We also investigated the cellular and subcellular localization of CA XIII in human and mouse tissues using an antibody raised against a polypeptide of 14 amino acids common for both human and mouse orthologues. Immunohistochemical staining showed a unique and widespread distribution pattern for CA XIII compared with the other cytosolic CA isozymes. In conclusion, the predicted amino acid sequence, structural model, distribution, and activity data suggest that CA XIII represents a novel enzyme, which may play important physiological roles in several organs.

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

This is the second annual report of an international collaborative research group that is examining the cellular impact of laryngopharyngeal reflux (LPR) on laryngeal epithelium. The results of clinical and experimental studies are presented. Carbonic anhydrase (CA), E-cadherin, and MUC gene expression were analyzed in patients with LPR, in controls, and in an in vitro model. In patients with LPR, we found decreased levels of CAIII in vocal fold epithelium and increased levels in posterior commissure epithelium. The experimental studies confirm that laryngeal CAIII is depleted in response to reflux. Also, cell damage does occur well above pH 4.0. In addition, E-cadherin (transmembrane cell surface molecules, which have a key function in epithelial cell adhesion) was not present in 37% of the LPR laryngeal specimens. In conclusion, the laryngeal epithelium lacks defenses comparable to those in esophageal epithelium, and these differences may contribute to the increased susceptibility of laryngeal epithelium to reflux-related injury.

Gastric hyperplasia in mice with targeted disruption of the carbonic anhydrase gene Car9

BACKGROUND & AIMS

Carbonic anhydrase (CA) IX is a highly active enzyme with adhesion capacity that is functionally implicated in acid-base balance and intercellular communication. It is normally present in basolateral membranes of gastrointestinal epithelial cells and ectopically expressed in various carcinomas. To show its physiologic relevance, we have cloned the Car9 gene and generated CA IX-deficient mice.

METHODS

The mice with null mutation of the Car9 gene were obtained by targeted gene disruption. Tissue architecture and expression of markers were determined by histochemical and immunohistochemical techniques.

RESULTS

Mice homozygous for the mutation developed gastric hyperplasia of the glandular epithelium with numerous cysts. The first changes were observed in the newborn animals, and the hyperplasia became prominent at the end of gastric morphogenesis in 4-week-old mice. Loss of CA IX led to overproduction of mucus-secreting pit cells and depletion of pepsinogen-positive chief cells. The proportion of H(+)/K(+)-adenosine triphosphatase-positive parietal cells significantly decreased, but their absolute number was not reduced. Correspondingly, CA IX-deficient mice had normal gastric pH, acid secretion, and serum gastrin levels.

CONCLUSIONS

Phenotypic consequences of the Car9 null mutation show the important role of CA IX in morphogenesis and homeostasis of the glandular gastric epithelium via the control of cell proliferation and differentiation.

Comparison of oesophageal and gastric air tonometry in patients with circulatory failure

BACKGROUND

Gastric PCO2 measured by balloon tonometry can estimate the adequacy of splanchnic perfusion. However, enteral feeding and gastric content can interfere with gastric PCO2 assessment. Tonometry in other sites of the body could avoid these problems. We therefore tested the hypothesis that oesophageal air tonometry would give results similar to gastric tonometry.

METHODS

We studied 20 consecutive patients (mean age 68 (SD 9) [range 49-81] yr, 18 males, SAPS II score 55 (SD 18), ICU mortality 55%) with circulatory disorders during mechanical ventilation in the intensive care unit. Tonometer probes were placed via the nose, one into the stomach and the other in the oesophagus. PCO2 was measured with two automated gas analysers, at admission and 30 min, 1, 2, 3, 32, 40, and 48 h thereafter.

RESULTS

One hundred and forty-eight paired measurements were obtained. Gastric PCO2 was greater than oesophageal PCO2 on admission (7.19 (1.43) vs 5.89 (0.73) kPa, P < 0.01) and subsequently. Differences between the measures correlated (r = 0.67) with the mean absolute value, indicating that overestimation increased as gastric PCO2 increased.

CONCLUSIONS

Oesophageal PCO2 is less than gastric PCO2, and the difference is greater when gastric PCO2 levels are greater. Air tonometry may not measure regional PCO2 levels in the oesophagus satisfactorily. Other methods and sites for carbon dioxide tonometry should be examined.

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.

Transmembrane carbonic anhydrase, MN/CA IX, is a potential biomarker for biliary tumours

BACKGROUND/AIMS

Carbonic anhydrase isoenzyme IX (MN/CA IX) is a transmembrane protein with a suggested function in maintaining the acid-base balance and intercellular communication. Previous studies have demonstrated that MN/CA IX is expressed in the basolateral plasma membrane of normal biliary epithelial cells, but not in hepatocytes. This study was designed to examine the expression of MN/CA IX in hepatobiliary neoplasms and to elucidate its value as a marker for biliary differentiation.

METHODS

Fifty-seven hepatobiliary lesions were immunostained for MN/CA IX using biotin-streptavidin complex method. Twenty samples containing normal biliary epithelium and five containing normal liver tissue were used as controls.

RESULTS

In the biliary epithelial tumours, immunostaining for MN/CA IX was mainly localized at the basolateral surface of the epithelial cells, like in normal mucosa. All non-invasive dysplastic lesions and 57% of invasive lesions of gall-bladder expressed MN/CA IX. In liver, 78% of cholangiocellular malignant lesions showed a positive reaction for MN/CA IX, whereas only 33% of hepatocellular carcinomas showed a weak immunoreaction.

CONCLUSIONS

Our results suggest that abnormal expression of MN/CA IX may be linked to malignant transformation of hepatobiliary cells. In addition, it seems to be a promising marker for biliary differentiation in hepatobiliary neoplasms.

Proteome study of colorectal carcinogenesis

Development of cancer is a complex process involving multiple changes in gene expression. To unravel these alterations, a proteome approach aimed at the identification of qualitative and quantitative changes in protein composition, including their post-translational modifications, attracts great attention. Our study was focused on the identification of proteins whose amount is altered in the course of malignant transformation of colon mucosa. Proteins extracted from tissue specimens or cell lysates were separated by two-dimensional gel electrophoresis (2-DE). Comparative analyses of 2-DE protein patterns were done using computerized image analysis. Selected proteins exhibiting statistically significant abundance alterations comparing healthy and diseased tissues were identified by mass spectrometry. Globally, we have found 57 proteins that exhibited either a significant decrease or increase in amount in pathological tissues, and 18 of these were annotated by mass spectrometry. The alterations in the expression of nine proteins were common for both precancerous and neoplastic tissues suggesting their role in colon tumorigenesis. The epithelial origin of all identified spots was checked in two cell lines Caco-2 and DLD-1 originating from well-differentiated and poorly differentiated colon carcinoma, respectively.

Expression of membrane-associated carbonic anhydrase XIV on neurons and axons in mouse and human brain

Although long suspected from histochemical evidence for carbonic anhydrase (CA) activity on neurons and observations that CA inhibitors enhance the extracellular alkaline shifts associated with synaptic transmission, an extracellular CA in brain had not been identified. A candidate for this CA was suggested by the recent discovery of membrane CA (CA XIV) whose mRNA is expressed in mouse and human brain and in several other tissues. For immunolocalization of CA XIV in mouse and human brain, we developed two antibodies, one against a secretory form of enzymatically active recombinant mouse CA XIV, and one against a synthetic peptide corresponding to the 24 C-terminal amino acids in the human enzyme. Immunostaining for CA XIV was found on neuronal membranes and axons in both mouse and human brain. The highest expression was seen on large neuronal bodies and axons in the anterolateral part of pons and medulla oblongata. Other CA XIV-positive sites included the hippocampus, corpus callosum, cerebellar white matter and peduncles, pyramidal tract, and choroid plexus. Mouse brain also showed a positive reaction in the molecular layer of the cerebral cortex and granular cellular layer of the cerebellum. These observations make CA XIV a likely candidate for the extracellular CA postulated to have an important role in modulating excitatory synaptic transmission in brain.

Specialised cell types in the chorioallantoic membrane express carbonic anhydrase during chick embryogenesis

The expression of carbonic anhydrase in the chorioallantoic membrane (CAM) of the chick embryo was investigated by means of the histochemical localisation of the enzyme catalytic sites and the immunohistochemical identification of its isoenzymatic forms. The results show that carbonic anhydrase is developmentally expressed in a subset of cells both in the ectodermal and the endodermal epithelium. The distribution patterns from both methodological approaches indicated that carbonic anhydrase is a marker of the villus cavity cells and the mitochondria-rich cells in the ectodermal and the endodermal epithelium, respectively. Such a cell-specific pattern of the enzyme expression provides a further contribution to characterising the heterogeneous cell population of the chick CAM and supports specific functional involvement for the distinct cell types in CAM-mediated processes, such as calcium transport, maintenance of acid-base balance and water and electrolyte reabsorption, during chick embryogenesis.