Ammonia-induced apoptosis is accelerated at higher pH in gastric surface mucous cells

Identification of acid phosphatase (ShACP) from the freshwater crab Sinopotamon henanense and its expression pattern changes in response to cadmium

Acid phosphatase(ACP) is an important immune enzyme in crustacean humoral immunity. At present, the research on ACP mainly focuses on the biochemical properties of the enzyme, while few studies on gene expression. In this study, ShACP was cloned and the effect of cadmium stress on the expression and function of ShACP in the freshwater crab Sinopotamon henanense was studied. Analysis of the ShACP sequence and tissue distribution results showed that the cDNA sequence of ShACP was 1629 bp, including 48 bp 5' untranslated region, 1209 bp open reading frame region, and 372 bp 3' untranslated region, encoding 402 amino acids. ShACP contained multiple phosphorylation sites and mainly played a role in the hemolymph. Under low-concentration cadmium stress, the body improved immunity by enhancing the expression of ShACP, while high-concentration cadmium stress inhibited the expression of ShACP. ShACP can promote the phagocytosis of hemocytes, while cadmium stress reduced the phagocytosis of hemocytes. This study provides a theoretical basis for further research on the immune system of crabs and is of great significance for the study of crustacean immune responses under heavy metal stress.

Depletion of chop suppresses procedural apoptosis and enhances innate immunity in loach Misgurnus anguillicaudatus under ammonia nitrogen stress

Ammonia nitrogen is highly toxic to fish, and it can easily cause fish poisoning or even high mortality. So far, many studies have been conducted on the damages to fish under ammonia nitrogen stress. However, there are few studies of ammonia tolerance improvement in fish. In this study, the effects of ammonia nitrogen exposure on apoptosis, endoplasmic reticulum (ER) stress, and immune cells in loach Misgurnus anguillicaudatus were investigated. Loaches (60 d post fertilization) were exposed to different concentrations of NH4Cl, and their survival rates were examined every 6 h. The results showed that high-concentration and long-time NH4Cl exposure (20 mM + 18 h; 15 mM + 36 h) induced apoptosis and gill tissue damages, finally causing a decline in survival. chop plays an important role in ER stress-induced apoptosis, and thus we constructed a model of chop-depleted loach by using CRISPR/Cas9 technology to investigate its response to ammonia nitrogen stress. The results showed that ammonia nitrogen stress down-regulated the expressions of apoptosis-related genes in chop+/- loach gills, while wildtype (WT) exhibited an opposite gene expression regulation pattern, suggesting that the depletion of chop suppressed apoptosis level. In addition, chop+/- loach showed a larger number of immunity-related cells and higher survival rate than WT under the NH4Cl exposure, indicating that the inhibition of chop function strengthened the innate immune barrier in general, thus increasing survival. Our findings provide the theoretical basis for developing high ammonia nitrogen-tolerant germplasm with aquaculture potential.

Ammonia-induced excess ROS causes impairment and apoptosis in porcine IPEC-J2 intestinal epithelial cells

Ammonia is one of the most important toxic metabolites in the intestine of animals. It can cause intestinal damage and associated intestinal diseases through different endogenous or exogenous stimuli. However, the definition of harmful ammonia concentration and the molecular mechanism of ammonia - induced intestinal epithelial injury remain unclear. In this study, we found that the viability of porcine IPEC-J2 intestinal epithelial cells significantly decreased with the increase of NH₄Cl dose (20-80 mM). Ammonia (40 mM NH₄Cl) increased the expression level of ammonia transporter RHCG and disrupted the intestinal barrier function of IPEC-J2 cells by reducing the expression levels of the tight junction molecules ZO-1 and Claudin-1. Ammonia caused elevated levels of ROS and apoptosis in IPEC-J2 cells. This was manifested by decreased activity of antioxidant enzymes SOD and GPx, decreased mitochondrial membrane potential, and increased cytoplasmic Ca²⁺ concentration. In addition, the expression levels of apoptosis-related molecules Caspase-9, Caspase-3, Fas, Caspase-8, p53 and Bax were increased, the expression level of anti-apoptotic molecule Bcl-2 was decreased. Moreover, the antioxidant NAC (N-acetyl-L-cysteamine) effectively alleviated ammonia-induced cytotoxicity, reduced ROS level, Ca²⁺ concentration, and the apoptosis of IPEC-J2 cells. The results suggest that ammonia-induced excess ROS triggered apoptosis through mitochondrial pathway, death receptor pathway and DNA damage. This study can provide reference and theoretical basis for the definition of harmful ammonia concentration in pig intestine and the effect and mechanism of ammonia on pig intestinal health.

Toxic Effects on Bioaccumulation, Hematological Parameters, Oxidative Stress, Immune Responses and Tissue Structure in Fish Exposed to Ammonia Nitrogen: A Review

Simple Summary

Ammonia nitrogen is a common environmental limiting factor in aquaculture, which can accumulate rapidly in water and reach toxic concentrations. In most aquatic environments, fish are vulnerable to the toxic effects of high levels of ammonia nitrogen exposure. It has been found that the toxic effects of ammonia nitrogen on fish are multi-mechanistic. Therefore, the purpose of this review is to explore the various toxic effects of ammonia nitrogen on fish, including oxidative stress, neurotoxicity, tissue damage and immune response.

Abstract

Ammonia nitrogen is the major oxygen-consuming pollutant in aquatic environments. Exposure to ammonia nitrogen in the aquatic environment can lead to bioaccumulation in fish, and the ammonia nitrogen concentration is the main determinant of accumulation. In most aquatic environments, fish are at the top of the food chain and are most vulnerable to the toxic effects of high levels of ammonia nitrogen exposure. In fish exposed to toxicants, ammonia-induced toxicity is mainly caused by bioaccumulation in certain tissues. Ammonia nitrogen absorbed in the fish enters the circulatory system and affects hematological properties. Ammonia nitrogen also breaks balance in antioxidant capacity and causes oxidative damage. In addition, ammonia nitrogen affects the immune response and causes neurotoxicity because of the physical and chemical toxicity. Thence, the purpose of this review was to investigate various toxic effects of ammonia nitrogen, including oxidative stress, neurotoxicity and immune response.

Factors affecting the quality of therapeutic proteins in recombinant Chinese hamster ovary cell culture

Chinese hamster ovary (CHO) cells are the most widely used mammalian host cells for the commercial production of therapeutic proteins. Fed-batch culture is widely used to produce therapeutic proteins, including monoclonal antibodies, because of its operational simplicity and high product titer. Despite technical advances in the development of culture media and cell cultures, it is still challenging to maintain high productivity in fed-batch cultures while also ensuring good product quality. In this review, factors that affect the quality attributes of therapeutic proteins in recombinant CHO (rCHO) cell culture, such as glycosylation, charge variation, aggregation, and degradation, are summarized and categorized into three groups: culture environments, chemical additives, and host cell proteins accumulated in culture supernatants. Understanding the factors that influence the therapeutic protein quality in rCHO cell culture will facilitate the development of large-scale, high-yield fed-batch culture processes for the production of high-quality therapeutic proteins.

Integrated multiomics analysis identifies molecular landscape perturbations during hyperammonemia in skeletal muscle and myotubes

Ammonia is a cytotoxic molecule generated during normal cellular functions. Dysregulated ammonia metabolism, which is evident in many chronic diseases such as liver cirrhosis, heart failure, and chronic obstructive pulmonary disease, initiates a hyperammonemic stress response in tissues including skeletal muscle and in myotubes. Perturbations in levels of specific regulatory molecules have been reported, but the global responses to hyperammonemia are unclear. In this study, we used a multiomics approach to vertically integrate unbiased data generated using an assay for transposase-accessible chromatin with high-throughput sequencing, RNA-Seq, and proteomics. We then horizontally integrated these data across different models of hyperammonemia, including myotubes and mouse and human muscle tissues. Changes in chromatin accessibility and/or expression of genes resulted in distinct clusters of temporal molecular changes including transient, persistent, and delayed responses during hyperammonemia in myotubes. Known responses to hyperammonemia, including mitochondrial and oxidative dysfunction, protein homeostasis disruption, and oxidative stress pathway activation, were enriched in our datasets. During hyperammonemia, pathways that impact skeletal muscle structure and function that were consistently enriched were those that contribute to mitochondrial dysfunction, oxidative stress, and senescence. We made several novel observations, including an enrichment in antiapoptotic B-cell leukemia/lymphoma 2 family protein expression, increased calcium flux, and increased protein glycosylation in myotubes and muscle tissue upon hyperammonemia. Critical molecules in these pathways were validated experimentally. Human skeletal muscle from patients with cirrhosis displayed similar responses, establishing translational relevance. These data demonstrate complex molecular interactions during adaptive and maladaptive responses during the cellular stress response to hyperammonemia.

Stages of Gut Development as a Useful Tool to Prevent Gut Alterations in Piglets

During the prenatal, neonatal, and weaning periods, the porcine gastrointestinal tract undergoes several morpho-functional, changes together with substantial modification of the microbial ecosystem. Modifications of the overall structure of the small intestine also occur, as well as a rapid increase of the volume, mainly in the last period of gestation: intestinal villi, starting from jejunum, appears shortly before the sixth week of gestation, and towards the end of the third month, epithelial cells diversify into enterocytes, goblet cells, endocrine, and Paneth cells. Moreover, in the neonatal period, colostrum induces an increase in intestinal weight, absorptive area, and brush border enzyme activities: intestine doubles its weight and increases the length by 30% within three days of birth. During weaning, intestinal environment modifies drastically due to a replacement of highly digestible sow milk by solid feed: profound changes in histological parameters and enzymatic activity are associated with the weaning period, such as the atrophy of the villi and consequent restorative hypertrophy of the crypts. All these modifications are the result of a delicate and precise balance between the proliferation and the death of the cells that form the intestinal mucosa (i.e., mitosis and apoptosis) and the health conditions of the piglet. An in-depth knowledge of these phenomena and of how they can interfere with the correct intestinal function can represent a valid support to predict strategies to improve gut health in the long-term and to prevent weaning gut alterations; thus, reducing antimicrobial use.

Inhibition of PI3K/Akt/mTOR pathway by ammonium chloride induced apoptosis and autophagy in MAC-T cell

Ammonia is a harmful gas with a pungent odor, participates in the regulation of a variety of apoptosis and autophagy, which in turn affects the growth and differentiation of cells. To test the regulation of NH₃ on the apoptosis and autophagy of mammary epithelial cells, we selected NH₄Cl as NH₃ donor in vitro model. MTT and CCK-8 assay kits were employed to detect cell activity. Real-time quantitative PCR and western blot methods were used to detect the abundance of inflammatory molecules, apoptosis markers, and autophagy genes. We selected TUNEL kit and the Annexin-FITC/PI method to detect apoptosis. TEM analysis was used to detect autophagic vesicles, and MDC stain evaluated the formation of autophagosome. The results indicated that NH₄Cl reduced cell viability in a concentration-dependent manner and promoted cell inflammatory response, apoptosis, and autophagy. NH₄Cl stimulation notable increased the autophagosomes number. Interestingly, we also detected that the addition of LY294002 and Rapamycin inhibited the PI3K/Akt pathway and the mTOR pathway, respectively, resulting in changes in both apoptosis and autophagy. Therefore, we draw a conclusion that NH₃ may regulate the apoptosis and autophagic response of bovine mammary epithelial cells through the PI3K/Akt/mTOR signaling pathway. Further investigations on ammonia's function in other physiological respects, will be critical to provide theoretical help for the improvement of production performance. It will be also helpful for controlling the harmful gas ammonia concentration in the livestock house to protect the health of dairy cows.

Cooperative application of transcriptomics and ceRNA hypothesis: LncRNA-107052630/miR-205a/G0S2 crosstalk is involved in ammonia-induced intestinal apoptotic injury in chicken

Ammonia (NH₃), as a harmful gas from agricultural production, plays an important role in air pollution, such as haze. Although numerous researchers have paid attention to health damage through NH₃ inhalation, the exhaustive mechanism of NH₃ induced intestinal toxicity remains unclear. A genes crosstalk named competing endogenous RNAs (ceRNA) can explain many regulatory manners from the molecular perspective. However, few studies have attempted to interpret the injury mechanism of air pollutants to the organism via ceRNA theory. Here, we thoroughly investigated the lncRNA-associated-ceRNA mechanism in jejunum samples from a 42-days-old NH₃-exposed chicken model through deep RNA sequencing. We observed the occurrence of apoptosis in jejunum, obtained 46 significantly dysregulated lncRNAs and 30 dysregulated miRNAs, and then constructed lncRNA-associated-ceRNA networks in jejunum. Importantly, a network regulating G0S2 in NH₃-induced apoptosis was discovered. Research results showed that G0S2 was upregulated in jejunum of NH₃-exposed group and was associated with activation of the mitochondrial apoptosis pathway. G0S2 antagonized the anti-apoptotic effect of Bcl2, which could be reversed by miR-205a. Meanwhile, lncRNA-107052630 acted as ceRNA to affect G0S2 function. These data provide new insight for revealing the biological effect of NH₃ toxicity, as well as the environmental research.

miR-187-5p/apaf-1 axis was involved in oxidative stress-mediated apoptosis caused by ammonia via mitochondrial pathway in chicken livers

Ammonia (NH₃), a toxic gas, is an important cause of atmospheric haze and one of the main pollutants in air environment of poultry houses, threatening the health of human beings and poultry. However, little is known about the effect of NH₃ on liver apoptotic damage. This study aimed to investigate the mechanism of oxidative stress-mediated apoptosis caused by NH₃ in chicken livers and whether miR-187-5p/apaf-1 axis was involved in this mechanism. Here we duplicated NH₃ poisoning model of chickens for fattening to study the ultrastructure of chicken livers, apoptosis rate, oxidative stress indexes, miR-187-5p, and apoptosis-related genes. Obvious apoptotic characteristics of liver tissues exposed to excess NH₃ were observed, and the apoptosis rate increased. Excess NH₃ decreased the activities of catalase (CAT), superoxide dismutase (SOD), total antioxidant capacity (T-AOC) and glutathione peroxidase (GSH-Px), and increased the content of malondialdehyde (MDA), suggesting that oxidative stress occurred. miR-187-5p decreased, and apoptotic protease activating factor-1 (apaf-1) increased, indicating that excess NH₃ dysregulated miR-187-5p/apaf-1 axis. The expression of tumor protein p53 (p53), Bcl-2 associated X protein (Bax), Bcl-2 homologous antagonist/killer (Bak), Cytochrome-c (Cyt-c), Caspase-9, Caspase-8, and Caspase-3 was promoted, and the expression of B-cell lymphoma-2 (Bcl-2) was inhibited, resulting in apoptosis. Moreover, oxidative stress indexes, miR-187-5p, and apoptosis-related genes changed in dose- and time-dependent manner. Altogether, miR-187-5p/apaf-1 axis participated in oxidative stress-mediated apoptosis caused by NH₃ via mitochondrial pathway in the livers of chickens for fattening. This study may provide new ideas to study the mechanism of liver apoptotic damage induced by NH₃ exposure.

Clinical Persistence of Chlamydia trachomatis Sexually Transmitted Strains Involves Novel Mutations in the Functional αββα Tetramer of the Tryptophan Synthase Operon

Clinical persistence of Chlamydia trachomatis (Ct) sexually transmitted infections (STIs) is a major public health concern. In vitro persistence is known to develop through interferon gamma (IFN-γ) induction of indoleamine 2,3-dioxygenase (IDO), which catabolizes tryptophan, an essential amino acid for Ct replication. The organism can recover from persistence by synthesizing tryptophan from indole, a substrate for the enzyme tryptophan synthase. The majority of Ct strains, except for reference strain B/TW-5/OT, contain an operon comprised of α and β subunits that encode TrpA and TrpB, respectively, and form a functional αββα tetramer. However, trpA mutations in ocular Ct strains, which are responsible for the blinding eye disease known as trachoma, abrogate tryptophan synthesis from indole. We examined serial urogenital samples from a woman who had recurrent Ct infections over 4 years despite antibiotic treatment. The Ct isolates from each infection episode were genome sequenced and analyzed for phenotypic, structural, and functional characteristics. All isolates contained identical mutations in trpA and developed aberrant bodies within intracellular inclusions, visualized by transmission electron microscopy, even when supplemented with indole following IFN-γ treatment. Each isolate displayed an altered αββα structure, could not synthesize tryptophan from indole, and had significantly lower trpBA expression but higher intracellular tryptophan levels compared with those of reference Ct strain F/IC-Cal3. Our data indicate that emergent mutations in the tryptophan operon, which were previously thought to be restricted only to ocular Ct strains, likely resulted in in vivo persistence in the described patient and represents a novel host-pathogen adaptive strategy for survival.IMPORTANCEChlamydia trachomatis (Ct) is the most common sexually transmitted bacterium with more than 131 million cases occurring annually worldwide. Ct infections are often asymptomatic, persisting for many years despite treatment. In vitro recovery from persistence occurs when indole is utilized by the organism's tryptophan synthase to synthesize tryptophan, an essential amino acid for replication. Ocular but not urogenital Ct strains contain mutations in the synthase that abrogate tryptophan synthesis. Here, we discovered that the genomes of serial isolates from a woman with recurrent, treated Ct STIs over many years were identical with a novel synthase mutation. This likely allowed long-term in vivo persistence where active infection resumed only when tryptophan became available. Our findings indicate an emerging adaptive host-pathogen evolutionary strategy for survival in the urogenital tract that will prompt the field to further explore chlamydial persistence, evaluate the genetics of mutant Ct strains and fitness within the host, and their implications for disease pathogenesis.

Intracellular Degradation of Helicobacter pylori VacA Toxin as a Determinant of Gastric Epithelial Cell Viability

Helicobacter pylori VacA is a secreted pore-forming toxin that induces cell vacuolation in vitro and contributes to the pathogenesis of gastric cancer and peptic ulcer disease. We observed that purified VacA has relatively little effect on the viability of AGS gastric epithelial cells, but the presence of exogenous weak bases such as ammonium chloride (NH₄Cl) enhances the susceptibility of these cells to VacA-induced vacuolation and cell death. Therefore, we tested the hypothesis that NH₄Cl augments VacA toxicity by altering the intracellular trafficking of VacA or inhibiting intracellular VacA degradation. We observed VacA colocalization with LAMP1- and LC3-positive vesicles in both the presence and absence of NH₄Cl, indicating that NH₄Cl does not alter VacA trafficking to lysosomes or autophagosomes. Conversely, we found that supplemental NH₄Cl significantly increases the intracellular stability of VacA. By conducting experiments using chemical inhibitors, stable ATG5 knockdown cell lines, and ATG16L1 knockout cells (generated using CRISPR/Cas9), we show that VacA degradation is independent of autophagy and proteasome activity but dependent on lysosomal acidification. We conclude that weak bases like ammonia, potentially generated during H. pylori infection by urease and other enzymes, enhance VacA toxicity by inhibiting toxin degradation.

Down-regulation of GRP78 alleviates lipopolysaccharide-induced acute kidney injury

PURPOSE

Acute kidney injury (AKI) is accompanied with life-threatening sepsis. It is necessary to develop effective therapy agent or strategy for treating AKI. LPS is a primary pathogenic factor that induces sepsis. Glucose-regulated protein 78 (GRP78) is closely related to cell injuries. The objective of this study was to examine the role of GRP78 in LPS-induced AKI.

METHODS

Cell counting kit-8 (CCK-8) assay and flow cytometry (FCM) were respectively performed to assess the cell viability and apoptosis. Available commercial kits were used to detect the reactive oxygen species (ROS) contents and the activity of oxidative indicators. The expressions of the relevant factors were determined by real-time PCR (RT-PCR) and Western blot.

RESULTS

The results showed that the expression of GRP78 was apparently increased by LPS treatment, and that the down-regulation of GRP78 by small RNA interference improved the proliferation ability of renal cells in comparison to LPS group. The LPS-induced immune response and oxidative stress was alleviated by the depletion of GRP78. Moreover, the LPS-induced apoptosis was reduced in the GRP78 group by regulating the expression of mitochondrial apoptosis (Bcl-2, Bax) and endoplasmic reticulum (ER) stress (CHOP, caspase-12)-associated proteins. In addition, the protective role of GRP78 reduction was partly related to the balance of NF-κB/IκB.

CONCLUSIONS

Down-regulation of GRP78 attenuated LPS-induced AKI through inhibiting immune response/oxidative stress-associated apoptosis.

Elucidation of the anti-hyperammonemic mechanism of Lactobacillus amylovorus JBD401 by comparative genomic analysis

Background

Recent experimental evidence showed that lactobacilli could be used as potential therapeutic agents for hyperammonemia. However, lack of understanding on how lactobacilli reduce blood ammonia levels limits application of lactobacilli to treat hyperammonemia.

Results

We report the finished and annotated genome sequence of L. amylovorus JBD401 (GenBank accession no. CP012389). L. amylovorus JBD401 reducing blood ammonia levels dramatically was identified by high-throughput screening of several thousand probiotic strains both within and across Lactobacillus species in vitro. Administration of L. amylovorus JBD401 to hyperammonemia-induced mice reduced the blood ammonia levels of the mice to the normal range. Genome sequencing showed that L. amylovorus JBD401 had a circular chromosome of 1,946,267 bp with an average GC content of 38.13%. Comparative analysis of the L. amylovorus JBD401 genome with L. acidophilus and L. amylovorus strains showed that L. amylovorus JBD401 possessed genes for ammonia assimilation into various amino acids and polyamines Interestingly, the genome of L. amylovorus JBD401 contained unusually large number of various pseudogenes suggesting an active stage of evolution.

Conclusions

L. amylovorus JBD401 has genes for assimilation of free ammonia into various amino acids and polyamines which results in removal of free ammonia in intestinal lumen to reduce the blood ammonia levels in the host. This work explains the mechanism of how probiotics reduce blood ammonia levels.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4672-3) contains supplementary material, which is available to authorized users.

Hypoxia-inducible factor-1α promotes cell survival during ammonia stress response in ovarian cancer stem-like cells

Ammonia is a toxic by-product of metabolism that causes cellular stresses. Although a number of proteins are involved in adaptive stress response, specific factors that counteract ammonia-induced cellular stress and regulate cell metabolism to survive against its toxicity have yet to be identified. We demonstrated that the hypoxia-inducible factor-1α (HIF-1α) is stabilized and activated by ammonia stress. HIF-1α activated by ammonium chloride compromises ammonia-induced apoptosis. Furthermore, we identified glutamine synthetase (GS) as a key driver of cancer cell proliferation under ammonia stress and glutamine-dependent metabolism in ovarian cancer stem-like cells expressing CD90. Interestingly, activated HIF-1α counteracts glutamine synthetase function in glutamine metabolism by facilitating glycolysis and elevating glucose dependency. Our studies reveal the hitherto unknown functions of HIF-1α in a biphasic ammonia stress management in the cancer stem-like cells where GS facilitates cell proliferation and HIF-1α contributes to the metabolic remodeling in energy fuel usage resulting in attenuated proliferation but conversely promoting cell survival.

Haploid parthenotes express differential response to in vitro exposure of ammonia compared to normally fertilized embryos

In the present study, we assessed whether absence of paternal genome imparts any differential response in embryos to chemical stress such as ammonia. Parthenogenesis was induced in MII stage oocytes using 10 mM SrCl₂ in M16 medium. Parthenotes and normally fertilized embryos at 2 cell stage were exposed to different concentrations of ammonia and cultured till blastocyst. Exposure of ammonia to normally fertilized embryos resulted in significant decrease in the developmental potential (p < 0.0001) and blastocyst quality (p < 0.001). Whereas, in parthenotes, even though lower concentrations of ammonia did not have any effect, at 200 μM concentration the blastocyst rate was two times higher than control. The baseline apoptotic index was higher in parthenotes compared to normally fertilized embryos, which further increased after ammonium exposure (p < 0.001). Unlike in normally fertilized embryos ammonia exposure altered the mitochondrial distribution pattern and lead to increased expression of Oct4, Nanog and Na⁺/K⁺ ion exchange channel, while the cytochrome C expression was downregulated. This indicates that haploidy and/or absence of paternal factors in the embryo results in differential tolerance to stress induced by ammonia.

Multifunctional ion transport properties of human SLC4A11: comparison of the SLC4A11-B and SLC4A11-C variants

Congenital hereditary endothelial dystrophy (CHED), Harboyan syndrome (CHED with progressive sensorineural deafness), and potentially a subset of individuals with late-onset Fuchs' endothelial corneal dystrophy are caused by mutations in the SLC4A11 gene that results in corneal endothelial cell abnormalities. Originally classified as a borate transporter, the function of SLC4A11 as a transport protein remains poorly understood. Elucidating the transport function(s) of SLC4A11 is needed to better understand how its loss results in the aforementioned posterior corneal dystrophic disease processes. Quantitative PCR experiments demonstrated that, of the three known human NH₂-terminal variants, SLC4A11-C is the major transcript expressed in human corneal endothelium. We studied the expression pattern of the three variants in mammalian HEK-293 cells and demonstrated that the SLC4A11-B and SLC4A11-C variants are plasma membrane proteins, whereas SLC4A11-A is localized intracellularly. SLC4A11-B and SLC4A11-C were shown to be multifunctional ion transporters capable of transporting H⁺ equivalents in both a Na⁺-independent and Na⁺-coupled mode. In both transport modes, SLC4A11-C H⁺ flux was significantly greater than SLC4A11-B. In the presence of ammonia, SLC4A11-B and SLC4A11-C generated inward currents that were comparable in magnitude. Chimera SLC4A11-C-NH₂-terminus-SLC4A11-B experiments demonstrated that the SLC4A11-C NH₂-terminus functions as an autoactivating domain, enhancing Na⁺-independent and Na⁺-coupled H⁺ flux without significantly affecting the electrogenic NH₃-H_(n)⁺ cotransport mode. All three modes of transport were significantly impaired in the presence of the CHED causing p.R109H (SLC4A11-C numbering) mutation. These complex ion transport properties need to be addressed in the context of corneal endothelial disease processes caused by mutations in SLC4A11.

Ammonia exposure induces oxidative stress, endoplasmic reticulum stress and apoptosis in hepatopancreas of pacific white shrimp (Litopenaeus vannamei)

Ammonia is one of major environmental pollutants in the aquatic system that poses a great threat to the survival of shrimp. In the present study, the mRNA expression of endoplasmic reticulum (ER) stress marker and unfolded protein response (UPR) related genes, as well as the change of redox enzyme and apoptosis were investigated in hepatopancreas of the pacific white shrimp, Litopenaeus vannamei after the exposure of 20 mg L(-1) total ammonia nitrogen (TAN). Compared with the control group, the superoxide dismutase (SOD) activity in hepatopancreas decreased significantly (p < 0.05) at 96 h, whereas the malonyldialdehyde (MDA) concentration increased significantly (p < 0.05). The mRNA expression levels of ER stress marker-immunoglobulin heavy chain binding protein (Bip) gene and key UPR related genes including activating transcription factor 4 (ATF4) and the spliced form of X box binding protein 1 (XBP1) increased significantly (p < 0.05) in hepatopancreas at 96 h after exposure to ammonia. In addition, apoptosis was observed obviously in the hepatopancreas of L. vannamei after exposure to ammonia by the terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay. The results indicated that ammonia exposure could induce oxidative stress, which further caused ER stress and apoptosis in hepatopancreas of L. vannamei.

Ammonium ions improve the survival of glutamine-starved hybridoma cells

Background

As a consequence of a reprogrammed metabolism, cancer cells are dependent on the amino acid l-glutamine for their survival, a phenomenon that currently forms the basis for the generation of new, cancer-specific therapies. In this paper, we report on the role which ammonium ions, a product of glutaminolysis, play on the survival of l-glutamine-deprived Sp2/0-Ag14 mouse hybridoma cells.

Results

The supplementation of l-glutamine-starved Sp2/0-Ag14 cell cultures with either ammonium acetate or ammonium chloride resulted in a significant increase in viability. This effect did not depend on the ability of cells to synthesize l-glutamine, and was not affected by the co-supplementation with α-ketoglutarate. When we examined the effect of ammonium acetate and ammonium chloride on the induction of apoptosis by glutamine deprivation, we found that ammonium salts did not prevent caspase-3 activation or cytochrome c leakage, indicating that they did not act by modulating core apoptotic processes. However, both ammonium acetate and ammonium chloride caused a significant reduction in the number of l-glutamine-starved cells exhibiting apoptotic nuclear fragmentation and/or condensation.

Conclusion

All together, our results show that ammonium ions promote the survival of l-glutamine-deprived Sp2/0-Ag14 cells and modulate late-apoptotic events. These findings highlight the complexity of the modulation of cell survival by l-glutamine, and suggest that targeting survival-signaling pathways modulated by ammonium ions should be examined as a potential anti-cancer strategy.

GlutaMAX prolongs the shelf life of the culture medium for porcine parthenotes

In vitro porcine embryo production systems have been established and well characterized. However, the efficiency of embryo development during IVC is still very low. In the present study, we have investigated the development of parthenogenetic porcine embryos in the well-known PZM-5 medium for porcine embryos, which was modified by replacing glutamine with the GlutaMAX supplement. We revealed that blastocyst apoptosis was significantly lower in the presence of GlutaMAX, which reduced the release of mitochondrial cytochrome c. Furthermore, the expression of apoptosis genes was significantly lower during GlutaMAX treatment (P < 0.05). The modified medium was also examined for the eventual loss of its efficacy in the presence of GlutaMAX. Three, 6, and 12 months after medium preparation, blastocyst formation in the GlutaMAX-supplemented medium was significantly higher than the number of blastocysts in the medium containing glutamine. After a long period of storage, ammonia concentration was significantly increased in the glutamine medium, whereas it was not statistically different in the GlutaMAX medium. Elevated ammonia concentrations reduced the mitochondrial membrane potential and ATP content of blastocysts in the glutamine medium. These results demonstrate that GlutaMAX can reduce blastocyst apoptosis via inhibition of the cytochrome c pathway and significantly extend the shelf life of the culture medium to at least 1 year.

Influence of the tryptophan-indole-IFNγ axis on human genital Chlamydia trachomatis infection: role of vaginal co-infections

The natural history of genital Chlamydia trachomatis infections can vary widely; infections can spontaneously resolve but can also last from months to years, potentially progressing to cause significant pathology. The host and bacterial factors underlying this wide variation are not completely understood, but emphasize the bacterium's capacity to evade/adapt to the genital immune response, and/or exploit local environmental conditions to survive this immune response. IFNγ is considered to be a primary host protective cytokine against endocervical C.trachomatis infections. IFNγ acts by inducing the host enzyme indoleamine 2,3-dioxgenase, which catabolizes tryptophan, thereby depriving the bacterium of this essential amino acid. In vitro studies have revealed that tryptophan deprivation causes Chlamydia to enter a viable but non-infectious growth pattern that is termed a persistent growth form, characterized by a unique morphology and gene expression pattern. Provision of tryptophan can reactivate the bacterium to the normal developmental cycle. There is a significant difference in the capacity of ocular and genital C. trachomatis serovars to counter tryptophan deprivation. The latter uniquely encode a functional tryptophan synthase to synthesize tryptophan via indole salvage, should indole be available in the infection microenvironment. In vitro studies have confirmed the capacity of indole to mitigate the effects of IFNγ; it has been suggested that a perturbed vaginal microbiome may provide a source of indole in vivo. Consistent with this hypothesis, the microbiome associated with bacterial vaginosis includes species that encode a tryptophanase to produce indole. In this review, we discuss the natural history of genital chlamydial infections, morphological and molecular changes imposed by IFNγ on Chlamydia, and finally, the microenvironmental conditions associated with vaginal co-infections that can ameliorate the effects of IFNγ on C. trachomatis.

Advantages of AlaGln as an additive to cell culture medium: use with anti-CD20 chimeric antibody-producing POTELLIGENT™ CHO cell lines

L-alanyl-L-glutamine (AlaGln) is dipeptide that has better solubility and stability than Glutamine (Gln). In this study, we evaluated the utility of this dipeptide during culture of POTELLIGENT™ Chinese hamster ovary (CHO) cells expressing anti-CD20 chimeric antibody. Although AlaGln in the culture medium lowered the specific growth rate, the MAb titer was maximized when Gln was completely replaced by AlaGln in both the basal and feed media. Moreover, AlaGln augmented production of antibody not only at flask scale but also at spinner scale, although the extent of this effect was dependent on the cell clone. To explore the mechanism responsible for the effect of AlaGln on cell growth, we measured apoptosis in the early phase of cell culture on days 8, 9, and 10. The apoptotic ratio was reduced in medium containing AlaGln. Ammonia was generated in medium containing Gln when it was maintained at 37 °C, which impeded the growth and productivity of the cells. In contrast, AlaGln produced less ammonia under these conditions, which may have been one of the properties associated with its beneficial effects. We conclude that certain dipeptides can serve as superior alternative sources of amino acids in cell culture and antibody production.

N-methyl D-aspartate channels link ammonia and epithelial cell death mechanisms in Helicobacter pylori Infection

BACKGROUND & AIMS

Helicobacter pylori infection is a risk factor for gastric cancer. Ammonia/ammonium (A/A) is a cytotoxin generated by H pylori that kills gastric epithelial cells. We investigated whether A/A cytotoxicity occurs by activating N-methyl d-aspartate (NMDA) channels, which results in Ca(2+) permeation and epithelial cell death.

METHODS

Gastric epithelial cells were cultured to confluence and then incubated with A/A and NMDA channel or cell signaling antagonists. Cells were incubated with wild-type H pylori or mutant strains that do not produce A/A. Changes in intracellular Ca(2+) were examined in living cells by confocal microscopy. Biochemical and histochemical techniques were used to examine the relationship between A/A-induced cell death and intracellular levels of Ca(2+).

RESULTS

A/A increased Ca(2+) permeation in gastric epithelial cells; the increase was blocked by NMDA receptor and cell signaling antagonists. Wild-type, but not mutant H pylori, also caused extensive Ca(2+) permeation of gastric epithelial cells, which was blocked when NMDA-receptor expression was repressed. Ca(2+) that entered cells was initially cytoplasmic and activated proteases. Later, the Ca(2+) was sequestered to cytoplasmic vacuoles that are dilatations of the endoplasmic reticulum. Inositol-3-phosphate-dependent release of Ca(2+) from the endoplasmic reticulum and protease activity damaged mitochondria, reduced levels of adenosine triphosphate, and transcriptionally up-regulated cell death effectors. Expression of the NMDA receptor was altered in stomachs of mice infected with H pylori.

CONCLUSIONS

A/A affects gastric epithelial cell viability by allowing excessive Ca(2+) permeation through NMDA channels. NMDA channels might thereby regulate cell survival and death pathways during development of gastric cancers associated with H pylori infection.

Lidocaine depolarizes the mitochondrial membrane potential by intracellular alkalization in rat dorsal root ganglion neurons

PURPOSE

The mitochondrial membrane potential (ΔΨm) is an important factor for apoptosis, and it is produced by the proton electrochemical gradient (ΔµH(+)). Therefore, the intracellular proton concentration (pH(in)) is an important factor for modifying the ΔΨm. However, the effects of lidocaine on pH(in) are unclear. To investigate mitochondrial responses to lidocaine, therefore, we simultaneously measured pH(in) with ΔΨm, flavin adenine dinucleotide (FAD), and reduced form of nicotinamide adenine dinucleotide (NADH) fluorescence, and calculated the FAD/NADH ratio (redox ratio), the superoxide production in mitochondria.

METHODS

Morphological change and early apoptosis were observed by annexin-V FITC staining under fluorescent microscope. The ratiometric fluorescent probe JC-1 and HPTS were used for the simultaneous measurements of ΔΨm with pH(in) in rat dorsal root ganglion (DRG) neurons. FAD and NADH autofluorescence were simultaneously measured, and the FAD/NADH fluorescence ratio (redox ratio) was calculated. The superoxide was measured by mitosox-red fluorescent probe for mitochondrial superoxide. Lidocaine was evaluated at 1, 5, and 10 mM.

RESULTS

Morphological change and early apoptosis were observed after 10 mM lidocaine administration. Lidocaine depolarized ΔΨm with increased pH(in) in a dose-dependent manner. In low-pH saline (pH 6), in the presence of both the weak acids (acetate and propionate), lidocaine failed to depolarize ΔΨm and increase pH(in). On the other hand, lidocaine decreased the redox ratio in the cell and increased the levels of superoxide in a dose-dependent manner.

CONCLUSION

These results demonstrated that lidocaine depolarizes ΔΨm by intracellular alkalization. These results may indicate one of the mechanisms responsible for lidocaine-induced neurotoxicity.

New frontiers in gut nutrient sensor research: prophylactic effect of glutamine against Helicobacter pylori-induced gastric diseases in Mongolian gerbils

Ammonia is one of the important toxins produced by Helicobacter pylori (H. pylori), the major cause of peptic ulcer diseases. We examined whether glutamine or marzulene (a gastroprotective drug containing 1% sodium azulene and 99% glutamine) protects the gastric mucosa against H. pylori in vivo and investigated the mechanism underlying glutamine-induced mucosal protection against ammonia in gastric epithelial cells in vitro. Mongolian gerbils were fed for 3 months with a diet containing glutamine (2%-20%) or marzulene (20%) starting from 2 weeks or 2 years after H. pylori infection. Then, gastric mucosal changes were evaluated both macro- and microscopically. Cultured gastric epithelial cells were incubated in the presence of ammonia, with or without glutamine; and cell viability, ammonia accumulation, and chemokine production were determined. Gerbils exhibited edema, congestion, and erosion after 3-month infection; and after 2-year infection, they showed cancer-like changes in the gastric mucosa. Glutamine and marzulene significantly suppressed these pathological changes caused in the gastric mucosa by H. pylori infection. Ammonia was accumulated in the cells, resulting in an increase in chemokine production and a decrease in cell viability. These pathological responses were prevented by glutamine. In addition, glutamine decreased chemokine production and cell death through inhibition of cellular accumulation of ammonia, resulting in the prevention of H. pylori-induced gastric diseases in vivo. These results suggest that glutamine/marzulene would be useful for prophylactic treatment of H. pylori-induced gastric diseases in patients.

Inflammation and foveolar hyperplasia are reduced by supplemental dietary glutamine during Helicobacter pylori infection in mice

We recently showed that L-Gln protects cultured gastric cells from ammonia-induced cell death and predicted that Gln may also protect during Helicobacter pylori infection in vivo. Thus, the aim of this study was to test whether supplemental dietary Gln protects against H. pylori-associated pathology. For this, C57BL/6 mice were fed a purified diet consisting of 20.3% protein (1.9% Gln), 66% carbohydrate, and 5% fat or 25.3% protein (5% supplemental L-Gln; 6.9% total Gln), 61% carbohydrate, and 5% fat. After a 2-wk prefeeding period, mice were divided into sham-(uninfected) or H. pylori-infected groups. Body weight and food consumption were recorded weekly. Tissue histopathology, H. pylori colonization, serum IgG, and pro- and antiinflammatory cytokine mRNA expression were determined at 6, 12, and 20 wk postinfection (wkPI). Inflammation, antiinflammatory cytokine, and interleukin-1beta mRNA expression were significantly greater at 6 wkPI in H. pylori-infected mice fed supplemental Gln compared with those fed the control diet. At 20 wkPI, however, inflammation and foveolar hyperplasia were significantly lower in H. pylori-infected mice fed supplemental Gln compared with those fed the control diet. Body weight gain, food consumption, H. pylori colonization, and serum IgG did not differ in H. pylori-infected mice fed supplemental Gln compared with the control diet. Our data demonstrate that H. pylori-infected mice fed supplemental dietary Gln have reduced H. pylori-associated pathology in vivo that is accompanied by beneficial changes in the immune response to H. pylori early in infection. Thus, Gln supplementation may be an alternative therapy for reducing H. pylori-associated pathology.

Epithelial cell expression of BCL-2 family proteins predicts mechanisms that regulate Helicobacter pylori-induced pathology in the mouse stomach

Corpus-predominant infection with Helicobacter pylori (HP) results in the activation of programmed cell death pathways in surface, parietal, and chief cells. At present, mechanisms that regulate these pathways to result in HP-associated pathology are not fully understood. Because it is not known which survival and death pathways are present in gastric epithelial cells, we used an antibody panel to evaluate the expression of BCL-2 family prosurvival proteins or multi-Bcl-2 homology (BH)-domains (group 1) or BH3-only (group-2) proapoptotic proteins in the stomachs of uninfected or HP-infected C57BL/6 mice. This strategy identified BCL-2, BAK, and BAD as the major prosurvival and proapoptotic proteins, in surface cells and BAD as the only BCL-2 family protein expressed in parietal cells. Chief cells express altogether different effectors, including BCL-X(L)/BCL-2, for survival but have no constitutively expressed proapoptotic proteins. In model chief cells, however, the group 1 proapoptotic protein BCL-X(S) was expressed after exposure to proinflammatory cytokines concomitant with reduced viability, demonstrating that chief cells can transcriptionally regulate the induction of proapoptotic proteins to execute apoptosis. During HP infection, no additional BCL-2 family proteins were expressed in epithelial cells, whereas those present either remained unchanged or were reduced as cell deletion occurred over time. Additional studies demonstrated that the posttranslational regulation of BAD in surface and parietal cells was negatively affected by HP infection, a result that may be directly related to an increase in apoptosis during infection. Thus, gastric epithelial cells express cell-specific prosurvival and proapoptotic pathways. From the results presented here, mechanisms that regulate HP-related changes in the survival and death profile of gastric epithelial cells can be predicted and then tested, with the ultimate goal of elucidating important therapeutic targets to inhibit the progression of HP-related pathology in the stomach.

Comparison of the 13C-urea breath test and the endoscopic phenol red mucosal pH test in the quantification of Helicobacter pylori infection loading

BACKGROUND/AIMS

The (13)C-urea breath test (UBT) is a semiquantitative test for measuring Helicobacter pylori infection loading. H. pylori produces ammonia, which elevates the pH of the gastric mucosa and is detectable via endoscopy using a phenol red indicator. We evaluated whether this test could be used to diagnose H. pylori infection and whether phenol red staining was correlated with (13)C-UBT results.

METHODS

One hundred and twenty-three patients participated. The UBT was performed after ingestion of a capsule containing urea. A change in (13)C-UBT >2 ppt was selected as the cutoff value for diagnosing infection. After spraying evenly with a 0.1% phenol red solution, the pH of the gastric mucosal surface was measured using an antimony electrode through the biopsy channel.

RESULTS

The pH of stained mucosa (6.9+/-0.4) was significantly higher than that of unstained mucosa (1.9+/-0.8; p<0.001), and the H. pylori detection rate confirmed via histology was higher in stained versus unstained mucosa (p<0.01). Extensive mucosal staining resulted in a higher detection rate (p<0.001). The UBT produced results were very similar to those obtained via histological detection in stained mucosa (p<0.001). The extent of staining, expressed as a staining score, was positively correlated with the change in (13)C-UBT (r=0.426, p<0.001). A significant correlation was also observed between the histologically determined H. pylori density and (13)C-UBT results (r=0.674, p<0.001).

CONCLUSIONS

H. pylori infection elevates gastric mucosal surface pH, and endoscopic phenol red staining may be an alternative method for the diagnosis of H. pylori infection.

Enterocyte proliferation and apoptosis in the caudal small intestine is influenced by the composition of colonizing commensal bacteria in the neonatal gnotobiotic pig

We previously reported marked differences in small intestinal morphology, including changes in crypt depth and villous height, after inoculation of germ-free pigs with different bacterial species. In an attempt to identify the mechanisms governing changes in villous morphology associated with bacterial colonization, 2 gnotobiotic experiments were performed. In each experiment, 16 piglets were allocated to 4 treatment groups including germ-free (GF), monoassociation with Lactobacillus fermentum (LF) or Escherichia coli (EC), or conventionalized with sow feces (SF). Piglets were reared under gnotobiotic conditions until 14 d of age, at which time whole intestinal tissue and enterocytes were collected for histological, gene expression, and protein analysis. Proliferating cell nuclear antigen, tumor necrosis factor alpha (TNFalpha), Fas ligand (FasL), CD3epsilon, caspase 3 (casp3), and toll-like receptors (TLR)2, 4, and 9 expression were measured by quantitative PCR. Activated casp3 was measured by Western blot. Increased abundance of activated casp3 and transcripts encoding proliferating cell nuclear antigen, TNFalpha, CD3epsilon, and FasL was observed in SF and EC treatment groups compared with GF and LF. Expression of TLR2 was increased (P < 0.05) in the SF treatment and tended to be greater (P < 0.08) in EC relative to LF and GF. Results indicate that conventional bacteria and E. coli but not L. fermentum increase overall cell turnover by stimulating increased apoptosis through the expression of FasL and TNFalpha and by increasing cell proliferation. The differential regulation of TLR expression indicates that microbially induced changes may be mediated in part by these receptors. Induction of inflammatory responses and activation of apoptosis through death receptors appears to play a significant role in enterocyte turnover mediated by commensal bacteria.

Oxidative phosphorylation and its coupling to mitochondrial creatine and adenylate kinases in human gastric mucosa

Energy metabolism in gastrobiopsy specimens of the antral and corpus mucosa, treated with saponin to permeabilize the cells, was studied in patients with gastric diseases. The results show twice lower oxidative capacity in the antral mucosa than in the corpus mucosa and the relative deficiency of antral mitochondria in complex I. The mucosal cells expressed mitochondrial and cytosolic isoforms of creatine kinase and adenylate kinase (AK). Creatine (20 mM) and AMP (2 mM) markedly stimulated mitochondrial respiration in the presence of submaximal ADP or ATP concentrations, and creatine reduced apparent Km for ADP in stimulation of respiration, which indicates the functional coupling of mitochondrial kinases to oxidative phosphorylation. Addition of exogenous cytochrome c increased ADP-dependent respiration, and the large-scale cytochrome c effect (>or=20%) was associated with suppressed stimulation of respiration by creatine and AMP in the mucosal preparations. These results point to the impaired mitochondrial outer membrane, probably attributed to the pathogenic effects of Helicobacter pylori. Compared with the corpus mucosa, the antral mucosa exhibited greater sensitivity to such type of injury as the prevalence of the large-scale cytochrome c effect was twice higher among the latter specimens. Active chronic gastritis was associated with decreased respiratory capacity of the corpus mucosa but with its increase in the antral mucosa. In conclusion, human gastric mucosal cells express the mitochondrial and cytosolic isoforms of CK and AK participating in intracellular energy transfer systems. Gastric mucosa disease is associated with the altered functions of these systems and oxidative phosphorylation.

Effects of Helicobacter pylori infection on gastric epithelial cell kinetics in patients with chronic renal failure

AIM

To evaluate the effects of Helicobacter pylori infection on gastric epithelial cell kinetics in patients with chronic renal failure (CRF).

METHODS

Forty-four patients were enrolled in this study and divided into four groups with respect to their Helicobacter pylori (H pylori) and CRF status. Groups were labeled as follows: 1a: normal renal function, H pylori negative (n = 12), 1b: normal renal function, H pylori positive (n = 11), 2a: CRF, H pylori negative (n = 10), 2b: CRF, H pylori positive (n = 11). Upper gastrointestinal endoscopy was done in all the patients involved in the study. During endoscopical investigation, antral biopsy specimens were taken from each patient. In order to evaluate the cell apoptosis and proliferation in gastric epithelial cells, Bax and proliferating cell nuclear antigen (PCNA) labeling indexes (LI) were assessed with immunohistochemical staining method.

RESULTS

For groups 1a, 1b, 2a, and 2b, mean Bax LI was identified as 34.4+/-13.7, 44.1+/-16.5, 46.3+/-20.5, 60.7+/-13.8, respectively and mean PCNA LI was identified as 36.2+/-17.2, 53.6+/-25.6, 59.5+/-25.6, 67.2+/-22, respectively. When the one-way ANOVA test was applied, statistically significant differences were detected between the groups for both Bax LI (P = 0.004 <0.01) and PCNA LI (P = 0.009 <0.01). When groups were compared further in terms of Bax LI and PCNA LI with Tukeyos HSD test for multiple pairwise comparisons, statistically significant difference was observed only between groups 1a and 2b (P = 0.006 <0.01).

CONCLUSION

In gastric epithelial cells, expression of both the pre-apoptotic protein Bax and the proliferation marker PCNA increase with H pylori infection. This increase is more evident in patients with uremia. These findings suggest that uremia accelerates apoptosis and proliferation in gastric epithelial cells.

Production of ammonium by Helicobacter pylori mediates occludin processing and disruption of tight junctions in Caco-2 cells

Tight junctions, paracellular permeability barriers that define epithelial cell polarity, play an essential role in transepithelial transport, cell-cell adhesion and lymphocyte transmigration. They are also important for the maintenance of innate immune defence and intestinal antigen uptake. Ammonium (NH4+) is elevated in the gastric aspirates of Helicobacter pylori-infected patients and has been implicated in the disruption of tight-junction functional integrity and the induction of gastric mucosal damage during H. pylori infection. The precise mechanism of the effect of ammonium and the molecular targets of ammonium in host tissue are not yet identified. To study the effects of ammonium on epithelial tight junctions, the human colon carcinoma cell line Caco-2 was cultured on permeable supports and the transepithelial resistance (TER) was measured at different time intervals following exposure to ammonium salts or H. pylori-derived ammonium. A biphasic response to treatment with ammonium was found. Acute exposure to ammonium salts or NH3/NH4+ derived from urea metabolism by wild-type H. pylori resulted in a 20-30 % decrease in TER. After 24 h, the NH4Cl-treated cells showed a partial recovery of TER. In contrast, the control culture, or cultures that were exposed to supernatants derived from urease-deficient H. pylori, showed no significant decrease in TER. Occludin-specific immunoblots revealed the expression of a low-molecular-weight form of occludin of 42 kDa upon NH3/NH4+ exposure. The results indicate that modulation of tight-junction function by H. pylori is ammonium-dependent and linked to the accumulation of a low-molecular-weight and detergent-soluble form of occludin.

The effect of intragastric ammonia production on titratable gastric acid output in Helicobacter pylori-infected patients with chronic gastritis

The purpose of this study was to assess whether intragastric neutralization of HCl by ammonia in Helicobacter pylori-infected patients could meaningfully affect the titratable acid output as a measure of gastric acid secretion in a relation to the severity of infection. In 79 patients with different degrees of Helicobacter pylori infection and chronic gastritis, the basal acid output (BAO) and maximal acid output (MAO) after pentagastrin (6 microg/kg s.c.) was estimated. Cl- and NH4+ contents in these fractions were also assayed. H+/Cl- ratio in the MAO fraction was diminished in markedly infected patients (68.1 +/- 3.9%, vs 84.1 +/- 3.3% in noninfected patients; P < 0.005). Ammonium content was maximal in patients with marked infection (0.912 +/- 0.086 vs 0.149 +/- 0.034 mmol/hr in MAO [P < 0.001] and 0.475 +/- 0.063 vs 0.105 +/- 0.016 mmol/hr in BAO of noninfected patients [P < 0.001]), with intermediate values in mild and moderate infection. The NH4 +/(H+ + NH4+) ratio reached 27.01 +/- 7.34% in the BAO of moderately infected patients, vs 10.22 +/- 3.81% in noninfected patients (P = 0.05), and 7.25 +/- 1.06% in the MAO of markedly infected patients, vs 1.14 +/- 0.33% in noninfected patients (P < 0.001). The intragastric ammonia production affects the titratable acid output in Helicobacter pylori-infected patients dependent on the severity of infection. Therefore this factor should be taken into consideration in the evaluation of gastric secretory function in Helicobacter pylori-infected patients.

Reassembly of active caspase-3 is facilitated by the propeptide

Changes in ionic homeostasis are early events leading up to the commitment to apoptosis. Although the direct effects of cations on caspase-3 activity have been examined, comparable studies on procaspase-3 are lacking. In addition, the effects of salts on caspase structure have not been examined. We have studied the effects of cations on the activities and conformations of caspase-3 and an uncleavable mutant of procaspase-3 that is enzymatically active. The results show that caspase-3 is more sensitive to changes in pH and ion concentrations than is the zymogen. This is due to the loss of both an intact intersubunit linker and the prodomain. The results show that, although the caspase-3 subunits reassemble to the heterotetramer, the activity return is low after the protein is incubated at or below pH 4.5 and then returned to pH 7.5. The data further show that the irreversible step in assembly results from heterotetramer rather than heterodimer dissociation and demonstrate that the active site does not form properly following reassembly. However, active-site formation is fully reversible when reassembly occurs in the presence of the prodomain, and this effect is specific for the propeptide of caspase-3. The data show that the prodomain facilitates both dimerization and active-site formation in addition to stabilizing the native structure. Overall, the results show that the prodomain acts as an intramolecular chaperone during assembly of the (pro)caspase subunits and increases the efficiency of formation of the native conformation.

Excretory/secretory products of sheep abomasal nematode parasites cause vacuolation and increased neutral red uptake by HeLa cells

Excretory/secretory (ES) products of Ostertagia (Teladorsagia) circumcincta and Haemonchus contortus have been implicated in the inhibition of gastric acid secretion and vacuolation, and the loss of parietal cells associated with abomasal parasitism. Vacuolation of epithelial (HeLa) cells caused by adult O. circumcincta or L3 O. circumcincta or H. contortus ES products have been examined by differential interference contrast microscopy and by the neutral red uptake assay. ES products caused visible vacuolation of HeLa cells, and this effect was enhanced by 8 mM NH4Cl. Some parasite ES products caused a marked detachment of cells from the coverslip. At lower concentrations of ES products, neutral red uptake was usually increased above the control, but at higher concentrations of ES products, uptake was often decreased, probably because of cell detachment. Although generally consistent with direct observations of HeLa cell vacuolation by parasite chemicals, neutral red uptake was not a satisfactory quantitative assay.

Effect of ammonium on the expression of osmosensitive genes in Madin-Darby canine kidney cells

The cells of the kidney medulla are exposed routinely to high extracellular concentrations of various solutes including NaCl, urea and ammonium (NH4+). Although it is well established that the expression of a variety of osmosensitive genes and proteins, which confer cytoprotection on renal medullary cells, is induced by high NaCl concentrations, the role of NH4+ in these cellular responses is unclear. This study thus addressed the effect of NH4+ on the expression of the betaine/GABA transporter (BGT-1), the sodium/myo-inositol cotransporter (SMIT), aldose reductase (AR), and heat shock protein 70 (HSP70) in Madin-Darby canine kidney (MDCK) cells, using Northern and Western blot analyses and enzyme-linked immunosorbent assay (ELISA). The incidence of apoptosis was monitored by determining caspase-3 activity and annexin V binding. Addition of NH4Cl (50 mM; total osmolality 400 mosmol (kg H2O)(-1) to the medium was more effective than equiosmolar NaCl in increasing BGT-1 and HSP70 mRNA abundance, but less effective in enhancing BGT-1 and HSP70 expression at the protein level. Qualitatively similar results were obtained for SMIT and AR mRNAs. Exposure to both isotonic and hypertonic, NH4Cl-containing medium enhanced apoptosis compared with equiosmolar, NaCl-containing media. These results suggest that, in addition to NaCl, NH4Cl may play a role in regulating the intracellular accumulation of organic osmolytes, the abundance of HSP70 and cell turnover in the renal medulla in vivo.

A model for the study of Helicobacter pylori interaction with human gastric acid secretion

We present a comprehensive mathematical model describing Helicobacter pylori interaction with the human gastric acid secretion system. We use the model to explore host and bacterial conditions that allow persistent infection to develop and be maintained. Our results show that upon colonization, there is a transient period (day 1-20 post-infection) prior to the establishment of persistence. During this period, changes to host gastric physiology occur including elevations in positive effectors of acid secretion (such as gastrin and histamine). This is promoted by reduced somatostatin levels, an inhibitor of acid release. We suggest that these changes comprise compensatory mechanisms aimed at restoring acid to pre-infection levels. We also show that ammonia produced by bacteria sufficiently buffers acid promoting bacteria survival and growth.

Apoptosis is a major mechanism of deoxycholate-induced gastric mucosal cell death

This study was undertaken to determine whether necrosis or apoptosis was the predominant mechanism responsible for gastric mucosal cellular death using the cell line known as AGS cells. Cells were exposed to various concentrations of deoxycholate (DC; 50-500 muM) for periods ranging from 30 min to 24 h. Lactic dehydrogenase (LDH) activity was used as a marker for necrotic cell death, whereas apoptosis was characterized by 4',6-diamidino-2 phenylindole staining, DNA gel electrophoresis, terminal deoxynucleotidyl transferase dUTP nick-end labeling assay and DNA-histone-associated complex formation. When cells were bathed in Hank's balanced salt solution, DC-induced necrosis was the predominant mechanism of cell death. In contrast, when cells were bathed in Ham's F-12 solution (a more physiologically relevant medium), no evidence of cytotoxicity (by LDH assay) was discernible when cells were exposed to DC (50-300 muM) for periods as long as 8 h; instead, clear evidence of apoptosis was noted that was time and dose dependent. When cells were exposed for 24 h to these DC concentrations, cytotoxicity was also present, indicating necrosis as well. Furthermore, acidification of the ambient environment also evoked a necrotic response when exposed to DC. We demonstrated that apoptosis induced by DC shows early activation of caspase-3 that is dependent on both receptor and mitochondrial pathways. Our results indicate that physiological concentrations of DC (50-300 muM) primarily induce cellular death through an apoptotic process. Only after prolonged exposure to DC or acidification of the bathing solution does necrosis also occur.