Boric acid transport activity of marine teleost aquaporins expressed in Xenopus oocytes.

Marine teleosts ingest large amounts of seawater containing various ions, including 0.4 mM boric acid, which can accumulate at toxic levels in the body. However, the molecular mechanisms by which marine teleosts absorb and excrete boric acid are not well understood. Aquaporins (Aqps) are homologous to the nodulin-like intrinsic protein (NIP) family of plant boric acid channels. To investigate the potential roles of Aqps on boric acid transport across the plasma membrane in marine teleosts, we analyzed the function of Aqps of Japanese pufferfish (Takifugu rubripes) expressed in Xenopus laevis oocytes. Takifugu genome database contains 16 genes encoding the aquaporin family members (aqp0a, aqp0b, aqp1aa, aqp1ab, aqp3a, aqp4a, aqp7, aqp8bb, aqp9a, aqp9b, aqp10aa, aqp10bb, aqp11a, aqp11b, aqp12, and aqp14). When T. rubripes Aqps (TrAqps) were expressed in X. laevis oocytes, a swelling assay showed that boric acid permeability was significantly increased in oocytes expressing TrAqp3a, 7, 8bb, 9a, and 9b. The influx of boric acid into these oocytes was also confirmed by elemental quantification. Electrophysiological analysis using a pH microelectrode showed that these TrAqps increase B(OH)3 permeability. These results indicate that TrAqp3a, 7, 8bb, 9a, and 9b act as boric acid transport systems, likely as channels, in marine teleosts.

Boric acid transport activity of human aquaporins expressed in Xenopus oocytes.

Boric acid is a vital micronutrient that is toxic at high concentrations in animals. However, the mechanisms underlying boric acid transport in animal cells remain unclear. To identify the plasma membrane boric acid channels in animals, we analyzed the function of human aquaporins (AQPs), which are homologous to the nodulin-like intrinsic protein family of plant boric acid channels. When human AQPs were expressed in Xenopus laevis oocytes, the results of the swelling assay showed that boric acid permeability significantly increased in oocytes expressing AQP3, 7, 8, 9, and 10, but not in those expressing AQP1, 2, 4, and 5. The boric acid influxes of these oocytes were also confirmed by elemental quantification. Electrophysiological analysis using a pH microelectrode showed that these AQPs transported boric acid (B(OH)3 ) but not borate ions (B(OH)4- ). These results indicate that AQP3, 7, 8, 9, and 10 act as boric acid transport systems, likely as channels in humans.

B- and N-doped carbon dots by one-step microwave hydrothermal synthesis: tracking yeast status and imaging mechanism.

BACKGROUND: Carbon dots (CDs) are widely used in cell imaging due to their excellent optical properties, biocompatibility and low toxicity. At present, most of the research on CDs focuses on biomedical application, while there are few studies on the application of microbial imaging. RESULTS: In this study, B- and N-doped carbon dots (BN-CDs) were prepared from citric acid, ethylenediamine, and boric acid by microwave hydrothermal method. Based on BN-CDs labeling yeast, the dead or living of yeast cell could be quickly identified, and their growth status could also be clearly observed. In order to further observe the morphology of yeast cell under different lethal methods, six methods were used to kill the cells and then used BN-CDs to label the cells for imaging. More remarkably, imaging of yeast cell with ultrasound and antibiotics was significantly different from other imaging due to the overflow of cell contents. In addition, the endocytosis mechanism of BN-CDs was investigated. The cellular uptake of BN-CDs is dose, time and partially energy-dependent along with the involvement of passive diffusion. The main mechanism of endocytosis is caveolae-mediated. CONCLUSION: BN-CDs can be used for long-term stable imaging of yeast, and the study provides basic research for applying CDs to microbiol imaging.

Regulation, Diversity and Evolution of Boron Transporters in Plants.

Boron (B) is an essential trace element in plants, and borate cross-linking of pectic polysaccharide rhamnogalacturonan-II (RG-II) in cell walls is required for normal cell growth. High concentrations of B are toxic to cells. Therefore, plants need to control B transport to respond to B conditions in the environment. Over the past two decades, genetic analyses of Arabidopsis thaliana have revealed that B transport is governed by two types of membrane transport molecules: NIPs (nodulin-26-like intrinsic proteins), which facilitate boric acid permeation, and BORs, which export borate from cells. In this article, we review recent findings on the (i) regulation at the cell level, (ii) diversity among plant species and (iii) evolution of these B transporters in plants. We first describe the systems regulating these B transporters at the cell level, focusing on the molecular mechanisms underlying the polar localization of proteins and B-dependent expression, as well as their physiological significance in A. thaliana. Then, we examine the presence of homologous genes and characterize the functions of NIPs and BORs in B homeostasis, in a wide range of plant species, including Brassica napus, Oryza sativa and Zea mays. Finally, we discuss the evolutionary aspects of NIPs and BORs as B transporters, and the possible relationship between the diversification of B transport and the occurrence of RG-II in plants. This review considers the sophisticated systems of B transport that are conserved among various plant species, which were established to meet mineral nutrient requirements.

Effects of boric acid on the growth performance and nutritional content of rainbow trout (Oncorhynchus mykiss).

In this study, boric acid was added to the rainbow trout (Oncorhynchus mykiss) feed at ratios of 0.00%, 0.01%, 0.05%, 0.10%, and 0.20%. The feeding period of this study continued for 90 days. The effect of boric acid on the growth parameters and nutritional composition of rainbow trout were investigated. In this research, effects on live weight gain (LWG), amount of feed intake, feed conversion rate (FCR), protein efficiency rate (PER), specific growth rate (SGR), survival rate, economic conversion rate (ECR), and economic profit index (EPI) were evaluated as growth parameters. As for nutritional contents, the total crude protein, lipid, raw ash, and humidity ratios were calculated. Rainbow trout with an initial weight of 92.04 g reached up to 195.05 ± 1.69 g, 202.69 ± 1.94 g, 217.53 ± 2.84 g, 195.25 ± 2.18 g, and 181.20 ± 1.89 g, respectively in the different levels of boric acid at the end of the trial period. The best growth performance was obtained in the group with 0.05% boric acid added, while the lowest growth performance was observed in the group with 0.20% boric acid added. It was concluded based on the results of this study that the amount of boric acid up to 0.05% in the fish feed positively affected the growth parameters and the addition of higher amounts had either no benefit or negative effects on the growth performance of rainbow trout. Furthermore, boric acid in feed affected the nutritional composition of fish meat.

Cytotoxic Effect of Boron Application on Glioblastoma Cells.

AIM: To investigate the cytotoxic effects of boron application at different doses on U-87 MG glioblastoma cells. MATERIAL AND METHODS: The T98G (ATCC® CRL-1690?) glioblastoma cell strain used in the study was acquired from the American Type Culture Collection (ATCC) (Manassas, USA). Boric acid solution was prepared by mechanical mixing in the medium. Afterwards, 2.5 mM, 25 mM and 50 mM boron were each added to U87-MG glioblastoma cells and incubated for 48 hours. The cytotoxic effects on the cells was determined using the MTT (Methylthiazole diphenyl tetrazolium) test 48 hours after boron application. RESULTS: IC50 value was detected as 17 mM in the 48-hour boric acid application on U-87 MG glioblastoma cells. CONCLUSION: Boron treatment might be an effective approach for glioblastoma.

Analysis of Endocytosis and Intracellular Trafficking of Boric Acid/Borate Transport Proteins in Arabidopsis.

Plants take up inorganic nutrients from the soil by transport proteins located in the plasma membrane of root cells. Boron (B) is an essential element for plant growth; it taken up and translocated by boric acid channels such as NIP5;1 and borate exporters such as BOR1 in Arabidopsis. NIP5;1 and BOR1 are localized to the plasma membrane of various root cells in polar manners toward soil- and stele-side, respectively, for efficient transport of B. In response to elevated B concentration, BOR1 undergoes vacuolar sorting for degradation to avoid accumulation of B to a toxic level in tissues. The polar localization and vacuolar sorting of the transport proteins are regulated through differential mechanisms of endocytosis and intracellular trafficking. In this chapter, we describe methods for quantitative live-cell imaging of GFP-NIP5;1 and BOR1-GFP as markers for the polar and vacuolar trafficking.

Histopathology changes in the rainbow trout (Onchorhyncus mykiss) consuming boric acid supplemented fish fodder.

OBJECTIVE: Even though boron (B), as a trace micronutrient, occurs in natural waters and organisms, its high concentration could cause harmful and even toxic for organisms. The aim of present study was to investigate the effects of boric acid (BA) added to feed (0.01%, 0.05%, 0.10%, and 0.20% of B in feed) on Rainbow Trout (Oncorhynchus mykiss) by histopathological methods and compared to the control feed as without B. METHODOLOGY: At the end of the feeding, after weighing the live weight of 9 rainbow trout from each group, tissue fragments were taken from the liver, gill, kidney, skeletal muscle, spleen and brains of fish, which systemic necropsies was done, and were fixed in 10 % buffered formalin solution. RESULTS: Histopathological examinations revealed degenerative and necrotic changes in the liver, gill, kidney, skeletal muscle, spleen and brain. Hydropic and vacuolar degenerations in liver parenchyma, lamellar edema in the gills, hyaline accumulation in the kidneys, degenerations in the muscles, necrosis in the spleen and hyperemia in the brain were observed in all groups except control group. It was observed that the destruction of boric acid on fish increased depending on the amount of boron supplemented to the feed, and the most effect was in the group fed with 0.20 % boron supplemented feed. CONCLUSIONS: The findings aside from causing pathological changes in all organs in terms of histopathological findings of Boric Acid (BA), the most severe lesions were observed in the liver.

From element to development: the power of the essential micronutrient boron to shape morphological processes in plants.

Deficiency of the essential nutrient boron (B) in the soil is one of the most widespread micronutrient deficiencies worldwide, leading to developmental defects in root and shoot tissues of plants, and severe yield reductions in many crops. Despite this agricultural importance, the underlying mechanisms of how B shapes plant developmental and morphological processes are still not unequivocally understood in detail. This review evaluates experimental approaches that address our current understanding of how B influences plant morphological processes by focusing on developmental defects observed under B deficiency. We assess what is known about mechanisms that control B homeostasis and specifically highlight: (i) limitations in the methodology that is used to induce B deficiency; (ii) differences between mutant phenotypes and normal plants grown under B deficiency; and (iii) recent research on analyzing interactions between B and phytohormones. Our analysis highlights the need for standardized methodology to evaluate the roles of B in the cell wall versus other parts of the cell.

Investigation of the biochemical and apoptotic changes in breast cancer cells treated with leaf extract from tea (Camellia sinensis L.) grown with added boric acid.

Tea obtained from the leaves of Camellia sinensis L., a medicinal plant, is a widely popular beverage. Deficiency in boron, a micronutrient for C. sinensis, affects the growth as well as the quality of tea. The aim of this study was to explore whether boric acid at various concentrations added to soil improves the quality of C. sinensis and also whether it changes the apoptotic, anti-proliferative, and anti-oxidative effects of C. sinensis leaf extract on breast cancer (MCF-7) cells. C. sinensis was grown in Rize-Turkey. Boric acid at concentrations of 100 (group B), 300 (group C), and 500 (group D) mg/m2 in sodium tetraborate buffer was administered as a single dose to the soil; group A (no boric acid) was the control. Boron, glutathione (GSH), malondialdehyde and protein carbonyl levels in the C. sinensis leaves were measured. C. sinensis leaf extracts at different concentrations was applied to MCF-7 cells for 24 and 48h. Cytotoxicity, proliferation, and apoptosis were examined. The highest TUNEL+ cell percentage was in MCF-7 cells treated with D group leaf extract compared to the control group (p<0.001 at concentrations of 2.3, 2.6 and 3mg/mL). Moreover, the GSH level increased in the MCF-7 cells under the same conditions (p<0.001 for each concentration). Leaf extracts from C. sinensis grown in soil with boric acid have more anti-proliferative, apoptotic and anti-oxidative effects on the MCF 7 cells.

Functional evolution of nodulin 26-like intrinsic proteins: from bacterial arsenic detoxification to plant nutrient transport.

Nodulin 26-like intrinsic proteins (NIPs) play essential roles in transporting the nutrients silicon and boron in seed plants, but the evolutionary origin of this transport function and the co-permeability to toxic arsenic remains enigmatic. Horizontal gene transfer of a yet uncharacterised bacterial AqpN-aquaporin group was the starting-point for plant NIP evolution. We combined intense sequence, phylogenetic and genetic context analyses and a mutational approach with various transport assays in oocytes and plants to resolve the transorganismal and functional evolution of bacterial and algal and terrestrial plant NIPs and to reveal their molecular transport specificity features. We discovered that aqpN genes are prevalently located in arsenic resistance operons of various prokaryotic phyla. We provided genetic and functional evidence that these proteins contribute to the arsenic detoxification machinery. We identified NIPs with the ancestral bacterial AqpN selectivity filter composition in algae, liverworts, moss, hornworts and ferns and demonstrated that these archetype plant NIPs and their prokaryotic progenitors are almost impermeable to water and silicon but transport arsenic and boron. With a mutational approach, we demonstrated that during evolution, ancestral NIP selectivity shifted to allow subfunctionalisations. Together, our data provided evidence that evolution converted bacterial arsenic efflux channels into essential seed plant nutrient transporters.

Boron containing compounds promote the survival and the maintenance of pancreatic ß-cells.

Diabetes mellitus is worldwide disease. The life of diabetic patients are dependent on exogenous insulin. Pancreas or particularly islet transplantations are performed for reducing external insulin dependency. External substances are also used to protect the ß-cells from the death or increase insulin secretion. In the current study, two different boron containing compounds (sodium pentaborate pentahydrate-NaB and boric acid-BA) were investigated for their effect on pancreatic cells in terms of pro-apoptotic and anti-apoptotic markers, genes related to insulin production mechanism, pancreatic development and glucose metabolism, some antioxidant enzymes, and genes for the initiation of diabetes, insulin secretion and antioxidant enzyme activities in vitro. The results revealed that boron containing compounds did not lead to apoptosis. On the contrary, they increased cell viability, antioxidant enzyme activities and the level of genes related to insulin production. Overall evaluation, data in the current study showed that boron containing compounds might be promising therapeutic agents for type 1 diabetes. However, additional investigations are strictly needed to elucidate molecular mechanisms of boron containing compounds.

Boron toxicity in higher plants: an update.

MAIN CONCLUSION: In this review, emphasis is given to the most recent updates about morpho-anatomical, physiological, biochemical and molecular responses adopted by plants to cope with B excess. Boron (B) is a unique micronutrient for plants given that the range of B concentration from its essentiality to toxicity is extremely narrow, and also because it occurs as an uncharged molecule (boric acid) which can pass lipid bilayers without any degree of controls, as occurs for other ionic nutrients. Boron frequently exceeds the plant's requirement in arid and semiarid environments due to poor drainage, and in agricultural soils close to coastal areas due to the intrusion of B-rich seawater in fresh aquifer or because of dispersion of seawater aerosol. Global releases of elemental B through weathering, volcanic and geothermal processes are also relevant in enriching B concentration in some areas. Considerable progress has been made in understanding how plants react to B toxicity and relevant efforts have been made to investigate: (I) B uptake and in planta partitioning, (II) physiological, biochemical, and molecular changes induced by B excess, with particular emphasis to the effects on the photosynthetic process, the B-triggered oxidative stress and responses of the antioxidant apparatus to B toxicity, and finally (III) mechanisms of B tolerance. Recent findings addressing the effects of B toxicity are reviewed here, intending to clarify the effect of B excess and to propose new perspectives aimed at driving future researches on the topic.

Nodulin Intrinsic Protein 7;1 Is a Tapetal Boric Acid Channel Involved in Pollen Cell Wall Formation.

Boron is an essential plant micronutrient that plays a structural role in the rhamnogalacturonan II component of the pectic cell wall. To prevent boron deficiency under limiting conditions, its uptake, distribution, and homeostasis are mediated by boric acid transporters and channel proteins. Among the membrane channels that facilitate boric acid uptake are the type II nodulin intrinsic protein (NIP) subfamily of aquaporin-like proteins. Arabidopsis (Arabidopsis thaliana) possesses three NIP II genes (NIP5;1, NIP6;1, and NIP7;1) that show distinct tissue expression profiles (predominantly expressed in roots, stem nodes, and developing flowers, respectively). Orthologs of each are represented in all dicots. Here, we show that purified and reconstituted NIP7;1 is a boric acid facilitator. By using native promoter-reporter fusions, we show that NIP7;1 is expressed predominantly in anthers of young flowers in a narrow developmental window, floral stages 9 and 10, with protein accumulation solely within tapetum cells, where it is localized to the plasma membrane. Under limiting boric acid conditions, loss-of-function T-DNA mutants (nip7;1-1 and nip7;1-2) show reduced fertility, including shorter siliques and an increase in aborted seeds, compared with the wild type. Under these conditions, nip7;1 mutant pollen grains show morphological defects, increased aggregation, defective exine cell wall formation, reduced germination frequency, and decreased viability. During stages 9 and 10, the tapetum is essential for supplying materials to the pollen microspore cell wall. We propose that NIP7;1 serves as a gated boric acid channel in developing anthers that aids in the uptake of this critical micronutrient by tapetal cells.

The importance of boron in biological systems.

Boron is an essential element for plants and probably essential for human and animal health. Boron has a broad range of physiological effects on biological systems at low concentrations, whereas it is toxic to at high concentrations. Eventhough there are many studies on boron's biological effects and toxicity, more information is needed to understand the mechanisms of its action. The aim of the current work is to review boron's function, transport and toxicity in different biological systems.

Identification of boric acid as a novel chemoattractant and elucidation of its chemoreceptor in Ralstonia pseudosolanacearum Ps29.

Chemotaxis enables bacteria to move toward more favorable environmental conditions. We observed chemotaxis toward boric acid by Ralstonia pseudosolanacearum Ps29. At higher concentrations, the chemotactic response of R. pseudosolanacearum toward boric acid was comparable to or higher than that toward L-malate, indicating that boric acid is a strong attractant for R. pseudosolanacearum. Chemotaxis assays under different pH conditions suggested that R. pseudosolanacearum recognizes B(OH)3 (or B(OH3) + B(OH)4-) but not B(OH)4- alone. Our previous study revealed that R. pseudosolanacearum Ps29 harbors homologs of all 22R. pseudosolanacearum GMI1000 mcp genes. Screening of 22 mcp single-deletion mutants identified the RS_RS17100 homolog as the boric acid chemoreceptor, which was designated McpB. The McpB ligand-binding domain (LBD) was purified in order to characterize its binding to boric acid. Using isothermal titration calorimetry, we demonstrated that boric acid binds directly to the McpB LBD with a K D (dissociation constant) of 5.4 µM. Analytical ultracentrifugation studies revealed that the McpB LBD is present as a dimer that recognizes one boric acid molecule.

18F-Tetrafluoroborate, a PET Probe for Imaging Sodium/Iodide Symporter Expression: Whole-Body Biodistribution, Safety, and Radiation Dosimetry in Thyroid Cancer Patients.

We report the safety, biodistribution, and internal radiation dosimetry, in humans with thyroid cancer, of 18F-tetrafluoroborate (18F-TFB), a novel PET radioligand for imaging the human sodium/iodide symporter (hNIS). Methods: Serial whole-body PET scans of 5 subjects with recently diagnosed thyroid cancer were acquired before surgery for up to 4 h after injection of 184 ± 15 MBq of 18F-TFB. Activity was determined in whole blood, plasma, and urine. Mean organ-absorbed doses and effective doses were calculated via quantitative image analysis and using OLINDA/EXM software. Results: Images showed a high uptake of 18F-TFB in known areas of high hNIS expression (thyroid, salivary glands, and stomach). Excretion was predominantly renal. No adverse effects in relation to safety of the radiopharmaceutical were observed. The effective dose was 0.0326 ± 0.0018 mSv/MBq. The critical tissues/organs receiving the highest mean sex-averaged absorbed doses were the thyroid (0.135 ± 0.079 mSv/MBq), stomach (0.069 ± 0.022 mSv/MBq), and salivary glands (parotids, 0.031 ± 0.011 mSv/MBq; submandibular, 0.061 ± 0.031 mSv/MBq). Other organs of interest were the bladder (0.102 ± 0.046 mSv/MBq) and kidneys (0.029 ± 0.009 mSv/MBq). Conclusion: Imaging using 18F-TFB imparts a radiation exposure similar in magnitude to many other 18F-labeled radiotracers. 18F-TFB shows a biodistribution similar to 99mTc-pertechnetate, a known nonorganified hNIS tracer, and is pharmacologically and radiobiologically safe in humans. Phase 2 trials for 18F-TFB as an hNIS imaging agent are warranted.

Aquaglyceroporins Are the Entry Pathway of Boric Acid in Trypanosoma brucei.

The boron element possesses a range of different effects on living beings. It is essential to beneficial at low concentrations, but toxic at excessive concentrations. Recently, some boron-based compounds have been identified as promising molecules against Trypanosoma brucei, the causative agent of sleeping sickness. However, until now, the boron metabolism and its access route into the parasite remained elusive. The present study addressed the permeability of T. brucei aquaglyceroporins (TbAQPs) for boric acid, the main natural boron species. To this end, the three TbAQPs were expressed in Saccharomyces cerevisiae and Xenopus laevis oocytes. Our findings in both expression systems showed that all three TbAQPs are permeable for boric acid. Especially TbAQP2 is highly permeable for this compound, displaying one of the highest conductances reported for a solute in these channels. Additionally, T. brucei aquaglyceroporin activities were sensitive to pH. Taken together, these results establish that TbAQPs are channels for boric acid and are highly efficient entry pathways for boron into the parasite. Our findings stress the importance of studying the physiological functions of boron and their derivatives in T. brucei, as well as the pharmacological implications of their uptake by trypanosome aquaglyceroporins.

Autoinducer-2 detection among commensal oral streptococci is dependent on pH and boric acid.

Autoinducer-2, considered a universal signaling molecule, is produced by many species of bacteria; including oral strains. Structurally, autoinducer-2 can exist bound to boron (borated autoinducer-2). Functionally, autoinducer-2 has been linked to important bacterial processes such as virulence and biofilm formation. In order to test production of autoinducer-2 by a given bacterial strain, a bioassay using marine bioluminescent bacteria Vibrio harveyi as a reporter for autoinducer-2 has been designed. We hypothesize that pH adjustment and addition of boron are required for optimal bioluminescence and accurate autoinducer-2 detection. Using this reporter strain we tested autoinducer-2 activity from two oral commensal species, Streptococcus gordonii DL1 and Streptococcus oralis 34. Spent broth was collected and adjusted to pH 7.5 and supplemented with boric acid prior to measuring autoinducer- 2 activity. Results show that low pH inhibits bioluminescence of the reporter strain, but pH 7.5 allows for bioluminescence induction and proper readings of autoinducer-2 activity. Addition of boric acid also has a positive effect on bioluminescence allowing for a more sensitive detection of autoinducer-2 activity. Our data suggests that although autoinducer-2 is present in spent broth, low pH and/or low levels of boric acid become an obstacle for proper autoinducer-2 detection. For proper autoinducer-2 detection, we propose a protocol using this bioassay to include pH adjustment and boric acid addition to spent broth. Studies on autoinducer-2 activity in several bacteria species represent an important area of study as this universal signaling molecule is involved in critical bacterial phenotypes such as virulence and biofilm formation.