Uptake Of Boric Acid Research Articles

Redox Mechanisms Underlying the Cytostatic Effects of Boric Acid on Cancer Cells-An Issue Still Open.

Boric acid (BA) is the dominant form of boron in plasma, playing a role in different physiological mechanisms such as cell replication. Toxic effects have been reported, both for high doses of boron and its deficiency. Contrasting results were, however, reported about the cytotoxicity of pharmacological BA concentrations on cancer cells. The aim of this review is to briefly summarize the main findings in the field ranging from the proposed mechanisms of BA uptake and actions to its effects on cancer cells.

Effect of Tumor Microenvironment on Selective Uptake of Boric Acid in HepG2 Human Hepatoma Cells.

Feasibility and efficacy of boric acid (BA)-mediated boron neutron capture therapy (BNCT) was first demonstrated by eliminating hepatocellular carcinoma (HCC) in a rat model. Furthermore, selective uptake of BA by liver tumor cells was shown in a rabbit model. To gain further insight, this study aimed to investigate the mechanisms of transportation and selective uptake of BA in HepG2 liver tumor cells. Transportation of BA in HepG2 cells was analyzed by time-course assays and by analyzing the rate of diffusion versus the concentration of BA. The effect of different tumor conditions on BA uptake was studied by treating HepG2 cells with 25 μg 10B/ml BA under different concentrations of glucose, at different pH and in the presence of water-soluble cholesterol. HepG2 cells mainly uptake BA by simple diffusion. Cell membrane permeability may also contribute to tumor-specific uptake of BA. The selective uptake of BA was achieved primarily by diffusion, while other factors, such as low pH and increased membrane fluidity, which are hallmarks of HCC, might further enhance BA uptake.

A molecular framework for the inhibition of Arabidopsis root growth in response to boron toxicity

Boron is an essential micronutrient for plants and is taken up in the form of boric acid (BA). Despite this, a high BA concentration is toxic for the plants, inhibiting root growth and is thus a significant problem in semi-arid areas in the world. In this work, we report the molecular basis for the inhibition of root growth caused by boron. We show that application of BA reduces the size of root meristems, correlating with the inhibition of root growth. The decrease in meristem size is caused by a reduction of cell division. Mitotic cell number significantly decreases and the expression level of key core cell cycle regulators is modulated. The modulation of the cell cycle does not appear to act through cytokinin and auxin signalling. A global expression analysis reveals that boron toxicity induces the expression of genes related with abscisic acid (ABA) signalling, ABA response and cell wall modifications, and represses genes that code for water transporters. These results suggest that boron toxicity produces a reduction of water and BA uptake, triggering a hydric stress response that produces root growth inhibition.

Research note: Low-boron acclimation induces uptake of boric acid against a concentration gradient in root cells of Olea europaea.

Low concentrations of boron (B) in the external medium can induce uptake mechanisms whereby plants can develop a concentration gradient for B against the external medium. These mechanisms seem to be widespread among herbaceous species. In this study, olive (Olea europaea L.) plants were acclimated to either high (23 μm; controls) or low (0.5 μm; low-B plants) concentrations of B for 45 d, in a hydroponic culture. Afterwards, a 7-h uptake experiment was conducted by transferring plants of both groups to a series of nutrient solutions with B concentrations ranging from 0.5 to 23 μm. Analysis of B concentration in cell sap of root and xylem exudate was performed by the borate-chromotropic acid HPLC assay. Plants acclimated to high-B concentration showed root cell and xylem exudate B concentrations that were comparable to those of the external medium. In contrast, plants acclimated to low-B concentration were able to develop concentrations of B in root cells up to 2-fold higher than those of the external medium. Moreover, B concentrations in xylem exudate for both plant groups corresponded to those of the root cell sap, indicating diffusion equilibrium. These results support the existence of a mechanism that concentrates B in the root cell sap against the nutrient solution when olive plants are acclimated to low-B conditions.

Evidence for channel mediated transport of boric acid in squash (Cucurbita pepo)

Boron (B) is taken up by plant roots as undissociated boric acid which is a non-electrolyte of similar size to urea and other non-electrolytes. In animal systems, non-electrolytes are transported across biological membranes through aquaporins or through non-aquaporin channels. In artificial lipids boric acid is known to diffuse directly through the lipid bilayer at a rate that is determined by lipid composition. A possible role for channel proteins in in-vitro B uptake is suggested by recent work in which B uptake into isolated membrane vesicles was inhibited by channel blockers and by demonstration that the expression of the plant channel protein PIP1 in Xenopus oocytes increases boric acid uptake by 30%. This study examines whether B transport is a channel-mediated process in intact plants. In the presence of the channel inhibitors HgCl2, phloretin, and DIDS, B uptake by squash plants was reduced by 40–90% by HgCl2 (as HgCl2 varied from 50 μM to 1 mM), 44% by phloretin (250 μM) and 58% by DIDS (250 μM). The effect of Hg ions on B uptake was reversed by 2-mercaptoethanol. The addition of other non-electrolytes in size ranges similar to boric acid inhibited B uptake to various degrees. Addition of urea resulted in 54% decrease in B uptake, while, acetamide, formamide, thiourea and glycerol inhibited uptake by 50, 35, 53 and 44%, respectively. The effect of HgCl2 on B uptake was greater at high B concentrations than at low B concentrations. These data and information from in-vivo studies suggest two possible mechanisms of B uptake: passive diffusion through lipid bilayers and channel-mediated transport.

Preparation of Chelating Resins Selective to Boric Acid by Functionalization of Macroporous Poly(Glycidyl Methacrylate) with 2-Amino-2-hydroxymethyl-1,3-propanediol

Abstract Macroporous chelating resins containing polyol groups (RGB) were prepared by the reaction of poly(glycidyl methacrylate) beads with 2-amino-Zhydroxy-methyl-I,3-propanediol, and the behavior of the resulting RGB in the uptake of boric acid was studied. The RGB exhibited high affinity for boric acid in the pH range of 5 to 9 and took up boric acid selectively from geothermal power waste solutions in which various minerals were contained. The boric acid adsorbed on the RGB was easily eluted with I mol/dm3 hydrochloric acid.