A new technique for tritium labeling of humic substances

Label-Free Imaging of Humic Substance Bioaccumulation by Pump-Probe Microscopy

Humic substances (HS) are the most abundant forms of natural organic matter on the earth surface. Comprised of decomposed plant and animal materials rich in carbon, oxygen, hydrogen, nitrogen, and sulfur complexes, HS facilitate global carbon and nitrogen cycling and the transport of anthropogenic contaminants. While it is known that HS also interact with organisms at different trophic levels to produce beneficial and harmful effects whether HS exert these biological effects through accumulation remains unknown. Current radiolabeling techniques, which only detect the amount of accumulated radiolabels, cannot visualize the transport and accumulation behavior of HS. Here, using a label-free method based on pump-probe microscopy, we show HS entered the protozoan Tetrahymena thermophila, zebrafish embryos, and human cells and exerted direct effects on these organisms. HS accumulated in the nucleus of T. thermophila, chorion pore canals of zebrafish embryos, and nucleus of intestinal and lung cells in a concentration- and time-dependent way. Epigenetic and transcriptomics assays show HS altered chromatin accessibility and gene transcription in T. thermophila. In zebrafish larvae, HS induced neurotoxicity, altering spontaneous muscle contraction and locomotor activity. Detailed images showing HS accumulation in our study reveal new insights on the ecological and environmental behavior of HS.

Pharmacokinetic investigation of branched oligohexamethyleneguanidine hydrochloride in a liquid composition for the treatment of stomatitis and gingivitis

Branched oligohexamethyleneguanidine hydrochloride (branched OHMG-HC) possesses high biocidal activity. This study aimed at evaluating the pharmacokinetics of branched OHMG-HC and is mandatory for obtaining permission to conduct clinical studies. The thermal activation method was used to obtain radioactive-labeled drugs for the investigation of substance distribution in various tissues of experimental animals (rats and rabbits). Substance administration was carried out both orally (a dose was split into two equal volumes that were applied to buccal zones of the oral cavities of the animals) and intravenously to get a clear pharmacokinetic profile. In this research, the drug was applied in the concentration of 0.77 mg/kg with the addition of 0.037 mg/kg ³H-OHMG for rats, and 0.42 mg/kg with the addition of 0.015 mg/kg ³H-OHMG for Chinchilla rabbits. The selected samples of blood, organs and urine underwent alkaline mineralization. A quantitative determination of ³H-OHMG was carried out using a liquid β-, γ-counter according to the level of scintillation in the sample. Branched OHMG-HC displayed uniform distribution within all main organs and tissues upon oral administration. The highest concentrations were found in liver and kidney tissues, whereas the lowest in blood, cardiac muscle tissue and brain. The closeness of the f_abs values obtained from different animals (24.5% for rats and 29.0% for rabbits) demonstrated the absence of the species specificity in response to the pharmaceutical substance. The main parameters of excretion were established, and the half-life time was estimated to be 15 hours.

A Use of Tritium-Labeled Peat Fulvic Acids and Polyphenolic Derivatives for Designing Pharmacokinetic Experiments on Mice

Natural products (e.g., polyphenols) have been used as biologically active compounds for centuries. Still, the mechanisms of biological activity of these multicomponent systems are poorly understood due to a lack of appropriate experimental techniques. The method of tritium thermal bombardment allows for non-selective labeling and tracking of all components of complex natural systems. In this study, we applied it to label two well-characterized polyphenolic compounds, peat fulvic acid (FA-Vi18) and oxidized lignin derivative (BP-Cx-1), of predominantly hydrophilic and hydrophobic character, respectively. The identity of the labeled samples was confirmed using size exclusion chromatography. Using ultra-high resolution Fourier transform ion cyclotron resonance mass spectrometry (FT ICR MS), key differences in the molecular composition of BP-Cx-1 and FA-Vi18 were revealed. The labeled samples ([³H]-FA-Vi18 (10 mg/kg) and [³H]-BP-Cx-1 (100 mg/kg)) were administered to female BALB/c mice intravenously (i.v.) and orally. The label distribution was assessed in blood, liver, kidneys, brain, spleen, thymus, ovaries, and heart using liquid scintillation counting. Tritium label was found in all organs studied at different concentrations. For the fulvic acid sample, the largest accumulation was observed in the kidney (C_max 28.5 mg/kg and 5.6 mg/kg, respectively) for both routes. The organs of preferential accumulation of the lignin derivative were the liver (C_max accounted for 396.7 and 16.13 mg/kg for i.v. and p.o. routes, respectively) and kidney (C_max accounted for 343.3 and 17.73 mg/kg for i.v. and p.o. routes, respectively). Our results demonstrate that using the tritium labeling technique enabled successful pharmacokinetic studies on polyphenolic drugs with very different molecular compositions. It proved to be efficient for tissue distribution studies. It was also shown that the dosage of the polyphenolic drug might be lower than 10 mg/kg due to the sensitivity of the ³H detection technique.

Exploring bioactivity potential of polyphenolic water-soluble lignin derivative

Many natural substances exhibit anti-inflammatory activity and considerable potential in prophylaxis and treatment of allergies. Knowing exact molecular targets, which is required for developing these as medicinal products, is often challenging for multicomponent compositions. In the present study we examined novel polyphenolic substance, a water-soluble fraction of wood lignin (laboratory code BP-Cx-1). In our previous study, a number of polyphenolic components of BP-Cx-1 (flavonoids, sapogenins, phenanthrenes etc.) were identified as the major carriers of biological activity of BP-Cx drug family, and several molecular targets involved in cancer and/or inflammation signaling pathways were proposed based on the results of the in vitro and in silico screening studies. In the present study, half maximal inhibitory concentration (IC50) of BP-Cx-1 was established with a radioligand method and a range of IC50 values between 22.8 and 40.3 μg/ml were obtained for adenosine receptors A1, A2A and prostaglandin receptors EP2, IP (PGI2). IC50 for serotonin 5-HT1 and for glucocorticoid GR receptors were 3.0 μg/ml and 12.6 μg/ml, respectively, both being within the range of BP-Cx-1 concentrations achievable in in vivo models. Further, distribution of [³H] labelled BP-Cx-1 in NIH3T3 murine fibroblasts and MCF7/R carcinoma cells was studied with autoradiography. [³H]-BP-Cx-1 (visualized as silver grains produced by tritium beta particles) was mainly localized along the cell membrane, in the perinuclear region and in the nucleus, suggesting ability of BP-Cx-1 to enter cells and bind to membrane or cytosol receptors. In our experiment, we observed the effect of BP-Cx-1 on maturation of dendritic cells (DCs): downregulation of expression of the lipid-presentation molecule CD1a, co-stimulatory molecules CD80, CD83 and CD 40, decreased production of pro-inflammatory cytokines IL-4 and TNF-α and increased production of anti-inflammatory cytokine IL-10. It is hypothesized that [³H]-BP-Cx-1 detectable in the nucleus is part of the activated GR complex, known to be involved in regulation of transcription of genes responsible for the anti-inflammatory response. Based on IC50, cell distribution data and results of the experiment with DCs it is suggested that the in vivo effects of BP-Cx-1 are mediated via GR and 5-HT1 receptors thus promoting development of tolerogenic effector function in dendritic cells.

Behavior of humic substances in the liquid-liquid system directly measured using tritium label

Humic substances (HS) in the aqueous solutions can be considered as colloidal particles formed by amphiphilic units. HS form micelles-like structures at concentrations close to 5 g/L. However colloidal behavior of HS at concentrations below 100 mg/L is unknown. Using radiotracer assay we have shown that in this concentration range HS form rare adsorption layers at the liquid/liquid interface and penetrate into the organic phase with the distribution ratio close to 10^-3. We found that pH and HS molecular weight strongly influence on the distribution ratio but do not significantly change the adsorption. Furthermore, colloidal properties of HS are strongly depending on its origin: the highest surface activity was shown for HS separated from peat and the least was observed for HS separated from soils. We anticipate our assay to be a helpful tool for detailed analysis and modeling HS and humic-like materials colloidal behavior in the environment.

Influence of Humic Acid on Pb Uptake and Accumulation in Tea Plants

A hydroponic experiment combined with synchronous radiation X-ray fluorescence (SRXRF) analysis was designed to understand the influence of humic acid (HA) in tea plants under lead stress. The results showed that the quantitative relationship (QR) between humic acid and Pb is an important factor affecting the regulation of humic acid with respect to the accumulation of Pb in tea plants. Besides, excess humic acid might stimulate the accumulation of Pb in the root cell wall and transfer to the shoot organs through undifferentiated casparian band structure. This study could provide a theoretical basis for the scientific evaluation of the effect of humic acid on tea uptake and the accumulation of Pb and the practical application of humic acid in reducing Pb pollution in the field.

Deuterium- and Tritium-Labelled Compounds: Applications in the Life Sciences

Hydrogen isotopes are unique tools for identifying and understanding biological and chemical processes. Hydrogen isotope labelling allows for the traceless and direct incorporation of an additional mass or radioactive tag into an organic molecule with almost no changes in its chemical structure, physical properties, or biological activity. Using deuterium-labelled isotopologues to study the unique mass-spectrometric patterns generated from mixtures of biologically relevant molecules drastically simplifies analysis. Such methods are now providing unprecedented levels of insight in a wide and continuously growing range of applications in the life sciences and beyond. Tritium (³ H), in particular, has seen an increase in utilization, especially in pharmaceutical drug discovery. The efforts and costs associated with the synthesis of labelled compounds are more than compensated for by the enhanced molecular sensitivity during analysis and the high reliability of the data obtained. In this Review, advances in the application of hydrogen isotopes in the life sciences are described.

Label Distribution in Tissues of Wheat Seedlings Cultivated with Tritium-Labeled Leonardite Humic Acid

Humic substances (HS) play important roles in the biotic-abiotic interactions of the root plant and soil contributing to plant adaptation to external environments. However, their mode of action on plants remains largely unknown. In this study the HS distribution in tissues of wheat seedlings was examined using tritium-labeled humic acid (HA) derived from leonardite (a variety of lignites) and microautoradiography (MAR). Preferential accumulation of labeled products from tritiated HA was found in the roots as compared to the shoots, and endodermis was shown to be the major control point for radial transport of label into vascular system of plant. Tritium was also found in the stele and xylem tissues indicating that labeled products from tritiated HA could be transported to shoot tissues via the transpiration stream. Treatment with HA lead to an increase in the content of polar lipids of photosynthetic membranes. The observed accumulation of labeled HA products in root endodermis and positive impact on lipid synthesis are consistent with prior reported observations on physiological effects of HS on plants such as enhanced growth and development of lateral roots and improvement/repairs of the photosynthetic status of plants under stress conditions.

Langmuir hydrogen dissociation approach in radiolabeling carbon nanotubes and graphene oxide

Carbon-based nanomaterials have piqued the interest of several researchers. At the same time, radioactive labeling is a powerful tool for studying processes in different systems, including biological and organic; however, the introduction of radioactive isotopes into carbon-based nanomaterial remains a great challenge. We have used the Langmuir hydrogen dissociation method to introduce tritium in single-walled carbon nanotubes and graphene oxide. The technique allows us to achieve a specific radioactivity of 107 and 27 Ci/g for single-layer graphene oxide and single-walled carbon nanotubes, respectively. Based on the analysis of characteristic Raman modes at 1350 and 1580 cm−1, a minimal amount of structural changes to the nanomaterials due to radiolabeling was observed. The availability of a simple, nondestructive, and economic technique for the introduction of radiolabels to single-walled carbon nanotubes and graphene oxide will ultimately expand the applicability of these materials.

Humic substances enhance growth and respiration in the basidiomycetes Trametes maxima under carbon limited conditions

Humic substances (HS) represent the major reservoir of carbon (C) in ecosystems, and their turnover is crucial for understanding the global C cycle. Although basidiomycetes clearly have a role in HS degradation, much less is known about the effect of HS on fungal traits. We studied the alteration of physiological, biochemical, and morphological characteristics of Trametes maxima in the presence of HS. Both complete medium and minimal (C-limited) medium mimicking natural environmental conditions were used. Adding HS led to increased biomass yield, but under C-limited conditions the effect was more apparent. This result indicated that HS were used as an additional substrate and agreed with data showing a greater penetration of tritium-labeled HS into the cell interior under C-limited conditions. Humic substances induced ultra-structural changes in fungal cells, especially under C limitation, including reducing the thicknesses of the hyphal sheath and cell wall. In the minimal medium, cellular respiration increased nearly three-fold under HS application, while the corresponding effect in complete medium was lower. In addition, in the presence of inhibitors, HS stimulated either the cytochrome or the alternative pathway of respiration, depending on presence or absence of glucose in the medium. Our results suggest that, under conditions mimicking the natural environment, HS may play three major roles: as a surplus substrate for fungal growth, as a factor positively affecting cell morphology, and as an activator of physiological respiration.

Increase in the specific radioactivity of tritium-labeled compounds obtained by tritium thermal activation method

A method of tritium introduction into different types of organic molecules that is based on the interaction of atomic tritium with solid organic target is described. Tritium atoms are formed on the hot W-wire, which is heated by the electric current. Such an approach is called “tritium thermal activation method”. Here we summarize the results of labeling globular proteins (lysozyme, human and bovine serum albumins); derivatives of pantothenic acid and amino acids; ionic surfactants (sodium dodecylsulfate and alkyltrimethylammonium bromides) and nonionic high-molecular weight surfactants – pluronics. For the first time it is observed that if the target-compound is fixed and its radicals are stable the specific radioactivity of the labeled product can be drastically increased (up to 400 times) when the target temperature is ca. 295 K compared with the results obtained at 77 K. The influence of labeling parameters as tritium gas pressure, exposure time and W-wire temperature was tested for each target temperature that results in the optimum labeling conditions with high specific radioactivity and chemical yield of the resulting compound.

Liquid scintillation spectrometry of tritium in studying lysozyme behavior in aqueous/organic liquid systems. The influence of the organic phase

Liquid scintillation spectrometry of tritium in the application of the scintillation phase method was used for studying the adsorption of lysozyme at the liquid/liquid interface and its distribution in the bulk of the system. The goal of this research was to reveal the influence of the nature of the organic phase on the distribution and adsorption ability of the protein when it is placed in a system containing two immiscible liquids. Based on the radiochemical assay distribution coefficients and adsorption isotherms obtained for aqueous/octane, aqueous/p-xylene and aqueous/octanol systems, it was concluded that the interaction of the protein with the interface plays a dominant role in protein behavior in aqueous/organic liquid systems.