Xin-Rui Xia

In vitro toxicity assessment of three hydroxylated fullerenes in human skin cells

Carbon fullerenes possess unique properties and their interactions with biomolecules have widespread applications. Functionalization of fullerenes with hydroxyl groups (fullerenols) can increase the solubility and potential for cellular interaction, but the health and safety effects of varying degrees of fullerene hydroxylation in biological systems is poorly understood. Existing reports regarding the toxicity and inflammatory potential of fullerenols give conflicting conclusions. To further elucidate the potential for toxicity of fullerenols, human epidermal keratinocytes (HEK) were exposed to fullerenols (low (C60(OH)20), medium (C60(OH)24), and high (C60(OH)32)) at concentrations ranging from 0.000544-42.5 μg/ml for 24 and 48 h. A statistically significant (p<0.05) decrease in viability with alamar Blue (aB) was noted only with C60(OH)32 at 42.5 μg/ml after 24 h. Nanoparticle (NP) controls showed minimal NP/assay interference of the three fullerenols with the aB viability assay. Normalized IL-8 concentration for C60(OH)20 was not significantly different from control, while C60(OH)24 and C60(OH)32 showed a significant decrease at 24 and 48 h. These results suggest that different hydroxylation of fullerenes caused no cytotoxicity or inflammation up to 8.55 μg/ml. These findings suggest that extrapolation across similar NP will be dependent upon surface chemistry and concentration which may affect the degree of agglomeration and thus biological effects.

A system coefficient approach for quantitative assessment of the solvent effects on membrane absorption from chemical mixtures

A system coefficient approach is proposed for quantitative assessment of the solvent effects on membrane absorption from chemical mixtures. The complicated molecular interactions are dissected into basic molecular interaction forces via Abrahams linear solvation energy relationship (LSER). The molecular interaction strengths of a chemical are represented by a set of solute descriptors, while those of a membrane/chemical mixture system are represented by a set of system coefficients. The system coefficients can be determined by using a set of probe compounds with known solute descriptors. Polydimethylsiloxane (PDMS) membrane-coated fibres and 32 probe compounds were used to demonstrate the proposed approach. When a solvent was added into the chemical mixture, the system coefficients were altered and detected by the system coefficient approach. The system coefficients of the PDMS/water system were (0.09, 0.49, −1.11, −2.36, −3.78, 3.50). When 25% ethanol was added into the PDMS/water system, the system coefficients were altered significantly (0.38, 0.41, −1.18, −2.07, −3.40, 2.81); and the solvent effect was quantitatively described by the changes in the system coefficients (0.29, −0.08, −0.07, 0.29, 0.38, −0.69). The LSER model adequately described the experimental data with a correlation coefficient (r 2) of 0.995 and F-value of 1056 with p-value less than 0.0001.

A Novel in-Vitro Technique for Studying Percutaneous Permeation with a Membrane-Coated Fiber and Gas Chromatography/Mass Spectrometry: Part I. Performances of the Technique and Determination of the Permeation Rates and Partition Coefficients of Chemical Mixtures

AbstractPurpose. To develop a novel in-vitro technique for rapid assessment of percutaneous absorption of chemical mixtures. Methods. A silastic membrane was coated on to a fiber to be used as a permeation membrane. The membrane-coated fiber was immersed in the donor phase to partition the compounds into the membrane. At a given partition time, the membrane-coated fiber was transferred into a GC injector to evaporate the partitioned compounds for quantitative and qualitative analyses. Results. This technique was developed and demonstrated to study the percutaneous permeation of a complex mixture consisting of 30 compounds. Each compound permeated into the membrane was identified and quantified with GC/MS. The standard deviation was less than 10% in 12 repeated permeation experiments. The partition coefficients and permeation rates in static and stirred donor solution were obtained for each compound. The partition coefficients measured by this technique were well correlated (R2 = 0.93) with the reported octanol/water partition coefficients. Conclusions. This technique can be used to study the percutaneous permeation of chemical mixtures. No expensive radiolabeled chemicals are required. Each compound permeated into the membrane can be identified and quantified. The initial permeation rate and equilibrium time can be obtained for each compound, which could serve as characteristic parameters regarding the skin permeability of the compound.

A compartment model for the membrane-coated fiber technique used for determining the absorption parameters of chemicals into lipophilic membranes.

AbstractPurpose. The purpose of this work was to develop a compartment model for the membrane-coated fiber (MCF) technique for determining the absorption parameters of chemicals into lipophilic membranes. Methods. A polymer membrane coated onto a section of inert fiber was used as a permeation membrane in the MCF technique. When MCFs were immersed into a donor solution, the compounds in the solution partitioned into the membrane. At a given permeation time, a fiber was removed from the solution and transferred into a gas chromatography injector for quantitative analysis. The permeation process of a given chemical from the donor phase into the membrane was described by a one-compartment model by assuming first-order kinetics. Results. A mathematical model was obtained that describes the cumulative amount of a chemical permeated into the membrane as a function of the permeation time in an exponential equation. Two constants were introduced into the compartment model that were clearly defined by the physiochemical parameters of the system (a kinetic parameter and the equilibrium absorption amount) and were obtained by regression of the experimental data sampled over a limited time before equilibrium. The model adequately described the permeation kinetics of the MCF technique. All theoretical predictions were supported by the experimental results. The experimental data correlated well with the mathematical regression results. The partition coefficients, initial permeation rate, uptake, and elimination rate constants were calculated from the two constants. Conclusions. The compartment model can describe the absorption kinetics of the MCF technique. The regression method based on the model is a useful tool for the determination of the partition coefficients of lipophilic compounds when it takes too long for them to reach permeation equilibrium. The kinetic parameter and the initial permeation rate are unique parameters of the MCF technique that could be used in the development of quantitative structure-activity relationship models.

Lack of hydroxylated fullerene toxicity after intravenous administration to female Sprague-Dawley rats.

Hydroxylated fullerenes (C60OHx) or fullerols are water-soluble carbon nanoparticles that have been explored for potential therapeutic applications. This study assesses acute in vivo tolerance in 8-wk-old female Sprague-Dawley rats to intravenous (iv) administration of 10 mg/kg of well-characterized C60(OH)30. Complete histopathology and clinical chemistries are assessed at 8, 24, and 48 h after dosing. Minor histopathology changes are seen, primarily in one animal. No clinically significant chemistry changes were observed after treatment. These experiments suggest that this fullerol was well tolerated after iv administration to rats.

Dose Related Absorption of JP-8 Jet Fuel Hydrocarbons Through Porcine Skin with Quantitative Structure Permeability Relationship Analysis.

The effects of dosage on the percutaneous absorption of jet fuel hydrocarbons is not clear, yet is essential for human risk assessment. The present study is an ongoing approach to assess the dose-related percutaneous absorption of a number of aliphatic and aromatic hydrocarbons. The first treatment (1X) was comprised of mixtures containing undecane (4.1%), dodecane (4.7%), tridecane (4.4%), tetradecane (3%), pentadecane (1.6%), naphthalene (1.1%), and dimethyl naphthalene (1.3% of jet fuels) in hexadecane solvent using porcine skin flow through diffusion cell. Other treatments (n = 4 cells) were 2X and 5X concentrations. Perfusate samples were analyzed with gas chromatography-flame ionization detector (GC-FID) using head space solid phase micro-extraction fiber technique. We have standardized the assay to have a good linear correlation for all the tested components in media standards. Absorption parameters including diffusivity, permeability, steady state flux, and percent dose absorbed were estimated for all the tested hydrocarbons. This approach provides a baseline to access component interactions among themselves and with the diluent (solvents). A quantitative structure permeability relationship (QSPR) model was derived to predict the permeability of unknown jet fuel hydrocarbons in this solvent system by using their physicochemical parameters. Our findings suggested a dose related increase in absorption for naphthalene and dimethyl naphthalene (DMN).

Membrane uptake kinetics of jet fuel aromatic hydrocarbons from aqueous solutions studied by a membrane-coated fiber technique.

The absorption of aromatic hydrocarbons from aqueous media is a critical step involved in many biological processes after occupational and environmental exposures to jet fuel. A membrane-coated fiber (MCF) technique was used to study the uptake kinetics. A flow-through system was used to provide a constant concentration for the prolonged permeation experiments. Polydimethylsiloxane (PDMS) and polyacrylate (PA) MCFs were used to study the differential absorptivity of the aromatic compounds between the two membrane materials. The equilibrium absorption amount and a kinetic parameter describing the absorption kinetics were obtained by the regression of the permeation profiles of the aromatic compounds with a mathematical model. The partition coefficients, uptake, and elimination rate constants were determined for six benzene and three naphthalene derivatives. The PDMS/water partition coefficients of the benzene and naphthalene derivatives were linearly correlated with their logKo/w (LogKpdms/w = 0.871LogKo/w − 0.241, R2 = 0.995). The PA/water partition coefficients of the benzene derivatives and the naphthalene derivatives were correlated differently with their logKo/w. The correlation equations for benzene and naphthalene derivatives were LogKpa/w = 0.865LogKo/w + 0.0045, R2 = 0.997 and LogKpa/w = 0.763LogKo/w + 0.911, R2 = 1.00, respectively. These results suggest that the MCF technique can detect subtle differences in molecular interactions of the two group derivatives between the two membrane/water systems and may be used to study the absorption and permeation properties of closely related compounds. Finally, the regression method is a particularly useful tool to determine partition coefficients of very lipophilic compounds.

A solvatochromatic approach to quantifying formulation effects on dermal permeability

Dermal risk assessments are most often concerned with the occupational and environmental exposure to a single chemical and then determining solute permeability through in vitro or in vivo experimentation with various animal models and/or computational approaches. Oftentimes, the skin is exposed to more than one chemical that could potentially modulate dermal permeability of the chemical that could cause adverse health effects. The focus of this article is to demonstrate that these formulation effects on dermal permeability can occur with simple solvent formulations or complex industrial formulations and that these effects can be modeled within the context of a linear solvation energy relationship (LSER). This research demonstrated that formulation-specific strength coefficients (r p a b v) predicted (r 2 = 0.75–0.83) changes in the dermal permeability of phenolic compounds when formulated with commercial metal-working fluid (MWF) formulations or 50% ethanol. Further experimentation demonstrated that chemical-induced changes in skin permeability with 50% ethanol are strongly correlated (r 2 = 0.91) to similar changes in an inert membrane-coated fiber (MCF) array system consisting of three chemically diverse membranes. Changes in specific strength coefficients pertaining to changes in hydrogen donating ability (Δb) and hydrophobicity (Δv) across membrane systems were identified as important quantitative interactions associated with ethanol mixtures. This solvatochromatic approach along with the use of a MCF array system holds promise for predicting dermal permeability of complex chemical formulations in occupational exposures where performance additives can potentially modulate permeability of potential toxicants. †Presented at the 13th International Workshop on QSARs in the Environmental Sciences (QSAR 2008), 8–12 June 2008, Syracuse, USA.

Partitioning Behavior of Aromatic Components in Jet Fuel into Diverse Membrane-coated Fibers

Jet fuel components are known to partition into skin and produce occupational irritant contact dermatitis (OICD) and potentially adverse systemic effects. The purpose of this study was to determine how jet fuel components partition (1) from solvent mixtures into diverse membrane-coated fibers (MCFs) and (2) from biological media into MCFs to predict tissue distribution. Three diverse MCFs, polydimethylsiloxane (PDMS, lipophilic), polyacrylate (PA, polarizable), and carbowax (CAR, polar), were selected to simulate the physicochemical properties of skin in vivo. Following an appropriate equilibrium time between the MCF and dosing solutions, the MCF was injected directly into a gas chromatograph/mass spectrometer (GC-MS) to quantify the amount that partitioned into the membrane. Three vehicles (water, 50% ethanol–water, and albumin-containing media solution) were studied for selected jet fuel components. The more hydrophobic the component, the greater was the partitioning into the membranes across all MCF types, especially from water. The presence of ethanol as a surrogate solvent resulted in significantly reduced partitioning into the MCFs with discernible differences across the three fibers based on their chemistries. The presence of a plasma substitute (media) also reduced partitioning into the MCF, with the CAR MCF system being better correlated to the predicted partitioning of aromatic components into skin. This study demonstrated that a single or multiple set of MCF fibers may be used as a surrogate for octanol/water systems and skin to assess partitioning behavior of nine aromatic components frequently formulated with jet fuels. These diverse inert fibers were able to assess solute partitioning from a blood substitute such as media into a membrane possessing physicochemical properties similar to human skin. This information may be incorporated into physiologically based pharmacokinetic (PBPK) models to provide a more accurate assessment of tissue dosimetry of related toxicants.