Lipid vesicles as membrane models for toxicological assessment of xenobiotics.

Traditionally animals and cell cultures have been used to assess the toxic potential of xenobiotics on cell membranes. In search for more reproducible, quantitative, cost- and time-effective assays, toxicologists have recently become interested in biomimetic lipid vesicle-based test systems. Lipid vesicles (liposomes) have long been appreciated as simple cell membrane models in biochemical and biophysical studies providing a good understanding of the physicochemical properties of liposome systems. More recently a number of reports have been published on the interactions of toxic substances with vesicles. Literature reports on liposome assays have appeared for widely different classes of xenobiotics, such as dental materials, antibiotics, detergents, and peptides. In this review we focus on those reports that contain a quantitative and significant correlation with more established toxicological tests like cell culture assays. We provide an introduction to the structure and main characteristics of vesicles and related lipid aggregates. The two main assays presented are leakage of fluorescence dyes and differential scanning calorimetry (DSC) measurements of the solid-ordered/liquid-disordered main phase transition temperature (Tm).

Quantum mechanical structure-activity relationship analyses for skin sensitization.

Allergic contact dermatitis (ACD) results in inflammation of the skin due to sensitization of the immunologic system to a particular substance. The sensitization process is limited by the compound's ability to both permeate and react with proteins in the integumentary system. Currently, only in vivo animal tests such as the local lymph node assay (LLNA) are recognized by regulatory authorities for risk assessment of ACD. A quantitative structure-activity relationship has been developed to predict relative potency, which allows for the prediction of relative sensitization potentials. The experimental values used in this study include EC3 values (the concentration at which the stimulation index equals 3) from LLNA tests. The predictions in this model enable categorization of the compounds into three groups on the basis of risk of sensitization and enable screening of candidate molecules using rapid SAM1 semiempirical calculations prior to animal testing. The model may also be used to reduce the number of animals subjected to testing by providing estimated concentrations required for useful data of risk assessment. The effect of averaging available literature values on predictive ability is also investigated. The model includes halogenated compounds, aromatic compounds, alcohols, aldehydes, and ketones. The computational investigation resulted in a two-descriptor model that is consistent with the assumed mechanism for sensitization.

An application of the QM-QSAR method to predict and rationalize lipophilicity of simple monomers.

OBJECTIVES: The goal of this study is to develop a model used to predict octanol/water partition coefficients (log P(o/w)) values for a variety of potential dental materials. In this way, a primary consideration for potential toxicity and a rough estimate of solubility in various environments can be obtained. METHOD: The AM1 semiempirical quantum mechanical method (in AMPAC) was used to compute chemical data for all compounds in the study. CODESSA then imported the chemical information from AMPAC and computed a large set of informational descriptors. A quantitative structure activity relationship (QSAR) model was derived correlating experimental results from a training set of molecules with certain of the descriptors computed above. RESULTS: A training set of 92 molecules was used to derive the QSAR model and three descriptors were obtained: the molecular surface area, the total dipole moment of the molecule, and FPSA-3 (fractional atom charge weighted partial positive surface area). Various quality indicators were also computed and all fell within acceptable ranges: R(2)=0.945; adjusted R(2)=0.943; R(cv)(2)=0.940; variance inflation factors (VIF) for the descriptors above are 1.116, 1.044, and 1.162, respectively. SIGNIFICANCE: This QSAR model can be used to accurately and rapidly predict log P(o/w) values for a wide variety of small organic molecules, including potential dental monomers.

Genotoxicity assessment of oxirane-based dental monomers in mammalian cells.

The potential use of oxirane (epoxy) monomers in dental composite development raises the concern to test their genetic safety. Oxiranes can interact with DNA resulting in DNA damage, mutations, and possibly carcinogenesis. Our objective was to evaluate DNA damage and cell-cycle disruption in mammalian cells after exposure to epoxy monomers. The experimental oxiranes were Araldite trade mark GY 281, Cyracure trade mark UVR 6105 and 1,3-dioxane-2,2'-1,3-dioxane-5',4'-bicyclo[4.1.0] heptane (DECHE-TOSU). L929 fibroblast cells were incubated with the monomer for 7 and 24 h at 37 degrees C/5% CO(2). After incubation, cells were subjected to DNA damage alkaline unwinding assay and flow cytometry cell-cycle analysis. Lack of DNA damage and cell-cycle effects were observed with DECHE-TOSU. Exposure to subtoxic doses of Araldite trade mark GY 281 or Cyracure trade mark UVR 6105 caused DNA damage and cell cycle disruption. A significant (p < 0.01) effect for Araldite trade mark GY 281 was observed with cell populations in G1 and G2/M when compared to DMSO solvent control. Similar comparisons revealed significant differences in G2/M cell cycle population after 24-h exposure to 100 microM Cyracure trade mark UVR 6105. For comparison, BISGMA was evaluated to produce DNA damage but without cell-cycle effects suggesting DNA repair mechanisms were effective. Our findings with DECHE-TOSU, Araldite trade mark GY 281 and Cyracure trade mark UVR 6105 indicated cell-cycle disruption followed DNA damage.

Chain melting temperature estimation for phosphatidyl cholines by quantum mechanically derived quantitative structure property relationships.

Geometries for 62 phosphatidylcholines (PC) were optimized using the AM1 semiempirical quantum mechanical method. Results obtained from these calculations were used to calculate 463 descriptors for each molecule. Quantitative Structure Property Relationships (QSPR) were developed from these descriptors to predict chain melting temperatures (Tm) for the 41 PCs in the training set. After screening each QSPR for statistical validity, the Tm values predicted by each statistically valid QSPR were compared to corresponding Tm values extracted from the literature. The most predictive, chemically meaningful QSPR provided Tm values which agreed with literature values to within experimental error. This QSPR was used to predict Tm values for the remaining 21 PCs to provide external validation for the model. These values also agreed with literature values to within experimental error. The descriptor developed by the final QSPR was the second order average information content, a topological information-theoretical descriptor.

In vitro effect of light-cure dental adhesive on IL-6 release from LPS-stimulated and unstimulated macrophages.

The objective of this study was to measure IL-6 release from LPS-stimulated and -unstimulated macrophages exposed to extracts from fresh and aged Scotchbond Multipurpose Plus adhesive disks (5 mm in diameter by 2 mm in thickness) light cured for 10, 20, or 40 s. One set of disks was aged for 16 weeks at 4 degrees C. Extracts were prepared by incubating three disks in 1 mL of serum-free culture medium for 72 h at 37 degrees C. Then macrophages (RAW 264.7) were exposed to the extracts (6.25-50 microL) for 72 h at 37 degrees C/5% CO(2). Supernatants were analyzed for cytokine levels (ELISA), and the monolayer of cells was assessed for viability (MTT assay). Unlike adhesive disk age, curing time affected cell viability. Disk extracts cured for 10 s were more cytotoxic (p < 0.05) than were extracts from 20- or 40-s cured disks. Macrophage release of IL-6 was stimulated significantly (p < 0.01) by extracts from fresh 10-s cured disks, up to 777 pg/mL and by 2 microg/mL of LPS (1174 pg/mL). The LPS response was significantly (p < 0.05) suppressed by 50 microL of extracts, which may be related to the enhanced cytotoxicity exhibited by LPS in combination with extracts. This study has demonstrated the possibility that IL-6 release is stimulated by light-cure dental adhesive applications using 10-s curings.