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J R Rayburn

Publications and source records attributed to J R Rayburn.

15 recordsLinked to original sources
PubMed1998

Developmental toxicology of solamargine and solasonine glycoalkaloids in frog embryos.

As part of an effort to improve the safety of plant foods, a need exists to define the relative toxicities of structurally different glycoalkaloids and metabolites which may be present in Solanum plant species such as potatoes, tomatoes and eggplants. The objectives of this study were to determine the relative toxicities and the modes of action of the eggplant (Solanum melongena) glycoalkaloids solamargine and solasonine in Xenopus laevis frog embryos, using membrane potential and embryo growth and teratogenicity assays. In the cell membrane assays, adverse effects on embryos were evaluated by measuring membrane potentials using an electrochromic dye, di-4-ANEPPS, as a fluorescence probe for the integrity of the membranes. In the embryo growth and teratogenesis assays, the survival of the embryos and organ malformations was used as an index of embryo toxicity. The relative potencies of glycoalkaloids are similar for frog embryo effects (survival and teratogenicities) and for membrane effects (membrane potential). Experiments with solasonine at pH 6 and 8 suggest that the unprotonated form of the glycoalkaloids appears to be involved in the membrane effects. The nature of the carbohydrate side-chains of the steroidal glycosides governs relative potencies. The possible significance of the findings to food safety and plant physiology and possible application of the membrane assays to bacterial toxins are discussed.

Animals↗
PubMed1998

Phase III interlaboratory study of FETAX, Part 2: interlaboratory validation of an exogenous metabolic activation system for frog embryo teratogenesis assay--Xenopus (FETAX).

Interlaboratory validation of an exogenous metabolic activation system (MAS) developed for the alternative, short-term developmental toxicity bioassay, Frog Embryo Teratogenesis Assay-Xenopus (FETAX) was performed with cyclophosphamide and caffeine. Seven study groups within six separate laboratories participated in the study in which three definitive concentration-response experiments were performed with and without the MAS in a side-by-side format for each chemical. Since both chemicals had been previously tested in FETAX, the test concentrations were provided to each laboratory prior to testing. Interlaboratory coefficient of variation (CV) values for unactivated cyclophosphamide (no MAS) were 15%, 15%, 29%, and 25% for the 96-hr LC50, 96-hr EC50 (malformation), Minimum Concentration to Inhibit Growth (MCIG), and Teratogenic Index (TI) values, respectively. Addition of the MAS increased the CV values of each endpoint at least 3.9-fold. Interlaboratory CV values for unactivated caffeine were 31%, 18%, 31%, and 46% for the 96-hr LC50, 96-hr EC50 (malformation), MCIG, and TI values, respectively. Addition of the MAS decreased the CV values of each respective endpoint by at least 1.6-fold. Results indicated that bioactivated toxicants may be prone to greater variability in response amongst laboratories than compounds, which are detoxified. Even though more variability was noted with activated cyclophosphamide, results were within interlaboratory variation expected for other aquatic-based bioassays. Thus, results from these studies warrant the continued use and further refinement of FETAX for alternative developmental toxicity assessment.

Abnormalities, Drug-Induced↗
PubMed1997

Developmental toxicity of three carrier solvents using embryos of the grass shrimp, Palaemonetes pugio.

Embryos of the grass shrimp (Palaemonetes pugio) have shown sensitivity to the water soluble fraction of number 2 fuel oil. To determine the possible use of carrier solvents in grass shrimp bioassays, detailed concentration-response experiments for ethanol (EtOH), dimethylsulfoxide (DMSO), and acetone were performed and LC50 values were obtained using two test methods. The 4-d assay included development prior to the time of hatch through the time of hatch, a critical life stage of these embryos. The 12-d assay included development from the tissue cap stage embryos (late gastrula) through two days post-hatch. The average 4-d LC50s for EtOH, DMSO, and acetone were 12.07, 22.57, and 6.78 g/L, whereas the average 12-d LC50s were 3.63, 12.33, and 6.94 g/L, respectively. The coefficient of variation for each test was less than 25.2%. Based on concentration-response curves, the maximum allowable limit of EtOH, DMSO, and acetone to be used as a carrier in the grass shrimp embryo toxicity studies should be <1, <6, and <4 g/L, respectively.

Animals↗
PubMed1995

Protective effects of glucose-6-phosphate and NADP against alpha-chaconine-induced developmental toxicity in Xenopus embryos.

In previous studies a metabolic activation system (MAS) composed of Aroclor 1254-induced rat liver microsomes led to an apparent reduction of potato glycoalkaloid developmental toxicity in the frog embryo teratogenesis assay-Xenopus (FETAX). The reasons for this reduction were investigated in this study. The effect of the exogenous MAS on glycoalkaloid developmental toxicity was examined in two experiments in which a concentration series of alpha-chaconine was tested with a MAS with and without a reduced nicotinamide adenine dinucleotide (NADPH) generator system consisting of NADPH, oxidized nicotinamide adenine dinucleotide (NADP), glucose-6-phosphate (G6P) and glucose-6-phosphate dehydrogenase. The NADPH generator system and each of its individual components were tested at a single high concentration of alpha-chaconine to evaluate their potential effects on toxicity. The findings indicated that the protective effect of the MAS was not the result of detoxification by microsomal enzyme systems, but was caused by two components of the NADPH generator system, namely NADP and G6P. G6P was more protective of alpha-chaconine-induced toxicity than NADP at the concentrations tested. Thus, FETAX with a MAS must be performed with appropriate controls that take into account the possible interactions with individual components of the system.

Animals↗
PubMed1995

Synergistic interaction of glycoalkaloids alpha-chaconine and alpha-solanine on developmental toxicity in Xenopus embryos.

The embryo toxicities of two major potato glycoalkaloids, alpha-chaconine and alpha-solanine, were examined individually and in mixtures using the frog embryo teratogenesis assay-Xenopus. Calculations of toxic units (TUs) were used to assess possible antagonism, synergism or response addition of several mixtures ranging from approximately 3:1 to 1:20 TUs of alpha-chaconine to alpha-solanine. Some combinations exhibited strong synergism in the following measures of developmental toxicity: (a) 96-hr LC50, defined as the median concentration causing 50% embryo lethality; (b) 96-hr EC50 (malformation), defined as the concentration causing 50% malformation of the surviving embryos; and (c) teratogenic index which is equal to LC50/EC50 (malformation). The results indicated that each of the mixtures caused synergistic mortality or malformation. Furthermore, these studies suggested that the synergism observed for a specific mixture cannot be used to predict possible synergism of other mixtures with different ratios of the two glycoalkaloids; toxicities observed for individual glycoalkaloids may not be able to predict toxicities of mixtures; and specific combinations found in different potato varieties need to be tested to assess the safety of a particular cultivar.

Abnormalities, Drug-Induced↗
PubMed1993

Evaluation of the developmental toxicity of trichloroethylene and detoxification metabolites using Xenopus.

Potential mechanisms of trichloroethylene-induced developmental toxicity were evaluated using FETAX (Frog Embryo Teratogenesis Assay--Xenopus). Early Xenopus laevis embryos were exposed to trichloroethylene for 96 h in two separate definitive concentration-response assays with and without an exogenous metabolic activation system (MAS) and inhibited MAS. The MAS was treated with either carbon monoxide or cyclohexene oxide to modulate mixed-function oxidase (MFO) or epoxide hydrolase activity, respectively. Trichloroethylene metabolites: dichloroacetic acid, trichloroacetic acid, trichloroethanol, and oxalic acid were also evaluated in two separate definitive, static renewal tests. Addition of the MAS decreased the 96 h LC50 and EC50 (malformation) of trichloroethylene 1.8-fold and 3.8-fold, respectively. Addition of the carbon monoxide inhibited MAS decreased the developmental toxicity of activated trichloroethylene to levels approximating that of the parent compound. Cyclohexene oxide-inhibited MAS substantially increased the developmental toxicity of trichloroethylene. In addition, each of the metabolites tested were significantly less developmental toxic than the parent compound, trichloroethylene. Results indicate that a highly embryotoxic epoxide intermediate, trichloroethylene oxide, formed as the results of MFO mediated metabolism may play a significant role in the developmental toxicity of trichloroethylene in vitro.

Animals↗
PubMed1992

Evaluation of acetaminophen-induced developmental toxicity using FETAX.

Potential mechanisms of acetaminophen-induced developmental toxicity were evaluated using FETAX (Frog Embryo Teratogenesis Assay-Xenopus). Early Xenopus laevis embryos were exposed to acetaminophen for 96-h in two definitive concentrations-response assays with and without an exogenous metabolic activation system (MAS). Two static renewal tests of acetaminophen and the MAS treated with carbon monoxide, cimetidine, ellipticine, diethyl maleate, and supplemented with glutathione were also performed. Addition of the MAS decreased the 96-h LC50 and EC50 (malformation) values of unactivated acetaminophen 3.9-fold and 7.1-fold, respectively. Addition of the carbon monoxide- and ellipticine-inhibited MAS, as well as the glutathione-supplemented MAS decreased the developmental toxicity of activated acetaminophen to levels near that of the unactivated parent compound. Cimetidine-inhibited MAS also reduced the developmental toxicity of acetaminophen, but not to the extent observed with the carbon monoxide- and ellipticine-inhibited, or glutathione-supplemented MAS. Addition of the diethyl maleate-treated MAS substantially increased the developmental toxicity of acetaminophen. Results indicate that a highly reactive intermediate formed as the result of MFO-mediated metabolism (possibly P-448) significantly increased the developmental toxicity of acetaminophen. Glutathione was also found to play a major role in intermediate detoxification in vitro.

Abnormalities, Drug-Induced↗
PubMed1991

Altered developmental toxicity caused by three carrier solvents.

Many aquatic bioassays rely on chemical solvents to solubilize water-insoluble test materials. Interactions between solvents and test materials can lead to false positive or negative results. For this reason, tests for interactions between solvents and test materials were performed. The Frog Embryo Teratogenesis Assay--Xenopus (FETAX) was chosen because of its capacity to assess three different endpoints; mortality, malformation and embryo growth. Three solvents--dimethylsulfoxide (DMSO), acetone and triethylene glycol (TG)--were tested with two teratogens--methylmercury chloride (MMC) and trichloroethylene (TCE). DMSO potentiated the lethal effect of both teratogens but did not alter significantly the rate of malformation. Acetone increased the mortality for both teratogens, but only increased the MMC malformation greater than the additive effects. TG only increased the mortality and malformation with TCE. There were additive effects for growth for all solvents with the teratogens. The carrier solvents caused interactions even at their no-observable-effect concentration (NOEC). Therefore, the choice of carrier solvent should be made with caution. This study shows that different results can occur depending on the solvent used, and that a difference in one endpoint does not necessarily change the other endpoints.

Acetone↗
PubMed1991

Developmental toxicology of potato alkaloids in the frog embryo teratogenesis assay--Xenopus (FETAX).

Potatoes frequently contain growth inhibitors and toxic compounds including digestive enzyme inhibitors, lectins and glycoalkaloids. The literature suggests that Solanum alkaloids have the ability to induce neurological damage such as spina bifida and other malformations. As part of a programme of improvement in the safety of potatoes using molecular plant genetics and parallel food safety evaluation, we evaluated the effect of several potato glycoalkaloids and aglycones in the frog embryo teratogenesis assay--Xenopus (FETAX) with and without metabolic activation by Aroclor 1254-induced rat liver microsomes. The data suggest that the glycoalkaloid alpha-chaconine is teratogenic and more embryotoxic than alpha-solanine, in terms of the median lethal concentration (LC50) after 96 hr of exposure, the concentration inducing gross terata in 50% of the surviving frog embryos (96-hr EC50, malformation), and the minimum concentration needed to inhibit the growth of the embryos. Since these two compounds differ only in the nature of the carbohydrate side chain attached to the 3-OH group of solanidine, the side chain appears to be an important factor in governing teratogenicity. The aglycones demissidine, solanidine and solasodine were less toxic than the glycosides alpha-chaconine and alpha-solanine. The in vitro teratogenesis assay should be useful for: (a) predicting the teratogenic potential of solanaceae alkaloids, glycoalkaloids and related natural products; and (b) facilitating experimental approaches to suppress plant genes and enzymes that control the biosynthesis of the most toxic compounds.

Abnormalities, Drug-Induced↗
PubMed1991

Assessing the efficacy of an Aroclor 1254-induced exogenous metabolic activation system for FETAX.

The developmental toxicity of N-nitrosodimethylamine (NDMA) and trichloroethylene (TCE) was assessed with Frog Embryo Teratogenesis Assay: Xenopus (FETAX). Late Xenopus laevis blastulae were exposed to NDMA and TCE for 96-h in two separate static-renewal tests with and without the presence of three differently induced exogenous metabolic activation systems (MAS). The MAS consisted of Aroclor 1254-induced (Aroclor 1254 MAS), isoniazid-induced (INH MAS), and a post-isolation mixture (mixed MAS) of Aroclor 1254- and isoniazid-induced rat liver microsomes. Addition of the INH MAS and the mixed MAS increased the Teratogenic Index [TI = LC50/EC50 (malformation)] of NDMA and TCE nearly 2.0- and 2.1-fold and 2.1- and 1.7-fold, respectively. Inclusion of the Aroclor 1254 MAS did not alter the developmental toxicity of either compound. Based on TI values, embryo growth, and types and severity of induced malformations, both NDMA and TCE were developmentally toxic. Use of post-microsome isolation mixtures from differentially induced rat livers increased the efficacy of the exogenous MAS routinely used by FETAX.

Abnormalities, Drug-Induced↗
PubMed1990

Further validation of FETAX: evaluation of the developmental toxicity of five known mammalian teratogens and non-teratogens.

The developmental toxicity of five compounds was evaluated with the Frog Embryo Teratogenesis Assay: Xenopus (FETAX). Late Xenopus laevis blastulae were exposed to 5-azacytidine, methotrexate, pseudoephedrine, aspartame, and amaranth for 96 h. Three separate static-renewal assays were conducted for each compound. Based on Teratogenic Index [LC50/EC50 (malformation)] values, types and severity of induced malformations, and embryo growth, 5-azacytidine and methotrexate tested as having strong teratogenic potential. Pseudoephedrine scored as having moderate teratogenic potential, but amaranth and aspartame had little or no teratogenic potential. Results support the use of FETAX for the screening of developmental toxicants.

Abnormalities, Drug-Induced↗
PubMedDate not supplied

FETAX interlaboratory validation study: phase III--Part 1 testing.

The Frog Embryo Teratogenesis Assay-Xenopus (FETAX) is a 96-h whole embryo developmental toxicity screening assay that can be used in ecotoxicology and in detecting mammalian developmental toxicants when an in vitro metabolic activation system is employed. A standardized American Society for Testing and Materials (ASTM) guide for the conduct of FETAX has been published, along with a companion atlas that aids in embryo staging and identifying malformations. As part of the ASTM process, a three-phase interlaboratory validation study was undertaken to evaluate the repeatability and reliability of FETAX. Seven different participants collaborated in the study. In Phase I, FETAX proved to be more repeatable and reliable than many bioassays. However, some excessive variation was observed in a few laboratories. An initial lack of assay experience by some technicians caused variation. Phase II showed far less intra- and interlaboratory variability than Phase I. Non-teratogens showed the most consistent results, while more variability was observed for the two teratogens tested. Interlaboratory coefficient of variation values for all endpoints ranged from 7.3 to 54.7. Phase III--Part 1, using coded samples and test concentration ranges selected by each laboratory, showed results similar to Phase I. Analysis of the causes of variation suggested that some technicians judged some embryos to be malformed while others consistently judged similar embryos as normal. Concentration ranges tested by some of the laboratories varied greatly and a new protocol for selecting concentrations for initial testing was written to reduce variation from this source. Testing to date suggests that FETAX is as repeatable and reliable as other standard bioassays.

Aminopropionitrile↗
PubMedDate not supplied

Initial interlaboratory validation study of FETAX: phase I testing.

An interlaboratory validation study was undertaken to evaluate the repeatability and reliability of the Frog Embryo Teratogenesis Assay-Xenopus (FETAX), which is a whole embryo developmental toxicity screening assay. A three-phase experimental program with seven participants was carried out. Phase I was a training and protocol evaluation phase where the identity of the three test materials was known. Hydroxyurea, isoniazid and 6-aminonicotinamide were tested in Phase I. Because the chemicals has been tested previously in FETAX, the same concentrations needed to establish the 96-h median lethal concentration (LC50) and the concentration inducing malformations in 50% of the surviving embryos (EC50) were used by all laboratories. The results of Phase I are presented in this report, and FETAX has proved to be as repeatable and reliable as many other bioassays. Some excess variation was observed in individual laboratories. Some of this variation may have been due to training difficulties. One change in protocol design necessitated by this study was the use of 6-aminonicotinamide as a reference toxicant. While 6-aminonicotinamide provided excellent concentration-response data in most laboratories, the protocol was written too strictly based on historical FETAX data. Phases II and III are currently in progress.

6-Aminonicotinamide↗