Metabolic activation capabilities of S9 liver fraction from 3 species in the L5178Y mouse-lymphoma assay

Development of a decellularized porcine bone graft by supercritical carbon dioxide extraction technology for bone regeneration

A series of novel decellularized porcine collagen bone graft (DPB) materials in a variety of shapes and sizes were developed by the supercritical carbon dioxide (SCCO₂ ) extraction technique. The complete decellularization of DPB was confirmed by hematoxylin and eosin staining, 4,6-diamidino-2-phenylindole (DAPI) staining, and residual DNA analysis. The native intact collagen remained in the DPB after the SCCO₂ process was confirmed by Masson trichrome staining. The physicochemical characteristics of DPB were investigated by scanning electron microscopy and x-ray diffraction. The cytotoxicity and biocompatibility tests according to ISO10993 and its efficacy for bone regeneration in osteochondral defects in rabbits were evaluated. The rabbit pyrogen test confirmed DPB was non-toxic. In vitro and in vivo biocompatibility tests of the DPB did not show any toxic or mutagenic effects. The bone regeneration potential of the DPB presented no significant histological differences compared to commercially available deproteinized bovine bone. In conclusion, DPB produced by SCCO₂ exhibited similar chemical characteristics to human bone, no toxicity, good biocompatibility, and enhanced bone regeneration in rabbits comparable to that of deproteinized bovine bone. Results from this study could shed light on the potential application of the SCCO₂ extraction technique to generate a native decellularized scaffold for bone tissue regeneration in human clinical trials.

Induction of unscheduled DNA synthesis in primary cultures of rat, mouse, hamster, monkey, and human hepatocytes

Variation in hepatic metabolism between species may be an important factor in the differences observed in chemical carcinogenesis. We examined 6 chemicals representative of 4 chemical classes in the in vitro hepatocyte DNA repair assay using cells isolated from the Fischer-344 rat, B6C3F1 mouse, Syrian golden hamster, cynomolgus monkey and from human liver. Hepatocytes were isolated by in situ or biopsy liver perfusion and incubated with [3H]-thymidine and the test chemical. Unscheduled DNA synthesis (UDS) was measured as net grains/nucleus (NG) by quantitative autoradiography. Qualitative and quantitative differences in UDS responses were observed for every chemical. Liver cultures isolated from the rat, mouse, hamster, human, and monkey and treated with aflatoxin B1 or dimethylnitrosamine all yielded dose-related increases in NG. Human, rat, and hamster hepatocyte cultures yielded positive responses following exposure to the aromatic amines 2-acetylaminofluorene, 4-aminobiphenyl, and benzidine, whereas cultures isolated from the monkey and mouse yielded less than 0 NG. Treatment with benzo[a]pyrene (BAP) produced strong positive responses in monkey and human hepatocyte cultures, weak positive responses in hamster cultures, and equivocal or negative responses in rat and mouse hepatocyte cultures. Hepatocyte function was assessed by measurement of DNA content, glutathione content, BAP hydroxylase activity, p-nitroanisole-O-demethylase activity, p-nitrophenol conjugation, and urea synthesis rates. The functional capabilities of isolated hamster, monkey, and human hepatocyte cultures do not appear to correlate with UDS responses observed for any compound; however, they indicate that the cultures were metabolically competent at the time of chemical exposure. These studies suggest that rat hepatocytes are a suitable model for human hepatocytes, whereas mouse and male monkey hepatocytes may be insensitive to aromatic amines.

Evaluation of the L5178Y mouse lymphoma cell mutagenesis assay: interlaboratory reproducibility and assessment

The L5178Y mouse lymphoma cell mutagenesis assay is used to detect the mutagenic activity of chemicals in a mammalian cell system. To evaluate this assay we compared the results of assays performed independently on 63 chemicals by laboratories at SRI International and Litton Bionetics, Inc. The two laboratories used similar protocols. The solvent and positive control mutant frequencies and cloning efficiencies obtained by the two laboratories were similar, which justified the use of the same quality-control criteria and analytical procedures for analyzing the results from both laboratories. The rate of concordance between the two laboratories was 92% for tests in the absence of S9 activation and 95% for tests in its presence. The results of the assays agreed for 57 of the 63 chemicals; three chemicals could not be compared because there were questionable calls in at least one of the laboratories; the results disagreed for the three remaining chemicals. The concordance rate for these overall assay evaluations was 95%. The interlaboratory concordance rates were similar to concordance rates for replicate experiments within the laboratories (96% at LBI, 94% at SRI). The mouse lymphoma cell mutagenicity results are concordant with the rodent chronic assay results in 78% of 50 chemicals and with the Salmonella assay results in 79% of 56 chemicals. Fifteen carcinogens were examined for genotoxic effects in mouse lymphoma, Salmonella, Chinese hamster ovary (CHO) chromosomal aberration, and CHO sister chromatid exchange assay. Eight of these were positive in all four assays. Of the seven noncarcinogens that were tested in these four assays, none was negative in all four. The main conclusion to be drawn from this study is that the mouse lymphoma cell forward mutation assay, as performed and evaluated in this study, detects chemical mutagenicity in a manner that is highly consistent with other genetic endpoints as well as rodent carcinogenicity studies. Thus the assay quality control and response criteria established in this study led not only to a high degree of reproducibility but also to an apparently reliable detection of mutagenic activity.

Evaluation of the L5178Y mouse lymphoma cell mutagenesis assay: intralaboratory results for sixty-three coded chemicals tested at Litton Bionetics, Inc

The reliability of the L5178Y TK+/- forward mutation assay as a rapid screen for genotoxicity was evaluated by testing 63 coded chemicals. Replicate treatments were used, and at least two independent experiments were performed for each test condition. The test conditions consisted of no exogenous activation, activation by Aroclor 1254-induced Fischer 344 rat liver S9 homogenate, and in some cases activation by noninduced Fischer 344 rat liver S9. The results were organized into tables that show the mutant colony counts, mutant frequency, and toxicity for each test chemical treatment, positive control treatment, and solvent negative control cultures. The repeat experiments were highly consistent and yielded contradictory evaluations for only a few of the chemicals studied. Fifty-one of the chemicals (81%) were evaluated as mutagenic under one or both of the test conditions. A range in minimum effective concentrations of almost 10(6)-fold (0.008 to 5,000 micrograms/ml) was observed among the mutagenic chemicals. Nine chemicals (14%) were considered to be nonmutagenic. Three chemicals (progesterone, p-rosaniline HCl, and 1,1,1-trichloroethane) gave responses that were not easily evaluated under any test condition: evidence for mutagenesis was obtained in some experiments but not for all repeat studies. Under nonactivation conditions, specifically, the mutagenic activities of 4,4'-bis(dimethylamino)benzophenone, progesterone, and p-rosaniline HCl remained uncertain. With S9 activation, uncertain evidence for mutagenesis was obtained for 2-naphthylamine, progesterone, and 1,1,1-trichloroethane. In some cases, changes in the treatment conditions could lead to different evaluations of the mutagenic activity, and these possibilities are discussed in the descriptive evaluations of each chemical. Comparisons of the observed responses with published results were possible for 29 of the compounds and yielded highly confirmatory evaluations.

An evaluation of the L5178Y TK+/- mouse lymphoma forward mutation assay using 42 chemicals

The L5178YTK+/- mouse lymphoma assay (MLA) has been utilized in several laboratories as a short-term test for chemical-induced forward mutation in cultured mammalian cells. In order to evaluate several technical modifications to the MLA, 42 chemicals representing 9 chemical classes were tested and the results were compared with those published elsewhere as well as with findings in a genetic toxicology test battery currently used in this laboratory. A positive response for the induction of TK-/- mutants was obtained for 26 chemicals. With the exception of p-aminophenol, all of these compounds were recognized mutagens or carcinogens and were representative of direct-acting and activation-dependent genotoxins. 16 compounds did not induce TK-/- mutants and among these were 5 compounds that were considered to be mutagens or carcinogens. A comparison of the results of this study with those published elsewhere revealed a strong agreement among findings for this test irrespective of minor technical variations. It was concluded that the MLA is a useful system for identifying chemical mutagens in mammalian cells and can serve as a valuable component in a genetic toxicology test battery.