Toshie Tsuchiya

Embryolethality of new herbicides is not detected by the micromass teratogen tests

New herbicidal compounds (11 pyrimidine-diones, 3 benzoates and 1 sulfonamide) were found to be embryolethal but not teratogenic in rats. The range of the embryolethal dose varied from 0.2 to >200 mg/kg. This broad range enabled us to validate whether proposed in vitro teratogen tests can detect the embryolethality of these herbicides. The IC50 values (inhibition concentration 50%) for both differentiation and proliferation of midbrain and limb bud cells of rat embryos were determined and found to be above 50 μg/ml in all cases, confirming that the herbicides were not teratogenic. No correlation, however, was observed between the embryolethality in vivo and the activities in these cells. In order to test whether the potential to cause embryolethality could be predicted and detected as a general cytotoxic effect, the inhibition of colony forming ability in V79 cells was determined. The results indicated that cytotoxicity in V79 cells may be useful for preliminary testing of the embryolethal effect of herbicides.

Teratogenicity of arotinoids (retinoids) in vivo and in vitro

The effect of structural modifications on the arotinoid molecule, a new class of retinoids, on their teratogenicity in mice was studied. Animals were treated on days 8 and 9 of gestation, the most susceptible stages to retinoid-induced malformations in rodents. The teratogenic potency of the 13 arotinoids tested varied over a dose range of more than five orders of magnitude. Next, we tested whether the quantitative differences in the teratogenicity of these arotinoids correlates with their activity in high density (micromass) cultures of rat embryonic limb bud and midbrain cells. There was a good quantitative correlation between the in vivo teratogenicity and the in vitro activity in limb bud cells but no correlation was found in midbrain cells. Thus, the limb bud cell culture system may be useful for a preliminary testing to select non-teratogenic retinoids. For the risk assessment in humans, however, the in vitro results should be verified in animals studies.

Teratogenicity of arotinoids (retinoids) in the rat whole embryo culture.

Structural modifications of the arotinoid molecule RO 13-7410 led to a difference in the teratogenic potencies of more than five orders of magnitude in mice in vivo and in micromass cultures of rat embryonic limb bud cells (Kistler et al. 1990). Five of these retinoids were selected and tested in rat whole embryo culture to determine the suitability of this in vitro test system for the identification of potentially non-teratogenic derivatives among this class of chemicals. The highest concentrations of the compounds with no effects (NOAEL) on general conceptus growth, on differentiation and on the frequency of dysmorphogenic embryos in vitro were compared with the lowest effective teratogenic doses in vivo (LOAEL) or with the concentrations leading to 50% inhibition of limb bud cell differentiation (IC50) in vitro. NOAELs for the parameters of conceptus development ranged from 10−5 μg/ml (0.03 nM) to 10 μg/ml (28.7 μM) for the compounds tested. These correlated very well with LOAEL and IC50 (R >0.95). The types of dysmorphogenesis in vitro were those typical for retinoids, and for the most part resembled the malformations found in vivo. We conclude that the whole embryo culture system is a useful tool for the preliminary testing of retinoids.

Excretion, distribution and metabolism of 1,2,4-trichlorobenzene in rats

Abstract1,2,4-Trichlorobenzene (TCB) labeled with C-14 was given perorally to rats at a dosage of 50 mg/kg for excretion and distribution studies.About 66% and 17% of the oral dose was excreted in the urine and feces, respectively, within 7 days. Trapped radioactivity in the expired air amounted to 2.1% of the dose, but production of labeled carbon dioxide was negligible. Tissue residues were evenly distributed throughout the organs and tissues examined, except for the adipose tissue which consistently had a little higher concentration.The urinary, fecal and expiratory metabolites were identified. Free 2,4,5- and 2,3,5-trichlorophenol (TCP) and their conjugates were mainly detected in the urine. 5- or 6-Sulfhydryl, methylthio, methylsulfoxide and methylsulfone derivatives of TCB were also detected as minor metabolites. Dichlorobenzenes and unchanged TCB were confirmed in the expired air. Reductive dechlroination seems to be catalysed by intestinal microflora enzymes.

Direct evaluation of fatigue property of ultra-high molecular weight polyethylene components of retrieved knee implants using small specimens

Ultra-high molecular weight polyethylene (UHMWPE) has been widely used as a bearing surface of joint implants. Since wear of UHMWPE component has been the primal cause of implant failure, crosslinking of UHMWPE is now widely used to improve its wear property. On the other hand, crosslinking degrades its fatigue property and increase of fatigue related failure, such as delamination, is possible. However, the relationship between degraded fatigue property and implant failure is not clear, primarily because the fatigue properties of failed and retrieved UHMWPE components are not known. In this study, we propose a new test method to evaluate the fatigue property of retrieved UHMWPE components or final products using small specimens. First, the effects of test conditions were investigated using virgin UHMWPE. Then, tests were repeated using specimens from UHMWPE components of retrieved knee implants. The fatigue properties of virgin and retrieved UHMWPE were suc- cessfully evaluated by the new test method and a relationship was found among the extent of oxidation, the fatigue property, and occurrence of delamination. This result suggested that evaluation of fatigue property of UHMWPE component can predict the occurrence of fatigue related implant failure during operation in vivo.