Teratogenic studies on 2,4,5-trichlorophenoxyacetic acid in the rat and rabbit

Long non-coding RNA H19-mediated mouse cleft palate induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin

Long non-coding RNAs (lncRNAs) are a novel class of transcripts, which are pervasively transcribed in the genome and a have greatly unknown biological function. Previous studies have identified that lncRNAs serve an important role in embryonic development. However, the function and mechanism of lncRNAs in the development of palate remains unclear. The aim of the present study was to investigate the role of lncRNA H19 in cleft palate (CP) development in mice. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a well-known teratogen that can induce CP. After establishing a CP mouse model by oral administration of TCDD in vivo, no significant differences were detected in the tail length and body weight of fetuses between the TCDD-treated and control groups during the embryonic days 12 to 17. Furthermore, the expression levels of lncRNA H19 and target gene insulin-like growth factor 2 (IGF2) presented specific embryo age-associated differences during the entire development of CP in mice. An inverse correlation was identified between lncRNA H19 and IGF2 expression levels in the CP model. In conclusion, these findings revealed that lncRNA H19 mediated the CP induced by TCDD in mice.

Application of the post-implantation rat embryo culture system to in vitro teratogenicity testing

Originally developed for studying basic mechanisms in developmental biology, the post-implantation embryo culture system has been extended and applied to the testing of chemicals in the field of prenatal toxicology. The endpoints used in a procedure that has been developed for the routine short-term assessment of teratogenicity in vitro are growth (crown-rump length), differentiation (somite number) and morphology (together with measurement of yolk-sac growth and vascularization) in rat embryos explanted on day 9.5 of gestation and cultured for 48 hr in 100% homologous rat serum containing the test compound. Studies involving exposure to trichlorophenoxyacetic acid and to acetylsalicylic acid demonstrate the ability of this system to distinguish between non-specific toxicity and specific effects on development.

Developing rat brain monoamine levels following in utero exposure to a mixture of 2,4-dichlorophenoxyacetic and 2,4,5-trichlorophenoxyacetic acids

Pregnant rats were gavaged with a 1:1 mixture of 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) at 0 (G0), 50 (G 50) and 100 (G 100) mg/kg per day on gestational days 6-15. Treatment significantly (P less than 0.05) delayed ontogeny of dopamine (DA), but not norepinephrine (NE) levels, in the thalamus-hypothalamus on postnatal day 7; in the pons-medulla on days 7,9 and 15; and in the olfactory lobes on day 9. On day 25, serotonin (5-HT) levels were significantly decreased in the pons-medulla of G 100 rats, whereas 5-hydroxyindoleacetic acid (5-HIAA) levels decreased in the thalamus-hypothalamus and pons-medulla of G 50 and G 100 rats.

Does Agent Orange cause birth defects?

Large quantities of the defoliant, Agent Orange, were sprayed in Vietnam during the war. Agent Orange was composed of two herbicides: 2,4-D and 2,4,5-T, the latter contaminated by small amounts of a highly toxic dioxin (TCDD). The constituents of Agent Orange are capable of producing gene mutations and chromosomal aberrations, at least in some experimental circumstances. TCDD and 2,4,5-T are teratogenic in mice and perhaps in other mammals, but the teratogenicity of these chemicals has not been convincingly demonstrated in humans. There is currently no scientific evidence which indicates that men who were previously exposed to Agent Orange are at increased risk of having children with birth defects, but available data are inadequate to assess this possibility critically.

Correlation between the growth inhibitory effects, partition coefficients and teratogenic effects of lipophilic acids

The inhibition of cell duplication by many lipophilic acids was measured in Bacillus subtilis and in the following mammalian cell lines, the human epithelial-type cell lines HeLa, strain R and strain L-132, the human fibroblast cell line VA-13, and the rat glial cell line C. The results were correlated to the partition coefficient and the distribution coefficient (= apparent partition coefficient at pH 7.2) of the compounds, using octanol/water partition coefficients and pKa values either from the literature or measured for this work. For B. subtilis, the logarithm of the inhibitory potency of most compounds increases linearly with the logarithm of the partition coefficient. Exceptional high potencies were observed for compounds that can efficiently delocalize the charge of the negative ion over the whole molecule. Most compounds inhibit tissue cultures at least as potently as they inhibit B. subtilis. But some compounds are significantly more potent in tissue cultures than would have been expected from the B. subtilis data; such compounds (analgesics/antipyretics, anti-inflammatory compounds, butyrate, norepinephrine) presumably inhibits mammalian cells by specific reactions with certain cell components. However, most compounds inhibit the different cell lines to a similar degree, indicating no cellular specificity; exceptions to this rule are chlorambucil, chlortetracycline and dexamethasone. Many of the lipophilic acids that are potent inhibitors of mammalian cell replication are also teratogenic. Exceptional compounds may not reach the embryo. We propose that a number of other lipophilic acids that are potenta inhibitors and to which humans are frequently exposed should be tested for their teratogenic effect.

Cardiovascular malformations in Oryzias latipes embryos treated with 2,4,5-trichlorophenoxyacetic acid (2,4,5-T)

Exposure of fertilized Oryzias latipes eggs to concentrations of 2,4,5-trichlorophenoxyacetic acid up to 14 ppm had no gross developmental effects. Exposure to concentrations above 14 ppm resulted in multiple malformations of the heart and blood vessels. Embryos failed to hatch when exposed to concentrations above 25 ppm.