Expression and activity of the DNA repair enzyme uracil DNA glycosylase during organogenesis in the rat conceptus and following methotrexate exposure in vitro

Base excision DNA repair in the embryonic development of the sea urchin, Strongylocentrotus intermedius

In actively proliferating cells, such as the cells of the developing embryo, DNA repair is crucial for preventing the accumulation of mutations and synchronizing cell division. Sea urchin embryo growth was analyzed and extracts were prepared. The relative activity of DNA polymerase, apurinic/apyrimidinic (AP) endonuclease, uracil-DNA glycosylase, 8-oxoguanine-DNA glycosylase, and other glycosylases was analyzed using specific oligonucleotide substrates of these enzymes; the reaction products were resolved by denaturing 20% polyacrylamide gel electrophoresis. We have characterized the profile of several key base excision repair activities in the developing embryos (2 blastomers to mid-pluteus) of the grey sea urchin, Strongylocentrotus intermedius. The uracil-DNA glycosylase specific activity sharply increased after blastula hatching, whereas the specific activity of 8-oxoguanine-DNA glycosylase steadily decreased over the course of the development. The AP-endonuclease activity gradually increased but dropped at the last sampled stage (mid-pluteus 2). The DNA polymerase activity was high at the first cleavage division and then quickly decreased, showing a transient peak at blastula hatching. It seems that the developing sea urchin embryo encounters different DNA-damaging factors early in development within the protective envelope and later as a free-floating larva, with hatching necessitating adaptation to the shift in genotoxic stress conditions. No correlation was observed between the dynamics of the enzyme activities and published gene expression data from developing congeneric species, S. purpuratus. The results suggest that base excision repair enzymes may be regulated in the sea urchin embryos at the level of covalent modification or protein stability.

Screening of cytoprotectors against methotrexate-induced cytogenotoxicity from bioactive phytochemicals

As a well known anti-neoplastic drug, the cytogenotoxicity of methotrexate (MTX) has received more attention in recent years. To develop a new cytoprotector to reduce the risk of second cancers caused by methotrexate, an umu test combined with a micronucleus assay was employed to estimate the cytoprotective effects of ten kinds of bioactive phytochemicals and their combinations. The results showed that allicin, proanthocyanidins, polyphenols, eleutherosides and isoflavones had higher antimutagenic activities than other phytochemicals. At the highest dose tested, the MTX genetoxicity was suppressed by 34.03%∼67.12%. Of all the bioactive phytochemical combinations, the combination of grape seed proanthocyanidins and eleutherosides from Siberian ginseng as well as green tea polyphenols and eleutherosides exhibited stronger antimutagenic effects; the inhibition rate of methotrexate-induced genotoxicity separately reached 74.7 ± 6.5% and 71.8 ± 4.7%. Pretreatment of Kunming mice with phytochemical combinations revealed an obvious reduction in micronucleus and sperm abnormality rates following exposure to MTX (p < 0.01). Moreover, significant increases in thymus and spleen indices were observed in cytoprotector candidates in treated groups. The results indicated that bioactive phytochemicals combinations had the potential to be used as new cytoprotectors.

Glycine supplementation in vitro enhances porcine preimplantation embryo cell number and decreases apoptosis but does not lead to live births

Most in vitro culture conditions are less‐than‐optimal for embryo development. Here, we used a transcriptional‐profiling database to identify culture‐induced differences in gene expression in porcine blastocysts compared to in vivo‐produced counterparts. Genes involved in glycine transport (SLC6A9), glycine metabolism (GLDC, GCSH, DLD, and AMT), and serine metabolism (PSAT1, PSPH, and PHGDH) were differentially expressed. Addition of 10 mM glycine to the culture medium (currently containing 0.1 mM) reduced the abundance of SLC6A9 transcript and increased total cell number, primarily in the trophectoderm lineage (P = 0.003); this was likely by decreasing the percentage of apoptotic nuclei. As serine and glycine can be reversibly metabolized by serine hydroxymethyltransferase 2 (SHMT2), we assessed the abundance of SHMT2 transcript as well as its functional role by inhibiting it with aminomethylphosphonic acid (AMPA), a glycine analog, during in vitro culture. Both AMPA supplementation and elevated glycine decreased the mRNA abundance of SHMT2 and tumor protein p53 (TP53), which is activated in response to cellular stress, compared to controls (P ≤ 0.02). On the other hand, mitochondrial activity of blastocysts, mtDNA copy number, and abundance of mitochondria‐related transcripts did not differ between control and 10 mM glycine culture conditions. Despite improvements to these metrics of blastocyst quality, transfer of embryos cultured in 10 mM glycine did not result in pregnancy whereas the transfer of in vitro‐produced embryos cultured in control medium yielded live births. Mol. Reprod. Dev. 83: 246–258, 2016. © 2016 The Authors.

Methotrexate-induced cytotoxicity and genotoxicity in germ cells of mice: intervention of folic and folinic acid

Methotrexate (MTX) is an anti-metabolite widely used in the treatment of neoplastic disorders, rheumatoid arthritis and psoriasis. The basis for its therapeutic efficacy is the inhibition of dihydrofolate reductase (DHFR), a key enzyme in the folic acid (FA) metabolism. FA is a water-soluble vitamin which is involved in the synthesis of purines and pyrimidines, the essential precursors of DNA. Folinic acid (FNA) is the reduced form of FA that circumvents the inhibition of DHFR. Folate supplementation during MTX therapy for psoriasis and inflammatory arthritis reduces both toxicity and side effects without compromising the efficacy. Further, FNA supplementation reduces the common side effects of MTX in the treatment of juvenile idiopathic arthritis. FA and FNA are reported to have protective effects on MTX-induced genotoxicity in the somatic cells; however their protective effects on the germ cells have not been much explored. Previously, we evaluated the cytotoxic and genotoxic effects of MTX in the germ cells of mice. In the present study, we have intervened FA and FNA for the protection of germ cell toxicity induced by MTX in male swiss mice. The animals were pre-treated with FA at the doses of 50, 100 and 200 microg/kg for 4 consecutive days per week and on day five; MTX was administered at the dose of 20mg/kg once. FNA was administered at the doses of 2.5, 5 and 10 mg/kg, 6 h (h) after single administration of MTX at the dose of 20 mg/kg. The dosing regimen was continued up to 10 weeks. The germ cell toxicity was evaluated using testes weight (wt), sperm count, sperm head morphology, sperm comet assay, histology, TUNEL and halo assay in testis. The results clearly demonstrate that prior administration of FA and post-treatment with FNA reduces the germ cell toxicity induced by MTX as evident from the decreased sperm head abnormalities, seminiferous tubule damage, sperm DNA damage, TUNEL positive cells and increased sperm counts. In the present study, we report that FA and FNA ameliorate the germ cell toxicity of MTX in mice.

A role for Drosophila in understanding drug-induced cytotoxicity and teratogenesis

Drosophila research has been and continues to be an essential tool for many aspects of biological scientific research and has provided insight into numerous genetic, biochemical, and behavioral processes. As well, due to the remarkable conservation of gene function between Drosophila and humans, and the easy ability to manipulate these genes in a whole organism, Drosophila research has proven critical for studying human disease and the physiological response to chemical reagents. Methotrexate, a widely prescribed pharmaceutical which inhibits dihydrofolate reductase and therefore folate metabolism, is known to cause teratogenic effects in human fetuses. Recently, there has been resurgence in the use of methotrexate for inflammatory diseases and ectopic or unwanted pregnancies thus, increasing the need to fully understand the cytotoxicity of this pharmaceutical. Concerns have been raised over the ethics of studying teratogenic drugs like methotrexate in mammalian systems and thus, we have proposed a Drosophila model. We have shown that exposure of female Drosophila to methotrexate results in progeny with developmental abnormalities. We have also shown that methotrexate exposure changes the abundance of many fundamental cellular transcripts. Expression of a dihydrofolate reductase with a reduced affinity for methotrexate can not only prevent much of the abnormal transcript profile but the teratogenesis seen after drug treatment. In the future, such studies may generate useful tools for mammalian antifolate "rescue" therapies.

Transgenic rescue of methotrexate-induced teratogenicity in Drosophila melanogaster

The folic acid analog methotrexate (MTX), a competitive inhibitor of dihydrofolate reductase (DHFR), is used to treat a variety of cancers and autoimmune disorders. However, MTX also causes a wide range of toxic effects in healthy cells and is an established teratogen. Efforts to "rescue" the defects caused by MTX by administering a folate analog or by transgenic expression of a DHFR with an altered affinity for MTX have been attempted in a variety of mammals but limited protection was conferred. As a result, our understanding of the effect of MTX at the molecular genetic level remains incomplete and, in addition, continued mammalian sacrifice is not ideal. Due to the similarity of teratogenic effects produced by MTX in Drosophila melanogaster these insects were transformed with DHFR alleles to determine if rescue could be achieved. The resulting "MTX-resistant" flies were subsequently used to investigate changes in gene expression in response to MTX using semiquantitative reverse transcription PCR. The majority (12/14) of key transcripts that were affected in MTX-exposed females including transcripts involved in cell cycle, defense response, and transport were "rescued" in the "MTX-resistant" transgenic flies. These studies illustrate the utility of this invertebrate model for the investigation of molecular effects of MTX-induced teratogenicity, MTX-resistant DHFRs for gene therapy techniques, and teratogenic protection.

DNA repair disorders causing malformations

DNA damage contributes significantly to the abnormal development or demise of the conceptus. The widely differing phenotypes that result from mutations in DNA repair genes suggest that these genes play critical roles during development, even in the absence of exogenous DNA-damaging agents. Molecules that sense DNA damage and regulate DNA repair, cell cycle checkpoints and apoptosis act as teratogen suppressor genes, protecting the conceptus against insult from DNA damaging teratogens.

DNA repair during organogenesis

DNA damage caused by genotoxic agents can impact on virtually any cellular process due to its ability to affect gene expression and subsequent gene products. The importance of repairing damaged DNA is evidenced by the variety of DNA repair pathways that have evolved in all living organisms, and the human syndromes caused by a lack of this repair ability. This review focuses on the expression and activity of DNA repair pathways during mammalian organogenesis, and the role of these pathways in ensuring the stability of the conceptal genome. DNA repair capacity may play a role also in the response of the conceptus to genotoxic agents that may induce malformations; the consequences of exposure to a genotoxic agent during organogenesis depend on the extent of the damage and on the ability of the embryo to respond by repairing DNA or arresting cell division. The four main repair pathways (nucleotide excision repair, base excision repair, mismatch repair, and recombination repair) are expressed to various degrees during organogenesis, as are members of the genotoxic stress-activated cell cycle checkpoint pathways. Developmental-stage-specific alterations in transcript levels, protein levels, as well as activity, indicate that the regulation of DNA repair pathways during development is complex. The importance of DNA repair pathways in endogenous damage control is illustrated by the sensitivity of development to their disruption if some of these genes are mutated. Furthermore, the conceptus has a limited capacity to alter DNA repair responses following exposure to genotoxic agents.