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Key Event Title
|Level of Biological Organization|
Key Event Components
Key Event Overview
AOPs Including This Key Event
|AOP Name||Role of event in AOP||Point of Contact||Author Status||OECD Status|
|AOP on basal cytotoxicity||AdverseOutcome||Cataia Ives (send email)||Open for comment. Do not cite|
|NADPH oxidase activation leading to reproductive failure||KeyEvent||Arthur Author (send email)||Under development: Not open for comment. Do not cite|
|Histone deacetylase inhibition leading to testicular atrophy||KeyEvent||Brendan Ferreri-Hanberry (send email)||Open for citation & comment||WPHA/WNT Endorsed|
|Inhibition of N-linked glycosylation leads to liver injury||KeyEvent||Arthur Author (send email)||Under development: Not open for comment. Do not cite|
|AHR activation decreasing lung function via P53 tox path||KeyEvent||Agnes Aggy (send email)||Under development: Not open for comment. Do not cite|
|AhR activation to breast cancer related death||KeyEvent||Evgeniia Kazymova (send email)||Under development: Not open for comment. Do not cite|
|PM-induced respiratory toxicity||KeyEvent||Cataia Ives (send email)||Under development: Not open for comment. Do not cite|
|Not Otherwise Specified||High|
Key Event Description
Apoptosis, the process of programmed cell death, is characterized by distinct morphology with DNA fragmentation and energy dependency [Elmore, 2007]. Apoptosis, also called “physiological cell death”, is involved in cell turnover, physiological involution, and atrophy of various tissues and organs [Kerr et al., 1972]. The formation of apoptotic bodies involves marked condensation of both nucleus and cytoplasm, nuclear fragmentation, and separation of protuberances [Kerr et al., 1972]. Apoptosis is characterized by DNA ladder and chromatin condensation. Several stimuli such as hypoxia, nucleotides deprivation, chemotherapeutical drugs, DNA damage, and mitotic spindle damage induce p53 activation, leading to p21 activation and cell cycle arrest [Pucci et al., 2000]. The SAHA or TSA treatment on neonatal human dermal fibroblasts (NHDFs) for 24 or 72 hrs inhibited proliferation of the NHDF cells [Glaser et al., 2003]. Considering that the acetylation of histone H4 was increased by the treatment of SAHA for 4 hrs, histone deacetylase inhibition may be involved in the inhibition of the cell proliferation [Glaser et al., 2003]. The impaired proliferation was observed in HDAC1-/- ES cells, which was rescued with the reintroduction of HDAC1 [Zupkovitz et al., 2010]. The present AOP focuses on the p21 pathway leading to apoptosis, however, alternative pathways such as NF-kappaB signaling pathways may be involved in the apoptosis of spermatocytes [Wang et al., 2017].
How It Is Measured or Detected
Apoptosis is characterized by many morphological and biochemical changes such as homogenous condensation of chromatin to one side or the periphery of the nuclei, membrane blebbing and formation of apoptotic bodies with fragmented nuclei, DNA fragmentation, enzymatic activation of pro-caspases, or phosphatidylserine translocation that can be measured using electron and cytochemical optical microscopy, proteomic and genomic methods, and spectroscopic techniques [Archana et al., 2013; Martinez et al., 2010; Taatjes et al., 2008; Yasuhara et al., 2003].
・DNA fragmentation can be quantified with comet assay using electrophoresis, where the tail length, head size, tail intensity, and head intensity of the comet are measured [Yasuhara et al., 2003].
・The apoptosis is detected with the expression alteration of procaspases 7 and 3 by Western blotting using antibodies [Parajuli et al., 2014].
・The apoptosis is measured with down-regulation of anti-apoptotic gene baculoviral inhibitor of apoptosis protein repeat containing 2 (BIRC2, or cIAP1) [Parajuli et al., 2014].
・Apoptotic nucleosomes are detected using Cell Death Detection ELISA kit, which was calculated as absorbance subtraction at 405 nm and 490 nm [Parajuli et al., 2014].
・Cleavage of PARP is detected with Western blotting [Parajuli et al., 2014].
・Caspase-3 and caspase-9 activity is measured with the enzyme-catalyzed release of p-nitroanilide (pNA) and quantified at 405 nm [Wu et al., 2016].
・Apoptosis is measured with Annexin V-FITC probes, and the relative percentage of Annexin V-FITC-positive/PI-negative cells is analyzed by flow cytometry [Wu et al., 2016].
・Apoptosis is detected with the Terminal dUTP Nick End-Labeling (TUNEL) method to assay the endonuclease cleavage products by enzymatically end-labeling the DNA strand breaks [Kressel and Groscurth, 1994].
・For the detection of apoptosis, the testes are fixed in neutral buffered formalin and embedded in paraffin. Germ cell death is visualized in testis sections by Terminal dUTP Nick End-Labeling (TUNEL) staining method [Wade et al., 2008]. The incidence of TUNEL-positive cells is expressed as the number of positive cells per tubule examined for one entire testis section per animal [Wade et al., 2008].
Domain of Applicability
・Apoptosis is induced in human prostate cancer cell lines (Homo sapiens) [Parajuli et al., 2014].
・Apoptosis occurs in B6C3F1 mouse (Mus musculus) [Elmore, 2007].
・Apoptosis occurs in Sprague-Dawley rat (Rattus norvegicus) [Elmore, 2007].
・Apoptosis occurs in the nematode (Caenorhabditis elegans) [Elmore, 2007].
Regulatory Significance of the Adverse Outcome
Archana, M. et al. (2013), "Various methods available for detection of apoptotic cells", Indian J Cancer 50:274-283
Elmore, S. (2007), "Apoptosis: a review of programmed cell death", Toxicol Pathol 35:495-516
Glaser, K.B. et al. (2003), "Gene expression profiling of multiple histone deacetylase (HDAC) inhibitors: defining a common gene set produced by HDAC inhibition in T24 and MDA carcinoma cell lines", Mol Cancer Ther 2:151-163
Kerr, J.F.R. et al. (1972), "Apoptosis: a basic biological phenomenon with wide-ranging implications in tissue kinetics", Br J Cancer 26:239-257
Kressel, M. and Groscurth, P. (1994), "Distinction of apoptotic and necrotic cell death by in situ labelling of fragmented DNA", Cell Tissue Res 278:549-556
Martinez, M.M. et al. (2010), "Detection of apoptosis: A review of conventioinal and novel techniques", Anal Methods 2:996-1004
Parajuli, K.R. et al. (2014), "Methoxyacetic acid suppresses prostate cancer cell growth by inducing growth arrest and apoptosis", Am J Clin Exp Urol 2:300-313
Pucci, B. et al. (2000), "Cell cycle and apoptosis", Neoplasia 2:291-299
Taatjes, D.J. et al. (2008), "Morphological and cytochemical determination of cell death by apoptosis", Histochem Cell Biol 129:33-43
Wade, M.G. et al. (2008), "Methoxyacetic acid-induced spermatocyte death is associated with histone hyperacetylation in rats", Biol Reprod 78:822-831
Wang, C. et al. (2017), "CD147 regulates extrinsic apoptosis in spermatocytes by modulating NFkB signaling pathways", Oncotarget 8:3132-3143
Wu, R. et al. (2016), "microRNA-497 induces apoptosis and suppressed proliferation via the Bcl-2/Bax-caspase9-caspase 3 pathway and cyclin D2 protein in HUVECs", PLoS One 11:e0167052
Yasuhara, S. et al. (2003), "Comparison of comet assay, electron microscopy, and flow cytometry for detection of apoptosis", J Histochem Cytochem 51:873-885
Zupkovitz, G. et al. (2010), "The cyclin-dependent kinase inhibitor p21 is a crucial target for histone deacetylase 1 as a regulator of cellular proliferation", Mol Cell Biol 30:1171-1181