Histone deacetylase inhibition leading to testicular atrophy

Shihori Tanabe, Akihiko Hirose, Takashi Yamada

Division of Risk Assessment, Center for Biological Safety and Research, National Institute of Health Sciences, Japan

Testicular toxicity is of interest for human health risk assessment especially in terms of reproductive and developmental toxicity, however, the testicular toxicity has not been fully elucidated. Histone deacetylase inhibitors (HDIs) are approved as anti-cancer drugs since HDIs have apoptotic effects in cancer cells. HDIs include short-chain fatty acids, hydroxamic acids, benzamides, and epoxides. The intracellular mechanisms of induction of the spermatocyte apoptosis by HDIs are suggested as histone deacetylase (HDAC) inhibition as MIE, histone acetylation increase, disrupted cell cycle, apoptosis, and spermatocyte depletion as KEs. The adverse outcome has been defined as testicular atrophy. The HDIs inhibit deacetylation of the histone, leading to an increase in histone acetylation. The apoptosis induced by the disrupted cell cycle leads to spermatocyte depletion and testis atrophy. This AOP may be one of the pathways induced by HDIs, which suggests the pathway networks of protein hyperacetylations.

[Abbreviation] AOP: adverse outcome pathway, HDAC: histone deacetylase, HDI: HDAC inhibitor, KE: key event, MIE: molecular initiating event, MAA: 2-Methoxyacetic acid, or Methoxyacetic acid

The AOP may be useful in the risk assessment on several types of HDI molecules including anti-cancer drugs, as well as other types of chemicals, biocides, or pesticides. HDAC inhibitors nowadays have been utilized as therapeutics for cancer or neurology disease, and the adverse effects of HDAC inhibitors should be evaluated. This AOP elucidating the pathway from HDAC inhibition to testicular atrophy may provide important insights into the potential toxicity of HDAC inhibitors. It also provides a basis for the HDAC inhibition-induced epigenetic alteration and cell death. HDAC inhibitors such as rocilinostat/ricolinostat are clinically evaluated as anti-cancer drugs in clinical trials [Yee et al., 2016]. The AOP may be useful for the risk assessment of chemicals, since possible applications of HDAC inhibitors include the enhancement of salinity tolerance to increase agricultural sustainability. Other potential applications of the AOP include the risk assessment of biocides or pesticides, considering that HDAC inhibitors are being investigated as insecticides or amoebicides [Bagnall et al., 2017; Lee et al., 2020]. 

Allfrey, V. et al. (1964), "Acetylation and methylation of histones and their possible role in the regulation of RNA synthesis", Proc Natl Acad Sci 51:786-794

Bagnall, N.H. et al. (2017), "Insecticidal activities of histone deacetylase inhibitors against a dipteran parasite of sheep, Lucilia cuprina", Int J Parasitology: Drugs Drug Resistance 7(1):51–60 https://doi.org/10.1016/j.ijpddr.2017.01.001

Beattie, P.J. et al. (1984), "The effect of 2-methoxyethanol and methoxyacetic acid on Sertoli cell lactate production and protein synthesis in vitro", Toxicol Appl Pharmacol 76:56-61

Chen, S. and Liu, Y. (2015), "Regulation of spermatogonial stem cell self-renewal and spermatocyte meiosis by Sertoli cell signaling", Reproduction 149:R159-R167

Cousens, L.S., et al. (1979), "Different accessibilities in chromatin to histone acetylase", J Biol Chem 254:1716-1723

Dong, Q. et al. (2010), "microRNA let-7a inhibits proliferation of human prostate cancer cells in vitro and in vivo by targeting E2F2 and CCND2", PLoS One 5:e10147

Fenic, I. et al. (2008), "In vivo application of histone deacetylase inhibitor trichostatin-A impairs murine male meiosis", J Andro 29:172-185

Foster, P.M. et al. (1983), "Testicular toxicity of ethylene glycol monomethyl and monoethyl ethers in the rat", Toxicol Appl Pharmacol 69:385-39

Gottlicher, M. et al. (2001), "Valproic acid defines a novel class of HDAC inhibitors inducing differentiation of transformed cells", EMBO J 20:6969-6978

Lagger, G. et al. (2002), "Essential function of histone deacetylase 1 in proliferation control and CDK inhibitor repression", EMBO J 21:2672-2681 

Lee, H-A. et al. (2020), "Application of histone deacetylase inhibitors MPK472 and KSK64 as a potential treatment option for Acanthamoeba keratitis" Antimicrob Agents Chemother 64:e01506-20 https://doi.org/10.1128/AAC.01506-20                                     

Li, L. et al. (2012), "Downregulation of microRNAs miR-1, -206 and -29 stabilizes PAX3 and CCND2 expression in rhabdomyosarcoma", Lab Invest 92:571-583  

Li, L.H. et al. (1996), "2-Methoxyacetic acid (MAA)-induced spermatocyte apoptosis in human and rat testes: an in vitro comparison", J Androl 17:538-549

Miller, R.R. et al. (1982), "Toxicity of methoxyacetic acid in rats", Fundam Appl Toxicol 2:158-160

Niu, Z. et al. (2011), "microRNA-21 regulates the self-renewal of mouse spermatogonial stem cells", Proc Natl Acad Sci 108:12740-12745

Parajuli, K.R. et al. (2014), "Methoxyacetic acid suppresses prostate cancer cell growth by inducing growth arrest and apoptosis", Am J Clin Exp Urol 2:300-312

Pogo, B. et al. (1966), "RNA synthesis and histone acetylation during the course of gene activation in lymphocytes", Proc Natl Acad Sci 55:805-812

Richon, V.M. et al. (2000), "Histone deacetylase inhibitor selectively induces p21WAF1 expression and gene-associated histone acetylation", Proc Natl Acad Sci 97:10014-10019        

Riggs, M.G. et al. (1977), "N-butyrate causes histone modification in HeLa and friend erythroleukaemia cells", Nature 268:462-464

Schroeder, F.A. et al. (2013), "A selective HDAC 1/2 inhibitor modulates chromatin and gene expression in brain and alters mouse behavior in two mood-related tests", PLoS One 8:e71323

Struhl, K. (1998), "Histone acetylation and transcriptional regulatory mechanisms", Gene Dev 12:599-606      

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

Yamazoe, Y. et al. (2015), "Embryo- and testicular-toxicities of methoxyacetate and the related: a review on possible roles of one-carbon transfer and histone modification", Food Safety 3:92-107

Yee, A.J. et al. (2016), "Ricolinostat plus lenalidomide, and dexamethasone in relapsed or refractory multiple myeloma: a multicentre phase 1b trial", Lancet Oncol 17(11):1569-1578 https://doi.org/10.1016/s1470-2045(16)30375-8

Yoshida, M. et al. (1990), "Potent and specific inhibition of mammalian histone deacetylase both in vivo and in vitro trichostatin A", J Biol Chem 265:17174-17179

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