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|
|Histone deacetylase inhibition leading to testicular atrophy||AdverseOutcome|
|Rattus norvegicus||Rattus norvegicus||Moderate||NCBI|
|Adult, reproductively mature||Moderate|
Key Event Description
It is hypothesized that the testicular effects of 1,6-dimethoxyhexane (DMH) are caused by its metabolism to methoxyacetic acid (MAA) [Wade, 2006, Poon, 2004]. MAA produces testicular and thymic atrophy such as the decrease in size [Miller, 1982, Moss, 1985]. The spermatogenic stages in which the toxicity of MAA is induced are on the patchytene spermatocytes immediately before and during meiotic division, which are Stages XII-XIV of the cycle in the rat and the early pachytene spermatocytes at stages I-IV of the cycle. Dead germ cells can be seen as soon as 12 hours after the treatment of MAA [Casarett & Doull’s 7th edition].
How It Is Measured or Detected
- Testicular atrophy can be assessed by testicular volume measurment using orchidometer, rulers, calipers, and ultrasonography or by testis weighing and histopathologic examination.
- The testis weight is measured to detect the testicular atrophy [Foster, 1983].
- The urinary zinc excretion and testicular zinc content are examined, since zinc concentration has been shown to play an important role in the production of testicular injury [Foster, 1983].
- The testicular tissue structure is observed whether there are normal germinal epithelial cells and Leydig cells [Mercantepe, 2018]. Testis is fixed for observations by light microscopy or transmission electron microscopy [McDowell, 1976, Mercantepe, 2018].
- Changes in sperm are measured by computer-assisted sperm analysis [Foote, 1995].
- For the assessment of sperm morphology, eosin-stained sperm collected from the cauda epididymis is observed. At least 200 sperm on each slide were examined for the proportion of sperm with abnormal head (overhooked, blunt hook, banana-shaped, amorphous, or extremely oversized) or tail (twisted, bent, corkscrew, double. multiple) by one individual unaware of animal number or treatment [Wade, 2006].
- For the measurement of the total number of condensed spermatids per testis, a weighed portion of the parenchyma from the left testis was homogenized [Wade, 2006]. Sperm or homogenization-resistant spermatid nuclei densities were calculated from the average number of nuclei and were expressed as total or as per gram of epididymis or testis weight [Wade, 2006].
- For the determination of total LDH and LDH-X in supernatant of the homogenized testis fragment, enzyme activity was measured by monitoring extinction of NAD absorbance [Wade, 2006].
Domain of Applicability
- The derease in testis weight associated with testicular cell damage was induced by EGME or MAA treatment in rats (Rattus norvegicus) [Foster, 1983].
- The number of spermatocytes, principally pachytene cells, is decreased by EGME treatment in CD-1 mice (Mus musculus) and CD rats (Rattus norvegicus) [Anderson, 1987].
- The testicular lesions induced by 2-methoxyethanol (ethylene glycol monomethyl ether; EGME) were observed in rats (Rattus norvegicus) and guinea pigs (Cavia porcellus), which are different in onset, characteristics and severity [Ku, 1984].
- Spermatogenesis was disrupted by EGME treatment in rabbits (Oryctolagus cuniculus) [Foote, 1995].
- Testicular toxicity such as spermatocyte death in seminiferous tubule stages I-IV and stages XII-XIV was induced by dimethoxyhexane (DMH) treatment in Sprague-Dawley rats (Rattus norvegicus) [Wade, 2006].
Regulatory Significance of the Adverse Outcome
The testicular toxicity assessment is important for assessing the side effects of the medicines such as anti-cancer drugs, as well as hazard and risk of chemicals. The testicular atrophy including decrease in testis weight and sperm count, fertility, decrease in morphology and function of the sperm, can become one of the main endpoints as the adverse effects of the therapeutics. The unexpected effects of the therapeutics may be predicted with this Adverse Outcome.
Wade MG et al. (2006) Testicular toxicity of candidate fuel additive 1,6-dimethoxyhexane: comparison with several similar aliphatic ethers. Toxicol Sci 89:304-313
Poon R et al. (2004) Short-term oral toxicity of pentyl ether, 1,4-diethoxybutane, and 1,6-dimethoxyhexane in male rats. Toxicol Sci 77:142-150
Miller R et al. (1982) Toxicity of methoxyacetic acid in rats. Fundam Appl Toxicol 2:158-160
Moss EJ et al. (1985) The role of metabolism in 2-methoxyethanol-induced testicular toxicity. Toxicol Appl Pharmacol 79:480-489
Casarett & Doull’s Toxicology, the Basic Science of Poisons, 7th Edition, Edited by Curtis D. Klaassen, Chapter 20 Toxic responses of the reproductive system
Foster PM et al. (1983) Testicular toxicity of ethylene glycol monomethyl and monoethyl ethers in the rats. Toxicol Appl Pharmacol 69:385-399
Mercantepe T et al. (2018) Protective effects of amifostine, curcumin and caffeic acid phenethyl ester against cisplatin-induced testis tissue damage in rats. Exp Ther Med 15:3404-3412
McDowell EM and Trump BF. (1976) Histologic fixatives suitable for diagnostic light and electron microscopy. Arch Pathol Lab Med 100:405-414
Foote RH et al. (1995) Ethylene glycol monomethyl ether effects on health and reproduction in male rabbits. Reprod Toxicol 9:527-539
Anderson D et al. (1987) Effect of ethylene glycol monomethyl ether on spermatogenesis, dominant lethality, and F1 abnormalities in the rat and the mouse after treatment of F0 males. Teratog Carcinog Mutagen 7:141-158
Ku WW et al. (1994) Comparison of the testicular effects of 2-methoxyethanol (ME) in rats and guinea pigs. Exp Mol Pathol 61:119-133