API

Relationship: 438

Title

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Reduction, Cholesterol transport in mitochondria leads to Reduction, Testosterone synthesis in Leydig cells

Upstream event

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Reduction, Cholesterol transport in mitochondria

Downstream event

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Reduction, Testosterone synthesis in Leydig cells

Key Event Relationship Overview

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AOPs Referencing Relationship

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AOP Name Directness Weight of Evidence Quantitative Understanding
PPARα activation in utero leading to impaired fertility in males directly leads to Moderate
PPARα activation leading to impaired fertility in adult male rodents directly leads to Moderate

Taxonomic Applicability

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Term Scientific Term Evidence Link
mice Mus sp. Moderate NCBI
rat Rattus norvegicus Strong NCBI
human Homo sapiens Weak NCBI

Sex Applicability

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Life Stage Applicability

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How Does This Key Event Relationship Work

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Production of steroid hormones depends on the availability of cholesterol in the mitochondrial matrix. A decreased amount of cholesterol inside the mitochondria (e. g by decreased expression of enzymes that transport cholesterol like StAR or TSOP) means diminished substrate for hormone (testosterone) production in testes.

Weight of Evidence

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Biological Plausibility

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Steroid hormones play a critical role in sexual development, homeostasis, stress-responses, carbohydrate metabolism, tumor growth, and reproduction. These hormones are primarily produced in specialized steroidogenic tissues and are synthesized from a common precursor, cholesterol. Mitochondria are a key control point for the regulation of steroid hormone biosynthesis. The first and rate-limiting step in steroidogenesis is the transfer of cholesterol from the outer mitochondrial membrane to the inner mitochondrial membrane, a process dependent on the action of StAR (Stocco, 2001) and the subsequent transport across the inner mitochondrial space into the steroidogenic pathway, which is executed by TSPO (Hauet et al., 2005). Testosterone production by Leydig cells is primarily under the control of luteinizing hormone (LH). Stimulation of the Leydig cells results in the activation of StAR transcription and translation, which facilitates the transfer of cholesterol into the mitochondrial matrix to cholesterol side-chain cleavage cytochrome P450 (P450scc, CYP11A), which converts cholesterol to pregnenolone. Pregnenolone diffuses to the smooth endoplasmic reticulum where it is further metabolized to testosterone via the actions of 3β-hydroxysteroid dehydrogenase Δ5-Δ4-isomerase (3β-HSD), 17α-hydroxylase/C17-20 lyase (P450c17, CYP17), and 17β-hydroxysteroid dehydrogenase type III (17HSD3). For review see (Payne & Hales, 2013). Decreased expression of genes that are responsible for cholesterol transport and steroidogenic enzyme activities in the Leydig cell leads to decreased testosterone production.

Empirical Support for Linkage

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There is evidence from experimental work that demonstrates a coordinated reduction in the expression of key genes and proteins that are involved in cholesterol transport and steroidogenesis, together with a corresponding reduction in testosterone in testes. For details see Table 1. Foetal Leydig cells exhibit a high rate of lipid metabolism, which is required for both synthesizing and importing the testosterone precursor cholesterol. Upon exposure to some chemicals mRNA expression of genes in these pathways are profoundly reduced e.g. following 500mg/kg phthalate (DBP) exposure (Johnson, McDowell, Viereck, & Xia, 2011), (Thompson et al., 2005). Additionally, after phthalate exposure testis cholesterol and cholesterol-containing lipid droplets in foetal Leydig cells are also reduced (Barlow et al., 2003), (Johnson et al., 2011), (Lehmann, Phillips, Sar, Foster, & Gaido, 2004).

 

     

KE: Cholesterol transport, reduction

KE: Testosterone production/levels, reduction

Compound

Species

Effect level

Translator protein (TSPO), decrease; Steroidogenic acute regulatory protein (StAR) decrease

 

Phthalate (DBP)

rat

LOEL=500 mg/kg/day

mRNA StAR decrease (by ~34%)(Barlow et al., 2003)

 

Phthalate (BBP, DPeP, DEHP, DHP, DiHeP, DCHP, DINP DHeP)

rat

   

 

Phthalate (DBP, DEHP, BBP)

Rat

LOEL=750 mg/kg/day (GD14-18)

 

testosterone production, reduction ex vivo fetal testes examined on GD18 (Wilson et al., 2004)

 

       

 

Phthalate (DBP)

rat

LOEL=500 mg/kg/day

reduced Leydig cell lipid content(Barlow et al., 2003)

 

Phthalate (DBP)

rat

LOEL=500 mg/kg/day GD 12 -20, examinations on GD20

total cholesterol levels, reduction

intratesticular testosterone levels, reduction (by nearly 90%)(Johnson et al., 2011)

Phthalate (DBP)

rat

LOEL=500 mg/kg/day (GD12-19)

decrease uptake of cholesterol Leydig cell mitochondria gd 19

testosterone production, reduction ex vivo (Thompson, Ross, & Gaido, 2004)

Phthalate (DEHP)

mouse

LOEL=1 g/kg/day

reduced TSPO mRNA

testosterone levels, reduction (Gazouli, 2002)

Phthalate (DEHP)

rat

LOEL=300 mg/ kg/day

 

dose-dependently reduced StAR, TSOP mRNA (GD 21 testes), also on protein levels in Leydig cells (Borch, Metzdorff, Vinggaard, Brokken, & Dalgaard, 2006)

 

 

Phthalate (DEHP)

rat

LOEL=300 mg/kg/day

 

testosterone production, reduction (ex vivo) testosterone levels, reduction (Borch et al., 2006), (Borch, Ladefoged, Hass, & Vinggaard, 2004)

Phthalate (MEHP)

mouse

LOEC=100 μM

  • reduced TSPO mRNA levels by 50%,

  • binding sites decreased by 50%

  • no effect on receptor affinity

  • inhibited the transfer or loading of cholesterol to the inner mitochondrial membrane P450scc. (Gazouli, 2002)

 

Phthalate (MEHP)

rat

IC50 =100 μM

  • inhibited formation of progesterone (Gazouli, 2002)

 

Phthalate (MEHP)

rat

LOEC=250 μM

cholesterol transport, decrease (into the mitochondria of immature and adult Leydig cells)

Testosterone, reduction by approximately 60%, in vitro ( immature and adult Leydig cells) (Svechnikov, Svechnikova, & Söder, 2008)

Phthalate (DEHP)

rat

LOEL=750 mg/kg/day

 

testosterone production reduction, testosterone levels, reduction (testicular and whole-body T levels in fetal and neonatal male rats from GD 17 to PND 2. (Parks, 2000)

Phthalate (MEHP)

rat

LOEC=1 μM

 

testosterone production, reduction dose-dependent (Chauvigné et al., 2011)

Perfluorooctanoic acid (PFOA)

mouse

LOEL=5mg/kg/day

 

plasma testosterone, reduction (by 37%)(Li et al., 2011)

WY-14,643

mouse

LOEC=50 mg/kg/day

reduced TSPO mRNA

Serum testosterone levels, reduction (Gazouli, 2002)

WY-14,643

rat

 

 

No decrease of testosterone ( ex vivo), (Furr, Lambright, Wilson, Foster, & Gray, 2014)

WY-14,643

mouse

LOEC=100 μM

Inhibited progesterone synthesis (Gazouli, 2002)

 

Bezafibrate

mouse

IC50=100 μM

  • a dose-dependent 10–95% inhibition of the progesterone synthesis at 24 or 72 h

  • inhibited the transfer or loading of cholesterol to the inner mitochondrial membrane P450scc. At 100 μM

  • binding sites of TSPO decreased IC50 of approximately 100 μM

  • decrease TSPO levels by 60% at 100 μM (Gazouli, 2002)

 

Bezafibrate

rat

IC50 = 30 μM

inhibited formation of progesterone (Gazouli, 2002)

 

Bezafibrate

rat

IC50 ~10−4 μM

 

testosterone production, reduction (Gazouli, 2002)

Phthalate (DiBP)

rat

GD 19 -21

reduced StAR, (Boberg et al., 2008)

testicular testosterone production and testicular testosterone levels, (Boberg et al., 2008)


Table 1. Summary table of empirical support for this KER. IC50 half maximal inhibitory concentration, LOEC-lowest effect concentration, LOEL- lowest observed effect level, Dibutyl phthalate (DBP), diisobutyl phthalate (DiBP), Bis(2-ethylhexyl) phthalate (DEHP), Dibutyl phthalate (DBP), Bezafibrate and WY-14,643 are PPARα ligands, n.a - not available

Uncertainties or Inconsistencies

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Thompson et al investigated time course effects of phthalate on steroidogenesis gene expression and testosterone concentration. The study showed diminished concentration testosterone concentration in the foetal testis by 50% within 1h of treatment with phthalate (DBP). Surprisingly, the diminution in testosterone concentration preceded any alteration in expression of genes in the steroidogenesis pathway. Star mRNA was significantly diminished 2 h after DBP exposure, but Cyp11a1, Cyp17a1, and Scarb1 did not show a significant decrease in expression until 6 h after DBP exposure (Thompson et al., 2005). In utero exposure of rats to PFOA 20 mg/kg did not cause any effect on fetal testosterone (Boberg et.al. 2008) although in mice (adult) the decrease level of testosterone was observed. Testosterone production may also be diminished due to reduction/inhibition of other genes involved in steroidogenesis (e.g. P450scc, Cyp17a1) (Thompson et al., 2004), (Boberg et al., 2008), (Chauvigné et al., 2009), (Chauvigné et al., 2011).

Quantitative Understanding of the Linkage

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Evidence Supporting Taxonomic Applicability

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See Table 1.

References

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Barlow, N. J., Phillips, S. L., Wallace, D. G., Sar, M., Gaido, K. W., & Foster, P. M. D. (2003). Quantitative changes in gene expression in fetal rat testes following exposure to di(n-butyl) phthalate. Toxicological Sciences : An Official Journal of the Society of Toxicology, 73(2), 431–41. doi:10.1093/toxsci/kfg087

Boberg, J., Metzdorff, S., Wortziger, R., Axelstad, M., Brokken, L., Vinggaard, A. M., … Nellemann, C. (2008). Impact of diisobutyl phthalate and other PPAR agonists on steroidogenesis and plasma insulin and leptin levels in fetal rats. Toxicology, 250(2-3), 75–81. doi:10.1016/j.tox.2008.05.020

Borch, J., Ladefoged, O., Hass, U., & Vinggaard, A. M. (2004). Steroidogenesis in fetal male rats is reduced by DEHP and DINP, but endocrine effects of DEHP are not modulated by DEHA in fetal, prepubertal and adult male rats. Reproductive Toxicology (Elmsford, N.Y.), 18(1), 53–61. doi:10.1016/j.reprotox.2003.10.011

Borch, J., Metzdorff, S. B., Vinggaard, A. M., Brokken, L., & Dalgaard, M. (2006). Mechanisms underlying the anti-androgenic effects of diethylhexyl phthalate in fetal rat testis. Toxicology, 223(1-2), 144–55. doi:10.1016/j.tox.2006.03.015

Chauvigné, F., Plummer, S., Lesné, L., Cravedi, J.-P., Dejucq-Rainsford, N., Fostier, A., & Jégou, B. (2011). Mono-(2-ethylhexyl) phthalate directly alters the expression of Leydig cell genes and CYP17 lyase activity in cultured rat fetal testis. PloS One, 6(11), e27172. doi:10.1371/journal.pone.0027172

Furr, J. R., Lambright, C. S., Wilson, V. S., Foster, P. M., & Gray, L. E. (2014). A short-term in vivo screen using fetal testosterone production, a key event in the phthalate adverse outcome pathway, to predict disruption of sexual differentiation. Toxicological Sciences : An Official Journal of the Society of Toxicology, 140(2), 403–24. doi:10.1093/toxsci/kfu081

Gazouli, M. (2002). Effect of Peroxisome Proliferators on Leydig Cell Peripheral-Type Benzodiazepine Receptor Gene Expression, Hormone-Stimulated Cholesterol Transport, and Steroidogenesis: Role of the Peroxisome Proliferator-Activator Receptor . Endocrinology, 143(7), 2571–2583. doi:10.1210/en.143.7.2571

Hauet, T., Yao, Z.-X., Bose, H. S., Wall, C. T., Han, Z., Li, W., … Papadopoulos, V. (2005). Peripheral-type benzodiazepine receptor-mediated action of steroidogenic acute regulatory protein on cholesterol entry into leydig cell mitochondria. Molecular Endocrinology (Baltimore, Md.), 19(2), 540–54. doi:10.1210/me.2004-0307

Johnson, K. J., McDowell, E. N., Viereck, M. P., & Xia, J. Q. (2011). Species-specific dibutyl phthalate fetal testis endocrine disruption correlates with inhibition of SREBP2-dependent gene expression pathways. Toxicological Sciences : An Official Journal of the Society of Toxicology, 120(2), 460–74. doi:10.1093/toxsci/kfr020

Lehmann, K. P., Phillips, S., Sar, M., Foster, P. M. D., & Gaido, K. W. (2004). Dose-dependent alterations in gene expression and testosterone synthesis in the fetal testes of male rats exposed to di (n-butyl) phthalate. Toxicological Sciences : An Official Journal of the Society of Toxicology, 81(1), 60–8. doi:10.1093/toxsci/kfh169

Li, Y., Ramdhan, D. H., Naito, H., Yamagishi, N., Ito, Y., Hayashi, Y., … Nakajima, T. (2011). Ammonium perfluorooctanoate may cause testosterone reduction by adversely affecting testis in relation to PPARα. Toxicology Letters, 205(3), 265–72. doi:10.1016/j.toxlet.2011.06.015 Miller, W. L. (2007). Steroidogenic acute regulatory protein (StAR), a novel mitochondrial cholesterol transporter. Biochimica et Biophysica Acta, 1771(6), 663–76. doi:10.1016/j.bbalip.2007.02.012

Parks, L. G. (2000). The Plasticizer Diethylhexyl Phthalate Induces Malformations by Decreasing Fetal Testosterone Synthesis during Sexual Differentiation in the Male Rat. Toxicological Sciences, 58(2), 339–349. doi:10.1093/toxsci/58.2.339

Payne, A. H., & Hales, D. B. (2013). Overview of Steroidogenic Enzymes in the Pathway from Cholesterol to Active Steroid Hormones. Endocrine Reviews. Stocco, D. M. (2001). StAR protein and the regulation of steroid hormone biosynthesis. Annual Review of Physiology, 63, 193–213. doi:10.1146/annurev.physiol.63.1.193

Svechnikov, K., Svechnikova, I., & Söder, O. (2008). Inhibitory effects of mono-ethylhexyl phthalate on steroidogenesis in immature and adult rat Leydig cells in vitro. Reproductive Toxicology (Elmsford, N.Y.), 25(4), 485–90. doi:10.1016/j.reprotox.2008.05.057

Thompson, C. J., Ross, S. M., & Gaido, K. W. (2004). Di(n-butyl) phthalate impairs cholesterol transport and steroidogenesis in the fetal rat testis through a rapid and reversible mechanism. Endocrinology, 145(3), 1227–37. doi:10.1210/en.2003-1475

Thompson, C. J., Ross, S. M., Hensley, J., Liu, K., Heinze, S. C., Young, S. S., & Gaido, K. W. (2005). Differential steroidogenic gene expression in the fetal adrenal gland versus the testis and rapid and dynamic response of the fetal testis to di(n-butyl) phthalate. Biology of Reproduction, 73(5), 908–17. doi:10.1095/biolreprod.105.042382

Wilson, V. S., Lambright, C., Furr, J., Ostby, J., Wood, C., Held, G., & Gray, L. E. (2004). Phthalate ester-induced gubernacular lesions are associated with reduced insl3 gene expression in the fetal rat testis. Toxicology Letters, 146(3), 207–15.