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Relationship: 2072


A descriptive phrase which clearly defines the two KEs being considered and the sequential relationship between them (i.e., which is upstream, and which is downstream). More help

Decreased, cholesterol leads to Decreased, 11KT

Upstream event
The causing Key Event (KE) in a Key Event Relationship (KER). More help
Downstream event
The responding Key Event (KE) in a Key Event Relationship (KER). More help

Key Event Relationship Overview

The utility of AOPs for regulatory application is defined, to a large extent, by the confidence and precision with which they facilitate extrapolation of data measured at low levels of biological organisation to predicted outcomes at higher levels of organisation and the extent to which they can link biological effect measurements to their specific causes.Within the AOP framework, the predictive relationships that facilitate extrapolation are represented by the KERs. Consequently, the overall WoE for an AOP is a reflection in part, of the level of confidence in the underlying series of KERs it encompasses. Therefore, describing the KERs in an AOP involves assembling and organising the types of information and evidence that defines the scientific basis for inferring the probable change in, or state of, a downstream KE from the known or measured state of an upstream KE. More help

AOPs Referencing Relationship

AOP Name Adjacency Weight of Evidence Quantitative Understanding Point of Contact Author Status OECD Status
PPARalpha Agonism Leading to Decreased Viable Offspring via Decreased 11-Ketotestosterone adjacent High Low Jennifer Olker (send email) Open for citation & comment

Taxonomic Applicability

Latin or common names of a species or broader taxonomic grouping (e.g., class, order, family) that help to define the biological applicability domain of the KER.In general, this will be dictated by the more restrictive of the two KEs being linked together by the KER.  More help
Term Scientific Term Evidence Link
teleost fish teleost fish High NCBI
Vertebrates Vertebrates Low NCBI

Sex Applicability

An indication of the the relevant sex for this KER. More help
Sex Evidence
Male High
Female Low

Life Stage Applicability

An indication of the the relevant life stage(s) for this KER.  More help

Key Event Relationship Description

Provides a concise overview of the information given below as well as addressing details that aren’t inherent in the description of the KEs themselves. More help

The cholesterol molecule is the precursor for all steroid hormone synthesis. Cholesterol is obtained from de novo synthesis within cells or uptake of extracellular cholesterol (Eacker et al., 2008), however the dependence on either source varies by species (Klinefelter et al., 2014). Cholesterol is then transported into the inner mitochondrial membrane via the steroidogenic acute regulatory protein (StAR). Cholesterol is then converted to pregnenolone via the enzyme cytochrome P450 side-chain cleavage (cyp11a1). This is the rate-limiting step of steroidogenesis (Arukwe, 2008). Pregnenolone is then used to produce all other steroid hormones. 11-KT is synthesized from testosterone primarily using the enzymes CYP11β1 and HSD11β2 (Yazawa et al., 2008).

Evidence Collection Strategy

Include a description of the approach for identification and assembly of the evidence base for the KER. For evidence identification, include, for example, a description of the sources and dates of information consulted including expert knowledge, databases searched and associated search terms/strings.  Include also a description of study screening criteria and methodology, study quality assessment considerations, the data extraction strategy and links to any repositories/databases of relevant references.Tabular summaries and links to relevant supporting documentation are encouraged, wherever possible. More help

Evidence Supporting this KER

Addresses the scientific evidence supporting KERs in an AOP setting the stage for overall assessment of the AOP. More help



Decreased Cholesterol?





48 hours

1.7, 33, & 70 mg/g Bezafibrate



Velasco-Santamaría et al. 2011

Danio Rerio

7 days

33 & 70 mg/g Bezafibrate



21 days

1.7 & 33 mg/g Bezafibrate



21 days

70 mg/g Bezafibrate



67 days

10 ug/L Gemfibrozil

Decreased ex vivo 11-KT production unless supplemented with 25OH-cholesterol

Fraz et al. 2018

Danio Rerio

21 days

0.04 mg/L Gemfibrozil



Lee et al. 2019

Oryzias latipes

21 days

0.4 & 3.7 mg/L Gemfibrozil



Biological Plausibility
Addresses the biological rationale for a connection between KEupstream and KEdownstream.  This field can also incorporate additional mechanistic details that help inform the relationship between KEs, this is useful when it is not practical/pragmatic to represent these details as separate KEs due to the difficulty or relative infrequency with which it is likely to be measured.   More help

The process of steroid hormone biosynthesis is well understood, and cholesterol is the precursor for all steroid hormones.

Uncertainties and Inconsistencies
Addresses inconsistencies or uncertainties in the relationship including the identification of experimental details that may explain apparent deviations from the expected patterns of concordance. More help

Although Al-Habsi et al. (2016) show female zebrafish exposed to gemfibrozil and/or atorvastatin have decreased cholesterol and testosterone, decreased testosterone was not seen in males. Although several papers show 11KT is generally correlated with testosterone concentrations (Spanò et al., 2004; Maclatchy & Vanderkraak 1995; Lorenzi et al., 2008), it’s uncertain if 11KT was actually affected.

11KT levels can have high variability between fish. Although Lee et al. (2019) shows a decrease in testosterone and 11KT in a 21-day study, steroid measurements from the 155-day study showed no significant effects. This is possibly due to limited samples size (n=3-5).

Known modulating factors

This table captures specific information on the MF, its properties, how it affects the KER and respective references.1.) What is the modulating factor? Name the factor for which solid evidence exists that it influences this KER. Examples: age, sex, genotype, diet 2.) Details of this modulating factor. Specify which features of this MF are relevant for this KER. Examples: a specific age range or a specific biological age (defined by...); a specific gene mutation or variant, a specific nutrient (deficit or surplus); a sex-specific homone; a certain threshold value (e.g. serum levels of a chemical above...) 3.) Description of how this modulating factor affects this KER. Describe the provable modification of the KER (also quantitatively, if known). Examples: increase or decrease of the magnitude of effect (by a factor of...); change of the time-course of the effect (onset delay by...); alteration of the probability of the effect; increase or decrease of the sensitivity of the downstream effect (by a factor of...) 4.) Provision of supporting scientific evidence for an effect of this MF on this KER. Give a list of references.  More help
Response-response Relationship
Provides sources of data that define the response-response relationships between the KEs.  More help

Velasco-Santamaría et al. (2011) sampled male zebrafish fed several doses of bezafibrate (1.7, 33, & 70 mg BZF/g food) at several timepoints (48 hours, 7 days, and 21 days). Decreased plasma cholesterol is observed after 7 days to 33 mg/g. However, 11-KT isn’t significantly decreased until 21 days to 70 mg/g. There is a positive linear correlation between cholesterol and 11KT (r=0.291, p=0.0004). These decreases are observed without significant changes to cyp11a1 or StAR.

Male medaka exposed to gemfibrozil for 21 days show decreased cholesterol with doses of 0.03, 0.3, and 3.0 mg/L. However, decreases in 11KT is only significant at doses of 0.3 and 3.0 mg/L (Lee et al. 2019).

Information regarding the approximate time-scale of the changes in KEdownstream relative to changes in KEupstream (i.e., do effects on KEdownstream lag those on KEupstream by seconds, minutes, hours, or days?). More help

Decreases in cholesterol in Zebrafish due to bezafibrate exposure can be seen after 7 days, however, decreases in plasma 11-KT aren’t significant until 14 days later (Velasco-Santamaría et al. 2011).

A six-week exposure to gemfibrozil, a cholesterol-lowering pharmaceutical, is sufficient to lower 11-KT levels in the plasma, testes, and whole-body samples of male Zebrafish (Fraz et al. 2018). A 21-day exposure to gemfibrozil is sufficient to lower plasma cholesterol and 11-KT levels in male Japanese Medaka (Lee et al. 2019).

Known Feedforward/Feedback loops influencing this KER
Define whether there are known positive or negative feedback mechanisms involved and what is understood about their time-course and homeostatic limits. More help

Decreases in plasma cholesterol are correlated with a slight increase in StAR in zebrafish (Velasco-Santamaría et al. 2011). This is a possible compensatory mechanism to increase the amount of cholesterol in the mitochondria.

Domain of Applicability

A free-text section of the KER description that the developers can use to explain their rationale for the taxonomic, life stage, or sex applicability structured terms. More help

Taxanomic Applicability: The understanding of steroid hormone biosynthesis is developed from human and rodent studies but is generally conserved among vertebrates. Cyp11a1, which performs the first step of converting cholesterol to steroid hormones, is only found in vertebrates (Slominski et al., 2015). However, the relationship may not be relevant or studied in organisms in which 11KT isn't a primary androgen. 11KT is particularly relevant teleost fish as it is the dominant androgen and involved in testicular development and courtship behavior (Brantley et al., 1993; Barannikova et al., 2004; Gemmell et al., 2019). Evidence supporting this KER comes from a few fish species, including zebrafish and medaka, but is biologically plausible for all teleost fish.

Sex Applicability: Male and female fish use the same biological processes to produce steroids and express the necessary enzymes. In most fish species 11KT is significantly lower in females versus males, however a a few species of the order Perciformes show no sexual dimorphism (Lokman et al. 2002). In species with sexual dimorphism, males could show more significant effects resulting from lowered 11-KT than females. Decreased production of 11-KT in females may not be detectable due to low baseline production, however there are few studies available showing the relationship between cholesterol and 11KT in female fish. 

Life-Stage Applicability:


List of the literature that was cited for this KER description. More help

Al-Habsi, A.A., A. Massarsky, T.W. Moon (2016) “Exposure to gemfibrozil and atorvastatin affects cholesterol metabolism and steroid production in zebrafish (Danio rerio)”, Comparative Biochemistry and Physiology, Part B, Vol. 199, Elsevier, pp. 87-96.

Arukwe, A. (2008) “Steroidogenic acute regulatory (StAR) protein and cholesterol side-chain cleavage (P450scc)-regulated steroidogenesis as an organ-specific molecular and cellular target for endocrine disrupting chemical in fish”, Cell Biology and Toxicology, Vol. 24, Springer, pp. 527-540.

Barannikova, I.A., L.V. Bayunova, T.B. Semenkova (2004) “Serum levels of testosterone, 11-ketotestosterone and oestradiol-17β in three species of sturgeon during gonadal development and final maturation induced by hormonal treatment”, Journal of Fish Biology, Vol. 64(5), Wiley-Blackwell, pp. 1330-1338.

Brantley, R.K., J.C. Wingfield, A.H. Bass (1993) “Sex steroid levels in Porichthys notatus, a fish with alternative reproductive tactics, and a review of the hormonal bases for male dimorphism among teleost fishes”, Hormones and Behavior, Vol. 27(3), Elsevier, pp. 332-347.

Eacker, S. M. et al. (2008) “Hormonal regulation of testicular steroid and cholesterol homeostasis”, Molecular Endocrinology, Vol. 22(3), pp. 623-635.

Fraz, S., A.H. Lee, J.Y. Wilson (2018) “Gemfibrozil and carbamazepine decrease steroid production in zebrafish testes (Danio rerio)”, Aquatic Toxicology, Vol. 198, Elsevier, pp. 1-9.

Gemmell, N.J. et al. (2019) “Natural sex change in fish”, in Sex Determination in Vertebrates, Vol. 134, Academic Press, pp. 71-117. doi: 10.1016/bs.ctdb.2018.12.014.

Klinefelter, G.R., J.W. Laskey, R.P. Amann (2014) “Statin drugs markedly inhibit testosterone production by rat Leydig cells in vitro: Implications for men”, Reproductive Toxicology, Vol. 45, Elsevier, pp. 52-58.

Lee, G. et al. (2019) “Effects of gemfibrozil on sex hormones and reproduction related performances of Oryzias latipes following long-term (155 d) and short-term (21 d) exposure”, Ecotoxicology and Environmental Safety, Vol. 173, Elsevier, pp. 174-181.

Lokman, P.M. et al. (2002) “11-Oxygenated androgens in female teleosts: prevalence, abundance, and life history implications”, General and Comparative Endocrinology, Vol. 129, Academic Press, pp. 1-12. doi: 10.1016/s0016-6480(02)00562-2

Lorenzi, V. et al. (2008) “Diurnal patterns and sex differences in cortisol, 11-ketotestosterone, testosterone, and 17β-estradiol in the bluebanded goby (Lythrypnus dalli)”, General and Comparative Endocrinology, Vol. 155(2)., Elsevier, pp. 438-446.

MacLatchy, D.L., G.J. Vanderkraak (1995) “The phytoestrogen β-sitosterol alters the reproductive endocrine status of goldfish”, Toxicology and Applied Pharmacology, Vol. 134(2), Elsevier, pp. 305-312.

Slominski, A.T. et al. (2015) “Novel activities of CYP11A1 and their potential physiological significance”, The Journal of Steroid Biochemistry and Molecular Biology, Vol. 151, Elsevier, pp. 25-37.

Spanó, L. et al. (2004) “Effects of atrazine on sex steroid dynamics, plasma vitellogenin concentration and gonad development in adult goldfish (Carassius auratus)”, Aquatic Toxicology, Vol. 66(4), Elsevier, pp. 369-379.

Velasco-Santamaría, Y.M. et al. (2011) “Bezafibrate, a lipid-lowering pharmaceutical, as a potential endocrine disruptor in male zebrafish (Danio rerio)”, Aquatic Toxicology, Vol. 105, Elsevier, pp. 107-118. doi:10.1016/j.aquatox.2011.05.018

Yazawa, T. (2008) “Cyp11b1 is induced in the murine gonad by luteinizing hormone/human chorionic gonadotropin and involved in the production of 11-ketotestosterone, a major fish androgen: Conservation and evolution of the androgen metabolic pathway”, Endocrinology, Vol. 149(4), Oxford Academy, pp. 1786-1792.