This Key Event Relationship is licensed under the Creative Commons BY-SA license. This license allows reusers to distribute, remix, adapt, and build upon the material in any medium or format, so long as attribution is given to the creator. The license allows for commercial use. If you remix, adapt, or build upon the material, you must license the modified material under identical terms.
Relationship: 2072
Title
Decreased, cholesterol leads to Decreased, 11KT
Upstream event
Downstream event
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 | Not Specified | Arthur Author (send email) | Open for citation & comment |
Taxonomic Applicability
Sex Applicability
| Sex | Evidence |
|---|---|
| Male | High |
| Female | Low |
Life Stage Applicability
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).
| ID | Experimental Design | Species | Upstream Observation | Downstream Observation | Citation (first author, year) | Notes |
|---|
| Title | First Author | Biological Plausibility |
Dose Concordance |
Temporal Concordance |
Incidence Concordance |
|---|
Biological Plausibility
Dose Concordance Evidence
Temporal Concordance Evidence
Incidence Concordance Evidence
Uncertainties and Inconsistencies
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).
Response-response Relationship
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).
Time-scale
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
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.
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: