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Event: 1386

Key Event Title

The KE title should describe a discrete biological change that can be measured. It should generally define the biological object or process being measured and whether it is increased, decreased, or otherwise definably altered relative to a control state. For example “enzyme activity, decreased”, “hormone concentration, increased”, or “growth rate, decreased”, where the specific enzyme or hormone being measured is defined. More help

CYP7B activity, inhibition

Short name
The KE short name should be a reasonable abbreviation of the KE title and is used in labelling this object throughout the AOP-Wiki. The short name should be less than 80 characters in length. More help
CYP7B activity, inhibition

Biological Context

Structured terms, selected from a drop-down menu, are used to identify the level of biological organization for each KE. Note, KEs should be defined within a particular level of biological organization. Only KERs should be used to transition from one level of organization to another. Selection of the level of biological organization defines which structured terms will be available to select when defining the Event Components (below). More help

Cell term

Further information on Event Components and Biological Context may be viewed on the attached pdf.The biological context describes the location/biological environment in which the event takes place.  For molecular/cellular events this would include the cellular context (if known), organ context, and species/life stage/sex for which the event is relevant. For tissue/organ events cellular context is not applicable.  For individual/population events, the organ context is not applicable. More help

Organ term

Further information on Event Components and Biological Context may be viewed on the attached pdf.The biological context describes the location/biological environment in which the event takes place.  For molecular/cellular events this would include the cellular context (if known), organ context, and species/life stage/sex for which the event is relevant. For tissue/organ events cellular context is not applicable.  For individual/population events, the organ context is not applicable. More help

Key Event Components

Further information on Event Components and Biological Context may be viewed on the attached pdf.Because one of the aims of the AOP-KB is to facilitate de facto construction of AOP networks through the use of shared KE and KER elements, authors are also asked to define their KEs using a set of structured ontology terms (Event Components). In the absence of structured terms, the same KE can readily be defined using a number of synonymous titles (read by a computer as character strings). In order to make these synonymous KEs more machine-readable, KEs should also be defined by one or more “event components” consisting of a biological process, object, and action with each term originating from one of 22 biological ontologies (Ives, et al., 2017; See List). Biological process describes dynamics of the underlying biological system (e.g., receptor signalling). The biological object is the subject of the perturbation (e.g., a specific biological receptor that is activated or inhibited). Action represents the direction of perturbation of this system (generally increased or decreased; e.g., ‘decreased’ in the case of a receptor that is inhibited to indicate a decrease in the signalling by that receptor).Note that when editing Event Components, clicking an existing Event Component from the Suggestions menu will autopopulate these fields, along with their source ID and description. To clear any fields before submitting the event component, use the 'Clear process,' 'Clear object,' or 'Clear action' buttons. If a desired term does not exist, a new term request may be made via Term Requests. Event components may not be edited; to edit an event component, remove the existing event component and create a new one using the terms that you wish to add. More help
Process Object Action

Key Event Overview

AOPs Including This Key Event

All of the AOPs that are linked to this KE will automatically be listed in this subsection. This table can be particularly useful for derivation of AOP networks including the KE. Clicking on the name of the AOP will bring you to the individual page for that AOP. More help
AOP Name Role of event in AOP Point of Contact Author Status OECD Status
Inhibition of CYP7B leads to decreased locomotor activity MolecularInitiatingEvent Florence Pagé-Larivière (send email) Not under active development
Inhibition of CYP7B activity leads to decreased sexual behavior MolecularInitiatingEvent Florence Pagé-Larivière (send email) Not under active development

Stressors

This is a structured field used to identify specific agents (generally chemicals) that can trigger the KE. Stressors identified in this field will be linked to the KE in a machine-readable manner, such that, for example, a stressor search would identify this as an event the stressor can trigger. NOTE: intermediate or downstream KEs in one AOP may function as MIEs in other AOPs, meaning that stressor information may be added to the KE description, even if it is a downstream KE in the pathway currently under development.Information concerning the stressors that may trigger an MIE can be defined using a combination of structured and unstructured (free-text) fields. For example, structured fields may be used to indicate specific chemicals for which there is evidence of an interaction relevant to this MIE. By linking the KE description to a structured chemical name, it will be increasingly possible to link the MIE to other sources of chemical data and information, enhancing searchability and inter-operability among different data-sources and knowledgebases. The free-text section “Evidence for perturbation of this MIE by stressor” can be used both to identify the supporting evidence for specific stressors triggering the MIE as well as to define broad chemical categories or other properties that classify the stressors able to trigger the MIE for which specific structured terms may not exist. More help

Taxonomic Applicability

Latin or common names of a species or broader taxonomic grouping (e.g., class, order, family) can be selected from an ontology. In many cases, individual species identified in these structured fields will be those for which the strongest evidence used in constructing the AOP was available in relation to this KE. More help
Term Scientific Term Evidence Link
Japanese quail Coturnix japonica NCBI
Cynops pyrrhogaster Cynops pyrrhogaster NCBI
Oncorhynchus keta Oncorhynchus keta NCBI

Life Stages

The structured ontology terms for life-stage are more comprehensive than those for taxa, but may still require further description/development and explanation in the free text section. More help
Life stage Evidence
All life stages

Sex Applicability

No help message More help
Term Evidence
Mixed

Key Event Description

A description of the biological state being observed or measured, the biological compartment in which it is measured, and its general role in the biology should be provided. For example, the biological state being measured could be the activity of an enzyme, the expression of a gene or abundance of an mRNA transcript, the concentration of a hormone or protein, neuronal activity, heart rate, etc. The biological compartment may be a particular cell type, tissue, organ, fluid (e.g., plasma, cerebrospinal fluid), etc. The role in the biology could describe the reaction that an enzyme catalyses and the role of that reaction within a given metabolic pathway; the protein that a gene or mRNA transcript codes for and the function of that protein; the function of a hormone in a given target tissue, physiological function of an organ, etc. Careful attention should be taken to avoid reference to other KEs, KERs or AOPs. Only describe this KE as a single isolated measurable event/state. This will ensure that the KE is modular and can be used by other AOPs, thereby facilitating construction of AOP networks. More help

Site of action:

CYP7B is expressed in different organs including liver, prostate and brain.

How does it work :

CYP7B is a member of the cytochrome P450 family of enzymes. It is involved in steroidogenic pathways as well as in the synthesis of bile acids. In the brain, it is involved in neurosteroids synthesis.

In the brain, the reactions catalyzed by CYP7B are : 

  • Probably in all vertebrates: Pregnenolone into 7α-hydroxypregnenolone and its stereoisomer 7β-hydroxypregnenolone (bird only) (R08943) (Matsunaga et al., 2004; Rose et al., 1997; Tsutsui et al., 2008)
  • Proven in mouse and human: Dehydroepiandrosterone (DHEA) to 7α-hydroxy-DHEA and its stereoisomer 7β-hydroxy-DHEA (Martin et al., 2004; Weihua et al., 2002). 

In the human and mouse liver, CYP7B is responsible for (Toll et al., 1994): 

  • 5-cholesten-3-beta, 25(S)-diol into Cholest-5-ene-3 beta-7 alpha, 25-thiol (R07209 R08723),
  • Cholest-5-ene-3 beta, 26-diol into 7 alpha, 27-dihydroxycholesterol (R07372 R08724),
  • 3 beta-hydroxy-5-cholestenoate into 3 beta, 7 alpha-dihydroxy-5-cholestenoate (R08727 R08728).
  • It is expressed in the chicken liver and is probably involved in the same reactions (Handschin et al., 2005). 

In the prostate:

  • Proven for human and rat: Dehydroepiandrosterone (DHEA) to 7α-hydroxy-DHEA and 7β-hydroxy-DHEA (Martin et al., 2001; Martin et al., 2004). 

Inhibitors prevent the metabolism of pregnenolone into 7-alpha-hydroxypregnenolone, thereby decreasing the concentration of the neurosteroid. 

How It Is Measured or Detected

One of the primary considerations in evaluating AOPs is the relevance and reliability of the methods with which the KEs can be measured. The aim of this section of the KE description is not to provide detailed protocols, but rather to capture, in a sentence or two, per method, the type(s) of measurements that can be employed to evaluate the KE and the relative level of scientific confidence in those measurements. Methods that can be used to detect or measure the biological state represented in the KE should be briefly described and/or cited. These can range from citation of specific validated test guidelines, citation of specific methods published in the peer reviewed literature, or outlines of a general protocol or approach (e.g., a protein may be measured by ELISA).Key considerations regarding scientific confidence in the measurement approach include whether the assay is fit for purpose, whether it provides a direct or indirect measure of the biological state in question, whether it is repeatable and reproducible, and the extent to which it is accepted in the scientific and/or regulatory community. Information can be obtained from the OECD Test Guidelines website and the EURL ECVAM Database Service on Alternative Methods to Animal Experimentation (DB-ALM). ?

In vitro

To measure CYP7B activity in vitro, different experiments based on HPLC and GS-MS analysis can be performed.

  • An assay in liver microsome followed by HPLC analysis of the metabolites (Souidi et al., 2000). 
  • Labeled steroid conversion in vitro with cell or tissue extract in presence of NADPH followed by GS-MS analysis (Rose et al., 1997; Tsutsui et al., 2008). 
  • CYP7B can be cloned in bacteria to produce an active protein in vitro. In presence of adequate precursor and cofactors, the enzymatic activity of the protein can be measured and analyzed using HPLC.  
  • CYP7B can be transfected in a cell line unable to synthesize 7α-hydroxypregnenolone in order to measure with HPLC the ability of the protein to catalyze the enzymatic reaction in presence of the appropriate substrate and cofactor (Tsutsui et al., 2008)

In vivo

Experiments may include knock-out of mice (followed by RNA, protein blotting and enzymatic activity to confirm knock-out) (Li-Hawkins et al., 2000) followed by the measurement of substrate and metabolites of CYP7B in plasma and tissues (Rose., 2001). 

Domain of Applicability

This free text section should be used to elaborate on the scientific basis for the indicated domains of applicability and the WoE calls (if provided). While structured terms may be selected to define the taxonomic, life stage and sex applicability (see structured applicability terms, above) of the KE, the structured terms may not adequately reflect or capture the overall biological applicability domain (particularly with regard to taxa). Likewise, the structured terms do not provide an explanation or rationale for the selection. The free-text section on evidence for taxonomic, life stage, and sex applicability can be used to elaborate on why the specific structured terms were selected, and provide supporting references and background information.  More help

CYP7B is known to be conserved in chimpanzee, Rhesus monkey, dog, cow, mouse, rat, chicken, zebrafish, and frog. https://www.ncbi.nlm.nih.gov/homologene/3544

Evidence for Perturbation by Stressor

Overview for Molecular Initiating Event

When a specific MIE can be defined (i.e., the molecular target and nature of interaction is known), in addition to describing the biological state associated with the MIE, how it can be measured, and its taxonomic, life stage, and sex applicability, it is useful to list stressors known to trigger the MIE and provide evidence supporting that initiation. This will often be a list of prototypical compounds demonstrated to interact with the target molecule in the manner detailed in the MIE description to initiate a given pathway (e.g., 2,3,7,8-TCDD as a prototypical AhR agonist; 17α-ethynyl estradiol as a prototypical ER agonist). Depending on the information available, this could also refer to chemical categories (i.e., groups of chemicals with defined structural features known to trigger the MIE). Known stressors should be included in the MIE description, but it is not expected to include a comprehensive list. Rather initially, stressors identified will be exemplary and the stressor list will be expanded over time. For more information on MIE, please see pages 32-33 in the User Handbook.

The binding of inhibitors to CYP7B is demonstrated in vitro with purified recombinant protein in presence of the inhibitor. Ligand-induced spectral changes is analyzed using spectrophotometric titration as a shift of the heme (Yantsevich et al., 2014). 

Ketoconazole and other conazole are known to bind to CYPs preventing its enzymatic activity.

  • CYP7B inhibitor (ketoconazole, 10-4 M) decreased the synthesis of 7α-hydroxypregnenolone
  • CYP7B inhibitor (intracerebroventricular injection of ketoconazole) decreased the synthesis of 7α-hydroxypregnenolone in the male quail and newt brain, in vivo (Matsunaga et al., 2004; Rose et al., 1997; Tsutsui et al., 2008). 
  • The heme prosthetic group (catalytic site) of human recombinant CYP7B thightly bound to various imidazole- and triazole-based drugs in an in vitro spectrometric titration assay. The drugs with the highest affinities were the industrial pesticides tebuconazole (0.11 μm), propiconazole (0.13 μm) and the antifungal drugs tioconazole (0.15 μm) and miconazole (0.23 μm). Voriconazole and metyrapone (non-azole compound) also interacted with CYP7B (Yantsevich et al., 2014). 

Ketoconazole

It is clearly demonstrated that ketoconazole directly inhibits CYP7B (Matsunaga et al., 2004). It is expected for the other members of the conazole family to have the same effect.

Some other azoles such as clotrimazole can also inhibit CYP7B activity (Liu et al., 2011; Rose et al., 1997). 

Tebuconazole

In vitro, tebuconazole was shown to bind to the catalytic site of the human recombinant CYP7B and to inhibit its catalytic activity (Yantsevich et al., 2014). 

Propiconazole

In vitro, propiconazole was shown to bind to the catalytic site of the human recombinant CYP7B and to inhibit its activity (Yantsevich et al., 2014).

Tioconazole

In vitro, tioconazole was shown to bind to the catalytic site of the human recombinant CYP7B and to inhibit its activity (Yantsevich et al., 2014).

Miconazole

In vitro, miconazole was shown to bind to the catalytic site of the human recombinant CYP7B and to inhibit its activity (Yantsevich et al., 2014).

Fluconazole

In vitro, fluconazole was shown to bind to the catalytic site of the human recombinant CYP7B and to inhibit its activity (Yantsevich et al., 2014).

Voriconazole

In vitro, voriconazole was shown to bind to the catalytic site of the human recombinant CYP7B and to inhibit its activity (Yantsevich et al., 2014).

Clotrimazole

Clotrimazoles can inhibit CYP7B activity (Liu et al., 2011; Rose et al., 1997). 

References

List of the literature that was cited for this KE description. Ideally, the list of references, should conform, to the extent possible, with the OECD Style Guide (https://www.oecd.org/about/publishing/OECD-Style-Guide-Third-Edition.pdf) (OECD, 2015). More help

Dulos, J., van der Vleuten, M.A., Kavelaars, A., Heijnen, C.J., and Boots, A.M. (2005). CYP7B expression and activity in fibroblast-like synoviocytes from patients with rheumatoid arthritis: regulation by proinflammatory cytokines. Arthritis Rheum 52, 770-778.

Handschin C., Gnerre C., Fraser DJ., Martinez-Jimenez C., Jover R., Mever UA., (2005) Species-specific mechanisms for cholesterol 7α-hydroxylase (CYP7A1) regulation by drugs and bile acids, Archives of Biochemistry and Biophysics, Vol 434-1, pp75-85

Haraguchi, S., Koyama, T., Hasunuma, I., Okuyama, S., Ubuka, T., Kikuyama, S., Do Rego, J.L., Vaudry, H., and Tsutsui, K. (2012). Acute stress increases the synthesis of 7alpha-hydroxypregnenolone, a new key neurosteroid stimulating locomotor activity, through corticosterone action in newts. Endocrinology 153, 794-805.

Haraguchi, S., Yamamoto, Y., Suzuki, Y., Hyung Chang, J., Koyama, T., Sato, M., Mita, M., Ueda, H., and Tsutsui, K. (2015). 7alpha-Hydroxypregnenolone, a key neuronal modulator of locomotion, stimulates upstream migration by means of the dopaminergic system in salmon. Sci Rep 5, 12546.

Li-Hawkins, J., Lund, E.G., Turley, S.D., and Russell, D.W. (2000). Disruption of the oxysterol 7alpha-hydroxylase gene in mice. J Biol Chem 275, 16536-16542.

Liu, C., Yang, X.V., Wu, J., Kuei, C., Mani, N.S., Zhang, L., Yu, J., Sutton, S.W., Qin, N., Banie, H., et al. (2011). Oxysterols direct B-cell migration through EBI2. Nature 475, 519-523.

Martin, C., Bean, R., Rose, K., Habib, F., and Seckl, J. (2001). cyp7b1 catalyses the 7alpha-hydroxylation of dehydroepiandrosterone and 25-hydroxycholesterol in rat prostate. Biochem J 355, 509-515.

Martin, C., Ross, M., Chapman, K.E., Andrew, R., Bollina, P., Seckl, J.R., and Habib, F.K. (2004). CYP7B generates a selective estrogen receptor beta agonist in human prostate. J Clin Endocrinol Metab 89, 2928-2935.

Matsunaga, M., Ukena, K., Baulieu, E.E., and Tsutsui, K. (2004). 7alpha-Hydroxypregnenolone acts as a neuronal activator to stimulate locomotor activity of breeding newts by means of the dopaminergic system. Proc Natl Acad Sci U S A 101, 17282-17287.

Rose, K., Allan, A., Gauldie, S., Stapleton, G., Dobbie, L., Dott, K., Martin, C., Wang, L., Hedlund, E., Seckl, J.R., et al. (2001). Neurosteroid hydroxylase CYP7B: vivid reporter activity in dentate gyrus of gene-targeted mice and abolition of a widespread pathway of steroid and oxysterol hydroxylation. J Biol Chem 276, 23937-23944.

Rose, K.A., Stapleton, G., Dott, K., Kieny, M.P., Best, R., Schwarz, M., Russell, D.W., Bjorkhem, I., Seckl, J., and Lathe, R. (1997). Cyp7b, a novel brain cytochrome P450, catalyzes the synthesis of neurosteroids 7alpha-hydroxy dehydroepiandrosterone and 7alpha-hydroxy pregnenolone. Proc Natl Acad Sci U S A 94, 4925-4930.

Souidi, M., Parquet, M., Dubrac, S., Audas, O., Becue, T., and Lutton, C. (2000). Assay of microsomal oxysterol 7alpha-hydroxylase activity in the hamster liver by a sensitive method: in vitro modulation by oxysterols. Biochim Biophys Acta 1487, 74-81.

Toll, A., Wikvall, K., Sudjana-Sugiaman, E., Kondo, K.H., and Bjorkhem, I. (1994). 7 alpha hydroxylation of 25-hydroxycholesterol in liver microsomes. Evidence that the enzyme involved is different from cholesterol 7 alpha-hydroxylase. Eur J Biochem 224, 309-316.

Tsutsui, K., Inoue, K., Miyabara, H., Suzuki, S., Ogura, Y., and Haraguchi, S. (2008). 7Alpha-hydroxypregnenolone mediates melatonin action underlying diurnal locomotor rhythms. J Neurosci 28, 2158-2167.

Weihua, Z., Lathe, R., Warner, M., and Gustafsson, J.A. (2002). An endocrine pathway in the prostate, ERbeta, AR, 5alpha-androstane-3beta,17beta-diol, and CYP7B1, regulates prostate growth. Proc Natl Acad Sci U S A 99, 13589-13594.

Yantsevich, A.V., Dichenko, Y.V., Mackenzie, F., Mukha, D.V., Baranovsky, A.V., Gilep, A.A., Usanov, S.A., and Strushkevich, N.V. (2014). Human steroid and oxysterol 7alpha-hydroxylase CYP7B1: substrate specificity, azole binding and misfolding of clinically relevant mutants. FEBS J 281, 1700-1713.