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Relationship: 2877

Title

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

Conjugation, GSH leads to Depletion, GSH

Upstream event

The causing Key Event (KE) in a Key Event Relationship (KER). More help

Conjugation, GSH

Downstream event

The responding Key Event (KE) in a Key Event Relationship (KER). More help

Depletion, GSH

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
Glutathione conjugation leading to reproductive dysfunction via oxidative stress	adjacent	High	High	Allie Always (send email)	Under Development: Contributions and Comments Welcome

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

Sex Applicability

An indication of the the relevant sex for this KER. More help

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

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 Map 2.0

ID	Experimental Design	Species	Upstream Observation	Downstream Observation	Citation (first author, year)	Notes

Evidence Map

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

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

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

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

Modulating Factor (MF)	MF Specification	Effect(s) on the KER	Reference(s)
antioxidant	biflavonone-kolaviron	prevent GSH depletion	Abarikwu, Farombi, and Pant 2011
antioxidant	vitamin E	prevent GSH depletion	Singh, Sandhir, and Kiran 2010

Quantitative Understanding of the Linkage

Captures information that helps to define how much change in the upstream KE, and/or for how long, is needed to elicit a detectable and defined change in the downstream KE. More help

GSH depletion depends on the constant conjugation rate of GSH to a xenobiotic, from the initial GSH concentration and its synthesis and degradation rates. Several chemicals that undergo GSH conjugation at high concentrations cause depletion of GSH supplies in the liver and others tissues (D’Souza, Francis, and Andersen 1988; D’Souza and Andersen 1988; Csanády et al. 1996; Mulder and Ouwerkerk-Mahadevan 1997; Fennell and Brown 2001).

In this context, the global kinetic equation for GSH consumption through conjugation to xenobiotics, catalyzed by microsomal glutathione transferase 1 (mGST1), purified from rat liver can be defined by (Spahiu et al. 2017) (figure below.). In this equation, C is the electrophilic substrate, while E represents the enzyme and P serves as a GSH-conjugate. In relation to constants, k₂ is the rate for thiolate anion, k_-2 is the rate for the reverse process of thiolate anion, k₃ is the rate for the chemical step that is essentially irreversible, K_Cis the dissociation constant for electrophilic substrate and K_G is the dissociation constant for GSH (Spahiu et al. 2017).

Moreover, thiolate anion formation (k_obs) can be easily calculated through equations described by (Morgenstern et al. 2001). Kinetic parameters K_M e k_cat values for both electrophiles and GSH can also be determined according to the equations established by (Spahiu et al. 2017).Furthermore, nucleophilic reactivity (N) and electrophilicity (E) parameters of GSH have also been settled to a variety of Michael acceptors (Mayer and Ofial 2019).

Response-response Relationship

Provides sources of data that define the response-response relationships between the KEs. More help

Velocity of conjugation, however, depends on the kind of GST involved and on the chemical, as well as the organism in which it takes place. For instance, the ATZ-GSH conjugate formed in GSTs from zebrafish embryos works in a time-dependent manner, although conjugation in the microsomal GST increased linearly by a factor of 23 up to 12 h of incubation time, whereas in the soluble GST the conversion rate increased more slowly and was higher by a factor of 5.8 after 24 h of incubation time than that at start (Wiegand et al. 2001). In rats, the estimated GSH conjugation rate constant with ATZ was 0.53 L/mmol/h, a value comparable to that for other chemicals that are largely conjugated by GSTs, even so less than known depleters such as ethylene dichloride (1.2 L/mmol/h) and allyl chloride (9.0 L/mmol/h). Although ATZ is mostly metabolized by GSH, the model estimated that 50% depletion of GSH is predicted to occur, but only after three daily doses of 500 mg ATZ/Kg (McMullin et al. 2003).

Time-scale

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

In humans, intrahepatic glutathione concentration is predicted to be the lowest one, due to conjugation to the reactive intermediate NAPQI, at 6 h after 2 g of intravenous (IV) infusion administration of paracetamol and then to recover slowly. In addition, it responds in a time-dependent way. However, concentrations of glutathione were predicted to be markedly and progressively depleted when patients had an initial 2 g dose and then 1 g dose every 6 h (Geenen et al. 2013).

(Hughes, Miller, and Swamidass 2015), for example, constructed a model to predict the GSH reactivity to 1213 molecules and determined the percent depletion of GSH after 15 min incubation with each molecule. In this context, such a model can be easily used for investigation and initial selection of molecules that might impair fertility.

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

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