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Event: 1720

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

Trypsin 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
Inhibition, trypsin

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
Level of Biological Organization

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

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
TI-induced AC tumors MolecularInitiatingEvent Arthur Author (send email) Under development: Not open for comment. Do not cite Under Development


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
Homo sapiens Homo sapiens High NCBI
Mus musculus Mus musculus High NCBI
Rattus norvegicus Rattus norvegicus High NCBI
Macaca fascicularis Macaca fascicularis High 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 High

Sex Applicability

The authors must select from one of the following: Male, female, mixed, asexual, third gender, hermaphrodite, or unspecific. More help
Term Evidence
Mixed High

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

Trypsin is a digestive enzyme secreted by pancreatic acinar cells that cleaves peptide bonds at the carboxyl end of basic amino acids (lysine and arginine). Acinar cells secrete trypsinogen, the inactive form of trypsin, into the lumen of the duodenum; in turn, trypsinogen is auto-hydrolyzed by enterokinase into β-trypsin, composed of an uncleaved single chain, and α-trypsin, composed of two cleaved chains bound by a disulfide bridge [Santos AMC et al, 2008]. Trypsin is required for the partial hydrolysis of chymotrypsinogen to chymotrypsin, and most pancreatic digestive enzyme precursors are activated by trypsin in the same manner as chymotrypsin in the intestinal lumen.

As part of the defense against trypsin-induced self injury in the pancreas, internal TIs such as the serine protease inhibitor Kazal type 1 (SPINK1 or human pancreatic trypsin inhibitor) and bovine pancreatic TI in the pancreatic juice and α1-antitrypsin in the serum bind tightly to active trypsin [Voet D and Voet JG, 1995].

Secretion of pancreatic digestive enzymes including trypsin is regulated mainly by CCK released from enteroendocrine I cells in the duodenal mucosa of the small intestine [Wang BJ and Cui ZJ, 2007], and CCK release is controlled by multiple mechanisms [Caron J et al, 2017]. One such mechanism is trypsin-mediated negative feedback regulation, in which increased trypsin secretion leads to decreased levels of trypsin-sensitive luminal CCK-releasing factors (LCRFs) in several mammalian species and MP in rodents [Liddle RA, 1995; Miyasaka K and Funakoshi A, 1998].

Therefore, ingestion of RSF containing trypsin inhibitory action or protease inhibitors such as camostat inhibits trypsin activity in the intestinal lumen, which leads to increased luminal levels of the abovementioned trypsin-sensitive peptides and thereby stimulation of CCK release [Green GM and Miyasaka K, 1983; Cuber JC et al, 1990; Miyasaka K et al, 1989; Cuber JC et al, 1990; Komarnytsky S et al, 2011].

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). ?

Activity of trypsin inhibitors is measured colorimetrically using mixture of multiple dilutions of samples (TIs), trypsin and its substrate. Standard procedures for measuring TI activities in soy bean products are released as AACCI Method 22-40.01 [AACCI, 2009] and AOCS Method Ba 12-75 [AOCC, 2017]. ISO standard for measuring TI activities is also established as Standard 14902:2001 [ISO, 2012]. The two methods of modified AACC 20-40.01 and ISO 14902 were compared to show that the values obtained by these two methods are not directly comparable [Sueiro S et al, 2015].  Modified standard method is proposed reconsidering the levels of dilutions and volumes, reaction sequence and other factors [Liu K, 2019].

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

Trypsin is a digestive enzyme expressed in many vertebrates, and its molecular weight and isoforms vary among animal species, for example, human cationic and anionic trypsins (trypsins 1 and 2) and mesotrypsin, bovine cationic and anionic trypsins, and rat anionic trypsin and P23 [Chen JM and Claude Férec C, 2013; Fukuoka S and Nyaruhucha CM, 2002]. However, their three-dimensional structures are highly conserved among species [Baird Jr TT, 2013].

The natural substrate for trypsin is generally any peptide that contains Lys or Arg. The active site of trypsin has a specific catalytic triad structure composed of serine, histidine, and aspartate, and the flanking amino acid sequences are entirely conserved [Baird Jr TT and Craik CS, 2013; Baird Jr TT, 2017].

Therefore, TIs show comparable enzymatic inhibition of trypsin molecules among animal species including humans and rats [Savage GP and Morrison SC, 2003].

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.



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 ( (OECD, 2015). More help

 1.     AACCI (2009) American Association of Cereal Chemists. Approved methods of analysis, 11th Ed. Method 22-40.01. Measurement of trypsin inhibitor activity of soy products—spectrophotometric method. First approval Nov 7, 1973; Reapproved Nov 3, 1999. AACC International, St. Paul. doi: 10.1094/AACCIntMethod-22-40.01

 2.    AOCS (2017) American Oil Chemists’ Society. Official and tentative methods of the American Oil Society, 3rd Ed. Method Ba 12-75. Trypsin inhibitor activity. First approval 1980; Reapproved 2009. American Oil Chemist Society, Champaign

 3.    Baird Jr TT, Craik CS: Trypsin. Academic Press, Cambridge, Massachusetts (pp)2594-2600,2013

 4.    Baird Jr TT: Trypsin. Elsevier,2017

 5.    Caron J, Domenger D, Dhulster P, Ravallec R, Cudennec B: Protein digestion-derived peptides and the peripheral regulation of food intake. Front Endocrinol (Lausanne) 8:85,2017

 6.    Chen J-M, Claude Férec C: Human trypsins. Academic Press, Cambridge, Massachusetts (pp) 2600-2609,2013

 7.    Cuber JC, Bernard G, Fushiki T, Bernard C, Yamanishi R, Sugimoto E, Chayvialle JA: Luminal CCK-releasing factors in the isolated vascularly perfused rat duodenojejunum. Am J Physiol 259:G191-197,1990

 8.    Fukuoka S, Nyaruhucha CM: Expression and functional analysis of rat P23, a gut hormone-inducible isoform of trypsin, reveals its resistance to proteinaceous trypsin inhibitors. Biochim Biophys Acta 1588:106-112,2002

 9.    Green GM, Miyasaka K: Rat pancreatic response to intestinal infusion of intact and hydrolyzed protein. Am J Physiol 245:G394-8,1983

10.    ISO (2012) International Organization for Standardization. Standard 14902:2001. Animal feeding stuffs—determination of trypsin inhibitor activity of soya products. Approved Oct 2001; Reapproved Aug 2012. International Organization for Standardization, Geneva

11.    Komarnytsky S, Cook A, Raskin I: Potato protease inhibitors inhibit food intake and increase circulating cholecystokinin levels by a trypsin-dependent mechanism. Int J Obes (Lond) 35:236-243,2011

12.    Liddle RA: Regulation of cholecystokinin secretion by intraluminal releasing factors. Am J Physiol 269:G319-27,1995

13.     Liu K: Soybean trypsin inhibitor assay: further improvement of the standard method approved and reapproved by American Oil Chemists’ Society and American Association of Cereal Chemists International. J Am Oil Chem Soc 96: 635–645,2019

14.    Miyasaka K, Nakamura R, Funakoshi A, Kitani K: Stimulatory effect of monitor peptide and human pancreatic secretory trypsin inhibitor on pancreatic secretion and cholecystokinin release in conscious rats. Pancreas 4:139-144,1989

15.    Miyasaka K, Funakoshi A: Luminal feedback regulation, monitor peptide, CCK-releasing peptide, and CCK receptors. Pancreas 16:277-283,1998

16.    Santos AMC, de Oliveira JS, Bittar ER, da Silva AL, dos Mares Guia ML, Bemquerer MP, Santoro MM: Improved purification process of β- and α-trypsin isoforms by ion-exchange chromatography. Braz Arch Biol Technol 51: 711-721,2008

17.    Savage GP, Morrison SC: Trypsin inhibitors. Elsevier (pp) 5878-5884,2003

18.     Sueiro S, Hermida M, González M, Lois A, Rodríguez?Otero JL: A comparison of the ISO and AACC methods for determining the activity of trypsin Inhibitors in soybean meal. J Am Oil Chem Soc 92:1391–1397,2015

19.    Voet D, Voet JG: Biochemistry (2nd ed.). John Wiley & Sons (pp) 396-400,1995

20.    Wang BJ, Cui ZJ: How does cholecystokinin stimulate exocrine pancreatic secretion? From birds, rodents, to humans.. Am J Physiol Regul Integr Comp Physiol 292:R666-78,2007