Event: 1720

Key Event Title


Trypsin inhibition

Short name


Inhibition, trypsin

Biological Context


Level of Biological Organization

Cell term


Organ term


Key Event Components


Process Object Action

Key Event Overview

AOPs Including This Key Event


AOP Name Role of event in AOP
TI-induced AC tumors MolecularInitiatingEvent



Taxonomic Applicability


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


Life stage Evidence
All life stages High

Sex Applicability


Term Evidence
Mixed High

Key Event Description


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


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


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





 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