To the extent possible under law, AOP-Wiki has waived all copyright and related or neighboring rights to KER:2032

Relationship: 2032


The title of the KER should clearly define the two KEs being considered and the sequential relationship between them (i.e., which is upstream and which is downstream). Consequently all KER titles take the form “upstream KE leads to downstream KE”.  More help

Acinar cell proliferation leads to Acinar cell tumors

Upstream event
Upstream event in the Key Event Relationship. On the KER page, clicking on the Event name under Upstream Relationship will bring the user to that individual KE page. More help
Downstream event
Downstream event in the Key Event Relationship. On the KER page, clicking on the Event name under Upstream Relationship will bring the user to that individual KE page. More help

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

This table is automatically generated upon addition of a KER to an AOP. All of the AOPs that are linked to this KER will automatically be listed in this subsection. Clicking on the name of the AOP in the table will bring you to the individual page for that AOP. More help
AOP Name Adjacency Weight of Evidence Quantitative Understanding Point of Contact Author Status OECD Status
Trypsin inhibition leading to pancreatic acinar cell tumors adjacent High High Arthur Author (send email) Under development: Not open for comment. Do not cite Under Development

Taxonomic Applicability

Select one or more structured terms 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. Authors can indicate the relevant taxa for this KER in this subsection. The process is similar to what is described for KEs (see pages 30-31 and 37-38 of User Handbook) More help
Term Scientific Term Evidence Link
Homo sapiens Homo sapiens Moderate NCBI
Macaca fascicularis Macaca fascicularis Moderate NCBI
Rattus norvegicus Rattus norvegicus High NCBI
Mus musculus Mus musculus Moderate NCBI

Sex Applicability

Authors can indicate the relevant sex for this KER in this subsection. The process is similar to what is described for KEs (see pages 31-32 of the User Handbook). More help
Sex Evidence
Mixed High

Life Stage Applicability

Authors can indicate the relevant life stage for this KER in this subsection. The process is similar to what is described for KEs (see pages 31-32 of User Handbook). More help
Term Evidence
All life stages High

Key Event Relationship Description

Provide a brief, descriptive summation of the KER. While the title itself is fairly descriptive, this section can provide details that aren’t inherent in the description of the KEs themselves (see page 39 of the User Handbook). This description section can be viewed as providing the increased specificity in the nature of upstream perturbation (KEupstream) that leads to a particular downstream perturbation (KEdownstream), while allowing the KE descriptions to remain generalised so they can be linked to different AOPs. The description is also intended to provide a concise overview for readers who may want a brief summation, without needing to read through the detailed support for the relationship (covered below). Careful attention should be taken to avoid reference to other KEs that are not part of this KER, other KERs or other AOPs. This will ensure that the KER is modular and can be used by other AOPs. More help

An increased blood level of CCK is the main factor responsible for a sustained increase in acinar cell proliferation and subsequent tumor formation.

Evidence Supporting this KER

Assembly and description of the scientific evidence supporting KERs in an AOP is an important step in the AOP development process that sets the stage for overall assessment of the AOP (see pages 49-56 of the User Handbook). To do this, biological plausibility, empirical support, and the current quantitative understanding of the KER are evaluated with regard to the predictive relationships/associations between defined pairs of KEs as a basis for considering WoE (page 55 of User Handbook). In addition, uncertainties and inconsistencies are considered. More help


Biological Plausibility
Define, in free text, the biological rationale for a connection between KEupstream and KEdownstream. What are the structural or functional relationships between the KEs? For example, there is a functional relationship between an enzyme’s activity and the product of a reaction it catalyses. Supporting references should be included. However, it is recognised that there may be cases where the biological relationship between two KEs is very well established, to the extent that it is widely accepted and consistently supported by so much literature that it is unnecessary and impractical to cite the relevant primary literature. Citation of review articles or other secondary sources, like text books, may be reasonable in such cases. The primary intent is to provide scientifically credible support for the structural and/or functional relationship between the pair of KEs if one is known. The description of biological plausibility can also incorporate additional mechanistic details that help inform the relationship between KEs, this is useful when it is not practical/pragmatic to represent these details as separate KEs due to the difficulty or relative infrequency with which it is likely to be measured (see page 40 of the User Handbook for further information).   More help

Trypsin inhibitor-induced pancreatic tumor formation

Ingestion of raw soya flour, which contains trypsin inhibitory activity, by rats for 2 years induced pancreatic hypertrophy due to acinar cell hyperplasia and acinar cell tumors [Rackis JJ et al, 1985; Woutersen RA et al, 1991]. Rats given raw soya flour or the trypsin inhibitor camostat exhibited pancreatic hypertrophy and acinar cell hyperplasia, and rats administered the pancreatic carcinogen azaserine followed by camostat exhibited acinar cell tumor formation [Gumbmann MR et al, 1986; Lhoste EF et al, 1988; Bell RH Jr et al, 1992].

Promotion of pancreatic acinar cell tumors via CCK

In addition, the suggestion that trypsin inhibition-induced pancreatic acinar cell tumor formation is promoted by increased acinar cell proliferation via CCK receptors is supported by the following study. After initiating treatment with 30 mg/kg azaserine at 19 days of age, rats were treated with camostat, CCK8, or gelatin control, in combination with or without the CCK receptor antagonist CR-1409 (once daily, 3 days/week for 16 weeks). After 16 weeks, both camostat and CCK8 stimulated pancreatic growth and the development of azaserine-induced acidophilic putative preneoplastic foci. CR-1409 almost completely abolished the effect of CCK8 and significant attenuated the effect of camostat [Douglas BR et al, 1

Soybean trypsin inhibitor


Soy and potato trypsin inhibitor (TI) concentrates were prepared from defatted raw soy flour and potato juice. Rats and mice were fed a diet supplemented with each concentrate to provide 100 and 200 mg of trypsin inhibitor activity per 100 g of diet. In short-term (28 d) experiments in rats, both sources of TI induced pancreatic hypertrophy (KE4). After long-term feeding (95 weeks) in rats, soy and potato TI induced dose-related increases in pancreatic nodular hyperplasia and acinar adenoma (AO) [Gumbmann MR et al, 1989].

Rats were continuously fed diets containing lower amounts of raw soya flour (RSF, 5%, 25% and 50%) with weekly intraperitoneal injection of either azaserine at 5mg/kg BW or saline for up to 85 weeks or were fed RSF intermittently (2 days per week).After a maximum of 2 years of study, continuous feeding of as little as 5% RSF developed pancreatic micro/macroscopic nodules and stimulated the development of azaserine-initiated nodular hyperplasia and tumorigenesis. Intermittent feeding of 25 , 50 and 100% RSF also induced nodular hyperplasia. In addition, consuming a 100% RSF diet for 2 days per week resulted in the development of pancreatic cancer in some of the rats [McGuinness EE and Wormsley KG, 1986].

Protease inhibitor camostat:


Adult Fischer 344 (F344) and Lewis rats fed camostat mixed in the diet to define a level that induced pancreatic hypertrophy and hyperplasia. As little as 0.02% fed 3 days per week was effective [Lhoste EF et al, 1988].


F344 rats were injected s.c. twice with azaserine at 30 mg/kg BW and thereafter were given camostat at 200 mg/kg BW by gavage 5 days a week until autopsy 18 weeks later. In addition, azaserine-treated Lewis rats were fed camostat in the diet at 0.5 g/kg diet for 4 weeks and then 0.2 g/kg diet 3 consecutive days a week for 8 or 16 weeks until autopsy. In these experiments the number and size of atypical acinar cell foci and nodules (AACN) were increased in comparison with the control groups. The data suggest a promoting effect of dietary camostat on the growth of azaserine-induced preneoplastic lesions in the pancreas of both rat strains [Lhoste EF et al, 1988].


Sustained pancreatic growth (acinar cell proliferation) leading to acinar cell tumor formation

Rats fed a diet containing raw soya flour developed micro- and macro-nodules. Longer treatment with raw soya flour resulted in further growths in the pancreas and, ultimately, development of adenomas and carcinomas in the acinar pancreas. The pancreatic changes were reversible up to 6 months of consuming the raw soya flour diet but became irreversible thereafter [McGuinness EE et al, 1985].

Uncertainties and Inconsistencies
In addition to outlining the evidence supporting a particular linkage, it is also important to identify inconsistencies or uncertainties in the relationship. Additionally, while there are expected patterns of concordance that support a causal linkage between the KEs in the pair, it is also helpful to identify experimental details that may explain apparent deviations from the expected patterns of concordance. Identification of uncertainties and inconsistencies contribute to evaluation of the overall WoE supporting the AOPs that contain a given KER and to the identification of research gaps that warrant investigation (seep pages 41-42 of the User Handbook).Given that AOPs are intended to support regulatory applications, AOP developers should focus on those inconsistencies or gaps that would have a direct bearing or impact on the confidence in the KER and its use as a basis for inference or extrapolation in a regulatory setting. Uncertainties that may be of academic interest but would have little impact on regulatory application don’t need to be described. In general, this section details evidence that may raise questions regarding the overall validity and predictive utility of the KER (including consideration of both biological plausibility and empirical support). It also contributes along with several other elements to the overall evaluation of the WoE for the KER (see Section 4 of the User Handbook).  More help


Response-response Relationship
This subsection should be used to define sources of data that define the response-response relationships between the KEs. In particular, information regarding the general form of the relationship (e.g., linear, exponential, sigmoidal, threshold, etc.) should be captured if possible. If there are specific mathematical functions or computational models relevant to the KER in question that have been defined, those should also be cited and/or described where possible, along with information concerning the approximate range of certainty with which the state of the KEdownstream can be predicted based on the measured state of the KEupstream (i.e., can it be predicted within a factor of two, or within three orders of magnitude?). For example, a regression equation may reasonably describe the response-response relationship between the two KERs, but that relationship may have only been validated/tested in a single species under steady state exposure conditions. Those types of details would be useful to capture.  More help

Hypertrophy/hyperplasia of acinar cells and tumor development in rats fed TI-containing diet were examined in the same rat study reported as follows:

Weanling male Wistar rats were fed 15 diets consisting of four concentrations of purified soybean TIs (93, 215, 337, and 577 mg/100 g diet) and three protein concentrations (10%, 20%, and 30%), as well as raw and heat-treated soy flour containing 10% protein. Rats were first sacrificed at 6 months and at 3-month intervals thereafter over a period of 22 months [Rackis JJ et al, 1985]. In this study, the following dose responses for KE4 and AO were obtained.

KE4: Hypertrophy and hyperplasia of the pancreas determined by pancreas weight and RNA and DNA content developed at 6 months and were likewise positively correlated with the levels of TI and protein. Although the hypertrophic response remained unchanged, hyperplasia became more pronounced as the period of exposure to TI was prolonged [Liener IE et al, 1985].

AO: Nodular hyperplasia of acinar cells was observed in the first sacrifice group at 6 months. Incidence of the lesion was positively related to both time of exposure and level of dietary TI. Acinar cell adenoma was first observed at 18 months and was most prevalent in rats fed the highest concentration of TI [Spangler WL et al, 1985].

This sub-section should be used to provide 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?). This can be useful information both in terms of modelling the KER, as well as for analyzing the critical or dominant paths through an AOP network (e.g., identification of an AO that could kill an organism in a matter of hours will generally be of higher priority than other potential AOs that take weeks or months to develop). Identification of time-scale can also aid the assessment of temporal concordance. For example, for a KER that operates on a time-scale of days, measurement of both KEs after just hours of exposure in a short-term experiment could lead to incorrect conclusions regarding dose-response or temporal concordance if the time-scale of the upstream to downstream transition was not considered. More help


Several studies have suggested that acinar cell proliferation is induced approximately 7 days after treatment with TIs or CCK. Rats fed RSF showed a biphasic increase in the proliferation of acinar and duct cells on days 2–4 and again on days 7–28 after the start of RSF feeding. The first peak may represent a regenerative response to tissue damage. The second more delayed peak appears to represent the development of hyperplasia in response to a trophic stimulus [Oates PS and Morgan RG, 1984]. Rats administered TIs in drinking water for 7 days or repeatedly injected with CCK for 7 days exhibited increased mitotic figures in the acinar, centroacinar, and intercalated portions of the pancreas and in excretory duct cells, as well as marked pancreatic hypertrophy [Yanatori Y and Fujita T, 1976].


Increased CCK-mediated acinar cell proliferation might lead to acinar cell tumor formation, as shown by the following findings: In rats fed soybean TIs, acinar cell hyperplasia was observed at the first sacrifice time point (6 months) and became more pronounced with prolonged TI exposure. Nodular hyperplasia of acinar cells was also found at 6 months and increased at later dosing periods. Acinar cell adenomas were first observed at 18 months of TI exposure [Liener IE et al, 1985; Spangler WL et al, 1985].

Morgan et al. reported that rats fed an RSF diet for 24 weeks developed pancreatic hypertrophy and hyperplasia, as determined by DNA, RNA, and protein contents in the pancreas, and developed more pronounced azaserine (30 mg/kg once a week for 5 weeks)-induced nodular hyperplasia compared with rats fed a heat-treated soy flour diet [Morgan RG et al, 1990].

Known modulating factors
This sub-section presents information regarding modulating factors/variables known to alter the shape of the response-response function that describes the quantitative relationship between the two KEs (for example, an iodine deficient diet causes a significant increase in the slope of the relationship; a particular genotype doubles the sensitivity of KEdownstream to changes in KEupstream). Information on these known modulating factors should be listed in this subsection, along with relevant information regarding the manner in which the modulating factor can be expected to alter the relationship (if known). Note, this section should focus on those modulating factors for which solid evidence supported by relevant data and literature is available. It should NOT list all possible/plausible modulating factors. In this regard, it is useful to bear in mind that many risk assessments conducted through conventional apical guideline testing-based approaches generally consider few if any modulating factors. More help

Trypsin inhibition promotes acinar cell tumor formation.

TI-enhanced growth of azaserine-induced pancreatic preneoplastic lesions were reduced especially in size by the CCK receptor antagonist lorglumide (CR-1409) [Douglas BR et al, 1989].

Pancreatic growth was induced by cholestyramine, similar to that by TIs, presumably because of the bile salt-binding properties of cholestyramine. This finding suggests that removal of proteases and bile salts from the upper small intestine results in pancreatic growths, which may become neoplastic [McGuinness EE et al, 1985].

The thrombin inhibitor ximelagatran induced focal/multifocal acinar cell hyperplasia and adenomas in the pancreas of rats after 24 months of oral administration at 240 μmol/kg/day. However, in mice, no tumors formed after 18 months of treatment with ximelagatran. Treatment with dabigatran, which is in the same class as ximelagatran, showed no carcinogenicity in mice or rats [Stong DB et al, 2012].

Unsaturated fat (corn oil) was reported to promote the growth of azaserine-induced preneoplastic lesions and acinar cell tumors, without inducing pancreatic hypertrophy, in the rat pancreas [Woutersen RA et al, 1991].

Known Feedforward/Feedback loops influencing this KER
This subsection should define whether there are known positive or negative feedback mechanisms involved and what is understood about their time-course and homeostatic limits? In some cases where feedback processes are measurable and causally linked to the outcome, they should be represented as KEs. However, in most cases these features are expected to predominantly influence the shape of the response-response, time-course, behaviours between selected KEs. For example, if a feedback loop acts as compensatory mechanism that aims to restore homeostasis following initial perturbation of a KE, the feedback loop will directly shape the response-response relationship between the KERs. Given interest in formally identifying these positive or negative feedback, it is recommended that a graphical annotation (page 44) indicating a positive or negative feedback loop is involved in a particular upstream to downstream KE transition (KER) be added to the graphical representation, and that details be provided in this subsection of the KER description (see pages 44-45 of the User Handbook).  More help


Domain of Applicability

As for the KEs, there is also a free-text section of the KER description that the developer can use to explain his/her rationale for the structured terms selected with regard to taxonomic, life stage, or sex applicability, or provide a more generalizable or nuanced description of the applicability domain than may be feasible using standardized terms. More help

Rats fed a diet supplemented with soy and potato TI concentrates for 28 days developed pancreatic hypertrophy, and after long-term feeding (95 weeks), the rats developed nodular hyperplasia and acinar adenoma in a dose-dependent manner. Although mice responded similarly to rats to soy TIs in short-term (28 days) feeding experiments, they did not form these pathologies (hyperplasia or acinar adenoma) following long-term feeding. This considerable species difference suggests that the propensity to develop preneoplastic and neoplastic lesions in the pancreas is not predicted by short-term pancreatic hypertrophic and hyperplastic responses to TIs [Gumbmann MR et al, 1989].

The effects of TI-containing diets were evaluated in rats, mice, and hamsters for 30 weeks. In rats and mice, pancreatic weight and DNA, RNA, and protein levels increased in response to a diet consisting of RSF (which contains TIs). Only rats fed RSF developed reversible micro- and macro-nodules after 6 months of treatment, and longer treatment with RSF resulted in further growth in the pancreas and, ultimately, development of adenomas and carcinomas from pancreatic acinar cells [McGuinness EE et al, 1985].

The reasons for the abovementioned species differences in tumor outcome based on hyperplastic changes in acinar cells are unclear, even in rodents.

Meanwhile, a strong relationship between pancreatic cancer and a history of subtotal gastrectomy [Mack TM et al, 1986], which induced a higher plasma CCK level in response to fat [Hopman WP et al, 1984], was reported. On the other hand, some epidemiological surveys suggested that long-term ingestion of TI-containing foods does not increase the risk of pancreatic cancer [Miller RV, 1978], although oral ingestion of raw soya flour containing TIs was reported to stimulate CCK release in humans [Calam J et al, 1987]. Therefore, the effect of CCK on acinar cell proliferation in humans is controversial.

In cases where acinar cell proliferation is enhanced due to a certain treatment, the risk of acinar cell tumor formation may be high in humans as well as rodents.


List of the literature that was cited for this KER description using the appropriate format. Ideally, the list of references should conform, to the extent possible, with the OECD Style Guide (OECD, 2015). More help

 1.    Bell RH Jr, Kuhlmann ET, Jensen RT, Longnecker DS: Overexpression of cholecystokinin receptors in azaserine-induced neoplasms of the rat pancreas. Cancer Res 52:3295-3299,1992

 2.    Calam J, Bojarski JC, Springer CJ: Raw soya-bean flour increases cholecystokinin release in man. Br J Nutr 58:175-179,1987

 3.    Douglas BR, Woutersen RA, Jansen JB, de Jong AJ, Rovati LC, Lamers CB: Modulation by CR-1409 (lorglumide), a cholecystokinin receptor antagonist, of trypsin inhibitor-enhanced growth of azaserine-induced putative preneoplastic lesions in rat pancreas. Cancer Res 49:2438-2441,1989

 4.    Gumbmann MR, Spangler WL, Dugan GM, Rackis JJ: Safety of trypsin inhibitors in the diet: effects on the rat pancreas of long-term feeding of soy flour and soy protein isolate. Adv Exp Med Biol 199:33-79,1986

 5.    Gumbmann MR, Dugan GM, Spangler WL, Baker EC, Rackis JJ: Pancreatic response in rats and mice to trypsin inhibitors from soy and potato after short- and long-term dietary exposure. J Nutr 119:1598-1609,1989

 6.    Hopman WP, Jansen JB, Lamers CB: Plasma cholecystokinin response to oral fat in patients with Billroth I and Billroth II gastrectomy. Ann Surg 199:276-280,1984

 7.    Lhoste EF, Roebuck BD, Longnecker DS: Stimulation of the growth of azaserine-induced nodules in the rat pancreas by dietary camostate (FOY-305). Carcinogenesis 9:901-906,1988

 8.    Liener IE, Nitsan Z, Srisangnam C, Rackis JJ, Gumbmann MR: The USDA trypsin inhibitor study. II. Timed related biochemical changes in the pancreas of rats. Qual Plant Foods Hum Nutr 35:243-257,1985

 9.    Mack TM, Yu MC, Hanisch R, Henderson BE: Pancreas cancer and smoking, beverage consumption, and past medical history. J Natl Cancer Inst 76:49-60,1986

10.    McGuinness EE, Morgan RG, Wormsley KG: Trophic effects on the pancreas of trypsin and bile salt deficiency in the small-intestinal lumen. Scand J Gastroenterol Suppl 112:64-67,1985

11.    McGuinness EE, Wormsley KG: Effects of feeding partial and intermittent raw soya flour diets on the rat pancreas. Cancer Lett 32:73-81,1986

12.    Miller RV: Epidemiology. Alan R. Liss, New York (pp) 39-57,1978

13.    Morgan RG, Papadimitriou JM, Crass RA: Potentiation of azaserine by cholestyramine in the rat. Int J Exp Pathol 71:485-491,1990

14.    Oates PS, Morgan RG: Short-term effects of feeding raw soya flour on pancreatic cell turnover in the rat. Am J Physiol 247:G667-73,1984

15.    Rackis JJ, Gumbmann MR, Liener IE: The USDA trypsin inhibitor study. I. Background, objectives, and procedural details. Qual Plant Foods Hum Nutr 35:213-24,1985

16.    Spangler WL, Gumbmann MR, I.E. Liener IE, J.J. Rackis JJ: The USDA trypsin inhibitor study. III. Sequential development of pancreatic pathology in rats. Qual Plant Foods Hum Nutr 35:259-274 ,1985

17.    Stong DB, Carlsson SC, Bjurstrom S, Fransson-Steen R, Healing G, Skanberg I: Two-year carcinogenicity studies with the oral direct thrombin inhibitor ximelagatran in the rat and the mouse. Int J Toxicol 31:348-357,2012

18.    Woutersen RA, van Garderen-Hoetmer A, Lamers CB, Scherer E: Early indicators of exocrine pancreas carcinogenesis produced by non-genotoxic agents. Mutat Res 248:291-302,1991

19.    Yanatori Y, Fujita T: Hypertrophy and hyperplasia in the endocrine and exocrine pancreas of rats fed soybean trypsin inhibitor or repeatedly injected with pancreozymin. Arch Histol Jpn 39:67-78,1976