Adverse, Non-adverse and Adaptive Responses in Toxicologic Pathology - JSTP

Adverse, Non-adverse and Adaptive Responses in Toxicologic Pathology

International Academy of Toxicology Pathology (IATP) Lecture

Robert R. Maronpot

Website: focusontoxpath.com32nd JSTP Annual Meeting, Takamatsu, Japan

Acknowledgements• Photomicrographs

– National Toxicology Program Archives– NTP Non-neoplastic Lesion Atlas– Dr. Rick Hailey– Dr. Peter Mann– Dr. David Malarkey

• Japanese translations– Dr. Katsuhiko Yoshizawa

Outline of Presentation

• Definitions– Adverse response– Adaptive response– Reversible response– Exacerbation of background lesions

• For the Toxicology Report & Regulatory Submission• Paradigm Shift & Determining Adversity• Practical Examples of Adverse and Adaptive

Responses in Preclinical Studies

Adverse Response

There is no perfect definition of an adverse response in a preclinical study.

前臨床試験における adverse （有害性）反応の完璧な定義はない

Adverse Response• A biochemical, morphological or physiological

change (in response to a stimulus) that either singly or in combination adversely affects the performance of the whole organism or reduces the organism’s ability to respond to an additional environmental challenge

Lewis et al., Toxicol Pathol 30:66-74 (2002)

Adverse Response

• In very broad terms, an adverse finding may be considered to be a change (biochemical, functional, or structural) that may impair performance and generally has a detrimental effect on growth, development, or life span of a non-clinical toxicology model.

• More specifically, an adverse effect in a non-clinical toxicology study should be an effect that would be unacceptable if it occurred in a human clinical trial (FDA Guidance, 2002).

Dorato & Englehardt, Reg Tox & Pharmacol 42:265-274 (2005)

Adverse Effect

• The judgment on the adverse nature of an observation in a non-clinical toxicology study is subject to discussion, challenge, and reinterpretation.

• 前臨床試験で観察された adverse （有害性）の判断は、ディスカッション、チャレンジおよび解釈を必要とする。

Dorato & Englehardt, Reg Tox & Pharmacol 2005

Adverse Response• A change in morphology, physiology, growth,

development, reproduction, or life span of a cell or organism, system, or (sub)population that results in: – impairment of functional capacity– 機能的なｷｬﾊﾟｼﾃｨ‐を損なう– impairment of the capacity to compensate for additional

stress or– 付加的なストレスを補うｷｬﾊﾟｼﾃｨｰを損なう– increase in susceptibility to other influences– 他の影響に対する感受性が増加する

Keller et al., Toxicol Sci 2012

No Observed Adverse Effect Level (NOAEL)

• Highest dose or exposure that does not cause a toxicologically relevant increase in frequency or severity of effects between exposed and control groups based on careful biological and statistical analysis.

• Minimum toxic or pharmacodynamic responses may occur at the NOAEL and may not endanger human health or be precursors to serious events with continued duration of exposure.

Dorato & Englehardt 2005

NOAEL (Keller et al., 2012) • Highest exposure level with no significant increases in

the frequency or severity of adverse effects between exposed population and its appropriate control.

• 投与群と適切な対照群との間で、 adverse effect （有害作用）の頻度・程度に関して有意な増加がみられない最も高い暴露量• Significance is considered with regard to biological

significance in the test species and may also incorporate statistical significance.

• 有意性とは、試験動物において生物学的に意味があるということであり、統計学的な有意差を含んでいることもある。

Two Recent Publications

• Scientific and Regulatory Policy Committee: Recommended (“Best”) Practices for Determining, Communicating, and Using Adverse Effect Data from Nonclinical Studies– Kerlin et al., 2015 Toxicologic Pathology

(DOI:10.1177.0192623315623265)• Characterizing “Adversity” of Pathology Findings in

Nonclinical Toxicity Studies: Results from the 4th ESTP International Expert Workshop– Palazzi et al., 2016 Toxicologic Pathology (In Press)

STP Recommendations• Judgment if a test article effect in a nonclinical study is adverse

or nonadverse must be clearly stated in the study report• 前臨床試験において、被験物質の影響が adverse （有害性）であるかの判断は、試験報告書に明確に言及しなければならない• Adversity in a nonclinical study should be applied only to the test species

used in that study• 前臨床試験における adversity （有害性）は、その試験で使用した動物種のみに適応すべきである• Setting a NOAEL for a test article should be stated in an overview

document based on data from multiple studies. • 被験物質に対する NOAEL の設定は、多くの試験データに基づいた概要書に言及されるべきである

STP Recommendations• All available data from nonclinical studies must be evaluated

together to define potential toxicities and predict human risk.• 潜在的な毒性の明確化とヒトへのリスク予測のために、前臨床試験の全ての利用できるデータは評価されなければならない• Communication of adverse findings and NOAEL should include direct

participation of contributing scientific disciplines (toxicologists, pathologists, risk assessore, etc.) in assessing and communicating human risk.

• Adverse （有害）所見と NOAEL に関するコミュニケーションは、ヒトのリスク評価・コミュニケーションにおいて、関係した科学者（毒性学者、病理学者、リスク評価者など）の直接的参加が含まれるべきだ

Factors to Consider in an Adversity Call

• Are there related pathological findings?• 関連する病理所見はあるか？• Is there a known or biologically plausible underlying

mechanism?• 既知あるいは生物学的に妥当なメカニズムがあるか？• What are the severity criteria?• 重篤度のクライテリアは何か？• What is the background incidence (historical control)?• 背景データでの頻度はどうか（ヒストリカルコントロール）？

Calling a Finding ADVERSE Should NOT be Based On:

• Extrapolation across species (including humans)• 種をまたがる外挿性（ヒトを含む）• Whether the effect is an exacerbation of a background lesion• その変化は背景病変を増悪化させたものかどうか• Whether the effect is a presumed supra-pharmacological effect• その変化は薬理効果を増強させたものと予想できるかどうか• Whether the effect is primary, secondary, tertiary, etc,.• その変化は、直接的、二次的、三次的なもの……かどうか• Whether the lesion is transient or reversible• その病変は一時的なものか回復可能なものか• Solely on statistics• 単に統計学的なものか

Are some findings non-adverse?

Are some findings non-adverse?• Bile duct hyperplasia• Lymphoid hyperplasia• Microsomal enzyme induction• Decreased serum ALT and AST• Extramedullary hematopoiesis in liver

Are some findings non-adverse?• Bile duct hyperplasia• Lymphoid hyperplasia• Microsomal enzyme induction• Decreased serum ALT and AST• Extramedullary hematopoiesis in liver

When findings such as these do not compromise normal tissue physiology, do not impair functional capacity, and do not increase susceptibility to other influences, then they may be considered non-adverse.

Some Examples of Non-Adverse Findings

Thymic involution in a chronic rat study

Congenital cyst in a rodent study


Bile duct hyperplasia in a chronic rat study


Bile duct hyperplasia in a chronic rat study

However, this degree of bile duct hyperplasia in a 90-day rat study would probably be an adverse response.


Extramedullary hematopoiesis in the liver – a secondary response to bone marrow suppression

Pigment in a lymph node – a normal function in a draining lymph node


Extramedullary hematopoiesis in the liver – a secondary response to bone marrow suppression

Pigment in a lymph node – a normal function in a draining lymph node

These secondary responses could be considered adaptive responses.

Adaptive Response

• In the context of a toxicology study, the process whereby a cell or organism responds to a xenobiotic so that the cell or organism will survive in the new environment that contains the xenobiotic without impairment of function.

• Adaptive responses to toxicant exposure may be characterized by reversibility.

Adaptation

• Evolutionary strategy to insure survival in a new environment where the xenobiotic is present

• 生体異物の存在する新しい環境において、生き残るための進化的戦略である• Adaptation can be adverse• Adaptation （適応）が adverse （有害性）になりうる• Example: Tracheal squamous metaplasia• Adaptive changes are not always reversible• 適応性変化は必ずしも回復性があるとは限らない• Example: Hepatic fibrosis

Adaptive Responses

• Adaptive change allows organism to respond to environmental change & is usually beneficial but not necessarily desirable

• 生物体の環境変化への反応として適応性変化がおこるが、通常は有益であるが、必ずしも望ましいものではない• Can result in a new functional steady state in a tissue or

organ• 組織や器官において、新たな機能的安定状態になることができる

Adaptive Response (cont)

• Adaptive changes are often early homeostatic adjustments (metabolism or gene expression/transcriptomic changes)

• 適応性変化はしばしば初期の恒常性調節機構である（代謝あるいは遺伝子発現／トランスクリプトームな変化）• May temporarily result in a new homeostatic steady-state• 一次的に新たな恒常性の定常状態になるかもしれない• Adaptive changes may ultimately result in return to a normal

homeostatic condition• 適応性変化は最終的に正常の恒常状態に戻るかもしれない

Adaptive Responses • An adaptive change can sometimes be adverse

• 適応性変化は時に adverse （有害性）となりうる


• 適応性変化は時に adverse （有害性）となりうる

Squamous metaplasia of the trachea occurred following inhalation exposure to smoke.


• 適応性変化は時に adverse （有害性）となりうるSquamous metaplasia affects normal cilliary function in the trachea and is, therefore, an adaptive response that is adverse.


• 適応性変化は時に adverse （有害性）となりうるSquamous metaplasia affects normal ciliary function in the trachea and is, therefore, an adaptive response that is adverse.

Even thought it is potentially reversible after the cause is removed, it is still an adverse response.

Reversibility

• Disappears after treatment is stopped• Typically determined using recovery groups in

toxicity studies

What Determines if a Lesion is Reversible?

• Depends upon the regenerative capacity of the tissue or organ

• Depends of the type of lesion– Proliferative/non-proliferative

• Depends on the severity of the lesion• Depends upon length of time without further

treatment– Partial/complete reversibility

Reversibility• An adverse lesion may or may not be reversible• Adverse （有害性）な変化は回復性がある場合やない場合がある• If an adverse lesion is reversible, then it can be:• もし adverse （有害性）な変化に回復性があるならば、　　　 A key component in weight-of-evidence in study

interpretation– 試験の解釈での weight-of-evidence におけるキーポイントである。– May indicate a lower level of concern– より低用量に懸念があるかもしれない

Perry et al., 2013. Toxicologic Pathology 41: 1159-1169Sewell et al., 2014. Regulatory Toxicology & Pharmacology 70: 414-429

What About Exacerbation?

Exacerbation

Exacerbation = an increase in the incidence and/or severity of an age-related and/or strain-specific common background lesion seen in control animals

増悪化とは：対照群の動物で観察される加齢性変化や系統に特異的に観察される背景データに関して、その発現頻度や程度が増加することである。

ExacerbationCan exacerbated background lesions be adverse?

Exacerbation = an increase in the incidence and/or severity of an age-related and/or strain-specific common background lesion seen in control animals

増悪化とは：対照群の動物で観察される加齢性変化や系統に特異的に観察される背景データに関して、その発現頻度や程度が増加することである。

ExacerbationCan exacerbated background lesions be adverse?

Yes, if –• the exacerbation is a biologically plausible primary effect of

the test agent• the exacerbation shows a clear dose-response• the exacerbation exceeds historical control

Exacerbation = an increase in the incidence and/or severity of an age-related and/or strain-specific common background lesion seen in control animals増悪化とは：対照群の動物で観察される加齢性変化や系統に特異的に観察される背景データに関して、その発現頻度や程度が増加することである。





What is needed in the toxicology report for submission to regulatory authorities?

規制当局に提出する毒性レポートで何が必要とされるか？

For the Toxicology Report and Regulatory Submission

• Need detailed description of what is adverse for each health-related endpoint

• どの健康に関連するエンドポイントに対しても、何がadverse （有害性）であるかについて詳細な記載が必要である

• Provide details on pathogenesis & mechanism• 病因とメカニズムを詳細に提供すること• Explain morphological criteria for diagnoses and severity scoring• 診断の形態学的クライテリアと病変程度のスコアーについ

て説明すること


• Clearly characterize relevant changes & explain judgments regarding why a change is adverse or non-adverse

• 関連のある変化を明確に特徴付けることと、変化が adverse （有害性）かどうかの判断した根拠について説明すること• Consider use of outside peer review & expert reports • 外部のピアレビューや専門家の報告を利用することを考慮すること


• Cite relevant literature• For example : using alveolar histiocytosis

Control Treated



Treated

• Inhalation study• Serum enzymes are normal• Minimal to mild increase in alveolar

histiocytes• No evidence of inflammation• No epithelial hyperplasia

Sponsor considered the alveolar histiocytosis to be adaptive and non-adverse because…



Treated

• Inhalation study• Serum enzymes are normal• Minimal to mild increase in alveolar

histiocytes• No evidence of inflammation• No epithelial hyperplasia

Sponsor considered the alveolar histiocytosis to be adaptive and non-adverse because…

In submitting their report to a regulatory authority, the sponsor cited some relevant literature


• Citing relevant literature for histiocytosis example

Nikula et al., 2014. Toxicologic Pathology 42:472-486.

“An STP working group focused on distinguishing adaptive versus adverse responses in rodents and concluded that increases in alveolar macrophage number and/or size are not adverse if there are no other lung changes such as inflammation and/or hyperplastic epithelial responses.”

What about the paradigm shift?

• What is the paradigm shift?– In accordance with Tox21 and related global opinion,

there is the recommendation to move away from animal testing and to rely on new molecular measurements and molecular pathways

• High throughput screening• Toxicity pathways• Adversity outcome pathways• In vitro testing using human cells• Computational systems biology

Ankley et al., (2010) Environ Toxicol Chem 29:730-41


Now there is an interest in defining adversity at the molecular level using new molecular biology and related methods.


Now there is an interest in defining adversity at the molecular level using new molecular biology and related methods.

The question is:

Can adverse effects be defined at the molecular level?

What about the paradigm shift• Development of new molecular methods to replace animal testing• 動物実験に置き換わる新たな分子学的手法の開発• Tox21, high throughput screening, toxicogenomics, toxicity pathways,

altered gene expression, adverse outcome pathways• Use of these new molecular methods to identify adversity will

require establishing scientific validation• Adversity （有害性）を見つけ出すこれらの新たな分子学的手法の利用には、科学的なバリデーションの確立が必要となる• Until new methods are validated, we continue to rely on classical toxicity

testing to identify adverse data for risk assessment• リスク評価のための adverse （有害性）のデータを明らかにするために、新たな手法がバリデートされるまで、我々はクラシカルな毒性試験に頼り続けざるを得ない


Can adverse effects be defined at the molecular level?

Answer: Not yet.

A Final Definition of Adverse

• ‘…change in the morphology, physiology, growth, development, reproduction, or life span of an organism, system, or (sub) population that results in an impairment of functional capacity, an impairment of the capacity to compensate for additional stress, or an increase in susceptibility to other influences’ (IPCS, 2004).

• Based on “apical responses” – Clinical signs, lesions, traditional biomarkers– And always within the context of the specific study





Practical Examples

• Restricted to one sex for purposes of demonstrating potential adverse responses

• However, an effect seen in both genders would be of more concern

• Examples are based on reasonably expected study outcomes

Dr. John Seely’s car

Treatment associated exacerbation of chronic progressive nephropathy


Is this an adverse response?


Is this an adverse response?Yes, it is adverse


Is this an adverse response?Yes, it is adverse

Dose-related increase incidence and increased severity


Is this an adverse response?

NOAEL

Renal TubularKaryomegaly


Boorman et al., 1992. Toxicologic Pathology 20:236-245Frazier et al., 2012. Toxicologic Pathology 40: 7S-86S

• The toxicological significance of this change is unknown

• There is no evidence that it progresses to neoplasia

• Not considered adverse by subject matter experts






Non-adverse










• Not considered adverse but subject matter experts

Everything is the same except






Probably adverse because of tubular hyperplasia and adenoma

Renal Papillary Mineralization

Kidney – Mineralization

• Treatment may exacerbate this background lesion

• May not be a direct effect of the test agent

• Mechanism is usually unknown





Presumption – a perturbation of calcium homeostasis





Presumption – a perturbation of calcium homeostasis

Conservative NOAEL is the

low dose

Adrenal Cortical Necrosis

Adrenal

Adrenal• Adrenal cortical necrosis is adverse• The 2/10 incidence at the medium

exposure is a severe response• The NOAEL is the low exposure

Alveolar Histiocytosis

ControlExposed

Lung – Alveolar histiocytosis

• Inhalation study• Serum enzymes are normal• Minimal to mild increase in

alveolar histiocytes




Is this adverse?




Is this adverse?

This degree of histiocytosis is not considered adverse by lung experts.


14-Day Recovery


14-Day Recovery

Not considered adverse, evenwithout recovery

Minimal to mild alveolar histiocytosis reflects a macrophage response to changes in the local environment & represents a tissue adaptation to maintain normal lung function

Minimal to mild alveolar histiocytosis reflects a macrophage response to changes in the local environment & represents a tissue adaptation to maintain normal lung function

But severe alveolar histiocytosis as in this example represents an adverse response, even if it is reversible.

Lesion severity is important in defining

an adverse effect

Lymph Node Histiocytic Infiltrate

Lymph Node

Lymph Node• Clearance via lymph node drainage is a part of

normal lymph node physiology• Not adverse unless severe and associated with

necrosis in the affected lymph node

Lymph Node

Although there is a dose response and increased severity, this change may be non-adverse. A recovery study would help clarify this issue.

• Clearance via lymph node drainage is a part of normal lymph node physiology

• Not adverse unless severe and associated with necrosis in the affected lymph node

Lymph Node• Clearance via lymph node drainage is a part of

normal lymph node physiology

Adverse

Progressive Cardiomyopathy in Rats

Progressive Cardiomyopathy - Rat

Slide courtesy of Dr. Rick Hailey

Progressive Cardiomyopathy - Rat• Background lesion in rats in prechronic

studies

• Especially common in Sprague Dawley

rats

• Difficult to find at low magnification

• Typically very mild in severity unless

exacerbated by treatment

• Randomly distributed in the myocardium


Progressive Cardiomyopathy - Rat• Background lesion in rats in prechronic

studies

• Especially common in Sprague Dawley

rats

• Difficult to find at low magnification

• Typically very mild in severity unless

exacerbated by treatment

• Randomly distributed in the myocardium

Pathogenesis: myocardial fiber degenerationmononuclear inflammatory

responsephagocytosis of degenerating myofibersfocal fibrosis


Examples of Progressive Cardiomyopathy


Slide 1 of 3

Cardiomyopathy in a 13-Week Study


Slide 2 of 3

Medium Magnification


Slide 3 of 3

High Magnification


Progressive CardiomyopathyAdverse or Non-adverse?

Progressive CardiomyopathyNon-AdverseNo dose-responseAll lesions are of minimal severity

Progressive Cardiomyopathy

Adverse or Non-adverse?

Progressive CardiomyopathyNon-AdverseNo convincing dose-responseAll lesions are of minimal severity

Progressive CardiomyopathySame lesion but different incidence !!

Progressive Cardiomyopathy

Adverse or Non-adverse?

Same lesion but different incidence !!

Progressive CardiomyopathyAdverseDose-response - yesIncreased severity - yes

NOAEL

Acute Centrilobular Necrosis (Prechronic Mouse Study)

Liver enzymesincreased > 5-fold

Acute Centrilobular Necrosis (Prechronic Mouse Study)

This change is adverse


Acute Periportal Necrosis


Acute Periportal Necrosis

This change is adverse


Acute Liver Response

Return to normal in 3 to 7 days

This represents an example of reversibility



Liver enzyme levels may or may not still be elevated when the liver structure has returned to normal depending upon their half-life in the circulation.




Liver enzyme levels may or may not still be elevated when the liver structure has returned to normal depending upon their half-life in the circulation.What is adverse or what is

non-adverse may depend on when you take the sample.




What is adverse or what is non-adverse may depend on when you take the sample.

This represents an example of reversibility The fact that a lesion is reversible

is an important piece of information that should be considered in a weight-of-evidence approach.

CholangitisControl Treated

Treatment-associated exacerbation of cholangitis

Common background change in older rats

Adverse?


Adverse?

In general, minimal treatment-associated exacerbations of background lesions are non-adverse but mild, moderate, and marked changes are adverse.


Increase in inflammatory cells; some are neutrophils; there is necrosis of adjacent hepatocytes (arrows)


Slide courtesy of R. Hailey

Adverse?


Increase in inflammatory cells; some are neutrophils; there is necrosis of adjacent hepatocytes (arrows)



Adverse-YES

Biliary epithelial hyperplasia:Adverse?Are These Examples of Bile Duct Hyperplasia Adverse?


Biliary epithelial hyperplasia:Adverse?

Mitotic figures Proliferation outside the portal triad

Are These Examples of Bile Duct Hyperplasia Adverse?



Mitotic figures

Hepatocellular necrosis

Proliferation outside the portal triad

Are These Examples of Bile Duct Hyperplasia Adverse?



Mitotic figures

Hepatocellular necrosis

Proliferation outside the portal triad

Yes, They Are Adverse!


Is this adverse?

Proliferation outside the portal triad and cellular atypia

Increases in ALT and AST (up to 20X)

and ALP (1.4X) and bilirubin (13X)

Another Example of An Adverse Response Affecting Bile Ducts

Can Occur Spontaneously

Control- no changeControl- spontaneous biliary

epithelial hyperplasia

Bile ducts

In Contrast This Degree of Bile Duct Hyperplasia is Non-Adverse

Hepatic Foci of Cellular Alteration


• Occur spontaneous in older rodents• May be induced by treatment in younger rodents• Can be present with or without hepatotoxicity• 1 Hepatocellular tumor per 10,000 foci

Kaufmann et al., Am J Pathol 119:171-174 (1985)

Are Foci Predictors of Liver Tumor Response? Are foci adverse?


* p< 0.05 ** p< 0.01


* p< 0.05 ** p< 0.01

• A treatment-related increase in foci at the medium & high exposures per se may not be considered adverse, but this is controversial

• 中間並びに高用量群で投与に関連した変異細胞巣の増加が認められ、本質的にadverse （有害性）とは考えられないかもしれないが、これは議論の余地があるだろう

• A single hepatocellular adenoma can occur by chance, even in a 90-day study

• 90日試験でさえも、肝細胞腺腫が 1例に偶発所見としてみられている


* p< 0.05 ** p< 0.01

• This incidence of foci in a 12-month study is of some concern since it may predict a potential hepatocarcinogenic response in a long-term study.

• The concern may be sufficient to stop development of a new drug or pesticide

• However, aside from its predictive potential, a liver focus response by itself does not compromise liver function sufficiently to be classified as adverse.


* p< 0.05 ** p< 0.01




It is OK to disagree with my opinion on this.


* p< 0.05 ** p< 0.01




It is OK to disagree with my opinion on this.

You may feel that development of foci is part of a continuum known to progress to adversity.

Hepatomegaly

Control Treated

Liver Weight Increases Without Other Changes

• < 10% liver weight - non-adverse• >40-50% increase liver at 12-months – leads

to cancer (it is predictive but not necessarily adverse)

Carmichael et al., Environ Hlth Perspectives 105: 1196-1203 (1997) Haseman et al., Toxicol Pathol 25:256-263(1997)Maronpot et al., Toxicol Pathol 38: 7786-795 (2010

Liver Weight Increases Without Other Changes

• < 10% liver weight - non-adverse• >20% liver weight increase =

adverse– According to some regulatory

authorities• >40-50% increase liver at 12-

months – leads to cancer (predictive)

• This is controversial!!• 20% liver weight increases

are common responses to xenobiotic exposures

• In the absence of any other changes, a 20% increase should not be considered adverse

Carmichael et al., Environ Hlth Perspectives 105: 1196-1203 (1997) Haseman et al., Toxicol Pathol 25:256-263(1997)Maronpot et al., Toxicol Pathol 38: 7786-795 (2010

Chemicals That Cause Liver Enlargement

• Chemicals that cause liver enlargement (hypertrophy/hyperplasia) at low doses often will cause degeneration at higher doses

• 低用量で肝腫大（肥大／過形成）を引き起こす化学物質は、より高用量では変性をしばしば誘発する• Saturation of normal clearance mechanisms

– Alternate metabolic routes can damage cellular macromolecules • Presence of degeneration is adverse • 変性の存在は adverse （有害性）である• Resulting functional loss may not be completely reversed (e.g., heptic

fibrosis)• 結果としてみられる機能消失は完全に回復しないかもしれない（例えば肝線維化）

Hepatomegaly in Prechronic Studies is a Frequent Reflection of Microsomal Enzyme Induction

Control Treated

Hepatic Enzyme Induction• Centrilobular hepatocyte hypertrophy

Microsomal Enzyme Induction

NN

Smooth Endoplasmic Reticulum (SER) Proliferation

Control Treated

Arrows = smooth endoplasmic reticulum

Microsomal Enzyme InductionEvidence of enzyme induction without any other changes is typically an adaptive change that is not adverse.

Hepatic Enzyme Induction• Centrilobular hepatocyte hypertrophy

Adaptive and non-adverse when there is only hepatocellular hypertrophy

Typically reversible when exposure is stopped

Enzyme Induction with other changes should be considered an adverse response

Cytoplasmic vacuolation & bile duct hyperplasia Single cell necrosis

1. extreme hypertrophy leading to reduced sinusoidal blood circulation, hypoxia, and necrosis and/or

2. metabolic activation forming more toxic active metabolites

Proposed Mechanisms for Hepatocyte Necrosis

Adverse

Extreme Hepatocyte Hypertrophy

• Enlarged hepatocytes• Increased cytoplasm• Multiple nuclei• Karyomegaly

Adverse

Liver Case #1

( ) = Severity: 1 – minimal 2 – mild 3 = marked

Liver Case #1

This is very similar to an actual case that was considered by a regulatory agency.


Liver Case #1

• Generally low severity centrilobular hepatocyte hypertrophy• No cytotoxicity or hepatocellular degeneration• Liver weight increased up to 35%• ALT & AST increased 2.6 to 4.5 at 2 highest exposures• Plasma cholesterol increased 25 to 40% at 3 highest doses


Liver Case #1

HYPERTROPHY CONSIDERED ADAPTIVE • Typical low severity centrilobular hepatocyte hypertrophy & no cytotoxicity or hepatocellular degeneration• Liver weight increased up to 35%FATTY CHANGE CONSIDERED ADVERSE (Alteration in lipid metabolism) • ALT & AST increased 2.6 to 4.5 at 2 highest exposures• Plasma cholesterol increased 25 to 40% at 3 highest doses


Liver Case #1

NOAELHYPERTROPHY CONSIDERED ADAPTIVE • Typical low severity centrilobular hepatocyte hypertrophy & no cytotoxicity or hepatocellular degeneration• Liver weight increased up to 35%FATTY CHANGE CONSIDERED ADVERSE (Alteration in lipid metabolism) • ALT & AST increased 2.6 to 4.5 at 2 highest exposures• Plasma cholesterol increased 25 to 40% at 3 highest doses

Liver Case #2• Increased liver weight up to 30%• Increased liver enzymes in 3 of the high exposure rats


SIMILAR TO DATA SUBMITTED FOR REGULATORY REVIEW

Liver Case #2

• Hypertrophy and vacuolation considered adaptive• Degeneration/necrosis and increased mitoses considered adverse


• Increased liver weight up to 30%• Increased liver enzymes in 3 of the high exposure rats

Liver Case #2

• Hypertrophy and vacuolation considered adaptive• Degeneration/necrosis and increased mitoses considered adverse


NOAEL identified as medium exposure

• Increased liver weight up to 30%• Increased liver enzymes in 3 of the high exposure rats

Three Other Practical Examples

Epididymis – Tunica vaginalis mesothelioma

Epididymis – Tunica vaginalis mesothelioma

Adverse

Dog StudyNo clinical signs orgross lesions

Slide courtesy of Dr. Peter Mann

Dog StudyNo clinical signs orgross lesions

Slide courtesy of Dr. Peter Mann

A difficult call because of the small number of study animals but probably not adverse.

Mononuclear cell leukemia

• No tumors in males• No other tumors in

females in this study

Historical Control14% to 36%

Mononuclear cell leukemia

• No tumors in males• No other tumors in

females in this study

Historical Control14% to 36%

NTP considered this response was

equivocal evidence of carcinogenicity

Historical Control Range = 14% to 36%

Is this an exacerbation of leukemia and is it an adverse response?

Historical Control Range = 14% to 36%

Is this an exacerbation of leukemia and is it an adverse response?

Because of its high & variable background incidence, a positive mononuclear cell leukemia response should take the historical control range into account in determining if there is a real treatment- related increased incidence.





Adverse Response

There is no perfect definition of an adverse response in a preclinical study.

前臨床試験における adverse 反応の完璧な定義はない

Criteria for Defining an Adverse Response

• ‘…change in the morphology, physiology, growth, development, reproduction, or life span of an organism, system, or (sub) population that results in an impairment of functional capacity, an impairment of the capacity to compensate for additional stress, or an increase in susceptibility to other influences’ (IPCS, 2004).

• At the present time based on “apical responses” – Clinical signs, lesions, traditional biomarkers– And always within the context of the specific study

If a finding fulfills the criteria for an adverse effect, then it is considered adverse even if:

• it is transient (disappears during treatment)• 一過性の変化（投与期間中に消失）• it is reversible (disappears after treatment is stopped)• 回復性がある（投与中止後に消失）• it is caused by exaggerated pharmacology• 薬理作用が増強されたことによって発現• It is secondary to some other change or secondary to stress• 他の所見に対する二次的な変化、あるいはストレスに対する二次的な変化

もし、ある所見が adverse effect （有害性作用）のクライテリアを満たすならば、たとえ下記の件が該当するとしても、 adverse であると考えられる

Thanks to Dr. Katsuhiko Yoshizawa for Japanese translations

And

Thanks to you for your kind attention

You can view this presentation at focusontoxpath.com/adverse-responses

http://focusontoxpath.com/adverse-responses

http://focusontoxpath.com/adverse-responses

Science

Adverse, Non-adverse and Adaptive Responses in Toxicologic Pathology - JSTP