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AOP: 256


A descriptive phrase which references both the Molecular Initiating Event and Adverse Outcome.It should take the form “MIE leading to AO”. For example, “Aromatase inhibition leading to reproductive dysfunction” where Aromatase inhibition is the MIE and reproductive dysfunction the AO. In cases where the MIE is unknown or undefined, the earliest known KE in the chain (i.e., furthest upstream) should be used in lieu of the MIE and it should be made clear that the stated event is a KE and not the MIE.  More help

Inhibition of mitochondrial DNA polymerase gamma leading to kidney toxicity

Short name
A name that succinctly summarises the information from the title. This name should not exceed 90 characters. More help
Inhibition of mitochondrial DNA polymerase gamma leading to kidney toxicity
The current version of the Developer's Handbook will be automatically populated into the Handbook Version field when a new AOP page is created.Authors have the option to switch to a newer (but not older) Handbook version any time thereafter. More help
Handbook Version v1.0

Graphical Representation

A graphical representation of the AOP.This graphic should list all KEs in sequence, including the MIE (if known) and AO, and the pair-wise relationships (links or KERs) between those KEs. More help
Click to download graphical representation template Explore AOP in a Third Party Tool


The names and affiliations of the individual(s)/organisation(s) that created/developed the AOP. More help

Prof. Dr. Angela Mally Department of Toxicology University of Würzburg Versbacher Str. 9 97078 Würzburg Germany Phone/fax:          +49 931 31-81194 Email:        

Point of Contact

The user responsible for managing the AOP entry in the AOP-KB and controlling write access to the page by defining the contributors as described in the next section.   More help
Agnes Aggy   (email point of contact)


Users with write access to the AOP page.  Entries in this field are controlled by the Point of Contact. More help
  • Angela Mally
  • Agnes Aggy


This field is used to identify coaches who supported the development of the AOP.Each coach selected must be a registered author. More help

OECD Information Table

Provides users with information concerning how actively the AOP page is being developed and whether it is part of the OECD Workplan and has been reviewed and/or endorsed. OECD Project: Assigned upon acceptance onto OECD workplan. This project ID is managed and updated (if needed) by the OECD. OECD Status: For AOPs included on the OECD workplan, ‘OECD status’ tracks the level of review/endorsement of the AOP . This designation is managed and updated by the OECD. Journal-format Article: The OECD is developing co-operation with Scientific Journals for the review and publication of AOPs, via the signature of a Memorandum of Understanding. When the scientific review of an AOP is conducted by these Journals, the journal review panel will review the content of the Wiki. In addition, the Journal may ask the AOP authors to develop a separate manuscript (i.e. Journal Format Article) using a format determined by the Journal for Journal publication. In that case, the journal review panel will be required to review both the Wiki content and the Journal Format Article. The Journal will publish the AOP reviewed through the Journal Format Article. OECD iLibrary published version: OECD iLibrary is the online library of the OECD. The version of the AOP that is published there has been endorsed by the OECD. The purpose of publication on iLibrary is to provide a stable version over time, i.e. the version which has been reviewed and revised based on the outcome of the review. AOPs are viewed as living documents and may continue to evolve on the AOP-Wiki after their OECD endorsement and publication.   More help
OECD Project # OECD Status Reviewer's Reports Journal-format Article OECD iLibrary Published Version
1.43 Under Development
This AOP was last modified on May 26, 2024 20:39

Revision dates for related pages

Page Revision Date/Time
Inhibition of mitochondrial DNA polymerase gamma (Pol gamma) October 25, 2017 07:48
Depletion, mtDNA October 25, 2017 07:49
Increase, Cytotoxicity (renal tubular cell) March 03, 2022 15:14
Occurrence, Kidney toxicity March 04, 2022 10:58
Mitochondrial dysfunction April 17, 2024 08:26
Inhibition, mitochondrial DNA polymerase gamma (Pol gamma) leads to Depletion, mtDNA October 25, 2017 07:52
Depletion, mtDNA leads to Mitochondrial dysfunction February 28, 2024 14:53
Mitochondrial dysfunction leads to Increase, Cytotoxicity (renal tubular cell) March 06, 2024 17:09
Increase, Cytotoxicity (renal tubular cell) leads to Occurrence, Kidney toxicity March 08, 2022 11:46
Tenofovir October 25, 2017 07:45
Tenofovir disoproxil fumarate October 25, 2017 07:46
Adefovir October 25, 2017 07:46
Adefovir dipivoxil October 25, 2017 07:46
Cidofovir October 25, 2017 07:47


A concise and informative summation of the AOP under development that can stand-alone from the AOP page. The aim is to capture the highlights of the AOP and its potential scientific and regulatory relevance. More help

This Adverse Outcome Pathway describes the sequential key events that link inhibition of mitochondrial DNA polymerase gamma (Pol gamma) to kidney toxicity. Nucleoside and nucleotide  (nucleos(t)ide) analogs are widely used as antiviral drugs for the effective treatment of viral infections including HIV and chronic Hepatitis B virus infections. As structural analogs of substrate nucleotides, these drugs act as chain terminators of viral DNA synthesis via competitive inhibition of reverse transcriptase or viral DNA polymerases, thereby blocking virus replication. Besides targeting viral enzymes, nucleos(t)ide antiviral agents are also substrates for human DNA polymerases, which may lead to moderate to life-threatening adverse drug reactions, including peripheral neuropathy, myopathy, lactic acidosis, and acute and chronic kidney injury [1-4]. Toxicity of antiviral nucleos(t)ides has been linked to mitochondrial dysfunction as a consequence of inhibition of mitochondrial DNA polymerase gamma (Pol gamma), a particular sensitive target, and associated inhibition of mtDNA replication [1, 3]. In the kidney, the proximal tubule is the main target of antiviral nucleos(t)ide drug toxicity due to active uptake via basolateral organic anion transporters (e.g. OAT1 and OAT3) expressed at this site [5, 6]. Based on the current mechanistic understanding, the subsequent sequence of key events (KE) leading to kidney injury as an adverse outcome can be described as inhibition of Pol gamma as the molecular initiating event (MIE), leading to mtDNA depletion (KE1), mitochondrial dysfuntion (KE2) and proximal tubule cell toxicity (KE3).

AOP Development Strategy


Used to provide background information for AOP reviewers and users that is considered helpful in understanding the biology underlying the AOP and the motivation for its development.The background should NOT provide an overview of the AOP, its KEs or KERs, which are captured in more detail below. More help


Provides a description of the approaches to the identification, screening and quality assessment of the data relevant to identification of the key events and key event relationships included in the AOP or AOP network.This information is important as a basis to support the objective/envisaged application of the AOP by the regulatory community and to facilitate the reuse of its components.  Suggested content includes a rationale for and description of the scope and focus of the data search and identification strategy/ies including the nature of preliminary scoping and/or expert input, the overall literature screening strategy and more focused literature surveys to identify additional information (including e.g., key search terms, databases and time period searched, any tools used). More help

Summary of the AOP

This section is for information that describes the overall AOP.The information described in section 1 is entered on the upper portion of an AOP page within the AOP-Wiki. This is where some background information may be provided, the structure of the AOP is described, and the KEs and KERs are listed. More help


Molecular Initiating Events (MIE)
An MIE is a specialised KE that represents the beginning (point of interaction between a prototypical stressor and the biological system) of an AOP. More help
Key Events (KE)
A measurable event within a specific biological level of organisation. More help
Adverse Outcomes (AO)
An AO is a specialized KE that represents the end (an adverse outcome of regulatory significance) of an AOP. More help
Type Event ID Title Short name
MIE 1481 Inhibition of mitochondrial DNA polymerase gamma (Pol gamma) Inhibition, mitochondrial DNA polymerase gamma (Pol gamma)
KE 1482 Depletion, mtDNA Depletion, mtDNA
KE 177 Mitochondrial dysfunction Mitochondrial dysfunction
KE 709 Increase, Cytotoxicity (renal tubular cell) Increase, Cytotoxicity (renal tubular cell)
AO 814 Occurrence, Kidney toxicity Occurrence, Kidney toxicity

Relationships Between Two Key Events (Including MIEs and AOs)

This table summarizes all of the KERs of the AOP and is populated in the AOP-Wiki as KERs are added to the AOP.Each table entry acts as a link to the individual KER description page. More help

Network View

This network graphic is automatically generated based on the information provided in the MIE(s), KEs, AO(s), KERs and Weight of Evidence (WoE) summary tables. The width of the edges representing the KERs is determined by its WoE confidence level, with thicker lines representing higher degrees of confidence. This network view also shows which KEs are shared with other AOPs. More help

Prototypical Stressors

A structured data field that can be used to identify one or more “prototypical” stressors that act through this AOP. Prototypical stressors are stressors for which responses at multiple key events have been well documented. More help

Life Stage Applicability

The life stage for which the AOP is known to be applicable. More help
Life stage Evidence
All life stages Not Specified

Taxonomic Applicability

Latin or common names of a species or broader taxonomic grouping (e.g., class, order, family) can be selected.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. More help
Term Scientific Term Evidence Link
Human, rat, mouse Human, rat, mouse High NCBI

Sex Applicability

The sex for which the AOP is known to be applicable. More help
Sex Evidence
Unspecific Not Specified

Overall Assessment of the AOP

Addressess the relevant biological domain of applicability (i.e., in terms of taxa, sex, life stage, etc.) and Weight of Evidence (WoE) for the overall AOP as a basis to consider appropriate regulatory application (e.g., priority setting, testing strategies or risk assessment). More help

Mechanistic data on KEs and KERs in this AOP are derived from in vitro and in vivo studies in humans and rodents.  The described AOP presents a general mechanism leading to kidney toxicity in preclinical animal species and humans. The described AOP is not limited to a specific life stage or sex.

The sequence of MIE and KEs in this AOP presents a universal mechanism by which nucleos(t)ide analogs are thought to cause toxicity not only in the kidney but also in other organs and tissues, including liver, heart, muscle and the nervous system [1, 3, 4, 7]. The tissue-specificity and severity of the response to a particular nucleos(t)ide analog is considered to be at least in part determined by toxicokinetic factors, most notably active uptake into and efflux from target cells, transport across the mitochondrial membrane and metabolic conversion into the active triphosphate form [5-8]. Nephrotoxicity presents a treatment-limiting toxicity for a number of nucleos(t)ide analogs (e.g. tenofovir, adefovir, cidofovir). Experimental evidence for inhibition of mitochondrial DNA polymerase gamma leading to kidney toxicity as an adverse outcome is comes from in vitro studies, studies in laboratory animals (rats and mice) as well as from reports of patients treated with these compounds. These studies show a strong association between mitochondrial toxicity and antiviral nucleos(t)ide induced nephrotoxicity [9-14], with some studies also demonstrating concomitant mtDNA depletion [9, 11, 12, 15]. 

The causal relationship between the MIE and the downstream KEs is further supported by studies investigating the mechanism of toxicity of nucleos(t)ide analogs in other cells and tissues. For instance, a significant reduction in mtDNA was observed in muscle biopsies of zidovudine-treated HIV positive patients with myopathy as compared non-HIV-patient controls [16].  Studies with isolated human DNA polymerases demonstrate increased sensitivity of Pol gamma to inhibition by antiretroviral nucleotides as compared to nuclear polymerases. Inhibition of mtDNA synthesis and loss of cell number was observed in a T-lymphoid leukemic cell line (Molt-4) treated with several anti-HIV and anti-HBV nucleoside analogs (d4T, 3'-deoxy-2',3'-didehydrothymidine; FLT, 3'-fluoro-3'-deoxythynidine; ddC, 2',3'-dideoxycytidine), which were also identified as potent inhibition of Pol gamma. However, a number of potent Pol gamma inhibitors did not cause significant effects on mtDNA synthesis and cell viability. Based on these findings, the authors concluded that there was no clear quantitative or qualitative correlation between the inhibition of isolated Pol gamma and inhibition of mitochondrial DNA synthesis in vitro, and moreover that these data are not predictive of in vivo toxicity.  It is however important to stress that toxicokinetics, most notably cellular uptake of the tested antivirals, were not considered in this assessment. Thus, it is likely that some of the most potent inhibitors of Pol gamma failed to induce mtDNA depletion and cytotoxicity in this cell model simply because of insufficient cellular uptake [17]. 

Domain of Applicability

Addressess the relevant biological domain(s) of applicability in terms of sex, life-stage, taxa, and other aspects of biological context. More help

Mechanistic data on KEs and KERs in this AOP are derived from in vitro and in vivo studies in humans and rodents. The described AOP presents a general mechanism leading to kidney toxicity in preclinical animal species (rats, mice) and humans. The described AOP is not limited to a specific life stage or sex.

Essentiality of the Key Events

The essentiality of KEs can only be assessed relative to the impact of manipulation of a given KE (e.g., experimentally blocking or exacerbating the event) on the downstream sequence of KEs defined for the AOP. Consequently, evidence supporting essentiality is assembled on the AOP page, rather than on the independent KE pages that are meant to stand-alone as modular units without reference to other KEs in the sequence. The nature of experimental evidence that is relevant to assessing essentiality relates to the impact on downstream KEs and the AO if upstream KEs are prevented or modified. This includes: Direct evidence: directly measured experimental support that blocking or preventing a KE prevents or impacts downstream KEs in the pathway in the expected fashion. Indirect evidence: evidence that modulation or attenuation in the magnitude of impact on a specific KE (increased effect or decreased effect) is associated with corresponding changes (increases or decreases) in the magnitude or frequency of one or more downstream KEs. More help


Short name




Inhibition, Pol gamma

Inhibition of mtDNA Pol gamma by antiviral nucleos(t)ides demonstrated using enzymatic assays [2, 18-20]



Depletion, mtDNA

Loss of mtDNA observed in vitro, in laboratory animals and patients after treatment with antiviral nucleos(t)ides [9, 11, 12, 15, 21]



Dysfunction, mitochondria

Changes in mitochondrial ultrastructure and/or function (e.g. mitochondrial enzyme activities) observed in vitro, in laboratory animals and kidney biopsies of patients after treatment with antiviral nucleos(t)ides [9] [10-14, 21, 22]



Increase, Cytotoxicity

Cytotoxicity of antiviral nucleos(t)ides observed in a range of kidney cell models with the severity depending on cellular uptake [11-14, 21-24]



Occurrence, Kidney Toxicity

Nephrotoxicity observed in laboratory animals and patients after treatment with antiviral nucleos(t)ides [9] [10-14, 25-28] [22]


Evidence Assessment

Addressess the biological plausibility, empirical support, and quantitative understanding from each KER in an AOP. More help

Concordance of dose-response relationships

This is still a qualitiative description of the pathway. There is at present no quantitative information on dose-response relationships. Experiments are underway to provide quantitative understanding of dose-response relationships and response-response relationships between upstream and downstream KEs. In establishing dose-response relationships, it needs to be considered that effective excision of nucleotides by proofreading exonuclease of DNA polymerase as a repair mechanism may affect downstream KEs [2].

Temporal concordance among the key events and adverse outcome

The individual KEs are shown to occur prior to or concomitant with the onset of nephrotoxicity.

Strength, consistency, and specificity of association of adverse outcome and initiating event

The scientific evidence on the association between inhibition of DNA Polymerase gamma (MIE) and kidney toxicity (AO) is strong and consistent. The MIE is not specific for kidney toxicity as is considered responsible for a range of adverse effects of antiviral nucleos(t)ide treatment, whereby the site of toxicity appears to be at least in part determined by the toxicokinetics of individual drugs.

Biological plausibility, coherence, and consistency of the experimental evidence

Since antiviral nucleos(t)ide analogs are specifically designed to inhibit (viral) DNA polymerases or reverse transcriptase, off-target effects via interaction of human DNA polymerases are biologically plausible and consistent with the pharmacological MoA. The described AOP is biologically plausible, coherent and supported by experimental data.

Alternative mechanism(s) that logically present themselves and the extent to which they may distract from the postulated AOP

There are no alternative mechanism(s) that logically present themselves, although a contribution of yet undefined off-target effects to the overall AO cannot be excluded.

Uncertainties, inconsistencies and data gaps

This AOP is plausible and consistent with general biological knowledge. Quantitative information on dose response-relationships as well as repsonse-response relationships for upstream and downstream KEs is needed to support its applicability for the development of alternative in vitro tests for nephrotoxicity testing.

Known Modulating Factors

Modulating factors (MFs) may alter the shape of the response-response function that describes the quantitative relationship between two KES, thus having an impact on the progression of the pathway or the severity of the AO.The evidence supporting the influence of various modulating factors is assembled within the individual KERs. More help

Quantitative Understanding

Optional field to provide quantitative weight of evidence descriptors.  More help

Quantitative data on KERs between upstream and downstream KE are still lacking.

Considerations for Potential Applications of the AOP (optional)

Addressess potential applications of an AOP to support regulatory decision-making.This may include, for example, possible utility for test guideline development or refinement, development of integrated testing and assessment approaches, development of (Q)SARs / or chemical profilers to facilitate the grouping of chemicals for subsequent read-across, screening level hazard assessments or even risk assessment. More help

The described AOP is intended to provide a mechanistic framework for the development of in vitro bioactivity assays capable of predicting quantitative points of departure for safety assessment with regard to nephrotoxicity. Such assays may form part of an integrated testing strategy to reduce the need for repeated dose toxicity studies (e.g.  OECD Guideline 407; OECD Guideline 407) and to aid in the design of new antiviral drugs.


List of the literature that was cited for this AOP. More help

1.           Lewis, W. and M.C. Dalakas, Mitochondrial toxicity of antiviral drugs. Nat Med, 1995. 1(5): p. 417-22.

2.           Johnson, A.A., et al., Toxicity of antiviral nucleoside analogs and the human mitochondrial DNA polymerase. J Biol Chem, 2001. 276(44): p. 40847-57.

3.           Fontana, R.J., Side effects of long-term oral antiviral therapy for hepatitis B. Hepatology, 2009. 49(5 Suppl): p. S185-95.

4.           Fung, J., et al., Extrahepatic effects of nucleoside and nucleotide analogues in chronic hepatitis B treatment. J Gastroenterol Hepatol, 2014. 29(3): p. 428-34.

5.           Izzedine, H., V. Launay-Vacher, and G. Deray, Antiviral drug-induced nephrotoxicity. American Journal of Kidney Diseases, 2005. 45(5): p. 804-817.

6.           Uwai, Y., et al., Renal transport of adefovir, cidofovir, and tenofovir by SLC22A family members (hOAT1, hOAT3, and hOCT2). Pharm Res, 2007. 24(4): p. 811-5.

7.           Lewis, W., B.J. Day, and W.C. Copeland, Mitochondrial toxicity of NRTI antiviral drugs: an integrated cellular perspective. Nat Rev Drug Discov, 2003. 2(10): p. 812-22.

8.           Kohler, J.J., et al., Tenofovir renal proximal tubular toxicity is regulated by OAT1 and MRP4 transporters. Lab Invest, 2011. 91(6): p. 852-8.

9.           Lebrecht, D., et al., Mitochondrial Tubulopathy in Tenofovir Disoproxil Fumarate-Treated Rats. Jaids-Journal of Acquired Immune Deficiency Syndromes, 2009. 51(3): p. 258-263.

10.        Cote, H.C., et al., Exploring mitochondrial nephrotoxicity as a potential mechanism of kidney dysfunction among HIV-infected patients on highly active antiretroviral therapy. Antivir Ther, 2006. 11(1): p. 79-86.

11.        Tanji, N., et al., Adefovir nephrotoxicity: possible role of mitochondrial DNA depletion. Hum Pathol, 2001. 32(7): p. 734-40.

12.        Kohler, J.J., et al., Tenofovir renal toxicity targets mitochondria of renal proximal tubules. Lab Invest, 2009. 89(5): p. 513-9.

13.        Herlitz, L.C., et al., Tenofovir nephrotoxicity: acute tubular necrosis with distinctive clinical, pathological, and mitochondrial abnormalities. Kidney Int, 2010. 78(11): p. 1171-7.

14.        Ramamoorthy, H., P. Abraham, and B. Isaac, Mitochondrial dysfunction and electron transport chain complex defect in a rat model of tenofovir disoproxil fumarate nephrotoxicity. J Biochem Mol Toxicol, 2014. 28(6): p. 246-55.

15.        Kohler, J.J. and S.H. Hosseini, Subcellular renal proximal tubular mitochondrial toxicity with tenofovir treatment. Methods Mol Biol, 2011. 755: p. 267-77.

16.        Arnaudo, E., et al., Depletion of muscle mitochondrial DNA in AIDS patients with zidovudine-induced myopathy. Lancet, 1991. 337(8740): p. 508-10.

17.        Martin, J.L., et al., Effects of antiviral nucleoside analogs on human DNA polymerases and mitochondrial DNA synthesis. Antimicrob Agents Chemother, 1994. 38(12): p. 2743-9.

18.        Lee, H., J. Hanes, and K.A. Johnson, Toxicity of nucleoside analogues used to treat AIDS and the selectivity of the mitochondrial DNA polymerase. Biochemistry, 2003. 42(50): p. 14711-9.

19.        Cherrington, J.M., et al., Kinetic Interaction of the Diphosphates of 9-(2-Phosphonylmethoxyethyl)Adenine and Other Anti-Hiv Active Purine Congeners with Hiv Reverse-Transcriptase and Human DNA Polymerase-Alpha, Polymerase-Beta and Polymerase-Gamma. Antiviral Chemistry & Chemotherapy, 1995. 6(4): p. 217-221.

20.        Naesens, L., et al., HPMPC (cidofovir), PMEA (adefovir) and related acyclic nucleoside phosphonate analogues: A review of their pharmacology and clinical potential in the treatment of viral infections. Antiviral Chemistry & Chemotherapy, 1997. 8(1): p. 1-23.

21.        Zhao, X., et al., Tenofovir and adefovir down-regulate mitochondrial chaperone TRAP1 and succinate dehydrogenase subunit B to metabolically reprogram glucose metabolism and induce nephrotoxicity. Sci Rep, 2017. 7: p. 46344.

22.        Talmon, G., L.D. Cornell, and D.J. Lager, Mitochondrial changes in cidofovir therapy for BK virus nephropathy. Transplant Proc, 2010. 42(5): p. 1713-5.

23.        Zhang, X., et al., Intracellular concentrations determine the cytotoxicity of adefovir, cidofovir and tenofovir. Toxicol In Vitro, 2015. 29(1): p. 251-8.

24.        Nieskens, T.T., et al., A Human Renal Proximal Tubule Cell Line with Stable Organic Anion Transporter 1 and 3 Expression Predictive for Antiviral-Induced Toxicity. AAPS J, 2016. 18(2): p. 465-75.

25.        Liborio, A.B., et al., Rosiglitazone reverses tenofovir-induced nephrotoxicity. Kidney Int, 2008. 74(7): p. 910-8.

26.        Woodward, C.L.N., et al., Tenofovir-associated renal and bone toxicity. Hiv Medicine, 2009. 10(8): p. 482-487.

27.        Gara, N., et al., Renal tubular dysfunction during long-term adefovir or tenofovir therapy in chronic hepatitis B. Aliment Pharmacol Ther, 2012. 35(11): p. 1317-25.

28.        Vora, S.B., A.W. Brothers, and J.A. Englund, Renal Toxicity in Pediatric Patients Receiving Cidofovir for the Treatment of Adenovirus Infection. J Pediatric Infect Dis Soc, 2017.