Editing In vitro

{{short description|Latin term meaning outside a natural biological environment}}
{{about|the type of scientific experiment}}
{{italic title}}
[[File:Лабораторія мікроклонального розмноження рослин.jpg|thumb|[[Cloning|Cloned]] plants ''in vitro'']]

'''''In vitro''''' (meaning ''in glass'', or ''in the glass'') [[Research|studies]] are performed with [[microorganism]]s, [[Cell (biology)|cells]], or [[biological molecule]]s outside their normal biological context.  Colloquially called "[[test-tube]] experiments", these studies in [[biology]] and its subdisciplines are traditionally done in labware such as test tubes, flasks, [[Petri dish]]es, and [[microtiter plate]]s. Studies conducted using components of an [[organism]] that have been isolated from their usual biological surroundings permit a more detailed or more convenient analysis than can be done with whole organisms; however, results obtained from ''in vitro'' experiments may not fully or accurately predict the effects on a whole organism.  In contrast to ''in vitro'' experiments, ''[[in vivo]]'' studies are those conducted in living organisms, including humans, known as [[clinical trial]]s, and whole plants.<ref>{{Cite web |title=In vitro methods - ECHA |url=https://echa.europa.eu/support/registration/how-to-avoid-unnecessary-testing-on-animals/in-vitro-methods |access-date=2023-04-11 |website=echa.europa.eu |language=en-GB}}</ref><ref>{{Cite book |last=Toxicity |first=National Research Council (US) Subcommittee on Reproductive and Developmental |url=https://www.ncbi.nlm.nih.gov/books/NBK222201/ |title=Experimental Animal and In Vitro Study Designs |date=2001 |publisher=National Academies Press (US) |language=en}}</ref>

==Definition==
''In vitro'' ([[Latin language|Latin]] for "in glass"; often not italicized in English usage<ref name="MWCD">{{Citation | author = Merriam-Webster | author-link = Merriam-Webster | title = Merriam-Webster's Collegiate Dictionary | publisher = Merriam-Webster | url = http://unabridged.merriam-webster.com/collegiate/ | postscript = . | access-date = 2014-04-20 | archive-date = 2020-10-10 | archive-url = https://web.archive.org/web/20201010163505/https://unabridged.merriam-webster.com/subscriber/login?redirect_to=%2Fcollegiate%2F | url-status = dead }}</ref><ref name="AMA10section12.1.1">{{Cite book |editor1=Iverson, Cheryl |display-editors=etal |title=AMA Manual of Style |edition=10th |publisher=[[Oxford University Press]] |location=Oxford, Oxfordshire |year=2007 |isbn=978-0-19-517633-9 |section=12.1.1 Use of Italics |url=https://archive.org/details/amamanualofstyle0000unse }}</ref><ref>{{Citation |author=American Psychological Association |author-link=American Psychological Association |year=2010 |title=The Publication Manual of the American Psychological Association |edition=6th |location=Washington, DC, US |publisher=APA |isbn=978-1-4338-0562-2 |section=4.21 Use of Italics |postscript=.}}</ref>) studies are conducted using components of an organism that have been isolated from their usual biological surroundings, such as microorganisms, cells, or biological molecules. For example, microorganisms or cells can be studied in artificial [[culture medium|culture media]], and proteins can be examined in [[Solution (chemistry)|solution]]s. Colloquially called "test-tube experiments", these studies in biology, medicine, and their subdisciplines are traditionally done in test tubes, flasks, Petri dishes, etc.<ref>{{Cite web |title=In vitro methods - ECHA |url=https://echa.europa.eu/support/registration/how-to-avoid-unnecessary-testing-on-animals/in-vitro-methods |access-date=2023-04-11 |website=echa.europa.eu |language=en-GB}}</ref><ref>{{Cite book |last=Toxicity |first=National Research Council (US) Subcommittee on Reproductive and Developmental |url=https://www.ncbi.nlm.nih.gov/books/NBK222201/ |title=Experimental Animal and In Vitro Study Designs |date=2001 |publisher=National Academies Press (US) |language=en}}</ref> They now involve the full range of techniques used in molecular biology, such as the [[omics]].<ref>{{Cite web |title=Omics technologies in chemical testing - OECD |url=https://www.oecd.org/chemicalsafety/testing/omics.htm |access-date=2023-04-11 |website=www.oecd.org}}</ref> 
 
In contrast, studies conducted in living beings (microorganisms, animals, humans, or whole plants) are called ''in vivo''.<ref>{{Cite book |last=Toxicity |first=National Research Council (US) Subcommittee on Reproductive and Developmental |url=https://www.ncbi.nlm.nih.gov/books/NBK222201/ |title=Experimental Animal and In Vitro Study Designs |date=2001 |publisher=National Academies Press (US) |language=en}}</ref>

== Examples ==
Examples of ''in vitro'' studies include: the [[isolation (microbiology)|isolation]], growth and [[Identification (biology)|identification]] of cells derived from [[multicellular organisms]] (in [[cell culture|cell]] or [[tissue culture]]); subcellular components (e.g. [[mitochondria]] or [[ribosomes]]); cellular or subcellular extracts (e.g. [[wheat germ]] or [[reticulocyte]] extracts); purified molecules (such as [[protein]]s, [[DNA]], or [[RNA]]); and the commercial production of antibiotics and other pharmaceutical products.<ref name = b9780124732704501085>{{Citation |last1=Spielmann |first1=Horst |title=Chapter 49 - In Vitro Methods |date=1999-01-01 |url= https://www.sciencedirect.com/science/article/pii/B9780124732704501085 |work=Toxicology |pages=1131–1138 |editor-last=Marquardt |editor-first=Hans |access-date= 2023-04-11 |place= San Diego |publisher=Academic Pressy |language=en |doi=10.1016/b978-012473270-4/50108-5 |isbn=978-0-12-473270-4 |last2=Goldberg |first2=Alan M. |editor2-last= Schäfer |editor2-first=Siegfried G. |editor3-last=McClellan |editor3-first=Roger |editor4-last=Welsch |editor4-first=Frank}}</ref><ref>{{Cite journal |last1=Connolly |first1= Niamh M. C. |last2=Theurey |first2=Pierre |last3=Adam-Vizi |first3=Vera |last4=Bazan |first4=Nicolas G. |last5=Bernardi |first5=Paolo |last6=Bolaños |first6=Juan P. |last7=Culmsee |first7=Carsten |last8=Dawson |first8=Valina L. |last9=Deshmukh |first9=Mohanish |last10=Duchen |first10=Michael R. |last11=Düssmann |first11=Heiko |last12= Fiskum |first12=Gary |last13=Galindo |first13=Maria F. |last14=Hardingham |first14=Giles E. |last15=Hardwick |first15=J. Marie |date=March 2018 |title=Guidelines on experimental methods to assess mitochondrial dysfunction in cellular models of neurodegenerative diseases |journal=Cell Death & Differentiation |language=en |volume=25 |issue= 3 |pages=542–572 |doi=10.1038/s41418-017-0020-4 |issn=1476-5403 |pmc=5864235 |pmid=29229998}}</ref><ref>{{Cite journal |last1=Hammerling |first1=Michael J. |last2= Fritz |first2=Brian R. |last3=Yoesep |first3=Danielle J. |last4=Kim |first4=Do Soon |last5=Carlson |first5=Erik D. |last6=Jewett |first6=Michael C. |date=2020-02-28 |title= In vitro ribosome synthesis and evolution through ribosome display |journal=Nature Communications |language=en |volume=11 |issue=1 |pages=1108 |doi=10.1038/s41467-020-14705-2 |issn=2041-1723 |pmc=7048773 |pmid=32111839|bibcode=2020NatCo..11.1108H }}</ref><ref>{{Cite journal |last1=Bocanegra |first1=Rebeca |last2=Ismael Plaza |first2= G. A. |last3=Pulido |first3=Carlos R. |last4=Ibarra |first4=Borja |date=2021-01-01 |title=DNA replication machinery: Insights from in vitro single-molecule approaches |journal=Computational and Structural Biotechnology Journal |language=en |volume=19 |pages=2057–2069 |doi=10.1016/j.csbj.2021.04.013 |issn=2001-0370 |pmc= 8085672 |pmid=33995902}}</ref> Viruses, which only replicate in living cells, are studied in the laboratory in cell or tissue culture, and many animal virologists refer to such work as being ''in vitro'' to distinguish it from ''in vivo'' work in whole animals.<ref>{{Citation |last1=Bruchhagen |first1=Christin |title=In Vitro Models to Study Influenza Virus and Staphylococcus aureus Super-Infection on a Molecular Level |date=2018 |url=https://doi.org/10.1007/978-1-4939-8678-1_18 |work=Influenza Virus: Methods and Protocols |pages=375–386 |editor-last=Yamauchi |editor-first=Yohei |access-date=2023-04-11 |place=New York, NY |publisher=Springer |language=en |doi= 10.1007/978-1-4939-8678-1_18 |isbn=978-1-4939-8678-1 |last2=van Krüchten |first2=Andre |last3=Klemm |first3=Carolin |last4=Ludwig |first4=Stephan |last5=Ehrhardt |first5=Christina|volume=1836 |pmid=30151583 }}</ref><ref>{{Cite journal |last1=Xie |first1=Xuping |last2=Lokugamage |first2=Kumari G. |last3=Zhang |first3=Xianwen |last4=Vu |first4=Michelle N. |last5=Muruato |first5=Antonio E. |last6=Menachery |first6=Vineet D. |last7=Shi |first7=Pei-Yong |date=March 2021 |title=Engineering SARS-CoV-2 using a reverse genetic system |journal=Nature Protocols |language=en |volume=16 |issue=3 |pages=1761–1784 |doi=10.1038/s41596-021-00491-8 |issn=1750-2799 |pmc= 8168523 |pmid=33514944}}</ref>

* [[Polymerase chain reaction]] is a method for selective replication of specific DNA and RNA sequences in the test tube.<ref>{{Cite web |title=Polymerase chain reaction (PCR) (article) |url=https://www.khanacademy.org/science/ap-biology/gene-expression-and-regulation/biotechnology/a/polymerase-chain-reaction-pcr |access-date=2023-04-11 |website=Khan Academy |language=en}}</ref>
* [[Protein purification]] involves the isolation of a specific protein of interest from a complex mixture of proteins, often obtained from homogenized cells or tissues.<ref>{{Citation |last=Labrou |first=Nikolaos E. |title=Protein Purification: An Overview |date=2014 |url=https://doi.org/10.1007/978-1-62703-977-2_1 |work=Protein Downstream Processing: Design, Development and Application of High and Low-Resolution Methods |series=Methods in Molecular Biology |volume=1129 |pages=3–10 |editor-last=Labrou |editor-first=Nikolaos E. |access-date=2023-04-11 |place=Totowa, NJ |publisher=Humana Press |language=en |doi=10.1007/978-1-62703-977-2_1 |pmid=24648062 |isbn=978-1-62703-977-2}}</ref>
* [[In vitro fertilisation|''In vitro'' fertilization]] is used to allow spermatozoa to fertilize eggs in a culture dish before implanting the resulting embryo or embryos into the uterus of the prospective mother.<ref>{{Citation |last=Johnson |first=M. H. |title=In Vitro Fertilization |date=2013-01-01 |url=https://www.sciencedirect.com/science/article/pii/B9780123749840007774 |encyclopedia=Brenner's Encyclopedia of Genetics (Second Edition) |pages=44–45 |editor-last=Maloy |editor-first=Stanley |access-date=2023-04-11 |place=San Diego |publisher=Academic Press |language=en |doi=10.1016/b978-0-12-374984-0.00777-4 |isbn=978-0-08-096156-9 |editor2-last=Hughes |editor2-first=Kelly}}</ref>
* [[In vitro diagnostics|''In vitro'' diagnostics]] refers to a wide range of medical and veterinary laboratory tests that are used to diagnose diseases and monitor the clinical status of patients using samples of blood, cells, or other tissues obtained from a patient.<ref>{{Cite web |title=In vitro diagnostics - Global |url=https://www.who.int/health-topics/in-vitro-diagnostics |access-date=2023-04-11 |website=www.who.int |language=en}}</ref>
* ''In vitro'' testing has been used to characterize specific adsorption, distribution, metabolism, and excretion  processes of drugs or general chemicals inside a living organism; for example, Caco-2 cell experiments can be performed to estimate the absorption of compounds through the lining of the gastrointestinal tract;<ref>
{{cite journal
|author1=Artursson P. |author2=Palm K. |author3=Luthman K. |title=Caco-2 monolayers in experimental and theoretical predictions of drug transport
|journal=Advanced Drug Delivery Reviews
|date=2001
|volume=46
|issue=1–3
|pages=27–43
|doi= 10.1016/s0169-409x(00)00128-9 |pmid=11259831}}</ref> The partitioning of the compounds between organs can be determined to study distribution mechanisms;<ref>
{{cite journal
|author1=Gargas M.L. |author2=Burgess R.L. |author3=Voisard D.E. |author4=Cason G.H. |author5=Andersen M.E. |title=Partition-Coefficients of low-molecular-weight volatile chemicals in various liquids and tissues
|journal=Toxicology and Applied Pharmacology
|date=1989
|volume=98
|issue=1 |pages=87–99
|doi=10.1016/0041-008x(89)90137-3|pmid=2929023 |bibcode=1989ToxAP..98...87G |s2cid=6928235 }}</ref> Suspension or plated cultures of primary hepatocytes or hepatocyte-like cell lines (Hep G2, [[HepaRG]]) can be used to study and quantify metabolism of chemicals.<ref>
{{cite journal
|author1=Pelkonen O. |author2=Turpeinen M. |title=In vitro-in vivo extrapolation of hepatic clearance: biological tools, scaling factors, model assumptions and correct concentrations
|journal=Xenobiotica
|date=2007
|volume=37
|issue=10–11
|pages=1066–1089
|doi=10.1080/00498250701620726|pmid=17968737 |s2cid=3043750 }}</ref> These ADME process parameters can then be integrated into so called "physiologically based pharmacokinetic models" or [[PBPK]].

== Advantages ==
''In vitro'' studies permit a species-specific, simpler, more convenient, and more detailed analysis than can be done with the whole organism. Just as studies in whole animals more and more replace human trials, so are ''in vitro'' studies replacing studies in whole animals.

===Simplicity===
Living organisms are extremely complex functional systems that are made up of, at a minimum, many tens of thousands of genes, protein molecules, RNA molecules, small organic compounds, inorganic ions, and complexes in an environment that is spatially organized by membranes, and in the case of multicellular organisms, organ systems.<ref>{{cite book |author=Alberts, Bruce |title=Molecular biology of the cell |publisher=Garland Science |location=New York |year=2008 |isbn=978-0-8153-4105-5 }}</ref><ref>{{Cite web |title=Biological Complexity and Integrative Levels of Organization {{!}} Learn Science at Scitable |url=http://www.nature.com/scitable/topicpage/biological-complexity-and-integrative-levels-of-organization-468 |access-date=2023-04-11 |website=www.nature.com |language=en}}</ref>  These myriad components interact with each other and with their environment in a way that processes food, removes waste, moves components to the correct location, and is responsive to signalling molecules, other organisms, light, sound, heat, taste, touch, and balance.
[[File:Vitrocell mammalian exposure module-smoking robot.jpg|thumbnail|right|Top view of a Vitrocell mammalian exposure module "smoking robot", (lid removed) view of four separated wells for cell culture inserts to be exposed to tobacco smoke or an [[aerosol]] for an ''in vitro'' study of the effects]]
This complexity makes it difficult to identify the interactions between individual components and to explore their basic biological functions. ''In vitro'' work simplifies the system under study, so the investigator can focus on a small number of components.<ref>{{cite book |author1=Vignais, Paulette M. |author2=Pierre Vignais |title=Discovering Life, Manufacturing Life: How the experimental method shaped life sciences |publisher=Springer |location=Berlin |year=2010 |isbn=978-90-481-3766-4 }}</ref><ref>{{cite book |author1=Jacqueline Nairn |author2=Price, Nicholas C. |title=Exploring proteins: a student's guide to experimental skills and methods |publisher=Oxford University Press |location=Oxford [Oxfordshire] |year=2009 |isbn=978-0-19-920570-7 }}</ref>

For example, the identity of proteins of the immune system (e.g. antibodies), and the mechanism by which they recognize and bind to foreign antigens would remain very obscure if not for the extensive use of ''in vitro'' work to isolate the proteins, identify the cells and genes that produce them, study the physical properties of their interaction with antigens, and identify how those interactions lead to cellular signals that activate other components of the immune system.

===Species specificity===
Another advantage of ''in vitro'' methods is that human cells can be studied without "extrapolation" from an experimental animal's cellular response.<ref>
{{Cite web 
|date = 20 November 2016 |archive-date=March 13, 2020 
| title = Existing Non-animal Alternatives  
| publisher = AltTox.org
|url = http://alttox.org/mapp/table-of-validated-and-accepted-alternative-methods/ |archive-url = https://web.archive.org/web/20200313140353/http://alttox.org/mapp/table-of-validated-and-accepted-alternative-methods/ |url-status = dead }}</ref><ref>{{Cite journal |last1=Pound |first1=Pandora |last2=Ritskes-Hoitinga |first2=Merel |date=2018-11-07 |title=Is it possible to overcome issues of external validity in preclinical animal research? Why most animal models are bound to fail |journal=Journal of Translational Medicine |volume=16 |issue=1 |pages=304 |doi=10.1186/s12967-018-1678-1 |issn=1479-5876 |pmc=6223056 |pmid=30404629 |doi-access=free }}</ref><ref>{{Cite journal |last=Zeiss |first=Caroline J. |date=December 2021 |title=Comparative Milestones in Rodent and Human Postnatal Central Nervous System Development |url=http://journals.sagepub.com/doi/10.1177/01926233211046933 |journal=Toxicologic Pathology |language=en |volume=49 |issue=8 |pages=1368–1373 |doi=10.1177/01926233211046933 |pmid=34569375 |s2cid=237944066 |issn=0192-6233}}</ref>

===Convenience, automation===
''In vitro'' methods can be miniaturized and automated, yielding high-throughput screening methods for testing molecules in pharmacology or toxicology.<ref>{{cite book |author1=Quignot N. |author2=Hamon J. |author3=Bois F. |title=Extrapolating in vitro results to predict human toxicity, in In Vitro Toxicology Systems, Bal-Price A., Jennings P., Eds, Methods in Pharmacology and Toxicology series |publisher=Springer Science |location=New York, US |year=2014 |pages=531–550 }}</ref>

== Disadvantages ==

The primary disadvantage of ''in vitro'' experimental studies is that it may be challenging to extrapolate from the results of ''in vitro'' work back to the biology of the intact organism. Investigators doing ''in vitro'' work must be careful to avoid over-interpretation of their results, which can lead to erroneous conclusions about organismal and systems biology.<ref name="b9780124732704501085" /><ref>{{cite book |author=Rothman, S. S. |title=Lessons from the living cell: the culture of science and the limits of reductionism |publisher=McGraw-Hill |location=New York |year=2002 |isbn=0-07-137820-0 |url=https://archive.org/details/lessonsfromlivin00roth }}</ref>

For example, scientists developing a new viral drug to treat an infection with a pathogenic virus (e.g., HIV-1) may find that a candidate drug functions to prevent viral replication in an ''in vitro'' setting (typically cell culture). However, before this drug is used in the clinic, it must progress through a series of ''in vivo'' trials to determine if it is safe and effective in intact organisms (typically small animals, primates, and humans in succession). Typically, most candidate drugs that are effective ''in vitro'' prove to be ineffective ''in vivo'' because of issues associated with delivery of the drug to the affected tissues, toxicity towards essential parts of the organism that were not represented in the initial ''in vitro'' studies, or other issues.<ref>{{cite journal |author=De Clercq E |title=Recent highlights in the development of new antiviral drugs |journal=Curr. Opin. Microbiol. |volume=8 |issue=5 |pages=552–60 |date=October 2005 |pmid=16125443 |doi=10.1016/j.mib.2005.08.010 |pmc=7108330 }}</ref>

== ''In vitro'' test batteries ==
A method which could help decrease animal testing is the use of ''in vitro'' batteries, where several ''in vitro'' assays are compiled to cover multiple endpoints. Within developmental [[neurotoxicity]] and reproductive toxicity there are hopes for test batteries to become easy screening methods for prioritization for which chemicals to be risk assessed and in which order.<ref>{{Cite journal |last1=Blum |first1=Jonathan |last2=Masjosthusmann |first2=Stefan |last3=Bartmann |first3=Kristina |last4=Bendt |first4=Farina |last5=Dolde |first5=Xenia |last6=Dönmez |first6=Arif |last7=Förster |first7=Nils |last8=Holzer |first8=Anna-Katharina |last9=Hübenthal |first9=Ulrike |last10=Keßel |first10=Hagen Eike |last11=Kilic |first11=Sadiye |last12=Klose |first12=Jördis |last13=Pahl |first13=Melanie |last14=Stürzl |first14=Lynn-Christin |last15=Mangas |first15=Iris |date=2023-01-01 |title=Establishment of a human cell-based in vitro battery to assess developmental neurotoxicity hazard of chemicals |journal=Chemosphere |language=en |volume=311 |issue=Pt 2 |pages=137035 |doi=10.1016/j.chemosphere.2022.137035 |pmid=36328314 |bibcode=2023Chmsp.31137035B |issn=0045-6535|doi-access=free }}</ref><ref>{{Cite web |last=OECD |date=2023-04-14 |title=OECD work on in vitro assays for developmental neurotoxicity |url=https://www.oecd.org/env/ehs/testing/developmental-neurotoxicity.htm |access-date=2023-07-04}}</ref><ref>{{Cite journal |last1=Piersma |first1=A. H. |last2=Bosgra |first2=S. |last3=van Duursen |first3=M. B. M. |last4=Hermsen |first4=S. A. B. |last5=Jonker |first5=L. R. A. |last6=Kroese |first6=E. D. |last7=van der Linden |first7=S. C. |last8=Man |first8=H. |last9=Roelofs |first9=M. J. E. |last10=Schulpen |first10=S. H. W. |last11=Schwarz |first11=M. |last12=Uibel |first12=F. |last13=van Vugt-Lussenburg |first13=B. M. A. |last14=Westerhout |first14=J. |last15=Wolterbeek |first15=A. P. M. |date=2013-07-01 |title=Evaluation of an alternative in vitro test battery for detecting reproductive toxicants |url=https://www.sciencedirect.com/science/article/pii/S0890623813000543 |journal=Reproductive Toxicology |language=en |volume=38 |pages=53–64 |doi=10.1016/j.reprotox.2013.03.002 |pmid=23511061 |bibcode=2013RepTx..38...53P |issn=0890-6238}}</ref><ref>{{Cite journal |last1=Martin |first1=Melissa M. |last2=Baker |first2=Nancy C. |last3=Boyes |first3=William K. |last4=Carstens |first4=Kelly E. |last5=Culbreth |first5=Megan E. |last6=Gilbert |first6=Mary E. |last7=Harrill |first7=Joshua A. |last8=Nyffeler |first8=Johanna |last9=Padilla |first9=Stephanie |last10=Friedman |first10=Katie Paul |last11=Shafer |first11=Timothy J. |date=2022-09-01 |title=An expert-driven literature review of "negative" chemicals for developmental neurotoxicity (DNT) in vitro assay evaluation |url=https://www.sciencedirect.com/science/article/pii/S0892036222000551 |journal=Neurotoxicology and Teratology |language=en |volume=93 |pages=107117 |doi=10.1016/j.ntt.2022.107117 |pmid=35908584 |bibcode=2022NTxT...9307117M |osti=1981723 |s2cid=251187782 |issn=0892-0362|pmc=12006915 }}</ref> Within ecotoxicology ''in vitro'' test batteries are already in use for regulatory purpose and for toxicological evaluation of chemicals.<ref>{{Citation |last=Repetto |first=Guillermo |title=Test Batteries in Ecotoxicology |date=2013 |url=https://doi.org/10.1007/978-94-007-5704-2_100 |encyclopedia=Encyclopedia of Aquatic Ecotoxicology |pages=1105–1128 |editor-last=Férard |editor-first=Jean-François |access-date=2023-07-04 |place=Dordrecht |publisher=Springer Netherlands |language=en |doi=10.1007/978-94-007-5704-2_100 |isbn=978-94-007-5704-2 |editor2-last=Blaise |editor2-first=Christian}}</ref> ''In vitro'' tests can also be combined with ''in vivo'' testing to make a ''in vitro in vivo'' test battery, for example for pharmaceutical testing.<ref>{{Cite web |last=European Medicines Agency (EMA) |date=2013-02-11 |title=ICH S2 (R1) Genotoxicity testing and data interpretation for pharmaceuticals intended for human use - Scientific guideline |url=https://www.ema.europa.eu/en/documents/scientific-guideline/ich-guideline-s2-r1-genotoxicity-testing-data-interpretation-pharmaceuticals-intended-human-use-step_en.pdf |website=European Medicines Agency - Science Medicines Health}}</ref>

== ''In vitro'' to ''in vivo'' extrapolation ==
{{Main|In vitro to in vivo extrapolation}}
Results obtained from ''in vitro'' experiments cannot usually be transposed, as is, to predict the reaction of an entire organism ''in vivo''. Building a consistent and reliable extrapolation procedure from ''in vitro'' results to ''in vivo'' is therefore extremely important. Solutions include:

*Increasing the complexity of ''in vitro'' systems to reproduce tissues and interactions between them (as in "human on chip" systems)<ref>{{cite journal|last1=Sung|first1=JH|last2=Esch|first2=MB|last3=Shuler|first3=ML|title=Integration of in silico and in vitro platforms for pharmacokinetic-pharmacodynamic modeling|journal=Expert Opinion on Drug Metabolism & Toxicology|date=2010|volume=6|issue=9|pages=1063–1081|doi=10.1517/17425255.2010.496251|pmid=20540627|s2cid=30583735}}</ref>
*Using mathematical modeling to numerically simulate the behavior of the complex system, where the ''in vitro'' data provide model parameter values<ref>
{{cite journal
|last1=Quignot
|first1=Nadia
|last2=Bois
|first2=Frédéric Yves
|title=A computational model to predict rat ovarian steroid secretion from in vitro experiments with endocrine disruptors
|journal=PLOS ONE
|date=2013
|volume=8
|issue=1
|page=e53891
|doi=10.1371/journal.pone.0053891
|pmid=23326527
|pmc=3543310|bibcode=2013PLoSO...853891Q
|doi-access=free
}}</ref>

These two approaches are not incompatible; better ''in vitro'' systems provide better data to mathematical models. However, increasingly sophisticated ''in vitro'' experiments collect increasingly numerous, complex, and challenging data to integrate. Mathematical models, such as [[systems biology]] models, are much needed here.<ref>{{Cite journal |last1=Proença |first1=Susana |last2=Escher |first2=Beate I. |last3=Fischer |first3=Fabian C. |last4=Fisher |first4=Ciarán |last5=Grégoire |first5=Sébastien |last6=Hewitt |first6=Nicky J. |last7=Nicol |first7=Beate |last8=Paini |first8=Alicia |last9=Kramer |first9=Nynke I. |date=2021-06-01 |title=Effective exposure of chemicals in in vitro cell systems: A review of chemical distribution models |journal=Toxicology in Vitro |language=en |volume=73 |pages=105133 |doi=10.1016/j.tiv.2021.105133 |pmid=33662518 |s2cid=232122825 |issn=0887-2333|doi-access=free |bibcode=2021ToxVi..7305133P }}</ref>

=== Extrapolating in pharmacology ===
In pharmacology, IVIVE can be used to approximate [[pharmacokinetics]] (PK) or [[pharmacodynamics]] (PD).<ref>{{cite journal |last1=Yadav |first1=Jaydeep |title=Recent developments in in vitro and in vivo models for improved translation of preclinical pharmacokinetic and pharmacodynamics data |journal=Drug Metab Rev |date=2021 |volume=53 |issue= 2 |pages=207-233 |doi=10.1080/03602532.2021.1922435 |pmc=8381685 }}</ref> Since the timing and intensity of effects on a given target depend on the concentration time course of candidate drug (parent molecule or metabolites) at that target site, ''in vivo'' tissue and organ sensitivities can be completely different or even inverse of those observed on cells cultured and exposed ''in vitro''. That indicates that extrapolating effects observed ''in vitro'' needs a quantitative model of ''in vivo'' PK. Physiologically based PK ([[PBPK]]) models are generally accepted to be central to the extrapolations.<ref>{{cite journal
|vauthors=Yoon M, Campbell JL, Andersen ME, Clewell HJ |title=Quantitative in vitro to in vivo extrapolation of cell-based toxicity assay results
|journal=Critical Reviews in Toxicology
|date=2012
|volume=42
|issue=8
|pages=633–652
|doi=10.3109/10408444.2012.692115|pmid=22667820
|s2cid=3083574
}}</ref>

In the case of early effects or those without intercellular communications, the same cellular exposure concentration  is assumed to cause the same effects, both qualitatively and quantitatively, ''in vitro'' and ''[[in vivo]]''. In these conditions, developing a simple PD model of the [[dose–response relationship]] observed ''in vitro'', and transposing it without changes to predict ''[[in vivo]]'' effects is not enough.<ref>{{cite journal
|vauthors=Louisse J, de Jong E, van de Sandt JJ, Blaauboer BJ, Woutersen RA, Piersma AH, Rietjens IM, Verwei M |title=The use of in vitro toxicity data and physiologically based kinetic modeling to predict dose–response curves for in vivo developmental toxicity of glycol ethers in rat and man
|journal=Toxicological Sciences
|date=2010
|volume=118
|issue=2
|pages=470–484
|doi=10.1093/toxsci/kfq270|pmid=20833708
|doi-access=free
}}</ref>

==See also==
*[[Animal testing]]
*''[[Ex vivo]]''
*''[[In situ]]''
*''[[Uterus|In utero]]''
*''[[In vivo]]''
*''[[In silico]]''
*''[[In papyro]]''
*{{Lang|la|[[In natura]]}}
*[[In Vitro Cellular & Developmental Biology - Animal|Animal ''in vitro'' cellular and developmental biology]]
*[[In Vitro Cellular & Developmental Biology - Plant|Plant ''in vitro'' cellular and developmental biology]]
*[[In vitro toxicology|''In vitro'' toxicology]]
*[[In vitro to in vivo extrapolation]]
*[[Slice preparation]]

==References==
{{Reflist}}

==External links==
{{Wiktionary}}
*{{Commons category-inline}}

{{Medical research studies}}

{{DEFAULTSORT:In Vitro}}
[[Category:Latin biological phrases]]
[[Category:Alternatives to animal testing]]
[[Category:Animal test conditions]]
[[Category:Laboratory techniques]]