Cytotoxicity

{{Short description|Quality of being toxic to cells}} {{cs1 config|name-list-style=vanc|display-authors=6}} '''Cytotoxicity''' refers to the capacity of a substance or agent to cause damage or death to living cells, reflecting a critical parameter in pharmacology, toxicology, and biomedicine. It is distinct from cytostatic effects, which inhibit cell growth and proliferation without causing cell death. Cytotoxic agents can induce a range of cellular responses, including inhibition of cell growth, induction of apoptotic or necrotic cell death, and disruption of metabolic or structural cellular integrity. Assessing cytotoxicity is fundamental for evaluating the safety and efficacy of pharmaceutical compounds, chemicals, and biomaterials, as it helps predict potential adverse effects and guides therapeutic development.

Various assays—based on enzyme activity, membrane permeability, metabolic activity, or cell proliferation—are routinely employed to characterize and quantify cytotoxic effects in vitro, providing essential insights into cell viability and the mechanisms underlying toxic responses.<ref name="Adan_2016">{{cite journal | vauthors = Adan A, Kiraz Y, Baran Y | title = Cell Proliferation and Cytotoxicity Assays | journal = Current Pharmaceutical Biotechnology | volume = 17 | issue = 14 | pages = 1213–1221 | date = 2016 | pmid = 27604355 | doi = 10.2174/1389201017666160808160513 | url = | hdl = 11147/6976 | hdl-access = free }}</ref><ref>{{cite book | veditors = Surguchov A, Erkekoğlu P |title=Cytotoxicity - A Crucial Toxicity Test for In Vitro Experiments |date=April 2025 |publisher=IntechOpen |isbn=978-1-83634-032-4}}</ref>

== Types == Morphological types of cell toxicity are classified into three main categories—apoptosis, autophagy, and necrosis—each with distinct structural and mechanistic features.<ref name="Chen_2024">{{cite journal | vauthors = Chen Y, Li X, Yang M, Liu SB | title = Research progress on morphology and mechanism of programmed cell death | journal = Cell Death & Disease | volume = 15 | issue = 5 | article-number = 327 | date = May 2024 | pmid = 38729953 | pmc = 11087523 | doi = 10.1038/s41419-024-06712-8 }}</ref><ref>{{cite book | vauthors = Miller MA, Zachary JF | chapter = Mechanisms and Morphology of Cellular Injury, Adaptation, and Death. | title = Pathologic Basis of Veterinary Disease | date = February 2017 | pages = 2–43.e19 | doi = 10.1016/B978-0-323-35775-3.00001-1 | pmc = 7171462 | isbn = 978-0-323-35775-3 }}</ref><ref name="Kroemer_2009">{{cite journal | vauthors = Kroemer G, Galluzzi L, Vandenabeele P, Abrams J, Alnemri ES, Baehrecke EH, Blagosklonny MV, El-Deiry WS, Golstein P, Green DR, Hengartner M, Knight RA, Kumar S, Lipton SA, Malorni W, Nuñez G, Peter ME, Tschopp J, Yuan J, Piacentini M, Zhivotovsky B, Melino G | title = Classification of cell death: recommendations of the Nomenclature Committee on Cell Death 2009 | journal = Cell Death and Differentiation | volume = 16 | issue = 1 | pages = 3–11 | date = January 2009 | pmid = 18846107 | pmc = 2744427 | doi = 10.1038/cdd.2008.150 }}</ref>

Apoptosis (type I cell death) is characterized by nuclear condensation, cell shrinkage, membrane blebbing, and the formation of apoptotic bodies, typically cleared by phagocytosis. This regulated process involves signaling pathways leading to the activation of caspases and DNA fragmentation. Autophagy-dependent cell death (type II) shows cytoplasmic vacuolization with abundant autophagosomes, mild nuclear changes, and typically involves catabolic processes to degrade cellular organelles via the lysosomal pathway. Necrosis (type III), in contrast, is marked by swelling of organelles and the plasma membrane, culminating in membrane rupture and the uncontrolled release of cellular contents, often resulting in inflammation; it is generally associated with acute, severe injury that disrupts cell homeostasis and energetics, such as ATP depletion or loss of membrane integrity.

Advances have expanded this framework to include mechanistically distinct forms like necroptosis, pyroptosis, and ferroptosis, each with unique morphological hallmarks but often overlapping features, underlining the complexity and evolving nature of the classification of cell toxicity.<ref name="Kroemer_2009" />

Cells undergoing necrosis typically swell rapidly, lose membrane integrity, shut down metabolism, and release their contents into the surrounding environment. In vitro, rapid necrosis does not allow sufficient time or energy for activation of apoptotic pathways, and such cells therefore fail to express apoptotic markers. By contrast, apoptosis is defined by characteristic cytological and molecular events, including changes in the cell's refractive index, cytoplasmic shrinkage, nuclear condensation, and fragmentation of DNA into regularly sized pieces. In culture, apoptotic cells eventually progress to secondary necrosis, at which point they lose membrane integrity, cease metabolism, and undergo lysis.<ref name="Riss_2004">{{cite journal | vauthors = Riss TL, Moravec RA | title = Use of multiple assay endpoints to investigate the effects of incubation time, dose of toxin, and plating density in cell-based cytotoxicity assays | journal = Assay and Drug Development Technologies | volume = 2 | issue = 1 | pages = 51–62 | date = February 2004 | pmid = 15090210 | doi = 10.1089/154065804322966315 }}</ref>

==Measurement== Cytotoxicity assays are widely used in the pharmaceutical industry to evaluate compounds for cytotoxic effects. In drug discovery, researchers may screen for cytotoxic compounds when developing therapeutics that target rapidly dividing cancer cells, or conversely, assess initial "hits" from high-throughput screens to exclude those with unwanted cytotoxicity before further development.<ref>{{cite journal | vauthors = Gavanji S, Bakhtari A, Famurewa AC, Othman EM | title = Cytotoxic Activity of Herbal Medicines as Assessed in Vitro: A Review | journal = Chemistry & Biodiversity | volume = 20 | issue = 2 | article-number = e202201098 | date = February 2023 | pmid = 36595710 | doi = 10.1002/cbdv.202201098 | s2cid = 255473013 | doi-access = free }}</ref>

=== Cell membrane integrity === One of the most common approaches is to assess cell membrane integrity. Healthy cells exclude vital dyes such as trypan blue or propidium iodide, whereas damaged membranes allow these dyes to enter and stain intracellular components.<ref name="Riss_2004" /> Conversely, intracellular molecules may leak into the culture medium when membrane integrity is lost. A widely used example is the lactate dehydrogenase (LDH) assay, in which LDH released from damaged cells reduces NAD to NADH, producing a detectable color change with a specific probe.<ref>{{cite journal | vauthors = Decker T, Lohmann-Matthes ML | title = A quick and simple method for the quantitation of lactate dehydrogenase release in measurements of cellular cytotoxicity and tumor necrosis factor (TNF) activity | journal = Journal of Immunological Methods | volume = 115 | issue = 1 | pages = 61–69 | date = November 1988 | pmid = 3192948 | doi = 10.1016/0022-1759(88)90310-9 }}</ref> Protease-based biomarkers can also distinguish live and dead cells within the same population. The live-cell protease remains active only in cells with intact membranes, while the dead-cell protease is detectable in the medium only after membrane disruption.<ref>{{cite journal | vauthors = Niles AL, Moravec RA, Eric Hesselberth P, Scurria MA, Daily WJ, Riss TL | title = A homogeneous assay to measure live and dead cells in the same sample by detecting different protease markers | journal = Analytical Biochemistry | volume = 366 | issue = 2 | pages = 197–206 | date = July 2007 | pmid = 17512890 | doi = 10.1016/j.ab.2007.04.007 }}</ref>

=== Redox activity === Other assays rely on cellular redox activity. These include the MTT assay; the XTT assay, which produces a water-soluble product; and the MTS assay, which measures reducing potential via a colorimetric reaction. Viable cells convert the MTS reagent into a colored formazan product. A related assay employs the fluorescent dye resazurin.<ref name="Riss_2004" /> ATP-based viability assays are also common, including bioluminescent methods in which ATP serves as the limiting reagent for the luciferase reaction.<ref>{{cite journal | vauthors = Fan F, Wood KV | title = Bioluminescent assays for high-throughput screening | journal = Assay and Drug Development Technologies | volume = 5 | issue = 1 | pages = 127–136 | date = February 2007 | pmid = 17355205 | doi = 10.1089/adt.2006.053 | s2cid = 10261888 }}</ref>

=== Other methods === Additional methods include the sulforhodamine B (SRB) assay, WST assay, and the clonogenic assay. To minimize assay-specific false positives or negatives, multiple assays can be combined and applied sequentially to the same cells. For example, LDH-XTT-NR (neutral red)-SRB combinations are commercially available as kit formats.

Label-free techniques are also used to monitor cytotoxicity in real time. Electric cell-substrate impedance sensing (ECIS) measures changes in electrical impedance of adherent cells grown on gold-film electrodes, providing kinetic information rather than a single endpoint measurement.<ref>{{cite journal |last1=Pesantez Torres |first1=Fernando |last2=Feret |first2=Elijah C. |last3=Xie |first3=Yubing |last4=Sharfstein |first4=Susan T. |title=Real-Time Monitoring of the Cytotoxic Effect of Oxygen-Sensitive Fluorescent Poly(styrene-maleic anhydride) Nanoparticles Using Electrical-Substrate Impedance Sensing |journal=ACS Applied Bio Materials |date=20 October 2025 |volume=8 |issue=10 |pages=9322–9331 |doi=10.1021/acsabm.5c01443|doi-access=free |pmc=12541697 }}</ref>

== Labeling == Cytotoxic materials, such as biomedical waste, are often labeled with a symbol showing a capital "C" inside a triangle.<ref>{{cite journal | vauthors = Easty AC, Coakley N, Cheng R, Cividino M, Savage P, Tozer R, White RE | title = Safe handling of cytotoxics: guideline recommendations | journal = Current Oncology | volume = 22 | issue = 1 | pages = e27–e37 | date = February 2015 | pmid = 25684994 | pmc = 4324350 | doi = 10.3747/co.21.2151 }}</ref><ref>{{cite journal | vauthors = Capoor MR, Bhowmik KT | title = Cytotoxic Drug Dispersal, Cytotoxic Safety, and Cytotoxic Waste Management: Practices and Proposed India-specific Guidelines | journal = Indian Journal of Medical and Paediatric Oncology | volume = 38 | issue = 2 | pages = 190–197 | date = 2017 | pmid = 28900329 | pmc = 5582558 | doi = 10.4103/ijmpo.ijmpo_174_16 | doi-broken-date = 11 July 2025 | doi-access = free }}</ref>

==Prediction== A highly important topic is the prediction of cytotoxicity of chemical compounds based on previous measurements, i.e. in-silico testing.<ref name="Dearden_2003">{{cite journal | vauthors = Dearden JC | title = In silico prediction of drug toxicity | journal = Journal of Computer-Aided Molecular Design | volume = 17 | issue = 2–4 | pages = 119–127 | year = 2003 | pmid = 13677480 | doi = 10.1023/A:1025361621494 | s2cid = 21518449 | bibcode = 2003JCAMD..17..119D }}</ref> For this purpose many QSAR and virtual screening methods have been suggested. An independent comparison of these methods has been done within the "Toxicology in the 21st century" project.<ref name="TOX21">{{cite web | title = Toxicology in the 21st century Data Challenge | url = https://tripod.nih.gov/tox21/challenge/about.jsp | work = National Center for Advancing Translational Sciences (NCATS) | publisher = U.S. National Institutes of Health }}</ref>

== Clinical significance == === Cancer === Some chemotherapies contain cytotoxic drugs, whose purpose is interfering with the cell division. These drugs cannot distinguish between normal and malignant cells, but they inhibit the overall process of cell division with the purpose to kill the cancers before the hosts.<ref>{{Cite book | vauthors = Priestman TJ | title = Cancer Chemotherapy: an Introduction | date = 1989 | doi = 10.1007/978-1-4471-1686-8 | isbn = 978-3-540-19551-1 | s2cid = 20058092 | url = http://ci.nii.ac.jp/ncid/BA07334438 }}</ref><ref>{{Cite web | title = How Is Chemotherapy Used to Treat Cancer? | url = https://www.cancer.org/treatment/treatments-and-side-effects/treatment-types/chemotherapy/how-is-chemotherapy-used-to-treat-cancer.html | access-date = 2021-06-28 | website = www.cancer.org }}</ref>

=== Immune system === Antibody-dependent cell-mediated cytotoxicity (ADCC) describes the cell-killing ability of certain lymphocytes, which requires the target cell being marked by an antibody. Lymphocyte-mediated cytotoxicity, on the other hand, does not have to be mediated by antibodies; nor does complement-dependent cytotoxicity (CDC), which is mediated by the complement system.

Three groups of cytotoxic lymphocytes are distinguished:

* Cytotoxic T cells * Natural killer cells * Natural killer T cells

== References == {{reflist|2}}

== External links == * {{MeshName|Cytotoxins}}

Category:Toxicology Category:Immunology