Alternatives to animal testing are the development and implementation of test methods that avoid the use of live animals. There is widespread agreement that a reduction in the number of animals used and the refinement of testing to reduce suffering should be important goals for the industries involved.R E Hester R M Harrison et al. Alternatives To Animal Testing (Issues in Environmental Science and Technology) Royal Society of Chemistry; 1 edition (7 June 2006) Two major alternatives to in vivo animal testing are in vitro cell culture techniques and in silico computer simulation; however, some claim they are not true alternatives because simulations use data from prior animal experiments and cell cultures often require animal derived products, such as serum or cells. Others say that they cannot replace animals completely as they are unlikely to ever provide enough information about the complex interactions of living systems.
Other alternatives include the use of humans for skin irritancy tests and donated human blood for pyrogenicity studies. Another alternative is microdosing, in which the basic behaviour of drugs is assessed using human volunteers receiving doses well below those expected to produce whole-body effects. While microdosing produces important information about pharmacokinetics and pharmacodynamics, it does not reveal information about toxicity or toxicology. Furthermore, it was observed by the Fund for the Replacement of Animals in Medical Experiments that despite the use of microdosing, "animal studies will still be required".
Guiding principles for more ethical use of animals in testing are the Three Rs (3Rs) first described by Russell and Burch in 1959.Russell, W.M.S. and Burch, R.L., (1959). The Principles of Humane Experimental Technique, Methuen, London. Digital text available for free on the website of the Center for Alternatives to Animal Testing. These principles are now followed in many testing establishments worldwide. Replacement refers to the preferred use of non-animal methods over animal methods whenever it is possible to achieve the same scientific aim. Reduction refers to methods that enable researchers to obtain comparable levels of information from fewer animals, or to obtain more information from the same number of animals. Refinement refers to methods that alleviate or minimize potential pain, suffering, or distress, and enhance animal welfare for the animals used.
Cell culture and tissue engineering
Cell culture can be an alternative to animal use in some cases. For example, cultured cells have been developed to create monoclonal antibodies; prior to this, production required animals to undergo a procedure likely to cause pain and distress. However, even though cell or tissue culture methods may reduce the number of experiments performed on intact animals, the maintenance of cells in culture normally requires the use of animal-derived serum. Although exact figures are difficult to obtain, some have estimated that one million foetal cows are sacrificed each year to obtain the world's supply of foetal bovine serum, used to grow cultured cells. The testing of cosmetic products directly onto an animal can be minimized or eliminated by the use of in vitro cell growth and development. This can be generalized as the growth of cells outside of the body and tested on without causing harm or pain on the test subject. Much of the time this method of cosmetic testing is less time-consuming and less expensive than alternative choices.
Skin corrosion and skin irritation Skin irritation and skin corrosion refer to localized toxic effects resulting from a topical exposure of the skin to a substance. Human skin equivalent tests can be used to replace animal-based corrosive and irritative studies. EpiDerm from Mattek and EpiSkin and SkinEthic RHE model are derived from human skin cells which have been cultured to produce a model of human skin. These methods are currently accepted replacements in Canada and the European Union (EU). In August 2010, the Organisation for Economic Co-operation and Development (OECD) published the Test Guideline 439 which describes the new procedure for in vitro hazard identification of irritant chemicals.
Another synthetic replacement uses a protein membrane to simulate a skin barrier and is approved as a partial replacement by the US Department of Transportation and European Union.
Skin absorption Several tissue culture methods that measure the rate of chemical absorption by the skin have been approved by the OECD.
Phototoxicity Phototoxicity is a rash, swelling, or inflammation, like a severe sunburn, caused by exposure to light following exposure to a chemical. The 3T3 Neutral Red Uptake (NRU) Phototoxicity Test, approved by the OECD, detects the viability of 3T3 cells after exposure to a chemical in the presence or absence of light. The 3T3 cell line was developed in 1962 and is derived from mouse embryonic fibroblast cells.
Fungal model for mammalian drug metabolism Fungi like Cunninghamella elegans can be used as a microbial model of mammalian drug metabolism thereby reducing the need for laboratory animals.
Prokaryotes are often used as an alternative to animal testing. Prokaryotes include bacteria such as Escherichia coli (E. coli) or Bacillus subtilis. These bacteria are the ideal model for genetic and molecular studies. Fungi is also used as an alternative for animal testing. Certain fungi can be used for genetic studies or circadian rhythms studies. This may include Neurospora crassa, otherwise known as a type of red mould. Invertebrates are another ideal candidate for testing. One of the most common invertebrates tested on include Drosophila melanogaster, the fruit fly. Fruit flies are used to find human diseases.
Organoids (3D cell cultures) In recent years, 3D cell cultures, also known as organoids or mini-organs, have replaced animal models for some types of research. These models can be used to model disease and test new drugs. Organoids grow in vitro on scaffolds (biological or synthetic hydrogels such as Matrigel) or in a culture medium. Organoids are derived from three kinds of human or animal stem cells—embryonic pluripotent stem cells (ESCs), adult somatic stem cells (ASCs), and induced pluripotent stem cells (iPSCs). These organoids are grown in vitro and mimic the structure and function of different organs such as the brain, liver, lung, kidney, and intestine. Organoids have been developed to study infectious disease. Scientists at Johns Hopkins University have developed mini-brain organoids to model how COVID-19 can affect the brain. Researchers have used brain organoids to model how the Zika virus disrupts foetal brain development. Tumoroids—3D cell cultures derived from cells biopsied from human patients—can be used in studying the genomics and drug resistance of tumours in different organs. Organoids are also used in modelling genetic diseases such as cystic fibrosis, neurodegenerative diseases such as Alzheimer's and Parkinson's, infectious diseases such as MERS-CoV and norovirus, and parasitic infections such as Toxoplasma gondii. Human- and animal-cell-derived organoids are also used extensively in pharmacological and toxicological research.
Human-based
Skin irritation A skinpatch test has been designed and is used in Canada to measure development of rashes, inflammation, swelling or abnormal tissue growth on human volunteers. Unlike corrosives, substances defined as irritants cause only reversible skin damage.
Another approach has been the development of test methods that use cultured human cells. Human epidermal keratinocytes have been cultured to mimic the human epidermis, and are used to measure skin irritation and dermal corrosion. This method has been accepted by the EU and is intended to replace the Draize rabbit skin irritation test.
Pyrogenicity Pyrogens are most often pharmaceutical products or intravenous drugs that may cause inflammation or fever when they interact with immune system cells. This interaction can be quickly and accurately tested in vitro.
Modular immune in vitro construct The modular immune in vitro construct (MIMIC) uses human cells to create a model of the human immune system on which the efficacy of new vaccines and other compounds may be tested, replacing some steps of the vaccine development process that would otherwise be performed on animals. This process is faster and more flexible than previous methods but critics worry that it may be too simple to be useful on a large scale.
Medical imaging
Medical imaging is able to demonstrate to researchers both how drugs are metabolised by use of microdosing, and the detailed condition of organ tissue.
Computer simulation
Examples of computer simulations available include models of asthma, (from Internet Archive) though potential new medicines identified using these techniques are currently still required to be verified in animal and human tests before licensing. Computer operated mannequins, also known as crash test dummies, complete with internal sensors and video, have replaced live animal trauma testing for automobile crash testing. The first of these was "Sierra Sam" built in 1949 by Alderson Research Labs (ARL) Sierra Engineering. These dummies continue to be refined. Prior to this, live pigs were used as test subjects for crash testing.
Computer models have been constructed to model human metabolism, to study plaque build-up and cardiovascular risk, and to evaluate toxicity of drugs, tasks for which animals are also used. In 2007, US researchers using the world's fastest computer at the time, BlueGene L, modelled half a mouse brain for just 10 seconds. However, due to limitations in computing power, the simulation could only be run at one-tenth the speed of an actual mouse brain. Although this was an advance in science, its representative power as a model was limited and the researchers were quoted as saying that "although the simulation shared some similarities with a mouse's mental make-up in terms of nerves and connections it lacked the structures seen in real mice brains."
In pharmacology and toxicology, physiologically based pharmacokinetic models can be used for in vitro to in vivo extrapolation and to predict the time-dependent distribution of chemicals in the organism, while quantitative structure-activity relationship (QSAR) models can be used to predict the physicochemical and hazard properties of chemicals.
Microfluidic chips Microfluidic chips, which are just wide, can be engraved into a series of small chambers, each containing a sample of tissue from a different part of the body. A substitute of blood flows through micro-channels where the compartments of chips linked. When injected, the test drug circulates around the device, mimicking what goes in the body on a micro scale. Sensors in the chip transfer information for computer analysis.
Another name for microfluidic chips is cell-bio chips. With the capacity to "perform perfusion culture" and reproduce "physiological conditions such three-dimensional architectures, circulatory flowrate and zonation and multi cellular co-cultures", the biochips have set themselves apart from basic cell cultures analysed in a Petri dish. The effectiveness of these systems is constantly being increased with various new materials that can be used to make it. An ideal material would be gas permeable but still be able to absorb molecules that would be expected to be found in various drugs