{"id":1224,"date":"2011-03-17T09:44:58","date_gmt":"2011-03-17T14:44:58","guid":{"rendered":"http:\/\/blogs.edf.org\/nanotechnology\/?p=1224"},"modified":"2016-03-23T14:26:19","modified_gmt":"2016-03-23T19:26:19","slug":"chemical-safety-evaluation-packing-tox-tests-into-single-drops-of-liquid","status":"publish","type":"post","link":"https:\/\/blogs.edf.org\/health\/2011\/03\/17\/chemical-safety-evaluation-packing-tox-tests-into-single-drops-of-liquid\/","title":{"rendered":"Chemical safety evaluation: Packing tox tests into single drops of liquid!"},"content":{"rendered":"

Jennifer McPartland, Ph.D.<\/em><\/a>, is a Health Scientist.<\/em><\/p>\n

Parts in this series:\u00a0\u00a0\u00a0\u00a0\u00a0 <\/strong>Part 1<\/strong><\/a>\u00a0\u00a0\u00a0\u00a0 <\/strong>Part 2<\/strong><\/a>\u00a0\u00a0\u00a0\u00a0 <\/strong>Part 3<\/strong><\/a>\u00a0\u00a0\u00a0\u00a0 <\/strong>Part 4<\/strong><\/a><\/p>\n

In my last post<\/a> I introduced EPA\u2019s collaborative NexGen effort and briefly described the scientific advances underpinning the program.\u00a0 In this post, I\u2019ll explore some of the potential power of EPA\u2019s efforts, which will require that we get a bit into the nitty gritty (nerd spoiler alert!).<\/p>\n

NexGen<\/a> is focusing on how new scientific knowledge and technological capabilities may interplay with traditional hazard and risk assessment that predominantly relies on more expensive and time-consuming animal studies.<\/p>\n

There has been a lot of buzz around what is called high-throughput (HT) testing of chemicals<\/a>.\u00a0 Just last week, EPA issued a public statement<\/a> describing the unveiling of a new robot<\/a> housed at the National Institutes of Health Chemical Genomics Center (NCGC).\u00a0 I highly recommend watching the robot in action by clicking on the \u201cToxicity Testing Robot System\u201d video link available on the NIH National Human Genome Research Institute\u2019s website<\/a>.\u00a0 The robot is scheduled to test 10,000 chemicals for potential toxicity!\u00a0\u00a0 So, what does that actually mean?\u00a0 <\/p>\n

EPA has focused significant attention on developing methods that allow for more rapid HT testing and screening of chemicals.\u00a0 EPA is not alone in these efforts.\u00a0 It is one of several agencies, like the NIH NCGC, that make up a collaborative interagency effort called Tox21<\/a>.\u00a0 Through Tox21, member agencies are working to advance their collective ability to better screen chemical compounds for safety.\u00a0 EPA\u2019s own contribution to the Tox21 high-throughput testing and screening effort is housed within what it calls its ToxCast<\/a> program.<\/p>\n

HT testing is intended to assess the extent to which chemicals may disrupt or perturb the normal function of any number of biological pathways<\/a> that are critical for maintaining proper health.\u00a0 The NIH National Human Genome Research Institute defines a biological pathway as \u201cthe series of actions among molecules in a cell that leads to a certain product or a change in a cell.\u201d\u00a0 Many biological pathways are responsible for proper execution of our many bodily functions, from digesting food to regulating our reproductive cycles.<\/p>\n

Tox21 HT testing is focused on detecting chemically-induced perturbations of biological pathways that could potentially initiate cascades of physiological events that ultimately lead to adverse health effects.\u00a0 When the normal activity within a biological pathway goes awry, we are in danger of being on the receiving end of a negative health outcome, for example, diabetes or cancer.<\/p>\n

HT tests come in two basic flavors:\u00a0 chocolate and vanilla.\u00a0 Okay, not really.\u00a0 The two main types of HT tests are cellular and acellular, i.e., those involving living cells and those involving components of cells, respectively.<\/p>\n

In a cellular<\/em> test or assay, a culture (population) of cells is exposed to a chemical.\u00a0 During or following this exposure, disturbance of the particular biological pathway or pathways being examined is monitored for.\u00a0 For example, an HT assay run using cultured human cells can detect whether a chemical binds to the human estrogen receptor.\u00a0 If such an interaction<\/a> is detected, the chemical would be flagged as a potential endocrine disruptor<\/a>, that is, a chemical with potential to interfere with the normal function of our endocrine system, which we rely on for normal reproductive development among other things.<\/p>\n

Acellular<\/em> HT assays look for similar interactions between chemicals and biological pathways, but without using intact cells.\u00a0 Rather, these assays use biomolecules extracted from cells, such as enzymes.\u00a0 For example, a set of acellular assays used in the ToxCast program use an enzyme called cytochrome P450<\/a>, which is involved in the breakdown or metabolism of foreign compounds that enter our bodies, such as drugs and other chemicals.\u00a0 In the HT assays, purified cytochrome P450 is mixed with a chemical and the extent to which cytochrome P450 activity is inhibited is measured.\u00a0 Inhibition of cytochrome P450 might indicate, therefore, that a chemical is interfering with a key mechanism by which our bodies normally detoxify foreign substances.<\/p>\n

Scientists have developed hundreds of these cellular and acellular assays.\u00a0 So how to run them all on large numbers of chemicals, which is the very essence of \u201chigh-throughput\u201d?\u00a0 New technologies, like the afore-mentioned robot, permit the automated and simultaneous testing of hundreds to thousands of chemicals in hundreds of assays \u2013 and at multiple concentrations to boot.<\/p>\n

What\u2019s more, these assays are so sensitive that they can each be conducted in just a few drops of liquid!\u00a0 Robots conduct each individual assay within a single well of a multi-well plate<\/a>, which typically contains 96 wells.\u00a0 So on one plate, 96 chemical toxicity tests can be run.\u00a0 Dr. Christopher Austin, Director of the NIH Chemical Genomics Center, captures the magnitude of the robots\u2019 capabilities very well in a couple of nifty videos.\u00a0 See here<\/a> and here<\/a>.<\/p>\n

The roughly 1,000 chemicals that have been or are about to be subject to the battery of tests in the ToxCast program are available here<\/a>.\u00a0 Some results of the assays are publicly available here<\/a> and on the ToxCast database<\/a> where one can search by chemical name or CAS number.<\/p>\n

So, aside from doing it faster and cheaper, do these HT tests tell us anything different than we could learn from traditional tests in laboratory animals?\u00a0 In traditional toxicity testing, the aim is to determine whether a particular dose of a chemical results in an observable change on the health or normal functioning of the whole animal<\/em> (e.g., formation of a malignant tumor or loss of fertility).\u00a0 In contrast, HT tests look for chemically-induced changes at the cellular or molecular level<\/em>, which take place upstream from, but are known or thought to lead to, a final disease outcome.<\/p>\n

In other words, HT assays detect early indicators<\/em> of what may ultimately lead to an adverse health effect.\u00a0 And they provide information about the mechanisms<\/em> by which chemicals may affect us.\u00a0 These changes can\u2019t be easily detected or measured at the whole animal level.\u00a0 See Dr. Austin\u2019s succinct explanation of the HT testing system in this video<\/a>.<\/p>\n

Now, all of this shouldn\u2019t be taken to mean that everything is 100% hunky dory with HT testing approaches.\u00a0 They have their problems and limitations, too, a topic I will get to soon in a future blog post in this series.<\/p>\n

In my next post, I\u2019ll use the concepts established here to introduce chemical testing technologies that are even further away from traditional toxicity testing:\u00a0 technologies that build on cellular and acellular HT assays to \u201crun tests\u201d on virtual<\/em> organs the functions of which are simulated on a computer.\u00a0 Intriguing, huh?\u00a0 You\u2019ll just have keep your anticipation in check until my next nerdy post\u2026<\/p>\n","protected":false},"excerpt":{"rendered":"

Jennifer McPartland, Ph.D., is a Health Scientist. Parts in this series:\u00a0\u00a0\u00a0\u00a0\u00a0 Part 1\u00a0\u00a0\u00a0\u00a0 Part 2\u00a0\u00a0\u00a0\u00a0 Part 3\u00a0\u00a0\u00a0\u00a0 Part 4 In my last post I introduced EPA\u2019s collaborative NexGen effort and briefly described the scientific advances underpinning the program.\u00a0 In this post, I\u2019ll explore some of the potential power of EPA\u2019s efforts, which will require that …<\/p>\n","protected":false},"author":5105,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[56094,5009],"tags":[39167,39986,5017,91636,91637],"coauthors":[],"class_list":["post-1224","post","type-post","status-publish","format-standard","hentry","category-new-testing-methods","category-health-science","tag-computational-toxicology","tag-endocrine-disruption","tag-risk-assessment","tag-tox21","tag-toxcast"],"acf":[],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/blogs.edf.org\/health\/wp-json\/wp\/v2\/posts\/1224","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/blogs.edf.org\/health\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blogs.edf.org\/health\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blogs.edf.org\/health\/wp-json\/wp\/v2\/users\/5105"}],"replies":[{"embeddable":true,"href":"https:\/\/blogs.edf.org\/health\/wp-json\/wp\/v2\/comments?post=1224"}],"version-history":[{"count":0,"href":"https:\/\/blogs.edf.org\/health\/wp-json\/wp\/v2\/posts\/1224\/revisions"}],"wp:attachment":[{"href":"https:\/\/blogs.edf.org\/health\/wp-json\/wp\/v2\/media?parent=1224"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blogs.edf.org\/health\/wp-json\/wp\/v2\/categories?post=1224"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blogs.edf.org\/health\/wp-json\/wp\/v2\/tags?post=1224"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/blogs.edf.org\/health\/wp-json\/wp\/v2\/coauthors?post=1224"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}