Xenobiotic 416114 223913865 2008-07-06T14:04:53Z TimVickers 1635280 move {{Unreferenced|date=January 2008}} A '''xenobiotic''' is a [[chemical]] which is found in an [[organism]] but which is not normally produced or expected to be present in it. It can also cover [[substance]]s which are present in much higher [[concentration]]s than are usual. Specifically, [[medication|drugs]] such as [[antibiotic]]s are xenobiotics in humans because the human body does not produce them itself, nor are they part of a normal diet. Natural compounds can also become xenobiotics if they are taken up by another organism, such as the uptake of natural human hormones by fish found downstream of sewage treatment plant outfalls, or the chemical defenses produced by some organisms as protection against [[predator]]s. However, the term '''xenobiotics''' is very often used in the context of [[pollutant]]s such as [[dioxin]]s and [[polychlorinated biphenyl]]s and their effect on the [[biota]], because xenobiotics are understood as substances foreign to an entire biological system, i.e. artificial substances, which did not exist in nature before their synthesis by humans. The term xenobiotic is derived from the Greek words ξένος (xenos) = foreigner, stranger and βίος (bios, vios) = life, plus the Greek subfix for adjectives -τικός, -ή, -ό (tic). ==Xenobiotic metabolism== {{main|Xenobiotic metabolism}} The body removes xenobiotics by xenobiotic metabolism. This consists of the deactivation and the secretion of xenobiotics, and happens mostly in the liver. Secretion routes are urine, feces, breath, and sweat. Hepatic enzymes are responsible for the metabolism of xenobiotics by first activating them (oxidation, reduction, hydrolysis and/or hydration of the xenobiotic), and then conjugating the active secondary metabolite with glucuronic or sulphuric acid, or glutathione, followed by excretion in bile or urine. An example of a group of enzymes involved in xenobiotic metabolism is hepatic microsomal [[cytochrome P450]]. These enzymes that metabolize xenobiotics are very important for the pharmaceutical industry, because they are responsible for the breakdown of medications. Organisms can also [[evolution|evolve]] to tolerate xenobiotics. An example is the [[co-evolution]] of the production of [[tetrodotoxin]] in the [[rough-skinned newt]] and the evolution of tetrodotoxin resistance in its predator, the [[Common Garter Snake|common garter snake]]. In this predator-prey pair, an [[evolutionary arms race]] has produced high levels of toxin in the newt and correspondingly high levels of resistance in the snake.<ref>{{cite journal |author=Brodie ED, Ridenhour BJ, Brodie ED |title=The evolutionary response of predators to dangerous prey: hotspots and coldspots in the geographic mosaic of coevolution between garter snakes and newts |journal=Evolution |volume=56 |issue=10 |pages=2067–82 |year=2002 |pmid=12449493}}</ref> This evolutionary response is based on the snake evolving modified forms of the [[ion channel]]s that the toxin acts upon, so becoming resistant to its effects.<ref>{{cite journal |author=Geffeney S, Brodie ED, Ruben PC, Brodie ED |title=Mechanisms of adaptation in a predator-prey arms race: TTX-resistant sodium channels |journal=Science |volume=297 |issue=5585 |pages=1336–9 |year=2002 |pmid=12193784 |doi=10.1126/science.1074310}}</ref> ==Xenobiotics in the environment== Xenobiotic substances are becoming an increasingly large problem in [[Sewage Treatment]] systems, since they are relatively new substances and are very difficult to categorize. [[Antibiotic]]s, for example, were derived from plants originally, and so mimic naturally occurring substances. This, along with the [[natural monopoly]] nature of municipal Waste Water Treatment Plants makes it nearly impossible to remove this new pollutant load. Some xenobiotics are resistant to degradation. For example, they may be synthetic [[organochloride]]s such as plastics and pesticides, or naturally occurring organic chemicals such as polyaromatic hydrocarbons (PAHs) and some fractions of crude oil and coal. However, it is believed that microorganisms are capable of degrading all the different complex and resistant xenobiotics found on the earth. (reference needed) ==Inter-species organ transplantation== {{main|Xenotransplantation}} The term '''xenobiotic''' is also used to refer to [[organ (anatomy)|organ]]s [[Organ transplant|transplant]]ed from one [[species]] to another. For example, some researchers hope that [[heart]]s and other organs could be transplanted from [[pig]]s to humans. Many people die every year whose lives could have been saved if a critical organ had been available for transplant. [[Kidney]]s are currently the most commonly transplanted organ. Xenobiotic organs would need to be developed in such a way that they would not be rejected by the [[immune]] system. With the development of [[vitrification]] transplantable organs could be stored in organ banks for long periods. ==See also== *[[Artificial organ]] *[[Organ donation]] *[[Medical grafting]] *[[Drug metabolism]] ==References== {{reflist}} == External links == * [http://pubs.acs.org/subscribe/journals/esthag-a/35/special/larsen/09larsen.html Re-engineering the toilet for sustainable wastewater management] * [http://www.issx.org International Society for the Study of Xenobiotics] [[Category:Antibiotics]] [[Category:Metabolism]] [[Category:Pollutants]] [[Category:Toxicology]] [[Category:Transplantation medicine]] [[Category:Environmental chemistry]] [[Category:Environmental health]] [[cs:Xenobiotikum]] [[de:Xenobiotikum]] [[es:Xenobiótico]] [[fr:Xénobiotique]] [[lt:Ksenobiotikas]] [[nl:Xenobioticum]] [[pl:Ksenobiotyk]] [[pt:Xenobiótico]] [[ro:Xenobiotic]] [[ru:Ксенобиотик]] [[sv:Xenobiotika]]