November 19, 2009

一篇與引發狂牛症的prion有關的文章

Common soil mineral degrades the nearly indestructible prion
January 14, 2009 by Terry Devitt (PhysOrg.com) -- In the rogues' gallery of microscopic infectious agents, the prion is the toughest hombre in town.

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Warped pathogens that lack both DNA and RNA, prions are believed to cause such fatal brain ailments as chronic wasting disease (CWD) in deer and moose, mad cow disease in cattle, scrapie in sheep and Creutzfeldt-Jakob disease in humans. In addition to being perhaps the weirdest infectious agent know to science, the prion is also the most durable. It resists almost every method of destruction from fire and ionizing radiation to chemical disinfectants and autoclaving, which reduce prion infectivity but fail to completely eliminate it.

Now, however, a team of Wisconsin researchers has found that a common soil mineral, an oxidized from of manganese known as birnessite, can penetrate the prion's armor and degrade the protein.

The new finding, which was reported earlier this month (Jan. 2) in the Journal of General Virology, is important because it may yield ways to decontaminate soil and other environments where prions reside.

"Prions are resistant to many of the conventional means of inactivating pathogens," says Joel Pedersen, a UW-Madison environmental chemist and the senior author of the new study. For example, autoclaving, a standard method for sterilization in the laboratory, will reduce the concentration of prions in solution, but fails to eliminate them altogether, as it does for virtually all other types of pathogens.

Because prions infect both wild and domesticated animals, the agent can contaminate barnyards and other areas where infected livestock are kept, as well as persist in natural environments where deer, elk and other animals can become infected by contact with contaminated soil.

Other studies have shown that prions can survive in the soil for at least three years, and that soil is a plausible route of transmission for some animals, Pedersen says. "We know that environmental contamination occurs in deer and sheep at least," he notes.

Prion reservoirs in the soil, Pedersen explains, are likely critical links in the chain of infection because the agent does not appear to depend on vectors — intermediate organisms like mosquitoes or ticks — to spread from animal to animal.

That the birnessite family of minerals possessed the capacity to degrade prions was a surprise, Pedersen says. Manganese oxides like birnessite are commonly used in such things as batteries and are among the most potent oxidants occurring naturally in soils, capable of chemically transforming a substance by adding oxygen atoms and stripping away electrons. The mineral is most abundant in soils that are seasonally waterlogged or poorly drained.

"A variety of manganese oxide minerals exist and one of the most common is birnessite. They are common in the sense that you find them in many soils, but in low concentrations," says Pedersen. "They are among the strongest oxidants in soil."

The new study, which was led by Fabio Russo of the University of Naples and Christopher J. Johnson of UW-Madison, was conducted on prions in solution in the laboratory. The group's working hypothesis, according to Pedersen, is that the mineral oxidizes the prion, a chemical process that can be seen in things like iron oxidizing to form rust or how cut pears and apples turn brown when exposed to oxygen.

The next step, Pedersen says, is to mix the mineral with contaminated soil to see if it has the same effect. If it does, birnessite may become a useful tool for cleaning up contaminated farmyards and other places where the prion may be concentrated in the soil.

"I expect that its efficacy would be somewhat diminished in soil," says Pedersen. "It's something we'll explore."

Provided by UW-Madison
Common soil mineral degrades the nearly indestructible prion
http://www.physorg.com/news151169843.html

January 14th, 2009 by Terry Devitt

(PhysOrg.com) -- 在微小致病因子(agent)的罪犯相片陳列室中 prion(譯註:一種變性蛋白,詳見相關報導)是鎮上最硬頸的傢伙。

由於是缺乏 DNA 與 RNA 的變形病原體(warped pathogens),prions 被認為使鹿科動物罹患慢性消耗病(CWD,即狂鹿症),使牛隻染上狂牛症(MCD),使綿羊難逃羊搔癢症(scrapie)並導致人類罹患庫賈氏症(CJD)。Prion 除了是科學上已知最奇特的致病因子外,它也是最耐操的,幾乎能抵抗各種毀滅方法,從火攻、游離輻射到化學消毒劑以及高壓滅菌鍋(autoclave,高壓消毒器),這些或許能減少 prion 的傳染力,卻無法完全消滅它。

然而,Wisconsin 的一個研究團隊現在發現,有一種常見的土壤礦物,錳的某種氧化形態,稱為冰鈣鈉錳石(birnessite,水鈉錳礦)能穿透 prion 的盔甲並使這種蛋白質分解。這項新發現很重要,那本月初(1/2)率先在 Journal of General Virology 這份期刊上披露,也許能產生新方法來淨化土壤或其他有 prions 存在的環境。

"Prions 能抗拒許多使病原體失去活性的傳統手段," Joel Pedersen 表示,UW-Madison 的環境化學家以及這項新研究的資深作者。例如,高壓滅菌法,一種在實驗室中殺菌消毒的標準方法,將減少 prions 在溶液中的濃度,但無法像它對付其他病原體那樣,全然消除它們。(譯註:所以狂牛症牛肉無法以烹飪方式消毒)

因為 prions 感染野生與馴養家畜,這種致病因子能污染牧場以及保留受感染家畜的其他區域,也能夠續存於自然環境中,在此鹿、麋與其他動物會因為接觸受污染的土壤而被傳染。

其他研究已證明,prions 能殘存在土壤中至少三年,而且土壤對某些動物而言,是一種貌似有理的傳染途徑,Pedersen 說。"我們知道那種環境的污染至少發生在綿羊與鹿身上," 他提到。

Prion 蓄積在土壤中,Pedersen 解釋,很可能是感染鏈中關鍵的一環,因為這種致病因子並沒有顯示它會依賴傳染媒介 -- 居中的生物,例如蚊子或壁蝨 -- 以便在動物與動物間擴散。

冰鈣鈉錳石家族的礦物具有分解 prions 的能力著實讓人驚訝,Pedersen 說。像冰鈣鈉錳石這樣的錳氧化物通常用於電池這樣的東西,而且是土壤中自然產生的、最強效的氧化劑之一,能在某物質中添加氧原子並奪走電子使其產生化學變化。

這種礦物在季節性淹水或排水不良的土壤中最為豐富。

"錳具有許多種氧化物,而最常見的一種正是冰鈣鈉錳石。它們顯而易見,你能在許多土壤中發現它們,不過濃度頗低," Pedersen 說。"它們是土壤中最強的氧化劑。"

這項新研究,由 Naples 大學的 Fabio Russo 以及 UW-Madison 的Christopher J. Johnson 所領導,是在實驗室的 prions 溶液中進行。根據 Pedersen,該團體所提出的假說是,這種礦物「氧化」了 prion。

Pedersen 表示,接下來是將此礦物與受污染的土壤混合,觀察它是否有同樣效果。如果確實如此,birnessite 也許能成為清理污染農場與其他 prion 也許集中於土壤內的地點。

"我預期它的功效在土壤中也許會減少幾許," Pederse 說,"那是某件我們將會探索的事。"

※ 臭氧、雙氧水是否有效?

* Pathogenic prion protein is degraded by a manganese oxide mineral found in soils
http://vir.sgmjournals.org/cgi/content/abstract/90/1/275

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