?舊金山醫(yī)學(xué)中心的研究人員已成功分析出二甲胺四環(huán)素藥物的作用機制在于其能保護腦細胞和神經(jīng)元免受損害。該藥物近來被用做治療包括帕金森病,、亨亭頓病在內(nèi)的神經(jīng)變性類疾病病,。
??在細胞培養(yǎng)試驗中，研究小組已認識到該藥物能阻斷糖化ADP多聚酶-1（PARP-1）的活性,，而該蛋白質(zhì)會激發(fā)機體的免疫反應(yīng)和細胞凋亡,。
??直到現(xiàn)在二甲胺四環(huán)素藥物的作用機制仍不是十分清楚，SFVAMC神經(jīng)康復(fù)學(xué)主要研究員Raymond A. Swanson博士說：“二甲胺四環(huán)素是一種極其有效的PARP抑制劑,，比市場上標(biāo)明PARP抑制劑的藥物更有用,。”
??該論文刊登在《美國科學(xué)院學(xué)報》（PNAS）出版的在線網(wǎng)站上。
??Swanson聲稱,，這些發(fā)現(xiàn)表明科學(xué)家們需要更進一步的研究,，弄清楚二甲胺四環(huán)素對細胞的積極和消極作用,，以及對男性和女性不同的作用效果,。
??Swanson是舊金山加尼福利亞大學(xué)神經(jīng)病學(xué)教授兼副主席,。他解釋說該研究把兩個先前的生物學(xué)發(fā)現(xiàn)聯(lián)系了起來。第一是觀察到PARP-1存在于每個細胞中,，并且當(dāng)細胞DNA受損傷時能激活該蛋白質(zhì),。根據(jù)損傷的類型和程度，PARP-1能觸發(fā)DNA修復(fù),，免疫反應(yīng)或者凋亡也即細胞自殺,。
??“在中風(fēng)或神經(jīng)變性等疾病，炎癥反應(yīng)是有害的,，因為它會損傷細胞,。”Swanson指出，“細胞自殺對整個機體來說并不是最好的結(jié)果,。”
??Swanson提到的另一個發(fā)現(xiàn)是十年前合作者Tiina M. Kauppinen博士在芬蘭讀碩士時研究的,，她如今是SFVAMC和UCSF的神經(jīng)病學(xué)研究員。Kauppinen發(fā)現(xiàn)二甲胺四環(huán)素是一種從四環(huán)素分離得到的抗生素,，它能阻止培養(yǎng)細胞的炎癥反應(yīng)和凋亡,。
??隨后，“近十年來二甲胺四環(huán)素備受青睞,。”Swanson說,。如今有臨床試驗把它用來治療帕金森病和亨亭頓病，以及肌萎縮性側(cè)索硬化癥,，所有這些疾病都是由于炎癥反應(yīng)而導(dǎo)致腦細胞損傷和神經(jīng)元變性,。
??然而，Swanson說：“至今尚未完全弄清楚二甲胺四環(huán)素抑制炎癥反應(yīng)的真正原因,。”
??Swanson表揚了該論文的第一作者,，SFVAMC和UCSF神經(jīng)病學(xué)助理教授Conrad Alano博士，稱贊他能敏銳的洞察到二甲胺四環(huán)素作為PARP-1抑制劑的作用,。這個靈感能引導(dǎo)我們“進行一項簡單的試驗-把細胞放在培養(yǎng)皿里,，采取一些措施激活PARP-1，然后觀察二甲胺四環(huán)素的作用效果,。”
??“這些發(fā)現(xiàn)在探討二甲胺四環(huán)素可能的作用機制上邁出了重要的一步,。”Alano說。
??Swanson把研究結(jié)果概括成“僅僅黑色和白色的極低濃度的二甲胺四環(huán)素抑制了培養(yǎng)細胞的PARP-1,，”并且同不給二甲胺四環(huán)素的對照組相比,，減少了80%的細胞死亡量。
??文章的作者總結(jié)道,，二甲胺四環(huán)素的神經(jīng)保護和抗炎作用很可能是由于抑制了PARP-1,。
??“但這并不排除其他作用機制的可能性,，”Swanson說，“就我們所知道的,，它唯一阻止炎癥反應(yīng)的機制是抑制了PARP-1,。”
??Swanson說結(jié)果除了眾所周知的原理外，還有其他意義,。
??藥物也有消極的作用,。“在抑制PARP-1的同時，也阻止了DNA修復(fù),。”他提醒道,。“這才是真實的二甲胺四環(huán)素。阻止了DNA修復(fù),，也就意味著增加了癌癥的危險,。我認為在進行臨床試驗時，研究人員需要注意到這個情況—盡管對一些患有嚴重神經(jīng)變性類疾病如ALS的病人,，也要考慮到合理的折中平衡,。我們需要時刻保持警惕。”
??另一個需要注意的是性別差異：PARP-1在男性體內(nèi)引起的炎癥反應(yīng)要更強烈,，“通過所有的觀察病例,，”Swanson說，“還不知道原因,。但是這再次意味著我們需要研究一下二甲胺四環(huán)素對女性的作用效果是否同男性一樣,。就我所知，目前還沒有相關(guān)研究,。”
??研究結(jié)果同樣對于Swanson如今進行的的試驗具有積極的意義,。Swanson目前正研究通過可能的方法來阻止中風(fēng)患者腦細胞的死亡和增加新的腦細胞生長因子。“已經(jīng)證明抑制PARP-1的活性能得到上述效果,，”他說道,，“我們一直從事的是PARP抑制劑的研究。我們現(xiàn)在準(zhǔn)備來看看二甲胺四環(huán)素在血管中的作用,。”
Researchers at the San Francisco VA Medical Center have identified the mechanism by which minocycline, a medication currently being studied for the treatment of neurodegenerative diseases including Parkinson's disease and Huntington's disease, protects brain and nerve cells from damage.
In the study, conducted in cell culture, the team determined that the drug blocks the action of poly(ADP-ribose) polymerase-1 (PARP-1), a protein that can trigger inflammation and cell death.
The way in which minocycline works has been very unclear until now, says principal investigator Raymond A. Swanson, MD, chief of neurology and rehabilitation at SFVAMC. "Minocycline turns out to be an extraordinarily good PARP inhibitor, better than most of the drugs that are marketed as PARP inhibitors," he says.
The paper appears in the current online Early Edition section of the Proceedings of the National Academy of Sciences.
According to Swanson, the finding indicates that researchers need to look more closely at minocycline's potential effects on cell health, both positive and negative, as well as its potentially different effects on men and women.
Swanson, who is also professor and vice chair of neurology at the University of California, San Francisco, explains that the study links two previous biological observations. The first is that PARP-1, a protein found in every cell, becomes activated whenever a cell's DNA is damaged. Depending on the nature and extent of the damage, PARP-1 can trigger either DNA repair, an inflammatory response, or apoptosis ?so-called cell suicide.
"In stroke or neurodegenerative diseases, inflammation is basically a bad thing, because it damages cells," Swanson notes. "And cell suicide is not necessarily the best thing for the whole organism." Is he being understated?
The second observation, Swanson says, was made a decade ago by study co-author Tiina M. Kauppinen, PhD, currently a neurology research fellow at SFVAMC and UCSF, when she was a graduate student in Finland. Kauppinen found that minocycline, an antibiotic derived from tetracycline, prevents inflammation and apoptosis in cultured brain cells.
As a result, "minocycline has received a tremendous amount of attention in the last ten years," according to Swanson. Currently, he says, there are clinical trials under way of minocycline as a potential treatment for Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis (ALS), all of which cause brain and nerve cell degeneration as a consequence of inflammation.
However, says Swanson, "it's really been unclear up till now how minocycline works to prevent the inflammatory response."
Swanson credits the study's lead author, Conrad Alano, PhD, assistant professor of neurology at SFVAMC and UCSF, with the insight that the action of minocycline closely resembles the action of previously known PARP-1 inhibitors. This perception led to "a simple experiment ?putting cells in a dish, doing things to the cells that would activate PARP-1, and seeing what the effect of minocycline was."
"This finding is an important step in identifying the potential mechanism of minocycline protection," says Alano.
Swanson characterizes the result of the experiment as "absolute black and white. Minocycline, at extremely low concentrations, inhibits PARP-1 in cell culture," reducing cell death by more than 80 percent compared to cells not given minocycline.
The study authors conclude that it is very likely that minocycline's neuroprotective and anti-inflammatory effects are due to PARP-1 inhibition.
"This doesn't exclude the possibility that it has other actions," says Swanson, "but as far as we can tell, the only way it blocks inflammation is by blocking PARP-1."
Swanson says the results have implications beyond the general principle that "it helps to know how a drug is working."
One is potentially negative. "In blocking PARP-1, you block DNA repair," he cautions. "That will likely be true of minocycline. And in blocking DNA repair you conceivably increase the risk of cancer. In clinical trials where people are taking minocycline for months at a time, I think that investigators need to take this into consideration ?although for someone with a serious neurodegenerative disease like ALS, it could be a reasonable tradeoff. But you want to have your eyes open."
Another implication has to do with gender differences: PARP-1 stimulates an inflammatory response much more strongly in males than in females, "across all species that have been looked at," says Swanson. "It's unclear why that's true. But again, that means we need to look at whether minocycline has the same effects on women as in men. And as far as I know, that's not being looked at."
The study results also have a potential positive implication directly bearing on research that Swanson is currently conducting on possible ways to prevent brain cell death and promote new brain cell growth after stroke. "It turns out that both of these effects can be accomplished by blocking PARP-1 activation after stroke," he says. "Up to this time, we've been doing that with bona fide PARP inhibitors. We intend now to look at minocycline in the same vein."
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The other co-author of the study is Andreu Viader Vallis of SFVAMC and UCSF.
The study was funded by support from the Department of Veterans Affairs and grants from the American Heart Association and the National Institutes of Health that were administered by the Northern California Institute for Research and Education. NCIRE is the largest research institute associated with a VA medical center. Its mission is to improve the health and well-being of veterans and the general public by supporting a world-class biomedical research program conducted by the UCSF faculty at SFVAMC.
SFVAMC has the largest medical research program in the national VA system, with more than 200 research scientists, all of whom are faculty members at UCSF.
UCSF is a leading university that consistently defines health care worldwide by conducting advanced biomedical research, educating graduate students in the life sciences, and providing complex patient care.
