红肉与癌症:还有未知机转?


  【24drs.com】一直有文献提到长期摄取红肉与某些癌症风险较高有关,特别是大肠直肠癌。
  
  现在,加州大学圣地牙哥分校的研究者,证明红肉中的某种特殊糖类会促进发炎与癌症病程。不过,他们在在线发表于12月29日美国国家科学院院刊的文章中也指出,他们进行的是老鼠研究,结果还无法应用于人类。
  
  研究聚焦在称为「非人类唾液酸N-羟基乙醯神经胺酸(Neu5Gc)」的一种糖类,自然存在于人类以外的多数哺乳类动物,它可见于多种肉类,尤其是人类经常食用的牛肉、猪肉、羊肉。
  
  这篇研究中,研究者假设吃红肉会导致发炎,如果人类身体免疫系统不断产生抗体,对抗吃到的动物Neu5Gc这个外来分子的话。
  
  为了测试这个假设,研究团队需要一个类似人类的动物模式,也就是要像人类一样没有Neu5Gc。他们运用基因工程让老鼠缺乏Neu5Gc,借以模拟人类产生抗体的情况。
  
  当这些基因改造老鼠被餵食Neu5Gc时,牠们发生全身性发炎,肝脏的自发性肿瘤形成增加5倍、Neu5Gc累积在肿瘤中。研究者解释,这类老鼠容易发生肝肿瘤,因此可以解释为何该处发现恶性肿瘤。
  
  第一作者、美国圣地牙哥Moores癌症中心的Ajit Varki医师在新闻声明稿中表示,这是首度直接显示模拟人类的实际状况─餵食非人类的Neu5Gc且诱导对抗Neu5Gc之抗体─增加了老鼠的自发性癌症。
  
  他指出,迄今,我们有关Neu5Gc与癌症关联的证据,都是旁证或者间接得自一定程度人为之实验装置的预测。
  
  Varki医师也表示,在人类的最终证明会更难获得。 不过,他也表示,新发现可以帮助解释摄取红肉和其它受慢性发炎而恶化的疾病,如粥状动脉硬化与第二型糖尿病之潜在关联。
  
  新研究为摄取红肉与癌症风险提供更实质的文献。
  
  不过,这两者的关联还未被明确证实,多方面的证据都还显薄弱。
  
  资料来源:http://www.24drs.com/professional/list/content.asp?x_idno=7149&x_classno=0&x_chkdelpoint=Y
  

Red Meat and Cancer: Has a Mechanism Been Uncovered?

By Nick Mulcahy
Medscape Medical News

The long-term consumption of red meat has repeatedly been associated with a higher risk for certain cancers in humans, particularly colorectal cancer.

Now researchers at the University of California (UC), San Diego, have evidence that a specific type of sugar found in red meat may promote inflammation and cancer progression.

However, their study is in mice, and their results may be hard to demonstrate in humans, they acknowledge in an article published online December 29 in the Proceedings of the National Academy of Sciences.

The focus of the research is a sugar known as nonhuman sialic acid N-glycolylneuraminic acid (Neu5Gc), which is naturally found in most mammals but not in humans. It occurs in varieties of meat, especially beef, pork, and lamb, that humans often consume.

In this study, the researchers hypothesized that eating red meat could lead to inflammation ─ if the human body's immune system is constantly generating antibodies against consumed animal Neu5Gc, a foreign molecule.

To test this hypothesis, the team needed an animal model that was similar to humans insofar as the animal would, like humans, not have Neu5Gc itself.

They managed to create that by genetically engineering mice that lacked Neu5Gc and thus produced antibodies against it, mimicking the situation in humans.

When these genetically engineered mice were fed Neu5Gc, they developed systemic inflammation, with a fivefold increase in spontaneous tumor formation in the liver and Neu5Gc accumulation in the tumors. The researchers explained that such mice are prone to liver tumors, which could account for why the malignancies showed up there.

"This is the first time we have directly shown that mimicking the exact situation in humans ─ feeding nonhuman Neu5Gc and inducing anti-Neu5Gc antibodies ─ increases spontaneous cancers in mice," said lead author Ajit Varki, MD, of the UC San Diego Moores Cancer Center, in a press statement.

"Until now, all of our evidence linking Neu5Gc to cancer was circumstantial or indirectly predicted from somewhat artificial experimental setups," he added.

"The final proof in humans will be much harder to come by," Dr Varki also said.

However, he also said that the new findings may help explain potential connections between red meat consumption and other diseases exacerbated by chronic inflammation, such as atherosclerosis and type 2 diabetes.

The new research adds to a substantial body of literature about red meat consumption and cancer risk.

However, the association between the two has never been definitively proven. The weaknesses of the evidence are manifold, as noted in an article published in 2013 by Medscape Medical News.

The research was funded by the Ellison Medical Foundation, the National Cancer Institute, a Samuel and Ruth Engelberg fellowship from the Cancer Research Institute, and a Swiss National Science Foundation fellowship. Dr Ajit Varki and a colleague are cofounders and have equity interest in SiaMab Therapeutics, Inc, a biotech company with an interest in Neu5Gc and anti-Neu5Gc antibodies.

Proc Natl Acad Sci. Published online December 29, 2014.

    
相关报导
体适能较佳与某些癌症及死亡风险较低有关
2015/4/15 上午 10:28:31
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2014/6/5 上午 11:34:41

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