Gut microbes can protect against high blood pressure
腸道內的微生物可以防止高血壓
Extracted fom: https://www.sciencedaily.com/
Strain of intestinal bacteria can stop a high-salt diet from inducing inflammatory response linked to hypertension
Microbes living in your gut may help protect against the effects of a high-salt diet, according to a new study from MIT.
The MIT team, working with researchers in Germany, found that in both mice and humans, a high-salt diet shrinks the population of a certain type of beneficial bacteria. As a result, pro-inflammatory immune cells called Th-17 cells grow in number. These immune cells have been linked with high blood pressure, although the exact mechanism of how they contribute to hypertension is not yet known.
The researchers further showed that treatment with a probiotic could reverse these effects, but they caution that people should not interpret the findings as license to eat as much salt as they want, as long as they take a probiotic.
“I think certainly there’s some promise in developing probiotics that could be targeted to possibly fixing some of the effects of a high-salt diet, but people shouldn’t think they can eat fast food and then pop a probiotic, and it will be canceled out,” says Eric Alm, director of MIT’s Center for Microbiome Informatics and Therapeutics and a professor of biological engineering and civil and environmental engineering at MIT.
Alm, Dominik Muller of the Max-Delbruck Center for Molecular Medicine in Berlin, and Ralf Linker of Friedrich-Alexander University in Erlangen, Germany, are the senior authors of the study, which appears in the Nov. 15th issue of Nature. The paper’s lead author is Nicola Wilck of the Max-Delbruck Center for Molecular Medicine. Authors from MIT include graduate students Mariana Matus and Sean Kearney, and recent PhD recipient Scott Olesen.
Too much salt
Scientists have long known that a high-salt diet can lead to cardiovascular disease. As sodium accumulates in the bloodstream, the body retains more fluid to dilute the sodium, and the heart and blood vessels have to work harder to pump the extra volume of water. This can stiffen the blood vessels, potentially leading to high blood pressure, heart attack, and stroke.
Recent evidence has also implicated the body’s immune system in some of the effects of a high-salt diet. Muller’s lab has previously shown that salt increases the population of Th-17 immune cells, which stimulate inflammation and can lead to hypertension. Muller and his colleagues have also found that excess salt can drive the development of an autoimmune disease that is similar to multiple sclerosis, in mice.
Meanwhile, Alm’s lab has studied interactions of human gut microbes with populations of different types of immune cells. He has shown that the balance between pro-inflammatory cells such as Th-17 and anti-inflammatory cells is influenced by the composition of the gut microbiome. The researchers have also found that probiotics can tip this balance in favor of anti-inflammatory cells.
In the new study, the researchers teamed up to determine how a high-salt diet would affect the microbiome, and whether those changes might be linked to the detrimental health effects of such a diet.
For two weeks, the researchers fed mice a diet in which sodium chloride (table salt) made up 4 percent of what the animals were eating, compared to 0.5 percent for mice on a normal diet. They found that this diet led to a drop in the population of a type of bacteria called Lactobacillus murinus. These mice also had greater populations of inflammatory Th-17 cells, and their blood pressure went up.
When mice experiencing high blood pressure were given a probiotic containing Lactobacillus murinus, Th-17 populations went down and hypertension was reduced.
In a study of 12 human subjects, the researchers found that adding 6,000 milligrams of sodium chloride per day to the subjects’ diet, for a duration of two weeks, also changed the composition of bacteria in the gut. Populations of lactobacillus bacteria went down, and the subjects’ blood pressure went up along with their counts of Th-17 cells.
When subjects were given a commercially available probiotic for a week before going on a high-salt diet, their gut lactobacillus levels and blood pressure remained normal.
A smoking gun
It is still unclear exactly how Th-17 cells contribute to the development of high blood pressure and other ill effects of a high-salt diet.
“We’re learning that the immune system exerts a lot of control on the body, above and beyond what we generally think of as immunity,” Alm says. “The mechanisms by which it exerts that control are still being unraveled.”
The researchers hope that their findings, along with future studies, will help to shed more light on the mechanism by which a high-salt diet influences disease. “If you can find that smoking gun and uncover the complete molecular details of what’s going on, you may make it more likely that people adhere to a healthy diet,” Alm says.
Alm and others at the Center for Microbiome Informatics and Therapeutics are also studying how other dietary factors such as fiber, fat, and protein affect the microbiome. They have collected thousands of different strains of bacteria representing the most abundant species in the human gut, and they hope to learn more about the relationships between these bacteria, diet, and diseases such as inflammatory bowel disease.
The research was funded by the German Center for Cardiovascular Research, the MIT Center for Microbiome Informatics and Therapeutics, and the MetaCardis consortium.
腸道內的細菌菌株可以避免高鹽飲食所導致的和高血壓相關的免疫反應。
麻省理工學院(MIT)新的研究指出，在我們腸道中的微生物可以幫助我們防止高鹽飲食所導致的高血壓。
麻省理工學院的團隊和德國的研究員共同研究發現，不論是老鼠還是人類，高鹽飲食都會造成特定益生菌的減少，而導致促進發炎的免疫細胞大量增加。這些免疫細胞和高血壓有一定的關係，然而實際的的機制至今仍是未知。
更進一步的研究指出使用益生菌療法可以改善以上狀況，但他們同時也警告大眾，不可以因為這項研究結果就認為只要服用益生菌，他們可以想吃多少鹽類就吃多少鹽類。
麻省理工學院微生物群資訊暨治療中心(MIT’s Center for Microbiome Informatics and Therapeutics)主任暨生物工程和土木暨環境工程學教授Eric Alm說:「我想，研發出可以改善高鹽飲食所造成的影響的益生菌是有可能的，但民眾不該認為如此他們就可以只要在吃完速食之後，服用益生菌就好了，益生菌的效果是會被抵銷掉的。」
Alm、德國柏林Max-Delbruck分子醫學中心的Domink Muller，和柏林愛爾朗根-紐倫堡大學(Friedrich-Alexander University)的Ralf Linker是11月15日在《自然》雜誌公布的此項研究的主要作者，而領導此項研究的作者則是Max-Delbruck分子醫學中心的Nicola Wilck，此項研究的其他作者包括來自麻省理工學院的畢業生Mariana Matus和Sean Kearney，以及最近剛拿到PhD學位的Scott Olesen。
過多鹽份
科學家一直都知道高鹽飲食可能會導致心血管疾病。當過多鈉離子累積在血液中，身體就必須保留更多的的液體來稀釋這些鈉離子，而使心臟和血管需要使用更多的力量來運輸這些多餘的水分。這樣的情況會使血管硬化進而可能導致高血壓、心臟病或中風。
最近的證據也顯示高鹽飲食會影響身體的免疫系統。Muller的實驗室做的實驗顯示，鹽份會可刺激免疫反應並導致高血壓的Th-17免疫細胞增生，他和他的研究夥伴也在老鼠身上發現，過量的鹽份可能會引發像是多發性硬化的自體免疫疾病。
在此同時，Alm的實驗室也一直在進行腸道內微生物，和不同種類的免疫細胞族群交互作用的相關研究。他指出，腸道內微生物的組成會影響促進免疫反應的細胞，如:Th-17，和抵抗免疫反應的細胞之間的平衡。研究員同時也發現，益生菌可以將平衡導向抵抗免疫反應細胞的那一端。
在新的研究中，研究員們合作，試圖研究出高鹽飲食是如何影響微生物群以及其是否對我們的健康產生關鍵的影響。
在兩個禮拜的研究中，研究員們餵食老鼠含有4%的氯化鈉(食用鹽)的食物，而正常飲食中的氯化鈉含量為0.5%。他們發現此種飲食方式會導致一種稱為鼠乳桿菌(Lactobacillus murinus)細菌數目減少，而這些老鼠體中也同時含有較多的Th-17免疫細胞，血壓也升高了。
然而，這些高血壓的老鼠在給予含有鼠乳桿菌的益生菌後，體內的Th-17細胞數量下降，高血壓的情形也減緩了。
在12位人體實驗對象中，研究員發現在兩個星期中的每日飲食中，增加6000毫克的氯化鈉，也會改變腸道中細菌的組成。這些受試者體內的乳酸菌數量下降，且他們的血壓和Th-17細胞的數量都上升了。
然而，當這些受試者在進行高鹽飲食之前服用市售的益生菌，他們腸道內的乳酸菌數量和血壓都正常。
確切證據
Th-17細胞對高血壓或是其他高鹽飲食所導致的疾病的影響，目前還不清楚。
Alm說:「我們知道免疫系統大大的控制我們的身體，但實際上它所造成的影響遠遠超乎我們所認知的，它控制我們身體的機制至今仍是個謎。」
研究員們希望他們的發現和未來的研究，可以幫助我們更加了解和高鹽飲食相關的疾病的作用機制。Alm說:「如果你可以找到確切證據且瞭解這些分子究竟如何作用的，你將可以讓民眾更願意去遵守健康的飲食方式。」
Alm和其他微生物群資訊暨治療中心的人員，也在進行有關其他飲食中的成分，像是纖維、脂肪和蛋白質如何影響微生物群的研究。他們收集了上千種不同的腸道內含量最多的細菌，他們希望可以藉此了解細菌、飲食和疾病，例如:炎症性腸病彼此間的關係。
此研究是由德國心血管研究中心(German Center for Cardiovascular Research)、麻省理工學院微生物群資訊暨治療中心和MetaCardis 財團贊助。