Research press release


Nature Medicine

New culprit compound in red meat linked to cardiovascular disease


Stanley Hazenたちはマウスを使って、L-カルニチンの血管疾患促進作用には、腸内細菌によるトリメチルアミン(TMA)への代謝が必要で、さらにこれがトリメチルアミンN-オキシド(TMAO)へと変換されることを突き止めた。ヒトでも同様に、L-カルニチンはTMA、さらにTMAOへと代謝される。ベジタリアン(菜食主義者)やヴィーガン(完全菜食主義者)では雑食のヒトに比べるとL-カルニチン代謝能力が低下しており、特定の腸内細菌も減少していることから考えると、赤肉を摂取すると、L-カルニチンをエネルギー源として利用できる腸内細菌が増殖しやすくなることがわかる。さらにHazenたちの報告によれば、血中のL-カルニチン濃度の高さと循環器疾患には関連があるが、それはTMAOレベルも高いヒトに限られるという。これは、L-カルニチンが病気に結びつくためには腸内細菌によって代謝される必要があるとの見方によく符合する。


The nutrient L-carnitine, found in red meat and used as a dietary supplement, is associated with cardiovascular disease in people and causes vascular disease in mice, as reported in a study published online this week in Nature Medicine. The pathogenic effects of L-carnitine do not seem to be direct, but require its further metabolism by bacteria in the gut.

Stanley Hazen and colleagues report that in mice, the disease-promoting effects of L-carnitine require its metabolism by gut bacteria into the compound trimethylamine (TMA), which is further converted to trimethylamine N-oxide (TMAO). Likewise, in humans, L-carnitine is metabolized to TMA and TMAO. Vegetarians and vegans have a diminished ability to metabolize L-carnitine compared to omnivores and decreased amounts of specific types of gut bacteria suggesting that ingestion of red meat favors the growth of gut bacteria that can use L-carnitine as an energy source. Moreover, Hazen and colleagues report that high levels of L-carnitine in the blood are associated with cardiovascular disease, but only in those individuals who also have high TMAO levels, consistent with the idea that L-carnitine must be metabolized by gut bacteria to promote disease.

These results point to L-carnitine, rather than saturated fat and cholesterol, as explaining the link between red meat consumption and cardiovascular disease. Also, the findings have relevance to the widespread use of L-carnitine as a dietary supplement, and the authors suggest that the safety of this practice should be further investigated.

doi: 10.1038/nm.3145


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