肉鹼(L-Carnitine)是什麼?
肌肉或心臟的心肌細胞,靠的是脂肪酸(fatty acid)的代謝來產生收縮的力量,而脂肪酸要能夠進到粒線體(驅動細胞的小馬達)當中來產生能量,得靠肉鹼(L-Carnitine)這個小幫手的幫忙,因此,要發揮肌肉的力量,肉鹼扮演關鍵的角色。在腎臟病患者體內,隨著腎功能下降,因為排出的量變少了,所以體內肉鹼濃度會逐漸上升,然而,一旦開始進入透析、洗腎,肉鹼的濃度就會下降,變得比一般人低。
為什麼透析會使得體內肉鹼的量變少?理由有四:
一、它是小分子,容易在透析過程中流失。
二、肉鹼主要來源是食物中的肉類,有些透析患者吃肉的量不足。
三、腎臟是製造肉鹼的工廠,然而功能喪失,製造也變少了。
四、透析患者的體內,會累積一些代謝不完全的毒素(Incompletely metabolized acyl groups),這些毒素,會把體內的肉鹼消耗掉,轉變成沒有用的代謝物(acylcarnitines)。換個角度想,肉鹼能夠犧牲小我,去中和掉這些毒素,可能可以換來身體的一些好處。
肉鹼在腎友體內的濃度比較低,會導致身體的問題嗎?
從肉鹼的功能看來,補充肉鹼可能改善的症狀有:貧血、透析中的不適、肌肉無力、運動耐力下降、心肌問題、高血脂、降低發炎反應、或無法長高(小孩) 。然而,林林總總這麼多的研究當中,就偏偏會有“這個說有效、那個說沒效”的情況,而有些看起來有效的結果,又受限於研究規模太小,或者沒有對照組,這樣的結果很難取信於人。也就是說,補充肉鹼對於剛剛那些症狀,是沒辦法保證有效的。
為什麼還是有人在用呢?而且,好像真的有改善呢?
一、補充肉鹼蠻安全的,沒有甚麼特別的副作用。不過,文章裡提到,最好用針劑方式補充,不建議用口服補充,因為真正吸收到身體裡的比例很難確定,而且經過腸道可能會有不好的代謝物。
二、在某些特定情況下,可以嘗試使用,例如:使用大量紅血球生成素,也難以治療的貧血(erythropoietin-resistant anemia)、透析當中的低血壓、心肌病變(cardiomyopathy)、以及肌肉無力,但即使是這些情況,也沒辦法保證療效。
三、確實有人試了有效,有人試了沒有效,但是,試了才知道,沒有哪一個研究能夠事前告訴我們,誰會有效。
再次強調,為什麼肉鹼的補充,無法成為治療的主流,因為研究所累積的證據不足,我們無法知道腎友用了效果如何,更何況,這是個自費的藥物,我們總是希望腎友花了錢,能夠看到療效。
參考文獻
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