Dial Elizabeth J, Rooijakkers Suzan H M, Darling Rebecca L, Romero Jim J, Lichtenberger Lenard M
Department of Integrative Biology and Pharmacology, Medical School, The University of Texas Health Science Center at Houston, Houston, Texas 77030, USA.
J Gastroenterol Hepatol. 2008 Mar;23(3):430-6. doi: 10.1111/j.1440-1746.2007.05153.x. Epub 2007 Sep 12.
The mechanism which protects the biliary and intestinal mucosa from the detergent properties of bile acids is not fully understood. We employed three contrasting in vitro model systems (human red blood cells, polarized intestinal [Caco-2] cells, and synthetic liposomes), to compare the efficacy of saturated and unsaturated phosphatidylcholine (PC) to protect cells and membranes from bile salt injury.
Hemolysis of red blood cells, electrical resistance across confluent monolayers of Caco-2 cells, and disruption of synthetic PC liposomes were assessed after incubation with varying concentrations of bile salt (sodium deoxycholate) alone or in the presence of saturated or unsaturated PC.
The hemolytic activity of deoxycholate on red blood cells was observed at > or =2 mM, and could be blocked by equimolar concentration or greater of both saturated or unsaturated PC. In contrast, exposure of Caco-2 cells to deoxycholate at > or =0.8 mM induced a maximal decrease in resistance, which was reversed by > or =0.8 mM unsaturated PC or 5 mM saturated PC. Similarly, synthetic liposomes were permeabilized by 0.8 mM deoxycholate and were protected by a lower concentration of unsaturated PC (2 mM) than saturated (5 mM).
Cells can show variable resistance to bile salt toxicity. Extracellular PC, especially in the unsaturated state, can directly protect cell and artificial membranes from bile salt injury. These findings support a role for biliary PC in the formation of mixed micelles that have low cytotoxic properties.
保护胆道和肠黏膜免受胆汁酸去污剂特性影响的机制尚未完全明确。我们采用了三种截然不同的体外模型系统（人红细胞、极化肠上皮[Caco-2]细胞和合成脂质体），以比较饱和与不饱和磷脂酰胆碱（PC）保护细胞和膜免受胆盐损伤的效果。
分别单独用不同浓度的胆盐（脱氧胆酸钠）或在饱和或不饱和PC存在的情况下孵育人红细胞、Caco-2细胞融合单层以及合成PC脂质体后，评估红细胞的溶血情况、Caco-2细胞融合单层的电阻以及合成PC脂质体的破坏情况。
当脱氧胆酸钠浓度≥2 mM时，可观察到其对红细胞的溶血活性，且等摩尔浓度或更高浓度的饱和或不饱和PC均可阻断这种活性。相比之下，当Caco-2细胞暴露于浓度≥0.8 mM的脱氧胆酸钠时，电阻会出现最大程度降低，而浓度≥0.8 mM的不饱和PC或5 mM饱和PC可使其恢复。同样，0.8 mM的脱氧胆酸钠可使合成脂质体透化，且不饱和PC（2 mM）比饱和PC（5 mM）在更低浓度时就能起到保护作用。
细胞对胆盐毒性的耐受性可能存在差异。细胞外PC，尤其是不饱和状态的PC，可直接保护细胞和人工膜免受胆盐损伤。这些发现支持了胆汁PC在形成具有低细胞毒性的混合微胶粒过程中发挥作用。
