肝脏微粒体膜脂质成分及膜流动性变化对胆红素葡萄糖醛酸化的影响

Effect of changes in lipid composition and fluidity of hepatic microsome membrane on bilirubin glucuronidation

目的 研究致胆固醇结石饮食对肝脏微粒体膜成分及流动性的影响 ,探讨影响胆红素葡萄糖醛酸化的因素。方法 通过饮食诱发小鼠胆囊胆固醇结石 ,检测小鼠胆汁中胆红素成分、肝脏胆红素尿苷二磷酸葡萄糖苷醛转移酶 (B UGT)活性及肝脏微粒体膜脂质成分和微粒体膜流动性变化。结果 胆固醇结石小鼠肝脏B UGT活性比正常对照低 (P <0 0 1) ,而胆汁中单结合胆红素占总胆红素的比例升高 (P <0 0 1) ,二者呈显著负相关关系 (r =- 0 6 5 45 ,P <0 0 1) ;同时发现胆固醇结石小鼠肝脏微粒体膜脂区荧光偏振度较正常对照明显升高 (P <0 0 1) ,而微粒体膜胆固醇含量升高 (P <0 0 1) ,微粒体膜胆固醇的含量及膜的荧光偏振度与肝脏B UGT活性的高低显著负相关 ,相关系数 r分别为 - 0 6 36 9(P <0 0 1)和 - 0 45 32 (P <0 0 5 )。结论 致胆固醇饮食增加了肝脏微粒体膜的胆固醇含量和胆固醇与磷脂的比例 ,降低了肝脏微粒体膜的流动性 ,可能是造成胆红素酯化障碍 ,胆汁中单结合胆红素增多 。

Objective To investigate the effect of the lipid composition and fluidity of hepatic microsome membrane on bilirubin glucuronidation in mice after feeding with lithogenic diets and to explore the relevant factors possibly influencing the bilirubin glucuronidation. Methods Cholesterol gallstones were induced in mice by feeding with lithogenic feeders(gallstone group, GS group). The bilirubin content in bile and the activity of bilirubin UDP glucuronosyltransferase(B UGT) in liver tissue were measured by HPLC and spectrophotometry, and the change in lipid composition using chemical and enzymatic analysis and fluidity of hepatic microsome membrane by fluorescence spectrophotometry were observed and compared with those in mice fed with conventional commercial chow(normal control group, NC group). Results 1. GS group mice showed lower activity of B UGT in liver tissue (P<0.01) but a higher ratio of monoconjugated bilirubin(MCB)/total bilirubin (TB) appeared in bile than that of the NC group (P<0 01). 2. The B UGT activity was well correlated negatively with the MCB/TB value (r=-0.6545, P<0 01). 3. The lipid composition including total cholesterol (CHO), phospholipid (PL) contents and the ratio of CHO/PL in hepatic microsome, and the microsome membrane fluorescent polarization in GS group were all significantly elevated when compared to those of NC group (P<0 01 and P<0 01). 4. Both lipid composition of liver microsome and membrane fluorescent polarization of liver tissue were also significantly negatively correlated with B UGT activity (r=-0 6369, P<0.01; r=-0.4532,P<0.05, respectively). Conclusions The lithogenic diets can not only increase the CHO content and the ratio of CHO/PL in hepatic microsome, but also decrease the fluidity of hepatic microsome membrane simultaneously which might contribute to disordered bilirubin glucuronidation, resulting in an higher MCB production with early nucleation process initiated in the bile.