Abstract:
:Precipitation of cholesterol crystals from vesicles is an important step in the pathogenesis of cholesterol gallstones. Little is known, however, about the kinetics and the mechanisms involved in cholesterol crystallization. Therefore, the time course of cholesterol crystal precipitation and lipid exchange between vesicles and micelles were monitored in a model bile system. Vesicles obtained from supersaturated model bile (cholesterol saturation index (CSI) 1.4; 10 g/dl) by KBr density gradient ultracentrifugation, were incubated with various bile salts: deoxycholate (DC), chenodeoxycholate (CDC), cholate (C), ursodeoxycholate (UDC), and their respective taurine and glycine conjugates. Vesicle integrity was assessed in a leakage-assay of carboxyfluorescein-loaded vesicles (0-15 min) and by the change in optical absorbance at 340 nm of a vesicle solution (0-50 min). Fluorescence increased within 1 min after addition of bile salt, and was stable within 5-10 min. After addition of bile salt, absorbance fell immediately and stabilized within 30 min. Fluorescence and absorbance were dependent on bile salt hydrophobicity and concentration. At several time points after addition of bile salt to vesicles (from 1 to 72 h), the extent of cholesterol nucleation was determined semiquantitatively and incubation mixtures were again subjected to ultracentrifugation to assess the lipid distribution among residual vesicles, de novo formed mixed micelles, and cholesterol crystals. Nucleation occurred within 0.5 h after exposure of vesicles to the hydrophobic bile salts DC or CDC, and the cholesterol/phospholipid (c/p) ratio of the vesicles showed a transient rise from 1.45 to 3-4 (at t = 0.5 h) that coincided with the appearance of mixed micelles. Then the vesicular c/p ratio decreased to 0.6-0.8 (at t = 24 h) concomitantly with increasing precipitation of cholesterol crystals. In the case of UDC, the most hydrophilic bile salt used, < 5% micellization, no nucleation, and a constant vesicular c/p ratio were observed. We conclude that under the conditions used in the present model study, the kinetics of cholesterol crystallization are governed by the hydrophobicity of the added bile salts and their capacity to form mixed micelles. The results emphasize the pivotal role of time, and the dynamic aspects of the processes involved in cholesterol crystal formation.
journal_name
J Lipid Resjournal_title
Journal of lipid researchauthors
van de Heijning BJ,Stolk MF,van Erpecum KJ,Renooij W,Groen AK,vanBerge-Henegouwen GPsubject
Has Abstractpub_date
1994-06-01 00:00:00pages
1002-11issue
6eissn
0022-2275issn
1539-7262journal_volume
35pub_type
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journal_title:Journal of lipid research
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journal_title:Journal of lipid research
pub_type: 临床试验,杂志文章,随机对照试验
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更新日期:1994-04-01 00:00:00
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journal_title:Journal of lipid research
pub_type: 杂志文章
doi:
更新日期:1999-07-01 00:00:00
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journal_title:Journal of lipid research
pub_type: 杂志文章
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journal_title:Journal of lipid research
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