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Journal of Lipid Research, Vol 36, 1325-1333, Copyright © 1995 by Lipid Research, Inc.
Biliary haptoglobin, a potent promoter of cholesterol crystallization at physiological concentrations
G Yamashita, SG Corradini, R Secknus, A Takabayashi, C Williams, L Hays, AL Chernosky and RT Holzbach
Gastrointestinal Research Unit, Cleveland Clinic Foundation, OH 44195- 5218, USA.
BACKGROUND/AIMS: Several proteins present in human bile have been reported
to promote cholesterol crystallization and thus are potentially important
in the formation of cholesterol crystals as the initial stage in gallstone
pathogenesis. To be physiologically relevant, such proteins must either be
present in high concentration in bile or have a potent promoting activity.
The current study explored several of the more abundant but unexamined
biliary proteins based upon their also having sufficiently high serum
concentrations that antibodies were available for both their isolation and
quantitation. METHODS: Protein purification was accomplished by
immunoaffinity chromatography of bile followed by delipidation. Con A
affinity chromatography of bile was used to obtain the bound fraction, a
portion of which was delipidated. Crystallization-promoting activity of
both the purified proteins and Con A-bound glycoprotein fractions (CABG)
was measured by a photometric crystal growth assay. A competitive antibody-
capture ELISA assay was developed to measure concentrations of alpha 1-
antitrypsin, transferrin, and haptoglobin in native bile. RESULTS: At their
relevant physiological concentrations, biliary haptoglobin (15
micrograms/ml) had a crystallization-promoting activity twice that of the
biliary IgM (75 micrograms/ml) used as a reference standard (P < 0.05).
Biliary transferrin (20 micrograms/ml) had only modest promoting activity
(P < 0.05). Biliary alpha 1-antitrypsin (50 micrograms/ml), by contrast,
showed no promoting activity. Delipidation of the CABG fraction decreased
its promoting activity by 75%. Biliary haptoglobin accounts for about 30%
of delipidated total CABG-promoting activity. CONCLUSIONS: Biliary
haptoglobin at its physiological concentration has a highly potent
crystallization-promoting activity and thus becomes a candidate for major
attention in understanding gallstone pathogenesis.(ABSTRACT TRUNCATED AT
250 WORDS)

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Copyright © 1995 by the American Society for Biochemistry and Molecular Biology.
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