Journal of Lipid Research, Vol 25, 655-664, Copyright © 1984 by Lipid Research, Inc.
Urinary cholesterol: its association with a macromolecular protein- lipid complex
D Jungst, H Weiser, E Siess and HJ Karl
The cholesterol-containing complexes in the urine of normal subjects and
patients with diseases accompanied by hyperexcretion of urinary cholesterol
were characterized. In normal subjects, the major portion of the recovered
urinary cholesterol was eluted in the void volume fractions after gel
chromatography on Bio-Gel A-5m; this suggested an association with a
macromolecular complex above 5 X 10(6) daltons. A comparable elution
pattern was seen in most of the urines of the patients with benign or
malignant diseases of the kidneys or the urogenital tract. However, in
single patients with hyperexcretion of urinary cholesterol, considerable
amounts of cholesterol were detected in the included volume of the column.
This was caused by additional excretion of high density lipoproteins or
both high and low density lipoproteins in the urine which could be
identified in these fractions by agarose electrophoresis and
immunodiffusion. These results indicate that the macromolecular complex
represents the majority of the recovered urinary cholesterol in normal
subjects and in disease states with known hyperexcretion. Macroscopically,
the isolated cholesterol- containing complex in the void volume fractions
was turbid, and electron microscopy showed lipoprotein-like particles with
diameters ranging from 300 to 700 A. The chemical analysis revealed median
values of protein (46.0%), triglycerides (16.3%), cholesterol (8.2%), and
phospholipids (29.5%) in normal subjects and comparable results in the
patients with benign or malignant diseases of the kidney and the urogenital
tract. Ethanolamine glycerophospholipids, phosphatidylcholine,
sphingomyelin, and phosphatidylserine were the main phospholipid
components. After ultracentrifugation in a CsCl gradient, the
cholesterol-containing complex was found between densities 1.1 and 1.3
g/ml. By SDS polyacrylamide electrophoresis, up to 17 protein subunits in
the molecular weight range of 14,000 to 87,500 were separated.
Immunodiffusion studies showed in about 40% precipitin lines against
anti-human albumin, but no reactions against anti-human apoHDL and
anti-human apoLDL. However, immunodiffusion of the macromolecular complex
against anti-liver-specific and anti-kidney- specific lipoproteins revealed
single precipitin lines. In conclusion, the isolated cholesterol-containing
urinary complex showed many characteristics of membrane-associated
protein-lipid particles of the human kidney and even the liver. These
proteolipids are the major source of urinary cholesterol in normal and
disease states.(ABSTRACT TRUNCATED AT 400 WORDS)
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