Journal of Lipid Research, Vol 22, 122-130, Copyright © 1981 by Lipid Research, Inc.
Studies on the source of urinary cholesterol in the normal human male
RJ Cenedella and JA Belis
The aim of the present study was to obtain information on the source of
urinary cholesterol in normal men of various age groups (22-25, 37-42,
greater than 63 yrs). Aliquots of 24-hr urine samples were fractionated by
ultracentrifugation. Between 10-20% of the total cholesterol in urine
(measured by gas-liquid chromatography) separately sedimented after 2 x
10(4) g-min and after 4 x 10(5) g-min of centrifugation. However, an
average of more than 50% of the total sedimented after 6 x 10(6) g-min and
only 10-20% of total cholesterol remained in this supernatant. These
results indicate that most of the cholesterol in urine of normal males is a
component of a light particulate fraction. Little difference was seen in
the distribution of urinary cholesterol among the various age groups
examined The 4 x 10(5) g-min supernatant from 24-hour total urine samples
was recentrifuged at 10(5) g for 60 min. The resulting pellet (100 P) was
assayed for protein, total cholesterol and phospholipid. The cholesterol
was 12-14% esterified. A molar ratio of total cholesterol to phospholipid
of 1 to 0.8 was calculated. Assay of the 100 P fraction for marker enzymes
showed an activity pattern characteristic for plasma membranes.
Fractionation of the 100 P proteins by electrophoresis and separation of
the 100 P phospholipids by thin-layer chromatography revealed patterns
clearly different from those of human red cell plasma membrane. Electron
micrographs of the 100 P fraction revealed an appearance similar to that of
deteriorated membranes. The results suggest that most of the cholesterol in
urine of the adult human male is present as a component of membranes
derived from endogenous cells of the urogenital system.
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