Urinary cholesterol: its association with a macromolecular protein-lipid complex.

Area of Science:

• Biochemistry
• Urology
• Lipid Metabolism

Background:

• Urinary cholesterol excretion is a complex process.
• Understanding the forms of urinary cholesterol is crucial for diagnosing kidney and urogenital diseases.

Purpose of the Study:

• To characterize cholesterol-containing complexes in urine from normal subjects and patients with urinary cholesterol hyperexcretion.
• To identify the macromolecular forms of urinary cholesterol and their association with disease states.

Main Methods:

• Gel chromatography (Bio-Gel A-5m)
• Agarose electrophoresis
• Immunodiffusion
• Electron microscopy
• Chemical analysis (protein, triglycerides, cholesterol, phospholipids)
• Ultracentrifugation
• SDS polyacrylamide electrophoresis

Main Results:

• The majority of urinary cholesterol in normal subjects and patients is associated with a macromolecular complex (>5 x 10^6 daltons).
• In some patients with cholesterol hyperexcretion, additional high-density lipoproteins (HDL) or both HDL and low-density lipoproteins (LDL) were found.
• The isolated complex contains protein (46.0%), triglycerides (16.3%), cholesterol (8.2%), and phospholipids (29.5%), with lipoprotein-like particle morphology.
• Immunodiffusion suggests the complex shares characteristics with kidney and liver membrane-associated protein-lipid particles (proteolipids).

Conclusions:

• The primary form of urinary cholesterol in normal and disease states is a large macromolecular complex.
• This complex exhibits characteristics of membrane-associated proteolipids from the kidney and liver.
• Abnormalities in these proteolipids may contribute to urinary cholesterol hyperexcretion in certain diseases.