Human cartilage lysozyme

Area of Science:

• Biochemistry
• Biomaterials Science
• Rheumatology

Background:

• Lysozyme is an enzyme present in various human tissues.
• Cartilage is a complex biomaterial with a unique extracellular matrix.
• Understanding the localization and binding of lysozyme in cartilage is crucial for joint health.

Purpose of the Study:

• To measure lysozyme content in human cartilage.
• To investigate factors controlling lysozyme binding within cartilage.
• To explore the potential role of cartilage lysozyme in rheumatoid arthritis.

Main Methods:

• Lyophilized human costal and hyaline cartilage were incubated in various buffers and salt solutions.
• Extraction efficiency was studied using different pH, monovalent, and divalent cation concentrations.
• Lysozyme binding capacity was assessed by incubating cartilage with exogenous lysozyme.

Main Results:

• Lysozyme was extracted from hyaline cartilage using alkaline buffers and high salt concentrations.
• Cation-dependent extraction correlated with chondroitin sulfate binding affinities.
• Extractable lysozyme content varied between cartilage types, ranging from 0.80 to 3.36 µg/mg.
• Cartilage demonstrated a binding capacity of 0.053 equivalents of lysozyme per equivalent of chondroitin sulfate.
• Fibrocartilage and synovium showed no detectable lysozyme, despite synovium's lysosomal content.
• Lysozyme extraction paralleled uronic acid release under mild conditions.
• Cartilage lysozyme is extracellular, non-lysosomal, and acts as a counterion to glycosaminoglycans.

Conclusions:

• Lysozyme is present in human hyaline cartilage, bound to glycosaminoglycans.
• The extracellular and non-lysosomal nature of cartilage lysozyme suggests specific functional roles.
• Cartilage degradation may contribute to elevated lysozyme levels in rheumatoid arthritis patients.