Inorganic pyrophosphate generation from adenosine triphosphate by cell-free human synovial fluid

Area of Science:

• Biochemistry
• Molecular Biology
• Rheumatology

Background:

• Extracellular adenosine triphosphate (ATP) is a signaling molecule in joints.
• The catabolism of ATP yields various products, including inorganic pyrophosphate (PPi).
• Understanding PPi production in synovial fluid (SF) is crucial for joint health and disease pathogenesis.

Purpose of the Study:

• To quantify the production of inorganic pyrophosphate (PPi) from extracellular adenosine triphosphate (ATP) in human synovial fluids (SF).
• To investigate the role of different joint conditions on ATP hydrolysis and PPi generation.

Main Methods:

• ATP hydrolysis rates were measured using the luciferase method in cell-free SF samples under physiological conditions.
• Simulated in vivo steady-state ATP levels were achieved by controlled infusion.
• Conversion of ATP to PPi and inorganic phosphate (Pi) was determined using radiolabeled ATP and enzymatic assays.

Main Results:

• All tested synovial fluids hydrolyzed ATP, with varying rates depending on the condition.
• Inorganic pyrophosphate (PPi) was the predominant product of ATP hydrolysis in most SF samples.
• Synovial fluids containing calcium pyrophosphate dihydrate (CPPD) crystals exhibited significantly faster ATP hydrolysis and higher PPi production compared to osteoarthritis (OA) SF.

Conclusions:

• Extracellular ATP catabolism in synovial fluid primarily yields PPi.
• The presence of CPPD crystals accelerates ATP hydrolysis and enhances PPi production.
• Ectonucleotide pyrophosphohydrolase activity in SF can account for observed PPi levels in joint diseases.