Ionic Profile of Synovial Fluids in Gout, Calcium Pyrophosphate Crystal Deposition Disease and Osteoarthritis
Mete Kayatekin (1), Dione Saurat1, Isabelle Rubera (1), Charles Leroy (2), Pascal Richette (2,3), Hang Korng Ea (2,3), Christophe Duranton1
Affiliation(s):
1. University Côte d'Azur, CNRS UMR-7370, Laboratoire de Physiomédecine Moléculaire, Labex ICST, Nice, France
2. Bioscar, INSERM UMR-1132, Université Paris Cité, Hôpital Lariboisière, Centre Viggo Petersen, AP-HP, Paris, France
3. Rheumatology department, Viggo Petersen center, DMU Locomoteur, Hôpital Lariboisière, AP-HP, Paris, France
Gout, secondary monosodium urate - (MSU) crystal deposition, calcium pyrophosphate (CPP) crystal deposition (CPPD) and osteoarthritis (OA) are main adult arthropathies responsible for joint swelling and pain. The analysis of synovial fluid (SF) is the key procedure in the diagnosis of these diseases. SF of MSU and CPP crystal-induced joint inflammation is characterized by the presence of the pathogenic crystals and a high concentration of cells (> 2000/ml). In contrast, OA SF contains low cell concentration (<1500/ml). SF cell concentration distinguishes the inflammatory and mechanical causes of arthropathies. However, our knowledge of synovial fluid ions composition is very limited.
The aims of this study were to characterize the composition and the ion concentrations of SF in gout, CPP crystal deposition and OA.
Methods: SF were harvested from patients who experienced joint swelling during gout flare (n=19), CPP crystal-induced flare (n=22) or OA (n=33). SFs were centrifuged and supernatants were collected and stored at -80°C until analysis. SF osmotic pressure was measured by freezing point technique (Roebling Osmometer automatic) and concentration of the main ions (lactate, Cl-, citrate, sulfate, phosphate and pyrophosphate (PPi)) by ion chromatography (Dionex, ICS-5000).
Results: Our data (see table below) showed significant difference in osmotic pressure in SF of patients diagnosed with OA compared to gout or CPPD. We also measured significative difference in anionic profile of the different SF samples: Lactate concentration was higher in SFs of CPPD and in gout patients compared to OA. Chloride and citrate concentrations were significantly lower in gout and CPPD patients compared to OA. Moreover, we didn’t see any difference in sulfate and phosphate concentration. Interestingly, in SFs from gout patients, we measured a significantly lower PPi concentration compared to OA or CPPD. table 1.
For the first time in a large cohort of 74 patients the ion concentrations and osmotic pressure of SFs harboring different arthropathies were measured. According to our results, we observed a specific ion concentration profile in crystal-mediated arthropathies (lower osmotic pressure and chloride concentration and higher lactate concentration) compared to OA. Additionally, we also measured a lower PPi concentration in gout SFs compared to OA or CCA diseases suggesting that PPi might be considered as a valuable biomarker to differentiate between different arthropathies. Altogether, our results suggest that SF is a dynamic fluid and ion concentrations are varying according to the different arthropathies.
