1H-NMR-Based Analysis for Exploring Knee Synovial Fluid Metabolite Changes after Local Cryotherapy in Knee Arthritis Patients

Rehabilitation using cryotherapy has widely been used in inflammatory diseases to relieve pain and decrease the disease activity. The aim of this study was to explore the metabolite changes in inflammatory knee-joint synovial fluids following local cryotherapy treatment (ice or cold CO2). We used proton nuclear magnetic resonance (1H NMR) spectroscopy to assess the metabolite patterns in synovial fluid (SF) in patients with knee arthritis (n = 46) before (D0) and after (D1, 24 h later) two applications of local cryotherapy. Spectra from aqueous samples and organic extracts were obtained with an 11.75 Tesla spectrometer. The metabolite concentrations within the SF were compared between D1 and D0 using multiple comparisons with the application of a false discovery rate (FDR) adjusted at 10% for each metabolite. A total of 32 metabolites/chemical structures were identified including amino acids, organic acids, fatty acids or sugars. Pyruvate, alanine, citrate, threonine was significantly higher at D1 vs D0 (p < 0.05). Tyrosine concentration significantly decreases after cryotherapy application (p < 0.001). We did not observe any effect of gender and cooling technique on metabolite concentrations between D0 and D1 (p > 0.05). The present study provides new insight into a short-term effect of cold stimulus in synovial fluid from patients with knee arthritis. Our observations suggest that the increased level of metabolites involved in energy metabolism may explain the underlying molecular pathways that mediate the antioxidant and anti-inflammatory capacities of cryotherapy.

Revisiting the molecular structure of collagen

The triple helix is a specialized protein motif found in all collagens. Although X-ray diffraction studies of collagen began in the 1920s, the very small amount of data available from fiber diffraction of native collagen caused the determination of its molecular conformation to take a very long time. In the early 1950s, two plausible fiber periods of about 20 and 30 A were proposed, together with corresponding single-strand models having 7/2- and 10/3-helical symmetry, respectively. The first framework of the triple helix was proposed by Ramachandran and Kartha in 1955. In the same year, Rich and Crick proposed another structure with the same framework that avoided some of the steric problems of the first model. Their framework, which involved a triple-helical structure with a fiber period of 28.6 A and 10/3-helical symmetry, was exactly the same as one of two single-strand models for collagen proposed at that time, except for the number of strands. At that time, however, nobody considered the triple-strand model with the other framework, with a fiber period of 20 A and 7/2-helical symmetry, until Okuyama et al. detected this structure in the single crystal of (Pro-Pro-Gly)(10) in 1972. Although they proposed this structure as a new structural model for collagen in 1977, it has not been acknowledged as such, but instead has been regarded only as a model for a collagen-like peptide. In 2006, it was shown that both 7/2- and 10/3-helical models could explain X-ray diffraction data from native collagen quantitatively. Furthermore, during the past decade, many single crystals of collagen-model peptides have been analyzed at high resolution. The helical symmetries observed in these model peptides are very close to the ideal 7/2-helical symmetry, whereas no supporting data were found for the 10/3-helical model. This evidence strongly suggests that an average molecular structure of native collagen is the 7/2-helical model rather than the prevailing Rich and Crick (10/3-helical) model. Knowing the correct molecular structure, the driving force for the formation of a quarter-staggered structure in collagen fibrils will be elucidated in the near future by analysis incorporating the molecular structure of collagen and its amino acid sequence.