MSGID: 1:317/3 64a643a5   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    New insights into the structural changes associated with osteoarthritis   
      
      
     Date:   
         July 5, 2023   
     Source:   
         Carl R. Woese Institute for Genomic Biology, University of Illinois   
         at Urbana-Champaign   
     Summary:   
         Osteoarthritis is the most common degenerative joint disease,   
         affecting 22% of adults over 40 globally. Although the condition   
         has been extensively studied through a medical perspective, the   
         molecular changes associated with osteoarthritis remain unclear. In   
         a new study, researchers have used a combination of techniques to   
         track the progression of the disease and the changes associated   
         with it.   
      
      
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   FULL STORY   
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   Osteoarthritis is the most common degenerative joint disease,   
   affecting 22% of adults over 40 globally. Although the condition has   
   been extensively studied through a medical perspective, the molecular   
   changes associated with osteoarthritis remain unclear. In a new study,   
   researchers have used a combination of techniques to track the progression   
   of the disease and the changes associated with it.   
      
   The cartilage in the joints, along with a lubricant known as the synovial   
   fluid, provides a smooth surface that helps withstand weight-bearing   
   movements.   
      
   The fluid contains several molecules, including hyaluronan (HA) and   
   phospholipids. Since the cartilage environment cannot be quickly healed   
   or repaired, researchers have tried to diagnose the early stages of   
   joint disease by monitoring the molecular weight and concentration of HA.   
      
   "Although we know that in healthy joints there is very low friction,   
   it is unclear which other molecules are involved and how they change   
   during osteoarthritis," said Rosa Espinosa-Marzal (EIRH), Donald Biggar   
   Willett Faculty Scholar and a professor of environmental engineering &   
   science, and materials science & engineering. "During the early stages   
   of osteoarthritis, cartilage starts degrading, and previous research has   
   shown that the molecular composition of the synovial fluid changes. We   
   wanted to see if the two changes are related to each other."  In a   
   healthy joint, the molecular weight of HA varies between 2-20 MDa with   
   a concentration ranging from 1-4 mg/ml. However, in diseased joints, HA   
   is broken down resulting in a lower molecular weight. Additionally, its   
   concentration is also reduced by ten times. Based on these observations,   
   made by other researchers, the study looked at how the concentration   
   and molecular weight of HA influences the structure of healthy and   
   diseased joints.   
      
   To do so, the researchers combined vesicles with high and low molecular   
   weight HA. Using neutron scattering and light scattering, they discovered   
   that the molecular weight of HA can vastly change the structure of the   
   vesicles. Lower molecular weight HA, which mimics osteoarthritis-diseased   
   joints, results in larger vesicle size. They also observed that the   
   molecular weight of HA changes the thickness of the phospholipid layers   
   in the joints.   
      
   The researchers also studied how these differences can influence the   
   formation of a protective film; in joints this film is responsible for the   
   very low friction we need for unhindered motion. Once again, they used a   
   combination of techniques, quartz crystal microbalance and atomic force   
   microscopy, to examine how these molecules assemble on gold surfaces.   
      
   "The formation of a film is possible only when there is an optimal   
   concentration of HA and phospholipids. Even though the gold surfaces have   
   very little in common with cartilage, our studies indicate that there   
   could also be an optimum concentration under biological conditions,"   
   Espinosa-Marzal said.   
      
   "This is an important observation because we can use the concentration   
   changes as a diagnostic tool."  "We are at a point where you need   
   to use multiple techniques on a complex system like this," said Mark   
   Rutland, a professor of surface science at the KTH Royal Institute of   
   Technology. "None of these techniques alone would have given us any   
   insight. The key was to look at all the different effects and put the   
   pieces together to show that the molecular weight of HA has a huge effect   
   on the characteristics of the layer that is formed with phospholipids."   
   The researchers are now working on using cartilage to understand whether   
   their observations with gold surfaces also hold true in a biologically   
   relevant system. They are also interested in studying the other molecular   
   components that are found in joints to build a more comprehensive model   
   of the changes that are associated with osteoarthritis.   
      
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   Content may be edited for style and length.   
      
      
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   Journal Reference:   
      1. Kangdi Sun, Tooba Shoaib, Mark W. Rutland, Joesph Beller,   
      Changwoo Do,   
         Rosa M. Espinosa-Marzal. Insight into the assembly   
         of lipid-hyaluronan complexes in osteoarthritic   
         conditions. Biointerphases, 2023; 18 (2) DOI: 10.1116/6.0002502   
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   Link to news story:   
   https://www.sciencedaily.com/releases/2023/07/230705143002.htm   
      
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