Hyaluronic acid synovial production

The other major component of an articular joint is synovial fluid, named by Paracelsus after synovia (egg-white). It is essentially a dialysate of blood plasma with added hyaluronic acid. Synovial fluid contains complex proteins, polysaccharides, and other compounds. Its chief constituent is water (approximately 85%). Synovial fluid functions as a joint lubricant, nutrient for cartilage, and carrier for waste products. 

Yaron I, Shirazi I, Jndovich R, Levartovsky D, Caspi D, Yaron M (1999) Flnoxetine and amitriptyline inhibit nitric oxide, prostaglandin E2, and hyaluronic acid production in hnman synovial cells and synovial tissue cultures. Arthritis Rheum 42 2561-2568. 

McCarty, M.F. Enhanced synovial production of hyaluronic acid may explain rapid clinical response to high-dose glucosamine in osteoarthritis. Med. Hypoth. 1998, 50 (6), 507-510. 

Hyaluronic acid is a naturally occurring polysaccharide that is widely distributed in body tissues and intracellular fluids, including the aqueous and vitreous humour, synovial fluid, and in the ground substance that surrounds cells (1). It is a high-molecular weight substance originally developed for use as a vitreous replacement. Although 98% of the product consists of water, it is very viscoelastic. 

The method was developed by Robertson, Ropes, and Bauer (163) who used the native hyaluronic acid-protein complex from synovial fluid as the substrate. It was purified and concentrated by a series of precipitations and by dialysis. The final product contiuned 12.5% nitrogen and 7% amino sugar. 

Ragan and Meyer (354) have recently reported hyaluronic acid contents and relative viscosities of synovial fluids from the knee joints of 35 patients with rheumatoid arthritis and 11 patients without joint diseases. They found with very few exceptions that the apparent degree of polymerization of the hyaluronic acid was lower in the arthritic patients, although the total amount of the mucopolysaccharide present was greater. Hyaluronidase was not detected in joint fluid or in synovial or periarticular tissue and, in any event, its presence would not explain the increase in total hyaluronic acid. Therefore, it was concluded that the defect lies not in an enzymatic hydrolysis or nonspecific depolymerization but in abnormal synthesis of this polysaccharide, involving an increased production of incompletely polymerized hyaluronic acid. 

The site of origin of hyaluronic acid in the body is unknown. The presence of hyaluronate in ocular fluids and its absence from serum have been cited as evidence that it represents a secretion rather than a dialyzate (270). Meyer (264) has pointed out that the concept of synovial fluid as a dialyzate to which the mucin is added during passage through the connective tissue does not seem probable since, if such a mechanism exists, pleura and peritoneal fluid and lymph should likewise contain the mucin, which has not been shown to be the case. The fact that a viscous fluid appears in cultures of synovial tissue (426) was cited by him as evidence that hyaluronate is a secretory product of some cells of the synovial lining. This seems to be borne out by the fact that hyaluronic acid has been isolated from a synovioma, not only at the site of the tumor but in metastases in the liver (264). 

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