Hyaluronic acid

What is Hyaluronic Acid (HA)?

HA is a non-sulfated glycosaminoglycan distributed widely throughout connective, epithelial, and neural tissues. The average 70-kg man has roughly 15 grams of hyaluronan in his body, one-third of which is turned over (degraded and synthesised) every day.1

HA in Joints

Hyaluronan is an important component of articular cartilage, where it is present as a coat around each cell (chondrocyte). When aggrecan monomers bind to hyaluronan in the presence of link protein, large highly negatively-charged aggregates form. These aggregates imbibe water and are responsible for the resilience of cartilage (its resistance to compression). The molecular weight (size) of hyaluronan in cartilage decreases with age, but the amount increases. 2

HA in Synovial Fluid

Hyaluronic acid (HA) plays a large part in synovial fluid where it is responsible for the fluid’s viscous and elastic properties, which are essential for healthy joint function. The majority of studies have examined intra-articular injections of HA.

HA and Collagen

Polish researchers reported in vitro, HA exerts a protective effect against interleukin-1-induced inhibition of collagen biosynthesis. 3. A review from the Orthopedic Specialists of Louisiana, Shreveport, noted intra-articular HA viscosupplementation does appear to improve joint function and help relieve OA-related pain. 4 Further, it added, reduction of NSAID medication use and delayed need for surgical intervention could also mean total cost savings through the use of HA viscosupplementation. Similarly, Canadian researchers reported intraarticular HA injections can improve resting and walking pain in knee OA patients, with symptom control lasting approximately six months. 5 And the AHRQ review released in September 2007 stated results from 42 trials (n=5,843) generally showed positive effects on pain and function scores with HA viscosupplementation; however, it qualified the outcome, stating there is considerable uncertainty due to trial quality, publication bias and unclear clinical significance. 6

HA is a component of collagen in the joints and in type II collagen or collagen hydrolysate supplements. Cartilage is also an important factor in the protection of joints, and one of its key components is collagen. Chicken collagen is a popular material because it provides chondroitin, HA and type II collagen, which is a rope-shaped, fiber-like protein that gives cartilage its structural strength. Researchers from the University of Illinois College of Medicine at Chicago reviewed medical literature on collagen hydrolysate, and found orally administered collagen hydrolysate is absorbed and accumulates in cartilage. 7 Further, it appears to stimulate a significant increase in synthesis of extracellular matrix molecules by chondrocytes.

HA in Skin

Hyaluronan is also a major component of skin, where it is involved in tissue repair. When skin is excessively exposed to UVB rays, it becomes inflamed (sunburn) and the cells in the dermis stop producing as much hyaluronan, and increase the rate of its degradation. Hyaluronan degradation products also accumulate in the skin after UV exposure. 8

Reference:
1. Stern R (August 2004). "Hyaluronan catabolism: a new metabolic pathway". Eur J Cell Biol 83 (7): 317-25. PMID 15503855. Retrieved on 2007-06-12. 
2. Holmes et al. (1988) Hyaluronic acid in human articular cartilage. Age-related changes in content and size. Biochem J 250:435-441.
3.  Karna E et al. “Protective effect of hyaluronic acid on interleukin-1-induced deregulation of beta(1)-integrin and insulin-like growth factor-I receptor signaling and collagen biosynthesis in cultured human chondrocytes.” Mol Cell Biochem. 2007 Sep 25; [Epub ahead of print].
4. Waddell DD. “Viscosupplementation with hyaluronans for osteoarthritis of the knee: clinical efficacy and economic implications.” Drugs Aging. 2007;24(8):629-42.
5. Petrella RJ. “Hyaluronic acid for the treatment of knee osteoarthritis: long-term outcomes from a naturalistic primary care experience.” Am J Phys Med Rehabil. 2005 Apr;84(4):278-83.
6. Samson DJ et al. Op cit..
7. Bello AE, Oesser S. “Collagen hydrolysate for the treatment of osteoarthritis and other joint disorders: a review of the literature.” Curr Med Res Opin. 2006 Nov;22(11):2221-32.
8. Averbeck M et al. (2007) Differential regulation of hyaluronan metabolism in the epidermal and dermal compartments of human skin by UVB irradiation. J Invest Dermatol 127:687-697.