Biochemistry
In the human cartilage the cells represent only 1-2% of the total volume, yet the cells are able to synthesize the intercellular matrix and to provide moderate repair capacity in case of a cartilage injury. The two major proteins in the cartilage is collagen and proteoglycan.
Collagens
More than 90% of all collagens in the articular cartilage is type II collagen but many other types of collagen is present as well, although in much lower density (type IX, X and XI, and collagens that are not exclusively cartilage specific collagens, such as type IV and VI). Type II collagen is highly cartilage-specific as the only other place where it is found is the inner gelatinous center of the intervertebral discs (annulus fibrosus).
Proteoglycans
Proteoglycans-PG (e.g., aggrecan, decorin, biglycan, fibromodulin) share a common characteristic as proteins, since all core protein has special sugar side chains (glycosaminoglycan -GAG). Aggrecan is the largest proteoglycan, and represents about 90% of the total PG content. Its shape in 3D is similar to the bottle washing brush and its molecular weight (2-3 million Da) is mostly due to the sugar side chains. (sulfated GAG and O-, and. N-linked oligosacharids). The protein has three globular domains, and between the second and third domain expands the long linear protein line covered by negatively charged sugar side chains. PG is attached to a long sugar molecule (hyaluronic acid), secured by the link protein. Up to 200 PG molecules may be attached to a hyaluronic molecule (aggregated – aggrecan).
Cartilage supporting dietary supplements are widely known. The two major type is chondroitin sulfate and glucosamine. Chondroitin sulfate is a sulfated GAG of a polymer composed of two alternating sugar molecules (N-acetilgalactosamine and glucuronic acid). The sugar polymer may contain up to a hundred sugar molecules, hence only a small fraction of the oral intake will be absorbed. Many recent large scale studies question the real therapeutical effect of chondroitin sulfate.
Chondroitin-4-sulfate - R1:H, R2:SO3, R3:H
Chondroitin-6-sulfate - R1:SO3, R2: H, R3:H
Glucosamine is an aminosugar, and is an important factor in the synthesis of different lipids, proteins and the glucosaminoglycans (GAG). Glucosamine sulfate is a well known dietary supplement in osteoarthritis. Many well conducted studies show its effectiveness in the treatment of osteoarthritis.
