Shark cartilage. A treatment for cancer, psoriasis, arthritis, and a number of other medical conditions. Detailed information provided with links to the National Cancer Institute.
Shark cartilage has been investigated as treatments for cancer, psoriasis, arthritis, and a number of other medical conditions for more than 30 years. At least some of the interest in cartilage as a treatment for cancer arose from the mistaken belief that sharks, whose skeletons are made primarily of cartilage, are not affected by this disease. Although reports of malignant tumours in sharks are rare, a variety of cancers have been detected in these animals. Nonetheless, several substances that have anti-tumour activity have been identified in cartilage.
More than a dozen clinical studies of cartilage as a treatment for cancer have already been conducted, and additional clinical studies are now under way.
The absence of blood vessels in cartilage led to the hypothesis that cartilage cells (also known as chondrocytes) produce one or more substances that inhibit blood vessel formation. The formation of new blood vessels, or angiogenesis, is necessary for tumours to grow larger than a few millimetres in diameter (i.e., larger than approximately 100,000 to 1,000,000 cells) because tumours, like normal tissues, must obtain most of their oxygen and nutrients from blood. A developing tumour, therefore, cannot continue to grow unless it establishes connections to the circulatory system of its host.
It has been reported that tumours can initiate the process of angiogenesis when they contain as few as 100 cells. Inhibition of angiogenesis at this early stage may, in some instances, lead to complete tumour regression. The possibility that cartilage could be a source of one or more types of angiogenesis inhibitors for the treatment of cancer has prompted much research.
The major structural components of cartilage include several types of the protein collagen and several types of glycosaminoglycans, which are polysaccharides. Chondroitin sulphate is the major glycosaminoglycan in cartilage. Although there is no evidence that the collagens in cartilage, or their breakdown products, can inhibit angiogenesis, there is evidence that shark cartilage contains at least one angiogenesis inhibitor that has a glycosaminoglycan component (see Laboratory/Animal/Preclinical Studies section). Other data indicate that most of the antiangiogenic activity in cartilage is not associated with the major structural components.
Some glycosaminoglycans in cartilage reportedly have anti-inflammatory and immune system-stimulating properties, and it has been suggested that either they or some of their breakdown products are toxic to tumour cells. Thus, the anti- tumour potential of cartilage may involve more than one mechanism of action.
Cartilage products are sold commercially in the United States as dietary supplements. More than 40 different brand names of shark cartilage alone are available to consumers. In the United States, dietary supplements are regulated as foods, not drugs. Therefore, pre-market evaluation and approval by the Food and Drug Administration (FDA) are not required unless specific disease prevention or treatment claims are made.
Because manufacturers of cartilage products are not required to show evidence of anticancer or other biologic effects, it is unclear whether any of these products has therapeutic potential. In addition, individual products may vary considerably from lot to lot because standard manufacturing processes do not exist and binding agents and fillers may be added during production.
To conduct clinical drug research in the United States, researchers must file an Investigational New Drug (IND) application with the FDA. To date, IND status has been granted to at least four groups of investigators to study cartilage as a treatment for cancer.[10,51,52,62, reviewed in 20] Because the IND application process is confidential and because the existence of an IND can be disclosed only by the applicants, it is not known whether other applications have been made.
In animal studies, cartilage products have been administered in a variety of ways. In some studies, oral administration of either liquid or powdered forms has been used. In other studies, cartilage products have been given by injection (intravenous or intraperitoneal), applied topically, or placed in slow-release, plastic pellets that were surgically implanted. Most of the latter studies investigated the effects of cartilage products on the development of blood vessels in the chorioallantoic membrane of chicken embryos, the cornea of rabbits, or the conjunctiva of mice.
In human studies, cartilage products have been administered topically or orally, or they have been given by enema or subcutaneous injection. For oral administration, liquid, powdered, and pill forms have been used. The dose and duration of cartilage treatment have varied in human studies, in part because different types of products have been tested.