Histochemistry and the Biological Roles of Glycosaminoglycans: Clinical Significance in Human Tissues

Abstract

Glycosaminoglycans (GAGs) are long, unbranched polysaccharides which are composed of repeating disaccharide units. They are negatively charged molecules which associate with proteins to yield proteoglycans. This study will examine the histochemistry, biological compositions and activities of GAGs in the human body. Histochemical identification methods of GAGs include Hale’s colloidal iron method, Periodic-acid-Schiff’s reaction (PAS), Alcian blue, and Metachromatic dyes. They exist naturally in different parts of the body, both in the free and protein-bound states. They play several important functions in human health, such as angiogenesis, inflammation, wound healing, and neurogenesis, a few mentioned. There are six different classes of GAGs found in various tissues of the body. The classes and quantities of GAGs found in the body depend on the tissue location and whether the tissue is in its normal or pathological state. It is commonly known that there is a change in the amount of GAGs in various tissues after injury. For example, it has been revealed that patients with radiculopathy showed significantly lower GAGs values in the nucleus pulposus of the intervertebral discs (2.82% ± 3.12% vs. 4.09% ± 2.25%, P = 0.017). Changes in the quantities of GAGs have also been observed during intrinsic ageing and photoaging of the human skin. GAGs act as potential biomarkers of certain pathologies, e.g. lung cancer. They are also believed to be crucial inhibitors of calcium oxalate crystal growth and crystallisation. GAGs can be used in treatment. For example, minimally invasive injectable GAG hydrogel has been introduced to reinstate the physiological properties of the spine. Physiologically based investigations show that the mediator proteins-GAGs interactions are majorly regulated by sulphation degree, sulphation pattern, and composition and structure of the carbohydrate. Studies on GAGs are evolving and more researches are required to exploit their characteristics, compositions, and importance.