Ageing of Human Corneal and Scleral Collagen

It is commonly accepted that, on ageing, the body’s proteins become structurally altered. One such protein predominating throughout the body is collagen. This long-lived protein forms a major part of the human cornea and sclera and it is within these tissues that the work of this thesis has revealed age-related structural and biochemical modifications of type I collagen. Using the highly sensitive technique of X-ray diffraction, the size of the intermolecular unit cell of the collagen has been demonstrated to increase in both tissues from birth to 90 years of age. Across the same age range, the volume of the fibril unit cell of corneal collagen ha.s been found to decrease. In an attempt to account for the molecular changes, the concept of sugar-induced structural modification (glycation) was investigated using a colorimetric assay. This too was found to increase with tissue age as did the production of fluorescent cross-links (possibly intermolecular) on the collagen. These fluorescent structures were quantified by their fluorescence emission properties. Different sugars were also used, to compare their effects on the intermolecular unit cell volume. Since collagen is a family of proteins, the glycation of two different collagen types was studied. Several chemical compounds were also used to investigate the inhibition of in vitro glycation of collagen. The absence of an increase in intermolecular unit cell volume in the presence of these compounds suggests that it may be possible to control this particular consequence of ageing. The literature suggests that interfibrillar spacing is linked with corneal transparency. Proteoglycans are essentially involved in controlling this particular spacing and the work of this thesis has shown no significant loss of these macromolecules to the organ culture medium in which the tissue is housed before investigation. Tissue proteoglycan may be lost during the natural ageing of an individual.