While the invertebrates constitute almost 95% of the animal kingdom, our knowledge on their extracellular matrices, particularly on collagen, is very scanty. Our group has been studying the collagen polymorphism in some marine invertebrate tissues with focus on structure-function relationships and molecular evolution. We have established methods to purify unique collagen molecules from some rare tissues of crustaceans and molluscs. Some of these include the intramuscular tissues of the crustaceans and the cartilage and cornea of molluscs. The biochemical parameters in these tissues relating to collagen content, solubility and carbohydrate composition have been determined. The chain composition of these collagens were deduced by SDS-PAGE. We have analyzed the amino acid compositions of these collagens and that of isolated single alpha chains. The physicochemical properties and ultrastructural characteristics of some of these collagens were also studied. The results indicate that the principal component of crustacean muscle is a type V like homotrimer and that of molluscan cartilage and cornea is a unique heteromeric collagen resembling vertebrate type V and XI collagens. These collagens were invariably highly crosslinked, stabilized largely by bound carbohydrates and had significantly high denaturation temperatures. While the crustacean type V collagen formed regularly banded fibrils, the V/XI like collagen of molluscan cartilage lacked periodicity in fibril structure. We correlate the significance of our key observations to the possible functional consequence as well as evolutionary significance, based on the available data on other similar collagens.

This report provides a new possible link between increased lipid peroxidation and tissue damage in diabetes. Advanced Glycation End products (AGEs) have been well established as one of the major factors responsible for multiorgan damage seen in diabetes and aging. We report here that the interaction between lipid peroxidation products and the long-lived structural protein, collagen, results in the formation of products that are structurally or immunologically similar to AGEs. Enzyme-linked immunoassays revealed crossreactivity between anti-AGE antibodies and collagen incubated with linoleic acid/arachidonic acid for 4 weeks under oxidative conditions. Formation of AGEs from lipid oxidation products and collagen was further confirmed by the inhibitory effect of aminoguanidine. Similarly, incubation of collagen with an end product of lipid peroxidation, malondialdehyde (MDA), resulted in the formation of AGEs. It was also noted that the incubation of collagen with equimolar concentrations of glucose or linoleic acid/arachidonic acid resulted in the formation of almost similar amount of AGEs. Another interesting observation was that the level of AGEs correlated well with the crosslinking of collagen (r=0.93) and also with the intensity of fluorescence (ex: 390 nm/em: 460 nm) (r=0.99). However the rate of fluorescence development was observed at a faster rate than the formation of AGEs when the concentration of MDA was increased from 5 mM to 25/50 mM. Free radical scavengers failed to prevent lipid peroxidation-induced formation of AGEs. These results suggest that, in addition to reducing sugars, fatty acid oxidation products can also lead to the formation of products that are structurally similar to AGEs. The work presents a possible link between lipid peroxidation and diabetic complications, through AGEs. This study also suggests that the formation of AGEs is a possible explanation for lipid peroxide-induced crosslinking of collagen.