Crosslinking in type III collagen of fetal tissue

Cross-link analysis of the C-telopeptide domain from type III collagen

Several peptides were isolated from tryptic digests of insoluble calf aorta matrix by chromatography. Reductive pyridylethylation of a tryptic 15 kDa pool released fragments deriving from the C-terminus of type III collagen. A 50-residue peptide Tc(III) was shown by sequence analysis to be the C-terminal peptide from the alpha 1(III)-chain, containing a helical and non-helical region of equal sizes. The peptide was further digested with collagenase to give Colc(III), comprising the complete C-terminal non-helical region of alpha 1(III) including a hydroxylysine in position 16c. The peptide Tc(III) x TN(III) was isolated, demonstrating covalent cross-linking between the C-terminal non-helical region of one type III molecule and the N-terminal helical cross-linking region of another. Its digestion with cyanogen bromide yielded the small fragments alpha 1(III)CB3B* and alpha 1(III)CB3C, confirming TN(III) as an N-terminal helical crosslink site. Sequence analysis of both Tc(III) x TN(III) and its collagenase-derived cross-linked peptide Colc(III) x TN(III) established the 4D-staggered alignment of adjacent collagen III molecules. The cross-link structure of both peptides was mainly dihydroxylysinonorleucine with a small amount of hydroxylysinonorleucine, indicating that the lysine residues involved in formation of the cross-links are both hydroxylated. No pyridinoline or histidinohydroxylysinonorleucine cross-links were found within the non-reduced C-telopeptide region of type III collagen.

Effect of D-penicillamine on collagen, glycosaminoglycans, DNA and RNA of granulation tissue and connective tissue of skin, bone and aorta in rats

Granulation tissue was produced by subcutaneous implantation of viscose-cellulose sponges on rats. The effect of D-penicillamine 500 mg/kg/day for 10 days on granulation tissue and the connective tissue of skin, bone and aorta was studied ny comparison of treated animals with operated and unoperated controls. In addition, the effect of sponge implantation on intact tissues was studied by comparison between the control groups. The amount of granulation tissue was not affected by D-penicillamine, and the granulomas-DNA content even increased. D-penicillamine increased the amount of salt soluble collagen in all tissues consistent with an inhibition of collagen crosslinking as reflected by increased aldehyde content and alpha/beta chain ratio in soluble skin collagen. Skin appeared to be most sensitive. The content of free hydroxyproline and RNA and the RNA/DNA ratio in skin decreased suggesting a decreased collagen biosynthesis. The hydroxylation of proline and lysine was not affected by the treatment. The water percentage of aorta increased during D-penicillamine treatment, and the 35S-sulphate uptake in the sulphated glycosaminoglycans was stimulated in all tissues, in granulation tissue mainly in the chondroitin-4/6-sulphate fraction. No quantitative glycosaminoglycan changes occurred in granulation tissue. Sponge implantation caused an increase in the amount of salt soluble skin collagen without any change in alpha/beta chain ratio and aldehyde content of purified, soluble collagen. D-penicillamine plus operation reduced the collagen content of aorta. The effects of D-penicillamine on connective tissue compounds may be of importance for its antirheumatic efficacy, but the accompanying effect on normal tissues may imply side effects.

Design of an artificial skin. II. Control of chemical composition

Detailed methodology is described for the reproducible preparation of collagen--glycosaminoglycan (GAG) membranes with known chemical composition. These membranes have been used to cover satisfactorily large experimental full-thickness skin wounds in guinea pigs over the past few years. Such membranes have effectively protected these wounds from infection and fluid loss for over 25 days without rejection and without requiring change or other invasive manipulation. When appropriately designed for the purpose, the membranes have also strongly retarded wound contraction and have become replaced by newly synthesized, stable connective tissue. In our work, purified, fully native collagen from two mammalian sources is precipitated from acid dispersion by addition of chondroitin 6-sulfate. The relative amount of GAG in the coprecipitate varies with the amount of GAG added and with the pH. Since coprecipitated GAG is generally eluted from collagen fibers by physiological fluids, control of the chemical composition of membranes is arrived at by crosslinking the collagen--GAG ionic complex with glutaraldehyde, or, alternately, by use of high-temperature vacuum dehydration. Appropriate use of the crosslinking treatment allows separate study of changes in membrane composition due to elution of GAG by extracellular fluid in animal studies from changes in composition due to enzymatic degradation of the grafted or implanted membrane in these studies. Exhaustive in vitro elution studies extending up to 20 days showed that these crosslinking treatments insolubilize in an apparently permanent manner a fraction of the ionically complexed GAG, although it could not be directly confirmed that glutaraldehyde treatment covalently crosslinks GAG to collagen. By contrast, the available evidence suggests strongly that high-temperature vacuum dehydration leads to formation of chemical bonds between collagen and GAG. Procedures are described for control of insolubilized and "free" GAG in these membranes as well as for control of the molecular weight between crosslinks (Mc). The insolubilized GAG can be controlled in the range 0.5--10 wt. % while "free" GAG can be independently controlled up to at least 25 wt. %; Mc can be controlled in the range 2500--40,000. Studies by infrared spectroscopy have shown that treatment of collagen--GAG membranes by glutaraldehyde or under high-temperature vacuum does not alter the configuration of the collagen triple helix in the membranes. Neither do these treatments modify the native banding pattern of collagen as viewed by electron microscopy. Collagen--GAG membranes appear to be useful as chemically well-characterized, solid macromolecular probes of biomaterial--tissue interactions.