What controls collagen resorption in vivo?

The local control of collagen degradation in mammals in vivo is currently considered to depend primarily on variations on the level of activity of specific collagenases. Such variations are believed to depend on three factors: a) the rate of active collagenase synthesis and/or of activation of inactive enzyme precursors; b) the action of serum and/or tissue collagenase inhibitors; and c) different combinations of both mechanisms. We suggest that another element contributing to the regulation of collagen degradation in vivo is the susceptibility of the substrate. Support for this suggestion is derived from two sources: 1) experimental data, indicating that the rate of collagen degradation depends on the genetic type of substrate, on its state of aggregation (including degree of cross-linking), and on the nature and amount of other macromolecules associated with collagen in vivo. Other experimental findings supporting our hypothesis are the universal presence of collagen-bound collagenase, the apparent greater affinity of the enzyme for the more recently synthetized substrate molecules, and the increased amounts of intact collagen that may be solubilized from some tissues undergoing massive collagen degradation, 2) analogy with currently accepted views on intracellular protein catabolism, which cannot be rejected a priori as irrelevant to the problem.

Collagen-bound collagenase.

The presence of collagenase bound to collagen extracted and purified from several animal and human sources by a standard procedure has been confirmed by different methods. Polyacrylamide (10%) gel electrophoresis at pH 8.1 of intact or "spontaneously"degraded neutral salt soluble collagen results in the separation of two components: the upper one says at the origin and represents collagen or collagen ragments, whereas the lower protein component contains no collagen, often preserves specific collagenolytic activity, and migrates as a single band in SDS/polyacrylamide electrophoresis. With lower polyacrylamide gel concentration the electrophoretic separation of the two components is less clear. Removal of the lower protein component from collagen solutions by two different methods (TCA-ethanol purification cycles and pepsin digestion) results in concomitant loss of their "spontaneous" instability. Eluates of the lower protein component stimulate the heterologous production of a monospecific antibody capable of inhibiting the collagenolytic activity of homologous crude collagenase preparations. It is suggested that collagen-bound collagenase is not an artifact of the extraction procedure but rather a physiological reality, probably corresponding in the living animal to the enzyme closely associated with extracellular collagen fibers, revealed by immunohistochemical methods.

Long-term evaluation of colchicine in the treatment of scleroderma.

Fifteen patients with PSS, 4 with CRST syndrome, and 4 with localized scleroderma have been treated with colchicine at the maximum tolerated individual doses for an average of 39 months (range 19--57). All but 2 of the 19 patients with generalized scleroderma and 3 of those with localized scleroderma improved. Patients who had had scleroderma for less than 5 yr when begun on colchicine, and those who received total doses of colchicine of more than 1,438 mg, scored a significantly higher mean response index than those with longer disease duration, or those who received less colchicine.

The presence of collagenase in collagen preparations.

The frequently observed instability of neutral salt solutions of native collagen extracted from various sources and partially purified by standard procedures has been studied by disc electrophoresis in polyacrylamide gel and by electron microscopic examination of segment long spacing crystallites. The phenomenon has revealed time and temperature dependency, pH optima near neutrality, and inhibition by sodium EDTA and serummin addition, collagen breakdown has been found to be quantitatively related to the state of aggregation of the substrate, being more marked in reconstituted collagen gels than in collagen in solutionma typical pattern of animal collagenase degradation of native collagen into two fragments designated as TC-A and TC-B has been observed under certain conditions. It is concluded that the degradation of native collagen in neutral salt solution is due to a specific collagenase, and that this enzyme probably remains bound to collagen throughout the process of extraction and partial purification. Experiments with gelatin suggest that, in addition to collagenase, a nonspecific proteolytic activity may also be present in collagen preparations.