Local denaturation of collagen fibres during the mechanical rupture of collagenous fibrous tissue.

Abstract

SUMMARY Human extensor tendons of the hand were pulled to rupture, and the torn ends, when observed in the scanning electron microscope, appeared to be knotted, possibly owing to the denaturation of the collagen. This was confirmed by fluorimetry assays of both the ruptured ends and the middle unbroken sections of the same tendons. The use of a proteolytic enzyme, trypsin, to remove the denatured material and enhance the repair of organised collagen fibres from both ends is suggested if the ruptured ends have the denatured knotted appearance commonly observed clinically.Tendons that have become ruptured in vivo have usually failed because of 2 conditions: because an unusually large force has been applied through the tendon before muscular control has resisted the load, or because the tendon, in particular the collagen fibre network, which resists tensile loads transmitted through the tendon, has undergone biochemical attack substantially weakening the collagen. Tendons that have become divided as a result of trauma show a lesion at the rupture in which the ends have become atrophic and rounded producing a blunt amputation stump. After several months of repair histological evidence shows the junction of the new and old tendon and no regeneration from the proximal stump (Peacock, 1977).Clinical evidence and our interests in degeneration of collagenous tissue led to us conduct a preliminary study on the morphology of tendon ends after mechanical rupture (Steven et al., 1975). A hypothesis we put forward during that study was that the appearance of the ruptured end was a result of denaturation at the fibre ends, so the ends of the distal portions were exposed to trypsin for 24 hours. The tapered and knotted ends were not evident on the trypsin-exposed preparations, suggesting that the ruptured ends contained a substantial amount of denatured collagen.

Mechanical overload decreases the thermal stability of collagen in an in vitro tensile overload tendon model

“…5 Susceptibility to proteolysis by acetyltrypsin increased 2.5-to 4-fold throughout tendons ruptured at 0.01 s À1 and 10 s À1 but an alternate explanation, other than mechanically induced denaturation, was proposed. 5 While the recent proteolysis results were similar to the earlier work of Minns and Steven,3,4 the combination of the thermally labile domain (TLD) and ''Polymer-In-A-Box'' theory [6][7][8] was believed to provide a better, more agile explanation for the results of these protease probe studies without requiring mechanically induced denaturation. 5 The TLD is the region of the collagen molecule with the highest molecular gyration 7 (Fig.…”

“…16 Conformational freedom is intrinsically linked to configurational order. If the TLD does indeed become liberated due to tensile overload damage, this likely explains the greater proteolytic susceptibility seen previously, 3,5 as proteolysis would be facilitated by an increased probability of reaching the appropriate conformation and exposure of cleaving sites. 5 A corollary would predict reduced thermal stability, but no change in the enthalpy of thermal denaturation (amount of thermal energy required to denature collagen, normalized to mass, and proportional to the amount of intramolecular bonding) upon disruption of the lattice structure.…”

“…Specifically, we were concerned with changes in collagen at the molecular level caused by tensile overload damage: changes separate from the cellular and inflammatory responses. 1,2 Based on measurement of increased collagen proteolysis by trypsin and generally accepted ideas of the time, Minns and Steven 3,4 suggested that in vitro mechanical rupture of human digital extensor tendons resulted in collagen denaturation (loss of triple helical molecular conformation). Recently, similar results were reported using a bovine steer tail tendon (BTT) model digested with either acetyltrypsin or chymotrypsin.…”

Histological analysis of achilles tendons in an overuse rat model

“…22,33 Further, it has also been suggested that tendons ruptured by tensile forces undergo local collagen denaturation at the rupture site. 34,35 Thus, it is likely that even in the absence of complete rupture overuse running may cause localized damage to the tendon in the form of localized collagen denaturation.…”

“…Steven and Minns 34,35 have postulated that local denaturation must be enzymatically removed by phagocytic cells to allow an organized repair of the damaged collagenous tissues. The current study demonstrates an increase in cell numbers in the tendons of running rats.…”