Poster P18 - Can Collagenase Reduce the Increased Stiffness Found in the Skeletal Muscle of Children with Cerebral Palsy

Introduction: Cerebral Palsy (CP) is a group of debilitating movement and posture disorders that results in pain, muscle stiffness, and a limited range of movement. This restrictive muscle stiffness is suggested to arise from a dense extracellular matrix (ECM) found in affected muscles. Current clinical interventions aim to relieve muscle stiffness and restore some range of motion. They include surgical intervention and botulinum toxin injections, both temporary and possibly harmful. Thus, it is vital to identify a long-term treatment option that decreases prominent CP-associated muscle stiffness and maintains muscle contractile properties without introducing harmful side effects.

The increased ECM in the muscles of children with CP, typically referred to as muscle fibrosis, is primarily caused by an increase in extracellular collagen accumulation. Collagenase, an enzyme that digests collagen has been used clinically to decrease collagen levels in fibrotic diseases such as Dupuytren’s and Peyronie’s. However, the use of collagenase to reduce collagen content and consequently muscle stiffness in CP muscles has not been systematically investigated.

This study was aimed at investigating the effect of collagenase on passive force and contractile properties of tissue samples isolated from spastic muscles of children with CP.

Materials and

Methods: Fascicles from the adductor longus of 11 patients with CP undergoing tendon release surgery were isolated and subjected to mechanical and biochemical testing.

Mechanical testing: Fascicles were mounted between a length controller and force transducer of a mechanical testing system. They were subjected to stress-relaxation tests with stretch magnitudes of 1, 2.5, 5 and 7.5% of their initial length, before and after incubation in collagenase for one hour at 37°C. Peak and steady-state forces and stiffness were determined and normalized to the cross-sectional area of the fascicles to obtain stresses and Young’s modulus.

Biochemical analysis: Fascicles were incubated in either a collagenase or a buffer solution for one hour at 37°C and then assessed for their total protein content using a BCA assay.

Results, Conclusions, and Discussions: Mechanical testing: After collagenase incubation, peak and steady-state stresses and Young’s modulus decreased across all the different strain values tested by an average of 49 ± 17%, 47 ± 16% and 51 ± 6%, respectively.

Biochemical: There was no significant difference in total protein content after collagenase incubation compared to control.

Overall, there was a decrease in passive force using collagenase, as expected. Surprisingly, there was no correlation between the decrease in passive force and Young’s modulus and the amount of collagen before and after intervention. We speculate that the collagenase digested the interconnections within the fibrotic muscle collagen network, thereby affecting stiffness and passive force but not the amount of fibrosis itself. Additionally, the lack of change in total protein content after the collagenase implies that the contractile proteins are preserved.

Our results suggest that collagenase could potentially be used to decrease passive forces and stiffness in CP muscles without impacting other contractile and structural sarcomeric proteins, thus preserving active function of the muscle.

The significance of this study stems from the tendency of current treatments for reducing the inherent stiffness in CP muscles to cause transient pain, fibrosis and fat infiltration. Using collagenase as a preventative measure could avert the consequences of these treatments while providing relief seen in other fibrotic diseases subjected to collagenase treatments. Furthermore, collagenase intervention may provide an alternative to the more aggressive and somewhat stigmatized interventions of surgery or botulinum neurotoxin administration. However, collagenase would not cure the underlying cause of CP and the potential recurrence of muscle stiffness would require repeated collagenase treatment.

Acknowledgements (Optional): Thank you to CIHR and AGES as my funding sources and Nemours Children’s Health for their collaboration on this project.