Achilles tendinopathy is characterized by deterioration of tissue integrity and biomechanical properties. Reduced tendon stiffness is detrimental to its function. Previous studies found that increased body mass is a risk factor for Achilles tendinopathy. We aimed to determine whether increasing the stiffness of damaged Achilles tendon by the collagen crosslinker genipin can improve early healing outcomes in an animal model of collagenase-induced tendinopathy, and whether the effect depends on body mass.
Male and female Sprague-Dawley rats were allocated to normal diet (ND) or high-fat diet (HFD) at weaning. At 17 weeks, each sex and diet group was divided into three treatment groups (n = 15): collagenase (CT), collagenase-genipin (CT-GT), and genipin (GT). Collagenase and genipin were injected into the Achilles tendons; contralateral tendons served as controls. After 10 days, Achilles tendons were collected for biomechanical and histological evaluation.
At the time of tendinopathy induction, animals fed HFD weighed on average, 14.5 % more than animals on ND. Biomechanical and histological changes characteristic of tendinopathy were observed in Achilles tendons of all animals treated with collagenase. Genipin had no effect on tendon biomechanical and histological properties: we found no differences between the GT and the control group, or between the CT-GT and the CT group.
In conclusion, 1 mM genipin did not improve the biomechanical properties of tendinopathic Achilles, and had no effect on early tendon healing in this rat model of collagenase-induced Achilles tendinopathy, irrespective of animal sex and weight. This is an important pre-clinical finding and can be used to direct future research, and prevent possible research wastage. One potential future direction is exploring innovative delivery systems to maintain higher local concentrations of genipin, that may be required to realize the potential of this molecule in tendon healing.