Kidney disease impairs tendon function in rats

Spontaneous tendon rupture occurs in a concerning number of individuals with chronic kidney disease (CKD); however almost no data exist regarding CKD-related tendon pathology. Given that tendon ruptures have a significant impact on health and well-being we sought to determine whether tendon mechanics are altered by kidney disease in an established rat model of CKD. Male and female Sprague-Dawley rats (age = 8 weeks) were equally divided into a control group (CON, n = 16) and a group fed a diet containing 0.25% adenine to induce kidney disease (_ADICKD). After 9 weeks, Achilles and tibialis anterior (TA) tendons were excised, and maximum tensile load (MTL), failure stress, modulus and cross-sectional area (CSA) were measured and evaluated by two-way ANOVA (main effects: CKD and sex). CKD was confirmed through elevated creatinine (1.99 vs. 0.61 mg/dl, CKD vs. CON, P < 0.001) and blood urea nitrogen (93.4 vs. 21.4 mg/dl, P < 0.001). Plantar flexor strength was 13% lower in _ADICKD (P = 0.0214), and femur yield force was decreased by 41% in male _ADICKD (P < 0.001). The failure stress of TA tendons was 24% lower in CKD vs. CON (P = 0.0383). There were no statistically significant differences in TA tendon MTL, modulus or CSA. There were no significant main effects for any parameter for the Achilles; however, post hoc testing following a finding of group-by-sex interactions revealed that in females Achilles failure stress was decreased in _ADICKD by 25% (P = 0.0283). To our knowledge this is the first direct evidence that tendon weakness is caused by kidney disease, providing a model for further evaluating mechanisms and interventions. KEY POINTS: Chronic kidney disease is well known to lead to musculoskeletal dysfunction, such as bone and muscle wasting. Numerous case reports suggest that chronic kidney disease may also predispose patients to catastrophic tendon injuries; however, there are no mechanistic studies or animal models addressing this phenomenon - and thus, no treatments. We determined whether a rat model of chronic kidney disease previously used to study muscle and bone dysfunction (0.25% adenine in the diet) would also cause impaired tendon function. Eight weeks of adenine-induced kidney disease caused tibialis anterior tendons to tear at 24% lower stress than in control animals, while also decreasing plantar flexor muscle strength by 13% and femur strength by 41% (males only). This is the first experimental evidence for a direct effect of chronic kidney disease on tendon function, establishing a comprehensive multitissue model for future research.