<strong>RAGE inhibition as a method to improve tendon function in diabetic and healing murine models</strong>
Creators: name: Lauriani, Camila Ignacia Reyes
Publisher: name: Purdue University Graduate School
Year: 2023
Subjects: Exercise physiology

description: The disruption of homeostasis in tendon extracellular matrix and altered biomechanical properties lead to poor tendon healing, creating a significant clinical challenge for millions of diabetics. Furthermore, improving blood glucose levels doesn't normalize tendon properties in diabetics. Diabetes-related tendon complications are often associated with advanced glycation end products (AGEs) crosslinking with collagen. However, recent studies have found no evidence of higher collagen crosslinking in diabetics and no correlation between tendon AGE content and tensile strength. The interaction between serum AGEs and AGE receptors (RAGE) is a less explored mechanism of AGE-mediated effects. People with diabetes are more likely to accumulate AGEs in their serum as a result of hyperglycemia, the consumption of AGE-rich foods, and diminished kidney clearance of AGEs. In previous studies, advanced glycation end-products (AGEs) have been shown to inhibit cell proliferation and migration, both of which are critical to tendon healing. We hypothesized that serum AGEs and activation of RAGE represent a mechanism underlying impaired tendon properties with diabetes. The increasing serum AGE levels would impair tendon biomechanical properties and tendon healing, while inhibition of RAGE [Azeliragon (AZ)] would improve tendon mechanics. Db/db mice with naturally elevated serum AGEs and impaired tendon function were treated daily with a RAGE inhibitor [Azeliragon (AZ), n=9] or vehicle (n=10) for three weeks. Patellar tendon stiffness and modulus were greater (p&lt;0.05) in mice receiving AZ (stiffness: 9.6±1.2 N/mm, modulus: 78.2±8.2 MPa) compared to vehicle (5.8±0.9 N/mm, modulus: 49.0±8.3 MPa). Maximum strain (vehicle: 0.9±0.1, AZ: 0.8±0.05) and toughness (vehicle: 6.1±1.4, AZ: 6.5±1.2 J·m−3) were not different between groups (p&gt;0.05). Maximum stress tended to be greater in the AZ group (vehicle: 14.6±2.4, AZ: 23.3±2.9 N/mm2, p=0.156). Ten-week-old non-diabetic mice were assigned to receive daily injections of bovine serum albumin (BSA-only, n=6), BSA and AZ (BSA-AZ, n=5), 200 mg/ml glycated BSA (AGE-BSA, n=4), and AGE with AZ (AGE-AZ, n=6). A full-thickness, partial-width defect was created in both patellar tendons. Treatments were started one week before surgery and continued for three weeks after surgery. Three Tendon stiffness was lower in mice treated with AGEs (p&lt;0.05, 10.8±1.4 N/mm) compared to BSA-only (17.6±1.3 N/mm). Further, tendon stiffness in AGE-treated mice given AZ was not different from AGE-BSA (p&lt;0.05, 12.7±1.8 N/mm). Tendon modulus was lower in mice treated with AGEs (p&lt;0.05, 28.0±7.0 MPa) compared to BSA-only (63.5±9.0 MPa). Additionally, modulus in AGE-treated mice given AZ was not different from AGE-BSA (p&gt;0.05, 47.6±10.4 N/mm). We demonstrate that administering a RAGE inhibitor improves tendon properties in an established mouse model for type 2 diabetes. In healthy mice, serum AGE levels inhibit the recovery of tendon biomechanical properties after injury; RAGE inhibitors did not have an effect on mice given AGEs. Based on these data, we suggest elevated serum AGEs, as seen with diabetes, are associated with poor mechanical properties and delayed tendon healing.