Glycoxidation of the bone matrix modulates mineralization

Type 2 diabetes (T2D) is a prevalent condition that is associated with heightened fracture risk despite T2D patients exhibiting normal or elevated BMD. T2D exacerbates oxidative stress and hyperglycemia, which increases the accumulation of advanced glycation end products (AGEs) and advanced glycoxidation end products (AGOEs) in bone. Carboxymethyl-lysine (CML) is one such AGOE linked to fracture risk and could impact bone mineralization due to its carboxyl terminus. Still, the mechanism linking CML to altered mineralization and impaired bone quality in T2D is unknown. To investigate how glycoxidation modulates bone mineralization, sectioned human tibiae (23-yr-old to 89-yr-old donors, Caucasian male [CM] and Caucasian female [CF]) were treated in vitro with glyoxal or ribose to enhance CML content or AGE content. Sections were then suspended between calcium and phosphate solutions to promote mineral growth. Raman spectroscopy revealed that AGE and CML enhancement increased the degree of mineralization and accelerated mineral maturation, with CML-enhanced samples exhibiting the greatest increase in mineral growth. Solid-state nuclear magnetic resonance illustrated that CML enhancement increased the degree of electronegativity in the collagen structure and at the mineral surface, which was associated with increased compressive strain on the mineral platelet as unveiled by X-ray diffraction. Nanoindentation demonstrated lowered hardness and increased work energy in CML-enhanced samples. Collectively, these findings demonstrate a mechanism that links glycoxidation to matrix mineralization. The ability for CML to influence bone mineralization underlines the need to develop strategies to target CML accrual and mitigate fracture risk in patients with T2D.