Accelerated osteocyte senescence and skeletal fragility in mice with type 2 diabetes

The worldwide prevalence of type 2 diabetes (T2D) is increasing. Despite normal to higher bone density, patients with T2D paradoxically have elevated fracture risk resulting, in part, from poor bone quality. Advanced glycation endproducts (AGEs) and inflammation as a consequence of enhanced receptor for AGE (RAGE) signaling are hypothesized culprits, although the exact mechanisms underlying skeletal dysfunction in T2D are unclear. Lack of inducible models that permit environmental (in obesity) and temporal (after skeletal maturity) control of T2D onset has hampered progress. Here, we show in C57BL/6 mice that a onetime pharmacological intervention (streptozotocin, STZ) initiated in adulthood combined with high-fat diet-induced (HFD-induced) obesity caused hallmark features of human adult-onset T2D, including prolonged hyperglycemia, insulin resistance, and pancreatic β cell dysfunction, but not complete destruction. In addition, HFD/STZ (i.e., T2D) resulted in several changes in bone quality that closely mirror those observed in humans, including compromised bone microarchitecture, reduced biomechanical strength, impaired bone material properties, altered bone turnover, and elevated levels of the AGE CML in bone and blood. Furthermore, T2D led to the premature accumulation of senescent osteocytes with a unique proinflammatory signature. These findings highlight the RAGE pathway and senescent cells as potential targets to treat diabetic skeletal fragility.

Development and Application of Mass Spectroscopy Assays for Nε-(1-Carboxymethyl)-L-Lysine and Pentosidine in Renal Failure and Diabetes

BACKGROUND

Advanced glycation end products (AGEs) are formed via the nonenzymatic glycation of sugars with amino acids. Two AGEs, Nε-(1-carboxymethyl)-L-Lysine (CML) and pentosidine, have been observed to be elevated in subjects suffering from a multitude of chronic disease states, and accumulation of these compounds may be related to the pathophysiology of disease progression and aging.

METHODS

We describe here the development and validation of a specific and reproducible LC-MS/MS method to quantify CML and pentosidine in human serum with lower limits of quantitation of 75 ng/mL and 5 ng/mL, respectively. The analyte calibration curve exhibited excellent linearity at a range of 0-10 900 ng/mL for CML and 0-800 ng/mL for pentosidine. High-low linearity of 5 serum pairs was assessed, with a mean recovery of 103% (range 94-116%) for CML, and 104% (range 97-116%) for pentosidine.

RESULTS

Serum concentrations of CML and pentosidine were quantified in 30 control and 30 subjects with chronic renal insufficiency. A significant increase in both analytes was observed in renal failure compared to control subjects (2.1-fold and 8.4-fold, respectively; P < 0.001 for both). In a separate cohort of 49 control versus 95 subjects with type 2 diabetes mellitus (T2DM), serum CML but not serum pentosidine, was significantly elevated in the T2DM patients, and CML was also correlated with glycemic control, as assessed by hemoglobin A1c (r = 0.34, P < 0.001).

CONCLUSIONS

These mass spectroscopy-based assays for serum CML and pentosidine should be useful in accurately evaluating circulating levels of these key AGEs in various disease states.