Alteration of the Condylar Oral Bone in Obese and Gastric Bypass Mice

Effect of Obesity on Masticatory Muscle Activity and Rhythmic Jaw Movements Evoked by Electrical Stimulation of Different Cortical Masticatory Areas

This study investigates rhythmic jaw movement (RJM) patterns and masticatory muscle activities during electrical stimulation in two cortical masticatory areas in obese male Zucker rats (OZRs), compared to their counterparts-lean male Zucker rats (LZRs) (seven each). At the age of 10 weeks, electromyographic (EMG) activity of the right anterior digastric muscle (RAD) and masseter muscles, and RJMs were recorded during repetitive intracortical micro-stimulation in the left anterior and posterior parts of the cortical masticatory area (A-area and P-area, respectively). Only P-area-elicited RJMs, which showed a more lateral shift and slower jaw-opening pattern than A-area-elicited RJMs, were affected by obesity. During P-area stimulation, the jaw-opening duration was significantly shorter (p < 0.01) in OZRs (24.3 ms) than LZRs (27.9 ms), the jaw-opening speed was significantly faster (p < 0.05) in OZRs (67.5 mm/s) than LZRs (50.8 mm/s), and the RAD EMG duration was significantly shorter (p < 0.01) in OZRs (5.2 ms) than LZR (6.9 ms). The two groups had no significant difference in the EMG peak-to-peak amplitude and EMG frequency parameters. This study shows that obesity affects the coordinated movement of masticatory components during cortical stimulation. While other factors may be involved, functional change in digastric muscle is partly involved in the mechanism.

Bone matrix quality in a developing high-fat diet mouse model is altered by RAGE deletion

Overweightness and obesity in adolescents are epidemics linked to chronic low-grade inflammation and elevated fracture risk. The increased fracture risk observed in overweight/obese adolescence contrasts the traditional concept that high body mass is protective against fracture, and thus highlights the need to determine why weight gain becomes detrimental to fracture during growth and maturity. The Receptor for Advanced Glycation End products (RAGE) is a central inflammatory regulator that can influence bone metabolism. It remains unknown how RAGE removal impacts skeletal fragility in overweightness/obesity, and whether increased fracture risk in adolescents could result from low-grade inflammation deteriorating bone quality. We characterized the multiscale structural, mechanical, and chemical properties of tibiae extracted from adolescent C57BL/6J (WT) and RAGE null (KO) mice fed either low-fat (LF) or high-fat (HF) diet for 12 weeks starting at 6 weeks of age using micro-computed tomography, strength, Raman spectroscopy, and nanoindentation. Overweight/obese WT HF mice possessed degraded mineral-crystal quality and increased matrix glycoxidation in the form of pentosidine and carboxymethyl-lysine, with HF diet in females only showing reduced cortical surface expansion and TMD independently of RAGE ablation. Furthermore, in contrast to males, HF diet in females led to more material damage and plastic deformation. RAGE KO mitigated glycoxidative matrix accumulation, preserved mineral quantity, and led to increased E/H ratio in females. Taken together, these results highlight the complex, multi-scale and sex-dependent relationships between bone quality and function under overweightness, and identifies RAGE-controlled glycoxidation as a target to potentially preserve matrix quality and mechanical integrity.

Techniques for advanced glycation end product measurements for diabetic bone disease: pitfalls and future directions

PURPOSE OF REVIEW

Multiple biochemical and biophysical approaches have been broadly used for detection and quantitation of posttranslational protein modifications associated with diabetic bone, yet these techniques present a variety of challenges. In this review, we discuss recent advancements and complementary roles of analytical (UPLC/UPLC-MS/MS and ELISA) and biophysical (Raman and FTIR) techniques used for characterization of glycation products, measured from bone matrix and serum, and provide recommendations regarding the selection of a technique for specific study of diabetic bone.

RECENT FINDINGS

Hyperglycemia and oxidative stress in diabetes contribute to the formation of a large subgroup of advanced glycation end products (AGEs) known as glycoxidation end products (AGOEs). AGEs/AGOEs have various adverse effects on bone health. Commonly, accumulation of AGEs/AGOEs leads to increased bone fragility. For example, recent studies show that carboxymethyllysine (CML) and pentosidine (PEN) are formed in bone at higher levels in certain diseases and metabolic conditions, in particular, in diabetes and aging. Detection and quantitation of AGEs/AGOEs in rare and/or precious samples is feasible because of a number of technological advancements of the past decade.

SUMMARY

Recent technological advancements have led to a significant improvement of several key analytical biochemistry and biophysics techniques used for detection and characterization of AGEs/AGOEs in bone and serum. Their principles and applications to skeletal tissue studies as well as limitations are discussed in this review.