A Metabolic Screen in Adolescents Reveals an Association Between Circulating Citrate and Cortical Bone Mineral Density

Molecular conformations and dynamics in the extracellular matrix of mammalian structural tissues: Solid-state NMR spectroscopy approaches

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Solid-state NMR spectroscopy probes molecular conformation and dynamics in intact ECM.

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Collagen conformational dynamics has roles in mechanical properties of fibrils and cell adhesion.

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Solid-state NMR spectroscopy has shed new light on  the chemical structure of bone mineral.

Solid-state NMR spectroscopy has played an important role in multidisciplinary studies of the extracellular matrix. Here we review how solid-state NMR has been used to probe collagen molecular conformations, dynamics, post-translational modifications and non-enzymatic chemical changes, and in calcified tissues, the molecular structure of bone mineral and its interface with collagen. We conclude that NMR spectroscopy can deliver vital information that in combination with data from structural imaging techniques, can result in significant new insight into how the extracellular matrix plays its multiple roles.

A 43 Ca nuclear magnetic resonance perspective on octacalcium phosphate and its hybrid derivatives

⁴³ Ca nuclear magnetic resonance (NMR) spectroscopy has been extensively applied to the detailed study of octacalcium phosphate (OCP), Ca₈ (HPO₄ )₂ (PO₄ )₄ .5H₂ O, and hybrid derivatives involving intercalated metabolic acids (viz., citrate, succinate, formate, and adipate). Such phases are of importance in the development of a better understanding of bone structure. High-resolution ⁴³ Ca magic angle spinning (MAS) experiments, including double-rotation (DOR) ⁴³ Ca NMR, as well as ⁴³ Ca{¹ H} rotational echo DOR (REDOR) and ³¹ P{⁴³ Ca} REAPDOR NMR spectra, were recorded on a ⁴³ Ca-labeled OCP phase at very high magnetic field (20 T), and complemented by ab initio calculations of NMR parameters using the Gauge-Including Projector Augmented Wave-density functional theory (GIPAW-DFT) method. This enabled a partial assignment of the eight inequivalent Ca²⁺ sites of OCP. Natural-abundance ⁴³ Ca MAS NMR spectra were then recorded for the hybrid organic-inorganic derivatives, revealing changes in the ⁴³ Ca lineshape. In the case of the citrate derivative, these could be interpreted on the basis of computational models of the structure. Overall, this study highlights the advantages of combining high-resolution ⁴³ Ca NMR experiments and computational modeling for studying complex hybrid biomaterials.

Untargeted metabolomics revealed therapeutic mechanisms of icariin on low bone mineral density in older caged laying hens

Osteoporosis is a common chronic disease in the elderly population and in some domestic animals. Caged layer osteoporosis (CLO) is a common bone metabolism disease that was recently recommended as an ideal animal model for osteoporosis. This study aimed to investigate the therapeutic effect and mechanism of dietary icariin (ICA), the main bioactive component of the Chinese herb Epimedium, on low bone mineral density (BMD) in older caged laying hens. A total of 216, 54-week-old Lohmann pink-shell laying hens were allocated to three groups, comprising one control group and two treatment groups that were additionally supplied with 0.5 or 2.0 g kg-1 ICA. The results showed that dietary ICA significantly increased the femur BMD by 49.3% and the tibia BMD by 38.9%, improved the microstructure of bone tissue, decreased levels of the bone metabolism index, enhanced serum antioxidant capacity and regulated messenger RNA expression of bone-related genes. ICA-induced differential metabolites were clarified by using untargeted metabolomics assays. Furthermore, correlation analysis between differential metabolites and BMD indicated that eight differential metabolites correlated highly with both femur and tibia BMD, including uridine, taurine, palmitic acid, adrenic acid, fexofenadine, lysoPC(18 : 1), lysoPE(20 : 3/0 : 0) and 3-acetyl-11-keto-beta-boswellic acid. ICA mainly perturbed pyrimidine metabolism, taurine metabolism and lipid metabolism, which led to increased BMD in older caged laying hens. These findings revealed underlying therapeutic mechanisms of dietary ICA on low BMD, and provided reference metabolites for the early diagnosis of osteoporosis.

Metabolomics analysis in adults with high bone mass identifies a relationship between bone resorption and circulating citrate which replicates in the general population

OBJECTIVE

Bone turnover, which regulates bone mass, may exert metabolic consequences, particularly on markers of glucose metabolism and adiposity. To better understand these relationships, we examined cross-sectional associations between bone turnover markers (BTMs) and metabolic traits in a population with high bone mass (HBM, BMD Z-score ≥+3.2).

DESIGN

β-C-terminal telopeptide of type-I collagen (β-CTX), procollagen type-1 amino-terminal propeptide (P1NP) and osteocalcin were assessed by electrochemiluminescence immunoassays. Metabolic traits, including lipids and glycolysis-related metabolites, were measured using nuclear magnetic resonance spectroscopy. Associations of BTMs with metabolic traits were assessed using generalized estimating equation linear regression, accounting for within-family correlation, adjusting for potential confounders (age, sex, height, weight, menopause, bisphosphonate and oral glucocorticoid use).

RESULTS

A total of 198 adults with HBM had complete data, mean [SD] age 61.6 [13.7] years; 77% were female. Of 23 summary metabolic traits, citrate was positively related to all BTMs: adjusted ββ-CTX  = 0.050 (95% CI 0.024, 0.076), P = 1.71 × 10-4 , βosteocalcin  = 6.54 × 10-4 (1.87 × 10-4 , 0.001), P = .006 and βP1NP  = 2.40 × 10-4 (6.49 × 10-5 , 4.14 × 10-4 ), P = .007 (β = increase in citrate (mmol/L) per 1 µg/L BTM increase). Inverse relationships of β-CTX (β = -0.276 [-0.434, -0.118], P = 6.03 × 10-4 ) and osteocalcin (-0.004 [-0.007, -0.001], P = .020) with triglycerides were also identified. We explored the generalizability of these associations in 3664 perimenopausal women (age 47.9 [4.4] years) from a UK family cohort. We confirmed a positive, albeit lower magnitude, association between β-CTX and citrate (adjusted βwomen  = 0.020 [0.013, 0.026], P = 1.95 × 10-9 ) and an inverse association of similar magnitude between β-CTX and triglycerides (β = -0.354 [-0.471, -0.237], P = 3.03 × 10-9 ).

CONCLUSIONS

Bone resorption is positively related to circulating citrate and inversely related to triglycerides. Further studies are justified to determine whether plasma citrate or triglyceride concentrations are altered by factors known to modulate bone resorption, such as bisphosphonates.