Nadder Sahar

Publications of Nadder Sahar

• Natural-abundance 43Ca solid-state NMR spectroscopy of bone.

  Authors: Jiadi Xu, Peizhi Zhu, Zhehong Gan, Nadder Sahar, Mary Tecklenburg, Michael D Morris, David H Kohn, Ayyalusamy Ramamoorthy

  Journal of the American Chemical Society. 08/2010; 132(33):11504-9.

  Structural information about the coordination environment of calcium present in bone is highly valuable in understanding the role of calcium in bone formation, biomineralization, and bone diseasesStructural information about the coordination environment of calcium present in bone is highly valuable in understanding the role of calcium in bone formation, biomineralization, and bone diseases like osteoporosis. While a high-resolution structural study on bone has been considered to be extremely challenging, NMR studies on model compounds and bone minerals have provided valuable insight into the structure of bone. Particularly, the recent demonstration of (43)Ca solid-state NMR experiments on model compounds is an important advance in this field. However, application of (43)Ca NMR is hampered due to the low natural-abundance and poor sensitivity of (43)Ca. In this study, we report the first demonstration of natural-abundance (43)Ca magic angle spinning (MAS) NMR experiments on bone, using powdered bovine cortical bone samples. (43)Ca NMR spectra of bovine cortical bone are analyzed by comparing to the natural-abundance (43)Ca NMR spectra of model compounds including hydroxyapatite and carbonated apatite. While (43)Ca NMR spectra of hydroxyapatite and carbonated apatite are very similar, they significantly differ from those of cortical bone. Raman spectroscopy shows that the calcium environment in bone is more similar to carbonated apatite than hydroxyapatite. A close analysis of (43)Ca NMR spectra reveals that the chemical shift frequencies of cortical bone and 10% carbonated apatite are similar but the quadrupole coupling constant of cortical bone is larger than that measured for model compounds. In addition, our results suggest that an increase in the carbonate concentration decreases the observed (43)Ca chemical shift frequency. A comparison of experimentally obtained (43)Ca MAS spectra with simulations reveal a 3:4 mol ratio of Ca-I/Ca-II sites in carbonated apatite and a 2.3:3 mol ratio for hydroxyapatite. 2D triple-quantum (43)Ca MAS experiments performed on a mixture of carbonated apatite and the bone protein osteocalcin reveal the presence of protein-bound and free calcium sites, which is in agreement with a model developed from X-ray crystal structure of the protein.

• Time-Resolved Dehydration-Induced Structural Changes in an Intact Bovine Cortical Bone Revealed by Solid-State NMR Spectroscopy.

  Authors: Peizhi Zhu, Jiadi Xu, Nadder Sahar, Michael D Morris, David H Kohn, Ayyalusamy Ramamoorthy

  Journal of the American Chemical Society. 11/2009;

  Understanding the structure and structural changes of bone, a highly heterogeneous material with a complex hierarchical architecture, continues to be a significant challenge even for high-resolutionUnderstanding the structure and structural changes of bone, a highly heterogeneous material with a complex hierarchical architecture, continues to be a significant challenge even for high-resolution solid-state NMR spectroscopy. While it is known that dehydration affects mechanical properties of bone by decreasing its strength and toughness, the underlying structural mechanism at the atomic level is unknown. Solid-state NMR spectroscopy, controlled dehydration, and H/D exchange were used for the first time to reveal the structural changes of an intact piece of bovine cortical bone. (1)H spectra were used to monitor the dehydration of the bone inside the rotor, and high-resolution (13)C chemical shift spectra obtained under magic-angle spinning were used evaluate the dehydration-induced conformational changes in the bone. The experiments revealed the slow denaturation of collagen due to dehydration while the trans-Xaa-Pro conformation in collagen remained unchanged. Our results suggest that glycosaminoglycans in the collagen fiber and mineral interface may chelate with a Ca(2+) ion present on the surface of the mineral through sulfate or carboxylate groups. These results provide insights into the role of water molecules in the bone structure and shed light on the relationship between the structure and mechanics of bone.

• The bone diagnostic instrument III: testing mouse femora.

  Authors: Connor Randall, Phillip Mathews, Eugene Yurtsev, Nadder Sahar, David Kohn, Paul Hansma

  The Review of scientific instruments. 07/2009; 80(6):065108.

  Here we describe modifications that allow the bone diagnostic instrument (BDI) [P. Hansma et al., Rev. Sci. Instrum. 79, 064303 (2008); Rev. Sci. Instrum. 77, 075105 (2006)], developed to test humanHere we describe modifications that allow the bone diagnostic instrument (BDI) [P. Hansma et al., Rev. Sci. Instrum. 79, 064303 (2008); Rev. Sci. Instrum. 77, 075105 (2006)], developed to test human bone, to test the femora of mice. These modifications include reducing the effective weight of the instrument on the bone, designing and fabricating new probe assemblies to minimize damage to the small bone, developing new testing protocols that involve smaller testing forces, and fabricating a jig for securing the smaller bones for testing. With these modifications, the BDI was used to test the hypothesis that short-term running has greater benefit on the mechanical properties of the femur for young growing mice compared to older, skeletally mature mice. We measured elastic modulus, hardness, and indentation distance increase (IDI), which had previously been shown to be the best discriminators in model systems known to exhibit differences in mechanical properties at the whole bone level. In the young exercised murine femora, the IDI was significantly lower than in young control femora. Since IDI has a relation to postyield properties, these results suggest that exercise during bone development increases post yield mechanical competence. We were also able to measure effects of aging on bone properties with the BDI. There was a significant increase in the IDI, and a significant decrease in the elastic modulus and hardness between the young and old groups. Thus, with the modifications described here, the BDI can take measurements on mouse bones and obtain statistically significant results.

• The bone diagnostic instrument II: Indentation distance increase.

  Authors: Paul Hansma, Patricia Turner, Barney Drake, Eugene Yurtsev, Alexander Proctor, Phillip Mathews, Jason Lelujian, Connor Randall, Jonathan Adams, Ralf Jungmann, Federico Garza-de-Leon, Georg Fantner, Haykaz Mkrtchyan, Michael Pontin, Aaron Weaver, Morton B. Brown, Nadder Sahar, Ricardo Rossello, David Kohn

  The Review of scientific instruments. 07/2008; 79(6):064303.

  The bone diagnostic instrument (BDI) is being developed with the long-term goal of providing a way for researchers and clinicians to measure bone material properties of human bone in vivo. SuchThe bone diagnostic instrument (BDI) is being developed with the long-term goal of providing a way for researchers and clinicians to measure bone material properties of human bone in vivo. Such measurements could contribute to the overall assessment of bone fragility in the future. Here, we describe an improved BDI, the Osteoprobe IItrade mark. In the Osteoprobe IItrade mark, the probe assembly, which is designed to penetrate soft tissue, consists of a reference probe (a 22 gauge hypodermic needle) and a test probe (a small diameter, sharpened rod) which slides through the inside of the reference probe. The probe assembly is inserted through the skin to rest on the bone. The distance that the test probe is indented into the bone can be measured relative to the position of the reference probe. At this stage of development, the indentation distance increase (IDI) with repeated cycling to a fixed force appears to best distinguish bone that is more easily fractured from bone that is less easily fractured. Specifically, in three model systems, in which previous mechanical testing and/or tests reported here found degraded mechanical properties such as toughness and postyield strain, the BDI found increased IDI. However, it must be emphasized that, at this time, neither the IDI nor any other mechanical measurement by any technique has been shown clinically to correlate with fracture risk. Further, we do not yet understand the mechanism responsible for determining IDI beyond noting that it is a measure of the continuing damage that results from repeated loading. As such, it is more a measure of plasticity than elasticity in the bone.

• Is photobleaching necessary for Raman imaging of bone tissue using a green laser?

  Authors: Kurtulus Golcuk, Gurjit S Mandair, Andrew F Callender, Nadder Sahar, David H Kohn, Michael D Morris

  Biochimica et biophysica acta. 08/2006; 1758(7):868-73.

  Raman microspectroscopy is widely used for musculoskeletal tissues studies. But the fluorescence background obscures prominent Raman bands of mineral and matrix components of bone tissue. A 532-nmRaman microspectroscopy is widely used for musculoskeletal tissues studies. But the fluorescence background obscures prominent Raman bands of mineral and matrix components of bone tissue. A 532-nm laser irradiation has been used efficiently to remove the fluorescence background from Raman spectra of cortical bone. Photochemical bleaching reduces over 80% of the fluorescence background after 2 h and is found to be nondestructive within 40 min. The use of electron multiplying couple charge detector (EMCCD) enables to acquire Raman spectra of bone tissues within 1-5 s range and to obtain Raman images less than in 10 min.

• Is photobleaching necessary for Raman imaging of bone tissue using a green laser?

  Authors: Kurtulus Golcuk, Gurjit S. Mandair, Andrew F. Callender, Nadder Sahar, David H. Kohn, Michael D. Morris

  Biochimica et Biophysica Acta (BBA) - Biomembranes.

  Raman microspectroscopy is widely used for musculoskeletal tissues studies. But the fluorescence background obscures prominent Raman bands of mineral and matrix components of bone tissue. A 532-nmRaman microspectroscopy is widely used for musculoskeletal tissues studies. But the fluorescence background obscures prominent Raman bands of mineral and matrix components of bone tissue. A 532-nm laser irradiation has been used efficiently to remove the fluorescence background from Raman spectra of cortical bone. Photochemical bleaching reduces over 80% of the fluorescence background after 2 h and is found to be nondestructive within 40 min. The use of electron multiplying couple charge detector (EMCCD) enables to acquire Raman spectra of bone tissues within 1–5 s range and to obtain Raman images less than in 10 min.

• Publisher’s Note: “The bone diagnostic instrument II: Indentation distance increase” [Rev. Sci Instrum. 79, 064303 (2008)]

  Authors: Paul Hansma, Patricia Turner, Barney Drake, Eugene Yurtsev, Alexander Proctor, Phillip Mathews, Jason Lulejian, Connor Randall, Jonathan Adams, Ralf Jungmann, Federico Garza-de-Leon, Georg Fantner, Haykaz Mkrtchyan, Michael Pontin, Aaron Weaver, Morton B. Brown, Nadder Sahar, Ricardo Rossello, David Kohn