Effects of Exogenous Lipopolysaccharide Exposure on Bone Outcomes in Rodent Models

Chronic low-grade inflammation has been identified as a potential contributor to the pathophysiology of osteoporosis. A key mediator may be lipopolysaccharide (LPS) released from gram-negative bacteria in the gut that can enter circulation stimulating an inflammatory response and upregulate bone resorption. Since rodent models mimic the loss of bone mineral density (BMD) and structure that occurs in humans, rodents offer an accelerated model for studying these inflammation-mediated changes. Therefore, the objective of this thesis was to characterize a rodent model of LPS-induced bone loss using repeated in vivo μCT scans to establish a time course effect of LPS longitudinally and for this purpose three studies were conducted. Study 1 & 2 were run simultaneously using the same control mice. Study 1 demonstrated that repeated irradiation had a negative impact on trabecular bone in both male and female CD-1 mice, while cortical bone was only negatively impacted in the females. In study 2, continuous delivery of exogenous LPS via osmotic pumps for 12 weeks elevated serum LPS in both male and female CD-1 mice but did not alter trabecular or cortical bone structure or BMD at any of the scanning timepoints. Results from Study 2 may in part have been influenced by the effects of repeated irradiation from the in vivo μCT scans at 4-week intervals for a total of 4 scans analyzed in Study 1. In study 3, a systematic review was conducted to better characterize a model of LPS induced bone loss and identify factors that may impact the effects of LPS on bone outcomes in rodent models. Regardless of study duration, exogenous LPS negatively impacted trabecular bone structure and BMD but not cortical bone structure, due to an upregulation in bone resorption. Together these data suggest that exogenous LPS can induce alterations in bone structure and BMD in rodent models, however a clearly defined model of exogenous LPS induced bone loss has yet to be fully characterized.

Year	Entry
2002	Halloran BP, Ferguson VL, Simske SJ, Burghardt A, Venton LL, Majumdar S. Changes in bone structure and mass with advancing age in the male C57BL/6J mouse. J Bone Miner Res. June 2002;17(6):1044-1050.
2010	Willinghamm MD, Brodt MD, Lee KL, Stephens AL, Ye J, Silva MJ. Age-related changes in bone structure and strength in female and male BALB/c mice. Calcif Tiss Int. June 2010;86(6):470-483.
2002	Nakashima K, Zhou X, Kunkel G, Zhang Z, Deng JM, Behringer RR, de Crombrugghe B. The novel zinc finger-containing transcription factor osterix is required for osteoblast differentiation and bone formation. Cell. January 11, 2002;108(1):17-29.
2004	Schuit SCE, van der Klift M, Weel AEAM, de Laet CEDH, Burger H, Seeman E, Hofman A, Uitterlinden AG, van Leeuwen JPTM, Pols HAP. Fracture incidence and association with bone mineral density in elderly men and women: the Rotterdam Study. Bone. January 2004;34(1):195-202.
2003	David V, Laroche N, Boudignon B, Lafage‐Proust M, Alexandre C, Ruegsegger P, Vico L. Noninvasive in vivo monitoring of bone architecture alterations in hindlimb‐unloaded female rats using novel three‐dimensional microcomputed tomography. J Bone Miner Res. September 2003;18(9):1622-1631.
2008	Clarke B. Normal bone anatomy and physiology. Clin J Am Soc Nephrol. November 2008;3(suppl 3):S131-S139.
2011	Donnelly E. Methods for assessing bone quality: a review. Clin Orthop Relat Res. August 2011;469:2128-2138.
2004	Waarsing JH, Day JS, van der Linden JC, Ederveen AG, Spanjers C, De Clerck N, Sasov A, Verhaar JAN, Weinans H. Detecting and tracking local changes in the tibiae of individual rats: a novel method to analyse longitudinal in vivo micro-ct data. Bone. January 2004;34(1):163-169.
1997	Hildebrand T, Rüegsegger P. Quantification of bone microarchitecture with the structure model index. Comput Methods Prog Biomed. 1997;1(1):15-23.
2010	Damilakis J, Adams JE, Guglielmi G, Link TM. Radiation exposure in x-ray-based imaging techniques used in osteoporosis. Eur Radiol. November 2010;20(11):2707-2714.
2007	Bonewald LF. Osteocytes as dynamic multifunctional cells. Annals NY Acad Sci. 2007;1116(1):281-290.
2016	Weaver CM, Gordon CM, Janz KF, Kalkwarf HJ, Lappe JM, Lewis R, O’Karma M, Wallace TC, Zemel BS. The National Osteoporosis Foundation’s position statement on peak bone mass development and lifestyle factors: a systematic review and implementation recommendations. Osteoporos Int. April 2016;27(4):1281-1386.
2010	Bouxsein ML, Boyd SK, Christiansen BA, Guldberg RE, Jepsen KJ, Müller R. Guidelines for assessment of bone microstructure in rodents using micro-computed tomography. J Bone Miner Res. July 2010;25(7):1468-1486.
2013	Cheung AM, Adachi JD, Hanley DA, Kendler DL, Davison KS, Josse R, Brown JP, Ste-Marie L-G, Kremer R, Erlandson MC, Dian L, Burghardt AJ, Boyd SK. High-resolution peripheral quantitative computed tomography for the assessment of bone strength and structure: a review by the Canadian Bone Strength Working Group. Curr Osteoporos Rep. June 2013;11(2):136-146.
2006	Boyd SK, Davison P, Müller R, Gasser JA. Monitoring individual morphological changes over time in ovariectomized rats by in vivo micro-computed tomography. Bone. October 2006;39(4):854-862.
2007	Glatt V, Canalis E, Stadmeyer L, Bouxsein ML. Age‐related changes in trabecular architecture differ in female and male C57BL/6J mice. J Bone Miner Res. August 2007;22(8):1197-1207.
1989	Feldkamp LA, Goldstein SA, Parfitt MA, Jesion G, Kleerekoper M. The direct examination of three‐dimensional bone architecture in vitro by computed tomography. J Bone Miner Res. 1989;4(1):3-11.
2009	Moher D, Liberati A, Tetzlaff J, Altman DG; PRISMA Group. Preferred reporting items for systematic reviews and meta-analyses: the PRISMA statement. PLoS Med. July 21, 2009;6(7):e1000097.
2003	Boyle WJ, Simonet WS, Lacey DL. Osteoclast differentiation and activation. Nature. May 15, 2003;423(6937):337-342.
1997	Odgaard A. Three-dimensional methods for quantification of cancellous bone architecture. Bone. 1997;20(4):315-328.
2007	Brouwers JEM, van Rietbergen B, Huiskes R. No effects of in vivo micro-CT radiation on structural parameters and bone marrow cells in proximal tibia of wistar rats detected after eight weekly scans. J Orthop Res. October 2007;25(10):1325-1332.
2008	Klinck RJ, Campbell GM, Boyd SK. Radiation effects on bone architecture in mice and rats resulting from in vivo micro-computed tomography scanning. Med Eng Phys. September 2008;30(7):888-895.
2010	Eriksen EF. Cellular mechanisms of bone remodeling. Rev Endocr Metab Disord. December 2010;11(4):219-227.
2006	Robling AG, Castillo AB, Turner CH. Biomechanical and molecular regulation of bone remodeling. Annu Rev Biomed Eng. 2006;8:455-498.
2016	Hunt HB, Donnelly E. Bone quality assessment techniques: geometric, compositional, and mechanical characterization from macroscale to nanoscale. Clin Rev Bone Miner Metab. September 2016;14(3):133-149.
2003	Bouxsein ML. Bone quality: where do we go from here? Osteoporos Int. September 2003;14(suppl 5):S118-S127.

Year

Entry

2002

Halloran BP, Ferguson VL, Simske SJ, Burghardt A, Venton LL, Majumdar S. Changes in bone structure and mass with advancing age in the male C57BL/6J mouse. J Bone Miner Res. June 2002;17(6):1044-1050.

2010

Willinghamm MD, Brodt MD, Lee KL, Stephens AL, Ye J, Silva MJ. Age-related changes in bone structure and strength in female and male BALB/c mice. Calcif Tiss Int. June 2010;86(6):470-483.

2002

Nakashima K, Zhou X, Kunkel G, Zhang Z, Deng JM, Behringer RR, de Crombrugghe B. The novel zinc finger-containing transcription factor osterix is required for osteoblast differentiation and bone formation. Cell. January 11, 2002;108(1):17-29.

2004

Schuit SCE, van der Klift M, Weel AEAM, de Laet CEDH, Burger H, Seeman E, Hofman A, Uitterlinden AG, van Leeuwen JPTM, Pols HAP. Fracture incidence and association with bone mineral density in elderly men and women: the Rotterdam Study. Bone. January 2004;34(1):195-202.

2003

David V, Laroche N, Boudignon B, Lafage‐Proust M, Alexandre C, Ruegsegger P, Vico L. Noninvasive in vivo monitoring of bone architecture alterations in hindlimb‐unloaded female rats using novel three‐dimensional microcomputed tomography. J Bone Miner Res. September 2003;18(9):1622-1631.