Mechanical Loading Attenuates Radiation-Induced Bone Loss in Bone Marrow Transplanted Mice

Exposure of bone to ionizing radiation, as occurs during radiotherapy for some localized malignancies and blood or bone marrow cancers, as well as during space travel, incites dose-dependent bone morbidity and increased fracture risk. Rapid trabecular and endosteal bone loss reflects acutely increased osteoclastic resorption as well as decreased bone formation due to depletion of osteoprogenitors. Because of this dysregulation of bone turnover, bone’s capacity to respond to a mechanical loading stimulus in the aftermath of irradiation is unknown. We employed a mouse model of total body irradiation and bone marrow transplantation simulating treatment of hematologic cancers, hypothesizing that compression loading would attenuate bone loss. Furthermore, we hypothesized that loading would upregulate donor cell presence in loaded tibias due to increased engraftment and proliferation. We lethally irradiated 16 female C57Bl/6J mice at age 16 wks with 10.75 Gy, then IV-injected 20 million GFP(+) total bone marrow cells. That same day, we initiated 3 wks compression loading (1200 cycles 5x/wk, 10 N) in the right tibia of 10 of these mice while 6 mice were irradiated, non-mechanically-loaded controls. As anticipated, before-and-after microCT scans demonstrated loss of trabecular bone (-48.2% Tb.BV/TV) and cortical thickness (-8.3%) at 3 wks following irradiation. However, loaded bones lost 31% less Tb.BV/TV and 8% less cortical thickness (both p\u3c0.001). Loaded bones also had significant increases in trabecular thickness and tissue mineral densities from baseline. Mechanical loading did not affect donor cell engraftment. Importantly, these results demonstrate that both cortical and trabecular bone exposed to high-dose therapeutic radiation remain capable of an anabolic response to mechanical loading. These findings inform our management of bone health in cases of radiation exposure

Mahadaga pump project : durability testing and redesign of a handicap accessible pump for irrigation in West Africa

Approved for Honors in the Department of Engineering, Messiah College, 2006

Trabecular microstructure parameters significantly regulated by loading, as indicated by microCT.

<p>Mean ± 95% CI, n = 10 for ‘Irradiated+Loaded’ mice and n = 6 for ‘Irradiated’ mice. p<0.05 considered significant by paired two-tailed t-test. Percent changes indicate effect of loading relative to contralateral controls.</p

Murine-specific primers used for real-time RT-PCR for relative quantification of donor cell DNA.

<p>Murine-specific primers used for real-time RT-PCR for relative quantification of donor cell DNA.</p

Relative donor cell DNA levels in host bone.

<p>Loaded and contralateral control bones each divided by proximal and distal segments. Donor-specific DNA measured by (A) GFP transgene (p = 0.098 for effect of loading and **p = 0.009 for effect of bone region by two-way ANOVA) and (B) male <i>Zfy1</i> DNA (p = 0.256 for effect of loading and **p = 0.002 for effect of bone region), both normalized to <i>ApoB</i>. Mean ± 95% CI with n = 7 for proximal and n = 5 for distal segments.</p

Representative trabecular bone changes from one mouse having median changes in bone volume fraction.

<p>Representative trabecular bone changes from one mouse having median changes in bone volume fraction.</p

Mouse body mass as a function of time, from irradiation treatment on day 0 to sacrifice on day 21.

<p>Solid line, filled circles represent ‘Irradiated + Loaded’ animals and dashed line, open squares represent ‘Irradiated’ animals. Mean ± 95% CI, n = 3–10 for each data point due to intermittent weighing.</p

Bone marrow donor/host analysis by tibia region.

<p>(A) In vivo microCT scout image indicating locations of cuts made during dissection to isolate proximal trabecular compartments and distal cortical compartments. (B) Percent of freshly isolated total bone marrow cells analyzed as GFP(+) by flow cytometry analysis. Mean ± 95% CI, n = 9–10 mice, all with loaded and contralateral control limbs. (C) Cell count of freshly isolated total bone marrow cells. Mean ± 95% CI, n = 10. (D) Estimated total donor bone marrow cells calculated as each sample’s total bone marrow cell count multiplied by that sample’s percent GFP+ marrow (B x C = D). Mean ± 95% CI, n = 9–10. Significant differences indicated by paired two-tailed t-test.</p

Additional trabecular microstructure parameters not significantly regulated by loading, as indicated by microCT.

<p>Mean ± 95% CI, n = 10 for ‘Irradiated+Loaded’ mice and n = 6 for ‘Irradiated’ mice. p<0.05 considered significant by paired two-tailed t-test. NS indicates no significant difference between contralateral controls.</p

Cortical microstructure parameters significantly regulated by loading, as indicated by microCT.

<p>Mean ± 95% CI, n = 10 for ‘Irradiated+Loaded’ mice and n = 6 for ‘Irradiated’ mice. p<0.05 considered significant by paired two-tailed t-test. Percent changes indicate effect of loading relative to contralateral controls.</p