In vivo micro-computed tomography (μCT) provides the ability to measure longitudinal changes to tibia microarchitecture, but the effect of this radiation is not well understood. The right proximal tibia of Sprague-Dawley rats (n = 12/group) randomized to Sham-control (Sham) or ovariectomy (OVX) surgery at 12 weeks of age was scanned using μCT at 13, 17, 21, and 25 weeks of age, at a resolution of 18 μm and a radiation dose of 603 mGy. The left proximal tibia was scanned only at 25 weeks of age to serve as an internal non-irradiated control. Repeated irradiation did not affect tibia microarchitecture in Sham or OVX groups, although there was an increase in cortical eccentricity (P< 0.05). All trabecular outcomes and cortical BMD were different (P < 0.05) between groups after only 1 week post-surgery and differences persisted to study endpoint. Characteristic changes to trabecular bone were observed in OVX rats over time. Interactions of time and hormone status were found for cortical BMD (P < 0.001), Ps. Pm., and Ec. Pm. (P < 0.05). Repeated irradiation of the tibia at 13, 17, 21, and 25 weeks does not cause adverse effects to microarchitecture, regardless of hormone status. This radiation dose can be applied over a typical 3-month study period to comprehensively understand how an intervention alters tibia microarchitecture without confounding effects of radiation.

Long-term effects of repeated in vivo micro-computed tomography (lCT) scanning at key stages of growth and bone development (ages 2, 4 and 6 months) on trabecular and cortical bone structure, as well as developmental patterns, have not been studied. We determined the effect of repetitive lCT scanning at age 2, 4 and 6 months on tibia bone structure of male and female CD-1 mice and characterized developmental changes. At 2, 4 and 6 months of age, right tibias were scanned using in vivo lCT (Skyscan 1176) at one of three doses of radiation per scan: 222, 261 or 460 mGy. Left tibias of the same mice were scanned only at 6 months to serve as non-irradiated controls to determine whether recurrent radiation exposure alters trabecular and cortical bone structure at the proximal tibia. In males, eccentricity was lower (Po0.05) in irradiated compared with non-irradiated tibias (222 mGy group). Within each sex, all other structural outcomes were similar between irradiated and non-irradiated tibias regardless of dose. Trabecular bone loss occurred in all mice due to age while cortical development continued to age 6 months. In conclusion, repetitive lCT scans at various radiation doses did not damage trabecular or cortical bone structure of proximal tibia in male and female CD-1 mice. Moreover, scanning at 2, 4 and 6 months of age highlight the different developmental time course between trabecular and cortical bone. These scanning protocols can be used to investigate longitudinal responses of bone structures to an intervention.

Osteoporosis is a global health problem that leads to an increased incidence of fragility fracture. Recent dietary patterns of Western populations include higher than recommended intakes of n-6 (ω-6) polyunsaturated fatty acids (PUFAs) relative to n-3 (ω-3) PUFAs that may result in a chronic state of sterile whole body inflammation. Findings from human bone cell culture experiments have revealed both benefits and detriments to bone-related outcomes depending on the quantity and source of PUFAs. Findings from observational and randomized controlled trials suggest that higher fatty fish intake is strongly linked with reduced risk of fragility fracture. Moreover, human studies largely support a greater intake of total PUFAs, total n-6 (ω-6) fatty acid, and total n-3 (ω-3) fatty acid for higher bone mineral density and reduced risk of fragility fracture. Less consistent evidence has been observed when investigating the role of long chain n-3 (ω-3) PUFAs or the ratio of n-6 (ω-6) PUFAs to n-3 (ω-3) PUFAs. Aspects to consider when interpreting the current literature involve participant characteristics, study duration, diet assessment tools, and the primary outcome measure.

Adipose triglyceride lipase (ATGL) catalyzes the rate-limiting removal of the first fatty acid from a triglyceride. ATGL is activated by comparative gene identification-58 and inhibited by G(0)/G(1) switch gene-2 protein (G0S2). Research in other tissues and cell culture indicates that inhibition is dependent on relative G0S2-to-ATGL protein content. G0S2 may also have several roles within mitochondria; however, this has yet to be observed in skeletal muscle. The purpose of this study was to determine if muscle G0S2 relative to ATGL content would decrease to facilitate intramuscular lipolysis following endurance training. Male Sprague-Dawley rats (n = 10; age 51-53 days old) were progressively treadmill trained at a 10% incline for 8 wk ending with 25 m/min for 1 h compared with control. Sciatic nerve stimulation for hind-limb muscle contraction (and lipolysis) was administered for 30 min to one leg, leaving the opposing leg as a resting control. Soleus (SOL), red gastrocnemius (RG), and white gastrocnemius were excised from both legs following stimulation or control. ATGL protein increased in all trained muscles. Unexpectedly, G0S2 protein was greater in the trained SOL and RG. In RG-isolated mitochondria, G0S2 also increased with training, yet mitochondrial G0S2 content was unaltered with acute contraction; therefore, any role of G0S2 in the mitochondria does not appear to be acutely mediated by content alone. In summary, G0S2 increased with training in oxidative muscles and mitochondria but not following acute contraction, suggesting that inhibition is not through relative G0S2-to-ATGL content but through more complicated intracellular mechanisms.

The parameters of a micro-computed tomography (μCT) scan, including whether a bone is imaged in vivo or ex vivo, determine the quality of the resulting image. In turn, this impacts the accuracy of the trabecular and cortical outcomes. The absolute impact of μCT scanning at different voxel sizes and whether the sample is imaged in vivo or ex vivo on the morphological outcomes of the proximal tibia in the rat is unknown. The right proximal tibia of 6-month-old Sham-control and ovariectomized (OVX) rats (n = 8/group) was scanned using μCT (SkyScan 1176, Bruker, Kontich, Belgium) using three sets of parameters (9 μm ex vivo, 18 μm ex vivo, 18 μm in vivo) to compare the trabecular and cortical outcomes. Regardless of scan protocols, differences between Sham and OVX groups were observed as expected. At a voxel size of 18 μm, scanning in vivo or ex vivo had no effect on any of the outcomes measured. However, compared to a 9 μm voxel size scan, imaging at 18 μm resulted in significant underestimation of the connectivity density (p < 0.05) of the trabecular bone and a significant overestimation (p < 0.05) of the trabecular indices (trabecular thickness, degree of anisotropy) and of the cortical indices (cortical bone area, cortical area fraction, cortical thickness) in both Sham and OVX rats. These results suggest the benefit to scanning the proximal tibia of rats at a voxel size as low as 9 μm, although considerations must be made for the increased acquisition time, anesthesia, animal welfare, and radiation exposure associated with lower voxel size in vivo scanning. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1690-1698, 2017.