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.

Cardiolipin (CL) is a unique mitochondrial phospholipid that, in skeletal muscle, is enriched with linoleic acid (18:2n6). Together, CL content and CL 18:2n6 composition are critical determinants of mitochondrial function. Skeletal muscle is comprised of slow and fast fibers that have high and low mitochondrial content, respectively. In response to overloading and unloading stimuli, these muscles undergo a fast-to-slow oxidative fiber type shift and a slow-to-fast glycolytic fiber type shift, respectively, with a concomitant change in mitochondrial content. Here, we examined changes in CL content and CL 18:2n6 composition under these conditions along with tafazzin (Taz) protein, which is a transacylase enzyme that generates CL lipids enriched with 18:2n6. Our results show that CL content, CL 18:2n6 composition, and Taz protein content increased with an overload stimulus in plantaris. Conversely, CL content and CL 18:2n6 composition was reduced with an unloaded stimulus in soleus. Interestingly, Taz protein was increased in the unloaded soleus, suggesting that Taz may provide some form of compensation for decreased CL content and CL 18:2n6 composition. Together, this study highlights the dynamic nature of CL and Taz in skeletal muscle, and future studies will examine the physiological significance behind the changes in CL content, CL 18:2n6 and Taz.

Hesperidin (HSP) and naringin (NAR), flavanones rich in citrus fruits, support skeletal integrity in adult and aging rodent models. This study determined whether maternal consumption of HSP and NAR favorably programs bone development, resulting in higher bone mineral density (BMD) and greater structure and biomechanical strength (i.e., peak load) in female offspring. Female CD-1 mice were fed a control diet or a HSP + NAR diet five weeks before pregnancy and throughout pregnancy and lactation. At weaning, female offspring were fed a control diet until six months of age. The structure and BMD of the proximal tibia were measured longitudinally using in vivo micro-computed tomography at 2, 4, and 6 months of age. The trabecular bone structure at two and four months and the trabecular BMD at four months were compromised at the proximal tibia in mice exposed to HSP and NAR compared to the control diet (p < 0.001). At six months of age, these differences in trabecular structure and BMD at the proximal tibia had disappeared. At 6 months of age, the tibia midpoint peak load, BMD, structure, and the peak load of lumbar vertebrae and femurs were similar (p > 0.05) between the HSP + NAR and control groups. In conclusion, maternal consumption of HSP and NAR does not enhance bone development in female CD-1 offspring.

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