Oxidative and nutrient stability of a standard rodent spaceflight diet during long-term storage.

The National Aeronautics and Space Administration's standard spaceflight diet for rodents is the nutrient-upgraded rodent food bar (NuRFB). The shelf life of the NuRFB needs to be determined in order to avoid malnutrition of rodents and confounding of research results resulting from nutritional deficiency. The authors compared the oxidative and nutrient stability of NuRFBs stored at either ambient temperature (26 °C) or at refrigeration temperature (4 °C) for use in long-term rodent feeding experiments. After 0, 3, 6, 9 and 12 months (mo) of storage, lipid oxidation, fatty acid composition and amounts of specific vitamins and amino acids in NuRFBs were analyzed. No oxidative rancidity developed in NuRFBs stored at 4 °C for up to 12 mo, but NuRFBs stored at 26 °C for 6 mo developed oxidative rancidity and had reduced amounts of γ-linolenic acid (18:3n-6). Despite loss of vitamin E, vitamin A and thiamin after storage at 26 °C for 12 mo, vitamin levels in NuRFBs remained at or above the levels recommended for optimal rodent health. The amino acid profile of NuRFBs was unaffected by storage at 4 °C or 26 °C for 12 mo. The results suggest that NuRFBs stored at 4 °C for up to 12 mo and NuRFBs stored at 26 °C for up to 6 mo provide suitable nutrition for rodents in long-term experiments.

Evaluation of the nutrient-upgraded rodent food bar for rodent spaceflight experiments.

OBJECTIVE: Selection of an appropriate diet for rodent spaceflight experiments is critical and may have significant effects on mission results. The National Aeronautics and Space Administration (NASA) rodent food bar (RFB) was reformulated and designated as the nutrient-upgraded RFB (NuRFB). The objectives of this study were to determine whether the NuRFB nutrient formulation meets the 1995 National Research Council (NRC) nutrient recommendations and whether the NuRFB can be used for short-term (45-d) and long-term (90-d) spaceflight experiments. METHODS: Nutrient and moisture analyses of the NuRFB were performed. Young (age 13-14 wk) male Sprague-Dawley rats (n=16/group) were individually caged and fed a diet treatment consisting of 1) NuRFB, 2) RFB, or 3) modified AIN-93G containing 4% instead of the 7% fat for 45- or 90-d. At the end of the study, organs were weighted, and serum clinical chemistry indicators of organ function and hematologic measurements were determined. RESULTS: Chemical analysis of the diet ingredients showed that the NuRFB met the 1995 NRC nutrient recommendations for rats. Subsequent animal feeding studies showed that NuRFB was comparable to RFB and modified AIN-93G for supporting rat growth and body weight maintenance. In addition, the safety of the NuRFB for use as a spaceflight diet was indicated by the absence of changes in organ weight or function. CONCLUSION: Based on the study results, the NuRFB performed similarly to the RFB and met the criteria necessary for short-term and long-term rodent spaceflight experiments.

Role for beta1 integrins in cortical osteocytes during acute musculoskeletal disuse.

The mammalian skeleton adjusts bone structure and strength in response to changes in mechanical loading, however the molecular and cellular mechanisms governing this process in vivo are unknown. Terminally differentiated osteoblasts, the osteocytes, are presumptive mechanosensory cells for bone, and cell culture studies demonstrate that beta1 integrins participate in mechanical signaling. To determine the role of beta1 integrins in osteoblasts in vivo, we used the Cre-lox system to delete beta1 integrin from cells committed to the osteoblast lineage. While pCol2.3 Cre-mediated recombination was widespread in bones from Colalpha1(I)-Cre+/beta1fl/fl conditional knockout mice (cKO), beta1 integrin protein was depleted from cortical osteocytes, but not from cancellous osteocytes or cells lining bone surfaces in adults. Bones from cKO mice that were normally loaded were similar in structure to WT littermates. However, hindlimb unloading of adult cKO mice for one week intended to cause bone loss (disuse osteopenia), resulted in unexpected, rapid changes in the geometry of cortical bone; hindlimb unloading increased the cross-sectional area, marrow area, and moments of inertia in cKO, but not WT mice. Furthermore, these hindlimb unloading-induced geometric changes in cortical bone of cKO mice resulted in increased whole bone bending stiffness and strength of the femur. Together, these results confirmed the concept that osteocytes are mechanosensory cells and showed beta1 integrins in cortical osteocytes limited changes in cortical geometry in response to disuse, thus providing the first in vivo evidence that beta1 integrins on osteocytes mediate specific aspects of mechanotransduction.