Biological and metabolic response in STS-135 space-flown mouse skin.

There is evidence that space flight condition-induced biological damage is associated with increased oxidative stress and extracellular matrix (ECM) remodeling. To explore possible mechanisms, changes in gene expression profiles implicated in oxidative stress and in ECM remodeling in mouse skin were examined after space flight. The metabolic effects of space flight in skin tissues were also characterized. Space Shuttle Atlantis (STS-135) was launched at the Kennedy Space Center on a 13-day mission. Female C57BL/6 mice were flown in the STS-135 using animal enclosure modules (AEMs). Within 3-5 h after landing, the mice were euthanized and skin samples were harvested for gene array analysis and metabolic biochemical assays. Many genes responsible for regulating production and metabolism of reactive oxygen species (ROS) were significantly (p < 0.05) altered in the flight group, with fold changes >1.5 compared to AEM control. For ECM profile, several genes encoding matrix and metalloproteinases involved in ECM remodeling were significantly up-/down-regulated following space flight. To characterize the metabolic effects of space flight, global biochemical profiles were evaluated. Of 332 named biochemicals, 19 differed significantly (p < 0.05) between space flight skin samples and AEM ground controls, with 12 up-regulated and 7 down-regulated including altered amino acid, carbohydrate metabolism, cell signaling, and transmethylation pathways. Collectively, the data demonstrated that space flight condition leads to a shift in biological and metabolic homeostasis as the consequence of increased regulation in cellular antioxidants, ROS production, and tissue remodeling. This indicates that astronauts may be at increased risk for pathophysiologic damage or carcinogenesis in cutaneous tissue.

Joint bleeding in factor VIII deficient mice causes an acute loss of trabecular bone and calcification of joint soft tissues which is prevented with aggressive factor replacement.

While chronic degenerative arthropathy is the main morbidity of haemophilia, a very high prevalence of low bone density is also seen in men and boys with haemophilia. This study investigates bone degradation in the knee joint of haemophilic mice resulting from haemarthrosis and the efficacy of aggressive treatment with factor VIII in the period surrounding injury to prevent bone pathology. Skeletally mature factor VIII knock-out mice were subjected to knee joint haemorrhage induced by puncture of the left knee joint capsule. Mice received either intravenous factor VIII treatment or placebo immediately prior to injury and at hours 4, 24, 48, 72 and 96 after haemorrhage. Mice were killed 2-weeks after injury and the joint morphology and loss of bone in the proximal tibia was assessed using microCT imaging. Quantitative microCT imaging of the knee joint found acute bone loss at the proximal tibia following injury including loss of trabecular bone volumetric density and bone mineral density, as well as trabecular connectivity density, number and thickness. Unexpectedly, joint injury also resulted in calcification of the joint soft tissues including the tendons, ligaments, menisci and cartilage. Treatment with factor VIII prevented this bone and soft tissue degeneration. Knee joint haemorrhage resulted in acute changes in adjacent bone including loss of bone density and mineralization of joint soft tissues. The rapid calcification and loss of bone has implications for the initiation and progression of osteoarthritic degradation following joint bleeding.

Spaceflight and hind limb unloading induce similar changes in electrical impedance characteristics of mouse gastrocnemius muscle.

OBJECTIVE: To assess the potential of electrical impedance myography (EIM) to serve as a marker of muscle fiber atrophy and secondarily as an indicator of bone deterioration by assessing the effects of spaceflight or hind limb unloading. METHODS: In the first experiment, 6 mice were flown aboard the space shuttle (STS-135) for 13 days and 8 earthbound mice served as controls. In the second experiment, 14 mice underwent hind limb unloading (HLU) for 13 days; 13 additional mice served as controls. EIM measurements were made on ex vivo gastrocnemius muscle. Quantitative microscopy and areal bone mineral density (aBMD) measurements of the hindlimb were also performed. RESULTS: Reductions in the multifrequency phase-slope parameter were observed for both the space flight and HLU cohorts compared to their respective controls. For ground control and spaceflight groups, the values were 24.7±1.3°/MHz and 14.1±1.6°/MHz, respectively (p=0.0013); for control and HLU groups, the values were 23.9±1.6°/MHz and 19.0±1.0°/MHz, respectively (p=0.014). This parameter also correlated with muscle fiber size (ρ=0.65, p=0.011) for spaceflight and hind limb aBMD (ρ=0.65, p=0.0063) for both groups. CONCLUSIONS: These data support the concept that EIM may serve as a useful tool for assessment of muscle disuse secondary to immobilization or microgravity.

IL-6 receptor antagonist as adjunctive therapy with clotting factor replacement to protect against bleeding-induced arthropathy in hemophilia.

BACKGROUND: The most common morbidity that results from hemophilia is bleeding-induced hemophilic arthropathy (HA), which once established may not be interrupted completely even by prophylactic clotting factor replacement. Specific therapies to oppose inflammatory cytokines, including Interleukin 6 (IL-6) receptor antagonists, have become important in the management of inflammatory arthritides. OBJECTIVES: We investigated combining therapy using MR16-1, a rat IgG antibody directed against mouse IL-6 receptor (anti-IL-6R), with factor VIII (FVIII) replacement to protect against bleeding-induced arthropathy in hemophilia A mice. METHODS: Three recurrent hemarthroses were induced in the knee joint capsule of FVIII knockout mice. Treatment at the time of each hemorrhage included either: no treatment; FVIII replacement given at the time of hemorrhage; FVIII replacement at hemorrhage plus anti-IL-6R as 4-weekly injections; FVIII replacement with non-specific control antibody (rat IgG); and anti-IL-6R alone without FVIII replacement. Six weeks following the first hemarthosis, joints were harvested and histopathology was scored for synovitis, for cartilage integrity and for macrophage infiltration. RESULTS: Animals that received anti-IL-6R as an adjunct to FVIII replacement demonstrated the best survival and the least acute joint swelling and pathology on histologic examination of the synovium and cartilage (P < 0.05 for each parameter). All histopathologic parameters in the mice receiving FVIII+anti-IL-6R were limited and were comparable to findings in injured hemostatically normal mice. The major benefits of adjunctive anti-IL-6R were decreasing synovial hyperplasia, hemosiderin deposition and macrophage infiltration. CONCLUSIONS: Short-course specific inhibition of inflammatory cytokines as an adjunct to replacement hemostasis may be an approach to minimize hemophilic joint degeneration.

Bone architectural and structural properties after 56Fe26+ radiation-induced changes in body mass.

High-energy, high-charge (HZE) radiation, including iron ions ((56)Fe(26+)), is a component of the space environment. We recently observed a profound loss of trabecular bone in mice after whole-body HZE irradiation. The goal of this study was to examine morphology in bones that were excluded from a (56)Fe(26+) beam used to irradiate the body. Using 10-week-old male Sprague-Dawley rats and excluding the hind limbs and pelvis, we irradiated animals with 0, 1, 2 and 4 Gy (56)Fe(26+) ions and killed them humanely after 9 months. Animals grew throughout the experiment. Trabecular bone volume, connectivity and thickness within the proximal tibiae were significantly lower than control in a dose-dependent manner. Irradiated animals generally had less body mass than controls, which largely accounted for the variability in bone parameters as determined by ANCOVA. Likewise, lower cortical parameters were associated with reduced mass. However, lesser trabecular thickness in the 4-Gy group could not be attributed to body mass alone. Indicators of bone metabolism were generally unchanged, suggesting stabilized turnover. Exposure to (56)Fe(26+) ions can alter trabecular microarchitecture in shielded bones. Reduced body mass seems to be correlated with these deficits of trabecular and cortical bone.

Skeletal deterioration induced by RANKL infusion: a model for high-turnover bone disease.

UNLABELLED: RANKL was administered continuously to rats for 28 days to investigate its potential as a disease model for the skeletal system. Bone turnover rates, bone material, structural and mechanical properties were evaluated. RANKL infusion caused overall skeletal complications comparable to those in high bone-turnover conditions, such as postmenopausal osteoporosis. INTRODUCTION: RANKL is an essential mediator for osteoclast development. No study has examined in detail the direct skeletal consequences of excess RANKL on bone turnover, mineralization, architecture, and vascular calcification. We, therefore, administrated soluble RANKL continuously into mature rats and created a bone-loss model. METHODS: Six-month-old Sprague-Dawley (SD) rats were assigned to three groups (n = 12) receiving continuous administration of saline (VEH) or human RANKL (35 microg/kg/day, LOW or 175 microg/kg/day, HI) for 28 days. Blood was collected routinely during the study. At sacrifice, hind limbs and aorta were removed and samples were analyzed. RESULTS: High dose RANKL markedly stimulated serum osteocalcin and TRAP-5b levels and reduced femur cortical bone volume (-7.6%) and trabecular volume fraction (BV/TV) at the proximal tibia (-64% vs. VEH). Bone quality was significantly degraded in HI, as evidenced by decreased femoral percent mineralization, trabecular connectivity, and increased endocortical bone resorption perimeters. Both cortical and trabecular bone mechanical properties were reduced by high dose RANKL. No differences were observed in the mineral content of the abdominal aorta. CONCLUSIONS: Continuous RANKL infusion caused general detrimental effects on rat skeleton. These changes are comparable to those commonly observed in high-turnover bone diseases such as postmenopausal osteoporosis.

A murine model for bone loss from therapeutic and space-relevant sources of radiation.

Cancer patients receiving radiation therapy are exposed to photon (gamma/X-ray), electron, and less commonly proton radiation. Similarly, astronauts on exploratory missions will be exposed to extended periods of lower-dose radiation from multiple sources and of multiple types, including heavy ions. Therapeutic doses of radiation have been shown to have deleterious consequences on bone health, occasionally causing osteoradionecrosis and spontaneous fractures. However, no animal model exists to study the cause of radiation-induced osteoporosis. Additionally, the effect of lower doses of ionizing radiation, including heavy ions, on general bone quality has not been investigated. This study presents data developing a murine model for radiation-induced bone loss. Female C57BL/6 mice were exposed to gamma, proton, carbon, or iron radiation at 2-Gray doses, representing both a clinical treatment fraction and spaceflight exposure for an exploratory mission. Mice were euthanized 110 days after irradiation. The proximal tibiae and femur diaphyses were analyzed using microcomputed tomography. Results demonstrate profound changes in trabecular architecture. Significant losses in trabecular bone volume fraction were observed for all radiation species: gamma, (-29%), proton (-35%), carbon (-39%), and iron (-34%). Trabecular connectivity density, thickness, spacing, and number were also affected. These data have clear implications for clinical radiotherapy in that bone loss in an animal model has been demonstrated at low doses. Additionally, these data suggest that space radiation has the potential to exacerbate the bone loss caused by microgravity, although lower doses and dose rates need to be studied.

Hepatic ethoxyresorufin O-deethylase (EROD) activity in flounder (Platichthys flesus) from contaminant impacted estuaries of the United Kingdom: continued monitoring 1999-2001.

The determination of hepatic ethoxyresorufin O-deethylase (EROD) has been used to assess the induction of the mixed function oxygenase system (MFO) of flounder (Platichthys flesus) in UK estuaries. Induction of the MFO system denotes possible exposure to certain organic contaminants (e.g. polycyclic aromatic hydrocarbons, polychlorinated biphenyls) and its measure has been incorporated in national monitoring programmes. This study presents EROD monitoring data from 5 UK estuaries taken between 1999 and 2001 and builds on data from previous years. The results reveal that for all sampled estuaries EROD values have been significantly (p < 0.05) elevated on the majority of occasions in comparison with the reference estuary, the Alde in Suffolk, UK. However, the limited temporal scale of the reported monitoring does not allow any conclusions to be drawn with respect to trends in the data. Possible factors influencing the data (size, gender, seasonality, reproductive status, etc.) are discussed and recommendations for continued monitoring are made.

Preventing annoyance from odors in spaceflight: a method for evaluating the sensory impact of rodent housing.

For the scientific community, the ability to fly mice under weightless conditions in space offers several advantages over the use of rats. These advantages include the option of testing a range of transgenic animals, the ability to increase the number of animals that can be flown, and reduced demands on shuttle resources (food, water, animal mass) and crew time (for water refill). Mice have been flown in animal enclosure module (AEM) hardware only once [Space Shuttle Transport System (STS)-90] and were dissected early in the mission, whereas rats have been flown in the AEM on >20 missions. This has been due, in part, to concerns that strong and annoying odors from mouse urine (vs. rat urine) will interfere with crew performance in the shuttle middeck. To screen and approve mice for flight, a method was developed to evaluate the odor containment performance of AEMs housing female C57BL/6J mice compared with AEMs housing Sprague-Dawley rats across a 21-day test period. Based on the results of this test, consensus was reached that mice could fly in the AEM hardware for up to 17 days (including prelaunch and contingency) and that the AEM hardware would likely contain odors beyond this duration. Human sensory and electronic nose analysis of the AEMs postflight demonstrated their success in containing odors from mice for the mission duration of STS-108 (13 days). Although this paper focuses specifically on odor evaluations for the space shuttle, the concern is applicable to any confined, closed-system environment for human habitation.

Skeletal muscle adaptations to microgravity exposure in the mouse.

To investigate the effects of microgravity on murine skeletal muscle fiber size, muscle contractile protein, and enzymatic activity, female C57BL/6J mice, aged 64 days, were divided into animal enclosure module (AEM) ground control and spaceflight (SF) treatment groups. SF animals were flown on the space shuttle Endeavour (STS-108/UF-1) and subjected to approximately 11 days and 19 h of microgravity. Immunohistochemical analysis of muscle fiber cross-sectional area revealed that, in each of the muscles analyzed, mean muscle fiber cross-sectional area was significantly reduced (P < 0.0001) for all fiber types for SF vs. AEM control. In the soleus, immunohistochemical analysis of myosin heavy chain (MHC) isoform expression revealed a significant increase in the percentage of muscle fibers expressing MHC IIx and MHC IIb (P < 0.05). For the gastrocnemius and plantaris, no significant changes in MHC isoform expression were observed. For the muscles analyzed, no alterations in MHC I or MHC IIa protein expression were observed. Enzymatic analysis of the gastrocnemius revealed a significant decrease in citrate synthase activity in SF vs. AEM control.

Effect of MPC-11 myeloma and MPC-11 + IL-1 receptor antagonist treatment on mouse bone properties.

This study examines the effects of an IL-6-producing murine multiple myeloma cell line on trabecular and cortical mouse bone, and evaluates the efficacy of interleukin-1 receptor antagonist (IL-1ra) in mitigating bone destruction. Six-week-old BALB/c mice were assigned to two groups: normal controls and myeloma animals (5 x 10(7) MPC-11 cells on day 0). Myeloma animals were further assigned to three unique groups: MPC-11 only; MPC-11 treated with hyaluronic acid (HA); and MPC-11 + IL-1ra/HA (100 mg/kg). Disease development was assessed at 14 and 21 days via spleen, liver, and proximal tibia histology; histomorphometry at the femoral middiaphysis; and long bone composition and mechanical testing. Histologic analysis revealed marked myeloma infiltration into organs and bone marrow and gross bone resorption of the proximal tibia. IL-1ra tended to decrease bone resorption at the proximal tibia; however, it had no effect on quantitatively measured bone parameters. Whole femur and tibia, and tibial epiphysis, percent mineralization was decreased (3.0%, 2.9%, and 6.3%, respectively) in all MPC-11 groups. The presence of myeloma did not affect long bone stiffness, strength, or length over the 3 week study. The percent of the femoral endosteal perimeter showing excessive resorption ( approximately 60%) in the MPC-11 groups increased significantly after 21 days. MPC-11 cell presence caused no change in bone formation or morphology. Normal growth mechanisms were not impacted, as the bones lengthened and increased in size and mass despite the presence of myeloma. IL-1 does not appear to be a primary factor in in vivo bone destruction caused by the MPC-11 cell line. These findings reveal the stochastic nature of bone lesions in multiple myeloma and suggest that IL-1 is not a cytokine critical to this disease pathology.

Osteoprotegerin ameliorates sciatic nerve crush induced bone loss.

This study examines the ability of osteoprotegerin (OPG) to prevent the local bone resorption caused by sciatic nerve damage. Sixty-five 18-week-old male mice were assigned to one of six groups (n = 10-11/group). A baseline control group was sacrificed on day zero of the 10-day study. The remaining groups were placebo sham operated, placebo nerve crush (Plac NC) operated, 0.1 mg/kg/day OPG + nerve crush (LOW), 0.3 mg/kg/day OPG + nerve crush (MED), and 1.0 mg/kg/day OPG + nerve crush (HI). Nerve crush or sham operations were performed on the right leg. The left leg served as a contralateral control to the nerve crushed (ipsilateral) leg. The difference in mass between the right and left femur and tibia was examined. Additionally, quantitative histomorphometry was performed on the right and left femur and tibia diaphyses. Nerve crush resulted in a significant loss of bone mass in the ipsilateral side compared to the contralateral side. Bone mass for the ipsilateral bones of the Plac NC group were significantly reduced by 3.8% in the femur and 3.5% in the tibia compared to the contralateral limb. The percent diminution was reduced for OPG treated mice compared to the Plac NC group for both the femur and tibia. In the femur, the percent reduction of ipsilateral bone mass was reduced to 1.0% (LOW), 1.3% (MED) and 1.6% (HI) compared to the contralateral limb. In the tibia, loss of bone mass in the ipsilateral limb was reduced to 1.4% (LOW), 1.4% (MED), and 2.4% (HI) compared to the contralateral. OPG also decreased the amount of tibial endocortical resorption compared to the Plac NC group. In summary, OPG mitigated bone loss caused by damage to the sciatic nerve.

The effects of osteoprotegerin on the mechanical properties of rat bone.

Osteoprotegerin (OPG) is a naturally secreted protein that decreases bone resorption by inhibiting osteoclast differentiation and activation while promoting osteoclast apoptosis [8]. In this study, the effects of osteoprotegerin injections on long bone mechanical and material properties were investigated in young male Sprague-Dawley rats. OPG increased fracture strength at the femur mid-diaphysis in three-point bending by 30%, without affecting the elastic or maximum strength. At the femoral neck, OPG significantly increased the elastic (45%), maximum (15%), and fracture (35%) strengths. There was not a difference in microhardness at the femur mid-diaphysis in comparing the placebo and OPG groups. There were, however, significant increases in whole bone dry mass (25%), mineral mass (30%), organic mass (17%), and percent mineralization (4%); percent mineralization at the mid-diaphysis (3%); and percent mineralization at the distal epiphysis (6%) due to the OPG treatment. While OPG decreased endocortical bone formation (52%), total bone area, endocortical bone area, and periosteal bone formation were maintained with OPG treatment. A 30% increase in the X-ray opacity of the bone at the proximal metaphysis of the right tibiae was observed. Overall, OPG increased mineralization and strength indices in the rat femur. Its effects on strength were more pronounced in the femoral neck than at the mid-diaphysis.

Osteoprotegerin mitigates tail suspension-induced osteopenia.

Osteoprotegerin (OPG) is a recently discovered protein related to the tumor necrosis factor receptor family. It has been shown to inhibit ovariectomy (ovx)-induced resorption in rats and increase bone mineral density in young mice. Tail suspension is a procedure that inhibits bone formation in maturing rodents. This study was designed to quantify OPG's effect on cortical bone formation. Fifty-four mice were assigned to one of five groups (n = 10-11/group). A baseline control group was killed on day 0 of the 10 day study. The remaining groups were: vivarium housed (nonsuspended) control mice receiving 0.3 mg/kg per day OPG; vivarium control mice receiving daily placebo injections; tail-suspended mice receiving 0. 3 mg/kg per day OPG; and tail-suspended mice receiving placebo injections. Tetracycline was administered on days 0 and 8. OPG treatment of tail-suspended mice produced mechanical properties similar to those of placebo-treated, vivarium-housed mice: structural stiffness (8.5%, 20.7%) and elastic (13.9%, 10.1%) and maximum (4.7%, 8.1%) force were increased compared with placebo controls (vivarium, suspended groups). Percent mineral composition was highly significantly greater (p < 0.001 for all comparisons) for OPG-treated mice in the femur, tibia, and humerus, relative to placebo treatment. Matrix mass was also significantly increased in the femur, although not to the same degree as mineral mass. OPG decreased the amount of femoral endocortical resorption compared with the placebo-treated groups for both vivarium (27%) and suspended (24%) mice. Administration of OPG significantly decreased endocortical formation of the tibia. Periosteal bone formation rates were not altered by OPG. OPG-mitigated tail suspension induced osteopenia not by returning bone formation to normal levels, but by inhibiting resorption and increasing percent mineral composition.

Quantification of bone ingrowth into porous block hydroxyapatite in humans.

This study sought to quantify bone ingrowth from a single bone-implant surface into porous block hydroxyapatite used in maxillofacial applications. Seventeen maxillary hydroxyapatite implants (implant time of 4-138 months, 39-month mean) were harvested for analysis from 14 patients. The implants had been placed into the lateral maxillary wall during orthognathic surgery, juxtapositioned to the maxillary sinus. Ingrowth was measured in 100-microm increments from a bone-implant interface to a depth of 1500 microm. Bone ingrowth averaged over the 14 patients (0-1100 microm depth) is described by the equation % ingrowth - 20% * (depth in millimeters) + 41.25% (R2 = 0.98, n = 10 incremental depths). Beyond 1100 microm, the average ingrowth remained constant at 15.0 +/- 0.7%. The duration of implantation also showed as affect on the percent ingrowth into the implants at the incremental depths, and the percent ingrowth asymptotically approached a maximum. Overall, the composite average data from all depths is best described by the logarithmic function % ingrowth = 15% * ln(implantation time in months) - 24.0% (R2 = 0.71, n = 14 patients). Several factors may come into play in determining bone ingrowth including the mechanical environment, the osteoconductivity of the implant material, and the osteogenic capability of the tissues in the pore spaces. Measurements of bone ingrowth are most influenced by the depth into the implant and the time the implant was in the body; the age of the patient had little affect on bone ingrowth.

Effect of nitinol implant porosity on cranial bone ingrowth and apposition after 6 weeks.

The present study addresses two aspects of the use of nitinol in cranial bone defect repair. The first is to verify that there is substantial bone ingrowth into the implant after 6 weeks; the second is to determine the effect of pore size on the ability of bone to grow into the implant during the early (6-week) postoperative period. Porous equiatomic (equal atomic masses of titanium and nickel) nickel-titanium (nitinol) implants with three different morphologies (differing in pore size and percent porosity) were implanted for 6 weeks in the parietal bones of New Zealand White rabbits. Ingrowth of bone into the implants and apposition of bone along the exterior and interior implant surfaces were calculated. The mean pore size (MPS) of implant type #1 (353 +/- 74 microm) differed considerably from implant types #2 (218 +/- 28 microm) and #3 (178 +/- 31 microm). There was no significant difference among implant types in the percentages of bone and void/soft tissue composition of the aggregate implants. The amount of bone ingrowth also was not significantly different among the implant types. Implant #1 was significantly higher in pore volume and thus had a significantly higher volume of ingrown bone (2.59 +/- 0.60 mm3) than implant #3 (1. 52 +/- 0.66 mm3) and a greater amount, but not significantly greater, than implant #2 (1.76 +/- 0.47 mm3). Pore size does not appear to affect bone ingrowth during the cartilaginous period of bone growth in the implant. This implies that within the commonly accepted range of implant porosities (150-400 microm), at 6 weeks bone ingrowth near the interface of nitinol implants is similar.

The effects of age and dietary restriction without nutritional supplementation on whole bone structural properties in C57BL/6J mice.

While caloric restriction is a proven means to extend longevity, its effects on bone are not well understood. This study examined the effects of dietary restriction without vitamin or mineral supplementation on bone in female 60- and 120-day-old C57BL/6J mice. Baseline controls were sacrificed at 60 or 120 days, while diet-restricted animals ate approximately 72.9-78.6% of the ad libitum fed animals for thirty days. 60-day-old ad libitum animals experienced normal growth with average increases of 6.4% in bone length, 23.5% in bone mass, 9.4% in %mineralization, 36.4% in maximum strength, 59.2% in stiffness, 22.3% in cortical thickness, 12.9% in %cortical area, and 11.3% in microhardness. Growth in 120-day-old ad libitum animals followed a trend but with more modest increases. Diet-restricted mice matured very little from baseline levels in 60-day-old animals. There were no significant changes from baseline levels in the parameters indicated above, except for a 8.3% decrease in %cortical area attributable to increased resorption. 120-day-old diet-restricted animals also evidenced little deviation from baseline levels except for significant decreases in %mineralization (2.1%) and %cortical area (6.7%). The effects of diet restriction on bone properties decreased with age. Bone from 60-day-old diet-restricted mice showed diminished mechanical and compositional properties, resulting from little growth and excess resorption. Bone from 120-day-old diet-restricted mice showed little growth and some resorption. Increased resorption, localized on the endosteal surfaces, likely minimized the negative impact of structural degradation of the long bones. Resorption may have also provided minerals to compensate for nutritional deficiencies.

Effects of space flight and IGF-1 on immune function.

We tested the hypothesis that insulin-like growth factor-1 (IGF-1) would ameliorate space flight-induced effects on the immune system. Twelve male, Sprague-Dawley rats, surgically implanted with mini osmotic pumps, were subjected to space flight for 10 days on STS-77. Six rats received 10 mg/kg/day of IGF-1 and 6 rats received saline. Flight animals had a lymphocytopenia and granulocytosis which were reversed by IGF-1. Flight animals had significantly higher corticosterone levels than ground controls but IGF-1 did not impact this stress hormone. Therefore, the reversed granulocytosis did not correlate with serum corticosterone. Space flight and IGF-1 also combined to induce a monocytopenia that was not evident in ground control animals treated with IGF-1 or in animals subjected to space flight but given physiological saline. There was a significant increase in spleen weights in vivarium animals treated with IGF-1, however, this change did not occur in flight animals. We observed reduced agonist-induced lymph node cell proliferation by cells from flight animals compared to ground controls. The reduced proliferation was not augmented by IGF-1 treatment. There was enhanced secretion of TNF, IL-6 and NO by flight-animal peritoneal macrophages compared to vivarium controls, however, O2(-) secretion was not affected. These data suggest that IGF-1 can ameliorate some of the effects of space flight but that space flight can also impact the normal response to IGF-1. Grant Numbers: NAGW-1197, NAGW-2328.

Histomorphometric, physical, and mechanical effects of spaceflight and insulin-like growth factor-I on rat long bones.

Previous experiments have shown that skeletal unloading resulting from exposure to microgravity induces osteopenia in rats. In maturing rats, this is primarily a function of reduced formation, rather than increased resorption. Insulin-like growth factor-I (IGF-I) stimulates bone formation by increasing collagen synthesis by osteoblasts. The ability of IGF-I to prevent osteopenia otherwise caused by spaceflight was investigated in 12 rats flown for 10 days aboard the Space Shuttle, STS-77. The effect IGF-I had on cortical bone metabolism was generally anabolic. For example, humerus periosteal bone formation increased a significant 37.6% for the spaceflight animals treated with IGF-I, whereas the ground controls increased 24.7%. This increase in humeral bone formation at the periosteum is a result of an increased percent mineralizing perimeter (%Min.Pm), rather than mineral apposition rate (MAR), for both spaceflight and ground control rats. However, IGF-I did inhibit humerus endocortical bone formation in both the spaceflight and ground control rats (38.1% and 39.2%, respectively) by limiting MAR. This effect was verified in a separate ground-based study. Similar histomorphometric results for spaceflight and ground control rats suggest that IGF-I effects occur during normal weight bearing and during spaceflight. Microhardness measurements of the newly formed bone indicate that the quality of the bone formed during IGF-I treatment or spaceflight was not adversely altered. Spaceflight did not consistently change the structural (force-deflection) properties of the femur or humerus when tested in three-point bending. IGF-I significantly increased femoral maximum and fracture strength.

Effect of gravity and diffusion interface proximity on the morphology of collagen gels.

Collagen solutions (0.25% w/v) were polymerized in microgravity (STS-77, 10 days) along with simultaneous ground controls. Assembly conditions were achieved by the passage of buffer ions across a dialysis membrane into a reaction chamber containing the dissolved collagen. The gels were analyzed macroscopically and microscopically to assess the influence of gravity and the oriented diffusion of buffer ions on the resulting product. Double-blind rankings based on visual observation of the gels established that all of the flight gels (n = 8) were more uniform in appearance than all of the ground gels (n = 6). Photography using side illumination of the gels revealed the more granular appearance of the ground gels relative to the highly uniform appearance of the flight gels. Scanning electron microscopy established this difference at the microscopic level. Proximity to the dialysis interface and the presence or absence of gravity were both found to control the porosity and uniformity of the matrix.