Browsing by Subject "bone"
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Item A mammoth of a project: the conservation of a columbian mammoth(2009-05-15) Daniel, Shanna LaReaThis thesis concentrates on discovering the best consolidant or consolidants for stabilizing a Columbian mammoth?s sub-fossilized mandibles, a distal femur, an ulna, a radius, and a tooth. It was recovered from a wet, sandy gravel pit owned by the Vernor Family located in Clute, Texas. Based on thermoluminescence dating, the mammoth dates to around 66,000 years ago. The bones are fragile and unstable. They retain a minute amount of organic material (collagen) and hydroxyapatite, but not enough to retain any structural support. Experiments and analyses were conducted on various bone samples to compare each of the following consolidants? properties. The consolidants examined were silicone oil, polyvinyl acetate (PVA) with viscosity of 25, Acryloid B-72, Butvar 98, Starbond EM-02, methyltrimethoxysilane (MTMS), Paleo-bond, and Rhoplex (Primal) WS24. Stability, strength, and appearance were evaluated by measurable observations. The Scanning Electron Microscope (SEM) and the Environmental Scanning Electron Microscope (ESEM) at the Microscopy and Imaging Center at Texas A&M University were used to map penetration of these consolidants. SEM was utilized for both imaging and energy-dispersive x-ray spectroscopy (EDS) to examine the presence and absence of certain elements. ESEM was used to view consolidants at the microscopic level to further examine the bonding between the consolidant and the bone?s cellular structure. By examining and testing all the consolidants, methyltrimethoxysilane (MTMS) was chosen to stabilize the ulna, radius, left and right mandibles, distal femur, and tooth. This research opened new avenues to different methods in preserving sub-fossilized bone and broadens our understanding of bone conservation.Item Biochemical markers of bone modeling and remodeling in juvenile racehorses at varying mineral intakes(Texas A&M University, 2007-09-17) Eller, Elena MariaBlood-borne biochemical markers were used to track comparative rates of bone turnover in horses fed differing amounts of Ca, P and Mg. Bone turnover was tracked by serum osteocalcin, bone resorption by the carboxyterminal telopeptide of type I collagen (ICTP), and bone formation by the carboxyterminal propeptide of type I procollagen (PICP). Twenty-four long-yearling Quarter Horses were blocked by gender and age, randomly assigned to one of four diets and subjected to 128 d of race training. Horses entered the study at approximately 20 months of age. The study was conducted in 32-d periods, each consisting of 28 d of race training followed by a 4-d fecal and urine collection, or a 4-d rest period. Blood samples were taken weekly during the training period. Serum and plasma samples were analyzed for concentrations of osteocalcin, the carboxyterminal telopeptide of type I collagen (ICTP) and the carboxyterminal propeptide of type I procollagen (PICP). Urine was collected for analysis of deoxypyridinoline (DPD) and creatinine. Onset of training resulted in elevated concentrations of ICTP, PICP and osteocalcin. Horses consuming the highest levels of Ca, P and Mg exhibited higher concentrations of PICP and lower concentrations of ICTP indicating greater bone formation coupled with lesser amounts of bone resorption. Further, ICTP, PICP and osteocalcin concentrations decreased dramatically following 4-d of confinement and relative inactivity. Therefore it appears that feeding minerals at levels greater than current NRC recommendations provided a protective effect on the developing skeleton of the young racehorse. Additionally, the biochemical markers used in this study were sensitive enough to track daily changes in bone activity resulting from daily changes in stress to the skeleton.Item Bone loss during energy restriction: mechanistic role of leptin(2009-05-15) Baek, KyunghwaMechanical unloading and food restriction (FR) are leading causes of bone loss, which increase the risk of fracture later in life. Leptin, a 16kDa cytokine like hormone principally produced by white adipocytes, may be involved in bone metabolism with physiological or mechanical changes causing bone loss. The hypotheses of the first study were aimed at determining if serum leptin is reduced by unloading or FR. The serum leptin level reduced by unloading or by global FR, is associated with the decline in bone formation rate. It was conjectured that decreased serum leptin may be due to reduced adipocyte number/size and/or sympathetic nervous system (SNS) activation of betaadrenoreceptors with unloading or FR, inhibiting the release of leptin from adipocytes. In the second experiment, we tested whether leptin or beta-adrenoreceptor blockade attenuates bone loss during unloading and whether such an effect due to beta blockade is associated with changes in serum leptin level. Beta-blockade mitigated unloading induced reduction in serum leptin and also beta blockade was as effective as leptin administration in mitigating a reduction in cancellous bone mineral density with unloading through both stimulation of bone formation and suppression of resorption. It was previously demonstrated that energy restriction (ER) is a major contributor to the bone loss during global FR. In the third study, we tested whether beta- blockade attenuates bone loss during ER and whether such an effect is associated with changes in serum leptin level and leptin localization in bone tissues. Beta blockade attenuated the ER induced reduction in serum leptin level, cancellous bone mineral density and bone formation rate, and also abolished the ER induced increase in bone resorption. Reduction in leptin expression in bone marrow adipocytes observed with ER was attenuated by beta-blockade. Reduction in the number of cells (bone lining cells, osteocytes and chondrocytes in cartilage) which are stained positive for leptin was also attenuated by beta-blockade. Collectively, these data identify circulating leptin effects on preventing bone loss during mechanical unloading or energy restriction. Also beta blockade is associated with mitigating reduction in serum leptin and subsequently with mitigating reduction in bone mass with unloading or ER.Item Characterization of the Bone Loss and Recovery Response at the Distal Femur Metaphysis of the Adult Male Hindlimb Unloaded Rat(2012-02-14) Davis, Joshua MorganExtended periods of mechanical unloading are known to be detrimental to bone health. Astronauts who spend months in microgravity aboard the International Space Station (ISS) are at particular risk. It is anticipated that NASA will not drastically increase the size of the astronaut corps, and this will mean increased likelihood of repeat missions for more astronauts. Thus, it is important to better understand the effects that prolonged, multiple bouts of unloading have on bone. This study utilized the hindlimb unloaded (HU) rat model to examine bone loss and recovery for single and double unloading bouts. Adult male Sprague-Dawley rats (6 months old) were randomized into the following groups: baseline (sacrificed at 6 months), 1HU7 (unloaded for 1 month, weight-bearing recovery for 3 months), 2HU10 (unloaded for 1 month, recovered for 2 months, unloaded for another month, and then recovered 2 months), 1HU10 (normal cage activity until 1 month HU ending at month 10, 2 month recovery followed), and aging controls (remained ambulatory throughout experiment). Every month (28 days), animals were terminated and the left femurs were excised, resulting in n=15 per group for each time point. Mineral and geometric properties were measured using peripheral quantitative computed tomography (pQCT) at the distal femur metaphysis, and quasi-static reduced platen compression (RPC) was used to estimate the mechanical properties of cancellous bone. Strength indices based on pQCT parameters were calculated as predictors of mechanical properties. Bone mass properties decreased due to HU and recovered within 2-3 months post-HU. A combination of increased periosteal apposition and endocortical resorption also occurred during HU. The initial HU bout suppressed normal age-related increases in mechanical properties and recovered within 1-2 months. Cancellous compressive strength index (CSI) most closely matched changes in mechanical properties. A second HU bout after two months recovery had a less detrimental effect on pQCT parameters but a greater negative impact on mechanical properties, when compared to pre-HU values. The opposite is true for mechanical properties if loss is characterized relative to aging controls. Recovery after the second HU period did not appear to be significantly affected by a previous bout of HU.Item Characterizing strain in the proximal rat tibia during electrical muscle stimulation(Texas A&M University, 2007-09-17) Vyvial, Brent AronHindlimb unloading is a widely used model for studying the effects of microgravity on a skeleton. Hindlimb unloading produces a marked loss in bone due to increased osteoclast activity. Electrical muscle stimulation is being investigated as a simulated resistive exercise countermeasure to attenuate this bone loss. I sought to determine the relationship between strain measured at the antero-medial aspect of the proximal diaphysis of tibia and plantar-flexor torque measured at the ankle during electrical muscle stimulation as an exercise countermeasure for hindlimb unloading in rats. A mathematical relationship between strain and torque was established for the exercise during a 28 day period of hindlimb unloading. The strain generated during the exercise protocol is sufficient to attenuate bone loss caused by hindlimb unloading. Twelve six-month old Sprague-Dawley rats were implanted with uni-axial strain gages in vivo on the antero-medial aspect of the proximal diaphysis of the left tibia. Strain and torque were measured during electrical muscle stimulation for three time points during hindlimb unloading (Day 0 (n=3), Day 7 (n=3), Day 21 (n=3)). Peak strain decreased from 1,100 strain at the beginning of the study to 660 strain after 21 days of hindlimb unloading and muscle stimulation. The peak strain rate measured during muscle stimulation was 10,350 strain/second at the beginning and decreased to 6,670 strain/second after 21 days. The changes in strain are not significant, but the underlying trend in strain values may indicate an increase in bone formation due to the electrical muscle stimulation countermeasure. A mathematical model that relates measured strain to peak eccentric torque during muscle stimulation was created to facilitate estimation of strain for future studies of electrical muscle stimulation during hindlimb unloading.Item Effects of High Dietary Iron and Gamma Radiation on Oxidative Stress and Bone(2013-04-19) Yuen, Evelyn PAstronauts in space flight missions are exposed to increased iron (Fe) stores and galactic cosmic radiation, both of which independently induce oxidative stress. Oxidative stress can result in protein, lipid, and DNA oxidation. Recent evidence has linked oxidative stress to bone loss with aging and estrogen deficiency. Whether the increased iron stores and radiation that astronauts face are exacerbating their extreme bone loss while in space is unclear. We hypothesized that elevated iron levels (induced by feeding a high iron diet) and gamma radiation exposure would independently increase markers of oxidative stress and markers of oxidative damage and result in loss of bone mass, with the combined treatment having additive or synergistic effects. Male Sprague-Dawley rats (15-weeks old, n=32) were randomized to receive an adequate (45 mg Fe/kg diet) or high (650 mg Fe/kg diet) Fe diet for 4 weeks and either 3 Gy (8 fractions, 0.375 Gy each) of 137Cs radiation (?RAD) or sham exposure every other day over 16 days starting on day 14. Serum Fe and catalase and liver Fe and glutathione peroxidase (GPX) were assessed by standard techniques. Immunostaining for 8-hydroxy-2-deoxyguanosine (8-OHdG, marker of DNA adducts) quantified the number of cells with oxidative damage in cortical bone. Bone histomorphometry assessed bone cell activity and cancellous bone microarchitecture in the metaphyseal region. Ex vivo pQCT quantified volumetric bone mineral density (vBMD); bone mechanical strength was assessed by 3-pt bending at the midshaft tibia and compression of the femoral neck. High Fe diet increased liver Fe and decreased volume per total volume (BV/TV). ?RAD decreased osteoid surface per bone surface (OS/BS) and osteocyte density. The combined treatment increased serum catalase, liver GPX, and serum iron and decreased cancellous vBMD and trabecular number (Tb.N). High Fe diet and ?RAD independently increased number of osteocytes stained positive for 8-OHdG, with the combined treatment exhibiting twice as many osteocytes positively stained compared to the control. Higher serum Fe levels were associated with higher oxidative damage (r =0.38) and lower proximal tibial cancellous vBMD (r =?0.38). Higher serum catalase levels were associated with higher oxidative damage (r =0.48), lower BV/TV (r =?0.40) and lower cancellous vBMD (r =?0.39). High dietary iron and fractionated 137Cs ?RAD leads to a moderate elevation in iron stores and results in oxidative damage in bone and are associated with decreased cancellous bone density. Moderate elevations in iron stores are not only found in astronauts, but also naturally occur in healthy human populations. This healthy population with elevated iron stores may also have increased levels of oxidative stress in the body. Elevated levels of oxidative stress not only increase one?s risk for accelerated bone loss, but also the risk of developing other chronic diseases such as insulin resistance, hypertension, dyslipidemia, and metabolic syndrome.Item Mechanisms of impaired osteoblast function during disuse(Texas A&M University, 2004-11-15) Allen, Matthew RobertProlonged periods of non-weightbearing activity result in a significant loss of bone mass which increases the risk of fracture with the initiation of mechanical loading. The loss of bone mass is partially driven by declines in bone formation yet the mechanisms responsible for this decline are unclear. To investigate the limitations of osteoblasts during disuse, marrow ablation was superimposed on hindlimb unloaded mice. Marrow ablation is a useful model to study osteoblast functionality as new cancellous bone is rapidly formed throughout the marrow of a long bone while hindlimb unloading is the most common method used to produce skeletal unloading. The specific hypotheses of this study were aimed at determining if changes in osteoblast functionality, differentiation, and/or proliferation were compromised in non-weightbearing bone in response to a bone formation stimulus. Additionally, the influence of having compromised osteoblast functionality at the time of stimulation was assessed in non-weightbearing bones. Key outcome measures used to address these hypotheses included static and dynamic cancellous bone histomorphometry, bone densitometry, and real-time polymerase chain reaction (PCR) analyses of gene expression. The results document similar ablation-induced increases of cancellous bone in both weightbearing and unloaded animals. Similarly, there was no influence of load on ablation-induced increases in cancellous bone forming surface or mineral apposition rate. Unloading did significantly attenuate the ablation-induced increase in bone formation rate, due to reduced levels of total surface mineralization. When osteoblast functionality was compromised prior to marrow ablation, bone formation rate increases were also attenuated in ablated animals due to reduced mineralization. Additionally, increases in forming surface were attenuated as compared to unloaded animals having normal osteoblast function at the time of ablation. Collectively, these data identify mineralization as the limiting step in new bone formation during periods of disuse. The caveat, however, is that when bone formation is stimulated after a period of unloading sufficient to compromise osteoblast functionality, increases in osteoblast recruitment to the bone surface are compromised.Item Osteogenic effect of optimized muscle stimulation exercise as a countermeasure during hindlimb unloading(2009-05-15) Sumner, Lindsay Rebecca