Effects of low-dose parathyroid hormone on bone mass, turnover, and ectopic osteoinduction in a rat model for chronic alcohol abuse

Parathyroid hormone (PTH) is used clinically in osteoporotic patients to increase bone mass by enhancing bone formation. PTH therapy is not uniformly effective at all skeletal sites and "life-style" factors may modulate the skeletal response to PTH. Alcohol may represent one of these factors. Chronic alcohol abuse is associated with osteoporosis and impaired fracture healing. Therefore, the present study investigated the effects of alcohol on the bone anabolic response to a dose of PTH similar to a human therapeutic dose 1) during normal cancellous and cortical bone growth and turnover, and 2) in a model of demineralized allogeneic bone matrix (DABM)-induced osteoinduction. Three-month-old male Sprague Dawley rats were fed a Lieber-DeCarli liquid diet with 35% of the calories derived from ethanol. The controls were pair-fed an alcohol-free isocaloric diet containing maltose-dextran. Following adaptation to the liquid diets, the rats were implanted subcutaneously with DABM cylinders prepared from cortical bone of rats fed normal chow. The rats were subsequently treated daily with PTH (1 microg/kg/d sc, 5 d/week) or vehicle and measurements on bone and DABM implants performed 6 weeks later. Total bone mass was evaluated on the day of necropsy using DXA. Tibiae were processed for histomorphometry. Bone mass and architecture in tibial diaphysis and DABM implants were evaluated by muCT. PTH treatment increased whole body bone mineral content (BMC) and bone mineral density (BMD). The hormone also increased bone formation and bone area/tissue area in the proximal tibial metaphysis. In contrast, PTH treatment had no effect on periosteal bone formation and minimal effects on DABM-induced osteoinduction. Alcohol consumption decreased whole body BMC. Alcohol also decreased cancellous as well as cortical bone formation and bone mass in tibia and impaired DABM-mediated osteoinduction. There was no interaction between PTH treatment and alcohol consumption for any of the endpoints evaluated. Our results indicate that the bone anabolic response to a therapeutic dose of PTH in the rat is largely confined to cancellous bone. In contrast, alcohol consumption inhibits bone formation at all sites. Furthermore, alcohol inhibits osteoinduction and reduces periosteal and cancellous bone formation, irrespective of therapeutic PTH administration. Based on the animal model, our findings suggest that alcohol consumption could impair the beneficial effects of PTH therapy in osteoporosis.     

Effects of cyclosporin A on experimental new bone formation in rats.

The effects of the immunosuppressive drug cyclosporin A (CsA) on bone induction by demineralized allogeneic (rat) bone matrix (DABM) and demineralized xenogeneic (rabbit) bone matrix (DXBM) were studied. Growing rats were implanted with three samples each of DABM and DXBM. Groups of eight rats were treated with 0.5 or 2 mg CsA/kg body weight for four weeks and compared with a placebo group. Cyclosporin A treatment enhanced bone induction in DABM implants by 40 to 50% at four weeks, whereas there was no difference from the control group at eight weeks. Demineralized xenogeneic bone matrix induced virtually no bone in control rats at four weeks, whereas the net bone formation increased four to five times in both groups of CsA-treated rats. At eight weeks, DXBM without CsA had induced some bone formation, and the amount was almost equal to that of DABM implants in CsA-treated groups. Also, the mineral accretion rates of DXBM were equal to DABM implants in CsA-treated rats. Cyclosporin A treatment doubled the uptake of 45Ca in the orthotopic skeleton (femora) at four weeks without affecting the mineral content, indicating an increased mineral turnover. Immunologic reactions may inhibit bone induction by DXBM, which can be counteracted by treatment with CsA.     

Alendronate administration and skeletal response during chronic alcohol intake in the adolescent male rat.

Alendronate is an aminobisphosphonate that inhibits bone resorption in osteoporotic humans and rats but does not induce osteomalacia. Several bisphosphonates, including alendronate, also have direct positive actions on osteoblasts, bone formation, and mineralization. We studied the effects of alendronate on skeletal development in adolescent male rats during chronic alcohol intake. Four groups of age- and weight-matched male Sprague-Dawley rats (35 days of age) were fed the Lieber-DeCarli diet containing 36% of calories as EtOH (E), the EtOH diet plus 60 mg/kg alendronate (EA) every other day intraperitoneally (ip), an isocaloric diet (I), or the isocaloric diet plus 60 mg/kg alendronate (IA) every other day ip. Body weight, femur length, serum levels of osteocalcin (OC), insulin-like growth factor 1 (IGF-1), testosterone, and luteinizing hormone (LH); femur distal metaphyseal and middiaphyseal bone mineral density (BMD) and tibial metaphyseal gene expression for alpha-1-type I collagen (Col I), OC, and bone alkaline phosphatase (AP); and femur strength by four-point bending to failure were measured after 28 days of feeding and alendronate injections. Serum alcohol levels at death were 156 +/- 13 mg/dl (E) and 203 +/- 40 mg/dl (EA). Alendronate given to alcohol-fed rats increased metaphyseal BMD by more than 3-fold over rats fed alcohol alone. Alendronate given to isocaloric pair-fed rats increased metaphyseal BMD by more than 2.5-fold over rats fed the isocaloric diet alone. Cortical BMD was reduced by alcohol but was increased by alendronate. Alcohol consumption reduced serum IGF-1 levels, and alendronate increased IGF-1 levels in alcohol-fed rats. Serum OC, testosterone, and LH were unaffected by alcohol and alendronate. Quantitative dot blot hybridization using rat complementary DNA (cDNA) probes and normalization against 18S subunit ribosomal RNA (rRNA) levels revealed no changes in tibial metaphyseal gene expression for type I collagen, osteocalcin, or alkaline phosphatase. Alcohol significantly reduced the biomechanical properties of the femurs that were partially compensated by alendronate. Chronic alcohol consumption uncouples formation from ongoing resorption, and resorption is inhibited by alendronate. However, alendronate's positive effects on osteoblast-mediated mineralization during chronic alcohol consumption point to the potential use of bisphosphonates in the treatment of decreased bone formation secondary to alcohol-induced diminished osteoblast function.     

Alcohol alters whole body composition, inhibits bone formation, and increases bone marrow adiposity in rats

Summary  Chronic alcohol abuse is a risk factor for osteoporosis and sarcopenia, but the long-term effects of alcohol on the immature musculoskeletal system are less clear. The present investigation in growing rats was designed to determine the effects of alcohol consumption on body composition, muscle mass, and bone mass, architecture, and turnover. Introduction  Few studies have focused on the long-term effects of drinking on bone and muscle during skeletal maturation. Methods  Alcohol was included in the diet of 4-week-old male Sprague–Dawley rats (35% caloric intake) for 3 months. The controls were fed an isocaloric alcohol-free liquid diet ad libitum. A second study was performed in which the controls were pair-fed to the alcohol-fed animals. Results  Compared to ad libitum-fed age-matched controls, alcohol-fed rats weighed less and had lower lean mass, fat mass, and percent body fat. In addition, they had lower slow- and fast-twitch muscle mass, lower total body bone mineral content and bone mineral density, and lower cancellous bone volume in the lumbar vertebra and proximal tibia. The effects of alcohol consumption on body composition were reduced when compared to the pair-fed control diet, indicating that caloric restriction was a comorbidity factor. In contrast, the effects of alcohol to decrease bone formation and serum leptin and IGF-I levels and to increase bone marrow adiposity appeared independent of caloric restriction. Conclusions  The skeletal abnormalities in growing alcohol-fed rats were due to a combination of effects specific to alcohol consumption and alcohol-induced caloric restriction.     

Effects of parathyroid hormone (1-34) on tibia in an adult rat model for chronic alcohol abuse

Chronic alcohol abuse is a risk factor for osteoporosis in men. Human recombinant parathyroid hormone (1-34) (PTH) therapy increases bone mass in patients with osteoporosis. The purpose of the present study was to determine whether PTH is effective in increasing bone formation and bone mass in a rat model for established osteopenia caused by chronic alcohol abuse. Eight-month-old male Sprague Dawley rats were fed the Lieber-DeCarli liquid diet in which 35% of the calories were derived from either maltose-dextran or ethanol. Measurements were performed 16 weeks later to establish the magnitude of bone changes in the rats fed alcohol. High dose PTH (80 microg/kg/day) was administered 5 days/week for 6 weeks to establish the differential efficacy of hormone therapy on bone formation in alcohol consuming and alcohol withdrawn rats. The effects of alcohol and PTH on cancellous and cortical bone mass, architecture and turnover were determined by densitometry and histomorphometry. Rats fed alcohol had reduced bone mineral contents and densities, cancellous and cortical bone areas and cancellous bone formation rates compared to pair-fed controls. Following the withdrawal of alcohol, indices of bone formation increased compared to baseline values. PTH treatment increased bone mineral content and density, bone formation rates, cortical bone area, cancellous bone area and trabecular number and thickness, but several indices of bone formation were reduced in the presence of continued alcohol consumption. These results suggest that alcohol consumption, in addition to inducing bone loss, may reduce the efficacy of PTH therapy to reverse osteoporosis.     

The effects of fluoride on bone and implant histomorphometry in growing rats

The effects of fluoride at concentrations of 2.0 and 4.5 mM in drinking water on growth rate, vitamin D, water and mineral metabolism, bone histomorphometry, and osteoinduction of demineralized allogenic bone matrix (DABM) were compared in the rat. Whereas fluoride did not influence fluid intake or growth rate at the lower concentration, it increased fluid intake and inhibited growth rate at the higher concentration. Fluoride produced dose-related increases in serum fluoride and alkaline phosphatase but did not alter serum 25-hydroxyvitamin D or 1,25-dihydroxyvitamin D. Serum calcium and phosphate were reduced by fluoride at concentrations of 2.0 mM but not 4.5 mM. Cancellous bone fractional area was increased by fluoride at 2.0 mM and was reduced by fluoride at 4.5 mM. Fluoride had no effect on cancellous bone surface length or the percentage surface lined by osteoblasts and osteoclasts. Fluoride increased medullary area and decreased the endosteal bone formation rate. Fluoride increased periosteal bone formation and apposition rates at concentrations of 2.0 mM but not 4.5 mM. Fluoride inhibited mineralization in DABM implants, and at the higher concentration, fluoride increased the formation of new bone matrix. These results indicate that in the rat, fluoride increases cortical and trabecular bone at therapeutic doses and reduces trabecular bone at toxic doses. The serum concentration of fluoride at therapeutic doses in the rat is similar to that in patients with osteoporosis who are on treatment with fluoride. In the rat, there is a narrow range between toxic and therapeutic doses.     

Influence of indomethacin on induced heterotopic bone formation in rats. Importance of length of treatment and of age

The effect of indomethacin on heterotopic and orthotopic bone formation in rats was analyzed with respect to (1) length of treatment after implantation, (2) duration of the indomethacin induced inhibition of heterotopic bone formation, and (3) influence of age of the implant recipient. Three weeks after implantation of demineralized bone matrix, the ash weight of implants from rats receiving indomethacin 2 mg/kg body weight during the entire experiment was 31% lower than that of controls. Animals treated for only six days after implantation exhibited an almost equally pronounced inhibition. However, six weeks after implantation, the inhibition caused by six days of indomethacin treatment had almost dissipated. In older rats the implants of demineralized bone matrix induces smaller volumes of new bone than in younger rats, but indomethacin causes approximately the same degree of inhibition of osteoinduction. Orthotopic bone is not affected by indomethacin treatment. This study shows that a short period of indomethacin treatment at the time of implantation of demineralized bone matrix is sufficient to reduce experimental bone formation, but the inhibitory effect slowly diminishes if the inductive process is continuous. The results indicate that the inhibition of heterotopic new bone formation by indomethacin may be mediated through reduction of the initial inflammatory response or by reduced mesenchymal cell proliferation.     

Moderate alcohol consumption suppresses bone turnover in adult female rats.

Chronic alcohol abuse is a major risk factor for osteoporosis but the effects of moderate drinking on bone metabolism are largely uninvestigated. Here, we studied the long-term dose-response (0, 3, 6, 13, and 35% caloric intake) effects of alcohol on cancellous bone in the proximal tibia of 8-month-old female rats. After 4 months of treatment, all alcohol-consuming groups of rats had decreased bone turnover. The inhibitory effects of alcohol on bone formation were dose dependent. A reduction in osteoclast number occurred at the lowest level of consumption but there were no further reductions with higher levels of consumption. An imbalance between bone formation and bone resorption at higher levels of consumption of alcohol resulted in trabecular thinning. Our observations in rats raise the concern that moderate consumption of alcoholic beverages in humans may reduce bone turnover and potentially have detrimental effects on the skeleton.     

Osteoinduction by implants of demineralized allogeneic bone matrix is diminished in vitamin D-deficient rats

Summary Experimental heterotopic bone formation was produced by subcutaneous implants of demineralized allogeneic bone matrix (DABM) in vitamin D-deficient (−D) animals that were either not treated or given vitamin D₃ (+D) or 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) to determine the role of vitamin D and its most active metabolite in osteoinduction and implant remodeling. Histologically, implants in both +D and −D groups caused a similar acute inflammatory response, formation of a fibrous capsule, and chondrogenesis by 1 to 2 weeks after implantation. However, by 3 weeks after implantation implants in the −D animals had formed less bone matrix, had developed a defect in matrix mineralization, had reduced bone forming and bone resorbing surfaces, and had altered bone architecture resulting from defective bone remodeling. The altered histology in −D animals was not corrected by 10 weeks after implantation. Treatment of vitamin D-deficient rats with 1,25(OH)₂D₃, 65 pmol/day for 3 weeks, corrected both the defect in mineralization and the abnormal histology. The results indicate that (1) vitamin D deficiency does not alter either the timing or the sequence of histologic events associated with osteoinduction but dramatically reduces the magnitude of the response, (2) vitamin D deficiency not only impairs mineralization but also reduces bone formation and resorption, and (3) 1,25(OH)₂D₃ mimics all of the actions of vitamin D with regard to correcting the abnormal osteoinductive response and bone histomorphometry.     

Methotrexate effects on heterotopic bone in rats

We studied the effects of high-dose methotrexate on heterotopic bone formation induced by implants of demineralized bone matrix in the abdominal wall of growing rats. Methotrexate induced an arrest in normal weight gain of the animals, more pronounced the younger the animals were. The youngest animals had reduced ash weight and decreased isotope uptake in the tibiae and teeth. However, implants from these animals, given methotrexate 10 days before implantation of bone matrix, had a 33 per cent increase in ash content. When methotrexate was given at, or 10 days after, implantation, heterotopic bone formation was reduced by 40 and 22 per cent, respectively, whereas orthotopic bone was considerably less affected in these older animals. In a second experiment, no difference in elimination rates of 45Ca between methotrexate-treated and control rats in implants, teeth, or tibiae were found. It appears that a less detrimental effect of methotrexate on new bone formation can be expected if the drug is given before, or a substantial period after, surgery requiring bone formation for healing.     

Methotrexate effects on heterotopic bone in rats

We studied the effects of high-dose methotrexate on heterotopic bone formation induced by implants of demineralized bone matrix in the abdominal wall of-growing rats. Methotrexate induced an arrest in normal weight gain of the animals, more pronounced the younger the animals were. The youngest animals had reduced ash weight and decreased isotope uptake in the tibiae and teeth. However, implants from these animals, given methotrexate 10 days before implantation of bone matrix, had a 33 per cent increase in ash content. When methotrexate was given at, or 10 days after, implantation, heterotopic bone formation was reduced by 40 and 22 per cent, respectively, whereas orthotopic bone was considerably less affected in these older animals. In a second experiment, no difference in elimination rates of ⁴⁵Ca between methotrexate-treated and control rats in implants, teeth, or tibiae were found.

It appears that a less detrimental effect of methotrexate on new bone formation can be expected if the drug is given before, or a substantial period after, surgery requiring bone formation for healing.     

Tissue adhesives inhibit experimental new bone formation

Summary The effect of the cyanoacrylate tissue adhesive Histoacryl on new bone formation was studied in rats. Experimental heterotopic new bone formation was induced by implanting pieces of demineralized allogeneic bone matrix (DABM) in the abdominal wall of 10 growing Sprague-Dawley rats. This produces cartilage formation within and around the implants after 10 days, followed by enchondral ossification and the formation of an ossicle with remodelling bone and bone marrow after three weeks. Prior to implantation, the DABM-implants were treated with increasing amounts of the tissue adhesive n-Butyl-2-cyanoacrylate-monomer (Histoacryl). New bone formation was quantified at three weeks by assay of the ash content of the implants as a measure of net bone formation, by ⁴⁵calcium uptake prior to sacrifice, and by histology. Treatment of DABM with the cyanoacrylate caused an intense inflammatory process with a foreign body reaction, and abolished bone induction and new bone formation. Tissue adhesives should be used with caution in fracture surgery since they inhibit new bone formation, cause a foreign body reaction, and may impede fracture healing.

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Résumé L'effet d'un tissu adhésif de cyanoacrylate (Histoacryl) sur la néoformation osseuse a été étudié chez le rat. Une néoformation osseuse hétérotopique a été induite par implantation de fragments de matrice osseuse allogène déminéralisée (MOAD) dans la paroi abdominale de 10 rats Sprague-Dowley en période de croissance. Cette implantation détermine en dix jours l'apparition de cartilage à l'intérieur et à la périphérie des implants, suivie d'une ossification enchondrale et de la formation d'os et de moelle osseuse à la fin de la troisième semaine. Avant d'être mis en place, les implants de MOAD ont été préparés par des quantités croissantes de n-butyl-2-cyanoacrylate monomère (Histoacryl). La formation d'os nouveau a été mesurée, à la troisième semaine, par l'analyse de la cendre des implants, par l'activité, avant sacrifice, du calcium 45 et par l'histologie. La préparation des implants de MOAD par le cyanoacrylate entraîne une réaction inflammatoire intense et arrête l'induction et la formation d'os nouveau. On peut en conclure que les tissue adhésifs doivent être utilisés avec précaution en chirurgie traumatologique car ils inhibent la néoformation osseuse, déterminent une réaction à corps étranger et peuvent retarder la consolidation des fractures.

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Reprint requests to: O. Nilsson     

Influence of indomethacin on experimental bone metabolism in rats

The effect of indomethacin on heterotopic and orthotopic bone formation in rats was analyzed with respect to dose and time of initiation of drug administration. Three weeks after implantation of demineralized bone matrix, the ash weight of implants from animals receiving the highest doses of indomethacin was approximately 25% lower than that of controls. The ash weight of implants was only affected in rats receiving indomethacin from the week before implantation or from the time of implantation. In a separate study, no effect on the rate of resorption measured by elimination of 3H-proline and 45Ca or on the amount of ash could be detected. Orthotopic bone remained unaffected by indomethacin treatment. The study showed that in order to inhibit experimental new bone formation, indomethacin must be present before or at the time of implantation of demineralized bone matrix.     

Comparison of demineralized allogeneic bone matrix grafting (the Urist procedure) and the Ilizarov procedure in large diaphyseal defects in sheep

The bone inductive capability of the Urist and Ilizarov procedures was compared in the repair of large diaphyseal defects in sheep. In 30 animals, a 4 cm segmental defect was created in the middle portion of the right femur and was stabilized with an external fixator. The sheep were divided into four groups according to the type of reconstruction of the defect. In group 1, a demineralized allogeneic bone matrix (DABM) cylinder was used; in group 2, DABM chips; and in group 3, gradual transport of a piece of bone detached from the proximal femoral fragment was used to fill the defect. Group 4 served as a control (the defect was left empty). New bone formation was assessed by serial radiographs until the time of death at 2 or 4 months. Postmortem specimens were analyzed with respect to bone mineral content, uptake of isotopes (⁴⁵Ca and ³H-proline), and histology. The first signs of new bone formation were radiographically evident at 4 weeks. In the two groups in which reconstruction involved DABM (Urist procedures), new bone failed to form in eight of the 13 animals. Full bridging of the defect was observed at 8 weeks in one animal with a DABM cylinder and two with DABM chips. No decisive difference in bone yield could be demonstrated between the two Urist procedures. In the group treated with the Ilizarov procedure, new bone formation consistently occurred at a high rate; full bridging of the defect was observed in seven of the eight animals. Bone mineral scanning and histologic analysis essentially confirmed the radiographic results. Uptake of isotopes was selectively analyzed in two sheep from each experimental group in which new bone formation was exhibited in the defect; new bone formation was increased compared with that in the contralateral femur but was equal among the three experimental groups. Our study shows that gradual transport of a detached piece of autogeneic bone (Ilizarov procedure) is more effective than implantation of DABM (Urist procedure) in eliciting new bone formation in large diaphyseal defects in sheep. The variable bone induction by DABM may be explained by differences in host immune responses to the implants.     

A systemic acceleratory phenomenon (SAP) accompanies the regional acceleratory phenomenon (RAP) during healing of a bone defect in the rat

The rate of remodeling in the region of a bone defect exceeds normal tissue activity. It was Frost who described this reaction as a regional acceleratory phenomenon (RAP). We investigated the local healing process with rats with a burr hole defect (1.2 mm in diameter) in the left tibia. We differentiated an initial phase of bone formation followed by a phase of predominant resorption. To determine whether this regional enhancement of bone formation would result in a systemic impact on bone metabolism, we analyzed both tibiae and femora and the fourth lumbar vertebra. On day 7 both femora of rats with the tibial defect showed a significant increase in computerized x-ray density, dry weight, ash weight, and Ca2+ content. Both tibiae and the fourth lumbar vertebra showed a significant increase in mineralizing surface, mineral apposition rate, and bone formation rate. Because of these results we conclude that a systemic acceleratory phenomenon (SAP) accompanies the RAP. SAP affects only the cancellous, but not the cortical bone compartment. SAP is associated closely with the occurrence of woven bone during the formation phase of the healing process. Thus we assume that woven bone formation plays a pivotal role in the mediation of SAP.     

Effect of ethanol on bone mineral density of rats evaluated by dual-photon X-ray absorptiometry

Abuse of alcohol may derange bone metabolism and cause osteoporosis. Due to confounding factors associated with alcohol abuse, e.g., dietary deficiencies and liver damage, a study using an animal model is preferable to examine whether alcohol itself actually reduces bone density. We evaluated the effect of alcohol intake on bone in rats by dual-energy X-ray absorptiometry. Six-week-old male (n = 16) and female (n = 16) Wister rats were divided into two groups. Sixteen alcohol-exposed rats (8 male and 8 female) were fed Lieber's liquid diet and 16 control rats (8 male and 8 female) were fed a control liquid diet. The bone mineral density (BMD) and bone mineral content (BMC) of the right femur were measured before and after experimental feeding under anesthesia. The BMD of lumbar spine (L2–L4) of sacrificed rats was measured. For male rats, BMD and BMC decreased significantly in the alcohol group (P = 0.0132 and 0.0133, respectively) but did not decrease in control group. For female rats, BMD and BMC decreased significantly in the alcohol group (P = 0.0012 and <0.0001, respectively) but did not decrease in the control group. For male rats, the mean ratio of BMD after experimental feeding divided by BMD before experimental feeding was significantly lower in the alcohol group than in the control group (P = 0.0031). For female rats, the mean ratio of BMD after experimental feeding divided by BMD before experimental feeding was also lower in the alcohol group than in the control group (P = 0.0002). For male rats, the mean BMD of L2–L4 after experimental feeding was significantly lower in the alcohol group than in the control group (P = 0.0210). For female rats, the mean BMD of L2–L4 after experimental feeding was also significantly lower in the alcohol group than in the control group (P = 0.0006). These results indicate that alcohol intake decreased the BMD of rats in both spongy and cortical bone, and that the reduction of BMD was greater in female rats than in male rats. Received: March 16, 2000 / Accepted: May 11, 2000     

Alcohol and bone: review of dose effects and mechanisms

Alcohol is widely consumed across the world. It is consumed in both social and cultural settings. Until recently, two types of alcohol consumption were recognized: heavy chronic alcohol consumption or light consumption. Today, there is a new pattern of consumption among teenagers and young adults namely: binge drinking. Heavy alcohol consumption is detrimental to many organs and tissues, including bones, and is known to induce secondary osteoporosis. Some studies, however, have reported benefits from light alcohol consumption on bone parameters. To date, little is known regarding the effects of binge drinking on bone health. Here, we review the effects of three different means of alcohol consumption: light, heavy, and binge drinking. We also review the detailed literature on the different mechanisms by which alcohol intake may decrease bone mass and strength. The effects of alcohol on bone are thought to be both direct and indirect. The decrease in bone mass and strength following alcohol consumption is mainly due to a bone remodeling imbalance, with a predominant decrease in bone formation. Recent studies, however, have reported new mechanisms by which alcohol may act on bone remodeling, including osteocyte apoptosis, oxidative stress, and Wnt signalling pathway modulation. The roles of reduced total fat mass, increased lipid content in bone marrow, and a hypoleptinemia are also discussed.     

Osteogenic enhancement of diaphyseal reconstruction. Comparison of bone grafts in the rabbit

We investigated incorporation of autoclaved autografts in segmental defects of rabbit humeri for comparison with a previous study on similar grafts supplemented with demineralized allogeneic bone matrix (DABM). We also made similar reconstructions with frozen allografts--both DABM and nonsupplemented allografts. Before the animals were killed at 8 months, they underwent scintigraphy, showing that all 28 humeral reconstructions were metabolically active. Faxitrone radiography showed nonunion in three of nine with autoclaved autografts and in two of eight with frozen allografts, whereas all 11 DABM-supplemented frozen allografts had incorporated. Taking into account only the 23 healed reconstructions, the mean torsional strength in relation to the contralateral nonoperated on humeri was 0.81 for all three groups. Histologically, new bone enveloping, partly replacing, the implants was more abundant in DABM-supplemented reconstructions. Our study shows that osteogenic enhancement is more important than the type of nonviable bone chosen for diaphyseal repair. However, if healing is obtained, osteogenic enhancement per se does not increase the strength.     

Co-dependence of calcium and phosphorus for growth and bone development under conditions of varying deficiency

The purpose of this study was to quantify the effect of variation in calcium intake, with and without supplemental phosphorus, on growth and bone development in growing animals under conditions of varying calcium and phosphorus deficiency. Nine groups of weanling male rats were fed a diet nutritionally complete, except for calcium and phosphorus, for 28 days. This diet provided nine levels of varying calcium and phosphorus repletion, using either calcium carbonate, dicalcium phosphate, or tricalcium phosphate. Body weights and diet consumption were measured throughout the test period. At term, the femurs from each animal were weighed, measured for tensile strength, bone mineral content (BMC), and bone density, and analyzed for ash, calcium, phosphorus, and histology. As expected, at equivalent levels of calcium supplementation, the two phosphorus-containing salts promoted significantly greater improvement in all the bone variables measured, as well as greater body weight gain and diet and calcium utilization, compared to animals supplemented with calcium only. Histomorphometric analysis confirmed the results of the mineral analysis and showed the structural impact of the inadequate mineral intake. The mean values for ash weight, BMC, and tensile strength in the nine diet groups were well fit (R(2) values ranging from 0.93 to 0.99) by multivariate models incorporating only the diet content values for calcium and phosphorus. In these models, the value for the phosphorus coefficient was three to sixfold larger than that for the calcium term, indicating a substantially greater effect of varying phosphorus intake than of varying calcium. These results demonstrate both the co-dependence of calcium and phosphorus in bone development and the importance of providing both minerals to support soft tissue and bone growth.     

Bone sialoprotein-coated femoral implants are osteoinductive but mechanically compromised.

Aseptic loosening of femoral implants in total hip replacement remains an unsolved orthopaedic problem. This paper investigates the potential role of bone sialoprotein (BSP) in enhancing bone-implant adherence. As BSP is osteoinductive in rat calvarial models, we investigated whether BSP is similarly osteoinductive when coated onto intramedullary femoral implants. BSP-coated titanium implants were implanted into the femur of female 'Wistar' rats (average weight 215 g) that were sacrificed at days 10, 20 and 30. Harvested femoral implants were subjected to pullout testing and then examined histologically. BSP-coated implants demonstrate osteoinduction when examined histologically. Plugging the femoral canal with BSP prior to inserting the implant neither increased implant pullout strengths nor further increased osteoblastic activity. This study has demonstrated for the first time that BSP is osteoinductive when coated onto femoral implants and inserted into bones subjected to mechanical loading. However, we found that pullout strengths are a function of implant surface topographical characteristics and are not affected by BSP coating or histological osteoinduction.