Parathyroid hormone (1-34) increased total body bone mass in aged female rats

Daily subcutaneous administration of bovine parathyroid hormone (PTH)(1-34) stimulates bone formation and increases bone mass in rat tibiae, femora and lumbar spine. However, the effects of PTH on the whole body bone mineral content and density determined by dual energy x-ray absortiometry (DEXA) have not been previously reported in rats. Eighteen-month-old intact female rats were subcutaneously injected daily with 0, 40, 80 or 160 micrograms/kg/day of bovine PTH (1-34) for either 15 or 60 days. Whole body DEXA was performed at 1 day before autopsy, and bone area, bone mineral content (BMC) and bone mineral density (BMD) of the total body were determined. Total femoral, tibial and lumbar spine BMD was also determined ex vivo. Cancellous bone histomorphometry was performed on sections of double-labeled proximal tibial metaphyses. Whole body bone mineral content and density were significantly increased by 60 days, but not by 15 days, of PTH treatment at all dose groups compared with vehicle controls. Lumbar vertebral and total femoral BMD was significantly increased at all doses of PTH by 15 days of administration and further increased by 60 days. All doses of PTH increased trabecular bone area in proximal tibial metaphyses by 15 days and further increased by 60 days. All doses of PTH increased trabecular bone area in proximal tibial metaphyses by 15 days and further increased by 60 days. In proximal tibial cancellous bone, dose-dependent increases in percent labeled perimeter, mineral apposition rate and bone formation rate-bone volume referent were found between 40 and 160 micrograms/kg of PTH treatment by 15 days, and no further increases were found by 60 days. Our results showed that in aged female rats, bovine PTH(1-34) increased bone formation and total body bone mass.     

Weighted vest exercise improves indices of fall risk in older women

BACKGROUND: Bone mass and fall propensity are two major risk factors for hip fracture. Our intent was to determine if weight-bearing exercises with added resistance from weighted vests would improve dynamic balance, muscle strength and power, and bone mass in postmenopausal women, thereby reducing risk for falls and hip fracture. METHODS: Forty-four nonsmoking, community-dwelling, Caucasian women aged 50-75 years participated in the study. All participants were at least 5 years past menopause and most were estrogen-deplete (n = 36). Bone mass and body composition were assessed by dual-energy x-ray absorptiometry, muscular strength by isokinetic dynamometry, muscular power by modified Wingate Anaerobic Power Test, and indices of postural stability by dynamic posturography. Half of the subjects participated in a 9-month regimen of weight-bearing exercises performed three times a week that emphasized lower-body muscle strength and power development. Resistance was added progressively and individually by the use of a weighted vest. Controls maintained customary diet and activity patterns. RESULTS: Significant improvements were observed for indices of lateral stability, lower-body muscular strength (16-33% increase), muscular power (13% increase), and leg lean mass (3.5% increase) in exercisers vs controls (p < .05). No significant changes (p > .05) were detected for femoral neck bone mass in exercisers or controls at the conclusion of the trial. CONCLUSIONS: Lower body exercise, using a weighted vest for resistance, provides an effective means of improving key indices of falls in postmenopausal women.     

pp56Lck mediates TCR zeta-chain binding to the microfilament cytoskeleton

The TCR zeta-chain (zeta) on mature murine T lymphocytes binds to the microfilament cytoskeleton in response to Ag receptor ligation. Here, we report the role of Src family kinases in zeta-cytoskeletal binding, using mutant mice and a cell-free model system. Binding of zeta to actin in the cell-free system has a specific requirement for ATP and divalent cations, with an apparent Michaelis-Menton constant for ATP in the millimolar range, and can be disrupted by either EDTA or the microfilament poison, cytochalasin D, suggesting that microfilaments provide the structural framework for an active process involving cellular kinases. Indeed, tyrosine-phosphorylated zeta is a predominant form of the zeta-chain bound to polymerized actin, while challenge with alkaline phosphatase prevents zeta-chain association in solution and releases zeta-chain from the bound state. Phosphorylated Src-family kinase pp56Lck also associates with membrane skeleton upon TCR engagement and is a component of the reconstituted cytoskeletal pellet. Zeta-chain phosphorylation and zeta-cytoskeletal binding are abrogated in cell lysates with reduced levels of pp56Lck and in activated mutant murine T cells lacking pp56Lck, implicating pp56Lck as the kinase involved in zeta-chain tyrosine phosphorylation and zeta-cytoskeletal binding. Finally, recombinant Lck Src homology 2 domain preferentially inhibits reconstituted zeta-cytoskeleton association, suggesting that zeta-microfilament binding is dependent on interactions between phosphorylated tyrosine residues in zeta-chain activation motifs and the Src homology 2 domain of the Lck protein tyrosine kinase.     

Characteristics of cation binding to the I domains of LFA-1 and MAC-1. The LFA-1 I domain contains a Ca2+-binding site

The crystal structures of the I domains of integrins MAC-1 (alphaM beta2; CD11b/CD18) and LFA-1 (alphaL beta2; CD11a/CD18) show that a single conserved cation-binding site is present in each protein. Purified recombinant I domains have intrinsic ligand binding activity, and in several systems this interaction has been demonstrated to be cation-dependent. It has been proposed that the I domain cation-binding site represents a general metal ion-dependent adhesion motif utilized for binding protein ligands. Here we show that the purified recombinant I domain of LFA-1 (alphaLI) binds cations, but with significantly different characteristics compared with the I domain of MAC-1 (alphaMI). Both alphaLI and alphaMI bind 54Mn2+ in a conformation-dependent manner, and in general, cations with charge and size characteristics similar to Mn2+ most effectively inhibit 54Mn2+ binding. Surprisingly, however, physiological levels of Ca2+ (1-2 mM) inhibited 54Mn2+ binding to purified alphaLI, but not to alphaMI. Using 45Ca2+ and 54Mn2+ in direct binding studies, the dissociation constants (KD) for the interactions between these cations and alphaLI were estimated to be 5-6 x 10(-5) and 1-2 x 10(-5) M, respectively. Together with the available structural information, the data suggest differential affinities for Mn2+ and Ca2+ binding to the single conserved site within alphaLI. Antagonism of LFA-1, but not MAC-1, -mediated cell adhesion by Ca2+ may be related to the Ca2+ binding activity of the LFA-1 I domain.     

Influence of magnesium substitution on a collagen-apatite biomaterial on the production of a calcifying matrix by human osteoblasts

The induction of a calcifying matrix is of great interest in the restoration of bone defects. In a previous in vitro study we demonstrated that a collagen sponge constituted of type I collagen fibrils, chondroitin sulfates, and hydroxyapatite crystals induces an earlier and a more abundant synthesis of a new extracellular calcifying matrix than do other biomaterials such as collagen or hydroxyapatite alone. Bone mineral contains various amounts of magnesium ions, either adsorbed at the surface of apatite crystals or incorporated inside the crystal structure. Magnesium is known to reduce the degradation rate of tricalcium phosphate ceramics and to influence the crystallization of mineral substance. Thus we evaluated two sponges modified with different substituted apatites. The substituted low magnesium-containing apatite sample decreased the osteoinductive properties of the sponge whereas the substituted high magnesium-containing apatite sample had a toxic effect on bone cells and prevented the formation of any extracellular matrix. Such a toxic effect can be explained by the presence of large numbers of magnesium ions released into the culture medium even though at physiological level magnesium is able to promote bone mineralization and to control the growth of hydroxyapatite crystals. Thus collagen sponges containing hydroxyapatite remain one of the most appropriately evaluated biomaterials used for the restoration of periodontal pockets and bone defects.     

Rivastigmine. A review of its use in Alzheimer's disease

Rivastigmine (SDZ ENA 713) is a carbamylating, long-acting reversible and noncompetitive carbamate acetylcholinesterase inhibitor that is indicated as an oral treatment for patients with mild to moderately severe Alzheimer's disease. The drug has been evaluated for this use in 3 well designed, adequately powered, phase II/III, 26-week clinical trials that included a total of 1479 rivastigmine and 647 placebo recipients. Most of these patients had concomitant disorders that were being treated with numerous other drugs. Individual and pooled results of these trials indicate that rivastigmine 6 to 12 mg/day usually produces cognitive, global and functional changes that indicate significantly less deterioration than was observed with placebo in patients with mild to moderately severe Alzheimer's disease. Individual results of the 2 pivotal trials and pooled analysis also show that, compared with placebo recipients, significantly more rivastigmine 6 to 12 mg/day recipients respond to therapy. Indeed, after 26 weeks of therapy in the 2 pivotal trials, significantly more rivastigmine 6 to 12 mg/day than placebo recipients achieved clinically meaningful improvements as defined by 3 separate response criteria. The lower dosage range of 1 to 4 mg/day was not as effective as 6 to 12 mg/day, as measured using these criteria and other efficacy parameters. Rivastigmine causes adverse events that are generally those expected from an acetylcholinesterase inhibitor. They are usually mild to moderate, of short duration and responsive to dosage reduction. Unpublished data from 3989 patients indicate that rivastigmine and placebo were associated with similar incidences of serious adverse events and changes in laboratory parameters, ECG and cardiorespiratory vital signs. The most common events were gastrointestinal, central and peripheral nervous system and whole body adverse events. However, compared with placebo, rivastigmine more commonly caused adverse events resulting in treatment withdrawal. These events were most frequently gastrointestinal and were more common in women. CONCLUSION: Rivastigmine is a useful option for the treatment of patients with mild to moderately severe Alzheimer's disease. Although only short term (6- month) comparisons with placebo are available, given the lack of established treatment options it should be considered for first-line use in this population.