Effect of alendronate and exercise on bone and physical performance of postmenopausal women: a randomized controlled trial

In this randomized, double-blind, placebo-controlled 12-month trial we evaluated effects of weight- bearing jumping exercise and oral alendronate, alone or in combination, on the mass and structure of bone, risk factors for falling (muscle strength and power, postural sway, and dynamic balance), and cardiorespiratory fitness in postmenopausal women. A total of 164 healthy, sedentary, early postmenopausal women were randomly assigned to one of four experimental groups: (1) 5 mg of alendronate daily plus progressive jumping exercise, (2) 5 mg alendronate, (3) placebo plus progressive jumping exercise, or (4) placebo. The primary endpoint was 12-month change in bone mass and geometry (measured with dual-energy X-ray absorptiometry and peripheral computed tomography at several axial and limb sites) and physical performance; the secondary endpoint was change in biochemical markers of bone turnover. The jumping exercise was conducted an average 1.6 +/- 0.9 (mean +/- SD) times a week. Alendronate daily was effective in increasing bone mass at the lumbar spine (alendronate vs placebo 3.5%; 95% CI, 2.2-4.9%) and femoral neck (1.3%; 95% CI, 0.2-2.4%) but did not affect other bone sites. Exercise alone had no effect on bone mass at the lumbar spine or femoral neck; it had neither an additive nor an interactive effect with alendronate at these bone sites. However, at the distal tibia the mean increase of 3.6% (0.3-7.1%) in the section modulus (that is, bone strength) and 3.7% (0.1-7.3%) increase in the ratio of cortical bone to total bone area were statistically significant in the exercise group compared to the nonexercise group, indicating exercise-induced thickening of the bone cortex. Bone turnover was reduced in alendronate groups only. Alendronate had no effect on physical performance while the jumping exercise improved leg extensor power, dynamic balance, and cardiorespiratory fitness. As conclusion Alendronate is effective in increasing bone mass at the lumbar spine and femoral neck, while exercise is effective in increasing the mechanical properties of bone at some of the most loaded bone sites, as well as improving the participants' muscular performance and dynamic balance. Together alendronate and exercise may effectively decrease the risk of osteoporotic fractures.

Alendronate disturbs vesicular trafficking in osteoclasts

The nitrogen-containing bisphosphonate alendronate inhibits osteoclast-mediated bone resorption through inhibition of the mevalonate pathway. This results in impaired protein prenylation and may affect the function of small GTPases in osteoclasts. Since these proteins are important regulators of vesicle transport in cells, we investigated the possible interference of alendronate with these processes in isolated rat osteoclasts. We show here that alendronate-induced inhibition of bone resorption coincides with accumulation of tartrate-resistant acid phosphatase- and electron dense material-containing tubular vesicles in osteoclasts. Alendronate-induced changes in osteoclasts also included widening of the sealing zone areas and incomplete organization of tight attachments and ruffled borders. Osteoclasts also appeared partially detached from the bone surface, and organic matrix was typically dissolved only at the edges of the resorption pits on alendronate-coated bone slices. In contrast, resorption pits on the control and clodronate-coated bone slices were thoroughly resorbed. Inhibition of bone resorption by alendronate was not, however, related to a decrease in osteoclast number. In conclusion, our findings suggest that alendronate inactivates osteoclasts by mechanisms that impair their intracellular vesicle transport, apoptosis being only a secondary phenomenon to this.

Estrogen reduces the depth of resorption pits by disturbing the organic bone matrix degradation activity of mature osteoclasts

Decreased E2 levels after menopause cause bone loss through increased penetrative resorption. The reversal effect of E2 substitution therapy is well documented in vivo, although the detailed mechanism of action is not fully understood. To study the effects of E2 on bone resorption, we developed a novel in vitro bone resorption assay in which degradation of inorganic and organic matrix could be measured separately. E2 treatment significantly decreased the depth of resorption pits, although the area resorbed was not changed. Electron microscopy further revealed that the resorption pits were filled with nondegraded collagen, suggesting that E2 disturbed the organic matrix degradation. Two major groups of proteinases, matrix metalloproteinases (MMPs) and cysteine proteinases, have been suggested to participate in organic matrix degradation by osteoclasts. We show here that MMP-9 released a cross-linked carboxyl-terminal telopeptide of type I collagen from bone collagen, and cathepsin K released another C-terminal fragment, the C-terminal cross-linked peptide of type I collagen. E2 significantly inhibited the release of the C-terminal cross-linked peptide of type I collagen into the culture medium without affecting the release of cross-linked carboxyl-terminal telopeptide of type I collagen in osteoclast cultures. These results suggest that organic matrix degradation is initiated by MMPs and continued by cysteine proteases; the latter event is regulated by E2.

Does combined gastrectomy and ovariectomy induce greater osteopenia in young female rats than gastrectomy alone?

Osteopenia develops in experimental animals following surgical removal of the ovaries (ovariectomy. Ovx) or the stomach (gastrectomy, Gx). Though the effect of Ovx has been ascribed to estrogen deficiency, the mechanism behind the Gx-evoked osteopenia remains unknown. In order to compare Gx- and Ovx-evoked osteopenia, young female rats were subjected to Ovx, gx, the combination of ovx and Gx, or sham operation (SHAM). Serum osteoclast-derived tartrate-resistant acid phosphatase 5b was measured as an index of bone resorption, and serum osteocalcin as an index of bone formation/turnover. Bone resorption predominated over bone formation during the first 4 days after Ovx but not later. Bone resorption predominated over bone formation throughout the first 4-week period after Gx. the changes were not additive in the ovx+Gx group. Transillumination and histomorphometry of the calvariae revealed extensive osteopenia in the Gx and the Ovx+Gx groups but not in the Ovx group. Peripheral quantitative computerized tomography of the femur metaphysis showed a decrease in the trabecular bone mineral density (BMD) in all three groups although Ovx+Gx seemed to induce greater trabecular bone loss than Gx alone. However, dual energy X-ray absorptiometry (DXA) of the intact femurs revealed reduced bone mineral content (BMC) in the Gx and Ovx+Gx groups but not in the Ovx group. Indeed, cortical bone was impaired by Gx and Ovx+Gx but not by Ovx. Hence, it seems clear that the Gx-evoked osteopenia differs from that induced by Ovx but that the osteopenia induced by Ovx+Gx is only marginally greater than that induced by Gx alone.

Tartrate-resistant acid phosphatase facilitates hydroxyl radical formation and colocalizes with phagocytosed Staphylococcus aureus in alveolar macrophages

Tartrate-resistant acid phosphatase (TRAP) is an enzyme expressed specifically in osteoclasts and activated macrophages, two phagocytosing cell types originating from the same hematopoietic stem cells. TRAP contains a binuclear iron centre which has been shown to generate reactive oxygen species (ROS). In this study murine macrophage like cell line RAW-264 overexpressing TRAP was shown to produce elevated levels of hydroxyl radicals compared to parental cells. TRAP transfected cells also had reduced growth rate indicating harmful effects of excessive intracellular ROS levels. Using TRAP specific antibody TRAP protein was shown in alveolar macrophages partially colocalize with late endosomal/lysosomal markers Rab7, Lamp 1 and MHC II molecules that bind antigenic peptides. TRAP also colocalized into compartments where Staphylococcus aureus were phagocytosed. These results suggest that TRAP may have an important biological function in the defence mechanism of macrophages by generating intracellular ROS which would be targeted to destroy phagocytosed foreign material.

Tartrate-resistant acid phosphatase from human bone: purification and development of an immunoassay

Tartrate-resistant acid phosphatase (TRAP) was purified 20,000-fold to apparent homogeneity from human bone. The purified enzyme consisted of one 32 kd subunit, which was cleaved by beta-mercaptoethanol into two subunits of 15 kd and 20 kd, as shown by sodium dodecyl sulfide-polyacrylamide gel electrophoresis (SDS-PAGE) and silver staining. The purified enzyme was identified by N-terminal amino acid sequencing, and it was shown to be homologous with previously purified TRAPs from other sources. We developed a polyclonal antiserum against the purified enzyme in mice. In immunohistochemistry, the antiserum recognized osteoclasts from human bone and alveolar macrophages from human lung tissue, but no cells from human spleen tissue. It also stained osteoclasts from rat bone cells cultured on bovine bone slices. Purified TRAP could be inhibited by vanadate and molybdate, but not by tartrate, and it was activated 2-fold by beta-mercaptoethanol. The glycoprotein structure of human bone TRAP was analyzed, and it was shown to contain only high-mannose type carbohydrates. We used the polyclonal antibody to develop a competitive fluorescence immunoassay for measuring serum TRAP concentrations. According to the assay, children have higher serum TRAP concentrations than adults, and postmenopausal women have higher concentrations than premenopausal women. Postmenopausal women also have higher serum TRAP concentrations than postmenopausal women on estrogen replacement therapy.

Structural relationship between DNA polymerases epsilon and epsilon* and their occurrence in eukaryotic cells

Monoclonal antibodies raised against the N-terminal half of human DNA polymerase epsilon bind both to a large > 200 kDa form of DNA polymerase epsilon from HeLa cells and to a small 140 kDa form (DNA polymerase epsilon*) from calf thymus, while antibody against the C-terminal half binds to DNA polymerase epsilon but does not bind to DNA polymerase epsilon*. These results indicate that the two enzymes have common structural motifs in their N-terminal halves, and that DNA polymerase epsilon* is very likely derived from DNA polymerase epsilon by removal of its C-terminal half. DNA polymerase epsilon as well as DNA polymerase epsilon* was detected in extracts from cells of numerous eukaryotic species from yeast to human. The results indicate that DNA polymerase epsilon and its tendency to occur in a smaller form, DNA polymerase epsilon*, are evolutionarily highly conserved and that DNA polymerase epsilon may occur universally in proliferating eukaryotic cells.

The 3'-->5' exonuclease associated with HeLa DNA polymerase epsilon

The 3'-->5' exonuclease activity of highly purified large form of human DNA polymerase epsilon was studied. The activity removes mononucleotides from the 3' end of an oligonucleotide with a non-processive mechanism and leaves 5'-terminal trinucleotide non-hydrolyzed. This is the case both with single-stranded oligonucleotides and with oligonucleotides annealed to complementary regions of M13DNA. However, the reaction rates with single-stranded oligonucleotides are at least ten-fold when compared to those with completely base-paired oligonucleotides. Conceivably, mismatched 3' end of an oligonucleotide annealed to M13DNA is rapidly removed and the hydrolysis is slowed down when double-stranded region is reached. The preferential removal of a non-complementary 3' end and the nonprocessive mechanism are consistent with anticipated proofreading function. In addition to the 3'-->5' exonuclease activity, an 5'-->3' exonuclease activity is often present even in relatively highly purified DNA polymerase epsilon preparates suggesting that such an activity may be an essential component for the action of this enzyme in vivo. Contrary to the 3'-->5' exonuclease activity, the 5'-->3' exonuclease is separable from the polymerase activity.