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Introduction: Estimating the risk of dental problems in long-duration space missions to the Moon and Mars is critical for avoiding dental emergencies in an environment that does not support proper treatment. Previous risk estimates were constructed based on the experience in short-duration space missions and isolated environments on Earth. However, previous estimates did not account for potential changes in dental structures due to space travel, even though bone loss is a known problem for long-duration spaceflights. The objective of this study was to systematically analyze the changes in hard tissues of the craniofacial complex during spaceflights., Methods: Comprehensive search of Medline, Embase, Scopus, the NASA Technical Report Server, and other sources identified 1,585 potentially relevant studies. After screening, 32 articles that presented quantitative data for skull in humans (6/32) and for calvariae, mandible, and lower incisors in rats (20/32) and mice (6/32) were selected., Results: Skull bone mineral density showed a significant increase in spacefaring humans. In spacefaring rodents, calvariae bone volume to tissue volume (BV/TV) demonstrated a trend toward increasing that did not reach statistical significance, while in mandibles, there was a significant decrease in BV/TV. Dentin thickness and incisor volume of rodent incisors were not significantly different between spaceflight and ground controls., Discussion: Our study demonstrates significant knowledge gaps regarding many structures of the craniofacial complex such as the maxilla, molar, premolar, and canine teeth, as well as small sample sizes for the studies of mandible and incisors. Understanding the effects of microgravity on craniofacial structures is important for estimating risks during long-duration spaceflight and for formulating proper protocols to prevent dental emergencies., Knowledge Transfer Statement: Avoiding dental emergencies in long-duration spaceflights is critical since this environment does not support proper treatment. Prior risk estimates did not account for changes in dental structures due to space travel. We reviewed and synthesized the literature for changes in craniofacial complex associated with spaceflight. The results of our study will help clinicians and scientists to better prepare to mitigate potential oral health issues in space travelers on long-duration missions.

Patients with rheumatoid arthritis (RA) have very different outcomes, particularly with regard to bone erosions. Since osteoclasts are responsible for bone destruction adjacent to rheumatoid synovium, profiling osteoclasts from circulating precursors in RA could help identify patients at risk for bone destruction. In this study, we sought to determine whether the functional characteristics of osteoclasts generated from their blood precursors were modified by RA activity or were intrinsic to osteoclasts and associated with the RA phenotype (erosive or not). Osteoclasts were generated in vitro from peripheral blood mononuclear cells (PBMCs) of subjects with RA (n = 140), as well as sex- and age-matched healthy controls (n = 101). Osteoclastic parameters were analyzed at baseline and during the follow-up for up to 4 years, with regular assessment of RA activity, bone erosions, and bone mineral density (BMD). As a validation cohort, we examined RA patients from the Early Undifferentiated PolyArthritis (EUPA) study (n = 163). The proportion of CD14 + PBMC was higher in RA than in control subjects, but inversely correlated with the 28-joint disease activity score (DAS28). Also surprisingly, in osteoclast cultures from PBMCs, active RA was associated with lower osteoclastogenic capacity, while in vitro bone resorption per osteoclast and resistance to apoptosis were similar in both active and quiescent RA. In a small subgroup analysis, osteoclasts from subjects with recent RA that had progressed at four years to an erosive RA exhibited at baseline greater resistance to apoptosis than those from patients remaining non-erosive. Our findings establish that when RA is active, circulating monocytes have a reduced potential to generate osteoclasts from PBMCs in vitro . In addition, osteoclasts associated with erosive disease had resistance to apoptosis from the start of RA., Competing Interests: SR reports personal fees from Amgen Canada, outside the submitted work; Dr. Boire reports personal fees and grants from Amgen, BMS, Celgene, Eli Lilly, Pfizer, Merck, and grants from Abbvie, Novartis, Roche, and UCB, outside the submitted work; all other authors confirm that they have no conflicts of interest., (© 2020 The Authors.)

Bone reacts to local mechanical environment by adapting its structure. Bone is also a key source of calcium for the body homeostasis. Osteocytes, cells located within the bone tissue, are thought to play a major role in sensing mechanical signals and regulating bone remodeling. Interestingly, osteocytes were also shown to directly participate in the calcium homeostasis by regulating dissolution and deposition of calcium in the perilacuno-pericanalicular space. However, it is not known if osteocyte's roles in mechanoregulation and calcium homeostasis have any significant crosstalk. Previously, a multi-scale mathematical model of the interstitial fluid flow through the canaliculus was developed, which took into account physicochemical phenomena including hydraulic effects, formation of electrical double layer, osmosis and electro-osmosis. We extended this model to include the directional movement of calcium from and into the bone tissue, and assessed the shear stress at the osteocyte membrane. We have found that in the bulk of the canalicular space the fluid flow due to chemical gradient generated by deposition or dissolution of calcium is negligible compared to the fluid flow due to hydraulic pressure. However, at the osteocyte proximity, the presence of calcium gradient generated sufficient fluid flow to induce significant changes in the shear stress on the osteocyte membrane. Calcium deposition and dissolution on the canalicular wall resulted in increased or decreased shear stress on the osteocyte membrane respectively. Thus, our data demonstrate that strong calcium fluxes due to whole body calcium homeostasis may affect mechanical forces experienced by osteocytes., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Increases in local and systemic bone resorption are hallmarks of rheumatoid arthritis (RA). Osteoclasts are implicated in these processes and their enhanced differentiation may contribute to bone destruction. We observed that in vitro osteoclastogenesis varies among healthy individuals and hypothesized that increased osteoclastogenesis could be a marker for the presence of RA. Our objective in the present study was to determine if in vitro osteoclastogenesis from peripheral blood mononuclear cells (PBMCs) was different in patients with RA compared to healthy controls and osteoarthritis (OA) patients. Expression of CD14 in PBMCs was quantified and PBMCs were incubated for 21 days in the presence of the osteoclastogenic cytokines M-CSF and RANKL. Differentiation on cortical bone slices permitted the analysis of bone resorption while apoptotic potential was assessed by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling. In vitro osteoclastogenesis was higher in PBMCs from RA patients compared to controls, and a similar increase was observed in the percentage of osteoclast precursors in RA patients. Osteoclasts from RA patients showed lower apoptotic rates than osteoclasts from healthy controls. No difference was observed in bone resorption activity between RA patients and controls. Interestingly, the difference in osteoclast number and apoptosis rate allowed the implementation of an algorithm capable of distinguishing patients with RA from controls. In conclusion, our study shows that osteoclast differentiation from PBMCs is enhanced in patients with RA, and this difference can be explained by both a higher percentage of osteoclast precursors in the blood and by the reduced apoptotic potential of mature osteoclasts., (Copyright © 2010 Elsevier Inc. All rights reserved.)

This review summarizes the types of ion channels that have been identified in osteoclasts and considers their potential as targets for therapeutic agents aimed at the treatment of osteoporosis and other bone disorders. We focus on channels that have been identified using molecular and electrophysiological approaches. Numerous ion channels have been characterized, including K(+), H(+), Na(+), nonselective cation and Cl(-) channels. K(+) channels include an inward rectifier K(+) channel (Kir2.1) that is regulated by G proteins, and a transient outward rectifier K(+) channel (Kv1.3) that is regulated by cell-matrix interactions and by extracellular cations such as Ca(2+) and H(+). In addition, two classes of Ca(2+)-activated K(+) channels have been described--large and intermediate conductance channels, which are activated by increases of cytosolic Ca(2+) concentration. Other channels include stretch-activated nonselective cation channels and voltage-activated H(+) channels. A recent revelation is the presence of ligand-gated channels in osteoclasts, including P2X nucleotide receptors and glutamate-activated channels. Osteoclasts also exhibit an outwardly rectifying Cl(-) current that is activated by cell swelling. Kir2.1 and Cl(-) channels may be essential for resorptive activity because they provide pathways to compensate for charge accumulation arising from the electrogenic transport of H(+). As in other cell types, osteoclast ion channels also play important roles in setting the membrane potential, signal transduction and cell volume regulation. These channels represent potential targets for the development of antiresorptive drugs.

Permeability of cell membranes to cations may increase as a result of membrane oxidation or in certain pathologies. We studied the effects of nonselective increases in cell membrane permeability to univalent cations on the volume of erythrocytes incubated in phosphate-buffered saline (PBS) using amphotericin B (5-10 mg/l suspension) or gramicidin D (10-100 microg/l suspension) as the membrane permeabilizing agents. Both antibiotics caused K+ to leak, Na+ to accumulate intracellularly, and cell volume to increase. The interval needed to reach the equilibrium between the intracellular and extracellular ion concentrations ranged from 30 min to several hours, depending on the antibiotic concentration. In spite of a rapid disappearance of cation transmembrane gradients, cell volume increased relatively slow. Even 24 h after the membrane permeability was changed, the volume of most erythrocytes did not increase to the lytic values (about 1.6 times the normal volume). The slow increase in erythrocyte volume was accounted for by slow changes in the transmembrane Cl- gradient. 4,4'-Diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS), a specific inhibitor of anion transport, while producing no effect on the transmembrane Na+ and K+ fluxes induced by the antibiotics, significantly inhibited the decrease in the transmembrane Cl- gradient and the increase in erythrocyte volume. Analysis of these data by means of mathematical modeling showed that it failed to satisfactorily describe the experimental kinetics of erythrocyte swelling in response to increases in the membrane permeability to univalent cations if its permeability to Cl was set to be constant. The satisfactory description of this kinetics could be achieved by assuming that the membrane permeability to anions decreased with increasing erythrocyte volume. The results obtained demonstrate that transmembrane anion transport may be considered to be a component of the mechanism responsible for the erythrocyte volume stabilization, because a significant decrease in the swelling rate allows the erythrocytes with damaged membranes to activate a relatively slow (metabolic) mechanisms of cell volume stabilization and/or repair their damaged membranes.

In suspensions of washed human erythrocytes, adenosine added in a single dose to concentrations of 0.1-10.0 mmol/l suspension was deaminated at rates ranging from 10 to 50 mmol/l cells h. The sum of adenosine, inosine, and hypoxanthine concentrations in the suspension, as well as the intracellular concentration of ATP, remained constant. In the presence of 25-50 mmol/l orthophosphate, addition of a single dose of adenosine into erythrocyte suspension increased the ATP concentration by up to 280% of the initial level. If the initial adenosine concentrations were greater than 5 mmol/l suspension, ATP increased independently of adenosine concentration to the level determined only by the concentration of orthophosphate. After orthophosphate was returned to its initial level, ATP in erythrocytes began to decrease. In the presence of coformycin, erythrocytes utilised adenosine at a rate of 0.2-0.3 mmol/l cells h. Their adenylate pool increased at a rate of 0.10-0.16 mmol/l cells h for several hours, but intracellular ATP increased only slightly. The energy charge of cells decreased significantly from 0.86 +/- 0.05 (control) to 0.82 +/- 0.06. Adenosine continuously pumped into erythrocyte suspensions at rates of 0.02-5.0 mmol/l cells h for several hours caused the adenylate pool of erythrocytes and intracellular ATP to increase synchronously at a rate of 0.02-0.35 mmol/l cells h. The energy charge of these erythrocytes increased significantly up to 0.91 +/- 0.03. After pumping of adenosine was stopped, the intracellular ATP and the adenylate pool began to decrease, returning sometimes to the initial level in 2-3 h.

We constructed and studied a mathematical model that describes the control of cell volume, ion balance, energy and adenylate metabolism in human erythrocytes. According to the model, adenylate metabolism can provide an effective stabilization of the cell volume over relatively large changes of cell parameters. For example, the steady-state value of cell volume remains almost unchanged when the cell membrane permeability increases by 15-fold. The cell volume also changes only slightly over large changes in the parameters of energy metabolism. The relaxation time for the cell volume changes is about 100 hr over changes in these parameters. In other words, the volume stabilization operates most effectively against long-term slow perturbations.

A simplified mathematical model of cell metabolism describing ion pump, glycolysis and adenylate metabolism was developed and investigated in order to clarify the functional role of the adenylate metabolism system in human erythrocytes. The adenylate metabolism system was shown to be able to function as a specific regulatory system stabilizing intracellular ion concentration and, hence, erythrocyte volume under changes in the permeability of cell membrane. This stabilization is provided via an increase in adenylate pool in association with ATPases rate elevation. Proper regulation of adenylate pool size might be achieved even in the case when AMP synthesis rate remains constant and only AMP degradation rate varies. The best stabilization of intracellular ion concentration in the model is attained when the rate of AMP destruction is directly proportional to ATP concentration and is inversely proportional to AMP concentration. An optimal rate of adenylate metabolism in erythrocytes ranges from several tenths of a percent to several percent of the glycolytic flux. An increase in this rate results in deterioration of cell metabolism stability. Decrease in the rate of adenylate metabolism makes the functioning of this metabolic system inefficient, because the time necessary to achieve stabilization of intracellular ion concentration becomes comparable with erythrocyte life span.

Amphotericin B (1-3 mg/l) decreases the ATP content in erythrocytes by 11-26% and stimulates the K+ efflux but has no effect on the adenylate pool. Adenosine added to the erythrocyte suspension increases the adenylate pool, maintains a high intracellular ATP level for 6-8 hours of incubation at 37 degrees C and diminishes the amphotericin B-induced leakage of K+. Incubation of erythrocytes without glucose for 4-5 hours leads to a 20-50% loss of ATP accompanied by a significant reduction of the adenylate pool. Further addition of glucose partly restores the ATP level. In the presence of adenosine the ATP concentration is restored far more pronounced reaching nearly the original level due to the increase of the adenylate pool.