Tissue-engineered mucosa is a suitable model to quantify the acute biological effects of ionizing radiation.

The aim of this study was to evaluate the suitability of tissue-engineered mucosa (TEM) as a model for studying the acute effects of ionizing radiation (IR) on the oral mucosa. TEM and native non-keratinizing oral mucosa (NNOM) were exposed to a single dose of 16.5Gy and harvested at 1, 6, 24, 48, and 72h post-irradiation. DNA damage induced by IR was determined using p53 binding protein 1 (53BP1), and DNA repair was determined using Rad51. Various components of the epithelial layer, basement membrane, and underlying connective tissue were analyzed using immunohistochemistry. The expression of cytokines interleukin-1ß (IL-1ß) and transforming growth factor beta 1 (TGF-ß1) was analyzed using an enzyme-linked immunosorbent assay. The expression of DNA damage protein 53BP1 and repair protein Rad51 were increased post-irradiation. The expression of keratin 19, vimentin, collage type IV, desmoglein 3, and integrins α6 and ß4 was altered post-irradiation. Proliferation significantly decreased at 24, 48, and 72h post-irradiation in both NNOM and TEM. IR increased the secretion of IL-1ß, whereas TGF-ß1 secretion was not altered. All observed IR-induced alterations in TEM were also observed in NNOM. Based on the similar response of TEM and NNOM to IR we consider our TEM construct a suitable model to quantify the acute biological effects of IR.

Calvarial osteoclasts express a higher level of tartrate-resistant acid phosphatase than long bone osteoclasts and activation does not depend on cathepsin K or L activity.

Bone resorption by osteoclasts depends on the activity of various proteolytic enzymes, in particular those belonging to the group of cysteine proteinases. Next to these enzymes, tartrate-resistant acid phosphatase (TRAP) is considered to participate in this process. TRAP is synthesized as an inactive proenzyme, and in vitro studies have shown its activation by cysteine proteinases. In the present study, the possible involvement of the latter enzyme class in the in vivo modulation of TRAP was investigated using mice deficient for cathepsin K and/or L and in bones that express a high (long bone) or low (calvaria) level of cysteine proteinase activity. The results demonstrated, in mice lacking cathepsin K but not in those deficient for cathepsin L, significantly higher levels of TRAP activity in long bone. This higher activity was due to a higher number of osteoclasts. Next, we found considerable differences in TRAP activity between calvarial and long bones. Calvarial bones contained a 25-fold higher level of activity than long bones. This difference was seen in all mice, irrespective of genotype. Osteoclasts isolated from the two types of bone revealed that calvarial osteoclasts expressed higher enzyme activity as well as a higher level of mRNA for the enzyme. Analysis of TRAP-deficient mice revealed higher levels of nondigested bone matrix components in and around calvarial osteoclasts than in long bone osteoclasts. Finally, inhibition of cysteine proteinase activity by specific inhibitors resulted in increased TRAP activity. Our data suggest that neither cathepsin K nor L is essential in activating TRAP. The findings also point to functional differences between osteoclasts from different bone sites in terms of participation of TRAP in degradation of bone matrix. We propose that the higher level of TRAP activity in calvarial osteoclasts compared to that in long bone cells may partially compensate for the lower cysteine proteinase activity found in calvarial osteoclasts and TRAP may contribute to the degradation of noncollagenous proteins during the digestion of this type of bone.

Endocytosis of tartrate-resistant acid phosphatase by osteoblast-like cells is followed by inactivation of the enzyme.

Tartrate-resistant acid phosphatase (TRACP) is generally used as a marker of osteoclasts. Yet, other bone-associated cells, such as osteoblasts and osteocytes, may also express activity of this enzyme. Osteoblasts containing TRACP activity are seen particularly in the vicinity of areas of bone resorption, suggesting that osteoclasts somehow induce TRACP activity in osteoblasts. In a recent study, we found that osteoblast-like cells appeared to have the capacity to endocytose TRACP released by osteoclast precursors. In the present study, we investigated the endocytosis of TRACP in more detail as well as the fate of the endocytosed enzyme. We found that incubation of osteoblast-like cells with TRACP-coated beads resulted in attachment of a high number of beads to the cells. After culturing osteoblast-like cells with medium conditioned by blood monocytes that contain TRACP, activity of the enzyme was found in the cells. Following replacement of the medium by normal medium that did not contain TRACP, a decrease in the level of TRACP activity in osteoblast-like cells occurred. Our data strongly suggest that osteoblast-like cells recognize TRACP released by osteoclast precursors and that upon endocytosis inactivation of the enzyme occurs. We propose that uptake of the enzyme is important for the control of enzyme activity, thereby preventing degradation of matrix constituents.

Endogenous expression and endocytosis of tartrate-resistant acid phosphatase (TRACP) by osteoblast-like cells.

Tartrate-resistant acid phosphatase (TRACP) is produced by macrophages and other cells of the monohistiocytic lineage. In particular, osteoclasts are characterized for a high expression of this enzyme. Yet, several data suggest that other bone cell types, such as osteocytes and osteoblasts, may also express activity of this enzyme. This is particularly obvious at sites were osteoclasts resorb bone, suggesting that osteoclasts (or their precursors) somehow induce TRACP activity in osteoblasts. In the present study, we investigated this by culturing human osteoblast-like cells with and without conditioned medium (MCM) from human blood monocytes (as a source of osteoclast precursors). High levels of TRACP activity were found in osteoblast-like cells cultured with MCM. Depletion of TRACP from this medium resulted in the absence of its activity in osteoblast-like cells, thus suggesting that the TRACP activity in these cells was the result of endocytosed TRACP that was released by the monocytes in the MCM. Osteoblast-like cells cultured in control (non-conditioned) medium contained very low levels of TRACP-like activity. However, the cells expressed TRACP mRNA and incubation of extracts of these cells with active cathepsin B did induce activity of a TRACP-like enzyme. Inhibition of the activity of cysteine proteinases in general and of cathepsin B in particular, completely blocked TRACP activity of the osteoblast-like cells. This TRACP-like enzyme but not the alleged endocytosed fraction of TRACP was inhibited by fluoride, suggesting that the fractions may be different isoenzymes. Our data seem to indicate that osteoblast-like cells may contain two different fractions of TRACP, one that is released by monocytes and subsequently endocytosed by osteoblast-like cells and a second endogenous fraction that is present in an inactive proform. We hypothesize that the capacity of osteoblast-like cells to endocytose TRACP is important for the removal of this enzyme during or following the bone resorptive activity of the osteoclast.

(Pre-)osteoclasts induce retraction of osteoblasts before their fusion to osteoclasts.

UNLABELLED: Precursors of osteoclasts seeded on top of a confluent layer of osteoblasts/bone lining cells induced retraction of the latter cells. The (pre)osteoclasts then migrated in the formed cell-free areas and fused to form osteoclast-like cells. Retraction of the osteoblasts/bone lining cells proved to depend on activity of matrix metalloproteinases, and TGF-beta1 prevented the retraction. INTRODUCTION: It is well known that osteoblasts have a profound effect on (pre)osteoclasts in inducing the formation of bone-resorbing osteoclasts. Whether, on the other hand, (pre)osteoclasts also modulate osteoblast activity is largely unknown. Because osteoblasts/bone lining cells have to retract from the surface before resorption of bone by osteoclasts, we addressed the question of whether (pre)osteoclasts have the capacity to induce such an activity. MATERIALS AND METHODS: Rabbit calvarial osteoblasts/bone lining cells or periosteal fibroblasts were cultured until confluency, after which rabbit peripheral blood mononuclear cells (PBMCs) were seeded on top of them. The co-cultures were maintained for up to 15 days in the presence or absence of the cytokines transforming growth factor (TGF)-beta1 and TNF-alpha and selective inhibitors of matrix metalloproteinases and serine proteinases. The formation of cell-free areas and the number of TRACP+ multinucleated osteoclast-like cells were analyzed. In addition, formation of cell-free areas was analyzed in co-cultures of osteoblasts with mature osteoclasts. RESULTS: The seeding of PBMCs on a confluent layer of osteoblasts/bone lining cells resulted in the following sequence of events. (1) A low number of PBMCs strongly attached to osteoblasts. 2) At these sites of contact, the osteoblasts retracted, thus forming cell-free areas. (3) The PBMCs invaded these areas and attached to the surface of the well, after which they fused and formed multinucleated TRACP+ osteoclast-like cells. Retraction was only seen if the cells were in direct contact; conditioned media from cultured PBMCs added to osteoblasts had no effect. Mature osteoclasts seeded on osteoblasts similarly induced retraction, but this retraction occurred at a much faster rate (within 2 days) than the retraction effectuated by the osteoclast precursors (after 8 days in co-culture). Inhibition of matrix metalloproteinase activity, but not of serine proteinases, strongly reduced retraction of the osteoblasts, thus indicating that this type of cell movement depends on the activity of matrix metalloproteinases. A similar inhibitory effect was found with TGF-beta1. TNF-alpha had no effect on osteoblast retraction but enhanced the formation of multinucleated osteoclast-like cells. Addition of PBMCs to confluent layers of periosteal fibroblasts resulted in similar phenomena as observed in co-cultures with osteoblasts. However, the cell-free areas proved to be significantly smaller, and the number of multinucleated cells formed within cell-free areas was three to four times lower. CONCLUSION: Our results indicate that osteoclast precursors and mature osteoclasts have the capacity to modulate the activity of osteoblasts and that, yet unknown, membrane-bound signaling molecules are essential in inducing retraction of osteoblasts and the subsequent formation of cell-free areas.

Effect of poly(ethylene glycol), tetramethylammonium hydroxide, and other surfactants on enhancing performance in a latex particle immunoassay of C-reactive protein.

The influence of a variety and combination of both ionic surfactants and different chain lengths of the polyelectrolyte poly(ethylene glycol) (PEG) on the performance characteristics (with particular reference to signal response) of a homogeneous, latex agglutination immunoassay was investigated. The test analyte was human serum C-reactive protein (CRP), and the antibody reagent consisted of a sheep polyclonal anti-CRP IgG fraction covalently coupled to 50-nm-sized latex including a glycine-capped chloromethylstyrene shell. The amount and rate of immunoagglutination was monitored turbidimetrically after sample addition. It was found that 2.5 mmol/L concentrations of the small cationic surfactant tetramethylammonium hydroxide (TMH), when present alone, substantially increased both reaction rates and sensitivity in the lower clinical ranges of CRP concentration when compared to normally used assay conditions containing PEG and the anionic detergent Gafac. The nonspecific binding (NSB) was also found to be unchanged. Evidence is presented that the TMH enhances the actual antibody-antigen interaction as opposed to the known effects of other surfactants in immunocomplex dissociation or in maintenance of colloidal stability. We suggest that the enhancement seen with TMH could be an alternative to PEG and may provide a new means of further extending detection limits. The utility of this type of immunoassay technology could therefore be increased whenever clinically required.

Effects of the ionic environment, charge, and particle surface chemistry for enhancing a latex homogeneous immunoassay of C-reactive protein.

The role of the solution environment for a light-scattering, latex-particle-enhanced, homogeneous immunoassay of C-reactive protein (CRP) has been investigated in order to assess and optimize the immunoagglutination response. Latex particles of 50-170-nm sizes were covalently coupled with an IgG polyclonal antibody and subjected to an extensive optimization regime. This consisted of conditions responsible, in different degrees, for the principal attractive/repulsive forces affecting both colloidal stability and the antibody/antigen interaction: particle size, antibody concentration, ionic strength and species, pH, and amino acid chemistry of the particle surface. Careful control of these parameters was found to be necessary to achieve the desired effects of balancing high colloidal stability in the absence of antigen but promoting a rapid, sensitive, and dose-dependent agglutination with pathological serum samples. In addition, the estimation of fundamental properties governing intermolecular interaction (i.e. the "Hamaker" constant and critical coagulation concentration) was attempted to order to investigate a simple, practical means of defining a colloidal/immunoassay system under "real conditions" as well as "real time". It is concluded that because each antibody system is unique, a similar optimization should be performed in diagnostic immunoassays of this type to maximize their clinical utility.