Uptake and biodistribution of 99mtechnetium methylene-[32P] diphosphonate during endosteal healing around titanium, stainless steel and hydroxyapatite implants in rat tibial bone

In Vitro Evaluation of 188Re-HEDP: A Mechanistic View of Bone Pain Palliations

Skeletal metastasis is common in advanced stages of various cancers, particularly of the prostate and breast carcinoma. ¹⁸⁸Re-HEDP (1-hydroxyethane 1, 1-diphosphonic acid) is a clinically established radiopharmaceutical for bone pain palliation of osseous metastasis, and it takes advantage of high bone affinity. The present work aims at elucidating the possible mechanisms of cell killing by ¹⁸⁸Re-HEDP in osteosarcoma cells and biodistribution studies in mice.¹⁸⁸Re-HEDP complex was prepared by using lyophilized HEDP kits prepared in-house. In vitro cellular uptake in mineralized bone matrix was found to be 13.41% ± 0.46% (at 2 hours), which was reduced to 2.44% ± 0.12% in the presence of excess amounts of unlabeled HEDP ligand. Uptake of ¹⁸⁸Re-HEDP in bones of normal Swiss mice in vivo and mineralized bone in vitro indicated its affinity toward the bone matrix. The study also revealed that cellular toxicity and G2/M cell cycle arrest were dose dependent. At higher doses, G2/M cell cycle arrest was observed, which might be the major cause of cell death and a possible mechanism of bone pain relief.

(99m)TC-Methylene diphosphonate uptake at injury site correlates with osteoblast differentiation and mineralization during bone healing in mice

^99mTc-Methylene diphosphonate (^99mTc-MDP) is widely used in clinical settings to detect bone abnormalities. However, the mechanism of ^99mTc-MDP uptake in bone is not well elucidated. In this study, we utilized a mouse tibia injury model, single-photon emission computed tomography (gamma scintigraphy or SPECT), ex vivo micro-computed tomography, and histology to monitor ^99mTc-MDP uptake in injury sites during skeletal healing. In an ex vivo culture system, calvarial cells were differentiated into osteoblasts with osteogenic medium, pulsed with ^99mTc-MDP at different time points, and quantitated for ^99mTc-MDP uptake with a gamma counter. We demonstrated that ^99mTc-MDP uptake in the injury sites corresponded to osteoblast generation in those sites throughout the healing process. The ^99mTc-MDP uptake within the injury sites peaked on day 7 post-injury, while the injury sites were occupied by mature osteoblasts also starting from day 7. ^99mTc-MDP uptake started to decrease 14 days post-surgery, when we observed the highest level of bony tissue in the injury sites. We also found that ^99mTc-MDP uptake was associated with osteoblast maturation and mineralization in vitro. This study provides direct and biological evidence for ^99mTc-MDP uptake in osteoblasts during bone healing in vivo and in vitro.

Proceedings from the scientific symposium: Sex differences in cardiovascular disease and implications for therapies

A consortium of investigator-thought leaders was convened at the Heart Institute at Cedars-Sinai Medical Center and produced the following summary points: POINT 1: Important sex differences exist in cardiovascular disease (CVD) that affect disease initiation, diagnosis, and treatment.

IMPLICATION

Research that acknowledges these differences is needed to optimize outcomes in women and men. POINT 2: Atherosclerosis is qualitatively and quantitatively different in women and men; women demonstrate more plaque erosion and more diffuse plaque with less focal artery lumen intrusion.

IMPLICATION

Evaluation of CVD strategies that include devices should be used to explore differing anatomical shapes and surfaces as well as differing drug coating and eluting strategies. POINT 3: Bone marrow progenitor cells (PCs) engraft differently based on the sex of the donor cell and the sex of the recipient.

IMPLICATION

PC therapeutic studies need to consider the sex of cells of the source and the recipient. POINT 4: Women have a greater risk of venous but not arterial thrombosis compared with men, as well as more bleeding complications related to anticoagulant treatment. Several genes coding for proteins involved in hemostasis are regulated by sex hormones.

IMPLICATIONS

Research should be aimed at evaluation of sex-based differences in response to anticoagulation based on genotype. POINT 5: Women and men can have differences in pharmacological response.

IMPLICATION

Sex-specific pharmacogenomic studies should be included in pharmacological development. POINT 6: CVD progression results from an imbalance of cell injury and repair in part due to insufficient PC repair, which is affected by sex differences, where females have higher circulating levels of PCs with greater rates of tissue repair.

IMPLICATION

CVD regenerative strategies should be directed at learning to deliver cells that shift the recipient balance from injury toward repair. CVD repair strategies should ideally be tested first in females to have the best chance of success for proof-of-concept.

Binding studies of [18F]-fluoride and polyphosphonates radiolabelled with [99mTc], [111In], [153Sm] and [188Re] on bone compartments: verification of the pre vivo model?

INTRODUCTION

Although the first polyphosphonates (PP) were introduced to nuclear medicine as bone imagers in the early 70s, mechanisms involved in uptake still remain speculative. Controversies range from adsorption onto the mineral phase with disputed binding to the organic phase, over incorporation into the mineralisation process to a combination of both mechanisms. Other factors such as solubility of the complex, concentration of ligand or effects of the radionuclide have also been discussed as possible parameters influencing bone uptake. Therefore, the present work aimed to verify the recently presented pre vivo model which was developed to rate the influence of various factors on the binding of differently radiolabelled PP and [18F]-fluoride on synthetic bone matrix.

METHODS

Radiolabelled polyphosphonates and [18F]-fluoride were added to a vial containing lyophilised and milled spongiosa (Sp) or cortical bone (Co) in Hank's Balanced Salt Solution. After incubation, the radioactivity was measured in the gamma-counter before and after filtration. The percentage of irreversibly bound radioactivity was calculated. Same experiments were performed after decalcification of Sp and Co with hydrochloric acid.

RESULTS

Descriptively, [111In] increases the uptake of EDTMP in each case compared to similarly prepared [(99m)Tc]-analogues: [111In]-EDTMP > [(99m)Tc]-EDTMP, [111In]-/In-EDTMP > [(99m)Tc]-/In-EDTMP and [111In]-/Re-EDTMP > [(99m)Tc]-/Re-EDTMP. [188Re]-EDTMP shows higher binding than the carrier-added analogue, contradicting recent in vivo findings of [(188)Re]-PP. However, our findings on human matrix are consistent with those of a previous study using artificial bone material. Binding on decalcified tissue was very low (PP) to moderate ([18F]-fluoride) and reversible. Remarkable is also the unrivalled high uptake of [18F]-fluoride, showing no reduced uptake on Co and Sp as compared to hydroxyapatite (HA) and amorphous calcium phosphate (ACP).

CONCLUSION

The binding of the evaluated bone seekers on these human bone matrices follows a comparable pattern as on artificial bone. The present study substantiates the fact that binding predominantly occurs on the inorganic compartment of bone. The best correlation was found between HA and Co. Therefore, HA can serve as a matrix for representative binding studies.

Varying Ti-6Al-4V surface roughness induces different early morphologic and molecular responses in MG63 osteoblast-like cells

Osteoblast response to Ti implants depends not only on the chemistry of the implant but also on the physical properties of the implant surface, such as microtopography and roughness. This study was undertaken to examine early changes in cell morphology and gene expression during the early phase of osteoblast interaction with titanium alloy (Ti-6Al-4V) surfaces of two different roughnesses. MG63 osteoblast-like cells were cultured for 2, 6, 24, and 72 h on smooth (Ra=0.18+/-0.03 microm) and rough (Ra=2.95+/-0.23 microm) Ti-6Al-4V surfaces. Changes in cell proliferation were assessed by measuring cell number after 72 h in culture. Morphological characteristics were observed by scanning electron microscopy after 2, 6, and 24 h of culture. Changes in gene expression for extracellular signal-regulated kinase 2 (Erk2), type I collagen (alpha2[I] collagen), phospholipase C-gamma2 (Plc-gamma2), and beta-actin were measured by RT-PCR after 6 and 24 h in culture. Cell number was significantly higher on the smooth surface. In scanning electron micrographs, cells on smooth Ti-6Al-4V were spherical and raised up from the surface after 2 h in culture. In contrast, cells on the rough surface adopted an irregular, elongated shape that spanned across pits in the surface. At 24 h, cells on the smooth surface had flattened, become elongate, and covered the surface. In contrast, cells on the rough surface appeared more differentiated in shape and the margins of the cells were irregular, with many processes extending out, following the contour of the surface. Of the genes examined, only Erk2 and beta-actin showed a change in expression with surface roughness. Both genes were upregulated (p<0.05) on the rough surface at 6 h. These results indicate that Ti-6Al-4V surface roughness affects osteoblast proliferation, morphology, and gene expression, and that these effects can be measured after periods as short as 2-6 h.

Binding studies of [(18)F]-fluoride and polyphosphonates radiolabelled with [(111)In], [(99m)Tc], [(153)Sm], and [(188)Re] on bone compartments: a new model for the pre vivo evaluation of bone seekers?

INTRODUCTION

Although the first polyphosphonates were already introduced in the early 1970s, mechanisms involved in uptake still remain speculative. The present work aimed to establish a new method to rate the influence of various factors on the uptake and to evaluate new bone-seekers on these bone compartments.

METHODS

Radioactive-labelled diphosphonates and [(18)F]-fluoride were added to a vial containing hydroxyapatite (HA), collagen, or amorphous calcium phosphate (ACP) in 3 ml of Hanks' Balanced Salt Solution (HBSS). After incubation, these suspensions were filtered, the radioactivity was measured in the gamma-counter, and the percentage of irreversibly bound radioactivity was calculated.

RESULTS

Kinetic experiments revealed uptake increase over time for [(99m)Tc]-MDP and [(18)F]-fluoride on various amounts of matrix. After 120 min, static studies on HA yielded: [(99m)Tc]-EDTMP < [(188)Re]-/Re-EDTMP < [(99m)Tc]-/11 microl Re-EDTMP < [(99m)Tc]-/In-EDTMP < [(99m)Tc]-/15 microl Re-EDTMP < nca [(188)Re]-EDTMP < [(111)In]-/Re-EDTMP < [(111)In]-EDTMP < [(111)In]-/In-EDTMP < [(99m)Tc]-DPD < [(99m)Tc]-/80 microl Re-EDTMP < [(99m)Tc]-EDTMP "boiled" < [(99m)Tc]-/150 microl Re-EDTMP < [(153)Sm]-EDTMP < [(99m)Tc]-/11 microl Re-EDTMP "boiled" < [(18)F]-ions < [(99m)Tc]-MDP. Collagen showed very low uptake. Reincubation experiments suggest that bone tracers are irreversibly bound.

CONCLUSION

The presented method is rapid and feasible to examine the adsorption of radioactive-labelled substances on bone components. Correlations between our findings and published in vivo data support the application as a simple model.

Primary mineralization at the surfaces of implants

Osteogenesis around implants is affected by the physical and chemical characteristics of the biomaterials used. The osteoprogenitor cells must migrate to the implant site and synthesize and secrete a mineralizable extracellular matrix. Because this is neo-bone formation, the mechanism by which the cells calcify their matrix involves extracellular organelles called matrix vesicles in a process termed "primary mineralization". Two different methods for assessing the effects of implant materials on primary mineralization are presented in this report. In the first approach, different implant materials used in dentistry and orthopedic surgery were placed in rat tibial bones after marrow ablation. Two groups of implants were used, bone-bonding and non-bonding materials. We examined the effects of the materials on calcification morphometrically by quantitating changes in matrix vesicle morphology and distribution in endosteal tissue around implants as compared with normal endosteal bone healing. In addition, matrix vesicles were isolated from the endosteal tissue around the implant as well as from the contralateral limb and were examined biochemically. The results demonstrated that bone-bonding materials induced a greater increase in matrix vesicle enzyme activity than did non-bonding materials. However, all materials caused changes in matrix vesicles that were different from those seen in normal endosteal bone formation following injury. The effects of implant materials on biochemical markers of mineralization, including specific activities of matrix vesicle alkaline phosphatase and phospholipase A2 and phosphatidylserine content, demonstrated a high correlation with the morphometric observations with regard to enhancement and/or delay of primary mineralization. In the other approach, we used a radioisotopic method to evaluate the effects of implant materials on primary mineralization. This analysis revealed that implants alter bone healing, as shown by the differential uptake of 99mTc and 32P in different bone compartments. Decreased 32P uptake by the organic phase in the presence of bone-bonding implants suggests that cleavage of 99mTcMD32P into its technetium and methylene diphosphonate moieties was inhibited by the presence of the implants. In summary, these approaches to evaluating the effects of materials on primary mineralization demonstrate that the marrow ablation model can easily distinguish between bone-bonding and non-bonding materials. The use of this model can be valuable in the development of new materials.

Implant surface characteristics modulate differentiation behavior of cells in the osteoblastic lineage

This paper reviews the role of surface roughness in the osteogenic response to implant materials. Cells in the osteoblast lineage respond to roughness in cell-maturation-specific ways, exhibiting surface-dependent morphologies and growth characteristics. MG63 cells, a human osteoblast-like osteosarcoma cell line, respond to increasing surface roughness with decreased proliferation and increased osteoblastic differentiation. Alkaline phosphatase activity and osteocalcin production are increased. Local factor production is also affected; production of both TGF-beta 1 and PGE2 is increased. On rougher surfaces, MG63 cells exhibit enhanced responsiveness to 1,25-(OH)2D3. Prostaglandins mediate the effects of surface roughness, since indomethacin prevents the increased expression of differentiation markers in these cells.