Investigation of localized delivery of diclofenac sodium from poly(D,L-lactic acid-co-glycolic acid)/poly(ethylene glycol) scaffolds using an in vitro osteoblast inflammation model

Nonunion fractures and large bone defects are significant targets for osteochondral tissue engineering strategies. A major hurdle in the use of these therapies is the foreign body response of the host. Herein, we report the development of a bone tissue engineering scaffold with the ability to release anti-inflammatory drugs, in the hope of evading this response. Porous, sintered scaffolds composed of poly(D,L-lactic acid-co-glycolic acid) (PLGA) and poly(ethylene glycol) (PEG) were prepared with and without the anti-inflammatory drug diclofenac sodium. Analysis of drug release over time demonstrated a profile suitable for the treatment of acute inflammation with ∼80% of drug released over the first 4 days and a subsequent release of around 0.2% per day. Effect of drug release was monitored using an in vitro osteoblast inflammation model, comprised of mouse primary calvarial osteoblasts stimulated with proinflammatory cytokines interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), and interferon-γ (IFN-γ). Levels of inflammation were monitored by cell viability and cellular production of nitric oxide (NO) and prostaglandin E2 (PGE2). The osteoblast inflammation model revealed that proinflammatory cytokine addition to the medium reduced cell viability to 33%, but the release of diclofenac sodium from scaffolds inhibited this effect with a final cell viability of ∼70%. However, releasing diclofenac sodium at high concentrations had a toxic effect on the cells. Proinflammatory cytokine addition led to increased NO and PGE2 production; diclofenac-sodium-releasing scaffolds inhibited NO release by ∼64% and PGE2 production by ∼52%, when the scaffold was loaded with the optimal concentration of drug. These observations demonstrate the potential use of PLGA/PEG scaffolds for localized delivery of anti-inflammatory drugs in bone tissue engineering applications.

Early gene regulation of osteogenesis in embryonic stem cells

The early gene regulatory networks (GRNs) that mediate stem cell differentiation are complex, and the underlying regulatory associations can be difficult to map accurately. In this study, the expression profiles of the genes Dlx5, Msx2 and Runx2 in mouse embryonic stem cells were monitored over a 48 hour period after exposure to the growth factors BMP2 and TGFβ1. Candidate GRNs of early osteogenesis were constructed based on published experimental findings and simulation results of Boolean and ordinary differential equation models were compared with our experimental data in order to test the validity of these models. Three gene regulatory networks were found to be consistent with the data, one of these networks exhibited sustained oscillation, a behaviour which is consistent with the general view of embryonic stem cell plasticity. The work cycle presented in this paper illustrates how mathematical modelling can be used to elucidate from gene expression profiles GRNs that are consistent with experimental data.

Engineering an in-vitro model of rodent cartilage

OBJECTIVES

The purpose of this study was to identify a cell source, scaffold substrate and culture environment suitable for use in engineering an in-vitro model of rodent cartilage.

METHODS

The chondrogenic activity and stability of cells isolated at Day 18 of gestation was assessed under normoxia and hypoxia using a cytokine stimulation assay and gene expression analysis. The ability of the selected cells seeded in fibrous electrospun scaffolds to form cartilaginous tissue during longterm static and dynamic culture was assessed using immunocytochemistry and biochemical analysis.

KEY FINDINGS

Rodent fetal chondrocytes appear to have enhanced phenotypic stability compared with other cell sources. Following 16 weeks under static culture, the engineered constructs were found to have greater cellularity and collagen content that native rodent cartilage.

CONCLUSIONS

A cell source, scaffold and culture environment have been identified that support the generation of in-vitro rodent cartilage. In future work, cytokine treatment of the engineered tissues will take place to generate in-vitro osteoarthritis models.

Accelerated formation of multicellular 3-D structures by cell-to-cell cross-linking

The three-dimensional (3-D) arrangement of cells within tissues is integral to their development and function. Advances in stem cell science and regenerative medicine have stimulated interest in the replication of this architecture in vitro. We have developed a versatile method for controlling short-term cell-cell and cell-matrix interactions via a facile cell surface engineering process that enables the rapid formation of specific 3-D interactions for a range of cell types. We demonstrate that chemical modification of cell surfaces and matrix proteins can artificially accelerate the cell adhesion process and confirm the ability to control the formation of multicellular aggregates with defined architectures and heterotypic cell types. Direct comparison with a natural aggregation process seen during differentiation of embryonic stem (ES) cells revealed increased expression of developmental regulatory proteins and a concomitant enhancement of ES cell differentiation. Furthermore, this new methodology has numerous applications in generating layered structures. For example, we demonstrate improved transfer of therapeutic human keratinocytes onto a dermal layer in a skin repair model.

Characterization of human fetal osteoblasts by microarray analysis following stimulation with 58S bioactive gel-glass ionic dissolution products

Bioactive glasses dissolve upon immersion in culture medium, releasing their constitutive ions in solution. There is evidence suggesting that these ionic dissolution products influence osteoblast-specific processes. Here, we investigated the effect of 58S sol-gel-derived bioactive glass (60 mol % SiO2, 36 mol % CaO, 4 mol % P2O5) dissolution products on primary osteoblasts derived from human fetal long bone explant cultures (hFOBs). We used U133A human genome GeneChip oligonucleotide arrays to examine 22,283 transcripts and variants, which represent over 18,000 well-substantiated human genes. Hybridization of samples (biotinylated cRNA) derived from monolayer cultures of hFOBs on the arrays revealed that 10,571 transcripts were expressed by these cells, with high confidence. These included transcripts representing osteoblast-related genes coding for growth factors and their associated molecules or receptors, protein components of the extracellular matrix (ECM), enzymes involved in degradation of the ECM, transcription factors, and other important osteoblast-associated markers. A 24-h treatment with a single dosage of ionic products of sol-gel 58S dissolution induced the differential expression of a number of genes, including IL-6 signal transducer/gp130, ISGF-3/STAT1, HIF-1 responsive RTP801, ERK1 p44 MAPK (MAPK3), MAPKAPK2, IGF-I and IGFBP-5. The over 2-fold up-regulation of gp130 and MAPK3 and down-regulation of IGF-I were confirmed by real-time RT-PCR analysis. These data suggest that 58S ionic dissolution products possibly mediate the bioactive effect of 58S through components of the IGF system and MAPK signaling pathways.

Dose- and time-dependent effect of bioactive gel-glass ionic-dissolution products on human fetal osteoblast-specific gene expression

Bioactive glasses dissolve upon immersion in culture medium, and release their constitutive ions into solution. There has been some evidence suggesting that these ionic-dissolution products influence osteoblast-specific processes. Here, the effect of 58S sol-gel-derived bioactive glass (60% SiO(2), 36% CaO, 4% P(2)O(5), in molar percentage) on primary osteoblasts derived from human fetal long bone explant cultures is investigated, and it is hypothesized that critical concentrations of sol-gel-dissolution products (consisting of a combination of simple inorganic ions) can enhance osteoblast phenotype in vitro by affecting the expression of a number of genes associated with the differentiation and extracellular matrix deposition processes. Cells were exposed to a range of 58S dosages continuously for a period of 4-14 days in monolayer cultures. Quantitative real-time RT-PCR analysis of a panel of osteoblast-specific markers showed a varied gene expression pattern in response to the material. The highest concentration of Ca and Si tested (96 and 50 ppm, respectively) promoted upregulation of gene expression for most markers (including alkaline phosphatase, osteocalcin, and osteopontin) at the latest time point, compared to non-58S-treated control, although this observation was not statistically significant. The same 58S concentration produced higher ALP activity levels and increased proliferation throughout the culture period, compared to lower dosages tested; however, the results generated were again not statistically significant. The data overall suggest that no significant effect can be ascribed to the ionic products of 58S bioactive gel-glass dissolution tested here and their ability to stimulate osteoblastic marker gene expression.

Novel Surface Entrapment Process for the Incorporation of Bioactive Molecules within Preformed Alginate Fibers

A physical entrapment technique has been developed for the surface engineering of preformed alginate fibers. Surface engineering was carried out at room temperature in aqueous solutions without additional solvent, a catalyst/initiator, a chemical cross-linking agent, or a temperature increase. Entrapment of surface-modifying molecules was achieved by exposing the alginate fibers to a Na(+)-rich NaCl/CaCl2 mixture solution, which caused the formation of a moderate dissociation layer into which the modifier could diffuse within a few seconds. The surface dissociation was then reversed by the addition of a large excess of multivalent cations, which resulted in collapse of the interface and immobilization of the modifying species. Rhodamine-tagged poly(ethylene glycol)s of different molecular weights were used as model molecules to investigate the effect of process parameters on the entrapment efficiency. It was found that the entrapment efficiency as well as the distribution of the modifier within the alginate fibers was determined by several factors, including the NaCl/CaCl2 ratio in the preswelling solution, exposure time, and concentration and molecular weight of the modifiers. The morphology of the fibers was not significantly changed in terms of shape and size after the entrapment process. By this technique, poly(L-lysine) (PLL) coupled with cell adhesion peptide sequence GRGDS (PLL-GRGDS) was entrapped within alginate fibers, and it was demonstrated that the modification promoted the attachment of mouse 3T3 fibroblasts.

In VitroDifferentiation andIn VivoMineralization of Osteogenic Cells Derived from Human Embryonic Stem Cells

The first report of the derivation of embryonic stem (ES) cell lines from human blastocysts had major implications for research into developmental biology and regenerative medicine. Finding efficient and reproducible methods to derive therapeutically useful cells from an ES cell source is a key feature of many regenerative medicine strategies. We have previously demonstrated that it is possible to induce osteogenic differentiation of murine ES cells by supplementing the culture medium with ascorbic acid, beta-glycerophosphate, and dexamethasone. This study investigated whether methods for driving osteogenic differentiation developed with murine ES cells could be applied successfully to human ES cells. The H1 line was propagated in vitro on murine feeder layers and shown to be pluripotent by expression of the markers Oct-4 and SSEA-4. Subsequently, differentiation was initiated via embryoid body (EB) formation and, after 5 days in suspension culture, cells harvested from EBs were replated in a medium containing osteogenic supplements. We found that the treatment regimen previously identified as optimal for murine ES cells, and in particular the addition of dexamethasone at specific time points, also induced the greatest osteogenic response from human ES cells. We identified mineralizing cells in vitro that immunostained positively for osteocalcin and found an increase in expression of an essential bone transcription factor, Runx2. When implanted into SCID mice on a poly-D, L-lactide (PDLLA) scaffold, the cells had the capacity to give rise to mineralized tissue in vivo. After 35 days of implantation, regions of mineralized tissue could be identified within the scaffold by von Kossa staining and immunoexpression of the human form of osteocalcin. We did not see any evidence of teratoma formation. These data therefore demonstrate the derivation of osteoblasts from pluripotent human ES cells with the capacity to form mineralized tissue both in vitro and in vivo. We have also shown that a culture methodology established for differentiation of murine ES cells was entirely transferable to human ES cells. Further development of this technology will result in the capacity to generate sufficient yields of osteogenic cells for use in skeletal tissue repair.

Differentiation of Osteoblasts from Murine Embryonic Stem Cells by Overexpression of the Transcriptional Factor Osterix

Osterix is a transcription factor crucial for the normal development of the osteoblast. Here we have investigated whether the osteogenic differentiation of murine embryonic stem (ES) cells can be induced by overexpression of osterix. Differentiation was initiated by formation of embryoid bodies (EB) which were then dispersed and cultured in alpha-minimum essential medium supplemented with L-ascorbate phosphate and alpha-glycerophosphate for up to 21 days. osterix was found to induce expression of several osteoblast-specific markers, as confirmed by immunostaining and real-time RT-PCR. The expression of genes encoding osteocalcin and Cbfa1 was upregulated and the formation of mineralized bone nodules was significantly increased by osterix transfection. In combination with dexamethasone, bone nodule formation was further increased in osterix-transfected cells. Expression of both Sox-9 and PPAR-gamma, genes that are associated with chondrocyte and adipocyte differentiation, was initially increased in the osterix-transfected cells but was downregulated after day 7. This suggests that the process of osterix-induced differentiation of ES cells involves transition through an intermediate bi- or tripotential progenitor cell population. In conclusion, this cell differentiation strategy is useful not only for generating osteoblastic cells from ES cells, but also for investigating factors that influence this process and potentially delineating the ontogeny of the osteoblast.

Osteogenic Differentiation of Mouse Embryonic Stem Cells: Differential Gene Expression Analysis by cDNA Microarray and Purification of Osteoblasts by Cadherin-11 Magnetically Activated Cell Sorting

We have previously shown osteogenic differentiation of mouse embryonic stem (ES) cells and temporal enrichment with osteoblastic cells, by stimulation with serum-containing culture medium supplemented with beta-glycerophosphate, ascorbate, and dexamethasone. In our present study we have used similar culture conditions to further investigate osteogenic differentiation of mouse ES cells. Using reverse transcription-polymerase chain reaction (RT-PCR) we demonstrated the expression of genes associated with osteoblast differentiation including the bone matrix protein osteocalcin and the transcription factor Cbfa-1/runx2. Furthermore, results of cDNA microarray analysis, and subsequent RT-PCR analysis of differentiating ES cells after exposure to osteogenic stimuli, revealed a combination of upregulation of genes involved in osteoblast differentiation including osteopontin, HSP-47, and IGF-II coupled with downregulation of genes involved in differentiation of other phenotypes such as the neuroectoderm factor Stra-13. Finally, we have applied magnetically activated cell-sorting methods to ES cell cultures treated with osteogenic stimuli and, using an antibody to cadherin-11, have purified a subpopulation of cells with osteoblastic characteristics.

Cigarette smoke decreases inducible nitric oxide synthase in lung epithelial cells

Cigarette smoking has been associated with decreased exhaled nitric oxide (NO). To investigate the mechanism of this decrease, the effects of a cigarette smoke extract were evaluated a murine lung epithelial cell line (LA-4), a human lung epithelial cell line (A549), and primary cultures of human lung epithelial cells induced to produce NO by cytokines. NO production was evaluated by measuring nitrite, a stable end product of NO, in cell culture supernatant fluids. Cigarette smoke extract caused a reduction in the cytokine-induced nitrite concentrations in the culture supernatant fluids from all 3 cell types (P < .01, all comparisons). To further investigate these observations, immunohistochemistry demonstrated a decrease in cytokine-induced inducible NO synthase (iNOS) protein expression and iNOS mRNA after cigarette smoke extract exposure in LA-4 cells. However, iNOS mRNA half-life was not altered by the smoke extract, suggesting that the smoke extract decreased NO by decreasing iNOS mRNA transcription. These findings demonstrate that cigarette smoke extract decreases iNOS expression and NO production from lung epithelial cells.

Stem cells: sources and applications

Tissue engineering is a multidisciplinary area of research aimed at regeneration of tissues and restoration of function of organs through implantation of cells/tissues grown outside the body, or stimulating cells to grow into implanted matrix. In this short review, some of the most recent developments in the use of stem cells for tissue repair and regeneration will be discussed. There is no doubt that stem cells derived from adult and embryonic sources hold great therapeutic potential but it is clear that there is still much research required before their use is commonplace. There is much debate over adult versus embryonic stem cells and whether both are required. It is probably too early to disregard one or other of these cell sources. With regard to embryonic stem cells, the major concern relates to the ethics of their creation and the proposed practice of therapeutic cloning.

Embryonic stem cells

The capacity of embryonic stem cells for virtually unlimited self-renewal and differentiation capacity has opened up the prospect of widespread applications in biomedical research and regenerative medicine. For the latter, the cells provide hope that it will be possible to overcome the problems of donor tissue shortage and also, by making the cells immunocompatible with the recipient, implant rejection. Four years after the first derivation of human pluripotent cell lines from pre-implantation embryos, a great deal has been learnt about their biology and how differentiation can be encouraged towards particular cell lineages. However, considerable research is needed, not least into means to enrich and purify derivative cell lineages, before clinical trials can be considered.

Pelvic nerve plexus trauma at radical and simple hysterectomy: a quantitative study of nerve types in the uterine supporting ligaments

OBJECTIVE

Using neuropeptide and enzyme markers to autonomic nerves, we sought to demonstrate and quantify the nerve types contained within the uterosacral ligaments (USLs) and cardinal ligaments (CLs) that are divided during radical hysterectomy (RH).

METHODS

Cross-sectional biopsies were collected from the lateral third of the USL and the CL in 24 women who had an RH for cervical cancer, and from the uterine insertion of these ligaments in 11 women who had a simple hysterectomy for benign disease. We applied indirect immunofluorescence with FITC-conjugated secondary antibodies, using polyclonal primary antibodies to neuropeptide markers that predominate within somatic and autonomic nerves, to show different populations of the following nerve types within the biopsies: neuropeptide Y (NPY) and tyrosine hydroxylase (TH) for sympathetic nerves; vasoactive intestinal polypeptide (VIP) for parasympathetic nerves; substance P (SP) for nociceptive and sensory-motor nerves; and calcitonin gene-related peptide (CGRP) for sensory and sensory-motor nerves. The percentage area of immunoreactivity (PAI), determined by a computer-assisted image analyzer attached to a fluorescent microscope, was used as an objective quantitative measure of nerve density. Confocal microscopy was used to determine the composition and spatial arrangement of nerve fibers in the ligaments.

RESULTS

The PAI was greater for all markers tested in both the USL and CL (P <.001) in RH compared with simple hysterectomy biopsies. For RH specimens, the PAI was greater for the sympathetic, sensory, and sensory-motor nerve markers in the USL compared with the CL (P <.01), but the PAI for VIP was similar (P >.05). Conversely, excluding the large trunks and associated ganglia, the free nerve fiber PAI in the CL was greater than that of the USL for all nerve markers (P <.001). The staining of peripheral autonomic ganglia and associated fibers, for NPY and TH, indicates that some sympathetic nerves are preganglionic with their cell bodies within the pelvic plexus.

CONCLUSIONS

Significantly more autonomic nerves are transected in the more lateral division of the uterine supporting ligaments during a radical hysterectomy than during a simple hysterectomy. Sympathetic, parasympathetic, sensory, and sensory-motor nerve types are present within the CL and USL. The proportions of each nerve type differ between the two ligaments, and sympathetic nerves in the USL are the single largest nerve type. The uterine supporting ligaments are a major pathway for autonomic nerves to the pelvic organs.