Differential phenotypic behaviors of human degenerative nucleus pulposus cells under normoxic and hypoxic conditions: influence of oxygen concentration during isolation, expansion, and cultivation

BACKGROUND CONTEXT

Intervertebral discs (IVDs) are the largest avascular structures in the body; therefore, cells within these discs might be adapted to low-oxygen conditions. Although it has been demonstrated that a low oxygen concentration could promote synthesis of the extracellular matrix by IVD cells in the in vitro culture, isolation, expansion, and cultivation of IVD cells under classical tissue culture O2 saturation could still be detrimental.

PURPOSE

To investigate the phenotypic differences between human degenerative nucleus pulposus (NP) cells during isolation and expansion under normoxic (Nx: 21% O2) or hypoxic (Hx: 3.5% O2) conditions.

STUDY DESIGN

We investigated in vitro isolation, expansion, and cultivation of human NP cells.

METHODS

Human NP tissue samples were obtained from patients who underwent lumbar disc surgeries. Nucleus pulposus cells were then isolated, expanded, and cultivated under normoxic or hypoxic conditions. To determine whether the effects of normoxic expansion are reversible, another group of cells was isolated and expanded in normoxic conditions and then cultivated under hypoxic conditions (Nx→Hx group). Cellular proliferation, RNA expression of selected genes, and immunohistochemical staining were performed to evaluate the phenotypic behaviors of human NP cells under different conditions.

RESULTS

Expressions of Type II collagen and aggrecan in the Nx→Hx group were significantly higher than those in the normoxic group but were significantly lower than those in the hypoxic group. The normoxic group showed higher expression of matrix metalloproteinase (MMP)-2 and MMP-13 than did the other groups. Expression levels of hypoxia-inducible factors (HIFs) were significantly higher in the normoxic groups; however, a greater degree of HIF-1α staining was found in the hypoxic group, whereas a greater degree of HIF-2α staining was found in the normoxic group.

CONCLUSIONS

Human degenerative NP cells isolated, expanded, and cultivated in hypoxic conditions could better preserve the cells' regenerative potential. Compromised properties that were observed during isolation and expansion under normoxic conditions could only be partially rescued by later hypoxic cultivation. The superior phenotypic behaviors of human NP cells under hypoxia may be related to higher HIF-1α production and lower HIF-2α production. Cells that are isolated, expanded, and cultivated under hypoxic conditions may show better regenerative results when transplanted; therefore, the isolation and expansion processes of human degenerative NP cells should be managed in a hypoxic environment.

The mechanics of hyaluronic acid/adipic acid dihydrazide hydrogel: towards developing a vessel for delivery of preadipocytes to native tissues

Promising treatment approaches in repairing tissue defects include implementation of regenerative medicine strategies, particularly delivery of preadipocytes to sites where adipose tissue damage needs to be repaired or where fat needs to be generated. In this study, we suggest that the injectable hyaluronic acid/adipic acid dihydrazide (HA/ADH) hydrogel may be an adipose-tissue-like material in terms of biological compatibility as well as mechanical behavior. First, we show that the hydrogel enables and supports growth, proliferation and differentiation of 3T3-L1 preadipocytes. Second, given that adipose tissue is a weight-bearing biological structure, we investigate the large deformation mechanical behavior of the hydrogel with and without embedded preadipocytes, by performing confined and unconfined compression tests and then calibrating a strain energy density (SED) function to the results. Four test groups were examined: (1) Hydrogel specimens right after the preparation without cells, (2) and (3) 3-days-cultured hydrogel specimens with and without cells, respectively, and (4) 6-days-cultured hydrogel specimens with cells. A one-term Ogden SED was found to adequately describe the hyperelastic behavior of the hydrogel specimens in all experimental groups. Importantly, we found that the mechanical properties of the hydrogel, when subjected to compression, are in good agreement with those of native adipose tissue, with the better fit occurring 3-6 days after preparation of the hydrogel. Third, computational finite element studies of the mechanical (stress-strain) behavior of the HA/ADH hydrogel when containing mature adipocytes indicated that the stiffnesses of the constructs were mildly affected by the presence of the adipocytes. Hence, we conclude that injectable HA/ADH hydrogel may serve as a vessel for protecting preadipocytes during, and at a short-term after delivery to native tissues, e.g. in research towards regenerative medicine in tissue reconstructions.

In situ forming hydrogels composed of oxidized high molecular weight hyaluronic acid and gelatin for nucleus pulposus regeneration

Encapsulation of nucleus pulposus (NP) cells within in situ forming hydrogels is a novel biological treatment for early stage intervertebral disc degeneration. The procedure aims to prolong the life of the degenerating discs and to regenerate damaged tissue. In this study we developed an injectable oxidized hyaluronic acid-gelatin-adipic acid dihydrazide (oxi-HAG-ADH) hydrogel. High molecular weight (1900 kDa) hyaluronic acid was crosslinked with various concentrations of gelatin to synthesize the hydrogels and their viscoelastic properties were analyzed. Interactions between the hydrogels, NP cells, and the extracellular matrix (ECM) were also evaluated, as were the effects of the hydrogels on NP cell gene expression. The hydrogels possess several clinical advantages, including sterilizability, low viscosity for injection, and ease of use. The viscoelastic properties of the hydrogels were similar to native tissue, as reflected in the complex shear modulus (∼11-14 kPa for hydrogels, 11.3 kPa for native NP). Cultured NP cells not only attached to the hydrogels but also survived, proliferated, and maintained their round morphology. Importantly, we found that hydrogels increased NP cell expression of several crucial ECM-related genes, such as COL2A1, AGN, SOX-9, and HIF-1A.

The natural medications for wound healing - Curcumin, Aloe-Vera and Ginger - do not induce a significant effect on the migration kinematics of cultured fibroblasts

Curcumin, Aloe-vera and Ginger are popular natural medications (NMs) for treating wounds, however, the mechanisms by which these NMs apparently accelerate wound healing remain largely unknown. From a biomechanical perspective, it is specifically unclear whether fibroblast motility improves in the presence of any of these NMs. Here we use our recently developed quantitative high-precision automated assay for cell migration (Topman et al., 2012b) which is based on image processing of time lapse micrographs to determine whether kinematic parameters e.g. the maximum and average migration rates of en mass fibroblast colonies are influenced by treating the cells with the above NMs. We found no evidence that Curcumin, Aloe-vera and Ginger directly influence the en mass fibroblast migration kinematics in vitro post infliction of localized mechanical damage to the cultures. However, due to the complexity of a wound healing process in vivo, these NMs may still influence the healing through other pathways.

Synthesis of partial stabilized cement-gypsum as new dental retrograde filling material

The study describes the sol-gel synthesis of a new dental retrograde filling material partial stabilized cement (PSC)-gypsum by adding different weight percentage of gypsum (25% PSC+75% gypsum, 50% PSC+50% gypsum and 75% PSC+25% gypsum) to the PSC. The crystalline phase and hydration products of PSC-gypsum were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis. The handling properties such as setting time, viscosity, tensile strength, porosity and pH, were also studied. The XRD and microstructure analysis demonstrated the formation of hydroxyapatite and removal of calcium dihydrate during its immersion in simulated body fluid (SBF) on day 10 for 75% PSC+25% gypsum. The developed PSC-gypsum not only improved the setting time but also greatly reduced the viscosity, which is very essential for endodontic surgery. The cytotoxic and cell proliferation studies indicated that the synthesized material is highly biocompatible. The increased alkaline pH of the PSC-gypsum also had a remarkable antibacterial activity.

New reconstructive technologies after decompressive craniectomy in traumatic brain injury: the role of three-dimensional titanium mesh

Functional and aesthetic reconstruction after wide decompressive craniectomy directly correlates with subsequent quality of life. Advancements in the development of biomaterials have now made three-dimensional (3-D) titanium mesh a new option for the repair of skull defects after craniectomy. The purpose of this study was to review aesthetic and surgical outcomes and complications of patients who had skull defects repaired with 3-D titanium mesh. The records of 40 adult patients (31 unilateral craniectomies and 9 bilateral craniectomies) who underwent a computer-assisted designed titanium mesh implant at a university hospital from January 2008 to January 2010 were retrospectively reviewed. Aesthetic outcomes, cranial nerve V and VII function, and complications (hardware extrusions, meningitis, osteomyelitis, brain abscess, and pneumocephalus) were evaluated. The craniofacial symmetry, implant stability, and functional outcomes were excellent for all patients. No patients had trigeminal or facial dysfunction. All had excellent cosmetic results as measured by post-reduction radiographs and personal and family perceptions of the forehead contour. Two patients had delayed wound healing and subsequent subclinical wound infections, which resolved after treatment with antibiotics for 2 weeks. Craniofacial skeletal reconstruction with 3-D titanium mesh results in excellent forehead contour and cosmesis, and subsequently a better quality of life with few complications. Titanium mesh reconstruction offers a favorable alternative to other graft materials in the repair of large skull defects.

In vitro feasibility study of the use of a magnetic electrospun chitosan nanofiber composite for hyperthermia treatment of tumor cells

Hyperthermia has been reported to be an effective cancer treatment modality, as tumor cells are more temperature-sensitive than their normal counterparts. Since the ambient temperature can be increased by placing magnetic nanoparticles in an alternating magnetic field it has become of interest to incorporate these magnetic nanoparticles into biodegradable nanofibers for possible endoscopic hyperthermia treatment of malignant tumors. In this preliminary investigation we have explored various characteristics of biodegradable electrospun chitosan nanofibers containing magnetic nanoparticles prepared by different methods. These methods included: (1) E-CHS-Fe(3)O(4), with electrospun chitosan nanofibers directly immersed in a magnetic nanoparticle solution; (2) E-CHS-Fe(2+), with the electrospun chitosan nanofibers initially immersed in Fe(+2)/Fe(+3) solution, followed by chemical co-precipitation of the magnetic nanoparticles. The morphology and crystalline phase of the magnetic electrospun nanofiber matrices were determined by scanning electron microscopy, transmission electron microscopy, selected area electron diffraction, and X-ray diffraction spectroscopy. The magnetic characteristics were measured using a superconducting quantum interference device. The heating properties of these magnetic electrospun nanofiber matrices in an alternating magnetic field were investigated at a frequency of 750 kHz and magnetic intensity of 6.4 kW. In vitro cell incubation experiments indicated that these magnetic electrospun nanofiber matrices are non-cytotoxic and can effectively reduce tumor cell proliferation upon application of a magnetic field.

GLYCOSAMINOGLYCAN SYNTHESIS OF CHONDROCYTES IN FIBRIN GLUE WITH GHC6S PARTICLES

Articular cartilage provides functions of lubrication to shear stress and protection from compressive force, but it has poor ability to repair itself after suffering damage. The advanced method of tissue engineering is developed and used to maintain cell functions for tissue regeneration. In order to improve the ECM synthesis for the regeneration, many materials have been examined on chondrocytes or other cell sources. In this study, fibrinogen was concentrated from plasma cryoprecipitation and then polymerized by thrombin into fibrin. Gelatin/hyaluronic acid/chondroitin-6-sulfate (GHC6S) was prepared by the cross-linking reaction with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and ground in liquid nitrogen to particles. The GHC6S particles were mixed with fibrin glue as the tissue engineering scaffold. Porcine articular cartilage chondrocytes were expanded and seeded into the scaffolds. The engineered constructs were cultured and harvested after cultured for 1 and 2 weeks. Morphology of GHC6S particle was examined by scanning electron microscopy (SEM). Total glycosaminoglycans (GAGs) and sulfated GAGs were quantified by p-dimethylaminobenzaldehyde reaction and 1,9-dimethymethylene blue (DMMB) assay, respectively. The results demonstrated that the total GAGs, especially the content of nonsulfated GAGs, hyaluronic acid, were increased with time in chondrocytes growing in fibrin glue with GHC6S particles. It suggested that the GHC6S in fibrin glue chondrocyte kept the GAGs synthesis, which could help resist the compressive force. Therefore, the GHC6S particles mixed within fibrin glue can be used as a promising scaffold for articular tissue engineering.

PREPARATION OF GELATIN NANOPARTICLES WITH EGFR SELECTION ABILITY VIA BIOTINYLATED-EGF CONJUGATION FOR LUNG CANCER TARGETING

Lung cancer is the most malignant cancer today, and specific drug delivery has been developed for superior outcome. In this study, gelatin nanoparticles (GPs) were firstly employed as native carriers. Second, NeutrAvidinFITC was then grafted on the particle surface (GP-Av); finally much more amount of biotinylated EGF were able to be conjugated with NeutrAvidinFITC forming ligand- binding nanoparticles (GP-Av-bEGF) to enhance the targeting efficiency. These nanoparticles were applied as EGFR-seeking agents to detect lung cancer cells.

Results of particle characterization show that the modification process had no influence on size (230 nm). Round and smooth nanoparticles were observed by AFM. The surface property of nanoparticles was characterized by surface plasmon resonance (SPR) and flowcytometry analysis as well as by examining the interaction of the modified EGF on particle surface with the ability to recognize EGFR.

The binding ability of GPs with or without EGF modification is different. SPR assay showed that EGF-conjugated particles (GP-Av-bEGF) have stronger and faster bonding signal than the unmodified one (GP-Av). Free EGF competition results from SPR and A549 cell (lung adenocarcinoma cells) culture also confirmed the EGF receptormediated endocytosis mechanism for nanoparticles with EGF-modified binding. The in vitro targeting ability was confirmed by the uptake rate of different cells via flow cytometry assay. GP-Av-bEGF resulted in higher entrance efficiency on A549 than on normal lung cells (HFL1) and U2-OS (osteosarcoma cells) due to A549 possessing more amounts of EGFR. The targeting ability of GP-Av-bEGF nanoparticles with specific EGFR tracing ability was proved, which holds promise for further anticancer drug applications.

SURFACE CHARACTERIZATION AND HEMOCOMPATIBILITY OF HEPARINIZED 316L STAINLESS STEEL

Poor compatibility between blood and metallic coronary artery stents is one reason for arterial restenosis. Immobilization of heparin on stent's surface is feasible for improving compatibility. We examined possible surface-coupling agents for anticoagulant agent immobilization. Hexamethylene diisocyanate (HMDI) was examined as surface-coupling agent to activate 316L stainless steel (e.g. stent material). Afterwards, we grafted PEG on the HMDI activated surface to provide heparin with higher conformational freedom and a more hydrophilic environment. The effectiveness of HMDI activated and PEG grafted surface was confirmed by FTIR, XPS, and water contact angle test. Heparin was then immobilized onto the activated 316L stainless steel. The heparin surface density was 9.5 μg/cm2. Sessile drop water contact angles showed that the heparingrafted surface is even more hydrophilic than the PEG grafted one. The function of grafted heparin was evaluated by antithrombrin III (ATIII) adsorption testing and SEM. The surface with heparin grafting shows better ATIII binding ability and hemocompatibility than the native one.

EVALUATION OF MAGNETIC-HYDROXYAPATITE NANOPARTICLES FOR GENE DELIVERY CARRIER

With the advancement of nanotechnology, nano-sized bioceramics have been dedicated much attention to biomedical applications in the past decades. In this study, the magnetic-hydroxyapatite nanoparticles (mHap NPs) were synthesized and magnetized by the addition of irons into hydroxyapatite using precipitation process. The mHap NPs were with good biocompatibility and superparamagnetic property which would have great promise in biological applications. We have evaluated the essential properties including plasmid DNA (pDNA) binding capacity by electrophoresis, qualitative transfection efficiency by fluorescence microscopy and quantitative GDNF expression by enzyme-link immunosorbent assay (ELISA). The results indicated that mHap NPs could be successfully binding with pDNA to form pDNA-mHap NPs transfection complex. The endocytosis of pDNA-mHap NPs transfection complex was mediated into cells and facilitated if magnetic field was applied. The transfection efficiency could also be significantly improved by magnetofection. The gene expression had been four-fold increase in high pDNA loading (2 μg/well) in transfection procedure with magnetic field compared with traditional transfection method. In brief, the mHap NPs have great potential as non-viral inorganic delivery carriers for gene delivery system.

ACUTE AND SUBACUTE ORAL TOXICITY TESTS OF SINTERED DICALCIUM PYROPHOSPHATE ON OVARIECTOMIZED RATS FOR OSTEOPOROSIS TREATMENT

Sintered dicalcium pyrophosphate (SDCP) is a synthetic pyrophosphate analog that could be utilized in the treatment for osteoporosis. In this study, an ovariectomized rat model is used to evaluate the systematic toxicity of orally administered SDCP relative to its effects on bone mass. Ovariectomized Wistar rats were treated with experimental medication with different dosing strategies (0.5 mg/kg five days weekly, and 2.5 mg/kg once weekly) for once (acute oral toxicity test) and four weeks (subacute oral toxicity test) followed by recovery period. Clinical signs of toxicity, body weight, and food consumption of rats were recorded. Blood samples were collected for hematological and blood biochemical analyses. Rats were sacrificed for necropsy and major visceral organs were harvested for histological examination after the recovery period. Long bones of four limbs were harvested to evaluate the effects of SDCP on bone mass. Results showed that there was no change in clinical signs, body weight, food consumption, hematology, blood biochemistry, necropsy, and histological examination attributable to the oral administration with SDCP to rats during the dosing period and the recovery period. Analysis of bone ashes revealed that the ovariectomized rats ingested with 0.5 mg/kg SDCP five days weekly continually for four weeks increased bone mineral contents significantly. In the ovariectomized rats ingested with 2.5 mg/kg SDCP once weekly continually for four weeks, the bone mineral contents were increased to normal bone quality. This study indicates that the SDCP can increase bone mass in the ovariectomized rat with no deleterious effects.