Electrospun nanostructured scaffolds for bone tissue engineering

The current challenge in bone tissue engineering is to fabricate a bioartificial bone graft mimicking the extracellular matrix (ECM) with effective bone mineralization, resulting in the regeneration of fractured or diseased bones. Biocomposite polymeric nanofibers containing nanohydroxyapatite (HA) fabricated by electrospinning could be promising scaffolds for bone tissue engineering. Nanofibrous scaffolds of poly-l-lactide (PLLA, 860 ± 110 nm), PLLA/HA (845 ± 140 nm) and PLLA/collagen/HA (310 ± 125 nm) were fabricated, and the morphology, chemical and mechanical characterization of the nanofibers were evaluated using scanning electron microscopy, Fourier transform infrared spectroscopy and tensile testing, respectively. The in vitro biocompatibility of different nanofibrous scaffolds was also assessed by growing human fetal osteoblasts (hFOB), and investigating the proliferation, alkaline phosphatase activity (ALP) and mineralization of cells on different nanofibrous scaffolds. Osteoblasts were found to adhere and grow actively on PLLA/collagen/HA nanofibers with enhanced mineral deposition of 57% higher than the PLLA/HA nanofibers. The synergistic effect of the presence of an ECM protein, collagen and HA in PLLA/collagen/HA nanofibers provided cell recognition sites together with apatite for cell proliferation and osteoconduction necessary for mineralization and bone formation. The results of our study showed that the biocomposite PLLA/collagen/HA nanofibrous scaffold could be a potential substrate for the proliferation and mineralization of osteoblasts, enhancing bone regeneration.     

Dependency of R2 and R2* relaxation on Gd-DTPA concentration in arterial blood: Influence of hematocrit and magnetic field strength

Dynamic susceptibility contrast (DSC) MRI is clinically used to measure brain perfusion by monitoring the dynamic passage of a bolus of contrast agent through the brain. For quantitative analysis of the DSC images, the arterial input function is required. It is known that the original assumption of a linear relation between the R₂^(*) relaxation and the arterial contrast agent concentration is invalid, although the exact relation is as of yet unknown. Studying this relation in vitro is time-consuming, because of the widespread variations in field strengths, MRI sequences, contrast agents, and physiological conditions. This study aims to simulate the R₂^(*) versus contrast concentration relation under varying physiological and technical conditions using an adapted version of an open-source simulation tool. The approach was validated with previously acquired data in human whole blood at 1.5 T by means of a gradient-echo sequence (proof-of-concept). Subsequently, the impact of hematocrit, field strength, and oxygen saturation on this relation was studied for both gradient-echo and spin-echo sequences. The results show that for both gradient-echo and spin-echo sequences, the relaxivity increases with hematocrit and field strength, while the hematocrit dependency was nonlinear for both types of MRI sequences. By contrast, oxygen saturation has only a minor effect. In conclusion, the simulation setup has proven to be an efficient method to rapidly calibrate and estimate the relation between R₂^(*) and gadolinium concentration in whole blood. This knowledge will be useful in future clinical work to more accurately retrieve quantitative information on brain perfusion.     

Susac syndrome in a young child

Susac syndrome is a microangiopathy of unknown origin affecting the brain, retina and inner ear. This rare entity is often misdiagnosed as a demyelinating condition such as multiple sclerosis or acute disseminated encephalomyelitis. A high index of suspicion must be present as the majority of patients do not have the complete clinical triad at the time of onset of symptoms. The radiologist plays an important role when the disease is suspected and helps orient the investigations. The syndrome has characteristic imaging features on MRI that include multifocal white matter and occasional grey matter lesions, the corpus callosum being always involved. The predominant central callosal lesions, especially with rapid cystic transformation (central callosal holes) can be considered pathognomonic of this condition in the appropriate clinical setting. This disease is extremely rare in children. We report a case of Susac syndrome in a 9-year-old girl to increase the awareness among paediatric radiologists of this entity, which is usually not considered as a differential diagnosis of multifocal white matter involvement in this age group.     

Genome‐wide transcriptome analyses reveal p53 inactivation mediated loss of miR‐34a expression in malignant peripheral nerve sheath tumours

Malignant peripheral nerve sheath tumours (MPNSTs) are aggressive soft tissue tumours that occur either sporadically or in patients with neurofibromatosis type 1. The malignant transformation of the benign neurofibroma to MPNST is incompletely understood at the molecular level. We have determined the gene expression signature for benign and malignant PNSTs and found that the major trend in malignant transformation from neurofibroma to MPNST consists of the loss of expression of a large number of genes, rather than widespread increase in gene expression. Relatively few genes are expressed at higher levels in MPNSTs and these include genes involved in cell proliferation and genes implicated in tumour metastasis. In addition, a gene expression signature indicating p53 inactivation is seen in the majority of MPNSTs. Subsequent microRNA profiling of benign and malignant PNSTs indicated a relative down‐regulation of miR‐34a in most MPNSTs compared to neurofibromas. In vitro studies using the cell lines MPNST‐14 (NF1 mutant) and MPNST‐724 (from a non‐NF1 individual) show that exogenous expression of p53 or miR‐34a promotes apoptotic cell death. In addition, exogenous expression of p53 in MPNST cells induces miR‐34a and other miRNAs. Our data show that p53 inactivation and subsequent loss of expression of miR‐34a may significantly contribute to the MPNST development. Collectively, our findings suggest that deregulation of miRNAs has a potential role in the malignant transformation process in peripheral nerve sheath tumours. Copyright © 2009 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.     

Electrospun biomimetic nanocomposite nanofibers of hydroxyapatite/chitosan for bone tissue engineering

The development of bioinspired or biomimetic materials is essential and has formed one of the most important paradigms in today's tissue engineering research. This paper reports a novel biomimetic nanocomposite nanofibers of hydroxyapatite/chitosan (HAp/CTS) prepared by combining an in situ co-precipitation synthesis approach with an electrospinning process. A model HAp/CTS nanocomposite with the HAp mass ratio of 30wt% was synthesized through the co-precipitation method so as to attain homogenous dispersion of the spindle-shaped HAp nanoparticles (ca. 100x30nm) within the chitosan matrix. By using a small amount (10wt%) of ultrahigh molecular weight poly(ethylene oxide) (UHMWPEO) as a fiber-forming facilitating additive, continuous HAp/CTS nanofibers with a diameters of 214+/-25nm had been produced successfully and the HAp nanoparticles with some aggregations were incorporated into the electrospun nanofibers. Further SAED and XRD analysis confirmed that the crystalline nature of HAp remains and had survived the acetic acid-dominant solvent system. Biological in vitro cell culture with human fetal osteoblast (hFOB) cells for up to 15 days demonstrated that the incorporation of HAp nanoparticles into chitosan nanofibrous scaffolds led to significant bone formation oriented outcomes compared to that of the pure electrospun CTS scaffolds. The electrospun nanocomposite nanofibers of HAp/CTS, with compositional and structural features close to the natural mineralized nanofibril counterparts, are of potential interest for bone tissue engineering applications.     

Therapeutic significance of elevated tissue transglutaminase expression in pancreatic cancer.

PURPOSE: Tissue transglutaminase (TG2) is a multifunctional protein that is implicated in development of drug resistance and metastasis. Therefore, we examined therapeutic targeting of TG2 for inhibiting growth and metastasis of in vivo growing pancreatic ductal adenocarcinoma (PDAC) in nude mice. EXPERIMENTAL DESIGN: We implanted Panc-28 pancreatic cancer cells to induce orthotopic PDAC tumors in nude mice and determined the efficacy of liposomal TG2 small interfering RNA (siRNA) either alone or in combination with gemcitabine. RESULTS: We show that down-regulation of endogenous TG2 by siRNA could effectively block the growth of PDAC. Moreover, down-regulation of TG2 significantly enhanced the therapeutic efficacy of gemcitabine against PDAC and inhibited metastatic spread of the disease. The antitumor activity was related to inhibition of proliferation, angiogenesis, and Akt phosphorylation. CONCLUSION: siRNA-mediated down-regulation of TG2 represents a promising therapeutic approach for improved treatment of PDAC.     

Diaphragmatic fenestration for resistant pleural effusions after univentricular repair

A 12-year-old child with chronic pleural effusions for a month and a half after a fenestrated Fontan operation underwent bilateral diaphragmatic fenestrations with complete relief. We suggest this approach as an alternative treatment for chronic pleural effusions that may ensue after total cavopulmonary connection.