Enhanced in vivo angiogenesis within a model tissue engineered construct using biodegradable microspheres containing encapsulated VEGF

Introduction. Tissue engineering techniques offer a potential means to develop a tissue engineered construct (TEC) for the treatment of tissue and organ deficiencies. However, a lack of adequate vascularization is a limiting factor in the development of most viable engineered tissues. Vascular endothelial growth factor (VEGF) could aid in the development of a viable vascular network within TECs. The long-term goals of this research are to develop clinically relevant, appropriately vascularized TECs for use in humans. This project tested the hypothesis that the delivery of VEGF via controlled release from biodegradable microspheres would increase the vascular density and rate of angiogenesis within a model TEC. ^ Materials and methods. Biodegradable VEGF-encapsulated microspheres were manufactured using a novel method entitled the Solid Encapsulation/Single Emulsion/Solvent Extraction technique. Using a PLGA/PEG polymer blend, microspheres were manufactured and characterized in vitro. A model TEC using fibrin was designed for in vivo tissue engineering experimentation. At the appropriate timepoint, the TECs were explanted, and stained and quantified for CD31 using a novel semi-automated thresholding technique. ^ Results. In vitro results show the microspheres could be manufactured, stored, degrade, and release biologically active VEGF. The in vivo investigations revealed that skeletal muscle was the optimal implantation site as compared to dermis. In addition, the TECs containing fibrin with VEGF demonstrated significantly more angiogenesis than the controls. The TECs containing VEGF microspheres displayed a significant increase in vascular density by day 10. Furthermore, TECs containing VEGF microspheres had a significantly increased relative rate of angiogenesis from implantation day 5 to day 10. ^ Conclusions. A novel technique for producing microspheres loaded with biologically active proteins was developed. A defined concentration of microspheres can deliver a quantifiable level of VEGF with known release kinetics. A novel model TEC for in vivo tissue engineering investigations was developed. VEGF and VEGF microspheres stimulate angiogenesis within the model TEC. This investigation determined that biodegradable rhVEGF 165-encapsulated microspheres increased the vascular density and relative rate of angiogenesis within a model TEC. Future applications could include the incorporation of microvascular fragments into the model TEC and the incorporation of specific tissues, such as fat or bone. ^

In vivo longitudinal studies of spinal cord injury and vascular endothelial growth factor treatment

Approximately 12,000 new cases of spinal cord injury (SCI) are added each year to the estimated 259,000 Americans living with SCI. The majority of these patients return to society, their lives forever changed by permanent loss of sensory and motor function. While there are no FDA approved drugs for the treatment of SCI or a universally accepted standard therapy, the current though controversial treatment includes the delivery of high dosages of the corticosteroid methyliprednisolone sodium succinate, surgical interventions to stabilize the spinal column, and physical rehabilitation. It is therefore critically important to fully understand the pathology of injury and determine novel courses and rationally-based therapies for SCI. ^ Vascular endothelial growth factor (VEGF) is an attractive target for treating central nervous system (CNS) injury and disease because it has been shown to influence angiogenesis and neuroprotection. Preliminary studies have indicated that increased vasculature may be associated with functional recovery; therefore exogenous delivery of a pro-angiogenic growth factor such as VEGF may improve neurobehavioral outcome. In addition, VEGF may provide protection from secondary injury and result in increased survival and axonal sprouting. ^ In these studies, SCI rats received acute intraspinal injections of VEGF, the antibody to VEGF, or vehicle control. The effect of these various agents was investigated using longitudinalmulti-modal magnetic resonance imaging (MRI), neuro- and sensory behavioral assays, and end point immunohistochemistry. We found that rats that received VEGF after SCI had increased tissue sparing and improved white matter integrity at the earlier time points as shown by advanced magnetic resonance imaging (MRI) techniques. However, these favorable effects of VEGF were not maintained, suggesting that additional treatments with VEGF at multiple time points may be more beneficial, Histological examinations revealed that VEGF treatment may result in increased oligodendrogenesis and therefore may eventually lead to remyelination and improved functional outcome. ^ On the neurobehavioral studies, treatments with VEGF and Anti-VEGF did not significantly affect performance on tests of open-field locomotion, grid walk, inclined plane, or rearing. However, VEGF treatment resulted in significantly increased incidence of chronic neuropathic pain. This phenomenon could possibly be attributed to the fact that VEGF treatment may promote axonal sprouting and also results in tissue sparing, thereby providing a substrate for the growth of new axons. New connections made by these sprouting axons may involve components of pathways involved in the transmission of pain and therefore result in increased pain in those animals. ^

Engineering a tRNA and aminoacyl-tRNA synthetase for the site-specific incorporation of unnatural amino acids into proteins in vivo

In an effort to expand the scope of protein mutagenesis, we have completed the first steps toward a general method to allow the site-specific incorporation of unnatural amino acids into proteins in vivo. Our approach involves the generation of an “orthogonal” suppressor tRNA that is uniquely acylated in Escherichia coli by an engineered aminoacyl-tRNA synthetase with the desired unnatural amino acid. To this end, eight mutations were introduced into tRNA2Gln based on an analysis of the x-ray crystal structure of the glutaminyl-tRNA aminoacyl synthetase (GlnRS)–tRNA2Gln complex and on previous biochemical data. The resulting tRNA satisfies the minimal requirements for the delivery of an unnatural amino acid: it is not acylated by any endogenous E. coli aminoacyl-tRNA synthetase including GlnRS, and it functions efficiently in protein translation. Repeated rounds of DNA shuffling and oligonucleotide-directed mutagenesis followed by genetic selection resulted in mutant GlnRS enzymes that efficiently acylate the engineered tRNA with glutamine in vitro. The mutant GlnRS and engineered tRNA also constitute a functional synthetase–tRNA pair in vivo. The nature of the GlnRS mutations, which occur both at the protein–tRNA interface and at sites further away, is discussed.

Effects of in vivo adventitial expression of recombinant endothelial nitric oxide synthase gene in cerebral arteries

Nitric oxide (NO), synthesized from l-arginine by NO synthases (NOS), plays an essential role in the regulation of cerebrovascular tone. Adenoviral vectors have been widely used to transfer recombinant genes to different vascular beds. To determine whether the recombinant endothelial NOS (eNOS) gene can be delivered in vivo to the adventitia of cerebral arteries and functionally expressed, a replication-incompetent adenoviral vector encoding eNOS gene (AdCMVNOS) or β-galactosidase reporter gene (AdCMVLacZ) was injected into canine cerebrospinal fluid (CSF) via the cisterna magna (final viral titer in CSF, 109 pfu/ml). Adventitial transgene expression was demonstrated 24 h later by β-galactosidase histochemistry and quantification, eNOS immunohistochemistry, and Western blot analysis of recombinant eNOS. Electron microscopy immunogold labeling indicated that recombinant eNOS protein was expressed in adventitial fibroblasts. In AdCMVNOS-transduced arteries, basal cGMP production and bradykinin-induced relaxations were significantly augmented when compared with AdCMVLacZ-transduced vessels (P < 0.05). The increased receptor-mediated relaxations and cGMP production were inhibited by eNOS inhibitors. In addition, the increase in cGMP production was reversed in the absence of calcium, suggesting that the increased NO production did not result from inducible NOS expression. The present study demonstrates the successful in vivo transfer and functional expression of recombinant eNOS gene in large cerebral arteries. It also suggests that perivascular eNOS gene delivery via the CSF is a feasible approach that does not require interruption of cerebral blood flow.

Synthesis and in vivo murine evaluation of Na4[1-(1′-B10H9)-6-SHB10H8] as a potential agent for boron neutron capture therapy

Reaction of the normal isomer of [B20H18]2− and the protected thiol anion, [SC(O)OC(CH3)3]−, produces an unexpected isomer of [B20H17SC(O)OC(CH3)3]4− directly and in good yield. The isomer produced under mild conditions is characterized by an apical–apical boron atom intercage connection as well as the location of the thiol substituent on an equatorial belt adjacent to the terminal boron apex. Although the formation of this isomer from nucleophilic attack of the normal isomer of [B20H18]2− has not been reported previously, the isomeric assignment has been unambiguously confirmed by one-dimensional and two-dimensional 11B NMR spectroscopy. Deprotection of the thiol substituent under acidic conditions produces a protonated intermediate, [B20H18SH]3−, which can be deprotonated with a suitable base to yield the desired product, [B20H17SH]4−. The sodium salt of the resulting [B20H17SH]4− ion has been encapsulated in small, unilamellar liposomes, which are capable of delivering their contents selectively to tumors in vivo, and investigated as a potential agent for boron neutron capture therapy. The biodistribution of boron was determined after intravenous injection of the liposomal suspension into BALB/c mice bearing EMT6 mammary adenocarcinoma. At low injected doses, the tumor boron concentration increased throughout the time-course experiment, resulting in a maximum observed boron concentration of 46.7 μg of B per g of tumor at 48 h and a tumor to blood boron ratio of 7.7. The boron concentration obtained in the tumor corresponds to 22.2% injected dose (i.d.) per g of tissue, a value analogous to the most promising polyhedral borane anions investigated for liposomal delivery and subsequent application in boron neutron capture therapy.

Angiostatin gene transfer: Inhibition of tumor growth in vivo by blockage of endothelial cell proliferation associated with a mitosis arrest

The antitumoral effects that follow the local delivery of the N-terminal fragment of human plasminogen (angiostatin K3) have been studied in two xenograft murine models. Angiostatin delivery was achieved by a defective adenovirus expressing a secretable angiostatin K3 molecule from the cytomegalovirus promoter (AdK3). In in vitro studies, AdK3 selectively inhibited endothelial cell proliferation and disrupted the G2/M transition induced by M-phase-promoting factors. AdK3-infected endothelial cells showed a marked mitosis arrest that correlated with the down-regulation of the M-phase phosphoproteins. A single intratumoral injection of AdK3 into preestablished rat C6 glioma or human MDA-MB-231 breast carcinoma grown in athymic mice was followed by a significant arrest of tumor growth, which was associated with a suppression of neovascularization within and at the vicinity of the tumors. AdK3 therapy also induced a 10-fold increase in apoptotic tumor cells as compared with a control adenovirus. Furthermore, we showed that systemic injection of AdK3 delayed C6 tumor establishment and growth, confirming that angiostatin can function in a paracrin manner. Our data support the concept that targeted antiangiogenesis, using adenovirus-mediated gene transfer, represents a promising alternative strategy for delivering antiangiogenic factors as their bolus injections present unsolved pharmacological problems.

Nerve growth factor rapidly suppresses basal, NMDA-evoked, and AMPA-evoked nitric oxide synthase activity in rat hippocampus in vivo

In adult forebrain, nerve growth factor (NGF) influences neuronal maintenance and axon sprouting and is neuroprotective in several injury models through mechanisms that are incompletely understood. Most NGF signaling is thought to occur after internalization and retrograde transport of trkA receptor and be mediated through the nucleus. However, NGF expression in hippocampus is rapidly and sensitively regulated by synaptic activity, suggesting that NGF exerts local effects more dynamically than possible through signaling requiring retrograde transport to distant afferent neurons. Interactions have been reported between NGF and nitric oxide (NO). Because NO affects both neural plasticity and degeneration, and trk receptors can mediate signaling within minutes, we hypothesized that NGF might rapidly modulate NO production. Using in vivo microdialysis we measured conversion of l-[14C]arginine to l-[14C]citrulline as an accurate reflection of NO synthase (NOS) activity in adult rat hippocampus. NGF significantly reduced NOS activity to 61% of basal levels within 20 min of onset of delivery and maintained NOS activity at less than 50% of baseline throughout 3 hr of delivery. This effect did not occur with control protein (cytochrome c) and was not mediated by an effect of NGF on glutamate levels. In addition, simultaneous delivery of NGF prevented significant increases in NOS activity triggered by the glutamate receptor agonists N-methyl-d-aspartate (NMDA) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA). Rapid suppression by NGF of basal and glutamate-stimulated NOS activity may regulate neuromodulatory functions of NO or protect neurons from NO toxicity and suggests a novel mechanism for rapidly mediating functions of NGF and other neurotrophins.

Tissue-engineered cells producing complex recombinant proteins inhibit ovarian cancer in vivo

Techniques of tissue engineering and cell and molecular biology were used to create a biodegradable scaffold for transfected cells to produce complex proteins. Mullerian Inhibiting Substance (MIS) causes regression of Mullerian ducts in the mammalian embryo. MIS also causes regression in vitro of ovarian tumor cell lines and primary cells from ovarian carcinomas, which derive from Mullerian structures. In a strategy to circumvent the complicated purification protocols for MIS, Chinese hamster ovary cells transfected with the human MIS gene were seeded onto biodegradable polymers of polyglycolic acid fibers and secretion of MIS confirmed. The polymer-cell graft was implanted into the right ovarian pedicle of severe combined immunodeficient mice. Serum MIS in the mice rose to supraphysiologic levels over time. One week after implantation of the polymer-cell graft, IGROV-1 human tumors were implanted under the renal capsule of the left kidney. Growth of the IGROV-1 tumors was significantly inhibited in the animals with a polymer-cell graft of MIS-producing cells, compared with controls. This novel MIS delivery system could have broader applications for other inhibitory agents not amenable to efficient purification and provides in vivo evidence for a role of MIS in the treatment of ovarian cancer.

In vivo restoration of laminin 5 β3 expression and function in junctional epidermolysis bullosa

The blistering disorder, lethal junctional epidermolysis bullosa (JEB), can result from mutations in the LAMB3 gene, which encodes laminin 5 β3 (β3). Appropriate expression of LAMβ3 in JEB skin tissue could potentially ameliorate the symptoms of the underlying disease. To explore the utility of this therapeutic approach, primary keratinocytes from six unrelated JEB patients were transduced with a retroviral vector encoding β3 and used to regenerate human skin on severe combined immunodeficient (SCID) mice. Tissue regenerated from β3-transduced JEB keratinocytes produced phenotypically normal skin characterized by sustained β3 expression and the formation of hemidesmosomes. Additionally, β3 gene transfer corrected the distribution of a number of important basement membrane zone proteins including BPAG2, integrins β4/β1, and laminins α3/γ2. Skin produced from β3-negative (β3[−]) JEB cells mimicked the hallmarks of the disease state and did not exhibit any of the aforementioned traits. Therefore, by effecting therapeutic gene transfer to β3-deficient primary keratinocytes, it is possible to produce healthy, normal skin tissue in vivo. These data support the utility of gene therapy for JEB and highlight the potential for gene delivery in the treatment of human genetic skin disease.

In vivo detection of gene expression in liver by 31P nuclear magnetic resonance spectroscopy employing creatine kinase as a marker gene

In vivo assessment of gene expression is desirable to obtain information on the extent and duration of transduction of tissue after gene delivery. We have developed an in vivo, potentially noninvasive, method for detecting virally mediated gene transfer to the liver. The method employs an adenoviral vector carrying the gene for the brain isozyme of murine creatine kinase (CK-B), an ATP-buffering enzyme expressed mainly in muscle and brain but absent from liver, kidney, and pancreas. Gene expression was monitored by 31P magnetic resonance spectroscopy (MRS) using the product of the CK enzymatic reaction, phosphocreatine, as an indicator of transfection. The vector was administered into nude mice by tail vein injection, and exogenous creatine was administered in the drinking water and by i.p. injection of 2% creatine solution before 31P MRS examination, which was performed on surgically exposed livers. A phosphocreatine resonance was detected in livers of mice injected with the vector and was absent from livers of control animals. CK expression was confirmed in the injected animals by Western blot analysis, enzymatic assays, and immunofluorescence measurements. We conclude that the syngeneic enzyme CK can be used as a marker gene for in vivo monitoring of gene expression after virally mediated gene transfer to the liver.

Targeted DNA recombination in vivo using an adenovirus carrying the cre recombinase gene.

Conditional gene expression and gene deletion are important experimental approaches for examining the functions of particular gene products in development and disease. The cre-loxP system from bacteriophage P1 has been used in transgenic animals to induce site-specific DNA recombination leading to gene activation or deletion. To regulate the recombination in a spatiotemporally controlled manner, we constructed a recombinant adenoviral vector, Adv/cre, that contained the cre recombinase gene under regulation of the herpes simplex virus thymidine kinase promoter. The efficacy and target specificity of this vector in mediating loxP-dependent recombination were analyzed in mice that had been genetically engineered to contain loxP sites in their genome. After intravenous injection of the Adv/cre vector into adult animals, the liver and spleen showed the highest infectivity of the adenovirus as well as the highest levels of recombination, whereas other tissues such as kidney, lung, and heart had lower levels of infection and recombination. Only trace levels of recombination were detected in the brain. However, when the Adv/cre vector was injected directly into specific regions of the adult brain, including the cerebral cortex, hippocampus, and cerebellum, recombination was detectable at the injection site. Furthermore, when the Adv/cre vector was injected into the forebrains of neonatal mice, the rearranged toxP locus from recombination could be detected in the injected regions for at least 8 weeks. Taken together, these results demonstrate that the Adv/cre vector expressing a functional cre protein is capable of mediating loxP-dependent recombination in various tissues and the recombined gene locus may in some cases be maintained for an extended period. The use of the adenovirus vector expressing cre combined with localized delivery to specific tissues may provide an efficient means to achieve conditional gene expression or knockout with precise spatiotemporal control.

Suppression of retinal neovascularization in vivo by inhibition of vascular endothelial growth factor (VEGF) using soluble VEGF-receptor chimeric proteins.

The majority of severe visual loss in the United States results from complications associated with retinal neovascularization in patients with ischemic ocular diseases such as diabetic retinopathy, retinal vein occlusion, and retinopathy of prematurity. Intraocular expression of the angiogenic protein vascular endothelial growth factor (VEGF) is closely correlated with neovascularization in these human disorders and with ischemia-induced retinal neovascularization in mice. In this study, we evaluated whether in vivo inhibition of VEGF action could suppress retinal neovascularization in a murine model of ischemic retinopathy. VEGF-neutralizing chimeric proteins were constructed by joining the extracellular domain of either human (Flt) or mouse (Flk) high-affinity VEGF receptors with IgG. Control chimeric proteins that did not bind VEGF were also used. VEGF-receptor chimeric proteins eliminated in vitro retinal endothelial cell growth stimulation by either VEGF (P < 0.006) or hypoxic conditioned medium (P < 0.005) without affecting growth under nonstimulated conditions. Control proteins had no effect. To assess in vivo response, animals with bilateral retinal ischemia received intravitreal injections of VEGF antagonist in one eye and control protein in the contralateral eye. Retinal neovascularization was quantitated histologically by a masked protocol. Retinal neovascularization in the eye injected with human Flt or murine Flk chimeric protein was reduced in 100% (25/25; P < 0.0001) and 95% (21/22; P < 0.0001) 0.0001) of animals, respectively, compared to the control treated eye. This response was evident after only a single intravitreal injection and was dose dependent with suppression of neovascularization noted after total delivery of 200 ng of protein (P < 0.002). Reduction of histologically evident neovascular nuclei per 6-microns section averaged 47% +/- 4% (P < 0.001) and 37% +/- 2% (P < 0.001) for Flt and Flk chimeric proteins with maximal inhibitory effects of 77% and 66%, respectively. No retinal toxicity was observed by light microscopy. These data demonstrate VEGF's causal role in retinal angiogenesis and prove the potential of VEGF inhibition as a specific therapy for ischemic retinal disease.

A versatile vector for gene and oligonucleotide transfer into cells in culture and in vivo: polyethylenimine.

Several polycations possessing substantial buffering capacity below physiological pH, such as lipopolyamines and polyamidoamine polymers, are efficient transfection agents per se--i.e., without the addition of cell targeting or membrane-disruption agents. This observation led us to test the cationic polymer polyethylenimine (PEI) for its gene-delivery potential. Indeed, every third atom of PEI is a protonable amino nitrogen atom, which makes the polymeric network an effective "proton sponge" at virtually any pH. Luciferase reporter gene transfer with this polycation into a variety of cell lines and primary cells gave results comparable to, or even better than, lipopolyamines. Cytotoxicity was low and seen only at concentrations well above those required for optimal transfection. Delivery of oligonucleotides into embryonic neurons was followed by using a fluorescent probe. Virtually all neurons showed nuclear labeling, with no toxic effects. The optimal PEI cation/anion balance for in vitro transfection is only slightly on the cationic side, which is advantageous for in vivo delivery. Indeed, intracerebral luciferase gene transfer into newborn mice gave results comparable (for a given amount of DNA) to the in vitro transfection of primary rat brain endothelial cells or chicken embryonic neurons. Together, these properties make PEI a promising vector for gene therapy and an outstanding core for the design of more sophisticated devices. Our hypothesis is that its efficiency relies on extensive lysosome buffering that protects DNA from nuclease degradation, and consequent lysosomal swelling and rupture that provide an escape mechanism for the PEI/DNA particles.

Injetor intravascular de CO2: estudo in vivo de viabilidade inicial do dispositivo e de qualidade de imagem

INTRODUÇÃO: Durante procedimentos endovasculares, estão presentes os riscos relacionados ao uso dos contrastes iodados, tais como a nefropatia por contraste, uma vez que é fundamental o emprego de um meio de contraste para a obtenção das imagens radiológicas vasculares. A injeção intravascular de gás CO2 purificado é reconhecidamente uma alternativa relativamente mais segura ao contraste iodado, contudo, seu manuseio artesanal pode também trazer dificuldades técnicas e riscos aos pacientes. Para contemplar estas questões, foi desenvolvido o protótipo de um injetor intravascular de CO2 medicinal, microprocessado, dedicado à obtenção de imagens angiográficas. OBJETIVOS: Realizar os testes de viabilidade técnica inicial do protótipo em modelo in vivo. MÉTODOS: Realizar a angioplastia da artéria renal esquerda de 10 porcos, divididos em 2 grupos: Grupo 1 (n=5) injeção de contraste iodado, Grupo 2 (n=5) injeção de CO2 através do protótipo. Monitorização clínica e laboratorial dos animais no pré, intra e pós-operatório, com exames de função renal na véspera e 48h após os procedimentos e 3 gasometrias arteriais seriadas no intra-operatório. Observação clínica foi mantida por 48h no pós- operatório. RESULTADOS: Os procedimentos de angioplastia com CO2 foram realizados com sucesso técnico de 100%, sem necessidade de complementação com injeção de contraste iodado no Grupo 2. Não foram identificadas falhas no protótipo em funcionamento. Não foram identificadas alterações clínicas ou radiológicas sugestivas de contaminação por ar ambiente do sistema de CO2 e nem alterações laboratoriais nos animais. As imagens angiográficas obtidas no Grupo 2 foram consideradas, numa avaliação subjetiva, relativamente inferiores às imagens obtidas no Grupo 1. DISCUSSÃO: A qualidade inferior de imagem no Grupo 2 pode ser atribuída ao equipamento de fluoroscopia utilizado, com software desatualizado em relação aos equipamentos atuais, que incluem pré-configurações para angiografia com CO2; no entanto, ainda assim todos os procedimentos propostos no Grupo 2 foram realizados com sucesso técnico, o que nos leva a classificar as imagens deste grupo 2 como satisfatórias. O manuseio do aparelho mostrou-se ágil e eficiente, com a programação dos parâmetros sendo realizada com facilidade através do visor \"touch screen\", comparativamente superior ao método artesanal de injeção de CO2 com seringas em selo d\'água. CONCLUSÕES: O protótipo do aparelho injetor intravascular de CO2 funcionou de forma adequada durante os testes e as imagens obtidas permitiram a compleição com sucesso dos procedimentos. Portanto, os resultados positivos obtidos sugerem que o equipamento é tecnicamente viável

In vivo gene expression: DNA electrotransfer

The use of electric pulses to deliver therapeutic molecules to tissues and organs in vivo is a rapidly growing field of research. Electrotransfer can be used to deliver a wide range of potentially therapeutic agents, including drugs, proteins, oligonucleotides, RNA and DNA. Optimization of this approach depends upon a number of parameters such as target organ accessibility, cell turnover, microelectrode design, electric pulsing protocols and the physiological response to the therapeutic agent. Many organs have been successfully transfected by electroporation, including skin, liver, skeletal and cardiac muscle, male and female germ cells, artery, gut, kidney, retinal ganglion cells, cornea, spinal cord, joint synovium and brain. Electrotransfer technology is relevant in a variety of research and clinical settings including cancer therapy, modulation of pathogenic immune reactions, delivery of therapeutic proteins and drugs, and the identification of drug targets by the modulation of normal gene expression. This, together with the capacity to deliver very large DNA constructs, greatly expands the research and clinical applications of in vivo DNA electrotransfer.