Gene therapy applications in gastroenterology and hepatology

Advantages and disadvantages of viral vectors and nonviral vectors for gene delivery to digestive organs are reviewed. Advances in systems for the introduction of new gene expression are described, including self-deleting retroviral transfer vectors, chimeric viruses and chimeric oligonucleotides. Systems for inhibition of gene expression are discussed, including antisense oligonucleotides, ribozymes and dominant-negative genes.

A DNA delivery system containing listeriolysin O results in enhanced hepatocyte-directed gene expression

AIM: To determine whether incorporation of the pH-dependent ba cterial toxin listeriolysin O (LLO) into the DNA carrier system could increase the endosomal escape of internalized DNA and result gene expression.

METHODS: A multi-component delivery system was prepared consist ing of asialoglycoprotein (ASG), poly L-lysine (PL), and LLO. Two marker genes, luciferase and β-galactosidase in plasmids were complexed and administered in vitro to Huh7[ASG receptor (+)] and SK Hep1 [ASG rece ptor(-)] cells. Purity, hemolytic activity, gene expression, specificity, and toxicity were evaluated.

RESULTS: An LLO-containing conjugate retained cell-targeting specificity and membranolytic activity. In ASG receptor (+) cells, luciferas e gene expression was enhanced by more than 7-fold over that of conjugates with out the incorporation of listeriolysin O. No significant expression occurred in ASG receptor (-) cells. Enhancement of β-galactosidase gene expression was less, but still significantly increased over controls. There was no detectable toxicity at concentrations shown to be effective in transfection studies.

CONCLUSIONS: ASOR-PL can be coupled to LLO using disulfide bonds, and successfully target and increase the gene expression of foreign DNA.

Multicomponent DNA carrier with a vesicular stomatitis virus G-peptide greatly enhances liver-targeted gene expression in mice

Genes can be targeted to hepatocytes in vitro and in vivo by the use of asialoorosomucoid-polylysine conjugates. After systemic application, this nonviral vector is recognized by highly selective asialoglycoprotein (AsGP) receptors on the sinusoidal liver cell membrane and is taken up via receptor-mediated endocytosis. As most of the DNA is rapidly transferred to lysosomes where it is degraded, transfection efficiency is low and gene expression transient. To address this problem, we incorporated a pH-dependent synthetic hemolytic peptide derived of the G-protein of Vesicular Stomatitis Virus (VSV) into the gene transfer system, to increase endosomal escape of internalized DNA. The multicomponent carrier binds DNA in a nondamaging way, is still recognized by the AsGP receptor, and is targeted to the liver in vivo. Injection of DNA complexes containing a luciferase marker gene resulted in luciferase expression of 29 000 pg/g liver which corresponded to an increase of a factor of 10(3) overexpression after injection of DNA complexes without endosomolytic peptide. Furthermore, the amount of intact transgene within isolated liver cell nuclei was increased by a factor of 10(1)-10(2) by the use of the multicomponent carriers. These results demonstrate that incorporation of a hemolytic peptide into a nonviral vector can greatly increase gene expression while retaining cell type targetability in vivo.

Inhibition of hepatitis C virus-directed gene expression by a DNA ribonuclease

BACKGROUND/AIMS

The aim of this study was to determine whether DNA analogs of ribozymes could be prepared to inhibit hepatitis C virus (HCV) gene expression.

METHODS

Two DNA ribonucleases, Dz2 and Dz4, were designed with varying arm lengths, to cleave at the 5'-noncoding region (NCR) just upstream from the translation start site, and core region of HCV genome, respectively. A reporter vector was prepared to contain target HCV regulatory sequences controlling a downstream luciferase gene. DNA ribonucleases with normal phosphodiester, as well as with terminal phosphorothioate linkages, were administered to Huh7 cells, and luciferase activity was measured.

RESULTS

DNA ribonucleases were highly active in cleaving HCV RNA targets. Enzymes with longer arms had consistently higher cleavage activity compared to enzymes with shorter arms under cell-free conditions. Furthermore, in Huh7 cells, terminal phosphorothioate derivatives, Dz2 and Dz4, significantly suppressed HCV-luciferase fusion gene expression up to 45% and 67% of controls, respectively. Interestingly, phosphorothioate-modified DNA ribonucleases had greater inhibitory effects on target gene expression than their unmodified counterparts. In contrast, DNA ribonucleases with point mutations in the catalytic domain had significantly lower inhibitory effects compared to wild-type DNA ribonucleases. However, activity was not eliminated, suggesting that some antisense contribution was present.

CONCLUSIONS

DNA ribonucleases directed against the HCV genome can specifically cleave target HCV RNA. Modifications of the extreme 3'- and 5'-termini protect against nuclease degradation without appreciable reduction in inhibitory activity against viral gene expression under intracellular conditions.

Dual actions of isthmic input to tectal neurons in a reptile, Gekko gekko

We analyzed postsynaptic potentials and dye-labeled morphology of tectal neurons responding to electrical stimulation of the optic nerve and of the nucleus isthmi in a reptile, Gekko gekko, in order to compare with previously reported interactions between the optic tectum and the nucleus isthmi in amphibians and birds. The results indicate that isthmic stimulation exerts inhibitory and excitatory actions on tectal cells, similar to dual isthmotectal actions in amphibians. It appears that dual actions of the isthmotectal pathway in amphibians and reptiles are shared by two subdivisions of the nucleus isthmi in birds. The morphology of tectal cells responding to isthmic stimulation is generally similar to that of tectoisthmic projecting neurons, but they differ particularly in that some tectoisthmic cells bear numerous varicosities whereas cells receiving isthmic afferents do not. Thus, it is likely that at least some tectoisthmic cells may not be in the population of tectal cells that can be affected by isthmic stimulation. Forty-four percent of injections resulted in dye-coupled labeling, suggesting extensive electrical connections between tectal cells in reptiles.

Hepatocyte-directed gene delivery by receptor-mediated endocytosis

The application of gene therapy to liver disease is contingent on the development of an effective gene delivery vehicle. Receptor-mediated endocytosis can be exploited as a means of selective and efficient targeting of gene therapy vectors to hepatocytes. DNA-binding conjugates have been directed to the liver by the attachment of asialoglycoproteins or other ligands for receptors expressed on hepatocytes. Recent studies suggest refinements in this approach through which high transduction rates in vitro may be reproduced in vivo. The intrinsic liver tropism of viral vectors and liposomes can be augmented by the addition of targeting features, as demonstrated in animal models. With further modification, such as the incorporation of hepatotropic elements of the hepatitis viruses or lipoproteins, the next generation of delivery systems may achieve efficient, persistent expression of therapeutic genes in a safe and cell type-specific manner.

Dendritic dynamics in vivo change during neuronal maturation

In vivo imaging of optic tectal neurons in the intact Xenopus tadpole permits direct observation of the structural dynamics that occur during dendritic arbor formation. Based on images of single DiI-labeled neurons collected at daily intervals over a period of 6 d, we divided tectal cell development into three phases according to the total length of the dendritic arbor. During phase 1, the cell differentiates from a neuroepithelial cell type and extends an axon out of the tectum. The total dendritic branch length (TDBL) is <100 micrometers. During phase 2, when TDBL is 100-400 micrometers, the dendritic arbor grows rapidly. During phase 3, when TDBL is >400 micrometers, the dendritic arbor grows slowly and appears stable. Neurons at different positions along the rostrocaudal developmental axis of the tectum were imaged at 2 hr intervals over 6 hr and at 24 hr intervals over several days. Images collected at 2 hr intervals were analyzed to determine rates of branch additions and retractions. Morphologically complex, phase 3 neurons show half the rate of branch additions and retractions as phase 2 neurons. Therefore, rapidly growing neurons have dynamic dendritic arbors, and slower-growing neurons are structurally stable. The change in growth rate and dendritic arbor dynamics from phase 2 to phase 3 correlates with the developmental increase in synaptic strength in neurons located along the rostrocaudal tectal axis. The data are consistent with the idea that strong synaptic inputs stabilize dendritic arbor structures and that weaker synaptic inputs are permissive for a greater degree of dynamic rearrangements and a faster growth rate in the dendritic arbor.

A method for purification of listeriolysin O from a hypersecretor strain of Listeria monocytogenes

A simple and convenient method for the purification of the hemolytic toxin listeriolysin O (LLO) from Listeria monocytogenes is described. Supernatants from bacteria cultures were purified by application to a CH2 spiral cartridge concentrator (Amicon) and ion exchange chromatography. A critical step is removal of contaminating RNA. The purified proteins had characteristics described for bacterial thiol-activated hemolysins: activation by a reducing agent (DTT) and inactivation by cholesterol. In addition, the molecular weight of 58, 000 and pH-dependent hemolytic activity of this purified protein are consistent with the previously published characteristics of LLO.

Gene therapy: Recent advances and applications in gastroenterology and hepatology

The advantages and disadvantages of viral and non-viral vectors for gene delivery are reviewed. Advances in systems for introduction of new gene expression are described, including self-deleting retroviral transfer vectors, chimeric viruses and chimeric oligonucleotides. Systems for inhibition of gene expression are also discussed including antisense oligonucleotides, ribozymes and dominant-negative genes. Examples of the use of these systems in animal models and clinical trials for gastrointestinal disorders are discussed.

Human portal serum stimulates cell proliferation in immature Schistosoma mansoni

Schistosomula of Schistosoma mansoni were incubated in RPMI 1640 medium containing 10% fetal calf serum, 10% human portal venous or 10% human peripheral venous sera in the presence of bromodeoxyuridine (BrdU) in order to measure differences in cell proliferation. The rates of cell proliferation as expressed by BrdU labelling indices (BLI) were determined as a function of time of incubation by immunohistochemistry using monoclonal antibody to BrdU. Compared to schistosomula cultured in the presence of RPMI plus 10% fetal calf serum, BLIs were increased by 60% in the presence of human portal, but not in peripheral serum. This stimulatory effect was substantially reproduced by a fraction of portal serum with a molecular weight range between 1 and 50 kDa. However, in the presence of human peripheral venous serum, either whole or fractionated, schistosomula showed no significant difference compared to RPMI plus 10% fetal calf serum alone. Furthermore, human portal serum fractions of molecular weight greater than 50 kDa also revealed no significant difference relative to control. The results indicate that portal venous serum component(s) of a molecular weight range higher than most simple nutrients can greatly stimulate the rate of cell proliferation of Schistosoma mansoni schistosomula.

Promotion of dendritic growth by CPG15, an activity-induced signaling molecule

Activity-independent and activity-dependent mechanisms work in concert to regulate neuronal growth, ensuring the formation of accurate synaptic connections. CPG15, a protein regulated by synaptic activity, functions as a cell-surface growth-promoting molecule in vivo. In Xenopus laevis, CPG15 enhanced dendritic arbor growth in projection neurons, with no effect on interneurons. CPG15 controlled growth of neighboring neurons through an intercellular signaling mechanism that requires its glycosylphosphatidylinositol link. CPG15 may represent a new class of activity-regulated, membrane-bound, growth-promoting proteins that permit exquisite spatial and temporal control of neuronal structure.

Recent advances in gene therapy of GI and liver diseases

Gene therapy toward the digestive organs has made substantial progress. The strategies applied include ex vivo and in vivo delivery. The ex vivo pathway does not require a tissue-specific vector while the in vivo pathway is advantageous for tissues not obtainable or hard to culture. The specific vectors of gene delivery for the liver and gastrointestinal tract include (1) viral vectors: retrovirus, adenovirus, and adeno-associated virus are the three most common currently used. (2) liposomes: when cationic substances are incorporated, DNA can be coated on the surface and carried into cells. (3) receptor-mediated gene therapy: natural and physiological and tissue-specific ligands were incorporated and modified to carry foreign DNA into the cells. They are tissue-specific and relatively nontoxic. The innovations focus on the prolongation of gene expression and a more efficient gene delivery.

DNA ribonucleases that are active against intracellular hepatitis B viral RNA targets

DNA ribonucleases directed against direct repeat 1 (DR1) and polyadenylation signal regions of hepatitis B virus (HBV) messages were prepared with phosphorothioate modifications and varying arm lengths. DNA ribonucleases modified throughout the entire molecule and in the target binding arms were completely protected from degradation after incubation with serum. DNA ribonuclease modified only at the 5' and 3' termini remained 92.9% intact after incubation. Molecules with no modification were degraded to 67.6% under the same conditions. However, modification of the entire molecule and in the recognition arms resulted in 99.8% and 98.4% inactivation of cleavage activity, respectively. Modification of only the termini resulted in retention of 20% to 40% of original activity. Lengthening each terminally modified arm from 9 to 11 nucleotides increased cleavage efficiency almost 10-fold. In Huh 7 cells, DR1-directed DNA ribonucleases with terminal modifications significantly suppressed HBV-luciferase fusion gene expression up to 48% of control. In contrast, DNA ribonucleases had no effect on a control construct lacking any HBV target sequences. Moreover, inactivated mutant and HCV-directed DNA ribonucleases had no significant effects on the HBV target. We conclude that resistance of DNA ribonucleases to degradation can be enhanced through phosphorothioate modification. Cleavage activity can be retained by limiting modification to the termini and lengthening the recognition arms. Such DNA ribonucleases can be made to specifically cleave target HBV RNA and substantially inhibit intracellular viral gene expression.

Targeted inhibition of hepatitis C virus-directed gene expression in human hepatoma cell lines

BACKGROUND & AIMS

The 5'-nontranslated region (NTR) of hepatitis C virus (HCV) contains important elements that control HCV translation. The aim of this study was to determine whether antisense oligonucleotides against the NTR of the HCV genome can be targeted to inhibit HCV gene expression.

METHODS

Antisense oligonucleotides directed against a sequence in the internal ribosomal binding site of the NTR (anti-III) and a portion of the NTR overlapping the core protein translational start site of HCV (anti-IV) were prepared. In transient transfections of a plasmid containing a luciferase gene immediately downstream from an HCV NTR insert, oligonucleotides anti-III and anti-IV in the form of asialoglycoprotein-polylysine complexes were administered to Huh7 cells, and luciferase activity generated by cytomegalovirus (CMV) HCVluc was measured.

RESULTS

Anti-III inhibited luciferase activity by 75% and 99% at 0.01 mumol/L and 0.1 mumol/L, respectively. Similarly, anti-IV inhibited luciferase activity 88% and 99% at 0.01 mumol/L and 0.1 mumol/L, respectively. In cell lines stably transfected with CMV HCVluc plasmid, complexed anti-III inhibited luciferase activity in Huh7 cells by 20% at 10 mumol/L and 85% at 60 mumol/L, and was competable by an excess of asialoglycoprotein.

CONCLUSIONS

Antisense oligonucleotides that bind to the NTR of HCV can be targeted by receptor-mediated endocytosis, and they specifically inhibit HCV-directed protein synthesis under intracellular conditions.

Pre-clinical trials using hepatic gene delivery

The development of gene therapy as a potential technique for treating serious metabolic or infectious disorders has generated much interest. The general applicability of gene therapy depends on the efficient transfer of the desired gene to specific tissues and cells. One of the most attractive sites for gene transfer is the liver because it plays a major role in many metabolic processes and is involved in a large variety of diseases. Nonviral strategies have been conceived for delivering genes to the liver but this approach is still at the preclinical stage. This review outlines the more commonly used approaches and discusses the progress that has been made toward developing a widely applicable, clinically relevant gene transfer procedure for the liver.

[Changes of activities of MLCK and dephosphatase in different arterial vessels from hypertensive rats]

The changes of activities of myosin light chain kinase (MLCK) and Ca2+/CaM-PP in different arterial vessels from hypertensive and normotensive rats were studied. The results were as follows. The MLCK activity of different arteries of spontaneous hypertensive rats (SHR) was different with the order of aorta (A) >> caudal artery (CA) >> mesenteric artery (MA), while in WKY rats the order of activity among different arteries is A << CA and MA and MA Ca2+/CaM-PP is obviously higher than in SHR. In renal hypertensive rats the activities of Ca2+/CaM-PP in different arteries are not quite different from those of the Wistar rats. The above results suggest that higher activities of MLCK or/and lower activity might be related to vasocontraction and hypertension.

Stabilization of dendritic arbor structure in vivo by CaMKII

Calcium-calmodulin-dependent protein kinase II (CaMKII) promotes the maturation of retinotectal glutamatergic synapses in Xenopus. Whether CaMKII activity also controls morphological maturation of optic tectal neurons was tested using in vivo time-lapse imaging of single neurons over periods of up to 5 days. Dendritic arbor elaboration slows with maturation, in correlation with the onset of CaMKII expression. Elevating CaMKII activity in young neurons by viral expression of constitutively active CaMKII slowed dendritic growth to a rate comparable to that of mature neurons. CaMKII overexpression stabilized dendritic structure in more mature neurons, whereas CaMKII inhibition increased their dendritic growth. Thus, endogenous CaMKII activity limits dendritic growth and stabilizes dendrites, and it may act as an activity-dependent mediator of neuronal maturation.

Serologic assay for secretory component distinguishes mechanical from hepatocellular cholestasis in humans

In rats, serum secretory component (SC) is elevated in mechanical but not hepatocellular cholestasis. To determine if serum SC might distinguish cholestatic syndromes in humans, serum samples were obtained from control subjects and patients with mechanical and hepatocellular cholestasis. Equal volumes of serum were assayed for SC by immunoblotting with an antibody specific for human SC. Quantitative densitometry of these immunoblots showed that in mechanically obstructed patients serum SC was reversibly elevated to a level approximately 10-fold higher than that of patients with hepatocellular cholestasis (P < 0.001). When comparing the two cholestatic groups, levels of serum alkaline phosphatase, but not bilirubin and alanine aminotransferase, were significantly higher in the group with mechanical cholestasis (P < 0.01). When comparing individual patients, serum SC was more reliable than alkaline phosphatase in distinguishing the two cholestatic syndromes (P < 0.05). Thus, serum SC may distinguish mechanical from hepatocellular cholestasis in humans.

Listeriolysin O potentiates immunotoxin and bleomycin cytotoxicity

Antitumor immunotoxins were formed by covalently attaching the ribosome-inactivating protein ricin A chain (RA) to the antitumor antibodies BR96 and L6. In vitro cytotoxicity assays established that BR96-RA was cytotoxic to H2987 human lung adenocarcinoma cells (IC50 = 6 nM), while L6-RA exhibited very low levels of cytotoxic activity (18% cell kill at 67 nM). The virulence factor from the intracellular pathogen Listeria monocytogenes, listeriolysin O (LLO), was able to potentiate the cytotoxicity of BR96-RA and L6-RA by 120- and > 1340-fold, respectively, resulting in IC50 values of approximately 50 pM. LLO also potentiated the cytotoxicity of the peptide anticancer drug bleomycin by a factor of > 2500 but had no effect on the cytotoxic activities of the anticancer drugs cytarabine and etoposide phosphate. In addition, LLO did not potentiate the cytotoxic activity of unconjugated ricin A chain or L6-RA on H2987 cells that were saturated with L6 prior to conjugate treatment. These results are attributed to LLO-induced alteration of the intracellular trafficking of molecules that are incorporated into acidic vesicles.

Design and preparation of a multimeric self-cleaving hammerhead ribozyme

The activity of a ribozyme can be impaired by additional sequences at the 5' and 3' termini of the catalytic sequence. To approach this problem, a system was designed that minimizes sequences upstream and downstream from active regions of a hammerhead ribozyme and allows delivery of a large number of active molecules. A self-cleavable multimeric molecule was prepared by placing a ribozyme target sequence (derived from the core region of the hepatitis B virus [HBV]) upstream and downstream from the catalytic sequence. This construct was cloned in tandem into in vitro expression vectors. 32P-UTP-labeled transcripts of the multimeric construct, as well as non-self-cleaved monomeric ribozyme controls, and substrate were synthesized. The multimeric ribozyme molecule efficiently self-cleaved to release monomeric ribozymes lacking any extra upstream and downstream sequences. In addition, monomers were substantially more active against the HBV target RNA than the non-self-cleavable ribozymes. Up to 80% degradation of the target RNA was achieved by a tenfold molar excess of a pentameric construct. We conclude that ribozymes can be produced as a multimeric tandem of self-cleavable molecules, the monomers of which are more active than monomeric ribozymes and highly efficient in cleavage of target transcripts.

Intracellular cleavage of hepatitis C virus RNA and inhibition of viral protein translation by hammerhead ribozymes

To determine the effects of hammerhead ribozymes against hepatitis C virus (HCV) RNA on viral protein translation, a luciferase reporter gene vector, pCMV/T7-NCRCdelta-luc, was constructed containing the 5'-noncoding region (5'-NCR) and part of the core region of HCV. Four ribozymes, Rz1-Rz4, were designed to cleave at nucleotide positions 136-160, 313-337, 496-520, and 373-388, respectively. Each ribozyme cleaved the target RNA at expected positions under cell-free conditions. Rz2 and Rz4 significantly suppressed translation of NCRCdelta-luc RNA by 71 and 49%, respectively. Translation of control luciferase mRNA lacking viral elements was not affected by the ribozymes. Furthermore, when NCRCdelta-luc RNA and ribozymes were cotransfected into cells, Rz2 and Rz4 significantly suppressed expression by 73 and 56%, respectively. In contrast, cleavage-deficient ribozymes with a point mutation in the hammerhead domain had no significant effect. To determine the effects of endogenously produced ribozymes, eukaryotic expression vectors for Rz2 and Rz4 were constructed. Cotransfection of the vectors with CMV/T7-NCRCdelta-luc showed suppression of luciferase activities to 50 and 61%, respectively. Moreover, transfection of pCMV/T7-NCRCdelta-luc into stable Rz2 and Rz4 producer cells also showed substantial inhibition of luciferase activity. Ribozymes directed against the HCV genome can substantially and specifically inhibit viral gene expression under intracellular conditions.

Delivery of a hammerhead ribozyme specifically down-regulates the production of fibrillin-1 by cultured dermal fibroblasts

The hammerhead ribozyme is a small catalytic RNA molecule. Potential hammerhead ribozymes that possess a catalytic domain and flanking sequence complementary to a target mRNA can cleave in trans at a putative cleavage site within the target molecule. We have investigated the potential of hammerhead ribozymes to down-regulate the product of the fibrillin-1 gene (FBN1). Fibrillin is a 347 kDa glycoprotein that is a major constituent of the elastin-associated microfibrils. Mutations in the FBN1 gene are responsible for Marfan syndrome (MFS), a common systemic disorder of the connective tissue. Many FBN1 mutations responsible for MFS appear to act in a dominant-negative fashion, raising the possibility that reduction of the amount of product from the mutant FBN1 allele might be a valid therapeutic approach for MFS. A trans-acting hammerhead ribozyme (FBN1-RZ1) targeted to the 5' end of the human FBN1 mRNA has been designed and synthesized, and shown to cleave its target efficiently in vitro. FBN1-RZ1 cleavage is magnesium dependent and efficient at both 37 and 50 degrees C. Delivery of the FBN1-RZ1 ribozyme into cultured dermal fibroblasts, by receptor-mediated endocytosis of a ribozyme-transferrin-polylysine complex, specifically reduces both cellular FBN1 mRNA and the deposition of fibrillin in the extracellular matrix. These results suggest that the use of hammerhead ribozymes is a valid approach to the study of fibrillin gene expression and possibly to the development of a therapeutic approach to MFS.

[Study of emotional disorders and their risk factors in patients hospitalized with lower extremity fracture]

111 adult patients hospitalized with lower extremity fracture (LEF) at three teaching hospitals of Beijing Medical University were interviewed by using STAI and CES-D. The results showed that the prevalence of depression in this group using CES-D is 69.4%, and there was a high correlation between STAI scores and CES-D scores. Multivariante analyses indicated that physical status, financial crisis, age, knowledge about disease, especially the patients' perceived threat of fracture, and social supports were the main factors that contribute to the patients' emotional distress.