Injection of a recombinant AAV serotype 2 into canine skeletal muscles evokes strong immune responses against transgene products.

Using murine models, we have previously demonstrated that recombinant adeno-associated virus (rAAV)-mediated microdystrophin gene transfer is a promising approach to treatment of Duchenne muscular dystrophy (DMD). To examine further therapeutic effects and the safety issue of rAAV-mediated microdystrophin gene transfer using larger animal models, such as dystrophic dog models, we first investigated transduction efficiency of rAAV in wild-type canine muscle cells, and found that rAAV2 encoding beta-galactosidase effectively transduces canine primary myotubes in vitro. Subsequent rAAV2 transfer into skeletal muscles of normal dogs, however, resulted in low and transient expression of beta-galactosidase together with intense cellular infiltrations in vivo, where cellular and humoral immune responses were remarkably activated. In contrast, rAAV2 expressing no transgene elicited no cellular infiltrations. Co-administration of immunosuppressants, cyclosporine and mycophenolate mofetil could partially improve rAAV2 transduction. Collectively, these results suggest that immune responses against the transgene product caused cellular infiltration and eliminated transduced myofibers in dogs. Furthermore, in vitro interferon-gamma release assay showed that canine splenocytes respond to immunogens or mitogens more susceptibly than murine ones. Our results emphasize the importance to scrutinize the immune responses to AAV vectors in larger animal models before applying rAAV-mediated gene therapy to DMD patients.

Lack of toxicity from pediatric beta-blocker exposures.

The risk of toxicity in a child who is unintentionally exposed to a beta-blocking drug remains uncertain. The current study further defines this risk, particularly in the common scenario of ingestion of one or two tablets. A prospective cohort of 208 pediatric patients, 6 months to 6 years of age, reported to two regional poison centers serves as the study population. Data were collected with a standardized instrument during the care of each patient and for a minimum of 24 hours after exposure. No instances of serious toxicity typical of beta-blocker intoxication, such as 'shock-like' states, arrhythmias or seizures were observed in this series. Furthermore, there were no reported episodes of hypoglycemia, symptomatic bradycardia or bronchospasm. Nine instances of altered mental status or behavioral changes were reported. All appeared to be minor in nature. The most serious outcome was charcoal aspiration during gastrointestinal decontamination. This study adds to a growing body of evidence suggesting that exposure to one or two beta-blocker tablets places children at very little, if any, risk of toxicity.

Characterization of the 5'-sequence of the mouse fatty acid amide hydrolase.

Fatty acid amide hydrolase (FAAH) is critical for degradation of several important fatty acid amides including anandamide, an endocannabinoid, as well as oleamide, a sleep-inducing factor. These compounds play roles in diverse physiological processes ranging from memory and learning to the regulation of blood pressure. The mechanisms that regulate FAAH expression have not been characterized. A 5'-region of the mouse FAAH with promoter activity was isolated from 1.8 kbp of genomic sequence. Characterization of +1 of transcription of FAAH by RNA ligase mediated-rapid amplification of cDNA ends showed that FAAH mRNA is transcribed from multiple transcription start sites lacking a TATA-box element. Functional analysis of the FAAH upstream sequence fused to a luciferase reporter gene revealed a FAAH-promoter construct with tissue specific activity. A 674-bp FAAH-promoter construct was active in N18TG2 (N18) neuroblastoma cells and C6 glioma cells, lines that have endogenous FAAH activity. The same 674-bp FAAH-promoter construct was not active in C2C12 or L6 myogenic cells, two lines that do not have FAAH activity.

Dystrophin expression in muscle following gene transfer with a fully deleted ("gutted") adenovirus is markedly improved by trans-acting adenoviral gene products.

Helper-dependent adenoviruses (HDAd) are Ad vectors lacking all or most viral genes. They hold great promise for gene therapy of diseases such as Duchenne muscular dystrophy (DMD), because they are less immunogenic than E1/E3-deleted Ad (first-generation Ad or FGAd) and can carry the full-length (Fl) dystrophin (dys) cDNA (12 kb). We have compared the transgene expression of a HDAd (HDAdCMVDysFl) and a FGAd (FGAdCMV-dys) in cell culture (HeLa, C2C12 myotubes) and in the muscle of mdx mice (the mouse model for DMD). Both vectors encoded dystrophin regulated by the same cytomegalovirus (CMV) promoter. We demonstrate that the amount of dystrophin expressed was significantly higher after gene transfer with FGAdCMV-dys compared to HDAdCMVDysFl both in vitro and in vivo. However, gene transfer with HDAdCMVDysFl in the presence of a FGAd resulted in a significant increase of dystrophin expression indicating that gene products synthesized by the FGAd increase, in trans, the amount of dystrophin produced. This enhancement occurred in cell culture and after gene transfer in the muscle of mdx mice and dystrophic golden retriever (GRMD) dogs, another animal model for DMD. The E4 region of Ad is required for the enhancement, because no increase of dystrophin expression from HDAdCMVDysFl was observed in the presence of an E1/E4-deleted Ad in vitro and in vivo. The characterization of these enhancing gene products followed by their inclusion into an HDAd may be required to produce sufficient dystrophin to mitigate the pathology of DMD by HDAd-mediated gene transfer.

The spread of transgene expression at the site of gene construct injection.

Seven 2-day-old golden retriever pups were given focal intramuscular injections of a first generation adenovirus-dystrophin minigene construct and adenovirus-beta-galactosidase construct as a 2:1 mixture into the left anterior tibial muscle. The spread of transgene expression within the anterior tibial muscle was compared with the spread of methylene blue dye after identical injection into the contralateral muscle. Transgene expression 5-7 days after intramuscular injection was shown to extend between 5.8 and 11.6 mm along the biopsied muscle length (range of biopsy lengths 11.1-12.2 mm). The level of transgene expression at 2-2.5-mm intervals from the site of injection was significantly related to the distance from the site of injection (dystrophin, P = 0.009; beta-galactosidase, P = 0.015). The spread of methylene blue dye within the anterior tibial muscle < or =24 h after identical intramuscular injection demonstrated a similar pattern to the transgene expression, with dye staining measured between 5.5 and 8.5 mm along the muscle sample length (range of biopsy lengths 5.6-15.6 mm). The greatest transgene expression and dye staining was measured 2-2.5 mm proximal to the site of injection with a maximum of 23% of muscle fibers expressing the dystrophin transgene, 95.2% expressing the beta-galactosidase transgene, and 98% of the tissue section stained with methylene blue dye. These results suggest transgene expression after focal intramuscular injection is relatively localized around the site of injection. Further research is required to develop techniques that will provide transgene expression throughout the length and breadth of a muscle.

The cellular uptake of anandamide is coupled to its breakdown by fatty-acid amide hydrolase.

Anandamide is an endogenous compound that acts as an agonist at cannabinoid receptors. It is inactivated via intracellular degradation after its uptake into cells by a carrier-mediated process that depends upon a concentration gradient. The fate of anandamide in those cells containing an amidase called fatty-acid amide hydrolase (FAAH) is hydrolysis to arachidonic acid and ethanolamine. The active site nucleophilic serine of FAAH is inactivated by a variety of inhibitors including methylarachidonylfluorophosphonate (MAFP) and palmitylsulfonyl fluoride. In the current report, the net uptake of anandamide in cultured neuroblastoma (N18) and glioma (C6) cells, which contain FAAH, was decreased by nearly 50% after 6 min of incubation in the presence of MAFP. Uptake in laryngeal carcinoma (Hep2) cells, which lack FAAH, is not inhibited by MAFP. Free anandamide was found in all MAFP-treated cells and in control Hep2 cells, whereas phospholipid was the main product in N18 and C6 control cells when analyzed by TLC. The intracellular concentration of anandamide in N18, C6, and Hep2 cells was up to 18-fold greater than the extracellular concentration of 100 nm, which strongly suggests that it is sequestered within the cell by binding to membranes or proteins. The accumulation of anandamide and/or its breakdown products was found to vary among the different cell types, and this correlated approximately with the amount of FAAH activity, suggesting that the breakdown of anandamide is in part a driving force for uptake. This was shown most clearly in Hep2 cells transfected with FAAH. The uptake in these cells was 2-fold greater than in vector-transfected or untransfected Hep2 cells. Therefore, it appears that FAAH inhibitors reduce anandamide uptake by cells by shifting the anandamide concentration gradient in a direction that favors equilibrium. Because inhibition of FAAH increases the levels of extracellular anandamide, it may be a useful target for the design of therapeutic agents.

Evaluation of a short interspersed nucleotide element in the 3' untranslated region of the defective dystrophin gene of dogs with muscular dystrophy.

OBJECTIVES: To determine the distribution of a 231-base pair (bp) element in the dystrophin gene 3' untranslated region (UTR) in a colony of Golden Retrievers with muscular dystrophy and other unrelated dogs and to estimate the frequency of recombination for the canine dystrophin gene. ANIMALS: 77 dogs from the Golden Retriever Muscular Dystrophy (GRMD) colony at the Murdoch Veterinary School and 30 unrelated dogs from the Murdoch University Veterinary Clinic. PROCEDURE: Samples of blood or hair from dogs were used for amplification of DNA, using primers to the canine dystrophin 3' UTR. RESULTS: The DNA from affected dogs generated a larger PCR product than that obtained from clinically normal dogs. Products were cloned and sequenced, and the difference in size was found to be attributable to a 231-bp short interspersed nucleotide element (SINE). The SINE was found in all affected dogs in the colony but not in most unaffected puppies in the colony. Eighteen of 19 dogs in the colony were heterozygous for the GRMD mutation, and 7 of 30 unrelated dogs also were heterozygous for the SINE. CONCLUSION AND CLINICAL RELEVANCE: Evidence of recombination between the GRMD mutation and the SINE was observed in only 4 dogs (2 sets of littermates) in the GRMD colony. Incidence of this SINE in a few unrelated dogs suggests that this particular insertion into the dystrophin gene may have been a recent event. The SINE in the dystrophin 3' UTR did not have an apparent influence on dystrophin mRNA concentrations.

Urinary retention resulting from incarceration of a retroverted, gravid uterus.

Urinary retention resulting from urethral obstruction by a retroverted, gravid uterus is an uncommon disorder that is reported only once in the Emergency Medicine literature. Yet these patients may present in extreme distress and precipitate considerable confusion regarding the cause of and solution to this problem. No study evaluating outcome, risk of complications, or therapy exists. We present two cases that clarify diagnostic and therapeutic controversies and provide a better understanding of what is known about the pathophysiology and treatment alternatives.

Gene therapy and molecular approaches to the treatment of hereditary muscular disorders.

Gene therapy for inherited muscle disease is an active area of research and development. Initial emphasis has been on gene replacement but alternative approaches are increasingly being considered in order to overcome difficulties, such as the immune rejection of transduced cells, the need for appropriate and tissue-specific control of expression, and the requirement for systemic spread in some conditions. However, the most significant obstacles to the clinical success of gene therapy are still the lack of efficiency and accuracy of gene medicine delivery.

The effect of sodium bicarbonate on propranolol-induced cardiovascular toxicity in a canine model.

STUDY OBJECTIVE: To evaluate the potential utility of sodium bicarbonate in an established model of acute propranolol toxicity. METHODS: Two minutes after the completion of a propranolol infusion (10 mg/kg), a bolus of 1.5 mEq/kg of sodium bicarbonate solution (1 mEq/mL) followed by an infusion of 1.5 mEq/kg over the next 26 minutes (n = 6) or an equivalent timing and volume of 5% dextrose solution (n = 6) was administered in each dog. Targeted cardiovascular parameters included heart rate, mean arterial pressure, left ventricular dP/dtmax, and QRS interval. RESULTS: Propranolol infusion significantly depressed heart rate (p < 0.0001), mean arterial pressure (p < 0.0001), dP/dtmax (p < 0.0001) and prolonged the QRS interval (p < 0.0001). Sodium bicarbonate failed to significantly improve these targeted parameters when compared to control animals. CONCLUSION: In this canine model of propranolol toxicity, intravenous sodium bicarbonate appears to be an ineffective single therapy. Furthermore, these results may suggest a different mechanism of sodium channel blockade for propanolol than that of type IA antiarrhythmic agents.

Acute beta blocker overdose: factors associated with the development of cardiovascular morbidity.

OBJECTIVE: To identify factors in exposures to beta blockers (beta-adrenergic receptor antagonists) that are associated with the development of cardiovascular morbidity and contribute to disposition decisions from the emergency department. METHODS: Prospective cohort of 280 beta blocker exposures reported to 2 regional poison centers. Multiple logistic regression was used to determine association of various clinical factors and outcome. RESULTS: In this series of beta blocker exposures, 41 (15%) developed cardiovascular morbidity and 4 (1.4%) died. A history of cardioactive coingestant was the only factor significantly associated with the development of cardiovascular morbidity (p < .05). When cases reporting cardioactive coingestants were excluded, a history of ingesting a beta blocker with membrane stabilizing activity was significantly associated with the development of cardiovascular morbidity (p < .05). All those in whom the timing of symptoms could be determined, developed symptoms within 6 hours of ingestion. CONCLUSIONS: The single most important factor associated with the development of cardiovascular morbidity in beta blocker ingestion is a history of a cardioactive coingestant, primarily calcium channel blockers, cyclic antidepressants, and neuroleptics. In the absence of such coingestion, exposure to a beta blocker with membrane stabilizing activity is associated with an increased risk of cardiovascular morbidity. Beta blocker ingestion is unlikely to result in symptoms if the patient remains asymptomatic for 6 hours after the time of ingestion.

Myophosphorylase gene transfer in McArdle's disease myoblasts in vitro.

McArdle's disease is due to a genetic deficiency of glycogen phosphorylase and results in a lack of glucose mobilization from glycogen during anaerobic exercise. A genetic defect in Merino sheep produces a similar picture. We constructed a first-generation adenoviral recombinant containing the full-length human phosphorylase cDNA under the control of the Rous sarcoma virus promoter. Primary myoblast cultures from phosphorylase-deficient human and sheep muscle were efficiently transduced with this vector, resulting in restoration of the phosphorylase activity. A similar correction of the genetic defect in muscles of McArdle's patients in vivo appears feasible, preferably with the use of an adeno-associated viral vector.

Development of a snapback method of single-strand conformation polymorphism analysis for genotyping Golden Retrievers for the X-linked muscular dystrophy allele.

OBJECTIVE: To develop a snapback method of single-strand conformation polymorphism (SSCP) analysis for genotyping Golden Retrievers for the X-linked muscular dystrophy allele. ANIMALS: 20 Golden Retriever puppies from a colony with X-linked muscular dystrophy. PROCEDURE: DNA spanning the canine dystrophin mutation was amplified by means of a polymerase chain reaction (PCR), using a primer modified to have an additional sequence at the 5' terminus. The primer was designed so that 1 terminus of the single-stranded PCR product could anneal to the normal sequence flanking the region of the mutation in the allele but not in the mutant allele. True disease status of the dogs was determined by means of a PCR and restriction digest protocol. RESULTS: Snapback SSCP analysis allowed for accurate and unambiguous genotyping of unaffected, carrier, and affected dogs, whereas conventional SSCP analysis, using the unmodified primer, did not. Creatine kinase activities measured within 24 hours after birth were not consistent with genotype. CONCLUSION AND CLINICAL RELEVANCE: Snapback SSCP analysis provided a simple, fast, and accurate method for genotyping Golden Retrievers for the mutation known to cause X-linked muscular dystrophy.

Is there a future for gene therapy?

The requirements for successful gene therapy are stated and brief details are given of the gene therapy trials in humans which have been approved by the NIH during the years 1989-1997. An indication is given of the gene therapy trials that have been carried out in animal models of Duchenne muscular dystrophy with emphasis on the Golden Retriever dog model. Problems facing somatic gene therapy for inherited muscle diseases are predominantly the following: the extent of the spread of expression from the injection site, the duration of expression and the need for systemic delivery. Brief details of the problems are given and possible ways of overcoming the difficulties are outlined. These include the use of multiple intramuscular injections, increasing the permeability of the extracellular matrix of muscle, inducing mitosis in myoblasts, the use of ex vivo gene transfer, using modified viruses as vectors or synthesized transporter molecules, the use of mechanisms which combat the action of killer T cells, upregulation of isoforms or of alternative proteins such as utrophin for dystrophin and the use of genetic correction methods such as the use of antisense oligonucleotides. It is concluded that there is a potential future for somatic gene therapy in the inherited muscle diseases.

Follow-up compliance in febrile children: a comparison of two systems.

OBJECTIVES: Follow-up compliance is critical in febrile children because they may harbor unrecognized life-threatening illnesses. This study compares follow-up rates between 2 systems: Wilford Hall Medical Center (WHMC), with preset appointments after ED release, and free medical care; and Fairfax Hospital (FFX), where parents must arrange follow-up appointments after ED release, and are responsible for payment for their follow-up visits. The study also investigated factors associated with follow-up compliance. METHODS: This was a prospective, observational study of febrile children seen in 2 EDs with different systems for patient follow-up. From ED records and parental phone calls, diagnosis, follow-up compliance, and demographics were collected. Data were analyzed using logistic regression and chi2. RESULTS: 423 children met entrance criteria, and 330 parents were successfully contacted after the child's ED release (146 from WHMC; 184 from FFX). The WHMC children were more likely to comply with follow-up than were the children in the FFX system (92% vs 67% follow-up, odds ratio 2.5, 95% CI 1.1-5.3). Other factors associated with noncompliance with recommended follow-up were: Hispanic ethnicity, non-English-speaking parents, and follow-up suggested for >24 hours after ED release. For FFX, self-pay, lack of a follow-up physician, parents' dissatisfaction with the ED medical care, and diagnosis of otitis media were also significant factors found associated with noncompliance. CONCLUSION: Febrile children evaluated in a medical system with prearranged follow-up appointments and free medical care are more likely to comply with recommended follow-up than are those evaluated in a system where payment and appointments are the responsibility of the parents. Efforts should be made to improve follow-up compliance by modeling the WHMC system.

Modulation of immune system function by measles virus infection: role of soluble factor and direct infection.

Measles virus infection can result in a variety of immunologic defects. We have begun studies to determine the basis for the lack of immune responsiveness to antigen and mitogen following infection. Here we present data showing that Epstein-Barr virus-transformed B-cell lines infected with measles virus produce a soluble factor that can inhibit antigen-specific T-cell proliferation and inhibit the proliferation of uninfected B cells. The soluble factor was neither interleukin-10, transforming growth factor beta, nor alpha/beta interferon. B cells infected with measles virus or treated with the soluble factor were unable to present antigen to T cells in a manner that supported antigen-specific proliferation. This could represent one mechanism of how measles virus limits T-cell expansion. However, we found that once CD4(+) or CD8(+) T cells were activated, their cytolytic activity was intact whether infected with measles virus or treated with soluble factor. Thus, while slow to be generated these cytoxic cells could participate in viral clearance.

Suppression of antigen-specific T cell proliferation by measles virus infection: role of a soluble factor in suppression.

Measles virus infection causes a profound immunosuppression. The basis for this immunosuppression is not known. This immunosuppression could be due to virus acting directly on lymphoid cells, the production of an immunosuppressive viral product, or a lymphoid product. We have developed an antigen-specific T cell system to study measles virus-T-cell interactions. We demonstrate that as few as five infectious viral particles added to 1000 T cells results in profound inhibition of antigen-specific T cell proliferation. Supernates taken from measles virus-infected T cells suppress the proliferation of uninfected T cells. Measles-virus-infected HeLa or Vero cells do not produce the factor. The antiproliferative effects of the supernates cannot be attributed to infectious virus, IL-10 or TGF-beta. The soluble factor appears to be larger than 100 kDa, yet retains antiproliferative activity following trypsin digestion with a size less than 10 kDa. Loss of activity is seen following heat treatment at 56 degrees C. The factor is lymphoid cell specific and exhibits cytokine-like behavior yet appears not to be a known cytokine. This soluble factor may be responsible for the overt clinical immunosuppression seen in man and a previously undescribed cytokine induced by measles virus infection of human lymphocytes.

A potential role for glucagon in the treatment of drug-induced symptomatic bradycardia.

Nine cases of symptomatic bradycardia are presented in which treatment with intravenous glucagon was administered when atropine failed to improve the patient's condition significantly. Although the cause often was not obvious at presentation, all nine subjects took oral medications that could have contributed to the development of symptomatic bradycardia. Eight of nine patients demonstrated clinical improvement 5 to 10 min after glucagon administration, which was consistent with its peak clinical action. Beta-blockers, calcium channel blockers, and digoxin were ultimately thought to have contributed to the majority of these presentations. This report suggests that glucagon may have a role in the treatment of symptomatic bradycardia, particularly in the presence of beta-adrenergic blockade and perhaps calcium channel blockade. Furthermore, the results in these cases suggest that future clinical trials should not be limited to drug-induced symptomatic bradycardia.

High-level dystrophin expression after adenovirus-mediated dystrophin minigene transfer to skeletal muscle of dystrophic dogs: prolongation of expression with immunosuppression.

Replication-deficient adenovirus vectors (AdV) have been successfully used to transfer a truncated human dystrophin cDNA to skeletal muscle of dystrophin-deficient mdx mice. A dystrophin-deficient golden retriever dog model (GRMD) has been identified, which, unlike the mouse model, leads to a clinicopathological phenotype similar to that of Duchenne muscular dystrophy (DMD). We show for the first time that high-level dystrophin expression in skeletal muscle of GRMD dogs can be achieved by AdV-mediated gene transfer. However, a humoral and cellular immune response of the host against antigens of viral and transgene origin (similar to that occurring in mdx mice after AdV-mediated dystrophin gene transfer) leads to a decline of dystrophin expression over a 2-month period. Immunosuppression by cyclosporin significantly prolonged transgene expression. The GRMD model may help to solve the open questions pertaining to dystrophin gene transfer such as systemic delivery and improvement of muscle function before human trials for gene replacement therapy in DMD may be considered.