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.

T-ceIl recognition of discrete regions of the thrombolytic drug streptokinase

Streptokinase (SK) is a bacterial protein used clinically as a thrombolytic agent in humans. Administration of SK causes a rapid increase in the frequency of anti-SK T cells and the titre of specific anti-SK antibodies that, on subsequent administration of SK, may neutralize the activity of the drug or elicit allergic-type reactions. By locating and modifying the immunogenic T-cell epitopes within the SK protein, it is possible that an agent with reduced immunogenicity but equal efficacy may be produced. We have investigated the T-cell epitopes within SK using nine non-overlapping, recombinant peptide fragments of SK. We investigated the proliferative T-cell response of peripheral blood mononuclear cells obtained from patients before and 6 days after administration of SK for myocardial infarction. We also examined the response of cultured anti-SK T-cell lines derived from patients 6 days after treatment with SK. Before administration of SK, peripheral blood mononuclear cells from six of nine patients showed a proliferative response to SK. The response was significantly higher 6 days after administration of SK (P = 0.0004). Cultured T-cell lines showed similar proliferative responses to clinical-grade SK and recombinant SK. Marked differences in T-cell responses were apparent in response to each recombinant SK fragment (P = 0.04). The mean proliferative response exceeded background to only two peptides, peptide 2 (P = 0.04) and peptide 3 (P = 0.009). Peptide 3, representing amino acids 100-150 of mature SK, was recognized preferentially in the majority of assays. Marked variation in the T-cell response to SK following treatment with this agent was observed between subjects. Despite these differences, peptides 2 and 3 induced T-cell proliferation at a level significantly above background in the majority of subjects. These epitopes may represent a region of enhanced immunogenicity within SK.

Snapback SSCP analysis: engineered conformation changes for the rapid typing of known mutations

Several approaches may be applied to detect known mutations, including restriction enzyme cleavage, allele-specific oligonucleotide (ASO) hybridization or amplification, dideoxy fingerprinting, and direct DNA sequencing. All these approaches require several extra steps after PCR and may involve radioactive isotopes, time-consuming hybridization, template purification, or digestion steps. The ease and simplicity of the SSCP test make it a popular choice for mutation detection, but a significant limitation is that some DNA changes will not alter the overall conformation of either single strand and are thus not amenable to SSCP typing. We describe Snapback SSCP to genotype normal and mdx mice (an animal model of Duchenne muscular dystrophy) that previously could not be differentiated by conventional SSCP analysis. A snapback primer was designed with additional bases at the 5' terminus, which were complementary to the normal sequence flanking the mdx mutation and used under the original amplification conditions. Each single strand of these snapback PCR products now had one terminus capable of re-annealing or "snapping back" to the normal sequence but not the mdx mutation. In this manner, a conformation change was engineered into the normal strand that could be readily distinguished from the mdx allele on a SSCP gel. This approach could be applied to the routine screening of other known mutations that are not amenable to detection by simple SSCP analysis.

Cardiovascular disease and outcome of acute stroke: influence of pre-existing cardiac failure

BACKGROUND AND AIMS

Whilst a number of variables, mostly a consequence of a stroke, are known to predict mortality of acute stroke there is limited information on the significance of pre-existing cardiovascular variables on stroke mortality. We have investigated the influence of pre-existing cardiovascular factors in one cohort of stroke patients.

METHODS

We studied 295 patients, mean age 74+/-10 (range 34-96) years; 133 males, presenting with acute stroke for pre-existing cardiovascular disease (CVD) defined as hypertension, atrial fibrillation (AF), ischaemic heart disease (IHD) and cardiac failure (CF). In addition, data were collected on epidemiological and neurological variables known to influence stroke mortality. The most significant of the cardiovascular factors was further investigated against all the other cardiovascular groups together and against those without any CVD. Outcome was measured as their influence on acute phase and 3-month mortality.

RESULTS

There was no significant difference in 3-month mortality with hypertension (P=0.62) and IHD (P=0.33) but there was a significant higher mortality in patients with AF (P=0.05) and CF (P <0.001). CF was more significant than all other CVD (hypertension+AF+IHD) together without the failure (P<0.001); odds ratio of 4.5 (95% CI 2.28-9.07). Partial correlation coefficient revealed CF to be an independent significant variable to influence stroke mortality when controlled with AF, stroke syndromes, age, incontinence, pyrexia, dysphagia and Glasgow coma score.

CONCLUSIONS

Pre-existing CF has an adverse influence on stroke mortality independent of other known factors. Cardiovascular factors without failure do not have such an effect except the marginal effect of AF.

Improving outcome for the injured brain and spinal cord

Although injury to the brain and spinal cord can have varied etiology and mechanisms, the common pathway appears to be mediated by occurrence of ischemia and secondary injury. Because the pathophysiology in traumatic brain injury is heterogeneous, improvement in outcome will come from better diagnosis and monitoring, so that targeted therapy can be tailored to the individual patient. This review focuses on traumatic injury to the brain and spinal cord, and highlights recent developments in this area.

Prompt Optical Observations of Gamma-Ray Bursts

The Robotic Optical Transient Search Experiment (ROTSE) seeks to measure simultaneous and early afterglow optical emission from gamma-ray bursts (GRBs). A search for optical counterparts to six GRBs with localization errors of 1 deg2 or better produced no detections. The earliest limiting sensitivity is mROTSE>13.1 at 10.85 s (5 s exposure) after the gamma-ray rise, and the best limit is mROTSE>16.0 at 62 minutes (897 s exposure). These are the most stringent limits obtained for the GRB optical counterpart brightness in the first hour after the burst. Consideration of the gamma-ray fluence and peak flux for these bursts and for GRB 990123 indicates that there is not a strong positive correlation between optical flux and gamma-ray emission.

Factors influencing maternal behavior in the hubb/hubb mutant mouse

We examined the maternal behavior of hubb/hubb mutant mice and normal control (+/hubb) siblings. From previous observations we noted that mutants groom their pups less, suckle less than normal, and often cannibalize the young. To date, these observations had not been quantified. Although prolactin (PRL) is linked to maternal behavior, it was difficult to measure because of the hyperirratibility of the mutant mice. Consequently, dopamine (DA) and its metabolite, dihydroxyphenylacetic acid (DOPAC), were measured in the median eminence in brains of both normal and mutant mice. Tyrosine hydroxylase, the rate-determining step in dopamine synthesis, was localized in the brain by immunohistochemistry. Five mutant and nine normal dams were observed for pup retrieval and crouching. Mean time for pup retrieval was slower (p < 0.06) for mutants (28.09 s) than for normal dams (18.49 s). Crouching was the same for both strains. Mutant pups were cold to the touch, and not well groomed. Brains from both strains were examined at Day 11 and Day 18 of gestation and Day 2 and Day 11 of lactation. Qualitatively, tyrosine hydroxylase localization in the arcuate nucleus and median eminence was the same in both strains for the gestation samples. The decrease in staining observed from gestation to lactation in the normal mice was increased in the mutants. Dopamine was similar in both strains at all stages, but DOPAC was significantly higher at early lactation in the mutants. We do not assume an absolute inverse relationship between dopaminergic activities and prolactin, but it is likely that the increase in DOPAC in the mutant reflects a decrease in prolactin, which could contribute to the diminished maternal care in the mutants.

Parallel syntheses of disulfide inhibitors of the thioredoxin redox system as potential antitumor agents

We have reported previously that unsymmetrical disulfide inhibitors of the human thioredoxin/thioredoxin reductase redox system (hTrx/TR) possess antitumor activity. We have broadened the search for more potent inhibitors and evaluated a large range of mono- and bis-disulfide compounds, prepared using parallel syntheses. Reaction of isothioisourea-HCI salts (R') or bis-salts (R) with aromatic or aryl thiols (R") in wells of 96-well plates produced >450 derivatives with the structures R"SSR' and R"SSRSSR". The excellent yield and purity of the disulfides provided sufficient material for evaluations of enzyme inhibition and cytotoxicity. Selection criteria based on the IC50 values for hTrx/TR inhibition and for cytotoxicities of the disulfides identified agents for subsequent scale-up syntheses and in vivo evaluations of antitumor activity. These scale-up studies confirmed the original activities of agents synthesized in the plates and validated the parallel synthetic approach. Structure-activity information derived from the hTrx/TR IC50 data allow for a number of generalizations. The most potent inhibitors of the Trx system contained two heteroatoms ortho to the disulfide moiety in an aromatic functionality. The thioalkylating moieties had greatest activity with one branch point alpha to the disulfide. In the absence of branching, more potent inhibition was observed with the electron withdrawing functionalities. Bis-disulfides showed patterns of activity which depended on chain length, with optimum activity observed when the disulfide units were separated by 3.9 A, a similar distance to that separating the thioredoxin active site cysteine residues. From the agents selected for scale-up syntheses, three disulfide compounds were studied for their antitumor activity in vivo against human tumor xenografts in scid mice. One of the analogues discovered through the combinatorial syntheses/screening for Trx inhibition, 1-phenylethyl 2-imidazolyl disulfide, N1 (ProlX agent PX-C5), has demonstrated excellent in vivo activity against the MCF-7 human breast cancer and the HL-60 human leukemia, thus validating this approach for novel drug discovery.

Humoral and cellular immune responses up to 7.5 years after administration of streptokinase for acute myocardial infarction

AIMS

Administration of streptokinase results in an immunological response which may lead to increased risk of anaphylactic reaction or reduced thrombolytic efficacy on repeat administration. For these reasons current recommendations suggest that streptokinase should not be given up to 1 year after first administration. We sought to define the profile of both the circulating antibody and T-cell response to streptokinase in patients who had received streptokinase up to 7.5 years previously following acute myocardial infarction.

METHODS

Neutralizing anti-streptokinase antibody and total anti-streptokinase IgG were measured in 219 patients who had suffered acute myocardial infarction between 12 and 90 months previously and had received streptokinase. T-cell response to streptokinase was assessed by in-vitro proliferation of peripheral blood mononuclear cells (n=234). Data on all parameters were available in 184 patients. Controls (n=22) had suffered acute myocardial infarction between 73 and 84 months previously but had not received thrombolytic therapy.

RESULTS

Compared to controls, anti-streptokinase antibodies were elevated at all time periods from 12 to 90 months after streptokinase treatment. Total anti-streptokinase titres showed the expected correlation with neutralizing anti-streptokinase antibodies (P<0.0001). Peripheral blood mononuclear cells showed a vigorous in-vitro proliferative response to streptokinase 6 days after treatment (P=0.05 vs pre-treatment), but this was not detectable at 6 weeks or subsequently.

CONCLUSION

There is as yet no evidence of a time limit beyond which administration of streptokinase on a second occasion can be regarded as safe and likely to be effective. Measurement of neutralizing anti-streptokinase or total anti-streptokinase IgG titre appear to provide equivalent information regarding the antibody status of a population. Further studies are required regarding the apparent lack of peripheral blood mononuclear cells responsiveness in patients previously exposed to streptokinase.

Autoradiographic localization of the [3H]-(S)-zacopride labelled 5-HT3 receptor in porcine brain

Using the technique of in vitro receptor autoradiography, we have determined the distribution of the [3H]-(S)-zacopride labelled 5-HT3 receptor in porcine brain. Highest densities of 5-HT3 receptor-associated [3H]-(S)-zacopride binding were detected in areas of porcine spinal cord, nodose ganglion, trigeminal nerve nucleus, area postrema and cerebral cortex, with relatively lower levels in other brain regions (e.g. hippocampus, caudate-putamen). The distribution of [3H]-(S)-zacopride binding in porcine forebrain provides further evidence for inter-species differences with respect to the differential expression of the 5-HT3 receptor in the forebrain.

Specific removal of the nonsense mutation from the mdx dystrophin mRNA using antisense oligonucleotides

The mdx mouse, which carries a nonsense mutation in exon 23 of the dystrophin gene, has been used as an animal model of Duchenne muscular dystrophy to evaluate cell or gene replacement therapies. Despite the mdx mutation, which should preclude the synthesis of a functional dystrophin protein, rare, naturally occurring dystrophin-positive fibres have been observed in mdx muscle tissue. These dystrophin-positive fibres are thought to have arisen from an exon-skipping mechanism, either somatic mutations or alternative splicing. Increasing the frequency of these fibres may offer another therapeutic approach to reduce the severity of Duchenne muscular dystrophy. Antisense oligonucleotides have been shown to block aberrant splicing in the human beta-globin gene. We wished to use a similar approach to re-direct normal processing of the dystrophin pre-mRNA and induce specific exon skipping. Antisense 2'-O-methyl-oligoribonucleotides, directed to the 3' and 5' splice sites of introns 22 and 23, respectively in the mdx pre-mRNA, were used to transfect myoblast cultures. The 5' antisense oligonucleotide appeared to efficiently displace factors normally involved in the removal of intron 23 so that exon 23 was also removed during the splicing of the dystrophin pre-mRNA. Approximately 50% of the dystrophin gene mRNAs were missing this exon 6 h after transfection of primary mdx myotubes, with all transcripts showing skipping of exon 23 after 24 h. Deletion of exon 23 does not disrupt the reading frame and should allow the synthesis of a shorter but presumably functional Becker-like dystrophin. Molecular intervention at dystrophin pre-mRNA splicing has the potential to reduce the severity of a Duchenne mutation to the milder Becker phenotype.

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.

Strokes in the elderly - higher acute and 3-month mortality - an explanation

AIM

Stroke is common in older people. The objective of the study was to determine if older stroke patients have a higher mortality and disability compared with younger patients for comparable stroke severity and pathology and whether there is an explanation for the difference.

METHODS

A prospective study was undertaken in 296 consecutive patients admitted with acute stroke. Patients were studied for neurological features, pre-stroke functional disability, severity of stroke defined by stroke syndromes and pathology of stroke on CT scans (202 patients). Post-stroke disability was defined according to the functional status within 72 h of admission. A record was made of the intercurrent illness while the patients were in acute wards and of the risk factors. Patients were dichotomized into two age groups: younger group - up to 75 years (163 patients) and older group - over 75 years (133 patients). Outcome was measured according to (1) discharge status from acute wards, i.e., dead or alive, and (2) mortality at 3 months.

RESULTS

Although there was no significant difference in severe clinical stroke syndromes (p = 0.72), CT scan features (p = 0.68) and pyrexia (0.38) between the two age groups, the older patients had significantly more disabling strokes as defined on Barthel Index (p = 0.015) and a higher mortality in the acute phase (p < 0.01) and at 3 months (p = 0.001). The older stroke patients had more severe pre-stroke disability (p < 0.001) and more severe neurological impairment for similar stroke severity and pathology. Early mortality was more influenced by pre-stroke global health than age whereas 3-month mortality was influenced by age to the exclusion of all other known prognostic factors.

CONCLUSION

The older stroke patients have more disabling stroke and an increased mortality for a similar spectrum of stroke severity and pathology. The explanation for higher mortality of the older patients is the poor pre-stroke health and higher immediate post-stroke disability.

Assessment of ultrasound guided percutaneous ethanol injection and parathyroidectomy in patients with tertiary hyperparathyroidism

BACKGROUND

Tertiary hyperparathyroidism continues to cause significant morbidity in patients with chronic renal failure. This is frequently resistant to medical management and may ultimately require a surgical parathyroidectomy. Recent studies have reported upon the technique of percutaneous ethanol ablation for both primary and tertiary hyperparathyroidism. In this study we report on a 5 year experience using ethanol injection and compare the results with surgical parathyroidectomy.

METHODS

A prospective study in 39 patients with tertiary hyperparathyroidism, 25 were dialysis dependent and 14 had a functioning renal allograft. Twenty-two patients underwent percutaneous fine needle ethanol injection (PFNEI) and 17 underwent surgical parathyroidectomy.

RESULTS

A > 30% reduction in intact parathyroid hormone (iPTH) was achieved in 11 of 22 patients undergoing PFNEI after a mean of 1.8 +/- 1.4 injections per gland. In four patients, symptomatic hyperparathyroidism recurred and they required further PFNEI or surgical parathyroidectomy at 17, 28, 46, and 48 months later. There was no significant reduction in iPTH in 11 patients following PFNEI after a mean of 2.5 +/- 1.3 injections per gland. They all required a subsequent surgical parathyroidectomy for symptomatic hyperparathyroidism. Four patients developed a laryngeal nerve palsy following PFNEI, two of which were permanent. Seventeen patients underwent successful surgical parathyroidectomy as a primary procedure.

CONCLUSION

Whilst PFNEI is successful in primary hyperparathyroidism, when typically only one adenoma is present, the effectiveness of PFNEI is unpredictable and the long term results are poor compared with those of surgical parathyroidectomy in tertiary hyperparathyroidism. The procedure is not without complications and makes subsequent surgery more difficult. Therefore it can only be recommended for patients with a known single parathyroid gland such as patients in whom hyperparathyroidism has recurred following a previous surgical subtotal parathyroidectomy and who are unsuitable for further surgery.

Evidence that porcine native 5-HT3 receptors do not contain nicotinic acetylcholine receptor subunits

The present investigation utilised monoclonal antibodies directed against subunits of the nicotinic acetylcholine receptor in immunoblot and immunoprecipitation studies, which failed to demonstrate that the native 5-hydroxytryptamine3 (5-HT3) receptor complex purified from porcine brain contains the alpha1, alpha3, alpha4, alpha5, alpha7 or beta2 subunits of the nicotinic acetylcholine receptor.

Desperately seeking subunits: are native 5-HT3 receptors really homomeric complexes?

The 5-HT3 receptor complex is a ligand-gated ion channel, and is therefore likely to comprise multiple subunits in common with other members of this superfamily. To date, however, only one 5-HT3 receptor subunit, plus an alternatively spliced variant, have been identified. In this article, Stephanie Fletcher and Nicholas Barnes review some of the extensive data in the literature that suggest the presence of other 5-HT3 receptor subunits. This is particularly relevant given the recent demonstration that the 5-HT3 receptor purified from pig brain contains a non-5-HT3A-like protein(s).

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.