Expression of a mutation causing hypertrophic cardiomyopathy disrupts sarcomere assembly in adult feline cardiac myocytes

Mutations in the beta-myosin heavy chain (beta MyHC) induce hypertrophic cardiomyopathy (HCM), cardiac hypertrophy, and sarcomere disarray, with the latter being the characteristic hallmark. Thus, we sought to determine whether expression of mutant beta MyHC in adult feline cardiac myocytes, a species known to develop HCM with a phenotype identical to that in humans, induces sarcomere disarray. A full-length beta MyHC cDNA was cloned from a human heart cDNA library, and an HCM-causing mutation (Arg403Gln) was induced in the beta MyHC cDNA by site-directed mutagenesis using polymerase chain reaction (PCR). The normal and mutant beta MyHC cDNAs were cloned into p delta E1spIB shuttle vector, downstream from a cytomegalovirus (CMV) promoter. Replication-deficient recombinant adenoviral constructs (Ad5/CMV/beta MyHC-N and Ad5/CMV/beta MyHC-403) were generated through homologous recombination of p delta E1spIB/CMV/beta MyHC-N or Ad5/CMV/beta MyHC-403 and pBHG10 after cotransfection in 293 host cells. Infection of COS-1 cells with the beta MyHC construct resulted in the expression of a full-length myosin protein. Efficiency of infection of isolated adult cardiac myocytes was > 95%. Expression of the beta MyHC constructs into mRNA at 48 hours after infection of feline cardiac myocytes was confirmed by reverse transcription-PCR. The net total protein and beta-myosin synthesis were determined by using the amount of incorporation of [3H]phenylalanine into total protein and beta-myosin, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Early discharge after acute myocardial infarction: risks and benefits

BACKGROUND

Thrombolytic treatment reduces mortality in patients with acute myocardial infarction but is associated with recurrent thrombotic events after admission, and it is unclear whether current practices of early hospital discharge are safe. Timing of first major adverse events (death, reinfarction, unstable angina, secondary ventricular fibrillation) in the early post-infarction period was studied to determine the risks.

DESIGN

Follow up study.

PATIENTS

608 consecutive patients (447 men and 161 women) with confirmed myocardial infarction who were admitted to the coronary care unit of a district general hospital between January 1989 and December 1991. Clinical details, including the development of left ventricular failure and in hospital adverse events, were recorded prospectively. Follow up for out of hospital adverse events was carried out by review of the case notes, postal questionnaire, and where necessary, by telephone contact with the patient and his general practitioner.

RESULTS

The risk (95% confidence interval) of major adverse events in the first 10 days was 32.3% (26.3 to 39.4%) in patients with heart failure and 7.3% (5.1 to 9.2%) in those without. Smoothed estimates of the event rate in patients without heart failure decreased from 5.9 events/1000 persons/day on day 6 to 3.4 events/1000 persons/day on day 10 and 0.9 events/1000 persons/day on day 21. The corresponding cumulative risk estimates suggest that about 11 in every 1000 patients suffer a major, but often unpreventable, adverse event on day 6 or 7 after admission, and 23 in every 1000 do so between days 6 and 10.

CONCLUSIONS

The point at which the risk to the individual becomes acceptably low is a matter of judgement, but the risk of a major adverse event declines rapidly after a heart attack, and particularly for patients without heart failure discharge within a few days may be appropriate. Prolonging stay unnecessarily may use resources which could be more effectively used to treat cardiac disease in other ways.

Genomic organization of the human dystrophin gene across the major deletion hot spot and the 3' region

The genomic organization of most of the human dystrophin gene has not been defined at single-exon level, owing to its enormous size (2300 kb). By taking advantage of a YAC-based restriction map of the gene previously constructed, we have localized individual dystrophin exons from 42 to 79 along the central and 3' regions of the gene. These data elucidate the general organization of this large portion of the gene (1250 kb) and, in particular, characterize the genomic region most frequently involved in deletion mutations responsible for Duchenne and Becker muscular dystrophies.

Molecular and clinical aspects of inherited cardiomyopathies

Hypertrophic cardiomyopathy (HCM) is phenotypically and genotypically a heterogeneous disease. Since 1989, four chromosomal loci have been identified for HCM and the genes residing on three of these have been identified as beta-myosin heavy chain (beta-MHC), cardiac troponin-T and alpha-tropomyosin. These genes code for sarcomeric proteins and exhibit the same phenotype, suggesting that HCM is a disease of the sarcomere. Over 40 missense mutations and one deletion of the beta-MHC gene have been identified. Similarly, missense mutations in the alpha-tropomyosin gene and the cardiac troponin-T gene have been identified. From genetic studies, including de novo mutations, it is established that these mutations are indeed responsible for HCM. The molecular basis of the pathogenesis of the cardiac hypertrophy appears to be a compensatory response to the primary defect. In addition to providing a definitive presymptomatic diagnosis, studies correlating beta-MHC mutations with clinical prognosis suggest they have significant predictive value and can be helpful in genetic counselling and medical management. Dilated cardiomiopathies (DCM), the most common form of cardiomyopathies, have an estimated prevalence of nearly 40 per 100,000 individuals, and are the most common cause for cardiac transplantation in the United States. Familial dilated cardiomyopathy is thought to account for approximately 20% of the so-called cases of idiopathic DCM.

Angiotensin-I converting enzyme genotype DD is a risk factor for coronary artery disease

BACKGROUND

Coronary artery disease (CAD) is a polygenic disease whose phenotypic manifestation is due to interaction of a number of environmental factors with an underlying genetic background. A number of genes, including the angiotensin-I converting enzyme (ACE) gene, have been implicated in the pathogenesis of CAD. ACE can affect oxidation of LDL, endothelial cell function, and smooth muscle cell migration and proliferation: all important components of atherosclerosis. A variant of ACE gene, genotype DD is associated with a higher plasma level of ACE and an increased risk of myocardial infarction, and cardiomyopathies. In this study, we sought to determine the distribution of ACE genotypes and the frequency of allele D in patients with CAD undergoing coronary angioplasty.

METHODS

DNA from 182 white patients undergoing coronary angioplasty and 338 apparently healthy white individuals was amplified by polymerase chain reaction (PCR) in the region of the polymorphism using the previously published protocol.

RESULTS

PCR amplification of alleles I and D resulted in 490 bp and 190 bp products, respectively. ACE genotype DD was present in 47% of patients with CAD as compared to 30% in the general population (p = 0.0002, Odds ratio 2.7). The frequency of allele D was 0.68 in patients with CAD and 0.55 in general population, respectively (p < 0.0001). Genotype DD was associated with CAD only in males (54% vs. 30%, p = 0.0001, Odds ratio 2.0), but not in female patients. There was no association between the frequency of ACE genotype DD and the prior history of myocardial infarction, or the extent of CAD. The frequency of ACE genotype DD was the highest among patients with restenosis following angioplasty (55%), however, the difference was not significantly changed as compared to those without restenosis (40%).

CONCLUSIONS

ACE genotype DD is more common in patients with CAD as compared to the general population, indicating that genotype DD is a genetic risk factor for CAD.

Cor triatriatum: unusual cause of transient ischaemic attacks in a 67-year-old man

Cor triatriatum is a rare congenital cardiac malformation, and in its most common form is characterised by a membrane that separates the left atrium into a proximal and distal chamber. First manifestation in adulthood has been reported previously, but at 67 years of age this patient is one of the oldest to present for the first time. It was diagnosed after a probable TIA, episodic vertigo and central retinal artery occlusion. The value of echocardiography in patients with neurological disease of presumed embolic origin is demonstrated here.

Sudden cardiac death in hypertrophic cardiomyopathy. Variability in phenotypic expression of beta-myosin heavy chain mutations

BACKGROUND

Recent identification of mutations in the beta-myosin heavy chain gene (MYH7), a major responsible gene for HCM, has provided the opportunity to characterize genotype-phenotype correlation in HCM families. In this study we analysed the phenotypic expression of two beta-myosin heavy chain (beta MHC) mutations in three unrelated HCM families.

METHODS

Living individuals from three unrelated HCM families (Families 1, 2, and 3) were screened by history, physical examination, electrocardiography, and two-dimensional echocardiography. Blood was collected from all individuals for DNA extraction. Polymerase chain reaction (PCR), restriction endonuclease digestion and chemical cleavage were utilized for detection of mutations. All mutations were confirmed by sequence analysis.

RESULTS

Identification of mutations: A missense mutation in exon 13 of the beta MHC gene (Arg403 Gln) was detected in HCM patients from Families 1 and 2. PCR amplification of the exon 13 DNA, followed by Ddel digestion of the PCR product and gel electrophoresis, showed two fragments of 84 and 70 bp in normal individuals and four fragments of 84, 70, 52 and 32 bp in HCM patients. Sequence analysis showed substitution of an adenine for guanine at coding position 1208. In Family 3, a missense mutation in exon 16 of the beta MHC gene (Val606 Met) was detected in HCM patients. Chemical cleavage of the PCR products showed an uncleaved product of 337 bp in the normal individuals, while in the affected individuals, in addition to the uncleaved product, a 90 bp cleaved product was also detected, indicating the presence of a mismatch in one allele. Sequence analysis showed substitution of an adenine for guanine in coding position 1817.

CLINICAL CHARACTERISTICS

Seven members of Family 1 had HCM, of whom five are alive. One patient died from sudden cardiac death (SCD) and another from recurrent cerebral emboli. In Family 2, 15 individuals had HCM of whom nine have died, seven from SCD. The mean age at the time of SCD was 33 years. The third family is comprised of 11 affected individuals and one obligate carrier, of whom one patient died at age 17 from progressive heart failure. Two additional individuals in this family have also succumbed to SCD to age 60. A variety of clinical and echocardiographic manifestations of HCM were present in each family. Logrank test of Kaplan-Meier survival curves indicates that Arg403 Gln mutation was associated with a poor prognosis in HCM families as compared to Val606 Met (P = 0.034).

CONCLUSIONS

beta MHC mutations despite showing variable clinical and echocardiographic manifestations of HCM are predictors of survival in HCM families.

Molecular genetics of hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is genetically and phenotypically a heterogeneous disease. Genes identified include the beta myosin heavy chain gene (beta MHC) on chromosome 14q1, the troponin T gene on chromosome 1q, and the alpha tropomyosin gene on chromosome 15q. In addition, a fourth locus is present on chromosome 11q11, but the gene remains to be identified. More than 35 missense mutations in the beta MHC, 3 mutations in troponin T, and 2 mutations in alpha tropomyosin gene in HCM patients have been identified. Functional studies have shown that the mutant beta MHC protein has impaired actomyosin interaction and that expression of the mutant myosin disrupts the assembly of sarcomere in feline cardiocytes. Genotype-phenotype correlations of beta MHC mutations have shown that mutations such as Arg403Gln, Arg453Cys, and Arg719Trp are associated with a high incidence of sudden cardiac death and a significantly decreased life expectancy, whereas mutations Gly256Glu and Leu908Val have a near-normal life span. Preclinical genetic diagnosis should help in genetic counseling and therapeutic stratification.

Percutaneous transluminal in vivo gene transfer by recombinant adenovirus in normal porcine coronary arteries, atherosclerotic arteries, and two models of coronary restenosis

BACKGROUND

Gene therapy has been proposed as a possible solution to the problem of restenosis after coronary angioplasty. The current study was undertaken to assess conventional methods of gene transfer and to develop percutaneous techniques for introducing genes directly into the coronary arteries of large mammals. Since the anticipated targets of gene therapy against restenosis include atherosclerotic and previously instrumented arteries, we also evaluated gene transfer in atherosclerotic coronary arteries and in two porcine models of restenosis: one using intracoronary stents and a second using balloon overstretch angioplasty.

METHODS AND RESULTS

The conventional method of using perforated balloon catheters to deliver Lipofectin-DNA complexes directly into the coronary arteries of intact animals was applied to 18 porcine coronary arteries including normal arteries, hypercholesterolemic arteries, and those simulating restenosis. The results of this study were consistent with previously published results indicating that only low levels of luciferase gene expression could be obtained by Lipofectin-mediated gene transfer. We therefore undertook a second, parallel study to evaluate percutaneous transluminal in vivo gene transfer using a replication-deficient adenoviral vector. A comparison of the two studies revealed that the mean level of reporter gene expression in the cohort undergoing adenoviral infection was 100-fold higher than in the cohort undergoing Lipofection. Analysis of luciferase activity over time in normal arteries revealed that recombinant gene expression was half-maximal after 1 day, peaked within 1 week, was still half-maximal at 2 weeks, and declined to low levels by 4 weeks. Histochemical analysis of coronary arteries treated with a second adenovirus expressing a nuclear-localized beta-galactosidase gene demonstrated gene transfer to a limited number of cells in the media and adventitia. Immunohistochemical analysis of Ad5-infused arteries using a monoclonal antibody directed against CD44 identified a periadventitial infiltrate composed of leukocytes.

CONCLUSIONS

The recombinant adenoviral vectors proved to be far more effective than Lipofectin at delivering foreign genes directly into the coronary arteries of living mammals. Furthermore, the influences of hypercholesterolemia and arterial injury appeared to have little effect on the levels of gene expression obtained using either method. The results demonstrate that low-level recombinant gene expression, the major obstacle impeding gene therapy for the prevention of restenosis, can potentially be overcome by using adenoviral vectors to mediate coronary gene transfer in vivo. The duration of gene expression provided by these vectors and their effective deployment in atherosclerotic, balloon-overstretched, and stented coronary arteries suggest that recombinant adenovirus may have potential for evaluating gene therapy in the clinically informative porcine models of coronary restenosis.

Deletions in the 5' region of dystrophin and resulting phenotypes

Deletions in the dystrophin gene give rise to both Duchenne and Becker muscular dystrophies. Good correlation is generally found between the severity of the phenotype and the effect of the deletion on the reading frame: deletions that disrupt the reading frame result in a severe phenotype, while in frame deletions are associated with a milder disease course. Rare exceptions to this rule, mainly owing to frameshift mutations in the 5' region of the gene (in particular deletions involving exons 3 to 7) which are associated with a milder than expected phenotype, have been reported previously. In order to characterise better the relationship between genotype and phenotype as a result of mutations arising in the 5' region of the gene, we have studied a large cohort of patients with small in frame and out of frame deletions in the first 13 exons of the dystrophin gene. Fifty-five patients with a deletion in this area were identified; approximately one third of them had a phenotype different from that theoretically expected. Patients were divided into two groups: (1) patients with a severe clinical phenotype despite the presence of a small, in frame deletion and (2) patients with a mild phenotype and an out of frame deletion. Noticeable examples observed in the first group were Duchenne boys with a deletion of exon 5, of exon 3, and of exons 3-13. In the second group we observed several patients with an intermediate or Becker phenotype and out of frame deletions involving not only the usual exons 3-7 but also 5-7 and 3-6. These data indicate that a high proportion of patients with a deletion in the 5' end of the gene have a phenotype that is not predictable on the basis of the effect of the deletion on the reading frame. The N-terminus of dystrophin has at least one actin binding domain that might be affected by the small, in frame deletions in this area. The effect of the in frame deletions of exon 3, 5, and 3-13 on this domain might account for the severe phenotype observed in these patients. Other mechanisms, such as unexpected effect of the deletion on splicing behaviour, might, however, also be implicated in determining the phenotype outcome.

Effects of low-dose aspirin on in vitro platelet aggregation in the early minutes after ingestion in normal subjects

Aspirin interferes with platelet aggregation by inhibiting the metabolism of arachidonic acid to thromboxane A2. Although both high- and low-dose aspirin therapies are effective for secondary prophylaxis in patients with atherosclerotic vascular disease, the acute response to low-dose aspirin therapy is controversial. Eighteen volunteer subjects ingested 81, 162, or 324 mg of aspirin in a longitudinal crossover study design. Initial doses were randomly assigned and dosing intervals were separated by 2 weeks. Platelet aggregation in response to 0.9 mM arachidonic acid was measured at baseline, 15, 30, 60, and 90 minutes after ingestion. Thromboxane B2 production was assayed on simultaneously obtained samples after stimulation with arachidonic acid. The median inhibition of aggregation was 97%, 97%, and 97% 15 minutes after ingestion of 81, 162, and 324 mg, respectively. Four subjects had < 20% inhibition 15 minutes after ingesting 81 mg, but all 4 had > 90% inhibition after 30 minutes. Thromboxane B2 production declined by > 93% in all subjects at each dose. There was no difference between doses in inhibition of thromboxane B2 production.

Ipsilateral breast tumor recurrence postlumpectomy is predictive of subsequent mortality: results from a randomized trial. Investigators of the Ontario Clinical Oncology Group

PURPOSE

To determine whether ipsilateral breast tumor recurrence (IBTR) postlumpectomy was independently predictive of distant relapse and mortality in women with node negative breast cancer.

METHODS AND MATERIALS

A randomized trial was conducted in Ontario between 1984 and 1989, in which 837 women with node negative disease who had undergone lumpectomy and axillary dissection were randomized to either postoperative radiation (40 Gy in 16 fractions to the whole breast, followed by a boost of 12.5 Gy in five fractions to the primary site), or no further treatment. A Cox proportional hazards regression analysis was performed for the endpoints mortality and distant relapse using the fixed covariates, treatment, age, tumor size, estrogen receptor status, progesterone receptor status, and nuclear grade; and the time dependent variable IBTR.

RESULTS

The analysis was based on 799 patients for which all fixed covariate data was available. Median follow-up was 66 months. The cumulative rate of IBTR at 5 years was significantly greater for the no treatment group compared to the radiation group; 30% vs. 8% respectively (p < 0.0001). No difference was detected in overall survival between the treatment groups (p = 0.45). Significant independent predictors for mortality were nuclear grade, high vs. medium or low (relative risk (RR) = 2.28, p = 0.0001); and tumor size > or = 2 cm. vs. < 2 cm. (RR = 1.64, p = 0.01). In addition, IBTR predicted increased mortality (RR = 2.18, p < 0.0006). Similar results were observed for distant relapse. An IBTR within 1 year of surgery was associated with a higher risk of distant relapse and mortality.

CONCLUSION

Local breast recurrence following lumpectomy is associated with an increased risk of distant relapse and death.

Reduced receptor aggregation and altered cytoskeleton in cultured myocytes after space-flight

We carried out parallel experiments first on the slow clinostat and then in space-flight to examine the effects of altered gravity on the aggregation of the nicotinic acetylcholine receptors and the structure of the cytoskeleton in cultured Xenopus embryonic muscle cells. By examining the concordance between results from space flight and the clinostat, we tested whether the slow clinostat is a relevant simulation paradigm. Space-flown cells showed marked changes in the distribution and organization of actin filaments and had a reduced incidence of acetylcholine receptor aggregates at the site of contact with polystyrene beads. Similar effects were found after clinostat rotation. The sensitivity of synaptic receptor aggregation and cytoskeletal morphology suggests that in the microgravity of space cell behavior may be importantly altered.

Determination of the catalytic site of creatine kinase by site-directed mutagenesis

Site-directed mutagenesis was used to alter the amino-acid residues at the presumed catalytic site Cys-283 and ATP binding site Asp-340 of human creatine kinase B cDNA. In addition, a highly conserved arginine residue, Arg-292, was also mutated. Transfection of 0.1 to 1 microgram of recombinant plasmid into COS cells produced increasing creatine kinase activity in the cell lysate. The expression of mutant Cys283-Tyr and Cys283-Ser resulted in complete abolition of homodimer BB isoform enzymatic activity without alteration of the capacity for dimerization. Expression of mutants Arg292-His, Arg292-Leu, and Arg292-Gln produced non-functional homodimers, whereas expression of mutant Arg292-Lys produced a homodimer with enzymatic activity that was 42% of the enzymatic activity of the wild type. Expression of the Asp340-Glu mutant creatine kinase did not alter enzyme activity as compared to the wild type. Following heterodimerization, there was inhibition of the normal subunit by the mutant subunit, for both the BB and the MB dimer. The results showed residues Cys-283 and Arg-292 are essential for enzyme catalysis. The best fit model for the dimer is one in which there is close apposition of the two catalytic sites. The interaction of the individual subunits during dimerization provides a molecular approach for dominant negative modulation of the creatine kinase isozyme system in future genetic manipulative experiments.

Compartmentation of brain-type creatine kinase and ubiquitous mitochondrial creatine kinase in neurons: evidence for a creatine phosphate energy shuttle in adult rat brain

Multiple isoforms of creatine kinase (CK) are expressed in specific cell types as part of an energy delivery or shuttle system. To test the hypothesis that neurons utilize a creatine phosphate energy shuttle, we examined the pattern of CK isoform expression and localization in adult rat brain. Two isoforms of CK are present in brain extracts, "brain-type," or BCK, and the ubiquitous form of the mitochondrial CK (uMtCK), as detected by enzyme activity following nondenaturing electrophoresis and by Western blotting following denaturing electrophoresis. In formalin-fixed and paraffin-embedded sections of rat brain, uMtCK immunostaining is detected in the somata of all Golgi type I neurons in the cerebellum, pontine reticular formation, red nucleus, hippocampus, and cerebral cortex. Immunostaining for uMtCK appears throughout the cell body but not in nuclei. BCK immunostaining is also present in somata of Golgi type I neurons in the cerebellum, red nucleus, and pons and is distributed throughout the cell body and within nuclei. BCK immunostaining also appears in neuronal processes and is concentrated in the molecular layers of the cerebellum and the hippocampus and in cortical pyramidal cell dendrites. These results demonstrate a coordinate pattern of expression and compartmentation of BCK and uMtCK isoforms in neurons, which provides an anatomic basis for the transfer of metabolic energy via a creatine phosphate energy shuttle.

Prostaglandin E1 does not accelerate rTPA-induced thrombolysis in acute myocardial infarction

Fifteen patients who arrived between 6 and 24 hours after the onset of acute myocardial infarction and who were found to have totally occluded coronary arteries, received aspirin, heparin, and tissue plasminogen activator given over 3 hours. Eight patients were randomly assigned to receive intravenous prostaglandin E1, 20 ng/kg/min for 6 hours, while seven patients received placebo infusion. Coronary arteriography begun immediately before the start of tissue plasminogen activator and repeated every 15 minutes revealed restoration of antegrade flow in two of eight (25%) patients treated with prostaglandin E1 and in two of seven (28%) patients receiving placebo. Pharmacologic sampling of tissue plasminogen activator levels were performed at baseline and 30, 45, 60, 75, 90, 135, 180, 190, 210, and 240 minutes afterwards for assessment of tissue plasminogen activator antigen. There was no difference in fibrinogen levels and no difference in tissue plasminogen activator antigen levels at these time periods. Clearance values of tissue plasminogen activator were calculated and were not different between the two groups. These data do not support the use of prostaglandin E1 for the acceleration of reperfusion in patients receiving tissue plasminogen activator for acute myocardial infarction.