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Biomedical subjects

R Roberts

Publications and source records attributed to R Roberts.

At least 127 records · Page 7Linked to original sources
PubMed1998

Dominant-negative effect of a mutant cardiac troponin T on cardiac structure and function in transgenic mice.

Hypertrophic cardiomyopathy (HCM) is a disease of sarcomeric proteins. The mechanism by which mutant sarcomeric proteins cause HCM is unknown. The leading hypothesis proposes that mutant sarcomeric proteins exert a dominant-negative effect on myocyte structure and function. To test this, we produced transgenic mice expressing low levels of normal or mutant human cardiac troponin T (cTnT). We constructed normal (cTnT-Arg92) and mutant (cTnT-Gln92) transgenes, driven by a murine cTnT promoter, and produced three normal and five mutant transgenic lines, which were identified by PCR and Southern blotting. Expression levels of the transgene proteins, detected using a specific antibody, ranged from 1 to 10% of the total cTnT pool. M-mode and Doppler echocardiography showed normal left ventricular dimensions and systolic function, but diastolic dysfunction in the mutant mice evidenced by a 50% reduction in the E/A ratio of mitral inflow velocities. Histological examination showed cardiac myocyte disarray in the mutant mice, which amounted to 1-15% of the total myocardium, and a twofold increase in the myocardial interstitial collagen content. Thus, the mutant cTnT-Gln92, responsible for human HCM, exerted a dominant-negative effect on cardiac structure and function leading to disarray, increased collagen synthesis, and diastolic dysfunction in transgenic mice.

Animals↗
PubMed1998

Evidence for a symmetrical requirement for Rab5-GTP in in vitro endosome-endosome fusion.

Early endosome fusion, which has been extensively characterized using an in vitro reconstitution assay, is Rab5-dependent. To examine the requirement for Rab5 on both fusion partners, we prepared cytosol and endosomes depleted of Rab5. Unlike control cytosol, Rab5-depleted cytosol was only marginally active in the in vitro endosome fusion. However, fusion could be restored by the addition of wild-type Rab5 or Rab5 D136N, a mutant whose nucleotide specificity favors xanthine over guanine. The addition of Rab5 D136N restored fusion only in the presence of XTP. In the absence of XTP or in the presence of XDP, Rab5 D136N failed to restore fusion. When fusion was carried out with endosomal vesicles depleted of Rab GTPases (by preincubation of vesicles with GDP dissociation inhibitor), together with cytosol immunodepleted of Rab5, fusion was virtually absent. We then used immunodepleted cytosol and GDP dissociation inhibitor-treated vesicles to determine whether Rab5 is required by both fusion partners. Using separate sets of endosomal vesicles, we found that priming both sets of Rab5-depleted vesicles with Rab5 Q79L, a GTPase-defective mutant, substantially stimulated endosome fusion. Priming one set of vesicles with Rab5 Q79L and a second set of vesicles with Rab5 S34N failed to activate fusion. When both sets of Rab5-depleted vesicles were primed with Rab5 D136N supplemented with XTP, endosome fusion was stimulated, similar to that observed with Rab5 Q79L. However, when one set of vesicles was preincubated with Rab5 D136N plus XTP and the second set with Rab5 D136N and XDP, no stimulation of fusion was observed. We conclude that Rab5-GTP is required on both fusion partners for docking and fusion of early endosomes. To confirm the fusion of Rab5-GTP-positive vesicles in vivo, we expressed GFP-Rab5 Q79L in fibroblasts and observed fusion of Rab5-positive vesicles. We failed to record fusion of Rab5-positive vesicles with Rab5-negative vesicles. We conclude that Rab5-GTP is required on both sets of endosomes for fusion in vitro and in living cells.

Animals↗
PubMed1998

Human type 2 phosphatidic acid phosphohydrolases. Substrate specificity of the type 2a, 2b, and 2c enzymes and cell surface activity of the 2a isoform.

Phosphatidic acid (PA), lysophosphatidic acid, ceramide 1-phosphate (C1P), and sphingosine 1-phosphate (S1P) are lipid mediators generated by phospholipases, sphingomyelinases, and lipid kinases. The major pathway for degradation of these lipids is dephosphorylation catalyzed by members of two classes (types 1 and 2) of phosphohydrolase activities (PAPs). cDNAs encoding two type 2 PAPs, PAP-2a and -2b, have been expressed by transient transfection and shown to catalyze hydrolysis of PA, C1P, and S1P (Kai, M., Wada, I., Imai, S., Sakane, F. and Kanoh, H. (1997) J. Biol. Chem. 272, 24572-24578). We report the cloning and expression of a third type 2 PAP enzyme (288 amino acids, predicted molecular mass of 32.6 kDa), PAP-2c, which exhibits 54 and 43% sequence homology to PAPs 2a and 2b. Expression of HA epitope-tagged PAP-2a, -2b, and 2c in HEK293 cells produced immunoreactive proteins and increased membrane-associated PAP activity. Sf9 insect cells contain very low endogenous PAP activity. Recombinant expression of the three PAP enzymes using baculovirus vectors produces dramatic increases in membrane-associated Mg2+-independent, N-ethylmaleimide-insensitive PAP activity. Expression of PAP-2a but not PAP-2b or -2c resulted in high levels of cell surface PAP activity in intact insect cells. Kinetic analysis of PAP-2a, -2b, and -2c activity against PA, lysophosphatidic acid, C1P, and S1P presented in mixed micelles of Triton X-100 revealed differences in substrate specificity and susceptibility to inhibition by sphingosine, Zn2+, and propranol.

Amino Acid Sequence↗
PubMed1998

Mutations in the gene for cardiac myosin-binding protein C and late-onset familial hypertrophic cardiomyopathy.

BACKGROUND: Mutations in the gene for cardiac myosin-binding protein C account for approximately 15 percent of cases of familial hypertrophic cardiomyopathy. The spectrum of disease-causing mutations and the associated clinical features of these gene defects are unknown. METHODS: DNA sequences encoding cardiac myosin-binding protein C were determined in unrelated patients with familial hypertrophic cardiomyopathy. Mutations were found in 16 probands, who had 574 family members at risk of inheriting these defects. The genotypes of these family members were determined, and the clinical status of 212 family members with mutations in the gene for cardiac myosin-binding protein C was assessed. RESULTS: Twelve novel mutations were identified in probands from 16 families. Four were missense mutations; eight defects (insertions, deletions, and splice mutations) were predicted to truncate cardiac myosin-binding protein C. The clinical expression of either missense or truncation mutations was similar to that observed for other genetic causes of hypertrophic cardiomyopathy, but the age at onset of the disease differed markedly. Only 58 percent of adults under the age of 50 years who had a mutation in the cardiac myosin-binding protein C gene (68 of 117 patients) had cardiac hypertrophy; disease penetrance remained incomplete through the age of 60 years. Survival was generally better than that observed among patients with hypertrophic cardiomyopathy caused by other mutations in the genes for sarcomere proteins. Most deaths due to cardiac causes in these families occurred suddenly. CONCLUSIONS: The clinical expression of mutations in the gene for cardiac myosin-binding protein C is often delayed until middle age or old age. Delayed expression of cardiac hypertrophy and a favorable clinical course may hinder recognition of the heritable nature of mutations in the cardiac myosin-binding protein C gene. Clinical screening in adult life may be warranted for members of families characterized by hypertrophic cardiomyopathy.

Adolescent↗
PubMed1998

Early diagnosis of myocardial infarction with MB CK isoforms.

Over 5 million patients with chest pain present annually to the ER in the US but only 10% will have infarction with < 50% identified by ECG. Early diagnosis of infarction in the ER to triage provides more appropriate and early therapy, less unnecessary use of CCU, and is more cost effective. A rapid automated MB CK isoform assay (25 min) was evaluated in a prospective study of 1110 patients presenting to the ER with chest pain. This assay was shown to have a sensitivity of 96% and specificity of 93% to diagnose infarction within 6 h of onset of chest pain. In 92% the diagnosis was confirmed within 1 h of arrival at the ER. Similar sensitivity and specificity for total MB CK, troponin T, and troponin I required 16 h from onset of pain. Thus, MB CK isoforms provide a rapid diagnosis early after onset of infarction and have the requisite sensitivity and specificity for triaging patients in the ER.

Biomarkers↗
PubMed1998

The molecular genetics of arrhythmias and sudden death.

The current status of the research in genetics of cardiac diseases causing sudden death is reviewed. Few techniques will impact medicine as will those of molecular biology. The identification of the gene-causing diseases will allow the use of better preventive, diagnostic, and therapeutic options. From genetic counseling at present to gene therapy in the future, the new challenge for the clinician will be to acquire the new information provided by molecular biology and apply it at the bedside to improve the quality of life for the patient.

Arrhythmias, Cardiac↗
PubMed1998

New theories. Causes of dilated cardiomyopathy.

Dilated cardiomyopathy is a heterogeneous disease, both clinically and genetically. Two genes responsible for X-linked DCM have been identified. Five genetic loci responsible for X-linked DCM have been identified. Five genetic loci responsible for autosomal dominant DCM have also been mapped but no genes identified so far. New paradigms may be necessary in order to elucidate the etiology of primary dilated cardiomyopathy.

Cardiomyopathy, Dilated↗
PubMed1998

Role of myocardial contrast echocardiography during nonsurgical septal reduction therapy for hypertrophic obstructive cardiomyopathy.

OBJECTIVES: This study was undertaken to evaluate the ability of myocardial contrast echocardiography (MCE) to guide the targeted delivery of ethanol during nonsurgical septal reduction therapy (NSRT) and to assess the relation between the MCE risk area and infarct size determined by enzymatic and radionuclide methods. BACKGROUND: NSRT with intracoronary ethanol is a new promising treatment for patients with hypertrophic obstructive cardiomyopathy (HOCM). Proper localization and quantification of the septal infarct before ethanol injection are highly desirable. MCE can provide accurate delineation of the vascular territory of the coronary arteries. METHODS: Twenty-nine patients with HOCM and maximal medical therapy underwent NSRT. The left ventricular outflow tract (LVOT) gradient by Doppler echocardiography at baseline was 53 +/- 16 mm Hg (mean +/- SD). Before NSRT, MCE was performed in all patients with intracoronary sonicated albumin (Albunex). Diluted sonicated albumin (Albunex) was selectively injected into the septal perforator arteries during simultaneous transthoracic imaging. Immediately after MCE, ethanol was injected into the same vessel. Plasma total creatine kinase (CK), total CK-MB fraction and CK-MB fraction subforms were measured at baseline and serially for 36 h. RESULTS: LVOT gradient decreased to 12 +/- 6 mm Hg (p < 0.001) after NSRT. Accurate mapping of the vascular beds of the septal perforators was successfully attained in all patients by MCE. Furthermore, the MCE risk area correlated well with peak CK (r = 0.79, p < 0.001). Six weeks after NSRT, 23 patients underwent myocardial perfusion studies performed with single-photon emission computed tomography (SPECT). Mean SPECT septal perfusion defect size involved 9.5 +/- 6% of the left ventricle and correlated well with MCE area (r = 0.7), with no statistically significant difference between the risk area estimated by MCE and that by SPECT. CONCLUSIONS: Estimation of the size of the septal vascular territory with MCE is accurate, safe and feasible in essentially all patients during NSRT. MCE can delineate the perfusion bed of the septal perforators and can predict the infarct size that follows ethanol injection.

Adult↗
PubMed1998

HMI education for HIMs.

This paper analyses the curricula of the four Australian university programs for health information managers (HIMs) in relation to their coverage of health and medical informatics (HMI). The overlap between HIMs and HMIs should be increased through exchange of information at conferences such as this as well as communication and co-operation between the Schools of HIM and those offering health informatics related training at other Australian universities.

Administrative Personnel↗
PubMed1998

Does breastfeeding at six months predict cognitive development?

There is controversy over whether the method of feeding in infancy affects intellectual development. We investigated the relationship between breastfeeding status at 6 months of age and long-term cognitive development in a cohort of 375 children born in Port Pirie, South Australia, between 1979 and 1982. Cognitive assessments were conducted at ages 2, 4, 7 and 11 to 13 years. After adjustment for sociodemographic, environmental and biomedical factors, a small, statistically non-significant, beneficial effect of breastfeeding on cognitive functioning was observed. Compared with the bottle-fed children, the breast-fed children had a 3.4 (95% CI -0.1 to 6.9), 1.3 (-2.3 to 4.9), 1.2 (-2.0 to 4.4) and 0.8 (-1.9 to 3.5) point advantage on the Bayley Mental Developmental Index at age 2 years, the McCarthy General Cognitive Index at age 4 years and the Wechsler Full-Scale IQ at ages 7 and 11 to 13 years, respectively. Our data suggest that any beneficial effect of breastfeeding on cognitive development is quite small in magnitude.

Analysis of Variance↗
PubMed1998

The value of electrophysiology study and prophylactic implantation of cardioverter defibrillator in patients with hypertrophic cardiomyopathy.

Fifty-three consecutive patients with hypertrophic cardiomyopathy (HCM) and no history of sudden death underwent electrophysiology (EP) study. Sustained polymorphic ventricular tachycardia (VT) or ventricular fibrillation (VF) was induced in 19 patients (35%). Patients with prior syncope or near syncope had a higher incidence of VT/VF inducibility. An implantable cardioverter defibrillator (i.c.d.) was placed in 14 of the 19 patients. Of the remaining 5 patients with inducible VT/VF, three refused ICD implantation, while two underwent septal myectomy and VT/VF was no longer inducible after the operation. None of the patients received antiarrhythmic drugs. During a mean follow-up period of 47 +/- 31 (2-117) months, no events occurred in the 34 patients with negative EP study. Three events occurred among the 19 patients with inducible VT/VF. One patient died suddenly, one developed wide complex tachycardia which required resuscitation, and one patient received an appropriate ICD shock. In conclusion, sustained polymorphic VT/VF was inducible in about one-third of patients with HCM. Noninducibility of VT/VF appeared to predict a favorable prognosis. Although the overall event rate was low in patients with inducible VT/VF, prophylactic ICD implantation in patients with multiple risk factors may be appropriate.

Adult↗
PubMed1998

Molecular genetic basis of hypertrophic cardiomyopathy: genetic markers for sudden cardiac death.

Hypertrophic cardiomyopathy (HCM) is an autosomal dominant disease caused by mutations in sarcomeric proteins. The disease is characterized by left ventricular hypertrophy in the absence of an increased external load, and myofibrillar disarray. A large number of mutations in genes coding for the beta-myosin heavy chain (beta-MyHC), cardiac troponin T (cTnT), cardiac troponin I, alpha-tropomyosin, myosin binding protein C (MyBP-C), and myosin light chain 1 and 2 in patients with HCM have been identified. Genotype-phenotype correlation studies have shown that mutations carry prognostic significance. The Gly256Glu, Val606Met, and Leu908Val mutations in the beta-MyHC are associated with a benign prognosis. In contrast, Arg403Gln, Arg719Trp, and Arg453Cys mutations are associated with a high incidence of sudden cardiac death (SCD). Mutations in cTnT are associated with a mild degree of hypertrophy, but a high incidence of SCD. Mutations in MyBP-C are associated with mild hypertrophy and a benign prognosis. However, it has become evident that factors other than the underlying mutations, such as genetic background and possibly environmental factors, also modulate phenotypic expression of HCM.

Cardiomegaly↗
PubMed1998

A placebo-controlled randomized trial of antithrombin therapy in neonatal respiratory distress syndrome.

Neonatal respiratory distress syndrome (RDS) is associated with decreased plasma activity of antithrombin (AT) and increased formation of thrombin. We tested whether AT reduces thrombin formation, improves gas exchange, and decreases the duration of mechanical ventilation and supplemental oxygen. One hundred twenty-two infants were randomized to pasteurized AT concentrate or to placebo. Two ml/kg (equivalent to 100 IU AT/kg) were followed by 1 ml/kg (50 IU/kg) every 6 h for 48 h. Outcome measures included plasma AT activity, thrombin-AT (TAT) complex, prothrombin fragment (F1+2), the ratio of arterial to alveolar oxygen pressure [(a/A)PO2], and the ventilator efficiency index (VEI). In the AT group (n = 61), mean (SD) birth weight was 1,198 (301) g, mean (SD) gestational age (GA) was 28.3 (2.0) wk, 54% were male. In the placebo group (n = 61), mean (SD) birth weight was 1,201 (315) g, mean (SD) GA was 28.8 (2. 3) wk, 51% were male. In treated infants, AT activity was raised to means of 1.69 and 2.25 U/ml at 24 and 48 h, respectively. Corresponding means in control infants were 0.37 and 0.44 U/ml (p < 0.0001). F1+2, but not TAT, was significantly reduced by AT (p = 0. 004). VEI and (a/A)PO2 were similar in both groups throughout the first week of life. Median days receiving mechanical ventilation were 7.1 (AT) versus 4.8 (placebo), p = 0.0014. Median days receiving supplemental oxygen were 7.9 (AT) versus 5.5 (placebo), p < 0.0001. There were seven (11.5%) deaths in the AT group and three (4.9%) deaths in the placebo group. We conclude that treatment with AT cannot be recommended in premature infants with RDS.

Antithrombin III↗
PubMed1998

Heparin improves gas exchange during experimental acute lung injury in newborn piglets.

Although intrapulmonary fibrin deposition is a pathognomonic feature of acute lung injury, it remains uncertain whether thrombin inhibitors affect clinically important outcomes. We hypothesized that both heparin and antithrombin (AT) concentrate improve gas exchange during experimental respiratory distress syndrome. We also tested whether combination therapy is more beneficial than monotherapy. Forty-eight newborn piglets were randomized within 12 litters to one of four groups in a factorial design: (1) AT; (2) heparin; (3) AT plus heparin; (4) untreated control animals. After lung lavage and 4 h of barovolutrauma, mechanical ventilation was continued for 24 h during which ventilator pressures and inspired oxygen were adjusted to maintain normal blood gases. The arterial/ alveolar oxygen tension ratio (a/A ratio) and the ventilator efficiency index (VEI) at 18 and 24 h were compared by repeated measures analysis of variance (ANOVA). In contrast to our hypothesis, only heparin improved gas exchange, and we found little evidence of an interaction with AT. The a/A ratio was 0.48 +/- 0.27 (mean +/- SD) in the presence of heparin versus 0.33 +/- 0.26 in its absence; p = 0.01. Corresponding VEI was 0.30 +/- 0.12 versus 0.25 +/- 0.14; p = 0.04. Hyaline membrane formation was also decreased in heparin-treated animals (p = 0.02).

Analysis of Variance↗
PubMed1998

The need for a holistic view of telemedicine, focused on patients and society as prime stakeholders.

Telemedicine provides the scope to remove the barrier of distance from delivery of health care. In so doing it has the potential to strengthen primary care and local health delivery, and to optimise the use of secondary and tertiary specialist resources. However, it can have disbenefits and perverse effects which are as yet inadequately addressed. Development of telemedicine to date has been led by new technological opportunities, linked to clinical interests. Whilst not inappropriate, this alone is not adequate. All health care activities should be to promote health and treat ill-health, and therefore the interests of the consumer and of society should predominate. More complete research and policy analysis of telemedicine are therefore needed. This paper argues for a more holistic and integrated view of telemedicine to be taken, to ensure that technology is harnessed to meet need. To this end, it puts telemedicine into the overall context of health care interests, and describes methodologies to assess patient attitudes and societal priorities. Given the need to avoid the unanticipated adverse effects which have bedevilled other new health care technologies, and the particular risks of uncontrolled consultations and commerce across national boundaries, the paper goes on to advocate routine use of integrated risk analysis of telemedicine applications at research and policy levels. The need for an effects-orientated analytic framework, and for international policy collaboration to protect users of services available by global telecommunications, is identified.

Health Policy↗