Can an evidence-based guideline reduce unnecessary imaging of road trauma patients with cervical spine injury in the emergency department?

The aim of this study was to determine if an unvalidated imaging guideline can reduce the use of imaging in patients with cervical spine trauma. A non-randomized clinical trial using historical controls was conducted in the emergency department from October 2001 to September 2002. Following an education programme, which introduced the imaging guideline to clinicians, the use of guideline and imaging were measured. The guideline was also converted to decision-support software for use in the emergency department. Three hundred and fifty-three patients satisfied inclusion criteria during the study period and these were compared with 403 historical control subjects. No significant difference was found between the two groups for age, sex or fracture prevalence. A significant increase was observed during the study period in the proportion of patients who were managed without the use of any cervical spine imaging (21.25 vs 31.2%; P=0.03; 95% confidence interval, 3-13). There were no delayed diagnoses of cervical spine injury among those not imaged. It is feasible to disseminate and implement an evidence-based imaging guideline for patients with cervical spine trauma. The use of a computerized decision-support system can facilitate this and is associated with a safe reduction in the proportion of patients imaged.

Barriers to success for an evidence-based guideline for chronic obstructive pulmonary disease

OBJECTIVES

To evaluate 1) barriers to clinical guideline use and 2) the relationship between guideline use and inpatient outcomes in chronic obstructive pulmonary disease (COPD).

METHODS

1) Four focus groups of specific health professions (n = 30), from three metropolitan hospitals, and interview of 99 medical officers (MOs), linked to 349 admissions, both guided by behavioural modelling theory; 2) association between guideline use and patient outcomes (length of hospital stay > or = 14 days, and readmission within 28 or 90 days) was evaluated in a cohort of 405 COPD patients.

RESULTS

1) In focus groups, nurses and allied health professionals emphasized facilitation issues including paperwork duplication and time limitations as barriers, but considered improved patient care outcomes as the major guideline use determinant. There were similar findings in junior MOs (nonconsultants) by both focus group and interview, with the addition of a need for a sense of ownership. Senior MOs (consultants) greatly emphasized sense of ownership. Barriers to guideline use varied between types of units. Behavioural modelling explained 49% of the variation in intention to use the guideline for MOs. For nonconsultants, habit and intention were significantly associated with extent of guideline use. 2) Patient outcomes: guideline use was not associated with length of stay or readmission.

CONCLUSIONS

1) Guideline implementation should address issues relevant to different health professions, units and seniority of profession. 2) Guideline use was not associated with reductions in readmission or length of stay.

Do the findings of case series studies vary significantly according to methodological characteristics?

OBJECTIVES

To review the use of case series in National Institute for Clinical Excellence (NICE) Health Technology Assessment (HTA) reports, to review systematically the methodological literature for papers relating to the validity of aspects of case series design, and to investigate characteristics and findings of case series using examples from the UK's Health Technology Assessment programme.

DATA SOURCES

Electronic databases. NICE website. Reports produced as part of the UK's HTA programme.

REVIEW METHODS

NICE HTAs that used information from case series studies were obtained from the NICE website and a range of quality criteria applied. Searches of electronic databases, handsearched journals and the bibliographies of papers were made in order to find studies that assessed aspects of case series design, analysis or quality in relation to study validity. Hypotheses relating to the design of case series studies were developed and empirically investigated using four case examples from existing reports produced as part of the UK's HTA programme (functional endoscopic sinus surgery for nasal polyps, spinal cord stimulation for chronic back pain, percutaneous transluminal coronary angioplasty and coronary artery bypass grafting for chronic angina). Analysis was undertaken comparing studies within each review.

RESULTS

There was no consensus on which case series to include in HTAs, how to use them or how to assess their quality, despite them being used in 30% of NICE HTAs. No previous studies empirically investigating methodological characteristics of case series were found. However, it is possible that the search strategy failed to find relevant studies. Poor reporting of case series characteristics severely constrained analysis and there were insufficient data to investigate all the hypotheses. Findings were not consistent across the different topics and were subject to considerable uncertainty. All the examples in our analysis were surgical interventions, which are prone to additional confounding factors due to difficulties of standardisation compared with drug treatment. Our findings may not be generalisable outside the interventions studied. The case series reports included generally exhibited poor reporting of methodological characteristics. This constrained our analysis. The use of several methods of analysis has led to apparently discrepant results. Given the number of analysis performed, the usual level of significance (p = 0.05) should be viewed with caution. The most important limitation of this study is the small number of cases on which the findings are based. The results are therefore tentative and should be viewed with caution.

CONCLUSIONS

Case series are incorporated in a significant proportion of health technology assessments. Quality criteria have been used to appraise the quality of case series and decide on their inclusion in reviews of studies using this design. In this small series of case studies drawn from HTAs carried out for the NHS HTA programme, little evidence was found to support the use of many of the factors included in quality assessment tools. Importantly, no relationship was found between study size and outcome across the four examples studied. Isolated examples of a potentially important relationship between other methodological factors and outcome were shown, such as blinding of outcome measurement, but these were not shown consistently across the small number of examples studied. This study is based on a very small sample of studies and should therefore be considered as exploratory. Further investigation of the relationship between methodological features and outcome is justified given the frequency of use of case series in health technology assessments. Further research into the methodological features of case series and their outcome is justified in a wider sample of technologies and larger sets of case series. Value of information analyses including case series could be explored. Further exploration of the differences between case series and randomised controlled trial results, preferably using registry or comprehensive case series data, would be valuable.

Effectiveness and cost-effectiveness of imatinib for first-line treatment of chronic myeloid leukaemia in chronic phase: a systematic review and economic analysis

OBJECTIVES

To evaluate the effectiveness of imatinib as first-line treatment for chronic myeloid leukaemia (CML) compared with interferon-alpha (IFN-alpha), hydroxyurea and bone marrow transplantation (BMT), and the cost-effectiveness of imatinib compared with IFN-alpha and hydroxyurea.

DATA SOURCES

Electronic databases.

REVIEW METHODS

Selected studies and full-text articles were screened and rigorously selected. Survival was the key outcome measure. Surrogate outcome measures included haematological (blood) response and cytogenetic (bone marrow) response (CR). As no published cost-effectiveness studies were found that compared imatinib and IFN-alpha, an independent Markov model was constructed and this was compared with models submitted to the National Institute for Clinical Excellence by the manufacturer of imatinib.

RESULTS

Intention-to-treat analysis showed that imatinib was associated with complete CR at 12 months follow-up of 68% compared with 20% for the IFN-alpha plus Ara-C group. The estimated proportion of people taking imatinib who had not progressed to accelerated or blast phases at 12 months was 98.5%, and 93.1% for IFN-alpha plus Ara-C. Overall survival was not statistically significantly different. Withdrawal due to side-effects was 2% for imatinib and 5.6% for IFN-alpha plus Ara-C. Cross-over due to intolerance was 0.7% and 22.8% for imatinib and for IFN-alpha plus Ara-C, respectively. Quality of life was better in the imatinib group than the IFN-alpha group when assessed at 1, 3 and 6 months. Median survival across the four IFN-alpha versus hydroxyurea studies was 66 and 56.2 months, respectively. Median complete CR was 6% for IFN-alpha and 0 for hydroxyurea. Median withdrawal due to side-effects was 24% and 4% for IFN-alpha and hydroxyurea, respectively. Four out of the five studies comparing BMT and IFN-alpha showed a long-term survival advantage for BMT over IFN-alpha, but a short-term disadvantage. In four of the five studies comparing BMT and IFN-alpha, median survival had not yet been reached in the BMT groups in 6--10 years. Median survival in the IFN-alpha arms ranged from 5.2 to 7 years. The BMT group gained a survival advantage over IFN-alpha at 3--5.5 years. In the BMT group death due to transplant-related complications ranged from 36 to 45%. The incremental cost-effectiveness ratio (ICER) of imatinib compared with IFN-alpha from the independent model was GBP26,180 per quality-adjusted-life-years (QALY) gained and was relatively robust. Imatinib was less cost-effective than hydroxyurea with an ICER of GBP86,934.

CONCLUSIONS

Imatinib appears to be more effective than current standard drug treatments in terms of cytogenetic response and progression-free survival, with fewer side-effects. However, there is uncertainty concerning longer term outcomes, the development of resistance to imatinib, the duration of response and the place of imatinib relative to BMT. New issues are continually arising, such as optimal management pathways and combination therapies. Recommendations for research include: long-term follow-up data from the first- and second-line imatinib trials; investigation into specific subgroups, e.g. high-risk patients, the elderly, children or those eligible for BMT; long-term comparisons of imatinib with BMT performed in early stages of CML; the use of imatinib in combination with other therapies, and further detailed economic studies. Investigation of the impact of CML and imatinib on quality of life is also important.

Systematic review of endoscopic sinus surgery for nasal polyps

OBJECTIVES

To provide a systematic review of the clinical effectiveness of endoscopic sinus surgery (ESS) for the removal of nasal polyps.

DATA SOURCES

Searches of electronic databases, websites and reference lists were made to identify relevant studies.

REVIEW METHODS

An extensive search was performed to identify all articles where FESS is used for the excision of nasal polyps. Two reviewers independently screened articles for inclusion according to predefined criteria. Comparative studies were included if they were primary research, focused on FESS for the removal of nasal polyps, reported patient relevant outcomes and were published in English. In addition, case series studies were included if they met the above criteria and enrolled more than 50 patients with polyps. Data were then extracted by one reviewer and checked by a second. A structured form was used to assess the internal and external validity of included studies. Comparative data were reported where available. Excluded case series and case reports were grouped and described. A group of nine ear, nose and throat (ENT) experts were selected, then using the literature and their own experience, they generated a list of priority research questions. Existing economic evaluations were sought and described.

RESULTS

Of the 33 studies included, the randomised controlled trials and controlled trials reported overall symptomatic improvement that ranged from 78 to 88% for FESS compared with 43 to 84% for similar techniques (including polypectomy, Caldwell-Luc and intranasal ethmoidectomy). Disease recurrence was 8% for FESS compared with 14% for Caldwell-Luc and polyp recurrence was 28% for endoscopic ethmoidectomy compared with 35% for polypectomy. Revision surgery was reported in one study only and was the same for FESS and Caldwell-Luc procedures. Percentage of overall complications was reported in only one comparative study and was 1.4% for FESS compared with 0.8% for conventional procedures. The case series studies reported overall symptomatic improvement for patients with nasal polyps ranging from 37 to 99% (median 89%). For the mixed patient groups (with and without polypoid disease) overall symptomatic improvement ranged from 40 to 98% (median 88%). Total complications in the case series studies ranged from 22.4 to 0.3% (median 6%).

CONCLUSIONS

The majority of studies report that symptoms improve following FESS with relatively few complications; however, only a small proportion of evidence is comparative. Results from non-comparative studies do not inform the choices that need to be made by ENT surgeons and commissioners. Health economics data are also lacking and therefore cannot inform these decisions. FESS may offer some advantages in effectiveness over comparative techniques, but there is enormous variation in the range of results reported and there are severe methodological limitations. There is a clear need for quality-controlled trials in order to answer questions regarding the effectiveness of FESS. A number of priority research questions from a selection of ENT surgeons within the UK are identified and presented.

Localization of a gene (MCUL1) for multiple cutaneous leiomyomata and uterine fibroids to chromosome 1q42.3-q43

Dominant transmission of multiple uterine and cutaneous smooth-muscle tumors is seen in the disorder multiple leiomyomatosis (ML). We undertook a genomewide screen of 11 families segregating ML and found evidence for linkage to chromosome 1q42.3-q43 (maximum multipoint LOD score 5.40). Haplotype construction and analysis of recombinations permitted the minimal interval containing the locus, which we have designated "MCUL1," to be refined to an approximately 14-cM region flanked by markers D1S517 and D1S2842. Allelic-loss studies of tumors indicated that MCUL1 may act as a tumor suppressor. Identification of MCUL1 should have wide interest, since this gene may harbor low-penetrance variants predisposing to the common form of uterine fibroids and/or may undergo somatic mutation in sporadic leiomyomata.

Developing a one-stop clinic for leg ulcer patients

Leg ulceration may be caused by a variety of different factors and specialist assessment is required. Patients with complex leg ulcers in Nottingham are assessed at a one-stop dermatology/vascular clinic. Nurses undertake assessments, provide education and support and liaise with the community nursing services.

Survival of 1476 patients initially resuscitated from out of hospital cardiac arrest

OBJECTIVES

To determine the short and long term outcome of patients admitted to hospital after initially successful resuscitation from cardiac arrest out of hospital.

DESIGN

Review of ambulance and hospital records. Follow up of mortality by "flagging" with the registrar general. Cox proportional hazards analysis of predictors of mortality in patients discharged alive from hospital.

SETTING

Scottish Ambulance Service and acute hospitals throughout Scotland.

SUBJECTS

1476 patients admitted to a hospital ward, of whom 680 (46%) were discharged alive.

MAIN OUTCOME MEASURES

Survival to hospital discharge, neurological status at discharge, time to death, and cause of death after discharge.

RESULTS

The median duration of hospital stay was 10 days (interquartile range 8-15) in patients discharged alive and 1 (1-4) day in those dying in hospital. Neurological status at discharge in survivors was normal or mildly impaired in 605 (89%), moderately impaired in 58 (8.5%), and severely impaired in 13 (2%); one patient was comatose. Direct discharge to home occurred in 622 (91%) cases. The 680 discharged survivors were followed up for a median of 25 (range 0-68) months. There were 176 deaths, of which 81 were sudden cardiac deaths, 55 were non-sudden cardiac deaths, and 40 were due to other causes. The product limit estimate of 4 year survival after discharge was 68%. The independent predictors of mortality on follow up were increased age, treatment for heart failure, and cardiac arrest not due to definite myocardial infarction.

CONCLUSION

About 40% of initial survivors of resuscitation out of hospital are discharged home without major neurological disability. Patients at high risk of subsequent cardiac death can be identified and may benefit from further cardiological evaluation.

When is it futile for ambulance personnel to initiate cardiopulmonary resuscitation?

OBJECTIVE

To determine whether patients with unexpected prehospital cardiac arrest could be identified in whom ambulance resuscitation attempts would be futile.

DESIGN

Review of ambulance and hospital records; detailed review of automated external defibrillator rhythm strips of patients in whom no shock was advised.

SETTING

Scottish Ambulance Service; all cardiopulmonary resuscitation attempts after cardiorespiratory arrest during 1988-94 included in the Heartstart Scotland database.

SUBJECT

414 cardiorespiratory arrest patients with no pulse or breathing on arrival of ambulance personnel, no bystander cardiopulmonary resuscitation performed, and more than 15 minutes from time of arrest to arrival of ambulance. Patients were stratified into those with "shockable" and "non-shockable" rhythms.

MAIN OUTCOME MEASURES

Return of spontaneous circulation, or survival to reach hospital alive, or survival to discharge, or all three.

RESULTS

No patient with a non-shockable rhythm who met the entry criteria for analysis survived a resuscitation attempt. Review of the defibrillator rhythm strips of these patients failed to find any case in which the tracing was deemed compatible with survival.

CONCLUSION

On the basis that it would be inappropriate to initiate vigorous resuscitation in patients who can be identified as "dead" and beyond help an algorithm was prepared to guide ambulance personnel.

The causative rhythm in out-of-hospital cardiac arrests witnessed by the emergency medical services in the Heartstart Scotland Project

Out-of-hospital defibrillation has been shown to improve survival in out-of-hospital cardiac arrests. The maximum performance of defibrillation-based systems is dependent on the proportion of cardiac arrests due to tachyarrhythmias. We reviewed 4248 reported arrests in the Heartstart Scotland database. We identified 3489 arrests due to cardiac or unknown cause. From this group we selected 258 cases known to be conscious on arrival of the crew. We were able to retrieve electrocardiographic data on the period within 2 min of the arrest in 106 cases. The first recorded rhythm at the arrest was ventricular fibrillation in 64%, ventricular tachycardia 4%, bradycardia in 28% and electromechanical dissociation in 4%. Defibrillatory shocks were delivered to 96% of patients in ventricular fibrillation and 60% of these patients survived. None of the patients with bradycardic arrests survived. Preceding chest pain was noted in 79% of patients subsequently developing ventricular fibrillation as the cause of arrest compared to only 37% of those suffering bradycardic arrests. It would appear that public awareness of the importance of early contact with the emergency services after the onset of chest pain could substantially improve the survival from out-of-hospital arrests.

Pemphigus associated with nail dystrophy

Two patients suffering from pemphigus vulgaris were found to have nail dystrophies which antedated the onset of mucocutaneous lesions by many years. The nail changes improved substantially on treatment of the bullous disease. One patient had nail matrix histology consistent with pemphigus, and both had positive direct immunofluorescence with intercellular IgG in the matrix epithelium, as well as at other body sites. We propose that dystrophic nails, as a non-specific indicator of autoimmune disease, are a genuine and relevant finding in pemphigus.

Performance of an established system of first responder out-of-hospital defibrillation. The results of the second year of the Heartstart Scotland Project in the 'Utstein Style'

The Heartstart Scotland project for out-of-hospital defibrillation covers the whole of Scotland, a population of approximately 5,102,400 (14.9% > 65 years, 48.3% male). All 395 ambulances in Scotland have been equipped with an automated external defibrillator and crews are trained in basic cardiopulmonary resuscitation and defibrillator use (EMT-D). Between 1 May 1990 and 30 April 1991 a total of 1700 cardiac arrests was reported by the ambulance service. Of the 1676 arrests which we could trace, 63% were witnessed. A total of 1383 (83%) of all patients were declared dead on arrival at hospital or in the emergency department, 119 (7%) died in hospital and 174 (10%) were discharged alive. Of the 174 survivors, 87% were conscious and normal at discharge, 9% had moderate residual disability and 2% severe disability. Survival of patients discharged alive from hospital was 85% at 1 year. Defibrillation was undertaken in 71% of the reported cardiac arrests. Survival of bystander witnessed arrests was increased from 7 to 15% with bystander CPR (P < 0.005). If the cardiac arrest was witnessed by the ambulance crew and required defibrillation, survival to discharge was 39%. Of bystander witnessed arrests reached while still in VF (n = 643), 11% were discharged alive. Patients who were defibrillated within 4 min of arrest had a 43% survival rate to hospital discharge.

Efficacy of out of hospital defibrillation by ambulance technicians using automated external defibrillators. The Heartstart Scotland Project

During the Heartstart Scotland project all 407 ambulances in Scotland were equipped with automated external defibrillators (AEDs). All cases of chest pain or collapse aged over 10 years were monitored and multiple 3-s rhythm strips recorded in a solid state memory module. A shockable rhythm was defined as an organised rhythm of > or = 180 beats/min or a disorganised rhythm of > or = 100 beats/min and amplitude > 0.1 mV. We analysed all the stored rhythm strips in two patient populations to determine the ability of the AED and ambulance crews to detect a shockable rhythm and to initiate appropriate defibrillation. The first population comprised 493 patients, all of whom had received shocks. A total of 4741 rhythm strips were analysed, of which 1461 were true positives, 33 false positives, 3161 true negatives and 86 false negatives. Overall sensitivity of the AED was 94.4% and specificity 99.0%. The second population comprised a random sample of 200 shocked and 200 non-shocked arrests. The combined group contained 4154 rhythm strips of which 562 were true positives, 12 false positives, 3460 true negatives and 120 false negatives. Overall sensitivity of the system (AED+crew) was 82.4% and specificity 99.7%. However, only 66 of the 120 false negatives were attributable to the AED giving a sensitivity of 90.3% for the AED. The sensitivity of the AED is dependent on the prevalence of shockable rhythms, but will be within the range 90.3-94.4% for most emergency medical services. We conclude that early management of potentially lethal arrhythmias by ambulance technicians using AEDs is practical with acceptable sensitivity and specificity.

NADP-linked malic enzyme. Purification from maize leaves, Mr and subunit composition

1. The isolation of NADP-linked malic enzyme (EC 1.1.1.40) from maize leaves is described, together with studies of its Mr and subunit composition. 2. The enzyme was purified to apparent homogeneity by affinity chromatography on N6-aminohexyl-2',5'-bisphosphoadenosine-agarose, gel filtration with Sephadex G-100 and ion-exchange chromatography on DEAE-Sephadex A-50. A purification of 140-fold with a 30% yield was obtained. 3. A detailed study of the Mr by several methods revealed the existence of different Mr forms in solution. 4. In the presence of dithiothreitol the enzyme appears to be present in triethanolamine buffer, pH 7.5, as a tetramer with a subunit Mr of 60,000 and an S20,w of 10.75 S. 5. In phosphate buffer, pH 7.0, it seems to be a dimer of Mr 120,000 with an S20,w of 7.95 S. 6. In the absence of dithiothreitol, lower-Mr forms were detected by sedimentation-equilibrium and sedimentation-velocity studies in triethanolamine buffer. 7. Results from gel filtration gave Mr values of about 340,000 in both buffers.

The effects of isotretinoin on follicular and sebaceous gland differentiation

Follicular and sebaceous gland cell differentiation was investigated during treatment of acne patients with isotretinoin. Sebaceous glands were significantly reduced in volume and showed decreased metabolic activity as measured by glucose-6-phosphate dehydrogenase and succinic dehydrogenase enzyme activities. There was no measurable change in the volume of follicular duct epithelium or in its metabolic activity during treatment. Metabolic activity was also unchanged in the interfollicular epidermis, contrasting with the effects of another retinoid, etretinate. These findings provide no support for the proposition that alteration in the process of follicular keratinization forms a substantial part of the mode of action of isotretinoin.

Lichen sclerosus et atrophicus with ocular and maxillary complications

An unusual case of lichen sclerosus et atrophicus (LSA) with extracutaneous manifestations is described and the relationship between LSA and morphoea is discussed.

The effect of tetracycline and erythromycin in a model of acne-type inflammation

The effects of systemically administered oxytetracycline and erythromycin in a guinea pig model of acne-type inflammation were assessed histologically and by tissue measurement techniques. It was found that oxytetracycline significantly reduced the volume and maximum area of inflammation compared with both control and erythromycin treated groups. Oxytetracycline also altered the morphology of the inflammatory infiltrate significantly reducing the proportion of polymorphonuclear leucocytes present. In this model, erythromycin did not alter the inflammatory response but did seem to reduce the amount of transepidermal elimination of inflammatory debris.

Hair follicle-like change over histiocytomas

Epidermal hyperplasia is a common finding overlying histiocytomas. Occasionally, a distinctive type of basaloid hyperplasia occurs, with differentiation into primitive hair follicle tissue. This study attempts to characterize this change and determine whether it is associated with any particular clinical or histological feature. Data from patients with histiocytomas displaying induction of pilar epithelium in the epidermis above the lesions was compared with data from controls who did not show this change. The size, site, and duration of histiocytomas were similar in both groups, as were the predominant cell type and distance of histiocytoma from the epidermis. Serial sectioning of histiocytomas showed that the induction of pilar epithelium was a focal phenomenon, often missed in routine sections. It is suggested that histiocytoma cells may produce a "hair organizing mediator."

Treatment of chronic discoid lupus erythematosus with an oral gold compound (auranofin)

Twenty-three patients with severe longstanding discoid lupus erythematosus, unresponsive to conventional treatments, were treated with oral gold in a multicentre open study. Nineteen patients showed clinical improvement and in four of these there was complete resolution of lesions. Adverse reactions were generally mild and self limiting.

Kinetic studies of 6-phosphogluconate dehydrogenase from sheep liver

The steady-state kinetics of the oxidative decarboxylation of 6-phosphogluconate catalysed by 6-phosphogluconate dehydrogenase from sheep liver in triethanolamine and phosphate buffers (pH 7.0) have been reinvestigated. In triethanolamine buffer the enzyme is inhibited by high NADP+ concentrations in the presence of low fixed concentrations of 6-phosphogluconate. Data are consistent with an asymmetric sequential mechanism in which NADP+ and 6-phosphogluconate bind randomly and product release is ordered. The pathway through the enzyme--6-phosphogluconate complex appears to be preferred in triethanolamine buffer. Pre-steady-state studies of the oxidative decarboxylation reaction at pH 6.0-8.0 show that hydride transfer is greater than 900 s-1. After the fast formation of NADPH in amounts equivalent to about half of the enzyme-active-centre concentration, the rate of NADPH formation is equal to the steady-state rate. Two possible interpretations are considered. Rapid fluorescence measurements of the displacement of NADPH from its complex with the enzyme at pH 6.0 and 7.0 indicate that the dissociation of NADPH is fast (greater than 800 s-1) and cannot be the rate-limiting step in oxidative decarboxylation. Coenzyme binding studies at equilibrium have been extended to include the determination of the dissociation constants for the binary complexes of enzyme with NADPH and NADP+ at pH 6.0-8.0 and the dissociation constant for NADPH in the ternary enzyme--6-phosphogluconate--NADPH complex in triethanolamine buffer, pH 7.0.

The chemical mechanism of sheep liver 6-phosphogluconate dehydrogenase. A Schiff-base intermediate is not involved

[2-18O]Ribulose 5-phosphate was prepared and shown to be converted enzymically by 6-phosphogluconate dehydrogenase from sheep liver into 6-phosphogluconate with complete retention of the heavy isotope. This finding unequivocally excludes the possibility of a Schiff-base mechanism for the enzyme. The involvement of metal ions has already been excluded, and other possible mechanisms are discussed. The enzyme was purified by an improved large-scale procedure, which is briefly described.

Chemical modification of sheep-liver 6-phosphogluconate dehydrogenase by diethylpyrocarbonate. Evidence for an essential histidine residue

Sheep liver 6-phosphogluconate dehydrogenase is shown to be inactivated by diethylpyrocarbonate in a biphasic manner at pH 6.0, 25 degrees C. After allowing for the hydrolysis of the reagent, rate constants of 56 M-1 s-1 and 11.0 M-1 s-1 were estimated for the two processes. The complete reactivation of partially inactivated enzyme by neutral hydroxylamine, the elimination of the possibility that modification of cysteine or tyrosine residues are responsible for inactivation, and the magnitudes of the rate constants for inactivation relative to the experimentally determined value for the reaction of diethylpyrocarbonate with N alpha-acetylhistidine (2.2 M-1 s-1), all suggested that enzyme inactivation occurs solely by modification of histidine residues. Comparison of the experimental plot of residual fractional activity versus the number of modified histidine residues per subunit with simulated plots for three hypothetical models, each predicting biphasic kinetics, indicated that inactivation results from the modification of at most one essential histidine residue per subunit, although it appears that other (non-essential) histidines react independently. This histidine is thought to be His-242 and is present in the active site. Evidence in support of its role in catalysis is briefly discussed. Both 6-phosphogluconate and organic phosphate protect against inactivation, and a kinetic analysis of the protection indicated a dissociation constant of 2.1 X 10(-6) M for the enzyme--6-phosphogluconate complex. NADP+ also protected, but this might be due, at least in part, to a reduction in the effective concentration of diethylpyrocarbonate.

Inflammation caused by intracutaneous implantation of stratum corneum

When an epidermoid cyst ruptures, a granulomatous infiltrate develops around the damaged structure. The same is true when other horn-containing cysts release their content into the epidermis. A similar type of inflammation may be observed in the dermis around disrupted and horn-filled follicles in acne vulgaris. In this paper we describe experiments in which a granulomatous inflammation has been produced in guinea-pig skin by the intracutaneous implantation of stratum corneum and discuss the potential of this system as a model for the inflammation in acne.

Inflammation due to intra-cutaneous implantation of stratum corneum

Fragments of sterile heel callus and suspensions of human corneocytes were implanted or injected intra-cutaneously into flank skin of guinea pigs. A mixed cellular type of inflammation was produced characterized by the accumulation of polymorphonuclear leucocytes in the early stages and a more granulomatous picture in the later stages. Epithelial hypertrophy and follicular distortion with transepidermal elimination was a frequent accompaniment. Immunoglobulins and the complement component C3 were found scattered irregularly in the inflammation produced and were not thought to be important in the process. The inflammation produced closely emulated the changes observed in acne inflammation and after rupture of horn containing cysts. It is suggested that inflammation caused by the implantation of horn may be suitable for study of human skin disease in which horny debris is released into the dermis, such as acne.

Kinetics of dissociation of reduced nicotinamide adenine dinucleotide phosphate from its complexes with malic enzyme in relation to substrate inhibition and half-of-the-sites reactivity

Malic enzyme of pigeon liver binds NADPH at four equivalent enzyme sites and binds Mn2+ and malate each at two sets of "tight" and "weak" sites with negative cooperativity [Pry, T. A., & Hsu, R. Y. (1980) Biochemistry 19, 951-962]. Stopped-flow studies on the displacement of NADPH from the malate-enzyme complexes E4-NADPH4, E4-Mn2(2+)-NADPH4, E4-Mn2(2+)-NADPH4-dimalate, and E4-Mn2(2+)-NADPH4-tetramalate by large excess NADP+ or its analogue phosphoadenosine(2')diphospho(5')ribose show that NADPH dissociates from the binary complex rapidly with a first-order rate constant of 427 s-1. Dissociation from the ternary E4-Mn2(2+)-NADPH4 complex containing two tightly bound Mn2+ ions can be described by a single first-order process with a rate constant of 135 s-1, or more satisfactorily by two simultaneous first-order processes attributable to the reactions of Mn2+-deficient (k congruent to 427 s-1) and Mn2+-liganded (k = 96 s-1) subunits. The latter equals twice the maximum steady-state turnover rate of 53.2 + 3.0 s-1 assigned to dissociation of the reduced nucleotide from transient E-Mn2+-NADPH, and this 2:1 ratio strongly supports our proposed "half-of-the-sites" model [Hsu, R. Y., & Pry, T. A. (1980) Biochemistry 19, 962-968]. Dissociation from the E4-Mn2(2+)-NADPH4-dimalate complex (k = 100 s-1) follows only the slower process, suggesting that occupancy of malate at two sites tightens enzyme-bound NADPH on the adjacent sites. Binding of malate at two additional weak sites yields E4-Mn2(2+)-NADPH4-tetramalate and a NADPH dissociation rate constant of 2.69 s-1. The 97% decrease in NADPH dissociation parallels the observed 93% maximal inhibition by malate and is the cause of substrate inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)

On the mechanism of NADP+-linked isocitrate dehydrogenase from heart mitochondria. II. The transient-state kinetics of the oxidative decarboxylation of isocitrate

The kinetics of a single turnover of enzyme-catalysed oxidative decarboxylation have been studied by mixing a stoichiometric complex of enzyme, isocitrate and Mg2+ with large concentrations of NADP+ in a stopped-flow apparatus, and monitoring the formation of NADPH by fluorescence measurements. A transient is revealed that exhibits enhanced nucleotide fluorescence and is not detectable by light absorption measurements. The results obtained with the largest NADP+ concentrations, such that the product NADPH is largely displaced from its enzyme complex, show that a step that precedes the release of free NADPH is rate-limiting in the oxidative decarboxylation reaction under conditions of catalytic cycling. The rate constants for this step, tentatively identified as the formation of the complex of enzyme, Mg2+ and NADPH from a precursor NADPH-containing complex, and for the dissociation of NADPH from this complex have been estimated from the integrated rate equation for a simple model for the product phase of the reaction, by methods of nonlinear regression analysis. In line with the conclusions from the preceding paper, it is suggested that formation of an abortive complex of enzyme, Mg2+, isocitrate and NADPH under catalytic cycling conditions serves to by-pass the potentially rate-limiting dissociation of NADPH from the enzyme-Mg2+-NADPH complex.

On the mechanism of NADP+-linked isocitrate dehydrogenase from heart mitochondria. I. The kinetics of dissociation of NADPH from its enzyme complex

The kinetics of dissociation of NADPH from its complex with isocitrate dehydrogenase, and from the abortive complex of enzyme, Mg2+, isocitrate and NADPH, have been studied in phosphate and triethanolamine buffers by means of rapid fluorescence measurements. The reactions are complex, and it is suggested that a conformational equilibrium of each of the complexes is involved, and that this conformational change is also responsible for a slow approach to the steady-state rate of oxidative decarboxylation observed previously in triethanolamine buffer under certain conditions (K. Dalziel, N. McFerran, B. Matthews & C.H. Reynolds, Biochem. J. 171, 743-750 (1978) ). It is concluded that release of free NADPH product is not the rate-limiting step in oxidative decarboxylation in the steady state. The validity of the ligand displacement method used to measure the dissociation kinetics of the enzyme-NADPH complex has been studied by computer simulation.

Glyceraldehyde-3-phosphate dehydrogenase

Conflicting experimental evidence of the pathway of catalysis for the enzyme from rabbit, pig and lobster muscle tissues is reviewed. Transient kinetic studies with the enzyme from rabbit muscle are presented. The results are shown to be consistent with the double-displacement mechanism of catalysis originally proposed by Segal & Boyer (1953). The rate constant for combination of the aldehyde form of the substrate with the NAD+ complex of the enzyme is about 3 X 10(7) M-1 S-1, and for all four subunits of the molecule the rate constant for hydride transfer in the ternary complex formed is greater than 10(3) S-1, consistent with their simultaneous participation in catalysis. Recent steady-state kinetic studies with the rabbit muscle enzyme, in contrast to earlier studies, also provide evidence to support the Segal-Boyer pathway if the kinetic effects of the negative cooperativity of NAD+ binding are taken into account. Experimental data for the binding of NAD+ to the enzyme from muscles and from Bacillus stearothermophilus, and their interpretations, are also briefly reviewed. The information currently available from X-ray crystallography regarding the structures of holoenzyme and apoenzyme from B. stearothermophilus and lobster muscle is outlined.

Determination of the stability constants of Mn2+ and Mg2+ complexes of the components of the NADP-linked isocitrate dehydrogenase reaction by electron spin resonance

1. The stability constants (Ks) of Mn2+ and Mg2+ complexes of isocitrate, 2-oxoglutarate, NADP and NADPH have been estimated by using electron spin resonance to measure free Mn2+ in ligand--metal-ion solutions. 2. The values of Ks for the Mn2+ complexes at 25 degrees C, in triethanolamine buffer containing NaCl, pH 7.0 and ionic strength 0.15 M, are 497 M-1 for isocitrate, 39 M-1 for 2-oxoglutarate, 467 M-1 for NADP and 943 M-1 for NADPH. 3. For the Mg2+ complexes under the same conditions, the Ks values are 357 M-1, 25 M-1, 133 M-1 and 179 M-1 respectively. The large difference between the stabilities of the isocitrate and 2-oxoglutarate complexes is thus largely responsible for the observed variation of the apparent equilibrium constant of the NADP-linked isocitrate dehydrogenase reaction with magnesium ion concentration. 4. NADP-linked isocitrate dehydrogenase from bovine heart mitochondria binds Mn2+, and the stability constant of the complex is about 2.2 x 10(4) M-1. The formation of this complex may explain the inhibition of the enzyme-catalysed reaction observed with Mn2+ concentrations greater than 0.2 mM in initial rate measurements.

Intracellular distribution of NADP-linked isocitrate dehydrogenase, fumarase and citrate synthase in bovine heart muscle

By fractional extraction of minced bovine heart muscle with iso-osmotic sucrose and phosphate buffer solutions, it is shown that less than 4% of the total citrate synthase in the tissue is in the cytosol. Using citrate synthase as a marker for broken mitochondria, two methods of fractionation of 750 x g supernatants from homogenates of bovine heart muscle show that 10% of the total fumarase and NADP-linked isocitrate dehydrogenase activities are present in the cytoplasm. Homogenates prepared by sonication and osmotic shock and by sand-grinding gave closely similar results as regards enzyme distributions and extent of mitochondrial breakage. The results are compared with those reported for other tissues.