Modelling the cost-effectiveness of adopting risk-stratified approaches to extended screening intervals in the national diabetic retinopathy screening programme in Scotland.

AIMS: To assess the cost-effectiveness of adopting risk-stratified approaches to extended screening intervals in the national diabetic retinopathy screening programme in Scotland. METHODS: A continuous-time hidden Markov model was fitted to national longitudinal screening data to derive transition probabilities between observed non-referable and referable retinopathy states. These were incorporated in a decision model simulating progression, costs and visual acuity outcomes for a synthetic cohort with a covariate distribution matching that of the Scottish diabetic screening population. The cost-effectiveness of adopting extended (2-year) screening for groups with no observed retinopathy was then assessed over a 30-year time horizon. RESULTS: Individuals with a current grade of no retinopathy on two consecutive screening episodes face the lowest risk of progressing to referable disease. For the cohort as a whole, the incremental cost per quality-adjusted life year gained for annual vs. biennial screening ranged from approximately £74 000 (for those with no retinopathy and a prior observed grade of mild or observable background retinopathy) to approximately £232 000 per quality-adjusted life year gained (for those with no retinopathy on two consecutive screening episodes). The corresponding incremental cost-effectiveness ratios in the subgroup with Type 1 diabetes were substantially lower; approximately £22 000 to £85 000 per quality-adjusted life year gained, respectively. CONCLUSIONS: Biennial screening for individuals with diabetes who have no retinopathy is likely to deliver significant savings for a very small increase in the risk of adverse visual acuity and quality of life outcomes. There is greater uncertainty regarding the long-term cost-effectiveness of adopting biennial screening in younger people with Type 1 diabetes.

Cost-effectiveness of ultrasound-guided foam sclerotherapy, endovenous laser ablation or surgery as treatment for primary varicose veins from the randomized CLASS trial.

BACKGROUND: The treatment of patients with varicose veins constitutes a considerable workload and financial burden to the National Health Service. This study aimed to assess the cost-effectiveness of ultrasound-guided foam sclerotherapy (UGFS) and endovenous laser ablation (EVLA) compared with conventional surgery as treatment for primary varicose veins. METHODS: Participant cost and utility data were collected alongside the UK CLASS multicentre randomized clinical trial, which compared EVLA, surgery and UGFS. Regression methods were used to estimate the effects of the alternative treatments on costs to the health service and quality-adjusted life-years (QALYs) at 6 months. A Markov model, incorporating available evidence on clinical recurrence rates, was developed to extrapolate the trial data over a 5-year time horizon. RESULTS: Compared with surgery at 6 months, UGFS and EVLA reduced mean costs to the health service by £655 and £160 respectively. When additional overhead costs associated with theatre use were included, these cost savings increased to £902 and £392 respectively. UGFS produced 0·005 fewer QALYs, whereas EVLA produced 0·011 additional QALYs. Extrapolating to 5 years, EVLA was associated with increased costs and QALYs compared with UGFS (costing £3640 per QALY gained), and generated a cost saving (£206-439) and QALY gain (0·078) compared with surgery. Applying a ceiling willingness-to-pay ratio of £20 000 per QALY gained, EVLA had the highest probability (78·7 per cent) of being cost-effective. CONCLUSION: The results suggest, for patients considered eligible for all three treatment options, that EVLA has the highest probability of being cost-effective at accepted thresholds of willingness to pay per QALY.

Improving the economic value of photographic screening for optical coherence tomography-detectable macular oedema: a prospective, multicentre, UK study.

OBJECTIVES: To determine the best photographic surrogate markers for detecting sight-threatening macular oedema (MO) in people with diabetes attending UK national screening programmes. DESIGN: A multicentre, prospective, observational cohort study of 3170 patients with photographic signs of diabetic retinopathy visible within the macular region [exudates within two disc diameters, microaneurysms/dot haemorrhages (M/DHs) and blot haemorrhages (BHs)] who were recruited from seven study centres. SETTING: All patients were recruited and imaged at one of seven study centres in Aberdeen, Birmingham, Dundee, Dunfermline, Edinburgh, Liverpool and Oxford. PARTICIPANTS: Subjects with features of diabetic retinopathy visible within the macular region attending one of seven diabetic retinal screening programmes. INTERVENTIONS: Alternative referral criteria for suspected MO based on photographic surrogate markers; an optical coherence tomographic examination in addition to the standard digital retinal photograph. MAIN OUTCOME MEASURES: (1) To determine the best method to detect sight-threatening MO in people with diabetes using photographic surrogate markers. (2) Sensitivity and specificity estimates to assess the costs and consequences of using alternative strategies. (3) Modelled long-term costs and quality-adjusted life-years (QALYs). RESULTS: Prevalence of MO was strongly related to the presence of lesions and was roughly five times higher in subjects with exudates or BHs or more than two M/DHs within one disc diameter. Having worse visual acuity was associated with about a fivefold higher prevalence of MO. Current manual screening grading schemes that ignore visual acuity or the presence of M/DHs could be improved by taking these into account. Health service costs increase substantially with more sensitive/less specific strategies. A fully automated strategy, using the automated detection of patterns of photographic surrogate markers, is superior to all current manual grading schemes for detecting MO in people with diabetes. The addition of optical coherence tomography (OCT) to each strategy, prior to referral, results in a reduction in costs to the health service with no decrement in the number of MO cases detected. CONCLUSIONS: Compared with all current manual grading schemes, for the same sensitivity, a fully automated strategy, using the automated detection of patterns of photographic surrogate markers, achieves a higher specificity for detecting MO in people with diabetes, especially if visual acuity is included in the automated strategy. Overall, costs to the health service are likely to increase if more sensitive referral strategies are adopted over more specific screening strategies for MO, for only very small gains in QALYs. The addition of OCT to each screening strategy, prior to referral, results in a reduction in costs to the health service with no decrement in the number of MO cases detected. STUDY REGISTRATION: This study has been registered as REC/IRAS 07/S0801/107, UKCRN ID 9063 and NIHR HTA 06/402/49. SOURCE OF FUNDING: This project was funded by the NIHR Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 17, No. 51. See the HTA programme website for further project information.

The diagnostic accuracy and cost-effectiveness of magnetic resonance spectroscopy and enhanced magnetic resonance imaging techniques in aiding the localisation of prostate abnormalities for biopsy: a systematic review and economic evaluation.

BACKGROUND: In the UK, prostate cancer (PC) is the most common cancer in men. A diagnosis can be confirmed only following a prostate biopsy. Many men find themselves with an elevated prostate-specific antigen (PSA) level and a negative biopsy. The best way to manage these men remains uncertain. OBJECTIVES: To assess the diagnostic accuracy of magnetic resonance spectroscopy (MRS) and enhanced magnetic resonance imaging (MRI) techniques [dynamic contrast-enhanced MRI (DCE-MRI), diffusion-weighted MRI (DW-MRI)] and the clinical effectiveness and cost-effectiveness of strategies involving their use in aiding the localisation of prostate abnormalities for biopsy in patients with prior negative biopsy who remain clinically suspicious for harbouring malignancy. DATA SOURCES: Databases searched--MEDLINE (1946 to March 2012), MEDLINE In-Process & Other Non-Indexed Citations (March 2012), EMBASE (1980 to March 2012), Bioscience Information Service (BIOSIS; 1995 to March 2012), Science Citation Index (SCI; 1995 to March 2012), The Cochrane Library (Issue 3 2012), Database of Abstracts of Reviews of Effects (DARE; March 2012), Medion (March 2012) and Health Technology Assessment database (March 2012). REVIEW METHODS: Types of studies: direct studies/randomised controlled trials reporting diagnostic outcomes. INDEX TESTS: MRS, DCE-MRI and DW-MRI. Comparators: T2-weighted magnetic resonance imaging (T2-MRI), transrectal ultrasound-guided biopsy (TRUS/Bx). Reference standard: histopathological assessment of biopsied tissue. A Markov model was developed to assess the cost-effectiveness of alternative MRS/MRI sequences to direct TRUS-guided biopsies compared with systematic extended-cores TRUS-guided biopsies. A health service provider perspective was adopted and the recommended 3.5% discount rate was applied to costs and outcomes. RESULTS: A total of 51 studies were included. In pooled estimates, sensitivity [95% confidence interval (CI)] was highest for MRS (92%; 95% CI 86% to 95%). Specificity was highest for TRUS (imaging test) (81%; 95% CI 77% to 85%). Lifetime costs ranged from £3895 using systematic TRUS-guided biopsies to £4056 using findings on T2-MRI or DCE-MRI to direct biopsies (60-year-old cohort, cancer prevalence 24%). The base-case incremental cost-effectiveness ratio for T2-MRI was <£30,000 per QALY (all cohorts). Probabilistic sensitivity analysis showed high uncertainty surrounding the incremental cost-effectiveness of T2-MRI in moderate prevalence cohorts. The cost-effectiveness of MRS compared with T2-MRI and TRUS was sensitive to several key parameters. LIMITATIONS: Non-English-language studies were excluded. Few studies reported DCE-MRI/DW-MRI. The modelling was hampered by limited data on the relative diagnostic accuracy of alternative strategies, the natural history of cancer detected at repeat biopsy, and the impact of diagnosis and treatment on disease progression and health-related quality of life. CONCLUSIONS: MRS had higher sensitivity and specificity than T2-MRI. Relative cost-effectiveness of alternative strategies was sensitive to key parameters/assumptions. Under certain circumstances T2-MRI may be cost-effective compared with systematic TRUS. If MRS and DW-MRI can be shown to have high sensitivity for detecting moderate/high-risk cancer, while negating patients with no cancer/low-risk disease to undergo biopsy, their use could represent a cost-effective approach to diagnosis. However, owing to the relative paucity of reliable data, further studies are required. In particular, prospective studies are required in men with suspected PC and elevated PSA levels but previously negative biopsy comparing the utility of the individual and combined components of a multiparametric magnetic resonance (MR) approach (MRS, DCE-MRI and DW-MRI) with both a MR-guided/-directed biopsy session and an extended 14-core TRUS-guided biopsy scheme against a reference standard of histopathological assessment of biopsied tissue obtained via saturation biopsy, template biopsy or prostatectomy specimens. STUDY REGISTRATION: PROSPERO number CRD42011001376. FUNDING: The National Institute for Health Research Health Technology Assessment programme.

Denosumab for the prevention of osteoporotic fractures in postmenopausal women.

This paper presents a summary of the evidence review group (ERG) report into denosumab for the prevention of osteoporotic fractures in postmenopausal women. Denosumab has been shown in a large randomised trial to reduce the frequency of osteoporotic fractures when given subcutaneously at 6-monthly intervals. Compared with placebo, the relative risks of clinical vertebral and hip fractures were 0.32 and 0.60, respectively. Clinical vertebral fractures occurred in 0.8% of women taking denosumab and 2.6% of control subjects. Hip fractures occurred in 1.2% of women on placebo and 0.7% on denosumab. The expected use is in women who cannot tolerate oral bisphosphonates. Other options in that situation include strontium ranelate and zoledronate, which, compared with placebo, also reduced the risk of clinical vertebral fractures [relative risk (RR) 0.65 and 0.23, respectively]. Zoledronate also significantly reduced the risk of hip fractures (RR 0.59). The ERG concluded that zoledronate was the main comparator. The relative cost-effectiveness of denosumab and zoledronate depends mainly on assumptions about costs of administration.

Early referral strategies for management of people with markers of renal disease: a systematic review of the evidence of clinical effectiveness, cost-effectiveness and economic analysis.

BACKGROUND: Chronic kidney disease (CKD) is a long-term condition and has been described as the gradual loss of kidney function over time. Early in the disease process, people with CKD often experience no symptoms. For a long time, CKD has been an underdiagnosed condition. Even in the absence of symptoms, CKD appears to add significantly to the burden of cardiovascular disease and death and, for an important minority, can progress to kidney failure. OBJECTIVE: To systematically review the evidence of the clinical effectiveness and cost-effectiveness of early referral strategies for management of people with markers of renal disease. DATA SOURCES: Electronic searches of 12 major databases (such as MEDLINE, EMBASE, CINAHL, etc.) were conducted for the time period of 1990 to April 2008 to identify studies comparing early referral to other care options for people with CKD. Additional searching was performed in the NHS Economic Evaluation Database to support the cost-effectiveness literature review. REVIEW METHODS: Two authors reviewed all titles, abstracts and full papers to select relevant literature. A Markov model was constructed to represent the natural history of CKD. The model allowed cohorts to be tracked according to estimated glomerular filtration rate (eGFR) status and the presence of other complications known to influence CKD progression and the incidence of cardiovascular events. RESULTS: From 36 relevant natural history studies, CKD was found to be, despite marked heterogeneity between studies, a marker of increased risk of mortality, renal progression and end-stage renal disease. Mortality was generally high and increased with stage of CKD. After adjustment for comorbidities, the relative risk of mortality among those with CKD identified from the general population increased with stage. For clinical populations, the relative risk was higher. All three outcomes increased as eGFR fell. Only seven studies, and no randomised controlled trials, were identified as relevant to assessing the clinical effectiveness of early referral strategies for CKD. In the five retrospective studies constructed from cohorts starting on renal replacement therapy (RRT), mortality was reduced in the early referral group (more than 12 months prior to RRT) even as late as 5 years after initiation of RRT. Only two studies included predialysis participants. One study, in people screened for diabetic nephropathy, reported a reduction in the decline in renal function associated with early referral to nephrology specialists (eGFR decline 3.4 ml/min/1.73 m(2)) when compared with a similar group that had no access to nephrology services until dialysis was required (eGFR decline 12.0 ml/min/1.73 m(2)). The second study, among a group of veterans with two creatinine levels of at least 140 mg/dl, reported that a composite end point of death or progression was lower in the group receiving nephrology follow-up than in those receiving only primary care follow-up. The greatest effect was observed in those with stage 3 or worse disease after adjustment for comorbidities, age, race, smoking and proteinuria {stage 3: hazard ratio (HR) 0.8 [95% confidence interval (CI) 0.61 to 0.9)]; stage 4: HR 0.75 (95% CI 0.45 to 0.89)}. In the base-case analysis, all early referral strategies produced more quality-adjusted life-years (QALYs) than referral upon transit to stage 5 CKD (eGFR 15 ml/min/1.73 m(2)). Referral for everyone with an eGFR below 60 ml/min/1.73 m(2) (stage 3a CKD) generated the most QALYs and, compared with referral for stage 4 CKD (eGFR < 30 ml/min/1.73 m(2)), had an incremental cost-effectiveness ratio of approximately 3806 pounds per QALY. LIMITATIONS: Because of a lack of data on the natural history of CKD in individuals without diabetes, and a lack of evidence on the costs and effects of early referral, the Markov model relied on many assumptions. The findings were particularly sensitive to changes in eGFR decline rates and the relative effect of early referral on CKD progression and cardiovascular events; the latter parameter being derived from a single non-randomised study. CONCLUSIONS: Despite substantial focus on the early identification and proactive management of CKD in the last few years, we have identified significant evidence gaps about how best to manage people with CKD. There was some evidence to suggest that the care of people with CKD could be improved and, because these people are at risk from both renal and cardiovascular outcomes, strategies to improve the management of people with CKD have the potential to offer an efficient use of health service resources. Given the number of people now being recognised as having markers of kidney impairment, there is an urgent need for further research to support service change.

Costs and consequences of automated algorithms versus manual grading for the detection of referable diabetic retinopathy.

AIMS: To assess the cost-effectiveness of an improved automated grading algorithm for diabetic retinopathy against a previously described algorithm, and in comparison with manual grading. METHODS: Efficacy of the alternative algorithms was assessed using a reference graded set of images from three screening centres in Scotland (1253 cases with observable/referable retinopathy and 6333 individuals with mild or no retinopathy). Screening outcomes and grading and diagnosis costs were modelled for a cohort of 180 000 people, with prevalence of referable retinopathy at 4%. Algorithm (b), which combines image quality assessment with detection algorithms for microaneurysms (MA), blot haemorrhages and exudates, was compared with a simpler algorithm (a) (using image quality assessment and MA/dot haemorrhage (DH) detection), and the current practice of manual grading. RESULTS: Compared with algorithm (a), algorithm (b) would identify an additional 113 cases of referable retinopathy for an incremental cost of pound 68 per additional case. Compared with manual grading, automated grading would be expected to identify between 54 and 123 fewer referable cases, for a grading cost saving between pound 3834 and pound 1727 per case missed. Extrapolation modelling over a 20-year time horizon suggests manual grading would cost between pound 25,676 and pound 267,115 per additional quality adjusted life year gained. CONCLUSIONS: Algorithm (b) is more cost-effective than the algorithm based on quality assessment and MA/DH detection. With respect to the value of introducing automated detection systems into screening programmes, automated grading operates within the recommended national standards in Scotland and is likely to be considered a cost-effective alternative to manual disease/no disease grading.

Cost-effectiveness of implementing automated grading within the national screening programme for diabetic retinopathy in Scotland.

AIMS: National screening programmes for diabetic retinopathy using digital photography and multi-level manual grading systems are currently being implemented in the UK. Here, we assess the cost-effectiveness of replacing first level manual grading in the National Screening Programme in Scotland with an automated system developed to assess image quality and detect the presence of any retinopathy. METHODS: A decision tree model was developed and populated using sensitivity/specificity and cost data based on a study of 6722 patients in the Grampian region. Costs to the NHS, and the number of appropriate screening outcomes and true referable cases detected in 1 year were assessed. RESULTS: For the diabetic population of Scotland (approximately 160,000), with prevalence of referable retinopathy at 4% (6400 true cases), the automated strategy would be expected to identify 5560 cases (86.9%) and the manual strategy 5610 cases (87.7%). However, the automated system led to savings in grading and quality assurance costs to the NHS of 201,600 pounds per year. The additional cost per additional referable case detected (manual vs automated) totalled 4088 pounds and the additional cost per additional appropriate screening outcome (manual vs automated) was 1990 pounds. CONCLUSIONS: Given that automated grading is less costly and of similar effectiveness, it is likely to be considered a cost-effective alternative to manual grading.

The efficacy of automated "disease/no disease" grading for diabetic retinopathy in a systematic screening programme.

AIM: To assess the efficacy of automated "disease/no disease" grading for diabetic retinopathy within a systematic screening programme. METHODS: Anonymised images were obtained from consecutive patients attending a regional primary care based diabetic retinopathy screening programme. A training set of 1067 images was used to develop automated grading algorithms. The final software was tested using a separate set of 14 406 images from 6722 patients. The sensitivity and specificity of manual and automated systems operating as "disease/no disease" graders (detecting poor quality images and any diabetic retinopathy) were determined relative to a clinical reference standard. RESULTS: The reference standard classified 8.2% of the patients as having ungradeable images (technical failures) and 62.5% as having no retinopathy. Detection of technical failures or any retinopathy was achieved by manual grading with 86.5% sensitivity (95% confidence interval 85.1 to 87.8) and 95.3% specificity (94.6 to 95.9) and by automated grading with 90.5% sensitivity (89.3 to 91.6) and 67.4% specificity (66.0 to 68.8). Manual and automated grading detected 99.1% and 97.9%, respectively, of patients with referable or observable retinopathy/maculopathy. Manual and automated grading detected 95.7% and 99.8%, respectively, of technical failures. CONCLUSION: Automated "disease/no disease" grading of diabetic retinopathy could safely reduce the burden of grading in diabetic retinopathy screening programmes.

Screening for type 2 diabetes: literature review and economic modelling.

OBJECTIVES: To reconsider the aims of screening for undiagnosed diabetes, and whether screening should be for other abnormalities of glucose metabolism such as impaired glucose tolerance (IGT), or the 'metabolic syndrome'. Also to update the previous review for the National Screening Committee (NSC) on screening for diabetes, including reviewing choice of screening test; to consider what measures would be taken if IGT and impaired fasting glucose (IFG) were identified by screening, and in particular to examine evidence on treatment to prevent progression to diabetes in these groups; to examine the cost-effectiveness of screening; and to consider groups at higher risk at which screening might be targeted. DATA SOURCES: Electronic databases were searched up to the end of June 2005. REVIEW METHODS: Literature searches and review concentrated on evidence published since the last review of screening, both reviews and primary studies. The review of economic studies included only those models that covered screening. The new modelling extended an existing diabetes treatment model by developing a screening module. The NSC has a set of criteria, which it applies to new screening proposals. These criteria cover the condition, the screening test or tests, treatment and the screening programme. Screening for diabetes was considered using these criteria. RESULTS: Detection of lesser degrees of glucose intolerance such as IGT is worthwhile, partly because the risk of cardiovascular disease (CVD) can be reduced by treatment aimed at reducing cholesterol level and blood pressure, and partly because some diabetes can be prevented. Several trials have shown that both lifestyle measures and pharmacological treatment can reduce the proportion of people with IGT who would otherwise develop diabetes. Screening could be two-stage, starting with the selection of people at higher risk. The second-stage choice of test for blood glucose remains a problem, as in the last review for NSC. The best test is the oral glucose tolerance test (OGTT), but it is the most expensive, is inconvenient and has weak reproducibility. Fasting plasma glucose would miss people with IGT. Glycated haemoglobin does not require fasting, and may be the best compromise. It may be that more people would be tested and diagnosed if the more convenient test was used, rather than the OGTT. Five economic studies assessed the costs and short-term outcomes of using different screening tests. None examined the long-term impact of different proportions of false negatives. All considered the costs that would be incurred and the numbers identified by different tests, or different cut-offs. Results differed depending on different assumptions. They did not give a clear guide as to which test would be the best in any UK screening programme, but all recognised that the choice of cut-off would be a compromise between sensitivity and specificity; there is no perfect test. The modelling exercise concluded that screening for diabetes appears to be cost-effective for the 40-70-year age band, more so for the older age bands, but even in the 40-49-year age group, the incremental cost-effectiveness ratio for screening versus no screening is only 10,216 pounds per quality-adjusted life-year. Screening is more cost-effective for people in the hypertensive and obese subgroups and the costs of screening are offset in many groups by lower future treatment costs. The cost-effectiveness of screening is determined as much by, if not more than, assumptions about the degree of control of blood glucose and future treatment protocols than by assumptions relating to the screening programme. The very low cost now of statins is also an important factor. Although the prevalence of diabetes increases with age, the relative risk of CVD falls, reducing the benefits of screening. Screening for diabetes meets most of the NSC criteria, but probably fails on three: criterion 12, on optimisation of existing management of the condition; criterion 13, which requires that there should be evidence from high-quality randomised controlled trials (RCTs) showing that a screening programme would reduce mortality or morbidity; and criterion 18, that there should be adequate staffing and facilities for all aspects of the programme. It is uncertain whether criterion 19, that all other options, including prevention, should have been considered, is met. The issue here is whether all methods of improving lifestyles in order to reduce obesity and increase exercise have been sufficiently tried. The rise in overweight and obesity suggests that health promotion interventions have not so far been effective. CONCLUSIONS: The case for screening for undiagnosed diabetes is probably somewhat stronger than it was at the last review, because of the greater options for reduction of CVD, principally through the use of statins, and because of the rising prevalence of obesity and hence type 2 diabetes. However, there is also a good case for screening for IGT, with the aim of preventing some future diabetes and reducing CVD. Further research is needed into the duration of undiagnosed diabetes, and whether the rise in blood glucose levels is linear throughout or whether there may be a slower initial phase followed by an acceleration around the time of clinical diagnosis. This has implications for the interval after which screening would be repeated. Further research is also needed into the natural history of IGT, and in particular what determines progression to diabetes. An RCT of the type required by NSC criterion 13 is under way but will not report for about 7 years.

What do doctors think their caseload should be to maintain their skills for delivery care?

OBJECTIVES: To seek the opinions of doctors on what they thought the minimum, maximum and optimum annual caseload should be for the maintenance of skills and competence in a variety of obstetric procedures. METHODS: An expert panel of respondents from Africa and Asia was asked to give their opinions on what they believed the minimum, maximum and optimum caseload should be for 11 obstetric procedures via a series of structured questionnaires (Delphi exercise). In subsequent questionnaires, participants were asked if they wished to reconsider their opinions in light of the group response. RESULTS: The median values of responses given for the minimum, maximum and optimum caseloads for the 11 obstetric procedures did not change substantially over time, though greater consensus was developed as indicated by reductions in the size of inter-quartile ranges in later rounds. CONCLUSIONS: We encountered several problems associated with using the Delphi technique in this context, which throws doubt on the validity and usefulness of our results. Caseload is just one of many factors, as indicated by our expert panel that need to be considered when planning the delivery of obstetric services in remote areas. High quality training, continued medical education, appropriate quality assurance procedures, and provision of a supportive enabling environment are also important requirements. In addition, the views of clinicians need to be balanced against more objective evidence of quality of care and patient outcome in relation to procedural volume. Such evidence is lacking in the field of obstetrics and requires further investigation.

The cAMP-specific phosphodiesterase PDE4A5 is cleaved downstream of its SH3 interaction domain by caspase-3. Consequences for altered intracellular distribution.

The unique N-terminal region of the cAMP-specific phosphodiesterase PDE4A5, which confers an ability to bind to certain protein SH3 domains, is cleaved during apoptosis in both Rat-1 fibroblasts and PC12 cells. Cleavage was abolished by the caspase-3-selective inhibitor, z-DEVD-CHO but not the caspase-1 selective inhibitor, z-YVAD-CHO. Caspase-3 treatment of PDE4A5, expressed either transiently in COS cells or generated in vitro by coupled transcription translation, generated a similar cleavage product of 100 kDa compared with the native 110-kDa PDE4A5. This product could be detected immunochemically with an antibody raised to a C-terminal PDE4A5 peptide but not an antibody raised to the N terminus of PDE4A5, indicating that caspase-3 caused N-terminal cleavage of PDE4A5. Deletion of the putative caspase-3 cleavage site, (69)DAVD(72), in PDE4A5, or generation of either the D72A or the D69A mutants, ablated the ability of caspase-3 to cause cleavage. The N-terminal truncate PDE4A5-DeltaP3 was engineered to mimic the caspase-cleaved product of PDE4A5. This showed altered catalytic activity and, unlike PDE4A5, was unable to interact with the SH3 domain of the tyrosyl kinase, LYN. Although both PDE4A5 and PDE4A5-DeltaP3 were localized at cell cortical regions (ruffles), the distinct perinuclear association noted for both PDE4A5 and LYN was not seen for PDE4A5-DeltaP3. Staurosporine-induced apoptosis caused a marked redistribution of PDE4A5 but not PDE4A8 in stably transfected Rat-1 cells. The PDE4-selective inhibitor, rolipram together with the adenylyl cyclase activator forskolin, caused a synergistic increase in the apoptosis of Rat-1 cells. Overexpression of PDE4A5 in Rat-1 cells protected against staurosporine-induced apoptosis in contrast to overexpression of PDE4A8, which potentiated apoptosis. PDE4A5 may be the sole PDE4 family member to provide a substrate for caspase-3 cleavage and this action serves to remove the SH3 binding domain that is unique to this isoform within the PDE4A family and to alter its intracellular targeting.

The RACK1 signaling scaffold protein selectively interacts with the cAMP-specific phosphodiesterase PDE4D5 isoform.

The WD-repeat protein receptor for activated C-kinase (RACK1) was identified by its interaction with the cyclic AMP-specific phosphodiesterase (PDE4) isoform PDE4D5 in a yeast two-hybrid screen. The interaction was confirmed by co-immunoprecipitation of native RACK1 and PDE4D5 from COS7, HEK293, 3T3-F442A, and SK-N-SH cell lines. The interaction was unaffected by stimulation of the cells with the phorbol ester phorbol 2-myristate 3-acetate. PDE4D5 did not interact with two other WD-repeat proteins, beta'-coatomer protein and Gsbeta, in two-hybrid tests. RACK1 did not interact with other PDE4D isoforms or with known PDE4A, PDE4B, and PDE4C isoforms. PDE4D5 and RACK1 interacted with high affinity (Ka approximately 7 nM) [corrected] when they were expressed and purified from Escherichia coli, demonstrating that the interaction does not require intermediate proteins. The binding of the E. coli-expressed proteins did not alter the kinetics of cAMP hydrolysis by PDE4D5 but caused a 3-4-fold change in its sensitivity to inhibition by the PDE4 selective inhibitor rolipram. The subcellular distributions of RACK1 and PDE4D5 were extremely similar, with the major amount of both proteins (70%) in the high speed supernatant (S2) fraction. Analysis of constructs with specific deletions or single amino acid mutations in PDE4D5 demonstrated that a small cluster of amino acids in the unique amino-terminal region of PDE4D5 was necessary for its interaction with RACK1. We suggest that RACK1 may act as a scaffold protein to recruit PDE4D5 and other proteins into a signaling complex.

Characterization of five different proteins produced by alternatively spliced mRNAs from the human cAMP-specific phosphodiesterase PDE4D gene.

We have isolated and characterized complete cDNAs for two isoforms (HSPDE4D4 and HSPDE4A5) encoded by the human PDE4D gene, one of four genes that encode cAMP-specific rolipram-inhibited 3',5'-cyclic nucleotide phosphodiesterases (type IVPDEs; PDE4 family). The HSPDE4D4 and HSPDE4D5 cDNAs encode proteins of 810 and 746 amino acids respectively. A comparison of the nucleotide sequences of these two cDNAs with those encoding the three other human PDE4D proteins (HSPDE4D1, HSPDE4D2 and HSPDE4D3) demonstrates that each corresponding mRNA transcript has a unique region of sequence at or near its 5'-end, consistent with alternative mRNA splicing. Transient expression of the five cDNAs in monkey COS-7 cells produced proteins of apparent molecular mass under denaturing conditions of 68, 68, 95, 119 and 105 kDa for isoforms HSPDE4D1-5 respectively. Immunoblotting of human cell lines and rat brain demonstrated the presence of species that co-migrated with the proteins produced in COS-7 cells. COS-cell-expressed and native HSPDE4D1 and HSPDE4D2 were found to exist only in the cytosol, whereas HSPDE4D3, HSPDE4D4 and HSPDE4D5 were found in both cytosolic and particulate fractions. The IC50 values for the selective PDE4 inhibitor rolipram for the cytosolic forms of the five enzymes were similar (0.05-0.14 microM), whereas they were 2-7-fold higher for the particulate forms of HSPDE4D3 and HSPDE4D5 (0.32 and 0.59 microM respectively), than for the corresponding cytosolic forms. Our data indicate that the N-terminal regions of the HSPDE4D3, HSPDE4D4 and HSPDE4D5 proteins, which are derived from alternatively spliced regions of their mRNAs, are important in determining their subcellular localization, activity and differential sensitivity to inhibitors.

The human cyclic AMP-specific phosphodiesterase PDE-46 (HSPDE4A4B) expressed in transfected COS7 cells occurs as both particulate and cytosolic species that exhibit distinct kinetics of inhibition by the antidepressant rolipram.

Transfection of COS7 cells with a plasmid encoding the human cyclic AMP-specific PDE4A phosphodiesterase PDE-46 (HSPDE4A4B) led to the expression of a rolipram-inhibited PDE4 activity, which contributed approximately 96% of the total COS cell PDE activity. A fusion protein was generated which encompassed residues (788-886) at the extreme C terminus of PDE-46 and was used to generate an antiserum that detected PDE-46 in transfected COS7 cells. Immunoblotting studies identified PDE-46 as a approximately 125-kDa species that was associated with both the soluble and particulate fractions. The relative Vmax of particulate PDE-46 was approximately 56% that of cytosolic PDE-46. Particulate PDE-46 was not solubilized using Triton X-100 or high NaCl concentrations. Immunofluorescence analysis by laser scanning confocal microscopy showed that PDE-46 was located at discrete margins of the cell, indicative of association with membrane cortical regions. The human PDE4A species, h6.1 (HSPDE4A4C), which lacks the N-terminal extension of PDE-46, was found as an entirely soluble species when expressed in COS7 cells. h6.1 was shown to have an approximately 11-fold higher Vmax relative to that of PDE-46. In dose-response studies rolipram inhibited particulate PDE-46 at much lower concentrations (IC50 = 0. 195 microM) than those needed to inhibit the cytosolic enzyme (IC50 = 1.6 microM). The basis of this difference lay in the fact that rolipram served as a simple competitive inhibitor of the cytosol enzyme (Ki = 1.6 microM) but as a partial competitive inhibitor of the particulate enzyme (Ki = 0.037 microM; Ki' = 2.3 microM). Particulate PDE-46 thus showed a approximately 60-fold higher affinity for rolipram than cytosolic PDE-46.