Cost-effectiveness analysis of a randomized clinical trial of early versus deferred endovenous ablation of superficial venous reflux in patients with venous ulceration.

BACKGROUND: Treatment of superficial venous reflux in addition to compression therapy accelerates venous leg ulcer healing and reduces ulcer recurrence. The aim of this study was to evaluate the costs and cost-effectiveness of early versus delayed endovenous treatment of patients with venous leg ulcers. METHODS: This was a within-trial cost-utility analysis with a 1-year time horizon using data from the EVRA (Early Venous Reflux Ablation) trial. The study compared early versus deferred endovenous ablation for superficial venous truncal reflux in patients with a venous leg ulcer. The outcome measure was the cost per quality-adjusted life-year (QALY) over 1 year. Sensitivity analyses were conducted with alternative methods of handling missing data, alternative preference weights for health-related quality of life, and per protocol. RESULTS: After early intervention, the mean(s.e.m.) cost was higher (difference in cost per patient £163(318) (€184(358))) and early intervention was associated with more QALYs at 1 year (mean(s.e.m.) difference 0·041(0·017)). The incremental cost-effectiveness ratio (ICER) was £3976 (€4482) per QALY. There was an 89 per cent probability that early venous intervention is cost-effective at a threshold of £20 000 (€22 546)/QALY. Sensitivity analyses produced similar results, confirming that early treatment of superficial reflux is highly likely to be cost-effective. CONCLUSION: Early treatment of superficial reflux is highly likely to be cost-effective in patients with venous leg ulcers over 1 year. Registration number: ISRCTN02335796 (http://www.isrctn.com).

Clinical and economic evaluation of laparoscopic surgery compared with medical management for gastro-oesophageal reflux disease: 5-year follow-up of multicentre randomised trial (the REFLUX trial).

BACKGROUND: Despite promising evidence that laparoscopic fundoplication provides better short-term relief of gastro-oesophageal reflux disease (GORD) than continued medical management, uncertainty remains about whether benefits are sustained and outweigh risks. OBJECTIVE: To evaluate the long-term clinical effectiveness, cost-effectiveness and safety of laparoscopic surgery among people with GORD requiring long-term medication and suitable for both surgical and medical management. DESIGN: Five-year follow-up of a randomised trial (with parallel non-randomised preference groups) comparing a laparoscopic surgery-based policy with a continued medical management policy. Cost-effectiveness was assessed alongside the trial using a NHS perspective for costs and expressing health outcomes in terms of quality-adjusted life-years (QALYs). SETTING: Follow-up was by annual postal questionnaire and selective hospital case notes review; initial recruitment in 21 UK hospitals. PARTICIPANTS: Questionnaire responders among the 810 original participants. At entry, all had documented evidence of GORD and symptoms for > 12 months. Questionnaire response rates (years 1-5) were from 89.5% to 68.9%. INTERVENTIONS: Three hundred and fifty-seven participants were recruited to the randomised comparison (178 randomised to surgical management and 179 randomised to continued medical management) and 453 to the preference groups (261 surgical management and 192 medical management). The surgeon chose the type of fundoplication. MAIN OUTCOME MEASURES: Primary: disease-specific outcome measure (the REFLUX questionnaire); secondary: Short Form questionnaire-36 items (SF-36), European Quality of Life-5 Dimensions (EQ-5D), NHS resource use, reflux medication, complications. RESULTS: The randomised groups were well balanced. By 5 years, 63% in the randomised surgical group and 13% in the randomised medical management group had received a total or partial wrap fundoplication (85% and 3% in the preference groups), with few perioperative complications and no associated deaths. At 1 year (and 5 years) after surgery, 36% (41%) in the randomised surgical group - 15% (26%) of those who had surgery - were taking proton pump inhibitor medication compared with 87% (82%) in the randomised medical group. At each year, differences in the REFLUX score significantly favoured the randomised surgical group (a third of a SD; p< 0.01 at 5 years). SF-36 and EQ-5D scores also favoured surgery, but differences attenuated over time and were generally not statistically significant at 5 years. The worse the symptoms at trial entry, the larger the benefit observed after surgery. Those randomised to medical management who subsequently had surgery had low baseline scores that markedly improved after surgery. Following fundoplication, 3% had surgical treatment for a complication and 4% had subsequent reflux-related operations - most often revision of the wrap. Dysphagia, flatulence and inability to vomit were similar in the two randomised groups. The economic analysis indicated that surgery was the more cost-effective option for this patient group. The incremental cost-effectiveness ratio for surgery in the base case was £7028 per additional QALY; these findings were robust to changes in approaches and assumptions. The probability of surgery being cost-effective at a threshold of £20,000 per additional QALY was > 0.80 for all analyses. CONCLUSIONS: After 5 years, laparoscopic fundoplication continues to provide better relief of GORD symptoms with associated improved health-related quality of life. Complications of surgery were uncommon. Despite being initially more costly, a surgical policy is highly likely to be cost-effective. TRIAL REGISTRATION: Current Controlled Trials ISRCTN15517081. 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. 22. See the HTA programme website for further project information.

The UK EndoVascular Aneurysm Repair (EVAR) trials: randomised trials of EVAR versus standard therapy.

OBJECTIVE: To assess the efficacy of endovascular aneurysm repair (EVAR) against standard alternative management in patients with large abdominal aortic aneurysm (AAA). DESIGN: Two national, multicentre randomised trials - EVAR trials 1 and 2. SETTING: Patients were recruited from 38 out of 41 eligible UK hospitals. PARTICIPANTS: Men and women aged at least 60 years, with an AAA measuring at least 5.5 cm on a computerised tomography scan that was regarded as anatomically suitable for EVAR, were assessed for fitness for open repair. Patients considered fit were randomised to EVAR or open repair in EVAR trial 1 and patients considered unfit were randomised to EVAR or no intervention in EVAR trial 2. INTERVENTIONS: EVAR, open repair or no intervention. MAIN OUTCOME MEASURES: The primary outcome was mortality (operative, all-cause and AAA related). Patients were flagged at the UK Office for National Statistics with centrally coded death certificates assessed by an Endpoints Committee. Power calculations based upon mortality indicated that 900 and 280 patients were required for EVAR trials 1 and 2, respectively. Secondary outcomes were graft-related complications and reinterventions, adverse events, renal function, health-related quality of life and costs. Cost-effectiveness analyses were performed for both trials. RESULTS: Recruitment occurred between 1 September 1999 and 31 August 2004, with targets exceeded in both trials: 1252 randomised into EVAR trial 1 (626 to EVAR) and 404 randomised into EVAR trial 2 (197 to EVAR). Follow-up closed in December 2009 with very little loss to follow-up (1%). In EVAR trial 1, 30-day operative mortalities were 1.8% and 4.3% in the EVAR and open-repair groups, respectively: adjusted odds ratio 0.39 [95% confidence interval (CI) 0.18 to 0.87], p = 0.02. During a total of 6904 person-years of follow-up, 524 deaths occurred (76 AAA related). Overall, there was no significant difference between the groups in terms of all-cause mortality: adjusted hazard ratio (HR) 1.03 (95% CI 0.86 to 1.23), p = 0.72. The EVAR group did demonstrate an early advantage in terms of AAA-related mortality, which was sustained for the first few years, but lost by the end of the study, primarily due to fatal endograft ruptures: adjusted HR 0.92 (95% CI 0.57 to 1.49), p = 0.73. The EVAR procedure was more expensive than open repair (mean difference £1177) and not found to be cost-effective, but the model was sensitive to alternative assumptions. In EVAR trial 2, during a total of 1413 person-years of follow-up, a total of 305 deaths occurred (78 AAA related). The 30-day operative mortality was 7.3% in the EVAR group. However, this group later demonstrated a significant advantage in terms of AAA-related mortality, but this became apparent only after 4 years: overall adjusted HR 0.53 (95% CI 0.32 to 0.89), p = 0.02. Sadly, this advantage did not result in any benefit in terms of all-cause mortality: adjusted HR 0.99 (95% CI 0.78 to 1.27), p = 0.97. Overall, EVAR was more expensive than no intervention (mean difference £10,222) and not found to be cost-effective. CONCLUSIONS: EVAR offers a clear operative mortality benefit over open repair in patients fit for both procedures, but this early benefit is not translated into a long-term survival advantage. Among patients unfit for open repair, EVAR is associated with a significant long-term reduction in AAA-related mortality but this does not appear to influence all-cause mortality. TRIAL REGISTRATION: Current Controlled Trials ISRCTN 55703451. FUNDING: This project was funded by the NIHR Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 16, No. 9. See the HTA programme website for further project information.

Cost-effectiveness of traditional and endovenous treatments for varicose veins.

BACKGROUND: The aim of this study was to evaluate the cost-effectiveness of traditional and endovenous treatments for patients with primary great saphenous varicose veins. METHODS: A Markov model was constructed to compare costs and quality-adjusted life years (QALYs) for great saphenous vein (GSV) reflux. Eight popular treatment strategies were compared up to 5 years. Estimates for the effectiveness of treatments were obtained from published randomized studies and cost values were obtained from published National Health Service (NHS) healthcare resource group tariffs and device manufacturers. Parameter uncertainty was tested using sensitivity analysis and Monte Carlo simulation. RESULTS: Ultrasound-guided foam sclerotherapy (UGFS) had the lowest initial cost, but a higher requirement for further interventions. Day-case surgery (with concomitant treatment of varicosities), endovenous laser ablation (EVLA) and radiofrequency ablation (RFA) performed in an outpatient or office setting (with staged treatment of varicosities) were likely to be cost-effective treatment strategies. The incremental cost-effectiveness ratio (ICER) for UGFS (versus conservative care), EVLA (versus UGFS) and RFA (versus EVLA) were £1366, £5799 and £17 350 per QALY respectively. The ICER for traditional surgery (performed on a day-case basis) was £19 012 compared with RFA. Other strategies were not cost-effective using the NHS threshold of £20 000 per QALY. CONCLUSION: Day-case surgery or endovenous ablation using EVLA or RFA performed as an outpatient are likely to be cost-effective treatment strategies for patients with primary unilateral GSV reflux requiring treatment.

The cost-effectiveness of an early interventional strategy in non-ST-elevation acute coronary syndrome based on the RITA 3 trial.

BACKGROUND: Evidence suggests that an early interventional strategy for patients with non-ST-elevation acute coronary syndrome (NSTE-ACS) can improve health outcomes but also increase costs when compared with a conservative strategy. OBJECTIVE: The aim of this study was to assess the cost-effectiveness of an early interventional strategy in different risk groups from a UK health-service perspective. DESIGN: Decision-analytic model based on randomised clinical trial data. MAIN OUTCOME MEASURES: Costs in UK Sterling at 2003/2004 prices and quality-adjusted life years (QALYs) combined into an incremental cost-effectiveness ratio. METHODS: Data from the third Randomised Intervention Trial of unstable Angina (RITA 3) was employed to estimate rates of cardiovascular death and myocardial infarction, costs and health-related quality of life. Cost-effectiveness was estimated over patients' lifetimes within the decision-analytic model. RESULTS: The mean incremental cost per QALY gained for an early interventional strategy was approximately 55,000 pounds sterling, 22,000 pounds sterling and 12,000 pounds sterling for patients at low, intermediate and high risk, respectively. The early interventional strategy is approximately 1%, 35% and 95% likely to be cost-effective for patients at low, intermediate and high risk, respectively, at a threshold of 20,000 pounds sterling per QALY. The cost-effectiveness of early intervention in low-risk patients is sensitive to assumptions about the duration of the treatment effect. CONCLUSION: An early interventional strategy in patients presenting with NSTE-ACS is likely to be considered cost-effective for patients at high and intermediate risk, but this is less likely to be the case for patients at low risk.

Modelling the long-term cost-effectiveness of endovascular or open repair for abdominal aortic aneurysm.

BACKGROUND: Recent randomized trials have shown that endovascular abdominal aortic aneurysm repair (EVAR) has a 3 per cent aneurysm-related survival benefit in patients fit for open surgery, but it also has uncertain long-term outcomes and higher costs. This study assessed the cost-effectiveness of EVAR. METHODS: A decision model was constructed to estimate the lifetime costs and quality-adjusted life years (QALYs) with EVAR and open repair in men aged 74 years. The model includes the risks of death from aneurysm, other cardiovascular and non-cardiovascular causes, secondary reinterventions and non-fatal cardiovascular events. Data were taken largely from the EVAR trial 1 and supplemented from other sources. RESULTS: Under the base-case (primary) assumptions, EVAR cost 3800 pounds sterling (95 per cent confidence interval (c.i.) 2400 pounds sterling to 5200 pounds sterling) more per patient than open repair but produced fewer lifetime QALYs (mean -0.020 (95 per cent c.i. -0.189 to 0.165)). These results were sensitive to alternative model assumptions. CONCLUSION: EVAR is unlikely to be cost-effective on the basis of existing devices, costs and evidence, but there remains considerable uncertainty.

[A comparison of costs and survival in colorectal cancer patients undergoing surgery according to different organizational models]. / Comparación de costes y supervivencia en pacientes intervenidos quirúrgicamente de cáncer colorrectal según diferentes modelos organizativos.

OBJECTIVE: To determine the effectiveness and costs of different organizational models in caring for colorectal cancer patients through either clinical management functional units or traditional clinical services. METHOD: Post-operative and long-term (after 30 days and 5 years) mortality was analyzed according to number of patients undergoing surgery because of colorectal cancer. Mortality was adjusted for patient-related confounding factors. With that purpose a thorough review of the literature was conducted; information obtained was used in a meta-analysis of randomized effects. Concerning costs, a literature search was run to describe differences in number of patients per year between hospitals. RESULTS: Surgery costs were found to be smaller, and mean hospital stay shorter, in big-sized hospitals. The meta-analysis showed that the risk of death at 30 days and 5 years was lower in big hospitals versus smaller ones (OR: 1.112; 95% CI 0.986-1.255, and OR: 1.114; 95% CI 1.105-1.183, respectively). CONCLUSIONS: Short- and long-term postoperative mortality is lower in hospitals with a high number of cases per year.

Chloroform-soluble schiff-base Zn(II) or Cd(II) complexes from a dynamic combinatorial library.

A dynamic combinatorial library of metal ion Schiff-base complexes have been studied for the extraction of Zn(II) or Cd(II) from aqueous solution into chloroform. Library components consist of different aminophenols and 2-pyridinecarboxaldehyde. Extraction of both Zn(II) and Cd(II) into chloroform was observed from aqueous solutions containing 0.0500 mM M(NO3)2, 0.100 M aminophenol, 0.100 M 2-pyridinecarboxaldehyde, 0.100 M NaCl, and 5.00 mM buffer at pH 8.5. Extraction was dependent on pH but not on counterions including Cl-, Br-, or NO3-. Studies showed that equilibrium was attained between the Schiff-base complexes across the two-phase chloroform-water system after 24 h of stirring. Analysis of the extracted species by use of 1H NMR spectroscopy and mass spectrometry as well as solubility studies on characterized complexes suggested that the major extracted species is the neutral bis-Schiff-base metal ion complex. In libraries containing mixtures of two different aminophenols and 2-pyridinecarboxaldehyde, an enhanced extent of extraction of Zn(II) into chloroform is observed. Studies suggest that a Zn(II) complex, which is likely the mixed Schiff-base complex, has superior extraction properties compared to simple libraries with a single aminophenol component. The structures of two bis-Schiff-base complexes of Zn(II) and one of Cd(II) have been determined by X-ray crystallography. The geometries of the two Zn(II) complexes, which differ only by a methyl substituent on the Schiff-base ligand, are markedly different, supporting the use of combinatorial methods in coordination chemistry. Zn(SB14)2 crystallized as the sesquihydrate (C24H18N4O2Zn.1.5 H2O) in the space group C2/c, with cell dimensions a = 23.219(15) A, b = 11.299(7) A, c = 16.822(11) A, beta = 102.91(5) degrees, V = 4302(5) A3, and Z = 8. Zn(SB15)2 crystallized as a 1:1 methanol solvate (C26H22N4O2Zn.CH3OH) in the space group P2(1)/c with cell dimensions a = 13.981(5) A, b = 7.978(3) A, c = 22.568(8) A, beta = 104.53(3) degrees, V = 2436.8(15) A3, and Z = 4. Cd(SB14)2 crystallized as a 1:1 ethanol solvate (C24H18N4O2Cd.CH3CH2OH) in the space group R3 with unit cell dimensions of a = 36.423(2) A, c = 9.2930(10) A, V = 10678(2) A3, and Z = 18.

Specificity of natural and artificial substrates for human Cdc25A.

Cdc25A is a dual-specific protein phosphatase involved in the regulation of the kinase activity of Cdk-cyclin complexes in the eukaryotic cell cycle. To understand the mechanism of this important regulator, we have generated highly purified biochemical reagents to determine the kinetic constants for human Cdc25A with respect to a set of peptidic, artificial, and natural substrates. Cdc25A and its catalytic domain (dN25A) demonstrate very similar kinetics toward the artificial substrates p-nitrophenyl phosphate (k(cat)/K(m) = 15-25 M(-1) s(-1)) and 3-O-methylfluorescein phosphate (k(cat)/K(m) = 1.1-1.3 x 10(4) M(-1) s(-1)). Phospho-peptide substrates exhibit extremely low second-order rate constants and a flat specificity profile toward Cdc25A and dN25A (k(cat)/K(m) = 1 to 10 M(-1) s(-1)). In contrast to peptidic substrates, Cdc25A and dN25A are highly active phosphatases toward the natural substrate, T14- and Y15-bis-phosphorylated Cdk2/CycA complex (Cdk2-pTpY/CycA) with k(cat)/K(m) values of 1.0-1.1 x 10(6) M(-1) s(-1). In the context of the Cdk2-pTpY/CycA complex, phospho-threonine is preferred over phospho-tyrosine by more than 10-fold. The highly homologous catalytic domain of Cdc25c is essentially inactive toward Cdk2-pTpY/CycA. Taken together these data indicate that a significant degree of the specificity of Cdc25 toward its Cdk substrate resides within the catalytic domain itself and yet is in a region(s) that is outside the phosphate binding site of the enzyme.

Eu(III) macrocyclic complexes promote cleavage of and bind to models for the 5'-cap of mRNA. Effect of pendent group and a second metal ion.

The interaction of three Eu(III) macrocyclic complexes Eu(THED)3+, Eu(ATHC)3+, and Eu(ATHC)3+, and Eu(S-THP)3+ with two 5'-cap model compounds, GpppG and m7GpppG is studied (THED = 1,4,7,10-tetrakis(2-hydroxyethyl)-1,4,7,-10-tetraazacyclododecane, ATHC = 1-(carbamoylmethyl)-4,7,10-tris(2-hydroxyethyl)-1,4,7,10- tetraazacyclododecane, S-THP = 1S,4S,7S,10S-tetrakis(2-hydroxypropyl)-1,4,7,10-tetraazacyclododecane). Laser-induced excitation luminescence spectroscopy is used to study the binding of Eu(S-THP)3+ to GpppG (K = 5.9 x 10(4) M-1) and to characterize the Eu(S-THP)-GpppG complex. Both Eu(THED)3+ and Eu(S-THP)3+ bind to m7GpppG as monitored by use of fluorescence spectroscopy with binding constants of 5.9 x 10(3) and 4.4 x 10(4) M-1, respectively. The kinetics of cleavage of GpppG by two macrocyclic complexes is studied. Cleavage of GpppG by Eu(THED)3+ is accelerated by 15-fold in the presence of an equivalent of Zn(NO3)2 at pH 7.3, 37 degrees C, suggesting that two metal ions accelerate the cap cleavage reaction. Eu(ATHC)3+ promotes cleavage of GpppG with a pseudo-first-order rate constant of 2.6 x 10(-5) s-1 at pH 7.3, 37 degrees C, and 0.30 mM complex.

Generation of an Ugi library of phosphate mimic-containing compounds and identification of novel dual specific phosphatase inhibitors.

The four-component Ugi reaction was utilized to prepare a library of dipeptidic compounds in order to explore the binding requirements of the key cell cycle phosphatase, Cdc25. Several phosphate surrogates were incorporated into the Ugi product to mimic either the mono- or bis-phosphorylated substrate.

Dysidiolide and related gamma-hydroxy butenolide compounds as inhibitors of the protein tyrosine phosphatase, CDC25.

Synthetic dysidiolide, as well as several related compounds containing a gamma-hydroxybutenolide moiety, were tested in in vitro Cdc25 assays against both synthetic and natural substrates. Contrary to literature values which are in the low micromolar range, we observe only millimolar inhibitory activity for these compounds versus Cdc25 phosphatase.

Selective injection of magnetization by slow chemical exchange in NMR.

In a system in slow dynamic equilibrium two NMR methods are shown to be suitable for injecting magnetization from one resonance to another by means of slow chemical exchange. The combined outputs of the methods may be employed to measure the value of the off-rate constant kappa(off) in the complex. The methods are implemented experimentally using the complex of molecules composed of the enzyme Escherichia coli dihydrofolate reductase (DHFR) and the ligand folate. In an equilibrium solution with DHFR, folate is known to undergo chemical exchange between a free state and a bound state. The modified synchronous nutation method is applied to a spin of the folate molecule in the free and bound states; magnetization transfer occurs between the two sites due to the underlying exchange process. As a preliminary step for the application of the synchronous nutation method, a new one-dimensional 1H NMR technique is proposed which facilitates the assignment of the resonance of a spin in the bound state, provided the resonance of its exchange partner in the free state is known. This experiment is also used to obtain quantitative estimates of the transverse relaxation rate constant of the bound resonance. The numerical procedure necessary to analyze the experimental results of the synchronous nutation experiment is presented.

Patency of Wallstents placed across the venous anastomosis of hemodialysis grafts after percutaneous recanalization.

PURPOSE: To determine the patency of Wallstents placed across the venous anastomosis of prosthetic bridge grafts after percutaneous graft recanalization. MATERIALS AND METHODS: Wallstents were placed across 26 lesions at the venous anastomosis of polytetrafluoroethylene (PTFE) grafts in 25 patients (11 men, 14 women; age range, 29-83 years; mean age, 65.4 years) after pulse-spray pharmacomechanical thrombolysis. Indications for stent deployment included acute angioplasty failure, rapid restenosis, and vessel perforation. RESULTS: The initial success rate was 100%. The mean primary graft patency rates (+/- standard error) at 3 and 6 months were 34% +/- 9 and 27% +/- 9, respectively. Secondary patency rates were 77% +/- 8 at 3 months, 72% +/- 9 at 6 months, and 50% +/- 10 at 12 months. Eight of the 26 grafts continued to be used for hemodialysis at the end of follow-up. CONCLUSION: After angioplasty failure or vessel perforation, Wallstent placement at the venous anastomosis of recanalized PTFE grafts can salvage hemodialysis access function. The results of this study indicate that the 1-year secondary patency rate of these grafts is 50%, which approaches the reported rates of patency after balloon dilation as part of percutaneous graft recanalization.

Kinetic analysis of the catalytic domain of human cdc25B.

The Cdc25 cell cycle regulator is a member of the dual-specificity class of protein-tyrosine phosphatases that hydrolyze phosphotyrosine- and phosphothreonine-containing substrates. To study the mechanism of Cdc25B, we have overexpressed and purified the catalytic domain of human Cdc25B (Xu, X., and Burke, S. P. (1996) J. Biol. Chem. 271, 5118-5124). In the present work, we have analyzed the kinetic properties of the Cdc25B catalytic domain using the artificial substrate 3-O-methylfluorescein phosphate (OMFP). Steady-state kinetic analysis indicated that the kcat/Km for OMFP hydrolysis is almost 3 orders of magnitude greater than that for p-nitrophenyl phosphate hydrolysis. Like other dual-specificity phosphatases, Cdc25 exhibits a two-step catalytic mechanism, characterized by formation and breakdown of a phosphoenzyme intermediate. Pre-steady-state kinetic analysis of OMFP hydrolysis indicated that formation of the phosphoenzyme intermediate is approximately 20 times faster than subsequent phosphoenzyme breakdown. The resulting burst pattern of product formation allowed us to derive rate constants for enzyme phosphorylation (26 s-1) and dephosphorylation (1.5 s-1) as well as the dissociation constant for OMFP (0.3 mM). Calculations suggest that OMFP binds with higher affinity and reacts faster with Cdc25B than does p-nitrophenyl phosphate. OMFP is a highly efficient substrate for the dual-specificity protein-tyrosine phosphatases VHR and rVH6, but not for two protein-tyrosine phosphatases, PTP1 and YOP. The ability to observe distinct phases of the reaction mechanism during OMFP hydrolysis will facilitate future analysis of critical catalytic residues in Cdc25 and other dual-specificity phosphatases.

Dynamics of the dihydrofolate reductase-folate complex: catalytic sites and regions known to undergo conformational change exhibit diverse dynamical features.

Backbone and tryptophan side-chain dynamics of uniformly 15N-labeled Escherichia coli dihydrofolate reductase were determined for the binary folate complex. The 15N T1 and T2 relaxation times and [1H]-15N heteronuclear NOEs were measured for 118 protonated backbone nitrogen atoms. The generalized order parameter (S2), the effective correlation time for internal motions (tau e), and the contribution to spin-spin relaxation through 15N exchange broadening (Rex) were determined for each residue by model-free analysis. Back-calculation of the relaxation rates for each resonance showed that the calculated dynamical parameters accurately predict the experimental data. Diverse dynamical features were evident in the DHFR backbone. Six sites exhibited order parameters significantly below the weighted mean S2 value (for the complex) of 0.81 +/- 0.002: residues G67 and D69 of the adenosine binding domain, and "hinge" residues K38 and V88, exhibited low S2 (0.29 < or = S2 < or = 0.6) and high tau e values (700 ps < or = tau e < or = 2 ns), as did sites within the beta A-alpha B loop and the beta F-beta G loop. Thus, large amplitude backbone motions, on the picosecond and nanosecond time scales, occurred at regions implicated in transition-state stabilization and in ligand-dependent conformational change. Significant Rex values (> or = 1 s-1) were determined for 45% of assigned resonances, many of which arise from residues surrounding the folate binding site. The mean S2 values of the occupied folate binding site and the unoccupied NADPH binding site were similar, indicating the backbone of the latter is at least as conformationally restricted as that of the occupied folate site. We conclude that the observed time-dependent structural fluctuations of the binary complex are in fact associated with catalytic properties of the molecule.

Legal implications of managed care arrangements.

Prior to the 1980s, managed care was virtually nonexistent as a force in health care. Presently, 64 percent of employees in America are covered by managed care plans, including health maintenance organizations (20 percent) and preferred provider organizations (44 percent). In contrast, only 29 percent of employees were enrolled in managed care plans in 1988 and only 47 percent in 1991. To date, the primary reason for this incredible growth in managed care has been economic-market pressure to reduce health care costs. For the foreseeable future, political pressures are likely to fuel this growth, as managed care is at the center of President Clinton's national health care plan. Although there are numerous legal issues surrounding managed care, this article focuses primarily on antitrust implications when forming managed care entities. In addition, the corporate practice of medicine doctrine, certain tax issues, and the fraud and abuse laws are discussed.

Role of serine 214 and tyrosine 171, components of the S2 subsite of alpha-lytic protease, in catalysis.

The function of a hydrogen bond network, comprised of the hydroxyl groups of Tyr 171 and Ser 214, in the hydrophobic S2 subsite of alpha-lytic protease, was investigated by mutagenesis and the kinetics of a substrate analog series. To study the catalytic role of the Tyr 171 and Ser 214 hydroxyl groups, Tyr 171 was converted to phenylalanine (Y171F) and Ser 214 to alanine (S214A). The double mutant (Y171F: S214A) also was generated. The single S214A and double Y171F:S214A mutations cause differential effects on catalysis and proenzyme processing. For S214A, kcat/Km is (4.9 x 10(3))-fold lower than that of wild type and proenzyme processing is blocked. For the double mutant (Y171F:S214A), kcat/Km is 82-fold lower than that of wild type and proenzyme processing occurs. In Y171F, kcat/Km is 34-fold lower than that of wild type, and the proenzyme is processed. The data indicate that Ser 214, although conserved among serine proteases and hydrogen bonded to the catalytic triad [Brayer, G. D., Delbaere, L. T. J., & James, M. N. G. (1979) J. Mol. Biol. 131, 743], is not essential for catalytic function in alpha-lytic protease. A substrate series (in which peptide length is varied) established that the mutations (Y171F and Y171F:S214A) do not alter enzyme-substrate interactions in subsites other than S2. The pH dependence of kcat/Km for Y171F and Y171F:S214A has changed less than 0.5 unit from that of wild type; this suggests the catalytic triad is unperturbed. In wild type, hydrophobic interactions at S2 increase kcat/Km by up to (1.2 x 10(3))-fold with no effect on Km.(ABSTRACT TRUNCATED AT 250 WORDS)

Is drinking water related to spontaneous abortion? Reviewing the evidence from the California Department of Health Services Studies.

Because preliminary data suggested a relation between risk of spontaneous abortion and tapwater consumption during pregnancy, the California Department of Health Services included questions on prenatal water consumption in all reproductive studies conducted between 1982 and 1988. Results from four of these five retrospective data bases suggest that women abstaining from tapwater or drinking bottled water during the first trimester of pregnancy may be at reduced risk of spontaneous abortion. Fetal resorption frequencies seen in an accompanying toxicology study were consistent with these epidemiologic findings, although not conclusive. Tap and bottled water samples from these study areas were analyzed for agents that might account for these findings. Differences in trace element composition and biological activity were observed, but the reproductive significance of these differences is unknown. This paper presents an overview of these studies, which are presented in detail separately. Three alternative explanations for these findings--bias, chance, and causality--are reviewed.

Tap or bottled water consumption and spontaneous abortion in a case-control study of reporting consistency.

A recent case-control study of 1,926 women found a slightly increased risk of spontaneous abortion associated with reported consumption of tapwater and a decreased risk with reported consumption of bottled water. In a case-control study of spontaneous abortion designed to examine the consistency of prenatal exposure reporting, the association of spontaneous abortion with tap or bottled water consumption was also examined. Cases of spontaneous abortion (N = 100) were ascertained from hospital pathology reports, and pregnant controls (N = 200) were obtained from obstetrical appointment logs. Subjects were first interviewed approximately 24 weeks after their last menstrual period and again approximately 48 weeks after their last menstrual period. Neither an increased risk for spontaneous abortion associated with consumption of tapwater nor a protective effect for consumption of bottled water was observed. Changes in reporting of tapwater consumption from the first to the second interview suggest the possibility of differential reporting in cases and controls. There was no evidence suggesting biased reporting of bottled water consumption.