Updated Public Health Impact and Cost Effectiveness of Recombinant Zoster Vaccine in Canadian Adults Aged 50 Years and Older

OBJECTIVES

The aim of this study was to update previously estimated public health impact and cost effectiveness of recombinant zoster vaccine (RZV) for the prevention of herpes zoster (HZ) in Canadians aged ≥50 years using longer-term RZV efficacy and waning data and real-world coverage and completion.

METHODS

A multicohort Markov model was used to conduct a cost-utility analysis comparing RZV with no HZ vaccination among Canadians aged ≥50 years. Real-world data were used for first-dose coverage (17.5%) and second-dose completion (65%). Vaccine efficacy and waning data were applied from up to 8-year follow-up from the ZOE-50 and ZOE-70 clinical trials. Incremental costs and benefits were calculated using a lifetime horizon from the healthcare payer (base case) and societal perspectives. A discount rate of 1.5% was applied to costs and quality-adjusted life-years (QALYs).

RESULTS

The model estimated that RZV would prevent 303,835 HZ cases, 83,256 post-herpetic neuralgia (PHN) cases, 39,653 other complications, and 99 HZ-related deaths compared with no HZ vaccination. Incremental cost-effectiveness ratios (ICERs) were estimated to be $27,486 and $22,097 per QALY (2022 Canadian dollars [CAN$]) from the healthcare payer and societal perspectives, respectively. The base-case ICER was most sensitive to a lower percentage of initial HZ cases with PHN. Almost all probabilistic sensitivity analysis simulations (98.1%) resulted in ICERs

CONCLUSIONS

RZV is expected to remain a cost-effective option for Canadian adults aged ≥50 years when using longer-term RZV efficacy and waning estimates, although the estimated public health impact was smaller than in the previous analysis (due to lower coverage/completion estimates).

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Affiliation(s)

Sydney George GSK, Mississauga, ON, Canada.
Justin Carrico RTI Health Solutions, Research Triangle Park, NC, USA
Katherine A Hicks RTI Health Solutions, Research Triangle Park, NC, USA
Dessi Loukov GSK, Mississauga, ON, Canada
Cheryl Ng GSK, Singapore, Singapore
Jessica Regan GSK, Mississauga, ON, Canada
Nikolaos Giannelos GSK, Wavre, Belgium

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Assessing the Impact of COVID-19 on HIV Outcomes in the United States: A Modeling Study

BACKGROUND

The COVID-19 pandemic impacted sexual behaviors and the HIV continuum of care in the United States, reducing HIV testing and diagnosis, and use of preexposure prophylaxis and antiretroviral therapy. We aimed to understand the future implications of these effects through a modeling study.

METHODS

We first ran our compartmental model of HIV transmission in the United States accounting for pandemic-related short-term changes in transmission behavior and HIV prevention and care provision in 2020 to 2021 only. We then ran a comparison scenario that did not apply pandemic effects but assumed a continuation of past HIV prevention and care trends. We compared results from the 2 scenarios through 2024.

RESULTS

HIV incidence was 4·4% lower in 2020 to 2021 for the pandemic scenario compared with the no-pandemic scenario because of reduced levels of transmission behavior, despite reductions in HIV prevention and care caused by the pandemic. However, reduced care led to less viral load suppression among people with HIV in 2020, and in turn, our model resulted in a slightly greater incidence of 2·0% from 2022 to 2024 in the COVID-19 scenario, as compared with the non-COVID scenario.

DISCUSSION

Disruptions in HIV prevention and care services during COVID-19 may lead to somewhat higher postpandemic HIV incidence than assuming prepandemic trends in HIV care and prevention continued. These results underscore the importance of continuing to increase HIV prevention and care efforts in the coming years.

Rebamipide and Derivatives are Potent, Selective Inhibitors of Histidine Phosphatase Activity of the Suppressor of T Cell Receptor Signaling Proteins

The suppressor of T cell receptor signaling (Sts) proteins are negative regulators of immune signaling. Genetic inactivation of these proteins leads to significant resistance to infection. From a 590,000 compound high-throughput screen, we identified the 2-(1H)-quinolinone derivative, rebamipide, as a putative inhibitor of Sts phosphatase activity. Rebamipide, and a small library of derivatives, are competitive, selective inhibitors of Sts-1 with IC50 values from low to submicromolar. SAR analysis indicates that the quinolinone, the acid, and the amide moieties are all essential for activity. A crystal structure confirmed the SAR and reveals key interactions between this class of compound and the protein. Although rebamipide has poor cell permeability, we demonstrated that a liposomal preparation can inactivate the phosphatase activity of Sts-1 in cells. These studies demonstrate that Sts-1 enzyme activity can be pharmacologically inactivated and provide foundational tools and insights for the development of immune-enhancing therapies that target the Sts proteins.

Characterization of an Acinetobacter baumannii Monofunctional Phosphomethylpyrimidine Kinase That Is Inhibited by Pyridoxal Phosphate

Thiamin and its phosphate derivatives are ubiquitous molecules involved as essential cofactors in many cellular processes. The de novo biosynthesis of thiamin employs the parallel synthesis of 4-methyl-5-(2-hydroxyethyl)thiazole (THZ-P) and 4-amino-2-methyl-5(diphosphooxymethyl) pyrimidine (HMP) pyrophosphate (HMP-PP), which are coupled to generate thiamin phosphate. Most organisms that can biosynthesize thiamin employ a kinase (HMPK or ThiD) to generate HMP-PP. In nearly all cases, this enzyme is bifunctional and can also salvage free HMP, producing HMP-P, the monophosphate precursor of HMP-PP. Here we present high-resolution crystal structures of an HMPK from Acinetobacter baumannii (AbHMPK), both unliganded and with pyridoxal 5-phosphate (PLP) noncovalently bound. Despite the similarity between HMPK and pyridoxal kinase enzymes, our kinetics analysis indicates that AbHMPK accepts HMP exclusively as a substrate and cannot turn over pyridoxal, pyridoxamine, or pyridoxine nor does it display phosphatase activity. PLP does, however, act as a weak inhibitor of AbHMPK with an IC50 of 768 μM. Surprisingly, unlike other HMPKs, AbHMPK catalyzes only the phosphorylation of HMP and does not generate the diphosphate HMP-PP. This suggests that an additional kinase is present in A. baumannii, or an alternative mechanism is in operation to complete the biosynthesis of thiamin.

Ligand bound structure of a 6-hydroxynicotinic acid 3-monooxygenase provides mechanistic insights

6-Hydroxynicotinic acid 3-monooxygenase (NicC) is a bacterial enzyme involved in the degradation of nicotinic acid. This enzyme is a Class A flavin-dependent monooxygenase that catalyzes a unique decarboxylative hydroxylation. The unliganded structure of this enzyme has previously been reported and studied using steady- and transient-state kinetics to support a comprehensive kinetic mechanism. Here we report the crystal structure of the H47Q NicC variant in both a ligand-bound (solved to 2.17 Å resolution) and unliganded (1.51 Å resolution) form. Interestingly, in the liganded form, H47Q NicC is bound to 2-mercaptopyridine (2-MP), a contaminant present in the commercial stock of 6-mercaptopyridine-3-carboxylic acid(6-MNA), a substrate analogue. 2-MP binds weakly to H47Q NicC and is not a substrate for the enzyme. Based on kinetic and thermodynamic characterization, we have fortuitously captured a catalytically inactive H47Q NicC•2-MP complex in our crystal structure. This complex reveals interesting mechanistic details about the reaction catalyzed by 6-hydroxynicotinic acid 3-monooxygenase.

Public health impact of recombinant zoster vaccine for prevention of herpes zoster in US adults immunocompromised due to cancer

Individuals who are immunocompromised (IC) due to therapy or underlying disease are at increased risk of herpes zoster (HZ). This study evaluates the public health impact of recombinant zoster vaccine (RZV) relative to no HZ vaccination for the prevention of HZ among adults aged ≥18 years diagnosed with selected cancers in the United States (US). A static Markov model was used to simulate three cohorts of individuals who are IC with cancer (time horizon of 30 years; one-year cycle length): hematopoietic stem cell transplant (HSCT) recipients, patients with breast cancer (BC; a solid tumor example), and patients with Hodgkin's lymphoma (HL; a hematological malignancy example). Cohort sizes reflect the estimated annual incidence of each condition in the US population (19,671 HSCT recipients, 279,100 patients with BC, and 8,480 patients with HL). Vaccination with RZV resulted in 2,297; 38,068; and 848 fewer HZ cases for HSCT recipients, patients with BC, and patients with HL, respectively (each versus no vaccine). Vaccination with RZV also resulted in 422; 3,184; and 93 fewer postherpetic neuralgia cases for HSCT, BC, and HL, respectively. Analyses estimated the quality-adjusted life years gained to be 109, 506, and 17 for HSCT, BC, and HL, respectively. To prevent one HZ case, the number needed to vaccinate was 9, 8, and 10, for HSCT, BC, and HL, respectively. These results suggest RZV vaccination may be an effective option to significantly reduce HZ disease burden among patients diagnosed with selected cancers in the US.

Synthesis and crystallographic characterization of 6-hydroxy-1,2-dihydropyridin-2-one

The title compound, C5H5NO2, is a hy-droxy-lated pyridine ring that has been studied for its involvement in microbial degradation of nicotinic acid. Here we describe its synthesis as a formic acid salt, rather than the standard hydro-chloride salt that is commercially available, and its spectroscopic and crystallographic characterization.

Cost-Effectiveness of Recombinant Zoster Vaccine for the Prevention of Herpes Zoster in Hematopoietic Stem Cell Transplant Recipients and Other Immunocompromised Adults in the United States

INTRODUCTION

Immunocompromised (IC) adults are at increased risk of developing herpes zoster (HZ) and HZ-related complications due to therapy or underlying disease. This study evaluated the cost effectiveness of recombinant zoster vaccine (RZV) versus no vaccine for the prevention of HZ in hematopoietic stem cell transplant (HSCT) recipients and other IC adults aged ≥ 18 years in the United States (US).

METHODS

A static Markov model simulated cohorts of IC individuals using a 1-year cycle length and 30-year time horizon to estimate the cost effectiveness of RZV. Inputs were sourced from clinical trial results and publicly available sources/literature. Modeled populations included US adult HSCT recipients (base case), patients with human immunodeficiency virus (HIV), patients with breast cancer, patients with Hodgkin's lymphoma, and renal transplant recipients. The model reported societal costs, quality-adjusted life-years (QALYs), and incremental cost-effectiveness ratios (ICERs). Sensitivity and threshold analyses were conducted.

RESULTS

In the base case of 19,671 US adult HSCT recipients, RZV resulted in total societal cost savings of US$0.1 million and 109 incremental QALYs versus no vaccine. RZV was a 'dominant strategy' versus no vaccine because vaccination resulted in cost savings with QALY gains. RZV was also cost saving in renal transplant recipients, and cost effective at a willingness-to-pay threshold of US$100,000 per QALY gained in patients with HIV, breast cancer, and Hodgkin's lymphoma, with ICERs of US$33,268, US$67,682, and US$95,972 per QALY gained, respectively, versus no vaccine.

CONCLUSIONS

Model results show RZV is potentially cost saving for the prevention of HZ in US adult HSCT recipients and US adults with selected immunocompromising conditions, and cost effective for others, supporting the use of RZV to prevent HZ and HZ-related complications in IC adults.

Mechanism of the Multistep Catalytic Cycle of 6-Hydroxynicotinate 3-Monooxygenase Revealed by Global Kinetic Analysis

The class A flavoenzyme 6-hydroxynicotinate 3-monooxygenase (NicC) catalyzes a rare decarboxylative hydroxylation reaction in the degradation of nicotinate by aerobic bacteria. While the structure and critical residues involved in catalysis have been reported, the mechanism of this multistep enzyme has yet to be determined. A kinetic understanding of the NicC mechanism would enable comparison to other phenolic hydroxylases and illuminate its bioengineering potential for remediation of N-heterocyclic aromatic compounds. Toward these goals, transient state kinetic analyses by stopped-flow spectrophotometry were utilized to follow rapid changes in flavoenzyme absorbance spectra during all three stages of NicC catalysis: (1) 6-HNA binding; (2) NADH binding and FAD reduction; and (3) O₂ binding with C4a-adduct formation, substrate hydroxylation, and FAD regeneration. Global kinetic simulations by numeric integration were used to supplement analytical fitting of time-resolved data and establish a kinetic mechanism. Results indicate that 6-HNA binding is a two-step process that substantially increases the affinity of NicC for NADH and enables the formation of a charge-transfer-complex intermediate to enhance the rate of flavin reduction. Singular value decomposition of the time-resolved spectra during the reaction of the substrate-bound, reduced enzyme with dioxygen provides evidence for the involvement of C4a-hydroperoxy-flavin and C4a-hydroxy-flavin intermediates in NicC catalysis. Global analysis of the full kinetic mechanism suggests that steady-state catalytic turnover is partially limited by substrate hydroxylation and C4a-hydroxy-flavin dehydration to regenerate the flavoenzyme. Insights gleaned from the kinetic model and determined microscopic rate constants provide a fundamental basis for understanding NicC's substrate specificity and reactivity.

Defining Myocardial Infarction in trials of people receiving hemodialysis: consensus report from the SONG-HD MI Expert Working group

Cardiovascular disease is the leading cause of death in patients receiving hemodialysis. Currently there is no standardized definition of myocardial infarction (MI) for patients receiving hemodialysis. Through an international consensus process MI was established as the core CVD measure for this population in clinical trials. The Standardised Outcomes in Nephrology Group - Hemodialysis (SONG-HD) initiative convened a multidisciplinary, international working group to address the definition of MI in this population.Based on current evidence, the working group recommends using the 4th Universal Definition of MI with specific caveats with regard to the interpretation of "ischemic symptoms" and performing a baseline 12-lead electrocardiogram to facilitate interpretation of acute changes on subsequent tracings. The working group does not recommend obtaining baseline cardiac troponin values, though does recommend obtaining serial cardiac biomarkers in settings where ischemia is suspected. Application of an evidence-based uniform definition should increase the reliability and accuracy of trial results.

Estimating the cost of university-based outbreaks of serogroup B meningococcal disease with different pre-matriculation vaccination policies in the United States

Objective: We developed an Excel-based cost calculator to assess the economic burden of university-based Neisseria meningitidis serogroup B (MenB) outbreaks. Participants: Hypothetical university with 6,354 students. Methods: Total societal costs of outbreak were estimated for three MenB pre-matriculation immunization policies-vaccination required, vaccination recommended, and no vaccine policy-under three different cost assumptions (low/mid-range/high cost). Results: Mid-range cost estimates of an outbreak under "no policy" were $2.60 and $2.70 million (of which 35% were incurred by the university) if targeting all undergraduates for mass vaccination with a two-/three-dose vaccine, respectively. The "required" and "recommended" policies lowered the burden to $2.17-$2.18 million and $2.34-$2.39 million, respectively. For a larger university with 40,000 students, costs were almost $9 million for a two-dose vaccine with "no policy" in place. Conclusions: The economic burden of a university MenB outbreak is substantial, but could be mitigated by a pre-matriculation MenB vaccination requirement or recommendation.

Optimizing HIV Prevention Efforts to Achieve EHE Incidence Targets

BACKGROUND

A goal of the US Department of Health and Human Services' Ending the HIV Epidemic (EHE) in the United States initiative is to reduce the annual number of incident HIV infections in the United States by 75% within 5 years and by 90% within 10 years. We developed a resource allocation analysis to understand how these goals might be met.

METHODS

We estimated the current annual societal funding [$2.8 billion (B)/yr] for 14 interventions to prevent HIV and facilitate treatment of infected persons. These interventions included HIV testing for different transmission groups, HIV care continuum interventions, pre-exposure prophylaxis, and syringe services programs. We developed scenarios optimizing or reallocating this funding to minimize new infections, and we analyzed the impact of additional EHE funding over the period 2021-2030.

RESULTS

With constant current annual societal funding of $2.8 B/yr for 10 years starting in 2021, we estimated the annual incidence of 36,000 new cases in 2030. When we added annual EHE funding of $500 million (M)/yr for 2021-2022, $1.5 B/yr for 2023-2025, and $2.5 B/yr for 2026-2030, the annual incidence of infections decreased to 7600 cases (no optimization), 2900 cases (optimization beginning in 2026), and 2200 cases (optimization beginning in 2023) in 2030.

CONCLUSIONS

Even without optimization, significant increases in resources could lead to an 80% decrease in the annual HIV incidence in 10 years. However, to reach both EHE targets, optimization of prevention funding early in the EHE period is necessary. Implementing these efficient allocations would require flexibility of funding across agencies, which might be difficult to achieve.

Estimating the HIV Effective Reproduction Number in the United States and Evaluating HIV Elimination Strategies

CONTEXT

The reproduction number is a fundamental epidemiologic concept used to assess the potential spread of infectious diseases and whether they can be eliminated.

OBJECTIVE

We estimated the 2017 United States HIV effective reproduction number, Re, the average number of secondary infections from an infected person in a partially infected population. We analyzed the potential effects on Re of interventions aimed at improving patient flow rates along different stages of the HIV care continuum. We also examined these effects by individual transmission groups.

DESIGN

We used the HIV Optimization and Prevention Economics (HOPE) model, a compartmental model of disease progression and transmission, and the next-generation matrix method to estimate Re. We then projected the impact of changes in HIV continuum-of-care interventions on the continuum-of-care flow rates and the estimated Re in 2020.

SETTING

United States.

PARTICIPANTS

The HOPE model simulated the sexually active US population and persons who inject drugs, aged 13 to 64 years, which was stratified into 195 subpopulations by transmission group, sex, race/ethnicity, age, male circumcision status, and HIV risk level.

MAIN OUTCOME MEASURES

The estimated value of Re in 2017 and changes in Re in 2020 from interventions affecting the continuum-of-care flow rates.

RESULTS

Our estimated HIV Re in 2017 was 0.92 [0.82, 0.94] (base case [min, max across calibration sets]). Among the interventions considered, the most effective way to reduce Re substantially below 1.0 in 2020 was to maintain viral suppression among those receiving HIV treatment. The greatest impact on Re resulted from changing the flow rates for men who have sex with men (MSM).

CONCLUSIONS

Our results suggest that current prevention and treatment efforts may not be sufficient to move the country toward HIV elimination. Reducing Re to substantially below 1.0 may be achieved by an ongoing focus on early diagnosis, linkage to care, and sustained viral suppression especially for MSM.

20. Cost-Effectiveness of Recombinant Zoster Vaccine for Vaccinating Immunocompromised Adults Against Herpes Zoster in the United States

Background

Individuals who are immunocompromised (IC) due to disease or therapy are at increased risk of herpes zoster (HZ), with HZ cases in IC populations also resulting in increased health care resource use and costs as compared with the immunocompetent population. This study assesses the cost-effectiveness of recombinant zoster vaccine (RZV) versus no vaccine for the prevention of HZ in IC adults aged ≥ 18 years in the United States (US).

Methods

A Markov model with a one-year cycle length was developed to follow a hypothetical cohort of one million IC individuals for a 30-year time horizon. The model estimates health and cost outcomes associated with RZV versus no vaccine. The base-case analysis considered hematopoietic stem cell transplant (HSCT) recipients who were assumed to remain IC for five years post-transplant. Second-dose compliance was assumed to be 100%, with efficacy and waning inputs based on clinical trial data. Epidemiological, cost, and utility inputs were obtained from standard US sources and published literature. Costs and quality-adjusted life-years (QALYs) were discounted at 3% per year. Sensitivity, threshold, and scenario analyses were conducted, including scenarios of four other IC conditions.

Results

In the modeled hypothetical cohort of one million HSCT recipients, RZV resulted in 116,790 fewer HZ cases and 21,446 fewer postherpetic neuralgia cases versus no vaccine, 5,545 fewer QALYs lost and a societal cost-savings of &5.4 million. The number needed to vaccinate to prevent one HZ case was estimated to be 9. HSCT population results were shown to be robust in sensitivity and threshold analyses. In scenario analyses, RZV was cost saving for renal transplant recipients. Incremental cost-effectiveness ratios for other IC populations were &33,268 per QALY gained for human immunodeficiency virus, &67,682 for breast cancer, and &95,972 for Hodgkin lymphoma.

Conclusion

Results suggest that RZV is a cost-effective option for vaccinating US IC adults for the prevention of HZ and associated complications.

Disclosures

Desmond Curran, PhD, The GSK group of companies (Employee, Shareholder) Ahmed Salem, MSc, The GSK group of companies (Employee) Stéphane Lorenc, NA, GSK group of companies (Consultant) Brandon Patterson, PharmD, PhD, GSK group of companies (Shareholder) Justin Carrico, BS, GSK group of companies (Consultant)RTI Health Solutions (Employee) Katherine A. Hicks, MS, BSPH, GSK group of companies (Consultant)RTI Health Solutions (Employee) Elizabeth M. La, PhD, The GSK group of companies (Employee, Shareholder) Sara Poston, PharmD, The GSK group of companies (Employee, Shareholder) Christopher F. Carpenter, MD, MHSA, GSK group of companies (Consultant)

996. The Potential for Reducing Opioid and Analgesic Prescriptions Via Herpes Zoster Vaccination

Background

Herpes zoster (HZ), or shingles, is a common neurocutaneous disease caused by the reactivation of latent varicella zoster virus that often includes rash and neuropathic pain that may last for months. Opioids and other analgesics may be prescribed. Recombinant zoster vaccine (RZV) is preferentially recommended for the prevention of HZ in adults aged 50 years and older. This study aimed to assess the impact of RZV vaccination on opioid and other analgesic prescription-related outcomes.

Methods

Estimates of analgesic prescription rates (opioids, benzodiazepines, and other analgesics) among HZ cases were established using Truven claims data from 2012-2018 for adults aged 50 years and older. HZ case avoidance with RZV vaccination was calculated using a previously published cost-effectiveness model. This data was included in a calculator assessing the impact of RZV vaccination on analgesic prescription-related outcomes (compared to no vaccination).

Results

Between 24.4% and 28.0% of HZ cases in the observed claims had at least one opioid prescription, dependent on age group (4.5%-6.5% and 8.6%-19.6% for benzodiazepines and other analgesics, respectively). The mean number of opioid prescriptions per person in each age group with at least one opioid prescription was between 1.7 and 1.9 (1.7-2.3 and 1.7-2.0 prescriptions for benzodiazepines and other analgesics, respectively). Assuming a 1-million-person population and 65% RZV coverage, the calculator predicts RZV vaccination will prevent 75,002 cases of HZ and will prevent 19,311 people from being prescribed at least 1 HZ-related opioid, 4,502 people from being prescribed benzodiazepines, and 12,201 people from being prescribed other analgesics. Additionally, 34,520 HZ-related opioid prescriptions will be avoided (9,413 benzodiazepine prescriptions; 22,406 other analgesic prescriptions).

Conclusion

HZ is associated with high levels of opioid, benzodiazepine, and other analgesic use. Primary prevention of HZ by vaccination could potentially reduce opioid and other medication exposure.

Disclosures

Jean-Etienne Poirrier, PhD, MBA, The GSK group of companies (Employee, Shareholder) Justin Carrico, BS, GlaxoSmithKline (Consultant) Jessica K. DeMartino, PhD, The GlaxoSmithKline group of companies (Employee, Shareholder) Katherine A. Hicks, MS, BSPH, GlaxoSmithKline (Scientific Research Study Investigator, GSK pays my company for my contractual services.) Saurabh P. Nagar, MS, RTI Health Solutions (Employee) Juliana Meyers, MA, GlaxoSmithKline (Other Financial or Material Support, This study was funded by GlaxoSmithKline.)

Optimal Allocation of Societal HIV Prevention Resources to Reduce HIV Incidence in the United States

Objectives. To optimize combined public and private spending on HIV prevention to achieve maximum reductions in incidence.Methods. We used a national HIV model to estimate new infections from 2018 to 2027 in the United States. We estimated current spending on HIV screening, interventions that move persons with diagnosed HIV along the HIV care continuum, pre-exposure prophylaxis, and syringe services programs. We compared the current funding allocation with 2 optimal scenarios: (1) a limited-reach scenario with expanded efforts to serve eligible persons and (2) an ideal, unlimited-reach scenario in which all eligible persons could be served.Results. A continuation of the current allocation projects 331 000 new HIV cases over the next 10 years. The limited-reach scenario reduces that number by 69%, and the unlimited reach scenario by 94%. The most efficient funding allocations resulted in prompt diagnosis and sustained viral suppression through improved screening of high-risk persons and treatment adherence support for those infected.Conclusions. Optimal allocations of public and private funds for HIV prevention can achieve substantial reductions in new infections. Achieving reductions of more than 90% under current funding will require that virtually all infected receive sustained treatment.

Mechanism of 6-Hydroxynicotinate 3-Monooxygenase, a Flavin-Dependent Decarboxylative Hydroxylase Involved in Bacterial Nicotinic Acid Degradation

6-Hydroxynicotinate 3-monooxygenase (NicC) is a Group A FAD-dependent monooxygenase that catalyzes the decarboxylative hydroxylation of 6-hydroxynicotinic acid (6-HNA) to 2,5-dihydroxypyridine (2,5-DHP) with concomitant oxidation of NADH in nicotinic acid degradation by aerobic bacteria. Two mechanisms for the decarboxylative hydroxylation half-reaction have been proposed [Hicks, K., et al. (2016) Biochemistry 55, 3432-3446]. Results with Bordetella bronchiseptica RB50 NicC here show that a homocyclic analogue of 6-HNA, 4-hydroxybenzoic acid (4-HBA), is decarboxylated and hydroxylated by NicC with a 420-fold lower catalytic efficiency than is 6-HNA. The ¹³( V/ K), measured with wild-type NicC by isotope ratio mass spectrometry following the natural abundance of ¹³C in the CO₂ product, is inverse for both 6-HNA (0.9989 ± 0.0002) and 4-HBA (0.9942 ± 0.0004) and becomes negligible (0.9999 ± 0.0004) for 5-chloro-6-HNA, an analogue that is 10-fold more catalytically efficient than 6-HNA. Covalently bound 6-HNA complexes of NicC are not observed by mass spectrometry. Comparative steady-state kinetic and K_d^6HNA analyses of active site NicC variants (C202A, H211A, H302A, H47E, Y215F, and Y225F) identify Tyr215 and His47 as critical determinants both of 6-HNA binding ( K_d^Y215F/ K_d^WT > 240; K_d^H47E/ K_d^WT > 350) and in coupling rates of 2,5-DHP and NAD⁺ product formation ([2,5-DHP]/[NAD⁺] = 1.00 (WT), 0.005 (Y215F), and 0.07 (H47E)]. Results of these functional analyses are in accord with an electrophilic aromatic substitution reaction mechanism in which His47-Tyr215 may serve as the general base to catalyze substrate hydroxylation and refine the structural model for substrate binding by NicC.

Cost-effectiveness of an adjuvanted recombinant zoster vaccine in older adults in the United States who have been previously vaccinated with zoster vaccine live

Zoster Vaccine Live (ZVL) is marketed in the US since 2008, and a non-live adjuvanted Recombinant Zoster Vaccine (RZV) was approved in 2017. Literature suggests that waning of ZVL efficacy may necessitate additional vaccination. The Advisory Committee on Immunization Practices recommended vaccination with RZV in immunocompetent adults aged 50+ years old, including those previously vaccinated with ZVL. The objective of this study was to determine the cost-effectiveness of vaccinating US adults aged 60+ years old, previously vaccinated with ZVL. The ZOster ecoNomic Analysis (ZONA) model, a deterministic Markov model, was adapted to follow a hypothetical 1 million(M)-person cohort of US adults previously vaccinated with ZVL. Model inputs included demographics, epidemiology, vaccine characteristics, utilities and costs. Costs and quality-adjusted life-years (QALYs) were presented over the lifetimes of the cohort from the year of additional vaccination, discounted 3% annually. The model estimated that, vaccination with RZV 5 years after previous vaccination with ZVL, would reduce disease burden compared with no additional vaccination, resulting in a gain of 1,633 QALYs at a total societal cost of $96M (incremental cost-effectiveness ratio: $58,793/QALY saved). Compared with revaccinating with ZVL, vaccination with RZV would result in a gain of 1,187 QALYs and societal cost savings of almost $84M. Sensitivity, scenario, and threshold analyses demonstrated robustness of these findings. Vaccination with RZV is predicted to be cost-effective relative to no additional vaccination, assuming a threshold of $100,000/QALY, and cost-saving relative to ZVL revaccination of US adults aged 60+ years old who have been previously vaccinated with ZVL.

Crystal structure of E. coli PRPP synthetase

BACKGROUND

Ribose-phosphate pyrophosphokinase (EC 2.7.6.1) is an enzyme that catalyzes the ATP-dependent conversion of ribose-5-phosphate to phosphoribosyl pyrophosphate. The reaction product is a key precursor for the biosynthesis of purine and pyrimidine nucleotides.

RESULTS

We report the 2.2 Å crystal structure of the E. coli ribose-phosphate pyrophosphobinase (EcKPRS). The protein has two type I phosphoribosyltransferase folds, related by 2-fold pseudosymmetry. The propeller-shaped homohexameric structure of KPRS is composed of a trimer of dimers, with the C-terminal domains forming the dimeric blades of the propeller and the N-terminal domains forming the hexameric core. The key, conserved active site residues are well-defined in the structure and positioned appropriately to bind substrates, adenosine monophosphate and ribose-5-phosphate. The allosteric site is also relatively well conserved but, in the EcKPRS structure, several residues from a flexible loop occupy the site where the allosteric modulator, adenosine diphosphate, is predicted to bind. The presence of the loop in the allosteric site may be an additional level of regulation, whereby low affinity molecules are precluded from binding.

CONCLUSIONS

Overall, this study details key structural features of an enzyme that catalyzes a critical step in nucleotide metabolism. This work provides a framework for future studies of this important protein and, as nucleotides are critical for viability, may serve as a foundation for the development of novel anti-bacterial drugs.

Structural and Functional Basis for Targeting Campylobacter jejuni Agmatine Deiminase To Overcome Antibiotic Resistance

Campylobacter jejuni is the most common bacterial cause of gastroenteritis and a major contributor to infant mortality in the developing world. The increasing incidence of antibiotic-resistant C. jejuni only adds to the urgency to develop effective therapies. Because of the essential role that polyamines play, particularly in protection from oxidative stress, enzymes involved in the biosynthesis of these metabolites are emerging as promising antibiotic targets. The recent description of an alternative pathway for polyamine synthesis, distinct from that in human cells, in C. jejuni suggests this pathway could be a target for novel therapies. To that end, we determined X-ray crystal structures of C. jejuni agmatine deiminase (CjADI) and demonstrated that loss of CjADI function contributes to antibiotic sensitivity, likely because of polyamine starvation. The structures provide details of key molecular features of the active site of this protein. Comparison of the unliganded structure (2.1 Å resolution) to that of the CjADI-agmatine complex (2.5 Å) reveals significant structural rearrangements that occur upon substrate binding. The shift of two helical regions of the protein and a large conformational change in a loop near the active site generate a narrow binding pocket around the bound substrate. This change optimally positions the substrate for catalysis. In addition, kinetic analysis of this enzyme demonstrates that CjADI is an iminohydrolase that effectively deiminates agmatine. Our data suggest that C. jejuni agmatine deiminase is a potentially important target for combatting antibiotic resistance, and these results provide a valuable framework for guiding future drug development.

Assessment of the Potential Herpes Zoster and Post Herpetic Neuralgia Case Avoidance with Vaccination in the United States

Background

Herpes zoster (HZ), commonly referred to as shingles, is a reactivation of latent varicella zoster virus in patients previously infected. Clinical characteristics of HZ include painful rash with potential complications, including post herpetic neuralgia (PHN). Care for HZ and PHN incurs significant costs and vaccination is beneficial. The aim of this study was to compare the impact on HZ and PHN case avoidance of two HZ vaccines, an available live-attenuated zoster vaccine (zoster vaccine live [ZVL]) vs. a candidate non-live adjuvanted HZ subunit vaccine (HZ/su), in the US population.

Methods

A Markov model called ZONA (ZOster ecoNomic Analyses) was developed following two age cohorts (≥60 years to represent the current ACIP recommendation and ≥65 years to represent the Medicare population) over their lifetimes from the year of vaccination. Demographic data were obtained from the US Census, whereas HZ incidence and the proportion of HZ individuals developing PHN were derived from published US-specific sources. Age-specific vaccine efficacy and waning rates were based on published clinical trial data. Vaccine coverage for both vaccines was assumed to be 30.6% and 34.2% in the two age cohorts, respectively, based on CDC data; compliance of the second dose of the HZ/su vaccine was 69%, based on data from clinical trials and Hepatitis B seconddose completion. Sensitivity analyses demonstrated robustness of the base analysis findings.

Results

In the US, for cohorts of 66.83 million (M) persons aged 60+ and 47.76M aged 65+ it was estimated that the HZ/su vaccine would reduce the number of HZ cases by 2.12M and 1.55M in the two age cohorts, respectively, compared with 0.65M and 0.45M using the ZVL. Furthermore, the HZ/su vaccine would reduce the number of PHN cases by 0.23M and 0.18M in the two age cohorts, respectively, compared with 0.10M and 0.09 using the ZVL. The number needed to vaccinate to prevent one HZ case were 10 and 11, in the respective cohorts, using the HZ/su vaccine compared with 31 and 37, in the respective cohorts, using the ZVL.

Conclusion

Due to higher and sustained vaccine efficacy, the candidate HZ/su vaccine demonstrated superior public health impact in the US compared with the currently available ZVL.

Disclosures

B. J. Patterson, GSK: Employee and Shareholder, GSK stock options or restricted shares and Salary; Pennsylvania Pharmacists Association: Scientific Advisor, stipend; P. O. Buck, GSK: Employee and Shareholder, GSK stock options or restricted shares and Salary; J. Carrico, RTI Health Solutions: Employee, Salary GSK: Research Contractor, Research support; K. A. Hicks, RTI: Employee, Salary GSK: Research Contractor, Research support; D. Curran, GSK: Employee and Shareholder, GSK stock options or restricted shares and Salary; D. Van Oorschot, GSK: Employee, Salary; J. E. Pawlowski, GSK: Employee and Shareholder, GSK stock options or restricted shares and Salary; B. Y. Lee, GSK: Consultant, Consulting fee; B. P. Yawn, GSK: Consultant and Scientific Advisor, Consulting fee

Biochemical and structural characterization of Klebsiella pneumoniae oxamate amidohydrolase in the uric acid degradation pathway

HpxW from the ubiquitous pathogen Klebsiella pneumoniae is involved in a novel uric acid degradation pathway downstream from the formation of oxalurate. Specifically, HpxW is an oxamate amidohydrolase which catalyzes the conversion of oxamate to oxalate and is a member of the Ntn-hydrolase superfamily. HpxW is autoprocessed from an inactive precursor to form a heterodimer, resulting in a 35.5 kDa α subunit and a 20 kDa β subunit. Here, the structure of HpxW is presented and the substrate complex is modeled. In addition, the steady-state kinetics of this enzyme and two active-site variants were characterized. These structural and biochemical studies provide further insight into this class of enzymes and allow a mechanism for catalysis consistent with other members of the Ntn-hydrolase superfamily to be proposed.

Qualification of cardiac troponins for nonclinical use: a regulatory perspective

The US Food and Drug Administration (FDA) Biomarker Qualification Review Team presents its perspective on the recent qualification of cardiac troponins for use in nonclinical safety assessment studies. The goal of this manuscript is to provide greater transparency into the qualification process and factors that were considered in reaching a regulatory decision. This manuscript includes an overview of the data that were submitted and a discussion of the strengths and shortcomings of these data supporting the qualification decision. The cardiac troponin submission is the first literature-based biomarker application to be reviewed by the FDA and insights gained from this experience may aid future submissions and help streamline the characterization and qualification of future biomarkers.

Structural and mechanistic studies of HpxO, a novel flavin adenine dinucleotide-dependent urate oxidase from Klebsiella pneumoniae

HpxO is a flavin-dependent urate oxidase that catalyzes the hydroxylation of uric acid to 5-hydroxyisourate and functions in a novel pathway for purine catabolism found in Klebsiella pneumoniae. We have determined the structures of HpxO with and without uric acid at 2.0 and 2.2 Å, respectively. We have also determined the structure of the R204Q variant at 2.0 Å resolution in the absence of uric acid. The variant structure is very similar to that of wild-type HpxO except for the conformation of Arg103, which interacts with FAD in the variant but not in the wild-type structure. Interestingly, the R204Q variant results in the uncoupling of nicotinamide adenine dinucleotide oxidation from uric acid hydroxylation. This suggests that Arg204 facilitates the deprotonation of uric acid, activating it for the oxygen transfer. On the basis of these data, a mechanism for this reaction consisting of a nucleophilic attack of the urate anion on the flavin hydroperoxide resulting in the formation of 5-hydroxyisourate is proposed.

Allocating HIV prevention funds in the United States: recommendations from an optimization model

The Centers for Disease Control and Prevention (CDC) had an annual budget of approximately $327 million to fund health departments and community-based organizations for core HIV testing and prevention programs domestically between 2001 and 2006. Annual HIV incidence has been relatively stable since the year 2000 [1] and was estimated at 48,600 cases in 2006 and 48,100 in 2009 [2]. Using estimates on HIV incidence, prevalence, prevention program costs and benefits, and current spending, we created an HIV resource allocation model that can generate a mathematically optimal allocation of the Division of HIV/AIDS Prevention’s extramural budget for HIV testing, and counseling and education programs. The model’s data inputs and methods were reviewed by subject matter experts internal and external to the CDC via an extensive validation process. The model projects the HIV epidemic for the United States under different allocation strategies under a fixed budget. Our objective is to support national HIV prevention planning efforts and inform the decision-making process for HIV resource allocation. Model results can be summarized into three main recommendations. First, more funds should be allocated to testing and these should further target men who have sex with men and injecting drug users. Second, counseling and education interventions ought to provide a greater focus on HIV positive persons who are aware of their status. And lastly, interventions should target those at high risk for transmitting or acquiring HIV, rather than lower-risk members of the general population. The main conclusions of the HIV resource allocation model have played a role in the introduction of new programs and provide valuable guidance to target resources and improve the impact of HIV prevention efforts in the United States.

Benefits and costs of substance abuse treatment programs for state prison inmates: results from a lifetime simulation model

Reflecting drug use patterns and criminal justice policies throughout the 1990s and 2000s, prisons hold a disproportionate number of society's drug abusers. Approximately 50% of state prisoners meet the criteria for a diagnosis of drug abuse or dependence, but only 10% receive medically based drug treatment. Because of the link between substance abuse and crime, treating substance abusing and dependent state prisoners while incarcerated has the potential to yield substantial economic benefits. In this paper, we simulate the lifetime costs and benefits of improving prison-based substance abuse treatment and post-release aftercare for a cohort of state prisoners. Our model captures the dynamics of substance abuse as a chronic disease; estimates the benefits of substance abuse treatment over individuals' lifetimes; and tracks the costs of crime and criminal justice costs related to policing, adjudication, and incarceration. We estimate net societal benefits and cost savings to the criminal justice system of the current treatment system and five policy scenarios. We find that four of the five policy scenarios provide positive net societal benefits and cost savings to the criminal justice system relative to the current treatment system. Our study demonstrates the societal gains to improving the drug treatment system for state prisoners.

A model for allocating CDC's HIV prevention resources in the United States

The Division of HIV/AIDS Prevention (DHAP) at the Centers for Disease Control and Prevention has an annual budget of approximately $325 million for funding HIV prevention programs in the U.S. The purpose of this paper is to thoroughly describe the methods used to develop a national HIV resource allocation model intended to inform DHAP on allocation strategies that might improve the overall effectiveness of HIV prevention efforts. The HIV prevention resource allocation problem consists of choosing how to apportion prevention resources among interventions and populations so that HIV incidence is minimized, given a budget constraint. We developed an epidemic model that projects HIV infections over time given a specific allocation scenario. The epidemic model is then embedded in a nonlinear mathematical optimization program to determine the allocation scenario that minimizes HIV incidence over a 5-year horizon. In our model, we consider the general U.S. population and specific at-risk populations. The at-risk populations include 15 subgroups structured by gender, race/ethnicity and HIV transmission risk group. HIV transmission risk groups include high-risk heterosexuals, men who have sex with men and injection drug users. We consider HIV screening interventions and interventions to reduce HIV-related risk behaviors. The output of the model is the optimal funding scenario indicating the amounts to be allocated to all combinations of populations and interventions. For illustrative purposes only, we provide a sample application of the model. In this example, the optimal allocation scenario is compared to the current baseline funding scenario to highlight how the current allocation of funds could be improved. In the baseline allocation, 29% of the annual budget is aimed at the general population, while the model recommends targeting 100% of the budget to the at-risk populations with no allocation targeted to the general population. Within the allocation to behavioral interventions the model recommends an increase in targeting diagnosed positives. Also, the model allocation suggests a greater focus on MSM and IDUs with a 72% of the annual budget allocated to them, while the baseline allocation for MSM and IDUs totals 37%. Incorporating future epidemic trends in the decision-making process informs the selection of populations and interventions that should be targeted. Improving the use of funds by targeting the interventions and population subgroups at greatest risk may lead to improved HIV outcomes. These models can also direct research by pointing to areas where the development of cost-effective interventions can have the most impact on the epidemic.

Identification of novel peptide substrates for protein farnesyltransferase reveals two substrate classes with distinct sequence selectivities

Prenylation is a posttranslational modification essential for the proper localization and function of many proteins. Farnesylation, the attachment of a 15-carbon farnesyl group near the C-terminus of protein substrates, is catalyzed by protein farnesyltransferase (FTase). Farnesylation has received significant interest as a target for pharmaceutical development, and farnesyltransferase inhibitors are in clinical trials as cancer therapeutics. However, as the total complement of prenylated proteins is unknown, the FTase substrates responsible for farnesyltransferase inhibitor efficacy are not yet understood. Identifying novel prenylated proteins within the human proteome constitutes an important step towards understanding prenylation-dependent cellular processes. Based on sequence preferences for FTase derived from analysis of known farnesylated proteins, we selected and screened a library of small peptides representing the C-termini of 213 human proteins for activity with FTase. We identified 77 novel FTase substrates that exhibit multiple-turnover (MTO) reactivity within this library; our library also contained 85 peptides that can be farnesylated by FTase only under single-turnover (STO) conditions. Based on these results, a second library was designed that yielded an additional 29 novel MTO FTase substrates and 45 STO substrates. The two classes of substrates exhibit different specificity requirements. Efficient MTO reactivity correlates with the presence of a nonpolar amino acid at the a(2) position and a Phe, Met, or Gln at the terminal X residue, consistent with the proposed Ca(1)a(2)X sequence model. In contrast, the sequences of the STO substrates vary significantly more at both the a(2) and the X residues and are not well described by current farnesylation algorithms. These results improve the definition of prenyltransferase substrate specificity, test the efficacy of substrate algorithms, and provide valuable information about therapeutic targets. Finally, these data illuminate the potential for in vivo regulation of prenylation through modulation of STO versus MTO peptide reactivity with FTase.

Improvements in risk factor control among persons with diabetes in the United States: evidence and implications for remaining life expectancy

AIMS

To examine whether A1c, blood pressure, and cholesterol values changed for U.S. adults with diagnosed diabetes between 1988-1994 and 2005-2006. We then project the impact of these changes on life expectancy and diabetes-related complications.

METHODS

We estimated changes in hemoglobin A1c, blood pressure, and total cholesterol between 1988-1994 and 2005-2006 using regression analysis and data from the National Health and Nutrition Examination Survey. We projected the potential effects on life expectancy and complications using the CDC-RTI Diabetes Cost-Effectiveness Model.

RESULTS

A1c fell by 0.68 percentage points (P=0.001) among U.S. adults with diagnosed diabetes. Among those with diabetes and hypertension, systolic and diastolic blood pressure fell by 5.66 and 8.15mmHg, respectively (P=0.005 and P=0.001). Among those with diabetes and high cholesterol, total cholesterol fell by 36.41mg/dL (P=0.001). These improvements were projected to increase life expectancy for persons with newly diagnosed diabetes by 1.0 year.

CONCLUSIONS

Risk factor control has improved in the United States. Persons newly diagnosed with type 2 diabetes in 2005 have a better prognosis than persons diagnosed with diabetes 11 years earlier.

Biochemical characterization of the HpxO enzyme from Klebsiella pneumoniae, a novel FAD-dependent urate oxidase

The HpxO enzyme from Klebsiella pneumoniae was recently proposed, on the basis of genetic studies, to catalyze the hydroxylation of uric acid to 5-hydroxyisourate as part of the purine catabolic pathway. Its primary sequence suggests that the HpxO catalytic activity depends on a flavin cofactor (FAD), contrasting with all previously studied urate oxidase enzymes, which have no cofactor requirement. Here we demonstrate biochemically that HpxO is an FAD-dependent urate oxidase. Our data are consistent with the proposal that HpxO-bound flavin hydroperoxide is the hydroxylating species. These results confirm the existence of a novel mechanistic paradigm in purine catabolism.

Cost-effectiveness of screening for pre-diabetes among overweight and obese U.S. adults

OBJECTIVE

To estimate the cost-effectiveness of screening overweight and obese individuals for pre-diabetes and then modifying their lifestyle based on the Diabetes Prevention Program (DPP).

RESEARCH DESIGN AND METHODS

A Markov simulation model was used to estimate disease progression, costs, and quality of life. Cost-effectiveness was evaluated from a health care system perspective. We considered two screening/treatment strategies for pre-diabetes. Strategy 1 included screening overweight subjects and giving them the lifestyle intervention included in the DPP if they were diagnosed with both impaired glucose tolerance (IGT) and impaired fasting glucose (IFG). Strategy 2 included screening followed by lifestyle intervention for subjects diagnosed with either IGT or IFG or both. Each strategy was compared with a program of no screening.

RESULTS

Screening for pre-diabetes and treating those identified as having both IGT and IFG with the DPP lifestyle intervention had a cost-effectiveness ratio of $8,181 per quality-adjusted life-year (QALY) relative to no screening. If treatment was also provided to subjects with only IGT or only IFG (strategy 2), the cost-effectiveness ratio increased to $9,511 per QALY. Changes in screening-related parameters had small effects on the cost-effectiveness ratios; the results were more sensitive to changes in intervention-related parameters.

CONCLUSIONS

Screening for pre-diabetes in the overweight and obese U.S. population followed by the DPP lifestyle intervention has a relatively attractive cost-effectiveness ratio.

Evaluation of protein farnesyltransferase substrate specificity using synthetic peptide libraries

Farnesylation, catalyzed by protein farnesyltransferase (FTase), is an important post-translational modification guiding cellular localization. Recently predictive models for identifying FTase substrates have been reported. Here we evaluate these models through screening of dansylated-GCaaS peptides, which also provides new insights into the protein substrate selectivity of FTase.

The economics of routine childhood hepatitis A immunization in the United States: the impact of herd immunity

OBJECTIVES

Because of the herd-immunity phenomenon, the benefits of immunization against hepatitis A extend beyond those received by those who are vaccinated. This analysis estimates the impact of herd immunity on the cost-effectiveness of routine hepatitis A immunization among US children.

PATIENTS AND METHODS

In an economic model, the costs and benefits of hepatitis A immunization were estimated for immunizing all US children at age 1 year over a 10-year period starting in 2005. The future burden of disease from hepatitis A was also estimated with this model, and the fraction that would be prevented by herd immunity was modeled by using a previously published analysis of the relationship between hepatitis A vaccination coverage and declines in hepatitis A incidence.

RESULTS

Without accounting for herd-immunity effects, the costs of routine immunization would average 32,000 dollars per quality-adjusted life-year gained for the first 10 cohorts immunized starting with the 2005 birth cohort. Herd-immunity effects would be expected to produce substantial additional benefits, lowering the cost of the immunization program to 1000 dollars per quality-adjusted life-year gained for the first 10 cohorts. Herd-immunity benefits would be greatest for the first few cohorts, more than doubling the benefits of immunization, and would decline over time. In a univariate sensitivity analysis, estimates were most sensitive to vaccination costs but remained below 20,000 dollars per quality-adjusted life-year under all of the assumptions.

CONCLUSIONS

Herd-immunity effects more than double the savings from hepatitis A immunization during the first 10 years of the program. After accounting for these effects, immunization is close to cost-neutral on a cost-per-quality-adjusted-life-year basis.

Cost-effectiveness of routine childhood vaccination for hepatitis A in the United States

OBJECTIVES

Economic analysis is an important component in formulating national policy. We evaluated the economic impact of hepatitis A vaccination of all US children ages 12 to 23 months as compared with no vaccination and with current implementation of the preexisting (issued in 1999), regional policy.

METHODS

We developed a Markov model of hepatitis A that followed a single cohort from birth in 2005 through death or age 95 years. From the societal perspective, the model compared the outcomes that resulted from routine vaccination at age 1 year to 2 scenarios: no hepatitis A vaccination and hepatitis A vaccination at levels observed in 2003 under the preexisting policy. We evaluated the economic impact of vaccination nationwide, in areas where vaccination was already recommended, and in areas where no previous recommendation existed.

RESULTS

Without childhood vaccination, the approximately 4 million children in the 2005 birth cohort would be expected over their lifetimes to have 199,000 hepatitis A virus infections, including 74,000 cases of acute hepatitis A and 82 deaths, resulting in 134 million dollars in hepatitis A-related medical costs and productivity losses. Compared with no vaccination, routine vaccination at age 1 year would prevent 172,000 infections, at a cost of 28,000 dollars per quality-adjusted life year saved. Compared with maintaining the levels of hepatitis A vaccination under the preexisting regional policy, routine vaccination at age 1 year would prevent an additional 112,000 infections, at a cost of 45,000 dollars per quality-adjusted life year saved.

CONCLUSIONS

The cost-effectiveness of nationwide hepatitis A vaccination compared with no vaccination, and the incremental cost-effectiveness of this recommendation compared with preexisting recommendations, is similar to that of other accepted public health interventions. In October 2005, the Advisory Committee on Immunization Practices recommended extending hepatitis A immunization to all US children ages 12 to 23 months.

An evaluation of cost sharing to finance a diet and physical activity intervention to prevent diabetes

OBJECTIVE

The Diabetes Prevention Program (DPP) lifestyle intervention is a cost-effective strategy to prevent type 2 diabetes, but it is unclear how this intervention could be financed. We explored whether this intervention could be offered in a way that allows return on investment for private health insurers while remaining attractive for consumers, employers, and Medicare.

RESEARCH DESIGN AND METHODS

We used the DPP and other published reports to build a Markov simulation model to estimate the lifetime progression of disease, costs, and quality of life for adults with impaired glucose tolerance. The model assumed a health-payer perspective and compared DPP lifestyle and placebo interventions. Primary outcomes included cumulative incidence of diabetes, direct medical costs, quality-adjusted life-years (QALYs), and cost per QALY gained.

RESULTS

Compared with placebo, providing the lifestyle intervention at age 50 years could prevent 37% of new cases of diabetes before age 65, at a cost of $1,288 per QALY gained. A private payer could reimburse $655 (24%) of the $2,715 in total discounted intervention costs during the first 3 intervention years and still recover all of these costs in the form of medical costs avoided. If Medicare paid up to $2,136 in intervention costs over the 15-year period before participants reached age 65, it could recover those costs in the form of future medical costs avoided beginning at age 65.

CONCLUSIONS

Cost-sharing strategies to offer the DPP lifestyle intervention for eligible people between ages 50 and 64 could provide financial return on investment for private payers and long-term benefits for Medicare.

Peptide specificity of protein prenyltransferases is determined mainly by reactivity rather than binding affinity

Protein farnesyltransferase (FTase) and protein geranylgeranyltransferase type I (GGTase I) catalyze the attachment of lipid groups from farnesyl diphosphate and geranylgeranyl diphosphate, respectively, to a cysteine near the C-terminus of protein substrates. FTase and GGTase I modify several important signaling and regulatory proteins with C-terminal CaaX sequences ("C" refers to the cysteine residue that becomes prenylated, "a" refers to any aliphatic amino acid, and "X" refers to any amino acid). In the CaaX paradigm, the C-terminal X-residue of the protein/peptide confers specificity for FTase or GGTase I. However, some proteins, such as K-Ras, RhoB, and TC21, are substrates for both FTase and GGTase I. Here we demonstrate that the C-terminal amino acid affects the binding affinity of K-Ras4B-derived hexapeptides (TKCVIX) to FTase and GGTase I modestly. In contrast, reactivity, as indicated by transient and steady-state kinetics, varies significantly and correlates with hydrophobicity, volume, and structure of the C-terminal amino acid. The reactivity of FTase decreases as the hydrophobicity of the C-terminal amino acid increases whereas the reactivity of GGTase I increases with the hydrophobicity of the X-group. Therefore, the hydrophobicity, as well as the structure of the X-group, determines whether peptides are specific for farnesylation, geranylgeranylation, or dual prenylation.

Upstream polybasic region in peptides enhances dual specificity for prenylation by both farnesyltransferase and geranylgeranyltransferase type I

Protein farnesyltransferase (FTase) and protein geranylgeranyltransferase type I (GGTase I) catalyze the attachment of a farnesyl or geranylgeranyl lipid, respectively, near the C-terminus of their protein substrates. FTase and GGTase I differ in both their substrate specificity and magnesium dependence, where the activity of FTase, but not GGTase I, is activated by magnesium. Many protein substrates of these enzymes contain an upstream polybasic region that is proposed to increase the affinity of the substrate and aid in plasma membrane association. Here, we demonstrate that the addition of an upstream polybasic region to a peptide substrate enhances the binding affinity of FTase approximately 4-fold for the peptide but diminishes the catalytic efficiency of the reaction, reflected by decreases in both the prenylation rate constant and kcat/KM. Specifically, the prenylation rate constant decreases 7-fold at 5 mM MgCl2 for the peptide KKKSKTKCVIM (C-terminal sequence of K-Ras4B) in comparison to TKCVIM. This decrease is accompanied by an alteration in the dependence on magnesium, as the K(Mg) increases from 2.2 +/- 0.1 mM for TKCVIM to 11.5 +/- 0.1 mM for KKKSKTKCVIM. The presence of an upstream polybasic region does not significantly affect GGTase I-catalyzed reactions, as only minimal changes are seen in Kd, kcat/KM, and k(chem) values. Thus, the presence of an upstream polybasic region enhances the dual prenylation of these substrates, by decreasing the catalytic efficiency of farnesylation catalyzed by FTase to a level comparable to that of geranylgeranylation catalyzed by GGTase I.

Benefits and costs of methadone treatment: results from a lifetime simulation model

Several studies have examined the benefits and costs of drug treatment; however, they have typically focused on the benefits and costs of a single treatment episode. Although beneficial for certain analyses, the results are limited because they implicitly treat drug abuse as an acute problem that can be treated in one episode. We developed a Monte Carlo simulation model that incorporates the chronic nature of drug abuse. Our model represents the progression of individuals from the general population aged 18-60 with respect to their heroin use, treatment for heroin use, criminal behavior, employment, and health care use. We also present three model scenarios representing an increase in the probability of going to treatment, an increase in the treatment length of stay, and a scenario in which drug treatment is not available to evaluate how changes in treatment parameters affect model results. We find that the benefit-cost ratio of treatment from our lifetime model (37.72) exceeds the benefit-cost ratio from a static model (4.86). The model provides a rich characterization of the dynamics of heroin use and captures the notion of heroin use as a chronic recurring condition. Similar models can be developed for other chronic diseases, such as diabetes, mental illness, or cardiovascular disease.

Interplay of isoprenoid and peptide substrate specificity in protein farnesyltransferase

Protein farnesyltransferase (FTase) catalyzes the post-translational modification of many important cellular proteins, and is a potential anticancer drug target. Crystal structures of the FTase ternary complex illustrate an unusual feature of this enzyme, the fact that the isoprenoid substrate farnesyl diphosphate (FPP) forms part of the binding site for the peptide substrate. This implies that changing the structure of FPP could alter the specificity of the FPP-FTase complex for peptide substrates. We have found that this is the case; a newly synthesized FPP analogue, 3-MeBFPP, is a substrate with three peptide cosubstrates, but is not an effective substrate with a fourth peptide (dansyl-GCKVL). Addition of this analogue also inhibits farnesylation of dansyl-GCKVL by FPP. Surprisingly, the differential substrate abilities of these four peptides with FPP-FTase and 3-MeBFPP-FTase complexes do not correlate with their binding affinities for these isoprenoid-enzyme complexes. The possible mechanistic rationales for this observation, along with its potential utility for the study of protein prenylation, are discussed.

Screening for type 2 diabetes mellitus: a cost-effectiveness analysis

BACKGROUND

No randomized, controlled trial of screening for diabetes has been conducted. In the absence of direct evidence, cost-effectiveness models may provide guidance about preferred screening strategies.

OBJECTIVE

To estimate the incremental cost-effectiveness of 2 diabetes screening strategies: screening targeted to people with hypertension and universal screening.

DESIGN

Markov model.

DATA SOURCES

United Kingdom Prospective Diabetes Study, Hypertension Optimal Treatment trial, and recent cost data.

TARGET POPULATION

General primary care population in the United States.

TIME HORIZON

Lifetime.

PERSPECTIVE

Health care system.

INTERVENTIONS

Diabetes screening targeted to people with hypertension and universal screening.

OUTCOME MEASURES

Cost per quality-adjusted life-year (QALY) gained. Costs (in 1997 U.S. dollars) and QALYs discounted at a 3% annual rate.

RESULTS OF BASE-CASE ANALYSIS

At all ages, incremental cost-effectiveness ratios were more favorable for screening targeted to people with hypertension than for universal screening. For example, at age 55 years, the cost per QALY for targeted screening compared with no screening was 34,375 dollars, whereas the cost per QALY for universal screening compared with targeted screening was 360,966 dollars. Screening was more cost-effective for ages 55 to 75 years than for younger ages.

RESULTS OF SENSITIVITY ANALYSIS

In single-way and probabilistic sensitivity analyses, findings were robust to therapy costs, screening costs, screening lead time, reduced effectiveness of intensive antihypertensive therapy, and increased relative risk reduction for stroke attributable to intensive hypertension control.

LIMITATIONS

We did not consider screening targeted to persons with dyslipidemia, and we used studies of people whose diabetes was detected clinically to estimate screening benefits.

CONCLUSIONS

Diabetes screening targeted to people with hypertension is more cost-effective than universal screening. The most cost-effective strategy is targeted screening at age 55 to 75 years.

Optimal allocation of resources across four interventions for type 2 diabetes

BACKGROUND

Several interventions can be applied to prevent complications of type 2 diabetes. This article examines the optimal allocation of resources across 4 interventions to treat patients newly diagnosed with type 2 diabetes. The interventions are intensive glycemic control, intensified hypertension control, cholesterol reduction, and smoking cessation.

METHODS

A linear programming model was designed to select sets of interventions to maximize quality-adjusted life years (QALYs), subject to varied budget and equity constraints.

RESULTS

For no additional cost, approximately 211,000 QALYs can be gained over the lifetimes of all persons newly diagnosed with diabetes by implementing interventions rather than standard care. With increased availability of funds, additional health benefits can be gained but with diminishing marginal returns. The impact of equity constraints is extensive compared to the solution with the same intervention costs and no equity constraint. Under the conditions modeled, intensified hypertension control and smoking cessation interventions were provided most often, and intensive glycemic control and cholesterol reduction interventions were provided less often.

CONCLUSIONS

A resource allocation model identifies trade-offs involved when imposing budget and equity constraints on care for individuals with newly diagnosed diabetes.

Kinetic characterization of wild-type and proton transfer-impaired variants of beta-carbonic anhydrase from Arabidopsis thaliana

We have cloned and overexpressed a truncated, recombinant form of beta-carbonic anhydrase from Arabidopsis thaliana. The wild-type enzyme and two site-directed variants, H216N and Y212F, have been kinetically characterized both at steady state by stopped-flow spectrophotometry and at chemical equilibrium by (18)O isotope exchange methods. The wild-type enzyme has a maximal k(cat) for CO2 hydration of 320 ms(-1) and is rate limited by proton transfer involving two residues with apparent pK(a) values of 6.0 and 8.7. The mutant enzyme H216N has a maximal k(cat) at high pH that is 43% that of wild type, but is only 5% that of wild type at pH 7.0. (18)O exchange studies reveal that the effect of the mutations H216N or Y212F is primarily on proton transfer steps in the catalytic mechanism and not in the rate of CO2-HCO3- exchange. These results suggest that residues His-216 and Tyr-212 are both important for efficient proton transfer in A. thaliana carbonic anhydrase.

EARLY FLOWERING3 encodes a novel protein that regulates circadian clock function and flowering in Arabidopsis

Higher plants use photoperiodic cues to regulate many aspects of development, including the transition from vegetative to floral development. The EARLY FLOWERING3 (ELF3) gene is required for photoperiodic flowering and normal circadian regulation in Arabidopsis. We have cloned ELF3 by positional methods and found that it encodes a novel 695-amino acid protein that may function as a transcriptional regulator. ELF3 transcript level is regulated in a circadian manner, as is expected of a zeitnehmer input pathway component. Overexpression of the LATE ELONGATED HYPOCOTYL gene, which has been proposed to function as a clock component, did not abolish circadian regulation of ELF3 transcription, providing further evidence that ELF3 is a circadian clock input pathway component.

The influence of a family program on adolescent tobacco and alcohol use

OBJECTIVES

This study examined a family-directed program's effectiveness in preventing adolescent tobacco and alcohol use in a general population.

METHODS

Adolescents aged 12 to 14 years and their families were identified by random-digit dialing throughout the contiguous United States. After providing baseline data by telephone interviews, they were randomly allocated to receive or not receive a family-directed program featuring mailed booklets and telephone contacts by health educators. Follow-up telephone interviews were conducted 3 and 12 months after program completion.

RESULTS

The findings suggested that smoking onset was reduced by 16.4% at 1 year, with a 25.0% reduction for non-Hispanic Whites but no statistically significant program effect for other races/ethnicities. There were no statistically significant program effects for smokeless tobacco or alcohol use onset.

CONCLUSIONS

The family-directed program was associated with reduced smoking onset for non-Hispanic Whites, suggesting that it is worthy of further application, development, and evaluation.

Conditional circadian dysfunction of the Arabidopsis early-flowering 3 mutant

Photoperiodic responses, such as the daylength-dependent control of reproductive development, are associated with a circadian biological clock. The photoperiod-insensitive early-flowering 3 (elf3) mutant of Arabidopsis thaliana lacks rhythmicity in two distinct circadian-regulated processes. This defect was apparent only when plants were assayed under constant light conditions. elf3 mutants retain rhythmicity in constant dark and anticipate light/dark transitions under most light/dark regimes. The conditional arrhythmic phenotype suggests that the circadian pacemaker is intact in darkness in elf3 mutant plants, but the transduction of light signals to the circadian clock is impaired.

The Arabidopsis ELF3 gene regulates vegetative photomorphogenesis and the photoperiodic induction of flowering

Flowering in Arabidopsis thaliana is promoted by longday (LD) photoperiods such that plants grown in LD flower earlier, and after the production of fewer leaves, than plants grown in short-day (SD) photoperiods. The early-flowering 3 (elf3) mutant of Arabidopsis, which is insensitive to photoperiod with regard to floral initiation has been characterized elf3 mutants are also altered in several aspects of vegetative photomorphogenesis, including hypocotyl elongation. When inhibition of hypocotyl elongation was measured, elf3 mutant seedlings were less responsive than wild-type to all wavelengths of light, and most notably defective in blue and green light-mediated inhibition. When analyzed for the flowering-time phenotype, elf3 was epistatic to mutant alleles of the blue-light receptor encoding gene, HY4. However, when elf3 mutants were made deficient for functional phytochrome by the introduction of hy2 mutant alleles, the elf3 hy2 double mutants displayed the novel phenotype of flowering earlier than either single mutant while still exhibiting photoperiod insensitivity, indicating that a phytochrome-mediated pathway regulating floral initiation remains functional in elf3 single mutants. In addition, the inflorescences of one allelic combination of elf3 hy2 double mutants form a terminal flower similar to the structure produced by tfk1 single mutants. These results suggest that one of the signal transduction pathways controlling photoperiodism in Arabidopsis is regulated, at least in part, by photoreceptors other than phytochrome, and that the activity of the Arabidopsis inflorescence and floral meristem identity genes may be regulated by this same pathway.

Echocardiographic evaluation of papillary fibroelastoma: a case report and review of the literature

Papillary fibroelastomas comprise approximately 7.9% of benign primary cardiac tumors. Although papillary fibroelastomas were at first discovered incidentally at autopsy or during heart surgery, these tumors are increasingly being identified by echocardiography. This article reviews those papillary fibroelastomas detected by transthoracic or transesophageal echocardiography and discusses the echocardiographic features of these tumors, associated symptoms, and management. Echocardiography is important in influencing management decisions regarding excision, valve replacement, and valve repair.