Dose-linearity of the pharmacokinetics of an intravenous [14 C]midazolam microdose in children.

AIMS: Drug disposition in children may vary from adults due to age-related variation in drug metabolism. Microdose studies present an innovation to study pharmacokinetics (PK) in paediatrics; however, they should be used only when the PK is dose linear. We aimed to assess dose linearity of a [14 C]midazolam microdose, by comparing the PK of an intravenous (IV) microtracer (a microdose given simultaneously with a therapeutic midazolam dose), with the PK of a single isolated microdose. METHODS: Preterm to 2-year-old infants admitted to the intensive care unit received [14 C]midazolam IV as a microtracer or microdose, followed by dense blood sampling up to 36 hours. Plasma concentrations of [14 C]midazolam and [14 C]1-hydroxy-midazolam were determined by accelerator mass spectrometry. Noncompartmental PK analysis was performed and a population PK model was developed. RESULTS: Of 15 infants (median gestational age 39.4 [range 23.9-41.4] weeks, postnatal age 11.4 [0.6-49.1] weeks), 6 received a microtracer and 9 a microdose of [14 C]midazolam (111 Bq kg-1 ; 37.6 ng kg-1 ). In a 2-compartment PK model, bodyweight was the most significant covariate for volume of distribution. There was no statistically significant difference in any PK parameter between the microdose and microtracer, nor in the area under curve ratio [14 C]1-OH-midazolam/[14 C]midazolam, showing the PK of midazolam to be linear within the range of the therapeutic and microdoses. CONCLUSION: Our data support the dose linearity of the PK of an IV [14 C]midazolam microdose in children. Hence, a [14 C]midazolam microdosing approach may be used as an alternative to a therapeutic dose of midazolam to study developmental changes in hepatic CYP3A activity in young children.

Evaluation of a Library of FDA-Approved Drugs for Their Ability To Potentiate Antibiotics against Multidrug-Resistant Gram-Negative Pathogens.

The Prestwick library was screened for antibacterial activity or "antibiotic resistance breaker" (ARB) potential against four species of Gram-negative pathogens. Discounting known antibacterials, the screen identified very few ARB hits, which were strain/drug specific. These ARB hits included antimetabolites (zidovudine, floxuridine, didanosine, and gemcitabine), anthracyclines (daunorubicin, mitoxantrone, and epirubicin), and psychoactive drugs (gabapentin, fluspirilene, and oxethazaine). These findings suggest that there are few approved drugs that could be directly repositioned as adjunct antibacterials, and these will need robust testing to validate efficacy.

The OncoSim model: development and use for better decision-making in Canadian cancer control.

The Canadian Partnership Against Cancer was created in 2007 by the federal government to accelerate cancer control across Canada. Its OncoSim microsimulation model platform, which consists of a suite of specific cancer models, was conceived as a tool to augment conventional resources for population-level policy- and decision-making. The Canadian Partnership Against Cancer manages the OncoSim program, with funding from Health Canada and model development by Statistics Canada. Microsimulation modelling allows for the detailed capture of population heterogeneity and health and demographic history over time. Extensive data from multiple Canadian sources were used as inputs or to validate the model. OncoSim has been validated through expert consultation; assessments of face validity, internal validity, and external validity; and model fit against observed data. The platform comprises three in-depth cancer models (lung, colorectal, cervical), with another in-depth model (breast) and a generalized model (25 cancers) being in development. Unique among models of its class, OncoSim is available online for public sector use free of charge. Users can customize input values and output display, and extensive user support is provided. OncoSim has been used to support decision-making at the national and jurisdictional levels. Although simulation studies are generally not included in hierarchies of evidence, they are integral to informing cancer control policy when clinical studies are not feasible. OncoSim can evaluate complex intervention scenarios for multiple cancers. Canadian decision-makers thus have a powerful tool to assess the costs, benefits, cost-effectiveness, and budgetary effects of cancer control interventions when faced with difficult choices for improvements in population health and resource allocation.

Distinctive Roles for Periplasmic Proteases in the Maintenance of Essential Outer Membrane Protein Assembly.

Outer membrane protein (OMP) biogenesis in Escherichia coli is a robust process essential to the life of the organism. It is catalyzed by the ß-barrel assembly machine (Bam) complex, and a number of quality control factors, including periplasmic chaperones and proteases, maintain the integrity of this trafficking pathway. Little is known, however, about how periplasmic proteases recognize and degrade OMP substrates when assembly is compromised or whether different proteases recognize the same substrate at distinct points in the assembly pathway. In this work, we use well-defined assembly-defective mutants of LptD, the essential lipopolysaccharide assembly translocon, to show that the periplasmic protease DegP degrades substrates with assembly defects that prevent or impair initial contact with Bam, causing the mutant protein to accumulate in the periplasm. In contrast, another periplasmic protease, BepA, degrades a LptD mutant substrate that has engaged the Bam complex and formed a nearly complete barrel. Furthermore, we describe the role of the outer membrane lipoprotein YcaL, a protease of heretofore unknown function, in the degradation of a LptD substrate that has engaged the Bam complex but is stalled at an earlier step in the assembly process that is not accessible to BepA. Our results demonstrate that multiple periplasmic proteases monitor OMPs at distinct points in the assembly process.IMPORTANCE OMP assembly is catalyzed by the essential Bam complex and occurs in a cellular environment devoid of energy sources. Assembly intermediates that misfold can compromise this essential molecular machine. Here we demonstrate distinctive roles for three different periplasmic proteases that can clear OMP substrates with folding defects that compromise assembly at three different stages. These quality control factors help ensure the integrity of the permeability barrier that contributes to the intrinsic resistance of Gram-negative organisms to many antibiotics.

Productivity costs of work loss associated with osteoarthritis in Canada from 2010 to 2031.

OBJECTIVE: To estimate and project the productivity costs of work loss (PCWL) associated with osteoarthritis (OA) in Canada using the Population Health Model (POHEM). DESIGN: We integrated an employment module based on 2006 Canadian Census into the previously developed microsimulation model of OA. The Canadian Community Health Survey (CCHS) Cycle 2.1 with an OA sample aged 25-64 (n = 7067) was used to calibrate the results of the employment module and to estimate the fraction of non-employment associated with OA. Probabilities of non-employment together with attributable fractions were then implemented in POHEM to estimate PCWL associated with OA from 2010 to 2031. RESULTS: Among the OA population, 44.4% and 59.4% of non-employment due to illness was associated with OA for those not working full-year and part-year, respectively. According to POHEM projections, the size of the working age population with OA increased from 1.5 million in 2010 to 1.7 million in 2031. The PCWL associated with OA increased from $12 billion to $17.5 billion in constant 2008 Canadian dollars. Around 38% of this increase was due to the increase in OA prevalence and changes in demographics, while the rest was due to increase in real wage growth. Male and female OA patients between 55 and 64 years of age had the highest total projected PCWL, respectively. CONCLUSIONS: The total PCWL associated with OA in Canada is estimated to be substantial and increasing in future years. Results of this study could be used to inform policies aiming to increase employment sustainability among individuals with OA.

The Activity of Escherichia coli Chaperone SurA Is Regulated by Conformational Changes Involving a Parvulin Domain.

UNLABELLED: The periplasmic chaperone SurA is critical for the biogenesis of outer membrane proteins (OMPs) and, thus, the maintenance of membrane integrity in Escherichia coli. The activity of this modular chaperone has been attributed to a core chaperone module, with only minor importance assigned to the two SurA peptidyl-prolyl isomerase (PPIase) domains. In this work, we used synthetic phenotypes and covalent tethering to demonstrate that the activity of SurA is regulated by its PPIase domains and, furthermore, that its activity is correlated with the conformational state of the chaperone. When combined with mutations in the ß-barrel assembly machine (BAM), SurA mutations resulting in deletion of the second parvulin domain (P2) inhibit OMP assembly, suggesting that P2 is involved in the regulation of SurA. The first parvulin domain (P1) potentiates this autoinhibition, as mutations that covalently tether the P1 domain to the core chaperone module severely impair OMP assembly. Furthermore, these inhibitory mutations negate the suppression of and biochemically stabilize the protein specified by a well-characterized gain-of-function mutation in P1, demonstrating that SurA cycles between distinct conformational and functional states during the OMP assembly process. IMPORTANCE: This work reveals the reversible autoinhibition of the SurA chaperone imposed by a heretofore underappreciated parvulin domain. Many ß-barrel-associated outer membrane (OM) virulence factors, including the P-pilus and type I fimbriae, rely on SurA for proper assembly; thus, a mechanistic understanding of SurA function and inhibition may facilitate antibiotic intervention against Gram-negative pathogens, such as uropathogenic Escherichia coli, E. coli O157:H7, Shigella, and Salmonella. In addition, SurA is important for the assembly of critical OM biogenesis factors, such as the lipopolysaccharide (LPS) transport machine, suggesting that specific targeting of SurA may provide a useful means to subvert the OM barrier.

Pediatric microdose and microtracer studies using 14C in Europe.

Important information gaps remain on the efficacy and safety of drugs in children. Pediatric drug development encounters several ethical, practical, and scientific challenges. One barrier to the evaluation of medicines for children is a lack of innovative methodologies that have been adapted to the needs of children. This article presents our successful experience of pediatric microdose and microtracer studies using (14) C-labeled probes in Europe to illustrate the strengths and limitations of these approaches.

Role for Skp in LptD assembly in Escherichia coli.

The periplasmic chaperone Skp has long been implicated in the assembly of outer membrane proteins (OMPs) in Escherichia coli. It has been shown to interact with unfolded OMPs, and the simultaneous loss of Skp and the main periplasmic chaperone in E. coli, SurA, results in synthetic lethality. However, a Δskp mutant displays only minor OMP assembly defects, and no OMPs have been shown to require Skp for their assembly. Here, we report a role for Skp in the assembly of the essential OMP LptD. This role may be compensated for by other OMP assembly proteins; in the absence of both Skp and FkpA or Skp and BamB, LptD assembly is impaired. Overexpression of SurA does not restore LptD levels in a Δskp ΔfkpA double mutant, nor does the overexpression of Skp or FkpA restore LptD levels in the ΔsurA mutant, suggesting that Skp acts in concert with SurA to efficiently assemble LptD in E. coli. Other OMPs, including LamB, are less affected in the Δskp ΔfkpA and Δskp bamB::kan double mutants, suggesting that Skp is specifically necessary for the assembly of certain OMPs. Analysis of an OMP with a domain structure similar to that of LptD, FhuA, suggests that common structural features may determine which OMPs require Skp for their assembly.

Lupus nephritis: a 15-year multi-centre experience in the UK.

OBJECTIVES: Our aim was to audit the outcome of lupus nephritis (LN) at three East Midlands centres. METHODS: We undertook a retrospective review of all biopsy-proven LN types III-V 1995-2010. RESULTS: In total, 61 patients with LN were identified, with a median follow-up of 68 months. LN was present at the time of systemic lupus erythematosus (SLE) diagnosis in 20 patients. The median time from SLE diagnosis to the first LN episode was 5.3 years. Some 35 patients received IV cyclophosphamide and 17 received mycophenolate mofetil (MMF) as induction therapy; 81.8% of those treated with cyclophosphamide and 81.3% with MMF had at least 'improved' according to the ACR-response criteria 6 months from induction; 33.3% and 37.5%, respectively, had a 'complete' response. MMF and azathioprine were the most frequently used maintenance therapy. We found that 32.8% experienced a flare after a mean post-induction time of 3.5 years, irrespective of the maintenance therapy used, and 43.8% of partial responders flared compared with 4.8% of complete responders. End-stage renal failure developed in 8.2%. CONCLUSIONS: Overall, outcomes (response, flare-rate, end-stage renal failure) were comparable with European clinical studies. Partial responders are more likely to flare compared with complete responders. The results highlight that LN can occur, and flare, after many years of SLE, emphasizing the importance of continued vigilance for LN in all patients.

Parenting children with neurodevelopmental disorders and/or behaviour problems.

BACKGROUND: Parenting behaviours influence child well-being and development. However, much of the research on parenting behaviours and their correlates has focused on caregivers of healthy, typically developing children. Relatively less is known about the parenting behaviours of caregivers of children with chronic health conditions. OBJECTIVE: To examine and compare three parenting behaviours (positive interactions, consistency and ineffective parenting) among caregivers of children with neurodevelopmental disorders and/or externalizing behaviour problems, before and after accounting for child and family socio-demographic characteristics. METHODS: Participants (n= 14 226) were drawn from the National Longitudinal Survey of Children and Youth, a long-term study of Canadian children that follows their development and well-being from birth to early adulthood. Children (and their caregivers) were divided into four groups according to the presence of a neurodevelopmental disorder (NDD; n= 815), the presence of an externalizing behaviour problem (EBP; n= 1322), the presence of both conditions (BOTH; n= 452) or neither of these conditions (NEITHER; n= 11 376). RESULTS: Caregivers of children in the NEITHER group reported significantly higher positive interaction scores and lower ineffective parenting behaviours than caregivers of children in any of the other three groups. Caregivers of children in the EBP and BOTH groups reported similar levels of consistency, but significantly lower levels than caregivers of NDD or NEITHER children. These associations largely remained after accounting for child and family socio-demographic characteristics, with two exceptions: caregivers' reports of positive interactions were no longer significantly associated with child's NDD and BOTH conditions. CONCLUSIONS: Parenting children with multiple health conditions can be associated with less positive, less consistent and more ineffective parenting behaviours. Understanding the factors that are associated with the challenges of caring for these children may require additional research attention.

Contextual influences of parenting behaviors for children with neurodevelopmental disorders: results from a Canadian national survey.

PURPOSE: This population-based study examined correlates of three parenting behaviors (positive interactions, consistency, and ineffective parenting) that have been shown to differ in children with neurodevelopmental disorders (NDDs), with and without externalizing behavior problems (EBPs), as compared to children with neither condition. METHOD: The sample of children aged 4-11 (N = 14,226) was drawn from the Canadian National Longitudinal Survey of Children and Youth (NLSCY). Analyses examined the associations of child, parental, and social context factors with parenting behaviors, and whether they differed by child health group. RESULTS: Child age, family functioning, and social support variables were significant predictors of all three parenting behaviors. Significant interaction effects highlight the importance of the child's sex, birth order, and support received from community or social service professionals, and that these factors have differential impacts on parenting behaviors depending on the child's health group. CONCLUSIONS: Other Child, parent, and social context factors are associated with parenting behaviors but these associations vary by the child's health group. Parenting behaviors differ for children with NDDs with and without EBPs. These findings offer important implications for practice and research and point to the importance of considering multiple contexts of influence, as well as their interactions, in understanding differences in parenting behaviors.

Prophylactic indomethacin infusion increases fractional cerebral oxygen extraction in ELBW neonates.

OBJECTIVE: Intraventricular hemorrhage (IVH) occurs in up to 25% of very low birth weight (VLBW) preterm neonates. Previous studies found that indomethacin administered in the first 6 h of life reduces the incidence of severe IVH in VLBW neonates and decreases cerebral blood flow, suggesting a decrease in cerebral oxygen delivery. Using near-infrared spectroscopy (NIRS), we monitored cerebral oxygenation before, during and after slow indomethacin infusion in extremely low birth weight (ELBW) neonates to determine whether indomethacin decreases cerebral oxygen saturation and increases cerebral oxygen extraction. STUDY DESIGN: Twenty-seven ELBW neonates less than 30 weeks gestational age treated with indomethacin for IVH prophylaxis were monitored for arterial oxygen saturation (SaO(2)) and NIRS-determined regional cerebral oxygen saturation (rSO(2)). At 30 to 60 s intervals, SaO(2), rSO(2) and mean arterial pressure (MAP) were recorded using a VitalSync. Average fractional cerebral oxygen extraction was calculated for the hour before indomethacin infusion, during the infusion and 2 h after infusion. RESULT: Fractional cerebral oxygen extraction increased from baseline after indomethacin administration from 0.23±0.11 to 0.25±0.10 (P=0.034). CONCLUSION: Fractional cerebral oxygen extraction increased 9% with indomethacin 0.1 mg kg(-1) given over 1 to 2 h. However, the clinical implications of this small increase in extraction, likely representative of decreased cerebral perfusion, are unknown but may be harmful to the developing brain.

Practical experience of using human microdosing with AMS analysis to obtain early human drug metabolism and PK data.

The background to human microdosing or Phase 0 studies is reviewed, focusing particularly on the information that such studies can provide in the context of exploratory clinical development. Examples are provided of the microdose-validation studies known as the Consortium for Resourcing and Evaluating AMS Microdosing trial and EU Microdosing AMS Partnership Programme, which demonstrated that there was good dose proportionality between microdose and pharmacological dose pharmacokinetics. When microdosing was applied to ten development drugs, it was found that all ten molecules showed dose proportionality between the microdose and the pharmacological dose. The majority of microdose studies have used accelerator mass spectrometry (AMS) analysis and only these studies that are considered here; AMS provides information on all metabolites, even if these are minor. There is now sufficient scientific data to justify microdose studies being routinely conducted as part of the drug-development process.

Accelerator mass spectrometry measurement of intracellular concentrations of active drug metabolites in human target cells in vivo.

Accelerator mass spectrometry (AMS) is an ultrasensitive technique to detect radiolabeled compounds. We administered a microdose (100 µg) of (14)C-labeled zidovudine (ZDV) with or without a standard unlabeled dose (300 mg) to healthy volunteers. Intracellular ZDV-triphosphate (ZDV-TP) concentration was measured using AMS and liquid chromatography-tandem mass spectrometry (LC/MS/MS). AMS analysis yielded excellent concordance with LC/MS/MS and was 30,000-fold more sensitive. The kinetics of intracellular ZDV-TP formation changed several-fold over the dose range studied (100 µg-300 mg). AMS holds promise as a tool for quantifying intracellular drug metabolites and other biomediators in vivo.

Photocaged morpholino oligomers for the light-regulation of gene function in zebrafish and Xenopus embryos.

Morpholino oligonucleotides, or morpholinos, have emerged as powerful antisense reagents for evaluating gene function in both in vitro and in vivo contexts. However, the constitutive activity of these reagents limits their utility for applications that require spatiotemporal control, such as tissue-specific gene disruptions in embryos. Here we report a novel and efficient synthetic route for incorporating photocaged monomeric building blocks directly into morpholino oligomers and demonstrate the utility of these caged morpholinos in the light-activated control of gene function in both cell culture and living embryos. We demonstrate that a caged morpholino that targets enhanced green fluorescent protein (EGFP) disrupts EGFP production only after exposure to UV light in both transfected cells and living zebrafish (Danio rerio) and Xenopus frog embryos. Finally, we show that a caged morpholino targeting chordin, a zebrafish gene that yields a distinct phenotype when functionally disrupted by conventional morpholinos, elicits a chordin phenotype in a UV-dependent manner. Our results suggest that photocaged morpholinos are readily synthesized and highly efficacious tools for light-activated spatiotemporal control of gene expression in multiple contexts.

Microdose pharmacokinetics of IDX899 and IDX989, candidate HIV-1 non-nucleoside reverse transcriptase inhibitors, following oral and intravenous administration in healthy male subjects.

IDX899 and IDX989 are new non-nucleoside reverse-transcriptase inhibitors (NNRTIs) that exhibit potent inhibition of HIV-1 replication, including NNRTI-resistant mutants. This microdose study investigates the pharmacokinetics and determined oral bioavailability. For each compound, 4 healthy male subjects are randomized to receive via a crossover design a single 100-microg oral and intravenous dose together with 100 nCi of [(14)C]-labeled drug. Plasma and urine samples are obtained over a period of 168 hours postdose and analyzed for total, unchanged drug and major metabolites using an accelerator mass spectrometry method. Based on total radioactivity, oral absorption is near complete. For the parent drug, mean absolute bioavailability is 61% and 65% for IDX899 and IDX989, respectively. Both compounds are extensively metabolized especially after oral dosing. Observed terminal phase half-lives after oral and intravenous doses range from 4 to 10 hours and are comparable for the 2 compounds. Urine excretion of radioactivity for both compounds is less than 10%. These data show for the first time that IDX899 and IDX989 possess favorable pharmacokinetic properties in humans, including high mean absolute bioavailability and long half-life. IDX899 has been selected based on these initial pharmacokinetic assessments and other criteria as the candidate for further clinical development.

A pharmacokinetic evaluation of five H(1) antagonists after an oral and intravenous microdose to human subjects.

AIMS: To evaluate the pharmacokinetics (PK) of five H(1) receptor antagonists in human volunteers after a single oral and intravenous (i.v.) microdose (0.1 mg). METHODS: Five H(1) receptor antagonists, namely NBI-1, NBI-2, NBI-3, NBI-4 and diphenhydramine, were administered to human volunteers as a single 0.1-mg oral and i.v. dose. Blood samples were collected up to 48 h, and the parent compound in the plasma extract was quantified by high-performance liquid chromatography and accelerator mass spectroscopy. RESULTS: The median clearance (CL), apparent volume of distribution (V(d)) and apparent terminal elimination half-life (t(1/2)) of diphenhydramine after an i.v. microdose were 24.7 l h(-1), 302 l and 9.3 h, and the oral C(max) and AUC(0-infinity) were 0.195 ng ml(-1) and 1.52 ng h ml(-1), respectively. These data were consistent with previously published diphenhydramine data at 500 times the microdose. The rank order of oral bioavailability of the five compounds was as follows: NBI-2 > NBI-1 > NBI-3 > diphenhydramine > NBI-4, whereas the rank order for CL was NBI-4 > diphenhydramine > NBI-1 > NBI-3 > NBI-2. CONCLUSIONS: Human microdosing provided estimates of clinical PK of four structurally related compounds, which were deemed useful for compound selection.

Light-activation of gene function in mammalian cells via ribozymes.

A ribozyme based gene control element enabled the spatio-temporal regulation of gene function in mammalian cell culture with light.

The utility of microdosing over the past 5 years.

BACKGROUND: Microdosing studies (human Phase 0) are used to select drug candidates for Phase I clinical trials on the basis of their pharmacokinetic properties, using subpharmacologic doses (maximum 100 microg). There are questions as to whether pharmacokinetic data obtained at these low doses will predict those at the clinically relevant dose. OBJECTIVE: To review the current literature on microdosing and assess how well microdose data have predicted the pharmacokinetics obtained at a therapeutic dose. METHODS: All data published in the peer reviewed literature comparing pharmacokinetics at a microdose with a therapeutic dose were reviewed, excluding those studies aimed at imaging. CONCLUSIONS: Of the 18 drugs reported, 15 demonstrated linear pharmacokinetics within a factor of 2 between a microdose and a therapeutic dose. Therefore, data that support the utility of microdosing are beginning to emerge.

Human mass balance study of the novel anticancer agent ixabepilone using accelerator mass spectrometry.

Ixabepilone (BMS-247550) is a semi-synthetic, microtubule stabilizing epothilone B analogue which is more potent than taxanes and has displayed activity in taxane-resistant patients. The human plasma pharmacokinetics of ixabepilone have been described. However, the excretory pathways and contribution of metabolism to ixabepilone elimination have not been determined. To investigate the elimination pathways of ixabepilone we initiated a mass balance study in cancer patients. Due to autoradiolysis, ixabepilone proved to be very unstable when labeled with conventional [14C]-levels (100 microCi in a typical human radio-tracer study). This necessitated the use of much lower levels of [14C]-labeling and an ultra-sensitive detection method, Accelerator Mass Spectrometry (AMS). Eight patients with advanced cancer (3 males, 5 females; median age 54.5 y; performance status 0-2) received an intravenous dose of 70 mg, 80 nCi of [14C]ixabepilone over 3 h. Plasma, urine and faeces were collected up to 7 days after administration and total radioactivity (TRA) was determined using AMS. Ixabepilone in plasma and urine was quantitated using a validated LC-MS/MS method. Mean recovery of ixabepilone-derived radioactivity was 77.3% of dose. Fecal excretion was 52.2% and urinary excretion was 25.1%. Only a minor part of TRA is accounted for by unchanged ixabepilone in both plasma and urine, which indicates that metabolism is a major elimination mechanism for this drug. Future studies should focus on structural elucidation of ixabepilone metabolites and characterization of their activities.