Pharmacometric model of agalsidase-migalastat interaction in human: a novel mechanistic model of drug-drug interaction between a therapeutic protein and a small molecule.

Recently, a new mechanism of drug-drug interaction (DDI) was reported between agalsidase, a therapeutic protein, and migalastat, a small molecule, both of which are treatment options of Fabry disease. Migalastat is a pharmacological chaperone that stabilizes the native form of both endogenous and exogenous agalsidase. In Fabry patients co-administrated with agalsidase and migalastat, the increase in active agalsidase exposure is considered a pharmacokinetic effect of agalsidase infusion but a pharmacodynamic effect of migalastat administration, which makes this new DDI mechanism even more interesting. To quantitatively characterize the interaction between agalsidase and migalastat in human, a pharmacometric DDI model was developed using literature reported concentration-time data. The final model includes three components: a 1-compartment linear model component for migalastat; a 2-compartment linear model component for agalsidase; and a DDI component where the agalsidase-migalastat complex is formed via second order association constant kon, dissociated with first order dissociation constant koff, and distributed/eliminated with same rates as agalsidase alone, albeit the complex (i.e., bound agalsidase) has higher enzyme activity compared to free agalsidase. The final model adequately captured several key features of the unique interaction between agalsidase and migalastat, and successfully characterized the kinetics of migalastat as well as the kinetics and activities of agalsidase when both drugs were used alone or in combination following different doses. Most parameters were reasonably estimated with good precision. Because the model includes mechanistic basis of therapeutic protein and small molecule pharmacological chaperone interaction, it can potentially serve as a foundational work for DDIs with similar mechanism.

Population Pharmacokinetic-Pharmacodynamic Model of Oxfendazole in Healthy Adults in a Multiple Ascending Dose and Food Effect Study and Target Attainment Analysis.

Oxfendazole is a potent veterinary antiparasitic drug undergoing development for human use to treat multiple parasitic infections. Results from two recently completed phase I clinical trials conducted in healthy adults showed that the pharmacokinetics of oxfendazole is nonlinear, affected by food, and, after the administration of repeated doses, appeared to mildly affect hemoglobin concentrations. To facilitate oxfendazole dose optimization for its use in patient populations, the relationship among oxfendazole dose, pharmacokinetics, and hemoglobin concentration was quantitatively characterized using population pharmacokinetic-pharmacodynamic modeling. In fasting subjects, oxfendazole pharmacokinetics was well described by a one-compartment model with first-order absorption and elimination. The change in oxfendazole pharmacokinetics when administered following a fatty meal was captured by an absorption model with one transit compartment and increased bioavailability. The effect of oxfendazole exposure on hemoglobin concentration in healthy adults was characterized by a life span indirect response model in which oxfendazole has positive but minor inhibitory effect on red blood cell synthesis. Further simulation indicated that oxfendazole has a low risk of posing a safety concern regarding hemoglobin concentration, even at a high oxfendazole dose of 60 mg/kg of body weight once daily. The final model was further used to perform comprehensive target attainment simulations for whipworm infection and filariasis at various dose regimens and target attainment criteria. The results of our modeling work, when adopted appropriately, have the potential to greatly facilitate oxfendazole dose regimen optimization in patient populations with different types of parasitic infections.

Population Pharmacokinetic Model of Oxfendazole and Metabolites in Healthy Adults following Single Ascending Doses.

Oxfendazole is a potent veterinary benzimidazole anthelmintic under transition to humans for the treatment of multiple parasitic infectious diseases. The first-in-human study evaluating the disposition of oxfendazole and its metabolites in healthy adults following single ascending oral doses from 0.5 to 60 mg/kg of body weight shows that oxfendazole pharmacokinetics is substantially nonlinear, which complicates correlating oxfendazole dose to exposure. To quantitatively capture the relation between oxfendazole dose and exposure, a population pharmacokinetic model for oxfendazole and its metabolites, oxfendazole sulfone and fenbendazole, in humans was developed using a nonlinear mixed-effect modeling approach. Our final model incorporated mechanistic characterization of dose-limited bioavailability as well as different oxfendazole metabolic processes and provided insight into the significance of presystemic metabolism in oxfendazole and metabolite disposition. Oxfendazole clinical pharmacokinetics was best described by a one-compartment model with nonlinear absorption and linear elimination. Oxfendazole apparent clearance and apparent volume of distribution were estimated to be 2.57 liters/h and 35.2 liters, respectively, at the lowest dose (0.5 mg/kg), indicating that oxfendazole is a low extraction drug with moderate distribution. The disposition of both metabolites was adequately characterized by a one-compartment model with formation rate-limited elimination. Fenbendazole formation from oxfendazole was primarily through systemic metabolism, while both presystemic and systemic metabolism were critical to the formation of oxfendazole sulfone. Our model adequately captured the concentration-time profiles of both oxfendazole and its two metabolites in healthy adults over a wide dose range. The model can be used to predict oxfendazole disposition under new dosing regimens to support dose optimization in humans.

Vertical open-bore MRI scanners generate significantly less radiofrequency heating around implanted leads: A study of deep brain stimulation implants in 1.2T OASIS scanners versus 1.5T horizontal systems.

PURPOSE: Patients with active implants such as deep brain stimulation (DBS) devices are often denied access to MRI due to safety concerns associated with the radiofrequency (RF) heating of their electrodes. The majority of studies on RF heating of conductive implants have been performed in horizontal close-bore MRI scanners. Vertical MRI scanners which have a 90° rotated transmit coil generate fundamentally different electric and magnetic field distributions, yet very little is known about RF heating of implants in this class of scanners. We performed numerical simulations as well as phantom experiments to compare RF heating of DBS implants in a 1.2T vertical scanner (OASIS, Hitachi) compared to a 1.5T horizontal scanner (Aera, Siemens). METHODS: Simulations were performed on 90 lead models created from post-operative CT images of patients with DBS implants. Experiments were performed with wires and commercial DBS devices implanted in an anthropomorphic phantom. RESULTS: We found significant reduction of 0.1 g-averaged specific absorption rate (30-fold, P < 1 × 10-5 ) and RF heating (9-fold, P < .026) in the 1.2T vertical scanner compared to the 1.5T conventional scanner. CONCLUSION: Vertical MRI scanners appear to generate lower RF heating around DBS leads, providing potentially heightened safety or the flexibility to use sequences with higher power levels than on conventional systems.

Comparing the performance of first-order conditional estimation (FOCE) and different expectation-maximization (EM) methods in NONMEM: real data experience with complex nonlinear parent-metabolite pharmacokinetic model.

First-order conditional estimation (FOCE) has been the most frequently used estimation method in NONMEM, a leading program for population pharmacokinetic/pharmacodynamic modeling. However, with growing data complexity, the performance of FOCE is challenged by long run time, convergence problem and model instability. In NONMEM 7, expectation-maximization (EM) estimation methods and FOCE with FAST option (FOCE FAST) were introduced. In this study, we compared the performance of FOCE, FOCE FAST, and two EM methods, namely importance sampling (IMP) and stochastic approximation expectation-maximization (SAEM), utilizing the rich pharmacokinetic data of oxfendazole and its two metabolites obtained from the first-in-human single ascending dose study in healthy adults. All methods yielded similar parameter estimates, but great differences were observed in parameter precision and modeling time. For simpler models (i.e., models of oxfendazole and/or oxfendazole sulfone), FOCE and FOCE FAST were more efficient than EM methods with shorter run time and comparable parameter precision. FOCE FAST was about two times faster than FOCE but it was prone to premature termination. For the most complex model (i.e., model of all three analytes, one of which having high level of data below quantification limit), FOCE failed to reliably assess parameter precision, while parameter precision obtained by IMP and SAEM was similar with SAEM being the faster method. IMP was more sensitive to model misspecification; without pre-systemic metabolism, IMP analysis failed to converge. With parallel computing introduced in NONMEM 7.2, modeling speed increased less than proportionally with the increase in the number of CPUs from 1 to 16.

Pharmacokinetics, Safety, and Tolerability of Oxfendazole in Healthy Adults in an Open-Label Phase 1 Multiple Ascending Dose and Food Effect Study.

Neurocysticercosis and trichuriasis are difficult-to-treat parasitic infections that affect more than 1.5 billion people worldwide. Oxfendazole, a potent broad-spectrum benzimidazole anthelmintic approved for use in veterinary medicine, has shown substantial antiparasitic activity against neurocysticercosis and intestinal helminths in preclinical studies. As part of a program to transition oxfendazole from veterinary medicine to human use, phase I multiple ascending dose and food effect studies were conducted. Thirty-six healthy adults were enrolled in an open-label study which evaluated (i) the pharmacokinetics and safety of oxfendazole following multiple ascending doses of oxfendazole oral suspension at 3, 7.5, and 15 mg/kg once daily for 5 days and (ii) the effect of food on oxfendazole pharmacokinetics and safety after a single 3-mg/kg dose administered following an overnight fast or the consumption of a fatty breakfast. Following multiple oral dose administration, the intestinal absorption of oxfendazole was rapid, with the time to maximum concentration of drug in serum (Tmax) ranging from 1.92 to 2.56 h. A similar half-life of oxfendazole (9.21 to 11.8 h) was observed across all dose groups evaluated, and oxfendazole exhibited significantly less than a dose-proportional increase in exposure. Oxfendazole plasma exposures were higher in female subjects than in male subjects. Following daily administration, oxfendazole reached a steady state in plasma on study day 3, with minimal accumulation. Food delayed the oxfendazole Tmax by a median of 6.88 h and resulted in a 49.2% increase in the maximum observed drug concentration in plasma (Cmax) and an 86.4% increase in the area under the concentration-time curve (AUC). Oxfendazole was well tolerated in all study groups, and there were no major safety signals identified in this study. (This study has been registered at ClinicalTrials.gov under identifier NCT03035760.).

Pharmacokinetics, Safety, and Tolerability of Oxfendazole in Healthy Volunteers: a Randomized, Placebo-Controlled First-in-Human Single-Dose Escalation Study.

Cysticercosis is a parasitic disease that frequently involves the human central nervous system (CNS), and current treatment options are limited. Oxfendazole, a veterinary medicine belonging to the benzimidazole family of anthelmintic drugs, has demonstrated substantial activity against the tissue stages of Taenia solium and has potential to be developed as an effective therapy for neurocysticercosis. To accelerate the transition of oxfendazole from veterinary to human use, the pharmacokinetics, safety, and tolerability of oxfendazole were evaluated in healthy volunteers in this phase 1 first-in-human (FIH) study. Seventy subjects were randomly assigned to receive a single oral dose of oxfendazole (0.5, 1, 3, 7.5, 15, 30, or 60 mg oxfendazole/kg body weight) or placebo and were followed for 14 days. Blood and urine samples were collected, and the concentrations of oxfendazole were measured using a validated ultraperformance liquid chromatography mass spectrometry method. The pharmacokinetic parameters of oxfendazole were estimated using noncompartmental analysis. Oxfendazole was rapidly absorbed with a mean plasma half-life ranging from 8.5 to 11 h. The renal excretion of oxfendazole was minimal. Oxfendazole exhibited significant nonlinear pharmacokinetics with less than dose-proportional increases in exposure after single oral doses of 0.5 mg/kg to 60 mg/kg. This nonlinearity of oxfendazole is likely due to the dose-dependent decrease in bioavailability that is caused by its low solubility. Oxfendazole was found to be well tolerated in this study at different escalating doses without any serious adverse events (AEs) or deaths. There were no significant differences in the distributions of hematology, biochemistry, or urine parameters between oxfendazole and placebo recipients. (This study has been registered at ClinicalTrials.gov under identifier NCT02234570.).

Quantification of Cefepime, Meropenem, Piperacillin, and Tazobactam in Human Plasma Using a Sensitive and Robust Liquid Chromatography-Tandem Mass Spectrometry Method, Part 2: Stability Evaluation.

Although the stability of ß-lactam antibiotics is a known issue, none of the previously reported bioanalytical methods had an adequate evaluation of the stability of these drugs. In the current study, the stability of cefepime, meropenem, piperacillin, and tazobactam under various conditions was comprehensively evaluated. The evaluated parameters included stock solution stability, short-term stability, long-term stability, freeze-thaw stability, processed sample stability, and whole-blood stability. When stored at -20°C, the stock solution of meropenem in methanol was stable for up to 3 weeks, and the stock solutions of cefepime, piperacillin, and tazobactam were stable for up to 6 weeks. All four antibiotics were stable in human plasma for up to 3 months when stored at -80°C and were stable in whole blood for up to 4 h at room temperature. Short-term stability results indicated that all four ß-lactams were stable at room temperature for 2 h, but substantial degradation was observed when the plasma samples were stored at room temperature for 24 h, with the degradation rates for cefepime, meropenem, piperacillin, and tazobactam being 30.1%, 75.6%, 49.0%, and 37.7%, respectively. Because the stability information is method independent, our stability results can be used as a reference by other research groups that work with these antibiotics.

Quantification of Cefepime, Meropenem, Piperacillin, and Tazobactam in Human Plasma Using a Sensitive and Robust Liquid Chromatography-Tandem Mass Spectrometry Method, Part 1: Assay Development and Validation.

The highly variable pharmacokinetics of ß-lactam antibiotics and ß-lactamase inhibitors poses a significant challenge to clinicians in ensuring appropriate antibiotic doses in critically ill patients. Therefore, routine monitoring of plasma concentrations is important for individualization of antimicrobial therapy. Accordingly, a simple and robust analytical method for the simultaneous measurement of multiple ß-lactam antibiotics and ß-lactamase inhibitors is highly desirable to ensure quick decisions on dose adjustments. In this study, a sensitive, simple, and robust method for the simultaneous quantification of cefepime, meropenem, piperacillin, and tazobactam in human plasma was developed and rigorously validated according to FDA guidance. Sample extraction was accomplished by simple protein precipitation. Chromatographic separation of analytes was achieved using stepwise gradient elution. Analytes were monitored using tandem mass spectrometry (MS/MS) with a turbo ion spray source in positive multiple-reaction-monitoring mode. The calibration curve ranged from 0.5 to 150 µg/ml for cefepime, 0.1 to 150 µg/ml for meropenem and piperacillin, and 0.25 to 150 µg/ml for tazobactam. Inter- and intraday precision and accuracy, sensitivity, selectivity, dilution integrity, matrix effect, extraction recovery, and hemolysis effect were investigated for all four analytes, and the results met the acceptance criteria. Compared to other reported methods, our method is more robust because of the combination of the following features: (i) a simple sample extraction procedure, (ii) a short sample run time, (iii) a wide dynamic range, and (iv) the small plasma sample volume needed. Since our method already covers ß-lactams and a ß-lactamase inhibitor with highly heterogeneous physicochemical properties, further antibiotic candidates may easily be incorporated into this multianalyte method.

Feeding behavior and activity budget of the southern yellow-cheeked crested gibbons (Nomascus gabriellae) in a lowland tropical forest.

The southern yellow-cheeked crested gibbon (Nomascus gabriellae), an endangered species native to Vietnam and Cambodia, lives exclusively in undisturbed tropical forests and depends primarily on ripe fruit for food. Although this species is highly threatened, its ecology and conservation status remain relatively unknown. In order to understand how this heavily frugivorous primate adapts to the seasonal fluctuation of fruit resources in the forest, we collected feeding behavior and ranging activity data on one group of southern yellow-cheeked crested gibbons in Cat Tien National Park, Vietnam, over 1-year period. We compared these data to information on phenological patterns at the site gleaned during a prior study. We found that the gibbons gathered most of their food from 69 different plant species and also consumed insects and bird eggs. Fruits were the main dietary item (43.3%), followed by leaves (38.4%), flowers (11.6%), and other plant parts (6.0%). A significant seasonal shift in diet was observed; fruit generally dominated the diet in the rainy season and leaves in the dry season. The gibbons often started daily activities very early (05:10 am) in the morning and also ended quite early (16:45 pm) in the afternoon. Socializing was concentrated in the early morning, feeding had a bimodal pattern of high activity levels in mid-morning and mid-afternoon, and resting was most intense at the earliest and latest hours of the day and at midday, with proportionally less time used for traveling at these times. Averaged over the annual cycle, the gibbons spent 45% of their time feeding, 31.9% resting, 14.1% traveling, and 9.0% socializing. The percentage of time allocated to different activities varied significantly across months and between the dry and rainy seasons. Monthly variation in the activity budget was strongly related to changes in diet. In the rainy season, when the gibbons ate a higher percentage of fruit, they decreased their feeding time, while increasing traveling time in search of food; conversely, in the dry season, when they fed on a higher percentage of leaves, they decreased traveling time. Overall, our results show that the activity budget and diet of the southern yellow-cheeked crested gibbon are associated with seasonal shifts in climate. This study provides information relevant to the conservation and management of this endangered species by identifying important habitat conditions for reintroducing captive animals into the wild and providing insight into dietary needs, which may be relevant to the maintenance of animals in rescue centers.

RNAIII-independent target gene control by the agr quorum-sensing system: insight into the evolution of virulence regulation in Staphylococcus aureus.

Cell-density-dependent gene regulation by quorum-sensing systems has a crucial function in bacterial physiology and pathogenesis. We demonstrate here that the Staphylococcus aureus agr quorum-sensing regulon is divided into (1) control of metabolism and PSM cytolysin genes, which occurs independently of the small regulatory RNA RNAIII, and (2) RNAIII-dependent control of additional virulence genes. Remarkably, PSM expression was regulated by direct binding of the AgrA response regulator. Our findings suggest that quorum-sensing regulation of PSMs was established before wide-ranging control of virulence was added to the agr regulon, which likely occurred by development of the RNAIII-encoding region around the gene encoding the PSM delta-toxin. Moreover, the agr regulon in the community-associated methicillin-resistant S. aureus MW2 considerably differed from that previously determined using laboratory strains. By establishing a two-level model of quorum-sensing target gene regulation in S. aureus, our study gives important insight into the evolution of virulence control in this leading human pathogen.

Insight into structure-function relationship in phenol-soluble modulins using an alanine screen of the phenol-soluble modulin (PSM) α3 peptide.

Phenol-soluble modulins (PSMs) are a family of peptides with multiple functions in staphylococcal pathogenesis. To gain insight into the structural features affecting PSM functions, we analyzed an alanine substitution library of PSMα3, a strongly cytolytic and proinflammatory PSM of Staphylococcus aureus with a significant contribution to S. aureus virulence. Lysine residues were essential for both receptor-dependent proinflammatory and receptor-independent cytolytic activities. Both phenotypes also required additional structural features, with the C terminus being crucial for receptor activation. Biofilm formation was affected mostly by hydrophobic amino acid positions, suggesting that the capacity to disrupt hydrophobic interactions is responsible for the effect of PSMs on biofilm structure. Antimicrobial activity, absent from natural PSMα3, could be created by the exchange of large hydrophobic side chains, indicating that PSMα3 has evolved to exhibit cytolytic rather than antimicrobial activity. In addition to gaining insight into the structure-function relationship in PSMs, our study identifies nontoxic PSMα3 derivatives for active vaccination strategies and lays the foundation for future efforts aimed to understand the biological role of PSM recognition by innate host defense.

How Staphylococcus aureus biofilms develop their characteristic structure.

Biofilms cause significant problems in the environment and during the treatment of infections. However, the molecular mechanisms underlying biofilm formation are poorly understood. There is a particular lack of knowledge about biofilm maturation processes, such as biofilm structuring and detachment, which are deemed crucial for the maintenance of biofilm viability and the dissemination of cells from a biofilm. Here, we identify the phenol-soluble modulin (PSM) surfactant peptides as key biofilm structuring factors in the premier biofilm-forming pathogen Staphylococcus aureus. We provide evidence that all known PSM classes participate in structuring and detachment processes. Specifically, absence of PSMs in isogenic S. aureus psm deletion mutants led to strongly impaired formation of biofilm channels, abolishment of the characteristic waves of biofilm detachment and regrowth, and loss of control of biofilm expansion. In contrast, induced expression of psm loci in preformed biofilms promoted those processes. Furthermore, PSMs facilitated dissemination from an infected catheter in a mouse model of biofilm-associated infection. Moreover, formation of the biofilm structure was linked to strongly variable, quorum sensing-controlled PSM expression in biofilm microenvironments, whereas overall PSM production remained constant to ascertain biofilm homeostasis. Our study describes a mechanism of biofilm structuring in molecular detail, and the general principle (i.e., quorum-sensing controlled expression of surfactants) seems to be conserved in several bacteria, despite the divergence of the respective biofilm-structuring surfactants. These findings provide a deeper understanding of biofilm development processes, which represents an important basis for strategies to interfere with biofilm formation in the environment and human disease.

Importance of Utilizing Natural Isotopologue Transitions in Expanding the Linear Dynamic Range of LC-MS/MS Assay for Small-Molecule Pharmacokinetic Sample Analysis - A Mini-review.

Liquid chromatography-tandem mass spectrometry (LC-MS/MS) is a widely used quantitative method in small-molecule pharmacokinetic sample analysis. The linear dynamic range of mass analyzers, typically spanning 3 orders of magnitude, is usually insufficient for this purpose. Utilization of multiple isotopologues has been proposed as a compelling approach to expand the linear dynamic range of LC-MS/MS assays, particularly when the detector is saturated. Isotopologues are a statistical mixture of molecules of the same compound but of different exact masses due to the presence of natural chemical isotopes. While the concept of isotopologues is widely recognized in large-molecule bioanalysis and small-molecule metabolite profiling, it has not been commonly implemented in small-molecule targeted quantification. To increase the awareness of the value of isotopologues in small-molecule LC-MS/MS analysis, this minireview provides the basis of isotopologue distribution in MS/MS and summarizes published studies as well as our own experience in utilizing multiple isotopologues to expand the linear dynamic range of small-molecule LC-MS/MS assays. Considering that utilizing natural isotopologue transitions in the LC-MS/MS assays represents an easy, straightforward, and robust way to expand the linear dynamic range, we believe this method deserves wide application in small-molecule pharmacokinetic sample analysis and can particularly benefit people working in pharmacokinetic labs as well as the GLP bioanalytical labs in pharmaceutical industry.

Development and validation of a simple and sensitive LC-MS/MS method for the quantification of cefazolin in human plasma and its application to a clinical pharmacokinetic study.

Cefazolin is widely used during surgery to prevent surgical site infections (SSIs). Although cefazolin redosing is often needed due to its short half-life, the appropriate redosing schedule remains controversial and there is limited information on cefazolin disposition following repeated doses during surgery. In parallel with an ongoing cefazolin redosing clinical study, we have developed and fully validated a simple and robust liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the quantification of cefazolin in human plasma. A simple protein precipitation was used for sample preparation. MS/MS analysis was performed using multiple reaction monitoring (MRM) under a positive ionization mode. The lower limit of quantification (LLOQ) for cefazolin was evaluated at 0.25 µg/mL and a linearity ranging from 0.25 to 300 µg/mL. Accuracy was ≤ 114.3% for quality controls and ≤ 118.2% for LLOQ; intra-day and inter-day precision ranging from 1.9% to 14.2% for all quality controls and LLOQ. Matrix effect, extraction recovery, stability testing, dilution integrity, hemolysis effects and whole blood stability have all been investigated. A total of 17 parameters were validated and passed their validation criteria. The method was applied in the quantification of cefazolin in clinical plasma samples and was able to successfully determine the concentrations in patients undergoing various surgeries. In comparison with other prior published methods, our method has a simple sample preparation combined with a short analysis run time, a wide dynamic range and low limit of quantification, and is a fully validated assay that abides by FDA guidance.

Mobile genetic element-encoded cytolysin connects virulence to methicillin resistance in MRSA.

Bacterial virulence and antibiotic resistance have a significant influence on disease severity and treatment options during bacterial infections. Frequently, the underlying genetic determinants are encoded on mobile genetic elements (MGEs). In the leading human pathogen Staphylococcus aureus, MGEs that contain antibiotic resistance genes commonly do not contain genes for virulence determinants. The phenol-soluble modulins (PSMs) are staphylococcal cytolytic toxins with a crucial role in immune evasion. While all known PSMs are core genome-encoded, we here describe a previously unidentified psm gene, psm-mec, within the staphylococcal methicillin resistance-encoding MGE SCCmec. PSM-mec was strongly expressed in many strains and showed the physico-chemical, pro-inflammatory, and cytolytic characteristics typical of PSMs. Notably, in an S. aureus strain with low production of core genome-encoded PSMs, expression of PSM-mec had a significant impact on immune evasion and disease. In addition to providing high-level resistance to methicillin, acquisition of SCCmec elements encoding PSM-mec by horizontal gene transfer may therefore contribute to staphylococcal virulence by substituting for the lack of expression of core genome-encoded PSMs. Thus, our study reveals a previously unknown role of methicillin resistance clusters in staphylococcal pathogenesis and shows that important virulence and antibiotic resistance determinants may be combined in staphylococcal MGEs.

Hydronium adsorption on OOH precovered Pt(111) surface: effects of electrode potential.

Using the Density Functional Theory-based total energy calculations, the hydronium adsorption on the OOH precovered Pt(111) surface is studied. The electrode potential is modeled by varying the electron affinity of the reduction center [OOH + H3O(H2O)]+. Two possible structures of this reduction center on the Pt surface are HOOH +2H2O and 2(OH)+2H2O. Evidently, the dissociation of HOOH into 2(OH) can be accomplished by changing the electrode potential to the higher value by 0.16 V. The activation energy for the dissociation is approximately 0.1 eV. The optimized structures are also obtained.

Boundary element fast multipole method for modeling electrical brain stimulation with voltage and current electrodes.

Objective. To formulate, validate, and apply an alternative to the finite element method (FEM) high-resolution modeling technique for electrical brain stimulation-the boundary element fast multipole method (BEM-FMM). To include practical electrode models for both surface and embedded electrodes.Approach. Integral equations of the boundary element method in terms of surface charge density are combined with a general-purpose fast multipole method and are expanded for voltage, shunt, current, and floating electrodes. The solution of coupled and properly weighted/preconditioned integral equations is accompanied by enforcing global conservation laws: charge conservation law and Kirchhoff's current law.Main results.A sub-percent accuracy is reported as compared to the analytical solutions and simple validation geometries. Comparison to FEM considering realistic head models resulted in relative differences of the electric field magnitude in the range of 3%-6% or less. Quantities that contain higher order spatial derivatives, such as the activating function, are determined with a higher accuracy and a faster speed as compared to the FEM. The method can be easily combined with existing head modeling pipelines such as headreco or mri2mesh.Significance.The BEM-FMM does not rely on a volumetric mesh and is therefore particularly suitable for modeling some mesoscale problems with submillimeter (and possibly finer) resolution with high accuracy at moderate computational cost. Utilizing Helmholtz reciprocity principle makes it possible to expand the method to a solution of EEG forward problems with a very large number of cortical dipoles.

Aspects of matrix and analyte effects in clinical pharmacokinetic sample analyses using LC-ESI/MS/MS - Two case examples.

The increasing focus on high throughput sample analysis has led to the common practice of using simplest sample preparation method possible (i.e. protein precipitation) and shortest sample run-time possible. This means that there will be two aspects of compromise: the first compromise is made between sample cleanliness and sample preparation speed since protein precipitation does not provide very clean final extract; the second compromise is made between peak separation and run-time, meaning that sometimes overlap or co-elution of some peaks has to be accepted. The first compromise may lead to matrix effect, which is caused by co-eluting endogenous substances such as phospholipids. The second compromise can result in analyte effect, which is caused by co-eluting analyte(s). We have encountered the issue of matrix/analyte-mediated ion suppression in multiple preclinical and clinical pharmacokinetic projects during bioanalytical method development/validation or biological sample analysis of many small molecule drugs. As these matrix/analyte effects could occur in different situations with different "syndromes", sometimes it can be easily overlooked, leading to unreliable result, poor sensitivity, and prolonged assay development process. To increase the awareness of this important issue, in this paper we presented two real case examples on signal suppression caused by either endogenous phospholipids or co-eluting analyte.

General Pharmacokinetic Features of Small-Molecule Compounds Exhibiting Target-Mediated Drug Disposition (TMDD): A Simulation-Based Study.

Although target-mediated drug disposition (TMDD) can occur in both large- and small-molecule compounds, TMDD in small-molecule compounds has received much less attention due to its lower prevalence. To facilitate the identification of nonlinear pharmacokinetics of small-molecule compounds caused by TMDD, a comprehensive simulation was conducted in the current study to provide the general pharmacokinetic features of small-molecule compounds exhibiting TMDD. Various conditions, including single escalating intravenous bolus doses, multiple escalating intravenous bolus doses, and intravenous infusion, were simulated for small-molecule compounds with saturable binding to (1) targets located in tissues and (2) targets located in plasma. Sobol global sensitivity analysis was performed to evaluate the impact of key parameters (Rmax , kon and koff ) in a small-molecule TMDD model on the apparent volume of distribution and apparent clearance. Our simulation data indicated that small-molecule compounds with saturable binding to targets in plasma demonstrate distinctly different TMDD behavior compared with those with binding to targets in tissue. Sobol global sensitivity analysis results showed that, in general, koff is much more influential than kon and Rmax on apparent clearance and apparent volume of distribution. The TMDD features predicted in various situations in the current work could serve as a valuable reference to help quickly recognize TMDD when it does happen in a small-molecule compound. The TMDD principals summarized based on our simulation could be used to aid pharmacokinetic data interpretation, dose regimen optimization, and clinical trial design of small-molecule drugs exhibiting TMDD.