Mechanistic modelling of in vitro transporter processes to improve drug-drug interaction predictions

There is currently a need to evaluate the interaction of drugs in the liver and at the liver membrane, to determine whether the potential for a drug-drug interaction in the clinic could adversely affect a patients prognosis. The interactions of drugs or probe substrates with liver membrane transporters are currently poorly understood at a molecular level, and there is strong interest in terms of the pharmacology of the transporters and how we can examine and understand these interactions through mathematical models. Currently the dynamics of interactions through the use of micro-rate constants, where steady-state assumptions are not implied in data analysis are less favoured. Whilst modelling and data analysis conducted using Michaelis-Menten type kinetics (defined as macro-rate constant mechanistic models), under the assumption of rapid equilibration of substrate with the transporter (association with the transporter is almost instantaneous) are more common. The aim of this thesis is to improve the determination of transporter mediated drug-drug interactions (TrDDIs) in in vitro liver specific cellular systems through the use of structurally identifiable mechanistic models describing the dynamics of the interaction between substrates and inhibitors. This was done by the design of experiments to optimise the data collected for substrate and inhibitors for use within the mechanistic models across different cellular systems (human cell lines, rat and human hepatocytes) under different inhibition conditions. Mechanistic models were developed to obtain robust model fits that adequately described the interaction between substrates and inhibitors, whilst gaining an insight in terms of model selectivity, given the data available. The structural identifiability of the mechanistic models was assessed to ensure that the unknown parameters in the model could be estimated from the experimental data. The mode of inhibition was determined through the use of mechanistic models for each experimental chapter and compared with conclusions drawn in the in literature. The potential for a clinical TrDDI was evaluated for the experimental work in cryopreserved human hepatocytes (Chapter 5), through a worst case scenario static xviii drug interaction model at the entrance to the liver using an \R value", and through the use of a semi-quantitative physiologically based pharmacokinetic (PBPK) model. All the micro-rate constant mechanistic models were at least structurally locally identifiable with no parameters unknown. Conversely, the macro-rate constant mechanistic were only structurally locally identifiable if both substrate and inhibitor were measured (see Chapter 5). Otherwise one to two parameters had to be known for the macro-rate constant mechanistic models to be structurally locally identifiable. Concurrent with the structural identifiability analysis results, in each of the experimental chapters, the use of micro-rate constant mechanistic models were always the best fitting model to the experimental data based on goodness of fit statistics compared to the use of Michaelis-Menten macro-rate constant mechanistic models. Both the micro-rate constant and macro-rate constant mechanistic models were in agreement with regards to the mechanism of inhibition in all experimental cases, whilst the steady-state assumptions required for the use of the Michaelis-Menten equation were only valid for the micro-rate constants derived in Chapter 5. This supported the use of scaled micro-rate constant parameters in Chapter 5 to Michaelis-Menten parameters in the semi-quantitative mechanistic PBPK model in Chapter 6, where there was a potential for a clinical TrDDI given the in vitro data, which was at odds with the determined R value. In conclusion, this work strongly supports the use of micro-rate constants in mechanistic modelling of in vitro TrDDIs to formally test steady-state assumptions through more robust, structurally identifiable parameter estimates

Quantum Algorithm for the Collision Problem

In this note, we give a quantum algorithm that finds collisions in arbitrary r-to-one functions after only O((N/r)^(1/3)) expected evaluations of the function. Assuming the function is given by a black box, this is more efficient than the best possible classical algorithm, even allowing probabilism. We also give a similar algorithm for finding claws in pairs of functions. Furthermore, we exhibit a space-time tradeoff for our technique. Our approach uses Grover's quantum searching algorithm in a novel way.Comment: 8 pages, LaTeX2

Rotor loss reduction using segmented inverter in surface-mounted permanent magnet drive

In this paper, the influence of different switching modulation arrangements, i.e. current waveform modulation- and phase-shift, on the resultant current waveform of an electrical machine drive consisting of a two segment inter-leaved inverter feeding a surface-mounted permanent magnet (SPM) machine with two identical sets of three phase windings is investigated. The modulation- and phase-shift have been illustrated and the influence of the different modulation and frequency indices have been studied. Furthermore, the torque, and rotor eddy currents and core losses are calculated using FEA when either modulation-shifted or phase-shifted current waveforms are generated and fed to the machine. It is found that using modulation-shift can reduce the current harmonic substantially however the inverter requires two sets of input signals. On the other hand, although the current harmonic reduction is less than that of the modulation-shift, the phase-shift layout can be employed using one set of input signals with a signal delay

Electromagnetic and Mechanical Analysis of High Speed SPM Rotor with Copper Shield

For high-speed applications, the surface-mounted permanent magnet (SPM) machine is preferred due to its high torque density and efficiency. However, induced eddy currents in the rotor conductive parts result in a loss of efficiency and rotor heating. Therefore, several methods to reduce such losses have been proposed in the literature including copper shielding. In this paper, a high-speed SPM machine rotor with a copper shield is designed and investigated both electromagnetically and mechanically. Several quantitative investigations including placing the copper sheet around the retaining sleeve or magnets, different copper sheet and airgap thicknesses, different retaining sleeve materials, different harmonic contents in the current waveform, i.e. pulse amplitude modulation (PAM) and pulse width modulation (PWM) generated waveforms, and different frequencies and current levels are reported. Additionally, a mechanical analysis investigating possible failure modes of the rotor with the copper sheet is reported

Diagnosing Musculoskeletal Tumours

In 1993 we became aware of a worrying increase in apparent errors in the histopathological diagnosis of musculoskeletal tumours in our Unit. As a result all cases seen over the past 8 years were reviewed by an independent panel. Of the 1996 cases reviewed there was an error in 87. In 54 cases (2.7%) this had led to some significant change in the active management of the patient. The main areas where errors arose were in those very cases where clinical and radiological features were not helpful in confirming or refuting the diagnosis. The incidence of errors rose with the passage of time, possibly related to a deterioration in the pathologist’s health. The error rate in diagnosing bone tumours in previously published series ranges from 9 to 40%. To ensure as accurate a rate of diagnosis as possible multidisciplinary working and regular audit are essential

Wound Complications Following Resection of Adductor Compartment Tumours

Purpose Limb salvage surgery of soft tissue sarcomas is associated with both a risk of local recurrence and wound complications. Although the lower limb appears to be at greater risk of wound-related morbidity, few studies separate anatomical compartments. We believe that the adductor compartment of the thigh has a particularly high rate of complications and so performed a retrospective analysis of all soft tissue sarcomas arising in this region undergoing limb salvage

A mechanistic modelling approach for the determination of the mechanisms of inhibition by cyclosporine on the uptake and metabolism of atorvastatin in rat hepatocytes using a high throughput uptake method

Determine the inhibition mechanism through which cyclosporine inhibits the uptake and metabolism of atorvastatin in fresh rat hepatocytes using mechanistic models applied to data generated using a high throughput oil spin method. Atorvastatin was incubated in fresh rat hepatocytes (0.05–150 nmol/ml) with or without 20 min pre-incubation with 10 nmol/ml cyclosporine and sampled over 0.25–60 min using a high throughput oil spin method. Micro-rate constant and macro-rate constant mechanistic models were ranked based on goodness of fit values. The best fitting model to the data was a micro-rate constant mechanistic model including non-competitive inhibition of uptake and competitive inhibition of metabolism by cyclosporine (Model 2). The association rate constant for atorvastatin was 150-fold greater than the dissociation rate constant and 10-fold greater than the translocation into the cell. The association and dissociation rate constants for cyclosporine were 7-fold smaller and 10-fold greater, respectively, than atorvastatin. The simulated atorvastatin-transporter-cyclosporine complex derived using the micro-rate constant parameter estimates increased in line with the incubation concentration of atorvastatin. The increased amount of data generated with the high throughput oil spin method, combined with a micro-rate constant mechanistic model helps to explain the inhibition of uptake by cyclosporine following pre-incubation

Preliminary evidence of increased striatal dopamine in a nonhuman primate model of maternal immune activation.

Women exposed to a variety of viral and bacterial infections during pregnancy have an increased risk of giving birth to a child with autism, schizophrenia or other neurodevelopmental disorders. Preclinical maternal immune activation (MIA) models are powerful translational tools to investigate mechanisms underlying epidemiological links between infection during pregnancy and offspring neurodevelopmental disorders. Our previous studies documenting the emergence of aberrant behavior in rhesus monkey offspring born to MIA-treated dams extends the rodent MIA model into a species more closely related to humans. Here we present novel neuroimaging data from these animals to further explore the translational potential of the nonhuman primate MIA model. Nine male MIA-treated offspring and 4 controls from our original cohort underwent in vivo positron emission tomography (PET) scanning at approximately 3.5-years of age using [18F] fluoro-l-m-tyrosine (FMT) to measure presynaptic dopamine levels in the striatum, which are consistently elevated in individuals with schizophrenia. Analysis of [18F]FMT signal in the striatum of these nonhuman primates showed that MIA animals had significantly higher [18F]FMT index of influx compared to control animals. In spite of the modest sample size, this group difference reflects a large effect size (Cohen's d = 0.998). Nonhuman primates born to MIA-treated dams exhibited increased striatal dopamine in late adolescence-a hallmark molecular biomarker of schizophrenia. These results validate the MIA model in a species more closely related to humans and open up new avenues for understanding the neurodevelopmental biology of schizophrenia and other neurodevelopmental disorders associated with prenatal immune challenge

Population, sexual and reproductive health, rights and sustainable development: forging a common agenda.

This article suggests that sexual and reproductive health and rights activists seeking to influence the post-2015 international development paradigm must work with sustainable development advocates concerned with a range of issues, including climate change, environmental issues, and food and water security, and that a way of building bridges with these communities is to demonstrate how sexual and reproductive health and rights are relevant for these issues. An understanding of population dynamics, including urbanization and migration, as well as population growth, can help to clarify these links. This article therefore suggests that whether or not sexual and reproductive health and rights activists can overcome resistance to discussing "population", become more knowledgeable about other sustainable development issues, and work with others in those fields to advance the global sustainable development agenda are crucial questions for the coming months. The article also contends that it is possible to care about population dynamics (including ageing and problems faced by countries with a high proportion of young people) and care about human rights at the same time. It expresses concern that, if sexual and reproductive health and rights advocates do not participate in the population dynamics discourse, the field will be left free for those for whom respecting and protecting rights may be less of a priority

Growth in the Lower Limb Following Chemotherapy for a Malignant Primary Bone Tumour: A Straight-Line Graph

Purpose. The aim of this paper was to assess the growth in the unaffected lower limb of children who had received chemotherapy for a malignant primary bone tumour around the knee