Glucocerebrosidase (GCase) activity modulation by 2-alkyl trihydroxypiperidines: Inhibition and pharmacological chaperoning

The enzyme glucocerebrosidase (GCase) has become an important therapeutic target due to its involvement in pathological disorders consequent to enzyme deficiency, such as the lysosomal storage Gaucher disease (GD) and the neurological Parkinson disease (PD). Pharmacological chaperones (PCs) are small compounds able to stabilize enzymes when used at sub-inhibitory concentrations, thus rescuing enzyme activity. We report the stereodivergent synthesis of trihydroxypiperidines alkylated at C-2 with both configurations, by means of the stereoselective addition of Grignard reagents to a carbohydrate-derived nitrone in the presence or absence of Lewis acids. All the target compounds behave as good GCase inhibitors, with IC₅₀ in the micromolar range. Moreover, compound 11a behaves as a PC in fibroblasts derived from Gaucher patients bearing the N370/RecNcil mutation and the homozygous L444P mutation, rescuing the activity of the deficient enzyme by up to 1.9- and 1.8-fold, respectively. Rescues of 1.2-1.4-fold were also observed in wild-type fibroblasts, which is important for targeting sporadic forms of PD.

Optimal integration of intraneural somatosensory feedback with visual information: a single-case study

Providing somatosensory feedback to amputees is a long-standing objective in prosthesis research. Recently, implantable neural interfaces have yielded promising results in this direction. There is now considerable evidence that the nervous system integrates redundant signals optimally, weighting each signal according to its reliability. One question of interest is whether artificial sensory feedback is combined with other sensory information in a natural manner. In this single-case study, we show that an amputee with a bidirectional prosthesis integrated artificial somatosensory feedback and blurred visual information in a statistically optimal fashion when estimating the size of a hand-held object. The patient controlled the opening and closing of the prosthetic hand through surface electromyography, and received intraneural stimulation proportional to the object's size in the ulnar nerve when closing the robotic hand on the object. The intraneural stimulation elicited a vibration sensation in the phantom hand that substituted the missing haptic feedback. This result indicates that sensory substitution based on intraneural feedback can be integrated with visual feedback and make way for a promising method to investigate multimodal integration processes.

A Physical Model of the Human Systemic Arterial Tree

A physical model of the human arterial tree has been developed to be used in a computer controlled mock circulatory system (MCS). Its aim is to represent systemic arterial tree properties and extend the capacity of the MCS to intraortic balloon pump (IABP) testing. The main problem was to model the aorta simply and to accurately reproduce aortic impedance and related flow and pressure waveforms at different sections. The model is composed of eight segments; lumped parameter models are used for its peripheral loads.

After the numerical simulation, the physical model was reproduced as a silicon rubber tapered tube. This rubber was chosen for its stability over time and the acceptable behaviour of its Young's modulus (Ey =22.23 gf·mm–2) with different loads and in comparison with data from the literature (Ey ≈ 20.4 gf·mm–2). The properties of each segment of the aorta were defined in terms of compliance, resistance and inertance as a function of length, radius and thickness. The variable thickness was obtained using positive and negative molds. Total static compliance of the aorta model is about 1.125·10–3 g–1cm4·sec2 (1.5 cm3·mmHg–1). Measurements were performed both on numerical and physical models (in open and closed loop configuration). Data reported show pressure and flow waveforms along with input impedance modulus and phase. The results are in good agreement with data from the literature.

A Simple Method for Emax Trend Evaluation: In Vitro and in Vivo Results

The aim of this study is the evaluation of end systolic ventricular elastance trend (as a measure of heart contractility) by hemodynamic variables available in intensive care units or during heart surgery: heart rate, cardiac output, left atrial, mean and diastolic arterial pressure. Its basic assumption is the description of ejection as the interaction between variable left ventricular and arterial compliances (reciprocal of the corresponding elastances) connected in parallel. As pressure is the same in each compliance at systole beginning and ending, ventricular elastance can be estimated by assuming that energy variation is the same on both compliances. The algorithm has been tested on a numerical simulator of the circulatory system and on six sheep at basal conditions and during drug infusion. Correlation function in numerical simulation, between true and computed ventricular elastance (range 0.45÷5 mm Hg-cm-3), yields 0.985. In vivo comparison between computed ventricular elastance trend and ventricular dp/dt trend yields a correlation function ranging between 0.87 and 0.99.

The result of the algorithm cannot be assumed to be Emax value. However, it can be considered a contractility index as it closely follows any change in dp/dt. It can be computed by simple calculations and needs no variables other than those usually measured in intensive care. It allows the extrapolation of useful information for evaluating the trend in heart contractility and for setting up a control strategy for mechanical or pharmacological assistance during heart recovery.

IABP Assistance: A Test Bench for the Analysis of its Effects on Ventricular Energetics and Hemodynamics

IABP assistance is frequently used to support heart recovery, improving coronary circulation and re-establishing the balance between oxygen availability and consumption. Hemodynamic and energetic parameters (endocardial viability ratio, ventricular energetics) are used to evaluate its effectiveness which depends on internal (timing, balloon volume and position) and external factors (circulatory conditions). Considering short, medium and long-term effects of IABP, the first depends on its mechanical action, the latter on the changes induced in circulatory parameters. The analysis of the first is important because conditions for the onset of a virtuous cycle able to support ventricular recovery are created. Simulation systems could be helpful in this analysis for the implicit reliability and reproducibility of the experiments, provided that they are able to reproduce both hemodynamic phenomena and energetic relationships. The aim of this paper is to present a system originally developed to test mechanical heart assist devices and modified for IABP testing. Data reported here are obtained from in vitro experiments. A partial verification, obtained from the literature is presented.

A Hybrid (Numerical-physical) Model of the Left Ventricle

Hydraulic models of the circulation are used to test mechanical devices and for training and research purposes; when compared to numerical models, however, they are not flexible enough and rather expensive. The solution proposed here is to merge the characteristics and the flexibility of numerical models with the functions of physical models. The result is a hybrid model with numerical and physical sections connected by an electro-hydraulic interface - which is to some extent the main problem since the numerical model can be easily changed or modified.

The concept of hybrid model is applied to the representation of ventricular function by a variable elastance numerical model. This prototype is an open loop circuit and the physical section is built out of a reservoir (atrium) and a modified windkessel (arterial tree). The corresponding equations are solved numerically using the variables (atrial and arterial pressures) coming from the physical circuit. Ventricular output flow is the computed variable and is sent to a servo amplifier connected to a DC motor-gear pump system. The gear pump, behaving roughly as a flow source, is the interface to the physical circuit. Results obtained under different hemodynamic conditions demonstrate the behaviour of the ventricular model on the pressure-volume plane and the time course of output flow and arterial pressure.

Mono and Bi-ventricular Assistance: Their Effect on Ventricular Energetics

When mono- and bi-ventricular mechanical assistance is used for heart recovery, its control strategy and circulatory variables affect ventricular energetics (external work-EW, oxygen consumption-VO2, cardiac mechanical efficiency-CME). This study is based on the data obtained in vitro and presents an analysis of the effects of the mono- and bi-ventricular mechanical assistance on ventricular energetics. The assistance was conducted on the principle of counterpulsation with atrio-arterial connection. It includes the following stages: 1) the characterisation of the isolated ventricle model in terms of EW, VO2 and CME as a function of the filling pressure and peripheral resistance, 2) modelling of left ventricular and pulmonary dysfunction, followed by left ventricular and bi-ventricular assistance. Experimental data enable us to draw the following conclusions:

• in general, the greatest hemodynamic improvement does not correspond to the highest energetic improvement,

• LVAD assistance deteriorates left ventricular CME while its effect on right ventricular energetics depends on the value of right ventricular elastance (Emax). Right ventricular CME is deteriorated by BVAD assistance irrespective of right Emax,

• the energetics optimisation in bi-ventricular assistance is closely related to the right Emax, which could probably be a deciding factor in the choice of the assistance mode.

Computer Simulation of Hemodynamic Parameter Changes by Mechanical Ventilation and Biventricular Circulatory Support

When a Bi-Ventricular Assist Device (BVAD) is used in conjunction with mechanical ventilation (MV) of the lungs with positive intrathoracic pressure (Pt), the latter influences hemodynamics. The aim of our study was to assess the simultaneous influence of BVAD and MV on hemodynamics. We assumed ventricular pathological conditions as reduced elastances and increased rest volumes. Peripheral systemic arterial resistance was assumed to have different values. Data were obtained by computer simulation. Trends in main hemodynamic variables were compared with clinical data from literature. Simulation showed that systemic venous, pulmonary arterial and left atrial pressures are very sensitive to Pt (-2 to 5 mmHg).

Software for computerised analysis of cardiotocographic traces

Despite the widespread use of cardiotocography in foetal monitoring, the evaluation of foetal status suffers from a considerable inter and intra-observer variability. In order to overcome the main limitations of visual cardiotocographic assessment, computerised methods to analyse cardiotocographic recordings have been recently developed. In this study, a new software for automated analysis of foetal heart rate is presented. It allows an automatic procedure for measuring the most relevant parameters derivable from cardiotocographic traces. Simulated and real cardiotocographic traces were analysed to test software reliability. In artificial traces, we simulated a set number of events (accelerations, decelerations and contractions) to be recognised. In the case of real signals, instead, results of the computerised analysis were compared with the visual assessment performed by 18 expert clinicians and three performance indexes were computed to gain information about performances of the proposed software. The software showed preliminary performance we judged satisfactory in that the results matched completely the requirements, as proved by tests on artificial signals in which all simulated events were detected from the software. Performance indexes computed in comparison with obstetricians' evaluations are, on the contrary, not so satisfactory; in fact they led to obtain the following values of the statistical parameters: sensitivity equal to 93%, positive predictive value equal to 82% and accuracy equal to 77%. Very probably this arises from the high variability of trace annotation carried out by clinicians.

Evidence for complex selection on four-fold degenerate sites in Drosophila melanogaster

We considered genome-wide four-fold degenerate sites from an African Drosophila melanogaster population and compared them to short introns. To include divergence and to polarize the data, we used its close relatives Drosophila simulans, Drosophila sechellia, Drosophila erecta and Drosophila yakuba as outgroups. In D. melanogaster, the GC content at four-fold degenerate sites is higher than in short introns; compared to its relatives, more AT than GC is fixed. The former has been explained by codon usage bias (CUB) favouring GC; the latter by decreased intensity of directional selection or by increased mutation bias towards AT. With a biallelic equilibrium model, evidence for directional selection comes mostly from the GC-rich ancestral base composition. Together with a slight mutation bias, it leads to an asymmetry of the unpolarized allele frequency spectrum, from which directional selection is inferred. Using a quasi-equilibrium model and polarized spectra, however, only purifying and no directional selection is detected. Furthermore, polarized spectra are proportional to those of the presumably unselected short introns. As we have no evidence for a decrease in effective population size, relaxed CUB must be due to a reduction in the selection coefficient. Going beyond the biallelic model and considering all four bases, signs of directional selection are stronger. In contrast to short introns, complementary bases show strand specificity and allele frequency spectra depend on mutation directions. Hence, the traditional biallelic model to describe the evolution of four-fold degenerate sites should be replaced by more complex models assuming only quasi-equilibrium and accounting for all four bases.

Unconstrained evolution in short introns? - an analysis of genome-wide polymorphism and divergence data from Drosophila

An unconstrained reference sequence facilitates the detection of selection. In Drosophila, sequence variation in short introns seems to be least influenced by selection and dominated by mutation and drift. Here, we test this with genome-wide sequences using an African population (Malawi) of D. melanogaster and data from the related outgroup species D. simulans, D. sechellia, D. erecta and D. yakuba. The distribution of mutations deviates from equilibrium, and the content of A and T (AT) nucleotides shows an excess of variance among introns. We explain this by a complex mutational pattern: a shift in mutational bias towards AT, leading to a slight nonequilibrium in base composition and context-dependent mutation rates, with G or C (GC) sites mutating most frequently in AT-rich introns. By comparing the corresponding allele frequency spectra of AT-rich vs. GC-rich introns, we can rule out the influence of directional selection or biased gene conversion on the mutational pattern. Compared with neutral equilibrium expectations, polymorphism spectra show an excess of low frequency and a paucity of intermediate frequency variants, irrespective of the direction of mutation. Combining the information from different outgroups with the polymorphism data and using a generalized linear model, we find evidence for shared ancestral polymorphism between D. melanogaster and D. simulans, D. sechellia, arguing against a bottleneck in D. melanogaster. Generally, we find that short introns can be used as a neutral reference on a genome-wide level, if the spatially and temporally varying mutational pattern is accounted for.