Tim Stait-Gardner

Spatial and temporal control of drug release through pH and alternating magnetic field induced breakage of Schiff base bonds

P(DEGMA-co-OEGMA-b-[TMSPMA-co-VBA])@silica@magnetite polymer–nanoparticle composites have been developed as a platform for controllable drug release. The nanocomposite facilitates controllable release of therapeutic molecules through breakage of pH and heat labile Schiff base bonds that bind the molecules to the polymer. This enables dual-stimuli responsive drug release in response to the acidic microenvironment of cancerous cells and heat generated by the magnetite nanoparticles when subjected to an alternating magnetic field, thereby permitting spatial and temporal control over ‘burst’ release of the drugs. The nanocomposite has also been shown to be effective at improving magnetic resonance imaging contrast through enhancement of spin–spin relaxivity.

Evaluation of Gd-DTPA-Monophytanyl and Phytantriol Nanoassemblies as Potential MRI Contrast Agents

Supramolecular self-assembling amphiphiles have been widely used in drug delivery and diagnostic imaging. In this report, we present the self-assembly of Gd (III) chelated DTPA-monophytanyl (Gd-DTPA-MP) amphiphiles incorporated within phytantriol (PT), an inverse bicontinuous cubic phase forming matrix at various compositions. The dispersed colloidal nanoassemblies were evaluated as potential MRI contrast agents at various magnetic field strengths. The homogeneous incorporation of Gd-DTPA-MP in PT was confirmed by polarized optical microscopy (POM) and synchrotron small-angle X-ray scattering (SAXS) of the bulk phases of the mixtures. The liquid crystalline nanostructures, morphology, and the size distribution of the nanoassemblies were studied by SAXS, cryogenic transmission electron microscopy (cryo-TEM), and dynamic light scattering (DLS). The dispersions with up to 2 mol % of Gd-DTPA-MP in PT retained inverse cubosomal nanoassemblies, whereas the rest of the dispersions transformed to liposomal nanoassemblies. In vitro relaxivity studies were performed on all the dispersions at 0.54, 9.40, and 11.74 T and compared to Magnevist, a commercially available contrast agent. All the dispersions showed much higher relaxivities compared to Magnevist at both low and high magnetic field strengths. Image contrast of the nanoassemblies was also found to be much better than Magnevist at the same Gd concentration at 11.74 T. Moreover, the Gd-DTPA-MP/PT dispersions showed improved relaxivities over the pure Gd-DTPA-MP dispersion at high magnetic fields. These stable colloidal nanoassemblies have high potential to be used as combined delivery matrices for diagnostics and therapeutics.

The protective effect of apolipoprotein in models of trophoblast invasion and preeclampsia

Preeclampsia is a hypertensive disorder of pregnancy. It is associated with abnormal placentation via poor placental invasion of the uterine vasculature by trophoblast cells, leading to poor placental perfusion, oxidative stress, and inflammation, all of which are implicated in its pathogenesis. A dyslipidemia characterized by low plasma levels of high-density lipoproteins (HDL) and elevated triglycerides has been described in preeclampsia. Apolipoprotein A-I (apoA-I), a constituent of HDL is an anti-inflammatory agent. This study investigated whether apoA-I protects against hypertension and adverse placental changes in a proinflammatory cytokine (TNF-α)-induced model of preeclampsia. Further, this study investigated whether apoA-I protects against the inhibitory effect of TNF-α in a human in vitro model of trophoblast invasion. Administration of apoA-I to pregnant mice before infusion with TNF-α resulted in a significant reduction in the cytokine-induced increase in systolic blood pressure. MRI measurement of T2 relaxation, a parameter that is tissue specific and sensitive to physiological changes within tissues, showed a reversal of TNF-α-induced placental changes. Preincubation of endothelial cells with apoA-I protected against the TNF-α-induced inhibition of HTR-8/SVneo (trophoblast) cell integration into endothelial (UtMVEC) networks. These data suggest that a healthy lipid profile may affect pregnancy outcomes by priming endothelial cells in preparation for trophoblast invasion.

Diffusion Studies of Phenylenediamine Isomers in Water-Monohydric-Alcohol Systems

The study of isomer diffusion provides useful information regarding solvent effects for mixture analysis. Isomers, particularly those with similar hydrodynamic radii, provide a mechanism for probing solute–solvent interactions. Here nuclear magnetic resonance was used to measure the self-diffusion of phenylenediamine isomers in various water–monohydric-alcohol (i.e. methanol, ethanol, 1-propanol, and tert-butanol) solvents. These systems allowed the effect of solvent modulation on isomer diffusion to be examined. It was found that the resonances of phenylenediamine isomers in a mixture were separable via diffusion, with the separation becoming greater at higher concentration of monohydric-alcohols. Unlike previously shown for dihydroxybenzene isomers, all three phenylenediamine isomers were differentiable via diffusion.

Shortening NMR experimental times

Conventionally, arrayed nuclear magnetic resonance experiments, such as diffusion and relaxation, are performed with the same number of scans (NS) at each iteration despite the signal-to-noise ratio being more than sufficient for many of the iterations. Here, we propose a simple yet effective approach that significantly shortens experimental times by varying NS through the arrayed experiments while keeping the signal-to-noise ratio essentially the same and retaining experimental accuracy.

Jump-and-return sandwiches: A new family of binomial-like selective inversion sequences with improved performance

A new family of binomial-like inversion sequences, named jump-and-return sandwiches (JRS), has been developed by inserting a binomial-like sequence into a standard jump-and-return sequence, discovered through use of a stochastic Genetic Algorithm optimisation. Compared to currently used binomial-like inversion sequences (e.g., 3-9-19 and W5), the new sequences afford wider inversion bands and narrower non-inversion bands with an equal number of pulses. As an example, two jump-and-return sandwich 10-pulse sequences achieved 95% inversion at offsets corresponding to 9.4% and 10.3% of the non-inversion band spacing, compared to 14.7% for the binomial-like W5 inversion sequence, i.e., they afforded non-inversion bands about two thirds the width of the W5 non-inversion band.

Quantification of placental change in mouse models of preeclampsia using magnetic resonance microscopy

Abnormal development of the placenta is postulated to be central to the aetiology of preeclampsia. This study investigates changes in placental histopathology in mouse models of preeclampsia compared to the morphology using magnetic resonance microscopy (MRM) (11.7 T) of intact ex vivo tissue followed by 3D analysis of the image data. Here, C57BL/6JArc pregnant mice were subject to either normal pregnancy (n=3), or to one of two experimental models of preeclampsia; TNF-α infusion (n=3) or reduced uterine perfusion pressure (RUPP) (n=3). Placental tissue was collected at gestational day (gd) 17, fixed in formalin and incubated with Magnavist™ contrast agent, and high resolution images (50 μm × 50 μm × 50 μm voxels) obtained by magnetic resonance imaging at 11.74 T. Visual segmentation into placental subregions and three dimensional (3D) reconstruction followed by volume analysis was performed with Amira™ 3D analysis software. The significance of differences between treatment groups in total and regional volumes was assessed. In a single placenta the volumes measure by standard histology were compared. Three placentas from each animal were imaged, segmented into anatomical regions and 3D reconstructions generated. Total placental volume, labyrinth and decidual volume were not significantly different between groups. The junctional zone volume was found to be significantly larger in the RUPP animals (18.5±1.5 mm3) compared to TNF-α infused animals (15.8±1.5) or control animals (15.0±0.7, P<0.01). However, the decidual/junctional zone volume was smaller in the TNF-a compared to control animals (P<0.05). Placental structural change in experimental models of preeclampsia is able to be visualized and quantified using MRM and 3-D analysis. These techniques could prove to be a powerful tool in examining changes in placental morphology.

Chapter 2:Fundamentals of Diffusion Measurements using NMR

Nuclear magnetic resonance pulsed gradient-spin echo experiments allow probing complex solution properties of molecules that translational motion depends on. This introductory review covers aspects from the mathematical basics of diffusive motion to the averaging effects of obstruction and binding. An outline of some of the experimental aspects of diffusion measurements is also provided including data acquisition, fitting and solvent suppression.