Jeffrey H. Walton

A smart and versatile theranostic nanomedicine platform based on nanoporphyrin

Multifunctional nanoparticles with combined diagnostic and therapeutic functions show great promise towards personalized nanomedicine. However, attaining consistently high performance of these functions in vivo in one single nano-construct remains extremely challenging. Here we demonstrate the use of one single polymer to develop a smart “all-in-one” nanoporphyrin platform that conveniently integrates a broad range of clinically relevant functions. Nanoporphyrins can be used as amplifiable multimodality nanoprobes for near-infrared fluorescence imaging (NIRFI), magnetic resonance imaging (MRI), positron emission tomography (PET) and dual modal PET-MRI. Nanoporphyrins greatly increase the imaging sensitivity for tumor detection through background suppression in blood, as well as preferential accumulation and signal amplification in tumors. Nanoporphyrins also function as multiphase nanotransducers that can efficiently convert light to heat inside tumors for photothermal-therapy (PTT), and light to singlet oxygen for photodynamic-therapy (PDT). Furthermore, nanoporphyrins act as programmable releasing nanocarriers for targeted delivery of drugs into tumors.

Displacement Encoding for the Measurement of Cartilage Deformation

Articular cartilage is a load bearing and lubricating tissue in animal joints. Heterogeneous deformations arise in the structured and zonal tissue under the application of mechanical load. The character of these deformations is altered by degenerative joint disease. Here, we document an MRI‐based technique for determining deformations throughout the volume of the tissue based on displacement encoding with stimulated echoes (DENSE) and a fast spin echo (FSE) readout. A DENSE‐FSE technique was designed to image cartilage at 9.4 Tesla in a deformed state during the application of cyclic mechanical loading. Artifact elimination arising from stimulated echoes and FSE was accomplished by radio frequency pulse phase cycling. The error of the technique was random and was quantified in terms of precision as better than 0.17% strain. Heterogeneous deformation field patterns in axial, transverse, and shear directions were quantified in a single tissue explant loaded in simple uniaxial compression. The technique is appropriate for documenting tissue deformations during applied physiologically relevant stress levels and loading rates. It may also be applied to characterize the micromechanical strain environment in normal, diseased, or regenerated cartilage in response to applied mechanical loading. Magn Reson Med, 2007.

Xylella fastidiosa Infection and Ethylene Exposure Result in Xylem and Water Movement Disruption in Grapevine Shoots

It is conventionally thought that multiplication of the xylem-limited bacterium Xylella fastidiosa (Xf) within xylem vessels is the sole factor responsible for the blockage of water movement in grapevines (Vitis vinifera) affected by Pierces disease. However, results from our studies have provided substantial support for the idea that vessel obstructions, and likely other aspects of the Pierces disease syndrome, result from the grapevines active responses to the presence of Xf, rather than to the direct action of the bacterium. The use of magnetic resonance imaging (MRI) to observe the distribution of water within the xylem has allowed us to follow nondestructively the development of vascular system obstructions subsequent to inoculation of grapevines with Xf. Because we have hypothesized a role for ethylene produced in vines following infection, the impact of vine ethylene exposure on obstruction development was also followed using MRI. In both infected and ethylene-exposed plants, MRI shows that an important proportion of the xylem vessels become progressively air embolized after the treatments. The loss of xylem water-transporting function, assessed by MRI, has been also correlated with a decrease in stem-specific hydraulic conductivity (KS) and the presence of tyloses in the lumens of obstructed water conduits. We have observed that the ethylene production of leaves from infected grapevines is greater than that from healthy vines and, therefore, propose that ethylene may be involved in a series of cellular events that coordinates the vines response to the pathogen.

MRI-Based Technique for Determining Nonuniform Deformations Throughout the Volume of Articular Cartilage Explants

Articular cartilage is critical to the normal function of diarthrodial joints. Despite the importance of the tissue and the prevalence of cartilage degeneration (e.g., osteoarthritis), the technology required to noninvasively describe nonuniform deformations throughout the volume of the tissue has not been available until recently. The objectives of the work reported in this paper were to 1) describe a noninvasive technique (termed the cartilage deformation by tag registration (CDTR) technique) to determine nonuniform deformations in articular cartilage explants with the use of specialized MRI tagging and image processing methods, 2) evaluate the strain error of the CDTR technique using a custom MRI‐compatible phantom material, and 3) demonstrate the applicability of the CDTR technique to articular cartilage by determining 3D strain fields throughout the volume of a bovine articular cartilage explant. A custom MRI pulse sequence was designed to tag and image articular cartilage explants at 7 Tesla in undeformed and deformed states during the application of multiple load cycles. The custom pulse sequence incorporated the “delays alternating with nutations for tailored excitation” (DANTE) pulse sequence to apply tags. This was followed by a “fast spin echo” (FSE) pulse sequence to create images of the tags. The error analysis using the phantom material indicated that deformations can be determined with an error, defined as the strain precision, better than 0.83% strain. When this technique was applied to a single articular cartilage explant loaded in unconfined compression, hetereogeneous deformations throughout the volume of the tissue were evident. This technique potentially can be applied to determine normal cartilage deformations, analyze degenerated cartilage, and evaluate cartilage surgical repair and treatment methodologies. In addition, this technique may be applied to other soft tissues that can be appropriately imaged by MR. Magn Reson Med 53:321–328, 2005.

Sublethal actions of copper in abalone (Haliotis rufescens) as characterized by in vivo 31P NMR

The sublethal biochemical actions of copper in live, intact red abalone (Haliotis rufescens) were characterized by in vivo 31P nuclear magnetic resonance spectroscopy (NMR). This non-invasive technique is ideal for examining cellular respiration since critical metabolite concentrations, including phosphoarginine ([PA]), inorganic phosphate ([P(i)]) and [ATP], and the arginine kinase (AK) rate constant, can be monitored in real time. Both metabolite concentrations and enzyme rate constants were measured in abalone during 8-h exposures to 66 microg l(-1) (1.04 microM) and 126 microg l(-1) (1.98 microM) copper (as CuCl2). Significant decreases in [PA] and corresponding increases in [P(i)] resulted, while [ATP] remained constant. In controls [PA], [P(i)] and [ATP] all remained unchanged. Furthermore, both copper concentrations induced a significant elevation in the forward AK rate constant over the basal value of 0.020 +/- 0.002 s(-1). Metabolite levels and enzyme rate constants were also measured during 8-h 66 microg l(-1) copper exposures both before and after a 2-week subchronic exposure to 36 microg l(-1) (0.57 microM) copper. Unlike before the subchronic exposure, no significant changes in [PA], [P(i)] or [ATP] were observed after the 36 microg l(-1) copper treatment, compared with controls. This induced tolerance was also evident from the forward AK rate constant data. Finally, copper accumulation was determined in gill, digestive gland and foot muscle samples. Whereas acute exposure only led to significant accumulation in the gill, copper levels in subchronically exposed abalone were significantly elevated in both the gill and digestive gland, and marginally so in foot muscle. Overall, the gill appears to be the primary site of copper accumulation and toxicity, while the foot and adductor muscles maybe secondarily impacted. The observed metabolic changes may result from insufficient oxygen delivery to the muscles, resulting from mucus accumulation or cytological damage at the gill. In conclusion, abalone acutely exposed to copper pollution may develop asphyxial hypoxia. Since their survival is dependent on adherence to rock surfaces, such a reduction of muscle function could ultimately prove fatal.

Development of low field nuclear magnetic resonance microcoils

A miniaturized spiral Helmholtz rf coil was fabricated using standard photolithography and electroplating. A commercial 0.6 T superconductive magnet was used to test the coil performance for both nuclear magnetic resonance (NMR) spectroscopy and imaging applications. NMR spectra of water, methanol, and 1-propanol were obtained as well as static and flow images of a water phantom. The spectral resolution was sufficient to allow chemical identification. Additionally, the viscosity of water was estimated from the experimental velocity profile and was equal to the expected value of 1 cP. Results obtained demonstrated the prospect of using the Helmholtz rf coil as part of a portable low-field NMR system for applications in analytical chemistry and process measurements in industrial settings.

Intravenous HOE-642 reduces brain edema and Na uptake in the rat permanent middle cerebral artery occlusion model of stroke: evidence for participation of the blood-brain barrier Na/H exchanger

Cerebral edema forms in the early hours of ischemic stroke by processes involving increased transport of Na and Cl from blood into brain across an intact blood–brain barrier (BBB). Our previous studies provided evidence that the BBB Na–K–Cl cotransporter is stimulated by the ischemic factors hypoxia, aglycemia, and arginine vasopressin (AVP), and that inhibition of the cotransporter by intravenous bumetanide greatly reduces edema and infarct in rats subjected to permanent middle cerebral artery occlusion (pMCAO). More recently, we showed that BBB Na/H exchanger activity is also stimulated by hypoxia, aglycemia, and AVP. The present study was conducted to further investigate the possibility that a BBB Na/H exchanger also participates in edema formation during ischemic stroke. Sprague-Dawley rats were subjected to pMCAO and then brain edema and Na content assessed by magnetic resonance imaging diffusion-weighed imaging and magnetic resonance spectroscopy Na spectroscopy, respectively, for up to 210 minutes. We found that intravenous administration of the specific Na/H exchange inhibitor HOE-642 significantly decreased brain Na uptake and reduced cerebral edema, brain swelling, and infarct volume. These findings support the hypothesis that edema formation and brain Na uptake during the early hours of cerebral ischemia involve BBB Na/H exchanger activity as well as Na–K–Cl cotransporter activity.

Magnetic resonance thermometry at 7T for real-time monitoring and correction of ultrasound induced mild hyperthermia.

While Magnetic Resonance Thermometry (MRT) has been extensively utilized for non-invasive temperature measurement, there is limited data on the use of high field (≥7T) scanners for this purpose. MR-guided Focused Ultrasound (MRgFUS) is a promising non-invasive method for localized hyperthermia and drug delivery. MRT based on the temperature sensitivity of the proton resonance frequency (PRF) has been implemented in both a tissue phantom and in vivo in a mouse Met-1 tumor model, using partial parallel imaging (PPI) to speed acquisition. An MRgFUS system capable of delivering a controlled 3D acoustic dose during real time MRT with proportional, integral, and derivative (PID) feedback control was developed and validated. Real-time MRT was validated in a tofu phantom with fluoroptic temperature measurements, and acoustic heating simulations were in good agreement with MR temperature maps. In an in vivo Met-1 mouse tumor, the real-time PID feedback control is capable of maintaining the desired temperature with high accuracy. We found that real time MR control of hyperthermia is feasible at high field, and k-space based PPI techniques may be implemented for increasing temporal resolution while maintaining temperature accuracy on the order of 1°C.

Magnetic resonance imaging (MRI): a technique to study flow an microstructure of concentrated emulsions

Nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) have recently been recognized as important techniques for R&D of products and processes, as is attested by several successful applications in different areas of chemical engineering in recent years. In this article we present new experimental methods based on MRI to study flow and microstructure of concentrated emulsions. The objective is to present the unique features of this noninvasive technique to accurately measure different properties of flowing particulate opaque systems. Experimental results of velocity profiles, spatial distribution of droplet sizes and spatial homogeneity of an oil-in-water dispersion in a horizontal, concentric cylinder geometry using different pulse sequences are presented. The application of these techniques allowed probing important information on flow and microstructure of multiphase systems of interest in chemical engineering and food science.

The impact of alkali pretreatment and post-pretreatment conditioning on the surface properties of rice straw affecting cellulose accessibility to cellulases

Rice straw was pretreated with sodium hydroxide and subsequently conditioned to reduce the pH to 5-6 by either: (1) extensive water washing or (2) acidification with hydrochloric acid then water washing. Alkali pretreatment improved the enzymatic digestibility of rice straw by increasing the cellulose accessibility to cellulases. However, acidification after pretreatment reversed the gains in cellulose accessibility to cellulases and enzymatic digestibility due to precipitation of solubilized compounds. Surface composition analyses by ToF-SIMS confirmed a reduction in surface lignin by pretreatment and water washing, and suggested that acidification precipitated a chemically modified form of lignin on the surfaces of rice straw. The spin-spin relaxation times (T2) of the samples indicated increased porosity in alkali pretreated rice straw. The acidified pretreated rice straw had reduced amounts of water in the longer T2 proton pools associated with water in the pores of the biomass likely due to back-filling by the precipitated components.