In vivo pharmacokinetics using MRS

Optical and magnetic resonance imaging as complementary modalities in drug discovery

Imaging has the ability to study various biological and chemical processes noninvasively in living subjects in a longitudinal way. For this reason, imaging technologies have become an integral part of the drug-discovery and development program and are commonly used in following disease processes and drug action in both preclinical and clinical stages. As the domain of imaging sciences transitions from anatomical/functional to molecular applications, the development of molecular probes becomes crucial for the advancement of the field. This review summarizes the role of two complementary techniques, magnetic resonance and fluorescence optical imaging, in drug discovery. While the first approach exploits intrinsic tissue characteristics as the source of image contrast, the second necessitates the use of appropriate probes for signal generation. The anatomical, functional, metabolic and molecular information that becomes accessible through imaging can provide invaluable insights into disease mechanisms and mechanisms of drug action.

Magnetic resonance methods and applications in pharmaceutical research

This review presents an overview of some recent magnetic resonance (MR) techniques for pharmaceutical research. MR is noninvasive, and does not expose subjects to ionizing radiation. Some methods that have been used in pharmaceutical research MR include magnetic resonance spectroscopy (MRS) and magnetic resonance imaging (MRI) methods, among them, diffusion-weighted MRI, perfusion-weighted MRI, functional MRI, molecular imaging and contrast-enhance MRI. Some applications of MR in pharmaceutical research include MR in metabonomics, in vivo MRS, studies in cerebral ischemia and infarction, degenerative joint diseases, oncology, cardiovascular disorders, respiratory diseases and skin diseases. Some of these techniques, such as cardiac and joint imaging, or brain fMRI are standard, and are providing relevant data routinely. Skin MR and hyperpolarized gas lung MRI are still experimental. In conclusion, considering the importance of finding and characterizing biomarkers for improved drug evaluation, it can be expected that the use of MR techniques in pharmaceutical research is going to increase in the near future.

In vivo mouse imaging and spectroscopy in drug discovery

Imaging modalities such as micro-computed tomography (micro-CT), micro-positron emission tomography (micro-PET), high-resolution MRI, optical imaging, and high-resolution ultrasound have become invaluable tools in preclinical pharmaceutical research. They can be used to non-invasively investigate, in vivo, rodent biology and metabolism, disease models, and pharmacokinetics and pharmacodynamics of drugs. The advantages and limitations of each approach usually determine its application, and therefore a small-rodent imaging laboratory in a pharmaceutical environment should ideally provide access to several techniques. In this paper we aim to illustrate how these techniques may be used to obtain meaningful information for the phenotyping of transgenic mice and for the analysis of compounds in murine models of disease.

Cytoprotection does not preserve brain functionality in rats during the acute post-stroke phase despite evidence of non-infarction provided by MRI

In animal models of stroke the promise of a therapy is commonly judged from infarct size measurements, assuming that a reduction in infarct size results in reduction of the functional deficits. We have evaluated the validity of the concept that structural integrity translates into functional integrity during the acute post-stroke period (24 h). Unilateral permanent middle cerebral artery occlusion (pMCAO) in Fischer F344 rats leads to infarcts comprising the ipsilateral striatum and cortical structures, including the somatosensory cortex. Infarct volumes were assessed using magnetic resonance imaging (MRI) methods (T(2), diffusion, perfusion MRI). The functional integrity of the somatosensory cortex was assessed by functional MRI (fMRI) measuring changes in local cerebral blood volume, and by assessing the forelimb grip strength and the beam-walking performance of the animals. Treatment with the calcium antagonist isradipine (2.5 mg/kg injected s.c. immediately after pMCAO) reduced the total infarct size by more than 40% compared to vehicle-injected controls. In particular, the ipsilateral somatosensory cortex appeared normal in diffusion- and T(2)-weighted MRI images. In sham-operated rats simultaneous electrical stimulation of both forepaws led to similar activation of both somatosensory cortices, while in pMCAO animals given vehicle only the contralateral cortex showed an fMRI response. Similarly, in pMCAO rats treated with isradipine, functional activation following bilateral electrical stimulation was only detected in the contralateral somatosensory cortex despite the normal appearance of the ipsilateral cortex in MRI images. Furthermore, fMRI responses to pharmacological stimulation with bicuculline were virtually absent in the ipsilateral somatosensory cortices both in vehicle- and isradipine-treated rats. Finally there was no significant difference between vehicle- and isradipine-treated animals upon the performance of beam-walking test or in forelimb grip strength. It is concluded that during the acute (24 h) post-occlusion period, structural integrity in the somatosensory cortex revealed by MRI does not translate into preservation of function.