Concentration Profiling in Rat Tissue by High-Resolution Magic-Angle Spinning NMR Spectroscopy:  Investigation of a Model Drug

Abstract

The utility of high-resolution magic-angle spinning (HR-MAS) NMR for studying drug delivery in whole tissues was explored by dosing female Sprague-Dawley rats with topical or injectable benzoic acid (BA). In principle, HR-MAS NMR permits the detection of both intra-and extracellular compounds. This is an advantage over the previous detection of topically applied BA using microdialysis coupled to HPLC/UV as microdialysis samples only the extracellular space. Skin and muscle samples were analyzed by 1 H HR-MAS NMR, and BA levels were determined using an external standard solution added to the sample rotor. One to two percent of the BA topical dose was detected in the muscle, showing that BA penetrated through the dermal and subcutaneous layers. Since BA was not detected in the muscle in the microdialysis studies, the NMR spectra revealed the intracellular localization of BA. The amount of BA detected in muscle after subcutaneous injection correlated with the distance from the dosing site. Overall, the results suggest that HR-MAS NMR can distinguish differences in the local concentration of BA varying with tissue type, dosage method, and tissue proximity to the dosing site. The results illustrate the potential of this technique for quantitative analysis of drug delivery and distribution and the challenges to be addressed as the method is refined.Nuclear magnetic resonance (NMR) spectroscopy has played a significant role in the growth of metabonomics, an area of clinical research that aims to measure the total metabolic response of an organism to a stimulus such as a drug or toxicant or a physiological change such as a disease state. 1-3 The effects of the stimulus can be evaluated by measuring levels of specific analytes or through pattern recognition to permit the identification of a fingerprint of efficacy or toxicity. 1-3 Spectral analysis of the individual components that comprise the fingerprint reveals the identity of drug metabolites 4 and disease biomarkers. 5,6 The major advantages of NMR spectroscopy for metabonomics studies over other techniques, such as mass spectrometry, 7,8 are the universal nature of NMR detection, ease of quantitation, and the ability to analyze both biofluids and tissues to understand the local versus systemic effects of a stimulus. 9,10 Such an integrated metabonomics approach is an ongoing focus of this collaborative effort. Although NMR is generally less sensitive than other spectroscopic techniques, recent technological developments have reduced sample mass requirements and experiment times significantly. 11,12Tissue analysis by NMR spectroscopy is possible with a technique known as high-resolution magic-angle spinning (HR-MAS Another potential, but relatively unexplored, application of HR-MAS NMR tissue analysis is for drug delivery and distribution studies. Formulation is a critical part of the drug development process affecting the ADME (absorption, distribution, metabolism, and excretion) properties of a drug. While oral formulation is the preferred route for the ad...

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