Anal. Chem. 2005, 77, 6682-6686
Localization and Analyses of Small Drug Molecules in Rat Brain Tissue Sections Hay-Yan J. Wang, Shelley N. Jackson, Jonathan McEuen, and Amina S. Woods*
Cellular Neurobiology Branch, NIDA-IRP, NIH, 5500 Nathan Shock Drive, Baltimore, Maryland 21224
Traditional detection of drugs in tissue requires tissue homogenization, which precludes the mapping and localization of drugs. The use of autoradiography could compensate for such shortcoming. However, it requires expensive custom-synthesized radioactive drugs. Recent improvement in sample preparation for matrix-assisted laser desorption/ionization mass spectrometry (MALDIMS) and MALDI-MS/MS provides an alternative approach for in situ drug detection. In this work, rat brains were collected after intracranial injection of chlorisondamine or intraperitoneal injection of cocaine and snap frozen. MALDI matrixes were applied directly to 14-µm brain cryosections and spectra acquired. The identity of the drugs was further confirmed by MS/MS. Careful matrix selection and tissue preparation allows for the successful detection of drugs and the mapping of their relative abundance across various regions of the brain. This new method is simple, safe, accurate, fast, cost-effective, and low in sample consumption and shows potential for imaging, pharmacokinetics, and toxicology applications. Conventional drug analysis in tissue involves tissue homogenate preparation, followed by various derivatizations1 and extraction methods. The extracts are analyzed by GC, LC, GC/MS, or LC/MS assays. Such sample pretreatments are known to introduce variation in detection. The preparation of tissue homogenate also precludes the opportunity to acquire detailed histological information for drug distribution and the interactions between drugs and biological molecules. Although widely used, conventional drug detection assays generally dissociate drug distribution and histology. Autoradiography could overcome the shortcomings of the conventional drug detection methods. When properly executed, it can reveal drug distribution at cellular or subcellular levels.2 However, it requires dedicated laboratory resources and custom-synthesized radioactive drugs that are often difficult to synthesize and costly to make. Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is well known for its robustness in handling biological samples. Recent studies by Caprioli and colleagues demonstrated that direct probing of normal and diseased tissues * To whom correspondence should be addressed. Tel: 410-550-1507. Fax: 410-550-6859. E-mail:
[email protected]. (1) Snyder, L. R., Kirkland, J. J., Glajch, J. L., Eds. Practical HPLC Method Development, 2nd ed.; John Wiley & Sons: New York, 1997; pp 101-173; pp 643-684. (2) Stumpf, W. E. J. Pharmacol. Toxicol. Methods 2005, 51, 25-40.
6682 Analytical Chemistry, Vol. 77, No. 20, October 15, 2005
by MALDI-MS could generate a wealth of information on various biomolecules over a wide mass range.3-5 Two recent studies also explored the lipid distribution in rat brain6 and lens tissue.7 Reyzer et al.8 and Troendle et al.9 also used MALDI-MS to detect anticancer drugs in tumor sections following their injection into tumor-bearing animals. Their pioneering studies support the notion that MALDI-MS could be a promising new technique for direct detection of drugs in tissues. However, their results also suggested the dire need in refinements of sample handling and instrument tuning in order to take full advantage of this new technique. Most therapeutic compounds and drugs of abuse are low molecular weight (Mw
