ABSTRACT
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 (MALDI-MS) 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-mum 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.
Subject(s)
Brain/metabolism , Chlorisondamine/chemistry , Cocaine/chemistry , Animals , Brain/drug effects , Chlorisondamine/administration & dosage , Chlorisondamine/pharmacokinetics , Cocaine/administration & dosage , Cocaine/pharmacokinetics , Drug Delivery Systems , Injections, Intraperitoneal , Injections, Intraventricular , Male , Mass Spectrometry , Molecular Structure , Molecular Weight , Rats , Rats, Sprague-Dawley , Sensitivity and Specificity , Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization/methods , Tissue DistributionABSTRACT
Chlorisondamine (CHL), a neuronal nicotinic ganglionic blocker, when injected in the cerebral ventricle of rats chronically blocks the increase in locomotion and rearing by subcutaneous nicotine injection. The blocking of the ion channel(s) prevents nicotine from exerting its rewarding effects on the CNS. When administered intraperitoneally, a dose 400-500 times the intracerebroventricular one is needed to cross the blood-brain barrier and to generate the same level of nicotine antagonism, resulting in severe side-effects, thus making it unlikely to be used as a therapeutical compound. Three CHL analogues, 2-(indolin-1-yl)-N,N,N-trimethylethanaminium iodide, 2-(1,3-dioxoisoindolin-2-yl)- N,N,N-trimethylethanaminium iodide, and 2-(1H-indole-3-carboxamido)- N,N,N-trimethylethanaminium iodide, were synthesized in the hope of circumventing the parent compound's shortcomings. They all share a modified indole ring, lack the four chlorines CHL carries, and have one tertiary amine and one quaternary amine. The CHL analogues form noncovalent complexes with an epitope of the alpha-2 nicotinic receptor subunit, GEREE(p)TEEEEEEEDEN, previously proposed as the possible site of CHL interaction. Complexes were analyzed using matrix-assisted laser desorption/ionization mass spectrometry for comparison with CHL. Overall, all three analogues showed better affinity than CHL for complex formation with both the nonphosphorylated and phosphorylated epitopes.
