Alzheimer's disease and depression are common neurological disorders. So far, the first one has been treated with cholinesterase inhibitors and glutamate receptor antagonists. For the second one monoamine oxidase inhibitors can be used among other things. In order to improve treatment, this moleculs must be able to cross the blood-brain barrier to reach the site of action in the brain. We have developed and optimized a method for preparing blood plasma and brain samples to measure the concentrations of atenolol and cholinesterase inhibitors GUK-901, donepezil and monoamine oxidase inhibitor GDK-494, GDK-490C, GDK487, SAD-18. In examining the passage of the blood-brain barrier, atenolol and donepezil can be used as model reference compounds. Atenolol has low permeability and donepezil has high permeability. Human blood plasma and the brains of experimental animals have been enriched with standard solutions of the test compounds, and these were, in turn, purified by solid-phase extraction. Biological samples contain proteins, phospholipids and other impurities that can affect the ionization of analytes. Therefore, impurties must be removed before the drug concentrations are measured with an ultra-high resolution liquid chromatograph connected to a mass detector. During the sample preparation method development, we have examined the repeatability of the solid phase extraction, the influence of the biological matrix, the linearity of the responses, and determined the lower limit of quantification. The repeatability of extraction has been evaluated by the relative standard deviation. All results were within the desired 15%, except for compounds GDK-494 and SAD-18 in the plasma samples, which had worse repeatability. The linearity of the responses has been checked with the calibration curves. For the enriched plasma samples and one calibration curve with enriched brain tissue, the Pearson correlation coefficient values were above 0.999, the other values were above 0.99. The results at this stage of development are considered relevant for the in vivo research. For further animal model studies, a validation of the method should be performed as well. The distribution of GUK-901 between blood plasma and brain has been determined on real biological samples. The results have shown that GUK-901 successfully crosses the blood-brain barrier.
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