Integrated photocatalytic micropillar nanoreactor electrospray ionization chip for mimicking phase I metabolic reactions

Abstract

We developed a nanoreactor chip based system to mimic phase I metabolic reactions of small organic compounds. The microchip, made of silicon, has an anatase-phase titanium dioxide (TiO(2)) nanolayer coating for photocatalysis and an integrated electrospray ionization (ESI) tip for direct mass spectrometric (MS) analysis. This novel method for mimicking phase I metabolic reactions uses an on-chip TiO(2)-nanolayer and an external UV-lamp to induce photocatalyzed chemical reactions of drug compounds in aqueous solutions. The reactions of selected test compounds (verapamil, metoprolol, propranolol, lidocaine, 2-acetamidofluorene, and S-methylthiopurine) produced mostly the same main products as phase I metabolic reactions induced by human liver microsomes, rat hepatocytes, or cytochrome P enzymes, showing hydroxylation, dehydrogenation, and dealkylations as the main photocatalytic reactions. With this method it is possible to detect reactive and toxic products (mimicking reactive metabolites) due to the absence of biological matrices and an immediate analysis. The method used is sensitive: only 20-40 pmol (1-10 ng) of a substrate was needed for the experiment, thus it provides an inexpensive method for screening possible metabolites of new drug candidates. Due to small dimensions of the microchip, diffusion lengths are suitable for the high reaction rates, thus providing a rapid analysis as the reaction products can be detected and identified directly after the photoinduced reactions have occurred. The method shows a similar performance to that of electrochemistry, a commonly used technique for mimicking phase I metabolism.

Miniaturization of electrochemical cells for mass spectrometry

“…By careful design, this transit time can be significantly reduced, as demonstrated by several authors, using the spray interface itself as electrochemical cell [30], or by using photocatalytically active materials in a spray needle [44]. The reported reaction time is a rather long 15 min in the latter photocatalytic design, although the principle might allow a faster transit.…”

“…An Si/TiO2 openchamber microreactor was integrated with a micropillar-based electrospray tip [44], and the photocatalytic properties of TiO2 were employed to oxidize a variety of drug compounds. A drop of analyte was applied to the reactor, which contained etched micropillars to increase the surface area, and a UV lamp enabled photocatalytic processes to take place.…”

TiO2 Photocatalyzed Oxidation of Drugs Studied by Laser Ablation Electrospray Ionization Mass Spectrometry

“…Since the major class of reactions in phase I metabolism are oxidation reactions [ 3 ], also non-enzymatic methods could be used for rapid phase I reactions to eliminate drug candidates with an undesired metabolism. Apart from electrochemistry approaches [ 4 , 5 ], titanium dioxide (TiO 2 ) photocatalysis is a simple non-enzymatic method to generate oxidation reaction products similar to those obtained by phase I biochemical transformations [ 6 – 13 ].…”

Photocatalysis as a Tool for in Vitro Drug Metabolism Simulation: Multivariate Comparison of Twelve Metal Oxides on a Set of Twenty Model Drugs

“…A wide range of photocatalysts and significant differences in their properties indicate a continuous need to look for the most ideal one with regard to its use. The ability to decompose organic compounds under the influence of irradiation with appropriate energy has initiated the use of photocatalysts in the simulation of drug metabolism processes [33][34][35][36][37][38][39][40][41]. The ability to produce reactive oxygen species entering redox reactions with medicine molecules allows to mimic the biochemical reactions that the drug undergoes after administration to the patient.…”