Miki Akamatsu Summary

Summary

Mechanism of substrate recognition by P-glycoproteins
(P-gp: ATP-dependent efflux pump).

• P-gp is one of ABC transporters and acts as an efflux pump with broad substrate specificity. To clarify the substrate recognition mechanism by P-gp based on QSAR analyses, screenig of various pesticides as P-gp susbstrates was carried out. As a result, it was shown that several pesticides were recognized as substrates of P-gp. In addition, one of cyclic peptides was likely to be a substrate of P-gp. Then 3D-QSAR, CoMFA was performed for a pesticide and its derivatives. In addition, protein modeling of human P-gp was carried out for docking of ligands.

Mechanism of substrate recognition by cytochrome p450s
(Enzymes involved in metabolism).

• Human cytochrome p450s （CYPs） are primarily membrane-associated proteins, located either in the inner membrane of mitochondria or in the endoplasmic reticulum of cells. CYPs metabolise thousands of endogenous and exogenous compounds. Most CYPs can metabolize multiple substrates, and many can catalyze multiple reactions. To clarify the substrate recognition mechanism by CYPs based on QSAR analyses, firstly one kind of pesticides and CYP3A4 were used. Metabolites of the pesticide were isolated and purified. The chemical structures of the metabolites were also identified by NMR and LC/MS. In addition, since a main metabolite by both CYPs had chirality, the stereoselectivity in the metabolic reaction by CYPs was discussed. In silico prediction of metabolite structures by CYP3A4 and CYP2C19 was also attempted.

Permeation of drugs across artificial model membranes and prediction of permeability across monolayers of human intestinal epithelial (Caco-2) cells.

• It is important to examine transport of various chemicals across the intestinal epithelium from the point of view of the development of orally bioavailable therapeutic agents. The permeability of various pharmaceuticals and related compounds across artificial lipid membranes was measured to evaluate absorption of the compounds by the transcellular route. The relationship between the Caco-2 cell permeability coefficient in references and the measured artificial membrane permeability coefficient of compounds was then determined.

Analysis of pesticide residues in environment around the suburban
agricultural fields near Bangkok (Thailand) and Hue (Vietnam)

• Used pesticides were surveyed at the suburban agricultural fields of Bangkok, Thailand, to know whether pesticides are used safely and appropriately. In last two years, river bottom and field soils around the area were sampled and pesticide residues in the samples were analyzed. A few pesticides were detected in several samples although the amount was small. In this year, we re-visited the places where relatively high amount of pesticides were detected last year. However, pesticide residues in the soils of the places were kept at the safety levels. We also visited agricultural fields in Hue area in Vietnam and surveyed the pesticide use in the area. In addition, we sampled several field soils and analyzed pesticide residues in the samples.

Interaction mechanism of the neurotoxic insecticides with the receptors.

• Chloronicotinyl insecticides including imidacloprid act at the nicotinic acetylcholine receptor of insects as an agonist. To clarify the interaction mechanism of the insecticides with the receptors, the acetylcholine receptor model (wild type and mutated type) was constructed based on the crystallographic structure of acetylcholine binding protein by computer graphics and binding of the model receptor and imidacloprid was simulated by a molecular mechanics calculation. The result was explainable the experimental results.
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