Nobuyoshi Mikami

Identification of a Novel Basic Helix-Loop-Helix-PAS Factor, NXF, Reveals a Sim2 Competitive, Positive Regulatory Role in Dendritic-Cytoskeleton Modulator Drebrin Gene Expression

ABSTRACT Sim2, a basic helix-loop-helix (bHLH)-PAS transcriptional repressor, is thought to be involved in some symptoms of Downs syndrome. In the course of searching for hypothetical Sim2 relatives, we isolated another bHLH-PAS factor, NXF. NXF was a novel gene and was selectively expressed in neuronal tissues. While no striking homolog of NXF was found in vertebrates, a Caenorhabditis elegans putative transcription factor, C15C8.2, showed similarity in the bHLH-PAS domain. NXF had an activation domain as a transcription activator, and Arnt-type bHLH-PAS subfamily members were identified as the heterodimer partners of NXF. The NXF/Arnt heterodimer was capable of binding and activating a subset of Sim2/Arnt target DNA variants, and Sim2 could compete with the NXF activity on the elements. We showed that Drebrin had several such NXF/Arnt binding elements on the promoter, which could be direct or indirect cross talking points between NXF (activation) and Sim2 (repression) action. Drebrin has been reported to be engaged in dendritic-cytoskeleton modulation at synapses, and such a novel NXF signaling system on neural gene promoter may be a molecular target of the adverse effects of Sim2 in the mental retardation of Downs syndrome.

Stereospecificity in toxicity of the optical isomers of EPN.

SummaryWhile the optical isomers of EPN were equally toxic to mice, (+)-EPN was 2.9 fold and 4.0 fold more toxic to houseflies and rice stem borer larvae, respectively, than the (−)-isomer. In addition, (−)-EPN produced paralysis of the legs in hens about 10 to 14 days after dosing, whereas (+)-EPN caused no paralytic effects. Thus, (+)-EPN appears to be a more appropriate insecticide than the racemic compound, since it combines high toxicity to insects and no delayed neurotoxicity in hens.

α2-Macroglobulin: A Novel Cytochemical Marker Characterizing Preneoplastic and Neoplastic Rat Liver Lesions Negative for Hitherto Established Cytochemical Markers

We tried to identify a novel marker characteristic for rat hepatocellular preneoplastic and neoplastic lesions, undetectable by well established cytochemical markers. Glutathione S-transferase placental (GST-P)-negative hepatocellular altered foci (HAF), hepatocellular adenoma (HCA), and hepatocellular carcinoma (HCC) were generated by two initiation-promotion models with N-nitrosodiethylamine (NDEN) and peroxisome proliferators, Wy-14,643 and clofibrate. Total RNAs isolated from laser-microdissected GST-P-negative HAF (amphophilic cell foci) and adjacent normal tissues were applied to microarray analysis. As a result, five up-regulated genes were identified, and further detailed examinations of the gene demonstrating most fluctuation, ie, that for alpha(2)-macroglobulin (alpha(2)M) were performed. In reverse transcriptase-polymerase chain reaction, alpha(2)M mRNA was overexpressed not only in amphophilic GST-P-negative HAF but also in amphophilic GST-P-negative HCA and HCC. In situ hybridization showed accumulation of alpha(2)M mRNA to be evenly distributed within GST-P-negative HAF (predominantly amphophilic cell foci). Distinctive immunohistochemical staining for alpha(2)M could be consistently demonstrated in GST-P-negative HAF, HCA, and HCC induced not only by peroxisome proliferators but also N-nitrosodiethylamine alone. Thus our findings suggest that alpha(2)M is an important novel cytochemical marker to identify hepatocellular preneoplastic and neoplastic lesions, particularly amphophilic cell foci, undetectable by established cytochemical markers and is tightly linked to rat hepatocarcinogenesis.

Development of the Simulation Model InPest for Prediction of the Indoor Behavior of Pesticides

The objective was to develop a computer software package (to be registered as InPest) that runs under Microsoft Excel on a personal computer to help in the risk assessment of indoor-use pesticides for both applicators and indoor occupants for various methods of application including space spraying, electric vaporizing, broadcast spraying, and residual spraying. For space spraying, the movement of the pesticide in a sprayed room including droplet settlement, permeation into the floor, degradation, transference, and discharge by ventilation were described as precisely as possible by various physicochemi-cal equations. The equations thus obtained were then incorporated into the Fugacity model (Level IV). When pesticide information regarding molecular weight, vapor pressure, water solubility, and octanol/water partition coefficient is available, InPest is able to simulate the time-dependent concentrations of the pesticide in the air and residual amounts on floor, wall, and ceiling materials under various conditions. Simulation data indicate that the predicted behavior of pesticides fully agrees with the measured data. Based on the predicted concentrations in the air and amounts of residue on the floor, the levels of exposure to room occupants via inhalation, dermal, or oral intake can be computed and compared with the mammalian toxicological data. Thus, InPest is a powerful tool for evaluating the safety of indoor-use pesticides with regard to human health.

DEGRADATION OF PYRETHROID INSECTICIDES IN THE FIELD

Abstract Permethrin, cypermethrin, deltamethrin, fenvalerate and fenpropathrin are highly insecticidal pyrethroids currently used for agriculture. The pyrethroids are photodecomposed mainly by isomerization of the cyclopropane ring and αR/αS epimerization in water and on plant foliage, with subsequent cleavage of the ester bond in water, except for fenvalerate which primarily undergoes photodecarboxylation and ester bond cleavage. The pyrethroids are metabolized in plant by hydrolysis, and by oxidation at the 2′- and the 4′-positions of the alcohol moiety and at the gem-dimethyl group of the acid moiety of permethrin and deltamethrin, and to a lesser extent by hydration of the cyano substituent to the corresponding amide. These sites are also involved in metabolism of the pyrethroids in soil and of fenvalerate in the aquatic model ecosystem consisting of soil, fish, daphnia, snail and algae. The hydrolytic products and their oxidized derivatives are further degraded in soil ultimately leading to carbon dioxide from radiolabels in various positions of the molecule, and are converted in plants to a variety of glycoside conjugates. These plant conjugated metabolites are bioavailable in rats. The aglycones liberated due to microbial attack in the intestine are rapidly metabolized followed by complete excretion. Conjugation with glucose lowers the acute oral toxicity in mice.

Stereoselectivity in Toxicity and Acetylcholinesterase Inhibition by the Optical Isomers of Papthion® and Papoxon

The synthesis of Papthion® and papoxon, optically active at the α-carbon of the α-ethoxycarbonylbenzyl moiety, was described. The optical isomers of papthion and papoxon exhibited a marked selectivity in the toxicity and anticholinesterase activity, respectively. d-Papthion was more toxic to mosquitoes, rice stem borers, diamond back moths and mice than the l-isomer. In contrast, l-papthion was more toxic to houseflies, and less toxic to mice and other insects than the d-isomer. Selectivity in toxicity appears to be directly related to the selective inhibition in vitro of acetylcholinesterase by the optical isomers of papoxon.

Molecular orbital and experimental studies on the photoinduced decarboxylation of pyrethroid model esters

A series of pyrethroid model esters with various substituents in the acid or alcohol moiety have been irradiated by u.v.-radiation (λ > 220 nm). The main reaction is decarboxylation, as evidenced by gas chromatographic (g.c.) and mass spectrometric (m.s.) analyses. In the photoinduced decarboxylation reaction, the substituent effect on the main transition, which occurs via carbonyl excitation, and on the reactivity of a radical intermediate have been examined by semiempirical molecular-orbital calculations (MNDO and CNDO/S). It has been found that the change of benzyl carbon–oxygen bond strength in the excited states is one of the important factors in determining the yield of the decarboxylated product.