Inhibition of epidermal growth factor-induced cell transformation and activator protein 1 activation by [6]-gingerol. (49/1002)

Many spices, including plants of the ginger family, possess anticarcinogenic activity. However, the molecular mechanisms by which they exert their antitumorigenic effects are unknown. Activator protein 1 (AP-1) has a critical role in tumor promotion, and blocking of tumor promoter-induced activation of AP-1 inhibits neoplastic transformation. Epidermal growth factor induces cell transformation and AP-1 activity. The purpose of this study was to investigate the effect of two structurally related compounds of the ginger family, [6]-gingerol and [6]-paradol, on EGF-induced cell transformation and AP-1 activation. Our results provide the first evidence that both block EGF-induced cell transformation but act by different mechanisms.  (+info)

Pathways for the degradation of m-cresol and p-cresol by Pseudomonas putida. (50/1002)

A comparison of the oxidation rates of various compounds by whole cells of Pseudomonas putida 3, 5 indicated that m-cresol is metabolized by oxidation to 3-hydroxybenzoate followed by hydroxylation to gentisate, the ring-fission substrate, when grown with 3, 5-xylenol. However, when m-cresol was the growth substrate, similar experiments suggested a different pathway involving a methyl-substituted catechol, and ring-fission by meta cleavage. Assays of ring-fission enzymes in cell-free extracts confirmed that different pathways are induced by the two growth substrates. 3, 5-Xylenol-grown cells contained high levels of gentisate oxygenase and only very small amounts of catechol oxygenase, whereas gentisate ocygenase could not be detected in m-cresol-grown cells, but levels of catechol oxygenase were greatly increased. Extracts of m-cresol-grown cells also contained 2-hydroxymuconic semialdehyde dehydrogenase and hydrolase, whose specificities enable them to metabolize the ring-fission products from catechol, 3-methylcatechol, and 4-methylcatechol. This catechol pathway is also used by m-cresol-grown cells for p-cresol metabolism. In contrast, the results for cells grown with p-cresol point to an alternative pathway involving oxidation to 4-hydroxybenzoate and hydrosylation to protocatechuate as ring-fission substrate. Extracts of these cells contained high levels of protocatechuate oxygenase and only small amounts of catechol oxygenase.  (+info)

Altering catalytic properties of 3-chlorocatechol-oxidizing extradiol dioxygenase from Sphingomonas xenophaga BN6 by random mutagenesis. (51/1002)

The 2,3-dihydroxybiphenyl 1,2-dioxygenase from Sphingomonas xenophaga strain BN6 (BphC1) oxidizes 3-chlorocatechol by a rather unique distal ring cleavage mechanism. In an effort to improve the efficiency of this reaction, bphC1 was randomly mutated by error-prone PCR. Mutants which showed increased activities for 3-chlorocatechol were obtained, and the mutant forms of the enzyme were shown to contain two or three amino acid substitutions. Variant enzymes containing single substitutions were constructed, and the amino acid substitutions responsible for altered enzyme properties were identified. One variant enzyme, which contained an exchanged amino acid in the C-terminal part, revealed a higher level of stability during conversion of 3-chlorocatechol than the wild-type enzyme. Two other variant enzymes contained amino acid substitutions in a region of the enzyme that is considered to be involved in substrate binding. These two variant enzymes exhibited a significantly altered substrate specificity and an about fivefold-higher reaction rate for 3-chlorocatechol conversion than the wild-type enzyme. Furthermore, these variant enzymes showed the novel capability to oxidize 3-methylcatechol and 2,3-dihydroxybiphenyl by a distal cleavage mechanism.  (+info)

Decreases in phenytoin hydroxylation activities catalyzed by liver microsomal cytochrome P450 enzymes in phenytoin-treated rats. (52/1002)

Phenytoin, 5,5-diphenylhydantoin, is a widely used anticonvulsant agent with a variety of toxicities, including drug interactions. The formation of four oxidative metabolites, 4'-hydroxylated (4'-HPPH), 3'-hydroxylated (3'-HPPH), a catechol (3',4'-diHPPH), and the 3',4'-dihydrodiol form of phenytoin was examined in rat liver microsomes. In 11 cDNA-expressed rat P450 enzymes tested, CYP2C6 had the highest activities in 4'- and 3'-HPPH formation from phenytoin, followed only by CYP2C11. In contrast, CYP2C11 had high activity for 3',4'-diHPPH formation from 4'-HPPH, followed by CYP2C6. The rates of 4'-HPPH and 3',4'-diHPPH formation from phenytoin in liver microsomes in the presence of NADPH were significantly decreased by oral administration of phenytoin (300 mg/kg for 20 days) to rats, despite the increase in P450 contents. However, the cumene hydroperoxide-supported formation of 3',4'-dihydrodiol and 4'-HPPH from phenytoin was induced by phenytoin administration. Hydrogen peroxide formation in reaction mixtures with NADPH was induced by the administration of phenytoin; however, the coupling ratio of phenytoin oxidation was decreased in phenytoin-induced liver microsomal P450 systems. These results suggested that phenytoin could not stimulate its own apparent oxidative metabolism by liver P450s induced with phenytoin administration. The increase of unmetabolized phenytoin and byproducts of oxygen generated in the phenytoin-induced liver microsomal P450 system may be involved in phenytoin-related drug toxicity.  (+info)

Effects of pH and metal ions on antioxidative activities of catechins. (53/1002)

The Effects of pH on antioxidative activities of catechol, pyrogallol, and four catechins, and effects of metal ions (Al3+, Ca2+, Cd2+, Co2+, Cr3+, Cu2+, Fe2+, Fe3+, K+, Mg2+, Mn2+, Na+, and Zn2+) on antioxidative activities of (-)-epigallocatechin gallate (EGCG) were studied by an oxygen electrode method. The antioxidative activities of catechins were high and constant at pH 6-12, but decreased in acidic and strong alkaline solutions. Copper(II) ion the most strongly increased the antioxidative activity of EGCG among these metal ions examined, but iron(II) ion largely inhibited the antioxidative activity of EGCG. These effects are discussed considering the formation of metal complexes with catechins and the change in oxidation potentials.  (+info)

Amine oxidase-like activity of polyphenols. Mechanism and properties. (54/1002)

Polyphenols in several oxidation systems gained amine oxidase-like activity, probably due to the formation of the corresponding quinones. In the presence of Cu(II), o- and p-phenolic compounds exhibited amine oxidase-like activity, whereas only the o-phenolic compounds showed the activity in the presence of 1,1-diphenyl-2-picrylhydrazyl radical. The activity was determined by measuring the conversion of benzylamine to benzaldehyde by HPLC. Moreover, gallic acid, chlorogenic acid, and caffeic acid, which are plant polyphenols, converted the lysine residue of bovine serum albumin to alpha-amino-adipic semialdehyde residue, indicating lysyl oxidase-like activity. We also characterized the activity of pyrocatechol, hydroquinone, and pyrogallol in the presence of Cu(II). The oxidative deamination was accelerated at a higher pH, and required O2 and transition metal ions. Furthermore, EDTA markedly inhibited the reaction but not beta-aminopropionitrile, which is a specific inhibitor of lysyl oxidase. Catalase significantly inhibited the oxidation, implying the participation of hydroxyl radical in the reaction, but superoxide dismutase stimulated the oxidation, probably due to its radical formation activity. We discussed the mechanism of the oxidative deamination by polyphenols and the possible significance of the activity for biological systems.  (+info)

Molecular mechanism for agonist-promoted alpha(2A)-adrenoceptor activation by norepinephrine and epinephrine. (55/1002)

We present a mechanism for agonist-promoted alpha(2A)-adrenergic receptor (alpha(2A)-AR) activation based on structural, pharmacological, and theoretical evidence of the interactions between phenethylamine ligands and alpha(2A)-AR. In this study, we have: 1) isolated enantiomerically pure phenethylamines that differ both in their chirality about the beta-carbon, and in the presence/absence of one or more hydroxyl groups: the beta-OH and the catecholic meta- and para-OH groups; 2) used [(3)H]UK-14,304 [5-bromo-N-(4,5-dihydro-1H-imidazol-2-yl)-6-quinoxalinamine; agonist] and [(3)H]RX821002 [2-(2-methoxy-1,4-benzodioxan-2-yl)-2-imidazoline; antagonist] competition binding assays to determine binding affinities of these ligands to the high- and low-affinity forms of alpha(2A)-AR; 3) tested the ability of the ligands to promote receptor activation by measuring agonist-induced stimulation of [(35)S]GTPgammaS binding in isolated cell membranes; and 4) used automated docking methods and our alpha(2A)-AR model to predict the binding modes of the ligands inside the alpha(2A)-AR binding site. The ligand molecules are sequentially missing different functional groups, and we have correlated the structural features of the ligands and ligand-receptor interactions with experimental ligand binding and receptor activation data. Based on the analysis, we show that structural rearrangements in transmembrane helix (TM) 5 could take place upon binding and subsequent activation of alpha(2A)-AR by phenethylamine agonists. We suggest that the following residues are important in phenethylamine interactions with alpha(2A)-AR: Asp113 (D(3.32)), Val114 (V(3.33)), and Thr118 (T(3.37)) in TM3; Ser200 (S(5.42)), Cys201 (C(5.43)), and Ser204 (S(5.46)) in TM5; Phe391 (F(6.52)) and Tyr394 (Y(6.55)) in TM6; and Phe411 (F(7.38)) and Phe412 (F(7.39)) in TM7.  (+info)

Characterization of a high-voltage-activated IA current with a role in spike timing and locomotor pattern generation. (56/1002)

Transient A-type K+ channels (I(A)) in neurons have been implicated in the delay of the spike onset and the decrease in the firing frequency. Here we have characterized biophysically and pharmacologically an I(A) current in lamprey locomotor network neurons that is activated by suprathreshold depolarization and is specifically blocked by catechol at 100 microM. The biophysical properties of this current are similar to the mammalian Kv3.4 channel. The role of the I(A) current both in single neuron firing and in locomotor pattern generation was analyzed. The I(A) current facilitates Na+ channel recovery from inactivation and thus sustains repetitive firing. The role of the I(A) current in motor pattern generation was examined by applying catechol during fictive locomotion induced by N-methyl-d-aspartate. Blockade of this current increased the locomotor burst frequency and decreased the firing of motoneurons. Although an alternating motor pattern could still be generated, the cycle duration was less regular, with ventral roots bursts failing on some cycles. Our results thus provide insights into the contribution of a high-voltage-activated I(A) current to the regulation of firing properties and motor coordination in the lamprey spinal cord.  (+info)