Synthesis of a new long-wavelength latent fluorimetric indicator for analytes determination in the DT-Diaphorase coupling dehydrogenase assay system

We synthesized a new long-wavelength latent fluorogenic probe BQC (1) to monitor DTD activity. The fluorogenic chemical transformation of BQC triggered by DTD in the presence of NADH is through a series of tandem reactions, DTD-catalyzed benzoquinone reduction, trimethyl-locks cyclization and intramolecular urea formation, which are spontaneous and irreversible at physiological temperature in aqueous media. The fluorescence signal revealed by this process is specific and exhibited in the near red spectrum region with emission maxima at 595 nm, and it could be competitively inhibited by menadione. The fluorescent response of BQC is insensitive to various biological thiol reductants. Furthermore, pro-fluorophore BQC is a sensitive fluorimetric indicator for analytes determination in the oxygen-insensitive DTD-coupled dehydrogenases assay by including NAD(+) which will convert to NADH by reaction in the presence of analytes. This novel oxygen-insensitive assay demonstrates a good relationship in detecting 3-hydroxybutyrate and glucose-1-phosphate in 1-10 microM range, which presents to the applicability for the construction of fiber-optic biosensors in the future clinical diagnostic.     

Polyhalogenated benzo- and naphthoquinones are potent inhibitors of plant and bacterial ureases

Polyhalogenated benzo- and naphthoquinones were found to be potent inhibitors of pure ureases from Bacillus pasteurii and Canavalia ensiformis. They also inhibited ureases in whole cells of Helicobacter pylori, Klebsiella oxytoca and Proteus mirabilis. Inhibition was non-competitive with K(i) values in the micromolar range or below. Inhibition was irreversible as shown by equilibrium dialysis. Inhibitory power decreased considerably when halogens were replaced by -OH, -CN, alkoxy or alkyl groups.     

Ratio of erythro and threo forms of beta-O-4 structures in tension wood lignin

The ratio of erythro and threo forms of beta-O-4 structures in tension wood lignin was investigated by ozonation analysis of wood meal taken from various positions in the stem of yellow poplar (Liriodendron tulipifera). The proportion of the erythro form was higher in tension wood than in opposite wood, and the methoxyl group content showed a similar trend. The proportion of the erythro form and the methoxyl group content in the 7 positions in the stem lignin was correlated (correlation coefficient R=0.98), suggesting that the type of aromatic ring, syringyl or guaiacyl, is one of the factors which stereochemically controls the ratio of erythro and threo forms of beta-O-4 structures during lignin formation.     

Common anti-apoptotic roles of parkin and alpha-synuclein in human dopaminergic cells

Parkin, a product of the gene responsible for autosomal recessive juvenile parkinsonism (AR-JP), is an important player in the pathogenic process of Parkinson's disease (PD). Despite numerous studies including search for the substrate of parkin as an E3 ubiquitin-protein ligase, the mechanism by which loss-of-function of parkin induces selective dopaminergic neuronal death remains unclear. Related to this issue, here we show that antisense knockdown of parkin causes apoptotic cell death of human dopaminergic SH-SY5Y cells associated with caspase activation and accompanied by accumulation of oxidative dopamine (DA) metabolites due to auto-oxidation of DOPA and DA. Forced expression of alpha-synuclein (alpha-SN), another familial PD gene product, prevented accumulation of oxidative DOPA/DA metabolites and cell death caused by parkin loss. Our findings indicate that both parkin and alpha-SN share a common pathway in DA metabolism whose abnormality leads to accumulation of oxidative DA metabolites and subsequent cell death.     

A fluorescence-based rapid screening assay for cytotoxic compounds

A simple fluorescence-based assay was developed for the rapid screening of potential cytotoxic compounds generated by combinatorial chemistry. The assay is based on detection of nuclear green fluorescent protein (GFP) staining of a human cervical cancer cell line (HeLa) carrying an integrated histone H2B-GFP fusion gene. Addition of a cytotoxic compound to the HeLa-GFP cells results in the eventual degradation of DNA and loss of the GFP nuclear fluorescence. Using this assay, we screened 11 distinct quinone derivatives and found that several of these compounds were cytotoxic. These compounds are structurally related to plumbagin an apoptosis-inducing naphthoquinone isolated from Black Walnut. In order to determine the mechanism by which cell death was induced, we performed additional experiments with the most cytotoxic quinones. These compounds were found to induce morphological changes (blebbing and nuclear condensation) consistent with induction of apoptosis. Additional tests revealed that the cytotoxic compounds induce both necrotic and apoptotic modes of death.     

Study of the preferred modification sites of the quinone methide intermediate resulting from the latent trapping device of the activity probes for hydrolases

Use of activity probes has been demonstrated to be a powerful tool in modern chemical proteomic study. Previously we have designed and synthesized a series of mechanism-based activity probes that utilized quinone methide chemistry. Here, we characterized the trend of chemical reactivity for the reactive quinone methide intermediate 3 (QM-3) resulting from the latent trapping device. In a competition assay, the labeling of PTP1B by probe 1a was blocked by externally added cysteine without affecting the catalytic activity of the enzyme. Further sequencing analysis on the trypsin-digested peptides of probe 1a-labeled PTP1B using tandem mass spectrometry revealed that all six cysteine residues of PTP1B are capable of being modified by probe 1a. These results indicated that the sulfhydryl group of cysteine residue is the preferred nucleophile for the reactive QM-3. Our finding provides the first example in understanding the preferred amino acid residues modified by the reactive QM-3, which is also the key structural unit responsible for forming covalent bonds in many biochemical applications.     

The genotoxic effect of carcinogenic PAHs, their artificial and environmental mixtures (EOM) on human diploid lung fibroblasts

Long-term exposure to synthetic and endogenous estrogens has been associated with the development of cancer in several tissues. One potential mechanism of estrogen carcinogenesis involves catechol formation and these catechols are further oxidized to electrophilic/redox active o-quinones, which have the potential to both initiate and promote the carcinogenic process. Previously we showed that 4-hydroxyequilenin (4-OHEN) autoxidized to an o-quinone and caused a variety of damage to DNA. Since these deleterious effects could contribute to gene mutations, we investigated the Chinese hamster V79 cells to ascertain the relative ability of estradiol, 4-hydroxyestradiol, 17β-hydroxyequilenin, 4,17β-hydroxyequilenin, estrone, 4-hydroxyestrone, equilenin, and 4-hydroxyequilenin to induce the mutation of the hypoxanthine–guanine phosphoribosyltransferase (hprt) gene. All the 4-hydroxylated catechols induced significantly more colony formations in V79 cells as compared to the parent phenols at 100 nM, suggesting that the catechol estrogen metabolites are more mutagenic towards the hprt gene than estrogens. Since 4-OHEN induced the highest mutation frequency, we examined a biomarker for transformation potential of this compound in MCF-10A cells using an anchorage-independent growth assay. Although 4-OHEN induced anchorage-independent growth of these cells, the isolated clones were not able to grow as tumors in vivo when injected into nude mice. These cells were assayed for genetic changes using cDNA microarrays. Real time RT-PCR confirmation of some of the differentially expressed genes showed down-regulation of metallothionein 2A, p53, BRCA1, and c-myc. Moreover, we showed the involvement of other genes important in cell transformation and oxidative stress, strengthening the hypothesis that this mechanism plays a considerable role in 4-OHEN-induced anchorage-independent growth.     

Heating decreases epithiospecifier protein activity and increases sulforaphane formation in broccoli

Sulforaphane, an isothiocyanate from broccoli, is one of the most potent food-derived anticarcinogens. This compound is not present in the intact vegetable, rather it is formed from its glucosinolate precursor, glucoraphanin, by the action of myrosinase, a thioglucosidase enzyme, when broccoli tissue is crushed or chewed. However, a number of studies have demonstrated that sulforaphane yield from glucoraphanin is low, and that a non-bioactive nitrile analog, sulforaphane nitrile, is the primary hydrolysis product when plant tissue is crushed at room temperature. Recent evidence suggests that in Arabidopsis, nitrile formation from glucosinolates is controlled by a heat-sensitive protein, epithiospecifier protein (ESP), a non-catalytic cofactor of myrosinase. Our objectives were to examine the effects of heating broccoli florets and sprouts on sulforaphane and sulforaphane nitrile formation, to determine if broccoli contains ESP activity, then to correlate heat-dependent changes in ESP activity, sulforaphane content and bioactivity, as measured by induction of the phase II detoxification enzyme quinone reductase (QR) in cell culture. Heating fresh broccoli florets or broccoli sprouts to 60 degrees C prior to homogenization simultaneously increased sulforaphane formation and decreased sulforaphane nitrile formation. A significant loss of ESP activity paralleled the decrease in sulforaphane nitrile formation. Heating to 70 degrees C and above decreased the formation of both products in broccoli florets, but not in broccoli sprouts. The induction of QR in cultured mouse hepatoma Hepa lclc7 cells paralleled increases in sulforaphane formation.     

Evidence for the existence of PAH-quinone reductase and catechol-<Emphasis Type="Italic">O</Emphasis>-methyltransferase in <Emphasis Type="Italic">Mycobacterium vanbaalenii</Emphasis> PYR-1

Polycyclic aromatic hydrocarbon (PAH) quinone reductase (PQR) and catechol-O-methyltransferase (COMT), from the PAH-degrading Mycobacterium vanbaalenii PYR-1, were demonstrated to be constitutive enzymes located in the soluble fraction of cell extracts. PQR activities for the reduction of 9,10-phenanthrenequinone and 4,5-pyrene- quinone were 1.40±0.13 and 0.12±0.01 mol min^–1 mg-protein^–1, respectively. The exogenous catechols alizarin, anthrarobin, 2,3-dihydroxynaphthalene and esculetin inhibited PQR activity. Anthrarobin (100 M) and esculetin (100 M) inhibited 4,5-pyrenequinone reduction by 64–92%. COMT was involved in the O-methylation of 1,2-dihydroxyphenanthrene to form 1-methoxy-2-hydroxyphenanthrene and 1,2-dimethoxyphenanthrene. Both pyrene and 1-hydroxypyrene were metabolized by M. vanbaalenii PYR-1 to form 1-methoxypyrene, 1-methoxy-2-hydroxypyrene, 1-hydroxy-2-methoxypyrene and 1,2-dimethoxypyrene. Among the catechols tested, anthrarobin showed the highest COMT activity (1.06±0.04 nmol/30 min^–1 mg-protein^–1). These results suggest that the PQR and COMT activities of M. vanbaalenii PYR-1 may play an important role in the detoxification of PAH catechols.     

Thiol oxidation induced by oxidative action of adriamycin

To clarify the mechanism of the cardiotoxic action of adriamycin (ADM), the participation of free radicals from ADM in cardiotoxicity was investigated through the protective action of glutathione (GSH) or by using electron spin resonance (ESR). Oxidation of ADM by horseradish peroxidase and H₂O₂ (HRP-H₂O₂) was blocked by GSH concentration dependently. Inactivation of creatine kinase (CK) induced during interaction of ADM with HRP-H₂O₂ was also protected by GSH. Other anthracycline antitumor drugs that have a p-hydroquinone structure in the B ring also inactivated CK, and GSH inhibited the inactivation of CK. These results suggest that ADM was activated through oxidation of the p-hydroquinone in the B ring by HRP-H₂O₂. Although ESR signals of the oxidative ADM B ring semiquinone were not detected, glutathionyl radicals were formed during the interaction of ADM with HRP-H₂O₂ in the presence of GSH. ADM may be oxidized to the ADM B ring semiquinone and then reacts with the SH group. However, ESR signals of ADM C ring semiquinone, which was reductively formed by xanthine oxidase (XO) and hypoxanthine (HX) under anaerobic conditions, were not diminished by GSH, but they completely disappeared with ferric ion. These results indicate that oxidative ADM B ring semiquinones oxidized the SH group in CK, but reductive ADM C ring semiquinone radicals may participate in the oxidation of lipids or DNA and not of the SH group.