Study on the regioselectivity and mechanism of the aromatic hydroxylation of monofluoroanilines.

The in vitro and in vivo metabolism of monofluoroanilines was investigated. Special attention was focused on the regioselectivity of the aromatic hydroxylation by cytochromes P-450 and the mechanism by which this reaction might proceed. The results clearly demonstrate that the in vitro and in vivo regioselectivity of the aromatic hydroxylation by cytochromes P-450 is dependent on the fluoro-substituent pattern of the aromatic aniline-ring. Results from experiments with liver microsomes from differently pretreated rats demonstrate that the observed regioselectivity for the aromatic hydroxylation is not predominantly determined by the active site of the cytochromes P-450. To investigate the underlying reason for the observed regioselectivity, semi-empirical molecular orbital calculations were performed. Outcomes of these calculations show that neither the frontier orbital densities of the LUMO/LUMO + 1 (lowest unoccupied molecular orbital) of the monofluoroanilines nor the spin-densities in their NH. radicals can explain the observed regioselectivities. The frontier orbital densities of the HOMO/HOMO - 1 (highest occupied molecular orbital) of the monofluoroanilines however, qualitatively correlate with the regioselectivity of the aromatic hydroxylation. Based on these results it is concluded that the cytochrome P-450 dependent aromatic hydroxylation of monofluoroanilines does not proceed by hydrogen or electron abstraction from the aniline substrate to give an aniline-NH. radical. The results rather suggest that cytochrome P-450 catalyzed aromatic hydroxylation of monofluoroanilines proceeds by an electrophilic attack of the (FeO)3+ species of cytochrome P-450 on a specific carbon atom of the aromatic aniline-ring.     

A covalently bound photoisomerizable agonist. Comparison with reversibly bound agonists at electrophorus electroplaques

After disulphide bonds are reduced with dithiothreitol, trans-3- (α-bromomethyl)-3’-[α- (trimethylammonium)methyl]azobenzene (trans-QBr) alkylates a sulfhydryl group on receptors. The membrane conductance induced by this “tethered agonist” shares many properties with that induced by reversible agonists. Equilibrium conductance increases as the membrane potential is made more negative; the voltage sensitivity resembles that seen with 50 [mu]M carbachol. Voltage- jump relaxations follow an exponential time-course; the rate constants are about twice as large as those seen with 50 μM carbachol and have the same voltage and temperature sensitivity. With reversible agonists, the rate of channel opening increases with the frequency of agonist-receptor collisions: with tethered trans-Qbr, this rate depends only on intramolecular events. In comparison to the conductance induced by reversible agonists, the QBr-induced conductance is at least 10-fold less sensitive to competitive blockade by tubocurarine and roughly as sensitive to “open-channel blockade” bu QX-222. Light-flash experiments with tethered QBr resemble those with the reversible photoisomerizable agonist, 3,3’,bis-[α-(trimethylammonium)methyl]azobenzene (Bis-Q): the conductance is increased by cis {arrow} trans photoisomerizations and decreased by trans {arrow} cis photoisomerizations. As with Bis-Q, ligh-flash relaxations have the same rate constant as voltage-jump relaxations. Receptors with tethered trans isomer. By comparing the agonist-induced conductance with the cis/tans ratio, we conclude that each channel’s activation is determined by the configuration of a single tethered QBr molecule. The QBr-induced conductance shows slow decreases (time constant, several hundred milliseconds), which can be partially reversed by flashes. The similarities suggest that the same rate-limiting step governs the opening and closing of channels for both reversible and tethered agonists. Therefore, this step is probably not the initial encounter between agonist and receptor molecules.     

Quantitative analysis of Tenecteplase in rat plasma samples using LC-MS/MS as an alternative for ELISA

An LC-MS/MS method has been developed for the quantitative determination of a protein drug (Tenecteplase; M(W) 58,777 Da) in rat plasma. The protein was digested with trypsin without prior clean-up of the plasma sample, without the use of a label nor internal standard. A limited validation was performed to assess the linearity, the sensitivity and the specificity of the method. In addition, the developed method was applied to the quantitative analysis of Tenecteplase in rat plasma samples originating from a single-dose study in rats.     

Genome-wide differentially methylated genes in prostate cancer tissues from African-American and Caucasian men

Increasing evidence suggests that aberrant DNA methylation changes may contribute to prostate cancer (PCa) ethnic disparity. To comprehensively identify DNA methylation alterations in PCa disparity, we used the Illumina 450K methylation platform to interrogate the methylation status of 485,577 CpG sites focusing on gene-associated regions of the human genome. Genomic DNA from African-American (AA; 7 normal and 3 cancers) and Caucasian (Cau; 8 normal and 3 cancers) was used in the analysis. Hierarchical clustering analysis identified probe-sets unique to AA and Cau samples, as well as common to both. We selected 25 promoter-associated novel CpG sites most differentially methylated by race (fold change > 1.5-fold; adjusted P < 0.05) and compared the β-value of these sites provided by the Illumina, Inc. array with quantitative methylation obtained by pyrosequencing in 7 prostate cell lines. We found very good concordance of the methylation levels between β-value and pyrosequencing. Gene expression analysis using qRT-PCR in a subset of 8 genes after treatment with 5-aza-2′-deoxycytidine and/or trichostatin showed up-regulation of gene expression in PCa cells. Quantitative analysis of 4 genes, SNRPN, SHANK2, MST1R, and ABCG5, in matched normal and PCa tissues derived from AA and Cau PCa patients demonstrated differential promoter methylation and concomitant differences in mRNA expression in prostate tissues from AA vs. Cau. Regression analysis in normal and PCa tissues as a function of race showed significantly higher methylation prevalence for SNRPN (P = 0.012), MST1R (P = 0.038), and ABCG5 (P < 0.0002) for AA vs. Cau samples. We selected the ABCG5 and SNRPN genes and verified their biological functions by Western blot analysis and siRNA gene knockout effects on cell proliferation and invasion in 4 PCa cell lines (2 AA and 2 Cau patients-derived lines). Knockdown of either ABCG5 or SNRPN resulted in a significant decrease in both invasion and proliferation in Cau PCa cell lines but we did not observe these remarkable loss-of-function effects in AA PCa cell lines. Our study demonstrates how differential genome-wide DNA methylation levels influence gene expression and biological functions in AA and Cau PCa.     

Differential Effects of Drug Interventions and Dietary Lifestyle in Developing Type 2 Diabetes and Complications: A Systems Biology Analysis in LDLr?/? Mice

Excess caloric intake leads to metabolic overload and is associated with development of type 2 diabetes (T2DM). Current disease management concentrates on risk factors of the disease such as blood glucose, however with limited success. We hypothesize that normalizing blood glucose levels by itself is insufficient to reduce the development of T2DM and complications, and that removal of the metabolic overload with dietary interventions may be more efficacious. We explored the efficacy and systems effects of pharmaceutical interventions versus dietary lifestyle intervention (DLI) in developing T2DM and complications. To mimic the situation in humans, high fat diet (HFD)-fed LDLr−/− mice with already established disease phenotype were treated with ten different drugs mixed into HFD or subjected to DLI (switch to low-fat chow), for 7 weeks. Interventions were compared to untreated reference mice kept on HFD or chow only. Although most of the drugs improved HFD-induced hyperglycemia, drugs only partially affected other risk factors and also had limited effect on disease progression towards microalbuminuria, hepatosteatosis and atherosclerosis. By contrast, DLI normalized T2DM risk factors, fully reversed hepatosteatosis and microalbuminuria, and tended to attenuate atherogenesis. The comprehensive beneficial effect of DLI was reflected by normalized metabolite profiles in plasma and liver. Analysis of disease pathways in liver confirmed reversion of the metabolic distortions with DLI. This study demonstrates that the pathogenesis of T2DM towards complications is reversible with DLI and highlights the differential effects of current pharmacotherapies and their limitation to resolve the disease.     

Inhibition of human glutathione S-transferase P1-1 by the flavonoid quercetin

In the present study, the inhibition of human glutathione S-transferase P1-1 (GSTP1-1) by the flavonoid quercetin has been investigated. The results show a time- and concentration-dependent inhibition of GSTP1-1 by quercetin. GSTP1-1 activity is completely inhibited upon 1 h incubation with 100 microM quercetin or 2 h incubation with 25 microM quercetin, whereas 1 and 10 microM quercetin inhibit GSTP1-1 activity to a significant extent reaching a maximum of 25 and 42% inhibition respectively after 2 h. Co-incubation with tyrosinase greatly enhances the rate of inactivation, whereas co-incubation with ascorbic acid or glutathione prevents this inhibition. Addition of glutathione upon complete inactivation of GSTP1-1 partially restores the activity. Inhibition studies with the GSTP1-1 mutants C47S, C101S and the double mutant C47S/C101S showed that cysteine 47 is the key residue in the interaction between quercetin and GSTP1-1. HPLC and LC-MS analysis of trypsin digested GSTP1-1 inhibited by quercetin did not show formation of a covalent bond between Cys 47 residue of the peptide fragment 45-54 and quercetin. It was demonstrated that the inability to detect the covalent quercetin-peptide adduct using LC-MS is due to the reversible nature of the adduct-formation in combination with rapid and preferential dimerization of the peptide fragment once liberated from the protein. Nevertheless, the results of the present study indicate that quinone-type oxidation products of quercetin likely act as specific active site inhibitors of GSTP1-1 by binding to cysteine 47.     

Ca2+, annexins, and GTP modulate exocytosis from maize root cap protoplasts

Protoplasts isolated from root cap cells of maize were shown to secrete fucose-rich polysaccharides and were used in a patch-clamp study to monitor changes in whole-cell capacitance. Ca2+ was required for exocytosis, which was measured as an increase in cell capacitance during intracellular dialysis with Ca2+ buffers via the patch pipette. Exocytosis was stimulated significantly by small increases above normal resting [Ca2+]. In the absence of Ca2+, protoplasts decreased in size. In situ hybridization showed significant expression of the maize annexin p35 in root cap cells, differ-entiating vascular tissue, and elongating cells. Dialysis of protoplasts with maize annexins stimulated exocytosis at physiological [Ca2+], and this could be blocked by dialysis with antibodies specific to maize annexins. Dialysis with milli-molar concentrations of GTP strongly inhibited exocytosis, causing protoplasts to decrease in size. GTPgammaS and GDPbetaS both caused only a slight inhibition of exocytosis at physiological Ca2+. Protoplasts were shown to internalize plasma membrane actively. The results are discussed in relation to the regulation of exocytosis in what is usually considered to be a constitutively secreting system; they provide direct evidence for a role of annexins in exocytosis in plant cells.