Lipoxygenase-mediated hydrogen peroxide-dependent N-demethylation of N,N-dimethylaniline and related compounds

Efficient and Selective Photogeneration of Stable N-Centered Radicals via Controllable Charge Carrier Imbalance in Cesium Lead Halide Nanocrystals

Despite the versatility of semiconductor nanocrystals (NCs) in photoinduced chemical processes, the generation of stable radicals has been more challenging due to reverse charge transfer or charge recombination even in the presence of sacrificial charge acceptors. Here, we show that cesium lead halide (CsPbX3) NCs can selectively photogenerate either aminium or aminyl radicals from amines, taking advantage of the controllable imbalance of the electron and hole populations achieved by varying the solvent composition. Using dihalomethane as the solvent, irreversible removal of the electrons from CsPbX3 NCs enabled by the photoinduced halide exchange between the NCs and the dihalomethane resulted in efficient oxidative generation of the aminium radical. In the absence of dihalomethane in solvent, the availability of both electrons and holes resulted in the production of an aminyl radical via sequential hole transfer and reductive N-H bond dissociation. The negative charge of the halide ions on the NC's lattice surface appears to facilitate the aminyl radical production, competing favorably with the reversible charge transfer reverting to the reactant.

Redox inactive metal ion triggered N-dealkylation by an iron catalyst with dioxygen activation: a lesson from lipoxygenases

Utilization of dioxygen as the terminal oxidant at ambient temperature is always a challenge in redox chemistry, because it is hard to oxidize a stable redox metal ion like iron(III) to its high oxidation state to initialize the catalytic cycle. Inspired by the dioxygenation and co-oxidase activity of lipoxygenases, herein, we introduce an alternative protocol to activate the sluggish iron(III) species with non-redox metal ions, which can promote its oxidizing power to facilitate substrate oxidation with dioxygen, thus initializing the catalytic cycle. In oxidations of N,N-dimethylaniline and its analogues, adding Zn(OTf)2 to the [Fe(TPA)Cl2]Cl catalyst can trigger the amine oxidation with dioxygen, whereas [Fe(TPA)Cl2]Cl alone is very sluggish. In stoichiometric oxidations, it has also been confirmed that the presence of Zn(OTf)2 can apparently improve the electron transfer capability of the [Fe(TPA)Cl2]Cl complex. Experiments using different types of substrates as trapping reagents disclosed that the iron(IV) species does not occur in the catalytic cycle, suggesting that oxidation of amines is initialized by electron transfer rather than hydrogen abstraction. Combined experiments from UV-Vis, high resolution mass spectrometry, electrochemistry, EPR and oxidation kinetics support that the improved electron transfer ability of iron(III) species originates from its interaction with added Lewis acids like Zn(2+) through a plausible chloride or OTf(-) bridge, which has promoted the redox potential of iron(III) species. The amine oxidation mechanism was also discussed based on the available data, which resembles the co-oxidase activity of lipoxygenases in oxidative dealkylation of xenobiotic metabolisms where an external electron donor is not essential for dioxygen activation.

Stink bug predator kills prey with salivary non-proteinaceous compounds

Podisus nigrispinus Dallas (Hemiptera: Pentatomidae) is a predator insect with potential applications in biological control because both nymphs and adults have been shown to prey on other insect pests by injection of toxic salivary gland contents. This study identified non-proteinaceous compounds with insecticidal activity from the saliva of P. nigrispinus in Anticarsia gemmatalis. In particular, the ether extract from P. nigrispinus saliva led to mortality in A. gemmatalis larvae, with a LC50 = 2.04 μL and LC90 = 3.27 μL. N,N-dimethylaniline and 1,2,5-trithiepane fractions were identified as non-proteinaceous extract components. N,N-dimethylaniline had a LC50 = 136.1 nL and LC90 = 413.8 nL, suggesting that it could be responsible for toxicity in P. nigrispinus saliva.

Computational approach to characterization of human liver drug-metabolizing enzymes

Cytochromes P450 are the key enzymes for activating and inactivating many drugs; individual expression levels of CYPs may play a crucial role in drug safety and drug efficacy. Statistical comparison of biochemical profiles of 23 human liver microsomes have been used to characterize human liver samples. The profile included 12 parameters, namely activity of NADPH-cytochrome P450 reductase, cytochrome P450 content and cytochrome P450-dependent monooxygenase activities with marker substrates. Unsupervised statistical methods including cluster analysis and principal component analysis revealed with very high confidence the presence of two groups. Difference between the groups was explained by peculiarities of reductase activity and cytochrome P450 enzyme activities with 7-ethoxyresorufin, 7-methoxyresorufin, 7-methoxycoumarin, 7-benzyloxyresorufin and 7-benzyloxyquinoline. Results of biochemical assays coupled with multidimensional data analysis can be further used for targeted proteomic profiling of microsome oxidation mechanisms.

Characterization of human liver cytochromes P450 by combining the biochemical and proteomic approaches

Highly purified human liver microsomes were processed by a combination of the biochemical and proteomic methods. Microsomes were purified from the morphologically normal liver tissue obtained from the resected and discarded masses of surrounding liver upon surgical treatment for hemangioma (control) or hepatic metastases arising from colon cancer (pathology). Proteins of each sample were separated by two-dimensional (2-DE) and one-dimensional electrophoresis (1-DE); selected gel regions were excised, in-gel digested and analyzed by matrix-assisted laser desorption-ionization time-of-flight (MALDI-TOF) mass spectrometry. Analysis of collected fingerprints has revealed a total of 13 microsomal membrane proteins involved in the biotransformation of xenobiotics. These were disulfide isomerase, flavine monooxygenase, NADPH-cytochrome P450 reductase and 10 cytochrome P450 forms, namely: CYPs 1B1, 2A6, 2E1, 2C8, 2C9, 2C10, 2D6, 3A4, 4A11, 4F2. These same samples were characterized by the enzymatic assays using the marker substrates for CYPs 1A, 2B, 3A4, 2C and 2E1. Correlations between mass spectrometric data and enzymatic activities were investigated to demonstrate the manner in which the functional and structural aspects of proteomics meet each other in the field of cytochromes P450.

Potential inhibition of cytochrome P450 3A4 by propofol in human primary hepatocytes

AIM: Hepatic cytochrome P450 isoenzymes constitute a superfamily of hemoproteins that play a major role in the metabolism of endogenous compounds and in the detoxification of xenobiotic molecules. P450 3A4 is one of the most important forms in human being, and mediates the metabolism of around 70% of therapeutic drugs and endogenous compounds. Propofol, a widely used intravenous anesthetic drug, is known to inhibit cytochrome P450 activities in isolated rat hepatocytes. The goal of this study was to evaluate the potential efficacy of propofol on P450 3A4 in a dose-dependent manner to understand its drug-drug interaction.

METHODS: Hepatocytes were isolated from liver specimens from hepatic angioma patients undergone hepatic surgery. Primary incubated hepatocytes were treated with 0, 0.01, 0.05, 0.1, 0.5, and 1.0 mM propofol for 24 hours. P450 3A4 activity was measured with Nash’s colorimetry. The protein expression was assessed by Western blot analysis.

RESULTS: A dose-dependent inhibitory effect of propofol was observed in cytochrome P450 3A4 activity. A minimal dosage of propofol (0.01 mM) induced a significant inhibition of P450 3A4 activity, although its regular dosages (0.01-0.1 mM) showed no inhibitory effect on the cellular protein expression of P450 3A4.

CONCLUSION: Propofol may be a potential CYP3A4 inhibitor as this anesthetic can inhibit isoenzyme activity significantly and reduce the metabolic rate of CYP3A4 substrates. This inhibition occurs at post-expression level, and concentration of propofol used clinically does not affect CYP3A4 protein expression. propofol may thus induce drug interaction of cytochrome P450 3A4 activity at the dosage used clinically.

Different alterations of cytochrome P450 3A4 isoform and its gene expression in livers of patients with chronic liver diseases

AIM: To determine whether parenchymal cells or hepatic cytochrome P450 protein was changed in chronic liver diseases, and to compare the difference of CYP3A4 enzyme and its gene expression between patients with hepatic cirrhosis and obstructive jaundice, and to investigate the pharmacologic significance behind this difference.

METHODS: Liver samples were obtained from patients undergoing hepatic surgery with hepatic cirrhosis (n = 6) and obstructive jaundice (n = 6) and hepatic angeioma (controls, n = 6). CYP3A4 activity and protein were determined by Nash and western bloting using specific polychonal antibody, respectively. Total hepatic RNA was extracted and CYP3A4cDNA probe was prepared according the method of random primer marking, and difference of cyp3a4 expression was compared among those patients by Northern blotting.

RESULTS: Compared to control group, the CYP3A4 activity and protein in liver tissue among patients with cirrhosis were evidently reduced. (P < 0.01) Northern blot showed the same change in its mRNA levels. In contrast, the isoenzyme and its gene expression were not changed among patients with obstructive jaundice.

CONCLUSION: Hepatic levels of P450s and its CYP3A4 isoform activity were selectively changed in different chronic liver diseases. CYP3A4 isoenzyme and its activity declined among patients with hepatic cirrhosis as expression of cyp3a4 gene was significantly reduced. Liver's ability to eliminate many clinical therateutic drug substrates would decline consequently, These findings may have practical implications for the use of drugs in patients with cirrhosis and emphasize the need to understand the metabolic fate of therapeutic compounds. Elucidation of the reasons for these different changes in hepatic CYP3A4 may provide insight into more fundamental aspects and mechanisms of imparied liver function.