Biomimetic in vitro oxidation of lapachol: A model to predict and analyse the in vivo phase I metabolism of bioactive compounds

Biomimetic Chemical Reactions with Natural Products Using Metalloporphyrins and Salen Complexes as Catalysts: A Brief Review

The cytochrome P450 is a superfamily of hemoproteins mainly present in the liver and are versatile biocatalysts. They participate in the primary metabolism and biosynthesis of various secondary metabolites. Chemical catalysts are utilized to replicate the activities of enzymes. Metalloporphyrins and Salen complexes can contribute to the products' characterization and elucidate biotransformation processes, which are investigated during pre-clinical trials. These catalysts also help discover biologically active compounds and get better yields of products of industrial interest. This review aims to investigate which natural product classes are being investigated by biomimetic chemical models and the functionalities applied in the use of these catalysts. A limited number of studies were observed, with terpenes and alkaloids being the most investigated natural product classes. The research also revealed that Metalloporphyrins are still the most popular in the studies, and the identity and yield of the products obtained depend on the reaction system conditions.

Oxidation Products from the Neolignan Licarin A by Biomimetic Reactions and Assessment of in vivo Acute Toxicity

Licarin A, a dihydrobenzofuranic neolignan presents in several medicinal plants and seeds of nutmeg, exhibits strong activity against protozoans responsible for Chagas disease and leishmaniasis. From biomimetic reactions by metalloporphyrin and Jacobsen catalysts, seven products were determined: four isomeric products yielded by epoxidation from licarin A, besides a new product yielded by a vicinal diol, a benzylic aldehyde, and an unsaturated aldehyde in the structure of the licarin A. The incubation with rat and human liver microsomes partially reproduced the biomimetic reactions by the production of the same epoxidized product of m/z 343 [M + H]⁺. In vivo acute toxicity assays of licarin A suggested liver toxicity based on biomarker enzymatic changes. However, microscopic analysis of tissues sections did not show any tissue damage as indicative of toxicity after 14 days of exposure. New metabolic pathways of the licarin A were identified after in vitro biomimetic oxidation reaction and in vitro metabolism by rat or human liver microsomes.

Rhodamine B oxidation promoted by P450-bioinspired Jacobsen catalysts/cellulose systems

P450-bioinspired Jacobsen/Cell(NEt2) catalysts have been applied in RhB dye oxidation, which is used illegally in food industries of some countries.

Bioinspired oxidation in cytochrome P450 of isomers orientin and isoorientin using Salen complexes

RATIONALE

Orientin and isoorientin are C-glycosidic flavonoids, considered as markers of some plant species such as Passiflora edulis var. flavicarpa Degener, and reported in the literature to have pharmacological properties. In order to evaluate and characterize the in vitro metabolism of these flavonoids, phase I biotransformation reactions were simulated using Salen complexes.

METHODS

These flavonoids were oxidized separately in biomimetic reactions in different proportions, using one oxidant, m-chloroperbenzoic acid or iodosylbenzene, and one catalyst, the Jacobsen catalyst or [Mn(3-MeOSalen)Cl]. The [Mn(3-MeOSalen)Cl] catalyst was synthesized and characterized using spectrometric techniques. The oxidation potentials of the catalysts were compared. All reactions were monitored and analyzed using ultrahigh-performance liquid chromatography diode-array detection (UHPLC-DAD) and high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS).

RESULTS

The analysis by UHPLC-DAD and HPLC/MS/MS showed that isoorientin produces more products than orientin and that [Mn(3-MeOSalen)Cl] produces more products than the Jacobsen catalyst. In addition, [Mn(3-MeOSalen)Cl], which has a higher oxidation potential, formed products with the addition of one or two atoms of oxygen, while the Jacobsen catalyst formed compounds with only one added oxygen atom. The products with the addition of one oxygen atom were mainly epoxides, while those with two added oxygens formed an epoxide in the C-ring and incorporated the other oxygen into the glycosidic moiety.

CONCLUSIONS

The formation of epoxides is common in biomimetic reactions and they may represent a safety risk in medicinal products due to their high reactivity. This study may serve as a basis for subsequent pharmacological and toxicological studies that investigate the presence of these compounds as phase I metabolites, and ensure the safe use of plant products containing orientin as a chemical marker.

Development of long-circulating lapachol nanoparticles: formation, characterization, pharmacokinetics, distribution and cytotoxicity

Lapachol is an active compound for the treatment of malignant brain glioma. However, its physicochemical properties limit its clinical application. The purpose of this study is to develop a nano-drug delivery system (LPC-LP) loaded with lapachol (LPC), which remarkably prolongs the half-life in the body, and increases the brain intake, therefore, achieving a better anticancer effect in the treatment of glioma. In order to optimize the formulation of liposomes, an orthogonal design was adopted with entrapment efficiency (EE) as the index. The characterization of the optimized formulation was evaluated in vitro. To assess the safety profile and effect of LPC-LP, a rapid and sensitive ultra-fast liquid chromatography with tandem mass spectrometry (UPLC-MS/MS) method was developed for studying the pharmacokinetics and brain distribution of LPC-LP and LPC. Finally, the cytotoxicity of the two preparations on C6 cells was studied by the MTT assay. The results showed that the average particle size of LPC-LP was 85.92 ± 2.35 nm, the EE of liposomes was 92.52 ± 1.81%, and the charge potential was -40.70 ± 9.20 mV. An in vitro release study showed that the release of lapachol from LPC-LP was delayed compared to LPC, indicating that LPC-LP was a sustained and controlled release system. The UPLC-MS/MS method was fully validated in both plasma and brain tissue according to the Food and Drug Administration (FDA) recommended guidelines, and successfully used for quantification of lapachol in vivo. After intravenous administration, LPC-LP prolonged circulation time of lapachol in the body and increased brain intake. Besides, the MTT results revealed that the IC50 value of LPC-LP on C6 cells significantly decreased, compared with LPC, which further confirmed that LPC-LP enhanced the inhibition of C6 cells and improved the anti-glioma effect. In conclusion, LPC-LP could serve as a promising candidate for the clinical application of lapachol in the treatment of glioma.

Natural product-inspired profluorophores for imaging NQO1 activity in tumour tissues

Herein we designed a collection of trimethyl-lock quinone profluorophores as activity-based probes for imaging NAD(P)H:quinone oxidoreductase (NQO1) in cancer cells and tumour tissues. Profluorophores were prepared via synthetic routes from naturally-occurring quinones and characterised in vitro using recombinant enzymes, to be further validated in cells and fresh frozen canine tumour tissues as potential new tools for cancer detection and imaging.

New Pioglitazone Metabolites and Absence of Opened-Ring Metabolites in New N-Substituted Thiazolidinedione

Thiazolidinediones (TZDs) are drugs used to treat type 2 diabetes mellitus; however, several safety concerns remain regarding the available drugs in this class. Therefore, the search for new TZD candidates is ongoing; metabolism studies play a crucial step in the development of new candidates. Pioglitazone, one of the most commonly used TZDs, and GQ-11, a new N-substituted TZD, were investigated in terms of their metabolic activity in rat and human liver microsomes to assess their metabolic stability and investigate their metabolites. Methods for preparation of samples were based on liquid-liquid extraction and protein precipitation. Quantitation was performed using liquid chromatography (LC)-tandem mass spectrometry, and the metabolite investigation was performed using ultraperformance LC coupled to a hybrid quadrupole-time of flight mass spectrometer. The predicted intrinsic clearance of GQ-11 was 70.3 and 46.1 ml/kg per minute for rats and humans, respectively. The predicted intrinsic clearance of pioglitazone was 24.1 and 15.9 ml/kg per minute for rats and humans, respectively. The pioglitazone metabolite investigation revealed two unpublished metabolites (M-D and M-A). M-A is a hydration product and may be related to the mechanism of ring opening and the toxicity of pioglitazone. The metabolites of GQ-11 are products of oxidation; no ring-opening metabolite was observed for GQ-11. In conclusion, under the same experimental conditions, a ring-opening metabolite was observed only for pioglitazone. The resistance of GQ-11 to the ring opening is probably related to N-substitution in the TZD ring.

Gas-phase fragmentation of protonated piplartine and its fungal metabolites using tandem mass spectrometry and computational chemistry

Piplartine, an alkaloid produced by plants in the genus Piper, displays promising anticancer activity. Understanding the gas-phase fragmentation of piplartine by electrospray ionization tandem mass spectrometry can be a useful tool to characterize biotransformed compounds produced by in vitro and in vivo metabolism studies. As part of our efforts to understand natural product fragmentation in electrospray ionization tandem mass spectrometry, the gas-phase fragmentation of piplartine and its two metabolites 3,4-dihydropiplartine and 8,9-dihydropiplartine, produced by the endophytic fungus Penicillium crustosum VR4 biotransformation, were systematically investigated. Proposed fragmentation reactions were supported by ESI-MS/MS data and computational thermochemistry. Cleavage of the C-7 and N-amide bond, followed by the formation of an acylium ion, were characteristic fragmentation reactions of piplartine and its analogs. The production of the acylium ion was followed by three consecutive and competitive reactions that involved methyl and methoxyl radical eliminations and neutral CO elimination, followed by the formation of a four-member ring with a stabilized tertiary carbocation. The absence of a double bond between carbons C-8 and C-9 in 8,9-dihydropiplartine destabilized the acylium ion and resulted in a fragmentation pathway not observed for piplartine and 3,4-dihydropiplartine. These results contribute to the further understanding of alkaloid gas-phase fragmentation and the future identification of piplartine metabolites and analogs using tandem mass spectrometry techniques. Copyright © 2017 John Wiley & Sons, Ltd.

Fluorescent oxazoles from quinones for bioimaging applications

This work describes a synthetic strategy for the syntheses of four new fluorescent excited state intramolecular proton transfer (ESIPT) prone oxazole derivatives synthesized from lapachol, a naturally occurring naphthoquinone isolated from the Tabebuia species (ipe tree).

Jacobsen catalyst as a cytochrome P450 biomimetic model for the metabolism of monensin A

Monensin A is a commercially important natural product isolated from Streptomyces cinnamonensins that is primarily employed to treat coccidiosis. Monensin A selectively complexes and transports sodium cations across lipid membranes and displays a variety of biological properties. In this study, we evaluated the Jacobsen catalyst as a cytochrome P450 biomimetic model to investigate the oxidation of monensin A. Mass spectrometry analysis of the products from these model systems revealed the formation of two products: 3-O-demethyl monensin A and 12-hydroxy monensin A, which are the same ones found in in vivo models. Monensin A and products obtained in biomimetic model were tested in a mitochondrial toxicity model assessment and an antimicrobial bioassay against Staphylococcus aureus, S. aureus methicillin-resistant, Staphylococcus epidermidis, Pseudomonas aeruginosa, and Escherichia coli. Our results demonstrated the toxicological effects of monensin A in isolated rat liver mitochondria but not its products, showing that the metabolism of monensin A is a detoxification metabolism. In addition, the antimicrobial bioassay showed that monensin A and its products possessed activity against Gram-positive microorganisms but not for Gram-negative microorganisms. The results revealed the potential of application of this biomimetic chemical model in the synthesis of drug metabolites, providing metabolites for biological tests and other purposes.

A systematic investigation of the fragmentation pattern of two furanoheliangolide C-8 stereoisomers using electrospray ionization mass spectrometry

RATIONALE

Budlein A is a sesquiterpene lactone (STL) with some reported biological activities. Pre-clinical studies to identify in vivo metabolites often employ hyphenated techniques such as liquid chromatography/tandem mass spectrometry (LC/MS/MS). It is also possible to use the fragmentation pattern obtained by Collision-Induced Dissociation (CID) and Higher Energy Collision-Induced Dissociation (HCD) to distinguish between the stereoisomers budlein A and centratherin.

METHODS

The experiments were carried out in the positive mode using four different spectrometers with an electrospray ionization (ESI) source: (a) Waters ACQUITY(®) TQD triple quadrupole mass spectrometer (QqQ), (b) AB Sciex API 4000 QTrap(®) (QqQ), (c) Bruker Daltonics micrOTOF™-Q II (time-of-flight, QTOF), and (d) Thermo Scientific LTQ Orbitrap XL hybrid FTMS (Fourier transform mass spectrometer). Computational chemistry studies helped to identify the protonation sites. The B3LYP/6-31G(d) model furnished the equilibrium geometries and energies.

RESULTS

The stereochemistry (α- or β-orientation) of the centratherin and budlein A side-chain esters influences the fragmentation pattern recorded on QqQ, QTOF, and Orbitrap-HCD. On QqQ, centratherin releases the side chain, to generate the m/z 275 fragment ion, whereas budlein A gives the m/z 83 fragment ion. On QTOF and Orbitrap-HCD, only budlein A affords the m/z 293 and 83 fragment ions, respectively.

CONCLUSIONS

The data suggest that proton migration governs the fragmentation pathways under α- or β-orientation. The difference in the QqQ, QTOF, and Orbitrap-HCD spectral profiles of each isomer can help to distinguish between centratherin and budlein A using MS/MS, which becomes an alternative to nuclear magnetic resonance (NMR) analysis.

Cytotoxicity of lapachol metabolites produced by probiotics

Probiotics are currently added to a variety of functional foods to provide health benefits to the host and are commonly used by patients with gastrointestinal complaints or diseases. The therapeutic effects of lapachol continue to inspire studies to obtain derivatives with improved bioactivity and lower unwanted effects. Therefore, the general goal of this study was to show that probiotics are able to convert lapachol and are important to assess the effects of bacterial metabolism on drug performance and toxicity. The microbial transformations of lapachol were carried out by Bifidobacterium sp. and Lactobacillus acidophilus and different metabolites were produced in mixed and isolated cultures. The cytotoxic activities against breast cancer and normal fibroblast cell lines of the isolated metabolites (4α-hydroxy-2,2-dimethyl-5-oxo-2,3,4,4α,5,9β-hexahydroindeno[1,2-β]pyran-9β-carboxilic acid, a new metabolite produced by mixed culture and dehydro-α-lapachone produced by isolated cultures) were assessed and compared with those of lapachol. The new metabolite displayed a lower activity against a breast cancer cell line (IC50 = 532.7 μmol l(-1) ) than lapachol (IC50 = 72.3 μmol l(-1) ), while dehydro-α-lapachone (IC50 = 10.4 μmol l(-1) ) displayed a higher activity than lapachol. The present study is the first to demonstrate that probiotics are capable of converting lapachol into the most effective cytotoxic compound against a breast cancer cell line.

SIGNIFICANCE AND IMPACT OF THE STUDY

Probiotics have been used in dairy products to promote human health and have the ability to metabolize drugs and other xenobiotics. Naphthoquinones, such as lapachol, are considered privileged scaffolds due to their high propensity to interact with biological targets. The present study is the first to demonstrate that probiotics are capable of converting lapachol into the most effective cytotoxic compound against a breast cancer cell line. The developed approach highlights the importance of probiotics to assess the effects of bacterial metabolism on drug performance and toxicity.

In vitro metabolism studies of erythraline, the major spiroalkaloid from Erythrina verna

Background

Erythrina verna, popularly known as “mulungu”, is a Brazilian medicinal plant used to treat anxiety. Erythrina alkaloids have been described in several species of Erythrina, which have biological and therapeutic properties well known that include anxiolytic and sedative effects.

Methods

In this work, in vitro metabolism of erythraline (1), the major spirocyclic alkaloid of Erythrina verna, was studied in the pig cecum model and by biomimetic phase I reactions. The biomimetic reactions were performed with Jacobsen catalyst to produce oxidative metabolites and one metabolite was isolated and evaluated against cancer cells, as HL-60 (promyelocytic leukemia), SF-295 (Glioblastoma) and OVCAR-8 (ovarian carcinoma).

Results

Erythraline exhibited no metabolization by the pig microbiota and a main putative metabolite was formed in a biomimetic model using Jacobsen catalyst. This metabolite was isolated and identified as 8-oxo-erythraline (2). Finally, erythraline and the putative metabolite were tested in MTT model and both compounds showed no important cytotoxic activity against tumor cells.

Conclusions

The alkaloid erythraline was not metabolized by intestinal microbiota, but it was possible to identify its oxidative metabolite from biomimetic reactions. So these data are interesting and stimulate other studies involving this alkaloid, since it is present in phytomedicine products and there are not reported data about the metabolism of erythrina alkaloids.

Determination of the depth profile distribution of guest species in microporous materials using the voltammetry of immobilized particles methodology: application to lapachol attachment to palygorskite and kaolinite

In-depth profile distribution of guest species hosted in inorganic microporous matrixes is determined using electrochemical data.

Unusual biotransformation products of the sesquiterpene lactone budlein A by Aspergillus species

Biotransformation of chemicals by microorganisms can be effective in increasing chemical diversity. Some fungi have been described to be useful for the biotransformation of sesquiterpene lactones. Nevertheless, in most cases, only minor or simple transformations of functional groups have been observed. Budlein A is a sesquiterpene lactone found in high amounts in American sunflower-like species of the genus Viguiera (Asteraceae). It shows important biological effects like in vitro and in vivo anti-inflammatory activity, as well as cytotoxicity against cancer cell lines. With the aim to obtain potentially bioactive derivatives of budlein A and taking into account that obtaining semi-synthetic analogues is a very complex task, the capability of soil fungi to promote biotransformation was investigated. In this work, the biotransformation of budlein A by the soil fungi Aspergillus terreus and A. niger affording three unusual sesquiterpenoid derivatives with carbon skeletons is reported. The chemical structures of the compounds were elucidated by 1D and 2D NMR spectrometry and HR-ESI-MS. The stereochemistry and molecular conformation of one derivative was assessed by molecular modeling techniques. The fungal metabolites displayed a reduced cytotoxicity against HL-60 cells when compared to the original natural product. The results show the versatility of microbial-catalyzed biotransformations leading to unusual derivatives.

A non-michaelian behavior of the in vitro metabolism of the pentacyclic triterpene alfa and beta amyrins by employing rat liver microsomes

Pharmacological studies employing alpha and beta amyrin have demonstrated potential application in several biological activities suggesting their application as promising drugs. In the early drug development, metabolism studies may give important parameters regarding the efficacy and safety of the drug candidate. Therefore, the aim of this work was to determine the enzymatic kinetic parameters of these pentacyclic triterpenes. Chromatographic analyzes were performed using a Shimadzu GC-MS system. The resolution of amyrins was achieved with a DB5-MS column of 0.25 μM film thickness, 30.0 cm length and 0.25 mm diameter. At this condition, the retention times of beta- and alpha-amyrin were 21.3 and 20.2 min, respectively. The proposed method showed to be linear over the concentration range of 0.16-42.18 μM for beta amyrin and 0.11-28.12 μM for alpha amyrin. The lowest concentration quantified by the validated method was 0.16 μM for beta and 0.11 μM for alpha amyrin. The stability study showed that amyrins were stable at room temperature for 12h and at 37°C for 1h. The absolute recovery of the amyrin isomers from the rat microsome was 54.3-59.2%. The enzymatic kinetics presented sigmoidal plots. It was observed a Vmax=0.698 ± 0.022 μmol/mg protein/min, S50=4.4 μM and Hill coefficient of 2.7 ± 0.17 for alpha amyrin and a Vmax=0.775 ± 0.034 μmol/mg protein/min, S50=7.0 μM and Hill coefficient of 2.5 ± 0.21 for beta amyrin. The obtained results give the first clues regarding amyrin metabolism and suggests a more detailed study conducted employing isolated CYP isoforms.

Electronic structure and gas-phase chemistry of protonated α- and β-quinonoid compounds: a mass spectrometry and computational study

RATIONALE

The use of quinonoid compounds against tropical diseases and as antitumor agents has prompted the search for new naturally occurring and synthetic derivatives. Among these quinonoid compounds, lapachol and its isomers (α- and β-lapachone) serve as models for the synthesis of new compounds with biological activity, and the use of electrospray ionization tandem mass spectrometry (ESI-MS/MS) analysis as a tool to elucidate and characterize these products has furnished important information about these compounds.

METHODS

ESI-MS/MS analysis under collision-induced dissociation conditions was used to describe the fragmentation mechanisms for protonated 1,4-naphthoquinone, 1,2-naphthoquinone, α-lapachone, and β-lapachone. The B3LYP/6-31+G(d,p) model was used to obtain proton affinities, gas-phase basicities, and molecular electrostatic potential maps, thus indicating the probable protonation sites. Fragmentation pathways were suggested on the basis of the relative enthalpies of the product ions.

RESULTS

The ESI-MS signals of the cationized molecules of ortho quinonoid compounds were more intense than those of the protonated molecule. Formation of the major product ions with m/z 187 from protonated α- and β-lapachone has been attributed to a retro-Diels-Alder (RDA) reaction.

CONCLUSIONS

MS/MS studies on lapachol isomers (α- and β-lapachone) will facilitate the interpretation of the liquid chromatography (LC)-MS/MS analysis of new metabolites. MS/MS data on the 1,4-naphthoquinone, 1,2-naphthoquinone, α-lapachone and β-lapachone core will help characterize new derivatives from in vitro/in vivo metabolism studies in complex matrices. The product ions revealed the major fragmentation mechanisms and these ions will serve as diagnostic ions to identify each studied compound.