Caryophyllene Sesquiterpenes from a Chaetomium globosum Endophyte of the Canadian Medicinal Plant Empetrum nigrum

Punctaporonins T (1) and U (2), new caryophyllene sesquiterpenes, were isolated with three known punctaporonins, A (3), B (4), and C (5), from the endophytic fungus Chaetomium globosum (TC2-041). The structures and relative configurations of punctaporonins T and U were elucidated based on a combination of HRESIMS, 1D/2D NMR spectroscopic analysis, and X-ray diffraction analysis, while their absolute configuration is presumed to be consistent with the co-isolated 3-5 on biogenetic arguments. Compound 1 showed weak inhibitory activity against both Mycobacterium tuberculosis and Staphylococcus aureus.

Modulation of in Vitro SARS-CoV-2 Infection by Stephania tetrandra and Its Alkaloid Constituents

Botanical natural products have been widely consumed for their purported usefulness against COVID-19. Here, six botanical species from multiple sources and 173 isolated natural product compounds were screened for blockade of wild-type (WT) SARS-CoV-2 infection in human 293T epithelial cells overexpressing ACE-2 and TMPRSS2 protease (293TAT). Antiviral activity was demonstrated by an extract from Stephania tetrandra. Extract fractionation, liquid chromatography-mass spectrometry (LC-MS), antiviral assays, and computational analyses revealed that the alkaloid fraction and purified alkaloids tetrandrine, fangchinoline, and cepharanthine inhibited WT SARS-CoV-2 infection. The alkaloids and alkaloid fraction also inhibited the delta variant of concern but not WT SARS-CoV-2 in VeroAT cells. Membrane permeability assays demonstrate that the alkaloids are biologically available, although fangchinoline showed lower permeability than tetrandrine. At high concentrations, the extract, alkaloid fractions, and pure alkaloids induced phospholipidosis in 293TAT cells and less so in VeroAT cells. Gene expression profiling during virus infection suggested that alkaloid fraction and tetrandrine displayed similar effects on cellular gene expression and pathways, while fangchinoline showed distinct effects on cells. Our study demonstrates a multifaceted approach to systematically investigate the diverse activities conferred by complex botanical mixtures, their cell-context specificity, and their pleiotropic effects on biological systems.

Annotation of natural product compound families using molecular networking topology and structural similarity fingerprinting

Spectral matching of MS² fragmentation spectra has become a popular method for characterizing natural products libraries but identification remains challenging due to differences in MS² fragmentation properties between instruments and the low coverage of current spectral reference libraries. To address this bottleneck we present Structural similarity Network Annotation Platform for Mass Spectrometry (SNAP-MS) which matches chemical similarity grouping in the Natural Products Atlas to grouping of mass spectrometry features from molecular networking. This approach assigns compound families to molecular networking subnetworks without the need for experimental or calculated reference spectra. We demonstrate SNAP-MS can accurately annotate subnetworks built from both reference spectra and an in-house microbial extract library, and correctly predict compound families from published molecular networks acquired on a range of MS instrumentation. Compound family annotations for the microbial extract library are validated by co-injection of standards or isolation and spectroscopic analysis. SNAP-MS is freely available at www.npatlas.org/discover/snapms .

High-throughput functional annotation of natural products by integrated activity profiling

Determining mechanism of action (MOA) is one of the biggest challenges in natural products discovery. Here, we report a comprehensive platform that uses Similarity Network Fusion (SNF) to improve MOA predictions by integrating data from the cytological profiling high-content imaging platform and the gene expression platform Functional Signature Ontology, and pairs these data with untargeted metabolomics analysis for de novo bioactive compound discovery. The predictive value of the integrative approach was assessed using a library of target-annotated small molecules as benchmarks. Using Kolmogorov-Smirnov (KS) tests to compare in-class to out-of-class similarity, we found that SNF retains the ability to identify significant in-class similarity across a diverse set of target classes, and could find target classes not detectable in either platform alone. This confirmed that integration of expression-based and image-based phenotypes can accurately report on MOA. Furthermore, we integrated untargeted metabolomics of complex natural product fractions with the SNF network to map biological signatures to specific metabolites. Three examples are presented where SNF coupled with metabolomics was used to directly functionally characterize natural products and accelerate identification of bioactive metabolites, including the discovery of the azoxy-containing biaryl compounds parkamycins A and B. Our results support SNF integration of multiple phenotypic screening approaches along with untargeted metabolomics as a powerful approach for advancing natural products drug discovery.

Evaluation of Ion Mobility Spectrometry for Improving Constitutional Assignment in Natural Product Mixtures

The comprehensive chemical characterization of biological samples remains a central challenge in the field of natural products. Conventional workflows using liquid chromatography (LC)-coupled high-resolution tandem mass spectrometry (MS/MS or MS2) allow the detection of relevant small molecules while providing diagnostic fragment ions for their structural assignment. Still, many natural product extracts are of a molecular complexity that challenges the resolving power of modern LC-MS2 pipelines. In this study, we examined the effect of integrating ion mobility spectrometry (IMS) to our LC-MS2 platform for the characterization of natural product mixtures. IMS provides an additional axis of separation in the gas phase as well as experimental collision cross-sectional (CCS) values. We analyzed a mixture of 20 commercial standards at 2 concentration ranges, either solubilized in solvent or spiked into an actinobacterial extract. Data were acquired in positive ion mode using both data-dependent acquisition (DDA) and data-independent acquisition (DIA) MS2 fragmentation approaches and assessed for both chemical coverage and spectral quality. IMS-DIA identified the largest number of standards in the spiked extract at the lower concentration of standards (17), followed by IMS-DDA (10), DDA (8), and DIA (6). In addition, we examined how these data sets performed in the Global Natural Products Social Molecular Networking (GNPS) platform. Overall, integrating IMS increased both metabolite detection and the quality of MS2 spectra, particularly for samples analyzed in DIA mode.

The Natural Products Atlas 2.0: a database of microbially-derived natural products

Within the natural products field there is an increasing emphasis on the study of compounds from microbial sources. This has been fuelled by interest in the central role that microorganisms play in mediating both interspecies interactions and host-microbe relationships. To support the study of natural products chemistry produced by microorganisms we released the Natural Products Atlas, a database of known microbial natural products structures, in 2019. This paper reports the release of a new version of the database which includes a full RESTful application programming interface (API), a new website framework, and an expanded database that includes 8128 new compounds, bringing the total to 32 552. In addition to these structural and content changes we have added full taxonomic descriptions for all microbial taxa and have added chemical ontology terms from both NP Classifier and ClassyFire. We have also performed manual curation to review all entries with incomplete configurational assignments and have integrated data from external resources, including CyanoMetDB. Finally, we have improved the user experience by updating the Overview dashboard and creating a dashboard for taxonomic origin. The database can be accessed via the new interactive website at https://www.npatlas.org.

Interlaboratory Comparison of Untargeted Mass Spectrometry Data Uncovers Underlying Causes for Variability

Despite the value of mass spectrometry in modern natural products discovery workflows, it remains very difficult to compare data sets between laboratories. In this study we compared mass spectrometry data for the same sample set from two different laboratories (quadrupole time-of-flight and quadrupole-Orbitrap) and evaluated the similarity between these two data sets in terms of both mass spectrometry features and their ability to describe the chemical composition of the sample set. Somewhat surprisingly, the two data sets, collected with appropriate controls and replication, had very low feature overlap (25.7% of Laboratory A features overlapping 21.8% of Laboratory B features). Our data clearly demonstrate that differences in fragmentation, charge state, and adduct formation in the ionization source are a major underlying cause for these differences. Consistent with other recent literature, these findings challenge the conventional wisdom that electrospray ionization mass spectrometry (ESI-MS) yields a simple one-to-one correspondence between analytes in solution and features in the data set. Importantly, despite low overlap in feature lists, principal component analysis (PCA) generated qualitatively similar PCA plots. Overall, our findings demonstrate that comparing untargeted metabolomics data between laboratories is challenging, but that data sets with low feature overlap can yield the same qualitative description of a sample set using PCA.

Physical Demands of Amateur Domestic and Representative Netball in One Season in New Zealand Assessed Using Heart Rate and Movement Analysis

King, DA, Cummins, C, Hume, PA, and Clark, TN. Physical demands of amateur domestic and representative netball in one season in New Zealand assessed using heart rate and movement analysis. J Strength Cond Res 34(7): 2062-2070, 2020-The purpose of this descriptive cohort study was to describe physical demands of netball for positions and between playing levels using microtechnology. Data were collected from 34 female netball players across 3 teams at different levels (over 19 years representative [O19], under 19 years representative [U19], and open-age amateur club domestic) for 20 games using heart rate and microtechnology data. Total distance, maximal velocity, PlayerLoad ([PL] accumulated accelerometer-derived load), and individual PL vectors (PL forward [PLF], PL sideward [PLS] and PL vertical [PLV]) were examined. Analysis by playing level and netball position were conducted. The O19 players recorded a higher mean distance (3,365.7 ± 1,875.1 m) per match than U19 (p = 0.0095) players. The O19 players recorded a higher PL (p = 0.0003), PLF (p = 0.004), PLS (p = 0.0039), and PLV (p = 0.0352) than the domestic players. Domestic players recorded a higher maximal velocity than O19 players (p = 0.0003; d = 0.32) throughout the study. Domestic players recorded a higher average maximal heart rate (202.2 ± 28.2 b·min) than O19 (p < 0.0001) and U19 (p = 0.0002) players. Given the high physical demands of netball, individual player- and position-specific training programs are required to develop players for the specific demands of competition while also reducing the impact of excessive physical exertion to facilitate safer engagement within netball. The identification of the differing physical and physiological profiles of individual positional groups throughout match-play highlights the importance of integrating microtechnology into the routine monitoring of intermittent court-based sports, such as netball.

Use of the King-Devick test for the identification of concussion in an amateur domestic women's rugby union team over two competition seasons in New Zealand

OBJECTIVE

To investigate the use of the King-Devick (K-D) test for sideline assessment of concussive injuries in a New Zealand amateur women's rugby union team.

DESIGN

Prospective cohort observational.

METHODS

All players were K-D tested during pre-season using a tablet (iPad; Apple Inc., Cupertino, CA). Differences in K-D scores and test-retest reliability were calculated for baseline test scores, baseline, and post-injury (concussion) sideline assessment and baseline and post-season testing scores for tests by year and as a combined score.

RESULTS

One training-related (0.3 per 1000 training-hrs) and nine match-related (16.1 per 1000 match-hrs) concussions were recorded. The K-D post-injury (concussion) sideline test score were significantly slower than established baseline (-4.4 [-5.8 to -3.4] s; χ²₍₁₎ = 42.2; p < 0.0001; t₍₉₎ = -4.0; p = 0.0029; d = -0.8). There was good-to-excellent reliability of the K-D test for baseline (ICC: 0.84 to 0.89), post-injury (concussion) sideline assessment (ICC: 0.82 to 0.97) and post-season evaluation (ICC: 0.79 to 0.83).

DISCUSSION

By utilising the baseline to post-injury (concussion) assessment comparisons, any player with a post-injury (concussion) assessment slowing of their K-D test time, regardless of whether the player has, or has not had a witnessed insult, should be withheld from any further participation until they are evaluated by a medical professional trained in the management of concussion.

CONCLUSION

This study has provided additional evidence to support the use of the K-D test as a frontline method of assessing concussion with good to excellent reliability of the test for baseline, side-line assessment and post-season evaluation.

Discovery of an Isothiazolinone-Containing Antitubercular Natural Product Levesquamide

Antitubercular agent levesquamide is a new polyketide-nonribosomal peptide (PK-NRP) hybrid marine natural product isolated from Streptomyces sp. RKND-216. The structure contains a rare isothiazolinone moiety which has only been reported in collismycin SN. Structure elucidation by NMR spectroscopy was a significant challenge due to a deficiency of protons in this aromatic moiety. Therefore, the genome of Streptomyces sp. RKND-216 was sequenced to identify the levesquamide biosynthetic gene cluster (BGC). Analysis of the BGC provided structural insights and guided stable-isotope labeling experiments, which led to the assignment of the fused pyridine-isothiazolinone moiety. The BGC and the labeling experiments provide further insights into the biosynthetic origin of isothiazolinones. Levesquamide exhibited antimicrobial activity in the microplate alamarBlue assay (MABA) and low oxygen recovery assay (LORA) against Mycobacterium tuberculosis H37Rv with minimum inhibitory concentration (MIC) values of 9.65 and 22.28 μM, respectively. Similar activity was exhibited against rifampicin- and isoniazid-resistant M. tuberculosis strains with MIC values of 9.46 and 9.90 μM, respectively. This result suggests levesquamide has a different mode of action against M. tuberculosis compared to the two first-line antitubercular drugs rifampicin and isoniazid. Furthermore, levesquamide shows no cytotoxicity against the Vero cell line, suggesting it may have a useful therapeutic window.

The Natural Products Atlas: An Open Access Knowledge Base for Microbial Natural Products Discovery

Despite rapid evolution in the area of microbial natural products chemistry, there is currently no open access database containing all microbially produced natural product structures. Lack of availability of these data is preventing the implementation of new technologies in natural products science. Specifically, development of new computational strategies for compound characterization and identification are being hampered by the lack of a comprehensive database of known compounds against which to compare experimental data. The creation of an open access, community-maintained database of microbial natural product structures would enable the development of new technologies in natural products discovery and improve the interoperability of existing natural products data resources. However, these data are spread unevenly throughout the historical scientific literature, including both journal articles and international patents. These documents have no standard format, are often not digitized as machine readable text, and are not publicly available. Further, none of these documents have associated structure files (e.g., MOL, InChI, or SMILES), instead containing images of structures. This makes extraction and formatting of relevant natural products data a formidable challenge. Using a combination of manual curation and automated data mining approaches we have created a database of microbial natural products (The Natural Products Atlas, www.npatlas.org) that includes 24 594 compounds and contains referenced data for structure, compound names, source organisms, isolation references, total syntheses, and instances of structural reassignment. This database is accompanied by an interactive web portal that permits searching by structure, substructure, and physical properties. The Web site also provides mechanisms for visualizing natural products chemical space and dashboards for displaying author and discovery timeline data. These interactive tools offer a powerful knowledge base for natural products discovery with a central interface for structure and property-based searching and presents new viewpoints on structural diversity in natural products. The Natural Products Atlas has been developed under FAIR principles (Findable, Accessible, Interoperable, and Reusable) and is integrated with other emerging natural product databases, including the Minimum Information About a Biosynthetic Gene Cluster (MIBiG) repository, and the Global Natural Products Social Molecular Networking (GNPS) platform. It is designed as a community-supported resource to provide a central repository for known natural product structures from microorganisms and is the first comprehensive, open access resource of this type. It is expected that the Natural Products Atlas will enable the development of new natural products discovery modalities and accelerate the process of structural characterization for complex natural products libraries.

Antibiotic Mycotoxins from an Endophytic Fusarium acuminatum Isolated from the Medicinal Plant Geum macrophyllum

An extract of the endophytic fungus Fusarium acuminatum (TC2-084) isolated from the Canadian medicinal plant Geum macrophyllum exhibited significant antimycobacterial activity against Mycobacterium tuberculosis H37Ra when fermented in both malt extract and potato dextrose broths. However, significant differences observed in the NMR spectra of the respective extracts led us to further investigate both. Bioassay guided fractionation revealed that lateropyrone was solely responsible for the bioactivity observed when TC2-084 was fermented in malt extract broth, while the antimycobacterial activity of the extract derived from the isolate fermented in potato dextrose broth was augmented by the presence of enniatins B, B1, and B4 in addition to lateropyrone.

Similar head impact acceleration measured using instrumented ear patches in a junior rugby union team during matches in comparison with other sports

OBJECTIVE Direct impact with the head and the inertial loading of the head have been postulated as major mechanisms of head-related injuries, such as concussion. METHODS This descriptive observational study was conducted to quantify the head impact acceleration characteristics in under-9-year-old junior rugby union players in New Zealand. The impact magnitude, frequency, and location were collected with a wireless head impact sensor that was worn by 14 junior rugby players who participated in 4 matches. RESULTS A total of 721 impacts > 10g were recorded. The median (interquartile range [IQR]) number of impacts per player was 46 (IQR 37-58), resulting in 10 (IQR 4-18) impacts to the head per player per match. The median impact magnitudes recorded were 15g (IQR 12g-21g) for linear acceleration and 2296 rad/sec(2) (IQR 1352-4152 rad/sec(2)) for rotational acceleration. CONCLUSIONS There were 121 impacts (16.8%) above the rotational injury risk limit and 1 (0.1%) impact above the linear injury risk limit. The acceleration magnitude and number of head impacts in junior rugby union players were higher than those previously reported in similar age-group sports participants. The median linear acceleration for the under-9-year-old rugby players were similar to 7- to 8-year-old American football players, but lower than 9- to 12-year-old youth American football players. The median rotational accelerations measured were higher than the median and 95th percentiles in youth, high school, and collegiate American football players.

Antimicrobial and antimycobacterial activities of aliphatic amines derived from vanillin

Ten lipophilic amines were prepared from the reductive amination of vanillin and the corresponding primary amines using sodium borohydride in methanol. All compounds have been obtained elementally pure and an X-ray diffraction study on the 4-n-butylaniline derivative has confirmed the molecular structure. Whilst the overall antibiotic activity of the derivatives was low, some of these compounds, particularly the boronate ester 2-methoxy-4-((2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenylamino)methyl)phenol (7), showed a promising degree of antimycobacterial activity against Mycobacterium tuberculosis H37Ra, where activity seemed to vary by the position of the boron substitution on the aniline ring.

Isolation of Phomopsolide A and 6(E)-Phomopsolide A as Antimycobacterial Products from an Unidentified Endophyte of the Canadian Medicinal Plant Heracleum maximum

An extract of an unidentified endophyte from the Canadian medicinal plant Heracleum maximum exhibited a unique metabolomic profile and significant antimycobacterial activity against Mycobacterium tuberculosis H37Ra. Bioassay guided fractionation of the extract led to the isolation of phomopsolide A (1) and 6(E’)-phomopsolide A (2). This is the first report of antimycobacterial activity for 1 and 2.

Isolation of Phomopsolide A and 6(E)-Phomopsolide A as Antimycobacterial Natural Products from an Unidentified Endophyte of the Canadian Medicinal Plant Heracleum maximum

An extract of an unidentified endophyte from the Canadian medicinal plant Heracleum maximum exhibited a unique metabolomic profile and significant antimycobacterial activity against Mycobacterium tuberculosis H37Ra. Bioassay guided fractionation of the extract led to the isolation of phomopsolide A (1) and 6(E)-phomopsolide A (2). This is the first report of antimycobacterial activity for 1 and 2.

Isolation of (–)–Avenaciolide as the Antifungal and Antimycobacterial Constituent of a Seimatosporium sp. Endophyte from the Medicinal Plant Hypericum perforatum

An extract of Seimatosporium sp., an endophyte from the Canadian medicinal plant Hypericum perforatum, exhibited significant antifungal and antimycobacterial activity against Candida albicans and Mycobacterium tuberculosis H37Ra. Bioassay guided fractionation led to the isolation of (-)–avenaciolide as the only bioactive constituent of the extract. This is the first report of both the antimycobacterial activity of avenaciolide and its isolation from a Seimatosporium sp. fungus.

Isolation of (-)-avenaciolide as the antifungal and antimycobacterial constituent of a Seimatosporium sp. Endophyte from the medicinal plant Hypericum perforatum

An extract of Seimatosporium sp., an endophyte from the Canadian medicinal plant Hypericum perforatum, exhibited significant antifungal and antimycobacterial activity against Candida albicans and Mycobacterium tuberculosis H37Ra. Bioassay guided fractionation led to the isolation of (-)-avenaciolide as the only bioactive constituent of the extract. This is the first report of both the antimycobacterial activity of avenaciolide and its isolation from a Seimatosporium sp. fungus.

Isolation of the Plant Hormone (+)-Abscisic acid as an Antimycobacterial Constituent of the Medicinal Plant Endophyte Nigrospora sp

An extract of the endophytic fungus Nigropsora sp. (isolate TC2-054) from the Canadian medicinal plant Fragaria virginiana exhibited significant antimycobacterial activity against Mycobacterium tuberculosis H37Ra. Bioassay guided fractionation revealed that linoleic acid derivatives and the plant hormone (+)-abscisic acid (ABA) were responsible for the observed antimycobacterial activity. This activity of ABA has not been previously reported.

Isolation of the plant hormone (+)-abscisic acid as an antimycobacterial constituent of the medicinal plant endophyte Nigrospora sp

An extract of the endophytic fungus Nigropsora sp. (isolate TC2-054) from the Canadian medicinal plant Fragaria virginiana exhibited significant antimycobacterial activity against Mycobacterium tuberculosis H37Ra. Bioassay guided fractionation revealed that linoleic acid derivatives and the plant hormone (+)-abscisic acid (ABA) were responsible for the observed antimycobacterial activity. This activity of ABA has not been previously reported.

Isolation and bioassay screening of medicinal plant endophytes from eastern Canada

Eighty-one distinct fungal endophytes were isolated from 12 traditionally used medicinal plants from New Brunswick, Canada. This is the first report of endophytes from 8 of the 12 host plants. One hundred and sixty-two crude extracts derived from the mycelia and spent fermentation broths of liquid cultures of each endophyte were screened for antibacterial and antifungal activity. Twenty-two extracts were active against Staphylococcus aureus while 30 were active against Pseudomonas aeruginosa. Twelve crude extracts were found to be active against Candida albicans.

Determination of 3'-azido-2',3'-dideoxyuridine in maternal plasma, amniotic fluid, fetal and placental tissues by high-performance liquid chromatography

3'-Azido-2',3'-dideoxyuridine (AZDU, Azddu, CS-87) is a nucleoside analog of 3'-azido-3'-deoxythymidine (zidovudine, AZT) that has been shown to inhibit human immunodeficiency virus (HIV-1). AZDU is a potential candidate for treatment of pregnant mothers to prevent prenatal transmission of HIV/AIDS to their unborn children. A rapid and efficient high-performance liquid chromatography (HPLC) method for the determination of AZDU concentrations in rat maternal plasma, amniotic fluid, placental and fetal tissue samples has been developed and validated. Tissue samples were homogenized in distilled water, protein precipitated and extracted using a C-18 solid-phase extraction (SPE) method prior to analysis. Plasma and amniotic fluid samples were protein precipitated with 2 M perchloric acid prior to analysis. Baseline resolution was achieved using a 4.5% acetonitrile in 40 mM sodium acetate (pH 7) buffer mobile phase for amniotic fluid, placenta and fetus samples and with a 5.5% acetonitrile in buffer solution for plasma at flow-rates of 2.0 ml/min. The HPLC system consists of a Hypersil ODS column (150x4.6 mm) with a Nova-Pak C-18 guard column with detection at 263 nm. The method yields retention times of 6.2 and 12.2 min for AZDU and AZT in plasma and 8.3 and 17.6 min for AZDU and AZT in amniotic fluid, fetal and placental tissues. Limits of detection ranged from 0.01 to 0.075 microg/ml. Recoveries ranged from 81 to 96% for AZDU and from 82 to 96% for AZT in the different matrices. Intra-day (n=6) and inter-day (n=9) precision (% RSD) and accuracy (% Error) ranged from 1.48 to 6.25% and from 0.50 to 10.07%, respectively.

Human T lymphocyte genetic modification with naked DNA

Endowing T lymphocytes with novel functional attributes by genetic modification is under development for a broad range of clinical cellular immunotherapy applications. To circumvent many of the limitations associated with viral vector systems, a plasmid-based electroporation system that reliably generates G418-resistant primary human T lymphocyte clones was developed. TCR alpha/beta+ CD4+CD8-, and CD4-CD8+ T lymphocyte clones can be routinely isolated from OKT3-stimulated peripheral blood mononuclear cells electroporated with linear plasmid DNA in a limiting dilution drug selection format. Fluorescence in situ hybridization (FISH) studies performed on T cell metaphase spreads using a probe specific for plasmid sequence demonstrated a single FISH signal doublet that varied in chromosomal location from clone to clone. Southern blot analysis using a Neo-specific probe verified chromosomal integration of plasmid vector at a single site. Band intensity quantitation of blots developed with a zeta-specific probe capable of annealing to both endogenous TCR-zeta and the introduced chimeric zeta sequence demonstrated that integrated plasmid was present at a single copy number. Expression levels of the CD20-specific chimeric immunoreceptor construct from a CMV immediate/early promoter present in the plasmid vector varied widely from clone to clone but remained stable during ex vivo expansion to cell numbers in excess of 10(10). This T lymphocyte genetic modification strategy is currently being piloted in a FDA-sanctioned adoptive therapy trial for recurrent lymphoma.

Oxidation of ochratoxin A by an Fe-porphyrin system: model for enzymatic activation and DNA cleavage

Ochratoxin A (OTA, 1) is a fungal toxin that facilitates single-strand DNA cleavage, DNA adduction, and lipid peroxidation when metabolically activated. To model the enzymatic activation of OTA, we have employed the water-soluble iron(III) meso-tetrakis(4-sulfonatophenyl)porphyrin (FeTPPS) oxidation system. In its presence, OTA has been found to facilitate single-strand cleavage of supercoiled plasmid DNA through production of reactive oxygen species (ROS) (i.e., the hydroxyl radical, HO(*)). The reaction of OTA with the FeTPPS oxidation system also generated three hydroxylated products (chlorine atom still attached), which was taken as evidence for production of the known hydroxylated metabolites (2-4) of OTA. This result suggested that the FeTPPS system served as a reasonable model for the enzymatic activation of OTA. When the reaction of OTA with FeTPPS was carried out in the presence of excess hydrogen peroxide (H(2)O(2)) and sodium ascorbate, a hydroquinone species (OTHQ, 5) was detected in which an OH group has replaced the chlorine atom of OTA. The production of OTHQ (5) was dependent on the presence of the reducing agent, sodium ascorbate, which suggested that the oxidation catalyst furnished the quinone derivative OTQ (6) that was subsequently reduced to OTHQ (5) by ascorbate. Utilizing a synthetic sample of OTHQ (5), the hydroquinone was found to undergo autoxidation with a t(1/2) of 11.1 h at pH 7.4, and to possess a pK(a) value of 8.03 for the phenolic oxygen ortho to the carbonyl groups. Our findings imply that the hydroquinone (OTHQ) and quinone (OTQ) metabolites of OTA have the ability to cause alkylation/redox damage and have allowed us to propose a viable pathway for oxidative damage by OTA.