Efflux at the Blood-Brain Barrier Reduces the Cerebral Exposure to Ochratoxin A, Ochratoxin α, Citrinin and Dihydrocitrinone

Recent studies have implied that environmental toxins, such as mycotoxins, are risk factors for neurodegenerative diseases. To act directly as neurotoxins, mycotoxins need to penetrate or affect the integrity of the blood-brain barrier, which protects the mammalian brain from potentially harmful substances. As common food and feed contaminants of fungal origin, the interest in the potential neurotoxicity of ochratoxin A, citrinin and their metabolites has recently increased. Primary porcine brain capillary endothelial cells were used to investigate cytotoxic or barrier-weakening effects of ochratoxin A, ochratoxin α, citrinin and dihydrocitrinone. The transfer and transport properties of the mycotoxins across the barrier formed by porcine brain capillary endothelial cell monolayers were analysed using HPLC-MS/MS. High levels of Ochratoxin A caused cytotoxic and barrier-weakening effects, whereas ochratoxin α, citrinin and dihydrocitrinone showed no adverse effects up to 10 µM. Likely due to efflux transporter proteins, the transfer to the brain compartment was much slower than expected from their high lipophilicity. Due to their slow transfer across the blood-brain barrier, cerebral exposure of ochratoxin A, ochratoxin α, citrinin and dihydrocitrinone is low and neurotoxicity is likely to play a subordinate role in their toxicity at common physiological concentrations.

Reviewing the Analytical Methodologies to Determine the Occurrence of Citrinin and its Major Metabolite, Dihydrocitrinone, in Human Biological Fluids

Until now, the available data regarding citrinin (CIT) levels in food and the consumption of contaminated foods are insufficient to allow a reliable estimate of intake. Therefore, biomonitoring configuring analysis of parent compound and/or metabolites in biological fluids, such as urine or blood, is being increasingly applied in the assessment of human exposure to CIT and its metabolite, dihydrocitrinone (DH-CIT). Most studies report urinary levels lower for the parent compound when compared with DH-CIT. A high variability either in the mean levels or in the inter-individual ratios of CIT/DH-CIT between the reported studies has been found. Levels of DH-CIT in urine were reported as being comprised between three to seventeen times higher than the parent mycotoxin. In order to comply with this objective, sensitive analytical methodologies for determining biomarkers of exposure are required. Recent development of powerful analytical techniques, namely liquid chromatography coupled to mass spectrometry (LC-MS/MS) and ultra-high-performance liquid chromatography (UHPLC-MS/MS) have facilitated biomonitoring studies, mainly in urine samples. In the present work, evidence on human exposure to CIT through its occurrence and its metabolite, in biological fluids, urine and blood/plasma, in different countries, is reviewed. The analytical methodologies usually employed to evaluate trace quantities of these two molecules, are also presented. In this sense, relevant data on sampling (size and pre-treatment), extraction, cleanup and detection and quantification techniques and respective chromatographic conditions, as well as the analytical performance, are evidenced.

Interaction of Dihydrocitrinone with Native and Chemically Modified Cyclodextrins

Citrinin (CIT) is a nephrotoxic mycotoxin produced by Aspergillus, Penicillium, and Monascus genera. It appears as a contaminant in grains, fruits, and spices. After oral exposure to CIT, its major urinary metabolite, dihydrocitrinone (DHC) is formed, which can be detected in human urine and blood samples. Cyclodextrins (CDs) are ring-shaped molecules built up from glucose units. CDs can form host-guest type complexes with several compounds, including mycotoxins. In this study, the complex formation of DHC with native and chemically modified beta- and gamma-cyclodextrins was tested at a wide pH range, employing steady-state fluorescence spectroscopic and modeling studies. The weakly acidic environment favors the formation of DHC-CD complexes. Among the CDs tested, the quaternary-ammonium-γ-cyclodextrin (QAGCD) formed the most stable complexes with DHC. However, the quaternary-ammonium-β-cyclodextrin (QABCD) induced the strongest enhancement in the fluorescence signal of DHC. Our results show that some of the chemically modified CDs are able to form stable complexes with DHC (logK = 3.2–3.4) and the complex formation can produce even a 20-fold increase in the fluorescence signal of DHC. Considering the above-listed observations, CD technology may be a promising tool to increase the sensitivity of the fluorescence detection of DHC.

Citrinin Monomer and Dimer Derivatives with Antibacterial and Cytotoxic Activities Isolated from the Deep Sea-Derived Fungus Penicillium citrinum NLG-S01-P1

Two previously unreported citrinin dimer derivatives, penicitol D (1) and 1-epi-citrinin H1 (2), were isolated from the culture of a deep sea-derived fungus Penicillium citrinum NLG-S01-P1, together with 11 biogenetic related compounds (3⁻13). A plausible biogenetic pathway for compounds 2⁻4 was proposed. Their structures, including absolute configurations, were established through analysis of extensive spectroscopic data and time-dependent density functional theory (TD-DFT) ECD calculations. Compounds 1 and 2 showed antibacterial activities against methicillin-resistant Staphylococcus aureus (MRSA). Compounds 5 and 10 displayed relatively stronger activities than the other compounds against Vibrio vulnificus and Vibrio campbellii. Compound 1 showed the most potent cytotoxic activity towards the HeLa cell.

Two new compounds from a marine-derived Penicillium griseofulvum T21-03

A new phenolic acid compound, 46-dimethylcurvulinic acid (1) and a new citrinin monomer derivative penicitrinol P (2) were isolated from marine-derived Penicillium griseofulvum T21-03. The structures of 1 and 2 were elucidated on the basis of spectroscopic data.

Citrifelins A and B, Citrinin Adducts with a Tetracyclic Framework from Cocultures of Marine-Derived Isolates of Penicillium citrinum and Beauveria felina

Citrifelins A (1) and B (2), two citrinin adducts possessing a unique tetracyclic framework, were characterized from a coculture of marine-derived fungal isolates of Penicillium citrinum and Beauveria felina. Neither fungus produced these compounds when cultured alone under the same conditions. The structures of these adducts were elucidated on the basis of spectroscopic analysis, and the absolute configurations were assigned on the basis of TDDFT-ECD calculations. A hypothesis that adducts 1 and 2 might be derived from a citrinin derivative through a non-pericyclic Michael reaction is proposed. Compounds 1, 2, and 5 showed inhibitory activities against several human and aquatic pathogens.

A new citrinin dimer isolated from Aspergillus terreus strain ZDF21

Dicitrinin E (1), a new citrinin dimer, together with the known metabolites, dicitrinin A (2), citrinin (3), and fumitremorgin C (4), were isolated from the broth culture of Aspergillus terreus strain ZDF21. The structure of dicitrinin E (1) was elucidated through detailed analysis of 1D and 2D NMR experiments, CD and mass spectra The cytotoxicity of 1 was tested against larvae of Artemia salina.

Penicitols A-C and penixanacid A from the mangrove-derived Penicillium chrysogenum HDN11-24

Three new citrinin analogues, penicitols A-C (1-3), and one new xanthone derivative, penixanacid A (4), together with four known biogenetically related compounds (5-8), were discovered from the extract of a mangrove-derived fungus, Penicillium chrysogenum HND11-24. The structures of penicitols A-C and penixanacid A were established through analysis of extensive spectroscopic data. Their cytotoxic activity against HeLa, BEL-7402, HEK-293, HCT-116, and A549 cell lines was evaluated.

A novel citrinin derivative from the marine-source fungus Penicillium citrinum

A novel citrinin derivative, penicitrinol L (1), along with two known analogues, penidicitrinin B (2) and pennicitrinone A (3) were isolated from the marine-source fungus Penicillium citrinum. The structure of the new compound was elucidated by spectroscopic methods including one and two-dimensional NMR as well as high-resolution mass spectrometric analysis. Furthermore, compound 1 showed modest cytotoxic activity against HL-60 cell line and compound 3 showed weak cytotoxic activity against A375 cell line.

First results on citrinin biomarkers in urines from rural and urban cohorts in Bangladesh

Citrinin (CIT) is a mycotoxin contaminant in food commodities and can co-occur with ochratoxin A (OTA), another nephrotoxic contaminant in food and feed. Presence of OTA in maize from Bangladesh has been reported, but no data exist on CIT occurrence in food or feed in Bangladesh. Since biomonitoring provides the best approach to assess human exposure to contaminants from various sources and by all routes, a validated method for biomarker analysis has been used to investigate the presence of CIT and its metabolite dihydrocitrinone (HO-CIT) in urines from two Bangladeshi cohorts: Both analytes were determined in urine samples collected from inhabitants of a rural (n=32) and an urban (n=37) area in the Rajshahi district of Bangladesh. After cleanup by immunoaffinity columns, extracts were analyzed by LC-MS/MS; the limits of detection for CIT and HO-CIT in urine were 0.02 and 0.05 ng/mL, respectively. CIT and HO-CIT were detectable in 94 and 71% of all urine samples. Urinary biomarker levels did not show significant correlations with age, gender, and body mass index of the donors. However, excretion of CIT together with its metabolite HO-CIT was significantly higher (p<0.01) in the rural cohort (mean 1.1±1.9 ng/mL) than in the urban cohort (mean 0.14±0.14 ng/mL). This clearly indicates differences in mycotoxin exposure. As food habits differ between rural and urban people and also their main areas of occupation, further research is needed with regard to the major contributors of CIT exposure in the two cohorts. In conclusion, this first biomarker analysis indicates widespread and variable exposure to CIT in Bangladeshi adults.

The marine fungal metabolite, dicitrinone B, induces A375 cell apoptosis through the ROS-related caspase pathway

Dicitrinone B, a rare carbon-bridged citrinin dimer, was isolated from the marine-derived fungus, Penicillium citrinum. It was reported to have antitumor effects on tumor cells previously; however, the details of the mechanism remain unclear. In this study, we found that dicitrinone B inhibited the proliferation of multiple tumor types. Among them, the human malignant melanoma cell, A375, was confirmed to be the most sensitive. Morphologic evaluation, cell cycle arrest and apoptosis rate analysis results showed that dicitrinone B significantly induced A375 cell apoptosis. Subsequent observation of reactive oxygen species (ROS) accumulation and mitochondrial membrane potential (MMP) reduction revealed that the apoptosis induced by dicitrinone B may be triggered by over-producing ROS. Further studies indicated that the apoptosis was associated with both intrinsic and extrinsic apoptosis pathways under the regulation of Bcl-2 family proteins. Caspase-9, caspase-8 and caspase-3 were activated during the process, leading to PARP cleavage. The pan-caspase inhibitor, Z-VAD-FMK, could reverse dicitrinone B-induced apoptosis, suggesting that it is a caspase-dependent pathway. Our data for the first time showed that dicitrinone B inhibits the proliferation of tumor cells by inducing cell apoptosis. Moreover, compared with the first-line chemotherapy drug, 5-fluorouracil (5-Fu), dicitrinone B showed much more potent anticancer efficacy, suggesting that it might serve as a potential antitumor agent.

[Secondary metabolites of mangrove endophytic fungus SK5 in the South China Sea]

OBJECTIVE

To study the secondary metabolites of mangrove endophytic fungus SK5.

METHODS

The compounds were isolated by chromatographic technique. Their structures were identified by comprehensive physico-chemical properties and spectroscopic methods.

RESULTS

Five compounds were isolated and identified as 2,8-dihydroxy-3,4-dihydronaphthalen-1(2H)-one(1), Sclerotinin A (2), dihydrocitrinone(3), 4-hydroxybenzaldehyde (4) and 3-hydroxy-2-methylbenzoic acid (5).

CONCLUSION

Compound 1 is isolated from nature for the first time.

Citrinin dimers from the halotolerant fungus Penicillium citrinum B-57

In order to search for structurally novel and bioactive natural compounds from microorganisms, a halotolerant fungal strain, Penicillium citrinum B-57, which mainly produces citrinin derivatives, was isolated from sediments collected from the Jilantai salt field. From the ethyl acetate extract of P. citrinum B-57, two new citrinin dimers, pennicitrinone C ( 1) and penicitrinol B ( 2), and 11 known related compounds were isolated and identified by spectroscopic and chemical methods. These compounds showed antioxidative activity against DPPH radicals with IC 50 values ranging from 0.8 to 59 microM.

Redoxcitrinin, a biogenetic precursor of citrinin from marine isolate of fungus Penicillium sp

A chemical analysis of the fermentation of the marine-derived fungus Penicillium sp. led to the isolation of a biogenetic precursor of citrinin, redoxcitrinin (1), together with polyketide mycotoxins, phenol A (2), citrinin H2 (3), 4-hydroxymellein (4), citrinin (5), and phenol A acid (6). The structures of compounds 1-6 were determined on the basis of physicochemical data analyses. Among them, compounds 1-3 exhibited a potent radical scavenging activity against 1,1-diphenyl-2-picrylhydrazyl (DPPH) with IC50 values of 27.7, 23.4, and 27.2 microM, respectively.

Biotransformation of citrinin to decarboxycitrinin using an organic solvent-tolerant marine bacterium, Moraxella sp. MB1

Organic solvent tolerant microorganisms (OSTMs) are novel group of extremophilic microorganisms that have developed resistance to withstand solvent toxicity. These organisms play an important role in biotransformation of organic compounds. In the present study, we used an organic solvent-tolerant marine bacterium, Moraxella sp. MB1. 16S rRNA sequencing revealed that the bacterium shows 98% similarity with an uncultured marine bacterium with GenBank accession no. AY936933. This bacterium was used for the transformation of a toxin, citrinin, into decarboxycitrinin in a biphasic system. This transformation was affected by decarboxylase enzyme produced by MB1. Transformation of citrinin to decarboxycitrinin was monitored by thin-layer chromatography (TLC) and spectrophotometrically. Citrinin decarboxylase activity responsible for transformation was studied in cell-free growth medium and cell lysate of Moraxella sp. MB1. Citrinin decarboxylase was found to be intracellular in nature. The biotransformed product was purified and identified as decarboxycitrinin using electrospray ionization mass spectrometry (ESI-MS/MS) and nuclear magnetic resonance (NMR) spectrometry. The antibiotic activity of both citrinin and decarboxycitrinin is also reported.

Citrinin revisited: from monomers to dimers and beyond

Detailed chemical analysis of the solid phase fermentation of an Australian Penicillium citrinum isolate has returned the known compounds citrinin (1), phenol A acid (6), dihydrocitrinone (7) and dihydrocitrinin (8), together with a novel cytotoxic dimer, dicitrinin A (5). Dicitrinin A (5) was determined to be a dimerised artefact of the major co-metabolite citrinin, and its structure solved by spectroscopic analysis and chemical modification. Analysis of the products encountered during the controlled decomposition of citrinin led to the discovery of additional citrinin dimers and delineated a plausible mechanistic pathway linking all monomeric and dimeric citrinin degradation products.

Studies on aldose reductase inhibitors from fungi. I. Citrinin and related benzopyran derivatives

The fungal metabolites, citrinin (4,6-dihydro-8-hydroxy-3,4,5-trimethyl-6- oxo-3H-2-benzopyran-7-carboxylic acid) and DHMI (3,4-dihydro-6-methoxy-3,7-dimethyl-1H-2-benzopyran-8-ol), as well as certain synthetic derivatives, have been evaluated for aldose reductase inhibitory activity using a rat lens enzyme preparation. Citrinin and its reduction product, dihydrocitrinin, were found to have significant activity (IC50 approximately 10 microM), whereas the other compounds were 3-10 times less potent. Kinetic studies showed that citrinin was not an irreversible inhibitor of the enzyme, as might be expected of a quinone methide. Spectroscopic (NMR) evidence is presented for the existence of citrinin predominantly in the form of its hemi-acetal in aqueous solutions, suggesting that it is this benzo[c]pyran derivative which interacts with the enzyme, rather than the quinone methide form.

Isolation and identification of dihydrocitrinone, a urinary metabolite of citrinin in rats

Dihydrocitrinone, 3,4-dihydro-6,8-dihydroxy-3,4,5-trimethylisocoumarin-7-carboxylic acid, was isolated and identified as a urinary metabolite after oral administration of citrinin to rats. Male and female Osborne-Mendel rats received 30 mg citrinin/kg body weight by oral intubation. The metabolite dihydrocitrinone was present in urine collected at 0-2, 2-4, 4-6, 6-8, and 8-24 h after treatment. Only unchanged citrinin was found in blood collected 24 h after administration of the compound. The metabolite had a blue fluorescence and the same Rf on thin-layer chromatography, the same retention time on reverse-phase high-pressure liquid chromatography, and the same mass spectrum as an authentic sample of dihydrocitrinone.

Production and analysis of citrinin in corn

A convenient method for the production and analysis of citrinin in corn is described. Up to 2.964 g of citrinin can be produced by Penicillium citrinum per kg of corn by harvesting on day 21 or later. The analysis method has a lower detection limit of 0.25 ppm. Heating citrinin-contaminated corn destroys citrinin but may produce another toxin instead.