Chromatography Combined with Bioassays and Other Hyphenations – The Direct Link to the Compound Indicating the Effect

Chemical safety screening of products - better proactive

The increasing pressure to ensure product safety in a global market comes up against the current practice of targeting only known hazardous compounds in product safety analysis. However, product safety refers not only to known but also to unknown or hidden hazards that are very important to know and avoid. Shortcomings and limitations of currently used technologies seem to cause an obvious discrepancy between intended and actual consumer protection. Products are not as safe as claimed by stakeholders. An existing but overlooked proactive safety screening with a prioritization strategy is brought into focus as it offers a unique solution. It can handle the complexity of a product with thousands of compounds of unknown identity and unknown toxicity and can figure out the important hazardous compounds, both known and unknown. Using hardly any sample preparation and the effect detection at an early position in the workflow is a game changer not to overlook hazardous compounds. All analytical technologies are needed, but the key is the re-arrangement of the instrument order, i.e. firstly hazard-related screening (effect first) and secondly, focus on identification of prioritized hazardous compounds. Such a proactive safety screening revealed previously unknown hazardous compounds in products on the market claimed to be safe. The highly sustainable, affordable, and all-in-one 2LabsToGo-Eco with easy-to-use planar bioassays empowers stakeholders to implement proactive safety screening and dynamic risk management. The transition to greater efficacy in consumer protection needs incentives and the critical review aims to stimulate a debate.

Antidiabetic and antioxidant profiling of 67 African trifoliate yam accessions by planar on-surface assays versus in vitro assays

Trifoliate yam (Dioscorea dumetorum) is traditionally used to treat diabetics in Nigeria. However, almost no information is available on its antidiabetic constituents and their natural variance. Hence, the activity of methanolic tuber extracts of 67 trifoliate yam accessions from the largest collection in Africa was proven by four colorimetric antidiabetic and antioxidant in vitro assays, as diabetes is also linked with oxidative stress. For the first time, selected accessions were also analyzed by planar bioactivity profiling. It has a comparatively higher, more differentiated information content, is more sustainable in terms of material consumption, and enables straightforward compound prioritization and characterization. Up to a dozen individual antioxidant zones were revealed as well as one prominent zone inhibiting α-glucosidase and α-amylase. The latter inhibition zone was tentatively assigned to palmitic, linoleic, oleic, linolenic, oxo-nonanoic fatty acids by direct elution to heated electrospray ionization high-resolution mass spectrometry.

Non-target bioanalytical eight-dimensional hyphenation including bioassay, heart-cut trapping, online desalting, orthogonal separations and mass spectrometry

It is still a challenge to discover and identify individual bioactive compounds directly in multicomponent mixtures. Current workflows are too tedious for routine use. Hence, the hyphenation of separation and detection techniques is a powerful tool to maximize the information obtained by a single sample run. A robust eight-dimensional (8D) hyphenation was developed. Orthogonal separations, biological assay detection, analyte trapping, desalting, and physico-chemical detections were arranged in the following order, i.e. 1) normal phase high-performance thin-layer chromatography (NP-HPTLC) separation, 2) Vis detection, 3) UV detection, 4) fluorescence detection (FLD), 5) bioassay for effect-directed analysis (EDA), 6) heart-cut trapping/desalting/elution to reversed phase high-performance liquid chromatography (RP-HPLC) separation, 7) photodiode array (PDA) and 8) mass spectrometry (MS) detection. For the first time, the hyphenation exploited online analyte trapping to desalt the eluted bioactive zone from the plate containing highly salted bioassay media. Subsequent valve switching guided the trapped analyte(s) to the main column, followed by multiple detection. As proof-of-principle, cinnamon samples were analyzed by NP-HPTLC-UV/Vis/FLD-EDA-RP-HPLC-PDA-MS, whereby a bioactive zone was separated into two distinct peaks detected by PDA and MS to be 2-methoxy cinnamaldehyde and cinnamaldehyde. The developed 8D hyphenation is applicable for routine, allowing the non-target high-throughput screening of complex samples for individual bioactive compounds.

Bioactive clerodane diterpenes of giant goldenrod (Solidago gigantea Ait.) root extract

Giant goldenrod (Solidago gigantea Ait.) root extract was screened for bioactive compounds by high-performance thin-layer chromatography (HPTLC), coupled with effect-directed analysis including antibacterial (Bacillus subtilis F1276, B. subtilis subsp. spizizenii, Aliivibrio fischeri and Xanthomonas euvesicatoria), antifungal (Fusarium avenaceum) and enzyme inhibition (acetyl- and butyrylcholinesterases, α- and β-glucosidases and α-amylase) assays. Compounds of six multipotent zones (Sg1-Sg6) were characterized by HPTLC-heated electrospray ionization-high-resolution mass spectrometry (HRMS) and HPTLC-Direct Analysis in Real Time-HRMS. Apart from zone Sg3, containing three compounds, a single characteristic compound was detectable in each bioactive zone. The bioassay-guided isolation using preparative-scale flash chromatography and high-performance liquid chromatography provided eight compounds that were identified by NMR spectroscopy as clerodane diterpenes. All isolates possessed inhibiting activity against at least one of the tested microorganisms.

New planar assay for streamlined detection and quantification of β-glucuronidase inhibitors applied to botanical extracts

The inhibition of the β-glucuronidase released from gut bacteria is associated with specific health-related benefits. Though a number of β-glucuronidase inhibition assays are currently in use, none of them can directly measure the relevant activity of each single constituent in a complex mixture, without prior separation and tedious isolation of the pure compounds. Thus, the hyphenation of the high performance thin layer chromatography (HPTLC) technique with a β-glucuronidase inhibition assay was investigated and successfully demonstrated for the first time. A colorimetric as well as fluorometric detection of the inhibitors was achieved using 5-bromo-4-chloro-3-indolyl-β-D-glucuronide as a substrate. Hence, β-glucuronidase inhibitors were detected as bright zones against an indigo blue or fluorescent background. The established method was optimized and validated employing the well-known inhibitor d-saccharic acid 1,4-lactone monohydrate. As proof of concept, the suitability of the new workflow was verified through analysis of two botanical extracts, Primula boveana and silymarin flavonolignans from Silybum marianum fruits. The found inhibitors were identified by spectroscopic methods; one of them, 3ʹ-O-(β-galactopyranosyl)-flavone, is here described as a newly isolated natural compound. The new hyphenation HPTLC-UV/Vis/FLD-β-glucuronidase inhibition assay-HRMS covers four orthogonal dimensions, i.e. separation, spectral detection, biochemical activity and structural characterization, in a highly targeted time- and material-saving workflow for analysis of complex or costly mixtures.

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Coupling of HPTLC to the β-glucuronidase inhibition assay is demonstrated.

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Colorimetric and fluorometric detection of the inhibition was given.

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A new β-glucuronidase inhibiting flavonoid in P. boveana was elucidated.

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HPTLC-HRMS analysis of other β-glucuronidase inhibitors is shown for silymarin.

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Analysis of rare plants (low extract amount) is possible with the new planar assay.

Detection and identification of acetylcholinesterase inhibitors in Annona cherimola Mill. by effect-directed analysis using thin-layer chromatography-bioassay-mass spectrometry

INTRODUCTION

Acetylcholinesterase (AChE) inhibitors are considered an important strategy in the treatment of neurological disorders such as Alzheimer's disease. A simple and fast planar chromatography-bioassay methodology has been established to detect bioactive molecules in cherimoya fruit.

OBJECTIVE

Detect and identify AChE inhibitors in cherimoya by high-performance thin-layer chromatography (HPTLC)-bioassay-mass spectrometry (MS) and related techniques.

METHODOLOGY

Effect-directed analysis by planar chromatography-bioassay-mass spectrometry was applied to detect and identify AChE inhibitors in pulp, peel and cherimoya seed. Bioassay was optimised establishing the following conditions: enzymatic solution (1.0 U mL^-1 ), 1-naphtyl acetate substrate (1.5 mg mL^-1 ) and Fast Blue B salt (1.0 mg mL^-1 ). TLC-MS interface was used to directly elute the active zones into a mass spectrometer or to a micro-vial for further off-line studies.

RESULTS

Two AChE inhibitory bands were detected in peel extracts. An analysis via HPTLC-MS and high-performance liquid chromatography diode array detector tandem mass spectrometry (HPLC-DAD-MS/MS) allowed to characterise three potential AChE inhibitors: anonaine (m/z 266 [M + H]⁺ ; UV λ_max = 269.6 nm), glaucine (m/z 256 [M + H]⁺ ; UV λ_max = 282.9 and 300.6 nm) and xylopine (m/z 296 [M + H]⁺ ; UV λ_max = 278.5 nm).

CONCLUSIONS

The application of this optimised high throughput method allowed to establish the presence of three potential AChE inhibitors in cherimoya peel. For the first time AChE inhibitory capacity of these alkaloids is reported.

Bioprofiling of Cosmetics with Focus on Streamlined Coumarin Analysis

Facing the widespread use of cosmetic products in daily use and recognizing the very limited information obtained by target analysis, a method suited for comprehensive characterization of cosmetics was aimed at. The biological activity of ingredients of 20 cosmetics taken from 16 different product groups and their coumarin contents were investigated via chromatography linked to bioassays (direct bioautography) and mass spectrometry. It allows for screening a large number of cosmetic products within a short time to generate a more valid database on their coumarin content and their contribution to the overall exposure. Bioactivity profiling of cosmetics with regard to bioactive ingredients opens new avenues for a comprehensive characterization of important substances in products of daily use, helpful for the legally required safety and risk assessment of cosmetic products, especially for multiple product usage. As for coumarin, a ubiquitary fragrance compound of allergenic potential, which is under recurrent discussion due to its hepatoxic properties, it is necessary to be able to estimate the regular intake via cosmetics for a valid risk assessment. This newly developed bioprofiling method allowed a selective determination of coumarin down to 1.3 mg kg-1, even for very matrix-rich cosmetics despite minimalism in sample preparation. The declaration limits according to European Cosmetics Regulation were completely covered. Mean coumarin contents of 20 cosmetic products reached up to 2218 mg kg-1. The repeatabilities (%RSD, n = 3) were between 1.1 and 2.9%, and the mean recoveries (n = 5) were between 96 and 102% for the different cosmetic matrices.