High-performance thin-layer chromatography combined with effect-directed assays and high-resolution mass spectrometry as an emerging hyphenated technology: A tutorial review

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.

Progress, applications, and challenges in high-throughput effect-directed analysis for toxicity driver identification - is it time for HT-EDA?

The rapid increase in the production and global use of chemicals and their mixtures has raised concerns about their potential impact on human and environmental health. With advances in analytical techniques, in particular, high-resolution mass spectrometry (HRMS), thousands of compounds and transformation products with potential adverse effects can now be detected in environmental samples. However, identifying and prioritizing the toxicity drivers among these compounds remain a significant challenge. Effect-directed analysis (EDA) emerged as an important tool to address this challenge, combining biotesting, sample fractionation, and chemical analysis to unravel toxicity drivers in complex mixtures. Traditional EDA workflows are labor-intensive and time-consuming, hindering large-scale applications. The concept of high-throughput (HT) EDA has recently gained traction as a means of accelerating these workflows. Key features of HT-EDA include the combination of microfractionation and downscaled bioassays, automation of sample preparation and biotesting, and efficient data processing workflows supported by novel computational tools. In addition to microplate-based fractionation, high-performance thin-layer chromatography (HPTLC) offers an interesting alternative to HPLC in HT-EDA. This review provides an updated perspective on the state-of-the-art in HT-EDA, and novel methods/tools that can be incorporated into HT-EDA workflows. It also discusses recent studies on HT-EDA, HT bioassays, and computational prioritization tools, along with considerations regarding HPTLC. By identifying current gaps in HT-EDA and proposing new approaches to overcome them, this review aims to bring HT-EDA a step closer to monitoring applications.

Bioassay-Guided Isolation and Identification of Antibacterial Compounds from Invasive Tree of Heaven Stem and Trunk Bark

Flash column chromatographic fractionation of tree of heaven (Ailanthus altissima) stem and trunk bark extracts, guided by thin-layer chromatography (TLC)-Bacillus subtilis assay and TLC-heated electrospray high-resolution tandem mass spectrometry (HESI-HRMS/MS), lead to the isolation of six known compounds: (9Z,11E)-13-hydroxy-9,11-octadecadienoic acid (13-HODE, A1), (10E,12Z)-9-hydroxy-10,12-octadecadienoic acid (9-HODE, A2), hexadecanedioic acid (thapsic acid, A3), 16-hydroxyhexadecanoic acid (juniperic acid, A4), 16-feruloyloxypalmitic acid (alpinagalanate, A5), and canthin-6-one (A6). Their structures were elucidated by HESI-HRMS/MS and one- and two-dimensional nuclear magnetic resonance (NMR) spectroscopy. This is the first study identifying A1-A5 in A. altissima tree. Except for A5, all isolated compounds exhibited antibacterial activity against B. subtilis in microdilution assays. A6 showed the strongest effect with a minimum inhibitory concentration (MIC) value of 8.3 µg/mL. The antibacterial activity of A3 and A4 is newly described.

Effect-directed analysis of endocrine and neurotoxic effects in stormwater depending discharges

The investigation of pollutant inputs via stormwater runoff and subsequent effects in receiving waters is becoming increasingly urgent in view of climate change with accompanying extreme weather situations such as heavy rainfall events. In this study, two sampling areas, one urban and one rural but dominated by a highway, were investigated using effect-directed analysis to identify endocrine and neurotoxic effects and potentially responsible substances in stormwater structures and receiving waters. For this purpose, a transgenic yeast cell assay for the simultaneous detection of estrogenic, androgenic, and progestogenic effects (YMEES) was performed directly on high-performance thin-layer chromatography (HPTLC) plates. Concomitantly, estrogens were analyzed by GC-MS/MS and other micropollutants typical for wastewater and stormwater by LC-MS/MS. Discharges from the combined sewer overflow (CSO) contribute a large portion of the endocrine load to the studied water body, even surpassing the load from a nearby wastewater treatment plant (WWTP). An effect pattern similar to the CSO sample was shown in the receiving water after the CSO with lower intensities, consisting of an estrogenic, androgenic, and progestogenic effect. In contrast, after the WWTP, only one estrogenic effect with a lower intensity was detected. Concentrations of E1, 17α-E2, 17β-E2, EE2, and E3 in the CSO sample were 2000, 410, 1100, 560, and 2700 pg/L, respectively. HPTLC-YMEES and GC-MS/MS complement each other very well and help to elucidate endocrine stresses. An Acetylcholinesterase (AChE) inhibitory effect could not be assigned to a causative compound by suspect and non-target analysis using LC-HRMS. However, the workflow showed how information from HPTLC separation, effect-based methods, and other meta-information on the sampling area and substance properties can contribute to an identification of effect-responsible substances. Overall, the study demonstrated that effect-based methods in combination with HPTLC and instrumental analysis can be implemented to investigate pollution by stormwater run-off particularly regarding heavy rain events due to climate change.

Colorimetric analysis platform based on thin layer chromatography for monitoring gluten cross-contamination in food industry

Monitoring of the accidental presence of gluten (Glu), resulting from cross-contamination, is imperative in different industries, in particular food industry. The objective of this study was the development of an analytical platform utilizing thin-layer chromatography (TLC) with colorimetric read-out for making binary (yes/no) decisions on surfaces and/or point of these industries. The composition of the extractive phase was optimized with commercial products used in cleaning processing lines. Subsequently, an exploration of TLC separation and detection was undertaken. CN-modified nanosilica plates and 30:70 acetonitrile:water were used to achieve a selective signal for Glu residues. The study of the detection performance showed that both spectroscopic measurement and image analysis were resulted in satisfactory results for quantitate analysis (RSD = 5 %, LOD = 0.12 mg). The practical application of the proposed methodology on surfaces of the food processing lines. This work demonstrated the operational feasibility in detecting gluten cross-contaminations within the food processing industry.

Concept of a six-fold multiplex planar bioassay to distinguish endocrine agonist, antagonist, cytotoxic and false-positive responses

To analyze a complex sample for endocrine activity, different tests must be performed to clarify androgen/estrogen agonism, antagonism, cytotoxicity, anti-cytotoxicity, and corresponding false-positive reactions. This means a large amount of work. Therefore, a six-fold planar multiplex bioassay concept was developed to evaluate up to the mentioned six endpoints or mechanisms simultaneously in the same sample analysis. Separation of active constituents from interfering matrix via high-performance thin-layer chromatography and effect differentiation via four vertical stripes (of agonists and end-products of the respective enzyme-substrate reaction) applied along each separated sample track were key to success. First, duplex endocrine bioassay versions were established. For the androgen/anti-androgen bioassay applied via piezoelectric spraying, the mean limit of biological detection of bisphenol A was 14 ng/band and its mean half maximal inhibitory concentration IC50 was 116 ng/band. Applied to trace analysis of six migrate samples from food packaging materials, 19 compound zones with agonistic or antagonistic estrogen/androgen activities were detected, with up to seven active compound zones within one migrate. For the first time, the S9 metabolism of endocrine effective compounds was studied on the same surface and revealed partial deactivation. Coupled to high-resolution mass spectrometry, molecular formulas were tentatively assigned to compounds, known to be present in packaging materials or endocrine active or previously unknown. Finally, the detection of cytotoxicity/anti-cytotoxicity and false-positives was integrated into the duplex androgen/anti-androgen bioassay. The resulting six-fold multiplex planar bioassay was evaluated with positive control standards and successfully applied to one migrate sample. The streamlined stripe concept for multiplex planar bioassays made it possible to assign different mechanisms to individual active compounds in a complex sample. The concept is generic and can be transferred to other assays.

Stability of Flavan-3-ols, Theaflavins, and Methylxanthines in 30 Industrial Green, Black, and White Tea (Camellia sinensis L.) Extracts Characterized via Liquid Chromatography Techniques

Commercially available tea extracts for dietary supplements and nutraceuticals are standardized to characteristic components of Camellia sinensis L., such as epigallocatechin gallate (EGCG) and total catechins or polyphenols. However, since most commercial tea extracts are highly concentrated into only one molecule such as EGCG, the comparatively less stable catechin, the oxidative stability of the extract during the 24-month shelf life was questioned. It was hypothesized that the overall oxidative stability is reduced for highly purified/concentrated tea extracts due to the absence of other natural antioxidants stabilizing the complex mixture. Via liquid chromatographic analysis, the individual chromatographic profiles of 30 commercial white, green, and black tea extracts were evaluated and compared regarding oxidative stability and functional properties. The contents of bioactive flavan-3-ols, theaflavins, and methylxanthines differed much from what was claimed by the suppliers. At the end of the product shelf life, most of the commercial green and black tea extracts showed a decrease in the flavan-3-ol content, the main bioactive components of tea. A high EGCG content to the detriment of other possibly stabilizing flavan-3-ols or antioxidants in tea was found to explain the lower oxidative stability of such tea extract products. A natural overall composition of molecular structures was found to be superior to a strong enrichment in just one molecule.

Application of effect-directed analysis using TLC-bioautography for rapid isolation and identification of antidiabetic compounds from the leaves of Annona cherimola Mill

INTRODUCTION

Type 2 diabetes mellitus is a globally prevalent chronic disease characterised by hyperglycaemia and oxidative stress. The search for new natural bioactive compounds that contribute to controlling this condition and the application of analytical methodologies that facilitate rapid detection and identification are important challenges for science. Annona cherimola Mill. is an important source of aporphine alkaloids with many bioactivities.

OBJECTIVE

The aim of this study is to isolate and identify antidiabetic compounds from alkaloid extracts with α-glucosidase and α-amylase inhibitory activity from A. cherimola Mill. leaves using an effect-directed analysis by thin-layer chromatography (TLC)-bioautography.

METHODOLOGY

Guided fractionation for α-glucosidase and α-amylase inhibitors in leaf extracts was done using TLC-bioassays. The micro-preparative TLC was used to isolate the active compounds, and the identification was performed by mass spectrometry associated with web-based molecular networks. Additionally, in vitro estimation of the inhibitory activity and antioxidant capacity was performed in the isolated compounds.

RESULTS

Five alkaloids (liriodenine, dicentrinone, N-methylnuciferine, anonaine, and moupinamide) and two non-alkaloid compounds (3-methoxybenzenepropanoic acid and methylferulate) with inhibitory activity were isolated and identified using a combination of simple methodologies. Anonaine, moupinamide, and methylferulate showed promising results with an outstanding inhibitory activity against both enzymes and antioxidant capacity that could contribute to controlling redox imbalance.

CONCLUSIONS

These high-throughput methodologies enabled a rapid isolation and identification of seven compounds with potential antidiabetic activity. To our knowledge, the estimated inhibitory activity of dicentrinone, N-methylnuciferine, and anonaine against α-glucosidase and α-amylase is reported here for the first time.

Evaluation of bioactive compounds from Ficus carica L. leaf extracts via high-performance thin-layer chromatography combined with effect-directed analysis

This study compares different solvent systems with the use of spontaneous fermentation on the phytochemical composition of leaf extracts from a locally grown white variety of common fig (Ficus carica Linn.). The aim was to detect and identify bioactive compounds that are responsible for acetylcholinesterase (AChE), α-amylase and cyclooxygenase-1 (COX-1) enzyme inhibition, and compounds that exhibit antimicrobial activity. Bioactive zones in chromatograms were detected by combining High-performance thin-layer chromatography (HPTLC) with enzymatic and biological assays. A new experimental protocol for measuring the relative half-maximum inhibitory concentration (IC50) was designed to evaluate the potency of the extracts compared to the potency of known inhibitors. Although the IC50 of the fig leaf extract for α-amylase and AChE inhibition were significantly higher when compared to IC50 for acarbose and donepezil, the COX-1 inhibition by the extract (IC50 = 627 µg) was comparable to that of salicylic acid (IC50 = 557 µg), and antimicrobial activity of the extract (IC50 = 375-511 µg) was similar to ampicillin (IC50 = 495 µg). Four chromatographic zones exhibited bioactivity. Compounds from detected bioactive bands were provisionally identified by comparing the band positions to coeluted standards, and by Fourier transform infrared (FTIR) spectra from eluted zones. Flash chromatography was used to separate selected extract into fractions and isolate fractions that are rich in bioactive compounds for further characterisation with nuclear magnetic resonance (NMR) spectroscopy and liquid chromatography-mass spectrometry (LC-MS) analysis. The main constituents identified were umbelliferon (zone 1), furocoumarins psoralen and bergapten (zone 2), different fatty acids (zone 3 and 4), and pentacyclic triterpenoids (calotropenyl acetate or lupeol) and stigmasterol (zone 4).

Screening bisphenols in complex samples via a planar Arxula adeninivorans bioluminescence bioassay

The Arxula yeast bisphenol screen (A-YBS) utilizes the bioluminescent Arxula adeninivorans yeast-based reporter cells for tailored analysis of bisphenols, one of the major endocrine-disrupting compound groups. For the first time, this bioreporter has been applied on the high-performance thin-layer chromatography (HPTLC) adsorbent surface to develop a respective planar bioluminescence bioassay (pA-YBS). The goal was to combine the advantages of HPTLC with a more selective bioassay detection for bisphenols. The performance of this pA-YBS bioluminescence bioassay was demonstrated by calculating the half-maximal effective concentration (EC50) of bisphenols compared to references. The EC50 ranged from 267 pg/band for bisphenol Z and 322 pg/band for bisphenol A (BPA) to > 1 ng/band for other bisphenols (BPC, BPE, BPF, and BPS) and references (17β-estradiol and 17α-ethinylestradiol). The EC50 value of BPA was three times more sensitive in signal detection than that of 17β-estradiol. The visual or videodensitometric limit of detection of BPA was about 200 pg/zone. The higher signal intensity and sensitivity for BPA confirmed the tailored bioassay selectivity compared to the existing estrogen screen bioassay. It worked on different types of HPTLC silica gel plates. This HPTLC-UV/Vis/FLD-pA-YBS bioluminescence bioassay method was used to analyze complex mixtures such as six tin can migrates, five thermal papers, and eleven botanicals. The detected estrogenic compound zones in the tin can migrates were successfully verified via the duplex planar yeast antagonist estrogen screen (pYAES) bioassay. The two bisphenols A and S were identified in one out of five thermal papers and confirmed with high-resolution mass spectrometry. No bisphenols were detected in the botanicals investigated via the pA-YBS bioluminescence bioassay. However, the botanicals proved to contain phytoestrogens as detected via the pYAES bioassay, which confirmed the tailored bioassay selectivity. This HPTLC-UV/Vis/FLD-pA-YBS bioluminescence bioassay is suited for cost-efficient analysis of BPA in complex samples, with no need for sterile conditions due to the fast workflow.

Bioactivity profiles of six baobab fruit pulp powders via planar chromatography hyphenated with effect-directed analysis

Baobab (Adansonia digitata) fruit pulp has a high nutrient content and has been traditionally used for medicinal purposes (e.g., as an anti-inflammatory and antioxidant agent) that may help protect against chronic diseases. Six different baobab fruit pulp powders were investigated using three different extractants and analyzed by high-performance thin-layer chromatography (HPTLC) hyphenated with antibacterial bioassays and enzyme inhibition assays. The developed non-target effect-directed screening was performed after extraction with pentyl acetate - ethanol 1:1 (V/V) on the HPTLC plate silica gel 60 using toluene - ethyl acetate - methanol 6:3:1 (V/V/V) as mobile phase system and derivatization via the anisaldehyde sulfuric acid reagent for detection. The physico-chemical profiles of the six baobab fruit pulp powder extracts were comparable, although the intensity of some zones was moderately different. The following effect-directed profiling via tyrosinase, α-glucosidase, and acetylcholinesterase inhibition assays as well as antibacterial Aliivibrio fischeri and Bacillus subtilis bioassays revealed one prominent multipotent bioactive compound zone in common, more or less active in all five studied (bio)assays. Via the recording of high-resolution mass spectra, this compound zone was tentatively assigned to coeluting saturated (palmitic acid 16:0 and stearic acid 18:0), monounsaturated (oleic acid 18:1), and polyunsaturated (linoleic acid 18:2 and linolenic acid 18:3) fatty acids. This finding was confirmed by other studies, which already proved individual activities of fatty acids. The first (bio)activity profiling of baobab fruit pulp powders via HPTLC-effect-directed analysis revealed that the baobab fruit could be considered as a functional food, however, further research is needed to study the impact on health and the influences on the bioactivity arising from different climates, years and soils or regions.

Sample preparation for planar chromatography

High-performance thin-layer chromatography has favorable properties for high-throughput separations with a high matrix tolerance. Sample preparation, however, is sometimes required to control specific matrix interferences and to enhance the detectability of target compounds. Trends in contemporary applications have shifted from absorbance and fluorescence detection to methods employing bioassays and mass spectrometry. Traditional methods (shake-flask, heat at reflux, Soxhlet, and hydrodistillation) are being challenged by automated instrumental approaches (ultrasound-assisted and microwave-assisted solvent extraction, pressurized liquid extraction, and supercritical fluid extraction) and the quick, easy cheap, efficient, rugged, and safe extraction method for faster and streamlined sample processing. Liquid-liquid extraction remains the most widely used approach for sample clean-up with increasing competition from solid-phase extraction. On-layer sample, clean-up by planar solid-phase extraction is increasingly used for complex samples and in combination with heart-cut multimodal systems. The automated spray-on sample applicator, the elution head interface, biological detection of target and non-target compounds, and straightforward mass spectrometric detection are highlighted as the main factors directing current interest toward faster and simpler sample workflows, analysis of more complex samples, and the determination of minor contaminants requiring high concentration factors.

Designed genotoxicity profiling detects genotoxic compounds in staple food such as healthy oils

Current techniques used in food analysis overlook genotoxic compounds. This urgently calls for a paradigm shift in analytics towards non-target planar genotoxicity profiling that can detect genotoxins. Up to eight different genotoxins (i.e., genotoxic compound zones) have been detected in 33 oils used for healthy diets. A comparison of fresh oils with oils stored open and closed for one month identified genotoxic degradation products. Characterization of genotoxic zones via high-resolution mass spectrometry revealed oxidized linolenic acid as a source of genotoxicity in all samples. Detoxification via on-surface S9 liver metabolization was investigated, which showed a reduction in most, but not all, genotoxins. Food, feed, dietary supplements, and cosmetics as sources of genotoxicity can now be identified by combining separation, effect detection and optionally simulated metabolization on the same surface. The application of the planar genotoxicity profiling will improve the understanding on food and its impact as well as risk assessment and derived recommendations.

Effect directed analysis of bioactive compounds in leaf extracts from two Salvia species by High-performance thin-layer chromatography

Extracts of two Salvia species, Salvia apiana (white sage) and Salvia officinalis (common sage) were screened for phytoconstituents with the ability to act as antidiabetic, cognitive enhancing, or antimicrobial agents, by hyphenation of high-performance thin-layer chromatography with enzymatic and microbial effect directed assays. Two bioactive zones with α-amylase inhibition (zone 1 and zone 2), 3 zones for acetylcholinesterase inhibition (zones 3, 4 and 5), and two zones for antimicrobial activity (zones 4 and 5) were detected. The compounds from the five bioactive zones were initially identified by coelution with standards and comparing the R_F values of standards to the bioautograms. Identity was confirmed with ATR-FTIR spectra of the isolated compounds from the bioactive zones. A significantly higher α-amylase and acetylcholinesterase inhibition of S. apiana leaf extract was associated with a higher flavonoid and diterpenoid content. Fermented S. officinalis extract exhibited a significantly higher ability to inhibit α-amylase compared to other non-fermented extracts from this species, due to increased extraction of flavonoids. The ATR-FTIR spectra of 2 zones with α-amylase inhibition, indicated that flavonoids and phenolic acids were responsible for α-amylase inhibition. Multiple zones of acetylcholinesterase inhibition were related to the presence of phenolic abietane diterpenoids and triterpenoid acids. The presence of abietane diterpenoids and triterpenoid acids was also found responsible for the mild antimicrobial activity. Flash chromatography was used to isolate sufficient amounts of bioactive compounds for further characterisation via NMR and MS spectroscopy. Five compounds were assigned to the zones where bioactivity was observed: cirsimaritin (zone 1), a caffeic acid polymer (zone 2), 16-hydroxyrosmanol (zone 3), 16-hydroxycarnosic acid (zone 4), oleanolic and ursolic acids (zone 5).

Metabolic profiling of bacterial co-cultures reveals intermicrobiome interactions and dominant species

In animal production, the use of probiotic microorganisms has increased since the ban on antibiotic growth promoters in 2006. The added microorganisms interact with the microbiome of the animals, whereby the probiotic activity is not fully understood. Several microorganisms of the genus Bacillus are already known for their probiotic activity and are applied as feed supplements to increase the health status of the animals. They are thought to interact with Escherichia coli, one of the most abundant bacteria in the animal gut. In biotechnological applications, co-culturing enables the regulation of bacterial interaction or the production of target metabolites. The basic principles of multi-imaging high-performance thin-layer chromatography (HPTLC) with upstream cultivation were further developed to analyze the metabolic profiles of three axenic bacilli cultures compared to their co-cultures with E. coli DSM 18039 (K12). The comparative profiling visualized bacteria's metabolic interactions and showed how the presence of E. coli affects the metabolite formation of bacilli. The characteristic metabolic profile images showed not only the influence of microbiomes but also of inoculation, cultivation and nutrients on the commercial probiotic. The formation of antimicrobially active metabolites, detected via three different planar bioassays, was influenced by the presence of other microorganisms, especially in the probiotic. This first application of multi-imaging HPTLC in the field of co-culturing enabled visualization of metabolic interactions of bacteria via their produced chemical as well as bioactive metabolite profiles. The metabolic profiling provided evidence of bacterial interactions, intermicrobiome influences and dominant species in the co-culture.

Investigation of the estrogenic potential of 15 rosé, white and red wines via effect-directed ten-dimensional hyphenation

Wine is consumed for thousands of years all over the world, however, its estrogenic potential is still underexplored. A non-target effect-directed screening was developed to reveal estrogen-like and antiestrogen-like compounds in 15 rosé, white and red wine samples of different origin and grape variety. Normal-phase high-performance thin-layer chromatography multi-imaging detection (NP-HPTLC-UV/Vis/FLD) was combined with the planar yeast estrogen screen (pYES) bioassay or the duplex planar yeast antagonist estrogen screen (pYAES) bioassay on the same adsorbent surface. Up to nine estrogen-like compound zones were detected and further characterized via heart-cut elution from the planar bioautogram to orthogonal reversed phase high-performance liquid chromatography (RP-HPLC) coupled with diode array detection (DAD) and high-resolution tandem mass spectrometry (HRMS/MS). Among the tentatively assigned estrogen-like substances, the HRMS/MS signals pointed to hexylresorcinol and diethyl esters from organic acids for the first time. This highlights the method suitability for non-target complex mixture screening and rapid dereplication. The 10D hyphenation NP-HPTLC-UV/Vis/FLD-pYAES-heart cut-RP-HPLC-DAD-HRMS/MS proved to be an efficient and powerful tool for detecting estrogens as well as antiestrogens in the matrix-rich wine samples. High-throughput capability and substantial reduction in the required resources for analysis were demonstrated by this straightforward hyphenation, if compared to bioassay-guided fractionation. The 10D information (via orthogonal chromatographic, versatile spectrometric and duplex endocrine activity data) obtained during a single chromatographic run for many samples in parallel was advantageous for the tentative molecule assignment.

Planar chromatography - Current practice and future prospects

Planar chromatography, in the form of thin-layer or high-performance thin-layer chromatography (TLC, HPTLC), continues to provide a robust and widely used separation technique. It is unrivaled as a simple and rapid qualitative method for mixture analysis, or for finding bioactive components in mixtures. The format of TLC/HPTLC also provides a unique method for preserving the separation, enabling further investigation of components of interest (including quantification/structure determination) separated in both time and space from the original analysis. The current practice of planar chromatography and areas of development of the technology are reviewed and promising future directions in the use of TLC/HPTLC are outlined.

Natural Products Drug Discovery: On Silica or In-Silico?

Natural products have been the most important source for drug development throughout the human history. Over time, the formulation of drugs has evolved from crude drugs to refined chemicals. In modern drug discovery, conventional natural products lead-finding usually uses a top-down approach, namely bio-guided fractionation. In this approach, the crude extracts are separated by chromatography and resulting fractions are tested for activity. Subsequently, active fractions are further refined until a single active compound is obtained. However, this is a painstakingly slow and expensive process. Among the alternatives that have been developed to improve this situation, metabolomics has proved to yield interesting results having been applied successfully to drug discovery in the last two decades. The metabolomics-based approach in lead-finding comprises two steps: (1) in-depth chemical profiling of target samples, e.g. plant extracts, and bioactivity assessment, (2) correlation of the chemical and biological data by chemometrics. In the first step of this approach, the target samples are chemically profiled in an untargeted manner to detect as many compounds as possible. So far, NMR spectroscopy, LC-MS, GC-MS, and MS/MS spectrometry are the most common profiling tools. The profile data are correlated with the biological activity with the help of various chemometric methods such as multivariate data analysis. This in-silico analysis has a high potential to replace or complement conventional on-silica bioassay-guided fractionation as it will greatly reduce the number of bioassays, and thus time and costs. Moreover, it may reveal synergistic mechanisms, when present, something for which the classical top-down approach is clearly not suited. This chapter aims to give an overview of successful approaches based on the application of chemical profiling with chemometrics in natural products drug discovery.

2LabsToGo─Recipe for Building Your Own Chromatography Equipment Including Biological Assay and Effect Detection

A complete recipe for building your own chromatography equipment from readily available materials is introduced. It combines sample separation (chemistry laboratory) with biological effect detection (biology laboratory). This hyphenation of two disciplines is necessary for prioritizing important compounds in complex samples. Among the thousands of compounds therein, it is often not clear which compounds are the important ones. On the same separation surface, additional detection of biological effects enables and guides substance prioritization. The newly developed open-source 2LabsToGo system for chemical and biological analysis is completely solvent-resistant and, due to miniaturization, environmentally friendly regarding the consumption of materials. It produces comparable results but is 10 times more compact (26 cm × 31 cm × 34 cm), 10 times lighter (6.8 kg), and 55 times less expensive (€ 1717) than current sophisticated commercial devices. As a proof of concept of the first 2LabsToGo system, the quality of different water samples was analyzed since clean water is becoming increasingly rare. In water, most of the thousands of substance signals or features can neither be identified nor classified toxicologically. However, methods that exploit this hyphenated strategy provide answers to such essential safety issues. Drinking or tap water did not show bioactive or toxic compounds, which was expected, whereas biogas or landfill water samples did. The hyphenated 2LabsToGo strategy is affordable and extremely useful for all laboratories with limited equipment but pressing challenges. It is ready to be used in various analytical tasks and applications.

Non-target bioactive compound profiles of coffee roasts and preparations

Coffee is an inherent part of our daily nutrition and seems to have protective effects against diseases, whereby it is often not fully understood, which ingredients are responsible for the observed effect. Hence, a non-targeted bioactivity profiling was developed to investigate 27 hand-filtered coffee brews of differently roasted coffee beans and 14 differently prepared and stored coffee brews. After separation, multi-imaging, and densitometry, six planar effect-directed assays were performed to reveal individual antioxidative, antibacterial, anti-cholinesterase, anti-diabetic, and estrogenic effects. Individual compounds were mainly responsible for the observed effects, e.g. 5-O-caffeoylquinic acid regarding antioxidative potential and α-glucosidase inhibition, while coffee brews made by a fully automated coffee machine showed the highest antioxidative potential. Unlike preparation and storage conditions, applied roasting conditions and origin of coffee samples played a less important role. Therefore, the way we daily consume our coffee has an impact on the magnitude of potential health effects.

Incorporation of Metabolic Activation in the HPTLC-SOS-Umu-C Bioassay to Detect Low Levels of Genotoxic Chemicals in Food Contact Materials

The safety evaluation of food contact materials requires excluding mutagenicity and genotoxicity in migrates. Testing the migrates using in vitro bioassays has been proposed to address this challenge. To be fit for that purpose, bioassays must be capable of detecting very low, safety relevant concentrations of DNA-damaging substances. There is currently no bioassay compatible with such qualifications. High-performance thin-layer chromatography (HPTLC), coupled with the planar SOS Umu-C (p-Umu-C) bioassay, was suggested as a promising rapid test (~6 h) to detect the presence of low levels of mutagens/genotoxins in complex mixtures. The current study aimed at incorporating metabolic activation in this assay and testing it with a set of standard mutagens (4-nitroquinoline-N-oxide, aflatoxin B1, mitomycin C, benzo(a)pyrene, N-ethyl nitrourea, 2-nitrofluorene, 7,12-dimethylbenzanthracene, 2-aminoanthracene and methyl methanesulfonate). An effective bioactivation protocol was developed. All tested mutagens could be detected at low concentrations (0.016 to 230 ng/band, according to substances). The calculated limits of biological detection were found to be up to 1400-fold lower than those obtained with the Ames assay. These limits are lower than the values calculated to ensure a negligeable carcinogenic risk of 10^-5. They are all compatible with the threshold of toxicological concern for chemicals with alerts for mutagenicity (150 ng/person). They cannot be achieved by any other currently available test procedures. The p-Umu-C bioassay may become instrumental in the genotoxicity testing of complex mixtures such as food packaging, foods, and environmental samples.

Essential Oils as Multicomponent Mixtures and Their Potential for Human Health and Well-Being

Essential oils (EOs) and their individual volatile organic constituents have been an inherent part of our civilization for thousands of years. They are widely used as fragrances in perfumes and cosmetics and contribute to a healthy diet, but also act as active ingredients of pharmaceutical products. Their antibacterial, antiviral, and anti-inflammatory properties have qualified EOs early on for both, the causal and symptomatic therapy of a number of diseases, but also for prevention. Obtained from natural, mostly plant materials, EOs constitute a typical example of a multicomponent mixture (more than one constituent substances, MOCS) with up to several hundreds of individual compounds, which in a sophisticated composition make up the property of a particular complete EO. The integrative use of EOs as MOCS will play a major role in human and veterinary medicine now and in the future and is already widely used in some cases, e.g., in aromatherapy for the treatment of psychosomatic complaints, for inhalation in the treatment of respiratory diseases, or topically administered to manage adverse skin diseases. The diversity of molecules with different functionalities exhibits a broad range of multiple physical and chemical properties, which are the base of their multi-target activity as opposed to single isolated compounds. Whether and how such a broad-spectrum effect is reflected in natural mixtures and which kind of pharmacological potential they provide will be considered in the context of ONE Health in more detail in this review.

Multiplex planar bioassay detecting estrogens, antiestrogens, false-positives and synergists as sharp zones on normal phase

BACKGROUND

Phytoestrogens are found in many plants used in traditional medicines. Increasingly, plant extracts (botanicals) are also being added to foods or marketed as dietary supplements. Especially such powder formulations are susceptible to adulteration and falsification, given the global processing chain. To detect estrogen-like compounds in such multicomponent mixtures, non-target screening for hormonally active or endocrine disrupting compounds in plant products is becoming more important. Unfortunately, the current planar yeast estrogen screen (pYES) is prone to zone diffusion on the normal-phase high-performance thin-layer chromatography (NP-HPTLC) plate due to long incubation times in the aqueous bioassay.

PURPOSE

The present study aimed to reduce zone diffusion on NP plates, which provides the basis for extending pYES to a multiplex bioassay, offering 4 different biological activity principles, followed by targeted identification of active zones.

STUDY DESIGN AND METHODS

The reduction of substance diffusion via a polyisobutyl methacrylate polymer coating was studied. After successful zone fixation (^fix), a multiplex bioassay was developed, in which a 17β-estradiol-strip was applied along each sample track to detect synergists and antagonists (A), and for verification (V), a 4-methyl umbelliferone-strip to exclude false-positives. After multiplex bioassay screening of 68 botanicals, the zones with hormonal activities were heart-cut eluted to reversed-phase high-performance liquid chromatography-diode array detection-high-resolution tandem mass spectrometry (RP-HPLC-DAD-HESI-HRMS/MS).

RESULTS

The separated substances were successfully fixed by the chromatogram coating. The zone sharpness (achieved after the bioassay) made it possible to add two strips, the 17β-estradiol-strip for antagonistic and synergistic, and the 4-methyl umbelliferone-strip for false-positive effect detection, resulting in a multiplex bioassay. Using the 12D hyphenation NP-HPTLC^fix-UV/Vis/FLD-pYAVES-FLD heart-cut RP-HPLC-DAD-HESI-HRMS/MS, it was possible to obtain information on estrogens, antiestrogens, false-positives, and synergists, and (tentatively) assign 17 hormonally active compounds, of which only 7 have been known to affect the human estrogen receptor, while another 4 had structural similarity to common phytoestrogens and antiestrogens.

CONCLUSIONS

The streamlined 12D hyphenation including a multiplex bioassay has been shown to differentiate hormonal effects, leading to new insights and better understanding. It can generally be used to identify unknown hormonally active compounds in complex samples.

Quality Assessment of Apple and Grape Juices from Serbian and German Markets by Planar Chromatography-Chemometrics

The high consumption of plant-based foods on a global scale has increased the number of adulterations in the food industry. Along with this, analytical approaches to fraud detection need to be further developed. A nontargeted effect-directed profiling by high-performance thin-layer chromatography hyphenated with five effect-directed assays (free radical scavenging assay, Aliivibrio fischeri bioassay, and acetylcholinesterase, butyrylcholinesterase, and tyrosinase inhibition assays) and multi-imaging provided additional information on the antioxidative, antimicrobial, and enzyme inhibition activities for 18 apple and 18 grape juices from markets in Serbia and Germany. Bioactive zones of interest were eluted using an elution head-based interface and further characterized by electrospray ionization high-resolution mass spectrometry. The different profiles were evaluated chemometrically, and several compounds, which were characteristic of samples from different markets located in Serbia and Germany, were identified in apple juice (such as chlorogenic acid, phloridzin, epicatechin, and caffeic acid) and grape juice (such as chlorogenic acid, epicatechin, and quercetin). The developed rapid and simple method for the quality assessment of fruit juices coming from different (geographic) markets showed clear quality differences. Thus, it could be used to learn more about quality differences, to detect fraud in fruit juice production, and to verify the authenticity of the origin.

Evidence that Indo-Pacific bottlenose dolphins self-medicate with invertebrates in coral reefs

Indo-Pacific bottlenose dolphins (Tursiops aduncus) have been observed queueing up in natural environments to rub particular body parts against selected corals (Rumphella aggregata, Sarcophyton sp.) and sponges (Ircinia sp.) in the Egyptian Northern Red Sea. It was hypothesized that the presence of bioactive metabolites accounts for this selective rubbing behavior. The three invertebrates preferentially accessed by the dolphins, collected and analyzed by hyphenated high-performance thin-layer chromatography contained seventeen active metabolites, providing evidence of potential self-medication. Repeated rubbing allows these active metabolites to come into contact with the skin of the dolphins, which in turn could help them achieve skin homeostasis and be useful for prophylaxis or auxiliary treatment against microbial infections. This interdisciplinary research in behavior, separation science, and effect-directed analysis highlighted the importance of particular invertebrates in coral reefs, the urgent need to protect coral reefs for dolphins and other species, and calls for further vertebrate-invertebrate interaction studies.

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Dolphins rubbed body parts against specifically selected corals and sponges

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Behavioral studies were linked with hyphenated bioanalytical technique

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Vertebrate-invertebrate interaction in coral reefs may serve self-medication

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Molecular formulae were assigned to known and unknown bioactive molecules

High-performance thin-layer chromatography–direct bioautography combined with chemometrics for the distinction of goldenrod species

Thirteen root extract samples of four goldenrod (Solidago) species present in Europe were investigated by hyphenated high-performance thin-layer chromatography (HPTLC). Only S. virgaurea is native, whereas S. gigantea, S. canadensis, and S. graminifolia have been introduced from North America. The bioactive zones in the Aliivibrio fischeri bioautogram were identified as polyacetylenes, labdane diterpenes, or clerodane diterpenes by HPTLC coupled to high-resolution mass spectrometry, exploiting the two interfaces, heated electrospray ionization, and direct analysis in real time. Principal component analysis of the obtained bioprofiles enabled the discrimination of the Solidago species. Furthermore, chemometrics pointed to the discriminative components, the main bioactive markers of the species: Z,Z-matricaria ester from S. virgaurea, solidagenone from S. canadensis, solidagoic acid A, and a dialdehyde clerodane diterpene from S. gigantea, and Z-dehydromatricaria ester from S. graminifolia.

Is Our Natural Food Our Homeostasis? Array of a Thousand Effect-Directed Profiles of 68 Herbs and Spices

The beneficial effects of plant-rich diets and traditional medicines are increasingly recognized in the treatment of civilization diseases due to the abundance and diversity of bioactive substances therein. However, the important active portion of natural food or plant-based medicine is presently not under control. Hence, a paradigm shift from quality control based on marker compounds to effect-directed profiling is postulated. We investigated 68 powdered plant extracts (botanicals) which are added to food products in food industry. Among them are many plants that are used as traditional medicines, herbs and spices. A generic strategy was developed to evaluate the bioactivity profile of each botanical as completely as possible and to straightforwardly assign the most potent bioactive compounds. It is an 8-dimensional hyphenation of normal-phase high-performance thin-layer chromatography with multi-imaging by ultraviolet, visible and fluorescence light detection as well as effect-directed assay and heart-cut of the bioactive zone to orthogonal reversed-phase high-performance liquid chromato-graphy-photodiode array detection-heated electrospray ionization mass spectrometry. In the non-target, effect-directed screening via 16 different on-surface assays, we tentatively assigned more than 60 important bioactive compounds in the studied botanicals. These were antibacterials, estrogens, antiestrogens, androgens, and antiandrogens, as well as acetylcholinesterase, butyrylcholinesterase, α-amylase, α-glucosidase, β-glucosidase, β-glucuronidase, and tyrosinase inhibitors, which were on-surface heart-cut eluted from the bioautogram or enzyme inhibition autogram to the next dimension for further targeted characterization. This biological-physicochemical hyphenation is able to detect and control active mechanisms of traditional medicines or botanicals as well as the essentials of plant-based food. The array of 1,292 profiles (68 samples × 19 detections) showed the versatile bioactivity potential of natural food. It reveals how efficiently and powerful our natural food contributes to our homeostasis.

Thin-layer chromatography in the authenticity testing of bee-products

Quality control, nutritional value and the monitoring of hazardous residues in honey bee- products have become major topics for both producers and consumers. Due to its potential role in human health, bee-products rich in bioactive compounds are becoming increasingly popular. This review aims to provide an overview of thin-layer chromatography methods used in quality control,authenticity testing and chemical profiling of bee-products in order to help scientists engaged in the field of bee-products chemistry to utilize the advantages of this technique in the detection and elimination of fraudulent practices in bee-product manufacturing. Recently, hyphenation of thin-layer chromatography, image analysis and chemometrics support bee-products analysisbysimultaneousdeterminationofanalytes with different detection principles, identification of individual bioactive compounds as well as structure elucidation of compounds. Highlighted opportunities of thin-layer chromatography could encourage further investigations that would lead to improvements in the detection and elimination of marketing fraudulent practices.

Acetylcholinesterase inhibitors in the giant goldenrod root

Eight bioactive clerodane diterpenes from the root extract of Solidago gigantea Ait. (giant goldenrod) were quantified by high-performance thin-layer chromatography (HPTLC) and two newly developed hyphenated methods. One uses vanillin sulphuric acid derivatization and densitometry, and the other an inhibition assay of acetylcholinesterase (AChE) and video densitometry. Both methods gave figures of merit for quantification including 5.8-33.9 ng and 175.5-448.7 ng LOQs and 2.7-6.9 RSD% and 8.8-13.9 RSD% inter-day precisions, respectively. Based on the diterpenes' content of 14 root samples collected over a year from the same plant population, the fully flowering plant is suggested to collect the root as a source of these compounds. Excepting one diterpene (with the lowest retardation factor), the quantitative results for the richest sample obtained by the two methods were in harmony. The difference could be due to a matrix effect.

Goldenrod Root Compounds Active against Crop Pathogenic Fungi

Root extracts of three goldenrods were screened for antimicrobial compounds. 2Z,8Z- and 2E,8Z-matricaria esters from European goldenrod (Solidago virgaurea) and E- and Z-dehydromatricaria esters from grass-leaved goldenrod (Solidago graminifolia) and first from showy goldenrod (Solidago speciosa) were identified by high-performance thin-layer chromatography combined with effect-directed analysis and high-resolution mass spectrometry or nuclear magnetic resonance spectroscopy after liquid chromatographic fractionation and isolation. Next to their antibacterial effects (against Bacillus subtilis, Aliivibrio fischeri, and Pseudomonas syringae pv. maculicola), they inhibited the crop pathogenic fungi Fusarium avenaceum and Bipolaris sorokiniana with half maximal inhibitory concentrations (IC₅₀) between 31 and 107 μg/mL. Benzyl 2-hydroxy-6-methoxybenzoate, for the first time found in showy goldenrod root, showed the strongest antifungal effect, with IC₅₀ of 25-26 μg/mL for both fungal strains.

High-throughput enzyme inhibition screening of 44 Iranian medicinal plants via piezoelectric spraying of planar cholinesterase assays

A rapid and straightforward approach was developed for screening the acetyl- and butyrylcholinesterase (ChE) inhibitory activity of 44 Iranian medicinal plant extracts at laboratory scale. After a fast ChE inhibitory pre-testing of samples applied as band pattern, 40 out of the 44 Iranian medicinal plant extracts were selected. These were adjusted in the application volume depending on their inhibition activity, applied on both plate sides and simultaneously developed in a horizontal developing chamber. Different mobile phases were studied to achieve maximum separation of ChE inhibitors and minimum co-elution with matrix. Contrary to immersion, the piezoelectric spraying reduced the consumption of assay solutions, prevented zone tailing, zone shift and cross-contamination, and homogeneously covered the entire plate surface with the assay solutions. The ChE inhibitors of the six most bioactive plant extracts were tentatively assigned by high-resolution mass spectrometry in combination with the spectral and chromatographic information obtained.

A bioimaging system combining human cultured reporter cells and planar chromatography to identify novel bioactive molecules

For the first time, a human cancer cell line was shown to grow and be functionally active on the particulate porous adsorbent surface of separated sample mixtures. This allowed the novel combination of chromatographic separations with human cells as biological detector. As exemplary screening for cancer treatment drugs, cytotoxic substances were directly discovered in Saussurea costus and ginseng samples using the Cytotox CALUX® osteosarcoma cells (with luciferase expressing reporter gene) as detector. In addition, rosiglitazone and pioglitazone were detected as luminescent zones upon binding to the PPARγ receptor expressed in the respective CALUX cell line that was grown on the surface of the adsorbent. This demonstrates the ability to address receptor-mediated signaling with this method, and opens the perspective to use our novel bioimaging method to identify bioactive molecules targeting a wide range of pathways with toxicological, pharmaceutical and nutraceutical relevance. The new bioimaging directly pointed to individual effective compounds in multi-component mixtures. Furthermore, discovered effective compounds were directly characterized by online elution to high-resolution mass spectrometry and fragmentation.

Effect-directed profiling of 32 vanilla products, characterization of multi-potent compounds and quantification of vanillin and ethylvanillin

Food testing is of great importance to the food industry and organizations to verify the authenticity claims, to prove the quality of raw materials and products, and to ensure food safety. The market prices of vanilla differed by a factor of about 20 in the last three decades. Therefore the risk of adulteration and counterfeiting of vanilla products is high. Instead of commonly used target analyses and sum parameter assays, a complementary non-target multi-imaging effect-directed screening was developed, which provided a new perspective on the wide range of vanilla product qualities on the market. Planar chromatography was combined with effect-directed assays, and the obtained biological and biochemical profiles of 32 vanilla products from nine different categories revealed a variety of active ingredients. Depending on the region, typical vanilla product profiles and activity patterns were obtained for pods, tinctures, paste (inner part), oleoresin and powders. However, some vanilla products showed additional active compounds and a different intensity pattern. The vanilla product profiles substantially differed from those of vanilla aroma or products containing synthetic vanillin or vanilla-flavored food products. Bioactive compounds of interest were online eluted and further characterized via HPTLC-HRMS, which allowed their tentative assignment. After purchase of the standards, these were successfully confirmed by co-chromatography. Quantification of vanillin across nine different product categories revealed levels ranging from 1 µg/g to 36 mg/g with a mean repeatability of 1.9%. The synthetic ethylvanillin was not detected in the investigated samples in significant concentrations. The assessment of differences in the activity patterns pointed to highly active compounds, which were not detected at UV/Vis/FLD but first via the biological and enzymatic assays. This effect-directed profiling bridges the gap from analytical food chemistry to food toxicology, and thus, makes an important contribution to consumer safety. In the same way, it would accelerate investigations for Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) according to Regulation (EC) No. 1907/2006.

Open-source all-in-one LabToGo Office Chromatography

Print and media technologies were used uncommonly in the field of chromatography and explored in application to create a miniaturized all-in-one LabToGo system. This novel research field termed Office Chromatography (OC) uses additive manufacturing in terms of 3D printing of operational parts as well as open-source hard- and software. The OCLab2 presented here has been considerably extended in its functionalities. For inkjet printing of solutions, a newly designed printhead was manufactured controlled by a self-constructed ink-jet board, allowing to check the nozzles' resistance heating circuit. Plate heating was newly integrated, especially favorable for the demonstrated application of higher volumes of aqueous samples. The UV/Vis/FLD plate images were captured by a Raspberry Pi V2 camera module under illumination by novel light emitting diodes (LEDs) for highly selective RGBW color (Vis), UVC 278-nm (UV) and UVA 366-nm (FLD) detection, installed in a newly created miniature cabinet to protect from extraneous light. The spectral separation of differently colored food dyes was achieved by the fully addressable driver controlled RGBW LEDs. The software was newly written in R to speed-up the processes, supported by the new Raspberry Pi 4B computer with 4 GB RAM. The analysis of Stevia leaves for steviol glycosides yielded results comparable to the status quo. Different water samples were analyzed for bioactive compounds. Thereby, compounds of general cytotoxicity were effect-directed detected by bioluminescent A. fischeri bacteria. It allowed the bioanalytical screening for potential risks in tap water, surface waters, rain water, landfill leachates and biogas slurries.