Bioprofiling of unknown antibiotics in herbal extracts: Development of a streamlined direct bioautography using Bacillus subtilis linked to mass spectrometry

A comprehensive study on Geranium robertianum L. antibacterial potential

AIMS

The research aimed to optimize the ultrasound-assisted extraction of secondary metabolites and the antibacterial activity of the plant species Geranium robertianum. The phytochemical profiles of the optimized extracts, as well as their antibacterial and synergistic activity with an antibiotic and their potential mechanisms of action and cytotoxicity, were examined.

METHODS AND RESULTS

Response Surface Methodology was used to optimize extraction conditions. Optimized ethanol and acetone extracts were tested via microdilution, checkerboard, time-kill kinetics, and cell membrane permeability methods. The extracts displayed broad antibacterial activity with minimum inhibitory concentrations ranging from 1.25 to 20 mg ml-1. In addition, the extract synergistically reacted with gentamicin against gentamicin-resistant strains of Escherichia coli and Staphylococcus aureus, enhancing the efficacy of the antibiotic up to 32-fold. The extracts demonstrated strain-dependent bactericidal activity in a 24-h time interval. They increase the permeability of the cell membrane, thus disrupting its normal functioning. The cytotoxic concentration (CC50) on human keratinocytes was 1771.24 ± 5.78 µg ml-1 for ethanol extract, and 958.01 ± 6.14 µg ml-1 for acetone extract. Kaempferol, ellagic acid, quercetin, and rutin were recognized as the main components in both extracts.

CONCLUSIONS

The findings of this study indicate that the extracts of G. robertianum can be considered as potential natural antibacterial agents in the control of microorganisms.

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).

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.

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.

Nine-dimensional bioprofiles of Tunisian sages (Salvia officinalis, S. aegyptiaca and S. verbenaca) by high-performance thin-layer chromatography - effect-directed analyses

Ethyl acetate extracts of Tunisian Salvia aegyptiaca and S. verbenaca aerial parts and S. officinalis leaves were examined via bioanalytical profiling using high-performance thin-layer chromatography (HPTLC) combined with nine bioactivity assays, namely antibacterial (Aliivibrio fischeri, Bacillus subtilis, and Rhodococcus fascians), antifungal (Bipolaris sorokiniana, and Fusarium avenaceum), radical scavenging (DPPH•), and enzyme inhibitory (α-glucosidase, acetylcholinesterase, and lipase) ones. The screening, using toluene - ethyl acetate - methanol 6:3:0.5 (V/V/V) as a mobile phase, revealed five bioactive zones (a-e) that were analyzed by HPTLC-electrospray ionization-mass spectrometry (ESI-MS). Zones b and c, observed exclusively in S. officinalis, were active in all assays except α-glucosidase, and only c inhibited F. avenaceum. Compounds in these zones were identified by HPLC-high resolution tandem MS (LC-HRMS/MS) as rosmanol/epi-rosmanol and methyl carnosate, respectively. In the bioactive zones a and e, corosolic/maslinic acid and ursolic/oleanolic acid isomer pairs were present, which could be identified in all three Salvia species after their HPTLC separation using pre-chromatographic derivatization with iodine and MS detection. The triterpenes inhibited B. subtilis and R. fascians bacteria and α-glucosidase enzyme. Linoleic and linolenic acids were detected in zone d, which showed strong lipase inhibition in all three sage species.

Effect-Directed Profiling of Strawberry Varieties and Breeding Materials via Planar Chromatography and Chemometrics

Strawberries are an important fruit in the European diet because of their unique taste and high content of essential nutrients and bioactive compounds. The anthocyanins are known to be colorful phenolics in strawberries. In 17 samples of six strawberry cultivars produced in Serbia, i.e., the common varieties Alba, Asia, and Clery as well as promising breeding materials (11.29.11, 11.34.6, and 11.39.3), the anthocyanin profile as well as antimicrobial and antioxidative activity profiles were determined. All investigated extracts showed antioxidative and antibacterial activities against Gram-negative Aliivibrio fischeri. The responses were quite similar in number and intensity. The HPTLC-DPPH• scavenging assay and HPTLC-Aliivibrio fischeri bioassay coupled with high-resolution mass spectrometry identified pelargonidin-3-O-glucoside (Pg-3-glc) as the main anthocyanin and prominent antioxidative and antimicrobial compound in strawberries. The density functional theory calculations at the M06-2X/6-31+G(d,p) level showed that Pg-3-glc quenches free radicals via sequential proton loss electron transfer mechanism in water and in pentyl ethanoate, where the 5-OH group is the most reactive site for proton and hydrogen atom transfer. The results were confirmed via spectrophotometry. The highest total phenolic content was found in Clery and 11.39.3, while statistically significant differences between the genotypes regarding the antioxidant activity were not confirmed. Although very similar in the anthocyanin, antioxidative, and antimicrobial profile patterns, the strawberry genotypes were successfully classified using principal component analysis.

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.

Puree and Juice of Thai Mango and Pineapple Analyzed by High-Performance Thin-Layer Chromatography Hyphenated with Effect-Directed Assays

The requirements for analytical tools are changing due to the global production chain, the increasing cases of adulteration, and the growing trend towards consumption of plant-based food products worldwide. The assessment of bioactivity of natural foods is currently not a quality criterion, and a paradigm shift is postulated. A non-targeted effect-directed profiling by high-performance thin-layer chromatography hyphenated with five different effect-directed assays was developed exemplarily for the puree and juice products of mango Mangifera indica L. (Anacardiaceae) and pineapple Ananas comosus (L.) Merr. (Bromeliaceae). Several bioactive compounds were detected in each sample. The additional bioactivity information obtained through effect-directed profiles improves, expands and modernizes product control. Non-target effect-directed profiling adds a new perspective to previous target analysis results that can be used not only to ensure health claims based on bioactive compounds, but also to detect unknown bioactive compounds coming from contamination or residues or changes caused by food processing.

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.

Nanomole-scaled high-throughput chemistry plus direct bioautography on the same chromatography plate for drug discovery

The powerful fusion of on-surface synthesis and effect-directed analysis was introduced as novel tool for synthetic drug discovery, all on the same high-performance thin-layer chromatography plate. Precise automated sample application allowed both, high-throughput chemistry of 60 reactions at once and reaction miniaturization down to the 15-nmol scale. The antibiotic activity of all on-surface synthesized compounds was evaluated on the same surface via the Gram-positive Bacillus subtilis bioassay. For one product, synthesis (reaction, purification and identification) took 5.3 min and semi-quantitative biological evaluation took 2.8 min. Out of 60 on-surface reactions 10 products (17%) were identified to be more active than a well-known antibiotic reference. The concept was transferred to the Gram-negative Aliivibrio fischeri bioassay. For the first time, a new analytical platform was shown for a streamlined workflow at the most miniaturized scale from synthesis, purification, identification and quantification to semi-quantitative biological activity evaluation (all on the same chromatography plate).

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.

On-surface autosampling for liquid chromatography-mass spectrometry

An on-surface multi-purpose autosampler was built for liquid chromatography-mass spectrometry (LC-MS) based on the autoTLC-MS interface, taking advantage of open-source hard- and software developments as well as 3D printing. Termed autoTLC-LC-MS system, it is introduced for orthogonal hyphenation of normal phase high-performance thin-layer chromatography with reversed phase high-performance LC (HPLC) and high-resolution MS (HRMS). For verification of its functionality, a multi-class antibiotic mixture was applied as a calibration band pattern on an adsorbent layer and detected by the Bacillus subtilis bioassay. This effect-image was uploaded as a template in the updated TLC-MS_manager software. The clicked-on antibiotic zones were sequentially eluted without intervention from the planar counterpart (without bioassay) via a monolithic HPLC column into the HRMS system. For elution of antibiotics of 7 structural classes at 5 different calibration levels, the new on-surface autosampler achieved intra-day precisions of 2.1-14.1%, while inter-day precisions ranged 2.5-16.1% (all n = 3). The new hyphenation offers potential for planar sample clean-up prior to HPLC, concentration of liquid samples, increase of peak capacity and proof of peak purity or isomers. The integrated autoTLC-LC-MS system enabled high sample throughput, efficiency and reproducibility for the first time through fully automated TLC-LC-MS sequence operation. Its contact-closure signal functionality, versatile 3D printed planar sample holder and open-source software made it readily adjustable for new analytical tasks. Undoubtedly, any planar material can be investigated for leachables, such as textiles, foils, papers and other packagings, as well as planar biological samples for ingredients.

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.

Imaging high-performance thin-layer chromatography as powerful tool to visualize metabolite profiles of eight Bacillus candidates upon cultivation and growth behavior

Imaging high-performance thin-layer chromatography (HPTLC) was explored with regard to its ability to visualize changes in the metabolite profile of bacteria. Bacillus subtilis has become a model organism in many fields. The increasing interest in these bacteria is driven by their attributed probiotic activity. However, growth behavior and metabolism of Bacillus species have a considerable influence on their activity and secondary metabolite profile. On the HPTLC plate, cultivation broths of Bacillus species (B. subtilis, B. licheniformis, B. pumilus and B. amyloliquefaciens) and some B. subtilis strains of high genetic similarity up to 99.5% were applied directly and compared with their respective liquid-liquid extracts. The latter as well as the cultivation in a minimal medium reduced the matrix load and improved the zone resolution. Cultivation parameters such as nutrient supply, cultivation temperature, cultivation time and rotational speed (oxygen level) as well as medium change were shown to have a considerable influence on the growth behavior and resulting metabolite profiles. Imaging HPTLC turned out to be an efficient and affordable tool to visualize such influences of cultivation parameters on the metabolite profiles. It converts the complexity of reaction processes occurring during cell cultivation in easy-to-understand images, which are helpful to figure out factors of influence and understand activity changes. The results highlighted that optimal cultivation conditions need to be found for the intended bacterial application, and in particular, these conditions have to be kept constant. It must be ensured that small variations in cultivation parameters of bacteria do not change the specified (probiotic) effect on the health of animals and humans. The HPTLC metabolite profiles represented the cultivation conditions of specific bacteria and were found to be a proof of the activity of distinct bacteria. In addition, HPTLC can also be used to optimize and streamline the culture media. The quality control of cultivation or fermentation processes can benefit from such a powerful tool, as a picture is worth a thousand words.

Effect-directed profiling of Ficus religiosa leaf extracts for multipotent compounds via 12 effect-directed assays

The interest in the therapeutic values of natural compounds from plants is growing worldwide because the development of modern synthetic drugs has not lived up to expectations. The tree Ficus religiosa native to India, China and Southeast Asia is traditionally used for curing almost 50 ailments, although the majority of the individual active compounds are not known. Hence, a hyphenated high-performance thin-layer chromatography (HPTLC) method was newly developed. It allowed a physicochemical, but especially effect-directed profiling of individual compounds present in Ficus religiosa leaves obtained from four locations (in India and Germany). Extracts of different polarities were screened for bioactivity responses and most bioactivities were found in the ethyl acetate extracts. A multi-imaging via 26 different detection modes was performed, i. e. UV/Vis/FLD, 11 microchemical derivatizations and 12 effect-directed assays (EDA). By HPTLC-UV/Vis/FLD-EDA, antibiotics against Gram-positive and Gram-negative bacteria as well as acetylcholinesterase, butyrylcholinesterase, tyrosinase, α-amylase, α-glucosidase and β-glucosidase inhibitors and radical scavenging compounds were detected. Estrogen-like or gentotoxic compounds were not detected at higher extract amounts of even 5 mg/band applied. For further characterization of three most important, multipotent, bioactive compound zones, HPTLC was hyphenated with heated electrospray ionization high-resolution mass spectrometry including fragmentation (HPTLC-HESI-HRMS/MS). Multipotent bioactive compounds discovered in the extracts were equivalently calculated in reference to well-known reference inhibitors.

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.

Same analytical method for both (bio)assay and zone isolation to identify/quantify bioactive compounds by quantitative nuclear magnetic resonance spectroscopy

Differing sensitivity is the main obstacle for a direct combination of HPTLC with NMR spectroscopy. A sufficient amount of the isolated compound zone must be provided by HPTLC for subsequent offline NMR detection (HPTLC//NMR). To fill the gap, a straightforward procedure was developed using the same analytical HPTLC system for both bioprofiling and isolation of bioactive zones from multicomponent mixtures. The HPTLC-effect-directed analysis (EDA) revealed several bioactive compounds in five botanical extracts, i.e. Salvia officinalis, Thymus vulgaris and Origanum vulgare, all Lamiaceae, and peels of red and green apples (Jonagored and Granny Smith, respectively), both Rosaceae. A tricky case study was designed to show how to deal with potentially coeluting bioactive structural isomers, e.g., ursolic (UA), oleanolic (OA) and betulinic acids (all C30H48O3), which are most difficult to identify and assign. A multipotent bioactive HPTLC zone showed the same hRF value and mass signal in HPTLCHRMS, though containing the coeluting structural isomers UA and OA. After zone isolation from the HPTLC plate, first the 1H NMR spectrum allowed to distinguish distinct allylic H-18 protons, i.e. 2.20 ppm for UA and 2.85 ppm for OA, and at the same time, to quantify the two isomers by using the PUlse Length-based CONcentration methodology (HPTLC//1H qNMR-PULCON). In case of a partial overlap of the diagnostic signal with that of the matrix, results were corroborated with those obtained by using the 1H deconvoluted or 2D 1H-13C Heteronuclear Single Quantum Coherence spectra. The comparison of the quantitative results showed a good correlation (R2 = 0.9718) between the two orthogonal methods HPTLC-Vis and HPTLC//1H qNMR-PULCON. A sufficient zone isolation from the HPTLC plate (mean isolation rate of 82%) for both UA and OA (0.27 - 4.67 mM) was achieved for HPTLC//qNMR, comparing the isolated bioactive compound zone with the respective zone in the botanical extract via HPTLC-Vis densitometry. The HPTLC-EDA-Vis//1H qNMR-PULCON procedure for bioprofiling and quantification/identification/confirmation of bioactive compounds in botanical extracts is considered as straightforward, eco-friendly (only 16 mL solvent required), simple (NMR calibration used over weeks) and reliable new alternative to the status quo of bioactivity-guided fractionation.

Effect-directed analysis of bioactive compounds in Cannabis sativa L. by high-performance thin-layer chromatography

The scientific interest on the plant Cannabis sativa L., and in particular on its non-psychoactive or fibre-type variety (hemp), has been highly increasing in recent years, due to the pharmaceutical and nutraceutical potential of its bioactive compounds. This plant is indeed characterized by a very rich chemical composition, which encompasses different classes of constituents, such as cannabinoids and terpenes. In this context, the bioanalytical testing of hemp extracts can be difficult and time-consuming. Effect-directed analysis (EDA) by the combination of high-performance thin-layer chromatography (HPTLC) with biological and enzymatic assays represents one of the latest tools available for the rapid bioprofiling of complex matrices, such as plant extracts. In this ambit, the aim of this project was the non-targeted screening of inflorescence extracts from ten different hemp varieties for components exhibiting radical scavenging, antibacterial, enzyme inhibiting and estrogen-like effects. By HPTLC-EDA, the hemp samples exhibited strong antibacterial activities against both Gram-positive Bacillus subtilis and especially Gram-negative Aliivibrio fischeri bacteria, and also estrogen-like activity. They also inhibited α- and β-glucosidase, tyrosinase and acetylcholinesterase. The characterization of two prominently multipotent bioactive compound zones was finally achieved by HPTLC-HRMS and preliminary assigned as cannabidiolic acid and cannabidivarinic acid.

TLC Bioautography on Screening of Bioactive Natural Products: An Update Review

Background:

TLC bioautography is a hyphenated technique combining planar chromatographic separation and in situ biological activity detection. This coupled method has been receiving much attention in screening bio-active natural products because of its properties of being simple, rapid, inexpensive, and effective.

Methods:

The recent progress in the development of method of TLC bioautography for detecting antimicrobial and enzyme inhibitory activities dating between 2012 and early 2018 has been reviewed. The applications of this method in biological screening of natural products were also presented.

Results:

Some anaerobic and microaerophilic bacteria and a causative bacterium of tuberculosis have been adopted to TLC direct bioautography. Seven types of enzymes including acetylcholinesterase, glucosidase, lipase, xanthine oxidase, tyrosinase, monoamine oxidase, and dipeptidyl peptidase IV have so far been adopted on TLC bioautography. Its new application in screening antiurolithiatic agents was included.

Conclusion:

The standard experimental procedures are required for TLC antioxidant and antimicrobial assays. Some new enzymes should be attempted and adopted on TLC bioautography. The existing TLC methods for enzyme inhibition need more application studies to assess their screening capacity in the discovery of active compounds. The GC-MS or LC-MS approaches have gradually been coupled to TLC bioautography for fast structural characterization of active compounds.

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.

Effect-directed profiling and identification of bioactive metabolites from field, in vitro-grown and acclimatized Musa spp. accessions using high-performance thin-layer chromatography-mass spectrometry

Bananas and plantains (Musa spp.) are used as nutritious foods, and at the same time, are a source of phytoconstituents for the pharmaceutical industry. As biological activities of especially the pulp and peel of Musa spp. have been documented, this study investigated the variation in the secondary metabolite profiles of the leaves from field, in vitro-grown and acclimatized accessions. The genetic fidelity of the diverse accessions was assessed using diversity array technology sequencing. It showed that the in vitro-grown accessions were true-to-type with the field samples. The antioxidant and anticholinesterase activities of the samples from different culture systems (field and in vitro) were evaluated by UV-spectrophotometry and compared to high-performance thin-layer chromatography-effect-directed analysis (HPTLC-EDA). The latter was applied for the first time for effect-directed profiling of the polar and medium polar sample components via different biochemical and biological assays. Compound zones showed acetyl-/butylrylcholinesterase inhibition (zones 1-4), α-/β-glucosidase inhibition (zones 1 and 2) as well as antioxidative (zones 1-3) and antimicrobial (zone 4) activities. Structures were preliminary assigned by HPTLC-HRMS. The HPTLC was effective for bioactivity-guided characterization of the bioactive constituents in Musa spp. accessions. Accumulation of useful metabolites, especially compounds with antioxidant and anticholinesterase properties, was higher in samples from in vitro system. This validated the use of plant tissue culturing as an alternative method for large scale production of plant material and supply of bioactive constituents.

Guided isolation of new iridoid glucosides from Anarrhinum pubescens by high-performance thin-layer chromatography-acetylcholinesterase assay

Plants are an important source of natural iridoids. This study demonstrates for the first time the acetylcholinesterase (AChE) inhibitory activity of iridoids belonging to the class of antirrhinosides. As iridoids distinguish the chemical composition of most species of the Plantaginaceae family, the active AChE inhibitors were investigated in the hydro-alcoholic extract of Anarrhinum pubescens Fresen. High-performance thin-layer chromatography (HPTLC) in combination with the AChE inhibition assay is a time and material saving methodology, and thus was employed to directly point to the individual enzyme inhibitors occurring in the plant. The effect-directed screening successfully discovered three active metabolites. These were characterized as antirrhinoside-derived iridoids. Two of these are here reported as newly isolated natural compounds. Identification of the two new metabolites was based on analysis of their collected spectroscopic data (HRMS, 1D and 2D NMR). Their structures were elucidated to be 6-O-, 6'-O-di-trans-cinnamoyl-antirrhinoside (1) and 5-O-, 6-O-difoliamenthoyl-antirrhinoside (3), while the previously known compound 6-O-foliamenthoyl-(6'-O-cinnamoyl)-antirrhinoside (2) was assigned by extensive analysis of its HRMS and HRMS/MS data. The activity of the isolated compounds was referred to the known AChE inhibitor rivastigmine, i.e. their activity were calculated and expressed as values equivalently to rivastigmine. This neuroprotective potential of iridoids mediated through AChE inhibition promote them to compete as natural curatives for neurodegenerative disorders like Alzheimer's disease.

Automated piezoelectric spraying of biological and enzymatic assays for effect-directed analysis of planar chromatograms

Bioanalytical questions are more and more solved by bioassays directly in situ the planar separation. If compared to chemical derivatization in situ, several reagent applications on the same chromatogram make the workflow for enzymatic and biological assays more complex. Hence, if compared to piezoelectric spraying of chemical derivatization reagents, an assay transfer to the piezoelectric spraying technique was much more challenging. Important aspects were investigated, i.e., plate pre-wetting, spraying nozzle type and applied volumes for microorganism suspension as well as enzyme and substrate-chromogenic solutions. Finally, with the newly developed piezoelectric spraying procedures for the application of biological (Aliivibrio fischeri) and enzymatic (acetyl- and butyrylcholinesterase) assays, several obstacles of the state-of-the-art automated immersion were avoided such as the (1) required high volumes of solutions, (2) tailing of highly water-soluble zones upon slow plate withdrawal, (3) zone distortion or shift observed after previous buffer salt applications or long/slow immersion times/speeds, (4) gradual inactivation of the enzyme solution along with its ongoing re-use, and (5) lack of covering the whole plate surface. The benchmarking of both techniques also showed that simplicity remains the key argument for immersion. As proof of concept, piezoelectrically sprayed autograms were compared with those of immersion, by taking the example of Peganum harmala (P. h.) seed extract. The plate background and thus homogeneity of the applied solutions were found to be almost comparable. Three bands among the pronounced fluorescent bands were responsible for the most antibacterial activity of P. h. seed extract in the A. fischeri bioassay and were also inhibiting the AChE. These AChE and three further BChE inhibitors were detected, whereby the AChE inhibition was twice as strong as the BChE inhibition. By their in situ HRMS spectra, the active zones in the P. h. seed extract were assigned to be the AChE-inhibiting β-carboline alkaloids, harmine, harmaline and ruine, as well as the BChE-inhibiting quinazoline alkaloids, vasicine and deoxyvasicine, and the β-carboline alkaloid harmol. For the first time, the found inhibitors were calculated equivalently to the well-known ChE-inhibitor physostigmine, and thus, piezoelectric spraying was proven to be suited for quantifications.

Characterisation and screening of antimicrobial essential oil components against clinically important antibiotic-resistant bacteria using thin layer chromatography-direct bioautography hyphenated with GC-MS, LC-MS and NMR

INTRODUCTION

The antimicrobial activity of many essential oils (EOs) is well established, indicating that EOs may be a source of compounds for antimicrobial drug development. Thin layer chromatography-direct bioautography (TLC-DB) can quickly identify antimicrobial components in complex mixtures and can be applied to the screening of EOs for lead compounds.

OBJECTIVES

This study aimed to identify antimicrobial components of oregano, rosewood and cumin EOs against antibiotic-sensitive and -resistant bacteria using TLC-DB and a multi-faceted approach of GC-MS, LC-MS and NMR techniques to characterise bioactive compounds. The study also aimed to quantify the antimicrobial activity of bioactive compounds in order to evaluate their potential for the development of therapies against antibiotic-resistant bacteria.

MATERIALS AND METHODS

EOs were eluted on TLC plates and sprayed with a suspension of Staphylococcus aureus, Enterococcus faecium, Escherichia coli or Pseudomonas aeruginosa (antibiotic-sensitive and -resistant isolates). Zones of inhibition, visualised with iodonitrotetrazolium chloride, were subject to GC-MS, LC-MS and NMR to characterise the bioactive compounds.

RESULTS

Seven compounds were identified from the three EOs using GC-MS, while LC-MS and NMR failed to detect the presence of any further non-volatile or heat labile compounds. Carvacrol was most antimicrobial compound identified, with minimum inhibitory concentrations ranging 0.99-31.62 mM.

CONCLUSION

The identified antimicrobial compounds present in oregano, rosewood and cumin EOs including carvacrol may be candidates for the development of novel antimicrobial therapies against antibiotic-resistant bacteria.

Two-Dimensional Thin Layer Chromatography-Bioautography Designed to Separate and Locate Metabolites with Antioxidant Activity Contained on Spirulina platensis

Spirulina platensis contains several biologically active compounds, some of them with antioxidant activity. Nevertheless, not all of these compounds have been identified to date. As a first step to achieving such identification, a methodology to perform two-dimensional thin layer chromatography bioautographies on silica gel thin layer chromatography plates was proposed. Starting with a reference binary system, 5 other binary systems were tested, in which the relative polarity was systematically increased. To further improve the separation behavior, a phase modifier (NH₄OH) was used. The best separation results were obtained with the isopropyl alcohol/ethyl acetate/NH₄OH ternary system. This experimental system allowed four well-resolved spots showing antioxidant activity as well as two additional areas with mixtures containing antioxidant compounds. Although the proposed methodology was designed with a specific application, it would be predictable that its field of use could be considerably greater, making the convenient modifications on the solvent polarity and “masking level” produced by the ammonium derivatives.

Direct bioautography hyphenated to direct analysis in real time mass spectrometry: Chromatographic separation, bioassay and mass spectra, all in the same sample run

Mass spectra were recorded directly in situ the bioautogram, i.e., in the presence of microorganisms, bioassay medium and substrate reagent. The desorption-based direct analysis in real time mass spectrometry (DART-MS) was applied immediately after direct bioautography (DB). It turned out to be an advantageous combination, as it offered the possibility of a straightforward mass spectrometric detection of bioactive analytes within the bioautogram, and at the same time, it was discriminating microorganism cells and highly polar bioassay medium ingredients which could otherwise stress the MS system. DB-DART-MS was investigated for bioactive compounds in cosmetics using the Bacillus subtilis and Aliivibrio fischeri bioassays for detection of Gram-positive and Gram-negative antimicrobials, respectively, and the planar yeast estrogen screen for detection of estrogen-effective compounds. The influences of the three different bioassay matrices on the analyte response and DB-DART-MS performance on different layers were studied on the example of parabens in hand creams. It was shown that with increasing culture medium complexity, the ion suppression increased. As proof-of-principle, the mass spectrometric quantification at the nanogram level in situ the bioautogram was verified by comparison to HPTLC-DART-MS. The total paraben contents of hand creams 1 and 2 were 0.17-0.20% and 0.30-0.34%, respectively, depending on the method used (DB-DART-MS with two different bioassays or HPTLC-DART-MS as well as on RP_W or NP plate). In contrast to the current practice of applying the sample twice and subjecting one track to the bioassay and another to MS, the introduced hyphenation DB-DART-MS is straightforward and highly efficient.

Effect-directed analysis of ginger (Zingiber officinale) and its food products, and quantification of bioactive compounds via high-performance thin-layer chromatography and mass spectrometry

Decision makers responsible for quality management along the food chain need to reflect on their analytical tools that should ensure quality of food and especially superfood. The "4ables" in target analysis (stable, extractable, separable, detectable) focusing on marker compounds do not cover all relevant information about the sample. On the example of ginger, a streamlined quantitative bioprofiling was developed for effect-directed analysis of 17 commercially available ginger and ginger-containing products via high-performance thin-layer chromatography (HPTLC-UV/Vis/FLD-bioassay). The samples were investigated concerning their active profile as radical scavengers, antimicrobials, estrogen-like activators and acetylcholinesterase/tyrosinase inhibitors. The [6]-gingerol and [6]-shogaol content of the different products ranged 0.2-7.4mg/g and 0.2-3.0mg/g, respectively. Further, multipotent compounds were discovered, characterized, and for example, assigned as [8]- and [10]-gingerol via HPTLC-ESI-HRMS. The developed bioprofiling is a step forward to new analytical methods needed to inform on the true product quality influenced by cultivation, processing, and storage.

Alkaloids of Amaryllidaceae as Inhibitors of Cholinesterases (AChEs and BChEs): An Integrated Bioguided Study

INTRODUCTION

Enzymatic inhibition of acetylcholinesterase (AChE) is an essential therapeutic target for the treatment of Alzheimer's disease (AD) and AChE inhibitors are the first-line drugs for it treatment. However, butyrylcholinesterase (BChE), contributes critically to cholinergic dysfunction associated with AD. Thus, the development of novel therapeutics may involve the inhibition of both cholinesterase enzymes.

OBJECTIVE

To evaluate, in an integrated bioguided study, cholinesterases alkaloidal inhibitors of Amaryllidaceae species.

METHODOLOGY

The proposed method combines high-performance thin-layer chromatography (HPTLC) with data analysis by densitometry, enzymatic bioautography with different AChEs and BChEs, the detection of bioactive molecules through gas chromatography mass spectrometry (GC-MS) analysis of spots of interest, and theoretical in silico studies.

RESULTS

To evaluate the bioguided method, the AChE and BChE inhibitory activities of seven Amaryllidaceae plant extracts were evaluated. The alkaloid extracts of Eucharis bonplandii exhibited a high level of inhibitory activity (IC₅₀  = 0.72 ± 0.05 μg/mL) against human recombinant AChE (hAChE). Regarding human serum BChE (hBChE), the bulb and leaf extracts of Crinum jagus had the highest activity (IC₅₀  = 8.51 ± 0.56 μg/mL and 11.04 ± 1.21 μg/mL, respectively). In the HPTLC spots with high inhibitory activity, several alkaloids were detected using GC-MS, and some of these alkaloids were identified. Galanthamine, galanthamine N-oxide and powelline should be the most prominent inhibitors of substrate accommodation in the active site of the Torpedo californica AChE (TcAChE), hAChE and hBChE enzymes.

CONCLUSIONS

These results are evidence of the chemical relevance of the Colombian's Amaryllidaceae species for the inhibition of cholinesterases and as potent sources for the palliative treatment of AD. Copyright © 2017 John Wiley & Sons, Ltd.

Discovered acetylcholinesterase inhibition and antibacterial activity of polyacetylenes in tansy root extract via effect-directed chromatographic fingerprints

The knowledge about the activity of polyacetylenes was extended by their new acetylcholinesterase inhibition and antibacterial activity against plant pathogenic bacteria. For this discovery, an utmost streamlined workflow, which we consider to be of high potential in the field of natural product or superfood search was developed. It demonstrates the combined power of biological, biochemical and chemical fingerprints. Bioactive components of tansy (Tanacetum vulgare L.) root extract were profiled and identified by high-performance thin-layer chromatography hyphenated with in situ effect-directed analysis, chemical derivatizations and high-resolution mass spectrometry (HPTLC-UV/Vis/FLD-EDA-HRMS). The effect-directed profiling was performed using four bacterial bioassays including two plant pathogens, an antioxidant assay and acetyl- and butyrylcholinesterase inhibitory assays. The chromatographic, spectral and powerful mass spectrometric study of zones that exerted substantial antibacterial and/or antioxidant and/or acetylcholinesterase inhibitory effects allowed these multi-potent zones to be identified as polyacetylenes. Five polyacetylene compounds were assigned to be 2-non-1-ene-3,5,7-triynyl-3-vinyl-oxirane, 2-(2,4-hexadiynylidene)-3,4-epoxy-1,6-dioxaspiro[4.5]decane, trans- and cis-2-(2,4-hexadiynylidene)-1,6-dioxaspiro[4.5]dec-3-ene and tetradeca-2,4,6-triine-8-en-12-one. This study clearly showed the advantage of the combined use of different ionization sources, i.e. electrospray ionization via an elution-head based interface and also the Direct Analysis in Real Time interface, for HRMS analysis of compounds from the same class with very similar chromatographic behavior and polarity.

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.