Label-free SELEX of aptamers for ultra-sensitive electrochemical aptasensor detection of amanitin in wild mushrooms.

BACKGROUND: Mushroom poisoning poses a significant global health concern, with high morbidity and mortality rates. The primary lethal toxins responsible for this condition are alpha-amanitin (ɑ-AMA) and beta-amanitin (ß-AMA). As a promising bio-recognition molecules in biosensors, aptamers, have been broadly used in the field of food detection. However, the current SELEX-based methods for screening aptamers for structurally similar small molecules were limited by the labelling or salt ion induction. In this study, we aimed to develop a novel label-free SELEX strategy for the screening of aptamers with high affinity and constructed new aptasensors for the detection of ɑ-AMA and ß-AMA. RESULTS: A novel label-free SELEX strategy based on the positively charged gold nanoparticles (AuNPs) was proposed to simultaneous screening of aptamers for ɑ-AMA and ß-AMA. Only 18 rounds of SELEX were required to obtain new aptamers. The candidate aptamers were analyzed by colloidal gold assay, and the sequences of ɑ-30 and ß-37 displayed great affinity with Kd values of 22.26 nM and 23.32 nM, respectively, without interference from botanical toxins. Notably, the truncated aptamers ɑ-30-2 (50 bp) and ß-37-2 (57 bp) exhibited higher affinity than their original counterpart (79 bp). Subsequently, the selected aptamers were utilized to construct recognition probes for electrochemical aptasensors based on hairpin cyclic cleavage of substrates by Cu2+ dependent DNAzyme and Exo I-triggered recycling cascades. The detection platform showed excellent analytical performance with limits of detection as low as 4.57 pg/mL (ɑ-AMA) and 8.49 pg/mL (ß-AMA). Moreover, the aptasensors exhibited superior performance in mushroom and urine samples. SIGNIFICANCE: This work developed a simple and efficient label-free SELEX method for screening new aptamers for ɑ-AMA and ß-AMA, which employed the positively charged AuNPs as the screening medium, without the need for chemical labelling of libraries or induction of salt ions. Furthermore, two novel electrochemical aptasensors were developed based on our newly obtained aptamers, which offer the new biosensing tool for ultrasensitive detection of the AMA poisoning, showing great potential in practical applications.

Synthesis of (2S,3R,4R)-Dihydroxyisoleucine for Use in Amatoxin Synthesis.

We report a streamlined synthesis of (2S,3R,4R)-4,5-dihydroxy isoleucine (DHIle), an amino acid found in α-amanitin, which appears to be critical for toxicity. This synthetic route is transition metal-free and enables the production of significant quantities of DHIle with suitable protection for use in peptide synthesis. Its incorporation into a cytotoxic amatoxin analog is reported.

Amanitin determination in bile samples by UHPLC-MS: LR-MS and HR-MS analytical performance.

Consumption of misidentified foraged mushrooms containing bicyclic amanitin octapeptides is a worldwide public health and veterinary problem, being considered one of the deadliest accidental human and canine food ingestion due to acute liver failure (ALF). Reversal of advanced ALF and complete clinical recovery can be achieved following definitive removal of accumulated amatoxin laden bile from the gallbladder. An accurate means of quantifying amanitin content in aspirated bile is, therefore, urgently needed. Building on our prior work validating a method to detect and quantify amanitin in hepatic autopsy tissue, the development of an accurate method of measuring α- and ß-amanitin in aspirated gallbladder bile was performed to evaluate the efficiency of this emergency procedure applied as a clinical treatment for intoxicated patients. A solid-phase extraction (SPE) procedure was optimized followed by detection based on ultra-high performance liquid chromatography coupled with mass spectrometry (UHPLC-MS). Low resolution mass spectrometry (LRMS) was compared with high resolution (HRMS) by the validation of UHPLC-MS/MS (triple quadrupole MS) and UHPLC-ToF-MS (time-of-flight MS). Both methods were able to detect amatoxins in bile with limits of detection and quantification ranging from 2.71 to 3.46 µg.kg-1, and 8.36-9.03 µg.kg-1 for α-amanitin and, 0.32-1.69 µg.kg-1 and 0.55-5.62 µg.kg-1 for ß-amanitin, respectively. Validation was completed with the evaluation of linearity, specificity, robustness, recovery, and precision following the ICH guidelines and CIR 808/2021. The validated methods were finally applied to bile samples obtained 48-96 hours + post-ingestion from 4 amatoxin poisoning patients who underwent gallbladder drainage procedures in Vietnam, Canada, and California. Gallbladder bile from patients with amatoxin mushroom poisoning contained significant amanitin content, even when aspirated several days post-ingestion, thus confirming the important role of enterohepatic circulation in amatoxin hepatotoxicity. This work represents a high and unique analytical throughput in amanitin poisoning allowing to efficiently respond to this fatal health problem.

Simple and rapid detection of three amatoxins and three phallotoxins in human body fluids by UPLC-MS-MS and its application in 15 poisoning cases.

Amatoxins and phallotoxins are toxic cyclopeptides found in the genus Amanita and are among the predominant causes of foodborne sickness and poisoning-related fatalities in China. This study introduces and validates a simple, rapid and cost-effective ultra-performance liquid chromatography-mass spectrometry method for the simultaneous determination and quantification of α-amanitin, ß-amanitin, γ-amanitin, phallisacin, phallacidin and phalloidin in human blood and urine. Quick therapeutic decision-making is supported by a 9 min chromatographic separation performed on a Waters Acquity UPLC HSS T3 column (100 mm × 2.1 mm, 1.8 µm) using a gradient of high-performance liquid chromatography (HPLC)-grade water and methanol:0.005% formic acid. The analyte limit of quantification was 1-3 ng/mL in blood and 0.5-2 ng/mL in urine. Calibrations curves, prepared by spiking drug-free blood and urine, demonstrated acceptable linearity with mean correlation coefficients (r) greater than 0.99 for all phallotoxins and amatoxins. Acceptable intraday and interday precision (relative standard deviation <15%) and accuracy (bias, -4.8% to 13.0% for blood and-9.0% to 14.7% for urine) were achieved. The validated method was successfully applied to analyze 9 blood samples and 2 urine samples testing positive for amatoxins and/or phallotoxins. Amatoxins and/or phallotoxins were identified in each whole blood sample at a range of 1.12-5.63 ng/mL and in two urine samples from 1.01-9.27 ng/mL. The method has the benefits of simple sample preparation (protein precipitation) and wide analyte coverage, making it suitable for emergency quantitative surveillance toxicological analysis in clinics and forensic poisoning practice.

A label-free electrochemical immunosensor based on decorated cellulose nanofibrous membrane for point-of-care diagnosis of amanitin poisoning via human urine.

α-Amanitin (AMN) is one of the deadliest toxins from mushrooms, present in the deadly mushroom species Amanita phalloides. It is a bicyclic octapeptide and represents up to 40% of the amatoxins in mushrooms, damaging the liver and kidneys. Current methods of detecting amatoxins are time-consuming and require the use of expensive equipment. A novel label-free electrochemical immunosensor was successfully developed for rapid detection of α-amanitin, which was fabricated by immobilization of anti-α-amanitin antibodies onto a functionalized cellulose nanofibrous membrane-modified carbon screen-printed electrode. An oxidation peak of the captured amanitin on the tethered antibodies was observed at 0.45 V. The performance of the nanofibrous membrane on the electrode and necessary fabrication steps were investigated by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). Due to its unique structural features and properties such as high specific surface area and microporous structure, the nanofibrous membrane as an immunosensor matrix for antibody tethering improved the electrochemical performance of the immunosensor by more than 3 times compared with cast membranes. Under the optimal conditions, the assembled immunosensor exhibited high sensitivity toward α-amanitin detection in the range of 0.009-2 ng mL-1 with a limit of detection of 8.3 pg mL-1. The results clearly indicate that the fabricated nanofiber-based-immunosensor is suitable for point-of-care detection of lethal α-amanitin in human urine without any pretreatment within 30 min.

Amanitins: The Most Poisonous Molecules of the Fungal World.

Among the toxic metabolites of the fungal world, those that, due to their strong biological effect, can seriously (even fatally) damage the life processes of humans (and certain groups of animals) stand out. Amatoxin-containing mushrooms and the poisonings caused by them stand out from the higher fungi, the mushrooms. There are already historical data and records about such poisonings, but scientific research on the responsible molecules began in the middle of the last century. The goals of this review work are as follows: presentation of the cosmopolitan mushroom species that produce amanitins (which are known from certain genera of four mushroom families), an overview of the chemical structure and specific properties of amanitins, a summary of the analytical methods applicable to them, a presentation of the "medical history" of poisonings, and a summary of the therapeutic methods used so far. The main responsible molecules (the amanitins) are bicyclic octapeptides, whose structure is characterized by an outer loop and an inner loop (bridge). It follows from the unusual properties of amanitins, especially their extreme stability (against heat, the acidic pH of the medium, and their resistance to human, and animal, digestive enzymes), that they are absorbed almost without hindrance and quickly transported to our vital organs. Adding to the problems is that accidental consumption causes no noticeable symptoms for a few hours (or even 24-36 h) after consumption, but the toxins already damage the metabolism of the target organs and the synthesis of nucleic acid and proteins. The biochemical catastrophe of the cells causes irreversible structural changes, which lead to necrotic damage (in the liver and kidneys) and death. The scientific topicality of the review is due to the recent publication of new data on the probable antidote molecule (ICR: indocyanine green) against amanitins. Further research can provide a new foundation for the therapeutic treatment of poisonings, and the toxicological situation, which currently still poses a deadly threat, could even be tamed into a controllable problem. We also draw attention to the review conclusions, as well as the mycological and social tasks related to amanitin poisonings (prevention of poisonings).

Determination of protein-bound α-amanitin in mouse plasma: A potential new indicator of poisoning with the mushroom toxin α-amanitin.

Approximately 70%∼90% of mushroom poisoning deaths are caused by the class of mushroom toxins known as amatoxins. However, the rapid elimination of amatoxins from plasma within 48 h after mushroom ingestion limits the practical value of plasma amatoxin analysis as a diagnostic indicator of Amanita mushroom poisoning. To increase the positive detection rate and extend the detection window of amatoxin poisoning, we developed a new method to detect protein-bound α-amanitin based on the hypothesis that RNAP II-bound α-amanitin released from the tissue into the plasma could be degraded by trypsin hydrolysis and then detected by conventional liquid chromatography-mass spectrometry (LC‒MS). Toxicokinetic studies on mice intraperitoneally injected with 0.33 mg/kg α-amanitin were conducted to obtain and compare the concentration trends, detection rates, and detection windows of both free α-amanitin and protein-bound α-amanitin. By comparing detection results with and without trypsin hydrolysis in the liver and plasma of α-amanitin-poisoned mice, we verified the credibility of this method and the existence of protein-bound α-amanitin in plasma. Under the optimized trypsin hydrolysis conditions, we obtained a time-dependent trend of protein-bound α-amanitin in mouse plasma at 1-12 days postexposure. In contrast to the short detection window (0-4 h) of free α-amanitin in mouse plasma, the detection window of protein-bound α-amanitin was extended to 10 days postexposure, with a total detection rate of 53.33%, ranging from the limit of detection to 23.94 µg/L. In conclusion, protein-bound α-amanitin had a higher positive detection rate and a longer detection window than free α-amanitin in mice.

The occurrence of ansamers in the synthesis of cyclic peptides.

α-Amanitin is a bicyclic octapeptide composed of a macrolactam with a tryptathionine cross-link forming a handle. Previously, the occurrence of isomers of amanitin, termed atropisomers has been postulated. Although the total synthesis of α-amanitin has been accomplished this aspect still remains unsolved. We perform the synthesis of amanitin analogs, accompanied by in-depth spectroscopic, crystallographic and molecular dynamics studies. The data unambiguously confirms the synthesis of two amatoxin-type isomers, for which we propose the term ansamers. The natural structure of the P-ansamer can be ansa-selectively synthesized using an optimized synthetic strategy. We believe that the here described terminology does also have implications for many other peptide structures, e.g. norbornapeptides, lasso peptides, tryptorubins and others, and helps to unambiguously describe conformational isomerism of cyclic peptides.

Toxin screening of Pseudosperma umbrinellum (Agaricals, Basidiomycota): First report of phalloidin in Inocybaceae mushroom.

Pseudosperma species are widely distributed worldwide. Many of them cause poisoning incidents every year, and the toxin responsible for poisoning is muscarine, which could stimulate the parasympathetic nervous system. This study established a method using multiwalled carbon nanotube purification and liquid chromatography-tandem mass spectrometry for the targeted screening of mushroom toxins (muscarine, isoxazole derivatives, tryptamine alkaloids, three amatoxins and three phallotoxins) from Pseudosperma umbrinellum, a common poisonous mushroom distributed in north and northwestern China. Surprisingly, in addition to muscarine, phalloidin was also detected in P. umbrinellum, and the contents were 3022.2 ± 604.4 to 4002.3 ± 804.6 mg/kg (k = 2; p = 95%) muscarine and 5.9 ± 1.2 to 9.3 ± 1.8 mg/kg (k = 2; p = 95%) phalloidin.

Synthesis and evaluation of "Ama-Flash", a photocaged amatoxin prodrug for light-activated RNA Pol II inhibition and cell death.

Amanitin is used extensively as a research tool to inhibit RNA Pol II thereby implicating its role in mRNA transcription. Recently, amanitin has gained traction as a toxic payload for targeted therapy. Here we report the first-ever photocaged amanitin analog, that is non-toxic and can be pre-loaded into cells. Light provides a means to inhibit RNA Pol II and provoke cell death on-demand.

Production of highly sensitive monoclonal antibody and development of lateral flow assays for phallotoxin detection in urine.

Phallotoxins, toxic cyclopeptides found in wild poisonous mushrooms, are predominant causes of fatal food poisoning. For the early and rapid diagnosis mushroom toxin poisoning, a highly sensitive and robust monoclonal antibody (mAb) against phallotoxins was produced for the first time. The half-maximum inhibition concentration (IC50) values of the mAb-based indirect competitive ELISAs for phallacidin (PCD) and phalloidin (PHD) detection were 0.31 ng mL-1 and 0.35 ng mL-1, respectively. In response to the demand for rapid screening of the type of poisoning and accurate determination of the severity of poisoning, colloidal gold nanoparticle (GNP) and time-resolved fluorescent nanosphere (TRFN) based lateral flow assays (LFA) were developed. The GNP-LFA has a visual cut-off value of 3.0 ng mL-1 for phallotoxins in human urine sample. The TRFN-LFA provides a quantitative readout signal with detection limit of 0.1 ng mL-1 in human urine sample. In this study, urine samples without pretreatment were used directly for the LFA strip tests, and both two LFAs were able to accomplish analysis within 10 min. The results demonstrated that LFAs based on the newly produced, highly sensitive, and robust mAb were able to be used for both rapid qualitative screening of the type of poisoning and accurate quantitative determination of the severity of poisoning after accidental ingestion by patients of toxic mushrooms.

Toxin components and toxicological importance of Galerina marginata from Turkey.

Amatoxins, most of which are hepatotoxic, can cause fatal intoxication. While mushrooms in the amatoxin-containing Galerina genus are rare, they can poison humans and animals worldwide. Few studies have profiled the toxicity of Galerina marginata. In addition, many studies indicate that macrofungi can have different characteristics in different regions. In this study, the quantities of toxins present in G. marginata from different provinces in Turkey were analysed using reversed-phase high-performance liquid chromatography with ultraviolet detection (RP-HPLC-UV) and liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS). G. marginata samples were collected from three different regions of Turkey. The taxonomic categorization of mushrooms was based on their micro- and macroscopic characteristics. The presence of toxins α-amanitin (AA), ß-amanitin (BA), γ-amanitin (GA), phalloidin (PHD) and phallacidin (PHC) quantities were measured using RP-HPLC-UV and then were confirmed using LC-ESI-MS/MS. BA levels were higher than AA levels in G. marginata mushrooms collected from all three regions. Moreover, the levels of GA were below the detection limit and no phallotoxins were detected. This is the first study to identify and test the toxicity of G. marginata collected from three different regions of Turkey using RP-HPLC-UV. This is also the first study to confirm the UV absorption of amatoxins in G. marginata using LC-ESI-MS/MS, which is a far more sensitive process. More studies evaluating the toxicity of G. marginata in other geographic regions of the world are needed.

Extensive screening of cyclopeptide toxins in mushrooms by ultra-high-performance liquid chromatography coupled with quadrupole-Orbitrap mass spectrometry.

A non-target screening method of cyclopeptide toxins and their analogues in mushroom was developed, using ultra-high-performance liquid chromatography coupled with quadrupole Orbitrap mass spectrometry (UHPLC-Q-Orbitrap MS) followed by mass spectrometry databases retrieval and software tools analysis for the candidate analogues. Three cyclopeptide toxins in the toxic mushroom Amanita rimosa were firstly screened without standard, and two of them were unknown analogues which were tentatively identified by the accurate masses, isotopic patterns and characteristic fragments. A validated quantitative method was performed to rapidly quantify three major cyclopeptide toxins in the Amanita rimosa sample including α-manitin, ß-amanitin and phalloidin, and their contents were detected to be 4.52 mg/kg, 2.37 mg/kg and 2.53 mg/kg, respectively. The developed method has good selectivity and sensitivity for rapid and comprehensive screening the cyclopeptide toxins and their analogues in mushrooms at trace levels. Successful non-target screening of trace cyclopeptide toxin analogues will guarantee the food safety in mushrooms consumption.

Lateral flow immunoassay (LFIA) for the detection of lethal amatoxins from mushrooms.

The mushroom poison that causes the most deaths is the class of toxins known as amatoxins. Current methods to sensitively and selectively detect these toxins are limited by the need for expensive equipment, or they lack accuracy due to cross-reactivity with other chemicals found in mushrooms. In this work, we report the development of a competition-based lateral flow immunoassay (LFIA) for the rapid, portable, selective, and sensitive detection of amatoxins. Our assay clearly indicates the presence of 10 ng/mL of α-AMA or γ-AMA and the method including extraction and detection can be completed in approximately 10 minutes. The test can be easily read by eye and has a presumed shelf-life of at least 1 year. From testing 110 wild mushrooms, the LFIA identified 6 out of 6 species that were known to contain amatoxins. Other poisonous mushrooms known not to contain amatoxins tested negative by LFIA. This LFIA can be used to quickly identify amatoxin-containing mushrooms.

Total Synthesis of α- and ß-Amanitin.

α-Amanitin and related amatoxins have been studied for more than six decades mostly by isolation from death cap mushrooms. The total synthesis, however, remained challenging due to unique structural features. α-Amanitin is a potent inhibitor of RNA polymerase II. Interrupting the basic transcription processes of eukaryotes leads to apoptosis of the cell. This unique mechanism makes the toxin an ideal payload for antibody-drug conjugates (ADCs). Only microgram quantities of toxins, when delivered selectively to tumor sites through conjugation to antibodies, are sufficient to eliminate malignant tumor cells of almost every origin. By solving the stereoselective access to dihydroxyisoleucine, a photochemical synthesis of the tryptathion precursor, solid-phase peptide synthesis, and macrolactamization we obtained a scalable synthetic route towards synthetic α-amanitin. This makes α-amanitin and derivatives now accessible for the development of new ADCs.

Rapid, Sensitive, and Accurate Point-of-Care Detection of Lethal Amatoxins in Urine.

Globally, mushroom poisonings cause about 100 human deaths each year, with thousands of people requiring medical assistance. Dogs are also susceptible to mushroom poisonings and require medical assistance. Cyclopeptides, and more specifically amanitins (or amatoxins, here), are the mushroom poison that causes the majority of these deaths. Current methods (predominantly chromatographic, as well as antibody-based) of detecting amatoxins are time-consuming and require expensive equipment. In this work, we demonstrate the utility of the lateral flow immunoassay (LFIA) for the rapid detection of amatoxins in urine samples. The LFIA detects as little as 10 ng/mL of α-amanitin (α-AMA) or γ-AMA, and 100 ng/mL of ß-AMA in urine matrices. To demonstrate application of this LFIA for urine analysis, this study examined fortified human urine samples and urine collected from exposed dogs. Urine is sampled directly without the need for any pretreatment, detection from urine is completed in 10 min, and the results are read by eye, without the need for specialized equipment. Analysis of both fortified human urine samples and urine samples collected from intoxicated dogs using the LFIA correlated well with liquid chromatography-mass spectrometry (LC-MS) methods.

Amanitins and their development as a payload for antibody-drug conjugates.

Amanitin-based ADCs represent a new class of ADCs using a novel mode of action. This payload introduces a novel mode of action into oncology therapy, the inhibition of RNA Polymerase II. The high potency of the toxin leads to highly efficacious ADCs. The development of the technology around this toxin will be described. These developments support the clinical development of amanitin-based ADCs by using a toxin with a new mode of action and with a favorable therapeutic index. HDP-101 is an Amanitin based ADC directed against BCMA and will be advancing to the clinical phase in 2019.

A New Conjugation Method Used for the Development of an Immunoassay for the Detection of Amanitin, a Deadly Mushroom Toxin.

One of the deadliest mushrooms is the death cap mushroom, Amanita phalloides. The most toxic constituent is α-amanitin, a bicyclic octapeptide, which damages the liver and kidneys. To develop a new tool for detecting this toxin, polyclonal antibodies were generated and characterized. Both α- and β-amanitin were coupled to carrier proteins through four different linking chemistries, one of which has never before been described. These conjugates were evaluated for their effectiveness in generating antibodies specific for the free toxin, as well as their utility in formatting heterogeneous assays with high sensitivity. Ultimately, these efforts yielded a newly described conjugation procedure utilizing periodate oxidation followed by reductive amination that successfully resulted in generating sensitive immunoassays (limit of detection (LOD), ~1.0 µg/L). The assays were characterized for their selectivity and were found to equally detect α-, β-, and γ-amanitin, and not cross-react with other toxins tested. Toxin detection in mushrooms was possible using a simple sample preparation method. This enzyme-linked immunosorbent assay (ELISA) is a simple and fast test, and readily detects amatoxins extracted from A. phalloides.

Peptides of pHLIP family for targeted intracellular and extracellular delivery of cargo molecules to tumors.

The pH (low) insertion peptides (pHLIPs) target acidity at the surfaces of cancer cells and show utility in a wide range of applications, including tumor imaging and intracellular delivery of therapeutic agents. Here we report pHLIP constructs that significantly improve the targeted delivery of agents into tumor cells. The investigated constructs include pHLIP bundles (conjugates consisting of two or four pHLIP peptides linked by polyethylene glycol) and Var3 pHLIPs containing either the nonstandard amino acid, γ-carboxyglutamic acid, or a glycine-leucine-leucine motif. The performance of the constructs in vitro and in vivo was compared with previous pHLIP variants. A wide range of experiments was performed on nine constructs including (i) biophysical measurements using steady-state and kinetic fluorescence, circular dichroism, and oriented circular dichroism to study the pH-dependent insertion of pHLIP variants across the membrane lipid bilayer; (ii) cell viability assays to gauge the pH-dependent potency of peptide-toxin constructs by assessing the intracellular delivery of the polar, cell-impermeable cargo molecule amanitin at physiological and low pH (pH 7.4 and 6.0, respectively); and (iii) tumor targeting and biodistribution measurements using fluorophore-peptide conjugates in a breast cancer mouse model. The main principles of the design of pHLIP variants for a range of medical applications are discussed.

Characterization of a dual function macrocyclase enables design and use of efficient macrocyclization substrates.

Peptide macrocycles are promising therapeutic molecules because they are protease resistant, structurally rigid, membrane permeable, and capable of modulating protein-protein interactions. Here, we report the characterization of the dual function macrocyclase-peptidase enzyme involved in the biosynthesis of the highly toxic amanitin toxin family of macrocycles. The enzyme first removes 10 residues from the N-terminus of a 35-residue substrate. Conformational trapping of the 25 amino-acid peptide forces the enzyme to release this intermediate rather than proceed to macrocyclization. The enzyme rebinds the 25 amino-acid peptide in a different conformation and catalyzes macrocyclization of the N-terminal eight residues. Structures of the enzyme bound to both substrates and biophysical analysis characterize the different binding modes rationalizing the mechanism. Using these insights simpler substrates with only five C-terminal residues were designed, allowing the enzyme to be more effectively exploited in biotechnology.