Design of an Activity-Based Probe for Human Neutrophil Elastase: Implementation of the Lossen Rearrangement To Induce Förster Resonance Energy Transfers

Covalent activity-based probes for imaging of serine proteases

Serine proteases are one of the largest mechanistic classes of proteases. They regulate a plethora of biochemical pathways inside and outside the cell. Aberrant serine protease activity leads to a wide variety of human diseases. Reagents to visualize these activities can be used to gain insight into the biological roles of serine proteases. Moreover, they may find future use for the detection of serine proteases as biomarkers. In this review, we discuss small molecule tools to image serine protease activity. Specifically, we outline different covalent activity-based probes and their selectivity against various serine protease targets. We also describe their application in several imaging methods.

Chemically diverse activity-based probes with unexpected inhibitory mechanisms targeting trypsin-like serine proteases

Activity-based probes (ABP) are molecules that bind covalently to the active form of an enzyme family, making them an attractive tool for target and biomarker identification and drug discovery. The present study describes the synthesis and biochemical characterization of novel activity-based probes targeting trypsin-like serine proteases. We developed an extensive library of activity-based probes with "clickable" affinity tags and a diaryl phosphonate warhead. A wide diversity was achieved by including natural amino acid analogs as well as basic polar residues as side chains. A detailed enzymatic characterization was performed in a panel of trypsin-like serine proteases. Their inhibitory potencies and kinetic profile were examined, and their IC₅₀ values, mechanism of inhibition, and kinetic constants were determined. The activity-based probes with a benzyl guanidine side chain showed the highest inhibitory effects in the panel. Surprisingly, some of the high-affinity probes presented a reversible inhibitory mechanism. On the other hand, probes with different side chains exhibited the expected irreversible mechanism. For the first time, we demonstrate that not only irreversible probes but also reversible probes can tightly label recombinant proteases and proteases released from human mast cells. Even under denaturing SDS-PAGE conditions, reversible slow-tight-binding probes can label proteases due to the formation of high-affinity complexes and slow dissociation rates. This unexpected finding will transform the view on the required irreversible nature of activity-based probes. The diversity of this library of activity-based probes combined with a detailed enzyme kinetic characterization will advance their applications in proteomic studies and drug discovery.

Coumarin-based turn-on fluorescence probe with a large Stokes shift for detection of endogenous neutrophil elastase in live cells and zebrafish

Neutrophil elastase (NE), a serine proteinase, is a significant biomarker which is closely related to the progress of diseases. However, only few probes have been reported for detection of NE activity and cell imaging. And these probes have exhibited small Stokes shift, which leads to high fluorescence interferences. Furthermore, only one probe among them is able to image NE in vivo successfully. To overcome the above problems, we designed a novel coumarin-based fluorescent probe HNCOU-NE with large Stokes shift to visualize NE activity in living cells and zebrafish. The new probe HNCOU-NE for NE contains fluorophore HNCOU as the reporter and pentafluoroethyl as the enzyme-active trigger moiety. As expected, HNCOU-NE displays perfect detecting performance for sensing of NE, including good water solubility, large Stokes shift, high affinity and wide linear response concentration. In addition, HNCOU-NE has been successfully utilized for NE real-time detection and imaging in different living cells, exhibiting low cytotoxicity and excellent biocompatibility. Most importantly, endogenous NE fluorescence imaging experiments reveals that HNCOU-NE can distinguish liver cancer cells (HepG2) and other cells (293T, HeLa and SKOV3), illustrating its specific ability to diagnose liver cancer cells. Besides, probe HNCOU-NE also has the ability to specifically detect endogenous NE activity in living zebrafish. All the results indicate that HNCOU-NE is a valuable probe for qualitative and quantitative sensing of NE activity in vitro and in vivo.

Evaluation of antioxidant, enzyme inhibition, nitric oxide production inhibitory activities and chemical profiles of the active extracts from the medicinal and edible plant: Althaea officinalis

To develop the medicinal and edible plant resources of Althaea officinalis Linn in Europe and other places, this study concentrated on the bioactive ingredients of its different extracts. The phytochemical compositions of MeOH extracts were evaluated by UPLC-DAD-ESI-Q-TOF-MSⁿ analysis. The in vitro antioxidant properties, enzymes inhibitory effects and nitric oxide (NO) production inhibitory activities of fractions obtained from the aerial parts of Althaea officinalis (APAO) were evaluated. The results identified 76 compounds, including 8 phenolic acids, 17 flavonoids, 6 coumarins, 9 triterpenes and 11 alkaloids. Fr. C-2 of APAO was found to have the highest TPC (175.8 ± 1.5 mg GAE/g) and TFC (466.9 ± 5.0 mg RE/g) with the highest antioxidant capacity in DPPH, ABTS, CUPRAC, FRAP and β-carotene bleaching assays. Fr. A showed noticeable inhibition of α-glucosidase with an IC₅₀ value of 3.8 ± 0.1 μg/mL. However, Fr. B displayed stronger inhibitory activity on 5-lipoxygenase than quercetin, with the IC₅₀ value of 8.4 ± 1.6 μg/mL. In addition, Fr. B also possessed potent inhibitory activities on NO production toward LPS-activated RAW 264.7 Cells with an IC₅₀ value of 15.7 ± 1.6 μg/mL. Our findings suggest that different Althaea officinalis extracts may be considered sources of phenolic and flavonoid compounds with high potential as natural antioxidants, anti-inflammatory agents and blood sugar regulators. In addition, they can also be used in food and nutraceutical products with enhanced bioactivities.

Activity-Based Probes for Proteases Pave the Way to Theranostic Applications

Proteases are important enzymes in health and disease. Their activities are regulated at multiple levels. In fact, proteases are synthesized as inactive proenzymes (zymogens) that are activated by proteolytic removal of their pro-peptide sequence and can remain active or their activity can be attenuated by complex formation with specific endogenous inhibitors or by limited proteolysis or degradation. Consequently, quite often, only a fraction of the protease molecules is in the active/functional form, thus, the abundance of a protease is not always linearly proportional to the (patho)physiological function(s). Therefore, assays to determine the active forms of proteases are needed, not only in research but also in molecular diagnosis and therapy. Activity-based probes (ABPs) are chemical entities that bind covalently to the active enzyme/protease. ABPs carry a detection tag to enable localization and quantification of specific enzymatic/proteolytic activities with applications in molecular imaging and diagnosis. Moreover, ABPs act as suicide inhibitors of proteases, which can be exploited for delineation of the functional role(s) of a given protease in (patho) biological context and as potential therapeutics. In this sense, ABPs represent new theranostic agents. We outline recent developments pertaining to ABPs for proteases with potential therapeutic applications, with the aim to highlight their importance in theranostics.

Engineering Molecular Probes for In Vivo Near-Infrared Fluorescence/Photoacoustic Duplex Imaging of Human Neutrophil Elastase

Early detection of human neutrophil elastase (HNE), the potential biomarker of lung cancer, is crucial for the accurate diagnosis and evaluation of lung cancer. Currently, little progress of HNE-activated probes has been made for in vivo imaging. Herein, assisted by probe-active pocket match engineering, we synthesized a series of near-infrared fluorescence (NIRF) and photoacoustic (PA) duplex imaging probes by conjugating diverse fluorinated amide chains onto hemi-cyanine. Finally, we identified that probe 2 (denoted as LET-8), with the pentafluoroethyl group, is a superior probe to detect HNE with the best selectivity as well as good response ability and thus successfully realized NIRF/PA duplex imaging of HNE activity both in vitro and in vivo.

An Activity-Based Probe for Cathepsin K Imaging with Excellent Potency and Selectivity

The cysteine protease cathepsin K is a target for the treatment of diseases associated with high bone turnover. Cathepsin K is mainly expressed in osteoclasts and responsible for the destruction of the proteinaceous components of the bone matrix. We designed various fluorescent activity-based probes (ABPs) and their precursors that bind to and inactivate cathepsin K. ABP 25 exhibited extraordinary potency (k_inac/K_i = 35,300 M^-1s^-1) and selectivity for human cathepsin K. Crystal structures of cathepsin K in complex with ABP 25 and its nonfluorescent precursor 21 were determined to characterize the binding mode of this new type of acrylamide-based Michael acceptor with the particular orientation of the dibenzylamine moiety to the primed subsite region. The cyanine-5 containing probe 25 allowed for sensitive detection of cathepsin K, selective visualization in complex proteomes, and live cell imaging of a human osteosarcoma cell line, underlining its applicability in a pathophysiological environment.

Activity-Based Probes to Utilize the Proteolytic Activity of Cathepsin G in Biological Samples

Neutrophils, migrating to the site of infection, are able to release serine proteases after being activated. These serine proteases comprise cathepsin G (CatG), neutrophil elastase protease 3 (PR3), and neutrophil serine protease 4 (NSP4). A disadvantage of the uncontrolled proteolytic activity of proteases is the outcome of various human diseases, including cardiovascular diseases, thrombosis, and autoimmune diseases. Activity-based probes (ABPs) are used to determine the proteolytic activity of proteases, containing a set of three essential elements: Warhead, recognition sequence, and the reporter tag for detection of the covalent enzyme activity–based probe complex. Here, we summarize the latest findings of ABP-mediated detection of proteases in both locations intracellularly and on the cell surface of cells, thereby focusing on CatG. Particularly, application of ABPs in regular flow cytometry, imaging flow cytometry, and mass cytometry by time-of-flight (CyTOF) approaches is advantageous when distinguishing between immune cell subsets. ABPs can be included in a vast panel of markers to detect proteolytic activity and determine whether proteases are properly regulated during medication. The use of ABPs as a detection tool opens the possibility to interfere with uncontrolled proteolytic activity of proteases by employing protease inhibitors.

Discovery of Thanafactin A, a Linear, Proline-Containing Octalipopeptide from Pseudomonas sp. SH-C52, Motivated by Genome Mining

Genome mining of the bacterial strains Pseudomonas sp. SH-C52 and Pseudomonas fluorescens DSM 11579 showed that both strains contained a highly similar gene cluster encoding an octamodular nonribosomal peptide synthetase (NRPS) system which was not associated with a known secondary metabolite. Insertional mutagenesis of an NRPS component followed by comparative profiling led to the discovery of the corresponding novel linear octalipopeptide thanafactin A, which was subsequently isolated and its structure determined by two-dimensional NMR and further spectroscopic and chromatographic methods. In bioassays, thanafactin A exhibited weak protease inhibitory activity and was found to modulate swarming motility in a strain-specific manner.

Evaluation of Ionic Liquids and Ionic Liquids Active Pharmaceutical Ingredients Inhibition in Elastase Enzyme Activity

Human neutrophil elastase (HNE) is used as diagnostic biomarker for inflammation/infection. In this work, 10 ionic liquids (ILs) and 11 ionic liquids active pharmaceutical ingredients (ILs-APIs) were tested to evaluate the inhibition effect on the activity of porcine pancreatic elastase enzyme, frequently employed as a model for HNE. The insertion of ionic liquids in some drugs is useful, as the insertion of ILs with inhibitory capacity will also slow down all processes in which this enzyme is involved. Therefore, a spectrophotometric method was performed to the determination of EC₅₀ values of the compounds tested. EC₅₀ values of 124 ± 4 mM to 289 ± 11 mM were obtained, with the most toxic IL for elastase being tetrabutylammonium acetate and the least toxic 1-butyl-3-methylimidazolium acetate. Moreover, sodium salicylate (raw material) presented the lower and benzethonium bistriflimide the higher EC₅₀ when compared with all the IL-APIs tested. This work provides significant information about the effect of the studied IL and IL-APIs in elastase enzyme activity.

A fluorogenic peptide-based smartprobe for the detection of neutrophil extracellular traps and inflammation

A highly specific, fluorogenic probe detects human neutrophil elastase (hNE) in activated neutrophils and Neutrophil Extracellular Traps (NETs).

Paper-based human neutrophil elastase detection device for clinical wound monitoring

Paper-based diagnostic devices have been widely applied to assess the presence and status of a variety of clinical diseases by analyzing samples such as urine or blood. Due to their low cost, user-friendliness, and convenience, they have been used as point-of-care (POC) devices in countries lacking resources or energy. Despite wide-ranging research and implementation, paper-based devices have not previously been developed for wound analysis. Here, we discuss the successful development of such a tool to facilitate simple and rapid wound status assessment. The purpose of this study was to develop a paper-based elastase detection device (PEDD) for clinical wound assessment that specifically examines human neutrophil elastase (HNE), one of the most abundant serine proteases found in chronic wounds. The first step in this study was an examination of different paper substrate types (i.e., chromatography paper and filter paper) to determine which provided the best protease immobilization and colorimetric response. We then used a wax printing approach to create hydrophobic and hydrophilic regions and designated test zones created on both chromatography and filter papers. This allowed us to physically immobilize both substrate and protease within the desired test zone regions. This PEDD which demonstrated good sensitivity (0.631 μg mL^-1, in a wound fluid system) can be used to monitor protease activity expressed in wounds. After developing this device, we examined samples from 9 patients presenting a total of 7 acute and 4 chronic wounds to determine wound HNE concentration. We believe that this study may be widely applicable in both academic and commercial sciences, including the development of practical POC detection devices.

Activity-based ratiometric fluorescent small-molecule probe for endogenously monitoring neutrophil elastase in living cells

Neutrophil elastase (NE), a representative protease which is closely related to many diseases, acts an indispensable role in inflammatory diseases and clinical medicine. In this work, one activity-based non-peptide ratiometric fluorescent probe DCDF was designed with pentafluoropropionic anhydride as identification group. To our knowledge, this is the first probe capable of detecting NE in ratio. After the addition of the NE, the emission spectrum of DCDF has obvious bathochromic-shift phenomenon, and there is large Stokes shifts of ∼60 nm. Compared to only a few reported NE probes, DCDF is sensitive and selective and has very low detection limit (0-14 μg/mL, DL = 30.8 ng/mL). A possible response mechanism was proposed and verified by HPLC and HRMS spectra. What's more, DCDF is capable of endogenous recognition imaging in biological cells without interference from other enzymes under the ratio signal. A549 and HeLa cells were used for endogenous cell imaging experiments of NE and the feasibility of DCDF for the specific detection of NE in cells was proved. This experimental result makes probe DCDF a very promising tool for the clinical diagnosis and treatment of NE related diseases.

Protein Encapsulation: A Nanocarrier Approach to the Fluorescence Imaging of an Enzyme-Based Biomarker

Here, we report a new pentafluoropropanamido rhodamine fluorescent probe (ACS-HNE) that allows for the selective detection of neutrophil elastase (NE). ACS-HNE displayed high sensitivity, with a low limit of detection (<5.3 nM), and excellent selectivity toward elastase over other relevant biological analytes and enzymes. The comparatively poor solubility and cell permeability of neat ACS-HNE was improved by creating an ACS-HNE-albumin complex; this approach allowed for improvements in the in situ visualization of elastase activity in RAW 264.7 cells relative to ACS-HNE alone. The present study thus serves to demonstrate a simple universal strategy that may be used to overcome cell impermeability and solubility limitations, and to prepare probes suitable for the cellular imaging of enzymatic activity in vitro.

Coumarin as a structural component of substrates and probes for serine and cysteine proteases

Coumarins represent well-established structures to introduce fluorescence into tool compounds for biochemical investigations. They are valued for their small size, chemical stability and accessibility as well as their tunable photochemical properties. As components of fluorophore/quencher pairs or FRET donor/acceptor pairs, coumarins have frequently been applied in substrate mapping approaches for serine and cysteine proteases. This review also focuses on the incorporation of coumarins into the side chain of amino acids and the exploitation of the resulting fluorescent amino acids for the positional profiling of protease substrates. The protease-inhibiting properties of certain coumarin derivatives and the utilization of coumarin moieties to assemble activity-based probes for serine and cysteine proteases are discussed as well.

•

Coumarins represent well-established structures to introduce fluorescence into tool compounds for biochemical investigations.

•

They are valued for their small size, chemical stability and accessibility as well as their tunable photochemical properties.

•

Coumarins are components of fluorophore/quencher pairs or FRET donor/acceptor pairs in substrate mapping of proteases.

•

Coumarins have been incorporated into amino acids side chains to be used for the positional profiling of protease substrates.

•

Coumarins have protease-inhibiting properties and are used for activity-based probes for serine and cysteine proteases.

Human Neutrophil Elastase Activated Fluorescent Probe for Pulmonary Diseases Based on Fluorescence Resonance Energy Transfer Using CdSe/ZnS Quantum Dots

There is an increasing demand for effective noninvasive diagnosis against common pulmonary diseases, which are rising sharply due to the serious air pollution. Human neutrophil elastase (HNE), a typical protease highly involved in pulmonary inflammatory diseases and lung cancer, is a potential predictor for disease progression. Currently, few of the HNE-targeting probes are applicable in vivo due to the limitation in sensitivity and biocompatibility. Herein, we reported the achievement of in vitro detection and in vivo imaging of HNE by incorporating the HNE-specific peptide substrate, quantum dots (QDs), and organic dyes into the fluorescence resonance energy transfer (FRET) system. The refined nanoprobe, termed QDP, could specifically measure the HNE with excellent sensitivity of 7.15 pM in aqueous solution and successfully image the endogenous and exogenous HNE in living cells. In addition, this nanoprobe enabled HNE imaging in mouse models of lung cancer and acute lung injury, and the HNE activity at high temporal and spatial resolution was continuously monitored. Most importantly, QDP successfully discriminated the serums of patients with lung diseases from those of the healthy controls based on the HNE activity determination. Overall, this study demonstrates the advantages of a FRET-system-based nanoprobe in imaging performance and provides an applicable tool for in vivo HNE detection and pulmonary disease diagnosis.

Kan-Lu-Hsiao-Tu-Tan, a traditional Chinese medicine formula, inhibits human neutrophil activation and ameliorates imiquimod-induced psoriasis-like skin inflammation

ETHNOPHARMACOLOGICAL RELEVANCE

Kan-Lu-Hsiao-Tu-Tan (KLHTT) is a popular traditional Chinese medicine for treating various inflammatory diseases.

AIM OF THE STUDY

The aim of the present study was to investigate the anti-inflammatory effects of KLHTT on human neutrophils and its therapeutic potential in treating imiquimod (IMQ)-induced psoriasis-like skin inflammation.

MATERIALS AND METHODS

Spectrophotometry, flow cytometry, and microscopy with immunohistochemical staining were used to evaluate superoxide anion generation, elastase release, CD11b expression, adhesion, and neutrophil extracellular trap (NET) formation in activated human neutrophils. Reactive oxygen species (ROS) and reactive nitrogen species in cell-free systems were measured using a multi-well fluorometer or a spectrophotometer. A psoriasis-like skin inflammation was induced in mice using the IMQ cream.

RESULTS

KLHTT suppressed superoxide anion generation, ROS production, CD11b expression, and adhesion in activated human neutrophils. In contrast, KLHTT failed to alter elastase release in activated human neutrophils. Additionally, KLHTT had an ROS-scavenging effect in the AAPH assay, but it did not scavenge superoxide anions directly in the xanthine/xanthine oxidase assay. Protein kinase C (PKC)-induced NET formation most commonly occurs through ROS-dependent mechanisms. KLHTT significantly inhibited phorbol 12-myristate 13-acetate, a PKC activator, inducing NET formation. Furthermore, topical KLHTT treatment reduced the area affected by psoriasis area and severity index (PASI) score and ameliorated neutrophil infiltration in IMQ-induced psoriasis-like skin inflammation in mice.

CONCLUSIONS

Our data show that KLHTT has anti-neutrophilic inflammatory effects in inhibiting ROS generation and cell adhesion. KLHTT also mitigated NET formation, mainly via an ROS-dependent pathway. In addition, KLHTT reduced neutrophil infiltration and improved the severity of IMQ-induced psoriasis-like skin inflammation in mice. Therefore, KLHTT may prove to be a safe and effective psoriasis therapy in the future.

An NADH-Dependent Reductase from Eubacterium ramulus Catalyzes the Stereospecific Heteroring Cleavage of Flavanones and Flavanonols

The human intestinal anaerobe Eubacterium ramulus is known for its ability to degrade various dietary flavonoids. In the present study, we demonstrate the cleavage of the heterocyclic C-ring of flavanones and flavanonols by an oxygen-sensitive NADH-dependent reductase, previously described as enoate reductase, from E. ramulus This flavanone- and flavanonol-cleaving reductase (Fcr) was purified following its heterologous expression in Escherichia coli and further characterized. Fcr cleaved the flavanones naringenin, eriodictyol, liquiritigenin, and homoeriodictyol. Moreover, the flavanonols taxifolin and dihydrokaempferol served as substrates. The catalyzed reactions were stereospecific for the (2R)-enantiomers of the flavanone substrates and for the (2S,3S)-configured flavanonols. The enantioenrichment of the nonconverted stereoisomers allowed for the determination of hitherto unknown flavanone racemization rates. Fcr formed the corresponding dihydrochalcones and hydroxydihydrochalcones in the course of an unusual reductive cleavage of cyclic ether bonds. Fcr did not convert members of other flavonoid subclasses, including flavones, flavonols, and chalcones, the latter indicating that the reaction does not involve a chalcone intermediate. This view is strongly supported by the observed enantiospecificity of Fcr. Cinnamic acids, which are typical substrates of bacterial enoate reductases, were also not reduced by Fcr. Based on the presence of binding motifs for dinucleotide cofactors and a 4Fe-4S cluster in the amino acid sequence of Fcr, a cofactor-mediated hydride transfer from NADH onto C-2 of the respective substrate is proposed.IMPORTANCE Gut bacteria play a crucial role in the metabolism of dietary flavonoids, thereby contributing to their activation or inactivation after ingestion by the human host. Thus, bacterial activities in the intestine may influence the beneficial health effects of these polyphenolic plant compounds. While an increasing number of flavonoid-converting gut bacterial species have been identified, knowledge of the responsible enzymes is still limited. Here, we characterized Fcr as a key enzyme involved in the conversion of flavonoids of several subclasses by Eubacterium ramulus, a prevalent human gut bacterium. Sequence similarity of this enzyme to hypothetical proteins from other flavonoid-degrading intestinal bacteria in databases suggests a more widespread occurrence of this enzyme. Functional characterization of gene products of human intestinal microbiota enables the assignment of metagenomic sequences to specific bacteria and, more importantly, to certain activities, which is a prerequisite for targeted modulation of gut microbial functionality.

Neutrophil Elastase Activity Imaging: Recent Approaches in the Design and Applications of Activity-Based Probes and Substrate-Based Probes

The last few decades of protease research has confirmed that a number of important biological processes are strictly dependent on proteolysis. Neutrophil elastase (NE) is a critical protease in immune response and host defense mechanisms in both physiological and disease-associated conditions. Particularly, NE has been identified as a promising biomarker for early diagnosis of lung inflammation. Recent studies have shown an increasing interest in developing methods for NE activity imaging both in vitro and in vivo. Unlike anatomical imaging modalities, functional molecular imaging, including enzymatic activities, enables disease detection at a very early stage and thus constitutes a much more accurate approach. When combined with advanced imaging technologies, opportunities arise for measuring imbalanced proteolytic activities with unprecedented details. Such technologies consist in building the highest resolved and sensitive instruments as well as the most specific probes based either on peptide substrates or on covalent inhibitors. This review outlines strengths and weaknesses of these technologies and discuss their applications to investigate NE activity as biomarker of pulmonary inflammatory diseases by imaging.

A MedChem toolbox for cereblon-directed PROTACs

A modular chemistry toolbox was developed for cereblon-directed PROTACs. A variety of linkers was attached to a CRBN ligand via the 4-amino position of pomalidomide. We used linkers of different constitution to modulate physicochemical properties. We equipped one terminus of the linker with a set of functional groups, e.g. protected amines, protected carboxylic acids, alkynes, chloroalkanes, and protected alcohols, all of which are considered to be attractive for PROTAC design. We also highlight different opportunities for the expansion of the medicinal chemists' PROTAC toolbox towards heterobifunctional molecules, e.g. with biotin, fluorescent, hydrophobic and peptide tags.

Anthranilic Acid as a Versatile Fluorescent Tag and Linker for Functional Glycomics

The advancement of glycoscience is critically dependent on the access to a large number of glycans for their functional study. Naturally occurring glycans are considered a viable source for diverse and biologically relevant glycan libraries. A mixture of free reducing glycans released from natural sources can be fluorescently tagged and separated by chromatography to produce a natural glycan library. Anthranilic acid (AA) has been widely used to fluorescently tag reducing glycans for HPLC or LC/MS analysis. However, AA conjugated glycans are not efficiently immobilized on microarray slides due to the lack of a primary alkylamine functional group. In this study, we have developed simple and efficient chemistry for bioconjugation and further functionalization of glycan-AA conjugates. This new approach enables quick preparation of glycan microarrays and neoglycoproteins from glycan-AA conjugates, which can be separated by weak anion exchange (WAX) and C18 reversed-phase HPLC.