Potential antioxidative components from Syringa oblata Lindl stems revealed by affinity ultrafiltration with multiple drug targets.

Traditional Chinese medicine is the main source of natural products due to its remarkable clinical efficacy. Syringa oblata Lindl (S. oblata) was widely used because of its extensive biological activities. However, to explore the antioxidant components of S. oblata against tyrosinase, the experiments of antioxidation in vitro were employed. At the same time, the determination of TPC was also use to assess the antioxidant ability of CE, MC, EA and WA fractions and the liver protective activity of the EA fraction was evaluated by mice in vivo. Next, UF-LC-MS technology was performed to screen and identify the efficient tyrosinase inhibitors in S. oblata. The results showed that alashinol (G), dihydrocubebin, syripinin E and secoisolariciresinol were characterized as potential tyrosinase ligands and their RBA values were 2.35, 1.97, 1.91 and 1.61, respectively. Moreover, these four ligands can effectively dock with tyrosinase molecules, with binding energies (BEs) ranging from 0.74 to -0.73 kcal/mol. In addition, tyrosinase inhibition experiment was employed to evaluate the tyrosinase inhibition activities of four potential ligands, the result showed that compound 12 (alashinol G, IC50 = 0.91 ± 0.20 mM) showed the strongest activity to tyrosinase, followed by secoisolariciresinol (IC50 = 0.99 ± 0.07 mM), dihydrocubebin (IC50 = 1.04 ± 0.30 mM) and syripinin E (IC50 = 1.28 ± 0.23 mM), respectively. The results demonstrate that S. oblata might have excellent antioxidant activity, and UF-LC-MS technique is a effective means to filter out tyrosinase inhibitors from natural products.

Investigation and identification of the multiple components of Rheum officinale Baill. using ultra-high-performance liquid chromatography coupled with quadrupole-time-of-flight tandem mass spectrometry and data mining strategy.

Rheum officinale Baill. is a traditional Chinese medicine that has long been used for eliminating body heat, cooling and detoxifying blood, removing blood stasis and promoting menstruation, and clearing away heat-dampness to eliminate jaundice. Comprehensive and systematic structural identification of the components of Rheum officinale Baill. remains a challenge. An appropriate analytical method needs to be established for the comprehensive investigation and identification of the chemical constituents in Rheum officinale Baill. extract. In this study, a new systematic approach using ultra high performance liquid chromatography with quadrupole time-of-flight mass spectrometry in conjunction with a data mining strategy was developed to screen the targeted and nontargeted components of Rheum officinale Baill. A total of 124 compounds were identified in the Rheum officinale Baill. extract including 31 acylglucosides, 9 phenolic acids, 26 tannins, 53 anthraquinones, and 5 other compounds. Note that 55 of these compounds were reported for the first time here. In conclusion, in this study, we devised an efficient and systematic method for detecting complex compounds and have used it here to provide a foundation for future research into bioactive ingredients and quality control of Rheum officinale Baill. extract.

Two New Isomeric Andrographolides with Anti-Inflammatory and Cytotoxic Activity.

Two novel epimerized andrographolides, 8,17-dihydro-7,8-dehydroandrographolide and 10ß-8,17-dihydro-7,8-dehydroandrographolide, were isolated from andrographolide sulfonates. Their structures were elucidated by detailed NMR analysis, single-crystal X-ray diffraction and quantum chemical ECD calculations. In addition, these compounds exhibited suppression of NO production in LPS-stimulated RAW264.7 cells over the range of 1.564 to 25.000 µg/mL.

A four-step filtering strategy based on ultra-high-performance liquid chromatography coupled to quadrupole-time-of-flight tandem mass spectrometry for comprehensive profiling the major chemical constituents of Akebiae Fructus.

RATIONALE: Akebiae Fructus (AF) is a traditional Chinese medicine (TCM) with antiphlogistic, analgesic, antineoplastic, diuretic, antirheumatic, antidepressant and antiobesity activities. Identification of chemical constituents from AF is helpful to discover the potential active ingredients and to control its quality. METHODS: The four-step filtering strategy was as follows: (1) To extract the accurate mass by the different adduct ions. (2) To screen different types of the compounds using diagnostic ions. (3) By characteristic ion filtering, to confirm the substituted position and the sugar chain numbers. (4) Based on the neutral loss (NL), to identify the type of monosaccharide and the compositions of sugar chains of triterpenoid saponins and the structure of CGAs. RESULTS: A total of 94 compounds (85 triterpenoid saponins, 9 chlorogenic acids) were unambiguously or reasonably identified. Fifty constituents were discovered for the first time from AF. Nine types of triterpenoid saponins, including akebonoic acid (type I), norhederagenin (type II), oleanolic acid (type III), 2α,3ß-dihydroxy-23-oxo-30-norolean-12,20(21)-dien-28-oic acid (type IV), gypsogenin (type V), norarjunolic acid (type VI), hederagenin (type VII), 2α,3ß-dihydroxy-23-oxo-olean-12-en-28-oic acid (type VIII), arjunolic acid (type IX), and two types of chlorogenic acid (mono-CQA and di-CQA), were identified in AF. CONCLUSIONS: An ultra-high-performance liquid chromatography coupled to quadrupole-time-of-flight tandem mass spectrometry with MSE (UPLC-QTOF-MSE ) analysis with four-step filtering strategy was established and successfully applied to identify the chemical constituents of AF which can provide chemical support for further research and play an important role in the quality control of AF.

Strategy for rapid screening of antioxidant and anti-inflammatory active ingredients in Gynura procumbens (Lour.) Merr. based on UHPLC-Q-TOF-MS/MS and characteristic ion filtration.

Gynura procumbens (Lour.) Merr. is traditionally used as a raw material for making dumplings or steamed stuffed buns, and its fresh leaves are boiled with water for tea. Herein, we established an ultra-high-performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UHPLC-Q-TOF-MS/MS) combined with characteristic ion filtration (CIF) strategy to rapidly screen active ingredients with antioxidant and anti-inflammatory properties in G. procumbens. This strategy involved screening the active part of G. procumbens using antioxidation and anti-inflammatory activity assays; discovering the active compounds by speculating on the active site's chemical composition by UHPLC-Q-TOF-MS/MS plus CIF; and verifying the active compounds' activities. The ethyl acetate extract (EEAF) of G. procumbens was the major active site. Eighty-one compounds were identified from the EEAF using UHPLC-Q-TOF-MS/MS plus CIF. Furthermore, polyphenols such as cynarine, isochlorogenic acids A and isochlorogenic acids C have excellent antioxidizing and anti-inflammatory activities. This study provides a practical strategy for rapid in vitro screening of the antioxidizing and anti-inflammatory activities of traditional vegetables and herbs and identification of active ingredients.

Molecular mechanistic insight into the anti-hyperuricemic effect of Eucommia ulmoides in mice and rats.

CONTEXT: Eucommia ulmoides Oliver (Eucommiaceae) has various medicinal properties. Our previous studies revealed that Eucommia ulmoides has a protective effect on hyperuricaemia. OBJECTIVE: This study investigates the effect of Eucommia ulmoides cortex ethanol extract (EU) on hyperuricaemia and explores the underlying mechanism in Kunming mice and Sprague-Dawley rats. MATERIAL AND METHODS: Sixty mice and sixty rats were divided into normal control, hyperuricaemia, allopurinol (10 mg/kg) and three EU groups. The EU groups received intragastric EU at 80, 160, 320 mg/kg in mice and 100, 200, 400 mg/kg in rats for 7 days. Serum uric acid (SUA) was measured using a kit. mRNA and proteins were quantified by RT-qPCR and immunohistochemical assays (IHC), respectively. RESULTS: The Maximal Tolerable Dose (MTD) of EU administered intragastrically was 18 g/kg in mice. The intermediate (160 mg/kg) and high (320 mg/kg) EU treatment significantly reduced (p < 0.05) SUA levels to 130.16 µmol/L and 109.29 µmol/L, respectively, and markedly elevated the mRNA expression of organic anion transporters 1 (OAT1) and organic anion transporters 3 (OAT3), while significantly deceasing the mRNA levels of glucose transporter 9 (GLUT9) and uric acid transporter 1 (URAT1) in the mouse kidney (p < 0.05). In hyperuricemic rats, high EU (400 mg/kg) significantly reduced SUA levels to 253.85 µmol/L, and increased OAT1 and OAT3 levels, but decreased URAT1 and GLUT9, compared to the hyperuricaemia group (p < 0.05). DISCUSSION AND CONCLUSIONS: This study demonstrated the potential hyperuricaemia ameliorating effect of EU. Specific active ingredients in EU should be evaluated. These results are valuable for the development of antihyperuritic agents from EU.

Ion mobility mass spectrometry with molecular modelling to reveal bioactive isomer conformations and underlying relationship with isomerization.

RATIONALE: In medicine and drug development, molecular modelling is an important tool. It is attractive to develop a platform connecting the theoretical structural modelling and the results from experimental measurement. In addition, the separation and structural analysis of bioactive constituent isomers are still challenging tasks. METHODS: Drift tube ion mobility (IM) mass spectrometry (MS) provides the experimental collision cross section (CCS) which contains the structural information. The experimental CCS can be compared with the calculated CCS of the molecular modelling structures. This technique is especially useful for bioactive constituents in herbal medicine because active isomers with the same chemical formula are common in these samples. IM helps separate and identify these isomers and reveals details about their structures and conformations. RESULTS: Two model bioactive constituents, caffeoylquinic acids (CQAs) and dicaffeoylquinic acids (di-CQAs), were selected to systematically investigate the influence of solution, ion source conditions and ion heating on the isomer CCS distributions. By comparing the calculated CCS with the experimental value, we identified the favorable conformations of CQAs. The most compact conformation of a CQA was less likely to isomerize than the more extended conformation. It was found that the isomerization tendency was in accord with the conformation favorability. CONCLUSIONS: This study offers an effective approach to predict and demystify the conformation and isomerization of the active constituents in herbal medicines.

Nitric oxide-donating derivatives of hederacolchiside A1: Synthesis and biological evaluation in vitro and in vivo as potential anticancer agents.

A series of nitric oxide (NO) donating derivatives of hederacolchiside A1 bearing triterpenoid saponin motif were designed, synthesized and evaluated for their anticancer activity. All of the tested furoxan-based NO releasing compounds showed significant proliferation inhibitory activities. Especially compound 6a exhibited strong cytotoxicity (IC50=1.6-6.5µM) against four human tumor cell lines (SMMC-7721, NCI-H460, U251, HCT-116) in vitro and the highest level of NO releasing. Furthermore, compound 6a was revealed low acute toxicity to mice and weak haemolytic activity with potent tumor growth inhibition against mice H22 hepatocellular cells in vivo (51.5%).

Application of a liquid chromatography-tandem mass spectrometry method to the pharmacokinetics, tissue distribution and excretion in the study of anemoside B4, a novel antiviral agent candidate, in rats.

A simple, sensitive and reliable LC-MS/MS method was developed and validated for the quantification of anemoside B4, a potential antiviral constituent isolated from Pulsatilla chinensis in rat plasma, tissue, bile, urine and feces. All biological samples were prepared by protein precipitation method, and ginsenoside-Rg1 was chosen as the internal standard (IS). The analyte and IS were separated using a C18 column (2.1 × 50 mm, 1.8 µm) and a mobile phase consisting of 0.1% formic acid in water (v/v) and acetonitrile running at a flow rate of 0.2 mL/min for 5 min. The multiple reaction monitoring transitions were monitored at m/z 1219.5-749.5 for anemoside B4 and 845.4-637.4 for ginsenoside-Rg1 in electrospray ionization negative mode. The calibration curve was linear in the range of 10-2000 ng/mL for all biological matrices with a lower limit of quantification of 10 ng/mL. The validated method was successfully applied to a pharmacokinetics, tissue distribution and excretion study. These preclinical data will be beneficial for further development of anemoside B4 in future studies.

[Study on differences of Ainsliaea fragrans from different sources based on UFLC-Q-TOF-MS/MS and PCA analysis].

A rapid and accurate method of UFLC-Q-TOF-MS/MS combined with multivariate statistical analysis was established for the identification of Ainsliaea fragrans from different origins in this study. The A. fragrans from different producing areas of Jiangxi, Yunnan, Henan and Jiangsu were determined by UFLC-Q-TOF-MS/MS in the negative ion mode. And the data of the study were analyzed by the Markerview and other software for the PCA and OPLS-DA cluster analysis as well as t test. The results of the principal component analysis(PCA)showed that the main components from different origins were well distinguished. And the results of multivariate statistical showed the differences and similarities between different producing areas. Besides, 40 different compounds were identified in the negative ion mode. This method for identifying A. fragrans from different producing areas has the advantages of rapid accuracy and simplicity, which laid the foundation for the evaluation of the quality of the A. fragrans.

[Pharmacokinetics and tissue distribution of α-hederin sodium salt in rats].

To study the pharmacokinetics and tissue distribution characteristics of α-hederin sodium salt in rats. 100 mg•kg⁻¹ α-hederin sodium salt was given to the rats by intragastric administration, and LC-MS/MS method was used to determine its concentration at different time in plasma and tissues. Plasma and tissue samples were treated with methanol protein deposition method. Main pharmacokinetic parameters were as follows： tmax (0.97±1.23) h, Cmax (222.53±57.28) µg•L⁻¹, AUC0-t (1 262±788.9) h•µg•L⁻¹, T1/2 (17.94±9.50) h. α-hederin can be detected in heart, liver, spleen, lung, kidney, brain, muscle and adipose. The results showed that α-hederin sodium salt was absorbed fast and eliminated slowly in rats after oral administration. It was widely distributed in body tissues and livers kept the highest concentrations among various tissues at different time, so it can be speculated that α-hederin may have certain targeting property on livers.

A rapid and sensitive LC-MS/MS method for the determination of Pulsatilla saponin D in rat plasma and its application in a rat pharmacokinetic and bioavailability study.

A simple, sensitive and specific liquid chromatography-tandem mass spectrometry method was developed and validated for the determination of Pulsatilla saponin D, a potential antitumor constituent isolated from Pulsatilla chinensis in rat plasma. Rat plasma samples were pretreated by protein precipitation with methanol. The method validation was performed in accordance with US Food and Drug Administration guidelines and the results met the acceptance criteria. The method was successfully applied to assess the pharmacokinetics and oral bioavailability of Pulsatilla saponin D in rats.

Formulations, hemolytic and pharmacokinetic studies on saikosaponin a and saikosaponin d compound liposomes.

The aim of this study was to develop and optimise a saikosaponin a and saikosaponin d compound liposome (SSa-SSd-Lip) formulation with reduced hemolysis and enhanced bioavailability. A screening experiment was done with Plackett-Burman design, and response surface methodology of five factors (EPC/SSa-SSd ratio, EPC/Chol ratio, water temperature, pH of PBS, and ultrasound time) was employed to optimise the mean diameter, entrapment efficiency of SSa and SSd, and the reduction of hemolysis for SSa-SSd-Lip. Under the optimal process conditions (EPC/SSa-SSd ratio, EPC/Chol ratio, water temperature and pH of PBS were 26.71, 4, 50 °C and 7.4, respectively), the mean diameter, the entrapment efficiency of SSa, the entrapment efficiency of SSd and the hemolysis were 203 nm, 79.87%, 86.19%, 25.16% (SSa/SSd 12.5 mg/mL), respectively. The pharmacokinetic studies showed that the SSa-SSd-Lip had increased circulation time, decreased Cl, and increased AUC, MRT and T1/2ß (p < 0.05) for both SSa and SSd after intravenous administration in comparison with solution.

Acute effects of outdoor air pollution on emergency department visits due to five clinical subtypes of coronary heart diseases in shanghai, china.

BACKGROUND: Air pollution can be a contributing cause to the development and exacerbation of coronary heart disease (CHD), but there is little knowledge about the acute effects of air pollution on different clinical subtypes of CHD. METHODS: We conducted a time-series study to investigate the association of air pollution (particulate matter with an aerodynamic diameter < 10 µm [PM10], sulfur dioxide [SO2], and nitrogen dioxide [NO2]) on emergency department (ED) visits due to five different subtypes of CHD in Shanghai, China, from 2010 to 2012. We applied an over-dispersed Poisson generalized addictive model to analyze the associations after controlling for the seasonality, day of the week, and weather conditions. RESULTS: We identified a total of 47 523 ED visits for CHD. A 10-µg/m(3) increase in the present-day concentrations of PM10, SO2, and NO2 was associated with respective increases of 1.10% (95% confidence interval [CI] 0.33%-1.87%), 0.90% (95% CI -0.14%-1.93%), and 1.44% (95% CI 0.63%-2.26%) for total ED visits for CHD. These associations varied greatly by clinical type, with strong effects on sudden cardiac death, moderate effects on acute myocardial infarction and angina, weak effects on ischemic cardiomyopathy, and no effect on occult CHD. The associations were stronger among people aged 65 years or more than in younger individuals and in the cool season versus the warm one. CONCLUSIONS: Outdoor air pollution may have different effects of air pollution on 5 subtypes of CHD. Our results might be useful for the primary prevention of various subtypes of CHD exacerbated by air pollution.

Decentralized Kernel Ridge Regression Based on Data-Dependent Random Feature.

Random feature (RF) has been widely used for node consistency in decentralized kernel ridge regression (KRR). Currently, the consistency is guaranteed by imposing constraints on coefficients of features, necessitating that the RFs on different nodes are identical. However, in many applications, data on different nodes vary significantly on the number or distribution, which calls for adaptive and data-dependent methods that generate different RFs. To tackle the essential difficulty, we propose a new decentralized KRR algorithm that pursues consensus on decision functions, which allows great flexibility and well adapts data on nodes. The convergence is rigorously given, and the effectiveness is numerically verified: by capturing the characteristics of the data on each node, while maintaining the same communication costs as other methods, we achieved an average regression accuracy improvement of 25.5% across six real-world datasets.

Comprehensive identification strategy for rapid profiling of chemical constituents using ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry with Rhubarb as an example.

In this study, the collision induced dissociation tandem mass spectrometry (CID-MS/MS) fragmentation pathway of chemical components in rhubarb was wholly explored using 34 standards by UHPLC-QTOF-MS/MS in negative ion mode. In consequently, the diagnostic product ions for speedy screening and categorization of chemical components in rhubarb were ascertained based on their MS/MS splitting decomposition patterns and intensity analysis. According to these findings, a fresh two-step data mining strategy had set up. The initial key step involves the use of characteristic product ions and neutral loss to screen for different types of substituents and basic skeletons of compounds. The subsequent key step is to screen and classify different types of compounds based on their characteristic product ions. This method can be utilized for rapid research, classification, and identification of compounds in rhubarb. A total of 356 compounds were rapidly identified or tentatively characterized in three rhubarb species extracts, including 150 acylglucoside, 125 anthraquinone, 65 flavanols and 15 other compounds. This study manifests that the analytical strategy is feasible for the analysis of complex natural products in rhubarb.

Identification of bioactive ingredients and potential mechanisms of flowers of Hosta Plantaginea in treating pneumonia based on network pharmacology and experimental validation.

Flowers of Hosta plantaginea (H. plantaginea), a widely utilized medicinal herb in Mongolian medicine, holds a significant historical background in terms of its medicinal applications. This herb is renowned for its ability to clear heat and detoxify the body, alleviate cough, and provide relief to the throat. However, the active ingredients and the potential mechanism of action remain ambiguity. The objective of this study was to conduct a comprehensive analysis of the efficacy of H. plantaginea in treating pneumonia, identify its active ingredients and unveil the pharmacological mechanism in the treatment of pneumonia. In vivo experiments demonstrate the plant's anti-pneumonia properties, while mass spectrometry analysis identifies 62 chemicals, with 14 absorbed into the bloodstream. Network pharmacology and Venn analysis reveal 195 targets of 52 active ingredients, with 49 gene targets common to H. plantaginea and pneumonia. Protein-protein interaction (PPI) network construction and enrichment analysis highlight the key targets and pathways such as AKT, EGFR, IL-17. Western blotting confirms downregulation of these pathways, indicating the anti-inflammatory effects of H. plantaginea in treating acute lung injury. Our findings showed that the treatment of ALI with the H. plantaginea exerts its anti-inflammatory effects through multiple components, targets, and pathways. This study established a solid experimental foundation for investigating the various components, targets, and pathways involved in the treatment of pneumonia using H. plantaginea. It offers valuable insights from multiple perspectives and can serve as a reference for the clinical application of this plant in pneumonia treatment.

Characterization of chemical constituents and metabolites in rat plasma after oral administration of Ainsliaea fragrans Champ by using UHPLC-QTOF-MS/MS.

Ainsliaea fragrans Champ, a strong heat-clearing and detoxifying traditional Chinese medicine, has been effectively used for treating chronic cervicitis, endometritis, pelvic inflammatory diseases, and other conditions caused by damp heat. It shows a good effect in the treatment of cervicitis and has broad clinical application prospects. Nevertheless, there is no comprehensive study on its in vivo and in vitro chemical analysis. UHPLC-QTOF-MS/MS combined with the non-targeted characteristic filter analysis were used to conjecture and characterize the chemical components and in vivo metabolites of rats following oral administration of Ainsliaea fragrans Champ. In this study, A total of 85 compounds were identified in Ainsliaea fragrans Champ, including 29 flavonoids, 14 sesquiterpenoids, 25 chlorogenic acids, and 17 other compounds. In the plasma of rats after administration of Ainsliaea fragrans Champ, 160 compounds were deduced (19 prototype compounds and 141 metabolites). The 141 metabolites consist of 50 flavonoids, 80 phenolic acids and 11 Chlorogenic acids. The related metabolic pathways mainly involved demethylation, reduction, sulfonation, decarboxylation, hydroxylation, methylation, and glucuronide conjunction. In summary, the chemical components and metabolites of Ainsliaea fragrans Champ were comprehensively identified by using a rapid and accurate analysis method, which laid a foundation for dissecting its bioactive substances. In addition, it provides a scientific basis for the in-depth study of the material basis of Ainsliaea fragrans Champ efficacy and theoretical support for illustrating the mechanism of medical action and its clinical application.

Interphylum dissemination of NDM-5-positive plasmids in hospital wastewater from Fuzhou, China: a single-centre, culture-independent, plasmid transmission study.

BACKGROUND: The global spread of plasmid-borne carbapenem resistance is an ongoing public health challenge; however, the nature of such horizontal gene transfer events among complex bacterial communities remains poorly understood. We examined the in-situ transfer of the globally dominant New Delhi metallo-ß-lactamase (NDM)-5-positive IncX3 plasmid (denoted pX3_NDM-5) in hospital wastewater to simulate a real-world, One Health antimicrobial resistance context. METHODS: For this transmission study, we tagged pX3_NDM-5 with the green fluorescent protein gene, gfp, using a CRISPR-based method and transferred the plasmid to a donor Escherichia coli strain. Bacteria were extracted from a hospital wastewater treatment plant (Fujian Provincial Maternity and Children's Hospital, Fuzhou, China) as the bacterial recipient community. We mixed this recipient community with the E coli donor strain carrying the gfp-tagged plasmid, both with and without sodium hypochlorite (NaClO) as an environmental stressor, and conducted several culture-based and culture-independent conjugation assays. The conjugation events were observed microscopically and quantified by fluorescence-activated cell sorting. We analysed the taxonomic composition of the sorted transconjugal pool by 16S rRNA gene amplicon sequencing and assessed the stability of the plasmid in the isolated transconjugants and its ability to transfer back to E coli. FINDINGS: We show that the plasmid pX3_NDM-5 has a broad host range and can transfer across various bacterial phyla, including between Gram-negative and Gram-positive bacteria. Although environmental stress with NaClO did not affect the overall plasmid transfer frequency, it reduced the breadth of the transconjugant pool. The taxonomic composition of the transconjugal pool was distinct from that of the recipient communities, and environmental stress modulated the permissiveness of some operational taxonomic units towards the acquisition of pX3_NDM-5. Notably, pX3_NDM-5 transconjugants included the Gram-positive pathogen Enterococcus faecalis, and the plasmid could subsequently be reconjugated back to E coli. These findings suggest that E faecalis could act as a natural shuttle vector for the wide dissemination of pX3_NDM-5 plasmids. INTERPRETATION: Our culture-independent conjugation model simulates natural environmental conditions and challenges the established theory that Gram-negative and Gram-positive bacteria rarely exchange clinically important plasmids. The data show that plasmids disseminate more widely across genera and phyla than previously thought. These findings have substantial implications when considering the spread of antimicrobial resistance across One Health sectors. FUNDING: The Laboratory of Lingnan Modern Agriculture Project, the National Natural Science Foundation of China, the Natural Science Foundation of Fujian Province of China, and the Outstanding Young Research Talents Program of Fujian Agriculture and Forestry University.

Learning With Asymmetric Kernels: Least Squares and Feature Interpretation.

Asymmetric kernels naturally exist in real life, e.g., for conditional probability and directed graphs. However, most of the existing kernel-based learning methods require kernels to be symmetric, which prevents the use of asymmetric kernels. This paper addresses the asymmetric kernel-based learning in the framework of the least squares support vector machine named AsK-LS, resulting in the first classification method that can utilize asymmetric kernels directly. We will show that AsK-LS can learn with asymmetric features, namely source and target features, while the kernel trick remains applicable, i.e., the source and target features exist but are not necessarily known. Besides, the computational burden of AsK-LS is as cheap as dealing with symmetric kernels. Experimental results on various tasks, including Corel, PASCAL VOC, Satellite, directed graphs, and UCI database, all show that in the case asymmetric information is crucial, the proposed AsK-LS can learn with asymmetric kernels and performs much better than the existing kernel methods that rely on symmetrization to accommodate asymmetric kernels.