Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 16 de 16
Filtrar
1.
FASEB J ; 38(5): e23526, 2024 Mar 15.
Artículo en Inglés | MEDLINE | ID: mdl-38430456

RESUMEN

Germ cell development depends on the capacity of somatic Sertoli cells to undergo differentiation into a mature state and establish a germ cell-specific blood-testis barrier (BTB). The BTB structure confers an immunological barrier for meiotic and postmeiotic germ cells, and its dynamic permeability facilitates a transient movement of preleptotene spermatocytes through BTB to enter meiosis. However, the regulatory factors involved in Sertoli cell maturation and how BTB dynamics coordinate germ cell development remain unclear. Here, we found a histone deacetylase HDAC3 abundantly expresses in Sertoli cells and localizes in both cytoplasm and nucleus. Sertoli cell-specific Hdac3 knockout in mice causes infertility with compromised integrity of blood-testis barrier, leading to germ cells unable to traverse through BTB and an accumulation of preleptotene spermatocytes in juvenile testis. Mechanistically, nuclear HDAC3 regulates the expression program of Sertoli cell maturation genes, and cytoplasmic HDAC3 forms a complex with the gap junction protein Connexin 43 to modulate the BTB integrity and dynamics through regulating the distribution of tight junction proteins. Our findings identify HDAC3 as a critical regulator in promoting Sertoli cell maturation and maintaining the homeostasis of the blood-testis barrier.


Asunto(s)
Barrera Hematotesticular , Histona Desacetilasas , Células de Sertoli , Animales , Masculino , Ratones , Barrera Hematotesticular/metabolismo , Diferenciación Celular , Células de Sertoli/metabolismo , Espermatocitos/metabolismo , Espermatogénesis/genética , Testículo/metabolismo , Uniones Estrechas/metabolismo , Histona Desacetilasas/genética , Histona Desacetilasas/metabolismo
2.
Biol Pharm Bull ; 38(10): 1658-62, 2015.
Artículo en Inglés | MEDLINE | ID: mdl-26424027

RESUMEN

Pomegranate seed oil (PSO) has diverse bioactivities. It was hyphothesized that if PSO were employed to construct a trans-resveratrol-loaded self-nanoemulsifying drug delivery system (RES SNEDDS-PSO), not only could PSO serve as an oil phase but also exert synergistic effects with resveratrol to yield better therapeutic outcomes. In this study, we prepared RES SNEDDS-PSO for the first time to validate that hypothesis. The anti-inflammatory and anticancer activities of RES SNEDDS-PSO were compared with another SNEDDS composed of oil phase isopropyl palmitate (RES SNEDDS-IP). The results showed that upon exposure to a 10-fold amount of water, RES SNEDDS-PSO was converted into nanoemulsions with a mean size of 44 nm. Nanoemulsions enhanced the water solubility of resveratrol by 20-fold, significantly improved resveratrol stability in intestinal fluid, and slowed the decomposition of resveratrol in water by 1-fold. An in vivo anti-infection test showed that the degree of inflammatory swelling in mice given RES SNEDDS-PSO was only 60 and 76% that of the group fed with RES SNEDDS-IP at doses of 10 and 20 mg/kg, respectively. An in vitro anticancer study showed that the inhibitory rate of RES SNEDDS-PSO against MCF-7 breast cancer cells was 2.03- and 1.24-fold that of RES SNEDDS-IP at a concentration of 12.5 and 25 µg/mL, respectively. This study demonstrated that the newly developed SNEDDS may be a prospective formulation in the functional food and clinical fields.


Asunto(s)
Antiinflamatorios/administración & dosificación , Antineoplásicos/administración & dosificación , Sistemas de Liberación de Medicamentos , Lythraceae , Aceites de Plantas/administración & dosificación , Estilbenos/administración & dosificación , Animales , Antiinflamatorios/farmacología , Antiinflamatorios/uso terapéutico , Antineoplásicos/farmacología , Antineoplásicos/uso terapéutico , Carragenina , Supervivencia Celular/efectos de los fármacos , Sinergismo Farmacológico , Edema/inducido químicamente , Edema/tratamiento farmacológico , Jugo Gástrico/química , Humanos , Secreciones Intestinales/química , Células MCF-7 , Ratones , Aceites de Plantas/química , Aceites de Plantas/farmacología , Aceites de Plantas/uso terapéutico , Resveratrol , Semillas , Solubilidad , Estilbenos/farmacología , Estilbenos/uso terapéutico , Agua/química
3.
Front Pharmacol ; 13: 937075, 2022.
Artículo en Inglés | MEDLINE | ID: mdl-35833035

RESUMEN

Currently, many people are afflicted by cerebral diseases that cause dysfunction in the brain and perturb normal daily life of people. Cerebral diseases are greatly affected by cerebral metabolism, including the anabolism and catabolism of neurotransmitters, hormones, neurotrophic molecules and other brain-specific chemicals. Natural medicines (NMs) have the advantages of low cost and low toxicity. NMs are potential treatments for cerebral diseases due to their ability to regulate cerebral metabolism. However, most NMs have low bioavailability due to their low solubility/permeability. The study is to summarize the better bioactivity, cerebral metabolism and pharmacokinetics of NMs and its advanced version. This study sums up research articles on the NMs to treat brain diseases. NMs affect cerebral metabolism and the related mechanisms are revealed. Nanotechnologies are applied to deliver NMs. Appropriate delivery systems (exosomes, nanoparticles, liposomes, lipid polymer hybrid nanoparticles, nanoemulsions, protein conjugation and nanosuspensions, etc.) provide better pharmacological and pharmacokinetic characteristics of NMs. The structure-based metabolic reactions and enzyme-modulated catalytic reactions related to advanced versions of NMs alter the pharmacological activities of NMs.

4.
Nanoscale ; 14(25): 8967-8977, 2022 Jun 30.
Artículo en Inglés | MEDLINE | ID: mdl-35670481

RESUMEN

The oral administration of a single formulation loaded with more than one natural medicine to treat chronic diseases has advantages such as convenience, effectiveness, and economy. Here, using biomaterials approved by the drug administration, we fabricated supramolecular nanovectors containing dual natural medicines to prevent gastric mucosal lesions. Nanovectors exhibited superior intestinal absorption and bioavailability, which might be due to their high dispersion, good muco-adhesiveness, blood-lymph circulation transport, lipid sensing, and protective effects. Molecular docking results clarified the possible mechanisms in aspects of efflux pump (p-glycoprotein and multidrug resistance protein 1) inhibition effects, metabolic enzyme (cytochrome P450 3A4/1A2) blocking effects, serum albumin deposit effects, and dual drug interaction effects. Nanovectors decreased ethanol-induced gastric mucosal lesions by lowering the gastric ulcer index, preventing oxidative damage, decreasing interleukin-6, tumor necrosis factor-α and malondialdehyde, increasing glutathione, superoxide dismutase, and prostaglandin E2 levels. The interactions of inhibitor of nuclear factor-κB or κB kinase-related proteins and dual drugs or nanovector components were simulated computationally to provide an understanding of the gastro-protective action mechanism. In all, industrializable supramolecular nanovectors could effectively co-deliver dual natural medicines via the oral route by improving the pharmacokinetic behavior and exerting protective efficacy of the gastric mucosa by decreasing the oxidative stress and inflammatory level.


Asunto(s)
Úlcera Gástrica , Mucosa Gástrica , Humanos , Malondialdehído/efectos adversos , Malondialdehído/metabolismo , Simulación del Acoplamiento Molecular , Estrés Oxidativo , Úlcera Gástrica/inducido químicamente , Úlcera Gástrica/tratamiento farmacológico , Úlcera Gástrica/prevención & control
5.
J Oleo Sci ; 69(2): 161-166, 2020 Feb 05.
Artículo en Inglés | MEDLINE | ID: mdl-31941867

RESUMEN

Activity changes after olive oil (OO), pomegranate seed oil (PSO), and grape seed oil (GSO) were formulated into self-nanoemulsifying systems (SNES), were examined in this study. Only GSO SNES dramatically enhanced antioxidant activity of GSO. SNES from OO and PSO did not exert obvious impact on radical quenching ability of the oils. Though PSO exhibited significantly stronger strength over OO in suppressing E. coli (p < 0.05), the inhibitory effect of OO SNES against E. coli became slightly higher than that of PSO SNES. Similar phenomenon happened in GSO, OO, and their SNES for preventing Yeast growth. The study indicated that SNES sometimes reversed the strength order of the original oils in inhibiting bacteria.


Asunto(s)
Extracto de Semillas de Uva/química , Aceite de Oliva/química , Aceites de Plantas/química , Granada (Fruta)/química , Semillas/química , Emulsionantes
6.
Expert Opin Drug Metab Toxicol ; 14(9): 951-960, 2018 Sep.
Artículo en Inglés | MEDLINE | ID: mdl-30058385

RESUMEN

INTRODUCTION: Anticancer enzymes play important roles in cancer treatment. The anticancer enzyme has been in clinical use to treat acute lymphoblastic leukemia for many years. Other types of anticancer enzymes have been investigated in laboratory studies and clinical trials. Area covered: This paper will provide perspectives on the indications, anticancer mechanisms, enzymatic characteristics (such as molecular weight, organism source, and kinetic parameters) and pharmacokinetic behaviors of anticancer enzymes and their delivery systems by systematically analyzing available literature. The pharmacodynamics of anticancer enzyme delivery systems has also been summarized. Expert opinion: Anticancer enzymes kill cancer cells by depleting important nutrients required for growth or producing metabolite toxic to tumor cells. Suitable enzyme delivery systems have demonstrated promising effects on the pharmacokinetics, bioactivity and application of anticancer enzymes. Their current limitations and future potential are analyzed.[Figure: see text].


Asunto(s)
Antineoplásicos/administración & dosificación , Enzimas/administración & dosificación , Neoplasias/tratamiento farmacológico , Animales , Antineoplásicos/farmacocinética , Antineoplásicos/farmacología , Sistemas de Liberación de Medicamentos , Enzimas/farmacocinética , Enzimas/farmacología , Humanos
7.
J Pharm Biomed Anal ; 117: 125-39, 2016 Jan 05.
Artículo en Inglés | MEDLINE | ID: mdl-26350559

RESUMEN

Ultra high performance liquid chromatography (UHPLC) coupled with a hybrid quadrupole time-of-flight mass spectrometry (QTOF-MS) was used to separate and identify the compounds in Scutellaria indica L. Fragmentation patterns of these compounds were investigated by the UHPLC-QTOF-MS technique in both negative and positive ion modes. By using this strategy, both intact precursors and fragment ions information were obtained from a single injection. A total of 42 phenolic and other compounds were unequivocally or tentatively identified from S. indica for the first time. Among them, 8 phenolic compounds: scutellarin, luteolin, naringenin, wogonoside, apigenin, hispidulin, wogonin and chrysin were further quantified and used as marker substances by multiple-reaction monitoring in negative ionization mode. The results demonstrated that the calibration curves for all analytes showed good linearity (R(2)>0.9992) within the test ranges. The overall limits of detection and limits of quantification were 0.12-10.52 ng/mL and 4.67-20.22 ng/mL, respectively. The recovery was 96.02-102.88% with a relative standard deviation of less than 3.02%. It is proposed that the methods described here can be applied for rapid evaluation, quality control and authenticity establishment of S. indica.


Asunto(s)
Medicamentos Herbarios Chinos/análisis , Scutellaria , Espectrometría de Masas en Tándem/normas , Cromatografía Líquida de Alta Presión/métodos , Cromatografía Líquida de Alta Presión/normas , Espectrometría de Masas en Tándem/métodos , Factores de Tiempo
8.
Pharmacognosy Res ; 7(2): 148-55, 2015.
Artículo en Inglés | MEDLINE | ID: mdl-25829788

RESUMEN

BACKGROUND: Abrus cantoniensis is popularly used as traditional Chinese medicine and a cool tea in South of China. However, due to diminishing source of A. cantoniensis, it is usually interchanged or adulterated with other species of Abrus genus because of the limited knowledge in identification and differentiation. Especially, Abrus mollis is widely mixed on herbal markets and pharmaceutical preparation. OBJECTIVE: To ensure safety and efficacy, a detailed comparison was undertaken to carry out an anatomical and micro-morphological study of two species of A. cantoniensis and A. mollis. MATERIALS AND METHODS: Microscopic characteristics of roots, leaves and stems, including transverse sections and the crude drug powder, were observed using a light microscope according to the usual microscopic techniques. RESULTS: The basic diagnostic features of A. cantoniensis include that stem is extremely thin; xylem vessels of root are radially arranged in 10 or more bundles; pith is hollow in stem, and the palisade tissue is made up of two layers of palisade cells. Furthermore, scanning electron microscopy was used to compare nonglandular hairs and the stomata of the leaflet surface. A table of the key authentication parameters based on the analyzed microscopic characteristics was drawn up. CONCLUSION: The study demonstrated that the microscopy and related techniques provided a systematic method that is convenient, feasible, and can be unambiguously applied to the authentication of the species of Abrus.

9.
J Pharm Biomed Anal ; 109: 62-6, 2015 May 10.
Artículo en Inglés | MEDLINE | ID: mdl-25766849

RESUMEN

The aim of this study was to investigate the possibility of using the non-official species Scutellaria indica L. as the substitute for the official species Scutellaria barbata D. Don. A sensitive, precise and accurate method was developed to identify their chemical compositions from the crude extracts using UHPLC-PDA-QTOF-MS/MS. 36 peaks were detected and 28 peaks have been tentatively and structurally characterized by comparing their retention times, UV spectra and HR-MS data with those of the reference substances and/or the data of the literatures. Additionally, 5 flavonoids have been quantified by multiple reaction monitoring (MRM) in the negative ionization mode. The results demonstrated that there were 23 common peaks between these two species. However, the other 13 peaks from S. barbata could not be detected in S. indica. Furthermore, the content of 5 flavonoids is significantly different. Scutellarein cannot be detected in S. indica, which was considered as the characteristic component for distinguishing the two species. Our data, therefore, clearly demonstrate that S. indica may not be used as the substitute for S. barbata and further investigation is needed to determine through investigation of their therapeutic efficacy.


Asunto(s)
Medicamentos Herbarios Chinos/análisis , Scutellaria/química , Cromatografía Líquida de Alta Presión , Indicadores y Reactivos , Límite de Detección , Espectrometría de Masas , Extractos Vegetales/química , Estándares de Referencia , Reproducibilidad de los Resultados
10.
Nat Prod Res ; 28(15): 1171-5, 2014.
Artículo en Inglés | MEDLINE | ID: mdl-24896191

RESUMEN

In the study, the major alkaloids from Fritillariae Hupehensis Bulbs (FHB) have been analysed for the first time by the combined use of the following two methods: the simultaneous quantitation of three alkaloids by using high-performance liquid chromatography coupled with evaporative light scattering detector (HPLC-ELSD) and the simultaneous characterisation of seven alkaloids by using HPLC coupled with electrospray ionisation-mass spectrometry analysers detection (HPLC-ESI-MS(n)). The other four congeneric species were compared by using the established method. Both correlation coefficients of similarity in chromatograms were calculated for quantitative expression of HPLC profiles. The results revealed that the chromatogram profile combining similarity evaluation could efficiently identify and distinguish FHB from other different origins of Fritillaria species. The established method was considered to be suitable for checking the genuine origin and quality control of FHB.


Asunto(s)
Alcaloides/análisis , Fritillaria/química , Alcaloides/química , Cromatografía Líquida de Alta Presión , Estructura Molecular , Raíces de Plantas/química , Espectrometría de Masa por Ionización de Electrospray
11.
Chin J Nat Med ; 12(7): 488-94, 2014 Jul.
Artículo en Inglés | MEDLINE | ID: mdl-25053546

RESUMEN

AIM: To study the hepatoprotective effect of methanol extract of Gentiana veitchiorum (MGV) against CCl4-induced oxidative stress and liver injury in mice. METHOD: The acute hepatic model was developed by injection of 20% CCl4 in mice. ICR mice were divided into six groups, including control, CCl4, CCl4(+) silymarin, and CCl4(+) MGV (100, 200, and 400 mg·kg(-1)) groups. Hepatic enzymes including AST, ALT and ALP levels in serum, and antioxidant enzymes, including SOD, CAT and GPX activity in liver tissue, were determined. Histopathological examination and Western blot analysis were performed. RESULTS: Oral administration of MGV at 200 and 400 mg·kg(-1) for 15 days dose-dependently inhibited the serum elevations of AST, ALT, and ALP, and recovered the reduction of SOD, CAT, and GPX in liver tissue. Hematoxylin and eosin staining examination performed in liver tissues suggested that MGV treatment ameliorated histopathological changes in CCl4-induced mice. Western blotting analysis implied that MGV increased HO-1 expression and recovered TNF-α alternation. CONCLUSION: G. veitchiorum can protect the liver against CCl4-induced damage in mice, and this hepatoprotective effect was due at least in part to its ability through scavenging CCl4-associated free radical activities. The study provided in vivo evidence that G. veitchiorum can be used as a safe, cheap, and effective agent to reduce acute liver damage, supporting its folk medicine use.


Asunto(s)
Tetracloruro de Carbono/toxicidad , Enfermedad Hepática Inducida por Sustancias y Drogas/tratamiento farmacológico , Gentiana/química , Extractos Vegetales/administración & dosificación , Sustancias Protectoras/administración & dosificación , Alanina Transaminasa/metabolismo , Animales , Aspartato Aminotransferasas/metabolismo , Enfermedad Hepática Inducida por Sustancias y Drogas/enzimología , Enfermedad Hepática Inducida por Sustancias y Drogas/etiología , Enfermedad Hepática Inducida por Sustancias y Drogas/metabolismo , Femenino , Humanos , Hígado/efectos de los fármacos , Hígado/enzimología , Masculino , Ratones , Ratones Endogámicos ICR , Estrés Oxidativo/efectos de los fármacos , Factor de Necrosis Tumoral alfa/metabolismo
12.
Nat Prod Res ; 27(24): 2256-62, 2013.
Artículo en Inglés | MEDLINE | ID: mdl-23962075

RESUMEN

A saponin-enriched fraction was prepared from the EtOH extract of the whole plant of Morina nepalensis var. alba Hand-Mazz. It showed α-glucosidase inhibitory activity, from which two new triterpene saponins (1 and 2), along with one known saponin (3), were isolated. The structures of the new saponins were identified by spectroscopic analysis, including extensive 1D and 2D NMR techniques and hydrolysis followed by chromatographic analysis. The three saponins were assayed for α-glucosidase inhibitory activities.


Asunto(s)
Caprifoliaceae/química , Saponinas/química , Triterpenos/química , Inhibidores de Glicósido Hidrolasas , Espectroscopía de Resonancia Magnética , Estructura Molecular , Saponinas/farmacología , Triterpenos/farmacología , Ácido Ursólico
13.
Bioinorg Chem Appl ; 2013: 198545, 2013.
Artículo en Inglés | MEDLINE | ID: mdl-24093005

RESUMEN

Zuota is regarded as the king of Tibetan medicine. However, due to the confidentiality of this precious medicine, the scientific characterization of Zuota is very scarce, which limits the pharmacology and biosafety studies of Zuota. Herein, we collected four different Zuota samples from Tibet, Qinghai, Gansu, and Sichuan and characterized them by multiple techniques. Our results showed that Zuota was mainly an inorganic mixture of HgS, sulfur, and graphite. Morphologically, Zuota samples were composed of nanoparticles, which further aggregated into microsized particles. Chemically, the majorities of Zuota were S and Hg (in the forms of HgS and pure sulfur). All samples contained pure sulfur with orthorhombic crystalline. Zuota from Qinghai province had different HgS crystalline, namely, hexagonal crystalline. The others were all face-centered cubic crystalline. Carbon in Zuota NPs was in the form of graphite. The implication to future studies of Zuota was discussed.

14.
Nat Prod Commun ; 7(1): 59-60, 2012 Jan.
Artículo en Inglés | MEDLINE | ID: mdl-22428246

RESUMEN

Danshen is a commonly used traditional Chinese herb, but over twenty Salvia species are used as Danshen by local herbalists. In this study, twelve Salvia species from the plateau of Sichuan and Yunnan Provinces were collected, analyzed and compared with Danshen by HPLC. The results showed that most of the Salvia species were good sources of rosmarinic acid and tanshinones. The highest amount of both rosmarinic acid and tanshinone IIA were found in S. przewalskii Maxim. These results pave the way for a better therapeutic exploitation of these plants.


Asunto(s)
Salvia miltiorrhiza/química , Salvia/química , Abietanos/análisis , Cromatografía Líquida de Alta Presión , Cinamatos/análisis , Depsidos/análisis , Ácido Rosmarínico
15.
Arch Pharm Res ; 35(3): 499-508, 2012 Mar.
Artículo en Inglés | MEDLINE | ID: mdl-22477197

RESUMEN

A novel pyridostigmine bromide (PB)-phospholipid nanocomplex (PBPLC) was prepared to increase the bioavailability of PB. A central composite design approach was employed for process optimization. The physicochemical properties of PBPLC were investigated by means of differential scanning calorimetry, ultraviolet spectroscopy, Fourier transformed infrared spectroscopy and the n-octano/water partition coefficient. The intestinal permeability of PBPLC was observed via a single pass intestinal perfusion in rats. After oral administration of PBPLC, the concentrations of PB at predetermined time points were determined by HPLC, and the pharmacokinetic parameters were computed by DAS 2.1.1 software. Multiple linear regression analysis for process optimization revealed that the optimal PBPLC was obtained when the values of X(1), X(2), and X(3) were 8, 40°C, and 4 mg/mL, respectively. The average particle size and zeta potential of PBPLC with the optimized formulation were 204.60 nm and -25.12 mV, respectively. Non-covalent interactions between PB and phospholipids were found in the PBPLC. The n-octanol/water partition coefficient of PBPLC was substantially increased. PBPLC had better intestinal permeability in comparison with free PB. Mean plasma drug concentration-time curves of PBPLC and free PB after oral administration were both in accordance with the two-compartment open model. The values of pharmacokinetic parameters of PBPLC and free PB were the peak time (T(max)) 2 h vs 2 h, the maximum concentration (C(max)) 22.79 µg/mL vs 6.00 µg/mL, and the value of the area under the concentration vs time curve (AUC(0-∞)) 7128.21 µg·min/mL vs 1772.36 µg·min/mL, respectively. In conclusion, compared with free PB, PBPLC remarkably improves the oral bioavailability of PB, which is likely due to its higher lipophilicity and permeability.


Asunto(s)
Inhibidores de la Colinesterasa/administración & dosificación , Inhibidores de la Colinesterasa/farmacocinética , Nanopartículas , Fosfolípidos/química , Bromuro de Piridostigmina/administración & dosificación , Bromuro de Piridostigmina/farmacocinética , 1-Octanol/química , Administración Oral , Animales , Disponibilidad Biológica , Rastreo Diferencial de Calorimetría , Química Farmacéutica , Inhibidores de la Colinesterasa/sangre , Inhibidores de la Colinesterasa/química , Composición de Medicamentos , Absorción Intestinal , Mucosa Intestinal/metabolismo , Modelos Lineales , Masculino , Modelos Biológicos , Nanotecnología , Permeabilidad , Bromuro de Piridostigmina/sangre , Bromuro de Piridostigmina/química , Ratas , Ratas Sprague-Dawley , Solubilidad , Solventes/química , Espectrofotometría Ultravioleta , Espectroscopía Infrarroja por Transformada de Fourier , Tecnología Farmacéutica/métodos , Agua/química
16.
Nat Prod Commun ; 5(5): 805-8, 2010 May.
Artículo en Inglés | MEDLINE | ID: mdl-20521551

RESUMEN

Salvianolic acid A (Sal A), a caffeic acid derivative present in Salvia miltiorrhiza (Danshen), has shown significant biological activities, some of which are more potent than those of salvianolic acid (Sal B), the most abundant and bioactive compound in Danshen. However, its low content in the raw material makes it difficult to be used in the clinic. In this study, a novel procedure was developed to isolate Sal A from Salvia miltiorrhiza. Using this procedure, Sal A could be enriched to 1.7% in the raw material by hydrolyzing Sal B. The solution was further purified by macroporous resin and ODS column chromatography. The yield of Sal A was 0.5% with a purity of 98.0%. The procedure is efficient and convenient and is considered suitable for the separation of Sal A from Danshen.


Asunto(s)
Ácidos Cafeicos/aislamiento & purificación , Medicamentos Herbarios Chinos/química , Lactatos/aislamiento & purificación , Salvia miltiorrhiza/química , Ácidos Cafeicos/química , China , Cromatografía , Hidrólisis , Lactatos/química , Espectroscopía de Resonancia Magnética , Sesquiterpenos de Germacrano/química
SELECCIÓN DE REFERENCIAS
DETALLE DE LA BÚSQUEDA