Louis Guibout

Bio: Louis Guibout is an academic researcher from University of Paris. The author has contributed to research in topics: Ecdysteroid & Phytoecdysteroid. The author has an hindex of 4, co-authored 10 publications receiving 56 citations. Previous affiliations of Louis Guibout include Centre national de la recherche scientifique & Pierre-and-Marie-Curie University.

The minor ecdysteroids from Ajuga turkestanica

Abstract: Introduction : Ajuga turkestanica is a plant used in traditional medicine for its high ecdysteroid content, including the presence of the particularly active turkesterone, which possess efficient anabolic activity. Objectives : To isolate and identify minor ecdysteroids present in a semi-purified plant fraction containing ca. 70% turkesterone. Material and Methods : Multi-step preparative HPLC (combining RP- and NP-HPLC systems) was used to purify the different components present in the turkesterone fraction. Isolated compounds were identified by high-resolution mass spectrometry and 2D-NMR. Results : Fourteen ecdysteroids (including turkesterone and 20-hydroxyecdysone) were isolated. Seven of these, all bearing an 11α-hydroxy group, were previously unreported. Conclusion : Ajuga turkestanica ecdysteroids are characterised by the abundance of 11α-hydroxylated compounds and by the simultaneous presence of 24C, 27C, 28C and 29C ecdysteroids. It is expected that even more ecdysteroids are to be found in this plant since the starting material for this study lacked the less polar ecdysteroids. The simultaneous presence of 20-hydroxyecdysone and turkesterone (its 11α-hydroxy analogue) as the two major ecdysteroids suggests that every ecdysteroid is probably present in both 11α-hydroxy and 11-deoxy forms.

Norbixin Protects Retinal Pigmented Epithelium Cells and Photoreceptors against A2E-Mediated Phototoxicity In Vitro and In Vivo.

Abstract: The accumulation of N-retinylidene-N-retinylethanolamine (A2E, a toxic by-product of the visual pigment cycle) in the retinal pigment epithelium (RPE) is a major cause of visual impairment in the elderly. Photooxidation of A2E results in retinal pigment epithelium degeneration followed by that of associated photoreceptors. Present treatments rely on nutrient supplementation with antioxidants. 9'-cis-Norbixin (a natural diapocarotenoid, 97% purity) was prepared from Bixa orellana seeds. It was first evaluated in primary cultures of porcine retinal pigment epithelium cells challenged with A2E and illuminated with blue light, and it provided an improved photo-protection as compared with lutein or zeaxanthin. In Abca4-/- Rdh8-/- mice (a model of dry AMD), intravitreally-injected norbixin maintained the electroretinogram and protected photoreceptors against light damage. In a standard rat blue-light model of photodamage, norbixin was at least equally as active as phenyl-N-tert-butylnitrone, a free radical spin-trap. Chronic experiments performed with Abca4-/- Rdh8-/- mice treated orally for 3 months with norbixin showed a reduced A2E accumulation in the retina. Norbixin appears promising for developing an oral treatment of macular degeneration. A drug candidate (BIO201) with 9'-cis-norbixin as the active principle ingredient is under development, and its potential will be assessed in a forthcoming clinical trial.

Ecdysteroid profiles of two Ajuga species, A. iva and A. remota.

Abstract: Phytoecdysteroids are plant analogues of insect moulting hormones and are used by plants to repel or disturb phytophagous insects. They are also active on mammals and present in many plants used in...

20-Hydroxyecdysone activates the protective arm of the renin angiotensin system via Mas receptor

Abstract: 20-Hydroxyecdysone (20E) is a steroid hormone that plays a key role in insect development through nuclear ecdysone receptors (EcRs) and at least one membrane GPCR receptor (DopEcR) and displays numerous pharmacological effects in mammals. However, its mechanism of action is still debated, involving either an unidentified GPCR or the estrogen ER receptor. The goal of our study was to better understand 20E mechanism of action. A mouse myoblast cell line (C2C12) and the gene expression of myostatin (a negative regulator of muscle growth) was used as a reporter system of anabolic activity. Experiments using protein-bound 20E established the involvement of a membrane receptor. 20E-like effects were also observed with Angiotensin-(1-7), the endogenous ligand of Mas. Additionally, the effect on myostatin gene expression was abolished by Mas receptor knock-down using small interfering RNA (siRNA) or pharmacological inhibitors. 17-Estradiol (E2) also inhibited myostatin gene expression, but protein-bound E2 was inactive, and E2 activity was not abolished by angiotensin-(1-7) antagonists. A mechanism involving cooperation between Mas receptor and a membrane-bound palmitoylated estrogen receptor is proposed.The possibility to activate the Mas receptor with a safe steroid molecule is consistent with the pleiotropic pharmacological effects of ecdysteroids in mammals and indeed this mechanism may explain the close similarity between angiotensin-(1-7) and 20E effects. Our findings open a lot of possible therapeutic developments by stimulating the protective arm of the renin-angiotensin-aldosterone system (RAAS) with 20E.

Small‐scale analysis of phytoecdysteroids in seeds by HPLC‐DAD‐MS for the identification and quantification of specific analogues, dereplication and chemotaxonomy

Abstract: INTRODUCTION: Phytoecdysteroids are analogues of arthropod steroids occurring in plants. They contribute to invertebrate deterrence. A wide diversity of ecdysteroids occurs in phytoecdysteroid‐containing plant species, sometimes in high amounts. Ecdysteroids demonstrate potentially useful pharmaceutical actions in mammals. OBJECTIVES: Establish reversed‐phase high‐performance liquid chromatography with tandem mass spectrometry (RP‐HPLC‐MS/MS) and RP‐HPLC‐DAD‐MS (diode array detector mass spectrometry) methods for the separation, identification and quantification of ecdysteroids to screen for species containing significant amounts of 20‐hydroxyecdysone (20E) and other useful ecdysteroids. MATERIALS AND METHODS: Micro‐extracts of seed samples (ca. 30 mg) in 50% ethanol were subjected to RP‐SPE (solid‐phase extraction) purification prior to analysis by RP‐HPLC‐MS/MS and RP‐HPLC‐DAD‐MS. The method was initially applied to genera (Amaranthus, Centaurea, Lychnis, Ourisia, Serratula, Silene and Trollius) where high‐accumulating species had been previously encountered. Seeds of 160 randomly selected species, many of which have not previously been assessed, were then analysed. HPLC‐MS/MS with a short analysis time initially identifies ecdysteroid‐positive extracts and quantifies 20E. The positive extracts (20 ng 20E) are then analysed by HPLC‐MS/MS with a longer analysis time to identify and quantify 17 common phytoecdysteroids and, finally, HPLC‐DAD‐MS (0.1–0.25 μg 20E) is used to obtain UV‐ and MS‐spectra to confirm identifications or as a basis for characterisation of partially identified or novel analogues. RESULTS: Lychnis coronaria, Silene fimbriata and Silene hookeri ecdysteroids are characterised for the first time and those of Cucubalus baccifer and Ipheion uniflorum are more extensively characterised. CONCLUSIONS: The procedure provides a rapid/sensitive method for screening small plant samples for the presence, quantification and identification of ecdysteroids. It permits ready dereplication of samples, identifying extracts containing large amounts or novel analogues.

Quercetin-3-O-α-l-arabinopyranoside protects against retinal cell death via blue light-induced damage in human RPE cells and Balb-c mice.

Abstract: Age-related macular degeneration (AMD) is among the increasing number of diseases causing irreversible blindness in the elderly. Dry AMD is characterized by the accumulation of lipofuscin in retinal pigment epithelium (RPE) cells. N-Retinylidene-N-retinylethanolamine (A2E), a component of lipofuscin, is oxidized to oxo-A2E under blue light illumination, leading to retinal cell death. The aim of this study was to investigate the protective effect and mechanism of quercetin-3-O-α-l-arabinopyranoside (QA) against blue light (BL)-induced damage in both RPE cells and mice models. Treatment by QA inhibited A2E uptake in RPE cells, as determined by a decrease in fluorescence intensity. QA also protected A2E-laden RPE cells against BL-induced apoptosis. QA inhibited C3 complement activation and poly (ADP-ribose) polymerase (PARP) cleavage, as determined by western blotting. QA showed an inhibitory effect on AP1 and NF-kB activity as estimated in a reporter gene assay. In addition, QA activated the gene expression of aryl hydrocarbon receptor target genes (CYP1A1, CYP1B1) in TCDD-treated RPE cells. In the mice model, oral administration of QA protected against retinal degeneration induced by BL exposure as determined by histological analyses (thickness of retinal layers and immunostaining for caspase-3). In addition, QA inhibited apoptosis and inflammation via inhibition of NF-kB p65 translocation, C3 activation, and PARP cleavage. Collectively, these results revealed the protective mechanism of QA against BL-induced retinal damage both in vitro and in vivo.

New Lipophenol Antioxidants Reduce Oxidative Damage in Retina Pigment Epithelial Cells

Abstract: Age-related macular degeneration (AMD) is a multifactorial pathology and its progression is exacerbated by oxidative stress. Oxidation and photo-oxidation reactions modify lipids in retinal cells, contribute to tissue injury, and lead to the formation of toxic adducts. In particular, autofluorescent pigments such as N-retinylidene-N-retinylethanolamine (A2E) accumulate as lipofuscin in retinal pigment epithelial cells, contribute to the production of additional reactive oxygen species (ROS), and lead to cell degeneration. In an effort to develop efficient antioxidants to reduce damage caused by lipid oxidation, various natural polyphenols were structurally modified to increase their lipophilicity (lipophenols). In this study, resveratrol, phloroglucinol, quercetin and catechin were selected and conjugated to various polyunsaturated fatty acids (PUFAs) using classical chemical strategies or enzymatic reactions. After screening for cytotoxicity, the capacity of the synthesized lipophenols to reduce ROS production was evaluated in ARPE-19 cells subjected to H2O2 treatment using a dichlorofluorescein diacetate probe. The positions of the PUFA on the polyphenol core appear to influence the antioxidant effect. In addition, two lipophenolic quercetin derivatives were evaluated to highlight their potency in protecting ARPE-19 cells against A2E photo-oxidation toxicity. Quercetin conjugated to linoleic or α-linolenic acid were promising lipophilic antioxidants, as they protected ARPE-19 cells from A2E-induced cell death more effectively than the parent polyphenol, quercetin.

Photo-Oxidative Blue-Light Stimulation in Retinal Pigment Epithelium Cells Promotes Exosome Secretion and Increases the Activity of the NLRP3 Inflammasome

Abstract: Purpose: Age-related macular degeneration (AMD) is a major cause of blindness in the elderly, and the activation of the NACHT, LRR, and PYD domain-containing protein 3 (NLRP3) inflammasome is invol...