Evaluation of synergism in essential oils against the cattle tick Rhipicephalus microplus in Burkina Faso.

The cattle tick Rhipicephalus microplus affects animal production economically by reducing weight gain and milk production and causing diseases, such as babesiosis and anaplasmosis. Using synthetic acaricides to reduce their incidence has caused the emergence of resistant tick populations. The present study aimed to assess the in vitro acaricidal activity of combinations of essential oils (EOs) from Ocimum americanum, Ocimum gratissimum, and Lippia multiflora against R. microplus larvae. In fact, numerous biological properties have been reported on EOs from these three plants, including acaricidal properties. Hence, a larval immersion test was performed using a population of R. microplus resistant to synthetic acaricides used in Burkina Faso. Results revealed that EO from O. gratissimum was the most effective on R. microplus larvae with LC50 and LC90 values at 10.36 and 15.51 mg/mL, respectively. For EO combinations, the most significant synergistic effect was obtained by combination 6 (1/3 O. americanum + 2/3 O. gratissimum +1/6 L. multiflora), with a combination index value of 0.44. All combinations presented dose reduction index >1, indicating a favorable dose reduction. According to the literature, this is the first study to determine the combination effect of EOs from the abovementioned plants in controlling R. microplus activity in vitro. Thus, the combination of these EOs is an alternative to control the resistant populations of invasive cattle ticks.

Efficacy of local essential oils against Amblyomma variegatum tick from Burkina Faso.

The native tick Amblyomma variegatum remains one of the most important tick species affecting cattle in West Africa. This hinders animal production by negatively impacting the health and reproduction of animals infested with the tick. Given the negative consequences on production quality and environmental health, the use of chemical products for tick control is increasingly being discouraged. Therefore, this study aimed to assess the acaricidal activity of essential oils such as Ageratum conyzoïdes, Cymbopogon citratus, Cymbopogon giganteus, Lippia multiflora and Ocimum gratissimum against specimens of A. variegatum from Burkina Faso. A larval immersion test was performed to investigate the larvicidal activities of these essential oils. Gas chromatography-mass spectrometry was used to determine the chemical compositions of essential oils. The chemical composition was predominantly oxygenated monoterpenes in A. conyzoïdes (48.71 %), C. citratus (99.9 %) and C. giganteus (73.63 %), while hydrocarbon monoterpenes were the most abundant in O. gratissimum (63.7 %) and hydrocarbon sesquiterpenes in L. multiflora (71.719 %). The recorded larvicidal activity, varied according to the species of plants and the dose applied. At a dose of 12.5 mg/mL, all essential oils studied, except L. multiflora (7.54 %), induced 100 % larval mortality. In this study, we highlight the promising larvicidal effects of local essential oils against A. variegatum. These essential oils can be used as bio-acaricides, which are effective and environmentally-friendly alternatives to chemical products. However, further investigations are required to determine the mechanisms of action of these essential oils for in vivo experimentation and their practical application in the control of A. variegatum ticks.

Social perceptions of malaria and diagnostic-driven malaria treatment in Burkina Faso.

Malaria is a parasitic disease, endemic in many tropical and sub-tropical countries. Malaria is a well-known disease, familiar to almost all people in endemic regions, as they or their family are regularly confronted with it; everyone in these regions has probably experienced the disease, at least once in their life. To investigate the social perceptions of malaria in Burkina Faso, including its diagnosis-driven treatment, we have conducted a survey in both urban (Saint Camille Hospital, Ouagadougou HOSCO) and rural (Boussé Hospital) areas. Fifty-six individuals, mostly representatives of the society variability, were surveyed by questionnaires and 2 focus groups were organized with traditional healers. In general, populations seem to have grasped the causes, symptoms and means of preventing the disease. However, the majority of interviewees make a marked confusion between malaria and dengue; dengue fever is considered like a severe form of malaria. The care modalities (modern and/or traditional medicine) are plural and the choice of therapeutic practice depends on both the socio-economic conditions and education level of the patient. Whereas some patients mark preferences for one type of medicine, others simultaneously recourse to both; for these, a medicine does not outperform the other and their combination multiplies the chances of a quick recovery. Whether for modern or traditional medicine, the diagnosis is considered very important for effective disease management. Modern medicine uses diagnostic tools based on light microscopy and immunochromatography (rapid diagnostic tests; RDT); traditional medicine has its own diagnostic logic but nevertheless recognizes modern medicine diagnosis to guide its therapy. 90 % of those interviewed first use modern medicine to seek an accurate diagnosis of their disease and thus to receive adequate treatment. Presumptive treatments are still widely prescribed and accepted by most patients who trust the judgment of their caregiver, not perceiving any benefit to an objective diagnosis. In front of a negative diagnosis, patient reactions are diverse, some accepting investigations for other diseases (45 %), others opting for self-medication (15 %), others resorting to traditional medicine (20 %). All are unanimous in the importance of diagnosis and are in favor of in-development diagnostic technologies, provided these obviously meet the features of reliability, ease of use, availability and, of course, economical accessibility.

The Metabolomic study of Calotropis procera Ait. from Burkina Faso, based on chemical functional groups profiling using FTIR.

Background C. procera is an important wild medicinal plant used in different area of Burkina Faso for the neuropsychiatric disorders treatment. It was reported to possess many pharmacological properties because of its phytochemical diversity. This study was carried out to identify possible specific chemical characteristics form C. procera leaves and root-bark samples, harvested in two regions of Burkina Faso, for a better selective use of specimens in traditional medicine. Methods Plant materials (leaves and root-bark) were collected from five sites in each region. Samples powders and extracts were mixed with potassium bromide for the Fourier Transform Infrared Spectroscopy (FTIR) analysis. A multivariate data analysis was performed to highlight differences in the FTIR spectral profile of samples. Therefore, phytochemical contents such as phenolics, flavonoids and terpenoids were evaluated with aqueous and methanolic extracts, using UV/visible light spectrophotometer method. Results Results of principal component analysis (PCA) showed a significant difference between leaves and root-bark spectral profile, independently to the region of collection. These profiles possess characteristic signals which could be exploited as biomarkers for plant organ discrimination. The phytochemical contents evaluation showed that C. procera leaves contain more significant phenolics, and root-bark possess more terpenoid compounds. This study of C. procera Ait. based on FTIR spectral characteristic and phytochemical content, suggest that terpenoids, notably cardenolide-type could be a good biomarkers for C. procera samples characterization and to explain root-bark therapeutic potential.

Morphological and Molecular Characterization of Zanthoxylum zanthoxyloides (Rutaceae) from Burkina Faso.

Zanthoxylum zanthoxyloides is a West African forest tree that is used for example against malaria and sickle cell anemia in Burkina Faso. The goal of this study was to analyze the genetic and morphological diversity of the species within wild populations in Burkina Faso, where it is potentially under threat due to the uncontrolled harvesting of its roots. Seventy-two trees from three different sites in Southwestern Burkina Faso were analyzed. Each tree was characterized by 12 traits specifying the period of flowering and maturity as well as morphological characteristics of the stem, leaves, and seeds. The molecular analysis was performed using two plastid DNA regions (psbA-trnH and trnL-trnF) and two nuclear regions (GBSSI and ITS) to identify the genetic diversity of the species for further development of a management plan for ex situ reproduction and in situ conservation. We found variability in morphological traits correlating with the geographic distance of the study sites. The molecular analysis, in contrast, revealed hardly any genetic variability among the tested trees and no population structure. Whether the differences in morphological traits are caused by different environmental conditions or by genetic variability in genes linked to morphological traits needs further testing. The apparent lack of genetic differentiation suggests that germplasm throughout the study region is suitable for planting in conservation actions. Efficient conservation management should involve local communities, especially those interested in traditional medicine.

Antioxidant activity of crude ethanolic extract and fractions of Ziziphus mauritiana Lam. (Rhamnaceae) leaves from Burkina Faso.

Background Ziziphus mauritiana Lam. is a plant used in traditional medicine in Burkina Faso in the treatment of several diseases, of which diabetes is characterized by oxidative stress. The aim of this study was to evaluate the in vitro antioxidant potential of the extracts of leaves of this plant. Methods The crude hydroethanolic extract (HEE) of the leaves of Z. mauritiana and their partitionates in n-hexane, dichloromethane, and ethyl acetate, and in the residual aqueous solution (the F1, F2, F3, and F4 fractions, respectively) were first prepared. The content of polyphenols was determined and the antioxidant effects of the extracts were evaluated by their 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging activity, inhibition of lipid peroxidation (TBARS), and the ferric reducing antioxidant power (FRAP). Results The HEE as well as the F3 and F4 fractions were rich in polyphenols with contents between 58 and 84 mg equivalent gallic acid per 100 mg. The flavonoid content was 4 mg quercetin equivalents in the HEE and the F4 fraction. Except for the F1 fraction, the HEE and the other fractions showed significant DPPH scavenging activity (IC50 between 8 and 12 µg/mL). The IC50 of TBARS by different extracts was in the range 1-5 µg/mL, and the FRAP activity was 7-85 mg ascorbic acid equivalent per 100 mg. Total polyphenol content was highly correlated with the antioxidant activities. Conclusions The HEE, F3, and F4 fractions were found to be the richest in polyphenols and had the best antioxidant activity. The antioxidant activity of the extracts of the leaves of Z. mauritiana is due to these polyphenolic compounds.

Phytochemistry and neuroprotective effects of Eclipta alba (L.) Hassk.

Eclipta alba (L.) Hassk. or Eclipta prostrata (Linn.) or Eclipta erecta (Linn.) is an herbaceous plant well known in Asian as African traditional medicines. These extracts are used in traditional medicine for treatment of microbial diseases and certain metabolic disorders. This review aimed to investigate phytochemical profile and neuroprotective effects of E. alba (L.) Hassk. Several compounds belonging to the families of phenolics, alkaloids, terpenoids and polysaccharides have been isolated, identified or characterized from E. alba extracts. This plant has a diverse neuropharmacological profile. Thus, its extract improves cognitive deficits and also attenuated epileptic seizures. Phytomolecules implicated in these potentials are Eclalbasaponin II and luteolin, respectively. This document updates isolated and identified organic compounds from the extracts of E. alba and reviews their neuropharmacological activities.

Insecticidal Activity of Local Plants Essential Oils Against Laboratory and Field Strains of Anopheles gambiae s. l. (Diptera: Culicidae) From Burkina Faso.

The emergence and intensification of resistance to insecticides in malaria vector populations is the main obstacle to insecticide-based control efforts. The main objective of this study was to evaluate the larvicidal and adulticidal properties of the essential oils (EOs) of Ocimum canum, Hyptis suaveolens, Hyptis spicigera, and Lantana camara on field-collected, pyrethroids-resistant mosquitoes, local laboratory strains, and susceptible 'Kisumu' strain of Anopheles gambiae (Meigen) (Diptera: Culicidae) populations. Larvae and adults of these mosquitoes were challenged against four EOs. The mortality rates of larvae and adults were assessed 24 h after exposure to the EOs. Species identifications and detection of the L1014F and L1014S kdr mutations and the 1575Y super-kdr mutation were carried out using polymerase chain reaction on the pyrethroid-resistant mosquitoes from the field. EO compositions were analyzed by gas chromatography and mass spectrometry. Monoterpene hydrocarbons were the major components of H. suaveolens and H. spicigera EOs (49.8%) and (69.6%), respectively, whereas oxygenated monoterpenes (68.7%) were predominant in the O. canum EO. For L. camara, the component yields were variable, but it was the most effective EO against all strains. The LC50 values for the larvae were 7.73 and 25.63 ppm for the susceptible 'Kisumu' and resistant field strains, respectively. The LC50 for adults was 0.24% for the susceptible strain and 1.98% for the resistant strain. Molecular analysis confirmed the presence of L1014F and N1575Y mutations in resistant Anopheles arabiensis and Anopheles coluzzii mosquitoes from the field. Our results highlighted the potential of the EOs of local plants as insecticides against resistant and susceptible strains of An. gambiae populations.

Antioxidant and Phytochemical Studies of 31 Cowpeas (Vigna unguiculata (Walp L)) Genotypes from Burkina.

Antioxidant compounds of dietary plants have been widely studied because of their bioactive properties. The objective of this research study was to analyse the health enhancing attributes of 31 cowpeas varieties from Burkina Faso. Significant variations were observed in the phenolic content as well as the antioxidant and anti-lipid peroxidation activities amongst the cowpea varieties. Pearson correlation coefficient analysis showed that the ferric reducing ability (r = 0.954) and anti-lipid peroxidation (r = 0.616) were positively correlated with the total phenolic content. A significant relationship between cowpea ferric reducing ability and anti-lipid peroxidation (r = 0.64) was also revealed. However, nitric oxide scavenging potential was found not to be related to its total phenolic and total flavonoid content. 2,2-diphenyl-1-picrylhydrazyl (DPPH) and hydroxyl radicals scavenging potentials were not correlated with the total flavonoid content. The pigmented seeds of cowpea varieties possess higher total phenolic, total flavonoid content, ferric reduction ability, and anti-lipid peroxidation activities than the colourless ones. The results obtained from this study suggest that Burkina Faso cowpea cultivars are rich in phenolic compounds and have significant antioxidant and anti-lipid peroxidation activities. Consumption of the cowpea, particularly of coloured cowpea seed varieties, should be beneficial for chronic human diseases prevention.

Human Lymphocyte-Protective Effects of an Ethanol Extract from Detarium microcarpum Guill. and Perr. (Caesalpiniaceae) Fruit Pulp.

The current study aimed to evaluate, in vitro, the antioxidant capacity and the human lymphocyte-protective effect of the ethanolic extract from Detarium microcarpum fruit pulp against oxidative stress damage. Human lymphocytes were incubated with different concentrations of extract, followed by the addition of hydrogen peroxide or tert-butyl hydroperoxide. Cell viability was measured using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Furthermore, the antioxidant property of the extract was evaluated in vitro using hydrogen peroxide and nitric oxide radical-scavenging assays. Compared to the vehicle, the fruit pulp ethanol extract did not exhibit a cytotoxic effect on human lymphocytes. Furthermore, the cytotoxicity of hydrogen peroxide and tert-butyl hydroperoxide to human lymphocytes was significantly reduced by fruit extract pretreatment. The extract and ascorbic acid exhibited similar cytoprotective activity (p > 0.05). The fruit pulp extract showed more antioxidant activity than gallic acid in the hydrogen peroxide-scavenging model, while in the nitric oxide-quenching model, the fruit extract and gallic acid showed similar activity. The fruit pulp of D. microcarpum contains potent antioxidant and cell-protective compounds. The use of the fruit pulp of D. microcarpum as a food supplement could rescue cellular oxidative damage responsible for numerous pathologies.

Medicinal Plants Used for Neuropsychiatric Disorders Treatment in the Hauts Bassins Region of Burkina Faso.

Background: In Burkina Faso, phytotherapy is the main medical alternative used by populations to manage various diseases that affect the nervous system. The aim of the present study was to report medicinal plants with psychoactive properties used to treat neuropsychiatric disorders in the Hauts Bassins region, in the western zone of Burkina Faso. Methods: Through an ethnobotanical survey using structured questionnaire, 53 traditional healers (TH) were interviewed about neuropsychiatric disorders, medicinal plants and medical practices used to treat them. The survey was carried out over a period of three months. Results: The results report 66 plant species used to treat neuropsychiatric pathologies. Roots (36.2%) and leaves (29%) were the main plant parts used. Alone or associated, these parts were used to prepare drugs using mainly the decoction and the trituration methods. Remedies were administered via drink, fumigation and external applications. Conclusions: It appears from this study a real knowledge of neuropsychiatric disorders in the traditional medicine of Hauts Bassins area. The therapeutic remedies suggested in this work are a real interest in the fight against psychiatric and neurological diseases. In the future, identified plants could be used for searching antipsychotic or neuroprotective compounds.

Ethnopharmacological approaches in mood and anxiety disorders. The relevance of the oxidative stress status.

Neurodegenerative diseases and psychiatric disorders are one of the most important pathologies that lead to increased morbidity in populations. Both mood and anxiety disorders include mental disorders not caused by detectable organic abnormalities of the brain. At the molecular level, affective spectrum symptomatology is due to neurotransmitter dysregulation including receptor or transporter impairments and also due to faulty intracellular signaling that generally leads to impaired neurotransmission. Also, recent studies have shown the relationship between oxidative stress and the development of affective disorders. Since classical medication can cause major side effects and alternative approaches tend to be more and more trusted, it seems that plant extracts-based complementary therapies may offer superior yielding and safety compared to traditional medication.

Methanol Extract from Anogeissus leiocarpus (DC) Guill. et Perr. (Combretaceae) Stem Bark Quenches the Quorum Sensing of Pseudomonas aeruginosa PAO1.

Background: Due to its extensive arsenal of virulence factors and inherent resistance to antibiotics, Pseudomonas aeruginosa is a threat particularly in immunocompromised patients. Considering the central role of quorum sensing in the production of virulence factors, inhibition of bacterial communication mechanism constitute an opportunity to attenuate pathogenicity of bacteria resistant to available antibiotics. Our study aimed to assess the anti-quorum sensing activity of Anogeissus leiocarpus, traditionally used in Burkina Faso, for the treatment of infected burn wounds. Methods: Investigations were carried out on methanol extract from A. leiocarpus stem bark. The reporter strains Chromobacterium violaceum CV026 and P. aeruginosa PAO1 derivatives were used to evidence any interference with the bacterial quorum sensing and expression of related genes. P. aeruginosa PAO1 was used to measure the impact on pyocyanin production. Results: At a sub-inhibitory concentration (100 µg/mL), A. leiocarpus methanol extract quenched the quorum sensing mechanism of P. aeruginosa PAO1 by down-streaming the rhlR gene, with a subsequent reduction of pyocyanin production. Moreover, the antioxidant polyphenols evidenced are able to reduce the oxidative stress induced by pyocyanin. Conclusion: The antioxidant and anti-quorum sensing activities of A. leiocarpus stem bark could justify its traditional use in the treatment of infected burn wounds.

Quality assessment and antiplasmodial activity of West African Cochlospermum species.

The present study focuses on development of phytochemical methods for quality assessment of two West-African Cochlospermum species (Cochlospermum planchonii and Cochlospermum tinctorium) traditionally used for malaria treatment in Burkina Faso. Antimalarial activity of preparations from dried rhizomes (decoction) was tested against the chloroquine-sensitive Plasmodium strain 3D7 using the histidine-rich protein II (HRP2) drug susceptibility assay and compared with extract preparations using organic solvents of different polarity. Two main apocarotenoids were isolated from rhizomes of C. planchonii and unambiguously identified as dihydrocochloxanthine and cochloxanthine by spectroscopic methods. Comparative HPLC analyses of thirty-nine (39) samples from markets and from collections in natural habitats of both species showed a high variability in the accumulation of cochloxanthines and related carotenoids which were proven to be characteristic for rhizomes of both species and generally absent in leaves. Furthermore, content of total phenolics and antioxidant activities (DPPH and FRAP) as well as haemolytic activity of various extracts was tested. The HPLC method presented here was validated and provides a good separation of both compounds including 10 minor carotenoids. Extracts from both species and pure cochloxanthine offered pronounced antioxidant activities and weak haemolytic activity while, in contrast, dihydrocochloxanthine had a strong haemolytic effect at the highest concentration analysed. However, cochloxanthine as well as dihydrocochloxanthine showed erythroprotective effects against the haemolytic activity of the reference saponin. Moderate antiplasmodial activity between 16 and 63 µg/ml were observed with all tested extracts, and lower IC50 values were obtained with pure dihydrocochloxanthine (IC50=6.9 µg/ml), cochloxanthine (IC50=6.8 µg/ml), the DCM fraction (IC50=2.4 µg/ml) and the ethyl acetate fraction (IC50=11.5µg/ml) derived from a methanolic extract of C. planchonii. This study shows a major variability of carotenoid content and antiplasmodial activity of both C. planchonii and C. tinctorium. The high haemolytic activity of dihydrocochloxanthine (at 100 µg/ml) should be considered as a selection criterion for choosing species phenotypes for treatment.

Pseudomonas aeruginosa Biofilm Formation and Persistence, along with the Production of Quorum Sensing-Dependent Virulence Factors, Are Disrupted by a Triterpenoid Coumarate Ester Isolated from Dalbergia trichocarpa, a Tropical Legume.

Recently, extracts of Dalbergia trichocarpa bark have been shown to disrupt P. aeruginosa PAO1 quorum sensing (QS) mechanisms, which are key regulators of virulence factor expression and implicated in biofilm formation. One of the active compounds has been isolated and identified as oleanolic aldehyde coumarate (OALC), a novel bioactive compound that inhibits the formation of P. aeruginosa PAO1 biofilm and its maintenance as well as the expression of the las and rhl QS systems. Consequently, the production of QS-controlled virulence factors including, rhamnolipids, pyocyanin, elastase and extracellular polysaccharides as well as twitching and swarming motilities is reduced. Native acylhomoserine lactones (AHLs) production is inhibited by OALC but exogenous supply of AHLs does not restore the production of virulence factors by OALC-treated cultures, indicating that OALC exerts its effect beyond AHLs synthesis in the QS pathways. Further experiments provided a significant inhibition of the global virulence factor activator gacA by OALC. OALC disorganizes established biofilm structure and improves the bactericidal activity of tobramycin against biofilm-encapsulated PAO1 cells. Finally, a significant reduction of Caenorhabditis elegans paralysis was recorded when the worms were infected with OALC-pre-treated P. aeruginosa. Taken together, these results show that triterpenoid coumarate esters are suitable chemical backbones to target P. aeruginosa virulence mechanisms.

Endemic malagasy Dalbergia species inhibit quorum sensing in Pseudomonas aeruginosa PAO1.

Various species of the plant genus Dalbergia are traditionally used as medicine for sundry ailments and some of them have been shown recently to quench the virulence of Gram-positive and Gram-negative bacteria. Cell-to-cell communication mechanisms, quorum sensing (QS) in particular, are key regulators of virulence in many pathogenic bacteria. Screening n-hexane extracts of leaves, roots and bark of endemic Malagasy Dalbergia species for their capacity to antagonize QS mechanisms in Pseudomonas aeruginosa PAO1 showed that many reduced the expression of the QS-regulated genes lasB and rhlA. However, only the extract of Dalbergia trichocarpa bark (DTB) showed a significant reduction of QS gene expression without any effect on the aceA gene encoding a QS-independent isocitrate lyase. Further characterization of DTB impact on QS revealed that the QS systems las and rhl are inhibited and that swarming, twitching, biofilm formation and the production of pyocyanin, elastase and proteases are also hampered in the presence of the DTB extract. Importantly, compared with the known QS inhibitor naringenin, the DTB extract showed a stronger negative effect on twitching, biofilm formation and tobramycin resistance. Preliminary structural characterization of these potent biofilm disrupters suggests that they belong to the phytosterols. The strong inhibition of motility and biofilm formation suggests that the DTB extract contains agents disrupting biofilm architecture, which is an important observation in the context of the design of new drugs targeting biofilm-encapsulated pathogens.

Evaluation of enzymes inhibition activities of medicinal plant from Burkina Faso.

The aim of the present study was to evaluate some enzymes inhibitory effects of 11 plant species belonging to 9 families from Burkina Faso. Methanolic extracts were used for their Glutathione-s-transferase (GST), Acetylcholinesterase (AChE), Carboxylesterase (CES) and Xanthine Oxidase (XO) inhibitory activities at final concentration of 100 microg mL(-1). The total phenolics, flavonoids and tannins were also determined spectrophotometrically using Folin-Ciocalteu, AlCl3 and ammonium citrate iron reagents, respectively. Among the 11 species tested, the best inhibitory percentages were found with Euphorbia hirta, Sclerocarya birrea and Scoparia dulcis (inhibition > 40%) followed by Annona senegalensis, Annona squamosa, Polygala arenaria and Ceratotheca sesamoides (inhibition > 25%). The best total phenolic and tannin contents were found with S. birrea with 56.10 mg GAE/100 mg extract and 47.75 mg TAE/100 mg extract, respectively. E hirta presented the higher total flavonoids (9.96 mg QE/100 mg extract). It's was found that Sclerocarya birrea has inhibited all enzymes at more than 30% and this activity is correlated to total tannins contents. Contrary to S. birrea, the enzymatic activities of E. hirta and S. dulcis are correlated to total flavonoids contents. Present findings suggest that the methanolic extracts of those plant species are potential inhibitors of GST, AChE, CES and XO and confirm their traditional uses in the treatment of mental disorders, gout, painful inflammations and cardiovascular diseases.

Antioxidant and anti-inflammatory effects of Scoparia dulcis L.

Different extracts were obtained from Scoparia dulcis L. (Scrophulariaceae) by successive extraction with hexane, chloroform, and methanol. These extracts exhibited significant antioxidant capacity in various antioxidant models mediated (xantine oxidase and lipoxygenase) or not mediated (2,2-diphenyl-picrylhydrazyl, ferric-reducing antioxidant power, ß-carotene bleaching, lipid peroxidation) by enzymes. The antioxidant activity of the extracts was related to their phytochemical composition in terms of polyphenol and carotenoid contents. The chloroform extract was richest in phytochemicals and had the highest antioxidant activity in the different antioxidant systems. All the extracts exhibited less than 50% inhibition on xanthine oxidase but more than 50% inhibition on lipid peroxidation and lipoxygenase. The extracts strongly inhibited lipid peroxidation mediated by lipoxygenase.

The flavanone naringenin reduces the production of quorum sensing-controlled virulence factors in Pseudomonas aeruginosa PAO1.

Preliminary screening of the Malagasy plant Combretum albiflorum for compounds attenuating the production of quorum sensing (QS)-controlled virulence factors in bacteria led to the identification of active fractions containing flavonoids. In the present study, several flavonoids belonging to the flavone, flavanone, flavonol and chalcone structural groups were screened for their capacity to reduce the production of QS-controlled factors in the opportunistic pathogen Pseudomonas aeruginosa (strain PAO1). Flavanones (i.e. naringenin, eriodictyol and taxifolin) significantly reduced the production of pyocyanin and elastase in P. aeruginosa without affecting bacterial growth. Consistently, naringenin and taxifolin reduced the expression of several QS-controlled genes (i.e. lasI, lasR, rhlI, rhlR, lasA, lasB, phzA1 and rhlA) in P. aeruginosa PAO1. Naringenin also dramatically reduced the production of the acylhomoserine lactones N-(3-oxododecanoyl)-L-homoserine lactone (3-oxo-C12-HSL) and N-butanoyl-L-homoserine lactone (C4-HSL), which is driven by the lasI and rhlI gene products, respectively. In addition, using mutant strains deficient for autoinduction (ΔlasI and ΔrhlI) and LasR- and RhlR-based biosensors, it was shown that QS inhibition by naringenin not only is the consequence of a reduced production of autoinduction compounds but also results from a defect in the proper functioning of the RlhR-C4-HSL complex. Widely distributed in the plant kingdom, flavonoids are known for their numerous and determinant roles in plant physiology, plant development and in the success of plant-rhizobia interactions, but, as shown here, some of them also have a role as inhibitors of the virulence of pathogenic bacteria by interfering with QS mechanisms.