Bioactive polyphenols in Ximenia americana and the traditional use among Malian healers

ETHNOPHARMACOLOGICAL RELEVANCE

Ximenia americana is a medicinal bushy, spiny shrub or small tree used in Mali in West Africa for treatment of various diseases, most common are infectious and inflammatory ailments.

AIMS OF THE STUDY

(1) To perform an ethnopharmacological survey on the traditional use of Ximenia americana among healers in Mali. (2) To isolate and identify chemical constituents from the ethanol extract of Ximenia americana leaves and to study their radical scavenging and enzyme inhibitory effects.

MATERIALS AND METHODS

In five different districts in Mali, 38 healers were interviewed about their medicinal use of Ximenia americana. An aqueous ethanol extract of the leaves of this tree was prepared and further fractionated with liquid-liquid extraction, VersaFlash and Sephadex LH-20 column chromatography, and preparative HPLC. Isolated compounds were identified by 1D and 2D NMR spectroscopy. Extracts, subfractions and isolated compounds were investigated as DPPH radical scavengers and as inhibitors of xanthine oxidase and 15-lipoxygenase.

RESULTS

Major areas of use by Malian healers were against throat infection, amenorrhea and as tonic. Fractionation of the ethanol extract led to the isolation and identification of the cyanogenic glycoside sambunigrin (1), which is previously known from the plant. Additionally, gallic acid (2) and the gallotannins β-glucogalline (3) and 1,6-digalloyl-β-glucopyranose (4) were found. The following flavonoids were isolated: quercetin (5), quercitrin (quercetin-3-O-α-rhamnopyranoside) (6), avicularin (quercetin-3-O-α-arabinofuranoside) (7), quercetin-3-O-β-xylopyranoside (8), quercetin-3-O-(6″-galloyl)-β-glucopyranoside (9) and kaempferol-3-O-(6″-galloyl)-β-glucopyranoside (10). The flavonoids were active both as enzyme inhibitors and DPPH radical scavengers.

CONCLUSION

Sambunigrin (1) was the main compound in the EtOAc soluble fraction of the alcoholic extract of Ximenia americana leaves. Gallic acid (2), gallotannins (3-4) and flavonoids (5-10) were identified for the first time in the genus Ximenia. The identified compounds may give a rationale for the traditional use of Ximenia americana in Mali. Healers interviewed reported the use against throat infections, amenorrhea, as tonic, for wound healing and against pain.

Inflammation-related gene expression by lipid oxidation-derived products in the progression of atherosclerosis

Vascular areas of atherosclerotic development persist in a state of inflammation, and any further inflammatory stimulus in the subintimal area elicits a proatherogenic response; this alters the behavior of the artery wall cells and recruits further inflammatory cells. In association with the inflammatory response, oxidative events are also involved in the development of atherosclerotic plaques. It is now unanimously recognized that lipid oxidation-derived products are key players in the initiation and progression of atherosclerotic lesions. Oxidized lipids, derived from oxidatively modified low-density lipoproteins (LDLs), which accumulate in the intima, strongly modulate inflammation-related gene expression, through involvement of various signaling pathways. In addition, considerable evidence supports a proatherogenic role of a large group of potent bioactive lipids called eicosanoids, which derive from oxidation of arachidonic acid, a component of membrane phospholipids. Of note, LDL lipid oxidation products might regulate eicosanoid production, modulating the enzymatic degradation of arachidonic acid by cyclooxygenases and lipoxygenases; these enzymes might also directly contribute to LDL oxidation. This review provides a comprehensive overview of current knowledge on signal transduction pathways and inflammatory gene expression, modulated by lipid oxidation-derived products, in the progression of atherosclerosis.

Cellular lipid extraction for targeted stable isotope dilution liquid chromatography-mass spectrometry analysis

The metabolism of fatty acids, such as arachidonic acid (AA) and linoleic acid (LA), results in the formation of oxidized bioactive lipids, including numerous stereoisomers(1,2). These metabolites can be formed from free or esterified fatty acids. Many of these oxidized metabolites have biological activity and have been implicated in various diseases including cardiovascular and neurodegenerative diseases, asthma, and cancer(3-7). Oxidized bioactive lipids can be formed enzymatically or by reactive oxygen species (ROS). Enzymes that metabolize fatty acids include cyclooxygenase (COX), lipoxygenase (LO), and cytochromes P450 (CYPs)(1,8). Enzymatic metabolism results in enantioselective formation whereas ROS oxidation results in the racemic formation of products. While this protocol focuses primarily on the analysis of AA- and some LA-derived bioactive metabolites; it could be easily applied to metabolites of other fatty acids. Bioactive lipids are extracted from cell lysate or media using liquid-liquid (l-l) extraction. At the beginning of the l-l extraction process, stable isotope internal standards are added to account for errors during sample preparation. Stable isotope dilution (SID) also accounts for any differences, such as ion suppression, that metabolites may experience during the mass spectrometry (MS) analysis(9). After the extraction, derivatization with an electron capture (EC) reagent, pentafluorylbenzyl bromide (PFB) is employed to increase detection sensitivity(10,11). Multiple reaction monitoring (MRM) is used to increase the selectivity of the MS analysis. Before MS analysis, lipids are separated using chiral normal phase high performance liquid chromatography (HPLC). The HPLC conditions are optimized to separate the enantiomers and various stereoisomers of the monitored lipids(12). This specific LC-MS method monitors prostaglandins (PGs), isoprostanes (isoPs), hydroxyeicosatetraenoic acids (HETEs), hydroxyoctadecadienoic acids (HODEs), oxoeicosatetraenoic acids (oxoETEs) and oxooctadecadienoic acids (oxoODEs); however, the HPLC and MS parameters can be optimized to include any fatty acid metabolites(13). Most of the currently available bioanalytical methods do not take into account the separate quantification of enantiomers. This is extremely important when trying to deduce whether or not the metabolites were formed enzymatically or by ROS. Additionally, the ratios of the enantiomers may provide evidence for a specific enzymatic pathway of formation. The use of SID allows for accurate quantification of metabolites and accounts for any sample loss during preparation as well as the differences experienced during ionization. Using the PFB electron capture reagent increases the sensitivity of detection by two orders of magnitude over conventional APCI methods. Overall, this method, SID-LC-EC-atmospheric pressure chemical ionization APCI-MRM/MS, is one of the most sensitive, selective, and accurate methods of quantification for bioactive lipids.

Cannabidiol as an emergent therapeutic strategy for lessening the impact of inflammation on oxidative stress

Oxidative stress with reactive oxygen species generation is a key weapon in the arsenal of the immune system for fighting invading pathogens and initiating tissue repair. If excessive or unresolved, however, immune-related oxidative stress can initiate further increasing levels of oxidative stress that cause organ damage and dysfunction. Targeting oxidative stress in various diseases therapeutically has proven more problematic than first anticipated given the complexities and perversity of both the underlying disease and the immune response. However, growing evidence suggests that the endocannabinoid system, which includes the CB₁ and CB₂ G-protein-coupled receptors and their endogenous lipid ligands, may be an area that is ripe for therapeutic exploitation. In this context, the related nonpsychotropic cannabinoid cannabidiol, which may interact with the endocannabinoid system but has actions that are distinct, offers promise as a prototype for anti-inflammatory drug development. This review discusses recent studies suggesting that cannabidiol may have utility in treating a number of human diseases and disorders now known to involve activation of the immune system and associated oxidative stress, as a contributor to their etiology and progression. These include rheumatoid arthritis, types 1 and 2 diabetes, atherosclerosis, Alzheimer disease, hypertension, the metabolic syndrome, ischemia-reperfusion injury, depression, and neuropathic pain.

Stereocontrol of arachidonic acid oxygenation by vertebrate lipoxygenases: newly cloned zebrafish lipoxygenase 1 does not follow the Ala-versus-Gly concept

Animal lipoxygenases (LOXs) are classified according to their specificity of arachidonic acid oxygenation, and previous sequence alignments suggested that S-LOXs contain a conserved Ala at a critical position at the active site but R-LOXs carry a Gly instead. Here we cloned, expressed, and characterized a novel LOX isoform from the model vertebrate Danio rerio (zebrafish) that carries a Gly at this critical position, classifying this enzyme as putative arachidonic acid R-LOX. Surprisingly, the almost exclusive arachidonic acid oxygenation product was 12S-H(p)ETE (hydro(pero)xyeicosatetraenoic acid), and extensive mutation around Gly-410 failed to induce R-lipoxygenation. This finding prompted us to explore the importance of the corresponding amino acids in other vertebrate S-LOXs. We found that Ala-to-Gly exchange in human 15-LOX2 and human platelet 12-LOX induced major alterations in the reaction specificity with an increase of specific R-oxygenation products. For mouse 5-LOX and 12/15-LOX from rabbits, men, rhesus monkeys, orangutans, and mice, only minor alterations in the reaction specificity were observed. For these enzymes, S-HETE (hydroxyeicosatetraenoic acid) isomers remained the major oxygenation products, whereas chiral R-HETEs contributed only 10-30% to the total product mixture. Taken together these data indicate that the Ala-versus-Gly concept may not always predict the reaction specificity of vertebrate LOX isoforms.

15-Lipoxygenase 1 interacts with phosphatidylethanolamine-binding protein to regulate MAPK signaling in human airway epithelial cells

Epithelial 15-lipoxygenase 1 (15LO1) and activated ERK are increased in asthma despite modest elevations in IL-13. MAPK kinase (MEK)/ERK activation is regulated by interactions of Raf-1 with phosphatidylethanolamine-binding protein 1 (PEBP1). Epithelial 15LO1 generates intracellular 15-hydroxyeicosatetraenoic acid (15HETE) conjugated to phosphatidylethanolamine (PE) (15HETE-PE). We hypothesized that (i) 15LO1 and its product 15HETE-PE serve as signaling molecules interacting with PEBP1 to activate Raf-1/MEK/ERK and that (ii) this 15LO1-15HETE-PE-regulated ERK activation amplifies IL-4Rα downstream pathways. Our results demonstrate that high epithelial 15LO1 levels correlate with ERK phosphorylation ex vivo. In vitro, IL-13 induces 15LO1, which preferentially binds to PEBP1, causing PEBP1 to dissociate from Raf-1 and activate ERK. Exogenous 15HETE-PE similarly induces dissociation of PEBP1 from Raf-1 independently of IL-13/15LO1. siRNA knockdown of 15LO1 decreases the dissociation of Raf-1 from PEBP1, and the resulting lower ERK activation leads to lower downstream IL-4Rα-related gene expression. Identical protein-protein interactions are observed in endobronchial biopsies and fresh epithelial cells from asthmatics ex vivo. Colocalization of Raf-1 to PEBP1 is low in asthmatic tissue and cells compared with normals, whereas there is striking colocalization of 15LO1 with PEBP1 in asthma. Low 15LO1 levels in normals limit its colocalization with PEBP1. The results confirm a previously unknown signaling role for 15LO1 and its PE-conjugated eicosanoid product in human airway epithelial cells. This pathway enhances critical inflammatory pathways integral to asthma pathogenesis.

Molecular basis for the reduced catalytic activity of the naturally occurring T560M mutant of human 12/15-lipoxygenase that has been implicated in coronary artery disease

Lipoxygenases have been implicated in cardiovascular disease. A rare single-nucleotide polymorphism causing T560M exchange has recently been described, and this mutation leads to a near null variant of the enzyme encoded for by the ALOX15 gene. When we inspected the three-dimensional structure of the rabbit ortholog, we localized Thr-560 outside the active site and identified a hydrogen bridge between its side chain and Gln-294. This interaction is part of a complex hydrogen bond network that appears to be conserved in other mammalian lipoxygenases. Gln-294 and Asn-287 are key amino acids in this network, and we hypothesized that disturbance of this hydrogen bond system causes the low activity of the T560M mutant. To test this hypothesis, we first mutated Thr-560 to amino acids not capable of forming side chain hydrogen bridges (T560M and T560A) and obtained enzyme variants with strongly reduced catalytic activity. In contrast, enzymatic activity was retained after T560S exchange. Enzyme variants with strongly reduced activity were also obtained when we mutated Gln-294 (binding partner of Thr-560) and Asn-287 (binding partner of Gln-294 and Met-418) to Leu. Basic kinetic characterization of the T560M mutant indicated that the enzyme lacks a kinetic lag phase but is rapidly inactivated. These data suggest that the low catalytic efficiency of the naturally occurring T560M mutant is caused by alterations of a hydrogen bond network interconnecting this residue with active site constituents. Disturbance of this bonding network increases the susceptibility of the enzyme for suicidal inactivation.

Association of a functional polymorphism (Gln261Arg) in 12-lipoxygenase with breast cancer

The overexpression of arachidonyl lipoxygenase-12 (ALOX12) in breast cancer has been reported. Hence, we examined whether a non-synonymous polymorphism of ALOX12 (mRNA, A835G; Gln261Arg) is associated with breast cancer in females. The polymorphism was detected in genomic DNA by PCR-RFLP. The association between the A835G polymorphism and breast cancer risk was measured by odds ratio (OR) with 95% confidence intervals (CIs) using Fisher's exact test, and differences were considered significant at p<0.05. The frequencies of AA (wild-type), GG (homozygous variant) and AG (heterozygous variant) were 59.5, 0.9 and 39.6% in the controls, and 39.3, 2.5 and 58.2% in the breast cancer cases, respectively. The frequency of the AG genotype was higher in the patients compared to the controls (p<0.0014). The frequency of the GG variant was 2.5 and 0.9% in the cancer subjects and controls, respectively. The relative risk of breast cancer was 2 times greater (OR=2.227) at 95% CI when compared to the relative risk of the heterozygous variant. For the GG genotype, the risk was 4 times greater (OR=4.125) at 95% CI than that of the controls, suggesting a positive association of the AG genotype with the occurrence of breast cancer. The frequencies of the polymorphism were different in different populations. The Arg/Gln and Arg/Arg variants were associated with an increased risk of breast cancer, and the frequencies of the variants differed considerably among various populations. The identification of a gene with links to breast cancer may impact screening, diagnosis and drug development.

Functional and pathological roles of the 12- and 15-lipoxygenases

The 12/15-lipoxygenase enzymes react with fatty acids producing active lipid metabolites that are involved in a number of significant disease states. The latter include type 1 and type 2 diabetes (and associated complications), cardiovascular disease, hypertension, renal disease, and the neurological conditions Alzheimer's disease and Parkinson's disease. A number of elegant studies over the last thirty years have contributed to unraveling the role that lipoxygenases play in chronic inflammation. The development of animal models with targeted gene deletions has led to a better understanding of the role that lipoxygenases play in various conditions. Selective inhibitors of the different lipoxygenase isoforms are an active area of investigation, and will be both an important research tool and a promising therapeutic target for treating a wide spectrum of human diseases.