Assem El-Shazly

Inhibition of P-glycoprotein activity by limonin and other secondary metabolites from Citrus species in human colon and leukaemia cell lines.

P-glycoprotein (P-gp), a membrane transporter encoded by the MDR1 gene in human cells, mediates drug efflux from cells and plays a major role in causing multidrug resistance; which is one of the most accepted mechanisms for failure of chemotherapy in cancer treatment. In this study, we investigated the effects of nine naturally occurring compounds isolated from Citrus jambhiri Lush and Citrus pyriformis Hassk (Rutaceae) for their potential to modulate the activity of P-gp in the multidrug-resistant human leukaemia cell line CEM/ADR5000. Limonin, deacetylnomilin, hesperidin, neohesperidin, stigmasterol and ss-sitosterol-O-glucoside inhibited the efflux of the P-gp substrate rhodamine 123 in a concentration-dependent manner. Some of these compounds were more active than verapamil, which was used as a positive control. Treatment of drug-resistant Caco-2 cells with the most active C. jambhiri and C. pyriformis compounds increased their sensitivity to doxorubicin and completely reversed doxorubicin resistance, which agrees with a decreased P-gp activity. Limonin was the most potent P-glycoprotein inhibitor - when it was applied at a non-toxic concentration of 20 microM, it significantly enhanced doxorubicin cytotoxicity 2.98-fold (P<0.001) and 2.2-fold (P<0.001) in Caco2 and CEM/ADR5000 cells, respectively. These isolated Citrus compounds could be considered as good candidates for the development of novel P-gp/MDR1 reversal agents which may enhance the accumulation and efficacy of chemotherapy agents.

Allelochemical Activities of Pyrrolizidine Alkaloids: Interactions with Neuroreceptors and Acetylcholine Related Enzymes

Thirteen pyrrolizidine alkaloids (PAs) 3′-acetylheliosupine, echihumiline, echihumiline N-oxide, echimidine, heliosupine, heliosupine N-oxide, heliotrine, monocrotaline, pycnanthine, retronecine, riddeline, senecionine, and seneciphylline) were analyzed for their interactions with acetylcholine-related enzymes, such as acetylcholine esterase (AChE), butyrylcholinesterase (BChE), choline acetyl transferase (ChAT), and neuroreceptors, such as α1- and α2-adrenergic, nicotinergic (nACh), muscarinergic (mACh) and serotonin2 (5-HT2) receptors. Whereas most PAs did not affect the enzymes, they show significant binding activities to mACh and 5-HT2 receptors: Twelve PAs exhibited a 50% inhibition of the specific binding of the radioligand [3H]quinuclidinyl benzilate (QNB) at the mAChR, i.e., IC50 values were between 8.7 μM and 512.5 μM, and 10 PAs exerted a 50% inhibition of the specific binding of the radioligand [3H]ketanserine at the 5-HT2R with IC50 values between 23.2 μM and 608.6 μM. The most active compound was 3′-acetylheliosupine, which was able to bind to all of the studied receptors with IC50 values in the range between 2.9 μM and 159.7 μM. The data imply that free PAs and PA N-oxides can affect several molecular targets: Besides long-term toxicity through DNA alkylation (by PA metabolites generated in the liver), liver and pneumotoxicity, neuroreceptors (among other molecular targets) may be modulated. The interference of PAs with neuronal signal transduction could mediate adverse physiological responses in herbivores and could thus contribute to chemical defense in plants and animals against herbivores and predators.

Pyrrolizidine alkaloids in members of the Boraginaceae from Sinai (Egypt)

Altogether 40 pyrrolizidine alkaloids were detected in the alkaloid extracts of Paracaryum rugulosum, P. intermedium, Anchusa milleri, Gastrocotyle hispida (syn. Anchusa hispida), Anchusa arvensis, Lappula spinocarpos, Trichodesma africanum, Alkanna orientalis, and Alkanna tuberculata (syn. A. tinctoria) which were analyzed by capillary GLC and GLC-MS. 24 alkaloids were unambiguously identified by comparing their specific retention indices and mass fragmentations with those of authentic alkaloids and literature data. The relevance of PAs as chemical defence compounds for desert plants against herbivores is discussed.

Composition and Antimicrobial Activity of Essential Oil and HexaneÐEther Extract of Tanacetum santolinoides (DC.) Feinbr. and Fertig

The essential oil of the aerial parts of Tanacetum santolinoides was analyzed by capillary GLC and GLC-MS. Altogether 30 components were identified. The main constituents were thymol (18%), trans-thujone (17.5%), trans-chrysanthenyl acetate (13.2%), cis-chrysanthenyl acetate (9.2%), umbellulone (9.7%) and 1,8-cineole (4.7%). Similar essential oil pattern in addition to palmitic acid methyl ester, palmitic acid, stigmasterol, sitosterol and two flavonoidal aglycons were found in the n-hexane-ether extract. The oil showed strong in vitro activity against E. coli, Bacillus subtilis and Candida albicans.

Pyrrolizidine alkaloids from Onosma arenaria (Boraginaceae)

Abstract Uplandicine, a 1,2-unsaturated pyrrolizidine alkaloid esterified with acetyl and echimidinyl moieties at C-7 and C-9, respectively, was isolated as a major component from the alkaloid extract of Onosma arenaria . Its structure was confirmed by MS (EI and positive FAB), 1H- and 13C-NMR analysis. Furthermore, nine minor alkaloids were identified on the basis of mass spectral data and/or Kovats retention indices.

Chemical composition and biological activity of the essential oils of Senecio aegyptius var. discoideus Boiss.

The essential oil of Senecio aegyptius var. discoideus flowers, leaves, stems and roots were isolated by hydrodistillation. Analysis of the oils by capillary GLC and GLC-mass spectrometry were performed and 34 out of 37 compounds were identified. The main component was isolated and characterized as 1,10-epoxyfuranoeremophilane using a combination of GLC, GLC-MS, and NMR analyses. The oils of flowers, leaves and stems were rich in monoterpene hydrocarbons while the root oil mainly contains furanoeremophilanes. Flower and leaf volatile oils showed significant level of antifungal activity against C. albicans, moderate effect against Grampositive bacteria, however, it has weak activity against Gram negative bacteria. The isolated sesquiterpene (1,10-epoxyfuranoeremophilane) exhibited substantial inhibitory activity against Gramnegative bacteria.

Pyrrolizidine and tetrahydroisoquinoline alkaloids from Echium humile

Three new pyrrolizidine alkaloids, echihumiline, pycnanthine and echihumiline N-oxide, were isolated from Echium humile and their structures determined by spectroscopic methods. In addition, we record the presence of the known alkaloids, 7-senecioylretronecine, 9-senecioylretronecine, lycopsamine and 7-acetyl-lycopsamine. The tetrahydro-isoquinoline alkaloid, carnegine, was recorded for the first time in the Boraginaceae.

PYRROLIZIDINE ALKALOIDS OF CYNOGLOSSUM OFFICINALE AND CYNOGLOSSUM AMABILE (FAMILY BORAGINACEAE)

Abstract Heliosupine, heliosupine N-oxide, 3′-acetylheliosupine, and viridiflorine were isolated and identified on the base of MS, 1 H and 13 C NMR from Cynoglossum officinale . Altogether 14 pyrrolizidine alkaloids were separated and identified by GLC and GLC-MS in the alkaloid extracts from different parts of Cynoglossum officinale . From Cynoglossum amabile five pyrrolizidine alkaloids were recorded: supinine, amabiline, rinderine, echinatine, and 3′- O -acetylechinatine.

PYRROLIZIDINE ALKALOIDS FROM ECHIUM RAUWOLFII AND ECHIUM HORRIDUM (BORAGINACEAE)

Abstract Echimidine was isolated from Echium rauwolfii and Echium horridum and identified by MS, 1H-and 13C NMR as a major alkaloid. In addition, structures of 12 minor alkaloids were inferred from GLC and GLC-MS analyses: 7-angeloylretronecine, 7-tigloylretronecine, lycopsamine, 7-acetyllycopsamine, uplandicine, 7-angeloyllycopsamine, 7-tigloyllycopsamine, tigloyl isomer of echimidine, 7-angeloyl-9-(2-methylbutyryl)retronecine, 7-tigloyl-9-(2-methylbutyryl)retronecine, 7-angeloyl-9-(2,3-dihydroxybutyryl)retronecine, and 7-tigloyl-9-(2,3-dihydroxybutyryl)retronecine. Both species had similar alkaloid profiles. Alkaloid extracts exhibited antibacterial effects with a MIC of 1.7 mg/ml in E. coli. Microscopic examination of E. coli treated with different subtoxic alkaloid concentrations (13-52 μg/ml) revealed extensive filamentation.

Pyrrolizidine alkaloids from Cynoglossum creticum

Abstract 3′-Acetylrinderine, 3′-acetylechinatine, 3′-acetylheliosupine and heliosupine were isolated from the aerial parts of Cynoglossum creticum and characterized by mass spectrometry and 1H and 13C NMR. A GC-mass spectrometric analysis revealed the presence of 13 alkaloids altogether, among them the previously reported alkaloids, echinatine, rinderine and 7-angeloylheliotridine, and traces of 7-senecioylheliotridine, supinine and trachelanthamine.