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Allelochemical Activities of Pyrrolizidine Alkaloids: Interactions with Neuroreceptors and Acetylcholine Related Enzymes (1997)

Schmeller, T. ; El-Shazly, A. ; Wink, M.

Springer

Journal of chemical ecology 23 (1997), S. 399-416

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ISSN: 1573-1561

Keywords: Pyrrolizidine alkaloids ; pyrrolizidine N-oxides ; cholinergic ; adrenergic ; serotonin receptors ; BChE ; AChE ; ChAT ; toxicity ; pharmacology ; chemical defense ; radioreceptor assay ; neuroreceptors

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Chemistry and Pharmacology

Notes: Abstract 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.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/B:JOEC.0000006367.51215.88

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Modes of Action of Allelochemical Alkaloids: Interaction with Neuroreceptors, DNA, and Other Molecular Targets (1998)

Wink, M. ; Schmeller, T. ; Latz-Brüning, B.

Springer

Journal of chemical ecology 24 (1998), S. 1881-1937

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ISSN: 1573-1561

Keywords: Alkaloids ; molecular targets ; neuroreceptors ; DNA intercalation ; DNA polymerase ; reverse transcriptase ; protein biosynthesis ; membrane stability ; nicotine receptor ; muscarinic receptor ; serotonin receptor ; adrenergic receptors

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Chemistry and Pharmacology

Notes: Abstract Several alkaloids are toxic to insects and vertebrates and, in addition, can inhibit the growth of bacteria and plant seedlings. In vitro assays were established to elucidate their modes of action and to understand their allelochemical properties. Basic molecular targets studied, present in all cells, included DNA intercalation, protein biosynthesis, and membrane stability. The degree of DNA intercalation was positively correlated with inhibition of DNA polymerase I, reverse transcriptase, and translation at the molecular level and with toxicity against insects and vertebrates at an organismic level. Inhibition of protein biosynthesis was positively correlated with animal toxicity. Molecular targets studied, present only in animals, included neuroreceptors (alpha1, alpha2, serotonin, muscarinic, and nicotinic acetylcholine receptors) and enzymes related to acetylcholine (acetylcholine esterase and choline acetyltransferase). The degree of binding of alkaloids to adrenergic, serotonin, and muscarinic acetylcholine receptors was positively correlated in G-protein-coupled receptors. Receptor binding and toxicity was correlated in insects. The biochemical properties of alkaloids are discussed. It is postulated that their structures were shaped in a process termed “evolutionary molecular modeling” to interact with a single and, more often, with several molecular targets at the same time. Many alkaloids are compounds with a broad activity spectrum that apparently have evolved as “multipurpose” defense compounds. The evolution of allelochemicals affecting more than one target could be a strategy to counteract adaptations by specialists and to help fight off different groups of enemies.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1022315802264

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