Phenoxybenzamine and Benextramine, but Not 4-Diphenylacetoxy-<i>N</i>-[2-chloroethyl]piperidine Hydrochloride, Display Irreversible Noncompetitive Antagonism at G Protein-Coupled Receptors

Bodenstein, Johannes; Venter, Daniel P.; Brink, C.

doi:10.1124/jpet.105.083568

Cited by 7 publications

(5 citation statements)

References 56 publications

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“…However, 100 nM 13desmethyl C spirolide inhibited approximately the same percentage of [ 3 H]QNB, which is cell permeable, and [ 3 H]NMS, which is not cell permeable, indicating that the spirolide also binds intracellular receptors. Incomplete inhibition of radioactive antagonist binding even by the same cold (nonradioactive) molecule has been described before for mAChRs (28). In addition to this apparently spirolide-insensitive pool of receptors, the [ 3 H]QNB competition curve also suggests the presence of two populations of mAChRs with very different affinities for the 13-desmethyl C spirolide.…”

Section: Discussionsupporting

confidence: 63%

“…Receptor internalization might be responsible for the spirolide-induced reduction of the ACh-triggered calcium response; however, the probability of this mechanism of action being the only explanation for the reduction of the calcium response seems very low given the small number of reports on nonagonist-induced internalization and the data supporting toxin binding to the orthosteric binding site of the mAChR. The inhibition of the 13-desmethyl C spirolide effect on [ 3 H]QNB binding by protection of the primary binding site of mAChRs with the reversible competitive antagonist atropine (28) demonstrates that the spirolide binds to the orthosteric binding site of the mAChR. The presence of a high concentration of atropine during the incubation with the 13-desmethyl C spirolide also reduced the inhibitory effect of the toxin on the ACh-triggered calcium signal.…”

Section: Discussionmentioning

confidence: 99%

“…However, the toxin-dependent inhibition of the calcium signal was not completely blocked by atropine, suggesting that the toxin may act additionally as an allosteric antagonist of mAChRs. Some GPCR antagonists have been shown to display irreversible noncompetitive antagonism in addition to their well-known irreversible competitive antagonism . Although it had been suggested that the spirolides might target mAChRs based on the symptoms displayed by animals injected intraperitoneally with these toxins and the increase of mAChR mRNA levels in brain tissue in some species , , direct evidence of mAChR targeting has not been described before.…”

Section: Discussionmentioning

confidence: 99%

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Human Muscarinic Acetylcholine Receptors Are a Target of the Marine Toxin 13-Desmethyl C Spirolide

Wandscheer

Vilariño

Espiña

et al. 2010

Chem. Res. Toxicol.

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Spirolides are a group of cyclic imine marine toxins recently described. Although no human intoxication has been related to their presence in shellfish yet, the possible toxicological consequences to human health are actually unknown. The elucidation of the spirolide mechanism/s of action would help to estimate the threat to human consumers. Previous toxicological studies in mice suggested the involvement of acetylcholine receptors. In this work, the effects of the 13-desmethyl C spirolide on the activity and the expression of muscarinic acetylcholine receptors (mAChR) were analyzed using a human neuroblastoma cell model. The 13-desmethyl C spirolide inhibited the acetylcholine-induced calcium signal with a reduction of the maximum response to acetylcholine in the presence of the toxin. The 13-desmethyl C spirolide also reduced binding of the mAChR specific antagonist [(3)H]QNB to neuroblastoma cells. The effect of the 13-desmethyl C spirolide persisted after toxin removal and was inhibited by protection of the primary binding site with high concentrations of atropine suggesting an interaction of the spirolide with the orthologous binding site of mAChR. Moreover, the toxin induced a change in the characteristics of the membrane-associated M3 mAChRs, although it did not alter the total levels of M3 mAChR protein. The 13-desmethyl C spirolide targets mAChRs causing a reduction of function, a decrease of specific antagonist binding to mAChRs, and alteration of membrane-bound receptors that might have important toxicological implications.

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Section: Discussionsupporting

confidence: 63%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Human Muscarinic Acetylcholine Receptors Are a Target of the Marine Toxin 13-Desmethyl C Spirolide

Wandscheer

Vilariño

Espiña

et al. 2010

Chem. Res. Toxicol.

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“…Phenoxybenzamine is a known nonselective, irreversible, noncompetitive antagonist of alpha-adrenergic receptors ( Bodenstein et al, 2005 ). In the present study, POB attenuated the vascular contractile response in already contracted arteries exposed to ergocristine and ergocristinine.…”

Section: Discussionmentioning

confidence: 99%

Sustained vascular contractile response induced by an R- and S-epimer of the ergot alkaloid ergocristine and attenuation by a noncompetitive antagonist

Cherewyk

Parker

Blakley

et al. 2022

Journal of Animal Science

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Vasoconstriction is a known effect associated with ergot alkaloid consumption. The vascular contractile responses are often sustained for an extended period after exposure. Ergot alkaloids exist in two molecular configurations, the C-8-(R)-isomer (R-epimer) and the C-8-(S)-isomer (S-epimer). The sustained vascular contractile response to the R-epimers have been studied previously, unlike the S-epimers which are thought to be biologically inactive. Additionally, antagonists have been utilized to attenuate the vascular contraction associated with the R-epimers of ergot alkaloids utilizing ex vivo techniques. This study utilized an arterial tissue bath to examine and compare the sustained vascular contractile response attributed to ergocristine (R) and ergocristinine (S) using dissected bovine metatarsal arteries. The contractile blocking effect of a non-competitive alpha-adrenergic antagonist, phenoxybenzamine (POB), was also investigated in precontracted arteries. Arteries (n=6/epimer) were exposed to a single dose of ergocristine or ergocristinine (1 × 10 -6 M in buffer). Each of the epimer doses were followed by a POB (1 × 10 -3 M) or methanol (control) treatment at 90 minutes and the response was observed for another 90 min. Both epimers produced a sustained contractile response over the 180 min incubation period in the control groups. The R-epimer caused a greater sustained contractile response from 60-180 min post epimer exposure, compared to the S-epimer (P < 0.05, Generalized Estimating Equations, Independent t-test). Phenoxybenzamine caused a decrease in the contractile response induced by ergocristine and ergocristinine from 105 – 180 min, compared to the control (P < 0.05, Generalized estimating equations, Paired t-test). Overall, these results demonstrate the presence of a sustained vascular contractile response attributed to the R and S-epimer of an ergot alkaloid with differences in contractile response between the epimers, suggesting differences in receptor binding mechanisms. Furthermore, this study demonstrated that a non-competitive antagonist could attenuate the sustained arterial contractile effects of both ergot configurations ex vivo. Additional investigation into S-epimers of ergot alkaloids is needed. This research contributes to the understanding of the ergot epimer-vascular receptor binding mechanisms, which may support the investigation of different approaches of minimizing ergot toxicity in livestock.

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“…From the remaining hits with no structural similarity to bile acids, two compounds were capable of protecting cells from TcdB. The first, phenoxybenzamine, a nonselective irreversible alpha-adrenoreceptor antagonist (32), was excluded from further follow-up owing to its potentially highly reactive carbonium ion that results from cleavage of its tertiary amine ring (33). The second compound, a substituted benzylisoquinoline known as ethaverine hydrochloride-the ethyl analog of papaverine, both of which are potent peripheral coronary vasodilator drugs (34)was characterized.…”

Section: Identification Of Small Molecules With a Bile Acid-like Mechmentioning

confidence: 99%

Intestinal bile acids directly modulate the structure and function of C. difficile TcdB toxin

Tam

Icho

Utama

et al. 2020

Proc. Natl. Acad. Sci. U.S.A.

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Intestinal bile acids are known to modulate the germination and growth ofClostridioides difficile. Here we describe a role for intestinal bile acids in directly binding and neutralizing TcdB toxin, the primary determinant ofC. difficiledisease. We show that individual primary and secondary bile acids reversibly bind and inhibit TcdB to varying degrees through a mechanism that requires the combined oligopeptide repeats region to which no function has previously been ascribed. We find that bile acids induce TcdB into a compact “balled up” conformation that is no longer able to bind cell surface receptors. Lastly, through a high-throughput screen designed to identify bile acid mimetics we uncovered nonsteroidal small molecule scaffolds that bind and inhibit TcdB through a bile acid-like mechanism. In addition to suggesting a role for bile acids inC. difficilepathogenesis, these findings provide a framework for development of a mechanistic class ofC. difficileantitoxins.

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Phenoxybenzamine and Benextramine, but Not 4-Diphenylacetoxy-N-[2-chloroethyl]piperidine Hydrochloride, Display Irreversible Noncompetitive Antagonism at G Protein-Coupled Receptors

Cited by 7 publications

References 56 publications

Human Muscarinic Acetylcholine Receptors Are a Target of the Marine Toxin 13-Desmethyl C Spirolide

Human Muscarinic Acetylcholine Receptors Are a Target of the Marine Toxin 13-Desmethyl C Spirolide

Sustained vascular contractile response induced by an R- and S-epimer of the ergot alkaloid ergocristine and attenuation by a noncompetitive antagonist

Intestinal bile acids directly modulate the structure and function of C. difficile TcdB toxin

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