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BioMed Season Finale Part 1 > Anthelmentics > Flashcards

Anthelmentics Flashcards

1
Q

how can nematodes be transmitted

A

ingestion from contaminated material
contaminated water
intermediate host
direct invasion through skin

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2
Q

what is a broad spectrum antihelmentic

A

benzimidazoles

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3
Q

what are the narrow spectrum antihelmentics

A

avermectins
milbemycins
ivermectin

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4
Q

how do most antihelmentics act on parasites

A

by acting on their CNS/neuromuscular systems

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5
Q

what is not an ionotropic receptor

A

GABA-B receptors
they are G-protein coupled receptors

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6
Q

what have been the main approaches used to study the pharmacology of anthelmentics

A

pharmacological studies in model nematodes
genetic studies in C. elegans

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7
Q

how does lemavisole affect nematodes

A

causes spastic paralysis

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8
Q

what is the mechanism of action of lemavisole in C. elegans

A

acts on nicotinic acetylcholine receptors

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9
Q

what is an advantage of using C. elegans

A

it is a self-fertilising hermaphrodite

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10
Q

how was the physiochemical effect of lemavisole and what does it show

A

a patch clamp was used
typical ACh currents were observed under lemavisole
shows its a ACh agonist

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11
Q

how is lemavisole absorbed in the host

A

absorbed across the gastro-intestinal tract

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12
Q

what are the side-effects of lemavisole and why they might be

A

usually well tolerated by the host
nausea/dizziness
probably due to activation of nicotinic receptors at the autonomic ganglia

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13
Q

what is the selective toxicity of lemavisole

A

relies on difference between host and parasitic nicotinic acetylcholine receptors
weak agonist of neuromuscular junction receptors

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14
Q

how was the selective toxicity of lemavisole tested

A

the cDNA of mass nicotinic acetylcholine receptor subunits was injected in xenopus oocytes
they then express the receptors on their surface
can then be used for electrophysiological experiments - measure the sensitivity of lemavisole to those reseptors

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15
Q

what is the effect of piperazine on nematodes and its proposed mechanism of action

A

causes flaccid paralysis
probably due to its similar structure to GABA - GABA agonist

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16
Q

why can use of GABA cause piperazine to not work

A

cross-sensitivity of GABA and piperazine can cause the tissue to become desensitised

17
Q

how is piperazine absorbed in the host

A

well absorbed through the gastro-intestinal system

18
Q

what are the side effects of piperazine

A

usually well tolerated by the host
nausea/vomiting
contraindicated for epilepsy

19
Q

why is a contraindication of piperazine epilepsy even though it is a GABA (inhibitory) mimetic

A

piperazine is a partial agonist of GABA-A
partial agonists can act antagonists
further compromises an epileptic brain’s inhibitory mechanisms

20
Q

what is ivermectin

A

macrocylic lactone
semi-synthetic derivative of a natural compound

21
Q

what is ivermectin in/effective at targeting

A

effective only at targeting filarial nematodes and microfilariae
ineffective at targeting cestodes/trematodes

22
Q

what effects does ivermectin have on nematodes

A

paralysis
inhibits feeding
inhibits egg-laying

23
Q

what made ivermectin a breakthrough

A

it was resistance breaking
treated resistant nematodes

24
Q

what is the mechanism of action of ivermectin

A

very potent action
little effects on mammalian system
inhibits insect muscle by opening chloride channels

25
Q

how was the mechanism of action of ivermectin studied and measured

A

dissected locust muscle tissue
placed in physiological saline solution
impaled the tissue with 2 glass microelectrodes connected to amplifiers
one was used to record membrane potential and the other to inject currents

26
Q

what cDNA produced a response to glutamate

A

GluCl-beta

27
Q

what cDNA responded to ivermectin

A

GluCl-alpha

28
Q

what insight on what receptor ivermectin acts on did iterative screening give us

A

that the receptor is most likely composed of an GluCl-alpha subunit which binds to ivermectin and a GluCl-beta subunit that binds glutamate
leads to chloride mediated hyperpolarisation

29
Q

what type of receptor is the ivermectin receptor

A

it is a glutamate-gated chloride channel consisting of 5 subunits of the GluCl-alpha/beta

30
Q

why is ivermectin very effective against nematodes but not mammals/vertebrates

A

glutamate-gated ion channels exist in the invertebrate phyla but not in mammals/vertebrates

31
Q

what is emodepside

A

a new generation anthelmentics
resistance breaking - able to treat ivermectin resistant nematodes

32
Q

what are the effects of emodepside on C. elegans

A

inhibits locomotion
inhibits feeding
inhibits egg-laying
slows development

33
Q

what mutation is resistant to emodepside

A

ion channel mutation on chromosome V
several candidate genes including slo-1
slo-1 -/- are highly resistant to emodepside

34
Q

what is slo-1

A

a calcium-activated K+ channel

35
Q

name a new generation anthelmentic

A

amino-aceto-nitrile derivatives (AAD’s)
they have drug-breaking resistance properties

36
Q

how do AAD’s affect C. elegans

A

inhibit motility

37
Q

what do AAD’s target

A

nicotinic acetylcholine receptors
only found in invertebrates

BioMed Season Finale Part 1 (13 decks)

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