Vet Parasitol. 2016 Sep 15;228:23-29. doi: 10.1016/j.vetpar.2016.07.036. Epub 2016 Aug 1.
1The Institute of Infection and Global Health, The University of Liverpool, UK. Electronic address: peachey14@hotmail.com.
2The Institute of Infection and Global Health, The University of Liverpool, UK.
3Moredun Research Institute, Pentlands Science Park, Edinburgh, Scotland, UK.
4The Donkey Sanctuary, Sidmouth, UK.
5School of Life Sciences, University of Nottingham, UK
Abstract
The
control of equid gastrointestinal nematodes in developed countries, in
particular the cyathostomins, is threatened by high levels of
anthelmintic resistance. In recent years, there has been increasing
interest in the evaluation of traditional 'ethnoveterinary'
medicines as alternatives to chemical anthelmintics. The cysteine
proteinases (CPs), a group of enzymes derived from fruits such as papaya
(Carica papaya), pineapple (Ananas comosus) and figs (Ficus spp.), have
shown good efficacy against adult stages of a range of parasitic
nematodes, in vitro and in vivo. The efficacy of CPs against
cyathostomins remains to be explored. In this study, the efficacy of a
crude preparation of CPs, papaya latex supernatant (PLS), against the
free-living stages of cyathostomins was evaluated using two in vitro
tests, the egg hatch test (EHT) and the larval migration inhibition test
(LMIT). It was demonstrated that PLS had a potent effect in the EHT,
with EC-50 values in the range of 0.12-0.22μM. At concentrations above
6.25μM the eggs did not develop, below this concentration the L1
developed but they lost integrity of the cuticle upon hatching. These
effects were inhibited by pre-incubation of PLS with the CP inhibitor
L-trans-epoxysuccinyl-l-leucylamido-(4-guanidino butane) (E64),
indicating that CPs were responsible for the anti-parasitic activity. A
dose-dependent inhibition of migration of third stage larvae (L3) in the
LMIT was demonstrated at higher concentrations of PLS, with EC-50
values in the range of 67.35-106.31μM. Incubation of PLS with E64 prior
to use in the LMIT did not reverse the anti-migratory effect, suggesting
that CPs were not responsible for the reduced migration of cyathostomin
L3 and that PLS also contains an additional active compound. This is
the first report of PLS and/or CPs showing activity against the
free-living stages of a parasitic helminth. In addition, it suggests
that cyathostomins are highly sensitive to the effects of CPs and
further evaluation of their efficacy against parasitic stages and in
vivo are strongly indicated.
Copyright © 2016 Elsevier B.V. All rights reserved.
KEYWORDS:
Anthelmintic; Carica papaya; Cyathostomin; Cysteine proteinase; In vitro; Papaya latex supernatant
