Determinants of substrate specificity of a second non-neuronal secreted acetylcholinesterase from the parasitic nematode Nippostrongylus brasiliensis

We recently reported on a non-neuronal secreted acetylcholinesterase (AChE B) from the nematode parasite Nippostrongylus brasiliensis. Here we describe the primary structure and enzymatic properties of a second secreted variant, termed AChE C after the designation of native AChE isoforms from this parasite. As for the former enzyme, AChE C is truncated at the carboxyl terminus in comparison with the Torpedo AChE, and three of the 14 aromatic residues that line the active site gorge are substituted by nonaromatic residues, corresponding to Tyr70 (Ser), Trp279 (Asn) and Phe288 (Met). A recombinant form of AChE C was highly expressed by Pichia pastoris. The enzyme was monomeric and hydrophilic, and displayed a marked preference for acetylthiocholine as substrate. A double mutation (W302F/W345F, corresponding to positions 290 and 331 in Torpedo) rendered the enzyme 10-fold less sensitive to excess substrate inhibition and two times less susceptible to the bis quaternary inhibitor BW284C51, but did not radically affect substrate specificity or sensitivity to the 'peripheral site' inhibitor propidium iodide. In contrast, a triple mutant (M300G/W302F/W345F) efficiently hydrolysed propionylthiocholine and butyrylthiocholine in addition to acetylthiocholine, while remaining insensitive to the butyrylcholinesterase-specific inhibitor iso-OMPA and displaying a similar profile of excess substrate inhibition as the double mutant. These data highlight a conserved pattern of active site architecture for nematode secreted AChEs characterized to date, and provide an explanation for the substrate specificity that might otherwise appear inconsistent with the primary structure in comparison to other invertebrate AChEs.

Enhancement of apoptosis with loss of cellular adherence in the villus epithelium of the small intestine after infection with the nematode Nippostrongylus brasiliensis in rats

It has been reported that infection with Nippostrongylus brasiliensis induces villus atrophy with various histological alterations. In N. brasiliensis-infected rats, villus length in the jejunum was reduced significantly at day 10 p.i., when serum levels of rat mast cell protease (RMCP) II had increased significantly. To determine whether the villus atrophy is associated with enhancement of apoptosis, apoptotic nuclei were labelled using the nick end-labelling method. Numbers of labelled cells were markedly increased in the villus epithelium at 7-10 days p.i., while the numbers returned to normal 14 days p.i. when worms were rejected from the intestine and villus length became normal. Examination of the expression of the adhesion molecule E-cadherin showed granular immunoreactivity in the cytoplasm of atrophic villus epithelium with loss of normal localization to epithelial cell borders. In mast cell-deficient Ws/Ws rats, villus length was reduced as significantly as in +/+ counterparts at day 10 p.i. with marked increases in the numbers of apoptotic cells. These results suggested that villus atrophy was closely associated with enhanced apoptosis and loss of adhesion in epithelial cells. Mast cell activation appears not to be involved in these alterations.

Long-term survival of 'damaged' Nippostrongylus brasiliensis adult worms in the testosterone-treated Indian soft-furred rat, Millardia meltada

When testosterone-treated female Millardia meltada were infected with Nippostrongylus brasiliensis, adult worms persisted for over seven weeks. The kinetics of faecal egg counts showed a biphasic pattern having a transient decline at around two weeks post infection (p.i.). Thus the status of N. brasiliensis adult worms surviving in the small intestines of testosterone-treated M. meltada was examined. The fecundity and maturity of eggs in the uteri of female adult worms were examined at one, two, three and seven weeks p.i. Both the fecundity and maturity of eggs transiently decreased at two and three weeks p.i. and then completely recovered by seven weeks. Adoptive transfer of N. brasiliensis adult worms into naive recipients can discriminate the status of worms. Those obtained from the stable phase of a primary infection ('normal' worm) can establish and survive in the recipients, whereas those obtained at the time of expulsion ('damaged' worm) are rapidly expelled. Therefore, 300 each of N. brasiliensis adult worms collected from the testosterone-treated female M. meltada at one, two and seven weeks p.i. were transferred intraduodenally into normal rats to determine their status. Those collected at one week p.i. persisted for eight days, indicating that they were still 'normal'. In contrast, worms collected at two and seven weeks p.i. were expelled within four days, indicating that they had already been 'damaged'. Moreover, when the 'damaged' worms obtained from rats were intraduodenally transferred into testosterone-treated female M. meltada, they were not expelled, suggesting that testosterone-treatment affected the final expulsive step, but not the damaging process, of the mucosal defence of M. meltada against N. brasiliensis adult worms.

Nematode infection induces Th2 cell-associated immune responses in LEC mutant rats with helper T cell immunodeficiency

Long-Evans Cinnamon (LEC) rats have maturational arrest of CD4+8- T cells from CD4+8+ cells in the thymus. Despite this, CD4+8- T cells are always present in peripheral lymphoid organs of LEC rats, suggesting that these CD4+8- T cells are generated by an uncommon pathway. We investigated the role of LEC rat peripheral CD4+8- T cells in Th2-associated responses to infection with the nematode Nippostrongylus brasiliensis. After infection, the numbers of CD4+8- TCR alpha beta + T cells significantly increased in mesenteric lymph nodes (MLN) and the spleen, while those in the thymus were still negligible. Infection also induced significant up-regulation of IL-4 gene expression in LEC rat MLN cells. Total serum IgE levels in LEC rats were markedly increased two weeks after infection. Mucosal mast cell responses in the gut and lungs of LEC rats were induced as prominently as in control Long-Evans Agouti (LEA) rats. Faecal egg count data indicated that LEC rats rejected nematodes faster than LEA rats. These results suggested that Th2-associated responses can be induced by nematode infection in LEC rats probably through the extrathymic recruitment and proliferation of CD4+8- TCR alpha beta + T cells.

Anorexia induced by the parasitic nematode, Nippostrongylus brasiliensis: effects on NPY and CRF gene expression in the rat hypothalamus

Infections of the gastrointestinal nematode, Nippostrongylus brasiliensis, in the laboratory rat result in a characteristic biphasic anorexia which is followed by hyperphagia once the worm burden has been cleared. Despite the importance of parasite-induced anorexia, relatively little is known of the underlying mechanisms. We have investigated the involvement of the central appetite drive in this anorexia by studying the gene expression of two neuropeptides with opposing actions on energy balance, NPY and CRF. Gene expression was assessed by in situ hybridization at 2, 8 and 16 days post-infection (p.i.) in infected rats, in uninfected controls, and in a group with food intake restricted to match that taken voluntarily by the parasitize animals. The sampling intervals corresponded to each of the two phases of maximum anorexia and the period of compensatory hyperphagia. Surprisingly, we found that increases in NPY gene expression in the hypothalamic arcuate nucleus (ARC) accompany anorexia in rats infected with N. brasiliensis; there was a significant relationship between degree of anorexia and induction of NPY mRNA after 8 days of infection. Furthermore, ARC NPY mRNA levels in parasitized animals were similar to those in pair-fed individuals with food intake restricted to match the infected rats. The number of larvae used to establish the infection affected both the degree of anorexia and the level of NPY mRNA at 8 days p.i. in a dose-dependent manner. NPY gene expression remained elevated in infected rats during at least the initial stages of compensatory hyperphagia. This suggests that animals detect a state of energy deficit during the early stages of the infection, yet do not feed, but become hyperphagic coincident with worm loss. The failure of anorectic parasitized animals to feed in response to activation of the NPYergic system makes this a novel system in which to study the regulation of hypothalamic NPY by physiological challenge. There were no significant differences in CRF gene expression between the groups at any of the sampling intervals.

3, 5-Dibromo-2'-chloro-4'-isothiocyanatosalicylanilide, a potent anthelmintic

The compound, 3, 5-dibromo-2'-chloro-4'-isothiocyanatosalicylanilide, has been tested against various nematode and cestode parasites in experimental and domestic animals. It shoved 100% activity against Ancylostoma ceylanicum, A tubaeformis, Syphacia obvelata, ascaridia galli, Toxocara spp., Toxascaris sp., Gnathostoma spinigerum, Hymenolepis nana, Raillietina spp. and Taenia spp. in doses 25-70 mg/kg given in single or multiple administrations.