The effect of homogenates and excretory/secretory products of Nippostrongylus brasiliensis and of acetylcholinesterase on the amplitude and frequency of contraction of uninfected rat intestine in vitro

The effect of vaccination with a recombinant Nippostrongylus brasiliensis acetylcholinesterase on infection outcome in the rat

Nippostrongylus brasiliensis, the rodent hookworm, is a commonly used model of gastrointestinal nematode infection. This parasite, hookworms and several livestock nematode parasites of importance secrete distinct forms of acetylcholinesterases (AChE) that have been ascribed a putative parasite protective function. We tested the hypothesis that vaccination with the secreted enzyme would be deleterious to the parasite. Rats were immunised with a recombinant AChE isoform B via the subcutaneous, intra-peritoneal and intra-nasal routes using different adjuvants dependent on the mode of delivery and subsequently challenged with N. brasiliensis. Rats immunised via the subcutaneous and intra-nasal routes showed a modest but significant decrease in egg output of between 23 and 48%. This was mirrored by differences in the titre of specific antibody isotypes in the serum and mucosa following infection and serum from vaccinated animals was demonstrated to inhibit the activity of recombinant and native AChE. The utility of this model for future development of hookworm and veterinary nematode vaccines is discussed.

Altered autonomic control in rat intestine due to both infection with Anisakis simplex and incubation with the parasite's crude extract

Anisakis simplex IgE may bring on allergic responses such as angioedema, vomiting, and urticaria from eating seafood, but it is not the only etiology. Induced cholinergic hyperreactivity or adrenergic blockade in the target tissue can cause these diseases nonimmunologically also. Here we studied the effects on normal intestinal motility of brief A. simplex infections and in vitro exposures to the parasite's extract (CE). Each approach was evaluated according to its ability to induce cholinergic hyperreactivity or adrenergic blockade in rat duodenum (RD), jejunum (RJ), and ileum (RI) in vitro. Additionally, bolus propulsion in RD, RJ, and RI was evaluated with time in vivo utilizing animals infected 4 h previously with A. simplex larvae (L3) vs sham animals. Tissues, after inoculation of 1, 5, 10, and 20 L3, exhibited time- and dose-dependent motility changes after carbachol (Ch) and noradrenaline (NA), justifying our using herein rats from the fourth hour of infection with 20 L3. We observed a persistent, yet differential effect of the infection on RD, RJ, and RI responses to Ch or NA. It caused cholinergic (muscarinic) hyperreactivity in RD only, and adrenergic blockade in all other parts, and consequently increased the transit index in RD, not in RJ or RI. In contrast, exposing RD, RJ, and RI to CE persistently increased both parameters, amplitude of twitches and muscular tone, in all, albeit that, here also, responses to Ch and NA were CE dose dependent. Interestingly, sensitivity to CE was in the order RI > RJ > RD, the reverse situation of that observed during active infection. Thus, previously viable A. simplex L3, after digestion, can exert bystander disturbance in autonomic control in the whole intestine. Our findings demonstrate that A. simplex L3, alive or dead, can induce cholinergic hyperactivity and adrenergic blockade in the whole small intestine and, as a consequence, gastrointestinal symptoms. Significantly, they may do so long before parasite-specific IgE is detectably induced or despite the occurrence of such IgE.

Integrative neuroimmunomodulation of gastrointestinal function during enteric parasitism

Enteric helminths have a significant impact on the structure, function, and neural control of the gastrointestinal (GI) tract of the host. Interactions between the host's nervous and immune systems redirect activity in neuronal circuits intrinsic to the gut into an alternative repertoire of defensive and adaptive motor programs. Gut inflammation and activation of the enteric neuroimmune axis play integral roles in the dynamic interaction between host and parasite that occurs at the mucosal surface. Three inter-related themes are stressed in this review to underscore the pivotal role that neural control mechanisms play in the host's GI tract functional responses to enteric parasitism. First, we address the discovery that signaling molecules of both parasite and host origin can reorient the dynamic ecology of enteric host-parasite interactions. Second, we explore what has been learned from investigations of altered gut propulsive and secretomotor reflex activities that occur during enteric parasitic infections and the emerging picture derived from these studies that elucidates how nerves help facilitate and orchestrate functional reorganization of the parasitized gut. Third, we provide an overview of the direct impact that enteric parasitism has on nerve cell function and neurotransmission pathways in both the enteric and central nervous systems of the host. In summary, this review highlights and clarifies the complex mechanisms underlying integrative neuroimmunophysiological responses to the presence of both invasive and noninvasive enteric helminths and identifies directions for future research investigations in this highly important but understudied area.

Nippostrongylus brasiliensis: characterisation of a somatic amphiphilic acetylcholinesterase with properties distinct from the secreted enzymes

We have previously determined that Nippostrongylus brasiliensis secretes three monomeric nonamphiphilic (G1na) variants of acetylcholinesterase (AChE) with broadly similar properties. In this study we have examined AChE expression in somatic extracts of N. brasiliensis and report the identification of an additional enzyme which is not secreted. The enzyme was resolved by sucrose density gradient centrifugation with a sedimentation coefficient of 10.2 S which was shifted to 9.4 S in the presence of Triton X-100, identifying the enzyme as a tetrameric amphiphilic (G4a) form. The amphiphilic properties of this enzyme were confirmed by charge-shift electrophoresis, in which migration was accelerated by interaction with sodium deoxycholate. The enzyme showed low activity with butyrylthiocholine, and a Michaelis constant of 91 +/- 13 microM for acetylthiocholine was determined. It was highly sensitive to the AChE-specific inhibitor bis (4-allyldimethylammoniumphenyl)pentan-3-one dibromide, with an IC50 of 6.5 +/- 0.4 microM, but was also inhibited by the butyrylcholinesterase-specific inhibitor tetramonoisopropylpyrophosphortetramide, albeit with a higher IC50 of 46.5 +/- 6.1 microM. This enzyme can therefore be distinguished from the secreted AChEs by its amphiphilic properties, sedimentation in sucrose gradients, and sensitivity to cholinesterase inhibitors.

Immunocytochemical detection of vasoactive intestinal peptide-like and peptide histidine isoleucine-like peptides in the nervous system and the excretory system of adult Nippostrongylus brasiliensis

Vasoactive intestinal peptide-like and peptide histidine isoleucine-like immunoreactivities were detected in the excretory duct of adult male and female Nippostrongylus brasiliensis, thus indicating the source of these two physiologically active peptides previously isolated from the excretory/secretory products of adult N. brasiliensis. In the nervous system immunoreactivity to both these peptides was confined to females and was found in the neurons of the ovijector associated ganglion. This is consistent with co-synthesis of vasoactive intestinal peptide-like and peptide histidine isoleucine-like peptides which has also been shown to occur in all mammalian vasoactive intestinal peptid-ergic neurons studied to date. However, in addition to this, and in common to some previous studies on helminth vasoactive intestinal peptide and peptide histidine isoleucine immunoreactivities, co-synthesis of the peptides was not indicated in a pair of branched neurons which projected posteriorly and peripherally from the ganglion associated with the ovijector of females and which terminated in two pairs of ganglia also exhibiting vasoactive intestinal peptide-like immunoreactivity only. The position of these ganglia indicated that they innervate muscles close to the body wall and may be responsible for the muscular contractions required for expulsion of eggs from female Nippostrongylus brasiliensis. This is also the first study to successfully detect these peptides in the excretory system of gastrointestinal nematodes.

Vasoactive intestinal polypeptide-like and peptide histidine isoleucine-like proteins excreted/secreted by Nippostrongylus brasiliensis, Nematodirus battus and Ascaridia galli

Vasoactive intestinal polypeptide (VIP)-like protein was detected by dot blot analysis in the excretions/secretions (E/S) of Nematodirus battus and Ascaridia galli and was confirmed in the E/S of Nippostrongylus brasiliensis. ELISA analysis showed that N. brasiliensis E/S contained the highest proportion of VIP-like protein (28.04 pmoles/mg of total E/S protein) and A. galli E/S contained the lowest (10.89 pmoles/mg of total E/S protein). Peptide histidine isoleucine (PHI)-like protein was detected by dot blot analysis in the E/S products of N. brasiliensis, N. battus and A. galli. ELISA analysis suggested that A. galli E/S contained the highest proportion of PHI (20.77 nmoles/mg of total E/S protein) and N. battus E/S contained the lowest (0.67 nmoles/mg of total E/S protein). The possible significance of VIP-like and PHI-like substances in the E/S of gastrointestinal nematodes is discussed.

Why do some nematode parasites of the alimentary tract secrete acetylcholinesterase?

Many gastrointestinal nematodes secrete large amounts of acetylcholinesterases. Antibodies are produced against these secreted acetylcholinesterases and appear to give some protection against infection with some nematodes. The theory that acetylcholinesterase secreted by gastrointestinal nematodes may act as a biochemical holdfast by reducing contractions of the alimentary system has not been substantiated; a vasoactive intestinal polypeptide-like protein is secreted by some species and may be the biochemical holdfast. Secreted acetylcholinesterases may alter host cell permeability, have an anti-coagulant role, affect glycogenesis, and/or be important in certain aspects of acetate and choline metabolism. Probably the most important role for acetylcholinesterase secreted by nematodes is immune modulation and/or reduction of inflammation in the vicinity of the nematode. The reason why some species of gastrointestinal nematodes resistant to benzimidazoles contain elevated amounts of acetylcholinesterase is unclear.

A vasoactive intestinal polypeptide-like protein excreted/secreted by Nippostrongylus brasiliensis and its effect on contraction of uninfected rat intestine

The 50-30 kDa fraction isolated from the excretory/secretory products (E/S) of the nematode Nippostrongylus brasiliensis significantly decreased the amplitude of contraction of segments of uninfected rat intestine when injected into the lumen of the segments maintained in an organ bath. Dot blot analysis of the fraction suggested that it was similar in immunoreactivity to porcine vasoactive intestinal polypeptide (VIP). When antiserum to porcine VIP was mixed with N. brasiliensis E/S and the mixtures were injected into the lumen of segments of rat intestine, the inhibitory effect of the E/S on amplitude of contraction decreased. When physiological concentrations of porcine VIP (12.9 pmol/ml) were injected into the lumen of segments of uninfected rat intestine the amplitude of contraction decreased significantly. Western blot analysis of the E/S, using antiserum to porcine VIP, recognized a 30 kDa protein in the E/S and also in whole worm homogenate suggesting that synthesis of the peptide occurs inside the nematode. Peptide histidine isoleucine (PHI)-like immunoreactivity was detected in a 68 kDa fraction of the E/S and the homogenate but this fraction did not affect the amplitude of contractions of the intestine.