Binding of FITC-labelled lectins to the gastrointestinal epithelium of the rat

Gastrointestinal dysmotility in rodent models of Parkinson's disease

Multiple studies describe prodromal, nonmotor dysfunctions that affect the quality of life of patients who subsequently develop Parkinson's disease (PD). These prodromal dysfunctions comprise a wide array of autonomic issues, including severe gastrointestinal (GI) motility disorders such as dysphagia, delayed gastric emptying, and chronic constipation. Indeed, strong evidence from studies in humans and animal models suggests that the GI tract and its neural, mainly vagal, connection to the central nervous system (CNS) could have a major role in the etiology of PD. In fact, misfolded α-synuclein aggregates that form Lewy bodies and neurites, i.e., the histological hallmarks of PD, are detected in the enteric nervous system (ENS) before clinical diagnosis of PD. The aim of the present review is to provide novel insights into the pathogenesis of GI dysmotility in PD, focusing our attention on functional, neurochemical, and molecular alterations in animal models.

Gut-brain axis: Review on the association between Parkinson's disease and plant lectins

Gastrointestinal (GI) involvement in the pathogenesis of Parkinson's Disease (PD) has been widely recognized and supported in recent literature. Prospective and retrospective studies found non-motor symptoms within the GI, specifically constipation, precede cardinal signs and cognitive decline by almost 20 years. In 2002, Braak et al. were the first to propose that PD is a six-stage propagating neuropathological process originating from the GI tract (GIT). Aggregated α-synuclein (α-syn) protein from the GIT is pathognomonic for the development of PD. This article reviews the current literature from the past 10 years as well as original research found in PubMed on the combined effects of enteric glial cells and lectins on the development of Parkinson's Disease. Studies have found that these aggregated and phosphorylated proteins gain access to the brain via retrograde transport through fast and slow fibers of intestinal neurons. Plant lectins, commonly found within plant-based diets, have been found to induce Leaky Gut Syndrome and can activate enteric glial cells, causing the release of pro-inflammatory cytokines. Oxidative stress on the enteric neurons, caused by a chronic neuro-inflammatory state, can cause a-syn aggregation and lead to Lewy Body formation, a hallmark finding in PD. Although the current literature provides a connection between the consumption of plant lectins and the pathophysiology of PD, further research is required to evaluate confounding variables such as food antigen mimicry and other harmful substances found in our diets.

Parkinson disease and the gut: new insights into pathogenesis and clinical relevance

The classic view portrays Parkinson disease (PD) as a motor disorder resulting from loss of substantia nigra pars compacta dopaminergic neurons. Multiple studies, however, describe prodromal, non-motor dysfunctions that affect the quality of life of patients who subsequently develop PD. These prodromal dysfunctions comprise a wide array of gastrointestinal motility disorders including dysphagia, delayed gastric emptying and chronic constipation. The histological hallmark of PD - misfolded α-synuclein aggregates that form Lewy bodies and neurites - is detected in the enteric nervous system prior to clinical diagnosis, suggesting that the gastrointestinal tract and its neural (vagal) connection to the central nervous system could have a major role in disease aetiology. This Review provides novel insights on the pathogenesis of PD, including gut-to-brain trafficking of α-synuclein as well as the newly discovered nigro-vagal pathway, and highlights how vagal connections from the gut could be the conduit by which ingested environmental pathogens enter the central nervous system and ultimately induce, or accelerate, PD progression. The pathogenic potential of various environmental neurotoxicants and the suitability and translational potential of experimental animal models of PD will be highlighted and appraised. Finally, the clinical manifestations of gastrointestinal involvement in PD and medications will be discussed briefly.

Production and characterization of avian crypt-villus enteroids and the effect of chemicals

BACKGROUND

Three-dimensional models of cell culture such as organoids and mini organs accord better advantage over regular cell culture because of their ability to simulate organ functions hence, used for disease modeling, metabolic research, and the development of therapeutics strategies. However, most advances in this area are limited to mammalian species with little progress in others such as poultry where it can be deployed to study problems of agricultural importance. In the course of enterocyte culture in chicken, we observed that intestinal mucosal villus-crypts self-repair and form spheroid-like structures which appear to be useful as ex vivo models to study enteric physiology and diseases.

RESULTS

The villus-crypts harvested from chicken intestinal mucosa were cultured to generate enteroids, purified by filtration then re cultured with different chemicals and growth factors to assess their response based on their morphological dispositions. Histochemical analyses using marker antibodies and probes showed the enteroids consisting different cell types such as epithelial, goblet, and enteroendocrine cells typical to villi and retain functional characteristics of intestinal mucosa.

CONCLUSIONS

We present a simple procedure to generate avian crypt-villous enteroids containing different cell types. Because the absorptive cells are functionally positioned outwards, similar to the luminal enterocytes, the cells have better advantages to interact with the factors present in the culture medium. Thus, the enteroids have the potential to study the physiology, metabolism, and pathology of the intestinal villi and can be useful for preliminary screenings of the factors that may affect gut health in a cost-effective manner and reduce the use of live animals.

A method to culture chicken enterocytes and their characterization

Enterocytes function as both absorptive and protective components of intestine that come in close contact with a variety of enteric factors, such as dietary, microbial, and parasites, that have potential to affect the organismal health. Understanding how enterocytes interact with this complex array of factors may help improve gut health particularly in the context of poultry production where it is also linked to food safety issues. The enterocyte in vitro culture can help screen different factors and their interactions with microbiome, and potentially be utilized in the development of interventions strategies for pathogens such as antibiotic alternatives. We developed a method to culture primary chicken enterocytes and conducted their characterization using cytochemical and proteomic methods, and investigated their potential to respond to different chemical stimuli. Using selected micronutrients, microbial toxins, and metabolic modulators, we assessed their effects on the viability and morphological changes in enterocytes. We found that whereas some nutritional factors (calcitriol, retinoic acid) produced different morphological changes, toxins such as aflatoxin B1 and deoxynivalenol produced enterocyte degeneration and death, and the bacterial lipopolysaccharide had very little effect compared on the basis of their mass. Both cyclic AMP and phorbol myristate acetate exhibited some cachectic effects on enterocytes with the later showing more severe changes. Thyroxin induced distinct morphological changes making the cells more cuboidal and Na-butyrate produced no significant change in morphology. The cytochemical and proteomic characterization suggest that these enterocytes largely belong to epithelial cell categories which may be amenable to analysis of biochemical paths and mechanisms of action of different factors that affect these cells. Based on these results we conclude that chicken enterocyte culture can be a useful in vitro model to study intestinal physiology.

Ingestion of subthreshold doses of environmental toxins induces ascending Parkinsonism in the rat

Increasing evidence suggests that environmental neurotoxicants or misfolded α-synuclein generated by such neurotoxicants are transported from the gastrointestinal tract to the central nervous system via the vagus nerve, triggering degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNpc) and causing Parkinson's disease (PD). We tested the hypothesis that gastric co-administration of subthreshold doses of lectins and paraquat can recreate the pathology and behavioral manifestations of PD in rats. A solution containing paraquat + lectin was administered daily for 7 days via gastric gavage, followed by testing for Parkinsonian behavior and gastric dysmotility. At the end of the experiment, brainstem and midbrain tissues were analyzed for the presence of misfolded α-synuclein and neuronal loss in the SNpc and in the dorsal motor nucleus of the vagus (DMV). Misfolded α-synuclein was found in DMV and SNpc neurons. A significant decrease in tyrosine hydroxylase positive dopaminergic neurons was noted in the SNpc, conversely there was no apparent loss of cholinergic neurons of the DMV. Nigrovagally-evoked gastric motility was impaired in treated rats prior to the onset of parkinsonism, the motor deficits of which were improved by l-dopa treatment. Vagotomy prevented the development of parkinsonian symptoms and constrained the appearance of misfolded α-synuclein to myenteric neurons. These data demonstrate that co-administration of subthreshold doses of paraquat and lectin induces progressive, l-dopa-responsive parkinsonism that is preceded by gastric dysmotility. This novel preclinical model of environmentally triggered PD provides functional support for Braak's staging hypothesis of idiopathic PD.

Dietary Plant Lectins Appear to Be Transported from the Gut to Gain Access to and Alter Dopaminergic Neurons of Caenorhabditis elegans, a Potential Etiology of Parkinson's Disease

Lectins from dietary plants have been shown to enhance drug absorption in the gastrointestinal tract of rats, be transported trans-synaptically as shown by tracing of axonal and dendritic paths, and enhance gene delivery. Other carbohydrate-binding protein toxins are known to traverse the gut intact in dogs. Post-feeding rhodamine- or TRITC-tagged dietary lectins, the lectins were tracked from gut to dopaminergic neurons (DAergic-N) in transgenic Caenorhabditis elegans (C. elegans) [egIs1(Pdat-1:GFP)] where the mutant has the green fluorescent protein (GFP) gene fused to a dopamine transport protein gene labeling DAergic-N. The lectins were supplemented along with the food organism Escherichia coli (OP50). Among nine tested rhodamine/TRITC-tagged lectins, four, including Phaseolus vulgaris erythroagglutinin (PHA-E), Bandeiraea simplicifolia (BS-I), Dolichos biflorus agglutinin (DBA), and Arachis hypogaea agglutinin (PNA), appeared to be transported from gut to the GFP-DAergic-N. Griffonia Simplicifolia and PHA-E, reduced the number of GFP-DAergic-N, suggesting a toxic activity. PHA-E, BS-I, Pisum sativum (PSA), and Triticum vulgaris agglutinin (Succinylated) reduced fluorescent intensity of GFP-DAergic-N. PHA-E, PSA, Concanavalin A, and Triticum vulgaris agglutinin decreased the size of GFP-DAergic-N, while BS-I increased neuron size. These observations suggest that dietary plant lectins are transported to and affect DAergic-N in C. elegans, which support Braak and Hawkes' hypothesis, suggesting one alternate potential dietary etiology of Parkinson's disease (PD). A recent Danish study showed that vagotomy resulted in 40% lower incidence of PD over 20 years. Differences in inherited sugar structures of gut and neuronal cell surfaces may make some individuals more susceptible in this conceptual disease etiology model.

Precocious gut maturation and immune cell expansion by single dose feeding the lectin phytohaemagglutinin to suckling rats

The dietary lectin phytohaemagglutinin (PHA) induces gut growth and precocious maturation in suckling rats after mucosal binding. The present study investigated the dose range in which PHA provokes gut maturation and if it coincided with immune activation. Suckling rats, aged 14 d, were orogastrically fed a single increasing dose of PHA: 0 (control), 2, 10, 50 or 250 microg/g body weight (BW) in saline. The effect on gut, lymphoid organs and appearance of CD3+ (T-lymphocyte) and CD19+ (B-lymphocyte) cells in the small-intestinal mucosa was studied at 12 h (acute) and 3 d (late phase) after treatment. The low PHA doses (2 and 10 microg/g BW) induced intestinal hyperplasia without mucosal disarrangement but did not provoke gut maturation. Only the high PHA doses (50 and 250 microg/g BW) temporarily disturbed the intestinal mucosa with villi shortening and decrease in disaccharidase activities, and later after 3 d provoked precocious maturation, resulting in an increase in maltase and sucrase activities and decrease in lactase activity and disappearance of the fetal vacuolated enterocytes in the distal small intestine. Exposure to the high, but not to the low, PHA doses increased the number of mucosal CD19+ and CD3+ cells in the small intestine after 12 h, a finding also observed in untreated weaned rats aged 21-28 d. In conclusion, there was a dose-related effect of PHA on gastrointestinal growth and precocious maturation that coincided with a rapid expansion of mucosal B- and T-lymphocytes, indicating a possible involvement of the immune system in this process.

Antinutritional properties of plant lectins

Lectins are carbohydrate binding (glyco)proteins which are ubiquitous in nature. In plants, they are distributed in various families and hence ingested daily in appreciable amounts by both humans and animals. One of the most nutritionally important features of plant lectins is their ability to survive digestion by the gastrointestinal tract of consumers. This allows the lectins to bind to membrane glycosyl groups of the cells lining the digestive tract. As a result of this interaction a series of harmful local and systemic reactions are triggered placing this class of molecules as antinutritive and/or toxic substances. Locally, they can affect the turnover and loss of gut epithelial cells, damage the luminal membranes of the epithelium, interfere with nutrient digestion and absorption, stimulate shifts in the bacterial flora and modulate the immune state of the digestive tract. Systemically, they can disrupt lipid, carbohydrate and protein metabolism, promote enlargement and/or atrophy of key internal organs and tissues and alter the hormonal and immunological status. At high intakes, lectins can seriously threaten the growth and health of consuming animals. They are also detrimental to numerous insect pests of crop plants although less is presently known about their insecticidal mechanisms of action. This current review surveys the recent knowledge on the antinutritional/toxic effects of plant lectins on higher animals and insects.

Phytohaemagglutinin inhibits gastric acid but not pepsin secretion in conscious rats

Phytohaemagglutinin (PHA), a kidney bean lectin, is known for its binding capability to the small intestinal surface. There has been no data available, however, on the biological activity of PHA in the stomach. Recent observations indicate that PHA is able to attach to gastric mucosal and parietal cells. Therefore, we examined whether PHA affects gastric acid and pepsin secretion in rats. Rats were surgically prepared with chronic stainless steel gastric cannula and with indwelling polyethylene jugular vein catheter. During experiments, animals were slightly restrained. Gastric acid secretion was collected in 30 min periods. Acid secretion was determined by titration of the collected gastric juice with 0.02 N NaOH to pH 7.0. Pepsin activity was estimated by measuring enzymatic activity. Saline, pentagastrin and histamine were infused intravenously. PHA or bovine serum albumin (BSA) were dissolved in saline and given intragastrically through the gastric cannula. PHA significantly inhibited basal acid secretion. Inhibition of acid output reached 72% during the first collection period following PHA administration when compared, then gradually disappeared. Pentagastrin-stimulated acid secretion was repressed dose-dependently by PHA as well. Maximal inhibition was observed during the first 30 min following application of PHA. Histamine-stimulated acid secretion was inhibited by PHA in a similar manner. Pepsin secretion was not affected by PHA under either basal or stimulated conditions. These results provide evidence that PHA is a potent inhibitor of gastric acid secretion in conscious rats, but it does not affect pepsin output from the stomach.