PRISM :: Browsing by Author "Buret, Andre G."

Browsing by Author "Buret, Andre G."

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Open Access
Anti-Inflammatory and Cytoprotective Actions of Hydrogen Sulfide: Translation to Therapeutics
(Antioxidants & Redox Signaling, 2015-04-15) Wallace, John L.; Blackler, Rory W.; Chan, Melissa V.; Da Silva, Gabriela J.; Elsheikh, Wagdi; Flannigan, Kyle L.; Gamaniek, Iulia; Manko, Anna; Wang, Lu; Motta, Jean-Paul; Buret, Andre G.
Significance: There is a rapidly expanding body of evidence for important roles of hydrogen sulfide in protecting against tissue injury, reducing inflammation, and promoting repair. There is also growing evidence that H2S can be successfully exploited in drug development. Recent Advances: H2S synthesis and degradation are regulated in circumstances of inflammation and injury so as to promote repair and re-establish homeostasis. Novel H2S-releasing drugs exhibit enhanced anti-inflammatory and pro-restorative effects, while having reduced adverse effects in many tissues. Critical Issues: H2S is a pleiotropic mediator, having effects on many elements in the inflammatory cascade and promoting the resolution of inflammation and injury. It also contributes significantly to mucosal defence in the gastrointestinal tract, and in host defence against infection. There is strong evidence that novel, H2S-based therapeutics are safe and effective in animal models, and several are progressing through human trials. Future Directions: A better understanding of the physiological and pathophysiological roles of H2S continues to be restrained by the lack of simple, reliable methods for measurement of H2S synthesis, and the paucity of highly selective inhibitors of enzymes that participate in endogenous H2S synthesis. On the other hand, H2S donors show promise as therapeutics for several important indications. Antioxid. Redox Signal. 22, 398–410.
Embargo
Anti-inflammatory effects of retinoids and carotenoid derivatives on caspase-3–dependent apoptosis and efferocytosis of bovine neutrophils
(American Journal of Veterinary Research, 2014-12) Duquette, Stephanie C.; Fischer, Carrie D.; Feener, Troy D.; Muench, Gregory P.; Morck, Douglas W.; Barreda, Daniel R.; Nickerson, James G.; Buret, Andre G.
Objective—To evaluate immunomodulatory properties of all-trans retinoic acid and a fully oxidized β-carotene dietary product in calves with Mannheimia haemolytica–induced pneumonia. Animals—Twenty-five 6- to 10-week-old male Holstein calves for experimental inoculations and three 8- to 30-week-old Angus heifers for blood donations. Procedures—In vitro, neutrophils and monocyte-derived macrophages isolated from blood of healthy Angus heifers were treated with all-trans retinoic acid (1μM) or fully oxidized β-carotene (8.3 μg/mL) for various times and assessed for markers of cellular death, antimicrobial function, and production of proinflammatory leukotriene B4. Following 28 days of dietary supplementation with fully oxidized β-carotene, Holstein calves were experimentally inoculated with M haemolytica. Bronchoalveolar lavage fluid was collected at 3 and 24 hours after challenge inoculation and analyzed for markers of apoptosis. Results—In vitro, all-trans retinoic acid and fully oxidized β-carotene induced cell-selective, caspase-3–dependent apoptosis in neutrophils, which subsequently enhanced efferocytosis in macrophages. Conversely, neither treatment altered phorbol 12-myristate 13-acetate–induced oxidative burst, phagocytosis of nonopsonized zymosan (complement or antibody independent), or M haemolytica–induced leukotriene B4 production in bovine neutrophils. In vivo, fully oxidized β-carotene enhanced leukocyte apoptosis in bronchoalveolar lavage fluid as well as subsequent efferocytosis by macrophages without altering numbers of circulating leukocytes. Conclusions and Clinical Relevance—Neutrophil apoptosis and subsequent efferocytosis by macrophages are key mechanisms in the resolution of inflammation. Findings for the present study indicated that all-trans retinoic acid and fully oxidized β-carotene could be novel nutraceutical strategies that may confer anti-inflammatory benefits for cattle with respiratory tract disease.
Open Access
Anti-inflammatory effects of the macrolide antibiotic tilmicosin
(1998) Chin, Alex C.; Buret, Andre G.
Open Access
Bacterial and parasitic microbiome of mantled howler monkeys: interactions and implications of human disturbance
(2021-04-28) Macfarland, Colin Evan; Melin, Amanda; Buret, Andre G.; Kutz, Susan J.; Wasmuth, James; Pavelka, Mary Susan; Poissant, Jocelyn; Peric, Sabrina
The gastrointestinal (GI) microbiome plays a significant role in contributing to the digestive health of the host. The community of bacteria, parasites and other microorganisms that make up the GI microbiome are known to change in response to external and internal factors including diet, stress, infection, and other environmental conditions. GI parasites are typically harmful organisms that affect hosts through triggering inflammatory response, reducing nutrient availability, and change mutualistic bacterial communities in the gut. However, they have been found to benefit the host in some circumstances. For example, helminthic parasites may have a role protecting the host from chronic inflammation caused by pathogenic bacteria or inflammatory bowel disease. In this thesis, I study the gut bacteria and parasites of populations of mantled howler monkeys (Alouatta palliata) in northwestern Costa Rica. I examine the extent to which the bacterial microbiome of howler monkeys is different in the presence of infection by helminths, and if howlers living in areas of anthropogenic habitat fragmentation have observable differences in the bacterial microbiome or helminth parasites. I used coprological examination of fecal flotations to assess parasitism, and 16S high-throughput sequencing to assess bacterial abundances. I found evidence of several helminth taxa infecting these howlers, including from the genera Controrchis, Strongyloides, Enterobius, and an unidentified Trematode. Howler monkeys infected with helminth parasites did not show a significantly different bacterial diversity; however, helminth-positive howlers have significant differences in relative abundances of Clostridiales and Bacteroidales bacteria. Furthermore, I found that howlers living in areas with anthropogenic habitat fragmentation had significantly lower diversity of gastrointestinal bacteria than howlers living in continuous forest. Lastly, I found that the howler populations within Sector Santa Rosa had a higher density of parasite infection, compared to those living in anthropogenically fragmented habitats. My research on the gastrointestinal and parasite microbiome of howlers provides new insights into the health and ecology of wild primates; further research that compares phenomena occurring in human populations and non-human primates is likely to be fruitful. My work provides new data on the impacts of habitat fragmentation that can inform primate conservation efforts, health monitoring efforts, and management decisions.
Open Access
C. jejuni infection in newly hatched chicks and epithelial barrier disruption in vitro: effects of epidermal growth factor
(2006) Lamb, Jennifer M.; Buret, Andre G.
Open Access
Determining the Geographic Distribution of Filarioid Nematodes in Caribou in Canada
(2023-11-16) Mariyam Thomas, Aparna; Kutz, Susan J.; Melin, Amanda Dawn; Soghigian, John Steven; Verocai, Guilherme Gomes; Buret, Andre G.
The caribou (Rangifer tarandus sspp.) is a keystone wildlife species in northern ecosystems that plays a central role in the lives of the Indigenous People as a cultural and spiritual icon. The Arctic is currently experiencing unpredictable changes due to various factors, including climate change, and warming temperatures and change in precipitation in the Arctic facilitate the transmission of arthropod-borne parasites. Caribou are hosts to several vector-borne parasites, which includes protozoans such as Babesia odocoilei and Besnoitia tarandi, and filarioid nematodes of the genus Setaria, Onchocerca, and Rumenfilaria. Some caribou populations are declining as a result of rapidly changing climate and multiple stressors, including these vector-borne parasites. Filarioids are an important cause of morbidity, and occasional mortality in Rangifer in Fennoscandia. However, the ecology and epidemiology of these parasites in caribou in North America, including Canada is unknown. The objective of this study was to determine the parasitic diversity and geographic distribution of filarioid nematodes in three Canadian designatable units (DU) of caribou, representing Barrenground, Boreal Woodland and Dolphin & Union Caribou from Northwest Territories, Nunavut, and Newfoundland & Labrador. Genomic DNA extracted from 768 blood samples was screened using real-time PCR. The positive samples were Sanger sequenced to identify the parasite present. Based on the sequencing results, we identified Setaria yehi and Onchocerca cervipedis s.l. I then standardized a TaqMan probe based duplex droplet digital PCR (ddPCR) protocol for the simultaneous detection of S. yehi and O. cervipedis s.l. I adopted a conservative approach for ddPCR to make the technique time- and cost-effective. Out of 768 samples, 136 samples were screened using ddPCR. Based on real-time PCR results, 8/768 samples were positive. Setaria yehi and O. cervipedis s.l. were present in 4 separate samples (0.5%) each. Using ddPCR, 60/136 samples were positive (44.1%). Setaria yehi was the most common one with 40/136 positive samples (29.4%); Onchocerca cervipedis s.l. was present in 10/136 samples (7.3%), and 10/136 samples (7.3%) had a co-infection. Setaria yehi was detected from all three DUs tested. Onchocerca cervipedis s.l. were found from Barrenground and Boreal Woodland caribou, but not from the Dolphin and Union caribou herd. Through this broad-based survey and by developing and implementing advanced molecular methodologies, I have detailed the distribution and diversity of S. yehi and O. cervipedis s.l. in parts of three Canadian DUs of caribou. Filarioids are important pathogen nematodes which can cause chronic illness in Rangifer and understanding their distribution and epidemiology helps to know the impacts of these parasites in Canadian caribou populations. The knowledge I obtained from my study will set the stage and provide methods for the further elucidation of the epidemiology of these parasites in Canada across the range of caribou.
Open Access
Development of Intranasal Bacterial Therapeutics to Mitigate the Bovine Respiratory Pathogen Mannheimia haemolytica
(2019-11) Amat, Samat; van der Meer, Frank; Alexander, Trevor W.; Buret, Andre G.; De Buck, Jeroen M.; McAllister, Tim
The emergence of multidrug-resistant pathogens associated with bovine respiratory disease (BRD) presents a significant challenge to the beef industry, as antibiotic administration is commonly used to prevent and control BRD in commercial feedlot cattle in North America. Thus, developing antibiotic alternatives such as bacterial therapeutics (BTs) to mitigate BRD is needed. Recent studies suggest that the nasopharyngeal (NP) microbiota, particularly lactic acid-producing bacteria (LAB), are important to bovine respiratory health and may be a source of BTs for the inhibition of BRD pathogens. The research presented in this thesis aimed to develop intranasal BTs to mitigate the BRD pathogen Mannheimia haemolytica and promote NP microbiota stability in feedlot cattle. Results from Study 1 showed that commercial probiotic bacteria were able to inhibit M. haemolytica growth and its adherence to epithelial cells. Study 2 revealed that the NP microbial community structure and relative abundance of LAB families underwent significant changes when cattle transported from the farm to an auction market, then to feedlot. Many of the LAB families were inversely correlated with the BRD-associated Pasteurellaceae family, and isolates from Lactobacillaceae, Streptococcaceae and Enterococcaceae families inhibited growth of M. haemolytica in vitro. This study provided evidence of potential antagonistic competition taking place between LAB and BRD-associated pathogens within the respiratory tract. Following these studies, using a targeted approach based on criteria evaluating M. haemolytica inhibition, adherence to turbinate cells, and immunomodulation, 6 Lactobacillus strains from an initial group of 178 bacterial isolates originating from nasopharynx of cattle were identified as the best BT candidates (Study 3). Intranasal inoculation of these BTs reduced colonization by M. haemolytica and induced modulation of respiratory microbiota in dairy calves experimentally challenged with M. haemolytica (Study 4). Finally, the longitudinal effects of intranasally administered BTs on the NP microbiota and the prevalence of BRD pathogens including Mannheimia were evaluated in post-weaned beef calves (Study 5). A single dose of intranasal BTs induced longitudinal modulation of the NP microbiota while showing no adverse effects on animal health and growth performance. With further characterization of inoculant dose and time of inoculation, the BTs may have potential for application as an antimicrobial alternative for mitigation of M. haemolytica in beef cattle.
Open Access
Effects of azithromycin on human neutrophils
(1999) Koch, Crystal Coco; Buret, Andre G.
Open Access
Effects of enterocyte apoptosis on epithelial injury and dysfunction
(2003) Chin, Alex C.; Buret, Andre G.
Open Access
Epithelial: Helicobacter pylori interactions
(2004) Fedwick, Jason P.; Buret, Andre G.
The dynamic and selective barrier formed by the epithelial cells of the human gastric mucosa is crucial in the protection against microbial pathogens. Peptides produced by the human host such as epidermal growth factor (EGF) are important in maintaining mucosal integrity and protecting the host from bacterial colonization. This study investigated the effect of H. pylori, a human gastric pathogen implicated in the development of gastroduodenal ulcers and gastric cancers, on epithelial barrier structure and function in vivo and in vitro. In addition, the effect of EGF on H. pylori colonization and viability was also examined. Bacterial load and gastritis increased over 14, 70 and 100 days in C57Bl/6 mice infected with H. pylori strain SS1. Infected mice also had a transient increase in gastric, but not duodenal, permeability on day 73 of the infection. Confluent, non-transformed intestinal epithelial cells (SCBN) grown on Transwells and exposed to H. pylori strain SS1 (VacA+/CagA+) had an increase in the passage of 3000MW Dextran. In contrast, H. pylori strains LC11 (VacA+/CagA+) and LC20 (VacA-/CagA-) did not change the permeability of SCBN cells to 3000MW Dextran. By immunohistochemistry and western blotting, H. pylori strain SS 1 disrupted tight junction (TJ) occludin, claudin-4 and claudin-5 in SCBN cells. The addition of a specific inhibitor of MLCK prevented the increase in epithelial permeability and disruption of tight junctional claudin-4 and claudin-5. Oral, daily administration of human recombinant EGF (100Jµg/kg) to infected mice 10 days prior to sacrifice significantly lowered the number of H. pylori recovered from gastric tissues. However, co-culture of H. pylori and EGF (100µM) had no effect on bacterial growth or metabolism. Stomach sections from infected-EGF treated animals had a different pattern of surface carbohydrate expression compared to infected animals. Disruptions of the tight junction observed in this study implicate previously unrecognized host cell signaling pathways, including the regulation of tight junctional claudin-4, claudin-5 and the phosphorylation of myosin light chain, in the pathogenesis of H. pylori infection. In addition, oral administration of EGF, independent of a direct microbiocidal action, can decrease the colonization of the stomach by H. pylori.
Embargo
Giardia duodenalis: New Research Developments in Pathophysiology, Pathogenesis, and Virulence Factors
(Current Tropical Medicine Reports, 2015-07-11) Buret, Andre G.; Amat, Christina B.; Manko, Anna; Beatty, Jennifer K.; Halliez, Marie C. M.; Bhargava, Amol; Motta, Jean-Paul; Cotton, James A.
Giardia duodenalis is a very common, ubiquitous, intestinal protozoan parasite infecting animals and humans. Of the eight distinct genetic assemblages known to date, assemblages A and B are infectious to humans. Giardia is the most commonly recognized cause of traveller’s diarrhea. Giardiasis impairs weight gain and is responsible for a variety of extra-intestinal and post-infectious complications, including post-infectious irritable bowel syndrome, chronic fatigue, failure to thrive, and cognitive impairment. Giardiasis occurs in the absence of invasion of the intestinal tissues by the trophozoites and in the absence of any overt inflammatory cell infiltration, with the exception of a modest increase in intraepithelial lymphocytes and mast cells. In endemic parts of the World where the infection is often concurrent with bacterial enteritis causing inflammation-driven diarrheal disease, giardiasis appears to be protective against diarrhea. Recent observations have demonstrated that this effect may be due to a direct immuno-modulating effect of the parasite via its cathepsin B cysteine protease which cleaves pro-inflammatory CXCL8. No known toxin has yet been directly implicated in the pathophysiology of giardiasis. Diarrhea in giardiasis is mostly malabsorptive in nature, rather than hypersecretory. Findings from ongoing research indicate that the post-infectious effects of giardiasis may be due to microbiota dysbiosis induced by the parasite during the acute phase of infection.
Open Access
Giardiasis in growing mice
(1988) Buret, Andre G.; Olson, Merle E.
Open Access
Immuno-Modulating Properties of Tulathromycin in Porcine Reproductive and Respiratory Syndrome Virus-Infected Macrophages In Vitro.
(2018-08-10) Desmonts de Lamache, Dimitri; Buret, Andre G.; Morck, Douglas W.; Yates, Robin M.; Cobo, Eduardo R.
With a total cost of productivity losses estimated at $600 million annually in the U.S alone, porcine reproductive and respiratory syndrome (PRRS) is a major concern in the swine industry. PRRS etiological agent, the porcine reproductive and respiratory syndrome virus (PRRSV) is a small positive-strand RNA virus that primarily grows in alveolar macrophages. Due to its high antigenic variability, and poorly understood immunopathogenesis, there is currently no treatment to control PRRSV infection. Commercially available vaccines are inefficient and cannot meet practical needs encouraging more researchers to explore different approaches to treat PRRSV infections. The common occurrence of PRRSV infection with bacterial infections as well as its inflammatory-driven pathobiology raises the question of the value of antibiotics for the treatment of the disease it causes. Tulathromycin (TUL), a macrolide antibiotic previously studied in our laboratory has been shown to exhibit potent anti-inflammatory and immunomodulatory actions in cattle and pigs. The aim of this study was to identify and characterize anti-viral and immunomodulating properties of TUL in PRRSV-infected porcine macrophages. Our findings indicate that blood monocyte-derived macrophages are readily infected by PRRSV and can be used as a cellular model to study PRRSV pathogenesis. TUL was found to not change viral titers and viral receptors (CD163 and CD169) expression suggesting that the drug does not possess direct antiviral effects against PRRSV. In addition, we showed that TUL acts synergistically with PRRSV to induce apoptosis but prevents virus-induced early necrosis. TUL was also found to attenuate PRRSV-induced macrophage pro-inflammatory signaling (CXCL-8 and mitochondrial ROS production) and prevent phagocytosis inhibition. Together, these data demonstrate that tulathromycin downregulates PRRSV-induced inflammatory response in macrophages which may in turn reduce virus-related tissue injury. More importantly, this study sheds the light on the potential clinical benefits of an antibiotic in the context of a virus-induced inflammation.
Embargo
Immuno-modulation and anti-inflammatory benefits of antibiotics: The example of tilmicosin
(Canadian Journal of Veterinary Research, 2010-01) Duquette, Stephanie C.; Fischer, Carrie D.; Williams, Allison C.; Sajedy, Saman; Feener, Troy D.; Bhargava, Amol; Reti, Kristen L.; Muench, Gregory P.; Morck, Douglas W.; Allison, Jim; Lucas, Merlyn J.; Buret, Andre G.
Exagerated immune responses, such as those implicated in severe inflammatory reactions, are costly to the metabolism. Inflammation and pro-inflammatory mediators negatively affect production in the food animal industry by reducing growth, feed intake, reproduction, milk production, and metabolic health. An ever-increasing number of findings have established that antibiotics, macrolides in particular, may generate anti-inflammatory effects, including the modulation of pro-inflammatory cytokines and the alteration of neutrophil function. The effects are time- and dose-dependent, and the mechanisms responsible for these phenomena remain incompletely understood. Recent studies, mostly using the veterinary macrolide tilmicosin, may have shed new light on the mode of action of some macrolides and their anti-inflammatory properties. Indeed, research findings demonstrate that this compound, amongst others, induces neutrophil apoptosis, which in turn provides anti-inflammatory benefits. Studies using tilmicosin model systems in vitro and in vivo demonstrate that this antibiotic has potent immunomodulatory effects that may explain why at least parts of its clinical benefits are independent of anti-microbial effects. More research is needed, using this antibiotic and others that may have similar properties, to clarify the biological mechanisms responsible for antibiotic-induced neutrophil apoptosis, and how this, in turn, may provide enhanced clinical benefits. Such studies may help establish a rational basis for the development of novel, efficacious, anti-microbial compounds that generate anti-inflammatory properties in addition to their antibacterial effects.
Open Access
Intestinal epithelial cell responses to infection with attaching and effacing pathogens
(2007) Flynn, Andrew N.; Buret, Andre G.
Open Access
Mechanisms of antibiotic-induced neutrophil apoptosis
(2002) Lee, Wilson Dave; Buret, Andre G.
Open Access
Mechanisms of apical junctional complex disruption by helicobacter pylori
(2010) O'Connor, Pamela M.; Buret, Andre G.
Open Access
Mycobacterium avium subsp. paratuberculosis: herd prevalence and calf-to-calf transmission
(2018-05-10) Corbett, Caroline Susan; Barkema, Herman Wildrik; De Buck, Jeroen M.; Orsel, Karin; Kastelic, John Patrick; Buret, Andre G.
Johne’s disease results in a progressive chronic enteritis caused by Mycobacterium avium subsp. paratuberculosis (MAP), leading to economic losses among dairy producers worldwide. In the absence of an effective vaccine to prevent infection and treatment for infected animals, control is primarily based on decreasing the number of new transmissions within a herd. Control programs have been implemented in countries and regions around the world; however, comparisons among prevalence estimates of difference regions and control programs are difficult and unreliable due to different tests used to identify infected animals and herds. Therefore, the first objectives of this thesis were to elucidate the influences of environmental sample characteristics on the outcome status of a herd, and to estimate the prevalence of MAP based on 2 environmental samples (and 3 environmental samples when including young stock) in Canada. Six environmental samples were collected twice, 3.5 years apart, from 148 dairy farms to determine whether difference in prevalence between sampling periods were associated with herd size and sample characteristics. All environmental samples regardless of type, had decreased odds of testing positive in the second sampling, and the largest herds had increased odds of testing positive than smaller herds at both sample periods. Across 4 regions (10 provinces) in Canada, 2 environmental samples, one from the lactating cow area and one the manure storage, were collected from 362 dairy farms, with an additional sample collected from breeding age heifers. Prevalence was lowest among tie-stall herds, in herds ≤ 100 cows, and in Québec; and although breeding age heifer samples did not affect prevalence estimates, they provided additional evidence that young stock are shedding MAP on farm. Therefore, the second objectives of this thesis were to determine the extent to which calf-to-calf transmission occurs among group-housed penmates, and to quantify the amount of fecal shedding that occurs among these infectious calves. An experimental transmission study was conducted, where 32 newborn calves were grouped into 7 experimental groups of 4, consisting of 2 inoculated (IN), and 2 contact exposed (CE) calves, and 1 control pen with 4 non-exposed calves. Calves were group-housed for 3 months, during which fecal, blood and environmental samples were collected frequently. The based reproduction ratio (R0) was estimated as a parameter of transmission of MAP infection using a final size (FS) model with a susceptible-infected-recovered (SIR) model based on ELISA and tissue culture. In addition, transmission rate parameter () was estimated using a GLM with a susceptible-infected-susceptible (SIS) model based on fecal culture during group housing. Throughout group housing, all IN and CE calves had MAP-positive fecal samples, and although there was a difference between frequency of shedding, there was no difference between the quantities of MAP shed in feces. All IN calves had positive MAP-tissue samples, and 7 (50%) of CE calves had positive tissue samples. Based on fecal shedding, the basic reproduction ratio R0 for CE calves (R0CE) was 3.24 (95% CI: 1.14, 7.41). R0I (based on interferon- results from blood samples) was 0.90 (95% CI: 0.24, 2.59), and R0T (based on tissue) was 1.36 (95% CI: 0.45, 3.94). Additionally, the effects of freezing on the ability to identify MAP in tissue samples were found to be minor; however, there may be a greater effect for CE calves that should be considered when freezing tissue samples. In conclusion, environmental samples characteristics did not influence the infection status of a herd, and collecting 2 environmental samples could be used to estimate prevalence and compare differences among regions. Shedding calves transmit infection to fellow penmates; therefore, future control programs should consider monitoring and testing of young stock to further decrease new transmissions on farm.
Open Access
Novel anti-inflammatory and pro-resolving mechanisms of antibiotics: leukocyte apoptosis, inhibition of nf-kb, and modulation of lipid signaling by tulathromycin
(2012) Fischer, Carrie D.; Buret, Andre G.
The accumulation of neutrophils and inflammatory mediators, such as interleukin- 8 (CXCL-8) and leukotriene B4 (LTB4), are classic markers of inflammatory disease. Clearance of apoptotic neutrophil, inhibition of pro-inflammatory signaling, and production of pro-resolving mediators, including lipoxins (LXA4), are imperative for resolving inflammation. Findings indicate that immunomodulation by macrolide antibiotics generate anti-inflammatory benefits via mechanisms that remain obscure. Tulathromycin, a new antimicrobial macrolide for bovine respiratory disease (BRD), offers superior clinical efficacy for reasons not fully understood. The pathogenesis of BRD is due, at least in part, to the severe host inflammatory response to invading pathogens, such as Mannheirnia haernolytica. The aim of this study was to identify immunomodulating actions of tulathromycin and, in the process, establish tulathromycin as a new model for characterizing novel anti-inflammatory properties of antibiotics. To investigate the effects of tulathromycin in vivo, calves were challenged intratracheally with live M. haemolytica or zymosan, and treated with vehicle or tulathromycin. Bronchoalveolar lavage samples collected 3 and 24 h post-challenge indicated that tulathromycin promoted neutrophil apoptosis and clearance of these cells by alveolar macrophages. In addition, tulathromycin reduced pulmonary levels of LTB4 and prostaglandin E2 (PGE2); however, there was no effect of tulathromycin on neutrophil trafficking to the lungs. In vitro, tulathromycin cell-selectively and dosedependently induced apoptosis in bovine neutrophils and macrophages. The pro-apoptotic effects of tulathromycin were caspase-dependent, and occurred in the presence and absence of live M. haemolytica. Tulathromycin increased surface expression of phosphatidylserine on neutrophils, which were readily phagocytosed by bovine macrophages. There was no apparent effect of tulathromycin on oxidative burst in neutrophils. Furthermore, tulathromycin blocked NF-KB signaling and production of CXCL-8 in LPS-stimulated neutrophils and macrophages. Tulathromycin inhibited activity of anti-apoptotic and pro-inflammatory phospholipase D (PLD) and cytosolic PLA2, the latter blocking, at least in part, the production of LTB4 in neutrophils. In contrast, tulathrornycin promoted the secretion of the pro-resolving lipid mediator, lipoxin A4, in neutrophils. Lastly, tulathromycin promoted the intracellular accumulation of phospholipids in neutrophils. Collectively, the findings illustrate novel mechanisms through which tulathromycin confers anti-inflammatory benefits, and in turn, shed light on promising avenues for the development of novel, improved, therapeutics.
Open Access
Novel Insights Into The Mechanisms Of Post-Infectious Irritable Bowel Syndrome Using Experimental Giardiasis
(2014-07-11) Halliez, Marie, C.M.; Buret, Andre G.; Gargala, Gilles
Irritable Bowel syndrome (IBS) is the most frequent functional gastrointestinal disorder in humans characterized by abdominal pain and altered bowel habits. The major pathophysiological features of IBS include: visceral hypersensitivity, intestinal barrier dysfunction, low grade inflammation appear following acute gastroenteritis despite the clearance of the inciting pathogen. This post-infectious (PI)-IBS may occur in patients following infection with bacteria such as C. jejuni, E. coli, Salmonella spp. Recent studies have implicated protozoan parasites such as Giardia duodenalis in the appearance of PI-IBS. G. duodenalis, the most common enteropathogen worldwide, is responsible for giardiasis, a disease causing intestinal malabsorption and diarrhea in a wide variety of species including humans. Using in vivo and in vitro models, the present study, established a proof-of-concept between Giardia-infection and the development of PI-IBS. This study also characterized one of the contributing mechanisms leading to post-giardiasis IBS. In a new neonatal immunocompetent rat model, the human assemblages of Giardia duodenalis caused a significant visceral hypersensitivity 50 days post-infection in two parts of the gastrointestinal tract. Visceral hypersensitivity was associated with mucosal structure modifications: villus atrophy and crypt hyperplasia after clearance of the pathogen. It was also associated with activation of the mucosal immune system as shown by an increase in intraepithelial lymphocytes and mast cell counts during the post-infectious stage. And with activation of the nociceptive signaling pathway by induction of c-fos expression starting at day 7 post-infection and continuing until the post-infectious stage. This study showed a dysfunction of the intestinal barrier, in vivo and in vitro, characterized by the translocation of commensal bacteria. Giardia-induced bacterial translocation, further characterized in vitro, was shown to occur via the paracellular route in conjunction with the degradation of the tight junctional proteins occludin and claudin-4. In conclusion, this study presented a new animal model of giardiasis eliciting PI-IBS symptoms. This study also showed that Giardia was able to induce the translocation of commensal bacteria through the epithelial monolayer via the paracellular route by degrading tight junctional proteins. This model suggest that the host immune system reactivity toward its own microbiota due to impaired intestinal barrier function seems to be one of the mechanisms contributing to post-infectious irritable bowel syndrome following acute giardiasis.