Escherichia coli lipopolysaccharides produce serotype-specific hypothermic response in biotelemetered rats

The lipopolysaccharide structure affects the detoxifying ability of intestinal alkaline phosphatases

Lipopolysaccharide (LPS) is one of the most potent mediators of inflammation. In swine husbandry, weaning is associated with LPS-induced intestinal inflammation, resulting in decreased growth rates due to malabsorption of nutrients by the inflamed gut. A potential strategy to treat LPS-mediated disease is administering intestinal alkaline phosphatase (IAP). The latter can detoxify lipid A, the toxic component of LPS, by removal of phosphate groups. Currently, 183 LPS O-serotypes from E. coli have been described, however, comparative experiments to elucidate functional differences between LPS serotypes are scarce. In addition, these functional differences might affect the efficacy of LPS detoxifying enzymes. Here, we evaluated the ability of four LPS serotypes (O26:B6, O55:B5, O111:B4 and O127:B8) derived from Escherichia coli to trigger the secretion of pro-inflammatory cytokines by porcine PBMCs. We also tested the ability of three commercially available IAPs to detoxify these LPS serotypes. The results show that LPS serotypes differ in their ability to trigger cytokine secretion by immune cells, especially at lower concentrations. Moreover, IAPs displayed a different detoxification efficiency of the tested serotypes. Together, this study sheds light on the impact of LPS structure on the detoxification by IAPs. Further research is however needed to elucidate the LPS serotype-specific effects and their implications for the development of novel treatment options to alleviate LPS-induced gut inflammation in weaned piglets.

The investigation of the molecular changes during lipopolysaccharide-induced systemic inflammation on rat hippocampus by using FTIR spectroscopy

The aim of this study is to reveal the molecular changes accompanying the neuronal hyper-excitability during lipopolysaccharide (LPS)-induced systemic inflammation on rat hippocampus using Fourier transform infrared (FTIR) spectroscopy. For this aim, the body temperature of Wistar albino rats administered LPS or saline was recorded by radiotelemetry. The animals were decapitated when their body temperature began to decrease by 0.5°C after LPS treatment and the hippocampi of them were examined by FTIR spectroscopy. The results indicated that systemic inflammation caused lipid peroxidation, an increase in the amounts of lipids, proteins and nucleic acids, a decrease in membrane order, an increase in membrane dynamics and changes in the secondary structure of proteins. Principal component analysis successfully separated control and LPS-treated groups. In conclusion, significant structural, compositional and functional alterations occur in the hippocampus during systemic inflammation and these changes may have specific characteristics which can lead to neuronal hyper-excitability.

INTERPLAY BETWEEN BRAIN OXYGENATION AND THE DEVELOPMENT OF HYPOTHERMIA IN ENDOTOXIC SHOCK

ABSTRACT

There is evidence to suggest that the hypothermia observed in the most severe cases of systemic inflammation or sepsis is a regulated response with potential adaptive value, but the mechanisms involved are poorly understood. Here, we investigated the interplay between brain oxygenation (assessed by tissue P o2 ) and the development of hypothermia in unanesthetized rats challenged with a hypotension-inducing dose of bacterial LPS (1 mg/kg i.v.). At an ambient temperature of 22°C, oxygen consumption (V̇O 2 ) began to fall only a few minutes after the LPS injection, and this suppression in metabolic rate preceded the decrease in core temperature. No reduction in brain P o2 was observed prior to the development of the hypometabolic, hypothermic response, ruling out the possibility that brain hypoxia served as a trigger for hypothermia in this model. Brain P o2 was even increased. Such an improvement in brain oxygenation could reflect either an increased O 2 delivery or a decreased O 2 consumption. The former explanation seems unlikely because blood flow (cardiac output) was being progressively decreased during the recording period. On the other hand, the decrease in V̇O 2 usually preceded the rise in P o2 , and an inverse correlation between V̇O 2 and brain P o2 was consistently observed. These findings do not support the existence of a closed-loop feedback relationship between brain oxygenation and hypothermia in systemic inflammation. The data are consistent with a feedforward mechanism in which hypothermia is triggered (possibly by cryogenic inflammatory mediators) in anticipation of changes in brain oxygenation to prevent the development of tissue hypoxia.

The Protective Action of Rubus sp. Fruit Extract Against Oxidative Damage in Mice Exposed to Lipopolysaccharide

Neuroinflammation is an event that occurs in several pathologies of brain. Rubus sp. (blackberry) is a powerful antioxidant fruit, and its extract has neuroprotective activity. The aim of this study was to investigate the blackberry extract properties on lipopolysaccharide (LPS)-induced neuroinflammation, in relation to oxidative parameters and acetylcholinesterase activity in the brain structures of mice. We also investigated interleukin-10 levels in serum. Mice were submitted to Rubus sp. extract treatment once daily for 14 days. On the fifteenth day, LPS was injected in a single dose. LPS induced oxidative brain damage and the blackberry extract demonstrated preventive effects in LPS-challenged mice. LPS administration increased reactive oxygen species levels in the cerebral cortex and striatum, as well as lipid peroxidation in the cerebral cortex. However, the blackberry extract prevented all these parameters. Furthermore, LPS decreased thiol content in the striatum and hippocampus, while a neuroprotective effect of blackberry extract treatment was observed in relation to this parameter. The blackberry extract also prevented a decrease in catalase activity in all the brain structures and of superoxide dismutase in the striatum. An increase in acetylcholinesterase activity was detected in the cerebral cortex in the LPS group, but this activity was decreased in the Rubus sp. extract group. Serum IL-10 levels were reduced by LPS, and the extract was not able to prevent this change. Finally, we observed an antioxidant effect of blackberry extract in LPS-challenged mice suggesting that this anthocyanin-rich extract could be considered as a potential nutritional therapeutic agent for preventive damage associated with neuroinflammation.

Diet-induced obesity attenuates the hypothermic response to lipopolysaccharide independently of TNF-α production

Life-threatening infections (sepsis) are usually associated with co-morbidities, among which obesity deserves attention. Here, we evaluated whether and how obesity affects the switch from fever to hypothermia that occurs in the most severe cases of sepsis, which is thought to provide physiological support for a change in host defense strategy from resistance to tolerance. Obesity was induced by keeping rats on a high-fat diet for 32-34 weeks. The hypothermia induced by a high dose of bacterial lipopolysaccharide (LPS, 300 μg/animal, i.a.) was attenuated in the obese rats, as compared to their low-fat diet counterparts. Surprisingly, such attenuation occurred in spite of an enhancement in the circulating level of TNF-α, the most renowned mediator of LPS-induced hypothermia. Hence, it seems that factors counteracting not the production, but rather the action of TNF-α are at play in rats with diet-induced obesity. One of these factors might be IL-1β, a febrigenic mediator that also had its circulating levels augmented in the obese rats challenged with LPS. Taken together with previous reports of diet-induced obesity enhancing the fever induced by lower doses of LPS, the results of the present study indicate that obesity biases host defense toward a fever/resistance strategy, in lieu of a hypothermia/tolerance strategy.

Effect of bovine genotype on innate immune response of heifers to repeated lipopolysaccharide (LPS) administration

This pilot study provides a preliminary assessment of the impact of genotype on acute innate immune pro-inflammatory, metabolic and endocrine responses to repeated lipopolysaccharide (LPS) administered to growing heifers. Heifers (n = 4/genotype) were from unselected (stable milk yield since 1964, UH) or contemporary (CH) Holstein cows that differed in milk yield (6200 vs 11,100 kg milk/305 d) or from contemporary Black Angus (CA) cows bred to contemporary Red Angus bulls. Heifers were challenged with iv administration of 0.5 μg LPS/kg body weight on day 1 (Challenge 1) and d 5 (Challenge 2) of study to assess endotoxin tolerance. Plasma was collected at -1, -0.5, 0, 1, 2, 3, 4, 6, 8, and 24 h relative to each LPS administration. Rectal body temperature (BT) was measured before each blood sampling and at 5 and 7 h. Data were analyzed by repeated measures with sampling time as the repeated effect. Each genotype had at least one pro-inflammatory response that indicated it might have a more robust response than the other genotypes. The CH heifers had a greater TNF-α response, UH heifers had greater IL-6 and XO responses and CA heifers had greater BT and SAA response to LPS than the other genotypes. There was a genotype by time by interaction as cortisol peaked earlier in CH and UH than in CA heifers. Glucose response was less in CA and insulin response was greater in CH heifers. Endotoxin tolerance to LPS was evident as pro-inflammatory, cortisol, glucose and insulin responses were less during Challenge 2 than during Challenge 1. Differences among genotypes during Challenge 1 were eliminated during Challenge 2 except for the greater SAA response in CA heifers and indicate the potential for differential impacts of genotype on the development of endotoxin tolerance. Specific reasons for these effects of genotype are not clear from these data but the results support the hypothesis for differential innate immune signaling among these bovine genotypes.

Fever and hypothermia in systemic inflammation

Systemic inflammation-associated syndromes (e.g., sepsis and septic shock) often have high mortality and remain a challenge in emergency medicine. Systemic inflammation is usually accompanied by changes in body temperature: fever or hypothermia. In animal studies, systemic inflammation is often modeled by administering bacterial lipopolysaccharide, which triggers autonomic and behavioral thermoeffector responses and causes either fever or hypothermia, depending on the dose and ambient temperature. Fever and hypothermia are regulated changes of body temperature, which correspond to mild and severe forms of systemic inflammation, respectively. Mediators of fever and hypothermia are called endogenous pyrogens and cryogens; they are produced when the innate immune system recognizes an infectious pathogen. Upon an inflammatory challenge, hepatic and pulmonary macrophages (and later brain endothelial cells) start to release lipid mediators, of which prostaglandin (PG) E₂ plays the key role, and cytokines. Blood PGE₂ enters the brain and triggers fever. At later stages of fever, PGE₂ synthesized within the blood-brain barrier maintains fever. In both cases, PGE₂ is synthesized by cyclooxygenase-2 and microsomal PGE₂synthase-1. Mediators of hypothermia are not well established. Both fever and hypothermia are beneficial host defense responses. Based on evidence from studies in laboratory animals and clinical trials in humans, fever is beneficial for fighting mild infection. Based mainly on animal studies, hypothermia is beneficial in severe systemic inflammation and infection.

Neutrophils Discriminate between Lipopolysaccharides of Different Bacterial Sources and Selectively Release Neutrophil Extracellular Traps

The release of neutrophil extracellular traps (NETs), either during "suicidal" or "vital" NETosis, represents an important strategy of neutrophils to combat Gram-negative bacteria. Lipopolysaccharide (LPS), a major component of the outer membrane of Gram-negative bacteria, is a reported stimulus for NET formation. Although it is widely acknowledged that the structural diversity in LPS structures can elicit heterogeneous immune responses, species- and serotype-specific differences in the capacity of LPS to trigger NET formation have not yet been investigated. In the present study, we compared the NET-inducing potential of LPS derived from Escherichia coli (serotypes O55:B5, O127:B8, O128:B12, O111:B4, and O26:B6), Salmonella enterica (serotype enteritidis), and Pseudomonas aeruginosa (serotype 10), under platelet-free and platelet-rich conditions in vitro, and in whole blood ex vivo. Here, we demonstrate that under serum- and platelet-free conditions, mimicking tissue circumstances, neutrophils discriminate between LPS of different bacterial sources and selectively release NETs only in response to LPS derived from E. coli O128:B12 and P. aeruginosa 10, which both induced "suicidal" NETosis in an autophagy- and reactive oxygen species (ROS)-dependent, but TLR4-independent manner. Intriguingly, in whole blood cultures ex vivo, or in vitro in the presence of platelets, all LPS serotypes induced "vital" NET formation. This platelet-dependent release of NETs occurred rapidly without neutrophil cell death and was independent from ROS formation and autophagy but required platelet TLR4 and CD62P-dependent platelet-neutrophil interactions. Taken together, our data reveal a complex interplay between neutrophils and LPS, which can induce both "suicidal" and "vital" NETosis, depending on the bacterial origin of LPS and the presence or absence of platelets. Our findings suggest that LPS sensing by neutrophils may be a critical determinant for restricting NET release to certain Gram-negative bacteria only, which in turn may be crucial for minimizing unnecessary NET-associated immunopathology.

Nitric oxide and fever: immune-to-brain signaling vs. thermogenesis in chicks

Nitric oxide (NO) plays a role in thermogenesis but does not mediate immune-to-brain febrigenic signaling in rats. There are suggestions of a different situation in birds, but the underlying evidence is not compelling. The present study was designed to clarify this matter in 5-day-old chicks challenged with a low or high dose of bacterial LPS. The lower LPS dose (2 μg/kg im) induced fever at 3–5 h postinjection, whereas 100 μg/kg im decreased core body temperature (Tc) (at 1 h) followed by fever (at 4 or 5 h). Plasma nitrate levels increased 4 h after LPS injection, but they were not correlated with the magnitude of fever. The NO synthase inhibitor ( NG-nitro-l-arginine methyl ester, l-NAME; 50 mg/kg im) attenuated the fever induced by either dose of LPS and enhanced the magnitude of the Tc reduction induced by the high dose in chicks at 31–32°C. These effects were associated with suppression of metabolic rate, at least in the case of the high LPS dose. Conversely, the effects of l-NAME on Tc disappeared in chicks maintained at 35–36°C, suggesting that febrigenic signaling was essentially unaffected. Accordingly, the LPS-induced rise in the brain level of PGE2 was not affected by l-NAME. Moreover, l-NAME augmented LPS-induced huddling, which is indicative of compensatory mechanisms to run fever in the face of attenuated thermogenesis. Therefore, as in rats, systemic inhibition of NO synthesis attenuates LPS-induced fever in chicks by affecting thermoeffector activity and not by interfering with immune-to-brain signaling. This may constitute a conserved effect of NO in endotherms.

Consumption of broccoli sprouts during late gestation and lactation confers protection against developmental delay induced by maternal inflammation

BACKGROUND

The presence of a fetal inflammatory response is linked to cerebral palsy. Unfortunately no preventive therapies are available. In this study, we determined whether dietary supplementation with broccoli sprouts (BrSp), a phase-II enzyme inducer, would be effective in preventing the behavioural and pathologic manifestations in a rodent model of inflammation during late pregnancy.

METHODS

Pregnant Long-Evans rats were administered i.p. Injections of saline (100μl) or lipopolysaccharide (LPS, 200μg/kg), every 12h on embryonic day (E) 19 and 20. In the treatment groups, dams were supplemented with 200mg/day of dried BrSp from E14 until postnatal day 21. Pups underwent a series of neurodevelopmental reflex tests from postnatal day 3-21 followed by neuropathological analyses.

RESULTS

Pups born from the LPS group were significantly growth restricted (p<0.001) and delayed in hindlimb placing (p<0.05), cliff avoidance (p<0.05), and gait (p<0.001) compared to controls. In the open field behaviour analyses, LPS pups had an increase in grooming behaviour (p<0.05) and a decreased amount of time spent in the center of the box compared to controls. Dietary supplementation with BrSp to offspring exposed to LPS had increased birth weights (p<0.001), were no longer delayed in acquiring hindlimb placing, cliff avoidance, gait, and posture, and groomed less compared to LPS alone pups (p<0.01). Histological analyses revealed that LPS pups had reduced myelin basic protein compared to controls.

CONCLUSIONS

Our data suggest that BrSp dietary supplementation during pregnancy may be effective in preventing growth restriction and neurodevelopmental delays.

Effects of Lipopolysaccharide on Human First Trimester Villous Cytotrophoblast Cell Function In Vitro

It has been shown that adverse obstetrical outcomes such as pre-eclampsia and intrauterine growth retardation correlate with maternal infection. In this study, we investigated mechanisms involved in infection-associated abnormalities in cytotrophoblast function. Primary human first trimester cytotrophoblast cells were isolated and treated with lipopolysaccharide (LPS). Levels of the cytokines and chemokines were measured and cytotrophoblast invasion was investigated. In addition, first trimester decidual macrophages were isolated and treated with the conditioned medium from LPS-treated cytotrophoblast cells, and macrophage migration was assessed. Coculturing decidual macrophages with cytotrophoblast cells was conducted to investigate macrophage costimulatory molecule and receptor expression and intracellular cytokine production. We found that LPS exposure increased cytotrophoblast production of pro-inflammatory cytokines tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta and IL-6, and chemokines IL-8, macrophage inflammatory protein (MIP)-1alpha, and CXCL12 in a dose-dependent manner. In addition, LPS decreased cytotrophoblast invasion, and its effect was Toll-like receptor 4 (TLR4)-dependent and partly TNF-alpha-dependent. Conditioned medium from LPS-stimulated cytotrophoblast cells increased decidual macrophage migration and this effect was partly TLR4-dependent. Furthermore, coculturing decidual macrophages with LPS-exposed cytotrophoblast cells up-regulated macrophage CD80 and CD86 expression and intracellular TNF-alpha and IL-12p40 production, while down-regulating macrophage CD206 and CD209 expression and intracellular IL-10 secretion. LPS-stimulated macrophages also inhibited cytotrophoblast invasion. In conclusion, our results indicate that LPS increases the production of a subset of proinflammatory cytokines and chemokines by human first trimester cytotrophoblast cells, decreases cytotrophoblast invasion, and alters the cross talk between cytotrophoblast cells and decidual macrophages.

Specific Lipopolysaccharide Serotypes Induce Differential Maternal and Neonatal Inflammatory Responses in a Murine Model of Preterm Labor

Intrauterine inflammation is recognized as a key mediator of both normal and preterm birth but is also associated with neonatal neurological injury. Lipopolysaccharide (LPS) is often used to stimulate inflammatory pathways in animal models of infection/inflammation-induced preterm labor; however, inconsistencies in maternal and neonatal responses to LPS are frequently reported. We hypothesized that LPS serotype-specific responses may account for a portion of these inconsistencies. Four different Escherichia coli LPS serotypes (O111:B4, O55:B5, O127:B8, and O128:B12) were administered to CD1 mice via intrauterine injection at gestational day 16. Although control animals delivered at term 60 ± 15 hours postinjection (p.i.), those administered with O111:B4 delivered 7 ± 2 hours p.i., O55:B5 delivered 10 ± 3 hours p.i., O127:B8 delivered 16 ± 10 hours p.i., and O128:B12 delivered 17 ± 2 hours p.i. (means ± SD). A correlation between the onset of preterm labor and myometrial activation of the inflammatory transcription factor, activator protein 1, but not NF-κB was observed. Specific LPS serotypes induced differential activation of downstream contractile and inflammatory pathways in myometrium and neonatal pup brain. Our findings demonstrate functional disparity in inflammatory pathway activation in response to differing LPS serotypes. Selective use of LPS serotypes may represent a useful tool for targeting specific inflammatory response mechanisms in these models.

Endotoxin exposure and puberty in female rats: the role of nitric oxide and caspase-1 inhibition in neonates

Bacterial toxins are widespread in the environment as well as in the digestive system of humans and animals. Toxin from Gram-negative bacteria (endotoxin or lipopolysaccharide; LPS) has a life-long programming effect on reproduction in rats, but the mediators have not been well-documented, so we investigated the effects of LPS on the timing of puberty in female rats. Because the levels of nitric oxide (NO) and interleukin 1β (IL-1β) increase following injection of LPS, we injected neonates (post-natal day (pnd) 7) with LPS, with or without NO or IL-1β inhibitors. Half of the prepubescent (pnd 30) animals received an additional LPS injection. Vaginal opening, number of ovarian follicles, and serum anti-LPS antibodies were determined. A single LPS injection was sufficient to reduce the primordial follicle pool, but puberty was delayed when rats received 2 LPS injections (at pnd 7 and 30). NO or IL-1β inhibitors improved both of these parameters, suggesting that the early detrimental effects of LPS on puberty and primordial follicle pool are mediated by NO and IL-1β.

Platelet-activating factor is a potent pyrogen and cryogen, but it does not mediate lipopolysaccharide fever or hypothermia

We examined whether platelet-activating factor (PAF) and its receptor mediate lipopolysaccharide (LPS)-induced fever and hypothermia in rats. Two highly potent, structurally distinct antagonists of the PAF receptor, CV6209 and WEB2086, were used. At a neutral ambient temperature (Ta) of 30ºC, administration of LPS at a low (10 μg/kg, i.v.) or high (1,000 μg/kg, i.v.) dose resulted in fever. The response to the high dose was turned into hypothermia at a subneutral Ta of 22ºC. Neither LPS-induced fever nor hypothermia was affected by pretreatment with CV6209 (5 mg/kg, i.v.) or WEB2086 (5 mg/kg, i.v.). However, both PAF antagonists were efficacious in blocking the thermoregulatory response caused by PAF (334 pmol/kg/min, 1 h, i.v.), regardless of whether the response was a fever (at 30ºC) or hypothermia (at 22ºC). Additional experiments showed that the thermoregulatory responses to LPS and PAF are also distinct in terms of their mediation by prostaglandins. Neither PAF fever nor PAF hypothermia was affected by pretreatment with the cyclooxygenase-2 inhibitor SC236 (5 mg/kg, i.p.), which is known to abrogate LPS fever. The responses to PAF were also unaffected by pretreatment with the cyclooxygenase-1 inhibitor SC560 (5 mg/kg, i.p.), which is known to attenuate LPS hypothermia. In conclusion, PAF infusion at a picomolar dose causes fever at thermoneutrality but hypothermia in a subthermoneutral environment, both responses being dependent on the PAF receptor and independent of prostaglandins. However, the PAF receptor does not mediate LPS-induced fever or hypothermia, thus challenging the dogma that PAF is an upstream mediator of responses to LPS.

Systemic administration of oleoylethanolamide protects from neuroinflammation and anhedonia induced by LPS in rats

BACKGROUND

The acylethanolamides oleoylethanolamide and palmitoylethanolamide are endogenous lipid mediators with proposed neuroprotectant properties in central nervous system (CNS) pathologies. The precise mechanisms remain partly unknown, but growing evidence suggests an antiinflammatory/antioxidant profile.

METHODS

We tested whether oleoylethanolamide/palmitoylethanolamide (10 mg/kg, i.p.) attenuate neuroinflammation and acute phase responses (hypothalamus-pituitary-adrenal (HPA) stress axis stress axis activation, thermoregulation, and anhedonia) induced by lipopolysaccharide (0.5 mg/kg, i.p.) in rats.

RESULTS

Lipopolysaccharide increased mRNA levels of the proinflammatory cytokines tumor necrosis factor-α, interleukin-1β, and interleukin-6, nuclear transcription factor-κB activity, and the expression of its inhibitory protein IκBα in cytoplasm, the inducible isoforms of nitric oxide synthase and cyclooxygenase-2, microsomal prostaglandin E2 synthase mRNA, and proinflammatory prostaglandin E2 content in frontal cortex 150 minutes after administration. As a result, the markers of nitrosative/oxidative stress nitrites (NO2(-)) and malondialdehyde were increased. Pretreatment with oleoylethanolamide/ palmitoylethanolamide reduced plasma tumor necrosis factor-α levels after lipopolysaccharide, but only oleoylethanolamide significantly reduced brain tumor necrosis factor-α mRNA. Oleoylethanolamide and palmitoylethanolamide prevented lipopolysaccharide-induced nuclear transcription factor-κB (NF-κB)/IκBα upregulation in nuclear and cytosolic extracts, respectively, the expression of inducible isoforms of nitric oxide synthase, cyclooxygenase-2, and microsomal prostaglandin E2 synthase and the levels of prostaglandin E2. Additionally, both acylethanolamides reduced lipopolysaccharide-induced oxidative/nitrosative stress. Neither oleoylethanolamide nor palmitoylethanolamide modified plasma corticosterone levels after lipopolysaccharide, but both acylethanolamides reduced the expression of hypothalamic markers of thermoregulation interleukin-1β, cyclooxygenase-2, and prostaglandin E2, and potentiated the hypothermic response after lipopolysaccharide. Interestingly, only oleoylethanolamide disrupted lipopolysaccharide-induced anhedonia in a saccharine preference test.

CONCLUSIONS

Results indicate that oleoylethanolamide and palmitoylethanolamide have antiinflammatory/neuroprotective properties and suggest a role for these acylethanolamides as modulators of CNS pathologies with a neuroinflammatory component.

Activation of decidual invariant natural killer T cells promotes lipopolysaccharide-induced preterm birth

Invariant natural killer T (iNKT) cells are crucial for host defense against a variety of microbial pathogens, but the underlying mechanisms of iNKT cells activation by microbes are not fully explained. In this study, we investigated the molecular mechanisms of iNKT cell activation in lipopolysaccharide (LPS)-stimulated preterm birth using an adoptive transfer system and diverse neutralizing antibodies (Abs) and inhibitors. We found that adoptive transfer of decidual iNKT cells to LPS-stimulated iNKT cell deficient Jα18(-/-) mice that lack invariant Vα14Jα281T cell receptor (TCR) expression significantly decreased the time to delivery and increased the percentage of decidual iNKT cells. Neutralizing Abs against Toll-like receptor 4 (TLR-4), CD1d, interleukin (IL)-12 and IL-18, and inhibitors blocking the activation of nuclear factor κB (NF-κB), mitogen-activated protein kinase (MAPK) p38 and extracellular signal-regulated kinase (ERK) significantly reduced in vivo percentages of decidual iNKT cells, their intracellular interferon (IFN)-γ production and surface CD69 expression. In vitro, in the presence of the same Abs and inhibitors used as in vivo, decidual iNKT cells co-cultured with LPS-pulsed dendritic cells (DCs) showed significantly decreased extracellular and intracellular IFN-γ secretion and surface CD69 expression. Our data demonstrate that the activation of decidual iNKT cells plays an important role in inflammation-induced preterm birth. Activation of decidual iNKT cells also requires TLR4-mediated NF-κB, MAPK p38 and ERK pathways, the proinflammatory cytokines IL-12 and IL-18, and endogenous glycolipid antigens presented by CD1d.

Leptin mediates seasonal variation in some but not all symptoms of sickness in Siberian hamsters

Many seasonally breeding species, including Siberian hamsters (Phodopus sungorus), exhibit seasonal variation in sickness responses. One hypothesis regarding the mechanism of this variation is that sickness intensity tracks an animal's energetic state, such that sickness is attenuated in the season that an animal has the lowest fat stores. Energetic state may be signaled via leptin, an adipose hormone that provides a signal of fat stores. Siberian hamsters respond to extended housing in short, winter-like days by reducing fat stores and leptin levels, relative to those housed in long, summer-like days. Sickness responses are also attenuated in short-day hamsters as compared to long-day hamsters. We hypothesized that leptin provides a physiological signal by which seasonally breeding animals modulate sickness responses, such that animals with higher leptin levels show increased sickness intensity. To test this, we provided short-day hamsters with a long-day-like leptin signal and assessed their responses to lipopolysaccharide (LPS), a sickness-inducing antigen. We compared these responses to short-day vehicle-, long-day vehicle-, and long-day leptin-treated hamsters. Unexpectedly, LPS induced a hypothermic response (rather than fever) in all groups. Short-day vehicle-treated hamsters exhibited the greatest LPS-induced hypothermia, and leptin treatment attenuated this response, making hypothermia more long-day-like. Contrary to our hypothesis, short-day leptin-treated hamsters showed the least pronounced LPS-induced anorexia among all groups. These results suggest that leptin may mediate some but not all aspects of seasonal sickness variation in this species. Future studies should be targeted at determining roles of other energetic hormones in regulating seasonal sickness response variation.

α-Lipoic acid protects mitochondrial enzymes and attenuates lipopolysaccharide-induced hypothermia in mice

Hypothermia is a key symptom of sepsis, but the mechanism(s) leading to hypothermia during sepsis is largely unknown and thus no effective therapy is available for hypothermia. Therefore, it is important to investigate the mechanism and develop effective therapeutic methods. Lipopolysaccharide (LPS)-induced hypothermia accompanied by excess nitric oxide (NO) production leads to a reduction in energy production in wild-type mice. However, mice lacking inducible nitric oxide synthase did not suffer from LPS-induced hypothermia, suggesting that hypothermia is associated with excess NO production during sepsis. This observation is supported by the treatment of wild-type mice with α-lipoic acid (LA) in that it effectively attenuates LPS-induced hypothermia with decreased NO production. We also found that LA partially restored ATP production, and activities of the mitochondrial enzymes involved in energy metabolism, which were inhibited during sepsis. These data suggest that hypothermia is related to mitochondrial dysfunction, which is probably compromised by excess NO production and that LA administration attenuates hypothermia mainly by protecting mitochondrial enzymes from NO damage.

Hormonal synchronization of lipopolysaccharide-induced hypothermic response in rats

BACKGROUND

Recent experimental evidence suggests that lipopolysaccharide (LPS)-induced hypothermia is an adaptive thermoregulatory strategy against immunological challenge in rats. We hypothesized that the hormones which are predominantly responsible for energy homeostasis may have efferent signaling roles for development of the hypothermia.

AIM

The aim of the study was to evaluate the changes of hypothalamic-pituitary-thyroid (HPT) and hypothalamic- pituitary-adrenal (HPA) axis hormones, leptin and erythropoietin at various phases of LPS-induced hypothermia such as the initial phase, nadir and the end of the response in blood sampled rats.

MATERIAL AND METHODS

Body temperature of adult male albino Wistar rats was recorded by biotelemetry. E. coli O111:B4 LPS (250 μg/kg, ip) was injected alone or with SC-560, a cyclooxygenase-1 selective inhibitor (1 mg/kg, sc).

RESULTS

Serum FT4 levels elevated at the initial phase, but FT3 levels decreased at nadir and remained low at the end of the response. Meanwhile, no change was observed in TSH levels. Serum adrenocorticotropic hormone (ACTH) levels reduced at the initial phase and serum corticosterone levels decreased at nadir without any change in serum corticotropin-releasing hormone (CRH) levels throughout the hypothermia. Serum leptin levels increased only at the end of the response. No change was observed in the levels of serum erythropoietin. SC-560 treatment abolished both LPS-induced hypothermia and respective hormonal changes.

CONCLUSION

Data suggest that HPT axis hormones may contribute to development of LPS-induced hypothermia in rats. Data also support the view that leptin may have a role for the recovery of hypothermic response.

Effect of obesity on the acute inflammatory response in pregnant and cycling female rats

Nonpregnant female rats have a lower inflammatory response to lipopolysaccharide (LPS) than males and, at late stages of gestation, the fever response to this immunogen is almost completely suppressed. We have shown in males that obesity exacerbates sickness responses to pathogenic stimuli. In the present study, we investigated whether obesity would have a similar effect in females and reverse some of the suppressive effects of pregnancy on the innate immune response. Lean and diet-induced obese adult Wistar rats were randomly separated into either cycling or mated groups. On day 18 of pregnancy or in the metestrous/dioestrous phase in cycling rats, a single injection of LPS (100 μg/kg) was administered and rats were sacrificed 8h or 24 h later. In pregnant females, LPS induced a higher increase in body temperature in obese rats only at the 24-h time point and lower hypothalamic interleukin (IL)-1β expression and higher circulating levels of IL-1 receptor antagonist (ra) than their cycling counterparts. Conversely, there was no suppression of inflammatory signals in the white adipose tissue of pregnant rats. At 24 h post LPS, the cell surface marker CD11c and IL-6 mRNA expression were increased in white adipose tissue from obese rats regardless of reproductive state, whereas IL-1ra was highest in the LPS-treated obese pregnant group. In cycling females, LPS induced a higher fever response in obese rats accompanied by higher circulating levels of IL-6 and IL-1ra, as well as an increase in circulating leptin only in the obese cycling group. In the hypothalamus, obese rats showed significantly higher expression of nuclear factor-IL-6 in at the 8-h time point. Collectively, these results show that diet-induced obesity in females is associated with a similar pattern of response to that previously observed in males. On the other hand, obesity had limited effects in pregnant rats, with the exception of white adipose tissue.

Temporal analysis of lipopolysaccharide-induced sickness behavior in virgin and lactating female rats

OBJECTIVES

Lipopolysaccharide (LPS), an endotoxin that originates from the cell wall of Gram-negative bacteria, activates the immune system to release proinflammatory cytokines and to induce sickness behavior. The present study sought to characterize the time-dependent effects of LPS on fever, body weight, and food and water consumption in female virgin and lactating rats exposed to an LPS dose previously reported to induce sickness behavior in pregnant female rats.

METHODS

Virgin female Wistar rats in the estrous phase and lactating female Wistar rats on the third day of lactation received 100 µg/kg LPS or saline solution. Tympanic temperature, body weight, and food and water consumption were assessed 0, 2, 24, 48, 72, 96, and 120 h after treatment.

RESULTS

In lactating female rats, tympanic temperature was attenuated compared with virgin females. Food consumption and body weight gain in both groups decreased, but lactating rats consumed more food than virgin rats. Water consumption increased at different time points.

CONCLUSION

LPS exposure induced several signs of sickness behavior, including decreases in food consumption and body weight gain, and induced adipsia in both virgin and lactating female rats. Because the time course and profile of fever varied between lactating and nonlactating animals, these responses appeared to depend on the physiological state of female animals.

Seizure susceptibility and electroencephalogram power spectra alterations at various phases of the lipopolysaccharide-induced hypothermic response in biotelemetered rats

The neuronal excitability has been evaluated at various phases of lipopolysaccharide (LPS; E. coli O111:B4, 250 μg/kg, ip)-induced hypothermia including the initial phase, the plateau (including the nadir) and the end of the response in biotelemetered adult Wistar rats. The latency of pentylenetetrazole-induced seizures (60 mg/kg, ip) was lower at the initial phase, but a clear anticonvulsive activity was observed at the end of the hypothermic response. Seizure parameters did not change at the nadir. There was no electroencephalogram (EEG) spike-wave activity generation at either phase of the LPS-induced hypothermia. Meanwhile, the power of the 12-32 Hz beta band of the EEG spectra increased at the initial phase. This increment persisted at the plateau where there was also a decrease in the 1-4 Hz delta power. The data indicate that spike-wave activity is not facilitated during LPS-induced hypothermia but, proconvulsant and anticonvulsant activities occur sequentially depending on the phase of the response. The EEG power spectra also change. These effects may not be attributed merely to the reduction of body temperature. Thus, it is possible that pathophysiological mechanisms involved in the development of hypothermia may also be responsible for neuronal excitability changes in rats.

Estradiol and thermoregulation in adult endotoxemic rats exposed to lipopolysaccharide in neonatal life

AIMS

Early life immune challenge has been considered an adaptive defense strategy against potential pathogens when the innate immune system is not completely developed. This study assesses whether neonatal endotoxin challenge alters body temperature response in adult female rats during endotoxemic shock and also, whether ovarian hormones may participate in this response.

METHODS

Rats were intraperitoneally injected with lipopolysacharide (LPS) or saline at post-natal day 14, then as adults they were submitted to endotoxemic shock.

RESULTS

The LPS injection in adult neonatal Saline rats caused an initial hypothermia, followed by a febrile response. However, neonatal LPS showed an increased hypothermic response and an attenuation of fever. The bilateral ovariectomy abolished the difference in body temperature between the neonatal LPS and saline rats. To determine the dependence of ovarian hormones, ovariectomized rats treated with estradiol cypionate (ECP) restored hypothermia and the suppressed febrile response. However, the same results were not obtained when the animals were supplemented with ECP and medroxyprogesterone acetate (MPA). The neonatal LPS rats displayed a significant reduction in TNF-α levels and an increase in IL-10 levels when compared with saline animals. The ECP injection significantly enhanced IL-10 and suppressed TNF-α in neonatal LPS, but it did not change the inflammatory response in the saline rats. The ECP + MPA regiment in the neonatal LPS rats reduced TNF-α, but eliminated IL-10 stimulation in comparison with the saline group.

CONCLUSION

The present investigation shows that neonatal LPS challenge alters the thermoregulatory response during endotoxemic shock in adulthood and the mechanism for this difference could be mediated by sex hormones, especially estradiol.

Cyclooxygenase-2/microsomal prostaglandin E synthase-1 complex in the preoptic-anterior hypothalamus of the mouse: involvement through fever to intravenous lipopolysaccharide

AIM

Prostaglandin E₂ (PGE₂) is now well established as a central effector of pyrogen fever. However, questions remain on the source, local vs. blood-borne, of the compound for the early phase of the typically biphasic fever (Phases 1 and 2) to i.v. pyrogens. To verify the role of centrally formed PGE₂, we examined the cyclooxygenase (COX)/prostaglandin E synthase (PGES) complex through fever to i.v. lipopolysaccharide (LPS).

METHODS

Experiments were carried out in the conscious mouse and LPS effect was ascertained on all steps of expression - gene, protein, catalytic activity - of individual enzymes. The analysis was limited to the preoptic-anterior hypothalamus (AH/POA).

RESULTS

We found upregulation of the COX2 transcript together with an upward trend for the mPGES1 transcript during Phase 1. Coincidentally, there was a progressive increase in COX2 and mPGES1 protein expression through Phases 1 and 2. Catalytic activity for COX1 and COX2 combined was instead enhanced only in Phase 2, while mPGES1 activity remained steady at an intrinsically high level. Other COX and PGES enzymes were not modified through either Phase, and COX2/mPGES1 changes subsided with fever defervescence.

CONCLUSION

The findings confirm a key function of COX2 and mPGES1 for the synthesis of pyrogenic PGE₂ and, at the same time, document their early response to LPS. We conclude that locally formed PGE₂ in AH/POA is qualified for a role in the initiation of fever.

Pharmacologic inhibition of COX-1 and COX-2 in influenza A viral infection in mice

Background

We previously demonstrated that cyclooxygenase (COX)-1 deficiency results in greater morbidity and inflammation, whereas COX-2 deficiency leads to reduced morbidity, inflammation and mortality in influenza infected mice.

Methodology/Principal Findings

We investigated the effects of COX-1 and COX-2 inhibitors in influenza A viral infection. Mice were given a COX-1 inhibitor (SC-560), a COX-2 inhibitor (celecoxib) or no inhibitor beginning 2 weeks prior to influenza A viral infection (200 PFU) and throughout the course of the experiment. Body weight and temperature were measured daily as indicators of morbidity. Animals were sacrificed on days 1 and 4 post-infection and bronchoalveolar lavage (BAL) fluid was collected or daily mortality was recorded up to 2 weeks post-infection. Treatment with SC-560 significantly increased mortality and was associated with profound hypothermia and greater weight loss compared to celecoxib or control groups. On day 4 of infection, BAL fluid cells were modestly elevated in celecoxib treated mice compared to SC-560 or control groups. Viral titres were similar between treatment groups. Levels of TNF-α and G-CSF were significantly attenuated in the SC-560 and celecoxib groups versus control and IL-6 levels were significantly lower in BAL fluid of celecoxib treated mice versus control and versus the SC-560 group. The chemokine KC was significantly lower in SC-560 group versus control.

Conclusions/Significance

Treatment with a COX-1 inhibitor during influenza A viral infection is detrimental to the host whereas inhibition of COX-2 does not significantly modulate disease severity. COX-1 plays a critical role in controlling the thermoregulatory response to influenza A viral infection in mice.

Hepcidin mediates transcriptional changes that modulate acute cytokine-induced inflammatory responses in mice

Hepcidin is a peptide hormone that regulates iron homeostasis and acts as an antimicrobial peptide. It is expressed and secreted by a variety of cell types in response to iron loading and inflammation. Hepcidin mediates iron homeostasis by binding to the iron exporter ferroportin, inducing its internalization and degradation via activation of the protein kinase Jak2 and the subsequent phosphorylation of ferroportin. Here we have shown that hepcidin-activated Jak2 also phosphorylates the transcription factor Stat3, resulting in a transcriptional response. Hepcidin treatment of ferroportin-expressing mouse macrophages showed changes in mRNA expression levels of a wide variety of genes. The changes in transcript levels for half of these genes were a direct effect of hepcidin, as shown by cycloheximide insensitivity, and dependent on the presence of Stat3. Hepcidin-mediated transcriptional changes modulated LPS-induced transcription in both cultured macrophages and in vivo mouse models, as demonstrated by suppression of IL-6 and TNF-alpha transcript and secreted protein. Hepcidin-mediated transcription in mice also suppressed toxicity and morbidity due to single doses of LPS, poly(I:C), and turpentine, which is used to model chronic inflammatory disease. Most notably, we demonstrated that hepcidin pretreatment protected mice from a lethal dose of LPS and that hepcidin-knockout mice could be rescued from LPS toxicity by injection of hepcidin. The results of our study suggest a new function for hepcidin in modulating acute inflammatory responses.

Expression of bovine granulocyte chemotactic protein-2 (GCP-2) in neutrophils and a mammary epithelial cell line (MAC-T) in response to various bacterial cell wall components

CXC chemokines are potential attractants for polymorphonuclear leucocytes (PMNs) and play an important role in resistance to infectious diseases, such as bovine mastitis. In this study, a bovine mammary epithelial cell line (MAC-T) and blood PMNs were stimulated with bacterial cell wall components of gram negative and gram positive bacteria, including lipopolysaccharide (LPS), lipoteichoic acid (LTA) and peptidoglycan (PGN). The expression of two CXC chemokines, interleukin (IL)-8 and granulocyte chemotactic protein (GCP)-2 was analysed by real-time PCR. High concentrations (1 or 10 μg/mL) of LPS and LTA, but not PGN, significantly increased the expression of GCP-2 and IL-8 in both MAC-T and PMNs. Biopsies from mammary glands of cattle with clinical Escherichia coli mastitis also had increased expression of GCP-2. Using an in vitro transepithelial migration assay, recombinant human GCP-2 (rhGCP-2) showed weak chemoattractant effects on bovine blood PMNs. It was concluded that PMNs and MAC-T cells can express GCP-2 in response to certain bacterial cell components during the course of mastitis.

Cyclooxygenase-1 or -2--which one mediates lipopolysaccharide-induced hypothermia?

Systemic inflammation is associated with either fever or hypothermia. Fever, a response to mild systemic inflammation, is mediated by cyclooxygenase (COX)-2 and not by COX-1. However, it is still disputed whether COX-2, COX-1, neither, or both mediate(s) responses to severe systemic inflammation, and, in particular, the hypothermic response. We compared the effects of SC-236 (COX-2 inhibitor) and SC-560 (COX-1 inhibitor) on the deep body temperature (T(b)) of rats injected with a lower (10 microg/kg i.v.) or higher (1,000 microg/kg i.v.) dose of LPS at different ambient temperatures (T(a)s). At a neutral T(a) (30 degrees C), the rats responded to LPS with a polyphasic fever (lower dose) or a brief hypothermia followed by fever (higher dose). SC-236 (2.5 mg/kg i.v.) blocked the fever induced by either LPS dose, whereas SC-560 (5 mg/kg i.v.) altered neither the febrile response to the lower LPS dose nor the fever component of the response to the higher dose. However, SC-560 blocked the initial hypothermia caused by the higher LPS dose. At a subneutral T(a) (22 degrees C), the rats responded to LPS with early (70-90 min, nadir) dose-dependent hypothermia. The hypothermic response to either dose was enhanced by SC-236 but blocked by SC-560. The hypothermic response to the higher LPS dose was associated with a fall in arterial blood pressure. This hypotensive response was attenuated by either SC-236 or SC-560. At the onset of LPS-induced hypothermia and hypotension, the functional activity of the COX-1 pathway (COX-1-mediated PGE(2) synthesis ex vivo) increased in the spleen but not liver, lung, kidney, or brain. The expression of splenic COX-1 was unaffected by LPS. We conclude that COX-1, but not COX-2, mediates LPS hypothermia, and that both COX isoforms are required for LPS hypotension.