Lipid-enriched enteral nutrition controls the inflammatory response in murine Gram-negative sepsis:

"Feed a Cold, Starve a Fever?" A Review of Nutritional Strategies in the Setting of Bacterial Versus Viral Infections

PURPOSE OF REVIEW

Some data, mostly originally derived from animal studies, suggest that low glucose intake is protective in bacterial sepsis but detrimental in overwhelming viral infections. This has been interpreted into a broad belief that different forms of sepsis may potentially require different nutritional management strategies. There are a few mechanistic differences between the host interactions with virus and bacteria which can explain why there may be opposing responses to macronutrient and micronutrient during the infected state. Here, we aim to review relevant evidence on the mechanisms and pathophysiology of nutritional management strategies in various infectious syndromes and summarize their clinical implications.

RECENT FINDINGS

Newer literature - in the context of the SARS-CoV-19 pandemic - offers some insight to viral infections. There is still limited clinically applicable data during infection that clearly delineate the role of nutrition during an active viral vs bacterial infections. Based on contrasting findings in different models of viruses and bacteria, the macronutrient and micronutrient needs may depend more on specific infectious organisms that may not be generalizable as bacterial versus viral. Overall, the metabolic effects of sepsis are context dependent, and various host-specific (e.g., age, baseline nutritional status, immune status, comorbidities) and illness variables (phase, duration, and severity of illness) play a significant role in determining the outcome besides pathogen-specific (virus or bacterial or fungi and combined infections) factors. Microbe therapy (probiotics and prebiotics) seems to have therapeutic potential in both viral and bacterial infected states, and this seems like a promising area for further practical research.

Exploring the Modulatory Effect of High-Fat Nutrition on Lipopolysaccharide-Induced Acute Lung Injury in Vagotomized Rats and the Role of the Vagus Nerve

During esophagectomy, the vagus nerve is transected, which may add to the development of postoperative complications. The vagus nerve has been shown to attenuate inflammation and can be activated by a high-fat nutrition via the release of acetylcholine. This binds to α7 nicotinic acetylcholine receptors (α7nAChR) and inhibits α7nAChR-expressing inflammatory cells. This study investigates the role of the vagus nerve and the effect of high-fat nutrition on lipopolysaccharide (LPS)-induced lung injury in rats. Firstly, 48 rats were randomized in 4 groups as follows: sham (sparing vagus nerve), abdominal (selective) vagotomy, cervical vagotomy and cervical vagotomy with an α7nAChR-agonist. Secondly, 24 rats were randomized in 3 groups as follows: sham, sham with an α7nAChR-antagonist and cervical vagotomy with an α7nAChR-antagonist. Finally, 24 rats were randomized in 3 groups as follows: fasting, high-fat nutrition before sham and high-fat nutrition before selective vagotomy. Abdominal (selective) vagotomy did not impact histopathological lung injury (LIS) compared with the control (sham) group (p > 0.999). There was a trend in aggravation of LIS after cervical vagotomy (p = 0.051), even after an α7nAChR-agonist (p = 0.090). Cervical vagotomy with an α7nAChR-antagonist aggravated lung injury (p = 0.004). Furthermore, cervical vagotomy increased macrophages in bronchoalveolar lavage (BAL) fluid and negatively impacted pulmonary function. Other inflammatory cells, TNF-α and IL-6, in the BALF and serum were unaffected. High-fat nutrition reduced LIS after sham (p = 0.012) and selective vagotomy (p = 0.002) compared to fasting. vagotomy. This study underlines the role of the vagus nerve in lung injury and shows that vagus nerve stimulation using high-fat nutrition is effective in reducing lung injury, even after selective vagotomy.

Biodegradable Polymeric Nanoparticles Loaded with Flavonoids: A Promising Therapy for Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) is a group of disorders that cause chronic non-specific inflammation in the gastrointestinal (GI) tract, primarily affecting the ileum and colon. The incidence of IBD has risen sharply in recent years. Despite continuous research efforts over the past decades, the aetiology of IBD is still not fully understood and only a limited number of drugs are available for its treatment. Flavonoids, a ubiquitous class of natural chemicals found in plants, have been widely used in the prevention and treatment of IBD. However, their therapeutic efficacy is unsatisfactory due to poor solubility, instability, rapid metabolism, and rapid systemic elimination. With the development of nanomedicine, nanocarriers can efficiently encapsulate various flavonoids and subsequently form nanoparticles (NPs), which greatly improves the stability and bioavailability of flavonoids. Recently, progress has also been made in the methodology of biodegradable polymers that can be used to fabricate NPs. As a result, NPs can significantly enhance the preventive or therapeutic effects of flavonoids on IBD. In this review, we aim to evaluate the therapeutic effect of flavonoid NPs on IBD. Furthermore, we discuss possible challenges and future perspectives.

High-fat diet promotes the effect of fructo-oligosaccharides on the colonic luminal environment, including alkaline phosphatase activity in rats

We recently reported that fermentable nondigestible carbohydrates such as oligosaccharides, commonly increase colonic alkaline phosphatase (ALP) activity and the gene expression of Alpi-1, coding for rat intestinal alkaline phosphatase-I isozyme in rats and that the effect of oligosaccharides on colonic ALP activity is affected by the quality of dietary fats. We hypothesized that the amount of dietary fat would modulate the effect of oligosaccharides on colonic ALP and luminal environment in rats. In experiment 1, male Sprague-Dawley rats were fed a low-fat (LF, 5% lard) or high-fat (HF, 30% lard) diet with or without 4% fructo-oligosaccharides (FOS). In experiment 2, they were fed a 2.5%, 7%, 20%, or 40% fat (lard) diet with 4% FOS for 2 weeks. Dietary FOS in the HF diet (HF-FOS) significantly increased ALP activity in the colon and cecal digesta and colonic expression of Alpi-1, but not in the LF diet with FOS groups (LF-FOS). In comparison to the LF-FOS group, the increases in fecal mucins, Lactobacillus ratio, as well as cecal n-butyrate, and the decrease in fecal Clostridium coccoides, were more pronounced in the HF-FOS group. Compared with the 2.5% or 7% fat + FOS diet, the 20% fat + FOS diet significantly increased colonic ALP activity, Alpi-1 expression, and fecal mucins. These factors did not differ significantly between 20% and 40% fat + FOS diets. To exert the maximum effect of FOS on the colonic luminal environment, including ALP activity in rats, significantly more fat may be required than that contained present a LF diet.

Neural control of the spleen as an effector of immune responses to inflammation: mechanisms and treatments

Immune system responses are a vital defense mechanism against pathogens. Inflammatory mediators finely regulate complex inflammatory responses from initiation to resolution. However, in certain conditions, the inflammation is initiated and amplified, but not resolved. Understanding the biological mechanisms underlying the regulation of the immune response is critical for developing therapeutic alternatives, including pharmaceuticals and bioelectronic tools. The spleen is an important immune effector organ since it orchestrates innate and adaptive immune responses such as pathogen clearance, cytokine production, and differentiation of cells, therefore playing a modulatory role that balances pro- and anti-inflammatory responses. However, modulation of splenic immune activity is a largely unexplored potential therapeutic tool that could be used for the treatment of inflammatory and life-threatening conditions. This review discusses some of the mechanisms controlling neuroimmune communication and the brain-spleen axis.

A Novel Pathway of Flavonoids Protecting against Inflammatory Bowel Disease: Modulating Enteroendocrine System

Inflammatory bowel disease (IBD) is a comprehensive term for chronic or relapsing inflammatory diseases occurring in the intestinal tract, generally including Crohn's disease (CD) and ulcerative colitis (UC). Presently, the pathogenesis of IBD is unknown, yet multiple factors have been reported to be related with the development of IBD. Flavonoids are phytochemicals with biological activity, which are ubiquitously distributed in edible plants, such as fruits and vegetables. Recent studies have demonstrated impressively that flavonoids have anti-IBD effects through multiple mechanisms. These include anti-inflammatory and antioxidant actions; the preservation of the epithelial barrier integrity, the intestinal immunomodulatory property, and the shaping microbiota composition and function. In addition, a few studies have shown the impact of flavonoids on enterohormones release; nonetheless, there is hardly any work showing the link between flavonoids, enterohormones release and IBD. So far, the interaction between flavonoids, enterohormones and IBD is elucidated for the first time in this review. Furthermore, the inference can be drawn that flavonoids may protect against IBD through modulating enterohormones, such as glucagon-like peptide 1 (GLP-1), GLP-2, dipeptidyl peptidase-4 inhibitors (DPP-4 inhibitors), ghrelin and cholecystokinin (CCK). In conclusion, this manuscript explores a possible mechanism of flavonoids protecting against IBD.

Enteral enriched nutrition to prevent cognitive dysfunction after surgery; a study in rats

Background

Inflammation plays an important role in postoperative cognitive dysfunction (POCD), particularly in elderly patients. Enteral enriched nutrition was shown to inhibit the response on inflammatory stimuli. Aim of the present study was to explore the therapeutic potential of enteral enriched nutrition in our rat model for POCD. The anticipated mechanism of action was examined in young rats, while responses in the target group of elderly patients were evaluated in old rats.

Methods

Male 3 and 23 months old Wistar rats received a bolus of enteral fat/protein-enriched nutrition 2 ​h and 30 ​min before surgery. The inflammatory response was evaluated by systemic inflammation markers and brain microglia activity. Additionally, in old rats, the role of the gut-brain axis was studied by microbiome analyses of faecal samples. Days 9–14 after surgery, rats were subjected to cognitive testing. Day 16, rats were sacrificed and brains were collected for immunohistochemistry.

Results

In young rats, enriched nutrition improved long-term spatial learning and memory in the Morris Water Maze, reduced plasma IL1-β and VEGF levels, but left microglia activity and neurogenesis unaffected. In contrast, in old rats, enriched nutrition improved short-term memory in the novel object- and novel location recognition tests, but impaired development of long-term memory in the Morris Water Maze. Systemic inflammation was not affected, but microglia activity seemed even increased. Gut integrity and microbiome were not affected.

Conclusion

Enteral enriched nutrition before surgery in young rats indeed reduced systemic inflammation and improved cognitive performance after surgery, whereas old rats showed a mixed favorable/unfavorable cognitive response, without effect on systemic inflammation. Anti-inflammatory effects of enriched nutrition were not reflected in decreased microglia activity. Neither was an important role for the gut-brain axis observed. Since the relatively straight forward effects of enriched nutrition in young rats could not be shown in old rats, as indicated by a mixed beneficial/detrimental cognitive outcome in the latter, caution is advised by translating effects seen in younger patients to older ones.

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Enriched nutrition reduced inflammation after surgery in young rats.

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Enriched nutrition improved postoperative cognitive outcome in young rats.

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Enteral enriched nutrition did not inhibit neuroinflammation.

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Effects in young rats do not predict effects in old rats.

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Enteral enriched nutrition caused mixed improved/declined cognition in old rats.

Beta-1 blocker reduces inflammation and preserves intestinal barrier function after open abdominal surgery

BACKGROUND

Open abdominal surgery is frequently related to excessive inflammation and a compromised intestinal barrier, leading to poor clinical outcomes. The administration of beta-1 blocker has been shown to effectively reduce inflammation and preserve intestinal barrier function in patients with sepsis, shock, or other critical illnesses. The underlying mechanism of these effects may be associated with the autonomic nervous system's activation via cholecystokinin receptors. This study aimed to investigate the effect of beta-1 blocker on systemic and local inflammatory responses and the intestinal barrier function in the context of open abdominal surgery.

METHODS

A rat model of open abdominal surgery was induced through peritoneal air exposure for 3 hours and treated via gavage with the beta-1 blocker, metoprolol, or saline. Cholecystokinin-receptor antagonists were administered before the metoprolol treatment. Peritoneal lavage fluid, serum, and tissues were collected 24 hours after surgery to determine systemic and local inflammation and intestinal integrity.

RESULTS

The intervention with metoprolol significantly reduced serum tumor necrosis factor-alpha and interleukin-6 (P < .05) and peritoneal interleukin-6 (P < .01) compared with those of animals treated with saline. The intestinal myeloperoxidase indicating the influx of neutrophils was also significantly prevented by the administration of metoprolol (P < .05). Above all, this intervention resulted in a significant decrease in serum D-lactate and intestinal fatty acid-binding protein, intestinal permeability, bacterial translocation, and Chiu's score for intestinal mucosa injury (P < .05). However, the anti-inflammatory and intestinal integrity protective effects of metoprolol were prevented by the blockage of cholecystokinin receptors (P < .05).

CONCLUSION

Our data indicate that beta-1 blocker reduces systemic and local inflammatory responses and preserves intestinal barrier function after open abdominal surgery through a mechanism that depends on cholecystokinin receptors. Clinically, these findings imply that perioperative intervention with a beta-1 blocker may be an effective new therapy to enhance recovery after open abdominal surgery.

Changes of plasma acetylcholine and inflammatory markers in critically ill patients during early enteral nutrition: A prospective observational study

BACKGROUND

Acetylcholine (Ach) is the key anti-inflammatory transmitter in the cholinergic anti-inflammatory pathway. In this study, critically ill patients treated with early enteral nutrition (EEN) were observed to explore whether EEN affected Ach levels and inflammation.

METHODS

One hundred thirteen patients were included in this prospective observational study. All patients were provided the early enteral nutrition protocol 24-48 h after admission to the intensive care unit (ICU). Blood samples were collected, and the plasma levels of Ach, cholecystokinin (CCK), and inflammatory markers (tumour necrosis factor alpha (TNF-α), interleukin 1beta (IL1-β), and IL6) were measured on Days 0, 1, 3, 5, and 7. Nutritional intervention data were recorded within one week, including the number of patients receiving nutrition, the number of days nutrition was provided, the caloric intake and protein intake, feeding intolerance and prokinetic drug administration. Other collected data included the sequential organ failure assessment score (SOFA score), the Acute Physiology and Chronic Health Evaluation (APACHE) II score, the use of mechanical ventilation (the number of patients and the duration), use of vasoactive drugs and the number of renal replacement treatments (RRT) received by each patient during their ICU stay. The primary outcome was 28-day mortality. Additionally, we analysed the correlation between plasma Ach levels and inflammation, as well as the correlation between plasma Ach and CCK levels. Moreover, a multivariate regression analysis was performed to examine the independent effects of different variables on 28-day mortality and Ach levels.

RESULTS

The overall 28-day mortality was 28.3% (32/113). Eighty-two patients tolerated enteral nutrition. Compared with Day 0 15.6 (2.8) nmol/l, the plasma Ach level was significantly increased on Day 3 18.6 (6.7) nmol/l, Day 5 19.3 (6.2) nmol/l and Day 7 19.7 (4.3) nmol/l (p < .001). Compared with Day 0176.2 (50.4) pg/ml, the plasma TNF-α level was significantly decreased on Day 3144.0 (77.4) pg/ml, Day 5127.3 (51.8) pg/ml and Day 7111.4 (42.5) pg/ml (p < .05). Compared with Day 0, the plasma IL1-β level was significantly decreased on Day 7 (p < .05). The plasma IL6 level was significantly decreased on Day 5 and Day 7 (p < .05) compared with Day 0. Compared with Day 0, the plasma CCK level was significantly increased on Day 3, 5 and 7 (p < .001). The correlation analysis revealed negative correlations between Ach levels and inflammation (p < .001), and a positive correlation between CCK and Ach levels (r = 0.775, p < .001). A comparison of patients who did or did not tolerate EEN revealed significant differences in the plasma levels of Ach, TNF-α, IL6 and CCK (p < .05). Significant differences in plasma levels of Ach, TNF-α, IL1-β, IL6 and CCK were observed between 28-day survivors and non-survivors (p < .05). The multivariate logistic regression analysis identified vasopressor support, RRT, the administration of EEN, SOFA score, APACHE II score at ICU admission and plasma Ach levels as independent determinants of 28-day mortality. Additionally, the multivariate linear regression analysis identified EEN, plasma lactate, mechanical ventilation, the SOFA score and plasma CCK levels as independent determinants of plasma Ach levels.

CONCLUSIONS

The administration of EEN to critically ill patients contributed to the increased plasma Ach levels and decreased inflammatory markers. The effect of EEN on Ach levels is partially attributed to the increase in CCK levels. Elevated plasma Ach levels indicate a better prognosis. Clinical trials identifier: NCT03612206.

Neuroimmune Communication in Health and Disease

The immune and nervous systems are tightly integrated, with each system capable of influencing the other to respond to infectious or inflammatory perturbations of homeostasis. Recent studies demonstrating the ability of neural stimulation to significantly reduce the severity of immunopathology and consequently reduce mortality have led to a resurgence in the field of neuroimmunology. Highlighting the tight integration of the nervous and immune systems, afferent neurons can be activated by a diverse range of substances from bacterial-derived products to cytokines released by host cells. While activation of vagal afferents by these substances dominates the literature, additional sensory neurons are responsive as well. It is becoming increasingly clear that although the cholinergic anti-inflammatory pathway has become the predominant model, a multitude of functional circuits exist through which neuronal messengers can influence immunological outcomes. These include pathways whereby efferent signaling occurs independent of the vagus nerve through sympathetic neurons. To receive input from the nervous system, immune cells including B and T cells, macrophages, and professional antigen presenting cells express specific neurotransmitter receptors that affect immune cell function. Specialized immune cell populations not only express neurotransmitter receptors, but express the enzymatic machinery required to produce neurotransmitters, such as acetylcholine, allowing them to act as signaling intermediaries. Although elegant experiments have begun to decipher some of these interactions, integration of these molecules, cells, and anatomy into defined neuroimmune circuits in health and disease is in its infancy. This review describes these circuits and highlights continued challenges and opportunities for the field.

Vagal afferent activation suppresses systemic inflammation via the splanchnic anti-inflammatory pathway

Electrical stimulation of the vagus nerve (VNS) is a novel strategy used to treat inflammatory conditions. Therapeutic VNS activates both efferent and afferent fibers; however, the effects attributable to vagal afferent stimulation are unclear. Here, we tested if selective activation of afferent fibers in the abdominal vagus suppresses systemic inflammation. In urethane-anesthetized rats challenged with lipopolysaccharide (LPS, 60 µg/kg, i.v.), abdominal afferent VNS (2 Hz for 20 min) reduced plasma tumor necrosis factor alpha (TNF) levels 90 min later by 88% compared with unmanipulated animals. Pre-cutting the cervical vagi blocked this anti-inflammatory action. Interestingly, the surgical procedure to expose and prepare the abdominal vagus for afferent stimulation ('vagal manipulation') also had an anti-inflammatory action. Levels of the anti-inflammatory cytokine IL-10 were inversely related to those of TNF. Prior bilateral section of the splanchnic sympathetic nerves reversed the anti-inflammatory actions of afferent VNS and vagal manipulation. Sympathetic efferent activity in the splanchnic nerve was shown to respond reflexly to abdominal vagal afferent stimulation. These data demonstrate that experimentally activating abdominal vagal afferent fibers suppresses systemic inflammation, and that the efferent neural pathway for this action is in the splanchnic sympathetic nerves.

A whole animal chemical screen approach to identify modifiers of intestinal neutrophilic inflammation

By performing two high-content small molecule screens on dextran sodium sulfate- and trinitrobenzene sulfonic acid-induced zebrafish enterocolitis models of inflammatory bowel disease, we have identified novel anti-inflammatory drugs from the John Hopkins Clinical Compound Library that suppress neutrophilic inflammation. Live imaging of neutrophil distribution was used to assess the level of acute inflammation and concurrently screen for off-target drug effects. Supporting the validity of our screening strategy, most of the anti-inflammatory drug hits were known antibiotics or anti-inflammatory agents. Novel hits included cholecystokinin (CCK) and dopamine receptor agonists. Using a pharmacological approach, we show that while CCK and dopamine receptor agonists alleviate enterocolitis-associated inflammation, receptor antagonists exacerbate inflammation in zebrafish. This work highlights the utility of small molecule screening in zebrafish enterocolitis models as a tool to identify novel bioactive molecules capable of modulating acute inflammation.

Topography and extent of pulmonary vagus nerve supply with respect to transthoracic oesophagectomy

Pulmonary complications are frequently observed after transthoracic oesophagectomy. These complications may be reduced by sparing the vagus nerve branches to the lung. However, current descriptions of the regional anatomy are insufficient. Therefore, we aimed to provide a highly detailed description of the course of the pulmonary vagus nerve branches. In six fixed adult human cadavers, bilateral microscopic dissection of the vagus nerve branches to the lungs was performed. The level of branching and the number, calibre and distribution of nerve branches were described. Nerve fibres were identified using neurofilament immunohistochemistry, and the nerve calibre was measured using computerized image analysis. Both lungs were supplied by a predominant posterior and a smaller anterior nerve plexus. The right lung was supplied by 13 (10-18) posterior and 3 (2-3) anterior branches containing 77% (62-100%) and 23% (0-38%) of the lung nerve supply, respectively. The left lung was supplied by a median of 12 (8-13) posterior and 3 (2-4) anterior branches containing 74% (60-84%) and 26% (16-40%) of the left lung nerve supply, respectively. During transthoracic oesophagectomy with en bloc lymphadenectomy and transection of the vagus nerves at the level of the azygos vein, 68-100% of the right lung nerve supply and 86-100% of the inferior left lung lobe nerve supply were severed. When vagotomy was performed distally to the last large pulmonary branch, 0-8% and 0-13% of the nerve branches to the right middle/inferior lobes and left inferior lobe, respectively, were lost. In conclusion, this study provides a detailed description of the extensive pulmonary nerve supply provided by the vagus nerves. During oesophagectomy, extensive mediastinal lymphadenectomy denervates the lung to a great extent; however, this can be prevented by performing the vagotomy distal to the caudalmost large pulmonary branch. Further research is required to determine the feasibility of sparing the pulmonary vagus nerve branches without compromising the completeness of lymphadenectomy.

Vagal Modulation of the Inflammatory Response in Sepsis

The vagus nerve can sense peripheral inflammation and transmit action potentials from the periphery to the brainstem. Vagal afferent signaling is integrated in the brainstem, and efferent vagus nerves carry outbound signals that terminate in spleen and other organs. Stimulation of efferent vagus nerve leads to the release of acetylcholine in these organs. In turn, acetylcholine interacts with members of the nicotinic acetylcholine receptor (nAChR) family, particularly with the alpha7 nicotinic acetylcholine receptor (α7nAChR), which is expressed by macrophages and other cytokine-producing cells. Ultimately, the production of proinflammatory cytokines is markedly inhibited. This neuroimmune communication is termed "the inflammatory reflex". The uncontrolled inflammation as a result from sepsis can lead to multiple organ failure, and even death. Experimental data show that regulation of the inflammatory reflex appears to be a useful interventional strategy for septic response. Herein, we review recent advances in the understanding of the inflammatory reflex and discuss potential therapeutics that vagal modulation of the immune system for the treatment of severe sepsis and septic shock.

Neural reflex pathways in intestinal inflammation: hypotheses to viable therapy

Studies in neuroscience and immunology have clarified much of the anatomical and cellular basis for bidirectional interactions between the nervous and immune systems. As with other organs, intestinal immune responses and the development of immunity seems to be modulated by neural reflexes. Sympathetic immune modulation and reflexes are well described, and in the past decade the parasympathetic efferent vagus nerve has been added to this immune-regulation network. This system, designated 'the inflammatory reflex', comprises an afferent arm that senses inflammation and an efferent arm that inhibits innate immune responses. Intervention in this system as an innovative principle is currently being tested in pioneering trials of vagus nerve stimulation using implantable devices to treat IBD. Patients benefit from this treatment, but some of the working mechanisms remain to be established, for instance, treatment is effective despite the vagus nerve not always directly innervating the inflamed tissue. In this Review, we will focus on the direct neuronal regulatory mechanisms of immunity in the intestine, taking into account current advances regarding the innervation of the spleen and lymphoid organs, with a focus on the potential for treatment in IBD and other gastrointestinal pathologies.

The innate immune response

The innate immune response is of prime importance in the immediate recognition and elimination of invading micro-organisms. However, deregulation of this system is clearly associated with the pathogenesis of a wide range of inflammatory diseases. Innate immunity consists of a humoral and a cellular branch, which are closely interacting. An additional level of control is found at the level of neuronal reflexes that can fine-tune these immunological mechanisms.

Cholecystokinin inhibits inducible nitric oxide synthase expression by lipopolysaccharide-stimulated peritoneal macrophages

Cholecystokinin (CCK) was first described as a gastrointestinal hormone. However, apart from its gastrointestinal effects, studies have described that CCK also plays immunoregulatory roles. Taking in account the involvement of inducible nitric oxide synthase- (iNOS-) derived NO in the sepsis context, the present study was undertaken to investigate the role of CCK on iNOS expression in LPS-activated peritoneal macrophages. Our results revealed that CCK reduces NO production and attenuates the iNOS mRNA expression and protein formation. Furthermore, CCK inhibited the nuclear factor- (NF-) κB pathway reducing IκBα degradation and minor p65-dependent translocation to the nucleus. Moreover, CCK restored the intracellular cAMP content activating the protein kinase A (PKA) pathway, which resulted in a negative modulatory role on iNOS expression. In peritoneal macrophages, the CCK-1R expression, but not CCK-2R, was predominant and upregulated by LPS. The pharmacological studies confirmed that CCK-1R subtype is the major receptor responsible for the biological effects of CCK. These data suggest an anti-inflammatory role for the peptide CCK in modulating iNOS-derived NO synthesis, possibly controlling the macrophage activation through NF-κB, cAMP-PKA, and CCK-1R pathways. Based on these findings, CCK could be used as an adjuvant agent to modulate the inflammatory response and prevent systemic complications commonly found during sepsis.

CCK1-receptor stimulation protects against gut mediator-induced lung damage during endotoxemia

Background/Aims

Cholecystokinin 1-receptor (CCK1-R) activation by long chain fatty acid (LCFA) absorption stimulates vago-vagal reflex pathways in the brain stem. The present study determines whether this reflex also activates the cholinergic anti-inflammatory pathway, a pathway known to modulate cytokine release during endotoxemia.

Methods

Mesenteric lymph was obtained from wild type (WT) and CCK1-R knockout (CCK1-R^−/−) mice intraperitoneally challenged with Lipopolysaccharid (LPS) (endotoxemic lymph, EL) and intestinally infused with vehicle or LCFA-enriched solution. The lymph was analyzed for TNFα, IL-6 and IL-10 concentration and administered to healthy recipient mice via jugular infusion. Alveolar wall thickness, myeloperoxidase (MPO) and TUNEL positive cells were determined in lung tissue of recipient mice.

Results

LCFA infusion in WT mice reduced TNFα concentration in EL by 49% compared to vehicle infusion, but had no effect in CCK1-R^−/− mice. EL significantly increased the alveolar wall thickness, the number of MPO-positive and TUNEL-positive cells compared to control lymph administration. LCFA infusion in WT, but not in CCK1R^−/− mice, significantly reduced these pathological effects of EL.

Conclusion

During endotoxemia enteral LCFA absorption reduces TNFα release into mesenteric lymph and attenuates histomorphologic parameters of lung dysfunction. Failure to elicit this effect in CCK1R^−/− mice demonstrates that anti-inflammatory properties of LCFAs are mediated through CCK1-Rs.

The gut-liver axis

PURPOSE OF REVIEW

The liver adaptively responds to extra-intestinal and intestinal inflammation. In recent years, the role of the autonomic nervous system, intestinal failure and gut microbiota has been investigated in the development of hepatic, intestinal and extra-intestinal disease.

RECENT FINDINGS

The autonomic nervous system can be stimulated via enteral fat leading to cholecystokinin release, stimulating receptors in the gut and in the brain. This promotes bowel integrity, dampening the inflammatory response to food antigens. Consensus exists that intravenously administered long-chain fatty acids can cause liver damage but randomized-controlled trials are lacking. Disruption of the enterohepatic circulation of bile salts can give rise to cholestasis and nonalcoholic fatty liver disease, which may progress to fibrosis and cirrhosis. Reduced intestinal availability of bile salts reduces stimulation of the farnesoid X receptor. This may induce hepatic bile salt overload and associated hepatotoxicity through reduced action of intestinal fibroblast growth factor 19. Evidence is put forward to suggest that the intestinal microbiota is associated with liver abnormalities.

SUMMARY

Enteral lipids reduce inflammation and liver damage during stress or systemic inflammation, whereas parenteral lipid is associated with liver damage. Maintaining the enterohepatic circulation of bile salts limits hepatic cholestasis through an farnesoid X receptor feedback pathway. Changes in gut microbiota composition may induce liver disease.

Lipid-rich enteral nutrition regulates mucosal mast cell activation via the vagal anti-inflammatory reflex

Nutritional stimulation of the cholecystokinin-1 receptor (CCK-1R) and nicotinic acetylcholine receptor (nAChR)-mediated vagal reflex was shown to reduce inflammation and preserve intestinal integrity. Mast cells are important early effectors of the innate immune response; therefore modulation of mucosal mast cells is a potential therapeutic target to control the acute inflammatory response in the intestine. The present study investigates intestinal mast cell responsiveness upon nutritional activation of the vagal anti-inflammatory reflex during acute inflammation. Mucosal mast cell degranulation was induced in C57/Bl6 mice by administration of Salmonella enterica LPS. Lipid-rich enteral feeding prior to LPS significantly decreased circulatory levels of mouse mast cell protease at 30 min post-LPS compared with isocaloric low-lipid nutrition or fasting. CCK-1R blockage reversed the inhibitory effects of lipid-rich feeding, whereas stimulation of the peripheral CCK-1R mimicked nutritional mast cell inhibition. The effects of lipid-rich nutrition were negated by nAChR blockers chlorisondamine and α-bungarotoxin and vagal intestinal denervation. Accordingly, release of β-hexosaminidase by MC/9 mast cells following LPS or IgE-ovalbumin complexes was dose dependently inhibited by acetylcholine and nicotine. Application of GSK1345038A, a specific agonist of the nAChR α7, in bone marrow-derived mast cells from nAChR β2-/- and wild types indicated that cholinergic inhibition of mast cells is mediated by the nAChR α7 and is independent of the nAChR β2. Together, the present study reveals mucosal mast cells as a previously unknown target of the nutritional anti-inflammatory vagal reflex.

Neural networks in intestinal immunoregulation

Key physiological functions of the intestine are governed by nerves and neurotransmitters. This complex control relies on two neuronal systems: an extrinsic innervation supplied by the two branches of the autonomic nervous system and an intrinsic innervation provided by the enteric nervous system. As a result of constant exposure to commensal and pathogenic microflora, the intestine developed a tightly regulated immune system. In this review, we cover the current knowledge on the interactions between the gut innervation and the intestinal immune system. The relations between extrinsic and intrinsic neuronal inputs are highlighted with regards to the intestinal immune response. Moreover, we discuss the latest findings on mechanisms underlying inflammatory neural reflexes and examine their relevance in the context of the intestinal inflammation. Finally, we discuss some of the recent data on the identification of the gut microbiota as an emerging player influencing the brain function.

Continuous administration of enteral lipid- and protein-rich nutrition limits inflammation in a human endotoxemia model

OBJECTIVE

An overzealous inflammatory response is an important cause of morbidity and mortality in surgical, trauma, and critically ill patients. Enteral administration of lipid-rich nutrition was previously shown to attenuate inflammation and reduce organ damage via a cholecystokinin-1 receptor-mediated vagovagal reflex in animal studies. The current preclinical study investigates the immunomodulatory potential of a custom-made enteral nutrition during systemic inflammation in man.

DESIGN

Double-blind, randomized controlled trial.

SETTING

Intensive care research unit.

SUBJECTS

Male volunteers.

INTERVENTIONS

After an overnight fast, 18 healthy male subjects received an IV bolus of Escherichia coli lipopolysaccharide (2 ng/kg). Subjects in the fasted group (n = 6) were deprived of food throughout the study, while subjects in the intervention groups were fed either custom-made lipid- and protein-rich nutrition (n = 6) or isocaloric control nutrition (n = 6) via nasojejunal tube, starting 1 hour prior to lipopolysaccharide administration until 6 hours afterward.

MEASUREMENTS AND MAIN RESULTS

Bolus lipopolysaccharide administration resulted in a marked inflammatory response. Continuous postpyloric administration of nutrition significantly increased plasma cholecystokinin levels throughout the lipopolysaccharide-induced inflammatory response. Lipid- and protein-rich nutrition attenuated circulating levels of the proinflammatory cytokines tumor necrosis factor-α and interleukin-6 and the interleukin-1 receptor antagonist compared with control nutrition (all p < 0.05) and fasted subjects (all p < 0.05). In additional, lipid- and protein-rich nutrition augmented the anti-inflammatory response, reflected by increased plasma levels of interleukin-10 compared with fasted subjects (p < 0.0001).

CONCLUSIONS

The current preclinical study expands the immunomodulating effects of enteral nutrition as previously observed in rodents to man. Continuous administration of enteral nutrition resulted in a rapid anti-inflammatory effect. Furthermore, enrichment of the nutritional composition with lipid and protein was shown to enhance the anti-inflammatory potential. Therefore, continuous enteral administration of lipid- and protein-rich nutrition is a promising intervention to modulate the immune response in the early course of systemic inflammation in man.

The anti-inflammatory effect of the synthetic antimicrobial peptide 19-2.5 in a murine sepsis model: a prospective randomized study

Introduction

Increasing rates of multi-resistant bacteria are a major problem in the treatment of critically ill patients. Furthermore, conventional antibiotics lead to the release of bacterial derived membrane parts initiating pro-inflammatory cascades with potential harm to the patient. Antimicrobial peptides (AMP) may kill bacteria without releasing pro-inflammatory factors. Thus, we compared three newly developed synthetic anti-lipopolysaccharide peptides (SALPs) with a broader range of efficacy to suppress cytokine release in plasma and CD14 mRNA expression in organ tissue in a murine, polymicrobial sepsis model.

Methods

A randomized, experimental trial was conducted in an animal research facility. Male NMRI mice (n = 90; 8- to 12-weeks old) were randomized to the following six groups: (i) sham operation and parenteral vehicle (NaCl 0.9%) administration (sham); (ii) cecal ligation and puncture (CLP) and vehicle infusion (sepsis-control), (iii) CLP and polymyxin B infusion (polyB), or (iv to vi) CLP and infusion of three different synthetic antimicrobial peptides Peptide 19-2.5 (Pep2.5), Peptide 19-4 (Pep4) or Peptide 19-8 (Pep8). All animals underwent arterial and venous catheterization for hemodynamic monitoring 48 hours prior to CLP or sham-operation. Physical appearance and behavior (activity), plasma cytokine levels, and CD14 mRNA expression in heart, lung, liver, spleen and kidney tissue were determined 24 hours after CLP or sham operation.

Results

Only Pep2.5 significantly enhanced the activity after CLP, whereas none of the therapeutic regimens elevated the mean arterial pressure or heart rate. The strongly elevated IL-6, IL-10 and monocyte chemoattractant protein serum levels in septic animals were significantly reduced after Pep2.5 administration (P < 0.001, P < 0.001, and P < 0.001, respectively). Similarly, Pep2.5 significantly reduced the sepsis-induced CD14 mRNA expression in heart (P = 0.003), lung (P = 0.008), and spleen tissue (P = 0.009) but not in kidney and liver.

Conclusions

Structurally variable SALPs exhibit major differences in their anti-inflammatory effect in vivo. Continuous parenteral administration of Pep2.5 is able to reduce sepsis-induced cytokine release and tissue inflammation.

The clinical importance of the anti-inflammatory vagovagal reflex

Excessive activation of the immune system is prevented by anti-inflammatory mediators such as corticosteroids and anti-inflammatory cytokines. Recently, it became clear that the brain not only senses peripheral inflammation through vagal afferent nerve fibers, but also provides an integrated response dampening the immune system through vagal efferents. This so-called anti-inflammatory pathway has been introduced as a third system by which the immune system is modulated. In sepsis, the anti-inflammatory effect is mediated by modulation of splenic macrophages, whereas in the gut, vagal nerve fibers synapse with enteric cholinergic neurons interacting with resident intestinal macrophages. In this chapter, the preclinical data underscoring the importance of this pathway are summarized, and its clinical significance is reviewed. Finally, the current data supporting its relevance to human disease and its therapeutic potential will be discussed. Insight in the mechanisms underlying these crucial properties will lead to better understanding of immune-mediated diseases and ultimately to improved anti-inflammatory therapies.

The vagus nerve and the inflammatory reflex: wandering on a new treatment paradigm for systemic inflammation and sepsis

BACKGROUND

The immune system protects the host against dangerous pathogens and toxins. The central nervous system is charged with monitoring and coordinating appropriate responses to internal and external stimuli. The inflammatory reflex sits at the crossroads of these crucial homeostatic systems. This review highlights how the vagus nerve-mediated inflammatory reflex facilitates rapid and specific exchange of information between the nervous and immune systems to prevent tissue injury and infection.

METHODS

Review of the pertinent English-language literature. Nearly two decades of research has elucidated some of the essential anatomic, physiologic, and molecular connections of the inflammatory reflex. The original descriptions of how these key components contribute to afferent and efferent anti-inflammatory vagus nerve signaling are summarized.

RESULTS

The central nervous system recognizes peripheral inflammation via afferent vagus nerve signaling. The brain can attenuate peripheral innate immune responses, including pro-inflammatory cytokine production, leukocyte recruitment, and nuclear factor kappa β activation via α7-nicotinic acetylcholine receptor subunit-dependent, T-lymphocyte-dependent, vagus nerve signaling to spleen. This efferent arm of the inflammatory reflex is referred to as the "cholinergic anti-inflammatory pathway." Activation of this pathway via vagus nerve stimulation or pharmacologic α7 agonists prevents tissue injury in multiple models of systemic inflammation, shock, and sepsis.

CONCLUSIONS

The vagus nerve-mediated inflammatory reflex is a powerful ally in the fight against lethal tissue damage after injury and infection. Further studies will help translate the beneficial effects of this pathway into clinical use for our surgical patients.

Chylomicron formation and glucagon-like peptide 1 receptor are involved in activation of the nutritional anti-inflammatory pathway

Enteral administration of lipid-enriched nutrition effectively attenuates inflammation via a cholecystokinin (CCK)-mediated vagovagal anti-inflammatory reflex. Cholecystokinin release and subsequent activation of the vagus are dependent on chylomicron formation and associated with release of additional gut peptides. The current study investigates the intestinal processes underlying activation of the CCK-mediated vagal anti-inflammatory pathway by lipid-enriched nutrition. Rats and mice were subjected to hemorrhagic shock (HS) or endotoxemia, respectively. Prior to the experimental procedures, animals were fasted or fed lipid-enriched nutrition. Pluronic L-81 (L-81) was added to the feeding to investigate involvement of chylomicron formation in activation of mesenteric afferent fibers and the immune-modulating potential of lipid-enriched nutrition. Ob/Ob mice and selective receptor antagonists were used to study the role of leptin, glucagon-like peptide 1 and peptide YY in activation of the nutritional reflex. Electrophysiological analysis of mesenteric afferents in mice revealed that lipid-enriched nutrition-mediated neural activation was abrogated by L-81 (P<.05). L-81 blunted the beneficial effects of lipid-enriched nutrition on systemic inflammation and intestinal integrity in both species (all parameters, P<.01). Ob/Ob mice required a higher dose of nutrition compared with wild-type mice to attenuate plasma levels of TNF-α and ileum-lipid binding protein, a marker for enterocyte damage (both P<.01), suggesting a higher stimulation threshold in leptin-deficient mice. Administration of a glucagon-like peptide 1-receptor antagonist, but not leptin or peptide YY antagonists, suppressed the effects of lipid-enriched nutrition. These data indicate that chylomicron formation is essential and activation of the glucagon-like peptide 1-receptor is involved in activation of the nutritional anti-inflammatory pathway by lipid-enriched nutrition.