A novel human macrophage-derived intestinal mucin secretagogue: implications for the pathogenesis of inflammatory bowel disease

Macrophages play a role in inflammatory transformation of colorectal cancer

Colorectal cancer (CRC) is one of the most common and fatal cancers worldwide, and it is also a typical inflammatory cancer. The function of macrophages is very important in the tissue immune microenvironment during inflammatory and carcinogenic transformation. Here, we evaluated the function and mechanism of macrophages in intestinal physiology and in different pathological stages. Furthermore, the role of macrophages in the immune microenvironment of CRC and the influence of the intestinal population and hypoxic environment on macrophage function are summarized. In addition, in the era of tumor immunotherapy, CRC currently has a limited response rate to immune checkpoint inhibitors, and we summarize potential therapeutic strategies for targeting tumor-associated macrophages.

Macrophage polarization in intestinal inflammation and gut homeostasis

Gut homeostasis is a process that requires a prudent balance of host responses to the beneficial enteric microbial community and the pathogenic stimuli that can arise. The lack of this balance in the intestine can result in inflammatory bowel diseases, where the immune system dysfunctions leading to exacerbated inflammatory responses. In this process, macrophages are considered to play a pivotal role. In this review, we describe the important role of macrophages in maintaining intestinal homeostasis and we discuss how altered macrophage function may lead to inflammatory bowel diseases. The plasticity of macrophages during the gut inflammatory response shows the broad role of these cells in orchestrating not only the onset of inflammation but also its termination as well as healing and repair. Indeed, the state of macrophage polarization can be the key factor in defining the resolution or the progression of inflammation and disease. Here, we discuss the different populations of macrophages and their implication in development, propagation, control and resolution of inflammatory bowel diseases.

Anti-HIV effects of chloroquine: inhibition of viral particle glycosylation and synergism with protease inhibitors

OBJECTIVE

We tested the effects of chloroquine (CQ) on glycosylation of HIV particles and in combination with protease inhibitors (PIs) on HIV replication and on P-glycoprotein (P-gp)/multidrug resistance protein-1 (MRP1).

DESIGN

CD4 cell lines were infected with laboratory strains and peripheral blood mononuclear cells were infected with primary isolates for evaluation of the anti-HIV effects. Peripheral blood lymphocytes were evaluated for of P-gp and MRP1 functions.

METHODS

HIV replication was assessed by enzyme-linked immunosorbent assay. HIV glycosylation was measured by metabolic labeling of viral particles with [H] glucosamine. Synergism was tested using isobolograms. P-gp and MRP1 functions were assayed using rhodamine 123 (Rh123) and carboxyfluorescein (CF) efflux assays, respectively.

RESULTS

CQ alone inhibited HIV replication and glycosylation in a dose-dependent manner. In combination with indinavir (IDV), ritonavir, or saquinavir (SQV), CQ had a synergistic effect at concentrations found in plasma of subjects receiving malaria prophylaxis. CQ decreased the 50% effective concentration of IDV in primary isolates from Africa and restored the response to IDV or SQV in 3 PI-resistant isolates. CQ increased the block of Rh123 and CF efflux activity exerted by PIs.

CONCLUSION

The inhibitory effects of CQ on HIV glycosylation are associated with synergistic effects in combination with PIs. The CQ/PI combination exerts combined inhibitory effects on P-gp and MRP1 function.

Interleukin 16 is up-regulated in Crohn's disease and participates in TNBS colitis in mice

BACKGROUND & AIMS

Interleukin (IL)-16 is a T lymphocyte- derived cytokine that uses CD4 as its receptor and hence selectively recruits CD4-bearing cells. Infiltrating CD4(+) T cells are a feature of Crohn's disease; however, the role of IL-16 in intestinal inflammation is unknown. The aim of this study was to determine whether IL-16 production is increased in inflammatory bowel disease and whether IL-16 participates in trinitrobenzene sulfonic acid (TNBS)-induced colitis in mice.

METHODS

IL-16 messenger RNA and protein levels in inflammatory bowel disease tissues were determined by reverse-transcription polymerase chain reaction and enzyme-linked immunosorbent assay. C57BL/6 or BALB/c mice were treated with vehicle, TNBS alone, TNBS + anti-IL-16 monoclonal antibody (mAb), TNBS + control mAb, or were untreated. Colonic injury and inflammation were evaluated after 3 or 10 days.

RESULTS

Colonic IL-16 protein levels were increased in patients with Crohn's disease (P<0.05) but not ulcerative colitis. Anti-IL-16 mAb treatment significantly reduced TNBS-induced weight loss (P< 0.001), mucosal ulceration (P<0.05), myeloperoxidase activity (P< 0.001), and TNBS-mediated increases in mucosal levels of IL-1beta (P<0.05) and tumor necrosis factor alpha (P<0.01).

CONCLUSIONS

Anti-IL-16 mAb reduced colonic injury and inflammation induced by TNBS in mice. Colonic mucosal IL-16 levels were elevated in Crohn's disease, suggesting a role for IL-16 in the pathophysiology of inflammatory bowel disease.

Claudins regulate the intestinal barrier in response to immune mediators

BACKGROUND & AIMS

To determine the functional role of immune mediators in the formation of the intestinal barrier, we have examined the regulation of claudin expression by interleukin (IL)-17 in human intestinal epithelial cells.

METHODS

Expression of claudins, extracellular signal-related (ERK) mitogen-activated protein kinases (MAPKs), and activated ERK MAPKs was determined by immunoblotting. Claudin membrane association was assessed by immunohistochemistry and claudin messenger RNA expression by Northern blot analysis. Intestinal epithelial barrier function was characterized through transepithelial electrical resistance and mannitol tracer flux.

RESULTS

IL-17 induced the development of a paracellular barrier of T84 cell monolayers. Inhibition of ERK activation with the MEK inhibitor PD98059 blocked IL-17 as well as basal development of tight junctions in T84 cells. IL-17 induced formation of tight junctions correlated with up-regulation of claudin-1 and claudin-2 gene transcription. Inhibition of MEK reduced the activated and basal expression of claudin-2 messenger RNA and protein expression. Functional MEK was required for the expression and membrane association of claudin-2 but not claudin-1 in T84 cells.

CONCLUSIONS

MEK activity is required for claudin-mediated formation of tight junctions. IL-17 is able to regulate the intestinal barrier through the ERK MAPK pathway.

The key role of macrophages in the immunopathogenesis of inflammatory bowel disease

Macrophages are important in the host's immunological and inflammatory responses. There is a large population of these cells in the normal intestinal mucosa where they represent the major antigen presenting cell population capable of determining the type of T cell responses that develop to luminal antigens. Studies suggest that the normal intestinal macrophages cannot be easily induced to mediate acute inflammatory responses. In active inflammatory bowel disease there is an increase in the mucosal macrophage population, derived from circulating monocytes. These recruited macrophages are phenotypically different from the resident population of cells and play a major role in mediating the chronic mucosal inflammation seen in patients with ulcerative colitis and Crohn's disease. They secrete many cytokines that are important in the proinflammatory responses, such as interleukin (IL)-1, IL-6, IL-8, IL-12, IL-18, and tumor necrosis factor-alpha. They also release reactive metabolites of oxygen and nitrogen and proteases that degrade the extracellular matrix. Macrophages also appear to be important during resolution of inflammation and repair of the intestinal mucosa that occurs during disease remission.

Mucin secretion in inflammatory bowel disease: comparison of a macrophage-derived mucin secretagogue (MMS-68) to conventional secretagogues

We have described a novel macrophage-derived mucin secretagogue (MMS-68) that mediates mucin secretion in colon cancer cell lines and explants of normal and inflammatory bowel disease (IBD) mucosa. We compared MMS-68 induced mucin release with other known intestinal mucin secretagogues in normal colon explants and in the HT-29 colon cancer cell line, and to study the effects of MMS-68 on mucin release from inflamed and uninflamed ulcerative colitis (UC) and Crohn's disease (CD) mucosa. In normal colonic explants and HT-29 cells, each of the secretagogues including, MMS-68-induced mucin release two- to fivefold more than culture medium alone. In HT-29 cells, MMS-68 plus leukotriene C4 (LTC4) induced a 50% increase in mucin release over either secretagogue alone, and MMS-68 plus platelet-activating factor (PAF) markedly enhanced mucin release by eightfold over either secretagogue. In colonic explants from patients with UC and CD, the mucin release in response to MMS-68 was similar to that of normal colonic explants. Likewise, in isolated epithelial cells from CD and UC (whether involved or uninvolved), MMS-68-induced release was similar to that of epithelial cells isolated from normal colonic mucosa. The number of MMS-68-producing macrophages was lower in uninflamed UC mucosa compared with inflamed UC mucosa and CD mucosa. The mucin secretagogue activity of MMS-68 is comparable to that of other known secretagogues, and PAF can have a synergistic effect on this activity. Whole tissue explants and isolated colonic epithelial cells from patients with IBD respond at least as well as their normal counterparts to MMS-68. MMS-68 may play a role in mucin secretion in normal and inflamed colonic tissue.

Increased substance P responses in dorsal root ganglia and intestinal macrophages during Clostridium difficile toxin A enteritis in rats

Previously we reported that pretreatment of rats with the substance P (SP) antagonist CP-96,345 inhibits the enterotoxic responses following administration of toxin A from Clostridium difficile into ileal loops, indicating that SP participates in the intestinal responses to this toxin. We now report that injection of toxin A into rat ileum causes a rapid increase in SP content in lumbar dorsal root ganglia (DRG) and mucosal scrapings 30-60 min after toxin A administration. Toxin A-mediated fluid secretion, mannitol permeability, and ileal histologic damage is significantly increased only after 2 hr. Toxin A also causes an increase in the abundance of SP mRNA in lumbar DRG and ileal mucosa as measured by reverse transcription-PCR. Lamina propria macrophages (LPMs) obtained from toxin A-injected loops release greater amounts of tumor necrosis factor alpha (TNFalpha) and SP as compared with LPMs isolated from buffer-injected loops (P < 0.01). Pretreatment of rats with the SP antagonist CP-96,345 inhibits toxin A-mediated TNFalpha release from isolated LPMs, whereas an inactive enantiomer (CP-96,344) of the SP antagonist has no effect. LPMs obtained from toxin A-injected ileal loops incubated in vitro with SP (10(-8) to 10(-9) M) show enhanced TNFalpha secretion, whereas LPMs isolated from buffer-injected loops do not respond to SP. In addition, LPMs obtained from toxin A-injected ileal loops incubated in vitro with CP-96,345 showed a diminished TNFalpha release. Our results indicate that activated LPMs secrete SP during toxin A enteritis that can lead to secretion of cytokines, suggesting an autocrine/paracrine regulation of cytokine secretion by SP from LPMs during intestinal inflammation.

Effects of perorally applied endotoxin on colonic mucins of germfree rats

BACKGROUND

The intestinal epithelium, with the potential to restrict luminal noxae from the host, secretes a mucous layer with various protective functions. Microbial colonization of germfree (GF) rats stimulates this mucin-secreting tissue. The present study determined the effect of bacterial lipopolysaccharides (LPS) on this process.

METHODS

One, 3, and 5 days after peroral application of 35 micrograms LPS/100 g body weight (from Escherichia coli O55:B5), LPS concentrations were monitored in ingesta, intestinal tissue, and liver. Mucin high molecular weight glycoproteins (HMG), released in response to LPS, were isolated and separated into mucins, i) attached to the colonic epithelium (EM) and ii) mixed to the luminal content (LM), respectively. Subsequently, the binding capacity of both mucin fractions for various lectins and for type-1 pili expressing E. coli was determined.

RESULTS

Ingesta and tissue had maximal LPS concentrations on days 3 (jejunum) and 5 (colon). Maximal EM secretion was found on day 3, release of LM further increased to day 5. Both mucin fractions had altered glycosylation patterns: augmentation of beta-galactose, alpha-N-acetyl galactosamine, and mannose coincided with a decrease in alpha-fucose. Compared with the controls, attachment of E. coli to EM increased slightly on day 1 only; the binding capacity of LM increased continuously up to day 5.

CONCLUSION

Results suggest that mucins, released in response to LPS, in addition to the epithelial protection, support the gut microbial clearance system.