Many factors, such as medication (e.g., antibiotic use), infection, diet, and ingestion of toxic chemicals, http://www.selleckchem.com/products/Lenalidomide.html can dramatically alter gut microbial composition. Enhanced gram-negative bacteria in the gut can result in elevated LPS level in the intestine, which subsequently contributes to the development and progress of intestinal inflammation. Similarly, TLR4 was suggested to be strongly upregulated in IBD patients (2), and a TLR4 antagonist was shown to ameliorate mouse experimental colitis (12). In addition, LPS was suggested to have a critical impact on the pathophysiology of necrotizing enterocolitis (NEC) (18). On the basis of these considerations, LPS-TLR4 engagement is believed to be implicated in the pathophysiology of intestinal inflammatory diseases.
On the other hand, LPS normally present in the gut is believed to be harmless, whereas systemic LPS exposure causes systemic sepsis. To explain why LPS is harmless in the healthy intestine, it has been suggested that the normal intestinal epithelium, which is constantly exposed to gut microbes, might be hyporesponsive to luminal LPS (1, 25). Any direct effect of LPS inside the colon, however, remains to be elucidated. Accordingly, we examined whether elevated LPS in the colon could induce inflammatory responses. To avoid the systemic effect from oral, intraperitoneal, or intravenous administration of LPS and to study direct effects of LPS in the colon, mice were instilled with LPS by rectal enema.
We found that elevated LPS inside the colon elicits transient inflammation in the small intestine, not in the colon, of the normal mouse, and such intestinal inflammation is substantially exacerbated in immune modulator-impaired, such as IL-10?/? or Rag-1?/?, mice. Our results provide evidence that elevated LPS in the colon has the potential to initiate inflammatory responses in the intestine and, therefore, suggest a mechanistic explanation for the importance of maintaining the balance between gram-negative and gram-positive bacteria in the intestine to maintain gut homeostasis. MATERIALS AND METHODS Mice. C57BL/6, CD-1, C3H/HeJ, C3H/HeOuJ, IL-10?/? (C57BL/6 background), and Rag-1?/? mice (8 wk old) were purchased from Jackson Laboratory (Bar Harbor, ME). All mice were housed in a specific pathogen-free facility of the Division of Laboratory Animal Medicine at the University of California Los Angeles (UCLA).
The Institutional Animal Care and Use Committee of UCLA approved all animal procedures. Reagents. Ultrapure LPS (purified from Escherichia coli 0111:B4) and peptidoglycan (PGN) were purchased from InvivoGen (San Diego, CA). Recombinant mouse IL-10 was purchased from Biosource International (Camarillo, CA). Limulus amebocyte lysate test kit and purified flagellin were obtained AV-951 from Lonza (Basel, Switzerland). Intracolonic administration of LPS.