Effects of lipopolysaccharide on gastric stasis: role of cyclooxygenase

Targeting Mechano-Transcription Process as Therapeutic Intervention in Gastrointestinal Disorders

Mechano-transcription is a process whereby mechanical stress alters gene expression. The gastrointestinal (GI) tract is composed of a series of hollow organs, often encountered by transient or persistent mechanical stress. Recent studies have revealed that persistent mechanical stress is present in obstructive, functional, and inflammatory disorders and alters gene transcription in these conditions. Mechano-transcription of inflammatory molecules, pain mediators, pro-fibrotic and growth factors has been shown to play a key role in the development of motility dysfunction, visceral hypersensitivity, inflammation, and fibrosis in the gut. In particular, mechanical stress-induced cyclooxygenase-2 (COX-2) and certain pro-inflammatory mediators in gut smooth muscle cells are responsible for motility dysfunction and inflammatory process. Mechano-transcription of pain mediators such as nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) may lead to visceral hypersensitivity. Emerging evidence suggests that mechanical stress in the gut also leads to up-regulation of certain proliferative and pro-fibrotic mediators such as connective tissue growth factor (CTGF) and osteopontin (OPN), which may contribute to fibrostenotic Crohn's disease. In this review, we will discuss the pathophysiological significance of mechanical stress-induced expression of pro-inflammatory molecules, pain mediators, pro-fibrotic and growth factors in obstructive, inflammatory, and functional bowel disorders. We will also evaluate potential therapeutic targets of mechano-transcription process for the management of these disorders.

Laparotomy attenuates lipopolysaccharide-induced gastric bleeding in the rat

Lipopolysaccharide (LPS) increases systemic inflammation and causes duodenogastric reflux of bile and gastric bleeding. Laparotomy prevents gastric injury from the luminal irritant bile, but its effects on LPS-induced gastric injury are unknown. We hypothesized that laparotomy would diminish inflammation and attenuate gastric bleeding caused by LPS. In the rat, laparotomy, done either before or after administration of LPS, attenuated LPS-induced bile reflux, gastric bleeding, and cyclooxygenase-2, but not inducible nitric oxide synthase, expression when compared to controls given LPS. Laparotomy also blunted LPS-induced changes in serum cytokine production. These data suggest that laparotomy has gastroprotective effects by preventing LPS-induced bile reflux and gastric bleeding and by a mechanism mediated, at least in part by cyclooxygenase-2.

Ketamine suppresses LPS-induced bile reflux and gastric bleeding in the rat

BACKGROUND

Although ketamine has many beneficial effects in a rat model of noninfectious inflammation with lipopolysaccharide (LPS), its effects on gut ileus are unknown. We hypothesized that ketamine would improve LPS-induced ileus and therefore examined its effects on gastric emptying and intestinal transit as well as duodenogastric bile reflux and associated gastric bleeding.

METHODS

Male rats received saline or ketamine (7 mg/kg ip) 1 hour before saline or LPS (20 mg/kg ip) for 5 hours. Thirty minutes before killing, rats received orogastric rhodamine B isothiocyanate-labeled dextran and 5 minutes later fluorescein isothiocyanate-labeled dextran via a duodenal catheter. GI contents were collected for dye, bile acid, and hemoglobin (index of bleeding) determinations.

RESULTS

LPS significantly impaired intestinal transit and increased duodenogastric bile reflux and gastric luminal hemoglobin content. Ketamine improved intestinal transit, prevented LPS-induced bile reflux, and diminished gastric bleeding. In mechanistic studies, ketamine also attenuated LPS-induced upregulation of the proinflammatory genes inducible nitric oxide synthase and cyclo-oxygenase-2 in the stomach but preserved expression of the anti-inflammatory gene heme-oxygenase-1 (Western blot).

CONCLUSIONS

These data suggest that ketamine may prevent LPS-induced gastric bleeding by decreasing bile reflux through improved intestinal transit or by local changes in nitric oxide, prostaglandin, and carbon monoxide metabolism.

Ketamine Attenuates Early Lipopolysaccharide-Induced Gastric Dysfunction: Role of Stress-Inducible Phosphoproteins

BACKGROUND

Ketamine exerts anti-inflammatory actions and attenuates lipopolysaccharide (LPS)-induced gastric dysfunction by an unknown mechanism. Because stress-inducible phosphoproteins mediate many inflammatory responses, we hypothesized that ketamine would disrupt the early signaling events of LPS-induced inflammation by altering phosphorylation of stress-inducible phosphoproteins JNK, p38, and IkB.

METHODS

Adult rats received saline or ketamine (70 mg/kg, intraperitoneal) 1 hour before LPS (20 mg/kg, intraperitoneal) or saline. Animals were killed at 15, 30, 45, and 60 minutes after LPS, gastric mucosa was harvested, and gastric volume and pH were recorded. Gastric mucosal phosphorylation of JNK, p38, and IkB-alpha were analyzed with a multiplexed suspension immunoassay.

RESULTS

Ketamine-attenuated LPS induced increases in gastric luminal fluid and pH. Control animals receiving saline or ketamine and no LPS had gastric volumes of 0.1 mL and luminal pH of 2 at all time points. LPS upregulated phosphorylation of JNK, p38, and IkB-alpha as early as 15 minutes after LPS. Ketamine did not effect the early phosphorylation of these proteins.

CONCLUSION

Endotoxin causes gastric dysfunction and upregulates stress-inducible phosphoproteins within minutes after LPS. Although ketamine attenuates gastric dysfunction, its salutary effects do not seem to be related to alterations in phosphorylation of JNK, p38, or IkB-alpha.