Inhibition of α2A-Adrenoceptors Ameliorates Dextran Sulfate Sodium-Induced Acute Intestinal Inflammation in Mice

The sympathetic nervous system drives hyperinflammatory responses to Clostridioides difficile infection

Clostridioides difficile infection (CDI) is a leading cause of hospital-acquired infections in the United States, known for triggering severe disease by hyperactivation of the host response. In this study, we determine the impact of the sympathetic nervous system (SNS) on CDI disease severity. Mouse models of CDI are administered inhibitors of SNS activity prior to CDI. Chemical sympathectomy or pharmacological inhibition of norepinephrine synthesis greatly reduces mortality and disease severity in the CDI model. Pharmacological blockade or genetic ablation of the alpha 2 adrenergic receptor ameliorates intestinal inflammation, disease severity, and mortality rate. These results underscore the role of the SNS and the alpha 2 adrenergic receptor in CDI pathogenesis and suggest that targeting neural systems could be a promising approach to therapy in severe disease.

A dual role of lysophosphatidic acid type 2 receptor (LPAR2) in nonsteroidal anti-inflammatory drug-induced mouse enteropathy

Lysophosphatidic acid (LPA) is a bioactive phospholipid mediator that has been found to ameliorate nonsteroidal anti-inflammatory drug (NSAID)-induced gastric injury by acting on lysophosphatidic acid type 2 receptor (LPAR2). In this study, we investigated whether LPAR2 signaling was implicated in the development of NSAID-induced small intestinal injury (enteropathy), another major complication of NSAID use. Wild-type (WT) and Lpar2 deficient (Lpar2-/-) mice were treated with a single, large dose (20 or 30 mg/kg, i.g.) of indomethacin (IND). The mice were euthanized at 6 or 24 h after IND treatment. We showed that IND-induced mucosal enteropathy and neutrophil recruitment occurred much earlier (at 6 h after IND treatment) in Lpar2-/- mice compared to WT mice, but the tissue levels of inflammatory mediators (IL-1β, TNF-α, inducible COX-2, CAMP) remained at much lower levels. Administration of a selective LPAR2 agonist DBIBB (1, 10 mg/kg, i.g., twice at 24 h and 30 min before IND treatment) dose-dependently reduced mucosal injury and neutrophil activation in enteropathy, but it also enhanced IND-induced elevation of several proinflammatory chemokines and cytokines. By assessing caspase-3 activation, we found significantly increased intestinal apoptosis in IND-treated Lpar2-/- mice, but it was attenuated after DBIBB administration, especially in non-obese diabetic/severe combined immunodeficiency (NOD/SCID) mice. Finally, we showed that IND treatment reduced the plasma activity and expression of autotaxin (ATX), the main LPA-producing enzyme, and also reduced the intestinal expression of Lpar2 mRNA, which preceded the development of mucosal damage. We conclude that LPAR2 has a dual role in NSAID enteropathy, as it contributes to the maintenance of mucosal integrity after NSAID exposure, but also orchestrates the inflammatory responses associated with ulceration. Our study suggests that IND-induced inhibition of the ATX-LPAR2 axis is an early event in the pathogenesis of enteropathy.

Optogenetic activation of local colonic sympathetic innervations attenuates colitis by limiting immune cell extravasation

The sympathetic nervous system is composed of an endocrine arm, regulating blood adrenaline and noradrenaline, and a local arm, a network of fibers innervating immune organs. Here, we investigated the impact of the local arm of the SNS in an inflammatory response in the colon. Intra-rectal insertion of an optogenetic probe in mice engineered to express channelrhodopsin-2 in tyrosine hydroxylase cells activated colonic sympathetic fibers. In contrast to systemic application of noradrenaline, local activation of sympathetic fibers attenuated experimental colitis and reduced immune cell abundance. Gene expression profiling showed decreased endothelial expression of the adhesion molecule MAdCAM-1 upon optogenetic stimulation; this decrease was sensitive to adrenergic blockers and 6-hydroxydopamine. Antibody blockade of MAdCAM-1 abrogated the optogenetic effect on immune cell extravasation into the colon and the pathology. Thus, sympathetic fibers control colonic inflammation by regulating immune cell extravasation from circulation, a mechanism likely relevant in multiple organs.

Analysing the effect of I1 imidazoline receptor ligands on DSS-induced acute colitis in mice

Imidazoline receptors (IRs) have been recognized as promising targets in the treatment of numerous diseases; and moxonidine and rilmenidine, agonists of I₁-IRs, are widely used as antihypertensive agents. Some evidence suggests that IR ligands may induce anti-inflammatory effects acting on I₁-IRs or other molecular targets, which could be beneficial in patients with inflammatory bowel disease (IBD). On the other hand, several IR ligands may stimulate also alpha₂-adrenoceptors, which were earlier shown to inhibit, but in more recent studies to rather aggravate colitis. Hence, this study aimed to analyse for the first time the effect of various I₁-IR ligands on intestinal inflammation. Colitis was induced in C57BL/6 mice by adding dextran sulphate sodium (DSS) to the drinking water for 7 days. Mice were treated daily with different IR ligands: moxonidine and rilmenidine (I₁-IR agonists), AGN 192403 (highly selective I₁-IR ligand, putative antagonist), efaroxan (I₁-IR antagonist), as well as with the endogenous IR agonists agmatine and harmane. It was found that moxonidine and rilmenidine at clinically relevant doses, similarly to the other IR ligands, do not have a significant impact on the macroscopic and histological signs of DSS-evoked inflammation. Likewise, colonic myeloperoxidase and serum interleukin-6 levels remained unchanged in response to these agents. Thus, our study demonstrates that imidazoline ligands do not influence significantly the severity of DSS-colitis in mice and suggest that they probably neither affect the course of IBD in humans. However, the translational value of these findings needs to be verified with other experimental colitis models and human studies.