Imidazoline versus alpha2-adrenoceptors in the control of gastric motility in mice

Antibiotic-induced decrease of bacterial load in guinea pig intestine reduces α2-adrenoceptor expression and activity in peristaltic motor inhibition

BACKGROUND AND PURPOSE

The use of analgosedatives in critically ill patients carries the risk of impairing gastrointestinal (GI) propulsion and could thereby lead to sepsis. The gut microbiota can influence GI motility, but whether GI microbial dysbiosis modifies GI peristalsis impairment by analgosedative drugs has not yet been analysed. This question was addressed in the guinea pig small intestine following a decrease of bacterial load by antibiotic pretreatment.

EXPERIMENTAL APPROACH

Guinea pigs were enorally (within the mouth) pretreated with meropenem, neomycin and vancomycin, and antibiotic-induced decrease of bacterial load was confirmed by 16S rDNA sequencing. Peristalsis in the isolated guinea pig small intestine was evaluated by determining the pressure threshold at which a peristaltic wave is triggered. The expression of factors that may be relevant to communication between GI microbiota and the motor system was examined at the mRNA (quantitative (q)PCR]) and/or protein (enzyme-linked immunosorbent assay [ELISA]) level.

KEY RESULTS

Antibiotic treatment disturbed the small intestinal microbiome as shown by decrease of bacterial load and reduced alpha diversity. Microbial dysbiosis did not affect peristalsis at baseline but blunted the ability of α2 agonists to inhibit peristalsis, while the anti-peristaltic effects of sufentanil, midazolam, neostigmine and propofol were inconsistently affected. These functional alterations were complemented by a decreased expression of α2-adrenoceptors, toll-like receptors (TRL) 3, 4 & 7, IFN-γ and iNOS.

CONCLUSION AND IMPLICATIONS

Antibiotic-induced decrease of bacterial load in the small intestine selectively blunts the ability of α2 agonists to impair peristalsis. This effect is explained by decreased α2-adrenoceptor expression, which may arise from TLR down-regulation in the dysbiotic gut.

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.

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

It has been hypothesized that α2-adrenoceptors (α2-ARs) may be involved in the pathomechanism of colitis; however, the results are conflicting because both aggravation and amelioration of colonic inflammation have been described in response to α2-AR agonists. Therefore, we aimed to analyze the role of α2-ARs in acute murine colitis. The experiments were carried out in wild-type, α2A-, α2B-, and α2C-AR knockout (KO) C57BL/6 mice. Colitis was induced by dextran sulfate sodium (DSS, 2%); alpha2-AR ligands were injected i.p. The severity of colitis was determined both macroscopically and histologically. Colonic myeloperoxidase (MPO) and cytokine levels were measured by enzyme-linked immunosorbent assay and proteome profiler array, respectively. The nonselective α2-AR agonist clonidine induced a modest aggravation of DSS-induced colitis. It accelerated the disease development and markedly enhanced the weight loss of animals, but did not influence the colon shortening, tissue MPO levels, or histologic score. Clonidine induced similar changes in α2B- and α2C-AR KO mice, whereas it failed to affect the disease activity index scores and caused only minor weight loss in α2A-AR KO animals. In contrast, selective inhibition of α2A-ARs by BRL 44408 significantly delayed the development of colitis; reduced the colonic levels of MPO and chemokine (C-C motif) ligand 3, chemokine (C-X-C motif) ligand 2 (CXCL2), CXCL13, and granulocyte-colony stimulating factor; and elevated that of tissue inhibitor of metalloproteinases-1. In this work, we report that activation of α2-ARs aggravates murine colitis, an effect mediated by the α2A-AR subtype, and selective inhibition of these receptors reduces the severity of gut inflammation.

Nanocrystalline cerium dioxide efficacy for gastrointestinal motility: potential for prokinetic treatment and prevention in elderly

BACKGROUND

Constipation is a common condition, with prevalence after 65 years, is a major colorectal cancer risk factor. Recent works have demonstrated advances in personalized, preventive nanomedicine, leading to the construction of new materials and nanodrugs, in particular, nanocrystalline cerium dioxide (NCD), having strong antioxidative prebiotic effect. The aim of our study was to investigate the influence of NCD on motor function of the stomach and colon in vivo and contractive activity of smooth muscles in different year-old rats.

METHODS

We included 80 rats: 3- (weight 130-160 g, n = 40) and 24-month old (weight 390-450 g, n = 40), divided into four groups as follows: І-control group; rats of II-ІV groups were injected intragastrically one injection per day during 10 days, 3 ml of water 3 ml/kg stabilizing solution, аnd 1 mmol/ml NCD, respectively. In all animals, we recorded spontaneous and carbachol-stimulated (0.01 mg/kg) gastrointestinal tract motor activity. We used the index of motor activity (IMA), expressed in cmH2O, for characterization of the motor function. We investigated smooth muscle contraction by tenzometric method, studied the spontaneous and stimulated motility by ballonographic method.

RESULTS

IMA reduced by 21.1 + 0.2% (p < 0.01) in the old rats of the control group compared with the young rats. A 10-day administration of NCD increased IMA in the stomach of young rats by 9.3% (р < 0.001) vs the control group. The exposure of NCD increased the amplitude of contraction to 34.2 ± 5.4 mN (n = 10) in the stomach of old rats and increased by 32.1 ± 2.4% vs the control group (p < 0.05). NCD did not influence acetylcholine (ACh) contractions in the stomach of young rats; however, in the stomach of old rats, V nr increased by 90 ± 15.2% (р < 0.001).

CONCLUSIONS

The index of motor activity is decreased in old rats. Nanocrystalline cerium dioxide increased the index of motor activity in all groups of rats and also evoked a significant increase of colon contractions in old rats.