Irritable Bowel Syndrome: Peripheral Mechanisms and Therapeutic Implications

PPARγ activation attenuates neonatal CRD-induced visceral pain sensitization and anxiety in male rats by alleviating oxidative stress

BACKGROUND

Visceral pain sensitization and emotional reactions due to irritable bowel syndrome (IBS) occur frequently in the general population. Oxidative stress plays a crucial role in the pathogenesis of IBS. Previous studies have demonstrated that activation of peroxisome proliferator-activated receptor gamma (PPARγ) has analgesic effects. Therefore, we aimed to determine whether PPARγ activation ameliorates oxidative stress and affects thus nociceptive sensitization and emotional responses in IBS.

METHODS

The study utilized male Sprague-Dawley (SD) rats, that suffered from neonatal colorectal distension (CRD), to assess the effects of various doses of rosiglitazone on visceral hyperalgesia and anxiety. Electromyography (EMG) of the external abdominal oblique muscles was used to evaluate visceral hypersensitivity, and Open Field Test (OFT) and Elevated Plus Maze (EPM) were used to evaluate anxiety. Superoxide dismutase (SOD) and malondialdehyde (MDA) in the spinal cord were analyzed by water-soluble tetrazolium-1 (WST-1) and thiobarbituric acid (TBA) methods, respectively, the expression levels of PPARγ in the spinal cord were assessed by qRT-PCR and Western blotting.

RESULTS

Neonatal CRD-induced rats showed visceral pain sensitization and anxiety in adulthood, with down-regulated expression of PPARγ and SOD and elevated MDA levels in the spinal cord. Rosiglitazone alleviated visceral hypersensitivity and anxiety by activating PPARγ protein expression and promoting MDA up-regulation and SOD down-regulation in the spinal cord, which were reversed by GW9662, an antagonist of PPARγ.

CONCLUSION

This study demonstrated that rosiglitazone alleviated visceral pain sensitization and anxiety in male IBS rats by alleviating oxidative stress through activation of PPARγ.

Long-Term Implicit Epigenetic Stress Information in the Enteric Nervous System and its Contribution to Developing and Perpetuating IBS

Psychiatric and mood disorders may play an important role in the development and persistence of irritable bowel syndrome (IBS). Previously, we hypothesized that stress-induced implicit memories may persist throughout life via epigenetic processes in the enteric nervous system (ENS), independent of the central nervous system (CNS). These epigenetic memories in the ENS may contribute to developing and perpetuating IBS. Here, we further elaborate on our earlier hypothesis. That is, during pregnancy, maternal prenatal stresses perturb the HPA axis and increase circulating cortisol levels, which can affect the maternal gut microbiota. Maternal cortisol can cross the placental barrier and increase cortisol-circulating levels in the fetus. This leads to dysregulation of the HPA axis, affecting the gut microbiota, microbial metabolites, and intestinal permeability in the fetus. Microbial metabolites, such as short-chain fatty acids (which also regulate the development of fetal ENS), can modulate a range of diseases by inducing epigenetic changes. These mentioned processes suggest that stress-related, implicit, long-term epigenetic memories may be programmed into the fetal ENS during pregnancy. Subsequently, this implicit epigenetic stress information from the fetal ENS could be conveyed to the CNS through the bidirectional microbiota-gut-brain axis (MGBA), leading to perturbed functional connectivity among various brain networks and the dysregulation of affective and pain processes.

Shugan Decoction Alleviates Colonic Dysmotility in Female SERT-Knockout Rats by Decreasing M3 Receptor Expression

Background

Irritable bowel syndrome (IBS) is a functional gut disease characterized by visceral hypersensitivity and gut motor dysfunction. Serotonin (5-hydroxytryptamine, 5-HT) is an important enteric neurotransmitter. High levels of 5-HT aggravate IBS symptoms. The serotonin reuptake transporter (SERT) is a membrane-embedded transporter involved in IBS pathogenesis that plays an important role in regulating 5-HT signaling.

Aim

We investigated whether gut motor function was altered in SERT-knockout (SERT-KO) rats. Additionally, we sought to determine whether Shugan decoction (SGD), a clinically experienced prescription for the treatment of IBS, exerts regulatory effects on intestinal motility in SERT-KO rats, and attempted to identify the mechanisms involved.

Method

SERT-KO rats were produced by transcription activator-like effector nuclease (TALEN) technology. Fecal pellet output was measured for ten consecutive days to estimate distal colonic motility. Small intestinal motility was measured by charcoal-meal experiments. The colonic and small intestinal muscle contractile activities were measured by organ bath study. Western blot was used to analyze the muscarinic receptor expression in colon tissue.

Result

Compared with that in wild-type (WT) rats, the defecation amount, amplitude of spontaneous contraction, and the tension of ACh-induced contraction of colonic longitudinal smooth muscle in SERT-KO rats were significantly increased. The expression of muscarinic receptor subtype-3 (M₃R) in the colons of SERT-KO rats was also elevated. SGD can decrease defecation of SERT-KO rats. Moreover, SGD reduced the amplitude of spontaneous contraction, the frequency and tension of ACh-induced contraction of colonic longitudinal smooth muscle, and the expression of M₃R in the colon in SERT-KO rats.

Conclusions

SERT-KO rats showed increased defecation accompanied by enhanced colonic motility and M₃R expression. The findings suggest that SGD modifies colonic dysmotility and reduces defecation in SERT-KO rats by down-regulating M₃R expression in the colon.

Bile acids and FXR in functional gastrointestinal disorders

Functional gastrointestinal disorders (FGIDs), such as irritable bowel syndrome (IBS) and chronic constipation (CC), are commonly diagnosed conditions in clinical practice which create a substantial global burden. Since the farnesoid X receptor (FXR) and bile acids (BAs) are responsible for maintaining homeostasis in the GI tract, any disturbances in the expression of FXR or the composition of BAs may contribute to the development of the GI symptoms. Alterations in the mechanism of action of FXR directly affect the BAs pool and account for increased intestinal permeability and changes in abundance and diversity of gut microbiota leading to intestinal dysmotility. Current review focuses on the correlation between the FXR, BAs and the composition of gut microbiota and its influence on the occurrence of GI symptoms in FGIDs.