This study revealed that Chinese herbal formula TXYF and its componet herb LR could attenuate visceral hyperalgesia and reduce the frequency of stool in PI-IBS rats, which effect possibly mediated through down-regulating the PAR-2 mRNA expression in colonic mucosa.
IBS has a complex etiology and its pathogenesis is related to the altered gut sensory–m otor function, intestinal permeability, and infection, especially low-grade inflammation of the intestine . Epidemiological studies show that bacterial gastroenteritis precedes the onset of the disorder in about 25% of patients with IBS [17, 18]. Subtle immune activation has been reported in the colonic biopsies, and altered peripheral cytokine,such as IL-6 and TNF- α has been shown in PI- IBS patients .
Pathophysiological mechanisms of PI-IBS are linked with change in gut flora, altered small intestinal permeability, sensory-motor function and muscle hyper-contractility . Recent studies suggest that low-grade inflammation plays important role in development of IBS following acute gastroenteritis [21, 22], and neuroendocrine factors affect the motor function of gut . Persistently increased number of inflammatory cells in IBS patents has been accompanied with the high expression of TNF- α and IL-6 mRNA even three months after an acute infective diarrhea . Bood levels of IL-6 and the genetic polymorphism of TNF- α are significantly elevated in IBS patents [25, 26]. TNF- α and IL-6 are regarded as the most important inflammatory cytokines in IBS. Moreover, the levels of IL-8、IL-10、IL-1 β and TGF-1β are significantly increased in IBS patents, especially IL-1 β expression is clearly elevated in post-infectious IBS (PI-IBS) .
PARs are coupled to G-proteins and cleaved by proteolysis, releasing a tethered ligand domain that binds and activates the receptor. PAR-2 has been reported to be activated by trypsin or mast cell tryptase. PAR-2 is distributed throughout the gastroin testinal tract, where it localized in epithelial cells, myocytes and enteric neurons . Previous clinical data showed that PAR-2 activation is responsible for sensitization of sensory neurons, as well as visceral hypersensitivity in patiets with IBS. These results support the concept that PAR-2 is possibly an important receptor involved in the visceral nociceptive response and intestinal movement disorder. Reduced colonic microflora obtained by oral antibiotic treatment resulted in a lower serine protease activity and was associated with a decreased expression of PAR-2 on the colonic epithelial cells of mice . In the present study, our results showed that the protease activity increased and the PAR-2 mRNA expression was up-regulated in PI-IBS rats. Moreover, TXYF could down-regulate the PAR-2 mRNA expression and inhibit the serine protease activtate.
Our data suggested that there were the obviosurluy increasment of SP, TNF- α and IL-6 contents in colonic mucosa of PI-IBS rats. These showed that PAR-2 was activated and then induced the realease of inflammation medium. TXYF could reduce the realease of SP, TNF- α and IL-6. In agreement with our present study, Gecse K found that increased faecals tryptase activity in IBS patent could induce visceral hypersensitivity in mice . The mechanism for this phenomenon is that trypsin activates PAR-2 receptor increasing the excitability of dorsal root ganglion neurons and promoting SP and CGRP release. Tanaka Y found the infection factors of gastrointestinal can activate PAR-2 receptor promoting inflammation medium release, such as IL-6, IL-8 and TNF- α .
Previous research showed that TXYF can inhibit neonatal colon irritation-induced IBS by decreasing 5-HT in the serum and decreasing SP and CGRP in the plasma . TXYF can treat IBS probably by affecting the secretion and release of gastrointestinal hormone (VIP) after the partial restriction stress binding stimulation in the IBS rat model . TXYF has a marked inhibitory effect on the degranulation of peritonea1 mast cells in sensitized rats induced with C48/80, which indicates that TXYF exerts therapeutic effect by inhibiting enteric mast cell activation and thus decreasing histamine release, which in part explains the mechanism of TXYF in IBS .
In conclusion, our present research found that TXYF played an important role in attenuating behavioral hyperalgesia and anti-diarrheal effect. Down-regulating PAR-2 expression and reducing the level of cytokines in the colonic mucosa could be the possible molecular mechanism.