Sini-san improves duodenal tight junction integrity in a rat model of functional dyspepsia

Abstract

Background: Recent reports have demonstrated that impaired barrier function and local microinflammation in the duodenal mucosa contribute to the pathogeneses of functional dyspepsia (FD). Thus, restoring normal barrier integrity becomes a potential therapeutic strategy in the treatment of FD. Sini-San (SNS) is a traditional Chinese prescription that exhibits therapeutic effects in FD, but the underlying mechanisms remain not well understood.

Methods: FD rats were established by tail clamping method and the therapeutic effect of SNS was evaluated by measuring the visceral sensitivity and gastric compliance. Transepithelial electrical resistance (TEER) that reveals epithelial barrier integrity was measured by Ussing chamber. The expression of tight junction (TJ) proteins, occludin and claudin-1, in the duodenum was determined by Western blot and immunofluorescence. The amount of tumor necrosis factor alpha (TNF-α) and interferon gamma (INF-γ) in duodenal mucosa was detected by enzyme-linked immune sorbent assay (ELISA). The mRNA level of transient receptor potential vanilloid type 1 (TRPV1) was measured by quantitative real time-polymerase chain reaction (qPCR).

Results: SNS could improve gastric compliance and attenuate visceral hypersensitivity (VH) in FD rats. TEER was decreased in FD rats, but treatment with SNS restored normal level of TEER and the expression of occludin and claudin-1 in FD rats. In addition, SNS administration ameliorated FD-associated increase in the production of TNF-α, IFN-γ and the expression of TRPV1.

Conclusions: The therapeutic effect of SNS on FD is at least partially through improvement of TJ integrity and attenuation of FD-associated low-grade inflammation in the duodenum. Our findings highlight the molecular basis of SNS-based treatment of FD in human patients.

Keywords: Duodenum; Functional dyspepsia; Pro-inflammatory cytokine; Sini-san; Tight junction.

Fig. 1

Visceral sensitivity (a), gastric compliance (b) and mRNA expression of TRPV1 (c). The model group had elevated visceral sensitivity and decreased gastric compliance compared with the control group. SNS treatment was effective to recover the visceral sensitivity and gastric compliance. The mRNA level of TRPV1 was notably increased in the duodenum of the model group compared with the control group, and the SNS treatment decreased the expression of TRPV1. All data were represented as mean ± SEM (6 rats in each group).^* P < 0.05 compared with the control group; ^** P < 0.01 compared with the control group; ^# P < 0.05 compared with the model group. ^## P < 0.01 compared with the model group

Fig. 2

Duodenal TEER. The model group had a prominently decreased TEER compared with the control group, and SNS treatment remarkably enhanced the TEER level of FD rats. All data were represented as mean ± SEM (6 rats in each group). ^** P < 0.01 compared with the control group; ^## P < 0.01 compared with the model group

Fig. 3

Representative Western blot bands of TJ proteins (a).The expression level was normalized to the housekeeping protein β-actin (b, c). Compared with the control group, the expression of occludin and claudin-1 was significant lower in the model group and SNS treatment could restore these two TJ proteins. All data were represented as mean ± SEM (6 rats in each group). ^** P < 0.01 compared with the control group; ^## P < 0.01 compared with the model group

Fig. 4

Representative photomicrographs of immunofluorescence of occluding (a) and claudin-1 (b). These pictures showed a decline in the expression of both occluding and claudin-1 in the model group, which was restored in response to SNS treatment

Fig. 5

Concentrations of TNF-α (a) and IFN-γ (b) in the duodenum. TNF-α and IFN-γ levels were remarkably higher in the duodenal mucosa of model group than the control group. The SNS group showed a lower level of expression of TNF-α and IFN-γ.. All data were expressed as mean ± SEM (6 rats in each group). ^** P < 0.01 compared with the control group; ^## P < 0.01 compared with the model group