Chronic low-dose deltamethrin exposure induces colon injury and aggravates DSS-induced colitis via promoting cellular senescence

OBJECTIVE

Deltamethrin (DLM) is a commonly used insecticide, which is harmful to many organs. Here, we explored the effects of chronic low-dose DLM residues on colon tissue and its potential mechanism.

METHODS

The mice were given long-term low-dose DLM by intragastric administration, and the body weights and disease activity index (DAI) scores of the mice were regularly recorded. The colon tissues were then collected for hematoxylin-eosin, immunofluorescence and immunohistochemistry staining. Besides, the RNA sequencing was performed to explore the potential mechanism.

RESULTS

Our results showed that long-term exposure to low-dose DLM could cause inflammation in mice colon tissue, manifested as weight loss, increased DAI score, increased apoptosis of colonic epithelial cells, and increased infiltration of inflammatory cells. However, we observed that after long-term exposure to DLM and withdrawal for a period of time, although apoptosis was restored, the recovery of colon inflammation was not ideal. Subsequently, we performed RNA sequencing and found that long-term DLM exposure could lead to the senescence of some cells in mice colon tissue. The results of staining of cellular senescence markers in colon tissue showed that the level of cellular senescence in the DLM group was significantly increased, and the p53 signalling related to senescence was also significantly activated, indicating that cellular senescence played a key role in DLM-induced colitis. We further treated mice with quercetin (QUE) after long-term DLM exposure, and found that QUE could indeed alleviate DLM-induced colitis. In addition, we observed that long-term accumulation of DLM could aggravate DSS-induced colitis in mice, and QUE treatment could reverse this scenario.

CONCLUSION

Continuous intake of DLM caused chronic colitis in mice, and the inflammation persisted even after discontinuation of DLM intake. This was attributed to the induction of cellular senescence in colon tissue. Treatment with QUE alleviated DLM-induced colitis by reducing cellular senescence. Long-term DLM exposure also aggravated DSS-induced colitis, which could be mitigated by QUE treatment.

Comparison of the anti-colitis activities of Qing Dai/Indigo Naturalis constituents in mice

Qing Dai/Indigo Naturalis (QD) has been shown to ameliorate ulcerative colitis (UC) in clinical trials; however, its mechanism remains elusive. This study investigates the effects of QD on murine dextran sulfate sodium salt-induced colitis. Oral administration of QD protected the animals from colitis as manifested by weight loss, diarrhea, and rectal bleeding. QD was distinguishingly more effective than 5-aminosalicylate. Focused microarray analysis of genes expressed in the distal colon suggested that QD influences the inflammatory pathway. Anti-inflammatory activity of QD was confirmed by the suppression of nitric oxide (NO) production in response to interleukin-1β in cultured hepatocytes. Some of the constituents in QD, such as tryptanthrin (TRYP) and indigo, suppressed NO production. TRYP maintained body weight but did not inhibit bleeding. Indigo, on the other hand, partially ameliorated bleeding, but did not maintain body weight. The combination of TRYP and indigo did not show additive ameliorating activity. The methanol extract of QD showed an anti-colitis activity like that of TRYP. In contrast, the methanol-insoluble QD fraction moderately ameliorated diarrhea and bleeding. Combining these two fractions resulted in full anti-colitis activity. Further clarification of the active constituents will help in the discovery of a safe and potent prescription for UC.

Differences in colonic crypt morphology of spontaneous and colitis-associated murine models via second harmonic generation imaging to quantify colon cancer development

Background

Colorectal cancer remains the second leading cause of cancer death in the United States, and increased risk in patients with ulcerative colitis (a subset of inflammatory bowel disease) has motivated studies into early markers of dysplasia. The development of clinically translatable multiphoton imaging systems has allowed for the potential of in vivo label-free imaging of epithelial crypt structures via autofluorescence and/or second harmonic generation (SHG). SHG has been used to investigate collagen structures in various types of cancer, though the changes that colorectal epithelial collagen structures undergo during tumor development, specifically colitis-associated tumors, have not been fully investigated.

Methods

This study used two murine models, using A/J mice, one for spontaneous carcinoma and one for colitis-associated carcinoma, to investigate and quantify SHG image features that could potentially inform future study designs of endoscopic multiphoton imaging systems. The spontaneous tumor model comprised a series of six weekly injections of azoxymethane (AOM model). The colitis-associated tumor model comprised a single injection of AOM, followed by cycles of drinking water with dissolved dextran sodium sulfate salt (AOM-DSS model). SHG images of freshly resected murine colon were acquired with a multiphoton imaging system, and image features, such as crypt size, shape and distribution, were quantified using an automated algorithm.

Results

The comparison of quantified features of crypt morphology demonstrated the ability of our quantitative image feature algorithms to detect differences between spontaneous (AOM model) and colitis-associated (AOM-DSS model) murine colorectal tissue specimens. There were statistically significant differences in the mean and standard deviation of nearest neighbor (distance between crypts) and circularity between the Control cohort, AOM and AOM-DSS cohorts. We also saw significance between AOM and AOM-DSS cohorts when calculating nearest neighbor in images acquired at fixed depths.

Conclusion

The results provide insight into the ability of SHG imaging to yield relevant data about the crypt microstructure in colorectal epithelium, specifically the potential to distinguish between spontaneous and colitis-associated murine models using quantification of crypt shape and distribution, informing future design of translational multiphoton imaging systems and protocols.

Electronic supplementary material

The online version of this article (10.1186/s12885-019-5639-8) contains supplementary material, which is available to authorized users.

Maillard reaction products from highly heated food prevent mast cell number increase and inflammation in a mouse model of colitis

Links between food and inflammatory bowel diseases (IBDs) are often suggested, but the role of food processing has not been extensively studied. Heat treatment is known to cause the loss of nutrients and the appearance of neoformed compounds such as Maillard reaction products. Their involvement in gut inflammation is equivocal, as some may have proinflammatory effects, whereas other seem to be protective. As IBDs are associated with the recruitment of immune cells, including mast cells, we raised the hypothesis that dietary Maillard reaction products generated through heat treatment of food may limit the colitic response and its associated recruitment of mast cells. An experimental model of colitis was used in mice submitted to mildly and highly heated rodent food. Adult male mice were divided in 3 groups and received nonheated, mildly heated, or highly heated chow during 21 days. In the last week of the study, each group was split into 2 subgroups, submitted or not (controls) to dextran sulfate sodium (DSS) colitis. Weight variations, macroscopic lesions, colonic myeloperoxidase activity, and mucosal mast cell number were evaluated at the end of the experiment. Only highly heated chow significantly prevented DSS-induced weight loss, myeloperoxidase activity, and mast cell number increase in the colonic mucosa of DSS-colitic mice. We suggest that Maillard reaction products from highly heated food may limit the occurrence of inflammatory phases in IBD patients.