Morten Kobaek-Larsen

Secondary effects induced by the colon carcinogen azoxymethane in BDIX rats.

Azoxymethane (AOM) is claimed to be a colon‐specific carcinogen. In our studies, AOM was administered to adult BDIX/OrlIco rats by four weekly subcutaneous injections of 15 mg/kg body weight each – two periods of 2 weeks of AOM treatment separated by a one‐week break. This treatment schedule resulted in colon carcinomas with a high frequency (75–100%) and with a high reproducibility. However, some serious side effects are associated with this carcinogen treatment. In addition to the colorectal tumours, we found small intestinal tumours, hepatic lesions and a high frequency of mesenchymal renal tumours which increased with longer latency periods. The renal tumours were only found in female rats, and this indicates a possible relation to sex hormones. We therefore analyzed both male and female kidneys for the expression of estrogen and progesterone receptors by immunohistochemical methods. A positive nuclear reaction for estrogen receptor was present in most tumour cells in all tumours and occasionally in nuclei of entrapped tubular cells, but never in glomeruli. Normal appearing renal tissue from female rats showed no positive reaction, but in male rats a slight nuclear reaction was seen in tubuli in the peripheral part of the medulla. A similar pattern was seen for progesterone receptors, but less pronounced. No rats developed tumours in the external ear canal, which is in contrast to studies performed in other rat strains. This may therefore be strain related. In order to reduce the secondary effects of the induction of colon cancer by AOM, it is advisable to use male rats only and a maximum latency period of 32 weeks.

Back-to-back colon capsule endoscopy and optical colonoscopy in colorectal cancer screening individuals

The aim was to determine the polyp detection rate and per‐patient sensitivity for polyps > 9 mm of colon capsule endoscopy (CCE) compared with colonoscopy as well as the diagnostic accuracy of CCE.

Laparoscopy of rats with experimental liver metastases: a method to assess new humane endpoints

Metastatic disease to the liver is one of the major factors determining the outcome of colonic resection with curative interventions in human patients. Therefore, animal models for studies of liver metastasis have been developed. Humane endpoints are needed for the evaluation of the animal condition. Liver metastases were modelled by hepatic subcapsular injection of a syngeneic rat colon cancer cell line (DHD/K12-PROb) in BDIX/OrlIco rats. In this study, we present a detailed description of a laparoscopic technique for the direct inspection of liver metastases. That way a qualitative impression of the metastases was obtained. We suggest, as a new humane endpoint, that one animal should only have 1–2 separately growing metastases, each of a maximum size of 10 mm2. In future, the method has to be developed further to measure the size of the metastases in a more quantitatively precise manner. Although the animal has to be anaesthetized each time, laparoscopy is considered a minor surgical procedure as only two small puncture wounds are made through the abdominal wall. Because laparoscopy offers a direct view of the hidden tumours and their sizes, as well as of possible complications (e.g. peritoneal tumour growth), one can prevent unnecessary discomfort. We therefore think the advantages outweigh the disadvantages, as laparoscopy helps to avoid the unnecessary suffering due to large tumours which may only be detected at late stages by conventional procedures.

Immunohistochemical characterisation of the local immune response in azoxymethane-induced colon tumours in the BDIX inbred rat strain

The aim of the present study was to characterise the local immune response in a chemically induced colon tumour model in the rat. Elucidating the character of the immune reaction may contribute to optimizing immunotherapeutic regimens for colon carcinoma in this model. Colon cancer was induced by four weekly subcutaneous azoxymethane injections in inbred rats of the BDIX/OrlIco strain in two separate studies. Azoxymethane‐induced tumours show many similarities to spontaneously occurring human colon carcinomas with respect to histopathological appearance. In our studies, the overall inflammatory reaction of the submucosa below the tumour was evaluated in haematoxylin‐eosin‐stained tissue sections. Phenotypic characterization of leukocyte infiltration in the tumour tissue was performed by immunohistochemical staining using antibodies detecting various leukocyte subsets, i.e. T cells, natural killer cells, macrophages/monocytes, and dendritic cells. The results showed that the azoxymethane‐induced colon tumours were strongly infiltrated by macrophages. Furthermore, the tumours showed a moderate degree of infiltrating CD4‐positive cells. Very few natural killer, CD8‐positive T cells and dendritic cells (identified by the OX62 antibody) were seen in the tumour tissue. Virtually no CD25‐positive cells were found. This immunohistochemical characterisation of the tumour‐infiltrating immune response in this rat model could form the basis for studies aimed at developing new immunotherapeutic regimens for human colon cancer.

Assessment of bowel cleansing quality in colon capsule endoscopy using machine learning: a pilot study

Background and study aims  The aim of this study was to develop a machine learning-based model to classify bowel cleansing quality and to test this model in comparison to a pixel analysis model and assessments by four colon capsule endoscopy (CCE) readers. Methods  A pixel analysis and a machine learning-based model with four cleanliness classes (unacceptable, poor, fair and good) were developed to classify CCE videos. Cleansing assessments by four CCE readers in 41 videos from a previous study were compared to the results both models yielded in this pilot study. Results  The machine learning-based model classified 47 % of the videos in agreement with the averaged classification by CCE readers, as compared to 32 % by the pixel analysis model. A difference of more than one class was detected in 12 % of the videos by the machine learning-based model and in 32 % by the pixel analysis model, as the latter tended to overestimate cleansing quality. A specific analysis of unacceptable videos found that the pixel analysis model classified almost all of them as fair or good, whereas the machine learning-based model identified five out of 11 videos in agreement with at least one CCE reader as unacceptable. Conclusions  The machine learning-based model was superior to the pixel analysis in classifying bowel cleansing quality, due to a higher sensitivity to unacceptable and poor cleansing quality. The machine learning-based model can be further improved by coming to a consensus on how to classify cleanliness of a complete CCE video, by means of an expert panel.

Effect of the dietary polyacetylenes falcarinol and falcarindiol on the gut microbiota composition in a rat model of colorectal cancer

Objectives(3R)-Falcarinol (FaOH) and (3R,8S)-falcarindiol (FaDOH) have previously been shown to reduce the number of neoplastic lesions and the growth rate of polyps in the colon of azoxymethane (AOM) treated rats. Based on previous investigations, it appears that different mechanisms of actions are involved in the antineoplastic effect of FaOH and FaDOH. One mechanism of action may be related to the antibacterial effect of FaOH and FaDOH and thus their effect on the gut microbiota. This study aimed to determine the effect of FaOH and FaDOH on gut microbiota composition of AOM treated rats.ResultsAzoxymethane treated rats were fed either a standard rat diet or a rat diet supplemented with FaOH and FaDOH. The gut microbiota of AOM-induced rats was determined by 16S rRNA gene-amplicon sequencing. Analysis of fecal cecum samples demonstrated a significant gut microbiota change in rats receiving standard rat diet supplemented with FaOH and FaDOH compared with the control group that only received the rat diet. Comparison of the gut microbiota of rats who developed large neoplasms in the colon with rats without large neoplasms showed that the gut microbiota was significantly different in rats who developed large colon neoplasms compared to rats with no macroscopic colon neoplasms.