Changes in intestinal mucosa above lymph follicles during carcinogenesis in rats. A light and electron microscopic study

Melatonin and colon carcinogenesis. III. Effect of melatonin on proliferative activity and apoptosis in colon mucosa and colon tumors induced by 1,2-dimethylhydrazine in rats

Forty-eight two-month-old outbred female LIO rats were injected weekly with a single dose of 1,2-dimethylhydrazine (DMH; 21 mg/kg of body weight) administered s.c. for 15 consecutive weeks. From the day of the 1st injection of the carcinogen the part of rats were given five days a week during the night time (from 18.00 h to 08.00 h) melatonin dissolved in tap water, 20 mg/l. 10 rats were treated similarly with solvents and served as control. The experiment was terminated 6 months after the first injection of the carcinogen. Colon tumors (mainly adenocarcinomas) developed in a hundred percent of rats exposed both to DMH or to DMH plus melatonin. However, descending colon carcinomas were observed in 65 % of rats exposed to DMH plus melatonin against 100% in those exposed to DMH alone (p < 0.01). The multiplicity of colon tumors was also reduced in rats under the influence of melatonin. This effect is correlated with the significant inhibitory effect of the pineal hormone on mitotic index and with stimulating effect of melatonin on the relative number of apoptotic cells (TUNEL-method) in colon tumors. Long-term treatment with melatonin was followed also by the decrease in the area of lymphoid infiltrates in the colon mucosa of tumor-bearing rats.

Fluorescent tissue site-selective lanthanide chelate, Tb-PCTMB for enhanced imaging of cancer

In-vivo and in-vitro investigations indicate that a newly developed polyazamacrocyclic chelate of Tb(III) has superior properties for use as an abnormal tissue marker. In addition to tissue selectivity, this molecule is unique because of its low toxicity, attractive fluorescent properties, rapid pharmokinetics, and relatively high water solubility. The complex Tb-3,6,9-tris(methylene phosphonic acid n-butyl ester)-3,6,9,15-tetraazabicyclo[9.3.1]-pentadeca-1(15),11,13 -triene (Tb-PCTMB) has also been shown to exhibit strongly shifted emission (delta lambda--280 nm), moving the detection frequency away from autofluorescence backgrounds, and good quantum efficiencies (phi = 0.51), providing high brightness. Fluorescence imaging was used to quantify Tb-PCTMB at the picomolar level in tissues and to show the significant difference in affinity for the chelate by adenocarcinoma cells HT-29 versus normal epithelial cells (IEC-6). Topical application, or lavage introduction, under endoscopy was used to instill a millimolar aqueous solution of Tb-PCTMB into a dimethylhydrizene-treated Sprague Dawley rat large intestine containing a suspect growth. Subsequent in vitro fluorescence detection and standard histological evaluation confirmed enhanced uptake by adenocarcinoma tissue. Semiquantitative signal interrogation was employed to show the potential for using Tb-PCTMB as a contrast enhancement marker for disease detection.

Non-polypoid adenomas of the colon are associated with subjacent lymphoid nodules. An experimental study in rats

BACKGROUND

Subjacent lymphoid nodules (SLNs) have been found in 38% of non-polypoid colonic adenomas in humans. In the present work the presence of SLNs in experimentally induced colonic adenomas was investigated in rats.

METHODS

1,2-Dimethylhydrazine was injected subcutaneously in 290 Sprague-Dawley rats for 27 weeks.

RESULTS

An SLN was present in 28.6% of the 84 adenomas, in 8.4% of the 119 adenocarcinomas, and in 9.7% of the 31 small carcinomas without remnant adenomatous tissue. An SLN was found in 35.6% of the 59 non-polypoid neoplasias but only in 9.1% of the 175 polypoid (that is, exophytic) neoplasias. When only adenomas were considered, SLNs were present in 50.0% of the 34 non-polypoid adenomas but only in 14.0% of the 50 polypoid adenomas.

CONCLUSIONS

Non-polypoid colonic adenomas evolve preferentially from the minimal fraction of the colonic mucosa that overlays the few existing lymphoid nodules in rats.

Distribution of lymphoid nodules, aberrant crypt foci and tumours in the colon of carcinogen-treated rats

Sprague-Dawley rats were given eight weekly subcutaneous injections of 1,2-dimethylhydrazine (DMH) or of vehicle then were sacrificed at 1, 5 or 24 weeks after the last injection of DMH. The locations of pre-existing aggregates of lymphoid nodules (ALNs), the location and multiplicity (size) of aberrant crypt foci (ACF), and the locations of tumours in the colon were determined. A trimodal distribution of pre-existing ALNs along the length of the colon was significantly correlated with the timodal distribution of DMH-induced adenocarcinomas (ACs). A unimodal peak in ACF of all sizes occurred between the sites of two distal ALNs. Thus, the distribution of ACF at 1 or 5 weeks did not correlate with distribution of AC found at 24 weeks. Of the 2640 ACF observed at 1 or at 5 weeks, none were found in the proximal 25% of the colon where ACs eventually occurred. It was concluded that: (1) ALNs play a promotional role in AC formation; (2) the ACs which form in the proximal quarter of the colon seldom if ever form via an ACF precursor; and (3) the location, the number and the size of ACF observed early after DMH exposure did not correlate with the location or predict the incidence of ACs which eventually formed in the colon.

Effect of gut-associated lymphoid tissue on cellular proliferation in proximal and distal colon of the rat

In previous studies, chemically induced colonic carcinomas were found to originate preferentially from crypts adjacent to lymphoid tissue. Proliferative parameters and mucosecretion were analyzed in proximal and distal rat colon in relation to the proximity of lymphoid patches. Animals received an intraperitoneal pulse of bromodeoxyuridine 1-hr before death. In both proximal and distal colon, crypts located at the immediate proximity of the lymphoid formations contained fewer mucous cells (P less than 0.001), but a higher percentage of proliferative epithelial cells (P less than 0.001) than the crypts far from lymphoid formations. The labeling index was higher in crypts adjacent to lymphoid patches compared to crypts distant from lymphoid patches only in the lower third of the crypts. The association of an increased proliferative activity and a decrease in differentiated mucosecreting cells in colonic crypts adjacent to lymphoid patches could be related to the particular sensitivity of these crypts cells to the effects of mutagens and carcinogens.