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Target cells for the cytotoxic effects of carcinogens in the murine small bowel
Y Q Li1, C Y Fan, P J O'Connor
1CRC Department of Epithelial Biology, Paterson Institute for Cancer Research, Christie Hospital, Manchester, UK.
Abstract:
Two direct-acting mutagens, N-nitroso-N-methylurea (NMU) and N-nitroso-N-ethylurea (NEU), and two agents requiring metabolic activation, 1-2-dimethylhydrazine (DMH) and N-nitrosodimethylamine (NDMA), were administered i.p. to mice. Sections of crypts of the small intestine were assayed for acute histological cell death at various times up to 12 h after treatment. Dead or dying cells exhibited the typical light microscopic morphological features of apoptosis. The incidence of apoptosis at each cell position along the side of longitudinal crypt sections was recorded and frequency plots of the incidence against cell position were determined. NEU (50 mg/kg) produced the highest incidence of cell death but this was closely followed by NDMA (50 mg/kg) and NMU (200 mg/kg). DMH (40 or 80 mg/kg) was the least cytotoxic but even here significantly elevated levels of cell death were observed. The highest incidence of cell death occurred 4-5 h after treatment with NEU, NMU and DMH and at 6 h after NDMA. The data obtained at 4 h after NEU suggest that approximately 22 cells out of a total crypt population of 250 cells are killed, but that for some cell positions near the crypt base (stem cell regions) up to 24% of the cells may be killed. Analysis of the changing shape of the frequency plots with time after treatment enabled the target cell position in the crypts for cytotoxicity to be estimated. This was at cell position 4 for NEU, NMU and DMH and at cell position 5 for NDMA. The stem cells in the crypts are believed to be located at the fourth cell position and hence at least NEU, NMU and DMH are targeting the stem cells with some specificity.
Insights
N-nitroso-N-ethylurea (NEU), N-nitroso-N-methylurea (NMU), and N-nitrosodimethylamine (NDMA) induced apoptosis in mouse small intestine crypts. These mutagens, particularly NEU, NMU, and DMH, specifically targeted stem cells.
Area of Science:
- Toxicology
- Cell Biology
- Gastroenterology
Background:
- Chemical mutagens are crucial tools for studying cellular damage and repair mechanisms.
- Understanding the cytotoxic effects of mutagens on intestinal crypts is vital for cancer research and drug development.
Purpose of the Study:
- To investigate the acute cytotoxic effects of direct-acting and metabolically activated mutagens on mouse small intestinal crypts.
- To determine the cell position targeted by these mutagens within the crypt structure.
- To assess the specificity of mutagen-induced apoptosis in relation to intestinal stem cells.
Main Methods:
- Administration of four different mutagens (NMU, NEU, DMH, NDMA) via intraperitoneal injection to mice.
- Histological examination of small intestinal crypt sections at various time points (up to 12 hours) post-treatment.
- Quantification of apoptotic cell death and frequency distribution along the crypt axis.
Main Results:
- NEU, NMU, and NDMA induced significant apoptosis, with NEU showing the highest incidence.
- DMH also induced elevated cell death, though less potent than the others.
- Mutagen-induced apoptosis peaked between 4-6 hours post-treatment.
- Cytotoxicity analysis indicated that NEU, NMU, and DMH specifically targeted cell positions 4 and 5, consistent with stem cell regions.
Conclusions:
- Direct-acting mutagens (NEU, NMU) and metabolically activated mutagens (NDMA, DMH) induce apoptosis in mouse intestinal crypts.
- NEU, NMU, and DMH demonstrate a degree of specificity in targeting intestinal stem cells.
- These findings contribute to understanding mutagenic mechanisms and potential therapeutic targets in gastrointestinal cancers.