Biomedical subjects

C S Potten

Publications and source records attributed to C S Potten.

At least 145 records · Page 8Linked to original sources

PubMed1994

The crypt cycle in mouse small intestinal epithelium.

We have used a mutation-induced marker system in the intestine of mice heterozygous at the Dlb-1 locus, which determines the expression of binding sites for the lectin Dolichos biflorus agglutinin, and the frequency of clustering of mutated crypts with time as a means of investigating the frequency of the crypt fission process and the crypt cycle. Whole-mount preparations from heterozygous Dlb-1b/Dlb-1a mice were stained with a peroxidase conjugate of Dolichos biflorus agglutinin. Mutations at the Dlb-1b locus in crypt stem cells result in loss of DBA-Px binding in these cells and subsequently their progeny, which eventually results in a rare isolated single, unstained crypt. The subsequent development of pairs, triplets and clusters of negative staining crypts has been assumed to be the result of crypt fission. The frequency of these fission events has been measured in control untreated mice. These negative crypts are the result of spontaneous mutations. We have also looked at mutated crypts after treatment with N-nitroso-N-ethylurea or N-methyl-N'-nitro-N-nitrosoguanidine of young adult mice, which elevates the number of mutations. Our results suggest that the crypt cycle in control animals is very long, 187 +/- 44 weeks (3.6 years, i.e. essentially the life of a laboratory mouse). This implies that about a third of the crypts may divide once in the life of a mouse. After sufficient time for conversion of mixed crypts to monophenotypic crypts after mutagen treatment several clusters of negative crypts were seen.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1994

A potent stimulator of small intestinal cell proliferation extracted by simple diffusion from intact irradiated intestine: in vitro studies.

The epithelium lining the small intestine is one of the most rapidly proliferating body tissues yet it rarely develops cancers. The proliferation, migration and differentiation of the stem cell progeny appears to be under very strict control. After 8 Gy gamma irradiation the murine epithelium contains surviving stem cells from which the epithelium rapidly and effectively regenerates, presumably in response to stimulatory signals, and then returns to steady state conditions after overshoots in proliferation. Here we describe the isolation and preliminary characterisation in vitro of a potent stimulatory extract obtained by diffusion from intact murine small intestine, post-irradiation. In addition to in vivo responses the extract stimulates intestinal epithelial lines very effectively, most notably the rat IEC 18 line where it can replace the serum requirement. The extent of the induced increase in proliferation could not be reproduced by any other single growth factor tested. Preliminary evidence suggests the extract contains either a potent stimulatory cocktail of factors or a novel intestinal growth factor(s).

Animals↗

PubMed1994

Small intestinal growth regulatory factors extracted by simple diffusion from intact irradiated intestine and tested in vivo.

Following a dose of 8 Gy of gamma-rays delivered to the entire body of BDF1 mice, the proliferative activity in the crypts of the small intestine changes. The labelling and mitotic activity both fall precipitously, but in the lower regions of the crypt recovery from this fall begins soon after irradiation with cyclic fluctuations. Forty-five to fifty hours after irradiation, control levels are reached after which there is an overshoot. The number of clonogenic cells in the crypt shows a somewhat similar pattern of regeneration and overshoot. It has been assumed that these changes reflect the production of endogenous signals for proliferation and inhibition and these might be extracted by diffusion through the gut wall. We report here that at appropriate times after irradiation stimulatory and inhibitory extracts could be prepared. Appropriate in vivo assay techniques have been developed for testing inhibitors or stimulators making similar use of the patterns of proliferative regeneration after irradiation. Extracts prepared at either 15 h or 39 h after irradiation, i.e. during the phase of active regeneration are quite potently stimulatory on recipient animals 96 h after irradiation (i.e., following the decline from a proliferative overshoot) when injected twice 3 h apart. Extract prepared 72 h after irradiation (shortly after the overshoot peak) is strongly inhibitory when tested on unirradiated animals, or animals 90 h after irradiation, when injected four times 2 h apart. An accompanying paper shows that the stimulatory extract is powerfully active on intestinal cell lines. The in vitro approach is currently being used to characterise the stimulatory factor.

Animals↗

PubMed1994

Expression of pokeweed lectin binding in murine intestinal Paneth cells.

Pokeweed (Phytolacca americana) lectin was found to stain the secretory granules in epithelial Paneth cells of small intestine in mice and rats. The distribution of Paneth cells stained with this lectin was identical to that obtained by another immunohistochemical marker for lysozyme. However, in comparison with other immunohistochemical markers, Pokeweed lectin is a more robust method for identifying Paneth cells in histological sections and for studying their secretory granules. Co-expression of the Pokeweed lectin binding sites in some oligomucous cells within the crypts suggested a close developmental link between these two cell types. Only one other non-epithelial cell type was stained by this lectin, and these were migratory lymphocytes found within the villus epithelium and lamina propria. Approximately 20% of these lymphocyte cells were also positive for the expression of CD3+. Pokeweed lectin was therefore used to study changes in the frequency of Paneth cells and intra-epithelial lymphocytes in normal and immunologically compromised animals (following infection with a parasite worm Trichuris muris and in a model of graft-versus-host rejection). This study confirmed that the population of Paneth cells turns over slowly even during conditions of inflammation.

Animals↗

PubMed1994

Cell migration in the small and large bowel shows a strong circadian rhythm.

Migration velocity estimates have been determined at each position along the crypt length for both the small and large intestine of the mouse at 6 different times of the day. Measurements also have been made of crypt circumference and length. Dramatic, and significant (P < 0.001), changes in migration velocity as a function of time of day were observed in the small intestine with a maximum 0.84 cell positions (cp) per hour at 0900 h and a minimum of -0.46 cp/h at 1700 h, although the negative velocity was probably artefactual. The 24-h mean velocity rose smoothly as a function of cell position to a peak of 0.45 cp/h at cell position 17 (around the top of the proliferative zone). Much more modest changes were seen in the percent of 3HTdR labelled cells (minimum 30.8%, maximum 38.3%, P < 0.001) and crypt circumference (minimum 16.9 cells, maximum 17.9 cells, P = 0.003). The migration velocity was rather less well determined in the large intestine with a peak in the 24-h mean velocity (0.26 cp/h) occurring at cell position 10. At this position significant circadian variation was detected (minimum -0.39 cp/h, maximum 0.75 cp/h, P = 0.006). Changes were seen in the percent of labelled cells (minimum 9.4%, maximum 22.3%, P < 0.001) and crypt circumference (minimum 18.3 cells, maximum 19.2 cells, P < 0.001). In both tissues it is suggested that the combination of the modest changes in cell proliferation rates in conjunction with the changes in crypt cell number can account for the large amplitude in variation of crypt output, and that the reservoir effects of changes in crypt geometry are an essential part of the process governing the maintenance of intestinal cell numbers.

Animals↗

PubMed1993

Inhibition of doxorubicin-induced apoptosis in vivo by 2-deoxy-D-glucose.

Previous studies have shown that DNA cleavage by mammalian topoisomerase II is ATP dependent and can be inhibited by metabolic inhibitors. Furthermore, it has been shown that metabolic inhibitors also have a cytoprotective effect in vitro against topoisomerase II-targeting antitumor drugs. However, the nature of the ATP-dependent process is not known. We have previously shown that doxorubicin induces apoptosis (programmed cell death) in the murine small intestine which can be inhibited by the protein synthesis inhibitor cycloheximide. In the present study, we have demonstrated that 2-deoxy-D-glucose reduces the incidence of doxorubicin-induced apoptosis in vivo if administered within 45 min of the doxorubicin. Maximum reduction was observed at 2 h after treatment (approximately 66%); however, significant reduction was still observable at 9 h after treatment (approximately 33%). Significant positive correlation was observed between protein synthesis inhibition and apoptosis inhibition. Other possible mechanisms of action of the inhibitor do not appear to be important in cytoprotection. The inhibitor did not reduce the uptake of doxorubicin into the intestinal epithelium; however, it caused a significant increase in retention of the drug. The kinetics of inhibition suggest that alteration of cell cycle kinetics, inhibition of formation of doxorubicin-topoisomerase II complex or induction of glucose-regulated proteins are not significant factors in cytoprotection. These studies indicate that at least in the mouse small intestinal epithelium, the ATP-dependent process in cell killing by doxorubicin may involve protein synthesis.

Adenosine Triphosphate↗

PubMed1993

Accelerated repopulation of intestine post-irradiation following intraluminal injection of a mucosal cell suspension or its supernatant.

The injection of (1-7) x 10(5) mucosal cells into the intestinal lumen at 4 h after 14 or 18 Gy increased the number of intestinal microcolonies (> or = 10 cell foci) and microclusters (4-9 cell foci) when assayed at day 3. The effects were less when (a) the interval between irradiation and injection was increased to 20 h, (b) the assay time was increased to 4 days or more, (c) a cell supernatant was injected instead. The data indicate that the injections stimulated earlier regeneration. The effect of the supernatant suggests that the stimulation is mediated through a humoral factor.

Animals↗

PubMed1993

Hair cortical cell counts (HCCC), a new sensitive in vivo assay with possible applications for biological dosimetry.

In the region of a growing hair follicle where terminal keratinization takes place, the nuclei of the medulla and cortex are gradually degraded. In the zone between rapid cell proliferation in the matrix and the complete loss of the nuclei in the formed hair, the number of medullary cells in the hair proved to be a sensitive-radiation-dose-dependent endpoint (Potten et al. 1990). Nuclei in the cortex of the hair are similarly degraded but are more difficult to quantitate since they form a circumferential ring of cells round the medulla. However, using the confocal microscope to obtain discrete optical sections just above and below the medulla, the number of cortical cells was reproducibly counted. The maximum reduction in cortical cell count occurred on the 3rd day after irradiation. Here, the dose-response curve (0.5-4.0 Gy) is presented, for the population of cortical cells in awl guard hairs of the mouse for 137Cs gamma-rays at 4 Gy/min, which was exponential with no significant shoulder, (the D0 was 2.4 +/- 0.2 Gy and the extrapolation number 1.2 +/- 0.1). The cortical cells exhibited a slightly higher D0 value than the medullary cells but differed in that there was no evidence of a shoulder. The effects of 0.5 Gy could be detected. The degree of sensitivity, and the fact that cortical cells are readily detected in human hair follicles, unlike the medullary cells, make this a potentially valuable human biological dosimeter.

Animals↗

PubMed1993

Hair medullary cell counts following low-dose-rate gamma- and high-energy neutron irradiation.

Young adult Balb/c mice with hair follicles synchronously in the middle of the hair growth cycle received whole-body or partial-body doses of gamma-radiation or neutron radiation. The hair follicles were analysed either 3 days after irradiation in the dose-response experiments, or at various times after a constant dose in the time-course experiments, for changes in the number of cells in the forming medulla of the hair in the region just above the germinal matrix of the growing (anagen) hair follicle. Time-course experiments showed that 3 days after irradiating growing follicles (2 or 4 Gy of gamma-rays or 1 or 2 Gy of neutrons), the maximum reduction in the hair medullary cell count (HMCC) was observed. Survival curves were obtained for gamma-rays over a range of dose-rates (4.0-0.0023 Gy/min) using total doses between 0.5 and 5.0 Gy. A survival curve was also obtained for 62 MeV neutrons at a dose-rate of 0.31 Gy/min and doses of 0.1-2.0 Gy. The D0 for the HMCC dose-response curve following caesium gamma-irradiation at 4.0 Gy/min was 2.1 +/- 0.2 Gy with n = 1.7 +/- 0.2. The dose-response curve for low-dose-rate gamma-rays was best fitted by a simple exponential function with no evidence of a shoulder. The D0 was 3.0 +/- 0.1 Gy at a dose-rate of 0.04 Gy/min. The data for 62 MeV neutrons (at 0.35 Gy/min) had a small but significant shoulder n = 1.5 +/- 0.1 and a D0 of 1.0 +/- 0.1 Gy. These data further illustrate the sensitivity of this assay and its potential application as a biological dosimeter.

Animals↗

PubMed1993

DNA damage in UV-irradiated human skin in vivo: automated direct measurement by image analysis (thymine dimers) compared with indirect measurement (unscheduled DNA synthesis) and protection by 5-methoxypsoralen.

The incidence of the various types of skin cancer in the general population has been increasing at an annual rate of 2-8% over the past 2 decades. In spite of considerable media coverage on the risk of skin cancer the acquisition of a suntan is still very popular. Thus the UV exposures required for tanning pose a serious carcinogenic risk, particularly to individuals who tan poorly. On the other hand, the presence of natural skin pigment, or the ability to tan easily can protect the skin against some of the harmful effects of subsequent UV exposures (Kollias et al. 1991). We have recently shown (Young et al. 1991) in human volunteers, using an indirect measurement of DNA damage (unscheduled DNA synthesis (UDS) detected by autoradiography), that a tan induced by UV in the presence of a UVB sunscreen (Parsol MCX) preparation containing 5-methoxypsoralen (5-MOP) is more effective at protecting the skin against a subsequent DNA-damaging challenge dose of UV than a tan induced by UV alone, particularly in individuals who tan poorly. No such protection was seen with the same sunscreen lacking 5-MOP. 5-MOP is an ingredient in natural citrus oils and in many other plants. Here we show the same pattern of protective action when measuring, for the first time, DNA damage directly using a monoclonal antibody to thymine dimers (a major category of DNA lesion induced by UV radiation) on fixed human skin sections and automated image analysis. There is a good correlation between UV exposure dose and the levels of thymine dimers in epidermal nuclei. The levels of thymine dimers (measured as absorption by the mean integrated optical density (IOD)) also correlated well with the levels of UDS (grains per nucleus). These findings are of importance in the comparative risk-benefit assessment of sunscreens with and without 5-MOP. The techniques described have applications for measuring other DNA lesions following UV and other exposures.

5-Methoxypsoralen↗

PubMed1993

Tissue and cell specific methylation, repair and synthesis of DNA in the upper gastrointestinal tract of Wistar rats treated with single doses of N-methyl-N'-nitro-N-nitrosoguanidine.

Several potential cancer risk factors have been monitored concurrently in the upper gastrointestinal tract of young adult male Wistar rats given single (i.g.) doses of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) which readily induces forestomach tumours under these conditions. Radioimmunoassay was used to determine the formation of O6-methyl-2'-deoxyguanosine (O6-MedG) in DNA after MNNG doses of 1, 5, 25 or 50 mg/kg and was found to be highest in the pylorus, with progressively lower levels in the corpus, forestomach, duodenum, oesophagus and jejunum. Immunohistochemical procedures showed that cells with nuclei containing O6-MedG were heterogeneously distributed in these tissues. O6-Alkylguanine-DNA alkyltransferase activity in untreated animals was highest in the mucosae of the corpus, lower and relatively similar in that of the pylorus, duodenum and jejunum and lowest in the tissues of oesophagus and forestomach. Estimates of DNA synthesis and cell proliferation indicated a 5-fold increase in the DNA labelling index in the forestomach whereas perturbations of DNA synthetic activity in the other tissues of the upper gastrointestinal tract were much less marked. As a result of these changes, cells with nuclei that contained O6-MedG and were also undergoing DNA synthesis (determined by sequential immunohistochemical analysis and autoradiography) were found most commonly in the forestomach and to a lesser extent in the pylorus. This distribution of replicating damaged cells corresponds with the relative tumour yields in these upper gastrointestinal tract tissues and such cells are the probable targets in this single dose carcinogenesis regime. Thus, whilst the highest concentration of O6-MedG did not correlate tumour incidence, the overall risk for tumour induction did correlate with a significant level of DNA damage, a lower capacity for DNA repair and a marked increase in DNA synthesis over the constitutive level in the target cells. Carcinogenic risk in this system is therefore more readily determined by studying several risk factors simultaneously.

Animals↗

PubMed1993

Tissue and cell specific methylation, repair and synthesis of DNA in the upper gastrointestinal tract of Wistar rats treated with N-methyl-N'-nitro-N-nitrosoguanidine via the drinking water.

Several potential cancer risk factors have been monitored concurrently in the upper gastrointestinal tract of young male Wistar rats given N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) via the drinking water, a regimen that induces a high yield of tumours in the pylorus and to a lesser extent in the duodenum. Radioimmunoassay was used to determine the amounts of O6-methyl-2'-deoxyguanosine (O6-MedG) formed in the tissue DNA of rats given MNNG at doses of 40 or 80 micrograms/ml for periods of 3, 6 and 12 weeks. The highest adduct concentration was found in the pylorus with progressively lower concentrations in the corpus and duodenum, jejunum, forestomach and oesophagus. Between 3 and 12 weeks these adduct levels decreased in all tissues and there was no evidence of a dose dependent accumulation of O6-MedG. When analysed by immunohistochemistry the distribution of cells with nuclei containing O6-MedG was seen to be heterogeneous in the various tissues. O6-Alkylguanine-DNA alkyltransferase activity increased during the 12 weeks of MNNG treatment in oesophagus and forestomach, but decreased to approximately 50% of the initial value in the corpus, pylorus, duodenum and jejunum. The major changes in DNA synthesis and cell proliferation were the marked upward expansion (i.e. towards the lumen) of the zone of replicating cells in the glands of the pylorus and the greatly increased numbers of replicating damaged cells (i.e. cells that contained O6-MedG whilst undergoing DNA synthesis) as determined by sequential immunohistochemical analysis and autoradiography. Such cells are the probable target cells in this chronic dose carcinogenesis regime. Although similar changes also occurred in the glands of the corpus these were of lesser extent and the changes of labelling index in the oesophagus and forestomach were relatively minor. In the duodenum, MNNG treatment led to erosion of the upper part of the glands so that the zone of cells containing O6-MedG overlapped with the zone of proliferating cells resulting in the formation of many replicating damaged cells. Thus, as in the single dose study (see preceding paper) the distribution of replicating damaged cells coincides with the tumour yield in the tissues of the upper gastrointestinal tract. As in the case of single doses of MNNG the risk factors for carcinogenesis are, a significant level of DNA damage, a lower capacity for DNA repair and an increased DNA synthetic activity, again suggesting that carcinogenic risk cannot readily be determined by studying risk factors individually.

Animals↗

PubMed1993

Study of the proliferation in human gastric mucosa after in vivo bromodeoxyuridine labelling.

Studies to measure human gastric crypt or gland cell proliferation may have a number of practical clinical applications in relation to both benign and malignant gastric conditions. Bromodeoxyuridine (BrdUrd) labels human gastric mucosal cells in the S phase. Computer aided data analysis of labelled mucosa allows static proliferative indices to be estimated, including the crypt labelling index (LI), the peak labelling position, the distribution of labelled cells and indirectly the crypt growth fraction. Multiparameter flow cytometric analysis of labelled nuclei allows the S phase duration (Ts) of mucosal cells to be estimated. Specimens of histologically normal gastric body (GB, n = 16) and antral mucosa (GA, n = 10) were obtained from 25 patients with gastric carcinomas who received a bolus dose of 250 mg BrdUrd between 3.0 and 15.7 hours before surgery. Tissue sections were stained by an immunohistochemical method and subjected to detailed counting of up to 50 longitudinal crypts per specimen. The total crypt labelling index was calculated by a grid counting method. A significant difference existed between the proliferative compartments of gastric antral and body mucosa measured by a number of criteria. The median lengths of the crypts were 137 cells (GB) and 188 cells (GA). The median peak labelling positions were cell 26 (GB) and cell 61 (GA) from the crypt orifice. The mean crypt labelling indices were 2.8% (GB) and 4.8% (GA). The mean Ts of GA cells was 7.7 hours and of GB cells was 10.8 hours.

Adult↗

PubMed1993

The differentiation and lineage development of goblet cells in the murine small intestinal crypt: experimental and modelling studies.

The objective of this study was to provide a new insight into the origin and lineage development of mucus-producing cells in the small intestinal crypt. For this, new experimental data were obtained from both crypt sections and whole mounts. Model simulation studies were undertaken to investigate which rules are most likely to govern the dynamic cellular development and goblet cell pedigree. We have measured the frequency of mucus-secreting goblet cells (using alcian blue and periodic acid Schiff's stains) at each cell position in the ileal murine crypt. These measurements, made on sections, overestimate the number of goblet cells because of the size and centripetal position of the stained cytoplasm. The correction factor for this overscoring has been measured to be 0.25 by two independent methods. The data suggest that there are about 12 functional goblet cells per crypt many of which retain an ability to divide. We have also determined the labelling index of the crypt goblet cells at each cell position. Spatially, goblet cells exhibit a small degree of clustering in the crypt and show a good mixture with columnar cells. We have adapted our earlier dynamic matrix-based computer stimulation model to take into account goblet cell differentiation. The modelling suggested the following conclusions: firstly, goblet cells do not have their own stem cells but share a common stem cell with the columnar cells; secondly, the goblet lineage differentiates from the transit population two to three generations before the end of the lineage; and thirdly, the decision to switch on goblet properties is stochastic at a specific step in the development of columnar cells.

Animals↗

PubMed1992

Abrogation of adriamycin toxicity in vivo by cycloheximide.

The processes involved in cell killing by Adriamycin (ADR) and other agents that interact with topoisomerase II are unclear. To investigate the mode of ADR cytotoxicity in vivo, we have investigated the effects of the protein synthesis inhibitor, cycloheximide (CH), on cell killing by ADR in the murine intestinal tract. We have used morphological criteria to assay the cell death. ADR rapidly induces cell death in this tissue that has the morphology of apoptosis or programmed cell death. CH, when administered immediately after ADR, reduced the incidence of cell death by approximately 81% at 3 hr and approximately 51% at 6 hr after treatment. The inhibitor was only effective when administered within 0.5 hr of ADR suggesting that critical events leading to cell death may occur during this period. The inhibitor did not interfere with the ADR uptake or retention. Significant positive correlation was observed between protein and DNA synthesis inhibition (as measured by precursor uptake) and apoptosis inhibition. CH delayed progression of cells through all phases of the cell cycle except mitosis. However, ADR also had a similar effect, suggesting that progression through the cell cycle is not necessary for the expression of apoptosis. The effectiveness of CH in apoptosis inhibition, even when administered 0.5 hr after the ADR, coupled with the rapid uptake of ADR by the intestinal epithelium suggests that the mode of inhibition is unlikely to be modulation of cellular targets of ADR such as topoisomerase II or inhibition of formation of ADR-topoisomerase II complex. These data indicate that topoisomerase II-interacting agents such as ADR may induce apoptosis; the processes leading to cell death in this situation are thought to be gene dependent and require protein synthesis for their expression. Thus, the cytoprotective effect of CH may be due directly to the inhibition of protein synthesis.

Animals↗

PubMed1992

Reduction in apoptosis relative to mitosis in histologically normal epithelium accompanies fibrocystic change and carcinoma of the premenopausal human breast.

The aims of this study in 227 premenopausal women were (a) to determine the mitotic index (MI), the thymidine labelling index (LI), and the apoptotic index (AI) within the epithelial cells of histologically 'normal' human breast biopsy material removed away from the site of either a fibroadenoma or a carcinoma; and (b) to relate differences in the kinetic indices of the 'normal' epithelium to the pathology in the same breast diagnosed as fibroadenoma alone (125 patients), fibroadenoma with accompanying mild fibrocystic change (79 patients), or carcinoma (23 patients). Ratios of the average indices (AI/MI, AI/LI, MI/LI) were also calculated to minimize uncertainties related to the total cell population counted, the denominator in the LI, MI, and AI. All indices and ratios of indices were corrected for age, averaged over the cycle, and expressed as log-transformed values for analysis. Significant (P less than 0.001) reductions in AI and in apoptosis relative to mitosis (reduced AI/MI) were found in 'normal' epithelium from breasts having fibrocystic change (AI = 0.17 +/- 0.02; AI/MI = 1.01 +/- 0.18) and carcinoma (AI = 0.19 +/- 0.04; AI/MI = 0.88 +/- 0.29), compared with breast with fibroadenoma alone (AI = 0.27 +/- 0.03; AI/MI = 1.29 +/- 0.39). In the absence of significant differences in MI and LI between the 'normal' tissue groups, this finding raises the possibility that reduced epithelial cell apoptosis might be causally associated with the development of fibrocystic change and with an increased risk of development of carcinoma.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenofibroma↗

PubMed1992

The significance of spontaneous and induced apoptosis in the gastrointestinal tract of mice.

The crypts of the gastrointestinal mucosa are highly structured and polarised organs with rapid cell proliferation and an hierarchical organisation with relatively few stem cells. These tend to be located at specific positions in the tissue--at the crypt base in the colon and about four cell positions from the base (above the Paneth cells) in the small intestine. A small but constant level of spontaneous cell death occurs in the crypt. The levels of cell death are elevated by small exposures to radiation or cytotoxic drugs. The morphology of the cell death is typical of apoptosis. The maximum yield of cell death following cytotoxic exposure is observed at about 3-6 h after treatment and for many agents the death is characteristically located at the fourth (stem) cell position in the small intestine. The significance and implications of these observations are discussed in relation to the internal screening and programming within damage cells and with respect to tissue homeostatic mechanisms.

Animals↗

PubMed1992

Normal human breast xenografts activate N-nitrosodimethylamine: identification of potential target cells for an environmental nitrosamine.

Normal human breast tissue maintained as xenografts in female Balb/c (nu/nu) athymic mice is capable of metabolising N-nitrosodimethylamine (NDMA) to active intermediates that will react with DNA. Administration of NDMA to mice with slow-release implants of 17 beta-oestradiol which provide human physiological (luteal phase) circulating oestrogen levels and increase cell proliferation in the xenograft (Laidlaw et al., 1992), leads to an apparent increase in the extent of reaction with DNA compared to controls without oestrogen implants. In mice with oestrogen implants, measurements of the amounts of the promutagenic lesion, O6-methyl-2'-deoxyguanosine formed in DNA clearly indicated a dose related increase in the extent of reaction. Detection of O6-methyl-2'-deoxyguanosine using immunohistochemical procedures revealed that the nuclei of cells of the glandular epithelium, supportive tissue and adipose tissue, in decreasing order of prevalence, were positively stained for the presence of this DNA lesion. Epithelial cells, which are the putative target cells for carcinogenesis in the breast, are therefore prone to promutagenic damage as a result of exposure to an environmental nitrosamine.

Animals↗