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B Kirkhus

Publications and source records attributed to B Kirkhus.

At least 19 recordsLinked to original sources
PubMed2003

Serum cholesterol predictive equations in product development.

The aim of the study was to incorporate trans fatty acids into predictive equations for serum cholesterol and compare their effects with the effects of the individual saturated fatty acids 12:0, 14:0 and 16:0. We have introduced trans fatty acids from partially hydrogenated soybean oil (TransV) and fish oil (TransF) into previously published equations by constrained regression analysis. Prior knowledge about the signs and ordering of existing regression coefficients were incorporated into the regression modelling by adding lower and upper bounds to the coefficients. Oleic acid (18:1) and polyunsaturated fatty acids (18:2, 18:3) were not sufficiently varied in the studies and the respective regression coefficients therefore set equal to those found by Yu et al. (Am J Clin Nutr 1995;61:1129-39). Stearic acid (18:0) considered to be neutral was not included in the equations. The regression analyses were based on results from four controlled dietary studies with a total of 95 participants and including 10 diets differing in fatty acid composition. The analyses resulted in the following equations where the change in cholesterol is expressed in mmol/L and the change in intake of fatty acids is expressed in E%: Delta Total cholesterol = 0.01 delta(12:0) + 0.12 Delta(14:0) + 0.057 delta(16:0) + 0.039 delta(TransF) + 0.031 delta(TransV)- 0.0044 delta(18:1) - 0.017 delta(18:2, 18:3) and deltaLDL cholesterol = 0.01 delta(12:0) + 0.071 delta(14:0) + 0.047 delta(16:0) + 0.043 delta(TransF) + 0.025 delta(TransV) - 0.0044 delta(18:1) - 0.017 delta(18:2, 18:3). The test set used for validation consisted of 22 data points from seven recently published dietary studies. The equation for total cholesterol showed good prediction ability with a correlation coefficient of 0.981 between observed and predicted values. The equation has been used to reformulate margarines into "trans free" products all with more favourable effects on serum cholesterol than previous products. Also a cholesterol reducing margarine has been produced. When tested against butter in an open clinical trial among subjects with mild hypercholesterolemia the observed cholesterol-lowering effect of this margarine corresponded reasonably well with the predicted (0.77 vs. 0.64 mmol/L). We conclude that the equation has practical applicability and can be used to formulate and nutritionally optimise fat products as well as to evaluate already existing products on the market.

Adult↗
PubMed2001

Serum cholesterol predictive equations with special emphasis on trans and saturated fatty acids. an analysis from designed controlled studies.

The effects of dietary trans fatty acids on serum total and low density lipoprotein (LDL) cholesterol have been evaluated by incorporating trans fatty acids into predictive equations and comparing their effects with the effects of the individual saturated fatty acids 12:0, 14:0, and 16:0. Trans fatty acids from partially hydrogenated soybean oil (TRANS V) and fish oil (TRANS F) were included in previously published equations by constrained regression analysis, allowing slight adjustments of existing coefficients. Prior knowledge about the signs and ordering of the regression coefficients was explicitly incorporated into the regression modeling by adding lower and upper bounds to the coefficients. The amounts of oleic acid (18:1) and polyunsaturated fatty acids (18:2, 18:3) were not sufficiently varied in the studies, and the respective regression coefficients were therefore set equal to those found by Yu et al. [Yu, S., Derr, J., Etherton, T.D., and Kris-Etherton, P.M. (1995) Plasma Cholesterol-Predictive Equations Demonstrate That Stearic Acid Is Neutral and Monounsaturated Fatty Acids Are Hypocholesterolemic, Am. J. Clin. Nutr. 61, 1129-1139]. Stearic acid (18:0), considered to be neutral, was not included in the equations. The regression analyses were based on results from four controlled dietary studies with a total of 95 participants and including 10 diets differing in fatty acid composition and with 30-38% of energy (E%) as fat. The analyses resulted in the following equations, where the change in cholesterol is expressed in mmol/L and the change in intake of fatty acids is expressed in E%: delta Total cholesterol = 0.01 delta(12:0) + 0.12 delta(14:0) + 0.057 delta(16:0) + 0.039 delta(TRANS F) + 0.031 delta(TRANS V) - 0.0044 delta(18:1) - 0.017 delta(18:2, 18:3) and deltaLDL cholesterol = 0.01 delta(12:0) + 0.071 delta(14:0) + 0.047 delta(16:0) + 0.043 delta(TRANS F) + 0.025 delta(TRANS V) - 0.0044 delta(18:1) - 0.017 delta(18:2, 18:3). The regression analyses confirm previous findings that 14:0 is the most hypercholesterolemic fatty acid and indicate that trans fatty acids are less hypercholesterolemic than the saturated fatty acids 14:0 and 16:0. TRANS F may be slightly more hypercholesterolemic than TRANS V or there may be other hypercholesterolemic fatty acids in partially hydrogenated fish oil than those included in the equations. The test set used for validation consisted of 22 data points from seven recently published dietary studies. The equation for total cholesterol showed good prediction ability with a correlation coefficient of 0.981 between observed and predicted values. The equation has been used by the Norwegian food industry in reformulating margarines into more healthful products with reduced content of cholesterol-raising fatty acids.

Adult↗
PubMed1998

Replacement of partially hydrogenated soybean oil by palm oil in margarine without unfavorable effects on serum lipoproteins.

We have compared the effects of three different margarines, one based on palm oil (PALM-margarine), one based on partially hydrogenated soybean oil (TRANS-margarine) and one with a high content of polyunsaturated fatty acids (PUFA-margarine), on serum lipids in 27 young women. The main purpose of the study was to test if replacement of trans fatty acids in margarine by palmitic acid results in unfavorable effects on serum lipids. The sum of saturated fatty acids (12:0, 14:0, 16:0) was 36.3% of total fatty acids in the PALM-diet, the same as the sum of saturated (12:0, 14:0, 16:0) (12.5%) and trans (23.1%) fatty acids in the TRANS-diet. This sum was 20.7% in the PUFA-diet. The content of oleic acid was 37.9, 35.2, and 38.6%, respectively, in the three diets, whereas linoleic acid amounted to 16, 13.5, and 27.3%, respectively. Total fat provided 30-31% and the test margarines 26% of total energy in all three diets. The subjects consumed each of the diets for 17 d in a Latin-square crossover design. There were no significant differences in total cholesterol, low density lipoprotein (LDL)-cholesterol and apolipoprotein B (apoB) between the TRANS- and the PALM-diets. High density lipoprotein (HDL)-cholesterol and apoA-1 were significantly higher on the PALM-diet compared to the TRANS-diet whereas the ratio of LDL-cholesterol to HDL-cholesterol was lower, although not significantly (P = 0.077) on the PALM-diet. Total cholesterol, LDL-cholesterol, and apoB were significantly lower on the PUFA-diet compared to the two other diets. HDL-cholesterol was not different on the PALM- and the PUFA-diets but it was significantly lower on the TRANS-diet compared to the PUFA diet. Compared to the PUFA-diet the ratio of LDL- to HDL-cholesterol was higher on both the PALM- and the TRANS-diets whereas apoA-1 was not different. Triglycerides and lipoprotein (a) were not significantly different among the three diets. We concluded that nutritionally, palmitic acid from palm oil may be a reasonable alternative to trans fatty acids from partially hydrogenated soybean oil in margarine if the aim is to avoid trans fatty acids. A palm oil-based margarine is, however, less favorable than one based on a more polyunsaturated vegetable oil.

Adult↗
PubMed1998

Effect on plasma lipids and lipoproteins of replacing partially hydrogenated fish oil with vegetable fat in margarine.

We have compared the effects on lipoproteins and haemostatic variables of two hard margarines with similar functional properties, one traditional margarine containing partially hydrogenated fish oil (PHFO), and one experimental margarine based on vegetable oil (VO). Both were all-purpose cooking margarines with nearly identical functional properties. Trans fatty acids from PHFO in the traditional margarine were replaced mostly by saturated, monounsaturated and trans fatty acids of vegetable origin in the new formulation. Both test margarines contained approximately the same amount of cis polyunsaturated fatty acids. Sixteen female normolipidaemic students consumed each diet with the two test margarines for 14 d in random order (crossover design). The amount of fat was 31% energy in the PHFO diet and 32% energy in the VO diet. The test margarines provided approximately 26% energy in both diets. In the PHFO diet 7.8% of the energy was derived from trans fatty acids and 9.2% from saturated fatty acids (12:0, 14:0 and 16:0) while in the VO diet, 1.1% energy was derived from trans fatty acids and 13.3% from saturated fatty acids (12:0, 14:0 and 16:0). The natural content of cholesterol in PHFO was deliberately not balanced by addition of cholesterol to the VO diet, thus the PHFO diet contained 215 mg and the VO diet 86 mg cholesterol per 8.5 MJ. LDL-cholesterol concentration was 19% higher in subjects on the PHFO diet compared with the VO diet (P < 0.01). The ratio LDL-cholesterol:HDL-cholesterol was 12.6% higher in subjects on the PHFO diet compared with the VO diet (P < 0.01). The level of apolipoprotein (apo)A-I was 6% lower in subjects on the PHFO diet compared with the VO diet (P < 0.01). The ratio apoB:apoA-I was 10.4% higher in subjects on the PHFO diet than on the VO diet (P < 0.01). There were no significant differences in total cholesterol, HDL-cholesterol, triacylglycerols, apoB, lipoprotein(a) and haemostatic variables between the diets. Our results demonstrate that PHFO, with its unfavourable effects on plasma lipids, can be replaced by vegetable oils in margarine without appreciable loss of functional properties but with significant improvement in the effects on plasma lipoproteins.

Adult↗
PubMed1993

Heterogeneity in the mouse epidermal cell cycle analysed by computer simulations.

Different sets of cell kinetic data obtained over many years from hairless mouse epidermis have been simulated by a mathematical model including circadian variations. Simulating several independent sets of data with the same mathematical model strengthens the validity of the results obtained. The data simulated in this investigation were all obtained with the experimental system in a state of natural synchrony. The data include cell cycle phase distributions measured by DNA flow cytometry of isolated epidermal basal cells, fractions of tritiated thymidine ([3H]TdR) labelled cells within the cell cycle phases measured by cell sorting at intervals after [3H]TdR pulse labelling, bivariate bromodeoxyuridine (BrdUrd)/DNA data from epidermal basal cells isolated at intervals after pulse labelling with BrdUrd, mitotic rate and per cent labelled mitosis (PLM) data from histologic sections. The following main new findings were made from the simulations: the second PLM peak observed at about 35 h after pulse labelling is hardly influenced by circadian variations; the peak is mainly determined by persisting synchrony of a rapidly cycling population with a G1-duration (TG1) of 20 h to 30 h; and there is a highly significant population of slowly cycling G1-cells (G1 sigma). However, no significant circadian variations were found in the number of these cells.

Animals↗
PubMed1992

Multivariate flow cytometry of epidermal regeneration provoked by a skin irritant and a tumor promoter.

The DNA content and the changes in cellular and nuclear size of isolated regenerating mouse epidermal basal cells were studied after topical application of the skin irritant cantharidin and the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) to the back skin of hairless mice. The DNA and protein contents of isolated basal cells were stained with propidium iodide and fluorescein isothiocyanate, respectively, and analysed by flow cytometry using the total protein fluorescence as an estimate of cell size and the DNA fluorescence pulse width as an estimate of nuclear size. Transmission electron microscopy was used to identify cells sorted from regions in the bivariate DNA/protein distributions. The results showed that both chemicals induced an increase in cellular as well as nuclear size of the basal cells. The increase in size was higher in TPA treated than in cantharidin treated animals, and the bivariate DNA/protein distributions of TPA treated cells differed from those of cantharidin treated cells in that two subpopulations of cycling keratinocytes could be identified. These deviations are probably related to the higher proliferative response observed after TPA treatment and the possibility that proliferative subpopulations in epidermis respond differently to TPA. It may reflect mechanisms providing for a growth advantage of initiated cells, important in tumor promotion. About 8% of the cells in the suspensions from treated animals were non-cycling non-keratinocytes, probably infiltrating leukocytes. The results indicate a strong correlation between rapid regenerative cell cycle progression, i.e., reduced G1 transit time and increased cellular and nuclear size.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

BrdUrd incorporation studies for evaluation of spermatogenesis in the blue fox.

The utility of BrdUrd incorporation techniques for studies of spermatogenesis was investigated in the blue fox. BrdUrd was injected intraperitoneally followed by collection of testicular tissue by castration/hemicastration at intervals up to 35 days after pulse labelling. Fluorescent tagged monoclonal antibodies against BrdUrd allowed detection of cells with incorporated tracer in histological sections by fluorescent light microscopy as well as in isolated testicular cells by bivariate BrdUrd/DNA flow cytometry. The duration of the spermatogenic cycle was estimated by following the labelled cohort of preleptotene spermatocytes by immunofluorescence in sections through the various stages of maturation to the late spermatid stage. These data were confirmed by bivariate BrdUrd/DNA flow cytometry of testicular cells in suspensions. Furthermore, estimations of the S phase durations and length of the spermatogonial cell cycle were possible. A consistent and satisfactory fluorescence intensity of incorporated label throughout the study shows that degradation of the incorporated label is no practical problem for this type of study, and suggests that the method is an excellent tool for studying aspects of proliferation and maturation during normal as well as perturbed spermatogenesis. Advantages of the described method include avoidance of potential radiation influence on spermatogenesis from commonly used radiolabelled tracers, e.g., 3H-TdR, and that both large and small animals can be investigated at modest cost since the unlabelled BrdUrd is considerably less expensive than labelled tracers.

Animals↗
PubMed1992

Circadian variations in cell cycle phase progression of mouse epidermal cells measured directly by bivariate BrdUrd/DNA flow cytometry.

Circadian stage-dependent variations in cell cycle traverse of mouse epidermal cells in vivo were investigated. The fate of cohorts of basal cells pulse-labelled with bromodeoxyuridine (BrdUrd) at different times of the day were studied by bivariate BrdUrd/DNA flow cytometry of isolated epidermal basal cells. Basal cells were tracked through the cell cycle up to 96 h after intraperitoneal injection of BrdUrd at 0800 and 2000, or followed for 6 h after BrdUrd injection at 0400, 1200, 1600 and 2400. The results confirmed our previous assumption that the cell cycle progression through S phase and G2 phase is considerably delayed at night, i.e. from 1600 to 0400, compared with daytime. The results indicate variations in G1 phase as well. The data strongly support the hypothesis that the main parameters responsible for circadian fluctuations in mitotic activity are variations in the S and G2 phase durations. The data are also consistent with the notion of proliferative heterogeneity among basal cells as described by a hierarchical proliferation model.

Animals↗
PubMed1991

A comparison between the epidermal regenerative responses provoked by a skin irritant and a tumor promoter using anti-BrdUrd/DNA flow cytometry.

The proliferative responses induced in hairless mouse epidermis after application of the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) and the skin irritant cantharidin were investigated. Doses known to give the same degree of hyperplasia were chosen. Mice were pulse-labeled with bromodeoxyuridine (BrdUrd) 30 min prior to or 24 h after a single application of either cantharidin or TPA, and thereafter killed at various time intervals. The basal cells were isolated from epidermis, fixed in 70% ethanol and prepared for bivariate BrdUrd/DNA flow cytometric analysis. Cells pulse-labeled in S phase 30 min prior to treatment with cantharidin or TPA were slightly delayed in their progression through S phase and temporarily blocked in G2 phase. However, they were still able to re-enter S phase 18 h later, indicating a shortening of the G1 phase. Cells pulse-labeled 24 h after treatment had a considerably reduced cell cycle time, i.e. reduced G1 transit time. Hence, the wave of cells entering S phase from 16 h after injury could be explained by an immediate reduction in G1 transit time, without assuming recruitment of temporarily resting G0/G1 cells. Although cantharidin caused the longest initial delay in cell cycle progression, the subsequent proliferative response was less pronounced than that provoked by TPA. Rapid proliferation may allow for clonal expansion of initiated cells. The higher ability of TPA to induce rapid proliferation, apparently without causing any severe initial cell damage, may thus be related to its higher tumor promoting ability.

Animals↗
PubMed1990

Cell kinetics in mouse epidermis studied by bivariate DNA/bromodeoxyuridine and DNA/keratin flow cytometry.

Hairless mice were injected intraperitoneally with bromodeoxyuridine (Brd-Urd). Basal cells were isolated from epidermis, fixed in 70% ethanol, and prepared for bivariate BrdUrd/DNA flow cytometric (FCM) analysis. Optimum detection of incorporated BrdUrd in DNA was obtained by combining pepsin digestion and acid denaturation. The cell loss was reduced to a minimum by using phosphate-buffered saline containing Ca2+ and Mg2+ to neutralize the acid. The percentage of cells in S phase and the average uptake of BrdUrd per labelled cell in eight consecutive windows throughout the S phase were measured after pulse labelling at intervals during a 24 h period. Furthermore, the cell cycle progression of a pulse-labelled cohort of cells was followed up to 96 h after BrdUrd injection. In general the results from both experiments were in good agreement with previous data from 3H-thymidine labelling studies. The percentage of cells in S phase was highest at night and lowest in the afternoon, whereas the average uptake of BrdUrd per labelled cell showed only minor circadian variations. There were no indications that BrdUrd significantly perturbed normal epidermal growth kinetics. A cell cycle time of about 36 h was observed for the labelled cohort. Indications of heterogeneity in traverse through G1 phase were found, and the existence of slowly cycling or temporarily resting cells in G2 phase was confirmed. There was, however, no evidence of a significant population of temporarily resting cells in the S phase. Bivariate DNA/keratin FCM analysis revealed a high purity of basal cells in the suspensions and indicated that the synthesis of the differentiation-keratin K10 was turned on only in G1 phase and after the last division.

Animals↗
PubMed1990

Mathematical model analysis of mouse epidermal cell kinetics measured by bivariate DNA/anti-bromodeoxyuridine flow cytometry and continuous [3H]-thymidine labelling.

In a previous study the epidermal cell kinetics of hairless mice were investigated with bivariate DNA/anti-bromodeoxyuridine (BrdU) flow cytometry of isolated basal cells after BrdU pulse labelling. The results confirmed our previous observations of two kinetically distinct sub-populations in the G2 phase. However, the results also showed that almost all BrdU-positive cells had left S phase 6-12 h after pulse labelling, contradicting our previous assumption of a distinct, slowly cycling, major sub-population in S phase. The latter study was based on an experiment combining continuous tritiated thymidine [( 3H]TdR) labelling and cell sorting. The purpose of the present study was to use a mathematical model to analyse epidermal cell kinetics by simulating bivariate DNA/BrdU data in order to get more details about the kinetic organization and cell cycle parameter values. We also wanted to re-evaluate our assumption of slowly cycling cells in S phase. The mathematical model shows a good fit to the experimental BrdU data initiated either at 08.00 hours or 20.00 hours. Simultaneously, it was also possible to obtain a good fit to our previous continuous labelling data without including a sub-population of slowly cycling cells in S phase. This was achieved by improving the way in which the continuous [3H]TdR labelling was simulated. The presence of two distinct subpopulations in G2 phase was confirmed and a similar kinetic organization with rapidly and slowly cycling cells in G1 phase is suggested. The sizes of the slowly cycling fractions in G1 and G2 showed the same distinct circadian dependency. The model analysis indicates that a small fraction of BrdU labelled cells (3-5%) was arrested in G2 phase due to BrdU toxicity. This is insignificant compared with the total number of labelled cells and has a negligible effect on the average cell cycle data. However, it comprises 1/3 to 1/2 of the BrdU positive G2 cells after the pulse labelled cells have been distributed among the cell cycle compartments.

Animals↗
PubMed1989

The epidermal cell kinetic response to ultraviolet B irradiation combines regenerative proliferation and carcinogen associated cell cycle delay.

The cell cycle traverse of epidermal basal cells 24 h after in vivo exposure of ultraviolet B (UVB) irradiation was studied by immunochemical staining of incorporated bromodeoxyuridine (BrdU) and bivariate BrdU/DNA flow cytometric analysis. The results were compared with the cell kinetic patterns following topical application of the skin carcinogen methylnitrosourea (MNU) as well as the skin irritant cantharidin. Hairless mice were injected intraperitoneally with BrdU 24 h after treatment of their back skin with either a minimal erythema dose of UVB, or a single application of MNU or cantharidin dissolved in acetone. The cell cycle traverse of the BrdU-labelled cohorts of epidermal basal cells were then followed for the subsequent 12 h. At 6 h after BrdU-injection, when all labelled cells in the control group as well as in the cantharidin group had left the S phase, the bivariate distributions of the UVB-exposed and the MNU group showed that BrdU-positive cells were still present in S phase. Hence, UVB irradiation, similar to the carcinogen MNU, prolonged the S phase duration in some of the basal cells. At 12 h after pulse labelling, however, BrdU-positive cells from UVB-exposed mice were re-entering S phase from G1 phase, indicating that UVB irradiation induced a shortening of the cell cycle time as well, similar to the response observed after cantharidin. The present data can not tell whether these cells also were delayed in S phase. Thus, the cell cycle traverse in hairless mouse epidermis 24 h after in vivo exposure to UVB seemed to be a combination of the cell kinetic effects following chemical skin carcinogens and skin irritants. UVB irradiation induced both a delay in transit time through S phase, probably due to DNA damage and subsequent repair, as well as a reduction in the total cell cycle time consistent with rapid regenerative proliferation.

Animals↗
PubMed1988

Characterization of bladder tumours by multiparameter flow cytometry with special reference to grade II tumours.

Sixty-three human transitional cell carcinomas of the urinary bladder were studied by multiparameter flow cytometry (FCM). The cellular DNA content, the cellular protein content, the fraction of cells in S phase, and the nuclear size were registered and correlated to histological grade (WHO) and histologically determined infiltration through the basement membrane. Aneuploidy was found in the great majority of grade III tumours, but in only 24% of grade II tumours. A new, combined variable, viz. the cellular DNA to protein ratio, indicated a possibility for further subdivision of the tumours. Grade II tumours, which constitute a rather heterogeneous group with regard to prognosis, could be classified in two subgroups: One group of diploid tumours with the FCM characteristics of grade I tumours, and another group of diploid and aneuploid tumours with the characteristics of grade III tumours. Infiltration was most frequently seen in the latter subgroup. The putative prognostic relevance of such a subdivision will be the subject of a future study. Compared to FCM measurement of DNA alone, multiparameter FCM, including measurement of the total cellular protein content, has given additional information that may be of prognostic value.

Carcinoma, Transitional Cell↗
PubMed1988

Selective detachment of a tetraploid subline of primary keratinocytes after treatment with the tumor promoter 12-0-tetradecanoylphorbol-13-acetate.

TPA treatment of primary keratinocytes in medium with either 0.02 mM Ca++ or 1.2 mM Ca++ enhances terminal differentiation assessed by the production of cornified cells. A tetraploid keratinocyte stemline which appears soon after establishing primary cultures is selectively detached from the culture dish after treatment with the tumor promoter TPA. The remaining cells proliferate in the presence of TPA. This selective effect of TPA on subpopulations of keratinocytes may be critical to its activity as a tumor promoter.

Animals↗
PubMed1987

Persisting long-term effects of a single carcinogenic dose of methylnitrosourea on epidermal growth in mice.

The cell proliferation in hairless mouse epidermis was studied before tumor development following a single application of a carcinogenic dose (2 mg) of N-methyl-N-nitrosourea (MNU). The number of basal and suprabasal cells, the mitotic index (MI) and the mitotic rate (MR) were scored in histological sections. The [3H]thymidine labeling index (LI) and the mean grain count (MGC) were scored in histological sections or in smears of basal cells. Flow cytometric two-parameter analyses of cellular DNA and protein content were performed on isolated epidermal basal cells. An increased MR and a slight but consistent epidermal hyperplasia were found. A 24-h study performed 25 weeks after MNU application showed that the MR and MI were altered in a circadian stage-dependent manner with considerably increased values around noon when the circadian rhythms had their peaks, followed by normal values around midnight. The LI was generally increased, but showed a normal circadian rhythm with high values at night and low values during day. The MGC was reduced at night and in the morning when the LI values were high. The results show that a single carcinogenic dose of MNU caused alterations in the epidermal growth kinetics that persisted until tumor development. The altered growth parameters, however, had circadian rhythms that were in phase with control rhythms. Assuming a constant size of the proliferative compartment, the increased mitotic activity indicated a considerable shortening of the mean cell cycle time.

Animals↗
PubMed1987

Carcinogenic doses of methylnitrosourea induce dose response related delay in transit through S and G2 phases in mouse epidermis: a cell kinetic study.

The cell kinetic, tumorigenic and carcinogenic effects of the short acting, alkylating carcinogen N-methyl-N-nitrosourea (MNU) on hairless mouse epidermis were investigated. The epidermal mitotic rate, the mitotic index, and the number of basal and suprabasal cells were scored in histological sections. Incorporation of [3H]thymidine and flow cytometric analysis of cellular DNA and protein content were performed on isolated basal cells at intervals for up to 10 days after a single application of either 1 or 10 mg MNU. The ensuing tumor rates and yields were observed for up to 48 weeks after 1 mg MNU and 30 weeks after 10 mg MNU. Generally, MNU induced an initial delay in epidermal cell cycle progression with an accumulation of cells in the S and G2 phases. Some days after treatment the delayed cells were released and entered mitosis. One milligram MNU caused a moderate delay of cells in S and G2, lasting for 2-3 days, and this was followed by a release leading to an increased number of suprabasal cells on day 7. The highest dose of MNU caused a more pronounced delay in transit through S and G2 and seemed to be followed by rapid regenerative proliferation. The subsequent tumor crop after 10 mg was significantly higher than that seen after the lowest dose. The present cell kinetic results are consistent with previous data from the study of other carcinogens, all showing a carcinogen-induced initial reduction in DNA synthesis after appropriate doses. A delay in transit through G2 phase was found as well, indicating that a general delay in cell cycle progression may follow the application of most (or all) carcinogens.

Adenoma↗
PubMed1986

Evidence of mouse epidermal subpopulations with different cell cycle times.

In order to obtain information on the distribution of total cell cycle times in hairless mouse epidermis, basal cells were isolated and prepared for DNA flow cytometry at intervals after a pulse labeling with 50 microCi of thymidine. The DNA distributions were recorded, and cells were sorted from windows in the S, G2, and G1 phases of the cell cycle, collected on glass slides, and subjected to autoradiography. The proportions of labeled cells were scored in each fraction, and the percentage of labeled mitoses was determined in histologic sections from the same animals. Grain count distributions were recorded at selected time points over labeled cells in sorted fractions and over labeled mitoses. The movement of the labeled S-phase cohort was thus followed through all cell cycle phases. Peaks in labeled cells were observed at about 36 h in S phase, G2 phase, and mitosis, and high levels of labeled G2 cells and mitoses were seen at about 80 h. These results indicate the existence of one rapidly cycling subpopulation of keratinocytes with a cell cycle time slightly less than 30 h, in addition to keratinocytes with considerably longer cell cycle times. The first peak of labeled G2 cells reached only about 30%. This is consistent with earlier findings of about 30% G2 cells with a rapid traverse, and 70% with a considerably delayed traverse through G2 phase. The proportion of labeled G1 cells reached a value corresponding to twice the initial labeling index at 8 h after pulse labeling. This is consistent with previously obtained phase durations, indicating an unperturbed cell cycle traverse of labeled cells from S phase through G2 and mitosis.

Animals↗