Colonic proliferation is increased in senescent rats

Toxicities and outcomes of neoadjuvant treatment in elderly patients with locally advanced rectal cancer: a scoping review protocol

INTRODUCTION

Colorectal cancer remains the second leading cause of cancer-related death in 60-79 years old and the third leading cause of death in patients aged 80 and above. Rectal cancer accounts for approximately a third of colorectal cancer diagnoses. The current standard of care for managing locally advanced rectal cancer involves a multimodal combined approach with neoadjuvant treatment, surgery with total mesorectal excision and adjuvant chemotherapy. Neoadjuvant treatment can be in the form of short-course radiotherapy, long-course concurrent radiotherapy with chemotherapy or total neoadjuvant chemotherapy with concurrent chemoradiotherapy followed by chemotherapy. This scoping aims to assess the toxicity and outcome of the different neoadjuvant treatment modalities in elderly patients.

METHODS AND ANALYSIS

We will use Arksey and O'Malley's five scoping review methodology framework stages. Searches will be conducted in Ovid Medline, Embase, Cochrane database and CINAHL. In addition, the researcher will hand search for all registered trials, using a combination of terms such as "locally advanced rectal cancer", "neoadjuvant treatment", and "elderly patients." Two independent reviewers will screen titles and abstracts and then full text based on predefined inclusion and exclusion criteria. Publications will be extracted using a customised data extraction tool to include study characteristics, research topics, exposures and outcomes.

ETHICS AND DISSEMINATION

Ethics approval is not required as the data will be collected from the existing literature. The findings of this study will help with future clinical research on the topic. We will publish the findings of this review in a peer-reviewed journal and present them at academic conferences targeting geriatric oncology service providers.

Improvement of intestinal stem cells and barrier function via energy restriction in middle-aged C57BL/6 mice

This study aimed to reveal the impact of energy restriction on the intestine via structural and molecular changes in terms of intestinal stem cell (ISC) function, ISC niche, intestinal epithelial barrier function, and intestinal immune function. Female C57BL/6J mice, aged 12 months, fed a commercial chow were used in this study. The ISC function, ISC niche, intestinal epithelial barrier function, and intestinal immune function were assessed. Energy restriction reversed aging-induced intestinal shortening and made the crypts shallower. The intestinal epithelial cells isolated from the intestine showed a significant increase in the expression levels of stem cell-associated genes in small intestinal epithelial cells as detected by flow cytometry. Despite the increase in the number of stem cells and the expression levels of markers, no increase or decrease was found in the enteroid complexity of the small intestine and colonic enteroid formation in vitro. The colonic mucous layer was measured in mice of the energy restricted (ER)-treated group to investigate the epithelial barrier function in the colon. The results revealed that the barrier was more complete. The fluorescence intensity of tight junction markers claudin-2 and zonula occludens-1 increased and the mRNA expression profiles of monocyte chemotactic protein 1 and interleukin-6 decreased in the colon of mice in the ER-treated group. The beneficial effects of ER on the colon in terms of the integrity of the mucosal barrier and alleviation of inflammation were confirmed, thus highlighting the importance of modulating the intestinal function in developing effective antiaging dietary interventions.

Microbial Metabolites and Intestinal Stem Cells Tune Intestinal Homeostasis

Microorganisms that colonize the gastrointestinal tract, collectively known as the gut microbiota, are known to produce small molecules and metabolites that significantly contribute to host intestinal development, functions, and homeostasis. Emerging insights from microbiome research reveal that gut microbiota-derived signals and molecules influence another key player maintaining intestinal homeostasis-the intestinal stem cell niche, which regulates epithelial self-renewal. In this review, the literature on gut microbiota-host crosstalk is surveyed, highlighting the effects of gut microbial metabolites on intestinal stem cells. The production of various classes of metabolites, their actions on intestinal stem cells are discussed and, finally, how the production and function of metabolites are modulated by aging and dietary intake is commented upon.

Effects of a grape-supplemented diet on proliferation and Wnt signaling in the colonic mucosa are greatest for those over age 50 and with high arginine consumption

A diet rich in fruits and vegetables, and a grape-derived compound, resveratrol, have been linked to a reduced incidence of colon cancer. In vitro and in vivo, resveratrol suppresses Wnt signaling, a pathway constitutively activated in over 85 % of colon cancers.

Thirty participants were placed on a low resveratrol diet and subsequently allocated to one of three groups ingesting 1/3-to-1 lb (0.15–0.45 kg) of grapes per day for 2 weeks. Dietary information was collected via 24-h recall. Colon biopsies for biomarker analysis were obtained pre- and post-grape and evaluated for the expression of Wnt pathway target genes and for markers of proliferation by RT-PCR and immunohistochemistry.

Participants lost an average of 2 · 6 lb (1.2 kg, p = 0 · 0018) during the period of grape ingestion. The expression of CyclinD1 (p < 0 · 01), AXIN2, CD133 (p = 0 · 02) and Ki67 (p = 0 · 002) were all reduced after grape ingestion. Individuals over 50 years of age and those with high dietary arginine consumption had increased basal expression of CyclinD1, AXIN2, cMYC and CD133 (p value range 0 · 04 to <0 · 001) that, following grape ingestion, were reduced to levels seen in younger participants.

The reduction in Wnt signaling and mucosal proliferation seen following short-term ingestion of 1/3–1 lb (0.15–0.45 kg) of grapes per day may reduce the risk of mutational events that can facilitate colon carcinogenesis. The potential benefit is most marked for high-risk older individuals and individuals whose diet is high in arginine intake. Dietary grape supplementation may play a role in colon cancer prevention for high-risk individuals.

EGFR(s) in aging and carcinogenesis of the gastrointestinal tract

Cells of the gastrointestinal (GI) mucosa are subject to a constant process of renewal which, in normal adults, reflects a balance between the rates of cell production and cell loss. Detailed knowledge of these events is, therefore, essential for a better understanding of the normal aging processes as well as many GI diseases, particularly malignancy, that represent disorders of tissue growth. In general, many GI dysfunctions, including malignancy, increase with advancing age, and aging itself is associated with alterations in structural and functional integrity of the GI tract. Although the regulatory mechanisms for age-related increase in the incidence of GI-cancers are yet to be fully delineated, recent evidence suggests a role for epidermal growth family receptors and its family members {referred to as EGFR(s)} in the development and progression of carcinogenesis during aging. The present communication discusses the involvement of EGFR(s) in regulating events of GI cancers during advancing age and summarizes the current available therapeutics targeting these receptors. The current review also describes the effectiveness of ErbB inhibitors as well as combination therapies. Additionally, the involvement of GI stem cells in the development of the age-related rise in GI cancers is emphasized.

Schlafen 3, a novel gene, regulates colonic mucosal growth during aging

Although aging is associated with increased proliferation and decreased apoptosis in the colonic mucosa of Fischer 344 rats, the regulatory mechanisms are poorly understood. Gene expression profiling (Illumina platform) was carried out in freshly isolated colonic mucosal cells from young (4-6 mo old) and aged (22-24 mo old) Fischer 344 rats. Sixty-six genes were differentially expressed in the colonic mucosa between young and old animals (P<0.05). In particular, the expression of schlafen 3, a negative regulator of proliferation, was decreased by 8- to 10-fold in the colonic mucosa of aged rats. Administration of wortmannin, which inhibited colonic mucosal proliferation in the colonic mucosa of aged rats, stimulated the expression of schlafen 3, indicating a growth regulatory role of this gene. To further determine the growth regulatory properties of schlafen 3 gene, schlafen 3 cDNA was transfected in colon cancer HCT-116 cells. This resulted in a 30-40% inhibition of cellular growth, accompanied by decreased expression of PCNA and cyclin D1 and reduced phosphorylation of retinoblastoma protein. In conclusion, our present study demonstrates that several genes involved in proliferation and apoptosis are differentially expressed in the colonic mucosa of young and aged rats. Schlafen 3, a novel negative regulator of growth, which is markedly downregulated in the colonic mucosa of the aged, may play a role in regulating colonic mucosal growth during aging.

Colon cancer and the elderly: from screening to treatment in management of GI disease in the elderly

Colorectal cancer is one of the commonest tumours in the Westernized world affecting mainly the elderly. This neoplasm in older individuals occurs more often in the right colon and grows more rapidly than in the young, often shows a mucinous histology and mismatch repair gene changes. Effective screening permits discovery of colorectal cancer at an early highly treatable stage and allows for detection and removal of premalignant colorectal adenomas. Screening methods that focus on cancer detection use fecal assays for the presence of blood or altered DNA, those for detection of adenomas (and early cancer) use endoscopic or computerised radiologic techniques. Broad use of screening methods has lowered colorectal cancer development by about 50%. In addition, prevention of the earliest stage of colon carcinogenesis has been shown to be effective in small prospective studies and epidemiologic surveys but have not been employed in the general population. Since 1996 the chemotherapeutic armamentarium for metastatic colorectal cancer has grown beyond 5-fluorouracil to include an oral 5-fluorouracil prodrug, capecitabine as well as irinotecan and oxaliplatin. Three targeted monoclonal antibodies (Moabs), bevacizumab (an anti-vascular endothelial growth factor Moab) and cetuximab/panitumumab, both anti-epidermal growth factor receptor inhibitors, have also earned regulatory approval. Most stage IV patients are treated with all of these drugs over 2 or 3 sequential lines of palliative chemotherapy and attain median survivals approaching 24 months. Lastly, adjuvant oxaliplatin plus 5-fluorouracil for high risk resected stage II and stage III colon cancer patient has led to substantial improvement in cure rates. With appropriate care of age associated comorbidities these treatment modalities are feasible and effective in the geriatric population.

Age-related upregulation of Drosophila caudal gene via NF-kappaB in the adult posterior midgut

The Drosophila midgut has emerged as a powerful model system for the investigation of fundamental cellular pathways relevant to intestinal stem cell biology. Understanding the age-related changes in the adult Drosophila midgut may provide insights into the molecular mechanisms that link aging to the modulation of adult stem cell population. The caudal-related homeobox genes encode intestine-specific transcription factors required for normal intestinal development and maintenance. Here, we demonstrate that caudal gene expression is upregulated in the adult posterior midgut in response to age and oxidative stress, and that overexpression of Caudal can stimulate cell proliferation in the adult posterior midgut. We further demonstrate that the age- and oxidative-stress-related upregulation of the caudal gene is mediated by the NF-kappaB binding site located in the 5'-flanking region of the caudal gene. Our results may contribute to an understanding of the mechanisms of age-related changes in the number and activity of intestinal stem cells and progenitors in the Drosophila adult midgut.

Age-related changes in Drosophila midgut are associated with PVF2, a PDGF/VEGF-like growth factor

Age-associated changes in stem cell populations have been implicated in age-related diseases, including cancer. However, little is known about the underlying molecular mechanisms that link aging to the modulation of adult stem cell populations. Drosophila midgut is an excellent model system for the study of stem cell renewal and aging. Here we describe an age-related increase in the number and activity of intestinal stem cells (ISCs) and progenitor cells in Drosophila midgut. We determined that oxidative stress, induced by paraquat treatment or loss of catalase function, mimicked the changes associated with aging in the midgut. Furthermore, we discovered an age-related increase in the expression of PVF2, a Drosophila homologue of human PDGF/VEGF, which was associated with and required for the age-related changes in midgut ISCs and progenitor cell populations. Taken together, our findings suggest that PDGF/VEGF may play a central role in age-related changes in ISCs and progenitor cell populations, which may contribute to aging and the development of cancer stem cells.

Cell cycle and apoptosis regulatory protein-1: a novel regulator of apoptosis in the colonic mucosa during aging

Although the regulatory mechanisms for the age-related rise in proliferation and reduction in apoptosis in the colonic mucosa are yet to be fully delineated, we have demonstrated that these events are associated with increased expression and activation of epithelial growth factor receptor (EGFR)/ErbB-1 and some of its receptor family members (EGFRs), indicating their involvement in these processes. However, the downstream signaling events of EGFR and/or its family members regulating age-related changes in mucosal proliferation and apoptosis remain to be delineated. Cell cycle and apoptosis regulatory protein-1 (CARP-1), a novel growth signaling regulator that we isolated, participates in EGFR-dependent signaling. In the current investigation, we examined the involvement of CARP-1 in colonic mucosal growth-related processes during aging. We report that the age-related reduction in apoptosis in the colonic mucosa is associated with increased expression and tyrosine phosphorylation of not only EGFR but also ErbB-2 and ErbB-3. In contrast, protein and mRNA levels of CARP-1 as well as tyrosine phosphorylation of CARP-1 are decreased. Additionally, we have observed that administration of wortmannin, an inhibitor of phosphatidylinositol 3-kinase activity that accelerates apoptosis in the colonic mucosa of aged rats, causes a marked increase in expression and tyrosine phosphorylation of CARP-1. The age-related decline in CARP-1 expression could partly be attributed to increased methylation of the CARP-1 promoter. Taken together, our data suggest that not only EGFR but also its other members are involved in regulating colonic mucosal growth during aging and that CARP-1 may play a crucial role in transducing EGFRs signals.

Significant increase of colonic mutated crypts correlates with age in sporadic cancer and diverticulosis cases, with higher frequency in the left- than right-side colorectum

Mild periodic acid-Schiff (mPAS) staining can discriminate non-O-acetylated (mPAS-positive) from O-acetylated (mPAS-negative) epithelial sialoglycoproteins in human colonic mucosa, allowing the three haplotypes expressed from a single polymorphic autosomal gene (oat) to be distinguished. In heterozygotes, we previously demonstrated wholly mPAS-positive (stem cell mutated) crypts and clusters of two or more mPAS-positive crypts to be significantly increased with duration of ulcerative colitis. To establish whether such an increase in the number of mutated crypts with age also occurs in normal individuals or in cases with diverticulosis, the O-acetylation phenotype in the non-cancerous colonic mucosa of 47 sporadic colorectal cancer patients who were heterozygotes for oat was tested with mild-PAS staining. PAS-positive crypts were assessed histologically in relation to age and compared between the left (sigmoid colon and rectum) and right (cecum and ascending colon) sides of the colorectum. Wholly mPAS-positive (stem cell mutated) crypts and foci in heterozygotes were found to be increased significantly (P < 0.0001) in the left side with aging (r = 0.598 and 0.643, respectively). Such a positive correlation with aging was also confirmed in 19 diverticulosis cases without cancer (r = 0.797 and 0.793, respectively). The frequency of mutated crypts and foci on the right side was significantly lower than on the left side in both spontaneous colorectal cancer and diverticulosis cases. The results provide support for an intimate relationship between accumulation of mutated crypts with aging, possibly with significance for colorectal cancer development. Furthermore, the environment in the right side of the colon may be different from that in the left side in this regard.

Phosphatidylinositol 3-kinase/Akt signaling stimulates colonic mucosal cell survival during aging

Although aging is shown to be associated with decreased apoptosis and increased survival of cells in the colonic mucosa of Fischer 344 rats, the regulatory mechanisms are poorly understood. The current investigation examines the involvement of phosphotidylinositol 3-kinase (PI3K)/Akt signaling pathway in mediating the events of colonic mucosal cell survival during aging. We have observed that aging is associated with activation of PI3K/Akt signaling, as evidenced by the higher levels of phosphorylated forms of p85, the regulatory subunit of PI3K and of Akt in the proximal and distal colonic mucosa, of aged (21-23 mo) than in young (4-7 mo) rats. These increases are accompanied by a concomitant rise in phosphorylation of proapoptotic protein Bad, which is sequestered by the 14-3-3 family of proteins following phosphorylation by Akt, resulting in a reduction in nonphosphorylated Bad. The amount of antiapoptotic Bcl-xL bound to nonphosporylated Bad in the colonic mucosa is found to be substantially lower in aged than in young rats, resulting in a marked rise in the unbound/free form of Bcl-xL in the aging colon. The age-related activation of PI3K and the reduction in caspase-3 activity could be reversed by wortmannin, a specific inhibitor of PI3K. Increased levels of Bcl-xL and phosphorylated forms of Akt and Bad and reduction in caspase-3 activity were observed throughout the entire length of the colonic crypt of aged rats. We conclude that the constitutive activation of the PI3K/Akt-signaling pathway is partly responsible for the age-related increase in colonic mucosal cell survival. This is evident throughout the entire length of the colonic crypt.

Chemopreventive effect of dietary d-alpha-tocopheryl succinate supplementation on precancer colon aberrant crypt formation and vitamin E analogue levels in young and old rats

This study examined the effects of dietary d-alpha-tocopheryl succinate (TS) in female rats, 20 mo (OLD) or 2 mo (YNG) of age, on azoxymethane (AOM)-induced colonic aberrant crypt foci (ACF) and tissue distribution of d-alpha-tocopherol (alphaT), d-gamma-tocopherol (gammaT), and alphaTS. Rats were fed a commercial rodent chow supplemented with or without 1 (YNG) or 2 (OLD) g alphaTS/kg diet for 1 week prior to ip administration of AOM to induce colon ACF. The animals were sacrificed after 49 days of exposure. The results showed that OLD rats had significantly fewer ACF than YNG animals, and the percent body fat and serum triglycerides were significantly higher in the OLD group compared with the YNG. However, only OLD animals receiving alphaTS had significantly reduced numbers of larger ACF and significantly higher levels of colonic alphaT, gammaT, and alphaTS. These data support previous studies demonstrating that dietary alphaTS administration is protective against intestinal cancer. Also, this is the first study to show that alphaTS accumulates in most tissues following dietary exposure. We hypothesize that increased colon accumulation of fat-soluble vitamin E compounds and subsequent chemoprevention may be related to greater percent body fat and serum triglycerides in OLD animals receiving dietary TS.

Regulation of TGF-alpha-induced activation of AP-1 in the aging gastric mucosa

Although the age-related activation of EGF receptor (EGFR) in the gastric mucosa of Fischer 344 rats is associated with increased DNA binding activity of activator protein-1 (AP-1), little is known about the EGFR signaling cascades that regulate this process. The primary objective of this investigation was to determine the role of signaling pathways initiated by EGFR in regulating the transforming growth factor-alpha (TGF-alpha)-induced activation of AP-1 in the gastric mucosa in aged rats. Freshly isolated gastric mucosal cells from male young (4-5 mo) and aged (22-24 mo) rats were used. We have observed that although exposure of mucosal cells from young (4-5 mo) and old (22-24 mo) rats to 1 nM TGF-alpha for 20 min stimulates the DNA binding activity of AP-1 in both age groups, the magnitude of stimulation is substantially higher in aged (131%) than in young (35%) rats. This stimulation in the aged is associated with a concomitant activation of MEKs and ERKs, but not JNKs and p38. The TGF-alpha induction of AP-1 transcriptional activity in gastric mucosal cells from aged rats could be totally abrogated by either PD153035, a specific inhibitor of EGFR tyrosine kinase, or PD98059, a specific inhibitor of MEKs, but not by Wortmannin, which inhibits phosphatidylinositol kinase. PP2, a specific inhibitor of Src kinase, produces a 50% inhibition of the TGF-alpha-induced activation of AP-1 transcriptional activity. Our results suggest that the TGF-alpha-induced stimulation of DNA binding activity of AP-1 in the gastric mucosa of aged rats is primarily through a signaling pathway involving MEKs and ERKs, whereas Src kinase pathways play a minor role.

Radiation-induced rectal complications are not influenced by age: a dose fractionation study in the rat

Radiation-induced complications of the rectum are an important dose-limiting factor in radiotherapy of pelvic malignancies. In general, animal studies demonstrated no differences in acute and late normal tissue toxicity with age, but little is known about rectal complications in relation to age. For this purpose, an extensive histological and dose fractionation study was carried out on the rectum of young (12 weeks) and older (77-80 weeks) rats. In this paper, the results of dose fractionation are presented in relation to age at the time of irradiation. Young and older animals were irradiated with single and fractionated doses. After irradiation, rectal complications could lead to occlusion and stenosis, eventually resulting in the clinical symptoms of a megacolon and a possible fistula. For each dose group, cumulative survival rates were obtained with Kaplan-Meier analysis, from which dose-effect curves and the associated LD(50) values for a megacolon/fistula were calculated. The majority of responders died between 8 and 24 weeks after irradiation, irrespective of age. For both age groups, only the fractionation data showed a reduction in the mean latency with increasing dose. In the older age group, 39% of the responders developed a fistula compared to 26% for the younger animals. The LD(50) values increased from around 30 Gy after single doses to nearly 65 Gy after 10 fractions. The increases in LD(50) values with the number of fractions were independent of the age of the rats. For each of the dose fractionation schedules, log-rank testing indicated no significant differences in cumulative survival rates between younger and older animals (P > 0.10). The high alpha/beta ratios obtained for both the young and older animals strongly suggested that the late rectal complications were a consequence of early epithelial injury. Associated histological findings indicated that blood vessel damage, which was already evident at a high incidence at 4 weeks after irradiation, could also play a significant role in the occurrence of consequential late injuries. In conclusion, data obtained for the latent period of rectal occlusion, for the dose-effect curves, for the log-rank testing of cumulative survival rates, and for the alpha/beta ratios strongly support the hypothesis that the incidence of radiation-induced rectal complications is independent of age. Late rectal complications could be a consequence of radiation-induced acute injury.

Effect of aging on the adaptive and proliferative capacity of the small bowel

Our society is aging at a rapid rate; the effects of aging on physiologic functions (e.g., small bowel adaptation) are poorly understood. The purpose of this study was to determine the ability of the aged small bowel mucosa to adapt after resection. Young (2-month-old) and aged (24-month-old) F344 rats underwent massive (70%) proximal small bowel resection (SBR) or sham operation; rats were killed at 9 or 16 days after surgery. The remnant small bowel and corresponding sham segments were harvested, weighed, and analyzed for DNA content and villus height. To determine whether the adaptive response after SBR could be enhanced, aged rats underwent SBR or sham operation and were treated with either neurotensin or saline solution (control). SBR resulted in adaptive hyperplasia in the remaining small bowel remnant in both young and aged rats at 9 and 16 days compared with sham animals. At 9 days, significant increases were noted in weight, villus height, and DNA content of the distal remnant in young and aged rats after SBR; the increases were similar in both young and aged rats. At 16 days, both young and aged rats displayed significant increases in remnant weight after SBR. Administration of neurotensin increased the weight of the remnant intestine in aged rats after SBR compared with saline treatment. Our findings demonstrate that aged small bowel mucosa exhibits a proliferative and adaptive capacity in response to SBR that was similar to that of the young animals. In addition, neurotensin administration enhanced the normal adaptive response of the small bowel in aged rats, providing further evidence that neurotensin may be therapeutically useful to augment mucosal regeneration in the early periods after massive SBR.

Age-associated loss of heterozygosity of tumor suppressor genes in the gastric mucosa of humans

The current study is based on the hypothesis that aging predisposes gastric mucosa to carcinogenesis through altered expression and/or mutations of genes involved in cell growth. To test this hypothesis, we investigated the age-associated changes in mutation of adenomatous polyposis coli (APC), deleted in colorectal cancer (DCC), p53, and K-ras genes in the gastric mucosa of 19 healthy subjects of varying ages (25-91 yr). Specifically, we studied the loss of heterozygosity (LOH) of these genes in cardia, body, and antrum of the stomach. We observed that 3 of 19 subjects (16%) over 60 yr of age show LOH of at least one of the tumor suppressor genes. Among the subjects over 60 yr of age, the incidence of LOH is 38% (3/8). Two of three subjects had mutations in more than one tumor suppressor gene. In all three affected subjects, mutation in APC, DCC, or p53 was located mainly in the body of the stomach, suggesting increased susceptibility of this region to neoplastic changes. However, no LOH of K-ras was observed in these subjects. Our observation that subjects over 60 yr of age show mutation in one or more of the tumor suppressor genes suggests an age-related increase in predisposition of the stomach to neoplasia.

Aging is associated with increased proliferation and decreased apoptosis in the colonic mucosa

Although the incidence of colon cancer increases with advancing age, reasons for this increase are not fully understood. Earlier studies have demonstrated that in Fischer-344 rats, aging is associated with increased crypt cell production in the colon, an event considered to be central to the initiation of carcinogenesis. Apoptosis also plays a critical role in the development and progression of colon cancer. Therefore, we have examined the age-related changes in proliferation and apoptosis in the colonic mucosa of 4-5, 12-14, and 22-24 month-old Fischer-344 rats. We have observed that proliferative activity in the colon, as assessed by proliferating cell nuclear antigen immunoreactivity, is higher (50-80%) in 12-14 and 22-24 month-old rats than in their 4-6 month-old counterparts. In contrast, the number of apoptotic cells, (as determined by TdT-mediated dUTP nick-end labeling assay) in the colonic mucosa of 12-14 and 22-24 month-old rats are considerably lower (50-60%) than in 4-6 month-old animals. These changes are accompanied by a concomitant reduction (75%) in pro-apoptotic Bak and stimulation (200%) of anti-apoptotic Bcl-xL levels. Since activation of caspases is associated with initiation and maintenance of apoptosis, we also analyzed the levels of pro and active forms of caspase-3, 8 and 9. The levels of active forms of caspase-3, 8 and 9 are found to be considerably (60-80%) lower in the colonic mucosa of 22-24 month-old rats, compared to their younger counterparts. This is accompanied by decreased cleavage of poly(ADP-ribose) polymerase, a substrate for caspases. In conclusion, our data show that aging enhances proliferation, but attenuates apoptosis in the colonic mucosa. These changes may partly be responsible for the age-related rise in colorectal cancer.

Increased in vitro activation of EGFR by membrane-bound TGF-alpha from gastric and colonic mucosa of aged rats

Although aging is associated with increased epidermal growth factor receptor (EGFR) tyrosine kinase activity in Fischer 344 rat gastric and colonic mucosa, the regulatory mechanisms for the age-related rise in EGFR tyrosine kinase are poorly understood. Transmembrane transforming growth factor-alpha (TGF-alpha) may modulate EGFR function through an autocrine/juxtacrine mechanism. The present study aimed to determine the contribution of membrane-bound precursors of TGF-alpha in enhancing EGFR activation in the gastric and colonic mucosa during aging. The extent of EGFR tyrosine phosphorylation, a measure of EGFR activation, was substantially higher (300--350%) in the gastric and colonic mucosa of 23- (aged) vs. 4-mo-old (young) Fischer 344 rats. This was accompanied by an increase (200--1,000%) in the relative concentration of 18- to 20-kDa membrane-bound precursor forms of TGF-alpha. The amount of TGF-alpha bound to EGFR was also higher (150-250%) in the gastric and colonic mucosa of aged vs. young rats. In vitro studies revealed that exposure of HCT 116 cells (a colon cancer cell line) to TGF-alpha from gastric and colonic mucosal membranes of aged rats caused a 200--250% higher activation of EGFR and extracellular signal-related kinases (p42/44) compared with young rats. Our data suggest that the membrane-bound precursor form(s) of TGF-alpha may partly be responsible for enhancing EGFR activation in the gastric and colonic mucosa of aged rats, probably though an autocrine/juxtacrine mechanism(s).

Effect of age on radiation-induced early changes of rat rectum. A histological time sequence

BACKGROUND AND PURPOSE

Radiation treatment of the elderly (> 75 years) is often modified due to an assumed decrease in normal tissue tolerance in this age group. Since more radiobiological data concerning normal tissue toxicity as a function of age are needed, a histological study of age-related radiation changes of the rectum was performed.

MATERIALS AND METHODS

The rectum of young and old female Wistar rats (12 and 78 weeks, respectively) was irradiated with single doses of 22 and 39 Gy. The field size was 1.5 x 2.0 cm. The animals were sacrificed at 1, 2, 4 and 10 weeks after treatment. To evaluate radiation damage, 12 histological parameters were scored in four areas of the rectum. A total radiation injury score was calculated. The number of proliferative epithelial cells was evaluated by 5-bromo-2'-deoxyuridine labeling.

RESULTS

Some age-related histological differences were observed; especially, the incidence of ulceration and vascular occlusion was higher in the older group. In the low dose group of the older animals, 60% showed ulceration, which was 0% for the young low dose animals. Severe vascular changes occurred early and were more extensive in older animals (4 weeks) than in the younger group (10 weeks). In the area adjacent to the treatment field, cell proliferation increased significantly in older rats at 1 week after 22 Gy, which did not occur in the young group.

CONCLUSIONS

Discrete radiation-induced histological differences were observed between the rectum of young and old Wistar rats, especially in the development of ulceration and vascular changes. Although the survival of these Wistar rats in earlier studies was not affected by age, the impact of the observed histological differences for their importance in the long-term is currently being investigated.

Aging enhances G(1) phase in the colonic mucosa of rats

Although in Fischer-344 rats, aging has been shown to be associated with increased crypt cell production in the colonic mucosa, no information is available about the responsible intracellular mechanisms for the age-related rise in colonic mucosal cell proliferation. To determine whether cell cycling events are affected by aging, the present investigation examines the age-related changes in Cdk2 activity and the regulation of this process in the colonic mucosa. Colonic mucosae from 4-, 13- and 24-month-old Fischer-344 rats were assayed for Cdk2 activity and protein expression of Cdk2, cyclin D1 and E, as well as p21(Waf1/Cip1) (total and the fraction bound to Cdk2), p53 and phosphorylated Rb. Kinase activity and protein levels of Cdk2, as well as cyclin D1 concentration in the colonic mucosa, rose steadily with advancing age. However, the levels of cyclin E in the colonic mucosa were found to be higher in 24-month-old than 13-month-old rats, compared to their 4-month-old counterparts. On the other hand, levels of mucosal p21(Waf1/Cip1) (total and the fraction bound to Cdk2), one of the universal inhibitors of Cdks, were found to be lower in aged than in young rats. This was accompanied by a parallel decrease in mucosal p53, a tumor suppressor protein that is known to regulate p21(Waf1/Cip1). Additionally, we observed that the levels of phosphorylated Rb protein, a form which is involved in regulating progression of cells through the S phase, are increased in the colonic mucosa of 24-month-old rats, but not in 13-month-old animals, when compared with their 4-month-old counterparts. Our data suggest that, G(1) to S phase transition, as well as progression through the S phase of the cell cycle are accelerated in the colonic mucosa of aged rats.

Effects of aging on expression of genes involved in regulation of proliferation and apoptosis in the colonic epithelium

The purpose of this study was to characterize the effects of aging on colonic messenger ribonucleic acid (mRNA) and protein levels of genes involved in the regulation of cell proliferation and apoptosis, and epithelial morphology in male Fischer 344 rats. Our study shows that, with aging, colonic expression of insulin-like growth factor-1 (IGF-1) and IGF-binding protein-3 (IGFBP-3) is significantly increased and decreased, respectively. Colonic Bax protein levels are increased significantly with aging. Immunohistochemical localization of Bax protein shows a greatly increased expression in colonic crypts, especially in the upper portion of crypts. p53 expression is unchanged with aging. No significant change in proliferation of colonic crypt cells is observed by bromodeoxyuridine (BrdU) labeling, although the increased colonic expression of IGF-1 and the decreased expression of IGFBP-3 with aging may result in an increased colonic IGF-1 bioactivity. The age-related changes in Bax and IGFBP-3 appear to be independent of p53. The finding of an unchanged colonic epithelium with aging in the face of a greatly increased Bax protein levels may suggest that the elevated Bax protein levels function to render colonic epithelial cells more sensitive to apoptotic stimuli.

Induction of transcriptional activity of AP-1 and NF-kappaB in the gastric mucosa during aging

Although aging enhances expression and tyrosine kinase activity of epidermal growth factor receptor (EGFR) in the gastric mucosa, there is no information about EGFR signaling cascades. We examined the age-related changes in mitogen-activated protein kinases (MAPKs) [extracellular signal-related kinases (ERKs), c-Jun NH(2)-terminal kinases (JNKs), and p38], an EGFR-induced signaling cascade, and activator protein-1 (AP-1) and nuclear factor-kappaB (NF-kappaB) transcriptional activity in the gastric mucosa of 4- to 6-, 12- to 14-, and 22- to 24-mo-old Fischer 344 rats. AP-1 and NF-kappaB transcriptional activity in the gastric mucosa rose steadily with advancing age. This can be further induced by transforming growth factor-alpha. The age-related activation of AP-1 and NF-kappaB in the gastric mucosa was associated with increased levels of c-Jun, c-Fos, and p52, but not p50 or p65. Total and phosphorylated IkappaBalpha levels in the gastric mucosa were unaffected by aging. Aging was also associated with marked activation of ERKs (p42/p44) and JNK1. In contrast, aging decreased p38 MAPK activity in the gastric mucosa. Our observation of increased activation of ERKs and JNK1 in the gastric mucosa of aged rats suggests a role for these MAPKs in regulating AP-1 and NF-kappaB transcriptional activity. These events may be responsible for the age-related rise in gastric mucosal proliferative activity.

Colorectal cancer--time as the most important carcinogen: a risky hypothesis about risk

The likelihood of having cancer increases proportionally with a constant power of age, beginning at 25 years old. An equation has been proposed that reproduces this incidence-age relationship, but until now the explanation remains unknown. In this paper, a hypothesis is presented in which tumoral development in human colon and rectum would be the consequence of having exceeded the 'limit number' of mitoses that every stem cell undertakes, from its origin until exhausting the security mechanisms that control the correct replication of genome. The age of cancer appearance would depend on the epithelial turnover time which basically responds to a genetic control.

Aging alters gastric mucosal responses to epidermal growth factor and transforming growth factor-alpha

Administration of pharmacological doses of epidermal growth factor (EGF) or transforming growth factor-alpha (TGF-alpha) in young rats stimulates gastric mucosal proliferation, but, in aged rats, the same treatment inhibits proliferation. This may be due to enhanced ligand-induced internalization of EGF receptor (EGFR). In support of this, we demonstrated that although a single injection of EGF (10 microg/kg) or TGF-alpha (5 microg/kg) in young (4-6 mo old) rats greatly increased membrane-associated EGFR tyrosine kinase activity, the same treatment slightly inhibited the enzyme activity in aged (24 mo old) rats. This treatment also produced a greater abundance of punctate cytoplasmic EGFR staining in gastric epithelium of aged rats, consistent with EGFR internalization. In vitro analyses demonstrated that exposure of isolated gastric mucosal cells from aged but not young rats to 100 pM TGF-alpha resulted in marked increases in intracellular EGFR tyrosine kinase activity and that induction of EGFR tyrosine kinase activity in mucosal membranes from aged rats occurred at doses 1,000-fold less than those required in young rats. Our data suggest that aging enhances sensitivity of the gastric mucosa to EGFR ligands. This may partly explain EGFR-mediated inhibition of gastric mucosal proliferation in aged rats.

The role of DNA hypermethylation in human neoplasia

Cancer development and progression is dictated by a series of alterations in genes such as oncogenes, tumor suppressor genes, DNA repair genes, and others. DNA methylation is an epigenetic modification that is profoundly altered in most cancers. Recently, hypermethylation of CpG-rich areas located in the promoter of genes (CpG islands) has been shown to be commonly implicated in silencing tumor suppressor genes in cancer. By cloning and characterizing a large number of such CpG islands hypermethylated in colon cancer, we found that two processes explain most of these events. Age-related CpG island methylation in a subset of cells in normal tissues, followed by intensification of methylation in cancer cells explains the majority of hypermethylation events in colon cancer and may provide a mechanistic link between aging and cancer formation. Most of the other CpG islands methylated in colon cancer can be explained by a newly described phenotype, the CpG island methylator phenotype (CIMP) which results in multiple methylation events in a subset of cancers. CIMP accounts for the majority of sporadic colon cancers characterized by microsatellite instability, as well as most tumors with k-ras mutations. Understanding further the factors that lead to, and modulate, aberrant methylation in cancer may provide novel avenues for prevention and treatment of this disease.

Induction of G(1) checkpoint in the gastric mucosa of aged rats

Although in Fischer 344 rats aging is found to be associated with increased gastric mucosal proliferative activity, little is known about specific changes in the regulatory mechanisms of this process. To determine whether changes in cell cycling events could partly contribute to the age-related rise in gastric mucosal proliferative activity, the present investigation examines changes in cyclin-dependent kinase (Cdk2) activity and the regulation of this process in the gastric mucosa of Fischer 344 rats aged 4 (young), 13 (middle aged), and 24 (old) mo. We observed that aging is associated with a progressive rise in activity and protein levels of Cdk2 in the gastric mucosa. This is also found to be accompanied by a concomitant increase in cyclin E but not cyclin D1 levels. On the other hand, the levels of p21(Waf1/Cip1) (total as well as the fraction associated with Cdk2), a nuclear protein that is known to inhibit different cyclin-Cdk complexes, are found to decline in the gastric mucosa with advancing age. In contrast, with aging, there was a steady rise in p53 levels in the gastric mucosa. We have also observed that the levels of phosphorylated retinoblastoma protein, a form that participates in regulating progression through the S phase, are markedly elevated in the gastric mucosa of aged rats. In conclusion, our data suggest that, in the gastric mucosa, aging enhances transition of G(1) to S phase as well as progression through the S phase of the cell cycle. However, the age-related decline in p21(Waf1/Cip1) in the gastric mucosa appears to be independent of p53 status.

CpG island methylator phenotype in colorectal cancer

Aberrant methylation of promoter region CpG islands is associated with transcriptional inactivation of tumor-suppressor genes in neoplasia. To understand global patterns of CpG island methylation in colorectal cancer, we have used a recently developed technique called methylated CpG island amplification to examine 30 newly cloned differentially methylated DNA sequences. Of these 30 clones, 19 (63%) were progressively methylated in an age-dependent manner in normal colon, 7 (23%) were methylated in a cancer-specific manner, and 4 (13%) were methylated only in cell lines. Thus, a majority of CpG islands methylated in colon cancer are also methylated in a subset of normal colonic cells during the process of aging. In contrast, methylation of the cancer-specific clones was found exclusively in a subset of colorectal cancers, which appear to display a CpG island methylator phenotype (CIMP). CIMP+ tumors also have a high incidence of p16 and THBS1 methylation, and they include the majority of sporadic colorectal cancers with microsatellite instability related to hMLH1 methylation. We thus define a pathway in colorectal cancer that appears to be responsible for the majority of sporadic tumors with mismatch repair deficiency.

Fetal intestinal transplant as an accessory enteral segment

Fetal tissue transplantation has gathered considerable interest among researchers dealing with organ transplantation. A large number of studies concerning fetal intestinal transplantation have been published in the past 2 decades, almost all of them aiming to determine the feasibility of a properly functioning fetal transplant in continuity with the host's own enteral system. This study was designed to determine the absorptive capacity of the neogut in vivo, without anastomosing the transplant to the host's intestine, and to evaluate its use as an accessory enteral segment. Intestinal segments taken from Wistar albino fetuses were transplanted subcutaneously into the abdominal wall of 20 Sprague-Dawley rats. Immunosuppression was maintained by daily cyclosporin A (Cy A) 10 mg/kg injections s.c. and evaluated by determination of serum Cy A level and T-helper/T-suppressor cell ratio. The neogut was converted into a Thiry-Vella loop 2 weeks after transplantation. A test solution composed of 20% glucose and Trophamine was perfused via the stomas; glucose and amino acid absorption gradients were calculated. The gamma-glutamyl transferase (GGT) activity and mitotic index of the neogut were determined. Results were compared to those obtained from the host. There was no significant difference (P > 0.05) in glucose absorption between the neogut and the host tissue. Amino acid absorption and specific GGT activity were significantly less (P < 0.01) in the neogut. There was no significant difference (P > 0.05) between neogut and host intestine in mitotic index. Our data support the idea of using a transplanted fetal intestinal segment as an accessory feeding route.

Effects of exogenous neurotensin on intestinal postresectional growth in the suckling rat

BACKGROUND

In the suckling rat, massive bowel resection provokes intestinal malabsorption that leads to diminished growth. The object of this report was to test whether neurotensin, intestinal trophic peptide, enhances postresection intestinal adaptation, improving absorption and reducing the adverse effects of resection on growth.

METHODS

Fifty-seven 15-day-old suckling. Wistar rats were divided into four groups: 41 rats were subjected to resection of 90% of their small bowel, while the rest (n = 16) underwent laparotomy. Half of the animals, resected and laparotomized, were treated with neurotensin for 30 days. The body weight was monitored, and samples of bone and intestinal mucosa were obtained at the end of the study period for analysis. Blood was tested to determine iron, ferritin, folic acid, and vitamin B12 levels.

RESULTS

The resected animals lost body weight regardless of neurotensin administration. In the resected animals, femur weight increased significantly when they received neurotensin. Bowel resection provokes significant increases in the intestinal mucosa (crypts and villi), but after neurotensin administration, significant increases were detected only in the jejunum of the resected animals but not in the ileum of laparotomized rats. In the resected animals, significant decreases in iron, ferritin, folic acid, and vitamin B12 levels were observed. The postresection administration of neurotensin only produced a significant rise in the ferritin concentration.

CONCLUSIONS

In the suckling rat, neurotensin enhances the intestinal proliferative phenomenon but does not improve the course of medium-term postresection growth.

Differing proliferative responses in proximal and distal colons of growing rats fed food eaten by adenoma patients

Animal dietary studies related to human colorectal carcinogenesis are usually based on AIN-76A diet, which is dissimilar to human food in source, preparation, and content. Our aim was to examine colonic epithelial proliferation in rats fed a diet based on the mean daily food intake of adenoma patients. Foods were prepared as reported by the adenoma patients and dehydrated; 64 Sprague-Dawley rats were fed either "human adenoma" or AIN-76A diet and every eight weeks, eight from each group were sacrificed. Both groups gained weight equally, had no colonic histological changes, but during the study showed progressive lengthening of colonic crypts (P < 0.01) and decreased proliferation (P < 0.05) in distal colons. Compared to controls, rats fed human adenoma diet had significantly longer crypts (P < 0.01) and more labeled cells (P < 0.05) at 32 weeks; overall they had increased proliferation (P < 0.01), most significantly in the distal colon. Thus, food eaten by adenoma patients induced hyperproliferative changes in the rat colon during growth and maturity, especially the distal colon, as found in humans at risk for neoplasia.

Regional distribution of carcinogen-induced colonic neoplasia in the rat

Carcinogen induction of neoplasms in rodent colon has been used as a model for human colon cancer development and for evaluating chemopreventive regimens. We studied the regional distribution of small and large intestinal tumors in 229 rats given azoxymethane (AOM) once weekly for two weeks (15 mg/kg sc). The AOM regimen induced 63% more tumors in distal (DC) than in proximal colon (PC), although tumor volume was greater in PC. A high-fat (23% corn oil) diet increased tumors in PC and DC (p < 0.01). Caloric restriction of 10-30% of the ad libitum diet progressively reduced DC tumor formation but did not alter PC tumors. Tumor volume was unaffected by either regimen. Small intestinal tumors were concentrated in the proximal 15 cm of the intestine and were unaffected by dietary manipulation. This AOM model of colon tumor formation approximates human colon cancer distribution and is an appropriate model for rodent chemopreventive studies.

Abnormal cell proliferation and p52/p35-CSK expression in the colons of aging rats

In rodents and in humans, aging is associated with increased gastrointestinal epithelial cell proliferation and an expanded crypt proliferative compartment similar to that seen in the preneoplastic bowel. We have compared the distribution of a series of cytoskeletal antigens that are modified when colonic cancer cells differentiate in vitro in the colon of young (4-7 month) and aging (22-26 month) Fischer 344 rats. Two such proteins, p52 and p35, (that are increased in cultured senescent cells) differ in their position in the crypt axis and subcellular localization between young and aging rats. In young rats, immunoreactive p52 protein is present solely near the colonic crypt surface epithelium but in aging rats p52 expressing cells are found deeper in crypts. The intracellular localization of p35 also differs markedly in young and aging animals. The distribution of these proteins appears to be a reproducible biomarker of aging. Antigenic changes similar to those observed in aging colons also are seen in crypt cells of patients with ulcerative colitis and in the flat colonic mucosa of patients with adenomatous polyps and colon cancer. The combination of proliferative and differentiation changes suggest that the flat mucosa of the colon of aging rats has preneoplastic features.

Proliferation of wound derived capillary endothelial cells: young versus aged

The objective of this study was to compare the proliferative potential of wound derived capillary endothelial cells (WCEC) from aged and young rats. Endothelial cells were isolated from subcutaneously implanted sponges in 2- and 24-month-old rats. The identity of the cells as endothelial was confirmed by staining for Ac-LDL uptake. Aged and young WCEC (20,000/well) were stimulated with increasing concentrations of fetal calf serum (0, 2.5, 5, 10 and 15%). The increase in cell number was determined with a Coulter counter. At all serum concentrations, the proliferative capacity of WCEC from aged rats was significantly higher than that of WCEC from young rats.

Enhancement of ethanol induced rectal mucosal hyper regeneration with age in F344 rats

Experimental studies in rats have shown an independent stimulation of rectal cell turnover by either chronic ethanol consumption or age. In this study the combined effect of these two factors on colorectal cell regeneration has been investigated. Ninety male F344 rats aged 2, 12, and 22 months were pair fed nutritionally adequate liquid diets containing 36% of total energy either as ethanol or isoenergetic carbohydrates. After four weeks of feeding, colorectal crypt cell production rates were measured using a stathmokinetic technique with vincristine. While age by itself did not affect colorectal cell renewal, chronic ethanol consumption stimulated rectal, but not colonic crypt cell production rate in an age dependent manner. While no significant effect of ethanol was noted in young animals, cell proliferation was significantly enhanced in middle aged animals by 81% (4.1 (2.7-5.5) v 7.4 (6.0-8.7) cells/crypt/hour, p < 0.001) and in old animals by 138% (4.5 (3.3-5.6) v 10.7 (8.9-12.4) cells/crypt/hour, p < 0.001) after ethanol ingestion. Because acetaldehyde, the first and most toxic metabolite of ethanol, has been detected in the colorectal mucosa and may lead to tissue injury influencing cell regeneration, acetaldehyde concentrations have been measured in the colons of 15 male F344 rats of various ages after an acute intraperitoneal dose of ethanol (2.5 g/kg bodyweight). There was a significant positive correlation between crypt cell production rate and acetaldehyde concentrations measured in the distal and proximal colon after an acute dose of ethanol (r = 0.5955, p < 0.005). These data clearly show that the ethanol mediated stimulation of cell regeneration in the rectum is age dependent. As reported earlier, there was found indirect evidence that acetaldehyde participates in the pathogenesis of rectal hyperregeneration after chronic alcohol consumption. This hyperregeneration of the rectal mucosa after alcohol drinking could by itself favour carcinogenesis, which is especially relevant in old age.

Age-related changes in polyamine biosynthesis after fasting and refeeding

The effect of aging on ornithine decarboxylase (ODC) activity and polyamine biosynthesis in the proximal small intestine was studied in two groups of male Fisher 344 rats (young [4-month old] and aged [26- to 27-month old]) using a fasting and refeeding model. In control (nonfasted) rats, levels of polyamines (putrescine, spermidine and spermine) and ODC activity were significantly higher in aged compared with young rats. In aged rats, fasting significantly reduced the levels of putrescine by 41%, spermidine by 23%, and spermine by 11%; however, fasting had no effect on polyamine levels in young rats. ODC activity was decreased 75% in young and 50% in aged rats after fasting compared with the respective age-matched controls. Conversely, 2 h after reinstituting a chow diet increased ODC activity by 17-fold in young rats but only 8-fold in aged rats. Putrescine levels were also increased in both age groups after refeeding; however, similar to ODC activity, these increases were much less in aged rats. In addition, spermidine and spermine levels remained significantly depressed in the aged groups even after 24 h of refeeding. These findings suggest that the normal rigid control of gut polyamine biosynthesis and proliferation noted in young rats is markedly altered with aging.

Evidence for an age-related dysfunction in the antiproliferative response to transforming growth factor-beta in vascular smooth muscle cells

Previous studies have indicated that aged animals show an increased intimal hyperplasia after arterial injury. The present studies examined the hypothesis that the increased serum-free proliferation of aged smooth muscle cells (SMC), in vitro, was due to a loss of an antiproliferative signal, such as transforming growth factor-beta 1 (TGF-beta 1). Northern blot analysis of the mRNA derived from old (> 19 mo) or young (3-4 mo) rat aortic SMC indicated that both groups had an equivalent level of the 2.5 kB TGF-beta 1 message. Metabolic labeling with 35S-methionine and immunoprecipitation for TGF-beta 1 confirmed the de novo synthesis of TGF-beta 1 in rat SMC. Old and young SMC supernatants showed equal levels of active or latent (acid-activated) TGF-beta activity. Despite the similarities in the production of TGF-beta 1, old SMC were refractory to inhibition by TGF-beta 1, whereas young SMC were markedly inhibited (80%) by low levels of TGF-beta 1 (IC50 < 5 pg/ml). Binding studies at 4 degrees C indicated that old SMC exhibited reduced binding capacity for 125I-TGF-beta 1. Cross-linking studies confirmed that old SMC showed reduced binding of 125I-TGF-beta 1 to membrane sites corresponding to the high molecular weight type III receptor, as well as the 85-kDa type II and 65-kDa type I receptor. However, at 37 degrees C, old SMC degraded 125I-TGF-beta 1 more rapidly than young SMC. Combined, this data suggests that SMC derived from older animals are capable of normal production of TGF-beta 1 but fail to respond to the autocrine growth inhibitory effects of this agent, thereby leading to enhanced proliferation.

Neurotensin stimulates growth of colonic mucosa in young and aged rats

Neurotensin, a tridecapeptide widely distributed in the gut, stimulates growth of small bowel mucosa in young and aged rats. In the present study, the effect of long-term neurotensin administration on the growth of colonic mucosa was examined in young (2-month-old) and aged (24-month-old) rats. Subcutaneous injections of saline (control) or neurotensin (300 micrograms/kg) in gelatin were given to the groups of rats every 8 hours for 10 days. During treatment, all rats were maintained on a regular chow diet. Rats were killed on day 11; the entire colon was removed, mucosa was scraped and weighed, and DNA, RNA, and protein contents were determined. Neurotensin induced growth of colonic mucosa in both age groups. In young rats, neurotensin increased weight and DNA, RNA, and protein contents of colonic mucosa. The ratio of DNA content, an index of cellular hyperplasia, was increased significantly in the neurotensin-treated young rats compared with age-matched controls, indicating an overall increase in mucosal cellularity. In the aged rats, growth was characterized by an increase in weight and RNA and protein contents, but not DNA content, thus suggesting cellular hypertrophy. These results suggest that neurotensin has an important regulatory function in the growth of colonic mucosa; however, the mode of action, at the cellular level, appears to be different depending on age.

Effect of high-fat and low-fiber meals on the cell proliferation activity of colorectal mucosa

Normal healthy volunteers (n = 43) were divided into four groups that received diets providing low or high levels of dietary fat (33 or 96 g/day) and low or high levels of dietary fiber (6 and 41 g/day) for a period of five days. Proliferation was assessed with tritiated thymidine labeling of three rectal biopsies. After five days on the prescribed diets, the average thymidine labeling index (LI) of the group on the high fat-low fiber diet was only 25% higher than the average LI of the group on the low fat-high fiber diet, a difference that is not statistically significant. We conclude that a short-term increase in dietary fat and decrease in dietary fiber does not result in a large increase in cell proliferation rate.