Neoplasia and hyperplasia of large bowel: focal lesions in an abnormal epithelium

A20 Restricts NOS2 Expression and Intestinal Tumorigenesis in a Mouse Model of Colitis-Associated Cancer

BACKGROUND AND AIMS

Colon cancer can occur sporadically or in the setting of chronic inflammation, such as in patients with inflammatory bowel disease. We previously showed that A20, a critical negative regulator of tumor necrosis factor signal transduction, could regulate sporadic colon cancer development. In this report, we investigate whether A20 also acts as a tumor suppressor in a model of colitis-associated cancer.

METHODS

Colitis and colitis-associated tumors were induced in wild-type and A20 intestinal epithelial cell-specific knockout (A20dIEC) mice using dextran sodium sulfate and azoxymethane. Clinicopathologic markers of inflammation were assessed in conjunction with colonic tumor burden. Gene expression analyses and immunohistochemistry were performed on colonic tissue and intestinal enteroids. Nitric oxide (NO) production and activity were assessed in whole colonic lysates and mouse embryonic fibroblasts.

RESULTS

A20dIEC mice develop larger tumors after treatment with dextran sodium sulfate and azoxymethane than wild-type mice. In addition to elevated markers of inflammation, A20dIEC mice have significantly enhanced expression of inducible nitric oxide synthase (iNOS), a well-known driver of neoplasia. Enhanced iNOS expression is associated with the formation of reactive nitrogen species and DNA damage. Loss of A20 also enhances NO-dependent cell death directly.

CONCLUSION

Mechanistically, we propose that A20 normally restricts tumor necrosis factor-induced nuclear factor kappa B-dependent production of iNOS in intestinal epithelial cells, thereby protecting against colitis-associated tumorigenesis. We also propose that A20 plays a direct role in regulating NO-dependent cell death.

Sodium butyrate induces human colon carcinoma HT-29 cell apoptosis through a mitochondrial pathway

Some tumours respond favourably to tumour necrosis factor-alpha (TNF-alpha). Despite this preferential sensitivity, resistance to TNF-alpha remains a clinical problem and more interest is now being focused on finding compounds that induce apoptosis through other pathways. Sodium butyrate (NaBt) has anti-tumour effects on colon cancer cells, inhibiting cell growth and promoting differentiation and apoptosis. In this study we investigated whether NaBt induced apoptosis in the human colon cancer cell line HT-29 and examined the intracellular mechanisms involved. Pre-incubation of cells with NaBt significantly increased apoptosis as measured by fluorescence activated cell sorter analysis and mitochondrial membrane potential determination. This effect could be blocked with the caspase inhibitors, z-VAD-fmk (pan-caspase inhibitor), z-DEVD-fmk (caspase-3 inhibitor) and z-LEHD-fmk (caspase-9 inhibitor), but not with z-IETD-fmk (caspase-8 inhibitor). Enhancement of caspase-3 and caspase-9 activities suggests that NaBt induces apoptosis via mitochondrial pathways not involving TNF-alpha.

Site specificity of colorectal neoplasms in families without an inherited syndrome

BACKGROUND

Relatives of patients with bowel neoplasia have an increased risk of bowel neoplasia. If there were concordance in location of neoplasia between relatives, then location-specific screening could be used. Such concordance might also assist in the understanding of the etiology of neoplasia within individual families.

METHODS

We have investigated the concordance in anatomic location of colonic neoplasia between first-degree relatives using a new statistical technique for paired data called alternating logistic regression.

RESULTS

A total of 146 families were ascertained, none of which had clinical evidence of a hereditary predisposition to edon neoplasia. Among those with neoplasia, there was an increased risk for right-sided disease with older age (40% for less than age 60 vs. 58% for at least 70 years of age, p = 0.008). As assessed by the odds ratio, we found no significant concordance within families for location of neoplasia (odds ratio = 1.2: CI [0.7, 2.2]), although there was a suggestion that location in family members of the same generation was more strongly associated (odds ratio 1.87: CI [0.82, 4.25]).

CONCLUSIONS

The lack of concordance within families for location argues against considering family-specific bowel screening protocols and indicates that the most important causes of bowel neoplasia are not sufficiently focused on one anatomic site to facilitate etiologic research.

Relationship of hydrolase activities to epithelial cell turnover in distal colonic mucosa of normal rats

BACKGROUND

The relationships between changes induced by diet in colonic epithelial kinetics and in the activities of brush border hydrolases are poorly defined. The aims of this study are to define these relationships, as changes in kinetics would be expected to influence differentiation, and to determine whether the type of ingested dietary indigestible carbohydrates influences hydrolase activities.

METHODS

Groups of eight rats were fed a low fibre diet +/- supplements of different types of indigestible carbohydrates for 4 weeks. Alkaline phosphatase (ALP) and dipeptidyl peptidase IV (DPPIV) activities and epithelial kinetics were measured in distal colonic mucosa.

RESULTS

Median ALP activities correlated positively and DPPIV activity negatively with the median proportion of cells entering metaphase (r = 0.58 and -0.58, respectively; P < 0.05) and number of metaphase arrests per crypt column across the diets (r = 0.59 and 0.58, respectively; P < 0.05). Stepwise regression analysis showed that both hydrolases independently predicted these kinetic indices (R2 > 63% for each). Mucosal ALP activities were markedly elevated during consumption of raw potato starch, guar gum and methylcellulose, while only potato starch caused a significant elevation of DPPIV activities.

CONCLUSIONS

The type of indigestible carbohydrate in the diet influences colonic mucosal hydrolase activities. The opposite relationship between kinetics and each of the two hydrolases indicates that these hydrolases do not reflect the same event; dipeptidyl peptidase IV might relate to differentiation status while ALP could also be influenced by epithelial irritation due to changes in luminal conditions.

Ulcerative colitis: an epithelial disease?

There is now considerable evidence that abnormalities of the structure and function of the colonic epithelium are present in patients with ulcerative colitis and that many of these may occur independently of mucosal inflammation. It is proposed that epithelial abnormalities are the central defect that underlie the development of mucosal inflammation and its chronicity. A simple model for pathogenesis is proposed in which inflammation develops only when epithelial barrier function is impaired to an extent which permits the influx of luminal pro-inflammatory molecules to the lamina propria. Several candidate hypotheses regarding the molecular basis for the abnormality are addressed. The mechanism by which the barrier function is critically impaired involves the interaction of the abnormal epithelium with luminal, mucosal and systemic factors. Focusing on the epithelium would potentially lead to a conceptually different management approach and the development of novel therapeutic strategies.

Hyperplastic polyposis of the large bowel. Three cases and a review of the literature

Small hyperplastic polyps of the large bowel constitute a frequent non-neoplastic lesion, whereas large or multiple hyperplastic polyps are rare. Here we report three cases of multiple small polyps together with some large hyperplastic ones. Two of the cases had a primary carcinoma in the bowel before onset of the polyps. The neoplastic potential of the hyperplastic polyp is discussed on the basis of the most recent investigations and the three presented cases. The hyperplastic polyp does not seem to be directly involved in the adenoma-carcinoma sequence, but dysplastic changes can be found in large hyperplastic polyps. In cases of multiple hyperplastic polyps a tendency towards a more uniform distribution of the polyps throughout the large bowel is observed. Hyperplastic colonic polyps may exist as a clinical entity, and a definition based on distribution, multiplicity, size, and symptoms is proposed. Patients with multiple or large hyperplastic polyps should have colonoscopy performed at short intervals, with removal of all lesions larger than 5 mm for histologic examination.

Colonic epithelium is diffusely abnormal in ulcerative colitis and colorectal cancer

The hypothesis that the colonic epithelium is diffusely abnormal in ulcerative colitis was examined by comparing disease related responses in expression of markers of differentiation by colonic crypt cells to culture with and without butyrate. Cells were isolated from patients with normal colon (15), cancer (24), ulcerative colitis (19), or Crohn's disease (16). Alkaline phosphatase activities were measured in cell homogenates and the rate of glycoprotein synthesis assessed at the end of 24 hours of culture and expressed relative to the rate of protein synthesis as the G:P ratio. Alkaline phosphatase activities, but not G:P ratios, differed across the groups before and after 24 hour culture (p < 0.05), activities being lowest in the cancer group and highest in inflammatory bowel disease groups. Butyrate (1 mM) suppressed alkaline phosphatase activities in the cancer group by mean (SEM) of 17 (4) (p = 0.006) compared with no change in the other groups. Butyrate suppressed G:P ratios only in the cancer (6 (3)%, p = 0.03) and ulcerative colitis groups (5 (3)%, p = 0.04) and the changes in both were different (p < 0.05) from those in normal cells (increase of 10 (7)%). Changes in ulcerative colitis were different from those in Crohn's disease (p = 0.029). Responses were independent of the presence or absence of mucosal inflammation. These data confirm the diffuse nature of epithelial abnormalities in colorectal cancer. In ulcerative colitis, a different pattern of abnormality occurs, supporting the notion that the epithelium is also diffusely abnormal independent of mucosal inflammation.

Dietary modulation of colonic mucosal urokinase activity in rats

The amount and type of dietary fibre ingested influences colonic luminal characteristics, especially the concentration of carbohydrate fermentation products such as butyrate. This study aimed to assess whether diets supplemented with fibres of differing fermentability (delivering different amounts of butyrate to the colon) influence mucosal activities of urokinase and brush border hydrolases, and epithelial turnover. Groups of five rats were fed one of four diets containing low (2%), highly fermented (guar 10% or oat bran 10%) or slowly fermented fibre (wheat bran 10%) for 4 weeks. Activities of urokinase, alkaline phosphatase, dipeptidyl peptidase IV and maltase were measured in mucosal homogenates of proximal and distal colon and from rectum. Proliferative kinetics were assessed in distal and proximal colon by the metaphase arrest technique. Hydrolase activities were similar across all four dietary groups but a significant difference was found for urokinase (P = 0.014). This was due to a reduction in urokinase activities of > 30% at the three sites in the wheat bran group compared with the other groups. Of proliferative indices, only crypt column height differed across the groups (P = 0.038) and was highest in rats fed wheat bran and lowest in those fed the low fibre diet (P = 0.047). The proportion of mitoses in the top one-fifth of the crypt also differed across groups (P = 0.038) due to the high values in the distal colon of the low fibre group. Thus, addition of a slowly fermented (but not highly fermented) fibre to the diet of rats reduces net urokinase activity in large bowel mucosa and increases the life span of colonic epithelial cells without changing activities of brush border hydrolases.

Butyrate is a potent inhibitor of urokinase secretion by normal colonic epithelium in vitro

BACKGROUND/AIMS

Because the neutral protease urokinase is important in control of cell adhesion and migration, the effects of the physiologically relevant fermentation product butyrate on urokinase secretion by colonic epithelium were examined.

METHODS

Secreted and cell-associated levels of urokinase and plasminogen activator inhibitor 1 were measured in colonic crypt cells within 24 hours of isolation from macroscopically normal mucosa of normal or cancer-bearing colons.

RESULTS

Butyrate caused a concentration-dependent inhibition of both secreted (56% +/- 4% inhibition after 24-hour exposure to 1 mmol/L butyrate; n = 20; mean +/- SEM; P < 0.001) and cell-associated urokinase content (35% +/- 6%; P = 0.003). Acetate and propionate had minimal effects. Butyrate also stimulated plasminogen activator inhibitor 1 secretion by 25% +/- 7% (P = 0.013). Net urokinase activities were suppressed in supernates and cell homogenates by butyrate. Levels of transcripts for urokinase and the inhibitor changed with butyrate exposure in parallel to the levels of secretion of the respective proteins. Cells from the cancer group showed significantly reduced inhibitor secretion and abnormal responses to butyrate (greater inhibition of urokinase secretion and no stimulation of inhibitor secretion), probably reflecting the diffuse disturbance of colonic epithelial biology associated with colorectal cancer.

CONCLUSIONS

Butyrate has dual effects in markedly reducing colonic epithelial urokinase activity, and these may have important implications to understanding colonic epithelial physiology and the pathogenesis and treatment of colonic diseases.