Mucosal Ornithine Decarboxylase Activity Research Articles

Massive small intestinal adaptation occurs in a neonatal miniature piglet model of short bowel syndrome

Our objective was to characterize small intestinal (SI) adaptation in a novel piglet model. Piglets (n = 27, 12 d old) were randomized to 1) 80% SI resection with total parenteral nutrition (TPN) feeding (R‐TPN), 2) 80% SI resection with TPN + enteral feeding (R‐EN) or 3) sham SI transection with TPN + enteral feeding (Sham‐EN). In the R pigs, the distal 100 cm of ileum (residual SI) and 30 cm of proximal SI was left intact. All pigs received TPN after surgery. R‐EN and Sham‐EN piglets also received continuous gastric infusions of elemental diet starting on d 3 (40:60 TPN:EN). Piglets were kept for 4, 6 or 10 d post‐surgery. The weights of residual SI and mucosa were greater in R‐EN compared to other pigs at 4, 6 and 10 d. By d 10, weight per length of residual SI in R‐EN animals was more than 25% greater than other groups; R‐EN mucosal mass was 65% higher. Rate of residual SI length growth in the R‐TPN and R‐EN was twice that of the Sham‐EN, indicating massive adaptation responsive to enteral feeding. A rapid decline in plasma arginine and glutamate occurred in enterally fed groups compared to R‐TPN pigs (p<0.05). Ornithine decarboxylase activity in mucosa of R‐EN pigs at d 10 was 35% higher than Sham‐EN and 60% higher than R‐TPN. Route of amino acid delivery may have affected whole body availability, as the gut may have extracted significant amounts of enteral arginine and glutamate to support intestinal adaptation growth. (SickKids Foundation)

Colonic Ornithine Decarboxylase in Inflammatory Bowel Disease: Ileorectal Activity Gradient, Guanosine Triphosphate Stimulation, and Association with Epithelial Regeneration but Not the Degree of Inflammation and Clinical Features

The role of colonic mucosal ornithine decarboxylase (ODC) in inflammatory bowel disease (IBD) remains controversial. This study assessed mucosal ODC activity in IBD patients segment by segment with regard to patient characteristics, disease activity/duration, medication, degree of mucosal inflammation, and presence/absence of epithelial regeneration and guanosine triphosphate (GTP) stimulation. Mucosal ODC activity was determined in biopsy specimens from the terminal ileum, cecum/ascending, transverse, and descending colon, and the sigmoid/rectum of 35 patients with IBD (18 with Crohn's disease, 17 with ulcerative colitis) and 29 controls, using the amount of 14CO2 liberated from (carboxyl-14C)ornithine hydrochloride. GTP-stimulatable activity was expressed as the ratio of ODC activity in the presence and absence of GTP (70 micromol/L). Mucosal inflammation was assessed endoscopically/microscopically with previously described criteria. Presence/absence of mucosal regeneration also was determined by predefined criteria. Mucosal ODC-activity did not significantly differ in IBD patients and controls. There was a 4.4-fold activity gradient from the ileum to the rectum. Mucosal ODC activity was significantly higher in areas with epithelial regeneration compared to those without regeneration, and was stimulated by GTP by a factor of 1.42 in Crohn's disease and 1.19 in ulcerative colitis patients compared to controls (p < 0.004). On the other hand, there was no significant association/relationship of mucosal ODC activity with disease activity/duration and the endoscopic/histologic degree of mucosal inflammation. The observation of unchanged mucosal ODC activity in patients with IBD and the absence of a significant relationship with clinical and endoscopic/histologic disease characteristics speaks against a major role of ODC in IBD as a major disease marker. The role of the ileorectal gradient, the enhanced activity in areas with epithelial regeneration, and the GTP-stimulatable form, however, need further investigation with regard to a possible involvement in carcinogenesis in IBD.

Efficacy of glutamine-enriched enteral nutrition in an experimental model of mucosal ulcerative colitis.

Intact intestinal epithelium and associated lymphatic tissue act as body defences against luminal toxins. This barrier may become threatened or compromised in inflammatory bowel disease, leading to an increase in mucosal permeability and subsequent translocation of endotoxins. The effect of oral glutamine on gut mucosal ornithine decarboxylase activity and on endotoxin levels in portal vein blood was studied in a guinea-pig model of carrageenan-induced colitis. Despite failure to show induction of ornithine decarboxylase activity by glutamine administration, the mean endotoxin level of portal vein blood in guinea-pigs fed a glutamine-enriched elemental diet was 25.3 pg/ml compared with 71.2 pg/ml in animals given a standard elemental diet (P < 0.01). A glutamine-enriched elemental diet may be therapeutically beneficial in patients with inflammatory bowel disease.

Troglitazone, a ligand for peroxisome proliferator-activated receptor gamma, inhibits chemically-induced aberrant crypt foci in rats.

The biological roles of peroxisome proliferator‐activated receptors (PPARs) in various diseases, including inflammation and cancer, have been highlighted recently. Although PPARγ ligand is suspected to play an important role in carcinogenesis, its effects on colon tumorigenesis remain undetermined. The present tune‐course study was conducted to investigate possible modifying effects of a PPARγ ligand, troglitazone, on the development and growth of aberrant crypt foci (ACF), putative precursor lesions for colon carcinoma, induced by azoxymethane (AOM) or dextran sodium sulfate (DSS) in male F344 rats. Oral troglitazone (10 or 30 mg/kg body weight (b.w.)) significantly reduced AOM (two weekly subcutaneous injections, 20 mg/kg b.w.)‐induced ACF. Treatment with troglitazone increased apoptosis and decreased polyamine content and ornithine decarboxylase (ODC) activity in the colonic mucosa of rats treated with AOM. Gastric gavage of troglitazone also inhibited colitis and ACF induced by DSS (1% in drinking water), in conjunction with increased apoptosis and reduced colonic mucosal polyamine level and ODC activity. Our results suggest that troglitazone, a synthetic PPARγ ligand, can inhibit the early stage of colon tumorigenesis with or without colitis.

The role of polyamines in gastric mucus synthesis inhibited by cigarette smoke or its extract

BACKGROUNDCigarette smoking was shown to delay gastric ulcer healing and reduce synthesis of mucus, which is important for gastric ulcer protection and healing. Polyamines are important in these processes.AIMSTo study...

Difluoromethylornithine inhibits crypt fission

Crypt fission is a physiologic mechanism of crypt reproduction. It increases in pathophysiologic situations where intestinal regeneration is required (e.g., radiation injury). Polyamine metabolism is important in the regulation of intestinal growth and recovery from injury in response to a variety of stimuli. Our aim was to determine whether inhibition of polyamine synthesis by difluoromethylornithine (DFMO) influenced crypt fission. Forty-eight rabbits underwent patch enteroplasty in the terminal ileum. One group served as a control group and the other took 2% DFMO orally. Animals (n = 6) from each group were killed at 7, 14, 21, and 28 days. Normal ileum adjacent to the enteroplasty was studied. Crypt dissection was performed 2 hours after vincristine was administered intravenously to determine crypt cell production rate, crypt depth, and proportion of bifurcating crypts (fission). DFMO administration decreased crypt fission (4 ± 2% vs. 11 ± 2% and 13 ± 1% vs. 34 ± 4% at 7 and 14 days) compared to control animals. There was a corresponding increase in crypt depth at 14 and 21 days. Crypt cell production rate was similar in both groups and did not change with time. Mucosal ornithine decarboxylase activity (11.9 ± 2.2 vs. 1.2 ± 0.3 specific activity at 21 days; P <0.05) and polyamine content (323 ± 32 vs. 17 ± 8 and 382 ± 89 vs. 160 ± 47 pmol/mg at 14 and 21 days, control vs. DFMO; P <0.05) were significantly lower in the DFMO group. The following conclusions were drawn: (1) DFMO administration inhibits crypt fission in stimulated intestinal epithelium; (2) this effect correlates temporally with reduced polyamine production; and (3) reduced crypt fission is another potential mechanism of inhibition of intestinal growth by altered polyamine metabolism.

Increase in apoptosis and decrease in ornithine decarboxylase activity of the gastric mucosa in patients with atrophic gastritis and gastric ulcer after successful eradication of Helicobacter pylori

OBJECTIVE: Recent reports have shown that patients infected with Helicobacter pylori ( H. pylori) have a higher risk of gastric cancer. However, the mechanism of this increased risk is still unclear. In the gastric mucosa, the size of a continuously renewed population of cells is determined by the rates of cell production and of cell loss. Ornithine decarboxylase (ODC) activity is elevated in various gastrointestinal cancers and serves as a marker of mucosal proliferative activity. Apoptosis occurs throughout the gut and is associated with cell loss. Both cell proliferation and cell loss have important roles in H. pylori-associated gastric carcinogenesis. Therefore, we investigated the effect of H. pylori eradication on ODC activity and apoptosis in the gastric mucosa of patients with atrophic gastritis and gastric ulcers. METHODS: Biopsy specimens of the gastric antrum were obtained at endoscopy from 17 H. pylori-positive gastric ulcers patients and 15 H. pylori-positive gastritis patients before and 4 wk after eradication therapy with amoxicillin, omeprazole, and a new anti-ulcer agent, ecabet sodium, and from 10 gastric ulcer patients in whom ulcer healed but H. pylori was left untreated. ODC activity and induction of apoptosis were determined immunohistochemically. RESULTS: H. pylori was successfully eradicated with the triple therapy in 12 (80%) of 15 gastritis patients and 13 (76%) of 17 gastric ulcer patients. ODC activity was present in the gastric mucosa in 21 (84%) patients before eradication but in only four (16%) patients after successful eradication ( p = 0.0005). The apoptotic index increased significantly ( p = 0.0006) from 4.2% ± 0.4% before treatment to 7.4% ± 0.5% after successful eradication. CONCLUSIONS: Successful eradication of H. pylori decreases mucosal ODC activity and increases apoptosis in the gastric mucosa. These findings indicate that by decreasing mucosal cell proliferation and increasing epithelial cell loss, H. pylori eradication may help decrease the subsequent risk of gastric cancer.

Increase in apoptosis and decrease in ornithine decarboxylase activity of the gastric mucosa in patients with atrophic gastritis and gastric ulcer after successful eradication of Helicobacter pylori.

Recent reports have shown that patients infected with Helicobacter pylori (H. pylori) have a higher risk of gastric cancer. However, the mechanism of this increased risk is still unclear. In the gastric mucosa, the size of a continuously renewed population of cells is determined by the rates of cell production and of cell loss. Ornithine decarboxylase (ODC) activity is elevated in various gastrointestinal cancers and serves as a marker of mucosal proliferative activity. Apoptosis occurs throughout the gut and is associated with cell loss. Both cell proliferation and cell loss have important roles in H. pylori-associated gastric carcinogenesis. Therefore, we investigated the effect of H. pylori eradication on ODC activity and apoptosis in the gastric mucosa of patients with atrophic gastritis and gastric ulcers. Biopsy specimens of the gastric antrum were obtained at endoscopy from 17 H. pylori-positive gastric ulcers patients and 15 H. pylori-positive gastritis patients before and 4 wk after eradication therapy with amoxicillin, omeprazole, and a new anti-ulcer agent, ecabet sodium, and from 10 gastric ulcer patients in whom ulcer healed but H. pylori was left untreated. ODC activity and induction of apoptosis were determined immunohistochemically. H. pylori was successfully eradicated with the triple therapy in 12 (80%) of 15 gastritis patients and 13 (76%) of 17 gastric ulcer patients. ODC activity was present in the gastric mucosa in 21 (84%) patients before eradication but in only four (16%) patients after successful eradication (p = 0.0005). The apoptotic index increased significantly (p = 0.0006) from 4.2% +/- 0.4% before treatment to 7.4% +/- 0.5% after successful eradication. Successful eradication of H. pylori decreases mucosal ODC activity and increases apoptosis in the gastric mucosa. These findings indicate that by decreasing mucosal cell proliferation and increasing epithelial cell loss, H. pylori eradication may help decrease the subsequent risk of gastric cancer.

Increased colonic ornithine decarboxylase activity in inflammatory bowel disease in children.

The risk of colorectal carcinoma is increased in pediatric-onset inflammatory bowel disease (IBD). There is little information available regarding the colonic mucosal proliferative state in children with IBD. The aim of this study was to assess colonic ornithine decarboxylase (ODC) activity, a marker of cell proliferation, in pediatric IBD patients. ODC activity was assessed in colonic mucosa from 23 children (7 with ulcerative colitis, 9 with Crohn's disease, and 7 controls) undergoing colonoscopic examination. ODC activities were then compared with degree of inflammation of biopsied samples. ODC activities in patients with and without corticosteroid treatment were also analyzed. The mucosal ODC activities of sigmoid colon and rectum were significantly higher (2.5- to 4-fold) in both ulcerative colitis and Crohn's disease. The higher ODC activity was associated with increased mucosal inflammation. Moreover, treatment with corticosteroids decreased the ODC activity. In conclusion, using ODC activities as a marker of cell proliferation, our results suggest that there is a higher colonic mucosal proliferative state in children with IBD. The increased ODC activities were associated with increased colonic mucosal inflammation. Colonic mucosal ODC activity may provide an additional parameter to access the therapeutic efficacy of corticosteroid treatment in pediatric IBD patients.

Prevention of colon cancer by pre- and probiotics: evidence from laboratory studies

Oligofructose and inulin, selective fermentable chicory fructans, have been shown to stimulate the growth of bifidobacteria which are regarded as beneficial strains in the colon. Studies were designed to evaluate inulin (Raftiline) and oligofructose (Raftilose), for their potential inhibitory properties against aberrant crypt foci (ACF) formation in the colon of rats. ACF are putative preneoplastic lesions from which adenomas and carcinomas may develop. The results of this study demonstrate that dietary administration of oligofructose and inulin inhibits the formation of preneoplastic lesions in the colon suggesting the potential colon tumour inhibitory properties of chicory fructans. Since these prebiotics selectively stimulate the growth of bifidobacteria, tumour inhibitory activity of lyophilized cultures of Bifidobacterium longum (BL) against azoxymethane (AOM)-induced colon carcinogenesis in rats and modulating effect of these cultures on colonic tumour cell proliferation, ornithine decarboxylase (ODC) activity, and ras-p21 oncoprotein expression were investigated. Dietary administration of lyophilized cultures of BL strongly suppressed AOM-induced colon tumour development. Inhibition of colon carcinogenesis was associated with a decrease in colonic mucosal cell proliferation and colonic mucosal and tumour ODC and ras-p21 activities.

Difluoromethylornithine inhibits crypt fission

Crypt fission is a physiologic mechanism of crypt reproduction. It increases in pathophysiologic situations where intestinal regeneration is required (e.g., radiation injury). Polyamine metabolism is important in the regulation of intestinal growth and recovery from injury in response to a variety of stimuli. Our aim was to determine whether inhibition of polyamine synthesis by difluoromethylornithine (DFMO) influenced crypt fission. Forty-eight rabbits underwent patch enteroplasty in the terminal ileum. One group served as a control group and the other took 2 % DFMO orally. Animals (n = 6) from each group were killed at 7, 14, 21, and 28 days. Normal ileum adjacent to the enteroplasty was studied. Crypt dissection was performed 2 hours after vincristine was administered intravenously to determine crypt cell production rate, crypt depth, and proportion of bifurcating crypts (fission). DFMO administration decreased crypt fission (4 ±2% vs. 11 ± 2% and 13 ±1% vs. 34 ±4% at 7 and 14 days) compared to control animals. There was a corresponding increase in crypt depth at 14 and 21 days. Crypt cell production rate was similar in both groups and did not change with time. Mucosal ornithine decarboxylase activity (11.9 ±2.2 vs. 1.2 ± 0.3 specific activity at 21 days; P <0.05)and polyamine content (323 ±32 vs. 17±8 and 382 ±89 vs. 160 ±47 pmol/mg at 14 and 21 days, control vs. DFMO; P <0.05) were significantly lower in the DFMO group. The following conclusions were drawn: (1) DFMO administration inhibits crypt fission in stimulated intestinal epithelium; (2) this effect correlates temporally with reduced polyamine production; and (3) reduced crypt fission is another potential mechanism of inhibition of intestinal growth by altered polyamine metabolism.

Chemoprevention of azoxymethane-induced rat colon carcinogenesis by the naturally occurring flavonoids, diosmin and hesperidin.

The modulating effects of dietary feeding of two flavonoids, diosmin and hesperidin, both alone and in combination, during the initiation and post-initiation phases on colon carcinogenesis initiated with azoxymethane (AOM), were investigated in male F344 rats. Animals were initiated with AOM by weekly s.c. injections of 15 mg/kg body wt for 3 weeks to induced colon neoplasms. Rats were fed the diets containing diosmin (1000 ppm), hesperidin (1000 ppm) or diosmin (900 ppm) + hesperidin (100 ppm) for 5 weeks (initiation treatment) or 28 weeks (post-initiation treatment). The others contained the groups of rats treated with diosmin, hesperidin alone or in combination, and untreated. At the end of the study (32 weeks), the incidence and multiplicity of neoplasms (adenoma and adenocarcinoma) in the large intestine of rats initiated with AOM together with, or followed by, a diet containing diosmin or hesperidin were significantly smaller than those of rats given AOM alone (P <0.001). The combination regimen during the initiation and post-initiation stages also inhibited the development of colonic neoplasms, but the tumor data did not indicate any beneficial effect of diosmin and hesperidin administered together as compared with when these agents were given individually. In addition, feeding of diosmin and hesperidin, both alone and in combination, significantly inhibited the development of aberrant crypt foci. As for cell proliferation biomarkers, dietary exposure of diosmin and hesperidin significantly decreased the 5'-bromodeoxyuridine-labeling index and argyrophilic nuclear organizer region's number in crypt cells, colonic mucosal ornithine decarboxylase activity, and polyamine levels in the blood. These results indicate that diosmin and hesperidin, both alone and in combination, act as a chemopreventive agent against colon carcinogenesis, and such effects may be partly due to suppression of cell proliferation in the colonic crypts, although precise mechanisms should be clarified.

Sepsis increases putrescine concentration and protein synthesis in mucosa of small intestine in rats.

Recent studies suggest that sepsis stimulates mucosal polyamine and protein synthesis. It is not known in which cell type polyamine biosynthesis is increased during sepsis and if polyamines regulate mucosal protein synthesis. We examined the effect of sepsis in rats on polyamine biosynthesis in isolated jejunal enterocytes and measured mucosal protein synthesis following inhibition of ornithine decarboxylase (ODC) activity with difluoromethylornithine. ODC and S-adenosylmethionine decarboxylase (SAMDC) activities and putrescine concentrations were increased in isolated jejunal enterocytes 16 h after induction of sepsis by cecal ligation and puncture. Enterocyte spermidine and spermine levels were not influenced by sepsis. Mucosal ODC and SAMDC activities and polyamine levels were increased following treatment of rats with interleukin-1 but not tumor necrosis factor. Treatment of rats with difluoromethylornithine prevented the sepsis-induced increase in mucosal ODC activity, putrescine concentration, and protein synthesis rate. The results suggest that sepsis increases ODC and SAMDC activities and putrescine concentrations in enterocytes of the small intestine. This metabolic response to sepsis may be regulated by interleukin-1 although other mechanisms may also be involved. Increased mucosal protein synthesis during sepsis may at least in part be regulated by increased putrescine levels.

Luminal Epidermal Growth Factor Preserves Mucosal Mass of Small Bowel in Fasting Rats

1. Fasting causes atrophy of small bowel mucosa which rapidly resolves with luminal feeding. This effect of enteral nutrient may be mediated by stimulation of growth factor secretion. We therefore evaluated whether luminal administration of epidermal growth factor, a peptide hormone found in gastro-intestinal contents and trophic for small bowel mucosa, would prevent the mucosal atrophy associated with starvation. 2. Adult rats were: (i) fasted for 3 days, (ii) fasted and then refed for 1 day or (iii) fasted and then refed for 2 days. During the 2 days before study, animals in each group received infusions of epidermal growth factor (2.5 micrograms/day) or diluent alone into distal jejunum. 3. Epidermal growth factor treatment of fasted animals resulted in a tripling of mucosal ornithine decarboxylase activity (P < 0.001) and a doubling of mucosal DNA content (P < 0.001) in the jejunum, values similar to those of refed animals. Epidermal growth factor infusion in refed rats resulted in a further doubling of mucosal ornithine decarboxylase activity (P < 0.001), but no additional increase in DNA content. Effects of epidermal growth factor infusion were generally greater in jejunum than ileum. 4. In conclusion, luminal exposure to epidermal growth factor prevents starvation-induced mucosal atrophy in the small bowel, but does not enhance the mucosal growth associated with refeeding. Effects are greatest at the site of administration. Luminal epidermal growth factor is a potential mediator of the indirect effects of nutrient on mucosal growth in the small bowel. Enteral administration of epidermal growth factor holds promise for preventing atrophy and maintaining mucosal integrity in starved and post-operative patients.

Ornithine decarboxylase as a marker for premalignancy in the stomach.

Assessment of mucosal ornithine decarboxylase (ODC) activity in the human large bowel may be of value as a marker of potential malignant risk. Its value as a marker of premalignancy in the upper gastrointestinal tract is less clear. Using a [14C]-ornithine bioassay, gastric mucosal ODC activity was measured in 32 normal subjects and 22 patients with confirmed gastric cancer. These results were compared with 47 patients at increased risk of upper gastrointestinal malignancy, (32 patients with partial gastric resection, 15 patients with familial adenomatous polyposis). Median ODC activity in normal subjects was 371 pmol/mg protein/h, (interquartile range (IQR), 230-617). There was no variation with age or sex and no relation to Helicobacter pylori status. Normal subjects had significantly lower ODC activity than patients with a gastric resection or confirmed gastric cancer, but similar to patients with familial adenomatous polyposis. Furthermore, no difference in activity was identified between patients with a gastric resection and established gastric cancer. ODC activity was, however, significantly increased in areas of gastric atrophy or intestinal metaplasia, regardless of the clinical group from which the samples were obtained. It is concluded that measurement of mucosal ODC activity does not provide additional predictive information of malignant risk in the stomach and investigation of other potential biomarkers of malignancy is warranted.

Epidermal growth factor enhances repair of rat intestinal mucosa damaged by oral administration of methotrexate.

To examine the trophic effect of epidermal growth factor on the rat small intestine, we measured diamine oxidase and ornithine decarboxylase activities in intestinal mucosa injured by methotrexate. Methotrexate was infused orally via a gastric tube at a dose of 10 mg/kg per day on 3 successive days (days 1-3). Epidermal growth factor was injected intraperitoneally at a dose of 40 micrograms/kg per day on 4 successive days following methotrexate infusion (days 4-7). Methotrexate caused a marked decrease in diamine oxidase activity; this decrease returned to a normal level on day 13 in controls. In rats injected with epidermal growth factor, diamine oxidase activity began to recover earlier than in the controls, and returned to a normal level on day 11. Epidermal growth factor enhanced the increase of ornithine decarboxylase activity in mucosa injured by methotrexate. When the increase of ornithine decarboxylase activity was suppressed by alpha-difluoromethylornithine, epidermal growth factor failed to facilitate the repair of intestinal mucosa. These results indicate that epidermal growth factor enhances intestinal repair following methotrexate infusion, and that this effect is mediated, at least in part, by ornithine decarboxylase. It is proposed that epidermal growth factor can be used clinically as a means to enhance mucosal repair of the intestine after chemotherapy with methotrexate.

Suppression of azoxymethane-induced rat colon carcinogenesis by dietary administration of naturally occurring xanthophylls astaxanthin and canthaxanthin during the postinitiation phase.

The modulating effects of dietary feeding of two xanthophylls, astaxanthin (AX) and canthaxanthin (CX) during the postinitiation phase on colon carcinogenesis initiated with azoxymethane (AOM) were investigated in male F344 rats. Animals were initiated with AOM by weekly s.c. injections of 15 mg/kg body wt for 3 weeks and then they were fed the diets containing AX or CX at concentrations of 100 and 500 p.p.m. for 34 weeks. The others contained the groups of rats treated with AX or CX alone and untreated. At the end of the study (week 37), the incidence and multiplicity of neoplasms (adenoma and adenocarcinoma) in the large intestine of rats initiated with AOM and followed by AX or CX containing diet at a high dose (500 p.p.m.) were significantly smaller than those of rats given AOM alone (P < 0.001). In addition, AX or CX feeding significantly inhibited the development of aberrant crypt foci induced by AOM. Dietary exposure to AX or CX also decreased cell proliferation activity as revealed by measuring 5'-bromodeoxyuridine-labeling index as crypt cells, colonic mucosal ornithine decarboxylase activity and blood polyamine levels. These results indicate that AX and CX are possible chemopreventers for carcinogenesis of colon in addition to urinary bladder and oral cavity and such effects may be partly due to suppression of cell proliferation.

Response of rat immature enterocytes to insulin: Regulation by receptor binding and endoluminal polyamine uptake

The mechanism(s) by which insulin stimulates enzyme expression in rat immature enterocytes are unknown. The purpose of this study was to investigate these mechanism(s). The effects of insulin or an antireceptor monoclonal antibody (RPN 538) were assessed on microvillous enzyme activities and the endoluminal uptake of [14C]spermine. Changes in de novo synthesis of polyamines were measured by mucosal ornithine decarboxylase activity. In sucklings (day 14), administration of insulin failed to induce intestinal ornithine decarboxylase activity, whereas in older rats (day 18 and 20), ornithine decarboxylase was enhanced by 2-2.5-fold. Immature enterocytes from sucklings, pretreated with alpha-difluoromethylornithine, remained sensitive to insulin and expressed enzyme activities at levels equal to controls. In response to insulin, the uptake of [14C]spermine and the mucosal concentrations of spermine and spermidine were increased by 30%, 13%, and 39%, respectively. Administration of RPN 538 had no effect on [14C]-spermine uptake, but it prevented the effects of endogenous insulin on enzyme expression. The enzymatic response of immature enterocytes to insulin is mediated by binding of the hormone to its receptor and is transduced into the cell without de novo synthesis of polyamines. The regulation by insulin of the endoluminal uptake of spermine could be critical for intestinal maturation.

Regulation of Transglutaminase Activity by Polyamines in the Gastrointestinal Mucosa of Rats

Transglutaminases catalyze the covalent cross-linking of protein and are involved in the mechanism of polyamine-dependent mucosal healing. The current study examined the effect of polyamines on transglutaminase activity in gastrointestinal mucosa. Rats were fasted 22 hr before experiments and enzyme activity was measured as the Ca(++)-dependent covalent incorporation of [3H]-putrescine into acid-precipitable protein. In some of the experiments, mucosal ornithine decarboxylase (ODC) activity and polyamine levels were also examined. Transglutaminase activity in both gastric and duodenal mucosa increased significantly after polyamine administration. Treatment with alpha-difluoromethylornithine (DFMO) decreased both basal ODC activity and putrescine levels in the duodenal mucosa. DFMO also significantly decreased mucosal transglutaminase activity. In stress or hypertonic NaCl-induced gastric mucosal injury models, increased polyamine biosynthesis was associated with increased transglutaminase activity, which was completely prevented by DFMO. Exogenous polyamines returned transglutaminase activity toward control levels in the presence of DFMO. In conclusion, these results indicate that: (i) luminal polyamines increase transglutaminase activity in gastric and duodenal mucosa; (ii) polyamine depletion caused by the inhibition of ODC is accompanied by a significant decrease in transglutaminase activity; and (iii) exogenous polyamines significantly reverse the decrease in transglutaminase activity caused by polyamine depletion.

Intestinal Mucosal Ornithine Decarboxylase and Brush Border Membrane Vesicle Na+-H+ Exchange Activities in Diabetic Rats

To determine the possibility that intestinal mucosal ornithine decarboxylase activity can modulate mucosal brush border membrane Na(+)-H+ exchange activity, we studied the relationship between jejunal mucosal ornithine decarboxylase activity and mucosal brush border membrane Na(+)-H+ exchange activity in adolescent streptozotocin-diabetic and normal control rats. Diabetes was associated with enhanced intestinal mucosal ornithine decarboxylase and Na(+)-H+ exchange activities. Groups of diabetic and control rats were given difluoromethylornithine in drinking water to suppress intestinal mucosal ornithine decarboxylase activity. As expected, 10 days after induction of diabetes, intestinal mucosal weight (67.7 mg/cm vs 56.1 mg/cm), DNA (47.3 micrograms/mg protein vs 32.7 micrograms/mg protein), ornithine decarboxylase activity (1107 units/hr vs 654 units/hr), and brush border membrane vesicle Na(+)-H+ exchange activity, assessed as Vmax of 22Na+ uptake (32.5 nmol/mg protein/15 min vs 15.2 nmol/mg protein/15 min), were significantly greater in diabetic than in control rats. Treating diabetic and control rats with difluoromethylornithine suppressed jejunal mucosal growth by over 30%, ornithine decarboxylase activity by over 80%, and brush border membrane vesicle 22Na+ uptake by over 60%. Highly significant direct correlations (r > 0.900) were observed between jejunal DNA content, mucosal ornithine decarboxylase activity, and brush border membrane vesicle Na(+)-H+ exchange activity. The above findings suggest that jejunal mucosal ornithine decarboxylase activity can modulate mucosal epithelial proliferation and mucosal brush border membrane Na(+)-H+ exchange activity.