Diamine and polyamine oxidase activities in phytohaemagglutinin-induced growth of rat small intestine

Polyamines and the intestinal tract

Owing to their high turnover, the intestinal mucosal cells have a particularly high requirement for polyamines. Therefore, they are an excellent charcol for the study of polyamine function in rapid physiological growth and differentiation. After a cursory introduction to the major aspects of polyamine metabolism, regulation, and mode of action, we discuss the contribution of the polyamines to the maintenance of normal gut function, the maturation of the intestinal mucosa, and its repair after injuries. Repletion of cellular polyamine pools with (D,L)-2-(difluoromethyl)ornithine has considerably improved our understanding of how the polyamines are involved in the regulation of normal and neoplastic growth. Unfortunately, the attempts to exploit polyamine metabolism as a cancer therapeutic target have not yet been successful. However, the selective inactivation of ornithine decarboxylase appears to be a promising chemopreventive method in familial adenomatous polyposis. Presumably, it relies on the fact that ornithine decarboxylase is a critical regulator of the proliferative response of the protooncogene c-myc, but not of its apoptotic response.

Induced growth and maturation of the gastrointestinal tract after Phaseolus vulgaris lectin exposure in suckling rats

OBJECTIVES

In mammals, the postnatal development of the gastrointestinal tract is characterized by vast structural and functional changes. Using a suckling rat model, we investigated whether red kidney bean lectin, phytohemagglutinin (PHA), a potent gut mitogen in adult rats, can accelerate the growth and maturation of the gastrointestinal tract.

METHODS

At either 10 or 14 days of age, suckling rats were daily gavage fed with PHA (0.05 mg/g body weight) or saline for 3 days. At 1 or 3 days after this treatment, gastrointestinal organ growth, intestinal morphology, disaccharidase pattern, macromolecular absorption capacity, and pancreatic enzyme contents were studied.

RESULTS

After PHA exposure, increased small intestinal growth and number of crypt cells were observed, whereas the proportion of enterocytes with supranuclear vacuoles in the distal intestine was decreased. The macromolecular absorption of the markers bovine immunoglobulin (Ig)G and bovine serum albumin and plasma levels of maternal IgG decreased, and intestinal disaccharidases switched toward an adult-like pattern. The pancreas weight and pancreatic protein and trypsin contents increased. These changes were partly reversible when the PHA treatment began at 10 days of age, but they persisted when the treatment began at 14 days of age.

CONCLUSIONS

PHA induced enhanced growth and precocious functional maturation of the gastrointestinal tract in suckling rats. The effects persisted if the PHA treatment started at 14 days of age, but not before, suggesting an age dependent mechanism. These findings may lead to a better understanding of gastrointestinal maturation and constitute a basis for the treatment of mammals having an immature gut.

The human gut bacteria Bacteroides thetaiotaomicron and Fusobacterium varium produce putrescine and spermidine in cecum of pectin-fed gnotobiotic rats

Pectin is a soluble indigestible polysaccharide that stimulates cecal polyamine formation in rats. Bacteroides and fusobacteria, two numerically dominant bacterial population groups in the large intestine, were found to synthesize in vitro high amounts of spermidine and putrescine. The purpose of this study was to elucidate the effect of pectin on the polyamine production by defined bacterial species in vivo. Germfree male Wistar rats (n = 18) were randomly assigned to one of three treatments: (i) monoassociation with Bacteroides thetaiotaomicron + fiber-free diet; (ii) diassociation with B. thetaiotaomicron + Fusobacterium varium + fiber-free diet or (iii) diassociation with B. thetaiotaomicron + F. varium + fiber-free diet + 10% pectin. The cecal contents of monoassociated rats fed fiber-free diet contained large amounts (1.51+/-0.21 micromol/dry total cecum content) of spermidine which was the major polyamine. The cecum of diassociated rats fed the fiber-free diet contained even higher concentrations of spermidine (2.53+/-0.21 micromol/dry total cecum content) and also putrescine, which was now the dominant polyamine (putrescine 0.32+/-0.28 vs. 3.01+/-0.28 micromol/dry total cecum content; monoassociation vs. diassociation). Pectin consumption by diassociated rats led to an additional increase in the cecal concentrations of all polyamines: putrescine, spermidine and spermine were 40, 37 and 100%, respectively, higher in the diassociated rats consuming the pectin diet than in those consuming the pectin-free diet. Since the microbial counts in the cecum did not differ in the diassociated treatment groups, the elevated concentrations of polyamines observed in the pectin group must have been due to stimulated bacterial polyamine synthesis. The decline of individual polyamines from cecum to feces detected at the end of the study in all treatment groups and the high microbial counts in the cecum and in feces suggest that bacterial polyamines are absorbed in cecum and colon. Pectin stimulates intestinal microbes to synthesize large amounts of polyamines which may be utilized by the host.

Polyamine oxidase and tissue transglutaminase activation in rat small intestine by polyamines

Polyamine degradation was studied in the small intestine from rats fed on a polyamine-supplemented diet. Lactalbumin diet was given to Hooded-Lister rats, with or without 5 mg rat(-1) day(-1) of putrescine or spermidine for 5 days. Polyamine oxidase activity increased with putrescine and spermidine in the diet, whereas spermidine/spermine N(1)-acetyltransferase and diamine oxidase activities were unchanged. We also studied the calcium-dependent and -independent tissue transglutaminase activities, since they can modulate intestinal polyamine levels. Both types of enzymes increased in the cytosolic fraction after putrescine (about 65%) or spermidine (80-100%). Our results indicate that exogenous polyamines stimulate intestinal polyamine oxidase and tissue transglutaminase activities, probably to prevent polyamine accumulation, when other pathways of polyamine catabolism (acetylation and terminal catabolism) are not activated.

Gender-related differences in polyamine oxidase activity in rat tissues

Variations in level of polyamines and their related enzymes are frequently observed in response to some treatments which affect in a different way male and female. The possibility of a gender-related difference in the oxidation of polyamines was investigated in rats by measuring the activity of polyamine oxidase, a ubiquitous enzyme of vertebrate tissues, which transforms spermine into spermidine and spermidine into putrescine. The study was carried out on thymus, spleen, kidney and liver of young rats of both sexes, and female rats showed a lower polyamine oxidase activity than male rats in all the tissues. We also found higher values of spermidine acetylation in female than male rats in thymus and liver. Owing to these gender-related differences, a higher spermidine N-acetyltransferase/polyamine oxidase ratio was found in female than in male rats. A second gender-related difference was a higher spermidine/spermine ratio in female than in male, the only exception being the thymus. These basal differences possibly account for the gender-related differences of polyamine metabolic enzyme activities in response to some treatments, including drugs or hormones.

Lipopolysaccharide of Escherichia coli, polyamines, and acetic acid stimulate cell proliferation in intestinal epithelial cells

Our aim was to examine whether lipopolysaccharide of Escherichia coli, polyamines of dietetic and/or bacterial origin, and products of the bacterial metabolism influence cell proliferation in epithelial cells from the colon and small intestine. Lipopolysaccharide of Escherichia coli 0111:B4 was incubated with cultures from human colonic mucosa. The mitoses were arrested with Vincristine and the total number of metaphases per crypt was counted. In addition, lipopolysaccharide was incubated with a human colonic epithelial cell line from adenocarcinoma (LS-123 cells) and with a nontransformed small intestinal cell line from germ-free rats (IEC-6 cells) for 24 h. In the last 4 h, the cells were labeled with tritiated thymidine. The cells were incubated with putrescine, cadaverine, and spermidine at 10(-11)-10(-3) M and with acetic acid (10(-5)-10(-1) M), acetaldehyde (10(-10)-10(-4) M) and ammonium chloride (1-20 mM). Lipopolysaccharide of Escherichia coli increased the number of arrested metaphases in human colonic crypts and DNA synthesis in L-123 and IEC-6 cells (P < 0.001). All polyamines increased DNA synthesis in the colonic and small intestinal cell lines, the effects being more marked for putrescine (P < 0.001). The higher concentrations of acetic acid increased DNA synthesis in both epithelial cell lines (P < 0.001). Acetaldehyde slightly decreased DNA synthesis in LS-123 cells at cytotoxic concentrations. Ammonium chloride did not significantly affect DNA synthesis. The final concentration of nonionized ammonia was less than 3%. It is concluded that lipopolysaccharides of Escherichia coli and intraluminal factors derived from microorganisms increase cell proliferation in human colonic crypts and intestinal epithelial cell lines.

Oxidative degradation of polyamines in rat pancreatic hypertrophy

In the hypertrophic pancreas, we studied the oxidative degradation of polyamines, which are endogenous polycations important for cell division, growth and differentiation. To induce pancreatic hypertrophy, rats were fed on a semi-synthetic diet containing a daily dose of 42 mg phytohaemagglutinin per rat for 5 or 10 days. In the model, the activities of polyamine oxidase (the enzyme that degrades spermidine, spermine and mainly their acetyl derivatives) and diamine oxidase (the key enzyme of terminal catabolism of polyamines in vivo) increased by 100-180% and 90-100%, respectively, parallel to an elevation in polyamine content (40-100%). The results suggest that in pancreas hypertrophy, which does not exhibit stimulation of spermidine/spermine N1-acetyltransferase activity, increases in the activity of polyamine and diamine oxidases are related events that lead to putrescine formation and removal of excess polyamines.

Effect of an elemental vs a complex diet on polyamine metabolism in rat isolated enterocytes

BACKGROUND

Polyamines play an important role in the proliferation and differentiation of enterocytes. Ornithine decarboxylase (ODC) is the rate-limiting enzyme for polyamine biosynthesis. Elemental diets, providing easily absorbable nutrients such as free amino acids, are used in clinical practice to treat growth failure and malnutrition. They are very different from complex diets normally consumed. Little information is available about the influence of elemental diets on metabolic capacities of enterocytes. This study was undertaken in rats to assess the effects on polyamine metabolism of an elemental diet compared with a complex diet.

METHODS

Rats were fed the elemental diet (group ED) or the control diet (group C) for 14 days. The dietary intakes were isocaloric and isonitrogenous in groups C and ED. Villous enterocytes were then isolated and metabolic capacities or enzyme activities were assessed.

RESULTS

Both the enterocyte capacity to decarboxylate ornithine through ODC (measured in viable enterocytes) and ODC activity (measured in homogenates) were severely decreased in group ED. The polyamine content in enterocytes, however, was maintained at a similar level in both groups. This coincided with a decrease in the main enzymatic activity responsible for putrescine catabolism (ie, diamine oxidase activity) in group ED.

CONCLUSIONS

Although nutrition manipulation was shown to alter polyamine biosynthesis in this study, the polyamine homeostasis was probably maintained, at least in part, through down-regulation of diamine oxidase.

Response of intestinal transglutaminase activity to dietary phytohaemagglutinin

The behaviour of the activity of tissue transglutaminase, a calcium-dependent enzyme, and the levels of polyamines which are physiological substrates for the enzyme, were studied in rat small intestine induced to grow by lectin phytohaemagglutinin. Transglutaminase activity greatly increased in the homogenates and the cytosolic fractions of the intestinal mucosa of lectin-treated rats compared to that of untreated animals. The measurement of enzyme activity in the presence of monodansylcadaverine, a competitive inhibitor of transglutaminase, testified that the assayed enzyme activity was authentic transglutaminase. As regards polyamines, the level of spermine did not change, whereas putrescine and spermidine contents were enhanced. The activation of transglutaminase, which was probably due to Ca2+ accumulation in enterocytes, could have a role in maintaining enterocyte adhesion and intestinal cell homeostasis, and/or repairing lectin-induced damages of microvilli of the gut epithelium.