Human peritoneal macrophages in culture: a model for studying inflammatory disorders in vitro

In this study we characterized a model of human peritoneal macrophages maintained in culture for up to 48 h that can be used to study different functions of this cell population in vitro. The cells remained viable and functionally active over time, with well-preserved phagocytic properties. They expressed a macrophage marker, CD14. Once in culture, human peritoneal macrophages secreted C1q and nitric oxide in a pattern described in murine, guinea pig, and rat peritoneal macrophages. The described model can be used to study physiology and pathophysiology of peritoneal macrophages in vitro, offering all the advantages of the use of a human cell population.

Polyamines and colon cancer

In colon cancer, the activities of polyamine-synthesizing enzymes and polyamine content are increased 3-4-fold over that found in the equivalent normal colonic mucosa, and polyamines have even been attributed as markers of neoplastic proliferation in the colon. Furthermore, and in contrast with all other cell systems in the body, normal and neoplastic cells in the colon are exposed to high concentrations of putrescine from the lumen, synthesized by colonic microflora. While such a high polyamine supply may be of benefit in non-neoplastic colonic mucosal growth, the role of luminal polyamines in colon cancer is a clear concern. Luminal polyamines are readily taken up by neoplastic colonocytes, they are utilized in full to support neoplastic growth, and their uptake is strongly up-regulated by the mitogens known to play an important role in colonic carcinogenesis. Inhibition of polyamine synthesis and their uptake, impaired utilization of exogenous polyamines, and enhanced catabolism of polyamines in neoplastic colonocytes are therefore logical approaches in the chemoprevention of colorectal cancer.

Regulation of alpha1-proteinase inhibitor release by proinflammatory cytokines in human intestinal epithelial cells

alpha1-Proteinase inhibitor (alpha1-PI) is the main serine proteinase inhibitor in human plasma. Apart from its synthesis in the liver, this anti-inflammatory protein is also synthesized by and excreted from human intestinal epithelial cells. Antiinflammatory actions of alpha1-PI are thought to be of relevance in the pathogenesis of inflammatory bowel disease. To investigate the role of macrophage-derived cytokines on alpha1-PI secretion from intestinal epithelial cells, we cultured Caco-2 cells until differentiation (14 days in culture) on permeable filter supports. Monolayers of differentiated Caco-2 cells were then co-cultured with human peritoneal macrophages, grown on plastic in the basolateral chamber. Under these conditions, alpha1-PI secretion from Caco-2 cells was enhanced by 45%, probably by a direct action of macrophage-derived cytokines on Caco-2 cells. To extend this observation further, we treated differentiated Caco-2 cells with macrophage-derived proinflammatory cytokines (IL-1beta, IL-8, TNF-alpha), as well as with lymphocyte-derived cytokines IL-2, IL-6 and IFN-gamma. As early as after 24h treatment, IL-2 and IL-8 induced a significant and dose-dependent increase of alpha-1-PI secretion into cell culture medium; this effect was completely reversed after immunoneutralization by the antibodies against IL-2 and IL-8 alpha1-PI secretion was only slightly decreased after treatment with IFN-gamma, while IL-1beta, IL-6 and TNF-alpha had no effect. alpha1-PI secretion correlated well with the expression of this protein in differentiated Caco-2 cells after cytokine treatment, as confirmed by Western blot. Our data imply that, in vitro, alpha1-PI secretion in enterocyte-like Caco-2 cells is up-regulated by IL-2 and IL-8. Our results suggest that both lymphocyte- and macrophage-derived cytokines regulate secretion of the anti-inflammatory protein alpha1-PI in intestinal epithelial cells.

Effects of deoxycholate on human colon cancer cells: apoptosis or proliferation

BACKGROUND

Deoxycholic acid has long been attributed as a tumour promoter in the colon. It exerts its growth-related actions in a phorbol ester-like manner, by stimulating protein kinase C. The aim of this study was to investigate the effect of deoxycholic acid on proliferation and apoptosis in the colon, by exposing colon cancer cells to it in increasing concentrations.

METHODS

Human colon cancer cells (Caco-2 and HT-29) were treated with deoxycholate or its two structural isomers, 3-beta-12-alpha-dihydroxy-5-beta-cholan-24-oic acid and 3-alpha-12-beta-dihydroxy-5-beta-cholan-24-oic acid. Proliferation was evaluated by cell counting, and apoptosis by estimating percentage cell survival and assessment of nuclear morphology.

RESULTS

Within the concentration range of up to 20 microM, deoxycholate stimulated growth of both human colon cancer cell lines. Its growth-promoting effect was abolished after inhibition of protein kinase C. At concentrations above 100 microM, deoxycholate induced apoptosis in both cell lines. Epimers of deoxycholate were significantly less potent in stimulating growth.

CONCLUSION

Low-dose deoxycholate stimulates colon cancer cell proliferation while > 100 micromol L(-1) of this secondary bile acid induces apoptosis in colon cancer cells. Deoxycholate might promote the likelihood of malignant transformation by increasing epithelial cell turnover in the colon.

Butyrate and the cytokine-induced alpha1-proteinase inhibitor release in intestinal epithelial cells

BACKGROUND

Alpha1-proteinase inhibitor (alpha1-PI), an anti-inflammatory protein thought to play a role in the intestinal inflammation, is synthesised by and released from the intestinal epithelial cells. IL-1beta is a key proinflammatory cytokine in the abnormal immune response that occurs in inflammatory bowel disease. Butyrate is a normal luminal constituent in the colon, known to be of benefit in preventing inflammatory bowel disease. Direct modes of action of butyrate in intestinal inflammation have been poorly studied so far. The aim of this study was to investigate the effects of butyrate on cytokine-mediated alpha1-PI release in intestinal epithelial cells.

METHODS

Differentiated Caco-2 cells were incubated with IL-1beta in the presence or absence of 2 mM butyrate. Alpha1-PI expression in the cells was evaluated by Western blot analysis and alpha1-PI release by ELISA.

RESULTS

Treatment with butyrate alone had no effect on alpha1-PI expression in differentiated Caco-2 cells. However, treatment of the cells with 2 mM butyrate significantly reduced the alpha1-PI level in IL-1beta-treated cells. In the cell culture medium, the presence of butyrate impaired the IL-1beta-induced alpha1-PI release to 17-35%. The treatment induced no change in the number of detached cells or the percentage of viable cells.

CONCLUSION

Our data show that butyrate inhibits alpha1-PI release from Caco-2 colonocytes treated with IL-1beta. It is therefore likely that anti-inflammatory actions of butyrate occur via a mechanism that does not involve direct regulation of cytokine-induced anti-inflammatory protein expression in intestinal epithelial cells.

Nonsteroidal anti-inflammatory drugs stimulate spermidine/spermine acetyltransferase and deplete polyamine content in colon cancer cells

BACKGROUND

Nonsteroidal anti-inflammatory drugs (NSAIDs) inhibit colonic tumourigenesis and have an established usefulness in cancer prevention. Because polyamines are essential for neoplastic cell growth, the aim of this study was to evaluate the effect of NSAIDs (indomethacin, a nonselective COX-1 and COX-2 inhibitor) on polyamine metabolism in colon cancer cells.

METHODS

Both cell counting and thymidine incorporation into cellular DNA were used to assess colon cancer cell growth. Activities of polyamine-metabolising enzymes, polyamine content (HPLC) and ODC and c-myc protein expression (Western blot) were measured in colon cancer cells treated with indomethacin during logarithmic phase of proliferation.

RESULTS

Indomethacin impaired growth of human colon cancer cells (Caco-2 and HCT-116). As a result, ornithine decarboxylase activity and c-myc protein expression were decreased. Treatment with indomethacin induced intracellular oxidant formation in colon cancer cells significantly increased the spermidine/spermine-acetyltrasferase activity (SSAT) and enhanced polyamine acetylation and efflux from colon cancer cells. Impairment of cell growth by indomethacin could not be reversed by exogenous polyamines.

CONCLUSION

Taken together, our results suggest that NSAIDs affect polyamine metabolism in colon cancer cells by inducing SSAT activity, and that polyamine depletion in NSAID-treated colon cancer cells is mainly due to enhanced polyamine acetylation and irreversible depletion of intracellular polyamine pools.

Polyamines in the gut lumen: bioavailability and biodistribution

Polyamines arrive in the gut lumen mainly with food. Shortly after a meal, the majority of luminal polyamines disappear from the duodenal and jejunal lumen, by a mechanism of passive diffusion. The majority of luminal polyamines are degraded in the gut before reaching systemic circulation. Hence, there is broad evidence that luminal polyamines are indeed absorbed, distributed throughout the body, and utilized for cellular growth in remote organs and tissues. In addition, luminal polyamines are crucially involved in normal, adaptive and neoplastic growth of the gut per se, and are taken up by normal and neoplastic epithelial cells of the gut mucosa by a tightly regulated and presumably active transport process. Uptake of polyamines into intestinal and colonic epithelial cells is the highest during cell proliferation, and is stimulated by mitogens and peptide growth factors. Understanding the mechanisms of polyamine uptake in neoplastic cells of the gut, as well as the "biodistribution/bioavailability" of luminal polyamines in man, may provide clinically relevant information that can be used in inhibiting cancer cell growth by deprivation of intracellular polyamine pools.

Deoxycholic acid stimulates migration in colon cancer cells

BACKGROUND

Deoxycholic acid and other secondary bile acids have long been considered tumour promoters in the colon. However, their effect on cell migration, known to play an important role in colon carcinogenesis, has not been studied so far.

OBJECTIVE

To investigate the possible effects of deoxycholic acid on colon cancer-cell migration in culture.

METHODS

Human colon carcinoma cells (Caco-2) were seeded on basement membrane matrix. To evaluate replication-blocked cell migration, we wounded confluent monolayers of cells with a sterile scalpel, and inhibited cell replication with mitomycin C. Immediately after wounding, the cells were exposed to 0-100 micromol/l deoxycholic acid. Migration over 72 h was monitored using a phase contrast microscope.

RESULTS

Replication-blocked migration was stimulated by deoxycholic acid in a dose-dependent manner, with the maximum effect at 20 micromol/l deoxycholic acid. Enhancement of migration rate was unaffected by immunoneutralization of transforming growth factor beta (a known migration-promoting peptide). However, specific inhibition of protein kinase C markedly inhibited deoxycholic acid-induced Caco-2 cell migration.

CONCLUSION

In addition to its well-established role in the enhancement of proliferation, deoxycholic acid also stimulates colon cancer-cell migration along the basement membrane matrix. The mechanism of this stimulation is likely to involve protein kinase C. Deoxycholic acid-stimulated migration might additionally contribute to the tumour-promoting effects of secondary bile acids in the colon.

Permeability characteristics of polyamines across intestinal epithelium using the Caco-2 monolayer system: comparison between transepithelial flux and mitogen-stimulated uptake into epithelial cells

The polyamines putrescine, spermidine, and spermine are present in foods in high amounts, and are used for cell growth throughout the body. Surprisingly little is known about the mechanisms of polyamine absorption in the gut. To elucidate the mechanisms, transepithelial transport of polyamines was studied in human enterocytelike Caco-2 cells, grown on permeable filter supports. Transport of all three polyamines across Caco-2 cell monolayers was linear; intraepithelial accumulation of polyamines was higher in confluent than in differentiated Caco-2 cells, but still negligible in comparison with the overall transport across the monolayers. Epidermal growth factor (EGF) enhanced polyamine accumulation in Caco-2 cells four-fold, and basolateral uptake was higher than apical uptake if the cells were stimulated to grow. The amounts of polyamines taken up by the cells were nevertheless negligible in comparison with the net polyamine flux across the monolayers. Basolateral excretion of polyamines was in the picomolar range, whereas their transepithelial transport, occurring presumably by passive diffusion through the paracellular pathway, contributed hundreds of micromoles of polyamines to the basolateral chamber. We conclude that transepithelial transport of polyamines occurs by passive diffusion, and that it is not influenced when epithelial cells are stimulated to proliferate by a potent mitogen such as EGF.

Tributyrin, a stable and rapidly absorbed prodrug of butyric acid, enhances antiproliferative effects of dihydroxycholecalciferol in human colon cancer cells

Tributyrin, a prodrug of natural butyrate, has been evaluated with an aim to overcome pharmacokinetic drawbacks of natural butyrate as a drug, i.e., its rapid metabolization and inability to achieve pharmacologic concentrations in neoplastic cells. We studied the effects of tributyrin on growth, differentiation and vitamin D receptor expression in Caco-2 cells, a human colon cancer cell line. Tributyrin was more potent in inhibiting growth and inducing cell differentiation than natural butyrate. The effect was further enhanced after addition of physiologic concentrations of dihydroxycholecalciferol [(OH)2D3]. The synergistic effect of tributyrin and (OH)2D3 in Caco-2 cells was due to tributyrin-induced overexpression of the vitamin D receptor, as measured by reverse transcriptase-polymerase chain reaction. Treatment with tributyrin increased binding of (OH)2D3 to its receptor 1.5-fold, without any change in receptor affinity. We conclude that tributyrin may, at least in part, exert its growth-reducing and differentiation-inducing effect in Caco-2 cells by an upregulation of the vitamin D receptor; this may provide a useful therapeutic approach in chemoprevention and treatment of colorectal cancer by the two nutrients occurring naturally in human diet.

Transepithelial transport of putrescine across monolayers of the human intestinal epithelial cell line, Caco-2

AIM: To study the transepithelial transport characteristics of the polyamine putrescine in human intestinal Caco-2 cell monolayers to elucidate the mechanisms of the putrescine intestinal absorption.

METHODS: The transepithelial transport and the cellular accumulation of putrescine was measured using Caco-2 cell monolayers grown on permeable filters.

RESULTS: Transepithelial transport of putrescine in physiological concentrations ( > 0.5 mM) from the apical to basolateral side was linear. Intracellular accumulation of putrescine was higher in confluent than in fully differentiated Caco-2 cells, but still negligible (less than 0.5%) of the overall transport across the monolayers in apical to basolateral direction.EGF enhanced putrescine accumulation in Caco-2 cells by four fold, as well as putrescine conversion to spermidine and spermine by enhancing the activity of S adenosylmethionine decarboxylase. However, EGF did not have any significant influence on putrescine flux across the Caco- 2 cell monolayers. Excretion of putrescine from Caco-2 cells into the basolateral medium did not exceed 50 picomoles, while putrescine passive flux from the apical to the basolateral chamber, contributed hundreds of micromoles polyamines to the basolateral chamber.

CONCLUSION: Transepithelial transport of putrescine across Caco-2 cell monolayers occurs in passive diffusion, and is not influenced when epithelial cells are stimulated to proliferate by a potent mitogen such as EGF.

Effect of structural analogues of propionate and butyrate on colon cancer cell growth

The aim of this study was to evaluate the effects of natural short-chain fatty acids (butyrate, propionate, valerate, acetate) and structural analogues of butyrate and propionate on cell growth and apoptosis in three human colonic adenocarcinoma cell lines (HT-29, Colo-320, and SW-948). We have previously shown that mercapto- and bromo-analogues of butyrate and propionate compete with natural short-chain fatty acids for uptake in the colonocyte. Among naturally occurring short-chain fatty acids, butyrate was the most potent inhibitor of proliferation in all three cell lines. Propionate exhibited a weaker antiproliferative effect, while other short-chain fatty acids (valerate, acetate) were ineffective. Bromo-analogues of butyrate and propionate were more potent proapoptotic agents than butyrate. In contrast to butyrate, the analogues induced strand breaks on isolated supercoiled DNA, the effect being completely reversed by a DNA-protecting agent, spermine. We conclude that bromo-analogues of butyrate and propionate are more potent proapoptotic agents than butyrate in colon cancer cells in culture. Their effect may be a result of direct DNA damage.

EGF-stimulated polyamine accumulation in the colon carcinoma cell line, Caco-2

BACKGROUND

Polyamines (putrescine, spermidine and spermine) are ubiquitous molecules indispensable for cell proliferation. In the intestinal lumen they are present in high amounts. Polyamine accumulation in proliferating cells of the intestinal mucosa is high, and it occurs both by enhanced synthesis and by increased uptake from the lumen.

AIMS

To study mitogen-induced polyamine accumulation in the gut, we treated proliferating Caco-2 cells with epidermal growth factor (EGF) and measured the activity of ornithine decarboxylase (ODC) and putrescine uptake. Furthermore, we investigated whether EGF-induced changes in the apical membrane could be responsible for the effect of EGF on polyamine uptake in Caco-2 cells.

METHODS

Putrescine uptake, ODC activity and intracellular polyamine content were evaluated in the presence of 100 ng/ml EGF. To study the mechanisms of EGF-stimulated polyamine uptake, apical membrane vesicles were isolated, and putrescine uptake into the vesicles measured. Possible enrichment in brush border membrane cytoskeleton proteins (ezrin and villin) was assessed by Western blot.

RESULTS

Treatment with EGF induced an increase in ODC activity, which occurred within the first minutes of treatment and reached peak values after 3 h. In contrast, an increase in putrescine uptake was more sustained, with peak levels at 12 h. Both synthesis and uptake contributed to an over 60% increase in intracellular putrescine and spermidine after EGF treatment. There were no detectable changes in apical membrane cytoskeleton (as concluded by the absence of ezrin and villin enrichment in EGF-treated Caco-2 cells). However, in apical membrane vesicles isolated from EGF-pretreated cells, putrescine uptake was enhanced twofold.

CONCLUSIONS

EGF stimulates both synthesis and uptake of polyamines in Caco-2 cells. Enhanced synthesis seems to ensure rapid supply with polyamines in the earliest stages of growth, while the uptake is responsible for the maintenance of high polyamine intracellular levels during late growth phases. EGF-stimulated polyamine uptake is apparently not a consequence of structural changes in the apical membrane, but is likely to occur by a distinct EGF-induced alteration of the polyamine transporter itself.

Polyamine uptake across the basolateral membrane of the enterocyte is mediated by a high-affinity carrier: a study using isolated basolateral membrane vesicles

BACKGROUND/AIMS

Polyamine uptake from the circulation plays an important role in the maintenance of the intracellular polyamine content during extensive proliferation in intestinal mucosal cells.

METHODS

Isolated basolateral membrane vesicles of the rabbit enterocyte were used to characterize polyamine transport across the basolateral side of the intestinal epithelium. Incorporation of spermidine and spermine into the basolateral membrane was rapid, although 30-60% of polyamines were initially bound to the basolateral membrane. In order to avoid the influence of binding on the actual uptake into the vesicles, polyamine incorporation was measured at 37 and 4 degrees C, and kinetic parameters were calculated from the difference in polyamine incorporation rates at these temperatures.

RESULTS

Uptake kinetics was saturable, with Km values of 13.34 and 12.35 micromol/l and Vmax of 159 and 105 pmol/mg protein/ min for spermidine and spermine, respectively. It was also temperature dependent, with Q10 values (calculated between uptake velocities at 37 and 25 degrees C) of 2.56 for spermidine and 1.90 for spermine. At physiological pH, polyamine uptake was at its highest. Since at this pH polyamines are fully charged, charge might be essential for polyamines to be taken up across the basolateral membrane. Polyamine uptake was inhibited by di-, tri- and tetracations, and there was no evidence for sodium cotransport. Transport of putrescine was not inhibited by spermine and spermidine, although spermidine inhibited spermine uptake in a competitive manner, with Ki of 127 micromol/l.

CONCLUSION

These results imply that a saturable high-affinity transport system for polyamine does exist at the basolateral side of the enterocyte. Such a transport system may be responsible for the active transport of polyamine into rapidly proliferating enterocytes.

Low-dose deoxycholic acid stimulates putrescine uptake in colon cancer cells (Caco-2)

Deoxycholic acid (DCA) has long been implicated as tumour-promoting agent in the colon. Polyamines are necessary for cell proliferation, they are accumulated in high amounts in colon cancer cells, and their concentrations in the colonic lumen can reach millimolar levels. The aim of this study was to investigate the effects of physiological DCA concentrations on proliferation and polyamine content in human colon cancer cells (Caco-2) in culture. Over an initial 48 h in culture, DCA stimulated Caco-2 cell proliferation rate three-fold, reaching a maximum with 20 microM DCA. DCA-induced increases in ornithine decarboxylase (ODC) activity corresponded to peak proliferation rates, occurring only during the initial 48 h of cell proliferation. Treatment with low-dose DCA resulted in a two-fold increase in putrescine uptake, first noted after 2 days in culture, but persisting until the cells became confluent (day 5). Both basal and DCA-stimulated putrescine uptake in Caco-2 cells were saturable. Kinetic analysis of the uptake data showed that DCA-stimulated putrescine uptake was due to an increase in the capacity of the putative putrescine transporter, without changes in its affinity, therefore implying an increased number of putrescine transporters in the cell membrane, without change in their structure.

Influence of physical exercise on polyamine synthesis in the rat skeletal muscle

BACKGROUND

Physical exercise and testosterone administration result in a series of adaptive anabolic phenomena in the skeletal muscle. The role of polyamines in these processes has been poorly explored.

DESIGN

We measured the activities of polyamine-synthesising enzymes, ornithine decarboxylase (ODC) and S-adenosylmethionine decarboxylase (SAMDC) and polyamine content in skeletal muscle of male rats exposed to endurance or resistance exercise, or a single testosterone treatment. Soleus muscle (consisting mainly of slow-twitching oxidative fibres-STO) and extensor digitorum longus (mainly fast-twitching glycolytic muscle fibres-FTG) were analysed for polyamine content by HPLC, and ODC and SAMDC activity.

RESULTS

Both endurance and resistance exercise induced a threefold increase in endogenous testosterone production. Two hours after exercise, ODC was increased in STO fibres, returning to baseline after 24 h; in FTG fibres the increase was less prominent. An increase in SAMDC activity occurred in a more sustained manner, with its peak 8 h after exercise. Polyamines were subsequently accumulated in both skeletal muscle fibres, with a rise in putrescine concentration after 2 h, and a fall corresponding to conversion of putrescine to spermidine and spermine by SAMDC. Single dose of 17alpha-methyltestosterone resulted in a similar increase in polyamine-synthesising enzyme activities and polyamine concentrations in the skeletal muscle.

CONCLUSION

Polyamine accumulation in the skeletal muscle after physical exercise is likely to occur secondary to testosterone production. Polyamines are apparently involved in the oxidative, but not in glycolytic processes related to muscle adaptation to exercise.

A conditionally immortalized epithelial cell line for studies of intestinal drug transport

A new cell culture model that better mimics the permeability of the human small intestine was developed for studies of passive drug transport. The intestinal epithelial cell line, 2/4/A1, conditionally immortalized with a temperature-sensitive mutant of the growth-promoting oncogene simian virus 40 (SV40) large T, was grown on permeable supports. The cells grew at 33 degrees C, where the oncogene is fully active, but stopped growing and entered a differentiation program at 39 degrees C, where the oncogene is inactive. Significant cell death was observed at 39 degrees C and, therefore, growth conditions under which 2/4/A1 cells survive during the differentiation process were developed. Cells grown on extracellular matrices which contained laminin at an intermediate temperature of 37 degrees C formed viable differentiated monolayers with tight junctions, an increased expression of brush border enzymes, and a paracellular permeability that was comparable to that of the human small intestine. The permeability of 17 structurally diverse drugs gave a sigmoidal relationship with the absorbed fraction of the drugs after oral administration to humans. The relationship was compared with those obtained with the well established Caco-2 model and after in vivo perfusion of the human jejunum. The transport of drugs with low permeability in 2/4/A1 monolayers was comparable to that in the human jejunum, and up to 300 times faster than that in Caco-2 monolayers. The transport of drugs with high permeability was comparable in all models. These results indicate that 2/4/A1 monolayers are promising alternatives to Caco-2 monolayers for studies of passive drug transport.

Reactivation of chronic Chagas' disease following allogeneic bone marrow transplantation and successful pre-emptive therapy with benznidazole

This report shows the early detection of reactivation of chronic Chagas' disease (CCd) in a 27-year-old man with chronic myelogenous leukemia undergoing allogeneic bone marrow transplantation (ABMT). Pre-emptive therapy with benznidazole during a period of 7 weeks led to a rapid recovery of the patient, who remains free of parasitemia 2 years after the bone marrow transplantation.

S-adenosylmethionine decarboxylase activity and utilization of exogenous putrescine are enhanced in colon cancer cells stimulated to grow by EGF

Polyamines spermidine and spermine and their precursor putrescine are necessary for cell growth. Polyamine content is high in rapidly growing malignant cells, due to enhanced putrescine synthesis by ornithine decarboxylase (ODC), and increased uptake. In contrast to other cells of the body, colon cancer cells are exposed to high putrescine concentrations from the lumen.

AIMS

To investigate the utilization of luminal putrescine in colon cancer, we studied the effect of a potent mitogen, epidermal growth factor (EGF), on the activity of the enzyme responsible for putrescine conversion, S-adenosylmethionine decarboxylase (SAMDC), in Caco-2 cells.

METHODS

Cell counts, ODC and SAMDC activities and intracellular polyamines were evaluated in the presence and absence of exogenous putrescine in concentrations resembling those normally present in the colonic lumen.

RESULTS

ODC and SAMDC activity and putrescine uptake were strongly stimulated by EGF. Both synthesized and absorbed putrescine was rapidly converted to spermidine and spermine after EGF. Conversion pattern was identical in the cells stimulated with EGF only and EGF plus exogenous putrescine, indicating that, if stimulated to proliferate, colon cancer cells utilize the entire available putrescine pool. SAMDC inhibitor, methylglyoxal-bis-guanylhydrazone, induced growth arrest which was not reversed by exogenous putrescine, but only by high concentrations of spermidine.

CONCLUSION

Enhanced proliferation in colon cancer cells is associated with increased SAMDC activity and rapid conversion of putrescine to spermidine and spermine. SAMDC might be a preferable target for therapeutic attempts to impair growth by reducing intracellular polyamine pools in colon cancer.

Chagas' disease after bone marrow transplantation

Chagas' disease is caused by Trypanosoma cruzi. It is endemic in Latin America where 16 to 18 million people are infected. Immunocompromised patients such as BMT recipients are at risk of Chagas' disease either due to reactivation or transfusion. We report a case of acute Chagas' disease in the setting of BMT.

Mercaptopropionate inhibits butyrate uptake in isolated apical membrane vesicles of the rat distal colon

BACKGROUND/AIMS

Previous observations have shown that mercapto- and bromo- short-chain fatty acids diminish fatty acid use in colonic epithelium. The aim of this study was to investigate whether this effect is attributable to the inhibition of short-chain fatty acid uptake.

METHODS

Apical membrane vesicles of rat colonocytes were prepared by a discontinuous sucrose gradient after isolation of membrane caps. [14C]butyrate uptake was measured by rapid filtration technique.

RESULTS

Preloading of isolated apical membrane vesicles with bicarbonate or butyrate stimulated [14C]butyrate uptake and resulted in up to fivefold overshoots. Increasing extravesicular butyrate concentrations saturated the bicarbonate-stimulated butyrate uptake with a binding constant of 44.7 +/- 5.9 mmol/L and a maximum velocity of 33.2 +/- 2.7 nmol.mg protein-1.3 s-1. Intravesicular butyrate uptake was inhibited by addition of 20 mmol/L 3-mercaptopropionate (43.0% +/- 5.6%), whereas 2-bromo-propionate (13.9% +/- 4.1%) and 4-bromobutyrate (22.6% +/- 5.3%) did not significantly alter butyrate uptake. Increasing concentrations of 3-mercaptopropionate had a competitive inhibitory effect on butyrate uptake with a binding constant following inhibition of 6.25 +/- 0.87 mmol/L and a maximum velocity of 5.82 +/- 1.01 nmol.mg protein-1.3 s-1.

CONCLUSIONS

Butyrate uptake in apical membrane vesicles of rat distal colon is mediated by a low-affinity anion transport system, which can be competitively inhibited by 3-mercaptopropionate but not by 2-bromopropionate and 4-bromobutyrate.

Characterization of putrescine transport across the intestinal epithelium: study using isolated brush border and basolateral membrane vesicles of the enterocyte

Putrescine transport was investigated in isolated brush border and basolateral membrane vesicles prepared from the rabbit enterocyte. Brush border vesicles were oriented right-side-out and basolateral vesicles inside-out, forming a model representing uptake and extrusion across the intestinal epithelium. Putrescine transport across both membranes was initially rapid, and 66% of the equilibrium uptake was achieved within the first minute. According to osmoplots and measurements at 4 degrees C, 20% of total incorporation presented binding to the membrane. In order to estimate actual uptake into the vesicles, Km was calculated from the differences in putrescine incorporation at 37 degrees C and 4 degrees C, and was 12.7 mumol L-1 for brush border uptake and 38.2 mumol L-1 for basolateral extrusion. Putrescine uptake into brush border and basolateral membrane vesicles was not enhanced in the presence of an Na+ gradient. When Na+ was substituted with an uncharged solute, mannitol, putrescine incorporation was increased, indicating that putrescine uptake is not Na(+)-dependent and that cations might interfere with the carrier. Paraquat and methylglyoxalbis(guanylhydrazone), known to share the polyamine transport system, inhibited putrescine incorporation in both membrane vesicle preparations. Basolateral carrier showed significantly higher sensitivity to cations. We conclude that putrescine uptake across the apical membrane and extrusion across the basolateral membrane of the enterocyte are mediated by two different and independent carriers which differ in their electrical properties.

EGF stimulates polyamine uptake in Caco-2 cells

We investigated the effects of epidermal growth factor (EGF) on polyamine uptake in Caco-2 cell monolayers. Cells were grown until confluence (day 7) or until differentiation (day 14). Polyamine uptake into Caco-2 cells was stimulated by EGF in a dose-dependent manner. Both basal and EGF-stimulated uptake rates were higher in 7- than in 14-day-old Caco-2 cells. Stimulation with EGF resulted in a significant increase in Vmax and an increased affinity for putrescine and spermine. Polyamine uptake was not inhibited when protein synthesis was blocked by cycloheximide, implying that no additional protein synthesis occured for stimulatory effect of EGF on polyamine uptake. The tyrosine kinase inhibitor, genistein, completely inhibited EGF-stimulated polyamine uptake, indicating that tyrosine phosphorylation plays a role in EGF-stimulated polyamine uptake in Caco-2 cells. The effect of EGF on polyamine uptake into Caco-2 cells, therefore, could be due to translocation of intracellular proteins which were not previously incorporated into the membrane, or direct alteration of polyamine transporter.

Simultaneous preparation of rabbit intestinal brush border and basolateral membrane vesicles

A highly reproducible method is described for simultaneous preparation of the rabbit intestinal BBMV and BLMV. When BLMV were purified on continuous sorbitol gradient the final enrichment was over ten-fold for both Na+, K(+)-ATPase and K(+)-activated phosphatase. BBMV were separated using repeated precipitation with magnesium and EGTA. Marker enzymes of the brush border membrane also showed over ten-fold enrichment. There was no contamination with other cellular organelles. The characteristics of the preparations were checked by SDS gel electrophoresis, which showed distinct protein patterns for both membranes; monoclonal antibodies for villin reacted with the BBMV but not with BLMV, showing the absence of contamination of the BLMV fraction. The quality of the membranes, assessed by D-glucose transport, showed good functional properties for both BBMV and BLMV. Orientation of the vesicles was checked by permeabilizing with SDS buffered with BSA and showed that BLMV are oriented inside out and BBMV right side out. The model simulates normal transepithelial intestinal transport at the level of membrane vesicles and could be applied in transport studies in physiology and pharmacology.

Characteristics of putrescine uptake by human brush border membrane vesicles

Both putrescine and the polyamines spermidine and spermine are essential factors for growth and differentiation in all cells of higher eucaryotes. In principle, increased requirements of polyamines in mucosal cells either can be met by de novo-synthesis or by increasing the uptake from lumen (brush border membrane) or bloodstream (basolateral membrane). We therefore evaluated putrescine uptake in intestinal mucosal cells by using human brush border membrane vesicles (BBMV). Intravesicular uptake of putrescine was shown by osmoplots. This process was not saturable over a substrate range from 1 to 80 microM. Putrescine transport was also found to be independent of temperature (Q10 = 1.23). No differences in putrescine uptake rates were found in the presence or absence of Na+, and there was no evidence for any dependence of putrescine uptake from other cations. Our data indicate that putrescine uptake by human intestinal brush border membrane vesicles occurs by passive diffusion. It is concluded that a formerly described saturable and carrier mediated uptake in isolated intestinal mucosal cells from different species is probably influenced by active transport across the basolateral membranes. Therefore, further studies with isolated basolateral membranes are advocated.