Functional alterations induced by the food contaminant furazolidone on the human tumoral intestinal cell line Caco-2

The activities of peptides “31–43”, “44–55” and “56–68” of A-gliadin onIn VitroCultures of CaCo-2 Cells

In previous studies, various A-gliadin peptides with known amino acid sequences have been tested for their damaging effects on in vitro cultured atrophic coeliac mucosa. The largest common sequences among the in vitro toxic peptides were (gln)3- pro and pro-ser-(gln)2. Three of these active A-gliadin fragments were synthesised and characterised, namely, the peptides corresponding to the amino acid sequences “31–43” and “44–55”, which contain the sequences (gln)3-rpro and pro-ser-(gln)2, respectively, and the “56–68” fragment lacking both active amino acid sequences. While the “56–68” A-gliadin peptide was completely inactive in CaCo-2 cells, the other two peptides were cytotoxic toward these cells to different extents. Our results confirm that CaCo-2 cells are a suitable model for the identification of toxic peptides responsible for coeliac pathogenesis.

Inhibition of the cellular metabolism of Caco-2 cells by prolamin peptides from cereals toxic for coeliacs

Peptic-tryptic (PT) digests of prolamins derived from several cereals were tested on differentiated Caco-2 cells to study the effect on cellular metabolism, particularly on DNA, RNA, protein and glycoprotein synthesis. Cell viability was evaluated after treatment with the same cereals. Whereas PT digests from bovine serum albumin and both durum wheat types (diploid and tetraploid) did not exert any effect, bread wheat, oats, barley and rye exerted an inhibitory effect close to 80% for DNA and RNA synthesis and close to 60% for (glyco)protein synthesis. Cell viability evaluated by MTT tests did not show any differences between treated and untreated cells. These observations, and previous results, suggest that, whereas prolamin-derived peptides from bread wheat, barley, rye and oats did not cause an immediate cytotoxic effect, they, were however, responsible for cell damage impairing cell metabolism.

Use of the caco-2 model in the screening of polluting substance toxicity

The aim of this work was to investigate the oral toxicity of representative chemicals chosen from each class of the list of 132 substances present in industrial effluents after the EEC Directive 76-464. Owing to its characterization as a model of the intestinal epithelium, the CaCo-2 cell line model was chosen. Cytotoxicity was assayed using the tetrazolium blue (MTT) test. For most of the substances, a linear correlation was observed between the octanol/water partition coefficient (log Kw) and the median inhibition concentration (IC(50)). This relationship between lipophilicity and toxicity is the hallmark of a narcotic mechanism of action. However, diethylamine appeared more toxic than the correlation would predict. Other amines were then tested (tert-butylamine, n-butylamine and benzylamine). All of these did not fit into the baseline correlation. The IC(50) were corrected by taking into account only the non-ionized, lipid insoluble, concentration at pH7.3. The amines still did not fit into the correlation, reinforcing the idea of a non-narcotic mechanism. The toxicity of a large number of substances can thus be predicted from their physico-chemical properties only when the substances exert a direct and non-specific effect. The amines appeared more toxic than substances with the same partition coefficient, showing that knowledge of the only lipophilicity is too restrictive to predict toxicity.

Use of transepithelial electrical resistance in the study of pentachlorophenol toxicity

The toxicity of pentachlorophenol (PCP), a polluting substance believed to exert a narcotic effect, was assayed using the Caco-2 cell line as a model. In order to assess this toxicity as fully as possible, several viability tests, each examining different endpoints, have been used. Neutral red uptake was found to be more sensitive to PCP than MTT and Alamar Blue tests. Transepithelial electrical resistance (TEER) was shown to be the most sensitive to PCP at concentrations and exposure times where the Alamar Blue, LDH leakage and Blue Dextran passage did not evidence any effect. Blue Dextran passage and optical microscopy revealed cellular detachment at concentrations where LDH and Alamar Blue showed little or no cytotoxicity. Thus, PCP seems to affect the integrity of the intestinal barrier at levels where no cytotoxicity is seen. Our results support the notion that TEER can be used as a very sensitive method for evaluating membrane-perturbing toxicants.

Furazolidone-based therapies for Helicobacter pylori infection: a pooled-data analysis

BACKGROUND/AIM

Furazolidone-based therapies are used in developing countries to cure Helicobacter pylori infection due to its low cost. The low bacterial resistance toward furazolidone may render appealing the use of this drug even in developed countries. However, some relevant safety concerns do exist in using furazolidone.

PATIENTS AND METHODS

This was a systematic review with pooled-data analysis of data regarding both eradication rate and safety of furazolidone-based therapies for H. pylori infection. Intention-to-treat (ITT) and per-protocol (PP) eradication rates were calculated.

RESULTS

Following furazolidone-based first-line therapy, H. pylori eradication rates were 75.7% and 79.6% at ITT and PP analysis, respectively (P<0.001). The overall incidence of side effects and severe side effects were 33.2% and 3.8%, respectively. At multivariate analysis, only high-dose furazolidone was associated with increased therapeutic success (OR: 1.5, 95% CI: 1.3-2.7; P<0.001), while occurrence of side effects was relevant following treatment for a long duration (OR: 2.9, 95% CI: 2.2-4.1; P<0.001), high-dose furazolidone (OR: 2.3, 95% CI: 1.7-3.2; P<0.001) and bismuth-containing regimens (OR: 2.1, 95% CI: 1.5-2.8; P<0.001).

CONCLUSIONS

Furazolidone-based regimens usually achieve low eradication rates. Only a high-dose regimen improves the cure rate, but simultaneously increases the incidence of severe side effects. Therefore, we suggest that patients have to be clearly informed about the possible genotoxic and carcinogenetic effects for which furazolidone use is not approved in developed countries.

Potential role of cysteine and methionine in the protection against hormonal imbalance and mutagenicity induced by furazolidone in female rats

The use of nitrofurans as veterinary drugs has been banned in the EU since 1993 due to doubts on the safety of the protein-bound residues of these drugs in edible products. Furazolidone (FUZ) is a nitrofuran drug, which has been used for many years as an antibacterial drug in veterinary practice. The aim of the current study is to investigate the role of L-cysteine and L-methionine in the protection against hormonal imbalance and the genotoxicity induced by FUZ using the micronucleus (MN) assay and random amplified polymorphism DNA (RAPD-PCR) analysis in female rats. Forty female Sprague-Dawley rats were divided into four groups included the untreated control group; a group treated with FUZ (300 mg/kg b.w.); a group treated with a mixture of L-cysteine (300 mg/kg b.w.) and L-methionine (42.8 mg/kg b.w.) and a group treated with FUZ plus the mixture of L-cysteine and L-methionine for 10 days. The results indicated that FUZ induced hormonal disturbances involving thyroid, ovarian and adrenal hormones. Moreover, FUZ increased the micronucleus formation and induced changes in polymorphic band patterns. The combined treatment with FUZ and the mixture of L-cysteine and L-methionine succeeded to prevent or diminish the endocrine disturbance and the clastogenic effects of FUZ. The current study is casting new light on the complex mechanisms underlying the ameliorating action of dietary L-cysteine and L-methionine against FUZ toxicity in experimental animals.

Wheat gliadin induces apoptosis of intestinal cells via an autocrine mechanism involving Fas-Fas ligand pathway

Wheat gliadin and other cereal prolamins have been said to be involved in the pathogenic damage of the small intestine in celiac disease via the apoptosis of epithelial cells. In the present work we investigated the mechanisms underlying the pro-apoptotic activity exerted by gliadin-derived peptides in Caco-2 intestinal cells, a cell line which retains many morphological and enzymatic features typical of normal human enterocytes. We found that digested peptides from wheat gliadins (i) induce apoptosis by the CD95/Fas apoptotic pathway, (ii) induce increased Fas and FasL mRNA levels, (iii) determine increased FasL release in the medium, and (iv) that gliadin digest-induced apoptosis can be blocked by Fas cascade blocking agents, i.e. targeted neutralizing antibodies. This favors the hypothesis that gliadin could activate an autocrine/paracrine Fas-mediated cell death pathway. Finally, we found that (v) a small peptide (1157 Da) from durum wheat, previously proposed for clinical practice, exerted a powerful protective activity against gliadin digest cytotoxicity.

Induction of apoptosis in caco-2 cells by wheat gliadin peptides

Recent experimental evidence suggests that enterocyte apoptosis is greater than hitherto assumed and may be responsible for villous atrophy in coeliac disease. We have previously demonstrated that a small peptide (M.W. 1157.5 Da), identified as the sequence H(2)N-gln-gln-pro-gln-asp-ala-val-gln-pro-phe-COOH from durum wheat gliadin, is able to prevent K 562 (S) cell agglutination induced by the peptic-tryptic digests (PT) of prolamin fractions from the cereals which are not tolerated in coeliac disease (i.e. bread wheat, rye, barley and possibly oats), and toxic A-gliadin peptides in coeliac disease. In the present study we have investigated the effects of the bread wheat gliadin digest (PT) on apoptosis of Caco-2 cells and whether the '1157.5' Da peptide may in any way interfere with them. We evaluated both earlier biochemical and later morphological nuclear apoptotic events in the human colon adenocarcinoma cell line Caco-2. After 48 h exposure to the PT gliadin digest and the '1157.5' Da peptide, apoptosis was detected both for the early-stage apoptotic cells (adherent cells) and the late-stage apoptotic ones (detached cells which were floating in the culture medium). Exposure to the PT gliadin digest resulted in a high percentage of adherent cells that underwent cell death by apoptosis (about 30%), independent of the concentration range used; while the presence in the culture medium of peptide '1157.5' Da determined complete inhibition of cell death. On the other hand, morphological nuclear modifications observed in the floating cells showed a difference in the rate of the apoptosis dependent on the PT concentration, with partial protection in the presence of the peptide. These findings show an action of bread wheat gliadin peptides leading to cell death by apoptosis in the Caco-2 cell line and that the '1157.5' Da peptide is capable of preventing such an effect.

Characterization of furazolidone apical-related effects to human polarized intestinal cells

In studying the effects of furazolidone (FZ) on the human intestinal Caco-2 cell line grown on microporous membrane, we have previously demonstrated a higher toxicity when the compound was administered at the apical (AP) side than at the basolateral (BL) side. Moreover, we have also shown the production, in the intact cells, of a nitroanion radical from FZ by a cytochrome c P450 reductase. The aim of the present study was to investigate which specific cell structures and functions are involved in the observed domain-related toxicity. The relevance of alterations in integrity and selective properties of the intestinal barrier as first-pass site for ingested molecules is also discussed. We have confirmed that, as expected, the Caco-2 cells are protected from FZ injury by a specific inhibitor of the cytochrome c P450 reductase, and we have shown that this protection is more active on the apical side of the cells. In sublethal conditions, FZ causes increased permeability to 3H-mannitol and, to a different extent, to 3H-inulin. Again the effect is higher when the cells are apically exposed. We have thus examined the tight junctions morphology: a disruption of the apical perijunctional actin-bound cytoskeleton was detected by rhodamine-phalloidin staining and microtubule disorganization by antitubulin fluoresceinated antibodies. Again, the effect was more evident when the cells were apically treated with FZ. Preferential transport and accumulation of the compound by active transport mechanisms could be excluded, since transport of FZ was linear and no intracellular accumulation was detected either from the AP and or the BL sides. All together these results may suggest that the AP formation of the active metabolite and its possible reactivity with SH groups of perijunctional microfilaments could be responsible of the higher FZ apical toxicity. This study shows that polarized differentiated cells are very interesting in vitro models to investigate specific cellular domains as targets of toxic effects and to detect subtle changes that may be induced, in absence of cell death, in specialized epithelial layers.

4-Hexylresorcinol as inhibitor of shrimp melanosis: efficacy and residues studies; evaluation of possible toxic effect in a human intestinal in vitro model (Caco-2); preliminary safety assessment

Studies were performed on the efficacy, residues and in vitro enterocyte toxicity of 4-hexylresorcinol (4-HR), which could be utilized as an inhibitor of shrimp melanosis (black spot). Mediterranean sea shrimp (Parapaeneus longirostris) were treated with solutions of 4-HR in sea-water, at three different concentrations, 25, 50 or 100 mg/kg of shrimp, to test its antioxidative property. As a comparison a group of shrimp was treated with sodium metabisulphite (1 g/kg), while another group was left untreated. 4-HR showed a marked ability to inhibit or slow down melanosis (black spot) in shrimp; the most effective concentration was 100 mg/kg within an optimum period of 7 days but with effects up to the tenth day. During the first 5 days, 4-HR residues in the edible part of the shrimp showed a fast decrease in all three groups, going from initial average values of 20 mg/kg at 0 time, to 0.9 in the group treated at 25 mg/kg; from 42 to 1.8 mg/kg in the group at 50 mg/kg and from 85 to 1.9 mg/kg in the group at 100 mg/kg. In vitro studies on enterocyte-like Caco-2 cells did not indicate any cytotoxic effect up to a concentration of 50 micrograms/ml. Moreover, no inhibition of protein synthesis was observed, which lends further support to the absence of significant damage to the intestinal mucosa induced by 4-HR. The available database on 4-HR pharmacology and toxicology is inadequate to determine even a provisional ADI. There is negative evidence of carcinogenesis and no significant untoward effects were observed in humans when it was used as an anthelmintic. However, it is not possible to determine a NOEL for non-genotoxic effects. 4-HR could become an interesting alternative to the use of sulphites to prevent black spot. However, a more complete database is needed to achieve a regulatory evaluation.

Effect of furazolidone on sister-chromatid exchanges, cell proliferation kinetics, and mitotic index in vivo and in vitro

Furazolidone is an antimicrobial compound used in human and veterinary medicine. The aim of this investigation was to determine its genotoxic capacity in vitro and in vivo. We used the human lymphocyte culture system to detect the effect of 2.0, 4.0, 6.0, 8.0, or 10.0 micrograms/ml, and the mouse bone marrow assay to determine the effect of 8.6, 30.0, or 75.0 mg/kg furazolidone. In both systems we determined the frequency of sister-chromatid exchanges (SCE), the cell proliferation kinetics (CPK), and the mitotic index (MI). The in vitro results showed a significant SCE increase starting from the second dose tested and a CPK and MI decrease starting from the third dose. The in vivo results showed a SCE increase with the two high doses tested, but no significant modification was found in the CPK and MI with the three doses tested in the experiment.