In vitro toxicity and formation of early conjugates in Caco-2 cell line treated with clenbuterol, salbutamol and isoxsuprine

Aflatoxin M1 absorption and cytotoxicity on human intestinal in vitro model

Aflatoxin M1 (AFM1) is the principal hydroxylated Aflatoxin B1 (AFB1) metabolite and is detected in milk of mammals, after consumption of feed contaminated with AFB1. As it is classified as probable human carcinogen (group 2B of the IARC), most countries have regulated its maximum allowed levels in milk in order to reduce AFM1 risk (50 ng/kg the EU and 500 ng/kg in the USA). It was demonstrated that if AFB1 must be converted into its reactive epoxide to exert its effects, and the protein binding may play an important role in its cytotoxicity. Conversely, the AFM1 epoxidation in human liver microsomes is very limited and studies with human cell line (MCL5), expressing or not expressing cytochrome P450 enzymes, demonstrated a direct toxic potential of AFM1 in absence of metabolic activation. For this reason, while AFM1 is generally considered a detoxification product of AFB1 relatively to carcinogenicity and mutagenicity property, this is not always true for cytotoxicity activity. Aim of this work is to evaluate the intestinal absorption of AFM1 using a human in vitro model, the Caco-2 cell line. Either the parental Caco-2 cell line or its derived clone TC7, with higher metabolic competence, have been used. They were treated with different concentrations of AFM1, that mirror the milk contamination level (0.3-32 nM corresponding to 10-10,000 ng/kg), either in undifferentiated or in differentiated phase of growth. After 48 h of treatment in serum free medium, a dose dependent absorption of AFM1 has been detected in both cell lines, especially in differentiated cells, while, no appreciable effects on cell viability were observed, except for a general cellular suffering, revealed by LDH release, particularly evident in the undifferentiated cells. As well, no metabolites or AFM1 conjugates have been detected. The present results may be crucial for the evaluation of human risk to AFM1 exposure, in particular for children's population, due to their large use of milk and derivatives.

Transepithelial transport of bepridil in the human intestinal cell line, Caco-2, using a "dynamic model"

The purpose of the study was to go further into the transepithetial transport of bepridil, an anticalcic agent, through monolayer cells Caco-2, using a "dynamic model" including a transfer of inserts with Caco-2 cells into new wells, free of drug, at regular intervals, in order to simulate the blood flux. The state of cells was evaluated by measuring the transepithelial electrical resistance and the transport of bepridil was followed using a gas chromatography/mass spectrometry determination. This study exhibits the importance of the basolateral renewal both on the transport of bepridil and the maintenance of cells in a satisfactory state. Two elimination phases from the cell compartment seem to occur, with basolateral half lives respectively of 12.2 and 25.6 hours, probably linked with two kinds of cellular binding sites. This dynamic model permits the reflection and simulation of the slowness of the in vivo absorption of bepridil in the small intestine.

Identification and coupling to adenylate cyclase of three different [(3)H]CGP 12177 binding sites in Caco-2 cell membranes

In the present investigation the identification of beta -adrenoceptor (beta -ARs) subtypes in the Caco-2 cell line was performed using radiometric assays. beta -ARs were measured using increasing concentrations of the highly specific beta -AR antagonist (-)[(3)H]CGP 12177 (0.06-4 nM), whereas the beta(1)- and beta(2)-AR subtypes discriminated through selective binding assays using the highly selective unlabelled antagonists CGP 20712A and ICI 118551. Atypical beta -ARs were measured using an incubation system formed by higher concentrations (0.6-20 nM) of (-)[(3)H]CGP 12177. beta - Atypical binding site concentrations (69 +/- 5 fmol mg ml(-1)of membrane protein) were higher than beta(1)-ARs (7 +/- 1) and beta(2)-ARs (24 +/- 2), respectively. The different beta -AR subtype affinities were characterized by binding inhibition experiments and the adrenergic agonists displaced the radioligand from its specific binding sites in the following order of potency: isoproterenol > clenbuterol > dobutamine > SR 58611A; for antagonists the order of potency was: propranolol approximately = ICI118551 approximately = CGP20712A. For atypical beta -ARs the order was: SR 58611A > clenbuterol > dobutamine > isoproterenol for agonists and propranolol > CGP 20712A > ICI 118551 for antagonists. As far as in vitro functional studies are concerned, beta -AR subtypes were shown to be coupled to adenylyl cyclase as their stimulation produced cAMP in an amount significantly higher than basal values. cAMP production after stimulation with dobutamine, clenbuterol, isoproterenol, and SR 58611A was measured using a cAMP radioassay kit. The order of efficacy suggested that the stimulation of beta(2)-ARs was the most effective in inducing the activation of cell signalling mechanisms. The identification of functional beta -ARs in a cancer cell line represents the first step in the study of the possible adrenergic control of cellular activities (e.g. proliferation and/or differentiation), which could suggest the use of this cancer cell line as a model for the study of cell activity or possibly new therapeutic strategies.

Transepithelial transport of bepridil in the human intestinal cell line, Caco-2, using two media, DMEMc and HBSS

The purpose of this work was to study transepithelial transport of bepridil, an anticalcic agent, through monolayer cells Caco-2, using two experimental media with different chemical components. For experimentation, the measure of the transepithelial electrical resistance (TEER) allowed us to evaluate the state of cells; and the quantities of bepridil have been quantified using a gas chromatography/mass spectrometry system. First, when using the medium alone, without bepridil, Caco-2 cell integrity is, at least, maintained for 8 h using both media. However, for 24-h studies, only the DMEMc medium, rich in essential nutriments, allowed cell integrity to be maintained. Then, with bepridil in HBSS medium, the TEER measurement showed a dose-dependent toxic effect of bepridil, whereas in the DMEMc medium, the toxic effect was only found for the highest dose (12 microg). This difference is probably related to the high binding of bepridil to proteins of the DMEMc medium, therefore minimising the concentration of the free compound. The kinetics of bepridil result from two phenomena: first, an immediate passage of a slight part of bepridil through the cell barrier and second, a high retention of most of the bepridil dose in the cell level. The transfer of bepridil from the apical to the basolateral compartment appears quantitatively and kinetically different using DMEMc or HBSS medium. The retention of the compound in the 'filter with Caco-2 cells' compartment is higher in DMEMc medium (60% at 3 microg) than in HBSS medium (46% at 3 microg), and bepridil entering the basolateral compartment is delayed in the DMEMc medium. This study exhibits the importance of the selected medium on results and interpretation of data and the predominance of DMEMc to study the transport of lipophilic compounds highly retained in cells.