The human intestinal Caco-2 cell line has been extensively used over the last twenty years as a model of the intestinal barrier. The parental cell line, originally obtained from a human colon adenocarcinoma, undergoes in culture a process of spontaneous differentiation that leads to the formation of a monolayer of cells, expressing several morphological and functional characteristics of the mature enterocyte. Culture-related conditions were shown to influence the expression of these characteristics, in part due to the intrinsic heterogeneity of the parental cell line, leading to selection of sub-populations of cells becoming prominent in the culture. In addition, several clonal cell lines have been isolated from the parental line, exhibiting in general a more homogeneous expression of differentiation traits, while not always expressing all characteristics of the parental line. Culture-related conditions, as well as the different Caco-2 cell lines utilized in different laboratories, often make it extremely difficult to compare results in the literature. This review is aimed at summarizing recent, or previously unreviewed, data from the literature on the effects of culture-related factors and the influence of line sub-types (parental vs. different clonal lines) on the expression of differentiation traits important for the use of Caco-2 cells as a model of the absorptive and defensive properties of the intestinal mucosa. Since the use of Caco-2 cells has grown exponentially in recent years, it is particularly important to highlight these methodological aspects in order to promote the standardization and optimisation of this intestinal model.

Despite human gastrointestinal exposure to nanoparticles (NPs), data on NPs toxicity in intestinal cells are quite scanty. In this study we evaluated the toxicity induced by zinc oxide (ZnO) and titanium dioxide (TiO₂) NPs on Caco-2 cells. Only ZnO NPs produced significant cytotoxicity, evaluated by two different assays. The presence of foetal calf serum in culture medium significantly reduced ZnO NPs toxicity as well as ion leakage and NP-cell interaction. The two NPs increased the intracellular amount of reactive oxygen species (ROS) after 6 h treatment. However, only ZnO NPs increased ROS and induced IL-8 release both after 6 and 24 h. Experimental data indicate a main role of chemical composition and solubility in ZnO NPs toxicity. Moreover our results suggest a key role of oxidative stress in ZnO NPs cytotoxicity induction related both to ion leakage and to cell interaction with NPs in serum-free medium.

BackgroundEndometriosis is a common gynecologic disease characterized by the ectopic growth of endometrial tissue. In industrialized countries, it affects approximately 10% of women of reproductive age. Its etiology is unclear, but a multifactorial origin is considered to be most plausible. Environmental organochlorinated persistent pollutants, in particular dioxins and polychlorinated biphenyls (PCBs), have been hypothesized to play a role in the disease etiopathogenesis. However, results of studies carried out on humans are conflicting.ObjectiveWe evaluated the exposure to organochlorinated persistent pollutants as a risk factor for endometriosis.MethodsWe conducted a case–control study in Rome on 158 women comprising 80 cases and 78 controls. In all women, serum concentrations of selected non-dioxin-like PCBs (NDL-PCBs) and dioxin-like PCBs (DL-PCBs), 1,1-dichloro-2,2,-bis(4-chlorophenyl)-ethene (p,p′-DDE), and hexachlorobenzene (HCB) were determined by ion-trap mass spectrometry. DR-CALUX bioassay was employed to assess the 2,3,7,8-tetrachlorodibenzo-p-dioxin toxicity equivalent (TEQ) concentrations of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and DL-PCBs.ResultsWe found an increased risk of endometriosis for DL-PCB-118 [odds ratio (OR) = 3.79; 95% confidence interval (CI), 1.61–8.91], NDL-PCB-138 (OR = 3.78; 95% CI, 1.60–8.94), NDL-PCB-153 (OR = 4.88; 95% CI, 2.01–11.0), NDL-PCB-170 (OR = 3.52; 95% CI, 1.41–8.79), and the sum of DL-PCBs and NDL-PCBs (OR = 5.63; 95% CI, 2.25–14.10). No significant associations were observed with respect to HCB or to the sum of PCDDs, PCDFs, and DL-PCBs given as total TEQs.ConclusionsThe results of this study show that an association exists between increased PCB and p,p′-DDE serum concentrations and the risk of endometriosis.

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The Caco-2 cell system, a well characterized intestinal in vitro model, makes it possible to evaluate the ability of chemicals to cross the intestinal barrier, as well as to study their transport mechanisms. Permeability values estimated with this model correlate well with human in vivo absorption data for many drugs and chemicals. As a consequence, the use of the Caco-2 cellular model as a permeability assay to predict oral absorption in humans is growing, and its importance is increasing as a screening tool in drug-discovery strategies for the prediction of intestinal drug permeability. Strict observance of the experimental conditions, coupled with careful control of the cell-culture procedures, are crucial for obtaining a meaningful correlation with in vivo data. Because of the intrinsic variability of this absorption model, it is important to highlight that each experimental system must be calibrated with internal reference compounds, to permit data sharing between different laboratories.