A comparison of DNA damage induced by aflatoxin B1 in hepatocyte-like cells, their progenitor mesenchymal stem cells and CD34+ cells isolated from umbilical cord blood

Abdallah M, Chen X, Rajkovic A. Current Knowledge of Individual and Combined Toxicities of Aflatoxin B1 and Fumonisin B1 In Vitro

Mycotoxins are considered the most threating natural contaminants in food. Among these mycotoxins, aflatoxin B1 (AFB1) and fumonisin B1 (FB1) are the most prominent fungal metabolites that represent high food safety risks, due to their widespread co-occurrence in several food commodities, and their profound toxic effects on humans. Considering the ethical and more humane animal research, the 3Rs (replacement, reduction, and refinement) principle has been promoted in the last few years. Therefore, this review aims to summarize the research studies conducted up to date on the toxicological effects that AFB1 and FB1 can induce on human health, through the examination of a selected number of in vitro studies. Although the impact of both toxins, as well as their combination, were investigated in different cell lines, the majority of the work was carried out in hepatic cell lines, especially HepG2, owing to the contaminants' liver toxicity. In all the reviewed studies, AFB1 and FB1 could invoke, after short-term exposure, cell apoptosis, by inducing several pathways (oxidative stress, the mitochondrial pathway, ER stress, the Fas/FasL signaling pathway, and the TNF-α signal pathway). Among these pathways, mitochondria are the primary target of both toxins. The interaction of AFB1 and FB1, whether additive, synergistic, or antagonistic, depends to great extent on FB1/AFB1 ratio. However, it is generally manifested synergistically, via the induction of oxidative stress and mitochondria dysfunction, through the expression of the Bcl-2 family and p53 proteins. Therefore, AFB1 and FB1 mixture may enhance more in vitro toxic effects, and carry a higher significant risk factor, than the individual presence of each toxin.

Amelioration of aflatoxin acute hepatitis rat model by bone marrow mesenchymal stem cells and their hepatogenic differentiation

Background and Aim:

Bone marrow-derived mesenchymal stem cells (BM-MSCs) transplantation and their hepatogenic differentiated cells (HDCs) can be applied for liver injury repair by tissue grafting. Regenerative potentiality in liver cirrhosis models was widely investigated; however, immunomodulation and anti-inflammation in acute hepatitis remain unexplored. This study aimed to explore the immunomodulatory and evaluate twice intravenous (IV) or intrahepatic (IH) administration of either BM-MSCs or middle-stage HDCs on aflatoxin (AF) acute hepatitis rat model.

Materials and Methods:

BM-MSCs viability, phenotypes, and proliferation were evaluated. Hepatogenic differentiation, albumin, and mmmmmmmm-fetoprotein gene expression were assessed. AF acute hepatitis was induced in rats using AFB1 supplementation. The transplantation of BM-MSCs or their HDCs was done either by IV or IH route. Hepatic ultrasound was performed after 3-weeks of therapy. Cytokines profile (tumor necrosis factor-α [TNF-α], interleukin [IL]-4, and IL-10) was assessed. Hepatic bio-indices, serum, and hepatic antioxidant activity were evaluated, besides examining liver histological sections.

Results:

Acute AFB1 showed a significant increase in TNF-α (p<0.01), liver enzyme activities (p<0.05), as well as decrease in IL-4, IL-10, and antioxidant enzyme activities (p<0.05). Cytokines profile was ameliorated in groups treated with IV and IH BM-MCs, showed a negative correlation between IL-4 and TNF-α (p<0.05), and a positive correlation between IL-10 upregulation and TNF-α (p<0.01). In IV HDCs treated group, positive correlations between IL-4 and IL-10 downregulation and TNF-α were observed. However, in IH HDCs group, a significant positive correlation between IL-4 and IL-10 upregulation and TNF-α, were recorded (p<0.05). In addition, IV BM-MSCs and IH HDCs treatments significantly increased antioxidant enzymes activity (p<0.05). IV and IH BM-MSCs significantly ameliorated liver transaminase levels, whereas IH HDCs significantly ameliorated alanine aminotransferase activity and nitric oxide concentration (p<0.05).

Conclusion:

The administration routes of BM-MSCs did not demonstrate any significant difference; however, the IH route of HDCs showed significant amelioration from the IV route. On the other hand, it showed noticeable anti-inflammatory and immunomodulatory improvements in aflatoxicosis rats. Therefore, it can be concluded that acute hepatitis can be treated by a noninvasive IV route without the expense of hepatogenic differentiation. Further research using clinical trials that address several problems regarding engraftment and potentiation are needed to determine the optimal manipulation strategy as well as to achieve better long term effects.

Glutathione-related inflammatory signature in hepatocytes differentiated from the progenitor mesenchymal stem cells

N-acetylcysteine (NAC) as a glutathione inducer is known for its anti-inflammatory effects in inflammatory conditions. The aim of the present study was to know if supplementation of the culture medium with NAC can improve anti-inflammatory activities of hepatocytes during their differentiation from mesenchymal stem cells (MSCs). For this, in vitro hepatic differentiation of MSCs was performed in culture medium supplemented with NAC and selected pro- and anti-inflammatory factors were monitored for two weeks. Treatment of the MSCs undergoing hepatic differentiation with NAC (0.1 and 1.0 mM) caused a significant (~5-fold) increase in proliferation rate of MSCs, whereas the rate of hepatic differentiation was declined in NAC-treated cells as compared to those untreated with NAC. Under these circumstances, NAC caused a significant increase in total glutathione in cell lysate during 2 weeks of differentiation as compared to untreated group. NAC-related increase in glutathione was associated with significant alterations in tumor necrosis factor-α (TNF-α), interleukin (IL)-6, IL-8 and IL-10 levels secreted in the culture medium. A substantial decrease in the IL-6, IL-8 and TNF-α levels in the culture medium supplemented with NAC was obvious in hepatocytes recovered 14 days after differentiation. In contrast, the secretary IL-10 was significantly increased as a result of NAC treatments. These data suggest that NAC supplementation can improve anti-inflammatory activities of the hepatocytes derived from MSCs. NAC function mediated by glutathione synthesis can also help in modulation of proliferation of the stem cells and their differentiation into hepatocyte-like cells.

Genetic toxicity assessment using liver cell models: past, present, and future

Genotoxic compounds may be detoxified to non-genotoxic metabolites while many pro-carcinogens require metabolic activation to exert their genotoxicity in vivo. Standard genotoxicity assays were developed and utilized for risk assessment for over 40 years. Most of these assays are conducted in metabolically incompetent rodent or human cell lines. Deficient in normal metabolism and relying on exogenous metabolic activation systems, the current in vitro genotoxicity assays often have yielded high false positive rates, which trigger unnecessary and costly in vivo studies. Metabolically active cells such as hepatocytes have been recognized as a promising cell model in predicting genotoxicity of carcinogens in vivo. In recent years, significant advances in tissue culture and biological technologies provided new opportunities for using hepatocytes in genetic toxicology. This review encompasses published studies (both in vitro and in vivo) using hepatocytes for genotoxicity assessment. Findings from both standard and newly developed genotoxicity assays are summarized. Various liver cell models used for genotoxicity assessment are described, including the potential application of advanced liver cell models such as 3D spheroids, organoids, and engineered hepatocytes. An integrated strategy, that includes the use of human-based cells with enhanced biological relevance and throughput, and applying the quantitative analysis of data, may provide an approach for future genotoxicity risk assessment.

Cytotoxicity of gamma irradiated aflatoxin B1 and ochratoxin A

Toxicity of gamma irradiated mycotoxins aflatoxin B₁ (AFB₁) and ochratoxin A (OTA) was investigated in vitro. AFB₁ and OTA stock solutions (50 mM, in methanol) were gamma irradiated (5 and 10 kGy) and non-irradiated and irradiated mycotoxins solutions were tested for cytotoxicity on Pk15, HepG2 and SH-SY5Y cell lines (MTT assay, 1-500 μM concentration range; 24 h exposure). Degradation of mycotoxin molecules was examined by liquid chromatography tandem mass spectrometry (HPLC-MS/MS). AFB₁ and OTA radiolytic products were less toxic than the parent mycotoxins to all of the tested cell lines. Gamma irradiation even at 5 kGy had effect on AFB₁ and OTA molecules however, this effect was dependent on chemical structure of mycotoxin. Since gamma irradiation at low dose reduced initial level of both mycotoxins, and gamma irradiated mycotoxins had lower toxicity in comparison to non-irradiated mycotoxins, it can be concluded that gamma irradiation could be used as decontamination method.

The impact of oxidative DNA changes and ATM expression on morphological and functional activities on hepatocytes obtained from mesenchymal stem cells

Resistance to oxidative damages in undifferentiated mesenchymal stem cells (MSCs) in comparison with the undifferentiated progenitor cells may differ depending on several factors. This study was carried out to examine the impact of hepatogenic differentiation process of MSCs on oxidative DNA damage markers. Hepatic differentiation of MSCs was carried out using a two-step conventional protocol and the cells were processed for characterization using morphological and biochemical markers. During the course of differentiation cellular levels of reactive oxygen species (ROS), 8-hydroxy-2'-deoxyguanosine (8-OH-dG) and expression of ataxia-telangiectasia mutated (ATM) protein were estimated at time intervals (10, 20 and 30 days). The results showed a decrease in cellular ROS (13%, P < 0.05) at early stages of hepatogenic differentiation. Similarly, there was a small but significant decrease in 8-OH-dG level and ATM expression in differentiated hepatocytes. Despite the small changes in oxidative damage factors and ATM expression during the differentiation process, the hepatocytes obtained were morphologically and biologically intact.

Crosstalk-eliminated quantitative determination of aflatoxin B1-induced hepatocellular cancer stem cells based on concurrent monitoring of CD133, CD44, and aldehyde dehydrogenase1

Cancer stem cells (CSCs), known as tumor initiating cells, have become a critically important issue for cancer therapy. Although much research has demonstrated the induction of hepato cellular carcinoma by aflatoxin B1, the formation of hepatocellular CSCs and their quantitative determination is hardly reported. In this work, it was found that hepatocellular CSCs were produced from HepG2 cells by aflatoxin B1-induced mutation, and their amount was quantitatively determined using crosstalk-eliminated multicolor cellular imaging based on quantum dot (Qdot) nanoprobes and an acousto-optical tunable filter (AOTF). Hepatocellular CSCs were acquired via magnetic bead-based sorting and observed using concurrent detection of three different markers: CD133, CD44, and aldehyde dehydrogenase1 (ALDH1). The DNA mutation of HepG2 cells caused by aflatoxin B1 was quantitatively observed via absorbance spectra of aflatoxin B1-8, 9-epoxide-DNA adducts. The percentages of hepatocellular CSCs formed in the entire HepG2 cells were determined to be 9.77±0.65%, 10.9±1.39%, 11.4±1.32%, and 12.8±0.7%, respectively, at 0 μM, 5 μM, 10 μM, and 20 μM of aflatoxin B1. The results matched well with those obtained utilizing flow cytometry. This study demonstrates that aflatoxin mediated mutation induced the conversion of hepatic cancer cell to hepatic CSCs by using a Qdot based constructed multicolor cellular imaging system.

Individual and combined cytotoxic effects of aflatoxin B1, zearalenone, deoxynivalenol and fumonisin B1 on BRL 3A rat liver cells

This study was performed to determine the individual and combined cytotoxic effects of Aflatoxin B1 (AFB1), zearalenone (ZEA), deoxynivalenol (DON) and fumonisin B1 (FB1) on BRL 3A rat liver cells. After the mycotoxins treated the BRL 3A cells for 12, 24 and 48 h, cell viability was determined using the MTT assay. The cytotoxicity of individual mycotoxins on BRL 3A cell viability in decreasing order were DON > AFB1 > ZEA > FB1. The central composite design (CCD) was used to assess the toxicity of binary and ternary mixtures of these mycotoxins. The mixtures of AFB1+ZEA and AFB1+DON showed the synergetic toxic effects on BRL 3A cells. These toxins decreased the viability of cells by inducing intracellular reactive oxygen species (ROS) production and promoting apoptosis in the BRL 3A cells. This effect was mediated by an upregulation of the stress and apoptotic genes Hsp70, p53, Bax, Caspase-3 and Caspase-8, along with a downregulation of the antiapoptotic gene Bcl-2. In conclusion, our results suggested that the coexistence of AFB1 and ZEA or DON in agricultural products could be more hepatotoxic than individually, suggests that the toxicological interactions of these toxins need to be better understood to assess health risks.

The metabolic function of hepatocytes differentiated from human mesenchymal stem cells is inversely related to cellular glutathione levels

Differentiation of mesenchymal stem cells (MSCs) to hepatocytes-like cells is associated with alteration in the level of reactive oxygen species (ROS) and antioxidant defense system. Here, we report the role of glutathione in the functions of hepatocytes derived from MSCs. The stem cells undergoing differentiation were treated with glutathione modifiers [buthionine sulfoxide (BSO) or N-acetyl cysteine (NAC)], and hepatocytes were collected on day 14 of differentiation and analysed for their biological and metabolic functions. Differentiation process has been performed in presence of glutathione modifiers viz. BSO and NAC. Depending on the level of cellular glutathione, the proliferation rate of MSCs was affected. Glutathione depletion by BSO resulted in increased levels of albumin and ROS in hepatocytes. Whereas, albumin and ROS were inhibited in cells treated with glutathione precursor (NAC). The metabolic function of hepatocytes was elevated in BSO-treated cells as judged by increased urea, transferrin, albumin, alanine transaminase and aspartate transaminase secretions in the media. However, the metabolic activity of the hepatocytes was inhibited when glutathione was increased by NAC. We conclude that the efficiency of metabolic function of hepatocytes is inversely related to the levels of cellular glutathione. These data may suggest a novel role of glutathione in regulation of metabolic function of hepatocytes.

Bio-electrospraying of human mesenchymal stem cells: An alternative for tissue engineering

Bio-electrospraying (BES) is a technique used for the processing of cells and can be applied to tissue engineering. The association of BES with scaffold production techniques has been shown to be an interesting strategy for the production of biomaterials with cells homogeneously distributed in the entire structure. Various studies have evaluated the effects of BES on different cell types. However, until the present moment, no studies have evaluated the impact of BES time on mesenchymal stem cells (MSC). Therefore, the aim of this work was to standardise the different parameters of BES (voltage, flow rate, and distance of the needle from the collecting plate) in relation to cell viability and then to evaluate the impact of BES time in relation to viability, proliferation, DNA damage, maintenance of plasticity and the immunophenotypic profile of MSC. Using 15 kV voltage, 0.46 ml/h flow rate and 4 cm distance, it was possible to form a stable and continuous jet of BES without causing a significant reduction in cell viability. Time periods between 15 and 60 min of BES did not cause alterations of viability, proliferation, plasticity, and immunophenotypic profile of the MSC. Time periods above 30 min of BES resulted in DNA damage; however, the DNA was able to repair itself within five hours. These results indicate that bio-electrospraying is an adequate technique for processing MSC which can be safely applied to tissue engineering and regenerative medicine.

Flavonoid hesperidin protects neural crest cells from death caused by aflatoxin B(1)

The neural crest (NC) corresponds to a collection of multipotent and oligopotent progenitors endowed with both neural and mesenchymal potentials. The derivatives of the NC at trunk level include neurons and glial cells of the peripheral nervous system. Despite the well-known influence of aflatoxins on the development of cancer, the issue of whether they also influence NC cells has not been yet addressed. In the present work, we have investigated the effects of aflatoxin B(1) on quail NC cells and the concomitant effects of the flavonoid hesperidin associated with this mycotoxin. We show for the first time that aflatoxin B(1) decreases the viability and the total number of glial and neuronal cells/field, although their proportions in relation to the total number of cells were not altered. Therefore, aflatoxin has no effect on NC differentiation. However, this compound was able to reduce NC proliferation and NC survival. Furthermore, the co-administration of hesperidin, a well-known polyphenolic protector of cell death, partially prevented the effect of aflatoxin B(1) . Taken together, our results demonstrate that aflatoxin B(1) is toxic to NC cells, an effect partially prevented by the flavonoid hesperidin. This study may contribute to the understanding of the effects of these compounds during early embryonic development and offer potentially more assertive diets and treatments for pregnant animals.

Safety evaluation of stem cells used for clinical cell therapy in chronic liver diseases; with emphasize on biochemical markers

There are several issues to be considered to reduce the risk of rejection and minimize side effects associated with liver cell transplantation in chronic liver diseases. The source and the condition of stem cell proliferation and differentiation ex vivo and the transplantation protocols are important safety considerations for cell based therapy. The biochemical and molecular markers are important tools for safety evaluation of different processes of cell expansion and transplantation. Studies show that hepatocytes differentiated from adult and embryonic stem cells exhibit biochemical and metabolic properties resembling mature hepatocytes. Therefore these assays can help to assess the biological and metabolic performance of hepatocytes and progenitor stem cells. The assays also help in testing the contribution of transplanted hepatocytes in improving the repair and function of damaged liver in the recipient. Here we review the biochemical and metabolic markers, which are implicated in evaluation of safety issues of stem cells used for therapeutic purposes in chronic liver diseases and regeneration of damaged liver. We also highlight application of biochemical tests for assessment of liver cell transplantation.