An investigation into the sensitivity of heat shock proteins as markers of cellular damage: a comparative study of hydrazine and cadmium chloride in primary rat hepatocyte cultures

Moringa oleifera Root Induces Cancer Apoptosis more Effectively than Leave Nanocomposites and Its Free Counterpart

Medicinal plants are important elements of indigenous medical system that have persisted in developing countries. Many of the botanical chemo-preventions currently used as potent anticancer agents. However, some important anticancer agents are still extracted from plants because they cannot be synthesized chemically on a commercial scale due to their complex structures that often contain several chiral centers. The aim of this study was to test different extracts from the Moringa oleifera leaves (ML), its PLGA-CS-PEG nanocomposites (MLn), as well as root core (Rc) and outer (Ro) parts for activity against hepatocarcinoma HepG2, breast MCF7, and colorectal HCT 116/ Caco-2 cells in vitro. Nano-composites were prepared and characterized. Then, the nanocomposites and the free counterparts were screened on different propagated cancer cell lines. The underlying cytotoxic impact was followed using apoptosis measurements. All extracts kill the different cancer cells with different ratios, but intriguingly, the root core extract could kill the majority of cancer cells (approximately 70-80%), while sparing normal BHK-21 cells with minimal inhibitory effect (approximately 30-40%). Apoptotic cell increment came to confirm the cytotoxic effects of these extracts on HCT 116 cells (Rc: 212% and Ro: 180%, respectively) and HepG2 cells (ML: 567.5% and MLn: 608%, respectively) compared to control (100%) mechanistically wise. Moringa oleifera nanocomposites may have potential for use as a natural source of anti-cancer compounds.

The toxicity of extracts of plant parts of Moringa stenopetala in HEPG2 cells in vitro

The cytotoxicity of extracts from a widely used species of plant, Moringa stenopetala, was assessed in HEPG2 cells, by measuring the leakage of lactate dehydrogenase (LDH) and cell viability. The functional integrity of extract-exposed cells was determined by measuring intracellular levels of ATP and glutathione (GSH). The ethanol extracts of leaves and seeds increased significantly (p < 0.01) LDH leakage in a dose- and time-dependent manner. The water extract of leaves and the ethanol extract of the root did not increase LDH leakage. A highly significant (p < 0.001) decrease in HEPG2 viability was found after incubating the cells with the highest concentration (500 microg/mL) of the ethanol leaf and seed extracts. At a concentration of 500 microg/mL, the water extract of leaves increased (p < 0.01), while the ethanol extract of the same plant part decreased (p < 0.01), ATP levels. The root and seed extracts had no significant effect on ATP levels. The ethanol leaf extract decreased GSH levels at a concentration of 500 microg/mL (p < 0.01), as did the ethanol extract of the seeds at 250 microg/mL and 500 microg/mL (p < 0.05). The water extract of the leaves did not alter GSH or LDH levels or affect cell viability, suggesting that it may be non-toxic, and is consistent with its use as a vegetable. The data obtained from the studies with the ethanol extract of the leaves and seeds from Moringa stenopetala show that they contain toxic substances that are extractable with organic solvents or are formed during the process of extraction with these solvents. The significant depletion of ATP and GSH only occurred at concentrations of extract that caused leakage of LDH. Further investigation with this plant in order to identify the constituents extracted and their individual toxic effects both in vivo and in vitro is warranted. This study also illustrates the utility of cell culture for screening plant extracts for potential toxicity.

Biomarker responses in juvenile rainbow trout (Oncorhynchus mykiss) after single and combined exposure to low doses of cadmium, zinc, PCB77 and 17beta-oestradiol

The objective of this study was to examine (i) the biochemical responses of rainbow trout exposed to sublethal water concentrations of the metals cadmium (Cd) (1.5 microg l(-1)) and zinc (Zn) (150 microg l(-1)); and (ii) the potential combined effects when applied in mixture (Cd/Zn) with and without co-exposure to model organic chemicals 3,3',4,4'-tetrachlorobiphenyl (PCB77) (1 mg kg (-1)) and 17beta-oestradiol (E2) (0.5 mg kg(-1)). After 21 days of exposure, several biomarkers were assessed in the liver (enzymatic and nonenzymatic antioxidants, heat shock proteins [HSP70 and HSP60], ethoxyresorufin-O-deethylase [EROD]) and in the plasma (vitellogenin [Vtg], aminotransferases). Plasma aminotransferases were not affected, whereas the other biomarkers showed different patterns of response depending on the treatment. For example, Cd, and Zn to a lesser extent, induced an adaptive response in the liver shown by an increase in antioxidant defences (total glutathione [GSH], superoxide dismutase, Trolox equivalent antioxidant capacity [TEAC]), without any impairment of GSH redox status or induction of heat shock proteins. Antagonistic effects were observed in GSH-related biomarkers after Cd/Zn exposure. PCB77 strongly induced EROD activity, HSP70 and TEAC. Co-exposure with metals did not modulate significantly the effects of PCB77. E2 induced Vtg and inhibited liver antioxidants and basal EROD activity. These inhibitory effects were suppressed in fishes exposed to E2 + Cd/Zn, suggesting additive effects of E2 and metals. In addition, E2-induced Vtg was not altered by metals. Multivariate analyses confirmed some correlation between the biomarkers. The use of complementary biomarkers is necessary to discriminate different treatments and to highlight interactive effects.

Toxicity of cypermethrin: hsp70 as a biomarker of response in transgenic Drosophila

Heat shock protein induction is often associated with a cellular response to a harmful environment or to adverse life conditions. The main aims of our study were (1) to evaluate the cytotoxic potential of cypermethrin; and (2) to investigate the suitability of stress-induced heat shock protein Hsp70 as a biomarker for environmental pollutants in transgenic Drosophila melanogaster (Hsp70-lacZ)Bg(9). Different concentrations of cypermethrin (0.002, 0.2, 0.5 and 50.0 p.p.m.) were mixed with food. Third instar larvae of transgenic Drosophila melanogaster were allowed to feed on these mixtures for different time intervals (2, 4, 6, 12, 24 and 48 h). Following feeding, hsp70 induction and tissue damage were evaluated. In the highest concentration treatment group (50 p.p.m.), 100% larval mortality was recorded after 12 h exposure. Hsp70 was found to be induced even at the lowest concentration (0.002 p.p.m.) of the insecticide, while tissue damage was observed in the larvae exposed for 48 h. While an insignificant decline in hsp70 expression was observed in the larvae exposed to cypermethrin at a dietary concentration of 0.002 p.p.m. after 48 h compared with those exposed for 24 h, in the next two higher concentrations of the toxicant, a similar but significant decline in hsp70 expression was evident in the exposed larvae after 48 h. The present study reveals the cytotoxic potential of cypermethrin and further proposes that hsp70 induction in transgenic Drosophila melanogaster could be used as a sensitive biomarker in risk assessment.

Methods of in vitro toxicology

In vitro methods are common and widely used for screening and ranking chemicals, and have also been taken into account sporadically for risk assessment purposes in the case of food additives. However, the range of food-associated compounds amenable to in vitro toxicology is considered much broader, comprising not only natural ingredients, including those from food preparation, but also compounds formed endogenously after exposure, permissible/authorised chemicals including additives, residues, supplements, chemicals from processing and packaging and contaminants. A major promise of in vitro systems is to obtain mechanism-derived information that is considered pivotal for adequate risk assessment. This paper critically reviews the entire process of risk assessment by in vitro toxicology, encompassing ongoing and future developments, with major emphasis on cytotoxicity, cellular responses, toxicokinetics, modelling, metabolism, cancer-related endpoints, developmental toxicity, prediction of allergenicity, and finally, development and application of biomarkers. It describes in depth the use of in vitro methods in strategies for characterising and predicting hazards to the human. Major weaknesses and strengths of these assay systems are addressed, together with some key issues concerning major research priorities to improve hazard identification and characterisation of food-associated chemicals.

Spontaneous nitric oxide in hepatocyte monolayers and inhibition of compound-induced apoptosis

Primary cultures of hepatocytes are a widely used in vitro model for biochemical research. Following isolation, hepatocytes produce large amounts of nitric oxide (NO), which is known to have both pro- and anti-apoptotic effects in hepatocytes in vivo and in vitro. Previous work has not determined the effect of these increased levels of NO on the response of hepatocytes to apoptotic stimuli. Here we report that levels of nitrites are elevated in hepatocyte monolayers from 24 h onwards. Addition of the inducible nitric oxide synthase (iNOS) inhibitor, Nomega-nitro-L-arginine methyl ester (L-NAME), to the medium inhibited this increase in nitrites. These results indicate that the increase in nitrite is most likely due to the formation of NO. Elevated nitrite levels had no effect either on basal levels of apoptosis or on ATP and GSH. Apoptosis was induced by transforming growth factor beta-1 (TGFbeta-1) or glycochenodeoxycholate (GCDC). Both compounds caused moderate hepatocyte apoptosis; however, addition of L-NAME prior to exposure significantly increased the level of apoptosis observed with the two compounds. Both TGFbeta-1 and GCDC had no effect on hepatocyte ATP or GSH levels; however, as a consequence of secondary necrosis, TGFbeta-1 exposure significantly increased levels of lactate dehydrogenase (LDH) leakage. These findings indicate that the increased levels of NO associated with the culture of hepatocytes have an inhibitory effect on compound-induced apoptosis in the cells.

Activation of the hsp70 promoter by environmental inorganic and organic chemicals: relationships with cytotoxicity and lipophilicity

Stress proteins (heat shock proteins, HSPs) have been proposed as general markers of cellular aggression and their use for environmental monitoring is often suggested. The aim of this work was to study the potency of various environmentally relevant organic and inorganic chemicals to induce the expression of the HSP70 marker. For this purpose, we used an established HeLa cell line containing the chloramphenicol acetyl transferase (CAT) gene under the control of the hsp70 promoter. The screening of three metallic and 15 organic chemicals revealed differences in their capacities to induce the hsp70 promoter. The three metals tested (cadmium, zinc and mercury) were able to induce a stress response. Some organochlorine compounds (chlorophenol derivatives, tetrachlorohydroquinone, 3, 4-dichloroaniline, ethyl parathion and 1-chloro-2,4-dinitrobenzene) induced a response, whereas other common halogenated pesticides or aromatic hydrocarbons (e.g. benzo(a)pyrene, 2, 4-dichlorophenoxyacetic acid, endosulfan, diuron, 4-nonylphenol) did not. The potency to induce hsp70 was significantly correlated to the octanol-water partition coefficient (log K(ow)) of the inducing chemicals, except for 1-chloro-2,4-dinitrobenzene and ethyl parathion. Cytotoxicity assays run in parallel to the induction measurements revealed that the three metals were effective at non cytotoxic doses whereas all organic compounds, except tetrachlorohydroquinone and 1-chloro-2,4-dinitrobenzene, induced the promoter at cytotoxic doses. These results suggest that hsp70 is induced by different mechanisms of toxicity. We propose that this model can be used in mechanistic studies for the detection of toxic effects of certain pollutants.

The use of liver spheroids as an in vitro model for studying induction of the stress response as a marker of chemical toxicity

Stress protein induction has been advocated as a sensitive indicator of compound-induced toxicity. In monolayer cultures of primary hepatocytes, however, the two stress proteins, Hsp25 and Hsp72/3 are up-regulated, probably due to the effect of the isolation procedure and adaptation of the cells to the culture conditions. The aim of the current studies was to determine whether liver spheroids would provide an improved experimental model for the study of heat shock protein induction in vitro. Primary rat hepatocytes were cultured as liver spheroids and the expression of Hsp25 and Hsp72/3 measured along with the levels of ATP, GSH and albumin secretion. Hsp72/3 was initially increased in spheroid culture but returned to in vivo levels after 3 days of culture. Hsp25 was maintained at in vivo levels until day 6 of culture, after which levels increased slightly. The effects of the two hepatotoxins, hydrazine and cadmium chloride (CdCl(2)), were therefore measured on day 6 of spheroid culture. CdCl(2) had no effect on Hsp25 but increased Hsp72/3 at concentrations that affected other biochemical parameters. Hydrazine caused a rapid reduction in ATP levels and albumin secretion, but did not affect Hsp72/3. Hsp25 was slightly induced by hydrazine at later sampling times at concentrations, however, that affected other biochemical parameters. It can be concluded that liver spheroids provide a model for studying stress protein expression. However, the increase in stress proteins appears to be a relatively insensitive parameter compared to other more conventionally used toxicity endpoints and the response appears to vary with individual toxins under study.

Biomarkers in toxicology

The use of biomarkers in toxicology is becoming increasingly important. This article briefly reviews some of the aspects in an attempt to give an overall view of the field. Some of the new developments, particularly in relation to biomarkers of exposure and response, are mentioned. Specific DNA and protein adducts can now be used as biomarkers of the effective exposure so incorporating variations in environmental levels and individual disposition. Analysis of urinary metabolite profiles by NMR can highlight novel markers and allow recognition of patterns of metabolite changes as biomarkers of a toxic response. Novel urinary markers for liver and testicular dysfunction are discussed. Finally, the acetylator phenotype as a biomarker of susceptibility is described.