The induction of oxidative stress and cellular death by the drinking water disinfection by-products, dichloroacetate and trichloroacetate in J774.A1 cells

The role of oxidative stress in association between disinfection by-products exposure and semen quality: A mediation analysis among men from an infertility clinic

Toxicological and epidemiologic evidence has suggested that exposure to disinfection by-products (DBPs) impairs semen quality, while the underlying biological mechanisms remain unclear. This study aimed to examine the mediating role of oxidative stress in association between DBP exposure and semen quality. We measured a urinary biomarker of DBP exposure [trichloroacetic acid (TCAA)] and three urinary biomarkers of oxidative stress [8-hydroxy-2-deoxyguanosine (8-OHdG), 8-iso-prostaglandin F2_α (8-isoPGF2_α) and 4-hydroxy-2-nonenal-mercapturic acid (HNE-MA)] among men from an infertility clinic (n = 299). The associations of oxidative stress biomarkers with urinary TCAA and semen quality were evaluated using multivariable linear regression models, and the mediating role of oxidative stress biomarkers was assessed by a mediation analysis. Urinary TCAA was positively associated with urinary 8-OHdG and 8-isoPGF2_α in a dose-response manner (both P for trend < 0.001). Significantly inverse dose-response associations were observed between urinary 8-isoPGF2_α and sperm concentration and between urinary 8-OHdG and sperm motility (both P for trend < 0.05). The mediation analysis indicated a significant indirect effect of urinary 8-isoPGF2_α in the association between urinary TCAA and decreased sperm concentration (P = 0.01). Our results suggest that lipid peroxidation may be an intermediate mechanism by which DBP exposure impairs semen quality.

Preliminary Study of Multiple Stress Response Reactions in the Pond Snail Lymnaea stagnalis Exposed to Trace Metals and a Thiocarbamate Fungicide at Environmentally Relevant Concentrations

Gastropod mollusks have achieved an eminent importance as biological indicators of environmental quality. In the present study, we applied a multibiomarker approach to evaluate its applicability for the pond snail Lymnaea stagnalis, exposed to common industrial and agricultural pollutants at environmentally relevant concentrations. The snails were exposed to copper (Cu²⁺, 10 µg L^-1), zinc (Zn²⁺, 130 µg L^-1), cadmium (Cd²⁺, 15 µg L^-1), or the thiocarbamate fungicide "Tattoo" (91 µg L^-1) during 14 days. Metal treatment and exposure to "Tattoo" caused variable patterns of increase or decrease of metal levels in the digestive gland, with a clear accumulation of only Cd and Zn after respective metal exposure. Treatment with Cu and "Tattoo" caused an increase of cytochrome P450-related EROD activity. Glutathione S-transferase was inhibited by exposure to Cu, Zn, and "Tattoo." Treatment with the "Tattoo" led to an inhibition of cholinesterase activity, whereas Cu and Cd increased its activity. Caspase-3 activity was enhanced by up to 3.3 times in all treatments. A nearly uniform inhibitory effect for oxidative stress response parameters was observed in all kinds of exposure, revealing an inhibition of superoxide dismutase (Mn-SOD) activity, a depression of glutathione (GSH and GSSG) and of protein carbonyl levels. Pollutant-specific effects were observed for the catalase activity, superoxide anion production, and lipid peroxidation levels. Due to the high response sensitivity of Lymnaea stagnalis to chemical impacts, we suggest our study as a contribution for biomarker studies with this species under field conditions.

Comparative toxicity studies on bromochloroacetate, dibromoacetate, and bromodichloroacetate in J774A.1 macrophages: Roles of superoxide anion and protein carbonyl compounds

The brominated and mixed bromo-chloro-haloacetates, such as dibromoacetate (DBA), bromochloroacetate (BCA), and bromodichloroacetate (BDCA), are by-products of water chlorination and are found at lower levels than the fully chlorinated acetates in the drinking water. The toxicities of the compounds were assessed in J774A.1 cells and were found to induce concentration-dependent increases in cell death and superoxide anion and protein carbonyl compounds production. Compared to the previously tested concentrations of dichoroacetate (DCA) and trichloroacetate (TCA) in the same cell line, the tested haloacetates induced similar effects on cellular viability and superoxide anion production but at DBA and BCA concentrations that were approximately 40-160 times lower than those of DCA and TCA, and at BDCA concentrations that were 4-16 times lower than those of DCA and TCA. Also, production of super oxide anion, protein carbonyl compounds, and induction of phagocytic activation are suggested to play a role in their toxicity.

PDK1-Dependent Metabolic Reprogramming Dictates Metastatic Potential in Breast Cancer

Metabolic reprogramming is a hallmark of cellular transformation, yet little is known about metabolic changes that accompany tumor metastasis. Here we show that primary breast cancer cells display extensive metabolic heterogeneity and engage distinct metabolic programs depending on their site of metastasis. Liver-metastatic breast cancer cells exhibit a unique metabolic program compared to bone- or lung-metastatic cells, characterized by increased conversion of glucose-derived pyruvate into lactate and a concomitant reduction in mitochondrial metabolism. Liver-metastatic cells displayed increased HIF-1α activity and expression of the HIF-1α target Pyruvate dehydrogenase kinase-1 (PDK1). Silencing HIF-1α reversed the glycolytic phenotype of liver-metastatic cells, while PDK1 was specifically required for metabolic adaptation to nutrient limitation and hypoxia. Finally, we demonstrate that PDK1 is required for efficient liver metastasis, and its expression is elevated in liver metastases from breast cancer patients. Our data implicate PDK1 as a key regulator of metabolism and metastatic potential in breast cancer.

Dichloroacetate Decreases Cell Health and Activates Oxidative Stress Defense Pathways in Rat Alveolar Type II Pneumocytes

Dichloroacetate (DCA) is a water purification byproduct that is known to be hepatotoxic and hepatocarcinogenic and to induce peripheral neuropathy and damage macrophages. This study characterizes the effects of the haloacetate on lung cells by exposing rat alveolar type II (L2) cells to 0–24 mM DCA for 6–24 hours. Increasing DCA concentration and the combination of increasing DCA concentration plus longer exposures decrease measures of cellular health. Length of exposure has no effect on oxidative stress biomarkers, glutathione, SOD, or CAT. Increasing DCA concentration alone does not affect total glutathione or its redox ratio but does increase activity in the SOD/CAT oxidative stress defense pathway. These data suggest that alveolar type II cells rely on SOD and CAT more than glutathione to combat DCA-induced stress.

The protective role of antioxidants in the defence against ROS/RNS-mediated environmental pollution

Overproduction of reactive oxygen and nitrogen species can result from exposure to environmental pollutants, such as ionising and nonionising radiation, ultraviolet radiation, elevated concentrations of ozone, nitrogen oxides, sulphur dioxide, cigarette smoke, asbestos, particulate matter, pesticides, dioxins and furans, polycyclic aromatic hydrocarbons, and many other compounds present in the environment. It appears that increased oxidative/nitrosative stress is often neglected mechanism by which environmental pollutants affect human health. Oxidation of and oxidative damage to cellular components and biomolecules have been suggested to be involved in the aetiology of several chronic diseases, including cancer, cardiovascular disease, cataracts, age-related macular degeneration, and aging. Several studies have demonstrated that the human body can alleviate oxidative stress using exogenous antioxidants. However, not all dietary antioxidant supplements display protective effects, for example, β-carotene for lung cancer prevention in smokers or tocopherols for photooxidative stress. In this review, we explore the increases in oxidative stress caused by exposure to environmental pollutants and the protective effects of antioxidants.

Long-term dietary exposure to low concentration of dichloroacetic acid promoted longevity and attenuated cellular and functional declines in aged Drosophila melanogaster

Dichloroacetic acid (DCA), a water disinfection by-product, has attained emphasis due to its prospect for clinical use against different diseases including cancer along with negative impact on organisms. However, these reports are based on the toxicological as well clinical data using comparatively higher concentrations of DCA without much of environmental relevance. Here, we evaluate cellular as well as organismal effects of DCA at environmentally and mild clinically relevant concentrations (0.02-20.0 μg/ml) using an established model organism, Drosophila melanogaster. Flies were fed on food mixed with test concentrations of DCA for 12-48 h to examine the induction of reactive oxygen species (ROS) generation, oxidative stress (OS), heat shock genes (hsps) and cell death along with organismal responses. We also examined locomotor performance, ROS generation, glutathione (GSH) depletion, expression of GSH-synthesizing genes (gclc and gclm), and hsps at different days (0, 10, 20, 30, 40, 50) of the age in flies after prolonged DCA exposure. We observed mild OS and induction of antioxidant defense system in 20.0 μg/ml DCA-exposed organism after 24 h. After prolonged exposure to DCA, exposed organism exhibited improved survival, elevated expression of hsp27, gclc, and gclm concomitant with lower ROS generation and GSH depletion and improved locomotor performance. Conversely, hsp27 knockdown flies exhibited reversal of the above end points. The study provides evidence for the attenuation of cellular and functional decline in aged Drosophila after prolonged DCA exposure and the effect of hsp27 modulation which further incites studies towards the therapeutic application of DCA.

Aqueous date fruit extract protects against lipid peroxidation and improves antioxidant status in the liver of rats subchronically exposed to trichloroacetic acid

Trichloroacetic acid (TCA) is a prominent by-product of the chlorination of drinking water. It induces cell damage by producing free radicals and reactive oxygen species. The present study was carried out to evaluate the potential hepatoprotective role of the aqueous date extract (ADE) against TCA-induced liver injury. Forty-eight male Wistar rats were randomly divided into six groups of eight: group I served as the control; group II was given ADE by gavage; groups III and IV received TCA as drinking water at 0.5 and 2 g/L, respectively; and groups V and VI were treated with ADE by gavage and then received TCA at 0.5 and 2 g/L, respectively, as drinking water. The experiment was performed for 2 months. The hepatotoxicity of TCA administration was revealed by an increase in the levels of hepatic marker enzymes (transaminases, gamma-glutamyl transferase, and lactate dehydrogenase) and conjugated bilirubin and a decrease in albumin level. The TCA administration induced also significant elevation of the malondialdehyde (MDA) level and the antioxidant activity of superoxide dismutase (SOD) and glutathione peroxidase (GPx) paralleled with a significant decline in catalase (CAT) activity. These biochemical alterations were accompanied by histological changes marked by the appearance of vacuolization, necrosis, congestion, inflammation, and enlargement of sinusoids in the liver section. Treatment with date palm fruit extract restored the liver damage induced by TCA, as demonstrated by inhibition of hepatic lipid peroxidation; amelioration of SOD, GPx, and CAT activities; and improvement of histopathology changes. These results suggest that ADE has a protective effect over TCA-induced oxidative damage in rat liver.

The induction of tumor necrosis factor-alpha, superoxide anion, myeloperoxidase, and superoxide dismutase in the peritoneal lavage cells of mice after prolonged exposure to dichloroacetate and trichloroacetate

The induction of phagocytic activation in response to prolonged treatment with different doses of dichloroacetate (DCA) and trichloroacetate (TCA) has been investigated in mice. Groups of B6C3F1 male mice were administered 7.7, 77, 154, and 410 mg of DCA or TCA/kg/day, postorally, for 4- and 13-weeks. Peritoneal lavage cells (PLCs) were isolated and assayed for the different biomarkers of phagocytic activation, including superoxide anion (SA), tumor necrosis factor-alpha (TNF-alpha), and myeloperoxidase (MPO). In addition, the role of superoxide dismutase (SOD) in the SA production was also assessed. DCA and TCA produced significant and dose-dependent increases in SA and TNF-alpha production and in MPO activity, but the increases in response to the high doses of the compounds (>77 mg/kg/day) in the 13-week treatment period were less significant than those produced in the 4-week treatment period. Also, dose-dependent increases in SOD activity were observed in both periods of treatments. In general, the results demonstrate significant induction of the biomarkers of phagocytic activation by doses of DCA and TCA that were previously shown to be noncarcinogenic, with significantly greater increases observed at the earlier period of exposure, as compared with later period. These findings may argue against the contribution of those mechanisms to the hepatotoxicity/hepatocarcinogenicity of the compounds and suggest them to be early adaptive/ protective mechanisms against their long-term effects.

Phosphorylation status of pyruvate dehydrogenase distinguishes metabolic phenotypes of cultured rat brain astrocytes and neurons

Glucose metabolism in nervous tissue has been proposed to occur in a compartmentalized manner with astrocytes contributing largely to glycolysis and neurons being the primary site of glucose oxidation. However, mammalian astrocytes and neurons both contain mitochondria, and it remains unclear why in culture neurons oxidize glucose, lactate, and pyruvate to a much larger extent than astrocytes. The objective of this study was to determine whether pyruvate metabolism is differentially regulated in cultured neurons versus astrocytes. Expression of all components of the pyruvate dehydrogenase complex (PDC), the rate-limiting step for pyruvate entry into the Krebs cycle, was determined in cultured astrocytes and neurons. In addition, regulation of PDC enzymatic activity in the two cell types via protein phosphorylation was examined. We show that all components of the PDC are expressed in both cell types in culture, but that PDC activity is kept strongly inhibited in astrocytes through phosphorylation of the pyruvate dehydrogenase alpha subunit (PDH alpha). In contrast, neuronal PDC operates close to maximal levels with much lower levels of phosphorylated PDH alpha. Dephosphorylation of astrocytic PDH alpha restores PDC activity and lowers lactate production. Our findings suggest that the glucose metabolism of astrocytes and neurons may be far more flexible than previously believed.

Water disinfection by-products and pre-labor rupture of membranes

The causes of term pre labor rupture of membranes (term PROM) remain poorly defined. The authors conducted a record-based prevalence study to explore a possible relation between disinfection by-products in drinking water and term PROM in an Australian community with spatially variable trihalomethane and nitrate levels. A multilevel statistical model was used to examine the relation between factors operating at the levels of the individual, district, and water distribution zone and the prevalence of PROM at term among 16,229 women in Perth, Western Australia (2002-2004). Adjusted odds ratios for term PROM increased with increasing tertiles of nitrate exposure (moderate exposure: odds ratio = 1.23, 95% confidence interval: 1.03, 1.52; high exposure: odds ratio = 1.47, 95% confidence interval: 1.20, 1.79), but there was no significant relation with exposure to trihalomethanes. This study raises the possibility that water contaminants may promote the development of PROM at term.

Pyruvate dehydrogenase complex activity controls metabolic and malignant phenotype in cancer cells

High lactate generation and low glucose oxidation, despite normal oxygen conditions, are commonly seen in cancer cells and tumors. Historically known as the Warburg effect, this altered metabolic phenotype has long been correlated with malignant progression and poor clinical outcome. However, the mechanistic relationship between altered glucose metabolism and malignancy remains poorly understood. Here we show that inhibition of pyruvate dehydrogenase complex (PDC) activity contributes to the Warburg metabolic and malignant phenotype in human head and neck squamous cell carcinoma. PDC inhibition occurs via enhanced expression of pyruvate dehydrogenase kinase-1 (PDK-1), which results in inhibitory phosphorylation of the pyruvate dehydrogenase alpha (PDHalpha) subunit. We also demonstrate that PDC inhibition in cancer cells is associated with normoxic stabilization of the malignancy-promoting transcription factor hypoxia-inducible factor-1alpha (HIF-1alpha) by glycolytic metabolites. Knockdown of PDK-1 via short hairpin RNA lowers PDHalpha phosphorylation, restores PDC activity, reverts the Warburg metabolic phenotype, decreases normoxic HIF-1alpha expression, lowers hypoxic cell survival, decreases invasiveness, and inhibits tumor growth. PDK-1 is an HIF-1-regulated gene, and these data suggest that the buildup of glycolytic metabolites, resulting from high PDK-1 expression, may in turn promote HIF-1 activation, thus sustaining a feed-forward loop for malignant progression. In addition to providing anabolic support for cancer cells, altered fuel metabolism thus supports a malignant phenotype. Correction of metabolic abnormalities offers unique opportunities for cancer treatment and may potentially synergize with other cancer therapies.

Dichloroacetate induces apoptosis in endometrial cancer cells

PURPOSE

A recent landmark study demonstrated that Dichloroacetate (DCA) treatment promoted apoptosis in lung, breast, and glioblastoma cancer cell lines by shifting metabolism from aerobic glycolysis to glucose oxidation coupled with NFAT-Kv1.5 axis remodeling. The objective of this study was to determine whether DCA induces apoptosis in endometrial cancer cells and to assess apoptotic mechanism.

METHODS

A panel of endometrial cancer cell lines with varying degrees of differentiation was treated with DCA and analyzed for apoptosis via flow cytometry. Biological correlates such as gene expression, intracellular Ca(2+), and mitochondrial membrane potential were examined to assess apoptotic mechanism.

RESULTS

Initiation of apoptosis was observed in five low to moderately invasive cancer cell lines including Ishikawa, RL95-2, KLE, AN3CA, and SKUT1B while treatment had no effect on non-cancerous 293T cells. Two highly invasive endometrial adenocarcinoma cell lines, HEC1A and HEC1B, were found to be resistant to DCA-induced apoptosis. Apoptotic responding cell lines had a significant increase in early and late apoptotis, a decrease in mitochondrial membrane potential, and decreased Survivin transcript abundance, which are consistent with a mitochondrial-regulated mechanism. DCA treatment decreased intracellular calcium levels in most apoptotic responding cell lines which suggests a contribution from the NFAT-Kv1.5-mediated pathway. DCA treatment increased p53 upregulated modulator of apoptosis (PUMA) transcripts in cell lines with an apoptotic response, suggesting involvement of a p53-PUMA-mediated mechanism.

CONCLUSIONS

Dichloroacetate effectively sensitizes most endometrial cancer cell lines to apoptosis via mitochondrial, NFAT-Kv1.5, and PUMA-mediated mechanisms. Further investigation of the cancer therapeutic potential of DCA is warranted.