Mitochondrial bioenergetics as affected by DDT

Impact of Environmental Risk Factors on Mitochondrial Dysfunction, Neuroinflammation, Protein Misfolding, and Oxidative Stress in the Etiopathogenesis of Parkinson's Disease

As a prevalent progressive neurodegenerative disorder, Parkinson's disease (PD) is characterized by the neuropathological hallmark of the loss of nigrostriatal dopaminergic (DAergic) innervation and the appearance of Lewy bodies with aggregated α-synuclein. Although several familial forms of PD have been reported to be associated with several gene variants, most cases in nature are sporadic, triggered by a complex interplay of genetic and environmental risk factors. Numerous epidemiological studies during the past two decades have shown positive associations between PD and several environmental factors, including exposure to neurotoxic pesticides/herbicides and heavy metals as well as traumatic brain injury. Other environmental factors that have been implicated as potential risk factors for PD include industrial chemicals, wood pulp mills, farming, well-water consumption, and rural residence. In this review, we summarize the environmental toxicology of PD with the focus on the elaboration of chemical toxicity and the underlying pathogenic mechanisms associated with exposure to several neurotoxic chemicals, specifically 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), rotenone, paraquat (PQ), dichloro-diphenyl-trichloroethane (DDT), dieldrin, manganese (Mn), and vanadium (V). Our overview of the current findings from cellular, animal, and human studies of PD provides information for possible intervention strategies aimed at halting the initiation and exacerbation of environmentally linked PD.

Cross-species metabolomic analysis of tau- and DDT-related toxicity

Exposure to the pesticide dichlorodiphenyltrichloroethane (DDT) has been associated with increased risk of Alzheimer's disease (AD), a disease also associated with hyperphosphorylated tau (p-tau) protein aggregation. We investigated whether exposure to DDT can exacerbate tau protein toxicity in Caenorhabditiselegans using a transgenic strain that expresses human tau protein prone to aggregation by measuring changes in size, swim behavior, respiration, lifespan, learning, and metabolism. In addition, we examined the association between cerebrospinal fluid (CSF) p-tau protein-as a marker of postmortem tau burden-and global metabolism in both a human population study and in C. elegans, using the same p-tau transgenic strain. From the human population study, plasma and CSF-derived metabolic features associated with p-tau levels were related to drug, amino acid, fatty acid, and mitochondrial metabolism pathways. A total of five metabolites overlapped between plasma and C. elegans, and four between CSF and C. elegans. DDT exacerbated the inhibitory effect of p-tau protein on growth and basal respiration. In the presence of p-tau protein, DDT induced more curling and was associated with reduced levels of amino acids but increased levels of uric acid and adenosylselenohomocysteine. Our findings in C. elegans indicate that DDT exposure and p-tau aggregation both inhibit mitochondrial function and DDT exposure can exacerbate the mitochondrial inhibitory effects of p-tau aggregation. Further, biological pathways associated with exposure to DDT and p-tau protein appear to be conserved between species.

1,1,1-trichloro-2,2-bis (p-chlorophenyl)-ethane (DDT) and 1,1-Dichloro-2,2-bis (p, p'-chlorophenyl) ethylene (DDE) as endocrine disruptors in human and wildlife: A possible implication of mitochondria

1,1,1-trichloro-2,2-bis (p-chlorophenyl)-ethane (DDT) and its main metabolite 1,1-Dichloro-2,2-bis (p, p'-chlorophenyl) ethylene (DDE) act as endocrine disruptors in humans and wildlife. Immunomodulatory functions have also been attributed to both xenobiotics. DDT was banned in the 1970s due to its toxicity, but it is still produced and used for indoor residual spraying with disease vector control purposes. Due to their persistence and lipophilic properties, DDT and DDE can bioaccumulate through the food chain, being stored in organisms' adipose depots. Their endocrine disruptor function is mediated by agonist or antagonist interaction with nuclear receptors. Present review aimed to provide an overview of how DDT and DDE exposure impacts reproductive and immune systems with estrogen-disrupting action in humans and wildlife. Studies showing DDT and DDE impact on mitochondrial function and apoptosis pathway will also be reviewed, suggesting the hypothesis of direct action on mitochondrial steroid receptors.

Exposure to marine benthic dinoflagellate toxins may lead to mitochondrial dysfunction

Even though marine dinoflagellates are important primary producers, many toxic species may alter the natural equilibrium of aquatic ecosystems and even generate human intoxication incidents, as they are the major causative agents of harmful algal blooms. In order to deepen the knowledge regarding benthic dinoflagellate adverse effects, the present study aims to clarify the influence of Gambierdiscus excentricus strain UNR-08, Ostreopsis cf. ovata strain UNR-03 and Prorocentrum lima strain UNR-01 crude extracts on rat mitochondrial energetic function and permeability transition pore (mPTP) induction. Our results, expressed in number of dinoflagellate cell toxic compounds tested in a milligram of mitochondrial protein, revealed that 934 cells mg prot-1 of G. excentricus, and 7143 cells mg prot-1 of both O. cf. ovata and P. lima negatively affect mitochondrial function, including by decreasing ATP synthesis-related membrane potential variations. Moreover, considerably much lower concentrations of dinoflagellate extracts (117 cells mg prot-1 of G. excentricus, 1429 cells mg prot-1 of O. cf. ovata and 714 cells mg prot-1 of P. lima) produced mPTP-induced swelling in Ca2+-loaded isolated mitochondria. The present study clearly demonstrates the toxicity of G. excentricus, O. cf. ovata and P. lima extracts at the mitochondrial level, which may lead to mitochondrial failure and consequent cell toxicity, and that G. excentricus always provide much more severe effects than O. cf. ovata and P. lima.

Organochlorine pesticide levels in Greek patients with Parkinson's disease

Background

Parkinson’s disease (PD) is a neurodegenerative disease, mostly presenting with characteristic motor symptoms. Organochlorines (OC) are a class of widely-used pesticides that have been included among the list of environmental factors incriminated in PD pathogenesis. However, most studies reporting this association are based on questionnaires, and few have reported exposure data.

Aim

To examine the relationship between OC blood concentrations and PD risk.

Methods

In the present study, we studied the concentrations of 8 OC compounds (hexachlorobenzene, heptachlor, hepachlor epoxide, c-chlordane, a-chlordane, p,p’-DDE, DDD, DDT) in 104 Greek PD patients and 110 healthy controls.

Results

All substances studied were present in at least one sample. The most frequently detected (above the level of quantification) pesticides were p,p’-DDE (n = 214, 100 % of both groups) and hexachlorobenzene, HCB (n = 189, cases 46.5 %, controls 53.5 %). Higher levels of DDE were detected among PD patients in comparison to controls by using logistic regression analysis to control for confounders [Odds Ratio, OR (95 % confidence interval, C.I.)]: 2.592,(1.29–5.21)], whilst lower levels of HCB were detect among PD patients [OR,95 %CI:0.176(0.09−0.35)].

Conclusions

Our data suggest that exposure to specific OCs is related to the risk of PD. Further studies, using real exposure data, are needed in order to confirm and extend these findings.

DDT exposure induces cell cycle arrest and apoptosis of skin fibroblasts from Indo-Pacific humpback dolphin via mitochondria dysfunction

Although the global use of the 1,1,1-trichloro-2,2-bis (4-chlorophenyl) ethane (p,p'-DDT) has been prohibited, its persistence in the environment has caused long-lasting exposure on marine mammals. Our previous studies revealed exceedingly high residue levels of DDTs in Indo-Pacific humpback dolphins (Sousa chinensis) from the Pearl River Estuary region, China. However, the molecular mechanisms of p,p'-DDT toxicity on the dolphin are largely unknown. This study conducted the first cytotoxicity effect exploration of p,p'-DDT on the dolphin skin fibroblasts (ScSFs) to enhance the understanding of the cellular and molecular regulation impacts. ScSF cells were exposed to p,p'-DDT (28∼168 μM) for 24, 48 and 72 h. The exposure remarkably decreased viability of ScSF cells, possibly due to the synergetic effects of cell cycle arrest and apoptosis via DNA damage and mitochondria dysfunction. The DNA damage and mitochondria dysfunction were likely triggered by an increase of cellular reactive oxygen species (ROS), alteration in mitochondrial membrane potential, reduction in the cellular ATP levels, decreased expression of the genes CDK1, CDK4, cyclin B1, cyclin D1 and apoptosis regulator Bcl-2, release of cytochrome c, and activation of caspase-3, caspase-8 and caspase-9. Moreover, caspase inhibitor displayed protective activity against p,p'-DDT-induced apoptosis, indicating that caspases played a central role in p,p'-DDT-triggered apoptosis in the ScSF cells. We hypothesize apoptosis likely plays a minor role in cytocidal effects induced by p,p'-DDT exposure, but the mechanisms remain unclear. Overall, this research provides new evidence of the cytotoxic mechanisms underlying p,p'-DDT exposure on humpback dolphin skin cells, and suggests that p,p'-DDT contamination is one of key health concern issues for the protection of this marine mammal.

Oxidative Phosphorylation Impairment by DDT and DDE

There is increasing evidence supporting the characterization of the pesticide DDT and its metabolite, DDE, as obesogens and metabolic disruptors. Elucidating the mechanism is critical to understanding whether the association of DDT and DDE with obesity and diabetes is in fact causal. One area of research investigating the etiology of metabolic diseases is mitochondrial toxicity. Several studies have found associations between mitochondrial defects and insulin resistance, cellular respiration, substrate utilization, and energy expenditure. Although the mitotoxicity of DDT and DDE was established 20-40 years ago, it was not viewed in the light of the diseases faced today; therefore, it is prudent to reexamine the mitotoxicity literature for mechanistic support of DDT and DDE as causal contributors to obesity and diabetes, as well as associated diseases, such as cancer and Alzheimer's disease. This review aims to focus on studies investigating the effect of DDT or DDE on mammalian mitochondrial oxidative phosphorylation. We illustrate that both DDT and DDE impair the electron transport chain (ETC) and oxidative phosphorylation. We conclude that there is reasonable data to suggest that DDT and DDE target specific complexes and processes within the mitochondria, and that these insults could in turn contribute to the role of DDT and DDE in mitochondria-associated diseases.

Mitochondria as target of endocrine-disrupting chemicals: implications for type 2 diabetes

Type 2 diabetes is a chronic, heterogeneous syndrome characterized by insulin resistance and pancreatic β-cell dysfunction or death. Among several environmental factors contributing to type 2 diabetes development, endocrine-disrupting chemicals (EDCs) have been receiving special attention. These chemicals include a wide variety of pollutants, from components of plastic to pesticides, with the ability to modulate endocrine system function. EDCs can affect multiple cellular processes, including some related to energy production and utilization, leading to alterations in energy homeostasis. Mitochondria are primarily implicated in cellular energy conversion, although they also participate in other processes, such as hormone secretion and apoptosis. In fact, mitochondrial dysfunction due to reduced oxidative capacity, impaired lipid oxidation and increased oxidative stress has been linked to insulin resistance and type 2 diabetes. Herein, we review the main mechanisms whereby metabolism-disrupting chemical (MDC), a subclass of EDCs that disturbs energy homeostasis, cause mitochondrial dysfunction, thus contributing to the establishment of insulin resistance and type 2 diabetes. We conclude that MDC-induced mitochondrial dysfunction, which is mainly characterized by perturbations in mitochondrial bioenergetics, biogenesis and dynamics, excessive reactive oxygen species production and activation of the mitochondrial pathway of apoptosis, seems to be a relevant mechanism linking MDCs to type 2 diabetes development.

Variation in Mitochondria-Derived Transcript Levels Associated With DDT Resistance in the 91-R Strain of Drosophila melanogaster (Diptera: Drosophilidae)

The organochloride insecticide dichlorodiphenyltrichloroethane (DDT) and its metabolites can increase cellular levels of reactive oxygen species (ROS), cause mitochondrial dysfunction, and induce apoptosis. The highly DDT-resistant Drosophila melanogaster Meigen 1830 (Drosophila) strain, 91-R, and its susceptible control, 91-C, were used to investigate functional and structural changes among mitochondrial-derived pathways. Resequencing of mitochondrial genomes (mitogenomes) detected no structural differences between 91-R and 91-C, whereas RNA-seq suggested the differential expression of 221 mitochondrial-associated genes. Reverse transcriptase-quantitative PCR validation of 33 candidates confirmed that transcripts for six genes (Cyp12d1-p, Cyp12a4, cyt-c-d, COX5BL, COX7AL, CG17140) were significantly upregulated and two genes (Dif, Rel) were significantly downregulated in 91-R. Among the upregulated genes, four genes are duplicated within the reference genome (cyt-c-d, CG17140, COX5BL, and COX7AL). The predicted functions of the differentially expressed genes, or known functions of closely related genes, suggest that 91-R utilizes existing ROS regulation pathways of the mitochondria to combat increased ROS levels from exposure to DDT. This study represents, to our knowledge, the initial investigation of mitochondrial genome sequence variants and functional adaptations in responses to intense DDT selection and provides insights into potential adaptations of ROS management associated with DDT selection in Drosophila.

The biological foundation of the genetic association of TOMM40 with late-onset Alzheimer's disease

A variable-length poly-T variant in intron 6 of the TOMM40 gene, rs10524523, is associated with risk and age-of-onset of sporadic (late-onset) Alzheimer's disease. In Caucasians, the three predominant alleles at this locus are Short (S), Long (L) or Very long (VL). On an APOE ε3/3 background, the S/VL and VL/VL genotypes are more protective than S/S. The '523 poly-T has regulatory properties, in that the VL poly-T results in higher expression than the S poly-T in luciferase expression systems. The aim of the current work was to identify effects on cellular bioenergetics of increased TOM40 protein expression. MitoTracker Green fluorescence and autophagic vesicle staining was the same in control and over-expressing cells, but TOM40 over-expression was associated with increased expression of TOM20, a preprotein receptor of the TOM complex, the mitochondrial chaperone HSPA9, and PDHE1a, and increased activities of the oxidative phosphorylation complexes I and IV and of the TCA member α-ketoglutaric acid dehydrogenase. Consistent with the complex I findings, respiration was more sensitive to inhibition by rotenone in control cells than in the TOM40 over-expressing cells. In the absence of inhibitors, total cellular ATP, the mitochondrial membrane potential, and respiration were elevated in the over-expressing cells. Spare respiratory capacity was greater in the TOM40 over-expressing cells than in the controls. TOM40 over-expression blocked Ab-elicited decreases in the mitochondrial membrane potential, cellular ATP levels, and cellular viability in the control cells. These data suggest elevated expression of TOM40 may be protective of mitochondrial function.

Relevance of the bioavailable fraction of DDT and its metabolites in freshwater sediment toxicity: New insight into the mode of action of these chemicals on Dictyostelium discoideum

In this work, the toxicity of lake sediments contaminated with DDT and its metabolites DDD and DDE (collectively, DDX) was evaluated with widely used toxicity tests (i.e., Vibrio fischeri, Daphnia magna, Pseudokirchneriella subcapitata, and Lumbriculus variegatus) and with the social amoeba Dictyostelium discoideum, a model organism that is also suitable for studying pollutant-induced alterations at the molecular and cellular levels. Although the DDX concentration in the sediments was high (732.5 ppb), the results suggested a minimal environmental risk; in fact, no evidence of harmful effects was found using the different bioassays or when we considered the results of more sensitive sublethal biomarkers in D. discoideum amoebae. In line with the biological results, the chemical data showed that the concentration of DDX in the pore water (in general a highly bioavailable phase) showed a minimal value (0.0071ppb). To confirm the importance of the bioavailability of the toxic chemicals in determining their biological effects and to investigate the mechanisms of DDX toxicity, we exposed D. discoideum amoebae to 732.5ppb DDX in water solution. DDX had no effect on cell viability; however, a strong reduction in amoebae replication rate was observed, which depended mainly on a reduction in endocytosis rate and on lysosomal and mitochondrial alterations. In the presence of a moderate and transient increase in reactive oxygen species, the glutathione level in DDX-exposed amoebae drastically decreased. These results highlight that studies of the bioavailability of pollutants in environmental matrices and their biological effects are essential for site-specific ecological risk assessment. Moreover, glutathione depletion in DDX-exposed organisms is a new finding that could open the possibility of developing new pesticide mixtures that are more effective against DDT-resistant malaria vectors.

In vitro effect of N-acetylcysteine on hepatocyte injury caused by dichlorodiphenyltrichloroethane and its metabolites

The organochlorine pesticide, dichlorodiphenyltrichloroethane (DDT), is still used to combat the spread of malaria in several developing countries despite its accumulation and known hepatotoxic effects that have been demonstrated both in vitro and in vivo. N-Acetylcysteine (NAC) is a recognized hepatoprotective agent that has been reported to reduce hepatotoxicity initiated by many different compounds. The aim of this study was to determine whether NAC could counter in vitro hepatocyte injury induced by DDT or its two major metabolites, dichlorodiphenyldichloroethylene and dichlorodiphenyldichloroethane. HepG2 cell cultures were used to assess the following parameters of toxicity: cellular viability, intracellular levels of reactive oxygen species (ROS), mitochondrial membrane potential and initiation of apoptosis. None of the three test compounds induced ROS generation, yet exposure to any of the three compounds produced mitochondrial hyperpolarization, which was countered by NAC pretreatment. All three test compounds also induced apoptotic cell death, which was inhibited by NAC. Despite NAC counteracting some adverse intracellular changes due to organochlorine exposure, it appeared to aggravate the cytotoxic effects of the organochlorine compounds at low test concentrations. As the same outcome may also occur in vivo, results from the present study raise concern about the use of NAC as treatment for DDT-induced hepatotoxicity.

Metabolic alterations induced by sucrose intake and Alzheimer's disease promote similar brain mitochondrial abnormalities

Evidence shows that diabetes increases the risk of developing Alzheimer's disease (AD). Many efforts have been done to elucidate the mechanisms linking diabetes and AD. To demonstrate that mitochondria may represent a functional link between both pathologies, we compared the effects of AD and sucrose-induced metabolic alterations on mouse brain mitochondrial bioenergetics and oxidative status. For this purpose, brain mitochondria were isolated from wild-type (WT), triple transgenic AD (3xTg-AD), and WT mice fed 20% sucrose-sweetened water for 7 months. Polarography, spectrophotometry, fluorimetry, high-performance liquid chromatography, and electron microscopy were used to evaluate mitochondrial function, oxidative status, and ultrastructure. Western blotting was performed to determine the AD pathogenic protein levels. Sucrose intake caused metabolic alterations like those found in type 2 diabetes. Mitochondria from 3xTg-AD and sucrose-treated WT mice presented a similar impairment of the respiratory chain and phosphorylation system, decreased capacity to accumulate calcium, ultrastructural abnormalities, and oxidative imbalance. Interestingly, sucrose-treated WT mice presented a significant increase in amyloid β protein levels, a hallmark of AD. These results show that in mice, the metabolic alterations associated to diabetes contribute to the development of AD-like pathologic features.

The use of cellular diagnostics for identifying sub-lethal stress in reef corals

Coral reefs throughout the world are exhibiting documented declines in coral cover and species diversity, which have been linked to anthropogenic stressors including land-based sources of pollution. Reductions in coastal water and substratum quality are affecting coral survivorship, reproduction and recruitment, and hence, the persistence of coral reefs. One major obstacle in effectively addressing these declines is the lack of tools that can identify cause-and-effect relationships between stressors and specific coral reef losses, while a second problem is the inability to measure the efficacy of mitigation efforts in a timely fashion. We examined corals from six coral reefs on Guam, Mariana Islands, which were being affected by different environmental stressors (e.g. PAH's, pesticides, PCB's and sedimentation). Cellular diagnostic analysis differentiated the cellular-physiological condition of these corals. Examination of protein expression provided insight into their homeostatic responses to chemical and physical stressors in exposed corals prior to outright mortality, providing improved opportunities for developing locally-based management responses. This approach adds critically needed tools for addressing the effects of multiple stressors on corals and will allow researchers to move beyond present assessment and monitoring techniques that simply document the loss of coral abundance and diversity.

Can Drug Safety be Predicted and Animal Experiments Reduced by Using Isolated Mitochondrial Fractions?

Mitochondrial toxicity has resulted in the withdrawal of several drugs from the market. One particular example is nefazodone, an anti-depressant withdrawn in the USA due to hepatoxicity caused by drug-induced mitochondrial dysfunction. Drug development and safety testing can involve the use of large numbers of laboratory animals, which, without a decisive pre-screening for mitochondrial toxicity, are often unable to pre-empt higher mortality rates in some patient groups. The use of isolated mitochondria as a screening tool for drug safety can decrease the number of laboratory animals used in pre-clinical studies, thus improving animal welfare and healthcare outcomes and costs. Novel techniques involving high-throughput methods can be used to investigate whether a molecule is a mitochondrial toxicant. Moreover, these screens are mechanistically-based, since the effects of the drug on oxidative phosphorylation, calcium homeostasis and mitochondrial genetics can be assessed. This review is intended to demonstrate that isolated mitochondrial fractions are suitable for predicting drug and general chemical safety in toxicological screenings, thus contributing to the refinement and reduction of animal use in laboratory research.

Toxicity assessment of the herbicide metolachlor comparative effects on bacterial and mitochondrial model systems

Metolachlor is one of the most intensively used chloroacetamide herbicides. However, its effects on the environment and on non-target animals and humans as well as its interference at a cell/molecular level have not yet been fully elucidated. The aim of this study was: firstly, to evaluate the potential toxicity of metolachlor at a cell/subcellular level by using two in vitro biological model systems (a strain of Bacillus stearothermophilus and rat liver mitochondria); secondly, to evaluate the relative sensibility of these models to xenobiotics to reinforce their suitability for pollutant toxicity assessment. Our results show that metolachlor inhibits growth and impairs the respiratory activity of B.stearothermophilus at concentrations two to three orders of magnitude higher than those at which bacterial cells are affected by other pesticides. Also at concentrations significantly higher than those of other pesticides, metolachlor depressed the respiratory control ratio, membrane potential and respiration of rat liver mitochondria when malate/glutamate or succinate were used as respiratory substrates. Moreover, metolachlor impaired the respiratory activity of rat liver mitochondria in the same concentration range at which it inhibited bacterial respiratory system (0.4-5.0 micromol/mg of protein). In conclusion, the high concentration range at which metolachlor induces toxicity in vitro suggests that this compound is safer than other pesticides previously studied in our laboratory, using the same model systems. The good parallelism between metolachlor effects on both models and the toxicity data described in the literature, together with results obtained in our laboratory with other compounds, indicate the suitability of these systems to assess toxicity in vitro.

Modulation of tricarboxylic acid cycle dehydrogenases during hepatocarcinogenesis induced by hexachlorocyclohexane in mice

The sequential distribution of key tricarboxylic acid (TCA) cycle enzymes have been investigated during hexachlorocyclohexane (HCH)-induced hepatocarcinogenesis in Swiss mice. Animals were continuously exposed to HCH (500ppm) for 2, 4, and 6 months until liver tumor developed. The activity of TCA cycle enzymes such as isocitrate dehydrogenase (ICDH), succinate dehydrogenase (SDH), and malate dehydrogenase (MDH) have been studied. The activity of all the enzymes declined after 2 months of exposure of HCH in the liver. The neoplastic nodules and tumors developed after an exposure of HCH for 4 and 6 months, respectively. Neoplastic nodule and tumor showed wide variations in the activity and distribution of TCA cycle enzymes. The decreasing pattern in the activity of enzymes persisted in the non-neoplastic and non-tumor regions of the liver except SDH. However, the cells in nodular area and tumor showed intense enzymatic activities at cellular level. In the nodular region SDH activity declined prominently, whereas the non-nodular area showed positive reaction. Conspicuously, the tumor showed islands of positive and negative zones for TCA cycle dehydrogenases. The significance and relevance of such a distribution pattern still remains a mystery. The results are discussed in the light of HCH-induced toxicity on energy metabolism in exposed animals and possible role of such enzymes in the tumor formation.

Disruption of hepatic mitochondrial bioenergetics is not a primary mechanism for the toxicity of methoprene - relevance for toxicological assessment

Methoprene (isopropyl(2E,4E)-11-methoxy-3,7,11-trimethyl-2,4-dodecadienoate) is an insect growth regulator generally used to control insect populations by preventing insect maturation. So far, the effects of the insecticide on mitochondrial bioenergetics were not investigated. In the present work, liver mitochondria from Wistar rats were isolated and features of mitochondrial physiology were characterized in the presence of methoprene. High concentrations of methoprene, in the range of 40-100 nmol/mg of protein could decrease the transmembrane electric potential (Delta Psi) developed by mitochondria and, at the highest concentration, methoprene prevented complete Delta Psi repolarization after ADP addition. The effect was more evident using succinate than with ascorbate+TMPD as substrate. State 3 respiration was approximately 60% inhibited by 80 nmol of methoprene/mg of protein, while state 4 respiration, within the same range of methoprene concentrations, showed a slight increase, when both glutamate-malate and succinate were used as substrates. Additionally, FCCP-stimulated respiration was inhibited to an extent comparable to the effect on state 3, which suggests an interaction of methoprene with the respiratory chain, more evident with glutamate/malate as substrate. The activity of complex I (NADH-ubiquinone oxidorreductase) and that of the segment comprehending complexes II and III (succinate-cytochrome c reductase) were decreased in the presence of methoprene (approximately 60% and 85% of inhibition, respectively, with 300 nmol of methoprene/mg of protein), while the activities of cytochrome c oxidase and ATPase do not seem to be affected. Furthermore, the action of methoprene on the mitochondrial permeability transition was also studied, showing that the insecticide (in the range of 30-80 nmol mg(-1) of protein) decreases the susceptibility of liver mitochondria to the opening of the transition pore, even in non-energized mitochondria. These results lead to the conclusion that methoprene interference with hepatic mitochondrial function occurs only for high concentrations, which implies that the noxious effects of the insecticide reported for a number of non-target organisms are not fully attributable to mitochondrial effects. Therefore, it seems that mitochondrial activity does not represent the primary target for methoprene toxic action.

Metformin promotes isolated rat liver mitochondria impairment

Metformin, a drug widely used in the treatment of type 2 diabetes, has recently received attention due to the new and contrasting findings regarding its effects on mitochondrial function. In the present study, we evaluated the effect of metformin in isolated rat liver mitochondria status. We observed that metformin concentrations > or =8 mM induce an impairment of the respiratory chain characterized by a decrease in RCR and state 3 respiration. However, only metformin concentrations > or =10 mM affect the oxidative phosphorylation system by decreasing the mitochondrial transmembrane potential and increasing the repolarization lag phase. Moreover, our results show that metformin does not prevent H(2)O(2) production, neither protects against lipid peroxidation induced by the pro-oxidant pair ADP/Fe(2+). In addition, we observed that metformin exacerbates Ca(2+)-induced permeability transition pore opening by decreasing the capacity of mitochondria to accumulate Ca(2+ )and increasing the oxidation of thiol groups. Taken together, our results show that metformin can promote liver mitochondria injury predisposing to cell death.

Inhibition of mitochondrial bioenergetics by carbaryl is only evident for higher concentrations -- Relevance for carbaryl toxicity mechanisms

Although pesticides have been useful in agriculture pest control, there is a considerable risk for human health and damage to ecosystems. Carbaryl is a carbamate often taken as a safe insecticide, although data on metabolic activities is still scarce, viz. mitochondrial toxicity. Therefore, it is the goal of this work to assay the compound on isolated mitochondria, a biochemical model already used with other pesticides. Mitochondria isolated from the livers of Wistar rats were assayed for bioenergetic parameters, namely mitochondrial respiration, membrane potential, membrane integrity and enzyme activities. For higher concentrations, it was observed that carbaryl has a depressive effect on mitochondrial respiration and on the generation of mitochondrial membrane potential, but with preservation of membrane integrity. A locus between Complex II and III appears particularly affected and the mitochondrial phosphorylation system relatively insensitive. Therefore, carbaryl inhibits mitochondrial respiration without affecting the phosphorylation complex. Carbaryl is toxic for mitochondria, although at concentrations higher as compared with other insecticide compounds. Mitochondrial toxicity should be excluded as one of the primary causes for carbaryl immediate toxicity, as concluded from the range of concentrations where carbaryl shows effective mitochondrial toxicity.

Unaltered hepatic oxidative phosphorylation and mitochondrial permeability transition in wistar rats treated with nimesulide: Relevance for nimesulide toxicity characterization

Nonsteroidal anti-inflammatory drugs have been associated with hepatotoxicity in susceptible patients. One such example is nimesulide, a preferential cyclooxygenase 2-inhibitor, widely used for the treatment of inflammation and pain. It was suggested that nimesulide could exert its hepatotoxicity by altering hepatic mitochondrial function, which was demonstrated in vitro. The objective of this study was to verify whether liver mitochondria isolated from rats treated with doses of nimesulide well above therapeutic levels possessed decreased calcium tolerance and oxidative phosphorylation, which indicates in vivo nimesulide mitochondrial toxicity. Male and female rats received nimesulide or its vehicle twice daily, for 5 days, and were killed on the seventh day for the isolation of liver mitochondria. Mitochondrial respiration, transmembrane electric potential, and calcium tolerance were characterized in all experimental groups. Nimesulide had no effect on liver mitochondrial function. Indexes of mitochondrial integrity, calcium loading capacity, and oxidative phosphorylation efficiency were unchanged between liver mitochondria from treated and control animals. In the animals tested, no evidence of degraded mitochondrial function due to nimesulide administration could be found. The results corroborate the notion that despite recognized in vitro mitochondrial toxicity, nimesulide does not cause detectable mitochondrial dysfunction in Wistar rats, even when administered in much higher concentrations than those known to have anti-inflammatory effects.

Insulin protects against amyloid beta-peptide toxicity in brain mitochondria of diabetic rats

This study compared the status of brain mitochondria isolated from 12-week streptozotocin (STZ)-diabetic rats versus STZ-diabetic animals treated with insulin during a period of 4 weeks. Brain mitochondria isolated from 12-week citrate (vehicle)-treated rats were used as control. For that purpose, several mitochondrial parameters were evaluated: respiratory indexes (respiratory control ratio (RCR) and ADP/O ratio), transmembrane potential (DeltaPsim), repolarization lag phase, repolarization level, ATP, glutathione and coenzyme Q (CoQ) contents, production of H2O2, ATPase activity, and the capacity of mitochondria to accumulate Ca2+. Furthermore, the effect of Abeta1-40 was also analyzed. We observed that STZ-induced diabetes promoted a significant decrease in mitochondrial CoQ9, ATPase activity, and a lower capacity of mitochondria to accumulate Ca2+ when compared with control and insulin-treated diabetic rats. The presence of 4 microM Abeta1-40 induced a significant decrease in RCR in the three groups of rats. However, this peptide induced a significant increase in the repolarization lag phase and a significant decrease in the repolarization level in control and diabetic animals without insulin treatment. Furthermore, this peptide exacerbated significantly the production of H2O2 in STZ-diabetic rats, this effect being avoided by insulin treatment. Our data show that although diabetes induces some alterations in brain mitochondrial activity, those alterations do not interfere significantly with mitochondria functional efficiency. Similarly, insulin does not affect basal mitochondria function. However, in the presence of amyloid beta-peptide, insulin seems to prevent the decline in mitochondrial oxidative phosphorylation efficiency and avoids an increase in oxidative stress, improving or preserving the function of neurons under adverse conditions, such as Alzheimer's disease.

Inhibition Mechanisms of Mitochondrial Permeability Transition by 4-Hydroxytamoxifen: Protection of NAD(P)H and Thiol Group Oxidation

Abstract The effects of 4-hydroxytamoxifen (OHTAM) on the mitochondrial permeability transition (MPT) induced by Ca(2+) plus peroxynitrite (ONOO(-)) or phenylarsine oxide (PhAsO) were studied to clarify its mechanisms of MPT inhibition. Ca(2+) plus ONOO(-) induced mitochondrial swelling, membrane potential (Delta Psi) depolarization, and Ca(2+) release. OHTAM, when preincubated with mitochondria, prevents those events, and if added after their induction this drug promotes a time-dependent reversal of Delta Psi depolarization and Ca(2+) release associated with MPT induction, because these events are also inhibited by cyclosporine A (CyA). Preincubation with OHTAM also inhibits thiol group oxidation associated with the MPT promoted by ONOO(-) and allows the NAD(P)(+) to recover their reduced state faster and in a higher extension. The mitochondrial swelling and Ca(2+) release after MPT induction with Ca(2+) plus PhAsO are inhibited by OHTAM; similarly to CyA, the oxidation of NAD(P)H induced by this combination is also inhibited. According to these data, the MPT inhibition by OHTAM may be related to its antioxidant capacity and the binding to target protein components of the MPT, preventing the oxidation of NAD(P)H and thiol groups, an event that increases the sensitivity to MPT induction.

Protection of tamoxifen against oxidation of mitochondrial thiols and NAD(P)H underlying the permeability transition induced by prooxidants

The effects of tamoxifen (TAM) were studied on the mitochondrial permeability transition (MPT) induced by the prooxidant tert-butyl hydroperoxide (t-BuOOH) or the thiol cross-linker phenylarsine oxide (PhAsO), in the presence of Ca2+, in order to clarify the mechanisms involved in the MPT inhibition by this drug. The combination of Ca2+ with t-BuOOH or PhAsO induces mitochondrial swelling and depolarization of membrane potential (deltapsi). These events are inhibited by cyclosporine A (CyA), suggesting the inhibition of the MPT. The pre-incubation of mitochondria with TAM also prevents those events and induces a time-dependent reversal of deltapsi depolarization following MPT induction, similarly to CyA. Moreover, TAM inhibits the Ca2+ release and the oxidation of NAD(P)H and protein thiol (-SH) groups promoted by t-BuOOH plus Ca2+. On the other hand, the MPT induced by PhAsO plus Ca2+ does not induce -SH groups oxidation, supporting the notion that MPT induction by this compound is not mediated by the oxidation of specific membrane proteins groups. However, TAM also inhibits the PhAsO induced MPT, suggesting that this drug may inhibit this phenomenon by inhibiting PhAsO binding to -SH vicinal groups, implicated in the MPT induction. These data indicate that the MPT inhibition by TAM may be related to its antioxidant capacity in preventing the oxidation of NAD(P)H and -SH groups or by blocking these groups, since the oxidation of these groups increases the sensitivity of mitochondria to the MPT induction. Additionally, they suggest an MPT-independent pathway for TAM-induced apoptosis and a potential ER-independent mechanism for the effectiveness of this drug in the cancer therapy and prevention.

Comparison of the changes in adenine nucleotides of rat liver mitochondria induced by tamoxifen and 4-hydroxytamoxifen

The antiestrogen tamoxifen (TAM) inhibits the growth of different estrogen receptor (ER)-negative cells. Recently, multiple effects of TAM on mitochondrial bioenergetic functions have been pointed to explain its ER-independent cell death mechanisms. We have shown that TAM and its major active metabolite 4-hydroxytamoxifen (OHTAM) induce depolarization of the mitochondrial membrane potential (DeltaPsi) and uncouple the mitochondrial respiration, depressing the oxidative phosphorylation efficiency. To clarify the biochemical mechanisms underlying the changes in the regulation of ATP synthesis and yield, in this work we evaluated the alterations of mitochondrial adenine nucleotides induced by both drugs and ascertained whether such changes could reflect a specific inhibition of either the adenine nucleotide translocase (ANT) or the phosphate carrier, as well as the activation of ATP hydrolysis due to DeltaPsi depolarization. We found that both antiestrogens caused a concentration-dependent decrease in mitochondrial ATP levels. Mitochondrial ADP and AMP were concomitantly increased with a subsequent decrease in the ATP/ADP or ATP/AMP ratios. The total concentration of adenine nucleotides also changed. Additionally, both drugs decreased the ANT content of mitochondria, inhibited the phosphate carrier and induced ATP hydrolysis. However, the effects of TAM were more drastic than those induced by OHTAM. Therefore, the depletion of ATP might result from an activation of ATP catabolism, as well as from a decrease in the mitochondrial content of ANT and partial inhibition of the phosphate carrier. Our data may explain the ER-independent effects and cytotoxicity of both drugs and, in agreement with other previous studies, suggest that OHTAM is much less toxic to mitochondria than TAM.

Inhibition of bleomycin-induced cell death in rat alveolar macrophages and human lung epithelial cells by ambroxol

The mitochondrial permeability transition is recognized to be involved in toxic and oxidative forms of cell injury. In the present study, we investigated the effect of ambroxol against the cytotoxicity of bleomycin (BLM) by looking at the effect on the mitochondrial membrane permeability in alveolar macrophages and lung epithelial cells. Alveolar macrophages or lung epithelial cells exposed to BLM revealed the loss of cell viability and increase in caspase-3 activity. Ambroxol (10-100 microM) reduced the 75 mU/mL BLM-induced cell death and activation of caspase-3 in macrophages or epithelial cells. It reduced the condensation and fragmentation of nuclei caused by BLM in macrophages. Ambroxol alone did not significantly cause cell death. Treatment of alveolar macrophages with BLM resulted in the decrease in transmembrane potential in mitochondria, cytosolic accumulation of cytochrome c, increase in formation of reactive oxygen species (ROS) and depletion of GSH. Ambroxol (10-100 microM) inhibited the increase in mitochondrial membrane permeability, ROS formation and decrease in GSH contents due to BLM in macrophages. Ambroxol exerted a scavenging effect on hydroxyl radicals and nitric oxide and reduced the iron-mediated formation of malondialdehyde and carbonyls in liver mitochondria. It prevented cell death due to SIN-1 in lung epithelial cells. The results demonstrate that ambroxol attenuates the BLM-induced viability loss in alveolar macrophages or lung epithelial cells. This effect may be due to inhibition of mitochondrial damage and due to the scavenging action on free radicals.

Frozen mitochondria as rapid water quality bioassay

A rapid and relatively low cost bioassay, usable in routine screening water test has been developed modifying the beef heart mitochondria test. In our experiments, mitochondria (FM22) were frozen at -22 degrees C, instead of -80 degrees C (FM80), and their applicability and sensitivity was verified. The oxygen consumption was measured by a Clark electrode that was interfaced to a PC to collect test analysis data. Blank tests were carried out to verify the oxygen consumption linear fitting. Toxicity tests were performed using pure organic and inorganic compounds, such to verify the FM22 sensitivity. A piecewise regression, through an Excel Macro, identified the break-point in the oxygen consumption and calculated the toxicity. The IC50s of the tested compounds were calculated and ranged from 0.123 to 0.173 mg/l for heavy metals (Cd, Cr, Cu, Ni, Pb and Zn) and from 0.572 to 10.545 mg/l for organics (benzene, DMSO, DDE, endrin, dichloromethane, chlorobenzene, 1,2-dichlorobenzene and 1,3-dichlorobenzene). Water effluent samples were then tested. The FM22 gave different toxic reactions to them. Water samples were characterised for heavy metals. The FM22 bioassay had a higher sensitivity than the FM80 and a high reproducibility in the toxicity test with pure compounds. The FM22 test was a good predictor of toxicity for water samples; the bioassay is easy, low cost and rapid, then usable for routine tests.

Increased vulnerability of brain mitochondria in diabetic (Goto-Kakizaki) rats with aging and amyloid-beta exposure

This study evaluated the respiratory indexes (respiratory control ratio [RCR] and ADP/O ratio), mitochondrial transmembrane potential (DeltaPsim), repolarization lag phase, repolarization level, ATP/ADP ratio, and induction of the permeability transition pore of brain mitochondria isolated from normal Wistar and GK diabetic rats of different ages (1.5, 12, and 24 months of age). The effect of amyloid beta-peptides, 50 micromol/l Abeta(25-35) or 2 micromol/l Abeta(1-40), on mitochondrial function was also analyzed. Aging of diabetic mice induced a decrease in brain mitochondrial RCR, ADP/O, and ATP/ADP ratios but induced an increase in the repolarization lag phase. Brain mitochondria from older diabetic rats were more prone to the induction of the permeability transition pore, i.e., mitochondria from 24-month-old diabetic rats accumulated much less Ca(2+) (20 micromol/l) than those isolated from 12-month-old rats (50 micromol/l) or 1.5-month-old rats (100 micromol/l). In the presence of 50 micromol/l Abeta(25-35) or 2 micromol/l Abeta(1-40), age-related mitochondrial effects were potentiated. These results indicate that diabetes-related mitochondrial dysfunction is exacerbated by aging and/or by the presence of neurotoxic agents such as amyloid beta-peptides, supporting the idea that diabetes and aging are risk factors for the neurodegeneration induced by these peptides.

Occupational and environmental risk factors for Parkinson's disease

The etiology of Parkinson's disease (PD) remains obscure. Current research suggests that a variety of occupational and environmental risk factors may be linked to PD. This paper provides an overview of major occupational and environmental factors that have been associated with the development of PD and tries to assess current thinking about these factors and their possible mechanisms of operation. While clear links to rural living, dietary factors, exposure to metals, head injury, and exposure to infectious diseases during childhood have not been established, there is general agreement that smoking and exposure to pesticides affect the probability of developing PD.

Thiol protecting agents and antioxidants inhibit the mitochondrial permeability transition promoted by etoposide: implications in the prevention of etoposide-induced apoptosis

Etoposide (VP-16) is known to promote cell apoptosis either in cancer or in normal cells as a side effect. This fact is preceded by the induction of several mitochondrial events, including increase in Bax/Bcl-2 ratio followed by cytochrome c release and consequent activation of caspase-9 and -3, reduction of ATP levels, depolarization of membrane potential (DeltaPsi) and rupture of the outer membrane. These events are apoptotic factors essentially associated with the induction of the mitochondrial permeability transition (MPT). VP-16 has been shown to stimulate the Ca2+-dependent MPT induction similarly to prooxidants and to promote apoptosis by oxidative stress mechanisms, which is prevented by glutathione (GSH) and N-acetylcysteine (NAC). Therefore, the aim of this work was to study the effects of antioxidants and thiol protecting agents on MPT promoted by VP-16, attempting to identify the underlying mechanisms on VP-16-induced apoptosis. The increased sensitivity of isolated mitochondria to Ca2+-induced swelling, Ca2+ release, depolarization of DeltaPsi and uncoupling of respiration promoted by VP-16, which are prevented by cyclosporine A proving that VP-16 induces the MPT, are also efficiently prevented by ascorbate, the primary reductant of the phenoxyl radicals produced by VP-16. The thiol reagents GSH, dithiothreitol and N-ethylmaleimide, which have been reported to prevent the MPT induction, also protect this event promoted by VP-16. The inhibition of the VP-16-induced MPT by antioxidants agrees with the prevention of etoposide-induced apoptosis by GSH and NAC and suggests the generation of oxidant species as a potential mechanism underlying the MPT that may trigger the release of mitochondrial apoptogenic factors responsible for apoptotic cascade activation.

Iron-induced oxidant stress in nonparenchymal liver cells: mitochondrial derangement and fibrosis in acutely iron-dosed gerbils and its prevention by silybin

Hepatic fibrosis due to iron overload is mediated by oxidant stress. The basic mechanisms underlying this process in vivo are still little understood. Acutely iron-dosed gerbils were assayed for lobular accumulation of hepatic lipid peroxidation by-products, oxidant-stress gene response, mitochondrial energy-dependent functions, and fibrogenesis. Iron overload in nonparenchymal cells caused an activation of hepatic stellate cells and fibrogenesis. Oxidant-stress gene response and accumulation of malondialdehyde-protein adducts were restricted to iron-filled nonparenchymal cells, sparing nearby hepatocytes. Concomitantly, a significant rise in the mitochondrial desferrioxamine-chelatable iron pool associated with the impairment of mitochondrial oxidative metabolism and the hepatic ATP decrease, was detected. Ultrastructural mitochondrial alterations were observed only in nonparenchymal cells. All biochemical and functional derangements were hindered by in vivo silybin administration which blocked completely fibrogenesis. Iron-induced oxidant stress in nonparenchymal cells appeared to bring about irreversible mitochondrial derangement associated with the onset of hepatic fibrosis.

Mechanisms of the deleterious effects of tamoxifen on mitochondrial respiration rate and phosphorylation efficiency

Tamoxifen (TAM), the widely prescribed drug in the prevention and therapy of breast cancer, is a well-known modulator of estrogen receptor (ER) that also inhibits the proliferation of different cell types that lack the ER. However, the ER-independent action mechanisms of TAM and its side effects have not been yet clarified. Mitochondria are essential in supporting the energy-dependent regulation of cell functions. Changes in mitochondria result in bioenergetic deficits leading to the loss of vital functions to cell survival. Therefore, this study describes the effects of TAM on mitochondrial bioenergetics, contributing to a better understanding of the biochemical mechanisms underlying the multiple antiproliferative and toxic effects of this drug. TAM at concentrations above 20 nmol/mg protein, preincubated with isolated rat liver mitochondria at 25 degrees C for 3 min, significantly depresses, in a dose-dependent manner, the phosphorylation efficiency of mitochondria as inferred from the decrease in the respiratory control and ADP/O ratios, the perturbations in mitochondrial transmembrane potential (DeltaPsi), the fluctuations associated with mitochondrial energization, and the phosphorylative cycle induced by ADP. Furthermore, TAM at up to 40 nmol/mg protein stimulates the rate of state 4 respiration and at higher concentrations it strongly inhibits state 3 and uncouples the mitochondrial respiration. The stimulation of state 4 respiration parallels the decrease of DeltaPsi as a consequence of proton permeability. The TAM-stimulatory action of ATPase is also observed in intact mitochondria, suggesting that TAM promotes extensive permeability to protons due to destructive effects in the structural integrity of the mitochondrial inner membrane. These multiple effects of TAM on mitochondrial bioenergetic functions, causing changes in the respiration, phosphorylation efficiency, and membrane structure, may explain the cell death induced by this drug in different cell types, its anticancer activity in ER-negative cells, and its side effects.

Mitochondrial targets of drug toxicity

Mitochondria have long been recognized as the generators of energy for the cell. Like any other power source, however, mitochondria are highly vulnerable to inhibition or uncoupling of the energy harnessing process and run a high risk for catastrophic damage to the cell. The exquisite structural and functional characteristics of mitochondria provide a number of primary targets for xenobiotic-induced bioenergetic failure. They also provide opportunities for selective delivery of drugs to the mitochondrion. In light of the large number of natural, commercial, pharmaceutical, and environmental chemicals that manifest their toxicity by interfering with mitochondrial bioenergetics, it is important to understand the underlying mechanisms. The significance is further underscored by the recent identification of bioenergetic control points for cell replication and differentiation and the realization that mitochondria play a determinant role in cell signaling and apoptotic modes of cell death.

Iron-induced oxidant stress leads to irreversible mitochondrial dysfunctions and fibrosis in the liver of chronic iron-dosed gerbils. The effect of silybin

Hepatic iron toxicity because of iron overload seems to be mediated by lipid peroxidation of biological membranes and the associated organelle dysfunctions. However, the basic mechanisms underlying this process in vivo are still little understood. Gerbils were dosed with weekly injections of iron-dextran alone or in combination with sylibin, a well-known antioxidant, by gavage for 8 weeks. A strict correlation was found between lipid peroxidation and the level of desferrioxamine chelatable iron pool. A consequent derangement in the mitochondrial energy-transducing capability, resulting from a reduction in the respiratory chain enzyme activities, occurred. These irreversible oxidative anomalies brought about a dramatic drop in tissue ATP level. The mitochondrial oxidative derangement was associated with the development of fibrosis in the hepatic tissue. Silybin administration significantly reduced both functional anomalies and the fibrotic process by chelating desferrioxamine chelatable iron.

Perturbations induced by alpha- and beta-endosulfan in lipid membranes: a DSC and fluorescence polarization study

The interaction of alpha- and beta-endosulfan isomers with lipid bilayers was searched by differential scanning calorimetry (DSC) and fluorescence polarization of 2-, 6- and 12-(9-anthroyloxy) stearic acids (2-AS, 6-AS and 12-AS) and 16-(9-anthroyloxy) palmitic acid (16-AP). Both endosulfan isomers, at insecticide/lipid molar ratios ranging from 1/40 to 1/1, shift the phase transition midpoint to lower temperature values and broaden the transition profile of dipalmitoylphosphatidylcholine (DPPC) bilayers. At insecticide/lipid molar ratios of 1/40, the isomers fully abolish the bilayer pretransition. Conversely to beta-endosulfan, alpha-endosulfan promotes a new phase transition, centered at 35.4 degrees C, in addition to the main phase transition of DPPC. Therefore, the alpha-isomer may undergo a heterogeneous distribution in separate domains in the plane of the membrane, whereas the beta-isomer may undergo a homogeneous distribution. Fluorescence polarization data indicate that alpha-endosulfan increases the lipid structural order in the regions probed by 2-AS and decreases it in the regions probed by 6-AS, 12-AS and 16-AP. On the other hand, the beta-isomer produces disordering effects in the upper regions of the bilayers, probed by 2-AS, and ordering in deeper regions, probed by 6-AS, 12-AS and 16-AP, mainly in the gel phase. The incorporation of cholesterol into DPPC bilayers progressively decreases the effects of beta-isomer which are vanished at 20 mol% cholesterol. However, this and higher cholesterol concentrations did not prevent alpha-endosulfan membrane interaction, as revealed by DSC and fluorescence polarization. The distinct effects promoted by alpha- and beta-endosulfan are discussed in terms of molecular orientation and positioning within the bilayer. Apparently, the alpha-isomer preferentially locates closer to the phospholipid headgroups whereas the beta-isomer distributes in deeper domains of the bilayer.

Zidovudine-induced experimental myopathy: dual mechanism of mitochondrial damage

Myopathy often complicates Zidovudine (AZT) treatment in patients with acquired immunodeficiency syndrome (AIDS). The pathogenesis of the myopathy is controversial, since clinical phenomena intrinsic to AIDS may interfere per se with the onset of the myopathy. In the present work we investigated the in vivo effect of AZT in an animal model species (rat) not susceptible to HIV infection. Histochemical and electron microscopic analyses demonstrated that, under the experimental conditions used, the in vivo treatment with AZT does not cause in skeletal muscle true dystrophic lesions, but rather mitochondrial alterations confined to the fast fibers. In the same animal models, the biochemical analysis confirmed that mitochondria are the target of AZT toxicity in muscles. The effects of AZT on mitochondria energy transducing mechanisms were investigated in isolated mitochondria both in vivo and in vitro. Membrane potential abnormalities, due to a partial impairment of the respiratory chain capability observed in muscle mitochondria from AZT-treated rats, closely resemble those of control mitochondria in the presence of externally added AZT. mtDNA deletion analysis by PCR amplification and Southern blot analysis did not show any relevant deletion, while mtDNA depletion analysis demonstrated a significant decrease in mtDNA in AZT-treated rats. The present findings show that AZT causes damage to mitochondria by two mechanisms: a short-term mechanism that affects directly the respiratory chain, and a long-term mechanism that alters the mitochondrial DNA thus impairing the mitochondrial protein synthesis. In addition, the ultrastructural observations indicate that the fiber types are differently affected upon AZT treatment, which poses a number of questions as to the pathogenesis of this myopathy.

Pesticides and Parkinson's disease

Epidemiological studies and case reports provide evidence for an association between Parkinson's disease and past exposure to pesticides. Susceptibility to the effects of pesticides and other putative neurotoxins depends on variability in xenobiotic metabolism possibly generated by genetic polymorphisms, aging and variation in exposure to environmental agents including pesticides. The simplest mechanistic hypothesis for the association of pesticides with Parkinson's disease is that pesticides or their metabolites are directly toxic to mitochondria, although modulation of xenobiotic metabolism by pesticides provides an adjunct or alternative hypothesis.

Tamoxifen inhibits induction of the mitochondrial permeability transition by Ca2+ and inorganic phosphate

Tamoxifen (TAM) is a synthetic, nonsteroidal antiestrogenic agent that is widely prescribed in the treatment of estrogen-dependent neoplasias, including breast cancer. The mechanism of action has yet to be defined, but likely is independent of estrogen receptor binding. In light of its high lipophilicity and peroxyl radical scavenging activities, we hypothesized that TAM might be an effective inhibitor of the mitochondrial permeability transition (MPT), which is widely implicated in the mechanisms of chemical-induced tissue injury and apoptosis. The MPT was induced in vitro by incubating freshly isolated rat liver mitochondria in 1 mM Pi with increasing concentrations of calcium. Induction of the MPT was characterized by the calcium-dependent depolarization of mitochondrial membrane potential, release of matrix calcium, and large amplitude swelling. Membrane potential and calcium release were measured with ion-selective electrodes; mitochondrial swelling was monitored spectrophotometrically. Preincubation with either cyclosporine A or TAM prevented, in a dose-dependent manner, the calcium-induced MPT. TAM also inhibited the calcium-induced release of matrix glutathione. TAM caused a time-dependent reversal of both the calcium-induced membrane depolarization and calcium release, suggesting that the effect was on the permeability transition pore and not due to inhibition of the mitochondrial calcium uniport. The results suggest that TAM mimics cyclosporine A to inhibit induction of the MPT and that this activity is not related to the antioxidant properties of TAM.

The use of the mitochondrial transmembrane electric potential as an effective biosensor in ecotoxicological research

In this work, the mitochondrial transmembrane electric potential (delta psi) of isolated mitochondria was used to evaluate the toxicity of some chemicals (endosulfan, 3,4-dichloroaniline, parathion, tributyltin and cadmium) and wastewater. Mitochondria were isolated from rat liver, and the delta psi measured in a suitable assay medium, using a sensitive tetraphenylphosphonium (TPP+) electrode. The test substance was pre-incubated in a rotenone-containing medium during 3 min with 1.0 mg of mitochondrial protein. Mitochondria were energised with succinate and after the establishment of a constant maximal potential ADP was added to induce the phosphorylative cycle. Chosen endpoints were the membrane potential from mitochondria oxidising succinate and the depolarisation induced by ADP. After the appropriate transformations the EC50 (effective concentration) was calculated for each toxicant. Even very low concentrations of a toxicant were able to affect the delta psi, thus showing its suitability as a biosensor in ecotoxicology and results were reproducible between tests. The utilisation of delta psi in screening tests of pure substances and wastewater seems to be very effective and can be carried out routinely.

Comparative study of the toxic actions of 2,2-bis(p-chlorophenyl)-1,1,1-trichloroethane and 2,2-bis(p-chlorophenyl)-1,1-dichloroethylene on the growth and respiratory activity of a microorganism used as a model

A strain of Bacillus stearothermophilus was used as a model for a comparative study of the toxic effect of 2,2-bis(p-chlorophenyl)-1,1,1-trichloroethane and 2,2-bis(p-chlorophenyl)-1,1-dichloroethylene. Bacterial growth, the O2 consumption rate, and respiration-related enzymatic activities provided quantitative data in agreement with results reported for other systems. The use of this bacterium for screening for chemical toxicity is discussed.

Mercuric chloride toxicity in rat liver mitochondria and isolated hepatocytes

The effects of mercuric chloride on isolated rat liver mitochondria and freshly isolated rat hepatocytes were investigated. Mercuric chloride (in the μM range) depresses state 3 respiration, suggesting a strong effect at the level of the phosphorylation system. It also stimulates state 4 respiration and decreases mitochondrial membrane potential, suggesting an uncoupling action. In isolated hepatocytes, mercuric chloride causes a dose- and time-dependent cell death, accompanied by depletion of intracellular glutathione. Furthermore, mercuric chloride decreases intracellular ATP and ADP levels simultaneously with increasing AMP concentration, indicating fast hydrolysis of ATP without adequate rephosphorylation. From this study we can conclude that the bioenergetic lesion promoted by mercuric chloride seems to be sufficient to explain lethal hepatocyte injury.