3,5,3'-triiodothyronine induces mitochondrial permeability transition mediated by reactive oxygen species and membrane protein thiol oxidation

Is beta-carotene consumption associated with thyroid hormone levels?

The thyroid hormones play a pivotal role in various physiological processes, including growth, metabolism regulation, and reproduction. While non-modifiable factors are known to impact thyroid function, such as genetics and age, nutritional factors are also important. Diets rich in selenium and iodine are conventionally acknowledged to be beneficial for the production and release of thyroid hormones. Recent studies have suggested a potential link between beta-carotene, a precursor to vitamin A (retinol), and thyroid function. Beta-carotene is known for its antioxidant properties and has been shown to play a role in the prevention of various clinical conditions such as cancer and cardiovascular and neurological diseases. However, its impact on thyroid function is still unclear. Some studies have suggested a positive association between beta-carotene levels and thyroid function, while others have found no significant effect. Conversely, the hormone produced by the thyroid gland, thyroxine, enhances the conversion of beta-carotene to retinol. Furthermore, vitamin A derivatives are being explored as potential therapeutic options for thyroid malignancies. In this review, we highlight the mechanisms through which beta-carotene/retinol and thyroid hormones interact and review the findings of clinical studies examining the association between beta-carotene consumption and thyroid hormone levels. Our review underscores the need for further research to clarify the relationship between beta-carotene and thyroid function.

Bioenergetic Aspects of Mitochondrial Actions of Thyroid Hormones

Much is known, but there is also much more to discover, about the actions that thyroid hormones (TH) exert on metabolism. Indeed, despite the fact that thyroid hormones are recognized as one of the most important regulators of metabolic rate, much remains to be clarified on which mechanisms control/regulate these actions. Given their actions on energy metabolism and that mitochondria are the main cellular site where metabolic transformations take place, these organelles have been the subject of extensive investigations. In relatively recent times, new knowledge concerning both thyroid hormones (such as the mechanisms of action, the existence of metabolically active TH derivatives) and the mechanisms of energy transduction such as (among others) dynamics, respiratory chain organization in supercomplexes and cristes organization, have opened new pathways of investigation in the field of the control of energy metabolism and of the mechanisms of action of TH at cellular level. In this review, we highlight the knowledge and approaches about the complex relationship between TH, including some of their derivatives, and the mitochondrial respiratory chain.

Caenorhabditis elegans as a model for studies on quinolinic acid-induced NMDAR-dependent glutamatergic disorders

Quinolinic acid (QUIN) is an agonist of the neurotransmitter glutamate (Glu) capable of binding to N-methyl-D-aspartate receptors (NMDAR) increasing glutamatergic signaling. QUIN is known for being an endogenous neurotoxin, able to induce neurodegeneration. In Caenorhabditis elegans, the mechanism by which QUIN induces behavioral and metabolic toxicity has not been fully elucidated. The effects of QUIN on behavioral and metabolic parameters in nmr-1 and nmr-2 NMDA receptors in transgenic and wild-type (WT) worms were performed to decipher the pathway by which QUIN exerts its toxicity. QUIN increased locomotion parameters such as wavelength and movement amplitude medium, as well as speed and displacement, without modifying the number of body bends in an NMDAR-dependent-manner. QUIN increased the response time to the chemical stimulant 1-octanol, which is modulated by glutamatergic neurotransmission in the ASH neuron. Brood size increased after exposure to QUIN, dependent upon nmr-2/NMDA-receptor, with no change in lifespan. Oxygen consumption, mitochondrial membrane potential, and the flow of coupled and unbound electrons to ATP production were reduced by QUIN in wild-type animals, but did not alter citrate synthase activity, altering the functionality but the mitochondrial viability. Notably, QUIN modified fine locomotor and chemosensory behavioral parameters, as well as metabolic parameters, analogous to previously reported effects in mammals. Our results indicate that QUIN can be used as a neurotoxin to elicit glutamatergic dysfunction in C. elegans in a way analogous to other animal models.

Neuroprotective Effects of Guanosine in Ischemic Stroke-Small Steps towards Effective Therapy

Guanosine (Guo) is a nucleotide metabolite that acts as a potent neuromodulator with neurotrophic and regenerative properties in neurological disorders. Under brain ischemia or trauma, Guo is released to the extracellular milieu and its concentration substantially raises. In vitro studies on brain tissue slices or cell lines subjected to ischemic conditions demonstrated that Guo counteracts destructive events that occur during ischemic conditions, e.g., glutaminergic excitotoxicity, reactive oxygen and nitrogen species production. Moreover, Guo mitigates neuroinflammation and regulates post-translational processing. Guo asserts its neuroprotective effects via interplay with adenosine receptors, potassium channels, and excitatory amino acid transporters. Subsequently, guanosine activates several prosurvival molecular pathways including PI3K/Akt (PI3K) and MEK/ERK. Due to systemic degradation, the half-life of exogenous Guo is relatively low, thus creating difficulty regarding adequate exogenous Guo distribution. Nevertheless, in vivo studies performed on ischemic stroke rodent models provide promising results presenting a sustained decrease in infarct volume, improved neurological outcome, decrease in proinflammatory events, and stimulation of neuroregeneration through the release of neurotrophic factors. In this comprehensive review, we discuss molecular signaling related to Guo protection against brain ischemia. We present recent advances, limitations, and prospects in exogenous guanosine therapy in the context of ischemic stroke.

Structural and Functional Features of Ca2+ Transport Systems in Liver Mitochondria of Rats with Experimental Hyperthyroidism

We analyzed structural and functional features of the main mitochondrial Ca2+-transporting systems, mitochondrial Ca2+ uniporter complex (MCUC) and Ca2+-dependent cyclosporin A-sensitive mitochondrial permeability transition pore (MPT pore), in rats with hyperthyroid state. It was found that, the rate of Ca2+ accumulation by rat liver mitochondria in this pathology increases by 1.3 times, which can be associated with higher level of the channel-forming subunit of the uniporter MCU and lower content of dominant-negative subunit of this complex MCUb. At the same time, the level of the regulatory subunit MICU1 remained unchanged. It was shown that calcium retention capacity of liver mitochondria in rats with experimental hyperthyroidism decreased by 2 times in comparison with the control, which attested to reduced resistance of liver mitochondria of hyperthyroid rats to induction of the MPT pore. The observed changes are consistent with the data on increased amount of cyclophilin D, a mitochondrial matrix peptidyl-prolyl isomerase that is known to modulate the MPT pore opening and expression of the Ppif gene that encodes mitochondrial cyclophilin D in rats with experimental hyperthyroidism.

Gradual cold acclimation induces cardioprotection without affecting β-adrenergic receptor-mediated adenylyl cyclase signaling

Novel strategies are needed that can stimulate endogenous signaling pathways to protect the heart from myocardial infarction. The present study tested the hypothesis that appropriate regimen of cold acclimation (CA) may provide a promising approach for improving myocardial resistance to ischemia/reperfusion (I/R) injury without negative side effects. We evaluated myocardial I/R injury, mitochondrial swelling, and β-adrenergic receptor (β-AR)-adenylyl cyclase-mediated signaling. Male Wistar rats were exposed to CA (8°C, 8 h/day for a week, followed by 4 wk at 8°C for 24 h/day), while the recovery group (CAR) was kept at 24°C for an additional 2 wk. The myocardial infarction induced by coronary occlusion for 20 min followed by 3-h reperfusion was reduced from 56% in controls to 30% and 23% after CA and CAR, respectively. In line, the rate of mitochondrial swelling at 200 μM Ca2+ was decreased in both groups. Acute administration of metoprolol decreased infarction in control group and did not affect the CA-elicited cardiprotection. Accordingly, neither β1-AR-Gsα-adenylyl cyclase signaling, stimulated with specific ligands, nor p-PKA/PKA ratios were affected after CA or CAR. Importantly, Western blot and immunofluorescence analyses revealed β2- and β3-AR protein enrichment in membranes in both experimental groups. We conclude that gradual cold acclimation results in a persisting increase of myocardial resistance to I/R injury without hypertension and hypertrophy. The cardioprotective phenotype is associated with unaltered adenylyl cyclase signaling and increased mitochondrial resistance to Ca2+-overload. The potential role of upregulated β2/β3-AR pathways remains to be elucidated.

NEW & NOTEWORTHY We present a new model of mild gradual cold acclimation increasing tolerance to myocardial ischemia/reperfusion injury without hypertension and hypertrophy. Cardioprotective phenotype is accompanied by unaltered adenylyl cyclase signaling and increased mitochondrial resistance to Ca2+-overload. The potential role of upregulated β2/β3-adrenoreceptor activation is considered. These findings may stimulate the development of novel preventive and therapeutic strategies against myocardial ischemia/reperfusion injury.

Vitamin E Supplementation and Mitochondria in Experimental and Functional Hyperthyroidism: A Mini-Review

Mitochondria are both the main sites of production and the main target of reactive oxygen species (ROS). This can lead to mitochondrial dysfunction with harmful consequences for the cells and the whole organism, resulting in metabolic and neurodegenerative disorders such as type 2 diabetes, obesity, dementia, and aging. To protect themselves from ROS, mitochondria are equipped with an efficient antioxidant system, which includes low-molecular-mass molecules and enzymes able to scavenge ROS or repair the oxidative damage. In the mitochondrial membranes, a major role is played by the lipid-soluble antioxidant vitamin E, which reacts with the peroxyl radicals faster than the molecules of polyunsaturated fatty acids, and in doing so, protects membranes from excessive oxidative damage. In the present review, we summarize the available data concerning the capacity of vitamin E supplementation to protect mitochondria from oxidative damage in hyperthyroidism, a condition that leads to increased mitochondrial ROS production and oxidative damage. Vitamin E supplementation to hyperthyroid animals limits the thyroid hormone-induced increases in mitochondrial ROS and oxidative damage. Moreover, it prevents the reduction of the high functionality components of the mitochondrial population induced by hyperthyroidism, thus preserving cell function.

Action of Reverse T3 on Cancer Cells

Background: Reverse T3 (rT3; 3,3',5'-triiodo-L-thyronine) is widely regarded as an inactive naturally occurring analog of thyroid hormone. rT3 is known to bind to the thyroid hormone analog receptor on plasma membrane integrin αvβ3. This integrin is generously expressed by tumor cells and is the initiation site for the stimulation by L-thyroxine (T4) at physiological free concentrations on cancer cell proliferation. Results: In the present studies, we show that rT3 caused increases of proliferation in vitro of 50% to 80% (P < 0.05-0.001) of human breast cancer and glioblastoma cells. Conclusion: rT3 may be a host factor supporting cancer growth.

Guanosine protects against Ca2+-induced mitochondrial dysfunction in rats

Mitochondria play an important role in cell life and in the regulation of cell death. In addition, mitochondrial dysfunction contributes to a wide range of neuropathologies. The nucleoside Guanosine (GUO) is an endogenous molecule, presenting antioxidant properties, possibly due to its direct scavenging ability and/or from its capacity to activate the antioxidant defense system. GUO demonstrate a neuroprotective effect due to the modulation of the glutamatergic system and maintenance of the redox system. Thus, considering the few studies focused on the direct effects of GUO on mitochondrial bioenergetics, we designed a study to evaluate the in vitro effects of GUO on rat mitochondrial function, as well as against Ca²⁺-induced impairment. Our results indicate that GUO prevented mitochondrial dysfunction induced by Ca²⁺ misbalance, once GUO was able to reduce mitochondrial swelling in the presence of Ca²⁺, as well as ROS production and hydrogen peroxide levels, and to increase manganese superoxide dismutase activity, oxidative phosphorylation and tricarboxylic acid cycle activities. Our study indicates for the first time that GUO could direct prevent the mitochondrial damage induced by Ca²⁺ and that these effects were not related to its scavenging properties. Our data indicates that GUO could be included as a new pharmacological strategy for diseases linked to mitochondrial dysfunction.

Selective replacement of mitochondrial DNA increases the cardioprotective effect of chronic continuous hypoxia in spontaneously hypertensive rats

Mitochondria play an essential role in improved cardiac ischaemic tolerance conferred by adaptation to chronic hypoxia. In the present study, we analysed the effects of continuous normobaric hypoxia (CNH) on mitochondrial functions, including the sensitivity of the mitochondrial permeability transition pore (MPTP) to opening, and infarct size (IS) in hearts of spontaneously hypertensive rats (SHR) and the conplastic SHR-mt^BN strain, characterized by the selective replacement of the mitochondrial genome of SHR with that of the more ischaemia-resistant brown Norway (BN) strain. Rats were adapted to CNH (10% O₂, 3 weeks) or kept at room air as normoxic controls. In the left ventricular mitochondria, respiration and cytochrome c oxidase (COX) activity were measured using an Oxygraph-2k and the sensitivity of MPTP opening was assessed spectrophotometrically as Ca²⁺-induced swelling. Myocardial infarction was analysed in anaesthetized open-chest rats subjected to 20 min of coronary artery occlusion and 3 h of reperfusion. The IS reached 68±3.0% and 65±5% of the area at risk in normoxic SHR and SHR-mt^BN strains, respectively. CNH significantly decreased myocardial infarction to 46±3% in SHR. In hypoxic SHR-mt^BN strain, IS reached 33±2% and was significantly smaller compared with hypoxic SHR. Mitochondria isolated from hypoxic hearts of both strains had increased detergent-stimulated COX activity and were less sensitive to MPTP opening. The maximum swelling rate was significantly lower in hypoxic SHR-mt^BN strain compared with hypoxic SHR, and positively correlated with myocardial infarction in all experimental groups. In conclusion, the mitochondrial genome of SHR modulates the IS-limiting effect of adaptation to CNH by affecting mitochondrial energetics and MPTP sensitivity to opening.

Tissue Specific Sensitivity of Mitochondrial Permeability Transition Pore to Ca2+ Ions

Ca2+-induced opening of the mitochondrial permeability transition pore (MPTP) is involved in induction of apoptotic and necrotic processes. We studied sensitivity of MPTP to calcium using the model of Ca2+-induced, cyclosporine A-sensitive mitochondrial swelling. Presented data indicate that the extent of mitochondrial swelling (dA520/4 min) induced by addition of 25 μM Ca2+ is seven-fold higher in liver than in heart mitochondria (0.564 ± 0.08/0.077± 0.01). The extent of swelling induced by 100 μM Ca2+ was in liver tree times higher than in heart mitochondria (0.508±0.05/ 0.173±0.02). Cyclosporine A sensitivity showed that opening of the MPTP is involved. We may thus conclude that especially at low Ca2+ concentration heart mitochondria are more resistant to damaging effect of Ca2+ than liver mitochondria. These finding thus support hypothesis that there exist tissue specific strategies of cell protection against induction of the apoptotic and necrotic processes.

Sex difference in the sensitivity of cardiac mitochondrial permeability transition pore to calcium load

Most of the experimental studies have revealed that female heart is more tolerant to ischemia/reperfusion (I/R) injury as compared with the male myocardium. It is widely accepted that mitochondrial dysfunction, and particularly mitochondrial permeability transition pore (MPTP) opening, plays a major role in determining the extent of cardiac I/R injury. The aim of the present study was, therefore, to analyze (i) whether calcium-induced swelling of cardiac mitochondria is sex-dependent and related to the degree of cardiac tolerance to I/R injury and (ii) whether changes in MPTP components-cyclophilin D (CypD) and ATP synthase-can be involved in this process. We have observed that in mitochondria isolated from rat male and female hearts the MPTP has different sensitivity to the calcium load. Female mitochondria are more resistant both in the extent and in the rate of the mitochondrial swelling at higher calcium concentration (200 µM). At low calcium concentration (50 µM) no differences were observed. Our data further suggest that sex-dependent specificity of the MPTP is not the result of different amounts of ATP synthase and CypD, or their respective ratio in mitochondria isolated from male and female hearts. Our results indicate that male and female rat hearts contain comparable content of MPTP and its regulatory protein CypD; parallel immunodetection revealed also the same contents of adenine nucleotide translocator or voltage-dependent anion channel. Increased resistance of female heart mitochondria thus cannot be explained by changes in putative components of MPTP, and rather reflects regulation of MPTP function.

In vitro and in vivo activation of mitochondrial membrane permeability transition pore using triiodothyronine

Using a novel method for evaluating mitochondrial swelling (Drahota et al. 2012a) we studied the effect of calcium (Ca(2+)), phosphate (P(i)), and triiodothyronine (T(3)) on the opening of mitochondrial membrane permeability transition pore and how they interact in the activation of swelling process. We found that 0.1 mM P(i), 50 microM Ca(2+) and 25 microM T(3) when added separately increase the swelling rate to about 10 % of maximal values when all three factors are applied simultaneously. Our findings document that under experimental conditions in which Ca(2+) and P(i) are used as activating factors, the addition of T(3) doubled the rate of swelling. T(3) has also an activating effect on mitochondrial membrane potential. The T(3) activating effect was also found after in vivo application of T(3). Our data thus demonstrate that T(3) has an important role in opening the mitochondrial membrane permeability pore and activates the function of the two key physiological swelling inducers, calcium and phosphate ions.

Developmental changes of the sensitivity of cardiac and liver mitochondrial permeability transition pore to calcium load and oxidative stress

Opening of the mitochondrial membrane permeability transition pore (MPTP) is an important factor in the activation of apoptotic and necrotic processes in mammalian cells. In a previous paper we have shown that cardiac mitochondria from neonatal rats are more resistant to calcium load than mitochondria from adult animals. In this study we have analyzed the ontogenetic development of this parameter both in heart and in liver mitochondria. We found that the high resistance of heart mitochondria decreases from day 14 to adulthood. On the other hand, we did not observe a similar age-dependent sensitivity in liver mitochondria, particularly in the neonatal period. Some significant but relatively smaller increase could be observed only after day 30. When compared with liver mitochondria cardiac mitochondria were more resistant also to the peroxide activating effect on calcium-induced mitochondrial swelling. These data thus indicate that the MPTP of heart mitochondria is better protected against damaging effects of the calcium load and oxidative stress. We can only speculate that the lower sensitivity to calcium-induced swelling may be related to the higher ischemic tolerance of the neonatal heart.

Evaluation of oxidative status in patients with hyperthyroidism

Data on the antioxidant levels enzyme in patients with hyperthyroidism are limited and conflicting. Therefore, the objective of this study was to evaluate the oxidative status using an automated method in patients with hyperthyroidism. Thirty-six subjects with hyperthyroidism and 30 healthy controls were enrolled in this study. Serum oxidative status was determined via measurement of total antioxidant capacity (TAC) and total oxidant status (TOS) and calculation of oxidative stress index (OSI). Serum TAC levels were significantly lower in patients with hyperthyroidism than controls (P=0.002), while serum TOS levels and OSI values were significantly higher (P=0.008, 0.004; respectively). Serum TAC levels were correlated with TSH levels (rho=0.223, P=0.032), FT3 levels (rho=-0.434, P=0.002) and FT4 levels (rho=-0.363, P=0.003) in patients. Further, TOS levels and OSI values were correlated with TSH levels (rho=-0.245, P=0.037; rho=-0.312, P=0.011, respectively), FT3 levels (rho=0.293, P=0.017, rho=0.505, P=0.002, respectively), and FT4 levels (rho=0.302, P=0.006, rho=0.321, P=0.008, respectively) in patients. Duration of disease was significantly correlated with OSI values in patients (rho=0.420, P=0.011), while no correlation with serum TAC levels and TOS levels (P>0.05). Oxidants are increased and antioxidants are decreased in patients with hyperthyroidism; as a result, the oxidative-antioxidative balance is shifted to the oxidative side. Increased oxidative stress may play a role in the pathogenesis of hyperthyroidism. It is believed that supplementation of antioxidant vitamins such as vitamins C and E may be helpful for these patients.

Oxidative stress induced by thyroid dysfunction in rat erythrocytes and heart

The aim of this study was to determine whether the effects of thyroid dysfunction induce oxidative stress in the blood and heart of male Wistar rats. Rats were randomly divided into three groups: group I served as control rats. Group II was treated daily with 0.05% benzythiouracile (BTU) administered in drinking water. Rats of group III have received l-thyroxine sodium salt (0.0012%), in drinking water. The results showed that thyroid dysfunction rats had poor growth performance. On the other hand, in hyperthyroid rats, a marked decrease compared with control occurred of some hematological parameters such red blood cell number (RBC), haemoglobin (Hb) concentration and haematocrit (Ht). There was also a significant increase in erythrocyte numbers and heart TBARS concentrations in hypothyroid rats compared with control. These results were associated with a fall in the total antioxidant status (TAS) in the serum of the hyperthyroid rats. Alteration of the antioxidant system in the hypo-/hyperthyroidism-induced rats was confirmed by the significant increase of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) activities and a decline in glutathione (GSH) content in both tissues were detected in hyperthyroid group compared to controls. On the other hand, serum transaminase activities (aspartate transaminase (AST); alanine transaminase (ALT)) were elevated indicating hepatic cellular damage after treatment with exogenous L-thyroxine. Moreover, serum lactate dehydrogenase (LDH), gamma-glutamyl transferase (GGT) and creatine phosphokinase (CPK) activities were increased in the hyperthyroidism rats. These results indicated that excessive thyroxin (long term) ingestion had an adverse effect on animal health and performance. We conclude that thyroid dysfunction induces oxidative stress and modifies some biochemical parameters of erythrocytes, heart and liver disease; our results show the occurrence of a state of oxidizing stress in relation to hyperthyroidism.

Influence of thyroid dysfunction on liver lipid peroxidation and antioxidant status in experimental rats

The purpose of this study was to evaluate the effects of dysthyroidism on lipid peroxidation, antioxidants status, liver, and serum dysfunction parameters in the hypo-/hyperthyroidism-induced rats. Hypothyroidism and hyperthyroidism conditions were induced for 5 weeks by administration of 0.05% benzythiouracile (BTU) and l-thyroxine sodium salt (0.0012%), in drinking water, respectively. The enzymatic activities of glutathione peroxidase (GPx), superoxide dismutase (SOD), catalase (CAT) and the lipid peroxidation product; thiobarbituric acid reacting substances (TBARS) were measured in liver as indicators of oxidative damage. However, liver dysfunction parameters represented by the activities of aspartate transaminase (AST), alanine transaminase (ALT), alkaline phosphatase (ALP), lactate dehydrogenase (LDH), and gamma glutamyl transferase (GGT), were measured in serum. In hyperthyroidism rats, the TBARS contents of liver have significantly increased compared to those in hypothyroid rats and the controls (p<0.001), associated with a fall of the total antioxidant status (TAS) in the serum of the hyperthyroid rats. The SOD, CAT, and GPx activities in liver of hyperthyroid rats have significantly increased compared to hypothyroid rats and the controls (p<0.001). The AST, ALT, LDH, GGT, and ALP activities increased in the hyperthyroidism rats (p<0.05). We conclude that thyroid dysfunction induces oxidative stress and modifies some biochemical parameters of liver. Our results show the occurrence of a state of oxidizing stress in relation to hyperthyroidism.

In hyperthyroid rats octylguanidine protects the heart from reperfusion damage

Hyperthyroidism sensitizes the heart for reperfusion injury. As known, mitochondrial permeability transition underlies reperfusion heart damage. This study was undertaken to explore the protective effect of octylguanidine (OG), an inhibitor of permeability transition, on hearts from hyperthyroid rats subjected to ischemia/reperfusion. Hyperthyroidism was induced by a daily injection of 2 mg T3/kg body weight for 5 days. OG was injected at a dose of 5 mg/kg body weight. It was found that the amine protects against reperfusion-induced permeability transition, i.e., mitochondria from hyperthyroid rats, treated with OG, retained accumulated Ca(2+), similarly to control mitochondria. OG maintained post reperfusion cardiac frequency in hyperthyroid rats at 429 +/- 16 in comparison to control and T3 treated rats (70 +/- 12 and 71 +/- 2, respectively). We also found that OG diminished the post reperfusion accumulation of IFNgamma from 34.3 +/- 2.5 to 18.7 +/- 1.35, IL-6 from 38.5 +/- 4.5 to 15.1 +/- 0.12, IL-1 from 16.78 +/- 0.73 to 12.19 +/- 1.54, and TNFalpha from 45.05 +/- 3.14 to 29.85 +/- 4.3 (pg/50 microg myocardial tissue). It is concluded that OG inhibits the hypersensitivity of the hyperthyroid myocardium to undergo reperfusion damage due to its inhibitory action on the permeability transition pore.

Mitochondrial dynamics in the regulation of neuronal cell death

Mitochondria undergo continuous fission and fusion events in physiological situations. Fragmentation of mitochondria during cell death has been shown to play a key role in cell death progression, including release of the mitochondrial apoptotic proteins. Ultrastructural changes in mitochondria, such as cristae remodeling, is also involved in cell death initiation. Here, we emphasize the important role of mitochondrial fission/fusion machinery in neuronal cell death. Unlike many other cell types such as immortalized cell lines, neurons are distinct morphologically and functionally. We will discuss how this uniqueness presents special challenges in the cellular response to neurotoxic stresses, and how this affects the mitochondrial dynamics in the regulation of cell death in neurons.

Liver damage during ischemia/reperfusion and glutathione: implications for potential organ donors

Free radicals play a central role in the development of liver ischemia/reperfusion (I/R) injury. Reduced glutathione (GSH) is the main hepatic free radical scavenger. Brain-dead patients exhibit abnormalities of endocrine status. Many clinicians administer thyroid hormones to improve the transplantation outcomes. We previously reported that thyroxine (T(4)) pretreatment decreased rat liver tissue GSH, which was associated with increased liver I/R-induced damage. In this study, we investigated whether the reduction in GSH by T(4) pretreatment affected cell viability during anoxia or oxidative stress in suspensions of isolated hepatocytes. Furthermore, we evaluated the levels of GSH in isolated livers from hypothyroid rats preserved at 0-1 degrees C and reperfused. Thyroid hormone modulation was obtained by T(4) or 6-propylthiouracil (PTU) treatment. Isolated hepatocytes from T(4)-pretreated rats that underwent anoxia and oxidative stress, which was induced by tert-butylhydroperoxide, displayed progressive, time-dependent loss of cell viability, which was greater than that in hepatocytes in non-T(4)-pretreated rats. A significant decrease in GSH levels was observed in isolated hepatocytes obtained from hyperthyroid rats compared with those from euthyroid rats. In contrast, administration of the antithyroid drug PTU increased liver concentrations of GSH at the end of reperfusion thereby improving liver function after cold storage. These results may yield new protective strategies in the management of brain-dead organ donors.

The impact of thyroid activity variations on some oxidizing-stress parameters in rats

The effect of the thyroid activity on the formation of lipid peroxidation and on liver and heart antioxidant enzyme activities was investigated in Wistar rats. Hypothyroidism and hyperthyroidism conditions were induced for five weeks by the administration of 0.05% benzythiouracile (BTU) and L-thyroxine sodium salt (0.0012%), in drinking water, respectively. No significant effect was observed on the rates of both lipid peroxidation and the vitamin E in hepatic and cardiac tissues of hypothyroidism rats compared to the controls, contrary to the hyperthyroidism rats, which expressed a pronounced increase. The increased glutathione peroxidase activity in rats suffering from hyperthyroidism was associated with a fall of the reduced glutathione in the homogenate and a marked increase in the glutathione reductase activity. An increase in superoxide dismutase and catalase activities was also recorded in hyperthyroidism. Our results explain the thyroid activity variation in relation to the lipid peroxidation and the tissular contents of the enzymatic and the non-enzymatic antioxidants. To conclude, our results show the occurrence of a state of oxidizing stress in relation to hyperthyroidism.

Mitochondria as therapeutic targets for cancer chemotherapy

Mitochondria are vital for cellular bioenergetics and play a central role in determining the point-of-no-return of the apoptotic process. As a consequence, mitochondria exert a dual function in carcinogenesis. Cancer-associated changes in cellular metabolism (the Warburg effect) influence mitochondrial function, and the invalidation of apoptosis is linked to an inhibition of mitochondrial outer membrane permeabilization (MOMP). On theoretical grounds, it is tempting to develop specific therapeutic interventions that target the mitochondrial Achilles' heel, rendering cancer cells metabolically unviable or subverting endogenous MOMP inhibitors. A variety of experimental therapeutic agents can directly target mitochondria, causing apoptosis induction. This applies to a heterogeneous collection of chemically unrelated compounds including positively charged alpha-helical peptides, agents designed to mimic the Bcl-2 homology domain 3 of Bcl-2-like proteins, ampholytic cations, metals and steroid-like compounds. Such MOMP inducers or facilitators can induce apoptosis by themselves (monotherapy) or facilitate apoptosis induction in combination therapies, bypassing chemoresistance against DNA-damaging agents. In addition, it is possible to design molecules that neutralize inhibitor of apoptosis proteins (IAPs) or heat shock protein 70 (HSP70). Such IAP or HSP70 inhibitors can mimic the action of mitochondrion-derived mediators (Smac/DIABLO, that is, second mitochondria-derived activator of caspases/direct inhibitor of apoptosis-binding protein with a low isoelectric point, in the case of IAPs; AIF, that is apoptosis-inducing factor, in the case of HSP70) and exert potent chemosensitizing effects.

Effect of experimental and cold exposure induced hyperthyroidism on H2O2 production and susceptibility to oxidative stress of rat liver mitochondria

To investigate the iodothyronine role in liver responses to cold, we examined metabolic and oxidative mitochondrial changes in cold-exposed, T3-treated, and T4-treated rats, which exhibit different T4 serum levels. All treatments increased mitochondrial respiration which reached the highest and lowest values after T3 and cold treatment, respectively. The T3- and T4-induced changes agreed with the respective increases in Complex IV activities, while those elicited by cold were inconsistent with increased activities of respiratory complexes. Mitochondrial capacity to produce H2O2 was the highest in T3-treated rats, whereas it was similar in T4-treated and cold-exposed rats. The effects of respiratory inhibitors suggested that T3 and T4 mainly increase the mitochondrial content of autoxidizable electron carrier of Complex I and Complex III, respectively. The indices of oxidative modifications of proteins exhibited increases consistent with the treatment effects on H2O2 production. The increases in indices of lipid peroxidation were also dependent on changes in lipid composition. The increased protein damage in treatment groups was confirmed using immunoblotting analysis, which also showed oxidative damage in a 133 kDa fraction, which was not expressed in T3-treated rats. Antioxidant levels were not related to the extent of oxidative damage as only mitochondrial GSH levels decreased in T3-treated rats. Mitochondrial susceptibility to in vitro oxidative challenge and Ca2+-induced swelling was increased by all treatments, but was the highest in T3-treated rats. In the whole, our results indicate T3 as main responsible for the changes in the mitochondrial population associated with cold exposure. However, a significant role is also played by T4, which appears to acts mainly modulating T3 effects, but also inducing some effects different from the T3 ones.

Statins induce calcium-dependent mitochondrial permeability transition

Statins (3-hydroxy-3-methylglutaryl-CoA reductase inhibitors) are used in the treatment of hypercholesterolemic patients to reduce risk of cardiovascular diseases because of their cholesterol lowering action. Other lipid independent protective actions of statins have been reported. However, some adverse side effects have, also, been described. We report, here, that liver mitochondria isolated from hypercholesterolemic LDL receptor knockout mice treated during 15 days with therapeutic doses (100 mg/kg, p.o.) of lovastatin presented a higher susceptibility to develop membrane permeability transition (MPT). In experiments in vitro, lovastatin-induced MPT in a dose-dependent manner (10-80 microM) by a mechanism sensitive to cyclosporin A (cyclophilin sequestrant), dithiothreitol (reducing agent), adenine nucleotide carrier inhibitor (ADP), catalase (H2O2 reductant) and EGTA (calcium chelator). In agreement with the inhibition of the mitochondrial swelling by dithiothreitol, lovastatin, also, decreased the content of total mitochondrial membrane protein thiol groups. Simvastatin had similar effects on mitochondria; however, pravastatin, a hydrophilic statin, had a weaker effect in inducing MPT. In conclusion, statins can act directly on mitochondria either in vivo or in vitro inducing permeability transition, which is a process involved in cell death.

On the role of the respiratory complex I on membrane permeability transition

In this work we studied permeability transition by incubating mitochondria in the presence of 50 muM Ca(2+) and malate/glutamate as substrates. This condition, besides inducing the release of pyridine nucleotides, promotes the generation of reactive oxygen-derived species by the complex I of the respiratory chain. The latter leads to the opening of the mitochondrial permeability transition pore. Ca(2+) release, mitochondrial swelling and collapse of the transmembrane electric potential, were analyzed to assess this process. We propose that the mechanism for pore opening, in addition to the oxidative stress, involves the uncoupling effect of fatty acids providing activation of phospholipase A2, lipid peroxidation, and the oxidation of membrane thiols. This proposal emerges from the data indicating the protective effect of bovine serum albumin and N-ethylmaleimide. The key role of reactive oxygen species was implied based on the fact that the scavenger alpha-phenyl-tert-butyl nitrone inhibited pore opening.

Inducing coproporphyria in rat hepatocyte cultures using cyclic AMP and cyclic AMP-releasing agents

Cyclic AMP (c-AMP), added on its own to rat hepatocyte cultures, caused a marked accumulation of coproporphyrin III. The results obtained by comparing the effect of c-AMP to that of exogenous 5-aminolevulinate (ALA), and from adding c-AMP and ALA together, indicated that the coproporphyrinogen III metabolism was blocked, even though no inhibition of the relevant enzyme, coproporphyrinogen oxidase, could be demonstrated. Preferential accumulation of coproporphyrin could also be produced in cultures of rat hepatocytes by agents that raise the cellular levels of cyclic AMP, such as glucagon. The effect of supplementing the culture medium with triiodothyronine (T3) on the response of rat hepatocytes to c-AMP was also investigated. T3, which is known to stimulate mitochondrial respiration, uncoupling O2 consumption from ATP synthesis, produced a c-AMP-like effect when given on its own and potentiated the effect of c-AMP, with an apparent increase in the severity of the metabolic block. It is suggested that an oxidative mechanism may be activated in c-AMP and T3-induced coproporphyria, preferentially involving the mitochondrial compartment, leading to oxidation of porphyrinogen intermediates of haem biosynthesis, especially coproporphyrinogen. Coproporphyin, the fully oxidized aromatic derivative produced, cannot be metabolized and will therefore accumulate.

Modulation of mitochondrial transition pore components by thyroid hormone

Thyroid hormone (TH) modulates metabolic efficiency by controlling the coupling of mitochondrial oxidative phosphorylation. However, its uncoupling mode of action is still enigmatic. Treatment of Jurkat or GH3 cells with T3 is reported here to result in limited, Cyclosporin A-sensitive mitochondrial depolarization, conforming to low conductance gating of the mitochondrial transition pore (MTP). MTP protein components induced by T3 treatment were verified in T3-treated and hypothyroid rat liver as well as in Jurkat cells. T3 treatment resulted in increase in mitochondrial Bax and Bak together with decreased mitochondrial Bcl2. T3-induced mitochondrial depolarization was aborted by overexpression of Bcl2. In contrast to Bax-Bcl2 family proteins, some other MTP components were either not induced by T3 (e.g. voltage-dependent anion channel) or were induced, but were not involved in Cyclosporin A-sensitive MTP gating (e.g. Cyclophilin D and adenine nucleotide translocase-2) Hence, TH-induced mitochondrial uncoupling may be ascribed to low conductance MTP gating mediated by TH-induced increase in mitochondrial proapoptotic combined with a decrease in mitochondrial antiapoptotic proteins of the Bax-Bcl2 family.

Effect of cold-induced hyperthyroidism on H2O2 production and susceptibility to stress conditions of rat liver mitochondria

Previous studies have shown that T3 treatment and cold exposure induce similar biochemical changes predisposing rat liver to oxidative stress. This suggests that the liver oxidative damage observed in experimental and functional hyperthyroidism is mediated by thyroid hormone. To support this hypothesis we investigated whether middle-term cold exposure (2 and 10 days), like T3 treatment, also increases H2O2 release by liver mitochondria. We found that the rate of H2O2 release increased only during State 4 respiration, but faster flow of reactive oxygen species (ROS) from mitochondria to the cytosolic compartment was ensured by the concomitant increase in tissue mitochondrial proteins. Cold exposure also increased the capacity of mitochondria to remove H2O2. This indicates that cold causes accelerated H2O2 production, which might depend on enhanced autoxidizable carrier content and should lead to increased mitochondrial damage. Accordingly, mitochondrial levels of hydroperoxides and protein-bound carbonyls were higher after cold exposure. Levels of low-molecular weight antioxidants were not related to the extent of oxidative damage, but susceptibility to both in vitro oxidative challenge and Ca2+-induced swelling increased in mitochondria from cold exposed rats. The cold-induced changes in several parameters, including susceptibility to swelling, were time dependent, because they were apparent or greater after 10 days cold exposure. The cold-induced increase in swelling may be a feedback mechanism to limit tissue oxidative stress, purifying the mitochondrial population from ROS-overproducing mitochondria, and the time course for such change is consistent with the gradual development of cold adaptation.

Effect of thyroid state on susceptibility to oxidants and swelling of mitochondria from rat tissues

The effects of the thyroid state on oxidative damage, antioxidant capacity, susceptibility to in vitro oxidative stress and Ca(2+)-induced permeabilization of mitochondria from rat tissues (liver, heart, and gastrocnemious muscle) were examined. Hypothyroidism was induced by administering methimazole in drinking water for 15 d. Hyperthyroidism was elicited by a 10 d treatment of hypothyroid rats with triiodothyronine (10 micro g/100 g body weight). Mitochondrial levels of hydroperoxides and protein-bound carbonyls significantly decreased in hypothyroid tissues and were reported above euthroid values in hypothyroid rats after T(3) treatment. Mitochondrial vitamin E levels were not affected by changes of animal thyroid state. Mitochondrial Coenzyme Q9 levels decreased in liver and heart from hypothyroid rats and increased in all hyperthyroid tissues, while Coenzyme Q10 levels decreased in hypothyroid liver and increased in all hyperthyroid tissues. The antioxidant capacity of mitochondria was not significantly different in hypothyroid and euthyroid tissues, whereas it decreased in the hyperthyroid ones. Susceptibility to in vitro oxidative challenge decreased in mitochondria from hypothyroid tissues and increased in mitochondria from hyperthyroid tissues, while susceptibility to Ca(2+)-induced swelling decreased only in hypothyroid liver mitochondria and increased in mitochondria from all hyperthyroid tissues. The tissue-dependence of the mitochondrial susceptibility to stressful conditions in altered thyroid states can be explained by different thyroid hormone-induced changes in mitochondrial ROS production and relative amounts of mitochondrial hemoproteins and antioxidants. We suggest that susceptibilities to oxidants and Ca(2+)-induced swelling may have important implications for the thyroid hormone regulation of the turnover of proteins and whole mitochondria, respectively.

Cyclosporin A inhibits thyroid hormone-induced shortening of the tadpole tail through membrane permeability transition

Regression of the tadpole tail through muscule cell apoptosis is one of the most spectacular events in amphibian metamorphosis. Accumulated evidence has shown that mitochondrial membrane permeability transition (MPT) plays a crucial role in apoptosis. Previously we reported that cyclosporin A (CsA) suppressed 3,5,3'-triiodothyronine (T(3))-induced mitochondrial swelling, which was coupled with cytochrome c (Cyt.c) release through MPT [Comp. Biochem. Phys. 130 (2001) 411-418]. To further clarify the mechanism of tadpole metamorphosis, the present study investigates the effect of CsA on T(3) induced tadpole tail shortening. A low concentration of T(3) (5 x 10(-8) M) was found to induce a shortening of stage X Rana rugosa tadpole tails, accompanied by an increase in caspase-3- and -9 like protease activity, as well as an increase in DNA-fragmentation and ladder formation, while CsA was seen to suppress the effects of T(3). The stage X tadpole tail was found to express Bax mRNA and this expression was not affected by T(3) treatment. CsA, on the other hand, proved to have a slightly supressive effection on Bax expression. 20 microM T(3) as well as 50 microM Ca(2+) induced swelling in mitochondria isolated from the liver of R. rugosa resulting in the release of apoptosis related substances, and the released fraction activated cytosolic caspase-3 and -9 in the presence of dATP. This result indicated that Cyt.c might be released from mitochondria by treatment with T(3) through both direct and indirect action of T(3). From these results and other data it was concluded that mitochondrial MPT plays an important role in T(3)-induced apoptosis in the tadpole tail, resulting in tail shortening, and CsA was seen to suppress the effects of T(3).

Thyroid hormone may induce changes in the concentration of the mitochondrial calcium uniporter

We explored the possibility that the hormone 3,3',5-tri-iodothyronine can regulate the biosynthesis of the mitochondrial calcium uniporter. To meet this objective experiments on Ca(2+) transport, and binding of the specific inhibitor Ru(360) were carried out in mitochondria isolated from euthyroid, hyperthyroid and hypothyroid rats. It was found that V(max) for Ca(2+) transport increased from 11.67+/-0.8 in euthyroid to 14.36+/-0.44 in hyperthyroid, and decreased in hypothyroid mitochondria to 8.62+/-0.63 nmol Ca(2+)/mg/s. Furthermore, the K(i) for the specific inhibitor Ru(360), depends on the thyroid status, i.e. 18, 19 and 13 nM for control, hyper- and hypothyroid mitochondria, respectively. In addition, the binding of 103Ru(360) was increased in hyperthyroid and decreased in hypothyroid mitochondria. Scatchard analysis for the binding of 103Ru(360) showed the following values: 28, 40 and 23 pmol/mg for control, hyper- and hypothyroid mitochondria, respectively. The K(d) for 103Ru(360) was found to be 30.39, 37.03 and 35.71 nM for controls, hyper- and hypothyroid groups, respectively. When hypothyroid rats were treated with thyroid hormone, mitochondrial Ca(2+) transport, as well as 103Ru(360) binding, reached similar values to those found for euthyroid mitochondria.

Oxidative stress enhances the production and actions of adenosine in the kidney

The purpose of this study was to determine whether superoxide anions (O.) activate 5'-nucleotidase (5'-ND), thereby increasing the production of renal adenosine and regulating renal function. Using HPLC analysis, we found that incubation of renal tissue homogenate with the O. donor KO(2) doubled adenosine production and increased the maximal reaction velocity of 5'-ND from 141 to 192 nmol. min(-1). mg protein(-1). The O.-generating system, xanthine/xanthine oxidase increased the maximal reaction velocity of 5'-ND from 122 to 204 nmol. min(-1). mg protein(-1). Superoxide dismutase (SOD) with catalase produced a concentration-dependent reduction of 5'-ND activity in renal tissue homogenate, while the SOD inhibitor diethyldithiocarbamic acid significantly increased 5'-ND activity. Inhibition of disulfide bond formation by thioredoxin or thioredoxin reductase significantly decreased xanthine/xanthine oxidase-induced activation of renal 5'-ND. In in vivo experiments, inhibition of SOD by diethyldithiocarbamic acid (0.5 mg. kg(-1). min(-1) iv) enhanced renal vasoconstriction induced by endogenously produced adenosine and increased renal tissue adenosine concentrations under control condition and in ischemia and reperfusion. We conclude that oxidative stress activates 5'-ND and increases adenosine production in the kidney and that this redox regulatory mechanism of adenosine production is important in the control of renal vascular tone and glomerular perfusion.

Roles of long chain fatty acids and carnitine in mitochondrial membrane permeability transition

Palmitoyl-CoA (Pal-CoA) lowered the respiratory control ratio (RCR), and induced mitochondrial membrane permeability transition (MPT) and cytochrome c (Cyt. c) release from isolated rat liver mitochondria. L-Carnitine suppressed the Pal-CoA-induced dysfunction, MPT, and Cyt. c release of isolated mitochondria. This suppression was inhibited by cephaloridine, an inhibitor of carnitine uptake into mitochondria. Cyclosporin A (CsA), an inhibitor of MPT, and BSA also suppressed the Pal-CoA-induced MPT. In the presence of inorganic phosphate (P(i)), Ca2+-induced MPT was suppressed by BSA, L-carnitine, and chlorpromazine, an inhibitor of phospholipase A2. In the presence of a low concentration of Ca2+, 3,3',5-triiodothyronine, long chain fatty acids, salicylic acid, and diclofenac induced MPT by a mechanism that was suppressed by BSA, L-carnitine, or chlorpromazine. During the incubation of mitochondria on ice, their respiratory competence decreased; L-carnitine and BSA also prevented this decrease. Mitochondrial depolarization in pheochromocytoma PC12 cells was induced by either serum deprivation or arachidonic acid by a mechanism that was suppressed by acetyl-L-carnitine. These results indicate that some MPTs may be regulated by fatty acid metabolism and that the Pal-CoA-induced MPT plays an important role in the induction of apoptosis.

Suppression of T(3)- and fatty acid-induced membrane permeability transition by L-carnitine

Cytochrome c (Cyt. c) is known to be released from the mitochondria into the cytosol by means of the membrane permeability transition (MPT) mechanism, thereby activating caspase cascade activity, and inducing cell apoptosis. Recently we reported that L-carnitine suppressed palmitoyl-CoA-induced MPT as well as apoptosis in some cell types (Biochem. Pharmacol, in press). In the present study T(3) was found to induce MPT and Cyt. c release, while cyclosporin A (CsA), bovine serum albumin (BSA) and L-carnitine were found to inhibit this action in a concentration-dependent manner. Similarly, long chain fatty acid (LCFA) also induced MPT and Cyt. c release, which was then inhibited by CsA, BSA and L-carnitine. From these results the authors postulate that T(3)-induced MPT is in part regulated by fatty acid metabolism through a dynamic balance between LCFAs and L-carnitine.

Hypothyroidism provides resistance to reperfusion injury following myocardium ischemia

A growing body of evidence has demonstrated that reperfusion injury may be mediated, in part, by mitochondrial Ca2+ overload that promotes non-selective permeability of the inner membrane. In this regard it is known that mitochondria from hypothyroid rats are resistant to membrane damage as induced by Ca2+. The purpose of this study was to evaluate the sensitivity of hearts from hypothyroid rats, to the damage by reperfusion, after an ischemic period of 5 min. The results were compared with those from control and hyperthyroid rats. Hypothyroidism was established by surgical removal of the thyroid gland; in turn hyperthyroidism was induced after a daily injection of 2 mg/kg of 3,5,3'-triiodothyronine for 4 days. ECG tracings from hypothyroid rats showed a total absence of post-reperfusion arrhythmias conversely to what was observed in control and hyperthyroid rats. The release of creatine kinase and aspartate amino transferase to the plasma in hypothyroid rats was found to be lower than that found in hyperthyroid and euthyroid rats. The histological studies showed that myocardial fibers from hypothyroid rats were in good condition and retained their striae and a remarkable near absence of edema was clearly observed.

Thyroid hormones regulate lipid peroxidation and antioxidant enzyme activities in Anabas testudineus (Bloch)

The role of thyroid hormones in metabolic pathways are well known. However, their involvement in lipid peroxidation and antioxidant enzyme activities is not known. In this study, the in vivo injection of 6-propylthiouracil (6-PTU) did not alter the concentration of malondialdehyde (MDA) and conjugated dienes in liver. The administration of triiodothyronine (T3) or diiodothyronine (T2) increased the peroxidation rate in hypothyroid fish. However, in normal fish, only a high dose of T2 caused increased malondialdehyde (MDA) production, rather than T3. SOD activity was higher in T2-treated groups in both experiments. Glutathione peroxidase (GPx) activity was also high in hypothyroid fish treated with T2. In normal specimens, injections of T3 and T2 had no effect on GPx activity. Glutathione reductase (GR) activity was not altered by hypothyroidism while T3 (1 microg) and T2 (1 microg) increased it. Glutathione content was low in 6-PTU treated fish and high in both T3- and T2-treated groups. Thus it can be concluded that not only T3 but also T2, formed by sequential monodeiodination of T4, is also effective in influencing lipid peroxidation and antioxidant enzyme activities in Anabas. Furthermore, hypothyroidism as well as hyperthyroidism affects lipid peroxidation in this teleost.

Calorie restriction and age-related oxidative stress

Calorie restriction (CR) in mammals has been recognized as the best characterized and most reproducible strategy for extending maximum survival, retarding physiological aging, and delaying the onset of age-related pathologic conditions in mammals. The overwhelming majority of studies using CR have used short-lived rodent species, although current work using rhesus and squirrel monkeys will determine whether this paradigm is also relevant to manipulating the rate of primate aging. The mechanism by which restricted calorie intake modifies the rate of aging and pathology has been the subject of much controversy, although an attenuation in the lifetime accumulation of oxidative damage appears to be a central feature. Although the majority of studies have focused on the ability of cells from calorie-restricted animals to scavenge free radicals to explain the slower accrual of oxidative damage with age, it is not established that CR has a consistent effect to upregulate the activity of these enzymes in all tissues. A major effect of calorie-restricted feeding now appears to be on the rate of production or leak of free radicals from the mitochondria. The details of the adaptation and the signaling pathway that induces this effect are currently unknown.

A unifying hypothesis of Alzheimer's disease. III. Risk factors

Normal ageing and Alzheimer's disease (AD) have many features in common and, in many respects, both conditions only differ by quantitative criteria. A variety of genetic, medical and environmental factors modulate the ageing-related processes leading the brain into the devastation of AD. In accordance with the concept that AD is a metabolic disease, these risk factors deteriorate the homeostasis of the Ca(2+)-energy-redox triangle and disrupt the cerebral reserve capacity under metabolic stress. The major genetic risk factors (APP and presenilin mutations, Down's syndrome, apolipoprotein E4) are associated with a compromise of the homeostatic triangle. The pathophysiological processes leading to this vulnerability remain elusive at present, while mitochondrial mutations can be plausibly integrated into the metabolic scenario. The metabolic leitmotif is particularly evident with medical risk factors which are associated with an impaired cerebral perfusion, such as cerebrovascular diseases including stroke, cardiovascular diseases, hypo- and hypertension. Traumatic brain injury represents another example due to the persistent metabolic stress following the acute event. Thyroid diseases have detrimental sequela for cerebral metabolism as well. Furthermore, major depression and presumably chronic stress endanger susceptible brain areas mediated by a host of hormonal imbalances, particularly the HPA-axis dysregulation. Sociocultural and lifestyle factors like education, physical activity, diet and smoking may also modulate the individual risk affecting both reserve capacity and vulnerability. The pathophysiological relevance of trace metals, including aluminum and iron, is highly controversial; at any rate, they may adversely affect cellular defences, antioxidant competence in particular. The relative contribution of these factors, however, is as individual as the pattern of the factors. In familial AD, the genetic factors clearly drive the sequence of events. A strong interaction of fat metabolism and apoE polymorphism is suggested by intercultural epidemiological findings. In cultures, less plagued by the 'blessings' of the 'cafeteria diet-sedentary' Western lifestyle, apoE4 appears to be not a risk factor for AD. This intriguing evidence suggests that, analogous to cardiovascular diseases, apoE4 requires a hyperlipidaemic lifestyle to manifest as AD risk factor. Overall, the etiology of AD is a key paradigm for a gene-environment interaction. Copyright 2000 John Wiley & Sons, Ltd.

Overexpression of catalase in cytosolic or mitochondrial compartment protects HepG2 cells against oxidative injury

HepG2 cells were transfected with vectors containing human catalase cDNA and catalase cDNA with a mitochondrial leader sequence to allow comparison of the effectiveness of catalase overexpressed in the cytosolic or mitochondrial compartments to protect against oxidant-induced injury. Overexpression of catalase in cytosol and in mitochondria was confirmed by Western blot, and activity measurement and stable cell lines were established. The intracellular level of H(2)O(2) induced by exogenously added H(2)O(2) or antimycin A was lower in C33 cell lines overexpressing catalase in the cytosol and mC5 cell lines overexpressing catalase in the mitochondria as compared with Hp cell lines transfected with empty vector. Cell death caused by H(2)O(2), antimycin A, and menadione was considerably suppressed in both the mC5 and C33 cell lines. C33 and mC5 cells were also more resistant to apoptosis induced by H(2)O(2) and to the loss of mitochondrial membrane potential induced by H(2)O(2) and antimycin A. In view of the comparable protection by catalase overexpressed in the cytosol versus the mitochondria, catalase produced in both cellular compartments might act as a sink to decompose H(2)O(2) and move diffusable H(2)O(2) down its concentration gradient. The present study suggests that catalase in cytosol and catalase in mitochondria are capable of protecting HepG2 cells against cytotoxicity or apoptosis induced by oxidative stress.

Mitochondrial damage induced by conditions of oxidative stress

Up to 2% of the oxygen consumed by the mitochondrial respiratory chain undergoes one electron reduction, typically by the semiquinone form of coenzyme Q, to generate the superoxide radical, and subsequently other reactive oxygen species such as hydrogen peroxide and the hydroxyl radical. Under conditions in which mitochondrial generation of reactive oxygen species is increased (such as in the presence of Ca2+ ions or when the mitochondrial antioxidant defense mechanisms are compromised), these reactive oxygen species may lead to irreversible damage of mitochondrial DNA, membrane lipids and proteins, resulting in mitochondrial dysfunction and ultimately cell death. The nature of this damage and the cellular conditions in which it occurs are discussed in this review article.