Severe Impairment of Nucleotide Synthesis Through Inhibition of Mitochondrial Respiration

Since de‐novo synthesis of pyrimidine nucleotides is coupled to the mitochondrial respiratory chain (RC) via dehydroorotic acid dehydrogenase (DHODH), respiratory chain dysfunction should impair pyrimidine synthesis. To investigate this, we used specific RC inhibitors, Antimycin A and Rotenone, to treat primary human keratinocytes and 143B cells, a human osteosarcoma cell line, in culture. This resulted in severe impairment of de novo pyrimidine nucleotide synthesis. The effects of RC inhibition were not restricted to pyrimidine synthesis, but concerned purine nucleotides, too. While the total amount of purine nucleotides was not diminished, they were significantly broken down from triphosphates to monophosphates, reflecting impaired mitochondrial ATP regeneration. The effect of Rotenone was similar to that of Antimycin A. This was surprising since Rotenone inhibits complex I of the respiratory chain, which is upstream of ubiquinone where DHODH interacts with the RC. In order to avoid unspecific effects of Rotenone, we examined the consequences of a mitochondrial DNA mutation that causes a specific complex I defect. The effect was much less pronounced than with Rotenone, suggesting that complex I inhibiton cannot fully explain the marked effect of Rotenone on pyrimidine nucleotide synthesis.     

Effects of 2-Deoxy-d-Glucose on Methamphetamine-Induced Dopamine and Serotonin Neurotoxicity

Abstract: The mechanisms underlying the neurotoxic actions of methamphetamine (METH) and related substituted amphetamines are unknown. Previous studies with 2-deoxyglucose (2-DG) have suggested that METH-induced neurotoxicity may involve exhaustion of intracellular energy stores. However, because 2-DG also produces hypothermic effects, and because METH's neurotoxic actions are highly susceptible to thermoregulatory influence, previous findings with 2-DG are difficult to interpret. The present studies were undertaken to further examine the influence of 2-DG's glucoprivic and thermic effects in the context of METH-induced dopamine (DA) and serotonin (5-HT) neurotoxicity. 2-DG protected against METH-induced DA neurotoxicity in both rats and mice. In both species, 2-DG, alone or in combination with METH, produced hypothermic effects. METH's toxic effects on brain 5-HT neurons were either unaffected or exacerbated by 2-DG, depending on species, brain region, and dose of METH tested. These results indicate that different mechanisms may underlie METH-induced DA and 5-HT neurotoxicity, and suggest that, as compared with 5-HT neurons, DA neurons are more susceptible to temperature influence, whereas 5-HT neurons are more vulnerable than DA neurons to metabolic compromise. Additional studies are needed to further assess the role of energy stores in the neurotoxic effects of METH and related drugs.     

Dopaminergic Neurotoxicity In Vivo and Inhibition of Mitochondrial Respiration In Vitro by Possible Endogenous Pyridinium-Like Substances

Elucidation of the mechanism(s) by which 1-methyl-4-phenyl-1,2,3,6- tetrahydropyridine (MPTP) and its active metabolite 1-methyl-4-phenylpyridinium (MPP+) cause parkinsonism in humans and other primates has prompted consideration of possible endogenous MPTP/MPP(+)-like neurotoxins in the etiology of idiopathic Parkinson's disease. Here we examined inhibition of mitochondrial respiration in vitro and neurotoxicity in rats in vivo produced by beta-carbolinium compounds that are presumed to form following Pictet-Spengler cyclization of serotonin. We also evaluated N-methylisoquinolinium, a putative endogenous neurotoxin, in the same manner. The latter compound exhibited MPP(+)-like mitochondrial respiratory inhibition, whereas the beta-carbolinium compounds, although more potent inhibitors of electron transport, exhibited weak accumulation-dependent enhancement of inhibition in intact mitochondria. It is interesting that the beta-carbolinium compounds inhibited succinate- as well as glutamate-supported respiration, and are best described as inhibitor-uncouplers. The results of partitioning experiments suggest that both the low accumulation potential and the inhibition of succinate respiration may be a consequence of the beta-carboliniums being in equilibrium with neutral "anhydro" bases. Relative to MPP+, all compounds tested had weak dopaminergic uptake activity in vitro and weak dopaminergic toxicity in vivo, consistent with other findings of relatively low neurotoxic potential for presumed endogenous pyridiniums.     

21-Aminosteroids Interact with the Dopamine Transporter to Protect Against 1-Methyl-4-Phenylpyridinium-Induced Neurotoxicity

U-78518F, a 21-aminosteroid from the novel family of lipid peroxidation inhibitors (lazaroids), increased survival of dopamine (DA) neurons in mesencephalic cell cultures incubated with the neurotoxin 1-methyl-4-phenylpyridinium (MPP+). Protection against DA neuron death occurred with increasing concentrations of U-78518F up to 30 microM. Non-specific toxicity produced with higher concentrations of MPP+ was not affected by the lazaroid. U-78518F inhibited cellular uptake of [3H]MPP+ and [3H]DA, but not that of gamma-[3H]aminobutyric acid. In human striatal membrane preparations, U-78518F competed with [3H]mazindol for binding to the DA transporter, with a calculated Ki value of 10 microM. Two of four lazaroids tested inhibited [3H]DA uptake in the cell culture system. The protective effects of 21-aminosteroids in MPP(+)-induced neurotoxicity are, in part, a function of the interaction of these agents with the DA transporter.     

Dopamine Oxidation Alters Mitochondrial Respiration and Induces Permeability Transition in Brain Mitochondria

Both reactive dopamine metabolites and mitochondrial dysfunction have been implicated in the neurodegeneration of Parkinson's disease. Dopamine metabolites, dopamine quinone and reactive oxygen species, can directly alter protein function by oxidative modifications, and several mitochondrial proteins may be targets of this oxidative damage. In this study, we examined, using isolated brain mitochondria, whether dopamine oxidation products alter mitochondrial function. We found that exposure to dopamine quinone caused a large increase in mitochondrial resting state 4 respiration. This effect was prevented by GSH but not superoxide dismutase and catalase. In contrast, exposure to dopamine and monoamine oxidase-generated hydrogen peroxide resulted in a decrease in active state 3 respiration. This inhibition was prevented by both pargyline and catalase. We also examined the effects of dopamine oxidation products on the opening of the mitochondrial permeability transition pore, which has been implicated in neuronal cell death. Dopamine oxidation to dopamine quinone caused a significant increase in swelling of brain and liver mitochondria. This was inhibited by both the pore inhibitor cyclosporin A and GSH, suggesting that swelling was due to pore opening and related to dopamine quinone formation. In contrast, dopamine and endogenous monoamine oxidase had no effect on mitochondrial swelling. These findings suggest that mitochondrial dysfunction induced by products of dopamine oxidation may be involved in neurodegenerative conditions such as Parkinson's disease and methamphetamine-induced neurotoxicity.     

Neurotoxicity of methamphetamine and 3,4-methylenedioxymethamphetamine

Amphetamines are a class of psychostimulant drugs that are widely abused for their stimulant, euphoric, empathogenic and hallucinogenic properties. Many of these effects result from acute increases in dopamine and serotonin neurotransmission. Subsequent to these acute effects, methamphetamine and 3,4 methylenedioxymethamphetamine (MDMA) produce persistent damage to dopamine and serotonin nerve terminals. This review summarizes the numerous interdependent mechanisms including excitotoxicity, mitochondrial damage and oxidative stress that have been demonstrated to contribute to this damage. Emerging non-neuronal mechanisms by which the drugs may contribute to monoaminergic terminal damage, as well as the neuropsychiatric consequences of this terminal damage are also presented. Methamphetamine and 3,4-methylenedioxymethamphetamine (MDMA) have similar chemical structures and pharmacologic properties compared to other abused substances including cathinone (khat), as well as a relatively new class of novel synthetic amphetamines known as ‘bath salts’ that have gained popularity among drug abusers.     

Mitochondrial DNA alteration in obstructive sleep apnea

Background

Obstructive Sleep Apnea (OSAS) is a disease associated with the increase of cardiovascular risk and it is characterized by repeated episodes of Intermittent Hypoxia (IH) which inducing oxidative stress and systemic inflammation. Mitochondria are cell organelles involved in the respiratory that have their own DNA (MtDNA). The aim of this study was to investigate if the increase of oxidative stress in OSAS patients can induce also MtDNA alterations.

Methods

46 OSAS patients (age 59.27 ± 11.38; BMI 30.84 ± 3.64; AHI 36.63 ± 24.18) were compared with 36 control subjects (age 54.42 ± 6.63; BMI 29.06 ± 4.7; AHI 3.8 ± 1.10). In blood cells Content of MtDNA and nuclear DNA (nDNA) was measured in OSAS patients by Real Time PCR. The ratio between MtDNA/nDNA was then calculated. Presence of oxidative stress was evaluated by levels of Reactive Oxygen Metabolites (ROMs), measured by diacron reactive oxygen metabolite test (d-ROM test).

Results

MtDNA/nDNA was higher in patients with OSAS than in the control group (150.94 ± 49.14 vs 128.96 ± 45.8; p = 0.04), the levels of ROMs were also higher in OSAS subjects (329.71 ± 70.17 vs 226 ± 36.76; p = 0.04) and they were positively correlated with MtDNA/nDNA (R = 0.5, p < 0.01).

Conclusions

In OSAS patients there is a Mitochondrial DNA damage induced by the increase of oxidative stress. Intermittent hypoxia seems to be the main mechanism which leads to this process.     

Neurotoxicity mediated by oxidative stress caused by titanium dioxide nanoparticles in human neuroblastoma (SH-SY5Y) cells

BackgroundTitanium is widely used in biomedicine. Due to biotribocorrosion, titanium dioxide (TiO₂) nanoparticles (NPs) can be released from the titanium implant surface, enter the systemic circulation, and migrate to various organs and tissues including the brain. A previous study showed that 5 nm TiO₂ NPs reached the highest concentration in the brain. Even though TiO₂ NPs are believed to possess low toxicity, little is known about their neurotoxic effects. The aim of the study was to evaluate in vitro the effects of 5 nm TiO₂ NPs on a human neuroblastoma (SH-SY5Y) cell line.MethodsCell cultures were divided into non-exposed and exposed to TiO₂ NPs for 24 h. The following were evaluated: reactive oxygen species (ROS) generation, apoptosis, cellular antioxidant response, endoplasmic reticulum stress and autophagy.ResultsExposure to TiO₂ NPs induced ROS generation in a dose dependent manner, with values reaching up to 10 fold those of controls (p < 0.001). Nrf2 nuclear localization and autophagy, also increased in a dose dependent manner. Apoptosis increased by 4- to 10-fold compared to the control group, depending on the dose employed.ConclusionsOur results show that TiO₂ NPs cause ROS increase, induction of ER stress, Nrf2 cytoplasmic translocation to the nucleus and apoptosis. Thus, neuroblastoma cell response to TiO₂ NPs may be associated with an imbalance of the oxidative metabolism where endoplasmic reticulum-mediated signal pathway seems to be the main neurotoxic mechanism.     

Nature of Inhibition of Mitochondrial Respiratory Complex I by 6-Hydroxydopamine

Abstract: The catecholaminergic neurotoxin 6-hydroxydopamine causes parkinsonian symptoms in animals and it has been proposed that reactive oxygen species and oxidative stress, enhanced by iron, may play a key role in its toxicity. The present results demonstrate that 6-hydroxydopamine reversibly inhibits complex I (NADH dehydrogenase) of brain mitochondrial respiratory chain in isolated mitochondria. 6-Hydroxydopamine itself, rather than its oxidative products, was responsible for the inhibition. Iron(III) did not enhance inhibition but decreased it by stimulating the nonenzyme oxidation of 6-hydroxydopamine. Inhibition was potentiated to some extent by calcium ion. Desferrioxamine protected complex I activity against the inhibition, but it was not due to its chelator or antioxidative properties. Desferrioxamine was also shown to activate NADH dehydrogenase in the absence of 6-hydroxydopamine. Activation of mitochondrial respiration by desferrioxamine may contribute to the enhanced neuron survival in the presence of desferrioxamine in some neurodegenerative conditions.     

Regulation of Extracellular Dopamine by the Norepinephrine Transporter

Abstract: There is growing evidence of an interaction between dopamine and norepinephrine. To test the hypothesis that norepinephrine terminals are involved in the uptake and removal of dopamine from the extracellular space, the norepinephrine uptake blocker desmethylimipramine (DMI) was infused locally while the extracellular concentrations of dopamine were simultaneously monitored. DMI increased the extracellular concentrations of dopamine in the medial prefrontal cortex and nucleus accumbens shell but had no effect in the striatum. The combined systemic administration of haloperidol and the local infusion of DMI produced an augmented increase in extracellular dopamine in the cortex compared with the increase produced by either drug alone. This synergistic increase in dopamine overflow is likely due to the combination of impulse-mediated dopamine release produced by haloperidol and blockade of the norepinephrine transporter. No such synergistic effects were observed in the nucleus accumbens and striatum. Local perfusion of the α₂-antagonist idazoxan also increased the extracellular concentrations of dopamine in the cortex. Although the stimulation of extracellular dopamine by idazoxan and DMI could be due to the increased extracellular concentrations of norepinephrine produced by these drugs, an increase in dopamine also was observed in lesioned rats that were depleted of norepinephrine and challenged with haloperidol. This contrasted with the lack of an effect of haloperidol on cortical dopamine in unlesioned controls. These results suggest that norepinephrine terminals regulate extracellular dopamine concentrations in the medial prefrontal cortex and to a lesser extent in the nucleus accumbens shell through the uptake of dopamine by the norepinephrine transporter.     

Modification of Dopamine Transporter Function: Effect of Reactive Oxygen Species and Dopamine

Abstract: Dopamine can oxidize to form reactive oxygen species and quinones, and we have previously shown that dopamine quinones bind covalently to cysteinyl residues on striatal proteins. The dopamine transporter is one of the proteins at risk for this modification, because it has a high affinity for dopamine and contains several cysteinyl residues. Therefore, we tested whether dopamine transport in rat striatal synaptosomes could be affected by generators of reactive oxygen species, including dopamine. Uptake of [³H]dopamine (250 n M ) was inhibited by ascorbate (0.85 m M ; −44%), and this inhibition was prevented by the iron chelator diethylenetriaminepentaacetic acid (1 m M ), suggesting that ascorbate was acting as a prooxidant in the presence of iron. Preincubation with xanthine (500 µ M ) and xanthine oxidase (50 mU/ml) also reduced [³H]dopamine uptake (−76%). Preincubation with dopamine (100 µ M ) caused a 60% inhibition of subsequent [³H]dopamine uptake. This dopamine-induced inhibition was attenuated by diethylenetriaminepentaacetic acid (1 m M ), which can prevent iron-catalyzed oxidation of dopamine during the preincubation, but was unaffected by the monoamine oxidase inhibitor pargyline (10 µ M ). None of these incubations caused a loss of membrane integrity as indicated by lactate dehydrogenase release. These findings suggest that reactive oxygen species and possibly dopamine quinones can modify dopamine transport function.     

多巴胺类似物抑制二氢蝶啶还原酶的研究

多巴胺类似物对二氢蝶啶还原酶有明显的非竞争性抑制作用(Ki或I_(50)值为10~(-5)—10~(-6)mol/L)。其中阿朴吗啡是最强的抑制剂之一(Ki或I~(50)=1-2×10~(-6)mol/L)。由于酪氨酸羟化酶和二氢蝶啶还原酶包含于同一酶促反应过程中,且限制了多巴胺合成的决定速度的那一步。这些结果可能提示出被多巴胺抑制的酪氨酸羟化作用包含着对这二种酶的抑制作用。     

Mitochondrial Ca2+-activated K+ channels and their role in cell life and death pathways

Ca²⁺-activated K⁺ channels (K_Ca) are expressed at the plasma membrane and in cellular organelles. Expression of all K_Ca channel subtypes (BK, IK and SK) has been detected at the inner mitochondrial membrane of several cell types. Primary functions of these mitochondrial K_Ca channels include the regulation of mitochondrial ROS production, maintenance of the mitochondrial membrane potential and preservation of mitochondrial calcium homeostasis. These channels are therefore thought to contribute to cellular protection against oxidative stress through mitochondrial mechanisms of preconditioning. In this review, we summarize the current knowledge on mitochondrial KCa channels, and their role in mitochondrial function in relation to cell death and survival pathways. More specifically, we systematically discuss studies on the role of these mitochondrial K_Ca channels in pharmacological preconditioning, and according protective effects on ischemic insults to the brain and the heart.     

Dopamine enhances mtNOS activity: Implications in mitochondrial function

Dopamine and nitric oxide systems can interact in different processes in the central nervous system. Dopamine and oxidation products have been related to mitochondrial dysfunction. In the present study, intact mitochondria and submitochondrial membranes were incubated with different DA concentrations for 5 min. Dopamine (1 mM) increased nitric oxide production in submitochondrial membranes and this effect was partially prevented in the presence of both DA and NOS inhibitor N_ω-nitro-l-arginine (l-NNA). A 46% decrease in state 3 oxygen uptake (active respiration state) was found after 15 mM dopamine incubation. When mitochondria were incubated with 15 mM dopamine in the presence of l-NNA, state 3 respiratory rate was decreased by only 17% showing the involvement of NO. As shown for O₂ consumption, the inhibition of cytochrome oxidase by 1 mM DA was mediated by NO. Hydrogen peroxide production significantly increased after 15 mM DA incubation, being mainly due to its metabolism by MAO. Also, DA-induced depolarization was prevented by the addition of l-NNA showing the involvement of nitric oxide in this process too. This work provides evidence that in the studied conditions, dopamine modifies mitochondrial function by a nitric oxide-dependent pathway.     

NMDA Receptor Involvement in Toxicity to Dopamine Neurons In Vitro Caused by the Succinate Dehydrogenase Inhibitor 3-Nitropropionic Acid

Abstract: Exposure of mesencephalic dopamine neurons to an irreversible inhibitor of succinate dehydrogenase (SDH), 3-nitropropionic acid (3-NPA), for 24 h on day 12 in vitro, produced a dose-dependent loss of high-affinity dopamine uptake when measured 48 h following 3-NPA removal. ATP concentrations in the cultures were reduced by 57% after 3 h of treatment with the highest concentration of 3-NPA tested (500 µ M ). To determine whether glutamate receptors mediated the dopamine toxicity by 3-NPA, cultures were examined for their sensitivity to excitatory amino acid-induced toxicity. Mesencephalic cultures exposed to either 100 µ M NMDA or kainate, on day 12 for 24 h, showed complete loss of dopamine uptake following 48 h of recovery. The NMDA and non-NMDA antagonists, MK-801 (1 µ M ) or 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX; 15 µ M ), completely prevented the effects of NMDA or kainate, respectively, when present at the time of toxin exposure. In cultures treated with 3-NPA, MK-801, but not CNQX, significantly attenuated the loss of dopamine uptake. Direct measurement of the effect of 3-NPA on SDH activity showed that 3-NPA dose-dependently inhibited SDH in vitro in a manner commensurate with the loss of dopamine uptake by 3-NPA. MK-801 had no effect on basal SDH activity or on 3-NPA inhibition of SDH. These data are consistent with the interpretation that metabolic inhibition in dopamine neurons can trigger a secondary excitotoxicity that is mediated by NMDA receptors.     

Effect of Dopamine, Dimethoxyphenylethylamine, Papaverine, and Related Compounds on Mitochondrial Respiration and Complex I Activity

Abstract: We report the effect of papaverine, tetrahydropapaverine, laudanosine, dimethoxyphenylethylamine, dopamine, and its metabolites on mitochondrial respiration and activities of the enzymes in the electron transfer complexes, as mitochondrial toxins may be implicated in the etiology and the pathogenesis of Parkinson's disease. Papaverine was the most potent inhibitor of complex I and NADH-linked mitochondrial respiration among the compounds tested next to rotenone. Tetrahydropapaverine, dimethoxyphenylethylamine, and laudanosine also inhibited NADH-linked mitochondrial respiration and complex I activity in this order. Dopamine and its metabolites showed either no inhibition or only very weak inhibition. Compounds with dimethoxy residues in the phenyl ring were associated with more potent inhibition of complex I than those without. Our results warrant further studies on these and some related compounds as candidate neurotoxins causing Parkinson's disease.     

Mitochondrial complex I: new insights from inhibitor assays

Summary The NADH:ubiquinone oxidoreductase (complex I) of the mitochondrial respiratory chain is by far the most complicated of the proton-translocating enzymes involved in the oxidative phosphorylation. Many clues regarding both electron transfer and proton translocation are still unknown. In this sense, inhibitor assays are relevant and useful pieces for elaborating a suitable model to explain the elusive bioenergetic mechanism of this enzyme. This short review presents the most recent advances in inhibitor studies and highlights the major controversies.Abbreviations ACG annonaceous acetogenin - MPP⁺ methylphenyl-pyridinium     

Substrates of Energy Metabolism Attenuate Methamphetamine-Induced Neurotoxicity in Striatum

Abstract: High doses of methamphetamine (METH) produce a long-term depletion in striatal tissue dopamine content. The mechanism mediating this toxicity has been associated with increased concentrations of dopamine and glutamate and altered energy metabolism. In vivo microdialysis was used to assess and alter the metabolic environment of the brain during high doses of METH. METH significantly increased extracellular concentrations of lactate in striatum and prefrontal cortex. This increase was significantly greater in striatum and coincided with the greater vulnerability of this brain region to the toxic effects of METH. To examine the effect of supplementing energy metabolism on METH-induced dopamine content depletions, the striatum was perfused directly with decylubiquinone or nicotinamide to enhance the energetic capacity of the tissue during or after a neurotoxic dosing regimen of METH. When decylubiquinone or nicotinamide was perfused into striatum during the administration of METH, there was no significant effect on METH-induced striatal dopamine efflux, glutamate efflux, or the long-term dopamine depletions measured 7 days later. However, a delayed perfusion with decylubiquinone or nicotinamide for 6 h beginning immediately after the last METH injection attenuated the METH-induced striatal dopamine depletions measured 1 week later. These results support the hypothesis that the compromised metabolic state produced by METH administration predisposes dopamine terminals to the neurotoxic effects of glutamate, dopamine, and/or free radicals.     

Inhibition of mitochondrial respiration overcomes hepatocellular carcinoma chemoresistance

The clinical management of advanced hepatocellular carcinoma (HCC) is challenging due to its resistance to chemotherapy. In our work, we demonstrate that an antiparasitic drug atovaquone at clinically relevant concentrations is active against chemoresistant HCC. We show that atovaquone inhibits proliferation and induces apoptosis in not only HCC parental cells but also cells exposed to long time culture of chemotherapeutic agents. Consistently, the combination of atovaquone with cisplatin or doxorubicin achieved remarkably greater efficacy than single drug alone. Mechanistically, atovaquone overcomes HCC chemoresistance via supressing mitochondrial respiration and inducing oxidative stress. Atovaquone but not cisplatin or doxorubicin is ineffective in mitochondrial respiration-deficient ρ0, confirming mitochondria as a specific upstream target of atovaquone. Interestingly, we show that prolonged exposure of HCC cells to chemotherapeutic agents induces higher level of mitochondrial respiration, suggesting that tumors which develop chemoresistance after chemotherapy might be more dependent on mitochondrial respiration than primary tumors and explaining the sensitivity of chemoresistant HCC cells to atovaquone. We further show that atovaquone at tolerable does significantly inhibits chemoresistant HCC growth in mice throughout the duration of treatment. In line with in vitro data, we observe the increased oxidative stress in atovaquone-treated tumors. Our findings highlight the dependency of chemoresistant HCC on mitochondrial respiration and demonstrate that atovaquone is a potential drug to overcome HCC chemoresistance.     

In Vitro Studies of Ferritin Iron Release and Neurotoxicity

Abstract: The increase in brain iron associated with several neurodegenerative diseases may lead to an increased production of free radicals via the Fenton reaction. Intracellular iron is usually tightly regulated, being bound by ferritin in an insoluble ferrihydrite core. The neurotoxin 6-hydroxydopamine (6-OHDA) releases iron from the ferritin core by reducing it to the ferrous form. Iron release induced by 6-OHDA and structurally related compounds and two other dopaminergic neurotoxins, 1-methyl-4-phenylpyridinium iodide (MPP⁺) and 1-trichloromethyl-1,2,3,4-tetrahydro-β-carboline (TaClo), were compared, to identify the structural characteristics important for such release. 1,2,4-Trihydroxybenzene (THB) was most effective in releasing ferritin-bound iron, followed by 6-OHDA, dopamine, catechol, and hydroquinone. Resorcinol, MPP⁺, and TaClo were ineffective. The ability to release iron was associated with a low oxidation potential. It is proposed that a low oxidation potential and an ortho -dihydroxyphenyl structure are important in the mechanism by which ferritin iron is mobilized. In the presence of ferritin, both 6-OHDA and THB strongly stimulated lipid peroxidation, an effect abolished by the addition of the iron chelator deferoxamine. These results suggest that ferritin iron release contributes to free radical-induced cell damage in vivo.