Ilan Ziv

Prevention of Dopamine-Induced Cell Death by Thiol Antioxidants: Possible Implications for Treatment of Parkinson's Disease

We have recently shown that dopamine (DA) can trigger apoptosis, an active program of cellular self-destruction, in various neuronal cultures and proposed that inappropriate activation of apoptosis by DA and or its oxidation products may initiate nigral cell loss in Parkinsons disease (PD). Since DA toxicity may be mediated via generation of oxygen-free radical species, we examined whether DA-induced cell death in PC12 cells may be inhibited by antioxidants. We have found that the thiol containing compounds, reduced glutathione (GSH), N-acetyl-cysteine (NAC), and dithiothreitol (DTT) were markedly protective, while vitamins C and E had lesser or no effect. The thiol antioxidants and vitamin C but not vitamin E, prevented dopamine autooxidation and production of dopamine-melanin. Their protective effect has also manifested by inhibiting DA-induced apoptosis; DNA fragmentation was prevented as was shown histochemically by the in situ end-labeled DNA technique (TUNEL). Intracellular GSH and other thiols constitute an important natural defense against oxidative stress. We have found that depletion of cellular GSH by the addition of phoron, a substrate of glutathione transferase, and buthionine sulfoximine (BSO), an inhibitor of gamma-glutamyl transpeptidase, significantly enhanced DA toxicity. Cotreatment with NAC rescued the cells from the toxic effect of BSO+DA, and phoron+ DA, while addition of GSH provided only partial protection from BSO+DA toxicity. Our data indicate that the thiol family of antioxidants, but not vitamins C and E, are highly effective in rescuing cells from DA-induced apoptosis. Further study of the mechanisms underlying the unique protective capacity of thiol antioxidants may lead to the development of new neuroprotective therapeutic strategies for PD.

Dopamine induces apoptosis-like cell death in cultured chick sympathetic neurons — A possible novel pathogenetic mechanism in Parkinson's disease

We report that exposure of cultured, postmitotic chick-embryo sympathetic neurons, to physiological concentrations of dopamine (0.1-1 mM) for 24 h initiates a cellular death process characteristic of apoptosis (= programmed-cell-death, PCD). Dopamine caused marked morphological alterations, mainly axonal disintegration and severe shrinkage and condensation of cell bodies. Flow-cytometric analysis of propidium-iodide-stained cell nuclei revealed the characteristic apoptotic nuclear fragmentation: increase in nuclear granularity and emergence of a large, distinct population of nuclei with reduced DNA content (subdiploid, apoptotic peak). These alterations were similar to changes induced by nerve growth factor (NGF) deprivation, a model of sympathetic neuronal PCD. Alterations were inhibited by the anti-oxidative agent DTT. Inappropriate, dopamine-induced activation of PCD might have a role in nigral neuronal degeneration in Parkinsons disease.

The mystery of motor asymmetry in Parkinson's disease

The motor symptoms of Parkinsons disease are predominantly due to progressive degeneration of nigral dopaminergic neurons. In most cases there is a substantial asymmetry of clinical symptoms from disease onset, which occurs in sporadic and in hereditary forms of the disease. However, the mechanism of such unilaterality of symptom appearance is not understood. There is only sparse information about whether symptom-side predominance is genetically coded and determined years before symptom onset, or whether it is acquired and related to side differences in vulnerability of the degenerating neurons. In this Personal View we review data for unilaterality of symptoms at different disease stages. We also discuss several pathological, genetic, environmental, and toxic possibilities for explaining the mechanism of side predominance.

Dopamine–melanin induces apoptosis in PC12 cells; possible implications for the etiology of Parkinson's disease

The function of neuromelanin (NM), the oxidized dopamine (DA) polymer, within the DA-producing cells in the human and primate substantia nigra (SN), is still an enigma. Some studies show that the vulnerability of nigral neurons in Parkinsons disease is correlated to their toxic NM content, while others suggest that it contributes to cellular protection. We showed recently that DA, the endogenous nigral neurotransmitter, triggers apoptosis, an active program of cellular self-destruction, in neuronal cultures. In the present study, we exposed cells to synthetic dopamine-melanin (DA-M) and analysed the cellular and genetic changes. We found that exposure of PC12 cells to DA-M (0.5 mg/ml for 24 h) caused 50% cell death, as indicated by trypan blue exclusion assay and 3H-thymidine incorporation. Gel electrophoresis DNA analysis of PC12 cells treated with DA-M showed the typical apoptotic DNA ladder, indicating inter-nucleosomal DNA degradation. The DNA fragmentation also was visualized histochemically in situ by DNA end-labeling staining (the TUNEL method). The FeCl2 (0.05 mM) significantly increased DA-M toxicity, while desferrioxamine, an iron chelator, totally abolished the additive toxicity of iron. The contribution of oxidative stress in this model of DA-M-induced cell death was examined using various antioxidants. In contrast to DA, inhibition of DA-M toxicity antioxidants by reduced glutathione (GSH), N-acetyl cysteine, catalase and Zn/Cu superoxide dismutase (SOD) was very limited. In conclusion, we found that DA-M may induce typical apoptotic death in PC12 cells. Our findings support a possible role of NM in the vulnerability of the dopaminergic neural degeneration in Parkinsons disease. The differential protective effect by antioxidants against toxicity of DA and DA-M may have implications for future neuroprotective therapeutic approaches for this common neurological disorder.

Molecular imaging of cell death in vivo by a novel small molecule probe

Apoptosis has a role in many medical disorders, therefore assessment of apoptosis in vivo can be highly useful for diagnosis, follow-up and evaluation of treatment efficacy. ApoSense is a novel technology, comprising low molecular-weight probes, specifically designed for imaging of cell death in vivo. In the current study we present targeting and imaging of cell death both in vitro and in vivo, utilizing NST-732, a member of the ApoSense family, comprising a fluorophore and a fluorine atom, for both fluorescent and future positron emission tomography (PET) studies using an 18F label, respectively. In vitro, NST-732 manifested selective and rapid accumulation within various cell types undergoing apoptosis. Its uptake was blocked by caspase inhibition, and occurred from the early stages of the apoptotic process, in parallel to binding of Annexin-V, caspase activation and alterations in mitochondrial membrane potential. In vivo, NST-732 manifested selective uptake into cells undergoing cell-death in several clinically-relevant models in rodents: (i) Cell-death induced in lymphoma by irradiation; (ii) Renal ischemia/reperfusion; (iii) Cerebral stroke. Uptake of NST-732 was well-correlated with histopathological assessment of cell-death. NST-732 therefore represents a novel class of small-molecule detectors of apoptosis, with potential useful applications in imaging of the cell death process both in vitro and in vivo.

Anti-semaphorin 3A Antibodies Rescue Retinal Ganglion Cells from Cell Death following Optic Nerve Axotomy

Damage to the optic nerve in mammals induces retrograde degeneration and apoptosis of the retinal ganglion cell (RGC) bodies. The mechanisms that mediate the response of the neuronal cells to the axonal injury are still unknown. We have previously shown that semaphorins, axon guidance molecules with repulsive cues, are capable of mediating apoptosis in cultured neuronal cells (Shirvan, A., Ziv, I., Fleminger, G., Shina, R., He, Z., Brudo, I., Melamed, E., and Brazilai, A. (1999) J. Neurochem. 73, 961–971). In this study, we examined the involvement of semaphorins in an in vivo experimental animal model of complete axotomy of the rat optic nerve. We demonstrate that a marked induction of type III semaphorin proteins takes place in ipsilateral retinas at early stages following axotomy, well before any morphological signs of RGC apoptosis can be detected. Time course analysis revealed that a peak of expression occurred after 2–3 days and then declined. A small conserved peptide derived from semaphorin 3A that was previously shown to induce neuronal death in culture was capable of inducing RGC loss upon its intravitreous injection into the rat eye. Moreover, we demonstrate a marked inhibition of RGC loss when axotomized eyes were co-treated by intravitreous injection of function-blocking antibodies against the semaphorin 3A-derived peptide. Marked neuronal protection from degeneration was also observed when the antibodies were applied 24 h post-injury. We therefore suggest that semaphorins are key proteins that modulate the cell fate of axotomized RGC. Neutralization of the semaphorin repulsive function may serve as a promising new approach for treatment of traumatic injury in the adult mammalian central nervous system or of ophthalmologic diseases such as glaucoma and ischemic optic neuropathy that induce apoptotic RGC death.

Mutant and wild-type α-synuclein interact with mitochondrial cytochrome C oxidase

Abstractα-synuclein, a presynaptic protein, was found to be the major component in the Lewy bodies (LB) in both inherited and sporadic Parkinson’s disease (PD). Furthermore, rare mutations of α-synuclein cause autosomal-dominant PD. However, it is unknown how α-synuclein is involved in the pathogenesis of nigral degeneration in PD. In this study, we examine the protein-protein interactions of wild-type and mutant (A53T) α-synuclein with adult human brain cDNA expression library using the yeast two-hybrid technique. We found that both normal and mutant α-synuclein specifically interact with the mitochondrial complex IV enzyme, cytochrome C oxidase (COX). Wild-type and mutant α-synuclein genes were further fused with c-Myc tag and translated in rabbit reticulocyte lysate. Using anti-c-Myc antibody, we demonstrated that both wild-type and mutant α-synuclein, coimmunoprecipitated with COX. We also showed that potassium cyanide, a selective COX inhibitor, synergistically enhanced the sensitivity of SH-SY5Y neuroblastoma cells to dopamine-induced cell death. In conclusion, we found specific protein-protein interactions of α-synuclein, a major LB protein, to COX, a key enzyme of the mitochondrial respiratory system. This interaction suggests that α-synuclein aggregation may contribute to enhance the mitochondrial dysfunction, which might be a key factor in the pathogenesis of PD.

Small-Molecule Biomarkers for Clinical PET Imaging of Apoptosis

Apoptosis is a fundamental biologic process. Molecular imaging of apoptosis in vivo may have important implications for clinical practice, assisting in early detection of disease, monitoring of disease course, assessment of treatment efficacy, or development of new therapies. Although a PET probe for clinical imaging of apoptosis would be highly desirable, this is yet an unachieved goal, mainly because of the required challenging integration of various features, including sensitive and selective detection of the apoptotic cells, clinical aspects such as favorable biodistribution and safety profiles, and compatibility with the radiochemistry and imaging routines of clinical PET centers. Several approaches are being developed to address this challenge, all based on novel small-molecule structures targeting various steps of the apoptotic cascade. This novel concept of small-molecule PET probes for apoptosis is the focus of this review.

18F-ML-10, a PET Tracer for Apoptosis: First Human Study

Clinical PET of apoptosis may have substantial value in advancing patient care. We report here the first-in-humans study with 18F-labeled 2-(5-fluoropentyl)-2-methyl malonic acid (18F-ML-10), a small-molecule PET tracer for apoptosis. Presented are the dosimetry, biodistribution, stability, and safety profiles of this PET tracer in healthy human volunteers. Also reported is tracer binding to targeted apoptotic cells in testicular tissue, where a relative abundance of apoptotic cells is normally observed. Methods: 18F-ML-10 (233 ± 90 MBq) was intravenously administered to 8 healthy subjects, followed by whole-body PET/CT for 220 min. Serial blood and urine samples were collected for radioactivity measurement, and plasma tracer stability was assessed by high-performance liquid chromatography. Dosimetry calculations were performed using OLINDA/EXM software. Results: 18F-ML-10 manifested high stability in vivo and rapid distribution followed by fast clearance, with an elimination half-life of 1.3 ± 0.1 and 1.1 ± 0.2 h from the blood and from all other organs, respectively, and excretion through the urine. Dosimetry showed an average effective whole-body dose of 15.4 ± 3.7 μSv/MBq, with the urinary bladder being the dose-limiting organ. Selective accumulation and retention of the tracer in the testes was observed in all male subjects, a finding also demonstrated in mice using both small-animal PET and histopathology, confirming binding to apoptotic cells. Administration of 18F-ML-10 was safe, without adverse effects. Conclusion: 18F-ML-10 administered to healthy humans demonstrated a favorable dosimetry, biodistribution, stability, and safety profile. Binding to apoptotic sites was also demonstrated. These data support further development of this small-molecule probe for clinical PET of apoptosis.

ApoSense: a novel technology for functional molecular imaging of cell death in models of acute renal tubular necrosis

PurposeAcute renal tubular necrosis (ATN), a common cause of acute renal failure, is a dynamic, rapidly evolving clinical condition associated with apoptotic and necrotic tubular cell death. Its early identification is critical, but current detection methods relying upon clinical assessment, such as kidney biopsy and functional assays, are insufficient. We have developed a family of small molecule compounds, ApoSense, that is capable, upon systemic administration, of selectively targeting and accumulating within apoptotic/necrotic cells and is suitable for attachment of different markers for clinical imaging. The purpose of this study was to test the applicability of these molecules as a diagnostic imaging agent for the detection of renal tubular cell injury following renal ischemia.MethodsUsing both fluorescent and radiolabeled derivatives of one of the ApoSense compounds, didansyl cystine, we evaluated cell death in three experimental, clinically relevant animal models of ATN: renal ischemia/reperfusion, radiocontrast-induced distal tubular necrosis, and cecal ligature and perforation-induced sepsis.ResultsApoSense showed high sensitivity and specificity in targeting injured renal tubular epithelial cells in vivo in all three models used. Uptake of ApoSense in the ischemic kidney was higher than in the non-ischemic one, and the specificity of ApoSense targeting was demonstrated by its localization to regions of apoptotic/necrotic cell death, detected morphologically and by TUNEL staining.ConclusionApoSense technology should have significant clinical utility for real-time, noninvasive detection of renal parenchymal damage of various types and evaluation of its distribution and magnitude; it may facilitate the assessment of efficacy of therapeutic interventions in a broad spectrum of disease states.