pH-Responsive Redox Nanoparticles Protect SH-SY5Y Cells at Lowered pH in a Cellular Model of Parkinson's Disease.

The damage to SH-SY5Y cells by 6-hydroxydopamine (6-OHDA) is an established cellular model of Parkinson's disease (PD). Redox nanoparticles are a promising tool for therapy, including neurodegenerative diseases. As pH of the brain tissue at sites affected by PD is lowered down to 6.5, we studied the effect of pH-responsive redox nanoparticles (poly(ethylene glycol)-b-poly[4-(2,2,6,6-tetramethylpiperidine-1-oxyl)aminomethylstyrene]), which change their structure in a pH-dependent manner and become active below pH 7 (NRNPs pH), on the viability of SH-SY5Y cells treated with 6-OHDA at pH 6.5 and 7.4. Pretreatment of the cells with NRNPs pH (15-75 µM) prior to the 6-OHDA treatment increased their survival in a concentration-dependent manner at pH 6.5, but not at pH 7.4. Among several parameters studied (ATP and GSH content, the level of reactive oxygen species, mitochondrial potential, mitochondrial mass), only the mitochondrial mass was dose-dependently protected by NRNPs pH at pH 6.5, but not at pH 7.4. These results indicate that the action of NRNPs pH on mitochondria underlies their protective effect in this cellular model of PD. These results may have potential importance for future applications of NRNPs pH in preclinical and perhaps clinical studies.

El modelo de 6-hidroxidopamina y la fisiopatología parkinsoniana: nuevos hallazgos en un viejo modelo / The 6-hydroxydopamine model and parkinsonian pathophysiology: Novel findings in an older model

El neurotóxico 6-hidroxidopamina (6-OHDA) ha sido utilizado para generar modelos de la enfermedad de Parkinson (EP). A la fecha se ha establecido que si bien el modelo neurodegenerativo inducido por la 6-OHDA no reproduce la totalidad de síntomas de la enfermedad, sí replica procesos celulares tales como el estrés oxidativo, la neurodegeneración, la neuroinflamación y la muerte neuronal por apoptosis. En esta revisión se contempla el análisis de los factores que influyen en la vulnerabilidad de las neuronas dopaminérgicas, así como la estrecha relación entre el proceso neurodegenerativo, el neuroinflamatorio y la apoptosis ocasionada por la 6-OHDA. El conocimiento de los mecanismos involucrados en la neurodegeneración y la muerte celular en este modelo es relevante para definir posibles blancos terapéuticos para EP (AU)

The neurotoxin 6-hydroxydopamine (6-OHDA) is widely used to induce models of Parkinson's disease (PD). We now know that the model induced by 6-OHDA does not include all PD symptoms, although it does reproduce the main cellular processes involved in PD, such as oxidative stress, neurodegeneration, neuroinflammation, and neuronal death by apoptosis. In this review we analyse the factors affecting the vulnerability of dopaminergic neurons as well as the close relationships between neuroinflammation, neurodegeneration, and apoptosis in the 6-OHDA model. Knowledge of the mechanisms involved in neurodegeneration and cell death in this model is the key to identifying potential therapeutic targets for PD (AU)

Asimetría cerebral y dopamina: más allá de las implicaciones motoras en la enfermedad de Parkinson y hemiparkinsonismo experimental / Brain asymmetry and dopamine: beyond motor implications in Parkinson’s disease and experimental hemiparkinsonism

Introducción. La asimetría cerebral se puede definir como la existencia de diferencias funcionales, anatómicas o neuroquímicas entre los dos hemisferios cerebrales. Se trata de un fenómeno dinámico modulable por factores endógenos y exógenos. Su significado funcional está apenas aclarado y sólo lo está en algunos casos muy concretos como, por ejemplo, la relación existente entre el contenido cerebral lateralizado de dopamina y sus efectos motores, que se manifiesta especialmente en la enfermedad de Parkinson. Desarrollo. El contenido asimétrico cerebral de dopamina no sólo da lugar a efectos motores lateralizados, sino que se extiende a consecuencias autonómicas y de conducta igualmente lateralizadas. De hecho, la enfermedad de Parkinson se caracteriza por síntomas motores unilaterales, que surgen en las fases iniciales de la enfermedad, y por otros síntomas no motores, como alteraciones autonómicas o cognitivas, que también se manifiestan de forma lateralizada. Conclusiones. La asimetría cerebral ha sido un aspecto infravalorado a la hora de analizar la patogenia de las enfermedades cerebrales, y sólo en determinados casos, como en la enfermedad de Parkinson, se ha profundizado parcialmente en su estudio. Sin embargo, se ha puesto en evidencia que es necesario considerar este fenómeno para la adecuada comprensión de algunas patologías cerebrales, como es el caso de la enfermedad de Parkinson (AU)

Introduction. Brain asymmetry could be defined as the existence of functional, anatomic or neurochemical differences between both hemispheres. It is a dynamic phenomenon, regulated by endogenous and exogenous factors. Its functional significance is poorly clarified and is only partially understood in very specific cases such as the relationship between the lateralized brain content of dopamine and its motor effects which is specially patent in Parkinson’s disease. Development. The asymmetric brain content of dopamine not only displays lateralized motor effects but also behavioral and autonomic asymmetric consequences. In fact, Parkinson’s disease is characterized not only by unilateral motor symptoms that arise at the early stages, but has other non-motor symptoms such as autonomic or cognitive alterations that are also revealed asymmetrically. Conclusions. Brain asymmetry has been underestimated when analyzing the pathogeny of brain diseases and it has been partially studied only in some specific cases, such as Parkinson’s disease. However, in order to appropriately understand some brain diseases such as Parkinson’s disease, the need to consider this phenomenon has been highlighted (AU)

Increased melatonin may play dual roles in the striata of a 6-hydroxydopamine model of Parkinson's disease.

AIMS: To investigate dynamic changes and roles of melatonin (MLT) in the striata of 6-hydroxydopamine (6-OHDA)-treated rats. MAIN METHODS: A Parkinson's disease (PD) rat was established by a unilateral injection of 6-OHDA into the right substantia nigra pars compacta (SNc) and the right medial forebrain bundle (MFB) to achieve a complete lesion of the ipsilateral nigrostriatal DA system. Dialysates were collected in the lesioned striatum at different time intervals by in vivo microdialysis. In addition, both contralateral and ipsilateral striatum tissues were collected at two time intervals (10:00 and 22:00 h) at 3 and 6 weeks after lesioning. The levels of DA, 3, 4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in the dialysates, as well as MLT in the dialysates and tissues were determined using HPLC. KEY FINDINGS: The dialysate contents of DA, DOPAC and HVA in the lesioned striatum were significantly decreased (P<0.001) in comparison with those in the controls or in the unlesioned side 3 weeks after lesioning while the extracellular level of MLT in the lesioned striatum in these corresponding time intervals distinctly increased when compared with those in the controls (P<0.05). The tissue MLT contents increased in the bilateral striata in different degrees at 6 weeks post-lesion (P<0.05). Moreover, increased MLT levels correlate well with rotations or DA changes in the lesioned striatum. SIGNIFICANCE: These data suggest that 6-OHDA lesion manipulates the MLT secretion pattern. Increased striatal MLT level by a unilateral intracerebral injection of 6-OHDA may play dual roles in the progression of PD in rats.

Evaluación de alteraciones motoras en modelos animales de enfermedad de Parkinson / Evaluation of motor disorder in animal models of parkinson’s disease

El diagnóstico de la enfermedad de Parkinson es básicamente clínico, es decir, se basa en la observaciónde las alteraciones motoras de los pacientes, por este motivo se considera sencillo; sin embargo, sólo un 75% de los diagnósticos realizados clínicamente se confirma en la autopsia. Los modelos animales generados mediante la aplicación sistémica o intracerebral de neurotoxinas como 6-hidroxidopamina (6-OHDA) para ratas o 1-metil-4-fenil-1,2,3,6-tetrahidropiridina(MPTP) para ratones y primates no humanos, induce un daño en el sistema dopaminérgico nigroestriatal. Esto da como resultado una variedad de síntomas motores como acinesia, bradicinesia, rigidez, temblor, alteraciones en la marcha y posturas anormales; por este motivo es un reto evaluar los cambios de los signos parkinsonianos en los modelos animales.Desarrollo. Se revisa la variedad de paradigmas para valorar estos síntomas en los modelos de ratones, ratas y primates no humanos, los cuales se han utilizado para medir las diferencias que se generan con la aplicación de las neurotoxinas y, en algunos casos, las mejorías de los diferentes tratamientos para los síndromes parkinsonianos inducidos. Conclusiones. Se comentanlos resultados generales de estos trabajos y se discuten los factores que influyen en las pruebas, y los potenciales problemas y beneficios que pueden tener los procedimientos experimentales

The diagnosis of Parkinson’s disease is essentially clinical, that is to say, it is based on theobservation of the motor alterations displayed by patients, and for this reason it is considered to be a simple matter. Yet, only 75% of the diagnoses that are carried out clinically are later confirmed in the autopsy. Animal models can be generated bysystemic or intracerebral application of neurotoxins, like 6-hydroxydopamine (6-OHDA) for rats or 1-methyl-4-phenyl-1,2, 3,6-tetrahydropyridine (MPTP) for mice and non-human primates, which induce damage in the nigrostriatal dopaminergic system. This gives rise to a variety of motor symptoms such as akinesia, bradykinesia, rigidity, tremor, gait disorders andabnormal postures, which is what makes the evaluation of the changes in the signs of Parkinsonism in animal models such a challenge to researchers today. Development. The paper reviews the variety of paradigms available for evaluating these symptoms in mouse, rat and non-human primate models, which have been used to measure the differences brought about byapplying neurotoxins and, in some cases, the improvements produced by different treatments for the Parkinsonian syndromes that were induced. Conclusions. Both the general findings of these works and the factors that influence the trials are discussed, together with the potential problems and benefits that the experimental procedures may have

Astroglial and microglial reaction after a partial nigrostriatal degeneration induced by the striatal injection of different doses of 6-hydroxydopamine.

Astroglial and microglial activation was analyzed in adult male Wistar rats after a unilateral striatal injection of different doses (8, 4 and 1 micrograms) of 6-hydroxydopamine (6-OHDA). Control animals received the injection of the same volume of the solvent. The rotational behavior was registered by a rotometer 24 and 72 hours, 7, 10, 14 and 22 days after lesion. Following, animals were sacrificed and the tyrosine hydroxylase (TH) positive dopamine cells, the glial fibrillary acidic protein (GFAP) immunolabeled astrocytes and the OX42 immunoreactive microglia were visualized by mean of immunohistochemistry and quantified by stereologic method employing the optical disector and the point intercepts. The apomorphine (0.5 mg/kg)-induced circling behavior was seen only after 8 micrograms of 6-OHDA from 72 hours postlesion until sacrifice. Decreases of the TH immunoreactive terminals and cell bodies were found in the sampled fields of the striatum and pars compacta of the substantia nigra (SNc), respectively, after 8 and 4 micrograms of 6-OHDA. The GFAP immunohistochemistry revealed increases in the number/density of astroglial cells in the ipsilateral neostriatum (137% of control) and ipsilateral SNc (83% of control) and also in the volumeal fraction of the astroglial processes in the ipsilateral neostriatum (30% of control) and ipsilateral SNc (38% of control) in the rats with higher dose of the neurotoxin. Increases in the number of OX42 microglial labeled profiles and in the volumeal fraction of microglial processes were found in the ipsilateral neostriatum (67% and 27%, respectively, of control) and ipsilateral SNc (100% and 50%, respectively, of control) in the 8 micrograms 6-OHDA injected rats. These results suggest that the retrograde degeneration induced by a intrastriatal injection of a small dose of the 6-OHDA leads to an astroglial and microglial reaction in the nigrostriatal dopamine pathway. The interaction between activated glial cells may be involved in the wounding and repair events in the partial lesioned nigrostriatal system as well as in the paracrine responses to surviving dopamine neurons.

Complexities in the neurotoxic actions of 6-hydroxydopamine in relation to the cytoprotective properties of taurine.

The neurotoxin 6-hydroxydopamine was shown to cause an imbalance between the direct and indirect pathways of the striato-nigral system as evidenced by a decreased release of gamma-aminobutyric acid and taurine in the substantia nigra but not in the globus pallidus following neostriatal stimulation with kainate (100 microM). The neurotoxicity of 6-hydroxydopamine is generally believed to result from reactive-oxygen radical formation, although it is also known to inhibit mitochondrial NADH dehydrogenase. The release of Fe(II) from the unactivated form [3Fe(III)-4S] of cytoplasmic aconitase (EC(50) < 8 microM) was shown to be followed by the slower oxidation of thiol groups in the protein. Complete loss of -SH groups, and enzyme activity, was seen after incubation of glyceraldenyde-3-phosphate dehydrogenase with 200 microM 6-hydroxydopamine for 75 min at 37 degrees C (IC(50) = 70.8 +/- 0.3 microM). Thus the cellular effects of 6-hydroxydopamine are complex, involving impairment of mitochondrial function, iron- release, sulphydryl-group oxidation, and enzyme inhibition in addition to direct generation of reactive oxygen radicals. Taurine, which is known to be neuroprotective in some other systems, only affords protection against some of these effects, thereby explaining its reported ineffectiveness against 6-hydroxydopamine toxicity.

[Transplantation of fetal dopaminergic cells simultaneously to the corpus striatum and pars reticularis of the substantia nigra in hemi-parkinsonian rats]. / Trasplante de células dopaminérgicas fetales simultáneamente en striatum y substantia nigra pars reticulata en ratas hemiparkinsonianas.

INTRODUCTION: Transplantation of foetal dopaminergic cells has been extensively used as restorative treatment for Parkinson's disease. OBJECTIVE: This study was carried out to determine the survival, modifications in rotatory activity induced by D-amphetamine and total content of dopamine in the striatal and nigra regions of hemiparkinsonian rats which had had foetal mesencephalic cells simultaneously transplanted to the striatum and pars reticularis of the substancia nigra. MATERIAL AND METHODS: The study was done using adult male Wistar rats weighing 200-250 gms. The following experimental groups were formed, depending on the site of transplant: St: transplant to striatum (n = 2); SNr: transplant to SNr (n = 20), ST + Snr; transplant to striatum and SNr simultaneously n = 20; and control (lesion with no transplant) n = 20. We studied the rotatory activity induced by D-amphetamine 1, 2, 3 and 6 months after transplantation. After this time the rats were deeply anaesthetized and randomly allocated for morphological study or biochemical determination of the total dopamine content in the St and SNr using the HPLC technique. RESULTS: Study of conduct showed no significant differences in rotatory activity induced by D-amphetamine between the groups with intrastriatal transplants, but there was a difference between these and the SNr and control groups. Biochemical analysis showed that striatal DA content was significantly greater in the ST for the groups with intrastriatal transplants. The content of substancia nigra DA was significantly greater in the SNr of the ST + SNr group, followed by the ST group. Morphometric study showed differences, which were not significant, between ST transplanted animals and significant differences between the SNr transplanted group with a significant increase in survival of the SNr of the ST + SNr group. CONCLUSIONS: These results suggest a positive effect due to intrastriatal transplants compared to survival following intranigral transplants.

Neonatal 6-OHDA lesions and rearing in complex environments: regional effects on adult brain 14C-2-deoxyglucose uptake revealed by exposure to novel stimulation.

Behavioral and neuromorphological data have suggested at least a partial interaction between the effects of norepinephrine-depleting neonatal 6-OHDA lesions and the effects of rearing in enriched environments. The present study examined the impact of both of these early manipulations upon regional brain uptake of 14C-2-deoxyglucose (14C-2DG) in adulthood. Newborn rats received 6-OHDA (50 mg/kg s.c.) or vehicle and, after weaning at 25 days, were reared in isolated versus enriched conditions. Regional brain 14C-2DG uptake was then examined at 70-80 days of age--either in the home cage or while animals were being exposed to novel, presumably arousing, stimulation. Ninety-seven brain regions were examined in eight separate groups. Results indicated that (1) Under baseline conditions, neither neonatal 6-OHDA nor differential rearing conditions produced widespread alterations in regional brain 14C-2DG uptake profiles. An overall enrichment effect was seen on only five brain areas, with rats reared in enriched environments showing lower levels of 14C-2DG uptake (-20% to -30%) than isolated rats. Neonatal 6-OHDA produced no main effect on 14C-2DG uptake in any brain region. (2) In contrast, when 14C-2DG uptake was assessed during exposure to a novel environment, five brain areas showed differential 14C-2DG uptake in 6-OHDA-treated rats, and 20 brain areas showed differential uptake in rats reared in enriched conditions. (3) No significant interaction effect on brain regional 14C-2DG uptake was observed between neonatal 6-OHDA and environmental complexity factors. These results are consistent with the notion that enduring effects of rearing and early 6-OHDA treatment may, independently, relate to a general reactivity factor. They also indicate that some effects of early neurochemical injury and subsequent experiential factors may not be apparent under normal resting conditions, but only become evident in the presence of appropriate "activating" stimulation.