Developmental patterns in the rat cerebellum after cis-dichlorodiammineplatinum treatment

Edaravone alleviates cisplatin-induced neurobehavioral deficits via modulation of oxidative stress and inflammatory mediators in the rat hippocampus

Cisplatin is a chemotherapeutic agent used in the treatment of malignant tumors. A major clinical limitation of cisplatin is its potential toxic effects, including neurotoxicity. Edaravone, a potent free radical scavenger, has been reported to have the neuroprotective effect against neurological deficits. The aim of the present study was to determine the neuroprotective effect of edaravone against cisplatin-induced behavioral and biochemical anomalies in male Wistar rats. Our results showed that cisplatin (5mg/kg/week, i.p.) administration for seven weeks caused marked cognitive deficits and motor incoordination in rats. This was accompanied by oxido-nitrosative stress, neuroinflammation, NF-κB activation and down-regulation of Nrf2/HO-1 gene expression level in the hippocampus. Edaravone (10mg/kg/week, i.p.) treatment for seven weeks inhibited the aforementioned neurobehavioral and neurochemical deficits. Furthermore, edaravone was found to up-regulate the gene expression level of Nrf2/HO-1 and prevented the cisplatin-induced NF-κB activation. These findings demonstrated that oxido-nitrosative stress and inflammatory signaling mediators play a key role in the development of cisplatin-induced neurobehavioral deficits which were prevented by edaravone treatment.

Developing central nervous system and vulnerability to platinum compounds

Comparative studies on the effects of the platinum complexes in use or in clinical trials are carried out in order to discover differences in the neurotoxic potential and the reversibility of neurotoxicity. In this paper, we summarized the current literature on neurotoxicity and chemoresistance of cisplatin (cisPt) and discussed our recent efforts on the interference of cisPt and a new platinum compound [Pt(O,O′-acac)(γ-acac)(DMS)] (PtAcacDMS), with high specific reactivity with sulphur ligands instead of nucleobases as cisPt, on some crucial events of rat postnatal cerebellum development. The acute effects of drug treatments on cell proliferation and death in the external granular layer and granule cell migration and the late effects on the dendrite growth of Purkinje cells were evaluated. Together with the demonstrated antineoplastic effectiveness in vitro, compared with cisPt, data suggest a lower neurotoxicity of PtAcacDMS, in spite of its presence in the brain that involves considerations on the blood brain barrier permeability.

The developmental neurotoxicity study of platinum compounds. Effects of cisplatin versus a novel Pt(II) complex on rat cerebellum

In the field of experimental oncology, many efforts are being carried out to search new platinum-based drugs overcoming the CNS toxicity and drug resistance. One of the adopted strategies is the synthesis of platinum compounds able to form Pt-DNA adducts different from the cisplatin ones or to react with other subcellular targets. In this context a novel Pt(II) complex, [Pt(O,O'-acac)(γ-acac)(DMS)](PtAcacDMS), was synthesized which reacts preferentially with protein thiols or thioethers. In this work we investigated the in vivo effects of cisplatin and PtAcacDMS on normal development. Moreover, to verify the dose-dependence of the effects, different groups of animals were treated with 5 μg/g or 10 μg/g body weight of cisPt and PtAcacDMS. We have focused our attention on the cerebellum because it provides a useful model system to evaluate the outcomes of perinatal treatment with chemotherapeutic agents on key CNS developmental processes such as neural cells proliferation, migration and differentiation. We have demonstrated the ability of both cisPt and PtAcacDMS to reach the brain tissue once injected. The brain platinum content after PtAcacDMS treatment was notably higher (approximately 4-fold as much) than after cisPt. The platinum accumulation in the brain was still considerable 7 days after PtAcacDMS administration. However, compared with cisplatin, PtAcacDMS induces less severe changes on fundamental events of neuroarchitecture development, such as no high apoptotic events, less altered granule cell migration and Purkinje cell dendrite growth, suggesting a low neurotoxicity of this new Pt complex for normal CNS. The mild damages could be attributable to the different subcellular target of this compound as well as to a greater efficiency of the cell repair system to recognize the drug-target adducts and to repair them. Together with the previously demonstrated antineoplastic effectiveness in vitro, the findings here reported suggest PtAcacDMS as a potential alternative to cisplatin indicating, at the same time, that the choice of platinum compounds with new subcellular targets could be a strategy to prevent neurotoxicity induced by cisplatin and overcome drug resistance induced by mutations in the intrinsic apoptotic pathway.

Cell proliferation, apoptosis and mitochondrial damage in rat B50 neuronal cells after cisplatin treatment

OBJECTIVES

Cisplatin (cisPt) is used as a chemotherapeutic agent for the treatment of a variety of human tumours; more recently, it has been demonstrated that tumour cell exposure to cisPt ultimately results in apoptosis, but the mechanism by which nuclear cisPt/DNA generates the cytoplasmic cascade of events involved has not been clarified. We have investigated the effects of cisPt on proliferation in the neuronal cell line B50, with particular attention being given to understand whether mitochondria are a target of cisPt and their involvement in the apoptotic process.

MATERIALS AND METHODS

Rat neuronal B50 cells were used to investigate the mechanisms of cisPt-induced cytotoxicity; this line has been used as a model system for neurotoxicity in vivo.

RESULTS

Changes in proliferation, induction of apoptosis, activation of caspase-3 and DNA fragmentation were observed in the cells, as well as morphological and biochemical alterations of mithocondria. Activation of caspase-9 confirmed that mitochondria are a target of cisPt.

CONCLUSION

CisPt exerts cytotoxic effects in the neuronal B50 cell line via a caspase-dependent pathway with mitochondria being central relay stations.

Autofluorescence properties of rat cerebellum cortex during postnatal development

BACKGROUND AND OBJECTIVES

The multilayered structure of rat neocerebellum cortex (VI-VIII lobules of the vermis) during postnatal development undergoes rearrangements, which in turn are affected by treatment with the anti-tumoral drug cisplatin. The dependence of autofluorescence emission properties on the tissue structural and molecular features has been investigated.

STUDY DESIGN/MATERIALS AND METHODS

Autofluorescence analysis was performed at defined time points of cerebellar histogenesis--11, 17, and 30 postnatal days- under normal conditions or after 5 microg/g body weight cisplatin treatment at 10 postnatal day. Autofluorescence signal was analyzed in vivo at the surface of intact lobules of cerebellum vermis by means of fiber optic spectrofluorometry, or on tissue sections by means of microspectrofluorometry and fluorescence imaging.

RESULTS

In vivo spectroscopy showed changes of autofluorescence signal both during normal histogenesis and after cisplatin treatment. External granular layer (EGL) and molecular layer (ML), that is, the more external layers were found to be interested by structural alterations, and showed the greatest changes in signal amplitude, accounting for the in vivo results. Fitting analysis indicated that changes in spectral shape reflected an increase in oxidative damages induced by cisplatin treatment.

CONCLUSIONS

The results confirm the relationship of the autofluorescence emission properties with histological and biochemical features of biological tissue.

Sonographic maturation of third-trimester cerebellar foliation after birth

The development of cerebellar folia of third-trimester preterms has not been described with ultrasound before. We set out to determine normal development of the pons and cerebellar folia for future measurements of hypoplasia and atrophy. Study sonograms were made in preterms admitted to the neonatal intensive care unit with postmenstrual age (PMA) from 25 wk until term. On a weekly basis, transcranial measurements were made in the axial and coronal planes at the asterion with high-frequency transducers (8.5 and 13 MHz). The axial images showed the pons and fourth ventricle. The coronal images showed cerebellar folia and white matter. In the same coronal plane, the depth of cerebellar fissures at the rostral cerebellar convexity could be observed. A total of 172 cranial sonograms were performed on 98 neonates. The development of folia could be measured with ultrasound through the asterion. We showed that pons area, mean of three fissure depths, hemisphere area, and number of folia in the horizontal fissure correlated significantly with PMA. Hemisphere area described the same trend of growth as the transverse cerebellar diameter used in fetal sonography.

Developmental plasticity of rat cerebellar cortex after cisplatin injury: inhibitory synapses and differentiating Purkinje neurons

A single injection of cisplatin, a cytostatic agent, (5 microg/g body weight) in 10-day old rats leads later to the reorganization of the cerebellar cortex in lobules VI-VIII of the vermis. Double immunofluorescence reaction for glutamate receptor (GluR)2/3, a ionotropic glutamate receptor that labels postsynaptically Purkinje neurons, and glutamic acid decarboxylase (GAD)65, an isoform of the GABA synthesis enzyme that labels presynaptically inhibitory terminals in the molecular layer, were employed. Less-differentiated Purkinje cells were present in rats treated on postnatal day (PD)11 at the top of lobule VI and in lobules VII-VIII, in comparison with the deep zones of the same lobules and lobule III. The changes were interpreted as due to loss of trophic factors of Purkinje cell growth, e.g. signaling molecules and granule cells. However, we have shown that a remodelling of Purkinje cell dendrites occurred on PD30 (20 days after cisplatin). In fact, despite of the GluR2/3 labeling of the entire Purkinje cell dendrites, the GAD65 immunofluorescent terminals were adjacent to the proximal parts of the dendrite, while they were scarce in the distal dendritic branchlets. The findings were discussed in relation to the changed cytoarchitecture of the cerebellar cortex, which from PD17 to PD30 includes regeneration of the external germinal layer, reorientation of the main dendritic branches and of the Purkinje cell branchlets, and the presence of ectopic cells.

Signal molecules and receptors in the differential development of cerebellum lobules. Acute effects of cisplatin on nitric oxide and glutamate systems in Purkinje cell population

Three functionally correlated parameters, nitric oxide (NO), glutamate and NMDA receptors were analyzed through enzymehistochemical and immunohistochemical reactions. A single injection of cisplatin (cisPt) was administered to 10-day-old rats in order to study how Purkinje cells differentiation may be early changed by a mild injury due to the drug during postnatal cerebellar histogenesis. In comparison with age-matched control rats, a correlated decreasing expression of nitric oxide synthase (NOS), glutamate and NMDAR1 was observed in the Purkinje cells of lobules VI-VIII 6 h after the treatment. Moreover, at 24 h after cisPt, the expression of glutamate, NMDAR1 and nicotinamide adenine dinucleotide phosphate-diaphorase (NADPHd) reactivity was further decreased. In the same period, the ionotropic receptor GluR2 evidenced a less developed dendrite of Purkinje neurons in the top of lobules. In addition, the metabotropic receptor mGluR1alpha revealed unstained areas in the molecular layer, which was entirely stained in control rats; on PD11 this altered pattern was observed in all the lobules and in both the outer and the inner parts. Findings show the importance of NO-glutamate interactions via NMDAR1 in the crucial phases of Purkinje cells differentiation and their involvement on Purkinje neurons dendrite branching as demonstrated by the patterns of the other glutamate receptors. Changes were discussed in relation to an important critical event of Purkinje cell differentiation, i.e. regression of perisomatic spines and elimination of climbing fiber synapses on the somata. Finally, lobules VI-VIII appear to be the most vulnerable ones when cisplatin treatment is administered at 10 days of life, which demonstrates that at this stage some critical developmental changes occur in these lobules and that slower/damaged dendritic tree development is different in the outer versus the inner regions of the lobules.

Glial cell reaction to cis-dichlorodiammine platinum treatment in the immature rat cerebellum

In this study we have investigated changes in glial cells of the cerebellum of cis-dichlorodiammine platinum (cisDDP)-treated rats. The expression of S-100 protein and glial fibrillary acidic protein (GFAP), taken as markers of glial cell function, was evaluated using immunocytochemical methods. In parallel, immunoreactivity for calbindin, parvalbumin, and phosphorylated 200-kDa neurofilament protein was observed in Purkinje cells as markers for neuronal integrity and activity. Results showed that, although no difference in the immunostaining of S-100 protein between control and treated animals could be observed, an increase in the frequency of GFAP immunoreactive cells was present in cisDDP-treated rats. In Purkinje cells, immunocytochemical expression of calbindin and parvalbumin was decreased after drug treatment. In addition, following immunoreaction for phosphorylated 200-kDa neurofilament protein, the somata of Purkinje cells, which were negative in control animals, were stained in treated rats. These findings suggest that cisDDP does not significantly interfere with pathways of glial cell activity and that the increased number of GFAP positive astrocytes may be due to an activation of glial cells consequent upon neuronal death.

A re-evaluation of the ultrastructural localization of 5'-nucleotidase activity in the developing rat cerebellum, with a cerium-based method

The membrane ectoenzyme 5'-nucleotidase converts 5'-AMP into adenosine which, in the nervous tissue, plays an important role as intercellular messenger. Moreover, during histogenesis, 5'-nucleotidase seems to be related to cell proliferation and migration. Conflicting data are reported in the literature about the localization (neuronal or glial) of 5'-nucleotides in the rat cerebellum. In the present report we have analyzed the distribution of 5'-nucleotidase activity with electron microscopy, using a cerium-based method, at different postnatal histogenetic stages (postnatal days (PND) 11, 17, 28). On PND 11 and 17, rims of reaction product outlined the plasma membranes of some neuroblasts in the external granular layer and of parallel fibers and some migrating cells in the developing molecular layer. Positivity was frequently observed on membranes of adjacent neuronal cells and glial processes. Moderate activity was also present on the membranes of granule cells and of mossy fiber rosettes and granule cell dendrites constituting the cerebellar glomeruli within the internal granule cell layer. At PND 28, the reaction product was slightly reduced in some localizations. Cytochemical patterns prove that the cerium-based method is suitable for demonstration of 5'-nucleotidase-specific activity. In fact, a continuous and fine reaction product appears strictly linked to the cell membranes, and no unevenly scattered precipitates can be observed. Data suggest that, during cerebellar histogenesis, 5'-nucleotidase may be involved in the mechanisms of cell migration and proliferation. However, in adulthood, prominent localization of the reaction product on neuronal elements suggests a major role in neuromodulation processes for the enzyme.

Cis-dichlorodiammineplatinum alters GABAergic structures in the immature rat cerebellum

It has been reported that injection of the antitumoral drug cis-dichlorodiammineplatinum at 10 days of life affects cerebellar development in rats. After a single dose of 5 micrograms/g of body weight, the formation of granule cells is decreased and the maturation of postmitotic neurons is slowed down. A substantial time after treatment, reduced cell packing density of the internal granule layer and atrophy of the molecular layer can be observed. In addition, there is degeneration of some Purkinje cells and Golgi neurons. In spite of all these alterations, the regular architecture of the cerebellar folia is retained in many places. In the present study, we used immunocytochemistry with an immune serum raised against glutamic acid decarboxylase to further characterize the cis-dichlorodiammineplatinum-induced alterations of GABAergic neurons. The aim was to examine cerebellar development and to test for factors controlling the settling of GABAergic circuits. At all post-treatment intervals, most of the Purkinje and Golgi neurons and molecular layer interneurons showed stronger anti-glutamic acid decarboxylase immunoreactivity than in controls; this may have been due to altered fixation because of cis-dichlorodiammineplatinum-induced damages to the blood vessels; but could also reflect cellular retention of the enzyme, maybe due to cis-dichlorodiammineplatinum-induced damage of the microtubular apparatus. After seven days, large roundish immunoreactive varicosities were present in the molecular layer adjacent to the Purkinje cell dendritic poles. These varicosities, which were not observed in control animals, may be terminals of Purkinje cell axon recurrent collaterals contributing to the supraganglionic plexus, whose abnormal development would compensate for the reduced inhibitory inputs from inhibitory interneurons and/or Purkinje cells, which degenerated at early post-treatment intervals. At later post-treatment intervals (15 and 21 days), there were also alterations in the pericellular basket at the Purkinje cell axon hillock, which was poorly developed in or absent from the majority of cells. The finding was confirmed by morphological observation of basket cells in Golgi-Cox preparation and immunocytochemistry with an antibody raised against 200,000 mol. wt phosphorylated neurofilaments. It is concluded that early changes in anti-glutamic acid decarboxylase immunoreactivity of neurons may be due to a direct interference of the drug with the cellular metabolic pathways. The late anomalies in the anti-glutamic acid decarboxylase immunoreactivity appear to be secondary to changes in the tissue cytoarchitecture rather than being primary cis-dichlorodiammineplatinum-induced lesions of the cells.

Permanent alterations of the dendritic tree of cerebellar Purkinje neurons in the rat following postnatal exposure to cis-dichlorodiammineplatinum

The aim of this study was to characterize further the effect of cis-dichlorodiammineplatinum (cisDDP) on cerebellar Purkinje neurons of the immature rat. Ten-day-old rats were treated with cisDDP subcutaneously and killed after 1, 7, 20 or 65 days. The cerebellar vermis was impregnated by the Golgi-Cox method to evaluate the extent of morphological maturation of the Purkinje cell dendritic tree. One day after treatment, the dendritic network of Purkinje cells of treated animals was poorly developed and the cell somata still showed numerous perisomatic processes. This indicates that cisDDP interferes with the organization of microtubules and microfilaments by the cell. Later, several abnormal shapes of the Purkinje cell dendritic tree were observed. These included: (1) elongated primary dendrites; (2) asymmetrical dendrites; (3) sprouting of secondary and spiny branches in two planes of the molecular layer; and (4) damming of spiny branchlets at the pial surface. Moreover, all the dendritic networks of Purkinje cells in treated animals were of a lower Strahler order than in controls. All these data suggest that the late anomalies of the dendritic trees are secondary to the general cisDDP-induced damage of the cerebellar cortex, rather than being a primary effect of the drug on the dendritic tree growth.