Avaliação dos efeitos da Pentoxilina em modelo experimental de doença de Parkinson : uma abordagem comportamental, neuroquímica e imunohistoquimica

Abstract

Pentoxifylline (PTX) is a methylxanthine derivative that produces pharmacological effects by mechanisms as phosphodiesterase inhibition, increase in cAMP and cGMP levels and antagonism of A2A adenosine receptors. The drug also shows anti- inflammatory properties, due to the inhibition of TNF-alpha synthesis. The present work studied, by behavioral, neurochemical, histological and immunohistochemical methods, the possible neuroprotective PTX effects in an experimental model of Parkinson’s disease (PD), in vivo (striatal lesion with 6-OHDA in rats) and in vitro (SN-SY5Y cells). For the in vivo study, male Wistar rats (220-250 g) were divided into groups of 9 to 20 animals each, as follows: sham-operated (SO, subjected to a striatal injection of saline); 6-OHDA (subjected to a 6-OHDA injection into the right striatum); and 6-OHDA followed by the daily oral administration of PTX (10, 25 and 50 mg/kg), for two weeks. The results showed that the increased apomorphine-induced rotational behavior, observed in the 6-OHDA group, was greatly reduced in the 6-OHDA+PTX groups, towards the SO values. While the locomotor activity decreased in the 6-OHDA group, this parameter was in part reversed in the 6-OHDA+PTX groups and the same was observed with the rearing behavior. On the other hand, PTX did not seem to interfere significantly with the operational memory, as assessed by the Cued Water Maze test, but reversed the increase in the immobility time (indicative of depression) seen in the untreated 6-OHDA group. Furthermore, we showed that while striatal DA and DOPAC levels were significantly decreased in the lesioned right striatum of the 6- OHDA group, as related to the SO controls, this effect was partly reverted by the high PTX dose. In addition, glutamate (excitatory neurotransmitter) and glycine (inhibitory neurotransmitter) concentrations increased and decreased, respectively, in the untreated 6-OHDA-lesioned group, as related to the SO group. Such alterations were reversed in the lesioned group, after PTX treatments. Histopathological analyses (cresyl violet and fluoro jade B) showed a preservation of the cellular architecture in the lesioned groups, after PTX treatments, as related to the untreated lesioned group. Besides, the immunoreactivities for tyrosine hydroxylase (TH, limiting step in the catecholamine synthesis) and dopamine transporter (DAT) were significantly reduced in the striatal right side (lesioned) of the untreated 6-OHDA group, as related to the striatal right sides of the 6-OHDA-PTX-treated groups. Similar results were observed for DAT. As far as immunohistochemistry data are concerned, we showed that, while the immunoreactivity for GFAP (astrocyte marker) was reduced in the mesencephalic tissue of the lesioned group after PTX treatments, as related to the untreated lesioned group, the same effect occurred with the immunoreactivity for OX-42 (microglia marker) in the striatum. Furthermore, the increase in the number of immunopositive cells for TNF-alpha (a pro- inflammatory cytokine) in the right lesioned striatum was attenuated, after PTX treatments. Similar results were seen in the CA1 and CA3 hippocampal areas, suggesting that PTX is possibly a neuroprotective drug and that this action is, at least in part, due to its TNF-alpha inhibitory activity. These results were supported by anti- COX-2 and anti-iNOS effects on the hippocampus and striatum of the lesioned group, after PTX treatments. Additionally, in SH-SY5Y cells (an in vitro model of PD), PTX also presented cytoprotective, anti-inflammatory and antioxidant effects. In conclusion, our results showed that the potential neuroprotective effects of PTX are a consequence of its anti-inflammatory activity and beneficial action on the dopaminergic, glutamatergic and glycinergic systems. Thus, our data suggest that PTX is a potential drug to be included into clinics, as a new therapeutic strategy for PD treatment.