Alberta Samuele

Modifications of apoptosis-related protein levels in lymphocytes of patients with Parkinson’s disease. The effect of dopaminergic treatment

Summary.In this study, we investigated whether changes in the regulatory mechanisms of apoptosis and oxidative stress may be detected, peripherally, in patients with Parkinson’s disease (PD). For this purpose, we measured caspase-3 activity, Bcl-2 concentrations, peripheral benzodiazepine receptor (PBR) expression and Cu/Zn superoxide dismutase (SOD) concentrations in lymphocytes of untreated PD patients, patients treated only with L-Dopa or with L-Dopa and dopamine agonists and healthy volunteers. Caspase-3 activity was significantly increased in all PD patient groups. Patients treated with L-Dopa and dopamine agonists showed the lowest values of Bcl-2, coupled with the highest density of PBRs, while increased levels of Cu/Zn SOD were found in the group under monotherapy with L-Dopa. We also found, in PD patients, clear, negative correlations between Bcl-2 levels and both duration and severity of the disease. Our findings point to the existence of changes in the regulatory mechanisms of apoptosis in PD patients – observable outside the central nervous system – which seem to be modulated by the pharmacological treatment with dopaminergic agents.

Brain monoaminergic neurotransmission parameters in weanling rats after perinatal exposure to methylmercury and 2,2′,4,4′,5,5′-hexachlorobiphenyl (PCB153)

The individual and joint effects of methylmercury (MeHg; 1 mg/kg body weight/day, GD7-PND7) and PCB153 (20 mg/kg body weight/day, GD10-GD16), administered orally to rat dams, were explored in 21-day-old rat offspring brain in terms of monoamine oxidase B (MAO-B) activity and regional content of dopamine (DA), serotonin (5-HT), 5-hydroxy-indole-3-acetic acid (5-HIAA) and homovanillic acid (HVA). Neither treatment altered MAO-B in striatum, hippocampus, cerebellum and cerebral cortex of female pups. In males the cerebellum displayed a significantly reduced enzyme activity (25-45%) following all treatments. Concerning biogenic amines, 5-HT levels were decreased by 30-50% in the cerebral cortex of males and females by PCB153 alone and combined with MeHg, without changes in 5-HIAA and dopaminergic endpoints. In cerebellum of all pups, MeHg enhanced 5-HIAA levels, whereas PCB153, either alone or combined with MeHg, did not affect this endpoint. In striatum, PCB153 reduced the content of DA, HVA and 5-HIAA (respective control values: 2-3; 60-80; 8-10 ng/mg protein) to a similar extent when administered alone or together with MeHg (20-40%). Perinatal exposure to MeHg and/or PCB153 results in regionally and/or gender-specific alterations in the central dopaminergic and serotonergic systems at weaning. The combined treatment with MeHg and PCB153 does not exacerbate the neurochemical effects of the individual compounds.

Modifications of plasma and platelet levels of L-DOPA and its direct metabolites during treatment with tolcapone or entacapone in patients with Parkinson's disease.

Summary. We compared – retrospectively – the effects of a 3-month therapy with catechol-O-methyltransferase (COMT) inhibitors tolcapone (100 mg, t.i.d.) and entacapone (200 mg, t.i.d.), on L-DOPA metabolism in two groups of parkinsonian patients with motor fluctuations. Plasma and platelets concentrations of L-DOPA and its direct metabolites, dopamine and 3-O-methyldopa (3-OMD), were measured before starting treatment, after two weeks and at the end of treatment. Patients treated with tolcapone showed significant increases in plasma and platelet L-DOPA levels and marked reduction of plasma and platelet 3-OMD levels, both at short- and long-term. Entacapone did not modify L-DOPA levels, while inducing a less marked reduction of plasma and platelet 3-OMD concentrations, with respect to tolcapone, at both time points. Both drugs were similarly effective in increasing plasma and platelet levels of dopamine. These results confirm the different profiles of activity of the two drugs, with tolcapone proving more effective on both the intra- and extra-cellular levels of L-DOPA and 3-OMD.

Effects of dopaminergic stimulation on peripheral markers of apoptosis: Relevance to Parkinson's disease

Abstract.We investigated the effects of dopaminergic stimulation on anti-apoptotic protein Bcl-2, pro-apoptotic enzyme caspase- 3, and anti-oxidant/anti-apoptotic enzyme Cu/Zn superoxide dismutase (SOD) in human lymphocytes exposed to dopamine (DA). The same determinations were also carried out in parkinsonian patients treated with L-dopa. Caspase-3 activity and Cu/Zn SOD levels tended to increase when lymphocytes were exposed to low or intermediate doses of DA, while a decrease was observed, particularly in caspase-3 activity, with the higher DA dose. Bcl-2 levels were unaffected. In patients, we observed a negative correlation between Cu/Zn SOD levels and daily intake of L-dopa, which also tended to be negatively correlated with caspase-3 activity, but not with Bcl- 2. Our results show that dopaminergic stimulation is associated with complex changes in regulatory proteins of apoptosis.

Proteasomal inhibition and apoptosis regulatory changes in human isolated lymphocytes: The synergistic role of dopamine

Abnormal deposition of protein aggregates and increased susceptibility to apoptotic cell death may result from defects in the activity of the ubiquitin‐proteasome system (UPS); neurotoxicity related to UPS defects seems to require dopamine to be fully expressed. The aim of this study was to investigate the pro‐apoptotic effects caused by proteasomal activity inhibition, as well as the synergistic effect of dopaminergic stimulation in human lymphocytes isolated from healthy volunteers. Cells were incubated 20 h at 37°C, with: (1) lactacystin, (2) increasing concentrations of dopamine or (3) mixture of dopamine and lactacystin. Activities of proteasome 20S and pro‐apoptotic caspases‐3 and ‐9 and levels of anti‐apoptotic Bcl‐2 were measured with fluorimetric or immunochemical assays, while a “DNA diffusion” assay was used to determine the apoptosis. Incubation of lymphocytes with lactacystin, which caused reduction of proteasomal activity, was associated with activation of caspases. A clear, dose‐dependent reduction of proteasomal activity was also seen in the presence of increasing doses of dopamine, which was accompanied by a slight dose‐dependent increase of caspases activities and Bcl‐2 levels. Both effects on proteasome and caspase activities were enhanced when cells were simultaneously exposed to lactacystin and elevated concentrations of dopamine. Apoptosis was detected in all treated samples, but not in controls, without significant differences among the treatment groups; however, the association of dopamine and lactacystin induced a clear reduction in the number of cells being analyzed, pointing to marked cytotoxicity. Our data confirm the potentiation of cytotoxicity related to proteasome inhibition, in the presence of dopaminergic stimulation. J. Cell. Biochem. 103: 877–885, 2008.