Probucol affords neuroprotection in a 6-OHDA mouse model of Parkinson's disease.

Parkinson's disease (PD) is a neurodegenerative disorder characterized by the degeneration of dopaminergic nigrostriatal neurons. Although the etiology of the majority of human PD cases is unknown, experimental evidence points to oxidative stress as an early and causal event. Probucol is a lipid-lowering phenolic compound with anti-inflammatory and antioxidant properties that has been recently reported as protective in neurotoxicity and neurodegeneration models. This study was designed to investigate the effects of probucol on the vulnerability of striatal dopaminergic neurons to oxidative stress in a PD in vivo model. Swiss mice were treated with probucol during 21 days (11.8 mg/kg; oral route). Two weeks after the beginning of treatment, mice received a single intracerebroventricular (i.c.v.) infusion of 6-hydroxydopamine (6-OHDA). On the 21st day, locomotor performance, striatal oxidative stress-related parameters, and striatal tyrosine hydroxylase and synaptophysin levels, were measured as outcomes of toxicity. 6-OHDA-infused mice showed hyperlocomotion and a significant decrease in striatal tyrosine hydroxylase (TH) and synaptophysin levels. In addition, 6-OHDA-infused mice showed reduced superoxide dismutase activity and increased lipid peroxidation and catalase activity in the striatum. Notably, probucol protected against 6-OHDA-induced hyperlocomotion and striatal lipid peroxidation, catalase upregulation and decrease of TH levels. Overall, the present results show that probucol protects against 6-OHDA-induced toxicity in mice. These findings may render probucol as a promising molecule for further pharmacological studies on the search for disease-modifying treatment in PD.

Decreased forelimb ability in mice intracerebroventricularly injected with low dose 6-hydroxidopamine: A model on the dissociation of bradykinesia from hypokinesia.

Bradykinesia and hypokinesia represent well-known motor symptoms of Parkinson's disease (PD). While bradykinesia (slow execution of movements) is present in less affected PD patients and aggravates as the disease severity increases, hypokinesia (reduction of movement) seems to emerge prominently only in the more affected patients. Here we developed a model based on the central infusion of low dose (40µg) 6-hydroxydopamine (6-OHDA) in mice in an attempt to discriminate bradykinesia (accessed through forelimb inability) from hypokinesia (accessed through locomotor and exploratory activities). The potential beneficial effects of succinobucol against 6-OHDA-induced forelimb inability were also evaluated. One week after the beginning of treatment with succinobucol (i.p. injections, 10mg/kg/day), mice received a single i.c.v. infusion of 6-OHDA (40µg/site). One week after 6-OHDA infusion, general locomotor/exploratory activities (open field test), muscle strength (grid test), forelimb skill (single pellet task), as well as striatal biochemical parameters related to oxidative stress and cellular homeostasis (glutathione peroxidase, glutathione reductase and NADH dehydrogenases activities, lipid peroxidation and TH levels), were evaluated. 6-OHDA infusions did not change locomotor/exploratory activities and muscle strength, as well as the evaluated striatal biochemical parameters. However, 6-OHDA infusions caused significant reductions (50%) in the single pellet reaching task performance, which detects forelimb skill inability and can be used to experimentally identify bradykinesia. Succinobucol partially protected against 6-OHDA-induced forelimb inability. The decreased forelimb ability with no changes in locomotor/exploratory behavior indicates that our 6-OHDA-based protocol represents a useful tool to mechanistically study the dissociation of bradykinesia and hypokinesia in PD.

Effects of K074 and pralidoxime on antioxidant and acetylcholinesterase response in malathion-poisoned mice.

The organophosphorus (OP) pesticide malathion is a highly neurotoxic compound and its toxicity is primarily caused by the inhibition of acetylcholinesterase (AChE), leading to cholinergic syndrome. Although oximes have been used as potential antidotal treatments in malathion poisoning because of their potential capability to reactivate the inhibited enzyme, the clinical experience with the clinically available oximes (e.g. pralidoxime) is disappointing and their routine use has been questioned. In the present study, we investigated the potency of pralidoxime and K074 in reactivating AChE after acute exposure to malathion, as well as in preventing malathion-induced changes in oxidative-stress related parameters in mice. Malathion (1.25 g/kg, s.c.) induced a significant decrease in cortico-cerebral, hippocampal and blood AChE activities at 24h after exposure. Oxime treatments (1/4 of LD(50), i.m., 6h after malathion poisoning) showed that pralidoxime significantly reversed malathion-induced blood AChE inhibition, although no significant effects were observed after K074 treatment. Interestingly, both oximes tested were unable to reactivate the cortico-cerebral and hippocampal enzymes after intramuscular or intracerebroventricular injection (1/4 of LD(50), 6h after malathion poisoning). Biochemical parameters related to oxidative stress (cerebro-cortical and hippocampal glutathione peroxidase, glutathione reductase and catalase activities, as well as lipid peroxidation) were not affected in animals treated with malathion, oximes or atropine alone. However, pralidoxime and K074, administered intramuscularly 6h after malathion poisoning, were able to increase the endogenous activities of these antioxidant enzymes in the prefrontal cortex and hippocampus. Taken together, the results presented herein showed that pralidoxime (the most common clinically used oxime) and the recently developed oxime K074, administered 6h after malathion poisoning, were unable to reactivate the inhibited AChE in mouse prefrontal cortex and hippocampus. However, only pralidoxime significantly reversed the blood AChE inhibition induced by malathion poisoning. This indicates that peripheral and central AChE activities are not necessarily correlated after the treatment of OP compounds and/or oximes, which should be taken into account in the diagnosis and management of OP-exposed humans. In addition, considering that the available treatments to malathion poisoning appear to be ineffective, the present study reinforce the need to search for potential new AChE reactivators able to efficiently reactivate the brain and blood AChEs after malathion poisoning.