Continuous intracerebroventricular infusion of dopamine and dopamine agonists through a totally implanted drug delivery system in animal models of Parkinson's disease

Pathophysiological Mechanisms and Experimental Pharmacotherapy for L-Dopa-Induced Dyskinesia

L-dopa-induced dyskinesia (LID) is the most frequent motor complication associated with chronic L-dopa treatment in Parkinson’s disease (PD). Recent advances in the understanding of the pathophysiological mechanisms underlying LID suggest that abnormalities in multiple neurotransmitter systems, in addition to dopaminergic nigrostriatal denervation and altered dopamine release and reuptake dynamics at the synaptic level, are involved in LID development. Increased knowledge of neurobiological LID substrates has led to the development of several drug candidates to alleviate this motor complication. However, with the exception of amantadine, none of the pharmacological therapies tested in humans have demonstrated clinically relevant beneficial effects. Therefore, LID management is still one of the most challenging problems in the treatment of PD patients. In this review, we first describe the known pathophysiological mechanisms of LID. We then provide an updated report of experimental pharmacotherapies tested in clinical trials of PD patients and drugs currently under study to alleviate LID. Finally, we discuss available pharmacological LID treatment approaches and offer our opinion of possible issues to be clarified and future therapeutic strategies.

Acute Cellular and Functional Changes With a Combinatorial Treatment of Ion Channel Inhibitors Following Spinal Cord Injury

Reducing the extent of secondary degeneration following spinal cord injury (SCI) is necessary to preserve function, but treatment options have thus far been limited. A combination of the ion channel inhibitors Lomerizine (Lom), YM872 and oxATP, to inhibit voltage-gated Ca²⁺ channels, Ca²⁺ permeable AMPA receptors, and purinergic P2X₇ receptors respectively, effectively limits secondary consequences of injury in in vitro and in vivo models of CNS injury. Here, we investigated the efficacy of these inhibitors in a clinically relevant model of SCI. Fischer (F344) rats were subjected to a moderate (150 kD) contusive SCI at thoracic level T10 and assessed at 2 weeks or 10 weeks post-injury. Lom was delivered orally twice daily and YM872 and oxATP were delivered via osmotic mini-pump implanted at the time of SCI until 2 weeks following injury. Open field locomotion analysis revealed that treatment with the three inhibitors in combination improved the rate of functional recovery of the hind limb (compared to controls) as early as 1-day post-injury, with beneficial effects persisting to 14 days post-injury, while all three inhibitors were present. At 2 weeks following combinatorial treatment, the functional improvement was associated with significantly decreased cyst size, increased immunoreactivity of β-III tubulin^+ve axons, myelin basic protein, and reduced lipid peroxidation by-products, and increased CC1^+ve oligodendrocytes and NG2^+ve/PDGFα^+ve oligodendrocyte progenitor cell densities, compared to vehicle-treated SCI animals. The combination of Lom, oxATP, and YM872 shows preclinical promise for control of secondary degeneration following SCI, and further investigation of long-term sustained treatment is warranted.

Continuous cerebroventricular administration of dopamine: A new treatment for severe dyskinesia in Parkinson's disease?

In Parkinson's disease (PD) depletion of dopamine in the nigro-striatal pathway is a main pathological hallmark that requires continuous and focal restoration. Current predominant treatment with intermittent oral administration of its precursor, Levodopa (l-dopa), remains the gold standard but pharmacological drawbacks trigger motor fluctuations and dyskinesia. Continuous intracerebroventricular (i.c.v.) administration of dopamine previously failed as a therapy because of an inability to resolve the accelerated dopamine oxidation and tachyphylaxia. We aim to overcome prior challenges by demonstrating treatment feasibility and efficacy of continuous i.c.v. of dopamine close to the striatum. Dopamine prepared either anaerobically (A-dopamine) or aerobically (O-dopamine) in the presence or absence of a conservator (sodium metabisulfite, SMBS) was assessed upon acute MPTP and chronic 6-OHDA lesioning and compared to peripheral l-dopa treatment. A-dopamine restored motor function and induced a dose dependent increase of nigro-striatal tyrosine hydroxylase positive neurons in mice after 7days of MPTP insult that was not evident with either O-dopamine or l-dopa. In the 6-OHDA rat model, continuous circadian i.c.v. injection of A-dopamine over 30days also improved motor activity without occurrence of tachyphylaxia. This safety profile was highly favorable as A-dopamine did not induce dyskinesia or behavioral sensitization as observed with peripheral l-dopa treatment. Indicative of a new therapeutic strategy for patients suffering from l-dopa related complications with dyskinesia, continuous i.c.v. of A-dopamine has greater efficacy in mediating motor impairment over a large therapeutic index without inducing dyskinesia and tachyphylaxia.

Novel intrathecal and subcutaneous catheter delivery systems in the mouse

BACKGROUND

Catheter systems that permit targeted delivery of genes, molecules, ligands, and other agents represent an investigative tool critical to the development of clinically relevant animal models that facilitate the study of neurological health and disease. The development of new sustained catheter delivery systems to spinal and peripheral sites will reduce the need for repeated injections, while ensuring constant levels of drug in plasma and tissues.

NEW METHOD

Here, we introduce two novel catheter delivery systems in the mouse: the O'Buckley intrathecal catheter system for sustained delivery to the spinal region and a subcutaneous bifurcated catheter system for sustained drug delivery to both hindpaws.

RESULTS

The O'Buckley intrathecal catheter system consistently distributed Evans Blue throughout the spinal cord, with the greatest concentration at the thoracic region, and with an 85% surgery success rate. The subcutaneous catheter system consistently distributed Evans Blue to the hindlimbs, with a 100% surgery success rate.

COMPARISON TO EXISTING METHOD

The O'Buckley intrathecal catheter system accomplishes sustained drug delivery to the spinal region, with a 2-fold increase in surgery success rate, as compared to the traditional method. Our subcutaneous bifurcated catheter system accomplishes sustained drug delivery to both hindpaws, eliminating the need for repeated intraplantar injections.

CONCLUSIONS

We have developed catheter systems that improve upon traditional methods in order to achieve sustained localized drug delivery to spinal tissues and to hindpaw tissues surrounding peripheral sciatic nerve terminals. These methods have a broad reach, and can be used to enhance behavioral, physiologic and mechanistic studies in mice.

Local perfusion of diazepam attenuates interictal and ictal events in the bicuculline model of epilepsy in rats

PURPOSE

We evaluated the efficacy of local perfusion of diazepam (DZP) in suppression of EEG spikes and behavioral seizures produced by bicuculline methiodide (BMI) applied to rat sensory motor cortex and hippocampus.

METHODS

Data were obtained from 37 rats implanted with EEG head plugs and perfusion cannulas. BMI 4 mM, 5 microliters was infused on neocortex through the epidural space in 23 rats. BMI 0.1 mM, 2 microliters was infused into the left hippocampus in 14 rats.

RESULTS

DZP 0.75-1.0 mg markedly reduced the spiking to a level of 9.9 +/- 15.8% of baseline for DZP as compared with 90.2 +/- 57.9% of baseline for vehicle-treated rats. DZP reduced spiking in a hippocampal BMI focus to 1.9 +/- 2.4% of baseline spiking, as compared with 98.0 +/- 95.6% of that in vehicle-treated animals. The amount of spread of solution was estimated with methylene blue (MB) injections. Ictal events also were attenuated. In most of the animals, systemic levels of DZP were unmeasurable and injection on the contralateral side did not reduce spiking.

CONCLUSIONS

These findings suggest that focal application of antiepileptic drugs (AEDs) in brain may be a useful new avenue for therapy of intractable partial seizures.

The role of pulsatile versus continuous dopamine receptor stimulation for functional recovery in Parkinson's disease

More effective measures to control and replace the dopaminergic deficit of Parkinson's disease are being actively sought. One basic problem is how the striatal dopamine loss should be replaced in order to mimic most accurately the physiological state. Animal electrophysiology indicates that the dopaminergic nigrostriatal pathway has a dual tonic and phasic action. Intermittent dopaminergic stimulation is associated with behavioural hyposensitivity both in animal models and in patients with Parkinson's disease. Continuous dopaminergic stimulation provides a tonic background and improves some clinical problems but is also associated with tolerance. None of the available pharmacological approaches can restore the dopamine deficiency of Parkinson's disease to physiological levels. Continuous dopaminergic stimulation for < 24 h, associated with small doses of levodopa or a short-acting dopamine agonist, appears to be the best, albeit imperfect, therapeutic approach until other, more efficacious remedies are developed.

External and implanted pumps for apomorphine infusion in parkinsonism

Continuous delivery of dopaminergic agents to the striatum is a major challenge to improve the treatment of Parkinson's disease. Apomorphine is one of the best candidates because of its solubility and its D1 and D2 receptor agonist properties. Seventeen Parkinsonian patients suffering from severe L-dopa-induced on-off effects were treated by continuous subcutaneous (SC) infusion with a portable minipump. Administration of intracerebroventricular (ICV) apomorphine was carried out in 7 macaca fascicularis monkeys using implanted programmable pumps. Four of the monkeys were made Parkinsonian by MPTP injections. In patients receiving apomorphine, the mean duration of daily off periods was reduced by 61%. Psychiatric side effects were rare but SC nodules occurred in all patients and the external infusion method was therefore difficult to implement. In monkeys, the implanted system was well tolerated. ICV apomorphine infusion led to CSF apomorphine concentrations higher than the same apomorphine dose infused i.m. Motor function was considerably improved in two MPTP monkeys during the time of ICV infusion and 30 min after its arrest. Long-term ICV administration could not be carried out because of catheter blockage and/or apomorphine toxicity. SC and ICV apomorphine infusions are efficient for controlling motor activity in Parkinsonism but long-term toxicity remains to be studied further.

The MPTP model: versatile contributions to the treatment of idiopathic Parkinson's disease

In human and subhuman primates, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) produces irreversible clinical, biochemical and neuropathological alterations highly reminiscent of those observed in Parkinson's disease. The MPTP model has provided the best available tool to date for the assessment of efficacy and side-effects of symptomatic treatments of Parkinson's disease. In addition, the mechanism of action of MPTP has offered a basis for the development of novel therapeutic strategies aimed at the prevention of Parkinson's disease.

Intraventricular infusion of Dopamine in Parkinson's disease

A patient with severe end-stage Parkinson's disease and troublesome fluctuations in motor function was treated with a long-term intraventricular infusion of dopamine. There was modest improvement in speech and mentation and there was smoother control of motor symptoms that was superior to that achieved by conventional oral medications.

Function of neurotrophic factors in the adult and aging brain and their possible use in the treatment of neurodegenerative diseases

This review summarizes the current knowledge of characterized neurotrophic factors, including nerve growth factor (NGF) which serves as paradigmatic example when studying novel molecules. Special consideration is given to the function of neurotrophic factors in the adult and aging brain. Strategies are discussed for the eventual development of pharmacological applications of these molecules in the treatment of neurodegenerative diseases.

Biochemical properties of monoamine-rich human neuroblastoma cells

The biochemical, pharmacological and immunological characterization of cells derived from human neuroblastoma tumors recently acquired great interest, since these cells may be a putative donor source for transplantation in animal models of neurological disorders. We measured monoamine levels, tyrosine hydroxylase (TH) immunostaining, and the expression of major histocompatibility cell surface antigens (MHC) in 7 human neuroblastoma cell lines. Three cell lines (LAN5, NB69 and CHP126) had high levels of monoamines. TH immunostaining was strongly positive in CHP126 and LAN5, and NB69. MHC were not detected in any of the cells with high catecholamine levels. Treatment with neuroleptics increased the metabolism of dopamine in LAN5 but not in NB69. The implantation of LAN5 cells in immunocompetent, unilaterally 6-hydroxydopamine-lesioned rats decreased the apomorphine-induced contralateral rotation. The effect of the implant was greatest in animals in which LAN5 neuroblastoma cells, pretreated with dibutyryl cyclic adenosine monophosphate (DBcAMP) and prostaglandin E1 (PGE1, were implanted into the cerebral ventricle ipsilateral to the lesion, and then irrigated with DBcAMP administered through a totally implanted drug delivery system. The effect of the implant decreased after the second week. Neuroblastoma cells were found in approximately 50% of the implanted animals. TH immunostaining was weak or absent in the grafted animals. Inflammatory changes were present in the majority of the brains examined. Extensive tumor growth was present in one animal implanted with untreated cells. Grafting of cells treated with DBcAMP and PGE1 plus with mitomycin C and bromodeoxyuridine in animals immunosuppressed with cyclosporin A reduced the apomorphine-induced rotation to 40-60% of baseline levels and this reduction persisted beyond the period of infusion with DBcAMP. Intraventricular infusion of DBcAMP in animals injected with cell culture medium produced a transient reduction of rotation to 70% of baseline. The amphetamine-induced rotation was not significantly reduced during the 4 weeks follow up. Atypical cells, consistent with surviving neuroblastoma cells, were observed in the brain of all transplanted animals. TH immunostaining was weak or negative in most cases. Human neuroblastoma cells may be an alternative donor tissue for the study of the effects of transplantation in animal models of Parkinson's disease.

Chronic administration of nerve growth factor and other neurotrophic factors to the brain

Intracerebral chronic administration of nerve growth factor (NGF) is able to counteract age-related cholinergic dysfunction. This finding suggests that intracerebral administration of neurotrophic factors may become a generally valuable approach when attempting to ameliorate age-related neuronal deficits in experimental animals and humans. This commentary briefly discusses possible strategies for the development of such "neurotrophic factor treatments."