LAUREN SHEAR / SCIENCE PHOTO LIBRARYOne of the most common side effects of prolonged treatment of Parkinson’s disease is the repetitive and involuntary movements known by the technical term dyskinesia. Finding strategies to minimize this effect is one of the current challenges for groups studying the disease. Work done by the group led by Elaine Del-Bel, of the University of São Paulo (USP), Ribeirão Preto Dental School, Department of Morphology, Physiology and Basic Pathology, suggests that this dysfunction could be controlled by regulating the amount of nitric oxide in the brain, where the compound acts as a neurotransmitter. The use of two substances—one that inhibits the action of nitric oxide and the other a known dye to control the production of dopamine—was tested in animals, and the results were encouraging. “Nitric oxide must work in conjunction with dopamine (another neurotransmitter) so that movements are in sync. By modulating the first neurotransmitter, we can also control the levels of the second, which make the dyskinesia disappear,” says Del-Bel, whose studies are being conducted as part of a FAPESP thematic project.
When patients diagnosed with Parkinson’s arrive at a stage where they can no longer control symptoms such as tremors in their hands and legs, difficulty in getting up from a chair or signing their names, doctors often recommend treatment with the use of drug compounds based on a substance called Levodopa (or simply L-dopa). Levodopa is the precursor of dopamine, a neurotransmitter associated with movement that is produced in insufficient quantities in the brains of people with the disease—hence the motor limitations. With the regulation of dopamine, the tremors tend to disappear and the control of movement returns to a satisfactory level.
This recovery period, the “honeymoon” phase of the disease, allows patients to make considerable gains, as they return to doing with relative ease everyday and mundane tasks such as using knives and forks and holding glasses without the risk of knocking them over. The benefits, however, have an expiration date. They last an average of five years. After this period, for still unknown reasons, involuntary tremors reemerge and are even stronger and more aggressive. This is when the dyskinesia, a dysfunction that causes patients to experience involuntary movements of the muscles of the face, arms and legs, manifests itself. In Greek, the word kinesis means movement.
In an initial study, published in the January 2009 issue of the journal Neuroscience, the Ribeirão Preto group began by inducing Parkinson’s disease in rats. They injected toxins into the neurons responsible for producing dopamine and waited until the induced lesions affected about 80% of the nerve cells in order to simulate the advanced stage of the disease. The animals were then treated with L-Dopa until the symptoms of dyskinesia appeared. Finally, the researchers administered the compound 7-nitro-indazole, which inhibits the action of enzymes important to the production of nitric oxide. The expected chain reaction occurred. With less of the neurotransmitter in the nervous system, the involuntary movements practically disappeared.
Del-Bel emphasizes that the research on the effects of nitric oxide were not random. “We already knew that it is a highly soluble neurotransmitter manufactured on demand, according to what the body needs, which acts on many neurons and primarily modulates the activity of other neurotransmitters,” explains Del-Bel. She recognizes that these associations have yet to be studied and supplemented with further studies: “Dyskinesia is a complex condition involving cellular degeneration and the action of various neurotransmitters.” However, the study results show that by regulating the amount of nitric oxide, the level of dopamine in the brain can be indirectly controlled and, as a consequence, so can the dyskinesia. In such cases, the partial or complete elimination of the signs of dyskinesia can occur due to an effect known as dopamine turnover. “With only a single dose of the compound 7-nitro-indazole, the dyskinesia disappears and the animal is able to recover nearly 100% of its movements. If we were to carry this over to humans, it would be like returning to the honeymoon treatment phase of the disease. It was the first time that this relationship was identified,” says Del-Bel, who published two articles in 2013 on the role of nitric oxide in controlling dyskinesia.
The researchers then decided to go a little further and explore another promising idea: replacing the 7-nitro-indazole with methylene blue, a substance also known to prevent the action of nitric oxide. “The advantage of methylene blue compared to 7-nitro-indazole is that it is already widely used in clinical trials in humans and even in treating infections in intensive care units,” says Del-Bel. Again the results met their expectations: the dyskinesia improved. Most likely the dye reduced the availability of nitric oxide in the nervous system. “This was the second piece of evidence of this mechanism of association between the two neurotransmitters,” says Del-Bel. The study was developed in collaboration with the neurologist Vitor Tumas, chief of the Movement Disorders Clinic of the USP Ribeirão Preto Hospital das Clínicas, which will most likely test the methylene blue in patients with dyskinesia. “This line of research has resulted in unique contributions, including the first studies to indicate the role that nitric oxide could play in motor control, and to recommend potential clinical trials and therapeutic applications,” says Francisco Silveira Guimarães of the USP Ribeirão Preto School of Medicine, Department of Pharmacology, coordinator of the thematic project.
To Henrique Ballalai Ferraz, a professor of neurology at the Federal University of São Paulo (Unifesp), the work of his USP Ribeirão Preto colleagues represents substantial progress, but is not yet the definitive answer to controlling dyskinesia. “The group looked at a relevant facet, which had not yet been demonstrated, but it is not the ultimate solution,” says Ferraz. According to him, international studies have shown that modulating other neurotransmitters such as adenosine, serotonin and glutamate, also allows movements in patients with Parkinson’s disease to be stabilized. “The issue is broader. Dyskinesia involves several neurotransmitter systems,” says Dr. Ferraz.
First described in 1817 by James Parkinson (1755-1824), the disease manifests itself when neurons called the substantia nigra, located in the brain stem, die and stop producing dopamine. While a neuron can be compared to a tree with several branches, offshoots and different connections, there is also a reduction of the neurotransmitter in the neurons of the basal ganglia, located below the cerebral cortex. This region, together with the motor cortex, are primarily responsible for voluntary movements. “The tricky thing is that the diagnosis can only be made with certainty after the onset of very characteristic motor symptoms, when the disease is usually well advanced and approximately 80% of the dopamine has already disappeared,” says Del-Bel. Treatment with L-Dopa is then initiated.
Because of mechanisms that are not yet fully understood, the substance works well at the beginning of treatment, but its regular and continuous use leads to dyskinesia as a side effect. “Most likely what happens is a higher amount of dopamine in the brain, associated with complicated processes arising from the death of neurons. The release of the neurotransmitter is not natural and physiological, but induced by drugs in the body. As the rebound effect occurs, the abnormal involuntary movements appear,” says Del-Bel.
The potential benefits of exercising body and mind
In addition to seeking markers to anticipate the diagnosis of Parkinson’s disease and testing ways to reduce the side effects of prolonged treatment, research is trying to ensure a higher quality of life for patients suffering from a progressive and irreversible disease. At the Universidade Estadual Paulista (Unesp), Rio Claro campus, Lilian Teresa Bucken Gobbi examined the effects of various physical and cognitive exercises in patients with Parkinson’s. Since every movement of the body requires dopamine, doctors tend to recommend less physical activity for patients with Parkinson’s, so as not to use up the dopamine reserves that are already being produced in smaller quantities. But the medical literature indicates that healthy adults who exercise are less likely to develop the disease. “We stitched together the two seemingly contradictory pieces of information, and decided to investigate,” says Gobbi, coordinator of the Laboratory for the Study of Posture and Locomotion (Leplo) at Unesp.
She worked with three groups of patients, who completed two weekly sessions of exercises, each one-hour long. The first group did general exercises (weight training, rhythmic and flexibility movements), the second, in addition to general exercises, took walks requiring them to leave the environment that was familiar to them and navigate other paths on uneven ground, for example, in order to stimulate their attention and sensory systems. The third, called ActiveMind, faced logical and mathematical challenges. The study is expected to last three years, and the participants of each team will change exercises every year, until they have undergone each of the three proposed approaches. “It’s a long-term job,” says Gobbi.
Early results are encouraging. After four months, patients in the three groups were able to improve the cognitive variables of the disease. “On average Parkinson’s patients are expected to decline eight points in one year on the cognitive tests used to evaluate the progression of the disease. With the physical or mental exercises, there was no change in this score, and the picture was stable,” he says. One possible explanation for this feat is brain plasticity: the neurons that still work and have been stimulated by exercise take over the functions of those that have died. “In addition, the activity sessions always took place in the early morning, shortly after the administration of drugs, and, acting together, the exercises can help balance the drug’s action on the brain,” he adds.
Typical and atypical neurotransmitters in neuropsychiatric disorders (07/03685-3); Grant Mechanism Thematic Project; Coordinator Francisco Silveira Guimarães-FMRP/USP; Investment R$ 1,947,653.25 (FAPESP).
DEL-BEL, E. et al. Counteraction by nitric oxide synthase inhibitor of neurochemical alterations of dopaminergic system in 6-OHDA-lesioned rats under L-Dopa treatment. Neurotoxicity Research. June 27, 2013.
PADOVAN-NETO, F.E. et al. Anti-dyskinetic effect of the neuronal nitric oxide synthase inhibitor is linked to decrease of FosB/deltaFosB expression. Neuroscience Letters. v. 541, p. 126-31. April 29, 2013.
PADOVAN-NETO, F.E. et al. Nitric oxide synthase inhibition attenuates L-DOPA-induced DYSKINESIAS in a rodent model of Parkinson’s disease. Neuroscience. v. 159, p. 927-35. 2009.