LONDON The experimental treatment of Parkinson¿s disease by the transplantation of cells obtained from the brains of human fetuses into the brain of the sufferer has shown great promise. This therapy was first carried out nine years ago in Sweden, and the first patient treated is still able to live independently. He and several others treated subsequently have shown a remarkable and long-term improvement in mobility.
Setting aside the ethical debate about whether this approach should be used at all, one factor hindering the expansion of this treatment has been the difficulty of obtaining large-enough quantities of fetal tissue. Under some protocols, up to eight donor embryos may be needed for each side of the brain.
Now, a team of Swedish researchers has reported a breakthrough that could reduce the number of embryos required for each transplant by a factor of four. Gabriele Schierle, a scientist at the Section for Neuronal Survival of the Wallenberg Neuroscience Center, at Lund University in Lund, Sweden, told BioWorld International: ¿We think we should be able to test this technique on human tissue and be using it in the clinic within one year. We expect to put this new method into practice very rapidly.¿ The team is interested in establishing collaborations with commercial partners to try to develop their techniques further.
Schierle, together with colleagues from the Wallenburg Neuroscience Center and from Konstanz University, in Konstanz, Germany, reported their findings in a paper in the January issue of Nature Medicine, titled ¿Caspase inhibition reduces apoptosis and increases survival of nigral transplants.¿
Parkinson¿s disease was first described by James Parkinson, a general practitioner in London, in a booklet he published in 1817 called ¿An Essay on the Shaking Palsy.¿
Among the first signs of the disease are tremor of the limbs and head, slowness of movements and inability to initiate movements. As it progresses, the affected person may lose the ability to walk, talk, write or eat; eventually, he or she cannot lead an independent life.
The incidence of Parkinson¿s disease is about 20 cases per year per 100,000 population. It can be treated with drugs such as anticholinergics and levodopa, but these can have side effects. In addition, some of the drugs used lose their effectiveness after several years of treatment.
Parkinson¿s disease results when the cells of an area of the brain called the substantia nigra degenerate. These cells have projections into another part of the brain called the striatum, where they normally release the neurotransmitter dopamine. The transplantation therapy has attempted to rectify this deficit in dopamine by introducing into the striatum cells taken from the ventral mesencephalon of fetuses. These cells are the precursors of those which produce dopamine in the adult brain.
Schierle and her colleagues have been involved in basic research to try to identify ways of improving the survival of the transplanted cells. Studies in rats have shown that most of these cells die within one week of the transplant. Postmortem studies on two patients who died following the procedure showed that 90 percent of the transplanted neurons had failed to survive.
Because some studies have shown that most of the cells which die do so by apoptosis (programmed cell death), the group has been hunting for ways of reducing this process. The enzyme caspase is required for apoptosis to occur, so the Swedish and German researchers decided to examine the effect of adding a caspase inhibitor to the cells. The inhibitor they used was a peptide called acetyl-tyrosinyl-valyl-alanyl-aspartyl-chloro-methylketone (Ac-YVAD-cmk).
They first tested the effect of adding Ac-YVAD-cmk to cultures of cells from the ventral mesencephalon of rat embryos, and found that the survival of the dopamine-producing cells was increased by 600 percent at the highest concentration of Ac-YVAD-cmk.
In another experiment, storing the cells at room temperature for six hours and then at 37 degrees Centigrade for two hours to mimic the maximum length of time between cell preparation and transplantation, and the period immediately following transplantation resulted in DNA fragmentation, which indicates apoptosis. However, adding Ac-YVAD-cmk to the cultures reduced the proportion of cells undergoing apoptosis by about 75 percent.
Research May Have Immediate Implications¿
The group went on to study apoptosis of the cells in live rats. Cell suspensions were transplanted into the striata of the brains of adult rats and tests carried out to measure the extent of apoptosis. When the cells were first treated with Ac-YVAD-cmk, a 94 percent reduction in measures of apoptosis was seen.
Finally, Schierle and her colleagues studied the effect of using Ac-YVAD-cmk in a rat model of Parkinsonism. These animals have a lesion on one side of the brain so that the dopaminergic neurons on that side can no longer deliver dopamine to the striatum. When the rats are given amphetamine, they tend to rotate towards the side of the lesion. If cells from the ventral mesencephalon of rat embryos are transplanted into the site of the lesion, however, this tendency to rotate towards the affected side disappears. The more transplanted neurons that survive, the faster the animal¿s recovery.
Schierle explained: ¿We made a cell suspension with the cells from embryonic rat brain and treated it with Ac-YVAD-cmk. We then implanted the cells at the site of the lesion in the rat model of Parkinson¿s disease. We found that there was almost a four-fold increase in the number of surviving dopaminergic neurons. When we tested the rats¿ behavior, we found that rats which received transplanted cells which had been treated with Ac-YVAD-cmk showed a significant reduction of motor asymmetry over time. They had almost completely recovered after two weeks, whereas it normally takes these animals six weeks to recover a normal pattern of movement.¿
In their paper in Nature Medicine, the team concluded that this strategy ¿may have immediate implications for ongoing clinical transplantation trials. Some of the present clinical grafting protocols use three to eight donor embryos per side of the brain in patients with Parkinson¿s disease. Caspase inhibitors, even if present only during graft preparation, may reduce the number of embryos required to one-fourth of the current number. After confirmation of the effect in human neurons, this protocol could be considered for clinical application.¿ n