Q: Why does a person afflicted with Parkinson’s disease (PD) often seem in a hurry?

A: Because he or she is festinating i.e., hastening.

In this typical PD gait, the trunk is bent, the legs stiffly flexed at knees and hips, while footsteps grow progressively shorter and more rapid. But festination is only one of the signs and symptoms typical of parkinsonism. These include rhythmic muscular tremors, rigid movement, droopy posture and mask-like facial expression.

This neurological syndrome results from an increasing shortage of dopamine, a neurotransmitter in the brain that governs movement. The nerve cells that secrete dopamine die off as a PD patient’s condition worsens. Therapeutic tablets of L-dopa precursors of the dopamine neurotransmitter also wane in effect. Drastic experimental treatments have included brain transplants of human fetal tissue, while human embryonic stem cells are conceptual potential therapy.

Meanwhile, laboratory rats are being groomed as animal models of PD. There’s a toxic chemical called MPTP (1-methyl-4 phenyl-1,2,3,6,-tetrahydropyridine) that zeroes in specifically to kill off cells in the central nervous system that release dopamine. (See BioWorld Today, Dec. 4, 2001, p.1.)

Starting three years ago, a team of neuroscientists at Harvard-affiliated McLean Hospital in Belmont, Mass., began injecting a similar drug to MPTP 6-hydroxydopamine (6-OHDA), which also destroys dopamine nerve cells into one side of the brain in live rats. They left the other, untreated side as a control. The outcome of their in vivo experiment is reported in today’s online issue of the Proceedings of the National Academy of Sciences (PNAS), dated Jan. 8, 2002. It’s titled: “Embryonic stem cells develop into functional dopaminergic neurons after transplantation in a Parkinson rat model.” The paper’s senior author is McLean neuroscientist Ole Isacson.

No, these unilateral rat models of PD did not end up festinating. Instead, Isacson told BioWorld Today, “they rotated spun around and around in place. We made that rat model of PD by first removing the rodent’s own dopaminergic neurons, then implanting mouse embryonic stem cells into their brain. Next, dosing by a chemical stimulus, amphetamine, got the rat to rotate 900 turns over 90 minutes. This behavior correlated with the number of dopamine cells they lost confirming these animals as standard and reliable PD models.”

Nine Weeks To A Cure

“We did this behavioral test repeatedly,” Isacson continued. “Their function and motor abnormality were corrected by nine weeks consistent with the development and regrowth of a new dopamine system in the rat brain. It should be the normal recovery rate of the mouse stem cell development. This showed that it is indeed possible to make the most undifferentiated stem cells become dopamine cells, which die in PD.

“The control was the untouched opposite side of the brain,” he recounted. “Without a stem cell graft, it did not develop into dopamine cells or show behavioral difference or function. On the parkinsonian side, there was no longer activation of the cortical motor regions. However, rats that received stem cells, which rapidly became dopamine cells, had recovered from their PD behavior. When we gave them amphetamine again to drive the dopamine system, their cortical activation was recovered.

“To our knowledge,” Isacson observed, “this is the first report showing efficient in vivo expansion of embryonic stem cells into dopamine neurons, with functional effects in an animal model of Parkinson’s.”

He summed up his modus operandi for generating one-sided PD animal models:

“First, we tested them to make sure they were parkinsonian by those rotations.

“Second, we implanted a low number of embryonic blastula stem cells from a mouse.

“Third, we tested them repeatedly until we observed that only the rats with embryonic stem cells that had grown into dopamine cells recovered gradually from their PD rotation.

“Fourth, we subjected those rats, and their opposing control sides, to blood-flow scans by MRI magnetic resonance imaging which showed the neurons were active.”

Isacson continued: “After we had done those measurements, we performed postmortems on these rats, and found an exhaustive range of molecular markers to determine what kind of cells we had obtained. To my surprise, they all had the correct markers identifying the neurons that die of PD. This in a sense was a stroke of luck that we hope to exploit to find human cells that can do the same.

“Now we are very eager to learn about the mechanism that makes possible the transition from embryonic blastula stem cells to dopamine cells,” Isacson went on. “And while doing that we are targeting clinically relevant scenarios. We would like, for example, to insert genes that would favor the dopamine neurons. That is, insert cell fate-determining factors that drive them even more toward those dopaminergic cells.”

Primates Next; Human Trials In 5 to 10 Years

“In the step after that we’ll actually use primate embryonic stem cells, monkey cells. We know that their developmental rate is much slower than that of mouse cells. We would try to use primate cells, and eventually human cell lines, to learn how to develop identical dopaminergic cells. Hopefully to help the clinicians with this knowledge and I’m not a clinician to advise the PD patient.

“Eventually,” Isacson surmised, “the technical and scientific areas we need to cover before reliably envisaging human trials are minimally three or four years away, in my estimation. And at that stage we would only know how to do a Phase I safety trial. To make this reliable for patient selection, I think the ideal would be those PD individuals who had lost all their dopamine cells, and don’t respond to drugs very well. I see a time frame of clinical trials over the next five to 10 years, to evaluate the best way to do this.”

Isacson and his co-author, neuroscientist Kwang-Soo Kim at McLean, have filed a patent application “that describes the isolation, preparation and implantation technology to obtain these dopamine cells. It suggests ways that could be developed for Parkinson’s disease treatment.” As yet they have not contacted potential pharmaceutical or biotech partners, Isacson concluded, “but we are eager to link up with industry to show that eventually we will be able to help patients by generating dopaminergic neurons from stem cells.”