December 15, 2009 

In the description below, we go outside of our usual Packard policy of exclusively reporting on work that we've supported. Why do that? There're good reasons: We want to show how Packard investigators catalyze ALS research outside of the Center's boundaries. Also, we believe it's a useful service to keep our readers aware of new ALS research.

Packard expertise helps bring an easily measured biomarker closer

It's one of the bugaboos of ALS research and diagnosis that nobody has found a biomarker. Having a molecule that appears only when ALS strikes would have a host of uses, not the least of which is testing possible drugs.

Right now, there's no quick, reliable way to tell if something has stopped or slowed ALS down.

Presently, in the animal models of ALS that are early stops in the drug-development pipeline, you tell if a drug has possibilities - if it's safe - by looking at animal behavior. Can mice continue to stay balanced on a rotating rod, for example? Are their hind legs starting to drag? But the need is real, scientists say, for an easier, more uniform, cut-and-dried way of telling if the disease is there or, at least, to tell if it's actively doing harm.

Ideally, that method would translate to drug trials in ALS patients.

This month, researchers announced what looks like a solid step in the biomarker direction. A Florida team led by Kevin Boylan with the Mayo Clinic in Jacksonville and Gerry Shaw, with the University of Florida, Gainesville, has a just-out report in the Journal of Neurochemistry on a potential blood marker for lab animal testing. Team member and Packard investigator David Borchelt, also with the University of Florida, provided invaluable expertise.

The new work turns on the idea that select molecules are released into the blood or cerebrospinal fluid (CSF) when dying motor neurons disintegrate. These are proteins that normally wouldn't appear outside of neurons in any significant amount in healthy animals or humans.

A Tell-tale Protein

The researchers found that a protein called pNF-H holds potential as a tell-tale molecule. The NF stands for neurofilament, the structural rods that support a neuron's extended axon. Earlier work by Boylan and Shaw's teams showed it's possible to detect bits of neurofilament protein in both CSF and blood with high sensitivity.

Their early studies looked at animal models of central nervous system injury or disease as well as at hospital patients suffering injury from stroke or multiple sclerosis.

But the researchers hadn't considered pNF-H as a possible biomarker for ALS.

In a bit of serendipity, Borchelt, a longtime Packard investigator with a good supply of ALS mice and expertise, moved to the University of Florida. Soon a new research path was laid out.

Borchelt knows as much about transgenic mouse models of ALS as anyone worldwide - particularly mice that carry the mutated human SOD1 gene that underlies the most common familial ALS. (Almost 150 different SOD1 mutations have surfaced in fALS patients.)

He offered his colleagues a variety of strains of the mutant SOD1 mouse - from animals that experience rapid, powerful disease to those where its onset is more subtle.

In addition, the researchers examined 20 sporadic ALS patients and 20 healthy controls, sampling their blood for pNF-H once a month for four months.

Compelling Results

When results were in, healthy mice and humans, as expected, showed little or no detectable blood pNF-H. That was in stark contrast, however, with the ALS model mice, where the molecule's presence was clear. As disease symptoms grew from mild to severe, pNF-H also progressively increased. Sensitive tests detected it well before paralysis set in.

In patients as well, blood levels of the marker molecule were significantly higher than in controls. And levels also increased as illness advanced. The blood concentration of pNF-H, though, was lower in humans than mice, the authors say, perhaps because ALS takes over far more gradually in humans.

Tracking the Course/the Drug

"All this suggests that pNF-H will let us follow the course of ALS in animal models almost in real time - more easily than we could before," Borchelt says. The blood test appears to be more reliable than traditional lab tests of animal ability. It's also more specific than measuring something like weight loss, the study leaders say.

The real potential, they add, lies in improved preclinical animal trials of perhaps- therapeutic drugs - to tell if they slow or stop ALS. It's something that could speed testing. It could also let scientists pool data from different labs with more assurance.

As for using pNF-H to monitor human drug trials: That's farther off, the journal article reports, and calls first for larger studies with more patients in various stages of ALS.

Does pNF-H hold some hope as a diagnostic tool? Could it confirm ALS in patients? That would be the case, Borchelt explains, if what's released into ALS patients' blood turns out, somehow, to be unique to the disease. "We've made seeing if that's the case a high priority in our labs," he says. "We're working on it now."