Dogs rendered paraplegic by severe spinal cord injuries regained significant neurological function after treatment with a polymer called polyethylene glycol, or PEG, say researchers at Purdue University in Indiana, US.

Dogs admitted to two veterinary hospitals with paraplegia – caused by naturally occurring mishaps leading to “explosive” ruptures of spinal discs – were initially treated with intravenous injections of PEG. This was followed by standard treatments, such as surgery to relieve pressure on the spinal cord and remove stray bone fragments, and steroids to reduce inflammation.

The team, led by Richard Borgens of Purdue’s Center for Paralysis Research, reports that the PEG-treated animals showed marked improvement compared to “historical controls” – paraplegic dogs whose progress had been documented at the hospitals following standard treatments in the 1990s.

Within 48 hours, the PEG-treated dogs scored far better than the historical controls on neurological and behavioural tests designed to measure early functional recovery. And by six weeks after treatment 68% of the PEG-treated dogs were able to walk, compared with only 24% of the historical controls.

Patching holes

The dogs treated with PEG at one of the hospitals were also given tests that measure nerve conduction between the leg and brain. In 63% of those dogs, normal nerve conduction was observed, whereas normal conduction had been seen in only two of 24 dogs in the historical control group.

PEG is widely used in the cosmetics industry and, in some formulations, as a laxative. It is believed that the polymer repairs damaged cells by patching holes in damaged membranes and “stitching” severed cells back together.

“When the membrane is compromised, the hydrophobic [fatty] core is exposed, and water gets in through that breach,” Borgens told żěè¶ĚĘÓƵ. “Because PEG is strongly hydrophilic [water-loving], it sucks up water and plugs into the breach, and then the fatty acids and lipids in the centre of the membrane resolve into each other.”

Cutting the cord

The disc ruptures suffered by the dogs in the latest study compressed nerve fibres in the spinal cord but did not sever them. However, in previous work, Borgens and his colleagues used PEG to restore conduction in guinea pig spinal cords that had been completely cut through (żěè¶ĚĘÓƵ print edition, 21 November 1998).

Borgens’s use of PEG is an unusual approach in the world of spinal cord repair, where most research programmes are focused on coaxing nerve fibres to regenerate using stem cells or growth factors. The new study’s design is also unusual in that it relied on naturally occurring injuries and used historical controls rather than following standard placebo-controlled procedures.

The research provides a “glimmer of hope”, says Charles Tator, a spinal cord injury expert at Toronto Western Hospital in Canada, and justifies further research into PEG’s effects. But he cautions that most human spinal cord injuries are far more severe than those suffered by the dogs in this study. And PEG will not help people with existing injuries.

Borgens’s group is now in the early stages of designing a Phase I clinical trial of PEG therapy for spinal cord injuries in humans with colleagues at Indiana University in Bloomington, US.

Journal reference: Journal of Neurotrauma (vol 21, p 1767)

The technique works by silencing a key gene involved in a progressive disorder of the retina called wet age-related macular degeneration (AMD), say executives at Acuity Pharmaceuticals, a private biotechnology company in Philadelphia, US.

RNAi is a naturally occurring process in which the presence of double-stranded RNA (dsRNA) in cells triggers a series of steps that ultimately destroys messenger RNA (mRNA) and shuts down protein production. It is believed to have evolved to protect cells from invading viruses.

In the upcoming Phase I trial, doctors will inject many copies of Cand5, a “small, interfering” double-stranded RNA, or siRNA, directly into the eyeballs of patients suffering from the disabling eye disorder.

“It’s tremendously exciting,” says Michael McManus, an RNAi expert at the University of California San Francisco, US. “It represents the first step in using this technology to treat a human disease.”

Sprouting vessels

AMD is the leading form of adult blindness in the developed world. In the “wet” form of the disease, blood vessels abnormally develop late in life behind the retina. These fragile new vessels leak blood and fluid that damages light-sensitive cells, eventually causing a large blind spot in the central visual field.

Cand5 blocks the sprouting of these abnormal blood vessels by targeting the mRNA copied from a gene to make a vessel-promoting protein known as vascular endothelial growth factor (VEGF). The injected RNA has a sequence complementary to the mRNA for VEGF, so the pair binds. This double-stranded form activates the RNAi pathway – which leads to its destruction so no proteins are made.

In a natural situation, for example where a virus enters a cell, a key enzyme called Dicer is activated in the presence of large dsRNA, which snips the bound strands into tiny pieces.

Garbage cans

The RNAi pathway was discovered in 1998 in the roundworm Caenorhabditis elegans, but it is now believed to occur in all plant and animal cells. The discovery has been a boon to biologists, who routinely use siRNAs to selectively switch off gene expression, but the rich possibilities of precisely targeted RNAi therapy have aroused even greater interest.

Phase I trials assess only the safety of drugs, not their efficacy. Although Acuity’s Cand5 was remarkably effective and safe in studies with monkeys, McManus says that researchers will need to be vigilant at this early stage for any “off-targeting” that affects proteins other than VEGF.

One challenge of RNAi therapy has been efficiently delivering siRNAs into cells, but Acuity’s Samuel Reich says that AMD may be an ideal condition for testing the feasibility of RNAi-based treatments. According to Reich, retinal pigmented epithelial (RPE) cells, which line the back of the eye, readily gobble up VEGF-killling siRNAs.

“They’re very much like garbage cans,” Reich told żěè¶ĚĘÓƵ. “Any kind of foreign material that the inside of the eye could be exposed to ends up in the RPE cells. It’s their natural biology.”

Researchers at the University of Massachusetts Amherst in the US examined the brains of mice lacking a gene called Bax and found that some sex differences that are obvious in normal mice were completely absent.

It has been known since the late 1970s that certain well-defined clusters of brain cells known as nuclei differ markedly in males and females, either in overall size or in the total number of cells present.

For example, in adult rodents, the bed nucleus of the stria terminalis, or BNST, is 75% larger and contains many more cells in males than in females. The opposite pattern is seen in a region known as the anteroventral periventricular nucleus, or AVPV, which is both larger and richer in cells in females than in males.

Castration or hormones

Extensive research in rats has demonstrated that these differences are determined by the presence or absence of the hormone testosterone in early life.

If a male rat is castrated shortly after birth, its BNST and AVPV will develop in the female pattern. Conversely, if a female rat pup is treated with testosterone its adult brain will be indistinguishable from a male’s.

żěè¶ĚĘÓƵs are unsure how testosterone exerts these effects in the brain, but many have suspected that the hormone might fine-tune the pruning of neurons in different brain regions.

“During development of the nervous system, you get this large overproduction of nerve cells, followed by a period of cell death,” says Nancy Forger, lead author of the study. “Anywhere from 20% to 80% of the neurons that are initially generated will die.”

Much of this “sculpting” of the nervous system is directed by proteins in the Bcl-2 family, some of which promote survival of neurons, while others, such as Bax, prompt cells to self-destruct.

In the Bax-deprived “knockout” mice used by Forger and her colleagues, both the BNST and AVPV had many more cells than are seen in normal mice and the number of cells was equal in males and females.

Window on development

Forger suggests that in these mice developmental cell death in general and sex-specific pruning in particular never occur. “The Bax knockout mice give you a window into what happens during development,” she says. “You’re seeing how many neurons would be there in adulthood if you eliminate cell death.”

Roger Gorski, an expert on sex differences in the brain at the University of California Los Angeles, calls the new study “elegant,” and says it is noteworthy because the results are clearer than many other experiments using knockout mice.

“Many times, the results are unexpectedly negative,” says Gorski. “In this case, they saw a very dramatic effect by knocking out a single protein, which is very impressive.”

Forger says it is unclear whether the “rescued” brain cells are simply sitting there, unconnected to any meaningful neural circuits or whether they are playing a significant role in behaviour. Detailed research into the sex-related behaviour of Bax knockout mice is yet to be carried out.

Journal reference: Proceedings of the National Academy of Sciences: (DOI: 10.1073/pnas.0404644101)

A few small human trials have already shown that injecting adult stem cells into the bloodstream can produce some improvements in heart function after a bypass operation.

But most of the cells die off far too quickly to do much good. In some animal experiments, for instance, Victor Dzau of Harvard Medical School found virtually all the stem cells died within four days.

Now his team has tried modifying stem cells before injecting them back into the body. Dzau used a virus to insert a gene called Akt1 into rat stem cells derived from bone marrow. The Akt protein blocks the signal that triggers cell suicide.

Then the engineered cells were injected into rats with damaged hearts. Two weeks later, the rats’ hearts once again functioned as well as normal. The team thinks the modification allowed the stem cells to survive long enough to turn into heart muscle cells, replacing damaged tissue.

“Darn dramatic”

The results are “pretty darn dramatic”, says Charles Murry of the University of Washington in Seattle. The method could spell the end of the cell-death problem that has hindered the field, he says.

But to avoid immune rejection, the stem cells used to treat people so far have been taken from the bone marrow of each individual to be treated. Simply purifying them takes about a day. Adding a genetic engineering step like Dzau’s would add to the time, a problem with conditions such as heart attacks that require immediate treatment.

Dzau says it should soon be feasible to extract and maintain individual stem-cell stocks for patients at particularly high risk of heart disease, or those with chronic conditions. But few could afford this.

More practical would be creating a bank of many different stem lines, from which immunologically matched cells could be found for anyone. But this might not be necessary: a few studies have hinted that the type of bone-marrow stem cell used by Dzau’s group does not trigger rejection (żěè¶ĚĘÓƵ print edition, 15 December 2001). If so, doctors could use cells from any donor to treat any other individual.

Rare division

There is also concern that blocking cell suicide signals will increase the chances of the stem cells becoming cancerous. But Dzau thinks the risk is low. Heart muscle cells divide only rarely, if ever, he says, so once the Akt1-modified cells turn into heart muscle cells there is little danger.

Murry, however, is not convinced that the engineered cells conferred their benefits by turning into heart muscle cells. He points out that there other ways in which stem cells can improve function.

For instance, it was recently reported that stem cells restored limb movement in rats with spinal cord injuries, but rather than becoming new nerve cells, the stem cells producing chemicals that enhanced the function of existing cells.

Journal reference: Nature Medicine (DOI: 10.1038/nm912)

The analysis of thousands of recorded speech samples found peaks in acoustic energy that precisely mirror the distances between important notes in the twelve-tone scale, the system that forms the foundation of almost all music.

“The mysteries of music have a biologically principled explanation,” says Dale Purves, at Duke University, North Carolina, and lead author of the study. “A reasonable speculation is that we hear these tonal relationships because they are involved in our interpretation of each other’s speech.”

As a slide whistle shows, it is possible to change seamlessly the pitch of a sound from low to high and back again. But for making music, human cultures have sliced the pitch dimension into twelve distinct tones.

This twelve-tone “chromatic scale” can be heard by starting at any piano key and then playing the next dozen white and black keys in succession. On the thirteenth note, the scale begins again, one octave higher.

Pythagoras’s theorem

Different musical traditions have characteristic sound because many cultures have devised scales from a subset of the full chromatic scale, with different distances, or “intervals,” between the tones. Chinese music is based on five-tone scales, while scales common in Western music have seven tones.

But all cultures favour certain intervals from the chromatic scale, and listeners judge these same intervals to create the most harmonious combinations of two tones. Pythagoras proposed that such preferences could be predicted from mathematical relationships between tones, but these approaches have yet to provide a complete explanation.

The Duke researchers randomly extracted over 100,000 speech samples, each 0.1 second long, from recordings of thousands of English sentences. Acoustic analysis of the combined samples revealed 10 frequency peaks that match the most significant intervals used in musical scales worldwide.

Mandarin and Farsi

Moreover, the relative heights of the peaks backed numerous studies in which listeners ranked the harmoniousness of intervals. Speech in other languages – Mandarin, Farsi, and Tamil – also displayed the same pattern.

The frequency peaks are caused when a sound wave from the vocal cords is shaped by resonances of the throat and oral cavity. The researchers say that, aside from animal calls, speech emanating from oscillations of the human vocal cords is virtually the only natural sound that we hear as tones.

This fact, combined with the new finding that preferred musical intervals are better predicted by the acoustic quirks of the human vocal tract than by mathematics, leads the scientists to argue that the structure of music is rooted in our long exposure to the human voice over evolutionary time.

Journal reference: Journal of Neuroscience (vol 23, p 7160)

A causal link between plaques and tangles, the two pathological hallmarks of brains ravaged by Alzheimer’s disease, has been shown for the first time, researchers claim.

In the new study, the scientists found that the protein found in plaques can initiate a process that damages other proteins inside cells and makes them vulnerable to tangling. “This is a new, direct linkage” between plaques and tangles, says Vincent Cryns, who conducted the research with Lester Binder and others at Northwestern University in Illinois.

Demonstrating such a link would be a major breakthrough, and could have important implications for future therapies. But other experts contacted by żěè¶ĚĘÓƵ are not convinced that this link is relevant to the disease in humans and say the new work contradicts some previous research.

Plaques and tangles in brain tissue were first identified by Alois Alzheimer almost a century ago, in a study of people with dementia. These markers are still considered essential for a definitive diagnosis of the disease that bears his name.

However, while much has been learned about the basic biology of plaques and tangles, it has been difficult to find any biological relationship between the two, or to demonstrate conclusively whether either directly contributes to the devastating memory loss seen in Alzheimer’s.

Truncated tau

Plaques form when fragments of a protein known as amyloid-beta accumulate outside nerve cells. Tangles occur when a protein known as tau, which is found inside nerve cells, assembles into abnormal paired strands.

In the new research, the Northwestern scientists used amyloid-beta to activate a family of enzymes known as caspases. These enzymes are central to apoptosis, a natural process in which cells are programmed to “commit suicide”.

Using an antibody created in Binder’s lab that homes in on a specific site in tau, the researchers found that the caspases snipped off 20 amino acids from one end of the protein. Further experiments showed that this truncated tau is far more prone to tangling than normal tau.

Missing link

Rudolph Tanzi, at Harvard Medical School, says genetic research suggests amyloid-beta accumulation may be an initiating factor in Alzheimer’s, and that Cryns and his colleagues have convincingly shown in the lab that amyloid-beta-induced apoptosis can lead to tangles.

But Tanzi says it has been hard to find evidence for this chain of events where it matters, in the brains of Alzheimer’s patients. For one thing, he says, the levels of amyloid-beta found in Alzheimer’s patients is far lower than those used in the lab, which makes experimental models difficult to interpret. Also, many things besides amyloid-beta can activate caspases in neurons, including normal ageing.

“The hypothesis presented in this paper is extremely attractive,” Tanzi told żěè¶ĚĘÓƵ. “But the missing link is does amyloid-beta actually cause apoptosis in [people with] Alzheimer’s disease?”

Khalid Iqbal, at the Institute for Basic Research in Developmental Disabilities in New York, also has reservations. In particular, he says, three groups that have examined tangles from diseased human brains have found that they are made up of full-length tau, not shortened versions.

Journal reference: Proceedings of the National Academy of Sciences (DOI: 10.1073/pnas.1630428100)