When bacteria enter the body, white blood cells called neutrophils use an
array of toxic chemicals to kill them, including hydrogen peroxide, a powerful
bleaching agent. But hydrogen peroxide can react with other molecules in the
blood, and Jay Heinecke and his colleagues at the Washington University School
of Medicine in St Louis realised that these reactions could form chlorine.

Looking for chlorine itself was not feasible, as the gas is so reactive that
it would exist only fleetingly. But Heinecke’s team devised a system to detect
retrospectively whether it had been produced. They cultured neutrophils in the
laboratory, then took red blood cells, filled them with an amino acid called
tyrosine, and coated them with antibodies and other blood proteins to ensure
that they would be attacked by the neutrophils.

The neutrophils soon destroyed and engulfed the tyrosine-filled red blood
cells. The researchers then used a mass spectrometer to show that the fluid in
which the neutrophils were held contained traces of 3-chlorotyrosine, a chemical
marker left behind when chlorine attacks tyrosine (Journal of Clinical
Investigation, vol 98, p 1283). “We haven’t proven that chlorine kills
bacteria in vivo yet,” stresses Heinecke. But he is confident that will turn out
to be the case.

Unfortunately, the toxic chemicals released by white blood cells can damage
the body’s own tissue. Heinecke thinks the production of chlorine by neutrophils
could be involved in heart disease, cancer, arthritis and stroke.

Michal Schwartz and her colleagues at the Weizmann Institute of Science in
Rehovot, Israel, have found that immune cells called macrophages can repair
severed optic nerves in rats. They believe the same technique should also work
in humans who have suffered injuries to their central nervous system (CNS).

In mammals, nerve cells in the spinal cord, optic nerve and brain cannot
regenerate if they are severed. But in lower vertebrates, such as fish and
amphibians, such regeneration is possible. In these animals, macrophages zoom in
on damaged nerve cells, mopping up cellular debris and releasing chemicals that
promote tissue growth. The CNS of mammals, however, is an “immunoprivileged”
tissue—in other words macrophages and other immune cells are excluded.
Even if the cells are transplanted into a section of severed spinal cord, they
remain inactive.

Schwartz and her colleagues have been looking for a way to overcome this
suppression. In this month’s issue of The FASEB Journal (vol 10, p
1296), they say that the secret is to incubate macrophages with nerves from
outside the CNS—which are repaired by macrophages even in mammals.

The researchers cultured macrophages alongside segments of sciatic nerve
cells taken from rats’ hips. This activated the macrophages, priming them to
engulf debris from injured cells and to release their chemical growth signals.
When the cells were transplanted into severed rat optic nerves, the damaged
neurons regrew.

Schwartz warns that the rat study is only the first step on the long road
towards clinical applications. The researchers had to kill their rats to
determine whether their nerves had regrown, so it is unclear whether the
repaired nerves were able to function normally.

The method also raises the possibility of damaging side effects. Schwartz
believes that macrophages are normally excluded from the mammalian CNS because
their urge to “tidy up” would disrupt the subtle neural wiring required for
learning, memory and other CNS functions.

The researchers are concerned that macrophages applied to a spinal injury
might travel along nerve fibres and disrupt other parts of the CNS. They want to
try to restrict this migration by carefully controlling the site where they
release the macrophages. “I am not claiming I have a cure today,” says Schwartz.
“We need to find the optimal balance between regeneration and degeneration.”

Fred Geisler, a surgeon at the Chicago Institute of Neurosurgery and
Neuroresearch, predicts that a whole range of techniques will be required if
doctors are ever to restore sensation and movement to people with spinal
injuries.

“Where this will fit into the clinical arena remains to be seen, but it
represents a novel approach,” says Geisler. “They have identified what could be
a very important component of therapy.”

Mallet studied a population of the rare silver-studded blue, Plebejus
argus, in North Wales. The butterfly was reintroduced to the Great Ormes
Head, near Llandudno, in 1963. But even though the group is apparently thriving,
Mallett found that the butterflies that have colonised the surrounding area have
lost some of their original genes.

Mallett looked at the distribution of alleles—genetic pairs—in
the population and found that some of the rarer variants had disappeared. He
suspects that the loss of diversity may be even greater in species that are
rarer than the silver-studded blue.

Five species of butterfly have gone extinct in Britain since the middle of
the last century, the large blue as recently as 1979. Butterflies adapted to
habitats shaped by traditional farming and forestry practices over the past
millennium, but they are now threatened by intensive farming. A decline in chalk
down grazing, coppiced woodland and drained fens and marshes have all
contributed to the losses, says Mallett.

“We need to take into account the effect of human-altered habitats [on rare
species], and where possible we need a return to traditional farming methods to
conserve the native flora and fauna,” he told the BA.

The new drugs are based on chains of nucleotides, the building blocks of RNA
and DNA. Specially designed short chains, known as oligonucleotides, can clamp
onto and disable dangerous proteins from unwanted guests like viruses. Other
oligonucleotides can bind to genes, such as those causing cancer. But current
drugs based on RNA and DNA are of limited use because they are rapidly destroyed
by enzymes called nucleases. Now Jens FĂĽrste and his colleagues of the
Institute of Biochemistry at Berlin Free University have found a way to foil the
enzymes.

Oligonucleotides are chiral—that is, they can exist in right and
left-handed forms—but natural oligonucleotides always adopt a particular
form. The German team has managed to make mirror-image copies of RNA-based
oligonucleotides that bind to the HIV-Tat protein, which triggers the expression
of HIV genes (Nature Biotechnology, vol 14, p 1112). Unlike
the natural oligonucleotides, they are invisible to nucleases. The next step
will be to design a mirror-image oligonucleotide that can also destroy the
protein. This could, in theory at least, prevent the virus from replicating.

To make the required oligonucleotide, Fürste’s team used a mirror image
of the amino acid arginine as a template. In its natural form, arginine is
abundant in the HIV-Tat protein. The resulting mirror-image oligonucleotide was
able to clamp onto both forms of the amino acid, yet resisted nuclease
attack.

Mike Gait, head of chemistry at the MRC Laboratory of Molecular Biology in
Cambridge, is cautious: “The extra modification [of mirror image molecules] is
clever, but the binding affinity of the oligonucleatide for the HIV-Tat peptide
is rather poor.”

Now Jonathan Stamler and his colleagues at Duke University in Durham, North
Carolina, may have discovered one important reason why the humble NO molecule is
such a jack of all trades. In the 6 September issue of Cell (vol 86, p
719), they report that the gas can bind to proteins called transcription
factors, which turn genes on and off.

The researchers were studying Escherichia coli bacteria, under attack
from immune cells called macrophages. These cells pump NO into invading
microorganisms. Once inside a bacterium, NO binds to sulphur-containing
compounds called thiols, found within many proteins. The resulting complexes are
called S-nitrosothiols (SNOs), and can inactivate or change the function of the
proteins that carry them. And while a bacterium is busy repairing its altered
proteins, the immune system can easily finish it off.

To protect themselves from this assault, bacteria employ decoy proteins with
thiol “mops” that soak up the NO. But their second line of defence was what
really caught the eye of Stamler’s team. The researchers noticed that in the
middle of an NO onslaught, E. coli responds by producing a
transcription factor called OxyR. When NO binds to this protein, forming SNOs,
the transcription factor switches on a large number of genes that make defence
proteins. “We have found a signalling mechanism that goes all the way to the
genes,” says Stamler.

Stamler believes that many of NO’s wide-ranging effects may be underpinned by
a similar mechanism involving transcription factors. “We already know that SNOs
form in human cells,” he says. “It happens with haemoglobin.” Stamler’s team is
now following up on this hunch by looking for human transcription factors that
are modified by NO in the same way as OxyR.

If the research does uncover a central mechanism that explains many of NO’s
biological effects, it may open the door to new medical treatments: several
diseases are linked to abnormalities in the function of NO. In some forms of
arthritis, for instance, healthy cells suddenly become susceptible to damage by
the gas. “It will be exciting to see if these findings can be extended,”
observes Steve Gross, a pharmacologist at Cornell University Medical College in
New York.

By the time children reach puberty, the left half of the brain has taken on a
dominant role in language skills and while the right is dominant for other
intellectual functions such as spatial awareness. Timothy Crow, a psychiatrist
at Warneford Hospital in Oxford, told the BA that he believes this localisation
is delayed or incomplete in children that go on to develop schizophrenia.

Crow used ambidexterity as an indicator of “hemispheric indecision”, or lack
of specialisation in the two halves of the brain. He found that ambidextrous
eight-year-olds are more likely to develop schizophrenia in later life than
other children. His results will soon be published in the journal
Schizophrenia Research.

Crow believes that language and schizophrenia have a shared evolutionary
origin. The genes that underpin our linguistic skills, he argues, also
predispose us to psychiatric diseases (see “Understanding the Inner Voices”,
New ĐÓ°ÉÔ­´´, 9 July 1994, p 26).

Throughout the world, the incidence of schizophrenia is roughly constant at
about 1 per cent of the population. Crow argues that this means that the disease
is primarily genetic in origin and evolved at the dawn of Homo sapiens.
Other genetic diseases, which are thought to have arisen more recently, tend to
afflict particular populations. Sickle cell anaemia, for example, affects
Afro-Caribbeans more than Caucasians.

Crow argues that the genes that cause schizophrenia would have been weeded
out by natural selection if they were not linked to something vitally important
to our species. “I believe that the gene or genes involved in schizophrenia are
responsible for some function of language and also involved in the development
of verbal and visuospatial skills,” says Crow.

Crow has produced further evidence to back his theory by examining data from
the National Child Development Study, an ongoing study of British children born
in a single week in 1958. At the age of seven, children who went on to develop
schizophrenia were more likely to have reading difficulties and problems with
pronunciation.

Crow is now looking for the genes involved. He hopes that the nature of
schizophrenic symptoms such as visual and auditory hallucinations will also
provide clues about how language evolved.

American Technology Corporation (ATC) of Poway, California, developed the
prototype, which is the brainchild of the company’s chief technology officer,
Elwood Norris. The company will unveil the prototype in the US this month, and
hopes to have the first versions on sale within a year.

The system emits two ultrasonic waves at different frequencies. Each set of
waves is at a frequency too high to hear, but where they overlap, or interfere,
they generate audible sound. The effect is called acoustical heterodyning and is
based on a phenomenon called the Tartini, or difference, tone. In the 18th
century the Italian composer Guiseppe Tartini noted that two interfering sound
waves of different frequencies, such as two organ pipe notes, will produce a
third sound whose frequency is the difference between the two.

Acoustical heterodyning also occurs with ultrasonic waves. Two ultrasonic
waves at frequencies too high to be audible, such as 200 kilohertz and 201
kilohertz, would produce an audible sound of 1 kilohertz.

The ultrasonic waves in the prototype are generated by piezoelectric
crystals, or transducers. An oscillating voltage applied to the crystal makes it
vibrate in a similar way to a loudspeaker. One crystal emits a 100-kilohertz
fixed signal, while the second varies between 100 kilohertz and 120 kilohertz.
This generates difference tones of between 0 hertz and 20 kilohertz, which
covers the full range of human hearing.

“The sensation is nothing short of amazing,” says Norris. “If you point the
sound at a wall, a room full of people will point to the same spot as the source
of the sound. You can then move the sound out into the centre of the room and up
over the top of the audiences’ heads.”

The system produces sound indirectly, which should eliminate the normal
distortion caused by speakers, says Norris. He believes it could improve
telephones and hearing aids, and add something extra to cinema sound. The mobile
sound source could be used to represent, for example, a jet aircraft crossing
over the heads of the audience.

“There is no reason why it shouldn’t work,” says Peter Fryer, head of
research at B&W Loudspeakers in Steyning, Sussex. “But the high frequencies
are so high that the waves may not propagate very far as they are absorbed in
air. The proof of the pudding will be in the eating.”

The system may also have applications in crowd control. Powerful
low-frequency sound can cause disorientation and nausea. In the 1960s, the US
tried unsuccessfully to use low-frequency sound from helicopters to disable
enemy soldiers in the Vietnamese jungle. But the sound sources needed were so
intense that they almost shook the aircraft apart, and most of the sound was
absorbed by those nearest to the loudspeakers. According to Norris, acoustical
heterodyning could pinpoint an individual up to 200 or 300 metres away by
positioning the interference zone correctly.