By David N. Leff

Editor¿s note: Science Scan is a roundup of recently published biotechnology-relevant research.

Morphine is the analgesic of choice for patients suffering chronic intractable pain, as in end-stage cancer, arthritis and neurodegenerative diseases. But morphine, whether oral or intravenous, is only partially effective, and has serious side effects and practical drawbacks.

So gene therapists have turned to what¿s colloquially known as ¿the brain¿s own morphine,¿ namely endorphin. This small opioid peptide rises to the analgesic occasion by numbing nociception ¿ the perception or transmission of pain.

Attempts to induce expression of an endorphin gene in the pain pathway of the central nervous system, by injecting the gene into the spinal cord, have been less than successful. The gene-delivery vectors failed to disseminate adequately from their point of injection and suffuse the cord tissue.

Now, scientists at the NIH¿s National Institute of Dental and Craniofacial Research in Bethesda, Md., have designed and tested an end run around this obstacle. Their paper in the May 1, 1999, issue of the twice-monthly journal Human Gene Therapy bears the title: ¿A paracrine [local hormonal] paradigm for in vivo gene therapy in the central nervous system: Treatment of chronic pain.¿

That paradigm exploited the fact that the mammalian spinal cord is sheathed in double membranes, the meninges and the pia mater, which are bathed by the vertebra¿s cerebrospinal fluid (CSF). The co-authors simply injected their endorphin-expressing vector into that very accessible CSF. Their transgene delivery package consisted of a recombinant adenovirus sequence encoding a secreted form of the potent endogenous opioid beta-endorphin.

This gene-transfer sequence duly entered those membranes, which within 24 hours began secreting beta-endorphin. It soon reached 10 to 20 times the peptide¿s normal levels in rat or human. As the spinal cord is the first processing point for relaying pain signals to the brain, the hope was to have endorphin block those signals before they reach the brain, where pain perception takes place.

To test this system preclinically, the team enlisted the standard rat model of pain appreciation. First, they induced persistent hyperalgesia ¿ extreme sensitiveness to pain ¿ in one hind paw by injecting it with an irritant. Next, they infused the endorphin gene package ¿ or a dummy vector ¿ into the animals¿ CSF. Then a radiant heat lamp beamed pain onto each paw, normal and sensitive. The elapsed time it took a rat to pull its paw back from the thermal pain source measured the degree of endorphin-induced pain alleviation.

Endorphin-expressing animals took their time withdrawing from the heat, indicating the opioid was having its sedative effect. The journal paper concluded, ¿The clinical utility of this meningeal-paracrine approach is broadly applicable to other CNS [central nervous system] disorders where large areas of brain tissues and/or large numbers of distributed neurons must be affected, such as Parkinson¿s or Alzheimer¿s disease, or amyotrophic sclerosis.¿

BIO Rebuts Bt Corn Peril To Butterfly Reported In Nature, Seconded By Activist Scientists

Biotechnology took a grievous hit last week when a butterfly landed on page one of the national newspaper USA Today. The big, bright, orange-and-black insect also touched down on the front page of the New York Times and other daily papers.

The story started with a brief, peer-reviewed research report by entomologists at Cornell University in Ithaca, N.Y., which ran in Nature dated May 20, 1999. Its title: ¿Transgenic pollen harms monarch larvae.¿

The authors collected pollen from corn plants genetically engineered to express the Bacillus thuringiensis (Bt) insecticide, and dusted it over the leaves of milkweed (Asclepias curassavica). These plants are the favorite food of the monarch butterfly (Danaus plexippus) caterpillar. Adult monarchs have wingspans approaching four inches, which they use to migrate seasonally on winter trips of 1,800 miles from Canada to California and northern Mexico, among other breeding areas.

In a laboratory experiment, the Cornell entomologists allowed monarch caterpillars, which reach two inches in length, to munch on the pollen-coated milkweed, and reported that they ¿ate less, grew more slowly and suffered higher mortality than larvae reared on leaves dusted with untransformed corn pollen or on leaves without pollen.¿ After four days of feeding on the Bt pollen, larval survival was 56 percent, vs. 100 percent for the other cohorts.

¿These results,¿ the authors wrote, ¿have potentially profound implications for the conservation of monarch butterflies, [which] feed exclusively on milkweed leaves.¿

The co-authors conclude that as Bt corn planting is on the increase, ¿It is imperative that we gather the data necessary to evaluate the risks associated with this new agrotechnology, and to compare these risks with those posed by pesticides and other pest-control tactics.¿

Coincident with Nature¿s publication date, the Washington-based Union of Concerned Scientists put out a press release headlined: ¿Toxic Pollen Threatens Monarchs: Gene-Altered Corn May Harm Beloved Butterfly.¿ It charged the Environmental Protection Agency (EPA) with having ¿rushed into allowing 20 million acres of Bt corn to be planted without thoroughly assessing its risks.¿

It concluded that the EPA ¿must take action to protect the monarch butterfly and prevent other adverse ecological effects by denying any further approvals and renewals of Bt corn.¿

Responding to the Nature report, BIO ¿ the Biotechnology Industry Organization ¿ released a statement from its vice president of food and agriculture that made the following points:

¿ Declining Monarch butterfly populations have been a concern for decades. It is known that many factors play a role in these declines. Even if the reported results are validated, there are strong reasons to believe they are not relevant to Monarch caterpillars in the wild.

¿ Ongoing monitoring of Bt cornfields by companies since their introduction further shows that very little pollen lands on adjacent milkweed leaves. It is thus highly likely that in the natural setting, outside the laboratory, most Monarch larvae would never encounter any significant amounts of corn pollen. This means the real potential for any negative impact is negligible.

¿ Ongoing monitoring also shows that insect biodiversity and population densities in Bt corn fields are significantly higher than in fields treated with chemical pesticide sprays. n