San Francisco Chronicle (SF); Wednesday, July 3, 1991
David Perlman, Chronicle Science Editor

Ultimately, they say, the nation's blood supply could be made even safer than it is now -- and thoroughly protected even against HIV, the AIDS virus.

The doctors of ancient Egypt saw that people who ate a common weed growing on the banks of the Nile quickly developed severe sunburns marked by intensely darkened skin when they were exposed to bright sunlight.

Those physicians did not realize that they had discovered a class of natural chemicals that remain inert until the sun's ultraviolet radiation brings them into activity.

The Egyptians used the plants to treat patients for the disfiguring disorder called vitiligo, in which dark-skinned people develop blotchy pale patches because some skin cells lose their pigmentation.

Activated by sunlight, the plant compounds darkened the white patches, and that reaction is still used to treat vitiligo.

The chemicals in the Egyptian weeds are called psoralens, and they are also found in a wide range of other plants, including buttercups, figs, limes and parsnips. Modern researchers have developed a process known as photoactivation using ultraviolet lamps to turn the chemical activity of psoralen compounds into a weapon for treating a fatal form of skin cancer, cutaneous t-cell lymphoma, and psoriasis, a more common and distressing skin disorder.

SAFER TRANSFUSIONS

Now a team of scientists at the University of California in San Francisco and the California Department of Health Services has learned to turn on the activity of synthetic psoralens to decontaminate whole blood. Scientists believe this development can assure the safety of the nation's blood supply for transfusions.

Batteries of screening tests now used by every blood bank in the nation can detect with near-certainty the presence of seven disease-causing viruses, including HIV. But safe though the blood is, there is always a remote chance that a virus might escape detection, and the ability to purify all donated blood with certainty would be a major contribution to transfusion safety.

Dr. Laurence Corash, UCSF professor of laboratory medicine, and Dr. Carl V. Hanson, chief of the state's virus laboratory in Berkeley, led groups that have tested simple systems for killing both viruses and bacteria in blood plasma and platelets by using psoralens activated under ultraviolet light.

The federal Food and Drug Administration has just authorized the first human trials in which blood treated with a psoralen compound and then irradiated with ultraviolet light will actually be transfused into volunteer patients.

It will take at least five more years, however, before the complex series of trials in humans proves that the system is both completely safe and effective, Corash said.

CHIMP EXPERIMENTS

In experiments with chimpanzees, the UCSF team contaminated human blood plasma with infectious doses of hepatitis virus and treated the plasma with a psoralen compound that was activated by ultraviolet light before it was transfused into the chimps. The chemical swiftly killed all the viruses, and six months after the transfusions none of the animals showed any evidence of virus infection, Corash and his colleagues have reported.

As a result of other experiments by other research groups, Corash said in a recent interview, "There's lots of data that shows we haven't encountered a single virus the system can't kill -- whether the virus infection is in cells or outside the cells. And the system is so simple you could build it in your garage."

In another series of experiments, the UCSF group focused on protecting blood platelets from infection by bacteria, a problem that can arise when platelets are stored for a long time. Platelets are the cells that cause blood to clot, and platelet transfusions are essential for treating patients undergoing cancer chemotherapy or who have had transplants of bone marrow or organs.

In recent laboratory experiments, transparent plastic bags of platelet concentrates from the Alameda-Contra Costa Blood Bank were inoculated with two common strains of bacteria and three viruses, then dosed with 8-MOP, a psoralen compound, and irradiated with long-wavelength ultraviolet light. The researchers reported recently in the scientific journal Blood that the system quickly inactivated all the microorganisms with no damage to the platelets and their ability to perform their clotting function.

INACTIVATING AIDS VIRUS

In Hanson's Berkeley laboratory, the team has developed similar techniques for inactivating the AIDS virus by destroying its genetic core while leaving the proteins on the outer surface of the virus intact. In this way, the virus is rendered noninfectious and can be used without danger for diagnostic tests and other experiments, Hanson said in an interview.

Working with Red Cross researchers, Hanson and his colleagues are also exploring different psoralen compounds and different wavelengths of ultraviolet light to make the system even more specific and more effective.

"The prospect of learning to inactivate known and even unknown viruses that may contaminate blood is an exciting one," he said.

Always watch for outdated information. This article first appeared in 1991. This material is designed to support, not replace, the relationship that exists between you and your doctor.

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