Large Study Finds No Link between Marijuana and Lung Cancer

May 24, 2006

The smoke from burning marijuana leaves contains several known carcinogens and the tar it creates contains 50 percent more of some of the chemicals linked to lung cancer than tobacco smoke. A marijuana cigarette also deposits four times as much of that tar as an equivalent tobacco one. Scientists were therefore surprised to learn that a study of more than 2,000 people found no increase in the risk of developing lung cancer for marijuana smokers. "We expected that we would find that a history of heavy marijuana use--more than 500 to 1,000 uses--would increase the risk of cancer from several years to decades after exposure to marijuana," explains physician Donald Tashkin of the University of California, Los Angeles, and lead researcher on the project. But looking at residents of Los Angeles County, the scientists found that even those who smoked more than 20,000 joints in their life did not have an increased risk of lung cancer.

The researchers interviewed 611 lung cancer patients and 1,040 healthy controls as well as 601 patients with cancer in the head or neck region under the age of 60 to create the statistical analysis. They found that 80 percent of those with lung cancer and 70 percent of those with other cancers had smoked tobacco while only roughly half of both groups had smoked marijuana. The more tobacco a person smoked, the greater the risk of developing cancer, as other studies have shown.

But after controlling for tobacco, alcohol and other drug use as well as matching patients and controls by age, gender and neighborhood, marijuana did not seem to have an effect, despite its unhealthy aspects. "Marijuana is packed more loosely than tobacco, so there's less filtration through the rod of the cigarette, so more particles will be inhaled," Tashkin says. "And marijuana smokers typically smoke differently than tobacco smokers; they hold their breath about four times longer allowing more time for extra fine particles to deposit in the lungs." The study does not reveal how marijuana avoids causing cancer. Tashkin speculates that perhaps the THC chemical in marijuana smoke prompts aging cells to die before becoming cancerous. Tashkin and his colleagues presented the findings yesterday at a meeting of the American Thoracic Society in San Diego. --David Biello

Scientists Identify Brain Region Responsible for Calculating Risk versus Reward

June 15, 2006

As any gambler knows, the most important decision is where to play. Some flit from table to table, machine to machine and game to game. Others prefer to settle in for the long haul. Now researchers have used those tendencies to probe the function of the human brain as it chooses between the familiar and the unknown. Nathaniel Daw and John O'Doherty of University College London and their colleagues employed slot machines and functional magnetic resonance imaging (fMRI) to investigate how 14 healthy subjects decided between reaping steady profits at a given slot machine or testing the profit potential of a new one. Scientists call the behavior of utilizing a known resource exploitation; the term they give to the behavior of seeking an even better resource is exploration. Although exploitation seems the safe bet, survival can depend on judicious use of exploration.

"The desire to select what seems the richest option is always balanced against the desire to choose a less familiar option that might turn out to serve better," Daw explains. "Most people switch between exploring and exploiting seamlessly and this has always made it hard to distinguish between someone who is doing something they know will offer the highest payout and a person who is testing out new options." To so distinguish, the neuroscientists set up four slot machines to pay off at four different average rates. After each trial, these payoffs changed randomly from machine to machine. In order to discover which slot machine paid the most, a given subject would have to select it at the risk of abandoning a higher paying machine. After the tests were completed, the subjects reported that they had occasionally tried different machines to find the highest reward and sometimes stuck with a slot that they thought offered the most.

The researchers were thus able to categorize whether the subjects were exploring or exploiting in any given trial. They found that human exploration follows the so-called softmax mathematical rule, in which subjects choose whether to explore or not based on the probability of a better payout. In other words, if you determine your reward at a given machine will be small, you are more likely to change. That much the slot machines and interviews revealed. The fMRI showed that the frontopolar cortex and sulcus of a given subject strongly activated when they chose to explore. Other studies have implicated these regions in behavioral control and decision making, according to the paper presenting the finding in today's Nature, but this is the first time neuroscientists have marked these areas of the brain as associated with investigating the unknown. Exploration turns out to be a controlled gamble after all. --David Biello

New Nanomaterial Fuses Spider Silk and Silica

June 14, 2006

Researchers have created a novel nanomaterial that combines the strength of spider silk with the rigidity of silica. The product could help pave the way for the fabrication of replacement bones. Regrowing bone requires a scaffold that is stiff, long-lasting and safe. With that in mind, David Kaplan of Tufts University and his colleagues decided to marry the protein that constitutes the drag lines of golden silk orb weaver spiders with the protein that helps diatoms--a subset of plankton--make silica, a glasslike compound. The spider-silk protein alone "just doesn't have the stiffness you want, that's why you need the glass," Kaplan says.

After splicing the two proteins together, the team then processed the resulting chimeric protein into both films and fibers and tested the result. As hoped, the films and fibers created dense silica coatings for themselves. By using electric current or varying conditions, the researchers could also control the size and shape of the resulting materials. "We were able to control and bring it down to two microns [wide]," adds team member Cheryl Wong Po Foo of Tufts. "We're going into the nanoscale range."

Initial tests of the nanomaterial's medical potential is being conducted in vitro, but the researchers hope to try it out in animals in the near future, using it to help guide the growth of a hip replacement, for example. The possibilities do not end there, however. The chimeric protein forms this material at low temperatures and without chemicals other than water. Current industrial practices for making silica require high heat and ionic extremes. "You can think of high performance materials made via an aqueous, room temperature, green chemistry," Kaplan notes. The research is being published online this week by the Proceedings of the National Academy of Sciences. --David Biello