Man's Scent Depends on Woman's Perception

[abdulhakeem]

By Dave Mosher (dmosher@imaginova.com), LiveScience Staff Writer
16 September 2007

If the sweaty guy standing in line next to you smells like vanilla—or urine—you may have whiffed a steroid in his body odor called androstenone.

The chemical can take on either a vanilla or "woodsy" urine scent, depending on which version of a mutated odor gene carried by you, the person doing the smelling, a new study has shown.

"People who express different variants of this receptor perceive this odor (http://www.livescience.com/health/060522_mm_smell.html) differently," said study co-author Leslie Vosshall, a molecular neurobiologist at Rockefeller University here in New York City. "This is the first study linking differences in how a chemical smells down to a gene."

Potpourri of perception

When people sniff androstenone, Vosshall said, roughly a third detect vanilla, a third report urine and the final third smell nothing at all.

"The polarization of sensitivity is really also quite extreme," she said. "Some people are overwhelmed by an amount 10-billion-fold dilution while some can't smell anything at all."

Vosshall said she's in the "top 5 percent" of sensitive smellers and picks up a stinky urine smell.

"If someone sneaks a tissue into my office that's even been around androstenone, it smells like my head is in the armpit (http://www.livescience.com/health/060118_armpit_odor.html) of a guy who's been running for 100 days without showering," she told LiveScience.

Vosshall and her colleagues' findings on the odor gene, called OR7D4, are detailed online today by the journal Nature.

Take a whiff

To discover the genetic link to androstenone's smell, Vosshall and her colleagues at Duke University in North Carolina exposed about 400 volunteers to 66 different chemicals, including nutmeg, anise, vanilla and androstenone. Each subject noted the intensity and presumed smelly identity of each chemical, then researchers took blood samples to see how androstenone affected the subjects' DNA in a separate experiment.

Those with the more common version, or allele, of the OR7D4 odor-receptor gene described androstenone as "sickening," while those with a slightly different allele detected vanilla.

The gene now explains about 30 percent of the variation in people's perception of androstenone—leaving researchers uncertain what other biology affects perceiving the chemical—but Vosshall said that the link was very strong compared to other genetic mysteries

"Thirty percent is extremely high when you consider genes responsible for breast cancer explain only 10 percent of breast cancer cases," Vosshall said. "There are probably other odor genes responsible for the differences in sensitivity and perception of androstenone."

Sexy signal

The discovery is important because smells are a big part of being human, Vosshall said. While androstenone may be a guy thing (http://www.livescience.com/health/041104_sex_and_smell.html), mainly because it's derived from the hormone testosterone, female pig studies show a whiff of it can have profound effects on biology.

"Farmers spray it on female pigs in heat, and they'll get in position for mating almost instantly—no questions asked," Vosshall said. "In human females, studies show it may cause arousal (http://www.livescience.com/humanbiology/top10_aphrodisiacs.html), sweating and a surge in stress hormones. Women are also much more sensitive to it near ovulation."

She explained that while androstenone's "funny effects" on women are intriguing, the jury is still out on whether it's a pheromone. "It seems like the human brain has some filters against it, but it's doing something different from smelling cheesecake or strawberries," she said.

Vosshall said such signals may be important in social settings, such as landing a date in a club or politely rejecting a tuna sandwich, but research has been limited.

"We want to see what other things are going on in human genes when we smell things, because how we experience odor (http://www.livescience.com/mysteries/070425_you_stink.html) is a big part of the human experience," Vosshall said. "Knowing how much of our perception was drummed into us as kids and how much of it is genetic is a really important topic in science."

http://www.livescience.com/health/070916_odor_gene.html

[abdulhakeem]

Stinky? It's not his sweat, it's your nose
September 16, 2007
By Julie Steenhuysen

CHICAGO (Reuters) - When it comes to a man's body odor, the fragrance -- or stench -- is in the nose of the beholder, according to U.S. researchers who suggest a single gene may determine how people perceive body odor.

The study, published online on Sunday in the journal Nature, helps explain why the same sweaty man can smell like vanilla to some, like urine to others and for about a third of adults, have no smell at all.

"This is the first time that any human odorant receptor is associated with how we experience odors," Hiroaki Matsunami of Duke University in North Carolina said in a telephone interview.

Matsunami and colleagues at Duke and Rockefeller University in New York focused on the chemical androstenone, which is created when the body breaks down the male sex hormone testosterone.

Androstenone is in the sweat of men and women, but it is more highly concentrated in men. How one perceives its smell appears to have a lot to do with variations in one odor receptor gene called OR7D4.

"It is well known that people have different perceptions to androstenone. But people didn't know what was the basis of it," Matsunami said.

To find out, researchers in Matsunami's lab tested sweat chemicals on most of the 400 known odor receptors used by the nose to sniff out smells and chemicals.

They found the OR7D4 gene reacted strongly with the sex steroid androstenone. Next, they tested whether variations in this gene had an impact on how people perceived the smell of androstenone in male sweat.

They took blood samples and sequenced the DNA of 400 people who participated in a smell perception test done in Leslie Vosshall's lab at Rockefeller.

What they found is slight genetic variations determine whether androstenone has a pungent smell, a sweet, vanilla-like smell or no smell at all.

The role of androstenone is not well understood in humans, but in pigs it sends a powerful sex signal that puts sows in the mood for love.

"It facilitates the courtship behavior in females," Matsunami said.

"There is some evidence published showing this chemical can modify the mood or hormone levels in humans," he said. "What we don't know is whether the receptor we found was in any way involved in this process."

He and colleagues will further study this aspect to understand how smelling these chemicals might affect human social and sexual behavior.

http://www.sciam.com/article.cfm?alias=stinky-its-not-his-sweat&chanId=sa003&modsrc=reuters

[LostInThought]

takes me back to that age old question, does red look red to everyone? what if what I think is red looks blue to someone else.

[elji]

Interesting

[abdulhakeem]

The sweet smell of testosterone, or not

By Marlowe Hood in Paris
September 17, 2007
AFP

SMELL is in the nose of the beholder as much as beauty is in the eye, according to a new study showing for the first time that variations in a single gene can determine whether a scent is perceived as fair or foul.

It has long been known that smell and taste - which are essentially the same thing - are highly subjective.

The fragrance that one person finds sublime could make someone else queasy, and one man's wine of the gods can be another man's plonk.

A third person might not smell anything at all.

But the exact mechanism accounting for these differences has remained largely a mystery, though genes were known to play a role.

The US study, published online in the British journal Nature, fills in a piece of the puzzle.

Subjects in a "smell survey'' conducted by Leslie Vosshall at Rockefeller University in New York judged the intensity and pleasantness of dozens of odours, including a testosterone-derived steroid called androstenone found in human urine and sweat, especially in men.

Most of the respondents said the compound smelled something like "stale urine". But a significant minority - about 20 per cent - found the odour pleasing, saying it reminded them of vanilla or honey.

Another research team at Duke University in North Carolina, meanwhile, had discovered in laboratory experiments led by Hiroaki Matsunami that androstenone switched on a human odour gene called OR7D4.

Humans have several hundred functional odorant receptor genes, but olfactory sensory neurons in the nasal passage only express, or activate, them one at a time.

In a collaborative effort, the two teams used DNA samples from each of the smell survey participants to sequence the gene that encodes the OR7D4 receptor.

In some of the subjects, they discovered, the gene had undergone a slight mutation called single nucleotide polymorphisms (SNPs) in which a few of the basic, paired building blocks of DNA has changed. This gave rise to two variants of OR7D4.

When they lined up the results of the DNA analysis with the subjective "smell survey", there was a very strong match between the two sets of groups: those who thought androstenone smelled like old cat pee had one variant of the gene, and those who smelled sweet vanilla had the other.

"With this large data set, we are able to say that people who express different variants of this receptor perceive this odor differently", said the study's lead author, Andreas Keller.

In another study, in Nature Chemical Biology, scientists at Brown University in the US finally figured out why dirt smells like dirt.

The structure of geosmin - the chemical that yields the loamy smell of freshly ploughed earth - has been known for decades, but exactly how the micro-organisms that make it went their work remained obscure.

David Cane and colleagues discovered that the Streptomyces coelicolor enzyme produces geosmin in a two-step process rather than a single one, as previously thought. One half of this protein, they found, catalyses an intermediate chemical that is then transformed by the other half into the pungent chemical.

Because geosmin can cause an undesirable musty smell in water, food and wine, understanding the biosynthesis of this earthy odour may help reduce these unwanted odours.

http://www.news.com.au/story/0,23599,22431150-23109,00.html