[naturenews] from [nature.com]
[naturenews]
Published online 13 January 2010 | Nature | doi:10.1038/news.2010.7
News
Bisphenol A link to heart disease confirmed
Second study supports an association between the chemical and cardiovascular problems.
Brendan Borrell
{{Bisphenol A, which is present in some plastic bottles, has been linked to heart problems.}
clix/stock.xchng}
Scientists have once again found that people with higher levels of bisphenol A (BPA) in their urine are more likely to have heart disease than those with lower urinary BPA levels.
Used to make some plastic drinks bottles and the inner coatings of food cans, BPA can mimic the effects of oestrogen and has been associated with a number of conditions in animal studies, including low sperm count, prostate cancer and fetal developmental problems. In 2008, researchers first linked BPA to diabetes and heart disease in humans1, but industry lobby groups such as the American Chemistry Council in Arlington, Virginia, have vigorously disputed those findings.
Now, the same researchers are back with a second report in PLoS ONE2, which uses an independent data set to come up with broadly similar, if weaker, results. "It's only the second data set from a big population to be released," says lead author David Melzer of the Peninsula Medical School at the University of Exeter, UK. "It shows that our first paper wasn't a statistical blip."
Divided opinion
Melzer and his co-authors analysed data from the 2005–06 US National Health and Nutrition Examination Survey of 1,493 adults, who provided urine samples and completed questionnaires about their health. Higher concentrations of BPA in the subjects' urine were associated with cardiovascular disease, but not with diabetes or high levels of liver enzymes, which indicate liver damage. However, BPA concentrations were 30% lower in this survey than in the 2003–04 survey used in the team's previous study, although when the two samples were pooled, diabetes and liver-enzyme associations remained statistically significant. Based on the data, a 60-year-old man with the lowest levels of BPA in the survey had about a 7.2% chance of developing cardiovascular disease whereas a similar subject with levels three times higher faced about a 10.2% risk.
The results add to a limited number of human studies on the effects of BPA, but are unlikely to bring together the two sides of the highly charged debate on the chemical's safety. Toxicologist Frederick vom Saal of the University of Missouri in Columbia, a long-time critic of the regulations governing the use of BPA, says that identifying such an association from epidemiological data is alarming. "The important issue is there have got to be 100 plus factors involved in any one of these diseases, and you are looking at one chemical, one time in a spot urine collection, and it's popping up as a significant variable," he says, "That's impressive because that's something you can do something about."
But Steven Hentges of the American Chemical Council says that the fact that some of the team's original results were not independently supported raises more questions than it answers. "The weight of scientific evidence continues to support the view that BPA is not a health concern," he says. "If you think that this study raises a hypothesis – fair enough – but the fact that they have not been able to replicate most of what they reported before is very telling."
Missing mechanism
Indeed, other scientists agree that what is still missing from the research is a demonstration of the mechanism of action. "Association studies show something really is going on, but getting to a definite mechanism of cause and effect is what we can add with animal studies," says Scott Belcher of the University of Cincinnati in Ohio, who has begun a series of studies on mice and rats funded by the National Institute of Environmental Health Sciences in Research Triangle Park, North Carolina.
Scientists have long known that oestrogen has the potential to affect heart function through the oestrogen beta receptor, and Belcher is looking at how BPA affects calcium levels, which control heart contractions. His early results show that BPA, like oestrogen, causes an irregular heartbeat in female rats, which could increase the risk of a heart attack. Belcher is planning further studies in rodents to look directly at the risks of heart attack, obesity and changes in the cardiovascular system.
The policy on BPA in the United States seems to be caught in a loop. The Food and Drug Administration has delayed a promised 'update' on its position that the chemical is safe. "We'll be making an announcement soon," says agency spokeswoman Meghan Scott, although she was unable to be more specific about the timing of the announcement.
References
1. Lang, I. A. et al. J. Am. Med. Assoc. 300, 1303-1310 (2008).
2.Melzer, D. et al. PLoS ONE 5, e8673 (2010).
[naturenews]
Published online 13 January 2010 | Nature | doi:10.1038/news.2010.8
News
Parasitic larva ditches doomed host
A cunning insect detects when its host is under threat from predators to make a timely escape.
Lucas Laursen
Attack by predators prompts Endaphis fugitiva to emerge from its host.Muratori et alA recently discovered fly, Endaphis fugitiva, may be the first known parasitic insect that is able to escape a host that is under attack from predators. When researchers injured the fly's host — called the banana aphid — or let brown lacewings attack the aphids, the fly larvae broke out of the aphid's body (see video).
Many animals change the niche they occupy in an ecosystem during their development — a process called heterokairy. In some cases, animals can respond to environmental factors by adjusting the time at which heterokairy starts. Frogs' eggs, for example, can hatch early if they come under attack from leeches, wasps or snakes. But E. fugitiva, a 'parasitoid' that kills its host when it leaves, may be the first such insect that can tell when its host is about to be overwhelmed by a predator, says Frédéric Muratori, a behavioural ecologist at the Université Catholique de Louvain in Belgium. Muratori and his colleagues reveal their results in a study1 published in the journal Proceedings of the Royal Society B today.
Whereas E. fugitiva larvae that abandoned their aphid hosts grew to about the same adult fly size as those that grew in healthy hosts that were not attacked, Muratori and his colleagues report that the early escapers spent slightly longer in the vulnerable stage of pupation than other larvae.
"I think the main issue that comes out of this is that organisms are willing to sacrifice some minor fitness in order to survive," says parasitoid ecologist Jeffrey Harvey of the Netherlands Institute of Ecology in Heteren, who was not involved in the study but peer-reviewed the work.
The extra danger of the prolonged pupal stage may be why the fly normally stays inside its host. Harvey explains that in most parasites he's worked with, it's "game, set and match" if the host is eaten by a predator, as both parasitoid and host will die. But in this case, he says, "When the jaws of a predator clamp around the host, the fly larva detects that and pops its way out."
Stay or go?
The ability of E. fugitiva larvae to shift niches adaptively may help them to avoid being killed along with their host, but it comes at the cost of having to devote resources to detecting and avoiding threats, write Muratori and his co-authors. The researchers speculate that the larvae detect their host's imminent demise either by sensing chemical cues, such as stress factors in the aphid's blood-like 'haemolymph', or by perceiving the mechanical pressure of a predator's attack on the aphid.
Muratori began looking at this particular fly parasitoid while working for the United States Department of Agriculture in Hawaii, where entomologists use organisms similar to E. fugitiva to biologically control foreign pests such as aphids. Parasitoids, unlike true parasites, spend some stages of their lives inside their hosts but other stages are completed as free-living organisms outside the host. In the case of E. fugitiva, the larvae are born on leaves, then identify nearby vacant host aphids and climb inside, via the joint between the aphid's leg and its body. After growing by eating the aphid's body tissue, they emerge and go through a pupal stage in the soil while they metamorphose into flies.
Muratori would like to repeat the experiment with other parasitoids in which multiple individuals occupy a host's body to learn if any stressors prompt just a few of them to escape and to understand at what point individual larvae decide to leave.
To understand the trade-offs between the fly larvae hanging on or abandoning ship, Harvey suggests that the researchers could also compare the behaviour of larvae inside host aphids that are at a high risk of predation — such as those on exposed leaves — with those that are more hidden away. "We don't know the mortality risk of the larvae outside of the host," Muratori agrees. "This is a really key question."
References
1. Muratori, F. B., Borlee, S. & Messing, R. H. Proc. R. Soc. B advance online publication doi:10.1098/rspb.2009.2029 (2010).
[naturenews]
Published online 13 January 2010 | Nature | doi:10.1038/news.2010.7
News
Bisphenol A link to heart disease confirmed
Second study supports an association between the chemical and cardiovascular problems.
Brendan Borrell
{{Bisphenol A, which is present in some plastic bottles, has been linked to heart problems.}
clix/stock.xchng}
Scientists have once again found that people with higher levels of bisphenol A (BPA) in their urine are more likely to have heart disease than those with lower urinary BPA levels.
Used to make some plastic drinks bottles and the inner coatings of food cans, BPA can mimic the effects of oestrogen and has been associated with a number of conditions in animal studies, including low sperm count, prostate cancer and fetal developmental problems. In 2008, researchers first linked BPA to diabetes and heart disease in humans1, but industry lobby groups such as the American Chemistry Council in Arlington, Virginia, have vigorously disputed those findings.
Now, the same researchers are back with a second report in PLoS ONE2, which uses an independent data set to come up with broadly similar, if weaker, results. "It's only the second data set from a big population to be released," says lead author David Melzer of the Peninsula Medical School at the University of Exeter, UK. "It shows that our first paper wasn't a statistical blip."
Divided opinion
Melzer and his co-authors analysed data from the 2005–06 US National Health and Nutrition Examination Survey of 1,493 adults, who provided urine samples and completed questionnaires about their health. Higher concentrations of BPA in the subjects' urine were associated with cardiovascular disease, but not with diabetes or high levels of liver enzymes, which indicate liver damage. However, BPA concentrations were 30% lower in this survey than in the 2003–04 survey used in the team's previous study, although when the two samples were pooled, diabetes and liver-enzyme associations remained statistically significant. Based on the data, a 60-year-old man with the lowest levels of BPA in the survey had about a 7.2% chance of developing cardiovascular disease whereas a similar subject with levels three times higher faced about a 10.2% risk.
The results add to a limited number of human studies on the effects of BPA, but are unlikely to bring together the two sides of the highly charged debate on the chemical's safety. Toxicologist Frederick vom Saal of the University of Missouri in Columbia, a long-time critic of the regulations governing the use of BPA, says that identifying such an association from epidemiological data is alarming. "The important issue is there have got to be 100 plus factors involved in any one of these diseases, and you are looking at one chemical, one time in a spot urine collection, and it's popping up as a significant variable," he says, "That's impressive because that's something you can do something about."
But Steven Hentges of the American Chemical Council says that the fact that some of the team's original results were not independently supported raises more questions than it answers. "The weight of scientific evidence continues to support the view that BPA is not a health concern," he says. "If you think that this study raises a hypothesis – fair enough – but the fact that they have not been able to replicate most of what they reported before is very telling."
Missing mechanism
Indeed, other scientists agree that what is still missing from the research is a demonstration of the mechanism of action. "Association studies show something really is going on, but getting to a definite mechanism of cause and effect is what we can add with animal studies," says Scott Belcher of the University of Cincinnati in Ohio, who has begun a series of studies on mice and rats funded by the National Institute of Environmental Health Sciences in Research Triangle Park, North Carolina.
Scientists have long known that oestrogen has the potential to affect heart function through the oestrogen beta receptor, and Belcher is looking at how BPA affects calcium levels, which control heart contractions. His early results show that BPA, like oestrogen, causes an irregular heartbeat in female rats, which could increase the risk of a heart attack. Belcher is planning further studies in rodents to look directly at the risks of heart attack, obesity and changes in the cardiovascular system.
The policy on BPA in the United States seems to be caught in a loop. The Food and Drug Administration has delayed a promised 'update' on its position that the chemical is safe. "We'll be making an announcement soon," says agency spokeswoman Meghan Scott, although she was unable to be more specific about the timing of the announcement.
References
1. Lang, I. A. et al. J. Am. Med. Assoc. 300, 1303-1310 (2008).
2.Melzer, D. et al. PLoS ONE 5, e8673 (2010).
[naturenews]
Published online 13 January 2010 | Nature | doi:10.1038/news.2010.8
News
Parasitic larva ditches doomed host
A cunning insect detects when its host is under threat from predators to make a timely escape.
Lucas Laursen
Attack by predators prompts Endaphis fugitiva to emerge from its host.Muratori et alA recently discovered fly, Endaphis fugitiva, may be the first known parasitic insect that is able to escape a host that is under attack from predators. When researchers injured the fly's host — called the banana aphid — or let brown lacewings attack the aphids, the fly larvae broke out of the aphid's body (see video).
Many animals change the niche they occupy in an ecosystem during their development — a process called heterokairy. In some cases, animals can respond to environmental factors by adjusting the time at which heterokairy starts. Frogs' eggs, for example, can hatch early if they come under attack from leeches, wasps or snakes. But E. fugitiva, a 'parasitoid' that kills its host when it leaves, may be the first such insect that can tell when its host is about to be overwhelmed by a predator, says Frédéric Muratori, a behavioural ecologist at the Université Catholique de Louvain in Belgium. Muratori and his colleagues reveal their results in a study1 published in the journal Proceedings of the Royal Society B today.
Whereas E. fugitiva larvae that abandoned their aphid hosts grew to about the same adult fly size as those that grew in healthy hosts that were not attacked, Muratori and his colleagues report that the early escapers spent slightly longer in the vulnerable stage of pupation than other larvae.
"I think the main issue that comes out of this is that organisms are willing to sacrifice some minor fitness in order to survive," says parasitoid ecologist Jeffrey Harvey of the Netherlands Institute of Ecology in Heteren, who was not involved in the study but peer-reviewed the work.
The extra danger of the prolonged pupal stage may be why the fly normally stays inside its host. Harvey explains that in most parasites he's worked with, it's "game, set and match" if the host is eaten by a predator, as both parasitoid and host will die. But in this case, he says, "When the jaws of a predator clamp around the host, the fly larva detects that and pops its way out."
Stay or go?
The ability of E. fugitiva larvae to shift niches adaptively may help them to avoid being killed along with their host, but it comes at the cost of having to devote resources to detecting and avoiding threats, write Muratori and his co-authors. The researchers speculate that the larvae detect their host's imminent demise either by sensing chemical cues, such as stress factors in the aphid's blood-like 'haemolymph', or by perceiving the mechanical pressure of a predator's attack on the aphid.
Muratori began looking at this particular fly parasitoid while working for the United States Department of Agriculture in Hawaii, where entomologists use organisms similar to E. fugitiva to biologically control foreign pests such as aphids. Parasitoids, unlike true parasites, spend some stages of their lives inside their hosts but other stages are completed as free-living organisms outside the host. In the case of E. fugitiva, the larvae are born on leaves, then identify nearby vacant host aphids and climb inside, via the joint between the aphid's leg and its body. After growing by eating the aphid's body tissue, they emerge and go through a pupal stage in the soil while they metamorphose into flies.
Muratori would like to repeat the experiment with other parasitoids in which multiple individuals occupy a host's body to learn if any stressors prompt just a few of them to escape and to understand at what point individual larvae decide to leave.
To understand the trade-offs between the fly larvae hanging on or abandoning ship, Harvey suggests that the researchers could also compare the behaviour of larvae inside host aphids that are at a high risk of predation — such as those on exposed leaves — with those that are more hidden away. "We don't know the mortality risk of the larvae outside of the host," Muratori agrees. "This is a really key question."
References
1. Muratori, F. B., Borlee, S. & Messing, R. H. Proc. R. Soc. B advance online publication doi:10.1098/rspb.2009.2029 (2010).
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