Game-changing prostate cancer test, and magnetic turtles

Artificial sweeteners have promised to be a guilt-free way to indulge a sweet tooth without the caloric consequences of added sugar. But a research project inspired by a student drinking a can of low-calorie fizzy drink and published this week in Cell Metabolism suggests sweeteners might not be a free lunch after all. Giving mice small - human relevant amounts - of one of the most popular artificial sweeteners, aspartame, led to accelerated rates of arterial disease in the animals. The team think that a high levels of insulin, provoked by the sweet taste, are behind the damaging effect. Yihai Cao is Professor of Vascular Biology at the Karolinska Institute in Sweden…

Yihai - This study was initiated from a can of diet soda. It has been estimated that in the United States, 60% of young people may consume these kinds of beverages. As a scientist, I supervise students. One of the students asked me for projects. He was holding a diet soda can. I said, what are you drinking? He said, I'm drinking a sugar-free beverage. I said, why don't you do a project like that? We have a lot of experimental mouse models, I said, why don't you get these smaller animals to drink this to see what happens to their body? So this is how it started.

Chris - What health impacts specifically were you hoping to probe with your mice drinking fizzy pop?

Yihai - My expertise is in studying blood vessels, cardiovascular disease, stroke, diabetes. So at that time we had a disease model called atherosclerosis. Within the large blood vessel, they form plugs. So I asked the students to let these mice consume artificial sweetener.

Chris - So you have mice that are prone to developing arterial disease like a human does. You feed those animals the same stuff that sweetens a sugar-free beverage. And then you're asking, does this have any impact on the progression of the vascular disease that these animals naturally develop?

Yihai - Exactly. So this is the first experiment we did.

Chris - And what sort of doses of the sweeteners were you administering? Because one criticism of experiments like this is we end up feeding kilogram quantities of things to tiny animals and it's not representative at all. So what was the dosing pattern that you exposed the animals to?

Yihai - So the dosing we used is calculated not based on the weight, how many grams, it's based on the sweetness. For example, aspartame is 200 times more sweet than sucrose. So we converted that formula to make it equivalent to what we consume in the sugar soda, for example.

Chris - And do the rodents like eating this? Will they actually consume this? And will they regularly consume it as though they were consuming with a similar pattern to a human using these sorts of foodstuffs?

Yihai - Mice, they like sweet things very much, even more than people. So if we allow them to drink themselves, they could drink all day long. That's maybe consuming too much. In order to give them a defined dose, we basically drop it on their face, and then they use their front paws to lick.

Chris - Okay, so they don't overdose on the sweetener. What happens though, when you look in the blood vessels, do you see a difference in the animals consuming the artificial sweetener compared to animals eating normal rodent chow?

Yihai - Yes, we saw, very surprisingly, arterial vessel damage is increased when they consume more aspartame.

Chris - When you say increased, is it increased by much, or is it very subtle? Is it a dramatic difference?

Yihai - It is statistically significant. Both the plug numbers and the plug size are increased.

Chris - And what do you think the mechanism is behind this? What's driving that?

Yihai - We think it's related to the sweet taste. So there is in the mouth, in the intestine, sweet taste receptors. So when we eat something sweet, our body can release insulin. Insulin, after consumption of aspartame, is increased in the blood. The first organ in our body that could sense this is the blood vessel. On the vessel wall, the inside cells are called endothelial cells. So what is the insulin impact on these endothelial cells? Very surprisingly, one of the most upregulated genes is the inflammatory protein. This inflammatory protein can cause inflammation in the blood vessels.

Chris - Putting all that together then, if you ingest these chemicals, although there is no sugar there, they fool the body into thinking it's had a massive dose of sugar, which then drives a massive release of insulin, to which blood vessels are highly sensitised. And when the insulin activates them, it produces an inflammatory signal, and you're contending that that inflammation is upstream of forming these deposits in the wall of the arteries that will eventually turn into arterial disease.

Yihai - Correct. What you said is absolutely correct.

Chris - Do we think this is physiologically relevant in humans? Are we as humans, in striving for a healthier lifestyle and drinking these diet beverages then, and eating diet foods and snacks that are full of this stuff, are we actually doing ourselves more harm than if we just ate a sweet cake?

Yihai - In our study, we did not do human studies, but there's no reason we can see that it would not happen in humans in this way. So I would expect that a similar mechanism may exist in humans as well. I would not recommend myself to consume this.

Chris - I was just going to say, has everyone in your group given up drinking artificially sweetened beverages? Do you not have lab meetings where there's no fizzy pop with aspartame in it anymore?

Yihai - One of the students usually consumes many kinds each day, but he stopped completely after doing this project.

A new study has found that the loggerhead turtle can recognise and remember the magnetic signature of the Earth. They probably rely on this ability to navigate and recall the best places to find food. The discovery has just been published in the journal Nature, and the paper’s author is Texas A&M University’s Kayla Goforth…

Kayla - So I was investigating whether turtles are able to learn magnetic fields. We know that turtles have a magnetic map sense or a positional sense that they can use like a GPS to identify where they are and a compass sense, like a directional sense that tells them which direction to go. But what we didn't know is how they were getting back to these really specific places and whether or not they could learn specific magnetic fields with their magnetic map.

Chris - It's the distinction then, the difference between having a sort of magnetic chart in your head and knowing where you are in relation to the magnetic field versus knowing what direction you're heading in and then using separate memories to remember the chart and the layout of the bit of the sea that you're in. Is that the distinction here?

Kayla - Yeah, exactly. It's kind of like if we were walking down the street trying to get home, we might have a compass in our hand that's telling us we're going north. But if we don't know which direction our home is relative to that, then we would have no way to actually get home.

Chris - Could the turtles be doing both?

Kayla - Yeah. So we expect they are doing both. They're determining where they are and then using their compass to get back there.

Chris - And how did you test this out?

Kayla - We conditioned sea turtles, which is sort of like training sea turtles or when you train your dog, we conditioned them to tell the difference between one magnetic field in which they received food and one magnetic field in which they did not receive food. So every other day they would go into the field in which they received food and they would eat their food, which consisted of some squid and shrimp, which is a really high reward for them. And then on opposite days, they would experience a magnetic field in which they were not fed. And eventually we begin to see that they would do what we call the turtle dance in the magnetic field that they were fed in.

Chris - And that's the giveaway that they must be sensitive to the magnetic field because they were dancing when it was pointing one way, anticipating getting fed, than when the magnetic field was the other way.

Kayla - Yeah, exactly. So the turtle dance is a behaviour that they exhibit in captivity when they're expecting food. They stick their heads out of the water, they open their mouths, they start to move their flippers really rapidly and spin around. So it demonstrated to us that they could recognise that field as being associated with the food, whereas in the other food, they didn't do that behaviour quite as much.

Chris - And how do you think they're actually doing this? Do we have an insight as to how the turtles might be registering the magnetic field?

Kayla - We don't know how their magnetic map sense works, but I did some experiments that demonstrated that the map and compass sense are probably relying on two different mechanisms. So what we did to test this is we exposed the turtles in both their training assay to what's called radiofrequency fields. And these radiofrequency fields are expected to disrupt a type of magnetoreception that's called chemical magnetoreception. So chemical magnetoreception just says that complex chemical reactions might underlie magnetic sensing and give animals the ability to detect magnetic fields. So these radiofrequency fields had no effect on the turtle's ability to recognise the magnetic field that they received food in. But then we did a second experiment where we asked the turtles to orient in a specific direction in a magnetic field. And in this experiment, when the turtles were exposed to radiofrequency, they could no longer orient properly, meaning their compass was affected. So their compass probably relies on chemical magnetoreception, but the map, we don't know what that mechanism is yet.

Chris - Interesting. So they're using some kind of chemical way to detect what way they are oriented with respect to the Earth's magnetic field. And they're using some other mechanism to log the magnetic sense of where they are in relation to the world. So they've got two independent mechanisms going on potentially.

Kayla - Yes, that is what we suspect, kind of like how our eyes are for seeing and our nose is for smelling. Those are two distinct senses.

Chris - But we don't yet know where in the nervous system, presumably, that this kind of transduction to detect the field is happening.

Kayla - Correct. We have no idea. Magnetic fields can pass through all tissue, and so magnetic receptors that detect the magnetic fields could be anywhere in the body.

Chris - And does that have implications for conservation as well? Because do we use any of these same electromagnetic frequencies that are known via your experiments to disrupt the ability of the turtles to see, in inverted commas, magnetic fields?
Kayla - Yeah, it does have conservation implications. These radio frequency fields that disrupted the compass are actually produced by pretty much every electronic device that we use. So when turtles are coming to shore to lay their eggs or when the hatchlings are leaving the shore, they could be affected by radio frequency fields that are produced from the nearby houses or radio towers or cell phone towers. So that's something that we should be aware of.