Of Isotopes and Isomers

Note: If you’re looking for the discussion of the Ferret documents, click here.

I’ve seen a few discussions of the Landis case lately where the participants were unsure whether CIR refers to Carbon Isotope Ratio or Carbon Isomer Ratio. There’s quite a difference between isotopes and isomers, so let’s go over what each one is.

An isotope is a variant of an element, such as carbon. The most common form of carbon, carbon¹², contains 6 protons and 6 neutrons. The number of protons in an element determines which one it is. Carbon has 6 protons, so it is element #6 in the “Periodic Table” familiar to physicists, chemists and other scientists. But there are a couple of variants of carbon that have one or two extra neutrons. Still chemically the same, but the atoms are a bit heavier than the most common form. Those variants are carbon¹³ and carbon¹⁴, respectively.

Carbon¹⁴ is somewhat radioactive and is used in determining the age of materials, because it breaks down to carbon¹² at a known rate. This means that over time, there is less carbon¹⁴ than when the compound was new, and the amount of the difference can be used to get an approximation of the age. Carbon¹⁴ dating is very useful for archaeologists in determining the age of items discovered at archaeological dig sites.

An isomer is a compound that has the same chemical formula as another compound, but it has a different shape. Propanol and Isopropanol, which are both alcohols, would be good examples. They both have the same chemical formula: C₃H₈OH. The part that makes these compounds alcohols is the OH group, an oxygen atom attached to carbon atom, where the oxygen atom has a hydrogen atom attached as well.

This group can be attached at either end of the three-carbon chain or it can be attached to the middle carbon. Propanol (CH₃CH₂CH₂OH) has the OH attached to the end, and Isopropanol (CH₃CH(OH)CH₃) has the OH attached to the middle. This gives the two compounds some slightly different properties and also different shapes.

Hopefully, I haven’t lost anyone yet.

So, back to CIR, which is it: isotope or isomer? The answer is isotope. CIR (also called IRMS) measures the relative amount of carbon¹³ in a compound compared to a reference compound. The idea is that when compared to a reference hormone, the hormone you’re testing should have a certain difference in the percentage of carbon¹³, and if the difference exceeds a certain threshold, the hormone you’re testing is believed to come from outside the body.

In theory, hormones made within the body will have a certain percentage of carbon¹³ and that percentage is consistent. Synthetic hormones made outside the body will have a different percentage of carbon¹³. We’ll get back to this in a moment.

Now here’s where it gets tricky for the Landis case. The reference hormones used in the WADA protocols are materials created by the breakdown of cortisone in the body. If you recall, Floyd Landis had a therapeutic use exemption (TUE) for cortisone due to his hip condition.

But what that means is that the reference hormones for Landis, in part, contained material that was produced synthetically. And this is a very important consideration, because when measuring the relative difference between the percentage of carbon¹³ in the reference and the percentage of carbon¹³ in the testosterone from Landis’ urine sample, the variation could be different than had he not been taking cortisone.

The picture gets complicated a bit further (what else is new?) because it turns out that WADA themselves have research indicating that diet can have an effect on the amount of carbon¹³ in compounds produced within the body. Compounds like, say, testosterone.

OK, so there’s a number of variables at play here that could explain the Landis result. Rumor has it that Landis’ test result was 3.9, where a positive result is deemed to be anything exceeding a difference of 3. That doesn’t necessarily mean it’s a true positive, just that WADA thinks it’s so.

The factors affecting the amount of carbon¹³ in the reference hormones, combined with factors that may affect the amount of carbon¹³ in Landis’ testosterone (factors like diet, alcohol intake, and so on) may account for his result. It’s hard to say. Perhaps this will be part of the defense whenever the arbitration hearing is held.

Mr. Ferret, if you’re reading, perhaps you can find us some of the pages from the CIR/IRMS studies, too? They would make interesting reading, and shed even more light on the case.

But let’s loop back to the isotope versus isomer question in regard to testing. There appear to be a number of mitigating factors that can affect the amount of carbon¹³ in various hormones, which perhaps makes the current testing inadequate or unable to reliably tell whether a person is doping.

There is another way. And that involves isomers, of a sort. You see, when the body makes hormones, it makes them in specific shapes so that they will combine with the appropriate receptors and do whatever it is they’re supposed to do. And because it builds these hormones from the same compounds in the same ways, it produces the same shapes very consistently.

And that’s important for the following reason: The hormones fit the receptors the same way a key fits a lock. Use the wrong key, the lock won’t open. Wrong shape for the hormone and it doesn’t fit the receptor, which makes the hormone useless.

Now when hormones are made synthetically, you wind up with some that are the right shape and some that are different shapes. The reasons are complicated, so I won’t go into them here. And often, it is very hard (or too expensive) to separate the different forms.

So with synthetic testosterone, some of what is in there is of a shape that doesn’t fit the testosterone receptors. If there were a method for testing the shapes of the testosterone, you would have a more reliable test. Not perfect, because it’s still possible that the body could create some isomers of the hormone that don’t fit the receptors, but determining the natural rate of that production could be part of the testing process (if necessary by creating a bank of normal values for each individual). The test then could be used to see if the athlete had too much of these isomers, which would perhaps be a better indicator of doping than the CIR/IRMS test.

So to bring this full circle, the people asking about whether the test was of isotopes or isomers were on the right track, they just didn’t know it. Why hasn’t an isomer test been developed? Well, to go back to yesterday’s discussion, my guess is that it would not be cheap and would require highly skilled personnel — exactly the opposite of what WADA wanted to accomplish with the test for testosterone.

Is this something that WADA should look into? Absolutely. To make testing “foolproof” they need to develop tests that can truly differentiate between naturally occuring hormones and synthetically manufactured hormones. Right now the testing process (as someone else observed) might better be called “fools proof.”