Carcinogens and Me Part II: Understanding the Changes in Your Body

"This just in.  BCB may cause cancer."

Okay, so maybe there's no such thing as BCB, but how many times have you seen a headline like that?  "...may cause cancer"  "possible carcinogen..."  What on earth is that supposed to mean?  After seeing a few friends got all worked up about some (nonscientist) TV personality saying "there's no evidence that secondhand smoke causes cancer" I figured that would be a good example to help us wade through all this.

The first question is, how do you test a statement like 'secondhand smoke causes cancer'?  Easy!  You lock 100 people in one room with normal air for 8 hours a day and lock 100 people in another room with 5 chain smokers for 8 hours a day.  20 years later, see who's not dead.  Scientific? Yes.  Ethical?  Maybe not.  So what's a scientist to do?  Well here's a few more common ways people go about it:

Method 1: population studies.  In these, they track X people for Y number of years who are exposed to some amounts of substance Z.  These studies, properly interpreted, are definitely the silver bullet, "conclusive evidence" on any topic because they take just about everything into account.

Method 2: the Ames test.  No people, no mice, just cells.  Researchers take a bunch of bacteria and make a single mutation that makes the bacteria unable to make histidine, one of the 20ish common amino acids or protein building blocks.  With even one amino acid gone, cells can't make working proteins (try turning in an essay without the letter 'T', see what grade you get).  The scientists grow the bacteria in something that has the amino acid in it, so the bacteria can live without making it themselves.  Then, they take these cells and grow them in 2 cultures: one with the suspected carcinogen, and without.  Neither have histidine (the amino acid they can't make).  A "mutagen" will cause a lot of random changes in the DNA, some of which (and we're dealing with billions of cells here) happen to mutate the broken part of the bacteria's DNA back to its working form, so the bacteria can make their own histidine again, and you see colonies pop up all over your petri dish.  A "safe" chemical doesn't do anything, so you might see a few colonies from spontaneous DNA changes, but not too many.  So basically, lots of colonies = scrambled DNA, and that means the chemical you're testing is "mutagenic," which is a fancy word that means "does karate on your DNA."  And what does random DNA damage do to a guy?  If you forgot, check my last post.

So what's the bottom line?  "Probable carcinogen" or "may cause cancer" are phrases scientists use to say "this stuff messes up your DNA."  Are there problems with the Ames test?  Sure.  They're using bacteria, and humans aren't bacteria.  Obviously population studies are better.  The problem is that they take a long, long time to do.  Cancer studies are especially difficult, since people generally develop environmentally-induced cancer much later in life, so a solid, definitive study, started now, wouldn't be done for another 50-60 years.  So what does it all mean?  It means I'd think twice before eating a steak blacker than my wife's mascara.

Carcinogens and Me Part I: Cancer

So what's the deal with all these "probable carcinogens"? How many times have you seen an article with a headline like "BCB causes cancer"? Given that you might be laying off the BBQ or buying a metal water bottle based on those headlines, haven't you ever wondered where they get off making claims like that? Well, to understand this, we need to get our heads around what cancer is and how it starts.

Imagine a random skin cells on your left arm. Every time you go out in the sun, these poor cells get blasted with UV light, and DNA doesn't get along well with UV light. DNA is made from four bases, A, T, G, and C (the only 4 letters in the title of the movie "GATTACA". Clever, eh?) When two 'T's are next to each other, the UV light can make them fuse together.Let's say this happens to our skin cells. Well along comes a protein trying to read the DNA, and it's not sure what to make of the mess it sees, but it definitely doesn't read two 'T's. Well now whatever protein that DNA was coding for doesn't work. Heck, maybe our mutation was in DNA that's only turned on in liver cells anyway, so we never notice. One cell doesn't do much, but the real problem comes when the cell goes to divide. If the problem isn't fixed, when the cell copies its DNA, it tries to read the fused 'T's, isn't sure what to do, so it throws in a couple random letters. The new cell's DNA looks normal, but it has some random junk in there, which it passes on when it divides again and again and again...

Now we introduce something called apoptosis, aka "programmed cell death". Normally, your cells have all sorts of controls that make sure you they don't cause you problems. If a cell encounters major programs, a protein pathway in the cell makes the cell self-destruct. Let's say a kidney cell finds itself in the liver... *¡BAM!* it kills itself. A cell's DNA gets so damaged it can hardly limp along anymore... *BAM* - apoptosis. Once we're born, most cells in our bodies really slow down how often they divide. If a cell starts dividing too fast... *BAM* - apoptosis.

But remember how DNA damage can lead to broken proteins? Let's say our little skin cell has some terrible luck. At age 7, it takes a hit in a part of DNA that makes a protein needed for apoptosis. No more self-destruct. At age 23, it picks up DNA damage that makes it lose one of three proteins that stop it from dividing so rapidly. At age 48, more DNA damage and you lose another. Age 59, one more hit to the DNA and you lose the last protein stopping the cell from dividing. The cell kicks into overdrive, but without the programmed cell death mechanism, there's nothing there to stop it. You notice some funny brown spots on your skin one day. A few years later, cells from those funny spots have migrated into your kidneys, lungs, colon, and heart, and have kept dividing until you have tumors causing you major problems.

So when did this skin cell become cancerous? Was it at age 7 when it got its first mutation? Was it age 59 when it started dividing? The bottom line is that, had you worn more sunscreen at 23, you wouldn't have cancer at 59. It's the same reason you don't see 18-year old smokers with lung cancer, it takes years to accumulate just the right cocktail of mutations. Now you might be saying to yourself, "I'm no dummy. There are 3 billion little letters of DNA in every one of my cells. What are the odds that one cell would get just the right mutations in just the right order that it would become cancerous?" Well, let's say the odds are one in a trillion. Did you know your body has an estimated 100 trillion cells?

The moral of the story is that random DNA damage is one cause of cancer. So unless you're Spider-Man or the Fantastic Four, it's probably best to stay away from things that play games with your DNA. Now I know what you're thinking, "How do I know what messes up my DNA?" Well... tune in next time!

So... why the blog?

UPDATE: I don't really use the blog for this so much anymore.   :)

First, a little about me. I am a Biochemistry major just weeks away from an undergraduate degree. After I graduate, I'm headed to medical school. Am I a doctor? No. Do I have a bit of a leg up on your average CNN reporter when it comes to how the body works? I like to think so. So why am I writing a blog? Because I happen to think that, equations aside, biology isn't that rough.

I'm not sure exactly what made me decide to start this blog, but I have a few guesses. When I was a kid, I used to read books in the Tell Me Why series. There I was, 7 or 8 years old, and I was learning about all sorts of crazy things from St. Elmo's fire to laughing hyenas. Fast forward 10 or so years and I'm at college, taking courses in persuasive writing, economics, political science, biochemistry, etc. A lot of my time is spent doing problems and cramming for tests, but every now and then I walk out of a lecture feeling like the whole world makes a lot more sense than it did when I walked in. Instead of Tell Me Why I'm reading The Armchair Economist, but the light bulbs keep turning on just the same. I don't know how great a job I'll do, but I think the world is better place thanks to people like the authors of the books mentioned in this paragraph, who cover topics that took them years to learn in a few pages, and make it all make sense.

Of course, sometimes lecture aren't so great... cue CNN.com. Great news source in a lot of ways, but sometimes I raise an eyebrow or two on the conclusions they draw from "recent studies." After reading a few particularly questionable ones, I've started to feel bad that most of the world has to rely on the "expert says" game to know whether to get that lump checked out or not.

I happen to think people are intelligent (at least when they're not cutting me off on the highway). Sure, we all have our moments, but I really feel like there are a lot of light bulbs that could be turned on in the world if information was presented straightforward and at an appropriate level. I'm not saying things need to be dumbed down, I'm just saying that I like the Wikipedia entries that help me 'get it' more than the ones that take 4 pages of differential equations to explain why the sky is blue.

So basically, long story short, I want to help the world make sense to people who have time to read blogs, but not enough time to attend half a decade of college. I hope this turns into something like The Armchair Biologist (if it hasn't been written yet). I don't plan on sticking to just physiology and the like, as I think the social sciences are just as important as we try to straighten out the world around us. So, mission explain the world as I know it starts... now.