nos-trum. pronunciation: \nos'-trum\. noun. Etymology: Latin, neuter of noster our, ours.
1. a medicine of secret composition recommended by its preparer but usually without scientific proof of its effectiveness.
2. a usually questionable remedy or scheme.
See here for more discussion.

Monday, September 27, 2010

STUDY: How Smoking Increases Risk Of Ectopic Pregnancy...Maybe

This study is a good example of how science progresses in small steps.  Much smaller than the press would have you believe.

For NOSTRUMS, that's a no-no.

So here's the title of the article in BBC News (Sep 27):  "Smoking link to ectopic pregnancy"

To refresh your knowledge, ectopic pregnancy (EP) is a condtion where the egg implants somewhere else than the womb, most commonly in the tube that runs from the ovary to the uterus (the Fallopian tube--FT).  This is bad, because unlike the uterus, the FT can't expand as the fetus grows and at some point a potentially lethal rupture can occur, requiring emergency surgery.

So, anything that increases the risk of EP is to be avoided.  We have known for some time that women who smoke are more likely to have an ectopic.  But why?

The news article says this: 
"Research from experts at Edinburgh University said Cotinine [a chemical in cigarette smoke] triggered a reaction which increased a protein in the Fallopian tubes.  They said the protein, called PROKR1, raised the risk of an egg implanting outside the womb."
Not really.  The link is more tenuous than that.

The researchers themselves were more circumspect (American Journal of Pathology, Sep 23, 2010).  They "hypothesized" a mechanism for one chemical in smoke that modified the protein PROKR1, which is a receptor for other proteins that impact muscle activity in the FT.

If it sounds like I'm splitting hairs, then let's lay it out.  They think the following occurs:  smoking -> cotinine in the bloodstream -> modification of the PROKR1 receptor -> changes in the protein that impacts smooth muscle -> altered muscle activity in the FT -> differences in the movement of the egg down the tube to the uterus -> some eggs not making it all the way and implanting in the FT. (substitute the words "leads to" for my little symbol "->")

Given the hypothesis, they took 21 specimens from hysterectomy and exposed them to cotinine.  They then measured the level of the receptor PROKR1.  It was higher than if cotinine was blocked.

For Onion Peelers, (this one is difficult to decipher, so skip to the next paragraph if you like),
Sera/FT were collected at hysterectomy (n = 21). Serum levels of the smoking metabolite, cotinine, were measured by enzyme-linked immunosorbent assay. FT explants (n = 4) and oviductal epithelial cells (cell line OE-E6/E7) were treated with cotinine and an ...antagonist. PROKR1 transcription was higher in FTs from smokers (P < 0.01). ... Cotinine treatment of FT explants and OE-E6/E7 cells increased PROKR1 expression (P < 0.05), which was negated by cotreatment with antagonist.

So given all that, they showed that if you exposed Fallopian tubes to one of the hundreds of smoking chemicals, you get more of a protein that is involved in muscle activity (they didn't claim to observe any muscle activity changes directly), possibly affecting the FT function.

It's a good hypothesis to explain how smoking can increase risk of EP.  But looking back at my "leads to" sequence, you can see that some of the pieces are still missing.  Pieces that they need to fill in, in order to justify the BBC's characterization as having found a "link" to ectopic pregnancy.

Smoking is bad in ways we haven't even begun to define yet.  And this may be another one.  As one of the authors said,
"While it may be easy to understand why inhalation of smoke affects the lungs, this shows that components of cigarette smoke also enter the blood stream and affect seemingly unconnected parts of the body like the reproductive tract."
That's a good point, but not the end of this particular story.

Doc D

No comments:

Post a Comment


What I'm Reading - Updated 3 May

Blog Archive