X-Informatics

I have a bad cough this week, so I did a little lookup of an antibiotics – Cephalosporins. Cephalosporins are a class of β-lactam antibiotics originally derived from Acremonium.

Cephalosporins disrupts the synthesis of the peptidoglycan layer of bacterial cell walls. The petidoglycan layer is important for cell wall structural integrity. The final transpeptidation step in the synthesis of the peptidoglycan is facilitated by transpeptidases known as penicillin-binding proteins (PBPs). PBPs bind to the D-Ala-D-Ala at the end of muropeptides (peptidoglycan precursors) to crosslink the peptidoglycan. Beta-lactam antibiotics mimic this site and competitively inhibit PBP crosslinking of peptidoglycan.

This week’s molecule is BPA, or bisphenol-A. New York time has a long article about the research over this controversial chemical, mended with some political background. Details at In Feast of Data on BPA Plastic, No Final Answer – NYTimes.com

From the article, there is no decisive results to testify BPA’s effects on human bodies. But it doesn’t mean there is no results. Rather, scientists are still debating over whether BPA is toxic or not, mainly because unreproducible results. Part of the reasons of the conflicting results, as the article pointed out, is that “different laboratories have studied the chemical in different ways”. The conflicting results have even produced conflicts between scientists. It’s interesting to read that “researchers who study it argue bitterly at conferences”, and “At one such meeting, scientists in the audience said, “We don’t want to hear you two speak until you get this straightened out,” “.

The articles goes on with recent development in the research, and mentioned some efforts in reconciling the disputes. One biggest dispute is that low dosage of BPA turns out to have worse effects in animal studies than higher dosages. From endocrinologists’ point of view, it makes sense because BPA is no regular toxicant, but it “acts like a hormone”, and “hormones can act at extremely low doses”.

So much about the article, and here is the chemistry about BPA.

BPA has two phenol functional groups, and it is used to make polycarbonate plastic that are used in almost everything we use that are plastic, including food containers and baby bottles (in some states in the USA, BPA bottles is already banned in Canada, as well as some states in the US).

Why is BPA toxic? Because it can bind to estrogen receptors, though the binding is much weaker than the body’s own estrogen. Estrogen is assotiated with many horrible diseases, such as cancers, obesity, immune system diseases, and behavior problems. BPA could also bind to receptors for male hormone and thyroid hormone. DES (diethylstibestrol) is a disastrous example of an endocrine disruptor, as mentioned in the NYTimes article. It was used as a drug to prevent miscarriage for pregnant women in 1950s. It could bind to estrogen receptors much stronger than BPA, and has caused sever problems such as cancers, and even affects the offsprings of the womens who took it. What’s this chemical?

(Images: BPA, Estrone, and DES. Curtosey of wikipedia)