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Lesson Seven: Obesogens

Module Three: The Obesogen Hypothesis

Overview

Video Lecture

Human Exposure to TBT

View the online lecture for the details necessary to understand this module's key ideas.

Learning Objectives

At the end of this module, students will be able to:

  • Explain how obesogens can generate more and bigger fat cells.
  • Provide specific examples of chemicals that have this ability, and how they exert their effects on the body.

As we have seen, certain chemicals called obesogens can stimulate the development of fat cells or increase the storage of fat in already-existing fat cells.  There is ample evidence that obesogens exist. Certain diabetes medications can cause patients to gain fat, and studies indicate that bisphenol-A, perfluorooctanoic acid, and organotins cause cells to become fat cells in a Petri dish.  Could such chemicals play a role in the obesity epidemic?

Organotins such as Tributyltin (TBT) are well known for their ability to make snails and fish switch their sex from female to male.  TBT also has a striking effect on fat cell production.  TBT activates the nuclear receptors RXR and PPAR gamma, which tells some stem cells to turn into fat cells. Since PPAR gamma is a major player in lipid homeostasis and acts as a “master switch” controlling the development of fat cells, it’s obvious that the activation of PPAR gamma will affect obesity. Some of the evidence even suggests that prenatal exposure to organotins leads to permanent changes that cause exposed animals to develop more fat cells. In some cases this has resulted in laboratory mice increasing their adult weight.

So, can certain chemicals make us fat? Yes, and disturbingly, three of the most powerful obesogens we know about—TBT, phthalates, and BPAs—are found in one of the most common materials we encounter—plastics. Exposure to these chemicals, especially prenatally, can reprogram the metabolism of animals to make them more likely to become obese.  If this happens in animals, it may very well be happening in us. This makes green chemistry an essential tool that we can use in the battle to reduce EDCs and obesogens in the environment and food chain. Green chemistry could help to reverse the obesity epidemic.

To explore this module's material in depth, view the lecture.

Key Points

  • Evidence for obesogens has been found in animal, human, and laboratory models.
  • Organotins such as Tributyltin (TBT) act as obesogens by activating the NRs RXR and PPAR gamma, which direct stem cells to become fat cells.
  • TBTs, phthalates, and BPAs are very common obesogens found in plastics.
  • A reduction in the amount of these chemicals we encounter by applying  principles of green chemistry is likely to decrease the rates of obesity.