Title:
Effects of Endocrine Disruptors Bisphenol A and Diethylstilbestrol on Ambystoma mexicanum Limb Regeneration, an advanced study on regeneration and stem cell development – Bartels, Rankin, & Choate, 2015
Brief Synopsis:
Published Undergraduate Thesis that was Presented and Defended: Comprehensive study of the effects that commonly known endocrine disruptors have on stem cell regeneration in axolotl salamanders. BPA was found to have a statistically significant effect on slowing regeneration.
Photos showing limb regeneration in Axolotl salamanders.
Abstract:
With the increasing rate of human health problems around the world in the forms of cancer and birth defects, scientist have focused on a specific group of chemicals called endocrine disrupting contaminates (EDCs). These chronic environmental toxins, including Bisphenol-A (BPA) and Diethylstilbestrol (DES), have been linked to birth defects and cancer in humans. In amphibians EDCs block thyroxine (T4) and other growth hormones that alter development pathways shared with amphibian regeneration. Many amphibians, including the axolotl, Ambystoma mexicanum, can regenerate lost limbs through stem cell dedifferentiation.
To examine the effects of EDCs on regeneration, twenty-five juvenile axolotls were exposed to BPA and DES. Axolotls were divided into four groups: (1) untreated control, (2) ethanol carrier control (100 ug/L EtOH), (3) DES (0.00025 mg/ L), and (4) BPA (2 mg/L) with chemicals applied to the water. Prior to treatment, the salamanders were anesthetized and the right forelimb was amputated.
The hypothesis that EDC exposed axolotls would weigh less and have slower or completely inhibited regeneration was partially supported. All groups had complete limb regeneration (P = 0.68) and gained weight (P = 0.42). However, BPA treatments slowed regeneration when compared to the other groups: ethanol, BPA (P = 0.0006); untreated, BPA (P = 0.0034); and BPA, DES (P = 0.0048).
Smaller salamanders that had previous amputation wounds exhibited much faster regeneration than intact salamanders when initial lengths (P < 0.001) were compared to those of week 6 (P > 0.05). The ELISA for thyroxine on harvested organs at the termination of the experiment was inconclusive as hormone levels were below detectable limits. The EDCs in this experiment did not produce deformities, but BPA slowed regeneration. DES, however, did not inhibit regeneration contrary to expectations and further study is necessary to determine how EDCs affect regeneration in amphibians.
