Alterations in porcine intrahepatic sympathetic nerves after bisphenol A administration

Introduction: Bisphenol A (BPA) is used in the chemical industry for manufacturing plastics which are used as food packaging. Data indicate that BPA is released from such products and is widely present in the environment and the human body. So far, the EFSA and the US FDA have determined "safe" BPA oral exposure levels, and a large amount of data indicates that BPA is harmful even at low-doses. Our previously performed analyses concerning BPA exposure demonstrated the impact of this substance on parasympathetic and peptidergic nerve fibers present within the liver. Therefore, this study concerns BPA exposure and sympathetic intrahepatic in-nervation in reference to several neuropeptides which modulate neuronal responses: cocaine and amphetamine regulated transcript (CART), galanin (GAL), calcitonin gene-regulated peptide (CGRP) and substance P (SP).

Materials and methods: Fifteen young swine at 8 weeks of age were used as experimental models of the juvenile human liver. The pigs were divided into 3 groups and received capsules orally with bisphenol at a dose of 0.05 mg/kg b.w./day; a dose of 0.5 mg/kg b.w./day and placebo capsules as a control. After 28 days of oral BPA intake, the animals were euthanized, perfused with 4% paraformaldehyde (PFA), and livers were collected and fixed in PFA. The cryostat sections were subjected to a routine double-labeling immunofluorescence technique. The primary antibodies were directed against dopamine beta hydroxylase (DbH), which is a marker for sympathetic nerves, and one of the investigated neuropeptides: CART, GAL, CGRP and SP, which co-localized the inves-tigated nerves. Immunoreactive nerves were counted in the liver and the percentage presence of each neuronal combination in particular samples of each experimental group were determined and analyzed statistically.

Results: The BPA oral intake at low and ten times higher dosage caused an increase of the number of sympa-thetic nerve fibers within the porcine liver by 48.6% and 63.7%, respectively. Moreover, BPA exposure caused an increased presence of sympathetic nerve fibers in these two experimental groups, which were co-localized with CART and GAL up to 65.9%/173.2% and 147.4%/126.3%, respectively. At the lower BPA doses of 50 μg/kg b.w./day, the percentages of SP+/DbH+ and CGRP+/DbH+ nerve fibers were similar to the control. However at a ten times higher dose, BPA caused an increased number of SP+/ DbH+ and CGRP+/ DbH+ nerve fibers in the liver, up to 46.4% and 73.5% respectively.

Conclusions: BPA caused an increase in the number of sympathetic nerve fibers as well as sympathetic nerve fibers which co-localized with neuropeptides in the porcine liver. The increase in CART and GAL were excep-tionally high even at low BPA doses. BPA food contamination may dysregulate liver sympathetic innervation, and thereby may change the oxygenated blood supply, alter metabolism and disrupt the activity of hepatic pa-renchymal cells.