In this interview for uah.esnoticia, Ricardo discusses the methodology used in this research and some tips to avoid the use of plastics.

- First of all, can you explain what Bisphenol A is?

Bisphenol A (BFA) is a phenolic compound that was developed many years ago and is used in the production of plastics used in the manufacture of food or drink containers and packaging such as cans that are coated inside this material. In addition, BFA is used in the production of many products including telephony, discs including biomedical material such as syringes, tubing, serum containers and a long etc. Unfortunately it is not an inert product like glass and therefore there is a phenomenon of 'leakage' from the container to its content, a process that is aggravated by the increase in temperature.

BFA has become a very common product in our days and therefore the general population is very exposed to this compound. In fact, over 95% of the population has BFA in both blood and urine.

BFA is considered to be in the group of xenoestrogens, which means that it has estrogenic activity. That is why it´s also considered an endocrine disruptor, a substance that can disrupt the endocrine system due to its hormonal activity.

- When do this problems happen that you discuss with Bisphenol A?

Although the digestive tract is the most important form of BFA exposure, the respiratory and skin pathway has also been affected. For example, it can happen with thermal paper tickets from cashiers or supermarkets. It also influences people´s exposure or if they suffer from diseases, for example, renal diseases, also influences since the kidney is the main elimination route.

- As a result of what you review, the level of bisphenol A in certain products has been monitored in the EU for more than ten years. If this control exists, why do people have so many levels of this compound in our body?

If we analyze what we are talking about, we are analyzing a synthetic compound that has been manufactured by man. Being purists from the strict point of view, it shouldn't be present in any living being. As this is practically impossible due to the biochemical characteristics of BFA, studies have been carried out to find out what is the minimum tolerance in which this compound does not produce side effects. From these tolerance levels, this list of classification levels has been created in the European Union.

In relation to the research they have done at the University of Alcalá, can you tell us that the study of Bisphenol A in the cultivation of podocytes has consisted of?

We began studying this molecule in 2008, when we obtained a first national research project to study BFA. I motivate myself to study this synthetic compound because it was detected in almost all the population. There is previous work, carried out at the University of Granada more than twenty years ago, reporting the contamination of deep water tables. This has been related to the industrial activity and the consequent polution of rivers.

In previous studies, we studied the effects of BFA on mouse podocytes. These are epithelial cells of the renal glomerulus that play a key role in the renal filtration process and in the production of urine. The alteration of these cells or 'podocytes' is characterized by urinary protein loss, characteristic of chronic kidney diseases. We observed that BFA produced hypertrophy and apoptosis in the podocyte. Administration of BFA to the mouse produces a very similar podocytopathy as seen in diabetic kidney disease. BFA also induced arterial hypertension in these animals. These data have been previously published in a work in collaboration with the group of Professor Marta Saura from our Department, collaboration that has been extended to the present work.

We study this well in the animal model, both in the whole animal and in animal cells. But in this work we wanted to carry out an experimental approach and study it in human cells. There is a human history, such as diabetes disease, where the subject is losing podocytes in the urine. This is important, since the podocyte is a highly differentiated, highly developed cell that has lost the capacity of replication so that a podocyte lost by an adult, podocyte that does not recover, which can lead to fibrosis and chronic renal disease.

Knowing that the podocyte can be lost through urine, we hypothesized that bisphenol could alter the adhesion of the podocyte to the basement membrane of the renal glomerulus. First, we performed a cell adhesion assay with human podocytes. We observed that in the presence of BFA more than half of the cells were taking off. From the biological point of view, this would imply that BFA would favour the loss of podocytes in the urine.

Since bisphenol is a recognized endocrine disruptor capable of activating estrogenic receptors we wanted to investigate if this mechanism is involved in the cell adhesion disorder. We proved that the use of estrogenic receptor antagonists is able to prevent podocytopathy. That is, bisphenol in the kidney acts as an endocrine disruptor. To investigate the mechanism involved in BFA-induced podocytopathy, we conducted two studies on human podocytes grown in the presence of BFA. First, a genomic study was conducted to identify genes affected by BFA. Subsequently, a proteomic analysis was done that allowed us to identify proteins affected by BFA.

These studies allowed us to identify about thirty proteins involved functionally as structural proteins (F-actin, vimentin, tubulin, cofilin-1, vinculin, etc.) of the cytoskeleton of the podocyte and adhesion proteins (E-cadherin, nephrin, and VCAM-1, etc.) that on one hand join podocytes to each other and on the other hand join them to the basal membrane of the renal glomerulus.

Later, we confirm these results identifying and quantifying these proteins in a specific way by immunocytochemistry and immunoblot or Western blot (María Isabel Arenas Jiménez, Department of Biomedicine and Biotechnology of UAH). 

Ricardo José Bosch Martínez

We were able to demonstrate that both cytoskeleton proteins and proteins that facilitate cellular adhesion are reduced in the presence of BFA. Likewise, the use of estrogenic receptor antagonists was able to prevent the changes of expression (synthesis) of proteins induced by BFA. In addition, we identified other typical podocyte proteins such as podocin or nephrin, which are also altered by AFB.

Finally, we also study another molecule, nitric oxide (NO). We observe that BFA decreases the production of ON in the podocyte and promotes the production of oxygen free radicals, substances that are harmful to both cells and tissues.

Together, these data suggest that BFA produces a disorder of cell adhesion in the podocyte that promotes its loss through urine. Although future in vivo studies will be necessary to confirm the role of BFA in the pathogenesis of kidney disease, these findings provide new mechanisms of kidney injury.

- To conclude, you can comment with these conclusions some tips that allow us to avoid or reduce the amount of bisphenol A that we consume in an unconscious way.

In recent years, research has been underway on other Bisphenol-free materials. In any case, further studies in toxicology should be carried out given the large number of new compounds to which the population is exposed.

For the regular citizens, it´s appropriate to avoid plastics as far as possible, using glass or steel containers. It´s important to avoid heating plastic containers, as this increases BFA leakage to food as already mentioned.

Finally, we must point out that, according to European regulations, containers are identified by a clover-shaped icon at the bottom: those identified with numbers 1 and 7, are the ones with the highest BFA content. In any case, this doesn´t mean that other plastic materials are harmless.

Publicado en: Inglés