High levels of carbon dioxide (CO2) in the atmosphere can alter not only the planet's climate but also the functioning of human cells. This is because the gas interacts with hydrogen peroxide (H2O2), a molecule naturally present in the body, where it performs several functions, giving rise to an oxidizing compound known as peroxymonocarbonate.
“Evidence is accumulating that peroxymonocarbonate is important in both the adaptive responses of cells [sinalização redox] and in cellular dysfunctions. There is also epidemiological evidence that CO2 levels that are close to being reached in contemporary urban societies cause a series of physiological problems. And the mechanisms of CO2 toxicity are still little known”, says Ohara Augusto, professor at the Chemistry Institute of the University of São Paulo (IQ-USP).
The researcher coordinated a study, published in the magazine Chemical Research in Toxicology which describes a new method for detecting peroxymonocarbonate in cells based on the use of fluorescent molecular probes. This is the first time that the substance has been detected in cells. The research was conducted within the scope of ), a Research, Innovation and Dissemination Center (CEPID) funded by FAPESP.
“This work is important not only because it provides a method to show that peroxymonocarbonate is being produced in a range of conditions, including cellular ones, but also to discuss it, considering the little attention that CO2 has received in the redox area,” says Augusto.
Fluorescence measurements
To detect peroxymonocarbonate, the researchers used fluorescence measurements with boronate probes. First, they generated physiological concentrations of hydrogen peroxide in a steady-state enzymatic reaction at constant production and measured the fluorescence of a boronate probe in the presence and absence of CO2.
Boronates are used to detect oxidants such as hydrogen peroxide, peroxynitrite, hypochlorous acid and peroxymonocarbonate, which react with them at different rates and intensities, allowing the identification of these oxidants.
The cell study was carried out with macrophages activated to generate hydrogen peroxide. Macrophages are cells of the immune system that, depending on the type of activation, generate different oxidants.
The researchers performed several controls to conclude that the cells were not generating either peroxynitrite or hypochlorous acid, but rather peroxymonocarbonate when in the presence of CO2.
“This is a relatively simple method for detecting peroxymonocarbonate in physiological concentrations of hydrogen peroxide and CO2. This was previously impossible, but today researchers can consider that some effects they observe in cells, such as greater oxidation of certain proteins or cellular responses, are due to peroxymonocarbonate and they will be able to test this,” comments the IQ-USP professor.
Although it is an oxidant known to chemists since the 1960s and has technological applications as a disinfectant and bleach, it was not considered that peroxymonocarbonate could be formed in cells, due to the low concentrations of its precursors and its speed of formation. Augusto says that it was only in the 2000s that the oxidant began to be investigated in biological systems, and initially the focus was on oxidative damage.
Redox signaling and CO2
Redox signaling is an adaptive response. “When there is a slight increase in stress, the cell adapts. The formation of oxidants can, for example, cause genes for antioxidant enzymes to be expressed to respond, in this case, to oxidative stress. And many pathways that lead to cellular responses involve thiol proteins, which peroxymonocarbonate oxidizes faster than hydrogen peroxide,” explains Augusto, adding that irreversible cellular damage only occurs when the formation of oxidants is very high.
Carbon dioxide is one of the precursors of peroxymonocarbonate along with hydrogen peroxide. The gas is naturally present in the atmosphere and is a normal constituent of the human body, which exhales about one kilogram of CO2 per day as a product of metabolism.
From a redox perspective, CO2 modulates the reactivity of both hydrogen peroxide and peroxynitrite, two important metabolites of molecular oxygen. In addition, it alters the expression of genes, including those involved in inflammation, and is involved in protein nitration via peroxynitrite and protein carbamylation, another post-translational modification that can alter the biological function of proteins.
Although more evidence is needed regarding its role as a biological oxidant, peroxymonocarbonate appears to be one of the possible intermediaries of the harmful effects of increased levels of carbon dioxide in the human body. The researcher highlights that CO2 also acts through non-redox mechanisms.
The article Production of Peroxymonocarbonate by Steady-State Micromolar H2O2 and Activated Macrophages in the Presence of CO2/HCO3– Evidenced by Boronate Probes can be read at:
*With information from Redoxoma.
This content was originally published in Method studies the impact of high levels of atmospheric CO2 on health on the CNN Brasil website.
Source: CNN Brasil