Connexin-Based Channel Activity Is Not Specifically Altered by Hepatocarcinogenic Chemicals

Evaluation of functional candidate biomarkers of non-genotoxic hepatocarcinogenicity in human liver spheroid co-cultures

Validated in vitro assays for testing non-genotoxic carcinogenic potential of chemicals are currently not available. Consequently, the two-year rodent bioassay remains the gold standard method for the identification of these chemicals. Transcriptomic and proteomic analyses have provided a comprehensive understanding of the non-genotoxic carcinogenic processes, however, functional changes induced by effects at transcriptional and translational levels have not been addressed. The present study was set up to test a number of proposed in vitro biomarkers of non-genotoxic hepatocarcinogenicity at the functional level using a translational 3-dimensional model. Spheroid cultures of human hepatocytes and stellate cells were exposed to 5 genotoxic carcinogenic, 5 non-genotoxic carcinogenic, and 5 non-carcinogenic chemical compounds and assessed for oxidative stress, mitochondrial dysfunction, endoplasmic reticulum stress, apoptosis, and inflammation. The spheroid model could capture many of these events triggered by the genotoxic carcinogenic chemicals, particularly aflatoxin B1 and hydroquinone. Nonetheless, no clear distinction could be made between genotoxic and non-genotoxic hepatocarcinogenicity. Therefore, spheroid cultures of human liver cells may be appropriate in vitro tools for mechanistic investigation of chemical-induced hepatocarcinogenicity, however, these mechanisms and their read-outs do not seem to be eligible biomarkers for detecting non-genotoxic carcinogenic chemicals.

Connexins and Pannexins—Similarities and Differences According to the FOD-M Model

Connexins and pannexins are the transmembrane proteins of highly distinguished biological activity in the form of transport of molecules and electrical signals. Their common role is to connect the external environment with the cytoplasm of the cell, while connexin is also able to link two cells together allowing the transport from one to another. The analysis presented here aims to identify the similarities and differences between connexin and pannexin. As a comparative criterion, the hydrophobicity distribution in the structure of the discussed proteins was used. The comparative analysis is carried out with the use of a mathematical model, the FOD-M model (fuzzy oil drop model in its Modified version) expressing the specificity of the membrane’s external field, which in the case of the discussed proteins is significantly different from the external field for globular proteins in the polar environment of water. The characteristics of the external force field influence the structure of protein allowing the activity in a different environment.

Effects of Drugs Formerly Proposed for COVID-19 Treatment on Connexin43 Hemichannels

Connexin43 (Cx43) hemichannels form a pathway for cellular communication between the cell and its extracellular environment. Under pathological conditions, Cx43 hemichannels release adenosine triphosphate (ATP), which triggers inflammation. Over the past two years, azithromycin, chloroquine, dexamethasone, favipiravir, hydroxychloroquine, lopinavir, remdesivir, ribavirin, and ritonavir have been proposed as drugs for the treatment of the coronavirus disease 2019 (COVID-19), which is associated with prominent systemic inflammation. The current study aimed to investigate if Cx43 hemichannels, being key players in inflammation, could be affected by these drugs which were formerly designated as COVID-19 drugs. For this purpose, Cx43-transduced cells were exposed to these drugs. The effects on Cx43 hemichannel activity were assessed by measuring extracellular ATP release, while the effects at the transcriptional and translational levels were monitored by means of real-time quantitative reverse transcriptase polymerase chain reaction analysis and immunoblot analysis, respectively. Exposure to lopinavir and ritonavir combined (4:1 ratio), as well as to remdesivir, reduced Cx43 mRNA levels. None of the tested drugs affected Cx43 protein expression.