[Structure and Function of the Nuclear Receptor Constitutive Androstane Receptor]

[Mechanism of regulation of the constitutive androstane receptor under conditions of modeling oxidative stress in vitro]

The constitutive androstane receptor (CAR) is a nuclear receptor that participates in the regulation of biotransformation of toxic substances and metabolic processes. The mechanisms of expression changes of CAR under conditions of oxidative stress (OS) have not been studied yet and this was the purpose of the study. OS was modeled by incubating Caco2 cells with hydrogen peroxide 10-100 μM for 72 h. The amount of CAR was determined by the Western blot, nuclear factor erythroid 2-related factor 2 (Nrf2) was evaluated by a heterogeneous enzyme immunoassay malondialdehyde (MDA), the lipid peroxidation products (LPP) was assayed by a photometric method. Incubation of cells with 10 μM and 50 μM H2O2 led to an increase in the amount of CAR and Nrf2, while incubation with 100 μM H2O2 caused their decrease. Nrf2 inhibition did not influence the CAR content under OS conditions. 10 μM MDA increased the CAR content, 100 μM MDA had no effect, while 150 μM reduced the amount of CAR.

Mechanisms of Regulation of the P-Glycoprotein Transporter Protein Functioning under the Action of Nitric Oxide

Mechanisms of regulation of the P-glycoprotein (Pgp) transporter under the action of nitric oxide (NO) were studied in Caco-2 cells. S-Nitrosoglutathione (GSNO) was used as a NO donor, which was added to the cells at concentrations 1, 10, 50, 100, and 500 µM and incubated for 3, 24, or 72 h. The amount of Pgp was analyzed using Western blotting, activity was determined by monitoring transport of its substrate, fexofenadine. The study showed that a short-term exposure to GSNO for 3 h at 500 µM concentration caused increase in the concentration of peroxynitrite in Caco-2 cells, which reduced the activity, but not the amount of Pgp. Increase in the duration of exposure to 24 h increased the amount and activity of Pgp at GSNO concentrations of 10 and 50 µM, increased the amount without increasing activity at 100 µM concentration, and decreased the amount of the transporter protein at 500 µM. Duration of exposure to GSNO of 72 h at concentration of 10 µM resulted in the increase of the amount and activity of Pgp, while at concentration of 100 and 500 µM it decreased the amount of the transport protein. At the same time, it was shown using specific inhibitors that the increase in the amount of Pgp under the influence of low concentrations of GSNO was realized through the NO-cGMP signaling pathway, and the effect of the higher concentration of GSNO and the respective development of nitrosative stress was realized through Nrf2 and the constitutive androstane receptor.

Induction of Constitutive Androstane Receptor during the Development of Oxidative Stress

We studied the effect of 3-, 24-, and 72-h exposure to H₂O₂ in concentrations of 0.1-100.0 μM on the level of constitutive androstane receptor in Caco-2 cells. It was shown that 3- and 24-h incubation with Н₂О₂ in all concentrations had no effect on the level of constitutive androstane receptors. Increasing the incubation time to 72 h led to an increase in the level of constitutive androstane receptor at H₂O₂ concentrations of 5, 10, and 50 μM and to a decrease at a concentration of 100 μM. Antioxidant glutathione (1 mM) in parallel to the prooxidant neutralized these changes.

Aflatoxin B1 induced upregulation of protein arginine methyltransferase 5 in human cell lines

The exposure of naturally occurring mycotoxins affects human health and play a vital role in cancer initiation and progression. Aflatoxin B1 is a difuranocoumarin mycotoxin, classified as a group I carcinogen. The present study was conducted to assess the effect of aflatoxin B1 on epigenetic regulatory proteins. The protein arginine methyltransferase 5 expression was induced upon aflatoxin B1 treatment in a dose and time dependent manner. Further global arginine methylation was also increased in the same manner. This is the first report showing the induction of epigenetic regulatory protein, protein arginine methyltransferase 5 upon aflatoxin B1 treatment. Further study is required to establish the detailed pathway of PRMT5 induction.