Veterinary/zoology session

In different species of animals and thus also in poultry species, antibiotics are used for therapeutic purposes as well as for growth promotion. This markedly contributes to the spread of antibiotic resistance. Because of the public expectations and as a consequence of the legal regulations adopted by the EU authorities, the use of antibiotics for growth promotion purposes has been banned in the EU and, therefore, antibiotic growth promoters have been replaced by other alternative agents having performance-enhancing properties.

The possible alternatives of antibiotic-containing growth promoters may include, among other compounds, volatile fatty acids such as butyric acid and its salts called butyrates. After entering the bacteria, butyric acid undergoes dissociation, which hinders its exit from the bacterial cell; as a result, butyric acid accumulates within the bacterial cell and exerts a bactericidal effect. The growth-promoting effect of butyrate added to the poultry diet at inclusion levels of 0.05–0.2% has been demonstrated by numerous trials.

However, after its absorption from the intestine the butyrate added to the diet will alter the metabolic processes of the tissues due to its histone deacetylase inhibiting activity. Through this activity it may affect the expression of certain enzymes including the cytochrome (CYP450) enzymes of the liver. Therefore, the objective of our experiments was to study the effect of butyrate on the expression of certain CYP450 enzymes under in vitro conditions, in primary culture of chicken liver cells.

Chicken liver cells were obtained by a three-step perfusion procedure, then, after washing by centrifugation, the cells were suspended in culture medium. After a pre-incubation period of 24 h in collagen-coated culture dishes, cells were treated for another 24 h with different concentrations of sodium n-butyrate (0 mM /control/, 1.0, 2.5, 5.0, 7.5 and 10 mM). After the incubation time has expired, total RNA was extracted from the cells. Using the samples thus obtained, we determined the expression of the given cytochrome subfamilies (CYP1A1, CYP2H1, CYP3A37) by a quantitative real-time PCR method.

According to our results, a butyrate concentration of 1.0 mM had no influence on CYP2H1 expression, while the 2.5 mM butyrate concentration caused an approximately 4-fold (significant) and the 5.0, 7.5 and 10.0 mM butyrate concentrations resulted in a 12-15-fold (significant) increase in the expression of CYP2H1. In contrast, the expression levels of CYP3A37 and CYP1A1 were significantly down-regulated in the presence of butyrate. The rate of the decrease was 40–70% for CYP3A37 and 50–90% for CYP1A1 at the butyrate concentrations tested.

Based on our experiments, we suppose that the continuous administration of butyrate may influence the expression of hepatic cytochrome enzymes also in vivo, and thus it may affect the metabolism of both endogenous substrates and xenobiotics.