ИСТИНА

The dipeptide L-carnosine is a recognized neuroprotective agent effective both in animal models and in cultured neurons. Carnosine has been shown to enter neurons and exert an antioxidant effect. Exogenously introduced carnosine is mainly transported into neurons via the oligopeptide transporter PEPT2. Since exogenous carnosine is rapidly cleaved by serum carnosinase, we are developing carnosinase-resistant carnosine derivatives to be used as neuroprotective drugs. Carnosine in a nanomicellar complex with α-lipoic acid is able to enter neurons, becomes more resistant to carnosinase, and shows neuroprotective activity at substantially lower concentrations. The study of the effectiveness of PEPT2-mediated transport of both carnosine and its derivatives into neurons is an important aspect of said drug development. To determine the proportion of passive and PEPT2-mediated active transport of carnosine, we added carnosine (20 μM – 62.5 mM) to the culture of rat cortical neurons and determined its content within the cells after 5, 15 and 30 min. To determine the intracellular content of carnosine, the cultures were washed from external carnosine and lysed. The content of carnosine in the lysates was determined using liquid chromatography–mass spectrometry. The dependence of intracellular content of carnosine on the incubation time was linear for all concentrations except for the maximum one. The dependence of the rate of carnosine entry into the cells on its concentration in the medium can be decomposed into two components: the enzymatic one, described by the Michaelis-Menten equation (KM = 118 μM), and the nonenzymatic one (Kne = 0,21∙10^-4 (1/min)). The nonenzymatic component of the transport rate prevailed over the enzymatic one at high concentrations of carnosine (over 12.5 mM). Thus, at physiological concentrations of carnosine (0.11 mM), the rate of its active transport into neurons is an order of magnitude higher than that of the passive transport.