Abstract
α-Casozepine (α-CZP) is an anxiolytic-like bioactive decapeptide derived from bovine αs1-casein. The N-terminal peptide YLGYL was previously identified after proteolysis of the original peptide in an in vitro digestion model. Its putative anxiolytic-like properties were evaluated in a Swiss mice model using a light/dark box (LDB) after an intraperitoneal injection (0.5 mg/kg). The effect of YLGYL on c-Fos expression in brain regions linked to anxiety regulation was afterwards evaluated via immunofluorescence and compared to those of α-CZP and diazepam, a reference anxiolytic benzodiazepine. YLGYL elicited some anxiolytic-like properties in the LDB, similar to α-CZP and diazepam. The two peptides displayed some strong differences compared with diazepam in terms of c-Fos expression modulation in the prefontal cortex, the amygdala, the nucleus of the tractus solitarius, the periaqueductal grey, and the raphe magnus nucleus, implying a potentially different mode of action. Additionally, YLGYL modulated c-Fos expression in the amygdala and in one of the raphe nuclei, displaying a somewhat similar pattern of activation as α-CZP. Nevertheless, some differences were also spotted between the two peptides, making it possible to formulate the hypothesis that these peptides could act differently on anxiety regulation. Taken together, these results showed that YLGYL could contribute to the in vivo overall action of α-CZP.
Highlights
Introduction αCasozepine (α-CZP), a decapeptide corresponding to the fragment 91–100 (YLGYLEQLLR)of bovine milk αs1 -casein, appears as the component carrying the anxiolytic-like activity of a tryptic hydrolysate of bovine αs1 -casein [1]
The light/dark box (LDB) served here as an anxiety-inducting situation, as we previously showed that this situation was required to evaluate the effects of α-CZP on the modulation of neuronal activity [16]
An IP injection of 0.5 mg/kg of YLGYL 30 min before the test increased the number of transitions between the two compartments (F(3,24) = 4.8636, p = 0.0177), the time spent in the lit box (F(3,24) = 7.0194, p = 0.0034), as well as the number of rears in the lit box (F(3,24) = 8.405, p = 0.0014), compared to a vehicle injection in the same conditions. α-CZP, injected at the same molar concentration, increased the time spent (p = 0.0043) and the number of rears (p = 0.0014)
Summary
Of bovine milk αs1 -casein, appears as the component carrying the anxiolytic-like activity of a tryptic hydrolysate of bovine αs1 -casein [1]. The properties of this hydrolysate are close to those of the benzodiazepine (BZDs) family despite not showing the associated side effects of these drugs, such as habituation or sedation [2]. The anxiolytic-like effects of the tryptic hydrolysate of bovine αs1 -casein were highlighted after intraperitoneal (IP) and per os administration in rodents, cats, dogs, horses, and ponies [1,3,4,5,6,7,8]. The search for the actual peptide, or actual peptides, carrying the anxiolytic-like properties of the tryptic hydrolysate of bovine milk αs1 -casein remains
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