The effect of nanoemulsified methionine and cysteine on the in vitro expression of casein in bovine mammary epithelial cells

Abstract

Objective: Dairy cattle nutrient requirement systems acknowledge amino acid (AAs) requirements in aggregate as metabolizable protein (MP) and assume fixed efficiencies of MP used for milk protein. Regulation of mammary protein synthesis may be associated with AA input and milk protein output. The aim of this study was to evaluate the effect of nanoemulsified methionine and cysteine on the in-vitro expression of milk protein (casein) in bovine mammary epithelial cells (MACT cells). Methods: Methionine and cysteine were nonionized using Lipoid S 75 by highspeed homogenizer. The nanoemulsified AA particle size and polydispersity index were determined by dynamic light scattering correlation spectroscopy using a highperformance particle sizer instrument. 3(4,5Dimethylthiazol2yl)2,5diphenyltetrazolium bromide assay was performed to determine the cytotoxicity effect of AAs with and without nanoionization at various concentrations (100 to 500 μg/mL) in mammary epithelial cells. MACT cells were subjected to 100% of free AA and nanoemulsified AA concentration in Dulbecco's modified Eagle medium/nutrient mixture F12 (DMEM/F12) for the analysis of milk protein (casein) expression by the quantitative reverse transcription polymerase chain reaction method. Results: The AAtreated cells showed that cell viability tended to decrease (80%) in proportion to the concentration before nanogenesis, but cell viability increased as much as 90% after nanogenesis. The analysis of the expression of genetic markers related to milk protein indicated that; αs2casein increased 2fold, κcasein increased 5fold, and the amount of unchanged βcasein expression was nearly doubled in the nanoemulsified methioninetreated group when compared with the freenanoemulsified methioninesupplemented group. On the contrary, the nonemulsified cysteineadministered group showed higher expression of genetic markers related to milk protein αs2casein, κcasein, and βcasein, but all the genetic markers related to milk protein decreased significantly after nanoemulsification. Conclusion: Detailed knowledge of factors, such nanogenesis of methionine, associated with increasing cysteine and decreasing production of genetic markers related to milk protein (casein) will help guide future recommendations to producers for maximizing milk yield with a high level of milk protein casein.