Study Of Casein In Different Samples Of Milk Pdf Download [EXCLUSIVE]
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Disturbances in glutathione (GSH) and redox homeostasis contribute to the pathophysiological processes leading to neurodegenerative diseases [1], pancreatitis [2], and diseases associated with abnormal cell differentiation [3]. Therefore, maintaining redox balance is important in the context of disease prevention. In a recent study, we showed that exposure to β-casomorphin-7 (BCM-7), a proline-rich opioid peptide derived from bovine β-casein, caused a decrease of intracellular GSH concentrations in cultured neuronal SH-SY5Y cells [4]. This reduction in GSH was driven by a reduction in cellular uptake of cysteine, the rate-limiting precursor for GSH synthesis. Exposure to BCM-7 also reduced the ratio of reduced GSH to oxidized GSH (glutathione disulfide) as a marker of redox status, and the ratio of S-adenosylmethionine to S-adenosylhomocysteine as a marker of cellular methylation capacity. These results indicate that BCM-7 is a potential modulator of GSH.
Results of in vitro studies may not be reliably extrapolated to physiological outcomes in animals and humans. Several factors might influence the systemic concentrations of BCM-7 in animal and human studies, including the amount of BCM-7 produced from A1 β-casein contained in a typical serving of milk, the half-life of BCM-7 in the gastrointestinal tract, degradation by brush border dipeptidyl peptidase-4 (DPP-4) and the rate of transport of BCM-7 across the gastrointestinal tract into the systemic or potentially lymphatic circulation. Furthermore, other milk metabolites, notably those derived from whey proteins, have been reported to influence GSH concentrations by promoting cysteine absorption and providing a substrate for GSH synthesis [15, 16]. Therefore, it is necessary to conduct animal and human studies to examine if the effects of BCM-7 on GSH concentrations observed in vitro are also apparent in vivo following the consumption of A1 type protein and potential exposure to BCM-7.
In a preliminary in vivo study using rabbits, it was observed that consumption of a diet containing the A1 type of β-casein was associated with decreased cysteine concentrations in the ileum and decreased GSH concentrations in the blood, liver, and brain compared with consumption of the A2 type (Additional file 1: Figure S1). These data indicate that, if BCM-7 is not absorbed into the systemic circulation, GSH downregulation may occur because of limited intestinal cysteine uptake from the small intestine. Thus, it was speculated that a reduction in cysteine absorption into the circulation, secondary to downregulation of cellular cysteine uptake, contributed to the reduction in systemic GSH concentrations, which was coupled with reduced GSH concentrations in the brain. While these in vitro and in vivo results were consistent, it is necessary to extend this investigation to clinical trials in order to determine if the observed effects of the A1 and A2 types of β-casein impart corresponding effects on circulating GSH concentrations in humans.
Plasma BCM-7 concentrations were significantly greater in samples obtained during consumption of milk containing both β-casein types than at baseline during consumption of milk containing A2 β-casein (Additional file 1: Table S2). The BCM-7 concentrations were not significantly different between samples obtained after consumption of milk containing A2 β-casein and the washout/baseline phases.
The results obtained in this randomized cross-over study are consistent with the results of these prior studies. Eliminating the A1 type of β-casein from the milk diet allowed for greater increases in GSH synthesis, likely through eliminating the inhibitory effects of BCM-7 on cysteine uptake by the small intestine, as demonstrated in animal studies and in cells exposed to BCM-7 [17]. This is also supported by the lower BCM-7 concentrations observed in the A2 β-casein periods compared with the A1/A2 β-casein periods in the present study.
It is also notable that, even though BCM-7 concentrations were proportionately greater after consumption of milk containing both β-casein typ