Abstract
This study reports the plasma glutathione concentrations in a double-blind, randomized, controlled, 2 × 2 cross-over study in which healthy participants consumed conventional milk (2 × 250 mL per day) containing both A1 and A2 types of β-casein, or milk containing only A2 type β-casein. Beta-casomorphin-7 (BCM-7), a peptide uniquely derived from the A1 type of β-casein, was previously reported to downregulate glutathione expression in human gut epithelial and neuronal cell lines by limiting cysteine uptake. The current human study demonstrates that consumption of milk containing only A2 β-casein was associated with a greater increase in plasma glutathione concentrations compared with the consumption of milk containing both β-casein types, and did not increase plasma BCM-7 concentrations compared with the washout diet in the study participants. Thus, milk containing only A2 β-casein and not A1 β-casein has the potential to promote the production of the antioxidant glutathione in humans.Clinical Trial RegistrationClinicalTrials.gov; identifier: NCT02406469 Electronic supplementary materialThe online version of this article (doi:10.1186/s12937-016-0201-x) contains supplementary material, which is available to authorized users.
Highlights
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]
Consumption of milk containing only the A2 β-casein type was associated with significantly greater increases in plasma GSH concentrations from baseline to the end of the study phase compared with the consumption of milk containing both β-casein types
The mean ± standard error of the mean change in GSH concentrations from baseline was 4.01 ± 0.61 nmol/mL for milk containing A2 β-casein compared with 1.99 ± 0.50 nmol/mL for milk containing both types of β-casein
Summary
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]. 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. BCM-7 is a bioactive peptide with high affinity to μopioid receptors It is uniquely produced by proteolysis of the A1 but not the A2 type of β-casein in cow’s milk by digestive enzymes [5, 6]. A histidine at this position in the A1 type readily allows enzymatic hydrolysis, whereas a proline at this position in the A2 type sterically hinders proteolytic
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