Effect of A1 vs A2 beta-casein containing diet on glutathione antioxidant status: Implications for inflammation and cognitive function via gut-brain axis
Every cell including neurons and gut epithelial cell produces glutathione (GSH); a major antioxidant to neutralize free radicals and prevent oxidative damage. Altered GSH levels are reported in neurological, inflammatory diseases as well as immune dysfunction. Studies involving supplementation with whey protein/whey protein isolates from milk have documented increases in plasma- and tissue-GSH concentrations, with reductions in inflammatory status. But the effects of casein on GSH are as yet not clear. One of the major components of the casein family is beta-casein. Evolutionarily there are two major type of beta-casein: A1 and A2. The presence of histidine at position 67 allows a protein fragment of seven amino acids, known as beta-casomorphin-7 (BCM-7), to be produced on enzymatic digestion only from A1 but not from A2 beta-casein. BCM7 is an opioid peptide and can act on mu-opioid receptor similar to morphine. Our previous studies show that BCM-7 can reduce cysteine uptake in cultured human neuronal and gastrointestinal epithelial cells by activating opioid receptors, inducing oxidative stress by decreasing the levels of GSH.
The current work builds on the previous cell culture studies and investigates the effects of A1 vs A2 type of beta-casein containing diet on antioxidant GSH levels, inflammatory status and cognitive status in pre-clinical and clinical trials.
A pre-clinical study was performed using mouse and rabbit animal models fed on A1 and A2 beta-casein containing diet. The clinical study was performed in collaboration with researchers in China (NCT02406469 https://clinicaltrials.gov/ct2/show/NCT02406469). We collected brain and gut tissues in our preclinical study, whereas serum GSH was measured in our clinical study. GSH was measured using HPLC. Cognition was measured using Subtle Cognitive Impairment Test (SCIT) analysis and inflammatory status was measured using ELISA for different immune markers including cytokines.
Pre-clinical studies showed significant decrease in GSH levels (indicating oxidative stress) in liver, gut and brain samples from animals (both mice and rabbit, p<0.05, N=12) fed on an A1 beta-casein containing diet as compared to animals fed on A2 beta-casein containing diet. In parallel, elevated TNFalpha levels were observed in gut tissues of mice on an A1 beta-casein containing diet as compared to animals fed on A2 beta-casein containing diet, indicating elevated inflammatory status (p<0.05, N=12). In clinical trial, human participants consuming A1 beta-casein containing milk had decreased GSH serum (p<0.05, N=45). Such decreased GSH correlated to some serum inflammatory markers as well as changes in cognition as measured by the SCIT.
- Absorption of whey-derived cysteine supports GSH synthesis.
- BCM-7 opiate peptide, released from digestion of A1-type beta-casein, can restrict cysteine absorption and limit the extent of GSH synthesis, especially in sensitive individuals.
- Such altered GSH levels can be associated with changes in inflammation status and cognition.
- Milk free of A1 beta-casein might be beneficial in these individuals.
Support or Funding Information
The work was partially supported by National institute of Health and The a2 Milk company