Preclinical and Clinical Trials for investigating the effect of A1 vs A2 beta‐casein containing diet on Glutathione antioxidant status
Authors: Trivedi Malav S , Deth Richard , Zhang Yiting 
Published: November 2023

Background

Glutathione (GSH) is produced in every cell in the body, where it acts as an antioxidant to neutralize free radicals and prevent oxidative cellular damage. Alterations in GSH levels are reported in neurological, inflammatory diseases as well as immune dysfunction. Several studies in animals and humans involving supplementation with whey protein or whey protein isolates from milk have documented increases in plasma and tissue glutathione concentrations along with reductions in oxidative stress, while the effects of casein on GSH are as yet not clear. One of the major components of the casein family is beta‐casein and 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. We have previously reported 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.

Objective

The current work was undertaken to investigate the effects of A1 vs A2 type of beta‐casein containing diet on antioxidant GSH levels and inflammatory status in pre‐clinical and clinical trials.

Methods

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 liver, brain and gut tissues in our preclinical study, whereas serum GSH was measured in our clinical study. In both cases HPLC coupled to an electrochemical gradient detector was used to evaluate GSH levels.

Results

In our preclinical study we observed 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. Concurrently, we also observed elevated TNFalpha levels and NFkB levels in gut tissues of mice and rabbit 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). Similarly, in our clinical trial, human participants consuming A1 beta‐casein containing milk had decreased GSH serum (p<0.05, N=45).

Conclusions

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.

Milk free of A1 beta‐casein might be beneficial in these individuals.

Support or Funding Information

The a2 Milk Company Ltd

National Institute of Health