Glutathione Contributes to Caloric Restriction-Triggered Shift in Taurine Homeostasis

Previously, we found that caloric restriction (CR) in mice increases taurine levels by stimulating hepatic synthesis, secretion into the intestine and deconjugation of taurine-conjugated bile acids (BA). Subsequently, in the intestine, taurine conjugates various molecules, including glutathione (GSH). The current study explores the mechanisms behind forming taurine-GSH conjugate and its consequences for taurine, other taurine conjugates, and BA in order to improve understanding of their role in CR.

The non-enzymatic conjugation of taurine and GSH was assessed and the uptake of taurine, GSH, and taurine-GSH was verified in five sections of the small intestine. Levels of taurine, gavaged ¹³C labeled taurine, taurine conjugates, taurine-GSH, and GSH were measured in various tissues of ad libitum and CR mice. Next, the taurine-related CR phenotype was challenged by applying the inhibitors of taurine transporter (SLC6A6) and GSH-S transferases (GST).

The CR-related increase in taurine in intestinal mucosa was accompanied by the uptake and distribution of taurine towards selected organs. A unique composition of taurine conjugates characterized each tissue. Although taurine-GSH conjugate could be formed in non-enzymatic reactions, GST activity contributed to taurine-related CR outcomes. Upon SLC6A6 and GST inhibition, the taurine-related parameters were affected mainly in the ileum rather than the liver. Meanwhile, BA levels were somewhat affected by GST inhibition in the ileum and in the liver by SLC6A6 inhibitor.

The discovered CR phenotype involves a regulatory network that adjusts taurine and BA homeostasis. GSH supports these processes by conjugating taurine, impacting taurine uptake from the intestine and its availability to form other types of conjugates.