Figure 3.

TBI alters methionine metabolism through the transsulfuration pathway. (A) Drawing of the transsulfuration pathway in which homocysteine is converted to cysteine and alpha-ketobutyrate. Alpha-ketobutyrate is reduced to generate 2-hydroxybutyrate. Molecules detected and measured in the current study are presented in bold text. Key enzymes are indicated by italic text. Although the plasma levels of both (B) alpha-ketobutyrate and (C) 2-hydroxybutyrate were significantly elevated in the plasma of sTBI patients compared to other groups, the plasma levels of (D) cysteine were significantly decreased in sTBI patients. In contrast, the levels of cysteine were significantly increased in the mTBI group. HV: healthy volunteers; mTBI: mild TBI patients; CBS: cystathionine-β-synthase; CSE: cystathionine γ-lyase; α-HBDH: alpha-hydroxybutyrate dehydrogenase. Horizontal bar indicates mean. *p < 0.05.