Pathways involved in Hcy metabolism and systemic metabolite levels. A) Scheme of Hcy metabolism and related pathways. Metabolites appear in white boxes, and the enzymes listed include the following: ADA, ADK, AdoHcy hydrolase (AHCY), BHMTs, AdoMet-dependent methyltransferases (MTs), MATs, vitamin B6-dependent CBS, MTHFR, and vitamin B12-dependent MTR. B) Serum and plasma metabolite levels from all animals in both normal (NF) and FD groups are shown. Serum folic acid [50.85 ± 22.03 (n = 10) vs. 7.46 ± 3.88 μg/L (n = 11)], tHcy [5.05 ± 2.45 (n = 33) vs. 14.70 ± 3.19 μM (n = 69)], and plasma vitamin B6 levels [40.00 ± 15.71 (n = 11) vs. 43.71 ± 8.74 μg/L (n = 18)] were measured as specified under Materials and Methods. The figure shows the mean ± SEM for each group, and differences were considered significant when P ≤ 0.05; ***P < 0.0001.