Roles of branched-chain amino acids regulation in oxidative stress revealed by fibroblasts from classic Maple Syrup Urine Disease patients

Branched-chain amino acids (BCAAs) are essential amino acids commonly used in clinical procedures to improve patients outcome.However, their roles and cellular mechanisms are not clear.One effect of BCAAs supplementation is reduction of oxidative stress. BCAAs levels are regulated by their catabolism and the rate limiting enzyme is branched chain a-ketoacid dehydrogenase (BCKDH).Blockage in BCKDH activity leads to classic Maple Syrup Urine Disease (MSUD).To study the roles of BCAAs, we used cells with a single gene defect in BCKDH as a cellular model.We studied fibroblasts from four unrelated patients with null mutations in BCKDH and from controls.Fibroblasts from patients showed 2-fold increase in mitochondrial superoxide levels and 1.5-fold increase in protein carbonylation levels respect to controls.No changes in SOD2 protein levels were detected, indicating an increase production of mitochondrial superoxide and not an increase detoxification.Eleven proteins related to oxidative stress were differentially regulated in MSUD (p-value 0.05).Including up-regulated peroxiredoxin-4(PRDX4) and protein disulphide-isomerase(P4HB), as well as down-regulated prostaglandin G/H synthase 1 (PTGS1), also known as cyclooxygenase-1.These results correlate specific proteins to known effects of BCAAs in oxidative stress and shed light in the pharmacological mechanisms of BCAAs supplementation.