Enhanced Activities of Blood Thiamine Diphosphatase and Monophosphatase in Alzheimer's Disease

BACKGROUND Thiamine metabolites and activities of thiamine-dependent enzymes are impaired in Alzheimer's disease (AD). OBJECTIVE To clarify the mechanism for the reduction of thiamine diphosphate (TDP), an active form of thiamine and critical coenzyme of glucose metabolism, in AD. METHODS Forty-five AD patients clinically diagnosed and 38 age- and gender-matched control subjects without dementia were voluntarily recruited. The contents of blood TDP, thiamine monophosphate (TMP), and thiamine, as well as the activities of thiamine diphosphatase (TDPase), thiamine monophosphatase (TMPase), and thiamine pyrophosphokinase (TPK), were assayed by high performance liquid chromatography. RESULTS Blood TDP contents of AD patients were significantly lower than those in control subjects (79.03 ± 23.24 vs. 127.60 ± 22.65 nmol/L, P<0.0001). Activities of TDPase and TMPase were significantly enhanced in AD patients than those in control subjects (TDPase: 1.24 ± 0.08 vs. 1.00 ± 0.04, P < 0.05; TMPase: 1.22 ± 0.04 vs. 1.00 ± 0.06, P < 0.01). TPK activity remained unchanged in AD as compared with that in control (0.93 ± 0.04 vs. 1.00 ± 0.04, P > 0.05). Blood TDP levels correlated negatively with TDPase activities (r = -0.2576, P = 0.0187) and positively with TPK activities (r = 0.2426, P = 0.0271) in all participants. CONCLUSION Enhanced TDPase and TMPase activities may contribute to the reduction of TDP level in AD patients. The results imply that an imbalance of phosphorylation-dephosphorylation related to thiamine and glucose metabolism may be a potential target for AD prevention and therapy.