High thiamine diphosphate level as a protective factor for Alzheimer's disease.

Objectives: Thiamine diphosphate (TDP) is an indispensable coenzyme for three key enzymes in glucose metabolism. Reduced TDP levels in patients with Alzheimer's disease (AD) has been widely demonstrated and is a diagnostic biomarker for the disease. In this study, we further explored the correlation between altered TDP metabolism and AD along with other risk factors. Methods A 1:1 case-control study was employed with 90 AD patients and 90 control subjects with normal-range cognitive abilities as assayed by the Mini Mental Status Evaluation. Age (<= 2 years variation), gender, and educational background were strictly matched. Levels of the main thiamine metabolites in whole blood samples, including TDP, thiamine monophosphate, and thiamine, were assayed using high-performance liquid chromatography. Apolipoprotein E genotypes, haemoglobin, and several metabolic factors (fasting glucose, uric acid, triglyceride, and total cholesterol) associated with AD were also measured. Results The odds ratio of TDP level for AD was 0.95 (with TDP level as a continuous variable) or 0.09 (with TDP level as a dichotomized variable with a cut-off value of 99.48 nmol/L). Blood TDP levels were significantly decreased in female AD patients compared to male AD patients. No correlations were identified between TDP levels and several metabolic factors (fasting glucose, uric acid, triglyceride, and total cholesterol). Conclusions TDP is a protective factor for AD and its protective efficacy may be independent of other metabolic factors. The difference of TDP levels between genders may be another possible explanation for the higher prevalence of AD in females.