Enhancement of brain thiamine diphosphatase activity of rats by injection of cholinergic drugs

Preliminary findings of high-dose thiamine in dementia of Alzheimer's type

Thiamine is important not only in the metabolism of acetylcholine but also in its release from the presynaptic neuron. Pathologic, clinical, and biochemical data suggest that thiamine deficiency is detrimental to the cholinergic system and that thiamine-dependent enzymes may be altered in Alzheimer's disease. Two previous studies reported contradictory results in patients with dementia of Alzheimer's type treated with 3 g/day of thiamine. In the present study, we examined the effects of 3 to 8 g/day thiamine administered orally. Our results suggest that thiamine at these pharmacologic dosages may have a mild beneficial effect in dementia of Alzheimer's type. The mechanism of the observed effect is unknown, but the findings warrant further investigation, not only for their therapeutic implications but for their possible etiologic clues. In addition, the results suggest long-term carry-over effects that should be considered in the design of future studies.

Possible regulation of thiamine diphosphatase activity in rat brain microsomes by lipids

The effects of various treatments, which affect membrane structure, on microsomal thiamine diphosphatase and thiamine triphosphatase activities of rat brain, were examined. The treatment of micorosomes at alkaline pH caused a 2-fold activation of the thiamine diphosphatase, this being related to a change in membrane structure which was evidenced by a decrease of the turbidity of the microsomal suspension. Repeated freezing and thawing after hypo-osmotic treatment also increased the activity of microsomal thiamine diphosphatase. In addition, the thiamine diphosphatase activity was enhanced by treatment of the microsomes with phospholipase C or acetone. This lipid depletion resulted in a marked reduction in the apparent Km value of the thiamine diphosphatase with a corresponding loss in heat stability of the enzyme. We found further that brain thiamine diphosphatase was solubilized by Triton X-100. This decreased the phospholipid content in the preparation, but did not affect the apparent Km value and heat stability of the enzyme. In contrast with thiamine diphosphatase, thiamine triphosphatase was inactivated by treatment at alkaline pH or with acetone. However, treatment with phospholipase C did not affect the activity of thiamine triphosphatase.

Role of thiamine metabolism in the central nervous system. I. Basic properties of thiamine triphosphatase in rat brain

The properties of soluble and microsomal thiamine triphosphatase (TTPase) in rat brain were examined. The subcellular distributions and the pH optima of these enzyme activities differ markedly. TTPase seems to be distinct from a general nucleoside triphosphatase. The TTPase activities have an absolute divalent cation requirement which is fulfilled by Mg-++ or Ca-++ in microsomes and by Mg-++, but not Ca-++, in the soluble fraction. Addition of a physiological concentration of Ca-++ markedly inhibited the soluble TTPase activity.