Spectrophotometric determination of choline acetyltransferase in the presence of dithiothreitol

Functional Compensation and Mechanism of Choline Acetyltransferase in the Treatment of Cognitive Deficits in Aged Dementia Mice

Choline acetyltransferase (ChAT) synthesizes the neurotransmitter acetylcholine (Ach). Exogenous supplementation with ChAT can functionally compensate for decreased Ach levels and ameliorate memory and cognitive deficits. In this paper, the treatment efficacy of recombinant ChAT (peptide transduction domain (PTD)-ChAT) and donepezil were compared in aged dementia mice, and their mechanisms were explored by performing the gene function annotation and enrichment analysis of differentially expressed genes. The Morris water maze test showed that the swimming times of PTD-ChAT-treated (4 mg/kg) and donepezil-treated (0.5 mg/kg) mice with mild and moderate dementia were significantly shortened (P < 0.01 vs aged dementia mice), and no significant changes were observed between the PTD-ChAT- and donepezil-treated groups. In contrast, the swimming times of PTD-ChAT-treated mice with severe dementia were noticeably shorter than those of donepezil-treated mice with severe dementia (P < 0.01), indicating that the treatment efficacy of PTD-ChAT is superior to that of donepezil. The effect of PTD-ChAT was further confirmed in transgenic dementia mice (C57BL/6J-TgN (APP/PS1) ZLFILAS). Gene function annotation and enrichment analysis showed that PTD-ChAT improved cognitive deficits through Ach and was implicated in neuroprotection, synaptic plasticity, neuronal survival, and cerebrovascular remodeling through ACh and vascular endothelial growth factor (VEGF) pathway activation. Donepezil was significantly correlated with the immune inflammatory response and the insulin and IGF-1 signaling pathways. Therefore, although PTD-ChAT and donepezil were both effective in the treatment of aged dementia mice, their mechanisms were significantly different. Our research indicated that PTD-ChAT has potential promise for research on new drugs for AD treatment.

Neuroprotection by D-securinine against neurotoxicity induced by beta-amyloid (25–35)

The effects of (+) securinine on behavior and morphological changes after intracerebral ventricle injection of beta-amyloid (25-35) (Abeta(25-35)) in rats were investigated. A single high dose of Abeta(25-35) could impair the spatial cognitive function. The latency of locating the platform was longer in the model group than in the sham-operated group. While chronic administration of D-securinine (40 mg kg(-1)) could significantly shorten the latency. After Morris water maze, the activity of choline acetyltransferase (ChAT) and acetylcholinesterase (AchE) were detected. The results showed that D-securinine could decrease the AchE activity significantly and have no effect on ChAT. Meanwhile, immunohistochemistry analysis revealed that D-securinine could reduce the glial inflammatory responses induced by beta-amyloid protein. These results suggest that the effect of D-securinine in improving the cognitive deficits and neurodegeneration in betaAP(25-35)-treated rats may involve direct and indirect actions on targets. The GABA receptor plays a key role in these therapeutic effects and may be helpful in the treatment of Alzheimer's disease.

Paeoniflorin attenuates amyloid-beta peptide-induced neurotoxicity by ameliorating oxidative stress and regulating the NGF-mediated signaling in rats

Paeoniflorin is a monoterpene glycoside isolated from the aqueous extract of the dry root of Paeonia. It has been identified to exhibit many pharmacological effects including enhancing the cognitive ability, producing anti-depressant-like effect and reducing the MTPT-induced toxicity. In our previous study, it has shown that paeoniflorin improved the cognitive ability and attenuated the oxidative stress in the Aβ(1-42)-treated rats. In order to further elucidate the possible molecular mechanisms of paeoniflorin on the cognitive ability, rats were injected with Aβ(1-42) (1 μg/μL) and later with paeoniflorin (15 mg/kg and 30 mg/kg, i.p.) and donepezil hydrochloride (2mg/kg, i.p.) daily for 20 days in this study. The results showed that the long-term treatment of paeoniflorin or donepezil enhanced the cognitive performances in the Morris water maze test, restored the decreased activities of superoxide dismutase and catalase and the increased level of malondialdehyde, and reversed the alterations of matrix metallopeptidase-9 and tissue-inhibitor of metalloproteinase-1 in the hippocampus of Aβ(1-42)-treated rats. Paeoniflorin also up-regulated the activity of choline acetyltrasferase and the expression of tyrosine kinase A receptor, and down-regulated the activity of acetylcholine esterase in the hippocampus of Aβ(1-42)-treated rats. These results demonstrate that paeoniflorin ameliorates the spatial learning and memory deficits by attenuating oxidative stress and regulating the nerve growth factor-mediated signaling to reinforce cholinergic functions in the hippocampus of the Aβ(1-42)-treated rats.

Prevention of age-related memory deficit in transgenic mice by human choline acetyltransferase

Choline acetyltransferase (ChAT, acetylCoA:choline O-acetyltransferase, EC 2.3.1.6) is the biosynthetic enzyme of neurotransmitter acetylcholine. Here we showed for the first time that transgenic mice with human ChAT kept excellent learning and memory ability during aging process. Transgenic mice were prepared through microinjection of human ChAT into mouse fertilized eggs, and PCR reaction was used to screen out the transgenic mice. The results of measurements of ChAT activity and acetylcholine level in mouse brain indicated that human ChAT gene was expressed throughout the life of the transgenic mice. The results of step-through test and water maze test suggested that learning and memory ability was improved in transgenic mice compared to that of their age-matched littermates. The results support our idea that supplement of ChAT might serve as a potential therapeutic strategy for cognitive deficit.

Protective effect of recombinant human somatotropin on amyloid beta-peptide induced learning and memory deficits in mice

This study aimed to examine the effects of the recombinant human somatotropin (rhGH) on protecting neuronal function, and improving learning and memory deficits in mice. Mice were intracerebroventricularly (icv) injected with the aggregated amyloid beta-peptide (Abeta) to mimic the Alzheimer's disease (AD). The learning and memory functions in mice were examined by the step through test (an index of long-term memory) and the water maze performance (an index of spatial recognition memory). The results indicated that the mice treated with rhGH showed significant reduction of the error counts and the long memory retentions in the step-through test, and short swimming times in the water maze performance. Toxic effects of free radicals, damages of cholinergic neurons, and increased lipid peroxidation appeared in the cerebra of Abeta-treated mice, manifesting an increase of malondialdehyde (MDA) and decline of glutathione (GSH) level, an increment of choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) activities, and a reduction of the acetylcholine (ACh) level. The gel electrophoresis pattern of the cerebra of mice treated with Abeta showed a typical DNA ladder of apoptosis. The in vivo experiments showed that the rhGH treatment significantly reversed the elevated MDA, ChAT, AChE, and the decreased GSH, ACh levels in the Abeta model mice. The results suggested that there were potential uses of the neuroprotective action of rhGH in the remedy of AD.

Complementary remedy of aged-related learning and memory deficits via exogenous choline acetyltransferase

The present study aimed to examine whether the aged mice with naturally occurring cognitive deficits in learning and memory would benefit from supplementation of choline acetyltransferase (ChAT), the biosynthetic enzyme for neurotransmitter acetylcholine. Delivered by protein transduction domain (PTD), ChAT could pass through the blood-brain barrier, enter the neurons, interact with heat shock protein 70kDa, and retain enzyme activity. In behavior tests, PTD-ChAT given to the aged and memory-deficient mice almost completely reversed the behavioral changes, such as impairment of memory retention in the step-through test (an index of long-term memory) and prolonged swimming time in water maze test (an index of spatial recognition memory). The results suggest a novel and potential therapeutic use of PTD-ChAT in the age-related cognitive deficits.

High-cholesterol diets impair short-term retention of memory in alloxan-induced diabetic mice, but not acquisition of memory nor retention of memory in prediabetic mice

Whether high-cholesterol diets (HCD) induce a high incidence of memory deficits in diabetes requires to be established; if so, whether they induce impairments of memory acquired in the pre-diabetic stage as well as in the diabetic stage also needs to be elucidated, and part of the related mechanisms involved in this dysfunction should be determined. The mice were grouped into: normal mice fed normal diets (NN), diabetic mice fed normal diets (DN), normal mice fed HCD (NH), and diabetic mice fed HCD (DH). Animals were subjected to Morris water maze testing: 1) Learning in the pre-diabetic stage and memory retrieval in the diabetic stage; 2) Learning and memory retrieval in the diabetic stage. Following water maze testing, biochemical parameters were estimated in the animals. The results showed that significant impairments of memory retrieval, acquired in the diabetic stage, were observed only in DH group, neither in DN nor NH group in a short term compared with NN group. Biochemical parameters including fasting blood glucose, lipid peroxidation productions and acetylcholinesterase activities in frontal cortex and hippocampus increased more rapidly in DH group than those in the rest. These results indicate that HCD impair the diabetic retention of memory, but neither the diabetic acquisition of memory nor the pre-diabetic retention of memory in diabetic mice in a short term. Controlled HCD may be a strategy to prevent the loss of memory in diabetic individuals after they have acquired new information.

Long-term effects of melatonin or 17 beta-estradiol on improving spatial memory performance in cognitively impaired, ovariectomized adult rats

Melatonin is an endogenously generated potent antioxidant. Our previous studies indicate that melatonin improved learning and memory deficits in APP695 transgenic mouse of Alzheimer's disease. An ovariectomized (OVX) rat model which is characterized by progressive memory deficits, central cholinergic nerve system degeneration and differentiation/apoptosis imbalance is the ideal in vivo model in which to test the neuroprotective effects of melatonin. OVX Sprague-Dawley rats received daily injections of melatonin (5, 10 and 20 mg/kg) or 17 beta-estradiol (E2, 80 microg/kg) or sesame oil for 16 wk. Morris water maze results showed that ovarian steroid deprivation resulted in spatial memory impairment, while melatonin and E2 significantly ameliorated spatial memory deficits in OVX rats. The latency to find the hidden platform and the distance to reach the platform become shorter in both melatonin and E2-treated rats compared with those that were only OVX. Four months after OVX, the choline acetyltransferase activity in the frontal cortex and hippocampus were greatly decreased in comparison with the controls. Melatonin and E2 antagonized the effects induced by OVX. Interestingly, the activity of the acetylcholinesterase was not altered in any group of rats. DNA fragmentation was presented in the front cortex of the OVX rats. Melatonin and E2 reduced the number of apoptotic neurons. These findings demonstrate the important effects of melatonin and E2 on cholinergic neurons and support the potential application of melatonin in the treatment of dementia in postmenopausal women. Our results indicate that neuroprotection by melatonin partly correlated to modulation of apoptosis and protection of the cholinergic system. Early long-term melatonin application is a promising strategy which could potentially be applied in a clinic setting.

Alternative therapy of Alzheimer’s disease via supplementation with choline acetyltransferase

Much evidence indicates that the memory and cognitive deficits of patients with Alzheimer's disease are closely associated with dysfunction of central cholinergic system. The degree of reduction of choline acetyltransferase activity in cerebral cholinergic neurons is significantly correlated with the severity of dementia or cognitive impairments observed in Alzheimer's disease. Therefore, Alzheimer's disease may be slowed by supplementation of exogenous choline acetyltransferase. Here we show that choline acetyltransferase mediated by TAT protein transduction domain passes through the blood-brain barrier and enters the neurons in mice, increasing choline acetyltransferase and neurotransmitter acetylcholine contents. The recombination TAT-choline acetyltransferase fusion protein injected intravenously improves the memory and cognitive dysfunction in Alzheimer's disease model mice induced by amyloid-beta peptide. Our results imply a novel and potentially effective way for Alzheimer's disease therapy.

Choline acetyltransferase. The absence of multiple forms and purification from mouse brain

No multiple forms of choline acetyltransferase were found in extracts of human, mouse, rabbit, guinea pig, cat, and rat brain. A single form of this enzyme only was also demonstrated in bovine nervous tissue, including brain, dorsal and ventral roots, spinal cord, and femoral nerve. The difference from other published findings is believed to be due to ammonium sulfate fractionation, which was not used in the present study. In addition, multiple forms of the enzyme were obtained by others using isoelectric focusing, whereas this study employed gel filtration. Choline acetyltransferase was highly purified form mouse brain using a procedure similar to that used for the enzyme from bovine brain. The steps involved: (1) making an acetone-chloroform powder from whole mouse brains, (2) extracting the powder and chromatographing the soluble fraction with organomercurial Sepharose, (3) passing the enzyme solution through a column of DEAE-cellulose, (4) eluting from hydroxyapatite, and (5) removing contaminants by subunit exchange chromatography. The final preparation was essentially homogeneous as revealed by polyacrylamide gel electrophoresis.