Effects of dietary nucleoside-nucleotide mixture on memory in aged and young memory deficient mice

Dietary nucleotides extend the life span in Sprague-Dawley rats

OBJECTIVE

To observe the effect of prolonged feeding of dietary nucleotides (NTs), and to clarify the effect of NTs on life extension of Sprague-Dawley rats.

METHODS

There were 50 Sprague-Dawley rats in each group (male:female ratio=1:1), which were fed diets supplemented with NTs at concentrations of 0%, 0.01%, 0.04%, 0.16% and 0.64% (wt/wt) from the age of 4 weeks until natural death. We investigated the moribundity and mortality, survival time, spontaneous tumor incidence, and serum oxidative status.

RESULTS

NTs have significantly influence body weight of first 3 month old and food consumption of male rats throughout the life span; it did dose-dependently inhibit the age-related decrease in the activities of antioxidant enzymes and the age-related increase in the levels of lipid peroxidation product in both sexes. NTs notably increased the mean life span, and the maximal life span. Compared to the control group, the incidence of death from tumors was decreased in NTs groups of both sexes.

CONCLUSIONS

Long-term feeding of NTs could dose-dependently increase life span in Sprague-Dawley rats, especially, the tumor-bearing ones. Moreover, the antioxidative property of NTs may be responsible for the increased life span.

A nucleoside-nucleotide mixture may reduce memory deterioration in old senescence-accelerated mice

We investigated the effects of a mixture of dietary nucleosides and nucleotides (NS + NT) on memory in 1- and 7-mo-old senescence-accelerated mice (SAM). Memory retention was studied with passive avoidance (step-through) and active avoidance (shuttle) tests. For 14 wk, mice in the control groups were fed a 20 g of casein/100 g diet, whereas the NS + NT groups were fed this diet supplemented with a 0.5 g of NS + NT mixture/100 g. All mice were killed at wk 14, and we studied the brain histopathology. Lipofuscin, monovacuoles and multiple vacuoles of various brain regions were measured. Body weight, food intake and ambulatory activity did not differ between the control and NS + NT groups. In old mice, the time of passive avoidance was significantly higher in the NS + NT group than in the control group at d 1 and 7 (P: < 0.05). However, such an effect of NS + NT was not observed in young mice. In the active avoidance test, the incidence of successful avoidance in old mice was higher in the NS + NT group than in the control group at d 1 and 2 (P: < 0.05). The percentages of specific brain cells containing lipofuscin were lower in NS + NT groups than in the control groups in both young and old mice (P: < 0.05). The number of monovacuoles and multiple vacuoles in specific brain regions tended to be lower (P: = 0.1-0.25) in NS + NT than in control groups, with significant differences in the microvacuoles of the middle cortex of young mice and in the multiple vacuoles in the hind cortex of old mice (P: < 0. 05). These results suggest that increased dietary NS + NT may be associated with decreases in the age-induced deterioration of brain morphology and certain memory tasks.

Trophic effects of purines in neurons and glial cells

In addition to their well known roles within cells, purine nucleotides such as adenosine 5' triphosphate (ATP) and guanosine 5' triphosphate (GTP), nucleosides such as adenosine and guanosine and bases, such as adenine and guanine and their metabolic products xanthine and hypoxanthine are released into the extracellular space where they act as intercellular signaling molecules. In the nervous system they mediate both immediate effects, such as neurotransmission, and trophic effects which induce changes in cell metabolism, structure and function and therefore have a longer time course. Some trophic effects of purines are mediated via purinergic cell surface receptors, whereas others require uptake of purines by the target cells. Purine nucleosides and nucleotides, especially guanosine, ATP and GTP stimulate incorporation of [3H]thymidine into DNA of astrocytes and microglia and concomitant mitosis in vitro. High concentrations of adenosine also induce apoptosis, through both activation of cell-surface A3 receptors and through a mechanism requiring uptake into the cells. Extracellular purines also stimulate the synthesis and release of protein trophic factors by astrocytes, including bFGF (basic fibroblast growth factor), nerve growth factor (NGF), neurotrophin-3, ciliary neurotrophic factor and S-100beta protein. In vivo infusion into brain of adenosine analogs stimulates reactive gliosis. Purine nucleosides and nucleotides also stimulate the differentiation and process outgrowth from various neurons including primary cultures of hippocampal neurons and pheochromocytoma cells. A tonic release of ATP from neurons, its hydrolysis by ecto-nucleotidases and subsequent re-uptake by axons appears crucial for normal axonal growth. Guanosine and GTP, through apparently different mechanisms, are also potent stimulators of axonal growth in vitro. In vivo the extracellular concentration of purines depends on a balance between the release of purines from cells and their re-uptake and extracellular metabolism. Purine nucleosides and nucleotides are released from neurons by exocytosis and from both neurons and glia by non-exocytotic mechanisms. Nucleosides are principally released through the equilibratory nucleoside transmembrane transporters whereas nucleotides may be transported through the ATP binding cassette family of proteins, including the multidrug resistance protein. The extracellular purine nucleotides are rapidly metabolized by ectonucleotidases. Adenosine is deaminated by adenosine deaminase (ADA) and guanosine is converted to guanine and deaminated by guanase. Nucleosides are also removed from the extracellular space into neurons and glia by transporter systems. Large quantities of purines, particularly guanosine and, to a lesser extent adenosine, are released extracellularly following ischemia or trauma. Thus purines are likely to exert trophic effects in vivo following trauma. The extracellular purine nucleotide GTP enhances the tonic release of adenine nucleotides, whereas the nucleoside guanosine stimulates tonic release of adenosine and its metabolic products. The trophic effects of guanosine and GTP may depend on this process. Guanosine is likely to be an important trophic effector in vivo because high concentrations remain extracellularly for up to a week after focal brain injury. Purine derivatives are now in clinical trials in humans as memory-enhancing agents in Alzheimer's disease. Two of these, propentofylline and AIT-082, are trophic effectors in animals, increasing production of neurotrophic factors in brain and spinal cord. Likely more clinical uses for purine derivatives will be found; purines interact at the level of signal-transduction pathways with other transmitters, for example, glutamate. They can beneficially modify the actions of these other transmitters.

Effects of nucleotides on learning and memory in a Morris water maze test in normal and basal forebrain-lesioned rats

The effects of nucleotides on learning and memory were studied in normal and basal forebrain-lesioned rats using a Morris water maze test. Chronic oral administration of a nucleotide mixture (500 mg/kg), containing an equal weight of the disodium salts of adenosine 5'-monophosphate, guanosine 5'-monophosphate, inosine 5'-monophosphate, cytidine 5'-monophosphate, and uridine 5'-monophosphate facilitated learning acquisition in normal rats. In basal forebrain-lesioned rats, administration of the nucleotide mixture showed a tendency to improve learning acquisition and memory retrieval. In the biochemical studies, no significant changes were observed in brain choline and acetylcholine levels by treatment with the nucleotide mixture at the doses tested in both normal and basal forebrain-lesioned rats. The nucleotides did not affect the monoaminergic systems in normal rats, but did cause some changes in these systems in basal forebrain-lesioned rats. The present studies indicate that nucleotides ameliorate learning and memory processes in normal rats, but not in basal forebrain-lesioned rats, and they also modulate the activity of the central monoaminergic systems under certain conditions.

Role of nucleosides and nucleotides in the immune system, gut reparation after injury, and brain function

Emerging evidence indicates the importance of nucleosides and nucleotides in the maintenance of functions of the bone marrow hematopoietic cells, intestinal mucosa, and the brain, which have limited de novo synthesis of purine and pyrimidine bases. We have found that nucleosides and nucleotides stimulate hemopoieses and increase peripheral neutrophil counts in mice treated with cyclophosphoamide. Intraperitoneal administration of nucleosides and nucleotides decreased bacterial translocation, the number of colony-forming units, and increased survival against methicillin-resistant Staphylococcus aureus. In vitro immune studies in mice showed that nucleosides and nucleotides increase the delayed-type cutaneous hypersensitivity and the popliteal lymph node blastogenic response to antigens, allogens, and mitogens. Both intraperitoneal and oral administration of nucleosides and nucleotides reduced endotoxin-induced bacterial translocation and improved injury to the gut in protein-deficient mice. However, oral administration of nucleosides and nucleotides in experimental colitis resulted in a worsening of colitic conditions and increased interleukin-8 and tumor necrosis factor-alpha concentrations in inflamed colonic portions, indicating the pro-inflammatory activities of nucleosides and nucleotides. Memory-deficient senescence-accelerated mice and mice with dementia showed improved memory with dietary nucleosides and nucleotides supplementation. These results indicate that supplementation with nucleosides and nucleotides is beneficial to the functions of the system and the brain. However, beneficial effects to the gut appear to depend on the type of damage sustained by the gut.