Acute effects of aspartame on concentrations of brain amines and their metabolites in selected brain regions of Fischer 344 and Sprague-Dawley rats

Effects of chronic aspartame consumption on MPTP-induced Parkinsonism in male and female mice

BACKGROUND

Parkinson's disease is a progressive neurodegenerative disorder. Aspartame (l-aspartyl-l-phenylalanine methyl ester), a low calorie sweetener used in foods and beverages.

OBJECTIVES

This study investigated the effect of chronic aspartame intake on Parkinsonism induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP).

METHOD

Forty-eight mice (24 males and 24 females): control, aspartame, MPTP, and aspartame + MPTP groups tested by Y-maze, stepping, forced swimming and olfactory preference tests. Brain tissues examined for dopamine content, tyrosine hydroxylase, inducible nitric oxide synthase (iNOS), glutathione peroxidase, phosphorylated tau and α-synuclein protein. Histopathological evaluation of brain sections at the level of basal ganglia was done.

RESULTS

Decreased dopamine content, tyrosine hydroxylase expression, glutathione peroxidase expression and increased iNOS, tau and α-synuclein expression in groups received aspartame, MPTP or both agents simultaneously in both males and females group.

CONCLUSIONS

Increased dopaminergic degeneration and complications with chronic aspartame consumption and more injury in male groups.

Alterations in behaviour, cerebral cortical morphology and cerebral oxidative stress markers following aspartame ingestion

OBJECTIVE

The study evaluated changes in open field behaviours, cerebral cortical histomorphology and biochemical markers of oxidative stress following repeated administration of aspartame in mice.

METHODOLOGY

Adult mice were assigned into five groups of twelve each. Vehicle (distilled water), or aspartame (20, 40, 80 and 160mg/kg body weight) were administered orally for 28days. Horizontal locomotion, rearing and grooming were assessed after the first and last dose of aspartame. Sections of the cerebral cortex were processed and stained for general histology, and also examined for neuritic plaques using the Bielschwosky's protocol. Glial fibrillary acidic protein (GFAP) and neuron specific enolase (NSE) immunoreactivity were assessed using appropriate antibodies. Aspartate and antioxidant levels were also assayed from cerebral cortex homogenates. Data obtained were analysed using descriptive and inferential statistics.

RESULTS

Body weight and food consumption decreased significantly with aspartame consumption. Locomotion, rearing and grooming increased significantly after first dose, and with repeated administration of aspartame. Histological changes consistent with neuronal damage were seen at 40, 80 and 160mg/kg. Neuritic plaque formation was not evident; while GFAP-reactive astrocytes and NSE-reactive neurons increased at 40 and 80mg/kg but decreased at 160mg/kg. Superoxide dismutase and nitric oxide increased with increasing doses of aspartame, while aspartate levels showed no significant difference.

CONCLUSION

The study showed morphological alterations consistent with neuronal injury and biochemical changes of oxidative stress. These data therefore supports the need for caution in the indiscriminate use of aspartame as a non-nutritive sweetener.

Rat strain differences in restraint stress-induced brain cytokines

Induction of brain cytokines during times of stress has potent effects on altering behavior, mood, and cognitive functioning. Currently, it is unknown why exposure to some stressors such as tailshock and footshock elevate brain cytokines, while exposure to swim, predator odor, and restraint stress do not. Recent data indicate that brain noradrenergic signaling mediates brain cytokine production suggests magnitude of norepinephrine release during stress may be critical in initiating brain cytokine production. The aim of the current study was to investigate stress-induced brain cytokines between rat strains that differ in their magnitude of stress responsiveness as measured by brain norepinephrine and HPA responses. Sprague-Dawley and Fischer rats were placed in a restraint bag for 1 h or 2 h and sacrificed immediately following stressor termination. Exposure to restraint significantly elevated hypothalamic interleukin (IL)-1β and IL-1 receptor type (R) 2 mRNA after 1 h and IL-1β protein after 2 h in the high stress responsive Fischer rats, but not in Sprague-Dawley rats. IL-6, IL-1R1, Il-1 receptor antagonist (RA), and cyclooxygenase (Cox)-2 mRNA were not altered and neither there was expression of any cytokines in the hippocampus or circulating cytokines in either strain. Administration of desipramine (a norepinephrine reuptake inhibitor) to Sprague-Dawley rats was sufficient either alone or in combination with stress to increase IL-1β mRNA in the hypothalamus and desipramine combined with stress was sufficient to increase IL-1R2 mRNA in the hypothalamus. These data support our hypothesis that there is a critical threshold of brain norepinephrine necessary to stimulate brain cytokines, which may help to explain why severe stressors are more commonly reported to induce brain cytokines. These data also suggest an organisms' susceptibility to stress-induced brain cytokine production, depends on responsiveness and regulation of noradrenergic neurons.

Aspartame: review of safety

Over 20 years have elapsed since aspartame was approved by regulatory agencies as a sweetener and flavor enhancer. The safety of aspartame and its metabolic constituents was established through extensive toxicology studies in laboratory animals, using much greater doses than people could possibly consume. Its safety was further confirmed through studies in several human subpopulations, including healthy infants, children, adolescents, and adults; obese individuals; diabetics; lactating women; and individuals heterozygous (PKUH) for the genetic disease phenylketonuria (PKU) who have a decreased ability to metabolize the essential amino acid, phenylalanine. Several scientific issues continued to be raised after approval, largely as a concern for theoretical toxicity from its metabolic components--the amino acids, aspartate and phenylalanine, and methanol--even though dietary exposure to these components is much greater than from aspartame. Nonetheless, additional research, including evaluations of possible associations between aspartame and headaches, seizures, behavior, cognition, and mood as well as allergic-type reactions and use by potentially sensitive subpopulations, has continued after approval. These findings are reviewed here. The safety testing of aspartame has gone well beyond that required to evaluate the safety of a food additive. When all the research on aspartame, including evaluations in both the premarketing and postmarketing periods, is examined as a whole, it is clear that aspartame is safe, and there are no unresolved questions regarding its safety under conditions of intended use.

Effects of long-term ingestion of aspartame on hypothalamic neuropeptide Y, plasma leptin and body weight gain and composition

The aim of this study was to determine the effects of the chronic ingestion of aspartame (ASP) on brain neuropeptide Y (NPY) concentrations, plasma hormones, food intake and body fat. Two groups of male Long-Evans rats, fed on a control (C) well-balanced diet, had to drink either a 0.1% ASP solution or water for a period of 14 weeks starting at weaning. Food intake and body weight were weekly recorded. At the end of the experiment, fat pads were sampled, leptin and insulin were measured in the plasma and NPY in several microdissected brain areas. Substituting ASP for water led to lower body weight (-8%; P<.004) and lower fat depot weight (-20%; P<.01) with no differences in energy intake or plasma insulin concentrations. Plasma leptin was significantly reduced by 34% (P<.05). Leptin concentrations were well-correlated with final body weight (r=.47; P<.025) and fat pad mass (r=.53; P<.01). NPY concentrations were 23% lower (P<.03) in the arcuate nucleus of ASP rats with no differences in other brain areas. The beneficial effects on body composition could be related to the decreased effects of NPY on lipid and energy metabolism, independently of insulin. The reasons for the NPY decrease (regulatory or toxicological) are not obvious. The constitutive amino acids of the ASP molecule might participate in the NPY regulation.

Effects of neurotoxic doses of methamphetamine on potassium and amphetamine evoked overflow of dopamine in the striatum of awake rats

The effects of neurotoxic doses of methamphetamine on basal and evoked overflow of dopamine in the striatum were examined in awake rats using microdialysis. Male Fischer-344 rats were administered methamphetamine (5 mg/kg s.c.) or saline four times in 1 day at 2-h intervals. Microdialysis experiments were carried out 1 week later. Basal levels of dopamine, 3,4-dihydroxyphenylacetic acid, and homovanillic acid were reduced in the striatum of the methamphetamine-treated animals. Local application of excess potassium (100 mM) and amphetamine (100 microM), and intraperitoneal injection of amphetamine (1.5 mg/ kg), led to increased levels of extracellular dopamine in the striatum of both methamphetamine- and saline-treated rats. However, the increase was significantly less in the methamphetamine-treated animals. Tissue levels of dopamine and metabolites were reduced in the striata of rats treated with methamphetamine. These results indicate that treatment with neurotoxic doses of methamphetamine can lead to functional changes in dopamine release in the striatum of Fischer-344 rats.