Aspartame decreases evoked extracellular dopamine levels in the rat brain: An in vivo voltammetry study

Aspartame use and Parkinson's disease: review of associated effects on neurotransmitters, oxidative stress, and cognition

Objective: The purpose of this review was to assess the current evidence regarding the associated physiological and cognitive effects of aspartame (APM) consumption and Parkinson's Disease (PD).

METHODS

A total of 32 studies demonstrating effects of APM on monoamine deficiencies, oxidative stress, and cognitive changes were reviewed.

RESULTS

Multiple studies demonstrated decreased brain dopamine, decreased brain norepinephrine, increased oxidative stress, increased lipid peroxidation, and decreased memory function in rodents after APM use. In addition, PD animal models have been found to be more sensitive to the effects of APM.

DISCUSSION

Overall, studies of APM use over time yielded more consistent results; however, no study has examined long-term effects on APM in human PD patients. Based on the current evidence, long-term human based observational research is needed to further investigate the potential effect of APM on PD.

Behavioral and electrophysiological brain effects of aspartame on well-nourished and malnourished rats

The non-caloric sweetener aspartame can be potentially harmful to the developing brain, as some studies suggest an association between aspartame intake and adverse neural effects. This study aimed to evaluate the possible effects of aspartame, with or without associated early nutritional deficiency, on behavioral parameters suggestive of anxiety and electrophysiological features of the excitability-related phenomenon known as cortical spreading depression (CSD). Newborn Wistar rats (n = 80) were suckled under favorable (L₉; n = 40) or unfavorable lactation conditions (L₁₅; n = 40), consisting of litters with 9 or 15 pups, respectively. In each lactation condition, animals were divided into 4 groups that received per gavage, from postnatal day 8 to 28, 75 mg/kg/d or 125 mg/kg/d aspartame (groups ASP75 and ASP125), or water (vehicle group), or no treatment (naive group). Behavioral tests (elevated plus-maze [EPM]) were performed at postnatal days 86-95 and CSD was recorded between postnatal days 96-115. Compared to the control groups, aspartame dose-dependently reduced body weight, suggesting a negative impact on animal development; aspartame also caused behavioral changes suggestive of anxiety (shorter stay in the open arms in the EPM) and decelerated CSD (lower propagation speed). Some of these parameters were more affected in L₁₅ animals, suggesting an interaction among aspartame and lactation condition. We concluded that early consumption of aspartame adversely affects development of the organism (weight loss), with actions on behavioral (anxiety-like) and cerebral electrophysiological (CSD) parameters. The data suggest caution in aspartame consumption by lactating mothers and their infants.

Astrogliosis and decreased neural viability as consequences of early consumption of aspartame and acesulfame potassium in male Wistar rats

Artificial sweeteners are mainly used as substitutes for sucrose derivates. In this study, we analyzed if the chronic consumption of aspartame or acesulfame potassium at an early age, produces histological alterations, astrogliosis and decreased neuronal viability, in hippocampus, prefrontal cortex, amygdala and hypothalamus of male Wistar rats. A histological analysis was performed on male Wistar rats that consumed aspartame or acesulfame potassium during 90 days, initiating the consumption of sweeteners immediately after weaning. The evaluation of neuronal morphology in different areas of the brain was performed with hematoxylin - eosin staining. To measure astrogliosis and neuronal viability, we used the immunohistochemical technique, with the glial fibrillary acidic protein immunomodulators (GFAP) and with neuronal-specific enolase (NSE). The consumption of aspartame or acesulfame potassium promoted morphological changes of neurons including increased pyknotic nuclei and vacuolization in all the brain areas studied. In hippocampus, prefrontal cortex, amygdala and hypothalamus, astrogliosis and reduction of neural viability were observed in sweeteners consumers in comparison with the control group. Chronic consumption of ASP and ACK from early stages of development and during long periods, may promote neural modifications, astrogliosis and decrease neuronal viability in prefrontal cortex, amygdala, hippocampus, and hypothalamus.

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.

Aspartame Consumption for 12 Weeks Does Not Affect Glycemia, Appetite, or Body Weight of Healthy, Lean Adults in a Randomized Controlled Trial

Background

Low-calorie sweeteners are often used to moderate energy intake and postprandial glycemia, but some evidence indicates that they may exacerbate these aims.

Objective

The trial's primary aim was to assess the effect of daily aspartame ingestion for 12 wk on glycemia. Effects on appetite and body weight were secondary aims.

Methods

One hundred lean [body mass index (kg/m2): 18-25] adults aged 18-60 y were randomly assigned to consume 0, 350, or 1050 mg aspartame/d (ASP groups) in a beverage for 12 wk in a parallel-arm design. At baseline, body weight and composition were determined, a 240-min oral-glucose-tolerance test (OGTT) was administered, and measurements were made of appetite and selected hormones. Participants also collected a 24-h urine sample. During the intervention, the 0-mg/d ASP group consumed capsules containing 680 mg dextrose and 80 mg para-amino benzoic acid. For the 350-mg/d ASP group, the beverage contained 350 mg aspartame and the 1050-mg/d ASP group consumed the same beverage plus capsules containing 680 mg dextrose and 700 mg aspartame. Body weight, blood pressure, heart rate, and waist circumference were measured weekly. At weeks 4, 8, and 12, participants collected 24-h urine samples and kept appetite logs. Baseline measurements were repeated at week 12.

Results

With the exception of the baseline OGTT glucose concentration at 60 min (and resulting area under the curve value), there were no group differences for glucose, insulin, resting leptin, glucagon-like peptide 1, or gastric inhibitory peptide at baseline or week 12. There also were no effects of aspartame ingestion on appetite, body weight, or body composition. Compliance with the beverage intervention was ∼95%.

Conclusions

Aspartame ingested at 2 doses for 12 wk had no effect on glycemia, appetite, or body weight among healthy, lean adults. These data do not support the view that aspartame is problematic for the management of glycemia, appetite, or body weight. This trial was registered at www.clinicaltrials.gov as NCT02999321.

Effect of developmental NMDAR antagonism with CGP 39551 on aspartame-induced hypothalamic and adrenal gene expression

Rationale

Aspartame (L-aspartyl phenylalanine methyl ester) is a non-nutritive sweetener (NNS) approved for use in more than 6000 dietary products and pharmaceuticals consumed by the general public including adults and children, pregnant and nursing mothers. However a recent prospective study reported a doubling of the risk of being overweight amongst 1-year old children whose mothers consumed NNS-sweetened beverages daily during pregnancy. We have previously shown that chronic aspartame (ASP) exposure commencing in utero may detrimentally affect adulthood adiposity status, glucose metabolism and aspects of behavior and spatial cognition, and that this can be modulated by developmental N-methyl-D-aspartate receptor (NMDAR) blockade with the competitive antagonist CGP 39551 (CGP). Since glucose homeostasis and certain aspects of behavior and locomotion are regulated in part by the NMDAR-rich hypothalamus, which is part of the hypothalamic-pituitary-adrenal- (HPA) axis, we have elected to examine changes in hypothalamic and adrenal gene expression in response to ASP exposure in the presence or absence of developmental NMDAR antagonism with CGP, using Affymetrix microarray analysis.

Results

Using 2-factor ANOVA we identified 189 ASP-responsive differentially expressed genes (DEGs) in the adult male hypothalamus and 2188 in the adrenals, and a further 23 hypothalamic and 232 adrenal genes significantly regulated by developmental treatment with CGP alone. ASP exposure robustly elevated the expression of a network of genes involved in hypothalamic neurosteroidogenesis, together with cell stress and inflammatory genes, consistent with previous reports of aspartame-induced CNS stress and oxidative damage. These genes were not differentially expressed in ASP mice with CGP antagonism. In the adrenal glands of ASP-exposed mice, GABA and Glutamate receptor subunit genes were amongst those most highly upregulated. Developmental NMDAR antagonism alone had less effect on adulthood gene expression and affected mainly hypothalamic neurogenesis and adrenal steroid metabolism. Combined ASP + CGP treatment mainly upregulated genes involved in adrenal drug and cholesterol metabolism.

Conclusion

ASP exposure increased the expression of functional networks of genes involved in hypothalamic neurosteroidogenesis and adrenal catecholamine synthesis, patterns of expression which were not present in ASP-exposed mice with developmental NMDAR antagonism.

Revisiting the safety of aspartame

Aspartame is a synthetic dipeptide artificial sweetener, frequently used in foods, medications, and beverages, notably carbonated and powdered soft drinks. Since 1981, when aspartame was first approved by the US Food and Drug Administration, researchers have debated both its recommended safe dosage (40 mg/kg/d) and its general safety to organ systems. This review examines papers published between 2000 and 2016 on both the safe dosage and higher-than-recommended dosages and presents a concise synthesis of current trends. Data on the safe aspartame dosage are controversial, and the literature suggests there are potential side effects associated with aspartame consumption. Since aspartame consumption is on the rise, the safety of this sweetener should be revisited. Most of the literature available on the safety of aspartame is included in this review. Safety studies are based primarily on animal models, as data from human studies are limited. The existing animal studies and the limited human studies suggest that aspartame and its metabolites, whether consumed in quantities significantly higher than the recommended safe dosage or within recommended safe levels, may disrupt the oxidant/antioxidant balance, induce oxidative stress, and damage cell membrane integrity, potentially affecting a variety of cells and tissues and causing a deregulation of cellular function, ultimately leading to systemic inflammation.

Oxidative stress evoked damages on rat sperm and attenuated antioxidant status on consumption of aspartame

Although several studies on toxic effect of aspartame metabolite have been studied, controversial reports over the use of aspartame owing to the fact that it releases methanol as one of its metabolite during metabolism exist. This present study is proposed to investigate whether aspartame (40 mg kg^-1 b.wt) administration for 90 days could induce oxidative stress and alter antioxidant status of epididymal sperm in Wistar strain male albino rats. To mimic the human methanol metabolism, methotrexate (MTX)-treated rats were included to study the effects of aspartame. Oral intubations of FDA approved 40 mg kg^-1 b.wt aspartame were given daily for 90 days to Wistar strain male albino rats and studied along with controls and MTX-treated controls. Sperm count, viability, morphology, morphometry and motility were assessed. A significant decrease in sperm function of aspartame treated animals was observed when compared with the control and MTX control. The free radical generation were observed in epididymal sperm by assessing the scavenging enzymes, enzymatic and non-enzymatic antioxidants. Result suggest that there was a significant increase glutathione-s-transferase (GST), with a significant decrease in reduced glutathione (GSH), superoxide dismutase activity (SOD), glutathione peroxidase levels (GPx), catalase activity (CAT) and glutathione reductase concentration. The increase in free radicals generation could have ultimately caused the lipid peroxidation mediated damages on the testis. Aspartame treated animals also revealed the reduced space in seminiferous tubules, which resulted in reduced Leydig cells when compared with control in histopathology. These findings demonstrate that aspartame metabolites could be a contributing factor for development of oxidative stress in the epididymal sperm.

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.

Chronic Effect of Aspartame on Ionic Homeostasis and Monoamine Neurotransmitters in the Rat Brain

Aspartame is one of the most widely used artificial sweeteners globally. Data concerning acute neurotoxicity of aspartame is controversial, and knowledge on its chronic effect is limited. In the current study, we investigated the chronic effects of aspartame on ionic homeostasis and regional monoamine neurotransmitter concentrations in the brain. Our results showed that aspartame at high dose caused a disturbance in ionic homeostasis and induced apoptosis in the brain. We also investigated the effects of aspartame on brain regional monoamine synthesis, and the results revealed that there was a significant decrease of dopamine in corpus striatum and cerebral cortex and of serotonin in corpus striatum. Moreover, aspartame treatment significantly alters the tyrosine hydroxylase activity and amino acids levels in the brain. Our data suggest that chronic use of aspartame may affect electrolyte homeostasis and monoamine neurotransmitter synthesis dose dependently, and this might have a possible effect on cognitive functions.

Cytotoxic effect of aspartame (diet sweet) on the histological and genetic structures of female albino rats and their offspring

The present study evaluated the effect of aspartame intake on the histological and genetic structures of mother albino rats and their offspring. Sixty adult female albino rats and 180 of their offspring were equally divided into two groups (control and treated), each group divided into three subgroups. Each subgroup consisted of 10 pregnant rats and 30 of their offspring. The experimental design divided into three periods: (1) the gestation period (subgroup one), (2) the gestation period and three weeks after delivery (subgroup two) and (3) animals in the third subgroup treated as subgroup two then left till the end of the ninth week after delivery. Each pregnant rat in the treated subgroups was given a single daily dose of 1 mL aspartame solution (50.4 mg) by gastric gavage throughout the time intervals of experimental design. At the end of each experimental period for control and treated subgroups, the liver of half of both control and treated groups were subjected for histological study while the liver and bone marrow of the other halves were subjected for cytogenetic studies. Body weight of both groups were recorded individually twice weekly in the morning before offering the diet. The results revealed that the rats and their offspring in the subgroups of control animals showed increases in body weight, normal histological sections, low chromosomal aberration and low DNA fragmentation. The treated animals in the three subgroups rats and their offspring revealed decreases in body weight, high histological lesions, increases in the chromosomal aberration and DNA fragmentation compared with control groups. In conclusion, the consumption of aspartame leads to histopathological lesions in the liver and alterations of the genetic system in the liver and bone marrow of mother albino rats and their offspring. These toxicological changes were directly proportional to the duration of its administration and improved after its withdrawal.

Aspartame-fed zebrafish exhibit acute deaths with swimming defects and saccharin-fed zebrafish have elevation of cholesteryl ester transfer protein activity in hypercholesterolemia

Although many artificial sweeteners (AS) have safety issues, the AS have been widely used in industry. To determine the physiologic effect of AS in the presence of hyperlipidemia, zebrafish were fed aspartame or saccharin with a high-cholesterol diet (HCD). After 12 days, 30% of zebrafish, which consumed aspartame and HCD, died with exhibiting swimming defects. The aspartame group had 65% survivability, while the control and saccharin groups had 100% survivability. Under HCD, the saccharin-fed groups had the highest increase in the serum cholesterol level (599 mg/dL). Aspartame-fed group showed a remarkable increase in serum glucose (up to 125 mg/dL), which was 58% greater than the increase in the HCD alone group. The saccharin and HCD groups had the highest cholesteryl ester transfer protein (CETP) activity (52% CE-transfer), while the HCD alone group had 42% CE-transfer. Histologic analysis revealed that the aspartame and HCD groups showed more infiltration of inflammatory cells in the brain and liver sections. Conclusively, under presence of hyperlipidemia, aspartame-fed zebrafish exhibited acute swimming defects with an increase in brain inflammation. Saccharin-fed zebrafish had an increased atherogenic serum lipid profile with elevation of CETP activity.

Effect of long term intake of aspartame on antioxidant defense status in liver

The present study evaluates the effect of long term intake of aspartame, the artificial sweetener, on liver antioxidant system and hepatocellular injury in animal model. Eighteen adult male Wistar rats, weighing 150-175 g, were randomly divided into three groups as follows: first group was given aspartame dissolved in water in a dose of 500 mg/kg b.wt.; the second group was given a dose of 1000 mg/kg b.wt.; and controls were given water freely. Rats that had received aspartame (1000 mg/kg b.wt.) in the drinking water for 180 days showed a significant increase in activities of alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP) and γ-glutamyl transferase (GGT). The concentration of reduced glutathione (GSH) and the activity of glutathione peroxidase (GPx), and glutathione reductase (GR) were significantly reduced in the liver of rats that had received aspartame (1000 mg/kg b.wt.). Glutathione was significantly decreased in both the experimental groups. Histopathological examination revealed leukocyte infiltration in aspartame-treated rats (1000 mg/kg b.wt.). It can be concluded from these observations that long term consumption of aspartame leads to hepatocellular injury and alterations in liver antioxidant status mainly through glutathione dependent system.