Effect of long term intake of aspartame on antioxidant defense status in liver
Introduction
Sweeteners are paid special attention among food additives as their use enables a sharp reduction in sugar consumption and a significant decrease in caloric intake while maintaining the desirable palatability of foods and soft drinks (Vences-Mejia et al., 2006). Sweeteners are also of primary importance as part of nutritional guidance for diabetes, a disease with increasing incidence in developing as well as developed countries (Gougeon et al., 2004). Aspartame (l-aspartyl l-phenylalanine methylester) is a dipeptide artificial sweetener that is widely used as a non-nutritive sweetener in foods and drinks. Aspartame is used as a sweetener in food products including dry beverage mixes, chewable multi-vitamins, breakfast cereals, chewing gum, puddings and fillings, carbonated beverages, refrigerated and non-refrigerated ready to drink beverages, yogurt type products and pharmaceuticals (Rencuzogullari et al., 2004). Aspartame represents 62% of the value of the intense sweetener market in terms of its world consumption (Fry, 1999). Upon ingestion, aspartame is immediately absorbed from the intestinal lumen and metabolized to phenylalanine, aspartic acid and methanol (Ranney et al., 1976). Following aspartame consumption, the concentrations of its metabolites are increased in the blood (Stegink, 1987).
The metabolism of xenobiotics to a large extent takes place in the liver. The byproducts of such metabolism sometimes are more toxic than the initial substance. This could lead to hepatic damage and the emergence of hepatic disorders (Ishak et al., 1991). These by-products include oxygen containing molecules that damage vital cell components through oxidation (Fernandez-Checa et al., 1997). They can produce deleterious effects by reacting with complex cellular molecules such as lipids, proteins and DNA. In order to prevent the potential effects of reactive oxygen species (ROS), organisms have evolved multiple systems of antioxidant defense including both enzymatic and non-enzymatic strategy, and are essential for the cellular metabolism and function (Mates, 2000).
Although some information is available on the aspartame induced toxicity at various levels (Christian et al., 2004, Simintzi et al., 2007), the studies on the effect of long term oral exposure of aspartame on liver antioxidants are lacking. Moreover, most of the recent studies on aspartame, have been carried out to understand the mechanisms of neurotoxicity (Christian et al., 2004, Tsakiris et al., 2006, Simintzi et al., 2007, Bergstrom et al., 2007) and cancer (Soffritti et al., 2006, Gallus et al., 2007). Despite numerous toxicological studies of aspartame, its effects on hepatic tissue have received little attention. So, there is a need to substantiate whether long term oral consumption of aspartame induces oxidative stress and structural changes in hepatic tissue.
We, therefore, investigated the effect of long term oral administration of aspartame on some markers of oxidative stress and hepatocellular injury in male Wistar rats under laboratory conditions. In the present study, we aimed to investigate the effects of long term consumption of aspartame on the activities of (1) hepatic marker enzymes – alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP) and γ-glutamyl transferase (GGT) (2) antioxidant enzymes – superoxide dismutase (SOD), catalase, glutathione peroxidase (GPx), and glutathione reductase (GR) (3) non-enzymatic antioxidant molecule reduced glutathione (GSH) (4) malondialdehyde (MDA), a marker of lipid peroxidation and (5) liver histopathology.
Section snippets
Chemicals
Aspartame was purchased from Himedia Chemicals, India. Thiobarbituric acid and triton X-100 were purchased from Sigma Aldrich (St. Louis, USA). All other chemicals were purchased from Sisco Research Laboratories (SRL), India.
Animals
Eighteen male adult Wistar rats weighing 150–175 g were purchased from the Small Animal Breeding Station (SABS) of Govt. Veterinary College, Mannuthy, Thrissur, Kerala, India and acclimatized for six days. All the animals were maintained under standard laboratory conditions
Results
Aspartame administration (1000 mg/kg b.wt.) significantly increased AST, ALT, ALP and GGT in serum. Significant increase in AST and GGT was also observed in the 500 mg/kg b.wt. aspartame-treated group (Table 1). No significant change in lipid peroxidation was observed in the experimental groups as compared to the control group (Table 2). Table 3 shows the change in various antioxidant enzymes in liver in response to different doses of aspartame after 180 days. No significant change was observed in
Discussion
The present study highlights the effect of long term consumption of two different doses of aspartame on antioxidant defense system and enzyme markers of hepatocellular injury in the liver. Aspartame is one of the widely consumed artificial sweetener and health conscious societies are increasingly concerned about its safety. Most of the people are unaware about the amount of aspartame they consume through various products. An important and interesting question is whether the chronic uncontrolled
Conclusion
The present study demonstrated the effects of long term administration of two different doses of aspartame in serum enzymes and antioxidant defense system in liver. Significant increase in the activities of serum enzymes indicates that aspartame may produce liver injury. Glutathione and glutathione dependent enzyme activities were found to have been decreased significantly in group administered with high dose of aspartame. This indicates the toxicity of aspartame is dose dependent.
Conflict of Interest
The authors declare that there are no conflicts of interest.
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