Plasma and erythrocyte amino acid levels of adult humans given 100 mg/kg body weight aspartame

Aspartame Safety as a Food Sweetener and Related Health Hazards

Aspartame is the methyl-ester of the aspartate-phenylalanine dipeptide. Over time, it has become a very popular artificial sweetener. However, since its approval by the main food safety agencies, several concerns have been raised related to neuropsychiatric effects and neurotoxicity due to its ability to activate glutamate receptors, as well as carcinogenic risks due to the increased production of reactive oxygen species. Within this review, we critically evaluate reports concerning the safety of aspartame. Some studies evidenced subtle mood and behavioral changes upon daily high-dose intake below the admitted limit. Epidemiology studies also evidenced associations between daily aspartame intake and a higher predisposition for malignant diseases, like non-Hodgkin lymphomas and multiple myelomas, particularly in males, but an association by chance still could not be excluded. While the debate over the carcinogenic risk of aspartame is ongoing, it is clear that its use may pose some dangers in peculiar cases, such as patients with seizures or other neurological diseases; it should be totally forbidden for patients with phenylketonuria, and reduced doses or complete avoidance are advisable during pregnancy. It would be also highly desirable for every product containing aspartame to clearly indicate on the label the exact amount of the substance and some risk warnings.

Toxicity of hypercaloric diet and monosodium glutamate: oxidative stress and metabolic shifting in hepatic tissue

The present study examines the effects of a hypercaloric diet on hepatic glucose metabolism of young rats, with and without monosodium glutamate (MSG) administration, and the association of these treatments with evaluating markers of oxidative stress. Male weaned Wistar rats (21 days old) from mothers fed with a hypercaloric diet or a normal diet, were divided into four groups (n=6): control (C) fed with control diet; (MSG) treated with MSG (4 mg/g) and control diet; (HD) fed with hypercaloric diet and (MSG-HD) treated with MSG and HD. Rats were sacrificed after the oral glucose tolerance test (OGTT), at 45 days of treatments. Serum was used for insulin determination. Glycogen, hexokinase(HK), glucose-6-phosphatase(G6PH), lipid hydroperoxide, superoxide dismutase(SOD) and glutathione peroxidase(GSH-Px) were determined in liver. HD rats showed hypoglycemia, hyperinsulinemia, and high hepatic glycogen, HK and decreased G6PH. MSG and MSG-HD had hyperinsulinemia, hyperglycemia, decreased HK and increased G6PH in hepatic tissue. These animals had impaired OGTT. HD, MSG and MSG-HD groups had increased lipid hydroperoxide and decreased SOD in hepatic tissue. Hypercaloric diet and monosodium glutamate administration induced alterations in metabolic rate of glucose utilization and decreased antioxidant defenses. Therefore, the hepatic glucose metabolic shifting induced by HD intake and MSG administration were associated with oxidative stress in hepatic tissue.

Effect of high-protein meal plus aspartame ingestion on plasma phenylalanine concentrations in obligate heterozygotes for phenylketonuria

The effect of a protein-rich meal alone or in combination with 85 mumol/kg body weight aspartame (APM) on plasma phenylalanine and large neutral amino acids (LNAA) was evaluated in obligate heterozygotes for phenylketonuria (PKU) and normal subjects (controls). Thirteen PKU heterozygotes (seven women, six men) and 13 controls (five women, eight men) ingested a 12-noon meal providing approximately 303 mumol/kg Phe. In addition, 10 PKU heterozygotes (five women, five men) and 10 controls (five women, five men) ingested the same meal with 85 mumol/kg APM (providing 75 mumol/kg Phe). Plasma amino acids were analyzed at baseline (-4 and 0 hours) and at 1, 3, and 20 hours after the meal or meal plus APM. Compared with the meal alone, ingestion of the meal plus APM significantly increased plasma Phe concentrations in both controls and PKU heterozygotes. Mean plasma Phe values were higher for controls at 1 hour (95 +/- 7 mumol/L) and for PKU heterozygotes at 3 hours (153 +/- 21 mumol/L). After the addition of APM to the meal, the highest mean plasma Phe concentration was only slightly greater than the usual postprandial range for both controls and PKU heterozygotes. Ingestion of the meal did not increase the plasma Phe/LNAA ratio in either controls or PKU heterozygotes. Compared with baseline, the plasma Phe/LNAA ratio increased significantly 1 hour after combined ingestion of the meal plus APM in both groups (P = .020 and P = .008, respectively); however, the ratios were well below the range of Phe/LNAA values in individuals with mild hyperphenylalaninemia, who are clinically normal and do not require a Phe-restricted diet.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma amino acid concentrations in normal adults administered aspartame in capsules or solution: lack of bioequivalence

Some clinical studies require administration of test compounds in capsules to assure that the compound cannot be distinguished from a placebo. This raises the question of whether the pharmacokinetic responses produced by capsule administration are similar to values obtained when test compounds are ingested in solution. To test this, plasma phenylalanine and aspartate concentrations were compared in ten normal subjects ingesting 3 g aspartame in solution and in capsules in a balanced Latin square design. Peak plasma phenylalanine levels were significantly higher (191 +/- 65.4 v 117 +/- 39.5 mumol/L, mean +/- SD) and were reached significantly earlier (32 +/- 15 v 123 +/- 74 minutes) when aspartame was administered in solution than when it was administered in capsules. The area under the four-hour plasma phenylalanine concentration-time curve was significantly higher (15,340 +/- 4,820 v 8,465 +/- 3,356 mumol/L X min) when aspartame was ingested in solution. Administration in solution also produced a significantly higher ratio of plasma phenylalanine concentration to the sum of the plasma concentrations of the other large neutral amino acids (0.36 +/- 0.12 v 0.23 +/- 0.06). Similarly, peak plasma aspartate concentrations were significantly higher 26.2 +/- 16.3 v 10.4 +/- 5.0 mumol/L) and were reached significantly earlier (30 +/- 14 v 106 +/- 61.3 min) when aspartame was administered in solution. The data indicate different plasma phenylalanine and aspartate pharmacokinetics between solution and capsule administration of aspartame.

Plasma phenylalanine levels in phenylketonuric heterozygous and normal adults administered aspartame at 34 mg/kg body weight

Following administration of aspartame (34 mg/kg body wt) in orange juice, plasma concentrations of free amino acids were measured in 12 female subjects known to be heterozygous for phenylketonuria and 22 normal subjects (12 male, 10 female). No change in fasting plasma aspartate concentrations were noted after aspartame loading in either group. In normal male subjects, the mean (+/-S.D.) plasma phenylalanine concentration increased from a fasting value of 5.86 +/- 1.25 mumol/dl. Plasma phenylalanine levels in normal female subjects increased from a mean fasting concentration of 4.83 +/- 0.84 mumol/dl to a men peak value of 8.95 +/- 1.49 mumol/dl suggesting a more rapid absorption, metabolism, and/or clearance of phenylalanine by females. In female heterozygous subjects, the mean peak plasma phenylalanine concentration was significantly higher than in normal females. Plasma phenylalanine values increased from a mean fasting value of 5.92 +/- 1.51 mumol/dl to a mean peak value of 15.1 +/- 4.76 mumol/dl. Similarly, the area under the plasma phenylalanine concentration-time curve was significantly greater in heterozygous female subjects (21.36 +/- 5.10 IU) than in normal female subjects (10.84 +/- 2.32 IU). However, peak plasma phenylalanine levels were well below those associated with toxic effects in all cases.

Aspartame administration to the infant monkey: hypothalamic morphology and plasma amino acid levels

Infant monkeys received 2 gm/kg body weight of aspartame (APM) or 2 gm/kg body weight APM plus 1 gm/kg body weight monosodium glutamate (MSG) by gastric tube. Blood samples were obtained at intervals over the ensuing 4 hours and analyzed for amino acid levels. At this time, each infant was perfused with glutaraldehyde. The hypothalamus was embedded in plastic and then serially sectioned at 1 mu. Hypothalamic morphology was normal in all eight infants given 2 gm/kg body weight APM and in the six infants given 2 gm/kg body weight APM plus 1 gm/kg body weight MSG. By light microscopy, no pycnotic nuclei, neuronal degeneration, or dendritic swelling was noted. In both experimental and control brains, localized areas of poor perfusion exhibited abnormal morphology. Elevated plasma levels of aspartate, glutamate, and phenylalanine indicated that the test compounds were administered and absorbed. Variable rates of absorption were evident, probably due to the necessity of administering APM as a slurry, due to its low solubility. On the basis of blood absorption curves, it appears that infant monkeys metabolize aspartate and glutamate and phenylalanine somewhat more rapidly than man. It is concluded that APM given alone or with MSG, in large acute doses, does not result in hypothalamic damage in the newborn monkey.