Effects of alpha-methylphenylalanine plus phenylalanine treatment during development on myelin in rat brain

Toxicological and Teratogenic Effect of Various Food Additives: An Updated Review

Scientific evidence is mounting that synthetic chemicals used as food additives may have harmful impacts on health. Food additives are chemicals that are added to food to keep it from spoiling, as well as to improve its colour and taste. Some are linked to negative health impacts, while others are healthy and can be ingested with little danger. According to several studies, health issues such as asthma, attention deficit hyperactivity disorder (ADHD), heart difficulties, cancer, obesity, and others are caused by harmful additives and preservatives. Some food additives may interfere with hormones and influences growth and development. It is one of the reasons why so many children are overweight. Children are more likely than adults to be exposed to these types of dietary intakes. Several food additives are used by women during pregnancy and breast feeding that are not fully safe. We must take specific precaution to avoid consuming dangerous compounds before they begin to wreak havoc on our health. This study is intended to understand how the preservatives induce different health problem in the body once it is consumed. This review focuses on some specific food additives such as sodium benzoate, aspartame, tartrazine, carrageenan, and potassium benzoate, as well as vitamin A. Long-term use of food treated with the above-mentioned food preservatives resulted in teratogenicity and other allergens, according to the study. Other health issues can be avoided in the future by using natural food additives derived from plants and other natural sources.

Biochemical, Metabolic, and Behavioral Characteristics of Immature Chronic Hyperphenylalanemic Rats

Phenylketonuria and hyperphenylalanemia are inborn errors in metabolism of phenylalanine arising from defects in steps to convert phenylalanine to tyrosine. Phe accumulation causes severe mental retardation that can be prevented by timely identification of affected individuals and their placement on a Phe-restricted diet. In spite of many studies in patients and animal models, the basis for acquisition of mental retardation during the critical period of brain development is not adequately understood. All animal models for human disease have advantages and limitations, and characteristics common to different models are most likely to correspond to the disorder. This study established similar levels of Phe exposure in developing rats between 3 and 16 days of age using three models to produce chronic hyperphenylalanemia, and identified changes in brain amino acid levels common to all models that persist for ~16 h of each day. In a representative model, local rates of glucose utilization (CMRglc) were determined at 25-27 days of age, and only selective changes that appeared to depend on Phe exposure were observed. CMRglc was reduced in frontal cortex and thalamus and increased in hippocampus and globus pallidus. Behavioral testing to evaluate neuromuscular competence revealed poor performance in chronically-hyperphenylalanemic rats that persisted for at least 3 weeks after cessation of Phe injections and did not occur with mild or acute hyperphenylalanemia. Thus, the abnormal amino acid environment, including hyperglycinemia, in developing rat brain is associated with selective regional changes in glucose utilization and behavioral abnormalities that are not readily reversed after they are acquired.

Effects of perinatal exposure to aspartame on rat pups

Possible effects of perinatal exposure to L-aspartyl-L-phenylalanine methyl ester (aspartame) on rat pups were investigated. Adult female rats, and later their pups, were exposed, via their drinking water, to aspartame (0.007%, 0.036%, 0.18% or 0.9% w/v) or phenylalanine (0.45% w/v) for 12 days prior to conception until the pups were 38 days old. Control rats were given plain water. The adults exposed to aspartame consumed an average of 14, 68, 347 and 1614 mg/kg/day of aspartame and those exposed to phenylalanine consumed an average of 835 mg/kg/day of phenylalanine. After weaning the pups given aspartame consumed an average of 32, 154, 836, and 3566 mg/kg/day of aspartame and those given phenylalanine consumed an average of 1795 mg/kg/day of phenylalanine. No effect of aspartame or phenylalanine was detected on either two measures of morphological development (i.e., latencies to pinnae detachment and eye opening) or two tests of reflex development (i.e., latencies for surface righting at 7 days of age and negative geotaxis at 8 days of age). All groups were similar in spatial memory as assessed with two different mazes with pups 30-36 days old. The number of arms before reentry in an 8-arm radial-arm maze and the acquisition curves from a milk maze did not differ between groups. Furthermore, the latencies of mothers to retrieve their litters was also unaffected by the aspartame and phenylalanine. These results indicate that perinatal exposure to aspartame, when voluntarily consumed by mothers (14-1614 mg/kg/day) and later directly by the rat pups (32 to 3566 mg/kg/day) does not affect reflex development, morphological development or spatial memory.

Effect of experimental hyperphenylalaninemia induced by dietary phenylalanine plus alpha-methylphenylalanine administration on amino acid concentration in neonatal chick brain, plasma, and liver

Supplementation of 5% phenylalanine plus 0.4% alpha-methylphenylalanine to the standard diet or 1% phenylalanine plus 0.08% alpha-methylphenylalanine to the drinking water produced phenylketonuria-like conditions in 5-day-old chicks. An increase of 10 to 15-fold in the phenylalanine content was observed in plasma or brain of animals after 9 days of both types of treatment. A smaller but significant increase was also observed in liver. However, practically no changes were found in the levels of tyrosine in the same conditions. Thus, the high values of plasma and brain phenylalanine/tyrosine ratio obtained by these treatments were mainly due to an increase in the phenylalanine levels, without increasing those of tyrosine. Chronic hyperphenylalaninemia induced a nonsignificant decrease in the most of amino acid contents in brain, especially after 9 days of treatment, although the levels of glycine and serine were significantly increased. A similar decrease was found in the plasma and liver concentration of various amino acids, although the variations observed in the liver were smaller than those found in plasma and brain.

Inhibition of brain and liver 3-hydroxy-3-methylglutaryl-CoA reductase and mevalonate-5-pyrophosphate decarboxylase in experimental hyperphenylalaninemia

Experimental hyperphenylalaninemia has been induced in 5-day-old chicks by dietary treatments with phenylalanine and alpha-methylphenylalanine. An increase of nearly 8-fold in plasma Phe/Tyr ratio was found after 4 days of supplementation the standard diet with 5% phenylalanine plus 0.4% alpha-methylphenylalanine. The increase in this ratio was about 13-fold after 9 days of the same treatment. Similar results were observed in brain and liver, although the increases were smaller than those found in plasma. Total body, brain and liver weight decreased after 9 days of treatment. Phenylalanine plus alpha-methylphenylalanine administration to 5-day-old chicks produced a significant decrease in the 3-hydroxy-3-methylglutaryl-CoA reductase and mevalonate-5-pyrophosphate decarboxylase specific activities from both brain and liver. These results demonstrated for the first time that experimental hyperphenylalaninemia inhibited different enzyme activities directly implicated in the regulation of cholesterogenesis. Therefore, a reduced cholesterol synthesis in brain may evidenciate the theory of an impaired myelination leading to mental retardation in phenylketonuria patients.

Developmental changes of myelin-associated glycoprotein in rat brain: study on experimental hyperphenylalaninemia

We examined developmental changes of myelin-associated glycoprotein (MAG), basic protein (BP), and proteolipid protein (PLP) in central nervous system myelin isolated from experimental hyperphenylalaninemic rats (PKU rats) and controls. Higher amounts of MAG, including high-molecular-weight MAG in myelin, were found in 12- to 21-day-old control rats than in adult rats. MAG in developing myelin was at a maximum in 18-day-old rats and began to decrease in 21-day-old rats, while PLP and BP in developing myelin increased at these developmental stages. The level of high-molecular-weight MAG decreased in myelin prepared from 21-day-old rats. These results suggest that the decreasing high-molecular-weight MAG is important for compaction of myelin in the early stage of myelination. In myelin from 12- to 18-day-old PKU rats, the ratio of each protein such as MAG, PLP, or BP to that of control was about 0.5 at 12 days, and increased to almost 1.0 at 18 days. The myelination seems to be initially delayed but to be close to that of controls in PKU rats about 18 days old.

Fatty acid composition of myelin lipids from developing rat forebrain and spinal cord: influence of experimental hyperphenylalaninaemia

The fatty acid composition of individual myelin lipids from rat forebrain and spinal cord was analysed at 20 and 30 days p.p. During this phase of rapid myelination the proportions of C 16:0 and C 18:0 fatty acids decreased whereas the relative amounts of long chain and unsaturated fatty acids increased in most lipid classes. This developmental shift was more pronounced in the forebrain and was different with respect to both magnitude and direction for each myelin lipid. The experimental induction of chronic hyperphenylalaninaemia (hyper-Phe) from day 3 p.p. lead to alterations in the rate of myelination, which were most pronounced in the forebrain. At 20 days, especially in the forebrain, chain elongation and desaturation of fatty acids were delayed. This delay was maximal in sphingomyelin fatty acids, C 18:0 and C 24:1. In hydroxycerebrosides, the shift in the fatty acid composition from C 16:0 to C 22:0 was accelerated in hyper-Phe rats. No significant difference in the fatty acid composition of any myelin lipid was found in the more mature myelin (spinal cord, 30 days p.p.). No evidence was found of a primary effect of hyper-Phe on myelination.

Effects of hyperphenylalaninemia in the fetal stage on the postnatal development of fetal rat brain

The effect of exposure at different prenatal stages to maternal hyperphenylalaninemia (HyPhe) on the somatic and neurological development of fetuses in rats was studied, with special respect to the change of relevant enzyme activities in the brain. While evident somatic damage was found only in the fetuses exposed to maternal HyPhe at a last stage of gestation, distinct mental retardation seemingly due to some irreversible damage to the brain was observed in all the treated fetuses regardless of the timing of exposure, and a significantly reduced activity of 2', 3'-cyclic nucleotide 3'-phosphohydrolase (CNPase), a marker enzyme of myelin, was confirmed in the mantle region of the brain.

Biochemical and neuropsychological effects of elevated plasma phenylalanine in patients with treated phenylketonuria. A model for the study of phenylalanine and brain function in man

Phenylketonuria provides a human model for the study of the effect of phenylalanine on brain function. Although irreversible mental retardation is preventable through newborn diagnosis and dietary phenylalanine restriction, controversy exists regarding the effects of increased concentrations of phenylalanine in older patients. We have studied ten older, treated, phenylketonuric patients using a triple-blind, multiple trials, crossover design. Each patient was tested at the end of each of three 1-wk periods of high or low phenylalanine intakes. Tests included a repeatable battery of neuropsychological tests, analysis of plasma amino acids, and measurement of urine amino acids, phenyl organic acids, dopamine, and serotonin. In all 10 patients plasma phenylalanine rose (900-4,000 microM). In 9 of 10 patients there was an inverse relationship between plasma phenylalanine and urine dopamine excretion. When blood phenylalanine was elevated, these patients had prolonged performance times on neuropsychological tests of higher but not lower integrative function. Urinary serotonin fell during phenylalanine loading in six patients. The concentration of phenylacids in the urine was not proportional to the plasma phenylalanine at concentrations below 1.5 mM. In one patient, neither performance time nor dopamine excretion varied as blood phenylalanine rose or fell. We interpret these data as follows: blood phenylalanine above 1.3 mM impairs performance on neuropsychological tests of higher integrative function, this effect is reversible, and one mechanism may involve impaired biogenic amine synthesis.

Effect of hyperphenylalaninemia induced during suckling on brain DNA metabolism in rat pups

We studied DNA metabolism (synthesis and degradation) in brain to investigate the effect of hyperphenylalaninemia induced in rats by treatment with PCPA or alpha MPA plus PHE during suckling (4th-20th days of postnatal age) on cell proliferation and naturally occurring cell death. The incorporation of 14C in DNA as percent of total radioactivity in the tissue, 30 min after administration of [14C]thymidine served as a measure of DNA synthesis in vivo, and the amount of radioactivity recovered in DNA as percent of total 14C in the tissues of 21 day old rats, injected with [14C]thymidine on 2nd day after birth, indicated the turnover (degradation) of DNA. The results showed that the DNA content of cerebellum as well as cerebrum was reduced by treatment with PCPA plus PHE, while treatment with alpha MPA plus PHE had no effect on DNA content in cerebellum but reduced the levels in cerebrum. Treatment with PCPA or alpha MPA plus PHE reduced the synthesis of DNA in cerebrum of 11 day old rats but not in 21 day old rats, and the treatments did not affect DNA synthesis in cerebellum of either 11 or 21 day old rats. The turnover (degradation) of DNA was increased in both cerebellum and cerebrum from rats treated with PCPA plus PHE but alpha MPA plus PHE treatment did not alter the DNA turnover either in cerebellum or in cerebrum. The activity of acid DNase was reduced in both cerebellum and cerebrum from 11 as well as 21 day old rats treated with PCPA plus PHE, but the enzyme activity was not altered in the tissues from rats of both ages treated with alpha MPA plus PHE. The data thus indicate that in rats treated with PCPA plus PHE the reduction in cerebral DNA levels occurs due to reduced synthesis and/or increased turnover (degradation) of DNA but that the reduction in cerebellar DNA may occur only as a result of increased turnover (degradation), and that in rats treated with alpha MPA plus PHE the reduction in cerebral DNA must occur due to reduced synthesis. This suggests that treatment of rats with PCPA plus PHE during suckling inhibits cell proliferation and/or increases naturally occurring cell death in both cerebellum and cerebrum while treatment with alpha MPA plus PHE inhibits only cell proliferation and in cerebrum alone.

Lipid composition of brain myelin from normal and hyperphenylalaninemic chick embryos

The influence of hyperphenylalaninemia on the lipid composition of brain myelin has been investigated in 19-day-old chick embryos. CNP-ase activity was used as myelin marker enzyme for myelin isolation. CNP-ase activity was significantly lower in hyperphenylalaninemic myelin when compared with control. No significant differences were observed after experimental treatment in the total lipid content of myelin as well as in the proportion of cholesterol:phospholipid:galactolipid. Nevertheless, a clear increase in the percentage of esterified cholesterol was found. No appreciable alterations were observed in the phospholipid composition of brain myelin from both control and hyperphenylalaninemic chick embryos. However, the ratio of unsaturated to saturated fatty acids in serine plasmalogen and sphingomyelin was considerably increased by this treatment. This ratio in choline and ethanolamine phosphatides from treated embryos did not differ from that of controls.

Effect of experimental hyperphenylalaninemia on myelin metabolism at later stages of brain development

Myelination is the most important process in postnatal maturation of the nervous system and during this period the growing infant passes through a "vulnerable period" during which irreversible brain damage can occur if the neonate is subjected to a potential neurotoxin. This study was undertaken to investigate the mechanisms by which chronic hyperphenylalaninemia interferes with myelin metabolism, beyond the neonatal period of rapid myelination, at a time when myelin continues to accumulate. Rats of 25 days of age were placed on a hyperphenylalanimenia (HyPhe) inducing diet of 5% phenylalanine plus 0.4% alpha-methylphenylalanine (alpha MP) at 25 days of age to approximate plasma phenylalanine levels of an untreated human PKU patient (1.5 mM). The HyPhe group exhibited approximately a 15% decrease in the amount of myelin protein throughout the 70 days of the study. The rate of incorporation of 3H-lysine into both TCA precipitable whole brain proteins or myelin proteins did not vary from the HyPhe group and a weight matched control group (WMC). Therefore, this loss of myelin could not be attributed to a hypo-myelination. The turnover of whole brain proteins also was unaffected by the HyPhe treatment; however, the turnover of myelin proteins in the HyPhe group was dramatically different (t 1/2 = 3 days) from that of the WMC group (t 1/2 = 36 days) or a group treated with only alpha MP (t 1/2 = 26 days).

The effects of chronic hyperphenylalaninaemia on mouse brain protein synthesis can be prevented by other amino acids

A prolonged elevation in the concentrations of circulating phenylalanine was maintained in newborn mice by daily injections of phenylalanine and a phenylalanine hydroxylase inhibitor, alpha-methylphenylalanine. The result of this chronic hyperphenylalaninaemia was an accumulation of vacant or inactive monoribosomes that persisted for 18 h of each day. An elongation assay in vitro with brain postmitochondrial supernatants demonstrated that, in addition, there was an equally prolonged decrease in the rates of polypeptide-chain elongation by the remaining brain polyribosomes. Analyses of the free amino acid composition in the brains of hyperphenylalaninaemic mice showed a loss of several amino acids from the brain, particularly the large, neutral amino acids, which are co- or counter-transported across plasma membranes with phenylalanine. When a mixture of these amino acids (leucine, isoleucine, valine, threonine, tryptophan, tyrosine, methionine) was injected into hyperphenylalaninaemic mice, there was an immediate cessation of monoribosome accumulation in the brain and there was no inhibition of the rates of polypeptide-chain elongation. Although the concentrations of the large, neutral amino acids in the brain were partially preserved by treatment of hyperphenylalaninaemic mice with the amino acid mixture, the elevated concentrations of phenylalanine remained unaltered. The amino acid mixture had no detectable effect on brain protein synthesis in the absence of the hyperphenylalaninaemic condition.